Plastic Flow in Two-Dimensional Solids

A time-dependent Ginzburg-Landau model of plastic deformation in two-dimensional solids is presented. The fundamental dynamic variables are the displacement field \bi u and the lattice velocity {\bi v}=\p {\bi u}/\p t. Damping is assumed to arise from the shear viscosity in the momentum equation. The elastic energy density is a periodic function of the shear and tetragonal strains, which enables formation of slips at large strains. In this work we neglect defects such as vacancies, interstitials, or grain boundaries. The simplest slip consists of two edge dislocations with opposite Burgers vectors. The formation energy of a slip is minimized if its orientation is parallel or perpendicular to the flow in simple shear deformation and if it makes angles of $\pm \pi/4$ with respect to the stretched direction in uniaxial stretching. High-density dislocations produced in plastic flow do not disappear even if the flow is stopped. Thus large applied strains give rise to metastable, structurally disordered states. We divide the elastic energy into an elastic part due to affine deformation and a defect part. The latter represents degree of disorder and is nearly constant in plastic flow under cyclic straining.Comment: 16pages, Figures can be obtained at http://stat.scphys.kyoto-u.ac.jp/index-e.htm

The use of camu-camu (Myrciaria dubia) for the production of a fermented alcoholic beverage

The high levels of ascorbic acid in camu-camu (Myrciaria dubia McVaugh, Myrtaceae) have stimulated interest of extractivists, farmers and consumers. This has led to a need to develop adequate technology for it's production on non-flooded land and the industrial use of this fruit. This study had as its main objective to verify if camu-camu is adequate for the production of fermented alcoholic beverages, measuring the effect of blanching the fruit and the incorporation of the fruit peel with the fruit pulp on the nutritional and sensory characteristics of the drink. The fruits were separated into 4 groups, two being blanched (90 ºC for 7 minutes). After the pulp was removed, the peels of one group from each blanching treatment were incorporated into the respective pulps and their chemical composition evaluated. After sugar correction of the must, pasteurisation, fermentation (25 days), decanting, pasteurisation (70 ºC for 15 minutes), filtering and clarification, the beverages were evaluated as to their chemical composition, sweetened and submitted to sensory analysis. Blanching reduced the concentration of ascorbic acid in the pulps (33 %) and the addition of the peel increased the amount of dry matter (39 % in pulp), ascorbic acid (33 % in pulp, 23 % in must and 50 % in drink) and phenolic compounds (50 % in drink). The sensory profile and acceptability suggest that camu-camu is adequate for the production of fermented alcoholic beverages and that the addition of the peel to the pulp contributes positively to it's acceptability (6.7 with versus 6.2 without, of 9 points possible). The beverage had flavour characteristic of the fruit, a orangish-red color and agreeable taste.", 'enO elevado teor de ácido ascórbico no camu-camu (Myrciaria dubia McVaugh, Myrtaceae) desperta o interesse de extrativistas, agricultores e consumidores, e leva à necessidade de desenvolvimento de tecnologias adequadas para produção em terra firme e aproveitamento industrial do fruto. Este trabalho teve por objetivo verificar a adequação do camu-camu para a produção de bebida alcoólica fermentada, assim como o efeito do branqueamento do fruto e da incorporação da casca à polpa nas características nutricionais e sensoriais da bebida. Os frutos foram separados em quatro lotes, sendo dois branqueados (90 ºC por 7 min). Após a despolpa, as cascas de um lote de cada tratamento (com e sem branqueamento) foram incorporadas às respectivas polpas e avaliadas quanto à composição química (umidade, pH, acidez, sólidos solúveis, açúcares, ácido ascórbico, compostos fenólicos, antocianinas e flavonóides). Após a correção do mosto com açúcar, pasteurização, fermentação (25 dias), trasfega, pasteurização (70 ºC por 15 min), filtragem e clarificação, as bebidas foram avaliadas quanto a composição química, edulcoradas e submetidas à análise sensorial. O branqueamento reduziu a concentração de ácido ascórbico das polpas (33 %) e a agregação da casca aumentou os teores de matéria seca (39 % polpa), ácido ascórbico (33 % na polpa, 23 % no mosto e 50 % na bebida) e fenólicos (50 % bebida). O perfil sensorial e a aceitabilidade sugerem que o camu-camu é adequado para a produção de bebida alcoólica fermentada e que a agregação da casca à polpa contribuiu positivamente para a aceitabilidade (6,7 com casca e 6,2 sem casca, na escala de 9 pontos). As bebidas apresentaram flavor característico do fruto, limpidez, coloração vermelho-laranjada e sabor agradável

Dark energy and dark matter from an inhomogeneous dilaton

A cosmological scenario is proposed where the dark matter (DM) and dark energy (DE) of the universe are two simultaneous manifestations of an inhomogenous dilaton. The equation of state of the field is scale-dependent and pressureless at galactic and larger scales and it has negative pressure as a DE at very large scales. The dilaton drives an inflationary phase followed by a kinetic energy-dominated one, as in the "quintessential inflation" model introduced by Peebles & Vilenkin, and soon after the end of inflation particle production seeds the first inhomogeneities that lead to galaxy formation. The dilaton is trapped near the minimum of the potential where it oscillates like a massive field, and the excess of kinetic energy is dissipated via the mechanism of "gravitational cooling" first introduced by Seidel & Suen. The inhomogeneities therefore behave like solitonic oscillations around the minimum of the potential, known as "oscillatons", that we propose account for most DM in galaxies. Those regions where the dilaton does not transform enough kinetic energy into reheating or carry an excess of it from regions that have cooled, evolve to the tail of the potential as DE, driving the acceleration of the universe.Comment: 9 pages, 8 figures, uses revtex, submitted PR

A Note on Inflation with Tachyon Rolling on the Gauss-Bonnet Brane

In this paper we study the tachyonic inflation in brane world cosmology with Gauss-Bonnet term in the bulk. We obtain the exact solution of slow roll equations in case of exponential potential. We attempt to implement the proposal of Lidsey and Nunes, astro-ph/0303168, for the tachyon condensate rolling on the Gauss-Bonnet brane and discuss the difficulties associated with the proposal.Comment: RevTex4, 5 pages, no figures, Minor clarifications added and references updated, To appear in PR

Fusion of secretory vesicles isolated from rat liver

Secretory vesicles isolated from rat liver were found to fuse after exposure to Ca2+. Vescle fusion is characterized by the occurrence of twinned vesicles with a continuous cleavage plane between two vesicles in freeze-fracture electron microscopy. The number of fused vesicles increases with increasing Ca2+-concentrations and is half maximal around 10–6 m. Other divalent cations (Ba2+, Sr2+, and Mg2+) were ineffective. Mg2+ inhibits Ca2+-induced fusion. Therefore, the fusion of secretory vesiclesin vitro is Ca2+ specific and exhibits properties similar to the exocytotic process of various secretory cells. Various substances affecting secretionin vivo (microtubular inhibitors, local anethetics, ionophores) were tested for their effect on membrane fusion in our system. The fusion of isolated secretory vesicles from liver was found to differ from that of pure phospholipid membranes in its temperature dependence, in its much lower requirement for Ca2+, and in its Ca2+-specificity. Chemical and enzymatic modifications of the vesicle membrane indicate that glycoproteins may account for these differences

Concept of temperature in multi-horizon spacetimes: Analysis of Schwarzschild-De Sitter metric

In case of spacetimes with single horizon, there exist several well-established procedures for relating the surface gravity of the horizon to a thermodynamic temperature. Such procedures, however, cannot be extended in a straightforward manner when a spacetime has multiple horizons. In particular, it is not clear whether there exists a notion of global temperature characterizing the multi-horizon spacetimes. We examine the conditions under which a global temperature can exist for a spacetime with two horizons using the example of Schwarzschild-De Sitter (SDS) spacetime. We systematically extend different procedures (like the expectation value of stress tensor, response of particle detectors, periodicity in the Euclidean time etc.) for identifying a temperature in the case of spacetimes with single horizon to the SDS spacetime. This analysis is facilitated by using a global coordinate chart which covers the entire SDS manifold. We find that all the procedures lead to a consistent picture characterized by the following features: (a) In general, SDS spacetime behaves like a non-equilibrium system characterized by two temperatures. (b) It is not possible to associate a global temperature with SDS spacetime except when the ratio of the two surface gravities is rational (c) Even when the ratio of the two surface gravities is rational, the thermal nature depends on the coordinate chart used. There exists a global coordinate chart in which there is global equilibrium temperature while there exist other charts in which SDS behaves as though it has two different temperatures. The coordinate dependence of the thermal nature is reminiscent of the flat spacetime in Minkowski and Rindler coordinate charts. The implications are discussed.Comment: 12 page

Cosmology With Non-Minimally Coupled K-Field

We consider non-minimally coupled (with gravity) scalar field with non-canonical kinetic energy. The form of the kinetic term is of Dirac-Born-Infeld (DBI) form.We study the early evolution of the universe when it is sourced only by the k-field, as well as late time evolution when both the matter and k-field are present. For the k-field, we have considered constant potential as well as potential inspired from Boundary String Field Theory (B-SFT). We show that it is possible to have inflationary solution in early time as well as late time accelerating phase. The solutions also exhibit attractor property in a sense that it does not depend on the initial conditions for a certain values of the parameters.Comment: 10 pages, Revtex style, 14 eps figures, to appear in General Relativity and Gravitatio

Magnetic fields in supernova remnants and pulsar-wind nebulae

We review the observations of supernova remnants (SNRs) and pulsar-wind nebulae (PWNe) that give information on the strength and orientation of magnetic fields. Radio polarimetry gives the degree of order of magnetic fields, and the orientation of the ordered component. Many young shell supernova remnants show evidence for synchrotron X-ray emission. The spatial analysis of this emission suggests that magnetic fields are amplified by one to two orders of magnitude in strong shocks. Detection of several remnants in TeV gamma rays implies a lower limit on the magnetic-field strength (or a measurement, if the emission process is inverse-Compton upscattering of cosmic microwave background photons). Upper limits to GeV emission similarly provide lower limits on magnetic-field strengths. In the historical shell remnants, lower limits on B range from 25 to 1000 microGauss. Two remnants show variability of synchrotron X-ray emission with a timescale of years. If this timescale is the electron-acceleration or radiative loss timescale, magnetic fields of order 1 mG are also implied. In pulsar-wind nebulae, equipartition arguments and dynamical modeling can be used to infer magnetic-field strengths anywhere from about 5 microGauss to 1 mG. Polarized fractions are considerably higher than in SNRs, ranging to 50 or 60% in some cases; magnetic-field geometries often suggest a toroidal structure around the pulsar, but this is not universal. Viewing-angle effects undoubtedly play a role. MHD models of radio emission in shell SNRs show that different orientations of upstream magnetic field, and different assumptions about electron acceleration, predict different radio morphology. In the remnant of SN 1006, such comparisons imply a magnetic-field orientation connecting the bright limbs, with a non-negligible gradient of its strength across the remnant.Comment: 20 pages, 24 figures; to be published in SpSciRev. Minor wording change in Abstrac

Virtual Compton Scattering and Neutral Pion Electroproduction in the Resonance Region up to the Deep Inelastic Region at Backward Angles

We have made the first measurements of the virtual Compton scattering (VCS) process via the H$(e,e'p)\gamma$ exclusive reaction in the nucleon resonance region, at backward angles. Results are presented for the $W$-dependence at fixed $Q^2=1$ GeV$^2$, and for the $Q^2$-dependence at fixed $W$ near 1.5 GeV. The VCS data show resonant structures in the first and second resonance regions. The observed $Q^2$-dependence is smooth. The measured ratio of H$(e,e'p)\gamma$ to H$(e,e'p)\pi^0$ cross sections emphasizes the different sensitivity of these two reactions to the various nucleon resonances. Finally, when compared to Real Compton Scattering (RCS) at high energy and large angles, our VCS data at the highest $W$ (1.8-1.9 GeV) show a striking $Q^2$- independence, which may suggest a transition to a perturbative scattering mechanism at the quark level.Comment: 20 pages, 8 figures. To appear in Phys.Rev.