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CN 11-1958/O4
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Electronic and optical properties of n-pr co-doped anatase TiO2 from first-principles
Zhang Li-Li, Xia Tong, Liu Gui-An, Lei Bo-Cheng, Zhao Xu-Cai, Wang Shao-Xia, Huang Yi-Neng
Acta Physica Sinica, 2019, 68 (1): 017401
Point-contact Andreev reflection spectroscopy on Re3W superconductor
Wang Zong, Hou Xing-Yuan, Pan Bo-Jin, Gu Ya-Dong, Zhang Meng-Di, Zhang Fan, Chen Gen-Fu, Ren Zhi-An, Shan Lei
Acta Physica Sinica, 2019, 68 (1): 017402
Photoinduced charge carrier dynamics and spectral band filling in organometal halide perovskites
Zhao Wan-Ying, Ku Zhi-Liang, Jin Zuan-Ming, Liu Wei-Min, Lin Xian, Dai Ye, Yan Xiao-Na, Ma Guo-Hong, Yao Jian-Quan
Acta Physica Sinica, 2019, 68 (1): 018401
Current Issue Accepts In Press Earlier Issues Top Downloaded SCI Top Cited
  Acta Physica Sinica--2019, 68 (1)   Published: 05 January 2019
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INVITED REVIEW

Excitonic magnetic polarons and their luminescence in II-VI diluted magnetic semiconductor micro-nanostructures

Zou Shuang-Yang, Muhammad Arshad, Yang Gao-Ling, Liu Rui-Bin, Shi Li-Jie, Zhang Yong-You, Jia Bao-Hua, Zhong Hai-Zheng, Zou Bing-Suo
Acta Physica Sinica. 2019, 68 (1): 017101 doi: 10.7498/aps.68.20181211
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Spin is an intrinsic nature of the angular momentum of elementary particle like electron and photon. Currently the collective spin behaviors of the multi-electrons in condensed matter, such as GMR, CMR and topological insulator which are the behaviors of ground state, have been a research focus in the condensed matter physics, due to the fact that the collective spin is related to electronic transports. Exciton is another type of bosonic quasiparticle, an excited state of electronhole pair in solid, which has a short lifetime and can recombine to emit light. Whether excitons can also exhibit the spin-polarized dominance before they recombine, has not been understood yet. It is proposed that excitons form condensate by themselves or light binding. Can coupled spins conduce to the formation of the exciton condensate in solid? Excitonic magnetic polaron (EMP) is the composite exciton of ferromagnetically coupled spins and free excitons in magnetic semiconductors, which may lead to ferromagnetic Bose-Einstein condensate (BEC) due to the binding of collective spins in a microstructure, like the photon binding excitons (exciton polaritons) in an optical cavity However, this subject has not been a research focus yet. Here in this paper, we review the progress of the EMP formation, its dynamic behaviors and spin polarized collective EMP emission and lasing in Ⅱ-VI dilute magnetic semiconductor micro-structures in our group Besides, we also present some expectations for the applications or advances in the quantum phenomena such as spin-related emission and lasing, spin induced BEC, photon induced magnetism and Hall effect, etc. Even more achievements of EMP could be expected in the future.
SPECIAL TOPIC—Critical topics in water research

Research progress of molecular structure and dynamics of biological water

Ye Shu-Ji, Li Chuan-Zhao, Zhang Jia-Hui, Tan Jun-Jun, Luo Yi
Acta Physica Sinica. 2019, 68 (1): 013101 doi: 10.7498/aps.68.20181273
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The specific water molecules that are confined within the solvation shell adjacent to the surface of biological macromolecules (including protein, enzyme, DNA, RNA, cell membrane, etc.) are called biological water molecules. Such water around the biomolecule surface plays a very important role in the structure, stability, dynamics, and function of biological macromolecules. A molecular-level understanding of the structure and dynamics of biological water, as well as the nature of its influence on biological structure and function is the key to revealing the mechanism of the biological functions. However, the researches in this field are still in the initial stage. Here in this paper, we review the relevant researches and recent progress of hydration water from three aspects. The first aspect is about the influence of hydration water on biological structure and function. It is evident that water actively participates in many biological processes such as protein folding, proton donation and migration, ligand binding and drug design, and allosteric effects. For example, water mediates the collapse of the chain and the search for the native topology through a funneled energy landscape. The second aspect is about the structure of water molecules around the biomolecules investigated by nuclear magnetic resonance (NMR), dielectric relaxation, neutron scattering, X-ray diffraction and ultrafast optical spectroscopy. The third aspect is about the dynamic behaviors of biological water, including the relaxation time scale, dynamic property, dynamic coupling between biomolecules and water molecules, and sub-diffusive motion of the water molecules along the protein surfaces. Different techniques measure different timescales for the motion of proteins and their hydration environment. While NMR and dielectric relaxation methods reveal the motion of biological water on a time scale from several tens of picoseconds to nanoseconds, ultrafast optical spectroscopy such as fluorescence and vibrational spectroscopy probes the hydrogen-bonding fluctuations of water on a time scale from the femtosecond to picosecond. It is therefore highly necessary to acquire a real and complete picture of the structure and dynamics of biological water by combining several different techniques. Finally, some unsolved scientific problems are also summarized in this review.

Definition and quantification of hydration water in aqueous solutions

Wang Qiang, Cao Ze-Xian
Acta Physica Sinica. 2019, 68 (1): 015101 doi: 10.7498/aps.68.20181742
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Water molecules in the very proximity to the solute differ a lot from those in the far and the bulk water in both structure and property, they are usually referred to as hydration water or bound water. There is no doubt about the effect of hydration water on the property and structure of solute in solution, in particular when biological macromolecules are of concern. However, by far, there are even significant controversies over the understanding of hydration water, including the accurate definition and quantification of hydration water, the quantitative evaluation of the difference in the properties between the hydration water and free water, and how the hydration water is involved in the various biological processes, etc. For resolving the aforementioned issues, it would be of essential importance to formulate a quantification scheme for the hydration water on a sound footing. In the present article, the principles of various spectrometric techniques for determining hydration water are briefly examined, and the main deficiency in quantification of hydration water for the individual techniques is analyzed. Those techniques based on the inflection point of the concentration dependence of some physical properties of the solution are also scrutinized. Finally, we present in detail a quantification scheme for hydration water based on the concentration dependence of glass transition temperature, which leads to quite a universal categorization of an aqueous solution into three distinct zones. Also the crystallization dynamics thus revealed might be helpful for understanding the water-involved processes in other circumstances.

Recent advances in probing surface/interfacial water by scanning probe microscopy

You Si-Fan, Sun Lu-Ye, Guo Jing, Qiu Xiao-Hui, Jiang Ying
Acta Physica Sinica. 2019, 68 (1): 016802 doi: 10.7498/aps.68.20182201
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Surface and interfacial water is ubiquitous in nature and modern technology.It plays vital roles in an extremely wide range of basic and applied fields including physics,chemistry,environmental science,material science,biology,geology, etc.Therefore,the studies of surface/interfacial water lies at the heart of water science.When water molecules are brought into contact with various materials,a variety of phenomena can show up,such as wetting,corrosion,lubrication, nanofluidics,ice nucleation,to name just a few.Due to the complexity of hydrogen-bonding interactions between water molecules and the competition between water-water interaction and water-solid interaction,surface/interfacial water is very sensitive to local environment,which makes it necessary to study the structure and dynamics of water at the molecular level.In recent years,the development of new scanning probe techniques allows detailed real-space research on surface/interfacial water at single-molecule or even submolecular scale.In Section 2,several representative scanning probe techniques and their applications in surface/interfacial water are reviewed.The first one is ultra-high vacuum scanning tunneling microscopy,which allows molecular imaging of single water molecules,water clusters,wetting layers,and even water multilayers on metal surfaces as well as ultrathin insulating films.Based on scanning tunneling microscopy,the single-molecule vibrational spectroscopy can be further developed to probe the vibration and movement of individual water molecules,which assist us in understanding water diffusion,dissociation and quantum nature of hydrogen bonds.As a versatile tool at liquid/solid interfaces,electrochemical scanning tunneling microscopy opens up the unique possibility of probing the double electric layer and identifying water dynamics during electrochemical reactions. Moreover,non-contact atomic force microscopy yields higher resolution than scanning tunneling microscopy,such that the topology of hydrogen-bonding skeleton of surface/interfacial water and even the degree of freedom of hydrogen atoms can be discerned.To conclude this review,the challenges and future directions of this field are discussed in Section 3, focusing on non-invasive imaging under ambient conditions,ultrafast molecular dynamics,and novel structures under high pressures.

Interfacial water and catalysis

Hu Jun, Gao Yi
Acta Physica Sinica. 2019, 68 (1): 016803 doi: 10.7498/aps.68.20182180
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Catalysis of water, normally occurring at the interface, is crucial for the development of renewable energy and the environmental protection. Understanding the structures and chemical/physical properties of interfacial water during catalysis is of paramount importance for the sustainable development of human society, such as clean energy, wastewater treatment, and etc. However, owing to its complexity structure and mysterious property, the effect of water during catalysis is still an open question. The role of water during reactions, as reactant, catalyst, solvent, or both, has not been resolved. Recently, with the fast-development of in-situ experimental techniques and the computational capacity, the scientists started to investigate the behaviors of interfacial water using the real-time characterization and theoretical modeling at the atomic level, which provides the evidences and pictures to understand the effects of interfacial water. This paper will briefly introduce the current opportunities and challenges in studying the interfacial water, and the latest development and facing difficulty in experiment and theory, which will be beneficial for the future design of efficient catalysts for their applications in water.

Water photosplitting: Atomistic mechanism and quantum dynamics

Shen Yu-Tian, Meng Sheng
Acta Physica Sinica. 2019, 68 (1): 018202 doi: 10.7498/aps.68.20181312
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Directly splitting water into carbon-free H2 fuel and O2 gases by sunlight is one of the most environmentally-friendly and potentially low cost approaches to solving the grand global energy challenge. Recent progress of electronic structure theory and quantum simulations allow us to directly explore the atomistic mechanism and ultrafast dynamics of water photosplitting on plasmonic nanoparticles. Here in this paper, we briefly introduce the relevant researches in our group. First we propose that the supported gold nanoparticles on oxide thin film/mental should be able to potentially serve as efficient photocatalysts for water splitting. Then, under the light illumination, we identify a strong correlation among light intensity, hot electron transfer rate, and water splitting reaction rate. The rate of water splitting is dependent not only on respective optical absorption strength, but also on the quantum oscillation mode of plasmonic excitation, which can help to design nanoparticles in water photosplitting cells. Finally, we simulate the ultrafast electron-nuclear quantum dynamics of H2 generation with plasmonic gold cluster on a time scale of~100 fs in liquid water. We identify that the water splitting is dominated by field enhancement effect and associated with charge transfer from gold to antibonding orbital of water molecule. Based on all atomistic mechanism and quantum dynamics above, we present a “chain-reaction” H2 production mechanism via high-speed (much higher than their thermal velocity) collision of two hydrogen atoms from different water molecules under light illumination.

Structure and properties of nature clathrate and its application in energy and enviromental science

Zhu Jin-Long, Zhao Yu-Sheng, Jin Chang-Qing
Acta Physica Sinica. 2019, 68 (1): 018203 doi: 10.7498/aps.68.20181639
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Clathrate hydrates are energy and environmental related materials for energy storage and extraction, as well as for waste gas sequestration. The three general structures of natural clathrates, structure I, structure Ⅱ and structure H are reviewed in the aspects of stability, cage size, and preferred guest molecule encapsulation. Neutron scattering technique has its unique advantage of clathrate hydrates characterization, such as large bulk property determination, penetration of high pressure vessel and the clathrate sample inside, sensitive to light elements (clathrate hydrates mainly containing C, H, and O atoms). Neutron diffraction and inelastic neutron scattering of clathrate hydrates are covered on the abilities of H/D atoms positions and anisotropic thermal parameters, pressure-temperature-dependent guest molecule occupancy, the disordered distributions of guest molecules and the nuclear density distributions, the thermodynamic and kinetic process of formation and decomposition, the translational and rotational vibration models of guest molecules and their quantum state transitions. Using CO2 to gently replace CH4 in methane hydrate is one of the most attractive exploiting schemes for its benefits to both geologic hazard consideration and cost efficiency (energy extraction and CO2 sequestration).

Water and mass transport in low-dimensional confined structures

Zhang Xi-Qi, Wen Li-Ping, Jiang Lei
Acta Physica Sinica. 2019, 68 (1): 018801 doi: 10.7498/aps.68.20182131
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Water and mass transport in low-dimensional confined structures is of great importance in solving many challenging problems in interface chemistry and fluid mechanics,and presents versatile applications including mass transport,catalysis,chemical reaction,and nanofabrication.Recent achievements of water and mass transport in low-dimensional confined structures are summarized.Water flow confined in nanochannels with different wettability reveals the viscosity in the interface region increases as the contact angle decreases,whereas the flow capacity of confined water increases as the contact angle increases.Small difference in the nanochannel size has a big effect on the confined water flow,especially for nanochannels with a diameter smaller than 10 nm.The phenomena of ultrafast mass transport are universal in the nanochannels with smaller diameter (<10 nm),e.g.,ultrafast ionic transport across the biological and artificial ionic channel;ultrafast water flow through aligned carbon nanotube (CNT) membrane;ultrafast water permeation through GO membranes with hydrophilic end-group.From the classical hydrodynamics,the penetration barrier in such a small channel in both biological and artificial systems is huge,which is contradictory with the actual phenomena.Thus,we propose a concept of quantum-confined superfluid (QSF) to understand this ultrafast fluid transport in nanochannels.Molecular dynamic simulations of water confined in 1D nanochannel of CNTs (with diameter of 0.81 nm) and 2D nanochannel of graphene (two graphene layers distance <2 nm) demonstrate ordered chain of water molecules and pulse-like transmission of water through the channel,further provide proof for the QSF concept.Reversible switching of water wettability in the nanochannel via external stimuli (temperature and voltage) are presented,raising the temperature causes water wettability switching from hydrophilic to hydrophobic state,while increasing the voltage induces water wettability change from hydrophobic to hydrophilic state.The ultrafast liquid transport performance promotes the application of nanochannels in separation.There exist an upper limit for the surface tension of the liquid (≈ 180mN/m) below which the nanochannels of CNTs can be wetting.Then,we summarized versatile applications of low-dimensional confined structures in catalysis,chemical reaction,nanofabrication,and battery.Despite considerable advances over the last few decades,many challenging issues on water and mass transport in low-dimensional confined structures are still unresolved.The biggest obstacle is focused on understanding the physical origin of the non-classical behavior of liquid under confinement.In this situation,our proposed QSF concept will provide new ideas for the fluidic behavior in the nanochannels,and the introduction of QSF concept might create QSF-based chemistry.By imitating enzyme synthesis,the reactant molecules can be arranged in a certain order,and the reaction barrier will be greatly reduced to achieve highly efficient and selective chemical synthesis.Some previous works including organic reaction and polymeric synthesis have approached the example of QSF-like chemical reactions.On the other hand,the advances in nanomechanical techniques such as surface forces apparatus,atomic force microscope,and sum-frequency vibrational spectroscopy will provide useful experimental approaches to understand the mechanism of water and mass transport in low-dimensional confined structures,and promote wider application of nanoconfined structures.

Mechanism of soil environmental regulation by aerated drip irrigation

Yang Hai-Jun, Wu Feng, Fang Hai-Ping, Hu Jun, Hou Zheng-Chi
Acta Physica Sinica. 2019, 68 (1): 019201 doi: 10.7498/aps.68.20181357
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Soil is the foundation of food security, water safety and wider ecosystem security. China's water resources is featured by its poverty and uneven distribution. Flood irrigation in traditional agriculture not only uses large amount of water, but also destroys soil aggregate structure, resulting in soil degradation, such as soil compaction and soil salinization. Underground drip irrigation have obvious water saving efficiency with the effective utilization rate of water larger than 95%, but it will also destroy the soil structure to a certain extent. It has been reported in many researches that using aerated water drip irrigation can not only increase crop yields, but also improve crop quality. The influence of several factors such as the burial depth of drop head, the frequency of dripping, the amount of irrigation, the growth period of plant, the mode of aerating and the equipment and so on, and the effects of the aerated drip irrigation on the water environment, the air environment, the microbial environment, the nutrient environment and the mineral environment of soil are summarized. And the regulation mechanism of soil environment by the aerated drip irrigation is put forward. The changes in water, gas, microorganism, nutrition and minerals are the result of the change of soil structure. The experimental results of in situ synchrotron radiation X-ray computed tomography confirmed that aerated drip irrigation can change the structure of soil.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Correlation between electrical resistivity and strength of copper alloy and material classification

Li Hong-Ming, Dong Chuang, Wang Qing, Li Xiao-Na, Zhao Ya-Jun, Zhou Da-Yu
Acta Physica Sinica. 2019, 68 (1): 016101 doi: 10.7498/aps.68.20181498
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Low electrical resistivity and high strength are a basic requirements for copper alloys.However,it has been widely known that these two properties are contradictory to each other:high electrical resistivity means extensive electron scattering by obstacles in the alloy,which in turn blocks dislocation movement to enhance mechanical strength.That is to say,any increase in strength necessarily brings about an increase in electrical resistivity.Essentially,strength and electrical resistivity are coupled in metal alloy as both are issued from a similar microstructural mechanism. That is why it is generally difficult to evaluate these alloys comprehensively and to select the materials appropriately. #br#The present work addresses this fundamental problem by analyzing the dependence of hardness (in relation to strength) and electrical resistivity on solute content for deliberately designed ternary[Moy/(y+ 12)Ni12/(y+12)]xCu100-x alloys (at.%),where x=0.3-15.0 is the total solute content,y=0.5-6.0 is the ratio between Mo and Ni.The Mo-centered and Ni-nearest-neighbored[Mo1-Ni12]cluster structure are used to construct a short-range-order structure model of solid solution.The cluster[Mo1-Ni12]in solution enhances the strength,without increasing the electrical resistivity much,for the solutes are organized into cluster-type local atomic aggregates that reduce the dislocation mobility more strongly than electron scattering.The short-range-order structure has an essentially identical function for strength and electrical resistivity. In this solution state,both hardness and resistivity increase linearly with solute content increasing.When the solute constituents do not meet the requirement for ideal solution,i.e.,Mo-Ni ratio exceeds 1/12,the maximum value that the cluster[Mo1-Ni12]can accommodate,the solid solution should be destabilized and precipitation should occur,such as Mo precipitation in this case.The deviation from the linear change of resistivity and strength with solute content are caused by different alloy states,that is,solid solution and precipitation,which contribute to the resistivity and strength differently.Here we define a new term,the ratio of residual tensile strength to residual electrical resistivity,i.e.the “strength/resistivity ratio” in short,which represents an essential property of the alloy system.This ratio is 7×108 MPa/Ω· m) for the Cu-Ni-Mo alloy in complete solid solution state,and it is in a range of (310-490) 108 MPa/Ω·m) for the Cu-Ni-Mo alloys in a fully precipitation state (i.e.,most of Mo solute atoms precipitate out of the Cu matrix). #br#Finally this new parameter is applied to the classification of common copper industrial alloys for the purpose of laying the basis for material selection.It is found that the strength/resistivity ratio of 310 effectively marks the boundary between the fully precipitated state and precipitation plus solution state.Using this criterion,it is concluded that alloys based on Cu-(Cr,Zr,Mg,Ag,Cd) are suitable for high-strength and high-conductivity applications.However,alloys based on binary systems Cu-(Be,Ni,Sn,Fe,Zn,Ti,Al) cannot realize the same purpose.The finding of the line dividing the characteristic properties of alloy having a strength-resistivity-ratio of 310 provides a key quantitative basis for comprehensively evaluating the alloy performance,which can effectively guide material selection and development of high strength and high conductivity copper alloys.

Influence of stiffness gradient on friction between graphene layers

Dong Yun, Duan Zao-Qi, Tao Yi, Gueye Birahima, Zhang Yan, Chen Yun-Fei
Acta Physica Sinica. 2019, 68 (1): 016801 doi: 10.7498/aps.68.20181905
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According to the molecular dynamics simulations and the mechanism of energy dissipation of nanofriction, we construct a model system with a flake sliding in commensurate configuration on a monolayer suspended graphene anchored on a bed of springs. The system is to analyze the contributions of different regions (T1-T7) of the graphene flake to friction force, with the substrate characterized by different stiffness gradients and midpoint stiffness.#br#The results indicate that the soft region of contact (T1) always contributes to the driving force, whereas the hard region (T7) leads to the biggest friction force on all column atoms of the flake. Moreover, as the support stiffness increases, when the stiffness gradient and the midpoint stiffness are equal to 1.34 nN/nm2 and 12 nN/nm, respectively, the contribution ratio of T7 to the total friction increases from 33% to 47%, which is approximately 4-15 times greater than those of each column atoms in T3-T6. The results also indicate that the energy barrier decreases with the increase of support stiffness along the stiffness gradient direction of the substrate, which induces the resistance forces on the relative motion to decrease. Meanwhile, the amplitude of the thermal atomic fluctuation is higher in the softer region while lower in the harder one. This difference in amplitude leads to the considerable potential gradient that ultimately causes the driving force. Finally, for a given point at the end of the flake (T1 or T7), the intensity of the van der Waals potential field is mainly determined by the nearest substrate atoms at that point. Part of these nearest atoms lie inside the contact region while the others do not. Consequently, the thermal vibration of the atoms inside the contact region is different from that of the atoms outside the confinement. The different thermal vibrations induce the greater edge barriers. In addition, T1 lies in the soft edge region and T7 in the hard one. As a result, the normal deformations of these two regions are always different, and therefore they also generate the driving force.#br#At these points, the results reported here suggest that the friction force in each contact region is caused by the coupling of the energy barrier and the elastic deformation between the graphene surfaces. The former contribution, i.e.the energy barrier, includes the interfacial potential barrier in commensurate state which is against the sliding of the surfaces with respect to each other, and the potential gradient caused by the different vibration magnitudes of the substrate atoms against the different spring stiffness in the direction of stiffness gradient. The latter contribution, i.e. the elastic deformation, is the unbalanced edge energy barrier resulting from the asymmetrical deformation and the different degrees of freedom between the edge atoms of the slider and atoms inside and outside the contact area of the substrate. Results of this paper are expected to be able to provide theoretical guidance in considering the influence of stiffness gradient on friction between commensurate surfaces and in designing the nanodevices.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Dynamics of A-exciton and spin relaxation in WS2 and WSe2 monolayer

Yu Yang, Zhang Wen-Jie, Zhao Wan-Ying, Lin Xian, Jin Zuan-Ming, Liu Wei-Min, Ma Guo-Hong
Acta Physica Sinica. 2019, 68 (1): 017201 doi: 10.7498/aps.68.20181769
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Two-dimensional transitional metal dichalcogenide (2D TMD) emerges as a good candidate material in optoelectronics and valleytronics due to its particular exciton effect and strong spin-valley locking. Owing to the enhancement of quantum confinement effect and the decline of dielectric shielding effect, the optical excitation of electron-hole pair is enhanced substantially, which makes large TMD exciton binding energy and makes excitons observed easily at room temperature or even higher temperature. Optical response of 2D TMD is dominated by excitons at room temperature, which provides an ideal medium for studying the generation, relaxation and interaction of excitons or trions. By employing ultrafast time resolved spectroscopy, we investigate experimentally the dynamic behaviors of A-exciton and spin relaxations for two types of TMDs, i.e. WS2 and WSe2 monolayers, respectively. By tuning the excitation wavelength of the degenerate pump and probe laser beam, the WS2 monolayer and WSe2 monolayer are excited at their A-exciton resonance transition position or near their A-exciton resonance transition position in order to compare the dynamical evolutions of band structure and exciton polarization of the two similar WS2 and WSe2 monolayer structures. Our experimental results reveal that the relaxation of A exciton in WS2 shows biexponential decay, while that of WSe2 shows triexponential decay, and the A-exciton life time in WSe2 is much longer than that of WS2 counterpart. The spin relaxation of A exciton in WS2 shows a monoexponential feature with a lifetime of 0.35 ps, which is dominated by the electron-hole exchange interaction. For the case of WSe2, the spin relaxation can be well fitted with biexponential function, the fast component has a lifetime of 0.5 ps and the slow one has a lifetime of 28 ps. The fast relaxation is dominated by the electron-hole exchange interaction, and the slow one comes from the formation of dark exciton via spin-lattice coupling. By tuning the excitation wavelength around A-exciton transition, the formation of dark exciton in WSe2 is demonstrated to be much more effective than that in WS2 monolayer. Our experimental results provide qualitative physical images for an in-depth understanding of the relationship between exciton and TMD structure, and also provide reference for further designing and regulating the TMDs based optoelectronic devices.

White organic light emitting devices based on ultrathin emitting layer and bipolar hybrid interlayer

Yu Hao-Jian, Yao Fang-Nan, Dai Xu-Dong, Cao Jin, Chulgyu Jhun
Acta Physica Sinica. 2019, 68 (1): 017202 doi: 10.7498/aps.68.20181803
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In this paper, efficient phosphorescent white organic light-emitting diodes (WOLEDs) with stable spectra are fabricated based on doping-free ultrathin emissive layers and mixed bipolar interlayers. To achieve WOLEDs, at least three kinds of light-emitting layers, i.e. blue, green and red, are needed. The traditional method to fabricate emissive layers is by co-evaporation, which can improve electroluminescent efficiency. However, the co-evaporation rate and dopant concentration are difficult to control, which leads to a bad reproducibility and thus goes against commercialization. In order to simplify the structures of WOLEDs and improve repeatability, several doping-free ultrathin emissive layers are used in this paper with 3 nm mixed bipolar interlayers separating them. The optimal ratio of bipolar hybrid material is determined by hole-only device, electron-only device and blue phosphorescent OLED. In addition, green, orange and red monochromatic OLED have also been fabricated separately, which are used to prove that mixed bipolar material is also suitable for the three phosphorescent emitting material. The WOLED with TCTA interlayers is fabricated to confirm that mixed bipolar material is beneficial to the characteristics of WOLEDs. The energy transfer process between different emitting materials is verified by studying the transient photoluminescence lifetime. The maximum efficiency of three-color and four-color doping-free WOLED are 52 cd/A (53.5 lm/W) and 13.8 cd/A (13.6 lm/W), respectively, and the maximum external quantum efficiency of three-color and four-color doping-free WOLED are 17.1% and 11.2%, respectively. Due to the sequential energy transfer structure between different emitting layers, the Commission Internationale de L'Eclairage coordinates shows a very slight variation of (0.005, 0.001) from 465 cd/m2 to 15950 cd/m2 for three-color WOLED. The Commission Internationale de L'Eclairage coordinates shows a variation of (0.023, 0.012) from 5077 cd/m2 to 14390 cd/m2 for four-color WOLED. The four-color WOLED shows a maximum color rendering index of 92.7 at 884 cd/m2, and it reaches 88.5 at 14390 cd/m2. In addition, the lifetime of phosphorescent OLED is usually poor due to the trap formed by triplet-polaron annihilation. The exciton distribution can be broadened and the exciton concentration can be reduced by using ultrathin light emitting layers (< 1 nm) and mixed bipolar interlayers. Therefore, triplet-polaron annihilation will be reduced, and the lifetime of OLEDs will be improved.

Effects of AlGaN interlayer on scattering mechanisms in InAlN/AlGaN/GaN heterostructures

Chen Qian, Li Qun, Yang Ying
Acta Physica Sinica. 2019, 68 (1): 017301 doi: 10.7498/aps.68.20181663
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Recent studies showed that the nominal AlN interlayers in InAlN/AlN/GaN heterostructures had high GaN mole fractions, especially those grown by metalorganic chemical vapor deposition. The Al and Ga mole fraction in the AlGaN interlayer determine the electron wave function and penetration probability, and thus affecting the scattering mechanism related to the InAlN/AlGaN potential layers. In this paper we study the effects of Al mole fraction of the AlGaN interlayer on three scattering mechanisms related to the potential layer, i.e. alloy disorder scattering, subband energy fluctuation scattering and conduction band fluctuation scattering induced by In compositionally inhomogeneous InAlN layer. The wave function and penetration probability in the InAlN/AlGaN/GaN heterostructure are determined by self-consistently calculating the Schrödinger-Poisson equations and then used to calculate the scattering mechanisms. The results show that penetration probabilities in the InAlN and AlGaN both decrease with increasing Al mole fraction. The combination of the contribution of the screening effect and the two-dimensional electron gas (2DEG) density inhomogeneity results in an initial decrease and subsequent increase in the subband energy fluctuation scattering-limited mobility with increasing Al mole fraction, and the heterostructure with a smaller InAlN thickness has a larger mobility increase. The penetration probability and non-periodic arrangement of Al and Ga in the AlGaN predict an Al mole fraction dependence of the alloy disorder scattering-limited mobility similar to the subband energy fluctuation scattering-limited mobility, and the alloy disorder scattering occurs mainly in the AlGaN because the penetration probability in the AlGaN is much higher than in the InAlN. The conduction band fluctuation scattering-limited mobility monotonically increases with increasing Al mole fraction due to the decrease of the penetration probability. The subband energy fluctuation scattering-limited mobility is less sensitive to variation in the Al mole fraction than the other two scattering mechanisms-limited mobilities. In a small Al mole fraction range around 0.1, the alloy disorder scattering is a dominant scattering mechanism, while the subband energy fluctuation scattering dominates the mobility beyond this compositional range. When Al mole fraction is above 0.52, the three scattering mechanisms-limited mobility exceeds that in the InAlN/GaN heterostructure without the AlGaN interlayer, indicating the promotion of the mobility by the AlGaN interlayer. The mobility is raised by more than 50 percent in the InAlN/AlN/GaN heterostructure with an AlN interlayer compared with that in the InAlN/GaN heterostructure without the interlayer.

Electronic and optical properties of n-pr co-doped anatase TiO2 from first-principles Hot!

Zhang Li-Li, Xia Tong, Liu Gui-An, Lei Bo-Cheng, Zhao Xu-Cai, Wang Shao-Xia, Huang Yi-Neng
Acta Physica Sinica. 2019, 68 (1): 017401 doi: 10.7498/aps.68.20181531
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ZnO is a wide bandgap semiconductor with the advantages of good stability, strong radiation resistance, and low cost. It has become a hot material in the field of photocatalysis, but it can only absorb purple light. Therefore, it is a valuable problem to study how to expand the response range of ZnO to visible light. Doping modification is a common method to solve this problem. In order to carry out the relevant research, the calculation in this paper are carried out by the CASTEP tool in Materials Studio software based on the first-principles of ultrasoft pseudopotential of density functional theory, the geometric structures of ZnO, Zn0.875Pr0.125O, ZnO0.875N0.125, Zn0.875Pr0.125O0.875N0.125, Zn0.75Pr0.25O0.875N0.125, Zn0.625Pr0.375O0.875N0.125 are constructed. All the models are based on the optimization of the geometry structure. By using the method of generalized gradient approximation plus U, we calculate the band structure, density of states, population, absorption spectra and dielectric functions of the models. The results show Co-doped system is easier to form than single-doped system, and the stability of the co-doped system increases first and then decreases with the increase of Pr concentration. The population ratio of the shortest Zn-O bond to the longest Zn-O bond in the same system increases first and then decreases with the impurity concentration, which shows that the doping of impurities has a great influence on the lattice distortion of the system, and the distortion is benefit for the separation of photogenerated hole-electron pairs. Therefore, the photocatalytic activity of the materials can be improved. Hybridization of N-2p and Pr-4f states destroys the integrity of crystals and forms crystal fields around impurity atoms, which results in splitting of energy levels and narrowing of bandgap. Compared with intrinsic ZnO, the static dielectric constant of all doped systems increases, especially the constant of Pr-N co-doped systems increases with the increase of doped Pr concentration, which indicates that the polarization ability of the co-doped systems increases with the increase of doped Pr atomic concentration. The main peaks of the dielectric function imaginary part of the doping systems move to the low energy region, and the absorption spectrums are red-shifted. As the concentration of impurity Pr atom increases, in the visible region, the absorption capacity of each co-doped system increases, their response range is enlarged in turn, showing the co-doping of N and Pr is benefit for improving the photocatalytic activity of ZnO.

Point-contact Andreev reflection spectroscopy on Re3W superconductor Hot!

Wang Zong, Hou Xing-Yuan, Pan Bo-Jin, Gu Ya-Dong, Zhang Meng-Di, Zhang Fan, Chen Gen-Fu, Ren Zhi-An, Shan Lei
Acta Physica Sinica. 2019, 68 (1): 017402 doi: 10.7498/aps.68.20181996
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Non-centrosymmetric superconductors have received considerable attention because of their possible possession of unconventional spin-triplet pairing.For this reason,the non-centrosymmetric Re3W with α -Mn structure has been widely concerned.However,almost all the previous studies support that the non-centrosymmetric phase of Re3W is a conventional weak-coupling s-wave superconductor.Later on,it is proved that Re3W has two different superconducting phases,one is the non-centrosymmetric phase and the other has a centrosymmetric hexagonal structure.Thus,a comparative study of these two superconducting phases could provide more information about the effect of non-centrosymmetric structure on the pairing symmetry of Re3W.
In this paper,point-contact Andreev reflection experiments are carried out on Re3W/Au and the data can be well fitted by isotropic s-wave Blonder-Tinkham-Klapwijk (BTK) theory.In combination with our previous researches,we find that both centrosymmetric and non-centrosymmetric phases have similar temperature dependence of superconducting gap () with almost the same gap ratio of /Tc.These results present strong evidence that both phases of Re3W are weak coupling Bardeen-Cooper-Schrieffer superconductors.
Another interesting finding is that both phases of Re3W could easily form an ideal point-contact junction (i.e.,inelastic scatterings at the interface can be ignored) with a normal metal tip.This is manifested as an extremely small broadening factor (Γ) used in the fitting process,and indicates a clean (and possibly transparent) interface.Keeping this in mind,we can assume that the effective barrier (Z) at the interface mainly comes from the mismatch between the Fermi velocity of the superconductor and that of the normal metal,which can be estimated from the formula Z2=(1-r)2/4r,where r is the ratio between those two Fermi velocities.From this formula,we can obtain the Fermi velocity of Re3W by using the known value of Au's Fermi velocity and the fitting parameter Z for the Re3W/Au point contacts.It is interesting to find that the chemical property of Re3W is stable in the atmospheric environment.Even if the samples are exposed to the atmospheric environment for nearly six months,the inelastic scatterings are still very weak,and the superconducting properties are unchanged.
Such an exceptional performance of Re3W can be utilized to study the physical properties of its counter electrode in a point contact.As an attempt,we build a point contact between Re3W and a ferromagnetic Ni tip,and measure its Andreev reflection spectra which are then fitted with a modified BTK model by considering spin polarization.The determined spin polarization of Ni is in good agreement with previously reported result. Moreover,using the Fermi velocities of Re3W and Ni,we can calculate the effective barrier to be around 0.3 in the Re3W/Ni interface,which coincides with the fitting parameter Z.These results self-consistently demonstrate the validity of the determination of Re3W's Fermi velocity and the cleanness/transparency of the studied point-contact interface.

Modeling of stress-regulated AND (OR) logic gate based on flipping preference of tilted nanomagnet

Liu Jia-Hao, Yang Xiao-Kuo, Wei Bo, Li Cheng, Zhang Ming-Liang, Li Chuang, Dong Dan-Na
Acta Physica Sinica. 2019, 68 (1): 017501 doi: 10.7498/aps.68.20181621
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Nano-magnetic logic device (NMLD) is a novel nanoelectronic device that stores, processes, and transfers information by dipole-coupled magneto-static interactions between nanomagnets. In the NMLD, long axis tilted nanomagnet attracts the attention of researchers due to its flexibility in magnetic logic design. Edge-slanted nanomagnet is wildly used, whose long axis is tilted due to its asymmetric shape. However, there are three defects in edge-slanted nanomagnets. 1) This type of nanomagnet requires a larger size, thus increasing the nano-magnetic logic (NML) space and introducing the C-shape and vortex clock errors that are often found in large-sized nanomagnets. 2) The irregular shape of nanomagnet increases the requirements for fabrication. 3) Complex calculations caused by the irregular shape are inevitable.#br#In this paper, the tilt of the long axis of the nanomagnet is realized by placing the regular-shaped (elliptical cylinder) nanomagnet (50 nm×100 nm×20 nm) obliquely. According to the flipping preference of tilted nanomagnet, the authors design a two-input AND (OR) logic gate clocked by stress. The authors choose PMN-PT (Pb (Mg1/3Nb2/3) O3-PbTiO3) as the piezoelectric layer material to use its high piezoelectric coefficient. For magnetic materials, the authors choose Terfenol-D (Tb0.7Dy0.3Fe2), whose magnetic crystal anisotropy is smaller. The material of the subatrate is not discussed in this paper, which will be further studied in future experimental work. The mathematical model is established, and the dynamic magnetization of the gate is calculated. A stress of 90 MPa is applied to the output nanomagent for 3 ns. The nanomagnet is flipped to “NULL” at 1.8 ns and is then flipped to the final stable state after the stress has been removed for 0.9 ns. The output will become logic “0” (“1”) only if the input is logic “00” (“11”), otherwise the output will be logic “1” (“0”), thus successfully implementing OR (AND) logic. In addition, the gate is simulated by using the micromagnetic method. The results are basically consistent with our model. Unlike the designs based on edge-slanted nanomagnets, the basic logic gate based on tilted nanomagnets has three advantages. 1) This design allows high-aspect-ratio (2:1) nanomagnets to be used in logic functions. Therefore, less vortex and C-shaped error will be generated. 2) The regular shape can reduce the fabrication requirements and computational complexities. 3) Using stress as a clock, the energy consumption is greatly reduced, which can be only one-tenth of the general designs clocked by spin electronics.#br#This model provides a greater energy efficiency and reliable basic logic unit for NML design. In the experimental preparation, there may be a large preparation error tilting the nanomagnet. As a solution, the stress electrodes can be tilted instead. So the stress will also make an angle with respect to the long axis of the nanomagnet.

Refractive index and thermo-optic coefficient of Ge-Sb-Se chalcogenide glass

Yang An-Ping, Wang Yu-Wei, Zhang Shao-Wei, Li Xing-Long, Yang Zhi-Jie, Li Yao-Cheng, Yang Zhi-Yong
Acta Physica Sinica. 2019, 68 (1): 017801 doi: 10.7498/aps.68.20181869
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Ge-Sb-Se chalcogenide glass is environmentally friendly, and has wide infrared transmitting window, high optical nonlinearity, as well as good mechanical property. These make it a good material for infrared transmission and nonlinear optics. In optical designs, the refractive index (n) and thermo-optic coefficient (ζ) of the glass are key technical parameters. In order to predict and tailor the n and ζ of Ge-Sb-Se glass, compositions with different chemical and topological features are prepared, their n, ζ, density (d) and volume expansion coefficient (β) are measured, and the composition dependence of the parameters is systematically investigated. The chemical feature of the glass is quantified by the percentage deviation of the composition from the stoichiometric ratio and denoted as dSe. The topological feature is represented by the mean coordination number <r> of each atom in the composition. It is shown that the n of Ge-Sb-Se glass increases with d increasing; the ζ decreases almost linearly with β increasing; and the β decreases with dSe decreasing or <r> increasing. When the Ge content is fixed, the d increases with dSe decreasing or <r> increasing; when the Sb concentration is fixed, the d has a minimum value at dSe=0. Based on the measured d and n, the molar refractivity (Ri) of Ge, Sb and Se elements in a spectral range of 2-12 μm are calculated. The obtained value of RGe is in a range of 10.16-10.50 cm3/mol, RSd in a range of 16.71-17.08 cm3/mol, and RSe in a range of 11.15-11.21 cm3/mol. When the Ri and d are used to compute n of any composition, the discrepancy between the calculated value and the measured one is less than 1%. According to the measured ζ and β, the thermal coefficients of the molar refractivity (φi) of Ge, Sb, and Se elements in a wavelength region of 2-12 μm are computed. The optimal value of φGe is in a range of 21.1-22.6 ppm/K, φSb in a range of 7.2-8.4 ppm/K, and φSe in a range of 90.2-94.2 ppm/K. When the φi and β are used to compute ζ of any composition, the discrepancy between the calculated value and the measured value is less than 6 ppm/K.

Fabrication and photovoltaic performance of counter electrode of 3D porous carbon composite

Chen Zhuo, Fang Lei, Chen Yuan-Fu
Acta Physica Sinica. 2019, 68 (1): 017802 doi: 10.7498/aps.68.20181833
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Dye-sensitized solar cell (DSSC) has been widely investigated due to its low cost, simple fabrication process, and excellent photoelectric conversion efficiency. Generally, the DSSC is composed of photoanode, electrolyte and counter electrode. At present, platinum (Pt) film delivers the highest photoelectric conversion efficiency in the available counter electrode materials. However, Pt film is very expensive and prepared by relatively complicated and high-cost magnetron sputtering, which seriously hinders the large-scale applications in DSSC. Therefore, it is of highly academic and engineering significance to develop novel counter electrode materials with low cost and high photoelectric conversion efficiency to replace expensive Pt counter electrode. Previous research shows that carbon-based nanomaterials such as graphene and carbon nanotubes ard promising to be used as highly efficient counter electrode materials. However, the high-cost and complicated fabrication process restrict their practical applications in DSSC. To address such issues, here in this work, we present and fabricate a highly efficient and low-cost three-dimensional porous carbon composite, which is constructed by the relatively dense and conductive graphite film as bottom layer (PC layer), and the porous carbon nanoparticle film as top layer (CC layer). Our fabricated DSSC consists of commercial TiO2 photoanode (m 4 mm×4 mm), and PC, CC, CC/PC composite, or Pt counter electrode with a size of m 8 mm×8 mm. The results show that under illumination (100 mW/cm2) provided by a solar simulator, the short circuit current densities (open circuit voltages) of DSSCs with PC, CC, CC/PC, and Pt counter electrodes are 11.45 mA/cm2 (0.72 V), 11.88 mA/cm2 (0.73 V), 12.00 mA/cm2 (0.75 V), and 13.46 mA/cm2 (0.74 V), respectively. The filling factors of DSSCs with PC, CC, and CC/PC are 56.09%, 59.80%, 65.28%, and 62.69%, respectively; the photoelectric conversion efficiencies of DSSCs with PC, CC, and CC/PC are 4.61%, 5.20%, 5.90%, and 6.26%, respectively. It is noted that compared with CC layer or PC layer counter electrode, the CC/PC counter electrode delivers better photovoltaic performance. Particularly, the filling factor of DSSC with CC/PC (65.28%) is even 4.10% higher than that of DSSC with commercial Pt (62.69%), and the photoelectric conversion efficiency of the CC/PC-based DSSC is as large as 5.90%, which reaches 94.2% of the Pt-based DSSC (6.26%). The excellent performance of DSSC with CC/PC counter electrode is attributed to the unique three-dimensional porous structure, which can not only facilitate the transfer of electrons and ions, but also provide abundant catalytic sites; these synergistic effects greatly enhance the photovoltaic conversion performance of CC/PC-based DSSC.

Research on fluorescence lifetime dynamics of quantum dot by single photons modulation spectrum

Zhang Qiang-Qiang, Hu Jian-Yong, Jing Ming-Yong, Li Bin, Qin Cheng-Bing, Li Yao, Xiao Lian-Tuan, Jia Suo-Tang
Acta Physica Sinica. 2019, 68 (1): 017803 doi: 10.7498/aps.68.20181797
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Fluorescence lifetime is an important characteristic parameter of quantum dot, which plays an important role in studying the optical properties of quantum dot. As a common method to obtain fluorescence lifetime, fluorescence decay curve fitting has been broadly accepted. The least squares fitting to the fluorescence decay curve is performed by using the exponential decay function to obtain fluorescence lifetime with taking the instrument response function into account. However, since the fluorescence decay curve inevitably involves noise photons such as dark counts and stray photons, there is a certain error in the fluorescence lifetime obtained by the method. In order to reduce the error and improve the accuracy of the results, enough photons are required. Nevertheless, too many photons will result in low efficiency of lifetime analysis and temporal resolution, and therefore this method can hardly extract dynamic information on a smaller temporal scale. In this paper, we propose a new method of obtaining the fluorescence lifetime of quantum dot, namely the single photons modulation spectrum. The basic idea is based on the relationship between the fluorescence lifetime and the signal amplitude of pulse repetition frequency in a single dynamic process. The experimental results show that the fluctuation errors and deviation errors of lifetime obtained by our method are significantly lower than those of the previous method when the same number of photons is used. Therefore, high-accuracy fluorescence lifetime can be obtained. When the fluctuation error is 5%, the accuracy is increased by more than one order of magnitude. And to obtain the fluorescence lifetime of the same error level, the number of photons required for our method is much smaller than that of the previous one, which indicates that our method can effectively suppress the disturbance of noise photons and enables the lifetime measurement with high efficiency and temporal resolution. When the fluctuation error and deviation error are both 5%, the efficiency and temporal resolution are increased by more than four times. Finally, real-time lifetime trajectory corresponding to the photoluminescence intensity time trajectory is obtained by our method, where rich dynamic information can be obtained on a sub-second temporal scale. The method of obtaining fluorescence lifetime with powerful anti-noise capability, high efficiency and temporal resolution proposed in this paper can play an important role in studying the fluorescence dynamics of single quantum systems.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Mechanism of influence of separator microstructure on performance of lithium-ion battery based on electrochemical-thermal coupling model

Zeng Jian-Bang, Guo Xue-Ying, Liu Li-Chao, Shen Zu-Ying, Shan Feng-Wu, Luo Yu-Feng
Acta Physica Sinica. 2019, 68 (1): 018201 doi: 10.7498/aps.68.20181726
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Separator is an important component of lithium-ion battery,and the microstructure of separator has an important influence on the performance of lithium-ion battery.In the present paper,an electrochemical-thermal full coupling model is developed to accurately describe the complex physicalchemical phenomena in lithium-ion battery in charge and discharge process.The simulation results by the present model are closer to the experimental results than those by the previously published model.What is more,the present model is widely used to investigate the effects of the separator porosity and tortuosity on the performance of lithium-ion battery,respectively.The simulation results show that with separator porosity decreasing or separator tortuosity increasing,the output voltage,maximum discharge capacity and average output power of lithium-ion battery decrease,and the lithium-ion battery surface temperature and its rising rate increase.In the initial stage of discharge,when the separator porosity decreases or separator tortuosity increases to a certain degree,the output voltage of lithium-ion battery first decreases and then increases.The smaller the separator porosity or the higher the separator tortuosity,the larger the range and rate of reducing the output voltage of lithium-ion battery become and the longer the rise time needs in the initial stage of discharge.To ensure that the output voltage of lithium-ion battery is higher than the cut-off voltage,the separator tortuosity must be less than the critical tortuosity (It is equal to the separator tortuosity of the lithium-ion battery with the lowest output voltage,which is just equal to the cut-off voltage in the initial stage of discharge).Finally,a comprehensive analysis is conducted on the dynamic distribution of the electrochemical parameters and various heat productions in lithium-ion battery during charge and discharge.It can be clearly found that the electrochemical reactions in the end of discharge,the diffusion coefficients and the conduction coefficients of Li+ of electrolyte in the initial and middle stage of discharge are mainly influenced by the separator porosity and tortuosity.The research results in the present paper not only provide theoretical and technical support for the separator microstructure design and optimization,but also has important realistic meanings for improving or perfecting the preparation technology of the separator.

Photoinduced charge carrier dynamics and spectral band filling in organometal halide perovskites Hot!

Zhao Wan-Ying, Ku Zhi-Liang, Jin Zuan-Ming, Liu Wei-Min, Lin Xian, Dai Ye, Yan Xiao-Na, Ma Guo-Hong, Yao Jian-Quan
Acta Physica Sinica. 2019, 68 (1): 018401 doi: 10.7498/aps.68.20181854
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In recent years, the solution-processed organic-inorganic perovskite solar cells have attracted considerable attention because of their advantages of high energy conversion efficiency, low cost, and easily processing. Organometallic halide perovskite solar cells have gradually demonstrated particular superior properties in energy field due to their excellent photoelectric properties. This has been triggered by the unprecedented increase in its overall power conversion efficiency reaching 23% in just a few years, and it is becoming a direct competitor against the existing leading technology silicon. In this paper, 5-AVA-doped organometal halide perovskite films, (5-AVA)0.05(MA)0.95PbI3 and (5-AVA)0.05(MA)0.95PbI3/Spiro-OMeTAD, are prepared by the two-step method. The generation and recombination mechanism of charge carriers in two kinds of film samples are discussed in detail. The bivalent band structure of perovskite film material CH3NH3PbI3 is determined by ultraviolet-visible absorption spectra of perovskite film (5-AVA)0.05(MA)0.95PbI3 and (5-AVA)0.05(MA)0.95PbI3/Spiro-OMeTAD. We investigate the photocarrier dynamics and band filling effects in these two organometal halide perovskite films by using femtosecond transient absorption spectroscopy. For (5-AVA)0.05(MA)0.95PbI3, the photoinduced bleach recovery at 760 nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via the recombination of free electrons and holes. With regard to the perovskite film (5-AVA)0.05(MA)0.95PbI3 and (5-AVA)0.05(MA)0.95PbI3/Spiro-OMeTAD, the signal is photoinduced absorption from 550 nm to 700 nm. As the delay time increases, the electrons and holes are recombined, which results in a red shift of absorption spectrum in (5-AVA)0.05(MA)0.95PbI3. This can be referred to as Moss-Burstein band filling model. In contrast, the electrons and holes of (5-AVA)0.05(MA)0.95PbI3/Spiro-OMeTAD perovskite film sample are separated after photoexcitation. The holes rapidly transfer to the hole transport layer of Spiro-OMeTAD. It will lead to an increase in sample absorbance and a rapid recovery of bleaching signals. Consequently, electron-hole recombination is no longer a dominant pathway to the relaxation of photocarriers and the band filling effect is not significant in the composite film. Our findings provide a valuable insight into the understanding of the charge carrier dynamics and spectral band filling in mixed perovskites. These results conduce to the understanding of the intrinsic photo-physics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications, and provide a reference for the future research of perovskite solar cells.

Mathematical model of memristor with sensory memory

Shao Nan, Zhang Sheng-Bing, Shao Shu-Yuan
Acta Physica Sinica. 2019, 68 (1): 018501 doi: 10.7498/aps.68.20181577
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In Atkinson-Shiffrin model, the formation of human memory includes three stages:sensory memory (SM), short-term memory (STM), and long-term memory (LTM). A similar memory formation process has been observed and reported in the experimental studies of memristors fabricated by different materials. In these reported experiments, the increase and decrease of the memristance (resistance of a memristor) would normally be regarded as the loss and formation of the memory of the device. These memristors can be divided into two types based on the memory formation process. The memory formation of some memristors consists of only STM and LTM, and these memristors in this paper are called STM → LTM memristors; the memory formation of other memristors contains all three stages like human memory, and these memristors here are named SM → STM → LTM memristors. The existing mathematical model of this kind of memristor can only describe the STM → LTM memristor. Three state variables are included in this model:w describes the memory of the device, wmin describes the long-term memory, and τw0 is the time constant of the forgetting curve of the short-term memory. In this paper, a phenomenological memristor model is proposed for SM → STM → LTM memristors. The model is designed by redefining a+, a constant in the existing STM → LTM memristor model, as a state variable, and the design of corresponding state equation is based on the reported experimentally observed behaviors of SM → STM → LTM memristors during the SM period. Simulations of the proposed model show its ability to describe the behavior of SM → STM → LTM memristors. Stimulated by repeated positive pulses starting from the high-memristance state, the memristor stays in the SM state during the stimulation of first several pulses, and no obvious memory is formed during this period; STM and LTM would be gradually formed when the following pulses are applied. A faster memory formation speed can be achieved by applying pulses with longer duration, shorter interval, or higher amplitude. The formation and annihilation of the conductive channel between two electrodes of a memristor is a commonly used explanation for the change of the memristance. In this model, w can be understood as the normalized area index of the conductive channel, wmin is the normalized area index of the stable part of the conductive channel, τw0 describes the amount of time taken by the annihilation of the unstable part, and a+ determines the variation of the conductive channel when different positive voltages are applied.

Network heterogeneity based on K-order structure entropy

Huang Li-Ya, Huo You-Liang, Wang Qing, Cheng Xie-Feng
Acta Physica Sinica. 2019, 68 (1): 018901 doi: 10.7498/aps.68.20181388
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Structure entropy can evaluate the heterogeneity of complex networks, but traditional structure entropy has deficiencies in comprehensively reflecting the global and local network features. In this paper, we define a new structure entropy based on the number of the K-order neighbor nodes which refer to those nodes which a node can reach within K steps. It can be supposed that the more K-order neighbors a node has, the more important role the node plays in the network structure. Combining the formula of Shannon entropy, the K-order structure entropy can be defined and figured out to explain the differences among the relative importance among nodes. Meanwhile, the new structure entropy can describe the network heterogeneity from the following three aspects. The first aspect is the change tendency of structure entropy with the value of K. The second aspect is the structure entropy under a maximum influence scale K. The last aspect is the minimum value of the K-order structure entropy. The simulation compares the heterogeneities of five classic networks from the above three aspects, and the result shows that the heterogeneity strengthens in the from-weak-to -strong sequence:regular network, random network, WS (Watts-Strogatz) small-world network, BA (Barabási-Albert) scale-free network and star network. This conclusion is consistent with the previous theoretical research result, but hard to obtain from the traditional structure entropy. It is remarkable that the K-order structure entropy can better evaluate the heterogeneity of WS small-world networks and suggests that the greater small-world coefficients a network has, the stronger heterogeneity the network has. Besides, the K-order structure entropy can fully reflect the heterogeneity variation of star networks with network size, and reasonably explain the heterogeneity of regular networks with additional isolated nodes. It suggests that when i additional isolated nodes are added to a regular network with n nodes, the new network has weaker heterogeneity than the old one, but has stronger heterogeneity than the regular network with n+i nodes. Finally, the validity of the K-order structure entropy is further confirmed by simulations for the western power grid of the United States. Based on the minimum value of the K-order structure entropy, the heterogeneity of the western power grid is the closest to that of WS small-world networks.
REVIEW

Recent progress of solidification of suspensions

You Jia-Xue, Wang Jin-Cheng, Wang Li-Lin, Wang Zhi-Jun, Li Jun-Jie, Lin Xin
Acta Physica Sinica. 2019, 68 (1): 018101 doi: 10.7498/aps.68.20181645
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Suspensions include solvent and uniformly dispersed particles. Solidification of suspensions is to freeze the solvent while numerous particles disturb the pattern formation during the growth of the solid/liquid interface. It is a new interdisciplinary subject, involving the fields of freeze-casting porous materials, frost heaving, sea ice and biological tissue engineering and so on. Especially in recent years, many advanced materials with excellent properties were developed based on the processing of suspension solidification. Experimental phenomenon in suspension solidification is different from that in alloy solidification, such as the close-packed particle layer and self assembly, the ice lamellae structure and the periodic ice lenses and so on. Up to now, the formation mechanisms of these microstructures are still unclear. In this paper, we first review the historical development of suspension solidification in theory and in experiment. Then we demonstrate some recent progress of microstructural evolution and dynamical particle packing of suspension solidification. Finally, the outlooks of the future study on solidification of suspensions are also presented.
GENERAL

Geometric momentum distribution for three-dimensional isotropic hormonic oscillator

Liu Quan-Hui, Zhang Meng-Nan, Xiao Shi-Fa, Xun Da-Mao
Acta Physica Sinica. 2019, 68 (1): 010301 doi: 10.7498/aps.68.20181634
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The geometric momentum was originally introduced for defining the momentum of particle constrained on a hypersurface, but it is in fact not necessarily defined on a curved surface only. If a coordinate system contains a family of hypersurfaces and a normal vector on hypersurface used as a unit vector, the geometric momentum can be defined on the family of hypersurfaces and can be used to determine a complete set of commuting observables. For instance, the spherical polar coordinate system is such a kind of coordinate, in which for a given value of radial position, the spherical surface is a hypersurface. It is well-known that any vector in the space can be decomposed into components along each axis of the spherical polar coordinates, but the geometric momentum has a different decomposition, for it requires a projection of the momentum on the hypersurface, and then needs to decompose the projection into the Cartesian coordinates of the original space where the whole spherical coordinates are defined. Explicitly, with a relation-iħ▽=pΣ + pn where-iħ▽ can be usual momentum operator in Cartesian coordinates, and pΣ is the momentum component on the hypersurface which turns out to be the geometric momentum, and pn is the momentum component along the radial direction, we have a nontrivial definition of radial momentum as pn ≡-iħ▽-pΣ. Once-iħ▽ and pΣ are measurable, pn is then indirectly measurable. The three-dimensional isotropic harmonic oscillator can be described in both the Cartesian and the spherical polar coordinates, whose quantum states thus can be examined in terms of both momentum and geometric momentum distributions. The distributions of the radial momentum are explicitly given for some states. The radial momentum operator that was introduced by Dirac has clear physical significance, in contrast to widely spreading belief that it is not measurable due to its non-self-adjoint.

Chaotic motion of piezoelectric material hyperbolic shell under thermoelastic coupling

Li Lin-Li, Xue Chun-Xia
Acta Physica Sinica. 2019, 68 (1): 010501 doi: 10.7498/aps.68.20181714
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Piezoelectric material, which exhibits excellent electro-mechanical conversion properties, is widely used in smart sensors and structures for sonar systems, weather detection and remote sensing. Hyperbolic shell structure made of piezoelectric material is liable to break down when it is used in high temperature environment, which is caused by the unexpected chaotic dynamic motion under the coupling effect of thermal filed and force field. Therefore, the chaotic nonlinear dynamic vibration of simply-supported piezoelectric material hyperbolic shell is studied under the combined action of temperature field and simple harmonic excitation. Based on the theory of finite deformation, the non-linear vibration equation and coordination equation of the hyperbolic shell are established. The non-linear dynamic equation of the structure is obtained by the Bubnov-Galerkin principle. The corresponding undisturbed Hamilton system has a homoclinic orbit. Using Melnikov function, the chaotic motion condition of the dynamic system under the criterion of Smale-horseshoe transformation is obtained. Furthermore, the mathematical model is established by Simulink software and the numerical simulations are performed by the fourth-order Runge-Kutta method. The simulation results accord well with those from the Melnikov method. The bifurcation diagram, the Lyapunov exponent diagram, the phase diagram and Poincaré section diagram are acquired to analyze the influence of temperature field on the non-linear characteristic of piezoelectric material hyperbolic shell system. When the temperature is close to 32℃ and 41℃, the Lyapunov index is less than 0 and the corresponding movement of the system is in the periodic zone, which is the same as that for a temperature range from 36℃ to 37℃. When the Lyapunov index is greater than 0, the corresponding movement of the system is in chaos zone. Therefore, the change of temperature has an additional effect on the stiffness of the system which affects the vibration of the system. The chaos and periodic zones of the system alternate with the increase of temperature and the vibration characteristics of the system can be controlled by changing the temperature field. Therefore, adjusting the temperature field can control the motion state of the system, which helps to improve reliability of the structure.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Characteristics of convergence zone formed by bottom reflection in deep water

Zhang Peng, Li Zheng-Lin, Wu Li-Xin, Zhang Ren-He, Qin Ji-Xing
Acta Physica Sinica. 2019, 68 (1): 014301 doi: 10.7498/aps.68.20181761
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There appears a convergence effect on the sound filed under the condition of sound channel in the deep sea due to the refraction effect of the sea water. For the deep water environment with an incomplete channel, sea bottom has an important influence on sound propagation. A long-range sound propagation experiment was conducted in the South China Sea in April 2018. Hyperbolic frequency modulated (HFM) signals with a frequency band of 250-350 Hz are transmitted by an acoustic source which is towed at a speed of 4 knots away from a vertical line array (VLA). The VLA consists of 20 hydrophones which are arranged from 85 m to 3400 m with an unequal depth space. Using the data collected in the experiment, the effects of bathymetry variation on sound propagation are studied. The physical causes of the seafloor reflection convergence phenomenon are explained by using the parabolic equation combined with ray theory. The observed phenomenon is different from the convergence phenomenon in the typical deep water environment, the spatial variation of bathymetry contributes to the formation of the seafloor reflection convergence zone in advance, and the sound intensity in part of shadow zone is significantly increased. Due to the reflection from the seabed, two obvious seafloor reflection convergence zones are observed near the range of 20 km and 40 km respectively, in which both gains increase up to 10 dB, and a high sound intensity area is formed in the shadow zone near the range of 11 km, where the gain is less than the gains in the two convergence zones. In addition, the grazing angle of the sound ray reaching the second convergence zone is smaller than that reaching the first convergence zone when the receiving depth is the same as the source depth, and the rays with smaller glancing angle have less reflection loss, which leads to a higher gain in the second convergence zone. As the water depth becomes gradually shallower with range increasing, the convergence zone near the range of 51 km under the SOFAR channel is destroyed, and the sound field energy in the corresponding range is much smaller since the number of arriving refracted sound rays is reduced. In the first convergence zone, the path of arriving rays is gradually increased as the receiver becomes deeper. Therefore, the arrival structure tends to be complicated, and the multi-path effect is more obvious. The study result is meaningful for the performance analysis of sonar in complex deep water environment.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Photon spectrum and angle distribution for photon scattering with relativistic Maxwellian electrons

Li Shu
Acta Physica Sinica. 2019, 68 (1): 015201 doi: 10.7498/aps.68.20181796
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Description of photon scattering with relativistic Maxwellian electrons is numerically complex, and computationally time consuming for the final photon energy and angle distribution. A Monte Carlo method is used to simulate photon scattering with relativistic Maxwellian electrons. The main idea of this method is to transform the interaction of photonmoving electrons in the laboratory coordinate system into that in a new coordinate system in which the electrons are at rest, then to use the exact Klein-Nishina formula to describe this interaction and obtain the outgoing photon energy and angle, finally, to transform it into the primary laboratory coordinate system. In sum, there are eight steps, i.e.two two-dimensional (2D) transforms and two three-dimensional (3D) transforms and two Lorentz transforms, and two sampling. Repeating this process, summarizing and averaging all computed energy values and angles, the distribution of scattered energy and angle can be obtained.#br#A Monte Carlo processor is developed to simulate a photon of any energy interacting with electrons at any temperature. Some typical cases are simulated. The computed results indicate that the photon spectrum is different from that of the photon scattering with rest electrons remarkably, especially for a low energy photon scattering with the high temperature electrons. The main phenomena are Doppler broading and blue shifting. The moving electron can extend the distribution of the outgoing photon energy, and for a low energy photon scattering with the high temperature electrons, the photon maybe obtains the energy from electrons with significant probability. The angle distribution is very complicated, and it is determined by the incident photon energy, the outgoing photon energy, and the electron temperature. This processor can calculate the energy scattering differential cross-sections or energy-angle scattering double differential cross-sections, and provide the data in a tabulated form for other transport methods.
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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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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Uncertainty Quantification in the Calculation of keff Using Sensitity and Stochastic Sampling method

null
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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Total Dose Dependence of Hot Carrier Injection Effect in the NMOS Devices

null
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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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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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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A broadband low-frequency sound insulation structure based on two-dimensionally inbuilt Helmholtz resonators

null
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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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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Optimization design of a Gamma-to-Electron spectrometer for high energy gammas induced by fusion

null
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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A super-resolution infrared microscopy based on a doughnut pump beam

null
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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Influnence of Nonspherical Effects on the Secondary Bjerknes Force in a Strong Acoustic Field

null
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 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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The Principle and Application of Diagonal Reducing Method in the Complex Noise Fields

null
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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Combined noise source identification method based on spherical microphone array with random unifrom distribution of elements

null
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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First-principles study on the thermodynamic stabilities and electronic structures of long-period stacking ordered phases in the Mg-Y-Cu alloys

null
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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The effect of linear bubble vibration on wave propagation in unsaturated porous media containing air bubbles

null
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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Moving target compressive imaging based on improved row scanning measurement matrices

null
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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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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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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Calculation of Hamilton energy function of dynamical systems by using Helmholtz theorem

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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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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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Ballistic thermal rectification in the three-terminal graphene nanojunction with asymmetric connection angles

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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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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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Penta-decomposition of instantaneous field in spanwise-rotating turbulent plane Couette flow

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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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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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Ferroelectric phase transition of perovskite SnTiO3 based on first principles

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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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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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Research on the method of vibration suppression for high precision broadband laser frequency scanning interferometry

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Accept: 2016-08-18
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The paper studies the method of reducing environmental influence in broadband laser frequency scanning interferometer. Target displacement caused by vibration will resulting in Doppler shift on measurement beat frequency. The quantity of frequency shift is usually much larger than the actual target displacement, so if calculating the target distance directly will cause ranging precision reduction. This paper established the impact model of environmental vibration on the measurement and analyzed the influence of the vibration on the ranging result. To suppress vibration effect, the Kalman filter is combined with the overlapping ChirpZ transform to estimate the measured data. The general process is as follows, firstly, the tuning nonlinearity will lead to the frequency spectrum broadening, so this paper uses the frequency sampling method to correct the frequency modulation nonlinearity of the laser. The frequency sampling method has the advantages of high speed and high precision. Secondly, the measurement system has the dispersion mismatch effect due to the use of broadband frequency swept laser. To solve this problem, the influence of the dispersion on the measurement is reduced by using the method of dispersion chirp slope calibration. Thirdly, because of the long frequency sweep period of the external cavity swept frequency laser, the vibration process of the target can’t be recorded in real time by single sweep, so this paper proposes segmenting the measurement signal of single sweep and conducting ChirpZ transform to calculate target distance at different time. Compared with FFT algorithm, ChirpZ transform can achieve arbitrary narrow band spectrum subdivision, with the advantages of high accuracy and fast frequency measurement. Lastly, the ChirpZ ranging result is further combined with the method of Kalman filter to estimate the state of the target distance information. The experimental results indicate that the measurement standard is reduced from 185.4μm to 9μm by the proposed method. Without changing the absolute distance measuring device of broadband laser frequency scanning interferometer, this method provides a solution for further improving the ranging accuracy in the vibration environment, and reduces the complexity and cost of the device.
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Effect of Surface Regulation on Monolayer SbAs and BiSb

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Accept: 2016-08-18
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Using the first principle calculation based on the density functional theory (DFT), we systematically investigate the stability and the structural and electronic structures of fully hydrogenated and fully fluorinated SbAs and BiSb. The results show that the SbAs and BiSb transform the buckled structure into quasi-planar structure after fully hydrogenated or low-buckled structure after fully fluorinated. Stability studies show that all the SbAs and BiSb structures (intrinsic, full hydrogenated, and fully fluorinated) are highly stable, leading to the possibility to be obtained in experiment. The electronic structure study show that both SbAs and BiSb turn from wide band gap semiconductors into narrow direct-gap semiconductors after fully hydrogenated and fully fluorinated, meanwhile the band structures still have good linear dispersion. Based on further analysis of the electronic structures of quasi-planar or low-buckled SbAs and BiSb, the reason of the change of band structure is revealed. Calculations show that the fX-SbAs (X = H, F) films on h-BN substrate can maintain the direct band gap characteristics because of the weak coupling between them, indicating that they may have great applications in the field of optoelectronic devices in the future.
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Conductivity characterization of nanometer thickness organic film using reflectance spectroscopy

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Accept: 2016-08-18
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We propose an optical approach for analyzing the formation of the conductive layer during organic thin film growth. The relationship between the properties of multi-layer film, such as thickness and optical coefficients, and the corresponding differential reflectance spectrum (DRS) is derived as math formula based on effective medium approximation. With the deduced formula, the thickness of the deposited film, for example, electron transport layer in this paper, can be estimated according to the measured DRS data. But, in fact, the fitting error always exists. It is, on the other hand, a useful evidence to point out the actual situation of the thin film. A concept of the normalized fitting error (NFE) is offered here to equivalently assess the fitting results of all DRS data in the growth process. The curve of NFE over time is proposed to analyze the growth revolution of the thin film and reveal the inside physical mechanism. In order to demonstrate the performance of the proposed method, Organic Field Effect Transistor (OFET) with a bottom-gate structure are manufactured and pentacene organic thin film is deposited by vacuum thermal evaporation, as an electron transport layer, on the top of the transistor, i.e. an insulator substrate of Si/SiO2. The reflected optical spectrum and the current between the drain and the source of the OFET device are investigated in real time during the growth process. As reported that pentacene has three kinds of crystal structures and their optical properties differ, the actual phase of the pentacene film in our experiment is discussed at first. The fitting results show that the pentacene layer exists mainly in thin film phase here. Then, the thickness of SiO2 layer is determined as 296nm, which is close to the design value of 300nm. With those parameters, a four-layer model is applied to calculate the thickness of the organic film. The thickness data present that the film appears a linear growth and the growth rate is 0.2nm/min. Next, the NFE is plot as a function of time. In this plot, the curve of the NFE increases quickly at the beginning of the growth and reaches to a positive peak at 70min. After that, the NFE decreases and then keeps constant for a while. When the measured current curve over time is added into this plot, one finds that the increase of the current happens at the same time with the peak of the NFE. It implies that the NFE is related to the structure change of the organic film and thus linked indirectly to the electronic property. The peak of the NFE, to a certain extent, reveals the completeness of the organic conductive layer. As a result, the presented optical approach is valuable for analyzing the electronic status of the organic thin film, especially if the electronic test can’t be performed.
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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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2018 Vol.67      No.1      No.2      No.3      No.4      No.5      No.6
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2009 Vol.58      No.1      No.2      No.3      No.4      No.5      No.6
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2008 Vol.57      No.1      No.2      No.3      No.4      No.5      No.6
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2007 Vol.56      No.1      No.2      No.3      No.4      No.5      No.6
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1998 Vol.47      No.1      No.2      No.3      No.4      No.5      No.6
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1997 Vol.46      No.1      No.2      No.3      No.4      No.5      No.6
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1994 Vol.43      No.1      No.2      No.3      No.4      No.5      No.6
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1993 Vol.42      No.1      No.2      No.3      No.4      No.5      No.6
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1992 Vol.41      No.1      No.2      No.3      No.4      No.5      No.6
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1991 Vol.40      No.1      No.2      No.3      No.4      No.5      No.6
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1990 Vol.39      No.1      No.2      No.3      No.4      No.5      No.6
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1989 Vol.38      No.1      No.2      No.3      No.4      No.5      No.6
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1988 Vol.37      No.1      No.2      No.3      No.4      No.5      No.6
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1987 Vol.36      No.1      No.2      No.3      No.4      No.5      No.6
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1986 Vol.35      No.1      No.2      No.3      No.4      No.5      No.6
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1985 Vol.34      No.1      No.2      No.3      No.4      No.5      No.6
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1984 Vol.33      No.1      No.2      No.3      No.4      No.5      No.6
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1983 Vol.32      No.1      No.2      No.3      No.4      No.5      No.6
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1982 Vol.31      No.1      No.2      No.3      No.4      No.5      No.6
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1981 Vol.30      No.1      No.2      No.3      No.4      No.5      No.6
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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] (38554)
· Large-eddy simulation and experimental study of deflecting oscillation of planar opposed jets [2013, No.8:84704-084704] (38123)
· 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] (30687)
· Quasiparticle band structure calculation for SiC using self-consistent GW method [2012, No.13:137103-137103] (28988)
· Proximity-effect-induced superconductivity by granular Pb film on the surface of Bi2Te3 topological insulator [2013, No.16:167401-167401] (27028)
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