Vol. 59, No. 4 (2010)
2010-02-20
GENERAL
2010, 59 (4): 2173-2177.
doi: 10.7498/aps.59.2173
Abstract +
A box model of the interhemispheric thermohaline circulation in the disturbed sea-air for globe climate is considered. By using the homotopic mapping method，a class of nonlinear model is studied, and the approximate solution is obtained. The homotopic mapping solving method is an analytic method，the solution obtained can be analytically operated sequentially. And then we can also study the diversified qualitative and quantitative behaviors of corresponding physical quantities.
2010, 59 (4): 2178-2181.
doi: 10.7498/aps.59.2178
Abstract +
For nonlinear dust acoustic waves in unmagnetized dusty plasma containing cold dust grains and isothermal electrons and ions, small but finite amplitude nonlinear waves are governed by the Korteweg de Veries (KdV) equation. For weakly two-dimensional dust acoustic solitary waves in a dusty plasma with variable dust charge and two-temperature ions, we obtain a Kadomtsev-Petviashvili equation under higher order transverse disturbances for this system. The interactions between two solitons and three solitons propagating in arbitrary directions are investigated. It is found that the maximum amplitude in the interaction region between two same——amplitude solitons is about four times that of a single soliton, while for three solitons the maximum amplitude is nine times that of a single soliton. It suggests that the transverse perturbations for the weakly nonlinear solitary waves in dusty plasma with variable dust charge and two-temperature ions are stable.
2010, 59 (4): 2182-2186.
doi: 10.7498/aps.59.2182
Abstract +
Considering ambient uniform currents, a third-order analytic solution for short-crested waves arising from a general partial reflection from a vertical breakwater is presented, thus reaching a universal law: frequency-doubling route to short-crested waves.
2010, 59 (4): 2187-2192.
doi: 10.7498/aps.59.2187
Abstract +
The tunneling phenomena of cold atoms in double-well with different interaction (U) and tunnel coupling (J) were studied. Experiments cannot be interpreted completely by a two-site Bose-Hubbard model. Thus, a new model was introduced, in which the ground state and the first excited state of the double-well were used as state bases. The expression of Hamiltonian was derived under the new model, which explains the reason why the parameter isnot consistent with the experiment from a two-site Bose-Hubbard model. Furthermore, we figured out the fluctuation of entanglement degree of the atoms in the double-well, and directly described the whole process of tunneling with the population of particles in the three states.
2010, 59 (4): 2193-2199.
doi: 10.7498/aps.59.2193
Abstract +
From the classical selective repeat ARQ (Automatic Repeat-reQuest) protocol, a selective repeat ARQ quantum synchronous communication protocol in data link layer is presented by utilizing the intrinsic characteristics of quantum mechanics. The proposed protocol divides the link into the preparation and the send stages, where the message is sent via classical channel and the preparation and distribution of EPR (Einstein-Podolsky-Rosen) pairs are supposed to be accomplished at the preparation stage. The performances of several protocols in data link layer are compared and analyzed from the aspects of throughput and utilization ratio of the channel. It is shown that the proposed protocol enhances the maximum throughput and the utilization ratio of the channel effectively and improves the performance of the selective repeat ARQ protocol for date link layers. The proposed protocol is of great significance in military communications.
2010, 59 (4): 2200-2206.
doi: 10.7498/aps.59.2200
Abstract +
基于Duan-Lukin-Cirac-Zoller(DLCZ)方案，在时域上研究了扩散诱导的Ramsey压窄. 以87Rb热原子系综为研究对象，观测到缓冲气体，激光束尺寸和镀石蜡Rb池均可以导致Ramsey压窄现象. 实验结果和文献中重复相互作用模型预期的一致.
2010, 59 (4): 2207-2211.
doi: 10.7498/aps.59.2207
Abstract +
We have measured the Rb atomic spin lifetime in both of paraffin-coated cell and glass cell. The experimental results shows that the lifetime of Rb atomic spin in paraffin-coated cell is about 7 ms at temperature T=50 ℃, while the data in glass cell is about 20 μs, which is useful for quantum memory experiments based on atomic spin. Meanwhile, we discuss other potential materials which can be used to eliminate the inelastic collisions between alkali metal atoms and walls. Based on some experimental data and investigation, we think that BN and C60H60 may be the candidates.
2010, 59 (4): 2212-2216.
doi: 10.7498/aps.59.2212
Abstract +
We studied the entanglements of the Heisenberg XX chain with impurity in the presence of a uniform magnetic field along the z axes by means of negativity. Through analyzing NL-A and N1-A, we show that the critical temperatures for nonzero negativities depend on the impurity parameter J1 and the magnetic field B. It is also shown that as qubit L increases, the entanglements increase when L is odd but decrease when L is even. And the entanglements of the even-qubit chains are larger than those of the odd-qubit chains. The condition is similar with L=3 for NL-A when qubit L is odd, but the entanglements increase with the increase of even qubit L.
2010, 59 (4): 2217-2222.
doi: 10.7498/aps.59.2217
Abstract +
We extend the Damour-Ruffini method and discuss Hawking radiation of Kerr-Newman-de Sitter black hole. Under the condition that the total energy and angular momentum of spacetime are conserved, taking the reaction of the radiation of particles to the spacetime into consideration and considering the interrelation between the black hole event horizon and the cosmological horizon, we obtain the black hole radiation spectrum. This radiation is no longer a strictly pure thermal spectrum. It is related to the change in Bekenstein-Hawking(B-H) entropy corresponding to black hole event horizon and the cosmological horizon. It is shown that the result satisfies the unitary principle. We also derive the correction term of B-H entropy. It leads to a new understanding of thermal radiation of the black hole.
2010, 59 (4): 2223-2227.
doi: 10.7498/aps.59.2223
Abstract +
Using semiclassical approximation method, the fermion tunnels at cosmological horizon of higher dimensional de Sitter and Schwarzschild de Sitter space-times are researched in this paper. In our work, the Dirac equation, which describes the property of 1/2 spin particles, is simplified, and then the semiclassical Hamilton-Jacobi equation is obtained via the condition that there are non-trivial solutions of Dirac equation. The research has been simplified greatly, and the Hawking temperature and tunneling rate at cosmological horizon of static higher dimensional de Sitter space time is gotten finally.
2010, 59 (4): 2228-2234.
doi: 10.7498/aps.59.2228
Abstract +
The mechanism of erosion phase transition of Fe2Al5 coating in molten zinc was investigated. Experimental results indicated that etched grooves caused by interfacial tension equilibrium driving formed on sample surface. The Fe2Al5 phase, on where zinc did not adhere at the early stage of erosion, was infiltrated by zinc and solid solution Fe2Al5-Znx (η phase) was formed due to zinc atoms diffusing into Fe2Al5 phase. The erosion process of Fe2Al5 in molten zinc is directed melt at the interface caused by phase transition to drive. There were three types of phase interface，η/L,η/(η+δ)/L and η /(η+δ)/δ+L，formed in corroded area .The solid (S) / liquid (L) interface was phase-equilibrium interface and the S/S interface like η/(η+δ) and (η+δ)/δ were non phase-equilibrium interfaces at erosion temperature. The demand of phase-equilibrium interfaces and phase transitions of non-equilibrium interfaces, η→(η+δ) and (η+δ) →δ, made the S/L interface move towards to solid phase and Fe2Al5 phase was corroded by molten zinc.
2010, 59 (4): 2235-2239.
doi: 10.7498/aps.59.2235
Abstract +
The quasimonochromatic noise (QMN) is the “truly colored” noise, and in this paper the time derivative of entropy for a dynamical system driven by QMN is studied. The dimension of Fokker-Planck equation is reduced by way of linear transformation. The exact time dependence of the entropy is calculated based on the definition of Shannon’s information entropy. The relationship between the properties of QMN and dissipative parameters and their effect on the entropy is also discussed.
2010, 59 (4): 2240-2243.
doi: 10.7498/aps.59.2240
Abstract +
Effects of time delay on the active rate of a bistable system was investigated. Using the steepest-descent approximation method, the analytical expression of the mean first passage time and the active rate of the bistable system with time delay was derived under the condition of small delay time. The numerical computations show that the time delay enhances the resonance suppression in the system.
2010, 59 (4): 2244-2249.
doi: 10.7498/aps.59.2244
Abstract +
According the iterative algorithm of Koch curve, we generate a Koch network by considering tetrahedron as the basic unit of the iteration and investigate its structure properties, such as degree distribution, clustering coefficient, and average path length, degree correlation, analytically. The results show that the network is scale-free and the exponent of the degree distribution is γ≈332. The clustering coefficient tends to be 0870435 in the limit of large iteration and the study of the average path length proves that the network exhibits small world effect. We also find that the generated network is not degree uncorrelated because the function knn(k) is dependent on the degree of site.
2010, 59 (4): 2250-2255.
doi: 10.7498/aps.59.2250
Abstract +
For chaos control problem, in accordance with the constraints of control system energy, a quadratic objective function is first determined, and then a simple method for obtaining the optimal control law is proposed. This method gives the optimal control law by solving linear quadratic optimal control problem and avoids the difficulty of solving Hamilton-Jacobi-Bellman equation. Using Lyapnuov method, we prove the stability of the closed-loop system. For the unified chaotic system and Liu chaotic system the simulation results show the effectiveness of the control method.
2010, 59 (4): 2256-2263.
doi: 10.7498/aps.59.2256
Abstract +
The method of adaptive slope compensation and its circuit structure are proposed in this paper. With this method, bifurcation and chaos in double-loop current-mode buck DC/DC are controlled with good performance. The discrete model of double-loop current-mode buck DC/DC used in stability analysis is build and the condition for the system operating stably under double-loop control is derived theoretically. Further more, the relationship between the adaptive coefficient k and the maximum duty ratio on which the system will operate stably is derived. The agreement of simulation results with the theoretical analysis shows that adaptive slope compensation can control bifurcation and chaos effectively, and it extends the system working range and improves the dynamic response characteristics.
2010, 59 (4): 2264-2271.
doi: 10.7498/aps.59.2264
Abstract +
This article treats the modified function projective synchronization between the hyperchaotic Lorenz-Stenflo(LS) system and a novel hyperchaotic CYQY system, and also that between the LS system and hyperchaotic Chen system, which have completely unknown parameters. By utilizing Lyapunov stability theory and active control method, the adaptive controllers and parameter update laws are derived to make the states of different hyperchaotic systems to attain adaptive modified function projective synchronization. The systems unknown parameters can be identified simultaneously. Numerical simulations are presented to demonstrate the effectiveness of the proposed methods.
2010, 59 (4): 2272-2280.
doi: 10.7498/aps.59.2272
Abstract +
Peak current and valley current controlled switching DC-DC converters show symmetrical dynamic phenomenon within a wide circuit parameter range. The unified discrete iterative map model of peak current and valley current controlled buck, boost, and buck-boost converters is established, and the unified piecewise smooth iterative map and their corresponding characteristic equations are also derived. The forward and inverse bifurcation diagrams and Lyapunov exponent spectrums with duty ratio as parameter are obtained by numerical simulation. The research results indicate that the bifurcation diagrams and Lyapunov exponent of peak and valley current-mode controlled switching converters show symmetrical dynamic phenomenon corresponding to a symmetrical point or a symmetrical axis. The numerical simulation results are verified by the time-domain simulation, which further indicates that with the duty ratio varying, the peak and valley current-mode controlled switching converter reveals a symmetrical dynamic phenomenon, or a symmetrical dynamic phenomenon accompanying an asymmetrical dynamic phenomenon, or an asymmetrical dynamic phenomenon.
2010, 59 (4): 2281-2288.
doi: 10.7498/aps.59.2281
Abstract +
A two-dimensional time-delay chaotic system is designed and realized in an electronic circuit based on its dynamical behavior. Then a generalized synchronization chaotic system is designed by linear transformation method. The generalized synchronization condition is obtained by mathematical analysis, and generalized synchronization is realized in an electronic circuit. The results of numerical calculation conform the exactness and validity of theoretical analysis and circuit design.
2010, 59 (4): 2289-2297.
doi: 10.7498/aps.59.2289
Abstract +
A cyclic iteration structure pseudo-random sequence generating method based on combined LFSR and chaotic systems is presented. Firstly, a choice function is chosen based on LFSRs computing result, and the selected chaotic function is used for generating the corresponding chaotic sequence by using iterative computation. The chaotic sequence is processed by binary system transformation, and the generated binary sequence is output as the end pseudo-random sequence. At the same time, the generated binary sequence is used as feedback value and operates with the LFSRs feedback value, the corresponding result is taken as the final feedback of LFSR. This process can achieve random perturbation of LFSR. And a real number pseudo-random sequence generating method is also presented. Performance of pseudo-random sequence generated by using our method is also analyzed by experiment, and simulation results show that the generated sequences have qualities of randomicity and security.
2010, 59 (4): 2298-2304.
doi: 10.7498/aps.59.2298
Abstract +
Properties of logistic chaotic map is studied, and it is pointed out that phase space is not ergodic when parameters of the chaotic system change. Based on these analysis, a piecewise logistic chaotic map is constructed. The bifurcation diagram and Lyapunov exponent of logistic and piecewise logistic map are studied, and the properties of randomicity, correlation coefficient and power spectrum etc. of the sequences generated by these two maps are analyzed experimentally. A new performance evaluation index for chaotic system, the bifurcation iteration time, is defined. Simulation results show that the defined piecewise logistic map is not only ergodic in phase space, and its corresponding chaotic performance evaluation indices are also better.
2010, 59 (4): 2305-2309.
doi: 10.7498/aps.59.2305
Abstract +
Based on the fractional stability theory, the controller and recognizing rules of the uncertain parameters are designed. Tracking control and synchronization of fractional hyper chaotic Lorenz system is realized. Numerical simulation verifies the effectiveness of the approach of this paper.
2010, 59 (4): 2310-2318.
doi: 10.7498/aps.59.2310
Abstract +
A multiple kernel least squares support vector machine (MK-LSSVM) modeling method is proposed for the chaos of permanent magnet synchronous motor (PMSM). An equivalent kernel is built by linear-weighted combination of multi kernels to reduce the dependence of modeling accuracy on kernel function and parameters. The solutions of regression parameters and MK-LSSVM output are given in theory. C-C method is employed for the phase space reconstruction of PMSM chaos, then one-step and multi-step real-time online prediction of reconstructed chaotic series are investigated based on moving window learning method. The effect of different measurement noises on the proposed method is discussed. Simulations show that the proposed method can enhance the modeling accuracy and have strong anti-noise capability.
2010, 59 (4): 2319-2325.
doi: 10.7498/aps.59.2319
Abstract +
The Br model is considered. The influence of the defect, defined by failure of the diffusion effect, on dynamics of spiral wave is investigated by introducing in to the system some defects. These defects are uniformly distributed. It was found numerically that these defects can lead to the reduction of the excitability of medium and the wave speed. When the number of defects is large enough, these defects can induce the meandering or the breakage of an originally stable spiral wave. On the other hands, the defects can yet cause an unstable spiral wave to become a rigidly rotating or meandering spiral wave. The phenomenon that Doppler effect causes unstable spiral wave to break up into co-existing states of spatiotemporal chaos and small spiral waves is observed for the first time. The physical mechanism of these phenomena are briefly discussed.
2010, 59 (4): 2326-2333.
doi: 10.7498/aps.59.2326
Abstract +
By introducing the electrical controlling circuit composed of inductance and capacitance, a fourth order model of generalized Chuas circuit with fast-slow effect has been established for certain parameter conditions. The conditions for fold bifurcation as well as Hopf bifurcation of the fast subsystem are investigated with the variation of the slow variable. Furthermore, the dynamical evolution of the entire system is explored, in which the fast-slow effect existing in the system is focused. Two types of bursting phenomenon, namely, the symmetric fold/fold and fold/Hopf periodic bursters, as well as their mechanism, are presented, which discloses the difference between the two burstings from the view point of bifurcation.
2010, 59 (4): 2334-2338.
doi: 10.7498/aps.59.2334
Abstract +
The FitzHugh-Nagumo neuron model driven by a harmonic noise is investigated, whose dynamic behaviours are influenced by the frequency and the damping parameters of noise. The spikes train varies with these two parameters changing. The FitzHugh-Nagumo neuron has resonance characteristic and exhibits stronger response to noise with a given frequency. Undernoise with this frequency parameter, the spikes train is more regular and the coefficient of coherent resonance reaches the minimum. The larger the damping parameter of the noise is, the more the different ingredients are, thus the synchronization between neuron and noise becomes more imperfect and the coefficient of coherent resonance is larger.
2010, 59 (4): 2339-2344.
doi: 10.7498/aps.59.2339
Abstract +
The instability of the spiral wave in an excitable medium is investigated by using the lattice Boltzmann method. The velocity distribution of the system are obtained by computer simulation, and discussed in connection with the pattern and the tip trajectory of the spiral wave. We find that the velocity of the particle at the rotating center of spiral wave changes periodically, while the change of this particles velocity is quickened and then becomes random when the spiral wave becomes unstable, which leads to the random decomposition of the velocity group and random distribution of velocity. The system falls into the spatiotemporal chaos finally.
2010, 59 (4): 2345-2349.
doi: 10.7498/aps.59.2345
Abstract +
The electron transport through an energy transmission spectrum between two reservoirs with different temperatures and chemical potentials is studied. The heat flow carried by the electrons is obtained. Taking into account the radiative heat leaks between the two electron reservoirs, the performance parameters of the heat pump are derived by numerical calculation. The performance characteristic curves of the heat pump are plotted. The influence of the heat leaks, the position of resonance energy level and the width of the level on the operation performance of the heat pump is analyzed. When the width of resonance energy level is infinitely small, the coefficient of performance may reach the value of Carnot heat pump.
2010, 59 (4): 2350-2355.
doi: 10.7498/aps.59.2350
Abstract +
To correct the error in theoretical model of process stress accelerated test, a new calculation method is proposed. The new method, based on computer-aided calculation, can significantly reduce the error of the model. Theoretical data is calculated using both the novel model algorithm, which is the root test method, and the old model algorithm. The results shows that the old model algorithm can generate errors of more than 13% in the activation energy, and of errors more than 150% in the extrapolated lifetime（Q≤10 eV）,while the novel model algorithm generates errors in less than 1% in activation energy, and errors less than -41% in the extrapolated lifetime.
2010, 59 (4): 2356-2363.
doi: 10.7498/aps.59.2356
Abstract +
A new approach for accurate measurement of the absorbing film thickness and optical constants by combined ellipsometry and spectrophotometry is introduced. The details are studied in terms of the mathematical models and formulats in comparison with the commonly used method which is only dependent on the ellipsometry data specifically. Using variable angle spectroscopic ellipsometry (VASE), the diamond-like carbon film deposited by a glow discharge technique was characterized at the wavelength range of 250—1700 nm. The results indicate that, generally, it is rather difficult to determine the thickness and optical constants of absorbing film accurately and rapidly due to the strong correlation between thickness and n, k. By simultaneously fitting ellipsometry parameters and film transmittance, however, the optical constants could be obtained easily and accurately from a unique solution without any predetermined dispersion model. The fitting results of DLC show that this approach is a promising method to determine the thicknesses and optical constants of films, especially of the thin absorbing films.
EDITOR'S SUGGESTION
2010, 59 (4): 2364-2368.
doi: 10.7498/aps.59.2364
Abstract +
The intra-pulse spectroscopy based on room-temperature pulsed quantum cascade(QC) lasers was introduced. With a room-temperature pulsed QC laser centered at 1904 cm-1, the sample NO gas has been detected.The least-squared algorithm of baseline fitting and concentration retrieving method were introduced for the single line spectroscopy detection, and the gas concentration can be calculated with scan integration and the corresponding values from HITRAN04 database by direct-absorption technique, without calibration. The detection limit was obtained by analyzing the residual of the absorption spectroscopy as 34 ×10-6m.
NUCLEAR PHYSICS
2010, 59 (4): 2369-2374.
doi: 10.7498/aps.59.2369
Abstract +
The octupole deformation of even-even Raisotopes has been investigated systematically by the reflection asymmetric relativistic mean field (RAS-RMF) theory. The results are compared with the experimental data together with the results from FRDM. It is shown that RAS-RMF theory gives a good description for Ra isotopes. The calculated binding energy, two neutron separation energy and deformation agree with the experimental data well. In particular, RAS-RMF theory provides the neutron and proton densities which show clearly the shape evolution of these nuclei from nearly spherical to well-developed octupole and finally back to quadrupole deformation shapes. This is in accordance with experimental observation.
2010, 59 (4): 2375-2380.
doi: 10.7498/aps.59.2375
Abstract +
The prompt and delayed supercritical process of a nuclear reactor with temperature feedback is taken into consideration. The solutions of the point-reactor neutron kinetics equations under the condition of temperature feedback and negative inserted step reactivity are investigated. Different analytic models are given. The new solution is also proposed and compared with those published in literature. It is found that (1) the model and related solution for prompt supercritical can not be applied for the process of large negative inserted step reactivity; (2) under the condition of the same initial power the precursor prompt jump approximation model is better than the neutron prompt jump approximation model; and (3) the temperature prompt jump approximation model is always better than the precursor and neutron prompt jump approximation models for any initial power and negative inserted step reactivity, which is so far the most accurate analytical model.
2010, 59 (4): 2381-2390.
doi: 10.7498/aps.59.2381
Abstract +
The thermonuclear burn characteristics of compressed deuterium-tritium microspheres are simulated with LARED-S code based on the isochoric and isobaric models. Two examples of the isochoric model are simulated and compared with the other present data for validating the LARED-S code. For the isobaric model, numerical results characterizing the thermonuclear burn for a broad range of initial conditions are presenteal. It is shown that the yield and burn-up fraction increase with the total fuel mass, pressure and main-fuel density. It is necessary for the hot-spot to reach temperatures up to 70 to 80 MK and areal density 3 to 4 kg· m-2 to obtain considerable fusion energy. If the main-fuel density is increased high enough, the hot-spot condition for ignition could be broadened to a lower limit. Finally, the results of the isobaric model are compared with those of the actual ignition targets simulated with the LARED-S code.
2010, 59 (4): 2391-2395.
doi: 10.7498/aps.59.2391
Abstract +
The emission of a 41 THz quantum cascade laser (THz QCL) has been measured by a spectrally-matching terahertz quantum-well photodetector (THz QWP). The measured emission spectra have been analyzed with respect to the spectral shape and peak position. The relative light power of the laser under different drive currents have been estimated from the emission spectra and then the lasing domain and threshold current density of the laser has been determined. The temperature-dependent response of THz QWP to the laser has also been investigated. The analyzed results indicate that the THz QWPs could be a good detector for characterizing the emission properties of the THz QCLs and may be the receivers in the terahertz communications.
ATOMIC AND MOLECULAR PHYSICS
2010, 59 (4): 2396-2400.
doi: 10.7498/aps.59.2396
Abstract +
The results of research on fluorescence spectra of three kinds of probiotic bacteria (lactobacillus acidophilus, streptococcus mutans and lactobacillus bulgaricus) show that the bacteria emit fluorescence when irradiated by ultraviolet light. The spectra are in the range of 300—650 nm with the excitation wavelength of 290 nm. Wavelet transform is used to compress the 150 groups of spectra data, and the number of data points in each group is reduced from 1341 to 168, which not only keeps the character of original spectra unchanged, but also improves the processing speed of neural network. Radial basis function neural network is applied for processing the compressed data. 40 groups of data of each strain are used to be trained, and the other 30 groups of data of which the kinds of bacteria are not given are used for prediction. The result shows that radial basis function neural network can identify the unknown bacterial strain accurately.
EDITOR'S SUGGESTION
2010, 59 (4): 2401-2405.
doi: 10.7498/aps.59.2401
Abstract +
In this paper, we investigate the Stark effect of ultra-cold 39D cesium Rydberg atoms in low-field. The Stark structure of 39D Rydberg states is calculated numerically. The cold cesium atoms are excited to Rydberg states via two-step process and the Stark spectra are obtained by field-ionization method. The scalar and tenson polarizabilities of 39D cesium Rydberg atoms are measured to be α5/22=62(7) MHz·V-2cm2，α5/20=－146(13) MHz·V-2cm2, α3/22=73(6) MHz·V-2cm2，α3/20=－106(20) MHz·V-2cm2 respectively. The experimental values are in agreement with the theoretical results.
2010, 59 (4): 2406-2415.
doi: 10.7498/aps.59.2406
Abstract +
We investigate the secular motion of a single Paul-trapped ion in the Lamb-Dicke regime, which interacts with a sequence of standing laser pulses. By using the ansatz method, we get an exact quantum solution of the system. Based on the wave-packet trains described by the exact solution, we find that: i) The center, height and width of the wave-packet trains depend on the strength of laser pulses, the deformation and spread of the wave-packet trains can be controlled by adjusting the strength of laser. ii) Energy expectation values of the ion show jumps at the instantaneous switching on of the laser pulses. In the time intervals when the laser pulses are switched off some narrow energy bands are generated. iii) When the strength of laser pulses reaches a critical value, the system changes its stability.
2010, 59 (4): 2416-2422.
doi: 10.7498/aps.59.2416
Abstract +
The differential and partial wave scattering cross sections of Ne-H2(D2,T2) collisions have been calculated by close-coupling approximation method using Tang-Toennies potential model at the incident energy of 83.8 meV. The calculated differential cross sections are in good agreement with the experimental data and the partial wave cross sections match well with the published data. With the same method and potential model, the differential cross sections and the partial wave cross sections of Ne-H2(D2,T2) collisions have been derived and analyzed. The rules of the effect of symmetrical isotopic substitution are obtained.
2010, 59 (4): 2423-2427.
doi: 10.7498/aps.59.2423
Abstract +
We modify the distorted wave Bohn approximation method (DWBA) by introducing optical model potential into the distorted potential of DWBA in this paper.The triple differential cross section of the argon 2p orbital in a coplanar asymmetric geometry has been calculated，calculations using the modified DWBA method show that the optical model potential effects play an important role in the ionization of the argon 2p shell.
2010, 59 (4): 2428-2433.
doi: 10.7498/aps.59.2428
Abstract +
Relaxation and local structure changes of a molten Cu57 cluster during rapidly quenching have been studied by molecular dynamics simulation using embedded atom method. With decreasing quenching temperature, atom motion details are analyzed using three factors, including the mean square displacement, incoherent intermediate scattering function, and non-Gaussian parameter, while the local structure changes are identified by pair analysis. Simulation results reveal that after a drastic collective motion of atoms, the temperature greatly affects the relaxation processes of the cooled cluster. At a high quenching temperature, after atoms dramatically move in a β relaxation region, diffusion motion of the atoms plays a dominant roles followed by non-diffusion rearrangements of local atomic structures, and no nucleation occurs. When the temperature decreases, local structure changes of atoms occur as the initial dramatic motion, then through the diffusion of atoms in the α relaxation region, and some unstable icosahedral structures are observed. At a low quenching temperature, the structure changes in the α relaxation region result mainly from non-diffusion rearrangement of the atom positions, and a notable amount of icosahedral structures are formed.
CLASSICAL AREA OF PHENOMENOLOGY
2010, 59 (4): 2434-2442.
doi: 10.7498/aps.59.2434
Abstract +
In the framework of the generalized Lorenz-Mie theory (GLMT), the scattering of arbitrarily incident shaped beam by dielectric bi-sphere is investigated. By expressing the incident beam with arbitrary incidence angle in terms of the spherical vector wave function, we derive the scattering equations of bi-sphere arbitrarily illuminated by a single beam, and then extend to the case of scattering of dual-beam. As an example, numerical computations for the scattered intensities of bi-sphere randomly irradiated by a single Gaussian beam and by two Gaussian beams are presented respectively after numerical verifications. In particular, the scattering properties for the two cases are compared and discussed theoretically in detail with respect to different parameters such as incident angle, center-center separation, etc.
2010, 59 (4): 2443-2450.
doi: 10.7498/aps.59.2443
Abstract +
A novel technique for treating electrically thin dispersive layer with the finite difference time domain (FDTD) method is introduced. The proposed model is based on modifying the node update equations to account for the layer, where the electric and magnetic flux densities are locally averaged in the FDTD grid. Then, based on the characteristics that the complex permittivity and complex permeability of three kinds of general dispersive media model, i.e. Debye model, Lorentz model, and Drude model, may be described by rational polynomial fraction in jω, the shift operator method is then applied to obtain the recursive formulation for D and E, B and H available for FDTD computation is obtained. The model is validated with several numerical examples. The computed results illustrate the generality, memory and time step economy and the precision of presented scheme.
2010, 59 (4): 2451-2456.
doi: 10.7498/aps.59.2451
Abstract +
The modes in a double-layer of single-negative material have been investigated. The conditions for the existence of different modes have been analyzed. The relations between different modes and material parameters are considered. Tunneling mode appears when the general zero average permittivity and permeability conditions are satisfied. When the wave guide condition is satisfied, electromagnetic wave is evanescent outside the material, and the field is mainly localized at the interface of the two single-negative layers.
2010, 59 (4): 2457-2461.
doi: 10.7498/aps.59.2457
Abstract +
In the research of the color digital holography and digital holography measurement with multi-wavelength illumination, how to avoid the interpolation error in the wave-front reconstruction with variable magnification is an important subject to be studied. Since the Fresnel diffraction integral can be expressed as Fourier transformation as well as convolution form, there are two reconstruction approaches, one is the relay algorithm which divides the reconstruction distance into two parts, the other is the convolution algorithm which uses the spherical wave as reconstruction wave. In this paper, the two algorithms are theoretically analyzed and experimentally studied, and the condition satisfying the sampling theorem for the reconstruction calculation is discussed. The results show that the convolution approach satisfies the sampling theorem more readily, while higher quality reconstructed object wave field can be obtained with the convolution approach.
2010, 59 (4): 2462-2470.
doi: 10.7498/aps.59.2462
Abstract +
The theoretical model of the hexagonal fiber array is established based on Fraunhofer diffraction theory. The far field distribution of the hexagonal fiber array is presented. Energy contained in the central lobe and Strehl ratio are taken as the two evaluation parameters of coherent combined system. The effects of arrangement, amplitude，filling factor and phase errors on far field distribution are analyzed and simulated. A seven-element hexagonal fiber array with a hexagonal prism is experimentally constructed. The hill climbing method is employed to detect and lock the element phase. The filling factor of the coherent array achieves 066. The combined beam of Strehl ratio of 070 and energy contained in the central lobe of 040 is experimentally obtained. And the energy contained in the central lobe of two-element linear array and four-element square array are 045 and 018, respectively.
2010, 59 (4): 2471-2478.
doi: 10.7498/aps.59.2471
Abstract +
Deconvolution methods are not feasible in spectral domain optical coherence tomography (SD-OCT) system due to the linear space variant property of its axial point spread function (PSF). In order to improve the axial resolution and enhance the imaging quality of the SD-OCT system, a Lucy-Richardson algorithm based deconvolution method is implemented with the numerically compensated A-scan signals and the effective axial PSF in this paper. The main factors decreasing the value of PSF along the axial direction and blurring the images, as well as the deconvolution process, are theoretical studied. With the developed SD-OCT system, the axial modulation function of the PSF is retrieved by curve fitting of the measured peak values of the PSF at different axial positions. After compensating the A-scan signal with the modulation function, deconvolution is performed with the measured effective axial PSF. In vivo imaging on typical samples is conducted and reconstruction is done based on the deconvolution method. The comparing results demonstrate that the proposed deconvolution method not only enhances the axial resolution but also improves the depth dependent sensitivity fall-off in SD-OCT system.
2010, 59 (4): 2479-2484.
doi: 10.7498/aps.59.2479
Abstract +
A kind of flexible cantilever beam electromagnetic optical switch which is used in the wave length channel selection system was designed and fabricated. It was manufactured by micro-opto-electromechanical system technology and composed of a plane circular coil in flexible polyimide cantilever beam, a cylindrical permanent magnet，the substrate and a reflector prism with two reflecting surfaces. The switch′s motion depends on the current direction in the coils. The simulation of force between the coils and the permanent magnet was proceeded by finite element method. In the same way, the relationship between cantilever’s deflection and restoring force, and electromagnetic force were obtained. The switch′s actuation performance was tested and the results indicate that deflection of the cantilever is 0925 mm with 015 A current input，which satisfies the need of the wave length channel selection system of changing the propagation direction of the optical beam.
2010, 59 (4): 2485-2492.
doi: 10.7498/aps.59.2485
Abstract +
Nonclassical properties of a two-mode field initially in an SU(2) coherent state resonantly interacting with a three-level Λ-type atom are investigated by means of the quantum theory and numerical calculations. The dependence of the nonclassical properties on the total photon number of the two-mode, the partition parameter and the coupling constant is discussed for three cases: (1) no state-selective atomic measurement; (2) direct state-selective atomic measurement; and (3) state-selective atomic measurement after the application of a classical field. The results indicate that when the total photon number of the two-mode is increased or the state-selective measurement is performed on the atom, the difference squeezing of two-mode is distinctly enhanced; and when the partition parameter is decreased or the state-selective measurement is performed on the atom after the application of a classical field, the average intensity of the sub-Poisson statistic distribution of mode a is reduced and that of mode b is enhanced; when the total photon number of the two modes is increased or the direct state-selective measurement is performed on the atom, the anti-correlation character between the two modes is preserved, but the average intensity of the anti-correlation is reduced; and when the direct state-selective measurement is performed on the atom, the Cauchy-Schwartz inequality is violated.
2010, 59 (4): 2493-2497.
doi: 10.7498/aps.59.2493
Abstract +
One-way deterministic secure quantum communication protocol based on single photons is proposed in this paper, in which the XOR operation by bits of the information sequence and random sequence is performed and the checking sequence is inserted before the sender’s coding operation. When the photons arrive at the receiver, they are delayed at the receiver, and the sender then publishes the coding basis, so the photons can be measured in the correct basis. Then the two parties estimate the security of the quantum channel by the checking bits. When the channel is secure the sender publishes the random bits where the receiver has results, and the information sequence can be recovered by the receiver. Even the channel is not secure, what the eavesdropper gets is the random sending sequence, the information sequence is still secure. This protocol has the advantages of higher transmission efficiency and easier implementation compared with the two-way communication.
2010, 59 (4): 2498-2504.
doi: 10.7498/aps.59.2498
Abstract +
In this paper, we first find out the analytic solution of the time-dependent Fokker-Planck equation of the non-degenerate optical parametric amplification (NOPA) system under the consideration of the dispersion, the loss and the pump depletion effects. Then, through the numerical calculation, we obtain the squeezing characteristic of the degenerate optical parametric amplification (DOPA) system with dispersion. the research indicates: the dispersion effect stems from the nonlinear susceptibility change from χ″ toχ″/{1+σ2/}/+2, with the increasing of the dispersion effect, the general feature of the squeezing curves beeps unchanged, and the curves contract toward left. The maximum squeezing approaches to the linear theory 1/(1+μ). Finally, we obtain the entanglement characteristic of the NOPA system with dispersion. We find out when σ is given, with the increasing of pump parameter μ, he corresponding phase makes a large change. The nonlinear susceptibility changes many times. When the polarity is positive, the system obtains the gain, when the polarity is negative, the system suffers the loss, but the gain is mainly dissipated by the loss, so the net gain is small, the squeezing is also small. The minimum variance V1 reduces gradually, and the whole curve moves to the right, approaches to the linear theory 1/(1+μ).
2010, 59 (4): 2505-2511.
doi: 10.7498/aps.59.2505
Abstract +
We study spectral properties and photon statistical characteristics of a strongly driven two-level atom produced within a nonlinear photonic crystal. This study reveals that when a large discontinuity in the local photon density of states and the cavity field mode is resonant with the central component of the Mollow spectrum of atomic resonance fluorescence, there is squeezing of the cavity field below the quantum shot noise limit and the peak of the cavity field spectrum that is achieved in the nonlinear photonic crystal is higher than that in the linear photonic crystal. Furthermore, we can see the statistics of the photons emitted by the atom into the microcavity is sub-Poissonian and close to Poissonian when the frequency of the driving field is high.
2010, 59 (4): 2512-2518.
doi: 10.7498/aps.59.2512
Abstract +
A quasi-optical mode converter for a whispering-gallery mode gyrotron，consisting of a Vlasov helically-cut launcher and two curved-mirror reflectors, is studied and designed. Firstly, the operation mechanism of the Vlasov type quasi-optical mode converter is investigated using geometric optics theory. And then, applying the aperture field integration and the surface current source integration of the vector diffraction theory, a numerical simulation code is programmed. Finally, the code is used to study a quasi-optical converter system of a W-band whispering-gallery mode gyrotron, and the operation mechanism of the mode conversion in the converter is revealed in detail. Numerical results indicate that the TE12,2 whispering-gallery mode inside the W-band gyrotron is converted into a highly Gaussian-like beam at the output window.
2010, 59 (4): 2519-2524.
doi: 10.7498/aps.59.2519
Abstract +
The main factor of laser induced damage is the modulation caused by the scratch in the subsurface of the fused silica. The three-dimensional Hertzian conical scratch (HCS) model on the exit surface is establised in this article. Three-dimensional finite-difference time-domain method is used to calculate and simulate the electric field intensity distribution in the vicinity of HCS. The effects of depth, radius and gradient angle of the HCS on incident light field modulation are analyzed, respectively. The results show that the electric field enhancement in the center of HCS is the largest. This area is apt to be damaged. The maximal electric field intensity in the fused silica will be enhanced as the depth of the HCS changes from λ to 19λ/2. The fused silica is liable to be damaged while the radius of HCS is below 15λ. When the radius is larger than 175λ, the maximal electric fields in the fused silica tend to be 2.5 V/m. And the maximal electric fields are independent on the radius. The effect of light intensity enhancement is more obviously when total internal reflection occurs between internal interface of HCS and the rear surface of fused silica.
2010, 59 (4): 2525-2531.
doi: 10.7498/aps.59.2525
Abstract +
Three kinds of simulating models for optical pulse chirped amplifier (OPCPA) are introduced at first. Then the three-step way to determine the length of the nonlinear crystal for most stable output is put forward. In this method, all the there models are used. As the more complex models are used, the ranging length for simulation becomes shorter. So it is efficient and accurate to useing this method to determine the optimized nonlinear crystal length. Then the way is also studied to introduce some phase mismatching in OPCPA to detune the nonlinear crystal length for most stable output. Simulating results show that as the mismatching angles increases, the nonlinear crystal length for most stable output becomes longer. So it is suggested that the nonlinear crystal be manufactured longer than designed. Most stable output can be obtained by introducing some phase mismatching in the experiments.
2010, 59 (4): 2532-2536.
doi: 10.7498/aps.59.2532
Abstract +
The optical limiting effect of Methyl-red dye doped suspended carbon nanotube mixture on 532 nm lascr lighter is studied in experiment. The experiments were carried out with samples of different thickness radiated by laser with different repetition frequency, and the results are compared with the results got from pure suspended carbon nanotubes. The results showed that, if the suspended carbon nanotubes with 60% transmission is doped with some Methyl-red dye, its solubility can be improved and the input limiting threshold decreases from 250 μJ to 200 μJ. The clamped output energies for samples with 2 mm and 5 mm thickness decrease from 45 and 20μJ to 35 and 9 μJ, respectively.
2010, 59 (4): 2537-2545.
doi: 10.7498/aps.59.2537
Abstract +
In this paper, we obtain the analytical solution of the off-waist inputted complex argument Laguerre-Gaussian beams and their mean squared beam width in nonlocal nonlinear media. The propagation of the complex argument Laguerre-Gaussian beams in the nonlocal nonlinear media is investigated in detail. The examples show that the pattern shape of a (n,m) mode complex argument Laguerre-Gaussian beam varies periodically with the period Δz=πzc in strongly nonlocal nonlinear media if n≠0.But if n=0, its pattern shape remains unvaried and the beam width varies periodically during propagation. Under the off-waist incident condition, the propagation of the (0,m)mode complex argument Laguerre-Gaussian beam behaves as a breather during propagation, no matter what the power of the incident beam is. Only when the beam is input at the waist and the input power equals the critical power would the breather be reduced to a soliton.
2010, 59 (4): 2546-2550.
doi: 10.7498/aps.59.2546
Abstract +
The mixed SrF2-CaF2 thin films with the same thickness were deposited by the techniques of resistant evaporation and electron beam evaporation respectively. The physical and infrared optical properties of the thin films were investigated. The optical constants in the infrared region were determined quantitatively which fills the gap of these data. At the same time, we provided a method to obtain gradient index films. We also used the mixed SrF2-CaF2 with a proportion of 1∶1 as the lower index material to deposit multilayer coatings. A broadband antireflection coatings with high optical performance was developed.
2010, 59 (4): 2551-2555.
doi: 10.7498/aps.59.2551
Abstract +
The mode condition of electromagnetic wave is obtained by making use of restriction condition of horizondal direation electromagnetic wave in one-dimensional rectanglular doped photonic crystal and the mode characteristics of electromagnetic wave is studied. The response of the defect mode versus mode quantum number and length of the rectangle is calculated by the characteristic matrix method. Some new defect mode structure of rectangular doped photonic crystal is obtained.
2010, 59 (4): 2556-2563.
doi: 10.7498/aps.59.2556
Abstract +
In contrast to dielectric photonic crystals, the propagation characteristics of metallic photonic crystals are of great importance in millimeter wave and submillimeter wave applications. It is convenient and reliable to get the band diagrams and field distributions of photonic crystals after solutions of the eigenmode equations, which is derived from the Yee-mesh-based finite-difference frequency-domain method. However, this method cannot be used for the analysis of metallic photonic crystals because of the essential distinctions between metal and dielectric. Based on this method, we derive eigenmode equations for two-dimensional metallic photonic crystals by introducing the metal surface boundary conditions. And then, after some numerical calculations, the transverse electric mode and the transverse magnetic mode global band gaps of different lattice structures are obtained, including both square lattice and triangular lattice. Finally, we discuss the advantages of metallic periodic structures in mode selection and device integration by the comparison between metallic photonic band gap and dielectric photonic band gap.
2010, 59 (4): 2564-2570.
doi: 10.7498/aps.59.2564
Abstract +
The diffraction efficiency of freestanding x ray transmission gratings is discussed in relation to the wavelength and grating period using both scalar diffraction theory and rigorous coupled wave analysis, and the grating design is accordingly optimized. A gold freestanding x ray transmission grating with period of 300 nm, line/period ratio of 055, thickness of 200 nm a size of 1 mm ×1 mm and fractional grating area of 65% is fabricated. The absolute diffraction efficiency of the fabricated grating was tested at the National Synchrotron Radiation Laboratory in the wavelength region of 55— 38 nm. The test result shows that the grating has a maximum efficiency of nearly 10%. The grating also shows a stable diffraction efficiency in the wavelength region from 15 nm to 35 nm.
2010, 59 (4): 2571-2576.
doi: 10.7498/aps.59.2571
Abstract +
Based on multi-pole method theory, a kind of hybrid cladding photonic crystal fiber（PCF） is designed. It has been shown theoretically that it is possible to obtain fiattened dispersion charactor of dispersion absolute value 125 ps·km-1·nm-1 within the wave band of 144 μm to 20 μm by altering four structure parameters of the five-ring hybrid cladding in the PCF (namely the diameter of the inner ring hole, the diameter of the outer four ring holes, the pitch of the hexagon and the pitch of the octagon). Moreover, value simulation results show that in the PCF low confinement loss of 0005 dB/km in the 144—20 μm wavelength range can be achieved.
2010, 59 (4): 2577-2581.
doi: 10.7498/aps.59.2577
Abstract +
As the channel-space of the comb filter based on chirped sampled fiber Bragg grating and phase shift is not accurate and the multi-channel is unable to channel the standard frequency, we discussed and calculated the error between theory and practice, which has been verified by simulation. Then a compensation method by introducing phase shift between the samples was proposed, and a 100 channel comb filter with accurate 40 GHz channel-spacing was simulated, which lays a good foundation for fabricating comb filters with accurate transmission peak in the future.
2010, 59 (4): 2582-2588.
doi: 10.7498/aps.59.2582
Abstract +
Particle segregation processes in different vibration modes are simulated based on 3D discrete element method (DEM). The phenomena of wave motion of large particles in upper layer that appears in the segregation processes of linear vibration mode, accumulation and circulation that appear in circular and elliptical vibration mode are analyzed. And the influences of vibration intensity on the segregation pattern of the circular and elliptical mode were also discussed. The results show that the segregation behaviors in different modes can be well explained by a combination of three mechanisms: void filling, sidewall-driven transport of particles and nonequipartition of energy, and the distribution of particle velocity vectors. The vibration intensity has a great effect on the segregation pattern of circular and elliptical mode. For each vibration mode, fine particle segregation effect and stable particle moving state is obtained when the value of vibration intensity is about 3.
2010, 59 (4): 2589-2594.
doi: 10.7498/aps.59.2589
Abstract +
By using the one-dimensional Frenkel-Kontorova (FK) model, we study the maximum static friction force between the two surface layers which are in contact. The relation between the substrate potential and the static friction force is studied in this paper. The effect of parameters of the upper layer such as the elastic coefficient K on the static friction force are also investigated.Results are obtained for three cases for which the ratio of the atomic distance to the period of potential field is commensurate, or equal to the golden mean, or the spiral mean respectively. The results show that both the form of the substrate potential and the commensurability have sigificant effect on the static friction force.
2010, 59 (4): 2595-2600.
doi: 10.7498/aps.59.2595
Abstract +
The lattice Boltzmann method is used to simulate numerically the droplet motion driven by Marangoni effect, which is induced by surface tension gradient on the solid-liquid interface, with the consideration of interaction between solid and liquid molecules. The computation results are well compared with the theoretical prediction available for smaller surface tension gradient, whereas the translation velocity of droplet is smaller than the theoretical value for larger gradient, because some assumptions, such as the quasi-equilibrium and non-deformable droplet, are not satisfied in the theoretical analysis anymore. Vortical structure with a solid-like core is found in the droplet when it moves to the hydrophilic end. The variations of velocity and contact angle of droplet are found to be oscillating with time for larger gradient of wettability.
2010, 59 (4): 2601-2609.
doi: 10.7498/aps.59.2601
Abstract +
The flow phenomena such as spray，splash and especially the bell-like spray happening after a droplet impacts on the liquid film are observed in experiment. The relationship between the flow phenomena and the diameter and speed of the droplet, and the viscosity, the surface tension and the thickness of the film are probed. The condition for bell-like spray brought about after the collision of the droplet on the film is discussed.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2010, 59 (4): 2610-2616.
doi: 10.7498/aps.59.2610
Abstract +
Multi-pulse atmospheric-pressure glow discharges between two slightly unparallel electrodes were carried out in helium. The mode of discharge was investigated using an intensified charge-coupled device camera. The discharge current through gas gap and surface charge on the solid dielectric barrier were calculated. Based on analysis of surface charge on the solid barrier, space charges in gas gap, applied voltage across electrodes and field strength in gas gap, the formation mechanism of multi-pulse discharge was discussed. The discharge evolution pictures show that discharge is generated at the narrower side. At the other side, discharge is also generated at the first current peak. Physical process of the first pulse of atmospheric-pressure glow discharge in helium starts from a Townsend discharge leading to a glow discharge, and that of each subsequent current pulse is a glow discharge. Between two consecutive current pulses, a faint glow discharge is maintained in the gas gap. Theoretical analysis shows that multi-pulse discharge is a result of co-evolution of both surface charge as well as space charge and applied voltage, and the Townsend discharge does not appear during current pulse sequence of the same half cycle, except for discharge inception.
2010, 59 (4): 2617-2621.
doi: 10.7498/aps.59.2617
Abstract +
This paper presents a numerical simulation of the evolution of the main particles in H2/O2 mixture plasma under different initial temperature, and gives the time-variation laws of the density of the main charged and neutral particles in plasma after discharge begins. The results show that the density of main active particles in H2/O2 mixture plasma is reduced with time, and the required time for the equilibrium of chemical reactions reduces with increasing initial temperature.
2010, 59 (4): 2622-2628.
doi: 10.7498/aps.59.2622
Abstract +
The space-charge-limited currents of both solid electron beam and annular electron beam in cylindrical waveguide are derived from the nonlinear Poisson equation for potential in the region of electron beams. Corrections for the transverse motion of electrons are made to the solution, which bring more consistent with the results from PIC simulations. Though numerical computation, it is showed that electrons located along the axis and by outer radius of solid and annular electron beams respectively and electrons standing near to the outside of the beam has larger axial velocity than these inside. This approach is available for analyzing the characteristics of electron beam transporting in high power microwave generator with other configuration waveguide.
2010, 59 (4): 2629-2634.
doi: 10.7498/aps.59.2629
Abstract +
A novel configuration of vircator with coaxial waveguide generated by annular electron beam under low guiding magnetic field is presented and the 25-D particle-in-cell simulations are carried out using KARAT code. We obtain High power microwave with average power of 27GW, frequency of 38GHz, of which the beam-to-wave power efficiency and dominant mode are 12 % and TEM mode, respectively.
2010, 59 (4): 2635-2639.
doi: 10.7498/aps.59.2635
Abstract +
Poisson line technique is a method of generating a straight line by diffraction for high precision alignment，which can keep the center of Poisson spot in this line at long distances (several tens or hundreds of meters). Numerical simulation and experimental demonstration are proposed to research this technique. The intensity of the line increases asymptotically to the incident intensity as distance from the disk increases. The diameter of the line increases as the distances from the disk increases. Whereas it decreases as the diameter of the disks increases. The direction of the line is parallel to laser beam and propagates through the center of the disk，which is sensitive to center excursion and insensitive to the incline of the disk. Poisson line is sensitive to 10 μm excursion in simulation. And Poisson line technique can adjust 50 μm center excursion at long distance in experimental demonstration.
2010, 59 (4): 2640-2644.
doi: 10.7498/aps.59.2640
Abstract +
The cascade effect of cathode spots from vacuum micro-arcing has been observed by micro-channel plate (MCP) imager in divect current mode. The spots-track on MCP surface can be drawn out as a multiform dog-leg path，and betweencenters of spots is 200—300 μm. The first spot is always the lucida，and its intensity is about decuple of its sub-spots. The intensity between cascade sub-spots is at the same level，and sub-spots are nondestructive for MCP cathode surface. The experiments showed that arcing of sub-spots depends on emission of the first spot.
2010, 59 (4): 2645-2652.
doi: 10.7498/aps.59.2645
Abstract +
The method for deducing expressions of arbitrary geometrical structures is studied in detail by using the Fourier series expansion. The dispersion curves of the slow-wave structures (SWSs) with the cosinoidal，rapezoidal and rectangular corrugations are obtained by numerical calculation. Moreover，the longitudinal resonance properties of the finite-length coaxial SWS are investigated with the S-parameter method. It is proposed that the introduction of a well designed coaxial extractor to slow-wave devices can help to reduce the period-number of the SWS，which not only can make the devices more compact，but also can avoid the destructive competition between various longitudinal modes. Furthermore，a compact L-band coaxial relativistic backward wave oscillator (RBWO) is investigated and optimized in detail with particle-in-cell (PIC) methods (KARAT code). In the preliminary experiments，the measured microwave frequency is 161 GHz，with a peak power level of above 102 GW，when the diode voltage is 670 kV and the current is 107 kA. The pulse duration (full-width at half-maximum) of the radiated microwave is 22 ns.
2010, 59 (4): 2653-2660.
doi: 10.7498/aps.59.2653
Abstract +
The characteristics of the radio frequency plasma jets at atmospheric pressure in Ar/SiCl4/H2 gas mixture were studied in this paper by using optical emission spectroscopy. Firstly, the electron excitation temperature of plasmas was calculated from the Si atom spectral emission using Boltzmann plots, and then, based on the temperature, the number density of the Si atoms in the plasmas and the dissociation ratio of the SiCl4 were estimated. Finally, the dependence of the excitation temperature, the number density of the Si atoms and the dissociation ratio of the SiCl4 on the discharge power and the gas flow rate were presented.
2010, 59 (4): 2661-2665.
doi: 10.7498/aps.59.2661
Abstract +
This paper investigates the intermediate gas phase in the CHF3 dual-frequency capacitively couple plasma (DF-CCP) driven by the high-frequency (HF) of 1356 MHz，2712 MHz or 60 MHz and the low-frequency (LF) of 2 MHz power sources，which was used to etch the SiCOH low dielectric constant (low-k) films. The increasing of 2 MHz LF power led to the increase of F radical concentration，and the increasing of HF frequency from 1356 MHz and 2712 MHz to 60 MHz led to the increase of CF2 concentration and a poor spatial uniformity of F radical between the electrodes. According to the electron temperature distribution at different LF power and HF frequency，and the dependence of ion energy on the high frequency，the CF2radicals were found to come from the CHF3 dissociation by the electron-neutrals collisions，and the F radical from the CHF3 dissociation induced by the ions-neutrals thermal collisions.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2010, 59 (4): 2666-2671.
doi: 10.7498/aps.59.2666
Abstract +
The field emission characteristics of nano-diamond deposited on titanium substrate at various temperatures are studied. It was found that the emission current increases with increase of temperature and electric field，while the stability of the emission current basically does not change. The field emission characteristic deviates from classic Fowler-Nordheim theory. The mechanism of the emission current at different temperatures is analyzed. It may be due to the combined action of scale effect of the nano-diamond and masses of hot carrier produced by nano-diamonds in external electric field. In addition，the research indicates that larger current can be generated after titanium substrates being heated up to a certain degree in external electric field, which can have large effect on field emission，showing that the titanium substrate has a certain degree of temperature sensitivity and voltage sensitivity.
2010, 59 (4): 2672-2678.
doi: 10.7498/aps.59.2672
Abstract +
We have used molecular dynamics (MD) simulation to investigate the evaporation of the surface wall of multi-wall carbon nanotubes (MWCNTs) at high temperature，using the environment dependent interatomic potential (EDIP) to describe the C—C interaction in carbon nanotube. The simulation results show that the Stone-Wales defect in the surface wall of a multi-wall carbon nanotube vibrates violently，which causes C—C bond breaking and evaporation of atoms along the circumferential directions of the nanotube. The formation of Stone-Wales defect is attributed to the atomic thermal motion or tensile strain. Using the Lindemann index as a criterion，we found that the surface wall of MWCNT evaporates around 2290 K. Our simulation results agree very well with the observation of the surface wall evaporation of the MWCNT at 2000 ℃.
2010, 59 (4): 2679-2684.
doi: 10.7498/aps.59.2679
Abstract +
The effect of KrF pulsed excimer laser irradiation on intrinsic defects，ultra-violet (UV) emission and surface morphology of ZnO thin films was investigated，and also the origin of room temperature UV emission was discussed in detail. It was found that，the KrF laser can break the Zn—O bonds; therefore，the concentration of VO (or Zni) defects increases，leading to the decrease of resistivity and increase of carrier concentration. By adjusting the laser energy densities，the donor defect concentration can be controlled in a wide range. Simultaneously，under the heat of laser，the melting grains connect with each other，resulting in the great decrease of surface roughness. Room temperature UV emission of ZnO film is composed of contribution from free-exciton (FX) recombination and its longitudinal-optical phonon replica (FX-LO), the defect density determines the relative strengths of FX to FX-LO emission intensities，which strongly affect the peak position and intensity of UV emission of ZnO film. This investigation indicates that the laser irradiation is an effective technique to modulate the exciton emission by controlling the defect density，which is important for the application of high performance of UV emitting optoelectronic devices.
2010, 59 (4): 2685-2690.
doi: 10.7498/aps.59.2685
Abstract +
Introducing sine-squared potential，the particle motion equation in the crystalline undulator field is reduced to the generalized pendulum equation with a dampping and a force terms in the classical mechanics frame in the dipole approximation. The properties of the phase plane are ananysed for a non-peturbated system by means of Jacobian elliptic function and the elliptic integral，and the solution of the equation and the period of the particle motion for this system are expressed exactly. The global bifurcation and a chaotic behaviour with the Smale horseshoe for the 3 kinds of orbits in a phase plane are analysed by Melnikov method. The critical condition of the system entering into a bifurcation or a chaoc is found. The result shows that critical condition is related to the parameters of the system，by suitably regulating the parameters of the system，the bifurcation or the chaos can be avoided or controlled in principle.
2010, 59 (4): 2691-2696.
doi: 10.7498/aps.59.2691
Abstract +
The elastic properties and optic characteristics of shocked Z-cut quartz were carefully examined，by using symmetric plate impact and in situ measurement. Results show that Z-cut quartz exhibits a simple-wave elastic response and keeps transparent up to a pressure of no less than 10 GPa，and it can be used as the opical window for velocity measurement within this pressure range. The relation of elastic shock wave velocity and particle velocity satisfies linear function very well. On the other hand，the velocity correction of Z-cut quartz at incident laser wavelength of 1550 nm can be better represented by exponential function than linear one，while the relation between refractive index and density of Z-cut quartz at 1550 nm satisfies the linear function very well. The results in this paper lay a foundation for using Z-cut quartz as optical windows of interferometer systems working with laser at 1550 nm wavelength.
2010, 59 (4): 2697-2702.
doi: 10.7498/aps.59.2697
Abstract +
Based on density functional perturbation theory (DFPT) combined with the norm-conserving pseudopotential method，the lattice dynamic simulation is presented. The total phonon density of states，partial phonon density of states and phonon dispersion spectrum of YAG are obtained. By using the special point sampling method within the first Brillouin zone，the special heat capacity and the population averaged group speed of phonon of YAG are calculated. The anharmonic phonon mean free path is calculated theoretically within anharmonic interaction and by using the Fermis golden rule scheme combined with the special point sampling method within the first Brillouin zone. We comprehensively considered two types of the phonon scattering mechanisms，the thermal conductivity of YAG ceramic is obtained. The result indicates that the grain boundary scattering plays a major role in the thermal resistance at low temperature in YAG ceramic，while the three-phonon interaction contribution to the thermal resistance will prevail above a certain temperature. Meanwhile，the viewpoint held by Y. Sato et al. that the difference of the thermal conductivity of between YAG ceramic and single crystal can be ignored above room temperature is theoretically proved. The temperature variations of the calculated thermal conductivity and special heat capacity agree well with the experimental results.
2010, 59 (4): 2703-2707.
doi: 10.7498/aps.59.2703
Abstract +
The specific heat of polycrystalline La0.7Ca0.3MnO3 at different resistance states induced by electric pulses was studied. It was found that the specific heat decreases with decreasing resistance, and the change is reversible. The reversible change of specific heat was shown to be mainly due to the ferromagnetic-spin-waves component and charge carriers component by fitting the specific heat data. These results indicate that the electric pulses modulated the magnetic configuration of LCMO at low temperature, which would result in large variation in magnetization and specific heat associated with ferromagnetic-spin-waves.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2010, 59 (4): 2708-2713.
doi: 10.7498/aps.59.2708
Abstract +
The electronic structure of Mg alloy was calculated with the recursion method. The result shows that the density of states of Mg in grain is similar to that on the surface of Mg alloy，but it is obviously different when O or O，H atoms exist on the surface of Mg alloys. This indicates Mg has similar properties whether in grain or on surface，but the properties of Mg change apparently after oxygen or hydrogen atom permeated in the surface layer of Mg alloy. Al，Y or La atom diffuses from grain to the surface and segregates there，because each the doped atom embedding energy of Al，Y or La atom on the surface is lower than that in grain. The affinity energy of Al-O，Y-O，La-O，Mg-O，Mg-O-H is negative，so they can form compound. Because the affinity energy of Mg-O-H is lower than that of Mg-O，Mg(OH)2 is more stable than MgO. In the early stage of oxidation，oxygen combined with Mg，Al，Y or La forming oxide. When Mg alloy is in corrosive medium，MgO reacts with H2O forming Mg(OH)2. Al2O3，（Y，La）2O3 and Mg(OH)2 can protect Mg alloys from corrosion and improve corrosion resistance.
2010, 59 (4): 2714-2720.
doi: 10.7498/aps.59.2714
Abstract +
Based on the density-functional theory and the non-equilibrium Greens function method, a theoretical study of the electron transport for the systems consisting of the terphenyl molecule connected to two Au electrodes through end-group S (Se) is carried out. The results show that these systems have good rectifying performance and the maximum rectification ratio may reach approximately 6 at a bias of 2.8 V. The rectifying behavior is reduced significantly when one of the two S(Se) atoms located at right end of the molecule is replaced by H. The asymmetric coupling between the molecule and the metal interface leads to different spatial distributions of the MPSH and different shifts of molecular orbital energy levels under positive and negative biases, which is the mechanism of rectifying performance. The systems with S end-groups have obvious rectifying performance because the interaction between S and Au electrode is stronger than that between Se and Au electrode.
2010, 59 (4): 2721-2727.
doi: 10.7498/aps.59.2721
Abstract +
We have performed first-principle calculations of electronic band structure of C-doped anatase TiO2, and explained some experimental phenormena of C-doped TiO2s absorption spectrum. The results indicated that the band gap broaders and some new bands appears in the band gap. These new bands result from C 2p orbitals, they are separated, and their existance explains the visible light response. The electrons in the valence band can be excited to the new states and subsequently excited to the conduction band, leading to existence of two absorption edges. Theoretical result are in agreement with the experimental result.
2010, 59 (4): 2728-2733.
doi: 10.7498/aps.59.2728
Abstract +
GaAs/AlAs triple-quantum-well samples were grown by molecular beam epitaxy, and the middle GaAs quantum-well layer was delta-doped at the well centre with Be shallow acceptors. Then the far-infrared Teraherz prototype emitter was fabricated using the samples. Electroluminescence (EL) and current-voltage characteristics (I-V) were measured at 4.5 K. In the EL spectrum, a wide peak was observed clear 222 cm-1, which is attributed to the Be acceptor’s radiative transitions from the excited odd-parity states to the ground state. Nevertheless, the emission signal was weakened by non-radiative relaxation processes. In the I-V curve, the negative differential resistance characteristic at the position of 0.72 and 1.86 V was also observed clearly. This is attributed to the resonant tunneling between Be acceptor 1s3/2(Γ6+Γ7) energy level in the middle quantum-well and the HH1 band in the left-side non-doping quantum-well, as well as the resonant tunneling between the HH band in the right-side non-doping quantum-well and Be acceptor 2p5/2(Γ6+Γ7) energy level.
2010, 59 (4): 2734-2738.
doi: 10.7498/aps.59.2734
Abstract +
A vertical organic light-emitting transistor (VOLET) was fabricated by stacking a capacitor cell on top of an organic light emitting cell joined by a common source electrode，and the operation mechanism was analyzed. This unique device has the dual functions of emitting light as an OLED and switching current as a transistor. When the capacitor is under bias, the stored charges on the thin and coarse electrode shared by the two units modulate the charge injection of the OLED active unit, hence control the current flow and consequently tune the light emission. This device structure provides an extremely short channel in the nanometer range and a large conduction area (004 cm2), which supply enough output current (up to 02 mA) to drive the light emitting unit. As a result, thanks to the vertical integration, this device not only realizes multifunction but also operates at lower voltage, which provides a navel solution for the active-matrix OLED display application.
2010, 59 (4): 2739-2745.
doi: 10.7498/aps.59.2739
Abstract +
Based on the previous work (Li P, Deng W J 2009 Acta Phys. Sin. 58 02713), the quantum transportation of electron through arbitrary equilateral polygons quantum rings with Rashba spin-orbit interaction is studied. With the typical method of quantum network and the Landauer-Büttiker formalism, we analytically solve the scattering problem of electron through equilateral polygonal quantum ring, and obtain the relevant formula for spin transportation conductance. The characteristics of the conductance varying with the wave-vector of electron, the strength of spin-orbit interaction, the number of polygon edges, and the ways of leads connecting to quantum rings are discussed. In the limit of infinite number of edges of polygon, we prove that the formula is consistent with the results obtained directly from the circular model of quantum rings.
2010, 59 (4): 2746-2752.
doi: 10.7498/aps.59.2746
Abstract +
The effects of static surface states and bulk traps on output characteristics have been studied. The effects of surface charge and bulk traps on current collapse, saturation current and knee voltage are investigated, and their relationships have been determined. The results show that the increase of the surface charge can exhaust the two-dimensional electron gas, and reduce the current collapse effect and saturation current, inducing the abnormal shift of the knee voltage. At the same time, reducing the bulk traps can alleviate the current collapse effect and increase the saturation current with the slight change of the knee voltage. At low lattice temperature, the hot electron effect and quantum tunneling effect play an important role in the current collapse. By using the hydrodynamics model, possible physical mechanisms are discussed, and an approach is proposed to reduce the effects of the static surface states and bulk traps on the output characteristics.
2010, 59 (4): 2753-2759.
doi: 10.7498/aps.59.2753
Abstract +
Combined Ag nanoparticles with Al2O3 dielectric layer structure have been designed for molecular detection using surface enhanced Raman scattering. Optical absorption spectra studies reveal dipole plasmon resonance absorption property, which show regular red shift with the increasing of the thickness of Al2O3 layer. By use the combined structure as SERS substrates and rhodamine 6G as a test molecule, the results in this paper show that the scattering at 1064 nm increases with the thickness of Al2O3 dielectric layer which leads to the surrounding dielectric constant of Ag nanoparticles to increase.
2010, 59 (4): 2760-2766.
doi: 10.7498/aps.59.2760
Abstract +
A new model of quantum ring with multiple arms whose middle arm is curved was proposed in this article.This is an unequal arm quantum ring with a shortest upper arm and a longest lower arm.The results indicate that the persistent spin current shows nonperiodic vibration with the size of the semiconductor ring increasing when the total magnetic flux is zero.And it is related to the electrodes’ magnetic moment direction as well as the tunneling electrons’ spin orientation. The average persistent spin current in the lower arm is minimum on account of its longest length. When the AB magnetic flux strengthens, the persistent spin current in each arm generates periodic oscillation and shows mutual restriction.The difference in each arm is related to the arm length and the magnetic flux distribution. Furthermore,the Rashba spin-orbit interaction affects the phase and the phase difference of the persistent spin current. Our results also imply that the persistent spin currents which the two kind of wave functions correspond to are separated under definite conditions.
2010, 59 (4): 2767-2774.
doi: 10.7498/aps.59.2767
Abstract +
A new model of quantum ring with multiple arms containing δ barrier is proposed in this paper. The results imply that the persistent current shows behavior of nonperiodic oscillation with the size of the semiconductor ring increasing when the total magnetic flux is zero. The lower arm obtains minimal average persistent current because it contains the δ barrier. The persistent current generates periodic oscillation when the AB magnetic flux strengthens. It is related to not only the electrodes’ magnetic moment direction but also the tunneling electrons’ spin orientation. Furthermore, when the two magnetic moments are parallel, the Rashba spin-orbit interaction has the effect of changing the persistent current’s phase and phase difference. However, when the magnetic moments in the two electrodes are antiparallel, the Rashba spin-orbit interaction affects the amplitude of the persistent current. Our results also indicate that the difference of the persistent current in each arm is retated to the arm length and the magnetic flux’s distribution. The persistent currents which the two kind of wave functions correspond to are separated under definite conditions.
2010, 59 (4): 2775-2782.
doi: 10.7498/aps.59.2775
Abstract +
With a Nickel-Silicon alloy as a target of magnetron-sputtering under Ar /O2 mixed gases, a new type of Ni/Si oxide source called self-released nickel source is fabricated. This kind of nickel source is different with the pure nickel source at both crystallized phenomenon and remainder of Ni. Low temperature poly-Silicon crystallized by self-released nickel source has lower nickel-residua and a controllable crystallization rate related without the thickness of Ni source. That is useful for widen process window. The relations of surface roughness and electrical characters of poly-Si crystallized by different source have been studied and discussed.
2010, 59 (4): 2783-2788.
doi: 10.7498/aps.59.2783
Abstract +
Cu would be doped and form deep level centers easily in CdTe solar cells. The deep level centers in ZnTe back contact and graphite back contact CdTe solar cells were studied by deep level transient spectroscopy(DLTS). The electronic density of states on zinc blende CdTe，VCd system and CdTe doping Cu were analyzed with density functional theory. The d-orbital splitting of Cu2+ in C3v and Td fields was obtained. The results show that two deep centers Ev+0206 eV and Ev+0122 eV，respectively，are attributed to substitutional Cu，energy of CdTe is reduced after Cu doping，and Cu could replace Cd.
2010, 59 (4): 2789-2794.
doi: 10.7498/aps.59.2789
Abstract +
Positron annihilation lifetime spectroscopy (PALS) measurements of SmFeAsO polycrystalline sample were first carried out at 298 K. Two lifetime components of 1516 ps and 2903 ps were obtained. According to two-state capture model, the free annihilation lifetime in polycrystalline SmFeAsO is 1870 ps, which agrees well with the calculated value（in general gradient approximation） of 173 ps in SmFeAsO single crystal. Superposed-neutral-atom model and the finite-difference method (SNA-FD) were used to calculate the positron annihilation information in single-crystal SmFeAsO. The results show that the ratio of annihilation rate with valence electrons to annihilation rate with core electrons is 106, while the ratio of annihilation rate with electrons from Fe, As, Sm, and O atoms are 1∶13∶12∶1
2010, 59 (4): 2795-2800.
doi: 10.7498/aps.59.2795
Abstract +
Polycrystalline perovskite SrMn0.5Fe0.5O3 has been synthesized by solid state reaction method. The crystal structure, magnetic properties and valence states of Mn and Fe ions have been investigated. X ray diffraction (XRD) and subsequent Rietveld refinement confirmed that SrMn0.5Fe0.5O3 is found to be a primitive cubic crystal structure，Mn and Fe atoms randomly occupy the center of oxygen octahedron. Also with the measure of XPS which indicates that Mn ions show trivalent and tetravalent state, while Fe ions are in trivalent state. Paramagnetic phase was observed in high temperature (>230 K), the spin-glass behavior at low temperature (3+ ions located in the octahedral sites.
2010, 59 (4): 2801-2807.
doi: 10.7498/aps.59.2801
Abstract +
Through measurement of saturation magnetic moment and transport of La0.8Sr0.2Mn1-yCoyO3 (y≤02), the mechanism of magnetoresistance (MR) impacted by Co doping is investigated. The results show that Co3+ is in the low-spin state in La0.8Sr0.2 Mn1-yCoyO3(y≤02). The magnetic exchange interactions of the type Mn3+—O—Co3+—O—Mn3+ is weaker than that of the double exchange interaction between Mn3+-Mn4+, and the magnetoresistance near the Curie temperature TC decreases with the increase of Co concentration. On the contrary, low-temperature magnetoresistance increases with the increase of Co concentration owing to the antiferromagnetic exchange coupling between Co2+ and eg itinerant electron.
2010, 59 (4): 2808-2814.
doi: 10.7498/aps.59.2808
Abstract +
The inverse magnetostrictive effect, also called magnetomechanical effect, in Terfenol-D material, has been investigated in this paper. Based on Stoner-Wohlfarth (SW) model, taking into account magnetocrystalline and stress-induced anisotropy energy, and following the free energy minimization procedure, direction cosines of magnetization in Terfenol-D single crystal in demagnetized state have been obtained as a function of the compressive stress. The nonlinear equations for equilibrium have been solved numerically. The results indicated that under compressive stress, magnetic anisotropy in Terfenol-D is determined by a competition between magnetocrystalline and stress-induced anisotropy energy, and changes from cubic symmetry to uniaxial. A comparison between experimental and numerical results showed that there is a maximum magnetostriction in Terfenol-D at a certain stress. According to our numerical results, experimental observations that compressive stress makes Terfenol-D hard to be magnetized and leads to the maximum magnetostriction can be explained. The computation in this paper presents a more accurate approach to similar investigations, and its numerical results would be helpful for a better understanding of magnetization process of similar materials.
2010, 59 (4): 2815-2819.
doi: 10.7498/aps.59.2815
Abstract +
Polycrystalline bulk Tb0.8Eu0.2MnO3 was prepared by solid phase reaction. The XRD analysis of the sample showed that the Eu3+ had been doped in TbMnO3. Dielectric properties were examined as functions of temperature (100 K ≤T≤ 300 K) and frequency (200 Hz≤ f ≤100 kHz). Two dielectric relaxations were found in these ranges. By means of analysis the low-temperature relaxation was ascribed to the dipolar effects induced by carriers hopping; and the high-temperature relaxation was found to originate from the internal barrier-layer capacitor effects of ion conductivity. The measurement of resistivity showed that there is a marked transition around 230 K, indicating that different conductive mechanisms underlay the transport processes.
2010, 59 (4): 2820-2826.
doi: 10.7498/aps.59.2820
Abstract +
We report a low loss photonic crystal slab waveguide formed by deforming the innermost holes on either side of a single line defect so that the circular air holes are changed to elliptical holes. The group velocity and group velocity dispersion of this waveguide depend strongly on the innermost elliptical air holes. We obtain the photonic bands and group index of guided modes in this kind of photonic crystal waveguide by guided mode expansion method and investigate the dependence of photonic bands and group index of guided modes in this photonic crystal waveguide on the parameter of the innermost elliptical air holes. For waveguides with the optimum innermost elliptical air holes, we achieved a wider single mode region below the light line, in which light can easily propagate without intrinsic loss. At the same time, this kind of waveguide has nearly constant group velocity and vanishing group velocity dispersion in a 3—5 nm bandwidth. These results will be applicable to design and fabricate photonic crystal slab waveguides with low group velocity, low dispersion and low loss characteristics.
2010, 59 (4): 2827-2830.
doi: 10.7498/aps.59.2827
Abstract +
Bi2O3:BaF2 and BiF3:BaF2 crystals were prepared by TGT (temperature gradient method). Near-infrared broadband luminescence was observed in as-grown Bi2O3:BaF2 crystal. The emission band peaks at 961 nm in the range of 850—1250 nm，with FWHM about 202 nm. The luminescence of Bi2+ and Bi3+ ions in the visible region was observed in BiF3:BaF2 crystal, but there was no near-infrared emission. Then the BiF3: BaF2 crystal was exposed to γ-rays in order to reduce valence states of Bi ions. Near-infrared broadband luminescence was observed in γ-irradiated BiF3:BaF2 crystal. The emission band peaks at 1135 nm in the range of 850—1500 nm，with FWHM about 192 nm. The mechanisms of near-infrared luminescence in Bi2O3:BaF2 crystals and γ-irradiated BiF3:BaF2 crystals were discussed.
2010, 59 (4): 2831-2835.
doi: 10.7498/aps.59.2831
Abstract +
To gain an insight into the effect of electric field on the electro-luminescence of organic light emission diode, the ultrafast pump-probe spectroscopy is used to investigate the transient phenomena of the excitons induced by the electric field. Under the excitation density of 230 μJ/cm2, the decay of the singlet excitons shows a fast and a slow component. The amplitude factor and the relaxation time of fast component are field-dependent. Compared with the zero biascase, the relaxation time of the fast component becomes faster at a bias of 6.4×105 V/cm, its amplitude factor is increased from 22% to 72%, about 50% initial excitons are dissociated by the electric field. The slow component is field-independent, its relaxation time-constant is about 890 ps. The longitudinal acoustic phonons with sound velocity of 17 /ps generated by excitation pulse are observed.
2010, 59 (4): 2836-2842.
doi: 10.7498/aps.59.2836
Abstract +
The electronic structure of M’ type GdTaO4 is studied by first-principle pseudopotential calculation within the frame of density-functional theory. The calculated band structure of M’-GdTaO4 revealed that the top of the valence band is dominated by O-2p and the bottom of the conduction band is dominated by e orbits of Ta-5d. The spin-up and spin-down electrons of Gd-4f are located at 627 eV below the top of the valence band and at 301 eV above the bottom of the conduction band when on-site Coulomb interaction Ueff=8 eV is applied. The calculated refraction index of M’-GdTaO4 is 224 which is in good agreement with the result abtained from the Gladstone-Dale relation.
2010, 59 (4): 2843-2849.
doi: 10.7498/aps.59.2843
Abstract +
A novel slow-wave structure (SWS)， the folded double-ridged waveguide structure， is presented and its properties used for wide-band traveling-wave tube (TWT) are investigated. A Ka-band folded double-ridged waveguide TWT is modeled by Magic 3D and the beam-wave interaction is simulated and analyzed. Within the same beam condition， it is concluded from the comparison of folded double-ridged waveguide TWT and folded waveguide TWT that: in the condition of similar gain maximum， the folded double-ridged waveguide TWT has wider bandwidth of which is 22%， and higher electron efficiency of which is 9％.
2010, 59 (4): 2850-2854.
doi: 10.7498/aps.59.2850
Abstract +
second-order nonlinearity, solvent effect, harmonic oscillator
2010, 59 (4): 2855-2859.
doi: 10.7498/aps.59.2855
Abstract +
Aimming at the decay tendency of reflection-mode negative electron affinity (NEA) GaN photocathode and the different decay speeds of quantum efficiency corresponding to the different wave bands, and referring to the decay tendency of quantum efficiency curve provided by foreign authors for reflection-mode NEA GaN photocathode, the quantum efficiency decay mechanism for reflection-mode NEA GaN photocathode was studied. The surface model ［GaN (Mg) : Cs］: O-Cs for GaN photocathode after being activated with cesium and oxygen was used. And the change of surface barrier in the decay course of quantum efficiency was considered. The reduction of the effective dipole quantity is the basic reason causing quantum efficiency reduction. And it is the change of surface I, II barrier shape that causes the difference of dropping speeds of quantum efficiencies corresponding to different wave bands.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2010, 59 (4): 2860-2866.
doi: 10.7498/aps.59.2860
Abstract +
The single-phase InSb compounds have been prepared by novel melt spinning (MS) technique combined with spark plasma sintering (SPS) method, and the effects of melt spinning process on their microstructure and thermoelectric transport properties have been investigated. The results show that the free surface of ribbon obtained by MS consists of cubic grains with the size of 03—20 μm, and the contact surface of ribbon obtained by MS amorphous-like phases or finer nanostructures have formed, and after SPS the highly dense bulk material with lots of fine layered nanostructure has been obtained of about 40 nm in dimensions. By comparing the bulk InSb material prepared by melting method combined with SPS (Melt+SPS sample) with the bulk InSb material obtained by melting method combined with MS and SPS (Melt+MS+SPS sample)， we see that the MS process leads to a slight decrease in electrical conductivity, and an obvious increase in Seebeck coefficient, as well as a remarkable decrease in thermal conductivity and lattice thermal conductivity for bulk InSb in the testing temperature range of 300—700 K. At 300 K and 700 K, the lattice thermal conductivities of Melt+SPS sample and Melt+MS+SPS sample decrease by the scopes of 106% and 1664%, respectively. As a result, the maximum dimensionless figure of merit ZT of 0.49 is obtained at 700 K for the Melt+MS+SPS sample. Compared with that of Melt+SPS sample, it is increased by 29% at the same temperature.
2010, 59 (4): 2867-2872.
doi: 10.7498/aps.59.2867
Abstract +
In this work, a method to determine atmospheric aerosol optical density from multi axis differential optical absorption spectroscopy (MAX-DOAS) observations was described. It basically utilizes the differential absorption structures of the oxygen collision complex (O4) in the UV and visible wavelength regions to derive information on aerosol optical properties. Based on radiative transfer model with appropriate aerosol single scattering albedo, asymmetry parameter and profile, atmospheric aerosol optical density was retrieved in an iterative process by comparison with measured O4 slant column densities at 360 nm. The retrieved value was verified through comparisons with sun photometer CE318.
2010, 59 (4): 2873-2881.
doi: 10.7498/aps.59.2873
Abstract +
Timbre attribute is the most important feature to recognize a target. This paper presents a model of timbre features by multiple regression analysis applied in the recognition of underwater noise. At first, timbre attribute as a dependent variable is analyzed by the semantic differential evaluation and principal component analysis. And then an extended stepwise variables selection is proposed to select the optimal set as independent variables from auditory features that have been discussed in previous researches. Finally, the timbre features extracted by the regression model are used to recognize the underwater target. The results show that the extended regression analysis as a statistical method can find the relationship between timbre attribute and the auditory features. And the modeling timbre features calculated by several statistics of the sub-spectral features and the sub-temporal features are more effective than other features.
2010, 59 (4): 2882-2888.
doi: 10.7498/aps.59.2882
Abstract +
Superconducting quantum interference device (SQUID) can detect weak cardiac magnetic signals. By analyzing those detected cardiac magnetic signals can we provide the evidence for the diagnosis of cardiac diseases. In this paper, we reconstruct the cardiac current dipole array using minimum-norm least-squares method (MNLS), thus realize the imaging of equivalent cardiac current sources. In the process of doing inverse computation using MNLS for current dipole array reconstruction, we assume that the cardiac current sources are distributed in a plane layer in human heart and the cardiac magnetic signals needed for inverse computation are obtained with three methods: the simulation based on single current dipole and current multipole models, and the realistic measurements by SQUID. Using the three methods for obtaining the cardiac magnetic signals, we discuss the distributive characteristics of current dipoles from the inverse computation. Besides, we also add the constant noise and random noise to the cardiac magnetic signals and consider their influences on the reconstruction of current dipole array.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2010, 59 (4): 2889-2897.
doi: 10.7498/aps.59.2889
Abstract +
multiple solution scheme, two dimensional variational assimilation, generalized variational optimization analysis, regularization method
2010, 59 (4): 2898-2906.
doi: 10.7498/aps.59.2898
Abstract +
Partitioning and reconstruction problem of the wind in a limited region is a useful diagnostic technology. From the non-divergent and non-rotational wind component, one can know more about the structures of meso-scale systems. The effective way to wind partitioning and reconstruction in a limited region is to calculate the stream function and velocity potential in the same limited region. When the reconstructed wind approachs the original one, it means the partitioning process is successful and the calculated stream function and velocity potential is accurate. The most commonly used partitioning methods in the past are summarized in this paper, and the harmonic-sine/cosine method is emphasized. Case study shows that the harmonic-sine/cosine method can partition and reconstruct the wind in a limited region, and its results are encouraging for studying the dynamical structures of meso-scale systems.
2010, 59 (4): 2907-2913.
doi: 10.7498/aps.59.2907
Abstract +
Internal charging is generated by penetrative electrons from the outer radiation belt, and the resultant discharges usually occur inside spacecrafts or sdeeply in the surface dielectrics. Therefore it may produce more serious results in electronics on board compared with surface charging. In this article, the general characteristics of internal charging were introduced, and, as an example, an internal charging induced anomaly, which took place on Double Star (TC-1 and TC-2) was analyzed through correlation of the anomaly with high energetic electron enhancement. The analysis provides a typical instance for spacecraft anomaly diagnostics.
