Higher Dimensional FRW Cosmology with Variable G and Λ

We have considered higher dimensional cosmological models of the FRW model with variable G and Λ. The solutions have been obtained for flat model with particular form of cosmological constant. The cosmological parameters have also been obtained for dust, radiation and stiff matter. Physical parameters of the models are discussed.     

Canonical quantization of the massive vector supermultiplet: an example of higher-order derivative model

Time variations of solarv _e -flux induced by spin-flavor conversion in the magnetic field of the sun have been studied. Several models of spatial and temporal distributions of the magnetic fields have been considered. The observed variations of the Ar-production rate in the Cl–Ar-experiment are shown to be not reproducible by these models. Unnaturally large values and fine tuned spatial structure of the fields are needed to explain the data.     

Massive String Cloud Cosmologies in Saez-Ballester Theory of Gravitation

String cloud cosmological models are studied using spatially homogeneous and anisotropic Bianchi type VI₀ metric in Saez-Ballester Scalar-Tensor theory of gravitation. The field equations are solved for massive string cloud with particles attached to them. A more general linear equation of state of the cosmic string tension density with the proper energy density of the universe is considered instead of taking any particular relationships like pure geometric string or the case of the p-string. The pure geometric string and p-string solutions can be easily inferred from the models. For all viable models the possible limiting values of the linear connection between the proper energy density and string tension density have been calculated. The physical and kinematical properties of the models have been discussed in detail.     

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.     

Cylindrically symmetric inhomogeneous cosmological models with viscous fluid and varying Λ

Cylindrically symmetric non-static cosmological models representing a bulk viscous fluid distribution have been obtained which are inhomogeneous and anisotropic. Without assuming anyadhoc law, we obtain a cosmological constant as a decreasing function of time. Various physical and geometrical features of the models are also discussed.     

Alkali adsorption on the Al(001) surface

The chemisorption of Na on the Al(001) surface has been studied by 2D bandstructure calculations on slab models using a density functional STO-LCAO method. Two slab models of three and five layers of substrate atoms have been used. Overlayers of the structuresp(2×2),c(2×2) andp(1×1), representing coverages of a quarter, a half and a full atomic monolayer of sodium atoms, respectively, have been investigated. The electronic structure of the adatoms and the charge transfer to the substrate are discussed. Satisfactory agreement with experiment is obtained for the adsorption induced change of the work function, correctly reproducing its monotonic character.     

Phantom Appearance of Non-phantom Matter in Anisotropic Cosmological Model

Two cosmological models with non-phantom matter having the same expansion of the universe as phantom cosmologies are constructed in anisotropic Bianchi type-V universe. The exact solutions to the corresponding Einstein field equations have been obtained. The statefinder diagnostic pair i.e. {r,s} parameters have been obtained for disordered radiation i.e. γ=1/3. We have also discussed the well-known astrophysical phenomena, namely the look-back time, luminosity distance and event horizon with redshift.     

Theoretical analysis of coherent electron transport in structures containing multiband superconductors with different types of superconducting pairing

Coherent electron transport in structures with multiband superconductors described by models of intraorbital (the s _± model) and interorbital superconducting pairing has been theoretically considered. Conductivities of junctions of a single-band normal metal with superconducting pnictides for these pairing models have been calculated. Temperature and phase dependences of the Josephson current through junctions containing a conventional Bardeen-Cooper-Schrieffer superconductor and a superconducting pnictide have been calculated within the considered pairing models taking into account temperature dependences of superconducting order parameters.     

Bianchi Type-I String Cosmological Model in Creation-Field

Hoyle-Narlikar C-field has been introduced to study cosmic strings in Bianchi type-I space-time. The solutions have been studied when the creation field C is a function of time t only. The geometrical and physical aspects for the models have also been studied.     

Disturbances of Rotational Motions for String Models of Hadrons and the Stability Problem

Slight disturbances of a classical rotational motion (uniform rotation of a system) are considered for a relativistic string with massive ends and for the q-q-q and Y baryon string models. It is shown that for a string with massive ends this motion is stable in the linear approximation and the slight perturbations are representable by a series each term of which describes a standing wave of certain frequency. These modes make it possible to simulate various excited states of hadrons. At the same time, for the q-q-q and Y baryon string models the instability of rotational motions has been proved: exponentially growing modes have been detected in their perturbation spectra.     

Orientational ordering from molecular polarizabilities and an odd-even effect in nCB homologous series

The molecular polarizabilities of the homologous series of cyano-alkyl-biphenyl (C _n H_2n+1.φφ.CN for n = 5 to 9) have been calculated using two different internal field models. From these values the orientational order parameters have been obtained. The orientational ordering exhibits an odd-even alteration along the series. The variations of different parameters with the increase of alkyl chain length are discussed. The relative stabilities of the alkyl-cyano-biphenyls are also discussed in terms of the molecular parameters.     

Nonlinear chiral models: Soliton solutions and spatio-temporal chaos

Nonlinear effective Lagrangian models with a chiral symmetry have been used to describe strong interactions at low energy, for a long time. The Skyrme model and the chiral quark-meson model are two such models, which have soliton solutions which can be identified with the baryons. We describe the various kinds of soliton states in these nonlinear models and discuss their physical significance and uses in this review. We also study these models from the view point of classical nonlinar dynamical systems. We consider fluctuations around theB=1 soliton solutions of these models (B, being the baryon number) and solve the spherically symmetric, time-dependent systems. Numerical studies indicate that the phase space around the Skyrme soliton solution exhibits spatio-temporal chaos. It is remarkable that topological solitons signifying stability/order and spatio-temporal chaos coexist in this model. In contrast with this, the soliton of the quark-meson model is stable even for large perturbations.     

Analogue Models of and for Gravity

Condensed matter systems, such as acoustics in flowing fluids, light in moving dielectrics, or quasiparticles in a moving superfluid, can be used to mimic aspects of general relativity. More precisely these systems (and others) provide experimentally accessible models of curved-space quantum field theory. As such they mimic kinematic aspects of general relativity, though typically they do not mimic the dynamics. Although these analogue models are thereby limited in their ability to duplicate all the effects of Einstein gravity they nevertheless are extremely important—they provide black hole analogues (some of which have already been seen experimentally) and lead to tests of basic principles of curved-space quantum field theory. Currently these tests are still in the realm of gedanken-experiments, but there are plausible candidate models that should lead to laboratory experiments in the not too distant future.     

String cosmology in LRS Bianchi type-II dusty Universe with time-decaying vacuum energy density Λ

A model of a cloud formed by massive strings is used as a source of LRS Bianchi type-II with time-decaying vacuum energy density Λ. To construct string cosmological models, we have used the energy–momentum tensor for such strings as formulated by Letelier (1983). The high nonlinear field equations have been solved for two types of strings: (i) massive string and (ii) Nambu string. The expansion θ in the model is assumed to be proportional to the shear σ. This condition leads to A = βB ^m , where A and B are the metric coefficients, m is a constant and β is an integrating constant. Our models are in accelerating phase which is consistent with the recent observations of supernovae type-Ia. The physical and geometrical behaviour of these models are also discussed.     

Exclusive electroproduction of \rho^0 and J/\psi mesons at HERA

Exclusive production of and mesons in ep collisions has been studied with the ZEUS detector in the kinematic range GeV, GeV for the data and GeV, GeV for the data. Cross sections for exclusive and production have been measured as a function of , W and t. The spin-density matrix elements , and Re have been determined for exclusive production as well as and for exclusive production. The results are discussed in the context of theoretical models invoking soft and hard phenomena. Received: 20 August 1998 / Published online: 14 January 1999     

Speeds of sound and isothermal compressibility of ternary liquid systems: Application of Flory’s statistical theory and hard sphere models

Speeds of sound and densities of three ternary liquid systems namely, toluene + n-heptane + n-hexane (I), cyclohexane + n-heptane + n-hexane (II) and n-hexane + n-heptane + n-decane (III) have been measured as a function of the composition at 298.15 K at atmospheric pressure. The experimental isothermal compressibility has been evaluated from measured values of speeds of sound and density. The isothermal compressibility of these mixtures has also been computed theoretically using different models for hard sphere equations of state and Flory’s statistical theory. Computed values of isothermal compressibility have been compared with experimental findings. A satisfactory agreement has been observed. The superiority of Flory’s statistical theory has been established quite reasonably over hard sphere models.      

Well Behaved Charged Generalization of Buchdahl’s Fluid Spheres

In the present article, we have obtained a class of well behaved charged analogues of Buchdahl (Phys. Rev. 116:1027–1034, 1959) neutral perfect fluid solution, which reduces to its neutral counter part in the absence of charge. The solutions so obtained are utilized to depict the super-dense stars models such as models for neutron stars and strange star. It is observed that the models are well behaved for restricted range of the parameter K (1<K≤1.64). Over all the maximum mass and corresponding radius is 2.4495M _Θ and 16.7289 respectively and moment of inertia . Also the pulsars character of the super-dense stars so obtained and has been analyzed with the help of moment of inertia. The analysis of the models reveals both vela and crab pulsars.     

LRS Bianchi Type II Perfect Fluid Cosmological Models in Normal Gauge for Lyra’s Manifold

The present study deals with spatially homogeneous and locally rotationally symmetric (LRS) Bianchi type II cosmological models of perfect fluid distribution of matter for the field equations in normal gauge for Lyra’s manifold where gauge function β is taken as time dependent. 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. It has been found that the displacement vector β behaves like cosmological term Λ in the normal gauge treatment and the solutions are consistent with recent observations. Some physical and geometric behavior of these models are also discussed.     

Particle subgrid scale modelling in large-eddy simulations of particle-laden turbulence

This study is concerned with particle subgrid scale (SGS) modelling in large-eddy simulations (LESs) of particle-laden turbulence. Although many particle-laden LES studies have neglected the effect of the SGS on the particles, several particle SGS models have been proposed in the literature. In this research, the approximate deconvolution method (ADM) and the stochastic models of Fukagata et al. (Dynamics of Brownian particles in a turbulent channel flow, Heat Mass Transf. 40 (2004), 715–726) Shotorban and Mashayek (A stochastic model for particle motion in large-eddy simulation, J. Turbul. 7 (2006), 1–13) and Berrouk et al. (Stochastic modelling of inertial particle dispersion by subgrid motion for LES of high Reynolds number pipe flow, J. Turbul. 8 (2007), pp. 1–20) are analysed. The particle SGS models are assessed using both a priori and a posteriori simulations of inertial particles in a periodic box of decaying, homogeneous and isotropic turbulence with an initial Reynolds number of Re_λ = 74. The model results are compared with particle statistics from a direct numerical simulation (DNS). Particles with a large range of Stokes numbers are tested using various filter sizes and stochastic model constant values. Simulations with and without gravity are performed to evaluate the ability of the models to account for the crossing trajectory and continuity effects. The results show that ADM improves results but is only capable of recovering a portion of the SGS turbulent kinetic energy. Conversely, the stochastic models are able to recover sufficient SGS energy, but show a large range of results dependent on the Stokes number and filter size. The stochastic models generally perform best at small Stokes numbers, but are unable to predict preferential concentration.     

Spectroscopy of neutron-rich nuclei at REX-ISOLDE with MINIBALL

We report on “safe” Coulomb excitation of neutron-rich nuclei. The radioactive nuclei have been produced by ISOLDE at CERN and postaccelerated by the REX-ISOLDE facility. The γ rays emitted by the decay of excited states have been detected by the MINIBALL array. Recent results are presented and compared to theoretical models. on behalf of the MINIBALL and REX-ISOLDE Collaborations The text was submitted by the author in English.