The linear and nonlinear characteristics of time-resolved photoluminescence (PL) of n-type bulk semiconductor GaAs modulated with terahertz (THz) pulse are studied by using an ensemble Monte Carlo (EMC) method. In this paper the center energy valley (Γ valley) electron concentration changes with the pulse delay time, sampling time and the outfield are mainly discussed. The results show that the sampling time and the THz field should exceed certain thresholds to effectively excite photoluminescence quenching (PLQ). Adopting a direct current (DC) field makes the sampling time threshold shortened and the linear range of THz field-modulation PL expanded. Moreover, controlling the sampling time and the outfield intensity can improve the linear quality:with forward time, the larger outfield is used; with backward time, the smaller outfield is used. This study can provide a theoretical basis of THz field linear modulation in a larger range for new light emitting devices.

Local structure-preserving algorithms including multi-symplectic, local energy-and momentum-preserving schemes are proposed for the generalized Rosenau-RLW-KdV equation based on the multi-symplectic Hamiltonian formula of the equation. Each of the present algorithms holds a discrete conservation law in any time-space region. For the original problem subjected to appropriate boundary conditions, these algorithms will be globally conservative. Discrete fast Fourier transform makes a significant improvement to the computational efficiency of schemes. Numerical results show that the proposed algorithms have satisfactory performance in providing an accurate solution and preserving the discrete invariants.

Phage T7 RNA polymerase is a single-subunit transcription enzyme, transcribing template DNA to RNA. Nucleoside triphosphate (NTP) selection and translocation are two critical steps of the transcription elongation. Here, using all-atom molecular dynamics simulations, we found that between pre-and post-translocation states of T7 RNA polymerase an intermediate state exists, where the O helix C-terminal residue tyrosine 639, which plays important roles in translocation, locates between its pre-and post-translocation positions and the side chain of the next template DNA nucleotide has moved into the active site. NTP selection in this intermediate state was studied, revealing that the selection in the intermediate state can be achieved relying on the effect of Watson-Crick interaction between NTP and template DNA nucleotide, effect of stability of the components near the active site such as the nascent DNA-RNA hybrid and role of tyrosine 639. This indicates that another NTP-selection pathway can also exist besides the main pathway where NTP selection begins at the post-translocation state upon the entry of NTP.

The nonlinear Schrödinger (NLS) equation and Boussinesq equation are two very important integrable equations. They have widely physical applications. In this paper, we investigate a nonlinear system, which is the two-component NLS equation coupled to the Boussinesq equation. We obtain the bright-bright, bright-dark, and dark-dark soliton solutions to the nonlinear system. We discuss the collision between two solitons. We observe that the collision of bright-bright soliton is inelastic and two solitons oscillating periodically can happen in the two parallel-traveling bright-bright or bright-dark soliton solution. The general breather and rogue wave solutions are also given. Our results show again that there are more abundant dynamical properties for multi-component nonlinear systems.

In this study, we present the analytical solutions of bound states for the Schrödinger equation with the multiparameter potential containing the different types of physical potentials via the asymptotic iteration method by applying the Pekeris-type approximation to the centrifugal potential. For any n and l (states) quantum numbers, we derive the relation that gives the energy eigenvalues for the bound states numerically and the corresponding normalized eigenfunctions. We also plot some graphics in order to investigate effects of the multiparameter potential parameters on the energy eigenvalues. Furthermore, we compare our results with the ones obtained in previous works and it is seen that our numerical results are in good agreement with the literature.

In this paper, we investigate the simulation of violation of the Wright inequality by the classical optical experiment theoretically and experimentally. The feasibility of the simulation is demonstrated by theoretical analysis based on descriptions of the classical electrodynamics and quantum mechanics, respectively. Then, the simulation of violation of the Wright inequality is realized experimentally. The setup is based on a laser source, free-space optical devices and power meters. The experimental result violates the noncontextuality hidden variable bound, agreeing with the quantum bound. This method can be extended to other types of noncontextuality inequalities.

A modified continuous-variable quantum key distribution (CVQKD) protocol is proposed by originating the entangled source from a malicious third party Eve in the middle instead of generating it from the trustworthy Alice or Bob. This method is able to enhance the efficiency of the CVQKD scheme attacked by local oscillator (LO) intensity attack in terms of the generated secret key rate in quantum communication. The other indication of the improvement is that the maximum transmission distance and the maximum loss tolerance can be increased significantly, especially for CVQKD schemes based on homodyne detection.

We study the moving bright solitons in the weak attractive Bose-Einstein condensate with a spin-orbit interaction. By solving the coupled nonlinear Schrödinger equation with the variational method and the imaginary time evolution method, two kinds of solitons (plane wave soliton and stripe solitons) are found in different parameter regions. It is shown that the soliton speed dominates its structure. The detuning between the Raman beam and energy states of the atoms decides the spin polarization strength of the system. The soliton dynamics is also studied for various moving speed and we find that the shape of individual components can be kept when the speed of soliton is low.

In this note, the off-shell generalized Abbott-Deser-Tekin (ADT) formalism is applied to explore the mass of Kerr-anti-de Sitter (Kerr-AdS) black holes in various dimensions within asymptotically rotating frames. The cases in four and five dimensions are explicitly investigated. It is demonstrated that the asymptotically rotating effect may make the charge non-integrable or unphysical when the asymptotic non-rotating timelike Killing vector associated with the charge is allowed to vary and the fluctuation of the metric is determined by the variation of all the mass and rotation parameters. To obtain a physically meaningful mass, it is proposed that one can let the non-rotating timelike Killing vector be fixed or perform calculations in the asymptotically static frame. The results further support that the ADT formalism is background-dependent.

We investigate the prominent impacts of coupling strengths on the evolution of entanglement and quantum discord for a three-qubit system coupled to an XY spin-chain environment. In the case of a pure W state, more robust, even larger nonzero quantum correlations can be obtained by tailoring the coupling strengths between the qubits and the environment. For a mixed state consisting of the GHZ and W states, the dynamics of entanglement and quantum discord can characterize the critical point of quantum phase transition. Remarkably, a large nonzero quantum discord is generally retained, while the nonzero entanglement can only be obtained as the system-environment coupling satisfies certain conditions. We also find that the impact of each qubit's coupling strength on the quantum correlation dynamics strongly depends on the variation schemes of the system-environment couplings.

We simulate a two-dimensional model of a round soft boundary enclosed with self-propelled particles. Persistent motion drives these particles to accumulate near the boundary, thereby dramatically deforming the boundary shape through collisions. Quantitative analyses of the boundary shape and the particle distribution show that there are two typical regimes in the variation of the morphology with the increase of self-propulsion of particles. One is under small forces, characterized by the radially inhomogeneous distribution of particles and the suppression of local fluctuations of the almost round boundary, and the other is under large forces, featured by the angularly inhomogeneous distribution of particles and the global shape deformation of the boundary. These two features are strongly cooperative. We also find different mechanisms in the particle relocation at low and high particle concentrations.

In this paper, a new method, based on firefly algorithm (FA) and extreme learning machine (ELM), is proposed to control chaos in nonlinear system. ELM is an efficient predicted and classified tool, and can match and fit nonlinear systems efficiently. Hence, mathematical model of uncertain nonlinear system is obtained indirectly. For higher fitting accuracy, a novel swarm intelligence algorithm FA is drawn in our proposed way. The main advantage is that our proposed method can remove the limitation that mathematical model must be known clearly and can be applied to unknown nonlinear chaotic system.

In this paper, Adomian decomposition method (ADM) with high accuracy and fast convergence is introduced to solve the fractional-order piecewise-linear (PWL) hyperchaotic system. Based on the obtained hyperchaotic sequences, a novel color image encryption algorithm is proposed by employing a hybrid model of bidirectional circular permutation and DNA masking. In this scheme, the pixel positions of image are scrambled by circular permutation, and the pixel values are substituted by DNA sequence operations. In the DNA sequence operations, addition and substraction operations are performed according to traditional addition and subtraction in the binary, and two rounds of addition rules are used to encrypt the pixel values. The simulation results and security analysis show that the hyperchaotic map is suitable for image encryption, and the proposed encryption algorithm has good encryption effect and strong key sensitivity. It can resist brute-force attack, statistical attack, differential attack, known-plaintext, and chosen-plaintext attacks.

We study the dynamical energy equipartition properties in the integrable Toda model with additional uniform or disordered on-site energies by extensive numerical simulations. The total energy is initially equidistributed among some of the lowest frequency linear modes. For the Toda model with uniform on-site potentials, the energy spectrum keeps its profile nearly unchanged in a relatively short time scale. On a much longer time scale, the energies of tail modes increase slowly with time. Energy equipartition is far away from being attached in our studied time scale. For the Toda model with disordered on-site potentials, the energy transfers continuously to the high frequency modes and eventually towards energy equipartition. We further perform a systematic study of the equipartition time t_{eq} depending on the energy density ε and the nonlinear parameter α in the thermodynamic limit for the Toda model with disordered on-site potentials. We find t_{eq}∝ (1/ε)^{a}(1/α)^{b}, where b≈ 2a. The values of a and b are increased when increasing the strengths of disordered on-site potentials or decreasing the number of initially excited modes.

This paper investigates the stochastic bounded consensus of leader-following second-order multi-agent systems in a noisy environment. It is assumed that each agent received the information of its neighbors corrupted by noises and time delays. Based on the graph theory, stochastic tools, and the Lyapunov function method, we derive the sufficient conditions under which the systems would reach stochastic bounded consensus in mean square with the protocol we designed. Finally, a numerical simulation is illustrated to check the effectiveness of the proposed algorithms.

Shannon observed the relation between information entropy and Maxwell demon experiment to come up with information entropy formula. After that, Shannon's entropy formula is widely used to measure information leakage in imperative programs. But in the present work, our aim is to go in a reverse direction and try to find possible Maxwell's demon experimental setup for contemporary practical imperative programs in which variations of Shannon's entropy formula has been applied to measure the information leakage. To establish the relation between the second principle of thermodynamics and quantitative analysis of information leakage, present work models contemporary variations of imperative programs in terms of Maxwell's demon experimental setup. In the present work five contemporary variations of imperative program related to information quantification are identified. They are:(i) information leakage in imperative program, (ii) imperative multithreaded program, (iii) point to point leakage in the imperative program, (iv) imperative program with infinite observation, and (v) imperative program in the SOA-based environment. For these variations, minimal work required by an attacker to gain the secret is also calculated using historical Maxwell's demon experiment. To model the experimental setup of Maxwell's demon, non-interference security policy is used. In the present work, imperative programs with one-bit secret information have been considered to avoid the complexity. The findings of the present work from the history of physics can be utilized in many areas related to information flow of physical computing, nano-computing, quantum computing, biological computing, energy dissipation in computing, and computing power analysis.

Signal detection is both a fundamental topic of data science and a great challenge for practical engineering. One of the canonical tasks widely investigated is detecting a sinusoidal signal of known frequency ω with time duration T:I(t)=Acos ω t+Γ(t), embedded within a stationary noisy data. The most direct, and also believed to be the most efficient, method is to compute the Fourier spectral power at ω:B=|2/T∫_{0}^{T} I(t)e^{iωt}dt|. Whether one can out-perform the linear Fourier approach by any other nonlinear processing has attracted great interests but so far without a consensus. Neither a rigorous analytic theory has been offered. We revisit the problem of weak signal, strong noise, and finite data length T=O(1), and propose a signal detection method based on resonant filtering. While we show that the linear approach of resonant filters yield a same signal detection efficiency in the limit of T→∞, for finite time length T=O(1), our method can improve the signal detection due to the highly nonlinear interactions between various characteristics of a resonant filter in finite time with respect to transient evolution. At the optimal match between the input I(t), the control parameters, and the initial preparation of the filter state, its performance exceeds the above threshold B considerably. Our results are based on a rigorous analysis of Gaussian processes and the conclusions are supported by numerical computations.

When the ground state hyperfine splitting of alkali metal vapor atoms is well optically resolved, the spin coherence on one hyperfine sublevel can be generated directly or indirectly by pumping the same or the other sublevel respectively. We experimentally studied the pump power dependence of the field response of a Bell-Bloom magnetometer for the two pumping schemes in a paraffin coated ^{87}Rb vapor cell. We find that although the maximum field response is achieved by combining the two pumping schemes, indirect pumping alone can do nearly as good while being much simpler to operate. We have achieved a sensitivity of 100 fT/Hz^{1/2} with a single indirect pump at room temperature.

We report the fabrication of long-period gratings (LPGs) in elliptical microfibers with femtosecond laser. Based on the numerical analysis of the modes and the mode coupling condition of elliptical microfibers, an LPG is fabricated with a very short pitch of 10 μm by periodically modifying the fiber surface, which demonstrates very strong polarization-dependent resonances, a very low temperature sensitivity of a few picometers in air, and high temperature sensitivity of -1.62 nm/℃ in refractive index oil.

Grazing incidence optics (GIO) is the most important compound in an x-ray detection system; it is used to concentrate the x-ray photons from outer space. A nested planar GIO for x-ray concentration is designed and developed by authors in this paper; planar segments are used as the reflection mirror instead of curved segments because of the simple process and low cost. After the complex assembling process with a special metal supporter, a final circle light spot of φ 12 mm was obtained in the visible light testing experiment of GIO; the effective area of 1710.51 mm^{2}@1 keV and 530 mm^{2}@8 keV is obtained in the x-ray testing experiment with the GIO-SDD combination, which is supposed to be a concentrating detector in xray detection systems.

SPECIAL TOPIC—Non-equilibrium phenomena in soft matters

The Eu-doped Cu(In, Eu)Te_{2} semiconductors with chalcopyrite structures are promising materials for their applications in the absorption layer for thin-film solar cells due to their wider band-gaps and better optical properties than those of CuInTe_{2}. In this paper, the Eu-doped CuInTe_{2} (CuIn_{1-x}Eu_{x}Te_{2}, x=0, 0.1, 0.2, 0.3) are studied systemically based on the empirical electron theory (EET). The studies cover crystal structures, bonding regularities, cohesive energies, energy levels, and valence electron structures. The theoretical values fit the experimental results very well. The physical mechanism of a broadened band-gap induced by Eu doping into CuInTe_{2} is the transitions between different hybridization energy levels induced by electron hopping between s and d orbitals and the transformations from the lattice electrons to valence electrons for Cu and In ions. The research results reveal that the photovoltaic effect induces the increase of lattice electrons of In and causes the electric resistivity to decrease. The Eu doping into CuInTe_{2} mainly influences the transition between different hybridization energy levels for Cu atoms, which shows that the 3d electron numbers of Cu atoms change before and after Eu doping. In single phase CuIn_{1-x}Eu_{x}Te_{2}, the number of valence electrons changes regularly with increasing Eu content, and the calculated band gap E_{g} also increases, which implies that the optical properties of Eu-doped CuIn_{1-x}Eu_{x}Te_{2} are improved.

The high-resolution absorption spectra of the (2,0),(3,1),and (8,5) bands of the A^{2}Π_{u}-X^{2}∑_{g}^{+} system of ^{15}N_{2}^{+} have been recorded by using velocity modulation spectroscopy technique in the near infrared region.The rotational constants of the X^{2}∑_{g}^{+} and A^{2}Π_{u} states of ^{15}N_{2}^{+} were derived from the spectroscopic data.The isotope shifts of these bands of the A^{2}Π_{u}-X^{2}∑_{g}^{+} system of ^{14}N_{2}^{+} and ^{15}N_{2}^{+} were also analyzed and discussed.

Zigzag graphene nanoribbon (ZGNR) is a promising candidate for next-generation spintronic devices. Development of the field requires potential systems with variable and adjustable electromagnetic properties. Here we show a detailed investigation of ZGNR decorated with edge topological defects (ED-ZGNR) synthesized in laboratory by Ruffieux in 2015[Pascal Ruffieux, Shiyong Wang, Bo Yang, et al. 2015 Nature531 489]. The pristine ED-ZGNR in the ground state is an antiferromagnetic semiconductor, and the acquired band structure is significantly changed compared with that of perfect ZGNR. After doping heteroatoms on the edge, the breaking of degeneration of band structure makes the doped ribbon a half-semi-metal, and nonzero magnetic moments are induced. Our results indicate the tunable electronic and magnetic properties of ZGNR by deriving unique edge state from topological defect, which opens a new route to practical nano devices based on ZGNR.

Excitation energies, magnetic dipole, and electric quadrupole transition probabilities of the 3d ^{2}D_{3/2}-3d ^{2}D_{5/2} transition in the potassium-like (K-like) sequence with 26 ≤ Z ≤ 36 are investigated by using the multi-configuration Dirac-Hartree-Fock (MCDHF) method. The contributions of the electron correlations, Breit interaction, and the leading-order quantum electrodynamic (QED) effects on the transition properties are analyzed. The present results are interested in the laboratory tokamak and the astronomical observations. Furthermore, the feasibility of these ions for the highly charged ion (HCI) clocks is discussed. Considering the wavelength of lasers and manipulation process of the atomic clocks, Cu^{10+} and Zn^{11+} are recommended as promising candidates with achievable quality factors at the 10^{15} level.

The photodetachment dynamics of H^{-} ion in a harmonic potential plus an oscillating electric field is studied using the time-dependent closed orbit theory. An analytical formula for calculating the photodetachment cross section of this system is put forward. It is found that the photodetachment cross section of this system is nearly unaffected for the weak oscillating electric field strength, but oscillates complicatedly when the oscillating electric field strength turns strong. In addition, the frequency of the harmonic potential and the oscillating electric field (the frequency of the harmonic potential and the frequency of the oscillating electric field are the same in the paper, unless otherwise stated.) can also affect the photodetachment dynamics of this system. With the increase of the frequency in the harmonic potential and the oscillating electric field, the number of the closed orbits for the detached electrons increased, which makes the oscillatory structure in the photodetachment cross section much more complex. Our study presents an intuitive understanding of the photodetachment dynamics driven by a harmonic potential plus an oscillating electric field from a space and time dependent viewpoint. This study is very useful in guiding the future experimental research for the photodetachment dynamics in the electric field both changing with space and time.

Combining a low temperature liquidizing system with a transient Raman spectroscopy, a new experimental technique is established for the first time on a two-stage light-gas gun, and it is employed to study shock-compressed fluid silane. With this experimental technique, we first obtain a Raman peak shift relating to the Si-H stretching vibration mode of molecular liquid silane under shock loading conditions. The Raman peak of 2184 cm^{-1} at an initial state of 0 GPa and 85 K moves to 2223.4 cm^{-1} at a shocked state of 10.5 GPa and 950 K, and its full width of half maximum broadens from 33 cm^{-1} to 118 cm^{-1}. The shocked temperature, calculated by the thermodynamic equation of state, is well consistent with that estimated by the Doppler broadening function.

We theoretically investigate the high-order harmonic generation of the one-dimensional hydrogen molecular ion at fixed intermediate internuclear distance, driven by a multicycle laser field. Our results show that the initial electronic state of the hydrogen molecular ion affects the modulation of the high-order harmonic spectrum, especially the positions of the minima. Based on the two-state model, the underlying physical mechanism of the minimum is analyzed and discussed. Further analysis shows that the different positions of the minima in the different initial electronic states can be understood via the different interferences of the two phase-adiabatic states at the ionization times.

The presence of a solvent interacting with a system brings about qualitative changes from the corresponding gas-phase reactions. A solvent can not only change the energetics along the reaction pathway, but also radically alter the reaction mechanism. Here, we investigated the water-induced transition state of the OH^{-}+CO_{2}→HCO_{3}^{-} reaction using a multi-level quantum mechanics and molecular mechanics method with an explicit water model. The solvent energy contribution along the reaction pathway has a maximum value which induces the highest energy point on the potential of mean force. The charge transfer from OH^{-} to CO_{2} results in the breaking of the OH^{-} solvation shell and the forming of the CO_{2} solvation shell. The loss of hydrogen bonds in the OH^{-} solvation shell without being compensated by the formation of hydrogen bonds in the CO_{2} solvation shell induces the transition state in the aqueous solution. The calculated free energy reaction barrier at the CCSD(T)/MM level of theory, 11.8 kcal/mol, agrees very well with the experimental value, 12.1 kcal/mol.

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

Several major challenges need to be faced for efficient transient multiscale electromagnetic simulations, such as flexible and robust geometric modeling schemes, efficient and stable time-stepping algorithms, etc. Fortunately, because of the versatile choices of spatial discretization and temporal integration, a discontinuous Galerkin time-domain (DGTD) method can be a very promising method of solving transient multiscale electromagnetic problems. In this paper, we present the application of a leap-frog DGTD method to the analyzing of the multiscale electromagnetic scattering problems. The uniaxial perfect matching layer (UPML) truncation of the computational domain is discussed and formulated in the leap-frog DGTD context. Numerical validations are performed in the challenging test cases demonstrating the accuracy and effectiveness of the method in solving transient multiscale electromagnetic problems compared with those of other numerical methods.

In this paper, an optical radiative cooler with quasi-Cantor structure is theoretically proposed and analyzed. This simple and symmetrically designed optical structure operates upon continuous thermal sources in diurnal subtropical conditions, and its efficiency is much higher than natural cooling, for instance, when operating upon a typical 323.15 K continuous thermal source with a wind speed at 3 m·^{-1}, it can generate a net cooling power of 363.68 W·m^{-2}, which is 18.26% higher than that of non-radiative heat exchange (natural cooling) under the same conditions. Additionally, several aspects are considered in its design to ensure a low cost in application, which is of great economical and environmental significance.

The vectorial structure of an optical field with hybrid states of polarization (SoP) in the near-field is studied by using the angular spectrum method of an electromagnetic beam. Physical images of the longitudinal components of evanescent waves are illustrated and compared with those of the transverse components from the vectorial structure. Our results indicate that the relative weight integrated over the transverse plane of the evanescent wave depends strongly on the number of the polarization topological charges. The shapes of the intensity profiles of the longitudinal components are different from those of the transverse components, and it can be manipulated by changing the initial SoP of the field cross-section. The longitudinal component of evanescent wave dominates the near-field region. In addition, it also leads to three-dimensional shape variations of the optical field and the optical spin angular momentum flux density distributions.

The plenoptic camera is a single lens stereo camera which can retrieve the direction of light rays while detecting their intensity distribution. In this paper, to reveal more truths of plenoptic camera imaging, we present the wavefront analysis for the plenoptic camera imaging from the angle of physical optics but not from the ray tracing model of geometric optics. Specifically, the wavefront imaging model of a plenoptic camera is analyzed and simulated by scalar diffraction theory and the depth estimation is redescribed based on physical optics. We simulate a set of raw plenoptic images of an object scene, thereby validating the analysis and derivations and the difference between the imaging analysis methods based on geometric optics and physical optics are also shown in simulations.

The vibration is one of the important factors affecting imaging quality of conventional remote sensing imaging because the relative motion between the imaging system and the target can result in the degradation of imaging quality. The influence of the vibration of the detector in the test path on reflective ghost imaging (RGI) is investigated theoretically and experimentally. We analyze the effects of the vibrating amplitude and velocity. The results demonstrate that the microvibrations of the bucket detector have almost no impact on the imaging resolution and signal-to-noise ratio (SNR) of RGI, i.e., the degradation of imaging quality caused by the vibration of the detector can be overcome to some extent. Our results can be helpful for remote sensing imaging.

We experimentally report on the generation of single and multiple dissipative soliton via nonlinear polarization rotation technique. The spectrum of the mode-locked dissipative soliton exhibits typical steep edges with a flat top; the pulse duration is 10.07 ps. It is found that with the pump power increasing from 110 mW to 161 mW, the top of the mode-locked spectrum becomes flater and the 3-dB spectral bandwidth is broadened, which indicates that the gain-dispersion effect is lowered under stronger pump. However, the full bandwidth of the spectrum is narrowed, which proves that the spectral filter effect increases and overcomes the effect of self-phase modulation induced spectral broadening. Such a phenomenon was not noticed nor reported before. Our experiment also demonstrates that the pulse interval is highly dependent on the input pump power:with pump power increasing, the pulse interval tends towards more uniform. So our observation qualitatively analyzes the relationship between mode-locked pulse characteristics and input pump power.

We numerically study the self-compression of the optical pulses centered at 1.8-μm in a hollow-core fiber (HCF) filled with argon. It is found that the pulse can be self-compressed to 2 optical cycles when the input pulse energy is 0.2-mJ and the gas pressure is 500-mbar (1 bar=10^{5} Pa). Inducing a proper positive chirp into the input pulse can lead to a shorter temporal duration after self-compression. These results will benefit the generation of energetic few-cycle mid-infrared pulses.

Single-photon detectors possess the ultra-high sensitivity, but they cannot directly respond to signal intensity. Conventional methods adopt sampling gates with fixed width and count the triggered number of sampling gates, which is capable of obtaining photon counting probability to estimate the echo signal intensity. In this paper, we not only count the number of triggered sampling gates, but also record the triggered time position of photon counting pulses. The photon counting probability density distribution is obtained through the statistics of a series of the triggered time positions. Then Minimum Variance Unbiased Estimation (MVUE) method is used to estimate the echo signal intensity. Compared with conventional methods, this method can improve the estimation accuracy of echo signal intensity due to the acquisition of more detected information. Finally, a proof-of-principle laboratory system is established. The estimation accuracy of echo signal intensity is discussed and a high accuracy intensity image is acquired under low-light level environments.

The structures of pseudo-binary GeS_{2}-Sb_{2}S_{3}, GeS_{2}-CdS, Sb_{2}S_{3}-CdS, and pseudo-ternary GeS_{2}-Sb_{2}S_{3}-CdS chalcogenide systems are systematically investigated by Raman spectroscopy. It is shown that a small number of[S_{3}Ge-GeS_{3}] structural units (SUs) and -S-S-/S_{8} groups exist simultaneously in GeS_{2} glass which has a three-dimensional continuous network backbone consisting of cross-linked corner-sharing and edge-sharing[GeS_{4}] tetrahedra. When Sb_{2}S_{3} is added into GeS_{2} glass, the network backbone becomes interconnected[GeS_{4}] tetrahedra and[SbS_{3}] pyramids. Moreover, Ge atoms in[S_{3}Ge-GeS_{3}] SUs tend to capture S atoms from Sb_{2}S_{3}, leading to the formation of[S_{2}Sb-SbS_{2}] SUs. When CdS is added into GeS_{2} glass,[Cd_{4}GeS_{6}] polyhedra are formed, resulting in a strong crystallization tendency. In addition, Ge atoms in[S_{3}Ge-GeS_{3}] SUs tend to capture S atoms from CdS, resulting in the dissolution of Ge-Ge bond. Co-melting of Sb_{2}S_{3} or CdS with GeS_{2} reduces the viscosity of the melt and improves the homogeneity of the glass. The GeS_{2} glass can only dissolve up to 10-mol% CdS without crystallization. In comparison, GeS_{2}-Sb_{2}S_{3} glasses can dissolve up to 20-mol% CdS, implying that Sb_{2}S_{3} could delay the construction of[Cd_{4}GeS_{6}] polyhedron and increase the dissolving amount of CdS in the glass.

The growth of heterogeneous crystal has aroused a great deal of interest in recent years. In this study, KH_{2}PO_{4} (KDP)/KTaO_{3} (KT) heterogeneous crystal is acquired based on the KT substrate. Here, we report the observation of the oriented layer-by-layer structure in KDP/KT composite crystal by scanning electron microscopy (SEM). The structure of KDP/KT composite crystal is accurately identified by transmission electron microscopy (TEM) for the first time and we find that the KT crystals dope into KDP crystal in the growth process with the mode of doping. It can be obtained from the analysis of crystal structure that the structure difference leads to the doping growth mode. Our research demonstrates a facile method to fabricate a composite nonlinear optical crystal based on KDP/KT heterostructure, and might shed light on potential applications of the composite nonlinear optical crystal.

A systematic interpretation of laser-induced damage in the nanosecond regime is realized with a defect distribution buried inside the redeposited layer arising from a polishing process. Under the 355-nm laser irradiation, the size dependence of the defect embedded in the fused silica can be illustrated through the thermal conduction model. Considering CeO_{2} as the major initiator, the size distribution with the power law model is determined from the damage probability statistics. To verify the accuracy of the size distribution, the ion output scaling with depth for the inclusion element is obtained with the secondary ion mass spectrometer. For CeO_{2} particulates in size of the depth interval with ion output satisfied in the negative exponential form, the corresponding density is consistent with that of the identical size in the calculated size distribution. This coincidence implies an alternative method for the density analysis of photoactive imperfections within optical components at the semi-quantitative level based on the laser damage tests.

Surface plasmon resonance induced tunable polarization filters based on nanoscale gold film-coated photonic crystal fibers were proposed and analyzed. The characteristics of the polarization filter were calculated by finite element method (FEM). The gold film was selectively coated on the inner wall of one cladding air hole which was located near the fiber core along the y-axis direction. When the phase of core fundamental mode and surface plasmon polaritons (SPPs) mode matches, the two modes couple with each other intensely. Numerical results show that the resonance wavelength and strength vary with fiber structural parameters and the index of the infilling liquid. The fiber parameters were optimized to achieve specific functions. Under the optimal structure, we realized a dual channel filter at the communication wavelength of 1.31 μm and 1.55 μm for y polarization direction and x polarization direction. Then a single channel polarized filter at the communication wavelength of 1.55 μm is also achieved by adjusting the refractive index of the infilling liquid. The proposed polarization filters realized dual channel filtering and single channel filtering simultaneously under the same structure for the first time to the best of our knowledge.

Improvement of the heat transfer of the cold side is one of the approaches to enhance the performance of TEG systems. As a new type of heat transfer media, nanofluids can enhance the heat transfer performance of working liquid significantly. Based on a three-dimensional and steady-state numerical model,the heat transfer and thermoelectric conversion properties of TEG systems were studied. Graphene anoplatelet aqueous nanofluids were used as the coolants for the cold side of the TEG system to improve the heat transfer capacity of the cold side. The results showed that the heat absorbed by the hot side, voltage, output power, and conversion efficiency of the TEG system were increased greatly by the nanofluid coolants. The output power and the conversion efficiency using 0.1-wt% graphene nanoplatelet aqueous nanofluid as the coolant are enhanced by 26.39% and 14.74%, respectively.

In order to decrease the Schottky barrier height and sheet resistance between graphene (Gr) and the p-GaN layers in GaN-based light-emitting diodes (LEDs), some transparent thin films with good conductivity and large work function are essential to insert into Gr and p-GaN layers. In this work, the ultra-thin films of four metals (silver (Ag), golden (Au), nickel (Ni), platinum (Pt)) are explored to introduce as a bridge layer into Gr and p-GaN, respectively. The effect of a different combination of Gr/metal transparent conductive layers (TCLs) on the electrical, optical, and thermal characteristics of LED was investigated by the finite element methods. It is found that both the TCLs transmittance and the surface temperature of the LED chip reduces with the increase of the metal thickness, and the transmittance decreases to about 80% with the metal thickness increasing to 2 nm. The surface temperature distribution, operation voltage, and optical output power of the LED chips with different metal/Gr combination were calculated and analyzed. Based on the electrical, optical, and thermal performance of LEDs, it is found that 1.5-nm Ag or Ni or Pt, but 1-nm Au combined with 3 layered (L) Gr is the optimal Gr/metal hybrid transparent and current spreading electrode for ultra-violet (UV) or near-UV LEDs.

On the basis of transformation thermodynamics and compensation medium theory, we develop a method to design a two-dimensional thermal illusion device with arbitrary shape, and the general expression of thermal conductivity in the each region is obtained. Simulation results show that when an object is covered with the thermal illusion device, it will accurately perform the same temperature distribution signature as another object we have predetermined. Owing to the property of deceiving and interfering with the observer, the thermal illusion device can achieve generalized thermal stealth by using thermal metamaterials, which may have a potential application in military field.

Crowd force by the pushing or crushing of people has resulted in a number of accidents in recent decades. The aftermath investigations have shown that the physical interaction of a highly competitive crowd could produce dangerous pressure up to 4500 N/m, which leads to compressive asphyxia or even death. In this paper, a numerical model based on discrete element method (DEM) as referenced from granular flow was proposed to model the evacuation process of a group of highly competitive people, in which the movement of people follows Newton's second law and the body deformation due to compression follows Hertz contact model. The study shows that the clogs occur periodically and flow rate fluctuates greatly if all people strive to pass through a narrow exit at high enough desired velocity. Two types of contact forces acting on people are studied. The first one, i.e., vector contact force, accounts for the movement of the people following Newton's second law. The second one, i.e., scale contact force, accounts for the physical deformation of the human body following the contact law. Simulation shows that the forces chain in crowd flow is turbulent and fragile. A few narrow zones with intense forces are observed in the force field, which is similar to the strain localization observed in granular flow. The force acting on a person could be as high as 4500 N due to force localization, which may be the root cause of compressive asphyxia of people in many crowd incidents.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

The modulation of absorption manner in helicon discharge by changing the profile of low axial magnetic field is explored experimentally in this work. The experiments are carried out in Boswell-type antenna driven by 13.56-MHz power source in 0.35-Pa argon environment. The peak of the external non-uniform magnetic field (B_{ex}) along the axis is observed in a range from 0 Gs to 250 Gs (1 Gs=10^{-4} T), where the electron density varies from 0.5×10^{16} m^{-3} to 9×10^{16} m^{-3}. When B_{ex} is located near the tube upper end sealed by a dielectric plate, or near the tube bottom end connected with a diffusion chamber, the plasmas are centralized in the tube in the former case while the strong luminance appears between the edge of the tube and the axial line in the latter case. When B_{ex} is located in the middle of the antenna, moreover, an effective resistance (R_{eff}) peak appears apparently with increasing magnetic field. The glow moves toward first the edge of the tube and then the two antenna legs as the magnetic field increases. The discharge in this case is caused by the absorption of Trivelpiece-Gould (TG) wave. It is suggested that B_{ex} is located in the middle of the antenna to obtain a higher efficiency of power transfer.

Ignition energy is one of the important parameters of flammable materials, and evaluating ignition energy precisely is essential to the safety of process industry and combustion science and technology. By using electric spark discharge test system, a series of electric spark discharge experiments were conducted with the capacitor-stored energy in the range of 10 J, 100 J, and 1000 J, respectively. The evaluation method for energy consumed by electric spark, wire, and switch during capacitor discharge process has been studied respectively. The resistance of wire, switch, and plasma between electrodes has been evaluated by different methods and an optimized evaluation method has been obtained. The electric energy consumed by wire, electric switch, and electric spark-induced plasma between electrodes were obtained and the energy structure of capacitor-released energy was analyzed. The dynamic process and the characteristic parameters (the maximum power, duration of discharge process) of electric spark discharge process have been analyzed. Experimental results showed that, electric spark-consumed energy only accounts for 8%-14% of the capacitor-released energy. With the increase of capacitor-released energy, the duration of discharge process becomes longer, and the energy of plasma accounts for more in the capacitor-released energy. The power of electric spark varies with time as a damped sinusoids function and the period and the maximum value increase with the capacitor-released energy.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

The sheet size of a graphene oxide (GO) can greatly influence its electrical, optical, mechanical, electrochemical and catalytic property. It is a key challenge to how to control the sheet size during its preparation in different application fields. According to our previous theoretical calculations of the effect of temperature on the oxidation process of graphene, we use Hummers method to prepare GOs with different sheet sizes by simply controlling the temperature condition in the process of the oxidation reaction of potassium permanganate (KMnO_{4}) with graphene and the dilution process with deionized water. The results detected by transmission electron microscopy (TEM) and atomic force microscopy (AFM) show that the average sizes of GO sheets prepared at different temperatures are about 1 μm and 7 μm respectively. The ultraviolet-visible spectroscopy (UV-vis) shows that lower temperature can lead to smaller oxidation degrees of GO and less oxygen functional groups on the surface. In addition, we prepare GO membranes to test their mechanical strengths by ultrasonic waves, and we find that the strengths of the GO membranes prepared under low temperatures are considerably higher than those prepared under high temperatures, showing the high mechanical strengths of larger GO sheets. Our experimental results testify our previous theoretical calculations. Compared with the traditional centrifugal separation and chemical cutting method, the preparation process of GO by temperature control is simple and low-cost and also enables large-size synthesis. These findings develop a new method to control GO sheet sizes for large-scale potential applications.

Two-layer monoclinic (2M) muscovite mica sheets with a thickness of 12 μm are irradiated with Sn ions at room temperature with electronic energy loss (dE/dx)_{e} of 14.7 keV/nm. The ion fluence is varied between 1×10^{11} and 1×10^{13} ions/cm^{2}. Structural transition in irradiated mica is investigated by x-ray diffraction (XRD). The main diffraction peaks shift to the high angles, and the inter-planar distance decreases due to swift heavy ion (SHI) irradiation. Dehydration takes place in mica during SHI irradiation and mica with one-layer monoclinic (1M) structure is thought to be generated in 2M mica after SHI irradiation. In addition, micro stress and damage cross section in irradiated mica are analyzed according to XRD data. High resolution transmission electron microscopy (HRTEM) is used on the irradiated mica to obtain the detailed information about the latent tracks and structural modifications directly. The latent track in mica presents an amorphous zone surrounded by strain contrast shell, which is associated with the residual stress in irradiated mica.

We performe first-principles density functional theory calculations to investigate the stability and mechanical properties of various HfH_{x} (0 ≤ x ≤ 1) phases. For pure Hf phases, the calculated results show that the HCP and FCC phases are mechanically stable, while the BCC phase is unstable at 0 K. Also, as for various HfH_{x} phases, we find that H location and concentration could have a significant effect on their stability and mechanical properties. When 0 ≤ x ≤ 0.25, the HCP phases with H at (tetrahedral) T sites are energetically most stable among various phases. The FCC and BCC phases with H at T sites turn to be relatively more favorable than the HCP phase when H concentration is higher than 0.25. Furthermore, our calculated results indicate that the H solution in Hf can largely affect their mechanical properties such as the bulk moduli (B) and shear moduli (G).

Simulations of guiding of low-energy ions through a single nanocapillary in insulating polymers are reported. The nanocapillary has a diameter of 100 nm and a length of 10 μm. Different from previous work, in our simulations a hyperbolic function is used to describe the decay of the charges deposited on the capillary surface. The present simulations reproduce the self-organized charge-up process occurring in the capillary. It is shown that lower-energy ions undergo more oscillations to get guiding equilibrium than those of higher-energy ions, resulting in a longer charging time, which is in good agreement with previous experimental results. Moreover, the experimentally observed mass independence of ion guiding is proved in our simulations. In particular, it is found that the maximum of the repulsive field within the capillary is independent of the ion energy as well as the tilt angle. To counterbalance the increasing of the transversal energy caused by increasing the tilt angle or incident energy, the effective length of the repulsive field is expanded in a self-organizing manner.

The elastic, thermodynamic, electronic, and optical properties of recently discovered and potentially technologically important transition metal boride NbRuB, are investigated using the density functional formalism. Both generalized gradient approximation (GGA) and local density approximation (LDA) are used for optimizing the geometry and for estimating various elastic moduli and constants. The optical properties of NbRuB are studied for the first time with different photon polarizations. The frequency (energy) dependence of various optical constants complement quite well the essential features of the electronic band structure calculations. Debye temperature of NbRuB is estimated from the thermodynamical study. All these theoretical estimates are compared with published results, where available, and discussed in detail. Both electronic band structure and optical conductivity reveal robust metallic characteristics. The NbRuB possesses significant elastic anisotropy. Electronic features, on the other hand, are almost isotropic in nature. The effects of electronic band structure and Debye temperature on the emergence of superconductivity are also analyzed.

The hardness, electronic, and elastic properties of 5d transition metal diborides with ReB_{2} structure are studied theoretically by using the first principles calculations. The calculated results are in good agreement with the previous experimental and theoretical results. Empirical formulas for estimating the hardness and partial number of effective free electrons for each bond in multibond compounds with metallicity are presented. Based on the formulas, IrB_{2} has the largest hardness of 21.8 GPa, followed by OsB_{2} (21.0 GPa) and ReB_{2} (19.7 GPa), indicating that they are good candidates as hard materials.

The structural, electronic, and elastic properties of cubic HC(NH_{2})_{2}PbI_{3} perovskite are investigated by density functional theory using the Tkatchenko-Scheffler pairwise dispersion scheme. Our relaxed lattice parameters are in agreement with experimental data. The hydrogen bonding between NH_{2} and I ions is found to have a crucial role in FAPbI_{3} stability. The first calculated band structure shows that HC(NH_{2})_{2}PbI_{3} has a direct bandgap (1.02 eV) at R-point, lower than the bandgap (1.53 eV) of CH_{3}NH_{3}PbI_{3}. The calculated density of states reveals that the strong hybridization of s(Pb)-p(I) orbital in valence band maximum plays an important role in the structural stability. The photo-generated effective electron mass and hole mass at R-point along the R-Γ and R-M directions are estimated to be smaller:m_{e}^{*}=0.06m_{0} and m_{h}^{*}=0.08m_{0} respectively, which are consistent with the values experimentally observed from long range photocarrier transport. The elastic properties are also investigated for the first time, which shows that HC(NH_{2})_{2}PbI_{3} is mechanically stable and ductile and has weaker strength of the average chemical bond. This work sheds light on the understanding of applications of HC(NH_{2})_{2}PbI_{3} as the perovskite in a planar-heterojunction solar cell light absorber fabricated on flexible polymer substrates.

Molecular dynamics (MD) simulations are performed to explore the layering structure and liquid-liquid transition of liquid water confined between two graphene sheets with a varied distance at different pressures. Both the size of nanoslit and pressure could cause the layering and liquid-liquid transition of the confined water. With increase of pressure and the nanoslit's size, the confined water could have a more obvious layering. In addition, the neighboring water molecules firstly form chain structure, then will transform into square structure, and finally become triangle with increase of pressure. These results throw light on layering and liquid-liquid transition of water confined between two graphene sheets.

The structural compression mechanism and compressibility of gallium oxyhydroxide, α -GaOOH, are investigated by in situ synchrotron radiation x-ray diffraction at pressures up to 31.0 GPa by using the diamond anvil cell technique. The α -GaOOH sustains its orthorhombic structure when the pressure is lower than 23.8 GPa. The compression is anisotropic under hydrostatic conditions, with the a-axis being most compressible. The compression proceeds mainly by shrinkage of the void channels formed by the coordination GaO_{3}(OH)_{3} octahedra of the crystal structure. Anomaly is found in the compression behavior to occur at 14.6 GPa, which is concomitant with the equatorial distortion of the GaO_{3}(OH)_{3} octahedra. A kink occurs at 14.6 GPa in the plot of finite strain f versus normalized stress F, indicating the change in the bulk compression behavior. The fittings of a second order Birch-Murnaghan equation of state to the P-V data in different pressure ranges result in the bulk moduli B_{0}=199(1) GPa for P < 14.6 GPa and B_{0}=167(2) GPa for P > 14.6 GPa. As the pressure is increased to about 25.8 GPa, a first-order phase transformation takes place, which is evidenced by the abrupt decrease in the unit cell volume and b and c lattice parameters.

A solid solution of (HfSc)_{0.83}W_{2.25}P_{0.83}O_{12-δ} is synthesized by the high-temperature, solid-state reaction and fast-quenching method. It is shown that it possesses an orthorhombic structure with space group Pmmm (47) and exhibits negative thermal expansion (NTE) property with low anisotropy in thermal expansion. The coefficients of thermal expansion (CTEs) for a, b, and c axes are -1.41×10^{-6} K^{-1}, -2.23×10^{-6} K^{-1}, and -1.87×10^{-6} K^{-1}, respectively. This gives rise to volume and linear CTEs of -3.10×10^{-6} K^{-1} and -1.03×10^{-6} K^{-1}, respectively. Besides, it exhibits also intense photoluminescence from 360 nm to about 600 nm. The mechanism of NTE and the correlation of the PL with axial thermal expansion property are discussed.

Improving the thermal conduction across graphene sheets is of great importance for their applications in thermal management. In this paper, thermal transport across a hybrid structure formed by two graphene nanoribbons and carbon nanorings (CNRs) was investigated by molecular dynamics simulations. The effects of linker diameter, number, and height on thermal conductivity of the CNRs-graphene hybrid structures were studied respectively, and the CNRs were found effective in transmitting the phonon modes of GNRs. The hybrid structure with 2 linkers showed the highest thermal conductivity of 68.8 W·m^{-1}·K^{-1}. Our work presents important insight into fundamental principles governing the thermal conduction across CNR junctions and provides useful guideline for designing CNR-graphene structure with superior thermal conductivity.

Copper (Cu)-doped ZrO_{2} (CZO) films with different Cu content (0 at.%~8.07 at.%) are successfully deposited on Si (100) substrates by direct current (DC) and radio frequency (RF) magnetron co-sputtering. The influences of Cu content on structural, morphological, optical and electrical properties of CZO films are discussed in detail. The CZO films exhibit ZrO_{2} monocline (111) preferred orientation, which indicates that Cu atoms are doped in ZrO_{2} host lattice. The crystallite size estimated form x-ray diffraction (XRD) increases by Cu doping, which accords with the result observed from the scanning electron microscope (SEM). The electrical resistivity decreases from 2.63 Ω.cm to 1.48 Ω·cm with Cu doping content increasing, which indicates that the conductivity of CZO film is improved. However, the visible light transmittances decrease slightly by Cu doping and the optical band gap values decrease from 4.64 eV to 4.48 eV for CZO films.

Resonant radiation force exerted on a semiconductor quantum well nanostructure (QWNS) from intersubband transition of electrons is investigated by taking the nonlocal coupling between the polarizability of electrons and applied optical fields into account for two kinds of polarized states. The numerical results show the spatial nonlocality of optical response can induce the spectral peak position of the exerted force to have a blueshift, which is sensitively dependent on the polarized state and the QWNS width. It is also demonstrated that resonant radiation force is controllable by the polarization and incident directions of applied light waves. This work provides effective methods for controlling optical force and manipulating nano-objects, and observing radiation forces in experiment. This nonlocal interaction mechanism can also be used to probe and predominate internal quantum properties of nanostructures, and to manipulate collective behavior of nano-objects.

Interfacial gaseous nanobubbles which have remarkable properties such as unexpectedly long lifetime and significant potential applications, are drawing more and more attention. However, the recent dispute about the contamination or gas inside the nanobubbles causes a large confusion due to the lack of simple and clean method to produce gas nanobubbles. Here we report a convenient and clean method to effectively produce interfacial nanobubbles based on a pure water system. By adding the cold water cooled at 4 ℃ for more than 48 h onto highly oriented pyrolytic graphite (HOPG) surface, we find that the average density and total volume of nanobubbles are increased to a high level and mainly dominated by the concentrations of the dissolved gases in cold water. Our findings and methods are crucial and helpful for settling the newly arisen debates on gas nanobubbles.

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

The interface properties and electrical characteristics of the n-type 4H-SiC planar and trench metal-oxide-semiconductor (MOS) capacitors are investigated by measuring the capacitance voltage and current voltage. The flat-band voltage and interface state density are evaluated by the quasi-static method. It is not effective on further improving the interface properties annealing at 1250 ℃ in NO ambient for above 1 h due to the increasing interface shallow and fast states. These shallow states reduce the effective positive fixed charge density in the oxide. For the vertical MOS capacitors on the (1120) and (1100) faces, the interface state density can be reduced by approximately one order of magnitude, in comparison to the result of the planar MOS capacitors on the (0001) face under the same NO annealing condition. In addition, it is found that Fowler-Nordheim tunneling current occurs at an oxide electric field of 7 MV/cm for the planar MOS device. However, Poole-Frenkel conduction current occurs at a lower electric field of 4 MV/cm for the trench MOS capacitor. This is due to the local field crowded at the trench corner severely causing the electrons to be early captured at or emitted from the SiO_{2}/SiC interface. These results provide a reference for an in-depth understanding of the mobility-limiting factors and long term reliability of the trench and planar SiO_{2}/SiC interfaces.

In this work, the influence of C concentration to the performance of low temperature growth p-GaN is studied. Through analyses, we have confirmed that the C impurity has a compensation effect to p-GaN. At the same time we have found that several growth and annealing parameters have influences on the residual C concentration:(i) the C concentration decreases with the increase of growth pressure; (ii) we have found there exists a Ga memory effect when changing the Cp_{2}Mg flow which will lead the growth rate and C concentration increase along the increase of Cp_{2}Mg flow; (iii) annealing outside of metal-organic chemical vapor deposition (MOCVD) could decrease the C concentration while in situ annealing in MOCVD has an immobilization role to C concentration.

By using a multi-configurational time-dependent Hartree-Fock (MCTDHF) method for the time-dependent Schrödinger equation and a Newtonian equation of motion for lattice, we investigate the disorder effects on the dissociation process of excitons in conjugated polymer chains. The simulations are performed within the framework of an extended version of the Su-Schrieffer-Heeger model modified to include on-site disorder, off-diagonal, electron-electron interaction, and an external electric field. Our results show that Coulomb correlation effects play an important role in determining the exciton dissociation process. The electric field required to dissociate an exciton can practically impossibly occur in a pure polymer chain, especially in the case of triplet exciton. However, when the on-site disorder effects are taken into account, this leads to a reduction in mean dissociation electric fields. As the disorder strength increases, the dissociation field decreases effectively. On the contrary, the effects of off-diagonal disorder are negative in most cases. Moreover, the dependence of exciton dissociation on the conjugated length is also discussed.

Thermoelectric properties of Li-doped Sr_{0.70}Ba_{0.30}Nb_{2}O_{6-δ} ceramics were investigated in the temperature range from 323 K to 1073 K. The electrical conductivity increases significantly after lithium interstitial doping. However, both of the magnitudes of Seebeck coefficient and electrical conductivity vary non-monotonically but synchronously with the doping contents, indicating that doped lithium ions may not be fully ionized and oxygen vacancy may also contribute to carriers. The lattice thermal conductivity increases firstly and then decreases as the doping content increases, which is affected by competing factors.Thermoelectric performance is enhanced by lithium interstitial doping due to the increase of the power factor and the thermoelectric figure of merit reaches maximum value (0.21 at 1073 K) in the sample Sr_{0.70}Ba_{0.30}Li_{0.10}Nb_{2}O_{6}.

The thermoelectric performance of CdO ceramics was enhanced by simultaneously optimizing the electrical and thermal transport properties via a small amount of Zn doping (≤ 3%). The introduction of Zn can obviously increase the electrical conductivity of CdO due to the simultaneous increase of carrier concentration and mobility, and eventually results in an improvement in power factor. Zn doping is also effective in suppressing the thermal conductivity of CdO because of stronger phonon scatterings from point defects, Zn-riched second phase, and grain boundaries. A best ZT of about 0.45 has been achieved in the Cd_{1-x}Zn_{x}O systems at about 1000 K, which is comparable to the highest values reported for other n-type oxide TE materials.

In this work, we use a 3-nm-thick Al_{0.64}In_{0.36}N back-barrier layer in In_{0.17}Al_{0.83}N/GaN high-electron mobility transistor (HEMT) to enhance electron confinement. Based on two-dimensional device simulations, the influences of Al_{0.64}In_{0.36}N back-barrier on the direct-current (DC) and radio-frequency (RF) characteristics of InAlN/GaN HEMT are investigated, theoretically. It is shown that an effective conduction band discontinuity of approximately 0.5 eV is created by the 3-nm-thick Al_{0.64}In_{0.36}N back-barrier and no parasitic electron channel is formed. Comparing with the conventional InAlN/GaN HEMT, the electron confinement of the back-barrier HEMT is significantly improved, which allows a good immunity to short-channel effect (SCE) for gate length decreasing down to 60 nm (9-nm top barrier). For a 70-nm gate length, the peak current gain cut-off frequency (f_{T}) and power gain cut-off frequency (f_{max}) of the back-barrier HEMT are 172 GHz and 217 GHz, respectively, which are higher than those of the conventional HEMT with the same gate length.

The influences of the spacer-layer Ta on the structures and magnetic properties of NdFeB/NdCeFeB multilayer films are investigated via DC sputtering under an Ar pressure of 1.2 Pa. An obvious (00l) texture of the hard phase is observed in each of the films, which indicates that the main phase of the film does not significantly change with Ta spacer-layer thickness. As a result, both the remanence and the saturation magnetization of the magnet first increase and then decrease, and the maximum values of 4π M_{r} and H_{cj} are 10.4 kGs (1 Gs=10^{-4} T) and 15.0 kOe (1 Oe=79.5775 A·m^{-1}) for the film with a 2-nm-thick Ta spacer-layer, respectively, where the crystalline structures are columnar shape particles. The measured relationship between irreversible portion D (H)=-△ M_{irr}/2M_{r} and H indicates that the nucleation field of the film decreases with spacer layer thickness increasing, owing to slightly disordered grains near the interface between different magnetic layers.

Te-doped GaSb single crystals are studied by measuring Hall effect, infrared (IR) transmission and photoluminescence (PL) spectra. It is found that the n-type GaSb with IR transmittance can be obtained as high as 60% by the critical control of the Te-doping concentration and electrical compensation. The concentration of the native acceptor-associated defects is apparently low in the Te-doped GaSb compared with those in undoped and heavily Te-doped GaSb. The mechanism for the high IR transmittance is analyzed by considering the defect-involved optical absorption process.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Based on the detailed first-principles calculations, we have carefully investigated the defect induced band splitting and its combination with Dirac cone move in bandgap opening. The uniaxial strain can split the π -like bands into π_{a} and π_{z} bands with energy interval E_{strain} to shift the Dirac cone. Also, the inversion symmetry preserved antidot can split π_{a} (π_{z}) into π_{a1} and π_{a2} (π_{z1} and π_{z2}) bands with energy interval E_{defect} to open bandgap in the nanomesh with Γ as four-fold degenerate Dirac point according to the band-folding analysis. Though the E_{defect} would keep almost unaffected, the E_{strain} would be increased by enhancing the uniaxial strain to continuously tune the gap width. Then the bandgap can be reversibly switched on/off. Our studies of the inversion symmetry preserved nanomesh show distinct difference in bandgap opening mechanism as compared to the one by breaking the sublattice equivalence in the (GaAs)_{6} nanoflake patterned nanomesh. Here, the π-band gap remains almost unchanged against strain enhancing.

The growth process of GeO_{x} films formed by plasma post-oxidation (PPO) at room temperature (RT) is investigated using angle-resolved x-ray photoelectron spectroscopy (AR-XPS). The experimental results show that the distributions of the Ge^{4+} states, a mixture of the Ge^{2+} and Ge^{3+} states, and the Ge^{1+} states are localized from the GeO_{x} surface to the GeO_{x}/Ge interface. Moreover, the Ge^{1+} states are predominant when the two outermost layers of Ge atoms are oxidized. These findings are helpful for establishing in-depth knowledge of the growth mechanism of the GeO_{x} layer and valuable for the optimization of Ge-based gate stacks for future complementary metal-oxide-semiconductor (MOS) field-effect transistor (CMOSFET) devices.

The development of inverse synthetic aperture radar (ISAR) imaging techniques is of notable significance for monitoring, tracking and identifying space targets in orbit. Usually, a well-focused ISAR image of a space target can be obtained in a deliberately selected imaging segment in which the target moves with only uniform planar rotation. However, in some imaging segments, the nonlinear range migration through resolution cells (MTRCs) and time-varying Doppler caused by the three-dimensional rotation of the target would degrade the ISAR imaging performance, and it is troublesome to realize accurate motion compensation with conventional methods. Especially in the case of low signal-to-noise ratio (SNR), the estimation of motion parameters is more difficult. In this paper, a novel algorithm for high-resolution ISAR imaging of a space target by using its precise ephemeris and orbital motion model is proposed. The innovative contributions are as follows. 1) The change of a scatterer projection position is described with the spatial-variant angles of imaging plane calculated based on the orbital motion model of the three-axis-stabilized space target. 2) A correction method of MTRC in slant-and cross-range dimensions for arbitrarily imaging segment is proposed. 3) Coarse compensation for translational motion using the precise ephemeris and the fine compensation for residual phase errors by using sparsity-driven autofocus method are introduced to achieve a high-resolution ISAR image. Simulation results confirm the effectiveness of the proposed method.

In this paper we propose a two-pole varactor-tuned superconducting filter using coplanar waveguide (CPW) spiral-in-spiral-out (SISO) resonators. Novel internal and external coupling structures are introduced to meet the requirements for a tunable filter with a constant absolute bandwidth. The fabricated device has a frequency tuning range of 14.4% at frequencies ranging from 274.1 MHz to 317.7 MHz, a 3-dB bandwidth of 5.14 ±0.06 MHz, and an insertion loss of 0.08 dB-0.70 dB. The simulated and measured results are in excellent agreement with each other.

In this study, a novel self-embedding asymmetric stepped impedance resonator (SE-ASIR) topology is proposed. By embedding asymmetric stepped impedance resonators in themselves, circuit sizes of ASIRs can be reduced effectively, while the ability to control spurious modes of ASIRs remains. Therefore, SE-ASIRs are suitable for being used to design filters with wide stopbands and miniaturized sizes. Furthermore, the construction process of the SE-ASIR is described in detail, and an equivalent model of the SE-ASIR is proposed. For demonstration, a high-temperature superconducting bandpass filter centered at 1112 MHz is designed and fabricated. The measured result agrees well with the simulation result and shows that the out-of-band rejection is better than 60 dB up to 4088 MHz, which is about 3.7 times the center frequency. The filter circuit size is 31 mm×13 mm or 0.28 λ_{g}×0.12 λ_{g}, where λ_{g} is the guided wavelength at 1112 MHz.

The impact of negative bias temperature instability (NBTI) can be ascribed to three mutually uncorrelated factors, including hole trapping by pre-existing traps (△ V_{HT}) in gate insulator, generated traps (△ V_{OT}) in bulk insulator, and interface trap generation (△ V_{IT}). In this paper, we have experimentally investigated the NBTI characteristic for a 40-nm complementary metal-oxide semiconductor (CMOS) process. The power-law time dependence, temperature activation, and field acceleration have also been explored based on the physical reaction-diffusion model. Moreover, the end-of-life of stressed device dependent on the variation of stress field and temperature have been evaluated. With the consideration of locking effect, the recovery characteristics have been modelled and discussed.

We demonstrate high-speed blue 4×4 micro-light-emitting-diode (LED) arrays with 14 light-emitting units (two light-emitting units are used as the positive and negative electrodes for power supply, respectively) comprising multiple quantum wells formed of GaN epitaxial layers grown on a sapphire substrate, and experimentally test their applicability for being used as VLC transmitters and illuminations. The micro-LED arrays provide a maximum -3-dB frequency response of 60.5 MHz with a smooth frequency curve from 1 MHz to 500 MHz for an optical output power of 165 mW at an injection current of 30 mA, which, to our knowledge, is the highest response frequency ever reported for blue GaN-based LEDs operating at that level of optical output power. The relationship between the frequency and size of the device single pixel diameter reveals the relationship between the response frequency and diffusion capacitance of the device.

To overcome hole-injection limitation of p^{+}-n emitter junction in 4H-SiC light triggered thyristor, a novel high-voltage 4H-SiC light triggered thyristor with double-deck thin n-base structure is proposed and demonstrated by two-dimensional numerical simulations. In this new structure, the conventional thin n-base is split to double-deck. The hole-injection of p^{+}-n emitter junction is modulated by modulating the doping concentration and thickness of upper-deck thin n-base. With double-deck thin n-base, the current gain coefficient of the top pnp transistor in 4H-SiC light triggered thyristor is enhanced. As a result, the triggering light intensity and the turn-on delay time of 4H-SiC light triggered thyristor are both reduced. The simulation results show that the proposed 10-kV 4H-SiC light triggered thyristor is able to be triggered on by 500-mW/cm^{2} ultraviolet light pulse. Meanwhile, the turn-on delay time of the proposed thyristor is reduced to 337 ns.

X-ray grating interferometer has attracted widely attention in the past years due to its capability in achieving x-ray phase contrast imaging with low brilliance source. However, the widely used phase stepping information extraction method reduces system stability and prolongs data acquisition time by several times compared with conventional x-ray absorption-based imaging. The mechanical stepping can be avoided by using a staggered grating, but at the cost of low vertical spatial resolution. In this paper, employing a modified staggered grating and the angular signal radiography, we proposed a single-shot grating-based x-ray differential phase contrast imaging with decent vertical spatial resolution. The theoretical framework was deduced and proved by numerical experiments. Absorption, phase, and scattering computed tomography can be performed without phase stepping. Therefore, we believe this fast and highly stable imaging method with decent resolution would be widely applied in x-ray grating-based phase contrast imaging.

By inserting a thin highly doped crystalline silicon layer between the base region and amorphous silicon layer in an interdigitated back-contact (IBC) silicon solar cell, a new passivation layer is investigated. The passivation layer performance is characterized by numerical simulations. Moreover, the dependence of the output parameters of the solar cell on the additional layer parameters (doping concentration and thickness) is studied. By optimizing the additional passivation layer in terms of doping concentration and thickness, the power conversion efficiency could be improved by a factor of 2.5%, open circuit voltage is increased by 30 mV and the fill factor of the solar cell by 7.4%. The performance enhancement is achieved due to the decrease of recombination rate, a decrease in solar cell resistivity and improvement of field effect passivation at heterojunction interface. The above-mentioned results are compared with reported results of the same conventional interdigitated back-contact silicon solar cell structure. Furthermore, the effect of a-Si:H/c-Si interface defect density on IBC silicon solar cell parameters with a new passivation layer is studied. The additional passivation layer also reduces the sensitivity of output parameter of solar cell to interface defect density.

The aim of this work is to investigate the influence of rainy weather on traffic accidents of a freeway. The micro-scale driving behaviors in rainy weather and possible vehicle rear-end and sideslip accidents are analyzed. An improved CA model of two lanes one-way freeway is presented, where some vehicle accidents will occur when the necessary conditions are simultaneously satisfied. The characteristics of traffic flow under different rainfall intensities are discussed and the accident probabilities are analyzed via the simulation experiments by using variable speed limit (VSL) and incoming flow control. The results indicate that the measures are effective especially during heavy rainstorms or short-time heavy rainfall. According to different rainfall intensities, an appropriate strategy should be adopted in order to reduce the probability of vehicle accidents and enhance traffic flux as well.

A class of models for activity-driven networks is proposed in which nodes vary in two states:active and inactive. Only active nodes can receive links from others which represent instantaneous dynamical interactions. The evolution of the network couples the addition of new nodes and state transitions of old ones. The active group changes with activated nodes entering and deactivated ones leaving. A general differential equation framework is developed to study the degree distribution of nodes of integrated networks where four different schemes are formulated.

In this study, we deal with the holographic model of interacting dark components of dark energy and dark matter quadratic case of the equation of state parameter (EoS). The effective equations of states for the interacting holographic energy density are derived and the results are analyzed and compared with the solution of the linear form in the literature. The result of our work shows that the value of interaction term between dark components affects the fixed points at far future in the DE-dominated universe in the case of quadratic EoS parameter; it is a different result from the linear case in the theoretical results in the literature, and as the Quintom scenario the equations of state had coincidence at the cosmological constant boundary of -1 from above to below.

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