General properties of cosmological models with an Isotropic Singularity

Much of the published work regarding the Isotropic Singularity is performed under the assumption that the matter source for the cosmological model is a barotropic perfect fluid, or even a perfect fluid with a $\gamma$-law equation of state. There are, however, some general properties of cosmological models which admit an Isotropic Singularity, irrespective of the matter source. In particular, we show that the Isotropic Singularity is a point-like singularity and that vacuum space-times cannot admit an Isotropic Singularity. The relationships between the Isotropic Singularity, and the energy conditions, and the Hubble parameter is explored. A review of work by the authors, regarding the Isotropic Singularity, is presented.Comment: 18 pages, 1 figur

Natural scene statistics and the structure of orientation maps in the visual cortex

Visual activity after eye-opening influences feature map structure in primary visual cortex (V1). For instance, rearing cats in an environment of stripes of one orientation yields an over-representation of that orientation in V1. However, whether such changes also affect the higher-order statistics of orientation maps is unknown. A statistical bias of orientation maps in normally raised animals is that the probability of the angular difference in orientation preference between each pair of points in the cortex depends on the angle of the line joining those points relative to a fixed but arbitrary set of axes. Natural images show an analogous statistical bias; however, whether this drives the development of comparable structure in V1 is unknown. We examined these statistics for normal, stripe-reared and dark-reared cats, and found that the biases present were not consistently related to those present in the input, or to genetic relationships. We compared these results with two computational models of orientation map development, an analytical model and a Hebbian model. The analytical model failed to reproduce the experimentally observed statistics. In the Hebbian model, while orientation difference statistics could be strongly driven by the input, statistics similar to those seen in experimental maps arose only when symmetry breaking was allowed to occur spontaneously. These results suggest that these statistical biases of orientation maps arise primarily spontaneously, rather than being governed by either input statistics or genetic mechanisms

A Gendered Imperative: Does Sexual Violence Attract UN Attention in Civil Wars?

There is increasing awareness that sexual violence is distinct from other aspects of civilian victimization in civil wars. Few studies have examined the independent impact of such violence on responses to civil wars as compared to “traditional” forms of violence. This paper explores whether reports of high levels of rape and sexual violence increase the probability of UN attention to conflicts and calls to action. In so doing, we combine original data on UN Security Council resolutions with data on sexual violence in armed conflict and estimate the impact of sexual violence on UN attention to all civil wars from 1990-2009. We show that the effects of sexual violence on the number and level of UNSC resolutions are shown to be significant even when controlling for other important determinants of UN action. These findings have important implications for understanding how the UN has expanded its view on protecting civilians

The role of biophysical cohesion on subaqueous bed form size

Biologically active, fine-grained sediment forms abundant sedimentary deposits on Earth's surface, and mixed mud-sand dominates many coasts, deltas, and estuaries. Our predictions of sediment transport and bed roughness in these environments presently rely on empirically based bed form predictors that are based exclusively on biologically inactive cohesionless silt, sand, and gravel. This approach underpins many paleoenvironmental reconstructions of sedimentary successions, which rely on analysis of cross-stratification and bounding surfaces produced by migrating bed forms. Here we present controlled laboratory experiments that identify and quantify the influence of physical and biological cohesion on equilibrium bed form morphology. The results show the profound influence of biological cohesion on bed form size and identify how cohesive bonding mechanisms in different sediment mixtures govern the relationships. The findings highlight that existing bed form predictors require reformulation for combined biophysical cohesive effects in order to improve morphodynamic model predictions and to enhance the interpretations of these environments in the geological record

Attitudes of Mexican anesthesiologists to indicate preoperative fasting periods: A cross-sectional survey

BACKGROUND: In Mexico, guidelines for fasting periods, or any audits on this topic are unavailable, and therefore the attitudes of anesthesiologists for recommending preoperative fasting periods are unknown. MATERIAL AND METHODS: The study was a cross-sectional survey of anesthesiologists subscribed to the Annual Updated Course, organized by the Sociedad Mexicana de Anestesiologia in 2000. The response rate was 31.4%. RESULTS: Most respondents were general anesthesiologists, with 5 or more years experience in a clinical post, were working in both public and private hospitals, and were performing anesthetic procedures on both pediatric and adult patients and in both ambulatory and hospitalized patients. Approximately 23% of the respondents considered natural fruit juices to be clear liquids. For a pediatric patient ingesting breast milk 1 h before undergoing a surgical procedure, 45% thought that surgery should be delayed for 3h, followed by those delaying the surgical procedure for 6 to 8 h. Our results show that more than 50% of the anesthesiologists had better defined attitudes for fasting milk and clear liquids in patients of 6 month or under than for older children and adults. However, due to the poor definition or pre-operative fasting, using clear liquids, in all other patient groups, several patients are allowed to go without oral clear liquids administration for prolonged periods. CONCLUSION: Preoperative fasting periods recommended by Mexican anesthesiologists differ from international guidelines