On the Adequacy of Shell Models for Predicting Stresses and Strains in Thick-Walled Tubes Subjected to Detonation Loading

This paper analyzes the adequacy of shell models for predicting stresses and strains in thick-walled tubes subjected to detonation loads. Of particular interest are the large axial strains which are produced at the inner and outer surfaces of the tube due to bending along the tube axis. First, comparisons between simple shell theory and a static finite element model are used to show that the axial strain varies proportionally with wall thickness and inversely with the square of the axial wavelength. For small wavelengths, this comparison demonstrates nonlinear behavior and a breakdown of the shell model. Second, a dynamic finite element model is used to evaluate the performance of transient shell equations. This comparison is used to quantify the error of the shell model with increasing wall thickness and show that shell models can be inaccurate near the load front where the axial curvature is high. Finally, the results of these analyses are used to show that the large axial strains which are sometimes observed in experiments cannot be attributed to through-wall bending and appear to be caused instead by non-ideal conditions present in the experiments

Detonation and transition to detonation in partially water-filled pipes

Detonations and deflagration-to-detonation transition (DDT) are experimentally studied in horizontal pipes which are partially filled with water. The gas layer above the water is stoichiometric hydrogen-oxygen at 1 bar. For detonation cases, ignition and transition occur outside of the water-filled section. For DDT cases, ignition and transition occur over the surface of the water. Pressure and hoop strain are measured incrementally along the pipe, with pressure transducers located both above and below the water. The detonation wave produces an oblique shock train in the water, and the curvature of the pipe is seen to focus the shocks at the bottom, resulting in peak pressures that are 4–6 times higher than the peak detonation pressure. Such pressure amplification is observed for water depths of 0.25, 0.5, 0.75, 0.87, and 0.92 pipe diameters. For a water depth of 0.5 diameters, pressure is also recorded at several circumferential locations in order to measure the shock focusing phenomenon. Peak hoop strains are found to decrease with increasing water depth, and transition to detonation is seen to occur for water depths as high as 0.92 pipe diameters

Developmental expression of a functional TASK-1 2P domain K+ channel in embryonic chick heart

<p>Abstract</p> <p>Background</p> <p>Background K⁺channels are the principal determinants of the resting membrane potential (RMP) in cardiac myocytes and thus, influence the magnitude and time course of the action potential (AP).</p> <p>Methods</p> <p>RT-PCR and <it>in situ </it>hybridization are used to study the distribution of TASK-1 and whole-cell patch clamp technique is employed to determine the functional expression of TASK-1 in embryonic chick heart.</p> <p>Results</p> <p>Chicken TASK-1 was expressed in the early tubular heart, then substantially decreased in the ventricles by embryonic day 5 (ED5), but remained relatively high in ED5 and ED11 atria. Unlike TASK-1, TASK-3 was uniformly expressed in heart at all developmental stages. <it>In situ </it>hybridization studies further revealed that TASK-1 was expressed throughout myocardium at Hamilton-Hamburger stages 11 and 18 (S11 & S18) heart. In ED11 heart, TASK-1 expression was more restricted to atria. Consistent with TASK-1 expression data, patch clamp studies indicated that there was little TASK-1 current, as measured by the difference currents between pH 8.4 and pH 7.4, in ED5 and ED11 ventricular myocytes. However, TASK-1 current was present in the early embryonic heart and ED11 atrial myocytes. TASK-1 currents were also identified as 3 μM anandamide-sensitive currents. 3 μM anandamide reduced TASK-1 currents by about 58% in ED11 atrial myocytes. Zn²⁺(100 μM) which selectively inhibits TASK-3 channel at this concentration had no effect on TASK currents. In ED11 ventricle where TASK-1 expression was down-regulated, I_K1was about 5 times greater than in ED11 atrial myocytes.</p> <p>Conclusion</p> <p>Functional TASK-1 channels are differentially expressed in the developing chick heart and TASK-1 channels contribute to background K⁺conductance in the early tubular embryonic heart and in atria. TASK-1 channels act as a contributor to background K⁺current to modulate the cardiac excitability in the embryonic heart that expresses little I_K1.</p

A Simple Model for Axial Displacement in a Cylindrical Pipe With Internal Shock Loading

This paper describes a simplified model for predicting the axial displacement, stress, and strain in pipes subjected to internal shock waves. This model involves the neglect of radial and rotary inertia of the pipe, so its predictions represent the spatially averaged or low-pass–filtered response of the tube. The simplified model is developed first by application of the physical principles of conservation of mass and momentum on each side of the shock wave. This model is then reproduced using the mathematical theory of the Green's function, which allows other load and boundary conditions to be more easily incorporated. Comparisons with finite element simulations demonstrate that the simple model adequately captures the tube's axial motion, except near the critical velocity corresponding to the bar wave speed √(E/ρ). Near this point, the simplified model, despite being an unsteady model, predicts a time-independent resonance, while the finite element model predicts resonance that grows with time

Climate change projections and stratosphere–troposphere interaction

Climate change is expected to increase winter rainfall and flooding in many extratropical regions as evaporation and precipitation rates increase, storms become more intense and storm tracks move polewards. Here, we show how changes in stratospheric circulation could play a significant role in future climate change in the extratropics through an additional shift in the tropospheric circulation. This shift in the circulation alters climate change in regional winter rainfall by an amount large enough to significantly alter regional climate change projections. The changes are consistent with changes in stratospheric winds inducing a change in the baroclinic eddy growth rate across the depth of the troposphere. A change in mean wind structure and an equatorward shift of the tropospheric storm tracks relative to models with poor stratospheric resolution allows coupling with surface climate. Using the Atlantic storm track as an example, we show how this can double the predicted increase in extreme winter rainfall over Western and Central Europe compared to other current climate projection

Audit market structure, fees and choice in a period of structural change: evidence from the UK – 1998–2003

This paper presents evidence on audit market concentration and auditor fee levels in the UK market in the crucial period of structural change following the PricewaterhouseCoopers’ (PwC) merger and encompassing Andersen’s demise (1998–2003). Given the current interest in auditor choice, analysis is also undertaken at the individual audit firm level and by industry sector. There is evidence of significant upward pressure on audit fees since 2001 but only for smaller auditees. Audit fee income for top tier auditors (Big 5/4) did not change significantly while the number of auditees fell significantly, consistent with a move towards larger, less risky, clients. A decomposition analysis of the aggregate Big 5/4 concentration ratio changes over the period identifies the impact of four distinct consumer-based reasons for change: leavers; net joiners; non-par auditor switches; and (only for the audit fees measure) audit fee changes. Andersen’s demise markedly reduced the level of inequality among the top tier firms but PwC retained its position as a ‘dominant firm’. On switching to the new auditor, former Andersen clients experienced an initial audit fee rise broadly in line with inflation, with no evidence of fee premia or discounting. They also reported significantly lower NAS fees, consistent with audit firms and auditees responding to public concerns about perceptions of auditor independence. There is no general evidence of knowledge spillover effects or cross-subsidisation of the audit fee by NAS. The combined findings provide no evidence to indicate that recent structural changes have resulted in anticompetitive pricing; the key concerns remain the lack of audit firm choice and issues concerning the governance and accountability of audit firms