A thick shell Casimir effect

We consider the Casimir energy of a thick dielectric-diamagnetic shell under a uniform velocity light condition, as a function of the radii and the permeabilities. We show that there is a range of parameters in which the stress on the outer shell is inward, and a range where the stress on the outer shell is outward. We examine the possibility of obtaining an energetically stable configuration of a thick shell made of a material with a fixed volume

Photon Green's function and the Casimir energy in a medium

A new expansion is established for the Green's function of the electromagnetic field in a medium with arbitrary $\epsilon$ and $\mu$. The obtained Born series are shown to consist of two types of interactions - the usual terms (denoted $\cal P$) that appear in the Lifshitz theory combined with a new kind of terms (which we denote by $\cal Q$) associated with the changes in the permeability of the medium. Within this framework the case of uniform velocity of light ($\epsilon\mu={\rm const}$) is studied. We obtain expressions for the Casimir energy density and the first non-vanishing contribution is manipulated to a simplified form. For (arbitrary) spherically symmetric $\mu$ we obtain a simple expression for the electromagnetic energy density, and as an example we obtain from it the Casimir energy of a dielectric-diamagnetic ball. It seems that the technique presented can be applied to a variety of problems directly, without expanding the eigenmodes of the problem and using boundary condition considerations

Leaf Growth and Anatomy During Winter Droughting of Tetrachne Dregei Plants

The purpose of this work was to study the leaf growth and anatomy of Tetrachne dregei plants when they were subjected to a winter drought period. Plants were grown in semicontrolled conditions under two soil moisture regimes: irrigated and non-irrigated. Anatomical characterization was made using optical and scanning electron microscopy. No differences were found in stomatal index, stomatal length and epidermal cell size, between irrigated and non-irrigated plants. The adaxial epidermis of water stressed plants was more pubescent. Leaf abaxial epidermis of non-irrigated plants showed more intercostal plates of crystallized epicuticular wax than that of the irrigated ones. Leaf tissue distribution was not affected by the different moisture regimes. The effect of water deficit was neither detected on plant height, nor on leaf width and length. Except for the enhanced adaxial pubescence and abaxial wax crystal content, no other xeroplastic changes were noticed

Microhistological Analysis of Cows\u27 Diet during a Severe Drought in the Semi Arid Region of North Patagonia (Argentina)

The continuous use of the livestock fields of the Middle Valley of Río Negro, North Patagonia, Argentina, combined with adverse weather conditions that occur periodically, have contributed to the degradation of rangelands. The historical annual average rainfall regime in the Valle Medio of Río Negro is 303 mm but between 2002 and 2011, the average deficit was 33%. According to the Rural Society of Choele Choel, due to the decreased forage on offer, the existence of cattle in 2011 dropped to 85,000 animals, representing 50% of the normal amount for the area. During these critical times of drought, when grasslands decrease in quantity and quality, shrubs are supposed to contribute to the diet of cattle in this area. Knowledge of the diet of grazing animals is important in developing management standards that allow the proper use of natural grasslands. The utilization of epidermal characteristics to identify plant components in esophageal, ruminal, or fecal samples is a widespread technique used to study diet composition of free-ranging herbivores (Holechek et al. 1982, Bóo et al. 1993, Lindström et al. 1998). Our study was designed to evaluate cow\u27s diet from spring (September 2011) to early summer (January 2012), a particularly difficult period for breeders, in a plot of a field in this area of north Patagonia, Argentina

Effects of Water Stress on Germination and Seedling Growth of Lovegrass Species

Seeds of seven cultivars of lovegrass species Ermelo, Morpa and Tanganyika weeping lovegrass (Eragrostis curvula var. curvula, Don Eduardo INTA (E. curvula var. robusta), Cochise lovegrass (E. lehmanniana x E. trichophera), A-68 Lehmann lovegrass (E. lehmanniana Nees) and Catalina boer lovegrass (E. curvula var. conferta) were germinated at different water potentials. Total germination percentage differed within cultivars according to water availability, although there were no great differences between the germination of the cultivars within any given water potential. The only exception was Don Eduardo INTA which had lower germination values. A marked fall in germination was registered as from -0.6 MPa, which became practically non-existent at -1.5 MPa . Root and shoot length was measured on all cultivars of Eragrostis curvula var. curvula and shortening was observed when the water potential was reduced

Birman-Schwinger and the number of Andreev states in BCS superconductors

The number of bound states due to inhomogeneities in a BCS superconductor is usually established either by variational means or via exact solutions of particularly simple, symmetric perturbations. Here we propose estimating the number of sub-gap states using the Birman-Schwinger principle. We show how to obtain upper bounds on the number of sub-gap states for small normal regions and derive a suitable Cwikel-Lieb-Rozenblum inequality. We also estimate the number of such states for large normal regions using high dimensional generalizations of the Szego theorem. The method works equally well for local inhomogeneities of the order parameter and for external potentials.Comment: Final version to appear in Phys Rev

Forage Offer and Nutritive Value of Elaeagnus angustifolia in North Patagonia, Argentina

Fil: Klich, María G. Universidad Nacional de Río Negro. Escuela de Veterinaria. Río Negro, Argentina.Fil: Bondia, Pedro. Universidad Nacional del Sur. Departamento de Agronomia. Buenos Aires, Argentina.Fil: Fernandez, Osvaldo A. Universidad Nacional del Sur. Departamento de Agronomia. Buenos Aires, Argentina.The presence and growth cycle of the browse Elaeagnus angustifolia (olivillo, Russian olive), naturalized in the Mid Valley, Rio Negro, Argentina, must be considered in the yearly schedule of rangeland management. Field observations showed that cattle prefer the leaves of this species that are included on the reproductive branches which develop as a thyrse inflorescence. In this trial, authors studied the incidence of E. angustifolia in the breeding cow’s diet as determined by microhistological analysis of cow feces; mapped the distribution patterns in a cattle farm and quantified its abundance in different parcels; estimated the volume of forage produced by this species and determined the nutritive value of the edible parts of the plants. The quality and quantity of the thyrses accessible for cow’s browse suggest that E. angustifolia must be considered as an important feed input. The results are used to schedule grazing periods in a valley farm divided into plots with different abundances of E. angustifolia and a known floristic composition.La presencia y el ciclo de crecimiento del arbusto Elaeagnus angustifolia (olivillo, Russian olive), naturalizado en el Valle Medio, Rio Negro, Argentina, deben ser tenidos en cuenta al momento de planificar los esquemas de manejo ganadero. Observaciones a campo demuestran que los bovinos prefieren las hoas de esta especie que se encuentran en las ramas reproductivas que se desarrollan como una inflorescencia en tirso . Demos ramos la insidencia de E. angustifolia en la dieta de vacas de cria mediante microhistologua de heces, regitramos la distribucion de la especie en un establecimiento, cuantificamos su abundancia. estimamos el volumen de forraje producido y el valor nutritivo de las partes comestibles. Los resultados son utilizados para programar esquemas de manejo ganadero

Leaf Anatomy and Ultrastructure of Poa Ligularis After Defoliation and Water Stress

The objective of this study was to determine the effect of defoliation and water stress on leaf anatomy and the mesophyll cell ultrastructure of Poa ligularis. Anatomical differences were detected mainly at epidermal level. Under water stress, leaf roughness was enhanced since the epidermal-cell surface contours became conspicuous. Under defoliation the microscopic roughness decreased as a result of fewer epicuticular wax crystals being formed. Defoliation produced an enhancement of the interlamellar spaces in the irrigated plantís chloroplast. Under no defoliation conditions, chloroplast structure was not affected by water stress. When subjected to water stress, lightly defoliated plants presented chloroplasts with a bellowed outer membrane, irregular thylacoid distribution and the disorganization of peripheral grana. Severely defoliated plants showed disorganized internal chloroplast membranes and even the disappearance of the grana. No breakdown or disappearance of chloroplast external membranes was detected under the imposed growing conditions, suggesting that no irreversible changes were induced

Casimir energy of a dilute dielectric ball in the mode summation method

In the $(\epsilon_1-\epsilon_2)^2$--approximation the Casimir energy of a dilute dielectric ball is derived using a simple and clear method of the mode summation. The addition theorem for the Bessel functions enables one to present in a closed form the sum over the angular momentum before the integration over the imaginary frequencies. The linear in $(\epsilon_1-\epsilon_2)$ contribution into the vacuum energy is removed by an appropriate subtraction. The role of the contact terms used in other approaches to this problem is elucidated.Comment: 14 pages, REVTeX, no figures, no tables; presentation is made better, new references are adde

Entanglement entropy of fermions in any dimension and the Widom conjecture

We show that entanglement entropy of free fermions scales faster then area law, as opposed to the scaling $L^{d-1}$ for the harmonic lattice, for example. We also suggest and provide evidence in support of an explicit formula for the entanglement entropy of free fermions in any dimension $d$, $S\sim c(\partial\Gamma,\partial\Omega)\cdot L^{d-1}\log L$ as the size of a subsystem $L\to\infty$, where $\partial\Gamma$ is the Fermi surface and $\partial\Omega$ is the boundary of the region in real space. The expression for the constant $c(\partial\Gamma,\partial\Omega)$ is based on a conjecture due to H. Widom. We prove that a similar expression holds for the particle number fluctuations and use it to prove a two sided estimates on the entropy $S$.Comment: Final versio