Born-Infeld Cosmologies

We present a model for an inhomogeneous and anisotropic early universe filled with a nonlinear electromagnetic field of Born-Infeld (BI) type. The effects of the BI field are compared with the linear case (Maxwell). Since the curvature invaria nts are well behaved then we conjecture that our model does not present an initial big bang singularity. The existence of the BI field modifies the curvature invariants at t=0 as well as sets bounds on the amplitude of the conformal metric functionComment: 13 pages, latex, 6 eps figure

Bacterial carbon demand and growth efficiency in a coastal upwelling system

Eleven culture experiments were conducted in the coastal upwelling ­system of the Ría de Vigo (NW Iberian Peninsula) by inoculating GF/C filtrated (10%) in 0.2 µm filtrated (90%) surface seawater collected under contrasting hydrographic conditions. Short-term (4 d) laboratory incubations were performed in the dark at 15°C. Dissolved organic carbon (DOC) concentration, bacterial biomass (BB), bacterial production (BP) and electron transport system (ETS) activity were then monitored to: (1) study the course of bacterial carbon demand (BCD) and growth efficiency (BGE) during the incubation period; and (2) determine how BCD and BGE were linked with changing environmental conditions. Following the 4 d incubation, BP decreased by <4 times its initial values (range from 3 to 11 times) and ETS activity increased by 6 times its initial values (range from 1 to 75 times). As a result, BCD increased by 5 times (range from 1 to 16 times) and the BGE decreased by 15 times (range from 2 to 55 times) over the same period. BGE integrated over the 4 d incubation period ranged from 7 ± 1% to 55 ± 11% (mean ± SD: 27 ± 15%); integrated BGE increased significantly (R2 = 0.64, p < 0.003) with the initial concentration of dissolved inorganic nitrogen (DIN), and decreased significantly (R2 = 0.55, p < 0.01) with the C:N ratio of the bioavailable dissolved organic matter (BDOM). A multiple linear regression with DIN and the C:N ratio of BDOM explained 89% of the observed variability in the integrated BGE, demonstrating the strong dependence of growth efficiency on nutrient conditions and the quality of the organic substrate feeding the community of this coastal embayment.This study was funded by fellowships to C.L. from the early-stage training site ECOSUMMER (MESTCT-2004-020501) and the Carlsberg Foundation.Peer reviewe

Effects of the photochemical transformation of dissolved organic matter on bacterial physiology and diversity in a coastal system

8 páginas, 2 tablas, 1 figuraThe effect of solar radiation on dissolved organic matter (DOM) and the subsequent impact of photo-altered DOM on bacterial activity and community structure were assessed during two experiments in the coastal system of the Ría de Vigo (NW Iberian Peninsula). After exposure of 0.2 μm filtered seawater for 3.5 days to dark and full sunlight, an inoculum of the bacterial community collected at the same time as the exposed water was added and the mixture was incubated for 4 days in the dark at 15 °C. Changes in bacterial production (BP), diversity (assessed by Fluorescence in situ hybridization) and electron transport system (ETS) activity, dissolved organic carbon (DOC) and nitrogen (DON) and DOM humic-like absorption and fluorescence were followed. The exposure to sunlight had no effect on DOM concentrations while an average (±SD) decrease in DOM humic fluorescence of 45 ± 10% was found. The incubations with photo-altered DOM had lower BP (57 ± 11%), ETS (42 ± 9%) and bacterial carbon demand (BCD) (42 ± 8%) compared with the dark incubations, while bacterial growth efficiency (BGE) was unaffected. This suggests that DOM photo-alteration had a negative effect on bacterial metabolism in the study system. The bacterial growth on irradiated DOM resulted in a significant enrichment of the Gammaproteobacteria group compared with the dark control, indicating that solar exposure of DOM led to rapid changes in the bacterial community composition of the Ría de Vigo.This study was funded by fellowships to C.L from the early stage training site ECOSUMMER (MEST-CT-2004-020501) and the Carlsberg FoundationPeer reviewe

The development and first validation of the “Preterm social, cognitive, health and learning outcomes” (Pre-School) socioeconomics indicators inventory

Background: The consequences of preterm birth, to the individual and society at large, remain a major financial, emotional, social and personal burden in all countries. A complex infuence network between the family socioeconomic status, nutrition and infant social interactions determines early childhood environment. The socioeconomic characteristics of families and households define much of the starting conditions and the posible future development of any newborn. Aim: To develop a socioeconomics indicators inventory specifically focused on preterm children, in order to characterize their early childhood environment to evaluate potential social affordances of infants under 24 months of age. Methods: The process was divided into four phases: questionnaire development (items and domains generation), pilot testing, validation and exploratory analysis. The final version of the PRE-SCHOOL questionnaire consisted of 190 items, each related to one or more of eight domains (personal data, family situation, health status, economical situation, level of education, social network, leisure and residence conditions). For the exploratory and validation analysis, 52 children were recruited. The parent interview was conducted by two specially trained social workers when the child reached 24 months of age. Internal consistency of the questionnaire was high for all domains (Cronbach’s a coefficient of 0.964). Conclusions: The social and economic contexts define spaces of possibility that directly affect the evolution and life development of each newborn. The PRE-SCHOOL socioeconomics indicators inventory improves the anamnesis process in preterm infants at risk of cognitive impairement. We need to increased socioecnomical informations of the early childhood enviroment in order to propose focused family-centred cost-effective interventions to improve cognitive development

Possibility of culturing Pacific goliath grouper Epinephelus quinquefasciatus in water with different salinities

Objective. To assess the survival and growth of juvenile Pacific goliath grouper (Epinephelus quinquefasciatus) in captivity at low salinities. Materials and methods. We randomly selected twelve juvenile goliath groupers with an average standard length of 44.2 ± 6.1 cm and 1492 ± 476 g in body weight, and raised them for three months in the laboratory in waters of 32-26, 20, 10 and 5 parts per thousand of salinity. Results. All juvenile Pacific goliath groupers tolerated the initial gradual transfer from full strength seawater to salinities of 32-26, 20, 10, and 5 parts per thousand, which was done over a period of four days. All of them survived and grew in body weight and length during the course of the three-month experiment, in all the treatments of high and low salinity water. The body condition factor (K) for each fish was between 1.5 and 2.4. Conclusions. This is a first time trial that documents a randomized, controlled experiment demonstrating the ability of Pacific juvenile goliath grouper to gradually transfer from full strength seawater to water of lower salinity, and survive and grow well in these brackish waters.Key words: Aquaculture, euryhaline species, osmoregulation, water salinity (Source: BNA, NAL)

Resonant radiation pressure on neutral particles in a waveguide

A theoretical analysis of electromagnetic forces on neutral particles in an hollow waveguide is presented. We show that the effective scattering cross section of a very small (Rayleigh) particle can be strongly modified inside a waveguide. The coupling of the scattered dipolar field with the waveguide modes induce a resonant enhanced backscattering state of the scatterer-guide system close to the onset of new modes. The particle effective cross section can then be as large as the wavelength even far from any transition resonance. As we will show, a small particle can be strongly accelerated along the guide axis while being highly confined in a narrow zone of the cross section of the guide.Comment: RevTeX,4 pages,3 PS figure

Continuous variable quantum key distribution with two-mode squeezed states

Quantum key distribution (QKD) enables two remote parties to grow a shared key which they can use for unconditionally secure communication [1]. The applicable distance of a QKD protocol depends on the loss and the excess noise of the connecting quantum channel [2-10]. Several QKD schemes based on coherent states and continuous variable (CV) measurements are resilient to high loss in the channel, but strongly affected by small amounts of channel excess noise [2-6]. Here we propose and experimentally address a CV QKD protocol which uses fragile squeezed states combined with a large coherent modulation to greatly enhance the robustness to channel noise. As a proof of principle we experimentally demonstrate that the resulting QKD protocol can tolerate more noise than the benchmark set by the ideal CV coherent state protocol. Our scheme represents a very promising avenue for extending the distance for which secure communication is possible.Comment: 8 pages, 5 figure

Electric field effects on magnetotransport properties of multiferroic Py/YMnO3/Pt heterostructures

We report on the exchange bias between antiferromagnetic and ferroelectric hexagonal YMnO3 epitaxial thin films sandwiched between a metallic electrode (Pt) and a soft ferromagnetic layer (Py). Anisotropic magnetoresistance measurements are performed to monitor the presence of an exchange bias field. When the heteroestructure is biased by an electric field, it turns out that the exchange bias field is suppressed. We discuss the dependence of the observed effect on the amplitude and polarity of the electric field. Particular attention is devoted to the role of current leakage across the ferroelectric layer.Comment: Accepted for publication in Philosophical Magazine Letters (Special issue on multiferroics

El pabellón de Venezuela en la Expo 2000 de Hannover

The Bolivarian Republic of Venezuela had constructed a pavilion for the Hannover EXPO 2000, designed by the Architect Fruto Vivas, with the form ofa flower, the lightness of an steel and glass structure, the mobility of the roof.. The basic content of the exhibition was the biodiversity of the country.Para la EXPO 2000 de Hannover, la República Bolivariana de Venezuela construyó un pabellón proyectado por el Arquitecto Fruto Vivas, caracterizado por la forma de flor. la ligereza de la estructura de acero y vidrio, la movilidad de la cubierta y el contenido de la exposición basado en la biodiversidad del país