Vol. 62, No. 1 (2013)
2013, 62 (1): 017202. doi: 10.7498/aps.62.017202
Recently, the applications of vanadium dioxide film (VO2) in terahertz functional devices have attracted much attention because VO2 has a remarkable response to THz wave, In this work BK7 glass a material highly transparent to both THz and optical band is adopted as a substrate. High-quality VO2 film is deposited on a BK7 substrate using low temperature magnetron sputtering technology. The crystallinity and microstructure of the thin film are investigated by X-ray diffraction and atomic force microscopy. The results indicate that the as-deposited film crystallizes directly into single-phase VO2 with (011) preferred orientation and compact nanostructure. Under a heating-cooling cycle, the film undergos a metal-insulator transition with an abrupt resistivity change reaching more than 4 orders of magnitude. Terahertz transmission modulation is characterized by terahertz time domain spectrum, and a giant modulation depth of 89% is obtained. Due to the high transparence and the huge modulation effect, the VO2/BK7 can be widely used for THz devices such as modulators and switches.
2013, 62 (1): 017501. doi: 10.7498/aps.62.017501
Bulk Terfenol-D/PZT composite material with laminated structure is prepared by sticky combination method. The magnetoelectric hysteresis loops under different frequencies are measured and analyzed by new plotting method in the polar coordinates. The results show that tiny phase drift occur in a non-resonant-frequency magnetoelectric hysteresis loop and significant phase drift as large as 90 degrees accompanied with a giant magnetoelectric effect occurs in a resonant-frequency magnetoelectric hysteresis loop. Terfenol-D powder/Epoxy/PZT composite material is prepared by fill method and used as contrast material. Comparison reveals that the phase drift in the non-resonant frequency magnetoelectric hysteresis loop is induced by eddy current in the bulk ferromagnetic constituent, while around the resonant frequency, the significant phase drift is derived from the variation of the elastic property induced by the applying magnetic field.
2013, 62 (1): 018101. doi: 10.7498/aps.62.018101
Transparent thin-film transistor (TFT) with ZnO film as a channel layer is fabricated at room temperature. ZnO film has a high absorption in the UV region and ZnO-TFT is sensitive to the UV illumination. We investigate the ultraviolet photoresponse of ZnO-TFT and find that the illumination with 254 nm light results in an evident photoresponse. The residual conductivity is observed in ZnO channel even the UV light was removed one week before. The UV illumination can induce the formation of oxygen vacancy defects which will act as donors in ZnO channel.
2013, 62 (1): 010201. doi: 10.7498/aps.62.010201
The approximate solitary-like wave solution for a class of disturbed evolution equation is considered using a simple and valid technique. First, an approximate solution of a corresponding typical differential equation is introduced, and then the approximate solution for an original disturbed evolution equation is obtained using the functional mapping method. It is pointed out that the series of approximate solution is convergent. The accuracy of the approximate solution is also discussed using the analytic method.
Quantum system based on superconducting circuit is considered as one of the most promising schemes to realize quantum computers due to its controllability, low dissipation and scalability. To implement large scale quantum computation, coherent coupling between qubits is crucial for controlling and transferring quantum states. In this review paper, we summarize the progress of coupled superconducting qubits, including local coupling via capacitance or inductance, multiple qubits coherent interaction through one-dimensional resonator as circuit quantum electrodynamics, and superconducting qubits in a three-dimensional waveguide cavity. Hamiltonians of various coupling schemes are analyzed and classification of these coupling structures is summarized based on the coupling range and tunability.
2013, 62 (1): 010302. doi: 10.7498/aps.62.010302
A quantum information signature protocol based on weak nonlinearity and the symmetrical quantum cryptography is proposed. A sender can send classical messages and can judge whether the messages have been modified or replaced by an adversary. When the authentication of messages is completed, the fact of the communication can neither be disavowed by the sender nor be denied by the receiver because of the existence of an honest arbitrator.
2013, 62 (1): 010501. doi: 10.7498/aps.62.010501
To analyze the complexity of chaotic pseudo-random sequences accurately, spectral entropy (SE) algorithm is used to analyze chaotic pseudo-random sequences generated by Logistic map, Gaussian map or TD-ERCS system. The SE algorithm has few parameters, and has high robustness with the sequence length N (the only parameter) and the pseudo-random binary number K. Using sliding window method, the evolution features are analyzed, and complexity of discrete chaotic systems with different initial conditions and system parameters are calculated. The results show that SE algorithm is effective for analyzing the complexity of the chaotic pseudo-random sequences, and TD-ERCS is a high complexity system with wide parameter range, and has the best complex performance among the three chaotic systems. The complexity of the same chaotic system with different initial values fluctuates within a small range. It provides a theoretical and experimental basis for the applications of chaotic sequences in the field of information security.
2013, 62 (1): 010502. doi: 10.7498/aps.62.010502
Based on the classical Chua's circuit, a four-dimensional Generalized Chua's circuit with multiple interfaces is established by introducing feedback elements. For the appropriate condition, there exists a difference in order of magnitude between the variables of state and a fast-slow coupled system, thereby forming a fast- and slow-coupled system at time scale. Analyzing the equilibrium points and the characteristics of the fast subsystems, and combining the theory of Clarke differential inclusions, the singularities on the non-smooth boundaries are explored. Two types of periodic bursting phenomena for different conditions are presented. Fast-slow analysis is employed to explore the special cluster phenomenon while the system trajectory passes across multiple interfaces. The coexisting different bursting mechanisms for the case with multiple attractors are explored in detail, while the influence of non-smooth bifurcations on bursting behavior is revealed.
Numerical study on the dynamic behavior of internal structure of 1+1-dimensional ballistic deposition model
2013, 62 (1): 010503. doi: 10.7498/aps.62.010503
In this paper, the dynamic behavior of internal structure of 1+1-dimensional ballistic deposition model is simulated by means of Kinetic Monte Carlo. The dynamic behaviors of the porosity and internal interface are investigated. It is found that the porosity, with the standard Gaussian distribution, increases very fast at the initial times and reaches a saturation valve, which is independent of the linear substrates. In addition to the surface width, the new method of extreme statistics is also employed to analyze the dynamic behavior of internal interface. The results show that the evolution of the internal interface of 1+1-dimensional ballistic deposition model satisfies the standard Family-Vicsek scaling, and belongs to the universality class described by the Kardar-Parisi-Zhang equation. Finally, the finite-size effects obtained by the two theoretical methods, i.e., surface width and extreme statistics are compared.
2013, 62 (1): 010504. doi: 10.7498/aps.62.010504
By introducing ramp compensation current into the feedback control circuit of current controlled switching DC-DC converter it can not only effectively extend the stable operation range of the switching DC-DC converter to realize chaotic stability control, but also shift its operation mode from discontinuous conduction mode to continuous conduction mode to realize operation mode shift. Taking current-controlled buck-boost converter as example by establishing the two-dimensional discrete-time model and the corresponding Jacobian matrix of current-controlled buck-boost converter with ramp compensation and two inductor current borders, the dynamical mechanism of ramp compensation for switching DC-DC converter is investigated. By analyzing the conditions of the instability and border collision bifurcation, the effects of the ramp compensation on the stable period oscillation and operation mode shift of switching DC-DC converter are discussed, and the corresponding stability boundary and mode shift boundary are obtained. Finally, an experimental circuit is built and the results are observed, from which the physical significance of the ramp compensation for chaotic stability control and operation mode shift of switching DC-DC converter is illustrated and the correctness of theoretical analysis is verified.
2013, 62 (1): 010505. doi: 10.7498/aps.62.010505
In this paper, the effects of the aging and systole of heart on the dynamics of spiral wave are studied by using the Greenberg-Hasting cellular automaton model. In this model the neighbor radius and the excitation threshold are increased in order to simulate the aging of heart, and the neighbor radius is changed alternately to simulate heart systole and diastole. The results show that the aging of heart can induce some influences on spiral wave, such as make spiral wave meandering, and even cause spiral wave to disappear; in addition, it can shorten the wavelength and keep period fixed, and also elongate the wavelength and increase the period of spiral wave. If the aging and the regular systole of heart take place at the same time, we observe some phenomena, such as different spiral wave patterns, the spiral wave breakup and disappearance. We also obtain the probabilities of heart failure, ventricular fibrillation and death. These results are essentially consistent with the results of relevant epidemiological survey.
2013, 62 (1): 010506. doi: 10.7498/aps.62.010506
The modified floor field cellular automata model is used to simulate the pedestrian evacuation in rooms which are discretized into squared rhombus cells. This discretization can effectively stop pedestrians to move against walls or obstacles. The pedestrian transition probabilities from one cell to neighbor cells are computed by considering various factors influencing evacuation. Simulation results show that the pedestrian distribution nearby exit is basically the same as that indicated by the experimental snapshot, the evacuation time increases almost linearly with exit width, and the flow rate from exit is close to the one observed from experiment.
Recently, self-organized oscillation networks have aroused great interest in diverse natural and social fields. Genetic regulatory networks are one of the most typical examples of this kind. They control the growth and develop of organism. We investigate the control of few node genetic regulatory networks. We use a method of multiple phase advanced driving to control the networks, which can improve the control efficiency. The numerical simulation, results show that for the network in which system parameter is fixed, the control efficiency will reach 95% (for 10-node network), and the method will also applicable for the network in which system parameter is unfixed.
2013, 62 (1): 010508. doi: 10.7498/aps.62.010508
This paper focuses on the consistency problem of a complex delayed dynamical network with stochastic disturbance. The complex network under consideration includes not only stochastic disturbance but also the varying time-delay which appear in the coupling term and the node system simultaneously. Therefore, such a network is more general. Based on the stochastic Lyapunov stability theory, linear feedback control and linear matrix inequality, some new asymptotic consistency sufficient conditions are established which guarantee the consistency for the nodes of this network and an isolated system in the delay-independent and delay-dependent levels. Finally illustrative simulation is provided to verify the correctness and effectiveness of the proposed scheme.
2013, 62 (1): 010601. doi: 10.7498/aps.62.010601
Frequency of an internal-mirror He-Ne laser is stabilized by using a micro cooling fan, instead of traditional heating method. Both the relationship between driving voltage and rotating speed and the thermal expansion of the intermal-mirror laser are discussed. The cavity length of the laser is controlled and adjusted by air cooling. The frequency stabilization is based on a theory of power balance between two longitudinal modes. The average temperature of the laser tube is less than 50 ℃ when the frequency is stabilized. A frequency fluctuation of less than 1.4 MHz in 20 h and a frequency relative standard uncertainty of U=4.710-9 in 4 months are evaluated by measuring the beat signal with a high-precision laser stabilized by iodine.
Measurement of industrial gas pollutant emissions using differential optical absorption spectroscopy
2013, 62 (1): 010701. doi: 10.7498/aps.62.010701
In this paper, we present a method of measuring the industrial gas pollutant emissions concentration by using differential optical absorption spectroscopy (DOAS). The dust and water vapor which affect the spectrum fitting are filtered by the sample and pretreatment system. In order to avoid the photolysis of SO2 with high concentration, the pretreated smoke mixtures are heated to 150 ℃. In the process of DOAS retrieval, the reference absorption cross sections (185–235 nm) of SO2, NO and NO2 at high temperature are calculated by applying the Voigt broadening method to the original absorption cross sections at low temperature. The influences of temperature, pressure and instrument function are taken into account in the calculation. A validation study of SO2 and NO measurement is performed by comparing with the results measured by a non-dispersive infrared analyzer. The result shows that they are in good agreement with each other indicating that the DOAS technique has a potential application to industrial gas pollutant emissions measurement.
Self-consistent thermodynamical treatment to strange quark matter with density-dependent bag constant and properties of hybrid stars
2013, 62 (1): 012101. doi: 10.7498/aps.62.012101
Thermodynamics of strange quark matter with density-dependent bag parameter is given by making use of MIT bag model, and properties of strange and hybrid stars are investicated by using them. Our results indicate that an extra term should be appended to the pressure expression of strange quark matter but not to the energy density when the bag constant is density-dependent, which assures self-consistency of the system. With this extra term, strange quark matter equations of state soften, gravitational mass and corresponding radius of strange star decrease compared with the inconsistent case. The hybrid star equations of state soften and corresponding mass and radius for hybrid star decrease when this model is used to describe quark phase in hybrid star. These indicate that new thermodynamics for strange quark matter with density-dependent bag parameter has an important influence on properties of strnge star and hybrid star.
Relation analysis between cathode ablation and voltage for a magnetically insulated transmission line oscillator
2013, 62 (1): 012901. doi: 10.7498/aps.62.012901
Through the particle-in-cell simulation and experimental investigation, the relation between the cathode ablation and the input voltage waveform of a magnetically insulated transmission line oscillator (MILO) is analyzed. And the key factor that results in the cathode ablation is found. The figures and process that the electron beam bombards back the cathode are obviously presented. By waveform adjustment of the low impedance accelerator, the reverse voltage of the input voltage to MILO is restrained, and the cathode ablation problem of the MILO driven by the low impedance accelerator is solved. Analysis results show that the electron beam which has been hauled from the cathode by the right direction voltage moves back, which the reverse voltage with adequate amplitude driven, and the beam bombards back the the cathode. The reverse current is formed and the cathode of the MILO device is ablated. Therefore, the reverse voltage immediately following the down slope of the input voltage is a key factor.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (1): 013101. doi: 10.7498/aps.62.013101
The time-dependent multilevel approach (TDMA) and the B-spline expansion technique are used to study the properties of Rydberg lithium atom. The energy level structures of high excited states n = 7075, l = 05 and population transfer of lithium atom in a microwave field are studied by numerical calculation. The results show that the coherent control of the population transfer in microwave field from the initial to the target states can be accomplished by optimizing the microwave field parameters. and that each state plays a crucial role in the transition process.
Ab-initio calculations of the crystal-field parameters and energy level structure for Yb3+ doped in tantalate
2013, 62 (1): 013102. doi: 10.7498/aps.62.013102
In this paper, the DV-X method of ab-initio calculations and the effective Hamiltonian model are introduced to calculate the crystal-field and spin-orbit parameters of rare earth ions doped in various crystals, especially for the crystal with low-symmetry. For the low-symmetry crystal, the number of parameters is more than that of energy levels, thus experimental energy levels fitting cannot determine all parameters, while ab-initio calculations can determine all crystal-field and spin-orbit parameters accurately. Firstly, the crystal-field and spin-orbit parameters of Yb3+ doped in GdTaO4 crystal are calculated by this model, and then the energy level structure of Yb3+:GdTaO4 is given and the continuous emission band of Yb3+:GdTaO4 emission spectrum is analyzed, which is conducive to the laser tunable and laser mode-locking output, so Yb3+:GdTaO4 is a potential laser medium for high efficiency laser operation and new ultrashort pulse output. Also, the crystal-field and spin-orbit parameters of Yb3+ doped in YTaO4 and ScTaO4 are calculated by this model, and the energy level structures of Yb3+:YTaO4 and Yb3+ :ScTaO4 are given, which leads to a conclusion similar to that drawn from the Yb3+:GdTaO4 crystal.
In this paper, the ab initio quantum mechanics method is used for further investigating the He-N2 interactional potential energy function. By means of different methods and basis sets, the energy data in space are calculated. Finally the accurate He-N2 interactional potential energy function is obtained by using QCISD(T)/6-311++G(3df, 2pd) with Boy and Bernardi's Full Couterpoise to eliminate the basis set superposition error. The calculated differential cross sections of He-N2 collision are in good agreement with the experimental data. The rules of differential cross sections of He-N2 collision at different collision energies are derived.
2013, 62 (1): 013104. doi: 10.7498/aps.62.013104
Structure of the SnS ground state molecule is optimized by employing density functional theory (B3P86) method with 6-311++G** basis sets for S atom and SDB-cc-pVTZ for Sn atom. The effects of electric filed ranging from -0.04 to 0.04 a.u. are investigated on bond length, total energy, the highest occupied molecular orbital (HOMO) energy level, the lowest unoccupied molecular orbital (LUMO) energy level, energy gap, mulliken atomic charges, harmonic frequency and infrared intensity of SnS ground state molecule. The excited properties of SnS molecule under different electric fields are also studied by using time dependent density functional theory (TD-B3P86) method. The results show that the bond length and infrared intensity are proved to first decrease, then increase with the external field increasing, but the total energy, HOMO energy EH and harmonic frequency are found to first increase, then decrease. The LUMO energy EL and energy gap Eg are proved to decrease with positive direction electric field increasing. The transition wavelengths from the ground state to the first nine excited states increase with positive direction electric field increasing, but excited energies from the ground state to the first nine excited states decrease.
2013, 62 (1): 013105. doi: 10.7498/aps.62.013105
The potential energy curves (PECs) of X2+, A2 and B2+ low-lying electronic states of SiN radical are investigated using the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach combining the full valence complete active space self-consistent field method. In the present calculations, the basis sets used are correlation-consistent basis sets, aug-cc-pV6Z. The PECs determined by the MRCI calculations are corrected for size-extensivity errors by means of the Davidson modification (MRCI +Q). To obtain more reliable results, effects of the core-valence correlation and relativistic correction on the PECs are taken into account. The core-valence correlation correction is carried out with the cc-pCV5Z basis set The way to consider the relativistic correction is to use the second-order Douglas-Kroll Hamiltonian approximation, and the correction is performed at the level of cc-pV5Z basis set. With these PECs, the spectroscopic parameters are determined. A comparison with the experimental data shows that the present spectroscopic parameters are more accurate than the previous calculations.
2013, 62 (1): 013201. doi: 10.7498/aps.62.013201
The Stark effect of ultra-cold Cs Rydberg atom is investigated in a magneto-optical trap, and the avoided crossing between nS state and (n-4) manifold is observed. The ion spectrum near the avoided crossing is obtained by using state-selective field pulse ionization technique. By changing the intensity of the applied electric field, we find that the relative intensities of two Stark states near the avoided crossing exchange obviously. Furthermore, state transfer from nS Rydberg state to high-l state due to the avoided crossing is also obtained.
2013, 62 (1): 013401. doi: 10.7498/aps.62.013401
Based on the accurate singlet and triplet state interatomic potentials for Na2, a theoretical study of elastic scattering properties of sodium atoms at ultracold temperatures is reported in this paper. The s-wave scattering length, effective range, the p-wave scattering length and the number of bound states are calculated. The singlet and triplet elastic scattering cross section between sodium aotms at ultracold temperatures are dominated by s-wave scattering, and shape resonances occur with collision energy increasing. There exist pronounced f-wave and i-wave shape resonances for the singlet and triplet cross section. In addition, s-wave scattering length is calculated by using the degenerate internet state approximation for selected hyperfine states of sodium atoms. The results are in agreement with calculated values obtained by close-coupling method.
2013, 62 (1): 013402. doi: 10.7498/aps.62.013402
When an atomic ensemble is coupled with a cavity field governed by the well-known Dicke model , an important quantum phase transition (QPT) from the normal phase to the superradiant phase occurs, which was predicted more than 30 years ago. In this paper, both the atom-photon nonlinear interaction and the driving field are added to the Dicke's Hamiltonian. With the method of Holstein-Primafoff transformation, the ground state energy is given by the theoretical calculation, and the rich phase figures are presented. Meanwhile, these properties are observed experimentally. We mainly dicuss the effects of the atom-photon nonlinear interaction and the driving field on QPT.
Simulation and experiment demonstration of a polarization-independent dual-directional absorption metamaterial absorber
2013, 62 (1): 013701. doi: 10.7498/aps.62.013701
In this paper, we design and fabricat a polarization-independent dual-directional metamaterial absorber. The simulation results indicate that the absorber keeps good absorbing performance in a wide incidence angles for both transverse electric and transverse magnetic polarization, and that the high absorption is due to the dielectric loss of substrates. The experimental results indicate that the absorber achieves dual-directional high absorption at normal incidence, and that the peak absorptions are 95.9% and 90.8%, respectively. The metamaterial absorber is very thin, and its thickness is approximately 1/34 of the working wavelength. The metamaterial absorber has many advantages such as high absorption, small thickness, simple design and easy processing.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (1): 014201. doi: 10.7498/aps.62.014201
We provide detailed analytical expressions of group-delay dispersion and three-order dispersion for reflection grism-pair using angle dispersion and material dispersion. The dispersion formulas obtained in this study are consistent with the results of the ray-tracing method. The analytical expressions can be used to design a grism-pair for compensating for the dispersive material. Furthermore, the dispersion performances of the grism pair depending on structural parameters and temperature are comprehensively analyzed. The results show that the parameters have a large influence on the dispersion of grism, such as incidence angle, grating constant, and apex angle of the prism. To compensate for material dispersion of amplifying medium, we can adjust the above parameters to obtain group delay dispersion and third order dispersion.
Image reconstruction algorithm for steady-state diffuse optical tomography with structural priori information
2013, 62 (1): 014202. doi: 10.7498/aps.62.014202
Diffuse optical tomography is a non-invasive and non-ionizing optical imaging technique with low cost, while it suffers from low spatial resolution and is very difficult to achieve quantitative measurement. In order to improve the resolution and reconstruct the optical coefficients accurately, in this paper, we present an image reconstruction algorithm based on finite element method for steady-state diffuse tomography with structural priori information. Imaging model is characterized by the steady-state diffuse equation. The spatial structural information from micro-CT is introduced into the inverse problem by the Laplace regularization and Levenberg-Marquardt method to solve the inverse problem where the Jacobian matrix is obtained by adjoint method. The simulation results show that the algorithm presented is able to obtain the accurate distribution of optical coefficients and increase the convergence speed of iteration evidently.
Influence of digital averaging on the signal-to-noise improvement ratio of temperature control system used in single-photon detector at infrared wavelength
2013, 62 (1): 014203. doi: 10.7498/aps.62.014203
According to performance requirement of high precision temperature control system used in single-photon detector, the signal-to-noise improvement ratio (SNIR) achieved by digital averaging used in it is analyzed, and the functional relation between SNIR and average times, sampling period, length of sampling time and bandwidth of band limited white noise is given. Aiming at practical application, on condition that the total sampling time is limited, the influences of average time and sampling period on the SNIR of the system are calculated respectively, the expression of SNIR is given and the optimal sampling time is defined.
Preparation of graghene oxide/chitosan composite films and investigations on their nonlinear optical limiting effect
2013, 62 (1): 014204. doi: 10.7498/aps.62.014204
As a new kind of carbon nanostructured material, graphene and its derivatives have attracted extensive attention owing to their outstanding optical limiting (OL) properties. However, most of the current studies concentrate on liquid matrix. In this work, we use chitosan (CS) as matrix and homogeneously disperse graphene oxide (GO) into it to prepare GO-CS composite films. We comparatively study the different OL effects and mechanisms of GO in liquid and solid matrix. The results show that GO presents stronger nonlinear optical effect and weaker nonlinear optical scatter, which indicates that different from carbon nanotubes, GO may possess multi sort of nonlinear optical effects.
2013, 62 (1): 014205. doi: 10.7498/aps.62.014205
In this paper, we report on the study of quartz material characteristic variation with temperature for precision oscillator applications with a novel piezoelectric material precise characterization method. Electrical impedance resonant characteristics of AT cut quartz sample are measured at temperatures ranging from ambient temperature up to 100 ℃. These measured results are fitted with a simulated annealing optimization algorithm to accurately calculate complex material parameters comprising loss characteristics. Effects of temperature change on quartz material characteristics and their loss are analyzed. This paper offers theoretical and technical supports to the design of precision oscillators with stable temperature characteristics.
Effect of pro-proximity pulse voltage on the third-generation low light level image intensifiers halo effect
2013, 62 (1): 014206. doi: 10.7498/aps.62.014206
In order to explore the proper working voltage for the third-generation low light level image intensifier, the influence of pro-proximity pulse voltage on image intensifier halo effect is investigated. The pulse voltage is applied to photocathode of image intensifier. Respectively change the high and low level voltage and duty ratio, image intensifier halo images are collected by high-resolution charge-coupled device (CCD). The gray distributions for pixel points on halo image central line are given and comparatively analyzed. The results show that as high level voltage and duty ratio increase, the number of pixel points whose gray value is 255 increases and the border between signal and background becomes clear. When high level voltage is above 200 V and duty ratio is above 60%, the pro-proximity voltage has not great influence on image intensifier halo effect. When low level voltage is above 2 V, photoelectrons escaping from photocathode cannot reach microchannel plate under low level voltage stage. The present investigation is beneficial to the exploration of the optimal working voltage for image intensifier and energy range of photoelectrons escaping from photocathode, and provides an experimental support for the improvement of the third-generation low light level image intensifier performance.
Theoretical and experimental investigation of air breakdown on single high power microwave based on the mixed-atmosphere propagation model
2013, 62 (1): 014207. doi: 10.7498/aps.62.014207
Considering the series effects of high power microwave such as thermal fast electrons effect, collision frequency effect and ionization frequency effect, a unified high power microwave (HPM) propagation model is presented in this paper. A unified air-breakdown model for single-pulse HPM is discussed in detail and the breakdown threshold is determined. It is found that the frequency of plasma induced by high power microwave is greater than previous value. The threshold of air breakdown increases with altitude increasing under the same condition. When the threshold reaches a minimum, a reverse trend will appear. And the minimum value will be obtained in an area of 30-60 km. The typical phenomenon waveform and threshold are gained in the experiment of air breakdown in microwave darkroom. And a well uniform distribution of the air breakdown threshold is shown theoretically and experimentally.
2013, 62 (1): 014208. doi: 10.7498/aps.62.014208
We investigate the nonclassicality and decoherence of a photon-subtraction-addition coherent state (a++a)m|a in a thermal environment. Its nonclassicality is discussed by deriving analytically Mandel's Q parameter, photon number distribution, and Wigner function. It is shown that if the condition |2z*+ -*|2 1 is satisfied, the Wigner function always presents the negativity for the one-order photon-subtraction-addition coherent state (m=1). Based on the evolution formula of Wigner function, we derive a compact expression for Wigner function in the thermal environment. It is found that when t(1/2)ln[(2N+2)/(2N+1)] there is no negativity for the case of m=1. In addition, the evolution of nonclassicality is discussed in terms of the negative volume of Wigner function.
2013, 62 (1): 014701. doi: 10.7498/aps.62.014701
Low permeability oil reservoirs are usually accompanied with fracture development, forming fracture-matrix dual porosity medium. Spontaneous imbibition is a crucially important recovery mechanism in naturally fractured reservoir with water deriving, in which non-wetting phase is displaced in either co-current or counter-current manner. In this work, the criterion (inverse bond number) and fractal model for spontaneous imbibition mechanism of dual-porosity medium are developed, and the analytical expression for structure constant is also derived based on the fractal characteristics of pores in porous matrix. The improved fractal model for inverse bond number can be expressed as a function of porosity, pore fractal dimension, flow tortuosity, maximum pore diameter, height of matrix, density difference between oil and water, interfacial tension and contact angle. The present model predictions are shown to be in agreement with the available results. The dominion for criterion of imbibition mechanism is plotted, which provides a theoretical basis of adding surfactant in water for enhancing oil recovery in low permeability reservoirs.
2013, 62 (1): 014702. doi: 10.7498/aps.62.014702
We fabricate solar cells based on blends of poly(3-hexylthiophene) (P3HT) as the donor and [6, 6]-phenyl-C60-butyric acid methyl ester (PCBM) as the acceptor using various solvents such as pure chlorobenzene (CB), pure chloroform (CF) and mixed solvent (CB/CF) with different ratios.We investigate the influences of various solvents and mixed solvents with different ratios on the performances of solar cells. The results show that for the device by using a mixed solvent of CB/CF (3/1), its UV-Vis absorption spectrum and external quantum efficiency show a red-shift and its AFM image shows finely structured phase segregation between P3HT and PCBM. We obtain an open circuit voltage of 0.61 V, short circuit current density of 9 mA/cm2, fill factor of 57.9%, and power conversion efficiency of 3.2% under irratiation of light with a strength of 100 mW/cm2.
Experimental study of the interactions between a pulsating bubble and sand particles with different diameters
2013, 62 (1): 014703. doi: 10.7498/aps.62.014703
The interactions between a spark generated bubble and sand particles with different diameters are studied in this paper using a high speed camera. And distance between the bubble and sand particle is varied. The experimental results show that there are two distinct phenomena during the interaction between the bubble and sand particle. On the one hand, the jet formed is much like that near a rigid wall; on the other hand, a mushroom-shape bubble will form, which will split into two bubbles and two jets with opposite directions along the axes will be generated afterwards. Thus, it is found that the sand particle has the characteristics of a rigid wall and an elastic material. In addition, as the distance d between the bubble and sand particle increases, the pulsating period of the bubble will rise to a peak before it reduces. For different sand particles, the distance corresponding to the peak decreases as the diameter of sand particle increases.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (1): 015201. doi: 10.7498/aps.62.015201
The electron energy distribution function (EEDF) of weakly ionized air plasma (79% nitrogen and 21% oxygen) is investigated by solving the Boltzmann equation with the spherical harmonics expansion. It is found that the EEDF deceases sharply in an energy range from 2 to 3 eV for low reduced field (E/N 100 Td), and the high energy tail of the EEDF decreases more sharply than Maxwell distribution. When the reduced field increases to a range 400 to 2000 Td, the EEDF approaches to Maxwell distribution. When the reduced field is greater than 2000 Td, the high energy tail (200 eV) of the EEDF deceases more slowly than Maxwell distribution. It is shown that the EEDF approaches to Maxwell distribution in a high frequency field. The effective electron temperature is dependent only on E/ for vm, but on E/N for vm. The electron-electron collisions play no significant role until the ionization degree is bigger than 0.1%. This is different from the case of monatomic plasmas, in which the EEDF is influenced by electron-electron collisions for ionization degree greater than 10-6.
2013, 62 (1): 015202. doi: 10.7498/aps.62.015202
A highly-efficient magnetoelectric heating not only improves ion temperature of electron cyclotron resonance (ECR) plasma, but also reforms the radial and axial distribution of ions, thereby promoting the application of ECR plasma to the etching of chemical vapor deposition diamond films. In this paper, a ring-electrode is replaced by a cylinder-electrode, and the effects of cylinder-electrode on the ion temperature and density are studied. The ion heating effects in the cases of cylinder-electrode and ring-electrode are compared. The results indicate that cylinder-electrode can produce higher ion temperature than ring-electrode at the same anode voltage. Ion temperature at each radial point changes a lot when the cylinder-electrode is used to heat ions. The ion temperature inside cylinder-electrode has a big radial variation while it has a good radial uniformity at downstream of cylinder-electrode. The effect of magnetoelectric heating on ion density is small. Using cylinder-electrode to heat ion is beneficial to the transport and axial uniformity of ions.
Experimental study of L-H transition triggered by supersonic molecular beam injection in the HL-2A tokamak
2013, 62 (1): 015203. doi: 10.7498/aps.62.015203
Features of L-H transition are investigated using the supersonic molecular beam injection (SMBI) with directional velocity under low heating powers in the present paper. Comparing the edge density profiles, it is analyzed that the conventional gas puffing (GP) and SMBI have effects on L-H transition. Experimental results suggest that the SMBI does directly trigger L-H transition on HL-2A, and it considerably reduces the power threshold of L-H transition. After abundant experimental data are analyzed and processed, it is found that the minimum L-H transition power with SMBI decreases by 10% when it is compared with GP trigged H-mode under same conditions.
2013, 62 (1): 015204. doi: 10.7498/aps.62.015204
High flux, Multi-keV X-rays, can be efficiently produced from nano-second laser interaction with metal target. Multi-keV backlight X-ray source is very important in inertial confinement fusion and high-energy density physics research. The one-dimensional numerical simulation results propose a laser plasmas radiation model, and the model is compared well with Shenguang II experimental results. The pinhole-assisted point-projection (PAPP) backlight is improved by the model; the rear-on PAPP backlight for low-Z metal target and the side-on PAPP backlight for middle-Z metal target are developed. The experiment is performed on Shenguang II 9th laser facility. The static stream line obtained with novel PAPP backlight provides high-quality capsule image, and the spatial resolution is better than 10 μm. Results show that novel PAPP backlight has advantages of traditional PAPP in source brightness, spatial resolution and image contrast.
2013, 62 (1): 015205. doi: 10.7498/aps.62.015205
The numerical simulation of ship wake laser scattering mechanism and the detection process are important foundations for the laser detection and guidance of the ship wake. The feasibility that Monte Carlo method is introduced into the numerical simulation of lidar of ship wake is analyzed firstly. The Monte Carlo simulation model of laser detection of ship wake is developed with the actual parameters of self-developed lidar of ship wake. The causes of the large variance and low photon utilization of simulation results are in-depth analyzed by statistics on the simulation results. To resolve this problem, the method of photon collision forced in the receive optical fields, the photon splitting method with the total free pach of photon serving as a criterion, and the conbination of the two methods are put forward based on partial sampling theory and the basic principle of division-roulette bet. The comparative analyses of the simulation and the experimental results show that the proposed model simulation results fit to experimental data better, thus the correctness of the model is verified. The photon collision forced in the receive optical field and division-the roulette method can effectively reduce the variance and increase the photon utilization. In this paper, the Monte Carlo method is introduced into the simulation process of lidar of ship wake.
2013, 62 (1): 015206. doi: 10.7498/aps.62.015206
Two models (Ta and Nanbu) of Coulomb collisions are compared theoretically, and the difference in scatter angle between Ta model and Nanbu model is analyzed particularly. The model of Coulomb collisions between electrons in the code which is developed already with Ta model is rebuilded with Nanbu model. Then, the codes with Ta model and Nanbu model are used for simulating electron energy distribution in JAEA 10 A respectively. The results of simulation are compared with the experimental results, showing that the electron energy distribution is closer to Maxwell distribution with Coulomb collisions and the Nanbu model is more accurate than the Ta model.
2013, 62 (1): 015207. doi: 10.7498/aps.62.015207
Based on CHIPIC platform and the ionization physics mechanism between electron and gas, a full three-dimensional particle-in-cell/Monte Carlo (PIC/MCC) code is developed with the MCC ionized collision module. The simulations of a relativistic backward wave oscillator with helium gas are used to verify the code. The results show that the gas can enhance the current, peak power and pulse length, but too much gas leads to the reductions of peak power and pulse length.
2013, 62 (1): 015208. doi: 10.7498/aps.62.015208
To image a large-size object with a high spatial resolution in a kiloelectronvolt (keV) X-ray range, a method is proposed to analyze and simulate the imaging of an extended X-ray source by a Fresnel phase zone plate (FPZP), based on the translational invariance of the point spread function in a 1 mm square area on the objective plane. Using this method, the imaging of an extended source of a different size is simulated under a typical experimental condition of image-to-source magnification of 10 for an FPZP of an outmost zone width of 0.35 μm. The results show that the image contrast decreases with the increase of the source size, and the zeroth-order and the minus first-order diffractions of the FPZP contribute mainly to the image background enhancement and the contrast decrease. The spatial resolution to the objective plane is also found to be reduced. For a 1-mm-square-shape source with a sinusoidal-distribution intensity modulation of contrast 1, the image modulation contrast is below 0.4, and the spatial resolution is 0.75 μm.
2013, 62 (1): 015209. doi: 10.7498/aps.62.015209
Two kinds of films are deposited on 316L stainless steel substrates by radio frequency reactive magnetron sputtering technique. One is fluorinated diamond-like carbon film (F-DLC) deposited on the 316L stainless steel substrate directly and the other is F-DLC with SiC intermediate layer. This paper focuses on the changing regulation of film adhesion with preparation condition. As the result, the adhesion of fluorinated diamond-like carbon film with SiC intermediate layer is obviously much better than that of F-DLC, and the adhesion is dependent on preparation condition of preparation SiC intermediate layer. The adhesion of F-DLC can reach 8.7 N with 200 W RF input power and 5 min deposition time, which is much bigger than the adhesion of F-DLC without intermediate layer (4 N). The mechanism of the preparation condition of SiC influencing the adhesive force of F-DLC is studied by investigating the deposition rate curve, surface morphology and infrared spectrum.
2013, 62 (1): 015210. doi: 10.7498/aps.62.015210
In indirect driven inertial confinement fusion experiments, one-dimensional radiation hydrodynamics code is used to simulate radiation transport in material confined in a cylinder and large bias is generated due to two- or three-dimensional lateral effects like energy losses into the cylinder wall. Lateral X-ray radiation losses such as cylinder wall loss and direct leak from the detection holes are simulated through analytical view factor equations and albedo power laws. Modifications are made for a one-dimensional radiation hydrodynamics code MULTI which is successfully used in the simulation of measured hydrodynamic trajectory of X-ray-heated gold plasma and better result is obtained than without taking lateral effect into account, which proves that this modification is practical.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
On glass forming ability and thermal stability of Zr57Cu20Al10Ni8Ti5 bulk metallic glass by substituting each component with 1 at% Ag
2013, 62 (1): 016101. doi: 10.7498/aps.62.016101
Each component element of Zr57Cu20Al10Ni8Ti5 bulk metallic glass is substituted by 1 at% Ag element. Variations of glass forming ability and thermal-stability are studied using differential scanning calorimetry which gives the thermal-dynamic parameter of the bulk metallic glass, combined with X-ray diffraction of different diameter rods (Φ8, Φ10 and Φ12) which are prepared by copper mould suction casting, The results show that the glass forming ability and thermal-stability are greatly improved by substituting Ti element and the critical cooling rate is significantly reduced. While, no obvious law is found when substituting other elements. By analyzing the relevant data on glass forming ability, Inoue's atomic size rule show inconformity in this work, however, the mixing enthalpy rule dose not show conformity obviously. By calculating the packing density, we find that the packing density is obviously improved when substituting 1 at% Ti with Ag. Dynamic analysis is used and the mechanism of element substitution is also investigated on the aspects of crystallization activation energy and crystallization rate constant.
2013, 62 (1): 016102. doi: 10.7498/aps.62.016102
The mechanical behaviors of carbon nanocone (CNCs) with equivalent number of atoms under uniaxial extension and uniaxial compress are investigated using classical molecular dynamics simulations, exploring the Brenner and Lennard-Jones potentials to represent the interatomic interaction. The mechanical properties including elastic strain limit, ultimate longitudinal loading, and configuration evolution of CNC, are obtained and compared with those of carbon nanotube that consists of equivalent atoms. Under tension, CNC with larger apex angle presents a higher failure strength in general, as well as a larger maximum strain. However, the failure strength of the CNC with largest conical angle of 112.88° is the smallest one. The carbon nanotube with (15, 0) and 4 nm length presents a moderate strength and strain. Under compression, CNCs with conical angle of 112.88° and 83.62° have true chiral inversion without the chemical bond break. However, the other CNC exhibits unstable uniaxial compress and sudden lateral bend under compression. The force that buckles these carbon nanostructures decreases as the conical angle increases, except for the CNC of 38.94°. Results in the present study show that a certain CNC possesses more excellent mechanical properties than the equivalent CNT and is expected to substitute CNT and to be applied to some engineering fields such as nanosensors and nanoscale composites.
2013, 62 (1): 016103. doi: 10.7498/aps.62.016103
Based on the composite compounds Ho2Ni7-xFex (x=0-3.0), a method of describing the structure transition from rhombohedral to hexagonal is discussed in terms of free electron concentration. The transition is investigated by X-ray powder diffraction and magnetic analysis. The compounds crystallize into the rhombohedral Gd2Co7-type structure for x=0-0.5 and into the hexagonal Ce2Ni7-type structure for x=0.5-2.5. The values of lattice parameters a and c of the Ho2Ni7-xFex compounds increase with the addition of Fe, and the saturation magnetization Ms decreases with Fe content increasing at a rate of d Ms/d x=-2, manifesting antiparallel alignments of the Fe and Ho moment. The higher the free electron concentration, the stabler the rhombohedral structure is, otherwise the hexagonal structure is stabler, which provides a meaningful parameter to distinguish the two allotropies in composite structure intermetallics.
2013, 62 (1): 016104. doi: 10.7498/aps.62.016104
Study of ion guiding effect of capillaries in insulator is of significance for developing passive-type ionic optics. Interactions between ions with different values of Ep/q, such as 150 keV O3+, 0.32 MeV O+ and 2 MeV O2+, and alumina capillaries are investigated. For projectile ions of 150 keV O3+, a guiding effect exists during the passage of the projectile ions through the capillaries. As the capillaries are tilted with respect to the projectile ion beam, the projectile ions can still pass through the capillaries considerably and the charge state remains unchanged; the spectrum of angular distribution of the ions out of the capillaries shifts by an angle the same as the tilt angle of the capillaries; the penetrating rates of the projectile ions for different tilt angles of the capillaries can be fitted to Gaussion function. For 0.32 MeV O+ and 2 MeV O2+ ions impinging on alumina capillaries, no guiding effect occurs in the interaction process. The maximum value of Ep/q of the projectile ions for guiding effect to occur is less than 320 kV.
2013, 62 (1): 016105. doi: 10.7498/aps.62.016105
Macroporous -Al2O3 is synthesized by polyacrylamide gel technique. X-ray diffractor combined with a photoluminescence spectrophotometer is used to investigate the formation of Al2O3 phase and the light emission properties of xerogel sintered at different temperatures. It is demonstrated that high-purity -Al2O3 can be obtained at a sintering temperature of 1150 ℃. Scanning electron microscopy images reveal that the synthesized -Al2O3 has a monolithic structure. Photoluminescence spectra show that a major emission band around 365 nm and a weaker side band around 330 nm are observed when the excitation wavelength is 228 nm. The pore-formation and luminescence mechanisms of porous alumina are discussed based on the experimental results.
First-principles calculations of microstructure and thermodynamic properties of the intermetallic compound in Ag-Mg-Zn alloy under high pressure and high temperature
2013, 62 (1): 016106. doi: 10.7498/aps.62.016106
The structural stability, elastic and thermodynamic properties of the intermetallic compounds MgAg, Mg4Zn8 and Ag8Mg4Zn4 in Ag-Mg-Zn alloy under high pressure and high temperature are investigated by employing the first-principles method based on the density functional theory. The theoretical results are generally in good agreement with experimental results and similar to the theoretical calculations. The calculated results indicate that the intermetallic compounds AgMg, Mg4Zn8 and Ag8Mg4Zn4 are elastically stable at zero temperature and pressure. Mg4Zn8 and Ag8Mg4Zn4 are of the ductility phase, and AgMg is of the brittleness phase. The plasticity of Ag8Mg4Zn4 is the best in the three intermetallic compounds, and AgMg is the worst. Based on the quasi-harmonic Debye model the vibrational internal energy, vibrational Helmholtz free energy, vibrational entropy, heat capacity of constant volume, heat capacity at constant pressure, thermal expansion coefficient Grneisen parameter and Debye temperature of the intermetallic compounds in Ag-Mg-Zn alloy under high pressure and high temperature are all discussed.
2013, 62 (1): 016201. doi: 10.7498/aps.62.016201
The shock properties of C100 concrete are investigated by gas gun planar impact technique. The manganin pressure gauge is used to measure the pressure-time curves of the samples. The physical quantities are all obtained by the Lagrange method. Moreover, it is observed from the measured pressure-time curves that the decay factor is smaller in the steel reinforced high strength concrete. The dynamic response is analyzed.
2013, 62 (1): 016601. doi: 10.7498/aps.62.016601
Based on the distributed interconnect power model, a novel dynamic power model is presented in this paper, in which a non-uniform interconnection structure is adopted. This model takes into account the self-heating effect and is constrained by delay, bandwidth, area, minimum interconnect width and minimum interconnect space. The validity of the proposed model is verified by 90 nm and 65 nm complementary metal-oxide semiconductor technology. The results indicate that the proposed model can cause a power consumption reduction as high as 35%, and yet the delay, area, and bandwidth are not deteriorated, when compared with the conventional power model. The proposed optimal model can be used for designing large scale interconnect router and clock network in network-on-chip structure.
2013, 62 (1): 016801. doi: 10.7498/aps.62.016801
In order to reveal the relationship between modulation structure and superhardness effect, a series of c-VC/h-TiB2 nanomultilayers with different modulation structures is synthesized by magnetron sputtering technique. X-ray diffractometer, high-resolution transmission electron microscope and nanoindention device are employed to investigate the microstructures and mechanical properties of the multilayers. Based on the experimental results, a relation map of modulation structure and superhardness effect is established for the nanomultilayer composed of c-VC and h-TiB2 with four regions. In these regions, superhardness effect could be generated only in the region with sharp interface and coherent growth structure. In other regions, the change of modulation structure leads to the change of the microstructure, and the hardness will decrease accordingly. The map could provide reference for obtaining superhardness effect by designing modulation structure in those analogous heterogenous nanomultilayers.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (1): 017101. doi: 10.7498/aps.62.017101
Using molecular dynamics simulations, we investigate the structure and transport properties of solid-liquid interface in a model ordered alloy. Our results show that the studied interface is a smooth interface. Due to the coexistence of structural order and chemical order, the structure of this interface is remarkably different from heterogeneous or pure element solid-liquid interface. The number density oscillates in a complicated way along the interface normal direction, and this oscillation goes into liquid around 30 Å. The two-dimensional structural analysis shows that the atoms form two-dimensional ordered clusters in the transition layer. The diffusion constant gradually increases from zero to a saturation value in the liquid side far from the interface. In the vicinity of the interface, the diffusion constant parallel to the interface direction is large than that along interface normal.
2013, 62 (1): 017102. doi: 10.7498/aps.62.017102
The microstructures and optical properties of N and Co-codoped anatase TiO2 are investigated by using the plane-wave ultrasoft pesudopotential method of first-principles. The calculated results show that the octahedral dipole moment of anatase TiO2 increases after N and Co codoping, which is favorable for effective separation of photogenerated electron-hole pairs. Some new impurity energy levels of codoped TiO2 appear between the conduction band and the valence band, which results in the red shift of the absorption wavelength toward visible-light region and an apparent increase in performance of light absorption. These impurity energy levels can promote the effective separation of photogenerated electron-hole pairs, which facilitates the improvement of the photocatalytic efficiency of codoped TiO2. The band edge redox potential of codoped TiO2 is only slightly changed compared with that of pure TiO2, which means that the strong redox capacity of codoping photocatalyst is still excellent.
2013, 62 (1): 017103. doi: 10.7498/aps.62.017103
Using the pseudopotential plane-wave method within the density functional theory as implemented in the Vienna ab-initio simulation package, we investigate the crystal parameters, electronic structures and optical properties of rare earth Ce and Pr doped GaN. The local spin density approximation with Hubbard-U corrections method is used to treat the correlation effect of strongly localized rare-earth 4f electron states. The results show that the crystal parameters increase after doping Ce and Pr in GaN. The Ce impurity introduces defect level in the gap while for Pr the level lies near the valence band maximum, and the defect levels are contributed by Ce and Pr 4f electron states. In addition, the dopings of Ce and Pr give rise to spin polarization and magnetic-order. For GaN:Ce, there appear two new peaks, one is in the low energy region of imaginary dielectric function and the other is in the low energy region of absorption coefficient. These new peaks are probably related to the defect level in the gap. For GaN:Pr, red shifts of the dielectric peak and absorption edge duo to bandgap narrowing are observed.
2013, 62 (1): 017201. doi: 10.7498/aps.62.017201
With the two-impurity Anderson model Hamiltonian, we theoretically study the magneto-transport properties of the serially coupled double quantum dot system in a spin blockade regime, and solve Hamiltonian by the master equation approach. We find that the spin flip tunneling between dots due to the spin-orbit coupling can lift the quantum dot spin blocking. We also study the effects of the spin flip of quantum dots due to the hyperfine interactions and the spin exchange interaction on magnetic transport properties of the system. Some valuable results are obtained and the relevant problems are discussed.
2013, 62 (1): 017301. doi: 10.7498/aps.62.017301
In the paper, we study electronic transport property through a quantum point contact with the saddle-point potential. Our numerical approach is based on the Green's function technique which is evaluated at the Hartree-Fork level. We reproduce relevant features of 0.7 structure when the strength of electron-electron interaction has changed. Besides, we calculate spin accumulation and noise factor at zero temperature. We deepen the understanding of the effect of strong correlation interaction on spin transport in nanometer semiconductor device.
2013, 62 (1): 017302. doi: 10.7498/aps.62.017302
With the density of function with pesudopotentional and plane-wave method, we study the strain effect on band structure of multi-layered BN film. It is found that the band gap of BN film decreases linearly with the increase of tensile strain, and the slope of the band gap-strain curve is independent of the BN stacking and the number of the BN layers, indicating that the band structure of BN film is determined by the interlayer interaction rather than the intralayer interaction.
Prediction of the magneto-resistivity of manganese oxides La0.67Ca0.33MnO3 and Pr0.7Sr0.3MnO3 via temperature and magnetic field
2013, 62 (1): 017601. doi: 10.7498/aps.62.017601
The resistivity related to temperature and magnetic field is a crucial parameter for determining the physical properties of the perovskite-type manganese oxide. The first task of this work is to find out a suitable method to predict the resistivities of La0.67Ca0.33MnO3 and Pr0.7Sr0.3MnO3 in the process from insulator phase to the metal phase via the temperature and the magnetic field. Based on the nonlinear numerical fitting, an analytical expression showing the dependence of the resistivity on temperature both less than and higher than the metal-insulator transition Curie temperature (TC) at different magnetic fields, and the maximum resistivity (ρmax) corresponding to each Curie temperature is acquired. The second task of this work is to trace a mathematical relationship between the magnetic field and the maximum resistivity, and the Boltzmann function can be used successfully by numerical fitting. The lowest correlation coefficient and the largest average relative error between the actual and the calculated data are 0.998 and 4.35% in all considered cases respectively.
2013, 62 (1): 017701. doi: 10.7498/aps.62.017701
Based on the gaussian-type distributions of bond energy and coordination number for barium titanate systematic ferroelectrics doping with a certain quantity of dopants, the bond energy and coordination number fluctuation model is used to derive the relationship between peak of dielectric constant and testing frequency. The universal Vogel-Fulcher function of the relationship is demonstrated, when the fluctuations of bond energy and coordination number approach to each other. The frozen temperature of the Vogel-Fulcher function is related only to actuation energy and relative fluctuation of bond energy. The mechanisms of dispersion due to homogenous distribution of dopants in low doping concentration and relaxor due to gaussian-type distribution of dopants over a critical concentration are investigated. It is suggested that strong inhibitory effect of substituted ions on formation and growth of ferroelectric domain is the main source of bond energy fluctuation and coordination number fluctuation.
2013, 62 (1): 017702. doi: 10.7498/aps.62.017702
Aluminum gallium nitride (AlGaN) thin films are prepared by pulsed laser deposition with different silicon doping concentrations from 0.5% to 2%. The field emission measurement shows that the 1% Si-doped AlGaN film has the best field emission property. Compared with undoped film, the Si-doped film has a large emission current density and a low threshold field. The increase of doping concentration can increase the carrier concentration, which will add a number of supply electrons, thereby improving greatly the FE property of AlGaN film. With the doping concentration further increasing, the defect of film increases and the electron mobility reduces. The reduction of the internal supply electron is greater than the contribution of the increase of electrons concentration, which induces the field emission performance to deteriorate. This study will provide a reliable basis for designing high-performance field emission devices.
Investigation on three-photon-absorption fitting method and three-photon-absorption-induced optical stabilication effect of a fluorene derivative
2013, 62 (1): 017801. doi: 10.7498/aps.62.017801
Three-photon absorption coefficient obtained by current nonlinear transmittance method has large fitting error because of uneven laser radiation distribution. Relatively small three-photon absorption cross section values of present nonlinear molecules restrict their practical applications. In this paper, an accurate three-photon absorption coefficient fitting method is presented, which is applicable for a variety of laser distributions. A fluorene-based derivative, 2, 7-bis(4-methoxyphenylacetylene)-9-thoine-fluorene, is synthesized. Apparent three-photon-absorption-induced optical stabilization effect is shown.
2013, 62 (1): 017802. doi: 10.7498/aps.62.017802
The hydrogenous diamond-like carbon (DLC) films deposited on Si substrates using pulsed glow discharge method are investigated using Raman spectroscopy and X-ray photoelectron spectroscopy method. The UV Raman spectrum for excitation wavelength is 325 nm. UV Raman is particularly useful for hydrogenous DLC, as it gives clear measurements in the D and G peak spectral region even for highly hydrogenated samples, for which the visible Raman spectra are overshadowed by photoluminescence. The sp3 bonding of hydrogenous DLC film can be effectively studied by X-ray photoelectron spectroscopy method, and the data from the X-ray photoelectron spectroscopy method are compared with Raman results. It is found that G peak shows a shift to ward a higher wave under UV excitation. For the G peak, I(D)/I(G), G-FWHM and sp3, there exists a relationship among them.
2013, 62 (1): 017803. doi: 10.7498/aps.62.017803
Highly conductive and transparent hydrogen and tungsten co-doped zinc oxide (HWZO) thin films are prepared at room temperature by pulsed DC magnetron sputtering using a WZO (98.5 wt.% ZnO, 1.5 wt.% WO3) ceramic target with different H2 flow rates. The influence of H2 flow rate on the structural, compositional, elemental valence state as well as electrical and optical properties are systematically investigated. The results indicate that the incorporation of H does not change the structure of tungsten doped zinc oxide (WZO) namely, both WZO and HWZO films are polycrystalline with hexagonal structure and a preferred orientation along c-axis, respectively whereas the crystallinity is firstly improved and then deteriorated with the increase of H2 flow rate. Furthermore, the reaction between Zn and O can be promoted by the incorporated H. With an optimal H2 flow rate, the carrier concentration increases from 3.32×1020 cm-3 for WZO film to 5.44×1020 cm-3 for HWZO film, and the resistivity decreases from 1.20×10-3 Ω·cm to 7.71×10-4 Ω·cm. The average transmittance in a range of 400-1100 nm is improved from 69.2% to 82.4 %, and the optical band gap is widened from 3.42 eV to 3.58 eV.
2013, 62 (1): 017804. doi: 10.7498/aps.62.017804
In this paper, the Dy3+-doped borosilicate glasses are fabricated by high-temperature melting method. The excitation and emission spectra of the glasses are measured to discuss their spectroscopic properties. The effects of the glass composition and the Dy3+ doping concentration on the emission spectrum and the luminescence intensity of the sample are investigated. We also calculate their color coordinates, which are all in the white region. By adjusting the intensity ratio of the yellow band to the blue band, which varies with the composition of the glass host and the doped concentration of Dy3+ ions, we implemente the effective white light on a single host under the excitation of 387 nm long-wavelength UV.
Improvement of light extraction efficiency of GaN-based blue light-emitting diode by disorder photonic crystal
2013, 62 (1): 017805. doi: 10.7498/aps.62.017805
Sub-wavelength photonic crystal can effectively improve the light extraction efficiency (LEE) of the light emitting diode (LED). However, it is inevitable to have defects, (namely disorder structures) during its fabrication. In this study, the LED model with ideal quadrate photonic crystal is optimized by using the finite-different time domain method. Three different LED structures with various disordered photonic crystals are further simulated. We investigate the influences of several stochastic variables (including position, radius, and depth of an air hole) of the photonic crystal on the LEE of GaN based blue LEDs. It can be found that regarding photonic crystal LED whose air hole radius is optimized to 80 nm, the stochastic variables of the position and radius will reduce its LEE. However, an opposite trend is found when this radius is replaced by 60 nm, which is not optimized. Furhermore, the LEE fluctuates inside to an extent of 53.8% as two stochastic variables (including the randomized position and the randomized radius) change from 0 nm to ±20 nm. The influence of the stochastic variables of the depth of air hole can be neglected since this variation is very small. The results in this paper have an important reference value for designing and fabricating high-performance blue light photonic crystal LED.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Numerical simulation of coupled thermo-mechanical process of friction stir welding in quasi-steady-state
2013, 62 (1): 018102. doi: 10.7498/aps.62.018102
The flow field of plastic deformation and the temperature field during the process of friction stir welding can directly affect the structure evolution of the welded joint, and also have a great influence on mechanical properties of the final joint. In this respect, therfore, a lot of researches have been carried out. The recent research results show that this process is an extremely complex coupled thermal-mechanical process, the temperature field couples together with the flow field of plastic deformation of the material. In this paper, the coupled process is simulated based on hydromechanics and heat transfer theory; the flow field of plastic deformation and the temperature field are calculated; an experiment is designed to measure the temperature field, which indicates that the computed results can exactly describe the coupled thermal-mechanical condition of the friction stir welding in quasi-steady-state.
2013, 62 (1): 018103. doi: 10.7498/aps.62.018103
The high-strain dynamic behavior of NiTi shape memory alloy has significant applications in several fields such as military af- fairs, aerospace. In order to investigate the transformation behavior in NiTi alloy, induced by dynamic mechanics, the shock-loading experiments are performed using a single stage gas gun at different temperatures and different shock velocities. Differential scanning calorimeter (DSC) and comprehensive physical property measurement system are employed to analyze the phase transformation in- duced by residual effects of shock waves in NiTi alloy. Three endotherms are observed in the first heating cycle, showing the presence of three-step reverse phase transformation; whereas during the second heating only one endotherm is seen, because the other two en- dotherms attributed to stress-induced martensite have disappeared. The exothermic and endothermic peak, owing to the transformation of shock-treated specimens, become small and their transformation temperature regions are broadened. This tendency indicates that the internal defects in the specimens, introduced by shock-treated, increase the resistance of phase transformation. The exothermic peaks of specimens, shock-treated at low velocity and high velocity, all shift to the low-temperature-zone, because the dislocations increase the hindrance to martensitic transformation. However, the endothermic peaks of specimens with low velocity shock-treated shift to high-temperature-zone, illustrating that the reverse martensitic transformation is also opposed by dislocations; while the endothermic peaks shift to low-temperature-zone for high velocity shock-treated, due to the decrease of transformation energy, caused by the re-duction of recoverable martensite. A small shoulder is detected in exothermic peak, whose shape becomes sharper with shock rate increasing. This result reveals that the intermediate phase (R-phase) results in two-stage phase transformation. The electrical resistivity measurement result further confirms that the two types of phase transformations associated with austenite to rhombohedral (A→R) and rhombohedral to martensite (R→M) can occur at the same time in a certain temperature range.
2013, 62 (1): 018104. doi: 10.7498/aps.62.018104
Vanadium thin films are deposited by magnetron sputter. Then VOx thin films are fabricated by a series of rapid thermal processes (RTPs) in pure oxygen environment. X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscope are employed to analyze crystalline structure of the thin film, phase composition and surface morphology. Electrical and optical properties of VOx thin film are measured by the four-point probe method and THz time-domain spectroscopy technology, respectively. The results reveale that the VOx thin film which is composed mainly of V2O5 and VO2 has the properties of phase transition to a certain extent within the RTP condition of heat preservation temperature and time, and the overall valence of vanadium remains unchanged, no matter whether the RTP condition is the same. The best performance VOx thin film can be obtained under the moderate RTP condition, such as 500 ℃ 25 s, and this film can also modulate the THz wave.
Experimental study of the settling and melting characteristics of equiaxed crystals in a falling tube
2013, 62 (1): 018105. doi: 10.7498/aps.62.018105
The morphology evolution of NH4Cl equiaxed crystal settling in a falling tube filling with its superheated aqueous solution is studied. The effects of superheating and initial crystal size on settling rate and melting velocity are analyzed. The results show that for a non-spinning equiaxed crystal, it will transform from a "quasi-symmetrical" morphology to "quasi-delta" morphology, and for a spinning equiaxed crystal, it is more likely to sustain its initial "quasi-symmetrical" morphology. By analyzing the drag coefficients of equiaxed crystals settling in the solution at different superheating degrees, it is found that higher superheating leads to a smoother shape of the equiaxed crystal, thus increasing its settling rate. For a large equiaxed crystal, higher complexity in shape and increase in settling velocity will lead to a higher melting velocity. In the settling process of crystal in superheated melt, the solute transport condition on the melting interface is weakened by the gradually reducing the settling velocity, resulting in a relatively steady melting velocity for a certain equiaxed crystal.
2013, 62 (1): 018701. doi: 10.7498/aps.62.018701
Transmembrane lipid exchange is critical to membrane function and pharmaceutical application. The exchange process is not fully understood and it is explored by quartz crystal microbalance with dissipation monitor method in this paper. It is found that the vesicle deformation discrepancy is not significant for the supported-lipid-bilayer-attached vesicles under different thermal and ionic strength conditions. And hence the total intermembrane contact area is determined by the vesicle adsorption amount. The maximum total intermembrane contact area decreases with the increase of temperature and the decrease of ionic strength. The changes of the vesicle adsorption rate and the transmembrane lipid exchange rate induced by temperature and ionic strength are elucidated to understand the observation above. The study helps explain some physiological phenomena and provides some guidelines for drug delivery researches.
2013, 62 (1): 018901. doi: 10.7498/aps.62.018901
The synchronization in complex network model with time-delay nodes is investigated. The model is applicable for two sorts of complex networks. With linear feedback controller and adaptive feedback controller, positive definite functions are designed respectively. The sufficient conditions of synchronization are given by Lyapunov stability theory. Finally, numerical simulations show the effectiveness of the synchronization in complex networks.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Responses of the land-surface process and its parameters over the natural vegetation underlying surface of the middle of Gansu in loess plateau to precipitation fluctuation
2013, 62 (1): 019201. doi: 10.7498/aps.62.019201
The Loess Plateau is well known as a specific region sensitive to global climate change, and thus its land-surface process is significantly influenced by climatic fluctuation. Up to now, the land-surface physical process over the Loess Plateau has been basically understood under a specific climatic condition, but the dynamic variation regularity of land-surface process in different climatic states is still lacking in its knowledge. Utilizing the continuous five-year data collected at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) supported by the program 'the Loess Plateau Land-surface Process Experiment (LOPEX)', in this paper, we systematically analyze the regularity of responses of factors including land-surface water and energy budget as well as surface albedo and roughness to climatic fluctuation over the natural vegetation surface of Loess Plateau. The results show that the land-surface process and its relevant parameters are very sensitive to the fluctuations of annual precipitation. Besides, they respond markedly to annual rainfall amount and are also closely related to the nature of rainfall. Soil moisture fluctuales not fully with total amount of rainfall but rises with the increase of effective precipitation with which land-surface water and energy budget also vary. In addition, the vertical sensible heat advection goes up with rainfall increasing, while the trend of surface energy imbalance is opposite. The averaged albedo in summer half-year comes down with the increase of the ratio of effective precipitation to the climatic average, but yearly averaged albedo is evidently affected by the snow-accumulating winter time and rises with the increase of snow-accumulating hours. Soil thermal conductivity and surface roughness both increase with annual effective precipitation increasing to the climatic average, but they are more sensitive to the precipitation fluctuation under a low precipitation condition than under the normal precipitation condition. However, land-surface process parameters over the natural vegetable surface of Loess Plateau basically fluctuate between those of deserts and farmland, and have not yet broken the climatic restrictions. Fitting relationship is used to quantitatively reflect the regularity of response of the parameters to rainfall fluctuations so as to evidently eliminate possible bias brought to numerical models and microclimatic analysis by the previous fixed and un-dynamic changeable land-surface parameters.
2013, 62 (1): 019701. doi: 10.7498/aps.62.019701
Timing information of X-ray pulsar signal is of the vital significance for realizing the autonomous navigation of spacecraft in deep space. The accurate timing model (period and period derivation) is the foundation of achieving high-precision auto-navigation solutions. Because the data that the X-ray photons arrive at the detector are unevenly spaced, both χ2 evaluation method and Lomb algorithm are analyzed. The idea is brought forward that the initial value of pulsar period is gained using the χ2 evaluation method, then the result of period is refined by Lomb algorithm. Meanwhile, the Lomb algorithm is ameliorated by the idea of fast Fourier transform algorithm, the efficiency of operation is enhanced highly. Finally the exact pulsar period is estimated, and correct pulse profile is replicated using the measured timing data from the X-ray source simulation system which used to validate the algorithm.