Quantum theory of dissociative chemisorption on metal surfaces

Recent theoretical progress in gas-surface reaction dynamics, a field relevant to heterogeneous catalysis, is described. One of the most fundamental reactions, the dissociative chemisorption of H2 on metal surfaces, can now be treated accurately using quantum mechanics. Density functional theory is used to compute the molecule-surface interaction, and the motion of the hydrogen atoms is simulated using quantum dynamics, modeling all six molecular degrees of freedom. Theory is in good quantitative agreement with molecular beam experiments, offering useful interpretations, and allowing reliable predictions. The success of the approach calls for extensions to larger systems, such as dissociative chemisorption of polyatomic molecules.     

Information risk management and compliance — expect the unexpected

This paper sets out to demonstrate how establishing an effective information risk management programme is a key element in an enterprise’s overall operational risk and governance programme. Establishing such a programme provides a golden opportunity to rationalise and align a number of processes and disciplines into an overall effective risk and compliance programme. This paper provides the opening steps for establishing such a programme to open up the possibility of such an opportunity. The business need has been created through legislation and regulation, accounting standards, best practice or contractual commitments for effective governance and appropriate risk management while meeting the need to generate profit and be cost effective. Aspects of financial risk, e.g. credit risk, are supported through mature processes and there is wide commercial experience in many of these finance related areas; however, other aspects of risk may be of such low frequency that little or no experience has been accumulated. For some risks the processes have not been developed to manage the risk — or where a risk management process is present, they are either immature or ineffective.     

Weight-of-evidence evaluation in environmental assessment: Review of qualitative and quantitative approaches

Assessments of human health and ecological risk draw upon multiple types and sources of information, requiring the integration of multiple lines of evidence before conclusions may be reached. Risk assessors often make use of weight-of-evidence (WOE) approaches to perform the integration, whether integrating evidence concerning potential carcinogenicity, toxicity, and exposure from chemicals at a contaminated site, or evaluating processes concerned with habitat loss or modification when managing a natural resource. Historically, assessors have relied upon qualitative WOE approaches, such as professional judgment, or limited quantitative methods, such as direct scoring, to develop conclusions from multiple lines of evidence. Current practice often lacks transparency resulting in risk estimates lacking quantified uncertainty. This paper reviews recent applications of weight of evidence used in human health and ecological risk assessment. Applications are sorted based on whether the approach relies on qualitative and quantitative methods in order to reveal trends in the use of the term weight of evidence, especially as a means to facilitate structured and transparent development of risk conclusions from multiple lines of evidence.     

Effect of Low-Levels of Strontium on the Oxidation Behavior of Selected Molten Aluminum–Magnesium Alloys

The effects of small additions of strontium on the oxidation behavior of aluminum–magnesium alloy melts were investigated by thermogravimetry at 750 °C for times up to 48 h. Oxidized samples were examined by FEGSEM, and phases formed within the oxide layer and in the alloy were identified by EDS, WDS and low-angle X-ray diffraction techniques. In the absence of Sr, the Al–Mg samples gained substantial amounts of weight by formation of spinel (MgAl₂O₄) at the oxide–metal interface. Samples containing Sr had significantly lower weight gains. A very significant decrease (98%) of total weight gain was observed for small Sr additions in the low Mg-bearing Al–Mg alloys. This change in oxidation behavior was linked to the presence of Sr enrichment of the liquid beneath the initial MgO layer suppressing the formation of spinel crystals.     

Several Theoretical Perspectives of Ferrite-Based Materials—Part 2: Close Packing Model for Crystal Structure

The model for crystal structure involving close packing of equivalent spheres is simple and intuitive. It is a handy tool and is familiar to material scientists. In this work, the usefulness of this model is expanded. An intuitive presentation of the structure of ferrites is developed from the close spherical packing model instead of from group theory. It is demonstrated here that the model is versatile by revealing information about structure not previously presented with this model.     

Preparation of fine copper powders from organic media by reaction with hydrogen under pressure: Part II. The kinetics of particle nucleation,growth, and dispersion

The kinetics of very tine copper powder (1 to 2 μm) production by hydrogen reduction of solvent extracted copper chelates have been determined. The Avrami-Erafeer model for nucleation growth processes has been found to best describe the precipitation kinetics. The model parameters were correlated with reasonable success to the morphology of the copper powder. The chemically controlled particle formation process was found to exhibit 30 to 58 kJ/mol activation energy depending on the temperature range and a complex dependency (from first order to fractional/zero order) on hydrogen pressure. A steric stabilization model has been advanced to interpret the cooperative action of decanol and Versatic 10 in stabilizing the very fine copper powder dispersion.     

False negative cytogenetic results following amniocentesis

The effect of feeding rats with cassava diet (tapioca) has been investigated with respect to the activities of superoxide dismutase, catalase and levels of TBARS. By varying the levels of protein in the diet and cyanide content of cassava, the possible role of a high protein diet in the prevention of oxidant stress has been shown. Rhodanese which detoxifes cyanide is also found to be inhibited in rats fed low protein diet while the inhibition was only marginal in the high protein fed groups.     

Quantification of cytomegalovirus DNA in peripheral blood leukocytes by a branched-DNA signal amplification assay

Quantification of cytomegalovirus (CMV) DNA in blood may aid in the identification of patients at highest risk for developing CMV disease, the evaluation of new therapeutics, and the prompt recognition of drug-resistant CMV strains. A branched-DNA (bDNA) assay was developed for the reliable quantification of CMV DNA in peripheral blood leukocytes. The bDNA assay allowed for the highly specific and reproducible quantification of CMV DNA in clinical specimens. Furthermore, the bDNA assay was at least as sensitive as culture techniques and displayed a nearly 3 log10 dynamic range in quantification. Changes in CMV DNA levels measured by the bDNA assay in a human immunodeficiency virus-positive patient undergoing therapy were consistent with CMV culture, antigen, and genotype results and correlated with disease progression and resistance markers. The bDNA assay for the quantification of CMV DNA may provide a useful tool that can be used to aid physicians in monitoring disease progression, evaluating therapeutic regimens, and recognizing viral resistance and drug failure.     

Nanoconfinement degradation in NaAlH4/CMK-1

An ordered mesoporous carbon scaffold (CMK-1) has been synthesized and infiltrated with NaAlH₄ nanoparticles by solvent- and melt-infiltration techniques. Small angle X-ray scattering (SAXS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM) and energy dispersive spectroscopy (EDS) are used to characterize the structure, composition and morphology before and after thermal treatment. This study illuminates some of the problems that can be associated with nanoconfinement of hydrogen storage materials including scaffold contamination, residual solvent contamination, sample morphology changes after heating, and other factors that can be detrimental to the application of these systems. Of particular interest is the expulsion of NaAlH₄ decomposition products from the scaffold after heating beyond its melting point under vacuum. This results in the surface of mesoporous carbon particles having arrays of multi-micron-long Al filaments that are >100 nm in diameter.