Vol. 62, No. 17 (2013)
Perturbation method of travelling wave solution for (2+1) dimensional disturbed time delay breaking solitary wave equation
2013, 62 (17): 170201. doi: 10.7498/aps.62.170201
A class of (2+1) dimentional disturbed time-delay breaking solitary wave equation is studied. Firstly, the corresponding non-delay breaking equation is considered. The exact solitary wave solution is obtained by using the mapping method with undetermined coefficients. Then, the travelling asymptotic solution of disturbed breaking solitary wave equation is found by using the homotopic mapping and perturbed approximate method.
2013, 62 (17): 170202. doi: 10.7498/aps.62.170202
A class of generalized disturbed KdV-Burgers equation is studied by constructing a homotopy mapping. Based on the kinked solitary-wave solution of the corresponding typical undisturbed generalized KdV-Burgers equation with nonlinear terms of any order,the approximate solution with arbitrary degree of accuracy for the disturbed equation is researched. It is pointed out that the series of approximate solution is convergent. Finally,the efficiency and accuracy of the approximate solutions is also discussed by using the fixed point theorem.
2013, 62 (17): 170203. doi: 10.7498/aps.62.170203
Using the homotopy analysis method (HAM), the nonlinear equation of the jamming transition problem (JTP) in traffic flow is discussed, which is based on the Lorentz system. Through choosing different initial approximation solutions and different linear operators, approximation solutions of the JTP and the corresponding residual errors are obtained respectively. By comparing the present results with the previous related studies, the following conclusions can be drawn that the HAM is superior to the differential transform method; however, a linear operator should be chosen as best you can to approach the linear part of the original operator in using the HAM. A new method to choose the initial approximation solution (named double HAM) is given. The correctness of the theoretical analysis is verified by numerical simulation.
Electromagnetic scattering from missile target above sea surface with finite element/boundary integral method
2013, 62 (17): 170301. doi: 10.7498/aps.62.170301
In this work, the finite element/boundary integral method (FE/BIM) combined with the domain decomposition method is introduced to study the electromagnetic scattering from the target above the rough sea surface. As the integral boundary can be set at anywhere with an arbitrary shape, the conformal truncated boundary is built to reduce the unknowns of the computational region combined with the domain decomposition method. In the interior region, the finite element method is used to solve the problem, whereas the artificial boundary condition can be obtained by the boundary integral method. The strategy of hybrid FE/BIM and the modeling method are presented with their validity evaluated by the method of moment, then bistatic scattering properties of a missile above the sea surface are discussed, and their dependence upon different incident angles, target height, wind speed above the sea, and the size of the missile are discussed in detail. The information of targets and the target detection can be retrieved and analyzed by the results in this paper.
2013, 62 (17): 170302. doi: 10.7498/aps.62.170302
The quantum-information theoretic notation of the Winger-Yanse skew information has been used to analyze the process of information transfer between probe fields and atomic ensemble in the electromagnetically induced transparency. It is well known that the skew information is a well-defined measure that quantifies the amount of the information a quantum state contains. We have calculated the dynamical skew information of the probe fields and the atomic ensemble, and found that the information for the individual atom is dependent of the numbers of the particles and the photons, as well as the state of the probe field. For a sufficiently weak coherent driving field, the dark-state polaritons is a purely atomic state with no photons in the composite system, and the information of the individual atom reaches the maximum value. However, the information of the probe field is not completely transferred into the atomic ensemble.
Application of the composite adiabatic passage technique in the Landau-Zener model with harmonic interaction modulation
2013, 62 (17): 170303. doi: 10.7498/aps.62.170303
In quantum information processing, an extreme high fidelity is needed. We apply a composite adiabatic passage (CAP) technique in the Landau-Zener model with harmonic interaction modulation in order to study the transition probability of the system with different model parameters. We find that this method could suppress the non-adiabatic oscillations in the transition probability and reduce the admissible error. This method could also enlarge the parameter regimes of high transition probability. Because of these good results, the Landau-Zener model with harmonic interaction modulation and CAP technique could be potentially important tools for ultrahigh-fidelity quantum information processing.
2013, 62 (17): 170304. doi: 10.7498/aps.62.170304
A three-party quantum key agreement protocol based on EPR pairs is proposed, in which the three participants have equal status in the protocol and each participant is capable of contributing to the shared secret key in the same degree. In addition, any one or two parties cannot predetermine the value of shared key alone. The security analysis shows that our protocol can resist the outside attack and the dishonest participants attack.
2013, 62 (17): 170305. doi: 10.7498/aps.62.170305
In order to solve the damage problem during remote transmission of quantum signaling, a repeater model of signaling quantum is proposed. In this model, firstly purifying and distributing entanglement of the received signaling quantum state is carried out, to establish entangled channels between the signed sending and receiving. Secondly, through quantum entanglement swapping the quantum signaling is transmitted, for completing the quantum signaling relay. Simulation results show that the success rate of signaling relay can reach more than 97% under the condition that the fidelity is 0.98 and the entangled pairs successful establishing rate is 0.98; the throughput of quantum signaling relay is up to 183kbps when the probability of entanglement swapping, purification, and entangled pairs successful establishing is 0.98.
2013, 62 (17): 170501. doi: 10.7498/aps.62.170501
This paper proposed a modified chaotic ant swarm optimization under an effective termination condition. Numerical calculation verifies the validity of the modified algorithm. Simulation of the algorithm indicates that the algorithm can have a high-accuracy optimal solution. Through multiple chaotic searches, the modified algorithm gradually approaches the optimal solution which can be used to solve complex continuous domain optimization problem.
Realization of synchronization between hyperchaotic systems by using a scheme of intermittent linear coupling
2013, 62 (17): 170502. doi: 10.7498/aps.62.170502
Based on the Lyapunov stability theory, it is confirmed that complete synchronization can be realized under intermittent linear coupling. The linear controller is selected as ‘stop’ or ‘on control’ by using a switch function; while the first switch function is realized by using a rectangular wave with the same amplitude, and the controller turns on/off in the peiod Ta, Tb alternately. The second switch function is adjusted by a square wave with the same amplitude, and the interval period is marked as T0. At first, a class of exponential Lyapunov function is designed to discuss the reliability and possibility of complete synchronization induced by indirectional linear coupling when the controller is adjusted by two types of switch function. The averaged power consumption of controller within a transient period is defined to measure the cost and efficiency of this scheme. In numerical studies, for the case of first switch function (rectangular wave), the distribution of the largest conditional Lyapunov function for the response system is calculated in the two-parameter space for interval period Ta vs. Tb, the synchronization area vs. nonsynchronization area, the distribution of averaged power consumption in the parameter space Ta vs. Tb. It is also confirmed that complete synchronization can be reached at appropriate Ta, Tb, and coupling intensity. In the case of the second switch function, the distribution of the largest conditional Lyapunov function for the response system is calculated in the two-parameter space for coupling intensity k vs. interval period T0, and the series of error function and averaged power consumption. It is found that complete synchronization can be realized at appropriate coupling intensity and interval period T0. It is also found that the averaged power consumption of controller within a transient period can reach a smallest value at an appropriate coupling intensity. Numerical results are consistent with the theoretical analysis.
A modified feedback controlled car-following model considering the comprehensive information of the nearest-neighbor leading car
2013, 62 (17): 170503. doi: 10.7498/aps.62.170503
Congestion control is a process to achieve optimal decision-making and effective control of vehicles through the interaction of vehicular perception and control, it shows the typical characteristic of cyber physical systems. Based on the pioneer work of Konishi et al., we present a new feedback control scheme to suppress traffic jam in the coupled map car-following model under open boundary condition, which considers the effect of safe headway and optimal velocity difference on the traffic system from the perspective of tight conjoining between the transportation cyber system and the transportation physical system. According to the control theory, the condition under which traffic jam can be suppressed is analyzed. Both theoretical analyses and simulation results show that the suppression performance of our scheme is better than those of the previous schemes, although all the schemes can suppress traffic jam.
2013, 62 (17): 170504. doi: 10.7498/aps.62.170504
A new method for data assimilation is proposed using complex-variable differentiation (CVD), which can be used to estimate the initial conditions of the nonlinear physical system governed by the following equation:. Firstly, the gradient analysis of cost function in variational data assimilation is transformed into function numerical computation in complex domain, and the value of gradient is computed more efficiently and exactly. Secondly, the new algorithm of data assimilation is developed by combining an accurate gradient information from CVD with the classical optimization method. Finally, numerical simulations of typical chaotic systems and a humidity evolution equation with physical on-off process show that the new data assimilation method can reconstruct initial conditions of the nonlinear dynamical system very conveniently and accurately.
2013, 62 (17): 170505. doi: 10.7498/aps.62.170505
In this article, a kind of piecewise expanding linear system is constructed. It has a positive Lyapunov exponent as calculated. It is proved that the system has a uniform limit distribution The formula of the least period of the system is also presented. It is indicated that there is a contradictory relationship between the complexity and the least period of the system when the symbol entropy is applied to the system. The theoretical limit of the complexity of the system with changing parameters is presented. Simulation of the system shows that the sequence generated by the chaos is uniformly distributed. It also tells that the system can have higher complexity but longer least-period than the logistic system and the Tent-Map system. Experiments show that the system is suitable for constructing the cipher.
2013, 62 (17): 170506. doi: 10.7498/aps.62.170506
Because the problem of the extended Kalman filter localization and mapping algorithm priori noise model is difficult to manage, this paper proposes an improved wild geese particle swarm algorithm based on the fuzzy adaptive Kalman filter localization and mapping algorithm. We take advantage of the the fractional calculus to improve particle speed of evolution, and make use of chaos to improve the initialization of the particle and the precocious one when processing. The improvement of wild geese particle swarm algorithm is shown in convergence rate and avoiding premature, then they can improve geese particle swarm algorithm for fuzzy adaptive extended Kalman filter localization and mapping algorithm training. in contrast with geese particle swarm algorithm fuzzy adaptive extended Kalman filter simultaneous localization and mapping algorithm, the new algorithm positioning and composition has greatly improved.
2013, 62 (17): 170507. doi: 10.7498/aps.62.170507
Hopf bifurcation and chaotic properties of a simple second order time-delayed system, which includes bifrucation point, bifurcation direction and the stability of bifrucating periodic solutions, are analyzed. We obtain analytically the phase trajectory equations when the delay degenerates. Furthermore, through bifurcation diagram drawn by means of numerical simulation, the route from period-doubling bifurcation to chaos is reaveled; using single linearly combinating signals and the feedback control method, we achieve partial synchronization of the system. Combining the active-passive method with the linear feedback method, we have realized complete synchronization. In addition, we have designed and built an electronic experimental line, from which the same result as the theoretical analysis or numerical results are obtained.
2013, 62 (17): 170508. doi: 10.7498/aps.62.170508
Synchronization of bursting activities in pancreatic islets when pancreatic β-cells are coupled together by gap junctions plays an important role in the insulin secretion. A minimal and generic phantom bursting model proposed by Bertram et al is employed to produce compound bursting synchronization with anti-phase spikes of two electrical coupling pancreatic β-cells, where the membrane exhibits a transition between a burst episode composed of a long burst and several short bursts and a relatively long rest state with large amplitude on both sides but small at the middle. Two different fast/slow analyses for the moderate and the slower slow variables in three-dimensional spaces are combined to highlight better how these two slow variables with different time scales commonly or separately result in complex dynamics of the compound bursting of the two electrical coupling β-cells. Especially for the compound bursting synchronization with anti-phase spikes, more is stressed on how varying coupling strengths lead to a change of the number of the short bursts within the burst episode of different compound bursting.
2013, 62 (17): 170509. doi: 10.7498/aps.62.170509
In order to solve the problem why it was hard to observe the single-variable nonlinear system, this article proposed the 45 line method. In this method, the continuous signal changing with time was transformed into dots on the 45 line of the rectangular coordinates, so that it could be directly displayed on a general dual-trace oscilloscope (either analog or digital). In this way, it is convenient to directly observe and analyze various states of single-variable system while the system is running, such as the periodical stable states, the local and global non-stable states. The mechanism of this method was expounded in this paper. In addition, the key issues in physical circuit design and implementation of this method were researched and solved, i.e., the useful signal which reflected the state of the system could be extracted from the continuously changing signal. Since the Chuas circuit is a typical nonlinear system, and it could produce abundant states with variation of parameters, so it was chosen as the system under test to conduct a great number of physical experiments. The experimental results confirmed the effectiveness and practicability of this method.
2013, 62 (17): 170510. doi: 10.7498/aps.62.170510
For the chaotic systems with disturbance, a sampled-data controller is designed to achieve chaotic synchronization. Firstly, to handle the discontinuity introduced by the sampling activities, the input-delay approach is introduced to transform the discontinuous chaotic systems into continuous ones. Secondly, the worst possible case of performance is considered according to min-max robust strategy. Then the sufficient conditions for global asymptotic synchronization of such chaotic systems are derived and expressed in terms of linear matrix inequality (LMI). The proposed algorithm can achieve synchronization of the sampled-data chaotic systems for all admissible disturbances at the pre-computed set of disturbance realizations. The effectiveness is finally illustrated via numerical simulations of chaotic Chuas circuit, and the simulation results show that the proposed algorithm is suitable for secure communication.
Chaos synchronization of FitzHugh-Nagumo neurons via backstepping and adaptive dynamical sliding mode control
2013, 62 (17): 170511. doi: 10.7498/aps.62.170511
In this paper, backstepping and adaptive dynamical sliding mode control is used to achieve chaos synchronization of coupled FitzHugh-Nagumo (FHN) neurons. The proposed controller consists of a combination of dynamical sliding mode control and adaptive backstepping technique. Based on a new switching function, the combined algorithm yields a design of dynamical sliding mode control law, which can realize chaos synchronization of coupled FHN neurons with uncertain parameters. It is shown that the proposed approach can effectively remove the chattering characteristic of the system, so that the intrinsic dynamics of neurons can avoid to be destroyed. Furthermore, it has rapid control performance. The simulation results have demonstrated the effectiveness of the control scheme.
2013, 62 (17): 170601. doi: 10.7498/aps.62.170601
The concepts of shock pressure and shock temperature in the interaction of femtosecond laser pulse and solid target are defined. Then the relationship between the shock pressure and other physical parameters in the process of femtosecond laser ablation of aluminum, copper, and silicon targets are discussed. Absolute values of shock pressure are calculated by means of the time-resolved pump detection shadow-graph. Result of this investigation plays an important role in the secure femtosecond laser processing of energetic materials and the femtosecond laser propulsion technology.
2013, 62 (17): 170602. doi: 10.7498/aps.62.170602
Transmission grating spectrometer is applied in the area of inertial confinement fusion and other laser plasma interaction experiments. Accurate spectrum estimation depends on the measurement uncertainty. Based on the transmission grating diffraction efficiency calibration experiments, the uncertainty of diffraction efficiency is analyzed. Then the uncertainty of X-ray spectrum unfolding progress is investigated. The total uncertainty of the measured spectrum is obtained for 0.1 to 5 keV.
2013, 62 (17): 170603. doi: 10.7498/aps.62.170603
High-accuracy distance measurement plays an important role in many applications, such as industry measurement, Aerospace and scientific research. The continual development oflaser ranging technique is always a frontier topic of geometric measurement, therefore this paper develops the application of femtosecond optical frequency comb for length measurement. Time-of-flight principle for distance measurement is widely used by pulse laser, however, achievable resolution reaches only a few millimeters at best due to the limited bandwidth of electronics. In this paper, the temporal coherence of multiple pulse train is analyzed, and an arbitrary and absolute length measurement system is set up based on modified Michelson interferometer by combining multiple pulse train interference and time-of-flight method. The timing difference is separately calculated by the first-order and second-order optical cross-correlation signals, therefore the absolute distance is calculated. An experiment is conducted by measuring a 60 cm length, and the measurement result is compared with a high precision laser displacement sensor. The result shows a good measuring linearity, and the measurement precision of ±0.5 μm is achieved.
Experimental research on the technique of magnetic flux compression by explosive cylindrical implosion
2013, 62 (17): 170701. doi: 10.7498/aps.62.170701
The cylindrical magnetic flux compression by explosive implosion (MC-1) is a kind of unique high energy density dynamic technique. A metal cylinder was driven by explosive implosion to compress the primary magnetic flux inside and an ultrahigh magnetic field was realized, which could be used to achieve effective isentropic compression of the sample. This technique has anigue characters like ultrahigh isentropic pressure and ultrahigh magnetic field, and would find wide usage in areas like high pressure physics, new material synthesis and ultrahigh magnetic field physics. The Institute of Fluid Physics, Chinese Academy of Engineering Physics (IFP, CAEP) has begun to make experiments on MC-1 since 2011 and a one-stage MC-1 set-up has been built up. The primary experimental results including the movement of liner and typical turn-around character in MC-1 experiment were observed and recorded. In the experiment a dynamic magnetic field of about 430T was obtained. The MC-1 process was numerically simulated by the one-dimensional MHD code and the simulations are in accord with experiments. Numerical simulations show that this technique has advantages in isentropic compression of materials as compared with normal implosion experiment.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Noether-Lie symmetry and conserved quantities of Nielsen equations for a singular variable mass nonholonomic system with unilateral constraints
2013, 62 (17): 171101. doi: 10.7498/aps.62.171101
Under the infinitesimal transformations of Lie group, Noether-Lie symmetry of Nielsen equations for a singular variable mass nonholonomic system with unilateral constraints is studied. Differential equations of motion for Nielsen equations of the system are established. The definition, criteria and propositions for Nielsen equations of the system are given. Noether conserved quantity as well as generalized Hojman quantity is obtained. An example is given to illustrate the application of the results.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (17): 173401. doi: 10.7498/aps.62.173401
As the C6+ ion beam pulses, provided by the Heavy Ion Research Facility in Lanzhou-Cooling Storage Rings, impact on Au taget surface, the Lα-and Lβ-X spectra of Au atom are measured. Results show that the production cross section of Lα is larger than that of Lβ. The production cross sections increase with the kinetic energies of the projectiles. The PWBA and ECPSSR theoretical models are compared with the experimental resulms. The significant difference between experimental data and theoretical models was discussed.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Analysis of the dispersion and interaction impedance for a coupled cavity slow wave structure with double in-line slots in TWT
2013, 62 (17): 174101. doi: 10.7498/aps.62.174101
An analytical model is presented in this paper for a coupled cavity slow-wave structure (CCSWS) with double in-line slots, also known as the “Chodorow” structure. Under matching boundary conditions in conjunction with Green’s function techniques and moment method (MOM), the formulae for discussing the high frequency characteristics of the SWS, including dispersion and interaction impedance, are given. The frequency characteristics for an X band Chodorow structure are calculated using these formulae, Ansoft HFSS code and equivalent circuit model. Results show that the dispersion and interaction impedance obtained with the formulae are in good agreement with those calculated by Ansoft HFSS code, while its calculation rate is more rapid than that with the code, and its calculation precision is higher than that with equivalent circuit method, which is helpful for the engineering design.
2013, 62 (17): 174102. doi: 10.7498/aps.62.174102
Using the method of combination, we have made a communicational band (0.8 GHz to 3 GHz) dual-directional metamaterial absorber. Simulation and experimental results show that the absorber to the incident electromagnetic wave of different polarization and wide-angle has three stable absorbing bands(2.04, 2.34, and 2.65 GHz), and the absorptions can reach 92.3%, 95.3% and 94.7% respectively. This kind of absorber is very simple in design, having strong flexibility, perfect absorption, and easy processing, which works in a communicational band (0.8 to 3 GHz) so that it provides a new idea on electromagnetic shielding and anti interference.
2013, 62 (17): 174103. doi: 10.7498/aps.62.174103
Based on analyzing the equivalent circuit and electric field distribution of second-order square fractal frequency selective surface (FSS), the mechanism of its spurious resonance is discussed. To achieve a millimeter wave (MMW) spatial filter which exhibits high out-band suppression(≥13dB) and insensitive to the variation of oblique incident angles for both TE and TM polarized waves, a hybrid methodology of decoupling operation in conjunction with discrete particle swarm optimization (DPSO) procedure is proposed. The FSS array without spurious resonance and its evolutionary process by DPSO are described. It is also demonstrated that the measured results and DPSO-operated frequency characteristics are in excellent agreement.
2013, 62 (17): 174201. doi: 10.7498/aps.62.174201
Based on the vector angular spectrum of the electromagnetic beam and the method of stationary phase, the analytical vectorial structure of the Airy-Gaussian beam in the far field has been presented. According to the analytical electromagnetic representations of the TE and TM terms, the energy flux distributions of the TE term, the TM term, and the whole beam in the far field are investigated respectively. The formulas obtained are applicable not only in the paraxial case, but also in the nonparaxial case. The physical pictures of Airy-Gaussian beams are well illustrated from the vectorial structure, which may provide a new approach to manipulate laser beams.
2013, 62 (17): 174202. doi: 10.7498/aps.62.174202
Based on the angular spectrum theory, we establish a propagation model for vortex beam in reflection at an air-glass interface in the paraxial approximation, and investigate the cross polarization effects. When the horizontal polarization vortex beam is incident at different angles, the cross polarization component of the reflected beam shows a double-peak intensity distribution which is similar to the first-order Hermite-Gaussian mode. The distribution of horizontal polarization component is similar to that of the incident beam, and will show a double-peak intensity distribution which is perpendicular to the distribution of cross polarization components at the Brewster incidence. For the incident beam with arbitrary linear polarizations, we find that the polarized direction of cross polarization component is not perpendicular to the incident polarized direction, but exhibits an interesting rotational characteristic. The physical nature of this phenomenon is attributed to the different reflection coefficients of parallel and perpendicular polarizations. Experimental results agree well with our theoretical analysis.
2013, 62 (17): 174203. doi: 10.7498/aps.62.174203
Eye movement information is the key clue for recognizing the vision-dominated tasks, such as browsing the web, or watching a video. However, traditional wearable sensors are invasive and the vision-based eye trackers are very expensive and need time consuming calibration. Therefore, an activity recognition method based on eye movement analysis under one web camera is first proposed and the feasibility is assessed. First, an iris tracking method for the low quality image is proposed to acquire eye movement information. Then, five ten novel features are extracted from the horizontal and the vertical eye movement signals for activity recognition, and the optimal feature subset is selected. Finally, the support vector machine is used to assess the feasibility of the proposed method. Three experiments are designed for different applications: leave-one-out cross-validation, k-fold cross-validation, and validation after respective calibration. Experimental results show that their accuracies are 68.4%, 79.3% and 84.1%, respectively, which demonstrate the promise of eye based activity recognition using one web camera.
2013, 62 (17): 174204. doi: 10.7498/aps.62.174204
Since single image restoration algorithms using lots of priori information lead to high complexity and low computational efficiency, a gradient cepstrum analysis method is proposed to estimate the point spread function PSF for a single blurred image. Firstly, we present the basic principle of estimating PSF from gradient cepstrum of a single blurred image and use the phase retrieval algorithm to recover phase information of the two-dimensional PSF, which can obtain the estimated PSF rapidly, Secondly, to evaluate the accuracy of the proposed PSF estimation method, the total variation regularized image restoration model coupling with an image gradient fidelity term is established and an alternating direction method with rapid and stable convergence is adopted to optimize the energy function. Both synthetic and real blurred images are tested to verify the performance of our scheme. Results show that our scheme not only can estimate the PSF rapidly and accurately so that it overcomes shortcomings of traditional algorithm with slow convergence, but also suppresses ringing effects to preserve information in edges. These advantages provide theoretical and technical foundation of the real engineering requirement in single image deblurring, especially for large scale images.
2013, 62 (17): 174205. doi: 10.7498/aps.62.174205
Based on the results of constructing the wavelet transform in continuous variable quantum state and the classical continuous ridgelet transform, we construct the continuous complex ridgelet transform in the expression of quantum operators and representations. We study the theory of the complex ridgelet transform in quantum optic state via calculating the inner product and projection of quantum states.
2013, 62 (17): 174206. doi: 10.7498/aps.62.174206
We have investigated the entanglement time evolution of two coupled two-level atoms in Kerr medium. Entanglement of the system is calculated by making use of concurrence. The influences of initial state, Kerr medium, and dipole-dipole coupling intensity between two atoms on the entanglement degree of the two atoms are revealed. Results show that the appropriate choice for the nonlinear coupling constant of Kerr medium and the dipole-dipole coupling intensity can improve the degree of atom-atom entanglement and eliminate the entanglement sudden death completely. We also find that invariant and stable entanglement occurs for a particular initial state.
Experimental research on retrieval efficiency of atomic spin wave based on electromagnetically induced transparency
2013, 62 (17): 174207. doi: 10.7498/aps.62.174207
The retrieve process of stored light field is important for quantum information, nonlinear optics, and quantum optics. Electromagnetically induced transparency (EIT) is one of the popular methods. In this paper we demonstrate the co-propagating and counter-propagating scheme of EIT retrieved in vapor 87Rb atomic cell. Result indicates that the retrieval efficiency depends on the spatial distribution of the atomic spin waves. Our experimental results may be useful to quantum information and nonlinear optics with vapor atomic ensemble.
2013, 62 (17): 174208. doi: 10.7498/aps.62.174208
The instantaneous linewidth in the process of tuning is a very important parameter of laser, however only static linewidth in steady state could be obtained by all kinds of measurement at present. So we proposed a method of measuring instantaneous linewidth by time-frequency analysis based on local mean decomposition, and after its validity of extracting the instantaneous phase noise of simulation signal was proved, we set the heterodyne measurement system with ultrashort delay (about 0.5 ns) which came from 10 cm optical path difference. Finally, we not only extracted the time-frequency spectrum of the beat signal’s phase noise power, but also obtained the instantaneous linewidth of distributed-feedback diode laser under the pulse current for the first time so far as we Rnow.
Experimental characterization of polarization gain properties of 808nm semiconductor laser and analysis of energy band based on amplified spontaneous emissions from double facets
2013, 62 (17): 174209. doi: 10.7498/aps.62.174209
The information of optical gain of semiconductor lasers can be obtained through the amplified spontaneous emission from double facets. By utilizing this new approach, an experimental research about polarization (TE and TM) gain characteristics of continuously-operated 808 nm GaAs/AlGaAs quantum well laser is introduced in this paper. Through the measured gain spectra which are compared with the theoretical gain curves, we analyze the variations of hole subband corresponding to the polarizations along with the change of injection current, meanwhile the actual status of gain spectra and influential factors of the continuously-operated laser are discussed as well.
2013, 62 (17): 174210. doi: 10.7498/aps.62.174210
There was a problem in current cell gap measurement of liquid crystal (LC) lens. A method was proposed by adopting interference of linearly polarized light in this paper. It was claimed that the incident light was monochromatic light with a uniform distribution of light intensity. The polarization axis of the analyzer was perpendicular or parallel to the polarization axis of polarizer. The difference between light and dark interference fringes was the biggest when the angle was equal to 45° between the rubbing direction of alignment layer in the LC lens and the polarization axis of polarizer. The cell gap of LC lens can be calculated by the transmittance of LC lens center and the max transmittance of its other locations. The tilt angle was equal to the pre-tilt angle of LC at the LC lens center. This method was simple and reliable. Its accuracy is relatively high due to the use of optical interference principle.
Investigation on large-mode-area flat-topped optical fiber with microstructured core and its transmission characteristics
2013, 62 (17): 174211. doi: 10.7498/aps.62.174211
A novel microstructured-core optical fiber with large mode area and flat-topped mode field distribution is proposed. The core of the fiber is composed of high refractive index dielectric cylinders with a non-uniform distribution. Numerical simulation on the mode area, mode field distribution of the fundamental mode and other aspects of the fiber indicates that the fiber can effectively obtain flat-topped mode field distribution by tuning the parameters of the cladding and the core of the fiber. In addition, the flat-topped fiber has a large mode area of 1655 μm2 at the operating wavelength of 1064 nm.
2013, 62 (17): 174212. doi: 10.7498/aps.62.174212
Image reconstruction is one of the key technologies in the fields of physical imaging, which include optical imaging, photoacoustic imaging, sonar imaging, magnetic resonance imaging, and celestial imaging etc. Compressive sensing theory, the new research spot in recent years, describes that a small group of non-adaptive linear projections of a sparse or compressible signal contains enough information for signal reconstruction. Compressive sensing has been applied in many physical imaging systems. In this paper, we propose a new image reconstruction algorithm based on lp norm compressive sensing by combining the penalty function and revised Hesse sequence quadratic programming, and using block compressive sensing. Several images, such as “cameraman”, “barbara” and “mandrill”, are chosen as the images for image reconstruction. First, we take different sampling rates for image reconstruction to verify the algorithm. When the sampling rate is as low as 0.3, the signal-to-noise ratio of the reconstructed image can reach up to 32.23 dB. Then, when the sampling rate is above 0.5, by comparing with OMP algorithm, reconstructed images can be obtained with a higher signal-to-noise ratio and a shorter imaging time. Especially, when the sampling rate is 0.7, the imaging time is reduced by 88%. Finally compared with the existing algorithm based on lp norm compressive sensing, simulation results show that the new algorithm can improve the signal-to-noise ratio of reconstructed images, and greatly reduce the imaging time.
2013, 62 (17): 174701. doi: 10.7498/aps.62.174701
We have investigated the characteristics of gas flow in microchannels under the coupled effects of random surface roughness and velocity slip by the method of computational fluid dynamics. The random surface roughness is modeled by fractal geometry, and the velocity slip on boundary is described by second-order slip law. Results show that the simulated curves obtained by considering both second-order slip law and random surface roughness are in good agreement with experimental data in a range of averaged Knudsen number from 0.025 to 0.59, while the one gained by using Maxwell slip law are in agreement with experimental data in a range of averaged Knudsen number extending up to 0.1. Random surface roughness has an obvious effect on velocity slip: as relative surface roughness increases, velocity slip coefficients decrease. An approximate relation between relative surface roughness and velocity slip coefficients is given according to the results. Last but not least, random surface roughness has a significant effect on the pressure, velocity and Poiseuille number.
2013, 62 (17): 174702. doi: 10.7498/aps.62.174702
For the spreading of an insoluble surfactant-laden droplet over the corrugated topography, the lubrication theory is used to establish the physical and mathematical models of the spreading of droplet and to derive the base state and disturbance evolution equations for thin liquid film thickness and surfactant concentration. The stability of droplet spreading on topography surfaces, as well as the effects of several parameters are investigated based on the non-model stability theory. Results show that disturbance quantities reach minimum at the droplet center and spreading fronts, and achieve the maximum in thinning regions, and the negative disturbance of surfactant concentration is quite obvious. Disturbance wave number can enhance the stability of the droplet spreading, but with increasing wave number, the stability tends to be weak and even transform into instability. The spreading stability is distinctly promoted with decreasing Marangoni number or increasing corrugated topography height. The droplet evolution displays a much stable spreading for moderate values of Peclet number and topography wave number.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (17): 175101. doi: 10.7498/aps.62.175101
Viscosity is an important fluid transport property, and the viscosity data mostly are obtained from experimental measurements. The fixed path interference method with a cylindrical resonator is one of the most precise ways to gain the gaseous sound speed by measuring the resonance frequency and the half-width of the resonance peak. The gas viscosity affects the sound speed, leading to the offset of the resonance frequency and the increase of half-width of the resonance peak. Viscosity can be accurately acquired through the measurement of the resonance frequency and the half-width of the resonance peak, together with modifications due to the effect of the thermal boundary layer, the fill duct on the resonator shell, the transducer and the resonator shell vibration. In this paper, the way to acquire viscosity by the cylindrical resonator was developed and was verified by measuring argon (Ar) viscosity, and we find the result agreeing well with the data given in the literature.
2013, 62 (17): 175201. doi: 10.7498/aps.62.175201
The fluid model and the self-consistent dust charging model are used to investigate the Bohm criterion for the plasma sheath including two species of charged dust particles. Numerical calculation results are obtained using quasi-Newton method. Effects of two species of dust particles on the dust charging and the ion Mach number are discussed. As the number density of the fewer dust particles is enhanced, different changes will take place on the surface potential of the two species of dust particles. Either more number density or smaller radius of the fewer dust particle may result in a larger ion Mach number. In addition, the ion Mach number will reduce when the velocity of any kind of dust particles at the sheath edge increases.
2013, 62 (17): 175202. doi: 10.7498/aps.62.175202
Laser and plasma interaction (LPI) is the important part for the study of inertial confinement fusion (ICF). In order to have an investigation for the energy and spectrum of scattered light produced by laser-plasma interaction in Shen Guang-III prototype laser facility, a backscattered light diagnostic system was developed. This paper introduces the design and the damping factor of this system. The laser focus shape after using the coherent phase plate (CPP) has been analyzed. Experimental results with the energy and spectrum of backscattered light have been provided and compared after adding the CPP on the laser beam. It is found that the fraction of backscattered light can be reduced to below 5% under the laser condition 8×800 J after using the CPP. And the spectrum range with CPP is narrower than that without CPP on laser beam. These experimental data can improve the research on hohlraum energy.
2013, 62 (17): 175203. doi: 10.7498/aps.62.175203
The current division between the inner and the outer arrays is one of the key factors that impact the implosion dynamics and modes of nested wire array. This paper presents the first quantitative measurements of current division for nested wire array Z pinch on the Qiang Guang-I pulsed power facility. In experiments, the nested wire arrays, made of 3.8 μm-diameter tungsten wires, were 20 mm in height and 8 mm/16 mm in diameter for inner/outer array. Measurements for loads consisting of 42/21 wires in inner/outer array were compared with that of 21/42 in inner/outer array. Data of current versus time at various radial positions were obtained using magnetic probes until 20 ns before the current peak. Results show that the currents in inner and outer arrays increase during the rise of the driving current, the proportion of current in outer array decreases and that in inner array increases, while the current in outer array, for loads with 21/42 wires in inner/outer array, was larger than those with 42/21 wires in inner/outer array.
Two-dimensional simulation of atmospheric pressure cold plasma jets in a needle-plane electrode configuration
2013, 62 (17): 175204. doi: 10.7498/aps.62.175204
The propagation mechanisms of atmospheric pressure cold plasma jets have recently attracted much attention. In this paper, by using a self-consistent two-dimensional plasma fluid model, we have investigated the propagation problems in the cold atmospheric pressure helium plasma jets that are surrounded by helium itself and thin dielectric tube, respectively. The spatio-temporal distributions of electron density, ionization rate, electrical field, and electron temperature were obtained. It is found that both the radius and the permittivity of dielectric tube have an impact on the discharge characteristics. A new method of improving the electron density and plasma jet size was also proposed.
2013, 62 (17): 175205. doi: 10.7498/aps.62.175205
In order to better comprehend the dynamic behaviours of ion and electron during the Penning source discharge process under a low pressure and weak ionization condition, numerical simulation is carried out to study the penning source discharge and diffuse process. For constituting 2D axial symmetrical model and combining the particle simulation and Monte Carlo (PIC/MCC) method, elastic collision, excitation, and ionization reactions between electrons and hydrogen molecules, hydrogen atom and ions are taken into account. The effect of magnetic field configuration, secondary electron emission coefficient, derivational voltage, and gas pressure on the discharge characteristics is investigated. It has been found that the simulant discharge parameters, including electron and ion densities, anodic current and ionic current, H+ and H2+ densities, etc, are in good agreement with the experimental results. Based on our numerical simulation, the study of the hydrogen penning discharge is being changed from qualitative analysis to quantitative calculation, which is important for the design and optimization of the penning ion source.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (17): 176101. doi: 10.7498/aps.62.176101
The rheological behaviors of 5CB liquid crystal under the coupling effect of shear and electric field are investigated by theoretical and experimental study. Establish calculating equation of the system Gibbs free energy by adopting the continuum theory of liquid crystals which contains anchoring energy, elastic free energy, dielectric free energy and flow energy. Then the molecular orientation angle distribution and apparent viscosity of liquid crystal under the coupling effect are obtained by minimizing the Gibbs free energy, revealing the microscopic mechanism of rheological behaviors and influence rules of coupling effect from the molecular model. Meanwhile the calculated results are verified by rheological test. Comparative Analysis of the errors and reasons of theoretical and experimental results, which demonstrates that anchoring effect plays an important role in the molecular orientation and viscosity of liquid crystal. Both the theoretical and experimental results indicate that liquid crystals have electroviscous effect and behavior like non-Newtonian liquids under electric field. The viscosities of liquid crystals are determined by the coupling and competition action of shear and electric field, which can reach 4 times of its original value under electric field. This property of controllable viscosity is important in tribology, which can self-adaptively satisfy the requirement of viscosities for different working conditions as a "smart lubrication" under certain condition.
2013, 62 (17): 176102. doi: 10.7498/aps.62.176102
The MnO nanoparticles with uniform size (～15 nm) and shape have been synthesized in an inert atmosphers by high-temperature oil phase method. XRD patterns and HRTEM reveals that the as-synthesized MnO nanoparticles are of pure crystalline phase. TEM image shows that the MnO nanoparticles are in spherical shape with a narrow size distribution. Both oil phase and the nanoparticles protected with inert gas in the synthesis process can avoid the oxidization of Mn2+. The obvious exchange bias effect can be observed from the M-H loop of MnO nanoparticles under zero field cooling (ZFC) and FC measurements. Furthermore, the temperature-dependent AC susceptibility of the MnO nanoparticles reveals that the exchange bias effect originates from the antiferromagnetic MnO core and the spin-glass surface, rather than the superparamagnetic phase.
Molecular dynamics simulation of tensile deformation mechanism of the single crystal tungsten nanowire
2013, 62 (17): 176103. doi: 10.7498/aps.62.176103
Molecular dynamics method was used to simulate tensile deformation of the high-purity single-crystal tungsten nanowire prepared by the metal-catalyzed vapor-phase reaction method first proposed by our research group. Stress-strain curve and microscopic deformation structure were analyzed in order to reveal the tensile deformation characteristics and microscopic failure mechanism of the single-crystal tungsten nanowire. Results show that the whole stress-strain curve can be classified into five stages: elastic stage, damage stage, phase transition stage, hardening stage and failure stage, where the phase transition is the main reason for hardening of the single-crystal tungsten nanowire. The first stress drop is caused by irreversible change of the local atomic dislocation and twinning, and the second stress drop is due to lattice structure failure resulting from the local atomic dislocation of the strengthened material and the development of split-forming necking area leading to the fracture of single-crystal tungsten nanowires. Calculated result of the elastic modulus is in good agreement with the test results of elastic modulus of the single-crystal tungsten nanowire.
2013, 62 (17): 176104. doi: 10.7498/aps.62.176104
Using density functional theory, the structural parameters of α-U and bcc phases were obtained separately, in reasonable agreement with previous experimental and theoretical results. The enthalpy-pressure curve showed that the phase transition pressure was approximately 111 GPa. The structural behavior of γ-U under extreme loading conditions was exhibited by the ideal strength calculations. In addition, by analyzing the energy-strain relationship we found that the strain corresponding to the shear modulus c’ could decrease the total energy of U-Nb (6.25 at.%) alloy, indicating the instability of this structure.
2013, 62 (17): 176105. doi: 10.7498/aps.62.176105
Colloidal crystals composed of polystyrene micro-spheres (negatively charged, with a diameter of 300 nm) are fabricated by injecting aqueous suspensions of the micro-spheres with different volume fractions into sample cells which are made by gluing together two glass plates. Whose surfaces are coated with conductive films. The colloidal crystals have a face-centered-cubic structure with their (111) planes parallel to the surface of the sample cells. Laser diffraction is used to measure the structural changes of the colloidal crystals in an electric field. Structures of the colloidal crystals are characterized by using the Kossel-line method. It is found that the colloidal crystals are compressed isotropically in the electrical field. The lattice constants of the colloidal crystals decrease with the increase of the electric field, maintaining their face-centered-cubic structure. Results can be explained by the combined action of the electric field force, electrostatic repulsion and electrohydrodynamic force. The electric field makes all of the micro-spheres migrate to the positive plate of the sample cell and leads to a compression in the direction along the electric field. Then the electrohydrodynamic force produces an attractive interaction between the micro-spheres in the direction perpendicular to the electric field.
2013, 62 (17): 176106. doi: 10.7498/aps.62.176106
The single event effect of H-gate SOI NMOS devices in total dose ionizing are studied by means of numerical simulation. By analyzing the mobility degradation in the simulation process, the corrected mobility Lombardi model due to degradation at interfaces is obtained. As the simulated transfer characteristic curves of SOI transistor agree well with the experimental data, the single event effect of H-gate SOI NMOS devices in total dose ionizing is simulated by this corrected model. Results shows that the maximum drain currents of devices under the same conditions are slight increasing, but the transistors get a significant increase in the drain collected charge with increasing total dose level.
2013, 62 (17): 176401. doi: 10.7498/aps.62.176401
In this paper, the state of metastable equilibrium and the state of unstable equilibrium of water at a certain temperature are explored using an exact difference lattice Boltzmann model and the conditions of bubble (droplet) formation are investigated in the isothermal phase transition processes. From these simulation results, it is found that the model predictions are in good agreement with analytical results. Based on these works, a new model, which is based on exact difference lattice Boltzmann model and extended with an energy transfer equation to model heat transfer, is proposed to describe liquid-vapor phase transition process. The effects of the wall-fluid interaction strength on the bubble nucleation process in a pit are investigated using this new heterogeneous phase transition model. Simulation results accurately reproduce the characteristics of three stages of the bubble nucleation process. The changes of the contact angle, curvature radius, and volume with the bubble nucleation process are explored, and the relationship curve between curvature and bubble volume from the simulations is in qualitative agreement with the previous results.
2013, 62 (17): 176402. doi: 10.7498/aps.62.176402
The magnetism, stabilities and phase transition of Ru in hcp, fcc, bct and bcc structures are investigated with detailed first-principles calculations based on density-functional theory and quasiharmonic lattice dynamics approximation. Magnetic ground states and stability ranges of various phases are obtained. Calculated results indicate that the non-magnetic (NM)-hcp structure is the most stable in the entire pressure range at zero temperature, and the structural transition cannot be induced by pressure alone. NM-fcc structure is a metastable phase of bulk Ru, while both the NM-bcc and ferromagnetic (FM)-bct structures are dynamically unstable. At high pressure and temperature, a transformation from NM-hcp to NM-fcc structure will occur. Finally, the pressure-temperature phase diagram of Ru is presented.
Investigation on visible emission and n-type conductivity of ZnO thin films annealed at different temperatures
2013, 62 (17): 176801. doi: 10.7498/aps.62.176801
ZnO thin films with good visible emissions were deposited on Al2O3 substrates by pulsed laser deposition and subsequently annealed at different temperatures in oxygen ambient. The visible emission property of the films varied significantly with different annealing temperatures. The resistivity, carrier concentration and mobility of the films showed certain rules. From the results of X-ray diffraction, scanning electron microscope, photoluminescence and Hall measurements, the mechanism of visible emission and the reason of showing n-type conductivity in native ZnO thin films were analyzed in this paper.
Molecular simulations of adsorption and separation of natural gas on zeolitic imidazolate frameworks
2013, 62 (17): 176802. doi: 10.7498/aps.62.176802
Grand canonical Monte Carlo simulations were employed to investigate the adsorption and separation of C2H6, CO2 and CH4 on two zeolitic imidazolate frameworks (ZIF-2 and ZIF-71). The adsorption isotherm and isosteric heat of pure gas, the separation performance of C2H6-CH4, CO2-CH4 and C2H6-CO2 binary mixtures and C2H6-CO2-CH4 ternary mixtures on two ZIFs were simulated and discussed. For single component gas adsorption at a low pressure, the adsorption amount depended on isosteric heat; at a high pressure, due to the limited pore volume, ZIFs preferably adsorbed smaller size gas molecules. For gas mixture separation, energetic effect dominated at low pressure, therefore, ZIFs selectively adsorbed gas component with strong interactions; packing effect usually played an important role at high pressures, consequently, smaller size component would be more entropically favorable. Results demonstrated that both ZIF-2 and ZIF-71 were of good separation performance for these three binary mixtures. For the ternary mixture separation, it was found that ZIF-2 cowld effectively separate C2H6 and CO2 from CH4 at 3000-4000 kPa and room temperature.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (17): 177101. doi: 10.7498/aps.62.177101
Using first principle and based on the density functional theory, we have studied the effect of the single vacancy on the electronic properties of armchair graphene nanoribbons (AGNRs). Results show that the system is the most stable when the vacancy is at edge site. It is found that AGNRs always become metallic, regardless of the vacancy position. As the vacancy concentration decreases, the influence of the vacancy position on band structures becomes weaker and weaker. As the ribbon width increases, the particular value characterizing the strength of metallicity decreases in oscillation. Vacancy-induced semiconductor to metal transition in AGNRs provides the theoretical direction for the application of graphene in the electrionic devices.
First-principles study of structural stability and electronic properties of tetragonal and orthorhombic as well as monoclinic K0.5Na0.5NbO3
2013, 62 (17): 177102. doi: 10.7498/aps.62.177102
The energetic stability, structural and electronic properties of tetragonal, orthorhombic, as well as monoclinic K0.5Na0.5NbO3 are systematically studied using first-principles supercell model and virtual crystal approximation based on density functional theory with local density approximation and generalized gradient approximation. Our calculated results show that the total energy differences among the three K0.5Na0.5NbO3 phases are small, which are well consistent with the easy phase equilibrium at the phase boundary in the experiments. Furthermore, we also find that the total energy of the monoclinic phase is lower than that of the other two phases, which suggests that the monoclinic structure is energetically more stable than the others. Moreover, the calculated structural parameters are in good agreement with experimental values. In addition, the electronic structure results show that the bonding interaction in the monoclinic structure is stronger than that in the other structures, also indicating that the monoclinic structure is the most stable one.
2013, 62 (17): 177301. doi: 10.7498/aps.62.177301
Plasmonic excitations in mesoscopic-sized atomic chains are investigated by employing the tight-binding model. Based on the quantum response theory and random phase approximation, a plasma oscillation eigen-frequency equation is derived for calculation of the plasmon energy spectrum. The plasmon energy spectrum has been numerically calculated, and the eigen-oscillation of the system and the resonance behavior under the external electric field applied on the atom chain are investigated, respectively. Dependence of plasmonic excitation energy on the length of systems and electron density has been discussed. Results suggest that in the case of resonance, the resonant peak of dipole moment is corresponding to the plasmonic excitation, and this indicates that the external electric field excites the plasmon of the system. In resonance the oscillation amplitude of the charge is much larger than that in the case of non-resonance, especially the imaginary part of the charge has a more obvious enhancement. For the eigen-oscillations, the plasmonic excitation energy is greater than the single-particle excitation state at the same level; the length of atomic chains, the electron density, and the strength of Coulomb correlation have significant effects on the plasmon spectroscopy. For the given atom-chain length, with variation of number of electrons, the plasmonic excitation energy varies symmetrically around the half-filling. This indicates that the plasmon spectrum of the system is symmetrical for the electrons and holes.
The surface state properties (such as surface state density, time constant and level position related to the bottom of InAlN conduction band) of Ni/Au/-InAlN Schottky barrier diodes with nearly lattice matched (InN=18%) and tensilely (15%) or compressively (21%) strained InAlN barrier layer were evaluated, by using current-voltage (I-V), frequency-dependent capacitance-voltage (C-V) measurements and atomic force microscope (AFM) images. It was found that, with increasing content of In the surface state density increased and the barrier height of the Schottky contacts decreased, respectively. The C-V curves shifted toward the positive bias values with reducing measured frequencies, which became more apparent with increasing In content. It may be due to the hole emission from the surface states of Ni/Au/-InAlN Schottcky contacts. Atomic force microscope (AFM) images indicated that the InAlN surface became rougher with increasing In content, which may be the main reason for the increased surface state densities.
Analysis of characteristics and key influencing factors in magnetomechanical behavior for cable stress monitoring
2013, 62 (17): 177501. doi: 10.7498/aps.62.177501
Until recently the magnetomechanical behavior has been rather poorly understood with contradictory results and interpretations from different investigators in the study of stress monitoring by magnetic method. Based on the domain motion and field-induced magnetization process of magnetic material, the stress-induced magnetization process in two different magnetization states is analyzed in detail. Characteristics of the magnetomechanical behavior are revealed. Domain motion caused by stress always makes materials tend to stable state of free energy minimum and accordingly the magnetization will approach the anhysterestic magnetization. Moreover, it can be concluded that magnetization state is an essential factor influencing the magnetomechanical behavior. Experiments of magnetomechanical behavior for galvanized steel wire have been conducted for different magnetization state, and the results are in accord with the theoretical analyses. The magnetomechanical behavior is changed with magnetization state, which can be effectively used to explain the existing complex and diverse research results.
Preparation of nanostructured GaN films and their field emission enhancement for different substrates
2013, 62 (17): 177701. doi: 10.7498/aps.62.177701
Using pulsed laser deposition (PLD) method, we have prepared nanostructured GaN films of the same thickness on Si and SiC substrates, and analyzed their microstructure characterization and field emission properties. The results showed that the substrates of GaN nanostructured films had significant effect on the microstructure and field emission properties. Compared with the GaN nano-film on Si substrate, the field emission from the GaN nano-film on SiC substrate has been significantly improved: its field emission current was increased by orders of magnitude. The field emission enhancement should be originated from the nanocrystalline microstructure and its orientation polarization induced field enhancement effect. Results indicate that to prepare field emission films of outstanding performance, appropriate substrates and crystal microstructures of the films are the key issues.
2013, 62 (17): 177801. doi: 10.7498/aps.62.177801
Cr4+-doped transparent Li1.14Zn1.43SiO4 glass-ceramics were prepared by high-temperature melting and subsequent heat-treatment, and the crystalline, microstructural, and luminescence properties of the products prepared by different-temperature heat-treatment were investigated. Results showed that the glass-ceramics heat-treated at 580 ℃ for 2 h contained nano crystallines of about 5 nm in size, and a broadband infrared emission centered at 1226nm with full width at half maximum of more than 230 nm and a decay time of about 200.07 s were observed by exciting with an 808 nm laser diode. Mean while, it is believed that the crystalline field environment of Cr4+ is changed with the increase of heat-treatment temperature, which results in blue shift and red shift of absorption and fluorescence spectra, respectively.
Photoluminescence properties of selenium nanocrystals on Si(100) substrate formed by rapid thermal annealing
2013, 62 (17): 177802. doi: 10.7498/aps.62.177802
We have investigated the structure and photoluminescence (PL) properties of Se nanocrystals (NCs) obtained by rapid thermal annealing of a-Se films on Si substrate. The size of Se NCs in a trigonal phase increases linearly with increasing temperature. Moreover, three PL peaks located at 1.4, 1.7 and 1.83 eV are observed, which are attributed to the emission of defects in amorphous Se, donor-acceprter pair (DAP) recombination at the interface of amorphous Se and Se NCs, and interband transition of Se crystals, respectively.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (17): 178101. doi: 10.7498/aps.62.178101
Microstructure, characteristic and metamorphism of Mg2(Si,Sn) compound phase are studied in as-cast Mg-Sn-Si alloy. The results indicate that Sn atom can replace the partial Si of Mg2Si then form Mg2(Si,Sn) compound phase, and structure of the ternary compound is the same as Mg2Si and Mg2Sn, all belong to face-centered cubic. The element content of Mg2(Si,Sn) phase is not invariable, the Mg2(Si,Sn) phase with high Si content is in Si enrichment region, while it with low Si content is in Si poverty region. The property of Mg2(Si,Sn) phase with high Si content is close to Mg2Si phase, the property of the phase with high Sn content is close to Mg2Sn phase. In experiments, the nano-hardness, elastic modulus, vickers hardness and other physical properties of Mg2(Si,Sn) phase are between Mg2Si phase and Mg2Sn phase, in the metamorphism process of Chinese-script-like Mg2Si phase, Mg2(Si,Sn) compound phase plays a role as a bridge.
Hydrothermal synthesis of K, Na doped Cu-S nanocrystalline and effect of doping on crystal structure and performance
2013, 62 (17): 178102. doi: 10.7498/aps.62.178102
Cuprous sulfide (Cu2S) nanocrystals and K or Na doped KCu7S4 nanowires and NaCu5S3 micro-nanospheres have been synthesized successfully by using a simple hydrothermal method, using KOH or NaOH as mineralizing agent, CuCl22H2O and S powders as copper and Sulfur sources, respectively. The structure and morphology are characterized and analyzed by X-ray diffraction (XRD), energy dispersive X-ray spectrum (EDS), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results reveal that under conditions that the amount of KOH is below 1g or the amount of NaOH below 2 g, the product is of the orthorhombic chalcocite Cu2S, while with high alkali amount (no less than 3 g), K+ or Na+ is successfully incorporated into the Cu-S structure; KCu7S4 has the pure tetragonal single crystal structure, and its uniform nanowires can be up to several tens of micrometers in length. Na doping has no effect on the morphology of the product, which forms the hexagonal NaCu5S3. The formation and growth of the product are closely related to the reaction temperature, reaction time and mineralizing agent. And, the formation and doping mechanisms are discussed. Finally, the influence of the alkali metal ion doping on the optical properties of the product is investigated. The diffuse reflectance spectra demonstrate that the optical band gaps of Cu2S, NaCu5S3 and KCu7S4 nanocrystallines is 1.21, 0.49, 0.42 eV, respectively. And K+ or Na+ doping greatly affects the optical characteristics.
Structural characterization and magnetic properties of perpendicularly magnetized MnAl films grown by molecular-beam epitaxy
2013, 62 (17): 178103. doi: 10.7498/aps.62.178103
Perpendicularly magnetized MnAlx thin films with different Al contents have been epitaxied on GaAs (001) substrates by a molecular-beam epitaxy system. Crystalline quality of MnAlx films is closely related to Al content, and magnetic properties of MnAlx films are improved as crystalline quality of MnAlx fims increases. MnAl0.9 film shows the best crystalline quality and magnetic property among all samples. So we grew MnAl0.9 films at different growth temperatures to further optimize growth conditions. With increasing temperature, the chemical order parameter increases and the full width at half maximum of the τ(002) peak decreases, which reveal the improvement of crystalline quality. Higher perpendicular magnetization, coercivity and magnetic anisotropy are found as growth temperature increases. The best crystalline quality and perpendicularly magnetized properties are found at 350℃; the coercivity of 8.3 kOe, saturation magnetization of 265 emu/cm3, Mr/Ms of 0.933 and perpendicular magnetic anisotropy constant of 7.74 Merg/cm3 are achieved. These tunable perpendicularly magnetized properties and good compatibility associated with semiconductor materials make the noble-metal-free and rare-earth-free MnAl films attractive in the application of spintronic devices.
2013, 62 (17): 178104. doi: 10.7498/aps.62.178104
We experimentally achieved optical third harmonic generation (THG) from two-dimensional periodically arrayed gold-island films. The gold-island films were fabricated using micro-spherical lithography. By using a reflection-type optical system, these arrays can produce significant THG with the help of a spectrum-resolved femto-second laser. At the localized surface plasmon (LSP) excitation wavelength of the fundamental wave, THG is greatly enhanced due to the strong light localization effect. The radiation direction of THG satisfies the momentum matching condition.
2013, 62 (17): 178105. doi: 10.7498/aps.62.178105
The dendritic growth patterns in directional solidification with different amplitudes of solid-liquid interface energy anisotropy were investigated using the two-dimensional cellular automata (CA) model. It is shown that when the preferred growth direction of the crystal was the same as the direction of thermal gradient, the solidification pattern would transform from seaweed to dendrite with the increase of amplitude of interface energy anisotropy. The amplitude of interface energy anisotropy could also influence the morphology of dendritic tips. As the amplitude of interface energy anisotropy increased, the dendritic tip radius, the liquid concentration ahead of the tip and the tip undercooling decreased. A power law relationship evisted between the stability parameter of dendritic tip and the amplitude of interface energy anisotropy in directional solidification. The primary arm spacing changed little with the increase of interface energy anisotropy. When the angle between the preferred growth direction of the crystals and the direction of thermal gradient was-40, and the amplitude of interface energy anisotropy increased, the solidification pattern would transform from seaweed to degenerated dendrite and finally to tilted dendrite.
2013, 62 (17): 178401. doi: 10.7498/aps.62.178401
Coherent power-combining by using several magnetrons is essential because the output power of one single magnetron cannot meet the need of large-scale industrial applications. In order to obtain phase coherence condition of the power-combining of normal magnetrons, injection-locking technology should be adopted to make sure the stability of the operating frequency and phase difference. Under impedance matching conditions, equivalent circuit of injection-locked magnetron is analyzed with the conditions of the magnetron stable frequency. The small injection-ratio and large injection-ratio situations of the injection-locked magnetrons are both derived. Furthermore, large injection-ratio situation indicates a greater frequency-locked bandwidth than small injection-ratio situation. Theoretical results are analyzed by MATLAB and injection-locked theory is verified by three-dimensional particle-in-cell simulation. The frequency-locked bandwidth and phase differential equation are given and curves of the phase difference are drawn for different initial phases. Output power and frequency of A6 magnetron are obtained by simulation under both free and injection-locked oscillation conditions. Simulation results show that magnetron can be locked and working stably in frequency-locked bandwidth predicted by both situations. Moreover, in the large injection ratio status the large injection-ratio situation is more accurate than the small injection-ratio situation.
The impact of interface charges at the heterojunction on the carriers transport in abrupt InP/InGaAs heterojunction bipolar transistor
2013, 62 (17): 178501. doi: 10.7498/aps.62.178501
The carriers transport at the base-emitter interface of abrupt heterojunction bipolar transistors (HBTs) is controlled by thermionic emission and tunneling, which depends on the form and height of the energy barriers. The interface charges at the heterojunction disturb the energy barriers, thus bringing about the change of the electrical characteristics of HBT. Based on thermionic-field-diffusion model which combines the drift-diffusion transport in the bulk of the transistor with the thermionic emission and tunneling at the interface, a conclusion can be drawn that the positive interface charges can improve the electrical characteristics of abrupt InP/InGaAs HBT, while the negative interface charges deteriorate the devices.
Design of silicon based germanium metal-semiconductor-metal photodetector enhanced by surface plasmon resonance
2013, 62 (17): 178502. doi: 10.7498/aps.62.178502
Surface plasmon excited by metallic grating integrated on metal-semiconductor-metal can greatly improve the absorption of devices. In order to deeply explore the excitation and resonant discipline of surface plasmon, a design of metal-semiconductor-metal based on ultra-thin germanium is proposed. By using finite difference time domain (FDTD) method, the effects of grating period, grating depth, grating space, and thickness of the active layer on the performance of surface plasmon resonance supported device are investigated in detail. The structure parameters of the device are optimized, and the mechanism of surface plasmon excited by each interface as well as spectrum absorption enhanced by surface plasmon resonance is analyzed in detail. Simulation results show that the germanium device with an ultra-thin active layer of 400 nm has a high absorption in the communication band, especially at the wavelength of 1550 nm the normalized spectral absorption can be as high as 53.77% with an enhancement factor of 7.22. Surface plasmon resonance can greatly improve the optical response of high-speed optoelectronic device, thus an efficient way is provided to solve the trade-off between photodetector responsivity and speed of the device.
2013, 62 (17): 178701. doi: 10.7498/aps.62.178701
Mesoporous silica nanoparticles (MSN) with cationic and anionic surface charges were synthesized, Their adsorption behaviors to the supported lipid membranes at different pH values were also studied using QCM-D. We found that NH2-MSN could be adsorbed onto the membrane at pH values from 4 to 8, while the adsorption of COOH-MSN onto the membrane could not occur due to its charge being always the same as that of the membrane at any pH values. These results might provide the information for understanding and predicting the interactions between nanoparticles and cell membranes, and could be effectively used in drug delivery systems and disease treatment.
2013, 62 (17): 178801. doi: 10.7498/aps.62.178801
This paper studies the influence of poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) on solution-processable functionalized graphene oxide (SPFGO) composite film-based organic light emitting Diode (OLED) and organic photovoltaic (OPV) performance for different SPFGO concentrations. There is a strong quenching of photoluminescence when MEH-PPV is doped with SPFGO, which means there is a strong transfer of electron and energy between MEH-PPV and SPFGO. Doping SPFGO in MEH-PPV can improve the performance of OLED at low concentration, and the performance will be the best when the concentration of SPFGO is 0.2%; however, the performance of OPV remains unchanged. The performance of OPV could be improved by high doping concentration of SPFGO, the performance will be the best when the concentration of SPFGO reaches 15%, and there is a quenching in the electroluminescence (EL) of OLED. As shown in the statistics of the experiment, SPFGO can increase the injectivity of carriers, and when the SPFGO is of low concentration, it can increase the luminous intensity of OLED and reduce the threshold voltage. SPFGO can act as an electron acceptor, and when the concentration of SPFGO is high, the exciton dissociation at MEH-PPV/SPFGO interface can be improved, and the performance of OPV can be also improved. Therefore, the concentration of SPFGO should be the main factor in adjusting the performance of OLED and OPV separately.
2013, 62 (17): 178902. doi: 10.7498/aps.62.178902
This paper investigates the congestion and efficiency in complex traffic and transportation networks. Effects of different distributions of capacity and origin-destination traffic demand on the degree of congestion and efficiency are explored in different network topologies including scale-free networks, random networks and small-world networks. According to the increase of average traffic demand, the transition from free flow state to congested state is analyzed. For easy comparison, we discuss the reciprocal of the congestion degree, which is defined as the network unobstructedness. A linear relation between the degree of unobstructedness and efficiency in different networks is uncovered, and the linear proportional coefficients are different in scale-free networks, random networks and small-world networks. These coefficients can also be used to describe the different transport performance in different networks.
COMPREHENSIVE SURVEY FOR THE FRONTIER DISCIPLINES
Identifying the most important nodes, or ranking the node importance by using the method of quantitative analysis in large scale networks are important problems in the complex networks. In this article, the metrics for node importance ranking in complex networks are reviewed and the latest progresses in this field are summarized from two prospects: the network structure and the spreading dynamics. The merits, weaknesses and applicable conditions of different node importance ranking metrics are analyzed. Finally, several important open problems are outlined as possible future directions.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
A new method of forecasting initial formation temperature during the whole drilling process based on proportional-integral control principle
2013, 62 (17): 179101. doi: 10.7498/aps.62.179101
A strategy based on proportional-integral feedback control was applied to gradually feedback the error between simulation of transient heat transfer model and logged date to forecast initial formation temperature. In this study, based on the each control unit of mass, momentum and energy conservation principles in a wellbore, the transient heat transfer model was developed between circulation and shut-in stages under real casing program and drilling string assembly condition, which were solved by full implicit finite difference method. Meanwhile, the proportional-integral control principle was introduced to compare the error range between measured temperature and prediction temperature, which can precisely and quickly obtain initial formation temperature. Combined with a deep well basic data, the results show that the heat exchange efficiency of wellbore and formation was changed by the casing pipe depth, thus affecting formation temperature distribution of the near-well zone. What’s more, the initial and boundary conditions of each control unit in the down-hole was also changed by circulation and shut-in operating time during the drilling process, leading to the variation of distribution distance of the initial formation temperature of the near-well zone. Development of the numerical models and the research methods can provide accurately, economically and quickly to obtain theoretical basis for oil drilling, geothermal well exploiting and the initial formation temperature information.