A fractional-order phase-locked loop (PLL) with a time-delay is firstly proposed on the basis of the fact that a capacitor has memory. The existence of Hopf bifurcation of the fractional-order PLL with a time-delay is investigated by studying the root location of the characteristic equation, and the bifurcated periodic solution and its stability are studied simply by using "pseudo-oscillator analysis". The results are checked by numerical simulation. It is found that the fractional-order PLL with a time-delay reduces the locking time, and it minimizes the amplitude of the bifurcated periodic solution when the order is properly chosen.

A consistent tanh expansion (CTE) is used to solve the Broer–Kaup (BK) system. It is proved that the BK system is CTE solvable. Some exact interaction solutions among different nonlinear excitations such as solitons, rational waves, periodic waves, error function waves and any Burgers waves are explicitly given.

The arbitrary ?-wave solutions to the Schr?dinger equation for the deformed hyperbolic Eckart potential is investigated analytically by using the Nikiforov–Uvarov method. The centrifugal term is treated with the improved Greene and Aldrich approximation scheme. The wave functions are expressed in terms of the Jacobi polynomial or the hypergeometric function. The discrete spectrum is obtained and it is shown that the deformed hyperbolic Eckart potential is a shape-invariant potential and the bound state energy is independent of the deformation parameter q.

We calculate the magnitude of cross phase modulation (XPM) induced by classical channels, and analyze its impact on quantum secure key rate. The results show that the XPM induced by classical signals is small and its impact on the quantum key distribution can be neglected.

Taking into account the effect of the generalized Gor'kov and Melik–Barkhudarov (GMB) approximation, we calculate the radio-frequency spectra of balanced and homogeneous ultracold Fermi gases within the framework of the non-self-consistent T-matrix approximation at unitarity in the normal phase. The corresponding equations are numerically calculated on the real frequency axis directly. It is found that our results agree well with the experimental result of the radio-frequency spectroscopy [Phys. Rev. Lett. 101 (2008) 140403].

Employing the thermo-entangled state representation, the common eigenstates of relative position and the total momentum of a two-mode system, we solve the master equation of a damped harmonic oscillator driven by a time-dependent uniform force field.

We present an analytical study on the dynamics of dark solitons in superfluid Fermi gases. By using the modified lens-type transformation, the dynamical equation of superfluid Fermi gases is reduced to a modified one-dimensional nonlinear Shor?dinger equation (NLSE). Once again, by using the reductive perturbation method, the NLSE is reduced to a standard Korteweg-de Vries equation which may be useful for understanding the dynamics of dark solitons in superfluid Fermi gases. The existence of dark soliton solutions in the Fermi gases is provided. In particular, we show that, by manipulating and controlling the scattering length between Fermi atomics of different components and the external potential, the soliton's parameters (amplitude and width) can be changed in a controllable way.

We study theoretically the effect of second-order coupling (SOC) on the tunneling dynamics in a planar four-well system with only one well periodically modulated. We find that SOC between next-nearest neighboring wells facilitates localization. Due to SOC, the suppression of tunneling occurs over a finite range of parameters, in stark contrast to the normal coherent destruction of tunneling in the nearest-neighbor tight-binding approximation. This counter-intuitive phenomenon of SOC-enhanced localization can be attributed to the existence of a localized Floquet state rather than the degeneracy of quasi-energy levels in such a system.

The coupled flapping of two side-by-side identical flags in uniform flow is observed experimentally and numerically. Besides the early reported stable, in-phase, and out-of-phase modes, a transition mode between the in-phase and out-of-phase modes is newly presented. Essentially different from the other modes, the flapping in this transition mode is no longer a single cycle motion. Especially, the FFT analysis of the displacement-time curve indicates that there are multiple peaks of frequency in this mode, of which the smaller value is comparable to the frequency of the in-phase mode and the larger one is close to that of the out-of-phase mode. Changing of the weights of different single cycle motions may explain the mode transition.

Focusing on the problems in the process of simulation and experiment on a parafoil nonlinear dynamic system, such as limited methods, high cost and low efficiency, we present a semi-physical simulation platform. It is designed by connecting parts of physical objects to a computer, and remedies the defect that a computer simulation is divorced from a real environment absolutely. The main components of the platform and its functions, as well as simulation flows, are introduced. The feasibility and validity are verified through a simulation experiment. The experimental results show that the platform has significance for improving the quality of the parafoil fixed-point airdrop system, shortening the development cycle and saving cost.

We present an exact numerical method to calculate the mean first passage time for the random walk on the network between any source node and any target which contains an arbitrary number of nodes. For the network with the average degree <k>～O(1) and the effective diameter D ～lnN or less, the efficiency of our numerical approach is found to exceed all other general numerical methods presented in the literature. Our method can also calculate the average of any function of the first passage time, provided it is finite.

Based on the kernel methods and the nonlinear feature of chaotic time series, we develop a new algorithm called kernel least mean kurtosis (KLMK) by applying the kernel trick to the least mean kurtosis (LMK) algorithm, which maps the input data to a high dimensional feature space. The KLMK algorithm can overcome the shortcomings of the original LMK for nonlinear time series prediction, and it is easy to implement a sample by sample adaptation procedure. Theoretical analysis suggests that the KLMK algorithm may converge in a mean square sense in nonlinear chaotic time series prediction under certain conditions. Simulation results show that the performance of KLMK is better than those of LMK and the kernel least mean square (KLMS) algorithm.

We design a new chaotic oscillator based on the realistic model of the HP TiO_{2} memristor and Chua's circuit. Some basic dynamical behaviors of the oscillator, including equilibrium set, Lyapunov exponent spectrum and bifurcations with respect to various circuit parameters, are investigated theoretically and numerically. Chaotic attractors generated by the proposed oscillator are described with simulations and experiments, showing a good agreement. The main finding by analysis is that the proposed oscillator has no transient chaos and weak hyperchaos appears. Furthermore, its stability is insensitive to its initial values, thereby generating continuous and stable chaotic oscillation signals for chaos-based applications.

The standard model is a chiral gauge theory where the gauge fields couple to the right-hand and the left-hand fermions differently. The standard model is defined perturbatively and describes all elementary particles (except gravitons) very well. However, for a long time, we do not know if we can have a non-perturbative definition of the standard model as a Hamiltonian quantum mechanical theory. Here we propose a way to give a modified standard model (with 48 two-component Weyl fermions) a non-perturbative definition by embedding the modified standard model into an SO(10) chiral gauge theory. We show that the SO(10) chiral gauge theory can be put on a lattice (a 3D spatial lattice with a continuous time) if we allow fermions to interact. Such a non-perturbatively defined standard model is a Hamiltonian quantum theory with a finite-dimensional Hilbert space for a finite space volume. More generally, using the defining connection between gauge anomalies and the symmetry-protected topological orders, one can show that any truly anomaly-free chiral gauge theory can be non-perturbatively defined by putting it on a lattice in the same dimension.

The influences of laser pulses with negative frequency chirp and different pulse cycles on pair production are studied. By solving the quantum Vlasov equation, the momentum distribution and the number density of the created pairs are obtained numerically. It is found that the chirp rate can enhance the pair production rate in both supercycle and subcycle pulses. Moreover, there is an optimal cycle parameter corresponding to the maximum number density under the same chirp rate. The pair number density is sensitive to the cycle parameter when it is less than the optimal one. Compared to the positive frequency chirp, in the case of the negative frequency chirp, the optimal cycle parameter is increased.

Using the B_{s} meson wave function extracted from non-leptonic B_{s} decays, we evaluate the rare decays B_{s}→?^{+}?^{?} γ(?=e,μ) in the standard model, including contributions from all four kinds of diagrams. We focus on the contribution from the four-quark operators, which were not taken into account properly in previous studies. We find that the contribution is large, leading to the branching of B_{s}→?^{+}?^{?}γ being nearly enhanced by a factor 3 and up to 1.6×10^{?8}. The predictions for such processes can be tested in the LHC-b and B factories in the near future.

HE Chuang-Ye, WU Xiao-Guang, WANG Jin-Long, WU Yi-Heng, ZHENG Yun, LI Guang-Sheng, LI Cong-Bo, HU Shi-Peng, LI Hong-Wei, LIU Jia-Jian, LUO Peng-Wei, YAO Shun-He

Chin. Phys. Lett. 2013, 30 (11):
112101
.
DOI: 10.1088/0256-307X/30/11/112101

High-spin states in ^{189}Pt are populated through the heavy-ion fusion-evaporation reaction^{176}Yb (^{18}O, 5n)^{189}Pt at 87 MeV beam energy. An array consisting of 13 HPGe detectors is used in conjunction with the plunger device in CIAE. The lifetimes of two levels in the yrast band are determined by using the recoil distance Doppler shift method. The transition quadrupole moments Q_{t} are extracted. The results show that the 17/2^{+} state has a much larger Q_{t} value than that of the ground state, whereas the value deceases quickly with spin increasing. This may contribute to the shape driving effect of the quasi-neutron from the em_{13/2} orbital.

We present a theoretical study of the H+OCl system on an accurate ab initio potential energy surface (PES) investigated by Peterson et al. [J. Chem. Phys. 113 (2000) 6186]. Both the exact time-dependent quantum wave packet (TDWP) and quasi-classical trajectory (QCT) methods are employed. The results of reaction probabilities for total angular momentum J=0 and the integral cross section calculated by the TDWP are in good agreement with the QCT ones. Additionally, the nearly forward-backward symmetric product scattering angular distributions and the weak products' rotational alignment effect obtained by the QCT calculations are attributed to a long-lived intermediate reaction process.

Ionization channels of the molecular ion H_{2}^{+} for various initial vibrational states in intense laser field (80 fs, 800 nm, I=6.8×10^{13} W/cm^{2}) are theoretically investigated by numerically solving the time-dependent Schr?dinger equation. The results confirm that the channels largely depend on the selection of initial vibrational states by analyzing the variations of peak locations in the nuclear initial kinetic-energy-release spectra. Furthermore, the selection of the ionization channels is sensitive to the wavelength of the laser pulse. In addition, time-dependent competition between direct multi-photon ionization and charge-resonance-enhanced ionization are is discussed.

We theoretically demonstrate that the (2+1) resonance-enhanced multiphoton-ionization (REMPI) photoelectron spectrum in a cesium (Cs) atom can be effectively manipulated by two time-delayed femtosecond laser pulses, involving its photoelectron spectral structure and photoelectron energy. We show that the photoelectron spectrum exhibits interference fringes and the fringe spacing is determined by the time delay of the two laser pulses, and the photoelectron energy is periodically modulated and the modulation period is determined by the two-photon transition frequency of the excited state. Finally, we utilize the power spectrum of the two time-delayed laser pulses and the two-photon transition probability of the excited state to respectively explain the modulations of the photoelectron spectrum and photoelectron energy.

Atomic structure data and effective collision strengths for 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} and 54 fine-structure levels are contained in the configurations 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{9} 4l (l=s, p, d, f) for the nickel-like Ta ion. These data are used in the determination of the reduced population for the 55 fine structure levels over a wide range of electron densities (from 10^{21} to 10^{23}) and at various electron plasma temperatures. The gain coefficients for those transitions with a positive population inversion factor are determined and plotted against the electron density.

The stability of coiled carbon nanotubes under C ion irradiation is investigated by molecular dynamics simulations. The defect statistics shows that small curvature coiled carbon nanotubes have better radiation tolerance than normal straight carbon nanotubes. To understand the effect of the curvature on defect production, the threshold displacement energies for the upper and lower walls, as well as those for the side parts, are calculated. The results show that the lower wall has better radiation tolerance than the upper wall. For the upper wall, a small increase in the curvature of nanotube axis gives rise to an increase in the radiation tolerance and then a decrease with the curvature becomes larger. However, for the lower wall, as the curvature of the nanotube axis increases, the radiation tolerance increases as the bonds compressed slightly in our simulation.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

Linewidth of a laser diode stack with 5 bar is reduced to 0.2 nm from 1.8 nm through the use of an external volume Bragg grating (VBG) cavity. The temperature of the VBG is controlled efficiently to make the central wavelength tunable. The linewidth changes little in the wavelength-tuning experiments. Since the tunable range covers the rubidium D2 absorption line, the stack can be used to pump the rubidium laser efficiently.

A ridge waveguide distributed-feedback laser emitting at 1064 nm is demonstrated. Two low-temperature-grown In_{0.21}Ga_{0.79}As/GaAs quantum wells are employed as the active layer. A second-order grating is formed by holographic photolithography and wet-etching. The laser operates at a single-mode up to 255 mA, corresponding to an output power of 90 mW.

The effects of counter-rotating terms (CRTs) on Rabi splitting and the dynamic evolution of atomic population in the Jaynes–Cummings model are studied with a coherent-state approach. When the coupling strength increases, the Rabi splitting becomes of multi-Rabi frequencies for the initial state of an excited atom in a vacuum field, and the collapses and revivals gradually disappear, and then reappear with quite good periodicity. Without the rotating-wave approximation (RWA), the initial excited state contains many eigenstates rather than two eigenstates under the RWA, which results in the multi-peak emission spectrum. An analytical approximate solution for the strong coupling regime is obtained, which gives a new oscillation frequency and explains the recovery of collapses and revivals due to the equal energy spacing.

A nanosecond pulsed laser is demonstrated using the stimulated Brillouin scattering (SBS) effect in a nonlinear photonic crystal fiber (PCF). The Brillouin fiber laser (BFL) uses a 50-m-long PCF in a simple ring cavity to generate a self-starting pulse as the Brillouin power reaches 16.5 dBm based on the relaxation oscillation technique. The BFL generates a pulse train with repetition rates of 2.7 MHz and 5.4 MHz depending on the BP power. The pulse width of the laser is obtained to be 190 ns at the BP power of 16.5 dBm and is maintained at around 72 ns as the pump power is set within 17.7 dBm and 18.5 dBm. The maximum pulse energy of 20 nJ is obtained at BP power of 17.4 dBm. This SBS based pulse laser is fairly stable at room temperature.

We propose a scheme for controlling the coherent transport of a single electron through a closed three-level structure in coupled quantum dots. The coherent transport is externally controlled by applying a weak few-cycle pulse with an adjustable carrier-envelope phase (CEP). It is revealed numerically that there exists a significant dependence of the electron transport on the CEP. Our results illustrate the potential to utilize few-cycle pulses for the excitation in coupled quantum dot systems through control of the CEP, as well providing guidance in the design for possible experimental implementations.

A compact, tunable mid-IR difference-frequency generation (DFG) light source based on a dual-wavelength fiber laser and a 5mol% MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal is developed and evaluated. An output power of 233 μW is achieved with a conversion efficiency of 0.1%/W. The mid-IR wavelength can be tuned between 3308 nm and 3314 nm by changing the temperature of a pair of fiber Bragg grating (FBG) taking as cavity mirrors in the dual-wavelength fiber laser from 26.5°C to 106.5°C.

We experimentally demonstrate a kind of high-quantum correlated, practical quantum random generation based on the quantum phase noise of a laser, which uniformly distributes in the range of (?π,π] by driving the laser with a stream of narrow electrical pulses. We propose a working mode to further suppress the impact of phase drift after we use the passive measures (thermal and mechanical isolation) to slow it down. Moreover, a new method which ensures random numbers to be true representations of quantum characteristics is presented to quantify the quantum randomness. This scheme has an inherent advantage for multiplex generation.

By designing pivotal phase-only masks based on canonical catastrophe theory, finite-energy optical quinary-cusp beams are experimentally generated for the first time. Such beams are a kind of new accelerating beams having five sampling points. Their optical topological structures and propagation characteristics are investigated subsequently. Moreover, we also find that the acceleration of quinary-cusp beams can be controlled by changing the Fourier transform lens with the different local lengths. Such research results are believed to pave the way toward future potential scientific applications of quinary-cusp beams.

In Gaussian-modulated coherent-state quantum key distribution, the measurement of quadratures of coherent states is performed by using a homodyne detector. However, conventional detectors usually suffer from narrow bands. We present a method to design a high-speed shot-noise-limited balanced homodyne detector. A 300-MHz bandwidth detector is experimentally tested and the level of shot noise is 14 dB higher than the electronic noise. The results show that a detector with this method is potential to design a GHz bandwidth detector for continuous variable quantum key distribution at a low level of ratio of shot noise to electronic noise.

A coupled-mode method for three-dimensional acoustic propagation and scattering in two-dimensional waveguides is presented. This method synthesizes the three-dimensional field solution by using Fourier transform techniques based on a sequence of two-dimensional problems, each of which is solved by a numerical model recently developed by Luo et al. [Chin. Phys. Lett. 29 (2012) 014302]. Numerical results indicate that the present model is remarkably accurate, and thus can serve as benchmark against other numerical models. In addition, this model can be applied to realistic problems, and can also be used to analyze horizontal refraction in some range-dependent waveguides in reality, such as the continental shelf environment, ridge-like bathymetry, and underwater trenches.

An approximate collision-radiative method is developed to calculate energy level populations of atoms and applied to simulate radiative transfer in a shock layer. Considering nonequilibrium plasmas with the electronic temperature below 20000 K, we introduce correction factors to the Saha–Boltzmann equation and simplify the master equation of the full collision-radiative model. Based on the method, the error of heat flux is smaller than 5% in a two-cell problem and smaller than 7% in the Stardust re-entry flow field compared with the correlated-k method. Furthermore, almost a factor of 2 is obtained in the improvement of computational efficiency compared with the nonequilibrium air radiation (NEQAIR) code. The results show that the present method is reliable and efficient.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Rotation of dust clusters in an unmagnetized dusty plasma under different gas pressures is experimentally studied. Clusters containing different numbers of charged dust grains are found in different horizontal planes. The mechanism behind the dust rotation is investigated by using molecular dynamics simulations. The experimental and simulation results show that the radial confinement potential plays an important role in determining the properties of the cluster rotation under given gas pressure or temperature.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Zr-Ti binary alloys are prepared using a nonconsumable tungsten electrode under Ti-gettered inert atmosphere (argon). Microstructures are observed mainly as α phase using x-ray diffraction. A tensile test is performed to investigate the tensile strength of a series of Zr-Ti binary alloys at room temperature. The findings indicate that increasing Ti concentration results in an initial increase (<50at% of Ti) and then a decrease in tensile strength. The Zr55Ti45 (at%) component exhibits the maximum tensile strength of 1216.68 MPa, which is much higher than that of pure Ti (increased by approximately 200%) or pure Zr (increased by approximately 100%). The potential mechanisms for the remarkable tensile strength are solid solution strengthening and grain refinement.

Path integral Monte Carlo (PIMC) method is employed to study the thermal properties of the X@C_{50} [X=H_{2}, He, Ne, Ar] system at temperatures from 5 K to 300 K. The interaction energies and probability distribution functions of one noble gas atom or H_{2} inside D_{5h}-symmetry C_{50} are obtained. A rough sphere model is used in calculating interaction energies, as a comparison. This model gives much lower interaction energy than PIMC calculations on all X@C_{50}, except He@C_{50}. The PIMC method and the sphere model get nearly the same values of interaction energies on He@C_{50}. The spatial distributions are enlarged by the increase in temperature, while the interaction energies change slowly in a wide range of temperature. Temperature is not the major reason for the stability of the system. It is impossible to trap an X atom into C_{50}, except H_{2} because only the H_{2}@C_{50} has positive interaction energies from the PIMC calculations.

To explain different doping effects in a buffer layer, thermally annealed interface, and upper epilayers of GaAs/Si films grown by Metalorganic Chemical Vapor Deposition (MOCVD), the behaviors of unintentional doping in GaAs/Si films are investigated in detail. A third doping mechanism of arsine impurity incorporation during the growth process of GaAs/Si films, apart from conventional mechanisms of gas phase reaction and diffusion from the silicon substrate, is proposed. The experimental results reveal that the doping behavior in the buffer layer studied is determined by the three types of doping mechanisms together. However in the thermally annealed interface and upper epilayers, the third doping mechanism is dominant. According to the third mechanism, the background carrier concentration in GaAs/Si films grown by MOCVD could be properly controlled through the arsine flow rate.

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

The first principles calculations based on density functional theory are performed to investigate the stability, chemical bonding, elastic constants, hardness and Debye temperature of MB (M=V, Nb and Ta) compounds. The structures of these borides are optimized, and the lattice parameters are in good agreement with the experimental data. The calculated cohesive energy and formation enthalpy indicate that they are of a thermodynamically stable structure. The mechanical properties, including elastic constants C_{ij}, bulk modulus, Young's modulus, shear modulus and Poisson's ratio, are calculated. The bulk moduli of them ranging from 263.0 to 278.4 GPa are larger than many common Laves phases and TaB with 278.4 GPa being the largest bulk modulus value among them. The population analysis is used to analyze the chemical bonds in these compounds. The hardness of the compounds is also evaluated, and the result reveals that TaB is the hardest compound among them. The Debye temperature of MB is calculated. The results show that the values of MB compounds range from 419.3 to 794.3 K.

We comparatively study two representative ballistic transport models of nanowire metal-oxide-semiconductor field effect transistors, i.e. the Natori model and the Jiménez model. The limitations and applicability of both the models are discussed. Then the Jiménez model is extended to include atomic dispersion relations and is compared with the Natori model from the aspects of ballistic current and quantum capacitance. It is found that the Jiménez model can produce similar results compared with the more complex Natori model even at very small nanowire dimensions.

We investigate the electronic states of IC_{60}BA and PC_{71}BM using first-principles calculations and photoelectron spectroscopy (PES) measurements. The energy level structures for all possible isomers are reported and compared with those of C_{60}, C_{70} and PC_{61}BM. The attachment of the side chains can raise the LUMO energies and decrease the HOMO-LUMO gaps, and thus helps to increase the power-conversion efficiency of bulk heterojunction solar cells. In the PES studies, we prepared IC_{60}BA and PC_{71}BM films on Si:H(111) substrates to construct adsorbate/substrate interfaces describable with the integer charge-transfer (ICT) model. Successful measurements then revealed that one of the most important material properties for an electron acceptor, the energy of the negative integer charge-transfer state (E_{ICT?}), is 4.31 eV below the vacuum level for PC_{71}BM. The E_{ICT?} of IC_{60}BA is smaller than 4.14 eV.

The electrode effect of resistive switching memory devices on resistive switching behaviors is studied. Compared to TiN- or Ti-electrode devices, significantly reduced switching parameters such as resistance-ratio of high- and low-resistance states and set-voltage are observed experimentally in the Al-electrode devices when a positive voltage bias is applied to the Al-electrode during the forming process. An electric-field induced metal-ion-migration effect is proposed to elucidate the observed electrode dependence of the resistive switching behaviors in the resistive switching memory devices. The further measured data identify the validity of the proposed mechanism.

By in situ x-ray diffraction, an isostructural phase transition between two kinds of the cubic PbCrOperovskites at around 1.6 GPa and room temperature with a 9.8% volume change is discovered. Recently, we have synthesized this cubic PbCrO_{3}perovskite successfully. Here we report our high-pressure in situ electrical resistance measurements up to 4.1 GPa for this perovskite sample. At room temperature, the resistance shows special changes at 1.2 and 2.7 GPa. They may indicate the starting and ending points of this transformation. At 4.1 GPa, the negative temperature resistance coefficient is observed, which means that phase II could be considered as a semiconductor according to our present measurement.

Al_{0.5}Ga_{0.5}N-based metal-semiconductor-metal photodetectors (PDs) with a large device area of 5×5 mm^{2} are fabricated on a sapphire substrate, which are tested for vacuum ultraviolet light detection by using a synchrotron radiation source. The PD exhibits low dark current of less than 1 pA under 30 V bias and a spectral cutoff around 260 nm, corresponding to the energy bandgap of Al_{0.5}Ga_{0.5}N. A peak photo-responsivity of 14.68 mA/W at 250 nm with a rejection ratio (250/360 nm) of more than four orders of magnitude is obtained under 30 V bias. For wavelength less than 170 nm, the photoresponsivity of the PD is found to increase as wavelength decreases, which is likely caused by the enhanced photoemission effect.

Enhanced crystallization of Si nanocrystals (Si NCs) has been achieved in an Al_{2}O_{3}:Er/Si:Er multilayer structure, which is fabricated by pulsed laser deposition and subsequent rapid thermal annealing. The Er atoms introduce strains in the initial amorphous Si layers and serve as nucleation centers that enhance the crystallization of Si NCs at low annealing temperatures. The average size of Si NCs is well controlled by adjusting the Si layer thickness. Thanks to the formation of Si NCs and the favored chemical environment of Er^{3+ } after annealing around 600–700°C, optimized photoluminescence peaked at 1.54 μm has been obtained. The present results stress the importance of controlling the formation of Si NCs to improve the performance of Er^{3+} luminescence.

By using a pulse laser at 532.36 nm as the incident light, stimulated Raman scattering (SRS) of a series of a-cut and c-cut Nd:Lu_{x}Y_{1?x}VO_{4} (x=0, 0.10, 0.26, 0.41, 0.61, 0.67, 0.80) crystals is investigated. For the π-polarization (E||c), the gain coefficient reduced as x value increased. For the σ-polarization (E||a), the Raman gain of all of the mixed crystals is larger than the pure Nd:YVO_{4}, and the maximum value is obtained from the Nd:Lu_{0.1}Y_{0.9}VO_{4} crystal. Such results are also supported by the measurement of spontaneous Raman scattering spectra.

Experimental investigation of electrical transport properties is carried out by in situ transmission electron microscopy (TEM) to explore the effect of local strain in ZnSe nanowires (NWs) on improvement of electron transport of Au-ZnSe NW-Au (M-S-M) nanostructure. The results show that the threshold voltage due to the Schottky barrier at the metal-semiconductor NW (M-S) nanocontact is found to decrease significantly when the ZnSe NW bends at the Au-ZnSe junction by the movable probe which can apply longitudinal compression, leading to current-voltage (I–V) characteristics of the M-S-M nanostructure being transformed from a nearly symmetrical to an asymmetrical feature. Alternation of the I–V characteristic can be ascribed to significant depression of the Schottky barrier at the M-S nanocontact due to the band gap being narrowed by highly localized strain. As a result, the I–V characteristics of the M-S-M nanostructure are strain-sensitive and can be modified by local strain intentionally produced in the semiconductor NW. The modifiable I–V characteristics of M-S-M nanostructure confirm that the strain can be used for improvement of transport property of the semiconductor NW-based nanoelectronics with the M-S-M nanostructure.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

We report on fabrication of a rhodamine-6G-gold-nanoparticle doped polymer optical fiber. The gold nanoparticle is synthesized directly into the monomer solution of the polymer using laser ablation synthesis in liquid. The size of the particle is found from the transmission electron microscopy. Rhodamine-6G is then mixed with the nanoparticle-monomer solution and optical characterization of the solution is investigated. It is found that there is a pronounced quenching of fluorescence of rhodamine 6G due to fluorescence resonance energy transfer. The monomer solution containing rhodamine 6G and gold nanoparticles is now made into a cylindrical rod and drawn into a polymer optical fiber. Further, the photostability is calculated with respect to the pure dye doped polymer optical fiber.

Broadband light emission is obtained from a chirped multiple InAs/InGaAs/GaAs quantum dot (QD) structure. The thickness of the InGaAs strain-reducing layer (SRL) is used as the tuning parameter to adjust the light emission property of each QD layer in the chirped structure. It is shown from the photoluminescence (PL) measurement that the SRL thickness has a strong influence on the PL peak position, linewidth, and intensity. By constructing the chirped QD structure comprising five groups of QD layers with different SRL thicknesses, a broadband electroluminescence emission with the full width at half maximum of 202 nm is realized, indicating the feasibility of chirped multiple InAs QD layers on broadening the emission spectrum.

Er-doped Y_{2}O_{3}, Bi_{2}O_{3} and Sb_{2}O_{3} nanoparticles are synthesized using pulsed laser ablation in a liquid. Ceramic targets of Y_{2}O_{3}:Er^{3+}, Bi_{2}O_{3}:Er^{3+} and Sb_{2}O_{3}:Er^{3+} for ablation process are prepared by standard solid-state reaction technique and ablation is carried out in 5-ml distilled water using nanosecond Q-switched Nd:YAG laser. The morphology and size of the fabricated nanoparticles are evaluated by transmission electron microscopy and the luminescence emission properties of the prepared samples are investigated under different excitation wavelengths.

ZnO films are grown on c-sapphire substrates by laser molecular beam epitaxy. The band offsets of the ZnO/Al_{2}O_{3} heterojunction are studied by in situ x-ray photoelectron spectroscopy. The valence band of Al_{2}O_{3} is found to be 3.59±0.05 eV below that of ZnO. Together with the resulting conduction band offset of 2.04±0.05 eV, this indicates that a type-I staggered band line exists at the ZnO/Al_{2}O_{3} heterojunction.

Germanium-tin (Ge_{1?x}Sn_{x}) p-type metal-oxide-semiconductor field effect transistors (pMOSFETs) were fabricated using a strained Ge_{0.985}Sn_{0.015} thin film that was epitaxially grown on a silicon-on-insulator substrate with a relaxed Ge buffer layer. The Ge buffer was deposited using a two-step chemical vapor deposition growth technique. The high quality Ge_{0.985}Sn_{0.015} layer was grown by solid source molecular beam epitaxy. Ge_{0.985}Sn_{0.015} pMOSFETs with Si surface passivation, TaN/HfO_{2} gate stack, and nickel stanogermanide [Ni(Ge_{1?x}Sn_{x})] source/drain were fabricated on the grown substrate. The device achieves an effective hole mobility of 182 cm^{2}/V?s at an inversion carrier density of 1×10^{13} cm^{?2}.

The cytosolic calcium system is inhomogenous because of the discrete and random distribution of ion channels on the ER membrane. It is well known that the spiral tip can be pinned by the heterogenous area, and the field can detach the spiral from the heterogeneity. We use the adventive field to counteract the attractive force exerting on the calcium spiral wave by the heterogeneity, then the strength of the adventive field is used to quantify the attractive force indirectly. Two factors determining the attractive force are studied. It is found that: (1) the attractive force sharply increases with size of the heterogeneity for small-size heterogeneity, whereas the force increases to a saturated value for large-size heterogeneity; (2) for large-size heterogeneity, the force almost remains constant unless the level of the heterogeneity vanishes, the force decreases to zero linearly and sharply, and for small-size heterogeneity, the force decreases successively with the level of the heterogeneity. Furthermore, it is found that the forces exist only when the spiral tip is very close to the heterogenous area. Our study may shed some light on the control or suppression of the calcium spiral wave.

In typical experiments where magnetic tweezers are involved, precise measurement of the magnetic forces is of crucial importance. To achieve this, a widely applied method is to track the bead's Brownian motion trajectory and to calculate the force from its mean-squared-displacement. However, this method does not take into account the fact that the bead-tracking device always has a finite bandwidth, acting effectively as a low-pass filter. The result could be subjected to significant system errors, which overestimates the magnetic force. We analyze the power spectrum of the bead's Brownian motion, and provide a corrected formula to calculate the magnetic force, which is free of system errors induced by limited detection bandwidth. A dsDNA force-extension curve is experimentally measured. The curve is consistent with the WLC model, exhibiting correctness of the new formula. On the other hand, the force given by the traditional method shows significant deviation from the WLC model, which is 3 times larger at most.

TiO_{2} anode materials are prepared on ITO glass by spin-coated method. Dye-sensitized solar cells are assembled with these anodes and natural dyes extracted from radix ophiopogonis by different solvents. The formation and characterization of anode materials are confirmed by field-emission scanning electron microscopy, x-ray diffraction, UV-visible absorption spectroscopy. Photovoltaic testing results show that energy conversion efficiency could reach 1.67% with fill factor of 0.51, open-circuit voltage of 457 mV, and short-circuit photocurrent density of 7.2 mA/cm^{2}. The short-circuit photocurrent density can reach 7.6 mA/cm^{2} with efficiency of 1.33.

We employ a bipartite network to describe an online commercial system. Instead of investigating accuracy and diversity in each recommendation, we focus on studying the influence of recommendation on the evolution of the online bipartite network. The analysis is based on two benchmark datasets and several well-known recommendation algorithms. The structure properties investigated include item degree heterogeneity, clustering coefficient and degree correlation. This work highlights the importance of studying the effects and performance of recommendation in long-term evolution.

A cosmological model in Lyra's geometry is studied under the assumption that an effective cosmological term appears in the field equations as the result of interaction between the displacement vector field and an auxiliary Λ term. Some exact solutions to the model equations are obtained and preliminarily studied for the simplest cases in order to illustrate how such a model works.