The concept of smart city gives an excellent resolution to construct and develop modern cities, and also demands infrastructure construction. How to build a safe, stable, and highly efficient public transportation system becomes an important topic in the process of city construction. In this work, we study the structural and robustness properties of transportation networks and their sub-networks. We introduce a complementary network model to study the relevance and complementarity between bus network and subway network. Our numerical results show that the mutual supplement of networks can improve the network robustness. This conclusion provides a theoretical basis for the construction of public traffic networks, and it also supports reasonable operation of managing smart cities.

In this paper, we derive a universal function from a model based on statistical mechanics developed recently, and show that the function is well fitted to all the available experimental data which cannot be described by any function previously established. With the function predicting creep rate, it is unnecessary to consider which creep mechanism dominates the process, but only perform several experiments to determine the three constants in the function. It is expected that the new function would be widely used in industry in the future.

Three-dimensional imaging with single orientation is a potential and novel technique. We successfully demonstrate that three-dimensional (3D) structure can be determined by a single orientation diffraction measurement for a phase object of double-layer Mie-scattering silica spheres on a Si_{3}N_{4} membrane. Coherent diffraction pattern at high numerical aperture was acquired with an optical laser, and the oversampled pattern was projected from a planar detector onto the Ewald sphere. The double-layered spheres are reconstructed from the spherical diffraction pattern and a 2D curvature-corrected pattern, which improve convergence speed and stability of reconstruction.

We develop a nonlinear beam propagation method for signal generation in inhomogeneous medium for wide-field nonlinear wave mixing microscope. Experimental results performed in wide-field coherent anti-Stokes Raman imaging have shown good agreement with the developed theory.

Indacenodithiophene-co-benzothiadiazole (IDTBT) has emerged as one of the most exciting semiconducting polymers in recent years because of its high electronic mobility and charge transport along the polymer backbone. By using the recently developed ion gel gating technique we studied the charge transport of IDTBT at carrier densities up to 10^{21} cm^{-3}. While the conductivity in IDTBT was found to be enhanced by nearly six orders of magnitude by ionic gating, the charge transport in IDTBT was found to remain 3D Mott variable range hopping even down to the lowest temperature of our measurements, 12 K. The maximum mobility was found to be around 0.2 cm^{2}·V^{-1}·s^{-1}, lower than that of Cytop gated field effect transistors reported previously. We attribute the lower mobility to the additional disorder induced by the ionic gating.

This paper is concerned with the problem of delay-dependent robust H_{∞} control for a class of uncertain systems with two additive time-varying delays. A new suitable Lyapunov-Krasovskii functional (LKF) with triple integral terms is constructed and a tighter upper bound of the derivative of the LKF is derived. By applying a convex optimization technique, new delay-dependent robust H_{∞} stability criteria are derived in terms of linear matrix inequalities (LMI). Based on the stability criteria, a state feedback controller is designed such that the closed-loop system is asymptotically stable. Finally, numerical examples are given to illustrate the effectiveness of the proposed method. Comparison results show that our results are less conservative than the existing methods.

For the (2+1)-dimensional Broer-Kaup-Kupershmidt (BKK) system, the nonlocal symmetries related to the Schwarzian variable and the corresponding transformation group are found. Moreover, the integrability of the BKK system in the sense of having a consistent Riccati expansion (CRE) is investigated. The interaction solutions between soliton and cnoidal periodic wave are explicitly studied.

We study the hyperbolic-parabolic equations with rapidly oscillating coefficients. The formal second-order two-scale asymptotic expansion solutions are constructed by the multiscale asymptotic analysis. In addition, we theoretically explain the importance of the second-order two-scale solution by the error analysis in the pointwise sense. The associated explicit convergence rates are also obtained. Then a second-order two-scale numerical method based on the Newmark scheme is presented to solve the equations. Finally, some numerical examples are used to verify the effectiveness and efficiency of the multiscale numerical algorithm we proposed.

A generalized Boussinesq equation that includes the dissipation effect is derived to describe a kind of algebraic Rossby solitary waves in a rotating fluid by employing perturbation expansions and stretching transformations of time and space. Using this equation, the conservation laws of algebraic Rossby solitary waves are discussed. It is found that the mass, the momentum, the energy, and the velocity of center of gravity of the algebraic solitary waves are conserved in the propagation process. Finally, the analytical solution of the equation is generated. Based on the analytical solution, the properties of the algebraic solitary waves and the dissipation effect are discussed. The results point out that, similar to classic solitary waves, the dissipation can cause the amplitude and the speed of solitary waves to decrease; however, unlike classic solitary waves, the algebraic solitary waves can split during propagation and the decrease of the detuning parameter can accelerate the occurrence of the solitary waves fission phenomenon.

This paper considers the formation tracking problem under a rigidity framework, where the target formation is specified as a minimally and infinitesimally rigid formation and the desired velocity of the group is available to only a subset of the agents. The following two cases are considered: the desired velocity is constant, and the desired velocity is time-varying. In the first case, a distributed linear estimator is constructed for each agent to estimate the desired velocity. The velocity estimation and a formation acquisition term are employed to design the control inputs for the agents, where the rigidity matrix plays a central role. In the second case, a distributed non-smooth estimator is constructed to estimate the time-varying velocity, which is shown to converge in a finite time. Theoretical analysis shows that the formation tracking problem can be solved under the proposed control algorithms and estimators. Simulation results are also provided to show the validity of the derived results.

Neural mass models can simulate the generation of electroencephalography (EEG) signals with different rhythms, and therefore the observation of the states of these models plays a significant role in brain research. The structure of neural mass models is special in that they can be expressed as Lurie systems. The developed techniques in Lurie system theory are applicable to these models. We here provide a new observer design method for neural mass models by transforming these models and the corresponding error systems into nonlinear systems with Lurie form. The purpose is to establish appropriate conditions which ensure the convergence of the estimation error. The effectiveness of the proposed method is illustrated by numerical simulations.

This paper studies the distributed H_{∞} control problem of identical linear time invariant multi-agent systems subject to external disturbances. A directed graph containing a spanning tree is used to model the communication topology. Based on the relative states of the neighbor agents and a subset of absolute states of the agents, distributed static H_{∞} controllers are proposed. The concept of an H_{∞} performance region is extended to the directed graph situation. Then the results are used to solve the leader-follower H_{∞} consensus problem. Sufficient conditions are proposed based on bounded real lemma and algebraic graph theory. The effectiveness of the theoretical results is illustrated via numerical simulations.

Security against eavesdroppers is a critical issue in cognitive radio networks (CRNs). In this paper, a scenario consisting of one primary pair and multiple secondary pairs is considered. The secondary transmitters (STs) work in half-duplex mode and they are potential eavesdroppers on the primary transmission unless they are allowed to simultaneously transmit with the primary transmitter (PT). A modified second-price sealed-bid auction scheme is employed to model the interaction between the PT and STs. With the proposed auction scheme, the hostile relationship between the PT and STs is transformed into a cooperative relationship. An iterative algorithm based on the max-min criteria is proposed to find the optimal bidding power of the STs for an access chance in the presence of multiple eavesdroppers. Numerical results show that the proposed auction scheme not only improves the PT's security but also increases the access opportunities of the STs.

We investigate the ground-state Riemannian metric and the cyclic quantum distance of an inhomogeneous quantum spin-1/2 chain in a transverse field. This model can be diagonalized by using a general canonical transformation to the fermionic Hamiltonian mapped from the spin system. The ground-state Riemannian metric is derived exactly on a parameter manifold ring S^{1}, which is introduced by performing a gauge transformation to the spin Hamiltonian through a twist operator. The cyclic ground-state quantum distance and the second derivative of the ground-state energy are studied in different exchange coupling parameter regions. Particularly, we show that, in the case of exchange coupling parameter J_{a}=J_{b}, the quantum ferromagnetic phase can be characterized by an invariant quantum distance and this distance will decay to zero rapidly in the paramagnetic phase.

We find the time evolution law of a negative binomial optical field in a diffusion channel. We reveal that by adjusting the diffusion parameter, the photon number can be controlled. Therefore, the diffusion process can be considered a quantum controlling scheme through photon addition.

We study the effects of the interaction strength and the initial phase on the dynamics of quantum discord in a two-qubit system under both spontaneous emission and dephasing noisy channels. It is shown that the time evolution of quantum discord displays quicker oscillations with increasing inter-qubit interaction strength but the effect of the initial phase closely depends on the interaction between the qubits. Only for non-zero inter-qubit interaction cases, the evolution of quantum discord is affected by the initial phase and its oscillating amplitude increases with increasing initial phase. A comparison between evolutions of quantum discord and entanglement is also made.

We investigate the quantum-memory-assisted entropic uncertainty for an entangled two-qubit system in a local quantum noise channel with JJ-symmetric operation performing on one of the two particles. Our results show that the quantum-memory-assisted entropic uncertainty in the qubits system can be reduced effectively by the local JJ-symmetric operation. Physical explanations for the behavior of the quantum-memory-assisted entropic uncertainty are given based on the property of entanglement of the qubits system and the non-locality induced by the re-normalization procedure for the non-Hermitian JJ-symmetric operation.

In a practical quantum key distribution (QKD) system, imperfect equipment, especially the single-photon detector, can be eavesdropped on by a blinding attack. However, the original blinding attack may be discovered by directly detecting the current. In this paper, we propose a probabilistic blinding attack model, where Eve probabilistically applies a blinding attack without being caught by using only an existing intuitive countermeasure. More precisely, our countermeasure solves the problem of how to define the bound in the limitation of precision of current detection, and then we prove security of the practical system by considering the current parameter. Meanwhile, we discuss the bound of the quantum bit error rate (QBER) introduced by Eve, by which Eve can acquire information without the countermeasure.

In this paper, we suggest a controlled mutual quantum entity authentication protocol by which two users mutually certify each other on a quantum network using a sequence of Greenberger-Horne-Zeilinger (GHZ)-like states. Unlike existing unidirectional quantum entity authentication, our protocol enables mutual quantum entity authentication utilizing entanglement swapping; moreover, it allows the managing trusted center (TC) or trusted third party (TTP) to effectively control the certification of two users using the nature of the GHZ-like state. We will also analyze the security of the protocol and quantum channel.

The influence of intrinsic decoherence on various correlations and dense coding in a model which consists of two identical superconducting charge qubits coupled by a fixed capacitor is investigated. The results show that, despite the intrinsic decoherence, the correlations as well as the dense coding channel capacity can be effectively increased via the combination of system parameters, i.e., the mutual coupling energy between the two charge qubits is larger than the Josephson energy of the qubit. The bigger the difference between them is, the better the effect is.

Interaction between Rydberg atoms can be used to control the properties of interatomic interaction in ultracold gases by weakly dressing the atoms with a Rydberg state. Here we investigate the effect of the Rydberg-dressing interaction on the ground-state properties of a Bose-Einstein condensate imposed by Raman-induced spin-orbit coupling. We find that, in the case of SU(2)-invariant s-wave interactions, the gas is only in the plane-wave phase and the zero-momentum phase is absent. In particular, we also predict an unexpected magnetic stripe phase composed of two plane-wave components with unequal weight when s-wave interactions are non-symmetric, which originates from the Rydberg-dressing interaction.

With thermal Bose-Fermi mapping method, we investigate the Tonks-Girardeau gas at finite temperature. It is shown that at low temperature, the Tonks gas displays the Fermi-like density profiles, and with the increase in temperature, the Tonks gas distributes in wider region. The reduced one-body density matrix is diagonal dominant in the whole temperature region, and the off-diagonal elements shall vanish rapidly with the deviation from the diagonal part at high temperature.

The invariance of specific mass increments of crystalline structures that co-exist in the case of non-equilibrium growth is grounded for the first time by using the maximum entropy production principle. Based on the hypothesis of the existence of a universal growth equation, and through the dimensional analysis, an explicit form of the time-dependent specific mass increment is proposed. The applicability of the obtained results for describing growth in animate nature is discussed.

A cellular automaton model for the ventricular myocardium considering the layer structure has been established. The three types of cells in this model differ principally in the repolarization characteristics. For the normal travelling waves in this model, the computer simulation results show the R, S, and T waves and they are qualitatively in agreement with the standard electrocardiograph. Phenomena such as the potential decline of point J and segment ST and the rise of the potential line after the T wave appear when the ischemia occurs in the endocardium. The spiral wave has also been simulated, and the corresponding potential has a lower amplitude, higher frequency, and wider R wave, which accords with the distinguishing feature of the clinical electrocardiograph. Mechanisms underlying the above phenomena are analyzed briefly.

This paper estimates an off-policy integral reinforcement learning (IRL) algorithm to obtain the optimal tracking control of unknown chaotic systems. Off-policy IRL can learn the solution of the HJB equation from the system data generated by an arbitrary control. Moreover, off-policy IRL can be regarded as a direct learning method, which avoids the identification of system dynamics. In this paper, the performance index function is first given based on the system tracking error and control error. For solving the Hamilton-Jacobi-Bellman (HJB) equation, an off-policy IRL algorithm is proposed. It is proven that the iterative control makes the tracking error system asymptotically stable, and the iterative performance index function is convergent. Simulation study demonstrates the effectiveness of the developed tracking control method.

In this paper the synchronization for two different fractional-order chaotic systems, capable of guaranteeing synchronization error with prescribed performance, is investigated by means of the fractional-order control method. By prescribed performance synchronization we mean that the synchronization error converges to zero asymptotically, with convergence rate being no less than a certain prescribed function. A fractional-order synchronization controller and an adaptive fractional-order synchronization controller, which can guarantee the prescribed performance of the synchronization error, are proposed for fractional-order chaotic systems with and without disturbances, respectively. Finally, our simulation studies verify and clarify the proposed method.

This paper proposes cooperative adaptive control schemes for a train platoon to improve efficient utility and guarantee string stability. The control schemes are developed based on a bidirectional strategy, i.e., the information of proximal (preceding and following) trains is used in the controller design. Based on available proximal information (prox-info) of location, speed, and acceleration, a direct adaptive control is designed to maintain the tracking interval at the minimum safe distance. Based on available prox-info of location, an observer-based adaptive control is designed to achieve the same target, which alleviates the requirements of equipped sensors to measure prox-info of speed and acceleration. The developed schemes are capable of on-line estimating of the unknown system parameters and stabilizing the closed-loop system, the string stability of train platoon is guaranteed on the basis of Lyapunov stability theorem. Numerical simulation results are presented to verify the effectiveness of the proposed control laws.

This paper describes the standardization of the proton-induced x-ray emission (PIXE) technique for finding the elemental composition of thick samples. For the standardization, three different samples of standard reference materials (SRMs) were analyzed using this technique and the data were compared with the already known data of these certified SRMs. These samples were selected in order to cover the maximum range of elements in the periodic table. Each sample was irradiated for three different values of collected beam charges at three different times. A proton beam of 2.57 MeV obtained using 5UDH-II Pelletron accelerator was used for excitation of x-rays from the sample. The acquired experimental data were analyzed using the GUPIXWIN software. The results show that the SRM data and the data obtained using the PIXE technique are in good agreement.

Covalent bonds arise from the overlap of the electronic clouds in the internucleus region, which is a pure quantum effect and cannot be obtained in any classical way. If the intermolecular interaction is of covalent character, the result from direct applications of classical simulation methods to the molecular system would be questionable. Here, we analyze the special intermolecular interaction between two NO molecules based on quantum chemical calculation. This weak intermolecular interaction, which is of covalent character, is responsible for the formation of the NO dimer, (NO)_{2}, in its most stable conformation, a cis conformation. The natural bond orbital (NBO) analysis gives an intuitive illustration of the formation of the dimer bonding and antibonding orbitals concomitant with the breaking of the π bonds with bond order 0.5 of the monomers. The dimer bonding is counteracted by partially filling the antibonding dimer orbital and the repulsion between those fully or nearly fully occupied nonbonding dimer orbitals that make the dimer binding rather weak. The direct molecular mechanics (MM) calculation with the UFF force fields predicts a trans conformation as the most stable state, which contradicts the result of quantum mechanics (QM). The lesson from the investigation of this special system is that for the case where intermolecular interaction is of covalent character, a specific modification of the force fields of the molecular simulation method is necessary.

To improve the energy resolution (ΔE) of Nb/Al superconducting tunnel junctions (STJs), an ozone (O_{3}) oxidation process has been developed to fabricate a thin defect-free tunnel barrier that simultaneously shows high critical current J_{C} > 1000 A/cm^{2} and high normalized dynamic resistance R_{D}A > 100 MΩ · μm^{2}, where A is the size of the STJ. The 50-μm^{2} STJs produced by O_{3} exposure of 0.26 Pa· min with an indirect spray of O_{3} gas, which is a much lower level of exposure than the O_{2} exposure used in a conventional O_{2} oxidation process, exhibit a maximum J_{C} = 800 A/cm^{2} and a high R_{D}A= 372 MΩ · μm^{2}. The 100-pixel array of the 100-μm^{2} STJs produced using the same O_{3} oxidation conditions exhibits a constant leak current I_{leak} = 14.9 ± 3.2 nA at a bias point around Delta /e (where e is half the energy gap of an STJ), and a high fabrication yield of 87%. Although the I_{leak} values are slightly larger than those of STJs produced using the conventional O_{2} oxidation process, the STJ produced using O_{3} oxidation shows a ΔE = 10 eV for the C-Kα line, which is the best value of our Nb/Al STJ x-ray detectors.

The tunneling ionization rates of vibrationally excited N_{2} molecules at the ground electronic state are calculated using molecular orbital Ammosov-Delone-Krainov theory considering R-dependence. The results show that molecular alignment significantly affects the ionization rate, as the rate is mainly determined by the electron density distribution of the highest occupied molecular orbital. The present work indicates that the ratios of alignment-dependent rates of different vibrational levels to that of the vibrational ground level increase for the aligned N_{2} at the angle θ= 0°, and suggests that the alignment-dependent tunneling ionization rates can be used as a diagnostics for the influence of vibrational excitation on the strong field ionization of molecules.

By solving a time-dependent Schrödinger equation (TDSE), we studied the electron capture process in the He^{2+}+H collision system under a strong magnetic field in a wide projectile energy range. The strong enhancement of the total charge transfer cross section is observed for the projectile energy below 2.0 keV/u. With the projectile energy increasing, the cross sections will reduce a little and then increase again, compared with those in the field-free case. The cross sections to the states with different magnetic quantum numbers are presented and analyzed where the influence due to Zeeman splitting is obviously found, especially in the low projectile energy region. The comparison with other models is made and the tendency of the cross section varying with the projectile energy is found closer to that from other close coupling models.

We have employed recoil-induced resonance (RIR) with linewidth on the order of 10 kHz to demonstrate the fast thermometry for ultracold atoms. We theoretically calculate the absorption spectrum of RIR which agrees well with the experimental results. The temperature of the ultracold sample derived from the RIR spectrum is T=84± 4.5 μK, which is close to 85 μK that measured by the method of time-of-flight absorption imaging. To exhibit the fast measurement advantage in applying RIR to the ultracold atom thermometry, we study the dependence of ultracold sample temperature on the trapping beam frequency detuning. This method can be applied to determine the translational temperature of molecules in photoassociation dynamics.

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

The modern landmine's electronic fuse is susceptible to strong interference or can even be damaged by the ultra-wide band electromagnetic pulse (UWB-EMP). The finite-difference time-domain (FDTD) method in lossy media with cylindrical coordinates is used to study the interactions of the UWB-EMP with the landmine. First, the coupling of UWB-EMP into the landmine shielding shell through an aperture is numerically simulated. Second, the coupled electromagnetic field of mine shells made of different shielding materials and with apertures of different sizes is plotted. Third, the aperture coupling laws of UWB-EMP into shells are analyzed and categorized. Such an algorithm is capable of effectively preventing ladder similar errors, and consequently improving the calculation precision, and in addition to adopting the message passing interface (MPI) parallel method to divide the total calculating range into more sub-ranges, the overall calculating efficiency is greatly increased. These calculations are surely a constructive reference for modern landmine design against electromagnetic damage.

In this paper, the enhanced terahertz radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch, in a structure consisting of a monolayer graphene supported on a dielectric grating with arbitrary profile is investigated. The results show that the grating profile has significant influence on the dispersion curves and radiation characteristics including radiation frequency and intensity. The dependence of dispersion and radiation characteristics on the grating shape for both the symmetric and asymmetric gratings is studied in detail. Moreover, we find that, for an asymmetric grating with certain profile, there exist two different diffraction types, and one of the two types can provide higher radiation intensity comparing to the other one. These results will definitely facilitate the practical application in developing a room-temperature, tunable, coherent and miniature terahertz radiation source.

We analyze the distribution properties of phase and phase vortices in a speckle field generated by N-pinhole random screens, and find that the phase vortex distributions show similarity and clustering in local regions. The phase patterns have a lot of sets composed of two phase vortices with opposite signs or four phase vortices which are positive and negative vortices alternately. Cases are also found where two adjacent phase vortices have the same topological charges. The density of phase vortices becomes larger with the increase of the radius of circumference and the number of pinholes on screen. Then, the relative positions of phase vortices can be adjusted by changing the radius of circumference and the number of pinholes.

We study the Gaussian laser transmission in lithium niobate crystal (LiNbO_{3}) by using the finite element method to solve the electromagnetic field's frequency domain equation and energy equation. The heat generated is identified by calculating the transmission loss of the electromagnetic wave in the birefringence crystal, and the calculated value of the heat generated is substituted into the energy equation. The electromagnetic wave's energy losses induced by its multiple refractions and reflections along with the resulting physical property changes of the lithium niobate crystal are considered. Influences of ambient temperature and heat transfer coefficient on refraction and walk-off angles of O-ray and E-ray in the cases of different incident powers and crystal thicknesses are analyzed. The E-ray electrical modulation instances, in which the polarized light waveform is adjusted to the rated condition via an applied electrical field in the cases of different ambient temperatures and heat transfer coefficients, are provided to conclude that there is a correlation between ambient temperature and applied electrical field intensity and a correlation between surface heat transfer coefficient and applied electrical field intensity. The applicable electrical modulation ranges without crystal breakdown are proposed. The study shows that the electrical field-adjustable heat transfer coefficient range becomes narrow as the incident power decreases and wide as the crystal thickness increases. In addition, it is pointed out that controlling the ambient temperature is easier than controlling the heat transfer coefficient. The results of the present study can be used as a quantitative theoretical basis for removing the adverse effects induced by thermal deposition due to linear laser absorption in the crystal, such as depolarization or wave front distortion, and indicate the feasibility of adjusting the refractive index in the window area by changing the heat transfer boundary conditions in a wide-spectrum laser.

Based on Akaike's information criterion (AIC) for a coherently driven ensemble of cold rubidium atoms, we study the crossover between electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting from the dispersion as well as the absorption viewpoint. We find that the dispersion signal is more sensitive than the absorption signal, showing more pronounced features in the Akaike per-point weights spectrum, which provides a cleaner way of discerning EIT from AT splitting.

We study the optical properties of a two-level atomic ensemble controlled by a high-finesse cavity. Even though the cavity is initially in the vacuum state in the absence of external driving, the probe response of the atomic ensemble can be dramatically modified. When the collectively enhanced atom-cavity coupling is strong enough and the cavity decay rate is much smaller than the atomic damping rate, an electromagnetically induced transparency-like coherent phenomenon emerges with a dip absorption for the response of the two-level atoms in the cavity without driving, and thus is called vacuum induced transparency. We also show the slow light with very low group velocity in such an atomic ensemble.

Atomic density is a basic and important parameter in quantum optics, nonlinear optics, and precision measurement. In the past few decades, several methods have been used to measure atomic density, such as thermionic effect, optical absorption, and resonance fluorescence. The main error of these experiments stemmed from depopulation of the energy level, self-absorption, and the broad bandwidth of the laser. Here we demonstrate the atomic density of ^{87}Rb vapor in paraffin coated cell between 297 K and 334 K mainly using fluorescence measurement. Optical pumping, anti-relaxation coating, and absorption compensation approaches are used to decrease measurement error. These measurement methods are suitable for vapor temperature at dozens of degrees. The fitting function for the experimental data of ^{87}Rb atomic density is given.

In this paper we investigate the optical properties of an open four-level tripod atomic system driven by an elliptically polarized probe field and compare its properties with the corresponding closed system. Our results reveal that absorption, dispersion, group velocity, and optical bistability of the probe field can be manipulated by adjusting the phase difference between the two circularly polarized components of a single coherent field and cavity parameters, i.e., the atomic exit rate from cavity and atomic injection rates.

Terahertz quantum cascade lasers (THz QCLs) emitted at 4.4 THz are fabricated and characterized. An equivalent circuit model is established based on the five-level rate equations to describe their characteristics. In order to illustrate the capability of the model, the steady and dynamic performances of the fabricated THz QCLs are simulated by the model. Compared to the sophisticated numerical methods, the presented model has advantages of fast calculation and good compatibility with circuit simulation for system-level designs and optimizations. The validity of the model is verified by the experimental and numerical results.

For distributed fiber Raman amplifiers (DFRAs), stimulated Brillouin scattering (SBS) can deplete the pump once occurring and consequently generate gain saturation. On the basis of such a theory, theoretical gain saturation powers in DFRAs with various pump schemes are obtained by calculating SBS thresholds in them, and the experimental results show that they are in excellent agreement with the calculation results. The saturation power of the DFRA with a 300 mW forward pump is as low as 0 dBm, which needs to be enhanced by phase modulation, and the effect is quantitatively studied. A simple model taking both modulation frequency and index into consideration is presented by introducing a correction factor to evaluate the effect of phase modulation on the enhancement of saturation power. Experimentally, it is shown that such a correction factor decreases as the modulation frequency increases and approaches zero when the modulation frequency becomes high enough. In particular, a phase modulation with a modulation frequency of 100 MHz and a modulation index of 1.380 can enhance the saturation power by 4.44 dB, and the correction factor is 0.25 dB, in which the modulation frequency is high enough. Additionally, the factor is 1.767 dB for the modulation frequency of 25 MHz. On this basis, phase modulations with various indexes and a fixed frequency of 25 MHz are adopted to verify the modified model, and the results are positive. To obtain the highest gain saturation power, the model is referable. The research results provide a guide for the design of practical DFRAs.

Brillouin amplification is a new method to obtain high power hundred-picosecond laser pulses for shock ignition. The laser pulse's intensity can be amplified to 10 GW/cm^{2} through this method. In order to determine the near-field quality, the relationship between the Brillouin amplification gain and the B integral in the stimulated Brillouin scattering (SBS) energy transfer process was studied, and numerical simulations and calculations were carried out to explain the process. For achieving an output intensity of 10 GW/cm^{2} under the condition that the effect of small-scale self-focusing is insignificant in the Brillouin amplification, the influence of the configuration parameters on the Brillouin amplification and the B integral was investigated. The results showed that the 10 GW/cm^{2} high power output can be obtained by optimizing the intensities of the pump and Stokes light and choosing an appropriate SBS medium.

A correction considering the effects of atmospheric temperature, pressure, and Mie contamination must be performed for wind retrieval from a Rayleigh Doppler lidar (RDL), since the so-called Rayleigh response is directly related to the convolution of the optical transmission of the frequency discriminator and the Rayleigh-Brillouin spectrum of the molecular backscattering. Thus, real-time and on-site profiles of atmospheric pressure, temperature, and aerosols should be provided as inputs to the wind retrieval. Firstly, temperature profiles under 35 km and above the altitude are retrieved, respectively, from a high spectral resolution lidar (HSRL) and a Rayleigh integration lidar (RIL) incorporating to the RDL. Secondly, the pressure profile is taken from the European Center for Medium range Weather Forecast (ECMWF) analysis, while radiosonde data are not available. Thirdly, the Klett-Fernald algorithms are adopted to estimate the Mie and Rayleigh components in the atmospheric backscattering. After that, the backscattering ratio is finally determined in a nonlinear fitting of the transmission of the atmospheric backscattering through the Fabry-Perot interferometer (FPI) to a proposed model. In the validation experiments, wind profiles from the lidar show good agreement with the radiosonde in the overlapping altitude. Finally, a continuous wind observation shows the stability of the correction scheme.

Spectral and directional control of thermal emission based on excitation of confined electromagnetic resonant modes paves a viable way for the design and construction of microscale thermal emitters/absorbers. In this paper, we present numerical simulation results of the thermal radiative properties of a silicon carbide (SiC) thermal emitter/absorber composed of periodic microstructures. We illustrate different electromagnetic resonant modes which can be excited with the structure, such as surface phonon polaritons, magnetic polaritons and photonic crystal modes, and the process of radiation spectrum optimization based on a non-linear optimization algorithm. We show that the spectral and directional control of thermal emission/absorption can be efficiently achieved by adjusting the geometrical parameters of the structure. Moreover, the optimized spectrum is insensitive to 3% dimension modification.

We propose a novel two-dimensional photonic crystal structure consisting of two line defect waveguides and a cavity to realize mode conversion based on the coupling effect. The W1/cavity/W2 structure breaks the spatial symmetry and successfully converts the even (odd) mode to the odd (even) mode in the W2 waveguide during the forward (backward) transmission. When considering the incidence of only the even mode, the optical diode effect emerges and achieves approximate 35 dB unidirectionality at the resonant frequency. Moreover, owing to the narrow bandpass feature and the flexibility of the tuning cavity, utilization of the proposed structure as a wavelength filter is demonstrated in a device with a Y-branch splitter. Here, we provide a heuristic design for a mode converter, optical diode, and wavelength filter derived from the coupling effect between a cavity and adjacent waveguides, and expect that the proposed structure can be applied as a building block in future all-optical integrated circuits.

To improve the link efficiency and decrease the payloads in space explorations, a novel simultaneous communication and ranging method based on x-ray communication (XCOM) is proposed in this paper. A delicate signal symbol structure is utilized to achieve simultaneous data transmission and range measurement. With the designed symbol structure, the ranging information is imbedded into the communication signal and transmitted with it simultaneously. The range measurement is realized by the two-way transmission of the range information. To illustrate the proposed method, firstly, the principle of the method is introduced and the signal processing procedure is presented. Then, the performance of the proposed method is analyzed theoretically in various aspects, including the acquisition probability, the bit error rate, the ranging jitter, etc. Besides, numerical experiments are conducted to verify the proposed method and evaluate the system performance. The simulation results show that the proposed method is feasible and that the system performance is influenced by the parameters concerning the signal symbol structure. Compared with the previous methods, the proposed method improves the link efficiency and is beneficial for system miniaturization and integration, which could provide a potential option for future deep space explorations.

The 30 at.% Ho: BaY_{2}F_{8} crystals were grown by the Czochralski method, and their spectroscopic properties are analyzed systematically by standard Judd-Ofelt theory. The Judd-Ofelt intensity parameters are estimated to be Ω_{2}=6.74× 10^{-20}cm^{2}, Ω_{4}=1.20× 10^{-20} cm^{2}, and Ω_{6}=0.66× 10^{-20}cm^{2}, and the fluorescence branching ratios and radiative lifetimes for a series of excited state manifolds are also determined. The emission cross sections with our measured infrared luminescence spectra, especially important for 4.1 μm, are calculated to be about 4.37× 10^{-21} cm^{2}. The crystal quality is preliminarily tested through a mid-infrared laser emission experiment.

A model of an ultrasound-driven encapsulated microbubble (EMB) oscillation near biomaterial wall is presented and used for describing the microflow-induced shear stress on the wall by means of a numerical method. The characteristic of the model lies in the explicit treatment of different types of wall for the EMB responses. The simulation results show that the radius-time change trends obtained by our model are consistent with the existing models and experimental results. In addition, the effect of the elastic wall on the acoustic EMB response is stronger than that of the rigid wall, and the shear stress on the elastic wall is larger than that of the rigid wall. The closer the EMB to the wall, the greater the shear stress on the wall. The substantial shear stress on the wall surface occurs inside a circular zone with a radius about two-thirds of the bubble radius. This paper may be of interest in the study of potential damage mechanisms to the microvessel for drug and gene delivery due to sonoporation.

The mechanical properties, such as the elastic constants C_{11}, C_{12}, C_{44}, and bulk, Young's, and shear moduli, of a Ga_{x}In_{1-x}As_{y}P_{1-y} alloy lattice matching to a GaAs substrate are calculated for various As concentrations. The calculations are based on the pseudo-potential method within the virtual crystal approximation containing the effective disorder potential. The variations of the studied properties with pressure and temperature are investigated. A comparison between the calculated results and the available published data for binary parent compounds shows that they have good agreement, while the calculated results for the quaternary alloys at various temperature and pressure may be taken as a reference.

Laser-driven flier impact experiments have been designed and performed at the SG-III prototype laser facility. The continuum phase plate (CPP) technique is used for the 3 ns quadrate laser pulse to produce a relatively uniform irradiated spot of 2 mm. The peak laser intensity is 2.7× 10^{13} W/cm^{2} and it accelerates the aluminum flier with a density gradient configuration to a high average speed of 21.3 km/s, as determined by the flight-of-time method with line VISAR. The flier decelerates on impact with a transparent silica window, providing a measure of the flatness of the flier after one hundred microns of flight. The subsequent shock wave acceleration, pursuing, and decay in the silica window are interpreted by hydrodynamic simulation. This method provides a promising method to create unique conditions for the study of a material's properties.

The combustion of magnesium particles in water vapor is of interest for underwater propulsion and hydrogen production. In this work, the combustion process of a single magnesium particle in water vapor is studied both experimentally and theoretically. Combustion experiments are conducted in a combustor filled with motionless water vapor. Condensation of gas-phase magnesia on the particle surface is confirmed and gas-phase combustion flame characteristics are observed. With the help of an optical filter and a neutral optical attenuator, flame structures are captured and determined. Flame temperature profiles are measured by an infrared thermometer. Combustion residue is a porous oxide shell of disordered magnesia crystal, which may impose a certain influence on the diffusivity of gas phases. A simplified one-dimensional, spherically symmetric, quasi-steady combustion model is then developed. In this model, the condensation of gas-phase magnesia on the particle surface and its influence on the combustion process are included, and the Stefan problem on the particle surface is also taken into consideration. With the combustion model, the parameters of flame temperature, flame diameter, and the burning time of the particle are solved analytically under the experimental conditions. A reasonable agreement between the experimental and modeling results is demonstrated, and several features to improve the model are identified.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

We construct a cubically nonlinear theory of plural interactions between harmonics of the growing space charge wave (SCW) during the development of the two-stream instability. It is shown that the SCW with a wide frequency spectrum is formed when the frequency of the first SCW harmonic is much lower than the critical frequency of the two-stream instability. Such SCW has part of the spectrum in which higher harmonics have higher amplitudes. We analyze the dynamics of the plural harmonic interactions of the growing SCW and define the saturation harmonic levels. We find the mechanisms of forming the multiharmonic SCW for the waves with frequencies lower than the critical frequency and for the waves with frequencies that exceed the critical frequency.

The intrinsic radial magnetic field (B_{r}) in a tokamak is explored by the solution of the Grad-Shafranov equation in axisymmetric configurations through an expansion of the four terms of the magnetic surfaces. It can be inferred from the simulation results that at the core of the device, the tokamak should possess a three-dimensional magnetic field configuration, which could be reduced to a two-dimensional one when the radial position is greater than 0.6a. The radial magnetic field and the amzimuthal magnetic field have the same order of magnitude at the core of the device. These results can offer a reference for the analysis of the plasma instability, the property of the core plasma, and the magnetic field measurement.

In this work, a two-dimensional fluid model has been employed to study the characteristics of Ar/O_{2} radio frequency (RF) inductively coupled plasma discharges. The emphasis of this work has been put on the influence of the external parameters (i.e., the RF power, the pressure, and the Ar/O_{2} gas ratio) on the plasma properties. The numerical results show that the RF power has a significant influence on the amplitude of the plasma density rather than on the spatial distribution. However, the pressure and the Ar/O_{2} gas ratio affect not only the amplitude of the plasma density, but also the spatial uniformity. Finally, the comparison between the simulation results and the experimental data has been made at different gas pressures and oxygen contents, and a good agreement has been achieved.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Uniform InN nanowires were studied under pressures up to 35.5 GPa by using in situ synchrotron radiation x-ray diffraction technique at room temperature. An anomalous phase transition behavior has been discovered. Contrary to the results in the literature, which indicated that InN undergoes a fully reversible phase transition from the wurtzite structure to the rocksalt type structure, the InN nanowires in this study unusually showed a partially irreversible phase transition. The released sample contained the metastable rocksalt phase as well as the starting wurtzite one. The experimental findings of this study also reveal the potentiality of high pressure techniques to synthesize InN nanomaterials with the metastable rocksalt type structure, in addition to the generally obtained zincblende type one.

The clay force field (CLAYFF) was supplemented by fluorine potential parameters deriving from experimental structures and used to model various topazes. The calculated cell parameters agree well with the observed structures. The quasi-linear correlation of the b lattice parameter to different F/OH ratios calculated by changing fluorine contents in OH-topaz supports that the F content can be measured by an optical method. Hydrogen bond calculations reveal that the hydrogen bond interaction to H1 is stronger than that to H2, and the more fluorine in the structure, the stronger the hydrogen bond interaction of hydroxyl hydrogen. Defect calculations provide the formation energies of all common defects and can be used to judge the ease of formation of them. The calculated vibrational frequencies are fairly consistent with available experimental results, and the 1080-cm^{-1} frequency often occurring in natural OH-topaz samples can be attributed to Si-F stretching because of the F substitution to OH and the Al-Si exchange.

Yang Yi-Bin, Liu Ming-Gang, Chen Wei-Jie, Han Xiao-Biao, Chen Jie, Lin Xiu-Qi, Lin Jia-Li, Luo Hui, Liao Qiang, Zang Wen-Jie, Chen Yin-Song, Qiu Yun-Ling, Wu Zhi-Sheng, Liu Yang, Zhang Bai-Jun

Chin. Phys. B 2015, 24 (9): 096103; doi: 10.1088/1674-1056/24/9/096103
Full Text: PDF (527KB) (
505
) RICH HTML^{}

In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3× 2" Thomas Swan close coupled showerhead metal organic chemical vapor deposition (MOCVD) system. The reflectivity mapping method is usually used to measure the film thickness and growth rate. The wafer bowing caused by stresses (tensile and compressive) during the epitaxial growth leads to a temperature variation at different positions on the wafer, and the lower growth temperature leads to a faster growth rate and vice versa. Therefore, the wafer bowing can be measured by analyzing the discrepancy of growth rates at different positions on the wafer. Furthermore, the wafer bowings were confirmed by the ex-situ wafer bowing measurement. High-resistivity and low-resistivity Si substrates were used for epitaxial growth. In comparison with low-resistivity Si substrate, GaN grown on high-resistivity substrate shows a larger wafer bowing caused by the highly compressive stress introduced by compositionally graded AlGaN buffer layer. This transition of wafer bowing can be clearly in-situ measured by using the reflectivity mapping method.

The structural, elastic, and electronic properties of a series of lanthanide hexaborides (LnB_{6}) have been investigated by performing ab initio calculations based on the density functional theory using the Vienna ab initio simulation package. The calculated lattice and elastic constants of LnB_{6} are in good agreement with the available experimental data and other theoretical results. The polycrystalline Young's modulus, shear modulus, the ratio of bulk to shear modulus B/G, Poisson's ratios, Zener anisotropy factors, as well as the Debye temperature are calculated, and all of the properties display some regularity with increasing atomic number of lanthanide atoms, whereas anomalies are observed for EuB_{6} and YbB_{6}. In addition, detailed electronic structure calculations are carried out to shed light on the peculiar elastic properties of LnB_{6}. The total density of states demonstrates the existence of a pseudogap and indicates lower structure stability of EuB_{6} and YbB_{6} compared with others.

The effect of tilt interfaces and layer thickness of Cu/Ni multilayer nanowires on the deformation mechanism are investigated by molecular dynamics simulations. The results indicate that the plasticity of the sample with a 45° tilt angle is much better than the others. The yield stress is found to decrease with increasing the tilt angle and it reaches its lowest value at 33°. Then as the tilt angle continues to increase, the yield strength increases. Furthermore, the studies show that with the decrease of layer thickness, the yield strength gradually decreases. The study also reveals that these different deformation behaviors are associated with the glide of dislocation.

The oxidation of nanoscale 3C-SiC involving four polar faces (C(100), Si(100), C(111), and Si(111)) is studied by means of a reactive force field molecular dynamics (ReaxFF MD) simulation. It is shown that the consistency of 3C-SiC structure is broken over 2000 K and the low-density carbon chains are formed within SiC slab. By analyzing the oxygen concentration and fitting to rate theory, activation barriers for C(100), Si(100), C(111), and Si(111) are found to be 30.1, 35.6, 29.9, and 33.4 kJ·mol^{-1}. These results reflect lower oxidative stability of C-terminated face, especially along [111] direction. Compared with hexagonal polytypes of SiC, cubic phase may be more energy-favorable to be oxidized under high temperature, indicating polytype effect on SiC oxidation behavior.

The viscosities of a series of Cu-Ag melts in a temperature range from 1473 K to nearly liquid temperatures are measured by using an oscillating viscometer. At the same temperature, the value of viscosity increases first with silver content increasing, and reaches a maximum value at the eutectic component Cu_{40}Ag_{60}, then decreases. All the temperature dependences of the viscosities of Cu-Ag melts conform with the Arrhenius equation. The parameters of correlation length D of the studied Cu-Ag melts are calculated according to the experimental results of x-ray diffraction. The temperature dependence of correlation length D shows an exponential decay function, which is similar to the Arrhenius equation. Based on the values of viscosities and correlation length D, a direct correlation between viscosity and liquid structure is found for the investigated Cu-Ag melts through comparative analysis.

Molecular dynamics simulations show that the gas dissolved in water can be adsorbed at a hydrophobic interface and accumulates thereon. Initially, a water depletion layer appears on the hydrophobic interface. Gas molecules then enter the depletion layer and form a high-density gas-enriched layer. Finally, the gas-enriched layer accumulates to form a nanobubble. The radian of the nanobubble increases with time until equilibrium is reached. The equilibrium state arises through a Brenner-Lohse dynamic equilibrium mechanism, whereby the diffusive outflux is compensated by an influx near the contact line. Additionally, supersaturated gas also accumulates unsteadily in bulk water, since it can diffuse back into the water and is gradually adsorbed by a solid substrate.

AlGaN/AlN/GaN structures are grown by metalorganic vapor phase epitaxy on sapphire substrates. Influences of AlN interlayer thickness, AlGaN barrier thickness, and Al composition on the two-dimensional electron gas (2DEG) performance are investigated. Lowering the V/III ratio and enhancing the reactor pressure at the initial stage of the high-temperature GaN layer growth will prolong the GaN nuclei coalescence process and effectively improve the crystalline quality and the interface morphology, diminishing the interface roughness scattering and improving 2DEG mobility. AlGaN/AlN/GaN structure with 2DEG sheet density of 1.19× 10^{13} cm^{-2}, electron mobility of 2101 cm^{2}·V^{-1}·s^{-1}, and square resistance of 249 Ω is obtained.

An efficient interface modification is introduced to improve the performance of polymeric thin film transistors. This efficient interface modification is first achieved by 4-fluorothiophenol (4-FTP) self-assembled monolayers (SAM) to chemically treat the silver source-drain (S/D) contacts while the silicon oxide (SiO_{2}) dielectric interface is further primed by either hexamethyldisilazane (HMDS) or octyltrichlorosilane (OTS-C8). Results show that contact resistance is the dominant factor that limits the field effect mobility of the PTDPPTFT4 transistors. With proper surface modification applied to both the dielectric surface and the bottom contacts, the field effect mobilities of the bottom-gate bottom-contact PTDPPTFT4 transistors were significantly improved from 0.15 cm^{2}·V^{-1}·s^{-1} to 0.91 cm^{2}·V^{-1}·s^{-1}.

Li Xiao-Jing, Zhao De-Gang, Jiang De-Sheng, Chen Ping, Zhu Jian-Jun, Liu Zong-Shun, Le Ling-Cong, Yang Jing, He Xiao-Guang, Zhang Li-Qun, Liu Jian-Ping, Zhang Shu-Ming, Yang Hui

Chin. Phys. B 2015, 24 (9): 096804; doi: 10.1088/1674-1056/24/9/096804
Full Text: PDF (330KB) (
279
) RICH HTML^{}

The influence of a deep-level-defect (DLD) band formed in a heavily Mg-doped GaN contact layer on the performance of Ni/Au contact to p-GaN is investigated. The thin heavily Mg-doped GaN (p^{++}-GaN) contact layer with DLD band can effectively improve the performance of Ni/Au ohmic contact to p-GaN. The temperature-dependent I-V measurement shows that the variable-range hopping (VRH) transportation through the DLD band plays a dominant role in the ohmic contact. The thickness and Mg/Ga flow ratio of p^{++}-GaN contact layer have a significant effect on ohmic contact by controlling the Mg impurity doping and the formation of a proper DLD band. When the thickness of the p^{++}-GaN contact layer is 25 nm thick and the Mg/Ga flow rate ratio is 10.29%, an ohmic contact with low specific contact resistivity of 6.97× 10^{-4}Ω ·cm^{2} is achieved.

It is significant for low-cost preparation of YBa_{2}Cu_{3}O_{7-δ} (YBCO) coated conductors to make clear the mechanism of orientation, copper segregation, and nucleation density in BaF_{2}-derived YBCO crystallization. In the present work, a distinct nucleation mechanism was proposed based on a transient liquid phase induced by the size effect as well as near-equilibrium assumption. With this scheme the nucleation of YBCO prepared by metal-organic deposition (MOD) or the physical vapor deposition BaF_{2} process was semi-quantitatively analyzed, revealing that the direct driving force for nucleation is YBCO supersaturation in the liquid phase. The theoretical analysis on the nucleation orientation portion is evidenced by the experimental result.

We use the first-principles calculation method to study the interface effect on the structure and electronic properties of graphdiyne adsorbed on the conventional substrates of rough SiO_{2} and flat h-BN. For the SiO_{2} substrate, we consider all possible surface terminations, including Si termination with dangling bond, Si terminations with full and partial hydrogenation, and oxygen terminations with dimerization and hydrogenation. We find that graphdiyne can maintain a flat geometry when absorbed on both h-BN and SiO_{2} substrates except for the Si termination with partial hydrogenation (Si-H) SiO_{2} substrate. A lack of surface corrugation in graphdiyne on the substrates, which may help maintain its electronic band character, is due to the weak Van der Waals interaction between graphdiyne and the substrate. Si-H SiO_{2} should be avoided in applications since a covalent type bonding between graphdiyne and SiO_{2} will totally vary the band structure of graphdiyne. Interestingly, the oxygen termination with dimerization SiO_{2} substrate has spontaneous p-type doping on graphdiyne via interlayer charge transfer even in the absence of extrinsic impurities in the substrate. Our result may provide a stimulus for future experiments to unveil its potential in electronic device applications.

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

The elastic properties and point defects of thorium monocarbide (ThC) have been studied by means of density functional theory based on the projector-augmented-wave method. The calculated electronic and elastic properties of ThC are in good agreement with experimental data and previous theoretical results. Five types of point defects have been considered in our study, including the vacancy defect, interstitial defect, antisite defect, schottky defect, and composition-conserving defect. Among these defects, the carbon vacancy defect has the lowest formation energy of 0.29 eV. The second most stable defect (0.49 eV) is one of composition-conserving defects in which one carbon is removed to another carbon site forming a C_{2} dimer. In addition, we also discuss several kinds of carbon interstitial defects, and predict that the carbon trimer configuration may be a transition state for a carbon dimer diffusion in ThC.

Advanced GGA+U (Hubbard) and modified Becke-Johnson (mBJ) techniques are used for the calculation of the structural, electronic, and optical parameters of α-Al_{2-x}Co_{x}O_{3} (x= 0.0, 0.167) compounds. The direct band gaps calculated by GGA and mBJ for pure alumina are 6.3 eV and 8.5 eV, respectively. The mBJ approximation provides results very close to the experimental one (8.7 eV). The substitution of Al with Co reduces the band gap of alumina. The wide and direct band gap of the doped alumina predicts that it can efficiently be used in optoelectronic devices. The optical properties of the compounds like dielectric functions and energy loss function are also calculated. The rhombohedral structure of the α-Al_{2-x}Co_{x}O_{3} (x= 0.0, 0.167) compounds reveal the birefringence properties.

First-principle calculations with different exchange-correlation functionals, including LDA, PBE, and vdW-DF functional in the form of optB88-vdW, have been performed to investigate the electronic and elastic properties of two-dimensional transition metal dichalcogenides (TMDCs) with the formula of MX_{2}(M= Mo, W; X = O, S, Se, Te) in both monolayer and bilayer structures. The calculated band structures show a direct band gap for monolayer TMDCs at the K point except for MoO_{2} and WO_{2}. When the monolayers are stacked into a bilayer, the reduced indirect band gaps are found except for bilayer WTe_{2}, in which the direct gap is still present at the K point. The calculated in-plane Young moduli are comparable to that of graphene, which promises possible application of TMDCs in future flexible and stretchable electronic devices. We also evaluated the performance of different functionals including LDA, PBE, and optB88-vdW in describing elastic moduli of TMDCs and found that LDA seems to be the most qualified method. Moreover, our calculations suggest that the Young moduli for bilayers are insensitive to stacking orders and the mechanical coupling between monolayers seems to be negligible.

A series of CeMn_{2}(Si_{1-x}Ge_{x})_{2} (x=0.2, 0.4, 0.6, 0.8) compounds are prepared by the arc-melting method. All the samples primarily crystallize in the ThCr_{2}Si_{2}-type structure. The temperature dependences of zero-field-cooled (ZFC) and FC magnetization measurements show a transition from antiferromagnetic (AFM) state to ferromagnetic (FM) state at room temperature with the increase of the Ge concentration. For x=0.4, the sample exhibits two kinds of phase transitions with increasing temperature: from AFM to FM and from FM to paramagnetic (PM) at around T_{N} ～ 197 K and T_{C} ～ 300 K, respectively. The corresponding Arrott curves indicate that the AFM-FM transition is of first-order character and the FM-PM transition is of second-order character. Meanwhile, the coexistence of positive and negative magnetic entropy changes can be observed, which are corresponding to the AFM-FM and FM-PM transitions, respectively.

We investigated the properties of polarons in a wurtzite ZnO/Mg_{x}Zn_{1-x}O quantum well by adopting a modified Lee-Low-Pines variational method, giving the ground state energy, transition energy, and phonon contributions from various optical-phonon modes to the ground state energy as functions of the well width and Mg composition. In our calculations, we considered the effects of confined optical phonon modes, interface-optical phonon modes, and half-space phonon modes, as well as the anisotropy of the electron effective band mass, phonon frequency, and dielectric constant. Our numerical results indicate that the electron-optical phonon interactions importantly affect the polaronic energies in the ZnO/Mg_{x}Zn_{1-x}O quantum well. The electron-optical phonon interactions decrease the polaron energies. For quantum wells with narrower wells, the interface optical phonon and half-space phonon modes contribute more to the polaronic energies than the confined phonon modes. However, for wider quantum wells, the total contribution to the polaronic energy mainly comes from the confined modes. The contributions of the various phonon modes to the transition energy change differently with increasing well width. The contribution of the half-space phonons decreases slowly as the QW width increases, whereas the contributions of the confined and interface phonons reach a maximum at d ≈ 5.0 nm and then decrease slowly. However, the total contribution of phonon modes to the transition energy is negative and increases gradually with the QW width of d. As the composition x increases, the total contribution of phonons to the ground state energies increases slowly, but the total contributions of phonons to the transition energies decrease gradually. We analyze the physical reasons for these behaviors in detail.

A zinc oxide thin film in cubic crystalline phase, which is usually prepared under high pressure, has been grown on the MgO (001) substrate by a three-step growth using plasma-assisted molecular beam epitaxy. The cubic structure is confirmed by in-situ reflection high energy electron diffraction measurements and simulations. The x-ray photoelectron spectroscopy reveals that the outer-layer surface of the film (less than 5 nm thick) is of ZnO phase while the buffer layer above the substrate is of ZnMgO phase, which is further confirmed by the band edge transmissions at the wavelengths of about 390 nm and 280 nm, respectively. The x-ray diffraction exhibits no peaks related to wurtzite ZnO phase in the film. The cubic ZnO film is presumably considered to be of the rock-salt phase. This work suggests that the metastable cubic ZnO films, which are of applicational interest for p-type doping, can be epitaxially grown on the rock-salt substrates without the usually needed high pressure conditions.

Devices with copper phthalocyanine (CuPc):molybdenum trioxide (MoO_{3}) co-evaporated layer were fabricated and the current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured. It has been found that for a given voltage, the current of the device with a co-evaporated layer is higher than those without the co-evaporated layer and it reaches the highest value if the ratio of MoO_{3} to CuPc is 1:1. Meanwhile, the C-V characteristics showed that only free holes exist in the function layer consisting of pure CuPc. However, charge transfer (CT) complexes exist in the function layer of a CuPc:MoO_{3} mixture. The charge transfer complexes do not contribute to the transport of the device efficiently under low applied fields but are disassociated into free carriers rapidly at applied fields higher than 1.7× 10^{5} V/cm, which greatly increases the conductivity.

A new epitaxial structure of AlGaInP-based light-emitting diode (LED) with a 0.5-μm GaP window layer was fabricated. In addition, indium tin oxide (ITO) and localized Cr deposition beneath the p-pad electrode were used as the current spreading layer and the Schottky current blocking layer (CBL), respectively. The results indicated that ITO and the Schottky CBL improve the total light extraction efficiency by relieving the current density crowding beneath the p-pad electrode. At the current of 20 mA, the light output power of the novel LED was 40% and 19% higher than those of the traditional LED and the new epitaxial LED without CBL. It was also found that the novel LED with ITO and CBL shows better thermal characteristics.

The electronic structure of InAs/AlSb/GaSb quantum wells embedded in AlSb barriers and in the presence of a perpendicular magnetic field is studied theoretically within the 14-band k·p approach without making the axial approximation. At zero magnetic field, for a quantum well with a wide InAs layer and a wide GaSb layer, the energy of an electron-like subband can be lower than the energy of hole-like subbands. As the strength of the magnetic field increases, the Landau levels of this electron-like subband grow in energy and intersect the Landau levels of the hole-like subbands. The electron-hole hybridization leads to a series of anti-crossing splittings of the Landau levels. The magnetic field dependence of some dominant transitions is shown with their corresponding initial-states and final-states indicated. The dominant transitions at high fields can be roughly viewed as two spin-split Landau level transitions with many electron-hole hybridization-induced splittings. When the magnetic field is tilted, the electron-like Landau level transitions show additional anti-crossing splittings due to the subband-Landau level coupling.

We present an investigation of the one-dimensional ferromagnetism in Au-Co nanowires deposited on the Cu(110) surface. By using the density functional theory, the influence of the nonmagnetic copper substrate Cu(110) on the magnetic properties of the bimetallic Au-Co nanowires is studied. The results show the emergence of magnetic anisotropy in the supported Au-Co nanowires. The magnetic anisotropy energy has the same order of magnitude as the exchange interaction energy between Co atoms in the wire. Our electronic structure calculation reveals the emergence of new hybridized bands between Au and Co atoms and surface Cu atoms. The Curie temperature of the Au-Co wires is calculated by means of kinetic Monte Carlo simulation. The strong size effect of the Curie temperature is demonstrated.

The influences of dry-etching damage on the electrical properties of an AlGaN/GaN Schottky barrier diode with ICP-recessed anode was investigated for the first time. It was found that the turn-on voltage is decreased with the increase of dry-etching power. Furthermore, the leakage currents in the reverse bias region above pinch-off voltage rise as radio frequency (RF) power increases, while below pinch-off voltage, leakage currents tend to be independent of RF power. Based on detailed current-voltage-temperature (I-V-T) measurements, the barrier height of thermionic-field emission (TFE) from GaN is lowered as RF power increases, which results in early conduction. The increase of leakage current can be explained by Frenkel-Poole (FP) emission that higher dry-etching damage in the sidewall leads to the higher tunneling current, while below pinch-off voltage, the leakage is only related to the AlGaN surface, which is independent of RF power.

Negative bias temperature instability (NBTI) has become a serious reliability issue, and the interface traps and oxide charges play an important role in the degradation process. In this paper, we study the recovery of NBTI systemically under different conditions in the P-type metal-oxide-semiconductor field effect transistor (PMOSFET), explain the various recovery phenomena, and find the possible processes of the recovery.

Boundary characteristic orthogonal polynomials are used as shape functions in the Rayleigh-Ritz method to investigate vibration and buckling of nanobeams embedded in an elastic medium. The present formulation is based on the nonlocal Euler-Bernoulli beam theory. The eigen value equation is developed for the buckling and vibration analyses. The orthogonal property of these polynomials makes the computation easier with less computational effort. It is observed that the frequency and critical buckling load parameters are dependent on the temperature, elastic medium, small scale coefficient, and length-to-diameter ratio. These observations are useful in the mechanical design of devices that use carbon nanotubes.

YBa_{2}Cu_{3}O_{7-x} (YBCO) films with co-doping BaTiO_{3} (BTO) and Y_{2}O_{3} nanostructures were prepared by metal organic deposition using trifluoroacetates (TFA-MOD). The properties of the BTO/Y_{2}O_{3} co-doped YBCO films with different excess yttrium have been systematically studied by x-ray diffraction (XRD), Raman spectra, and scanning electron microscope (SEM). The optimized content of yttrium excess in the BTO/Y_{2}O_{3} co-doped YBCO films is 10 mol.%, and the critical current density is as high as ～ 17 mA/cm^{2} (self-field, 65 K) by the magnetic signal. In addition, the Y_{2}Cu_{2}O_{5} was formed when the content of yttrium excess increases to 24 mol.%, which may result in the deterioration of the superconducting properties and the microstructure. The unique combination of the different types of nanostructures of BTO and Y_{2}O_{3} in the doped YBCO films, compared with the pure YBCO films and BTO doped YBCO films, enhances the critical current density (J_{C}) not only at the self-magnetic field, but also in the applied magnetic field.

High-quality single crystals of A-site ordered perovskite oxides CaCu_{3}Ru_{4}O_{12} were synthesized by flux method with CuO serving as a flux. The typical size of these single crystals was around 1× 1× 1 mm^{3} and the lattice constant was determined to be 7.430± 0.0009 Å by using x-ray single crystal diffraction. The surfaces of the samples were identified to be (100) surface. The high quality of the single crystal samples was confirmed by the rocking curve data which have a full width at half maximum of approximately 0.02 degree. The x-ray photoelectron spectroscopy measurement was performed and the temperature-dependent specific heat, magnetic susceptibility, and electric resistivity were measured along the [100] direction of the single crystals. All these measurements showed that the physical properties of CaCu_{3}Ru_{4}O_{12} single crystals are similar to that of polycrystals. However, the single crystals have a lower Curie susceptibility tail and a smaller residual resistivity than polycrystals, which indicates that the amount of paramagnetic impurities can be controlled by tuning the number of defects in CaCu_{3}Ru_{4}O_{12} samples.

The magnetism and magnetocaloric effect in Er_{1-x}Gd_{x}CoAl (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1) were investigated. The Er_{1-x}Gd_{x}CoAl compounds were synthesized by arc melting. With the increasing Gd content, the Néel temperature (T_{N}) linearly increases from 14 K to 102 K, while the magnetic entropy change (-Δ S_{M}) tends to decrease nonmonotonously. Under the field change from 0 T to 5 T, the-Δ S_{M} of the compounds with x = 0.2-1 are stable around 10 J/kg ·K, then a cooling platform between 20 K and 100 K can be formed by combining these compounds. For x = 0.6, 0.8, 1.0, the compounds undergo two successive magnetic transitions, one antiferromagnetism to ferromagnetism and the other ferromagnetism to paramagnetism, with increasing temperature. The two continuous magnetic transitions in this series are advantageous to broaden the temperature span of half-peak width (δ T) in the-Δ x_{M}-T curve and improve the refrigeration capacity.

The magnetization dynamics of nanoelements with tapered ends have been studied by micromagnetic simulations. Several spin-wave modes and their evolutions with the sharpness of the element ends are characterized. The edge mode localized in the two ends of the element can be effectively tuned by the element shape. Its frequency increases rapidly with the tapered parameter h and its localized area gradually expands toward the element center, and it finally merges into the fundamental mode at a critical tapered parameter h_{0}. For nanoelements with h > h_{0}, the edge mode is completely suppressed. The standing spin-wave modes mainly in the internal area of the element are less affected by the element shape. The shifts of their frequencies are small and they display different tendencies. The evolution of the spin-wave modes with the element shape is explained by considering the change of the internal field.

Cu_{x}(Cu_{2}O)_{1-x} (0.09≤Cux≤1.00) granular films with thickness about 280 nm have been fabricated by direct current reactive magnetron sputtering. The atomic ratio x can be controlled by the oxygen flow rate during Cu_{x}(Cu_{2}O)_{1-x} deposition. Room-temperature ferromagnetism (FM) is found in all of the samples. The saturated magnetization increases at first and then decreases with the decrease of x. The photoluminescence spectra show that the magnetization is closely correlated with the Cu vacancies in the Cu_{x}(Cu_{2}O)_{1-x} granular films. Fundamentally, the FM could be understood by the Stoner model based on the charge transfer mechanism. These results may provide solid evidence and physical insights on the origin of FM in the Cu_{2}O-based oxides diluted magnetic semiconductors, especially for systems without intentional magnetic atom doping.

The influence of the RE-rich phase distribution in the precursor alloys on the anisotropy of the hydrogenation disproportionation desorption recombination (HDDR) processed powders is investigated. The homogenized ingot alloy and the as-cast strip casting (SC) alloy with a uniform RE-rich grain boundary phase lead to high anisotropy of the refined powders, acquiring degrees of alignment (DOA) of 0.62 and 0.54, respectively. The RE-rich phase aggregation results in a deteriorated DOA of the powders due to the drastic disproportionation rate, while a thin and uniform RE-rich phase distribution is beneficial for DOA. A reaction model of the initial particle microstructure is proposed for optimizing the HDDR powder anisotropy.

In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy (PMA) on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micromagnetic simulations. The results show that the horizontal and vertical motion can generally be monotonously enhanced by PMA. However, when the current is small, a nonmonotonic phenomenon for the horizontal motion is found. Namely, the velocity of the horizontal motion firstly decreases and then increases with the increase of the PMA. We find that the reason for this is that the PMA can firstly increase and then decrease the confining force induced by the confining potential energy. In addition, the PMA always enhances the driving force induced by the current.

An all-fiber laser using a single-walled carbon nanotube (SWCNT) as the saturable absorber (SA) for Q-switched operation in the 1031 nm region is demonstrated in this work. A lasing threshold as low as 17 mW was realized for continuous wave operation. By further increasing the pump power, stable Q-switched pulse trains are obtained when the pump power ranges from 38 mW to 125 mW, corresponding to repetition rate varying from 40.84 kHz to 66.24 kHz, the pulse width from 2.0 μs to 1.0 μs， and the highest single pulse energy of 40.6 nJ respectively.

A space monocrystalline silicon (c-Si) solar cell under low-energy (< 1 MeV) electron irradiation was investigated using noncontact photocarrier radiometry (PCR). Monte Carlo simulation (MCS) was employed to characterize the effect of different energy electron irradiation on the c-Si solar cell. The carrier transport parameters (carrier lifetime, diffusion coefficient, and surface recombination velocities) were obtained by best fitting the experimental results with a theoretical one-dimensional two-layer PCR model. The results showed that the increase of the irradiation electron energy caused a large reduction of the carrier lifetime and diffusion length. Furthermore, the rear surface recombination velocity of the Si:p base of the solar cell at the irradiation electron energy of 1 MeV was dramatically enhanced due to 1 MeV electron passing through the whole cell. Short-circuit current (I_{sc}) degradation evaluated by PCR was in good agreement with that obtained by electrical measurement.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Single-phase pristine and cation-substituted calcium manganite (Ca_{1-x}Bi_{x}Mn_{1-y}V_{y}O_{3-δ} ) polycrystalline samples were synthesized by the solid state reaction technique. Their thermoelectric properties were measured by a set up that was designed and assembled in the laboratory. The Ca_{1-x}Bi_{x}Mn_{1-y}V_{y}O_{3-δ} sample with x = y = 0.04 has shown a power factor (S^{2}σ) of 176 μW/m/K^{2} at 423 K, which is nearly two orders of magnitude higher than that of the pristine sample (2.1 μW/m/K^{2}). The power factor of the substituted oxide remains almost temperature independent as the Seebeck coefficient increases monotonically with temperature, along with the simultaneous decrease in electrical resistivity which is attributed to enhanced electron density due to co-doping of bismuth and vanadium and grain boundary scattering. These cation-substituted calcium manganites can be used as a potential candidate for an n-type leg in a thermoelectric generator (module).

We propose to achieve a high-efficiency wideband flat focusing reflector using metasurfaces. To obtain the wide band, the polarization conversion mechanism is introduced into the reflector design, based on the fact that the reflection phases of cross-polarized waves are linear in quite a wide band. This facilitates the design of wideband parabolic reflection phase profile. As an example, we design two reflective focusing metasurfaces with one- and two-dimensional in-plane parabolic reflection phase profiles based on elliptical split ring resonators (ESRRs). Both the simulation and experiment verify the wideband focusing performance in 10.0-22.0 GHz of the flat reflectors. Due to the wide operating band, such reflectors have important application values in communication, detection, measurement, imaging, etc.

The lutetium tantalate compounds obtained from Lu_{2}O_{3}-Ta_{2}O_{5} with a molar ratio of 0.515:0.485 were studied by Raman scattering and x-ray diffraction. The results of the room temperature Raman scattering indicate that the sample has a phase transition between 1830 ℃ and 1872 ℃, the polycrystalline is a mixture of M'-LuTaO_{4} and Lu_{3}TaO_{7} (Fm3m) when it is prepared at 1830 ℃, and a mixture of M-LuTaO_{4} (B112/b) and Lu_{3}TaO_{7} (Fm3m) when it is prepared at above 1872 ℃. The sample melts at a temperature of 2050 ℃. The phase transition of the sample prepared at 2050 ℃ was also investigated by the high-temperature Raman spectra, and the result indicates that no phase transition occurs between room temperature and 1400 ℃, which is consistent with the results from the x-ray diffraction.

Based on the density functional theory, we investigate negatively charged clusters Pt_{l}Au_{m}^{-} (l+m=4), which show significant catalytic properties in the simultaneous removal of N_{2}O and CO. We find that in these clusters, the platinum atom acts as the adsorption center for N_{2}O, the gold and Pt atoms act as electron donors during the reaction, and the charge transfers from the bimetallic cluster to the N_{2}O molecule. As the proportion of Au in the cluster increases, the d band center shifts down further away from the Fermi level, meanwhile more charge is transferred to the N_{2}O molecule, resulting in weaker N-O bond strength. Therefore bimetallic cluster PtAu_{3}^{-} shows better catalytic properties than the other clusters, especially pure Pt_{4}^{-} and Au_{4}^{-} clusters. This means that there is a synergetic effect between the Pt and Au atoms in the negatively charged bimetallic clusters. Our results help to reveal the mechanism of Pt_{l}Au_{m}^{-} bimetallic clusters as excellent catalysts.

In time-of-flight mass spectrometry (TOF MS), superconducting strip ion detectors (SSIDs) in the parallel configuration are promising for ideal ion detection with a nanosecond-scale time response and a practical large sensitive area. In the parallel configuration, the bias current in one strip is diverted into other parallel strips after each detection event. Under high bias current conditions, the diverted bias current induces cascade switching of all parallel strips. Studies show that cascade switching degrades the ion count rate of SSIDs made from niobium and hence is disliked in TOF MS applications. To suppress the bias current redistribution, we connected resistors in a series with the individual parallel strips using aluminum-bonding wires. Their effect was studied by measuring the pulse height distributions.

By investigating the interaction of an n-type silicon sample with the TM_{01} mode millimeter wave in a circular waveguide, a viable high-power TM_{01} millimeter wave sensor is proposed. Based on the hot electron effect, the silicon sample serving as a sensing element (SE) and appropriately mounted on the inner wall of the circular waveguide is devoted to the on-line measurement of a high-power millimeter wave pulse. A three-dimensional parallel finite-difference time-domain method is applied to simulate the wave propagation within the measuring structure. The transverse electric field distribution, the dependences of the frequency response of the voltage standing-wave ratio (VSWR) in the circular waveguide, and the average electric field amplitude within the SE on the electrophysical parameters of the SE are calculated and analyzed in the frequency range of 300-400 GHz. As a result, the optimal dimensions and specific resistance of the SE are obtained, which provide a VSWR of no more than 2.0, a relative sensitivity around 0.0046 kW^{-1} fluctuating within ± 17.3%, and a maximum enduring power of about 4.3 MW.

On the basis of Helfrich's bending energy model, we show that the adsorption process of a small spherical particle to a closed vesicle can be analytically studied by retaining the leading terms in an expansion of the shape equation. Our general derivation predicts the optimal binding sites on a vesicle, where the local membrane shape of the binding site could be non-axisymmetric before the continuous adhesion transition takes place. Our derivation avoids directly solving the shape equation and depends on an integration of the contact-line condition. The results are verified by several examples of independent numerical solutions.

In order to improve the accuracy of the battery state of charge (SOC) estimation, in this paper we take a lithium-ion battery as an example to study the adaptive Kalman filter based SOC estimation algorithm. Firstly, the second-order battery system model is introduced. Meanwhile, the temperature and charge rate are introduced into the model. Then, the temperature and the charge rate are adopted to estimate the battery SOC, with the help of the parameters of an adaptive Kalman filter based estimation algorithm model. Afterwards, it is verified by the numerical simulation that in the ideal case, the accuracy of SOC estimation can be enhanced by adding two elements, namely, the temperature and charge rate. Finally, the actual road conditions are simulated with ADVISOR, and the simulation results show that the proposed method improves the accuracy of battery SOC estimation under actual road conditions. Thus, its application scope in engineering is greatly expanded.

In this paper, a new continuum traffic flow model is proposed, with a lane-changing source term in the continuity equation and a lane-changing viscosity term in the acceleration equation. Based on previous literature, the source term addresses the impact of speed difference and density difference between adjacent lanes, which provides better precision for free lane-changing simulation; the viscosity term turns lane-changing behavior to a “force” that may influence speed distribution. Using a flux-splitting scheme for the model discretization, two cases are investigated numerically. The case under a homogeneous initial condition shows that the numerical results by our model agree well with the analytical ones; the case with a small initial disturbance shows that our model can simulate the evolution of perturbation, including propagation, dissipation, cluster effect and stop-and-go phenomenon.

This paper investigates event-triggered synchronization for complex networks with Markovian jumping parameters. Nonlinear dynamics with Markovian jumping parameters is considered for each node in a complex network. By utilizing the proposed event-triggered strategy, and based on the Lyapunov functional method and linear matrix inequality technology, some sufficient conditions for synchronization of complex networks are derived whether the transition rate matrix for the Markov process is completely known or not. Finally, a numerical example is presented to illustrate the effectiveness of the proposed theoretical results.

Many real communication networks, such as oceanic monitoring network and land environment observation network, can be described as space stereo multi-layer structure, and the traffic in these networks is concurrent. Understanding how traffic dynamics depend on these real communication networks and finding an effective routing strategy that can fit the circumstance of traffic concurrency and enhance the network performance are necessary. In this light, we propose a traffic model for space stereo multi-layer complex network and introduce two kinds of global forward-predicting dynamic routing strategies, global forward-predicting hybrid minimum queue (HMQ) routing strategy and global forward-predicting hybrid minimum degree and queue (HMDQ) routing strategy, for traffic concurrency space stereo multi-layer scale-free networks. By applying forward-predicting strategy, the proposed routing strategies achieve better performances in traffic concurrency space stereo multi-layer scale-free networks. Compared with the efficient routing strategy and global dynamic routing strategy, HMDQ and HMQ routing strategies can optimize the traffic distribution, alleviate the number of congested packets effectively and reach much higher network capacity.

[an error occurred while processing this directive]