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Barium as doping element tuning both toxicity and optoelectric properties of lead-based halide perovskites
Wang Xue-Ting, Fu Yu-Hao, Na Guang-Ren, Li Hong-Dong, Zhang Li-Jun
Acta Physica Sinica, 2019, 68 (15): 157101
Temperature-dependent properties of metastable graphene oxide
Mo Jia-Wei, Qiu Yin-Wei, Yi Ruo-Bing, Wu Jun, Wang Zhi-Kun, Zhao Li-Hua
Acta Physica Sinica, 2019, 68 (15): 156501
In situ observation of lithiation mechanism of SnO2 nanoparticles
Xiong Yu-Wei, Yin Kui-Bo, Wen Yi-Feng, Xin Lei, Yao Li-Bing, Zhu Chong-Yang, Sun Li-Tao
Acta Physica Sinica, 2019, 68 (15): 158201
Current Issue Accepts In Press Earlier Issues Top Downloaded SCI Top Cited
  Acta Physica Sinica--2019, 68 (15)   Published: 05 August 2019
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SPECIAL TOPIC—Perovskite optoelectronic devices and physics

Barium as doping element tuning both toxicity and optoelectric properties of lead-based halide perovskites Hot!

Wang Xue-Ting, Fu Yu-Hao, Na Guang-Ren, Li Hong-Dong, Zhang Li-Jun
Acta Physica Sinica. 2019, 68 (15): 157101 doi: 10.7498/aps.68.20190596
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Organic-inorganic halide perovskites ABX3 (A=CH3NH3, HC(NH2)2; B=Pb; X=Cl, Br, I) have recently attracted increasing attention due to their advanced optoelectronic properties. However, the poor stability and toxicity of organic lead halogen perovskites are still a major challenge for deploying the outdoor solar cells. Element substitution is a simple and effective strategy to solve these problems. For example, the substitution of the I ions with Cl and Br has been regarded as a reliable method to improve the device stability. A-site engineering, i.e., replacing organic ions with inorganic cations (such as Cs+, Rb+), has also been reported. The B-site alloying approach has been demonstrated with Zn, Sr, Sn, etc. Inorganic halide perovskites can be synthesized by the low-cost solution spin-coating method and have similar optoelectronic properties and improved stability to their organic counterparts. Here in this paper, we report a comprehensive study of the alloyed perovskite CsPb1-xBaxX3 (X=Cl, Br, I) by combining the disorder alloy structure search method with first-principles energy calculations. We find that it is not easy to dope barium into the perovskite lattice when Ba concentration is low and the stable disordered solid solution can exist in the high Ba concentration case. Carrier effective mass and bandgap increase with the increase of Ba concentration and the bandgap change range is wide, owing to the difference in both electronegativity and ionic radius between Pb and Ba. After inducing Ba into CsPb1-xBaxX3 (X=Cl, Br, I), the higher electron concentration on the I sites also enhances the Coulomb interaction of the Pb-I bonds. Moreover, the electrons and holes tend to be located on Pb sites, and this may give rise to the formation of local potential wells, which would further induce the large lattice deformation to accommodate the self-trapped excitons. Especially, CsPbI3-Pnma perovskite is metastable in the ambient environment with a suitable photon absorption threshold. The CsPb1-xBaxI3 can be used as a capping layer on CsPbI3 in solar cells, thereby significantly improving the power conversion efficiency and long-term stability. Overall, the alloyed perovskite CsPb1-xBaxX3 (X=Cl, Br, I) with high Ba concentration can be stable and less-toxic, and they can be used in short wave light-emitting diodes, radiation detectors or other fields because of their large bandgaps (> 2.8 eV).

Recent advances in photo-stability of lead halide perovskites

Lou Hao-Ran, Ye Zhi-Zhen, He Hai-Ping
Acta Physica Sinica. 2019, 68 (15): 157102 doi: 10.7498/aps.68.20190324
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Lead halide perovskites, which can be grown by solution process, are very suitable for various optoelectronic applications, such as in solar cells, light-emitting diodes, lasers and photo-detectors, due to their outstanding electrical and optical properties. However, lead halide perovskites are unstable under continuous light illumination, which severely degrades the performance and lifetime of optoelectronic devices based on them. Therefore, the photo-stability of perovskites and the mechanisms have received more and more attention. In this article we review the main phenomena in perovskites, induced by continuous light illumination, namely photo curing, photo dissociation, photo-induced phase separation, and photo-induced phase transition. The proposed mechanisms for the instability from the perspectives of defect states, ion migration, thermodynamics and chemical bonds, respectively, are also introduced. Finally, the complexity presented in the studying of photo-stability, and the issues should be addressed in the future are also briefly discussed.

Recent advances in perovskite solar cells: Space potential and optoelectronic conversion mechanism

Wang Yan-Bo, Cui Dan-Yu, Zhang Cai-Yi, Han Li-Yuan, Yang Xu-Dong
Acta Physica Sinica. 2019, 68 (15): 158401 doi: 10.7498/aps.68.20190569
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Perovskite solar cells, as a promising next-generation photovoltaic technology for large-scale application, have demonstrated the advantages of high absorption coefficient, tunable bandgap, considerable photoelectric conversion efficiency and low-cost fabrication. However, the photoelectric conversion process within the device is still not understood clearly. One of the major reasons is that it is difficult to directly observe the space potential inside the device and its effect on the photogenerated charge carriers. The direct measurement and analysis of the space potential inside the device and the clarification of the intrinsic relationship between the space potential and the charge carrier micro-process under illumination and different electric field conditions can reveal the photoelectric conversion mechanism in depth, and thus providing the scientific research basis for the further development. Kelvin probe force microscopy (KPFM), a testing technology that is non-contact, can detect the space potential distribution without any damage to the device, demonstrating the great potential to unveil the working mechanism of perovskite solar cells accurately. Such a characterization method can work under vacuum condition. The KPFM combines Kelvin method of measuring contact potential difference with the scan probe microscopy to characterize internal carrier dynamic behavior with high resolution on a nanometer scale. The study of the spatial potential distribution of semiconductor device plays an important role in understanding the working mechanism of new perovskite solar cells. For example, under an open-circuit condition, the intensity and width of the electric field and space charge region can be obtained from the spatial potential distribution, and the bending direction of the energy band can be judged according to the increase or decrease of the potential. While in a short-circuit case, the generation and transport of charge carriers can be obtained. In this review, we mainly introduce the research progress of the space potential distribution and optoelectronic conversion mechanism in perovskite solar cells. The key mechanism of charge carrier generation, separation, transport and recombination are revealed by using KPFM to directly observe the space potential variations caused by light or electric field. We also prospect the issues and challenges in the future research.

Blue perovskite light-emitting diodes: opportunities and challenges

Duan Cong-Cong, Cheng Lu, Yin Yao, Zhu Lin
Acta Physica Sinica. 2019, 68 (15): 158503 doi: 10.7498/aps.68.20190745
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The great progress of light-emitting diodes (LEDs) has been made based on perovskites, and the external quantum efficiency of near infrared, red and green devices have reached > 20%, exhibiting their great potential applications in lighting and displays. However, the performance of blue perovskite LEDs is very poor, thus limiting their applications in the field of full-color displays. The blue perovskite LEDs can be achieved through mixed halides or quantum confinement effect. In this paper, we review the research progress of blue perovskite LEDs based on these two strategies, discuss the challenges to achieve high-performance perovskite LEDs and present our perspectives.

Research progress of efficient green perovskite light emitting diodes

Qu Zi-Han, Chu Ze-Ma, Zhang Xing-Wang, You Jing-Bi
Acta Physica Sinica. 2019, 68 (15): 158504 doi: 10.7498/aps.68.20190647
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Perovskite light emitting diodes exhibit the advantages of high color purity, tunable wavelength and low producing cost. Considering these superiorities, one regards perovskite light emitting diodes as very promising candidates for solid state lighting and panel displaying. Human eyes are very sensitive to green light, thus green perovskite light emitting diodes receive the most attention from researchers. Since the advent of the very first green perovskite light emitting diode, the external quantum efficiency has climbed from only 0.1% to over 20%. In this review, we mainly discuss the history of green perovskite light emitting diodes, the basic concepts of perovskite materials and green perovskite light emitting diodes, and the common methods to improve the efficiency of green perovskite light emitting diodes. The bandgap of bromide perovskite is about 2.3 eV, which is located just on a green light wavelength scale and thus becomes the suitable emitting layer material for green emission. There are mainly two types of device structures, i.e. regular format and inverted format. The whole working process of green perovskite light emitting diodes can be divided into two stages, i.e. the injection and recombination of charge carriers. One engineers the energy levels of different layers to improve the injection of charge carriers. They also raise up the strategy so-called surface passivation to reduce the defect density at the interface in order to avoid the quenching phenomenon. One usually inserts a buffering layer to realize the surface passivation. Besides, perovskites possess very small exciton binding energy, which is at the same order of magnitudes as the kinetic energy at room temperature. Charge carriers become free in this case, which will severely reduce the radiation recombination probability due to the non-radiation recombination process such as Shockley-Read-Hall effect and Auger recombination. To solve the problem, people fabricate three types of perovskites, namely quasi two-dimensional perovskite, perovskite quantum dot, and perovskite nanocrystal. In this way, the charge carriers can be confined into a limited space and the exciton binding energy will hence be improved. From the efficiency perspective, the green perovskite light emitting diodes promise to be commercialized. However, another critical issue impeding the development of green perovskite light emitting diodes is the stability problem. Comparing with the organic light emitting diodes and inorganic quantum dot light emitting diodes, the lifetime of perovskite light emitting diodes is too limited, which is only approximately one hundred hours under normal conditions. The temperature, moisture and light exposure are all factors that influence the stability of perovskite light emitting diodes.

Applications of organic additives in metal halide perovskite light-emitting diodes

Li Zhen-Chao, Chen Zi-Ming, Zou Guang-Rui-Xing, Yip Hin-Lap, Cao Yong
Acta Physica Sinica. 2019, 68 (15): 158505 doi: 10.7498/aps.68.20190307
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In recent years, metal halide perovskites have received extensive attention due to their superior optoelectronic properties and solution processability, which also become a research hotspot in the field of optoelectronics. Among all the perovskite optoelectronics applications, perovskite light-emitting diode (LED) becomes one of the important research topics because it is likely to be used in the next-generation display technique. Based on the high photoluminescence quantum yield (PLQY), facilely tunable bandgaps, and sharp emission of perovskite material, the external quantum efficiency of perovskite LED has increased from less than 1% to over 20% within only five years, showing the most rapid development speed in the LED field. During the 5-year exploration of perovskite LEDs, researchers have focused their efforts on how to realize the crystal-growth control in the perovskite film formation process, enhance PLQY of the perovskite films, and improve the performance of perovskite LEDs. Among all the approaches, the utilization of organic additives including small molecules and polymers proves to be an effective strategy. Here, in this article, we review the recent advances in metal halide perovskite LEDs based on the strategy of organic-additive treatment. We also analyze and discuss the interaction between organic additive and perovskite crystal as well as its influence on the performance of perovskite LED. In the end, we discuss the challenges remaining in perovskite LEDs and the prospects for perovskite LEDs.

Rashba effect in perovskites and its influences on carrier recombination

Wei Ying-Qiang, Xu Lei, Peng Qi-Ming, Wang Jian-Pu
Acta Physica Sinica. 2019, 68 (15): 158506 doi: 10.7498/aps.68.20190675
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When there is a strong spin-orbit coupling in some direct semiconductor with an inversion-asymmetric structure, the Rashba effect will exist, splitting the spin-degenerated bands into two sub-bands with opposite spin states. These two sub-bands will deviate from the symmetry center of the Brillouin zone, making the semiconductor an indirect band gap semiconductor. Metal halide perovskites exhibit strong spin-orbit coupling and possess an inversion-asymmetric crystal structure, showing great potential in Rashba effect research. In this review, we systematically review the Rashba effects in perovskites, including the theoretical and experimental studies for demonstrating the Rashba effect in perovskites, the influence of Rashba effect on the carrier recombination, and the current debates concerning the Rashba effect in perovskites. Then, several problems that need to be solved urgently are proposed,they being 1) whether there exists the Rashba effect in the perovskite, 2) whether the Rashba effect can exert a significant influence on carrier recombination, and 3) what the relationship between the Rashba effect and the perovskite stucture is. The prospects are also given for the future research including the study of the Rashba effect in perovskites by various spectral methods and the applications of the Rashba effect in optical-electronic-magnetic devices.

Recent progress of ion migration in organometal halide perovskite

Wang Ji-Fei, Lin Dong-Xu, Yuan Yong-Bo
Acta Physica Sinica. 2019, 68 (15): 158801 doi: 10.7498/aps.68.20190853
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In recent years, metal halide perovskite solar cells have attracted widespread attention due to their unique technological superiority. Remarkable progress of device performance has been achieved in last few years. The certified efficiency has reached 24.2%, which is close to the efficiency of the commercial crystalline silicon solar cells. Halide perovskite is a kind of semiconductor and ionic conductor material, which not only has the ability to transfer charges, but also exhibits the phenomenon of ion migration under an external electric field. Ion migration can directly change the local chemical ratio of perovskite crystals, and can also greatly affect the electrical properties of materials and the working mechanisms of corresponding devices. In this review, the formation mechanism, basic characteristics and effects of ion migration on the working mechanism of the device (such as giant switchable photovoltaic phenomenon, current hysteresis, etc.) are summarized, and then some recent advances in the suppression of ion migration are introduced. Since there exist still many doubts about ion migration in perovskite materials, it is very important to understand the phenomenon of ion migration in perovskite materials in order to promote the development and application of perovskite solar cells.

Perovskite solar cells passivated by distorted two-dimensional structure

Fu Peng-Fei, Yu Dan-Ni, Peng Zi-Jian, Gong Jin-Kang, Ning Zhi-Jun
Acta Physica Sinica. 2019, 68 (15): 158802 doi: 10.7498/aps.68.20190306
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Hybrid perovskites are a series of solution-processable materials for photovoltaic devices. To achieve better performance and stability, interface passivation is an effective method. So far, the most commonly used passivators are organic amines, which can tailor perovskite into a lower-dimensional structure (Ruddlesden-Popper perovskite). Here, we select a biimizole (BIM) molecule as a new passivator for perovskite. The BIM based single layer perovskite has a more rigid structure. And multi-layered structure cannot be formed due to large lattice mismatching and structural rigidity. By inducing the excess MAI (methanaminium iodide) into the lattice, the layered structure is maintained, and half of the BIM molecules are replaced by MA (methylamine). The mixed layered structure is distorted, because of the difference in size between two kinds of cations. We then investigate passivation effect of BIM on perovskite solar cells. By carefully controlling the feed ratio in precursor solutions, we fabricate solar cells with different passivation structures. We find that the introduction of BIM can cause Voc to increase generally, indicating that MAPbI3 is well passivated. The peak at 7.5° and 15° in X-ray diffraction pattern are corresponding to a two-dimensional (2D) phase with a shorter layer distance. There are no peaks at lower degrees, so that no multi-layered structure is formed in the film either. We suppose that a dual-phase 2D-3D (where 3D represents three-dimensional) structure is formed in the perovskite film. To explain the passivation effect of the two 2D structures, we investigate their lattice matching towards MAPbI3. The distorted 2D structure is well matched with (110) face of o-MAPbI3, and the mismatching rate is lower 1% in the two directions. On the other hand, the BIM based 2D structure cannot well match with (-110) face of o-MAPbI3, nor with (001) face of c-MAPbI3. We also consider that the less rigidity of distorted structure contributes to better passivation. As a result, we achieve a BIM passivated perovskite solar cell with a power conversion efficiency up to 14%. This work paves a new way to the interface engineering of perovskite solar cells.

Research progress of interface passivation of n-i-p perovskite solar cells

Li Xiao-Guo, Zhang Xin, Shi Ze-Jiao, Zhang Hai-Juan, Zhu Cheng-Jun, Zhan Yi-Qiang
Acta Physica Sinica. 2019, 68 (15): 158803 doi: 10.7498/aps.68.20190468
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In recent years, organic-inorganic hybrid perovskite solar cells have aroused the interest of a large number of researchers due to the advantages of large optical absorption coefficient, tunable bandgap and easy fabrication. Recently, the power conversion efficiency of organic-inorganic hybrid perovskite solar cells has been enhanced to more than 23% in laboratory. In solution processed perovskite solar cells, perovskite and charge transport layer are stacked together, due to the different crystallization rates leading to lattice mismatch near the surface region of perovskite film, resulting in a lot of interface defects, especially at the interface between perovskite and charge transport layer. What is more, the photo-induced free carriers must transfer across the interfaces to be collected. But the defects near the interface can trap photogeneration electrons, thus reducing the carrier lifetime and causing the charges to be recombined, which greatly influence the performance and stability of perovskite solar cells. Therefore, reducing and passivating these defects is critical for obtaining the high performance perovskite solar cells. Now, there have been made tremendous efforts devoting to advancing passivation techniques, such as doping and surface modification, for high efficiency perovskite solar cell with improved stability and reduced hysteresis. These approaches also contribute to improving the energy band alignment between carrier transport layers and perovskite absorber improving device performance, or resistance moisture to enhance device stability. In this review we mainly introduce the formation and the effect of defects on perovskite solar cells, analyze the mechanism for passivating the interfacial defects between charge transport layer and perovskite photo absorption layer for different materials, compare the effects of different passivation materials on the photovoltaic performance of perovskite solar cells, and summarize the role of these materials in passivating the defects. Finally we discuss the research trend and development direction of passivation defects in perovskite solar cells.

Intrinsic stability of organic-inorganic hybrid perovskite

Zhang Yu, Zhou Huan-Ping
Acta Physica Sinica. 2019, 68 (15): 158804 doi: 10.7498/aps.68.20190343
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The power conversion efficiency of organic-inorganic hybrid perovskite solar cell has exceeded 24%. The rapid increase in efficiency coupled with its cost-effective fabrication has attracted tremendous attention toward the commercialization of perovskite solar cells. The biggest challenge that hinders the commercialization of perovskite solar cells is the long-term instability of materials and the corresponding devices, which cannot compete with other commercialized solar cells, such as Si cells, in terms of lifetime. The intrinsic instability of perovskite material itself is the most critical challenge faced by researchers. In this study, we discuss the intrinsic instability of organic-inorganic hybrid perovskite materials from the aspects of both chemical instability and phase instability. Suggestions for improving the stability of perovskite solar cell are provided from the perspective of composition design and fabrication process.

Organic ammonium salt surface treatment stabilizing all-inorganic CsPbI2Br perovskite

Liu Xiao-Min, Li Yi-Hui, Wang Xing-Tao, Zhao Yi-Xin
Acta Physica Sinica. 2019, 68 (15): 158805 doi: 10.7498/aps.68.20190303
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All-inorganic perovskite cesium lead halides with superior stability, suitable bandgap and high absorption efficient have become a promising candidate for photovoltaic application. In all-inorganic cesium lead halide perovskites, CsPbX3 (X=Br, I) exhibits excellent photoelectric properties, which are similar to those of organic-inorganic hybrid perovskites. The CsPbI3 faces a challenge of unideal tolerant factor for perovskite phase while CsPbI3-xBrx has better tolerant factor. Among them, CsPbI2Br is one of most popular candidates because of its good thermal stability. Nevertheless, CsPbI2Br shows instability due to the phase transition caused by moisture and lower efficiency because of defects. For all inorganic perovskite devices, the alkyl chain length of surface treatment agent should be taken into account when using organic cationic passivation method. In this paper, CsPbI2Br perovskite is treated with different organic ammonium salts to enhance its phase stability. The experimental results show that α-phase CsPbI2Br is more stable with the increase of the alkyl chain length. Butylamine iodine (BAI) among three kinds of surface treating agents is proved to have the best defect passivation and phase stabilization effect. With the increase of alkyl chain length, the hydrophobicity of the organic molecular layer increases, which plays a crucial role in protecting optically active CsPbI2Br. Meanwhile, it is found that the stability of perovskite is enhanced with the concentration of the BAI solution increasing. This should be related to the organic cation termination formed on the surface of CsPbI2Br film. Solar cell devices based on the CsPbI2Br thin films treated with different concentrations of BAI are assembled and then the effect of organic ion surface treatment on the photoelectric performance of batteries is further explored. The experimental results show that when the concentration of BAI is relatively high (4 mg/mL and 8 mg/mL), the device's photovoltaic performance decreases especially the photocurrent obviously decreases, while the post-treatment process using 2 mg/mL BAI will enhance not only the phase stability but also the photovoltaic parameters after defect passivation. Considering both humidity resistance and device efficiency, this work demonstrates that the CsPbI2Br thin film with suitable BAI treatment can improve the wet stability of perovskite, and enhance the photovoltaic performance.

Research progress of solution processed all-inorganic perovskite solar cell

Wang Ji-Ming, Chen Ke, Xie Wei-Guang, Shi Ting-Ting, Liu Peng-Yi, Zheng Yi-Fan, Zhu Rui
Acta Physica Sinica. 2019, 68 (15): 158806 doi: 10.7498/aps.68.20190355
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Photovoltaic technology, which can converse solar illumination into electricity, is crucial to the sustainable development of human civilization. Among them, the organic-inorganic hybrid perovskite solar cell (OIPSC) has become a research front due to its excellent photoelectric characteristics, low production cost and high power conversion efficiency (PCE). Although the PCE of OIPSC has exceeded 24%, the organic components in the perovskite system are sensitive to the decomposion caused by either being exposed to light or heated in high temperature environment. The stability defects have greatly limited the commercialization of perovskite solar cells. Therefore, it is urgent to improve the stability of perovskite solar cells, especially to solve the material decomposition problem. All-inorganic perovskite photovoltaic material, composed of all-inorganic elements, exhibits excellent heat and moisture resistance. Therefore, the development of all-inorganic perovskite solar cells is of great significance for solving the current stability problems in perovskite photovoltaics. In this work, we review the recent research progress of all-inorganic perovskite solar cells, discuss the solution approaches to processing all-inorganic perovskite films, and explore the enhancement of device stability. Our work provides a guideline for further promoting the device stability and PCE.

Inkjet printed perovskite solar cells: progress and prospects

Xia Jun-Min, Liang Chao, Xing Gui-Chuan
Acta Physica Sinica. 2019, 68 (15): 158807 doi: 10.7498/aps.68.20190302
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In the field of photovoltaic materials, perovskite has attracted extensive attention during the past years, owing to its excellent photovoltaic properties, including high charge carrier mobility, low exciton binding energy, long charge carrier diffusion length, broad light absorption spectrum, large absorption coefficient, and low-cost solution processability. However, due to the limitations of film preparation methods (typical spin coating), industrial large-scale production of perovskite solar cells is still in infancy. The inkjet printing technology is a significant manufacturing technology developed from home and office printing and widely used in various printing electronics industries. Compared with other deposition methods, it possesses many advantages, including low cost, high material utilization, high patterning precision, etc. As a direct writing technology, the inkjet printing has shown great industrial potential and is expected to be employed in the industrialization of perovskite solar cells. In this paper, we review the research progress of perovskite solar cells fabricated via the inkjet printing and the application of inkjet printing technology to various functional layers (electrode, hole transport layer, electron transport layer, perovskite active layer). Finally, the challenges of inkjet printed perovskite solar cells at this stage are discussed, and the commercialization direction of inkjet printed perovskite solar cells is also pointed out.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Kinematics and passing modes of a droplet impacting on a soap film

Yang Ya-Jing, Mei Chen-Xi, Zhang Xu-Dong, Wei Yan-Ju, Liu Sheng-Hua
Acta Physica Sinica. 2019, 68 (15): 156101 doi: 10.7498/aps.68.20190604
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Droplet passing through a film is a ubiquitous phenomenon in nature, such as a rain drop impacting on a rain bubble in paddle and pouring beer onto the beer foam, etc. This phenomenon has not been sufficiently investigated and many interfacial interaction mechanisms are still unknown. In this paper, the passing modes and the kinematics of a droplet impacting on a soap film are studied with the help of a high-speed cameral. The impacting Weber number of the droplet varies from 10 to more than 350. The droplet position and velocity are extracted from the video by a self-designed Matlab codes.
Experimental results show that the droplet may pass through the soap film in five modes, i.e., bouncing, bagless packaging, package peeling, bag packaging, and instaneous coalescence. A "drop-cushion-shell"-type compound droplet can be formatted in bag-[We ∈ (10.8, 60)] and bagless[We ∈ (120, 240)] packaging mode, while in the package peeling[We ∈ (60, 120)] and coalescence[We ∈ (240, 350)] mode it will form single phase droplets, however, with the surface coated with a soap solution layer (original soap film). Although compound droplets have three surfaces, i.e., the droplet's original surface and the inner and outer surface of the soap film, the apparent surface tension for the bagless-packed droplet is just that of the soap solution, while for the bag-packed droplet it is the sum of the three surface tensions. The outer shell of the compound droplet may peel off and eject a bubble when the Weber number is in the certain range (We ∈ (60, 120) for droplet with D0=3.0 mm), the lower limit decreases and the upper limit increases with the increase of the initial diameter of the droplets and thus expands the bubble-shooting range. The droplet performs a free fall motion, however, it is interfered by the soap film. The droplet can be stopped and rebounded when We < 10.8, and penetrate the film and start another free fall when We > 10.8. The velocity loss before and after the penetration decrease with impact velocity increasing, hence the motion of the higher We droplet is less retarded by the soap film, the motion curve approaches to the free fall curve. The approaching is not a linear but an accelerating behavior.

Temperature-dependent properties of metastable graphene oxide Hot!

Mo Jia-Wei, Qiu Yin-Wei, Yi Ruo-Bing, Wu Jun, Wang Zhi-Kun, Zhao Li-Hua
Acta Physica Sinica. 2019, 68 (15): 156501 doi: 10.7498/aps.68.20190670
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Monolayer of graphene oxide has great potential applications in ion and molecular screening, desalination and purification of water, gas separation, biosensing, proton conductors, lithium batteries, super capacitors and other fields, due to its excellent physical and chemical properties. However, the graphene oxide prepared by chemical and physical methods, such as the commonly used Hummers method is a metastable material. The transformation and regulation of the physical and chemical properties of the final morphology are essential, and systematic research is urgently needed. In this paper, the thermostat treatment method is used to control the metastable transformation of graphene oxide. The relationship of content, type, and morphology with temperature of oxygen-containing graphene oxide are detected by X-ray photoelectron absorption spectroscopy, Fourier infrared absorption spectroscopy, scanning electron microscope, etc.; and the effects of temperature on the stability of solution suspension stability, photon energy band and tensile strength of graphene oxide in the transformation process are analyzed by using Zeta potential, ultraviolet absorption spectrum, tensile force. The quantitative test results show that there exists a phenomenon in which the epoxy phase decreases, the hydroxyl group increases and the overall oxygen content decreases in the metastable transition process of graphene oxide, and the monolayer morphology of graphene oxide does not change significantly in this process. This structural transformation, however, greatly enhances the viscosity and hydrophilicity of the suspension, and remarkably reduces the energy band and considerably raises the tensile strength enhancement effect. When the transformation process is long enough, the hydrophilicity of the graphene oxide will decrease and precipitate. It is indicated that a further dehydration transition occurs between the hydroxyl groups. In addition, in the paper we also analyze the effect of constant temperature treatment time and concentration of suspension on this transformation process. The relevant research results are helpful in understanding the performance change of metastable graphene oxide suspension with temperature, and have certain reference value for the specific application of graphene oxide.

On the derivation of local mean pressure tensor for nonuniform systems and the analysis of uniform fluid

Cui Shu-Wen, Liu Wei-Wei, Zhu Ru-Zeng, Qian Ping
Acta Physica Sinica. 2019, 68 (15): 156801 doi: 10.7498/aps.68.20182189
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The expression of equilibrium pressure tensor for uniform systems derived from Virial theorem can be divided into two parts:dynamic pressure tensor and configuration pressure tensor. The local mean pressure tensor is obtained by physical analysis of the equilibrium non-uniform system. In this paper, this expression is derived in a more concise way. The theoretical relationship, with undetermined parameters, between the three parts (the volume contribution, the surface contribution and the line contribution) of the average configuration pressure of a homogeneous fluid system and the local average size L* with the atomic diameter as length unit greater than 8 is given. Taking argon as an example, molecular dynamics simulation is carried out by using the Lennard-Jones potential between atoms at temperature 180 K and density 0.8 (atomic diameter)-3. The simulation curves of configuration pressure and its three parts are given, and the undetermined coefficients in the theoretical relationship under the condition of L* > 8 are determined. It is found that for L* > 2, With the increase of L*, the volume contribution decreases monotonously from the positive pressure to the negative total configuration pressure, while the surface contribution and the line contribution both increase monotonously and tend to zero, but the line contribution tends to zero fastest. The complex characteristics of various behaviors are explained physically. It is concluded that the surface contribution and the line contribution can be neglected only if L* are large enough. In nanoscale, the neglect of the surface contribution and the line contribution, i.e., the neglect of the boundary effect, will bring obvious errors to the calculation. Finally, molecular dynamics simulation shows that the configuration pressure increases with the increase of temperature. These conclusions are significant for optimizing the selection of pressure tensor in molecular dynamics simulation.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Electronic structures and Li diffusion in cathode material Li2FeO2 of Li-ion batteries

Lin Chuan-Jin, Zheng Feng, Zhu Zi-Zhong
Acta Physica Sinica. 2019, 68 (15): 157201 doi: 10.7498/aps.68.20190213
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The electronic structures and lithium diffusion in the cathode material Immm-Li2FeO2 of lithium-ion batteries are calculated by the first-principles method based on the density functional theory. The calculated results show that Immm-Li2FeO2 is ferromagnetic, and the band structure indicates a semi-metal character. The d-electrons of Fe ions are in the low spin state, with a spin polarization of 8.01%. The spin-up and spin-down band structure are also analyzed by using the l-decomposed electronic density of states. Furthermore, the energy barriers for the lithium ion diffusion in different directions are calculated by the nudged elastic band method. For comparison, the potential barriers for the Li2MO2 (M=Co, Ni, Cu) are also calculated. The results suggest that it is easier for Li ion to diffuse in the c-axis directionof Li2FeO2, with an energy barrier of only 0.1 eV. The energy barrier is 0.21 eV for Li to diffuse in the ab-axis direction, while the diffusion barrier is 0.39 eV along the a-axis direction of Li2FeO2. All these values of energy barriers are lower than those in other Fe-based cathodes mentioned, indicating that the Li diffusion coefficient in Immm-Li2FeO2 should be larger than those of other materials, which also indicates that the Li2FeO2 is of great importance as cathode material.

Structure and half-metallic ferromagnetism of quaternary Heusler compounds CoMnZnZ

Xu Jia-Ling, Jia Li-Yun, Jin Xiao-Qing, Hao Xing-Nan, Ma Li, Hou Deng-Lu
Acta Physica Sinica. 2019, 68 (15): 157501 doi: 10.7498/aps.68.20190207
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Using the first principle full-potential linearized augmented wave method we study the electronic structure and elastic and magnetic properties of CoMnZnZ (Z=Si, Ge, Sn, Pb) LiMgPdSn-type Heusler alloys. These compounds have the composition CoMnZnZ with 1:1:1:1 stoichiometry, where Z denotes the main group element Si, or Ge, or Sn, or Pb. The exchange-correlations are treated within the generalized gradient approximation of Perdewe-Burke-Ernzerhof. For each of all studied Heusler alloys, the ferromagnetic state is considered to be more stable than the paramagnetic state, judged by the energy. The total energy of the magnetic calculation is lower than that of the nonmagnetic state for each of all three serise compounds at the equilibrium lattice constant, indicating that the magnetic state is more stable than the nonmagnetic state. We determine the elastic constants C11, C12 and C44, which have not been established previously in experiment nor in theory. The elastic constant indicates the weakened resistance to sheardeformation compared with the resistance to unidirectional compression. We derive other mechanical parameters, i.e., the shear modulus G, Young's modulus E, Poisson's ratio ν, and shear anisotropic factor A, which are the important elastic moduli for applications. These compounds each have a lower anisotropy and possess a low probability to develop micro-crack or structural defect in its growing process. The sound velocity and Debye temperature for each of the CoMnZnZ (Z=Si, Ge, Sn, Pb) compounds in their stable structure are calculated. The CoMnZnPb exhibits the lowest Debye temperature, and the highest value is observed for CoMnZnGe. The electronic structure calculations show that CoMnZnZ (Z=Si, Ge, Sn) each exhibit a gap in the band of minority states, and they are clearly half-metallic ferromagnets, except for the CoMnZnPb. The CoMnZnZ (Z=Si, Ge, Sn) compounds and their magnetic moments are in reasonable agreement with the Slater-Pauling rule, and they comply with a Slater-Pauling rule of Mt=Zt-28, which indicates the half metallicity and high spin polarization for these compounds. The CoMnZnSi compound has the largest half-metallic gap value and the gap is about 0.66 eV. The magnetic properties are primarily determined by the Mn atoms, which contribute the highest magnetic moments. The localmoment of the Z element atom is negligibly small. The hybridization of the d orbitals between Co and Mn can explain the origin of the Slater-Pauling rule in half-metallic quaternary Heusler alloys. The half-metallic gap comes mainly from the interaction between the Co and Mn atoms.

Software realization of physical property calculation model based on effective medium theory

Sun Nan-Nan, Shi Zhan, Ding Qi, Xu Wei-Wei, Shen Yang, Nan Ce-Wen
Acta Physica Sinica. 2019, 68 (15): 157701 doi: 10.7498/aps.68.20182273
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In this paper, a composite physical property calculation software-Composite Studio is developed based on the modified effective medium theory. The computing kernel of the software is written in C++ language and its GUI is designed by Qt. With the development of the computation technique, the material genome project is proposed, which tries to shorten the period of the material design by high-throughput computation, data mining and property database establishment. On a mesoscopic scale, there are several kinds of the models to calculate the physical properties of the composite materials. However, these models usually have the formula in quite a lot of kinds of forms. A general commercial software for physical property calculation on a mesoscopic scale is still leaking. The software uses Green's function to solve the constitutive equations. It calculates the effects of microstructural factors on physical properties. These factors include volume fraction, aspect ratio of reinforce particles, orientation distribution, and macroscopic orientation. It can obtain more than 10000 composites by freely combining four microstructure factors. The operation process of software includes 5 steps. The first step is to choose the materials of matrix and reinforcement. The second step is to select the shape type of reinforcement. The third step is to set the range of values for the microstructure factors of the composite materials. The fourth step is to choose the calculation model and start calculations. The last step is to plot and analyze the results. In addition, researchers can directly have the calculation results through the single point analysis module of the software. We use several two-dimensional line plots to display multi-dimensional calculation results. This is convenient and efficient for researchers to observe and analyze the results. Until now, two calculation modules were developed in Composite Studio, i.e. the elastic modulus calculation module and the dielectric constant calculation module. The software can be applied to different computer systems. In the future, the Composite Studio can be used as a general-purpose calculation tool embedded into an server platform for popular composite design.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Dynamic impact strength of diamond-SiC superhard composite

Li Yuan-Yuan, Yu Yin, Meng Chuan-Min, Zhang Lu, Wang Tao, Li Yong-Qiang, He Hong-Liang, He Duan-Wei
Acta Physica Sinica. 2019, 68 (15): 158101 doi: 10.7498/aps.68.20190350
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Unlike the ductile materials, the failure seriously limits the strength of the brittle medium. To understand the mechanism of controlling the dynamic impact strength of diamond-SiC superhard composite under shock wave compression, the numerical simulation is conducted with a lattice-spring model that can describe the mechanical properties of diamond-SiC superhard composite quantitatively. For the simulation, the diamond-SiC superhard composite is constructed by different volume content of diamond and SiC particles. The obtainted shock wave profiles indicate that the dynamic impact strength first increases and then decreases with the increase of diamond content in the sample. The analysis based on the meso-scale damage pattern reveals that such a variation of dynamic impact strength corresponds to three damage evolution modes. When the diamond content increases to a value between 10%-50% in volume percentage, the long slip bands are first dominated, and then becomes short slip bands when the diamond content is 70%, and damage happens mainly in SiC matrix whereas most of the diamond particles are not damaged. When the diamond content is above a critical value of 70% in volume percentage, even the short slip bands are limited heavily, which makes it difficult to relax the shear stress on diamond particles and causes serious damage to diamond particles, finally results in the reduction of dynamic strength.

In situ observation of lithiation mechanism of SnO2 nanoparticles Hot!

Xiong Yu-Wei, Yin Kui-Bo, Wen Yi-Feng, Xin Lei, Yao Li-Bing, Zhu Chong-Yang, Sun Li-Tao
Acta Physica Sinica. 2019, 68 (15): 158201 doi: 10.7498/aps.68.20190431
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Tin oxide (SnO2) has attracted a lot of attention among lithium ion battery anode materials due to its rich reserves, high theoretical capacity, and safe potential. However, the mechanism of the SnO2 nano materials in the lithiation-delithiation reaction, especially whether the first-step conversion reaction is reversible, is still controversial. In this paper, SnO2 nanoparticles with an average particle size of 4.4 nm are successfully prepared via a simple hydrothermal method. A nanosized lithium ion battery that enables the in situ electrochemical experiments of SnO2 nanoparticles is constructed to investigate the electrochemical behavior of SnO2 in lithiation-delithiation process. Briefly, the nanosized electrochemical cell consists of a SnO2 working electrode, a metal lithium (Li) counter electrode on a sharp tungsten probe, and a solid electrolyte of lithium oxide (Li2O) layer naturally grown on the surface of metal Li. Then, the whole lithiation-delithiation process of SnO2 nanocrystals is tracked in real time. When a constant potential of -2 V is applied to the SnO2 with respect to lithium, lithium ions begin to diffuse from one side of the nanoparticles, which is in contact with the Li/Li2O layer, and gradually propagate to the other side. Upon the lithiation, a two-step conversion reaction mechanism is revealed:SnO2 is first converted into intermediate phase of Sn with an average diameter of 4.2 nm which is then further converted into Li22Sn5. Upon the delithiation, a potential of 2 V is applied and Li22Sn5 phase can be reconverted into SnO2 phase when completely delithiated. It is because the interfaces and grain boundaries of nano-sized SnO2 may impede the Sn diffusing from one grain into another during lithiation/delithiation and then suppress the coarsening of Sn, and enable the Li2O and Sn to be sufficiently contacted with each other and then converted into SnO2. This work provides a valuable insight into an understanding of phase evolution in the lithiation-delithiation process of SnO2 and the results are of great significance for improving the reversible capacity and cycle performance of lithium ion batteries with SnO2 electrodes.

Electro-static discharge protection analysis and design optimization of interlayer Cu interconnection in InGaZnO thin film transistor backplane

Ma Qun-Gang, Wang Hai-Hong, Zhang Sheng-Dong, Chen Xu, Wang Ting-Ting
Acta Physica Sinica. 2019, 68 (15): 158501 doi: 10.7498/aps.68.20190646
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The InGaZnO thin film transistor (IGZO TFT) backplane combined with Cu interconnection has nearly an order of magnitude lower in the ability to withstand voltage than that of traditional a-Si TFT backplane on the production line. The breakdown voltage of Mo/Cu interconnection between data line and gate line is only about 60% of that of traditional a-Si TFT backplane. The electrostatic discharge (ESD) breakdown of Mo/Cu:SiNx/SiO2:Mo/Cu structure has become an important factor affecting the normal display of IGZO TFT ultra high definition (UHD) panel. We find that the anti-ESD damage ability of IGZO TFT devices needs matching with the anti-ESD damage ability of interlayer Cu interconnection in order to achieve a high-robustness IGZO TFT backplane. The position of ESD damage in IGZO TFT backplane is commonly in the climbing place where the data line crosses the scanning line. In this paper, a Cu diffusion model is proposed to explain the mechanism for the ESD failure of interlayer Cu interconnection. The Cu metal in gate line diffuses into SiNx/SiO2 gate insulator, and Cu metal at the corner of data line, where the date line crosses the gate line, diffuses into SiO2 film on the date line. The selection conditions of three kinds of protection architectures for ESD protection circuits around Cu interconnection, i.e. R-type, R-half-type, and Diode-type protection architectures, are proposed. On the basis of process optimization such as Cu metal film forming and Cu metal interface treatment, an ESD protection method for the Cu interconnection periphery of IGZO TFT backplane with high robustness is proposed. For the stable production process of IGZO TFT, combined with the design window of ESD protection circuit, the peripheral ESD protection circuit of Cu interconnect is designed with diode-type protection circuit on the IGZO TFT backplane of large-sized UHD and QUHD panel, which effectively improves the effect of interlayer Cu interconnection of IGZO TFT backplane on ESD damage. Through the production verification, it is proved that the metal diffusion of Cu interconnection on IGZO TFT backplane is the fundamental reason for reducing the anti-ESD damage ability of Mo/Cu:SiNx/SiO2:Mo/Cu structure. The rationality of the proposed ESD damage model for interlayer Cu interconnection is verified, which provides a theoretical basis for subsequent IGZO TFT backplane design with high robustness.

Demonstration of wide-bandgap GaN-based heterojunction vertical Hall sensors for high-temperature magnetic field detection

Cao Ya-Qing, Huang Huo-Lin, Sun Zhong-Hao, Li Fei-Yu, Bai Hong-Liang, Zhang Hui, Sun Nan, Yung C. Liang
Acta Physica Sinica. 2019, 68 (15): 158502 doi: 10.7498/aps.68.20190413
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Magnetic fields are generally sensed by a device that makes use of the Hall effect. Hall-effect sensors are widely used for proximity switching, positioning, speed detecting for the purpose of control and condition monitoring. Currently, the Hall sensor products are mainly based on the narrow-bandgap Si or GaAs semiconductor, and they are suitable for room temperature or low temperature environment, while the novel wide-bandgap GaN-based Hall sensors are more suitable for the application in various high-temperature environments. However, the spatial structure of the GaN-based sensor is mainly horizontal and hence it is only able to detect the magnetic field perpendicular to it. To detect the parallel field on the sensor surface, the vertical structure device is required despite encountering many difficulties in technology, for example reducing the vertical electric field in the two-dimensional electron gas (2-DEG) channel. The vertical Hall sensor has not been reported so far, so it is technically impossible to realize three-dimensional magnetic field detection on single chip. To address the mentioned issues, in this paper we propose a design of the vertical Hall sensor based on the wide-bandgap AlGaN/GaN heterojunction material, which adopts a shallow etching of 2-DEG channel barrier to form a locally trenched structure. The material parameters and physical models of the proposed device are first calibrated against real device test data, and then the key structural parameters such as device electrode spacing ratio, mesa width and sensing electrode length are optimized by using technology computer aided design, and the device characteristics are analyzed. Finally, the simulation results confirm that the proposed Hall sensor has a higher sensitivity of magnetic field detection and lower temperature drift coefficient (~600 ppm/K), and the device can work stably in a high-temperature (greater than 500 K) environment. Therefore, the vertical and horizontal devices can be fabricated simultaneously on the same wafer in the future, thus achieving a three-dimensional magnetic field detection in various high-temperature environments.

GENERAL

Control of maximum evolution speed of quantum states by two-mode entangled light field

Tian Cong, Lu Xiang, Zhang Ying-Jie, Xia Yun-Jie
Acta Physica Sinica. 2019, 68 (15): 150301 doi: 10.7498/aps.68.20190385
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We consider a two-mode entangled coherent light field, in which one mode of the light field is injected into the cavity and interacts with a two-level atom. According to the theory of cavity electrodynamics, the evolution state of atomic system is deduced. Aiming at the dynamic process from the initial state of an atomic system to the target evolution state, the quantum speed limit time is used to characterize the maximum evolution rate of the quantum state of an atomic system. The maximum evolution rate of an atomic system can be controlled by adjusting the coherent parameters of the two-mode entangled coherent light field. But up to now, which kind of quantum speed limit time can be better, universal and strict applicable to the quantum dynamics process of any system is still an unresolved important issue. Based on different methods of measuring the distance between two quantum states and different dynamic evolution channels, many definitions of the quantum speed limit time have been given. The quantum speed limit time proposed by Deffner and Lutz (Deffner S, Lutz E 2013 Phys. Rev. Lett. 111 010402) and the other deduced by Campaioli et al. (Campaioli F, Pollock F A, Binder F C, Modi K 2018 Phys. Rev. Lett. 120 060409; Campaioli F, Pollock F A, Modi K 2018 arXiv:1806.08742) have attracted extensive attention. In this paper, we first compare the advantages of two quantum speed limit times to characterize the maximum evolution rate of quantum states. We find that the quantum speed limit time expression given by Campaioli et al. (Campaioli F, Pollock F A, Modi K 2018 arXiv:1806.08742) in 2018 is a tighter bound when describing the boundary of the shortest time required for the quantum state evolution of a two-level atomic system. Therefore, this paper is mainly based on the quantum speed limit time given by Campaioli et al. to analyze how to achieve the maximum evolution rate of the quantum state of the atomic system by manipulating the parameters of a two-level entangled coherent light field. The results show that the maximum evolution speed of the quantum state of the atomic system can be significantly affected by the coherent parameters of the light field interacting with the atom under certain conditions. Furthermore, when the interacting light field parameters cannot well control the maximum evolution speed of the quantum state, the quantum correlation with the two-mode entangled coherent light field can realize the remote control of the maximum evolution speed of quantum state of atomic system by the light field parameters that are not involved in the atom-light interaction.

Dynamic analysis of rumor propagation model based on true information spreader

Zhang Ju-Ping, Guo Hao-Ming, Jing Wen-Jun, Jin Zhen
Acta Physica Sinica. 2019, 68 (15): 150501 doi: 10.7498/aps.68.20190191
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In the process of rumor propagation, people who know the truth or judge the truth can spread true information about rumors. Therefore, on the rumor propagation, it is significant to introduce the spreaders who spread true information in the rumor propagation. But the previous studies did not take into consideration the influence of true information spreading on the rumor propagation. In this paper, the susceptible-infective-true-removed (SITR) rumor propagation model with the true information spreader and the forgetting factor of rumors is established. The threshold K0 is obtained by using the method of the next generation matrix. If K0 < 1, the balance between no rumor and no true information spreader is locally asymptotically stable. The existence and stability of two boundary balance (that is, there are rumor spreaders but no true information spreaders, and there are no rumor spreaders but true information spreaders) are proved. The bistable region of two-boundary balance is given. Further, under different conditions we obtain the existence and locally asymptotical stability of positive balance (rumor spreaders and true information spreaders coexist). Finally, the theoretical results are verified by numerical simulations. We find that the initial value of the true information spreaders affects the peak value of the rumor spreaders and the duration of the rumor. The bigger the initial value of the true information spreaders, the smaller the peak value of the rumor spreaders is and the shorter the duration of the rumor is. The initial value of the rumor spreaders affects the peak value of the rumor spreaders, and the time when the rumor spreaders reach the peak value. The larger the initial value of the rumor spreaders, the larger the peak value of the rumor spreaders is and the earlier the peak value appears. But the initial value of the rumor spreaders does not affect the duration of the rumor. Therefore, in the process of rumor propagation, according to mathematical analysis of the rumor propagation model, we find that the rumor spread is a very complicated process. The results of mathematical analysis can provide theoretical basis to control the rumor propagation and reduce the negative effects of rumors.

NUCLEAR PHYSICS

Experimental study on fission reaction rate induced by D-T neutron in depleted uranium shell

Han Zi-Jie, Zhu Tong-Hua, Lu Xin-Xin, Qin Jian-Guo, Wang Mei, Jiang Li, Yang Bo
Acta Physica Sinica. 2019, 68 (15): 152501 doi: 10.7498/aps.68.20181717
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Fission reaction rate is an important index for validating and checking the neutron transportation and fission power in nuclear engineering. The experimental data can be used in benchmark validation of cross sections, and in studying the correlation of fission power with the thickness of uranium sphere shell. There are five assemblies of depleted uranium shells used in this work, the inner radii of which are all fixed at 13.1 cm, while their outer radii are 18.1, 19.4, 23.35, 25.4 and 28.5 cm, respectively. The D-T neutron source is generated in the center of the assemblies, the yield of which is about 3×1010-4×1010 s-1. In horizontal plane across the center of the assemblies, the fission rates at positions along the radial direction are measured in the direction with 45° inclining with respect to the incident D+ beam. Due to the disturbance to assemblies and neutron field, the activation foil of uranium is a suitable choice rather than fission chamber or capture detector. The material of activation foil is the same as that in the experimental assemblies. Considering the accurate fission yield of 143Ce, the objective nuclides are selected. The total fission yield of 143Ce is contributed by 238U and a little 235U. For calculating the total fission yiled of 143Ce, the neutron energy range of 0-15 MeV is divided into eight subranges. By measuring the 293 keV gamma rays from the fission product 143Ce in activation foils with a TRANS-SPEC-DX100 HPGe detector, with a relative efficiency 40%, the fission rates and the trends at positions along the radial direction in the five assemblies are obtained based on the 143Ce fission product yield. The fission rate ranges from 5.28×10-29 to 7.58×10-28 sn-1·nuclide-1, with the relative uncertainty in a range from 6% to 11%. The Monte Carlo transport code MCNP5 and continuous energy cross section library ENDF/BV.8 are used for analyzing the fission rate distribution in the assemblies, and the experiemtal configuration, including the wall of the experimental hall is described in detail in the model. The calculated results are compared with the experimental ones and their agreement is found to be in an uncertainty range.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Omnidirectional cloaking based on spoof surface plasmonic structure

Quan Jia-Qi, Sheng Zong-Qiang, Wu Hong-Wei
Acta Physica Sinica. 2019, 68 (15): 154101 doi: 10.7498/aps.68.20190283
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Surface plasmons include surface plasmon polaritons and localized surface plasmons, which are electromagnetic wave confined at the interface of the metal and dielectric. Spoof surface plasmonic structure has many special optical properties, which is of great significance for designing new-generation optical elements. In order to transfer the features of the surface plasmon polaritons and localized surface plasmons to microwave-terahertz region, Pendry et al. (Pendry J B, Martin-Moreno L, Garcia-Vidal F J 2004 Science 305 847) have proposed the spoof surface plasmon polaritons based on a metal structure with grooved stripes. In this paper, a hollow textured perfect electric conductor cylinder with periodic cut-through slits structure is designed to suppress the light scattering of the object in any direction and achieve the effect of omnidirectional cloaking while the transverse magnetic polarization wave propagates along the x direction. And the locations of the electrical and magnetic modes can be freely modulated by tailoring the structural geometric construction. In order to find the physical mechanism behind the abnormal phenomenon, through theoretical analysis and numerical simulation, we find that the strong scattering suppression of this spoof surface plasmonic polariton structure is caused by the interference between the background wave and Mie scattering of the structural unit, and it can be equivalent to a ring metamaterial due to the special structural design, in order to achieve the omnidirectional cloaking. It implies that we can hide objects in metal strips due to the fact that the metal in the microwave-to-terahertz region is equivalent to a perfect electrical conductor. This opens up a new way to analyzing the physical cloaking and optical response of spoof surface plasmonic polaritons structure. In addition, we also analyze the influence of the structure on the movement law of the scattering spectrum under different structural parameters. This enables us to have an in-depth understanding of the influence of structural parameters on the structural scattering spectrum. Our results can be applied to the microwave-to-terahertz region and a variety of advanced optic devices such as radars, cloaking coatings, sensors and detectors.

Theoretical analysis and design of G-band extended interaction klystron amplifier

Zeng Zao-Jin, Ma Qiao-Sheng, Hu Lin-Lin, Jiang Yi, Hu Peng, Chen Hong-Bin
Acta Physica Sinica. 2019, 68 (15): 154102 doi: 10.7498/aps.68.20190264
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Extended interaction klystron is a very important millimeter-wave and sub-millimeter-wave vacuum electron device with many actual and potential applications, such as space-borne cloud profiling radar, communication, imaging system, precision guided missiles, etc. Kinematical theory and space charge wave theory are extensively used to analyze the bunching process of electrons. Kinematical theory is precise when electron beam is especially small because the influence of space charge effect is ignored, while space charge wave theory is accurate when the modulation of electron beam is small since it is based on the premise of small amplitude. Based on kinematical theory, law of induce current, principle of charge conservation in a one-dimensioanl mode and small signal condition, the influence of electron beam on standing wave electric field in multiple-gap cavity is analyzed, and the expression of beam-loading conductance and beam-loading susceptance in multiple-gap cavity are derived. The influence of the direct current transmit angle of single gap, the number of multiple gaps and the direct current transmit angle of between center of adjacent gaps on beam-loading conductance and beam-loading susceptance are analyzed. The results show that the beam-loading conductance and beam-loading susceptance of multiple-gap cavity can change to a bigger extent when the number of cavity gaps is bigger, which means that the maximum beam-wave conversion efficiency and the range of loaded frequency increase with the number of cavity gaps increasing. The results also show that the direct current transmit angle between centers of adjacent gaps is the most important parameter for the beam-wave interaction effect. Based on the above analysis, a G-band extended interaction klystron amplifier consisting of three five-gap cavities is designed by an three-dimensional PIC code. An output power of 225.5 W at 217.94 GHz with an efficiency of 6.26%, whose gain and 3 dB bandwidth are 30.5 dB and 470 MHz respectively, is obtained by simulation. This study is of great significance for the physical design and process in engineering the G-band extended interaction klystron amplifier.

Generation and characteristics of shock optical pulses based on a fiber-loop time-lens system

Xiao Hong-Jing, Huang Chao, Tang Yu-Long, Xu Jian-Qiu
Acta Physica Sinica. 2019, 68 (15): 154201 doi: 10.7498/aps.68.20190246
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The shock ignition scheme has the advantages of low ignition energy threshold, high gain, and good hydrodynamic stability, which has become one of the key schemes for the potentially successful ignition of inertial confinement fusion. The crucial element of shock ignition is how to achieve a highly efficient shock laser pulse. We propose a new scheme based on a time-lens system combining the fiber-loop phase modulation and the grating-pair compression to generate a highly controllable shock pulse. Based on the asymmetric phase modulation in time-domain followed by linear dispersion compensation in frequency domain, the shock pulse can be actively controlled with high precision in both pulse duration and pulse contrast (peak power ratio of the compression part to the shock part of the pulse). We construct a theoretical model based on the nonlinear Schrödinger equation to simulate the evolution of the spectrum and temporal shape of the shock laser pulse. The influences of various key parameters of the proposed system on the characteristics of the generated shock pulse are analyzed in depth.
The time lens system consists of three parts, i.e. the seed pulse carving part, the phase modulation loop, and the chirp-compensating grating pair. The operation principle of this system for generating shock pulse is as follows. First, a single-mode continuous wave 1053 nm distributed feedback seed laser is chopped into pulses with a Mach-Zehnder intensity modulator. Then the pulses enter into a fiber-loop for phase modulation. Owing to different modulation frequencies exerted on the left and right side of the pulse, the amount of spectral broadening of these two sides of the spectrum are also different after phase modulation. The spectrally broadened pulses are linearly chirped when the phase-modulation function has a parabolic shape. Finally, the pulse transits through a grating pair system for chirp compensating. Just like an anomalous dispersion delay line, the grating pair applies an anomalous group velocity dispersion to the passing optical pulse. When the chirp is compensated for appropriately, the pulse will be compressed. What the target pulse can be finally shaped into is dependent on the combined optimization of all the above processes.
The simulation results show that by systematically designing the parameters such as chopping function, phase modulation function, modulation depth, modulation frequency, and chirp compensating, the target shock pulse can be actively controlled with high-precision in the pulse width, pulse rising edge, and peak-power contrast. In addition, we can also tune only one parameter (such as the pulse width) of the pulse, with the other parameters kept unchanged. This new design idea and the proposed system can actively and independently adjust the two key parameters (the peak power contrast and the pulse width) of the generated shock pulse, which is not only helpful in deepening our understanding of the principle of laser-pulse shaping, but also significant for the subsequent practical implement of shock ignition of inertial confinement fusion.

Continuously spacing-tunable dual-wavelength erbium-doped fiber laser based on polarization-dependent in-line multimode-single-mode-multimode fiber filter

Peng Wan-Jing, Liu Peng
Acta Physica Sinica. 2019, 68 (15): 154202 doi: 10.7498/aps.68.20190297
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A continuously spacing-tunable dual-wavelength erbium-doped all-fiber laser is proposed and experimentally demonstrated in this paper. The key component of the laser is a novel polarization-maintained multimode-single-mode-multimode fiber interference filter, which is composed of two single-mode-multimode-single-mode fiber mode converters with a polarization-maintaining fiber sandwiched between them. As the polarization-maintaining fiber gives rise to a polarization-dependent phase difference, the fiber filter shows good polarization-dependent characteristics in interference filtering. Based on the mode interference and polarization control, the good wavelength tuning results are obtained in experiment. An optimized length of 1.3 mm for multimode fiber and 1.5 mm for polarization-maintaining fiber are adopted based on the theoretical and experimental analysis. When the phase difference between the lasing in the fast axial direction and that in the slow axial direction is $ π, the peaks and valleys in the transmission spectrum of the fiber filter correspond exactly to the two orthogonal polarization states. In the test, when the pump power is 50 mW, a high-quality dual-wavelength lasing output (at 1544.82 nm and 1545.61 nm) is observed to have side-mode suppression ratio better than 45 dB, the wavelength spacing of 0.8 nm, the peak power difference of less than 1 dB, and the output keeps stable with a small power fluctuation less than 0.7 dB. By adjusting the polarization controller in the ring cavity, two different dual-wavelength outputs can be obtained, which are corresponding to tuning Ⅰ and tuning Ⅱ. In tuning Ⅰ, a dual-wavelength lasing output in a wavelength spacing tuning range of 0-1.2 nm can be obtained within 1 dB peak power difference, correspondingly, 0-1.6 nm tuning range within 10 dB peak power difference. In tuning Ⅱ, with continuously adjusting the polarization controller, the short wavelength signal of the dual-wavelength output stops resonating, and simultaneously another wavelength signal near 1547.8 nm is excited, the switching is continuous and the system remains dual-wavelength output. In tuning Ⅱ, a maximum tuning range of 1.6-3 nm is obtained. In both of tuning Ⅰ and tuning Ⅱ, a 0-3 nm continuously spacing-tunable dual-wavelength output is obtained, all of which keep stable single-polarization operation. The test results show that the polarization state of the dual-wavelength lasing varies with tuning; a maximum polarization extinction ratio of 35 dB is obtained as the two wavelengths are orthogonally polarized.

Dispersion characteristics of nonreciprocal gyroelectric silicon-on-insulator rectangular waveguide

Wang Hui-Ying, Wang Zhi, Cui Can, Li Hang-Tian, Li Qiang, Zhan Xiang-Kong, Wang Jian, Wu Chong-Qing
Acta Physica Sinica. 2019, 68 (15): 154203 doi: 10.7498/aps.68.20190109
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A C-band rectangular waveguide with gyroelectric semiconductor is designed to study the non-reciprocal propagation characteristics of surface magnetoplasmons (SMPs), which are generated by an external magnetic field. The effective refractive index method is used to obtain the effective refractive index and transverse electric field distribution of the waveguide, and a two-dimensional rectangular waveguide is approximately regarded as a combination of two one-dimensional planar waveguides. The dispersion equation of planar waveguide with Emnx mode in rectangular waveguide is derived. The influences of the structural parameters of rectangular waveguide and the refractive index of material on the non-reciprocal dispersion relation and time-delay characteristics are analyzed by numerical method. Due to the effect of external magnetic field, the off-diagonal elements of dielectric tensor in magnetic photonic crystal are changed. The generation of electrical anisotropy leads the time reversal symmetry to be broken. As a result, the dispersion curves of the rectangular waveguide are asymmetric with respect to propagation constant, and the complete one-way transmission of SMPs can be realized in the asymmetric frequency region. The dispersion curve tends to be a dispersion curve of planar waveguide as the width of rectangular waveguide increases, but the non-reciprocal frequency range is approximately unchanged. The width of the core region and the refractive index of the side material have a significant influence on the non-reciprocal dispersion characteristics:the group velocity of SMPs decreases with ω and propagation constant decreasing. The group velocity is related to the waveguide width, propagation constant and the operating wavelength. The relationship between the normalized group velocity and the width of the waveguide separately operating at 1530, 1550 and 1565 nm are studied. The group velocity is relatively slow when the width of waveguide's core region is between 140 nm and 233.5 nm, and the minimum group velocity reaches 5.43×10-2c. As for the slow light effect, the rectangular waveguide is better than planar waveguide. The rectangular waveguide has a large engineering tolerance in the width of core region, which is 93.5 nm. In addition, the dispersion curves of the rectangular waveguide with SiO2, Air, Au and Ag as the left and right cladding layers are calculated. As a result, the group velocity is proportional to the refractive index of the side material in the y direction of the rectangular waveguide. The slow light effect is the most obvious when the material is silver, and the minimum transmission speed can reach 2.8×10-3c.

Bouncing-with-spray mode and residence time of droplet impact on heated surfaces

Rong Song, Shen Shi-Quan, Wang Tian-You, Che Zhi-Zhao
Acta Physica Sinica. 2019, 68 (15): 154701 doi: 10.7498/aps.68.20190097
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The impact of droplets on surfaces is a ubiquitous phenomenon, and reducing the droplet residence time is the aim of many studies because of the potential applications in self-cleaning, anti-icing, corrosion resistance, etc. This study identifies a mode of droplet bouncing (bouncing-with-spray) that can reduce the residence time significantly. And compared with the way of using complex microstructures on the substrate employed in previous studies, simply heating the substrate to reduce the residence time is novel and simple. The dimensionless residence time decreases down to about 40% compared with that from the traditional retraction-bouncing mode. The reduction in the residence time is due to the burst of vapor bubbles in the liquid film, which results in holes forming in the liquid film and consequently the liquid film recoiling from the holes. The reduction in the recoiling distance leads to the reduction in the recoiling time. Then a simplified theoretical model with considering the energy balance and the critical condition of the bubble burst is proposed. According to this theoretical model, a scaling law is proposed for the transition boundary between the retraction-bouncing mode and the bouncing-with-spray mode in the film boiling regime, and it accords well with our experimental data. This model can also explain the transition boundary between these two modes in the transition boiling regime.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Proton imaging of relativistic laser-produced near-critical-density plasma

Li Yao-Jun, Yue Dong-Ning, Deng Yan-Qing, Zhao Xu, Wei Wen-Qing, Ge Xu-Lei, Yuan Xiao-Hui, Liu Feng, Chen Li-Ming
Acta Physica Sinica. 2019, 68 (15): 155201 doi: 10.7498/aps.68.20190610
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When ultrashort pulse laser interacts with near-critical-density plasma, extremely strong transient electromagnetic field will generate a great variety of nonlinear phenomena, such as efficient pulse absorption, magnetic self-channeling, nonlinear coherent structure, and electron and ion acceleration. It is of great significance to make a profound study of these physical processes for studying the laser-plasma interaction. Here in this work, we investigate the near-critical-density plasma structure and its temporal evolution by using proton radiography. The plasma is generated by the interaction of ultra-intense femtosecond laser (I~3.6×1018 W/cm2) with high-density gas-jet target, which can produce plasma with electron density ne~0.7nc (here, nc is the near-critical-density) for 800 nm laser. The proton beam is produced by the interaction of another ultra-intense femtosecond laser with stainless steel foil target. In the experiment, the proton beam is split into two asymmetric spots. On the one hand, the distance between two spots first increases rapidly and decreases slowly as time goes by. On the other hand, the size of proton beam spot on the right side is obviously lager than the one on the left side. The modification of proton beam profile indicates that a transient electric field with a maximum amplitude of 109 V/m is produced when ultrashort laser pulse interacts with the plasma. Besides, the electric field in the direction of laser propagation axis is stronger than that in the opposite direction. When the proton beam goes through the laser-plasma interaction area, most of the protons enter into the electric field in the direction of laser propagation axis, only a small number of protons enter into the electric field in the opposite direction, resulting in the fact that the proton beam is split into two asymmetric spots. The space-charge field in the plasma is induced by the laser ponderomotive force which expels the electrons piled up into a step-like profile. This field can be sustained for a long time, as the ions expand slowly because of the coulomb repulsion between ions, and the hot electrons continue to move forward with energy of a few MeV. At the end, these expanded ions gradually recombine with the reflowed electrons, causing the space-charge field to weaken until it disappears eventually. As a result, the deflection of the proton beam by the electric field in the plasma is also weakened, so the distance between proton beam splitting spots is correspondingly reduced. The hypothesis is justified by the particle-in-cell simulations. The results may have important implications in laser wake-field electron acceleration, ion acceleration and fast ignition scheme to inertial confinement fusion.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

On-orbit cross-calibration and assimilation for relativistic electron observations from FengYun 4A and GOES-13

Liu Zhen, Yang Xiao-Chao, Zhang Xiao-Xin, Zhang Shen-Yi, Yu Qing-Long, Zhang Xin, Xue Bing-Sen, Guo Jian-Guang, Zong Wei-Guo, Shen Guo-Hong, Bai Chao-Ping, Zhou Ping, Ji Wen-Tao
Acta Physica Sinica. 2019, 68 (15): 159401 doi: 10.7498/aps.68.20190433
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Magnetospheric relativistic electrons can destroy on-orbit spacecrafts completely by internal charging and discharging effects. As the characteristics and physical mechanism of this space particle are still unclear, magnetospheric relativistic electrons have always been an important object of space environment exploration and space science research. For studying the physical mechanisms and developing models relating to magnetospheric relativistic electrons, it is necessary to use the observations from different satellites and detectors at the same time. Eliminating the systematic deviation between different detection systems to assimilate the observations from different sources is essentially required by such researches. In this work, the on-orbit cross-calibration and assimilation for relativistic electron (> 2 MeV) observations from FengYun 4A and GOES-13 are performed. In this work, only the observations obtained under very quiet geomagnetic conditions (Kp < 2) are adopted to ensure that the objects of study are the radiation belt particles, which are stably captured by the geomagnetic field. According to the physical characteristics of the radiation belt particles, that is, the three adiabatic invariants, and based on the Liouville theorem, the phase space density of the stably captured particles is unchanged. In this paper, the relativistic electron flux data of energy > 2 MeV and instrument pitch angle are in the east and west direction respectively. If the particles' energy is the same, then their corresponding μ values are the same, and their particles' directions are the same, then their corresponding J values are the same, and the Liouville theorem can be simplified as the drift shell Lm is the same, the fluxes are the same, and the electron fluxes observed by the two satellites are compared in the drift shell Lm coordinate. The systematic deviation between the two satellites' relativistic electronic observations can be obtained. According to this result, the data assimilation is carried out, and the results show that the system deviation can be removed well. By this research work, the systematic deviation between two important relativistic electron detection systems in geosynchronous orbit is obtained. Based on the obtained systematic deviations, the assimilations for observations from the two detection systems are achieved. This work lays a solid foundation for the follow-up theoretical and applied researches, and also provides the methods for on-orbit cross-calibration and observation assimilation which could be referred to when other electronic observations on geosynchronous orbit are dealt with.

Acta Physica Sinica
Accepts
Note: The papers published below will continue to be available from this page until they are assigned to an issue. To see an article, click its [PDF] link. To review many abstracts, check the boxes to the left of the titles you want, and click the 'Selected articles' button. To see one abstract at a time, click its [Abstract] link.
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The Effect of Collision Parameter on a Magnetized Electronegative Plasma Sheath Structure

Accept: 2016-10-11
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The structure of an electronegative plasma sheath in an oblique magnetic field is investigated. More over, the collisions between positive ions and neutral particles are taken into account. It is assumed that the system consists of hot electrons, hot negative ions and cold positive ions. Also the negative ions and the electrons are assumed to be described by the Boltzmann distributions of their own temperatures, and the accelerated positive ions are treated by means of the continuity and momentum balance equations through the sheath region. In addition, the assumption that the collision cross section has a power law dependence on the positive velocity is introduced. After theoretical derivation, an exact of sheath criterion is obtained. The numerical simulation results include the distributions of the positive ions density for different invariable ion Mach number satisfying Bohm criterion, the comparison of net space charge distributions for variable and invariable ion Mach number. Furthermore, three species of charged particles density, the net space charge and the spatial electric potential in the sheath are studied numerically for different collision parameters under the condition of the fixed ion Mach number. The results show that the ion Mach number has not only the lower limit but also the upper limit. The ion Mach number affects the sheath structure by influencing the distribution of the positive ion density, and different conclusions can be obtained because ion Mach number is adopted as variable or invariable value while discussing the effects of the other variables which can result in the variety of the ion Mach number on the sheath formation. The reason is the actual sheath structure modification brought on by the variation of a parameter can be resolved into two parts. One is the sheath formation change caused directly by the variation of the parameter, the other is the sheath formation change caused by the Bohm criterion modification which the variation of the parameter results in. Therefore, an identical ion Mach number should be adopted when researching the direct effects of a parameter variety on plasma sheath structure. In addition, it is concluded that the collisions between positive ions and neutral particles make positive ions density curve higher and electrons’ lower than the case without collisions. Negative ions density does not alter significantly whether there exists collision or not. Besides there is a peak in the profile of the net space charge while in the presence of ion-neutral collision and the net space charge peak moves toward the sheath edge. The spatial potential increases and the sheath thickness decreases on account of the presence of the collisions between ions and neutral particles.
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Calculation of Hamilton energy function of dynamical systems by using Helmholtz theorem

null
Accept: 2016-10-11
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The Helmholtz theorem confirmed that any vector field could be decomposed of gradient and rotational field. The supply and transmission of energy occur during the propagation of electromagnetic wave accompanied by variation of electromagnetic field, thus the dynamical oscillators and neurons can absorb and release energy in presence of complex electromagnetic condition. Indeed, the energy in nonlinear circuit is often time-varying when the capacitor is in charged or discharged, and occurrence of electromagnetic induction is available. Those nonlinear oscillating circuits can be mapped into dynamical systems by using scale transformation. Based on mean field theory, the energy exchange and transmission between electronic field and magnetic field could be estimated by appropriate nonlinear dynamical equations for oscillating circuits. In this paper, it investigates the calculation of Hamilton energy for a class of dimensionless dynamical systems based on Helmholtz’s theorem. Furthermore, scale transformation could be used to develop dynamical equations from the realistic nonlinear oscillating circuit, so the Hamilton energy function could be approached effectively. These results could be much useful for self-adaptive control of dynamical systems.
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Ballistic thermal rectification in the three-terminal graphene nanojunction with asymmetric connection angles

null
Accept: 2016-10-11
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By using the nonequilibrium Green’s function method, the ballistic thermal rectification in the three-terminal graphene nanojunction is studied. The dynamics of atoms are described by the interatomic fourth-nearest neighbor force-constant model. The nanojunction has a Y-shaped structure, created by a combination of a straight graphene nanoribbon and a leaning branch as the control terminal holding a fixed temperature. No heat flux flows through the control terminal. There exists a temperature bias between the two ends of the graphene nanoribbon served as the left and right terminals, respectively. The primary goal of this paper is to demonstrate that the ballistic thermal rectification can be introduced by the asymmetric structure with different connection angles between terminals. The control terminal has a smaller connection angle with respect to the left terminal than to the right terminal. The forward direction is defined as being from the left terminal to the right terminal. The results demonstrate that, given the same control temperature and absolute temperature bias, the heat flux in the graphene nanoribbon tends to run preferentially along the forward direction. When the difference between the connection angles increases, the rectification ratio rises. Compared to the zigzag graphene nanoribbon, the rectification ratio of the armchair nanoribbon is more sensitive to the direction the control terminal. However, the greatest rectification ratio is found in the zigzag graphene nanoribbon which has a connection angle of 30 degrees with respect to the armchair branch. In addition, the direction of the control terminal can be adjusted to raise more than 50% of the rectification ratio of the graphene thermal recti?er based on the width discrepancy between the left and right terminals. The mechanism of the ballistic thermal recti?cation is also discussed. In the three-terminal graphene nanojunction, a smaller connection angle with respect to the control terminal leads to more phonon scattering. The confirmation of this conclusion comes from a comparison of phonon transmission between different couples of terminals, which shows that, in most of the frequency spectrum, the phonon transmission between the control terminal and the left terminal is smaller than that between the control terminal and the right terminal. Given the same control terminal temperature and temperature bias, the asymmetric connection angles therefore will introduce a higher average temperature of the left and right terminals, and a larger heat flux in the forward process. Moreover, the average temperature difference between in the forward process and in the reverse process is found to be proportional to the temperature bias, and the proportionality coefficient will get bigger if the asymmetry is strengthened.
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The Propagation Properties of Vortex Beams in a Ring Photonic Crystal Fiber

null
Accept: 2016-10-11
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In the last decade, the vortex beams have received lots of attention for their orbital angular momentum. When they are applied to optical fiber communication field, the data channels will increase and information propagation speed will be effectively improved. Recently, researchers have shown the capability of long length stably propagation, nonlinear frequency conversion and mode division multiplexing of vortex modes in a ring fiber. Due to the photonic crystal fiber (PCF) has very flexible design degrees of freedom, it will enable a wide range of propagation properties. In this paper, A SiO2 air-holes ring PCF is proposed for separation and propagation of optical vortex modes. By using COMSOL Multiphysics software, the vortex modes(TE01, HE_21^± and TM01) are simulated and calculated. The differences of the effective refractive index between them are 4.59×〖10〗^(-4) and 3.62×〖10〗^(-4) respectively. One can analyze the propagation properties of vortex beams in the ring PCF by changing the size of first layer air holes’ radius and air hole pitch. When the incident light wavelength of TE01 mode ranges from 1650 nm to 1950 nm, this ring PCF can achieve a total dispersion variation between 44.18 to 45.83 ps?nm^(-1)?km^(-1), which is tend to be flat. When incident light wavelength is 1550 nm, the nonlinear coefficient of TE01 mode vortex light is 1.37 W^(-1)?km^(-1); Due to the long wavelength light is easier to leakage through the cladding than the short wavelength light, the confinement loss increases with the wavelength. When incident light wavelength is 2000 nm, there is still an eight-orders-of-magnitude of the low confinement loss. Theoretically, flat dispersion and low loss vortex beams in this fiber can be beneficial to propagate stably, and the vortex modes lay the foundation for long distance propagation in the optical fiber. In the future, this ring PCF will be used in optical fiber communication field and application in aspects such as continuous spectrum research, which can make it have immense advantage to traditional fibers.
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Penta-decomposition of instantaneous field in spanwise-rotating turbulent plane Couette flow

null
Accept: 2016-10-11
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Spanwise-rotating turbulent plane Couette flow (RPCF) is one of the fundamental prototypes for wall-bounded turbulent flows in the rotating reference frames. In this turbulent problem, there are large-scale roll cells, which are widely studied. In this paper, a penta-decomposition method is proposed to separate the instantaneous velocity and the total kinetic energy into five parts, including a mean part, a streamwise part and a cross-flow part of the secondary flow, and a streamwise part and a cross-flow part of the residual field, aimed to explore the energy balance and transfer among different shares of the turbulent kinetic energy in RPCF at Reynolds number Rew=Uwh/ν=1300 (here, Uw is the half the wall velocity difference, and h is half channel-height) and rotation number Ro=2Ωzh/Uw (Ωz is the constant angular velocity in the spanwise direction) in the range of 0≤Ro≤0.9. The results show that the energy is transferred between streamwise part (cross-flow part) of secondary flows and residual field through the correlation between the vorticity of secondary flows and shear stress of residual field. The rotation term acts as a bridge to transfer the energy between streamwise part and cross-flow part of secondary flows (residual field). Moreover, pressure-strain redistribution term also plays an important role in the energy transfer between streamwise part and cross-flow part in residual field. For the streamwise part of residual field, in certain rotate rates, the energy obtained from the streamwise part of secondary flows is larger than that got from mean flow, implying that the streamwise motions of secondary flows have a significant impact on the streamwise motions of residual field.
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A fast particle simulation method for calculating the multipactor threshold based on the frequency domain solutions in microwave devices

null
Accept: 2016-10-11
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In order to compute the multipactor thresholds of microwave devices with high ef?ciency and precision, a novel fast particle-in-cell (PIC) method is proposed, which takes advantages of the frequency-domain (FD) electromagnetic field solver of CST Microwave Studio (MWS). At the initial stage of multipactor (when there are not many electrons in the devices), the self-consistent field generated by the electrons is much smaller than the applied electromagnetic field. Therefore it can be ignored in calculating the multipactor threshold and this will significantly reduce the computation burden. During simulations of multipactor processes, the FD fields pre-calculated by CST MWS are converted into time-domain (TD) scaling with the square root of the input power. Then the electrons are advanced by Boris algorithm. When the electrons hit the boundaries of the simulation region, where triangular facets from CST are used for discretization, the secondary electrons would be emitted. After series of simulations with variable input powers, the multipactor threshold is determined according to time evolutions of the electron number. As verifications, the multipactor thresholds in a parallel plate and a coaxial transmission line are investigated. Compared with the results of CST Particle Studio (PS), the fast method obtains almost the same thresholds, while the computational efficiency is improved more than 1 order of magnitude. Since the self-consistent field generated by the electrons is ignored in the fast method and it is considered in CST PS, the results validate that the self-consistent field can be ignored in calculating the multipactor threshold. Finally, taking a parallel plate transmission line and a stepped impedance transformer as examples, we studied the effects of the number of initial macro-particles on the calculation precision. When the initial particles are so few that it can hardly reflect the randomness of the multipactor process, it results in a higher calculated value. With the increase of the number of initial macro-particles, the calculated multipactor threshold is lower and more accurate. It is convergent when the number reaches about 2000 for the parallel plate transmission line and 4000 for the stepped impedance transformer, respectively. Taking into account other microwave devices with more complex electromagnetic field distribution, in order to ensure precision, it is recommended to select the number of initial macro-particles 8000. In addition, although CST MWS was used to obtain the electromagnetic fields and boundary information in this paper, of course, other electromagnetic software (such as HFSS) can also be adopted as an alternation.
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The effect of linear bubble vibration on wave propagation in unsaturated porous media containing air bubbles

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Accept: 2016-10-11
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Biot model is widely applied in geophysics, petroleum engineering, civil engineering and ocean engineering since it has been presented. This leads to a considerable development of the research on the wave propagation in saturated porous medium. However, fully saturated porous medium is rarely found in nature, almost all the rocks or soils contain two kinds of fluid, such as gas and petroleum. So many researches has been done on the wave propagation in unsaturated porous medium by domestic and abroad scholars. It is well known that the presence of a small volume of gas bubbles in a liquid can greatly alter the velocity and attenuation of acoustic waves in the liquid. Evidence is beginning to accumulate that the velocity and attenuation of acoustic waves in a saturated marine sediment can be affected by the presence of gas bubbles in the saturating liquid. To investigate the sound propagation in porous media when the pore water contains a small amount of air bubbles, this paper integrates the volume vibration of bubbles in pore water into the continuity equation of pore-fluid filtration in porous media based on Biot theory, so as to obtain the continuity equation of pore-fluid filtration with bubble volume vibration. On this basis, according to the relationship between the instantaneous radius of bubbles and the background pressure of the medium under the linear vibration of bubbles, as well as the equations of motion of the fluid medium and porous medium, a new displacement vector wave equation of porous media under the influence of bubbles is derived, which establishes the model for the sound velocity dispersion and attenuation prediction under the unsaturated porous media. The presence of air bubbles increases the compressibility of pore fluid, which leads to the decrease in the sound velocity of the bubbly saturated porous media. When the wave frequency equals to the resonance frequency of the bubbles, the bubbles in pore water will produce resonance; the medium will present to be highly dispersive and the velocity can greatly exceed the gas-free velocity, but these have not been measured in field data; and the absorption cross section of the air bubble can reach the maximum, which leads to the maximum attenuation of the porous media. It should be noted that the attenuation coefficient calculated with this model is related to the damping of bubble motion(radiation, thermal and internal friction) and the dissipation of the relative motion between the pore water and porous solid frame. The obtained numerical analysis is consistent with the above conclusions, which indicates that the volume concentration, the bubble size and the excitation frequency of sound field are important parameters affecting the sound wave propagation in the saturated porous media containing few bubbles.
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Ferroelectric phase transition of perovskite SnTiO3 based on first principles

null
Accept: 2016-10-11
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Due to their spontaneous polarization, ferroelectric materials have excellent dielectric, piezoelectric, pyroelectric and other properties, which enable them to be used in many applications, such as capacitors, filters, sensors, detectors, and transducers, among others. In this paper, we employ a first-principles-based effective Hamiltonian method to investigate perovskite SnTiO$_3$, obtaining essential coefficients for the effective Hamiltonian via ab initio computations, which are used in subsequent Monte-Carlo simulations to predict the phase transition temperature of SnTiO$_3$, and different structural phases involved in such phase transition.
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Nonlocal Symmetries and Interaction Solutions of the (2+1)-dimensional Higher Order Broer-Kaup System

xiangpeng xin Hanze Liu Xi-qiang LIU
Accept: 2016-10-11
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The (2+1)-dimensional higher-order Broer-Kaup (HBK) system is studied by nonlocal symmetry method and consistent tanh expansion (CTE) method. In this paper, via the localization of the residual symmetries, the nonlocal symmetries are localized to Lie point symmetries and symmetry groups are also obtained. Many types of soliton solutions and interaction solutions among different nonlinear excitations such as solitons, periodic waves etc. are constructed. In order to study their dynamic behaviors, corresponding images are explicitly given.
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Development of a intranuclear-cascade code CBIM applicable to the nuclear reaction with incident particle energy above 45MeV

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Accept: 2016-10-11
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The Monte Carlo intra-nuclear cascade program CBIM has been developed for describing nuclear reactions involving protons, neutrons and pions on complex nuclei. In order to describe cascade process, several simplifications have been made in the following: firstly, neither reaction, reflection, refraction, nor ionization will be taken into account before the incident particle enters the target nucleus; secondly, target nucleus is regarded as spherical and the atom number should be greater than 2; thirdly, the knocked nucleon is determined by cross section sampling; last, in the center-of-mass frame, the scattering angle is sampled based on differential cross section distribution.. The basis physics model bases on the above assumptions and Bertini intra-nuclear cascade model; meanwhile, nucleon-nucleon angle differential distributions of INCL in the center-of-mass frame have been introduced to overcome the shortage of Bertini model. The interactions between nucleon and nucleon or between nucleon and pion, for example, elastic scattering, pion production and charge exchange, are simulated in the code. In the particles collision, the nucleon density changes with the target nucleus radius; and the interaction cross sections refer to 22 kinds of experimental cross sections in Bertini model. The intra-nuclear cascades induced by 45MeV~3500MeV neutron, proton or pion below 2500MeV can be simulated by this code. Finally, comparisons with experiment on reaction cross section over the energy range 60~378MeV, and some simulation results by MCNPX, GEANT4 and PHITS over the energy range 65~3000MeV, the CBIM results are in reasonable agreement with them over the broad energy range considered.
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Omnidirectional photonic bandgap of the one-dimensional plasma photonic crystal based on a novel Fibonacci quasiperiodic structure

Accept: 2016-10-11
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Take the binary one-dimensional plasma photonic crystal based on Fibonacci quasiperiodic structure as an object, on the basis of the photonic bandgap characteristics of the structure with different initial sequence and number of period, a novel structure of one-dimensional plasma photonic crystal is proposed in this paper to enlarge the omnidirectional photonic bandgap (OPBG). Compared with previously reported structures in literatures, this structure is simpler in configuration with fewer layers and materials, and its OPBG width is wider. The influence of the parameters of the plasma material, such as the thickness, plasma frequency and collision frequency, on the OPBG characteristics of this structure is systematically discussed and compared with that of the structure in literatures. The research results can provide important theoretical guidance for the design of novel omnidirectional reflectors.
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Quantum secure direct communication protocol based on the mixture of Bell state particles and single photons

Zheng-Wen CAO
Accept: 2016-10-11
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By studying the properties of the mixture of Bell state particles and single photons, the paper designs a quantum code scheme with high coding capacity, and proposes a novel quantum secure direct communication protocol with high transmission efficiency. Alice prepares Bell state particles and single photons, and divides Bell state particles into two sequences $S_A$ and $S_B$. $S_B$ is sent to Bob for the first security check using quantum correlation properties of particles. When the check result shows that the quantum channel is safe, using designed quantum code scheme, Alice encodes her classical message on the mixed quantum state sequence of Bell sequence $S_A$ and single photon sequence $S_S$. Then, some single photons that are used for security check are re-inserted randomly into the encoded sequence, and the order of particles is rearranged to ensure to check Eve's attack. Alice sends the new sequence to Bob. Bob delays and receives it. And then, the quantum channel is conducted security check for the second time. The transmission error rate is calculated, if the error rate is lower than the tolerance threshold, the channel is safe. Bob decodes and reads Alice's message. The first security check is to determine whether quantum channel is safe. The second security check could test whether there are eavesdroppers during information transmission. Safety analysis is done by using quantum information theory to the proposed protocol. The error rate introduced by Eve and the amount of information by Eve are calculated. It is showed that this protocol can effectively resist measurement-resend attack, intercept-resend attack, auxiliary particle attack, denial of service attack and Trojan attack. Among them, auxiliary particle attack is analyzed in details. The transmission efficiency and coding capacity are also analyzed. The transmission efficiency is 2, the quantum bit rate is 1, and the coding capacity is that a quantum state can encode three bits of classical messages. We also compare the proposed protocol to many existing popular protocols in terms of efficiency, e.g., Ping-Pong protocol, Deng,F.G. et al.'s Two-step and One-pad-time quantum secure direct communication protocol, Wang,J. et al.'s quantum secure direct communication protocol based on entanglement swapping and Quan,D.X. et al.'s one-way quantum secure direct communication protocol based on single photon. It is proved that this proposed protocol has higher transmission efficiency. In addition, complex U operation and entanglement swapping are not used, and implementation process is simplified. However, this protocol is devoted to theoretical research of quantum secure direct communication. There are still some difficulties in the practical application. For example, the storage technology of quantum states is not mature at present. It is not easy to prepare and measure Bell state particles and combine them with single photons, and so on. The implementation of this protocol depends on the development of quantum technology in the future.
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The Relationship between Dielectric Properties and Nanoparticle Dispersion of Nano- SiO2/Epoxy Composites

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Accept: 2016-10-11
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Nano-SiO2 was modified by silane coupling agent and modified nano-SiO2 powder and nano-SiO2 dispersing liquid was obtained. Unmodified and modified nano-SiO2/Epoxy composites made by “mechanical mixing method”, and modified namo-Silica/Epoxy composites made by “bubble mixing method” were prepared, respectively. The content of nano-SiO2 in the composite is 2wt%, 3wt%, 4wt%, 5wt% and 6wt%. Breakdown strength and corona-resistance characteristics of the composites were tested. The results show that, with the increase of nano-SiO2 loading, the breakdown strength and corona-resistance of nano-SiO2/Epoxy composites increase. The maximum breakdown strength of namo-Silica/Epoxy composites was appeared when the nano-Silica content is 5wt%. The SEM images of 5wt% nano-Silica loading composites were analyzed by Software Image J, and the Morisita’s Index method was used to evaluate the dispersion of nano-Silica particles in the matrix quantitatively. The best dispersion was found in the composites made by “bubble mixing method”. The relationship between dielectric properties and nano-particle dispersions of nano-Silica/Epoxy composites was discussed.
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Combined noise source identification method based on spherical microphone array with random unifrom distribution of elements

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Accept: 2016-10-11
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As the developing of techlology, noise controlling is paied wide attention in recent years. Noise source identification is the key step for noise controlling. Spherical microphone array, which can located the noise source of arbitrary direction in three dimensional space, is widely used for noise source identification in recent years. Conventional methods for noise source localization include spherical near field acoustic holography and spherical focused beamforming. The acoustic quantities are reconstructed by using spherical near field acoustic holography method to realize the noise source identification, while the noise source can also be located by using focused beamforming based on spherical harmonic wave decomposition. However, both these methods have their own limitations while being used in noise source identification. Spherical near field acoustic holography has low resolution in high frequency with far distance from noise source to measurement array for noise source identification, whereas the spherical focused beamforming has low localization resolution in low frequency. Noise source identification is discussed here and a 64-element microphone spherical array with randomly uniform distribution of elements is designed. The combination methods of noise source identification by using spherical near field acoustic holography and mode decomposition focused beamforming are researched. The performance of the proposed combination methods is simulated, and an experiment of noise source identification is carried out based on the designed spherical microphone array to test the validity of proposed method. The dividing frequency point is when selecting noise source identification methods between near field acoustic holography of spherical wave decomposition by using the spherical array designed in this paper. Research results show that high resolution of noise source identification can be obtained by using near field acoustic holography when reconstruction frequency is with a distance from noise source to the center of spherical array, while high resolution of noise source localization can be achieved by using spherical wave decomposition beamforming when signal’s frequency is with a distance from noise source to the center of spherical array. Spherical array with random uniform distribution of elements maintains stable identification ability in all bearing. Spherical near field acoustic holography has high resolution distinguish ability in near field and low frequency, while focused beamforming method has high resolution distinguish ability in far field and high frequency. Therefore the noise source can be efficiently identified by using the proposed combined method of near field holography and focused beamforming with less elements and small aperture spherical microphone array.
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Optimization design of a Gamma-to-Electron spectrometer for high energy gammas induced by fusion

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Accept: 2016-10-11
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Apart from neutrons, the fusion core produces gamma rays during one fusion reaction. The spectrum of gamma ray can provide very important information for fusion diagnosis. However, due to the gamma energy and yield in one fusion pulse, the gamma spectrometer used should have high detection efficiency and energy resolution. The concept of a Gamma-to-Electron magnetic spectrometer GEMS provides the idea to build up such a spectrometer to meet this requirement. Based on this concept design, four important parts of this facility are investigated. The first part is the gamma-electron converter. The main physics processes include Compton scattering of gamma ray with converter material generating electron, the electron Multiple Coulomb scattering (MCS) inside the converter and the electron attenuation. Affected by the thickness of convector, these processes gives a complex influence on the detection efficiency and angular-energy distribution of the electrons which are emitted from the downstream face of the convector. The Monte Carlo code Geant4 is employed to investigated the functions of Compton scattering, MCS and converter thick on the angular-energy distribution. The second one is the collimation. The collimation is used to select the forward direction election, the performance of cutoff angle of the collimator on the detection efficiency and resolutions, as well as the correlation between electron transportation direction and energy, are also studied using Geant4 code. The third part is the dipole magnetic field. There are several parameters of geometric and magnetic, therefore, a multi-thread parallelized Genetic algorithm is developed to get the best result. Both the irregular geometry (shape) and dipole magnetic field strength are optimized to achieve the best energy resolution and detection efficiency. The obtained magnetic field has intensity less than 100 Gauss, and its performance on gathering elections is also verified by Geant4 code. The last one is the location of electron detectors. The study shows that all the electron detectors should be located according to not a straight line but a quadratic curve. Then the optimized spectrometer is simulated by Geant4 to get the responses of gamma rays with various energies. For the gammas provided by fusion reaction, the simulation shows that when the neutron yield is about 2.5×1015 and 1.2×1016, the energy resolution reaches 0.5 MeV and 0.25 MeV, respectively, provided that different thick Be converters are employed. All in all, this optimized GEMS can be employed to measure the spectrum of gamma rays generated by the fusion reaction.
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Influnence of Nonspherical Effects on the Secondary Bjerknes Force in a Strong Acoustic Field

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Accept: 2016-10-11
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The secondary Bjerknes force between bubbles in an acoustic field is a well-known acoustic phenomenon. The major theoretically researches of the secondary Bjerknes force were owing to two spherical bubbles. The secondary Bjerknes force between two spherical bubbles which is calculated based on the linear equations is very small and negligible, therefore these theoretically researches did not give a well explanation for the phenomenon, such as “streamer formation” and Multi-bubble sonoluminescence (MBSL). Experiments of sonoluminescence (SL) show that bubbles in a sound field are not entirely spherical bubbles. Nonspherical effects have an important influence on the secondary Bjerknes force when two bubbles come close to each other in a strong acoustic field (>1.0×〖10〗^5 Pa). How does the shape distortion of a nonspherical bubble cause the change of the secondary Bjerknes force between two bubbles, and the secondary Bjerknes force how to affect the oscillation and movement of bubbles are major problems which we wish to solve. The of the secondary Bjerknes force between a nonspherical bubble and a spherical bubble is obtained by considering the shape oscillation of a nonspherical bubble. We numerical simulate the secondary Bjerknes force between a nonspherical bubble and a spherical bubble based on the nonlinear oscillation equations of two bubbles, and compare the secondary Bjerknes force between a nonspherical bubble and a spherical bubble to the secondary Bjerknes force between two spherical bubbles in the same condition. We discuss the influence of nonspherical effects on the secondary Bjerknes force between two bubbles. The results show that when the amplitude of driving pressure is greater than the Blake threshold of a nonspherical bubble and makes the bubble oscillate stably, the secondary Bjerknes force between this nonspherical bubble and a spherical bubble is different to the secondary Bjerknes force between two spherical bubbles in direction and magnitude. The secondary Bjerknes force between a nonspherical bubble and a spherical bubble is much bigger than that of two spherical bubbles. The interactional distance of the secondary Bjerknes force between a nonspherical bubble and a spherical bubble is further than that of two spherical bubbles. The secondary Bjerknes force between a spherical bubble and a nonspherical bubble depends on the radii of two bubbles, distance between two bubbles, shape mode of the nonspherical bubble and the amplitude of driving pressure. Our research is more close to the actual bubbles in liquid. We also prove that big mutual interaction between bubbles is mainly cause for the formation of a stable structure between bubbles. For bubbles, big mutual interaction causes the cavitation become easier. These results are important to explain the phenomenon in an acoustic field, such as “streamer formation” and Multi-bubble sonoluminescence (MBSL).
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The Principle and Application of Diagonal Reducing Method in the Complex Noise Fields

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Accept: 2016-10-11
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Acoustic environment has low signal-to-noise ratio (SNR); hence, array signal processing is always used for noise reduction and signal enhancement. Because the delay-and-sum beamforming method performs robust, so it is almost widely used, but the array gain is limited by the array aperture. The actual underwater ambient noise is complex, which includes uncorrelated noise and correlated noise. The noise power of each array element is unequal. The noise covariance matrix is not a scaled identity matrix. Consequently, the performance of array signal processing method decreases obviously. Aiming at these two problems, the diagonal reducing method of the covariance matrix in the complex noise fields is proposed. Firstly, a reducing matrix, which is defined as a diagonal matrix with unequal diagonal elements, is subtracted from the covariance matrix so as to reduce the noise, and a new matrix is obtained. Secondly, the delay-and-sum beamforming is done by using the new matrix to obtain the beaming output. The analytic solution and approximate solution of reducing matrix are obtained under the constraint condition that the output SNR attains its maximum. Thirdly, the estimation of the reducing matrix is determined by minimizing the function that is defined as the error between the covariance matrix and the estimated covariance matrix. This minimization problem is accomplished in an iterative method. Fourthly, if the noise is uniform white noise or the nonuniform white noise, this proposed method performs well. While, under the complex noise field the performance of the proposed method may be deteriorated. So the effects of the correlation of the noise field and the input SNR on the estimated error is analyzed. In fact, the weaker the correlation is, or the smaller the input SNR is, the smaller the estimated error is. Lastly, the simulation experiment and the lake trial are implemented. The simulation results show that the diagonal reducing method of the covariance matrix reduces some ambient noise, the noise output power is decreased, the output SNR is increased, and the proposed method improves performance of array signal processing. The experimental results show that the output SNR of the target using the proposed method is increased by about 14 dB. The diagonal reducing method of covariance matrix has definite value to engineering application, and is computationally attractive.
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Moving target compressive imaging based on improved row scanning measurement matrices

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Accept: 2016-10-11
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Abstract: Moving target imaging (MTI) plays an important role in practical applications. How to capture dynamic images of the targets with high quality is a front-burner issue in the field of MTI. In order to improve the reconstruction quality, a new MTI model based on compressed sensing (CS) is proposed here, applying a sampling protocol of the row-scanning together with a motion measurement matrix constructed by our own. It is proved by the simulation and the experimental results that a relatively higher quality can be achieved through this approach. Furthermore, an evaluation criterion of reconstructed images is introduced to analyze the relationship between the imaging quality and the moving speed of the target. By contrast, the performance of our algorithm is much better than that of traditional CS algorithms under the same moving speed condition. As a result, it suggests that our imaging method may have a great application prospect in the earth observation of unmanned aerial vehicles, video monitoring in the product line and other fields.
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Spatial Correlation of Underwater Bubble clouds Based on Acoustic Scattering

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Accept: 2016-10-11
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Using effective medium theory to describe acoustic scattering from bubble clouds, one of the underlying assumptions shows that the probability of an individual bubble being located at some position in space is independent of the locations of other bubbles. However, bubbles within naturally occurring clouds are usually influenced by the motion of the fluids which makes they become preferentially concentrated or clustered. According to Weber’s method, it is a useful way to importing spatial correlation function to describe this phenomenon in bubble clouds. The spatial correlation function is contained in acoustic scattering and it is important to notice that the spatial correlation should be dependent of the position and radius of each bubble due to the ‘‘hole correction’’ or the effect of the dynamics of the fluids. Because of these reasons, it is hard to invert the spatial distribution of bubble clouds using spatial correlation function in acoustic scattering. A method is described here in which bubble clouds are separated into many small subareas and the conception called effective spatial correlation function which is the statistic of spatial correlation function used to describe the correlation between each subarea of bubble clouds. Since the effective spatial correlation function is independent of bubbles’ radius and positions, the bubble clouds’ distribution and the trend of clustering can be inverted by using this function. The result of simulation indicates that the effective spatial correlation function can precisely track the position of the clustering center, even the clustering center covered by other bubble clouds can be detected. Using multi-bean sonar measuring the bubbly ship wake generated by a small trial vessel, the method is used to invert the spatial distribution and clustering centers of bubble field in the ship wake. The results show that effective spatial correlation function accurately inverts the distribution and clustering centers of bubbles in ship wake. Furthermore, the method presented in this paper could distinguish the bubble clouds caused by different reasons and detect upper ocean bubble clouds covered by other bubbles generated by wave breaking.
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Uncertainty Quantification in the Calculation of keff Using Sensitity and Stochastic Sampling method

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Accept: 2016-10-11
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In the neutronics simulation of nuclear reactor, the uncertainties associated to the integral parameters due to the uncertainties in nuclear data are usually quantified using the sensitivity and uncertainty (S/U) analysis method based on the perturbation theory. S/U analysis method is only applicable to the linear model, moreover neutronics code generally can not be directly used in sensitivity analysis. Sampling approach, which evaluating the uncertainties by performing a set of stochastic simulations, is easy to implement and the uncertainties quantified is close to exact. The function of uncertainty quantification based on sampling approach have been added to uncertainty analysis code SURE. Before applying the sampling method to the uncertainty quantification in the simulation of complex problems, it is necessary to carry out a careful verification. The uncertainties of the calculated effective neutron multiplication factor keff for two selected simple critical benchmark experimental model are quantified using SU method and sampling method respectively. The keff uncertainties due to all nuclides and reaction types nuclear data quantified by two methods are in good agreement, and the correctness of the sampling function of SURE code is verified. The keffs distributions from sampling method obey normal distribution, which embodies a linear relation between input nuclear data and output keff in the range of the uncertainty range of nuclear data, and sensitivity analysis method is adaptable to quantify uncertainty of calculated keff.
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A super-resolution infrared microscopy based on a doughnut pump beam

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Accept: 2016-10-11
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This paper presents an approach to break through the diffraction limitation in infrared microscopies. In this method, instead of Gaussian pump beam, an intensive vortex beam is firstly focused on the sample, leading to saturation absorption of the peripheral molecules in the point spread function (PSF). The vortex beam is followed by a Gaussian beam with the same wavelength, which can only be absorbed by the molecules near the center, resulting in shrunken PSF which means higher resolution. Furthermore, the PSF of a system based on this approach is numerically simulated. With an 100 nJ pulse energy vortex beam and a 0.1 nJ pulse energy probe beam, the theoretical resolution (full width at half maximum, FWHM) is measured to be about 236 nm which is 14 times better than that of the traditional infrared microscopy.
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Fast Bayesian Blind Restoration for Single Defocus Image with Iterative Joint Bilateral Filters

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Accept: 2016-10-11
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It is significant to realize effective defocus image restoration for acquiring clear image in military and geological examination field. Most of existing algorithms have the problems of large computational cost, ringing and noise sensitivity, hence a novel approach by iterative joint bilateral filtering under Bayesian framework is proposed. Firstly, it utilizes defocus image depth estimation to compute the point spread function in the Bayesian framework. Then a minimum optimization problem is built to represent the blind restoration problem. After inferring the solution procedure of the minimum optimization problem, we find that the joint bilateral filters can be used to search the optimal solution, which not only simplify the searching procedure but also reduce the computational cost. Finally, an iterative joint bilateral filtering was designed to realize the image restoration. That means the original restored image obtained from the bilateral filtering is used to design the guide image for the joint bilateral filters, and the guide image will serve as the input of the optimization problem for acquiring the better optimal result. This procedure was repeated until convergence. The experiment results indicate that this method can yield the ringing, reduce the computational cost and remove the noise. Generally speaking, the average pixel error of 85% images is under 0.03, which has improved 19% comparing with the same error rang of existing algorithms. And 78% shorter than those of compared algorithms. It can be used in the engineering practice of blind restoration for single defocus image.
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First-principles study on the thermodynamic stabilities and electronic structures of long-period stacking ordered phases in the Mg-Y-Cu alloys

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Accept: 2016-10-11
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A first-principles method based on density functional theory has been used to investigate thermodynamic stability and electronic characteristics of long-period stacking ordered (LPSO) phases 14H and 18R (18R(m),18R(t)) in Mg–Y–Cu alloys. The present calculations are performed using Vienna Ab-initio Simulation Package (VASP) with projector augmented plane wave pseudopotential, and generalized gradient approximation is used to treat with and describe the exchange-correlation interaction. The plane wave cutoff energy is set to 360 eV, the forces on all the atoms is less than 0.02 eV/?. The calculated negative enthalpies of formation show that both 14H and 18R can exist in Mg–Y–Cu system, 14H and 18R are stable with respect to the Mg, Cu and Y elements, the reaction energies indicate that 14H is more stable than 18R. The density of states (DOS) of these phases reveals that the main bonding peaks of 14H is located at energy range between -6.82 eV and 2.09 eV, those of 18R(m) at energy range between -6.82 eV and 2.02 eV, and 18R(t) at energy range between -6.82 eV and 1.98 eV. The Cu 3d orbits, Y 4d orbits, Mg 3s and Mg 2p orbits are broadly distributed in the entire region, while Cu 4s orbits, Y 4s and Y 4p orbits are very weak in whole region. For 14H,18R(m) and 18R(t) phases, the bonding originates mainly from the valence electrons of Mg 3s, Mg2p, Cu 3d and Y 4d orbits. The presence of pseudogap indicates that the bonds in 14H and 18R phases are noticeable covalent. In addition, the charge density on (0 0 0 1) plane of 14H and 18R phases are analyzed, and the results indicate that the Cu-Y bonds exhibits covalent feature in 14H and 18R, the covalent bonding of 14H phase is stronger than that of 18R phase.
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A broadband low-frequency sound insulation structure based on two-dimensionally inbuilt Helmholtz resonators

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Accept: 2016-10-11
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A man-made acoustic structure with broadband low-frequency sound insulation property is designed based on circularly inbuilt Helmholtz resonators. Beyond this structure, a two-dimensional quiet zone can be created. Being the same as the simulating model, an experimental structure is fabricated. Experiments are carried out to study its sound insulation properties. The experimental results are very coincident with the simulating one, which show that this structure has an excellent sound insulation effect in the frequency band of 680-1050Hz, and the maximum insulation sound pressure level can reach 41dB. Meanwhile, the distribution of the two-dimensional sound field above this structure is measured. The results point out that the range of the insulation area can be changed with the change of the incident frequency. In addition, the sound insulation effect is sensitive to the resonant state of the Helmholtz resonators. This work will be of help for designing new sound protection devices.
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Total Dose Dependence of Hot Carrier Injection Effect in the NMOS Devices

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Accept: 2016-10-11
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The equipments and devices which were long-time running in space were affected by space radiation effects and hot carrier injection effects at the same time which would reduce their optional times. Normally, the single mechanism test simulation method was used on the ground simulation test but the multi-mechanism effects was affected the space equipments and devices, included total irradiation dose effect, hot carrier injection effect, and so on. The total dose dependence of hot carrier injection (HCI) effect in the 0.35μm NMOS Devices was studied in this paper. Three samples were test with different conditions (sample 1# with TID and HCI test, sample 2# with TID, annealing and HCI test, sample 3# only with HCI test). The results shows that threshold voltage of NMOS devices with 5000s HCI test after 100krad (Si) total dose radiation shift negatively then positively during total dose irradiation test and HCI test,and it was more than the devices without radiation test. But the threshold voltage shift of NMOS devices with 5000s HCI test and 200hours annealing test after TID test was more than the devices without radiation test and lower than the devices without annealing test. That was, the parameters of NMOS device varied faster with the association effects (included total dose irradiation effect and HCI effect) than with single mechanism effect. It was indicated that the hot electrons were trapped by the oxide trap charges induced by irradiation effect and then became recombination centre. And then the oxide trap charges induced by irradiation effect reduced and became to negative electronic. The interface trap charges induced by irradiation effect were reduced and then increased and it was because that the electrons of hole-electron pairs in the Si-SiO2 interface were recombined by oxide traps in the oxide during the forepart of HCI test but then the electrons were trapped by interface traps in the Si-SiO2 interface because the electrons from source area were injected to interface during the HCI test. So the threshold voltage shift was positively due to the negative oxide trap charges and interface trap charges. The association effect was attributed to the reduction of oxide traps induced by recombination with hot electrons and the increase of the interface traps induced by irradiating trapped with hot electrons.
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Optoelectronic properties of N/B doped graphene

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Accept: 2016-10-11
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Since its discovery in 2004, graphene has attracted great attention because of its unique chemical bonding structure, which has excellent chemical, thermal, mechanical, electrical and optical properties. Due to the zero band gap material, graphene has limited its development in the field of Nano Electronics. Only expanding the band gap of the graphene can promote the application of graphene in Nano Electronics. In this paper, we constructed three models of intrinsic graphene, N-doped graphene and B-doped graphene. The energy band structures, electronic density of states and optical properties of N/B doped graphene with intrinsic graphene and different doping concentrations were studied. The absorption spectra, the reflection spectra, the refractive index, the conductivity and the dielectric function were studied. The study shows that the electronic states near the Fermi level of N/B doped graphene are mainly composed of C-2p and N-2p/B-2p orbitals, and N/B doping can induce the change of the Fermi level and the photoelectric properties of graphene. The conclusion of this paper can provide a theoretical basis for the application of graphene in optoelectronic devices.
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The study of the dynamic of the slow electrons transmitted through straight glass capillary and tapered glass capillary

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Accept: 2016-08-18
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It was found that the transmission rate of the electrons through insulating capillaries as a function of the time/incident charge is not the same as that for the ions. The question arouse that, by using the electrons, if the negative charge patches can be formed to facilitate the transmission of the followed electrons, substantiating that the so-called guiding effect works also for electrons. This study aims to observe the time evolution of the transmission of electrons through a straight glass tube and a tapered glass capillary. This would reveal the details that how and/or if the negative charge patches can be formed when the electron are being transported through them. In this work, a set of MCP/phosphor two-dimensional detection system based on Labview platform was developed to obtain the time evolution of the angular distribution of the transmitted electrons. The pulsed electron beams through a small hole with the diameter of 0.5 mm was obtained to test our detection system. The time evolution of the angular profile of 1.5 keV electrons transmitted through the glass tube/capillary was observed. The transmitted electrons are observed on the detector for a very short time and disappear for a time and then back again for both the glass tube and tapered glass capillary, leading to an oscillation. The positive charge patches are formed in the insulating glass tube and tapered glass capillary since the secondary electron emission coefficient for the incident energy is larger than 1. It is due to the fast discharge of the deposited charge, leading to an increase of the transmission rate, while the fast blocking of the incident electrons due to the deposited positive charge, leads to a decrease of the transmission rate. The geometrical configuration of the taper glass capillary tends to make the secondary electrons deposited at the exit part to form the negative patches that facilitate transmission of electrons, similar to the guiding of positive charged ions. This suggests that if the stable transmission needs to be reached for the production of the electron micro-beam by using tapered glass capillaries, the steps has to be taken to have the proper grounding and shielding of the glass capillaries and tubes. Our results show a difference for electrons in transmission through the insulating capillary from that of highly charged ions.
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Accept: 2016-08-18
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internuclear-distance-dependent ionization of H$_2^+$ in strong laser fields in a classical perspective

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Accept: 2016-08-18
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The enhanced ionization of H$_2^+$ in strong laser fields is studied by numerically simulating the classical Hamiltonian equation with the fix-nuclei approximation. The classical trajectory of the electron shows the electron gains energy from the laser field by circulating one electron, then passes through the interatomic barrier and move around the other nucleus before ionization. The ionization probability is maximum when the energy difference between the ground state and the the higher value of the interatomic barrier and outatomic Coulomb barrier is minimum. The classical calculation offers a perspective to inspect the intriguing phenomena in quantum systems.
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Partition and growth of convection patterns in Poiseuille-Rayleigh-Benard flow

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Accept: 2016-08-18
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In this paper, the Simple algorithm is used to numerically simulate the two-dimensional fully hydrodynamic equations. Partition of convection pattern , growth and the effect of horizontal flow on the characteristical parameters of different patterns in Poiseuille-Rayleigh-Benard flow are studied. The result indicated that flow zone is divided into three zones by the upper and lower critical Reynolds numbers , such as traveling wave zone, localized traveling wave zone, horizontal flow zone.and increase with reduced Rayleigh number. In the growth stage of the convection pattern, the growth process of three kinds of patterns with time is different, but the convection rolls grow all from downstream; Variation of characteristic parameters with time is also different, maximum vertical velocity and Nusselt number of traveling wave and localized traveling wave enter into the stable stage of the cycle variation after the exponential growth stage;and of horizontal flow pattern down to a stable constant after slow growth. and of three types of patterns decrease with increasing Reynold number, there are different rules in the different pattern areas. In this paper, formulas on variation ofandwith and formulas on variation ofandwithin different convection patterns are suggested.
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     No.7      No.8      No.9      No.10      No.11      No.12
2002 Vol.51      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
2001 Vol.50      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
2000 Vol.49      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1999 Vol.48      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
     No.13
1998 Vol.47      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1997 Vol.46      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1996 Vol.45      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1995 Vol.44      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1994 Vol.43      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1993 Vol.42      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1992 Vol.41      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1991 Vol.40      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1990 Vol.39      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1989 Vol.38      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1988 Vol.37      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1987 Vol.36      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1986 Vol.35      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1985 Vol.34      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1984 Vol.33      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1983 Vol.32      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1982 Vol.31      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1981 Vol.30      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1980 Vol.29      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1979 Vol.28      No.1      No.2      No.3      No.4      No.5      No.6
1978 Vol.27      No.1      No.2      No.3      No.4      No.5      No.6
1977 Vol.26      No.1      No.2      No.3      No.4      No.5      No.6
1976 Vol.25      No.1      No.2      No.3      No.4      No.5      No.6
1975 Vol.24      No.1      No.2      No.3      No.4      No.5      No.6
1974 Vol.23      No.1      No.2      No.3      No.4      No.5      No.6
1973
1972
1971
1970
1969
1968
1967
1966 Vol.22      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9
1965 Vol.21      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1964 Vol.20      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1963 Vol.19      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1962 Vol.18      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1961 Vol.17      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1960 Vol.16      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8
1959 Vol.15      No.1      No.2      No.3      No.4      No.5      No.6
     No.7      No.8      No.9      No.10      No.11      No.12
1958 Vol.14      No.1      No.2      No.3      No.4      No.5      No.6
1957 Vol.13      No.1      No.2      No.3      No.4      No.5      No.6
1956 Vol.12      No.1      No.2      No.3      No.4      No.5      No.6
1955 Vol.11      No.1      No.2      No.3      No.4      No.5      No.6
1954 Vol.10      No.1      No.2      No.3      No.4
1953 Vol.9      No.1      No.2      No.3      No.4
1952
1951 Vol.8      No.1      No.2      No.3
1950 Vol.7      No.5      No.6
1949 Vol.7      No.4
1948 Vol.7      No.3
1947 Vol.7      No.1      No.2
1946 Vol.6      No.2
1945 Vol.6      No.1
1944 Vol.5      No.1      No.2
1943
1942
1941
1940 Vol.4      No.1
1939 Vol.3      No.2
1938
1937 Vol.3      No.1
1936 Vol.2      No.1      No.2
1935 Vol.1      No.3
1934 Vol.1      No.2
1933 Vol.1      No.1
物理学报
· Numerical simulation of soliton trapping of the supercontinuum in photonic crystal fiber [2012, No.12:124203-124203] (38671)
· Large-eddy simulation and experimental study of deflecting oscillation of planar opposed jets [2013, No.8:84704-084704] (38163)
· Effect of concentration of heavy oxygen vacancy in rutile and anatase (TiO2) on electric conductivity performance studied by simulation and calculation [2013, No.23:237101-237101] (30742)
· Quasiparticle band structure calculation for SiC using self-consistent GW method [2012, No.13:137103-137103] (29077)
· Proximity-effect-induced superconductivity by granular Pb film on the surface of Bi2Te3 topological insulator [2013, No.16:167401-167401] (27101)
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