Mechanisms for rate effects on interlaminar fracture toughness of carbon/epoxy and carbon/PEEK composites

The objective of this study was to investigate strain-rate dependent energy absorption mechanisms during interlaminar fracture of thermosetting (epoxy) and thermoplastic (PEEK) uni directional carbon fibre (CF) composites. A simple model addressing the translation of matrix toughness to mode I and mode II interlaminar toughness of the composite is presented, in conjunction with a fractographic examination of the fracture surfaces and the fracture process. The observed rate dependency of composite fracture toughness is attributed to the rate dependent toughness of the viscoelastic matrix and the size of the process zone around the crack tip. Other important factors identified are the roughness of the fracture surface and fibre bridging.     

Structure and activity of the hairpin ribozyme in its natural junction conformation: effect of metal ions

The natural form of the hairpin ribozyme consists of a four-way RNA junction of which the single-stranded loop-carrying helices are adjacent arms. The junction can be regarded as providing a framework for constructing the active ribozyme, and the rate of cleavage can be modulated by changing the conformation of the junction. We find that the junction-based form of the hairpin ribozyme is active in magnesium, calcium, or strontium ions, but not in manganese, cadmium, or sodium ions. Using fluorescence resonance energy transfer experiments, we have investigated the global structure of the ribozyme. The basic folding of the construct is based on pairwise helical stacking, so that the two loop-carrying arms are located on opposite stacked helical pairs. In the presence of magnesium, calcium, or strontium ions, the junction of the ribozyme undergoes a rotation into a distorted antiparallel geometry, creating close physical contact between the two loops. Manganese ions induce the same global folding, but no catalytic activity; this change in global conformation is therefore necessary but not sufficient for catalytic activity. Fitting the dependence of the conformation on ionic concentration to a two-state model suggests that cooperative binding of two ions is required to bring about the folding. However, further ion binding is required for cleavage activity. Cobalt hexammine ions also bring about global folding, while spermidine generates a more symmetrical form of the antiparallel structure. Cadmium ions generate a different folded form, interpreted in terms of close loop-loop association while the junction is unfolded. Sodium ions were unable to induce any folding of the ribozyme, which remained slightly parallel. These results are consistent with a folding process induced by the binding of two group IIA metal ions, distributed between the junction and the loop interface.     

MMPI alcoholic subtypes: Replicability and validity of the 2-8-7-4 subtype.

An empirical examination of previous alcoholism classifications that have used the Minnesota Multiphasic Personality Inventory reveals that one particular subtype emerges with considerable convergence. This article describes this subtype and outlines some of its implications for alcoholism theory and research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pyrographit – Eigenschaften und anwendung

Pyrolytic Graphite – Properties and Application The carbon material known as pyrolytic graphite is remarkable for its exceptional properties which make it capable of being used in fields and processes in which high thermal, chemical and electrical stress is required. Its technical importances has increased in recent years. A report is given of the preparation of pyrolytic graphite and also of its important application properties, and the most important fields of application are touched on.     

Bayesian Inference of Nanoparticle-Broadened X-Ray Line Profiles

A single-step, self-contained method for determining the crystallite-size distribution and shape from experimental x-ray line profile data is presented. It is shown that the crystallite-size distribution can be determined without invoking a functional form for the size distribution, determining instead the size distribution with the least assumptions by applying the Bayesian/MaxEnt method. The Bayesian/MaxEnt method is tested using both simulated and experimental CeO₂ data, the results comparing favourably with experimental CeO₂ data from TEM measurements.     

Waking up the gastric bypass patient

Waking up the gastric bypass patient in the post-anesthesia care unit (PACU) is a continual challenge. From January 1992 to November 1996, 961 gastric bypasses (GBP) have been performed at Columbia St Mark's Hospital. Of the 961 patients, 957 came to the PACU. Four patients went directly to ICU because of respiratory status requiring mechanical ventilation. There have been no deaths and no respiratory arrests in PACU. Continuous bedside monitoring of the patient's respiratory status coupled with pain management contributed to positive care of the GBP patient. Methods of care for the GBP patient include the use of O2 masks and cannulas, coughing and deep breathing, administering i.v. narcotics until patient controlled analgesia pumps are initiated, encouragement and emotional support, ongoing assessment of patients' status, and treating problems/needs appropriately.