Vol. 61, No. 11 (2012)
The third independent conserved quantity and its symmetry of the two-dimensional anisotropic harmonic oscillator
2012, 61 (11): 110201. doi: 10.7498/aps.61.110201
The energy and the two partial energies of two-dimensional anisotropic harmonic oscillator are conserved quantities, but only two of them are independent. The system possesses the third independent conserved quantity when the 1/2 is a rational number. The extended Prelle-Singer method is used to find the third independent conserved quantity for the five typical two-dimensional anisotropic harmonic oscillators. The Noether symmetry and the Lie symmetry of the third independent conserved quantities are also discussed.
2012, 61 (11): 110202. doi: 10.7498/aps.61.110202
By use of the method to construct the Lagrangian from the first integral, two families of Lagrangians and some Lagrangians and Hamiltonians are obtained for a class of Painleve equations.
2012, 61 (11): 110203. doi: 10.7498/aps.61.110203
To construct the infinite sequence soliton-like exact solutions of nonlinear evolution equations and develop the characteristics of constructivity and mechanization of the first kind of elliptic equation, new type of solutions and the corresponding Bcklund transformation of the equation are presented. Based on this, infinite sequence soliton-like exact solutions of Nizhnik-Novikov-Vesselov equation are obtained with the help of symbolic computation system Mathematica, which includes infinite sequence smooth soliton-like solutions, infinite sequence peak soliton-like solutions and infinite sequence compact soliton-like solutions.
The first-order approximate Lie symmetries and approximate conserved quantities of the weak nonlinear coupled two-dimensional anisotropic harmonic oscillator
2012, 61 (11): 110204. doi: 10.7498/aps.61.110204
The first-order approximate Lie symmetries and approximate conserved quantities of the weak nonlinear coupled two-dimensional anisotropic harmonic oscillator are studied. When the 1/2 is equal to 2/1, the system possesses six first-order approximate Lie symmetries and approximate conserved quantities, one of them is an exact conserved quantity, four of them are trivial conserved quantities, only one of them is a stable conserved quantity.
2012, 61 (11): 110205. doi: 10.7498/aps.61.110205
In this paper, considering the random motion of nodes, we propose an epidemic spreading model on network of mobile environment based on the mean-filed theory. Using the theory of differential dynamical system, the behaviors of epidemic spreading are further analyzed. It is shown that if R0 1, the epidemic always dies out and the disease-free equilibrium is globally asymptotically stable; and if R0 1, the epidemic is uniformly persistent and the endemic equilibrium is globally asymptotically stable. Numerical simulations are given to validate the results of theoretical analysis.
2012, 61 (11): 110206. doi: 10.7498/aps.61.110206
Based on the stretched coordinate perfectly matched layer (SC-PML) formulation and the auxiliary differential equation method, an absorbing boundary condition for general dispersive medium is presented, and applied to both the standard finite difference time domain (FDTD) method and the high-order FDTD method. The proposed D-H formulations are completely independent of the material properties of the FDTD computational domain. Thus they can be directly applied to the simulations involving arbitrary dielectrics. Numerical results show that compared with the CPML, the proposed method is versatile, has an improved absorbing performance and low computational complexity, and can substantially reduce the computational time.
2012, 61 (11): 110207. doi: 10.7498/aps.61.110207
In this paper, the stochastic series expansion quantum Monte Carlo method is employed to investigate the thermodynamic properties of hardcore Bose-Hubbard model in two-dimensional space. The two-dimensional hardcore Bose-Hubbard model can be mapped into the two-dimensional antiferromagnetic quasi-Heisenberg model under transform of bosonic operators. There is an additional term which is proportional to the total number of sites compared with real Heisenberg model and it is difficult for simulation. Using a nonlocal operator-loop update, it allows one to simulate thousands of sites. Our simulation results show that, first, energy decreases with the increase of density of particles in a range from 0 to 0.5, and finally approaches to a fixed value. Moreover, with the size of square lattice increasing, energy also increases. Second, when we fix the system size, energy and magnetization increase with temperature, but not with of chemical potential. When we increase the system size, energy increases, while, the magnetization decreases. Third, specific heat is independent of chemical potential, but it dramatically increases with temperature and approaches to a peak, then decreases slowly. According to Landau theory of superfluidity, the tends of curve for energy and specific heat fit the research of He II in the Landau two-fluid model. Fourth, different square lattice linear system sizes have a little influence on tiny differences to the reciprocal of uniform susceptibility. There are small fluctuations in a range from 0 to 0.5(J/kB), where J is the coupling energy, kB is the Boltzmann constant, but the reciprocal of uniform susceptibility increases with temperature increasing in a range from 0.5 to 2(J/kB). The tends of curve are similar to those of Kondo effect.
Runge-Kutta discontinuous Galerkin finite element method for two-dimensional gas dynamic equations in unified coordinate
2012, 61 (11): 110208. doi: 10.7498/aps.61.110208
In this paper we develop the Runge-Kutta discontinuous Galerkin finite element method for two-dimensional compressible gas dynamic equations in unified coordinate. The equations for fluid dynamics and geometry conservation laws are solved simultaneously. All the calculations can be performed on the fixed meshes. The information about the grid velocities is not needed in calculation. Some numerical examples are given to evaluate the efficiency and the reliability of the scheme. The numerical results show that the algorithm works well.
2012, 61 (11): 110209. doi: 10.7498/aps.61.110209
In this paper, the problem of finite-time stability for Lorenz-Haken laser chaotic system is studied by active control method. On the basis of the study for terminal attractor, and the consideration fo the uncertainties, an active control method with dynamic active compensation based on terminal attractor is proposed, which makes the controlled Lorenz-Haken laser chaotic system achieve the finite-time stability approximately. Meantime, in order to solve the uncertainties, a new observer is designed, which makes the estimate value follow the real value of uncertainties in a very short time. The approximate finite-time stability of the closed-loop system is analyzed in detail by introducing a singular perturbation theory. Simulation results show the effectiveness of the active control method and observer.
2012, 61 (11): 110301. doi: 10.7498/aps.61.110301
According to the classic theory of electromagnetic (EM) fields, we develop a propellantless microwave thruster system that can convert microwave power directly into thrust without the need of propellant. It is expected to be useful for spacecraft. Different from conventional space plasma propulsion, the system can obviate a large propellant storage tank and the issues related to plasma plume interference with the spacecraft surface. Different from huge solar sails and microwave-propelled sails, the system uses a cylindrical tapered resonance cavity as a thruster and uses an integrated microwave source to generate continuous EM wave so that the EM wave is radiated into and then reflected from the thruster to form a pure standing wave with amplified wave amplitude. The pure standing wave produces a non-uniform EM pressure distribution on the inner surface of the thruster. Consequently, a non-zero net EM thrust exerting on the symmetric axis and directing to the minor end plate of the thruster appears. In experiments a magnetron is used as a microwave source with an output microwave power of 2.45 GHz frequency. The generated net EM thrust is measured using a force-feedback test stand. The developed thruster system is experimentally demonstrated to produce thrust from 70 to 720 mN when the microwave output power is from 80 to 2500 W.
2012, 61 (11): 110302. doi: 10.7498/aps.61.110302
By introducing the Hermite-polynomial-operator Hn(X), where X is the coordinate operator (or the quadrature operator in quantum optics theory), and combining the technique of integration within an ordered product of operators, we derive some new operator identities about quantum squeezing, which are useful for studying the squeezed number state.
2012, 61 (11): 110401. doi: 10.7498/aps.61.110401
In this paper a method is presented to estimate the unknown parameters of nonlinear El Nio/La Nio-Southern Oscillation model based on the variational principle. Firstly, the equation of the coupled air-sea model is included into the objective functional. Secondly, the formulas of the adjoint equation and the functional gradient for unknown parameters are derived using the variational method. Finally, the algorithm to estimate unknown parameters of air-sea oscillator system is designed according to the above formulas. The numerical simulation results show that the proposed method is very effective and feasible to estimate the unknown parameters of nonlinear air-sea coupled dynamical system.
2012, 61 (11): 110402. doi: 10.7498/aps.61.110402
In this paper, we provide the analytical expression of acceleration of neutral experimental particle in the gravitational field of black hole involving a global monopole and discuss the contribution of global monopole to acceleration effect. The results indicate that the repulsion effect takes place due to the global monopole, and when v c, neutral particle in the gravitational field is subjected to a repulsive force, which does not exist in Newtonian mechanics.
2012, 61 (11): 110403. doi: 10.7498/aps.61.110403
Statistical entropy of scalar field outside Reissner-Nordstrm-de Sitter black hole is computed by the equation of state density corrected by the generalized uncertainty principle and by Wentzel-Kramers-Brillouin approximation method. The result shows that the entropy is proportional to the sum of the internal, the external and the cosmological horizon areas, which accords with these calculated by other methods. It shows internal relation between the entropy of black hole and horizon area. The entropy of black hole is the entropy of quantum state on horizon, which is a quantum effect.
2012, 61 (11): 110404. doi: 10.7498/aps.61.110404
The dynamical behavior of a class of coupled system to the Sine-Gordon equations with the Peierls-Nabarro force is considered in this paper. First, the existence of the continuous solution is shown in the semi-group approach, under the certain initial-boundary value condition. Then, using the decomposing technique of semi-group, we construct the compact positively invariant sets, and the global attractor is proved.
2012, 61 (11): 110501. doi: 10.7498/aps.61.110501
A new model of stochastic resonance, in which the pulse signal is modulated by noise, is established for a single-mode laser system. The corresponding intensity correlation function and the output signal-to-noise ratio of the system are calculated in the linear approximation. The phenomena of stochastic resonance are thoroughly discussed. Results reveal that due to the pulse signal modulated by noise, the single-mode laser exhibits a novel stochastic resonance phenomenon, that is, the optimization or the restraint of output signal-to-noise ratio can be controlled by the adjustment of the pulse signal period T.
Based on the construction patterns of Chen and Liu chaotic systems, a new chaotic system is proposed by developing the Lorenz chaotic system. The essential features of chaotic system are analyzed via equilibrium, stability, continuous spectrum, and Poincare mapping. The different dynamic behaviors of the system are analyzed especially when each system parameter changes. It is found that when parameters d and e vary, the Lyapunov exponent spectrum keeps invariable, and there exist the functions of global nonlinear amplitude adjuster for d and partial nonlinear amplitude adjuster for e. Finally, a practical circuit is designed to implement this new chaotic system, which confirms that the chaotic system can be achieved physically.
2012, 61 (11): 110503. doi: 10.7498/aps.61.110503
In this paper, a new three-dimensional autonomous chaotic system is constructed by adding a product term with variable coefficient to the first equation of Chen's system. The new system with different groups of coefficients can be chaotic or not by adjusting the variable coefficient, that is, by adjusting the variable coefficient, chaos occurs in new system when Chen's system is not chaotic, or chaos is suppressed in new system even if Chen's system is chaotic. The characteristics of the new chaotic system are analyzed in detail and the synchronization of new system is considered. Moreover, the simulation results are also presented.
2012, 61 (11): 110504. doi: 10.7498/aps.61.110504
A novel concept of switching block is presented via detecting the switching behavior of each switching period in piecewise smooth system of DC-DC switching converter, and logical arithmetic method of computer is used to obtain decimal system from binary system, so complex degree of the system during one switching period is quantized as switching block and the symbolic time sequence of the piece smooth system is established. Weight Lempel-Ziv (L-Z) complexity is derived based on the L-Z complexity and the symbolic time sequence, and the qualitative analysis of nonlinear and complex degree in piecewise smooth system from symbolic time sequence with single variable is carried out. The motion rule and the dynamics structure of the whole system are revealed. Finally, The present current mode controlled buck converter is studied as an example to establish symbolic time sequence and to illustrate the applications of weight L-Z complexity.
2012, 61 (11): 110505. doi: 10.7498/aps.61.110505
A linear single degree-of-freedom oscillator with fractional-order derivative is researched by the averaging method, and the approximately analytical solution is obtained. The effects of the parameters on the dynamical property, including the fractional coefficient and the fractional order, are characterized by the equivalent linear damping coefficient and the equivalent linear stiffness, and this conclusion is entirely different from the published results. The comparison of the analytical solution with the numerical results verifies the correctness of the approximately analytical results. The following analysis on the effects of the fractional parameters on the amplitude-frequency is fulfilled, and it is found that the fractional coefficient and the fractional order could affect not only the resonance amplitude through the equivalent linear damping coefficient, but also the resonance frequency by the equivalent linear stiffness.
2012, 61 (11): 110506. doi: 10.7498/aps.61.110506
A one-way hash function algorithm is proposed based on the chaos mapping and multiplicative congruential method. The initial value of the system is generated by the pseudo-random sequence which is obtained through the multiplicative congruential method. the normalized ASCII of the plaintext is used as the initial value of the chaos mapping. After a variable-step chaotic digital quantification, 128 bit hash value is extracted from the systems. Theoretical analysis and simulation results show that the proposed method has better characteristics of irreversibility, collision resistance, anti-forgery, initial sensitivity and higher operation speed.
2012, 61 (11): 110507. doi: 10.7498/aps.61.110507
A hybrid-crossover-based evolution algorithm is proposed to estimate the parameters of chaotic system. Through establishing an appropriate fitness function, the parameter estimation problem is coverted into a multi-dimensional functional optimization problem. In this approach, the individual generation based on good-point-set method is introduced into the evolutionary algorithm initial step, which reinforces the stability and global exploration ability of the evolutionary algorithm. In the evolution process, it not only can be explored to induce the new individuals generated by stochastic hybrid crossover operation to fly into the better subspace, but also can avoid the premature convergence and speed up the convergence. It coordinates the exploitation ability and the exploration ability of algorithm. Numerical simulations on the benchmark function and the Lorenz system are conducted. The results demonstrate the effectiveness of the proposed algorithm, which is shown to be an effective method of parameter estimation for chaotic systems.
2012, 61 (11): 110508. doi: 10.7498/aps.61.110508
With the help of the symbolic computation system Maple and using the improved projective method and the variable separation method, a series of excitations of the (2+1)-dimensional Bogoyavlenskii-Schiff system is derived. According to the derived solitary wave solution, we obtain some novel localized excitations of the system.
2012, 61 (11): 110701. doi: 10.7498/aps.61.110701
The multiple scattering of underwater lidar for wake happens in the near field, which leads ordinary receiving system to be saturated due to lack of dynamic range. The receiving system recovery time is usually up to several nanoseconds, which affects the receiving of the far-field signal. For this problem, the attenuation law of laser back-scattering intensity by water is analyzed and a front-end receiver of underwater lidar with energy consumption is developed. A high-speed reverse transient cancellation current is superimposed on the strong peak of near-field part signal to prevent the receiving system from being saturated, thereby restoring the two signals to integrated returned signal waveform. The technical difficulties are analyzed and the solutions are presented. The influence of generation time of transient cancellation current on intensity is discussed. The results of measurement and analysis prove that the transient cancellation current is 5 ns in pulse width, its adjustable step of 122 nA and the adjustable range is 135360 upA. The system suppresses the near-field strong scattering signal successfully and can meet the requirement for the underwater large dynamic range lidar for wake.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Lie symmetry and their conserved quantities of Tznoff equations for the vairable mass nonholonomic systems
2012, 61 (11): 111101. doi: 10.7498/aps.61.111101
The operational system of the spacecraft is general a variable mass one, of which the symmetry and the conserved quantity imply physical rules of the space system. In this paper, Tznoff equations of the variable mass nonholonomic system are derived, from which the Lie symmetries of Tznoff equations for the variable mass nonholonomic system and conserved quantities are derived and are researched. The function expressions of conserved quantities and the criterion equations which deduce these conserved quantities are presented. This result has some theoretical value for further research of the conservation laws obeyed by the variable mass system.
2012, 61 (11): 112101. doi: 10.7498/aps.61.112101
In the framework of the relativistic mean field (RMF) theory, the single-particle resonant states for spherical nuclei are studied by the complex scaling method. Taking 122Zr for example, we demonstrae the calculated details, and the obtained energies, widths, and wave functions for all the possiable resonant states. The results are in good agreement with those from the analytic continuation in the coupling constant method and the scattering phase shift method. Furthermore, we investigate the resonant states for all the Zr isotopes. The results are in satisfactory agreement with those from the scattering phase-shift method.
2012, 61 (11): 112601. doi: 10.7498/aps.61.112601
The influences of uncertainties in nuclear physics inputs on the Th/U, Th/Hf, Th/Eu, Th/Os, Th/Ir nucleo-chronometers are investigated in the framework of the classical r-process approach. A Monte-Carlo method is used to evaluate the age uncertainty originating from neutron separation energies for each nuclear mass model. It is found that the deduced age uncertainty for Th /U can be up to 1.66 Ga, and for the three chronometers, Th/Eu, Th/Os, Th/Ir, the uncertainties are 5.15 Ga, 3.93 Ga and 3.95 Ga, respectively. The recently proposed chronometer, Th/Hf, shows a clear model dependence, while Th/Os and Th/Ir chronometers tend to overestimate the age of Universe. Taking into account the uncertainties in nuclear physics inputs and observations, an up-to-date age estimation for the universe with the Th/U chronometer is 14.1? 3.8 Ga.
ATOMIC AND MOLECULAR PHYSICS
2012, 61 (11): 113401. doi: 10.7498/aps.61.113401
The X ray emissions from Arq+ (the kinetic energy 150 keV and 1.2 MeV) beams impinging on Au surface are measured. The results show that the about 2 keV minimum-potential energy of Ar11+ and Ar12+ (150 keV) is necessary for exciting Au atoms to emit M-X rays. The kinetic energy threshold for exciting target atomic X ray emission is estimated by the semiclassical approximation theory of binary collision.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2012, 61 (11): 114101. doi: 10.7498/aps.61.114101
The condition to realize the negative refraction in the uniaxially anisotropic chiral medium with an optical axis parallel to the interface has been investigated. The variations of refraction angles of two eigenwaves with the incident angle for different electromagnetic parameters and chirality parameters are also analyzed. The results show that the uniaxially anisotropic chiral medium is easy to realize the negative refraction, even though it has a small chirality parameter. And for the different permittivities, chirality parameters and incident angles, the phase refractive angles of the two eigenwaves in the uniaxially chiral medium are distinctly different. In a peculiar condition, one or two eigenwaves cannot propagate in the medium.
Line-imaging optical recording velocity interferometer at Shenguang-II laser facility and its applications
2012, 61 (11): 114102. doi: 10.7498/aps.61.114102
A line-imaging optical recording velocity interferometer (VISAR) is implemented at the Shenguang II laser facility. The spatial resolution is ～ 7 m, the effective field of view in the target plane is ～ 1 mm. We propose a new illumination method with increasing three times the luminosity of such a diagnostic. The VISAR is applied to experiments of laser-driven equation of state shockless compression, and shocktiming.
2012, 61 (11): 114201. doi: 10.7498/aps.61.114201
Silver superlens has a great influence on super-resolution lithography, imaging and the biosensing based on surface plasmon polaritons. In this paper, the surface plasmon resonance and the imaging of silver film are discussed in detail with optical transfer function of silver superlens. And the imaging process of silver superlens has also been simulated with the finite difference time domain. The simulation results are in agreement with those from the theoretical formulas, which fully proves the optical transfer function to be reliable. This may be an effective method of rapid parameter optimization for sensors, super-resolution imaging and enhance the interference lithography based on surface plasmon polaritons.
Dynamics of vertical-cavity surface-emitting laser subject to optical injection and positive optoelectronic feedback
2012, 61 (11): 114202. doi: 10.7498/aps.61.114202
Based on the spin-flip model (SFM), we theoretically investigate the dynamics of a vertical-cavity surface-emitting laser (VCSEL) subject to optical injection and positive optoelectronic feedback. The results show that under the joint action of positive optoelectronic feedback and optical injection from a master VCSEL (M-VCSEL), two polarization modes of a slave VCSEL (S-VCSEL) will show many dynamic states such as period one, period two, multi-period and chaos, and the evolution routes of these states are different for two polarization modes. Mapping of dynamic region as a function of feedback strength f and injection strength is varied with frequency detuning between M-VCSEL and S-VCSEL (=m-s, where m ands are the free-running frequencies of M-VCSEL and S-VCSEL, respectively). Compared with the case for zero or negative frequency detuning, the region of chaotic state is expanded significantly under positive . For a fixed , the influences of f and on the chaotic bandwidth of S-VCSEL are discussed. Through selecting proper f and , chaotic bandwidth of S-VCSEL can be improved obviously.
2012, 61 (11): 114203. doi: 10.7498/aps.61.114203
Introducing the gain competition is an effective way to suppress stimulated Brillouin scattering (SBS) in single frequency fiber amplifier. Steady rate equation describing two-tone single frequency Yb-doped double cladding fiber amplifier with gain competition is deduced based on single frequency amplifier. A theoretical model of this kind of amplifier is set up. With this model, simulation is performed to analyze the influences of wavelength difference between signals, signal power ratio, pump configuration and length of gain fiber on output efficiency of single frequency laser, and the effect of SBS suppression.
2012, 61 (11): 114204. doi: 10.7498/aps.61.114204
The output characteristics of a continuous-wave diode pumped free-running double-clad ytterbium-doped fiber laser are investigated. In the experiment, not only self-pulsing is observed, but also self-mode-locking is observed for the first time in the free-running fiber laser. The physical mechanism responsible for these phenomena is analyzed. The analysis reveals that the signal is absorbed in the weakly pumped or non-pumped part of the active fiber, which leads the self-pulsing to be present, and self-mode-locking is induced by axial mode beating and self-phase modulation, which are enhanced by nonlinear effects, stimulated Raman scattering, and stimulated Brillouin scattering. The pulse width of self-pulsing decreases as pump power increases. The pulse width of self-mode-locking pulses becomes narrow with the increase of the pump power. When the pump power is higher than 8 W, self-pulsing and self-mode-locking disappear. The interval between adjacent self-mode-locking pulses is 224 ns, corresponding to the cavity round-trip time. The maximum and the minimum durations (full width at half maximum) of self-mode locked pulses are about 35.0 ns and 6.3 ns respectively, and the maximum and minimum spectral widths (full width at half maximum) of signal light are about 7.05 nm and 2.01 nm respectively.
2012, 61 (11): 114205. doi: 10.7498/aps.61.114205
The complex refractive indices of the Cr film are obtained by terahertz time-domain spectroscopy. The penetration depth the Cr film is calculated based on the complex refractive indices, and then the effective cavity length and the emitted spectrum of the structure Cr/GaAs/Cr are simulated. The resonant frequencies are located at 0.32, 0.65, 0.98, 1.31 and 1.65 THz, respectively. The peak intensity of the cavity photo-conductive resource at 0.32 THz is 25 times higher than that of non-cavity one and the full width at half maximum is greatly narrowed. The relation between the emitting dipoles and the standing wave field in the cavity is also discussed. The results show that the emission intensity is enhanced when the emitting dipoles are located at the nodes of the standing wave field, but greatly suppressed at antinodes.
2012, 61 (11): 114206. doi: 10.7498/aps.61.114206
Shock ignition is a new concept for assembling and igniting thermonuclear fuel, in which compressed fusion fuel is separately ignited by a strong convergent shock launched in the target at the end of compression phase by a final intense laser pulse. Because of compression and ignition decoupling, target implosion velocities are significantly lower than those required for conventional hotspot ignition. As a result, shock ignition has the advantages of a low ignition energy threshold, high gain and good hydrodynamic stability properties. It offers a possibility for a high gain inertial confinement fusion to be used as green energy in the future, and could be tested on the projecting indirect drive laser fusion facilities like Shenguang-III facility (SG-III) in China. In this paper, we present the requirements for laser system used for shock ignition, delineate the critical issues and describe the research and development program that must be performed in order to test the high gain shock ignition in the future term.
Study on stimulated Brillouin scatting energy transfer to amplify laser pulses for shock ignition in laser fusion facilities
2012, 61 (11): 114207. doi: 10.7498/aps.61.114207
Shock ignition is considered as a relatively robust way to achieve the efficient fuel burn in inertial confinement fusion. However it requires intense laser pulses of sub-ns to launch strong convergent shock to ignite the pre-compressed target. Here we present a novel method, which has a substantially high extraction efficiency, to amplify laser pulses of ～200 ps for shock ignition. In this method, stacking pulse with a Stokes light of ～200 ps in the front and a pump light of ～5 ns following, is employed to propagate in the amplifier to extract the stored energy, then in the final system after harmonic conversion, laser energy is transferred from pump pulse to probe pulse by stimulated Brillouin scattering. Because of employing long pulse in the main amplifier, an output laser energy of 1520 kJ is achievable at fundamental frequency. Simulations show that the energy transfer efficiency is up to 75%, considering harmonic conversion efficiency of 60%80%, implying that 510 kJ laser pulses of ～200 ps can be produced using this scheme. As a result, only ～20 beams are required to generate the ignitor, reducing the cost for realizing the shock ignition.
2012, 61 (11): 114208. doi: 10.7498/aps.61.114208
In this paper, the Monte Carlo method is employed to simulate the ultraviolet light scattering transmission. The three modes of ultraviolet (UV) no-line-of-sight (NLOS) communication are analyzed. The UV NLOS transmission model based on the Monte Carlo method is proposed. The path losses of single and multiple scatterings and the coverage area of three UV NLOS modes are simulated by using the Monte Carlo method. Finally, we obtain the conclusion that multiple scattering and single scattering basically have the same path loss. The coverage of NLOS (a) is smallest, but omni-direction is good. The coverage of NLOS (b) is larger, but it is directional. The coverage of NLOS (c) is largest, but it is strongly directional.
Measurement of NO2 total vertical columns by direct-sun differential optical absorption spectroscopy in Hefei city
2012, 61 (11): 114209. doi: 10.7498/aps.61.114209
Direct-sun DOAS(DS-DOAS) technique is successfully applied to the measurement of atmospheric trace gas vertical column density(VCD). The DS-DOAS technique for continuously measuring NO2 total vertical column density is investigated based on the passive DOAS. The composition of system is introduced. The statistical method minimum-amount Langley-extrapolation is utilized to reduce the errors from the selected reference spectrum. The VCD measuring error is estimated and the error source is discussed. The NO2 total VCD is measured based on the system in Hefei city in a consecutive period of 11 days. And the results are analyzed. The experiment has verified the feasibility of the algorithm and proved that the technique can be used to continuously measure NO2 total vertical column density.
2012, 61 (11): 114210. doi: 10.7498/aps.61.114210
Rotating paraboloid model is establishd, and three-dimensional finite-difference time-domain method is used to simulate pit-shaped cracks on fused silica rear-surface. The light intensification with its depth, width, gap distance and etch value are investigated under 355 nm laser incident. Results show that the strongest modulation is located at the connection area between pit and pit, and the modulation become strong with approaching to the surface. The maximum light intensity enhancement factor (LIEF) is 11.53 when the breadth depth ratio ranges from 2.0 to 3.5 and gap distance close to 1/2 width. As gap distance greater than the width, the modulation reduces greatly, which is equal to a single pit. For 60-width, 30-depth and 30-gap distance cracks, the maximum LIEF is 11.0 during the acid etching. As the gap distance is less than 300 nm, the diffraction of the light field makes the neighbor pits connective.
Investigation of the tunable laser of one-dimensional photonic crystal with dye-doped nematic liquid crystal defect layer
2012, 61 (11): 114211. doi: 10.7498/aps.61.114211
We investigate the optical characteristics of the tunable laser of a one-dimensional photonic crystal (1D PC) containing Dye-doped nematic liquid crystal (NLC). The dielectric multilayer consisting of an alternating stack of SiO2 and TiO2 layers is used as the 1D PC whose defect layer is filled with the laser dye and NLC. The central wavelength of the stop band of the 1D PC is 650 nm. A second-harmonic light of a Q-switched Nd: YAG laser has a wavelength of 532 nm, and is used for excitation. With the temperature increasing from 25.5 ℃ to 48 ℃, the emission wavelength of the tunable laser is continuously shifted from 605.5 to 639.8 nm, the total wavelength shifts is 34.4 nm. With the external voltage increasing from 0 to 2.86 V, the emission wavelength of the tunable laser is shifted from 634.5 to 619.5 nm, the total wavelength shifts are 15 nm. The lasing threshold was about 12.3 J/pulse, and the linewidth of the emission peak was less than 1 nm.
Characterization and chemical/biosensing application of a high-sensitivity integrated optical polarimetric interferometer
2012, 61 (11): 114212. doi: 10.7498/aps.61.114212
A tapered thin film of Ta2O5 is sputtered on a single-mode slab glass waveguide to form a composite optical waveguide (COWG) for serving as a prism-coupled integrated optical polarimetric interferometer. The relationship between the refractive-index sensitivity (SRI) of the interferometer and the equivalent thickness (Teq) for the tapered layer of Ta2O5 is theoretically analyzed based on a four-layer homogeneous waveguide model. A comparison of the measured SRI with the simulated data leads to Teq 33.021 nm for the COWG used. The sensitivity of the interferometer to thickness of the protein adlayer is determined to be Sab (2.412 2)/nm. The acetic-acid concentration of a commercial Chinese vinegar is investigated, for the first time, by use of the interferometer combined with the Lorentz-Lorenz effective-medium theory. Water and methanol adulterations of a commercial Chinese liquor are detected with the interferometer. The results indicate that the refractive-index change induced by the adulteration is a quasi-linear function of the adulteration amount. Both the dynamic adsorption process of butyrylcholinesterase and the self-assembly process of cytochrome c/PSS multilayer film are monitored in real time with the sensor. The protein surface coverage is obtained from the combination of the measured phase-difference change and the adlayer-thickness sensitivity.
The three-photon resonant nondegenerate six-wave mixing via quantum interference in the middle level
2012, 61 (11): 114213. doi: 10.7498/aps.61.114213
We study the quantum interference in three-photon resonant nondegenerate six-wave mixing (NSWM) of a five-level system in which the middle level of six-wave mixing and other levels are coupled by a strong laser field. The coupling field-dependence of the NSWM signal intensity, and the spectrum of the NSWM with a coupling field, are discussed. We find that in the presence of a strong coupling field, the three-photon resonant NSWM spectrum exhibits Autler-Townes splitting, which reflects the levels of the dressed states. It also leads to either suppression or enhancement of the NSWM signal. Due to the enhancement of NSWM signal caused by quantum interference, the dressed state created by a coupling field can replace the atom intrinsic level and serve as the middle level of three-photon resonance. Thus the middle level of three-photon resonance can be controlled by a coupling field.
Measurement of the argon-gas-induced broadening and shifting of the barium Rydberg levels by two-photon resonant nondegenerate four-wave mixing
2012, 61 (11): 114214. doi: 10.7498/aps.61.114214
We apply two-photon resonant nondegenerate four-wave mixing with a resonant intermediate state for observing the broadening and the shifting of the barium Rydberg 6snd 1D2 series by collision with argon. The collision broadenings and the collision shifting cross sections are measured for n=1633. This technique is a purely optical means, and can achieve Doppler-free resolution of narrow spectral structures of Rydberg levels when the incident lasers have narrow bandwidths. Different from other experimental methods of studying the pressure dependence of the longitudinal relaxation rate of Rydberg states, our method is to investigate the pressure dependence of the transverse relaxation rate of the transition.
2012, 61 (11): 114401. doi: 10.7498/aps.61.114401
Thermal conductivity is one of the most important physical properties of thin films. Different from two- or three-dimensional measurement structures in most reports, in this work, one-dimensional (1D) two-end supported cantilever beam is provided. The structure of cantilever includes a metal heater (which also serves as a thermometer) and thin film(s) underneath for measurement. 1D heat flow equation is employed to obtain the expression of temperature rise distribution (T(x)) along the cantilever beam and voltage drop changes along the heater (U) when a direct current (DC) follows in the heater. To confirm the correctness of theoretical deduction, ANSYS finite element software is employed to simulate T(x) and U. Results demonstrate that the simulations are in good agreement with the theoretic calculations obtained from expressions of T(x) and U. Compared with conventional 3-times frequency (3 ) method, the DC method with 1D cantilever beam is relatively simple and accurate.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Study on the machining mechanism of fabrication of micro channels in fused silica substrates by laser-induced plasma
2012, 61 (11): 115201. doi: 10.7498/aps.61.115201
A Q-switched Nd: YAG laser was used to fabricate micro channels in the fused silica substrate by laser-induced plasma. The micro channels were observed with fluorescence microscope, no thermal cracks around the channels and the depth of the channels is up to 4 mm. There are coagulation layers around the inner surface. We studied the ionization mechanism of optical breakdown in solids by nanosecond laser pulses. For the 1064 nm laser, as the intensity of nanosecond pulse is not enough large, plasma formation in optical breakdown is the result of an electron avalanche process. We got the plasma formation model using the breakdown threshold of avalanche ionization and calculated the range of laser plasma based on the model. The theoretical analysis based on the model is shown to be mainly agreement with the experimental observations. The laser-supported detonation wave (LSDW) based on the principle of hydrodynamics was analyzed as well and calculated the characteristic parameters of plasma including the plasma temperature, pressure and velocity. The characteristics of micro channels were analyzed through the parameters. When the plasma passed, the melting quartz solidified with the effect of LSDW and produced the coagulation layers. The ablation of the high temperature and pressure plasma lead to a micro channel of high quality with a relatively smooth internal surface and no thermal cracks.
2012, 61 (11): 115202. doi: 10.7498/aps.61.115202
In laser plasmas interactions, the simulation of stimulated Brillouin scattering takes a long time. In order to decrease the simulation time, a hybrid Vlasov code is developed, in which the electrons are treated as Boltzmann fluid. The two-ion beam instability is simulated, and the simulation results are compared with the theoretical results. Stimulated Brillouin scattering is also simulated, the results show the code correctness.
2012, 61 (11): 115203. doi: 10.7498/aps.61.115203
In inertial confinement fusion experiments, the measurement of hydrodynamic instability growth factor is an important means of studying hydrodynamic instability. In this paper we use the calibration of the sample to gain the modulation transfer function of framing camera at a given space frequency. The calibration results are employed to measure the absolute hydrodynamic instability growth of sinusoidally perturbed sample, under the condition of the same configure, and the growth factors at different times are given. The results show that the method of measuring the absolute hydroponics instability growth is established successfully.
A large plasma sheet with a size of 60 cm60 cm2 cm is generated in an apparatus with a hollow cathode. The electron density distribution of the large area plasma sheet is measured. Since the duration of high voltage pulse is short, we change measurement methods. Besides, modification is used for electron saturation current to get the real density. The two-dimensional electron density and electrical field distribution are calculated at discharge currents ranging from 1 to 6 A. Meanwhile we discuss other parameters related to density distribution. The electron density distribution is important for plasma sheet to steer microwave. It is encouraging that the large area plasma sheet generated by the hollow cathode is uniform and has sufficient electron density to reflect X-band (812 GHz) microwaves.
2012, 61 (11): 115205. doi: 10.7498/aps.61.115205
Stable stripe pattern is observed in flowing argon at atmospheric pressure by using a dielectric barrier discharge device with two transparent water electrodes. Based on the photography and the electrical measurement, the formation mechanism of stripe is investigated. Results show that a stripe pattern can be obtained at a lower peak value of the applied voltage in flowing argon, and the discharge turns homogeneous at a higher voltage. Results show that the formation of stripe pattern results from the movement of discharge filament in the direction of gas flow. The moving velocity of filaments almost keeps constant during the voltage varying. However, the moving velocity increases with the increase of gas flow rate. The memory effect of active particles in the discharge space is very important for the formation of stripe pattern. Furthermore, the electric characteristics of discharge are studied in flowing gas in this paper. It is found that both the discharge current and the gas inception voltage decrease with the increase of the gas flow rate. A qualitative explanation is given for this experimental phenomenon. These results are of great importance for the research of pattern formation dynamics and industrial applications of dielectric barrier discharge.
2012, 61 (11): 115206. doi: 10.7498/aps.61.115206
A method of solving spatial distribution of shell density by inverse Abel transform is presented. CH sphere imaging on the micro-focus X-ray source is implanted to test the method of inverse Abel transform. The reversion of shell density is in agreement with real density, which verifies the correctness of the method. The 16-fram implosion target images are processed by inverse Abel transform, and the distributions of compressed shell density at different times are obtained. Qualitative analysis of back-lighter distribution, pinhole imaging and variation of shell thickness is proposed for inverse Abel transform.
2012, 61 (11): 115207. doi: 10.7498/aps.61.115207
The mechanisms of the synergy effects between electron-cyclotron and lower-hybrid current drive and the synergy current are revealed. The matching relationships required by synergy effect in phase space and on current profile are explained. The non-linear relationship between synergy current and wave power is shown by computer simulation, and its physical explanation is given. This work provides physical support for the design and analysis of relevant experiment.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2012, 61 (11): 116101. doi: 10.7498/aps.61.116101
Evolution of the dynamic recrystallization microstructure in the hot working process of metal is difficult to observe in real time experimentally. Based on Ginzburg-Landau kinetic equation, a physical metallurgy model with coupling multi-phase field method and the dislocation density calculation is used to simulate dynamic recrystallization in the thermal processing. The dynamic recrystallization processes at the different temperatures and different strain rates are investigated. The reason for the stress-strain curve changing from single peak state to the multi-peak state is explained. In addition, we systematically simulate the process of multi-stage deformation and the effect of static recovery on dynamic recrystallization, and analyze the influence of thermal processing parameters on the kinetics of dynamic recrystallization. The simulation results show that the grain size increases during suspension of deformation, and higher deformation temperature and lower deformation strain rate can accelerate the process of dynamic recrystallization.
2012, 61 (11): 116301. doi: 10.7498/aps.61.116301
A series of Er-doped silicate glasses is prepared by a conventional melting method under normal processing conditions, and the effects of gamma-ray radiation on absorption and emission properties of all samples are investigated. The radiation-induced darkening causes a strong broad optical absorption band that has a maximum around 400 nm and extends to the near infrared region. The point defects generated in the silicate matrix by irradiation around the Er3+ ion favor the activation of non-radiative relaxation channels thus modifying the photoluminescence quantum efficiency from specific excited levels, such as those emitting at 520 and 650 nm. Photobleaching effects are observed in Er-doped silicate glasses pumped by 980 nm LD at room temperature.
2012, 61 (11): 116401. doi: 10.7498/aps.61.116401
Angle dispersive X-ray diffraction measurements of -Ce are performed in a diamond anvil cell under up to 0.74 GPa at room temperature. The accurate high pressure bulk modulus data obtained from ultrasonic measurements are used to calculate the parameters of various equations of states (EOSs). We find that the three order Murnaghan EOS and three order Xu EOS are fitted best to the relationships of the pressure vs. volume and the pressure vs. bulk modulus for -Ce.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2012, 61 (11): 117101. doi: 10.7498/aps.61.117101
Optoelectronic and magnetic properties for Sn(O1-xNx)2 material were examined using quantum chemical ab initio calculation software WIEN2K based on the first principles of density functional theory. The density of states, the band structure, the magnetism, dielectric function and the refractive index are analyzed. The results show that the band gap frist narrowed and then increases with the increase of doping concentration of nitrogen substituting oxygen, the band gap of Sn(O1-xNx)2 becomes the narrowest when the concentration of nitrogen is 12.50%. As a result of the contribution of the electron of N 2p orbit, a low acceptor level appears in a range of 0.551.05 eV, and the level spliting and the orbit overlap appear in the valence band and conduction band. The SnO bond is stronger than the NO bond. From the magnetism, the magnetic moment is determined by N atoms. We know that the optical absorption edge is widened from the imaginary part of dielectric function. The main transition peak is red shifted and the refractive index is corresponding to the dielectric function related to the transition of electrons.
First-principles study of the electronic structure and absorption spectrum of heavily Nd-doped anatase TiO2
2012, 61 (11): 117102. doi: 10.7498/aps.61.117102
According to the plane wave ultra-soft pseudo potential technique of density function theory, we perform the first-principles study of the electronic structure and absorption spectrum of heavily Nd-doped anatase TiO2 with different Nd concentrations, along with those of pure anatase TiO2. The calculation results show that, within the concentration range of Nd set by this article, with the doping concentration decreasing, the band gap becomes narrow, and the absorption spectrum is red shifted more considerably. The experimental results are in accordance with the calculation results.
2012, 61 (11): 117103. doi: 10.7498/aps.61.117103
As the active areas and the connection part, semiconductor nanowires have ideal shapes which are beneficial to restricting the electron motion and atomic periodicity to one one-dimensional structure. The effective selection of material components in nanowires can enhance the advantages of low-dimensional structures by analyzing the features of bulk materials. Furthermore, the nanowire properties can also be tailored by controlling the internal or intrinsic characteristics such as diameters, crystallographic growth direction, structural phase, surface crystallographic plane or saturation degree, and by applying external influences such as electric, magnetic, thermal and force fields. The bulk InAs and GaSb have approximate lattice constants, thereby resulting in small lattice mismatch for InAs/GaSb heterostructures that can finally be grown into excellent infrared optoelectronic materials. Moreover, the bulk InAs has the lowest electron effective mass in binary III-V compound semiconductors, leading to high transport features for electrons distributing most in InAs layers of InAs/GaSb superlattices. In the present work, the zinc-blend (InAs)1/(GaSb)1 superlattice nanowires (subscript denotes the number of molecular or double-atomic layers) with  and  crystallographic wire-axes have been studied by first-principles calculations for their structural, electronic and mechanical properties together with the rule of different nanowire diameters (from ～0.5 to ～2.0 nm). We also analyze the stress effects from external forces and examine the electronic band-edge changes with strain in wire-axis direction to determine the deformation potentials.
2012, 61 (11): 117104. doi: 10.7498/aps.61.117104
The atomic structure, the mechanical properties, the electronic band structure, and the phonon structure of (InAs)1/(GaSb)1 superlattice atomic chain are investigated by first-principles pseudopotential plane wave method, and the quantum transport properties are also calculated by the density functional theory numerical atomic orbit pseudopotential method in combination with nonequilibrium Green's function formalism. Compared with two-dimensional layer structural (InAs)1/(GaSb)1 superlattice, the (InAs)1/(GaSb)1 superlattice atomic chains have obviously different band structures, and represent metal energy band characteristics in certain conditions. The calculated mechanical strength of (InAs)1/(GaSb)1 superlattice atomic chains indicates that such structures can sustain the strain as high as =0.19. The structural stability of (InAs)1/(GaSb)1 superlattice atomic chains is investigated by full Brillouin zone analysis for phonon structure. The electron transport calculations for (InAs)1/(GaSb)1 superlattice atomic chain segments in between Al electrodes show that the conductance exhibits nontrivial features as the chain length or strain is varied. The calculated optical absorption spectra represent precipitous cutoff absorptions in infrared regime, and the cutoff wavelength varies with chain structure. InAs/GaSb superlattice atomic chains are predicted to be applied to infrared optoelectronic nanodevices, modifying optoelectronic response wavelength range by changing the structures of superlattice atomic chains.
2012, 61 (11): 117105. doi: 10.7498/aps.61.117105
Based on the numerically solved Dirac equations, we study the electronic properties of the point vacancy of the graphene quantum dots with armchair boundary conditions under magnetic field. The size effect on the gap is analyzed. Without magnetic fields, quantum dot has finite energy gap which is proportional to the inverse of the radius of the dot. In the presence of the magnetic field, there appear Landau levels. The lowest Landau level has zero energy and is irrelevant to the magnetic field. With the increase of the magnetic field, the degeneracy of the Landau levels will increase. We further analyze the relationship between the lowest Landau level in the presence of magnetic field and the size of the quantum dot. The result shows that the degeneracy is linearly dependent on the magnetic field and the square of the radius. Our calculation will be possibly helpful in designing the device based on the graphene quantum dots.
2012, 61 (11): 117106. doi: 10.7498/aps.61.117106
Organic light-emitting diode (OLED) based on tris-(8-hydroxyquinoline) aluminum(III) (Alq3) is fabricated, and its magnetoconductance (MC) effects are measured at different bias voltages. When the bias voltage is small, the OLED exhibits apparently a negative MC effect. After the bias voltage is increased, the MC value changes from negative to positive, displaying a negative-positive inversion. The MC effects in N, N'-Di(naphthalen-1-yl)-N, N' diphenyl-benzidine (NPB) and Copper phthalocyanine (CuPc) unipolar devices show that the negative MC effect in OLED comes from the CuPc layer in device. The MC effect of bipolar current can be explained using the electron-hole pair model. The MC effect of unipolar current can be attributed to the polaron-bipolaron transition in device. The positive-negative MC inversion in OLED results from the simultaneous contributions of the above two mechanisms during the variation of the injection current.
First-principles study of interface relaxation effects on interface structure, band structure and optical property of InAs/GaSb superlattices
2012, 61 (11): 117301. doi: 10.7498/aps.61.117301
The first-principles all electron relativistic calculations within the general gradient approximation are performed to investigate the interface structure, the electronic and the optical absorption properties of quaternary InAs/GaSb superlattices with InSb or GaAs type of interface. Because of the complexity and low symmetry of the quaternary interfaces, the equilibrium structural parameters of relaxed interfaces are determined by the minimization of total electronic energy and strain in InAs/GaSb superlattices. The band structures and the optical absorption spectra of InAs/GaSb superlattices with special InSb or GaAs and normal (two types are alternate) interfaces are calculated, with the consideration of the superlattice interface atomic relaxation effects. The calculation of relativistic Hartree-Fock functional and local density approximation with the plane wave method is also implemented to demonstrate the calculated band structure results. The calculated band structures of InAs/GaSb superlattices with different types of interfaces are systematically compared. We find that the chemical bonding and ionicity of interfacial Sb atoms are essentially important in determining the interface structures, the band structures and the optical properties of InAs/GaSb superlattices.
2012, 61 (11): 117302. doi: 10.7498/aps.61.117302
Using the electric potential and the magnetic scalar potential formulas which contain Bessel function of zero-order of first kind and the constitute relations of topological insulator, we derive the induced electric potentials and induced magnetic scalar potentials which are induced by point electric charge in dielectric, topological insulator and earthing conductor. Further research shows that the induced magnetic monopoles and the induced electric charges are induced in dielectric, topological insulator and earthing conductor; the positive and negative induced magnetic monopoles and electric charges and their magnitudes are determined not only by the material parameter, point electric charge, but also by the space of the induced electric charge and induced magnetic monopole.
2012, 61 (11): 117501. doi: 10.7498/aps.61.117501
Using the plane-wave expansion method under supercell approximation, band structures of spin waves propagating in two-dimensional magnonic crystals with coupling multi-point defects and magnetization field distributions of some defect modes are calculated. The results indicate that the energies of point defect modes can couple each other, and propagate along the direction of the multi-point defects in these structures. Utilizing the coupling characteristics of defect modes, two-dimensional magnonic crystals can be used as the fabricating materials of spin-wave waveguides.
2012, 61 (11): 117801. doi: 10.7498/aps.61.117801
We synthesize MAl12O19 (M = Ca, Sr, Ba) singly doped with Eu2+ or Cr3+ and co-doped with Eu2+ and Cr3+ by high-temperature solid-state reaction under reducing atmosphere. It is observed that there exit energy transfers from Eu2+ to Cr3+ in MAl12O19 (M = Ca, Sr, Ba) hosts. Although the MAl12O19 (M= Ca, Sr, Ba) hosts have similar crystal structures, the energy transfer efficienies and the conversion rates of the blue light to the red light are different. Both experiment and calculation show that the energy transfer from Eu to Cr in CaAl12O19 host is most efficient, and the ratio of the red emission to the blue emission in CaAl12O19 host is the highest among the three different hosts.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2012, 61 (11): 118101. doi: 10.7498/aps.61.118101
The circuits of memristor with border constraint, connected with capacitance and inductance in series, and with capacitance and inductance in parallel are studied separately. The properties of the circuits and the influences of frequency and element parameters on circuit are analyzed. Theories are proved by simulation. Potential applications are predicted based on the properties of memristor with border constraint and its related circuits.
2012, 61 (11): 118102. doi: 10.7498/aps.61.118102
The effects of Al2O3 on micro-structure and crystallization of oxyfluoride glass are investigated by infrared spectra, Raman spectra and X-ray diffraction analyses. The results show that [AlO4] is connected with [SiO4] units by means of angle connection, thereby forming the basic network of glass. When the content of Al2O3 increases, the structures of monomer and dimer increase in oxide glass matrix. Under the condition, the size of nanocrystals has a minimum value, while the structure of nancrystals is not affected.
Phase field modeling of the growth and competition behavior of tilted dendrites in directional solidification
2012, 61 (11): 118103. doi: 10.7498/aps.61.118103
The multi-phase field model is employed to simulate the growth of tilted dendrites during directional solidification. In this simulation, the evolution of a single oriented dendritic array and the overgrowth behavior between two converging grains with different orientations are studied. The simulated results show that the dendritic tip undercooling increases with the tilt angle, which means that the tip position of tilted dendrite is always lower than that of the non-tilted in the same condition. The favorably oriented grain always blocks the unfavorably oriented one in the case of converging growth. However, when the pulling velocity is low, the growth of the preferred crystalline orientation dendrites at the grain boundary is lagged by the immediate unfavorably ones because of the solutal interaction, which may result in the fact that the unfavorably oriented grain overgrows the favorably oriented one.
2012, 61 (11): 118401. doi: 10.7498/aps.61.118401
Thick frequency selective surface has potential applications in the stealth curved streamlined radomes because it has advantages in broadening bandwidth and overcoming multi-layer FSS shortcoming of complex structure and low transmittance of central frequency due to the cascade. However, there are a drift of central frequency in a wide range of incident angle and an unsteadiness of polarization at big incident angle. To solve the problem, in this paper we provide a novel Y element thick FSS. The structure is analyzed using mode matching method. The bandwidth, the central frequency and its transmittance of the structure are investigated when some parameters including the incidence angle of TE and TM waves and the polarization at big incident angle are changed. The novel Y element thick FSS has better transmission properties with polarization independence and incident angle independence. The novel structure provides a valuable reference for the application in stealth curved streamlined radomes.
Action potential initial dynamical mechanism analysis in a minimum neuron model exposure to TMS induced electric field
2012, 61 (11): 118701. doi: 10.7498/aps.61.118701
Transcranial magnetic stimulation (TMS) is a kind of brain stimulation method of producing magnetic field at the designated area of brain employing electromagnetic coils. The principle of TMS is to apply an electric field which is generated through the electromagnetic induction to neuron, thereby influencing the excitability of neuron. Though it has been used for decades, its underlying mechanism, i.e., how TMS induction electric field changes neuronal excitability, is still unknown. To address this problem, we establish a minimum neuron model under action of TMS induced electric field, analyze the mechanism from the viewpoint of action potential initial dynamical mechanism which has been proved to be the decision factor of neural coding in previous studies. Through phase plane and bifurcation analysis, we reveal the dynamical mechanism of different firing patterns of neuron. Finally, we find that the physiological basis of different excitabilities under action of TMS induced electric field, which is the different outcomes of competition between ion currents of neuron with different kinetic behaviors in sub-threshold potential.
2012, 61 (11): 118801. doi: 10.7498/aps.61.118801
In order to optimize the multi-user subcarrier allocation of cognitive wireless network, it is converted into a constraint optimization problem. A chaotic immune optimization algorithm is proposed to solve it. The key techniques and implementation processes are given. The operators, such as coding, clonal, crossover, and mutation, are designed. The experimental results show that in conditions of user rate, the bit error rate and inference constraints, the algorithm minimizes the total transmit power and converges rapidly. It can obtain the better allocation scheme and improve the utilization efficiency of high frequency spectrum.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2012, 61 (11): 119101. doi: 10.7498/aps.61.119101
A novel stereo photography method is developed for ocean wave measurement, and the mathematical model and algorithm are also developed. A new exterior calibration technique is built by the least square method in combination with the sea wave theory. Compared with the conventional calibration technique, the present method does not need the sea control points are not needed. Thus, this novel stereo photography method can easily be extended to the measurement the sea waves on a mobile platform. The laboratory experiments show that the stereo photography system proposed in the present paper is accurate and can be used to measure Gravity-Capillary waves. Meanwhile, from the outfield experiments we can also find that our method is feasible to measure large-scale ocean wave and the measured area (overlay) is up to 104 m2.
2012, 61 (11): 119102. doi: 10.7498/aps.61.119102
Experiments are performed by Metravib dynamic mechanical analyzer (DMA+450) using the stress-strain method. The static load is fixed at 100 N, and the dynamic load amplitude of the sine wave is 60 N, so that the total loading force is controlled under yield stress. Temperature is controlled between -50 ℃ and 175 ℃, and the heating rate is 1 ℃ per min. The frequency ranges from 1 Hz to 1000 Hz. Pump-oil saturated arkoses and Pengshan sandstones are tested under uniaxial cyclic loading. The variations of attenuation, phase angle, Young's modulus, and velocity with temperature or frequency are obtained. The attenuation peak and the phase angle peak shift toward higher temperatures with frequency increasing, which can be considered as thermal relaxation regularity. The activation energy and the transition frequency corresponding to the thermal relaxation peak are determined by experimental results and explained by the sandstone characteristics. A new phase transition attenuation peak, which is corresponding to mineral ion exchange in rock, is observed in the present experiments. Some dynamic characteristics of rock minerals under thermal and vibration loading are used to explain the peak. The Young's modulus and the velocity increase with frequency increasing and decrease with temperature increasing. There is obvious frequency dispersion, and the dispersion weakens when temperature increases. This investigation is helpful for studying theoretical model and interprating seismic data.
2012, 61 (11): 119201. doi: 10.7498/aps.61.119201
A new method of predicting dryness and wetness based on evolutionary modeling (EM) is presented in this paper. Numerical tests indicate that the basic dynamic characteriscs can be captured by EM and the model obtained by EM is not only able to preferablely simulate historical evolution, but also can exactly predict the future evolutionary trend of a time series. For the model obtained by EM with relatively larger prediction errors, the secondary EM can improve the prediction accuracy obviously.
2012, 61 (11): 119202. doi: 10.7498/aps.61.119202
The influence of external forcing on chaotic character, Lorenz map structure and the predictability is studied with the Lorenz system which has a forcing term, and the atmospheric predictability forced by sea surface temperature (SST) is also analyzed. The chaotic attractors are related to the forcing term that changes the moving rules of system and makes randomicity of attractors reduce. The probability distribution function of Lorenz system in the x-y plane has a bimodal structure with two clearly separated peaks. In the absence of forcing, both peaks are equally likely. When an external forcing introduced, the probability of state moving around two Lorenz attractors is changed, and it makes the two peaks asymmetric. It is found that the single cusp of Lorenz map obtained in the absence of forcing splits into two cusps that represent two branches of the Lorenz attractor when the forcing is introduced. On Lorenz map, the moving directions of two cusps and the difference between two cusps and single cusp are determined by the sign and the magnitude of forcing term. The predictability of Lorenz system is also deeply affected by external forcing. The predictability is increased by introducing forcing, and especially the range of increasing is larger when the absolute value of forcing term is bigger. It is also found that the higher potential predictability is obtained by forcing with the stronger SST which causes the larger external variance.
A novel method to configure the parameters of the bilateral filtering for synthetic aperture radar images speckle reduction
2012, 61 (11): 119501. doi: 10.7498/aps.61.119501
Bilateral filtering can effectively smooth SAR images with the edges preserved, but it is difficult to optimally configure the parameters of bilateral filtering. Traditional method is based on an optimal trade-off hypothesis according to the despeckling estimation indexes, including the equivalent number of looks (ENL) and edge preserving index (EPI). However, the variance of gray value similarity obtained by traditional method has large error, and to improve accuracy, the computing time is increased linearly. In this paper, we present a novel method to configure the parameters of bilateral filtering based on the hypothesis and the monotone properties of the ENL and EPI curves. Experimental results show that the accuracy of variance of gray value similarity is increased by one order of magnitude in the case of almost the same computing time; the computing time is reduced by one order of magnitude for the same accuracy of variance of gray value similarity.
2012, 61 (11): 119701. doi: 10.7498/aps.61.119701
In order to reduce the observation time of X-ray pulsar signal identification, a new identification algorithm based on the photon distribution statistics is proposed. The influence of cumulation period variation on photons distribution is analyzed, according to whether the cumulation period is correct, two kinds of Poisson models are developed to characterize the cumulation profiles. The photon distribution statistics is constructed, and the difference of photon distribution statistics between two kinds of profiles is presented. Rossi X-ray timing explorer observation data is used for simulation, and the simulation result verifies the effectiveness of the suggested method.
To understand earthquake from the granular physics point of viewcauses of earthquakes, earthquake precursors and prediction
2012, 61 (11): 119103. doi: 10.7498/aps.61.119103
To recognize the seismogenic process, mechanism and behavior of seismic precursors, as well as look for the ways of earthquake prediction the granular physics principle is applied based on the basic structure of the crust and mantle and existing experimental observations, where we treat the earth crust and mantle as large scale discrete matters. Main outcomes are: A granular model of the structure and movement of the earth crust and mantle is established. A formation mechanism of the tectonic forces, which causes the earthquakes, and a model of propagation for precursive signals are proposed. Properties of the seismic precursive signal and its relevance with the earthquake occurrence are illustrated, and principle of ways to detect the effective seismic precursor is elaborated. In the paper the mechanism of palintectic earthquake is also explained by the jamming-unjamming transition of the granular flow. Some earthquake phenomena which were previously difficult to understand are explained, and the predictability of the earthquake is discussed. Due to the discrete nature of the earth crust and mantle, the continuum theory no longer applies during the quasi-static seismogenic process. In all in this paper, based on granular physics, we study the causes of earthquakes, earthquake precursors and earthquake prediction, and a new understanding, different from the traditional seismological point of view, is obtained.