Axisymmetric dynamic response of a penny-shaped crack to a pair of transient concentrated forces

The three-dimensional axisymmetric elastodynamic response of a penny-shaped crack embedded in an infinite elastic solid subjected to a pair of transient concentrated forces is investigated. The forces are applied on the symmetry axis perpendicular and symmetric to the crack surfaces, including the special case when the forces act precisely on the crack surfaces. A time-domain boundary integral equation method is applied for computing the crack-opening displacement and subsequently the time dependence of the dynamic stress intensity factors. Numerical calculations are carried out for various geometry parameters and the results are discussed. It is found that the location of the applied concentrated forces inducing the highest dynamic stress intensity factors differs from that producing the highest static values.     

Rat and human pancreatic islet cells contain a calcium ion independent phospholipase A2 activity selective for hydrolysis of arachidonate which is stimulated by adenosine triphosphate and is specifically localized to islet beta-cells

The recent demonstration that myocardial Ca(2+)-independent phospholipase A2 exists as a complex of catalytic and regulatory polypeptides that is modulated by ATP has suggested a novel mechanisms through which alterations in glycolytic flux can be coupled to the generation of eicosanoids which facilitate insulin secretion. To determine the potential relevance of this mechanism, we examined the kinetic characteristics, substrate specificities, and cellular locus of phospholipase A2 activity in pancreatic islets. Rat pancreatic islets contain a Ca(2+)-independent phospholipase A2 activity which is optimal at physiologic pH, preferentially hydrolyzes phospholipid substrates containing a vinyl ether linkage at the sn-1 position, and prefers arachidonic acid compared to oleic acid in the sn-2 position. Rat islet Ca(2+)-independent phospholipase A2 activity is inhibited by the mechanism-based inhibitor (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one and is stimulated by ATP. Purification of beta-cells from dispersed pancreatic islet cells by fluorescence-activated cell sorting demonstrated that beta-cells (but not non-beta-cells) contain Ca(2+)-independent, ATP-stimulated phospholipase A2 activity. Remarkably, clonal RIN-m5f insulinoma cells, which possess a defect in glucose-induced insulin secretion, contain a Ca(2+)-independent phospholipase A2 which is not modulated by alterations in ATP concentration. Collectively, these results and those of an accompanying paper [Ramanadham et al. (1993) Biochemistry (following paper in this issue)] implicate Ca(2+)-independent phospholipase A2 as a putative glucose sensor which can couple alterations in glycolytic metabolism to the generation of biologically active eicosanoids and thereby facilitate glucose-induced insulin secretion.     

Radiation chemical reactions of poly-p-chlorphenylmethacrylate by ESCA

Summary ESCA is used to characterize ion beam irradiated P(p-ClPhMA)-samples. The results show a chlorine abstraction. The experimental findings are in accordance with a recently proposed model for a crosslinking mechanism of halogenated aromatic polymers.     

The dominance of the K I-field for a crack under stress wave loading

The extent of the dominant singular field is investigated for a finite crack under stress wave loading. Using a boundary integral equation method the complete solution as well as the near field solution is determined. A comparison of the two fields indicates that the singular field dominates within a small domain at the crack tip. The size of the dominance region in the dynamic case may be very different from that in the static case.     

Contributions of Transformation and Microcracking to the Plastic Deformation of Magnesia-Partially-Stabilized Zirconia

The measured plastic deformation of Mg-PSZ under stress contains contributions from both transformation and microcracking. A method is described to separate the contributions from transformation and microcracking for samples deformed in uniaxial tension. Such a separation enables the ratio of the longitudinal to transverse strains arising from the transformation to be estimated. The results are compared to the predictions of the shear–dilatation model of Chen and Reyes-Morel. Serious discrepancies are found between the experimental results and the predictions of the model and the possible reason for this is discussed.     

Exposure plus response-prevention treatment of bulimia nervosa.

A controlled study evaluating the effectiveness of exposure plus response-prevention treatment of bulimia nervosa was conducted in a sample of 47 women. This was a four-group comparison involving three treatment conditions and a waiting-list control group. The three treatment conditions were (a) exposure plus response prevention conducted in a single setting (clinic), (b) exposure plus response prevention conducted in multiple settings (clinic, patients' homes, and restaurants), and (c) cognitive–behavioral therapy without exposure plus response prevention. All treatment was provided to groups of 3 patients at a time. Outcome was evaluated at posttreatment and at a 6-month follow-up. The three treatment groups improved significantly on most outcome measures, whereas the waiting-list control group showed little change. At follow-up, there was a slightly better outcome on vomiting behavior and amount of food consumed in one of the test meals for the exposure plus response-prevention groups relative to the no-exposure group. However, on all other measures, the degree of improvement from pretreatment to follow-up was the same for all three treatment groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simulation of macroscopic material behavior for uniaxial fiber-matrix composites, using a DAE-approach

The macroscopic deformation behavior of a fiber-reinforced aluminum-boron composite is investigated. Different periodic and random arrangements of the microstructure are considered with macroscopic hardening behavior due to the evolution of plastic zones on the microscale being taken into account.

For the solution of the initial boundary value problem, a non-standard algorithm is applied. It consists of the direct solution of the whole set of equations, treating all variables as global quantities. Together with a higher order time integration method (BDF2), an automatic step size control is used in the FEM calculations.     

FR139317, a specific ETA-receptor antagonist, inhibits cerebral activation by intraventricular endothelin-1 in conscious rats

A comprehensive series of time-related behavioral, physiological and cerebral metabolic studies was conducted using conscious Sprague-Dawley rats to discern the anti-endothelin (ET) properties of the specific ETA receptor antagonist, FR139317. Endothelin-1 (9 pmol given by injection into one lateral ventricle, i.c.v.) produced convulsions, acute arterial hypertension, arterial hyperglycemia, and hyperventilation. Brain structures close to the i.c.v. site of injection, such as the caudate nucleus, lateral septal nucleus, corpus callosum and hippocampal CA3 medial lamellae, as well as 14 other individual structures, displayed moderate-to-intense levels of metabolic activation after endothelin. Data were assessed quantitatively by means of the autoradiographic [14C]deoxyglucose technique combined with image analysis. Neural circuits in the efferent projection paths of the stimulated forebrain structures, such as the midbrain oculomotor complex, amygdaloid nuclei, substantia nigra pars reticulata and caudal subicular subregions of the hippocampal formation, were stimulated focally by endothelin. Specific medullary nuclei and cerebellar cortical subregions displayed high rates of glucose metabolism following endothelin injection at the time of maximum behavioral and physiological stimulation. I.c.v. treatment with > or = 14 nmol FR139317 before endothelin significantly inhibited the effects produced by the peptide. At the highest dose of FR139317 (28 nmol), there was only mild behavioral stimulation following endothelin injection, and hypermetabolic responses in the brain were abolished except in two specific areas of the cerebellar cortex (approx 40% increases in metabolic activity in the copula pyramis and paramedian lobule). The results indicate that the cerebral stimulatory effects of i.c.v. endothelin are mediated by the A type of endothelin receptor. By itself, i.c.v. FR139317 had no effects on the parameters assessed. Further evaluation of FR139317 is warranted as a possible therapeutic agent for neuropathologies suspected of deriving from central neural or vascular stimulation by endothelin, such as aneurysmal vasospasm, ischemia, excitotoxicity, and peptide-mediated epilepsies.