The Lie symmetry analysis is performed for coupled short plus (CSP) equation. We derive the infinitesimals that admit the classical symmetry group. Five types arise depending on the nature of the Lie symmetry generator. In all types, we find reductions in terms of system of ordinary differential equations, and exact solutions of the CSP equation are derived, which are compared with numerical solutions using classical fourth-order Runge-Kutta scheme.

In this paper, the complex variable reproducing kernel particle (CVRKP) method and the finite element (FE) method are combined as the CVRKP-FE method to solve transient heat conduction problems. The CVRKP-FE method not only conveniently imposes the essential boundary conditions, but also exploits the advantages of the individual methods while avoiding their disadvantages, then the computational efficiency is higher. A hybrid approximation function is applied to combine the CVRKP method with the FE method, and the traditional difference method for two-point boundary value problems is selected as the time discretization scheme. The corresponding formulations of the CVRKP-FE method are presented in detail. Several selected numerical examples of the transient heat conduction problems are presented to illustrate the performance of the CVRKP-FE method.

By means of singularity structure analysis, the integrability of a generalized fifth-order KdV equation is investigated. It is proven that this equation passes the Painlevé test for integrability only for three distinct cases. Moreover, the multi-soliton solutions are presented for this equation under three sets of integrable conditions. Finally, by selecting appropriate parameters, we analyze the evolution of two solitons, which is especially interesting as it may describe the overtaking and the head-on collisions of solitary waves of different shapes and different types.

The symmetries and the exact solutions of the (3+1)-dimensional nonlinear incompressible non-hydrostatic Boussinesq (INHB) equations, which describe the atmospheric gravity waves, are studied in this paper. The calculation on symmetry shows that the equations are invariant under the Galilean transformations, the scaling transformations, and the space-time translations. Three types of symmetry reduction equations and similar solutions for the (3+1)-dimensional INHB equations are proposed. Traveling and non-traveling wave solutions of the INHB equations are demonstrated. The evolutions of the wind velocities in latitudinal, longitudinal, and vertical directions with space-time are demonstrated. The periodicity and the atmosphere viscosity are displayed in the (3+1)-dimensional INHB system.

Optimizing train movement has a great significance for railway traffic. In this paper, based on the optimal velocity car-following model, we propose a new simulation model for optimizing train movement in railway traffic. Here a kind of single-track railway is considered. Our aim is to reduce the energy consumption of train movement and ensure the train being on time by controlling the velocity curve of train movement. The simulation results indicate that the proposed model is effective for optimizing train movement. And some major characteristics of train movement can be well captured. This method provides a new way to optimize train movement in railway traffic.

In this paper, a Petrov-Galerkin scheme named Runge-Kutta control volume (RKCV) discontinuous finite element method is constructed to solve the one-dimensional compressible Euler equations in the Lagrangian coordinate. Its advantages include preserving the local conservation and a high resolution. Compared with the Runge-Kutta discontinuous Galerkin (RKDG) method, the RKCV method is easier to be implemented. Moreover, the advantages of the RKCV and the Lagrangian methods are combined in the new method. Several numerical examples are given to illustrate the accuracy and the reliability of the algorithm.

A microwave thruster system that can convert microwave power directly to thrust without gas propellant is developed. In the system, a cylindrical tapered resonance cavity and a magnetron microwave source are used respectively as the thruster cavity and the energy source to generate the electromagnetic wave. The wave is radiated into and then reflected from the cavity to form a pure standing wave with a non-uniform electromagnetic pressure distribution. Consequently, a net electromagnetic thrust exerted on the axis of the thruster cavity appears, which is demonstrated through theoretical calculation based on the electromagnetic theory. The net electromagnetic thrust is also experimentally measured in the range from 70 mN to 720 mN when the microwave output power is from 80 W to 2500W.

Shannon entropy for lower position and momentum eigenstates of Pöschl-Teller-like potential is evaluated. Based on the entropy densities demonstrated graphically, we note that the wave through of the position information entropy density ρ(x) moves right when the potential parameter V_{1} increases and its amplitude decreases. However, its wave through moves left with the increase in the potential parameter |V_{2}|. Concerning the momentum information entropy density ρ(p), we observe that its amplitude increases with increasing potential parameter V_{1}, but its amplitude decreases with increasing |V_{2}|. The Bialynicki-Birula-Mycielski (BBM) inequality has also been tested for a number of states. Moreover, there exist eigenstates that exhibit squeezing in the momentum information entropy. Finally, we note that position information entropy increases with V_{1}, but decreases with |V_{2}|. However, the variation of momentum information entropy is contrary to that of the position information entropy.

We investigate the dynamics of correlations for two-parameter qubit-qutrit states under various local decoherence channels including depahsing, phase-flip, bit- and trit-flip, bit- and trit-phase-flip, and depolarizing channels. We find that, under certain conditions, the classical correlations may not be affected by the noise or decay monotonically. The quantum correlations measured by measurement-induced disturbance (MID) show three types of dynamical behaviors: (i) monotonic decay to zero, (ii) monotonic decay to a nonzero steady value, (iii) increase from zero and then decrease to zero in a monotonic way. Consequently, we find that, differing from the dynamics of entanglement, the present classical and quantum correlations do not reveal sudden death behavior.

Quantum walk, the quantum counterpart of random walk, is an important model and widely studied to develop new quantum algorithms. This paper studies the relationship between the continuous-time quantum walk and the symmetry of a graph, especially that of a tree. Firstly, we prove in mathematics that the symmetry of a graph is highly related to quantum walk. Secondly, we propose an algorithm based on the continuous-time quantum walk to compute the symmetry of a tree. Our algorithm has better time complexity O(N^{3}) than the current best algorithm. Finally, through testing three types of 10024 trees, we find that the symmetry of a tree can be found with an extremely high efficiency with the help of the continuous-time quantum walk.

By means of the cavity-assisted photon interference, a simple scheme is proposed to implement symmetric economical phase-covariant quantum cloning machine of two remote qubits, with each in a separate cavity. With our present scheme, a high-fidelity cloning machine is realized. Our scheme may be quite useful in terms of the distributed quantum information processing.

We propose two effective schemes for local and remote unknown atomic state comparisons with cavity-assisted single photon input-output process without any initial entanglement or auxiliary resource. And the unambiguous state discrimination is considered using the state comparison process as the basic module. All the implementation schemes here just involve common quantum logic gates and the single qubit measurement. The analysis shows that our schemes are feasible under the current experimental conditions.

We propose a scheme to generate a Greenberger-Horn-Zeilinger (GHZ) state of four atoms trapped in a two-mode optical cavity via an adiabatic passage. The scheme is robust against moderate fluctuations of the experimental parameters. Numerical calculations show that the excited probabilities of both the cavity modes and the atoms are tiny and depend on the pulse peaks of the classical laser fields. For certain decoherence due to the atomic spontaneous emission and the cavity decay, there exits a range of pulse peaks to get a high fidelity.

We show a scheme to generate entangled coherent states in a circuit quantum electrodynamics system, which consists of a nanomechanical resonator, a superconducting Cooper-pair box (CPB), and a superconducting transmission line resonator. In the system, the CPB plays the role of nonlinear medium and can be conveniently controlled by a gate voltage including direct-current and alternating-current components. The scheme provides a powerful tool for preparing the multipartite mesoscopic entangled coherent states.

A quantum steganography protocol with a large payload is proposed based on the dense coding and the entanglement swapping of the Greenberger-Horne-Zeilinger (GHZ) states. Its super quantum channel is formed by building up a hidden channel within the original quantum secure direct communication (QSDC) scheme. Based on the original QSDC, secret messages are transmitted by integrating the dense coding and the entanglement swapping of the GHZ states. The capacity of the super quantum channel achieves six bits per round covert communication, much higher than the previous quantum steganography protocols. Its imperceptibility is good, since the information and the secret messages can be regarded to be random or pseudo-random. Moreover, its security is proved to be reliable.

We first provide four new schemes for two-party quantum teleportation of an arbitrary unknown multi-particle state by using three-, four- and five-particle states as the quantum channel, respectively. The successful probability and fidelity of the four schemes reach 1. In the first two schemes, the receiver can only apply one of the unitary transformations to reconstruct the original state, making it easier for these two schemes to be directly realized. In the third and fourth schemes, the sender can preform Bell-state measurements instead of multipartite entanglement measurements of the existing similar schemes, which makes real experiments more suitable. It is found that the last three schemes may become tripartite controlled teleportation schemes of teleporting an arbitrary multi-particle state after a simple modification. Finally, we present a new scheme for three-party sharing an arbitrary unknown multi-particle state. In this scheme, the sender first shares three three-particle GHZ states with two agents. After setting up the secure quantum channel, an arbitrary unknown multi-particle state can be perfectly teleported if the sender performs three Bell-state measurements, and either of two receivers operates an appropriate unitary transformation to obtain the original state with the help of other receiver's three single-particle measurements. The successful probability and fidelity of this scheme also reach 1. It is demonstrated that this scheme can be generalized easily to the case of sharing an arbitrary unknown multi-particle state among several agents.

We develope the Hirota bilinear method and obtain the exact one and two superposition soliton solutions for two-component Bose-Einstein condensates. The conversion of three kinds of solitons including the superposition solitons, bright-bright solitons, and dark-bright solitons is discussed. With the energy analysis, we find that the superposition soliton state is an excitation state for this system. Moreover, the collision of two superposition solitons is found to be elastic.

We analyze the role of the electromagnetic field for the stability of a shearing viscous star with spherical symmetry. Matching conditions are given for the interior and the exterior metrics. We use a perturbation scheme to construct the collapse equation. The range of instability is explored in Newtonian and post Newtonian (pN) limits. We conclude that the electromagnetic field diminishes the effects of the shearing viscosity in the instability range and makes the system more unstable in both Newtonian and post Newtonian approximations.

Very recently, via the covariant form of the adiabatic invariant I=fp_{i}dq_{i} instead of I=∫ p_{i}dq_{i}, an equally spaced spectroscopy of a Schwarzschild black hole was derived. The emphasis was given to the covariant of results. In this paper, we extend that work in a spherically symmetric spacetime to the case of a rotating Bañados-Teitelboim-Zanelli (BTZ) black hole. It is noteworthy that the adiabatic covariant action I=fp_{i}dq_{i} gives the same value for the black hole spectroscopy in different coordinates. The result shows that the area spectrum is ΔA=8π l_{P}^{2}, which confirms the initial proposal of Bekenstein. And the result is consistent with that already obtained by other methods.

Depending on the excitability of the medium, a propagating wave segment would either contract or expend to fill the medium with spiral waves. This paper aims to introduce a simple mechanism of feedback control to stabilize such an expansion or contraction. To do this, we lay out a feedback control system in a block diagram and reduce it into a bare, universal formula. Analytical and experimental findings are compared through a series of numerical simulations of the Barkley model.

A new method of predicting chaotic time series is presented based on local Lyapunov exponent, by quantitatively measuring the exponential rate of separation or attraction of two infinitely close trajectories in state space. After reconstructing state space from one-dimensional chaotic time series, neighboring multiple-state vectors of the predicting point are selected to deduce the prediction formula using the definition of local Lyapunov exponent. Numerical simulations are carried out to test its effectiveness and verify its higher precision than two older methods. Effects of number of referential state vectors and added noise on forecasting accuracy are also studied numerically.

A digital image encryption scheme using chaotic map lattices has been proposed recently. In this paper, two fatal flaws of the cryptosystem are pointed out. According to these two drawbacks, cryptanalysts could recover the plaintext by applying chosen plaintext attack. Therefore, the proposed cryptosystem is not secure enough to be used in the image transmission system. Experimental results show the feasibility of the attack. As a result, we achieve some improvements to enhance the encryption scheme, which can completely resist our chosen plaintext attack.

This paper is concerned with the exponential synchronization problem of coupled memristive neural networks. In contrast to general neural networks, memristive neural networks exhibit state-dependent switching behaviors due to the physical properties of memristors. Under a mild topology condition, it is proved that a small fraction of controlled subsystems can efficiently synchronize the coupled systems. The pinned subsystems are identified via a search algorithm. Moreover, the information exchange network needs not to be undirected or strongly connected. Finally, two numerical simulations are performed to verify the usefulness and effectiveness of our results.

In this paper, we propose a new method to realize drive-response system synchronization control and parameter identification for a class of generalized Julia sets. By means of this method, the zero asymptotic sliding variables are applied to control the fractal identification. Furthermore, the problems of synchronization control are solved in the case of a drive system with unknown parameters, and the unknown parameters of the drive system can be identified in the asymptotic synchronization process. The results of simulation examples demonstrate the effectiveness of this new method. Particularly, the basic Julia set is also discussed.

The complexities of multi-wing chaotic systems based on the modified Chen system and multi-segment quadratic function are investigated by employing statistical complexity measure (SCM) and spectral entropy (SE) algorithm. How to choose the parameters of the SCM and SE algorithms is discussed. The results show that the complexity of the multi-wing chaotic system does not increase as the number of wings increases, and it is consistent with the results of the Grassberger-Procaccia (GP) algorithm and the largest Lyapunov exponent (LLE) of the multi-wing chaotic system. This conclusion is verified by other multi-wing chaotic systems.

We generate a directed weighted complex network by a method based on Markov transition probability to represent an experimental two-phase flow. We first systematically carry out gas-liquid two-phase flow experiments for measuring the time series of flow signals. Then we construct directed weighted complex networks from various time series in terms of a network generation method based on Markov transition probability. We find that the generated network inherits the main features of the time series in the network structure. In particular, the networks from time series with different dynamics exhibit distinct topological properties. Finally, we construct two-phase flow directed weighted networks from experimental signals and associate the dynamic behavior of gas-liquid two-phase flow with the topological statistics of the generated networks. The results suggest that the topological statistics of two-phase flow networks allow quantitatively characterizing the dynamic flow behavior in the transitions among different gas-liquid flow patterns.

In this paper, we propose a novel block cryptographic scheme based on spatiotemporal chaotic system and chaotic neural network (CNN). The employed CNN comprises a 4-neuron layer called chaotic neuron layer (CNL), where spatiotemporal chaotic system participates in generating its weight matrix and other parameters. The spatiotemporal chaotic system used in our scheme is the typical coupled map lattice (CML), which can be easily implemented in parallel by hardware. A 160-bit-long binary sequence is used to generate the initial conditions of the CML. The decryption process is symmetric relative to the encryption process. Theoretical analysis and experimental results prove that the block cryptosystem is secure and practical, and suitable for image encryption.

We investigate the extended (2+1)-dimensional shallow water wave equation. The binary Bell polynomials are used to construct bilinear equation, bilinear Bäcklund transformation, Lax pair, and Darboux covariant Lax pair for this equation. Moreover, the infinite conservation laws of this equation are found by using its Lax pair. All conserved densities and fluxes are given with explicit recursion formulas. The N-soliton solutions are also presented by means of the Hirota bilinear method.

By using the (G'/G)-expansion method and the variable separation method, a new family of exact solutions of the (3+1)-dimensional Jimbo-Miwa system is obtained. Based on the derived solitary wave solutions, we obtain some special localized excitations and study the interactions between two solitary waves of the system.

In this study, the consensus problem for a class of second-order multi-agent systems with nonuniform time delays is investigated. A linear consensus protocol is used to make all agents reach consensus and move with a constant velocity. By a frequency-domain analysis, a simplified sufficient condition is given to guarantee the consensus stability of the dynamic system. Finally, the effectiveness of the obtained theoretical results is illustrated through numerical simulations.

Based on an isotropic two spin-1/2 qubits Heisenberg model with the Dzyaloshinskii-Moriya interaction in an external magnetic field, we have constructed an entangled quantum refrigerator. Expressions for the basic thermodynamic quantities, i.e., the heat exchanged, the net work input, and the coefficient of performance, are derived. Some intriguing features and their qualitative explanations in zero and non zero magnetic fields are given. The influence of the thermal entanglement on the refrigerator is investigated. The results obtained here have general significance and will be helpful to understand the performance of an entangled quantum refrigerator.

We study the role of laser polarization in the diamagnetic spectrum for the transition from the ground state to the highly excited Rydberg states through a single photon absorption. For simplicity, one usually polarizes the irradiation laser to the selected main quantum axis, which is along the applied external electric or magnetic field. The transition selection rule is simply expressed as Δm=0, which corresponds to the π transition. When the polarization is circularly polarized around the main axis, the σ^{+} or σ^{-} transition occurs, corresponding to the selection rule of Δm=1 or Δm=-1, respectively. A slightly more complex case is that the laser is linearly polarized perpendicular to the main axis. The numerical calculation shows that we can decompose the transition into the sum of σ^{+} and σ^{-} transitions, it is noted as the σ transition. For the more complex case in which the laser is linearly polarized with an arbitrary angle with respect to the main axis, we have to decompose the polarization into one along the main axis and the other one perpendicular to the main axis. They correspond to π and σ transitions, respectively. We demonstrate that these transitions in the diamagnetic spectrum and the above spectral decomposition well explain the experimentally observed spectra.

The D_{1} line spectrally selective pumping process in Doppler-broadened cesium is analyzed by solving the optical Bloch equations. The process, described by a three-level model with the L scheme, shows that the saturation intensity of broadened atoms is three orders of magnitude larger than that of resting atoms. The |F_{g} =3>→|F_{e} =4> resonance pumping can result in the ground state |F_{g} =4, m_{F} =4i sublevel having a maximum population of 0.157 and the population difference would be about 0.01 in two adjacent magnetic sublevels of the hyperfine (HF) state F_{g} =4. To enhance the anisotropy in the ground state, we suggest employing dichromatic optical HF pumping by adding a laser to excite D_{1} line |F_{g} =4>→jF_{e} =3> transition, in which the cesium magnetometer sensitivity increases by half a magnitude and is unaffected by the nonlinear Zeeman effect even in Earth’s average magnetic field.

The ionization process of B^{2+} by H^{+} impact is studied using the continuum-distorted-wave eikonal-initial-state (CDW-EIS) method and the modified free electron peak approximation (M-FEPA), respectively. Total, single-, and double-differential cross sections from 1s and 2s orbital are presented for the energy range from 10 KeV/u to 10 MeV/u. Comparison between the results from the two methods demonstrates that the total and single-differential cross sections for the high-energy incident projectile case can be well evaluated using the simple M-FEPA model. Moreover, the M-FEPA model reproduces the essential features of the binary-encounter (BE) bump in the double-differential cross sections. Thus, BE ionization mechanism is discussed in detail by adopting the M-FEPA model. In particular, the double- and single-differential cross sections from the 2s orbital show a high-energy hip, which is different from those from the 1s orbital. Based on Ref. [1], the Compton profiles of B^{2+} for 1s and 2s orbitals are given, and the hips in DDCS and SDCS from the 2s orbital are explained.

Quasiclassical trajectory (QCT) calculations have been performed for the abstraction reaction, D' +DS(v = 0, j = 0)→D'D+S on a new LZHH potential energy surface (PES) of the adiabatic 3A'' electronic state [Lü et al. 2012 J. Chem. Phys. 136 094308]. The collision energy effect on the integral cross section and product polarization are studied over a wide collision energy range from 0.1 to 2.0 eV. The cross sections calculated by the QCT procedure are in good accordance with previous quantum wave packet results. The three angular distribution functions, P(θ_{r}), P(φ_{r}), and P(θ_{r},φ_{r}), together with the four commonly used polarization-dependent differential cross sections ((2π/σ)(ds_{00}/dω_{t}), (2π/σ)(ds_{20}/dω_{t}), (2π/σ)(ds_{22+}/dω_{t}), (2π/σ)(ds_{21-}/dω_{t})) are obtained to gain insight into the chemical stereodynamics of the title reaction. Influences of the collision energy on the product polarization are exhibited and discussed.

The mechanism of contact electrification between metals was studied using the first-principles method, taking the Ag-Fe contact as an example. Charge population, charge density difference, and the orbitals and densities of states (DOS) were calculated to study the electronic properties of the contacting interfacial atoms. Based on the calculation, the amount of contact charge was obtained. The investigation revealed that the electrons near Fermi levels with higher energies transfer between the outermost orbitals (s orbitals for Ag and d orbitals for Fe). Meanwhile, polarized covalent bonds form between the d electrons in the deep energy states. These two effects together lead to an increase of charge magnitude at the interface. Also, the electrons responsible for electrification can be determined by their energies and orbitals.

We theoretically investigate the orientation of the cold KRb molecules induced in a switched electrostatic field by numerically solving the full time-dependent Schrödinger equation. The results show that the periodic field-free molecular orientation can be realized for the KRb molecules by rapidly switching off the electrostatic field. Meanwhile, by varying the switching times of the electrostatic field, the adiabatic and nonadiabatic interactions of the molecules with the applied field can be realized. Moreover, the influences of the electrostatic field strength and the rotational temperature to the degree of the molecular orientation are studied. The investigations show that, the increasing of the electrostatic field will increase the degree of the molecular orientation, both in the constant-field regime and in the field-free regime, while the increasing of the rotational temperature of the cold molecules will greatly decrease the degree of the molecular orientation.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

A novel cloaking scheme to hide an object in a half space from electromagnetic (EM) detection without reflection is firstly presented. The proposed cloaking scheme contains a couple of matching strips, which consist of an isotropic material layer and an anisotropic UPML layer, located right under the bottom surface of a semi-cylindrical cloaking shell. Simple expressions for the material parameters of the cloaking scheme are derived. Numerical simulations are also performed, and good cloaking effect is achieved. The cloaking scheme is effective to hide the local object with strong scattering characters placed on mobile carriers, such as the radar antenna system on the aircraft.

In this paper, we propose a new structure of centralized-light-source wavelength division multiplexed passive optical network (WDM-PON) utilizing inverse-duobinary-return-to-zero (inverse-duobinary-RZ) downstream and DPSK upstream. It reuses downstream light for the upstream modulation, which retrenches lasers assembled at each optical network unit (ONU), and ultimately largely cuts down the cost of ONUs. Meanwhile, a 50-km-reach WDM-PON experiment with 10-Gb/s inverse-duobinary-RZ downstream and 6-Gb/s DPSK upstream is demonstrated here. It is revealed to be a novel cost-effective alternative for the next generation access network.

We report an integral imaging method with continuous imaging space. This method simultaneously reconstructs real and virtual images in the virtual mode, with a minimum gap that separates the entire imaging space into real and virtual space. Experimental results show that the gap is reduced to 45% of that in a conventional integral imaging system with the same parameters.

Mg:Ru:Fe:LiNbO_{3} crystals with various concentrations of MgO (in mole) and fixed content of RuO_{2} and Fe_{2}O_{3} (in mass) are grown with the Czochralski method from the congruent melt. Their infrared transmission spectra are measured and discussed to investigate the defect structure. With the increase of Mg^{2+} concentration the blue nonvolatile holographic storage capability is enhanced. The nonvolatile holographic storage properties of dual-wavelength recording of Mg(7 mol%):Ru:Fe:LiNbO_{3} nonvolatile diffraction efficiency, response time and nonvolatile sensitivity reach 59.8%, 70 s, and 1.04 cm/J, respectively. Comparing Mg(7 mol%):Ru:Fe:LiNbO_{3 } with Ru:Fe:LiNbO_{3} crystal, the response time is shortened apparently. The nonvolatile diffraction efficiency and sensitivity are raised largely. The mechanism in blue photorefractive nonvolatile holographic storage is discussed.

We theoretically investigate the emission spectrum for a Λ -type three-level atom trapped in the node of the standing wave. We show that the atomic center-of-mass motion not only directly affects the peak number, peak position, and peak height in atomic emission spectrum, but also influences the effects of the cavity field and the atomic initial state on atomic emission spectrum.

An electrically driven, single-longitudinal-mode GaAs based photonic crystal (PC) ridge waveguide (RWG) laser emitting at around 850 nm is demonstrated. The single-longitudinal-mode lasing characteristic with a single wavelength is achieved by introducing the PC to the RWG laser. The triangle PC is etched on both sides of the ridge by photolithography and inductive coupled plasma (ICP) etching. The lasing spectra of the RWG lasers with and without the PC are studied, and the result shows that the PC purifies the longitudinal mode. The power/facet and current-voltage characteristics have also been studied and compared.

A diode dual-end-pumped Nd:YVO_{4} regenerative amplifier was reported. The influence of the cavity stability on the performance of the regenerative amplifier was studied. The experimental results matched well with the analysis at high pump power. The mode locking seed pulses with 15 ps pulse width and 10 nJ single pulse energy at 86 MHz were amplified up to 4.7 mJ at 1 kHz, corresponding to the maximum amplification about 0.5×10^{6}, by our regenerative amplifier. And an average power of 4.7 W was obtained at the repetition rate from 1 kHz to 10 kHz.

The effect of defect density on the modulation of incident laser waves is investigated. First, based on the actual defect distribution in the subsurface of fused silica, a three-dimensional (3D) grid model of defect sites is constructed. The 3D finite-difference time-domain method is developed to solve the Maxwell equations. Then the electrical field intensity in the vicinity of the defect sites in the subsurface of fused silica is numerically calculated. The relationships between the maximal electrical field intensity in fused silica and the geometry of the defect sites are given. The simulated results reveal that the modulation becomes more remarkable with an increase of the defect density. In addition, the effect of the distribution mode of defects on modulation is discussed. Meanwhile, the underlying physical mechanism is analyzed in detail.

We propose a unified theory to construct exact rogue wave solutions of the (2+1)-dimensional nonlinear Schrödinger equation with varying coefficients. And then the dynamics of the first- and the second-order optical rogues are investigated. Finally, the controllability of the optical rogue propagating in inhomogeneous nonlinear waveguides is discussed. By properly choosing the distributed coefficients, we demonstrate analytically that rogue waves can be restrained or even be annihilated, or emerge periodically and sustain forever. We also figure out the center-of-mass motion of the rogue waves.

A new approach is presented to reveal the temporal structure of femtosecond laser pulses by recording the corresponding time-resolved shadowgraphs of the laser-induced air plasma. It is shown that the temporal structures of femtosecond laser pulses, normally not observable by the ordinary intensity autocorrelator, can be detected through intuitively analyzing the ultrafast evolution process of the air plasma induced by the femtosecond laser pulses under examination. With this method, existence of pre- and post-pulses has been clearly unveiled within the time window of ± 150 fs in reference with the main 50-fs laser pulses output from a commercial 1-kHz femtosecond laser amplifier. The unique advantage of the proposed method is that it can directly provide valuable information about the pulse temporal structures' effect on the laser-induced ionization or material ablation.

We demonstrated experimentally a synchronously pumped intracavity frequency-doubled femtosecond optical parametric oscillator (OPO) using a periodically-poled lithium niobate (PPLN) as the nonlinear material in combination with a lithium triborate (LBO) as the doubling crystal. A Kerr-lens-mode-locked (KLM) Ti:sapphire oscillator at the wavelength of 790 nm was used as the pump source, which was capable of generating pulses with a duration as short as 117 fs. A tunable femtosecond laser covering the 624-672 nm range was realized by conveniently adjusting the OPO cavity length. A maximum average output power of 260 mW in the visible was obtained at the pump power of 2.2 W, with a typical pulse duration of 205 fs assuming a sech^{2} pulse profile.

Monolithic integration of four 1.55-μ InGaAsP/InP distributed feedback (DFB) lasers using varied ridge width with a 4×1 multimode-interference (MMI) optical combiner and a semiconductor optical amplifier (SOA) is demonstrated. The average output power and the threshold current are 1.8 mW and 35 mA, respectively, when the injection current of the SOA is 100 mA, with a side mode suppression ratio (SMSR) exceeding 40 dB. The four channels have a 1-nm average channel spacing and can operate separately or simultaneously.

Sound propagation in a wedge-shaped waveguide with perfectly reflecting boundaries is one of the few range-dependent problems with an analytical solution, and hence provides an ideal benchmark for a full two-way solution to the wave equation. An analytical solution for the sound propagation in an ideal wedge with a pressure-release bottom was presented by Buckingham and Tolstoy [Buckingham and Tolstoy 1990 J. Acoust. Soc. Am.87 1511]. The ideal wedge problem with a rigid bottom is also of great importance in underwater acoustics. We present an analytical solution to the ideal wedge problem with a perfectly reflecting bottom, either rigid or pressure-release, which may be used to provide a means for investigating the sound field in depth-varying channels, and to establish the accuracy of numerical propagation models. Closed-form expressions for coupling matrices are also provided for the ideal waveguides characterized by a homogeneous water column bounded by perfectly reflecting boundaries. A comparison between the analytical solution and the numerical solution recently proposed by Luo et al. [Luo W Y, Yang C M and Zhang R H 2012 Chin. Phys. Lett.29 014302] is also presented, through which the accuracy of this numerical model is illustrated.

Double-diffusive stationary and oscillatory instabilities at the marginal state in a saturated porous horizontal fluid layer heated and salted from above are investigated theoretically under the framework of Darcy for porous medium. The contributions of Soret and Dufour coefficients are taken into account in the analysis. Linear stability analysis shows that the critical value of the Darcy-Rayleigh number depends on cross-diffusive parameters at marginally stationary convection, while the marginal state characterized by oscillatory convection does not depend on the cross-diffusion terms even if the condition and frequency of oscillatory convection depends on the cross-diffusive parameters. The critical value of the Darcy-Rayleigh number increases with increasing value of the solutal Darcy-Rayleigh number in the absence of cross-diffusive parameters. The critical Darcy-Rayleigh number decreases with increasing Soret number, resulting in destabilization of the system, while its value increases with increasing Dufour number, resulting in stabilization of the system at the marginal state characterized by stationary convection. The analysis reveals that the Dufour and Soret parameters as well as the porosity parameter play an important role in deciding the type of instability at the onset. This analysis also indicates that the stationary convection is followed by the oscillatory convection for certain fluid mixtures. It is interesting to note that the roles of cross-diffusive parameters on the double-diffusive system heated and salted from above are reciprocal to the double-diffusive system heated and salted from below.

The clustering behavior of a mono-disperse granular gas is experimentally studied in an asymmetric two-compartment setup. Unlike the random clustering in either compartment in the case of symmetric configuration when lowering the shaking strength to below a critical value, the directed clustering is observed, which corresponds to an imperfect pitchfork bifurcation. Numerical solutions of the flux equation using a modified simple flux function show qualitative agreements with the experimental results. The potential application of this asymmetric structure is discussed.

Sun Ya-Bin, Fu Jun, Xu Jun, Wang Yu-Dong, Zhou Wei, Zhang Wei, Cui Jie, Li Gao-Qing, Liu Zhi-Hong, Yu Yong-Tao, Ma Ying-Qi, Feng Guo-Qiang, Han Jian-Wei

Chin. Phys. B 2013, 22 (5): 056103; doi: 10.1088/1674-1056/22/5/056103
Full Text: PDF (595KB) (
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A study on single event transient (SET) induced by pulsed laser in silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) is presented in this work. The impacts of laser energy and collector load resistance on the SET are investigated in detail. The waveform, amplitude, and width of the SET pulse as well as collected charge are used to characterize the SET response. The experimental results are discussed in detail and it is demonstrated that the laser energy and load resistance significantly affect the SET in the SiGe HBT. Furthermore, the underlying physical mechanisms are analyzed and investigated, and a near-ideal exponential model is proposed for the first time to describe the discharge of laser-induced electrons via collector resistance to collector supply when both base-collector and collector-substrate junctions are reverse biased or weakly forward biased. Besides, it is found that an additional multi-path discharge would play an important role in the SET once the base-collector and collector-substrate junctions get strongly forward biased due to a strong transient step charge by the laser pulse.

We report ^{75}As NMR studies on single crystals of rare-earth doped iron pnictide superconductor Ca_{1-x}Pr_{x}Fe_{2}As_{2}. In both cases of x=0.075, 0.15, a large increase of ν_{q} upon cooling is consistent with the tetragonal-collapsed tetragonal structure transition. A sharp drop of the Knight shift is also seen just below the structural transition, which suggests the quenching of Fe local magnetism, and therefore offers important understanding of the collapsed tetragonal phase. At even low temperatures, the 1/^{75}T_{1} is enhanced and forms a peak at T≈ 25 K, which may be caused by the magnetic ordering of the Pr^{3+} moments or spin dynamics of mobile domain walls.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Based on the nonequilibrium plasma dynamics of air discharge, a dynamic model of zero-dimensional plasma is established by combining the component density equation, the Boltzmann equation, and the energy transfer equation. The evolution properties of nanosecond pulse discharge (NPD) plasma under different air pressures are calculated. The results show that air pressure has a significant impact on the NPD products and on the peak value of particle number density for particles such as O atoms, O_{3} molecules, N_{2}(A3) molecules in excited states, and NO molecules. It increases at first and then decreases with the increase of air pressure. On the other hand, the peak values of particle number density for N_{2}(B3) and N_{2}(C3) molecules in excited states are only slightly affected by the air pressure.

The accelerated skin layer may be used to ignite solid state fuels. The detailed analyses were clarified by solving the hydrodynamic equations for nonlinear force driven plasma block ignition. In this paper, the complementary mechanisms are included for the advanced fuel ignition: external factors such as laser, compression, shock waves, and spark. The other category is created within the plasma fusion as reheating of alpha particle, the Bremsstrahlung absorption, expansion, conduction, and shock waves generated by explosions. With the new condition for the control of shock waves, the spherical deuterium-tritium fuel density should be increased to 75 times of the solid state. The threshold ignition energy flux density for the advanced fuel ignition may be obtained using temperature equations, including the ones for the density profile obtained through the continuity equation and the expansion velocity for the r≠0 layers. These thresholds are significantly reduced in comparison with the ignition thresholds at x=0 for the solid advanced fuels. The quantum correction for the collision frequency is applied in the case of the delay in ion heating. Under the shock wave condition, the spherical proton-boron and proton-lithium fuel densities should be increased to densities 120 and 180 times of the solid state. These plasma compressions are achieved through a longer duration laser pulse or X ray.

The effect of the plasma with toroidal rotation on the resistive wall modes in tokamaks is studied numerically. An eigenvalue method is adopted to calculate the growth rate of the modes for changing plasma resistivity and plasma density distribution, as well as the diffusion time of magnetic field through the resistive wall. It is found that the resistive wall mode can be suppressed by the toroidal rotation of the plasma. Also, the growth rate of the resistive wall mode decreases when the edge plasma density is the same as the core plasma density, but it changes only slightly with the plasma resistivity.

A 2.3 kJ Mather type pulsed plasma focus device was used for the synthesis of a TiN/a-Si_{3}N_{4} thin film at room temperature. The film was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The XRD pattern confirms the growth of polycrystalline TiN thin film. The XPS results indicate that the synthesized film is non-stoichiometric and contains titanium nitride, silicon nitride, and a phase of silicon oxy-nitride. The SEM and AFM results reveal that the surface of the synthesized film is quite smooth with 0.59 nm roughness (root-mean-square).

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Sr_{3.96}Al_{14}O_{25}:Eu^{2+},Dy^{3+} long persistent materials with different weight of H_{3}BO_{3} prepared by the high temperature solid-state reaction method were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM), photoluminescence spectra (PL), and thermoluminescence (TL). The results of XRD indicate that the 3% addition of H_{3}BO_{3} is in favor of the formation of pure phase Sr_{4}Al_{14}O_{25}, and SrAl_{12}O_{19} was generated when H_{3}BO_{3} is in low content or high content. The average grain sizes of samples grow bigger during the increasing of H_{3}BO_{3}. PL spectra show that the emission peak does not shift evidently and the emission intensity changes a little, indicate that the different amount of H_{3}BO_{3} have a little inference to the crystal field. The decay characteristics and TL measurement show that H_{3}BO_{3} affect the afterglow properties of Sr_{3.96}Al_{14}O_{25}:Eu^{2+},Dy^{3+}, because the increasing of H_{3}BO_{3} lead to more defects in Sr_{4}Al_{14}O_{25} matrix.

Rare-earth compounds have been a subject of intensive research based on the unique electronic structures of the rare-earth elements. Novel ternary intermetallic compounds R_{2}TX_{3} (R=rare-earth element or U, T=transition-metal element, X=Si, Ge, Ga, In) is a significant branch of this research field due to their complex and intriguing physical properties, such as magnetic order at low temperature, spin-glass behavior, Kondo effect, heavy fermion behavior, and so on. The unique physical properties of R_{2}TX_{3} compounds are related to distinctive electronic structures, crystal structures, micro-interaction, and external environment. Most R_{2}TX_{3} compounds crystallize in AlB_{2}-type or derived AlB_{2}-type structure and exhibit many similar properties. This paper gives a concise review of the structures and physical properties of these compounds. Spin glass, magnetic susceptibility, resistivity, and specific heat of R_{2}TX_{3} compounds are discussed.

Effect of non-hydrostatic stress on X-ray diffraction in diamond anvil cell (DAC) is studied. Pressure gradient in sample chamber leads to the broadening of the diffraction peaks, which increase with the hkl index of the crystal. It is found that the difference between the determined d-spacing compressive ratio d/d_{0} and the real d-spacing compressive ratio d_{r}/d_{0} is determined by the yield stress of the pressure transmitting media (if used) and the shear modulus of the sample. On the basis of the corrected experiment data of Mao et al. (MXB86), which was used to calibrate the most widely used ruby fluorescence ruby scale, a new relationship of ruby fluorescence pressure scale is corrected, i.e., P=(1904/9.827)[(1+Δλ/λ_{0})^{9.827}-1].

Nb/Ta multilayer films deposited on Ti6Al4V substrate with Nb and Ta monolayer thicknesses of 30 nm, 120 nm, and 240 nm were irradiated by high current pulse electron beam (HCPEB) to prepare Nb-Ta alloyed layers. The microstructure and the composition of the outmost surface of melted alloyed layers were investigated using transmission electron microscope (TEM) equipped with X-ray energy dispersive spectrometer (EDS) attachment. The Ta content of the alloyed surface layer prepared from the monolayer of thickness 30 nm, 120 nm, and 240 nm was ～ 27.7 at.%, 6.37 at.%, and 0 at.%, respectively. It was found that the Ta content in the alloyed layer plays a dominant role in the microstructure of the films. The hardness and the wear rate of the alloyed layers decrease with the increasing content of Ta in the surface layer.

We have applied a thermodynamical model to calculate the diffusion coefficient of aluminum in MgO with the aid of bulk elastic properties. Our calculated diffusivities as a function of temperature and pressure are compared with the existing results derived from the experimental or theoretical investigations. We find that the present model provides a satisfactory estimation for the activation volume and the activation enthalpy.

We report a rapid evaporative cooling method using a hybrid trap which is composed of a quadrupole magnetic trap and a one-beam optical dipole trap. It contains two kinds of evaporative coolings to reach the quantum degeneracy: previously radio-frequency (RF) enforced evaporative cooling in the quadrupole magnetic trap and further runaway evaporative cooling in the optical dipole trap. The hybrid trap does not require a very high power laser such as that in the traditional pure optical trap, but still has a deep trap depth and a large trap volume, and has better optical access than the normal magnetic trap like the quadrupole-Ioffe-configuration (QUIC) cloverleaf trap. A high trap frequency can be easily realized in the hybrid trap to enhance the elastic collision rate and shorten the evaporative cooling time. In our experiment, pure Bose-Einstein condensates (BECs) with about 1×10^5 atoms can be realized in 6 s evaporative cooling in the optical dipole trap.

CoNiFe patterned films with rectangular elements, all 600 nm wide but of different lengths, were fabricated and investigated by ferromagnetic resonance experiment and micromagnetic simulation. An in-plane magnetic uniaxial anisotropy was exhibited, and its value increases with an increase in the aspect ratio of the elements, which was fitted by the model, including a quasi-ellipsoid demagnetizing field and a non-uniform demagnetizing field. The relative importance of the non-uniform demagnetizing field decreased from 0.26 to 0.16 with an increase in the length-width aspect ratio of the patterned element from 1.5 to 10. The demagnetizing factors in the three principal axes were determined from the experimental data of ferromagnetic resonance, which agreed reasonably well with the values calculated by micromagnetic simulation. The calculation also indicated that the interaction between elements could be neglected when the edge to edge spacing between neighboring elements was larger than 3 μ in our patterned films.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

First-principles calculations based on spin density functional theory are performed to study the spin-resolved electronic properties of ZnO codoped with Cu and N. (Cu, N)-codoped ZnO exhibits magnetism, and the total magnetic moment mainly originates from the p-d hybridization of Cu-N and Cu-O as well as p-p coupling interaction between N and O at the Fermi level. The Zn_{34}Cu_{2}O_{35}N_{1} favors energetically a ferromagnetic ground state due to the existence of stable Cu-N-Cu complex. These results imply that the (Cu, N)-codoped ZnO is a promising dilute magnetic semiconductor free of magnetic precipitates, which could broaden the horizon of currently known magnetic systems.

The structures and the phase transitions of ScH_{3} under high pressure are investigated using first-principles calculations. The calculated structural parameters at zero pressure agree well with the available experimental data. With increasing pressure, the transition sequence hcp (GdH_{3}-type)→C2/m→fcc→hcp (YH_{3}-type)→Cmcm of ScH_{3} is predicted first; the corresponding transition pressures at 0 K are 23 GPa, 25 GPa, 348 GPa, and 477 GPa, respectively. The C2/m symmetry structure is a possible candidate but not a good one as the intermediate state from hexagonal to cubic in ScH_{3}. On the other hand, via the analysis of the structures of hexagonal ScH_{2.9}, cubic ScH_{3}, and cubic ScH_{2}, we find that the repulsive interactions of H-H atoms must play an important role in the transition from hexagonal to cubic.

We perform first-principles calculations to investigate the structural, magnetic, electronic, and mechanical properties of face-centered cubic (fcc) PuH_{2} and fcc PuH_{3} using the full potential linearized augmented plane wave method (FP-LAPW) with the generalized gradient approximation (GGA) and the local spin density approximation (LSDA) taking account of both relativistic and strong correlation effects. The optimized lattice constant a_{0}= 5.371 Å for fcc PuH_{2} and a_{0}= 5.343 Å for fcc PuH_{3} calculated in the GGA + sp (spin polarization) + U (Hubbard parameter) + SO (spin-orbit coupling) scheme are in good agreement with the experimental data. The ground state of fcc PuH_{3} is found to be slightly ferromagnetic. Our results indicate that fcc PuH_{2} is a metal while fcc PuH_{3} is a semiconductor with a band gap about 0.35 eV. We note that the SO and the strong correlation between localized Pu 5f electrons are responsible for the band gap of fcc PuH_{3}. The bonds for PuH_{2} have mainly covalent character while there are covalent bonds in addition to apparent ionicity bonds for PuH_{3}. We also predict the elastic constants of fcc PuH_{2} and fcc PuH_{3}, which were not observed in the previous experiments.

In this paper, the effects of quantum and classical correlations on the excitation energy transfer in a three-quasi-spin-pigment system are investigated. We first study the dependence of the energy transfer efficiency on various initial correlations of the donor pigments, and find that the initial concurrence is crucial to the efficiency no matter whether the initial states are pure or mixed. We then demonstrate the dynamics of correlations of the system and observe the appearance of sudden death of quantum correlations in the donor pigments. The relation between the energy transfer efficiency and the dynamics of correlations in the donor pigments is also discussed.

The effect of an initially grown high-temperature AlN buffer (HT-AlN) layer's thickness on the quality of an AlN epilayer grown on sapphire substrate by metalorganic chemical vapor deposition (MOCVD) in a two-step growth process is investigated. The characteristics of AlN epilayers are analyzed by using triple-axis crystal X-ray diffraction (XRD) and atomic force microscopy (AFM). It is shown that the crystal quality of the AlN epilayer is closely related to its correlation length. The correlation length is determined by the thickness of the initially grown HT-AlN buffer layer. We find that the optimal HT-AlN buffer thickness for obtaining a high-quality AlN epilayer grown on sapphire substrate is about 20 nm.

AlSb/InAs quantum well (QW) structures and InAs films on GaAs (001) substrates were grown by molecular beam epitaxy (MBE). We investigated the dependence of electron mobility and two-dimensional electron gas (2DEG) concentration on the thickness of an InAs channel. It is found that electron mobility as high as 19050 cm^{2}·V^{-1}·s^{-1} has been achieved for an InAs channel of 22.5 nm. The Hall devices with high sensitivity and good temperature stability were fabricated based on the AlSb/InAs QW structures. Their sensitivity is markedly superior to Hall devices of InAs films.

Electrical transport and thermoelectric properties of Ni-doped YCo_{1-x}Ni_{x}O_{3} (0≤ x ≤0.07), prepared by using sol-gel process, are investigated in a temperature range from 100 to 780 K. The results show that with the increase of Ni doping content, the values of DC resistivity of YCo_{1-x}Ni_{x}O_{3} decrease, but carrier concentration increases. The temperature dependences of the resistivity for YCo_{1-x}Ni_{x}O_{3} are found to follow a relation of lnρ ∝ 1/T in a low-temperature rang (LTR) (T<～304 K for x=0; ～ 230 K < T <～500 K for x=0.02, 0.05, and 0.07) and high-temperature range (HTR) (T > ～ 655 K for all compounds), respectively. The estimated apparent activation energies for conduction E_{a1} in LRT and E_{a2} in HTR are both found to decrease monotonically with doping content increasing. At very low temperatures (T < ～ 230 K), Mott's law is observed for YCo_{1-x}Ni_{x}O_{3} (x ≥ 0.02), indicating that considerable localized states form in the heavy doping compounds. Although the Seebeck coefficient of the compound decreases after Ni doping, the power factor of YCo_{1-x}Ni_{x}O_{3} is enhanced remarkably in a temperature range from 300 to 740 K, i.e., a 6-fold increase is achieved at 500 K for YCo_{0.98}Ni_{0.02}O_{3}, indicating that the high-temperature thermoelectric property of YCoO_{3} can be improved by partial substitution of Ni for Co.

A combined frequency-swept and quasi-time-domain photocarrier radiometry (PCR) technique was developed to characterize thermally annealed silicon wafers with B^{+}, P^{+}, and As^{+} ion implantation at doses ranging from 1×10^{11} cm^{-2} to 1×10^{16} cm^{-2}. The implantation dose dependence of the PCR amplitude, the frequency dependencies of the PCR amplitude and phase, as well as the quasi-time-domain PCR waveforms were simultaneously employed to analyze all the ion-implanted silicon samples. The dependence of the effective lifetime on the implantation dose has been investigated and shown to be related to the trap density and lifetime extracted from the transient PCR signals.

We investigate the effects of a bar on optical transmission through Z-shaped metallic slit arrays by using finite-difference time domain (FDTD) method. A new hybrid Fabry-Perot (FP) surface plasmon polariton (SPP) mode emerges when changing the geometric parameters of the bar, and this mode can be viewed as a coupling between FP mode and SPP mode. In addition, an obvious dip appears in a featured area when the bar deviates from the central line, and a small displacement of the bar leads to tremendous change of the dip. These behaviors can be attributed to the phase resonance. In short, the structure is very sensitive to the metal bar. Furthermore, it combines photonic device miniaturization with sensitivity, which is useful for making optical switch.

The effects of polarization and related structural parameters on the intersubband transitions of AlGaN/GaN multi-quantum wells (MQWs) have been investigated by solving the Schrödinger and the Poisson equations self-consistently. The results show that the intersubband absorption coefficient increases with increasing polarization while the transition wavelength decreases, which is not identical to the case of the interband transitions. Moreover, it suggests that the well width has a greater effect on the intersubband transitions than the barrier thickness, and the intersubband transition wavelength of the structure when doped in the barrier is shorter than that when doped in the well. It is found that the influences of the structural parameters differ for different electron subbands. The mechanisms responsible for these effects have been investigated in detail.

Silicyne, a silicon allotrope, which is closely related to silicene and has the graphyne-like structure, is theoretically investigated in this work. Its optimized geometry and electronic band structure are calculated by means of the first-principles frozen-core projector-augmented wave method implemented in the Vienna ab initio simulation package (VASP). We find that the lattice parameter is 9.5 Å, the silicon chain between hexagons is composed of disilynic linkages (-Si≡Si-) rather than cumulative linkages (=Si=Si=), and the binding energy is -3.41 eV per atom. The band structure is calculated by adopting the generalized gradient approximation and hybrid functionals. The band gap produced by the HSE06 functional is 0.73 eV, which is nearly triple as much as that by the generalized gradient approximation of Perdew-Burke-Ernzerhof functional.

V-gate GaN high electron mobility transistors (HEMTs) are fabricated and investigated systematically. A V-shaped recess geometry is obtained using an improved Si_{3}N_{4 } recess etching technology. Compared with standard HMETs, the fabricated V-gate HEMTs exhibit a 17% higher peak extrinsic transconductance due to a narrowed gate foot. Moreover, both the gate leakage and current dispersion are dramatically suppressed simultaneously, although a slight degradation of frequency response is observed. Based on a two-dimensional electric field simulation using Silvaco "ATLAS" for both standard HEMTs and V-gate HEMTs, the relaxation in peak electric field at gate edge is identified as the predominant factor leading to the superior performance of V-gate HEMTs.

Co_{2}FeAl_{0.5}Si_{0.5} (CFAS) based multilayers sandwiched by MgO layers have been deposited and annealed at different temperatures. Perpendicular magnetic anisotropy (PMA) with the magnetic anisotropy energy density K_{u} ≈ 2.5×10^{6} erg/cm^{3} and the coercivity H_{c}=363 Oe has been achieved in the Si/SiO_{2}/MgO (1.5 nm)/CFAS (2.5 nm)/MgO (0.8 nm)/Pt (5 nm) film annealed at 300 ℃. The strong PMA is mainly due to the top MgO layer. The structure can be used as top magnetic electrodes in half-metallic perpendicular magnetic tunnel junctions.

We propose a Rashba three-terminal double-quantum-dot device to generate a spin-polarized current and manipulate the electron spin in each quantum dot by utilizing the temperature gradient instead of the electric bias voltage. This device possesses a nonresonant tunneling channel and two resonant tunneling channels. The Keldysh nonequilibrium Green's function techniques are employed to determinate the spin-polarized current flowing from the electrodes and the spin accumulation in each quantum dot. We find that their signs and magnitudes are well controllable by the gate voltage or the temperature gradient. This result is attribute to the change in the slope of the transmission probability at the Fermi levels in the low-temperature region. Importantly, an obviously pure spin current can be injected into or extracted from one of the three electrodes by properly choosing the temperature gradient and the gate voltages. Therefore, the device can be used as an ideal thermal generator to produce a pure spin current and manipulate the electron spin in the quantum dot.

Intrinsic Josephson junctions in misaligned Tl_{2}Ba_{2}CaCu_{2}O_{8} thin film were fabricated on LaAlO_{3} substrate. The temperature dependence of the critical current is investigated around liquid nitrogen temperature. In the current voltage characteristic, large voltage jump and free of resistive branch are observed, which shows good consistency with the intrinsic Josephson junctions. By analyzing the large gap voltage in the curve, great suppression of the energy gap is found. Through discussing the temperature dependence of the gap voltage in liquid nitrogen temperature, it is showed that this phenomenon can be caused by the nonequilibrium quasiparticle injection. The temperature influence on the excess current also confirms the nonequlibrium effect.

Magnetocaloric effect (MCE) in polycrystalline HoMn_{2}O_{5} was investigated by isothermal magnetization curves from 2 K to 50 K. A relatively large magnetic entropy change, ΔS_{M} = 7.8 J/(kg·K), was achieved with the magnetic field up to 70 kOe. The magnetic entropy change is reversible in the whole range of temperature. The contributions of elastic and magnetoelastic energy to the changing of the magnetic entropy are discussed in terms of the Landau theory. The reversibility of MCE with maximal refrigerant capacity R_{C} = 216.7 J/kg makes polycrystalline HoMn_{2}O_{5} be promising as a magnetic refrigerant.

Qin Yu-Feng, Yan Shi-Shen, Xiao Shu-Qin, Li Qiang, Dai Zheng-Kun, Shen Ting-Ting, Yang Ai-Chun, Pei Juan, Kang Shi-Shou, Dai You-Yong, Liu Guo-Lei, Chen Yan-Xue, Mei Liang-Mo

Chin. Phys. B 2013, 22 (5): 057503; doi: 10.1088/1674-1056/22/5/057503
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Amorphous Mn_{x}Ge_{1-x}:H ferromagnetic semiconductor films prepared in mixed Ar with 20% H_{2} by magnetron co-sputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of Mn_{x}Ge_{1-x}:H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding Mn_{x}Ge_{1-x} and other ferromagnetic semiconductors before. For Mn_{0.4}Ge_{0.6}:H film, the inverted Hall loop is also observed at 30 K, which is in consistence with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of Mn_{x}Ge_{1-x} films for the application in spintronics.

In this work, we use Monte Carlo simulations to study the magnetic properties of a nanowire system based on a honeycomb lattice, in the absence as well as in the presence of both an external magnetic field and crystal field. The system is formed with N_{L} layers having spins that can take the values σ =± 1/2 and S=± 1,0. The blocking temperature is deduced, for each spin configuration, depending on the crystal field Δ. The effect of the exchange interaction coupling J_{p} between the spin configurations σ and S is studied for different values of temperature at fixed crystal field. The established ground-state phase diagram, in the plane (J_{p}, Δ), shows that the only stable configurations are: (1/2,0), (1/2,+1), and (1/2,-1). The thermal magnetization and susceptibility are investigated for the two spin configurations, in the absence as well as in the presence of a crystal field. Finally, we establish the hysteresis cycle for different temperature values, showing that there is almost no remaining magnetization in the absence of the external magnetic field, and that the studied system exhibits a super-paramagnetic behavior.

The electronic structures, deformation charge density, dipole moment, and optical properties of N-La-codoped anatase titanium dioxide (TiO_{2}) are studied using the plane-wave ultrasoft pseudopotential method based on density functional theory (DFT). The optical properties of two-ion-doped TiO_{2}are analyzed via electronic structures, deformation charge density, and dipole moment. For the model of N-La-doped TiO_{2}, smaller atom fraction of N and La atoms induces better optical properties. The absorption edges of two doped TiO_{2} models redshift to the visible-light region.

The differential cross-section for electronic Raman scattering in double semi-parabolic quantum wells of typical GaAs/Al_{x}Ga_{1-x}As is investigated numerically with the effective-mass approximation. The dependence of the differential cross-section on structural parameters such as the barrier width and the well widths are studied. Our results indicate that the electronic Raman scattering is affected by the geometrical size and can be negligible in the symmetric double-well case.

A novel near-infrared (NIR) downconversion (DC) phosphor KSrPO_{4}:Eu^{2+}, Pr^{3+} is synthesized by the conventional high temperature solid-state reaction. The Eu^{2+} acts as an efficient sensitizer for Pr^{3+} in the KSrPO_{4} host. With broadband near-ultraviolet light excitation induced by the 4f→5d transition of Eu^{2+}, the characteristic NIR emission of Pr^{3+}, peaking at 974 nm and 1019 nm due to ^{3}P_{0} →^{1}G_{4} and ^{1}G_{4} →^{3}H_{4} transitions, is generated as a result of the energy transfer from Eu^{2+} to Pr^{3+}. The luminescence spectra in both the visible and the NIR regions and the decay lifetime curves of Eu^{2+} prove the energy transfer from Eu^{2+} to Pr^{3+}. This Eu^{2+} and Pr^{3+} co-doped KSrPO_{4} phosphor may be a promising candidate to modify the spectral mismatch behavior of crystalline solar cells and sunlight.

Ag island films with different sizes have been deposited on hydrogenated amorphous silicon carbide (α -SiC:H) films, and the influences of Ag island films on the optical properties of the α -SiC:H films are investigated. Atomic force microscope images show that Ag nanoislands are formed after Ag coating, and the size of the Ag islands increase with increasing Ag deposition time. The extinction spectra indicate that two resonance absorption peaks which correspond to out-of-plane and in-plane surface plasmon modes of the Ag island films are obtained, and the resonance peak shifts toward longer wavelength with increasing Ag island size. The photoluminescence (PL) enhancement or quenching depends on the size of Ag islands, and PL enhancement by 1.6 times on the main PL band is obtained when the sputtering time is 10 min. Analyses show that the influence of surface plasmons on the PL of α-SiC:H is determined by the competition between the scattering and absorption of Ag islands, and PL enhancement is obtained when scattering is the main interaction between the Ag islands and incident light.

The quantum tunneling effect (QTE) in a cavity-resonator-coupled (CRC) array was analytically and numerically investigated. The underlying mechanism was interpreted by treating electromagnetic waves as photons, and then was generalized to acoustic waves and matter waves. It is indicated that for the three kinds of waves, the QTE can be excited by cavity resonance in a CRC array, resulting in sub-wavelength transparency through the narrow splits between cavities. This opens up opportunities for designing new types of crystals based on CRC arrays, which may find potential applications such as quantum devices, micro-optic transmission, and acoustic manipulation.

Based on a simple classical model specifying that the primary electrons interact with the electrons of a lattice through the Coulomb force and a conclusion that the lattice scattering can be ignored, the formula for the average energy required to produce a secondary electron (ε) is obtained. On the basis of the energy band of an insulator and the formula for ε, the formula for the average energy required to produce a secondary electron in an insulator (ε_{i}) is deduced as a function of the width of the forbidden band (E_{g}) and electron affinity χ. Experimental values and the ε_{i} values calculated with the formula are compared, and the results validate the theory that explains the relationships among E_{g}, χ, and ε_{i} and suggest that the formula for ε_{i} is universal on the condition that the primary electrons at any energy hit the insulator.

SPECIAL TOPIC --- Non-equilibrium phenomena in soft matters

SPECIAL TOPIC—Recent advances in thermoelectric materials and devices

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Nanocomposite BaFe_{12}O_{19}/α-Fe microfibers with diameters of about 1-5 μm are prepared by the organic gel-thermal selective reduction process. The binary phase of BaFe_{12}O_{19} and α-Fe is formed after reduction of the precursor BaFe_{12}O_{19}/α-Fe_{2}O_{3}microfibers at 350 ℃ for 1 h. These nanocomposite microfibers are fabricated from α-Fe (16-22 nm in diameter) and BaFe_{12}O_{19} particles (36-42 nm in diameter) and basically exhibit a single-phase-like magnetization behaviour, with a high saturation magnetization and coercive force arising from the exchange-coupling interactions of soft α-Fe and hard BaFe_{12}O_{19}. The microwave absorption characteristics in a 2-18 GHz frequency range of the nanocomposite BaFe_{12}O_{19}/α-Fe microfibers are mainly influenced by their mass ratio of α-Fe/BaFe_{12}O_{19} and specimen thickness. It is found that the nanocomposite BaFe_{12}O_{19}/α-Fe microfibers with a mass ratio of 1:6 and specimen thickness of 2.5 mm show an optimal reflection loss (RL) of -29.7 dB at 13.5 GHz and the bandwidth with RL exceeding -10 dB covers the whole Ku-band (12.4-18.0 GHz). This enhancement of microwave absorption can be attributed to the heterotructure of soft, nano, conducting α-Fe particles embedded in hard, nano, semiconducting barium ferrite, which improves the dipolar polarization, interfacial polarization, exchange-coupling interaction, and anisotropic energy in the nanocomposite BaFe_{12}O_{19}/α-Fe microfibers.

A modified polyacrylamide gel route is applied to synthesize SnO_{2} nanoparticles. High-quality SnO_{2} nanoparticles with a uniform size are prepared using different chelating agents. The average particle size of the samples is found to depend on the choice of the chelating agent. The photoluminescence spectrum detected at λ_{ex }= 230 nm shows a new peak located at 740 nm due to the surface defect level distributed at the nanoparticle boundaries.

Optoelectronic characteristics of p-type CuO nanorods, synthesized by a simple hydrothermal method, were investigated at different atmospheres and oxygen pressures. The CuO nanorods have lower resistance in air than in vacuum, unlike the n-type semiconductors. This is explained in terms of the surface accumulation conduction. Measurements at different oxygen pressures indicate that oxygen has an important effect on the optoelectronic properties of p-type nanomaterials.

Self-assembled Ge nanodots with areal number density up to 2.33×10^{10} cm^{-2} and aspect ratio larger than 0.12 are prepared by ion beam sputtering deposition. The dot density, a function of deposition rate and Ge coverage, is observed to be limited mainly by the transformation from two-dimensional precursors to three-dimensional islands, and to be associated with the adatom behaviors of attachment and detachment from the islands. An unusual increasing temperature dependence of nanodot density is also revealed when high ion energy is employed in sputtering deposition, and is shown to be related with the breaking down of the superstrained wetting layer. This result is attributed to the interaction between energetic atoms and the growth surface, which mediates island nucleation.

The electrical conductivity and Hall effect for TlGaSeS crystals have been investigated over a wide temperature range. The crystals we used are grown by a modified Bridgman technique and possess p-type conductivity. The energy gap has been found to be 1.63 eV, whereas the ionization energy is 0.25 eV. The variations of the Hall mobility as well as the carrier concentration with temperature have been investigated. The scattering mechanisms of the carrier are checked over the whole investigated temperature range. Furthermore, the diffusion coefficient, relaxation time, and diffusion length of holes are estimated.

ZnO nanoparticles-embedded hydrogenated diamond-like carbon (ZnO-DLC) films have been prepared by electrochemical deposition in ambient conditions. The morphology, composition, and microstructure of the films have been investigated. The results show that the resultant films are hydrogenated diamond-like carbon films embedded with ZnO nanoparticles in wurtzite structure, and the content and size of the ZnO nanoparticles increase with increasing deposition voltage, which are confirmed by X-ray photoelectron spectroscopy (XPS), Raman, and transmission electron microscope (TEM). Furthermore, a possible mechanism used to describe the growth process of ZnO-DLC films by electrochemical deposition is also discussed.

We propose an evolution model of cooperative agent and noncooperative agent aggregates to investigate the dynamic evolution behaviors of the system and the effects of the competing microscopic reactions on the dynamic evolution. In this model, each cooperative agent and noncooperative agent are endowed with integer values of cooperative spirits and noncooperative spirits, respectively. The cooperative spirits of a cooperative agent aggregate and the noncooperative spirits of a noncooperative agent aggregate change via four competing microscopic reaction schemes: the win-win reaction between two cooperative agents, the lose-lose reaction between two noncooperative agents, the win-lose reaction between a cooperative agent and a noncooperative agent (equivalent to the migration of spirits from cooperative agents to noncooperative agents), and the cooperative agent catalyzed decline of noncooperative spirits. Based on the generalized Smoluchowski's rate equation approach, we investigate the dynamic evolution behaviors such as the total cooperative spirits of all cooperative agents and the total noncooperative spirits of all noncooperative agents. The effects of the three main groups of competition on the dynamic evolution are revealed. These include: (i) the competition between the lose-lose reaction and the win-lose reaction, which give rise to respectively the decrease and increase in the noncooperative agent spirits; (ii) the competition between the win-win reaction and the win-lose reaction, which give rise to respectively the increase and decrease in the cooperative agent spirits; (iii) the competition between the win-lose reaction and the catalyzed-decline reaction, which give rise to respectively the increase and decrease in the noncooperative agent spirits.

In a three-sphere system, the middle sphere is acted by two opposite depletion forces from the other two spheres. It is found that, in this system, the two depletion forces are coupled with each other and result in a strengthened depletion force. So the difference of the depletion forces of the three-sphere system and its corresponding two two-sphere systems is introduced to describe the coupling effect of the depletion interactions. The numerical results obtained by Monte-Carlo simulations show that this coupling effect is affected by both the concentration of small spheres and the geometrical confinement. Meanwhile, it is also found that the mechanisms of the coupling effect and the effect on the depletion force from the geometry factor are the same.

Apparent mass measurements at the bottom of silo have been carried out. An important parameter in the Janssen model known as the effective screening length has been investigated for different bead and silo diameters as well as of their ratios. It is found that the effective screening length augments with the grain diameter d in addition to the granular column size. It is also revealed that λ exhibits stronger correlation with the bead diameter than that of silo. This phenomenon is attributed to the reduced-shielding of the vertical stresses to the horizontal ones.

By solving 2D Poisson's equation, analytical models are proposed to calculate the surface potential and electric field distributions of lateral power devices with arbitrary vertical doping profiles. The vertical and the lateral breakdown voltages are formulized to quantify the breakdown characteristic in completely-depleted and partially-depleted cases. A new reduced surface field (RESURF) criterion which can be used in various drift doping profiles is further derived for obtaining the optimal trade-off between the breakdown voltage and the on-resistance. Based on these models and the numerical simulation, the electric field modulation mechanism and the breakdown characteristics of lateral power devices are investigated in detail for the uniform, linear, Gaussian, and some discrete doping profiles along the vertical direction in the drift region. Then, the mentioned vertical doping profiles of these devices with the same geometric parameters are optimized, and the results show that the optimal breakdown voltages and the effective drift doping concentrations of these devices are identical, which are equal to those of the uniform-doped device, respectively. The analytical results of these proposed models are in good agreement with the numerical results and the previously experimental results, confirming the validity of the models presented here.

P-InGaN/p-GaN superlattices (SLs) are developed for hole accumulation layer (HAL) of blue light emitting diode (LED). Free hole concentration as high as 2.6×10^{18} cm^{-3} is achieved by adjusting the Cp_{2}Mg flow rate during the growth of p-InGaN/p-GaN SLs. The p-InGaN/p-GaN SLs with appropriate Cp_{2}Mg flow rates are then incorporated between the multi-quantum well and AlGaN electron blocking layer as an HAL, which leads to the enhanced light output power by 29% at 200 mA, compared with the traditional LED without such SL HAL. Meanwhile, the efficiency droop is also effectively alleviated in the LED with the SL HAL. The improved performance is attributed to the increased hole injection efficiency, and the reduced electron leakage by inserting the p-type SL HAL.

The characteristics of a blue light-emitting diode (LED) with an AlInN/GaN superlattice (SL) electron-blocking layer (EBL) are analyzed numerically. The carrier concentrations in the quantum wells, energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results suggest that the LED with an AlInN/GaN SL EBL has better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in the active region than the LED with a conventional rectangular AlGaN EBL or a AlGaN/ GaN SL EBL. The results also indicate that the efficiency droop is markedly improved when an AlInN/GaN SL EBL is used.

The effect of lattice dimerization on the magnetoresistance (MR) in organic spin valves is investigated based on the Su-Schrieffer-Heeger (SSH) model and the Green's function method. By comparing with the results for a uniform chain, we find that the dimerization of the molecular chain modifies the monotonic dependence of the MR on the bias to an oscillatory one. A sign inversion of the MR is observed when the amplitude of the dimerization is adjusted. The results also show that at a low bias, the MR through a dimerized chain decreases with the increasing bias as well as the increasing chain length, which is consistent with the experimental reports. A further understanding can be achieved by analyzing the electronic states and the spin-dependent transmission spectrum with the parallel and antiparallel magnetization orientations of the two ferromagnetic electrodes.

In this paper we present a combined algorithm for the synchronization control of two gap junction coupled chaotic FitzHugh-Nagumo (FHN) neurons in the external electrical stimulation. The controller consists of a combination of dynamical sliding mode control and adaptive backstepping control. The combined algorithm yields an adaptive dynamical sliding mode control law which has advantages over static sliding mode-based controller of chattering-free, i.e., a sufficiently smooth control input signal is generated. It is shown that the proposed control scheme can not only compensate for the system uncertainty, but also guarantee the stability of the synchronized error system. In addition, numerical simulations are also performed to demonstrate the effectiveness of the proposed adaptive controller.

Based on the relationship between capacity and load, cascading failure on weighted complex networks is investigated, and a load-capacity optimal relationship (LCOR) model is proposed in this paper. Compared with other three kinds of load-capacity linear or non-linear relationship models in model networks as well as a number of real-world weighted networks including the railway network, the airports network and the metro network, the LCOR model is shown to have the best robustness against cascading failure with less cost. Furthermore, theoretical analysis and computational method of its cost threshold are provided to validate the effectiveness of the LCOR model. The results show that the LCOR model is effective for designing real-world networks with high robustness and less cost against cascading failure.

In this paper, we propose an adaptive strategy based on linear-prediction of queue length to minimize congestion in Barabási-Albert (BA) scale-free networks. This strategy uses local knowledge of traffic conditions and allows nodes to be able to self-coordinate their accepting probability to the incoming packets. We show that the strategy can delay remarkably the onset of congestion and systems avoiding the congestion can benefit from hierarchical organization of accepting rates of nodes. Furthermore, with the increase of prediction orders, we achieve larger values for the critical load together with a smooth transition from free-flow to congestion.

We introduce a thermal flux-diffusing model for complex networks. Based on this model, we propose a physical method to detect the communities in the complex networks. The method allows us to obtain the temperature distribution of nodes in time that scales linearly with the network size. Then, the local community enclosing a given node can be easily detected for the reason that the dense connections in the local communities lead to the temperatures of nodes in the same community being close to each other. The community structure of a network can be recursively detected by randomly choosing the nodes outside the detected local communities. In the experiments, we apply our method to a set of benchmarking networks with known pre-determined community structures. The experiment results show that our method has higher accuracy and precision than most existing globe methods and is better than the other existing local methods in the selection of the initial node. Finally, several real-world networks are investigated.

Structural and spectroscopic properties of Sr_{2}ZnTeO_{6} (SZTO) were investigated by angle-dispersive synchrotron X-ray powder diffraction and Raman spectroscopy in a diamond anvil cell up to 31 GPa at room temperature. Although SZTO remained stable up to the highest pressure, the different pressure coefficients of the normalized axial compressibility were obtained as β_{ab}=8.16×10^{-3} GPa^{-1} and β_{c}=7.61×10^{-3} GPa^{-1}. The bulk modulus B_{0} was determined to be 190(1) GPa by fitting the pressure-volume data using the Birch-Murnaghan equation of state. All the observed Raman modes exhibited a broadening effect under high pressure. The vibrational band ϒ _{1} around 765 cm^{-1}, which is associated with the Te-O stretching mode in the basal plane of the TeO_{6} octahedron, had the largest pressure coefficient, and the Grüneisen parameters for all the observed phonon modes also were calculated and presented. These parameters could be used to measure the amount of uniaxial or biaxial strain, providing a fundamental tool for monitoring the magnitude of the shift of phonon frequencies with strains.

We present a simulation on the spatial and temporal characteristics of the indoor propagation channel at 120 GHz. The simulation, applied to a dynamic scenario with randomly placed objects and moving people in a room, is based on a three-dimensional ray-tracing method. Propagation and reflection mechanisms of electromagnetic waves are discussed in the channel model. The received power in a 0.95-m-height plane is obtained. Comparison between walls and ceiling covered with dielectric mirrors and those with three common wall and ceiling materials are presented. The result shows that the holistic received power level with dielectric mirrors is about 10 dB higher than with other materials.

We investigate the impact of heavy ion irradiation on hypothetical static random access memory (SRAM) device. Influences of the irradiation angle, critical charge, drain-drain spacing, and dimension of device structure on the device sensitivity have been studied. These prediction and simulated results are interpreted with MUFPSA, a Monte Carlo code based on Geant4. The results show that the orientation of ion beams and device with different critical charge exert indispensable effects on multiple-bit upsets (MBUs), and that with the decrease in spacing distance between adjacent cells or the dimension of the cells, the device is more susceptible to single event effect, especially to MBUs at oblique incidence.

We analyze the attractor behaviour of the inflation field in braneworld scenarios using the Hamilton-Jacobi formalism, where the Friedmann equation has the form of H^{2}=ρ+ε√2ρ_{0}ρ or H^{2}=ρ+ερ^{2}/2σ, with ε=±1. We find that in all models the linear homogeneous perturbation can decay exponentially as the scalar field rolls down its potential. However, in the case of a -ρ^{2} correction to the standard cosmology with ρ < σ, the existence of an attractor solution requires (σ-ρ)/φ^{2} > 1. Our results show that the perturbation decays more quickly in models with positive-energy correction than in the standard cosmology, which is opposite to the case of negative-energy correction. Thus, the positive-energy modification rather than the negative one can assist the inflation and widen the range of initial conditions.

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