6,963 publications from this institution
Compressed sandwich structures, comprising two stiff face plates separated by a softer core material, while designed principally as efficient integral structures, can lose this quality when faces buckle locally. Interaction between overall (Euler) buckling and local buckling of one face suggests that failure will localize into the centre. A variational formulation, leading to a pair of nonlinear differential equations subject to integral constraints, describes the post–buckling response. These are solved by a combination of numerical shooting and continuation techniques, such that the response far into the unstable post–buckling regime can be portrayed. Solutions with both linear and nonlinear constitutive core relations are compared with the results of an engineering (body–force) approach, and with those of earlier (periodic) Rayleigh–Ritz analyses. The latter demonstrate the extra destabilization that comes with localization.
Coronary artery disease (CAD) represents a wide spectrum of underlying anatomical disease ranging from near normal, minor single-vessel disease (SVD), to extensive triple-vessel disease. Its presentation is similarly variable, from a single episode of chest pain to acute coronary syndrome (ACS) or even death. The aim of treatment in CAD is to relieve symptoms and improve quality of life, reduce cardiovascular (CV) events, and prolong survival. There have been vast improvements in management over the years, following a greater understanding of the underlying pathophysiology, the identification and appropriate management of risk factors, development of new medication, and advances in revascularization techniques, both percutaneous and surgical. These developments have resulted in a move towards an anatomic treatment for CAD even though it is the minor lesion, so-called vulnerable plaque, which is suggested as the most likely culprit for mortality. Nevertheless, in those patients presenting with ACS or ST-elevation myocardial infarction the long-term benefits of percutaneous coronary intervention (PCI) have been confirmed in multiple randomized trials; however, debate surrounds the ideal management of the majority of patients who have angina, and who have not experienced any previous CV events or had an interventional procedure, so-called stable CAD.
Viral infection may induce the expression of nitric oxide (NO) synthase, resulting in increased NO formation that has an antiviral effect. NO may be produced by various cells of the upper and lower respiratory tract, and may be detected in the exhaled air. We have studied the levels of exhaled NO in 18 normal subjects during symptomatic upper respiratory tract infections and during recovery 3 weeks later. Exhaled NO was measured using a modified chemiluminescence analyser. At the time of symptoms of upper respiratory tract infection, the peak exhaled NO values were 315 +/- 57 ppb (mean +/- SEM) and decreased to 87 +/- 9 ppb during recovery. Recovery values of exhaled NO were similar to those reported in age-matched normal control subjects (88 +/- 3 ppb, n = 72). These findings suggest that symptomatic upper respiratory tract infections markedly increase the concentration of NO in exhaled air. This may reflect the induction of nitric oxide synthase (NOS) in upper and lower respiratory tract, and may be relevant to viral exacerbations of asthma.
Vasoactive intestinal peptide (VIP), first isolated from porcine intestine (S. I. Said and V. Mutt, Science Wash. DC 169: 1217-1218, 1970), has been identified in postganglionic autonomic axons of many tissues. VIP has potent regulatory effects on the function of various cell types within these tissues, ranging from relaxation of smooth muscle to ion transport. Recently, VIP has been implicated in the regulation of mucus secretion in the respiratory tract, a process involving release of macromolecules from exocrine cells and transport of ions and water across the airway mucosa. However, because airway glands and mucosa both consist of mixed cell populations, it was unclear which specific cells contained VIP receptors and contributed to VIP-evoked responses. We identified these specific cells by using immunocytochemical techniques to monitor concentration changes in adenosine 3',5'-cyclic monophosphate (cAMP), the intracellular compound known to mediate VIP responses. Serous and mucous cells of ferret tracheal submucosal glands and ciliated and basal cells of dog tracheal mucosa all increased cAMP in response to VIP stimulation. We conclude that these cell types possess VIP receptors and thus participate in VIP-stimulated responses. In contrast, ferret tracheal epithelium and dog epithelial goblet cells showed little or no reactivity after VIP, and thus we believe that these cells lack VIP receptors.
Drug-eluting stents have shown to be superior over bare metal stents in clinical and angiographic outcomes after percutaneous treatment of coronary artery stenosis. However, long-term follow-up data are scarce and only available for sirolimus- and paclitaxel-eluting stents.To assess the feasibility and performance of the XIENCE V everolimus-eluting stent (EES) versus an identical bare metal stent after a 5-year follow-up period.SPIRIT FIRST was a First in Man, multicentre, prospective, single-blind, clinical trial, randomizing 60 patients with a single de novo coronary artery lesion in a ratio of 1:1 to either an everolimus eluting or a bare metal control stent.At 5-year clinical follow-up, data were available in 89% and 86% of patients in the everolimus and control arm, respectively. In the everolimus arm, no additional death, myocardial infarction, clinically driven target lesion revascularization (TLR), or clinically driven target vessel revascularization (TVR) events were observed between 1- and 5-year follow-up. The 5-year hierarchical major adverse cardiac events (MACE) and target vessel failure (TVF) rates for the everolimus arm were 16.7% (4/24) for both endpoints. In the control group, no additional cardiac death, myocardial infarction, or clinically driven TLR events were observed between 2- and 5-year follow-up. No additional clinically driven TVR events were observed between 3- and 5-year follow-up. The 5-year hierarchical MACE and TVF rates for the control arm were 28.0% (7/25) and 36.0% (9/25), respectively. No stent thromboses were observed in either the everolimus arm or the control arm up to 5 years.The favorable 5-year long term clinical outcome of the EES is consistent with the results from other studies of the EES with shorter follow-up.
Oxidative stress is implicated in the pathogenesis and progression of asthma (1,2), chronic obstructive respiratory disease (COPD) (3), and cystic fibrosis (4). Reactive oxygen species (ROS) are unstable compounds with unpaired electrons, capable of initiating oxidation. Several of the inflammatory cells which participate in the inflammatory response, such as macrophages, neutrophils, and eosinophils release increased amounts of ROS (1,5) exceeding the already reduced tissue antioxidant defences of asthmatic and COPD patients (2).
The local buckling behaviour and ultimate cross-sectional strength of tubular elliptical profiles in compression is examined in this study through numerical modelling. The numerical models were first validated against previous experimental data with good agreement observed, enabling an extensive parametric study to be performed. A total of 270 elliptical sections were simulated in order to examine the influence of cross-section aspect ratio, geometric imperfections and local slendernesses. The obtained ultimate capacities, load–deformation responses and failure modes are discussed. It was found that for lower cross-section aspect ratios the behaviour of the elliptical hollow sections (EHS) was similar to that of cylindrical shells across a number of metrics; however, as the aspect ratio increased, more plate-like stable postbuckling behaviour was observed. Imperfection sensitivity was found to decrease with increasing slenderness and aspect ratio. The influence of the shape of the initial imperfection on the strengths of the EHS columns was also assessed and was found to be generally limited. Finally, a design method has been proposed for Class 4 EHS members that reflects the reduction in capacity due to local buckling with increasing slenderness, but also recognises the improved postbuckling stability with increasing aspect ratio; the proposals were shown to provide safe and accurate predictions for the strengths of the EHS columns with nondimensional local slendernesses up to 2.5 and aspect ratios from 1.1 to 5.0.
Cold-formed structural sections are manufactured at ambient temperature and hence undergo plastic deformations which result in an increase in the yield stress and ultimate stress, but reduced ductility.This paper begins with a comparative study of existing predictive models to harness this strength increase.Modifications to the existing models are then made and an improved model is presented.Tensile coupon tests from the literature have been used to validate and compare the predictive models.A wide range of structural section types from both cold-rolling and press-braking fabrication processes and structural materials, including various grades of carbon steel and stainless steel, have been considered.
