A simplified nonlinear stability analysis of an imperfect rectangular two-bar frame

A simplified nonlinear stability analysis for moderately large rotations and small strains is performed on a rectangular two-bar frame subjected to a concentrated eccentrically applied joint load. Such a simplification consisting of adopting linear kinematic relations leads to very reliable results for the initial postbuckling path in the vicinity of the critical point of the above imperfect frame. The existence of an asymmetric bifurcation point is thoroughly discussed and a direct evaluation of the bifurcational load is readily obtained. Using this technique the effect of imperfection sensitivity is also addressed. A qualitative analysis associated with the physical phenomenon yields a substantial reduction of the computational work. The efficiency and reliability of this approximate nonlinear stability analysis proposed herein is illustrated by means of several examples for which a lot of numerical results based on a more accurate nonlinear analysis are available.     

Tidal turbines harness the power of the sea

Just as there were once 10?000 windmills across Europe, countless water mills helped power the rural economy and then the industrial revolution. And, just as reinforced plastics have supported the 21st century reincarnation of windmills as wind turbines, so they are beginning to contribute to the next likely large-scale commercial renewable energy source - water current power. George Marsh reports.     

Supplementation of the diet with the functional fiber PolyGlycoplex? is well tolerated by healthy subjects in a clinical trial

Background  

The relationship of dietary fiber to overall health is of great importance, as beneficial effects have been demonstrated with the use of fiber from diverse sources, some traditional, other novel. PolyGlycopleX^? (PGX^?) is a unique proprietary product composed of three water-soluble polysaccharides, that when processed using novel technology give rise to a final product – a soluble, highly viscous functional fiber.     

Adaptive mental mechanisms: Their role in a positive psychology.

Psychology needs a metric for positive mental health that would be analogous to the IQ tests that measure above average intelligence. The Defensive Function Scale of the DSM-IV offers a possible such metric. In the present article the author links the transformational qualities of defenses at the mature end of the Defensive Function Scale (altruism, suppression, humor, anticipation, and sublimation) to positive psychology. First, the methodological problems involved in the reliable assessment of defenses are acknowledged. Next, the use of prospective longitudinal study to overcome such difficulties and to provide more reliable definition and measurement of defenses is outlined. Evidence is also offered that, unlike many psychological measures, the maturity of defenses is quite independent of social class, education, and IQ. Last, evidence is offered to illustrate the validity of mature defenses and their contribution to positive psychology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of the copper chaperone Cox17 of Saccharomyces cerevisiae

Assembly of functional cytochrome oxidase in yeast requires Cox17, which has been postulated to deliver copper ions to the mitochondrion for insertion into the enzyme. This role for Cox17 is supported by the observation that it binds copper as a binuclear cuprous-thiolate cluster. X-ray absorption spectroscopy, together with UV-visible absorption and emission spectroscopy, indicates the presence of bound cuprous ions, trigonally coordinated by thiolate ligands. Analysis of the EXAFS shows three Cu-S bonds at 2.26 A, plus a short Cu-Cu distance of 2.7 A, indicating a binuclear cluster in Cox17. The cuprous-thiolate cluster in Cox17 is substantially more labile than structurally related clusters in metallothioneins.     

Buoyantly-driven two-phase countercurrent flow in liquid discharge from a vessel with an unvented gas space

This paper details experiments and analyses regarding the phenomenon of liquid discharge into a gaseous atmosphere from the bottom of a vessel with an unvented, upper gas space. The primary goal is the development of a simple model that predicts the rate of liquid discharge under the prevailing unvented condition. A literature survey of previous work on this phenomenon yielded only simple experiments and analyses that were limited in scope. Experiments were subsequently undertaken with an air-water system, using a larger volume and a wide range of drain line diameters. In addition to flowrate data, visual information was acquired regarding the physical mechanism possibly governing the prevalent flow regimes. The governing physical mechanism is identified as the stability of a gas-liquid interface, perturbed by buoyancy, at the drain line entrance. G.I. Taylor's fundamental analysis of interfacial stability lead to the determination of criteria for flow regime transition among the three prevalent flow regimes, corresponding to so-called small, medium, and large diameters. Also, analysis of the growth of interfacial instabilities lead to the application of flooding models for drainage rates within each regime. The models for moderate and large diameters were then compared against data, which confirmed their success in predicting discharge rates under the unvented condition.The motivation for this effort, besides the basic scientific significance of studying such a fundamental phenomenon, was its numerous applications, one of which is commercial nuclear reactor systems. Specifically, the phenomenon prevails in liquid coolant discharge from a PWR pressurizer, with an unvented steam volume, into a steam atmosphere existing in the adjoining hot coolant leg. Such a phenomenon could occur as part of a transient, or severe accident, scenario, entailing saturated conditions and steam production in the normally subcooled primary heat transport loop. The developed model was implemented in the Modular Accident Analysis Program (MAAP), a computer code designed to predict reactor system behavior in response to postulated off-normal conditions, including severe accident scenarios.     

CHEMICAL BASIS OF MIDDLE DISTILLATE FUEL INSTABILITY: Interactive Effects of Selected Nitrogen Heterocycles with Organic Bases in a Shale-Derived Diesel Fuel.

Fuel instability reactions are defined in terms of the formation of deleterious products such as filterable sediments and peroxides. Gravimetric stability tests have been carried out at 80^°C using two model nitrogen heterocycles: 2,5-dimethy1pyrrole, DMP, and 3-methylindole, 3-MI, in an otherwise stable shale derived middle distillate fuel. Potential interactive effects for these model nitrogen heterocycles have been described by the presence of organic base co-dopants. Organic bases employed included: tri-n-butylamine, N, N-dimethyl-aniline, and 4-dimethylaminopyridine. Simple organic amines exerted only minor interactive effects, usually an increase in filterable sediment in the range of 5-15%. However, the diamine species, 4-dimethylaminopyridine, interacted in a strong positive fashion to generate increased amounts, 22-44%, of sediment.     

Validity and construct contamination of the Racial Identity Attitude Scale—Long Form.

The Racial Identity Attitude Scale—Long Form (RIAS–L; J. E. Helms & T. A. Parham, 1996) is likely to be the instrument of choice in future research on African American racial identity development, but little is known about its psychometric properties. RIAS-L data from 275 African American community members and students were collected, and a series of analyses (i.e., correlations, multiple regressions, and confirmatory modeling) was conducted to explore convergent and discriminant validity. Overall, results were mixed, generally revealing limited support for the RIAS-L's convergent and discriminant validity and highlighting concerns regarding the Preencounter and Encounter subscales. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

微导通孔的电镀填孔技术

本文主介绍了电镀填孔技术,并探讨了DC和PPR电镀填孔技术的优缺点和影响填孔效果的相关因素。