Effects of fabric counts and weave designs on the properties of laminated woven kenaf carbon fibre reinforced epoxy hybrid composites

The effects of different fabric materials namely weave designs (plain and satin) and fabric counts (5 × 5 and 6 × 6) on the properties of laminated woven kenaf/carbon fibre reinforced epoxy hybrid composites were evaluated. The hybrid composites were fabricated from two types of fabric, i.e., woven kenaf that was made from a yarn of 500tex and carbon fibre, by using vacuum infusion technique and epoxy resin as matrix. The panels were tested for tensile, flexural, and impact strengths. The results have revealed that plain fabric is more suitable than satin fabric for obtaining high tensile and impact strengths. Using a fabric count of 5 × 5 has generated composites that are significantly higher in flexural modulus as compared to 6 × 6 which may be attributed to their structure and design. The scanned electron micrographs of the fractured surfaces of the composites demonstrated that plain woven fabric composites had better adhesion properties than satin woven fabric composites, as indicated by the presence of notably lower amount of fibre pull out

High-energy expansion of Coulomb corrections to the e+e- photoproduction cross section

First correction to the high-energy asymptotics of the total $e^+e^-$ photoproduction cross section in the electric field of a heavy atom is derived with the exact account of this field. The consideration is based on the use of the quasiclassical electron Green function in an external electric field. The next-to-leading correction to the cross section is discussed. The influence of screening on the Coulomb corrections is examined in the leading approximation. It turns out that the high-energy asymptotics of the corresponding correction is independent of the photon energy. In the region where both produced particles are relativistic, the corrections to the high-energy asymptotics of the electron (positron) spectrum are derived. Our results for the total cross section are in good agreement with experimental data for photon energies down to a few $MeV$. In addition, the corrections to the bremsstrahlung spectrum are obtained from the corresponding results for pair production.Comment: 22 pages, 7 figures, RevTeX.Typos are corrected. The numerical results, figures and conclusions remain unchanged as they were obtained using correct formula

Statistics of skyrmions in Quantum Hall systems

We analyze statistical interactions of skyrmions in the quantum Hall system near a critical filling fraction in the framework of the Ginzburg-Landau model. The phase picked up by the wave-function during an exchange of two skyrmions close to $\nu=1/(2n+1)$ is $\pi[S+1/2(2n+1)]$, where $S$ is the skyrmion's spin. In the same setting an exchange of two fully polarized vortices gives rise to the phase $\pi/(2n+1)$. Skyrmions with odd and even numbers of reversed spins have different quantum statistics. Condensation of skyrmions with an even number of reversed spins leads to filling fractions with odd denominators, while condensation of those with an odd number of reversed spins gives rise to filling fractions with even denominators.Comment: 6 pages in Latex. addendum - skyrmions with odd or even number of reversed spins have different quantum statistics. They condense to form respectively even or odd denominator filling fraction state

Constraint on teleportation over multipartite pure states

We first define a quantity exhibiting the usefulness of bipartite quantum states for teleportation, called the quantum teleportation capability, and then investigate its restricted shareability in multi-party quantum systems. In this work, we verify that the quantum teleportation capability has a monogamous property in its shareability for arbitrary three-qutrit pure states by employing the monogamy inequality in terms of the negativity.Comment: 4 pages, 1 figur

Quantum fluctuations of classical skyrmions in quantum Hall Ferromagnets

In this article, we discuss the effect of the zero point quantum fluctuations to improve the results of the minimal field theory which has been applied to study %SMG the skyrmions in the quantum Hall systems. Our calculation which is based on the semiclassical treatment of the quantum fluctuations, shows that the one-loop quantum correction provides more accurate results for the minimal field theory.Comment: A few errors are corrected. Accepted for publication in Rapid Communication, Phys. Rev.

Traveling length and minimal traveling time for flow through percolation networks with long-range spatial correlations

We study the distributions of traveling length l and minimal traveling time t through two-dimensional percolation porous media characterized by long-range spatial correlations. We model the dynamics of fluid displacement by the convective movement of tracer particles driven by a pressure difference between two fixed sites (''wells'') separated by Euclidean distance r. For strongly correlated pore networks at criticality, we find that the probability distribution functions P(l) and P(t) follow the same scaling Ansatz originally proposed for the uncorrelated case, but with quite different scaling exponents. We relate these changes in dynamical behavior to the main morphological difference between correlated and uncorrelated clusters, namely, the compactness of their backbones. Our simulations reveal that the dynamical scaling exponents for correlated geometries take values intermediate between the uncorrelated and homogeneous limiting cases

Stripes in Quantum Hall Double Layer Systems

We present results of a study of double layer quantum Hall systems in which each layer has a high-index Landau level that is half-filled. Hartree-Fock calculations indicate that, above a critical layer separation, the system becomes unstable to the formation of a unidirectional coherent charge density wave (UCCDW), which is related to stripe states in single layer systems. The UCCDW state supports a quantized Hall effect when there is tunneling between layers, and is {\it always} stable against formation of an isotropic Wigner crystal for Landau indices $N \ge 1$. The state does become unstable to the formation of modulations within the stripes at large enough layer separation. The UCCDW state supports low-energy modes associated with interlayer coherence. The coherence allows the formation of charged soliton excitations, which become gapless in the limit of vanishing tunneling. We argue that this may result in a novel {\it ``critical Hall state''}, characterized by a power law $I-V$ in tunneling experiments.Comment: 10 pages, 8 figures include

Constraints on scalar-tensor theories of gravity from observations

In spite of their original discrepancy, both dark energy and modified theory of gravity can be parameterized by the effective equation of state (EOS) $\omega$ for the expansion history of the Universe. A useful model independent approach to the EOS of them can be given by so-called Chevallier-Polarski-Linder (CPL) parametrization where two parameters of it ($\omega_{0}$ and $\omega_{a}$) can be constrained by the geometrical observations which suffer from degeneracies between models. The linear growth of large scale structure is usually used to remove these degeneracies. This growth can be described by the growth index parameter $\gamma$ and it can be parameterized by $\gamma_{0} + \gamma_{a} (1 - a)$ in general. We use the scalar-tensor theories of gravity (STG) and show that the discernment between models is possible only when $\gamma_a$ is not negligible. We show that the linear density perturbation of the matter component as a function of redshift severely constrains the viable subclasses of STG in terms of $\omega$ and $\gamma$. From this method, we can rule out or prove the viable STG in future observations. When we use $Z(\phi) =1$, $F$ shows the convex shape of evolution in a viable STG model. The viable STG models with $Z(\phi) = 1$ are not distinguishable from dark energy models when we strongly limit the solar system constraint.Comment: 19 pages, 20 figures, 2 tables, submitted to JCA

On the possibility of superconductivity in PrBa2Cu3O7

Recent reports about observations of superconductivity in PrBa2Cu3O7 raise a number of questions: (i) of various theories striving to explain the Tc suppression in PrxY{1-x}Ba2Cu3O7, are there any compatible with possible superconductivity in stoichiometric PrBa2Cu3O7? (ii) if this superconductivity is not an experimental artifact, are the superconducting carriers (holes) of the same character as in the other high-Tc cuprates, or do they represent another electronic subsystem? (iii) is the underlying mechanism the same as in other high-Tc superconductors? I present an answer to the first two questions, while leaving the last one open.Comment: 4 pages 4 eps fig

Skyrmions in Higher Landau Levels

We calculate the energies of quasiparticles with large numbers of reversed spins (``skyrmions'') for odd integer filling factors 2k+1, k is greater than or equals 1. We find, in contrast with the known result for filling factor equals 1 (k = 0), that these quasiparticles always have higher energy than the fully polarized ones and hence are not the low energy charged excitations, even at small Zeeman energies. It follows that skyrmions are the relevant quasiparticles only at filling factors 1, 1/3 and 1/5.Comment: 10 pages, RevTe