San Francisco State University

About: San Francisco State University is a education organization based out in San Francisco, California, United States. It is known for research contribution in the topics: Population & Planet. The organization has 5669 authors who have published 11433 publications receiving 408075 citations. The organization is also known as: San Francisco State & San Francisco State Normal School.

Reduction of Se(VI) to Se(-II) by zerovalent iron nanoparticle suspensions

Abstract: The reaction of selenate (Se(VI)) with zerovalent iron nanoparticles (nano Fe0) was studied using both conventional batch equilibrium and X-ray spectroscopic techniques. Nano Fe0 has a high uptake capacity for removal of dissolved Se(VI) reaching concentrations as high as 0.10 Se:Fe molar ratio in the solid product mixture. Kinetic studies of the Se(VI) uptake reaction in batch experiments showed an initial reaction rate (0–30 min) of 0.0364 min−1 which was four times greater than conventional Fe0 powder. Analysis of the oxidation state of Se in the solid products by X-ray absorption near edge structure (XANES) spectroscopy showed evidence for the reduction of Se(VI) to insoluble selenide (Se(-II)) species. Structural analysis of the product by extended X-ray absorption fine structure (EXAFS) spectroscopy suggested that Se(-II) was associated with nano Fe0 oxidation products as a poorly ordered iron selenide (FeSe) compound. The fitted first shell Se–Fe interatomic distance of 2.402 (±0.004) A matched closely with previous studies of the products of Se(IV)-treated Fe(II)-clays and zero-valent iron/iron carbide (Fe/Fe3C). The poorly ordered FeSe product was associated with Fe0 corrosion product phases such as crystalline magnetite (Fe3O4) and Fe(III) oxyhydroxide. The results of this investigation suggest that nano Fe0 is a strong reducing agent capable of efficient reduction of soluble Se oxyanions to insoluble Se(-II).

Imperfect drug penetration leads to spatial monotherapy and rapid evolution of multidrug resistance

Abstract: Infections with rapidly evolving pathogens are often treated using combinations of drugs with different mechanisms of action. One of the major goal of combination therapy is to reduce the risk of drug resistance emerging during a patient's treatment. Although this strategy generally has significant benefits over monotherapy, it may also select for multidrug-resistant strains, particularly during long-term treatment for chronic infections. Infections with these strains present an important clinical and public health problem. Complicating this issue, for many antimicrobial treatment regimes, individual drugs have imperfect penetration throughout the body, so there may be regions where only one drug reaches an effective concentration. Here we propose that mismatched drug coverage can greatly speed up the evolution of multidrug resistance by allowing mutations to accumulate in a stepwise fashion. We develop a mathematical model of within-host pathogen evolution under spatially heterogeneous drug coverage and demonstrate that even very small single-drug compartments lead to dramatically higher resistance risk. We find that it is often better to use drug combinations with matched penetration profiles, although there may be a trade-off between preventing eventual treatment failure due to resistance in this way and temporarily reducing pathogen levels systemically. Our results show that drugs with the most extensive distribution are likely to be the most vulnerable to resistance. We conclude that optimal combination treatments should be designed to prevent this spatial effective monotherapy. These results are widely applicable to diverse microbial infections including viruses, bacteria, and parasites.

Multiple stressors and amphibian declines: dual impacts of pesticides and fish on yellow-legged frogs.

Abstract: More than 40% of Earth's 5700+ amphibian species have undergone recent declines. Despite the likely involvement of multiple factors in driving these declines, most studies continue to focus on single stressors. In California (USA), separate studies have implicated either introduced fish or pesticides as causal agents. To date, however, no study has simultaneously evaluated the respective roles of these two potential stressors nor attempted to assess their relative importance, information critical for the development of effective conservation efforts and environmental policies. We examined the role and relative effect of fish and pesticides on the mountain yellow-legged frog (Rana muscosa) using unusually detailed data sets for a large portion of R. muscosa's historic range in California's Sierra Nevada. Habitat characteristics and presence/absence of R. muscosa and fish were quantified at each of 6831 sites during field surveys. Pesticide use upwind of each site was calculated from pesticide application records and predominant wind directions. Using generalized additive models, we found that, after accounting for habitat effects, the probability of R. muscosa presence was significantly reduced by both fish and pesticides, with the landscape-scale effect of pesticides much stronger than that of fish. The degree to which a site was sheltered from the predominant wind (and associated pesticides) was also a significant predictor of R. muscosa presence. Taken together, these results represent the strongest evidence to date that windborne pesticides are contributing to amphibian declines in pristine locations. Our results suggest that amphibian declines may have complex multi-factorial causes, and caution that single-factor studies that demonstrate the importance of one factor should not be used as evidence against the importance of other factors.

Evaluating domestic and international Web‐site strategies

Abstract: This paper presents the AIPD approach to the evaluation of commercial Web sites within or across borders. The author explains how benchmarking techniques can be used to compare attracting, informing, positioning, and delivering (AIPD) strategies of Web sites in order to clarify strategic opportunities or advantages. The AIPD model is then used to compare the Internet strategies of some Japanese and American banks. Results show that Japanese banks have created more dynamic and content rich Internet environments than their American counterparts. Cultural and institutional differences are given for the contrasting approaches to Web design, information and service delivery.

Are Social Networking Sites a Source of Online Harassment for Teens? Evidence from Survey Data

Abstract: Media reports on incidences of abuse on the internet, particularly amongst teenagers, are growing at an alarming rate causing much concern among parents of teenagers and legislations aimed at regulating internet use among teenagers. Past studies have found that one in five youth were exposed to sexual solicitation, one in seventeen were harassed or threatened and only a fraction reported these cases while more than 63% reported being upset, embarrassed or stressed as a result of these unwanted contacts. Social networking sites (SNS) have been blamed to be a major source of harassment for teen users. Despite several media reports, there is a serious paucity of research in this area that explicitly identifies risk factors that make teens prone to internet abuse, and strategies for prevention and intervention. This study examines the extent to which internet use and having SNS site memberships result in incidences of stranger contact and online harassment for teens in the United States. We also determine the characteristics of teens that make them more likely to be victims of online harassment. Using parental background information, we also seek to shed light on the relationship between parental awareness and teen abuse on the internet. We use 2006 round of Pew Internet American Life Survey for this study. Since data on social networking has been collected fairly recently and we do not have any past information, the limitation of this study is that we cannot draw causal links between internet use and online harassment.