Higher Dimensional Cosmology with Normal Scalar Field and Tachyonic Field

We have considered N-dimensional Einstein field equations in which four-dimensional space-time is described by a FRW metric and that of extra dimensions by an Euclidean metric. We have supposed that the higher dimensional anisotropic universe is filled with only normal scalar field or tachyonic field. Here we have found the nature of potential of normal scalar field or tachyonic field. From graphical representations, we have seen that the potential is always decreases with field φ increases.     

Field dependent specific heat and longitudinal magnetization of the quantum magnet layer Cs2CuCl4: Anisotropy effects

We have addressed the specific heat and magnetization of an anisotropic spin-1/2 triangular Heisenberg antiferromagnet Cs₂CuCl₄ in the presence of magnetic field at finite temperature. We have investigated the behavior of thermodynamic properties by means of excitation spectrum in terms of a hard core bosonic representation. The effect of in-plane anisotropy on thermodynamic properties has also been studied via the bosonic model by Green’s function approach. This anisotropy is considered for exchange constants that couple spin components perpendicular to magnetic field direction. We have found the temperature dependence of the specific heat and longitudinal magnetization in the gapped field induced spin-polarized phase for various magnetic fields and anisotropy parameters. Furthermore we have studied the magnetic field dependence of specific heat and magnetization for various anisotropy parameters. Our results show temperature dependence of specific heat includes a peak so that its temperature position goes to higher temperature with increase of magnetic field. We have found the magnetic field dependence of specific heat shows a monotonic decreasing behavior for various magnetic fields due to increase of energy gap in the excitation spectrum.     

Vector erf-Gaussian beams: fractional optical vortices and asymmetric TE and TM modes

We have considered the paraxial vector erf-Gaussian beams with field distribution in the form of the error function that are shaped by the cone of plane waves with a fractional step of the azimuthal phase distribution modulated by the Gaussian envelope. We have revealed that the initial distributions of the transverse electric and transverse magnetic fields have a far from standard form but at the far diffraction field the field distributions recover nearly the symmetric form.     

Quantum confined Stark effect in single self-assembled GaN/AlN quantum dots

We have experimentally and theoretically investigated quantum confined Stark effect in hexagonal self-assembled GaN/AlN quantum dots. We have observed a blueshift of up to 100 meV for vertical electric field applied against the built-in electric field while we have observed a redshift for the electric field along the built-in field. The experimental result is compared with a charge self-consistent effective mass calculation, taking into account strain, piezoelectric charge, and pyroelectric charge. The tunability of the emission energy and the exciton binding energy is discussed.     

Observation of phase-sensitive temporal correlations in the resonance fluorescence from two-level atoms

We have made what we believe is the first observation of phase-dependent temporal correlations in the fluorescent field emitted by coherently driven two-level atoms in free space. We measured the temporal fluctuations of the fluorescent field when the resonant driving field was in phase and out of phase with the local-oscillator field.     

Particle-like objects in a nonlinear field theory

We further discuss the field theory which we introduced in a previous paper. We find that it is possible for a component of the field to have a minimum at an arbitrary origin point as a consequence of the field equations.     

Effect of metallic nanoparticle sizes on the local field near their surface

We have used numerical calculations based on Mie theory to analyze the near field distribution patterns for 4–150 nm spherical silver nanoparticles (nanospheres). We have shown that as the nanoparticle sizes increase, the region where “hot spots” are concentrated is shifted to the forward hemisphere. We have observed a nonmonotonic dependence of the maximum attainable local field enhancement factor on the size of the silver nanospheres. We have determined a correlation between the optimal nanosphere size for the maximum attainable local field enhancement factor and the optical absorption efficiency factor. We have established a nonmonotonic dependence of the optimal size of the nanoparticles and the maximum attainable local field enhancement factor on the refractive index of the surrounding medium. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 831–837, November–December, 2008.     

The behavior of the critical current density below and above the first matching field in superconductors with periodic square arrays of pinning sites

We have studied the effect of the applied magnetic field on critical depinning force at zero and finite temperatures and for several values of pinning strength. This was achieved by conducting extensive series of molecular dynamic simulations on driven vortex lattices interacting with periodic square arrays of pinning sites. We have found that the critical depinning force decreases as the applied magnetic field is increased. We have also observed two distinct behaviors of dependence of the critical depinning force on the applied magnetic field below and above the first matching filed.     

Effect of interaction of electromagnetic fields with a resonant medium in epr when the saturating field is small compared with the local field

We propose a system of Bloch equations, modified to take into account the presence of a dipole-dipole reservoir (DDR), for the case when the saturating magnetic field is small compared with the local field. We take into account the transverse and longitudinal magnetizations in the equation for the DDR, in contrast to our previous papers in which we took into account only the longitudinal magnetization. Using the system obtained, we solve the problem of the interaction of three fields, where one is the saturating field, the second is the probe field, and the third is a combination field that is the result of the interaction of the first two fields in a resonant medium. We have studied the imaginary and real parts of the susceptibility of the system at the probe field frequency, both when the interacting waves have different frequencies and when they have matching frequencies (the degenerate case). We have compared the results with those we obtained previously. For the degenerate case, we consider the frequency dependence of the parametric coupling coefficient of the waves. We show that weak waves can be enhanced as they pass through a layer of a resonant absorbing medium. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 462–466, July–August, 2006.     

Photon sieve for reduction of the far-field diffraction spot size in the laser free-space communication system

In the free-space laser communication, there is sometimes a strong need for reduction of the diffraction spot size in the far field. In this paper, instead of the usage of the larger size aperture lens and super-resolution technology in the free-space laser communication system, we introduce photon sieve to compress the center spot in the diffractive far field, which can decrease the weight of the emitting lens. We have designed the photon sieve and calculated its far-field diffractive intensity. We have also calculated the far field Airy diffractive field intensity. Simulation proves that the photon sieve diffractive spot is smaller than the Airy spot with the same transmit aperture. We have set up an experimental system to simulate the far-field diffraction free-space laser communication. Experimental results are in good agreement with the theoretical results. Detailed experiments are presented.     

Analysis of antiferromagnetic resonance in KNiF3

We have compared theoretical calculations of the temperature dependence of the antiferromagnetic resonance field for KNiF₃, a cubic crystal, with the experimental data obtained by other authors. We have discussed the applicability to the cubic case of Kittel's equations for a uniaxial system. We have used experimental values from the literature for the magnetic susceptibilities and anisotropy in the expression for the antiferromagnetic resonance field.     

Effect of an electric field on photoluminescence of cadmium selenide nanocrystals

We have demonstrated a difference in the nature of the effect of a strong external electric field (>10⁵ V/cm) on the photoluminescence of cadmium selenide nanoparticles of different shapes. We have determined a correlation between the magnitude of the external electric field and the average photoluminescence decay time for two types of nanoparticles: "quantum dots" and nanorods. We discuss the mechanism for the effect of an electric field on the photoluminescence of both types of nanoparticles.     

Late-time acceleration and phantom divide line crossing with?non-minimal coupling and Lorentz-invariance violation

We consider two alternative dark-energy models: a Lorentz-invariance preserving model with a non-minimally coupled scalar field and a Lorentz-invariance violating model with a minimally coupled scalar field. We study accelerated expansion and the dynamics of the equation of state parameter in these scenarios. While a minimally coupled scalar field does not have the capability to be a successful dark-energy candidate with line crossing of the cosmological constant, a non-minimally coupled scalar field in the presence of Lorentz invariance or a minimally coupled scalar field with Lorentz-invariance violation have this capability. In the latter case, accelerated expansion and phantom divide line crossing are the results of the interactive nature of this Lorentz-violating scenario.     

Surface currents on a perfect conductor, induced by a magnetic dipole

An oscillating magnetic dipole located near a perfect conductor induces a current density on the surface of the metal. We have derived an expression for this current density, and studied its field line patterns for various orientations of the dipole moment. When the dipole moment is perpendicular to the surface, the field lines are circles which run clockwise and counterclockwise. For a linear dipole oriented parallel to the surface, the field line pattern is much more complex, and it contains singular points. When the dipole moment rotates in a plane parallel to the surface, the field lines are spirals. A field line spirals inward from infinity to some given point, after which it spirals outward back to infinity. We have also considered the Poynting vector of the electromagnetic field near the surface, and we found that its field lines can have singular points or exhibit a vortex.     

Orbital and epicyclic motion of charged test particles around non-rotating Einstein-Æther black holes

The study of charged test particle dynamics in the combined black hole gravitational field and magnetic field around it could provide important theoretical insight into astrophysical processes around such compact object. We have explored the orbital and epicyclic motion of charged test particles in the background of non-rotating Einstein-Æther black holes in the presence of external uniform magnetic field. We numerically integrate the equations of motion and analyze the trajectories of the charged test particles. We examined the stability of circular orbits using effective potential technique and study the characteristics of innermost stable circular orbits. We analyze the key features of quasi-harmonic oscillations of charged test particles nearby the stable circular orbits in an equatorial plane of the black hole, and investigate the radial profiles of the frequencies of latitudinal as well as radial harmonic oscillations in dependence on the strength of magnetic field, mass of the black hole and dimensionless coupling constants of the theory. We demonstrate that the magnetic field and dimensionless parameters of the theory have strong influence on charged particle motion around Einstein-Æther black holes.     

Band gap tuning of defective silicon carbide nanotubes under external electric field: Density functional theory

We have theoretically investigated the effect of applying longitudinal and transverse electric field on silicon carbide nanotubes with different orientations of Stone Wales defects. We found that each type of Stone Wales defects maintained different formation energy. We have also successfully proved that the orientation of Stone Wales defects in silicon carbide nanotubes response quite differently upon applying external electric field, whereas, two important and interesting phenomena were observed. First, the semiconductor-metal phase transition occurred in silicon carbide nanotubes as well as the three types of Stone Wales defects. However, clear band gap variations were observed in all silicon carbide nanotubes under study. Second, the band gap variations in pristine silicon carbide nanotubes and nanotubes with different orientations of Stone Wales defects have the same trend, even though all silicon carbide nanotubes have clear band gap values under different strengths of the applied external electric field. However, band gap tuning under longitudinal electric field is less significant compared to band gap tuning under the transverse electric field.     

Application of the short and long consecutive pairs model to the triplet-doublet interaction in molecular crystals

We have adapted the model of two consecutive pairs to the study of the triplet-doublet (T-D) interaction in molecular crystals. We have applied this model to the modulation of the photoconductivity in crystalline anthracene by a static magnetic field (MFE) and a microwave field (PDMR). We were able to reproduce, for the first time, quite perfectly two types of experiments with the same set of kinetic constants.     

Nonequivalent spectra of unpaired electrons in field and frequency modulation

We report a difference in the spectral lineshapes of continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy between field and frequency modulation. This finding addresses the long-standing question of the effect of modulation in EPR absorption. We compared the first-derivative EPR spectra at 1.1 GHz for lithium phthalocyanine crystals, which have a single narrow linewidth in the EPR absorption spectrum, using field and frequency modulation. The experimental findings suggest that unpaired electrons have different behaviors under perturbation due to field and frequency modulation.     

Significant reduction of the triggering electric field for half-metallicity in hydrogenated carbon nanotubes by optimized field direction

We have investigated the half-metallicity in hydrogenated carbon nanotubes under an electric field as a function of the electric field direction by using the density functional theory calculation. We found that the electric field required for the half-metallicity can be significantly reduced by controlling the field direction and the reduction rate increases with the nanotube diameter. The field direction effect can be understood in a simple model based on the electrostatic potential difference between the spatially-separated edges.     

Super Liouville black holes

We describe in superspace a classical theory of of two-dimensional (1,1) dilaton supergravity coupled to a super-Liouville field, and find exact super black hole solutions to the field equations that have non-constant curvature. We consider the possibility that a gravitini condensate forms and look at the implications for the resultant spacetime structure. We find that all such condensate solutions have a condensate and/or naked curvature singularity.