For waves in inhomogeneous media, variable-coefficient evolution equations can arise. It is known that the Manakov model can derive two models for propagation in uniform optical fibers. If the fiber is nonuniform, one would expect that the coefficients in the model are not constants. We present a variable-coefficient Manakov model and derive its Lax pair using the generalized dressing method. As an application of the generalized dressing method, soliton solutions of the variable-coefficient Manakov model are obtained.

By using the truncated Painlevé analysis and the generalized tanh function expansion approaches, many interaction solutions among solitons and other types of nonlinear excitations of the Konopelchenko–Dubrovsky (KD) equation can be obtained. Particularly, the soliton-cnoidal wave interaction solutions are studied by means of the Jacobi elliptic functions and the third type of incomplete elliptic integrals.

A multiparty controlled bidirectional quantum secure direct communication and authentication protocol is proposed based on EPR pair and entanglement swapping. The legitimate identities of communicating parties are encoded to Bell states which act as a detection sequence. Secret messages are transmitted by using the classical XOR operation, which serves as a one-time-pad. No photon with secret information transmits in the quantum channel. Compared with the protocols proposed by Wang et al. [Acta Phys. Sin. 56 (2007) 673; Opt. Commun. 266 (2006) 732], the protocol in this study implements bidirectional communication and authentication, which defends most attacks including the 'man-in-the-middle' attack efficiently.

We develop a frequency-tunable two-color continuous variable entangled state and demonstrate the entanglement distribution over a telecom single mode fiber. One beam of the entangled state (795 nm) can be continuously tuned over a range of 2.4 GHz and the hyperfine transitions of a rubidium D1 line are measured based on saturated absorption spectroscopy. The other beam (1560 nm) is injected into a 5-km single mode fiber to distribute the entanglement, and the entanglement evolution between the transmitted beam and its entangled counterpart is investigated. The system presented here will find potential applications in long-distance quantum information processing.

The collective excitations of a one-dimensional dipolar Bose–Einstein condensate trapped in an anharmonic potential are investigated theoretically. Using the variational approach, we obtain the coupled equations of motion for the center-of-mass coordinate of the condensate and its width. In particular, analytical expressions for the low-lying excitation modes are given. The results show that dipole-dipole interactions reduce the frequency shift induced by quartic distortion. The interplay between dipole-dipole interactions and anharmonic distortion for the collapse and revival of the collective excitations originating from the nonlinear coupling between the two modes are also discussed.

We study the decoherence of superradiant Rayleigh scattering from condensed atoms without confinement, by using two same pumping pulses with an interval time. The first pulse is to establish a matter-wave grating, and the coherence between different momentum modes is measured by the second pulse after a variable interval time. Different from the case in the trap, the distruction of the grating owing to the phase perturbation is very fast, and the superradiant process is inhibited very soon afterwards for released atoms. A semi-classical model is applied to simulate this phase perturbation, and the calculation agrees with our experimental results.

We experimentally demonstrate a quantum key distribution protocol using entangled photon pairs in orbital angular momentum (OAM). Here Alice uses a fixed phase hologram to modulate her OAM state on one photon with a spatial light modulator (SLM), while Bob uses the designed N different phase holograms for his N-based keys on the other photon with his SLM. With coincidences, Alice can fully retrieve the keys sent by Bob without reconciliation. We report the experiment results with N=3 and OAM eigenmodes |?=±1>, and discuss the security from the light path and typical attacks.

We study Bose–Einstein condensate vortical solitons under both a bichromatic optical lattice and anharmonic potential. The vortical solitons are built in the form of a layer-chain structure made up of two fundamental vortices along the bichromatic optical lattice direction, which have not been reported before in the three-dimensional Bose–Einstein condensate. A variation approach is applied to find the optimum initial solutions of vortical solitons. The stabilities of the vortical solitons are confirmed by the numerical simulation of the time-dependent Gross–Pitaevskii equation. In particular, stable Bose–Einstein condensate vortical solitons with fundamental vortices of different atomic numbers in the external potential within a range of experimentally achievable timescales are found. We further manipulate the vortical solitons to an arbitrary position by steadily moving the bichromatic optical lattice, and find a stable region for the successful manipulation of vortical solitons without collapse. These results provide insight into controlling and manipulating the Bose–Einstein condensate vortical solitons for macroscopic quantum applications.

Geometric quantum discord of fermionic systems in the relativistic regime, that is, beyond the single-mode approximation, is investigated. It is shown that geometric quantum discord for the fermionic systems in non-inertial frames converges at an infinite acceleration limit, which means that the fermionic systems become independent of the choice of Unruh modes (q_{R}) beyond single-mode approximation. The discord may vanish or be retained depending upon the level of mixedness of the fermionic system. The dynamics of geometric discord are investigated under amplitude damping, depolarizing, phase damping and flipping channels. The vanishing behavior of discord is seen for a higher level of decoherence in the infinite acceleration limit. The depolarizing channel dominantly affects the fermionic geometric discord as compared to the amplitude and phase damping channels. This implies that the depolarizing channel has most destructive influence on the discord of the fermionic systems. However, the flipping channels have a symmetrical effect on the discord. Moreover, the discord heavily depends on the mixedness parameter of the quantum state of the fermionic systems in accelerated frames beyond single-mode approximation.

We study the thermodynamics of a charged AdS black hole in the special f(R) correction with the constant Ricci scalar curvature. Our results show that the f(R) correction influences the Gibbs free energy and the phase transition of system. The ratio ρ_{c} occurring at the critical point increases monotonically with the derivative term f'(R_{0}). We also disclose that the critical exponents are the same as those of the liquid-gas phase transition in the van der Waals model, which does not depend on the f(R) correction considered here.

A photosensitive chaotic oscillator which can be controlled with light illumination under various control voltage levels is proposed. The oscillator consists of a photodiode for the light input, clock switches and capacitors for the sample and hold function, a nonlinear function that creates an adjustable chaos map, and a voltage shifter that adjusts the output voltage for feedback. After optimizing the photodiode sub-circuit by using an available photodiode model in PC-based simulation program with integrated circuit emphasis to obtain a suitable output, the full chaotic circuit is verified with standard 0.6-μm complementary metal oxide semiconductor parameters. Chaotic dynamics are analyzed as a function of the light intensity under different control voltage levels. The time series, frequency spectra, transitions in state spaces, bifurcation diagrams and the largest Lyapunov exponent are improved.

Utilizing the Wronskian technique, a new Wronskian representation is proposed for a variable-coefficient Kadomtsev–Petviashvili (vcKP) equation. Furthermore, some particular forms of Wronskian determinant solutions, including N-soliton solutions, trigonometric function solutions and rational solutions, are obtained for the equation.

Nonlinear spectroscopy has become a useful tool in laser cooling, frequency stabilization and so on. We use the 455.5 nm light beam output of an external cavity diode laser to perform the saturation spectroscopy signal and polarization spectroscopy signal on the 6S_{1/2} →7P_{3/2} transition in cesium. The measured linewidth of the F4→4,5 transition is as narrow as 1.40 MHz and that of the F3→2,3 transition is 1.67 MHz. Both of them are very close to the natural linewidth of about 1.2 MHz. Our result is the narrowest measured linewidth of Cs 455 nm saturation spectroscopy signal to our knowledge.

We report a quantitative analysis of by-pass current effect on the accuracy of resistivity measurement in a diamond anvil cell. Due to the by-pass current, the sample resistivity calculated by the van der Pauw method is obviously smaller than the actual value and the problem becomes more serious for a high-resistivity sample. For the consideration of high accuracy of resistivity measurement, a method is presented that the inside wall of the sample chamber should be covered by a polymethylmethane layer. With this highly insulating layer, the by-pass current is effectively prevented and the current density distribution inside the sample is very close to the ideal case.

A dual-frequency atomic force microscopy imaging system is set up to enhance the amplitude of higher harmonic signals. The experimental results of the dual-frequency imaging technology are given. Normally the image of the higher harmonic is helpful to optimize the imaging conditions in tapping mode and allows one to differentiate qualitatively between dissimilar materials that are hardly distinguishable by traditional atomic force microscopy.

We investigate the influence of the energy gap ( Δ) of the color-flavor locked (CFL) quark phase on the bulk properties of hybrid stars. The relativistic mean field model is used for hadronic matter and the MIT bag model for CFL quark matter. In our calculation results, we find that with the increase of the CFL energy gap there exists a transition behavior, which goes from the hadron star range through the transition range into the CFL quark star range. The observation data of PRS J1614-2230 are in the hadron star range (with Δ<40 MeV). We also find that with hyperons the equation of state (EOS) for the hybrid star matter with the CFL quark matter core has a small change, which can be disregarded.

We investigate the nucleon superfluidity in the ^{1}S_{0} channel in neutron star matter using the relativistic mean field theory and the BCS theory. We discuss particularly the influence of the isovector scalar interaction which is considered by exchanging δ meson on the nucleon superfluidity. It is found that the δ meson leads to a growth of the nucleon ^{1}S_{0} pairing energy gaps in a middle density range of the existing nucleon superfluidity. In addition, when the density ρ_{B}>0.36 fm^{?3}, the proton ^{1}S_{0} pairing energy gap obviously decreases. The density range of the proton ^{1}S_{0} superfluidity is narrowed due to the presence of δ mesons. In our results, the δ meson not only changes the EOS and bulk properties but also changes the cooling properties of neutron stars.

LI Li, SUN Ji, LI Jian, YU De-Yang, LIU Gong-Ye, ZHANG Wei-Tian, MA Ke-Yan, YANG Dong, MA Ying-Jun, WU Xiao-Guang, ZHU Li-Hua, HE Chuang-Ye, ZHENG Yun, YAO Shun-He, LI Cong-Bo, HU Shi-Peng, CAO Xue-Peng, WANG Jin-Long, YU Bei-Bei

Chin. Phys. Lett. 2013, 30 (6):
062301
.
DOI: 10.1088/0256-307X/30/6/062301

Excited states in ^{120}I are investigated utilizing in-beam gamma-ray spectroscopy following the ^{114}Cd(^{11}B,5n) reaction at 70 MeV bombarding energy. A level scheme is constructed with states up to 9 MeV. The levels are classified into several bands and their possible configurations at low spins are discussed briefly. Based on the linking transitions between different bands at higher spins, the excitation energy of the previously reported T_{1/2}=53 min isomer is ascertained to be 72 keV. Evidence showing the existence of an isomer at an excitation energy of 6.4 MeV is presented.

The pseudo-rapidity distribution of charged hadron multiplicity in Pb+Pb collisions at √s=2.76 TeV is studied by using Color Glass Condensate dynamics in the fixed coupling case. We fit the HERA experimental data with heavy parton mass effect to obtain saturation exponent λ=0.22. It is found that the charged hadron multiplicity can only describe after including heavy parton mass effect due to a large amount of heavy partons produced at large hadron collider (LHC) energy. The pomeron loop effect contribution to hadron production is also investigated. It shows that charged hadron multiplicity is underestimated by including the pomeron loop effect, which indicates that the pomeron loop effect may not exist at LHC energy.

We attempt to deal with the direct photon production phenomena in p+p, d+Au and Au+Au collisions at RHIC energy, √s_{NN}=200 GeV and in Pb+Pb-collisions at LHC energy, √s_{NN}=2.76 TeV on the basis of a non-standard framework outlined in the text. Comparisons of the model-based results with the measured data on some observables reveal fair agreement and they are modestly consistent with the results obtained by some other models of 'Standard' framework.

The isotopic effect on nuclear dynamics in Coulomb explosion for various initial vibrational states of H_{2}^{+} and HD^{+} in intense laser (80 fs, 800 nm, I=6.8×10^{13} W/cm^{2}) is theoretically investigated by numerically solving the time-dependent Schr?dinger equation. The calculated results confirm that the effect we discussed by paying close attention to the comparative analysis of peak locations in the nuclear kinetic-energy-release spectra largely depends on the selection of the initial vibrational states. Furthermore, it is the special isotope effect case about the vibrational state υ=5 that has been studied in depth. We also discuss the time-dependent spectrum at υ=7, which can reveal the difference in nuclear wavepacket motion between H_{2}^{+} and HD^{+} in the time region in which charge-resonance enhanced ionization takes place.

Detailed calculations are carried out for the electron-impact excitation cross sections from the ground state to the individual magnetic sublevels of the 1s2s^{2}2p_{3/2} J=2 excited state of highly-charged beryllium-like ions by using a fully relativistic distorted-wave (RDW) method. The contributions of the Breit interaction to the linear polarization of the 1s2s^{2}2p_{3/2} J=2→1s^{2}2s^{2} J=0 magnetic quadrupole (M2) line are investigated systematically for the beryllium isoelectronic sequence with 42≤Z ≤92. It is found that the Breit interaction depolarizes significantly the linear polarization of the M2 fluorescence radiation and that these depolarization effects increase as the incident electron energy and/or the atomic number is enlarged.

This study presents an experiment on diffuse light cooling of atoms in a cylindrical cavity. We focus on the controlling of the shape of the atom cloud by placing the cooling beams in appropriate positions. The Gauss-like shape of the atomic cloud is demonstrated. The number of cold atoms detected in the cavity is increased, thereby improving the signal-to-noise ratio of the clock signal.

FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

A novel radome is presented, which is transparent at operating frequency and is invisible out of band. In order to prevent reflection of the incoming power, frequency selective surfaces loaded with the lumped resistors are employed. To obtain the pass-band properties in lower frequencies, the convoluted slots are utilized. By comparison with the results obtained both by full wave analysis and by the measurements, the performance of the radome is verified. It performs with high transmission characteristics in band, and broadband absorbing properties out of band simultaneously. The oblique incidences are also investigated for both transmission coefficients and reflection ones.

The terahertz radiations generated through a slab of GaAs-based photoconductive antennas are calculated from the nonlinear model and measured by a time domain spectroscopy system. The calculated spectra for the different pulses are in agreement with our experimental observations. This consistency suggests that the description of the nonlinear model captures the basic features of this photoelectrical terahertz emission mechanism. Furthermore, 1/f background noise dominates the terahertz detection in our experiments when the frequency is larger than 3 THz.

We demonstrate continuous-wave (cw) operation of terahertz (THz) quantum cascade lasers emitting at 3.2 THz based on bound-to-continuum active region and semi-insulating surface-plasmon waveguide design. Optical power of 62 mW with a threshold current density of 285 A/cm^{2} is obtained at 10 K from a 130-μm-wide and 1.5-mm-long laser in cw operation. Maximum cw operation temperature is up to 60 K. In pulsed mode, peak optical power more than 100 mW at 10 K and 2.1 mW at 85 K are observed from a 230-μm-wide and 2-mm-long device.

We fabricate z-cut LiNbO_{3} nonlinear photonic crystal with two-dimensional dodecagonal superlattice by applying high voltage pulses. By using collinear quasi-phase matching technique, second-harmonics at five wavelengths 620 nm, 574 nm, 555 nm, 515nnm and 492 nm are observed simultaneously in one quasiperiodically poled crystal. The distributions of the reciprocal vectors and the diffraction spots in this quasiperiodic structure are theoretically and experimentally analyzed. The same results can be obtained by rotating around z-axis by intervals of 30°.

We investigate 750 nm and 532 nm dual-wavelength laser for applications in the internet of things. A kind of optical maser is developed, in which the semiconductor module outputs the 808 nm pump light and then it goes into a double-clad Nd^{3+}:YAG monocrystal optical fiber through the intermediate coupler and forms a 1064 nm laser. The laser outputs come from both left and right terminals. In the right branch, the laser goes into the right cycle polarization Li_{n}NbO_{3} (PPLN) crystal through the right coupler, produces the optical parametric oscillation and forms the signal light λ_{1} (1500 nm), the idle frequency light λ_{2} (3660.55 nm), and the second-harmonic of the signal light λ_{3} (750 nm). These three kinds of light and the pump light λ_{4} together form the frequency matching and the quasi-phase matching, then the four-wave mixing occurs to create the high-gain light at wavelength 750 nm. Meanwhile, in the left branch, the laser goes into the left PPLN crystal through the left coupler, engenders frequency doubling and forms the light at wavelength 532 nm. That is to say, the optical maser provides 750 nm and 532 nm dual-wavelength laser outputting from two terminals, which is workable.

A biconcave particle suspended in a Poiseuille flow is investigated by the multiple-relaxation-time lattice Boltzmann method with the Galilean-invariant momentum exchange method. The lateral migration and equilibrium of the particle are similar to the Segré-Silberberg effect in our numerical simulations. Surprisingly, two lateral equilibrium positions are observed corresponding to the releasing positions of the biconcave particle. The upper equilibrium positions significantly decrease with the increasing Reynolds number, whereas the lower ones are almost insensitive to the Reynolds number. Interestingly, the regular wave accompanied by nonuniform rotation is exhibited in the lateral movement of the biconcave particle. It can be attributed to the fact that the biconcave shape in various postures interacts with the parabolic velocity distribution of the Poiseuille flow. A set of contours illustrate the dynamic flow field when the biconcave particle has successive postures in a rotating period.

Temporally evolving high-temperature turbulent channel flows (at Ma_{∞}=6 and 10 and Re_{∞}=12000) are performed by using direct numerical simulation with the assumption of local thermal equilibrium and chemical non-equilibrium. The turbulent statistical characteristics are studied. We find that the Morkovin theory for the Van Direst transformed velocity remains valid, while the compressibility effects need to be considered since the turbulent Mach number is high enough, especially for the higher Mach number case. The dissociation/recombination reactions are excited, which are proved by the mean temperature, mass fractions and specific heat ratio. The importance of the mean property variations is studied from the rms velocity and mass fraction fluctuations.

Tomographic particle image velocimetry (TPIV) and static pressure measurements are performed in a wind tunnel on a scaled model of the rotor blade of a 5 kW horizontal-axis wind turbine designed by using the blade element momentum method. This study is to investigate the physics of the stall-delay phenomenon observed for a rotating blade. The TPIV experiments are conducted at several span-wise locations of the blade. The separated flow from the rotating blade is studied and compared with the case of the static stall at similar angles of attack and Reynolds number Re.

We present an inverse analysis of the conductive and radiative heat transfer problem in fibrous porous materials. The porosity and total heat transmission are simultaneously recovered in the finite-volume method and genetic algorithm scheme for both uniform and nonuniform porosity distributions. We solve the heat transfer equations directly to obtain the total heat transmission that defines the objective function to be minimized in the inverse analysis. The results show that the combined scheme is an effective tool for the inverse analysis of fibrous porous materials.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

The spectral broadening of motional Stark effect (MSE) is simulated in the HL-2A tokamak, which is in good agreement with the experimental observation. The divergence angle of the neutral beam, finite lens size and beam energy dissociation are the main broadening factors, while the lens size is the most important one. The experimental spectra fitted by multiple Gaussian distributions reveal that the Stark splitting and its full width at half maximum (FWHM) are ～0.07 nm and ～0.19 nm, respectively. Therefore, the π and σ components of the MSE will overlap since the Stark splitting is much smaller than its spectral broadening. A narrowband filter with the FWHM of about 0.16 nm is good enough to isolate the two components for providing the polarization fraction over 50%, which guarantees reasonable measurement precision for magnetic field pitch angle.

The synergy current driven by combined lower hybrid wave (LHW) and electron cyclotron wave (ECW) in two different polarizations is studied. It is shown that improvement of the current drive efficiency can be obtained during the synergy current drive, using either the fundamental ordinary mode (1O-mode) or the second harmonic extraordinary mode (2X-mode) ECW. Detailed comparison of using the two modes reveals that the 1O-mode is more effective than the 2X-mode. It is also found that the synergy current driven by LHW and 2X-mode ECW is more likely to become negative when the power of ECW is higher than that of LHW.

Nonlinear dependence of the synergetic current by the combined effect of electron-cyclotron current drive (ECCD) and lower-hybrid current drive (LHCD) on the power ratio is shown through the recent simulation research based on common parameters on HL-2A tokamak. Corresponding experiments have been demonstrated on HL-2A tokamak and these experimental results verify qualitatively the simulated ones.

Hydrogen is produced by direct dissociation of water vapor, i.e., splitting water molecules by the electrons in water plasma at low pressure (<10–50 Torr) using microwave plasma discharge. This condition generates a high electron temperature, which facilitates the direct dissociation of water molecules. A microwave plasma source is developed, utilizing the magnetron of a microwave oven and a TE_{10} rectangular waveguide. The quantity of the generated hydrogen is measured using a residual gas analyzer. The electron density and temperature are measured by a Langmuir probe, and the neutral temperature is calculated from the OH line intensity.

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

The structural and electronic properties of undoped and Ag-doped unpassivated wurtzite GaAs nanowires (NWs), as well as their stability, are investigated within the first-principles frame. The calculated formation energies show that the single Ag energetically prefers to substitute the surface Ga (E_{f}=?0.529 eV) under As-rich conditions, and creates a much shallower (0.19 eV above the Fermi) acceptor level, which is of typical p-type character. With the increase in the Ag concentration, the p-type behavior gradually weakens and the n-type character arises. Thus, one can expect to synthesize Ag-doped GaAs NWs for p-type or n-type applications by controlling their Ag concentration and microarrangement.

Using first-principles calculations, we investigate the structural, electronic and hydrogenated properties of the hexagonal BC_{7} sheet. The computed energy bands and density of states indicate that the BC_{7} sheet is a metal, and its metallicity mainly originates from the non-bonding p_{z} electrons of the diagonal carbon of the B atom. When these carbon atoms are fully passivated by H atoms, the BC_{7} sheet becomes a semiconductor with a band gap of 2.41 eV. Our studies demonstrate that changing both the proportion of the boron atoms in the boron carbon sheet and its hydrogenation can tune the electronic properties of boron carbon two-dimensional material.

We address the effects of various deformation modes, equibiaxial tension, uniaxial tension and pure shear on the energy diagrams and stability restrictions of a dielectric elastomer (DE) generator. It is shown that the stability restrictions, as well as the maximum energy that can be converted, are deformation-dependent. DE generators working under the pure shear state can avert electromechanical instability provided that tensile stress prevails over the membrane. The energy output in the pure shear state is lower than that of equibiaxial tension, but much higher than that of uniaxial tension.

NbH_{2} hydride is an important material in hydrogen storage materials. However, until now there have been no experimental and theoretical data on the elastic and thermodynamic properties. The structure and thermodynamic properties of cubic-NbH_{2} under high temperatures and pressure are investigated by first-principles study based on the pseudo-potential plane-wave density functional theory method using the generalized gradient approximation and quasi-harmonic Debye model. The results show that the calculated structural parameters of NbH_{2} are in good agreement with the available experimental results and other theoretical data. The obtained elastic constants satisfy the requirement for mechanical stability, indicating that the NbH_{2} crystal is stable in the investigated pressure and temperature ranges. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the thermodynamic properties of NbH_{2}, such as the thermal expansion coefficient and the heat capacity dependence of temperature and pressure in the ranges 0–1100 K and 0–70 GPa, are also obtained, respectively.

Shock compression experiments on a new kind of 47Zr45Ti5Al3V alloys at pressures between 28 and 200 GPa are performed using a two-stage light gas gun. The Hugoniot data are obtained by combining the impedance-match method and the electrical probe technique. The relationship between the shock wave velocity U_{s} and particle velocity u_{p} can be described linearly by U_{s}=4.324(±0.035) +1.177(±0.012) u_{p}. No obvious evidence of phase transition is found in the shock compression pressure range. The calculated U_{s}?u_{p} relationship obtained from the additive principle is different from the experimental data, indicating that the α→β phase transition occurs below 28 GPa. The Grüneisen parameter γ obtained from the experimental data can be expressed by γ=1.277(ρ_{0}/ρ). The zero-pressure bulk modulus B_{0s}=97.96 GPa and its pressure derivative B'_{0s}=3.68. The P–V–T equation of state for 47Zr45Ti5Al3V is given using the Vinet equation of state to describe the cold curve and the Debye model for the thermal contributions.

The adsorption behaviors of radioactive strontium and silver nuclides on the graphite surface in a high-temperature gas-cooled reactor are studied by first-principles theory using generalized gradient approximation (GGA) and local density approximation (LDA) pseudo-potentials. It turns out that Sr prefers to be absorbed at the hollow of the carbon hexagonal cell by 0.54 eV (GGA), while Ag likes to sit right above the carbon atom with an adsorption energy of almost zero (GGA) and 0.45 eV (LDA). Electronic structure analysis reveals that Sr donates its partial electrons of the 4p and 5s states to the graphite substrate, while Ag on graphite is a physical adsorption without any electron transfer.

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

The structural parameters, electronic structure, chemical bonding and optical properties of hexagonal LiIO_{3} are investigated in the framework of density functional theory. The calculated lattice parameters are in agreement with the previous experimental work. The band structure, density of states, and Mulliken charge population are obtained, and indicate that hexagonal LiIO_{3} has an indirect band gap of 2.81 eV. Furthermore, the optical properties are also calculated and analyzed in detail. It is shown that hexagonal LiIO_{3} is a promising dielectric material.

We theoretically study the quantum confinement effects on the self-energies of electrons and holes in quasi-one-dimensional semiconductor systems. It is found that the effective Coulomb interactions are enhanced with the increase in lateral confinement and the decrease in confinement size. The single-particle self-energies of electrons and holes are calculated in dynamic plasmon pole approximation within the GW approximation, where G refers to Green's function and W is the dynamically screened Coulomb interaction. The real and imaginary parts of the self-energies have a strong dependence on the effective Coulomb interactions.

A p-n junction composed of Ag^{+}-doped manganite La_{0.8}Ag_{0.2}MnO_{3}(LAMO) and Nb-0.5wt%-doped SrTiO_{3}(STON) was fabricated using the pulsed laser deposition method. The heterojunction exhibits a good rectifying property over a wide temperature range from 20 to 390 K. The minimum diffusion potential and the lowest leakage currents under different negative voltages both occur at 320 K, which is around the metallic-insulator transition temperature of the LAMO film. The photovoltage rises with the decreasing temperature and wavelength of the laser beam. Under the illumination of a 473 nm laser beam, the photovoltage grows as the light power increases and seems to be saturated at about 300 mW. The maximum V_{oc} is 0.76 V, which is close to the diffusion voltage.

The electron transport properties of a silicon atomic chain sandwiched between Au (100) leads are investigated by using the density functional theory combined with the non-equilibrium Green's function method. The breaking process of Au-Si_{4}-Au nanoscale junctions is simulated. The conductance and the corresponding cohesion energy as a function of distance d_{z} are obtained. With the increase of distance, the conductance decreases. When d_{z}=18.098 ?, there is a minimum value of cohesion energy. The nanoscale structure of junctions is most stable, and the equilibrium conductance is 1.71G_{0} (G_{0}=2e^{2}/h) at this time. The I–V curves of junctions at equilibrium position show linear characteristics.

We employ the first-principles technique based on the modified Becke–Johnson (BJ) exchange potential for the prediction of the electronic band structure, optical properties, and electron density of the cubic MgIn_{2}O_{4} spinel compound. It is found that the calculated band gap value with the modified BJ approximation is significantly improved over the results based on the generalized gradient approximation and the local density approximation in comparison to the experimental data. The band gap dependent optical parameters such as the dielectric constant, refractive index, reflectivity, optical conductivity, and electron density are predicted. The optical response suggests that MgIn_{2}O_{4} is an applicant material in optoelectronic devices in various parts of the energy spectrum like MgAl_{2}O_{4} and MgGa_{2}O_{4}.

High resolution laser-based angle-resolved photoemission measurements are carried out on Bi_{2}Sr_{2}CuO_{6+δ} superconductor covering a wide doping range from heavily underdoped to heavily overdoped samples. Two obvious energy scales are identified in the nodal dispersions: one is the well-known 50–80 meV high energy kink and the other is <10 meV low energy kink. The high energy kink increases monotonously in its energy scale with increasing doping and shows weak temperature dependence, while the low energy kink exhibits a non-monotonic doping dependence with its coupling strength enhanced sharply below T_{c}. These systematic investigations on the doping and temperature dependence of these two energy scales favor electron-phonon interactions as their origin. They point to the importance in involving the electron-phonon coupling in understanding the physical properties and the superconductivity mechanism of high temperature cuprate superconductors.

The laser damage resistances of four crystals (CaF_{2}, MgF_{2}, Al_{2}O_{3}, and SiO_{2}) and fused silica (JGS1) irradiated at 355 nm (8 ns, 300-on-1) are reported. The laser-induced damage threshold is measured using a tripled Nd:YAG laser system. The results obtained from the pure crystals are in accordance with their specific optical, mechanical, and thermal properties. An empirical law based on the Franz–Keldysh effect can interpret the experimental results.

The giant magnetoimpedance (GMI) effect and effective permeability ratio in a QFR/Cu/QFR sandwiched structure are studied, where QFR stands for the as-quenched FeNiCrSiB amorphous ribbon. Remarkable GMI effects are obtained in the QFR/Cu/QFR sandwiched structure without annealing. The maximum values of the longitudinal and transverse GMI ratios at 0.5 MHz are 282% and 408%, respectively. Correspondingly, the maximum effective permeability ratios at 0.5 MHz are 326% and 1013% in longitudinal and transverse field, respectively. These large GMI values are attributed to the high effective permeability of the sample due to the closed alternating current (ac) magnetic flux path in the sandwiched structure, and large permeability variation induced by the magnetic field.

A series of silicon nanoporous pillar array (Si-NPA) samples are prepared with different times of hydrothermal etching, and their surface morphologies are characterized. A systematic study on the evolution trend of the surface photovoltage and photoluminescence spectra discloses that the adoption of a prolonged etching time will increase the native degree of oxidation and decrease the interfacial states density localized in the SiO_{x} matrix. These results might be helpful for designing Si-NPA-based semiconductor nanosystems with optimized physical properties.

The polarized Raman spectra of deuterated potassium dihydrogen phosphate crystals with different deuterium concentrations are measured. With the increasing deuterium concentration, the Raman peaks which are assigned as the internal vibrations of the (H/D)_{2}PO_{4}^{?} anion shift to lower wavenumbers. This red-shift contributes to the decrease in the bonding force of the P–O bond as a result of the substitution of deuterium for hydrogen. Moreover, the intensity of the strongest peak of these crystals decreases first, and reaches the minimum value while the mole percentage of the deuterium content in the crystal is about 74%. After that, the intensity increases with the increase of the deuterium concentration in the crystal.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

We demonstrate InAs/InGaAsP/InP quantum dot (QD) lasers grown by metalorganic chemical vapor deposition. The active region of the lasers consists of five layers of InAs QDs. Ridge waveguide lasers with 6 μm width have been fabricated by standard optical lithography and wet etching. Under continuous wave operation at room temperature, a low threshold current density of 447 A/cm^{2} per QD layer is achieved for a QD laser with a cavity length of 2 mm. Moreover, the lasing redshifts from 1.61 μm to 1.645 μm as the cavity length increases from 1.5 mm to 4 mm. A high characteristic temperature of up to 88 K is obtained in the temperature range between 10°C and 40°C.

An indirect imager working at terahertz band is presented and implemented, which is suitable for high-resolution planar object detection. The proposed imager employs a simple quasi-optics design to transmit and to receive terahertz waves, and adopts incoherent detection technology to extract the intensity of echoed signal, which results in a relatively low complexity and cost. Moreover, the Fienup Fourier phase-retrieval algorithm is successfully modified and is applied to retrieve the phase of the echoed signal and reconstruct the target image. Imaging experiments on typical planar objects are performed with the imager working at 0.2 THz, and the experimental results demonstrate the good performance of the proposed imager and validate the effectiveness of the reconstruction algorithm.

Metalorganic chemical vapor deposition of a crack-free mirror-like surface of InGaN/GaN MQWs on Si (111) substrate is demonstrated, and an InGaN/GaN MQWs solar cell device is fabricated. Photo response measurement of the solar cell devices shows that the fill factor FF = 49.4%, open circuit voltage V_{oc}=0.32 V, and short circuit current J_{sc}=0.07 mA/cm^{2}, under AM 1.5 G illumination. In order to analyze the influence of material quality on the performance of solar cells, XRD, SEM and Raman scattering experiments are carried out. It is found that insertion of a proper top AlN layer can effectively improve the material quality, and therefore enhance the photovoltaic performance of the fabricated device.

The effects of a polarization field on the current transport mechanisms in ultraviolet light emitting diodes (UV-LEDs) are studied by analyzing forward current-voltage (I–V) characteristics based on the experimental data and theoretical simulation. The results indicate that polarization electric field suppresses the diffusion current and meanwhile enhances the tunneling current in the metal-face UV LEDs under forward bias. The presence of a large polarization field in the deep UV-LEDs is responsible for the current transport mechanism dominated by the tunneling process at a moderate forward bias.

The asymmetric underlap device for a floating body cell is proposed without any extra process or photomask during fabrication. The electric field in the gate-drain underlap region is quietly relaxed. It is found that memory operation would fail in bipolar-based floating body cells because band-to-band tunneling significantly alters the body potential. Measurements show the proposed structure could indeed suppress the undesirable band-to-band tunneling greatly so that the bistable state via the parasitic bipolar junction transistor is ensured in scaled floating body cells. The parasitic capacitances in both word line and bit line are also reduced.

A Microcantilevers resonator is used to detect a protein biomarker called prostate specific antigen (PSA), which is associated with prostate cancer. Different concentrations of PSA in a buffer solution are detected as a function of deflection of the beams. For this purpose, we use a surface micromachined, antibody-coated polycrystalline silicon micromechanical cantilever beam. Cantilevers have mass sensitivities of the order of 10–17 g/Hz, which result from their small mass. This matter allows them to detect an immobilized antibody monolayer corresponding to a mass of about 70 fg. With these devices, concentrations as low as 150 fg/mL, or 4.5 fM, could be detected from the realistic samples.

We apply electric fields at different frequencies of 0.1, 1, 10 and 100 kHz to the rat basophilic leukemia (RBL) mast cells in calcium-containing or calcium-free buffers. The stimuli cause changes of the intracellular calcium ion concentration [Ca^{2+}]_{i} as well as the histamine. The [Ca^{2+}]_{i} increases when the frequency of the external electric field increases from 100 Hz to 10 kHz, and then decreases when the frequency further increases from 10 kHz to 100 kHz, showing a peak at 100 kHz. A similar frequency dependence of the histamine release is also found. The [Ca^{2+}]_{i} and the histamine releases at 100 Hz are about the same as the values of the control group with no electrical stimulation. The ruthenium red (RR), an inhibitor to the TRPV (transient receptor potential (TRP) family V) channels across the cell membrane, is used in the experiment to check whether the electric field stimuli act on the TRPV channels. Under an electric field of 10 kHz, the [Ca^{2+}]_{i} in a calcium-concentration buffer is about 3.5 times as much as that of the control group with no electric stimulation, while the [Ca^{2+}]_{i} in a calcium-free buffer is only about 2.2 times. Similar behavior is also found for the histamine release. RR blockage effect on the [Ca^{2+}]_{i} decrease is statistically significant (～75%) when mast cells in the buffer with calcium are stimulated with a 10 kHz electric field in comparison with the result without the RR treatment. This proves that TRPVs are the channels that calcium ions inflow through from the extracellular environment under electrical stimuli. Under this condition, the histamine is also released following a similar way. We suggest that, as far as an electric stimulation is concerned, an application of ac electric field of 10 kHz is better than other frequencies to open TRPV channels in mast cells, and this would cause a significant calcium influx resulting in a significant histamine release, which could be one of the mechanisms for electric therapy.

Photo-generated charge collection is strongly correlated with the alignment and connectivity of the individual domains of donor and acceptor in bulk heterojunction polymer solar cells. It is found that CS_{2} vapor annealing on PCDTBT:PC_{71}BM (1:4) blend effectively improves the hole-transport pathways of PCDTBT domains, which reduces accumulation of photo-generated charges and improves charge collection efficiency. The PCDTBT:PC_{71}BM-based solar cells with the active layer subjected to CS_{2} vapor annealing demonstrate a high fill factor of 0.71–0.73 and a power conversion efficiency of 6.68%, about a 10% increase in comparison with the control cell.

The generalized f(R) gravity with coupling in five-dimensional (5D) spacetime is studied on the basis of both the 4D generalized f(R) gravity with coupling and the pure f(R) gravity without coupling in 5D spacetime. Specifically, by assuming a hypersurface-orthogonal space-like Killing vector field in 5D spacetime, the generalization of the 4D generalized f(R) gravity to 5D can be realized, which can give the reduced 4-metric coupled with two scalar fields. In particular, we discuss a special class of models, i.e., f_{1}(R)=f_{2}(R)=αR^{m} (m≠1), and choose B(L_{m})=L_{m}=?ρ in the homogeneous and isotropic cosmology with the 4D Friedmann–Robertson–Walker metric. The numerical analysis shows that the parameter m can be constrained by means of the current observations for the deceleration parameter, which implies that this generalized f(R) model with coupling in 5D spacetime can account for the present accelerated expansion of the universe.