Gravitational collapse with tachyon field and barotropic fluid

A particular class of space-time, with a tachyon field, $\phi $ , and a barotropic fluid constituting the matter content, is considered herein as a model for gravitational collapse. For simplicity, the tachyon potential is assumed to be of inverse square form i.e., $V(\phi )\sim \phi ^{-2}$ . Our purpose, by making use of the specific kinematical features of the tachyon, which are rather different from a standard scalar field, is to establish the several types of asymptotic behavior that our matter content induces. Employing a dynamical system analysis, complemented by a thorough numerical study, we find classical solutions corresponding to a naked singularity or a black hole formation. In particular, there is a subset where the fluid and tachyon participate in an interesting tracking behaviour, depending sensitively on the initial conditions for the energy densities of the tachyon field and barotropic fluid. Two other classes of solutions are present, corresponding respectively, to either a tachyon or a barotropic fluid regime. Which of these emerges as dominant, will depend on the choice of the barotropic parameter, $\gamma $ . Furthermore, these collapsing scenarios both have as final state the formation of a black hole.     

Linear-projection diffusion on smooth Euclidean submanifolds

To process massive high-dimensional datasets, we utilize the underlying assumption that data on manifold is approximately linear in sufficiently small patches (or neighborhoods of points) that are sampled with sufficient density from the manifold. Under this assumption, each patch can be represented (up to a small approximation error) by a tangent space of the manifold in its area and the tangential point of this tangent space.We extend previously obtained results (Salhov et al., 2012 [18]) for the finite construction of a linear-projection diffusion (LPD) super-kernel by exploring its properties when it becomes continuous. Specifically, its infinitesimal generator and the stochastic process defined by it are explored. We show that the resulting infinitesimal generator of this super-kernel converges to a natural extension of the original diffusion operator from scalar functions to vector fields. This operator is shown to be locally equivalent to a composition of linear projections between tangent spaces and the vector-Laplacians on them. We define a LPD process by using the LPD super-kernel as a transition operator while extending the process to be continuous. The obtained LPD process is demonstrated on a synthetic manifold.     

Heavily doped Si:P emitters of crystalline Si solar cells: recombination due to phosphorus precipitation

The measured saturation current density J_0e of heavily phosphorus‐doped emitters of crystalline Si solar cells is analysed by means of sophisticated numerical device modelling. It is concluded that Shockley–Read–Hall (SRH) recombination exceeds Auger recombination significantly; it is caused by inactive phosphorus. This explains the large discrepancies between measured and simulated J_0e values, observed persist‐ently over the last two decades in industrially fabricated Si solar cells. As a consequence, the heavily phosphorus‐diffused emitters still bear a significant potential to contribute to higher Si solar cell efficiency levels, if the amount of inactive phosphorus can be reduced. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Comparison of quasi-steady-state and unsteady-state formulations in a freeze dryer modeling

An unsteady-state model is developed for primary and secondary stages of freeze drying process of skim milk. The results are compared with those obtained from a quasi-steady-state (QSS) formulation. The QSS formulation is not valid where the applied heat load is high. The applied heat load affects on the drying time the most compared to other parameters like chamber pressure and the radiation surface temperature.     

Locally Rotationally Symmetric Vacuum Solutions in f(R) Gravity

This paper is devoted to find the Locally Rotationally Symmetric (LRS) vacuum solutions in the context of f(R) theory of gravity. Actually, we have considered the three metrics representing the whole family of LRS spacetimes and solved the field equations by using metric approach as well as the assumption of constant scalar curvature. It is mention here that R may be zero or non-zero. In all we found 10 different solutions.     

Thermal and Mechanical Properties of Ultra High Molecular Weight Polyethylene Fiber Reinforced High-Density Polyethylene Homocomposites: Effect of Processing Condition and Nanoclay Addition

A new method to prepare single-polymer high-density (HDPE)-ultra high molecular weight polyethylene (UHMWPE) fiber (PE-PE homocomposites) composed and also PE-PE homocomposites containing HDPE organo montmorillonite clay (OMMT) nanocomposites as a matrix (PE nanohomocomposites) was used. Owing to the major importance of fiber impregnation by the matrix and its effect on the adhesion of matrix/fiber and, consequently, the mechanical properties of the composite, a combination of powder impregnation and film stacking methods, utilizing compression molding, were used for manufacturing the PE-PE homocomposites and PE nanohomocomposites. In addition, PE nanohomocomposites with the matrix containing different amounts of nanoclay were prepared to investigate the effect of the clay on the interfacial and mechanical properties of the PE-PE nanohomocomposites. Several different processing conditions were examined to determine the best conditions for manufacturing of the PE-PE homocomposite and PE nanohomocomposites and it was concluded that 40 bar and 10 min of compression molding resulted in the highest overall mechanical properties. The PE-PE homocomposites and PE-PE nanohomocomposites showed identical trends for the relationship between the effects of processing conditions and mechanical properties. Mechanical results demonstrated that clay platelets could increase the interfacial strength by improving physical entanglements between fiber and matrix through better cocrystallization.     

Effect of Maleated Styrene/Ethylene-co-Butylene/Styrene on the Dispersed Particles Size and Mechanical Properties of Polyamide 6/Poly(styrene-co-acrylonitrile)/Poly(styrene-b-(ethylene-co-butylene)-b-styrene) Ternary Blends

In this study, the effect of several parameters, including composition, order of mixing, viscosity, and interfacial tension, on the phase structure and size of dispersed particles of polyamide 6 (PA6)/poly(styrene-co-acrylonitrile) SAN/poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) ternary blends was investigated. Moreover, the effect of addition of different ratios of reactive SEBS (maleic anhydride grafted-SEBS) and non-reactive SEBS at a fixed order of mixing and composition of 70/15/15 (PA6/SAN/SEBS + SEBS-g-MAH) on the mechanical properties of ternary blends was examined. Scanning electron microscopy (SEM) micrographs showed that among the studied parameters, interfacial tension and viscosity of dispersed phases were the leading factors in the formation of morphology and size of dispersed droplets. Mechanical results revealed that in contrast to the expectation, formation of core/shell structure of PA6/SAN/SEBS ternary blends did not result in a significant increasing of impact strength. The highest impact strength was achieved when a 50/50 weight ratio of SEBS/SEBS-g-MAH was used.     

Green׳s function method for piezoelectric energy harvesting beams

The development of validated mathematical models for piezoelectric harvesters is important as it provides predictive capabilities of their performance and insight to their coupled electromechanical behavior. Advanced solutions to these models allows for more realistic parameters to be considered. In this paper, we present a Fourier Transform–Green?s Function (FTGF) solution approach to the distributed parameter coupled electromechanical equations for a piezoelectric beam excited by an arbitrary external transverse force. This method, as opposed to modal analysis, allows for frequency-dependent material properties and damping coefficients to be considered. The special case of a harmonic base excitation is considered and closed-form expressions for the frequency response functions of the voltage generated by piezoelectric layer, relative tip displacement and local bending strain are obtained. Finally, the FTGF solution to these frequency response functions is compared with the modal analysis solution along with experimental data for validation.     

Applications of differential algebra for computing Lie algebras of infinitesimal CR-automorphisms

We perform detailed computations of Lie algebras of infinitesimal CR-automorphisms associated to three specific model real analytic CR-generic submanifolds in C9by employing differential algebra computer tools—mostly within the Maple package DifferentialAlgebra—in order to automate the handling of the arising highly complex linear systems of PDE’s.Before treating these new examples which prolong previous works of Beloshapka,of Shananina and of Mamai,we provide general formulas for the explicitation of the concerned PDE systems that are valid in arbitrary codimension k 1 and in any CR dimension n 1.Also,we show how Ritt’s reduction algorithm can be adapted to the case under interest,where the concerned PDE systems admit so-called complex conjugations.