The elastic and anelastic constants of a synthetic fluor-mica formed by glass-ceramic fabrication techniques

A tetrasilicic fluor mica, K2Mg5Si8O20F4, was synthesized using glass forming techniques. Density changes, weight losses, and shrinkage, as well as elastic and anelastic properties, were measured on bars heat-treated at selected temperatures between 500°C and 1150°C to determine the characteristics of this material. Phase changes were followed by determining thermal expansion, logarithmic decrement, and modulus of elasticity from room temperature to 800°C. It was found that the elastic and anelastic constants decreased gradually with heat treatments from 600°C to 1000°C. This indicated progressively increased structural ordering. Heat treatments above 1000°C produced appreciable decreases in the elastic constants and equally appreciable increases in the anelastic constants. This was evidence of increasing mica or crystal growth. Determinations of the modulus of elasticity, logarithmic decrement, and thermal expansion from room temperature to 800°C showed the transformation from an amorphous to ordered structure to occur at 600°C. There was also an indication of ionic arrangement prior to the actual transformation --Abstract, page ii

The damage assessment of thermally shocked high density, high purity aluminum oxide

The traditional approach to thermal shock testing in brittle materials has been to determine the temperature difference required to nucleate cracks in these materials. Recent work has indicated that the degree of damage after crack nucleation should be an additional consideration. The degree of damage resulting from cooling thermal shocks has been the primary consideration of the present work. Test specimens of two geometries: long, solid rods and short, solid cylinders were quenched from selected temperatures into ice water. The degree of damage was determined through strength measurements and sonic damping analysis. Initial damage occurred at a temperature difference above 150⁰C; this was characterized by significant decreases in strength, increases in strength data dispersion, and changes in sonic behavior. A model has been employed to predict degree of damage using crack depths as a criteria. Good agreement is seen between the predicted crack depths and observed crack depths at low temperature differences. At higher temperature differences, crack densities increase, and crack interactions affect the agreement between the predicted crack depths and those observed --Abstract, page ii

Clinical risk prediction models: the canary in the coalmine for artificial intelligence in healthcare?

From Europe PMC via Jisc Publications RouterHistory: ppub 2021-10-01Publication status: Publishe

An adaptive stabilized finite element method for the generalized Stokes problem

In this work we present an adaptive strategy (based on an a posteriori error estimator) for a stabilized finite element method for the Stokes problem, with and without a reaction term. The hierarchical type estimator is based on the solution of local problems posed on appropriate finite dimensional spaces of bubble-like functions. An equivalence result between the norm of the finite element error and the estimator is given, where the dependence of the constants on the physics of the problem is explicited. Several numerical results confirming both the theoretical results and the good performance of the estimator are given

Quinoline Sorption on Na-Montmorillonite: Contributions of the Protonated and Neutral Species

Dilute aqueous solutions of quinoline were contacted with Na-montmorillonite to elucidate the sorption process of the neutral and protonated species. Sorption occurs via a combination of ion exchange and molecular adsorption and yields S-type isotherms. Exchange between the quinolinium ion (QH+ and Na can be described by means of Vanselow selectivity coefficients and a thermodynamic exchange constant (Kex). Due to the apparent adsorption of the neutral species at high mole fractions (x) of the solid phase, the thermodynamic standard state was defined as 0.5 mole fraction. The selectivity at pH ~4.95 of the QH+ species over Na (at XQH+ 0.5) was determined to be Kv = 340. At pH ≥ 5.5 surface mole fractions of 0.5 could not he obtained without adsorption of the neutral species. This study suggests that at dilute solution concentrations quinoline is sorbed preferentially as the cation even at pHs \u3e\u3e pKa. A critical surface-solution concentration is apparently necessary for adsorption of the neutral species

Sorption of Binary Mixtures of Aromatic Nitrogen Heterocyclic Compounds on Subsurface Materials

Single and binary solute sorption of pyridine, quinoline, and acridine has been investigated on two low organic carbon subsurface materials with similar properties but different equilibrium pH when saturated with water. Single solute sorption for all compounds is higher in the acidic soil as compared to the basic soil, reflecting stronger sorption of the protonated organic cations. The protonated species exhibit high selectivity for the exchange complex at low aqueous concentration with selectivity increasing with ring number. Binary sorption experiments with quinoline/pyridine and quinoline/acridine demonstrate that competitive sorption occurs between compounds in the acidic subsoil where the protonated compound species predominate in solution. In contrast, competition is minimal in the basic subsoil when the compounds are neutral. The competition between compounds is consistent with their measured single solute sorption and suggests mass action on a common set of high-affinity surface sites. A simplified model based on ideal adsorbed solution theory (IAS) is used to provide simulations of binary solute sorption that are in good qualitative agreement with experimental results. It is suggested that competition between ionized solutes may significantly influence transport of organic mixtures when the groundwater pH is near the pKa of the compounds