Lie symmetry and conserved quantity deduced from Lie symmetry of Appell equations in a dynamical system of relative motion with Chetaev-type nonholonomic constraints are studied. The differential equations of motion of the Appell equation for the system, the definition and criterion of Lie symmetry, the condition and the expression of generalized Hojman conserved quantity deduced from Lie symmetry for the system are obtained. The condition and the expression of Hojman conserved quantity deduced from special Lie symmetry for the system under invariable time are further obtained. An example is given to illustrate the application of the results.

In this paper, Runge-Kutta Discontinuous Galerkin (RKDG) finite element method is presented to solve the one-dimensional inviscid compressible gas dynamic equations in Lagrangian coordinate. The equations are discretized by the DG method in space and the temporal discretization is accomplished by the total variation diminishing Runge-Kutta method. A limiter based on the characteristic field decomposition is applied to maintain stability and non-oscillatory property of the RKDG method. For multi-medium fluid simulation, the two cells adjacent to the interface are treated differently from other cells. At first, a linear Riemann solver is applied to calculate the numerical flux at the interface. Numerical examples show that there is some oscillation in the vicinity of the interface. Then a nonlinear Riemann solver based on the characteristic formulation of the equation and the discontinuity relations is adopted to calculate the numerical flux at the interface, which suppress the oscillation successfully. Several single-medium and multi-medium fluid examples are given to demonstrate the reliability and efficiency of the algorithm.

A quick and exact imaging method for one-dimensional layered rough surfaces is proposed in this paper to study the scattering characteristics of layered medium that exists widely in nature. The boundary integral equations of layered rough surfaces are solved by using the propagation-inside-layer expansion combining the forward and backward spectral acceleration method (PILE+FB-SA), and the back scattering data can be obtained. Then, a conventional synthetic aperture radar (SAR) imaging procedure called back projection method is used to generate two-dimensional (2D) image of the layered rough surfaces. Combining the relative dielectric permittivity of realistic soil, the random rough surfaces with Gauss spectrum are used to simulate the layered medium with rough interfaces. Since the back scattering data are computed by using the fast numerical method, this method can be used to study layered rough surfaces with any parameter, which has a great application value in the detection and remote sensing areas.

The composite systems can be non-uniquely decomposed into parts (subsystems). Not all decompositions (structures) of a composite system are equally physically relevant. In this paper we answer on theoretical ground why it may be so. We consider a pair of mutually un-coupled modes in the phase space representation that are subjected to the independent quantum amplitude damping channels. By investigating asymptotic dynamics of the degrees of freedom, we find that the environment is responsible for the structures non-equivalence. Only one structure is distinguished by both locality of the environmental influence on its subsystems and a classical-like description.

By virtue of the Weyl ordering method, we find a new formalism of optical field operator expansion in number state representation. Miscillaneous optical fields' (coherent state, squeezed field, Wigner operator, etc.) new expansions are therfore exhibited. Some new generating function of special polynomials are derived herewith.

We study the d-dimensional Schrödinger equation for Eckart plus modified deformed Hylleraas potentials using the generalized parametric form of Nikiforov-Uvarov method. We obtain energy eigenvalues and the corresponding wave function expressed in terms of Jacobi polynomial. We also discuss two special cases of this potential comprised of the Hulthen potential and the Rosen-Morse potential in three dimensions. Numerical results are also computed for the energy spectrum and the potentials.

In this paper, we investigate the quantum correlation of coupled qubits which are initially in maximally entangled mixed states in squeezed vacuum reservoir. We compare and analyse the effects of squeezed parameters on quantum discord and quantum concurrence. The results show that in squeezed vacuum reservoir, the quantum discord and quantum concurrence perform completely opposite behaviors to the change of squeezed parameters. Quantum discord survives longer with the increase of squeezed amplitude parameter, but entanglement death turns faster on the contrary. The results also indicate that the classical correlation of the system is smaller than quantum discord in vacuum reservoir, while it is bigger than quantum discord in squeezed vacuum reservoir. The quantum discord and classical correlation are more robust than quantum concurrence in the two reservoir environments, which indicates that the entanglement actually is easily affected by decoherence and quantum discord has stronger ability to avoid decoherence in squeezed vacuum reservoir.

We propose a novel deterministic protocol that two senders are capable of remotely preparing arbitrary two- and three-qubit states for a remote receiver using EPR pairs and GHZ state as the quantum channel. Compared with the existing deterministic protocols [An et al. 2011 Phys. Lett. A 375 3570 and Chen et al. 2012 J. Phys. A: Math. Theor. 45 055303], the quantum resources and classical information in our scheme are decreased, and the whole operation process is simplified.

We present an efficient entanglement concentration protocol (ECP) for the less-entangled W state with some same conventional polarized single photons. In the protocol, two of the parties say Alice and Charlie should perform the parity check measurements and they can ultimately obtain the maximally entangled W state with a certain success probability. Otherwise, they can obtain another less-entangled W state, which can be reconcentrated into the maximally entangled W state. By iterating this ECP, a high success probability can be achieved. This ECP may be an optimal one and it is useful in current quantum information processing.

We use the quantum renormalization-group (QRG) method to study the entanglement and quantum phase transition (QPT) in the one-dimensional spin-1/2 Heisenberg-Ising model [Lieb E, Schultz T and Mattis D 1961 Ann. Phys. (N.Y.) 16 407]. We find the quantum phase boundary of this model by investigating the evolution of concurrence in terms of QRG iterations. We also investigate the scaling behavior of system close to the quantum critical point, which shows that the minimum value of the first derivative of concurrence and the position of the minimum scale with an exponent of the system size. And the first derivative of concurrence between two blocks diverges at the quantum critical point, which is directly associated with the divergence of the correlation length.

Time evolution dynamics of three non-coupled two-level atoms independently interacting with their reservoirs is solved exactly by considering a damping Lorentzian spectral density. For three atoms initially prepared in Greenberger-Horne-Zeilinger-type state, quantum correlation dynamics in Markovian reservoir is compared with that in non-Markovian reservoir. By increasing detuning quantity in non-Markovian reservoir, three-atom correlation dynamics measured by negative eigenvalue presents a trapping phenomenon which provides long-time quantum entanglement. Then we compare the correlation dynamics of three atoms with that of two atoms, measured by quantum entanglement and quantum discord for initial robuster-entangled type state. The result further confirms that quantum discord is indeed different from quantum entanglement in identifying quantum correlation of many bodies.

The evolution of a system state is derived based on the nonresonant interaction of a three-level "Λ" type atom with two cavity modes at a pair coherent state and two classic fields, and a cavity field state is analysed in detail under conditional detecting. It is found that the quantized modified Bessel-Gaussian states as well as the superposition states consisting of the quantized vortex states with different weighted coefficients may be prepared through carefully preparing an initial atomic state and appropriately adjusting the interaction time. The scheme provides an additional choice to realize the two-mode quantized vortex state within the context of cavity quantum electrodynamics (QED).

A theory of (N+1)-dimensional gravity is developed on the basis of the teleparallel equivalent of general relativity (TEGR). The fundamental gravitational field variables are the (N+1)-dimensional vector fields, defined globally on a manifold M, and the gravitational field is attributed to the torsion. The form of Lagrangian density is quadratic in torsion tensor. We then, give an exact five-dimensional spherically symmetric solution (Schwarzschild (4+1)-dimensions). Finally, we calculate energy and spatial momentum using gravitational energy-momentum tensor and superpotential 2-form.

We use a semiclassical approximation to study the transport through the weakly open chaotic Sinai quantum billiards which can be considered as the schematic of a Sinai mesoscopic device, with the diffractive scatterings at the lead openings taken into account. The conductance of the ballistic microstructure which displays universal fluctuations due to quantum interference of electrons can be calculated by Landauer formula as a function of the electron Fermi wave number, and the transmission amplitude can be expressed as the sum over all classical paths connecting the entrance and the exit leads. For the Sinai billiards, the path sum leads to an excellent numerical agreement between the peak positions of power spectrum of the transmission amplitude and the corresponding lengths of the classical trajectories, which demonstrates a good agreement between the quantum theory and the semiclassical theory.

In this paper we propose a novel four-dimensional fractional order hyperchaotic system derived from Liu system. Electronics workbench (EWB) and Matlab simulations show the dynamical behavior of the proposed four-dimensional fractional order hyperchaotic system. Finally, after separately using EWB and Matlab, an electronic circuit is designed to realize the novel four-dimensional fractional order hyperchaotic system and the experimental circuit results are obtained which are identical to software simulations.

The entransy theory developed in the recent years is used to optimize the aspect ratio of plate fin in heat convection. Based on a two-dimensional model, the theoretical analysis shows that the minimum thermal resistance defined with the concept of entransy dissipation corresponds to the maximum heat transfer rate when the temperature of the heating surface is fixed. On the other hand, when the heat flux of the heating surface is fixed, the minimum thermal resistance corresponds to the minimum average temperature of the heating surface. The entropy optimization is also given for the heat transfer processes. It is observed that none of the minimum entropy generation, the minimum entropy generation number, and the minimum revised entropy generation number always corresponds to the best heat transfer performance. In addition, the influence factors on the optimized aspect ratio of plate fin are also discussed. The optimized ratio decreases with the enhancement of heat convection, while it increases with fin thermal conductivity increasing.

A method of fabricating multi-core polymer image fiber is proposed. Image fiber preform is fabricated by stacking thousands of polymer fibers each with a 0.25-mm diameter orderly in a die by only one step. The preform is heated and stretched into image fiber with an outer diameter of 2 mm. Then a portable eyewear-style three-dimensional (3D) endoscope system is designed, fabricated, and characterized. This endoscopic system is composed of two graded index lenses, two pieces of 0.35-m length image guide fibers, and a pair of oculars. It shows good flexibility and portability, and can provide the depth information accordingly.

The time-dependent multilevel approach (TDMA) and B-spline expansion technique are used to study the coherent population transfer between the quantum states of potassium atom by a single frequency-chirped microwave pulse. The Rydberg potassium atom energy levels of n=6-15, l=0-5 states in zero field are calculated and the results are in good agreement with other theoretical values. The time evolutions of the population transfer of the six states from n=70 to n=75 in different microwave fields are obtained. The results show that the coherent control of the population transfer from the lower states to the higher ones can be accomplished by optimizing the microwave pulse parameters.

In the present work we calculate the energies, quadrupole moments, and electric field gradients (EFGs) of molecules C_{2}, N_{2}, and O_{2} based on DIRRCI method with basis aug-cc-pVTZ-DK. We prove that the quadratic force constant k_{2} is the product of charge and EFG at its equilibrium nuclear distance. The dipole charge distributions for these symmetrical molecules are all in equilibrium, however, the quadrupole charge distributions are far from equilibrium, among these, there is the most remarkable deviation from equilibrium for N_{2}, for its many charges concentrate on two sides of molecule, which is in agreement with the well-known characteristic of nitrogen molecule. The relativistic effect is remarkable even for the same period.

The potential energy curves for neutrals and multiply charged ions of carbon monosulfide are computed with highly correlated multireference configuration interaction wavefunctions. The correlations of inner-shell electrons with the scalar relativistic effects are included in the present computations. The spectroscopic constants, dissociation energies, ionization energies for ground and low-lying excited states together with corresponding electronic configurations of ions are obtained, and a good agreement between the present work and existing experiments is found. No theoretical evidence is found for the adiabatically stable CS^{q+} (q > 2) ions according to the present ab initio calculations. The calculated values for 1st-6th ionization energies are 11.25, 32.66, 64.82, 106.25, 159.75, and 224.64 eV, respectively. The kinetic energy release data of fragments are provided by the present work for further experimental comparisons.

The equilibrium crystal structures, lattice parameters, elastic constants, and elastic moduli of the polymorphs α-, β-, and γ-Si_{3}N_{4}, have been calculated by first-principles method. β-Si_{3}N_{4} is ductile in nature and has an ionic bonding. γ-Si_{3}N_{4} is found to be a brittle material and has covalent chemical bonds, especially at high pressures. The phase boundary of the β → γ transition is obtained and a positive slope is found. This indicates that at higher temperatures it requires higher pressures to synthesize γ-Si_{3}N_{4}. On the other hand, the α → γ phase boundary can be described as P=14.37198+3.27×10^{-3}T-7.83911×10^{-7}T^{2}-3.13552×10^{10}T^{3}. The phase transition from α- to γ-Si_{3}N_{4} occurs at 16.1~GPa and 1700~K. Then, the dependencies of bulk modulus, heat capacity, and thermal expansion on the pressure P are obtained in the ranges of 0~GPa-30~GPa and 0~K-2000~K. Significant features in these properties are observed at high temperatures. It turns out that the thermal expansion of γ-Si_{3}N_{4} is larger than that of α-Si_{3}N_{4} over wide pressure and temperature ranges. The evolutions of the heat capacity with temperature for the Si_{3}N_{4} polymorphs are close to each other, which are important for possible applications of Si_{3}N_{4}.

We propose and demonstrate a scheme to implement photonic multi-shape ultra-wideband (UWB) signal generation using a semiconductor optical amplifier (SOA) based nonlinear optical loop mirror (NOLM). By employing the cross phase modulation (XPM) effect, cross gain modulation (XGM), or both, multi-shape UWB waveforms are generated including monocycle, doublet, triplet, and quadruplet pulses. Both the shapes and polarities of the generated pulses are flexible to adjust, which may be very useful in UWB pulse shape modulation and pulse polarity modulation.

The spectral properties of trivalent erbium ions (Er^{3+}) are systematically studied in a melt-quenched germanate glass (60~GeO_{2}-20PbO-10BaO-10K_{2}O-0.1Ag_{2}O) containing silver (Ag) particles. Thermal treatment of the material leads to the precipitation of Ag particles as observed by transmission electron microscopy and confirmed by absorption spectrum for the obvious surface plasmon resonance peak of Ag particles. The fluorescence from Er^{3+} in the 10-min-annealed sample with Ag particles is found to be 4.2 times enhancement compared with the unannealed sample excited by 488-nm Ar^{+} laser. A comparison is made between a spectral study performed on the unannealed Er^{3+}-doped sample and the one annealed for 20~min. The data of absorption cross section and Judd-Ofelt intensity parameters show the agreement between the two samples no matter whether there are Ag particles, indicating that the introduction of Ag particles by post-heat treatment has no effect on the crystal field environment of Er^{3+} ions. And the fluorescence enhancement is attributed to the surface plasmon oscillations of Ag particles in germanate glass.

Spectra of autoionizing states of the Sm atom in an energy region between 45948.9 cm^{-1} and 46943.6 cm^{-1} are systematically investigated by three-color multi-step resonant excition scheme with three different excitation paths. The three intermediate states, 4f^{6}6s7s ^{7}F_{3}, 4f^{6}6s7s ^{7}F_{4}, and 4f^{6}6s7s ^{9}F_{5} are employed for the three paths, respectively. Based on precise calibration of wavelength, the level energies of 112 autoionizing states are determined with the line widths and the relative line intensities of the related transitions. The possible influence of configuration interaction on the line shape of autoionizing state is also discussed. In addition, a unique value of J, the total angular momentum, is assigned to all detected states by comparing the three spectra obtained with the different excitation paths.

We demonstrate theoretically that the high-order harmonic of atom can be generated by a circularly polarized laser pulse. The harmonic spectrum shows a clear cutoff with an energy I_{p}+2U_{p}. Especially, the high-order harmonic generation comes from the multiple recombination of the ionized electron with non-zero initial velocity. These results are verified by the classical model theory and the time-frequency analysis of harmonic spectrum.

Quantum chemical calculations are performed to investigate the equilibrium C-COOH bond distances and the bond dissociation energies (BDEs) for 15 acids. These compounds are studied by utilizing the hybrid density functional theory (DFT) (B3LYP, B3PW91, B3P86, PBE1PBE) and the complete basis set (CBS-Q) method in conjunction with the 6-311G^{**} basis as DFT methods have been found to have low basis sets sensitivity for small and medium molecules in our previous work. Comparisons between the computational results and the experimental values reveal that CBS-Q method, which can produce reasonable BDEs for some systems in our previous work, seems unable to predict accurate BDEs here. However, the B3P86 calculated results accord very well with the experimental values, within an average absolute errors of 2.3 kcal/mol. Thus, B3P86 method is suitable for computing the reliable BDEs of C-COOH bond for carboxylic acid compounds. In addition, the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of studied compounds are estimated, based on which the relative thermal stabilities of the studied acids are also discussed.

The above-threshold ionization of argon in an intense 70-fs, 400-nm linearly polarized laser pulse has been investigated by the velocity map imaging techniques, combined with an attosecond-resolution quantum wave packet dynamics method. There is a quantitative agreement in all dominant features between the experiment and the theory. Moreover, a peak-splitting phenomenon in the first energy peak has been observed at high pulse intensity. Further, through the theoretical analysis, an ac Stark splitting with evident resonant and nonresonant ionization pathways has been found to be the physical reason for the experimental observations.

We investigate the two-step association process of NaCs using the time-dependent wave packet method. Ground state atoms can be photoassociated to the low vibrational levels of the ground state for NaCs molecule by the two-step association. The time-dependent Schrödinger equation of the association process is solved within a three-state model and the wave packet is propagated with the "split operator-Fourier transform" scheme and the rotating-wave approximation (RWA). The vibrational population distribution of the ground state can be obtained by projecting the wave packet to every vibrational level of the ground state. The results not only show that for NaCs achievement of photoassociation production is accompanied by the photodissociation of the higher vibrational molecules, but also show that the vibrational distribution in lower vibrational levels of the ground state changes with the laser parameters.

We report a momentum-space study on low-energy electron-CO collisions. Elastic differential cross sections (DCS) are obtained using a static-exchange-optical (SEO) model for the incident energies of 2, 3, 5, and 10 eV. Polarization effect of higher reaction channels, including the ionization continuum, on the elastic collision is represented by an ab initio equivalent-local optical potential. The cross sections are compared with experimental measurements and other theoretical results.

The original additivity rule method cannot give good results for electron scattering from SO, SO_{2}, SO_{2}Cl_{2}, SO_{2}ClF, and SO_{2}F_{2} molecules at low energy, because the electron-molecule scattering is simply reduced to electron-atom scattering. Considering the difference between the bound atom in a molecule and the corresponding free atom, the original additivity rule is revised. With the revised additivity rule, the total cross sections for electron scattering from these molecules are calculated over a wide energy range below 3000 eV and compared with the available experimental and theoretical data. Their better agreement with each other is obtained.

The decay pathways of structured ionization region of oxygen at different momentum transfers, i.e., 0, 0.23 a.u. (atomic unit), and 0.91 a.u., are studied by measuring the ion and the scattered electron coincidently. It is found that the dipole-forbidden superexcited states of (2σ_{u})^{-1}(c^{4}Σ_{u}^{-})npσ_{u}^{3}Σ_{g}^{-}≤←X^{3}Σ_{g}^{-} decay into different channels according to the principal quantum number n. The broad ridge above 35 eV, which may be due to inner-valence excited states of (2σ_{g})^{-1}nλ or multiply excited states, is observed both at small and large momentum transfers, and its decay channel of O^{+}+O is dominant.

Direct-write atom lithography, one of the potential nanofabrication techniques, is restricted by some difficulties in producing optical masks for the deposition of complex structures. In order to bring a further progress, a structured mirror array is developed to transversely collimate the chromium atomic beam in two dimensions. The best collimation is obtained when the laser red detunes by natural line-width of transition ^{7}S_{3} → ^{7}P_{4}^{0} of chromium atom. The collimation ratio is 0.45 vertically (in x axis), and it is 0.55 horizontally (in y axis). The theoretical model is also simulated, and a success of our structured mirror array is achieved.

This work experimentally demonstrates a new method of optimizing the transport of cold atoms via modulating the velocity profile imposed on a magnetic quadrupole trap. The trap velocity and corresponding modulation are controlled by varying the currents of two pairs of anti-Helmholtz coils. Cold ^{87}Rb atoms are transported in a non-adiabatic regime over 22 mm in 200 ms. For the transported atoms their final-vibration amplitude dependences of modulation period number, depth, and initial phase are investigated. With modulation period n=5, modulation depth K=0.55, and initial phase φ=0, cold atom clouds with more atom numbers, smaller final-vibration amplitude, and lower temperature are efficiently transported. Theoretical analysis and numerical simulation are also provided, which are in good agreement with experimental results.

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

In this paper we study the extraordinary optical transmission of one-dimensional multi-slit in an ideal metal film. The transmissivity is calculated as a function of various structural parameters. The transmissivity oscillates, with the period being just the light wavelength, as a function of the spacing between slits. As the number of slits increases, the transmissivity varies in one of the three ways. It can increase, attenuate, or remain basically unchanged, depending on the spacing between slits. Each way is in an oscillatory manner. The slit interaction responsible for the oscillating transmission strength that depends on slit spacing is the subject of more detailed investigation. The interaction most intuitively manifests as a current distribution in the metal surface between slits. We find that this current is attenuated in an oscillating fashion from the slit corners to the center of the region between two adjacent slits, and we present a mathematical expression for its waveform.

The nitrogen doping of ZnO film deposited by the magnetron sputtering method is subsequently realized by the hydrothermal synthesis method. The nitrogen-doped ZnO film is preferably (002) oriented. With the increase of hexamethylenetetramine (HMT) solution concentration, the average grain size of the film along the <002> direction almost immediately decreases and then monotonously increases, conversely, the lattice strain first increases and then decreases. The structural evolution of the film surface from compact and even to sparse and rough is attributed to the enhanced nitrogen doping content in the hydrothermal process. The transmission and photoluminescence properties of the film are closely related to grain size, lattice strain, and nitrogen-related defect arising from the enhanced nitrogen doping content with HMT concentration increasing.

LiNbO_{3}:Fe, Mn crystal has been suggested to be used for solving the problem of information volatility during the read-out process with all-optical facilities, but the minute order response time is far from the requirements for the real-time information processing. We present the nonvolatile holographic storage properties of LiNbO_{3}:Hf, Fe, Mn. The response time is shortened to 5.0 s, and the sensitivity S' is enhanced to 0.22 cm/J in this triply doped crystal. The experimental results show that the HfO_{2} doping threshold is 5.0 mol.%. Thus it seems that we have found a useful tetravalent dopant for LiNbO_{3}:Fe, Mn that can obviously improve the nonvoaltile holographic recording sensitivity.

We propose a feasible scheme to generate electromagnetically induced transparency (EIT) and quadripartite macroscopic entanglement in an optomechanical system with one fixed mirror and three movable perfectly reflecting mirrors. We explore the EIT phenomena in this optomechanical system. Results show the appearance of EIT dips in the output field. Moreover, we demonstrate how steady-state quadripartite entanglement can be generated via radiation pressure. We also quantify the bipartite entanglement in each field-mirror subsystem and in the mirror-mirror subsystem. Findings show that a high intensity of entanglement between two subsystems can be achieved.

The polarization of traditional photonic crystal (PC) vertical cavity surface emitting laser (VCSEL) is uncontrollable, resulting in the bit error increasing easily. Elliptical hole photonic crystal can control the transverse mode and polarization of VCSEL efficiently. We analyze the far field divergence angle, and birefringence of elliptical hole PC VCSEL. When the ratio of minor axis to major axis b/a=0.7, the PC VCSEL can obtain single mode and polarization. According to the simulation results, we fabricate the device successfully. The output power is 1.7 mW, the far field divergence angle is less than 10°, and the side mode suppression ratio is over 30 dB. The output power in the Y direction is 20 times that in the X direction.

We present an experimental study on tilt-tip (TT) and phase-locking (PL) control in coherent beam combination (CBC) system of adaptive fiber laser array. The TT control is performed using the adaptive fiber-optics collimator (AFOC), and the PL control is realized by the phase modulator (PM). Cascaded and simultaneous controls of TT and PL using stochastic parallel gradient descent (SPGD) algorithm are investigated in this paper. Two fiber lasers, four fiber lasers, and six fiber laser arrays are employed to study the TT and PL control. In the cascaded control system, only one high-speed CMOS camera is used to collect beam data and a computer is used as the controller. In a simultaneous control system one high-speed CMOS camera and one photonic detector (PD) are employed, and a computer and a control circuit based on field programmable gate array (FPGA) are used as the controllers. Experimental results reveal that both cascaded and simultaneous controls of TT using AFOC and PL using PM in fiber laser array are feasible and effective. Cascaded control is more effective in static control situation and simultaneous control can be applied to the dynamic control system directly. The control signals of simultaneous PL and TT disturb each other obviously and TT and PL control may compete with each other, so the control effect is limited.

Polarization spectroscopy of the D lines of rubidium atoms is investigated experimentally, especially with different pump powers and cell temperatures. We found that there are four candidate transitions suitable for frequency stabilization, and optimal pump powers and cell temperatures are also presented to obtain a perfect signal with maximal amplitude and slope. The optimal signal is insensitive to the fluctuations of laser power and the temperature, which can enhance the performance of frequency locking.

The operational parameters including the polarization controlling and the pump power in a nonlinear polarization rotation based passively mode-locked fiber laser are studied in this paper. The carrier rate equations of the activated erbium-doped fiber are first employed together with the nonlinear Shrödinger equations to reveal the relation between the operational parameters and the output state of the passively mode-locked fiber laser. The numerical and experimental results demonstrate that the output state of the mode-locked laser varies with the polarization controlling and the pump power. The periodicity of the polarization controlling is observed. With given pump power, there exists a set of polarization controlling under which the ultra-short pulse can be generated. With given polarization controlling, the mode-locked state can be maintained generally except for some particular values of pump power. Three shapes of the output optical spectra from the fiber cavity can be identified when the pump power changes. The results in this paper provide a comprehensive insight into the operation of the nonlinear polarization rotation-based passively mode-locked fiber laser.

We discuss the influences of two different types of mechanisms of quantum coherence on optical bistability in a semiconductor quantum well structure. In the first mechanism, only quantum coherence induced by the resonant coupling of a strong control laser is considered. In the second mechanism, the decay coherence is taken into account under the condition where the control field is weak. In two different cases, optical bistability can be obtained through choosing appropriate physical parameters. Our studies show quantum coherence makes the optical nonlinear effect of the system become stronger, which takes an important role in the process of generating optical bistability. Semiconductor quantum well with flexibility and easy integration in design could potentially be exploited in real solid-state devices.

In this paper, we present a novel ultrashort pulse shaper based on complex-modulated long-period-grating coupler (CM-LPGC). Temporal rectangular waveform with 2-ps full width at half maximum (FWHM) is obtained by transforming the input Gaussian pulse. Tolerances of the CM-LPGC-based shaper to various non-ideal excitation conditions and fabricating errors are investigated. Results confirm that CM-LPGC is stable and suitable for optical pulse shaping operation.

For the nonlinearity of Fabry-Perot interferometer (FPI) transmission spectrum, the measurement uncertainty of incoherent Mie Doppler wind lidar based on it increases evidently with the increase of backscattering signal Doppler shift. A method of repeating the use of the approximate linear part of FPI transmission spectra for reducing the high uncertainty of big Doppler shift is proposed. One of the ways of realizing this method is discussed in detail, in which the characteristics of FPI transmission spectrum changing with thickness and incident angle are utilized simultaneously. Under different atmosphere conditions, it has been proved theoretically that the range of measurement uncertainty drops to one-sixth while its minimum has no seriously change. This method can be used not only to guide the new system design, but also as a new working way for the fabricated system.

Grating couplers are widely investigated as coupling interfaces between silicon-on-insulator waveguides and optical fibers. In this work, a high-efficiency and complementary metal-oxide-semiconductor (CMOS) process compatible grating coupler is proposed. The poly-Si layer used as gate in CMOS metal-oxide-semiconductor field effect transistor (MOSFET) is combined with a normal fully etched grating coupler, which greatly enhances its coupling efficiency. With optimal structure parameters, a coupling efficiency can reach as high as ～ 70% at a wavelength of 1550 nm as indicated by simulation. From the angle of fabrication, all masks and etching steps are shared between MOSFETs and grating couplers, thereby making the high performance grating couplers easily integrated with CMOS circuits. Fabrication errors such as alignment shift are also simulated, showing that the device is quite tolerant in fabrication.

In most previous models, simulation of the temperature generation in tissue is based on the Pennes bio-heat transfer equation, which implies an instantaneous thermal energy deposition in medium. Due to the long thermal relaxation time τ (20 s-30 s) in biological tissues, the actual temperature elevation during clinical treatments could be different from the value predicted by the Pennes bioheat equation. Thermal wave model of bio-heat transfer (TWMBT) defines a thermal relaxation time to describe the tissue heating from ultrasound exposure. In this paper, COMSOL Multiphysics 3.5a, a finite element method software package, is used to simulate the temperature response in tissues based on Pennes and TWMBT equations. We further discuss different factors in the bio-heat transfer model on the influence of the temperature rising. And it is found that the temperature response in tissue under ultrasound exposure is a rising process with a declining rate. The thermal relaxation time inhibits the temperature elevation at the beginning of ultrasonic heating. Besides, thermal relaxation in TWMBT leads to lower temperature estimation than that based on Pennes equation during the same period of time. The blood flow carrying heat dominates most to the decline of temperature rising rate and the influence increases with temperature rising. On the contrary, heat diffusion, which can be described by thermal conductivity, has little effect on the temperature rising.

Numerical models based on boundary element method and Boussinesq equation are used to simulate the wave transform over a submerged bar for the regular waves. In the boundary-element-method model the linear element is used, and the integrals are computed by analytical formulas. The Boussinesq-equation model is the well-known FUNWAVE from the University of Delaware. We compare the numerical free surface displacements with the laboratory data on both gentle slope and steep slope, and find that both the two models simulate the wave transform well. We further compute the agreement indexes between the numerical result and laboratory data, and the results support that the boundary-element-method model has a stable good performance, which is due to the fact that its government equation has no restriction on nonlinearity and dispersion as compared with Boussinesq equation.

In this analysis, the magnetohydrodynamic boundary layer flow of Casson fluid over a permeable stretching/shrinking sheet in presence of wall mass transfer is studied. Using similarity transformations, the governing equations are converted to an ordinary differential equation and then solved analytically. The introduction of magnetic field changes the behavior of the entire flow dynamics in the shrinking sheet case and also has major impact in the stretching sheet case. The similarity solution is always unique in the stretching case, and in the shrinking case the solution shows dual nature for certain values of the parameters. For stronger magnetic field, the similarity solution for the shrinking sheet case becomes unique.

In this paper, we present a direct numerical simulation (DNS) of elastic turbulence of viscoelastic fluid at vanishingly low Reynolds number (Re=1) in a three-dimensional straight channel flow for the first time, using the Giesekus constitutive model for the fluid. In order to generate and maintain the turbulent fluid motion in the straight channel, a sinusoidal force term is added to the momentum equation, and then the elastic turbulence is numerically realized with an initialized chaotic velocity field and a stretched conformation field. Statistical and structural characteristics of the elastic turbulence therein are analyzed based on the detailed information obtained from the DNS. The fluid mixing enhancement effect of elastic turbulence is also demonstrated for the potential applications of this phenomenon.

A novel technique for simultaneous measurements of instantaneous whole-field density and velocity fields of supersonic flows has been developed. The density measurement is performed based on the nano-tracer planar laser scattering (NPLS) technique, while the velocity measurement is carried out using particle image velocimetry (PIV). The present experimental technique has been applied to a flat-plate turbulent boundary layer at Mach 3, and the measurement accuracy of the density and velocity are discussed. Based on this new technique, the Reynolds stress distributions were also obtained, demonstrating that this is an effective means for measuring Reynolds stresses under compressible conditions.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

It is shown that the rarefactive-type double layer structures exist in ultradense electron-positron plasma. For this purpose, an extended Korteweg de Vries equation is derived and solved analytically in low amplitude limit by employing the appropriate fluid equations. Strong influence of quantum degeneracy pressure of electrons and positrons, quantum diffraction effects and concentration of background positive ions on double layer is noticed. It is also pointed out that the amplitude and steepness of double layer increases with increase in ion concentration or ion charge number. The results are examined numerically for some interesting cases of dense plasmas with illustrations.

Parametric instabilities induced by the nonlinear interaction between high frequency quantum Langmuir waves and low frequency quantum ion-acoustic waves in quantum plasmas with the electron exchange-correlation effects are presented. By using the quantum hydrodynamic equations with the electron exchange-correlation correction, we obtain an effective quantum Zaharov model, which is then used to derive the modified dispersion relations and the growth rates of the decay and four-wave instabilities. The influences of the electron exchange-correlation effects and the quantum effects on the existence of quantum Langmuir waves and the parametric instabilities are discussed in detail. It is shown that the electron exchange-correlation effects and quantum effects are coupled strongly. The quantum Langmuir wave can propagate in quantum plasmas only when the electron exchange-correlation effects and the quantum effects satisfy a certain condition. The electron exchange-correlation effects tend to enhance the parametric instabilities, while quantum effects suppress the instabilities.

A reliable analytical expression for the potential of plasma waves with phase velocities near the speed of light is derived. The presented spheroid cavity model is more consistent than the previous spherical and ellipsoidal models and it explains the mono-energetic electron trajectory more accurately, especially at the relativistic region. The maximum energy of electrons is calculated and it is shown that the maximum energy of the spheroid model is less than that of the spherical model. The electron energy spectrum is also calculated and it is found that the energy distribution ratio of electrons ΔE/E for the spheroid model under the conditions reported here is half that of the spherical model and it is in good agreement with the experimental value in the same conditions. As a result, the quasi-mono-energetic electron output beam interacting with the laser plasma can be more appropriately described with this model.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Fe-doped ZnO film has been grown by laser molecular beam epitaxy (L-MBE) and structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), all of which reveal the high quality of the film. No secondary phase was detected. Resonant photoemission spectroscopy (RPES) with photon energies around the Fe 2p-3d absorption edge is performed to detect the electronic structure in the valence band. A strong resonant effect at a photon energy of 710 eV is observed. Fe^{3+} is the only valence state of Fe ions in the film and the Fe 3d electronic states are concentrated at binding energies of about 3.8 eV and 7 eV～ 8 eV. There are no electronic states related to Fe near the Fermi level. Magnetic measurements reveal a typical superparamagnetic property at room temperature. The absence of electronic states related to Fe near the Fermi level and the high quality of the film, with few defects, provide little support to ferromagnetism.

Strain-compensated InGaN quantum well (QW) active region employing tensile AlGaN barrier is analyzed. Its spectral stability and efficiency droop for dual-blue light-emitting diode (LED) are improved compared with those of the conventional InGaN/GaN QW dual-blue LED based on stacking structure of two In_{0.18}Ga_{0.82}N/GaN QWs and two In_{0.12}Ga_{0.88}N/GaN QWs on the same sapphire substrate. It is found that the optimal performance is achieved when the Al composition of strain-compensated AlGaN layer is 0.12 in blue QW and 0.21 in blue-violet QW. The improvement performance can be attributed to the strain-compensated InGaN-AlGaN/GaN QW that can provide a better carrier confinement and effectively reduce leakage current.

An AlGaN/GaN high-electron mobility transistor (HEMT) with a novel source-connected air-bridge field plate (AFP) is experimentally verified. The device features a metal field plate that jumps from the source over the gate region and lands between the gate and drain. When compared to a similar size HEMT device with conventional field plate (CFP) structure, the AFP not only minimizes the parasitic gate to source capacitance, but also exhibits higher OFF-state breakdown voltage and one order of magnitude lower drain leakage current. In a device with a gate to drain distance of 6 μm and a gate length of 0.8 μm, three times higher forward blocking voltage of 375 V was obtained at V_{GS}=-5 V. In contrast, a similar sized HEMT with CFP can only achieve a breakdown voltage no higher than 125 V using this process, regardless of device dimensions. Moreover, a temperature coefficient of 0 V/K for the breakdown voltage is observed. However, devices without field plate (no FP) and with optimized conventional field plate (CFP) exhibit breakdown voltage temperature coefficients of -0.113 V/K and -0.065 V/K, respectively.

Ab initio calculations, based on norm-conserving nonlocal pseudopotentials and density functional theory (DFT), are performed to investigate the structural, elastic, dielectric, and vibrational properties of aluminum arsenide AlAs with zinc-blende (B3) structure and nickel arsenide (B8_{1}) structure under hydrostatic pressure. Firstly, the path for the phase transition from B3 to B8_{1} is confirmed by analyzing the energies of different structures, which is in good agreement with previous theoretical results. Secondly, we find that the elastic constants, bulk modulus, static dielectric constants, and the optical phonon frequencies are varying in a nearly linear manner under hydrostatic pressure. What is more, the softening mode of transversal acoustic mode at X point supports the phase transition in AlAs.

The phase behaviors in binary mixture of diblock copolymers confined between two parallel walls are investigated by using cell dynamics simulation of the time-dependent Ginzburg-Landau theory. The morphological dependence of the wall-block interaction and the distance between walls (confinement degree) has been systematically studied, and the effect of repulsive interactions between different monomers is also discussed. It is interesting that multiple novel morphological transitions are observed by changing these factors, and various multilayered sandwich structures are formed in the mixture. Furthermore, the parametric dependence and physical reasons for the microdomain growth and orientational order transitions are discussed. From the simulation, we find that much richer morphologies can form in binary mixture of diblock copolymers than those in pure diblock copolymer. Our results provide an insight into the phase behaviors under parallel walls confinement and may provide guidance for experimentalists. This model system can also give a simple way to realize orientational order transition in soft materials through confinement.

The present paper discusses our investigation of InGaAs surface morphology annealed for different lengths of time. After annealing for 15 min, the ripening of InGaAs islands is completed. The real space scanning tunneling microscopy (STM) images show the evolution of InGaAs surface morphology. A half-terrace diffusion theoretical model based on thermodynamic theory is proposed to estimate the annealing time for obtaining flat morphology. The annealing time calculated by the proposed theory is in agreement with the experimental results.

Single-junction, lattice-mismatched In_{0.69}Ga_{0.31}As thermophotovoltaic (TPV) devices each with a bandgap of 0.6 eV are grown on InP substrate by metal-organic chemical vapour deposition (MOCVD). Compositionally undulating step-graded InAs_{y}P_{1-y} buffer layers with a lattice mismatch of ～1.2%, are used to mitigate the effect of lattice mismatch between the device layers and the InP substrate. With an optimized buffer thickness, the In_{0.69}Ga_{0.31}As active layers grown on the buffer displayed a high crystal quality with no measurable tetragonal distortion. High-performance single-junction devices are demonstrated, with an open-circuit voltage of 0.215 V and a photovoltaic conversion efficiency of 6.9% at a short-circuit current density of 47.6 mA/cm^{2}, which are measured under the standard solar simulator of air mass 1.5-global (AM 1.5 G).

We propose an optically pumped nonpolar GaN/AlGaN quantum well (QW) active region design for terahertz (THz) lasing in the wavelength range of 30 μm～ 40 μm and operating at room temperature. The fast longitudinal optical (LO) phonon scattering in GaN/AlGaN QWs is used to depopulate the lower laser state, and more importantly, the large LO phonon energy is utilized to reduce the thermal population of the lasing states at high temperatures. The influences of temperature and pump intensity on gain and electron densities are investigated. Based on our simulations, we predict that with a sufficiently high pump intensity, a room temperature operated THz laser using a nonpolar GaN/AlGaN structure is realizable.

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

An effective multiscale simulation which concurrently couples the quantum-mechanical and molecular-mechanical calculations based on the position continuity of atoms is presented. By an iterative procedure, the structure of the dislocation core in face-centered cubic metal is obtained by first-principles calculation and the long range stress is released by molecular dynamics relaxation. Compared to earlier multiscale methods, the present work couples the long-range strain to the local displacements of the dislocation core in a simpler way with the same accuracy.

The structural, elastic, and electronic properties of NiAl alloyed with rare earth elements Pr, Pm, Sm, and Eu are investigated by using density functional theory (DFT). The study suggests that Pr, Pm, Sm, and Eu are all tend to be substituted for Al site. Ni_{8}Al_{7}Pm possesses the largest ductility. Only the hardness and ductility of Ni_{8}Al_{7}Eu are enhanced simultaneously. The covalency strength of Ni-Al bond in Ni_{8}Al_{7}Pm is higher than that in Ni_{8}Al_{7}Eu. The covalency strength of Al-Al bond and that of Ni-Ni bond in Ni_{8}Al_{7}Eu are higher than that in Ni_{8}Al_{7}Pm. Ni-Pm bond and Ni-Eu bond are covalent, and the covalency strength of Ni-Pm bond is greater. Al-Pm bond and Al-Eu bond show great covalency strength and ionicity, respectively.

We report on a molecular dynamics study of swelling patterns of an Na-rich/Cs-poor montomorillonite and a Cs-montomorillonite. The recently developed CLAYFF force field is used to predict the basal spacing as a function of the water content in the interlayer. The simulations reproduce the swelling patterns of the Na and Cs-montomorillonite, suggesting a mechanism of its hydration different from that of the montomorillonite. In the meanwhile, we find that the differences in size and hydration energy of Na and Cs ions have strong implications for the structure and the internal energy of interlayer water. In particular, our results indicate that the hydrate difference in the presence of coexistent Na and Cs has a larger influence on the behavior of clay-water system. For Na-rich/Cs-poor montomorillonite, the hydration energy values of Na ions and water molecules each have a dramatic increase compared with those in Na-montomorillonite on the interlayer spacing, and the hydration energy values of Cs ions and water molecules decrease somewhat compared with those in Cs-montomorillonite.

Direct current (DC) reverse step voltage stress is applied on the gate of AlGaN/GaN high-electron mobility transistor (HEMT). Experiments show that parameters degenerate under stress. Large-signal parasitic source/drain resistance (R_{S}/R_{D}) and gate-source forward I-V characteristics are recoverable after breakdown of the device under test (DUT). Electrons trapped by both the AlGaN barrier trap and the surface state under stress lead to this phenomenon, and surface state recovery is the major reason for the recovery of device parameters.

A planar InP-based Gunn diode with a notch doping structure is designed and fabricated for being integrated into millimeter-wave and terahertz integrated circuits. We design two kinds of InP-based Gunn diodes. One has a fixed diameter of cathode area, but it has a variable spacing between anode and cathode; the other has a fixed spacing, but it has a varying diameter. The threshold voltage and saturated current exhibit their strong dependences on spacing (10 μm-20 μm) and diameter (40 μm-60 μm) of InP Gunn diode. The threshold voltage is approximately 4.5 V and the saturated current is in a range of 293 mA-397 mA. In this work, the diameter of the diode and the space between anode and athode are optimized. The devices are fabricated using wet etching technique and show excellent performances. The results strongly suggest that the low-cost and reliable InP planar Gunn diodes can be used as single chip terahertz sources.

We propose to use wavelength modulation approach, i.e., the spectroscopy of surface plasmon in frequency domain to characterize the optical dispersion property of gold film. Using this method, we determine the dispersion relationship of gold film in a wavelength range from 537.12 nm to 905.52 nm, and our results accord well with the reported results by other authors. This method is particularly suited for studying the optical dispersion properties of thin metal films, because a series of dielectric constants over a wide spectral range can be determined simultaneously via only a single scan of the incident angle, thereby avoiding the repeated measurements required when using angular modulation approach.

The fabrication of 4H-SiC vertical trench-gate metal-oxide-semiconductor field-effect transistors (UMOSFETs) is reported in this paper. The device has a 15-μm thick drift layer with 3×10^{15} cm^{-3} N-type doping concentration and a 3.1-μm channel length. The measured on-state source-drain current density is 65.4 A/cm^{2} at V_{g}=40 V and V_{DS}=15 V. The measured threshold voltage (V_{th}) is 5.5 V by linear extrapolation from the transfer characteristics. A specific on-resistance (R_{sp-on}) is 181 mΩ·cm^{2} at V_{g}=40 V and a blocking voltage (BV) is 880 V (I_{DS}=100 μA@880V) at V_{g}=0 V.

A high voltage (>600 V) integrable silicon-on-insulator (SOI) trench-type lateral insulated gate bipolar transistor (LIGBT) with a reduced cell-pitch is proposed. The LIGBT features multiple trenches (MTs): two oxide trenches in the drift region and a trench gate extended to the buried oxide (BOX). Firstly, the oxide trenches enhance electric field strength because of the lower permittivity of oxide than that of Si. Secondly, oxide trenches bring in multi-directional depletion, leading to a reshaped electric field distribution and an enhanced reduced-surface electric-field (RESURF) effect. Both increase the breakdown voltage (BV). Thirdly, oxide trenches fold the drift region around the oxide trenches, leading to a reduced cell-pitch. Finally, the oxide trenches enhance the conductivity modulation, resulting in a high electron/hole concentration in the drift region as well as a low forward voltage drop (V_{on}). The oxide trenches cause a low anode-cathode capacitance, which increases the switching speed and reduces the turn-off energy loss (E_{off}). The MT SOI LIGBT exhibits a BV of 603 V at a small cell-pitch of 24 μm, a V_{on} of 1.03 V at 100 A/cm^{-2}, a turn-off time of 250 ns and E_{off} of 4.1×10^{-3} mJ. The trench gate extended to BOX synchronously acts as dielectric isolation between high voltage LIGBT and low voltage circuits, simplifying the fabrication processes.

A low specific on-resistance (R_{on,sp}) integrable silicon-on-insulator (SOI) metal-oxide semiconductor field-effect transistor (MOSFET) is proposed and investigated by simulation. The MOSFET features a recessed drain as well as dual gates which consist of a planar gate and a trench gate extended to the buried oxide layer (BOX) (DGRD MOSFET). First, the dual gates form dual conduction channels, and the extended trench gate also acts as a field plate to improve the electric field distribution. Second, the combination of the trench gate and the recessed drain widens the vertical conduction area and shortens the current path. Third, the P-type top layer not only enhances the drift doping concentration but also modulates the surface electric field distributions. All of these sharply reduce R_{on,sp} and maintain a high breakdown voltage (BV). The BV of 233 V and R_{on,sp} of 4.151 mΩ·cm^{2} (V_{GS}=15 V) are obtained for the DGRD MOSFET with 15-μm half-cell pitch. Compared with the trench gate SOI MOSFET and the conventional MOSFET, R_{on,sp} of the DGRD MOSFET decreases by 36% and 33% with the same BV, respectively. The trench gate extended to the BOX synchronously acts as a dielectric isolation trench, simplifying the fabrication processes.

Wang Pei, Luo Xiao-Rong, Jiang Yong-Heng, Wang Qi, Zhou Kun, Wu Li-Juan, Wang Xiao-Wei, Cai Jin-Yong, Luo Yin-Chun, Fan Ye, Hu Xia-Rong, Fan Yuan-Hang, Wei Jie, Zhang Bo

Chin. Phys. B 2013, 22 (2): 027305; doi: 10.1088/1674-1056/22/2/027305
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An ultra-low specific on-resistance trench gate vertical double-diffused metal-oxide semiconductor with a high-k dielectric-filled extended trench (HK TG VDMOS) is proposed in this paper. The HK TG VDMOS features a high-k (HK) trench below the trench gate. Firstly, the extended HK trench not only causes an assistant depletion of the n-drift region, but also optimizes the electric field, which therefore reduces R_{on,sp} and increases the breakdown voltage (BV). Secondly, the extended HK trench weakens the sensitivity of BV to the n-drift doping concentration. Thirdly, compared with the super-junction (SJ) vertical double-diffused metal-oxide semiconductor (VDMOS), the new device is simplified in fabrication by etching and filling the extended trench. The HK TG VDMOS with BV=172 V and R_{on,sp}=0.85 mΩ·cm^{2} is obtained by simulation; its R_{on,sp} is reduced by 67% and 40% and its BV is increased by about 15% and 5%, in comparison with those of the conventional trench gate VDMOS (TG VDMOS) and conventional superjunction trench gate VDMOS(SJ TG CDMOS).

Using the nonequilibrium Green's function technique, electron transport through a laterally coupled vertical triple quantum dot is investigated. The conductance as a function of electron energy is numerically calculated. The evolution of the conductance strongly depends on the configuration of dot levels and interdot coupling strengths.

The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn^{+2} ion (S=5/2) are investigated by the non-equilibrium Green function method. We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering quantum dot are coupled into spin pair states with (2S+1) sublevels. In the sequential tunneling regime, the differential conductance exhibits (2S+1) possible peaks, corresponding to resonance tunneling via (2S+1) sublevels. At low temperature, Kondo physics dominates transport and (2S+1) Kondo peaks occur in the local density of states and conductance. These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states.

The magnetic properties of a mixed spin-2 and spin-1/2 ferromagnetic diamond chain are studied by effective-field theory and Monte Carlo (MC) simulation based on Ising model. The temperature dependences of magnetization, magnetic susceptibility, internal energy, and specific heat are studied, respectively. The exchange interaction dependences of magnetization and the critical temperature are calculated by MC simulation. The changes of magnetization depend on field increasing and then field decreasing under steady-static conditions are also given.

The magnetocaloric effect (MCE) in EuCu_{1.75}P_{2} compound is studied by the magnetization and heat capacity measurements. Magnetization and modified Arrott plots indicate that the compound undergoes a second-order phase transition at T_{C}～51 K. A large reversible MCE is observed around T_{C}. The values of maximum magnetic entropy change (-ΔS_{M}^{max}) reach 5.6 J·kg^{-1}·K^{-1} and 13.3 J·kg^{-1}·K^{-1} for the field change of 2 T and 7 T, respectively, with no obvious hysteresis loss in the vicinity of Curie temperature. The corresponding maximum adiabatic temperature changes (ΔT_{ad}^{max}) are evaluated to be 2.1 K and 5.0 K. The magnetic transition and the origin of large MCE in EuCu_{1.75}P_{2} are also discussed.

The geometry structures, electronic structures, and magnetic properties of Zn_{46}V_{2}O_{48} nanowires are studied by density functional theory (DFT) calculations. We find that the ferromagnitic (FM) coupling is more stable for six configurations of Zn_{46}V_{2}O_{48} nanowires, and is mediated by neighboring O as evidenced from the strong hybridization of V 3d and O 2p states, exhibiting strong spin polarization. The spin polarization is found to be 100% in the Zn_{46}V_{2}O_{48} nanowires, which confirms that it is a half-metallic ferromagnet and very suitable for the injection of the spin carriers, which shows that Zn_{46}V_{2}O_{48} nanowire is one of the ideal materials to realize spin electronic devices. At the same time, the magnetic coupling mechanisms of Zn_{46}V_{2}O_{48} nanowires are analyzed with V 3d and O 2p orbitals and their magnetic moments mainly come from the contributions of the unpaired electrons of V 3d orbitals. The above results provide theoretical basis for the preparation of 3d transition metal-doped ZnO nanowire materials.

We investigated the effect of low temperature annealing on magnetic anisotropy in 7-nm ultrathin Ga_{0.94}Mn_{0.06}As devices by measuring the angle-dependent planar Hall resistance (PHR). Obvious hysteresis loops were observed during the magnetization reversal through the clockwise and counterclockwise rotations under low magnetic fields (below 1000 Gs, 1 Gs=10^{-4} T), which can be explained by competition between Zeeman energy and magnetic anisotropic energy. It is found that the uniaxial anisotropy is dominant in the whole measured ferromagnetic range for both the as-grown ultrathin Ga_{0.94}Mn_{0.06}As and the annealed one. The cubic anisotropy changes more than the uniaxial anisotropy in the measured temperature ranges after annealing. This gives a useful way to tune the magnetic anisotropy of ultrathin (Ga,Mn)As devices.

This study focuses on the effect of V-doping on the ferromagnetism (FM) of 6H-SiC powder. The X-ray diffraction results indicate that V is inserted into the 6H-SiC lattice. The Raman spectra reveale that with a V concentration of 25 ppm, the crystalline quality and carrier concentration of 6H-SiC are hardly varied. It is found that after V-doping process, the saturation magnetization (M_{s}) and the vacancy concentration of 6H-SiC are both increased. From these results, it is deduced that the effect of V might contribute mainly to the increase of vacancy concentration, thus resulting in the increase of M_{s} of V-doped 6H-SiC.

In this paper, magnetic and dielectric properties of the quasi-two-dimensional triangular-lattice system CuCrS_{2} and its B-site-diluted analogs CuAl_{1-x}Cr_{x}S_{2} (x=0.01 and x=0.02) are investigated. Antiferromagnetic phase transition is observed at about 38.5 K by magnetization measurement without shift induced by a small amount of dopping Al. Magnetodielectric effect is found near T_{N} in each of the three compounds. The dielectric constant decreases and the magnetocapacitance increases with the increase of substitution of nonmagnetic Al^{3+} ions for the magnetic Cr^{3+} ions. The negative magnetocapacitive effect reaches ～13% for CuAl_{0.02}Cr_{0.98}S_{2}.

The effects of the oxygen-argon ratio on electric properties of Ta_{2}O_{5} film prepared by radio-frequency magnetron sputtering were investigated. The Ta_{2}O_{5} partially transforms from amorphous phase into crystal phase when annealing temperatures are 800℃ or higher. The lattice constant of Ta_{2}O_{5} decreases with the increase of the O_{2}/Ar ratio, which indicates that oxygen gas in the working gas mixture contributes to reducing the density of oxygen vacancies during the deposition process. For the films deposited in working gas mixtures with different O_{2}/Ar ratios and subsequently annealed at 700℃, the effective dielectric constant is increased from 14.7 to 18.4 with the increase of the O_{2}/Ar ratio from 0 to 1. Considering the presence of an SiO_{2} layer between the film and the silicon substrate, the optimal dielectric constant of Ta_{2}O_{5} film was estimated to be 31. Oxygen gas in the working gas mixture contributes to reducing the density of oxygen vacancies, and the oxygen vacancy density and leakage current of Ta_{2}O_{5} film both decrease with the increase of the O_{2}/Ar ratio. The leakage current decreases after annealing treatment and it is minimized at 700℃. However, when the annealing temperature is 800℃ or higher, it increases slightly, which results from the partially crystallized Ta_{2}O_{5} layer containing defects such as grain boundaries and vacancies.

A comparative study of two kinds of oxidants (H_{2}O and O_{3}) with the combinations of two metal precursors [trimethylaluminum (TMA) and tetrakis(ethylmethylamino) hafnium (TEMAH)] for atomic layer deposition (ALD) hafnium aluminum oxide (HfAlO_{x}) films is carried out. The effects of different oxidants on the physical properties and electrical characteristics of HfAlO_{x} films are studied. The preliminary testing results indicate that the impurity level of HfAlO_{x} films grown with both H_{2}O and O_{3} used as oxidants can be well controlled, which has significant effects on the dielectric constant, valence band, electrical properties, and stability of HfAlO_{x} film. Additional thermal annealing effects on the properties of HfAlO_{x} films grown with different oxidants are also investigated.

Hexagonal β-NaYF_{4} co-doped with Yb^{3+} and Er^{3+} is directly synthesized under mild conditions using a hydrothermal method. The variation of the ratio of Ln^{3+} to F^{-} and ethylenediaminetetraacetic acid (EDTA) causes the shape of the microcrystal to change from microplate to microcolumn. The NaYF_{4} powder is mixed with polydimethylsiloxane (PDMS) to create an up-converter for thin film amorphous silicon solar cells so as to evaluate the effectiveness of the synthesized material as up-converter. In order to overcome the difficulty in measuring the effectiveness of up-conversion material, a new method of using near infrared illumination to measure the short circuit current densities of solar cells both with and without up-converters is developed. Up-converter with pure hexagonal NaYF_{4}:Yb^{3+/}Er^{3+}microcrystal produces a high current output. Emission intensity data obtained by photoluminescence suggest that pure hexagonal NaYF_{4}:Yb^{3+/}Er^{3+} microcrystals are more efficient than nanocrystals when used as up-converting phosphors.

Ultrathin InSb thin films on SiO_{2}/Si substrates are prepared by radio frequency (RF) magnetron sputtering and rapid thermal annealing (RTA) at 300, 400, and 500℃, respectively. X-ray diffraction (XRD) indicates that InSb film treated by RTA at 500℃, which is higher than its melting temperature (about 485℃), shows a monocrystalline-like feature. High-resolution transmission electron microscopy (HRTEM) micrograph shows that melt recrystallization of InSb film on SiO_{2}/Si(111) substrate is along the (111) planes. The transmittances of InSb films decrease and the optical band gaps redshift from 0.24 eV to 0.19 eV with annealing temperature increasing from 300℃ to 500℃, which is indicated by Fourier transform infrared spectroscopy (FTIR) measurement. The observed changes demonstrate that RAT is a viable technique for improving characteristics of InSb films, especially the melt-recrystallized film treated by RTA at 500℃.

Novel Dy^{3+}-doped Gd(PO_{3})_{3} white light phosphors each with an orthorhombic system are successfully synthesized by solid-state reaction. The luminescence properties of white-light Gd_{1-x}(PO_{3})_{3}:xDy^{3+} (0<x≤ 0.25) under vacuum ultraviolet (VUV) excitation are investigated. The strong absorption at around 147 nm in excitation spectrum energy can be transferred to the energy levels of Dy^{3+} ion from the host absorption. Additionally, the white light phosphor is activated by a single Dy^{3+} ion. Therefore, the luminescence of Gd_{1-x}(PO_{3})_{3}:xDy (0<x≤ 0.25) under VUV excitation is effective, and it has the promise of being applied to mercury-free lamp.

Optical absorption, excitation, and fluorescence were investigated in Eu ion-doped CdWO_{4} single crystal grown by a modified Bridgman method. The results indicate that Eu^{2+} and Eu^{3+} ions coexist in CdWO_{4} crystal and an energy transfer occurs between these Eu^{2+} and Eu^{3+} ions. When the crystal is excited by 266-nm light, the energy corresponding to the 4f^{6}5d to ^{8}S_{7/2} transition of Eu^{2+} ions results in the excitation of the Eu^{3+} ions to the ^{ 5}D_{J} level. The effect on fluorescence of annealing in oxygen at various temperatures was investigated. The excitation intensity of Eu^{2+} ions at 266 nm decreases as annealing temperature increases from 300 K to 1073 K, but it remains at a certain equilibrium level when the annealing temperature is further increased.

Driving voltage of organic light-emitting diode (OLED) is lowered by employing molybdenum trioxide (MoO_{3})/N, N'-bis(naphthalene-1-yl)-N,N'-bis(phe-nyl)-benzidine (NPB) multiple quantum well (MQW) structure in hole transport layer. For the device with double quantum well (DQW) structure of ITO/ [MoO_{3} (2.5 nm)/NPB (20 nm)]_{2}/Alq_{3}(50 nm)/LiF (0.8 nm)/Al (120 nm)], the turn-on voltage is reduced to 2.8 V, which is lowered by 0.4 V compared with that of the control device (without MQW structures), the driving voltage is 5.6 V, which is reduced by 1 V compared with that of the control device at the 1000 cd/m^{2}. In this work, the enhancement of the injection and transport ability for holes could reduce the driving voltage for the device with MQW structure, which is attributed not only to the reducing energy barrier between ITO and NPB, but also to the forming charge transfer complex between MoO_{3} and NPB induced by the interfacial doping effect of MoO_{3}.

GaN samples 1-3 are cleaned by a 2:2:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%) to de-ionized water; hydrochloric acid (37%); or a 4:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%). The samples are activated by Cs/O after the same annealing process. X-ray photoelectron spectroscopy after the different ways of wet chemical cleaning shows: sample 1 has the largest proportion of Ga, N, and O among the three samples, while its C content is the lowest. After activation the quantum efficiency curves show sample 1 has the best photocathode performance. We think the wet chemical cleaning method is a process which will mainly remove C contamination.

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

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

In this paper, Raman shifts of a-plane GaN layers grown on r-plane sapphire substrates by low-pressure metal-organic chemical vapor deposition (LPMOCVD) are investigated. We compare the crystal qualities and study the relationships between Raman shift and temperature for conventional a-plane GaN epilayer and insertion AlN/AlGaN superlattice layers for a-plane GaN epilayer using temperature-dependent Raman scattering in a temperature range from 83 K to 503 K. The temperature-dependences of GaN phonon modes (A_{1} (TO), E_{2} (high), and E_{1} (TO)) and the linewidths of E_{2} (high) phonon peak are studied. The results indicate that there exist two mechanisms between phonon peaks in the whole temperature range, and the relationship can be fitted to the pseudo-Voigt function. From analytic results we find a critical temperature existing in the relationship, which can characterize the anharmonic effects of a-plane GaN in different temperature ranges. In the range of higher temperature, the relationship exhibits an approximately linear behavior, which is consistent with the analyzed results theoretically.

The stereodynamics of the abstraction reaction H+NeH^{+} (v=1-3, j=1, 3, 5)→ H_{2}^{+}+Ne is studied theoretically with quasi-classical trajectory method on a new ab initio potential energy surface [Lü S J, Zhang P Y, Han K L and He G Z 2012 J. Chem. Phys.132 014303]. The effects of vibrational and rotational excitation of reagent molecules on the polarization of product are investigated. The reaction cross sections, the distributions of P(θ_{r}), P(φ_{r}), and polarization-dependent differential cross sections (PDDCSs) are calculated. The obtained cross sections indicate that the title reaction is a typical barrierless atom (ion)-ion (molecule) reaction. The initial vibrational excitation and rotational excitation of reagent molecules have distinctly different influences on stereodynamics of title reaction, and the possible reasons for the differences are presented.

Single-event effect (SEE) is the most serious problem in space environment. The modern semiconductor technology worries about the feasibility of the linear energy transfer (LET) as metric in characterizing SEE induced by heavy ions. In the paper, we calibrate the detailed static random access memory (SRAM) cell structure model of advanced field programmable gate array (FPGA) device using the computer-aided design tool, and calculate the heavy ion energy loss in multi-layer metal utilizing Geant4. Based on the heavy ion accelerator experiment and numerical simulation, it is proved that the metric of LET at the device surface, with ignoring the top metal material in advanced semiconductor device, would underestimate the SEE. In the SEE evaluation in space radiation environment the top-layers on the semiconductor device must be taken into consideration.

In the present paper we conduct a theoretical study of the thermal accumulation effect of a typical bipolar transistor caused by high power pulsed microwave (HPM), and investigate the thermal accumulation effect as a function of pulse repetition frequency (PRF) and duty cycle. A study of the damage mechanism of the device is carried out from the variation analysis of the distribution of the electric field and the current density. The result shows that the accumulation temperature increases with PRF increasing and the threshold for the transistor is about 2 kHz. The response of the peak temperature induced by the injected single pulses indicates that the falling time is much longer than the rising time. Adopting the fitting method, the relationship between the peak temperature and the time during the rising edge and that between the peak temperature and the time during the falling edge are obtained. Moreover, the accumulation temperature decreases with duty cycle increasing for a certain mean power.

The effect of substrate doping on the flatband and threshold voltages of strained-Si/SiGe p metal-oxide semiconductor field-effect transistor (pMOSFET) has been studied. By physically deriving the models of the flatband and threshold voltages, which have been validated by numerical simulation and experimental data, the shift in the plateau from the inversion region to the accumulation region as the substrate doping increases has been explained. The proposed model can provide valuable reference to the designers of strained-Si devices and has been implemented in software for extracting the parameters of strained-Si MOSFET.

The electronic transport properties of a new kind of molecular switches -bi-OPE-monothiol molecular switches -were studied by applying first-principles calculations and generalized elastic scattering Green's function. The numerical results show that, for a bi-OPE-molecule junction, the offset face-to-face configuration induces more delocalized molecular orbitals, and results in higher conductivity than the parallel face-to-face configuration, so it can be used as a molecular switch. The side substituent groups containing more delocalized electrons can strengthen the intermolecular coupling and raise the conductivities of bi-OPE-monothiol molecular devices. On the basis of the investigations, we find a scheme to enhance the open-close ratios of bimolecular switches.

Manual acupuncture is widely used for pain treatment and stress control. Previous studies on acupuncture have shown its modulatory effects on functional connectivity associated with one or a few preselected brain regions. To investigate how manual acupuncture modulates the organization of functional networks at a whole-brain level, we acupuncture at ST36 of right leg to obtain electroencephalograph (EEG) signals. By coherence estimation, we determine the synchronizations between all pairwise combinations of EEG channels in three acupuncture states. The resulting synchronization matrices are converted into functional networks by applying a threshold, and clustering coefficients and path lengths are computed as a function of threshold. The results show that acupuncture can increase functional connections and synchronizations between different brain areas. For a wide range of threshold, the clustering coefficient during acupuncture and post-acupuncture period is higher than that during the pre-acupuncture control period, whereas characteristic path length is shorter. We provide further support for the presence of "small-world" network characteristics in functional networks by acupuncture. These preliminary results highlight the beneficial modulations of functional connectivity by manual acupuncture, which could contribute to the understanding of acupuncture effects on the entire brain, as well as the neurophysiological mechanisms underlying acupuncture. Moreover, the proposed method may be a useful approach to the further investigation of the complexity of patterns of interrelations between EEG channels.

To investigate whether and how manual acupuncture (MA) modulates brain activities, we design an experiment that acupuncture at acupoint ST36 of right leg to obtain electroencephalograph (EEG) signals in healthy subjects. We adopt autoregressive (AR) Burg method to estimate the power spectrum of EEG signals and analyze the relative powers in delta (0 Hz-4 Hz), theta (4 Hz-8 Hz), alpha (8 Hz-13 Hz), and beta (13 Hz-30 Hz) bands. Our results show that MA at ST36 can significantly increase the EEG slow wave relative power (delta band) and reduce the fast wave relative powers (alpha and beta bands), while there are no statistical differences in theta band relative power between different acupuncture states. In order to quantify the ratio of slow to fast wave EEG activity, we compute the power ratio index. It is found that the MA can significantly increase the power ratio index, especially in frontal and central lobes. All the results highlight the modulation of brain activities with MA and may provide potential helps in clinical treatment of acupuncture. The proposed quantitative method of acupuncture signals may be further used to make MA more standardized.

Information feedback strategies can influence the traffic efficiency of intelligent traffic systems greatly. Based on the more practical symmetrical two-route scenario with one entrance and one exit, an improved Weighted Mean Velocity Feedback Strategy (WMVFS) is proposed, which is not sensitive to the precision of Global Position System (GPS) devices. The applicability of WMVFS to different weight factors, aggressive probabilities, densities of dynamic vehicles, and different two-route scenarios (symmetrical scenario and asymmetrical scenario with a speed limit bottleneck) is analyzed. Results show that WMVFS achieves the best performance compared with three other information feedback strategies when considering the traffic flux and stability.

We report some key results in the theoretical investigations of configurations of lipid membranes and present several challenges in this field, which involve (i) the exact solutions to the shape equation of lipid vesicles, (ii) the exact solutions to the governing equations of open lipid membranes, (iii) the neck condition of two-phase vesicles in the budding state, (iv) the nonlocal theory of membrane elasticity, and (v) the relationship between the symmetry and the magnitude of the free energy.

In this paper, we describe the estimation of low-altitude refractivity structure from simulation and real ground-based GPS delays. The vertical structure of the refractive environment is modeled using three parameters, i.e., duct height, duct thickness, and duct slope. The refractivity model is implemented with a priori constraints on the duct height, thickness, and strength, which might be derived from soundings or numerical weather-prediction models. A ray propagation model maps the refractivity structure into a replica field. Replica fields are compared with the simulation observed data using a squared-error objective function. A global search for the three environmental parameters is performed using genetic algorithm. The inversion is assessed by comparing the refractivity profiles from the radiosondes to those estimated. This technique could provide near-real-time estimation of ducting effect. The results suggest that ground-based GPS provides significant atmospheric refractivity information, despite certain fundamental limitations of ground-based measurements. Radiosondes typically are launched just a few times daily. Consequently, estimates of temporally and spatially varying refractivity that assimilate GPS delays could substantially improve over-estimates using radiosonde data alone.

Estimation of lower atmospheric refractivity from radar sea clutter (RFC) is a complicated nonlinear optimization problem. This paper deals with the RFC problem in a Bayesian framework. It uses unbiased Markov Chain Monte Carlo (MCMC) sampling technique, which can provide accurate posterior probability distributions of the estimated refractivity parameters by using an electromagnetic split-step fast Fourier transform terrain parabolic equation propagation model within a Bayesian inversion framework. In contrast to the global optimization algorithm, the Bayesian-MCMC can obtain not only the approximate solutions, but also the probability distributions of the solutions, that is, uncertainty analyses of solutions. The Bayesian-MCMC algorithm is implemented on the simulation radar sea-clutter data and the real radar sea-clutter data. Reference data are assumed to be simulation data and refractivity profiles obtained with a helicopter. Inversion algorithm is assessed (i) by comparing the estimated refractivity profiles from the assumed simulation and the helicopter sounding data; (ii) the one-dimensional (1D) and two-dimensional (2D) posterior probability distribution of solutions.

This paper investigates the temperature dependence of single event transient (SET) in 90-nm complementary metat-oxide semiconductor (CMOS) dual-well and triple-well negative metal-oxide semiconductor field-effect transistors (NMOSFETs). Technology computer-aided design (TCAD) three-dimensional (3D) simulations show that the drain current pulse duration increases from 85 ps to 245 ps for triple-well but only increases from 65 ps to 98 ps for dual-well when the temperature increases from -55℃ to 125℃, which is closely correlated with the source of NMOSFETs. This reveals that the pulse width increases with temperature in dual-well due to the weakening of anti-amplification bipolar effect while increases with temperature in triple-well due to the enhancement of the bipolar amplification.

Using the technology computer-aided design three-dimensional simulation, the supply voltage scaled dependency of the recovery of single event upset and charge collection in static random-access memory cells are investigated. It reveals that the recovery linear energy transfer threshold decreases with the supply voltage reducing, which is quite attractive to the dynamic voltage scaling and subthreshold circuits radiation-hardened design. Additionally, the effect of supply voltage on charge collection is also investigated. It is concluded that the supply voltage mainly affects the bipolar gain of parasitical bipolar junction transistor (BJT) and the existence of the source plays an important role in the supply voltage variation.

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