Dynamic behaviour of AA 2024 under blast loading : experiments and simulations

The dynamic behaviour of AA2024-T3 is investigated. Dynamic tensile tests using a servo-hydraulic and a light weight shock testing machine (LSM) have been performed. The servo-hydraulic test machine proves to be more reliable and reaches higher strain rates. Neither test revealed any strain rate effect of AA2024-T3. Two types of fracture tests were carried out to determine the dynamic crack propagation behaviour of this alloy, using prestressed plates and pressurized barrels, both with the help of explosives. The prestressed plates proved to be not suitable, whereas the barrel tests were quite reliable, allowing to measure the crack speeds. Computer simulations with a user defined, rate dependent cohesive zone model were in agreement with experiments, capturing the rate toughening effect

Trial-by-Trial Changes in a Priori Informational Value of External Cues and Subjective Expectancies in Human Auditory Attention

Background: Preparatory activity based on a priori probabilities generated in previous trials and subjective expectancies would produce an attentional bias. However, preparation can be correct (valid) or incorrect (invalid) depending on the actual target stimulus. The alternation effect refers to the subjective expectancy that a target will not be repeated in the same position, causing RTs to increase if the target location is repeated. The present experiment, using the Posner’s central cue paradigm, tries to demonstrate that not only the credibility of the cue, but also the expectancy about the next position of the target are changedin a trial by trial basis. Sequences of trials were analyzed. Results: The results indicated an increase in RT benefits when sequences of two and three valid trials occurred. The analysis of errors indicated an increase in anticipatory behavior which grows as the number of valid trials is increased. On the other hand, there was also an RT benefit when a trial was preceded by trials in which the position of the target changed with respect to the current trial (alternation effect). Sequences of two alternations or two repetitions were faster than sequences of trials in which a pattern of repetition or alternation is broken. Conclusions: Taken together, these results suggest that in Posner’s central cue paradigm, and with regard to the anticipatory activity, the credibility of the external cue and of the endogenously anticipated patterns of target location are constantly updated. The results suggest that Bayesian rules are operating in the generation of anticipatory activity as

Methylphenidate produces selective enhancement of declarative memory consolidation in healthy volunteers

RATIONALE: Methylphenidate inhibits the reuptake of dopamine and noradrenaline and is used to treat children with attention deficit hyperactivity disorder (ADHD). Besides reducing behavioral symptoms, it improves their cognitive function. There are also observations of methylphenidate-induced cognition enhancement in healthy adults, although studies in this area are relatively sparse. We assessed the possible memory-enhancing properties of methylphenidate. OBJECTIVE: In the current study, the possible enhancing effects of three doses of methylphenidate on declarative and working memory, attention, response inhibition and planning were investigated in healthy volunteers. METHODS: In a double blind placebo-controlled crossover study, 19 healthy young male volunteers were tested after a single dose of placebo or 10, 20 or 40 mg of methylphenidate. Cognitive performance testing included a word learning test as a measure of declarative memory, a spatial working memory test, a set-shifting test, a stop signal test and a computerized version of the Tower of London planning test. RESULTS: Declarative memory consolidation was significantly improved relative to placebo after 20 and 40 mg of methylphenidate. Methylphenidate also improved set shifting and stopped signal task performance but did not affect spatial working memory or planning. CONCLUSIONS: To the best of our knowledge, this is the first study reporting enhanced declarative memory consolidation after methylphenidate in a dose-related fashion over a dose range that is presumed to reflect a wide range of dopamine reuptake inhibition

Voluntary task switching under load: contribution of top-down and bottom-up factors in goal-directed behavior

The present study investigated the relative contribution of bottom-up and top-down control to task selection in the voluntary task-switching (VTS) procedure. In order to manipulate the efficiency of top-down control, a concurrent working memory load was imposed during VTS. In three experiments, bottom-up factors, such as stimulus repetitions, repetition of irrelevant information, and stimulus task associations, were introduced in order to investigate their influence on task selection. We observed that the tendency to repeat tasks was stronger under load, suggesting that top-down control counteracts the automatic tendency to repeat tasks. The results also indicated that task selection can be guided by several elements in the environment, but that only the influence of stimulus repetitions depends on the efficiency of top-down control. The theoretical implications of these findings are discussed within the interplay between top-down and bottom-up control that underlies the voluntary selection of tasks

Appraisal of MC2010 shear resistance approaches coupled with a residual flexural strength prediction model

In the present work the predictive performance of the two approaches proposed by Model Code 2010 for the evaluation of the shear capacity of fiber reinforced concrete (FRC) elements flexurally reinforced with conventional steel bars is assessed considering a database (DBs) constituted by 80 FRC beams do not including conventional transverse reinforcements. The accuracy of these shear models is evaluated by statistical analysis of the prediction ratio between the experimental and estimated shear capacity of the beams of the DBs, and applying the Demerit Points Classification approach for further information about the reliability of the two approaches in design context. Due to the absence of the post-cracking experimental characterization of the FRC used in several beams considered in the DBs, an approach was developed for estimating the residual flexural strength parameters from the most relevant known variables of steel fiber reinforcement mechanisms for concrete, namely the fiber volume and aspect ratio, and the concrete compressive and tensile strength. The residual flexural strength prediction model is assessed and its influence on the performance of the shear resistance models is evaluatedSFRH/BDE/96381/2013 co-funded by CiviTest - Pesquisa de Novos Materiais para a Engenharia Civil, Lda. and by FCT - Portuguese Foundation for Science and Technology. The authors also acknowledge the support provided by the FCT project PTDC/ECM-EST/2635/201

Systematic Mutational Analysis of the Intracellular Regions of Yeast Gap1 Permease

The yeast general amino acid permease Gap1 is a convenient model for studying the intracellular trafficking of membrane proteins. Present at the plasma membrane when the nitrogen source is poor, it undergoes ubiquitin-dependent endocytosis and degradation upon addition of a good nitrogen source, e.g. ammonium. It comprises 12 transmembrane domains (TM) flanked by cytosol-facing N- and C-terminal tails (NT, CT). The NT of Gap1 contains the acceptor lysines for ubiquitylation and its CT includes a sequence essential to exit from the endoplasmic reticulum (ER).Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

α-Arrestins Aly1 and Aly2 Regulate Intracellular Trafficking in Response to Nutrient Signaling

Arrestins, known regulators of endocytosis, take on novel functions in nutrient-regulated endosomal recycling. Yeast α-arrestins, Aly1 and Aly2, redistribute the Gap1 permease from endosomes to the cell surface and interact with clathrin/AP-1. Aly2 is regulated by the Npr1 kinase and acts through mechanisms distinct from Aly1