In this paper, we present a new method to obtain the Lie symmetries and conserved quantities of the discrete wave equation with the Ablowitz-Ladik-Lattice equations. Firstly, the wave equation is transformed into a simple difference equation with the Ablowitz-Ladik-Lattice method. Secondly, according to the invariance of the discrete wave equation and the Ablowitz-Ladik-Lattice equations under infinitesimal transformation of dependent and independent variables, we derive the discrete determining equation and the discrete restricted equations. Thirdly, a series of the discrete analogs of conserved quantities, the discrete analogs of Lie groups, and the characteristic equations are obtained for the wave equation. Finally, we study a model of a biological macromolecule chain of mechanical behaviors, the Lie symmetry theory of discrete wave equation with the Ablowitz-Ladik-Lattice method is verified.

In this paper the pinning consensus of multi-agent networks with arbitrary topology is investigated. Based on the properties of M-matrix, some criteria of pinning consensus are established for the continuous multi-agent network and the results show that the pinning consensus of the dynamical system depends on the smallest real part of the eigenvalue of the matrix which is composed of the Laplacian matrix of the multi-agent network and the pinning control gains. Meanwhile, the relevant work for the discrete-time system is studied and the corresponding criterion is also obtained. Particularly, the fundamental problem of pinning consensus, that is, what kind of node should be pinned, is investigated and the positive answers to this question are presented. Finally, the correctness of our theoretical findings is demonstrated by some numerical simulated examples.

In this paper, we propose a general method to simultaneously identify both unknown time delays and unknown model parameters in delayed dynamical systems based on the autosynchronization technique. The design procedure is presented in detail by constructing a specific Lyapunov function and linearizing the model function with nonlinear parameterization. The obtained result can be directly extended to the identification problem of linearly parameterized dynamical systems. Two typical numerical examples confirming the effectiveness of the identification method are given.

The complex variable reproducing kernel particle method (CVRKPM) of solving two-dimensional variable coefficient advection-diffusion problems is presented in this paper. The advantage of the CVRKPM is that the shape function of a two-dimensional problem is formed with a one-dimensional basis function. The Galerkin weak form is employed to obtain the discretized system equation, and the penalty method is used to apply the essential boundary conditions. Then the corresponding formulae of the CVRKPM for two-dimensional variable coefficient advection-diffusion problems are obtained. Two numerical examples are given to show that the method in this paper has greater accuracy and computational efficiency than the conventional meshless method such as reproducing the kernel particle method (RKPM) and the element-free Galerkin (EFG) method.

Based on the pioneering work of Konishi et al.[Phys. Rev. E (1999) 60 4000], a new feedback control scheme is presented to suppress traffic jams based on the coupled map car-following model under the open boundary condition. The effect of the safe headway on the traffic system is considered. According to the control theory, the condition under which traffic jams can be suppressed is analyzed. The results are compared with the previous results concerning congestion control. The simulations show that the suppression performance of our scheme on traffic jams is better than those of the previous schemes, although all the schemes can suppress traffic jams. The simulation results are consistent with theoretical analyses.

In this paper, we discuss the influence of ratio of minor to major axis on the propagation property and focusing performance of a plasmonic lens with variant periodic concentric elliptical slits illuminating under a Gaussian beam. In order to analyse the influence theoretically, a finite-difference time-domain (FDTD) numerical algorithm is adopted for the computational numerical calculation and the design of the plasmonic structure. The structure is flanked with penetrated slits through a 200-nm metal film (Au) which is coated on a quartz substrate. Tunability of focusing capability of the plasmonic lenses is studied by tailoring the ratio. Our calculation results demonstrate that the ratio of the elliptical slits greatly affects the focusing capability of the lense. The plasmonic lenses with concentric elliptical slits illuminating under a Gaussian beam have ultra-elongated depth of focus. These results are very encouraging for the future study of the plasmonic lens-based applications.

The Cornell potential that consists of Coulomb and linear potentials has received a great deal of attention in particle physics. In this paper, we present the exact solutions of the Dirac equation with the pseudoscalar Cornell potential under spin and pseudospin symmetry limits. The energy eigenvalues and corresponding eigenfunctions are given in closed form.

Following the spirit of thermo field dynamics initiated by Takahashi and Umezawa, we employ the technique of integration within an ordered product of operators to derive the thermal vacuum state (TVS) for the Hamiltonian H of the two-coupled-oscillator model. The ensemble averages of the system are derived conveniently by using the TVS. In addition, the entropy for this system is discussed based on the relation between the generalized Hellmann-Feynman theorem and the entroy variation in the context of the TVS.

It has been common knowledge that the single-mode squeezing operator and the two-mode squeezing operator are independent of each other. However, in this work we find that after using the technique of integration within Q-ordering and P-ordering, we can detach two single-mode squeezing operators from the two-mode squeezing operator. In other words, we show that the two-mode squeezing operator can be split into a P-ordered two-mode squeezing operator (with a new squeezing parameter) and two single-mode squeezing operators (with another squeezing parameter). This tells us that the two-mode squeezing mechanism also involves some single-mode squeezing.

In this paper, we have applied the Lie algebraic model to nano-bio molecules to determine the vibrational spectra of different stretching and bending vibrational modes. The determined vibrational energy levels by the Lie algebraic model are compared with the experimental data. The results from the theoretical model are consistent with the experimental data. The vibrational energy levels are clustering in the excited states.

Approximate analytical solutions of the Dirac equation for Tietz-Hua (TH) potential including Coulomb-like tensor (CLT) potential with arbitrary spin-orbit quantum number κ are obtained within the Pekeris approximation scheme to deal with the spin-orbit coupling terms κ (κ±1)r^{-2}. Under the exact spin and pseudospin symmetric limitation, bound state energy eigenvalues and associated unnormalized two-component wave functions of the Dirac particle in the field of both attractive and repulsive TH potential with tensor potential are found using the parametric Nikiforov-Uvarov (NU) method. The cases of the Morse oscillator with tensor potential, the generalized Morse oscillator with tensor potential, and the non-relativistic limits have been investigated.

We present a new exactly solvable quantum problem for which the Schrödinger equation allows for separation of variables in oblate spheroidal coordinates. Namely, this is the quantum mechanical two-Coulomb-center problem for the case of an imaginary intercenter parameter and complex conjugate charges are considered. Since the potential is defined by the two-sheeted mapping whose singularities are concentrated on a circle rather than at separate points, there arise additional possibilities in the choice of boundary conditions. A detailed classification of the various types of boundary-value problems is given. The quasi-radial equation leads to a new type of boundary value problem which has never been considered before. Results of the numerical calculations, which allow conclusions to be drawn about the structure of the energy spectrum, are shown. Possible physical applications are discussed.

We investigate the roles of different qubit-environment decoherence models on the entanglement trapping of two qubits. By considering three environmental models (the single photonic band gap model, the common photonic band gap model, and the two independent photonic band gaps model), we note that the final values of entanglement trapping are determined by these different models. We also give the conditions of obtaining the larger entanglement trapping by comparing two-qubit entanglement dynamics in different decoherence models. Moreover, the comparison of entanglement trapping between two Bell-like states in the same decoherence model are also carried out.

We study the topological properties of a one-dimensional (1D) hardcore Bose-Fermi mixture using the exact diagonalization method. We firstly add a hardcore boson to a fermionic system and by examining the edge states we find that the quasi-particle manifests the topological properties of the system. Then we study a mixture with 7 fermions and 1 boson. We find that the mixture also exhibits topological properties and its behaviors are similar to that of the corresponding fermionic system. We present a qualitative explanation to understand such behaviors using the mapping between a hardcore boson and a spinless fermion. These results show the existence of topological properties in a 1D hardcore Bose-Fermi mixture and may be realized using cold atoms trapped in optical lattices experimentally.

We propose a method to construct an optical cluster-state analyzer based on cross-Kerr nonlinearity combined with linear optics elements. In the scheme, we employ two four-qubit parity gates and the controlled phase gate (CPG) from only the cross-Kerr nonlinearity and show that all the orthogonal four-qubit cluster states can be completely identified. The scheme is significant for the large-scale quantum communication and quantum information processing networks. In addition, the scheme is feasible and deterministic under current experimental conditions.

We investigate the acceleration of an adiabatic process with the same survival probability of the ground state by sweeping a parameter nonlinearly, fast in the wide gap region and slowly in the narrow gap region, in contrast to the usual linear sweeping. We find the expected acceleration both in the Landau-Zener tunneling model and in the adiabatic quantum computing model for factorizing the number N=21.

The distributed wireless quantum communication network (DWQCN) has a distributed network topology and transmits information by quantum states. In this paper, we present the concept of the DWQCN and propose a system scheme to transfer quantum states in the DWQCN. The system scheme for transmitting information between any two nodes in the DWQCN includes a routing protocol and a scheme for transferring quantum states. The routing protocol is on-demand and the routing metric is selected based on the number of entangled particle pairs. After setting up a route, quantum teleportation and entanglement swapping are used for transferring quantum states. Entanglement swapping is achieved along with the process of routing set up and the acknowledgment packet transmission. The measurement results of each entanglement swapping are piggybacked with route reply packets or acknowledgment packets. After entanglement swapping, a direct quantum link between source and destination is set up and quantum states are transferred by quantum teleportation. Adopting this scheme, the measurement results of entanglement swapping do not need to be transmitted specially, which decreases the wireless transmission cost and transmission delay.

Measurements of three-junction flux qubits, both single flux qubits and coupled flux qubits, using a coupled direct current superconducting quantum interference device (dc-SQUID) for readout are reported. The measurement procedure is described in detail. We performed spectroscopy measurements and coherent manipulations of the qubit states on a single flux qubit, demonstrating quantum energy levels and Rabi oscillations, with Rabi oscillation decay time T_{Rabi}=78 ns and energy relaxation time T_{1}=315 ns. We found that the value of T_{Rabi} depends strongly on the mutual inductance between the qubit and the magnetic coil. We also performed spectroscopy measurements on inductively coupled flux qubits.

The effects of the Dzyaloshinski-Moriya (DM) interaction on the ground-state properties of the anisotropic XY chain in a transverse field have been studied by means of correlation functions and entanglement. Different from the case without the DM interaction, the excitation spectra ε_{k} of this model are not symmetrical in the momentum space and are not always positive. As a result, besides the ferromagnetic (FM) and the paramagnetic (PM) phases, a gapless chiral phase is induced. In the chiral phase, the von Neumann entropy is proportional to log_{2}L (L is the length of a subchain) with the coefficient A≈1/3, which is the same as that of the XY chain in a transverse field without the DM interaction for γ=0 and 0<h ≤1. And in the vicinity of the critical point between the chiral phase and the FM (or PM) phase, the behaviors of the nearest-neighbor concurrence and its derivative are like those for the anisotropy transition.

We investigate how three-body interactions affect the elementary excitations and dynamic structure factor of a Bose-Einstein condensate trapped in a one-dimensional optical lattice. To this end, we numerically solve the Gross-Pitaevskii equation and then the corresponding Bogoliubov equations. Our results show that three-body interactions can change both the Bogoliubov band structure and the dynamical structure factor dramatically, especially in the case of the two-body interaction being relatively small. Furthermore, when the optical lattice is strong enough, the analytical results, combined with the sum-rule approach, help us to understand that: the effects of three-body interactions on the static structure factor can be significantly amplified by an optical lattice. Our predictions should be observable within the current Bragg spectroscopy experiment.

We investigate the particle-hole pair excitations of dipolar molecules in an optical lattice, which can be described with an extended Bose-Hubbard model. For strong enough dipole-dipole interaction, the particle-hole pair excitations can form bound states in one and two dimensions. With decreasing dipole-dipole interaction, the energies of the bound states increase and merge into the particle-hole continuous spectrum gradually. The existence regions, the energy spectra and the wave functions of the bound states are carefully studied and the symmetries of the bound states are analyzed with group theory. For a given dipole-dipole interaction, the number of bound states varies in momentum space and a number distribution of the bound states is illustrated. We also discuss how to observe these bound states in future experiments.

In this paper, an optimal tracking control scheme is proposed for a class of discrete-time chaotic systems using the approximation-error-based adaptive dynamic programming (ADP) algorithm. Via the system transformation, the optimal tracking problem is transformed into an optimal regulation problem, and then the novel optimal tracking control method is proposed. It is shown that for the iterative ADP algorithm with finite approximation error, the iterative performance index functions can converge to a finite neighborhood of the greatest lower bound of all performance index functions under some convergence conditions. Two examples are given to demonstrate the validity of the proposed optimal tracking control scheme for chaotic systems.

In this paper, the Padé approximant and analytic solution in the neighborhood of the initial value are introduced into the process of constructing the Shilnikov type homoclinic trajectories in three-dimensional nonlinear dynamical systems. The PID controller system with quadratic and cubic nonlinearities, the simplified solar-wind-driven-magnetosphere-ionosphere system, and the human DNA sequence system are considered. With the aid of presenting a new condition, the solutions of solving the boundary-value problems which are formulated for the trajectory and evaluating the initial amplitude values become available. At the same time, the value of the bifurcation parameter is obtained directly, which is almost consistent with the numerical result.

This paper deals with the cluster exponential synchronization of a class of complex networks with hybrid coupling and time-varying delay. Through constructing an appropriate Lyapunov-Krasovskii functional and applying the theory of the Kronecker product of matrices and the linear matrix inequality (LMI) technique, several novel sufficient conditions for cluster exponential synchronization are obtained. These cluster exponential synchronization conditions adopt the bounds of both time delay and its derivative, which are less conservative. Finally, the numerical simulations are performed to show the effectiveness of the theoretical results.

We study exact single-soliton solutions of an attractive Bose-Einstein condensate governed by a one-dimensional nonautonomous Gross-Pitaevskii system. For several different forms of time-dependent atom-atom interaction and external parabolic potential which satisfy the exact integrability scenario, we construct a set of new analytical nonautonomous deformed-soliton solutions, including the macroscopic wave function and the position of soliton’s center of mass. The soliton characteristics are modulated by the external field parameters and deformation factors related to the number of the condensed atoms and the initial conditions. The results suggest a simple and effective method for experimentally generating matter-wave deformed solitons and manipulating their motions.

An optical atomic clock with ^{171}Yb atoms is devised and tested. By using a two-stage Doppler cooling technique, the ^{171}Yb atoms are cooled down to a temperature of 6±3 μK, which is close to the Doppler limit. Then, the cold ^{171}Yb atoms are loaded into a one-dimensional optical lattice with a wavelength of 759 nm in the Lamb-Dicke regime. Furthermore, these cold ^{171}Yb atoms are excited from the ground-state ^{1}S_{0} to the excited-state ^{3}P_{0} by a clock laser with a wavelength of 578 nm. Finally, the ^{1}S_{0}-^{3}P_{0} clock-transition spectrum of these ^{171}Yb atoms is obtained by measuring the dependence of the population of the ground-state ^{1}S_{0} upon the clock-laser detuning.

A cardiac vector model is presented and verified, and then the forward problem for cardiac magnetic fields and electric potential are discussed based on this model and the realistic human torso volume conductor model, including lungs. A torso-cardiac vector model is used for a 12-lead electrocardiographic (ECG) and magneto-cardiogram (MCG) simulation study by using the boundary element method (BEM). Also, we obtain the MCG wave picture using a compound four-channel HT_{c}·SQUID system in a magnetically shielded room. By comparing the simulated results and experimental results, we verify the cardiac vector model and then do a preliminary study of the forward problem of MCG and ECG. Therefore, the results show that the vector model is reasonable in cardiac electrophysiology.

Vibrational transition spectra of H_{2}^{+} in an ultra-strong magnetic field are determined. The validity of Born-Oppenheimer approximation is analyzed based on one-center method and B-spline basis sets. It is shown that Born-Oppenheimer approximation is reliable for the investigation on the ground state and low excited states of H_{2}^{+} subjected to the strong magnetic field. Furthermore, it is found that the vibrational transition spectra from 1σ_{g}, 1π_{u}, and 1δ_{g} states lie in infrared, visible, and ultraviolet ranges with increasing magnetic field strength.

The potential energy curves (PECs) of four electronic states (X^{1}Σ_{g}+, e^{3}Δ_{u}, a^{3}Σ_{u}^{-}, and d^{3}Π_{g}) of an As_{2} molecule are investigated employing the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach in conjunction with the correlation-consistent aug-cc-pV5Z basis set. The effect on PECs by the relativistic correction is taken into account. The way to consider the relativistic correction is to employ the second-order Douglas-Kroll Hamiltonian approximation. The correction is made at the level of a cc-pV5Z basis set. The PECs of the electronic states involved are extrapolated to the complete basis set limit. With the PECs, the spectroscopic parameters (T_{e}, R_{e}, ω_{e}, ω_{e}x_{e}, ω_{e}y_{e}, α_{e}, β_{e}, γ_{e}, and B_{e}) of these electronic states are determined and compared in detail with those reported in the literature. Excellent agreement is found between the present results and the experimental data. The first 40 vibrational states are studied for each electronic state when the rotational quantum number J equals zero. In addition, the vibrational levels, inertial rotation and centrifugal distortion constants of d^{3}Π_{g} electronic state are reported which are in excellent agreement with the available measurements. Comparison with the experimental data shows that the present results are both reliable and accurate.

The ionization time in sequential double ionization with an elliptically polarized laser pulse has been examined theoretically using a semiclassical method. The significant discrepancy between the ionization time for parallel and anti-parallel electron emission is predicted numerically for the first time. The impact of the carrier envelope phase offset is also studied in this work.

The accurate theoretical expressions of the mean field operator associated with the multi-configuration time-dependent Hartree-Fock (MCTDHF) method are presented in this paper. By using a theoretical formula, derived without approximation, we can study the multi-electron correlation dynamics accurately. Some illustrative calculations are carried out to check the accuracy of the expression of the mean field operator. The results of illustrative calculations indicate the reliability of the accurate expression of the mean field operator. This theoretical calculation method for the mean field operator may be of considerable help in future studies of the correlated dynamics of many-electron systems in strong laser fields.

In this paper, ultracold cesium molecules are formed through photoassociation technology, which is carried out in a magneto-optical trap. High resolution photoassociaion spectra with the rotational progressions up to J=7 are obtained. Three rovibrational levels of the long-range 0_{u}^{+} state of Cs_{2} below the (6S_{1/2}+6P_{1/2}) dissociation limit are specifically investigated. By fitting their binding energy intervals to the non-rigid rotational model, the rotational constant of the long-range 0_{u}^{+} state is determined. A proportional dependence of the value of the rotational constant on the vibrational quantum number is demonstrated.

Ultracold polar RbCs molecules are produced via photoassociation in a laser-cooled mixture of ^{85}Rb and ^{133}Cs atoms. The a^{3}Σ^{+} state molecules which decay from electronically excited (2)0^{-} state RbCs molecules are detected by resonance-enhanced two-photon ionization. The new rovibrational levels (v=189, 190) in the (2)0^{-} state are also observed, which exist in theory and have not been observed in experiments yet. The corresponding rotational constants are measured by photoassociation spectroscopy, which are consistent with theoretical calculations using a nonrigid rotor model.

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

Ultra-wideband (UWB) microwave images are proposed for detecting small malignant breast tumors based on the large contrast of electric parameters between a malignant tumor and normal breast tissue. In this study, an antenna array composed of 9 antennas is applied to the detection. The double constrained robust capon beamforming (DCRCB) algorithm is used for reconstructing the breast image due to its better stability and high signal-to-interference-plus-noise ratio (SINR). The successful detection of a tumor of 2 mm in diameter shown in the reconstruction demonstrates the robustness of the DCRCB beamforming algorithm. This study verifies the feasibility of detecting small breast tumors by using the DCRCB imaging algorithm.

Graded negative refractive index-based photonic crystal (PC) lenses are designed by gradually modifying the sizes of air holes along the transverse direction for focusing the incident plane wave. To study the tunability of the graded negative index-based PC, we introduce filling factor A, gradually tune the filling factor, and use the finite-difference and time-domain (FDTD) algorithm for numerical calculation. Our calculation results indicate that the focal length and the spot size increase with A increasing. For the same A value, the focal length of a PC with elliptical air holes is the longest, and those of PC with square and rectangular air holes are the shortest. Moreover, when the focal length is greater than 1 μm, the focal parameters of the PC are highly insensitive to the variation of A. When the focal length is less than 1 μm, the PC lenses have higher transmittances and all well focus with a beam spot size breaking the diffraction limit. This feature possibly makes the graded negative index-based PC lenses have some new applications in optoelectronic systems.

A new technique for designing a varactor-tunable frequency selective surface (FSS) with an embedded bias network is proposed and experimentally verified. The proposed FSS is based on a square-ring slot FSS. The frequency tuning is achieved by inserting varactor diodes between the square mesh and each unattached square patch. The square mesh is divided into two parts for biasing the varactor diodes. Full-wave numerical simulations show that a wide tuning range can be achieved by changing the capacitances of these loaded varactors. Two homo-type samples using fixed lumped capacitors are fabricated and measured using a standard waveguide measurement setup. Excellent agreement between the measured and simulated results is demonstrated.

The effects of a Mg^{2+} ion on the dopant occupancy and upconversion luminescence of a Ho^{3+} ion in LiNbO_{3} crystal are reported. The birefringence gradient of the crystal is measured to investigate the optical homogeneity. The X-ray powder diffraction spectrum and the upconversion luminescence are used to investigate defect structure and spectroscopic properties of Mg,Ho:LiNbO_{3}. Under 808-nm excitation, blue, red, and very intense yellow-green bands are observed. Based on the energy levels of Ho^{3+} in LiNbO_{3}, and the pump intensity dependence of the observed emission, an excitation scheme is presented. The upconversion emission spectra reveal an enhancement of upconversion intensity when the Mg^{2+} ions are introduced into Ho:LiNbO_{3}. The main upconversion mechanism is discussed in this work.

Through a series of studies on arithmetic coding and arithmetic encryption, a novel image joint compression-encryption algorithm based on adaptive arithmetic coding is proposed. The contexts produced in the process of image compression are modified by keys in order to achieve image joint compression encryption. Combined with the bit-plane coding technique, the discrete wavelet transform coefficients in different resolutions can be encrypted respectively with different keys, so that the resolution selective encryption is realized to meet different application needs. Zero-tree coding is improved, and adaptive arithmetic coding is introduced. Then, the proposed joint compression-encryption algorithm is simulated. The simulation results show that as long as the parameters are selected appropriately, the compression efficiency of proposed image joint compression-encryption algorithm is basically identical to that of the original image compression algorithm, and the security of the proposed algorithm is better than the joint encryption algorithm based on interval splitting.

We study the dynamics of the Jaynes-Cummings model within transformed rotating-wave approximation (TRWA). We analyze this model coupled to a dephasing reservoir, through the Lindblad formalism in the master equation. Then, we examine the expectation value of the number operator. Finally, we investigate the validity of this model under dephasing using the Mandel parameter and the total number of quanta.

We report the measurement of the intensity difference squeezing via the non-degenerate four-wave mixing process in a rubidium atomic vapor medium. Two pairs of balanced detection systems are employed to measure the probe and the conjugate beams, respectively. It is convenient to get the quantum shot noise limit, the squeezed and the amplified noise power spectra. We also investigate the influence of the input extra quadrature amplitude noise of the probe beam. The influence of the extra noise can be minimized and the squeezing can be optimized under the proper parameter condition. We measure the-3.7-dB intensity difference squeezing when the probe beam has a 3-dB extra quadrature amplitude noise. This result is slightly smaller than-4.1 dB when the ideal coherent light (no extra noise) for the probe beam is used.

In theory, we study the quantum fluctuations of the subharmonic reflected field from a triple-resonant degenerate optical parametric amplifier (OPA) inside an optical cavity. We discuss two cases, where the linewidth of the harmonic field is either much narrower or broader than the subharmonic field. Since an electromagnetically-induced-transparency (EIT)-like effect can be simulated in a triple-resonant OPA, the output spectra from a triple-resonant OPA with a squeezed vacuum input may simulate the phenomenon of the response of an EIT medium for squeezed states. This scheme can be implemented with present experimental setups.

We present a continuous-wave squeezed vacuum generation system at a telecommunication wavelength of 1.3 μm. By employing a home-made single-frequency Nd:YVO_{4} laser with dual wavelength outputs as the pump source, via an optical parameter oscillator based on periodically poled KTP, a squeezed vacuum of 6.1 dB±0.1 dB below the shot noise limit at 1342 nm is experimentally measured. This system could be utilized for demonstrating practical quantum information networks.

The spontaneous emission spectrum from two quantum dots (QDs) that are strongly coupled with a single-mode nanocavity is investigated using rigorous numerical calculations and simple analytical solutions of quantum dynamics. The emission spectra both from the side and along the axis of the cavity are considered. Modification of two parameters, the coupling strength and the detuning between the transition frequencies of the two quantum dots, allows us to efficiently control the shape of the spontaneous emission spectrum. Different profiles and their physical origins can be well understood in the dressed-state picture for the light-QD interaction in the on-resonance and off-resonance situations. In the on-resonance situation, the emission spectra exhibit symmetric features, and they are not altered by the asymmetry in the coupling parameters. The axis spectra show two emission peaks while the side spectra have three emission peaks. In the off-resonance situation, the emission spectra always show an asymmetrical three-peak feature. When the two QDs have different decay parameters, singular features (a peak or a dip) can take place at the frequency of the cavity mode, and this is attributed to the unbalanced process of the emission and absorption of a single photon.

A high power GaSb-based laser diode with lasing wavelength at 2 μm was fabricated and optimized. With the optimized epitaxial laser structure, the internal loss and the threshold current density decreased and the internal quantum efficiency increased. For uncoated broad-area lasers, the threshold current density was as low as 144 A/cm^{2} (72 A/cm^{2} per quantum well), and the slope efficiency was 0.2 W/A. The internal loss was 11 cm^{-1} and the internal quantum efficiency was 27.1%. The maximum output power of 357 mW under continuous-wave operation at room temperature was achieved. The electrical and optical properties of the laser diode were improved.

A low cost and simply fabricated reflective graphene oxide is successfully made. By using this absorber, as well as an end reflector, we obtain a passively mode-locked Yb:LuYSiO_{5} laser operating at nearly 1 μm. When the pump power is increased up to 5.73 W, stable mode locking is achieved. The central wavelength of the laser spectrum is 1043.2 nm with a pulse duration of 5.0 ps. When the pump power reaches 8.16 W, dual-wavelength mode locking laser pulses at 1036.3 nm and 1043.5 nm are simultaneously detected.

The optical performance of a grating-coupled external cavity laser based on InAs/InP quantum dots is investigated. Continuous tuning from 1391 nm to 1468 nm is realized at an injection current of 1900 mA. With the injection current increasing to 2300 mA, the tuning is blue shifted to some extent to the range from 1383 nm to 1461 nm. By combining the effect of the injection current with the grating tuning, the total tuning bandwidth of the external cavity quantum-dot laser can reach up to 85 nm. The dependence of the threshold current on the tuning wavelength is also presented.

We theoretically investigate the propagation of few-cycle laser pulses in resonant two-level dense media with a subwavelength structure, which is described by the full Maxwell-Bloch equations without the frame of slowly varying envelope and rotating wave approximations. The input pulses can be shaped into shorter ones with a single or less than one optical cycle. The effect of the parameters of the subwavelength structure and laser pulses is studied. Our study shows that the media with a subwavelength structure can significantly shape the few-cycle pulses into a subcycle pulse, even for the case of chirp pulses as input fields. This suggests that such subwavelength structures have potential application in the shaping of few-cycle laser pulses.

The effects of clouds, sea surface temperature, and its diurnal variation on precipitation efficiency are investigated using grid-scale data from nine equilibrium sensitivity cloud-resolving model experiments driven without large-scale vertical velocity. The precipitation efficiencies are respectively defined in surface rainfall, cloud, and rain microphysical budgets. We mathematically and physically demonstrate the relationship between these precipitation efficiencies. The 2℃ increases in spatiotemporal invariant sea surface temperature (SST) from 27℃ to 29℃ and from 29℃ to 31℃, and the inclusion of diurnal SST difference 1℃ and the 1℃ increase in diurnal SST difference generate opposite changes in the precipitation efficiency by changing ice cloud-radiation interactions. The radiative and microphysical processes of ice clouds have opposite effects on the precipitation efficiency because of the rainfall increase associated with the reduction in the saturation mixing ratio caused by the exclusion of radiative effects and the decrease in rainfall related to the reduction in net condensation caused by the exclusion of deposition processes. The radiative effects of water clouds on the precipitation efficiency are statistically insensitive to the radiative effects of ice clouds.

An all-silicone zoom lens is fabricated. A tunable metal ringer is fettered around the side edge of the lens. A nylon rope linking a motor is tied, encircling the notch in the metal ringer. While the motor is operating, the rope can shrink or release to change the focal length of the lens. A calculation method is developed to obtain the focal length and the zoom ratio. The testing is carried out in succession. The testing values are compared with the calculated ones, and they tally with each other well. Finally, the imaging performance of the all-silicone lens is demonstrated. The all-silicone lens has potential uses in cellphone cameras, notebook cameras, micro monitor lenses, etc.

We propose a novel optical intensity modulator based on the combination of a symmetrical metal cladding optical waveguide (SMCW) and ferrofluid, where the ferrofluid is sealed in the waveguide to act as a guiding layer. The light matter interaction in the ferrofluid film leads to the formation of a regular nanoparticle pattern, which changes the phase match condition of the ultrahigh order modes in return. When two lasers are incident on the same spot of the waveguide chip, experiments illustrate all-optical modulation of one laser beam by adjusting the intensity of the other laser. A possible theoretical explanation may be due to the optical trapping and Soret effect since the phenomenon is considerable only when the control laser is effectively coupled into the waveguide.

A necessary and sufficient condition is obtained for the generalized eigenfunction systems of 2×2 operator matrices to be a block Schauder basis of some Hilbert space, which offers a mathematical foundation of solving symplectic elasticity problems by using the method of separation of variables. Moreover, the theoretical result is applied to two plane elasticity problems via the separable Hamiltonian systems.

The effects of variable fluid properties and variable heat flux on the flow and heat transfer of a non-Newtonian Maxwell fluid over an unsteady stretching sheet in the presence of slip velocity have been studied. The governing differential equations are transformed into a set of coupled non-linear ordinary differential equations and then solved with a numerical technique using appropriate boundary conditions for various physical parameters. The numerical solution for the governing non-linear boundary value problem is based on applying the fourth-order Runge-Kutta method coupled with the shooting technique over the entire range of physical parameters. The effects of various parameters like the viscosity parameter, thermal conductivity parameter, unsteadiness parameter, slip velocity parameter, the Deborah number, and the Prandtl number on the flow and temperature profiles as well as on the local skin-friction coefficient and the local Nusselt number are presented and discussed. Comparison of numerical results is made with the earlier published results under limiting cases.

A horizontally slotted photonic crystal nanobeam cavity with an embedded active nanopillar structure is proposed for ultrafast direct modulation. By designing the thicknesses of both the nanobeam and the horizontal slot layer, the quality factor (Q factor) and the mode volume (V_{n}) of the proposed cavity can be engineered independently. As a result, the spontaneous emission (SpE) rate is enhanced with a small V_{n} of 2.4 while the SpE rate and the cavity photon lifetime have an optimal Q factor of ～1000. In our simulation, the modulation bandwidth could be enhanced up to 170 GHz with different emission linewidths of the active nanopillar.

In order to understand the Kondo effect observed in molecular systems, first-principles calculations have been widely used to predict the ground state properties of molecules on metal substrates. In this work, the interaction and the local magnetic moments of magnetic molecules (3d-metal phthalocyanine and tetraphenylporphyrin molecules) on noble metal surfaces are investigated based on the density functional theory. The calculation results show that the d_{z2} orbital of the transition metal atom of the molecule plays a dominant role in the molecule-surface interaction and the adsorption energy exhibits a simple declining trend as the adsorption distance increases. In addition, the Au(111) surface generally has a weak interaction with the adsorbed molecule compared with the Cu(111) surface and thus serves as a better candidate substrate for studying the Kondo effect. The relation between the local magnetic moment and the Coulomb interaction U is examined by carrying out the GGA+U calculation according to Dudarev’s scheme. We find that the Coulomb interaction is essential for estimating the local magnetic moment in molecule-surface systems, and we suggest that the reference values of parameter U are 2 eV for Fe and 2-3 eV for Co.

The structure and photoluminescence (PL) properties of Sr_{3}SiO_{5}: Sm^{3+} and Li^{+}-doped Sr_{3}SiO_{5}: Sm^{3+} red-emitting phosphors were investigated. Samples were prepared by the high-temperature solid-state method. PL spectra show that the concentration quenching occurs when the Sm^{3+} concentration is beyond 1.3 mol% in Sr_{3}SiO_{5}: Sm^{3+} phosphor without doping Li^{+} ions. The concentration-quenching mechanism can be explained by the electric dipole-dipole interaction of Sm^{3+} ions. The incorporation of Li^{+} ions into Sr_{3}SiO_{5}: Sm^{3+} phosphors, as a charge compensator, improves the PL properties. The lithium ions also suppress the concentration quenching in Sm^{3+} with concentration increased from 1.3 mol% to 1.7 mol%.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

A quasi-linear formalism is developed for relativistic particles. It is self-consistent including spatial diffusion. An attempt is made to simulate the process of electron cyclotron resonant heating (ECRH) and electron cyclotron current drive (ECCD) for the HL-2A tokamak. Temperature oscillating regimes in Tore Supra diagnosed by MHD activity seem to be reproduced in the simulation. The special feature in this paper is to see the resonance in the long time scale for relativistic plasma.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

In the present work, three-dimensional molecular dynamics simulation is carried out to elucidate the nanoindentation behaviors of CuZr Bulk metallic glasses (BMGs). The substrate indenter system is modeled using hybrid interatomic potentials including both many-body Finnis Sinclair (FS) and two-body Morse potentials. A spherical rigid indenter (diameter=60 Å(1 Å=10^{10} m)) is employed to simulate the indentation process. Three samples of BMGs including Cu_{25}Zr_{75}, Cu_{50}Zr_{50}, and Cu_{75}Zr_{25} are designed and the metallic glasses are formed by rapid cooling from the melt state at about 2000 K. The radial distribution functions are analyzed to reveal the dynamical evolution of the structure of the atoms with different compositions and different cooling rates. The mechanical behavior can be well understood in terms of load-depth curves and Hardness-depth curves during the nanoindentation process. Our results indicate a positive linear relationship between the hardness and the Cu concentration of the BMG sample. To reveal the importance of cooling rate provided during the processing of BMGs, we investigate the indentation behaviors of Cu_{50}Zr_{50} at three different quenching rates. Nanoindentation results and radial distribution function (RDF) curves at room temperature indicate that a sample can be made harder and more stable by slowing down the quenching rate.

The molecular dynamics simulation technique with many-body and semi-empirical potentials (based on the embedded atom method potentials) has been used to calculate the interactions of point defects with (1 1 1), (1 1 3), and (1 2 0) twin boundaries in Au at different temperatures. The interactions of single-, di-, and tri-vacancies (at on-and off-mirror sites) with the twin interfaces at 300 K are calculated. All vacancy clusters are favorable at the on-mirror arrangement near the (1 1 3) twin boundary. Single-and di-vacancies are more favorable at the on-mirror sites near the (1 1 1) twin boundary, while they are favorable at the off-mirror sites near the (1 2 0) twin boundary. Almost all vacancy clusters energetically prefer to lie in planes closest to the interface rather than away from it, except for tri-vacancies near the (1 2 0) interface at the off-mirror site and for 3.3 and 3.4 vacancy clusters at both sites near the (1 1 1) interface, which are favorable away from the interface. The interaction energy is high at high temperatures.

Zhang Zhan-Gang, Liu Jie, Hou Ming-Dong, Sun You-Mei, Zhao Fa-Zhan, Liu Gang, Han Zheng-Sheng, Geng Chao, Liu Jian-De, Xi Kai, Duan Jing-Lai, Yao Hui-Jun, Mo Dan, Luo Jie, Gu Song, Liu Tian-Qi

Chin. Phys. B 2013, 22 (9): 096103; doi: 10.1088/1674-1056/22/9/096103
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Monte Carlo simulations reveal considerable straggling of energy loss by the same ions with the same energy in fully-depleted silicon-on-insulator (FDSOI) devices with ultra-thin sensitive silicon layers down to 2.5 nm. The absolute straggling of deposited energy decreases with decreasing thickness of the active silicon layer. While the relative straggling increases gradually with decreasing thickness of silicon films and exhibits a sharp rise as the thickness of the silicon film descends below a threshold value of 50 nm, with the dispersion of deposited energy ascending above±10%. Ion species and energy dependence of the energy-loss straggling are also investigated. For a given beam, the dispersion of deposited energy results in large uncertainty on the actual linear energy transfer (LET) of incident ions, and thus single event effect (SEE) responses, which pose great challenges for traditional error rate prediction methods.

There remain a number of unsolved problems about chemical reactions, and it is significant to explore new detection methods because they always offer some unique information about reactions from new points of view. For the first time, the solidification course of a modified two-component acrylic structural adhesive is measured by using reed-vibration mechanical spectroscopy for liquids (RMS-L) in this work, and results show that there are four sequential processes of mechanical spectra with time. The in-depth analyses indicate that RMS-L can detect in real-time the generation and disappearance of active free radicals, as well as the chemical cross-link processes in the adhesive. This kind of real-time detection will undoubtedly facilitate the study of the chemical reaction dynamics controlled by free radicals.

The in situ electrical resistance and transport activation energies of solid C_{60} fullerene have been measured under high pressure up to 25 GPa in the temperature range of 300-423 K by using a designed diamond anvil cell. In the experiment, four parts of boron-doped diamond films fabricated on one anvil were used as electrical measurement probes and a W-Ta thin film thermocouple which was integrated on the other diamond anvil was used to measure the temperature. The current results indicate that the measured high-pressure resistances are bigger than those reported before at the same pressure and there is no pressure-independent resistance increase before 8 GPa. From the temperature dependence of the resistivity, the C_{60} behaviors as a semiconductor and the activation energies of the cubic C_{60} fullerene are 0.49, 0.43, and 0.36 eV at 13, 15, and 19 GPa, respectively.

By using the Born-von Kármán theory of lattice dynamics and the modified analytic embedded atom method, we reproduce the experimental results of the phonon dispersion in fcc metal Cu at zero pressure along three high symmetry directions and four off-symmetry directions, and then simulate the phonon dispersion curves of Cu at high pressures of 50, 100, and 150 GPa. The results show that the shapes of dispersion curves at high pressures are very similar to that at zero pressure. All the vibration frequencies of Cu in all vibration branches at high pressures are larger than the results at zero pressure, and increase correspondingly as pressure reaches 50, 100, and 150 GPa sequentially. Moreover, on the basis of phonon dispersion, we calculate the values of specific heat of Cu at different pressures. The prediction of thermodynamic quantities lays a significant foundation for guiding and judging experiments of thermodynamic properties of solids under high pressures.

We have performed the cell dynamics simulation with the time-dependent Ginzburg-Landau theory to study the self-assembled morphology of A-B diblock copolymers and C homopolymers in a neutral nanopore. The nanopore diameter and length are systematically varied to examine their effects on the structures of various morphologies and their phase transition. From the simulation, it is observed that the equilibrium morphology of the confined system is sensitive to pore diameter D and pore length L_{pore}, the phase behavior in neutral nanopores is due to an interplay of two factors: the surface effect and the extension effect. When the nanopore length and the lamellae spacing are not commensurate, the surface effect prevails at small nanopores (small diameters or short lengths), the extension effect takes over at larger nanopores (large diameters or long lengths). When the nanopore length and the lamellae spacing are commensurate, the surface effect dominates. Furthermore, the interactions between different monomers are also discussed and we obtain a transition from a tilted pancakes/cylinder structure (L_{⊥}^{tilted}) to a concentric cylindrical structure with defects and to a concentric cylindrical structure (L_{‖}). We also investigate the effect of the relative concentrations of diblock copolymer-homopolymer and obtain a transition in which the position of the C blocks changes from the outer of the cylinder to the middle of the cylinder and then to the inner of the cylinder with the concentration of the C blocks decreasing.

We derive the coupled nonpolynomial nonlinear Schrödinger equations for a two-component Bose-Einstein condensate in a quasi-one-dimension geometry and investigate the effects of a tightly transverse trapping on the ground state and the miscibility-immiscibility threshold. We find that the density profile of the matter wavepacket is remarkably dependent on the transverse width and the effective one-dimension nonlinear coupling strengths in miscible and immiscible regimes.

We study systematically an extended Bose-Hubbard model on the triangular lattice by means of a meanfield method based on the Gutzwiller ansatz. Pair hopping terms are explicitly included and a three-body constraint is applied. The zero-temperature phase diagram and a variety of quantum phase transitions are investigated in great detail. In particular, we show the existence and the stability of the pair supersolid phase.

We propose a catalytically activated replication-decline model of three species, in which two aggregates of the same species can coagulate themselves, an A aggregate of any size can replicate itself with the help of B aggregates, and the decline of A aggregate occurs under the catalysis of C aggregates. By means of mean-field rate equations, we derive the asymptotic solutions of the aggregate size distribution a_{k}(t) of species A, which is found to depend strongly on the competition among three mechanisms: the self-coagulation of species A, the replication of species A catalyzed by species B, and the decline of species A catalyzed by species C. When the self-coagulation of species A dominates the system, the aggregate size distribution a_{k}(t) satisfies the conventional scaling form. When the catalyzed replication process dominates the system, a_{k}(t) takes the generalized scaling form. When the catalyzed decline process dominates the system, a_{k}(t) approaches the modified scaling form.

TOPICAL REVIEW—Low-dimensional nanostructures and devices

Topological insulators’ properties and their potential device applications are reviewed. We also explain why topological insulator (TI) nanostructures are an important avenue for research and discuss some methods by which TI nanostructures are produced and characterized. The rapid development of high-quality TI nanostructures provides an ideal platform to exploit salient physical phenomena that have been theoretically predicted but not yet experimentally realized.

Intercalations of metals and silicon between epitaxial graphene and its substrates are reviewed. For metal intercalation, seven different metals have been successfully intercalated at the interface of graphene/Ru(0001) and form different intercalated structures. Meanwhile, graphene maintains its original high quality after the intercalation and shows features of weakened interaction with the substrate. For silicon intercalation, two systems, graphene on Ru(0001) and on Ir(111), have been investigated. In both cases, graphene preserves its high quality and regains its original superlative properties after the silicon intercalation. More importantly, we demonstrate that thicker silicon layers can be intercalated at the interface, which allows the atomic control of the distance between graphene and the metal substrates. These results show the great potential of the intercalation method as a non-damaging approach to decouple epitaxial graphene from its substrates and even form a dielectric layer for future electronic applications.

Three-dimensional topological insulators are a new class of quantum matter which has interesting connections to nearly all main branches of condensed matter physics. In this article, we briefly review the advances in the field effect control of chemical potential in three-dimensional topological insulators. It is essential to the observation of many exotic quantum phenomena predicted to emerge from the topological insulators and their hybrid structures with other materials. We also describe various methods for probing the surface state transport. Some challenges in experimental study of electron transport in topological insulators will also be briefly discussed.

Plasmonics is a rapidly developing field concerning light manipulation at the nanoscale with many potential applications, of which plasmonic circuits are promising for future information technology. Plasmonic waveguides are fundamental elements for constructing plasmonic integrated circuits. Among the proposed different plasmonic waveguides, metallic nanowires have drawn much attention due to the highly confined electromagnetic waves and relatively low propagation loss. Here we review the recent research progress in the waveguiding characteristics of metallic nanowires and nanowire-based nanophotonic devices. Plasmon modes of both cylindrical and pentagonal metallic nanowires with and without substrate are discussed. Typical methods for exciting and detecting the plasmons in metallic nanowires are briefly summarized. Because of the multimode characteristic, the plasmon propagation and emission in the nanowire have many unique properties, benefiting the design of plasmonic devices. A few nanowire-based devices are highlighted, including quarter-wave plate, Fabry-Pérot resonator, router and logic gates.

Topological insulators (TIs) are bulk insulators that possess robust helical conducting states along their interfaces with conventional insulators. A tremendous research effort has recently been devoted to TI-based heterostructures, in which conventional proximity effects give rise to a series of exotic physical phenomena. This paper reviews our recent studies on the potential existence of topological proximity effects at the interface between a topological insulator and a normal insulator or other topologically trivial systems. Using first-principles approaches, we have realized the tunability of the vertical location of the topological helical state via intriguing dual-proximity effects. To further elucidate the control parameters of this effect, we have used the graphene-based heterostructures as prototypical systems to reveal a more complete phase diagram. On the application side of the topological helical states, we have presented a catalysis example, where the topological helical state plays an essential role in facilitating surface reactions by serving as an effective electron bath. These discoveries lay the foundation for accurate manipulation of the real space properties of the topological helical state in TIbased heterostructures and pave the way for realization of the salient functionality of topological insulators in future device applications.

The recent development of synthesis processes to assemble graphene sheets into porous three-dimensional (3D) macroscopic structures are reviewed, including our efforts on 3D graphene structures. Mechanisms for building 3D graphene architectures and their composite materials are also summarized. The functional systems based on 3D graphene architectures provide a significant enhancement in the efficacy due to their unique structures and properties.

Recent progress of research for graphene applications in electronic and optoelectronic devices is reviewed, and recent developments in circuits based on graphene devices are summarized. The bandgap-mobility tradeoff inevitably constrains the application of graphene for the conventional field-effect transistor (FET) devices in digital applications. However, this shortcoming has not dampened the enthusiasm of the research community toward graphene electronics. Aside from high mobility, graphene offers numerous other amazing electrical, optical, thermal, and mechanical properties that continually motivate innovations.

The preparation and electrical properties of diamond nanocones are reviewed, including a maskless etching process and mechanism of large-area diamond conical nanostructure arrays using a hot filament chemical vapor deposition (HFCVD) system with negatively biased substrates, and the field electron emission, gas sensing, and quantum transport properties of a diamond nanocone array or an individual diamond nanocone. Optimal cone aspect ratio and array density are investigated, along with the relationships between the cone morphologies and experimental parameters, such as the CH_{4}/H_{2} ratio of the etching gas, the bias current, and the gas pressure. The reviewed experiments demonstrate the possibility of using nanostructured diamond cones as a display device element, a point electron emission source, a gas sensor or a quantum device.

The controllable growth of nanostructures with desired geometric order and well-defined shapes has stimulated great interest due to its applicability in the development of microelectronic devices. Self-assembly is an efficient and versatile way to guide the atoms or molecules into low-dimensional nanostructures as a consequence of balancing complex interplay between adsorbate-adsorbate and adsorbate-substrate interfacial interactions. The tailoring of low-dimensional nanostructures by control of inter-adsorbate and adsorbate-substrate interfacial interactions is reviewed. Such inherent interactions greatly influence not only the size and shape of the growing nanostructures, but also their chemical identity. The degree of interaction between adsorbates can be controlled via preparation procedures, opening up the study of the influence of this phenomenon with respect to reactivity and catalytic behavior. The formation of well-defined molecular layers can be controlled not only by repulsive molecule-molecule interaction but also by symmetry matching or charge transfer between adsorbed molecules and the substrate. It has become obvious that inter-adsorbate and adsorbate-substrate interfacial interactions can be tuned to fabricate diverse surface nanostructures from semiconductor, metallic, and molecular materials.

Fullerene molecules are interesting materials because of their unique structures and properties in mechanical, electrical, magnetic, and optical aspects. Current research is focusing on the construction of well-defined fullerene nano/microcrystals that possess desirable structures and morphologies. Further tuning the intermolecular interaction of the fullerene nano/microcrystals by use of pressure is an efficient way to modify their structures and properties, such as creation of nanoscale polymer structures and new hybrid materials, which expands the potential of such nanoscale materials for direct device components. In this paper, we review our recent progress in the construction of fullerene nanostructures and their structural transformation induced by high pressure. Fullerene nano/microcrystals with controllable size, morphology and structure have been synthesized through the self-assembly of fullerene molecules by a solvent-assisted method. By virtue of high pressure, the structures, components, and intermolecular interactions of the assemblied fullerene nano/microcrystals can be finely tuned, thereby modifying the optical and electronic properties of the nanostructures. Several examples on high pressure induced novel structural phase transition in typical fullerene nanocrystals with C_{60} or C_{70} cage serving as building blocks are presented, including high pressure induced amorphization of the nanocrystals and their bulk moduli, high pressure and high temperature (HPHT) induced polymerization in C_{60} nanocrystals, pressure tuned reversible polymerization in ferrocene-doped C_{60}/C_{70} single crystal, as well as unique long-range ordered crystal with amorphous nanoclusters serving as building blocks in solvated C_{60} crystals, which brings new physical insight into the understanding of order and disorder concept and new approaches to the design of superhard carbon materials. The nanosize and morphology effects on the transformations of fullerene nanocrystals have also been discussed. These results provide the foundation for the fabrication of pre-designed and controllable geometries, which is critical in fullerenes and relevant materials for designing nanometer-scale electronic, optical, and other devices.

Field-effect transistors (FETs) for logic applications, based on two representative two-dimensional (2D) materials, graphene and MoS_{2}, are discussed. These materials have drastically different properties and require different considerations. The unique band structure of graphene necessitates engineering of the Dirac point, including the opening of the bandgap, the doping and the interface, before the graphene can be used in logic applications. On the other hand, MoS_{2} is a semiconductor, and its electron transport depends heavily on the surface properties, the number of layers, and the carrier density. Finally, we discuss the prospects for the future developments in 2D material transistors.

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

We investigate the resistive switching characteristics of a Cu/VO_{x}/W structure. The VO_{x} film is deposited by radio-frequency magnetron sputtering on the Cu electrode as a dielectric layer. The prepared VO_{x} sample structure shows reproducible bipolar resistive switching characteristics with ultra-low switching voltage and good cycling endurance. A modified physical model is proposed to elucidate the typical switching behavior of the vanadium oxide-based resistive switching memory with a sudden resistance transition, and the self-saturation of reset current as a function of compliance current is observed in the test, which is attributed to the growth pattern of the conducting filaments. Additionally, the related conducting mechanism is discussed in detail.

In this paper, a novel structure of a 4H-SiC lateral bipolar junction transistor (LBJT) with a base field plate and double RESURF in the drift region is presented. Collector-base junction depletion extension in the base region is restricted by the base field plate. Thin base as well as low base doping of the LBJT therefore can be achieved under the condition of avalanche breakdown. Simulation results show that thin base of 0.32 μm and base doping of 3×10^{17} cm^{-3} are obtained, and corresponding current gain is as high as 247 with avalanche breakdown voltage of 3309 V when the drift region length is 30 μm. Besides, an investigation of a 4H-SiC vertical BJT (VBJT) with comparable breakdown voltage (3357 V) shows that the minimum base width of 0.25 μm and base doping as high as 8×10^{17} cm^{-3} contribute to a maximum current gain of only 128.

A GaAs metal-oxide-semiconductor (MOS) capacitor with HfO_{2} as gate dielectric and silicon nitride (SiN_{x}) as the interlayer (IL) is fabricated. Experimental results show that the sample with the SiN_{x} IL has an improved capacitance-voltage characteristic, lower leakage current density (0.785×10^{-6} A/cm^{2} at V_{fb}+1 V) and lower interface-state density (2.9×10^{12} eV^{-1}·cm^{-2}) compared with other samples with N_{2-} or NH_{3-} plasma pretreatment. The influences of postdeposition annealing temperature on electrical properties are also investigated for the samples with SiN_{x} IL. The sample annealed at 600℃ exhibits better electrical properties than that annealed at 500℃, which is attributed to the suppression of native oxides, as confirmed by XPS analyses.

Zheng Liu, Zhang Feng, Liu Sheng-Bei, Dong Lin, Liu Xing-Fang, Fan Zhong-Chao, Liu Bin, Yan Guo-Guo, Wang Lei, Zhao Wan-Shun, Sun Guo-Sheng, He Zhi, Yang Fu-Hua

Chin. Phys. B 2013, 22 (9): 097302; doi: 10.1088/1674-1056/22/9/097302
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4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 mΩ·cm^{2} with a total active area of 2.46×10^{-3} cm^{2}. Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7 V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250℃ in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9×10^{-5} A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.

A novel source-connected field plate structure, featuring the same photolithography mask as the gate electrode, is proposed as an improvement over the conventional field plate (FP) techniques to enhance the frequency performance in GaN-based HEMTs. The influences of the field plate on frequency and breakdown performance are investigated simultaneously by using a two-dimensional physics-based simulation. Compared with the conventional T-gate structures with a field plate length of 1.2 μm, this field plate structure can induce the small signal power gain at 10 GHz to increase by 5-9.5 dB, which depends on the distance between source FP and dramatically shortened gate FP. This technique minimizes the parasitic capacitances, especially the gate-to-drain capacitance, showing a substantial potential for millimeter-wave, high power applications.

The momentum relaxation time of a photoexcited graphene in the THz frequency range has been studied by using terahertz time domain spectroscopy under optical pumping at room temperature. It is found that the momentum relaxation time of the graphene as a function of the optical pumping intensity exhibits a threshold behavior. The features of the momentum relaxation time as a function of the optical pumping intensity are also investigated. The results are useful for understanding the basic underlying physics of graphene scattering as well as finding the possible applications in carbon-based electronics.

Rhenium is a superconductor with a relatively weak tendency to oxidize, which is advantageous in superconducting quantum circuit and qubit applications. In this work, Re/Al-AlO_{x}/Re Josephson tunnel junctions were fabricated using a selective film-etching process similar to that developed in Nb trilayer technology. The Re films had a superconducting transition temperature of 4.8 K and a transition width of 0.2 K. The junctions were found to be highly reproducible using the fabrication process and their characteristics had good quality with a low leakage current and showed a superconducting gap of 0.55 meV.

A gold tetrahedral nanocage, i.e., a tetrananocage, that converts near-infrared (NIR) light into heat was fabricated by using a simple method. Silver tetrahedra with good homogeneity and dispersity were synthesized by a hydrothermal route. Gold tetrananocages were obtained using a galvanic replacement reaction between Ag tetrahedra and HAuCl_{4} solution. The surface plasmon resonance (SPR) of gold tetrananocages was tuned from 412 nm to 850 nm through controlling the volume of HAuCl_{4} solution added. This Au tetrananocage can effectively convert NIR light into heat when the SPR couples with the exciting light. When cancer cells are cultured with the gold tetrananocages for several hours and irradiated, the gold tetrananocages destroy the cancer cells effectively and demonstrate themselves to be a good candidate for combating cancer.

A composition-modulated (HfO_{2})_{x}(Al_{2}O_{3})_{1-x} charge trapping layer is proposed for charge trap flash memory by controlling the Al atom content to form a peak and valley shaped band gap. It is found that the memory device using the composition-modulated (HfO_{2})_{x}(Al_{2}O_{3})_{1-x} as the charge trapping layer exhibits a larger memory window of 11.5 V, improves data retention even at high temperature, and enhances the program/erase speed. Improvements of the memory characteristics are attributed to the special band-gap structure resulting from the composition-modulated trapping layer. Therefore, the composition-modulated charge trapping layer may be useful in future nonvolatile flash memory device application.

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

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

The present work is devoted to a study of the molecular mechanisms of the crystallization of polymer chains induced by graphene by using molecular dynamics (MD) simulations. From the atomic configuration translation, the number distribution of the atoms, and the order parameter S, the crystallization process can be summarized in two steps, the adsorption and the orientation. By analyzing the diffusion properties of the polymer chains, we find that a graphene substrate has a great adsorption for the polymer molecules and the polymer molecules need more time to adjust their configurations. Therefore, the adsorption step and the orientation step are highly cooperative.

Structural and optical properties of ～ 20 nm Ge nanoislands grown on Si(100) by radio frequency (rf) magnetron sputtering under varying annealing conditions are reported. Rapid thermal annealing at a temperature of 600℃ for 30 s, 90 s, and 120 s are performed to examine the influence of annealing time on the surface morphology and photoluminescence properties. X-ray diffraction spectra reveal prominent Ge and GeO_{2} peaks highly sensitive to the annealing time. Atomic force microscope micrographs of the as-grown sample show pyramidal nanoislands with relatively high-density (～ 10^{11} cm^{-2}). The nanoislands become dome-shaped upon annealing through a coarsening process mediated by Oswald ripening. The room temperature photoluminescence peaks for both as-grown (～ 3.29 eV) and annealed (～ 3.19 eV) samples consist of high intensity and broad emission, attributed to the effect of quantum confinement. The red shift (～ 0.10 eV) of the emission peak is attributed to the change in the size of the Ge nanoislands caused by annealing. Our easy fabrication method may contribute to the development of Ge nanostructure-based optoelectronics.

A cupric oxide (CuO) nanocrystal-doped NaCl single crystal and a pure NaCl single crystal are grown by using the Czochralski (Cz) method. A number of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, optical absorption in the UV-visible range, and photoluminescence (PL) spectroscopy are used to characterize the obtained NaCl and NaCl:CuO crystals. It is observed that the average radius of CuO crystallites in NaCl:CuO crystal is about 29.87 nm, as derived from the XRD data analysis. Moreover, FT-IR and Raman spectroscopy results confirm the existence of the monoclinic CuO phase in NaCl crystal. UV-visible absorption measurements indicate that the band gap of the NaCl:CuO crystal is 434 nm (2.85 eV), and it shows a significant amount of blue-shift (ΔE_{g}=1 eV ) in the band gap energy of CuO, which is due to the quantum confinement effect exerted by the CuO nanocrystals. The PL spectrum of the NaCl:CuO shows a broad emission band centred at around 438 nm, which is consistent with the absorption measurement.

The effect of far-field uniform flow on the morphological evolution of a spherical particle in a supersaturated solution affected by a far-field uniform flow is studied by using the matched asymptotic expansion method. The analytical solution for the interface shape, concentration field, and interface velocity of the particle growth shows that the convection induced by the far-field uniform flow facilitates the growth of the spherical particle, the upstream flow imposed on the particle enhances the growth velocity of the interface when the flow comes in, the downstream flow lowers the growth velocity of the surface when the flow goes out, and the interface morphology evolves into a peach-like shape.

In this paper, the dynamic behavior analysis of the electromechanical coupling characteristics of a flywheel energy storage system (FESS) with a permanent magnet (PM) brushless direct-current (DC) motor (BLDCM) is studied. The Hopf bifurcation theory and nonlinear methods are used to investigate the generation process and mechanism of the coupled dynamic behavior for the average current controlled FESS in the charging mode. First, the universal nonlinear dynamic model of the FESS based on the BLDCM is derived. Then, for a 0.01 kWh/1.6 kW FESS platform in the Key Laboratory of the Smart Grid at Tianjin University, the phase trajectory of the FESS from a stable state towards chaos is presented using numerical and stroboscopic methods, and all dynamic behaviors of the system in this process are captured. The characteristics of the low-frequency oscillation and the mechanism of the Hopf bifurcation are investigated based on the Routh stability criterion and nonlinear dynamic theory. It is shown that the Hopf bifurcation is directly due to the loss of control over the inductor current, which is caused by the system control parameters exceeding certain ranges. This coupling nonlinear process of the FESS affects the stability of the motor running and the efficiency of energy transfer. In this paper, we investigate into the effects of control parameter change on the stability and the stability regions of these parameters based on the averaged-model approach. Furthermore, the effect of the quantization error in the digital control system is considered to modify the stability regions of the control parameters. Finally, these theoretical results are verified through platform experiments.

The radiation effects on several properties (reference voltage, digital output logic voltage, and supply current) of dual 8-bit analog-to-digital (A/D) converters (AD9058) under various biased conditions are investigated in this paper. Gamma ray and 10-MeV proton irradiation are selected for a detailed evaluation and comparison. Based on the measurement results induced by the gamma ray with various dose rates, the devices exhibit enhanced low dose rate sensitivity (ELDRS) under zero and working bias conditions. Meanwhile, it is obvious that the ELDRS is more severe under the working bias condition than under the zero bias condition. The degradation of AD9058 does not display obvious ELDRS during 10-MeV proton irradiation with the selected flux.

This paper explores the band structure effect to elucidate the feasibility of an ultra-scaled GaAs Schottky MOSFET (SBFET) in a nanoscale regime. We have employed a 20-band sp^{3}d^{5}s^{*} tight-binding (TB) approach to compute E-K dispersion. The considerable difference between the extracted effective masses from the TB approach and bulk values implies that quantum confinement affects the device performance. Beside high injection velocity, the ultra-scaled GaAs SBFET suffers from a low conduction band DOS in the Γ valley that results in serious degradation of the gate capacitance. Quantum confinement also results in an increment of the effective Schottky barrier height (SBH). Enhanced Schottky barriers form a double barrier potential well along the channel that leads to resonant tunneling and alters the normal operation of the SBFET. Major factors that may lead to resonant tunneling are investigated. Resonant tunneling occurs at low temperatures and low drain voltages, and gradually diminishes as the channel thickness and the gate length scale down. Accordingly, the GaAs (100) SBFET has poor ballistic performance in nanoscale regime.

A novel red-emitting phosphor, CaYAl_{3}O_{7}: Eu^{3+}, Sm^{3+}, is synthesized by a combustion method at a low temperature (850℃), and the single phase of CaYAl_{3}O_{7} is confirmed by powder X-ray diffraction measurements. The photoluminescence property results reveal that the red emission intensity of Eu^{3+} is strongly dependent on the Sm^{3+} concentration. Only the Eu^{3+} luminescence is detected in the Eu^{3+}-Sm^{3+} co-doped CaYAl_{3}O_{7} phosphor with 393 nm excitation. However, under the characteristic excitation (402 nm) of Sm^{3+}, not only the Sm^{3+} emission but also the Eu^{3+} emission are observed. A possible mechanism of the energy transfer between Sm^{3+} and Eu^{3+} is investigated in detail.

The advantages of a blue InGaN-based light-emitting diode with a p-InGaN layer inserted in the GaN barriers is studied. The carrier concentration in the quantum well, radiative recombination rate in the active region, output power, and internal quantum efficiency are investigated. The simulation results show that the InGaN-based light-emitting diode with a p-InGaN layer inserted in the barriers has better performance over its conventional counterpart and the light emitting diode with p-GaN inserted in the barriers. The improvement is due to enhanced Mg acceptor activation and enhanced hole injection into the quantum wells.

The condensation of DNA induced by spermine is studied by atomic force microscopy (AFM) and molecular dynamics (MD) simulation in this paper. In our experiments, an equivalent amount of multivalent cations is added to the DNA solutions in different numbers of steps, and we find that the process of DNA condensation strongly depends on the speed of adding cations. That is, the slower the spermine cations are added, the slower the DNA aggregates. The MD and steered molecular dynamics (SMD) simulation results agree well with the experimental results, and the simulation data also show that the more steps of adding multivalent cations there are, the more compact the condensed DNA structure will be. This investigation can help us to control DNA condensation and understand the complicated structures of DNA-cation complexes.

The multiple instance regression problem has become a hot research topic recently. There are several approaches to the multiple instance regression problem, such as Salience, Citation KNN, and MI-ClusterRegress. All of these solutions work in batch mode during the training step. However, in practice, examples usually arrive in sequence. Therefore, the training step cannot be accomplished once. In this paper, an online multiple instance regression method “OnlineMIR” is proposed. OnlineMIR can not only predict the label of a new bag, but also update the current regression model with the latest arrived bag. The experimental results show that OnlineMIR achieves good performances on both synthetic and real data sets.

The neural system characterizes information in external stimulations by different spiking patterns. In order to examine how neural spiking patterns are related to acupuncture manipulations, experiments are designed in such a way that different types of manual acupuncture (MA) manipulations are taken at the ‘Zusanli’ point of experimental rats, and the induced electrical signals in the spinal dorsal root ganglion are detected and recorded. The interspike interval (ISI) statistical histogram is fitted by the gamma distribution, which has two parameters: one is the time-dependent firing rate and the other is a shape parameter characterizing the spiking irregularities. The shape parameter is the measure of spiking irregularities and can be used to identify the type of MA manipulations. The coefficient of variation is mostly used to measure the spike time irregularity, but it overestimates the irregularity in the case of pronounced firing rate changes. However, experiments show that each acupuncture manipulation will lead to changes in the firing rate. So we combine four relatively rate-independent measures to study the irregularity of spike trains evoked by different types of MA manipulations. Results suggest that the MA manipulations possess unique spiking statistics and characteristics and can be distinguished according to the spiking irregularity measures. These studies have offered new insights into the coding processes and information transfer of acupuncture.

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

Chin. Phys. B 2013, 22 (9): 098801; doi: 10.1088/1674-1056/22/9/098801
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The effects of Mg-induced net acceptor doping concentration and carrier lifetime on the performance of a p-i-n InGaN solar cell are investigated. It is found that the electric field induced by spontaneous and piezoelectric polarization in the i-region could be totally shielded when the Mg-induced net acceptor doping concentration is sufficiently high. The polarization-induced potential barriers are reduced and the short circuit current density is remarkably increased from 0.21 mA/cm^{2} to 0.95 mA/cm^{2} by elevating the Mg doping concentration. The carrier lifetime determined by defect density of i-InGaN also plays an important role in determining the photovoltaic properties of solar cell. The short circuit current density severely degrades, and the performance of InGaN solar cell becomes more sensitive to the polarization when carrier lifetime is lower than the transit time. This study demonstrates that the crystal quality of InGaN absorption layer is one of the most important challenges in realizing high efficiency InGaN solar cells.

Cadmium sulphide (CdS) and cadmium telluride (CdTe) thin films are deposited by electron beam evaporation. Atomic force microscopy (AFM) reveals that the root mean square (RMS) roughness values of the CdS films increase as substrate temperature increases. The optical band gap values of CdS films increase slightly with the increase in the substrate temperature, in a range of 2.42-2.48 eV. The result of Hall effect measurement suggests that the carrier concentration decreases as the substrate temperature increases, making the resistivity of the CdS films increase. CdTe films annealed at 300℃ show that their lowest transmittances are due to their largest packing densities. The electrical characteristics of CdS/CdTe thin film solar cells are investigated in dark conditions and under illumination. Typical rectifying and photovoltaic properties are obtained.

In this paper, a-Si:H/a-SiGe:H/μc-SiGe:H triple-junction solar cell structure is proposed. By the analyses of microelectronic and photonic structures (AMPS-1D) and our TRJ-F/TRJ-M/TRJ-B tunneling-recombination junction (TRJ) model, the most preferably combined bandgap for this structure is found to be 1.85 eV/1.50 eV/1.0 eV. Using more realistic material properties, optimized thickness combination is investigated. Along this direction, a-Si:H/a-SiGe:H/μc-SiGe:H triple cell with an initial efficiency of 12.09% (V_{oc}=2.03 V, FF=0.69, J_{sc}=8.63 mA/cm^{2}, area=1 cm^{2}) is achieved in our laboratory.

In order to exploit its potential applications, we experimentally study the dependence of ^{85}Rb-based coherent population trapping (CPT) resonance on N_{2} buffer gas with 6 vapor cells filled with natural rubidium and N_{2}. The experiments are carried out at different pressures and temperatures, and the results reveal that higher cell temperature makes the resonance more sensitive to N_{2} pressure. Thus, it is important to choose a proper buffer gas pressure at a given cell temperature. This work provides valuable data for the application of ^{85}Rb CPT resonance with a buffer gas of N_{2}.

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