The discontinuous Galerkin method is used for solving the two-dimensional equilibrium radiation diffusion equation. We construct the weighted interior penalty method based on the geometric average weight. The semi-implicit integration factor method is applied to the nonlinear ordinary differential equations obtained by the discontinuous Galerkin spatial discretization. Numerical results are presented to demonstrate the validity and reliability of using the discontinuous Galerkin method for solving the highly nonlinear radiation diffusion equation.

Quantum secret sharing (QSS) schemes are analyzed from an information theoretical perspective centered on the Araki–Lieb inequality. Based on this inequality, mathematical characterizations of QSS schemes and quantum error-correcting codes (QECCs) are given. Furthermore, we present a proof of the relation between QSS schemes and QECCs. This information theoretic description of QSS schemes is used to derive the quantum Singleton bound.

We try to find the analytical solutions to the time-independent Gross-Pitaevskii equation, a nonlinear Schr?dinger equation used in the simulation of Bose–Einstein condensates trapped in a harmonic potential. Both the homotopy analysis method and the Galerkin spectral method are applied. We investigate the one-dimensional case and obtain the approximate analytical solutions successfully. Comparison between the analytical solutions and the numerical solutions has been made. The results indicate that they agree very well with each other when the atomic interaction is not too strong.

We show theoretically that it is possible to optically control domain formation in a spinor-1 ^{87}Rb gas. A model is proposed to include the photoassociation (PA) interaction characterizing the symmetry breaking of M_{F}=±1 ferromagnetic condensate. We find that the dynamical process of the domain formation can be greatly controlled by the PA field. The PA field can enhance or suppress the spatial separation of domains, which can provide a flexible tool to modulate the domain structure and indicate an interesting research field of laser-catalyzed in spinor condensate.

Exact solutions of the Dirac equation are studied for the pseudo-harmonic oscillatory ring-shaped potential by using the Laplace transform approach and the Nikiforov–Uvarov (NU) method. The normalized eigenfunctions are expressed in terms of hyper-geometric series and use the NU and Laplace methods to obtain the eigenvalues equations. The obtained result of the eigenvalue equation is compared. At the end, one can find with a simple transformation the lower spinor component of the Dirac equation.

In the paper [Chin. Phys. Lett. 29 (2012) 050303] of Hong et al., two quantum secret sharing protocols were proposed. We study the security of the second protocol and find that it is insecure. Acting as the communication center, Trent may eavesdrop Alice's secret messages without introducing any error. Finally, a feasible improvement of the second protocol is given.

We analyze the time of formation of central singularities in (N+2)-dimensional spacetimes. It is shown that the time of formation of central singularity decreases with the increase in dimensions of the spacetime. The dynamics of trapped surface formation in different higher-dimensional spacetimes are studied and compared graphically.

Zr_{0.9}Mg_{0.1}O_{2?δ} nanofibers and ZrO_{2} nanofibers are synthesized using electrospinning and the calcination technique. The nanofibers are characterized using x-ray diffraction (XRD), a field emission scanning electron microscope (FE-SEM), and a Brunauer–Emmett–Teller (BET) surface analyzer. The humidity sensing properties of Zr_{0.9}Mg_{0.1}O_{2?δ} nanofiber sensors are analyzed and compared with those of ZrO_{2} nanofiber sensors. The Zr_{0.9}Mg_{0.1}O_{2?δ} nanofiber humidity sensors exhibit a broader humidity range of 11–97% relative humidity (RH), good linearity, small humidity hysteresis, and rapid response and recovery times. The complex impedance plots of the Zr_{0.9}Mg_{0.1}O_{2?δ} sensor at different RHs are drawn, and the humidity sensing mechanism is discussed via an equivalent circuit.

We investigate the effects induced by the interactions of the Kaluza–Klein graviton with the standard model (SM) particles on the triple Z^{0}-boson production process at the International Linear Collider in the framework of the large extra dimension (LED) model. We present the dependence of the integrated cross sections on the electron-positron colliding energy √s, and various kinematic distributions of final Z^{0} bosons and their subsequential decay products in both the SM and the LED model. We also provide the relationship between the integrated cross section and the fundamental scale M_{S} by taking the number of the extra dimensions (d) as 3, 4, 5, and 6, respectively. The numerical results show that the LED effect can induce an observable relative discrepancy for the integrated cross section (δ_{LED}). We find that the relative discrepancy of the LED effect can even reach a few dozen percent in the high transverse momentum area or the central rapidity region of the final Z^{0}-bosons and muons.

The currently accepted value for the upper limit on the photon rest mass comes from a rough estimate based on the solar wind method. We reconsider this method and present a more detailed analysis of the electromagnetic fields in interplanetary space. The simple analytic expressions for the solar wind magnetic field, electric field and current are obtained with a finite photon mass. The upper limit on the photon mass is re-estimated as m_{γ}<0.8×10^{?54} kg, which improves the current bound by up a factor of 2, and further confirms the reliability of the solar wind method.

Fully self-consistent relativistic random phase approximation (RRPA) is built on the relativistic mean field ground state with a non-linear relativistic Lagrangian. The consistency requires that the same effective interaction is adopted to simultaneously describe both the ground states and the excited states of the nucleus. Reliable and accurate numerical results of the nuclear giant resonances obtained in the RRPA require fully consistent calculations. In some excitation modes they are extremely sensitive to consistent treatment, e.g., such as isoscalar giant monopole and dipole resonances (ISGMR and ISGDR). In this work we perform the numerical calculations in the case of ISGDR for ^{208}Pb and check the consistency. The spurious state in the ISGDR vanishes once the full self-consistency is achieved.

Conventional nuclear fusion occurs in plasma at temperatures greater than 10^{7}°C or when energy higher than 10 keV is applied. We report a new result of anomalous neutron emission, also called cascade neutron burst emission, from deuterium-loaded titanium and uranium deuteride samples at room temperature. The number of neutrons in the large bursts is measured as up to 2800 in less than a 64-μs interval. We suggest that the anomalous cascade neutron bursts are correlated with deuterium-loaded metals and probably the result of nuclear reactions occurring in the samples.

Using the B-spline basis set method combined with model potential, the Stark energy level of rubidium atoms in the vicinity of n=30 is presented. By using a using time-dependent multilevel approach, we calculate the population redistribution of high Rydberg rubidium atoms under the interaction of external time-dependent half-cycle pulses. Our numerical results show that the population of rubidium atoms can be driven to lower or higher n levels with a train of half cycle pulses, the final population distribution of all the l states for the same n is observed after these interactions.

Detailed theoretical calculations are performed for the 4f and 5p inner-shell excitations of W-W^{3+} ions using the multiconfiguration Hartree–Fock method in order to better understand the origin of the XUV photoabsorption spectra of W atoms from the dual laser-produced plasma experiment (Costello et al. J. Phys. B 24 (1991) 5063 and the spectra of photon-induced single ionization of W^{q+} ions (q=1, 2, 3) (Müller et al. Phys. Scr. T1441 (2011) 014052) from photon-ions merged beam experiments, respectively. Two broad and strong resonances in the experimental spectra have also been theoretically identified mainly from 5p–5d resonance. The 4f–5d,6d and 5p–6d transitions also make a small contribution to each spectrum, which are superimposed on the 5p–5d transition arrays. Based on the assumption of a normalized Boltzmann distribution among the excited states, we succeed in reproducing spectra which are in good agreement with experiments.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

We report on fractal-featured square and ring-shaped apertures with a Sierpinski carpet pattern (SCP) on metallic and superconducting NbN films. Multiple extraordinary terahertz (THz) transmission peaks are studied in the transmission spectra using both THz time-domain spectroscopy and numerical simulation. The characteristic transmission peaks are found to be associated with the interaction of surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) for ring-shaped apertures. The effect of LSPs is less remarkable in the square apertures. For the superconducting NbN film, when the temperature is slightly lower than the critical transition temperature T_{c}, the peak magnitude of SPP resonances is most prominent due to the non-monotonic temperature dependence of kinetic inductance. These results provide a new way to design compact and efficient THz devices.

An improved compact ultra-wideband (UWB) microstrip antenna with metamaterials is proposed. The total size is slightly reduced and the measured impedance bandwidth operates from 3.84 to 22.77 GHz for a return loss of less than ?10 dB. Compared with the original patch antenna, the bandwidth of this antenna is about six times broader. Moreover, the antenna has an average gain of 6.2 dB, which is 1.2 dB larger than the original one. Both strong radiation in the horizontal direction and practical characteristics are observed. Thus, this antenna would have some specific applications for UWB wireless communications in the future.

The microwave slow-light delay-line has broad applications in signal processing systems, and the tunable slow-light delay-line is particularly important for adjusting the timing of wave packets and phased array beam shapers. We propose to construct multichannel microwave slow-light delay-lines using piezoelectric (PMN-PT) and piezomagnetic (CoFe_{2}O_{4}) superlattices(PPS). The group velocity can be slowed down by a factor of 14612 (31554) and a delay bandwidth product (DBP) of 25(47) can be achieved for the first (second) channels with a sample length of 1 cm around 10GHz (21 GHz). Furthermore, a tunable time-delay from 590 ps (590ps) to 480ns (1052 ns) can be realized by flipping the magnetic domains using an external magnetic field. The nonreciprocal polaritonic bands also contain the basic building blocks for designing the compact microwave isolator.

We demonstrate a simple, compact and low cost Q-switched erbium-doped fiber laser (EDFL) using single-wall carbon nanotubes (CNTs) as a saturable absorber for possible applications in metrology, sensing, and medical diagnostics. The EDFL operates at around 1560 nm with repetition rates of 16.1 kHz and 6.4 kHz with saturable absorbers SA1 and SA2 at a pump power of 120 mW. The absorbers are constructed by optically driven deposition and normal deposition techniques. It is observed that the optical deposition method produces a Q-switched EDFL with a lower threshold of 70 mW and better Q-switching performance compared to that of the normal deposition method. The EDFL also has pulse energy of 90.3 nJ and pulse width of 11.6 μs at 120 mW pump power.

We analyze the responsivity and signal-to-noise ratio (SNR) of a punchthrough enhanced phototransistor (PEPT). Measurement results show that the PEPT exhibits a good response to light over a wide range of intensity. Because the responsivity is still as high as 10^{6} A/W when the bias voltage is as low as 0.2 V, the device is suitable for ultra-low voltage applications. Meanwhile, with 1–10 μA bias current, the PEPT shows the best performance for the responsivity and SNR. When incident light is as low as 3.8×10^{?8} W/cm^{2}, the responsivity reaches approximately 10^{8} A/W. The super high responsivity of PEPTs makes it possible to fabricate small sized photodetector.

We study the post nonlinearity compensation of differential-phase-shift-keying links employing pure soliton transmissions over a large number of spans. In addition to the distributed amplified spontaneous noises added by the inline amplifiers, lumped intensity noises initially resulting from transmitter imperfections are also considered. Based on the soliton perturbation theory, we derive simple and accurate formulae for the optimum operating phase, the variance of the residue phase noise, and the phase Q-factor improvement of the post nonlinearity compensation. We validate these derived formulae by comparing their results with numerical simulations built upon the split-step Fourier method.

We investigate the photon counting for a pure number state passing through a laser channel. It is found that the pure number state evolves in the laser channel into a mixed state: the number state |m??m| evolves into a superposition of the photon-added thermal (chaotic) state, and the photon counting for the outcome state is a Gauss hypergeometric function.

ZHAO Jun-Qing, WANG Yong-Gang, YAN Pei-Guang, RUAN Shuang-Chen, CHENG Jian-Qun, DU Ge-Guo, YU Yong-Qin, ZHANG Ge-Lin, WEI Hui-Feng, LUO Jie, Yuen H. Tsang

Chin. Phys. Lett. 2012, 29 (11):
114206
.
DOI: 10.1088/0256-307X/29/11/114206

We demonstrate an erbium-doped ring-cavity fiber laser Q-switched by a graphene oxide-based saturable absorber (GOSA). The GOSA was fabricated by vertically evaporating GO-polyvinylalcohol (GO/PVA) composite dispersion, and has a good performance under room temperature. Utilizing a specially fabricated fiber Bragg grating (FBG), stable five-wavelength lasing is realized and stabilized at different pump powers under any polarization state. When the pump power increases from 78.4 mW to 379.3 mW, the output power ranging from 1.9 mW to 16.6 mW could be obtained, with pulse duration from 6.8 μs to 2.72 μs, single pulse energy from 123.73 nJ to 229.74 nJ, and pulse repetition rate from 15.36 kHz to 72.25 kHz. To the best of our knowledge, it is the first simultaneous realization of five-wavelength operation and pulse output in a GO Q-switched all fiber laser system.

An equivalent circuit model for the design and analysis of two-section gain lever quantum dot (QD) laser is presented. This model is based on the three level rate equations with two independent carrier populations and a single longitudinal optical mode. By using the presented model, the effect of gain lever on QD laser performances is investigated. The results of simulation show that the main characteristics of laser such as threshold current, transient response, output power and modulation response are affected by differential gain ratios between the two-sections.

We demonstrate an octave?spanning Kerr-lens mode-locked Ti:sapphire laser with double-chirped mirrors (DCMs), BaF_{2} wedges and plate, which generates laser pulses in the spectrum range from 600 nm to 1200 nm at -45 dB below the maximum and the duration of 8.5 fs at the repetition rate of 80 MHz. The average output power is 100 mW under 5 W pump power. By carefully adjusting the insertion of BaF_{2} wedges and the optimization position of Ti:sapphire crystal in the cavity, we can obtain the smooth swings in the interferometric autocorrelation trace due to good third-order dispersion compensation.

We investigate the effect of decay-induced interference on photon correlation in a nearly equispaced three-level driven ladder atom. It is found that the combination of destructive interference and two-photon resonance are responsible for the occurrence of nonclassical correlations. In addition, the bunching or antibunching behavior of the two emission processes can be controlled by the relative phase of the two applied fields attributed to the phase control spontaneous emission enhancement or cancellation.

ZnO thin films are grown on monocrystalline silicon by laser molecular-beam epitaxy. Silver quantum dot arrays as surface enhanced Raman scattering substrates are prepared on the surface of ZnO films by magnetron sputtering. Surface enhanced Raman spectra of ZnO films modified with silver quantum dots are recorded. Surface enhanced Raman spectra image and 378 cm^{?1} vibration intensity mapping image of Raman peak of ZnO thin films modified with silver quantum dots are obtained. It is indicated that Raman intensity is enhanced immensely on the surface of ZnO films nearby silver quantum dots. It is well known that Raman signals of nano films, nano particles or nano wires are very weak, which limits the applied range of Raman on the nano materials. It is an efficient method that expends Raman field of applications on nano scale materials by modifying with silver quantum dots on the surface.

A novel approach is proposed towards the design of fiber Bragg gratings with multi-channel right-angled triangular spectrum. Firstly, a single-channel grating is synthesized utilizing an adaptive quantum particle swarm optimization with the piecewise constant mutated factor. Meanwhile, the reflectivity spectrum with good linear edge for a short grating is obtained. Then, for its merits of easy fabrication, the superposition method is adopted to design multi-channel gratings with initial spectral distortion. Finally, this distortion is optimized by the method in the first step. It is shown that the design outcomes still retain the features of easy fabrication and short length. Such gratings would be useful as wavelength-interrogation devices with multiple physical parameters in optical sensor systems.

Beam manipulation by metallic nanoslit arrays with perpendicular cuts inside the slits was investigated numerically. The simulated results performed by the finite element method (FEM) show that perpendicular cuts with different heights can modulate phase retardation of the transmitted light through the slits. With the proper distribution of cut height, a focused beam is achieved in our metallic nanostructure with four-time amplitude at the focus point and half focal length compared to a slit array without cuts inside. By using asymmetric distribution of height amplitude, a beam deflection around 6° can also be realized in our design.

An effective top cladding for silicon-on-insulator grating coupler is designed and the validity of the design is confirmed experimentally. The proposed double-layer silicon oxide/silicon nitride (SiO_{2}/Si_{3}N_{4}) cladding demonstrates antireflection properties and affects a coupling strength of the grating structure. A coupling efficiency of 65% is obtained after cladding layer deposition.

Recently, the Kochen–Specker theorem has been demonstrated and quantum contextuality has been observed experimentally by using special and independent quantum states. On the other hand, recent investigations have shown that a thermal light source can mimic the two-photon entangled source to perform the imaging effects. We perform an all-or-nothing–type Kochen-Specker experiment using the thermal light source and obtain the same results as those using quantum sources. The physical origin for such a phenomenon is analyzed.

A novel master oscillator/power amplifier architecture for optical parametric conversion of high pulse energy from 1.064 μm to 1.572 μm in KTiOPO_{4} crystal is presented. A high gain of more than 80 at 1.572 μm pumped by a high energy Q-switched pulse laser is realized. With a seeding signal energy of 1 mJ, and 400 mJ pump pulse at 100 Hz, an amplified signal pulse energy of over 80 mJ is obtained. The total optical-optical conversion efficiency reaches 21%.

An organic optocoupler (OOC) is fabricated with a tandem organic light-emitting diode (OLED) as the light source (input unit) and an organic photodiode (OPD) as the detector (output unit). It is found that using the tandem OLED as the input unit can significantly increase the current transfer ratio of the organic optocoupler. When the tandem OLED operates under 8 V and the OPD operates under ?4 V, the current transfer ratio of the optocoupler reaches 5.4%. Simultaneously, the I_{ON}/I_{OFF} ratio of the optocoupler reaches 10^{5}, which can be attributed to the small leakage current of the OPD, and the high efficiency of the OPD and the tandem OLED.

We study theoretically and experimentally the properties of numerical aperture (N_{A}) of multimode graded-index plastic core silica (PCS) fibers by using an image technique. A He-Ne laser at wavelength 632.8 nm and output power 1 mW is used as the transmitter light source. The output beam images and intensity profiles of an optical fiber are investigated by using an imaging technique. The laser beam profiles captured by a sensitive digital Nikon camera are processed and analyzed by using a Gaussian intensity distribution in a 2D graph. A MathCAD 14 program is used for converting the image of the laser output beam into data. The theoretical and experimental values of the numerical aperture for the used optical fiber in this study are found to be 0.5 and 0.4924, respectively. The theoretical value of V-number is also calculated to be approximately 2482.

Broadband acoustic transmission enhancement (ATE) is realized for a periodically structured stiff plate without any opening that is conventionally thought to be only capable of supporting narrowband ATE, by introducing locally resonant (LR) elements. This exotic phenomenon is interpreted by analyzing the vibration pattern of the structure-induced LR modes, and is well modeled by a simple "spring-mass" system which reveals the contribution of the LR effect to the important broadband performance. Our findings should help to better understand the physical mechanism of ATE and may have potential impact on ultrasonic applications such as broadband acoustic filters or compact acoustic devices in subwavelength scale.

An approximation approach is proposed for realizing an arbitrarily shaped acoustic cloak. Based on the effective medium theory, the designed cloak is a discrete layered structure using homogeneous isotropic materials. The performance of the cloak is simulated, and the results demonstrate that the cloak possesses properties of low-reflection outside the cloak and wavefront-bending in the cloak shell. This work proves the feasibility of realizing an arbitrarily shaped acoustic cloak using normal materials.

The influence of simultaneously applied mechanical and thermal treatment is used for producing a geometrically complex shaft from 51CrV4 steel resulting in widely differing formations of microstructures. Materials' properties such as internal friction (IF), hardness and electrical resistivity are affected by this change of microstructure formations. The Snoek–K?ster peak is identified and analyzed in the actual steel structure.

Four different formation processes of spinning detonation in a narrow square tube are investigated by three-dimensional parallel simulations. High-resolution simulations are performed with a Riemann solver of the HLLC-type, high-order, parallel AMR reactive flow code. The simulations clearly show that the detonation structure transforms from rectangular and diagonal modes into spinning mode respectively during the propagation processes. Transverse wave dynamic and periodic oscillation of the front plays a significant role in the spinning detonations' formation.

Hydrophobic islands/patterns on a hydrophilic substrate could be employed to enhance boiling heat transfer, however the underlying mechanisms are far from clear. We perform boiling experiments on a copper wire coated with superhydrophobic micropatterns (contact angle >170°). The copper wire is as fine as 150 μm in diameter, greatly facilitating the observation of the bubble dynamic details. With the heat flux increasing, four regimes are characterized based on the bubble behavior. The superhydrophobic micropatterns are found to play critical roles in bubble formation and distribution as well as the interactions.

The boundary layer flow of power-law fluids over a shrinking sheet with mass transfer is revisited. Closed-form analytical solutions are found and presented for special cases. One of the presented solutions has an algebraic decay behavior. These analytical solutions might offer valuable insight into the nonlinear boundary layer flow for power-law fluids.

The mixed convection stagnation-point flow of an incompressible non-Newtonian fluid over a stretching sheet under convective boundary conditions is investigated. Mathematical formulation is presented for a Casson fluid. The resulting partial differential equations are converted into the ordinary differential equations by the suitable transformations. The velocity and temperature profiles are computed by employing the homotopy analysis method. The plotted graphs illustrate the flow and heat transfer characteristics and their dependence upon the embedded parameters. Numerical values of skin-friction coefficient and Nusselt number are given and examined. Comparison of the present results with the existing solution is also given.

Analytic and numerical techniques are presented to analyze the influence of temperature and wall slip conditions on the unsteady flow and heat transfer via viscous fluid squeezed between two parallel disks in the presence of an applied magnetic field. The governing partial differential equations for momentum and heat transfer are reduced to a system of coupled nonlinear ordinary differential equations using similarity transformations. The homotopy analysis method (HAM) is then utilized to find explicit series solution of the resulting problem. The convergence of the obtained solution is carefully analyzed. To check the reliability of the method the same problem is also solved by using the shooting method and an excellent agreement is observed between the two sets of results. Influence of various parameters of practical importance on the velocity and temperature profiles is studied and portrayed graphically. Values of skin friction coefficient and local Nusselt number are tabulated by assigning different values to various emerging parameters.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

The single-fluid Magnetohydrodynamic (MHD) equations for electrolytes in the presence of a magnetic field are derived from multi-fluid MHD equations with ion-neutral collisions in partially ionized conductive fluids. The dispersion relationship of MHD waves is also investigated, which is different from that for plasmas or liquid metals. Based on the equations, we find that MHD waves are dispersive in electrolytes, and the critical frequencies for excitation of Alfven waves vary with magnetic field or conductivity, so the exciting of MHD waves is severely restricted in electrolytes with relatively low conductivity except at an extremely low frequency or when it is permeated by a considerably strong ambient magnetic field. These theories are applied to seawater to estimate the magnetic field vibration caused by the large-scale motion of seawater (e.g., ocean currents or tides). It is found that high frequency waves are dampened severely in seawater, while low frequency waves can propagate over a long distance without much attenuation.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Determining the best set of beveling parameters is an advantageous characteristic of the geometrical conditions for a cubic high-pressure tungsten carbide (WC) anvil, but it is almost impossible to deduce experimentally (much affected by defects in the material). In order to remove the affection of defects in materials, we investigate computational stress analyses in different beveling parameters of WC anvils by the finite element method. The results indicate that the rate of cell pressure transmitting and failure crack in the WC anvil monotonically increases with the bevel angle from 42° to 45°. Furthermore, there are two groups of actual users of beveled anvils, one group preferring 41.5°, which can decrease the rate of failure crack in WC anvil, the other group preferring 42°, which can increase the rate of cell pressure transmitting. This work would give an effective solution to solve the problem of the design of a cubic high-pressure WC anvil experimentally and will greatly help to improve the cubic high-pressure WC anvil type high pressure techniques.

We present an analysis of thermal and thermoelastic behaviors of a functionally graded infinite plate taking into account electromagnetic wave absorption. To treat with the inhomogeneity of functionally graded wave-absorbing (FGWA) materials, the plate is approximated by subdividing it into thin homogeneous layers to solve the governing equations together with proper boundary and connecting conditions. The results illustrate that the FGWA plate is a broadband type absorber with electromagnetic wave absorption. By choosing proper material gradation character and the thickness of the FGWA plate, it is possible to obtain a good performance of electromagnetic wave absorption and thermoelastic stress characteristics.

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

The electronic structures and optical properties of Y-doped ZnO are calculated using first-principles calculations. It is found that the replacement of Zn by the rare-earth element Y presents a shallow donor, and the Fermi level moves into the conduction band (CB). The high dispersion and s-type character of CB is expected to result in an increase in conductivity. Moreover, the absorption spectrum of the Y-doped ZnO system exhibits a slight blue shift with an increase of Y concentration, and a higher transparency in visible light is expected. Therefore, the Y-doping in ZnO would enhance the mobility and hence increase the electrical conductivity without sacrificing the optical transparency, which is essential for the improvement of ZnO's behavior and its performance in extension applications.

Electronic, structural and optical properties of the cubic perovskite CsCaF_{3} are calculated by using the full potential linearized augmented plane wave (FP-LAPW) plus local orbitals method with generalized gradient approximation (GGA) in the framework of the density functional theory. The calculated lattice constant is in good agreement with the experimental result. The electronic band structure shows that the fundamental band gap is wide and indirect at (Γ–R) point. The contribution of the different bands is analyzed from the total and partial density of states curves. The charge density plots show strong ionic bonding in Cs-F, and ionic and weak covalent bonding between Ca and F. Calculations of the optical spectra, viz., the dielectric function, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are performed for the energy range 0–30 eV.

The non-polar a-plane (1120) In_{x}Ga_{1?x}N alloys with different indium compositions (0.074≤x≤0.555) were grown on r-plane (1012) sapphire substrates by metalorganic chemical vapor deposition, and the indium compositions x are estimated from x-ray diffraction measurements. The in-plane orientation of the In_{x}Ga_{1?x}N with respect to the r-plane substrate is confirmed to be [1100]_{sapphire}|| [1120]_{InxGa1?xN} and [1101]_{sapphire}|| [0001]_{InxGa1?xN}. The effects of substrate temperature, reactor pressure and trimethylindium input flow on the indium incorporation and growth rate are investigated. The morphology of the a-plane In_{x}Ga_{1?x}N is found to be significantly improved with the decreasing indium composition x and growth rate. Moreover, the in-plane anisotropic structural characteristics are revealed by high resolution x-ray diffraction employing azimuthal dependence, and the degree of anisotropy decreases with the increase of indium composition.

The structural transformation and electronic structure of ZnO under hydrostatic pressure are investigated using the HSE06 range-separated hybrid functional. We show that wurtzite ZnO under pressure undergoes a structural transition to a graphite-like phase. We also find that the band gap of wurtzite phase is always direct, whereas the new phase can display either direct or indirect band structure. Furthermore, the gap is greatly enhanced by pressure and no semi-metallic phase is observed. This is drastically different from our previous results of AlN and GaN [Appl. Phys. Lett. 100 (2012) 022104].

Photo-induced spin dependent electron transmission through a narrow gap InSb/InGa_{x}Sb_{1?x} semiconductor symmetric well is theoretically studied using transfer matrix formulism. The transparency of electron transmission is calculated as a function of electron energy for different concentrations of gallium. Enhanced spin-polarized photon assisted resonant tunnelling in the heterostructure due to Dresselhaus and Rashba spin-orbit coupling induced splitting of the resonant level and compressed spin-polarization are observed. Our results show that Dresselhaus spin-orbit coupling is dominant for the photon effect and the computed polarization efficiency increases with the photon effect and the gallium concentration.

In order to take advantage of organic and inorganic materials, we chose the polymer MEH-PPV as the luminous layer and ZnS as the electron transporting layer to prepare hybrid organic-inorganic light-emitting diodes (HOILEDs): ITO/MEH-PPV(～70 nm)/ZnS(20 nm)/Al by thermal evaporation and spin coating. Compared with the single-layer device ITO/MEH-PPV(～70 nm)/Al, spectral broadening and a slightly red shift are observed. Compared with the pure organic device ITO/MEH-PPV(～70 nm)/BCP (20 nm)/Al and combined with the energy level structure diagram, it is concluded that the spectral broadening and red shift are due to the exciplex luminescence at the interface between MEH-PPV and ZnS or BCP. In addition, the hybrid inorganic-organic device shows a lower turn-on voltage, but the current efficiency is lower than that of the pure organic device with the same structure.

We demonstrate how molecular states of coupled graphene quantum dots are probed in transport experiments. The applied method measures the sequential tunneling of electrons through the double dot and hence resolves the molecular state transport channel simultaneously. The overlap of the two dots' wavefunctions, and in turn, the tunnel coupling between the two dots are controlled by the local gates. These results imply the relevance of our graphene device for implementing a quantum manipulation by adjusting the electrodes.

Based on a simple classical model that primary electrons at high electron energy interact with the electrons of lattice by the Coulomb force, we deduce the energy of secondary electrons. In addition, the number of secondary electrons in the direction of velocity of primary electrons per unit path length, n, is obtained. According to the energy band of the insulator, n, the definition of the probability B of secondary electrons passing over the surface barrier of insulator into the vacuum and the assumption that lattice scattering is ignored, we deduce the expression of B related to the width of the forbidden band (E_{g}) and the electron affinity χ. As a whole, the B values calculated with the formula agree well with the experimental data. The calculated B values lie between zero and unity and are discussed theoretically. Finally, we conclude that the deduced formula and the theory that explains the relationships among B, χ and E_{g} are correct.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Controlled growth, synthesis, and characterization of a high density and large-scale Ge nanostructure by an easy fabrication method are key issues for optoelectronic devices. Ge quantum dots (QDs) having a density of ～10^{11} cm^{?2} and a size as small as ～8 nm are grown by radio frequency magnetron sputtering on Si (100) substrates under different heat treatments. The annealing temperature dependent structural and optical properties are measured using AFM, XRD, FESEM, EDX, photoluminescence (PL) and Raman spectroscopy. The effect of annealing is found to coarsen the Ge QDs from pyramidal to dome-shaped structures as they grow larger and transform the nanoislands into relatively stable and steady state configurations. Consequently, the annealing allows the intermixing of Si into the Ge QDs and thereby reduces the strain energy that enhances the formation of larger nanoislands. The room temperature PL spectra exhibits two strong peaks at ～2.87 eV and ～3.21 eV attributed to the interaction between Ge, GeO_{x} and the possibility of the presence of QDs core-shell structure. No reports so far exist on the red shift ～0.05 eV of the strongest PL peak that results from the effect of quantum confinement. Furthermore, the Raman spectra for the pre-annealed QDs that consist of three peaks at around ～305.25 cm^{?1}, 409.19 cm^{?1} and 515.25 cm^{?1} are attributed to Ge-Ge, Ge-Si, and Si-Si vibration modes, respectively. The Ge-Ge optical phonon frequency shift (～3.27 cm^{?1}) associated with the annealed samples is assigned to the variation of shape, size distribution, and Ge composition in different QDs. The variation in the annealing dependent surface roughness and the number density is found to be in the range of ～0.83 to ～2.24 nm and ～4.41 to ～2.14 × 10^{11} cm^{?2}, respectively.

Amorphous alloys with a composition (at.%) Fe_{48}Cr_{15}Mo_{14}C_{15}B_{6}Y_{2} were prepared by using either pure elements (alloy B1) or a commercial AISI430 steel as a base material (B2). When prepared from pure elements, alloy (B1) could be cast in plate form with a fixed thickness of 2 mm and variable lengths between 10 and 20 mm by means of copper-mold injection in an air atmosphere. In the case of alloy B2, prepared by using commercial grade raw materials, rods of 2 mm diameter are obtained. Ribbons (B1 and B2) of width 5 mm and thickness about 30 μm are prepared from the arc-melted ingots using a single roller melt spinner at a wheel speed of 40 m/s. The thermal and structural properties of the samples are measured by a combination of differential scanning calorimetry (DSC), x-ray diffraction and scanning electron microscopy. Chemical compositions are checked by energy dispersive spectroscopy analysis. X-ray diffraction and scanning electron microscopy observations confirm that an amorphous structure is obtained in all the samples. A minor fraction of crystalline phases (oxides and carbides) is detected on the as-cast surface. Values of hardness and Young modulus were measured by nanoindentation for both the alloys. The effects of adverse casting conditions (such as air atmosphere, non-conventional injection copper mold casting and the partial replacement of pure elements with commercial grade raw materials) on the glass formation and properties of the alloy are discussed.

GaAs nanowires (NWs) are grown on GaAs (311)B substrates by gold assisted molecular beam epitaxy technology. Combined scanning and transmission electron microscopy analyses, the crystallographic orientations of NWs are studied. It is found that crystallographic orientations of NWs are closely related to their crystal structures: NWs of zinc blende structure grow along ?001? directions and NWs of wurtzite structure grow along ?0001? directions. The influence of impinging Ga flux on morphology and crystal structure of the NWs is also discussed. It is observed that NWs prefer to grow along zinc blende ?001? directions at lower Ga flux, while NWs tend to grow along the wurtzite ?0001? directions with only a small portion along the zinc blende ?001? direction at a higher Ga flux. The control of crystal structure and orientation of NWs can be achieved effectively by changing the Ga flux.

A high-sensitivity magnetic field sensor based on the nano-polysilicon thin film transistors is proposed to adopt the nano-polysilicon thin films and the nano-polysilicon/single silicon heterojunction interfaces as the sensing layers. By using CMOS technology, the fabrication of the nano-polysilicon thin film transistors with Hall probes can be achieved on the ?100? high resistivity single silicon substrates, in which the thicknesses of the nano-polysilicon thin films are 120 nm and the length width ratio of the channel is 320 μm /80 μm . When V_{DS}=5.0 V, the magnetic sensitivity and linearity is 264 mV/T and 0.23%f.s. (full scale), respectively. The experimental results show that the magnetic sensors based on nano-polysilicon thin film transistors with Hall probes exhibit high sensitivity.

A combination of large mass, weak spring and nano-grating is the key for a nano-grating accelerometer to measure nano-G acceleration. A novel compact nano-grating accelerometer integrating a large mass with nano-grating is proposed. First, the numbers of diffraction orders are calculated. Then, structure parameters are optimized by finite element analysis to achieve a high sensitivity in an ideal vibration mode. Finally, we design the fabrication method to form such a compact nano-grating accelerometer and successfully fabricate the uniform and well-designed nano-gratings with a period of 847 nm, crater of 451 nm by an FIB/SEM dual beam system. Based on the ANSYS simulation, a nano-grating accelerometer is predicted to work in the first modal and enables the accelerometer to have displacement sensitivity at 197 nm/G with a measurement range of ±1 G, corresponding to zeroth diffraction beam optical sensitivity 1%/mG. The nano-gratings fabricated are very close to those designed ones within experimental error to lay the foundation for the sequent fabrication. These results provide a theoretical basis for the design and fabrication of nano-grating accelerometers.

A separate absorption, grading, charge and multiplication InGaAs/InP avalanche photodiode with ultra low dark current and high responsivity is demonstrated. It has a thin multiplication layer and a planar structure. Through the use of a well and a single floating guard ring to suppress edge breakdown, the device can easily be fabricated by one step epitaxial growth and one step diffusion. The dark current of a 30 μm diameter device is as low as 0.028 nA at punch-through and 0.1 nA at 90% of the breakdown voltage. The responsivity at 1.55 μm is 0.93 A/W at unity gain and the multiplication layer is estimated to be less than 300 nm.

Several hundred keV fast neutron radiography (HKFNR) can be a complementary technique to common thermal neutron radiography (TNR) and several MeV fast neutron radiography (MFNR). We tested HKFNR on a 4.5 MV Van de Graaff accelerator, and the experimental results show that the spatial resolution of this technique is better than MFNR and close to TNR. Several hundred keV fast neutrons can penetrate some thermal neutron absorbers such as Cd, and it is feasible to investigate its use on some materials which are transparent to cold/thermal neutrons, such as aluminum, using this technique.

We studied the effect of population density in a spatial public goods game. We found that the effect on the evolution of cooperation is very complex when the strategy learning and mobility of players in a long range are considered in a two-dimensional lattice. As the learning range is larger than the mobility range, the system is driven to enter into a cooperation state for a low population density, because a small local group is beneficial to sustain a high level of cooperation. As population density increases to a moderate range, the mobility of players from a domain invaded by defectors supports the evolution stability of cooperation. When the mobility range is larger than the learning range, a formation of compact domains of cooperators promotes cooperation as the population density becomes high.