University of North Carolina at Chapel Hill

About: University of North Carolina at Chapel Hill is a education organization based out in Chapel Hill, North Carolina, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 81393 authors who have published 185327 publications receiving 9948508 citations. The organization is also known as: University of North Carolina & North Carolina.

Measuring Tie Strength

Abstract: Little attention has been given to the measurement of the concept of tie strength. Using survey data on friendship ties, we apply multiple indicator techniques to construct and validate measures of tie strength. We conclude that: (1) there may be two distinct aspects of tie strength, having to do with the time spent in a relationship and the depth of the relationship; (2) a measure of "closeness" or intensity is the best indicator of strength; (3) there are difficulties with frequency and duration of contact as indicators of strength; (4) predictors of strength (e.g., kinship, neighboring) are not especially strongly related to the concept; and (5) the constructed measures of strength, particularly the one of "time spent," are valid in that they are related to predictor variables in anticipated directions. Tie strength is probably the network concept that has attracted the most research attention and the one that has led to the most in the way of substantive contributions. Research using the concept was initiated by the publication of Granovetter's (a) paper entitled "The Strength of Weak Ties," and Granovetter (c) has recently provided an overview of many of the studies that have invoked the concept. Substantive successes have been especially visible in the literature on the process of social mobility, where variations in tie strength have been shown to be systematically related to the outcomes of job search efforts, but there have been applications to other substantive concerns as well. These accomplishments based on the tie strength concept are notable ones. We find, however, an important gap in this literature. Little sustained attention has been given to the measurement of the concept of tie strength, and the (presumably differential) accuracy of the different mea*This paper was presented at the 1983 annual meeting of the American Sociological Association, session on Network Analysis. We thank Lois Verbrugge for help in understanding nuances of the data sources, and Mark Granovetter, Edward 0. Laumann, and Rachel Rosenfeld for helpful comments. Address correspondence to Peter V. Marsden, Department of Sociology, Hamilton Hall 070A, University of North Carolina, Chapel Hill, NC 27514. C) 1984 The University of North Carolina Press

Analysis of protein-coding genetic variation in 60,706 humans

Abstract: Large-scale reference data sets of human genetic variation are critical for the medical and functional interpretation of DNA sequence changes. Here we describe the aggregation and analysis of high-quality exome (protein-coding region) sequence data for 60,706 individuals of diverse ethnicities. The resulting catalogue of human genetic diversity has unprecedented resolution, with an average of one variant every eight bases of coding sequence and the presence of widespread mutational recurrence. The deep catalogue of variation provided by the Exome Aggregation Consortium (ExAC) can be used to calculate objective metrics of pathogenicity for sequence variants, and to identify genes subject to strong selection against various classes of mutation; we identify 3,230 genes with near-complete depletion of truncating variants, 79% of which have no currently established human disease phenotype. Finally, we show that these data can be used for the efficient filtering of candidate disease-causing variants, and for the discovery of human knockout variants in protein-coding genes.

Oxidative Stress and Vascular Disease

Abstract: Growing evidence indicates that chronic and acute overproduction of reactive oxygen species (ROS) under pathophysiologic conditions is integral in the development of cardiovascular diseases (CVD). These ROS can be released from nicotinamide adenine dinucleotide (phosphate) oxidase, xanthine oxidase, lipoxygenase, mitochondria, or the uncoupling of nitric oxide synthase in vascular cells. ROS mediate various signaling pathways that underlie vascular inflammation in atherogenesis: from the initiation of fatty streak development through lesion progress to ultimate plaque rupture. Various animal models of oxidative stress support the notion that ROS have a causal role in atherosclerosis and other cardiovascular diseases. Human investigations also support the oxidative stress hypothesis of atherosclerosis. Oxidative stress is the unifying mechanism for many CVD risk factors, which additionally supports its central role in CVD. Despite the demonstrated role of antioxidants in cellular and animal studies, the ineffectiveness of antioxidants in reducing cardiovascular death and morbidity in clinical trials has led many investigators to question the importance of oxidative stress in human atherosclerosis. Others have argued that the prime factor for the mixed outcomes from using antioxidants to prevent CVD may be the lack of specific and sensitive biomarkers by which to assess the oxidative stress phenotypes underlying CVD. A better understanding of the complexity of cellular redox reactions, development of a new class of antioxidants targeted to specific subcellular locales, and the phenotype-genotype linkage analysis for oxidative stress will likely be avenues for future research in this area as we move toward the broader use of pharmacological and regenerative therapies in the treatment and prevention of CVD.

Defect passivation in hybrid perovskite solar cells using quaternary ammonium halide anions and cations

Abstract: The ionic defects at the surfaces and grain boundaries of organic–inorganic halide perovskite films are detrimental to both the efficiency and stability of perovskite solar cells. Here, we show that quaternary ammonium halides can effectively passivate ionic defects in several different types of hybrid perovskite with their negative- and positive-charged components. The efficient defect passivation reduces the charge trap density and elongates the carrier recombination lifetime, which is supported by density-function-theory calculation. The defect passivation reduces the open-circuit-voltage deficit of the p–i–n-structured device to 0.39 V, and boosts the efficiency to a certified value of 20.59 ± 0.45%. Moreover, the defect healing also significantly enhances the stability of films in ambient conditions. Our findings provide an avenue for defect passivation to further improve both the efficiency and stability of solar cells. Losses in solar cells can be caused by material defects in the bulk or at interfaces. Here, Zheng et al. use quaternary ammonium halides to passivate various perovskite absorbers and prepare solar cells with certified efficiency above 20%, suggesting that both anionic and cation defects are affected.