Design considerations for mine workings under accumulations of water

The study outlines the effects of surface and underground subsidence patterns on the spatial distribution of in-situ permeability and its effects on groundwater inflow. The behaviour of strata surrounding a longwall face where limited knowledge exists has been outlined. The effects of mining subsidence on the surface flow pattern have been described with the remedial solutions. The mechanism of formation of sinkholes in certain chemical rockmass has been described. Factors affecting mine water inflow have been described in detail with the aid of a simplified conceptual model and case studies. Practical examples of undersea workings and those under a large accumulation of water are given, both in the United Kingdom and worldwide.     

The skin, free radicals, and oxidative stress

Oxidative stress involves the adverse effects of oxygen and other free radicals on living tissue. An overview of the various types of free radicals generated in the body, the basic chemistry of free radicals, and how they arise is presented. The importance of understanding the action of free radicals on specific target tissues in the skin and how this affects the physiology of the skin in relation to treatment is covered.     

Alkoxylation reaction catalysed by layered double hydroxides

Layered double hydroxides (LDHs) are extensively studied as precursors for catalysts, following a calcination at high temperatures to yield mixed oxides. However, these materials are less used as layered materials, i.e., without undergoing thermal activation. We have focused in this work on the use of a series of as-synthesised LDHs for the catalytic preparation of glycol ethers, which is a reaction of primary commercial importance. Two main systems are considered, namely the [Cu–Cr] and [Mg–Al] LDHs. The [Cu–Cr–Cl] LDH is obtained by the coprecipitation method, then through the appropriate chimie douce exchange reactions the original chloride anions are replaced by a variety of oxo- and polyoxometallates, (CrO₄)²⁻, (Cr₂O₇)²⁻, (V₂O₇)²⁻, (V₁₀O₂₈)⁶⁻ and (Mo₇O₂₄)⁶⁻. On the other hand, the [Mg–Al] hydrotalcites, intercalated by (V₂O₇)²⁻, (V₁₀O₂₈)⁶⁻ and [Fe^III(CN)₆]³⁻ anions, are obtained by structure regeneration. This was done by rehydration of a commercial calcined material (Kyowa) in aqueous solutions containing the desired anion. The different materials have been fully characterised by conventional analytical techniques to evidence their lamellar properties and chemical nature. They were then tested in the catalytic reaction involving butan-1-ol and one or more units of ethylene oxide to make butyl-monoglycol ether (BMGE), di-glycol ether (BDGE), tri-glycol ether (BTGE), etc. The reactions were carried out between 80 and 120°C, temperature range in which no collapse of the lamellar structure is normally observed. In this paper it is shown that decavanadate exchanged LDHs proved to be very selective catalysts for the preparation of the monoglycol adduct, some samples achieving up to 100% selectivity in the screening tests.     

Development of the technical capabilities needed to build and position a prepolarization coil for a magnetic resonance imaging magnet

An experiment to show that a magnetic resonance imaging (MRI) magnet could be assembled around a patient, and used as part of a prepolarization system in which substantial transient forces are applied to parts of it, is described. The paper describes the circumstances that develop as a result of the application of the large transient fields used in this type of study, and outlines the reason for the tolerances that are permissible on the alignment of the system components. It then describes a test rig used to evaluate how the various problems might be overcome, and reports on the performance achieved with this rig. On the basis of this work, it appears that a system could be developed that would allow the application of these methods in clinical MRI.     

Modelling metal cutting using modern ductile fracture mechanics: quantitative explanations for some longstanding problems

The assumption that negligible work is involved in the formation of new surfaces in the machining of ductile metals, is re-examined in the light of both current Finite Element Method (FEM) simulations of cutting and modern ductile fracture mechanics. The work associated with separation criteria in FEM models is shown to be in the kJ/m² range rather than the few J/m² of the surface energy (surface tension) employed by Shaw in his pioneering study of 1954 following which consideration of surface work has been omitted from analyses of metal cutting. The much greater values of surface specific work are not surprising in terms of ductile fracture mechanics where kJ/m² values of fracture toughness are typical of the ductile metals involved in machining studies. This paper shows that when even the simple Ernst–Merchant analysis is generalised to include significant surface work, many of the experimental observations for which traditional ‘plasticity and friction only’ analyses seem to have no quantitative explanation, are now given meaning. In particular, the primary shear plane angle φ becomes material-dependent. The experimental increase of φ up to a saturated level, as the uncut chip thickness is increased, is predicted. The positive intercepts found in plots of cutting force vs. depth of cut, and in plots of force resolved along the primary shear plane vs. area of shear plane, are shown to be measures of the specific surface work. It is demonstrated that neglect of these intercepts in cutting analyses is the reason why anomalously high values of shear yield stress are derived at those very small uncut chip thicknesses at which the so-called size effect becomes evident. The material toughness/strength ratio, combined with the depth of cut to form a non-dimensional parameter, is shown to control ductile cutting mechanics. The toughness/strength ratio of a given material will change with rate, temperature, and thermomechanical treatment and the influence of such changes, together with changes in depth of cut, on the character of machining is discussed. Strength or hardness alone is insufficient to describe machining. The failure of the Ernst–Merchant theory seems less to do with problems of uniqueness and the validity of minimum work, and more to do with the problem not being properly posed. The new analysis compares favourably and consistently with the wide body of experimental results available in the literature. Why considerable progress in the understanding of metal cutting has been achieved without reference to significant surface work is also discussed.     

Biomimetic hydroxyapatite coating on glass coverslips for the assay of osteoclast activity in vitro

The osteoclast (OC) is the cell type responsible for the resorption of bone. The activity of this cell is important in the aetiology of a large number of skeletal pathologies, and also for the biocompatibility and osseointegration of orthopaedic implant materials. OC mediated acid hydrolysis of calcium phosphate from the bone matrix offers a prime means of studying the biology and activity of this cell type. We have developed a method of coating glass coverslips with a hydroxyapatite (HA)-like mineral, using a biomimetic approach. Hydroxylation followed by formation of a self assembled monolayer (SAM) using the surfactant triethoxysilylpropyl succinic anhydride (TESPSA), allowed biomimetic deposition of HA-like mineral from a simulated body fluid (SBF). The biocompatibility of the TESPSA SAM-HA coated glass coverslips was tested by culturing human mature OC present in samples of giant cell tumour of bone (GCT). Parameters of OC activity were assayed, including F-actin ring formation, release of calcium and formation of osteoclastic resorption pits, confirming that OC were able to attach to and resorb the coated surface. This approach for the preparation of HA coatings on glass coverslips could have wide applicability for the study of osteoclast behaviour in vitro. Gerald J. Atkins and Peter Majewski share senior author status.     

立达C60型梳棉机使用经验

介绍了一印度尼西亚纺纱厂使用瑞士立达机械工程公司生产的C60型梳棉机在环锭细纱操作方面运转性能和质量的经验。     

Crack propagation in non-proportionally scaled elastic structures

Scaling laws for load, stress, displacement and crack velocity are given for crack propagation in non-proportionally scaled elastic structures where the scaling factors for height, width, thickness and crack length can all be different. Problems are addressed where only one or two of the scaling factors are important, in contrast to geometrically similar scaling where all factors are equal. Examples discussed include pipelines and plate-like structures of ships or bridges. The conditions under which strength of materials design criteria, based on yielding, prove inadequate for such large structures are investigated. In addition, the validity of determining “brittle” fracture toughness by “equivalent energy” scaling procedures from small laboratory specimens is discussed.     

Infrared Photochemistry with Shaped Laser Pulses

A relatively simple design for a hybrid CO₂ laser and electrooptic crystal switch is described, which can be used to produce pulses with fast (< 10 ns) rise and fall times with constant power over their duration (50–1000 ns). Gaussian beam profiles allow separate and quantitative determination of both fluence (J cm⁻²) and intensity (W cm⁻²) dependences of processes induced by IR multiple photon absorption (MPA). Visible luminescence accompanying MPA of OsO₄ is shown to depend on intensity, and the dependences of MPA cross sections in SF₆ on fluence and intensity are derived from optoacoustic and long path absorption measurements.     

Development and validation of the College Life Alcohol Salience Scale: A measure of beliefs about the role of alcohol in college life.

This article reports the development and validation of the College Life Alcohol Salience Scale (CLASS), which assesses college students’ beliefs about the centrality of alcohol to the college experience. Developed using procedures designed to increase its ecological validity, the CLASS was administered to three samples of college students (total N = 571). Its unidimensional factor structure was first established via exploratory factor analysis and parallel analysis on one sample and then verified via confirmatory factor analysis on a separate sample. Scores on the CLASS were predictably related to a nomological network of drinking and personality variables and it provided incremental validity in accounting for drinking frequency and amount, when added to drinking motive scores. The importance of assessing and developing interventions to target the types of beliefs measured by the CLASS is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)