Using adiabatic approximation, a two arbitrary qubits Rabi model has been studied in ultra-strong coupling. The analytical expressions of the eigenvalues and the eigenvalues are obtained. They are in accordance with the numerical determined results. The dynamical behavior of the system and the evolution of entanglement have also been discussed. The collapse and revival phenomena has garnered particular attention. The influence of inconsistent coupling strength on them is studied. These results will be applied in quantum information processing.

A polarization splitter based on dual-core soft glass photonic crystal fiber (PCF) filled with micron-scale gold wire is proposed. The characteristics of the polarization splitter are studied by changing the structural parameters of the PCF and the diameter of the gold wire with the finite element method (FEM). The simulation results reveal that the coupling length ratio of the soft glass-based PCF is close to 2 and the corresponding curve is more flat than that of the silica-based PCF. The broadband bandwidth is 226 nm in which the extinction ratio is lower than -20 dB by the soft glass-based PCF, i.e., from 1465 nm to 1691 nm which is competitive in the reported polarization splitters, and the bandwidth is just 32 nm by the silica-based PCF. The insertion loss by our polarization splitter is just 0.00248 dB and 0.43 dB at the wavelength of 1.47 μm and 1.55 μm. The birefringence is obviously increased and the coupling length is decreased by filling gold wire into the soft glass-based or the silica-based PCF. Also the birefringence based on the silica-based PCF is much larger than that based on the soft glass-based PCF whether or not the gold wire is introduced. The fabrication tolerance of the polarization splitter is also considered by changing the structural parameters. The polarization splitter possesses broad bandwidth, low insertion loss, simple structure and high fabrication tolerance.

We demonstrate a flexible erbium-doped pulsed fiber laser which achieves the wavelength and pulse width tuning by adjusting an intracavity filter. The intracavity filter is flexible to achieve any of the different wavelengths and bandwidths in the tuning range. The wavelength and width of pulse can be tuned in a range of ~20 nm and from ~0.8 ps to 87 ps, respectively. The flexible pulsed fiber laser can be accurately controlled, which is insensitive to environmental disturbance.

We study the spontaneous Raman scattering (RS) in taper-drawn micro/nano-fibers (MNFs) by employing the photon counting technique. The spectra of RS in five MNFs, which are fabricated by using different heating flames (hydrogen flame or butane flame) and with different diameters, are measured within a frequency shift range of 1435 cm^{-1}-3200 cm^{-1}. From the measured spectra, we observe the RS peaks originated from silica and a unique RS peak with a frequency shift of ~2905 cm^{-1} (~87.2 THz). Unlike the former ones, the latter one is not observable in conventional optical fibers. Furthermore, the unique peak becomes obvious and starts to rapidly increase with the decrease of the diameter of MNFs when the diameter is smaller than 2 μm, and the intensity of the unique peak significantly depends on the heating flame used in the fabricating process. Our investigation is useful for the entanglement generation or optical sensing using taper-drawn MNFs.

A new Raman process can be used to realize efficient Raman frequency conversion by coherent feedback at low light intensity[Chen B, Zhang K, Bian C L, Qiu C, Yuan C H, Chen L Q, Ou Z Y, and Zhang W P 2013 Opt. Express21, 10490]. We present a theoretical model to describe this enhanced Raman process, termed as cascade correlation-enhanced Raman scattering, which is a Raman process injected by a seeded light field. It is correlated with the initially prepared atomic spin excitation and driven by the quasi-standing-wave pump fields, and the processes are repeated until the Stokes intensities are saturated. Such an enhanced Raman scattering may find applications in quantum information, nonlinear optics, and optical metrology due to its simplicity.

We theoretically study the nonlinear compression of a 20-mJ, 1030-nm picosecond chirped pulse from the thin-disk amplifier in a krypton gas-filled hollow-core fiber. The chirp from the thin-disk amplifier system has little influence on the initial pulse, however, it shows an effect on the nonlinear compression in hollow-core fiber. We use a large diameter hollow waveguide to restrict undesirable nonlinear effects such as ionization; on the other hand, we employ suitable gas pressure and fiber length to promise enough spectral broadening; with 600-μm, 6-bar (1 bar=10^{5} Pa), 1.8-m hollow fiber, we obtain 31.5-fs pulse. Moreover, we calculate and discuss the optimal fiber lengths and gas pressures with different initial durations induced by different grating compression angles for reaching a given bandwidth. These results are meaningful for a compression scheme from picoseconds to femtoseconds.

The factors influencing the crosstalk of silicon-on-insulator (SOI) nanowire arrayed waveguide grating (AWG) are analyzed using the transfer function method. The analysis shows that wider and thicker arrayed waveguides, outsider fracture of arrayed waveguide, and larger channel space, could mitigate the deterioration of crosstalk. The SOI nanowire AWGs with different arrayed waveguide widths are fabricated by using deep ultraviolet lithography (DUV) and inductively coupled plasma etching (ICP) technology. The measurement results show that the crosstalk performance is improved by about 7 dB through adopting 800 nm arrayed waveguide width.

It is a difficult problem to study the stability of the rheonomic and nonholonomic mechanical systems. Especially it is difficult to construct the Lyapunov function directly from the differential equation. But the gradient system is exactly suitable to study the stability of a dynamical system with the aid of the Lyapunov function. The stability of the solution for a simple rheonomic nonholonomic constrained system is studied in this paper. Firstly, the differential equations of motion of the system are established. Secondly, a problem in which the generalized forces are exerted on the system such that the solution is stable is proposed. Finally, the stable solutions of the rheonomic nonholonomic system can be constructed by using the gradient systems.

The characteristics of lubricant film at head/disk interface (HDI) are essential to the stability of hard disk drives. In this study, the theoretical models of the lubricant flow and depletion are deduced based on Navier-Stokes (NS) and continuity equations. The air bearing pressure on the surface of the lubrication film is solved by the modified Reynolds equation based on Fukui and Kaneko (FK) model. Then the lubricant film deformations for a plane slider and double-track slider are obtained. The equation of lubricant film thickness is deduced with the consideration of van der Waals force, the air bearing pressure, the surface tension, and the external stresses. The lubricant depletion under heat source is simulated and the effects of different working conditions including initial thickness, flying height and the speed of the disk on lubricant depletion are discussed. The main factors that cause the lubricant flow and depletion are analyzed and the ways to reduce the film thickness deformation are proposed. The simulation results indicate that the shearing stress is the most important factor that causes the thickness deformation and other terms listed in the equation have little influence. The thickness deformation is dependent on the working parameter, and the thermal condition evaporation is the most important factor.

We report on an experiment on transferring an image through coherent population trapping (CPT) effect in a hot rubidium vapor. We demonstrate experimentally that an image can be transferred from a control light to a probe light. Moreover, we describe the demonstration that the image can be transferred from a control light to two different probes showing a feasibility of transferring an image onto multiple probes. We believe that this effect definitely has important applications in image metrology, high dimensional information transfer in quantum information field, etc.

K_{3}B_{6}O_{10}Cl (KBOC), a new nonlinear optical crystal, shows potential advantages for the generation of deep ultraviolet (UV) light compared with other borate crystals. In this paper we study for the first time the second harmonic generation (SHG) of a femtosecond Ti:sapphire amplifier with this crystal. Laser power is obtained to be as high as 220 mW at the central wavelength of 396 nm with a 1-mm-long crystal, and the maximum SHG conversion efficiency reaches 39.3%. The typical pulse duration is 83 fs. The results show that second harmonic (SH) conversion efficiency has the room to be further improved and that the new nonlinear crystal is very suited to generate the high efficiency deep ultraviolet laser radiation below 266 nm.

Modulation instabilities in the randomly birefringent two-mode optical fibers (RB-TMFs) are analyzed in detail by accounting the effects of the differential mode group delay (DMGD) and group velocity dispersion (GVD) ratio between the two modes, both of which are absent in the randomly birefringent single-mode optical fibers (RB-SMFs). New MI characteristics are found in both normal and anomalous dispersion regimes. For the normal dispersion, without DMGD, no MI exists. With DMGD, a completely new MI band is generated as long as the total power is smaller than a critical total power value, named by P_{cr}, which increases significantly with the increment of DMGD, and reduces dramatically as GVD ratio and power ratio between the two modes increases. For the anomalous dispersion, there is one MI band without DMGD. In the presence of DMGD, the MI gain is reduced generally. On the other hand, there also exists a critical total power (P_{cr}), which increases (decreases) distinctly with the increment of DMGD (GVD ratio of the two modes) but varies complicatedly with the power ratio between the two modes. Two MI bands are present for total power smaller than P_{cr}, and the dominant band can be switched between the low and high frequency bands by adjusting the power ratio between the two modes. The MI analysis in this paper is verified by numerical simulation.

The product of the cutoff frequency and breakdown voltage (f_{T}×BV_{CEO}) is an important figure of merit (FOM) to characterize overall performance of heterojunction bipolar transistor (HBT). In this paper, an approach to introducing a thin N^{+}-buried layer into N collector region in silicon-on-insulator (SOI) SiGe HBT to simultaneously improve the FOM of f_{T}×BV_{CEO} and thermal stability is presented by using two-dimensional (2D) numerical simulation through SILVACO device simulator. Firstly, in order to show some disadvantages of the introduction of SOI structure, the effects of SOI insulation layer thickness (T_{BOX}) on f_{T}, BV_{CEO}, and the FOM of f_{T}×BV_{CEO} are presented. The introduction of SOI structure remarkably reduces the electron concentration in collector region near SOI substrate insulation layer, obviously reduces f_{T}, slightly increases BV_{CEO} to some extent, but ultimately degrades the FOM of f_{T}×BV_{CEO}. Although the f_{T}, BV_{CEO}, and the FOM of f_{T}×BV_{CEO} can be improved by increasing SOI insulator SiO_{2} layer thickness T_{BOX} in SOI structure, the device temperature and collector current are increased due to lower thermal conductivity of SiO_{2} layer, as a result, the self-heating effect of the device is enhanced, and the thermal stability of the device is degraded. Secondly, in order to alleviate the foregoing problem of low electron concentration in collector region near SOI insulation layer and the thermal stability resulting from thick T_{BOX}, a thin N^{+}-buried layer is introduced into collector region to not only improve the FOM of f_{T}×BV_{CEO}, but also weaken the self-heating effect of the device, thus improving the thermal stability of the device. Furthermore, the effect of the location of the thin N^{+}-buried layer in collector region is investigated in detail. The result show that the FOM of f_{T}×BV_{CEO} is improved and the device temperature decreases as the N^{+}-buried layer shifts toward SOI substrate insulation layer. The approach to introducing a thin N^{+}-buried layer into collector region provides an effective method to improve SOI SiGe HBT overall performance.

Reconstructing the distribution of optical parameters in the participating medium based on the frequency-domain radiative transfer equation (FD-RTE) to probe the internal structure of the medium is investigated in the present work. The forward model of FD-RTE is solved via the finite volume method (FVM). The regularization term formatted by the generalized Gaussian Markov random field model is used in the objective function to overcome the ill-posed nature of the inverse problem. The multi-start conjugate gradient (MCG) method is employed to search the minimum of the objective function and increase the efficiency of convergence. A modified adjoint differentiation technique using the collimated radiative intensity is developed to calculate the gradient of the objective function with respect to the optical parameters. All simulation results show that the proposed reconstruction algorithm based on FD-RTE can obtain the accurate distributions of absorption and scattering coefficients. The reconstructed images of the scattering coefficient have less errors than those of the absorption coefficient, which indicates the former are more suitable to probing the inner structure.

In this paper, we provide a new kind of operator formula for anti-normally and normally ordering bosonic-operator functions in quantum optics, which can help us arrange a bosonic-operator function f(λ+ν) in its anti-normal and normal ordering conveniently. Furthermore, mutual transformation formulas between anti-normal ordering and normal ordering, which have good universality, are derived too. Based on these operator formulas, some new differential relations and some useful mathematical integral formulas are easily derived without really performing these integrations.

In quantum metrology we usually extract information from the reduced probe system but ignore the information lost inevitably into the environment. However, K. Mølmer[Phys. Rev. Lett.114, 040401 (2015)] showed that the information lost into the environment has an important effect on improving the successful probability of quantum process discrimination. Here we reconsider the model of a driven atom coupled to an environment and distinguish which of two candidate Hamiltonians governs the dynamics of the whole system. We mainly discuss two measurement methods, one of which obtains only the information from the reduced atom state and the other obtains the information from both the atom and its environment. Interestingly, for the two methods the optimal initial states of the atom, used to improve the successful probability of the process discrimination, are different. By comparing the two methods we find that the partial information from the environment is very useful for the discriminations.

We analyze the localization of quantum walks on a one-dimensional finite graph using vector-distance. We first vectorize the probability distribution of a quantum walker in each node. Then we compute out the probability distribution vectors of quantum walks in infinite and finite graphs in the presence of static disorder respectively, and get the distance between these two vectors. We find that when the steps taken are small and the boundary condition is tight, the localization between the infinite and finite cases is greatly different. However, the difference is negligible when the steps taken are large or the boundary condition is loose. It means quantum walks on a one-dimensional finite graph may also suffer from localization in the presence of static disorder. Our approach and results can be generalized to analyze the localization of quantum walks in higher-dimensional cases.

Any unknown unitary operations conditioned on a control system can be deterministically performed if ancillary subspaces are available for the target systems[Zhou X Q, et al. 2011 Nat. Commun.2 413]. In this paper, we show that previous optical schemes may be extended to general hybrid systems if unknown operations are provided by optical instruments. Moreover, a probabilistic scheme is proposed when the unknown operation may be performed on the subspaces of ancillary high-dimensional systems. Furthermore, the unknown operations conditioned on the multi-control system may be reduced to the case with a control system using additional linear circuit complexity. The new schemes may be more flexible for different systems or hybrid systems.

In the preparations of superconducting qubits, circuit design is a vital process because the parameters and layout of the circuit not only determine the way we address the qubits, but also strongly affect the qubit coherence properties. One of the most important circuit parameters, which needs to be carefully designed, is the mutual inductance among different parts of a superconducting circuit. In this paper we demonstrate how to design a gap-tunable flux qubit by layout design and inductance extraction using a fast field solver FastHenry. The energy spectrum of the gap-tunable flux qubit shows that the measured parameters are close to the design values.

In this paper we investigate the phase transition and geometrothermodynamics of regular electrically charged black hole in nonlinear electrodynamics theory coupled to general relativity. We analyze the types of phase transition of the thermodynamic system by calculating its temperature, heat capacity, and free energy, etc. We find that there are second-order phase transitions from the heat capacity for a large value of S. In addition, employing the geometrothermodynamics, we obtain a Legendre invariance metric and find the relationship between the thermodynamical phase transition and the singularity of the curvature scalar in the regular black hole with the nonlinear electrodynamics.

In the microwave ^{199}Hg^{+} trapped-ion clock, the frequency instability degradation caused by the Dick effect is unavoidable because of the periodical interrogating field. In this paper, the general expression of the sensitivity function g(t) to the frequency fluctuation of the interrogating field with Nπ-pulse (N is odd) is derived. According to the measured phase noise of the 40.5-GHz microwave synthesizer, the Dick-effect limited Allan deviation of our ^{199}Hg^{+} trapped-ion clock is worked out. The results indicate that the limited Allan deviations are about 1.75×10^{-13}/√τ and 3.03×10^{-13}/√τ respectively in the linear ion trap and in the two-segment extended linear ion trap under our present experimental parameters.

In this paper, a novel design procedure is proposed for synthesizing high-capacity auto-associative memories based on complex-valued neural networks with real-imaginary-type activation functions and constant delays. Stability criteria dependent on external inputs of neural networks are derived. The designed networks can retrieve the stored patterns by external inputs rather than initial conditions. The derivation can memorize the desired patterns with lower-dimensional neural networks than real-valued neural networks, and eliminate spurious equilibria of complex-valued neural networks. One numerical example is provided to show the effectiveness and superiority of the presented results.

The high-pressure polymorphs and structural transformation of Sn were experimentally investigated using angle-dispersive synchrotron x-ray diffraction up to 108.9 GPa. The results show that at least at 12.8 GPa β-Sn→bct structure transformation was completed and no two-phase coexistence was found. By using a long-wavelength x-ray, we resolved the diffraction peaks splitting and discovered the formation of a new distorted orthorhombic structure bco from the bct structure at 31.8 GPa. The variation of the lattice parameters and their ratios with pressure further validate the observation of the bco polymorph. The bcc structure appears at 40.9 GPa and coexists with the bco phase throughout a wide pressure range of 40.9 GPa-73.1 GPa. Above 73.1 GPa, only the bcc polymorph is observed. The systematically experimental investigation confirms the phase transition sequence of Sn as β-Sn→bct→bco→bco+bcc→bcc upon compression to 108.9 GPa at room temperature.

Using the first-principles plane-wave calculations within density functional theory, the perfect bi-layer and monolayer terminated WZ-CIS (100)/WZ-CdS (100) interfaces are investigated. After relaxation the atomic positions and the bond lengths change slightly on the two interfaces. The WZ-CIS/WZ-CdS interfaces can exist stably, when the interface bonding energies are -0.481 J/m^{2} (bi-layer terminated interface) and -0.677 J/m^{2} (monolayer terminated interface). Via analysis of the density of states, difference charge density and Bader charges, no interface state is found near the Fermi level. The stronger adhesion of the monolayer terminated interface is attributed to more electron transformations and orbital hybridizations, promoting stable interfacial bonds between atoms than those on a bi-layer terminated interface.

At the Douglas-Kroll-Hess (DKH) level, the B3PW91 functional along with the all-electron relativistic basis sets of valence triple and quadruple zeta qualities are used to determine the structure, stability, and electronic properties of the small silver clusters (Ag_{n}, n≤7). The results presented in this study are in good agreement with the experimental data and theoretical values obtained at a higher level of theory from the literature. Static polarizability and hyperpolarizability are also reported. It is verified that the mean dipole polarizability per atom exhibits an odd-even oscillation and that the polarizability anisotropy is directly related to the cluster shape. In this article, the first study of hyperpolarizabilities of small silver clusters is presented. Except for the monomer, the second hyperpolarizabilities of the silver clusters are significantly larger than those of the copper clusters.

The pseudopotential method has been used to investigate the structural, electronic and magnetic properties of La_{1-x}Eu_{x}GaO_{3} (x=0, 0.25, 0.5, 0.75, and 1) within the scheme of generalized gradient approximation. The spin-polarized calculations demonstrate that the ground state is an antiferromagnetic insulator for x≤0.5, while it is ferromagnetic half-metal at x>0.5. The substitutions of magnetic Eu ions for non-magnetic La ions produce and strength spin polarization, which forcefully urges the system from the insulator to the half metal. Meanwhile, Eu doping strengthens a stoner mechanism for ferromagnetism of La_{1-x}Eu_{x}GaO_{3} (x=0.75 and 1), which may lead to a rapid increasing in the total magnetic moment and therefore, antiferromagnetic-ferromagnetic transition happens.

The N(^{2}D)+HD (v=0, j=0) reaction has been studied by a quantum time-dependent wave packet approach with a second-order split operator on the potential energy surface of Li et al. (Li Y, Yuan J, Chen M, Ma F and Sun M J. Comput. Chem. 34 1686). The rovibrationally resolved reaction probability, vibrationally integral cross section, and differential cross section of the NH+D and ND+H channel are investigated at the state-to-state level of theory. The experimental data of the thermal rate constant of two output channels is very scare, but the sum of the two output channels is in excellent agreement with the experimental data which was reported by Umemoto et al. It may imply that the thermal rate constants of the two output channels are accurate and reliable.

The cold atom gravimeter offers the prospect of a new generation of inertial sensors for field applications. We accomplish a mobile atom gravimeter. With the compact and stable system, a sensitivity of 1.4×10^{-7} g·Hz^{-1/2} is achieved. Moreover, a continuous gravity monitoring of 80 h is carried out. However, the harsh outdoor environment is a big challenge for the atom gravimeter when it is for field applications. In this paper, we present the preliminary investigation of the thermal adaptability for our mobile cold atom gravimeter. Here, we focus on the influence of the air temperature on the performance of the atom gravimeter. The responses to different factors (such as laser power, fiber coupling efficiency, etc.) are evaluated when there is a great temperature shift of 10℃. The result is that the performances of all the factors deteriorate to different extent, nevertheless, they can easily recover as the temperature comes back. Finally, we conclude that the variation of air temperature induces the increase of noise and the system error of the atom gravimeter as well, while the process is reversible with the recovery of the temperature.

In order to seek a transition metal cluster with high ability to adsorb CO molecule, the author performs a density function theory calculation on COSc_{n} (n=2-8, 13) clusters. The results demonstrate that COSc_{n} (n=2-8, 13) clusters have the large adsorption energies of which the values are over 3.6 eV, and the elongations of C-O bond length exceed 20% in most calculated sizes. Adsorbing CO contributes to the improvement of the chemical activity, but reduces the magnetic moment of corresponding Sc_{n} cluster.

In this paper, we describe a modal expansion approach for the analysis of the selective generation of ultrasonic Lamb waves by electromagnetic acoustic transducers (EMATs). With the modal expansion approach for waveguide excitation, an analytical expression of the Lamb wave's mode expansion coefficient is deduced, which is related to the driving frequency and the geometrical parameters of the EMAT's meander coil, and lays a theoretical foundation for exactly analyzing the selective generation of Lamb waves with EMATs. The influences of the driving frequency on the mode expansion coefficient of ultrasonic Lamb waves are analyzed when the EMAT's geometrical parameters are given. The numerical simulations and experimental examinations show that the ultrasonic Lamb wave modes can be effectively regulated (strengthened or restrained) by choosing an appropriate driving frequency of EMAT, with the geometrical parameters given. This result provides a theoretical and experimental basis for selectively generating a single and pure Lamb wave mode with EMATs.

In this paper, acoustic scattering from the system comprised of a cloaked object and the multilayer cloak with only one single pair of isotropic media is analyzed with a recursive numerical method. The designed acoustic parameters of the isotropic cloak media are assumed to be single-negative, and the resulting cloak can reduce acoustic scattering from an acoustic sensor while allowing it to receive external information. Several factors that may influence the performance of the cloak, including the number of layers and the acoustic dissipation of the medium are fully analyzed. Furthermore, the possibility of achieving acoustic invisibility with positive acoustic parameters is proposed by searching the optimum value in the parameter space and minimizing the scattering cross-section.

Classical reciprocity relations have wide applications in acoustics, from field representation to generalized optical theorem. In this paper we introduce our recent results on the applications and generalization of classical Rayleigh reciprocity relation:higher derivative reciprocity relations as a generalization of the classical one and a theoretical proof on the Green's function retrieval from volume noises.

In this paper, we investigate the diffraction tomography for quantitative imaging damages of partly through-thickness holes with various shapes in isotropic plates by using converted and non-converted scattered Lamb waves generated numerically. Finite element simulations are carried out to provide the scattered wave data. The validity of the finite element model is confirmed by the comparison of scattering directivity pattern (SDP) of circle blind hole damage between the finite element simulations and the analytical results. The imaging method is based on a theoretical relation between the one-dimensional (1D) Fourier transform of the scattered projection and two-dimensional (2D) spatial Fourier transform of the scattering object. A quantitative image of the damage is obtained by carrying out the 2D inverse Fourier transform of the scattering object. The proposed approach employs a circle transducer network containing forward and backward projections, which lead to so-called transmission mode (TMDT) and reflection mode diffraction tomography (RMDT), respectively. The reconstructed results of the two projections for a non-converted S0 scattered mode are investigated to illuminate the influence of the scattering field data. The results show that Lamb wave diffraction tomography using the combination of TMDT and RMDT improves the imaging effect compared with by using only the TMDT or RMDT. The scattered data of the converted A0 mode are also used to assess the performance of the diffraction tomography method. It is found that the circle and elliptical shaped damages can still be reasonably identified from the reconstructed images while the reconstructed results of other complex shaped damages like crisscross rectangles and racecourse are relatively poor.

Anisotropic metamaterial with only one component of the mass density tensor near zero (ADNZ) is proposed to control the sound wave propagation. We find that such an anisotropic metamaterial can be used to realize perfect bending waveguides. According to a coordinate transformation, the surface waves on the input and output interfaces of the ADNZ metamaterial induces the sound energy flow to be redistributed and match smoothly with the propagating modes inside the metamaterial waveguide. According to the theory of bending waveguide, we realize the“T”-type sound shunting and convergence, as well as acoustic channel selection by embedding small-sized defects. Numerical calculations are performed to confirm the above effects.

International and domestic research progress in theory and experiment and applications of the air-to-water sound transmission are presented in this paper. Four classical numerical methods of calculating the underwater sound field generated by an airborne source, i.e., the ray theory, the wave solution, the normal-mode theory and the wavenumber integration approach, are introduced. Effects of two special conditions, i.e., the moving airborne source or medium and the rough air-water interface, on the air-to-water sound transmission are reviewed. In experimental studies, the depth and range distributions of the underwater sound field created by different kinds of airborne sources in near-field and far-field, the longitudinal horizontal correlation of underwater sound field and application methods for inverse problems are reviewed.

In this paper, we extensively study the higher-order harmonic generation of the general limited diffraction m-th-order Bessel beam. The analysis is based on successive approximations of the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation. Asymptotic expansions are presented for higher-order harmonic Bessel beams in near and far fields. The validity of asymptotic approximation is also analyzed. The higher-order harmonic of the Bessel beam with the lowest zero-order is taken as a special example.

Modelling and biomedical applications of ultrasound contrast agent (UCA) microbubbles have attracted a great deal of attention. In this review, we summarize a series of researches done in our group, including (i) the development of an all-in-one solution of characterizing coated bubble parameters based on the light scattering technique and flow cytometry; (ii) a novel bubble dynamic model that takes into consideration both nonlinear shell elasticity and viscosity to eliminate the dependences of bubble shell parameters on bubble size; (iii) the evaluation of UCA inertial cavitation threshold and its relationship with shell parameters; and (iv) the investigations of transfection efficiency and the reduction of cytotoxicity in gene delivery facilitated by UCAs excited by ultrasound exposures.

This paper presents a three-dimensional (3D) coupled-mode model using the direct-global-matrix technique as well as Fourier synthesis. This model is a full wave, two-way three-dimensional model, and is therefore capable of providing accurate acoustic field solutions. Because the problem of sound propagation excited by a point source in an ideal wedge with perfectly reflecting boundaries is one of a few three-dimensional problems with analytical solutions, the ideal wedge problem is chosen in this work to validate the presented three-dimensional model. Numerical results show that the field results by analytical solutions and those by the presented model are in excellent agreement, indicating that the presented model can serve as a benchmark model for three-dimensional sound propagation problems involving a planar two-dimensional geometry as well as a point source.

The spatial correlations of acoustic field have important implications for underwater target detection and other applications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterborne modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth.

Sound multipath propagation is very important for target localization and identification in different acoustical zones of deep water. In order to distinguish the multipath characteristics in deep water, the Northwest Pacific Acoustic Experiment was conducted in 2015. A low-frequency horizontal line array towed at the depth of around 150 m on a receiving ship was used to receive the noise radiated by the source ship. During this experiment, a bearing-splitting phenomenon in the direct zone was observed through conventional beamforming of the horizontal line array within the frequency band 160 Hz-360 Hz. In this paper, this phenomenon is explained based on ray theory. In principle, the received signal in the direct zone of deep water arrives from two general paths including a direct one and bottom bounced one, which vary considerably in arrival angles. The split bearings correspond to the contributions of these two paths. The bearing-splitting phenomenon is demonstrated by numerical simulations of the bearing-time records and experimental results, and they are well consistent with each other. Then a near-surface source ranging approach based on the arrival angles of direct path and bottom bounced path in the direct zone is presented as an application of bearing splitting and is verified by experimental results. Finally, the applicability of the proposed ranging approach for an underwater source within several hundred meters in depth in the direct zone is also analyzed and demonstrated by simulations.

Acoustic scattering from a rough sea bottom is recognized as a main source of reverberation. In this study, scattering properties from a layered bottom were exploited based on the finite element model. The scattering strength and loss from the layered rough seabed were investigated by ensembling the realizations of rough interface. They were found to be dependent on the thickness of sediment, and interference was significant in the case of thin sediment. Through verification of the finite element model, the scattering loss could be evaluated using the Eckart model with a proper sound speed in the thick sediment. The multiple scattering effect on the sound field was also exploited. It revealed that the effect depended strongly on the bottom type.

The controls of the pass-bands in an asymmetric acoustic transmission system are investigated numerically and experimentally, and the system consists of a periodical rectangular grating and two uniform brass plates in water. We reveal that the pass-band of the asymmetric acoustic transmission is closely related to the grating period, but is affected slightly by the brass plate thickness. Moreover, the transmittance can be improved by adjusting the grating period and other structural parameters simultaneously. The control method of the system has the advantages of wider frequency range and simple operation, which has great potential applications in ultrasonic devices.

Transdermal drug delivery (TDD) can effectively bypass the first-pass effect. In this paper, ultrasound-facilitated TDD on fresh porcine skin was studied under various acoustic parameters, including frequency, amplitude, and exposure time. The delivery of yellow-green fluorescent nanoparticles and high molecular weight hyaluronic acid (HA) in the skin samples was observed by laser confocal microscopy and ultraviolet spectrometry, respectively. The results showed that, with the application of ultrasound exposures, the permeability of the skin to these markers (e.g., their penetration depth and concentration) could be raised above its passive diffusion permeability. Moreover, ultrasound-facilitated TDD was also tested with/without the presence of ultrasound contrast agents (UCAs). When the ultrasound was applied without UCAs, low ultrasound frequency will give a better drug delivery effect than high frequency, but the penetration depth was less likely to exceed 200 μm. However, with the help of the ultrasound-induced microbubble cavitation effect, both the penetration depth and concentration in the skin were significantly enhanced even more. The best ultrasound-facilitated TDD could be achieved with a drug penetration depth of over 600 μm, and the penetration concentrations of fluorescent nanoparticles and HA increased up to about 4-5 folds. In order to get better understanding of ultrasound-facilitated TDD, scanning electron microscopy was used to examine the surface morphology of skin samples, which showed that the skin structure changed greatly under the treatment of ultrasound and UCA. The present work suggests that, for TDD applications (e.g., nanoparticle drug carriers, transdermal patches and cosmetics), protocols and methods presented in this paper are potentially useful.

Tool waves, also named collar waves, propagating along the drill collars in acoustic logging while drilling (ALWD), strongly interfere with the needed P- and S-waves of a penetrated formation, which is a key issue in picking up formation P- and S-wave velocities. Previous studies on physical insulation for the collar waves designed on the collar between the source and the receiver sections did not bring to a satisfactory solution. In this paper, we investigate the propagation features of collar waves in different models. It is confirmed that there exists an indirect collar wave in the synthetic full waves due to the coupling between the drill collar and the borehole, even there is a perfect isolator between the source and the receiver. The direct collar waves propagating all along the tool and the indirect ones produced by echoes from the borehole wall are summarized as the generalized collar waves. Further analyses show that the indirect collar waves could be relatively strong in the full wave data. This is why the collar waves cannot be eliminated with satisfactory effect in many cases by designing the physical isolators carved on the tool.

Ocean noise recorded during a typhoon can be used to monitor the typhoon and investigate the mechanism of the wind-generated noise. An analytical expression for the typhoon-generated noise intensity is derived as a function of wind speed. A“bi-peak”structure was observed in an experiment during which typhoon-generated noise was recorded. Wind speed dependence and frequency dependence were also observed in the frequency range of 100 Hz-1000 Hz. The model/data comparison shows that results of the present model of 500 Hz and 1000 Hz are in reasonable agreement with the experimental data, and the typhoon-generated noise intensity has a dependence on frequency and a power-law dependence on wind speed.

An acoustic vector sensor can measure the components of particle velocity and the acoustic pressure at the same point simultaneously, which provides a larger array gain against the ambient noise and a higher angular resolution than the omnidirectional pressure sensor. This paper presents an experimental study of array gain for a conformal acoustic vector sensor array in a practical environment. First, the manifold vector is calculated using the real measured data so that the effects of array mismatches can be minimized. Second, an optimal beamformer with a specific spatial response on the basis of the stable directivity of the ambient noise is designed, which can effectively suppress the ambient noise. Experimental results show that this beamformer for the conformal acoustic vector sensor array provides good signal-to-noise ratio enhancement and is more advantageous than the delay-and-sum and minimum variance distortionless response beamformers.

Parabolic equation (PE) method is an efficient tool for modelling underwater sound propagation, particularly for problems involving range dependence. Since the PE method was first introduced into the field of underwater acoustics, it has been about 40 years, during which contributions to extending its capability has been continuously made. The most recent review paper surveyed the contributions made before 1999. In the period of 2000-2016, the development of PE method basically focuses on seismo-acoustic problems, three-dimensional problems, and realistic applications. In this paper, a review covering the contribution from 2000 to 2016 is given, and what should be done in future work is also discussed.

The filamentation instability was observed in the interaction of two counter-streaming laser ablated plasma flows, which were supersonic, collisionless, and also closely relevant to astrophysical conditions. The plasma flows were created by irradiating a pair of oppositely standing plastic (CH) foils with 1ns-pulsed laser beams of total energy of 1.7 kJ in two laser spots. With characteristics diagnosed in experiments, the calculated features of Weibel-type filaments are in good agreement with measurements.

A microscale vortex laser is a new type of coherent light source with small footprint that can directly generate vector vortex beams. However, a microscale laser with controlled topological charge, which is crucial for virtually any of its application, is still unrevealed. Here we present a microscale vortex laser with controlled topological charge. The vortex laser eigenmode was synthesized in a metamaterial engineered non-Hermitian micro-ring cavity system at exceptional point. We also show that the vortex laser cavity can operate at exceptional point stably to lase under optical pumping. The microscale vortex laser with controlled topological charge can serve as a unique and general building block for next-generation photonic integrated circuits and coherent vortex beam sources. The method we used here can be employed to generate lasing eigenmode with other complex functionalities.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

In order to enhance the power capacity, an improved Ku-band magnetically insulated transmission line oscillator (MILO) with overmoded slow-wave-structure (SWS) is proposed and investigated numerically and experimentally. The analysis of the dispersion relationship and the resonant curve of the cold test indicate that the device can operate at the near π mode of the TM01 mode, which is useful for mode selection and control. In the particle simulation, the improved Ku-band MILO generates a microwave with a power of 1.5 GW and a frequency of 12.3 GHz under an input voltage of 480 kV and input current of 42 kA. Finally, experimental investigation of the improved Ku-band MILO is carried out. A high-power microwave (HPM) with an average power of 800 MW, a frequency of 12.35 GHz, and pulse width of 35 ns is generated under a diode voltage of 500 kV and beam current of 43 kA. The consistency between the experimental and simulated far-field radiation pattern confirms that the operating mode of the improved Ku-band MILO is well controlled in π mode of the TM01 mode.

Characteristics of a direct current (DC) discharge in atmospheric pressure helium are numerically investigated based on a one-dimensional fluid model. The results indicate that the discharge does not reach its steady state till it takes a period of time. Moreover, the required time increases and the current density of the steady state decreases with increasing the gap width. Through analyzing the spatial distributions of the electron density, the ion density and the electric field at different discharge moments, it is found that the DC discharge starts with a Townsend regime, then transits to a glow regime. In addition, the discharge operates in a normal glow mode or an abnormal glow one under different parameters, such as the gap width, the ballast resistors, and the secondary electron emission coefficients, judged by its voltage-current characteristics.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

The effects in electrostatic models of chevron surface-stabilized ferroelectric liquid crystals are investigated through numerical modeling. To study smectic C^{*} director distribution within the cell, we consider two nonlinear approaches:the chevron interface does not interplay with the electric field; the electric field interplays with the chevron interface. The obtained results of the director field distribution are compared with the earlier linearized studies. We find that whether or not the electric field interplays with the chevron interface, the electro-optic response requires a generalized approach for its description. The threshold electric field, which is necessary for switching between two stable director states in the chevron cell is evaluated. This study suggests that, in many cases of practical interest, electro-optic response to the electric field and the threshold electric field can be precisely estimated. We argue that, beside being numerically efficient, our approach provides a convenient and a novel standpoint for looking at the electro-optic response problem.

M-type Al-doped strontium ferrite powders (SrAl_{x}Fe_{2n-x}O_{19}, n=5.9) with nominal Al content of x=0-2.0 are prepared by traditional ceramic technology. The phase identification of the powders, performed using x-ray diffraction, shows the presence of purity hexaferrite structure and absence of any secondary phase. The lattice parameters decrease with increasing x. The average grain size of the powders is about 300 nm-400 nm at Al^{3+} ion content x=0-2.0. The room-temperature hysteresis loops of the powders, measured by using vibrating sample magnetometer, show that the specific saturation magnetization (σ_{s}) value continuously decreases while the coercivity (H_{c}) value increases with increasing x, and H_{c} reaches to 9759 Oe (1 Oe=79.5775 A/m) at x=2.0. According to the law of approach saturation, H_{c} value increases with increasing Al^{3+} ion content, which is attributed to the saturation magnetization (M_{s}) decreasing more rapidly than the magnetic anisotropy constant (K_{1}) obtained by numerical fitting of the hysteresis loops. The distribution of Al^{3+} ions in the hexaferrite structure of SrAl_{x}Fe_{2n-x}O_{19} is investigated by using ^{57}Co Mössbauer spectroscopy. The effect of Al^{3+} doping on static magnetic properties contributes to the improvement of magnetic anisotropy field.

Since knowledge of the structure and elastic properties of Ta at high pressures is critical for addressing the recent controversies regarding the high-pressure stable phase and elastic properties, we perform a systematical study on the high-pressure structure and elastic properties of the cubic Ta by using the first-principles method. Results show that the initial body-centered cubic phase of Ta remains stable even up to 500 GPa and the high-pressure elastic properties are excellently consistent with the available experimental results. Besides, the high-pressure sound velocities of the single- and poly-crystals Ta are also calculated based on the elastic constants, and the predications exhibit good agreement with the existing experimental data.

We report a lateral Ge-on-Si ridge waveguide light emitting diode (LED) grown by ultrahigh vacuum chemical vapor deposition (UHV-CVD). Direct-bandgap electroluminescence (EL) of Ge waveguide under continuous current is observed at room temperature. The heat-enhancing luminescence and thermal radiation-induced superlinear increase of edge output optical power are found. The spontaneous emission and thermal radiation based on the generalized Planck radiation law are calculated and fit very well to the experimental results. The Ge waveguides with different lengths are studied and the shorter one shows stronger EL intensity.

Using molecular dynamics simulation method, the plastic deformation mechanism of Fe nanowires is studied by applying uniaxial tension along the[110] direction. The simulation result shows that the bcc-to-hcp martensitic phase transformation mechanism controls the plastic deformation of the nanowires at high strain rate or low temperature; however, the plastic deformation mechanism will transform into a dislocation nucleation mechanism at low strain rate and higher temperature. Furthermore, the underlying cause of why the bcc-to-hcp martensitic phase transition mechanism is related to high strain rate and low temperature is also carefully studied. Based on the present study, a strain rate-temperature plastic deformation map for Fe nanowires has been proposed.

By using a mean-field approximation which describes the coupled oscillations of condensate and noncondensate atoms in the collisionless regime, Landau damping in a dilute dipolar Bose-Fermi mixture in the BEC limit where Fermi superfluid is treated as tightly bounded molecules, is investigated. In the case of a uniform quasi-two-dimensional (2D) case, the results for the Landau damping due to the Bose-Fermi interaction are obtained at low and high temperatures. It is shown that at low temperatures, the Landau damping rate is exponentially suppressed. By increasing the strength of dipolar interaction, and the energy of boson quasiparticles, Landau damping is suppressed over a broader temperature range.

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

Cd_{1-x}Zn_{x}S/Cu_{2}ZnSnS_{4} (CZTS)-based thin film solar cells usually use CdS as a buffer layer, but due to its smaller band gap (2.4 eV), CdS film has been replaced with higher band gap materials. The cadmium zinc sulfide (CdZnS) ternary compound has a higher band gap than other compounds, which leads to a decrease in window absorption loss. In this paper, the band offsets at Cd_{1-x}Zn_{x}S/Cu_{2}ZnSnS_{4} (CZTS) heterointerface are calculated by the first-principles, density-functional and pseudopotential method. The band offsets at Cd_{1-x}Zn_{x}S/CZTS heterointerface are tuned by controlling the composition of Zn in Cd_{1-x}Zn_{x}S alloy, the calculated valence band offsets are small, which is consistent with the common-anion rule. The favorable heterointerface of type-I with a moderate barrier height (<0.3 eV) can be obtained by controlling the composition of Zn in Cd_{1-x}Zn_{x}S alloy between 0.25 and 0.375.

Oxygen vacancies (OVs) play a critical role in the physical properties and applications of titanium dioxide nanostructures, which are widely used in electrochemistry and photo catalysis nowadays. In this work, OVs were artificially introduced in the surface of a pure TiO_{2} single crystal by pulsed laser irradiation. Raman spectra showed that the intensity of E_{g} mode was enhanced. Theoretical calculations disclose that this was caused by the strong coupling effect between the phonon vibration and plasmon induced by the OVs-related surface deformation, and good agreement was achieved between the experiments and theory.

It is studied in this paper that the electrical characteristics of the interface between SiO_{y}N_{x}/SiN_{x} stack and silicon wafer affect silicon surface passivation. The effects of precursor flow ratio and deposition temperature of the SiO_{y}N_{x} layer on interface parameters, such as interface state density D_{it} and fixed charge Q_{f}, and the surface passivation quality of silicon are observed. Capacitance-voltage measurements reveal that inserting a thin SiO_{y}N_{x} layer between the SiN_{x} and the silicon wafer can suppress Q_{f} in the film and D_{it} at the interface. The positive Q_{f} and D_{it} and a high surface recombination velocity in stacks are observed to increase with the introduced oxygen and minimal hydrogen in the SiO_{y}N_{x} film increasing. Prepared by deposition at a low temperature and a low ratio of N_{2}O/SiH_{4} flow rate, the SiO_{y}N_{x}/SiN_{x} stacks result in a low effective surface recombination velocity (S_{eff}) of 6 cm/s on a p-type 1 Ω·cm-5 Ω·cm FZ silicon wafer. The positive relationship between S_{eff} and D_{it} suggests that the saturation of the interface defect is the main passivation mechanism although the field-effect passivation provided by the fixed charges also make a contribution to it.

The influence of hydrostatic pressure, temperature, and impurity on the electronic and optical properties of spherical core/shell/well/shell (CSWS) nanostructure with parabolic confinement potential is investigated theoretically. The energy levels and wave functions of the structure are calculated by using shooting method within the effective-mass approximation. The numerical results show that the ground state donor binding energy as a function layer thickness very sensitively depends on the magnitude of pressure and temperature. Also, we investigate the probability distributions to understand clearly electronic properties. The obtained results show that the existence of the pressure and temperature has great influence on the electronic and optical properties.

In this study, the unipolar resistive switching (URS) and bipolar resistive switching (BRS) are demonstrated to be coexistent in the Ag/ZnO/Pt memory device, and both modes are observed to strongly depend on the polarity of forming voltage. The mechanisms of the URS and BRS behaviors could be attributed to the electric-field-induced migration of oxygen vacancies (V_{O}) and metal-Ag conducting filaments (CFs) respectively, which are confirmed by investigating the temperature dependences of low resistance states in both modes. Furthermore, we compare the resistive switching (RS) characteristics (e.g., forming and switching voltages, reset current and resistance states) between these two modes based on V_{O}- and Ag-CFs. The BRS mode shows better switching uniformity and lower power than the URS mode. Both of these modes exhibit good RS performances, including good retention, reliable cycling and high-speed switching. The result indicates that the coexistence of URS and BRS behaviors in a single device has great potential applications in future nonvolatile multi-level memory.

A novel ultralow turnoff loss dual-gate silicon-on-insulator (SOI) lateral insulated gate bipolar transistor (LIGBT) is proposed. The proposed SOI LIGBT features an extra trench gate inserted between the p-well and n-drift, and an n-type carrier stored (CS) layer beneath the p-well. In the on-state, the extra trench gate acts as a barrier, which increases the carrier density at the cathode side of n-drift region, resulting in a decrease of the on-state voltage drop (V_{on}). In the off-state, due to the uniform carrier distribution and the assisted depletion effect induced by the extra trench gate, large number of carriers can be removed at the initial turnoff process, contributing to a low turnoff loss (E_{off}). Moreover, owing to the dual-gate field plates and CS layer, the carrier density beneath the p-well can greatly increase, which further improves the tradeoff between E_{off} and V_{on}. Simulation results show that E_{off} of the proposed SOI LIGBT can decrease by 77% compared with the conventional trench gate SOI LIGBT at the same V_{on} of 1.1 V.

Shear-mode piezoelectric materials have been widely used to shunt the damping of vibrations where utilizing surface or interface shear stresses. The thick-shear mode (TSM) elastic constant and the mechanical loss factor can change correspondingly when piezoelectric materials are shunted to different electrical circuits. This phenomenon makes it possible to control the performance of a shear-mode piezoelectric damping system through designing the shunt circuit. However, due to the difficulties in directly measuring the TSM elastic constant and the mechanical loss factor of piezoelectric materials, the relationships between those parameters and the shunt circuits have rarely been investigated. In this paper, a coupling TSM electro-mechanical resonant system is proposed to indirectly measure the variations of the TSM elastic constant and the mechanical loss factor of piezoelectric materials. The main idea is to transform the variations of the TSM elastic constant and the mechanical loss factor into the changes of the easily observed resonant frequency and electrical quality factor of the coupling electro-mechanical resonator. Based on this model, the formular relationships are set up theoretically with Mason equivalent circuit method and they are validated with finite element (FE) analyses. Finally, a prototype of the coupling electro-mechanical resonator is fabricated with two shear-mode PZT5A plates to investigate the TSM elastic constants and the mechanical loss factors of different circuit-shunted cases of the piezoelectric plate. Both the resonant frequency shifts and the bandwidth changes observed in experiments are in good consistence with the theoretical and FE analyses under the same shunt conditions. The proposed coupling resonator and the obtained relationships are validated with but not limited to PZT5A.

To more in depth understand the doping effects of oxygen on SiGe alloys, both the micro-structure and properties of O-doped SiGe (including:bulk, (001) surface, and (110) surface) are calculated by DFT+U method in the present work. The calculated results are as follows. (i) The (110) surface is the main exposing surface of SiGe, in which O impurity prefers to occupy the surface vacancy sites. (ii) For O interstitial doping on SiGe (110) surface, the existences of energy states caused by O doping in the band gap not only enhance the infrared light absorption, but also improve the behaviors of photo-generated carriers. (iii) The finding about decreased surface work function of O-doped SiGe (110) surface can confirm previous experimental observations. (iv) In all cases, O doing mainly induces the electronic structures near the band gap to vary, but is not directly involved in these variations. Therefore, these findings in the present work not only can provide further explanation and analysis for the corresponding underlying mechanism for some of the experimental findings reported in the literature, but also conduce to the development of μc-SiGe-based solar cells in the future.

The magnetic properties and magnetocaloric effects (MCE) of HoNiGa compound are investigated systematically. The HoNiGa exhibits a weak antiferromagnetic (AFM) ground state below the Ńeel temperature T_{N} of 10 K, and the AFM ordering could be converted into ferromagnetic (FM) ordering by external magnetic field. Moreover, the field-induced FM phase exhibits a high saturation magnetic moment and a large change of magnetization around the transition temperature, which then result in a large MCE. A large -ΔS_{M} of 22.0 J/kg K and a high RC value of 279 J/kg without magnetic hysteresis are obtained for a magnetic field change of 5 T, which are comparable to or even larger than those of some other magnetic refrigerant materials in the same temperature range. Besides, the μ_{0}H^{2/3} dependence of |ΔS_{M}^{pk}| well follows the linear fitting according to the mean-field approximation, suggesting the nature of second-order FM-PM magnetic transition under high magnetic fields. The large reversible MCE induced by metamagnetic transition suggests that HoNiGa compound could be a promising material for magnetic refrigeration in low temperature range.

A novel AlGaN/GaN high electron mobility transistor (HEMT) with a source-connected T-shaped field-plate (ST-FP HEMT) is proposed for the first time in this paper. The source-connected T-shaped field-plate (ST-FP) is composed of a source-connected field-plate (S-FP) and a trench metal. The physical intrinsic mechanisms of the ST-FP to improve the breakdown voltage and the FP efficiency and to modulate the distributions of channel electric field and potential are studied in detail by means of two-dimensional numerical simulations with Silvaco-ATLAS. A comparison to the HEMT and the HEMT with an S-FP (S-FP HEMT) shows that the ST-FP HEMT could achieve a broader and more uniform channel electric field distribution with the help of a trench metal, which could increase the breakdown voltage and the FP efficiency remarkably. In addition, the relationship between the structure of the ST-FP, the channel electric field, the breakdown voltage as well as the FP efficiency in ST-FP HEMT is analyzed. These results could open up a new effective method to fabricate high voltage power devices for the power electronic applications.

Although the spin-reorientation transition from out-of-plane to in-plane in Fe/Si film is widely reported, the tuning of in-plane spin orientation is not yet well developed. Here, we report the thickness-, temperature- and Cu-adsorption-induced in-plane spin-reorientation transition processes in Fe/Si (557) film, which can be attributed to the coexistence of two competing step-induced uniaxial magnetic anisotropies, i.e., surface magnetic anisotropy with magnetization easy axis perpendicular to the step and volume magnetic anisotropy with magnetization easy axis parallel to the step. For Fe film thickness smaller than 32 monolayer (ML), the magnitudes of two effects under various temperatures are extracted from the thickness dependence of uniaxial magnetic anisotropy. For Fe film thickness larger than 32 ML, the deviation of experimental results from fitting results is understood by the strain-relief-induced reduction of volume magnetic anisotropy. Additionally, the surface and volume magnetic anisotropies are both greatly reduced after covering Cu capping layer on Fe/Si (557) film while no significant influence of NaCl capping layer on step-induced magnetic anisotropies is observed. The experimental results reported here provide various practical methods for manipulating in-plane spin orientation of Fe/Si films and improve the understanding of step-induced magnetic anisotropies.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

This letter reports the nanoscale spatial phase modulation of GaAs growth in V-grooved trenches fabricated on a Si (001) substrate by metal-organic vapor-phase epitaxy. Two hexagonal GaAs regions with high density of stacking faults parallel to Si {111} surfaces are observed. A strain-relieved and defect-free cubic phase GaAs was achieved above these highly defective regions. High-resolution transmission electron microscopy and fast Fourier transforms analysis were performed to characterize these regions of GaAs/Si interface. We also discussed the strain relaxation mechanism and phase structure modulation of GaAs selectively grown on this artificially manipulated surface.

An ultrathin micro-split Jerusalem-cross metasurface is proposed in this paper, which can efficiently convert the linear polarization of electromagnetic (EM) wave into the circular polarization in ultra-wideband. By symmetrically employing two micro-splits on the horizontal arm (in the x direction) of the Jerusalem-cross structure, the bandwidth of the proposed device is significantly extended. Both simulated and experimental results show that the proposed metasurface is able to convert linearly polarized waves into circularly polarized waves in a frequency range from 12.4 GHz to 21 GHz, with an axis ratio better than 1 dB. The simulated results also show that such a broadband and high-performance are maintained over a wide range of incident angle. The presented polarization converter can be used in a number of areas, such as spectroscopy and wireless communications.

An investigation of low temperature hot corrosion is carried out on a spray-formed nickel-based superalloy FGH100 pre-coated with Na_{2}SO_{4}-NaCl at 700℃ for 100 h. Mass gain measurement, x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy are used to study the corrosion behavior. Results reveal that corrosion behavior follows a sequence, that is, first rapidly proceeding, then gradually slowing down, and finally forming an outer layer composed of different types of oxides and an inner layer mainly comprised of sulfides. In-depth analysis reveals that the hot corrosion of FGH100 is a combined effect of oxidation-sulfidation and transfer of oxides.

Annealing effects on structural and compositional performances of Al_{2}O_{3} thin films on 4H-SiC substrates are studied comprehensively. The Al_{2}O_{3} films are grown by atomic layer deposition through using trimethylaluminum and H_{2}O as precursors at 300℃, and annealed at various temperatures in ambient N_{2} for 1 min. The Al_{2}O_{3} film transits from amorphous phase to crystalline phase as annealing temperature increases from 750℃ to 768℃. The refractive index increases with annealing temperature rising, which indicates that densification occurs during annealing. The densification and grain formation of the film upon annealing are due to crystallization which is relative with second-nearest-neighbor coordination variation according to the x-ray photoelectron spectroscopy (XPS). Although the binding energies of Al 2p and O 1s increase together during crystallization, separations between Al 2p and O 1s are identical between as-deposited and annealed sample, which suggests that the nearest-neighbour coordination is similar.

We report on the measurements of the electrical and dielectric properties of Na_{1/2}La_{1/2}Cu_{3}Ti_{4}O_{12} (NLCTO) ceramics prepared by high energy ball-milling and conventional sintering without any calcination steps. The x-ray powder diffraction analysis shows that pure perovskite-like CCTO phase is obtained after sintering at 1025℃-1075℃. Higher sintering temperatures result in multi-phase ceramics due to thermal decomposition. Scanning electron microscope observations reveal that the grain size is in a range of ~3 μm-5 μm for these ceramics. Impedance spectroscopy measurements performed in a wide frequency range (1 Hz-10 MHz) and at various temperatures (120 K-470 K) are used to study the dielectric and electrical properties of NLCTO ceramics. A good compromise between high ε' (5.7×10^{3} and 4.1×10^{3} at 1.1 kHz and 96 kHz, respectively) and low tanδ (0.161 and 0.126 at 1.1 kHz and 96 kHz, respectively) is obtained for the ceramic sintered at 1050℃. The observed high dielectric constant behavior is explained in terms of the internal barrier layer capacitance effect.

The formation mechanism of ice banding in the system of freezing colloidal suspensions, which is of significance in frost heaving, ice-templating porous materials and biological materials, is still a mystery. Recently, the theory of secondary nucleation and growth of ice has been proposed to explain the emergence of a new ice lens. However, this theory has not been quantitatively examined. Here, we quantitatively measure the initial interfacial undercooling of a new ice lens and the nucleation undercoolings of suspensions. We find that the interfacial undercooling cannot satisfy the nucleation undercooling of ice and hence disprove the secondary nucleation mechanism for ice banding.

A megawatt-level subterahertz surface wave oscillator (SWO) is proposed to obtain high conversion efficiency by using separated overmoded slow wave structures (SWSs). Aiming at the repetitive operation and practical applications, the device driven by electron beam with modest energy and current is theoretically analyzed and verified. Then,the functions of the two SWS sections and the effect of the drift tube are investigated by using a particle-in-cell code to reveal how the proposed device achieves high efficiency. The mode analysis of the beam-wave interaction region in the device is also carried out, and the results indicate that multi-modes participate in the premodulation of the electron beam in the first SWS section, while the TM_{01} mode surface wave is successfully and dominantly excited and amplified in the second SWS section. Finally, a typical simulation result demonstrates that at a beam energy of 313 keV, beam current of 1.13 kA, and guiding magnetic field of above 3.5 T, a high-power subterahertz wave is obtained with an output power of about 70 MW at frequency 146.3 GHz, corresponding to the conversion efficiency of 20%. Compared with the results of the previous subterahertz overmoded SWOs with integral SWS and similar beam parameters, the efficiency increases almost 50% in the proposed device.

A side band power re-injection locked (SBPRIL) magnetron is presented in this paper. A tuning stub is placed between the external injection locked (EIL) magnetron and the circulator. Side band power of the EIL magnetron is reflected back to the magnetron. The reflected side band power is reused and pulled back to the central frequency. A phase-locking model is developed from circuit theory to explain the process of reuse of side band power in SBPRIL magnetron. Theoretical analysis proves that the side band power is pulled back to the central frequency of the SBPRIL magnetron, then the amplitude of the RF voltage increases and the phase noise performance is improved. Particle-in-cell (PIC) simulation of a 10-vane continuous wave (CW) magnetron model is presented. Computer simulation predicts that the frequency spectrum's peak of the SBPRIL magnetron has an increase of 3.25 dB compared with the free running magnetron. The phase noise performance at the side band offset reduces 12.05 dB for the SBPRIL magnetron. Besides, the SBPRIL magnetron experiment is presented. Experimental results show that the spectrum peak rises by 14.29% for SBPRIL magnetron compared with the free running magnetron. The phase noise reduces more than 25 dB at 45-kHz offset compared with the free running magnetron.

Adaptation is one of the key capabilities of cognitive radio, which focuses on how to adjust the radio parameters to optimize the system performance based on the knowledge of the radio environment and its capability and characteristics. In this paper, we consider the cognitive radio adaptation problem for power consumption minimization. The problem is formulated as a constrained power consumption minimization problem, and the biogeography-based optimization (BBO) is introduced to solve this optimization problem. A novel habitat suitability index (HSI) evaluation mechanism is proposed, in which both the power consumption minimization objective and the quality of services (QoS) constraints are taken into account. The results show that under different QoS requirement settings corresponding to different types of services, the algorithm can minimize power consumption while still maintaining the QoS requirements. Comparison with particle swarm optimization (PSO) and cat swarm optimization (CSO) reveals that BBO works better, especially at the early stage of the search, which means that the BBO is a better choice for real-time applications.

The comprehensive understanding of the structure-dependent electrostatic discharge behaviors in a conventional diode-triggered silicon controlled rectifier (DTSCR) is presented in this paper. Combined with the device simulation, a mathematical model is built to get a more in-depth insight into this phenomenon. The theoretical studies are verified by the transmission-line-pulsing (TLP) test results of the modified DTSCR structure, which is realized in a 65-nm complementary metal-oxide-semiconductor (CMOS) process. The detailed analysis of the physical mechanism is used to provide predictions as the DTSCR-based protection scheme is required. In addition, a method is also presented to achieve the tradeoff between the leakage and trigger voltage in DTSCR.

A bright white quantum dot light-emitting device (white-QLED) with 4-[4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl]-2-[3-(tri-phenylen-2-yl)phen-3-yl]quinazoline deposited on a thin film of mixed green/red-QDs as a bilayer emitter is fabricated. The optimized white-QLED exhibits a turn-on voltage of 3.2 V and a maximum brightness of 3660 cd/m^{2}@8 V with the Commission Internationale de l'Eclairage (CIE) chromaticity in the region of white light. The ultra-thin layer of QDs is proved to be critical for the white light generation in the devices. Excitation mechanism in the white-QLEDs is investigated by the detailed analyses of electroluminescence (EL) spectral and the fluorescence lifetime of QDs. The results show that charge injection is a dominant mechanism of excitation in the white-QLED.

The electronic transport properties of a single thiolated arylethynylene molecule with 9,10-dihydroanthracene core, denoted as TADHA, is studied by using non-equilibrium Green's function formalism combined with ab initio calculations. The numerical results show that the TADHA molecule exhibits excellent negative differential conductance (NDC) behavior at lower bias regime as probed experimentally. The NDC behavior of TADHA molecule originates from the Stark effect of the applied bias voltage, by which the highest occupied molecular orbital (HOMO) and the HOMO-1 are pulled apart and become localized. The NDC behavior of TADHA molecular system is tunable by changing the electrode distance. Shortening the electrode separation can enhance the NDC effect which is attributed to the possible increase of coupling between the two branches of TADHA molecule.

In this paper, we investigate cooperatively surrounding control (CSC) of multi-agent systems modeled by Euler-Lagrange (EL) equations under a directed graph. With the consideration of the uncertain dynamics in an EL system, a backstepping CSC algorithm combined with neural-networks is proposed first such that the agents can move cooperatively to surround the stationary target. Then, a command filtered backstepping CSC algorithm is further proposed to deal with the constraints on control input and the absence of neighbors' velocity information. Numerical examples of eight satellites surrounding one space target illustrate the effectiveness of the theoretical results.

In this paper, a standard susceptible-infected-recovered-susceptible(SIRS) epidemic model based on the Watts-Strogatz (WS) small-world network model and the Barabsi-Albert (BA) scale-free network model is established, and a new immunization scheme–“the most common friend first immunization”is proposed, in which the most common friend's node is described as being the first immune on the second layer protection of complex networks. The propagation situations of three different immunization schemes–random immunization, high-risk immunization, and the most common friend first immunization are studied. At the same time, the dynamic behaviors are also studied on the WS small-world and the BA scale-free network. Moreover, the analytic and simulated results indicate that the immune effect of the most common friend first immunization is better than random immunization, but slightly worse than high-risk immunization. However, high-risk immunization still has some limitations. For example, it is difficult to accurately define who a direct neighbor in the life is. Compared with the traditional immunization strategies having some shortcomings, the most common friend first immunization is effective, and it is nicely consistent with the actual situation.

Conventional multiple breath-hold two-dimensional (2D) balanced steady-state free precession (SSFP) presents many difficulties in cardiac cine magnetic resonance imaging (MRI). Recently, a self-gated free-breathing three-dimensional (3D) SSFP technique has been proposed as an alternative in many studies. However, the accuracy and effectiveness of self-gating signals have been barely studied before. Since self-gating signals are crucially important in image reconstruction, a systematic study of self-gating signals and comparison with external monitored signals are needed. Previously developed self-gated free-breathing 3D SSFP techniques are used on twenty-eight healthy volunteers. Both electrocardiographic (ECG) and respiratory bellow signals are also acquired during the scan as external signals. Self-gating signal and external signal are compared by trigger and gating window. Gating window is proposed to evaluate the accuracy and effectiveness of respiratory self-gating signal. Relative deviation of the trigger and root-mean-square-deviation of the cycle duration are calculated. A two-tailed paired t-test is used to identify the difference between self-gating and external signals. A Wilcoxon signed rank test is used to identify the difference between peak and valley self-gating triggers. The results demonstrate an excellent correlation (P=0, R>0.99) between self-gating and external triggers. Wilcoxon signed rank test shows that there is no significant difference between peak and valley self-gating triggers for both cardiac (H=0, P>0.10) and respiratory (H=0, P>0.44) motions. The difference between self-gating and externally monitored signals is not significant (two-tailed paired-sample t-test:H=0, P>0.90). The self-gating signals could demonstrate cardiac and respiratory motion accurately and effectively as ECG and respiratory bellow. The difference between the two methods is not significant and can be explained. Furthermore, few ECG trigger errors appear in some subjects while these errors are not found in self-gating signals.

The bottleneck effect on bidirectional crowd dynamics is of great theoretical and practical significance, especially for the designing of corridors in public places, such as subway stations or airports. Based on the famous social force model, this paper investigates the bottleneck effects on the free flow dynamics and breakdown phenomenon under different scenarios, in which different corridor shapes and inflow ratios are considered simultaneously. Numerical simulation finds an interesting self-organization phenomenon in the bidirectional flow, a typical characteristic of such a phenomenon is called lane formation, and the existence of which is independent of the corridor's shape and inflow rate. However, the pattern of the lane formed by pedestrian flow is related to the corridor's shape, and the free flow efficiency has close relationship with the inflow rate. Specifically, breakdown phenomenon occurs when inflows from both sides of the corridor are large enough, which mostly originates from the bottleneck and then gradually spreads to the other regions. Simulation results further indicate that the leaving efficiency becomes low as breakdown occurs, and the degree of congestion is proportional to the magnitude of inflow. The findings presented in this paper match well with some of our daily observations, hence it is possible to use them to provide us with theoretical suggestions in design of infrastructures.

A new synchronization technique of inner and outer couplings is proposed in this work to investigate the synchronization of network group. Some Haken-Lorenz lasers with chaos behaviors are taken as the nodes to construct a few nearest neighbor complex networks and those sub-networks are also connected to form a network group. The effective node controllers are designed based on Lyapunov function and the complete synchronization among the sub-networks is realized perfectly under inner and outer couplings. The work is of potential applications in the cooperation output of lasers and the communication network.

In this paper, we study epidemic spreading on random surfer networks with infected avoidance (IA) strategy. In particular, we consider that susceptible individuals' moving direction angles are affected by the current location information received from infected individuals through a directed information network. The model is mainly analyzed by discrete-time numerical simulations. The results indicate that the IA strategy can restrain epidemic spreading effectively. However, when long-distance jumps of individuals exist, the IA strategy's effectiveness on restraining epidemic spreading is heavily reduced. Finally, it is found that the influence of the noises from information transferring process on epidemic spreading is indistinctive.

The genetic algorithm (GA) is a nature-inspired evolutionary algorithm to find optima in search space via the interaction of individuals. Recently, researchers demonstrated that the interaction topology plays an important role in information exchange among individuals of evolutionary algorithm. In this paper, we investigate the effect of different network topologies adopted to represent the interaction structures. It is found that GA with a high-density topology ends up more likely with an unsatisfactory solution, contrarily, a low-density topology can impede convergence. Consequently, we propose an improved GA with dynamic topology, named DT-GA, in which the topology structure varies dynamically along with the fitness evolution. Several experiments executed with 15 well-known test functions have illustrated that DT-GA outperforms other test GAs for making a balance of convergence speed and optimum quality. Our work may have implications in the combination of complex networks and computational intelligence.

Besides our previous experimental discovery (Zhao Y R, et al. 2015 Langmuir, 31, 12975) that acetonitrile (ACN) can tune the morphological features of nanostructures self-assembled by short peptides KⅢIK (KI4K) in aqueous solution, further experiments reported in this work demonstrate that ACN can also tune the mass of the self-assembled nanostructures. To understand the microscopic mechanism how ACN molecules interfere peptide self-assembly process, we conducted a series of molecular dynamics simulations on a monomer, a cross-β sheet structure, and a proto-fibril of KI4K in pure water, pure ACN, and ACN-water mixtures, respectively. The simulation results indicate that ACN enhances the intra-sheet interaction dominated by the hydrogen bonding (H-bonding) interactions between peptide backbones, but weakens the inter-sheet interaction dominated by the interactions between hydrophobic side chains. Through analyzing the correlations between different groups of solvent and peptides and the solvent behaviors around the proto-fibril, we have found that both the polar and nonpolar groups of ACN play significant roles in causing the opposite effects on intermolecular interactions among peptides. The weaker correlation of the polar group of ACN than water molecule with the peptide backbone enhances H-bonding interactions between peptides in the proto-fibril. The stronger correlation of the nonpolar group of ACN than water molecule with the peptide side chain leads to the accumulation of ACN molecules around the proto-fibril with their hydrophilic groups exposed to water, which in turn allows more water molecules close to the proto-fibril surface and weakens the inter-sheet interactions. The two opposite effects caused by ACN form a microscopic mechanism clearly explaining our experimental observations.

SPECIAL TOPIC—Soft matter and biological physics (Review)

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