Accelerated fuel cell tests of anodic Pt/Ru catalyst via identical location TEM: New aspects of degradation behavior

In the present work the stability, chemical composition and structure of a Pt/Ru catalyst alloy with a nominal ratio of 1/1 is investigated. The same catalyst particles are analyzed before and after potential cycling experiments using identical location transmission electron microscopy. The experiments were performed at room temperature at [0–1.0] V_RHE and [0–1.2] V_RHE to simulate conditions occurring during ramping up of fuel cells. With decreasing maximum potential value a higher stability is found. Dissolution and dealloying are identified to be the main degradation mechanisms during potential cycling with Ru being dissolved preferably. Also agglomeration and Ostwald ripening are taking place, the frequency decreasing the longer the experiment is performed. Advanced in-depth analysis of potential-dependent reshaping mechanisms are performed by calculating the three-dimensional volume of single particles both in the as-prepared state and after potential cycling experiments using electron tomography data. Evaluation of the volume-specific change of the accessible surface area of the catalyst helps to understand fuel cell performance deterioration.     

Lymphocyte-filled villi: comparison with other lymphoid aggregations in the mucosa of the human small intestine

BACKGROUND & AIMS: Solitary lymphoid structures that may be sites of primary extrathymic T-cell differentiation have been described recently in murine (cryptopatches) and rat (lymphocyte-filled villi) small intestine. This study tests the hypothesis that similar structures occur in human small intestine. METHODS: Normal small intestine was obtained during surgery. Fixed tissue was examined histologically, and frozen sections were examined by an indirect immunoperoxidase technique using a panel of mouse monoclonal antibodies. RESULTS: A new isolated lymphoid structure, with epithelium resembling follicle-associated epithelium of Peyer's patches, is described as a lymphocyte-filled villus. These structures contain major histocompatibility complex (MHC) class II-positive dendritic cells, a majority of memory T cells, a variable B-cell component, and no evidence of immature lymphocytes that express either c-kit or CD1a. Two previously described lymphoid aggregations (isolated lymphoid follicles and submucosal lymphoid aggregations) are components of a single structure. The complete structure contains a B-cell follicle, T cells with mainly memory (CD45RO-positive) phenotype, high endothelial venules, and no detectable population of immature lymphocytes. CONCLUSIONS: A new solitary lymphoid structure is described in the human small intestine. Neither these structures nor isolated lymphoid follicles appear to be similar to solitary primary lymphoid structures in rodent intestine.     

Sind "Biomedizin" und "Bioethik" behindertenfeindlich?

Ethik in der Medizin - Zwischen Medizinethik und Behindertenbewegung besteht Uneinigkeit darüber, ob von einer Diskriminierung von behinderten Menschen durch biomedizinische Verfahren, wie der...     

Electron Microscopy Study of γ-Al2O3 Supported Cobalt Fischer–Tropsch Synthesis Catalysts

Three supported catalysts containing 20 wt% cobalt and 0.5 wt% rhenium were subjected to electron microscopy studies in their calcined state. The catalysts were prepared by incipient wetness impregnation of γ-Al₂O₃ supports of different pore characteristics with aqueous solutions of cobalt nitrate hexahydrate and perrhenic acid. The influence of the support on the Co₃O₄ crystallite size and distribution was studied by X-ray diffraction and electron microscopy. There was a positive correlation between the pore diameter of the support and the post calcination Co₃O₄ crystallite size. On all three γ-Al₂O₃ supports, Co₃O₄ was present as aggregates of many crystallites (20–270 nm in size). Cobalt oxide did not crystallise as independent crystallites, but as an interconnected network, with a roughly common crystallographic orientation, within the matrix pore structure. The internal variations in crystallite size between the catalysts were maintained after reduction. Fischer–Tropsch synthesis was carried out in a fixed-bed reactor at industrial conditions (T = 483 K, P = 20 bar, H₂/CO = 2.1). Although the cobalt-time yields varied significantly (4.6–6.7 × 10^?3 mol CO/mol Co s), the site-time yields were constant (63–68 × 10^?3 s^?1) for the three samples. The C₅₊ selectivity could not be correlated to the cobalt oxide aggregate size and is more likely related to the cobalt particle size and chemical properties of the γ-Al₂O₃ support.     

Adsorption characteristics of selected pharmaceuticals and an endocrine disrupting compound-Naproxen, carbamazepine and nonylphenol-on activated carbon

The adsorption of two representative pharmaceutically active compounds (PhACs) (naproxen and carbamazepine) and one endocrine disrupting compound (nonylphenol) were evaluated on two types of activated carbon. When determining their isotherms at environmentally relevant concentration levels, it was found that at this low concentration range (10-800 ng/L), removals of the target compounds were contrary to expectations based on their hydrophobicity. Nonylphenol (log K(ow) 5.8) was most poorly adsorbed, whereas carbamazepine (log K(ow) 2.45) was most adsorbable. Nonylphenol Freundlich isotherms at this very low concentration range had a much higher 1/n compared to isotherms at much higher concentrations. This indicates that extrapolation from an isotherm obtained at a high concentration range to predict the adsorption of nonylphenol at a concentration well below the range of the original isotherm, leads to a substantial overestimation of its removals. Comparison of isotherms for the target compounds to those for other conventional micropollutants suggested that naproxen and carbamazepine could be effectively removed by applying the same dosage utilized to remove odorous compounds (geosmin and MIB) at very low concentrations. The impact of competitive adsorption by background natural organic matter (NOM) on the adsorption of the target compounds was quantified by using the ideal adsorbed solution theory (IAST) in combination with the equivalent background compound (EBC) approach. The fulfilment of the requirements for applying the simplified IAST-EBC model, which leads to the conclusion that the percentage removal of the target compounds at a given carbon dosage is independent of the initial contaminant concentration, was confirmed for the situation examined in the paper. On this basis it is suggested that the estimated minimum carbon usage rates (CURs) to achieve 90% removal of these emerging contaminants would be valid at concentrations of less than 500 ng/L in natural water.     

Measurement of oxygen reduction activities via the rotating disc electrode method: From Pt model surfaces to carbon-supported high surface area catalysts

The aim of this report is to scrutinize the thin-film rotating disc electrode (TF-RDE) method for investigating the electrocatalytic activity of high surface area catalysts. Special emphasis is given to the oxygen reduction reaction (ORR) on carbon-supported platinum catalysts. On the basis of measurements on four different Pt catalyst samples with various average particle sizes, it is demonstrated in detail how the intrinsic properties of the catalyst, i.e., the mass activity (A/g_Pt) and the specific activity (A/m²_Pt), are evaluated. The potential sources of error are critically discussed and guidelines for the measurements are given. Furthermore, the specific ORR activities determined for the different catalyst samples are analyzed and compared to polycrystalline Pt. The previously reported effect of the particle size on the specific activity for the ORR is interpreted on the basis of the shift in the potential of zero total charge and the concomitant alteration of the adsorption properties.     

Molecular criteria for discriminating adipose fat and milk from different species by NanoESI MS and MS/MS of their triacylglycerols: application to archaeological remains

A new multistep analytical methodology is described in this paper for the precise identification of triacylglycerols, which are biomarkers of dairy products and subcutaneous fats, that may be chemically identified in archaeological pottery. It consists of the analysis of the total lipid extract from different kinds of fats by high-temperature gas chromatography, performed in order to select the ceramic vessels in which animal fats are well preserved, followed by nanoelectrospray QqTOF mass spectrometry that allows for distinguishing the specific origins of the lipids detected (namely, cow, sheep, or goat). The analysis of model samples, cow and goat dairy products and cow and sheep adipose fats, was successfully achieved. The fatty acid composition of each triacylglycerol was identified, which allowed for the discrimination of subcutaneous fats and dairy fats and distinguishing between cow and goat milk. This methodology was then applied to archaeological samples, and the presence of goat milk, cow milk, and possibly sheep subcutaneous fat was assessed based on the discriminating criteria found on modern fats.     

Low-temperature fabrication of layered self-organized Ge clusters by RF-sputtering

In this article, we present an investigation of (Ge + SiO₂)/SiO₂ multilayers deposited by magnetron sputtering and subsequently annealed at different temperatures. The structural properties were investigated by transmission electron microscopy, grazing incidence small angles X-ray scattering, Rutherford backscattering spectrometry, Raman, and X-ray photoelectron spectroscopies. We show a formation of self-assembled Ge clusters during the deposition at 250°C. The clusters are ordered in a three-dimensional lattice, and they have very small sizes (about 3 nm) and narrow size distribution. The crystallization of the clusters was achieved at annealing temperature of 700°C.