Water Penetration—Its Effect on the Strength and Toughness of Silica Glass

When a crack forms in silica glass, the surrounding environment flows into the crack opening, and water from the environment reacts with the glass to promote crack growth. A chemical reaction between water and the strained crack-tip bonds is commonly regarded as the cause of subcritical crack growth in glass. In silica glass, water can also have a secondary effect on crack growth. By penetrating into the glass, water generates a zone of swelling and, hence, creates a compression zone around the crack tip and on the newly formed fracture surfaces. This zone of compression acts as a fracture mechanics shield to the stresses at the crack tip, modifying both the strength and subcritical crack growth resistance of the glass. Water penetration is especially apparent in silica glass because of its low density and the fact that it contains no modifier ions. Using diffusion data from the literature, we show that the diffusion of water into silica glass can explain several significant experimental observations that have been reported on silica glass, including (1) the strengthening of silica glass by soaking the glass in water at elevated temperatures, (2) the observation of permanent crack face displacements near the crack tip of a silica specimen that had been soaked in water under load, and (3) the observation of high concentrations of water close to the fracture surfaces that had been formed in water. These effects are consistent with a model suggesting that crack growth in silica glass is modified by a physical swelling of the glass around the crack tip. An implication of water-induced swelling during fracture is that silica glass is more resistant to crack growth than it would be if swelling did not occur.     

Shift Register Graphs and Permutation/Reset Automata

Abstract

This note completes the author's study of embedding of cascade products of permutation or reset automata in so-called shift register graphs.     

SPHERES, Jülich's high-flux neutron backscattering spectrometer at FRM II

SPHERES is a third-generation neutron backscattering spectrometer, located at the 20 MW German neutron source FRM II and operated by the Ju?lich Centre for Neutron Science. It offers an energy resolution (fwhm) better than 0.65 μeV, a dynamic range of ±?31 μeV, and a signal-to-noise ratio of up to 1750:1.     

Contribution of Solutes to Density Stratification in a Meromictic Lake (Waldsee/Germany)

Density differences are the key parameter for stratification stability. We used data from the iron-meromictic Waldsee, Germany, a lignite mine pit lake, to quantify the contribution of single solutes to water density and analyzed the density gradient. Iron meromictic lakes maintain their density gradient through chemical reactions. Hence, quantifying the contributions of separate solutes is essential for understanding the entire process. Based on solute concentrations and literature values of partial molal volumes, substance specific density contributions were quantitatively evaluated. Then, by direct measurements of the density of IHSS Waskish peat fulvic acid, we quantified the density contribution of dissolved organic carbon (DOC). While several solutes contributed to the density throughout the water column, only those substances that occurred at higher concentrations in the anoxic monimolimnion than in the oxic mixolimnion were crucial to sustaining the density difference between the two layers. In Waldsee, the density difference between monimolimnion and mixolimnion was attributed to dissolved Fe²⁺ (0.23?g/L, resulting in a 45?% of the density difference due to solutes) and to the carbonate system (HCO₃ ^?, about 0.16?g/L and CO₂, 0.03?g/L) while Ca²⁺ and DOC delivered only a small contribution. In summer, total density differences were dominated by temperature differences; during winter, solutes sustained meromixis. Finally, we present a complete list of specific density fractions for basically all of the density-relevant substances in fresh waters.     

Development and Performance of Crystallization with Additives Applied on Different Milk Samples

Crystallization with additives is developed on milk samples from different processing treatments. Performance tests are carried out based on structure analysis of the crystallization patterns. Crystallization with milk as additive is applied following changes in milk after different processing treatments. When an aqueous cupric chloride dihydrate solution crystallizes in the presence of milk as additive, specific patterns emerge, which can be evaluated by image analysis. Milk samples were heated and homogenized in a pilot plant and characterized by various parameters. Furthermore, milk samples from the market were tested. Patterns from milk after heat treatment and homogenization are significantly different from those derived from untreated milk. The experiments could be reproduced for other milk samples, on different days and in another laboratory.     

Residual tumor after laser ablation of human non-small-cell lung cancer demonstrated by ex vivo staining: correlation with invasive temperature measurements

Object   

Histology is the gold standard for confirming thermally induced necrosis. Generally, however, no specimen is obtained from thermal ablation therapy for pathological examination. The aim of this study was to provide evidence for the relationship between temperatures reached and resulting tissue coagulation during laser ablation in a near-physiological ex vivo lung tumor model by combining viability staining and direct temperature measurement.