Conductivity of a periodic two-component system of rhombic type

The conductivity and the distribution of electric field, current, and charge density in a periodic two-component system composed of rhombs with an arbitrary vertex angle of 2α are investigated. The effective conductivity of such a medium is represented by a tensor with components σ _eff ¹¹ (α) and σ _eff ²² (α) in the principal axes that satisfy the Dykhne relation σ _eff ¹¹ (α) σ _eff ²² (α)=σ ₁σ₂, where σ₁, σ₂ are the isotropic conductivities of media 1 and 2. In addition, the relation σ _eff ²² (α)=σ _eff ¹¹ (π/2?α) is satisfied. The principal axes are directed along the diagonals of the rhombs. It is shown that there are three lines in the rectangle 0<α ≤π/2,?1<Z<1((Z=σ₁?σ₂)/(σ ₁+σ₂)) on which the charge density is expressed in terms elliptic functions. An explicit expression is obtained for all physical quantities on these lines.     

Frequency and amplitude alterations of sound modes in a space-dependent random mass density field

We investigate the effect of a space-dependent random mass density field on small amplitude acoustic modes that are settled in a semi-infinite medium of a temperature growing linearly with depth. Using a perturbation method, the dispersion relation is derived in the form of Hill's determinant. Numerical solutions of this equation lead to the following conclusions: (a) a weak random field (with σ_eff = 0.05) essentially affects long waves which experience attenuation and a frequency reduction; (b) for a stronger random field (with σ_eff = 0.1), high-order sound modes behave as sound waves as they are attenuated and their frequencies are increased; (c) for a sufficiently strong random field (with σ_eff = 0.2), mode coupling occurs, as a result of which the dispersive curves cross each other, the sound modes loose their identities, and some modes are amplified. Here σ_eff denotes the effective strength of a random field.     

Magnetoelastic waves in an in-plane magnetized ferromagnetic plate

The spectrum of magnetoelastic waves propagating along the magnetic field in an in-plane magnetized ferromagnetic plate is numerically investigated in the exchangeless approximation. No restrictions are imposed either on the field pattern of backward volume magnetostatic waves (BVMSWs) or elastic waves supported by a plate of a given geometry across the plate or on the relationship between the sound velocity v _S and the phase velocity of the magnetoelastic waves v=ω/q (ω is the frequency, q is the wave number). The resonance interaction of the BVMSWs and elastic waves is accompanied, as a rule, by the formation of “stop” bands δω that are proportional to the magnetoelastic coupling constant b. When the BVMSWs are in resonance with Lamb and shear elastic modes the values of the magnetoelastic gaps δω at v≈v _S turn out to be of the same order. For v≫v _S , the efficiency of the interaction between the BVMSWs and transverse Lamb modes is almost one order of magnitude higher. If the frequency spacing Δω between the elastic modes is smaller than the mag-netoelastic gap in the spectrum (Δω≤δω), which takes place, particularly, in the region of crowding the elastic mode spectrum (v≈v _S), the resonant interaction results in mixing the dispersion laws for the elastic modes. Namely, a surface mode may transform into a volume one and a shear mode, into the Lamb mode or into a shear mode with another number. The resonance interaction of the shear and Lamb elastic modes not only forms the magnetoelastic gaps δω∼b ² but also changes the efficiency of elastic wave coupling with the magnetic subsystem. This may show up as the coexistence of the effects of “repulsing” both the dispersion laws and the damping decrements of the elastic waves at the resonance frequency. It is shown that magnetostriction splits the cutoff frequencies of both transverse Lamb modes and shear modes, as well as the long-wave (q → 0) frequency limits f ₀ of the BVMSW modes. This may cause the resonance interaction between BVMSW modes of equal evenness in a narrow frequency band Δ∼b near f ₀.     

Phantom expansion with non-linear Schrödinger-type formulation of scalar field cosmology

We describe non-flat standard Friedmann cosmology of canonical scalar field with barotropic fluid in form of non-linear Schrödinger-type (NLS) formulation in which all cosmological dynamical quantities are expressed in term of Schrödinger quantities as similar to those in time-independent quantum mechanics. We assume the expansion to be superfast, i.e. phantom expansion. We report all Schrödinger-analogous quantities to scalar field cosmology. Effective equation of state coefficient is analyzed and illustrated. We show that in a non-flat universe, there is no fixed w _eff value for the phantom divide. In a non-flat universe, even w _eff > ?1, the expansion can be phantom. Moreover, in open universe, phantom expansion can happen even with w _eff > 0. We also report scalar field exact solutions within frameworks of the Friedmann formulation and the NLS formulation in non-flat universe cases.     

A Light and X‐Ray Scattering Study of Aqueous Micellar Solutions of a Diblock Copolymer of Propylene Oxide and Ethylene Oxide with Solubilized Alkylcyanobiphenyl Liquid Crystals

Abstract

The temperature and concentration dependences of the physicochemical properties of aqueous solutions of the diblock copolymer P₄₃E₃₁₂ (P = oxypropylene, E = oxyethylene) with solubilized liquid crystal (LC) have been studied using static and dynamic light scattering (SLS and DLS), small‐angle x‐ray scattering (SAXS), and ultraviolet (UV) spectroscopy. Relaxation time distributions from DLS obtained from inverse Laplace transformation of intensity correlation functions are multimodal, where the two fastest modes are attributed to diblock copolymer unimers and micelles, respectively. The remaining modes at longer decay times reflect the presence of free LC with hydrodynamic radii (R _h) of hundreds of nm. The R _h of both unimers and micelles were independent of temperature (T), while the hydrodynamic virial coefficient k _D and the second virial coefficient, A ₂, decreased with increasing T. The UV spectroscopy measurements showed that there is a reduction in the amount of solubilized LC per gram of copolymer (c _s) as the copolymer concentration (c _p) is increased. The SAXS results agree well with a model of a homogeneous system of polydisperse interacting hard spheres. In solution, both the effective micellar radius of interaction (R _eff) and the hard‐sphere micellar radius (R¯_s) increase in the presence of LC due to solubilization of the latter in the hydrophobic micellar core. Both SAXS and SLS results show that intermicellar interactions become important at c _p > 1% (w/w) at high temperatures [T > the critical micelle temperature (cmt)].     

Mössbauer spectroscopic studies of spin crossover in tris(N, N′-dialkyldithiocarbamato) iron (III) complexes: effect of alkyl substituents

Spin crossover behavior in tris(N,N′-dialkyldithiocarbamato) iron(III) complexes with varying alkyl groups has been studied by variable temperature magnetic moment and Mössbauer spectral studies. All the complexes may be divided into three broad groups; high spin (μ _eff > 4.8 BM), intermediate spin (μ _eff?=?3.5???4.6 BM) and low spin (μ _eff?< 3.2 B.M). Room temperature (RT) Mössbauer spectra exhibit an asymmetric doublet resolved into two doublets corresponding to high and low spin states. Estimated % contributions of HS and LS states and calculated μ _eff were comparable with the experimentally determined values. It has been shown that some complexes undergo spin crossover, ⁶A₁g→²T₂g whereas others exhibit spin transitions ⁶A₁g →⁴T₁g or ⁴T₁g → ²T₂g. IR spectra show characteristic ν _(Fe???S) bands in the region 208–285 (HS) and 311–380 cm^???1 (LS). Nature of alkyl groups affects the spin state.     

Preparation, Structure and Near-infrared Luminescent Property of Yb(III) Complex with 2,4,6-Pyridinetricarboxylic Acid

A rare earth ytterbium complex with 2,4,6-pyridinetricarboxylic acid (H₃pta) has been synthesized by hydrothermal method, the formula is {[Yb₂(pta)₂(H₂O)₃]·H₂O}_n. The complex crystallized in monoclinic system, P2₁/c space group with lattice parameters a?=?11.6556(19)Å, b?=?7.8364(12), c?=?22.020(4), α?=?γ?=?90º, β?=?92.120(3), Z?=?4, GOF?=?1.026, R1?=?0.0334, wR2?=?0.0660. The pta anions connect four rare earth Yb(III) ions with two different coordination modes. The complex exhibit intense characteristic near-infrared luminescence of Yb(III) ions at 990 nm with excitation of UV-rays.     

Angular reflectance of suspended gold, aluminum and silver nanospheres on a gold film: Effects of concentration and size distribution

In this article, we describe a parametric study of the effects of the size distribution (SD) and the concentration of nanospheres in ethanol on the angular reflectance. Calculations are based on an effective medium approach in which the effective dielectric constant of the mixture is obtained using the Maxwell–Garnett formula. The detectable size limits of gold, aluminum, and silver nanospheres on a 50-nm-thick gold film are calculated to investigate the sensitivity of the reflectance to the SD and the concentration of the nanospheres. The following assumptions are made: (1) the total number of particles in the unit volume of suspension is constant, (2) the nanospheres in the suspension on a gold film have a SD with three different concentrations, and (3) there is no agglomeration and the particles have a log-normal SD, where the effective diameter, d _eff and the effective variance, ν _eff are given. The dependence of the reflectance on the d _eff, ν _eff, and the width of the SD are also investigated numerically. The angular variation of the reflectance as a function of the incident angle shows a strong dependence on the effective size of the metallic nanospheres. The results confirm that the size of the nanospheres (d _eff <100 nm) can be detected by reflected light from the bottom surface of a gold film with a reasonable sensitivity if a proper angle of incidence is chosen based on the type of metallic particles on a gold thin film at λ = 632 nm. We show that the optimum incident angle to characterize the size of nanospheres on a gold film is between 70° and 75° for a given concentration with a particular SD.     

Low-frequency dispersion of the effective transverse conductivity in inhomogeneous media in strong magnetic field

On crystalline silicon specimens with a nonuniform carrier concentration distribution produced by an optical method, a dispersion of the effective transverse conductivity σ _⊥ ^eff (ω) is observed near the frequency ω≈ω_c=τ _⊥ ^?1 ≡ε/4πσ _⊥ ^eff . At ω<ω_c, an anomalous transverse effective conductivity is observed: σ _⊥ ^eff (ω) is greater than the transverse conductivity of a homogeneous specimen σ _⊥ ^h (ω) (in the frequency range studied in the experiment σ _⊥ ^h (ω) = const). Near ω≈ω_c, the conductivity σ _⊥ ^eff decreases, and, at ω>ω_c it coincides with σ _⊥ ^h .     

Numerical study of dumbbell-shaped gold nanoparticles using in plasmonic waveguides in near infra-red spectrums

In this paper, we investigated plasmonic waveguides in near infra-red spectrum using dumbbell-shaped gold nanoparticles. It is possible to shift localized surface plasmon resonance (LSPR) to the desired wavelength with proper geometrical properties. 3-D FDTD simulations are used to determine the set of geometrical parameters of nanoparticles to obtain LSPR at 1310 and 1550 nm. Employing different configuration of nanoparticles chains, we not only can design waveguides with better optical characteristics but also achieve the demultiplexing function in V-form arrays. The proposed nanoparticles show sharp resonance peak, 168 FWHM bandwidth for λ?=?1310, and 204 nm for λ?=?1550 nm. Linear chains of particles can transport the electromagnetic energy at λ?=?1310 nm, with transmission losses γ_L?=?3 dB/452 and γ_T?=?3 dB/446 nm and group velocities v_gL?=?0.336C₀ and v_gT?=?0.256C₀ for longitudinal and transverse polarizations, respectively, where C₀ is the speed of light in the vacuum. At λ?=?1550 nm, γ_L?=?3 dB/490, γ_T?=?3 dB/604, v_gL?=?0.382C₀ and v_gT?=?0.260C₀. Moreover, we attained 8.13 as minimum ratio of averaged electric field intensity and 36.8 as minimum ratio of averaged Poynting vector as a function of position between two ports in demultiplexing function.     

Effect of magnetic field on the sound velocity of a dilute Kramers-ion glass at low temperature

Recent results on the effect of magnetic field on the sound velocity V in aluminosilicate glasses doped with dysprosium are analyzed on the basis of a minimal model for the ground state of Dy³⁺ (Kramers ion with J=15/2) described by a wave function ϕ _± = ϕ _± J _m + ηϕ _{± 1/2}. The first term represents a state with a large J projection on the local crystal field axis and the random parameter η(〈η〉=0, 〈η ²〉≪1) introduces a small admixture of the state ϕ _±1/2 into the ground state. The relative variation of V due to the resonance interaction of sound waves with this state split by H is determined as a function of H and T. It possesses a universal asymptotic behavior. Our results are in reasonable agreement with the experiment. A possible structure of the crystal fields that can induce this state is discussed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 4, 341–346 (25 February 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

First-principles study of structural,mechanical, lattice dynamical and thermal properties of nodal-line semimetals ZrXY (X=Si,Ge; Y=S,Se)

Abstract

The nodal-line semimetals are new and very promising materials for technological applications. To understand their structural, mechanical, lattice dynamical and thermal properties in detail, we have investigated theoretical study of ZrXY (X = Si,Ge; Y = S,Se) using Density Functional Theory for the first time. Obtained lattice parameters are in excellent agreement with previous experimental data. These nodal-line semimetals obey the mechanical stability conditions for tetragonal structure. We obtain Bulk modulus, Shear modulus, Poisson’s ratio, Pugh ratio, sound velocities and thermal conductivity using elastic constant. All the materials behave in brittle manner. Poisson’s ratio data and Bader charge analysis results indicate that the ionic bonding characters are dominant. Next, the lattice dynamical properties are calculated. Phonon density of states shows that nodal-line semimetals ZrXY are also dynamically stable in the tetragonal structure. Raman and IR active phonon modes are determined. Highest optical mode at gamma point corresponds to A_2u (IR active) and E_g (Raman active) modes for ZrXSe and ZrXS, respectively. Based on phonon density of states, thermal properties such as Helmholtz free energy, entropy, heat capacity at constant volume and Debye temperature are also presented and discussed.     

On the effective cross-section for recombination of free carriers with dipole centres

An approximate calculation of the effective cross-section for recombination δ_eff of free charge carriers with dipole centres for small mean path lenght l of free carriers and not very small gas-kinetical cross-section of recombination σ_k is conducted. A formula for the σ_eff suitable also for larger l and small σ_k is suggested.     

X-ray structure refinement,vibrational spectroscopy,and ionic conductivity of Na0.11Ca9.64Sm0.23(PO4)6F2

The present paper is interested in the study of compounds from the apatite family, which is an apatite structure of individual rare earth substituted fluorapatite. In fact, an Sm-Bearing fluorapatite Ca_10–2yNa_ySm_y(PO₄)₆A₂ with x?=?0.11 and y?=?0.23 has been synthesized by solid-state reaction and characterized by X-ray powder diffraction. The site occupancies of substituents are 0.01091 for Sm and 0.02601 for Na in the Ca(1) position and 0.05317 for Sm in the Ca(2) position. Besides, the observed frequencies in the Raman and infrared spectra were explained and discussed on the basis of unit cell group analyses and in comparison with fluorapatite and other fluorapatites. In addition to the proton conduction, the possibility of a Na⁺ contribution to the conductivity in the high-temperature phase is proposed. The highest overall conductivity values were found at σ_{475 °C}?=?2.03?×?10^?5 S cm^?1 and Ea?=?0.60 eV.     

Measurements of light scattering by a characterized random rough surface

Abstract

Measurements are presented of the angular distribution of four wavelengths of light scattered by a one-dimensional random rough surface, whose probability density function is Gaussian with a standard deviation σ=1.22±0.02 μm and whose lateral correlation function is also Gaussian with 1/e width τ=3.17±0.07 μm. The wavelengths used are 0.63, 1.15, 3.39 and 10.6 μm. The surface is used in two forms: coated with gold and as an almost lossless dielectric. The results are compared to those predicted by a double scattering form of the Kirchhoff formulation. Agreement is good at small angles of incidence but less good at larger angles of incidence.     

Laser-induced periodic surface structures on polymers for formation of gold nanowires and activation of human cells

Frequently observed coherent structures in laser-surface processing are ripples, also denoted as laser-induced periodic surface structures (LIPSS). For polyethylene terephthalate (PET) and polystyrene (PS), LIPSS can be induced by irradiation with linearly polarized ns-pulsed UV laser light. Under an angle of incidence of θ, their lateral period is close to the laser wavelength λ divided by (n _eff ? sinθ). Here, n _eff is the effective refractive index which is 1.32 and 1.23 for PET and PS, respectively. We describe potential applications of LIPSS for alignment and activation of human cells cultivated on polymer substrates, as well as for formation of separated gold nanowires which show pronounced surface plasmon resonances, e.g., at 775 nm for PET.     

Nonlinear coefficient and temperature dependence of the refractive index of lithium niobate crystals in the terahertz regime

The effective nonlinear coefficient d _eff of lithium niobate is determined to be 94 pm/V for a process that converts infrared light to 1.35 THz radiation. This value is inferred from the performance of a continuous-wave, singly-resonant optical parametric oscillator, in which the cavity-enhanced signal wave of a primary parametric process acts as a pump wave for a cascaded process, generating terahertz waves. To quantify the nonlinear coefficient, the coupled wave equations including absorption are evaluated. Furthermore, from our measurements we also determine the temperature dependence of the refractive index to be dn _THz/dT=0.0013/K around 1.4 THz.     

Photovoltaic properties of ZnO photoanode incorporating with CNTs for dye-sensitized solar cell application

Zinc oxide carbon nanotube (ZnO-CNTs) thin films were prepared by a chemical bath deposition (CBD) method and immersed in N719 dye for 24 h. The structure and surface morphology of the samples was captured by X-ray diffraction (XRD) and field effect scanning electron microscopy (FESEM) unit, respectively. The photovoltaic properties of ZnO- and ZnO-CNT-based dye-sensitized solar cells (DSSCs) were measured by considering the power conversion efficiency (η), photocurrent density (J _sc), open-circuit voltage (V _oc), and fill factor (FF). The cell's efficiency doped with single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) reached 0.65 and 0.28 %, respectively. ZnO-based DSSC generated only η?=?0.003 %. The electrochemical impedance spectroscopy (EIS) unit was employed to investigate the electron transport properties such as effective electron lifetime (τ _eff), effective electron chemical diffusion coefficient (D _eff), and effective electron diffusion length (L _n ). The addition of CNTs has enhanced the photovoltaic properties of the DSSCs and reduced the recombination effect inside the solar cell.     

One-dimensional numerical simulations of random sound impulses

Abstract

We perform one-dimensional numerical simulations of small-amplitude acoustic pulses in space- and time-dependent random mass density and time-dependent velocity fields. Numerical results reveal that: (a) random fields affect the speeds, amplitudes and, consequently, shapes of sound pulses; (b) for weak random fields and short propagation times the numerical data converge with the analytical results of the mean field theory which says that a space-dependent (time-dependent) random field leads to wave attenuation (amplification) and all random fields speed up sound pulses; (c) for sufficiently strong random fields and long propagation times numerical simulations reveal pulse splitting into smaller components, parts of which propagate much slower than a wave pulse in a non-random medium. These slow waves build an initial stage of a wave localization phenomenon. However, this effect can be very weak in a real three-dimensional medium.