Vol. 61, No. 12 (2012)
The asymptotic solving methodof traveling wave solution to a class of sea-air coupled oscillator model
2012, 61 (12): 120201. doi: 10.7498/aps.61.120201
The tropical sea-air oscillator is a complicated natural phenomenon. In this paper, based on a sea-air oscillator model, by a new method of combining the undetermined coefficients with the perturbation theory the asymptotic traveling wave solution of the corresponding model is obtained.
2012, 61 (12): 120202. doi: 10.7498/aps.61.120202
Porous structure can effectively reduce the loads caused by the water wave, which results in lowering the cost of engineering project. The double porous shelter performs even better. Therefore, it receives much attention from researches. However, most of the previous studies dealing with the analysis of the interaction between water wave are porous structure were based on two-dimensional plane wave assumption. This can hardly reflect the real phenomena of complex wave action. In this paper, a semi-analytical solution to the hydrodynamic interaction between the three-dimensional short-crested wave and the cylindrical structure with double porous shelters is performed by employing the scaled boundary finite element method (SBFEM). The SBFEM possesses the advantages of finite element method (FEM) and boundary element method (BEM): the spatial dimension of the problem is reduced by one, no fundamental solution is needed and no singularity occurs. Meanwhile, this method can meet the infinity of the boundary condition automatically. In the SBFEM, the total computational domain is divided into three sub-domains, two ring-shaped finite sub-domains and one outer infinite sub-domain. A variational principle approach is proposed to establish the SBFE governing equations, which describe the variation of the velocity potential of wave motion in the radial direction. Bessel functions and Hankel functions are chosen as the basis functions for the solution of bounded and unbounded sub-domain problems, respectively. Numerical examples show that the proposed approach achieves very high accuracy and converges rapidly with quite few discretized nodes at the outer boundary. In comparison with the cylindrical structure with single porous shelter, the former performs better for the reduction of the water wave force. In addition, The influences of the wave parameters and the configuration of the structure on the system hydrodynamics, including the wave force, wave and diffracted wave contour are extensively examined. This research provides a valuable insight into the hydrodynamic analysis of cylindrical structure with double porous shelters and their structural design.
2012, 61 (12): 120203. doi: 10.7498/aps.61.120203
The problem of uniform finite-time stability for a class of discrete-time switched descriptor systems is considered. Firstly, the concept of finite-time stability for continuous descriptor systems is extended to discrete-time switched descriptor systems. Secondly, based on the Lyapunov-like function method, and under arbitrary switching signal, sufficient conditions under which discrete-time switched descriptor systems are regular and causal, the uniform finite-time is bounded and uniform finite-time is stable, are derived. Then, the state feedback controllers are designed to guarantee the discrete-time switched descriptor system uniform finite-time stablility. Finally, some numerical examples show that the results obtained in this paper are effective.
2012, 61 (12): 120301. doi: 10.7498/aps.61.120301
Inspired by Lanyon (B. P. Lanyon et al. 2008 Nature Physics. 5 134) successfully simplifying the three-qubit Toffoli gate, we present a novel scheme that optimizes universal quantum logic circuits using assisted higher-dimensional Hilbert space. We construct a more efficient two-qubit circuit and a more effective three-qubit universal quantum circuit by using assisted dimension, Cosine-Sine Decomposition (CSD) and Quantum Shannon Decomposition (QSD). Meanwhile, we present the formula for the complexity of arbitrary n-qubit universal quantum gate. We propose the physical implementation of this scheme by linear optical circuits and cavity-QED. The results show that the two-qubit and three-qubit universal quantum circuits are respectively close and superior to the current optimal scheme in complexity. And with the increase of the number of qubits, the advantage of our scheme will become increasingly prominent.
2012, 61 (12): 120302. doi: 10.7498/aps.61.120302
Considering a moving two-level atom interacting with a single-mode thermal field through multi-photon process, in this paper we study the entropy exchange between the atom and the field by using quantum partial entropy and entanglement measured by using Concurrence, and investigate the effects of the initial atomic state, the atomic motion, the mean photon number and the transition photon number on entropy and entanglement. The results show that the entropy exchange and the entanglement exhibit the periodic evolution due to atomic motion, and entropy exchange occurs. The entanglement between the atom and the field is strengthened as the transition photon number increases. When the partial entropy exchange between atom and field is zero, the entanglement is also zero.
2012, 61 (12): 120401. doi: 10.7498/aps.61.120401
The purpose of this paper is to investigate the effects of the dynamical parameters, the spin-orbit coupling, the spin-spin coupling and the classification of orbits on the gravitational waveforms emitted by the conservative post-Newtonian Hamiltonian system for the spinning compact binaries by means of symplectic integrator and power spectrum. The numerical results show that the gravitational waveforms of ordered orbits vary periodically with time, while those of chaotic orbits are stochastic under the radiation--reaction force turning off. In particular, the chaotic dynamic behavior can enhance the strength of emission power. In addition, the magnitude of the spin parameter does exert a significant influence on the gravitational waveforms.
Dynamical modeling and border collision bifurcation in pulse train controlled discontinuous conduction mode buck converter
2012, 61 (12): 120501. doi: 10.7498/aps.61.120501
According to the charge variation of output capacitor in a switching cycle, the output voltage variation in a switching cycle can be obtained, from which an approximate discrete-time model of pulse train (PT) controlled buck converter operating in discontinuous conduction mode (DCM) is established. Based on the model, the border-collision bifurcations of the PT controlled DCM buck converter with the variations of the load resistance and the input voltage are studied. By constructing the corresponding iterative map curves, the stabilities of the fixed points, formed by the orbits of period-1, period-2, period-3 and so on, are analyzed, and the mechanisms of border-collision bifurcations of the converter under different operation states are revealed. The analysis results indicate that with the variation of parameters, the PT controlled DCM buck converter always operates in different periodic states, in which the change of the operation mode with periodic state is caused by the border-collision bifurcation and the lyapunov exponent is always less than zero. By using PSIM circuit simulation software, the time domain waveforms and phase portraits under different load resistances are obtained. Experimental results are provided to verify the correctnesses of theoretical analyses and circuit simulations and the feasibility of dynamical modelling.
2012, 61 (12): 120502. doi: 10.7498/aps.61.120502
A non-coherent blind detection method based on the generalized negative entropy mechanism for chaotic ultra-wideband system is proposed in this paper. In the case without knowing the transmission channel information, the chaotic impulse signals can be detected. The proposed method can overcome the practical application problem existing in the direct chaotic communication (DCC) scheme for impulse radio ultra-wideband (IR-UWB) communication system. Also, this method can overcome the complicated and unknown multipath channel effect. Analysis of simulation results show that the proposed approach has a good separating and detection performance in the case without the channel information. A new way for the noncoherent blind detection of chaotic UWB system under non-ideal unknown channel is established.
2012, 61 (12): 120503. doi: 10.7498/aps.61.120503
The security of a class of hyperchaotic image encryption algorithms is analysed. The results show that the shuffling process can be separated from the confusion process, and the formulas of encryption are simple, which makes the ciphertext cannot resist the attacks from chosen plaintext and ciphertext. Then we propose an improved and enhanced algorithm based on hyperchaos. The improved algorithm includes two rounds of encryption operation. The theoretical analyses and the experimental results indicate that the improved algorithm can overcome these flaws and has better cryptographic performances in resisting differential attacks and speed of encryption.
2012, 61 (12): 120504. doi: 10.7498/aps.61.120504
Sliding mode control method is used to study the synchronization of regular network. The method is extended from the single chaos control or synchronization between two chaotic systems to the synchronization of complex network. The sliding surface of the network and the control input are designed. Furthermore, the effectiveness of the method is analyzed based on the stability theory. The Duffing system and the Coullet system are taken as network nodes of the regular network, and the simulation is made to verify the method.
2012, 61 (12): 120505. doi: 10.7498/aps.61.120505
The node placement is the foundation of network operation in wireless sensor networks. In many applications, the positions of gateway node and sensor node are relatively fixed. To guarantee network connectivity and reliability, some relay nodes must be reasonably placed between the gateway node and the sensor node. In the context of the above applications, we introduce many constraint conditions into the existing placement model, and adopt a hybrid placement method based on enumeration and greedy optimization algorithms to determine relay node positions from their candidate location sets, and we finally achieve the relay node initial placement and follow-up adjustment strategies, owing to new sensor nodes joining the current network. The simulation results demonstrate that our operable and optimized relay node placement algorithm can ensure multi-restricted fault-tolerant relay node placement, and the presented new evaluation standard based on the minimum distance factor can significantly improve the energy-efficiency of relay node placement algorithm.
2012, 61 (12): 120506. doi: 10.7498/aps.61.120506
The Levins model subjected to the noise is employed to study the stability of a metapopulation. The analytic expressions of the stationary probability distribution function and the mean extinction time of the metapopulation are obtained according to the Fokker-Planck Equation. The results show that for the case of no correlation between the additive noise and the multiplicative noise (=0, is the intensity of correlation between multiplicative and additive noise), the increase of the additive noise intensity weakens the stability of a metapopulation; for the case of 0, enhances the stability of a metapopulation. For -(c-e-D)2/(4cD)1, can induce the resonance restrain phenomenon. Meantime, there exists a critical value of D. When D is lower than the critical value, the stability of the system is enhanced.
Steady state characteries of FitzHugh-Nagumo neural system subjected to two different kinds of colored noises
2012, 61 (12): 120507. doi: 10.7498/aps.61.120507
Making use of the unified colored noise approximation, the steady sate characteristics of the one-dimension of FitzHugh-Nagumo neural system with two different colored noises are investigated. The expressions of the steady state probability distribution function and the mean value are obtained. After numerical calculation, the results show that the self-correlated time of the multiplicative noise 1, the self-correlated time of the additive noise 2,the intensity of the additive noise , and the intensity of the multiplicative noise D can induce the transition. The increases of and D are conductive to the switch from the exciting state to the resting state. However, with 1 and 2 increasing, the switch from the resting state to the exciting state becomes obvious. The noise intensity and it self-correlated time play opposite roles.
Analysis the convergency speed of estimating the network topology based on the dynamical synchronization
2012, 61 (12): 120508. doi: 10.7498/aps.61.120508
Identifying convergent speed is an important but rarely discussed problem in estimating topologies of complex networks. In this paper, we discuss this problem mainly in both weakly and strongly coupled conditions. In the weakly coupled conditions, the convergent speed we defined increases linearly with coupling strength increasing. After analyzing the dynamics, we find that this relation is universal. In light of the repeatedly driving method we proposed recently, we generalize the definition of the convergent speed into the area of synchronization. In this case, there is a best length of the driving time series to maximize the convergent speed. The knowledge of convergent speed helps us understand the topological information embedded in the time series.
2012, 61 (12): 120509. doi: 10.7498/aps.61.120509
Dynamic behaviors of sparse and dense spirals are investigated numerically based on a Barkley model in heterogeneous excitable media. It is found that the rotating frequency of sparse spiral wave decreases rapidly with b increasing and then tends to saturation, which is different from that of dense spiral wave. The period and wavelength of dense spiral wave increase with the increase of parameter or the size R of localized inhomogeneity, which depends more sensitively on the size R than those of sparse sprial wave. The change of the speed of dense spiral wave tip with R is opposite to that of the sparse spiral wave tip. In addition, inhomogeneous effect gives rise to a defect point in arm of each of the two spiral waves when or b increases above a critical value.
Complex networks from multivariate time series for characterizing nonlinear dynamics of two-phase flow patterns
2012, 61 (12): 120510. doi: 10.7498/aps.61.120510
We use finite element analysis method to optimize and design a new curve half-ring conductance sensor for gas-liquid two-phase flow system. Then we carry out gas-liquid two-phase flow experiment in multiphase flow loop facility, and use the designed sensor to measure multivariate time series corresponding to different flow patterns. According to the measured signals, we construct complex networks from multivariate time series for different flow patterns by a network inference method. Through investigating the community structures of the constructed networks, we find that different communities correspond to different flow patterns and the network statistics in community can be used to effectively characterize the dynamic behavior of different flow patterns. In this regard, our method can be a powerful tool for identifying flow patterns and uncovering the nonlinear dynamics governing the evolution of different flow patterns.
2012, 61 (12): 120701. doi: 10.7498/aps.61.120701
A real-time measurement of gases based on QEPAS is introduced. For eliminating fluctuation of laser, a simple method, in which a digital PID algorithm and a software lock-in amplifier designed by using Lab-VIEW are employed, is utilized to lock the laser to the center of the absorption line. In order to test the system, an absorption line of water vapor near 1.396 m is chosen by using a fiber-coupled distributed feedback (DFB) diode laser. An over-40-hours continuous measurement is implemented, and the relevant results are presented and discussed. The detection limit of the system is 1 ppm. This method can also be used to measure the trace gases and monitor the industry gases.
2012, 61 (12): 120702. doi: 10.7498/aps.61.120702
The performance prediction of freestanding blazed transmission grating is discussed using scalar diffraction theory, and grating design parameters are accodingly given. A freestanding transmission grating with a period of 1 m, duty cycle of 0.10.2, aspect ratio of about 100, thickness of 10 m and fractional area of 65% is successfully fabricated by holographic lithography and anisotropic wet etching. The size of a single die is 15 mm 15 mm divided into four 5 mm 5 mm windows. The diffraction efficiency of the fabricated grating is tested at the National Synchrotron Radiation Laboratory in a wavelength region of 550 nm. The wavelength scanning results show a strong blazing effect in the direction of specular reflection from mirror-like grating sidewalls, as expected. The measured and normalized diffraction efficiency is consistent with the theoretical prediction within 38%49% due to grating structural imperfections. These experimental results prove not only the concept of blazed transmission grating but also practicability of the fabrication process.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2012, 61 (12): 121101. doi: 10.7498/aps.61.121101
In the paper, we use the method of super-symmetric quantum mechanics to study the spin-weighted spheroidal wave equation in the case of s=3/2. We first change the equation into Schrdinger's form, then calculate and derive the first four terms concerning E and super-potential W. we summarize the general formula of super-potential Wn and use mathematical induction to prove its correctness. In turn, this completely gives all the information about the ground eigenvalue and eigenfunction.
2012, 61 (12): 121301. doi: 10.7498/aps.61.121301
In this paper, we study the basic theory of field emission, thermionic emission and the thermal field emission, derive their current density formula, the initial distribution of the particles and their initial momentum. And then we achieve a field emission model, thermionic emission model and thermal field emission model on the basis of FDTD-PIC algorithm software. Finally, we verify its correctness using a wedge-shaped-cathode device.
ATOMIC AND MOLECULAR PHYSICS
Investigation on regulating the topological electronic structure of the half-Heusler compound LaPtBi
2012, 61 (12): 123101. doi: 10.7498/aps.61.123101
Using the full-potential linearized augmented plane-wave method based on the density functional theory, we investigate the influences of chemical substitution and uniaxial strain on the topological electronic structure of the half-Heusler compound LaPtBi. It is shown that the 8 band which is protected by the cubic symmetry of the C1b structure can open and form a gap by substituting Sc element for La or Pd for Pt in LaPtBi compound. However, in the case of distorting cubic lattice by using a uniaxial strain, not only the gap mentioned above appears, but also the Fermi level can be tuned regularly. Thus the LaPtBi compound becomes a real topological insulator.
2012, 61 (12): 123201. doi: 10.7498/aps.61.123201
We theoretically investigate the high-order harmonic generation from He+in the two-color laser pulse, which is composed of a multi-cycle 800 nm laser and 1600 nm laser. Compared with the case of the fundamental laser, the harmonic spectrum presents a two-plateau structure, and a broadband supercontinuum appears in the second plateau, of which the efficiency is approximately 2 orders of magnitude lower than that of the first plateau. Adding the 27th harmonic pulse to the two-color laser at a proper time, we can control the ionization mostly occurring at half the optical cycle, and the short quantum path can be picked out, the second plateau is heightened four orders of magnitude compared with the case of the two-color case. Furthermore, the supercontinuum spectrum is extended from the second plateau to the first one. An intense isolated pulse with a duration of 29 as is obtained by superposing the 190th285th harmonics in the continuous region.
2012, 61 (12): 123301. doi: 10.7498/aps.61.123301
The optical emission spectrum of the second positive system of N2(C3uB3g)isanalyzed and calculated based on the energy structure of nitrogen radical triplet system. Some key parameters of the equation for the radiative transition intensity are evaluated theoretically, including the potentials of the upper and lower states obtained from diagonalizing their Hamiltonian matrices, the electronic transition moments calculated by using r-centroid approximation, and the Einstein coefficients of different vib-rotational levels. For comparing with the theoretical spectrum, we achieve the measured results from corona discharge experiments of N2 and Ar. By fitting the measured spectral intensities and the calculated ones, the vibrational and the rotational temperatures are determined approximately to be 4300 K and 800 K. The results also demonstrate that with the reduction of nitrogen concentration, the intensity of N2 radiative state first increases and then decreases due to Penning excitation from argon metastable states. The experimental results verify the correctness of the theoretical calculations on the second positive system.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2012, 61 (12): 124101. doi: 10.7498/aps.61.124101
A double rectangular comb slow-wave structure with a round beam channel is proposed as the slow-wave structure (SWS) circuit of a broad bandwidth traveling-wave tube at W-band. The "cold" characteristic of the SWS and the transmission of the input/output structure are simulated and optimized in this paper. The results show that this circuit has a very broad bandwidth, and that the impedance of the structure with round beam channel can be the same as that of sheet beam by modifying the distance between the double vanes and the radius of the beam channel. Moreover, the transmission of the whole tube is so good that the VSWR can be kept at below 2 in a very broad bandwidth after optimization. The output performance is investigated by both the big signal theory MTSS and the PIC code MAFIA, and they have the same results that in 10 GHz bandwidth the output power is over 40 W and the gain is above 29 dB under a driven power of 50 mW.
2012, 61 (12): 124102. doi: 10.7498/aps.61.124102
By retrieving the constitutive effective parameters of bifilar spiral structure, it is proved that its permittivity and permeability are negative at different frequencies. With the electromagnetic waves incidence in the direction either perpendicular or parallel to the surface of bifilar spiral structure, it is found that the causes of negative permittivity are the same. Previously the investigation of single-sided left-handed materials was limited to microwave band. Through modifying bifilar spiral metamaterials, we design a new single-sided left-handed material in the terahertz regime and the design principle is explained with an LC equivalent circuit. The left-handed material generally consists of electric and magnetic resonators etched on each side of the dielectric substrate respectively Compared with these composite structures, the new single-sided left-handed material has the advantages of low loss, simple structure and easy operating
Analysis of symmetrical, periodic negative-permeability metamaterial using interdigital capacitance loading
2012, 61 (12): 124103. doi: 10.7498/aps.61.124103
The relations between the scattering matrix and relative Bloch permeability of periodic symmetric magnetic resonance metamaterial are investigated in detail by means of network theory and Floquet's theorem, and we retrieve the Bloch constitutive parameters for four split ring resonators using the relations. Full wave simulations in conjunction with numerical retrieval algorithms show that when we load the interdigital capacitance at the gap of split ring resonator, the magnetic resonance frequency drastically lowers. Our work provides not only theoretical foundation for the Bloch permeability parameter retrieval from periodic metamaterials, but also a novel design way of miniaturizing magnetic resonance metamaterial configurations.
2012, 61 (12): 124104. doi: 10.7498/aps.61.124104
A new fast far field approximation algorithm is introduced to calculate the composite scattering characteristics of rough surface and the target in near field, by using the reduced-order electromagnetic current iteration method. Also we use the multi-process parallel algorithm to reduce the simulation time and analyze the influence on the results of the reduced-order electromagnetic current iteration. The calculated results by the algorithm described in the paper and the results obtained by multi-level fast multi-pole method (MLFMM) are in good agreement, so the effectiveness of the algorithm is verified. At the same time, the use of tank to carry out the measurements of near-field complex scattering between the targets and rough surfaceshows that the test results and the calculation results are very consistent.
2012, 61 (12): 124201. doi: 10.7498/aps.61.124201
Interference imaging system for space target has close relation with atmospheric environment, and atmospheric turbulence disturbance distorts terribly the wavefront phase of any transported optics launched from any optics system. In the space target interference imaging system the phase-closure-principle is adopted, in order to eliminate possible effects of atmospheric turbulence on the target image. Based on the power spectrum method and the Fourier transform method, the numerical simulation of wavefront phase screen, which is distorted by atmospheric turbulence conforming to the statistical rules of kolmogonov model and modified Von Karmen model, is respectively implemented. Various images by several different phase-screen models on the interference imaging system are obtained. Simulation results show that, with the advantage of adopting phase-closure-principle, the possible effects of atmospheric turbulence imaging can be eliminated basically.
Smoothing of small on-target spots produced by frequency-tripled beams using lens array and spectral dispersion
2012, 61 (12): 124202. doi: 10.7498/aps.61.124202
The performances of the smoothing of small target spots with a lens array (LA) and two-dimensional smoothing by spectral dispersion (2D SSD) in frequency-tripled high-power laser driver are numerically studied. Intensity distributions and spatial power spectra of the spots are analyzed. Simulative results show that LA can reduce the near-field nonuniformity of the beam and control the envelope of on-target intensity distribution. The 2D SSD has obvious effects in eliminating high-contrast intensity modulation, even in the case that the spots are very small. The results indicate that SSD mainly smoothes the intensity modulation at low-to-middle spatial frequency for small spots, and this would lead to the modifying of the spot profile, while for large spots, SSD sweeps the fine speckle structure to reduce nonuniformity at middle-to-high frequency. These results are valuable for choosing the suitable beam smoothing method in indirect-drive experiment.
2012, 61 (12): 124203. doi: 10.7498/aps.61.124203
In this paper, we numerically study the soliton trapping of supercontinuum in photonic crystal fiber by solving generalized nolinear Schrödinger equation. Using the cross-correlation frequency resolved optical gating (X-FROG) technique, the propagation of the supercontinuum is recorded along the fiber and the evolution of soliton trapping is observed. When the phase-matching condition is met, new frequency of the pulse trapping is generated from four-wave mixing of soliton with nonsolitonic radiation, and is continuously blueshifted while the soliton is redshifted. Higher pump-power shows the strong interaction between soliton and nonsolitonic radiation. Provided in the paper is a theoretical basis for tunable ultra-short laser pulses and supercontinuum researches.
Study on the polarization mismatch in micro/millimeter-wave generation employing optical self-heterodyning technology
2012, 61 (12): 124204. doi: 10.7498/aps.61.124204
In this paper, we study the effect of polarization mismatch (POM) in micro/millimeter-wave (mm-wave) generation employing optical self-heterodyning technology. The calculation formula of POM-induced mm-wave power penalty is derived for the first time. Utilizing a mm-wave generator based on a homemade dual-wavelength polarization maintaining fiber grating laster, several-mm-wave with frequency around 30 GHz is generated. The experimental results accord well with the theoretical ones, which can prove that the theoretical analysis is correct. Finally the simulation of effect of POM on 60 GHz is performed. Under different conditions, the bit error rates (BERs) and the eye diagrams are obtained. BER below 10-9 and clear eye diagrams can be obtained if the POM is under control. So it is very important to control the POM in fiber-optic wireless link.
Study of the satellite line in measurement of the argon -gas-induced broadening of the barium Rydberg levels by two-photon resonant nondegenerate four-wave mixing
2012, 61 (12): 124205. doi: 10.7498/aps.61.124205
We study the satellite lines in measurement of the foreign-gas-induced broadening of the barium Rydberg levels by two-photon resonant nondegenerate four-wave mixing (NFWM). The NFWM spectra of the 6s2 1S0-6snd 1D2 (n=16, 22, 36) transitions at different argon pressures are measured. The plots of the center of satellite line principal quantum number and versus pressure are discussed. The contribution of satellite line to the NFWM spectral profile is analyzed. We find that the pressure-broadening rate coefficient can be corrected when the contribution of satellite line is considered.
The dynamic effect of a field with a time-varying frequency on the atom-atom entanglement in a double J-C model
2012, 61 (12): 124206. doi: 10.7498/aps.61.124206
The entanglement between the two atoms of two separate Jaynes-Commings models is investigated by means of the concurrence. We restrict our attention to two cases, the field frequency varying with time in the forms of sine and rectangle. When the field frequency varies with time in the form of sine, the period and the amplitude of the atom-atom concurrence will decrease as the amplitude of the sine frequency modulation increases. Not only the sine field frequency modulation but also the rectangular field frequency modulation can affect the interaction of the field with atom between resonance and off-resonance. The field frequency modulation can also affect the atom-atom entanglement. The suitable field frequency modulation is favorable for improving, enhancing and stabilizing the degree of the atom-atom entanglement. The suitable field frequency modulation can also prevent the atom-atom entanglement from entanglement sudden death and control it dynamically.
2012, 61 (12): 124207. doi: 10.7498/aps.61.124207
We obtain the exact solution of energy spectrum and dynamics for the two-site Hubbard-Holstein model by the coherent states orthogonal expansion method. The influences of coupling strength g, the average number of phonons n and the initial electronic state on the evolution of system entanglement and von Neumann entropy are discussed. Numerical results are as follows. (a) Entanglement evolution with time shows a good periodicity. When the other parameters are fixed, the evolution period decreases as the coupling strength g goes up but it is independent of the average number of phonons n. (b) The von Neumann entropy of the system demonstrates strict synchronia with the electronic state occupancy probability. (c) Under the weak coupling strength and low average number of phonons, the initial electronic state c2+ c2+|Oe or c1+ c1+|Oe shows larger maximum von Neumann entropy during its evolution than that of c1+c2+c1+c2++ but they gradually approach to each other with the increase of coupling strength or average number of phonons.
2012, 61 (12): 124208. doi: 10.7498/aps.61.124208
In this paper, we describe orbital angular momentum entangled photon pair entanglement in atmospheric channel. The Von Karman spectrum of turbulence is used to create a model of two-photon pair entanglement. The effects of atmospheric turbulence on the entanglement of entangled photon pairs of different orbital angular momentum bases are analyzed. The obtained results are as follows because of the presence of atmospheric turbulence, the entanglement of entangled photon pairs decreases with the increase of the propagation distance z in the atmosphere channel. The entanglement of the entangled photon pairs decreases with the increase of transmission distance. The bigger the turbulence intensity, the faster the entanglement decline and the shorter the propagation distanceis. In the same intensity of atmospheric turbulence of the atmospheric channel, the bigger the orbital angular momentum index, the slower the entanglement decline and the further the propagation distanceis.
2012, 61 (12): 124209. doi: 10.7498/aps.61.124209
The intensity distribution of the -2 to 4-order vector Bessel beams in the focal planes of a high numerical aperture lens are simulated based on the Richards-Wolf's vector diffraction integral model, and the distribution of gradient force capturing a glass ball in vacuum is also simulated. The simulated results show that the patterns, the areas of the focused light field and the variation of components are closely related to the order of the vector beams. Additionally, the distribution of the focused light field gradient force is closely related to the order of the vector beams, which can form optical traps with different shapes and scales.
A study of two-dimensional hexagonal phase array optical beam splitter modulated by external electric field
2012, 61 (12): 124210. doi: 10.7498/aps.61.124210
In this paper, we establish a theoretical model of reciprocal-lattice vector of the two-dimensional hexagonal phase array optical beam splitter modulated by an external electric field, perform the analysis of the tunable phase-difference array optical beam splitter according to the numerical simulation, and then obtain the images of intensity distribution with different values of fractional Talbot distance and external electric field. The two-dimensional hexagonal phase array optical beam splitter is designed and fabricated by lithium niobate. An experimental study of beam splitting is also given. When the applied voltage is 0.5 kV (with electric field of 1 kV/mm), we observe the phenomenon of the beam splitting in Talbot diffraction. As the external field increases, the images of beam splitting in diffraction become clearer, the experimental results are in agreement with theoretical results.
Coherence properties of the supercontinuum generated in anomalous dispersion region of photonic crystal fibers
2012, 61 (12): 124211. doi: 10.7498/aps.61.124211
We numerically calculated the coherence properties of the supercontinuum based on the definition of complex degree of mutual coherence, and obtained the spectral broadening of the pump pulse and the coherence properties of the generated supercontinuum under different pump powers. The results showed that the dominant underlying mechanisms of the spectral broadening are soliton self-frequency shift and dispersive wave generation when the pump wavelength located in the anomalous dispersion region of photonic crystal fiber. While the coherence properties are affected by the modulation instability which amplifies the stochastic noise of the pump pulse, thus the generated frequency components have stochastic phases and amplitudes, which induces the degradation of the coherence of the supercontinuum. The gain of modulation instability increases with the increasing of the pump power, and the effect of the noise on the supercontinuum will become greater which degrades the coherence properties. Low pump power is required to obtain high coherent supercontinuum, and suitable pump power should be adjusted to get wide bandwidth and high coherent supercontinuum.
2012, 61 (12): 124212. doi: 10.7498/aps.61.124212
Generation of triangular optical pulses in conventional normal dispersive (ND) fiber is experimentally realized using a passive nonlinear pulse shaping method based on a combination of pulse pre-chirping, group-velocity dispersion and self-phase modulation in a section of ND fiber. It is found that by optimizing the parameters of launching pulse power level and ND fiber length, high-quality triangular optical pulses with nearly constant gradients of leading and trailing edges and linear frequency chirp profiles can be obtained for a wide range of different pulse pre-chirping values. For different pulse pre-chirpings, high launch power is required for triangular optical pulse generation. The tolerance of triangular pulse formation to ND fiber length and launch power level is improved with the increase of pulse pre-chirping, which means that it is easy to obtain triangular pulses for higher pulse pre-chirping.
2012, 61 (12): 124213. doi: 10.7498/aps.61.124213
Based on the composite surface scattering model, the analytical formulas for Doppler shift and bandwidth of radar echoes return from time-varying sea surface are derived. In our derivations, the influences of the tilt modulation, the shadow and the curvature of large-scale undulating waves are all taken into account for achieving more reasonable results. Comparisons between the theoretical results and direct numerical simulations demonstrate that the analytical formulas can significantly improve the simulated results. And the effects of the tilt modulation, the shadow and the curvature on Doppler spectral properties are discussed in detail. From the simulated results, it is found that the predicted Doppler shifts are always larger in HH-polarization than in VV-polarization due to the tilt modulation of large-scale waves. In addition, at low-grazing angles, the shadow of large-scale waves results in a rapid increase of the predicted Doppler shift, and on the contrary maks the bandwidth narrower.
Near-field modulated simulation of repaired site contained crack or bubble in fused silica subsurface
2012, 61 (12): 124214. doi: 10.7498/aps.61.124214
Three-dimensional (3D) model of Gaussian repaired site contained crack or bubble is establishd, and 3D finite-difference time-domain method is used to simulate near-field modulation of 355 nm laser incidence by those defects on fused silica rear-surface. The results show that we should avoid any unrepaired cracks, especially cracks with incident angle of 65°, and the size of bubbles should be less than 5 λ. All of above contribute to weaken the modulation around repaired pit. When crack or bubble distributes in the near-surface area (<3 λ) and close to the edge of pit ring, the field modulation is obvious. With the increase of lateral gap, there will be a maximum due to electric field fluctuations near the surface area, especially when cracks are contained. And the electric field gradually stabilized when lateral gap is far from the surface. As the vertical gap increases, the number of large electric field decreases, and stabilized oscillation emerges when vertical gap is larger than 3 λ. If cracks or bubbles are located below Gauss repaired sites within a few wavelengths, its depth seems to be enlarged under irradiation.
2012, 61 (12): 124215. doi: 10.7498/aps.61.124215
Plastic fiber image bundle with 250 single fiber diameter, 4096 pixels, 15 m length is fabricated. The result indicates that 25% of the input image remains after it has translated though the 15m fiber bundle, which can meet the need of eye observation or CCD image capture. Based on the key component of image bundle, the eye observation life detection instrument prototype and intelligent life detection instrument prototype connected with CCD, image capture card and portable computer are designed and produced. The effectiveness of researching and rescuing the person from danger is demonstrated. The system can be used not only for researching and rescuing the buried person, but also for video monitoring some special occasions, such as strong electromagnetic interference environment, security department and explosive places.
Full-vectorial analysis of the directional couplers in horizontal multiple-slotted silicon wires with trapezoidal cross-section
2012, 61 (12): 124216. doi: 10.7498/aps.61.124216
Directional couplers are basic components for forming various kinds of photonic devices. In this paper, a directional coupler composed of two horizontal multiple-slotted waveguide structures with slanted sidewalls is characterized by using a full-vectorial finite element method in terms of the electric fields. The effective indexes of the even and the odd modes and the corresponding coupling lengths, both in quasi-TE and quasi-TM modes, are presented, where the strongly-hybrid nature of the guided-mode is effectively demonstrated. The results show that the coupling lengths in quasi-TE and quasi-TM modes exponentially increase with the increase of the gap between the coupled waveguides, where the value in quasi-TE mode is more sensitive to the variation of the angle of the sidewall, while the value in quasi-TM mode is more sensitive to variation of the height and the index of the slot. Properly choosing the structure and material parameters, polarization-independent directional couplers can be realized.
2012, 61 (12): 124301. doi: 10.7498/aps.61.124301
The dynamics of a cavitation bubble under acoustic field and an electric field is studied by regarding liquid as a working medium. The effects of the dimensionless frequency and strength of acoustic field and electric field on cavitation bubble dynamical behaviors by Rayleigh-Plesset equation are numerically investigated. The results show that when acoustic field and electric field are combined, chaos area range of cavitation bubble motion is larger than that when only acoustic field or single electric field exists. This is of significance not only for further research of acoustic cavitation but also for enhancing and improving the cavitation degration of organic pollutant technology.
Experimental research on cylindrical focused beamforming localization method of moving sound sources based on vector sensor array
2012, 61 (12): 124302. doi: 10.7498/aps.61.124302
Based on the passive synthetic aperture principle, a new cylindrically focused beamforming localization method of moving sound sources based on vector sensor array suited for both narrowband and broadband signal is proposed in this paper. By establishing the measurement model of moving sound sources, calculating the localization accuracy versus error, and analyzing the experimental results of cabin model, the performance of this new method can be verified. A comparison between the focused beamforming localization results and the shell vibration measurement results proveds that the proposed method not only can obtain the localization results, but also can reflect the relative contribution of each coherent source.
Analysis of thermal protection mechanism of leading structure embedded high directional thermal conductivity layer
2012, 61 (12): 124401. doi: 10.7498/aps.61.124401
The structure of embedded high thermal conductivity layer leading thermal protection is considered as thermal protection system to prevent hypersonic vehicle from the serious aerodynamic heating. By numerical method, we analyze the cooling effect of the leading thermal protection system under given conditions. The maximum outer surface temperature and the inner surface temperature are reduced by 9.1% and by 31.5% respectively. Both high temperature region and low temperature region are blocked in the external layer and the inner temperature distributions are more uniform. The transfer of heat from high temperature region to low one is achieved, the thermal load of the high temperature area is weakened, and the ability of leading thermal protection system is strengthened. The research shows that the cooling effect of leading system increases with the increases of aerodynamic flux ratio and the area ratio of radiative surfaces. The influences of structure parameters and materials properties on thermal protection are discussed, which provides some references for the design of the structure and the selection of materials.
2012, 61 (12): 124501. doi: 10.7498/aps.61.124501
The effects of particle density on the segregation of binary granular systems in a rotating drum are studied by the molecular dynamics simulation. The results show that the Brazil nut effect happens when the density of small granules is larger, whereas as the density of big granule increases, the segregation pattern is reversed and the reverse Brazil nut effect occurs. We also calculate the quantitative relationship between the segregation index and the density ratio. Finally, the mechanism of competition between percolation and condensation from Hong's theory is used to explain theoretically the reversion of segregation pattern.
2012, 61 (12): 124701. doi: 10.7498/aps.61.124701
A convective cooling platelet structure is a considered as thermal protection system to prevent the leading edge of airfoil from the serious aerodynamic heating. The cooling effect parameter is proposed in this paper. By the use of fluid structure interaction method, the cooling effect of convective cooling structure is investigated under given condition. The minimum that is 0.25 when the coolant is water occurs on the leading edge of airfoil head. The research shows that the increases with the increase of channel aspect radio () and reaches a stable value that indicates that the cooling effect is saturated. Situation unfavorable for cooling may occur if the keeps increasing. And the decreases with the radio of airfoil's head decreasing. With coolant flux increasing, the also increases to a stable value and the pressure drop between inlet and outlet increases rapidly when the structure and the material of the convective cooling platelet structure are fixed. Considering the pressure brought to the supply system due to the increase of flux, we should choose the optimal coolant flux value in order to obtain better cooling effect. Both the inner coolant groove and the external refractory protection should be of high thermal conductivity material which can strengthen the heat transfer of structure and enhance the cooling effect.
Time periodic electroosmotic flow of the generalized Maxwell fluids between two micro-parallel plates with high Zeta potential
2012, 61 (12): 124702. doi: 10.7498/aps.61.124702
In this study, semi-analytical solutions are presented for the time periodic (electroosmotic flow) of linear viscoelastic fluids between micro-parallel plates. The linear viscoelastic fluids used here are described by the general Maxwell model. The solution involves analytically solving the nonlinear Poisson-Boltzmann (P-B) equation, the Cauchy momentum equation and the general Maxwell constitutive equation. By numerical computations, the influences of the dimensionless wall Zeta potential0, the periodic EOF electric oscillating Reynolds number Re, and normalized relaxation times 1 on velocity profiles are presented. Results show that for prescribed electrokinetic width K, relaxation time 1 and oscillating Reynolds number Re, higher Zeta potential 0 will lead to larger amplitude of EOF velocity, and the variation of velocity is restricted to a very narrow region close to the Electric double-layer. In addition, with the increase of relaxation time 1, the elasticity of the fluid becomes conspicuous and the velocity variations can be expanded to the whole flow field. For prescribed Re, longer relaxation time 1 will lead to quick change of the EOF velocity profile, and the amplitude becomes larger gradually.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
SO-FDTD method of analyzing the reflection and transmission coefficient of weakly ionized dusty plasma layer
2012, 61 (12): 125201. doi: 10.7498/aps.61.125201
The complex permittivity of weakly ionized dusty plasma is presented as a fractional polynomial in j. A frequency-domain constitutive relation of weakly ionized dusty plasma is given by shift operator finite-difference time-domain (SO-FDTD) method in time domain. Also the recurrence relation on the electromagnetic properties of weakly ionized dusty plasma is deduced by the SO-FDTD. The reflection and transmission coefficients of the weakly ionized dusty plasma layer are calculated, and the influences which is caused by the change of the dust particle concentration and radius on reflection and transmission coefficients are also analyzed by the SO-FDTD method. The result shows that the reflection coefficient in the presence of dust particles is smaller than in the absence of dust particles, while the transmission coefficient in the former case is larger than in the latter case. Besides, it is found that the reflection coefficient decreases as the concentration or radius of dust particle increases.
Effects of size and electric field coupling on the surface plasmon properties of gold nanoring dimer structures
2012, 61 (12): 125202. doi: 10.7498/aps.61.125202
The extinction spectra and the electric field distribution of the surface plasmon coupling of gold nanoring dimer in horizontal and vertical arrangements are calculated by the discrete dipole approximation method. It is found that the peaks of extinction spectra and electric field distribution of the surface plasmon coupling are sensitive to the size and the separation gap between gold nanorings. It is demonstrated that the peaks of extinction spectra will be red-shifted or blue-shifted due to the different structure parameters of gold nanorings. Because of the effect of the polarization charge coupling between adjacent gold nanoring, the local electric field distribution is found to be stronger for the gold nanoring dimer and trimer in horizontal arrangement than for the single gold nanoring. The horizontal gold nanoring trimer has stronger enhancement of local electric field than the dimer. It shows that the greater separation gap has the weaker local electric field distribution for the gold nanoring dimer and trimer in horizontal arrangement. Therefore the gold nanoring horizontal array is predicted to be an ideal surface enhanced Raman scattering substrate and is expected to have potential applications in biological and chemical detections.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Wavelength tunable properties for distributed feedback lasing from dye-doped holographic polymer dispersed liquid crystal transmission grating
2012, 61 (12): 126101. doi: 10.7498/aps.61.126101
In this paper, we study the wavelength tunable properties for distributed-feedback lasing from 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) dye-doped holographic polymer dispersed liquid crystal grating. By preparing and pumping the DCM-doped HPDLC gratings with various grating spacings, we depict the tuning curve of the distributed-feedback lasing and confirm that only in a range from 574 nm to 685 nm, the lasing action can be observed. Then, we adjust the temperature of the sample and measure the lasing spectrum from the DCM-doped holographic polymer dispersed liquid crystal grating with a grating period of 610nm. There is an obvious 4.9 nm blueshift from 627.9 nm to 623 nm for the lasing wavelength with the temperature increasing from 20℃ to 65℃.
Growth and photoluminescence character research of aluminum nitride nanowires upon carbon foam substrate
2012, 61 (12): 126201. doi: 10.7498/aps.61.126201
To simplify preparation process of AlN/C composite foam, AlN nanomaterials are prepared via double decomposition reaction and then 800℃ annealing process to recrystallize hexagonal AlN (h-AlN) nanowires on carbon foam substrate. Fore the morphology characterization it follows that, h-AlN nanowires with straight cylindrical morphology grow along the direction on carbon microspheres surface and are about 50 nm in diameter and several micrometers in length. Meanwhile, the growth mechanism of nanowire is interpreted as vapor-liquid-solid(VLS) process. The photoluminescence(PL) spectrum of as-prepared sample also researched, and the results show that a sharp photoluminescence peak appears at 423 nm and shifts toward the red side with temperature increasing. The peak is attributed to the transition luminescence, owing to the substitution of C for N impurity energy level. The sample has good PL character in purple light band and is potential to be used the in photodetector field.
2012, 61 (12): 126202. doi: 10.7498/aps.61.126202
In this paper, the interfacial mechanical properties of carbon nanotube-polyethylene (CNT-PE) composite are investigated by using classical molecular dynamics simulation. Basd on the simulations for the CNT pulling-out process from the PE, the influences of the CNT sliding velocity, the chain length of PE and the radius of CNT on the interfacial shear stress are explored. As the chain length of PE increases, the critical interfacial shear stress increases remarkably while the sliding shear stress increases slightly. Both the critical shear stress and the sliding shear stress increase with the radius of CNT enlarging. Moreover, the mechanism for the variation of interfacial shear stress is analyzed and discussed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2012, 61 (12): 127101. doi: 10.7498/aps.61.127101
The electronic structures and the bond characters of bulk -Fe with Ti, C, N additions are studied using the first-principls pseudopotential plane-wave method. The total energy and the cohesive energy are calculated, and the Mulliken population, the overlap population, the density of states and the charge density are also analyzed, which can give a microscopic reason why the mechanical property is improved after the infiltration of Ti, C, N into bulk Fe. The calculated results show that with the alloying element Ti(012.5 at%), C(011.11 at%), N(011.11 at%) contents increasing, the cohesive energy of alloy increases slowly and the structure keeps stable. The additions of Ti, C, N into the alloy enhance the reciprocal hybridization in Fermi energy level, and the binding abilities of Ti, C, N, Fe become stronger. The pseudo-gap near the Fermi energy level means the coexistence of covalent and metallic bonds in alloy. With the contents of alloying elements increasing, the covalent bondings between C, N and Ti, Fe become stronger, and part of C and N atoms will be bound to Ti atoms and form TiC and TiN particles, thereby strengthening the dispersion.
2012, 61 (12): 127102. doi: 10.7498/aps.61.127102
High-mobility In0.53Ga0.47As/InP quantum well is fabricated by the chemical beam epitaxy technique. Clear Shubnikov-de Hass (SdH) oscillation and beating pattern due to zero-field spin splitting are observed by magnetotransport measurements at low temperature. We use an analytical method, involving the simultaneous fitting of fast Fourier transform spectra of SdH oscillations at different tilted fields, to extract the effective g-factor.
2012, 61 (12): 127103. doi: 10.7498/aps.61.127103
First-principles density functional calculations are performed to study the geometries, the electronic and the optical properties of AⅡAl2C4Ⅵ (A =Zn, Cd, Hg; C = S, Se) semiconductors each with a defect chalcopyrite structure. For the linear optical properties, five compounds show good transmissions of light in the IR and part of visible regions, and among them HgAl2S4 and HgAl2Se4 possess moderate birefringences. For the nonlinear optical properties, the strong second harmonic generation (SHG) response can be expected for these crystals, and the large static SHG coefficients ( 20 pm/V) are predicted in this work. The SHG response of AⅡAl2C4Ⅵ semiconductors can be attributed to the transitions from the bands near the top of valence band which are derived from S/Se p states to the unoccupied bands that are contributed by p states of Al and Hg atoms. By comparing with the optical properties of the commercialized AgGaC2 crystals, our results indicate that HgAl2S4 and HgAl2Se4 compounds are good candidates for the second-order nonlinear optical crystals in the IR region.
2012, 61 (12): 127104. doi: 10.7498/aps.61.127104
We present a first-principles calculation study of matal and nonmetal codoped anatase TiO2. We mainly investigate C/TM and N/TM (carbon and metal codoped, nitrogen and metal codoped) codoped TiO2, are calculate their bound energies, energy band structures and densities of states. We find that the metal and the nonmetal impurities have an aggregate tendenty by calculating the bound energy of codoping structure. Positive bound energy show that the doping atom and the peripheral atom will combine into a bond, the boding-effect-produced system energy is higher than the geometric-distortion-effect produced stress energy. We analyze the energy band structure and boding of N/V and C/Cr --codoped TiO2, and further find that if we want to extend TiO2 light absorb edge and improve TiO2 photocatalysis properties by metal and nonmetal codoped TiO2, we should make codoping by the codoped joint method, namely, below the conduction band and on the top of valence band can arise impurity energy levels contributed by metal 3d and nonmetal 2p orbits respectively
2012, 61 (12): 127201. doi: 10.7498/aps.61.127201
The geometry, the frontier molecular orbital and the charge transfer property of lithium (Li) doped tris (8-hydroxyquinoline) aluminum (Alq3) are investigated by the density functional theory (DFT) method. The calculated results show that in the Li-doped Alq3 system, Li-N and Li-O bonds are formed and Li-Alq3 electron transfer complexes are obtained. The incomplete electron transfer from Li atoms to the pyridine side of Alq3 results in donor level in the band gap of Alq3, a typical n-type doping formation, which can improve efficiently the electron transport efficiency. However heavy Li doping can induce the dissociation of Alq3, which leads to the decline of electron transport ability. When the Li:Alq3 doping ratio is about 2:1, the Li-doped Alq3 layer will have a maximal electron transport efficiency.
2012, 61 (12): 127202. doi: 10.7498/aps.61.127202
Previous studies of shot noise suppression in nano-MOSFET either ignored its suppression or emphasized only its existence but gave no deeper research. In this paper, based on the Navid model, the expressions of shot noise suppression factor (Fano) in quasi-ballistic transport nano-MOSFETs are derived with separately considering Fermi effect, Coulomb interaction and the combination of the two effects. The variations of suppression-factors with source-drain voltage, gate voltage, temperature and source-drain doping are investigated. The results we obtained with considering the combination of the two effects are consistent with those from experiments, and the theoretical explanation is given.
2012, 61 (12): 127501. doi: 10.7498/aps.61.127501
According to the exact analytical Bethe-ansatz solution of the one-dimensional spin-1/2 XXZ model, we perform a numerical study of one-dimensional spinless fermions in an optical lattice in the presence of harmonic potential by using a local density approximation. We study the density profile, and obtain the -u phase diagram (here =NfV2/t is the characteristic dimensionless density and u=V/t is the interaction strength scaled in units of the hopping parameter t). With the increases of particle density and nearest-neighbour interaction, the system undergoes five different quantum phases. Through calculating the thermodynamic stiffness S, we find that it can be used as an order parameter. Its singular points can measure the quantum phase transitions in such a confined system.
Room temperature absorption spectra analysis of Er3+/Yb3+-doped Hydrothermal Epitaxial Layer on LiNbO3 and LiTaO3 Single Crystal Substrates
2012, 61 (12): 127801. doi: 10.7498/aps.61.127801
In this paper we introduce the undetermined parameter kNL which is related to the concentration and thickness, and perform the fitting calculation that is on the basis of the absorption spectrum about the hydrothermal epitaxial polycrystalline sample on the surfaces of LiNbO3 and LiTaO3 doped with Er3+/Yb3+ single crystalline substrates according to the J-O theory at the room temperature. It is obtained that for LiNbO32=2.34 10-20 cm2,4=0.77 10-20 cm2,6=0.31 10-20 cm2, and kNL=4.32 10-2 molm-2. LiTaO32=1.68 10-20 cm2,4=0.84 10-20 cm2,6=0.45 10-20 cm2, kNL=9.17 10-3 mol m-2. This method can be extended to the systems in which the data of concentration and thickness such as powder or colloid are difficult to obtain. According to the up-conversion luminescence analysis and the calculation via spectrum parameters, it is confirmed that both the samples have the green up-conversion luminescence at Er3+:Yb3+=1:1, the method of reducing the energy of matrix phonon is tried to improve the quantum cutting yield of 4I13/2 to 2H11/2 and 4S3/2.
2012, 61 (12): 127802. doi: 10.7498/aps.61.127802
Influences of alkaline earth oxides on super broadband near infrared luminescence properties from Bi-doped RO-Al2O3-SiO2 (R=Ca, Sr, Ba) aluminosilicate glasses are investigated. The results show that under different pumping sources, the near infrared (NIR) luminescence shows different behaviors. Under 808 nm excitation, the infrared emission located at 1300 nm with lifetime more than 600 ms is observed, whose intensity increases with the increase of ionic radius. However, under 690 nm excitation, the luminescence at 1100 nm with a full width at half maximum of 400 nm decreases with the increase of ionic radius. According to the above results, it is suggested that infrared emissions may originate from Bi+ and BiO.
2012, 61 (12): 127803. doi: 10.7498/aps.61.127803
In order to research the factors that affect the current uniformity of Flip-chip LEDs, the three-dimensional model of LED chip is established by the finite-element analysis software COMSOL4.0. The influences of chip size, electrode structure and current injection bump on the electrical property of the LED are investigated. The simulation results show that the non-uniform current distribution of LED chip changes exponentially with the increase of the chip size. Interdigitated electrode structure can reduce the lateral resistance effectively by shorting the channel that current flows through. The reasonable design of the bump on the block electrode can also make current even by reducing the lateral resistance.
2012, 61 (12): 127804. doi: 10.7498/aps.61.127804
The vibronic spectra mainly depend on the nature of the defects in diamond. The strong sharp local vibronic modes are observed for the interstitial-related centres beyond their phonon cut-off energy (165meV), but not for the vacancy-related centres. The vibronic spectra of these vacancy-related centres show very strong and broad sidebands closely after the zero phonon lines. Further, the vibrations involving only one vacancy are due to two separate phonons or both, one has an energy of approximately 42 meV and the other has approximately 67 meV.
2012, 61 (12): 127805. doi: 10.7498/aps.61.127805
A novel electron trapped material Sr2SnO4:Sb3+ for optical storage is successfully obtained by conventional solid state method at 1300℃ It indicates that the 1S0 1P1 (208 nm) and 1S0 3P1 (265 nm) transitions of Sb3+ are the most efficient writing light source. Its emission covers 400700 nm and can be attributed to 3P0,1 1S0 transition of Sb3+. We can observe yellowish white light and its color coordination is (0.341, 0.395). The thermoluminescence of Sr2SnO4:Sb3+ contains four peaks at about 39 ℃, 124 ℃, 193 ℃ and 310 ℃, respectively. The intensity of peak at 39 ℃ is low and thus it has a weak afterglow which can last only 140 s. However, even after putting it in dark for 1 day, the peak at 310 ℃ can still keep 45.6% of its original intensity and can be efficiently stimulated by 980 nm infrared laser. As a conclusion, the Sr2SnO4:Sb3+ is a promising electron trapping material for application in optical storage.
2012, 61 (12): 127806. doi: 10.7498/aps.61.127806
Bi-doped BaO-B2O3 glasses are prepared by the melting method. Visible and infrared luminescence spectra, fluorescence decay curve and Raman scattering spectra are measured. NIR emissions, not only one broadband emission peak but also several emission peaks, appear in Bi-doped BaO-B2O3 glass under 808 nm LD pumping. The effect of the network structure of BaO-B2O3 glass on the NIR emission is discussed, and the mechanism for the emission is investigated preliminarily.
2012, 61 (12): 127807. doi: 10.7498/aps.61.127807
The GaN-based blue light LED with double layer photonic crystals is designed to enhance the vertical light extraction efficiency. The effective index approximation method is proposed and used to solve the distribution of the modes in the LED model. The geometrical parameters including the depth of the top photonic crystal d, the thickness of the embedded photonic crystal T, and the distance between the active layer and the embedded photonic crystal D are optimized. Compared with other numerical optimization, the mode analysis used in this work can dramatically save computation time and reduce complexity. In addition, it can provide more theoretical details about the influence of these geometrical parameters on light extraction efficiency. It can be found that when the surface photonic crystal satisfies the condition of d / nPhCs, high order modes localized in the structure are still not cut off but the low order modes obtain less power since they are pushed away from the active layer. Hence, the light extraction efficiency reaches its maximum. The cap layer modes can be excited by the embedded photonic crystals, when this layer satisfies 100 nm T 300 nm and 100 nm D 200 nm, the cap layer modes gather much power from the active layer and interact with the surface photonic crystals more efficiently. Hence the light extraction efficiency is dramatically improved. With our optimized parameters, the light extraction efficiency can be achieved to be up 4 times that of ordinary LED. These results shows a significant promise of designing a high-efficiency GaN-based blue light LED.
2012, 61 (12): 127808. doi: 10.7498/aps.61.127808
Based on the relationship between ionizing damage effect and displacement damage effect under radiation degradation mechanism of pn-junction diode, and combined with the noise theory of radiation degradation of pn-junction diode, a change law of low frequency noise of pn-junction diode under radiation found. The inconsistency between the change laws of of two kinds of effects is found. Based on the experimental result, the relationship between two kinds of effects is judged. This relationship can explain the experimental result. This is very important for the device hardening research.
2012, 61 (12): 127901. doi: 10.7498/aps.61.127901
The micro-vacuum electronic device is one of the most promising sources for the generation of high power THz-wave radiations. In this paper, the systematical theoretical analyses and computer simulations on the physical mechanism of a kind of micro-vacuum electronic THz radiation source based on the cathode of field-emission array (FEA) are carried out. The mode matching method is used to study the electromagnetic characteristics of the structure, and -mode is confirmed to be an optimal operation mode for its field distribution. Linear theory (small signal theory) is used to analyze the beam-wave interaction of this kind of source, and the starting condition of the -mode oscillation is derived. The premodulation of electron beam emitted from FEA and the electron transit time effect in the interaction gap are the physical cause of the electromagnetic oscillation. These results are well verified by the computer simulations.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Design and analysis of thermally tunable liquid-crystal-filled microstructured polymer optical fiber
2012, 61 (12): 128101. doi: 10.7498/aps.61.128101
A highly tunable bandgap-guiding microstructured polymer optical fiber (mPOF) is designed by infiltrating the cladding air holes with a liquid crystal. Bandgap is blue shifted as temperature is increased. A high thermal tuning sensitivity of -5.5 nm/℃ is achieved at the long-wavelength edge of the bandgap. Mode properties and effective mode area of the fundamental mode are investigated by using the full-vector finite element method. The designed fiber has a large effective area and high power transmission coefficient between the index guiding modes and the bandgap guiding modes. Our results provide theoretical references for applications of mPOF in sensing and tunable fiber-optic devices.
2012, 61 (12): 128102. doi: 10.7498/aps.61.128102
15at.%Yb3+:Gd2SiO5 crystal with a size of30 mm75 mm is grown by the Czochralski method, and its lattice parameters, atom coordinates and temperature factors are determined by the full-profile Rietveld refinement method. Its spectral parameters of oscillator strength, line strength, transition probability, energy lifetime and integral emission cross-section for Yb3+2F7/22F5/2 transition are calculated using the absorption spectraum. And the laser performance evaluation shows that this crystal is a potential laser crystal with relatively high threshold, and could be used as a medium of tunable or ultra-fast laser pumped by high-power laser diode.
2012, 61 (12): 128401. doi: 10.7498/aps.61.128401
The space charge limiting current in cylinder drifting tube and coaxial drifting tube and the energy that could be obtained and also the restrict magnetic field are analyzed, and the results show that it is propitious to change the energy of electron beam into microwave power in the coaxial conduit. The advantages of the tri-axial relativistic klystron amplifier and the multi-beam klystron amplifier are analyzed, then an x-band coaxial multi-beam relativistic klystron amplifier is designed by using a three-dimensional particle simulation software, and the transmition and the bunching of electron beam are analyzed. A 1.23 GW averaged microwave power over the oscillator period is generated by simulation with 600 kV electron beam voltage, 5 kA current and 0.8 T leading magnetic field density, the frequency is 9.37 GHz and the efficiency is 41%.
2012, 61 (12): 128501. doi: 10.7498/aps.61.128501
The characteristics of a double heterojunction bipolar transistor(DHBT) depend closely on the type of band alignment structure at the hetero-interface between emitter-base(E-B) heterojunction and base-collector(B-C) heterojunction. Based on thermionic-field-diffusion model, the comparisons are made of the DC and the RF characteristics between two novel HBTs, that is, InAlAs/GaSbAs/InP DHBT and InP/GaSbAs/InP DHBT, of which the former has a type-I E-B junction and a type-II B-C junction and the later has a type-II E-B junction and a type-II B-C junction. The simulation results show that DHBT with a type-I E-B junction and a type-II B-C junction has much better current driving capability, DC gain and RF performance, although it has a slightly high turn-on voltage.
2012, 61 (12): 128502. doi: 10.7498/aps.61.128502
Flip chip plastic ball grid array (FC-PBGA) is unique and has been widely used. During FC-PBGA's practical application, the analysis of its failure mechanisms under high temperature, electricity, water vapor and other comprehensive environmental stress conditions is very important for improving its application reliability. In this paper, with 0.13-μm m/6-level copper-based FPGA with FC-PBGA package, failure mode of the device is exposed under external stress, which is dominated with thermal-mechanical stress generated by high temperature thermal reflow process. And the failure mechanism corresponding to the failure mode is analyzed. Results show that the basic cause of the failure is the thermal-mechanical stress, which is induced by the combination of internal and external reflow temperature difference and high temperature reflow process when assembled. The thermal-mechanical stress makes the solder bumps on the flip chip melt again and bridges the adjacent solder bumps to lead to the device short failure. It also induces crack or delamination in the underfill, crack in solder bump or solder bump fallen off to lead to device open failure. The residual stress on Cu/low-k interconnect structures damages the structure integrity and affects the reliability of FC-PBGA packages.
2012, 61 (12): 128503. doi: 10.7498/aps.61.128503
One-dimensional nanomaterial possesses an electric field reinforcing effect, and its field emission properties have aroused much interest. In this paper, ZnO nanowire (NW) arrays are prepared by the thermal chemical vapor deposition (CVD) method, and the characteristic of field electron emission of ZnO NW arrays under the illumination of ultraviolet light is investigated. It is found that, upon ultraviolet light illumination, the turn-on voltage drops off and emission current increases. A process of field emission coupled with semiconducting properties of ZnO NWs is proposed. Ultraviolet photon-excited electron transition from valence band to conductance band and defect energy levels of ZnO NWs can lead the number of emitting electrons to increase, and the photoemission reduces the effective work function of zinc oxide emitters, which largely enhances the field emission performance. The characteristic of field emission of ZnO NWs under ultraviolet light illumination suggests an approach to tuning field emission of semiconductor emitters, which is promising for the applications in optical sensor, cold-cathode flat panel display and field electron source.
2012, 61 (12): 128504. doi: 10.7498/aps.61.128504
Quantum efficiency decay of reflection-mode GaN photocathode is small at short wavelengths and large at long wavelengths. In light of this experimental phenomenon, the emitted electron energy distribution is calculated by using the Boltzmann distribution and transfer matrix method based on Airy function, with the intervalley scattering considered. The effect of surface potential barrier change on quantum efficiency decay is investigated. The results of theoretical calculation are in good agreement with the experiments al results. The reduction of effective dipole in activated layer leads to inereased length and height of surface barrier, which causes more decay of the emitted electron energy distribution generated by longer wavelength photons, and less decay of the emitted electron energy distribution generated by shorter wavelength photons. It is the fundamental reason of phenomenon that the decay of quantum efficiency is small at short wavelengths and large at long wavelengths.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2012, 61 (12): 129101. doi: 10.7498/aps.61.129101
The electrical anisotropy in the crust and the upper mantle is the main link among geoelectrical model, underlying structure, and tectonic model. In recent years, great attention was paid to this phenomenon, which promotes the new research towards the structure model of electrical anisotropy and inversion theory. According to the Marquardt's inversion theory, in the paper we first improve the weighting factor and apply it to the apparent resistivity and impedance phase joint inversion. Then, the detailed example analysis of them proves the corrctness of the mentioned theory. Additionally, the processing and the interpretation of the measured magnetotelluric data in northwest of china not only indicate the practicability of the theory, but also provide a new method for the future research of deep electrical structures.
Relationship between the South China Sea summer monsoon and the first-landfall tropical cyclone over mainland of China
2012, 61 (12): 129201. doi: 10.7498/aps.61.129201
This study investigates the relationship between the South China Sea summer monsoon and the first tropical cyclone (TC) of the season to make landfall over mainland China (in short, the first-landfall TC) using the South China Sea summer monsoon index, NCEP/NCAR reanalysis monthly average data, and best-track TC data from Joint Typhoon Warning Center (JTWC) for 19482009. The results show that the characteristics of the first-landfall TC are closely associated with the frequency, active stage, and strength of subsequent landfall TCs in the same year. In detail, a stronger (weaker) South China Sea summer monsoon index year corresponds to more (fewer) landfall TCs over Mainland China, a later (earlier) date of the first-landfall TC, a lower (higher)-latitude landing point of the first-landfall TC, and a stronger (weaker) monsoon trough. The anomalous wind field and the track of the first-landfall TC are also significantly related to the strength of the index. The location of the first-landfall TC has shows a gradual trend toward higher latitudes over the analysis period, and there is a decreasing trend in the variability of the South China Sea summer monsoon index.
2012, 61 (12): 129202. doi: 10.7498/aps.61.129202
Affected by some factors such as external forcing and the measurement errors of instrument itself, observational data often contain noises, disturbances and some other false information. To solve this problem, the effects of different noises on moving cut data-approximate entropy (MC-ApEn) are investigated in this paper. The results indicate that MC-ApEn is little affected by random spikes and Gaussian white noise, which means that the MC-ApEn method has strong anti-noise ability. The results provide an essential experimental basis for the wide applications of the present method to observational data.
A method for temperature inversion in middle-upper atmosphere using FPI without laser calibration and its observational data preliminary analysis
2012, 61 (12): 129401. doi: 10.7498/aps.61.129401
In this paper we present a method, by which the temperature inversion is carried our without the calibration of the laser under the FPI observations. On the basis of 630 nm and 557.7 nm observational data are obtained by Wuhan University FPI atmospheric temperature measurement system, using the above method. The results of temperature inversion show that the method doesnot require the calibration of the laser, and can be used for FPI temperature inversion with different wavelengths.
2012, 61 (12): 129501. doi: 10.7498/aps.61.129501
In order to reduce the time delay of the liquid-crystal (LC) adaptive optics system (AOS) which reduces the image resolution of the observed objects, we present a new technique for the first time which is called recursive least square (RLS) modal prediction of turbulent wavefront. First, we introduce the structure of the open-loop LC AOS with RLS predictor. Second, we present the RLS modal prediction algorithm in detail. Third, an actual open-loop LC AOS is designed and built, and the RLS prediction is carried out on it. It is shown that under a pure time delay system and the turbulent condition with Greenwood frequency of 35Hz and Fried parameter of 6 cm, after prediction the residual wavefront error reduce to 0.15 wave (wave=785 nm) from 0.26 wave that is obtained through the direct open loop correction. The prediction gain reaches 42%. Finally, the images obtained by the open-loop AOS with and without prediction are demonstrated. With direct correction without prediction, the image resolution reache 25.4 cycles/mm. After the correction with RLS prediction, the image resolution reaches 32.0 cycles/mm which is equal to 0.9 of the diffraction limit resolution of the system. Therefore, with respect to correction without prediction, a relative gain of 26% in image resolution is achieved with RLS prediction. In conclusion, the RLS modal prediction can improve the image resolution of the open-loop LC AOS effectively.