Interfacial sliding near a free surface in a fibrous or layered composite during thermal cycling

This paper presents a simple shear lag model of interfacial sliding at a free surface in a layered or continuous fiber composite. The interface is characterized by a critical interfacial shear stress, τ₀, which might represent the critical stress for frictional sliding at a weakly bonded interface, or the shear flow stress of a thin, ductile interface layer at a well bonded interface. We calculate the history during heating and cooling of the relative normal displacement of the reinforcing inclusions and the matrix on a free surface cut normal to the inclusions. The calculated history is shown to depend on both the absolute value and the temperature dependence of τ₀, as well as on the magnitudes of the bulk residual stresses. Analytical results are obtained for the first few heating and cooling cycles and the equilibrium hysteresis loop under thermal cycling of uniform amplitude. The variety of possible displacement histories suggests that they are a rich source of information about τ₀ and the residual stresses. A discussion of feasible experiments and some results for continuous fiber titanium and titanium aluminide composites are presented in a companion paper.     

A computational model for defect prediction in shape castings based on the interaction of free surface flow, heat transfer, and solidification phenomena

High-integrity castings require sophisticated design and manufacturing procedures to ensure they are essentially macrodefect free. Unfortunately, an important class of such defects—macroporosity, misruns, and pipe shrinkage—are all functions of the interactions of free surface flow, heat transfer, and solidication in complex geometries. Because these defects arise as an interaction of the preceding continuum phenomena, genuinely predictive models of these defects must represent these interactions explicitly. This work describes an attempt to model the formation of macrodefects explicitly as a function of the interacting continuum phenomena in arbitrarily complex three-dimensional geometries. The computational approach exploits a compatible set of finite volume procedures extended to unstructured meshes. The implementation of the model is described together with its testing and a measure of validation. The model demonstrates the potential to predict reliably shrinkage macroporosity, misruns, and pipe shrinkage directly as a result of interactions among free-surface fluid flow, heat transfer, and solidification.     

Localization of the peritoneal reflection in the pelvis by endorectal ultrasound

BACKGROUND: Large adenomas and low-risk rectal carcinomas (T1) that are localized distal of the pelvic peritoneal reflection (PPR) are treated by transanal excision. However, the location of the PPR varies widely and cannot be detected reliably by preoperative methods. Therefore, we evaluated the value of endorectal ultrasound (EUS) for the prediction of an intraperitoneal location of rectal tumors. METHODS: Fourteen patients with rectal tumors measuring 相似文献   

Integration of free pulses in electrical self-stimulation of the rat brain.

Frequency thresholds for electrical self-stimulation of the medial forebrain bundle were estimated in rats while low frequencies of pulses were applied continuously. When continuous pulses were delivered to the same electrode that received the 0.5-sec trains of response-initiated stimulation, thresholds decreased by the free-pulse frequency (Experiment 1), consistently across current (Experiment 2). Estimates of the reward added by concurrent, response-contingent stimulation of the opposite electrode of a bilateral pair predicted the drop in threshold caused by the noncontingent pulses applied to the opposite hemisphere (Experiment 3), again, robustly across test current (Experiment 4). Continuous pulses restricted to times between self-initiated trains lost their effect (Experiment 5). The perception of reward was invariant despite changes in the overall activity of the self-stimulation substrate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Containment of a silicone fluid free surface in reduced gravity

In support of the Surface Tension Driven Convection Experiment planned for flight aboard the space shuttle, tests were conducted under reduced gravity in the 2.2-second drop tower and the 5.0-second Zero-G facility at the Lewis Research Center. The dynamics of controlling the test fluid, a 10-centi Stoke viscosity silicone fluid, in a low gravity environment were investigated using different container designs and barrier coatings. Three container edge designs were tested without a barrier coating: a square edge, a sharp edge with a 45-deg slope, and a saw-tooth edge. All three edge designs were successful in containing the fluid below the edge. G-jitter experiments were made in scaled-down containers subjected to horizontal accelerations. The data showed that a barrier coating is effective in containing silicone fluid under g-levels up to 10^•1 g₀. This paper is based on a presentation made in the symposium “Experimental Methods for Microgravity Materials Science Research” presented at the 1988 TMS-AIME Annual Meeting in Phoenix, Arizona, January 25-29, 1988, under the auspices of the ASM/MSD Thermodynamic Data Committee and the Material Processing Committee.     

Increased common carotid intima-media thickness. Adaptive response or a reflection of atherosclerosis? Findings from the Rotterdam Study

BACKGROUND AND PURPOSE: Carotid intima-media thickness (IMT) measurements are used widely to study atherosclerosis. Some have suggested that an increased IMT reflects a nonatherosclerotic adaptive response to changes in shear stress and tensile stress. This stems from the hypothesis that changes in shear stress and subsequently in lumen diameter are followed by changes in IMT to keep tensile stress constant. We studied the relation of common carotid IMT to common carotid end-diastolic lumen diameter and tensile stress, as approximated by mean arterial pressure (lumen diameter/IMT)]. METHODS: A cross-sectional analysis was performed with data obtained from the first 1715 participants in the Rotterdam Study, a population-based cohort study among 7983 subjects aged 55 years and over who underwent ultrasonographic examination of the carotid arteries. End-diastolic lumen diameter and IMT of the common carotid arteries were evaluated and quantified. RESULTS: With increasing IMT, inner and outer lumen diameters increased gradually, and beyond an IMT of 1.10 mm, the inner lumen diameter decreased. Tensile stress increased with increasing lumen diameter instead of being constant. The lumen-to-IMT ratio was constant across levels of mean arterial pressure. CONCLUSIONS: Our findings are compatible with the view that at lower degrees of IMT, the thickening appears to reflect an equilibrium state in which the effects of pressure and flow on the arteries are in balance, given a characteristic relation between shear stress and local transmural pressure. Beyond a certain level, IMT more likely may represent atherosclerosis. Regardless of whether common carotid IMT reflects local atherosclerosis, it may still serve as a graded marker for cardiovascular risk.     

Numerical investigation of the free surface in a continuous steel casting mold model

This article presents a numerical investigation of the turbulent flow in a water model, simulating a continuous steel casting mold. Special attention is given to the free-surface oscillations. The governing differential equations are discretized in a curvilinear coordinate system moving with the free surface by the Finite Volume Methodology (FVM). The results indicate that the free-surface wave has a predominant length and frequency and the wave amplitude scales with the flow dynamic head. Wave instability, which may be associated with emulsification, is predicted at a critical casting speed.     

Typical pathology during the free immersion of a man under water

The free immersion of a man under the water is accompanied by the threat of specific disorders which could cause the drowning. The article examines the causes, conditions and mechanisms of two most frequent pathological states, i.e. the compression of thorax and loss consciousness caused by CO2 action and hypoxia. The symptoms of these states, as well as prophylactic measures and first aid recommendations are enclosed.     

Plasma light reflection by free charge carriers in some compounds of the rare earth elements

Conclusions The results of our investigation of the reflection spectra of powders and sintered specimens of metallike lanthanum and praseodymium compounds have enabled us to determine the frequency of plasma oscillations of conduction electrons during interaction with light and assess the principal kinetic parameters with an error of 30%. The method employed is suitable for assessing the principal physical characteristics of charge carriers in those refractory compounds which cannot easily be produced in the form of monocrystalline or monolithic specimens with specular polished surfaces without disturbing their stoichiometry.Values of plasma frequency of free charge carrier oscillations determined in this investigation have made it possible to compare, for all the compounds studied, the optical values of kinetic parameters determined with their aid with those yielded by galvanomagnetic measurements.The optical values of electrical conductivity in the metal-like REE compounds and conduction electron mobility were found to be smaller than the values obtained in measurements involving the direct passage of current, probably as a result of the influence exerted by Interzonal electron transitions of similar energy on the plasma frequency of oscillations.Examination of the optical characteristics of lanthanum and praseodymium compounds leads to the conclusion that the high concentration of conduction electrons in Me³⁺X, Me³⁺B₆, and MeSb type refractory compounds is linked with a common feature of all these compounds, namely, the simple cubic lattice of their trivalent ion.Translated from Poroshkovaya Metallurgiya, No. 8(188), pp. 38–48, August, 1978.     

Release of nontransmembrane full-length Alzheimer''s amyloid precursor protein from the lumenar surface of chromaffin granule membranes

OBJECTIVE: To evaluate the effectiveness and safety of a single-dose treatment for acute repetitive seizure (ARS) episodes (e.g., clusters) administered in a nonmedical setting by caregivers. BACKGROUND: Patients with epilepsy may experience ARS episodes despite optimal anticonvulsant treatment. Such episodes require rapid treatment as medical emergencies. Typically, the patient is treated in an emergency medical setting with i.v. medication by trained medical personnel. METHODS: The authors undertook a multicenter, randomized, parallel, double-blind study of a single administration of Diastat (diazepam rectal gel) for treating episodes of ARS. ARS episodes and treatment criteria were defined for each patient at the start of the study. Caregivers were taught to determine ARS episode onset, administer a predetermined dose of study medication, monitor outcome, count respirations, and record seizures and adverse events. RESULTS: A total of 29 centers enrolled 158 patients, of whom 114 patients had a treated ARS episode (Diastat, n = 56; placebo, n = 58). Diastat treatment reduced median seizure frequency (p = 0.029). More Diastat patients were seizure free post-treatment (Diastat, 55%; placebo, 34%; p = 0.031). Kaplan-Meier analysis of the time to the next seizure favored Diastat treatment (p < 0.007). The most common adverse event was somnolence. CONCLUSION: Administration of a single rectal dose of Diastat was significantly more effective than placebo in reducing the number of seizures following an episode of ARS. Caregivers could administer treatment safely and effectively in a nonmedical setting.     

Effects of surface flow control on fluid flow phenomena and mixing time in a bottom blown bath

The intensity of mixing in a molten metal bath stirred by bottom gas injection can be represented by the mixing time. According to previous water model experiments, the mixing time is known to be dependent on the operational variables such as the bath diameter, bath depth, location of a bottom nozzle, and gas flow rate. It is not easy to control the former three variables during processing, and the dependence of the mixing time on the gas flow rate is weak. In this study, the possibility of changing the mixing time drastically due to the control of the surface flow in the bath is examined. Three kinds of boundary conditions were imposed on the bath surface, and the relation between the fluid flow phenomena resulting from the surface flow control and the mixing time was investigated. The mixing time was found to be significantly influenced by the surface flow control. In particular, when the surface flow was suppressed by bringing a circular cylinder into contact with the bath surface, the mixing time became very long.