On the Thermodynamic Stability of Amorphous Intergranular Films in Covalent Materials

The thermodynamic origin, structure, and stability of the thin amorphous films commonly found in grain boundaries in covalent ceramics are investigated by molecular-dynamics simulation. To focus on the purely thermodynamic aspects, any kinetic effects associated with impurity-controlled interface chemistry are excluded by investigating pure silicon (described by the Stillinger–Weber three-body potential). For this single-component covalent model material, we demonstrate that all high-energy boundaries exhibit a universal amorphous structure, with a width of }0.25 nm, whereas low-energy boundaries are crystalline and much sharper. We also demonstrate that introduction of an amorphous film into a crystalline interface lowers the excess energy to a level similar to the energy of two bulk crystalamorphous interfaces. The competition between a narrow crystalline boundary structure and a wider amorphous boundary structure is shown to be governed by the relative excess energies of the atoms in the grain boundaries and in the bulk amorphous phase. These observations suggest that, in principle, amorphous grain-boundary films do not require impurities for their stabilization and that, as first proposed by Clarke, an equilibrium grain-boundary phase of uniform thickness can be the result of purely thermodynamic rather than kinetic factors.     

Spatial and spectral correlations in MALDI mass spectrometry images by clustering and multivariate analysis

Matrix-assisted laser desorption/ionization mass spectrometry imaging is a technique for direct analysis of tissue sections without the use of molecular tags or contrast agents. The combination of spatial and mass resolution results in large and complex data sets that require powerful and efficient analysis and interpretation tools. Conventional images, derived from a specific analyte mass, do not identify the spatially localized correlations between analytes that are latent in the data. A new approach to find and visualize these correlations is presented. Clustering methods are used to classify pixels by spectral similarity, facilitating definition of distinct spatial regions. Principal component and discriminant analyses are combined to comprehensively identify changes in the mass spectra between regions. Images are generated by projecting the spectra of each pixel on the discriminant spectra; contrast is then a function of multiple correlated peaks.     

Physikalisch-chemische Eigenschaften oxidkeramischer Festelektrolyte bei Stahlschmelztemperaturen

Übersichtsbericht zur Beurteilung der Eignung von feuerfesten Oxiden, Mischoxiden und Oxidverbindungen als Festelektrolyte zur Sauerstoffmessung in Stahlschmelzen. Zusammenstellung und kritische Bewertung der physikalisch-chemischen Eigenschaften der in Frage kommenden oxidkeramischen Festelektrolyte.     

The pressure ratio of critical two-phase flows

Depressurization of a pressure vessel, containing a liquid or a gas is limited by the maximum possible mass flux. This flux occurs at a certain drop in pressure. The ratio of ambient pressure to that inside the vessel must be less than a certain critical value. The critical pressure ratio depends on the thermodynamic state of the fluid inside the vessel and on the geometry of the outlet cross-section. The outlet can be a pipeline, a safety valve or a rupture disk. The results of known theoretical and experimental work are presented. In previous experiments, saturated liquids, two-phase flows or pure vapours were examined. In order to predict the critical pressure ratio, certain assumptions are necessary. These are derived for three well-defined cross-sections of the vessel outlet.