Spikes in Cosmic Crystallography

If the universe is multiply connected and small the sky shows multiple images of cosmic objects, correlated by the covering group of the 3-manifold used to model it. These correlations were originally thought to manifest as spikes in pair separation histograms (PSH) built from suitable catalogues. Using probability theory we derive an expression for the expected pair separation histogram (EPSH) in a rather general topological-geometrical-observational setting. As a major consequence we show that the spikes of topological origin in PSH's are due to translations, whereas other isometries manifest as tiny deformations of the PSH corresponding to the simply connected case. This result holds for all Robertson-Walker spacetimes and gives rise to two basic corollaries: (i) that PSH's of Euclidean manifolds that have the same translations in their covering groups exhibit identical spike spectra of topological origin, making clear that even if the universe is flat the topological spikes alone are not sufficient for determining its topology; and (ii) that PSH's of hyperbolic 3-manifolds exhibit no spikes of topological origin. These corollaries ensure that cosmic crystallography, as originally formulated, is not a conclusive method for unveiling the shape of the universe. We also present a method that reduces the statistical fluctuations in PSH's built from simulated catalogues.Comment: 25 pages, LaTeX2e. References updated. To appear in Int. J. Mod. Phys. D (2002) in the present for

Derivation of an Abelian effective model for instanton chains in 3D Yang-Mills theory

In this work, we derive a recently proposed Abelian model to describe the interaction of correlated monopoles, center vortices, and dual fields in three dimensional SU(2) Yang-Mills theory. Following recent polymer techniques, special care is taken to obtain the end-to-end probability for a single interacting center vortex, which constitutes a key ingredient to represent the ensemble integration.Comment: 18 pages, LaTe

Topological Reverberations in Flat Space-times

We study the role played by multiply-connectedness in the time evolution of the energy E(t) of a radiating system that lies in static flat space-time manifolds M_4 whose t=const spacelike sections M_3 are compact in at least one spatial direction. The radiation reaction equation of the radiating source is derived for the case where M_3 has any non-trivial flat topology, and an exact solution is obtained. We also show that when the spacelike sections are multiply-connected flat 3-manifolds the energy E(t) exhibits a reverberation pattern with discontinuities in the derivative of E(t) and a set of relative minima and maxima, followed by a growth of E(t). It emerges from this result that the compactness in at least one spatial direction of Minkowski space-time is sufficient to induce this type of topological reverberation, making clear that our radiating system is topologically fragile. An explicit solution of the radiation reaction equation for the case where M_3 = R^2 x S^1 is discussed, and graphs which reveal how the energy varies with the time are presented and analyzed.Comment: 16 pages, 4 figures, REVTEX; Added five references and inserted clarifying details. Version to appear in Int. J. Mod. Phys. A (2000

Produção de etanol a partir de subproduto cervejeiro

O processo de fabricação de cerveja inevitavelmente envolve a geração de diversos resíduos e subprodutos. O mais comum dos subprodutos é o dresh, o qual é gerado a partir da principal matéria-prima usada para a elaboração da cerveja, o malte de cevada. O dresh é gerado em grandes quantidades ao longo do ano, mas seu uso ainda é limitado, sendo basicamente vendido para fazendeiros locais para ser utilizado como alimento para o gado, ou simplesmente é descartado na natureza. Tendo em conta a quantidade considerável em que este subproduto é continuamente gerado, e considerando que se trata de um material rico em açúcares, o nosso grupo de pesquisa investigou a possibilidade de reutilizar o dresh como matéria-prima para a produção de etanol de segunda geração. A possibilidade de produzir etanol combustível a partir de dresh foi confirmada e esta aplicação pode ser considerada uma alternativa de interesse para a valorização deste subproduto industrial

Marine Primary Productivity Is Driven by a Selection Effect

10 páginas, 6 figuras, 1 tabla.-- Pedro Cermeño ... et al.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these termsThe number of species of autotrophic communities can increase ecosystem productivity through species complementarity or through a selection effect which occurs when the biomass of the community approaches the monoculture biomass of the most productive species. Here we explore the effect of resource supply on marine primary productivity under the premise that the high local species richness of phytoplankton communities increases resource use through transient selection of productive species. Using concurrent measurements of phytoplankton community structure, nitrate fluxes into the euphotic zone, and productivity from a temperate coastal ecosystem, we find that observed productivities are best described by a population growth model in which the dominant species of the community approach their maximum growth rates. We interpret these results as evidence of species selection in communities containing a vast taxonomic repertory. The prevalence of selection effect was supported by open ocean data that show an increase in species dominance across a gradient of nutrient availability. These results highlight the way marine phytoplankton optimize resources and sustain world food stocks. We suggest that the maintenance of phytoplankton species richness is essential to sustain marine primary productivity since it guarantees the occurrence of highly productive speciesThis research was supported by grants CTM2011-25035, CTM2012-30680, and CGL2013-41256-P from the Spanish Government (SG). PC and SV are supported by Ramon y Cajal contracts from the SGPeer reviewe

Orientational transitions in a nematic confined by competing surfaces

The effect of confinement on the orientational structure of a nematic liquid crystal model has been investigated by using a version of density-functional theory (DFT). We have focused on the case of a nematic confined by opposing flat surfaces, in slab geometry (slit pore), which favor planar molecular alignment (parallel to the surface) and homeotropic alignment (perpendicular to the surface), respectively. The spatial dependence of the tilt angle of the director with respect to the surface normal has been studied, as well as the tensorial order parameter describing the molecular order around the director. For a pore of given width, we find that, for weak surface fields, the alignment of the nematic director is perpendicular to the surface in a region next to the surface favoring homeotropic alignment, and parallel along the rest of the pore, with a interface separating these regions (S phase). For strong surface fields, the director is distorted uniformly, the tilt angle exhibiting a linear dependence with the distance normal to the surface (L phase). Our calculations reveal the existence of a first-order transition between the two director configurations, which is driven by changes in the surface field strength, and also by changes in the pore width. In the latter case the transition occurs, for a given surface field, between the S phase for narrow pores and the L phase for wider pores. A link between the L-S transition and the anchoring transition observed for the semi-infinite case is proposed. We also provide calculations with a phenomenological approach that yields the same main result that DFT in the scale length where this is valid.Comment: submitted to PR

Deliriumin the ICU setting ‐ a subjective and theoretical survey before the implementation of the Confusion Assessment Method for the ICU in an unit

Background and Goal of Study: The current definition of delirium comprises acute change or fluctuation in mental status and inattention, accompanied by either altered level of consciousness or disorganized thinking. It is a frequent condition in the ICU and it is associated with longer hospital stay, increase in mortality at 6 months and long-term cognitive impairment, but remains under diagnosed. The Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) has been validated and implemented in many ICUs and its use is recommended by the Society of Critical Care Medicine. It is our purpose to evaluate the individual perspective and the objective knowledge of our staf f about delirium before the implementation of the CAM-ICU. Materials and Methods: Anonymous survey to our ICU clinical staf f which contained subjective and ‘true or false’ questions. Data was analised with the sof tware SPSS version 17.0. The Wilcoxon test was used to compare autoperception of knowledge about delirium and the content of answers regarding its definiton. Results: Forty two questionnaires were returned (participation rate of 73%), 11 from physicians and 31 from nurses. Overall, 61,9% of inquiries think they can give a definition for delirium in the ICU and 50% claim to be able to evaluate delirium. 28,6% of the respondents - 63,6% of the physicians and 16,1% of the nurses - know the CAM-ICU. From these only a quarter has received education on this method, 75% think it’s easy to apply and 66% don’t see its use as an increase in the daily workload. We found a high rate of wrong and ‘I don’t know’ answers to questions about operationalization, diagnosis and outcome. The subjects’ auto-perception on their knowledge about delirium [Likert scale] was compared to their ability to answer questions related to its definiton - ‘attention deficit is essencial for diagnosis’ [true], Wilcoxon test Z=-4,699 (p< 0,001); ‘disorganized thinking is essential for diagnosis’ [false], Wilcoxon test Z=-4,437 (p< 0,001). Conclusions: The respondents’ auto perception of knowledge about delirium doesn’t translate in the ability of giving an appropriate definition and making an adequate evaluation. Most of the inquiries don’t know the CAM-ICU, but those who do believe it’s easy to apply and its use won’t increase the workload. We performed educational sessions about delirium and the CAM-ICU in our unit to encourage our clinical staf f to deal properly with this hazardous condition