Operational systems of spacecraft are general variable mass mechanics systems, and their symmetries and conserved quantities imply profound physical rules of the space system. We study the Mei symmetry of Tzénoff equations for a variable mass nonholonomic system and the new conserved quantities derived. The function expression of the new conserved quantities and the criterion equation which deduces these conserved quantities are presented. This result has some theoretical values in further research of conservation laws obeyed by the variable mass system.

Based upon the group theoretical jet bundle formalism introduced by Wahlquist and Estabrook for discussing the complete integrability of soliton systems, we investigate the prolongation structure of Wadati–Konno–Ichikawa isospectral evolution equations. As a result, we unearth a new physical coupled system entailing a hidden structural symmetry SL(3,R) arising in the description of ultra−short pulse propagation in optical nonlinear media. As a matter of fact, we depict a graphical representation of one-breather and two-breather ultra-short pulses in motion with a non-zero angular momentum. By extending the previous study to multidimensional symmetry SL(n,R), we unearth a more general class of multicomponent coupled nonlinear ultra-short pulse system with its associated inverse scattering formulation particularly useful in soliton theory.

Two classes of periodic wave solutions to the (3+1)-dimensional soliton equation are derived by employing the Hirota bilinear method and theta function identities. These solutions are expressed in terms of Riemann theta functions of genus one and can be converted into an elliptic function format, both their long wave limit and extremum value are discussed in detail.

The anisotropy of dipole-dipole interaction is revealed by energy band, tunneling dynamics and stabilities of a dipolar condensate in one-dimensional optical lattices. It is demonstrated that the Bloch band structure, the tunneling rate between Bloch bands and the stabilities of Bloch states can be controlled by adjusting the effective aspect ratio of the condensate and the dipolar orientation.

The decoherence effect on multipartite entanglement in non-inertial frames is investigated. The GHZ state is considered to be shared between partners with one partner in the inertial frame whereas the other two are in accelerated frames. One-tangle and π−tangles are used to quantify the entanglement of the multipartite system influenced by phase damping and phase flip channels. It is seen that for the phase damping channel, entanglement sudden death (ESD) occurs for p>0.5 in the infinite acceleration limit. On the other hand, in the case of the phase flip channel, ESD behavior occurs at p=0.5. It is also seen that entanglement sudden birth (ESB) occurs in the case of phase flip channel just after ESD, i.e. p>0.5. Furthermore, it is seen that the effect of the environment on multipartite entanglement is much stronger than that of the acceleration of non-inertial frames.

The Schrödinger equation for the generalized Pöschl–Teller potential with the centrifugal term is investigated approximately. The Nikiforov–Uvarov method is used in the calculations and the eigenfunctions as well as the energy eigenvalues obtained after a proper Pekeris-type approximation. Some useful expectation values and the oscillator strength are reported.

We revisit Parikh–Wilczek tunneling through the de Sitter horizon and obtain the tunneling rate in Schwarzschild-de Sitter space, which is non-thermal and closely related to the change of entropy. We discuss the thermodynamics of Schwarzschild-de Sitter space and show existence of correlation which can ensure conservation of the total entropy in the transition process of Schwarzschild-de Sitter space to de Sitter space. The correlation and the conserved entropy provide a way to explain the entropy in empty de Sitter space.

We carry out the hidden structural symmetries embedded within a system comprising ultra-short pulses which propagate in optical nonlinear media. Based upon the Wahlquist–Estabrook approach, we construct the Lie-algebra valued connections associated to the previous symmetries while deriving their corresponding Lax-pairs, which are particularly useful in soliton theory. In the wake of previous results, we extend the above prolongation scheme to higher-dimensional systems from which a new (2+1)-dimensional ultra-short pulse equation is unveiled along with its inverse scattering formulation, the application of which are straightforward in nonlinear optics where an additional propagating dimension deserves some attention.

Time-delay Takagi-Sugeno fuzzy drive-response dynamical networks (TD-TSFDRDNs) are defined by extending the drive-response dynamical networks. Based on the LaSalle invariant principle, a simple and systematic adaptive control scheme is proposed to synchronize the TD-TSFDRDNs with a desired scalar factor. A sufficient condition for the generalized projective synchronization in TD-TSFDRDNs is derived. Moreover, numerical simulations are provided to verify the correctness and effectiveness of the scheme.

We investigate the third-order leader-following consensus problem of nonlinear multi-agent systems in undirected network topologies. Based on graph theory and Lyapunov stability theory, the adaptive control method is employed to achieve leader-following consensus in an undirected network of agents with nonlinear third-order dynamics against the perturbations. Simulation examples validate the correctness of the results and show that the control gains have a great influence on the convergence performance of errors for a short time.

Mechanisms for the evolution of a single spherical bubble subjected to sound excitation in water are studied from the viewpoint of nonlinear dynamics. First, the shooting method is combined with a Poincaré map to obtain the fixed point for the case of forced oscillation in volume. Then, the stabilities are judged by Floquet theory and the bifurcation theorem. Moreover, the transitions of bubble oscillation in volume due to sound excitation in water are explained from the viewpoint of nonlinear dynamics in detail. The results show that with an increase in sound frequency, the period-1 oscillation becomes unstable, and oscillation behaves in a double-periodic manner, then a quasi-periodic manner, and finally chaotically. Additionally, with an increase of the amplitude of the sound pressure, the bubble eventually oscillates with chaos via a series of period-doubling bifurcations.

The generalized projective synchronization of different dimensional fractional order chaotic systems is investigated. According to the stability theory of linear fractional order systems, a sufficient condition to realize synchronization is obtained. The fractional order chaotic and hyperchaotic systems are applied to achieve synchronization in both reduced and increased dimensions. The corresponding numerical results coincide with theoretical analysis.

In-Pd-Co-SnO_{2} composite nanofibers have been synthesized by an electrospinning method and characterized by x−ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Micro-sensors with a tiny area of 1×1 mm^{2} are fabricated by spinning the nanofibers on sensor substrates. Excellent CH_{4} sensing properties are found based on the micro−sensors. The sensitivity is up to 13 when the sensors are exposed to 10 ppm CH_{4} at 140°C, and the response and recovery times are about 8 and 14 s, respectively. High selectivity, good stability, and low power-consumption are also observed in the investigation.

We parameterize the vertexes Σ_{Q}Ξ_{Q}^{*}K^{*} and Ξ'_{Q}Σ_{Q}^{*}K^{*} with three tensor structures due to Lorentz invariance, and calculate the corresponding three coupling constants within light-cone QCD sum rules. We then obtain their numerical values taking into account all the uncertainties of the relevant parameters.

By using the worldline instanton method we investigate the electron-positron pair production rate from a vacuum in the presence of a time-dependent field with general elliptic polarization. It is found that as field polarization changes from a linear to a circular one, the pair production rate would change to some extent. When field strength is weak while frequency is high, the pair production rate changes significantly with polarization. However, when field strength is strong while frequency is low, the pair production rate from a vacuum is insensitive to field polarization and the results of the pair production rate are the same as those in a constant field. Our results are compared with previous work and the implications of our study are briefly discussed.

The ground bands and β−bands of four nuclei ^{230,232}Th and ^{232,234}U in the actinide region are investigated by introducing a collective D_{0} pair into the projected shell model. We discuss the collectivity of the D_{0} pair. The calculated energy schemes agree well with experimental data, and so do the E2 transition rates.

LI Shi-Cheng, SHI Yue, ZHANG Yu-Hu, ZHOU Xiao-Hong, XU Fu-Rong, FANG Yong-De, LIU Min-Liang, DING Bing, GUO Song, LI Guang-Shun, ZHOU Hou-Bing, M. Oshima, Y. Toh, M. Koizumi, A. Osa, A. Kimura, Y. Hatsukawa, H. Hayakawa, T. Shizuma, J. Katakura, M. Matsuda, T. Morikawa, M. Sugawara, H. Kusakari

Chin. Phys. Lett. 2012, 29 (2):
022102
.
DOI: 10.1088/0256-307X/29/2/022102

The high-spin level structure of ^{186}Au is re−investigated by means of in-beam γ−ray spectroscopy via the ^{172}Yb(^{19}F, 5nγ)^{186}Au reaction. The oblate bands previously reported are revised and extended to higher−spin states. A new I^{π}=(20^{+}) excited state has been identified and assigned to the πh_{11/2}^{−1} ⊗νi_{13/2}^{-2}h_{9/2}^{-1} configuration. The total Routhian surface and cranked shell model calculations suggest that the πh_{11/2}^{−1} ⊗νi_{13/2}^{-2}h_{9/2}^{-1} band in ^{186}Au has a non-axial deformation.

We look at some crucial aspects of J/Ψ-production in a few high energy nuclear collisions in the light of a non-standard model which is outlined in the text. The underlying physical ideas, assumptions and ansatzs are also enunciated in some detail. The results are in fairly in good agreement with both measured data and the results obtained on the basis of other models of the standard variety. The impact and implications of this comparative study are also discussed.

We present the pseudorapidity distributions of charged particles in nucleus-nucleus collisions as functions of beam energy and impact parameter through weighted superposition of the pseudorapidity distributions in the effective binary nucleon-nucleon collisions. Using the theoretical model we then analyze the experimental measurements carried out by the BNL-RHIC-PHOBOS collaboration in Cu+Cu collisions at s_{NN}^{1/2}=200, 62.4 and 22.4 GeV. The model has only two free parameters and the theoretical results favor the experimental measurements well.

We investigate the decay rate of an atom in a two-dimensional optical microcavity in which there exists a Bose–Einstein condensation of photons. It is found that below the critical temperature T_{c}, the atomic decay rate depends on the absolute temperature T. Especially, at absolute zero temperature almost all photons are in the condensate state, and the atom can be approximately treated as if it is in vacuum.

We present an experiment on the measurement of the spatial distribution of cold atoms in a ceramic cell. The atoms are first cooled by diffusing light produced by multiple scattering of laser light at the inner surface of the cell. An inhomogeneous magnetic field is applied after the atoms are cooled by using a pair of anti-Helmholtz coils, and thus the shift of atomic magnetic sub-levels is position-dependent. We move the anti-Helmholtz coils point by point while keeping the probe laser beam resonant with the cold atoms at zero magnetic field. The number of cold atoms at different positions can be extracted by detecting the absorption to the probe beam. The density of the cold atoms in the cell is measured in two dimensions perpendicular and parallel to the tube connecting to the vacuum system, respectively. The results show that at the center of the cell, fewer atoms exist due to the leakage of diffuse light into the hole connecting to the vacuum pump. The method we developed is used to detect cold atoms in a region where imaging is impossible.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

A 1.56 µm passively mode-locked laser diode with a two-section tensile strained multi-quantum-well structure is fabricated. Without any external pulse compression, a Lorentz pulse train with a pulse width of 1.03 ps and a repetition rate of 35.6 GHz is obtained, which is one of the best results that have been reported on similar devices. The optical pulse has a 300 kHz line width and a 50 dB peak over the noise floor in the photodetected radio-frequency electrical spectrum.

We experimentally observe the counterintuitive absorption peaks in the transition spectra of 5S_{1/2}–5P_{3/2}–4D_{5/2} and 5S_{1/2}–5P_{3/2}–4D_{3/2} in a hot ^{85}Rb vapor. These spectra are very different from the spectra observed via double resonance optical pumping or electromagnetically induced transparency in the same transitions. These absorption peaks are from electromagnetically induced absorption due to the two-photon atomic coherence effect. We also investigate the relations between these peaks and the powers of the coupling laser and the probe laser experimentally.

The three-dimensional thermal properties of 18-core photonic crystal fiber lasers operated under natural convection are investigated. The temperature sensing technique based on a fiber Bragg grating sensor array is proposed to measure the longitudinal temperature distribution of a 1.6-m-long ytterbium-doped 18-core photonic crystal fiber. The results show that the temperature decreases from the pump end to the launch end exponentially. Moreover, the radial temperature distribution of the fiber end is investigated by using the full-vector finite-element method. The numerical results match well with the experimental data and the coating temperature reaches 422.7 K, approaching the critical value of polymer cladding, when the pumping power is 40 W. Therefore the fiber end cooling is necessary to achieve power scaling. Compared with natural convection methods, the copper cooling scheme is found to be an effective method to reduce the fiber temperature.

We report a 31.2 W cw diode-pumped cryogenic Ho(0.4at.%),Tm(4at.%):GdVO_{4} laser in a dual−crystal cavity. The pumping sources are two fiber-coupled laser diodes with a fiber core diameter of 0.4 mm, both of which can supply 42 W near 802 nm. With an incident pump power of 70.3 W at 802.4 nm, a cw output power of 31.2 W at 2.05 µm is attained, corresponding to an optical−to-optical conversion efficiency of 44.4%. The M^{2} factor is measured as ∼1.3 under an output power of 20 W.

We build up a novel setup of a two-dimensional (2D) ^{85}Rb magneto−optical trap (MOT) with a high optical depth (OD) of 38. Such a MOT trap of ^{85}Rb has several advantages as compared to the normal three−dimensional ellipsoidal MOT. Firstly, it will greatly enhance atom-photon interaction due to the large OD. Then, the dephasing caused by the magnetic gradient will be decreased in the long axis of the 2D MOT, which we want to avoid from in the experiments. The metastable ground level dephasing rate was γ_{21}=0.008γ_{31}, which is much less than that in a normal MOT. The total number of atoms in this MOT was measured to be 9.1×10^{8}.

A diode-end-pumped electro-optic (EO) Q-switched adhesive-free bond composite Nd:YVO_{4} laser operating at a repetition rate of 200 kHz is reported. A pair of RbTiOPO_{4} (RTP) crystals are used as a high repetition EO Q-switch. At the repetition rate of 200 kHz, the maximum average output power of 11.8 W at wavelength 1064 nm and full width at half maximum of pulses of 16.65 ns are achieved at an incident pump power of 27 W, corresponding to an optical conversion efficiency of 43.7% and a slope efficiency of 44.6%, respectively. To the best of our knowledge, this is the highest repetition rate reported on the EO Q-switched laser by using RTP crystals.

We demonstrate the ultrafast imaging of a submillimeter bar chart that is either hidden behind glass diffusers or inside a solution of polystyrene spheres, using an ultrafast optical Kerr gate (OKG). The results show that the time-resolved imaging of the target in the turbid media with an optical depth of 11.4 is achieved using the OKG with a 1.6 ps opening time. The image contrast is improved by about 70% compared with the shadowgraph imaging.

A new time reversal method is proposed to infer the location of an unknown extending target in a complex environment. In our method, the wavelet analysis and scalogram of energy density are first introduced into the electromagnetic time reversal process to improve the accuracy and to eliminate noises. The computation results show that the new technique can refocus the unknown target better than using traditional time reversal.

By locating the emitters around the first and second antinode of the metal electrode, the escaped and trapped emission of small molecule based bottom emission organic light-emitting diodes is investigated by using an integrating sphere, a fiber spectrometer and a glass hemisphere. It is found that the external coupling ratio by locating the emitters at the second antinode (at a distance of 220 nm from the cathode) is 70%, which is higher than that of an emitter at the first antinode (60 nm from the cathode) in theory and experiment. Extending the "half-space" dipole model by taking the dipole radiation pattern into account, we also calculate the optical coupling efficiency for the emitter at both the first and second antinode. Our experimental and theoretical results will benefit the optimization of device structures for the higher out-coupling efficiency.

We investigate the Ramsey fringes of a single electron spin of the nitrogen-vacancy center in diamond with different microwave radiation frequency detunings. The fast Fourier transform demonstrates that the Ramsey fringes consist of three components caused by hyperfine interaction with ^{14}N nuclear spin, and the Ramsey fringes cannot be well explained without the phase term of the three components, which has not been mentioned before. Each phase is determined by the microwave frequency detuning and the resonant Rabi frequency as well as the π/2 pulse.

We provide alternatively a simple way of computing the Fresnel field integral, a further extension to the Gaussian-beam expansion. With a known result that the circ function is approximately decomposed into a sum of Gaussian functions, the zero-order Bessel function of the first kind is similarly expanded by the Bessel–Fourior transform. Two expansions are together inserted in this integral, which is then expressible in terms of the simple algebraic functions. The approach is useful in treatment of the field radiation problem for a large and important group of piston sources in acoustics. As examples, the calculation results for the uniform and the simply supported piston sources are presented, in a good agreement with those evaluated by numerical integration.

Surface acoustic wave (SAW) propagation in relaxor-based ferroelectric single crystals 0.93Pb(Zn_{1/3}Nb_{2/3})O_{3}−0.07PbTiO_{3} (PZN−7%PT ) poled along [011]_{c} has been analyzed theoretically. The results show that PZN−7%PT single crystals have excellent SAW properties, such as low phase velocities, very high electromechanical coupling coefficients and small power flow angles. It is also found that the SAW properties strongly depend on the propagation direction and the characteristic curves of SAW phase velocity, and the electromechanical coupling coefficients are symmetric with respect to θ=90°. Considering all related factors, the X−cut PZN-7%PT single crystal has the best performance. Based on our results, the X−cut PZN-7%PT single crystals poled along [011]_{c} are an excellent candidate for ultra-wide bandwidth low-frequency SAW devices.

A new semi-Lagrangian (SL) scheme is proposed by using finite spectral regional interpolation and adequate numerical dissipation to control the nonlinear instability. The finite spectral basis function is C^{1} continuous at the boundary and is easy to construct. Comparison between numerical and experimental results indicates that the present method works well in solving incompressible Navier–Stokes equations for unsteady flows around airfoil with different angles of attack.

We investigate the axisymmetric stagnation-point flow of a viscous fluid over a lubricated surface by imposing a generalized slip condition at the fluid-fluid interface. The power law non-Newtonian fluid is considered as a lubricant. The lubrication layer is thin and assumed to have a variable thickness. The transformed nonlinear ordinary differential equation governing the flow is linearized using quasilinearization. The method of superposition is adopted to convert the boundary value problem into an initial value problem and the solution is obtained numerically by using the fourth-order Runge–Kutta method. The results are discussed to see the influence of pertinent parameters. The limiting cases of Navier and no-slip boundary conditions are obtained as the special cases and found to be in excellent agreement with the existing results in the literature.

A computational simulation for the separation of red blood cells (RBCs) is presented. The deformability of RBCs is expressed by the spring network model, which is based on the minimum energy principle. In the computation of the fluid flow, the lattice Boltzmann method is used to solve the Navier–Stokes equations. Coupling of the fluid-membrane interaction is carried out by using the immersed boundary method. To verify our method, the motions of RBCs in shear flow are simulated. Typical motions of RBCs observed in the experiments are reproduced, including tank-treading, swinging and tumbling. The motions of 8 RBCs at the bifurcation are simulated when the two daughter vessels have different ratios. The results indicate that when the ratio of the daughter vessel diameter becomes smaller, the distribution of RBCs in the two vessels becomes more non-uniform.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

We present the results from 2D fluid modeling of the key roles controlling the glow dielectric barrier discharge (DBD) structure. A uniform DBD can be sustained at lower frequency when the space charge reaches uniformity due to plasma decay, while the patterned structure appears above a critical frequency when the space charge is nonuniform. The patterns start from the electrode edge where the electric field is significantly distorted, characterized by the patterned seed electrons that always form ahead of the surface charges. The formation of the patterned DBD structure is associated with the lateral inhibition of the local increase of space charges. The distribution of the volume seed electrons plays a key role in the DBD structure while the distribution of surface charge is a result of the formed structure.

Transport properties of lithium plasmas in local thermodynamic equilibrium at pressures from 0.0001 atm to 1 atm, and temperatures from 1000 K to 40000 K are presented. The calculations of transport coefficients are carried out using the Chapman–Enskog method. The evolutions of transport coefficients with temperature and pressure are reported and discussed. Comparisons of these values in the low temperature region with previously reported data show reasonable agreement.

The internal kink mode with a real frequency comparable with the bulk ion diamagnetic frequency is investigated in the case of lower hybrid wave injection. It is found that circulating supra-thermal electrons can directly destabilize the internal kink mode by resonance interaction in the neighborhood of the q=1 rational surface. The pressure gradient of circulating supra-thermal electrons on the resonance surface is crucial for excitation of the mode.

A three-dimensional (3D) dusty plasma crystalline with cubic configurations is considered. We calculate the interaction between particles up to distance √2a, implying the second−neighbor interactions for the simple cubic structure, the third-neighbor interactions for the body-centered cubic structure, and the forth-neighbor interactions the for face-centered cubic structure. Longitudinal and transverse dispersion relations are derived in arbitrary directions. The dispersion relations are studied in special directions, i.e. (1,0,0), (1,1,0)/√2, and (1,1,1)/√2. Study of dispersion relations with more neighbor interactions show that in some cases the results change physically.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Dislocation information and strain-related tetragonal distortion as well as crystalline qualities of a 2-µm −thick InN film grown by molecular beam epitaxy (MBE) are characterized by Rutherford backscattering/channeling (RBS/C) and synchrotron radiation x-ray diffraction (SR-XRD). The minimum yield χ_{min}=2.5% deduced from the RBS/C results indicates a fairly good crystalline quality. From the SR−XRD results, we obtain the values of the screw and edge densities to be ρ_{screw}=7.0027×10^{9} and ρ_{edge}=8.6115×10^{9} cm^{−2}, respectively. The tetragonal distortion of the sample is found to be −0.27% by angular scans, which is close to the −0.28% derived by SR-XRD. The value of |e^{⊥}/e^{||} |=0.6742 implies that the InN layer is much stiffer along the a axis than that along the c axis, where e^{||} is the parallel elastic strain, and e^{⊥} is the perpendicular elastic strain. Photoluminescence results reveal a main peak of 0.653 eV with the linewidth of 60 meV, additional shoulder band could be due to impurities and related defects.

The high-pressure and high-temperature structural behavior of FeP_{2} is investigated by means of synchrotron x−ray powder diffraction combined with a laser heating technique up to 70 GPa and at least 1800 K. No phase transition of FeP_{2} occurs up to 68 GPa at room temperature. While a new phase of FeP_{2} assigned to the CuAl_{2}−type structure (I4/mcm, Z=4) is observed at 70 GPa after laser-heating. This new phase presents a quenchable property on decompression to ambient conditions. Our results update previous experimental data and are consistent with theoretical studies.

The nickel sites of a D0_{22}−Ni_{3}V phase are subdivided into Ni1 and Ni2 sublattices according to their coordination sphere difference. The occupancy probability (OP) differences influenced by the coordination sphere are interpreted using the microscopic phase field model. The OP of regular atoms (Ni_{Ni1}, Ni_{Ni2}), antisite defects (V_{Ni1}, V_{Ni2}), and substitutional defects (Al_{Ni2}, Al_{Ni1}) have strong site preferences, as well as temperature−dependence features, on both sublattices. These features involve both redistribution of components, and phase transition from D0_{22} to L1_{2}.

We report the mechanical spectroscopy study of the cold-rolling induced dynamical behavior of crystalline defects in nanocrystalline (NC) nickel. The results show that internal friction (IF) peaks in NC nickel can be induced by cold-rolling. An IF peak, originating from dislocation activity, occurs when the strain is in the range of 9.7–32.8%. Two Bordoni peaks occur when the strain is 39.0% and an IF peak associated with deformation twinning appears when the strain is 42.6%. These results mean that deformation of NC nickel is mediated by different kinds of defects as the strain increases.

A compact temperature sensor based on a symmetrical metal-cladding optical waveguide using free-space coupling is proposed and demonstrated theoretically and experimentally. The symmetrical Au-cladding optical waveguide is based on a thin LiNbO_{3} slab sandwiched between two metal films, which serve as the coupling layer and reflecting panel, respectively. The sensitivity of this sensor of 9.08×10^{−2} deg/°C, 6.6×10^{−2} deg/°C and 4.8×10^{−2} deg/°C corresponding to 3238−order, 3237-order and 3236-order modes, respectively, are obtained. Higher resolution is predicted with a larger linear expansion coefficient material and a higher resolution θ/2θ goniometer.

SANG Ling, LIU Jian-Ming, XU Xiao-Qing, WANG Jun, ZHAO Gui-Juan, LIU Chang-Bo, GU Cheng-Yan, LIU Gui-Peng, WEI Hong-Yuan, LIU Xiang-Lin, YANG Shao-Yan, ZHU Qin-Sheng, WANG Zhan-Guo

Chin. Phys. Lett. 2012, 29 (2):
026801
.
DOI: 10.1088/0256-307X/29/2/026801

The morphological evolution of a-GaN deposited by metalorganic chemical vapor deposition (MOCVD) on r-sapphire is studied. The influences of V/III ratio and growth temperature on surface morphology are investigated. V−pits and stripes are observed on the surface of a-GaN grown at 1050°C and 1100°C, respectively. The overall orientation and geometry of V−pits are uniform and independent on the V/III molar ratio in the samples grown at 1050°C, while in the samples grown at 1100°C, the areas of stripes decrease with the adding of V/III ratio. We deduce the origin of V−pits and stripes by annealing the buffer layers at different temperatures. Because of the existence of inclined (1011) facets, V−pits are formed at 1050°C. The (1011) plane is an N terminated surface, which is metastable at higher temperature, so stripes instead of V−pits are observed at 1100°C. Raman spectra suggest that the growth temperature of the first layer in the two-step process greatly affects the strain of the films. Hence, to improve the growth temperature of the first layer in the two-step method may be an effective way to obtain high quality a-GaN film on r-sapphire.

The wetting behavior of dust by droplets is investigated by experiments and numerical simulation methods. Experimental observation reveals that the surface of a coal slice is hydrophilic in nature, while surfaces of coal dust stacks are hydrophobic. We show that water droplets settle on these surfaces following the Cassie–Baxter wetting model, as supported by theoretical, numerical analyses and experimental observations, i.e. water droplets only wet the first layer of coal dust. Our numerical simulation results also show that a water droplet could not enclose any coal dust inside it and many coal dust particles are adhered with a hexagonal close packing on a large water droplet. Based on these results, we conclude that the surface area of water droplets is an important factor on their wetting and capturing coal dust, and producing smaller water droplets can improve the efficiency of settling dust.

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

We propose three models of pairing ladders, in which two types of atoms, A and B, exist, and the corresponding atoms in different chains are pairng, i.e. if atom A is in a site of one chain, the atom in the corresponding site of another chain should be atom B. It is found that there are three resonant states in the ladder when the two types of atoms are both random dimers (RD) in the same chain. No extended state exists in the ladder when only one type of atom is RD distributed or two types of atoms both are random distributed in the same chain.

Nitrogen doped a-C/Silicon (a-C:N/Si) heterojunctions have been fabricated by using the pulsed laser deposition (PLD) technique and their current-voltage characteristics at various temperatures are investigated. For reverse applied voltages, a-C:N/Si heterojunctions exhibit metal-insulator transition characteristics and the transition temperature can be controlled by the applied voltages. After the excitation of repeated high reverse applied voltages, the current-voltage curves show obvious hysteresis behaviors at low temperatures. These hysteresis behaviors are reproducible and the ratio of the high/low resistance can be greater than 10^{4}.

We present a simplified structure made of periodic metallic layers on a glass substrate, which offers a potentially simpler approach to building photonic crystals. Using microwave experiments and Fresnel formulas, we investigate the refractive index properties of these structures. We make both transmission and reflection measurements and find that the refractive index of a periodic layered media decreases depending on the periodicity of the geometric arrangement, dielectric contrast and filling fraction of metallic layers. It is shown that metallic layers lead to a substantial change of interference pattern which can be interpreted as a result of interference in a uniform medium with a refractive index smaller than 1.

Electrical transport properties of the interface between a Nd_{0.7}Sr_{0.3}MnO_{3} ceramic and a Ag electrode are investigated using the ac impedance over a wide temperature and frequency ranges. The ac impedance measurements give the compressed semicircle arcs at different temperatures, which are used for the analysis of different contributions to electrical transport based on an electrical equivalent circuit. A significant interface-dependent electroresistance effect of 530% is clearly developed around the metal-insulator transition temperature 130 K, which is confirmed as the interface-layer dependent Curie temperature by the plot of interfacial conductance with frequency at different temperatures.

A new lateral double diffused MOS (LDMOS) transistor with a double epitaxial layer formed by an n-type substrate and a p-type epitaxial layer is reported (DEL LDMOS). The mechanism of the improved breakdown characteristic is that the high electric field around the drain is reduced by substrate reverse bias, which causes the redistribution of the bulk electric field in the drift region, and the vertical blocking voltage is shared by the drain side and the source side. The numerical results indicate that the trade-off between breakdown voltage and on-resistance of the proposed device is improved greatly in comparison to that of the conventional LDMOS.

The compressive pre-stress induced magnetostriction jump effect of an [110] oriented TbDyFe crystal is simulated by tracking the initial redistribution of magnetic domains and their volume fraction evolutions under external magnetic fields. Through searching for the free energy minima within both (110) and (110) planes, it is found that the axial compressive pre−stress not only switches magnetizations of the 35° domains toward the perpendicular plane, but also switches magnetizations of the 90° domains approaching the [110] direction. When increasing the stress magnitude, the volume fraction for 35° domains decreases and the one for the [110] domain increases rapidly. However, the volume fraction for the four 90° domains within the perpendicular plane first increases to a maximum under a certain stress magnitude and further decreases. The stress-induced anisotropy thereafter changes the volume fraction evolutions during the magnetization process, which explains well the magnetostriction jump effect.

In a strong magnetic field, the magnetic susceptibility χ and equivalent magnetic susceptibility λχ of some paramagnetic materials depend sensitively on the applied field H_{e}. Here λ is the coefficient of the effective field H_{m}, which relates to the superexchange interaction between the electrons in different magnetic ions. We present the forms of the adiabatic equivalent λχ and the effective field H_{m}. The adiabatic magneto−caloric and magneto-optical effects of paramagnetic terbium gallate garnet Tb_{3}Ga_{5}O_{12} are calculated at 6 K in strong magnetic fields. Our calculated results are in agreement with the experimental data.

The high-temperature permittivity of quartz fibre-reinforced silicon dioxide (SiO_{2}/SiO_{2}) nano−composites is studied on the basis of the multi-scale theoretical model. We obtain the permittivity of the SiO_{2}/SiO_{2} at high temperature, which is dependent on the temperature by data−mining. The result shows that the permittivity and loss tangent obtained by data-mining are well consistent with the measured ones. The high-temperature permittivity can be well predicted for SiO_{2}/SiO_{2} by the as-proposed model and the data-mining method.

Anatase TiO_{2} films are deposited on glass substrates at different oxygen partial pressures of 0.8–1.6 Pa. Room temperature N ion implantation is conducted in the films at ion fluences up to 5×10^{17} ions/cm^{2}. UV−visible absorption and photoluminescence (PL) are investigated. With the increase of N ion fluences, the band gap of TiO_{2} decreases and the absorbance increases. X-ray photoelectron spectroscopy (XPS) confirms the formation of O-Ti-N nitride after implantation, resulting in the red shift of the band gap. The PL intensity of the deposited films increases with the increasing oxygen partial pressure and decreases remarkably due to the irradiation defects induced by ion implantation.

We carry out a comparison of the thermoluminescence (TL) response of photon and electron irradiated Ge- and Al-doped SiO_{2} optical fibres, as well as cross-comparison with that of TLD-100. Irradiation is made with 6 MeV electrons and 6 MV photons, for doses ranging from 0.2 Gy to 4.0 Gy. The commercially available Al- and Ge-doped optical fibres produce a linear dose-TL response. The TL yield for both of the doped fibres and also for TLD-100 is greater for electron irradiation than for photon irradiation. The TL yield of the Al-doped fibres is a small fraction of that of Ge-doped fibres (by a factor of 25), the Ge-doped fibres offering a response of 59% of that of TLD-100.

In_{x}Ga_{1−x}N alloys with low indium composition x in the range 0.13≤x≤0.23 are systematically studied mainly based on a Raman scattering technique. Scanning electron microscopy and x−ray diffraction results show that our samples can be divided into two groups: pseudomorphic (0.13≤x≤0.16) and relaxed (0.18≤x≤0.23). The prominent enhancement of A_{1} longitudinal−optical (LO) mode is found with 325 nm laser excitation. For pseudomorphic samples, the frequencies of A_{1} (LO) phonons agree well with the theoretical predictions, which verifies that the samples are fully strained. For relaxed In_{x}Ga_{1−x}N samples, a linear dependence of the A_{1} (LO) mode frequency is obtained: Ω_{0} (x)=(740.8±3.3)−(143.1±16.0)x, which is the evidence of one-mode behavior in In_{x}Ga_{1−x}N ternary alloys. Residual strains in these partially relaxed samples are also evaluated.

Based on the guided mode resonance effect, single-layer transmission filters are presented. It is found that there is an intersection region in which the strong modulation waveguide modes TE_{0} and TE_{2} can be simultaneously excited by the second and first diffraction orders, respectively. A very high transmission peak emerges when the leaky modes interact with each other. Based on the normalized eigen−function of a single-layer waveguide grating, the high resonance transmission filters can be designed at any central wavelength. In order to demonstrate this concept, we design narrow line-shaped band pass filters with a central wavelength at 0.8, 1.06 and 10.6 µm .

A new scheme to realize an abnormal dielectric response at optical wavelength is developed on the basis of two-level electronic transition of rare-earth ion doped crystals. Based on the semi-classical theory and the Judd–Ofelt theory, the electric dipole transition under a weak field is analyzed, and a general expression for the frequency-dependent dielectric constant is obtained. As an example, the permittivity of (Er_{x}Y_{1−x})_{3}Al_{5}O_{12} is calculated numerically in consideration of the transition between ^{4}I_{15/2}and ^{4}F_{9/2}. An optimized dielectric property with a negative real part and low absorption is achieved. This proposes a new mechanism for building extraordinary electromagnetic media at optical frequencies by using a quantum process.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

We investigate the characteristics of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with a NbAlO/Al_{2}O_{3} lamination dielectric deposited by atomic layer deposition (ALD) as the gate insulator. A large gate voltage swing (GVS) of 3.96 V and a high breakdown voltage of −150 V for the MIS-HEMT were obtained. We present the gate leakage current mechanisms and analyze the reason for the reduction of the leakage current. Compared with traditional HEMTs, the maximum drain current is improved to 960 mA/mm, indicating that NbAlO layers could reduce the surface-related depletion of the channel layer and increase the sheet carrier concentration. In addition, the maximum oscillation frequency of 38.8 GHz shows that the NbAlO high-k dielectric can be considered as a potential gate oxide comparable with other dielectric insulators.

A novel reconfigurable threshold logic element (TLE) using single-electron transistors (SETs) and metal-oxide-semiconductor (MOS) transistors is proposed. The proposed TLE is highly reconfigurable, which can perform all two-variable logic functions directly or indirectly, including OR, NOR, AND, NAND, XOR and XNOR. The reconfiguration of the TLE is realized by simply configuring the input bits without changing the device parameters. The design methodology can also be applied in the design of a multi-variable TLE. The reconfigurable TLE demonstrates good performance at room temperature with a compact structure and ultralow power dissipation. The reconfigurable TLE can be useful in high-density high-performance reconfigurable systems and artificial neural networks.

The purpose of this work is to study the principle fluctuation modes of the global stock market, which is regarded as a complex system. It is proposed that the systematic risk can be reflected by the trace calculated from the cross-correlation matrix, and the integrity can be classified into clusters according to the plus-minus signs of the elements of the eigenvectors corresponding to several top largest eigenvalues whose total value accounts for more than 60 percent of the trace. The principle fluctuation modes of 30 stock markets are in the same direction in each year of 2005–2010. According to the classification criteria proposed here, the stock markets of the Americas, Europe and Asia & Oceania are automatically classified into different clusters, while Brazil, Russia and China are separated.

We introduce the variant rate and white noise into the susceptible-infected-removed (SIR) model for epidemics, discuss the epidemic dynamics of a multiple-compartment system, and describe this system by using master equations. For both the local epidemic spreading system and the whole multiple-compartment system, we find that a threshold could be useful in forecasting when the epidemic vanishes. Furthermore, numerical simulations show that a model with the variant infection rate and white noise can improve fitting with real SARS data.