On the matrix cracking stress and the redistribution of internal stresses in brittle-matrix composites

A concept is proposed to increase the matrix cracking stress of some brittle-matrix composites by taking advantage of the redistribution of internal stresses that occurs when a composite with phases that have dissimilar creep behavior is subjected to thermomechanical loading. The concept is elaborated through the stress analysis of a model unidirectional composite with constituents that exhibit linear viscoelastic behavior. It is shown that if a composite with a matrix that is less creep resistant than the fibers is subjected to a treatment involving both thermal and mechanical loading (e.g. creep test), stresses can be transferred from the matrix to the fibers, resulting in the stress–relaxation of the matrix. Furthermore, it is also shown that by the elastic recovery of the fibers, the matrix can be subjected to large compressive residual stresses at the end of the treatment. The conditions for the viability of this concept and the implications of fiber overloading and potential loss of composite-like behavior are discussed.     

Modeling the effects of hypoglycemia on a two-choice task in adult humans.

Objective: Previous research has demonstrated that hypoglycemia causes reaction times to be slower and more variable. Reaction time tests, however, use multiple cognitive and noncognitive processes. This study is the first to use a validated sequential sampling model (diffusion model) applied to results obtained from a simple 2-choice task in adult humans to assess the effects of hypoglycemia on the basic parameters of decision making. Method: Fourteen adult volunteers were tested on a numerosity discrimination task with and without reduced blood glucose concentrations. The results were analyzed with a model that dissects the components of processing that underlie decisions: the quality of the information on which a decision is based (drift rate), the critical amount of evidence that must be accumulated before a decision is made (boundary separation), and the time taken by nondecision processes. Results: Hypoglycemia resulted in a reduction of mean drift rate from 0.290 to 0.211, t(13) = 4.10, p     

Frequency, quality, and impact of life events in self-rated depressed, behavioral-problem, and normal children.

Assessed 60 self-rated depressed, behavioral-problem, and normal 3rd–6th grade children closely matched for sex, age, and socioeconomic status (SES) for the number, quality, and impact of stressful life events in the past year. Results indicate that dysphoria-reporting Ss experienced more life events and a higher qualitative index of stress than the other 2 groups. The impact of each event, however, was not greater for the depressed Ss than for the other 2 groups. The self-rated depressed Ss appeared to experience more major family disruptions than the other 2 groups of Ss. (6 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

问与答Wyld Stallyons

本期，我们邀请了新成立的移动成像公司Wyld Stallyons的Richard May坐客访谈栏目，进一步了解他们为内衣品牌Lascivious制作的颇受好评的病毒式短片The Doll以及他们为MTV、VH1和BMW等客户创作的作品。