Ag-Cu alloy surfaces in an oxidizing environment: a first-principles study

Recent experiments on model catalysts have shown that Ag-Cu alloys have improved selectivity with respect to pure silver for ethylene epoxidation. In this paper we review our first-principles investigations on the (111) surface of this alloy and present new findings on other low index surfaces. We find that, for every surface orientation, the presence of oxygen leads to copper segregation to the surface. Considering the alloy to be in equilibrium with an oxygen atmosphere and accounting for the effect of temperature and pressure, we compute the surface free energy and study the stability of several surface structures. Investigating the dependence of the surface free energy on the surface composition, we construct the phase diagram of the alloy for every surface orientation. Around the temperature, pressure and composition of interest for practical applications, we find that a limited number of structures can be present, including a thin layer of copper oxide on top of the silver surface and copper-free structures. Different surface orientations show a very similar behavior and in particular a single layer with CuO stoichiometry, significantly distorted when compared to a layer of bulk CuO, has a wide range of stability for all orientations. Our results are consistent with, and help explain, recent experimental measurements

Microtubules as a Critical Target for Arsenic Toxicity in Lung Cells in Vitro and in Vivo

To understand mechanisms for arsenic toxicity in the lung, we examined effects of sodium m-arsenite (As3+) on microtubule (MT) assembly in vitro (0–40 µM), in cultured rat lung fibroblasts (RFL6, 0–20 µM for 24 h) and in the rat animal model (intratracheal instillation of 2.02 mg As/kg body weight, once a week for 5 weeks). As3+ induced a dose-dependent disassembly of cellular MTs and enhancement of the free tubulin pool, initiating an autoregulation of tubulin synthesis manifest as inhibition of steady-state mRNA levels of βI-tubulin in dosed lung cells and tissues. Spindle MT injuries by As3+ were concomitant with chromosomal disorientations. As3+ reduced the binding to tubulin of [3H]N-ethylmaleimide (NEM), an -SH group reagent, resulting in inhibition of MT polymerization in vitro with bovine brain tubulins which was abolished by addition of dithiothreitol (DTT) suggesting As3+ action upon tubulin through -SH groups. In response to As3+, cells elevated cellular thiols such as metallothionein. Taxol, a tubulin polymerization agent, antagonized both As3+ and NEM induced MT depolymerization. MT–associated proteins (MAPs) essential for the MT stability were markedly suppressed in As3+-treated cells. Thus, tubulin sulfhydryls and MAPs are major molecular targets for As3+ damage to the lung triggering MT disassembly cascades

Geospatial information infrastructures

Manual of Digital Earth / Editors: Huadong Guo, Michael F. Goodchild, Alessandro Annoni .- Springer, 2020 .- ISBN: 978-981-32-9915-3Geospatial information infrastructures (GIIs) provide the technological, semantic,organizationalandlegalstructurethatallowforthediscovery,sharing,and use of geospatial information (GI). In this chapter, we introduce the overall concept and surrounding notions such as geographic information systems (GIS) and spatial datainfrastructures(SDI).WeoutlinethehistoryofGIIsintermsoftheorganizational andtechnologicaldevelopmentsaswellasthecurrentstate-of-art,andreflectonsome of the central challenges and possible future trajectories. We focus on the tension betweenincreasedneedsforstandardizationandtheever-acceleratingtechnological changes. We conclude that GIIs evolved as a strong underpinning contribution to implementation of the Digital Earth vision. In the future, these infrastructures are challengedtobecomeflexibleandrobustenoughtoabsorbandembracetechnological transformationsandtheaccompanyingsocietalandorganizationalimplications.With this contribution, we present the reader a comprehensive overview of the field and a solid basis for reflections about future developments

Social Media Data Can Be Used to Understand Tourists’ Preferences for Nature-Based Experiences in Protected Areas

Can social media data be used as an alternative to traditional surveys to understand tourists’ preferences for nature-based experiences in protected areas? We explored this by comparing preferences for biodiversity obtained from a traditional survey conducted in Kruger National Park, South Africa, with observed preferences assessed from over 13,600 pictures shared on Instagram and Flickr by tourists visiting the park in the same period. We found no significant difference between the preferences of tourists as stated in the surveys and the preferences revealed by social media content. Overall, large-bodied mammals were found to be the favorite group, both in the survey and on social media platforms. However, Flickr was found to better match tourists’ preference for less-charismatic biodiversity. Our findings suggest that social media content can be used as a cost-efficient way to explore, and for more continuous monitoring of, preferences for biodiversity and human activities in protected areas.Peer reviewe

Protective effects of selenium on oxidative damage and oxidative stress related gene expression in rat liver under chronic poisoning of arsenic

Arsenic (As) is a toxic metalloid existing widely in the environment, and chronic exposure to it through contaminated drinking water has become a global problem of public health. The present study focused on the protective effects of selenium on oxidative damage of chronic arsenic poisoning in rat liver. Rats were divided into four groups at random and given designed treatments for 20 weeks. The oxidative damage of liver tissue was evaluated by lipid peroxidation and antioxidant enzymes. Oxidative stress related genes were detected to reflect the liver stress state at the molecular level. Compared to the control and Na2SeO3 groups, the MDA content in liver tissue was decreased and the activities of antioxidant enzymes were increased in the Na2SeO3 intervention group. The mRNA levels of SOD1, CAT, GPx and Txnrd1 were increased significantly (P < 0.05) in the combined Na2SeO3 + NaAsO2 treatment group. The expressions of HSP70 and HO-1 were significantly (P < 0.05) increased in the NaAsO2 group and reduced in the combined treatment group. The results indicate that long-term intake of NaAsO2 causes oxidative damage in the rat liver, and Na2SeO3 protects liver cells by adjusting the expression of oxidative stress related genes to improve the activities of antioxidant enzymes. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved

Classical strong metal–support interactions between gold nanoparticles and titanium dioxide

Supported metal catalysts play a central role in the modern chemical industry but often exhibit poor on-stream stability. The strong metal–support interaction (SMSI) offers a route to control the structural properties of supported metals and, hence, their reactivity and stability. Conventional wisdom holds that supported Au cannot manifest a classical SMSI, which is characterized by reversible metal encapsulation by the support upon high-temperature redox treatments. We demonstrate a classical SMSI for Au/TiO2, evidenced by suppression of CO adsorption, electron transfer from TiO2 to Au nanoparticles, and gold encapsulation by a TiOx overlayer following high-temperature reduction (reversed by subsequent oxidation), akin to that observed for titania-supported platinum group metals. In the SMSI state, Au/TiO2 exhibits markedly improved stability toward CO oxidation. The SMSI extends to Au supported over other reducible oxides (Fe3O4 and CeO2) and other group IB metals (Cu and Ag) over titania. This discovery highlights the general nature of the classical SMSI and unlocks the development of thermochemically stable IB metal catalysts

Modification of Dust Grain Structure by Sputtering

We have applied the SRIM computer code to study the sputtering of some likely astrophysical grain materials, and we have shown that selective embedding of metallic projectiles offers a partial explanation of gas-phase depletions. We show that supernova shockwaves sweep a significantly larger mass of interstellar gas per unit time than the shockwaves generated by outflows in star-forming regions. We apply our sputtering model to the bombardment levels expected in a supernova shock, and show that net embedding may dominate over net sputtering, leading to grain growth under some circumstances, particularly when the bombarding gas is enriched with metals from the supernova progenitor star. A combination of short cooling times and net embedding mean that it is possible for a type II supernova to generate more dust that it destroys, and we conclude that, in general, the sputtering process often leads to a compositional change in the grain material rather than simply to grain erosion.Comment: tex file and nine postscript figure in tar.gz archiv

The Effects of Arsenic Trioxide on DNA Synthesis and Genotoxicity in Human Colon Cancer Cells

Colon cancer is the third leading cause of cancer-related deaths worldwide. Recent studies in our laboratory have demonstrated that arsenic trioxide is cytotoxic in human colon cancer (HT-29), lung (A549) and breast (MCF-7) carcinoma cells. The purpose of the present study is to investigate the effects of arsenic trioxide on DNA synthesis and the possible genotoxic effects on human colon cancer cells. HT-29 cells were cultured according to standard protocol, followed by exposure to various doses (0, 2, 4, 6, 8, 10, and 12 μg/mL) of arsenic trioxide for 24 h. The proliferative response (DNA synthesis) to arsenic trioxide was assessed by [3H]thymidine incorporation. The genotoxic effects of arsenic-induced DNA damage in a human colon cancer cell line was evaluated by the alkaline single cell gel electrophoresis. Results indicated that arsenic trioxide affected DNA synthesis in HT-29 cells in a biphasic manner; showing a slight but not significant increase in cell proliferation at lower levels of exposure (2, 4 and 6 μg/mL) followed by a significant inhibition of cell proliferation at higher doses (i.e., 8 and 10 μg/mL). The study also confirmed that arsenic trioxide exposure caused genotoxicity as revealed by the significant increase in DNA damage, comet tail-lengths, and tail moment when compared to non-exposed cells. Results of the [3H]thymidine incorporation assay and comet assay revealed that exposure to arsenic trioxide affected DNA synthesis and exhibited genotoxic effects in human colon cancer cells

A case-control study of GST polymorphisms and arsenic related skin lesions

BACKGROUND: Polymorphisms in GSTT1, GSTM1 and GSTP1 impact detoxification of carcinogens by GSTs and have been reported to increase susceptibility to environmentally related health outcomes. Individual factors in arsenic biotransformation may influence disease susceptibility. GST activity is involved in the metabolism of endogenous and exogenous compounds, including catalyzing the formation of arsenic-GSH conjugates. METHODS: We investigated whether polymorphisms in GSTT1, GSTP1 and GSTM1 were associated with risk of skin lesions and whether these polymorphisms modify the relationship between drinking water arsenic exposure and skin lesions in a case control study of 1200 subjects frequency matched on age and gender in community clinics in Pabna, Bangladesh in 2001–2002. RESULTS AND DISCUSSION: GSTT1 homozygous wildtype status was associated with increased odds of skin lesions compared to the null status (OR1.56 95% CI 1.10–2.19). The GSTP1 GG polymorphism was associated with greater odds of skin lesions compared to GSTP1 AA, (OR 1.86 (95%CI 1.15–3.00). No evidence of effect modification by GSTT1, GSTM1 or GSTP1 polymorphisms on the association between arsenic exposure and skin lesions was detected. CONCLUSION: GSTT1 wildtype and GSTP1 GG are associated with increased risk of skin lesions