University of Virginia

About: University of Virginia is a education organization based out in Charlottesville, Virginia, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 52543 authors who have published 113268 publications receiving 5220506 citations. The organization is also known as: U of V & UVa.

Intracluster Medium Entropy Profiles for a Chandra Archival Sample of Galaxy Clusters

Abstract: We present radial entropy profiles of the intracluster medium (ICM) for a collection of 239 clusters taken from the Chandra X-ray Observatory's Data Archive. Entropy is of great interest because it controls ICM global properties and records the thermal history of a cluster. Entropy is therefore a useful quantity for studying the effects of feedback on the cluster environment and investigating any breakdown of cluster self-similarity. We find that most ICM entropy profiles are well fitted by a model which is a power law at large radii and approaches a constant value at small radii: K(r) = K {sub 0} + K {sub 100}(r/100 kpc){sup {alpha}}, where K {sub 0} quantifies the typical excess of core entropy above the best-fitting power law found at larger radii. We also show that the K {sub 0} distributions of both the full archival sample and the primary Highest X-Ray Flux Galaxy Cluster Sample of Reiprich (2001) are bimodal with a distinct gap between K {sub 0} {approx} 30-50 keV cm{sup 2} and population peaks at K {sub 0} {approx} 15 keV cm{sup 2} and K {sub 0} {approx} 150 keV cm{sup 2}. The effects of point-spread function smearing and angular resolution on best-fitmore » K {sub 0} values are investigated using mock Chandra observations and degraded entropy profiles, respectively. We find that neither of these effects is sufficient to explain the entropy-profile flattening we measure at small radii. The influence of profile curvature and number of radial bins on best-fit K {sub 0} is also considered, and we find no indication that K {sub 0} is significantly impacted by either. For completeness, we include previously unpublished optical spectroscopy of H{alpha} and [N II] emission lines discussed in Cavagnolo et al. (2008a). All data and results associated with this work are publicly available via the project Web site.« less

Structural Rearrangements Underlying K+-Channel Activation Gating

Abstract: The intramembrane molecular events underlying activation gating in the Streptomyces K+ channel were investigated by site-directed spin-labeling methods and electron paramagnetic resonance spectroscopy. A comparison of the closed and open conformations of the channel revealed periodic changes in spin-label mobility and intersubunit spin-spin interaction consistent with rigid-body movements of the two transmembrane helices TM1 and TM2. These changes involve translations and counterclockwise rotations of both helices relative to the center of symmetry of the channel. The movement of TM2 increases the diameter of the permeation pathway along the point of convergence of the four subunits, thus opening the pore. Although the extracellular residues flanking the selectivity filter remained immobile during gating, small movements were detected at the C-terminal end of the pore helix, with possible implications to the gating mechanism.

Effects of Walking on Mortality among Nonsmoking Retired Men

Abstract: Background The potential benefit of low-intensity activity in terms of longevity among older men has not been clearly documented. We examined the association between walking and mortality in a cohort of retired men who were nonsmokers and physically capable of participating in low-intensity activities on a daily basis. Methods We studied 707 nonsmoking retired men, 61 to 81 years of age, who were enrolled in the Honolulu Heart Program. The distance walked (miles per day) was recorded at a base-line examination, which took place between 1980 and 1982. Data on overall mortality (from any cause) were collected over a 12-year period of follow-up. Results During the follow-up period, there were 208 deaths. After adjustment for age, the mortality rate among the men who walked less than 1 mile (1.6 km) per day was nearly twice that among those who walked more than 2 miles (3.2 km) per day (40.5 percent vs. 23.8 percent, P = 0.001). The cumulative incidence of death after 12 years for the most active walkers was ...

Wild-type microglia arrest pathology in a mouse model of Rett syndrome

Abstract: Rett syndrome is an X-linked autism spectrum disorder. The disease is characterized in most cases by mutation of the MECP2 gene, which encodes a methyl-CpG-binding protein. Although MECP2 is expressed in many tissues, the disease is generally attributed to a primary neuronal dysfunction. However, as shown recently, glia, specifically astrocytes, also contribute to Rett pathophysiology. Here we examine the role of another form of glia, microglia, in a murine model of Rett syndrome. Transplantation of wild-type bone marrow into irradiation-conditioned Mecp2-null hosts resulted in engraftment of brain parenchyma by bone-marrow-derived myeloid cells of microglial phenotype, and arrest of disease development. However, when cranial irradiation was blocked by lead shield, and microglial engraftment was prevented, disease was not arrested. Similarly, targeted expression of MECP2 in myeloid cells, driven by Lysm(cre) on an Mecp2-null background, markedly attenuated disease symptoms. Thus, through multiple approaches, wild-type Mecp2-expressing microglia within the context of an Mecp2-null male mouse arrested numerous facets of disease pathology: lifespan was increased, breathing patterns were normalized, apnoeas were reduced, body weight was increased to near that of wild type, and locomotor activity was improved. Mecp2(+/-) females also showed significant improvements as a result of wild-type microglial engraftment. These benefits mediated by wild-type microglia, however, were diminished when phagocytic activity was inhibited pharmacologically by using annexin V to block phosphatydilserine residues on apoptotic targets, thus preventing recognition and engulfment by tissue-resident phagocytes. These results suggest the importance of microglial phagocytic activity in Rett syndrome. Our data implicate microglia as major players in the pathophysiology of this devastating disorder, and suggest that bone marrow transplantation might offer a feasible therapeutic approach for it.

Creditor Control Rights and Firm Investment Policy

Abstract: We present novel empirical evidence that conflicts of interest between creditors and their borrowers have a significant impact on firm investment policy. We examine a large sample of private credit agreements between banks and public firms and find that 32% of the agreements contain an explicit restriction on the firm's capital expenditures. Creditors are more likely to impose a capital expenditure restriction as a borrower's credit quality deteriorates, and the use of a restriction appears at least as sensitive to borrower credit quality as other contractual terms, such as interest rates, collateral requirements, or the use of financial covenants. We find that capital expenditure restrictions cause a reduction in firm investment and that firms obtaining contracts with a new restriction experience subsequent increases in their market value and operating performance.