Vol. 59, No. 1 (2010)
2010, 59 (1): 1-6. doi: 10.7498/aps.59.1
In this paper we study the Lie symmetries and Noether conserved quantities of generalized nonholonomic mechanical systems， and establish the determining equations， the restriction equations and the additional restriction equations. The structure equation and the form of Noether conserved quantities are obtained. The inverse problems of Lie symmetries are discussed and an example to illustrate the application of the result is given.
2010, 59 (1): 7-10. doi: 10.7498/aps.59.7
A kind of conserved quantity which directly results from the Mei symmetry of general holonomic mechanical system is studied in the paper. The definition and criterion of Mei symmetry for the general holonomic mechanical system are given. The conditions under which Mei symmetry can lead to a conserved quantity and the form of the conserved quantity are deduced. An example is given to illustrate the application of the result.
2010, 59 (1): 11-14. doi: 10.7498/aps.59.11
In this article Noether symmetry of Lagrange systems, Hamilton systems and Birkhoff systems are discussed by geometric methods. And the corresponding Noether conserved quantities are deduced.
2010, 59 (1): 15-19. doi: 10.7498/aps.59.15
The Lagrangian image of the Birkhoffian representations is studied. The conditions that the second-order Lagrangians should satisfy are obtained, under which the generalized Lagrange equations are second-order differential equations. A new way for solving the inverse problem in Lagrange mechanics is presented. An error made in the study by some author is pointed out. Two examples are given to illustrate the application of the result.
2010, 59 (1): 20-24. doi: 10.7498/aps.59.20
The stability problem of equilibrium for a generalized Birkhoffian system is studied. The equations of equilibrium for the autonomous generalized Birkhoffian system are established. The equations of first approximation of the system are given, and the criterion of stability for equilibrium state of the system is established by using the Liapunovs first approximation theory. The Liapunovs function is constructed, and the criterion of stability for equilibrium state of the system is established by using the Liapunovs direct method. Some examples are given to illustrate the application of the results.
Dynamic modeling of a flexible beam with large overall motion and nonlinear deformation using the finite element method
2010, 59 (1): 25-29. doi: 10.7498/aps.59.25
In this paper, the dynamic modeling theory of a flexible beam, which incorporates large overall motion and nonlinear deformation, is investigated. As we knows, in spacecraft and space station, there are a lot of flexible appendices, the dynamic modeling of a flexible beam is essential. Yet existing such models, in our opinion, lack several important coupling terms. This paper supplies these important coupling terms. It is reasonable to use geometrically nonlinear deformation fields to demonstrate and simplify a flexible beam undergoing large overall motion. In this paper, the finite element method is used for the system discretization and the coupling dynamic equations of flexible beam are obtained by Lagrange’s equations. The complete expression of stiffness matrix and all coupling terms are included in the dynamic equations. The second order coupling terms among rigid large overall motion, arc length stretch, lateral flexible deformation kinematics and torsional deformation terms are concluded in the present exact coupling model to expand the theory of one-order coupling model. The dynamic properties of a planar flexible rotating beam in the non-inertial reference frame are developed.
2010, 59 (1): 30-37. doi: 10.7498/aps.59.30
Granular matter is a large assemblage of dense-packing particles. The interparticle forces are transmitted through heterogeneous chain architecture. The force chains would display different responses as external loading varies, and it would be directly related to the macroscopic mechanical properties of the granular system. Therefore, understanding the properties of force chains is fundamental to the study in granular systems. In this work, we firstly analyzed three characteristic time scales involved in processes occurring in granular systems, and proposed three dimensionless numbers to measure their relative importance. Secondly, a series of numerical simulations were conducted on a uniaxial compression system consisting of 12400 polydispersed particles. Our results showed that the shape of force distributions are unaffected by system preparation history and packing fractions in the range from 0855 to 0886, but mainly affected by the static surface friction. By defining three conditions for evaluating strong force chain, the probability distribution of force chain length was found in the form of power law with an exponent of 172, which is independent of packing fractions and static surface frictions in this static system.
Hopf bifurcation and stability of periodic solutions in a nonlinear relative rotation dynamical system with time delay
2010, 59 (1): 38-43. doi: 10.7498/aps.59.38
Hopf bifurcation in a nonlinear relative-rotation system with time delay is considerd, and the critical time delay associated with Hopf bifurcation is found. The time delays influence on the direction and stability of bifurcation are analyzed under the primary resonance condition with the aid of multiple scales. Finally, numerical simulations are performed to verify the analytical results.
2010, 59 (1): 44-53. doi: 10.7498/aps.59.44
Fourier-transformed method is used to investigate the problem of the rapid growth and decay of the disturbance energy of Rossby wave in barotropic atmosphere on the assumption that this kind of atmosphere is adiabatic, non-frictional, unforced, non-dissipative and quasigeostrophic on a beta plane. The analytical solution of linear barotropic potential vorticity equation is obtained for the first time and we go a step further to discuss the relations between the disturbance energy and the initial perturbation flow wave numbers, shear of basic flow and viscid coefficient by using the above analytical solution.
2010, 59 (1): 54-59. doi: 10.7498/aps.59.54
A new periodic wave solution for a (3+1)-dimensional soliton equation is found by using the Hirota method and Riemann theat function, from which the soliton solution can be obtained in an appropriate limiting procedure. In addition, the special three-dimensional surface graph of this equation is simulated with the help of Mathematica.
2010, 59 (1): 60-66. doi: 10.7498/aps.59.60
First, the relationships between the amplification or the attenuation of solitary waves and the initial amplitude of solitary waves as well as the structure parameters of the media are determined by direct perturbation method. Second, the solitary wave propagation in a microstructured solid layer is solved numerically using a four-order difference scheme constructed by linearization technique, and also the interaction of the solitary waves with different amplitudes are simulated. As a result, it is demonstrated that the solitary waves, under proper conditions, could be amplified or attenuated, even the solitary waves can propagate steadily in the microstructured solid layer, and the interaction of solitary waves does not influence their propagation characteristics.
2010, 59 (1): 67-74. doi: 10.7498/aps.59.67
We obtained a class of approximations and analytical solutions for the KdV-Burgers equation by using the homotopy analysis method (HAM). The solutions we got agree very well with the exact solutions. The results indicate that the HAM is still valid for solving a class of dissipative systems.
2010, 59 (1): 75-79. doi: 10.7498/aps.59.75
A new scheme with very simple implementations giving obvious experimental results has been demonstrated to reveal the particle and wave duality of light. The scheme demonspates the wave property of light by coherent superposition and the particle property of light by random path selection though a 50/50 beam splitter. Preliminary experiments showed high interference visibility of 99% and the particle nature of light as high as 90% by using a highly attenuated pulsed laser as a single photon source. This scheme displays both the wave and particle nature of light though a simple experimental setup, which makes it a quite promising schem for revealing the property of light.
The scattering of two-mode squeezed vacuum state and entangled coherent state through a one-dimensional potential barrier
2010, 59 (1): 80-86. doi: 10.7498/aps.59.80
We analyze the one-dimensional potential barrier scattering problem of two-mode squeezed vacuum state and entangled coherent state. We show that the entanglement of both the scattering states exhibits a parabolic relation with the transmission coefficient of the barrier, and valley of the parabola corresponds with a semi-anti-semi-permeable barrier. In addition, the entanglement of the former has a similar parabolic relation with the incident squeezed factor, and the entanglement of the latter has a linear relation with the incident entanglement. The fidelities of both the scattering states increase as the transmission coefficient increases, but the former decreases as the incident squeezed factor increases and the latter decreases as the incident module of coherent state increases.
2010, 59 (1): 87-91. doi: 10.7498/aps.59.87
In this paper, we propose a kind of degenerate optical parametric oscillator below threshold and use the thin crystal approximation to analyze the quantum noise reduction of the spectrum emitted from this cavity, and get the relation between the squeezing level and the pump field or the cavity detuning. We found that better squeezing level could be obtained only by properly choosing the phase of the local field, the amplitude of the pump field and the cavity detuning of the confocal cavity.
Based on the work of Majhi et al., we investigate the entropy correction to the Kerr-Newman black hole beyond semiclassical approximation by the Dirac equation. Because in the units G=c=kB=1,the Planck constant is proportional to the square of Planck Length,Planck Mass and Planck Charge,the proportionality parameter of quantum correction terms to the semiclassical term of action is taken as (Mrh-Q2/2)-1. With the aid of the differential form of horizon equation and the first law of black hole thermodynamics,we obtain the corrected entropy of charged stationary black hole and find that the correction terms also include the logarithmic and inverse terms to Bekenstein-Hawking entropy.
2010, 59 (1): 97-102. doi: 10.7498/aps.59.97
Single wire array Z-pinch experiments were carried out on the 3—4 MA Angara-5-1 facility employing a set of diagnostic equipment, including an X-ray power meter with platform response to record X-ray emission bursts and a time resolved pinhole camera to obtain soft X-ray images. Experimental results indicated that when the diameter of wire array was fixed, implosions of arrays with smaller wire diameter started earlier and had a larger convergence ratio. In addition, when the wire gap was larger, the wire plasma could not merge effectively but moved inward individually at an early imploding stage, and larger wire diameter with larger wire gap had longer instability wavelength. The results also showed that when the wire diameter was fixed, implosions of arrays with larger diameter started earlier and had higher implosion speeds and wider plasma dispersion during implosions. Implosions of arrays with larger wire and array diameter had longer pulse X-ray width.
According to the basic theories of Brownian motion, a mixed search model is proposed. By dividing every search process into two phases: single random walk search and multiple random walk searches, it improves the efficiency of a single random walk while reduces the hardware cost of multiple random walks. Compared with the mixing navigation model proposed by Tao Zhou, our model converges much faster on complex networks with lower hardware cost. We also compared two selection strategies: random selection and target selection, and found that our model improves the search efficiency further on complex networks when employed with target selection, which is prefered to the nodes of the highest degrees. Besides, by simulations on scale-free networks, we found the efficiency of our model is far higher than the single random walk and comparable to multiple random walks while the hardware cost of our model is far less. Finally, we give an absorption strategy to reduce the traffic load produced by the MS model.
2010, 59 (1): 111-115. doi: 10.7498/aps.59.111
The diffusion in a linear oscillator driven by white cross-correlation colored noises in which one of the noises is modulated by a biased period signal is studied. Effects on d versus Q curve, d versus D curve, and d versus Ω curve by multiplicative colored noise self-correlation time τ1 as well as additive colored noise self-correlation time τ2 are revealed. Here d, Q, D, and Ω denote the diffusion coefficient of the oscillator, the intensity of the signal modulated noise, the intensity of the pure additive noise, and the signal frequency, respectively. It is found that a minimum exists in the d versus Q curve and the d versus D curve respectirely. The diffusion coefficient as a function of signal frequency Ω exhibits a pronounced maximum at Ω=Ω, here Ω is the oscillator frequency. The condition of diffusion coefficient d=0 is derived.
2010, 59 (1): 116-122. doi: 10.7498/aps.59.116
On the basis of continuous chaos time scaling, dynamical design principle of continuous chaos frequency modulation signal (CCFMS) is proposed. Subsequently, a detailed implementation by taking Colpitts circuit as the example is given. Dynamical characteristics of CCFMS are analyzed by reconstructing the attractor and computing the Lyapunov exponent. Results show that the maximum Lyapunov exponent of CCFMS is the same as that of chaotic signal. Dynamical design of CCFMS can be simply realized and its system parameters can be easily controlled, meanwhile the signal expression is consistent with the mathematical expression of CCFMS.
2010, 59 (1): 123-130. doi: 10.7498/aps.59.123
Based on the nonlinear time series prediction，a feature extraction method for epileptic EEG signals using nonlinear prediction is proposed to automatically detect the epileptic EEG from EEG recordings. To reconstruct the phase space，the approach of determining the embedding dimension based on nonlinear predictability is used to determine the embedding dimension of the EEG signals. The experimental results show that the feature extracted with the method based on nonlinear prediction could clearly distinguish the epileptic EEG from the normal EEG，and the proposed nonlinear feature extraction method is fit for the small set time series and is stable to noise.
2010, 59 (1): 131-139. doi: 10.7498/aps.59.131
In this paper，we study a new chaotic system which is totally different from the Lorenz chaotic system，Chen chaotic system and Liu chaotic system. Firstly，the basic dynamical behaviors of new chaotic system are studied. The influence of system parameter on the chaotic system is discussed through Lyapunov exponent spectrum and bifurcation diagram. The results between simulation and experiment are in good agreement，thereby proving the veracity of analysis.
2010, 59 (1): 140-146. doi: 10.7498/aps.59.140
This article examines the theory of phase space reconstruction in complicated nonlinear system and further proposes a new method，an advanced Least Square Support Vector Machine (LS-SVM) model，to detect weak signals from a chaotic clutter. This method functions in following sequences：1) db3 wavelet decomposition of the signals，2) LS-SVM prediction，which includes increasing the symmetry constraint and improving the kernel function，3) Reconstruction. It is established a one-step predictive model that detects the weak signal，including transient signal and period signals，from the predictive error in the chaotic sequences. It is illustrated in the experiment，which is conducted to detect weak signals from Lorenz chaotic background and Sea Clutter，that this proposed method is highly effective to detect weak signals from a chaotic background as well as minimize the impact of noise on weak signals. Compare to conventional RBF neural network and LS-SVM models，the new method presents great value in prediction accuracy and detection threshold.
Fault tolerant control of master-slave synchronization for a class of chaos systems with multiple time-delays
2010, 59 (1): 147-156. doi: 10.7498/aps.59.147
The problem of master-slave fault tolerant synchronization for a class of chaotic systems with multiple time-delays is considered. A fault tolerant synchronization is designed for a fault occuring in chaotic systems. Whether the fault happens in the chaotic systems or not，the synchronization method not only guarantees that the error system is globally asymptotically stable，but also satisfies a prescribed performance level. The fault tolerant controller contains two parts：the state feedback controller and fault compensator. A delay-dependent condition based on linear matrix inequality (LMI) is proposed for fault tolerant controller. The effectiveness of proposed design method is demonstrated by a simulation example.
2010, 59 (1): 157-163. doi: 10.7498/aps.59.157
A tail-mapping is introduced to deal with the tail impacts caused by the chattering，and based on which，an effective numerical method is suggested to simulate the chattering in the vibro-impact system. As an illustrative example，a Duffing unilateral vibro-impact system is investigated. The results show the evidence of complete and incomplete chattering. We also investigate two novel chattering bifurcations，including transitions from complete to incomplete chattering and incomplete chattering period to aperiodic motion.
Generalization of mode decomposition approach to studies of the synchronization of non-identical coupled dynamical systems
2010, 59 (1): 164-170. doi: 10.7498/aps.59.164
In this paper the mode decomposition approach in the studies of the synchronization of the coupled dynamical systems is generalized to the case of the coupled non-identical dynamical systems by changing the coupling function. The synchronization of the non-identical periodic and quasi-periodic attractor systems is considered detailedly and the conditions for their local synchronization stability are obtained in this paper. The numerical simulation is performed and it was found that the dynamical behaviors of the synchronization are rich. The behaviors include stable synchronized periodic and quasi-periodic solutions in the coupled non-identical quasi-periodic attractor systems，and several stable synchronized periodic solutions in the coupled non-identical periodic attractors， where the new stable synchronized periodic solutions are born due to the coupling，and their attraction basins differe greatly，i.e.，in both of them the multiplicity of the synchronization appears. At the same time the validity of the mode decomposition is also verified.
2010, 59 (1): 171-177. doi: 10.7498/aps.59.171
Based on the multi-agent approach and the swarm platform，a macroscopic simulation of urban transportation system is developed. In the simulation，travelers are divided into three groups first，and then links，intersections and travelers are treated as agents respectively. Three different experiments，namely traveling scales，traveler groups and network structure experiments，are carried out by the simulation. Through comparing and analyzing the simulation results from the perspectives of system scale and structure，we try to find and explain the macroscopic phenomena and the possible emergence phenomena coming from the microscopic level in urban transportation system.
2010, 59 (1): 178-185. doi: 10.7498/aps.59.178
In this paper，a new single-component lattice Boltzmann method is proposed to describe liquid-vapor phase transition process. Water and ammonia phase transition process are simulated by using this new model for Redlich-Kwong，Redlich-Kwong Soave and Peng-Robinson equations of state. Compared with the experimental data of water and ammonia，the results show that the Peng-Robinson equation of state is more suitable to describe the phase transitions process of water，ammonia and other substance. In particularly，the simulation results of ammonia with Peng-Robinson equation of state are more close to the experimental data. In order to demonstrate the capability of this model for dealing with two-phase problems，the mass density profile across the interface of water or ammonia which is controlled by Peng-Robinson equation of state are simulated by this model for different temperatures. These simulation results agree with that of classical interface theory. Finally，the relationship between the bubble (droplet) inside and outside pressure difference and its radius is simulated when the bubble (droplet) is in equilibrium environment at different temperatures. The results agree with Laplace law. The surface tension of water and ammonia is obtained from simulation results at different temperature，which agree with experimental data and the critical theory of surface tension.
2010, 59 (1): 186-191. doi: 10.7498/aps.59.186
A method for calibrating the spectroscopic ellipsometry by X-ray reflectivity is presented. As an indirect method，spectroscopic ellipsometry does not have the traceability because the measured film thickness is dependent on its optical constant. In contrast，at the grazing angle，the X-ray reflectivity can be used to measure the absolute thickness of thin film with sub-nanometer precision，and is independent of the optical constant. Five SiO2 films were deposited on the substrate of single crystal silicon with the thickness of 2 nm，18 nm，34 nm，61 nm，and 170 nm，respectively. The results of spectroscopic ellipsometry and X-ray reflectivity were well fitted by a liner equation with slope of 1013±0013 and its intercept was set to zero，which means this calibration method is valid for spectroscopic ellipsometry in the determination of the thickness of thin films.
Numerical simulation of the near-field distribution of light spot of aperture pyramid-type optical probe with a metal tip
2010, 59 (1): 192-198. doi: 10.7498/aps.59.192
The finite-difference time-domain method (FDTD) is employed to investigate the near-field distribution of the light spot of aperture pyramid-type optical probe with a metal tip. The factors that have some influence on the electric field distribution such as the length，radius and position departed from aperture of the tip are investigated. The mechanism of electromagnetic wave transmitting from the aperture to metal tip by way of plasmon is discussed. Our calculation results are consistent with the results obtained by Taminiau with different methods. How and why Pohl etc. have obtained images with high resolution in the 20—25 nm range between 1984 and 1986 are analyzed. The imaging mechanism of their experiment system is discussed. Numerical simulation demonstrates that the imaging mechanism of Pohls experiment system may belong to a scattering-type near-field optical microscope (S-SNOM) rather than an aperture scanning near-field optical microscope (A-SNOM). This paper can help us to find optimized tip design in the future.
Study of proton beam spreading for a solid beam stopper double scattering method using Monte Carlo simulation
2010, 59 (1): 199-202. doi: 10.7498/aps.59.199
Beam spreading is the foundation of proton therapy for large area and depth tumor. The characteristics of proton lateral beam distribution for a solid beam stopper double scattering system are investigated using Monte Carlo multi-particle transport code Fluka and the results are compared with analytical computation by using Highland formula under the same conditions. It is found that proton fluence obtained by Fluka is lower than that by analytical computation with Highland formula in the region where the variation in uniformity is ±25% and they coincide better with thin-foil than with thick-foil. For a solid beam stopper double scattering system，as the thickness of foils increases，the radius of beam spreading increases，but the efficiency of beam use age increases firstly and then decreases，the maximum value is about 169%.
ATOMIC AND MOLECULAR PHYSICS
2010, 59 (1): 203-209. doi: 10.7498/aps.59.203
A parameter-free analytical formula for dissociation energy of diatomic system is suggested recently by Sun et al. Together with the algebraic method (AM) which was presented to obtain accurate full vibrational energies for diatomic molecules in their previous work，the new formula is applied to study the dissociation energies and the full vibrational spectra of some diatomic ions in this work. The results show that the AM vibrational spectra and dissociation energies have excellent agreement with experimental values.
2010, 59 (1): 210-214. doi: 10.7498/aps.59.210
Raman spectra of benzene have been obtained at pressure of 13 GPa. The results shows that with the increase of pressure，all the Raman bands blue shift，accompanied with the splitting and change of relative intensity of some spectral bands. For the vibrational Fermi resonance bands ν1+ν6—ν8，according to the Betran theory，the unperturbed peak separation Δ0 increases with pressure，which is due to the ratio of frequency-pressure of the combined ν1+ν6 bands is larger than that of fundamental ν8. As a consequence，the coupling coefficient ω and the intensity ratio Rf/a decrease. The Fermi resonance phenomenon disappears when the pressure is up to 11 Gpa，which can be explaned by high-pressure phase transition method. This report enriches the studies of environmental effect on the Fermi resonance，and provides positive reference value for the spectral certification and assignment.
Theoretical study of the influence of laser intensity on the population of the NO molecule electronic states
2010, 59 (1): 215-221. doi: 10.7498/aps.59.215
Using the time-dependent wavepacket method and employing the four-state model，the influence of the laser intensity on the population of the NO molecule electronic states are calculated in this paper. The populations of the electronic states of the NO are given by the wavefunctions obtained by solving the Schrdinger equation through the split-operator Fourier transform method. The calculated results show that different pump pulse intensities have different influences on the population of the electronic states of NO. By changing the pulse intensity，the ionization ratio can be controlled，which will benefit the light manipulation of atomic and molecular processes.
2010, 59 (1): 222-226. doi: 10.7498/aps.59.222
The transmission of 60 keV O+ ions through Al2O3 nanocapillaries at a series of different tilt angles is measured. The capillaries with diameters of 50 nm and 30 nm respectively and 10 μm in length are used. The angular distribution and the transmission yields of transported ions are investigated. Our results indicate both the existence of guiding effect when ions pass through the capillary and a significant dependence on the tilt angle. The results also show that the transmission yield increases as the diameter of capillary decreases，and the theoretical model used in our work explains it well.
Investigations on molecular structure and analytic potential energy function of the AsH(X3Σ-) and AsH2(C2v，X2B1) radicals
2010, 59 (1): 227-233. doi: 10.7498/aps.59.227
The CCSD(T) theory in combination with the cc-pV5Z basis set is used to determine the equilibrium geometry，dissociation energy and vibrational frequencies of AsH2(C2v，X2B1) radical. By comparison，excellent agreement can be found between the present results and the experiments. The values obtained at present are of 01508 nm for the equilibrium bond length RAs-H，912231° for the bond angle ∠HAsH，28795 eV for the dissociation energy De(HAs-H) and 10133361 cm-1，22251347 cm-1 and 22337565 cm-1 for the vibrational frequencies ν1(a1)，ν2(a1) and ν3(a1)，respectively. The equilibrium geometry，harmonic frequency and potential energy curve of the AsH(X3Σ-) radical are calculated at the CCSD(T)/cc-pV5Z level of theory. The ab initio results are fitted to the Murrell-Sorbie function with the least-square method. The spectroscopic parameters are in excellent agreement with the experiments. The analytic potential energy function of the AsH2(C2v，X2B1) radical is derived by using the many-body expansion theory. This function correctly describes the configuration and dissociation energy of the AsH2(C2v，X2B1) radical. Two symmetrical saddle points have been found at (0160 nm，0296 nm) and (0296 nm，0160 nm)，respectively. And the barrier height is equal to 01512×4184 kJ/mol.
2010, 59 (1): 234-238. doi: 10.7498/aps.59.234
Density functional theory has been employed to investigate the structure and stability of C@Al12Hn (1≤n≤7) clusters. Hydrogenated C@Al12 clusters exhibit pronounced stability for even numbers of H atoms. Large HOMO-LUMO gaps，large binding energy and increased ionization potentials imply that these clusters should be physically and chemically stable. The analysis of the charge density of the HOMO plot illustrates that a pair of hydrogen atoms prefer to occupy opposing on-top sites for clusters with an even n number. Studies of deformation charge density plots demonstrate that the bonding characteristic between the H atoms and the C@Al12 moiety is mainly covalent. The total magnetic moment is 1μB for C@Al12Hn with an odd number for n.
CLASSICAL AREA OF PHENOMENOLOGY
2010, 59 (1): 239-245. doi: 10.7498/aps.59.239
A method based on magnetization is proposed to predict the induced magnetic field of naval vessels. We first deduce a formula to calculate the magnetic field in the internal region of magnetized objects from the viewpoint of magnetization，and then use the formula to define the point-function demagnetizing tensor and prove some properties of the tensor. Finally we use this formula to develop a new method to predict the induced magnetic field of naval vessels in a nonuniform applied field，and we call it the Magnetization Method，in which the point-function demagnetizing tensor is used. Compared with traditional methods，the magnetization method features low computational cost，high precision and manifest physical meaning. A numerical simulation of ship model verifies the method.
2010, 59 (1): 246-255. doi: 10.7498/aps.59.246
The analytical expression for the propagation of partially coherent flat-topped vortex beams through a paraxial optical ABCD system is derived and used to study the coherence vortex properties of partially coherent vortex beams in the focal region and free space. It is shown that the coherence vortex depends on the beam order N，spatial coherence parameter α and position (x1，y1) of the reference point. Depending on the choice of the reference point，the zero point of the spectral degree of coherence may be present or absent. In particular，if x1=y1=0 is chosen，the phase at the zero point of the spectral degree of coherence may be determinate，thus the coherence vortex does not exist.
2010, 59 (1): 256-263. doi: 10.7498/aps.59.256
We studied the focusing properties of an anisotropic metamaterial slab lens by means of the angular spectrum representation of the vectorial electromagnetic field. The analytical expressions for vectorial fields in all the propagation regions are obtained，and the quantitative relationship between the focusing characteristics of the vectorial electromagnetic field and the anisotropic parameters of the anisotropic metamaterial slab lens is disclosed. The polarization state of the focusing beam is found to be changed due to the effect of anisotropy. As an application of the vectorial theory，we have analyzed the focusing property of an anisotropic metamaterial slab for which the permeability along longitudinal axis is -1. It is demonstrated that this slab lens can redirect a beam initially polarized along a transverse axis to a partial focus and give a clear polarization rotation of the beam.
Generation of helical beams with pre-determined energy distribution based on phase modulation gratings
2010, 59 (1): 264-270. doi: 10.7498/aps.59.264
The generation of helical beams with different pre-determined orbital angular momentum states based on computer-generated holograms is studied. The phase-type diffraction gratings are designed by using the Gerchberg-Saxton iterative method，and realized by using the spatial light modulator (SLM). In the experiments diffraction fields with different helical beams distribution are obtained by using the gratings. The theoretical simulation agrees with the experimental results. This method is meaningful for the information transmission based on the orbital angular momentum.
2010, 59 (1): 271-280. doi: 10.7498/aps.59.271
A pre-process of feature extraction and classification approach based on spectrum edges matching is proposed to analyze the complicated nonlinear fluorescence spectra emitted by the interaction between femto-second (fs) laser and the impurities in air. The spectra data is denoised and compressed from 3979 points to 664 points using wavelet (WT) transform. By similarity analysis we create the characteristic spectra of 3 kinds of gases and the weights for classification. A new method of classification is proposed based on the edges matching and the comparison with characteristic spectra. Compared with existing methods，our method can not only get 100% classification accuracy，but also gives the characteristic position and the matching degree. The analysis of the matching degree shows that our method works well at low concentrations and has a potential application of identifying gases of lower concentration.
2010, 59 (1): 281-286. doi: 10.7498/aps.59.281
Quantum key distribution (QKD) system must be robust enough in practical communication. The system performance is notably affected by phase drift. For the fiber-based phase-encoded quantum key distribution system, the Faraday-Michelson QKD scheme can auto-compensate the birefringence of fiber, but phase drift caused by environment variations is still a serious problem in practical operation. In this paper, the major schemes to compensate for the phase drift are analyzed in detail and an “five-phase”effective active phase compensation method is proposed. The comparison with other two major active phase compensation schemes also given. The result shows that this method uses less time to acquire the parameter of phase drift with the same precision and it can be used in phase-encoded QKD systems without introducing additional devices.
Nonorthogonal decoy-state quantum key distribution based on conditionally prepared down-conversion source
2010, 59 (1): 287-292. doi: 10.7498/aps.59.287
The decoy-state method and the non-orthogonal encoding protocol, being capable of resisting the photon-number splitting attack, have become attractive recently. Here, we combine both the methods and propose a new protocol using a conditionally prepared down-conversion source, following Poisson photon number distribution. In the protocol, Alice randomly changes the intensities of the pump light so that the intensity of signal photon of photon pair is randomly changed. The signal state is used for generating keys, the decoy states for detecting the eavesdropping and estimating the fraction of single-photon and two-photon pulses. We have simulated the final key rate over transmission distance, showing our scheme can enhance the performance of quantum key distribution.
2010, 59 (1): 293-299. doi: 10.7498/aps.59.293
We have studied the effect of optical bistability exhibited in the laser oscillation of Yb:LuVO4, Yb:YVO4, and Yb:GdVO4, the three Yb doped vanadate crystals. The bistability range can be in excess of 1 W in terms of the pump power absorbed by the crystal. At the high-power-end side of the bistability region, i.e., the upper threshold for laser oscillation, discontinuous growing in the output power takes place, along with large fluctuations in the laser intensity occurring on sub-millisecond time scale. It is found that the bistability effect is affected significantly by the output coupling of the resonator, the crystal thickness, and the thermal effect existing in the crystal.
Spectroscopic properties and Judd-Ofelt theory analysis of La, Nd codoped Y2O3 high refractivity transparent ceramics
2010, 59 (1): 300-306. doi: 10.7498/aps.59.300
Nd，La:Y2O3 nanocrystalline powder was prepared by co-precipitation method. The transparent ceramic was fabricated by vacuum sintering at 1700℃ for 4 h in vacuum. Transparent polycrystalline ceramics with uniform lanthanum distribution was obtained. The grain size was around 22 μm. No pores were found in the grain and grain boundary. The absorption spectrum and the fluorescence spectrum of the sample were measured. The highest absorption peak is centered at 821 nm and the absorption cross section is 43×10-24 m2 The main emission peak is at 1078 nm, and the fluorescence lifetime is 0287 ms. The Judd-Ofelt intensity parameter Ωλ（λ=2，4，6）, spontaneous transition probability, radiative lifetime and fluorescence branching ratio of Nd3+ were calculated by Judd-Ofelt theory. The calculated emission cross section of 4F3/2→4I11/2 transition is 20×10-24 m2 It was found that the addition of La ion can change the crystalline field of yttria, which helps to obtain suitable solid laser materials.
Experimental research on frequency doubling in periodically poled KTiOPO4 waveguide fabricated by femtosecond laser
2010, 59 (1): 307-310. doi: 10.7498/aps.59.307
We present in this paper the fabrication and characterization of type II waveguide in c-cut periodically poled KTiOPO4 crystal. The waveguide was fabricated by using a femtosecond laser，and the fabrication process was optimized. In our experiments single mode propagation was observed at optimal waveguide width of 145 μm and quasi-phase matching wavelength of 1064 nm. The second-harmonic conversion efficiency of 398% can be achieved.
Two-dimensional complex nano-micro patterning on GaP and ZnSe surface created by the interference of three femtosecond laser beams
2010, 59 (1): 311-316. doi: 10.7498/aps.59.311
In this paper, we reported the two-dimensional periodic nano-micro complex structures on GaP and ZnSe crystals surface created by the interference of three femtosecond laser beams. Different types of nano-patterns were obtained by arranging the laser polarization combination of the three beams. In order to understand the formation of these nanopatterns, we theoretically calculated the distributions of laser intensity and polarization. The experimental and theoretical results indicate that the long periodic microsturctures are determined by the interferential intensity pattern, and the short periodic nanostructures were determined by the interferential polarization pattern. These researches haue huge potential applications in nanopattering of semiconductors and dielectrics.
Effect of laser polarization direction on high order harmonic generation of oxygen molecule——A simulation via TDDFT
2010, 59 (1): 317-321. doi: 10.7498/aps.59.317
The high order harmonic generation (HHG) of O2 radiated by ultra-strong femto-second pulsed laser beam is simulated by the time dependent density functional theory (TDDFT) method with the general gradient approximation (GGA) of the exchange-correlation energy. The effect of different laser polarization directions on HHG is discussed. The results indicate that the HHG spectrum of O2 has the similar characteristic as the typical atom HHG spectrum. The HHG yields peaks when the molecules are aligned at about 45° from the polarization axis. Good agreements are found with the experiment.
Strong monochromatic harmonics generated by the interaction of two counter-propagating pulses with a foil target
2010, 59 (1): 322-328. doi: 10.7498/aps.59.322
This paper studies the strong harmonic generation in the interaction of two conter-propagating pulses with a foil target. When the thin target is irradiated by high-contrast circularly polarized laser pulse, the light pressure push high-density plasma forward.At the same time, because of the role of charge separation field, the ion beam and electron beam bunch well in longitudinal direction, and generate the plasma mirror with a forward movement at relativistic speed. When incidenting on a probe laser pulse on the plasma mirror in the opposite direction, they produce strong monochromatic N-order harmonics by Doppler shift, with the new duration of pulses compressed to 1/N of the original ones. This paper also discusses the effect of the laser and plasma parameters on plasma mirror movement which influences the order of harmonics, and also the effect of the stability of the relativistic plasma mirror on the harmonics.
2010, 59 (1): 329-335. doi: 10.7498/aps.59.329
We studied the steering of the nonlocal spatical optical soliton in thermal optical nonlinear lead glass theoretically and experimentally. By employing the conformal mapping method, the response function of the lead glass was obtained, and the influence of the boundary on the response function is discussed. Then we obtained the trajectory for the off-center soliton and the output displacement equation when the point of incidence is varied. We also observed experimentally the phenomenon of steering of the optical soliton in lead glass whose boundary shape is rectangular. The theoretical results are in good agreement with the experimental observations.
2010, 59 (1): 336-339. doi: 10.7498/aps.59.336
We experimentally investigate the discrete mode in the zero-average-refractive-index gap (the zero-n—gap) of the one-dimensional periodical structures containing left-handed materials (LHMs) and right-handed materials (RHMs). When the discrete mode conditions are satisfied in the zero-n gap, there are no discrete propagating modes, but the zero-n—gap completely vanishes. This behavior is attributed to the dispersive property of LHMs and RHMs. In addition, the theoretical expectation of the discrete modes with no sidelobes in the zero-n—gap never occurs in experiment because the LHMs is intrinsically dispersive.
2010, 59 (1): 340-350. doi: 10.7498/aps.59.340
It has been over 20 years since the concept of photonic crystal was proposed. Photonic crystal is now an important part of nano/micro-optics and quantum optics, and is also applied in many fields, such as information optics etc. The paper is focused on the progress in the fabrication of photonic crystals, especially the fabrication of two-dimensional and three-dimensional photonics. Meanwhile, the application of the photonic crystal is also reviewed. Then some perspectives are proposed.
Dispersion properties of two-dimensional dispersive and anisotropic-magnetized-plasma photonic crystals
2010, 59 (1): 351-359. doi: 10.7498/aps.59.351
Dispersion characteristics of two-dimensional dispersive and anisotropic-magnetized-plasma photonic crystals are studied using both the plane wave method and finite-difference time-domain method. When the wave vector lies in the periodic plane, due to the external magnetic field, two different regions of flat bands occur in the TE mode. Varying the values of external magnetic field will affect not only the location of flat bands, but also the position and size of band gaps. Increasing the background dielectric constant will make omnidirectional band gaps to be formed, and make the center of gaps reduced while making the width increase. When the wave vector lies in non-periodic plane, dispersion curves of magnetized plasma photonic crystal are no longer divided into TE and TM modes. With the increasing of the non-periodic wave vector, the location of gap shifts upward, and the gap width firstly increases and then varies little.
Simulation study on a negative refractive index material with high transmission at 748 THz——The violet end of the visible region
2010, 59 (1): 360-364. doi: 10.7498/aps.59.360
A left-handed material composed of unit cells of three-layered square nanoflake with four edges gapped is proposed in this paper. The S-parameters of the unit cell are caculated in the numeric simulation, and the property parameters such as the retrieved complex refractive index n, permittivity ε and permeability μ,etc. are analyzed. It is shown that, the frequency band in which the refractive index of this structure being negative lies from blue in the visible region to near ultraviolet, and the peak of negative refractive index lies at 748 THz, namely the violet end of the visible region. And the figure of merit of the material is 154, so it may have practical applications because of its low loss and high transmission.
2010, 59 (1): 365-369. doi: 10.7498/aps.59.365
Tunable Fabry-Perot filter (FPF) has high practical value in optic communications. Piezoelectric copolymer P(VDF-TrFE) can be used as spacer material in FPF to obtain large tunability in wide range because of its great electrostrictive effect. The filter has been fabricated with the structure of DBR/electrode/spacer/electrode/DBR. The copolymer is partly etched at where the light traverses. The transmittance spectra have been studied. The resonant wavelengths have been modulated by applied voltage. The optical length is measured to be 804 μm, which shrinks under the electric field. The filter exhibits a total optical path-length change of -0757% under an electric field of 140 V. The results indicate that the electrostrictive effect plays a major role.
Characterization of chirped pulses with modified-zero-additional-phase spectral phase interferometry for direct electric-field reconstruction
2010, 59 (1): 370-375. doi: 10.7498/aps.59.370
At present, pulse measurement systems based on spectral phase interferometry for direct electric-field reconstruction (SPIDER) may have problems in chirped pulse characterization. In this paper we propose and demostrate a Modified-ZAP SPIDER system to solve this problem. Femtosecond pulses from a KLM Ti:sapphire laser and the chirped pulses obtained by broadening by a 80 mm BK7 glass block are respectively measured. The experimental results show that the novel MZAP-SPIDER system performs well in chirped pulse measurement.
2010, 59 (1): 376-380. doi: 10.7498/aps.59.376
By multiple-scattering theory (MST), disorder effect on the focus image in steel/water phononic crystal panel with negative refraction was investigated. It was found that sonic waves within certain frequency range can propagate along certain directions in periodic crystal and form a focus image with negative refraction characteristics. These directional pathways depend on the periodic scattering in the crystal and are different from the ordinary positional guide. Obstacles in pathways have a deep influence on the focus image. With the increasing of degrec of positional disorder of cylinders, the periodic scattering decreases, pathways are broken, and the focus image becomes blurred or disappears.
2010, 59 (1): 381-386. doi: 10.7498/aps.59.381
By using multiple-scattering theory (MST), the imaging process was investigated in steel/water phononic crystal panel with negative refraction. It was found there are some channels for the scattering waves propagating in the panel. For a given source location, the scattering channel changes with incident angle and so does the strength of signal coupled to the channel. While small-angle incident wave can be coupled into the channel perfectly, large-angle incident wave which is strongly scattered in the incident surface can be coupled into the channel only weakly. In the non-ideal imaging case, imaging position changes with the angle of incidence signal,it further causes imaging aberration. These scattering channels are closely related to the anisotropic band structure of the crystal panel and multiple scattering of the rods, and vary with position change of the sound source.
2010, 59 (1): 387-392. doi: 10.7498/aps.59.387
Piezoelectric patches connected with shunting circuits are periodically placed along a base beam, forming a one-dimensional phononic crystal. Different types of shunting circuits will determine the band structure of the beam. Resistive shunting circuits can restrain the beam’s modal vibrations to some extent and the band gaps of the beam can be changed by weakening the piezoelectric effect. LC shunting circuits can produce locally resonant gaps induced by LC circuits’ electromagnetic oscillations excited by piezoelectric patches. When resistors are added to the LC circuits, the LC circuits’ oscillation will be weakened and the attenuation amplitude in the band gaps will be lowered, but the scope of band gaps are widened.
2010, 59 (1): 393-400. doi: 10.7498/aps.59.393
Acoustic band gaps in two-dimensional phononic crystal consisting of a finite-sized square array of parallel hollow aluminum cylinders in air are investigated with the finite difference time domain (FDTD) method. Experimental measurements were carried out to validate the theoretical predictions with excellent overall agreement achieved. The numerical method is used subsequently to study the band gap properties of phononic crystals composed of cylinder (both solid and hollow)/fluid systems for two different acoustic impedance ratios. For both types of system, the influence of the transverse size of the phononic crystal on the propagation properties is analyzed, and the minimum size to achieve the largest band gap width for different filling factors is determined.
2010, 59 (1): 401-410. doi: 10.7498/aps.59.401
Based on the finite deformation equation of protein bubble with viscoelastic film, and taking into account the Bjerknes effect that one oscillating bubble acts on the ather in Bingham liquid, a nonlinear equation describing the vibration of two equal-radius protein bubbles in Bingham fluid is built. The numerical simulation is used to solve the above nonlinear equation. The results show that, increasing the plastic viscosity of Bingham liquid the protein bubble wall will vibrate with higher decrement velocity of amplitude, and with lower frequency; shortening the distance between bubbles, the bubble wall will vibrate with a higher frequency and a higher decrement velocity of amplitude. Furthermore, the smaller the bubble size is, the higher the increment of frequency and decrement velocity of amplitude are. The two bubbles in Bingham fluid will vibrate with higher frequency and higher decrement velocity of amplitude than that of a single bubble.
Experimental studdy on relation between volume fraction of sandpiles and flow rate of forming sandpiles
2010, 59 (1): 411-416. doi: 10.7498/aps.59.411
The function of volume fraction η versus flow rate Q was determined. It is found that η decreases exponentially with increase of Q. The volume fraction η will reach saturation when Q is reduced or increased to certain extent. The increase of η slows down rapidly with decrease of Q when D/d decreases to a critical value. The decrease of η slows rapidly with increase of Q when d decreases to a critical size. The phenomenon is explained by the dissipation of granules, effect of air, effect of bottleneck and collision theory.Theoretical result about η-Q is in agreement with the experimental result.
2010, 59 (1): 417-421. doi: 10.7498/aps.59.417
The stress cracking and crack-healing effects in dimethyl phthalate, diethyl phthalate, dibutyl phthalate and dioctyl phthalate series glassy materials was measured by the recently invented method (RMS-L-CH) which measures the stress cracking and crack healing in situ and further analysis and discussions on the crack healing phenomenon as well as its relation to the glass transition are presented. The results validate that the RMS-L-CH method is effective and may provide a new means to characterize the glass transition and to probe into the glass transition mechanism.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2010, 59 (1): 422-429. doi: 10.7498/aps.59.422
In the paper, the influence of aggregation structure and traps on both DC and impulse flashover voltage of semi-crystalline cross-linked polyethylene (XLPE) in vacuum are investigated. After heat treatment at 135 ℃ for 10 min, the XLPE samples were quenched to -56 ℃ or -25 ℃, cooled normally, cooled at a rate of 1 ℃/min or 05 ℃/min to room temperature, respectively. The electrical properties, microstructure and trap distribution of heat-treated samples were studied. Compared with untreated samples, it is found that the dc and impulse flashover voltages of heat treated samples are raised by 76% and 19%, respectively. It is proposed that the aggregation structure and trap level is changed by heat treatment, leading to the improvement of surface flashover properties in vacuum. It is suggested that the vacuum flashover characteristics can be improved by controlling the aggregation structure and trap levels of semi-crystalline polymers.
Preliminary studies on the mechanism of radiation production in aluminum wire array Z-pinch implosion
2010, 59 (1): 430-437. doi: 10.7498/aps.59.430
The mechanism of energy conversion and radiation emission of aluminum wire array Z-pinch implosion has been studied by using a one-dimension non-equilibrium magnetohydrodynamic code. The energy transfer processes have been discused carefully, which shows that the accelerator feeds its stored energy to plasma via Poynting energy flux, and plasma kinetic energy is converted to plasma internal energy through pdV work and shock heating, thus producing radiation via several atomic processes including line radiation, recombination radiation and bremsstrahlung radiation. With the information of atomic populations, the mechanism of producing radiation has been anzlyzed. It is shown that in the implosion stage the ionization and excitation processes dominate, leading to the dominant yield of line radiation.While at stagnation most ions are in naked states, so the recombination radiation is the main radiation source. Corresponding to the two peak fractional populations of H-like and He-like ions, the line radiation also exhibits two radiation peaks at the time near peak compression. In the expansion stage, it is the radiative recombination that dominates the atomic processes, thus decreasing the share of line radiation in total radiation.
Field emission properties of amorphous carbon nanodot arrays in a novel anodic aluminum oxide template by self-assembly technique
2010, 59 (1): 438-442. doi: 10.7498/aps.59.438
Amorphous carbon nanodot arrays were successfully prepared through filtered cathodic arc plasma (FCAP) technique, and via a special widen process, the negative effect of the anion impurities distributed in the anodic aluminum oxide (AAO) template was avoided during carbon ions deposition. The morphology of the samples was studied by a field emission scanning electron microscopy (FESEM). The AAO template prepared by multi-steps combining anodization process and pore-widening process has special pore openings. The nanodot arrays are uniformly distributed and in good agreement with the AAO pore arrays. The diameter of the as-prepared nanodot is about 100 nm, and the density was estimated to be 1010 cm-2. Field emission properties of the nanodot arrays were investigated and a low threshold field of 37 V/mm at 10 mA/cm2 was obtained.
2010, 59 (1): 443-446. doi: 10.7498/aps.59.443
The filter-fluorescer method is an important X-ray diagnostic technique. For 14×107—16×107 K blackbody radiation, a four channel spectrometer consisting of filter-fluorescer combinations of V-Ti, Co-Fe, Cu-Ni and Zn-Cu was designed, and the corresponding supplementary channels were supplied for each primary channel. The calculation results show that the measurement of supplementary channel which has the same configuration as that of primary is not accurate, the postfilters of supplementary channels should be reconfigured to make an proper background measurement.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2010, 59 (1): 447-452. doi: 10.7498/aps.59.447
Purified multiwalled carbon nanotubes (MWCNTs) were irradiated by 60Co γ-ray with different doses. The structural change of the MWCNTs was revealed by high-resolution transmission electron microscopy and Raman spectroscopy. It was found that under γ-ray irradiation some amorphous structure homogeneously covers the inner tube walls with graphite structure in irradiated MWCNTs. Moreover, the amorphous structure continuously proceeds and the graphite structure is reduced during the γ-ray irradiation till the irradiated MWCNTs become amorphous nanowires with a hollow structure. Based on the interaction between photons and carbon nanotubes, the structural transformation process and the corresponding mechanisms are discussed. In MWCNTs, the collision of a photon with a carbon atom will result in displacement of the atom, i.e. formation of a vacancy (single- or multi- vacancy) and a number of primary knock-on atoms which, if their energy is high, leave the tube or displace other atoms in the MWCNTs. If their energy is low, they can be adsorbed onto the tube walls. These adsorbed atoms play the role of interstitials. All the displaced atoms can be sputtered from the MWSNTs. The carbon atoms sputtered from the MWCNTs can further create some damage in a nearby MWCNTs or be absorbed onto its surface. Along with the simple defects, a number of more complex defects can be formed. The behavior of complex irradiation-induced defects is governed in part by annealing and diffusion of original defects-vacancies and interstitials. The γ-ray irradiation induced structural transformation of MWCNTs was a unique graphite to amorphous structural transition from the outer walls to the inner walls of the irradiated MWCNTs due to the removal of carbon atoms by knock-on displacements.
2010, 59 (1): 453-457. doi: 10.7498/aps.59.453
The electronic structures of the perfect CsI crystal and the crystal containing iodine vacancy and F, F2 color centers are studied within the framework of the fully relativistic self-consistent Dirac-Slater theory, by using a numerically discrete variational (DV-Xα) method. Calculated results reveal that the existence of the iodine vacancy results in the band gap widening and does not introduce the new energy level in the forbidden band. However, the crystal containing F color centers and F2 color centers have their donor energy levels introduced in the forbidden band. The transition energy from energy level of F color center and F2 color center to the bottom of conduction band is 169 eV (736 nm) and 115 eV, respectively, which are consistent with the experimental results. This result indicates that the 750 nm absorption band originates from the F color center and the 11 eV absorption band originates from F2 color center.
2010, 59 (1): 458-465. doi: 10.7498/aps.59.458
The serrated yielding phenomenon is studied in an Al-Mg alloy during the tensile tests at ambient temperature and constant strain rate. The temperature field on the surface of the specimen changes with the increase of strain. An infrared camera is used to observe and record the temperature variations at very high time and space resolutions. According to these thermal data, the formation and propagation of the deformation bands (type A, B) are discussed and some characteristic parameters of the bands such as orientation, bandwidth, and apparent velocity are also obtained. Furthermore, the plastic deformation in the band is quantified from heat transfer equation. Both experimental and computational results show that elastic shrinkage deformation exists outside the band only during the formation of the type B band. Based on this, whether or not shrinkage deformation exists outside the band is proposed as a new standard to discriminate type A and B bands.
2010, 59 (1): 466-470. doi: 10.7498/aps.59.466
The effect of the nanoparticulate metal film on the heat radiation performance has been studied by evaluating the thermal conduction of different helix slow-wave structures (SWS). The heat dissipation capabilities of the SWSs with normal barrel, with normal Ir film deposited barrel and nano-Ir deposited barrel have been analyzed and compared by experiments and simulations. With the measured data, the radiation emissivities of the employed materials have been estimated, and the accuracy has been verified by computer simulation. The experimental results and the simulation results make perfect agreement, suggesting that the nanoparticulate metal film gives much better heat radiation performance.
2010, 59 (1): 471-475. doi: 10.7498/aps.59.471
Copper nanoparticles with average diameter of about 45 nm were compressed in a high-strength mold under different pressures at 523 K to produce nanocrystalline copper. The X-ray diffraction (XRD)， scanning electron microscopy (SEM)，and physics-property-measurement system (PPMS) were used to study the thermal capacity of nanocrystalline Cu as a function of temperature and the mass density at low temperatures. The experimental results indicate that the thermal capacity at low temperatures increases with decreasing density. The thermal capacity of nanocrystalline Cu is higher than that of the coarsed Cu and the increase ratio reaches maximum at around 10 K. The physical mechanism of the phenomenon is explored in this paper.
2010, 59 (1): 476-481. doi: 10.7498/aps.59.476
We investigate the important role of interface collisions on the thermal conduction behavior, especially on the thermal rectification effect, of the two-segment lattices. In the high-average temperature regime, it is found that the thermal diode effect may be significantly weaken and even eliminated. Meanwhile in the low-temperature regime, an interesting reversed thermal diode is realized. These behaviors are interpreted in terms of phonon bands mixing induced by interface collisions. The results proposed in this paper reveal that thermal diode effect can be qualitatively influenced if the interface collisions could not be neglected.
2010, 59 (1): 482-487. doi: 10.7498/aps.59.482
Path integral Monte Carlo (PIMC) simulation is a powerful tool in studying the interacting quantum systems at finite temperatures. In this article, we use PIMC to study the pair correlation function g(r) of the system consisting of 124 4He atoms in different conditions. At saturated-vapor-pressure (SVP), we calculated the pair correlation function g(r) at four different temperatures respectively, that is, T=138 K, 167 K, 250 K and 424 K. We also determined the changes in g(r) when either temperature or density is changed while the other remaines fixed, and found that for different densities and the same temperature, the change in g(r) is remarkable, while for different temperatures but same density, the change is not obvious. We used the microcosmic point of view for g(r) to explain the above phenomenon. Although finite size effects exist in the PIMC method, when comparing the pair correlation function belonging to systems consisted of 128 and 256 4He atoms respectively, differences between them are small. And we can conclude that as the increasing of the simulated system size, differences between simulated system and the real one becomes smaller and smaller. So in this particle, the properties educed from the simulated system consisted of 256 4He atoms can represent those of the real liquid system.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Study of the influence mechanism of additional elements on the corrosion behavior of bulk Cu-based amorphous alloys
2010, 59 (1): 488-493. doi: 10.7498/aps.59.488
The liquid state Cu-Al alloy system was simulated by using the molecular dynamics method, then Cu-Al amorphous alloy is obtained by cooling process simulation. This article firstly sets up crystalline Cu-Al alloy liquid by using the molecular dynamics. The models of Cu-Al-M bulk amorphous alloys, their clean surfaces and their surfaces with O adsorption are set up by computer programming. The influence mechanism of additional elements Zr, Nb, Ta, V, Y and Sc on the corrosion behavior of bulk Cu-based amorphous alloys are investigated by using real-place recursive method. Results show that the alloying elements do not aggregate on the clean surface of bulk Cu-based amorphous alloys, but tend to aggregate on the surface with O adsorption with the exception of Y, which indicates that the segregation of the bulk Cu-based amorphous alloy surface with O adsorption is reversed. Calculations of the total bond order integral show that additional element can interact with oxygen easily to form oxide film on the surface of Cu-based amorphous alloys, which can improve the corrosion resistance of bulk Cu-based amorphous alloys. The improvement in corrosion resistance of Cu-based metallic glass with Y addition may be due to the aggregation of Y to the interface between alloy and oxide film, which improves the adhesion.
2010, 59 (1): 494-498. doi: 10.7498/aps.59.494
The formation mechanism of the oxide film on Fe-Cr-Al alloy, the effects of sulfur on the adhesion of the oxide film, and the role of RE element Y on the improvement of the oxide film adhesion were systematically studied on an electronic level, so that the physical nature of oxidation of the alloy was revealed. The results show that Al atom (compared with Cr or Fe atom ) has the lowest environment-sensitive embedding energy when O atoms are present on the alloy surface, thus leading to an outward diffusion of Al atoms from the interior of the alloy, and hence to the segregation of Al atoms on the alloy surface. Oxygen atoms are easy to combine with Al atoms to form Al2O3 oxide films on the alloy surface due to its high affinity with Al atoms. The impurity S has a lower environment-sensitive embedding energy on the interface between the Al2O3 oxide film and the alloy matrix than within the alloy matrix, suggesting that S can diffuse (segregate) to the interface. S atoms segregated on the interface weakens the cohesion of Al2O3 oxide film with the alloy matrix. Y is easy to combine with sulfur to form a stable sulfide within the interior of the alloy matrix, which inhibits the diffusion of sulfur to the Al2O3 oxide film /matrix interface. Y added into the alloy can thus markedly increase the adhesion of the oxide film with the alloy matrix, and significantly improve the high-temperature oxidation resistance of the alloy.
2010, 59 (1): 499-503. doi: 10.7498/aps.59.499
The atomic cluster model of the interface between aluminum oxide film and the niobium matrix has been set up with our self-programmed software. By using recursion method, the atom embedding energy, the atomic binding energy and other electronic parameters have been calculated. The high temperature oxidation mechanism of niobium alloys is analysis from the electron levels. Our study shows that， aluminum segregates on the alloy surface through the grain boundary diffusion and combines with oxygen to form dense Al2O3 oxide film which blocks oxygen to diffuse into the niobium matrix. Grain boundary and rare earth elements can increase binding energy between the oxide film and the matrix and increase the bonding strength of the interface to enhance the adhesion between the oxide film and the niobium matrix. Thus, by adding rare earth elements in the alloy or refining the alloy grains, the performance of high temperature oxidation resistance of niobium alloys can be improved.
2010, 59 (1): 504-507. doi: 10.7498/aps.59.504
Optical absorption spectra for a series of GaMnN samples with different Mn content grown by metal-organic chemical vapor deposition have been investigated. Compared with GaN, the absorption coefficient of Ga1-xMnxN increases in the UV region and an absorption peak can be observed near 144 eV. In addition, the absorption coefficient increases with the increase of the Mn content. The experimental results are in excellent agreement with theoretical data based on density functional theory. Associated with theoretical data, the absorption peak near 144 eV is assigned to 5T2→5E internal transition between the e state and the t2 state of Mn3+ ion.
Numerical simulation of charge packet behavior in low-density polyethylene based on Gunn effect-like model
2010, 59 (1): 508-514. doi: 10.7498/aps.59.508
Packet-like space charge behavior usually induces the electric field distortion and strongly affects the electrical performance of low-density polyethylene. In this paper, we analyze the influence of charge injection, carriers migration and interaction between the free charge and trap in polyethylene on packet-like space charge behavior and introduce the mechanism of Gunn effect to describe the generating process of space charge packet. Based on this, we simulated two kinds of packet-like space charge behaviors with different variation trends and in different applied fields reported by different research groups. The simulated space charge packet shows very good fitting with the experiment data in both packet amplitude and migration velocity. The simulation results also indicate that the injection conditions and trap level depth play an important role in the diversity of packet-like space charge behavior.
2010, 59 (1): 515-520. doi: 10.7498/aps.59.515
The electronic structure of pure and Nb doped B2 NiTi have been calculated with the first-principle ultrasoft pseudopotential approach of the plane wave based on the density functional theory aiming at examining the effect of Nb on the electronic structure and bonding characteristic of NiTi. The point defect formation energy calculation results show that the introduction of Nb largely enhances the energy required to form the vacancies and anti-sites of both Ni and Ti sublattice. Furthermore, the calculation results on the partial density of states (PDOS) suggest that the addition of Nb increase the s-s, p-p and d-d electronic interactions between Nb and neighboring Ni and Ti atoms. The electron density of NiTi was also increased with the introduction of Nb. All these Nb-inuced results on electronic structure and bonding characteristic may hamper the hop of Ni and Ti atoms, which may facilitate to improve of oxidation resistance of NiTi intermetallic compound in the experimental findings.
A first-principles study of electronic structure, magnetism, response to pressure and tetragonal distortions of Ni2MnSi Heusler alloy
2010, 59 (1): 521-526. doi: 10.7498/aps.59.521
Crystal structure，magnetism，electronic structure，response to pressure and tetragonal distortions of stoichiometric Ni2MnSi were calculated by first-principles method based on the density functional theory within the projected augmented wave（PAW） appreach. The calculations show the contribution of the spin magnetic moments of Mn atom to the total moments is largest for Ni2MnSi. The low energy part of the total DOS is decided by Si-s-projected DOS, however, the high energy part of the total DOS is decided by the Ni -d-projected DOS, Mn -d-projected DOS and Si -p-projected DOS for Ni2MnSi. The entire energy surface for 095c/a2MnSi，which has significant implications for the growth and properties of thin films. We predict that the Ni2MnSi may also grow single crystal tetragonal structured thin film of ferromagnetic phase with high Curie temperature.
Study on the electronic structure and optical properties of B-doped single-walled carbon nanotubes for formaldehyde adsorption
2010, 59 (1): 527-531. doi: 10.7498/aps.59.527
The binding energy, electronic structures, optical absorption and reflection spectra of the formaldehyde (HCHO) adsorption on B-doped single-walled (8,0) carbon nanotubes have been investigated using density functional theory based on first principles. The calculated results show that the B-doped SWCNT is sensitive to HCHO, the binding energy increases, peaks in absorption and reflection spectra increase, the peak height decreases and shows blue shift in the lower energy region, and there appears a distinct peak in HCHO adsorption on B-doped carbon nanotubes at the energy of E=172 eV. The results have been discussed theoretically. B-doped single-walled carbon nanotubes are expected to be used to design sensors and photoelectric device for monitoring formaldehyde.
2010, 59 (1): 532-535. doi: 10.7498/aps.59.532
In this paper, we investigate the localization in a tight-binding one-dimensional model with long-range correlated disorder, which was proposed by de Moura and Lyra. The diagonal on-site energies are distributed in ［-W/2，W/2］ and the Fourier transform S(k) of the two-point correlation function 〈εiεj〉 satisfies S(k)∝k-α with α>0. Using the participation ratio, we confirm that there is a finite range of extended eigenstates for α>2 and Wα<2.
2010, 59 (1): 536-540. doi: 10.7498/aps.59.536
The first principles based on the density functional theory and the nonequilibrium Green's function method are adopted to research the electronic transmission of a zigzag single wall carbon tube with an implanted Li atom. The transmission model is built after optimizing the structure of the single wall carbon nano tube with the implanted Li atom. The electronic transmission and the density of states are obtained. The electronic transmission characteristics are analyzed when the electronic energy and the bias voltage vary. It is found that the conductivity changes obviously as SWCNT is implanted with the Li atom, the electronic transmission band is broadened and the quantum step effect is recovered.
2010, 59 (1): 541-544. doi: 10.7498/aps.59.541
In this paper, In2O3/SnO2 thin films deposited on the fabric for camouflage net are developed. Effect of the film thickness on the spectral reflective properties is investigated thoroughly. Results of the influence of the film thickness on the morphology and spectral properties are presented. Application of In2O3/SnO2 film in the infrared camouflage field is proposed.
2010, 59 (1): 545-549. doi: 10.7498/aps.59.545
The main problem of GaAs based AlGaInP series LED is the low light extraction efficiency and heat generation inside, which have serious impact on the LED' lifetime. In this paper, we introduce a kind of LED with new surface structure formed of surface texture and light anti-reflecting layers through the post-epitaxial processing. In this new structure, the inside light transmission route has been changed and the current spreading is enhanced, which makes much more light emit outside. With the same injected current, the new LED' output light intensity is in average 15 times as the normal LED with the same epitaxial structure, and the ratio is larger than 15 as the injected current increases. The new LED's saturation current is as high as 125 mA because of the heat is decreased inside, the accelerated aging test shows that the new LED' lifetime is as long as 13×104 h for packaged ones and 19×104 h for unpackaged ones, which is suitable for working at large injected current especially.
2010, 59 (1): 550-554. doi: 10.7498/aps.59.550
Piezoelectric discharge characteristic of semiconductor ZnO nanorod was studied with atomic force microscope in contact mode. The c-axial orientation ZnO nanorod array film was fabricated with two-step wet-chemical method. Electric pulses were got when Pt coated probe contact-scans the ZnO nanorod, their peak value reaches 120 pA. The electric pulse is related with the topography of ZnO nanorod and has a time duration of 30 ms. The contact of Pt coated probe and ZnO nanorod behaves as a Schottky diode. The I-V curve showed the piezoelectric voltage must be larger than 03 V to drive Schottky diode. The resistance of Schottky contact has a magnitude of GΩ order during piezoelectric discharge, which is the major factor impacting the output of piezoelectric potential.
2010, 59 (1): 555-559. doi: 10.7498/aps.59.555
The dynamical properties of a one-dimensional quantum ring with a constant magnetic flux are studied using the non-equilibrium Green’s function method. The ring is coupled through a single lead to an electron reservoir, which is driven by a stepped pulse bias. We provide a numerical method to calculate current in the presence of stepped bias. Our results reveal the relation between the evolution of tunneling current and electron energy levels of the ring.
2010, 59 (1): 560-565. doi: 10.7498/aps.59.560
Dielectric frequency spectra of ZnO-Bi2O3 based varistor ceramics were measured in the frequency range of 10-2Hz—106Hz from -100℃ to 20℃ by Novocontrol broadband dielectric spectrometer. The intrinsic defect structure of ZnO was calculated according to the theory which assumes that characteristics dielectric loss peaks of ZnO varistor ceramics origin from electronic relaxation process of intrinsic defects in depletion layer. At the same time the micro-electric parameters of grainboundary and the single grainboundary breakdown voltage Vb were obtained. The accordance of theory with experiment in Vb value indicates that the method to calculate grainboundary electronic structure by dielectric spectroscopy proposed in this paper is resonable.
2010, 59 (1): 566-570. doi: 10.7498/aps.59.566
A novel SiC semi-superjunction-Schottky Barrier Diode (Semi-SJ-SBD) structure is proposed, which is the combination of super-junction (SJ) structure and conventional drift region structure. The proposed structure can significantly reduce the specific on-resistance (Ron-sp) and improve the forward characteristics. The breakdown voltage (VB) and specific on-resistance (Ron-sp) in different SJ depth and width are studied using two-dimensional simulator Medici and compared with conventional SiC SBD. The results show that Ron-sp is greatly reduced (greater than 10%) with VB unchanged (less than 4%) when the SJ width is chosen as 2—3 μm and SJ depth is deeper than 5 μm.
2010, 59 (1): 571-578. doi: 10.7498/aps.59.571
This paper investigates a specific current saturation phenomenon in high-voltage LDMOS (lateral double-diffused MOS) transistors, i.e., the quasi-saturation effect. By means of simulation tool TCAD, we clarified that the physical mechanism of quasi-saturation effect is the carrier velocity saturation in the drift region. Further more, with the concept of intrinsic drain voltage Vk, a mathematical model is derived to describe the current saturation effect in LDMOS transistors. The proposed model has been primarily validated by Matlab program and exhibites excellent accuracy, speed and scalability. This model can be further implemented in SPICE circuit simulation.
2010, 59 (1): 579-582. doi: 10.7498/aps.59.579
There has been much interest in the Si-based strained technology lately. The research on the hole effective mass of Si-based strained material is the theoretical basis for the performance enhancement of Si-based strained PMOS devices. Based on the valence band E(k)-k relation of strained Si1-xGex/(111)Si, the hole effective mass along arbitrarily k wavevector direction were obtained. And the hole isotropic effective mass models were established. It was found that in comparison with relaxed Si, the more obvious anisotropy of the hole effective mass occurs in strained Si1-xGex/(111)Si and the hole isotropic effective mass of the top valence band decreases obviously with increasing Ge fraction. The results can supply valuable references to the conduction channel design related to stress and orientation in the Si-based strained PMOS devices.
2010, 59 (1): 583-586. doi: 10.7498/aps.59.583
A new and simple method of preparing the flexible YBCO/Polyacrylonitrile (PAN) thick film which is not dependent on substrate structure is reported. It is found that, when the PAN content increases from zero to 10wt%, the superconducting critical temperature (Tc) of all the YBCO/PAN specimens lies in the 900—920 K interval, and the specimens show good superconductivity. Moreover, when the PAN content is up to 10wt%, the YBCO/PAN hybridized film shows a certain degree of flexibility. The thickness of the film is about 35μm, and the critical current density (Jc) of the film is 29×104Acm-2 at (1 T, 10 K) and 46×103Acm-2 at (1 T, 40 K). The YBCO/PAN hybridized film, prepared without being treated at high temperature, is hopeful for application in electronics field.
The band structure of symmetrical structured one-dimensional photonic crystal with single-negative materials
2010, 59 (1): 587-591. doi: 10.7498/aps.59.587
The symmetrical structured one-dimensional photonic crystal in the form of (AB)N(BA)N, is prepared and studied by transfer matrix. The results show that this kind of symmetrical structured one-dimensional photonic crystal has a special photonic gap which is insensitive to the incident angle and the disorder of the lattice. Two tunneling modes appear in this gap which are also insensitive to the incident angle and the disorder of the lattice. But the energy bands and tunneling modes of the gap are sensitive to change in the scale length of crystal lattice and the number of periodicities. With the increasing of incident angle the tunneling modes on both sides of the gap tend to degenerate. This characteristic will have a certain reference value for designing a filter with this kind of structure.
We studied the intrinsic optical bistability(OB) of coated spherical particles with graded dielectric profiles.According to Maxwell equations, we obtained the spatial average of the local field in the core as a function of the external applied field. Numerical results for power-law graded profiles show that the optical bistable behavior is dependent on the shell thickness and the power-laws exponent k. The interval of optical bistability increases with increasing shell thickness or increasing k. In addition, the field-dependent reflectance at normal incidence R in random composites is also investigated, and a hysteretic loop is observed.
2010, 59 (1): 597-602. doi: 10.7498/aps.59.597
Transient spin grating, as a novel technique in ultrafast magneto-optical laser spectroscopy, is widely used to study the properties of spin transport in semiconductor low-dimensional structures. The principle of transient spin grating and the optical arrangement are described briefly in this paper, which includes the generation and detection of transient spin grating. The signal to noise ratio was significantly enhanced by using heterodyne detection. The spin diffusion coefficient Ds was determined by this technique to be about 551cm/s in (110) GaAs/AlGaAs single quantum well at room temperature.
2010, 59 (1): 603-608. doi: 10.7498/aps.59.603
On the basis of of local density approximation (LDA) and general gradient approximation (GGA), positron annihilation information has been calculated for five types of compound semiconductors, which are ZnO, GaN, GaAs, SiC and InP. The calculated information includes distribution of positron density, distribution of positron annihilation rate density, positron bulk lifetime, positron monovacancy lifetime and positron divacancy lifetime.
2010, 59 (1): 609-615. doi: 10.7498/aps.59.609
The BaWO4:Tm3+ single crystals of optical quality have been grown by the Czochralski technique. The lattice parameters of crystals with different doping concentrations were determined by XRD. The absorption spectra were measured at room temperature. And the optical parameters, such as transition line intensity, oscillator strength and absorption section were calculated by using Juud-Ofelt theory. The three intensity parameters were fitted to be Ω2=404×10-20cm2， Ω4=0509×10-20cm2，Ω6=0134×10-20cm2， respectively. The lifetime, branching ratio and integrated stimulated-emission cross section were obtained. Ultra-visible fluorescence was measured and analyzed. The red up-conversion luminescence with wavelengths 689 nm and 704 nm corresponding to the transition from 3F3 to 3H6 was observed under Ti-sapphire laser and LD laser, respectively.
The applications of ZnO nanorods in poly ［2-methoxy-5-(2-ethyl-hexyloxy)-1, 4-phenylene vinylene］solid state cathodoluminescence device
2010, 59 (1): 616-619. doi: 10.7498/aps.59.616
A solid state cathodoluminescence (SSCL) device in which ZnO nanorods act as the field emission electrode and SiO2 as the electronic accelerating layer and poly ［2-methoxy-5-(2-ethyl-hexyloxy)-1, 4-phenylene vinylene］ (MEH-PPV) polymer as the luminescent layer is first designed. Under AC bias, SSCL of MEH-PPV is realized. The luminescence peaks are located at 580 nm and 450 nm, respectively. Compared with the device without the accelerating layer, we find that mixed-excited mode device can achieve greater brightness at long wavelength.
2010, 59 (1): 620-624. doi: 10.7498/aps.59.620
The processes of transfer ionization in He2+-He collisions at energies ranging from 20 to 40 keV have been studied experimentally by means of cold target recoil ions momentum spectroscopy. From the longitudinal momentum spectra of recoil ions, different mechanisms of transfer ionization have been obtained. The results show that one of the electrons of helium atom being captured into the ground state of projectile ion He2+ and the other one emitted to the continuum state of projectile or target are the dominant mechanisms of transfer ionization. The autoionization cross section of projectile after two-electron capture into a double excited state is small. Transfer ionization for one target electron capture into ground state and the other one into the continuum of projectile mainly occurs at large impact parameter collisions.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
The effect of different preparation temperatures on the photoelectric properties of CdTe films and solar cells
2010, 59 (1): 625-629. doi: 10.7498/aps.59.625
In this research, the CdTe polycrystalline films are prepared at various temperatures by close-spaced sublimation. The experiment was conducted to investigate how difference in preparation temperature effects on CdTe/CdS solar cells by the characteration of I-V,C-V curves and deep level transient spectroscopy. The result shows that the difference of temperatures has some effect on Isc and FF, but not on Voc. The samples prepared at 580℃ have lowest dark saturated current density, higher carrier concentration and the photovoltaic performance is preferable. The response of deep-level impurities in CdTe films is unchanged with temperature and frequency, but the sample prepared at 580℃ has less deep-level impurity recombination because of lower hole trap concentration. Then, the CdS/CdTe solar cells with large area of 300 mm×400 mm have efficiency reaching 82% by improving the uniformity of temperature field.
The synthesis and thermoelectric properties of Yb/Sr double-atom-filled YbxSr8－xGa16Ge30 type-I clathrates
2010, 59 (1): 630-635. doi: 10.7498/aps.59.630
n-type Yb/Sr double-atom-filled YbxSr8-xGa16Ge30 (x=0, 05, 10, 15) clathrates have been synthesized by combining melting reaction with the spark plasma sintering (SPS) method. The effects of double-atom filling on thermoelectric properties have been investigated. The results show that the solubility limit of Yb in the Sr-Ga-Ge system is between 10 and 15 when it is expressed by the formula of YbxSr8-xGa16Ge30. With increasing Yb content x, the room-temperature carrier concentration of the YbxSr8-xGa16Ge30 samples increases, while the room-temperature carrier mobility decreases. For the double-atom-filled samples, the electrical conductivity raises with increasing x, while the Seebeck coefficient reduces, and in which the x=05 sample has a comparable electrical conductivity and a remarkably higher Seebeck coefficient compared with the single-atom-filled Sr8Ga16Ge30 sample in the temperature range of 300—800 K. The double-atom filling of Yb/Sr has significant influence on the lattice thermal conductivity of the YbxSr8-xGa16Ge30 samples and the lattice thermal conductivity decreases gradually with increasing x. Of all the YbxSr8-xGa16Ge30 samples, the maximum dimensionless figure of merit ZT of 081 is obtained at 800 K for the Yb10Sr70Ga16Ge30 sample. Compared with that of single-atom-filled Sr8Ga6Ge30 sample, it is 35% higher at the same temperature.
2010, 59 (1): 636-642. doi: 10.7498/aps.59.636
The results of UHV-STM investigation of C60 at various adsorption sites on Si(111)-7×7 surface using MBE were presented. At room temperature, molecules prefer the faulted half unit cell to unfaulted half unit cell. Through controlling the annealing temperature and time, C60 molecules could directionally move towards step edges where the density of electronic dangling bonds is the highest. The measurement of diameter and height at each adsorption site shows different intensities of interaction between molecules and Si atoms. We also studied the multilayer growth process of C60 molecules on Si(111)-7×7 surface, and observed the local ordering of the first layer after annealing at 600℃, which shows the realization of the growth mode transformation from Stankski-Krastanov to Frank-van der Merwe mode.
2010, 59 (1): 643-648. doi: 10.7498/aps.59.643
The dependence of photocurrent and photovoltage of dye-sensitized solar cell on the incident light intensity were investigated based on the electron continuity diffusion equation. For the first time a model was presented for power loss of series resistance in dye-sensitized solar cell, and were simulated the influence of the active-area width of nanoporous film, the effect of special contact resistance on the photo-electric conversion efficiency, as well as the silver impedance in lager-scale solar cells with active area greater than 1 cm2 under different illuminations. It was found that the efficiency strongly depends on the width of active area and the silver impedance under strong illumination, nevertheless, this dependence is not obvious under poor illumination.
2010, 59 (1): 649-654. doi: 10.7498/aps.59.649
Using 3-D mixed-mode simulation, bipolar amplification effect in an inverter chain of single event transient(SET) is studied, and compared with that in single NMOS. It is found that bipolar amplification component takes a large proportion in SET current pulse, but not in an inverter chain. The difference of source/substrate biases between them and the mechanism of amplification are explained, which validates the conclusion that bipolar amplification depends on the bias of source/substrate. The positive current component from source to drain and the mechanism of SET pulse are also studied, and results show that the source current change is positive in the plateau region because of the presence of carrier diffusion.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2010, 59 (1): 655-663. doi: 10.7498/aps.59.655
Based on homogeneous temeperature, precipitation and the Palmer Drought Severity Index (PDSI) data between 1958 and 2007 of 194 stations in China, quantitative measure of impact of global warming and precipitation variation on the formation of drought in China is made through a statistical model. Dividing China into eight regions, we analyzed the importance of global warming and precipitation variations in each region respectively. Under the background of global warming, the trend of drought in north China still persists. The most probable region of drought in the next five years shows a tendendy of expansion in north China, especially in the direction to the south. Decreased precipitation is still the key factor in drought formation in most regions. However, in the north, northeast and east-northwest China, global warming plays a bigger role in drought formation.
2010, 59 (1): 664-675. doi: 10.7498/aps.59.664
The Palmer Drought Severity Index (PDSI) was calculated by using monthly air temperature and precipitation data in China during the period 1960 to 2007 Based on the monthly PDSI of 614 stations in China from 1960 to 2007, we theoretically study the statistics of record-breaking monthly PDSI (RBMP) in recent 48 years. According to the theory of record-breaking event, we have developed the universal mathematical formula to evaluate the record-breaking events. Based on the existing Gaussian distribution of monthly PDSI and the RBMP as the initial conditions, we compute the universal mean of the RBMP. Compared with the results of iterative calculations using the theoretical value, the values computed using the former method are closer to the real values. Then the next possible RBMP in the future are evaluated and predicted by the former method. The results show that the changes of extreme drought differ much in different regions of China and have obvious regional features. The drought trend in North China will continue, and the degree of extreme drought event of these regions are rising fast, extreme drought events more likely happen again in nearly two decades in the future. On the other hand, in South area, it is very improbable for more serious occurrence of extreme drought events in recent decades. The polarization trend in China will be further enhanced.
2010, 59 (1): 676-682. doi: 10.7498/aps.59.676
Based on monthly data from 1960 to 2007 of 740 stations in China, we investigate the response of monthly extreme high-temperature (MEHT) to atmospheric oscillation through spatial Generalized Pareto Distribution (GPD) model. Here we take different groupings of North Atlantic Oscillation (NAO) and Southern Oscillation (SO) as forcing parameters in the model and evaluate the response of MEHT to atmospheric oscillation in 9 different scenarios. Results show that the impact of NAO/SO on MEHT of China is significant and different responsen to different regions, i.e. the regions showing significant dependence of MEHT on atmospheric oscillation are Northeast China, the eastern part of the Tibetan Plateau, reaches of Yangtze and Yellow river and part of South China. To be specific, 1) MEHT obviously dependent on NAO is the north-east areas, followed by the eastern Tibet Plateau; MEHT obviously dependent on SO is mainly the Eastern Tibet Plateau and the Yangtze River and Yellow River and etc.; 2) Nonlinear addition effect of NAO and SO is not obvious, their impact on MEHT is mainly one-way, that is, both acting as forcing factors， most of the region forced by them is not significantly weakened or strengthened, and the reason may be related to differences in the atmosphere oscillation spatial and temporal distribution.
2010, 59 (1): 683-691. doi: 10.7498/aps.59.683
By introducing the concept of information content and using Bayesian estimation theory, a scheme for calculating information contents in temperature, humidity, O3, SO2, CH4 and other atmospheric parameters in the remote sensing data is given. The scheme takes into account the channel sensitivity to the atmospheric parameters, the observation error of each channel as well as the error characteristics of the background atmosphere. The temperature and humidity information contents in the observation of HIRS, AMSU, AIRS, IAIS and three combinations of the instruments are calculated using the scheme. The results show that the scheme may have valuable applications in instrument designing, evaluating and comparing different instruments and usage of remote sensing data etc.
Influence of atmospheric turbulence on the spreading and directionality of radial Gaussian array beams
2010, 59 (1): 692-698. doi: 10.7498/aps.59.692
The analytical expressions for the mean-squared beam width and the far-field divergence angle of radial Gaussian array beams in atmospheric turbulence are derived. The influence of turbulence on the spreading and directionality is studied in detail. It is shown that for the coherent combination, the radial Gaussian array beams with smaller beam number N and larger radial radius r0 are less affected by the turbulence. The spreading of radial Gaussian array beams for the coherent combination is smaller than that for the incoherent case. However, the spreading of radial Gaussian array beams for the coherent combination is more affected by turbulence than that for the incoherent case. Specially, the mean-squared beam width in the far-field for the coherent combination is the same as that for the incoherent case when N is small enough or r0 is large enough. On the other hand, the condition under which radial Gaussian array beams for both coherent and incoherent combinations have the same far-field divergence angle as a single Gaussian beam is also given. The main results are interpreted physically.