Bianchi Type V Magnetized String Dust Bulk Viscous Fluid Cosmological Model with Variable Magnetic Permeability

Bianchi Type V magnetized string dust bulk viscous fluid cosmological model with variable magnetic permeability, is investigated. The magnetic field is due to an electric current produced along x-axis. Thus the magnetic fields is in yz-plane and F ₂₃ is the only non-vanishing component of electromagnetic field tensor F _ij . To get the deterministic model in terms of cosmic time t, we have also assumed the condition ζ θ=constant where ζ the coefficient of bulk viscosity and θ the expansion in the model. The behaviour of the model in presence and absence of magnetic field and bulk viscosity and singularities in the model are also discussed.      

Bianchi Type-IX viscous fluid cosmological model in general relativity

Bianchi Type-IX viscous fluid cosmological model is investigated. To get a deterministic model, we have assumed the conditiona = b ^m(m is a constant) between metric potentials andη ∞θ whereη is the coefficient of shear viscosity andθ the scalar of expansion in the model. The coefficient of bulk viscosity (ς) is taken as constant. The physical and geometrical aspects of the model are also discussed.     

Bulk Viscous Bianchi Type V Cosmological Models with Decaying Cosmological Term Λ

We present bulk viscous Bianchi type V cosmological models with time-dependent cosmological term Λ. Exact solutions of Einstein field equations have been obtained by assuming shear scalar σ proportional to volume expansion θ. The coefficient of bulk viscosity is taken to be power function of energy density ρ or volume expansion θ. In these models cosmological term Λ come out to be negative. It is found that models obtained are expanding, shearing and non-rotating. They do not approach isotropy for large values of time t. Some observational parameters for the model have also been discussed.     

Bianchi Type <Emphasis Type="Italic">VI</Emphasis><Subscript>0</Subscript> Magnetized Barotropic Bulk Viscous Fluid Massive String Universe in General Relativity

A model of a cloud formed by massive strings is studied in the context of the usual general relativity. This model is used as a source of Bianchi type VI ₀ massive with magnetic field and bulk viscosity. To get a determinate model, we assume that the expansion (θ) in the model is proportional to the shear (σ) and also the fluid obeys the barotropic equation of state. The behaviour of the models from physical and geometrical aspects in presence and absence of magnetic field and bulk viscosity is discussed.     

Bianchi Type I Magnetized Barotropic Perfect Fluid Cosmological Model in General Relativity

Bianchi Type I barotropic perfect fluid cosmological model in presence of magnetic field, is investigated. To get the deterministic model, we have also assumed that σ ₁¹ α θ where σ ₁¹ is the eigen-value of shear tensor σ _i ^j and θ the expansion in the model. The behavior of the model in presence and absence of magnetic field and singularities in the model are also discussed.     

Electron screening in backward elastic scattering

Abstact: The elastic scattering cross sections, σ (E,θ), for the systems He+Ta and He+W have been measured at θ_lab=165° and E _lab=76.1 keV to 3.988 MeV using targets with a thickness of a few atomic layers. The results are smaller than the results given by the Rutherford scattering law, σ_R(E,θ), due to the effects of electron screening and can be described by σ(E,θ)/σ_R(E,θ)=(1+U_e/E)⁻¹, where U _e is an atomic screening potential energy. The deduced average value, U _e=28 ± 3 keV, is consistent with the Moliére- and Lenz-Jensen-models as well as electron binding energies. Received: 25 May 1998     

Bulk Viscous Bianchi Type I Cosmological Models with Time-Dependent Cosmological Term Λ

Bianchi type I cosmological models with time-varying cosmological constant Λ and bulk viscous fluid are investigated. Cosmic matter is chosen to obey a barotropic equation of state. Exact solutions of Einstein’s field equations are obtained assuming the volume expansion θ proportional to the eigen values of shear tensor σ _ij . Physical and kinematical properties of the models are discussed considering bulk viscosity to be a power function of matter density.     

μ + Knight shift and spin relaxation in indium single crystalKnight shift and spin relaxation in indium single crystal

μ ⁺ SR measurements have been performed in a single crystal indium sample between 12 K and 300 K with a stroboscopic μSR spectrometer. The muonic Knight shiftK _μ and the muonic depolarization rate σ were obtained for various angles θ between the tetragonal crystallinec-axis and the direction of the external field. The isotropic part ofK _μ is only weakly temperature dependent and is consistent with the estimated Pauli spin susceptibility value. At a temperature of 12 K the angular dependence ofM ₂ (the second moment of the field distribution at the muon, obtained from the measured σ(θ) values) allows a clear determination of the muon location — the symmetric tetrahedral site. The observed anisotropicK _μ cannot be explained by the dipoles at the In atoms responsible for the bulk magnetic susceptibility but probably originates from an anisotropic Pauli spin susceptibility.     

Bianchi Type V Universe Models with Specific Expansion Anisotropy

We investigate Bianchi type V cosmological models for perfect fluid source with time varying cosmological term Λ. We examine the possibility of cosmological models assuming the expansion anisotropy (the ratio σ/θ of the shear scalar σ to the volume expansion θ) to be a function of average scale factor R. The resulting models begin with initial anisotropy and approach isotropy at late times. Our models present an initial epoch with decelerating expansion followed by late time acceleration consistent with observations.     

Stability of QED Vacuum and 3+1 Dimensional Scattering Problem in the Presence of a Coulomb Scalar Potential and Vector Field

We show that, in the presence of a scalar field the range of the value of external field parameters a and b, at which corresponding Hamiltonian operator is hermitian, essentially wider than in its absence. It allows us to study precisely the question on stability of QED vacuum in the presence of a strong electric field of a point charge Z|e| and external scalar Coulomb field with respect to electron-positron pair production. Also, we consider the scattering of Dirac particle by the specified fields in 3+1 dimensions. The phase shift and wave functions are obtained exactly. We calculate the scattering amplitude in a quasi-classical approximation as a partial wave series. By means of figures obtained for the cross section σ(θ) in general and special cases, such as a≠b and a=b, we find that σ(θ) is not exactly symmetric about θ=π.     

Simulation study of random sequential adsorption of mixtures on a triangular lattice

Random sequential adsorption of binary mixtures of extended objects on a two-dimensional triangular lattice is studied numerically by means of Monte Carlo simulations. The depositing objects are formed by self-avoiding random walks on the lattice. We concentrate here on the influence of the symmetry properties of the shapes on the kinetics of the deposition processes in two-component mixtures. Approach to the jamming limit in the case of mixtures is found to be exponential, of the form: θ(t) ∼ θ_jam - Δθ exp(- t/σ), and the values of the parameter σ are determined by the order of symmetry of the less symmetric object in the mixture. Depending on the local geometry of the objects making the mixture, jamming coverage of a mixture can be either greater than both single-component jamming coverages or it can be in between these values. Results of the simulations for various fractional concentrations of the objects in the mixture are also presented.     

Energy landscapes, lowest gaps, and susceptibility of elastic manifolds at zero temperature

We study the effect of an external field on (1 + 1) and (2 + 1) dimensional elastic manifolds, at zero temperature and with random bond disorder. Due to the glassy energy landscape the configuration of a manifold changes often in abrupt, “first order”-type of large jumps when the field is applied. First the scaling behavior of the energy gap between the global energy minimum and the next lowest minimum of the manifold is considered, by employing exact ground state calculations and an extreme statistics argument. The scaling has a logarithmic prefactor originating from the number of the minima in the landscape, and reads ΔE ₁∼L ^θ[ln(L _z L ^{- ζ})]^-1/2, where ζ is the roughness exponent and θ is the energy fluctuation exponent of the manifold, L is the linear size of the manifold, and L_z is the system height. The gap scaling is extended to the case of a finite external field and yields for the susceptibility of the manifolds ∼L ^{2D + 1 - θ}[(1 - ζ)ln(L)]^1/2. We also present a mean field argument for the finite size scaling of the first jump field, h ₁∼L ^{d - θ}. The implications to wetting in random systems, to finite-temperature behavior and the relation to Kardar-Parisi-Zhang non-equilibrium surface growth are discussed. Received December 2000 and Received in final form April 2001     

Beta-gamma-gamma directional correlation in103Rh

β-γ-γ directional correlation studies for the cascades (i)β-rays ofE _max=0.12 MeV,γ-rays of 557 keV andγ-rays of 53 keV and (ii)β-rays ofE _max=0.21 MeV,γ-rays of 444 keV andγ-rays of 53 keV have been made. The triple correlation functionsW(θ) were obtained to beW(θ)=1+(−0.153±0.031)P ₂(cosθ)+(0.004±0.035)P ₄(cosθ) forβ-rays ofE _max 0.12 MeV→557→53 keV cascade andW(θ)=1+(0.163±0.042)P ₂(cosθ)+(−0.035±0.058)P ₄(cosθ) forβ rays ofE _max=0.21 MeV→444 keV→53 keV cascade. Spins and parities of the 650, 537 and 93 keV levels of¹⁰³Rh are deduced by triple angular correlation and the internal conversion coefficient studies. Multipolarities of the transitions are also determined.     

Influence of the reagent vibration on the stereo-dynamics of the reactions D- + H2 and H- + D2

Employing the quasi-classical trajectory method and the potential energy surface of Panda and Sathyamurhy [Panda A N and Sathyamurthy N 2004 J. Chem. Phys. 121 9343], the effect of the reagent vibration on vector correlation of the ion-molecule reactions D^- + H₂ and H^- + D₂ is studied at a collision energy of 35.7 kcal/mol. Four generalized polarization-dependent differential cross sections (2π/σ)(dσ₀₀/dω_t),(2π/σ)(dσ₂₀/dω_t),(2π/σ)(dσ₂₂/dω_t), and (2π/σ)(dσ₂₀/dω_t) are presented in the centre-of-mass reference frame, separately. At the same time, the effects on the product angular distributions P(θ_r), P(φ_r) and P(θ_r,φ_r) of the title reactions are also analysed. The calculated results show that the scattering tendencies of the product HD, the alignment and the orientation of j' sensitively depend on reagent molecule vibration.     

LRS Bianchi Type II Bulk Viscous Fluid Universe with?Decaying Vacuum Energy Density Λ

The present study deals with spatially homogeneous and locally rotationally symmetric (LRS) Bianchi type II cosmological models with bulk viscous fluid distribution of matter and decaying vacuum energy density Λ. To get the deterministic models of the universe, we assume that the expansion (θ) in the model is proportional to the shear (σ). This leads to condition R=mS ⁿ , where R and S are metric potentials, m and n are constants. We have obtained two types of models of the universe for two different values of n. The vacuum energy density Λ for both models is found to be a decreasing function of time and it approaches a small positive value at late time which is supported by recent results from the observations of (SN Ia). Some physical and geometric behaviour of these models are also discussed.     

Bianchi Type III Cosmological Models for Barotropic Perfect Fluid Distribution with Variable <Emphasis Type="Italic">G</Emphasis> and <Emphasis Type="BoldItalic">Λ</Emphasis>

Bianchi type III cosmological model for perfect fluid distribution with variable G and Λ are investigated. To get the determinate models, we have assumed the barotropic condition p=γ ρ and shear (σ) is proportional to expansion (θ) where p is isotropic pressure, ρ the matter density and 0≤γ≤1. The physical and geometrical aspects related with the observations and singularities in the models are discussed.     

Similarity parameters evaluation in the Po Valley during convective situations with Sodar data

Summary In well-developed convection, the surface sensible-heat flux can be evaluated from Sodar data; by using these flux values, it is possible to estimate some scale parameters in the mixed layer (likeθ _* andw _*). The use ofθ _*,w _* and the height of the mixed layerz _i, obtainable from other sources (i.e. radiosoundings), allows to verify some similarity relationships. We analysed the vertical profiles of the ratioσ _w ² /w _* ² : we found that it follows the theoretical behaviour depending onz/z _i if we use numerical coefficients slightly different from those usually referred to in the literature.     

Calculation of the photoionization with deexcitation cross sections of He and helium-like ions

We discuss the results of the calculation of the photoionization with deexcitation of excited He and helium-like ions Li⁺ and B³⁺ at high but nonrelativistic photon energies θ. Several lower ¹ S and ³ S states are considered. We present and analyze the ratios R _d ⁺ * of the cross sections of photoionization with deexcitation, σ _(d) ⁺ *(θ), and of the photoionization with excitation, σ⁺*(θ). The dependence of R _d ⁺ * on the excitation of the target object and the charge of its nucleus is presented. In addition to theoretical interest, the results obtained can be verified using long-lived excited states such as 2³ S of He. The text was submitted by authors in English.     

Mathematical analysis of isobaric decay chain in alpha particle induced reactions

A detailed mathematical formalism is developed from the first principles, to separate out the fractional contributions of the cross-sectionσ _g andσ _p for the production of the two isobaric precursor nuclei- grand parent and parent, respectively, to the cross-sectionσ _d for the formulation of the residual nucleus of interest. The analytical work of separating out such contributions gives a meaningful picture to the comparison with the theoretical predictions of hybrid model, using the initial excition numbern ₀ = 4(4p0h).     

Separated cross-sections in \pi^{0}_{} electroproduction at threshold at Q2 = 0.05GeV2/c2

The differential cross-sections σ₀ = σ_T + εσ_L , σ_LT , and σ_TT of electroproduction from the proton were measured from threshold up to an additional center-of-mass energy of 40MeV, at a value of the photon four-momentum transfer of Q ² = 0.05 GeV²/c² and a center-of-mass angle of θ = 90^° . By an additional out-of-plane measurement with polarized electrons σ_LT' was determined. This showed for the first time the presence of an imaginary part of the s -wave above the threshold, which is usually interpreted as a unitary cusp. The predictions of the Heavy Baryon Chiral Perturbation Theory (HBChPT) are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological model and are in good agreement with the dynamical model DMT.