Electron irradiation induced reduction of the permittivity in chalcogenide glass (As2S3) thin film

We investigate the effect of electron beam irradiation on the dielectric properties of As2S3 Chalcogenide glass. By means of low-loss Electron Energy Loss Spectroscopy, we derive the permittivity function, its dispersive relation, and calculate the refractive index and absorption coefficients under the constant permeability approximation. The measured and calculated results show, to the best of our knowledge, a heretofore unseen phenomenon: the reduction in the permittivity of <40%, and consequently a modification of the refractive index follows, reducing it by 20%, hence suggesting a significant change on the optical properties of the material. The plausible physical phenomena leading to these observations are discussed in terms of the homopolar and heteropolar bond dynamics under high energy absorption.Comment: 22 pages, 7 figures, manuscript in preparation to send to Physical Review

The biogeochemical cycling of gold under surface and near-surface environmental conditions

The mobility of gold at near-surface environmental conditions, e.g., supergene weathering environments, lateritic weathering systems, saline to hypersaline systems and placer gold environments, takes place as oxidised, soluble gold complexes and as reduced elemental gold. The transformation between aqueous and solid states of gold is attributed to the varying geochemical conditions that occur in dynamic environments that are catalysed in part by the biosphere. The primary focus of this research is the investigation of biogeochemical processes that contribute to the cycling of gold using laboratory models to represent various natural systems including chemolithotrophic bacteria, e.g., iron-oxidising bacteria, and heterotrophic sulphate-reducing bacteria and nitrifying bacteria. Results from these studies demonstrate that bacteria initiate the gold cycle by liberating gold through the chemical weathering of gold-bearing minerals. Through oxidative-complexation, soluble gold complexes, e.g., gold (I) thiosulphate and gold (III) chloride, could be produced; however, destabilisation of these gold complexes coupled with bioprecipitation and biomineralisation can immobilise gold thereby completing the cycle. Since the biosphere has an influence on the geochemical conditions of natural environments, the duration of the mobility of gold as soluble complexes is finite and represents a brief “snap shot” of gold’s occurrence. Therefore under surface and near-surface environmental conditions gold will predominantly occur as secondary gold. Secondary gold occurs as nanometre-size to micrometre-size colloids, octahedral platelets, euhedral crystals and bacteriomorphic structures. Furthermore, when bacteria develop as a structurally cohesive biofilms, reduction and enrichment of gold can occur and produce macroscopic gold structures including foils, grains and nuggets. Therefore, bacteria can have a profound effect on the occurrence of gold in natural environments as long as nutrients necessary for microbial metabolism are sustained and gold is in the system. The direct and indirect biogenic effects on gold biogeochemistry will persist over geological time forming observed anomalous gold concentrations such as nugget formations and supergene gold enrichment. Characterising the morphology of gold grains and nuggets in association with understanding how biogeochemical conditions contribute to gold immobilisation is important for gold exploration as it has practical application in mineral vectoring

Particulate airborne impurities

The cumulative effects of air pollutants are of principal concern in research on environmental protection in Sweden. Post-industrial society has imposed many limits on emitted air pollutants, yet the number of reports on the negative effects from them is increasing, largely due to human activity in the form of industrial emissions and increased traffic flows. Rising concerns over the health effects from airborne particulate matter (PM) stem from in vitro, in vivo, and cohort studies revealing effects of mostly negative nature. Full insight into the health effects from PM can only be achieved through practical investigation of the mode of toxicity from distinct types of particles and requires techniques for their identification, monitoring, and the production of model fractions for health studies. To this effect, comprehensive collection and chemical analysis of particulates at the origin of emission was performed in order to provide clearer insight into the nature of the particulates at exposure and add detail to aid risk assessment. Methods of capturing particles and analyzing their chemical nature were devised using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). Furthermore, taking the approach of in vitro cytotoxicity testing, nanoparticles of types typical to automotive emissions, were synthesized and extensively characterized using SEM-EDS, X-ray diffraction (XRD), transmission electron microscopy (TEM),dynamic light scattering (DLS), and nanoparticle tracking analysis (NTA). The produced model magnetite and palladium nanoparticles were found to induce toxicity in human pulmonary epithelial cells (A549 and PBEC) as well as impact severely on immunological and renal cells (221 B- and 293T-cells) in a dose-dependent manner

Characterization of Electronic Cigarette Aerosol and Its Induction of Oxidative Stress Response in Oral Keratinocytes.

In this study, we have generated and characterized Electronic Cigarette (EC) aerosols using a combination of advanced technologies. In the gas phase, the particle number concentration (PNC) of EC aerosols was found to be positively correlated with puff duration whereas the PNC and size distribution may vary with different flavors and nicotine strength. In the liquid phase (water or cell culture media), the size of EC nanoparticles appeared to be significantly larger than those in the gas phase, which might be due to aggregation of nanoparticles in the liquid phase. By using in vitro high-throughput cytotoxicity assays, we have demonstrated that EC aerosols significantly decrease intracellular levels of glutathione in NHOKs in a dose-dependent fashion resulting in cytotoxicity. These findings suggest that EC aerosols cause cytotoxicity to oral epithelial cells in vitro, and the underlying molecular mechanisms may be or at least partially due to oxidative stress induced by toxic substances (e.g., nanoparticles and chemicals) present in EC aerosols