Constitution of Bone China: I, High-Temperature Phase Equilibrium Studies in the System Tricalcium Phosphate—Alumina—Silica

This investigation represents a first attempt to interpret the thermal behavior and constitution of bone china by means of a phase diagram of an idealized system. A consideration of the Tricalcium phosphate-alumina-sica phase diagram in relation to the quaternary system lime-alumina-phosphorus pentoxide-silica indicates that the composition of a normally tired commercial bone china body is β-tricalcium phosphate and anorthite in a siliceous glassy matrix. X-ray examinations of many such bodies confirm this interpretation. This preliminary investigation indicates the most profitable fields for further research.     

Microcomputer Solution of Large Structural Dynamic Problems

Microcomputers are currently used to solve linear problems in structural dynamics. However, realistic engineering applications require a large amount of processing operations such that computer execution time and storage requirements can become critical. It is shown in this paper that the solution of large three-dimensional linear dynamic problems using microcomputers is best accomplished by working with a reduced system of equilibrium equations expressed in generalized coordinates derived from a new load-dependent subspace Ritz-transformation method instead of the classical eigensolution procedure. Numerical applications on the microcomputer earthquake response analysis of a three-dimensional model of nearly 2000 dynamic degrees of freedom is used to illustrate the relative efficiency of the proposed solution algorithm as compared to the subspace iteration method.     

Thermodynamics in a hierarchically organized system: microcanonical ensembles with non-equiprobable states

The aim is to research equilibrium distributions for hierarchically organized systems. These systems are divided into weakly coupled groups. In the first step, equilibrium distributions are obtained for isolated groups considered as micro-canonical ensembles. In a second step, the couplings between the groups are taken into account and the equilibrium distribution is obtained for the whole hierarchical system. It is shown that the entropy of a hierachical multi-level system is the sum of entropies relative to each level and of coupling entropies. We particularly study the entropy exchanges between the hierarchical levels, or vertical exchanges of entropy. Microcanonical ensembles with non-equiprobable states are studied. The method is applied to an ecological example of coupled individual and population levels.     

Chitosan Gel Beads as a New Biosorbent for Molybdate Removal

Abstract

Metal ion sorption on chitosan is controlled by intraparticle mass transfer. This paper examines the suggestions of producing gel beads to enhance these diffusion properties. This technique consisted of two stages: firstly dissolving chitosan in acetic acid solution followed by dropping the resulting viscous solution through a thin nozzle into a casting alkaline solution (NaOH). This sorbent was tested for molybdate removal. The optimum pH range corresponded to an acid medium. A cross-linking stage in glutaraldehyde solution increases resistance to acid preventing gel beads dissolving. Metal ion concentration, particle size, chitosan conditioning and competitor ions were studied in terms of equilibrium and kinetic performances. The intraparticuiar diffusion coefficients were evaluated and sorption capacities as high as 750 mg (dry)g^?1 were obtained. Dynamic removal of molybdate in a fixed-bed reactor was also studied in terms of flow rate and column size effects.     

Non‐rigid alignment in electron tomography in materials science

Electron tomography is a key technique that enables the visualization of an object in three dimensions with a resolution of about a nanometre. High‐quality 3D reconstruction is possible thanks to the latest compressed sensing algorithms and/or better alignment and preprocessing of the 2D projections. Rigid alignment of 2D projections is routine in electron tomography. However, it cannot correct misalignments induced by (i) deformations of the sample due to radiation damage or (ii) drifting of the sample during the acquisition of an image in scanning transmission electron microscope mode. In both cases, those misalignments can give rise to artefacts in the reconstruction. We propose a simple‐to‐implement non‐rigid alignment technique to correct those artefacts. This technique is particularly suited for needle‐shaped samples in materials science. It is initiated by a rigid alignment of the projections and it is then followed by several rigid alignments of different parts of the projections. Piecewise linear deformations are applied to each projection to force them to simultaneously satisfy the rigid alignments of the different parts. The efficiency of this technique is demonstrated on three samples, an intermetallic sample with deformation misalignments due to a high electron dose typical to spectroscopic electron tomography, a porous silicon sample with an extremely thin end particularly sensitive to electron beam and another porous silicon sample that was drifting during image acquisitions.     

Validation of a Second-Order Slip Flow Model in Rectangular Microchannels

An analytical slip-flow model based on second-order boundary conditions was proposed for gaseous flow in rectangular microchannels. An experimental setup has been designed for the measurement of gaseous micro flow rates under controlled temperature and pressure conditions. Data relative to nitrogen and helium flows through rectangular microchannels, from 4.5 to 0.5 μm in depth and with aspect ratios from 1–9%, are presented and analyzed. A method is proposed to eliminate the main source of uncertainty, which is the imprecision when measuring the dimensions of the microchannel cross-section. It is shown that in rectangular microchannels, the proposed second-order model is valid for Knudsen numbers up to about 0.25, whereas the first-order model is no longer accurate for values higher than 0.05. The best fit is found for a tangential momentum accommodation coefficient σ = 0.93, both with helium and nitrogen.     

ON THE SWELLING OF SUBMERGED JETS OF DILUTE AND SEMI-DILUTE POLYMER SOLUTIONS

Profound jet swelling is shown to exist when a dilute or semi-dilute solution of PEO (POLYOX WSR 301) is ejected from a capillary tube into a stagnant fluid. The jet swells up to ten times the diameter of the capillary tube depending on the shear rate in the tube and on the density difference between the ejected and the stagnant fluid. The diameter ratio (jet/tube) grows as the 1/3 power of the shear rate, regardless of the density difference, tube diameter and polymer concentration and provided the tube is long enough for the development of the flow profile. For SEPARAN AP 45 solutions, displaying a non-Newtonian behaviour in shear, it is shown that the 1/3 power law holds between the diameter ratio and the shear stress, instead of the shear rate. The analogy between the swelling behaviour of these dilute and semi-dilute polymer solutions and the one observed in concentrated solutions and melts is discussed. The possibility of utilizing the submerged jet technique to compute the polymer solution normal stresses is considered.