Durham University

About: Durham University is a education organization based out in Durham, United Kingdom. It is known for research contribution in the topics: Population & Galaxy. The organization has 39385 authors who have published 82311 publications receiving 3110994 citations. The organization is also known as: University of Durham & Gallery of Durham University.

The Evolution of X-Ray Clusters in a Low-Density Universe

Abstract: We present results of N-body/gasdynamical simulations designed to investigate the evolution of X-ray clusters in a flat, low-density, ?-dominated cold dark matter (CDM) cosmogony. The simulations include self-gravity, pressure gradients, and hydrodynamical shocks, but neglect radiative cooling. The density profile of the dark matter component can be fitted accurately by the simple formula originally proposed by Navarro, Frenk, & White to describe the structure of clusters in a CDM universe with ? = 1. In projection, the shape of the dark matter radial density profile and the corresponding line-of-sight velocity dispersion profile are in very good agreement with the observed profiles for galaxies in the Canadian Network for Observational Cosmology sample of clusters. This suggests that galaxies are not strongly segregated relative to the dark matter in X-ray luminous clusters. The gas in our simulated clusters is less centrally concentrated than the dark matter, and its radial density profile is well described by the familiar ?-model. As a result, the average baryon fraction within the virial radius (rvir) is only 85%-90% of the universal value and is lower nearer the center. The total mass and velocity dispersion of our clusters can be accurately inferred (with ~15% uncertainty) from their X-ray emission-weighted temperature. We generalize Kaiser's scale-free scaling relations to arbitrary power spectra and low-density universes and show that simulated clusters generally follow these relations. The agreement between the simulations and the analytical results provides a convincing demonstration of the soundness of our gasdynamical numerical techniques. Although our simulated clusters resemble observed clusters in several respects, the slope of the luminosity-temperature relation implied by the scaling relations, and obeyed by the simulations, is in disagreement with observations. This suggests that nongravitational effects such as preheating or cooling must have played an important role in determining the properties of the observed X-ray emission from galaxy clusters.

Model selection and model averaging in behavioural ecology: the utility of the IT-AIC framework

Abstract: Behavioural ecologists often study complex systems in which multiple hypotheses could be proposed to explain observed phenomena. For some systems, simple controlled experiments can be employed to reveal part of the complexity; often, however, observational studies that incorporate a multitude of causal factors may be the only (or preferred) avenue of study. We assess the value of recently advocated approaches to inference in both contexts. Specifically, we examine the use of information theoretic (IT) model selection using Akaike’s information criterion (AIC). We find that, for simple analyses, the advantages of switching to an IT-AIC approach are likely to be slight, especially given recent emphasis on biological rather than statistical significance. By contrast, the model selection approach embodied by IT approaches offers significant advantages when applied to problems of more complex causality. Model averaging is an intuitively appealing extension to model selection. However, we were unable to demonstrate consistent improvements in prediction accuracy when using model averaging with IT-AIC; our equivocal results suggest that more research is needed on its utility. We illustrate our arguments with worked examples from behavioural experiments.

Enfuvirtide: the first therapy to inhibit the entry of HIV-1 into host CD4 lymphocytes

Abstract: Highly active antiretroviral therapy (HAART) based on combinations of drugs that target key enzymes in the life-cycle of human immunodeficiency virus (HIV) has considerably reduced morbidity and mortality from HIV infection since its introduction in the mid-1990s. However, the growing problem of the emergence of HIV strains that are resistant not only to individual drugs, but to whole drug classes, means that agents with new mechanisms of action are needed. Here, we describe the discovery and development of enfuvirtide (Fuzeon), the first drug to inhibit the entry of HIV-1 into host cells.

Plasma metabolomic profile in nonalcoholic fatty liver disease.

Abstract: The plasma profile of subjects with nonalcoholic fatty liver disease (NAFLD), steatosis, and steatohepatitis (NASH) was examined using an untargeted global metabolomic analysis to identify specific disease-related patterns and to identify potential noninvasive biomarkers. Plasma samples were obtained after an overnight fast from histologically confirmed nondiabetic subjects with hepatic steatosis (n = 11) or NASH (n = 24) and were compared with healthy, age- and sex-matched controls (n = 25). Subjects with NAFLD were obese, were insulin resistant, and had higher plasma concentrations of homocysteine and total cysteine and lower plasma concentrations of total glutathione. Metabolomic analysis showed markedly higher levels of glycocholate, taurocholate, and glycochenodeoxycholate in subjects with NAFLD. Plasma concentrations of long-chain fatty acids were lower and concentrations of free carnitine, butyrylcarnitine, and methylbutyrylcarnitine were higher in NASH. Several glutamyl dipeptides were higher whereas cysteine-glutathione levels were lower in NASH and steatosis. Other changes included higher branched-chain amino acids, phosphocholine, carbohydrates (glucose, mannose), lactate, pyruvate, and several unknown metabolites. Random forest analysis and recursive partitioning of the metabolomic data could separate healthy subjects from NAFLD with an error rate of approximately 8% and separate NASH from healthy controls with an error rate of 4%. Hepatic steatosis and steatohepatitis could not be separated using the metabolomic profile. Plasma metabolomic analysis revealed marked changes in bile salts and in biochemicals related to glutathione in subjects with NAFLD. Statistical analysis identified a panel of biomarkers that could effectively separate healthy controls from NAFLD and healthy controls from NASH. These biomarkers can potentially be used to follow response to therapeutic interventions.