Vol. 62, No. 2 (2013)
2013-01-20
GENERAL
2013, 62 (2): 020201.
doi: 10.7498/aps.62.020201
Abstract +
In this paper, the approximate symmetry reduction for the initial-value problem of perturbed diffusion equations with source term is studied by the approximate generalized conditional symmetry. The classification of governing equations is given, and the Cauchy problem of partial differential equations is reduced to initial-value problem of ordinary differential equations. Finally, the approximate solution is obtained by solving the reduced system of equations.
2013, 62 (2): 020202.
doi: 10.7498/aps.62.020202
Abstract +
Neural mass models can produce electroencephalography (EEG) like signals corresponding to interical, pre-ictal and ictal activities. In this paper, a novel closed-loop feedback control strategy based on algebraic estimation is proposed to eliminate epileptiform spikes in neural mass models. Algebraic estimation plays a role in observing the states of the model in order to construct the controller. For a network of coupled neural populations, the characteristics regarding the closed-loop feedback control strategy, including the relationship between the type of controlled populations and the ability of eliminating epileptiform spikes, the relationship between the number of controlled populations and control energy, the relationship between the model parameters and control energy, are determined by numerical simulations. The purpose is to establish the rules for the proper control of eliminating epileptiform spikes with as less control energy as possible. Moreover, the proposed control-loop control strategy is compared with a direct proportional feedback control strategy by numerical simulations. It is shown that the use of algebraic estimation makes a reduction of control energy.
2013, 62 (2): 020203.
doi: 10.7498/aps.62.020203
Abstract +
According to directed Email networks and the spread characteristics of Email virus, we study the behavior of the virus shock propagation in Email networks by using the mean field method to build delay differential equation model of viral spread. Then, the sufficient condition about the existence of shock solution's global attractor is given in theory. The existence and control of attractor are proved by numerical experiments. Our research indicates that spread probability between subgraphs determines the existence of attractor, and effective rate of spread determines the amplitude of attractor. Therefore these two parameters are significant in prediction of the scale of viral spread in networks.
2013, 62 (2): 020204.
doi: 10.7498/aps.62.020204
Abstract +
In complex networks, it is significant how to rank the nodes according to their importance. Most of the existing methods of ranking key nodes (e.g. degree-based, betweenness-based) only consider one factor but not the integration of whole complex network in evaluating the importance of nodes, so those methods each have a limited application range. In this paper, a multi-attribute decision-making method to identify the key nodes in complex networks is proposed. In our method, each node is regarded as a solution, and each importance evaluation criterion as one solution's attribute. After that, we calculate the closeness between each solution and the ideal solution in order to obtain the integration results of node importance in complex networks. The proposed method can be used in a variety of complex networks. It is also easy to evaluate the importance evaluation criteria. Finally, experimental results show that the proposed method is effective.
2013, 62 (2): 020301.
doi: 10.7498/aps.62.020301
Abstract +
There exist some disadvantages in the calculation of two-dimensional Poisson equation with several common methods. A new ameliorative algorithm is presented. It is based on a parallel successive over-relaxation (PSOR) method, by using the multi-objective genetic algorithm to search for optimal relaxation factor, with which the problem of optimal relaxation factor selection in PSOR is solved. The multi-objective fitness function is constructed, with which the genetic algorithm parameters are optimized. The analysis mainly focuses on algorithm computation, time cost and accuracy of error correction. The performance of the ameliorative algorithm is compared with those of Jacobi, Gauss-Seidel, Successive over relaxation iteration (SOR) and PSOR. Experimental results show that relaxation factor has a significant effect on the speed of solving Poisson equation, as well as the accuracy. The improved algorithm can increase the speed of iteration and obtain higher accuracy than traditional algorithm. It is suited for solving complicated finite difference time domain equations which need high accuracy. The higher the accuracy requirement, the better the performance of the algorithm is and the more computation time can also be saved.
2013, 62 (2): 020501.
doi: 10.7498/aps.62.020501
Abstract +
In order to study the dynamic scaling behavior of the space-fractional stochastic growth equation with correlated noise, we simulate numerically the space-fractional Edwards-Wilkinson (SFEW) equation driven by correlated noise in (1+1)-dimensional case based on the Riesz-and the Grmwald-Letnikov-type fractional derivatives. The scaling exponents including growth exponent, roughness exponent and dynamic exponent with different noise correlation factors and fractional orders are obtained, which are consistent with the corresponding scaling analysis. Our results show that the noise correlation factors and fractional orders affect the dynamic scaling behavior of the SFEW equation, which displays a continuous changing universality class.
2013, 62 (2): 020502.
doi: 10.7498/aps.62.020502
Abstract +
The research on the stability theory of fractional order nonlinear system has an important value for the application of synchronization and the control of fractional order chaotic system. The discussion that the stability discrimination of fractional order nonlinear system is converted into that of corresponding integer order nonlinear system has an important significance. In this paper, through the examples, for time-varying coefficient matrix, we point out the existing mistake of the discrimination theorem that states that if the integer system is stable, then its corresponding fractional system with order less than one is also stable. We also analyze the causes of the mistake.
2013, 62 (2): 020503.
doi: 10.7498/aps.62.020503
Abstract +
In the paper, the chaotic characteristic of the quadratic function in plane unit area is studied, and it is found that the standard quadratic mapping is Li-Yorke chaos, and also Devaney chaos, and that under certain conditions, there are a large number of quadratic functions that are chaotic. Some quadratic functions can transform into the standard quadratic functions by moving and zooming, without changing their chaotic characteristics. In addition, non-standard quadratic function is preliminary studied. The chaotic characteristic of the quadratic curve is analyzed by calculating Lyapunov exponents and drawing the bifurcation diagram of conic. The bifurcation diagram of the parameter variation and the area distributing diagram of parameter control points have certain research value. The study also shows that more conic curve cross iteration can generate a better chaotic sequence, and the chaotic sequence can be used to image encryption and other practical purposes.
2013, 62 (2): 020504.
doi: 10.7498/aps.62.020504
Abstract +
The complex dynamical evolution of a circuit system composed of two nonlinear circuit subsystems, which is switched by a periodic switching, is investigated. According to the fact that the magnification of an open-loop operational amplifier is maximum magnification, namely, the operational amplifier is always in a positive or negative saturated state, when an input voltage becomes positive from negative through zero, the output voltage jumps from the positive saturation into negative saturation. In this paper the jump function is selected as a nonlinear part in subsystems. Firstly through the stability analysis of the subsystems, their oscillation behaviors in the parameter space are given correspondingly. Secondly the complex oscillation behavior and mechanism of the switched system are discussed in the parameter space of one subsystem. The periodic orbit of the switched system is divided into four parts, influenced by non-smooth characteristics of the subsystems and switching. With the variation of the parameters, grazing bifurcation appears, and then the whole periodic orbit is separated into two symmetrical periodic oscillations. Finally the convesion of switching points into the periodic oscillation is given,and the mechanism at switching point is discussed.
2013, 62 (2): 020505.
doi: 10.7498/aps.62.020505
Abstract +
The output power spectrum and signal-to-noise ratio (SNR) of the first order linear system driven by sinusoidal and white noise signal are analyzed. The result shows that the linear system under additive noise does not perform traditional stochastic resonance (SR), but it reveals the parameter-adjusted SR in a broad sense, which means that a resonance peak appears in the curve of SNR versus system parameter. The output spectrum properties under different sampling frequencies are analyzed for a signal with an arbitrary frequency, leading to a conclusion that increasing sampling frequency properly can be beneficial to the detection of the character signal.
2013, 62 (2): 020506.
doi: 10.7498/aps.62.020506
Abstract +
The dependence of sensitivity on initial conditions is the essence of chaos. And the randomness of chaos originates from the high sensitivity to initial values, which is measured by the Lyapunov exponents. It is found in this paper that the cascade of chaotic systems can considerably improve the Lyapunov exponents of cascade chaos and other dynamic properties. Therefore, in this paper, we study the cascade of chaotic systems and the influence on dynamic performances of the cascade chaos, and we present the definition and conditions of chaotic system cascade. It is proved in theory that the Lyapunov exponent of cascade chaos system is a sum of Lyapunov exponents of cascade subsystems. Appropriate cascade for chaotic systems can increase system parameters and expand parameter regions of chaos mapping and full mapping, thereby enhancing initial condition sensitivity of chaotic map and security of chaotic pseudo-random sequences. For logistic map, cubic map and tent map, the dynamic characteristics of logistic-logistic, logistic-cubic and logistic-tent cascade are investigated in detail, verifying the improvements on dynamic characteristics of cascade chaos systems. The proposed chaotic cascade system can be used to generate better pseudo-random sequences for initial condition sensitivity and security.
2013, 62 (2): 020507.
doi: 10.7498/aps.62.020507
Abstract +
The Poincare section method is an effective method to simplify the analysis of complex dynamic system motion state. To achieve online observing system states conveniently, an arbitrary directional Poincare plane section physical electronic circuit in three-dimensional space is designed and realized. Firstly, the key problems of an arbitrary Poincare plane section circuit design are analyzed and studied in detail. And then the physical circuit is realized in classification. As Chua's circuit has rich dynamic behaviors, the typical Chua's circuit is chosen as the experimental dynamical system. And then a lot of the physical experiments with this Poincare plane section circuit are performed in real time. For example, Poincare plane section diagrams in different conditions of Chua's circuit are measured, and the test experiments in the same kind of chaotic state, with different plane sections chosen, are carried out. All Poincare section map diagrams and phase diagrams are measured by two double-channel oscilloscopes (analogue oscilloscope and digital oscilloscope). At the same time, computer simulation experiments are conducted by using Matlab. These results show the practicability and effectiveness of the Poincare plane section circuit.
2013, 62 (2): 020508.
doi: 10.7498/aps.62.020508
Abstract +
Complicated behaviors of a compound system with periodic switches between different types of Chen systems are investigated in detail. In the local analysis, the critical conditions such as fold bifurcation and Hopf bifurcation are derived to explore the bifurcations of the compound systems with different stable solutions in the two subsystems. Different types of oscillations of this switched system are observed, of which the mechanism is presented to show that the trajectories of the oscillations can be divided into several parts by the switching points, governed by the two subsystems respectively. Because of the non-smooth characteristics at the switching points, different forms of bifurcations may occur in the compound system, which may result in complicated dynamics such as chaotic oscillations, instead of the simple connections between the trajectories of the two subsystems. By the Poincaré mapping, the location of the fixed point and Floquet characteristic multiplier of switching system are discussed.With the variation of the parameter, the system can evolve into chaos via the cascading of period-doubling bifurcation. Besides, the system can evolve into chaos immediately by saddle-node bifurcations from period solutions.The non-smooth bifurcation mechanism of periodic switching system can be revealed by the research.
2013, 62 (2): 020509.
doi: 10.7498/aps.62.020509
Abstract +
Taking the modified Morris-Lecar neuron model for example, we consider the synchronous behaviour between "Hopf/homoclinic" bursting and "SubHopf/homoclinic" bursting. Firstly, the synchronization between two coupled bursting neurons with the same topological type is investigated numerically, and the results show that the coupling strength reaching the synchronization of the membrane potential of "Hopf/homoclinic" bursting is smaller than that of "SubHopf/homoclinic" bursting, that is to say, the former can reach complete synchrony of the membrane potential more easily than the latter. Secondly, we study the synchronous behavior of two coupled bursting neurons with different topological types by numerical analysis, and find that with the increase of the coupling strength the two different types of bursting neurons reach the bursting-synchrony first, and then they can reach complete synchrony of the membrane potential when the coupling strength is strong enough, and the type of synchronous state is inclined to the type of easy synchronization, namely, "Hopf/homoclinic" bursting. To our surprise, the slow variables exhibit phase synchronization instead of complete synchronization. Moreover, there is a linear relationship between the both slow variables. This point is distinctly different from the results of the existing documents.
2013, 62 (2): 020510.
doi: 10.7498/aps.62.020510
Abstract +
Topological horseshoe theory is fundamental for studying chaos rigorously, which, however, has rarely applied to hyperchaos. The reason is that it is too hard to find a topological horseshoe in a hyperchaotic system, due to the high dimension of the system and the multiple expansion directions in the state space. Therefore, in this paper a practical algorithm for three-dimensional (3D) hyperchaotic maps is proposed. Usually, a hyperchaotic system has a large negative Lyapunov exponent, its attractor is often contracted closely to a certain surface. Based on this feature, the algorithm first deducts the dimension along the direction of contraction to obtain a 2D projective system; then it detects a projective horseshoe with 2D expansion; finally, it constructs a 3D horseshoe for the original system. In order to verify the validity of the algorithm, it is applied to the classic hyperchaotic Lorenz system and the famous Saito hyperchaotic circuit, and their horseshoes with 2D expansion are successfully found from the Poincaré mapping.
2013, 62 (2): 020511.
doi: 10.7498/aps.62.020511
Abstract +
The stability of equilibrium of a T chaotic system is analyzed, and the system bifurcation, Lyapunov exponent, Poincare section with numerical analysis are studied. Also, the synchronization problem with T chaotic systems with known or unknown parameters is studied in this paper. According to the Lyapunov function, feedback controller of the system is designed and has been proved. An electronic circuit is designed to realize the controller using Multisim. The simulation results demonstrate the effectiveness and realizableness of the proposed method.
2013, 62 (2): 020512.
doi: 10.7498/aps.62.020512
Abstract +
A new method to generate multi-wing butterfly chaotic attractors is presented. Based on the three-dimensional Lorenz system, in this paper we propose a four-dimensional multi-wing chaotic system by appending a state variable and a piecewise linear function. The equilibrium points and Lyapunov exponent spectra of the system are studied. Furthermore, an electronic circuit is designed to implement the system. The experimental results are in agreement with numerical simulation results, which verify the feasibility and availability of this method.
2013, 62 (2): 020513.
doi: 10.7498/aps.62.020513
Abstract +
Spatiotemporal chaos synchronization of complex networks by Backstepping design is investigated. Backstepping design is extended from synchronization between two chaotic systems to the synchronization of complex network constituted spatiotemporal chaotic systems. The relation between the configuration coefficient and the control gain is identified according to the stability theory. When the control input is added to any node of the network, the network synchronization is realized. Furthermore, simulation is made to verify the effectiveness of the synchronization mechanism.
2013, 62 (2): 020514.
doi: 10.7498/aps.62.020514
Abstract +
Based on the finite time control Lyapunov function the synchronization control between unified chaotic system and chaotic Liu system with uncertain parameters and different structures is investigated. The feedback control law does not require to know the specific value of parameter, but only depends on the variation range of the parameter. Compared with existing control method, it can effectively overcome the effect of mismatched parameters, moreover, the feedback is relatively simple and robust. Simulation results verify the effectiveness of the proposed control method.
2013, 62 (2): 020701.
doi: 10.7498/aps.62.020701
Abstract +
A hybrid optimization approach with a combination of linear programming and nonlinear programming algorithm for designing a compact self-shielded magnetic resonance imaging (MRI) superconducting magnet system is presented. The designed coils possess advantages of low construction costs, simple coil structure and the maximum magnetic strength within coils, current margin and electromagnetic stress easy to control. Firstly, in the stage of linear programming optimization, the feasible rectangular region can be divided into two-dimensional meshes, and a current map is calculated for meeting the magnetic field constraints over the surfaces of DSV sphere and 5 gauss stray field ellipse; Secondly, the current map has many nonzero current clusters and each cluster can be discretized into a solenoid. A nonlinear programming algorithm is employed to optimize the positions of all solenoids for minimizing the total coil volume and meeting all constraints including magnetic field which is the same as linear programming stage, and maximum magnetic strength, current margin and the gap between neighborhood inner coils. A 1.5 T compact self-shielded MRI superconducting magnet system is studied, the total coil length is only 1.32 m and the peak-peak homogeneity over 50 cm DSV is 10 ppm. The design approach is flexible and efficient for designing symmetrical and asymmetrical horizontal MRI and also open bi-planar MRI system.
NUCLEAR PHYSICS
2013, 62 (2): 022801.
doi: 10.7498/aps.62.022801
Abstract +
Aiming at checking the conceptual design of the subcritical reactor, an experiment using activation technique was carried out on a depleted uranium shell of R19.4/30.0 cm with D-T neutrons. The 6 depleted uranium foils were activated at 90° with respect to the incident D beam in the shell, and distributions of 238U (n, γ) reaction rates, 238U (n, f) reaction rates, 238U (n, f) reaction rates and 238U (n, 2n) reaction rates were obtained, by measuring characteristic γ rays generated by corresponding uranium reactions. The relative uncertainties are 3.6%–3.7% for 238U (n, γ) reaction rates, 5.1%–5.9% for 238U (n, f) reaction rates and 238U (n, f) reaction rates, and 4.3%–4.7% for 238U (n, 2n) reaction rates. The experiment was simulated using MCNP5 code with ENDF66c library, and the calculation-to-experiment ratios are 0.972–1.034 for 238U (n, γ) reaction rates, 0.983–1.058 for 238U (n, f) reaction rates and 238U (n, f) reaction rates, and 0.979–1.019 for 238U (n, 2n) reaction rates.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (2): 023401.
doi: 10.7498/aps.62.023401
Abstract +
The stereodynamic properties of the reaction N(4S)+NO(X2Π)→N2(X3Σg-)+O(3P) in different initial reagent rotational states are studied theoretically by using the quasiclassical trajectory method on two lowest 3A" and 3A' potential energy surfaces at a collision energy of 0.6 eV. The vector properties of different rotational states on the two potential energy surfaces are discussed in detail. The results indicate that the rotational excitation of NO has a considerable influence on the stereodynamic property of reaction occurring on the 3A' potential energy surface, which can be ascribed to the early barrier on this potential energy surface.
2013, 62 (2): 023601.
doi: 10.7498/aps.62.023601
Abstract +
The possible equilibrium geometries of WnNim (n+m=8) clusters are optimized by using the density functional theory at the B3LYP/LANL2DZ level. For the ground state structures, the dipole moment, polarizability and vibrational spectrum are analyzed. The calculated results show that each of all the clusters of WnNim (n+m=8) has a polarity, and W-rich clusters which have a strong nonlinear optical effect each and are easy to be polarized by external electromagnetic field, that vibrational frequencies are mainly distributed in a 0–350 cm-1 range, but the cluster of W4Ni4, due to the particularity of vibration mode, has a obviously strong peak on IR spectrum and also on Raman spectrum, each at a frequency of 421.971 cm-1, and that the W5Ni3 cluster, with high symmetry of C3v point group, presents a resonance phenomenon on IR spectrum.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (2): 024101.
doi: 10.7498/aps.62.024101
Abstract +
Based on transformation optics theory, an elliptical scattering-shifting cloak is designed and the constitutive parameter tensor expressions are derived. Then full-wave simulations to mimic the ellptical dielectric and conductor cylinder are obtained by using finite-element software. The results of full-wave simulations validate the constitutive parameter tensors we derived and verify that the scattering-shifting cloak can imitate any object including dielectric and conductor: these results provide a new theoretical approach to design cloaks.
2013, 62 (2): 024102.
doi: 10.7498/aps.62.024102
Abstract +
Using the HFSS and MAGIC code, influences of the washer/rod structure on the high frequency characteristics and the basic operation of the wide-gap klystron amplifier (WKA) are presented. Generally, the rod structure has a great influence on the space-charge potential depression and the eigenmode resonant frequency of the cavity. Once the rods are employed, the space charge field can be nearly eliminated with only 4 washers. Moreover, the presence of the rods raises the cavity eigenmode resonant frequency by ～ 9.0% due to their comparable lumped inductance to the cavity's inherent inductance. Nevertheless, if only the cavities are tuned to the desired operation frequency, the effect of the rod size on the basic operation of the WKA is expected to be very small.
2013, 62 (2): 024103.
doi: 10.7498/aps.62.024103
Abstract +
In this paper, a folded waveguide is adopted as a slow wave structure (SWS) of the extended interaction oscillator (EIO). An EIO with frequency 105 GHz in sub-Terahertz band is studied in detail, including the dispersion relation and the impedance of the SWS, and the variation of starting current with the period number, which provides an effective way to reduce starting current. On this basis, from the PIC simulation studies are discussed the EIO beam-wave interaction and output characteristics under the operation modes of low current continuous wave and strong current pulse. Further, the tuning characteristic of the EIO is analyzed, showing that output power reaches 26-50 W and the corresponding frequency range is 105.26-105.31 GHz. By EDM technology two fabrication methods of the SWS are investigated and the transmission properties of the SWS and the window are tested indicating that they are in good agreement with the simulation results.
2013, 62 (2): 024201.
doi: 10.7498/aps.62.024201
Abstract +
Nonreciprocal transmission device is one of the fundamental elements in integrated optics, and mid-infrared is a widely used waveband in many areas, such as remote sensing or spectrum analysis. An all-optical diode based on self-phase modulation (SPM) effect is numerically demonstrated in mid-infrared waveband. The diode consists of a linear waveguide and double silicon ring resonators. The nonreciprocal transmission ratio can be more than 20 dB in a power range between 0.5 mW and 20 mW, while the transmission loss in forward direction is less than 10 dB. Moreover, the influences of linear absorption coefficient of ring resonators and the bi-stability effect on the performance of the diode are discussed.
2013, 62 (2): 024202.
doi: 10.7498/aps.62.024202
Abstract +
Formation of elliptical optical soliton in rectangular lead glass is theoretically investigated, and an anisotropic diffraction effect is introduced into our theoretical model. Using the variational approach, we obtain an analytic elliptic soliton solution in a strongly nonlocal medium with anisotropy, which demonstrates that anisotropic diffraction effect has a great influence on the formation of the elliptical optical soliton. To confirm the analytic solution, we work out the numerical solution by the Newton iterative method. And the analytic solution accords with the numerical solution very well.
2013, 62 (2): 024203.
doi: 10.7498/aps.62.024203
Abstract +
In this paper, we study the slow propagation characteristics of surface electromagnetic waves according to theoretical analysis in the MNG (μ-negative)-DPS (double-positive)-MNG waveguide, which is composed of two-dimensional (2D) metamaterials. The dispersion curves of this waveguide vary with circuit parameter (unit capacitors) of MNG metamaterial. At the cutoff frequency of the dispersion curve the group velocity of electromagnetic wave is equal to zero in theory. So we can obtain slow propagation of the surface waves at different cutoff frequencies just by changing the unit capacitor of the MNG metamaterial. Theoretical analysis also shows that the step changes in slow waves are obtained at some fixed frequencies through changing the unit circuit parameters. The experimental results are in good agreement with simulation results.
2013, 62 (2): 024204.
doi: 10.7498/aps.62.024204
Abstract +
Optical heterodyne detection is one of the key techniques for developing synthetic aperture ladar. The decoherence effect caused by the roughness of the target surface is particularly important for the practical use of the synthetic aperture ladar. The effect of the target surface roughness on the echo signal detection is discussed in the paper. One-dimensional and two-dimensional Gaussian random rough surface model are created by the use of the Monte Carlo method. The detection process of the target echo signal is simulated to study the effect of the target surface roughness on the intermediate frequency signal. And two optical heterodyne detection experiments are conducted in which the targets each include a rough surface and a smooth surface to verify the serious decoherence effect of the target roughness on the synthetic aperture laser radar echo signal. Meanwhile, the wavefronts of both the local oscillator and the signal beam are monitored at the position of the detector with a digital wavefront analyzer. The measured phase distribution accords well with the simulation result. It is shown that the phase of the echo signal from a rough surface has a serious distortion. The results obtained could be useful for designing the parameters of the laser source and the receiver, as well as for estimating the detection range of the ladar system.
2013, 62 (2): 024205.
doi: 10.7498/aps.62.024205
Abstract +
Existing static dispersive and interference imaging spectrometers use fixed spectral resolution to obtain a fixed spectral data cube. To satisfy a variety of application requirements, the spectral range must be large and the resolution must be fine. This will result in a huge data and reducing the S/N ratio of the instruments. To solve these problems, a novel birefringent Fourier transform imaging spectrometer with spectral zooming capability is proposed. Operating concept, theory and experimental demonstration are presented to validate that the designed setup has wide spectral zooming capability. It can adapt to different applications, significantly reduce the size of the imaging spectral data for capturing, saving and processing. This will effectively improve the system performance.
2013, 62 (2): 024206.
doi: 10.7498/aps.62.024206
Abstract +
The fiber-laser array technique has an extensive prospect of applications in the areas of coherent beam combination, free-space laser communications and so on. In this paper, considering the development trend of the fiber-laser array technique, the research progress of an adaptive fiber-optic collimator based on large-mode-area fiber is introduced, a 7-channel fiber-laser array is established, the tip/tilt control experiment of laser array under parallel-transmission configuration is conducted, and the tip/tilt control of laser array under conformal-transmission configuration using target-in-the-loop is explored. Finally, the tip/tilt control and phase locking of two 10-W level fiber lasers are achieved in the master-oscillator-power-amplifier (MOPA) system with three-stage all-fiber amplifiers. This paper presents a reference for using the fiber-laser array technique in real atmospheric environment.
2013, 62 (2): 024207.
doi: 10.7498/aps.62.024207
Abstract +
The digital image-plane holographic microscopy which has the same curvature radius in the object light path and the reference light path is studied for the first time to our knowledge. The configuration of this setup is analyzed and built. The point spread function of this system is derived. The factors corresponding to the imaging resolution and the imaging characteristics of this system are analyzed. The method to correct the linear phase distortion in the reconstructed optical field is discussed. The results show that this system has the largest information content, and the imaging resolution of the system is dependent on the numerical aperture of the microscope objective (MO) and on the CCD pixel size, but independent of the photosensitive surface size of the CCD. All frequency components of each point in the object wave which has passed through the MO can completely be recorded and reconstructed. And the size of illuminated region of object has no influence on the recording condition and the quality of the reconstructed image. The digital image-plane holographic microscopy with the same curvature radius in the object light path and the reference light path is an optimized holographic recording system, which can achieve high-quality imaging. The experimental results demonstrate the correctness of the theoretical analysis.
2013, 62 (2): 024208.
doi: 10.7498/aps.62.024208
Abstract +
In this paper, a chaotic synchronization system model of a chain mutually coupled semiconductor lasers is established by adding a relay laser between the mutually coupled semiconductor lasers with cavity. The isochronal chaos synchronization condition is theoretically analysed. The influences of injection current, mutual coupling strength and feedback strength on isochronal chaos synchronization are numerically studied. The distributions of synchronous quality in the two-dimensional parameter space for mutual coupling strength and feedback strength are revealed. We show that when the injection current is big enough and the mutual coupling conditions and feedback conditions are completely the same, the stable isochronal chaos synchronization with high quality can be obtained among all the lasers. Stable isochronal chaos synchronization between central laser and side laser is distributed in the area when both mutual coupling strength and feedback strength are small or similar. Two side lasers can easily achieve the stable isochronal chaos synchronization with high quality, because they receive the same injection from central laser at the same time. The system model can be further expanded into the realizing of remote two-way isochronal chaos synchronization or the isochronal chaos synchronization of the arrayed semiconductor laser system.
2013, 62 (2): 024209.
doi: 10.7498/aps.62.024209
Abstract +
In this paper, the mode-locked laser pulse with a maximum power of 366 mW is achieved by using Yb-ions-doped double-clad fiber as the gain medium and single-walled carbon nanotubes (SWCNTs) as the saturable absorber (SA). The saturable absorber with a modulation depth of 27% is fabricated by spreading the well-dispersed SWCNTs on the D-shaped segment of the fiber, which is directly etched on the standard single-mode fiber by water-assisted femtosecond laser ablation. The ring-cavity structure fiber laser is fabricated based on the SWCNT-SA. The mode-locked pulse width of 93.8 fs, central wavelength of 1083.8 nm, and 3 dB bandwith of 8.6 nm at the repetition rate of 5.59 MHz are obtained in the optimized polarization state under a pump power of 4 W.
2013, 62 (2): 024210.
doi: 10.7498/aps.62.024210
Abstract +
The thermal effects induced by high-power diode pumping in the Nd:YVO4 slab laser crystal are numerically modeled. Using three-dimensional (3D) finite volume method, an accurate numerical solution based on heat transfer equation is achieved. The transient temperature distribution curves and the steady state 3D temperature distributions of the diode double end-pumped, uniformly face-pumped and the periodical face-pumped Nd:YVO4 slab are presented.
Method of designing astigmatic compensation cavity for mode-locked laser based on propagation circle
2013, 62 (2): 024211.
doi: 10.7498/aps.62.024211
Abstract +
The cavities of ultrashort pulsed lasers are mostly based on folded resonators with multi-mirrors. Astigmatism is an important issue to affect the performance of the mode-locked laser. An effective method of astigmatic ally compensating a continuous-wave passively mode-locked laser is presented in this paper. This method, in which the resonator propagation circle graphic theory is used, is easy and intuitive to seek the optimal location of the semiconductor saturable absorber mirror (SESAM), where the astigmatism can be compensated. Theoretical results show that the tangential and the sagittal spot size at the SESAM are equal and that the astigmatism can be compensated, when an SESAM is located at the tangential and the sagittal propagation circle intersection. The mode-locked resonator is insensitive to external perturbation including the vibration and the change of the thermal lens focal length, which leads to the instability of the mode locking operation. The antijamming ability of the resonator is outstanding. The experimental results indicate that the mode-locked laser works in a stabilized continuous-wave mode locking state and operates extremely steadily, when the SESAM is located at the tangential and the sagittal propagation circle intersection. The experimental results of the mode locking lasers show good agreement with the theoretical studies.
EDITOR'S SUGGESTION
2013, 62 (2): 024212.
doi: 10.7498/aps.62.024212
Abstract +
The buleshift properties of high-harmonic generation with phase matching of different filling pressures and laser intensities are experimentally investigated in this paper. The laser buleshift generated in gas cell, with about 0.13 nm in plateau and 0.07 nm in cutoff is obtained. The buleshift is influenced by simply changing the filling pressure and laser intensity, namely, by varying the density of free electrons in gas cell.
2013, 62 (2): 024213.
doi: 10.7498/aps.62.024213
Abstract +
According to the coupled-mode theory for guided optical waves, the mechanism of magneto-optical four-wave mixing (MO-FWM) existing in a fiber with magneto-optic effect and nonlinear effect both serving as perturbation is analyzed. The influence of applied magnetic field on the polarization dependency of FWM is measured, and the experimental results are in agreement with the theoretical analyses. It is shown that the magnetic control function of FWM can be identified easily for the incident orthogonal states of polarization. The FWM efficiency is dependent on the MO coupling coefficient in the oscillation form and can be further improved under an appropriate bias magnetic field. The MO-FWM effect can also be applied to magnetic field sensing, and the operating range is determined by the Verdet constant of highly nonlinear fiber.
2013, 62 (2): 024214.
doi: 10.7498/aps.62.024214
Abstract +
The characteristics of laser transmission in atmosphere are an important issue that must be considered for applications in laser engineering. For 1.06 μm and 10.6 μm laser, the single scattering parameters of aerosols are calculated based on the Mie scattering theory. For the transmission attenuation of the laser in aerosol, the Monte Carlo simulation model is established. For dust-like, water-soluble, oceanic and soot four types of aerosols, the relations of transmittance to visibility and propagation distance are computed and analyzed using the program written in MATLAB language respectively. The results show that single scattering calculation has a larger error when the visibility is low, and albedo is high. Using the Monte Carlo method to calculate the attenuation of the laser transmission in aerosol can reveal multiple scattering phenomenon. For the 1.06 μm laser, the attenuation capacity of soot aerosol is strongest, and for the 10.6 μm laser, the attenuation capacity of dust-like aerosol is strongest.
2013, 62 (2): 024215.
doi: 10.7498/aps.62.024215
Abstract +
A design approach to guided-mode resonance filter containing an absentee layer with an antireflective surface is presented. This design approach is reliable for the design and analysis of guided-mode resonance filter containing an absentee layer with an antireflective surface at an arbitrary incidence. The antireflection condition of guided-mode resonance filter containing an absentee layer is obtained. For the absentee layer with a fixed optical thickness, the resonance wavelength can be selected, with the low-sideband features and the filter linewidth kept almost the same by using different materials. In addition, the resonance wavelength and its linewidth can be tuned almost linearly in a broad spectral band as the incident angle is varied due to high angular tolerance of the antireflection features of the filter in the range of small angle.
2013, 62 (2): 024216.
doi: 10.7498/aps.62.024216
Abstract +
We propose a unified theory, that is, similarity transformation, to construct exact optical rogue wave solution of (1+1)-dimensional nonlinear Schrödinger equation with variable coefficients. Moreover, we investigate propagation dynamics of the first-order optical rogue wave in an optical fiber amplifier. In the suitable regulation of parameters, we find that the properties of the optical rogue wave, such as width, amplitude and position, are controllable in a nonlinear medium. These results give edification in theory and practical application.
2013, 62 (2): 024217.
doi: 10.7498/aps.62.024217
Abstract +
Field-tracing based numerical simulation technique is investigated to design and analyze ultra-small self-focusing optical fiber probe. Firstly, the concept and principle of the field-tracing are described. Secondly, the method is discussed to implement the field-tracing technique in the physical optical software of VirtualLab. Finally, an ultra-small self-focusing optical fiber probe is simulated in the field-tracing based optical software of VirtualLab. In this paper, we find that under the conditions of a fiber spacer length of 0.36 mm and the self-focusing fiber lens lengths of 0.1 mm, 0.11 mm and 0.12 mm, the working distances of the probe are 0.75 mm, 0.63 mm and 0.51 mm, and the focus spot sizes are 32 μm, 24 μm and 19 μm respectively. The simulation results are in good agreement with the experimental data, showing that the field-tracing based numerical simulation technique is an effective tool for investigating ultra-small self-focusing optical fiber probe.
2013, 62 (2): 024218.
doi: 10.7498/aps.62.024218
Abstract +
The tunable optical power splitter is a key optical component used to dynamically control its optical power at its output ports, which has a wide application in many optical fields. A novel approach to controllable optical power splitter is proposed in this work, which is based on thermal expansion effect resulting in width variation of air gap at the branching point of Y-branch waveguide. The thermal expansion profile and the optical performance are simulated by using the finite element method (FEM). The simulation results show that the tunable optical power splitter can exhibit good performance such as large dynamical range, low dependence of operation wavelength and its optical polarization. In addition, the proposed splitter with a simple structure can be easily designed, fabricated and controlled, which is very useful for potential application in integrated optical system.
2013, 62 (2): 024301.
doi: 10.7498/aps.62.024301
Abstract +
Research on sound scattering from a finite quasi-periodic bulkhead cylindrical shell is conducted. The small deviation of bulkhead array exists. Firsts some applications are given to investigate the problem of backscattering from a periodic bulkhead cylindrical shell in order to verify the theory. Then the angle-frequency spectrum of the backscattering from quasi-periodic bulkhead cylindrical shell is calculated, and the angle-frequency spectrum shows that the quasi-periodic array of bulkhead results in the diffusion of Bloch-Floquet wave and background field. However, the resonance of bulkheads is covered by background field. Finally, the influences of the array random variable of bulkheads, the number of bulkheads and the spacing between bulkheads are discussed. The calculations show that the diffusion of Bragg waves is more evident with array random variable increasing; the power of Bragg waves is concentrated with the number of bulkheads increasing; with the spacing between bulkheads becoming broad, the number of Bragg waves increases and the diffusion of high modes Bragg waves becomes more serious. Based on the geometric characteristics of Bragg waves, the approximate calculation formula of the Bragg wave position on the angle-frequency spectrum is presented. The formula can forecast the position of Bragg wave on the angle-frequency spectrum exactly and the diffusion of Bragg waves roughly when the bulkheads array quasi-periodic.
2013, 62 (2): 024501.
doi: 10.7498/aps.62.024501
Abstract +
Under excitations of different periodical signals, the response of a fractional linear system is investigated. First, by the harmonic balance method, the approximate solutions of the fractional-order linear system excited by harmonica signals are obtained. The results in this paper are idenified with the existing results obtained by the average method (Shen Y J, Yang S P, Xing H 2012 Acta Phys. Sin. 61 110505). However, the solving process here is much simpler. Further, the value of the fractional-order is extended in this paper. Then, according to the Fourier expansion and the method of linear superposition, the response of the system to a general periodical signal is obtained, and two examples are given for the case of periodical square wave and modulus of sine wave respectively. The results in this paper show that the value of the factional-order influences the resonance frequency and resonance amplitude of each order harmonic. The monotonicity between the response amplitude and the value of the fractional-order is influenced mainly by the frequency of the external excitation. Besides the analytical analysis, the numerical simulations are also performed, and the approximate solutions are in good agreement with the numerical ones. Hence, the process of the analysis of this paper is feasible.
2013, 62 (2): 024502.
doi: 10.7498/aps.62.024502
Abstract +
For a vertically vibrating box filled with Cu grains or glass beads, we study power of dissipating energy of the granular system, by measuring acceleration of the box and force acting on it. It is found that for a given vibrating strength the power displays a wide peak structure centered at several tens Hz as vibrating frequency varies, and for a given frequency its variation with the strength obeys a power law, with an exponent smaller than that of a forced harmonic oscillator model 2. The results are considered to be useful for determining magnitudes of transport coefficients of granular liquids and gases, as well as difference in dissipative energy between their different dynamic patterns.
2013, 62 (2): 024701.
doi: 10.7498/aps.62.024701
Abstract +
The capillary flow in interior corners of infinite long cylinder under microgravity environment is investigated by the homotopy analysis method (HAM). Different from other approximate computational method, the HAM totally depends on small physical parameters, and thus it is suitable for most nonlinear problems. The HAM provides us with a great freedom to choose basis functions of solution series, so that a nonlinear problem can be more effectively approximated. The HAM can adjust and control the convergence region and the convergence rate of the series solution through introducing auxiliary parameter and the auxiliary function. The computed result indicates that this method has the advantage of high accuracy.
2013, 62 (2): 024702.
doi: 10.7498/aps.62.024702
Abstract +
In this article, we report on an experimental research on the probability density function (PDF) of temperature measured in the wake of a circular cylinder slightly heated and its relationships with the turbulent mixedness under different Reynolds numbers (1200-8600). The temperature is measured by a probe of cold-wire with 0.63-m in diameter. Results show that the temperature PDF varies significantly with location in the wake. An increase in Reynolds number speeds up this variation, particularly accelerates the evolution from totally non-Gaussianity to near-Gaussianity along the wake centreline.
2013, 62 (2): 024703.
doi: 10.7498/aps.62.024703
Abstract +
A three-dimensional coupled model for particle inertial migration in the presence of micro flows is proposed and implemented. In the present model, the kinetic theory based lattice Boltzmann method is used to describe the fluid flows, and the Newton dynamics equation based model is used to describe the translation and rotation of the particle. The fluid and particle model are coupled by the LBM bounceback scheme based moving boundary method. The processes of particle settlement under gravity and particle rotation in the condition of Couette flow take place. The reliability of the present model and algorithm is validated through comparisons between the present simulation and the benchmark tests in the literature. The simulations of particle migration with various radii in an annular curved channel are performed, and the classic velocity distribution of the secondary flow in the channel cross-section is reproduced successfully. The mechanism of the particle radius influencing the particle equilibrium position in the curved channel is discussed. The results show that the particle equilibrium position in the curved channel will approach to the channel inner wall with the increase of radius. The present model is of important value for detailed study of the particle dynamics in micro flows as well as for the design and development of new micro fluidic particle selective chips and devices.
2013, 62 (2): 024704.
doi: 10.7498/aps.62.024704
Abstract +
The effect of Reynolds number on a passive scalar field is investigated in the turbulent wake of a circular cylinder. The cylinder-diameter-based Reynolds number varies between 1200 and 8600. The temperature difference above the ambient temperature acts as a passive scalar quantity. In general, the Reynolds number is found to have significant influence on the scalar mixing characteristics in the wake flow. When Reynolds number increases, the mean scalar spreads out more rapidly and the scalar variance decays with downstream distance at a higher rate. It is also revealed that if is likely to have two regions where some relations for self-similarity are approximately valid, one is located in the late Karman vortex street and the other is the traditional self-preserving far-wake.
2013, 62 (2): 024705.
doi: 10.7498/aps.62.024705
Abstract +
Physical and mathematical models are established to simulate the phenomenon of single droplet impinging onto flat liquid film by using the coupled level set and volume of fluid method, and influences of viscosity and surface tension on the morphology of the crown liquid sheet are discussed. Besides, the mechanism of jet flow in the neck region is revealed and the theory of kinematic discontinuity proposed by Yarin and Weiss is verified by analyzing the distributions of pressure and velocity after impingement. The research result shows that the effect of surface tension on the crown morphology is far stronger than that of viscosity. Generation of jet flow is due to the higher pressure difference, the effect of which becomes weak with impact evolution and the jet flow is developed into the crown gradually with the help of radial flow in the liquid film.
2013, 62 (2): 024706.
doi: 10.7498/aps.62.024706
Abstract +
In this paper, the energy dissipation formulas of the several typical macroscopic continuum models of traffic flow are derived according to the loss of the kinetic energy of traffic flow on road. The calculation of energy dissipation via two traffic cases: two Riemann initial conditions and the traffic bottleneck on the road indicates the energy dissipation of macroscopic traffic mode is influenced by not only the velocity reduction of the vehicle, but also the velocity gradient of the vehicle and the traffic density along the road, which is different from the result obtained from the CA model.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (2): 025201.
doi: 10.7498/aps.62.025201
Abstract +
The corona discharge process in low pressure N2 in stepped impedance transformer (SIT) is simulated using 3-D particle-in-cell (PIC) software (VORPAL). The evolution of the charged particle spatial distribution during the discharge is obtained. The two main discharge mechanisms, i.e., multipactor and corona discharge, are analyzed. From the simulation results, it can be found that the threshold voltage of breakdown of the SIT first decreases and then increases. In addition, with the increase of the pressure, the multipactor effect weakens while the corona discharge effect strengthens. Through the comparison of the threshold voltages between two kinds of wall materials, i.e., Ag and Cu, the critical pressures between the two discharge mechanisms are achieved.
2013, 62 (2): 025202.
doi: 10.7498/aps.62.025202
Abstract +
It is found in the experiments on synergy between low hybrid wave (LHW) and electron cyclotron wave (ECW) that the LHW reflection coefficient decreases with the injection of ECW into plasmas in the presence of LHW. In the present paper, the coupling characteristics of LHW, and the pump-out phenomenon caused by ECW are analyzed theoretically. The analysis shows the law of pump-out and the increase of plasma density in the vicinity of the grill mouth caused by pump-out, there by improving LHW coupling. The conclusion is proved by the experiments. Also, considering the change of the plasma density in the vicinity of the grill mouth caused by pump-out in synergy experiments, the synergy current should be corrected.
2013, 62 (2): 025203.
doi: 10.7498/aps.62.025203
Abstract +
The analysis of nanosecond laser-induced plasma versus the lens-to sample distance(LTSD) is investigated by 532nm laser ablated Ti-Al alloys in air and vacuum condition. The results indicate that electron temperature and density increase rapidly with the LTSD changing from short distance to the focal length (f=111 mm). Moreover, the plasma parameters by laser ablation in vacuum condition will further increase with LTSD further increasing. As for ambient medium, the plasma parameters reach their maximum values at 107 mm and then substantially decrease. On the other hand, the electron temperature and density rise again, while the intensity of Ti(II)368.52 nm decreases rapidly when the LTSD extends 112 mm.
2013, 62 (2): 025204.
doi: 10.7498/aps.62.025204
Abstract +
The nanocrystal silicon films were prepared by using a pulsed laser to ablate a high-resistivity single crystalline Si target in an ambient pressure range of 0.01-0.5 Pa of pure argon gas. An argon gas flow is introduced in the horizontal direction of the ablation point in an axial range of 2 cm. Nanocrystal Si films are deposited on glass or single crystalline (111) Si substrates placed at a distance of 1 cm below the nozzle. Then the same device is used to prepare the ranocrystal Si films at a pressure of 0.08 Pa with gas flow being, respectively, 0, 2.5, 5, 7.5, 10 sccm. The morphologies and microstructurs of the samples are characterized by atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman scattering. The results show that the Si nanocrystal threshold pressure is 0.1 Pa without gasflow, and 0.05 Pa with gasflow. The size of Si nanocrystal decreases as the gasflow increases.
2013, 62 (2): 025205.
doi: 10.7498/aps.62.025205
Abstract +
The scalings of double tearing mode (DTM) with various values of resistivity and viscosity have been investigated numerically by using a magneto hydrodynamic model in slab geometry. It is found that the growth rate changes from γ∝η3/5ν0 to γ∝η5/6ν-1/6 when the distance between two rational surfaces 2xs is sufficiently large. On the other hand, when the distance between two rational surfaces 2xs is very small, the scaling of γ and η and ν changes from γ∝η1/3ν0 to γ∝η2/3ν-1/3 as the viscosity increases. Moreover, the nonlinear evolution of symmetrical DTM is investigated in this paper. The study shows that the symmetrical DTM transforms to unsymmetrical DTM in the final phase.
2013, 62 (2): 025206.
doi: 10.7498/aps.62.025206
Abstract +
The physical mechanism of the negative hydrogen ion transportation and extraction is investigated, the charge exchange reaction and coulomb collision process are analysed thearelically, and the corresponding numerical calculation module is also designed. Therefore, using the finite difference time domain method to calculate the lorentz force of the negative hydrogen ions, and through Monte Carlo method to deal with the collision between negative hydrogen ions and other particles. Finally, it is successful to develop the 3D MCC algorithm of the transportation and extraction of the surface-produced negative hydrogen ions, and simulate the foreign popular ion source JAEA 10 A. The results show that with the increase of the filter magnetic fiel, the bigger the number of extracted ions, the smaller the number of ions in negative hydrogen ions source is, that with the filter magnetic filed is small, the greater the pressure, the bigger the number of extracted ions is, and that when the filter magnetic filed is big, the smaller the pressure, the bigger the number of extracted ions is.
2013, 62 (2): 025207.
doi: 10.7498/aps.62.025207
Abstract +
In order to study the characteristics of the films deposited by pulsed plasma thruster plume and assess contamination arising from the exhaust plume, the compositions of the pulsed plasma thruster plume are studied by means of mass spectrum analysis, the structural properties of the films deposited at different angles on the cathode side of the thruster are investigated by X-ray photoelectron spectroscopy, Fourier transform infrared absorption spectroscopy, and the optical properties of the films are studied by ultraviolet-visible light spectrophotometry. The results show that the plume consists primarily of C, F, CF, CF2, CF3, that low fluorine-carbon ration carbon fluorine films are deposited by pulsed plasma thruster plume, and that the chemical bondings and structures of these films present different trends in different regions with 30 degree angle as the boundary. These films basically show that they have strong absorption properties for wavelengths below 500 nm and have enhanced reflective characteristics. Due to influence of the characteristics of the deposited films, the optical properties of these films present signigicant angular dependences.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (2): 026101.
doi: 10.7498/aps.62.026101
Abstract +
Thermal rectification has potential applications in the thermal management of electronics and energy saving. Discovering thermal rectification phenomena and understanding the mechanism are very essential. Reported in this paper is the thermal rectification in silicon nanofilm with triangle holes by the non-equilibrium molecular dynamics simulation. The results show that in the silicon nanofilm with triangle holes, the difference in thermal rectification coefficient is around 28% with the variation of heat flow direction in a temperature range from 300 K to 1100 K. The phonon wave packet dynamic simulations indicate that transverse phonons are generated during the scattering of longitudinal phonons in the nanofilms. When the phonon transport direction is reversed, the average phonon energy transmission coefficient is changed by about 22% in all the frequency range. The difference in phonon transmissity, which is caused by asymmetric structure, is regarded as being attributed mainly to the thermal rectification in silicon film with triangle holes.
2013, 62 (2): 026201.
doi: 10.7498/aps.62.026201
Abstract +
Ceramic Pr1-xCaxMnO3(x=0.3) samples are prepared by solid-state reaction and measured using direct current (DC) and alternating current (AC) methods in different magnetic and electrical fields. A Curie temperature of 150 K is determined by I-V measurements in field for Pr0.7Ca0.3MnO3, which is consistent with that from vibrating sample magnetometer (VSM). The AC measurement shows that the grain boundary resistance reduces with magnetic field increasing, while the grain almost keeps unchanged, and it indicates that the colossal magnetoresistance (CMR) effect in low field mainly comes from the grain boundary for the Pr0.7Ca0.3MnO3 ceramic. The barrier height of grain boundary is 117 meV for the Pr0.7Ca0.3MnO3 ceramic, obtained by fitting the temperature spectrum of impedance, and it is well coincident with that from fitting the R-T data. A trap state model is proposed to explain all the measured data.
EDITOR'S SUGGESTION
2013, 62 (2): 026202.
doi: 10.7498/aps.62.026202
Abstract +
Bulk titanium borides (TiB2) have been successfully synthesized from the stoichiometric boron and titanium powders at high pressure and high temperature (HPHT). The density of TiB2 is higher than 99%. The Vicker's hardness of TiB2 as synthesized is 39.6 GPa which is near to result of the supehard materials. While TiB2 show good metallic characters with the resistivity, 10-8 Ωm, which is near to the value of the single crystal of TiB2. The enhanced properties of TiB2 as synthesized may be attributed to the higher density and uniform crystal size.
2013, 62 (2): 026501.
doi: 10.7498/aps.62.026501
Abstract +
Concerning metallic nanoparticles, a statistical simulation method to predict the electron mean free path of a nanoparticleis developed. And the phonon-contributed specific heat and phonon group velocity are also analyzed. Then, the kinetic theory is used to obtain the electron thermal conductivity and the lattice thermal conductivity of the nanoparticles. The size dependence of these properties is further discussed. It turns out that the electron mean free path of a square nanoparticle approximates to that of a circle nanoparticle if nanoparticles are of the same characteristic length. The electron thermal conductivity is much higher than the lattice thermal conductivity on the nanoscale. Either electron or lattice thermal conductivity of nanoparticles declines with diameter decreasing, while the size dependence of electron thermal conductivity is more obvious. However, if the diameter decreases to quite a small size, the electron thermal conductivity will become as low as the lattice thermal conductivity. In addition, the electron/lattice thermal conductivity of a nanoparticle will become less size-dependent if its characteristic length is 4 times larger than corresponding bulk electron/phonon mean free path.
2013, 62 (2): 026701.
doi: 10.7498/aps.62.026701
Abstract +
Based on the linear stability analysis, the modulational instablilities (MIs) of two-component Bose-Einstein condensations (BECs) in the optical lattices are studied, especially the relation of MI with the different component and modulational wavevectors, and with the inter- and intra- interaction when the condition of atom current conversation is not satisfied. The results show that when the condition of atom current is not satisfied, the new MI areas of two-component BEC in the optical lattice with the component wavevectors, modulational wavevectors and the interaction between components can arise. The above results can gives us some useful information about manipulating two-component BECs in practice.
2013, 62 (2): 026801.
doi: 10.7498/aps.62.026801
Abstract +
The (Al0.1Ga0.9)0.5In0.5P, four-element alloy, whose band is direct, is used to make optoelectronic devices. The wavelength of the material is about 630nm. When it is epitaxially grown by low press-metalorganic chemical vapor deposition(LP-MOCVD), its quality will depend on temperature, one of the most important conditions. So it is essential to find out the best temperature of growth. The quantum wells of the (Al0.1Ga0.9)0.5In0.5P are grown at 700 ℃, 680 ℃, 670 ℃ and 660 ℃ respectively. The best temperature, which is found out by the results of photoluminescence PL, is about 670 ℃. The reasons are given by the results of PL, surfaces of wafers and the flow field simulation of MOCVD. The revaporization of In at high temperature and the incorporation of O at low temperature can lead to bad quality. An available path to solve growth at high temperature is to increase the effective density of In.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (2): 027101.
doi: 10.7498/aps.62.027101
Abstract +
Polycrystalline bulk samples of BaSn1-xMnxO3 with x=0, 0.05, 0.10 and 0.13 are prepared by the conventional solid state reaction method. The effects of Mn concentration on crystal structural, optical and magnetic properties of BaSn1-xMnxO3 are investigated systematically. Powder X-ray diffraction (XRD) shows that each of these compounds presens a perovskite structure (with the space group Pm3m) without the secondary crystalline phase. The Mn ions take the Sn sites which is revealed by the XRD, diffusion reflectance spectrum (DRS) and Raman scattering. With the increase of doping level x, the optical absorption edge shifts towards higher wavelength and is smoothened gradually, meanwhile the Raman spectrum shows that Raman mode is also changed. The photoluminescence spectrum under magnetic field shows that near-infrared luminescence is probably related to Sn ions. The magnetization measurement demonstrates that Mn-doped BaSnO3 system exhibits ferromagnetism at low temperature, which can be explained by the F-center exchange (FCE) mechanism.
2013, 62 (2): 027501.
doi: 10.7498/aps.62.027501
Abstract +
The Fe, Co-codoped Zn0.9FexCo0.1-xO (x=0, 0.03, 0.05, 0.07) thin films are fabricated on the glass substrates by sol-gel method. The surface morphologies, crystal structures, elements and optical properties of the films are investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectrum. The XRD results reveal that all the ZnO films are of wurtzite structure. The diffraction peaks of the clusters, oxide or other impurity phase related to Fe and Co are not observed in the samples. This indicates that codoped is beneficial to the improvement on the dispersion of Fe or Co in ZnO. XPS results reveal that Co elements exist as Co2+, Fe elements exist as Fe2+ and Fe3+, but the increase of relative concentration of Fe leads to the increase of Fe3+ content. The ultraviolet emission peak and blue double emission are observed in the PL spectra of all the samples. Compared with the undoped ZnO film, the Co-codoped ZnO film has a blue shift of ultraviolet emission peak of Fe, the unchanged position of the blue double emission peak, and the weakened luminous intensity. Moreover, the green luminescence peak of the doped ZnO film almost disappears. Finally, the luminescence mechanisms of Fe, Co-codoped ZnO films are discussed by combining the microstructures and compositions of the samples.
COMPREHENSIVE SURVEY FOR THE FRONTIER DISCIPLINES
2013, 62 (2): 027201.
doi: 10.7498/aps.62.027201
Abstract +
Organic solar cells have received extensive attention due to their light weight, low cost, flexible. Because a single organic material absorbs only part of the sun light, laminated structure of solar cell, consisting of different absorption band gaps of organic material through the middle connecting layer, can both cover a larger part of the solar flux, and improve the circuit voltage or short circuit current of the solar cells. In this paper, the recent progress of the blend laminated structure polymer solar cells is summarized. Structures, principles and performances of a variety of laminated organic solar cells are introduced. The present status of research and existing problems of the blend laminated structure polymer solar cells are described, which provides valuable referesce for the study of high-performance organic solar cells.
EDITOR'S SUGGESTION
2013, 62 (2): 028201.
doi: 10.7498/aps.62.028201
Abstract +
Graphene, which is regarded as a new carbon material, has attracted much attention of scientists. Graphene holds the promise for applications in optoelectronics and microelectronics, owing to many unique physical and chemical properties. The large-scale applications are restricted by controllable synthesis of large-size graphene. In this paper we present the advantages and disadvantages of preparation processes of graphene. The recent advances in the process of metal-catalyzed graphene in terms of lay number control and large area synthesis are discussed. The graphene prepared by metal-catalyzed solid carbon source has large area and high quality and is thin and homogeneous. We review the latest progress in graphene transformation mechanism, point out the limitations of current study and prospect the future development in the graphene transformation mechanism.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (2): 028401.
doi: 10.7498/aps.62.028401
Abstract +
Based on the Fermi-Dirac distribution, a typical numerical method to calculate photoelectric current by voltage between anode and cathode in vacuum is developed. The results of simulations agree very well with the observed curves consisting of photoelectric current and voltage. Then, the contribution of intensity of incident light to photoelectric current is obtained mathematically. Finally, the wavelength of incident light is related to photoelectric current theoretically. Hence, photoelectric current can be predicted.
2013, 62 (2): 028701.
doi: 10.7498/aps.62.028701
Abstract +
The experimental results confirmin that spiral wave can be observed in the cortex of brain and the electric signals in neurons can proprgate with spiral wave. The mechanism for the formation of spiral wave is investiaged in the regular network of Hodgkin-Huxley, which can measure the effect of ion channels, and the sprial waves with different periods are developed to occupy the network by blocking the travelling wave with defects. The basic condition for inducing spiral wave and the effect of the couling intensity are analyzed. The potential mechanism for developing spiral wave is discussed.
2013, 62 (2): 028702.
doi: 10.7498/aps.62.028702
Abstract +
A novel low-loss dual-core fiber directional coupler for terahertz raditional is proposed, Coupling properties, loss and group velocity dispersion of the fibers are investigated by the full-vector finite-element method (FEM). The simulation results demonstrate that the coupling length of this coupler is less than 1.8 cm between 1.55 and 1.80 THz, and the coupling broadband of 0.07THz can be realized. And the loss coefficient of the coupler is less than 0.02 cm-1. The directional coupler has potential applications in narrowband filtering, wavelength-division multiplexing, switching, polarization splitter and so on.
2013, 62 (2): 028901.
doi: 10.7498/aps.62.028901
Abstract +
The detrended fluctuation analysis (DFA) method is used to analyze the human on-line activities in e-commerce. We comprehensively investigate the scale laws of browse and purchase behaviors, which have received little attention before. The time series of browse and purchase behaviors each obviously show a periodical character, and their probability density distributions each have a significant bimodal form. Based on the Fourier transform method, the power spectra of time series indicate that each of them obeys a stochastic process with a long-range self-similar feature (i.e., deviation far from the Poisson process). After identifying and filtering the influence of periodic trend based on power spectra, the detrended fluctuation analysis is used to study the scaling law of time series. Several interesting results can be found that their scaling behaviors on small and large scales show similar values that confirm the long-range correlations rooting in the time series of human on-line activities, and their average scaling exponent approximately equaling 1 suggests that the human online activity may be associated with a self-organized criticality. Although the empirical results are only the observed phenomena like those found in the Internet traffic and stock price fluctuation of financial market, we still think that they may provide an important insight to deeply understand the mechanism of human dynamic behaviors in e-commerce and predict their fluctuation trend for the potential business application.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2013, 62 (2): 029201.
doi: 10.7498/aps.62.029201
Abstract +
The quasi-geostrophic theory is the theoretical basis of the short-term weather forecast. Quasi-geostrophic motion equations of mid-latitude synoptic -scale movement are the core of quasi-geostrophic theory. Based on baroclinic two-layer model, quasi-geostrophic potential tendency equation and vertical motion equation can more clearly explain the movement and development of upper and surface weather systems. The movement of 500 hPa upper trough depends on the vorticity advection of 500 hPa, its development is determined by 500 hPa vorticity advection and differential vorticity advection between 250 and 750 hPa . The movement and development of cyclone depend on the positive temperature advection at 500 hPa and differential vorticity advection between 250 and 750 hPa. A case of snoptic system evolution demonstrates that quasi-geostrophic theory based on baroclinic two-layer model is conducive to the quick recognition of the characteristics of mid-latitude synoptic scale baroclinic development system, the understanding of the objective law of the development of the weather systems and the physical basis of numerical products.
2013, 62 (2): 029202.
doi: 10.7498/aps.62.029202
Abstract +
In order to repeat the propagation and its distribution characteristics, the lightning electromagnetic field (LEMP) in the entire space is calculated by a modified finite difference time-domain (FDTD) approach in this paper. Different from issued results, in which the electromagnetic field operates only at some discrete points near the ground, the LEMP and its time derivatives, power density and energy density at each unit in the whole space under the ground are calculated and expressed as groups of pictures. We find LEMPs attenuate exponentially in the horizontal and vertical direction, in the area near the ground and far from the discharge channel. The peak values of horizontal electric field and azimuthal magnetic field each have an unaltered polarity and their contours are similar to double exponential functions in the entire space under the ground. However the peak values of vertical electric field can be divided into two opposite-polarity parts in the whole area under the ground, and the contours in the area near the strike channel are spherical in shape. The other components have similar features. We also calculate the LEMPs with different values of ground conductivity, ground permittivity, return model and base current, and the characteristics of distribution are not changed, although the values are enhanced integrally in some cases. And in the layered earth, the LEMP has similar contours inside the layers. Even in the case of striking to the lightning rod, the characteristics of distribution are not changed. These patterns and distribution characteristics of LEMP can provide support and reference in shielding design and route planning under the ground.
2013, 62 (2): 029203.
doi: 10.7498/aps.62.029203
Abstract +
Climate network is a new interesting field in the earth sciences. It has advantage in exploring the properties and associated structures of climate fields. In the past researches, only climate dataset for winter month of the years were used to construct climate networks, and the effect of other seasons was ignored. In this paper, how seasonal factors impact on climate networks is investigated. It is find that some of the global properties of climate networks keep stable regardless of season, on the contrary, the community structures of network and local topologies change significantly in different seasons. With this conclusion, the variation of global teleconnection patterns and local area climate in different seasons can be investigated on climate network.
2013, 62 (2): 029601.
doi: 10.7498/aps.62.029601
Abstract +
The control methods of ground-based teleoperation rendezvous with variable time delay are surveyed. With the help of root locus method, the influences of time delay on the stability and performance of the control system are analyzed. Then, a time-delay compensator is designed to transfer the variable delay into a constant. A predictive model is established based on the relative dynamic equations. After that, a multivariable Smith predictor is designed based on the principle of Smith predictor, which makes the control input state variables independent of variable time delay. At the same time, the fuzzy control method is introduced to alleviate the uncertainties in the teleoperation rendezvous system. Finally, semi-physical simulations are carried out to verify the methods presented in this paper. Simulation results show that time-delay compensation and Smith-Fuzzy control are effective in alleviating the variable time delay and model uncertainties in the process of teleoperation rendezvous, and the success probability and control accuracy can be improved.
