Vol. 59, No. 9 (2010)
Memoryless state observer-based adaptive control for uncertain nonlinear systems with multiple time delays
2010, 59 (9): 5925-5929. doi: 10.7498/aps.59.5925
In this paper,the problem of adaptive control based on memoryless state observer is considered for uncertain nonlinear systems with multiple time delays. The upper bound of the time-delay state disturbance is unknown. And an adaptive law is proposed to estimate the unknown parameter of the disturbance,and the estimated value is used to design a memoryless state observer and controller,which are both independent of time-delay. Based on the Lyapunov-Krasovskii function,it is shown that the observation error can converge asymtotically to zero. Simulation results illustrate the applicability of this method.
2010, 59 (9): 5930-5933. doi: 10.7498/aps.59.5930
The field method and the last multiplier method are general integral methods for solving the differential equations of motion. The two methods are applied to the generalized Birkhoff system,and the complete integrals of the basic partial differential equation are given. Furthermore,the solutions of the generalized Birkhoff equations are obtained by Jacobi last multiplier theorem. An example is given to illustrate the application of the results.
Estimation of unknown parameters and adaptive anti-synchronization of quadratic autonomous chaos systems via a scale controller
2010, 59 (9): 5934-5939. doi: 10.7498/aps.59.5934
Based on Lyapunov stability theory,a simple adaptive scalar controller was designed to realize the anti-synchronization of 3-D quadratic autonomous systems with known or unknown parameters. Furthermore,all the unknown parameters can be estimated dynamically from the time series of the drive and response systems. Numerical simulations show the effectiveness and feasibility of the proposed method.
2010, 59 (9): 5940-5948. doi: 10.7498/aps.59.5940
The aim of this paper is to study a chaotic oscillators stability and chaos behavior and to determine the conditions for the stability and chaotic behavior of the chaotic oscillator by theoretical analysis. Furthermore,this study also aims to control the chaotic oscillator by an exact feedback linearization method. Finally,both numerical simulations and circuit experiments verify the validity of the theoretical analysis.
2010, 59 (9): 5949-5953. doi: 10.7498/aps.59.5949
The present paper aims to investigate the phase synchronization in chaotic oscillator networks by using quantitative indexes. We define two new quantitative indexes, namely the mean phase locking value and mean frequency difference of two adjacent nodes of the network. Lorenz chaotic oscillators with several rotational centers are chosen as networks nodes. We convert the original Lorenz system into the dynamics of amplitude and phase. The chaotic oscillator networks are formed via amplitude coupling. We find that for star-coupled network and small-world network the adjacent oscillation phases are locked. Moreover, phase synchronization definitely comes along with the transition of the mean phase locking value and mean frequency difference by increasing the coupling strength.
2010, 59 (9): 5954-5958. doi: 10.7498/aps.59.5954
We present a systematic design procedure to anti-synchronize a class of chaotic systems. An adaptive control method for anti-synchronization of uncertain chaotic system is proposed based on the scheme,by which the uncertain parameters of response system are identified. Numerical simulations show the effectiveness of the developed approache.
2010, 59 (9): 5959-5965. doi: 10.7498/aps.59.5959
Based on the microcontroller (MCU), a universal digital hardware experimental circuit for four-dimensional chaotic system is designed, from which 9×7-grids scroll chaotic and hyperchaotic attractors are generated. Reference  has presented a four-dimensional multi-scroll hyperchaotic system extended from Colpitts oscillator model. In this paper, a new four-dimensional grid-scroll hyperchaotic system is constructed by introducing a unit sawtooth wave function to replace the triangular function in the original system, which is realized by utilizing MCU digital hardware implementation easily. Analysis and numerical simulations are performed for the formation mechanism of grid-scroll attractor in the new system. By using Euler algorithm to discretize the proposed grid-scroll hyperchaotic system, an attractor with more grid-scroll number than that of the original system can be generated in the effective dynamic range of the experimental circuit. Experimental results verified the feasibility of grid-scroll hyperchaotic system based on MCU implementation.
2010, 59 (9): 5966-5971. doi: 10.7498/aps.59.5966
The synchronization of spatiotemporal chaos in a nearest-neighbor coupled network is studied. Spatiotemporal chaos systems are taken as the nodes of the network,and the condition to realize global synchronization of the network is obtained by identifying the maximum Lyapunov exponent of the network according to Lyapunov stability theory. The nearest-neighbor coupled network with nodes of Fisher-Kolmogorov spatiotemporal chaos systems is taken as an example for simulation,the synchronization of spatiotemporal chaos for the network is checked. The synchronizing function of the network under bounded noise is further studied,and the results show that the method has good capability of anti-jamming.
The topological variance of neighborhood of a non-hyperbolic fixed point produced by truncation error
2010, 59 (9): 5972-5978. doi: 10.7498/aps.59.5972
In the paper,a direct evidence for truncation error to complicate a simple system is provided,which proves the existence of anti-degradation mechanism in chaotic systems. Both one-dimensional circular arc iterated system and one-dimensional parabola iterated system are constructed,respectively. In each system,there is a non-hyperbolic fixed point. The corresponding iterative sequences are theoretically proved to be simple convergent sequences. However,there are a lot of iterative sequences that could jump over the fixed point in digital experiments. It is clearly revealed by digital-cell analysis that the topological variance of neighborhood of a non-hyperbolic fixed point is produced by truncation error,either a channel of type-I intermittency or a ripple bifurcation is configured from the fixed point.
2010, 59 (9): 5979-5984. doi: 10.7498/aps.59.5979
The effect of small heterogeneous grains with different features and shapes on the evolution of spiral wave is investigated by using the simple model of discrete excitable medium. When the small grains are uniformly distributed in a medium,the instability of spiral wave relates to the shape,density and nature of the grain. The numerical results show that under suitable conditions,the heterogeneous grains can lead to the transition from stable spiral wave to meandering spiral wave in the medium in which it occurs, the spiral wave even drifts out of the boundary of system. The periodic pattern with irregular shape and the periodic maze-type pattern have been observed for the first time. The physical mechanism underlying these phenomena is discussed.
2010, 59 (9): 5985-5989. doi: 10.7498/aps.59.5985
Chua’s circuits are non-smooth systems. At first,by the generalized Hamiltonian system and observer approach,the problem of the chaotic synchronization of Chua’s circuits with nonlinear control is transformed into that of the stability of zero solution of smooth error systems with nonlinear control. Then,the sliding mode control is applied to the error systems, which stabilizes their zero solutions,and the synchronization conditions are obtained. At last,the numerical results are shown to be in very good agreement with the theoretical analysis.
2010, 59 (9): 5990-5995. doi: 10.7498/aps.59.5990
The traffic flow at the roundabout crossing with the inner roundabout lane and the outer roundabout lane is described by a cellular automaton traffic flow model with open boundary condition. Simulation results show that the boundary condition and bottlenecks affect the traffic flow at the roundabout crossing. The enter probability α and the out probability β can change the systemic flux in a certain range. Three phases of the system are differentiated by the relationship between the systemic flux and the enter probability α,the out probability β. The systemic phase diagram is also studied. The research can provide a reference for the realistic traffic control.
2010, 59 (9): 5996-6002. doi: 10.7498/aps.59.5996
This work studies the crossroad traffic model with low velocity vehicles,wherein the model consists of two one-lane roads. The parallel updating rule without traffic lights is obeyed by all the cars in our model. Based on the principle for constructing phase diagrams and the local occupation probability method,the phase diagrams are constructed,and in every phase diagram,the formulas of current in each region can be obtained. The deterministic FI model with the periodic boundary is applied in our numerical simulations. It turns out that the numerical results are in exact accordance with the theoretical analysis. Besides,the parallel updating rule is more common in the real crossroad traffic and thus our work may be helpful for the study of traffic management.
2010, 59 (9): 6003-6008. doi: 10.7498/aps.59.6003
Based on the properties of the car-following model,we present in this paper a formula of the kinetic energy change and use the formula to study the effect of the lane changing on the kinetic energy of the system. The numerical results show that the lane changing probability and the relative velocity have great effect on the kinetic energy,but the lane changing probability and the relative speed will respectively lessen the frequency and amplitude of the change of the kinetic energy. In addition,the enhanced average kinetic energy of the system will decrease with the increase of its maximum lane changing probability.
2010, 59 (9): 6009-6013. doi: 10.7498/aps.59.6009
In this article,information traffic dynamics in scale-free networks with limited queue resource is investigated firstly. It is found that the network transits from a free flow state to full congestion state with the increase in the packet generation rate. Then,a queue resource allocation model based on node degree is proposed. The core of this model is to make the queue length of node i proportional to kβi (ki being the degree of node i and β being an allocation parameter). Simulations show that the capacity of the scale-free network is maximal when β is about 1.25 for the shortest path algorithm used to transfer information. Furthermore,the optimal value of allocation parameter β is irrelevant to the network size and the amount of queue resource.
2010, 59 (9): 6014-6021. doi: 10.7498/aps.59.6014
A physical and revised mathematical droplet model was proposed for condensation heat transfer process near the cooled solid surface,according to the micro-physical mechanism and thermodynamic characteristics in condensation phase change process. The heat transfer model considering the effect of interfacial effects was used to calculate the temperature of clusters. The mathematical model based on the refined DM homogeneous nucleation model,introducing the wall conditions and making some correlations,was used to calculate the size distribution of clusters,and also describe the effect of the presence of non-condensable gases on the distribution of clusters. The present model explains quantitatively the fact that the presence of small amount of non-condensable gases deteriorate condensation heat transfer performance significantly. The predicted results of the model agree with the experimental results reported in the literature.
The evaluation function of weight similarity and its application in community detection in weighted networks
2010, 59 (9): 6022-6028. doi: 10.7498/aps.59.6022
An evaluation function of weight similarity in weighted network is proposed,and a spectral algorithm for detecting community structure based on the function is presented. The results show that the algorithm can divide the weighted network into several groups within each of them the edges weights distribute uniformly but at random between them. The algorithm is analyzed by constructing random weighted networks with known community structure. Compared with WEO and WGN,the algorithm has high accuracy when the threshold coefficient takes small values. For a network with n nodes and c communities,the computation complexity of the algorithm is O(cn2/2). By setting different threshold coefficients,a special hierarchical organization which describes the various steady connections between nodes in groups can be discovered by the algorithm. It is different from the conventional concept of community detection in weighted networks which divides the weighted network into several groups in which the edges weights are relatively larger than those in-between them,such that it extracts the information about the structure of weighted networks from another perspective.
2010, 59 (9): 6029-6035. doi: 10.7498/aps.59.6029
To meet the need of Beijing Synchrotron Radiation Facility (BSRF) in two-dimensional detectors, a two-dimensional position sensitive X-ray gas electron multiplier(GEM)detector based on PCB strips and anolog readout were designed and constructed. Through the test of two kinds of strip pitchs and based on the system of multi-channel charge sensitive preamplifier and VME buffer-ADC, the spatial resolution of soft X-ray was measured and pretty good spatial resolutions of about 84 μm and 75μm respectively were obtained. The effect of the sum of the voltages applied on the three GEM foils on the spatial resolution was studied and position veracity and linearity of GEM was tested. The principles of GEM based on anode readout and the anolog electronic system were clarified meanwhile.
ATOMIC AND MOLECULAR PHYSICS
2010, 59 (9): 6036-6043. doi: 10.7498/aps.59.6036
In the frame work of multi-channel quantum defect theory, the energy levels of three autoionization Rydberg series converging to Sc+ 3d4s(1D2) with Jπ=(3/2)-,(5/2)- are calculated from first principles by relativistic multi-channel theory at two levels of approximation, i.e., frozen core approximation and that with consideration of dipole polarization. Considering dipole polarization effect, the difference between calculated and experimental quantum defects for the 3d4s(1D2)np2D3/2 and 3d4s(1D2)nf2F5/2 series are smaller than 0.01, thus the dipole polarization effects are important for the two autoionization Rydberg series. While for 3d4s(1D2)nf2D3/2 series, the calculated data by frozen core approximation are close to those by considering dipole polarization effects, and the difference between calculated and experimental quantum defects are generally about 0.04.
2010, 59 (9): 6044-6051. doi: 10.7498/aps.59.6044
We studied the dielectronic recombination processe of Ni17+(3s) through the resonant doubly excited states Ni16+(3pnl,3dnl) (Δn=0) using the Flexible Atomic Code (FAC) which is based on a relativistic configuration interaction method. We obtained the cross sections and the rate coefficients and compared them with the experimental data and other theoretical results. The integrated cross sections through the resonant doubly excited states 3p3/210l and 3p1/211l are in a good agreement with the measurements within the experimental errors. In combination with quantum defect theory, we have found out that the radiative rates and the auger rates of the resonant doubly excited states involving high Rydberg states obey a good scaling law, by means of which we obtained the integrated cross sections and the rate coefficients of all the resonances close to the thresholds. A comparison of the series 3pnl and 3dnl indicates that the rate coefficients of the former are larger when the temperature is below ~100 eV, and are smaller when the temperature is higher.
The comparison of temporal bond polarizabilities of the nonresonant Raman excited virtual state of ethylene thiourea by two different algorithms
2010, 59 (9): 6052-6058. doi: 10.7498/aps.59.6052
We studied the temporal bond polarizabilities of ethylene thiourea (ETU) from the Raman intensities by two different algorithms. One algorithm includes only the bond stretching modes and the other includes all bond modes. Our analysis shows that, the algorithm using bond stretching modes, in which only the part of Raman peaks whose vibrational modes have relatively larger proportion in the bond stretching are considered, may have larger errors in certain situations where the stretching and bending modes have significant coupling. Otherwise, this algorithm is just suitable, although it may lose certain physical information. The bond polarizabilities provide much information concerning the electronic distribution of nonresonant Raman excited virtual state. At the initial moment of the 514.5 nm excitation, the tendency of the excited electrons is to spread to the molecular periphery. Meanwhile, the relaxation process of the bond polarizability and the characteristic times for these two models are almost the same.
2010, 59 (9): 6059-6063. doi: 10.7498/aps.59.6059
We studied the characteristic X-ray spectra produced by the interaction of highly charged ions of 129Xeq+(q=25,26,27)with surface of metallic Mo. The experimental result shows that highly charged ions can excite the characteristic X-ray spectra of L-shell of Mo when the beam’s intensity is not more than 120 nA. The X-ray yield of single ion reaches a quantitative level of 10-8 and increases with the increment of the ion’s kinetic energy and ionic charge (potential energy). By measuring the X-ray spectra of Mo-Lα1, the M-level lifetime of Mo atom is estimated by using Heisenberg uncertainty relation.
2010, 59 (9): 6064-6070. doi: 10.7498/aps.59.6064
The K X-rays emitted from the incident slow highly charged Ar17+ ions are investigated in the interaction with various metal target such as Be, Al, Ni, Mo and Au. The Kβ/Kα ratios and the mean energies of the emitted X-rays are extracted and analyzed from our previous experimental results . It is found that the ratios and the energies are almost independent of the ion velocity and the target element. Meanwhile, a model based on the conductive-electron capture and the cascading de-excitation model is proposed to interpret the experiment. Excellent agreement is found between the theoretical results and the experimental data.
CLASSICAL AREA OF PHENOMENOLOGY
2010, 59 (9): 6071-6077. doi: 10.7498/aps.59.6071
Arbitrary three-dimensional axiolitic cloaks are proposed and designed based on the coordinate transformation theory. The general expressions of constitutive tensors of the cloak are derived, and then some full-wave simulations of the cloaks based on the constitutive tensors that we derived are performed. The results of full-wave simulations validate the general expressions of constitutive tensors of the three-dimensional axiolitic cloaks.
2010, 59 (9): 6078-6083. doi: 10.7498/aps.59.6078
Based on the electromagnetic resonant characteristic of the metallic dendritic cells, we present a metamaterial absorber (MA) composed of periodic array of double dendritic cells. The unit cell of the absorber is composed of two metallic elements on the substrate, a two-level dendritic cell and a three-level dendritic cell are located on each side separately. Designing different impedance matching conditions, the effect of impedance matching on the absorptivity is found. The experimental results show that a maximum absorptivity of 90% can only occur when the MA layer is impedance-matched to free space. At the same time, increasing the number of MA layers can effectively enhance the absorptivity. For 3 layers, the absorptivity above 99% can be obtained, that is to say, a perfect MA is realized in the engineering sense.
2010, 59 (9): 6084-6088. doi: 10.7498/aps.59.6084
We studied the basic resonance structure of split ring resonator (SRR) and wire array at microwave X-band numerically. With proper design of parameters, this structure could achieve the absorptivity as high as 98% near the frequency of 10.91 GHz, and the FWHM of which is greater than 3.5 GHz. The scattering parameter retrieval method is employed to calculate the effective electromagnetic parameters. It is found that, close to the resonance frequency, the real components of the effective permittivity, permeability, and refractive index are all negative. However, the imaginary components of the electromagnetic parameters seem to be very large in the resonance region, which is the main reason of the high absorptivity. The broadband lefthanded metamaterial absorber presented in this paper has potential applications such as in electromagnetic heating and electromagnetic hiding.
A novel finite-difference time-domain scheme for electromagnetic scattering by stratified anisotropic plasma under oblique incidence condition
2010, 59 (9): 6089-6095. doi: 10.7498/aps.59.6089
A novel finite-difference time-domain(FDTD) implementation, by which electromagnetic(EM) wave scattering characteristic can be analyzed for oblique incidence on stratified anisotropic plasma, is proposed. This method transforms two-dimensional electromagnetic wave scattering question to one-dimensional question, and avoids two-dimensional scattering problem by 2D FDTD method, by which the computational efficiency can be greatly improved. FDTD iterative formula of EM scattering by layered anisotropic plasma are deduced in the TEz and TMz wave oblique incidence situations, and the connection boundary(CB) and the absorbing boundary condition (ABC) in the oblique incidence situation are carried out the revision. The EM wave reflection coeffientes of the anisotropic plasma slab are calculated in the oblique incidence situation by the method. The computed results and the analytic solutions are in good agreement. The results show the accuracy and validity of the method. Finally, the algorithm is applied to calculate the reflection coefficients of the metal plate coated with the stratified anisotropic plasma under different incidence angles. The numerical results show the incidence angle have a great impact on the reflection coefficients.
2010, 59 (9): 6096-6100. doi: 10.7498/aps.59.6096
Step refractive index axicon for generating bottle beam is proposed for the first time, and the two kinds of models-refractive index step-increase or decrease in radial direction are discussed. The principle of the bottle beam generation is analyzed by geometrical optics. The optical field distribution and 2D light spot image at different propagation distance behind the two kinds of axicons are numerically simulated using the diffraction integral theory. Research result shows that the step-decrease refractive index axicon generates single bottle beam, and the step-increase refractive index axicon generates periodic bottle beams. Bottle beam has a wild application in atom guiding and trapping,optical capture and optical tweezers. Research results in this paper give the significant guidance for the practical applications of the bottle beam.
A new method of generating bottle beam was proposed for the first time, which is compriecs a traditional axicon with a ring obstacle at its underside. When a plane wave illuminates the bottom of axicon with ring obstacle, a bottle beam is generated within the maximum non-diffractional distance, and the beam keeps as non-diffractional Bessel beam in front and behind the bottle beam. Controlling the size of bottle beam is realized by changing the size of obstacle or cone angle of axicon. The principle of generating bottle beam when a plane wave illuminates the ring obstacle-axicon was described using the diffraction theory. The transverse intensity distribution of the bottle beam in propagation and the three-dimensional intensity distribution of the whole process were analyzed and simulated, and the experiment results were presented. The result shows significant guidance value for the practical application of the bottle beam.
The tunneling properties of the bilayer structure composed of single negative materials based on transmission lines
2010, 59 (9): 6106-6110. doi: 10.7498/aps.59.6106
Epsilon-negative (ENG) and mu-negative (MNG) materials are fabricated by using transmission line (TL) approach, the electromagnetic tunneling properties of the bilayer structures with ENG-MNG materials are experimentally investigated. The results indicate that the two kinds of single negative materials do not support electromagnetic propagation modes, whereas the completely tunneling phenomenon occurs in the ENG-MNG pairs under special conditions when the average permittivity or average permeability equals zero respectively. Furthermore, the tunneling modes are insensitive to the scale length. Exponential amplification of the evanescent wave is also experimentally observed by simulating and measuring the electric field distributions in ENG-MNG structures at the tunneling frequency.
2010, 59 (9): 6111-6117. doi: 10.7498/aps.59.6111
To explore the applications of carbon nanofibers in passive interference by smoke screen, the integral equation of induced current for carbon nanofibers is established based the electromagnetic field theory. The method of moment (MOM) is used to solve the integral equation. The formulae of scattered field and extinction cross section are derived for carbon nanofibers. By comparing with variational method, our proposed method is proved to be valid. The relationships between infrared extinction cross section of carbon nanofiber and the wavelength, the angle of incidence, the fiber length and diameter are analyzed and calculated.The results provide a theoretical basis for the applicatrion of nanocarbon fiber in infrared smoke interference.
2010, 59 (9): 6118-6124. doi: 10.7498/aps.59.6118
The two-step phase-shifting algorithm proposed previously is optimized, the original object wave field can be reconstructed by only one phase shift value in (0, π) and two interferograms, with the removal (or suppression) of background intensity (or dc term), and the additional measurements such as the object wave intensity, reference wave intensity, etc., are no longer required. Together with double random phase encoding technique in the Fresnel domain, the optimized two-step phase-shifting algorithm is then applied to image encryption system. The feasibility of the proposed scheme is verified by computer simulation. Furthermore, the sensitivity of geometrical keys has also been tested and analyzed.
2010, 59 (9): 6125-6130. doi: 10.7498/aps.59.6125
When a radially-polarized beam passes through a wave plate, the polarization distribution of the beam strongly depends on the retardation angle and the spatial position. When the retardation angle is changed from 0 to π, the polarization of the beam becomes the local elliptic polarization with non-uniform polarization distribution. The rotating direction of polarization in the first and third quadrants is opposite to that in the second and fourth quadrants. In this paper we have numerically simulated the transverse and longitudinal electric field intensity, the transverse energy flux and the longitudinal angular momentum of the tightly focused beam in the focal plane. Our results show that the sum of the longitudinal angular momentum in the focal plane is zero, but it is varying in different quadrants. The liquid crystal variable retarder (LCVR) is adopted as a real-time continuous tunable wave plate with its retardation angle δ changing from 0 to π by varying the applied voltage. In this case the phase retardation angle δ introduced by the LCVR can be used as a control over the longitudinal electric field intensity and the longitudinal angular momentum.
The data processing method of the temporarily and spatially mixed modulated polarization interference imaging spectrometer
2010, 59 (9): 6131-6137. doi: 10.7498/aps.59.6131
A new method of the interferogram formation,recording and processing is proposed for the polarization interference imaging spectrometer. According to the regularities of the optical path difference distribution on the detector, the wide-field-of-view polarization interference imaging spectrometer (WPIIS) is proved to be much suitable for working under temporally and spatially mixed model. In addition, the originally experimental interferogram obtained by WPIIS is processed in this new way, the satisfactory result of interference data and reconstructed spectrum proved that the method is exact and useful.
Investigation on all-optical regeneration of asynchronous dual-wavelength signals based on fiber-optic parametric amplification
2010, 59 (9): 6138-6144. doi: 10.7498/aps.59.6138
With the continued development of the wavelength division multiplexing (WDM) network, there arises an urgent demand for the research of multi-wavelength all-optical 3R regeneration. In this paper, a novel multi-wavelength all-optical regeneration scheme has been proposed. Using phase clock in the fiber-optic parametric amplification and polarization multiplexing, all-optical regeneration of dual-wavelength signals generated by two independent WDM transmitter is realized. Theoretical analysis is carried out for the operation mechanism of the amplitude noise suppression using the gain saturation of the parametric amplification, and re-timing using phase modulation with cascading dispersion. Dual-wavelength 10 Gbit/s signal optical regeneration is demonstrated experimentally. Experimental results show that the inter-channel nonlinearities like four-wave mixing and cross phase modulation are effectively reduced. In the single and dual-wavelength cases, signal to noise ratio improvements of at least 6.5 dB and 4.5 dB have been achieved, respectively, after regeneration. Bit error rate test shows that about 2 dB power penalty improvement is obtained in both single- and dual-wavelength operations.
Correction method for phase-modulation deviation of liquid crystal spatial light modulator in full-color holographic display
2010, 59 (9): 6145-6151. doi: 10.7498/aps.59.6145
It is feasible to realize full-color holographic display based on liquid crystal spatial light modulator by use of multi-wavelength illumination combined with time division multiplexing (TDM) or space division multiplexing (SDM). However, the modulation characteristics of liquid crystal spatial light modulator (LC-SLM) vary with the wavelength of incident laser beam. Especially, the non-linearity and the modulation-depth mismatch of phase modulation curve are the important factors influencing the reconstruction quality of phase hologram in full-color holographic display. In order to solve this problem, a novel method is proposed to correct the gray-scale of phase holograms in the RGB channels with the established gray-mapping model according to the phase modulation curves measured under different wavelengths, and compensate the effects of non-linearity and the modulation-depth mismatch of phase modulation curves. Analysis of numerical and optical reconstruction results are carried out. It is verified that the method is effective to improve the qualities of reconstructed images in the RGB channels.
Nonclassical properties in the resonant interaction of a three level Λ-type atom with pair coherent states
2010, 59 (9): 6152-6158. doi: 10.7498/aps.59.6152
This paper is concentrated on the nonclassical properties of the pair coherent states during the interaction with a three-level Λ-type atom, such as antibunching effect, violation of Cauchy-Schwarz inequality and two-mode squeezing. Meanwhile, we find these nonclassical properties can be enhanced in the case that the atom is selectively measured.
2010, 59 (9): 6159-6163. doi: 10.7498/aps.59.6159
We describe the high order elliptic hermite gaussian beam and the average orbital angular momentum of single-photon, and analyze some situations of the change of orbital angular momentum, briefly by the simulation. Finally, the probability distribution and changes in the probability distribution within the range of space for the single-photon orbital angular momentum are analyzed. The results show that the change magnitude of the single-photons average orbital angular momentum varies with the material when the high order elliptic Hermite-Gaussian beam interacts with mater.
2010, 59 (9): 6164-6171. doi: 10.7498/aps.59.6164
One-dimensional photon counting detector with vernier position sensitive anode is reported. The decode principle and design of vernier position sensitive anode are described in detail. An ultraviolet photon counting system was built based on one-dimensional photon counting detector with vernier position sensitive anode. One-dimensional coordinates of single-photon events can be simultaneously measured when the detection system works in photon counting mode. The spatial distribution of pulse counts, which corresponds to one-dimensional spatial distribution of incident light intensity, was obtained. The resolution of this system is better than 100 mμ according to the resolution test. The detector can detect one-dimensional spatial distribution of the intensity of very weak particle flow such as high-energy photons, electrons and ions flow, so it can be used for deep space exploration, spectral measurement, high-energy physics and bio-luminescence detection.
Entanglement between a two-level atom and spontaneous emission field in anisotropic photonic crystal
2010, 59 (9): 6172-6177. doi: 10.7498/aps.59.6172
By means of Von Neumann entropy and Schmidt number K, we study the time evolution properties of the entanglement between a two-level atom and spontaneous emission field in anisotropic photonic crystal. The evolution properties of the atom-field entanglement are directly related to the relative position of the upper level from the band edge. The atom-field entanglement can keep steady when the atomic upper level is within the band gap. The atom-field entanglement increases to the maximum value firstly and then decay to zero when the atomic upper level is within the transmitting band. The atom-field entanglement also depends on the initial state of the atom. We can control the time evolution properties of the atom-field entanglement by choosing special atomic initial state and the relative position of the upper level from the band edge.
Influence of Kerr-effect on the quantum interference of the cavity field spectrum within two mode binomial initial field
2010, 59 (9): 6178-6184. doi: 10.7498/aps.59.6178
The cavity field spectrum of the nondegenerate two-photon Jayners-Cummings model with an additional Kerr medium is investigated. The results for the initial fields in binomial states are presented. The influence of the Kerr effect on the quantum interference of the two mode cavity field spectra is discussed. It is found that the quantum interference item shows a periodical damped oscillation irregularly when the Kerr effect is increased. The amplitude of the oscillation relate to the difference of the two field frequencies intimately. When the Kerr coefficient χg (g is coupling coefficient between atom and the fields), the change of the quantum interference item is strong with χ. And when χ>g, it is weakly. The cavity field spectra usually take on a complex asymmetric structure with many peaks when Kerr coefficient is large.
Theoretical investigation of infrared generation mechanism by quantum coherence in low-dimensional semiconductor heterostructures
2010, 59 (9): 6185-6192. doi: 10.7498/aps.59.6185
We present an infrared generation mechanism without population inversion between subbands in quantum well and quantum dot lasers. The infrared generation scheme is based on the resonant nonlinear mixing of the two optical laser fields. These two optical fields come from two interband transitions in the same active region and serve as the coherent drive for infrared field. This mechanism of frequency down conversion should work efficiently at room temperature with injection current pumping, not relying on any ad hoc assumptions of long-lived coherence in the semiconductor active medium. Under optimized waveguide and cavity parameters, the intrinsic down-conversion efficiency can reach the limiting quantum value corresponding to one infrared photon generated by one optical photon. Because the proposed infrared generation is parametric, the proposed scheme without population inversion is especially promising for long-wavelength infrared operation.
2010, 59 (9): 6193-6199. doi: 10.7498/aps.59.6193
An InGaAsP-InP transistor laser (TL) working at 1.5 μm and its epitaxy structure with MQW active layer buried between unsymmetrical upper and lower waveguides in base region has been designed and modeled. The simulation result shows that the proposed TL has good optical and lateral electrical current confinement. The result of epitaxial experiment by metalorganic chemical vapor deposition (MOCVD) shows that the diffusion of doped Zn2+ from heavily doped base contactor layer to active waveguide can induce serious degradation of quantum wells. By modeling the Zn2+ diffusion from heavily doped base contactor layer, a gradient doping profile with an average doping density of 1 ( 1018 cm-3 in the base contact layer has been used in the epitaxy process to constrain the Zn2+ diffusion to quantum wells. The test result of the epitaxy material has demonstrated high PL intensity at 1.51 μm and clear satellite diffraction peaks in the XRD spectrum.
2010, 59 (9): 6200-6204. doi: 10.7498/aps.59.6200
We have employed a nonlinear polarization rotation technique to realize the self-starting passive mode-locking in an erbium-doped fiber laser with positive dispersion. The laser can emit high-energy dissipative solitons without wave-breaking. The pulse-shaping mechanism, which is qualitatively distinct from the conservative solitons in negative dispersion cavity, may originate from the laser gain, loss, NPR, cavity dispersion, or other fiber nonlinearity effects. To our best knowledge, it is the first report on the experimental observations for high-energy wave-breaking-free dissipative solitons forming in a fiber laser with ultra-large net-normal cavity dispersion. The spectrum of these strongly chirped pulses covers the wavelength range from 1530 to 1660 nm. The FWHM width of the spectrum can be as large as 42 nm, and the maximal total energy of a single-pulse is estimated to be ~34.4 nJ.
Theoretical investigation of mode coupling to a microdisk system containing a three-level quantum-dot
2010, 59 (9): 6205-6212. doi: 10.7498/aps.59.6205
A full quantum mechanical approach is extended to a coupled waveguide-ring resonator interacting with a three-level quantum dot (QD). The transmission and reflection amplitudes, as well as the resonator and the QD responses, are solved exactly via a real-space approach, which shows the single-photon transport properties. One feature of the system is the coupling between the two degenerate whispering- gallery modes (WGMs) of the resonator at rate β due to backscattering caused by surface roughness of the cavity. Another feature is describing the coupling between QD and the cavity by two parameters g1 and g2. From the analytic numerical results we can see the difference from two-level system.It may better interpret the experiment of a quantum dot strongly coupled to WGMs in a cavity.
Nanosecond non-diffracting Bessel green beam generated directly from an unstable resonator by active method
2010, 59 (9): 6213-6218. doi: 10.7498/aps.59.6213
An intracavity frequency-doubled Nd∶YAG nanosecond Bessel green laser is designed in an axicon-based Bessel and Bessel-Gaussian resonator. The unstable laser resonator is composed of a refraction axicon and a convex mirror. The gain medium Nd∶YAG rod is pumped by a single flash-lamp which is working in a pulsed mode and a KTP crystal is used for intracavity second-harmonic generation. Nanosecond Bessel green beam is generated directly from the laser by active method when pumping voltage is 350 V. The pulse with width of 55.1 ns, central wavelength at 532 nm, spectral line width of 0.8 nm and diameter of central spot of 192 μm is obtained. Fresnel-Kirchhoff diffraction integral and the Fox-Li algorithm is used to extract the dominant mode of the cavity and the experimental results are consistent with those of the numerical simulation.
2010, 59 (9): 6219-6223. doi: 10.7498/aps.59.6219
The experiment for measuring Brillouin shift of optical fiber was set up. The Brillouin shift of a dispersion-shifted fiber was experimentally investigated in the range of 20 to 820 ℃, and the data was fitted. When the environment temperature changes in a wide range, the measured data when fitted by a linear relation, will bring about large errors. We set out our study on the basis of the structure and material properties of fused silica, including the thermal expansion coefficient, the density, the refractive index, the Young’s modulus, and the Poisson’s ratio. The mathematical model for the temperature dependence of each of the parameters was built up. Based on the relationships between Brillouin shift and the material properties, the Brillouin shift has been formulated as a second-order polynomial of temperature over a wide temperature range. Compared with our experimental results, the theoretical results are in good agreement, which lays a foundation for the wide-range Brillouin distributed temperature sensor.
The study of spatiotemporal perturbation in the nonlinear propagation of broadband chirped pulsed laser
2010, 59 (9): 6224-6230. doi: 10.7498/aps.59.6224
In the paper, we extended the propagation equation of the large chirped pulse based on the nonlinear Schrodinger equation, and then analyzed the spatiotemporal instability of chirped pulsed-beam by using the perturbation theory. The influence of the spatiotemporal noise and the effect of chirp on the perturbation modulation of noise of the broadband pulsed-laser with large chirp were investigated theoretically. The results showed that the chirp of pulse has no direct influence on the modulation growth of noise under the same value of γI0(the product of the nonlinear coefficient and the peak intensity). Then the spatial small-scale self-focusing of chirped pulse was measured in experiment using nonlinear medium, and the modulation growth of the temporal noise of the broadband chirped pulse were also simulated numerically, and the result was basically consistent with the analysis of perturbation theory.
Photon statistics of squeezed vacuum field from optical parametric oscillator far below the threshold
2010, 59 (9): 6231-6236. doi: 10.7498/aps.59.6231
Photon statistics of the weak squeezed vacuum field from an optical parametric oscillatior (OPO) is investigated both in theory and by experiment . The strong photon bunching effect of weak squeezed vacuum field, which can be used as an important source in quantum optics and quantum measurement, was demonstrated. We have experimentally produced the weak squeezed vacuum at the center wavelength of D2 line of the cesium atom by the OPO operating far below the threshold . The second-order correlation function was measured based on the Hanbury-Brown-Twiss scheme, and the result is consistent with theoretical analysis.
Theoretical study of tunable terahertz radiation based on stimulated polariton scattering in zinc blende crystal
2010, 59 (9): 6237-6242. doi: 10.7498/aps.59.6237
Based on the theory of stimulated polariton scattering, adopting reported experimental conditions that generate tuning terahertz wave utilizing nonlinear optical parametric oscillation as the theoretical analysis model,and taking GaAs, GaP, InP, ZnTe crystals as representatives, the absorption and gain characteristics in zinc blende crystal are calculated, and the output tuning characteristics of terahertz wave are also analyzed. We give detailed analysis of the cavity structure that efficiently outputs terahertz wave, and compare it with the terahertz parametric oscillator composed of MgO: LiNbO3 crystal.
2010, 59 (9): 6243-6249. doi: 10.7498/aps.59.6243
First, a frequency doubling model with 4-dimensional temperature-beam coupling was proposed in this paper on the assumption of an infinite transverse crystal section. The frequency doubling process, by using analytical formula and iterative method, was simulated in the BBO crystal pumped by a laser with watt-level power. The amplitudes and conversion efficiencies of the fundamental, and harmonic beams and temperature distributions were obtained, together with the time evolution of temperature field and beam intensities. The influence of the pumping power and crystal length on the conversion efficiency and temperature field was analyzed secondly. The results finally showed that the temperature distribution has great influence on the conversion efficiency and beam quality. A compensation for the phase mismatch induced by temperature can well improve the reduction of conversion efficiency induced by the thermal effect, which thus should be considered in practice.
The relationships study of structure-nonlinear optical property of two-dimensional charge transfer molecules substituted annulenes
2010, 59 (9): 6250-6255. doi: 10.7498/aps.59.6250
The molecular first hyperpolarizabilities β and ultraviolet spectra of two-dimensional charge transfer (2DCT) substituted annulenes by employing MP2 and TD-DFT approach, respectively. It is found that these 2DCT molecules 2—6 possess larger β values and blue-shifted absorption spectra in comparison with 1DCT molecules 8 and 9. It is helpful to solve the nonlinearity-transparency trade-off. For 2DCT molecules 2—7, values of β depend on the band length alternation (BLA) and when the BLA increases, the values of β decrease. Moreover, there is not a relationship between β and HOMO-LUMO energy gap ΔEHL for 2DCT molecules. The maximum absorption wavelength λmax of 2DCT molecules originates from deeper energy level orbital transition than HOMO→LUMO transition.
2010, 59 (9): 6256-6260. doi: 10.7498/aps.59.6256
Tm3+/Ho3+/Yb3+ codoped tellurite glass (TeO2-ZnO-La2O3) was prepared by conventional melt-quenching method. The absorption spectra and upconversion spectra of the glass were measured, and the upconversion luminescence mechanism was analyzed. Intensive red (662 nm), green (546 nm) and blue (480 nm) emissions of the tellurite glass were simultaneously observed at room temperature under 975 nm LD excitation. Upconversion red luminescence are due to the energy transition of Tm3+ ion: 1G4→3F4 and Ho3+ ion: 5F5→5I8, while upconversion green and blue are the results of Ho3+ ion: 5S2→5I8 and Tm3+ ion: 5S2(5F4) →5I8, respectively. With the increasing of Yb3+ content and the pump power, upconversion luminescence are also enhanced. The white light close to the standard white light emission has been obtained by adjusting the concentration of rare earth doping. Our result has practical significance for developing high-quality white LED.
The influence of thermodynamic equilibrium state prior to the phase transition on the alignment of ferroelectric liquid crystal
2010, 59 (9): 6261-6265. doi: 10.7498/aps.59.6261
In this experiment, devices of ferroelectric liquid crystal (FLC) were prepared by selecting ZLI-3654 FLC and SE-3140 alignment material. In order to study the influence of thermodynamic equilibrium state before the phase transition on the alignment of FLC, ten sets of experiments were carried out by changing the cooling rate during phase transition and thermodynamic equilibrium state before the phase transition. From experiments, a conclusion that the thermodynamic equilibrium state prior to chiral nematic-smectic A (N*-SmA) phase transition play an important role in realizing a uniform alignment of FLC devices, was obtained by comparing static contrasts of the devices. The static contrast ratio of our samples reached 620 ∶1 and the thermodynamic equilibrium state before N*-SmA phase transition was conducive to the formation of high contrast ratio FLC devices. The conclusion can provides a theoretical and practical guidance for the fabrication of FLC devices with I←→N*←→SmA←→S*mC←→Cr phase sequence.
2010, 59 (9): 6266-6272. doi: 10.7498/aps.59.6266
In the paper, a holographic storage experiment on laser optically induced light diffraction in acrylamide photopolymer thin film is reported, in which the semiconductor laser of 532nm is used as writing and reading light source, and fuchsin basic is used as sensibilizer. The appearance of diffraction rings can readily be explained as being holographic interference fringes formed by the original laser beam and light scattered from internal or surface inhomogeneities in the unexposed photopolymer. According to phase match condition of degenerate four-wave mixing theory, the diffraction cones of double laser beam holographic writing and single laser beam radiative reading are explained separately. The relationship between angle of incidence and diffraction cone angle is deeply studied by using holographic scattering theory with the help of trigonometric functions.
The design and optimization of high efficiency heterostructure four-wavelength wavelength division multiplexing
2010, 59 (9): 6273-6278. doi: 10.7498/aps.59.6273
A photonic crystal waveguide coupled structure can be constructed by placing two photonic crystal waveguides dosely and parallel to each other. A new type of high efficiency heterostructure four-wavelength wavelength division multiplexing is designed according to the theory of coupling and decoupling. The finite-difference time-domain method is used to simulate the efficiency of the device, and the simulated results show that higher transmittance is achieved by adjusting the refractive index of a row of dielectric rods. We further found that adding three pairs of rods in the incident medium can effectively reduce the reflection of the system to realize the efficient transport for four-wavelength and the transmittance can exceed 90%. The present device not only has a high transmission rate, but also its size is only 36 μm×17 μm and may have potential applications in future photonic integrated circuits.
Effect of defects outside the centre on dispersive properties of photonic band gap guiding photonic crystal fibers
2010, 59 (9): 6279-6283. doi: 10.7498/aps.59.6279
The dispersion properties of optical wave in photonic band gap guiding photonic crystal fibers (PBG-PCF) were analyzed by the finite differential time domain method. The result demonstrates that: the point defects and the dislocation of air holes make the zero-dispersion-point move to the long-wavelength side, but the change of the shape of the air columm makes it move in the opposite direction. All kinds of defects make the dispersion curves flatten.
2010, 59 (9): 6284-6289. doi: 10.7498/aps.59.6284
The compound X-ray refractive lens is a kind of optical components for X-rays focusing and imaging. This paper reports the authors’ research on focusing performance of the compound X-ray refractive lens with fabrication errors. Firstly SEM measurements of the semi-cylindrical PMMA compound X-ray refractive lens fabricated by means of deep X-ray lithography are performed, and accordingly the fabrication errors are measured. Then the theoretical analysis and simulations are done for the focusing performance of the compound X-ray refractive lens with the fabrication errors. Finally, X-ray microbeam experimental system is built on the 4W1A beamline of Beijing Synchrotron Radiation Facility (BSRF) for measuring the focusing performance of the semi-cylindrical PMMA X-ray refractive lenses we fabricated. And the focusing performances of the semi-cylindrical PMMA compound X-ray refractive lenses with and without distinct fabrication errors are measured and analyzed under 8 keV monochromatic X-rays.
2010, 59 (9): 6290-6298. doi: 10.7498/aps.59.6290
Precise physical experiments place strict requirements on target illumination uniformity in inertial confinement fusion. Currently, the main stream of beam smoothing technology adopted in solid-state laser driver is smoothing by spectral dispersion (SSD). The SSD based on wave-guide phase modulator is experimentally studied here. The experimental results indicate that this phase modulator can easily broaden the narrow-band light generated from a DFB laser to 0.1 nm to 1.5 nm bandwidth. The far-field analysis indicates the experimental results are in good accordance with the simulation results. In the meantime, nearfield modulation around 100 μm after the dispersion grating could be smoothed significantly. The research lays experimental basis for the optimization of beam smoothing in high-power laser facility.
2010, 59 (9): 6299-6305. doi: 10.7498/aps.59.6299
We present a method for quickly setting up the complex structure model of photonic crystal fiber (PCF) through directly reading the cross-section of photonic crystal fiber (PCF) by MATLAB, and numerically analyzing the band-gap and the modal field distribution in band-gap PCF (PBG-PCF) by combining plane wave method (PWM) with finite difference frequency domain (FDFD) method. Firstly, the frequency and modal effective index in PBG-PCF can be calculated by using PWM. Then, the modal field distribution and others properties of the PBG-PCF can be obtained in certain wavelength and index ranges by using the calculation results above and FDFD method. To validate its applicability, a type of commercial PBG-PCF was discussed and the influences of the structure parameters (crystal lattice structure, "atom" filling fraction, background material index and "atom" index) on the band-gap were systemically analyzed. This analytic method and calculation results may be useful for the design and preparation of the PCF with large band-gap.
2010, 59 (9): 6306-6311. doi: 10.7498/aps.59.6306
An ultraviolet photon counting imaging system based on charge induction readout was built and its structure, working principle and spatial resolution are reported. The single photon stream can be obtained via atmospheric dispersion, some weakeners, and narrow-band optical filters. A photo-electron produced in microchannel plate is multiplied, forming a charge cloud, which is collected on the Ge film and then detected through capacitive coupling by a PSA located a few millimeters behind the Ge film. The signal data from the anode is acquired and processed with software after being transformed, filtered and shaped by a charge-sensitive preamplifier and a main amplifier in sequence. Finally, a 30-minute counting image is obtained. The resolution of this system can reach 150 micrometers as tested with the resolution board, and the influence of Ge film resistivity and its substrate thickness on the performance of this system is also analyzed. The system is beneficial in good imaging properties and time resolution to bioluminescence, astronomy and nuclear radiant detection.
2010, 59 (9): 6312-6318. doi: 10.7498/aps.59.6312
We numerically demonstrate a kind of tapered hollow silver waveguide for optically guiding and focusing of light through finite-difference time-domain (FDTD) simulations. The results of numerical simulation reveal that the tapered hollow silver waveguide can efficiently guide and focus a laser light to a tiny, highly localized beam spot of 1 μm diameter. The physical mechanism of the cone-focused laser light is explored. The influence of incident angle and waveguide geometry on the focusing properties is also discussed. The results obtained here might have important reference value for applications in tapered optics, and designing the optimum cone shape for fast ignition and generating high energy charged particles.
Based on the earth-mine resonance model, a model combining resonance and anti-resonance was presented for acoustic mines detection. Considering the high compliance and low-frequency acoustics characters, a landmine and the earth on top of it were respectively equivalent to a spring and a mass, resulting in a mass-spring system. The model’s resonance and anti-resonance mechanisms were discussed by means of frequency response function. The experimental results showed that the vibration velocity ratios of the ground surface with and without mine buried under it show alternate maximum and minimum frequencies with the ratios greater than 1, and less than 1 respectively. The results consisted with the theoretical prediction and indicated that the earth-mine system’s resonance and anti-resonance mechanisms exist concurrently, which can be used to further study of the acoustic mine imaging.
Variational principle and its boundary and additional boundary conditions for inverse shape design problem of heat conduction
2010, 59 (9): 6326-6330. doi: 10.7498/aps.59.6326
Based on variable domain variational principle (VP), the variational theory of inverse shape design of heat conduction together with the boundary and the additional boundary conditions enforced on the unknown surface which must be satisfied by the problem is established. Incorporating the boundary and additional conditions into the functional makes the mathematic formulation very concise and compact. Through the established VP, both the temperature field and unknown boundary shape can be determined in a coupled way. The numerical method of the variational principle combined with finite element method is presented in the paper.
2010, 59 (9): 6331-6338. doi: 10.7498/aps.59.6331
The present study systematically investigates by experiment the influence of Reynolds number (Re) on a turbulent jet issuing from a smoothly-contracting round nozzle. Measurements were performed for seven Reynolds numbers varying from Re = 4,050 to Re = 20,100 using single hot-wire anemometry and over an axial distance of 30 nozzle exit diameters. Although all the exit velocity profiles are of "top-hat" shape, these measurements reveal significant dependence on Re of the exit and downstream flows. The effect of Re on both the mean and turbulent fields is substantial for Re ＜ 10,000 and becomes weak beyond Re = 10,000. The length of the jet’s potential core and the far-field rates of decay and spread all depend significantly on Re.
2010, 59 (9): 6339-6344. doi: 10.7498/aps.59.6339
The deep-sea area east of Dongsha Island is chosen as the research area. The relationship between dispersion and nonlinearity is studied using nonlinear Schrödinger equation which describes deep-sea internal waves in conjuction with the idea of chirps, then the propagation of internal waves in deep sea is simulated. The numerical simulation results are found to be in good agreement with the internal wave MODIS images, which validates the rationality of simulating internal wave propagation in deep sea using nonlinear Schrödinger equation.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2010, 59 (9): 6345-6350. doi: 10.7498/aps.59.6345
The electrical and dielectric properties of a commercial ZnO-based varistor ceramics were measured in the process of 8/20 μs impulse current degradation up to 5000 times of impulses. The characteristics of U-I in the region of low current and the loss tangent were mainly investigated. It was found that the varistor voltage U1mA will first increase rapidly with impulse times increasing, and then remain stable and finally decrease sharply. Furthermore, a new loss peak emerges at -100℃ in the dielectric spectra after 600 times of impulse degradation, which suggests a new trapping behavior introduced in the degradation process. Activation energy of the new peak first decreases, then becomes independent on impulse times. It was also found that the non-linear coefficient was more sensitive to the degradation process than varistor voltage U1mA. These phenomena have not been reported before, which revealed that the variation of the neutral Fermi level between positive bias Schottky barrier region and reverse bias Schottky barrier region is the origin which leads to the degradation of electrical properties.
2010, 59 (9): 6351-6361. doi: 10.7498/aps.59.6351
The dynamics of ablated plasma of wire-array Z-pinches are studied numerically in (r, θ) geometry by using 2D MHD simulation model, in which plausible mass injection boundary conditions are incorporated, and 2D spatio-temporal distribution of plasma parameters and magnetic field are obtained. The ablated-plasma dynamics involves 4 stages: drifting towards the axis, arriving at the axis and forming the precursor column, contraction and expansion of the precursor column, which is essentially reasonable. The relationships between the ablation velocity, the ratio of ablated plasmas to the total wire-array mass and the initial array load parameters are analyzed, and the results are in reasonablly good agreement with the experiment. The effects of the initial inter-wire separation on the structure of magnetic field are investigated and the results can give valuable suggestions to designing the wire array Z-pinch loads.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Molecular dynamical investigation on plastic behavior of Cu(100) twist-grain boundary under shear load
2010, 59 (9): 6362-6368. doi: 10.7498/aps.59.6362
By using molecular dynamics with EAM potential, yield strength of copper column with (100) twist grain boundary and twist grain boundary effect are investigated under shear load. The results reveal that dislocations nucleate at the misfit dislocation network of low-angle twist grain boundary and dislocations stacking influence the yield strength of copper column. For high-angle twist grain boundary, twist grain boundary sliding decreases the yield stress of copper column. Meanwhile it is found that, with increasing twist angle, copper column yielding strength increases firstly. When twist angle reaches the critical value, the yielding strength decreases with increasing twist angle. It is concluded that different mechanisms mediate the yielding of copper column. Dislocation nucleation controls the yield stress of copper column for low-angle twist grain boundary and yielding of copper column is dominated by grain boundary sliding for high-angle twist grain boundary.
Simulation of microstructure of liquid-crystalline polymers in nonhomogenous shear flow by EFG method
2010, 59 (9): 6369-6376. doi: 10.7498/aps.59.6369
Complex microstructures of liquid-crystalline polymers in nonhomogenous shear flow are studied by element free Galerkin (EFG) method based on the micro-macro dualscale model. The dualscale model combines the orientational diffusion equation in microscale with the flow governing equations in macroscale. The EFG method which has the merits of high accuracy and good stability can ensure the reliability of the simulation results. One simple and five composite structures of liquid-crystalline polymers in nonhomogenous shear flow are predicted by studying the influences of Deborah number on microstructures of liquid-crystalline polymers in plane Poiseuille flow. It shows that the instabilities in the transition region of the composite structures can cause some defects.
An atomistic simulation on melting and breaking relaxation characteristics of Ag nanorods at high temperature
2010, 59 (9): 6377-6383. doi: 10.7498/aps.59.6377
Based on the molecular dynamics simulation method, the evolution of Ag nanorods structure during the Ag nanorods relaxation process at various temperatures and lengths are intensively studied. The results show that there is a critical breaking temperature, which is decreasing with the increasing Ag naorods length. The Ag nanorod is melted to a highly disordered spherical cluster when the temperature is between the melting point and the critical breaking temperature. However, the Ag nanorod is melted to two spherical clusters when the temperature is above the critical breaking temperature.The physical mechanics of the structure evolution processe at various temperatures are presented.
The vacancy defect clusters in polycrystalline pure nickle induced by high-current pulsed electron beam
2010, 59 (9): 6384-6389. doi: 10.7498/aps.59.6384
High-current pulsed electron beam (HCPEB) technique is employed to irradiate the samples of polycrystalline pure nickel. The microstructures of the irradiated surface layers are investigated by using transmission electron microscopy (TEM). After HCPEB irradiation, very high value of residual stress is induced in the irradiated surface layer, which leads to the formation of dense dislocation walls and twins. Furthermore, a larger number of vacancy defect clusters including dislocation loops, stacking fault tetrahedra (SFT) and voids are also formed. Among three vacancy defect clusters, the number of SFT is much more than that of two other vacancy defect clusters. The lower dislocation density near the regions with dense SFT is observed and voids are likely to be present in these regions. It suggests that the stress with very high value and strain rate induced by rapid heating and cooling due to HCPEB irradiation could cause the shifting of the whole atomic plane synchronously.
2010, 59 (9): 6390-6393. doi: 10.7498/aps.59.6390
It is very important to consider the distribution of range, range straggling and lateral spread of ions implanted into semiconductor materials in design and fabrication of semiconductor integration devices by ion implantation. Er ions with energy of 400 keV were implanted in 6H-SiC crystal samples under the angles of 0°, 45° and 60°, respectively. The lateral spread of Er ions with dose of 5×1015 cm-2 at energy of 400 keV implanted in 6H-SiC crystal were measured by Rutherford backscattering technique. The measured lateral spread is compared with TRIM98 and SRIM2006 codes prediction. It is seen that the experimental lateral spread well justifies the theoretical values. The value from TRIM98 agrees somewhat better to the experimental data than the value obtained based on SRIM2006.
2010, 59 (9): 6394-6398. doi: 10.7498/aps.59.6394
Shock compression properties of polyethylene (CH2) were studied at SG-Ⅱ laser facility. The experimental results show that the self-emission is high,which emits from the shock-front in polyethylene. And the shock-front propagates through the polyethylene step almost with constant velocity. The Hugoniot equation of state (EOS) of polyethylene was measured by using the impedance-matching method with aluminum as standard material. Pressures are high up to 0.54 TPa in polyethylene, and the relative expanded uncertainties of the measured shockwave velocity are about 2% (K=2). Moreover, the consistency of our data is good, and our data are also consistent with existing experimental data and EOS model.
2010, 59 (9): 6399-6404. doi: 10.7498/aps.59.6399
Variation of graphene Raman G peak splitting due to uniaxial strain and absorption of polyaromatic moleculars on both sides are studied by fifth-nearest neighbor force-constant model. The calculation results show that symmetry lowering is responsible for the G peak splitting, where G peak splits into G+ and G- peaks by lifting the energy degeneracy of in-plane longitudinal and transverse optical phonons at Γ point. Under uniaxial strain, the elongation of C—C bonds reduces the force-constant and softens the in-plane optical phonons which induce red shifts of both G+ and G- peaks. The different strains produced by polyaromatic molecules along its long and short edges lead to red shift and blue shift of the two in-plane optical phonons relevant to G- and G+ peaks, which gives a plausible explanation to the different G peak splitting of the recent Raman experiment on graphene with uniaxial strain and graphene sandwiched by the polyaromatic molecules.
2010, 59 (9): 6405-6411. doi: 10.7498/aps.59.6405
Based on the SSH model, polaron dynamics in a system of highly ordered conjugated polymer chains is investigated, including polaron formation and transport in the presence of an external electric field. It is found that, beyond a certain strength of the interchain coupling, the injected electron will induce a two-dimensional delocalized polaron state, expanding over several chains. Dynamical simulations suggest that, under the same electric field, two-dimensional interchain delocalized polarons move faster than intrachain localized polarons, as suggested by earlier experiments.
2010, 59 (9): 6412-6416. doi: 10.7498/aps.59.6412
The electronic Grüneisen constant γe of Al is measured at room temperature using our homemade ultrafast electron diffraction (UED) equipment. The electronic contribution to the thermal expansion of solid is differentiated from the lattice contribution in the time domain when an Al film is heated rapidly by ultrashort laser pulse. By directly probing the associated thermal expansion in real time at room temperature, we differentiate the two in the time domain, and finally obtain the electronic Grüneisen constant γe. With this new method we overcome the restriction of the traditional low temperature methods in measuring the electronic Grüneisen constant γe of nonmagnetic metals.
2010, 59 (9): 6417-6422. doi: 10.7498/aps.59.6417
Pb(Zr0.3Ti0.7)O3(PZT)thin films have been grown by pulsed laser deposition (PLD) on LaSrAlTaO3 (LSATO),LaAlO3(LAO) and SrTiO3(STO) single crystal vicinal cut substrates. Laser-induced voltage(LIV) effect was also found in PZT thin films grown on the three vicinal cut substrates for the first time. LIV signals increased with the single-pulse laser energy following the linear relation in case of c-axis orientation of thin film; but this linear relation was not followed obviously in case of a-axis orientation of thin film. This result shows that the LIV effect in PZT thin film is the atomic layer thermopile effect, in the which anisotropy of Seebeck coefficient plays an important role. Through realizing impedance-matching of thin films and transmission line, LITV signal response time has been optimized, the time of rising edge dropped from 60 ns to 26 ns, the full width at half maximum dropped from 260 ns to 38 ns.
2010, 59 (9): 6423-6429. doi: 10.7498/aps.59.6423
The dynamics of magneto-optical trap loading by light-induced atom desorption (LIAD) are investigated theoretically and experimentally. The loading of the MOT has been described by a theoretical model. We have paid close attention to the background gases which are essentially important for the ultimate vacuum pressure. The experiment is done based on a glass cell and all the results are well in agreement with the theory. The decay process of the background vacuum pressure caused by the untrapped cesium atoms after shutting off the desorption light is explained quantitatively. The LIAD effect is proved to be an effective tool to control the loading of the MOT and the neutral single atoms in experiment.
2010, 59 (9): 6430-6437. doi: 10.7498/aps.59.6430
The influence of inhomogeneous interaction energy between deposited atoms and substrate atoms on island film growth is investigated by Monte Carlo simulation on a triangular lattice substrate. The Gaussian distribution is employed to describe the inhomogeneity of interaction energy. The results illustrate that the influence of inhomogeneous interaction energy on the growth of thin film is related to the degree of the inhomogeneity and the experimental conditions (such as substrate temperature).At medium temperature the inhomogeneity of interaction energy has notable influence on the island number and the island size. Increasing in temperature could counteract the influence of the inhomogeneity of interaction energy.
2010, 59 (9): 6438-6442. doi: 10.7498/aps.59.6438
Considering that free monatomic chain containing hundreds of atoms has not been prepared so far, an experiment method for preparing monatomic carbon chain from graphene by nano probe is proposed based on classical molecular dynamics simulation. We show that longer monatomic carbon chain can be pulled out from the zigzag edge of graphene by C60 tip with the pulling speed of 1 m/s at room temperature.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2010, 59 (9): 6443-6449. doi: 10.7498/aps.59.6443
The geometry, spin multiplicity, magnetic moment, electronic density of states and the spin density of single-layer trigonal graphene quantum dots with zigzag edges have been systematically investigated using density functional theory with the generalized gradient approximation under different sizes. The calculated results such as lattice constants are in good agreement with experimental data and indicate that the system behaves like metal, while the electrons with up spins occupy the Fermi energy. The influence of quantum size effect is remarkable in the system of small size. It is also found that the sp2 hybridization and nonbonding electrons play an important part in the single-layer trigonal graphene quantum dots, just like in graphene. The spin multiplicity and magnetic moment of the system increase with the increase of the system size. Based on our calculation, the total magnetic moment of the system mainly comes from the nonbonding electrons on the 2p orbital of the zigzag boundary. Our calculation may be helpful in designing devices based on trigonal graphene quantum dots.
2010, 59 (9): 6450-6456. doi: 10.7498/aps.59.6450
The geometry structure, electronic structure, total energy, Mulliken changes of He atom in the Al octahedral site and tetrahedral site were studied by first-principle plane-wave pseudopotential method and GGA. The calculation results indicated that the crystal lattice of Al was changed when He atom enter to the interstitial of Al, but the total results are the change of crystal lattice in octahedral site smaller than tetrahedral site. For Al system, the impurity formation energies of helium atom are 1.3367 and 2.4411 eV in the octahedral site and tetrahedral site, respectively. It is found that for He atom the best stable state is octahedral of Al. At the same time, the site occupancy and its effect of He atom in crystal cell was analysis in this article, and the effects of helium atom in Al system on band structure and density of states and valence electron density are discussed.
2010, 59 (9): 6457-6465. doi: 10.7498/aps.59.6457
Based on the density functional theory,the structure of pure ZnO and N, Li, and Li-N codoped wurtzite ZnO has been investigated by using first-principle plane wave ultrasoft pseudopotential method. The band structure, total density of states, partial density of states, and the number of charge population of pure ZnO and N, Li, Li-N codoped wurtzite ZnO were studied. The calculated results show that Li-N codoped wurtzite ZnO is more in favor of the formation of p-type ZnO.
2010, 59 (9): 6466-6472. doi: 10.7498/aps.59.6466
The electronic structures and optical properties of pure and Ga-doped wurtzite ZnO are studied by using first-principles plane wave pseudopotential method based on the density functional theory. The bonding of ZnO and changes in density of states are analyzed using of the crystal ligand field theory. Electron concentration is 2.42×1021 cm-3 by calculation, and carrier concentration of ZnO is raised 104 fold by doping Ga. Analysis of dielectric function, refractive index, absorption spectrum and reflectance spectrum of pure and Ga-doped ZnO shows that the optical absorption edge moving to high energy leads optical gap to broaden. In the visible light region, optical absorption coefficient and reflectivity are reduced and optical transmittance is increased significantly. Optical properties of ZnO are improved effectively by Ga doping.
2010, 59 (9): 6473-6479. doi: 10.7498/aps.59.6473
The effects of vacant, O defects and As doping on the structures and properties of Ge nanocrystals (Ge-ncs) are investigated by using first-principles calculation based on the density functional theory (DFT). The calculation results indicate that the O defects induced by thermal annealing cannot compensate for the defects caused by neutron irradiation in Ge nanocrystals, while the introduction of As produced by neutron transmutation doping (NTD) will do the jop. We also show that the strong attraction between O and Ge atoms inhibits the formation of vacant defects in Ge nanocrystals, and further improve the luminescent property of Ge-SiO2 system. This suggests that it is necessary to perform thermal annealing for Ge-ncs structures before NTD. Our calculations well support our previous experimental results.
2010, 59 (9): 6480-6486. doi: 10.7498/aps.59.6480
The first principle methods have been used to investigate the electronic structure and thermal property of VO2 in rutile or monoclinic phase. The strong electronic correlation of V(3d) was described by the local density plus Hubbard U approximation, and the phonon density of states of the two phases were calculated by using perturbation density function theory. Our calculated results showed that the energy level of x2-y2 orbital of V(3d) exhibits an separation in the electronic density of stats when VO2 transfer from metallic states to insulator state. The calculated equation of states of VO2 at zero temperature discovered a pressure-induced M—I phase transition at 68 GPa. The pressure-induced M—I phase transition can be due to the strong correlation between V(3d, 3s) and O(2p) orbital. Furthermore, based on the Gibbs free energy, we found that the temperature-induced phase transition is at 375 K. This is in agreement with the experimental result.
2010, 59 (9): 6487-6493. doi: 10.7498/aps.59.6487
Based on the collinear and non-collinear magnetic structures, the ground state, magnetism and electronic structure of the frustrated triangular antiferromagnet AgCrO2 have been investigated using the density functional theory (DFT) within the generalized gradient approximation (GGA) with the projected augmented wave (PAW) method. Detailed magnetic structure has been elucidated vividly from the theoretical view. The calculations show that AgCrO2 magnetic ground state has 120° helical-spin order with its spiral plane parallel to the (110)or (11-0) plane. Due to the strong intra- and interlayer geometric spin frustration, parallel helical-spin chains arise along the a,b or a+b direction with the screw-rotation angle 120°. From the non-collinear electronic structure calculation, it is found that due to the spin frustration Cr-3d orbital states near the Fermi level become more localized, indicating an enhanced interaction between Cr-Cr. Nevertheless, the spin-orbit coupling has weak influence on the electron structure.
2010, 59 (9): 6494-6500. doi: 10.7498/aps.59.6494
The structure and magnetic properties of the Eu1-xSrxMnO3 (ESMO x=0—1) system have been systematically studied. The results indicate that the substitution of Sr for Eu can greatly change the magnetic properties of antiferromagnetic EuMnO3 matrix. In the case of high doping compounds (Eu0.4Sr0.6MnO3 and Eu0.3Sr0.7MnO3), the abnormal magnetic and electrical properties result from the competition between their being ferromagnetic and antiferromagnetic. At low temperature, the conducting behavior of the Eu0.4Sr0.6MnO3 and Eu0.3Sr0.7MnO3 are well fitted by the Mott variable range hopping (VRH) model.
Theoretical study of local structure and ground-state splitting of Cs2NaMF6(M=Al, Ga):Cr3+ complex molecule systems
2010, 59 (9): 6501-6507. doi: 10.7498/aps.59.6501
Based on the two spin orbit coupling parameter model and the complete energy matrices for a d3 configuration ion in a trigonal ligand field, the local structure and the ground-state splitting of Cr3+ ion in Cs2NaMF6(M=Al, Ga):Cr3+ systems have been studied. By simulating the EPR parameter D and the optical spectra, the distorted angles of two inequivalent sites formed by Cr3+ replacing M3+ are determined and the obvious difference of the distorted angles Δθ calculated by using two spin orbit coupling parameter model and single spin orbit coupling parameter model is found. Our results indicate that the influence of ligand F- can not be ignored with respect to spin orbit coupling mechanism when the energy level fine structure and local structure distortion of fluoride complex molecules are studied. Meanwhile, the dependence of EPR parameter D on angle θ, average parameter ζ1 and divergent parameter ζ2 is discussed, respectively.
Significant influence of isothermal crystallization conditions on charge stability of fluorinated cellular polypropylene films
2010, 59 (9): 6508-6513. doi: 10.7498/aps.59.6508
On the basis of the measurement of open-circuit thermally stimulated discharge current and isothermal charge decay, the influence of isothermal crystallization conditions on charge stability of fluorinated cellular polypropylene (PP) film was systematically investigated. The results indicate that the time and temperature of isothermal crystallization of the fluorinated PP film have significant influences on its charge trap structure and charge stability. Charge traps and charge stability can be significantly deepened or improved even by isothermal crystallization at 90 ℃ for 0.5 h. And with the increase of crystallization temperature and time, charge traps are deepened further, presenting further improved charge stability, as observed in the case of isothermal crystallization at 130 ℃ for more than 2 h. Attenuated total reflection infrared analysis and wide angle X-ray diffraction measurement indicate that the improvement of charge stability results from the changes in chemical composition and structure of the PP film.
2010, 59 (9): 6514-6520. doi: 10.7498/aps.59.6514
The laminated fluoroethylenepropylene (FEP) and porous polytetrafluoroethylene (PTFE) films with regular void structure are prepared by using a rigid template with a periodic-structured surface. The porous PTFE film is firstly patterned with the rigid template surface by applying force on the stack of porous PTFE film and the template, then followed by the fusion bonding process to bond the FEP and patterned porous PTFE together. The corona charging technique is used to make the laminated film piezoelectric, i.e., to become piezoelectrets. The Young’s modulus of the laminated FEP/PTFE films is determined by dielectric resonance spectra. The thermal stability of the piezoelectric d33 coefficients are characterized by measuring the decay of d33 at elevated temperatures. The charge dynamics in such FEP/PTFE piezoelectrets is investigated by analying the thermally stimulated discharge current spectra in short circuit. The results show that laminated FEP/PTFE films with very regular void structure can be made by using rigid template and fusion bonding process. The Young's modulus of such films is about 0.53 MPa. The maximum quasi-static piezoelectric d33 coefficient up to 500 pC/N is achieved. The laminated FEP/PTFE films show improved thermal stability. For example, the remnant d33value is around 22% of the initial value for the sample annealed at 150 ℃ for 5000 min. For the samples after annealing treatment, the main drift path of the detrapped charges is through the solid dielectric layer.
2010, 59 (9): 6521-6526. doi: 10.7498/aps.59.6521
Spin-polarized transport in magnetic pn junction has been theoretically studied by using the drift-diffusive theory. The factors considered include bias voltage, equilibrium spin polarization,spin injection and spin life time, which could effectively affect the current density and resistance. The connection between spin-voltaic effect of the magnetic pn junction and thickness of the junction was also discussed. It is found that the equilibrium spin polarization makes the spin electrons with different orientations (up or down) have different barriers, which makes the current effectively modulated. However, the spin injection modulates the current by providing non-equilibrium spin electrons in the magnetic pn junction. It is also found that the spin-voltaic current is sensitive to quasi-neutral p-type region width.
2010, 59 (9): 6527-6531. doi: 10.7498/aps.59.6527
Exciton dissociation process and its mechanism at the NPB-Alq3 interface are studied by means of transient photovoltage techniques. For bilayer structured samples made from NPB and Alq3, the transient photovoltage upon 355 nm pulsed laser irradiation was measured. By analysis of the transient photovoltage of samples with different structures or with interface exciton blocking layer that climinates the effect of exciton dissociation at the external interface, it is concluded that the mechanism of exciton dissociation at the NPB-Alq3interface results in holes injected into NPB and electrons injected into Alq3.
2010, 59 (9): 6532-6537. doi: 10.7498/aps.59.6532
For a quantitative analysis of the detection performance of wavelength surface plasmon resonance sensor after the introduction of absorbing thin films, a mathematical model was established for the wavelength SPR biosensor. Based on absorption theory of dispersive media, the distribution of electromagnetic field in each film outside the prism is calculated. The results show that, after introducing the absorbing thin films, electromagnetic field energy distribution in each layer out of the prism surfaces was changed, the metal film contribution on the resonance absorption was reduced, which increases the half wave width of SPR curve and the minimum reflection coefficient, so the optimal film thickness of metal film was also changed. Then the effect of colloidal gold and immunogold on SPR biosensor has been theoretically and experimentally verified. The result shows that, compared with the 48 nm gold film SPR sensor, the sensitivity increases 1.5 times when 45nm gold film is surface-modified with 10nm nano-gold.
2010, 59 (9): 6538-6544. doi: 10.7498/aps.59.6538
In this paper the physical mechanism of the S-shaped J-V characteristics of (p) a-Si:H/(n) c-Si heterojunction solar cell at low working temperatures, low impurity concentrations in the a-Si:H layer, high valence band offsets or high interface defect densities is studied by heterojunction interface analysis and AMPS simulations. The results show that the barrier at the amorphous/crystalline interface hinders the collection of photogenerated holes. A high hole accumulation at the interface, in combination, causes a shift of the depletion region from the c-Si into the a-Si:H. This leads to the electric field decreasing, and the enhanced recombination inside the c-Si depletion region causes a significant current loss. It results in the S-shaped J-V characteristics.
2010, 59 (9): 6545-6548. doi: 10.7498/aps.59.6545
Strained Si CMOS technology is one of the most advanced technologies in present day microelectronics. Electronical conductivity effective mass of strained Si is a key parameter to study electron mobility enhancement. Using K ·P method with the help of perturbation theory, dispersion relation near conduction band valley was determined, including the longitudinal and transverse masses. And then, electronical conductivity effective masses of strained Si on (001),(101) and (111) planes were obtained with respect to stress, splitting energy and directions. It was found that both the and directional electronical conductivity effective masses of strained Si/(001)Si1-xGex and the directional one of strained Si/(101)Si1-xGex decrease with increasing Ge fraction or stress, and both values tend to be constant. The results provide valuable reference to the conduction channel design related to stress and orientation in the strained Si nMOS devices.
2010, 59 (9): 6549-6555. doi: 10.7498/aps.59.6549
TiO2 thin films doped with rare-earth yttrium and lanthanum were prepared on quartz plate by sol-gel/spin-coating technique. The samples were annealed at 700 to 1100 ℃ and the Raman spectra of the samples were obtained. Analysis of Raman spectra shows that with increasing annealing temperature, the anatase form of undoped TiO2 thin film transforms eventually into the rutile phase with mixed anatase/ rutil phase as an intermediate. Yttrium doping and lanthanum doping of TiO2 thin films can inhibit the phase transformation, and the latter effect is stronger. Rare-earth doping refines grain size of TiO2 thin films and increases the internal stress, thereby preventing lattice vibration. The effect of La doping is stronger than yttrium doping. The samples show significant phonon confinement effect. That is to say, the characteristic Raman peaks blue shift and the full widths at half height increase and the peak shap easymmetricaly stretches with decrease of grain size.
2010, 59 (9): 6556-6562. doi: 10.7498/aps.59.6556
By means of density functional theory on the basis of generalized gradient approximation, the equilibrium geometries and electronic properties of different hydrogenated diamond (100) surfaces were calculated. The results indicate that in the case of 2×1 reconstruction structure, the relaxation occurs along directions parallel and vertical to the surface. However, the relaxation does not appear in the direction parallel to the surface in the case of 1×1 structure. In addition, for the clean surfaces with C(100)-2×1, C(100)-2×1 ∶0.5H and C(100)-1×1 ∶1.5H structures, empty surface states exist in their band gaps. But with regard to the C(100)-1×1 ∶2H and C(100)-2×1 ∶H surface structures, which are configurations with full hydrogen coverage, the empty surface states shift upwards into the conduction band. With the help of analysis of charge density distribution, the inducing mechanisms of surface states were investigated.
Study of structural and electrical properties of phase-change materials Ge1Sb2Te4 and Ge2Sb2Te5 thin films
2010, 59 (9): 6563-6568. doi: 10.7498/aps.59.6563
The Ge1Sb2Te4 and Ge2Sb2Te5 thin films were deposited on quartz and silicon substrates by radio frequency magnetron sputtering from Ge1Sb2Te4 and Ge2Sb2Te5alloy targets. Structure properties and electrical transport characteristics of Ge1Sb2Te4 and Ge2Sb2Te5 thin films were studied and compared. X-ray diffraction spectra and atomic force microscopic images were used to characterize the structure of Ge1Sb2Te4 and Ge2Sb2Te5before and after thermal annealing. With increasing annealing temperature, Ge1Sb2Te4crystallized gradually and transformed to polycrystalline state from the amorphous state. Surface of Ge1Sb2Te4 thin films was uniform nanoparticles with roughness less than 10 nm. After thermal annealing, Ge2Sb2Te5 also transformed to polycrystalline state from amorphous state, but its surface morphology did not change significantly compared with the as-deposited film. Results of Hall effect measurement indicated the carrier concentrations of both the as-deposited and annealed films of Ge1Sb2Te4 were three orders of magnitude larger than those of Ge2Sb2Te5. From the above results, we conclude that Ge1Sb2Te4 tends to be more conductive than Ge2Sb2Te5 owing to the larger carrier concentration. Results of resistance versus time measurements under isothermal condition suggested Ge2Sb2Te5is more thermally stable and better fit for data storage than Ge1Sb2Te4.
2010, 59 (9): 6569-6574. doi: 10.7498/aps.59.6569
Polycrystalline Bi0.5Ca0.5Mn1-xCoxO3(0≤ x≤0.12) samples are synthesized by using the solid-state reaction. The effects of Co-doping on charge order of Bi0.5Ca0.5MnO3 are studied. The results show that Co doping leads to the melting of the charge order and the enhancement of the ferromagnetic correlation. For x≥0.08, the charge order transition is completely suppressed; however, there are still remaining antiferromagnetic domains inside the system. The phase separation or the coexistence of the charge order and ferromagnetic phase induced by Co-doping plays an important role in the low temperature properties for the system. Moreover, unlike in the case of rare-earth manganites, Co is more efficient to suppress charge order of Bi0.5Ca0.5MnO3 than Cr.
2010, 59 (9): 6575-6579. doi: 10.7498/aps.59.6575
Comparing with the experimental data, the composition dependence of atomic moment and Co-Mn exchange interaction in CuMnAl, CoMnAl and CuCoMnAl alloys have been investigated by KKR-CPA-LDA calculation. It has been found that, due to the different surrounding environments, the magnetic moment of excess Mn atom occupying Al sites is larger than that of the original Mn atoms on B sites in Cu50Mn25+xAl25-x alloys. When the Mn content increases in Co50Mn25+xAl25-x alloys, the moment of Co atom increases monotonically, while the Mn moment almost has the same value. In Cu50-xCoxMn25Al25 alloys, it has been revealed that the moment of Co decreases resulting from the decrease of the moment of Mn atom with the substitution of Co for Cu. These results indicate that the atomic moments of Mn and Co atoms are positively related. It has also been found that the Co-Mn exchange interaction can be enhanced by increasing Mn content and its strength comes not only from the added Co but also from the contribution of Mn.
Based on the spin diffusion theory and the Ohm’s law, we theoretically studied the magnetoresistance (MR) effect in an organic spin valve with structure of ferromagnetic/organic semiconductor/ferromagnetic system, which takes into account the special characteristics of organic semiconductors. Self-trapped states, such as spin polarons as well as spinless bipolarons are assumed to be the main carriers in organic semiconductors. From the calculation, it is found that MR ratio increases with the increasing of the polaron proportion and rapidly decreases with the increasing of the organic layer thickness. MR ratio can be enhanced remarkably when the interfacial resistances are spin related. Effects of the conductivity match and the spin polarization of the ferromagnetic layer on the MR are also discussed.
2010, 59 (9): 6585-6592. doi: 10.7498/aps.59.6585
We have fabricated c-axis-oriented Sr2CoO4-δ thin films under relatively low oxygen pressure by the pulsed laser deposition method (PLD) on LaAlO3 substrates. X-ray diffraction and high-pressure reflection high energy electron diffraction (RHEED) demonstrate that the films were well deposited. There exist two different characteristic temperatures, Tf and Ta, in the ZFC curve of temperature dependence of magnetization. Tf may correspond to the freezing temperature while Ta may be related with the anisotropic field of c-axis. Further investigations including magnetic relaxation, memory effect and hysteresis behaviour measurements suggest a main phase of spin glass, which starts the frozen-in process even above the freezing temperature. We ascribe the spin glass behaviour to the competition betwcen double-exchange and super-exchange interactions which could have originated from the coexistence of Co4+ and Co3+ caused by oxygen deficiency in the films.
2010, 59 (9): 6593-6598. doi: 10.7498/aps.59.6593
In this work, the issue of magentic hardening of soft phase in nanocomposite permanent magnetic materials has been investigated using one-and three-dimensional models. For the same microstructure, it is found that the coercivity is decreased and the low-field demagnetization curve keeps unchanged when the anisotropy constant of magnetic hard phase is decreased in anisotropic one-or three-dimensional samples. Therefore, the drop in anisotropy of magnetic hard phase will not lead to the increase of remanence and maximum energy product (BH)max. According to the simulation results of isotropic three-dimension samples, both the remanence and (BH)max will be obviously decreased by the drop in anisotropy. As a result, enhancing the anisotropy and/or enlarging the grain size of magnetic hard phase is one of the means to improve the hard magnetic properties of nanocomposite permanent magnetic materials.
2010, 59 (9): 6599-6605. doi: 10.7498/aps.59.6599
By using Karman’s plate theory of large deflection, the nonlinear equation of motion of a thin metal plate with the coaction of a transverse uniform magnetic field and a transverse load is established. These equations consider the magnetic Lorentz force induced by the eddy current. Based on the Bubnov-Galerkin method, the nonlinear partial differential equation is transformed into a third-order nonlinear ordinary differential equation. By using the sub-harmonic orbit Melnikov function method, the criterion of the Smale-horseshoe chaos is also acquired. Furthermore, the chaotic motion is numerically simulated with Matlab. The bifurcation diagram, the phase curve, the Poincaré map and the evolution curve are calculated. The digital characteristics of the chaotic motions are provided based on the analysis. The analysis results show that the magnetic induction intensity and the external load may affect the vibration of the system.
Synthesis and temperature dependence of permittivity of Ba1-xSrxTiO3 and Ba0.6-xPbxSr0.4TiO3 ceramics
2010, 59 (9): 6606-6612. doi: 10.7498/aps.59.6606
Ba1-xSrxTiO3 (BST) and Ba0.6-xPbxSr0.4TiO3 (BPST) ceramics were prepared by conventional solid-state reaction method. The analysis of XRD, FESEM and Raman spectroscopy showed the effects of Pb-doping on the crystal lattice,phase transition and surface morphology of Ba0.6Sr0.4TiO3, respectively. And the temperature dependence of permittivity (ε-T properties)for all ceramics were measured at a frequency of 10 kHz. The mechanism that Curie temperature and the peak value of permittivity are modulated by Sr and Pb content in BST and BPST perovskite has been revealed. In addition, all samples exhibit a diffused phase transition (DPT), especially for the ceramic Ba0.5Pb0.4Sr0.1TiO3, which can improve its temperature stability of tunability as phase shifter than others. Some ferroelectric parameters are calculated to interpret the DPT by adopting Smolenski’s theory and Curie-Wise law. For example, the values of diffuseness exponent α,Curie constant and transition region have changed from 1.29 to 1.73, from 1.25×105 to 2.87×105 K, and from 13.2 ℃ to 22.3 ℃, respectively.
2010, 59 (9): 6613-6619. doi: 10.7498/aps.59.6613
Ba(Zr0.06Ti0.94)MnxO3 ceramics were prepared by oxide solid state reaction method. The effects of Mn-doping on the phase structure, piezoelectric and dielectric properties of BZT ceramics were studied. Mn ions preferentially incorporated in the lattice acted as donors when the concentration of Mn ions is below 0.5 mol%, which improves the piezoelectric coefficient and decreases the dielectric loss. When the concentration of MnO2 doping is larger than 0.5 mol%, it accumulated at the grain boundaries and deteriorates the piezoelectric properties of BZT ceramics as a result of domain pinning effect. With the increase of MnO2 contew, the ferroelectric behaves more diffused. The BZT ceramics doped with x=0.3—0.4 mol% MnO2 showed improved properties with d33 value as high as 195—220 pC/N, dielectric permittivity εr of 7500 and loss tanδ of 2%.
2010, 59 (9): 6620-6625. doi: 10.7498/aps.59.6620
In this paper the phase transition temperature of epitaxial ferroelectric thin film is analyzed and discussed systematically via the dynamic Ginzburg-Landau (DGL) equation by taking the effective interior stress, surface eigenstrain relaxation and depolarization field. When the thickness of ferroelectric film is changed, external and internal factors, which affect phase transition temperature of ferroelectric thin films,are presented to explain the experimental observations. There is a good quantitative agreement between the theoretical results and experimental data for BaTiO3 thin film epitaxially grown on SrTiO3 substrate.
All-optical switching effect of the excited state proton transfer molecule 2-(2'-hydroxyphenyl) benzothiazole in different polar solvents
2010, 59 (9): 6626-6631. doi: 10.7498/aps.59.6626
An all-optical switching model system comprising a single pulsed pump beam at 355 nm and a cw He-Ne signal beam at 632.8 nm was demonstrated with 2-(2'-hydroxyphenyl) benzothiazole(HBT) in five different polar solvents. The origin of the optical switching effect was discussed, and it was verified that fast excited state intramolecular proton transfer (ESIPT) of HBT and the slow thermal effect of solvent together induced the change of the refractive index of HBT solutions, which lead to the signal beam deflection and dominated the optical switching "off" and "on" states, respectively. The slow thermal effect of solvent results in the "tail" phenomenon of the optical switching recovery, and reducing the signal beam waist radius is a viable means for accelerating the recovery of the optical switching. The results indicated that the HBT molecule could be an excellent candidate for high-speed and high-sensitivity optical switching devices. This work provides a theoretical as well as experimental basis for the production of ultra-fast all-optical switching device.
2010, 59 (9): 6632-6636. doi: 10.7498/aps.59.6632
A series of blue-emitting phosphors M2B5O9Cl: Eu2+(M=Ca, Sr) were synthesized by solid-state methods. And the phosphors were characterized by XRD and photoluminescence emission (PL) and excitation (PLE) spectra. The factors that affect the PL intensity of phosphor Sr2B5O9Cl have been investigated, and the optimal conditions to obtain the blue emitting phosphor are 8 mol% Eu2+concentration, 5.0mol % excess of SrCl2. As Ca partially or completely substituted Sr in the host Sr2B5O9Cl, the emission peak shifts from 425 to 453 nm. The most important is that the phosphors M2B5O9Cl: Eu2+(M=Ca, Sr) show strong absorption in the region of 350—400 nm, which matches well with the emission of the near-ultraviolet or purple LED chips. Comparison with the commercial blue-emitting phosphor, the PL intensity of phosphor Sr1.92Eu0.08B5O9Cl is about 1.8 times that of the commercial blue emitting phosphor BAM. Thus, the phosphors M2B5O9Cl: Eu2+ (M=Ca, Sr) show great potential as the candidate for blue phosphor in n-UV or purple based white LEDs.
2010, 59 (9): 6637-6641. doi: 10.7498/aps.59.6637
Er3 + /Yb3 + co-doped TeO2-WO3-Bi2O3 (TWB) glass has been prepared.The absorption spectra, fluorescence spectra and up-conversion luminescence of the glass were measured. The strength parameters of Er3+ in glass were calculated according to the Judd-Oflet theory. Along with Bi2O3 content increasing, Ω2 increases, Ω4, and Ω6 gradually decrease. The broad 1.5 μm fluorescence was observed under 976 nm excitation, and its full width at half maximum (FWHM) was 96 nm. The stimulated emissiow was calculated using the McCumber theory, and the peak emission cross-section was 0.70 × 10-20cm2 at 1.5 μm. The product of stimulated emission cross section and fluorescence of FWHM was 60.2 cm2 nm. At the same time, there is an obvious phenomenon of fluorescence up-conversion of Er3 +/Yb3 + co-doped TeO2-WO3-Bi2O3 glass under 976 nm pump, and the intensity of the conversion gradually weakened with the increasing of Bi2O3 content.
2010, 59 (9): 6642-6646. doi: 10.7498/aps.59.6642
The organic light emitting diodes with the structure of ITO/NPB(60 nm)/ Alq3 ∶Rubrene(1wt%,20 nm)/Alq3(3 nm)/Alq3:Rubrene(1wt%,20 nm)/ Alq3(20 nm)/LiF/Al, which have multiple quantum well structures (MQW), were fabricated and the magnetic field effects on the efficiency and current of the OLEDs were measured. The experiment showed that the current decreased monotoniocally, i.e. the resistance of the device increased under the magnetic field. At the same time, the magnetic field effect on efficiency was achieved. The changing ratio of efficiency increased 9.13% maximally when the magnetic field was below 20 mT. The changing ratio of efficiency decreased with the magnetic field increasing when the magnetic field was higher than 20 mT.
2010, 59 (9): 6647-6652. doi: 10.7498/aps.59.6647
Porous silicon (PS) prepared by electrochemical etching method has been studied by positron annihilation lifetime spectroscopy (PALS) and age-momentum correlation (AMOC) measurement in different atmospheres. The longest lifetime component in PALS results is ascribed to the annihilation of positronium in cavities of PS sample. It is found that 80% of the positrons implanted in PS film have formed positronium atoms. PALS results show that the lifetime of ortho-positronium has smaller value when the sample was in oxygen gas medium compared with those in other medium. AMOC results reveal that S parameter of three lifetime components in oxygen are all bigger than that in nitrogen atmosphere. These are probably caused by the oxygen leading to the spin-conversion of positronium atoms.
2010, 59 (9): 6653-6658. doi: 10.7498/aps.59.6653
In this paper a dielectric-loaded folded waveguide slow-wave circuit is presented. The "hot" dispersion relation for slow wave interaction between the traveling wave and linear beam is derived from the fluid dynamical treatment. In the special case where εr=1, the dispersion relation can be simplified with a closed form of the conventional Pierce’s small-signal equation, which confirms the validity of the derivations. By giving the specific parameters, the effects of dielectric loading on the small-signal gain have been studied. The results indicated that in the case of "weak loading" (where d/a<0.1), the gain is flattened and there is no need to readjust the structure parameters beyond a slight adjustment of beam parameters. By considering that the "weak loading" can reduce the ohmic loss of the conductor, this study will be also a guide to the research of the THz folded waveguide traveling-wave tube.
2010, 59 (9): 6659-6665. doi: 10.7498/aps.59.6659
A novel mm-wave high power microwave device, the ridge-loaded folded waveguide traveling wave tube (TWT), is presented and its linear gain properties are investigated. The perturbed dispersion equation is derived and the small signal growth rate is calculated for different dimensions of ridge and parameters of electron beam. For a cold beam, the linear theory predicts a gain of 1.15 dB/period and a 3-dB small-signal gain bandwidth of 18.51% in Kα-band. The investigation reveals that, with the same beam parameters, the novel slow-wave structure (SWS) has advantage over the folded waveguide SWS in its gain and efficiency. The dimensions of ridge and the beam current may be increased in order to raise the gain.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Microstructure and themoelectric properties of p-type filled skutterudite Ce0.3Fe1.5Co2.5Sb12 prepared by melt-spinning method
2010, 59 (9): 6666-6672. doi: 10.7498/aps.59.6666
Polycrystalline nanostructured bulk samples of p-type filled skutterudite Ce0.3Fe1.5Co2.5Sb12 have been prepared by melt-spinning (MS) method combined with spark plasma sintering (SPS). The effects of melt-spinning process on their microstructure and thermoelectric properties have been investigated. The results indicate that the ribbons have finer microstructure with the increasing cooling rate for melt-spun ribbons, resulting from the increasing copper wheel speed and decreasing ejection pressure. Compared with the sample prepared by traditional method, the samples prepared by MS-SPS method have higher power, factor due to the enhanced thermopower, despite the slightly reduced electrical conductivity. Meanwhile, the lattice thermal conductivity of the MS-SPS samples is significantly suppressed. Hence, the thermoelectric performance of the MS-SPS samples is greatly improved, and the figures of merit reach about 0.55 at 750 K.
2010, 59 (9): 6673-6680. doi: 10.7498/aps.59.6673
The properties of memristor as the fourth basic circuit element are studied. The mathematical models in integral form for memristors with and without border constraint are developed. The simulation is done for the memristor with border constraint. The influences of the source frequency and model parameters on the memristor’s properties are analyzed and some conclusions are drawn. The model parameters considered include the doping ratio and the initial doping width, and their influnce on the current, voltage-current relation and flux-charge relation of the memrister are investigaled.
2010, 59 (9): 6681-6688. doi: 10.7498/aps.59.6681
Kinetics of diffusion-limitied aggregation-annihilation processes on NW small-world networks is investigated by Monte Carlo simulation. In the system, if two clusters of the same species meet at the same node, they will aggregate and form a large one; while if two clusters of different species meet at the same node, they will annihilate each other. Simulation results show that, if the value of p (a parameter that quantifies the number of shortcuts) is large or small enough, the concentration of clusters c(t) and the concentration of particles g(t) follow power laws at large times, i.e.c(t)∝t-α and g(t)∝t－β. Moreover, the relation between the exponents α and β is found to satisfy α=2β. However, if p is of medium value, the concentration of clusters and the concentration of particles do not follow the power laws exactly. Our simulation results agree with the reported theoretical analysis very well.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2010, 59 (9): 6689-6696. doi: 10.7498/aps.59.6689
Using the daily main observational temperature data of 435 stations in China from 1961 to 2002, temperature change on 9-day scale has been compiled in network. Research on the connection between nodes and items in bipartite graph temperature (BGT) network, reveals the temperature change on 9-day scale and the topological statistics in the space. The nodes of RRRD, RrDD, eeed, DRRD and DDRR have remarkably high degree, which is helpful to predict the temperature change on 9-day scale. Calculation of the topological parameters of this network, including degree distribution and clustering coefficients, shows the normal school character of the bipartite graph model temperature network. The distribution of nodes’ degree diversity in each item presents quadruple type character, and has similar characteristics as the complex regions defined by the fluctuant temperature network(FT network), displaying the background information of temperature change in the region by this two kind of network respectively. Thus, temperature network modeled by bipartite graph model present a possible and available approach to research the characteristic and rule about temperature change from the combination of the time and space scale.
Study of the multi-system compatible receiver’s frequency selection problem based on fixed point theory and its genetic algorithm realization
2010, 59 (9): 6697-6705. doi: 10.7498/aps.59.6697
The problem of multi-system compatible receiver’s frequency selection is studied based on fixed point theory, and genetic algorithm is applied to resolve the problem. In the frequency space Banach fixed point theory was used to explain the fixed point physical property, which is presented through the evolution of the frequency set in the frequency space. By adequate reciprocal action of the frequency space operator any iterative sequence source frequency set in the frequency space will finally converge to the unique fixed-point object frequency set, the object frequencies of which are the frequency selection problem’s optimal solution. The study of and the solution to the frequency selection problem has been accomplished by a genetic algorithm. Simulation shows that the algorithm can resolve the problem of the multi-system compatible receiver’s frequency selection effectively.