Fracture Mechanisms And Size Effects Of Brittle Metallic Foams: In Situ Compression Tests Inside Sem

In situ compressive tests on specially designed small samples made from brittle metallic foams were accomplished in a loading device equipped in the scanning electron microscopy (SEM). Each of the small samples comprises only several cells in the effective test zone (ETZ), with one major cell in the middle. In such a system one can not only obtain sequential collapse-process images of a single cell and its cell walls with high resolution, but also correlate the detailed failure behaviour of the cell walls with the stress-strain response, therefore reveal the mechanisms of energy absorption in the mesoscopic scale. Meanwhile, the stress-strain behaviour is quite different from that of bulk foams in dimensions of enough large, indicating a strong size effect. According to the in situ observations, four failure modes in the cell-wall level were summarized, and these modes account for the mesoscopic mechanisms of energy absorption. Paralleled compression tests on bulk samples were also carried out, and it is found that both fracturing of a single cell and developing of fracture bands are defect-directed or weakness-directed processes. The mechanical properties of the brittle aluminum foams obtained from the present tests agree well with the size effect model for ductile cellular solids proposed by Onck et al. (C) 2008 Elsevier Ltd. All rights reserved.

Tensile Tests Of Micro Anchors Anodically Bonded Between Pyrex Glass And Aluminum Thin Film Coated On Silicon Wafer

Micro anchor is a kind of typical structures in micro/nano electromechanical systems (MEMS/NEMS), and it can be made by anodic bonding process, with thin films of metal or alloy as an intermediate layer. At the relative low temperature and voltage, specimens with actually sized micro anchor structures were anodically bonded using Pyrex 7740 glass and patterned crystalline silicon chips coated with aluminum thin film with a thickness comprised between 50 nm and 230 nm. To evaluate the bonding quality, tensile pulling tests have been finished with newly designed flexible fixtures for these specimens. The experimental results exhibit that the bonding tensile strength increases with the bonding temperature and voltage, but it decreases with the increase of the thickness of Al intermediate layer. This kind of thickness effect of the intermediate layer was not mentioned in the literature on anodic bonding. (C) 2008 Elsevier Ltd. All rights reserved.

Factors Resulting In Micron Indentation Hardness Descending In Indentation Tests

Some factors that affect the experimental results in nanoindentation tests such as the contact depth, contact area, load and loading duration are analyzed in this article. Combining with the results of finite element numerical simulation, we find that the creep property of the tested material is one of the important factors causing the micron indentation hardness descending with the increase of indentation depth. The analysis of experimental results with different indentation depths demonstrates that the hardness decrease can be bated if the continuous stiffness measurement technique is not adopted; this indicates that the test method itself may also be one of the factors causing the hardness being descended.

Attention deficit/hyperactivity disorder children with a 7-repeat allele of the dopamine receptor D4 gene have extreme behavior but normal performance on critical neuropsychological tests of attention

An association of the dopamine receptor D4 (DRD4) gene located on chromosome 11p15.5 and attention deficit/hyperactivity disorder (ADHD) has been demonstrated and replicated by multiple investigators. A specific allele [the 7-repeat of a 48-bp variable number of tandem repeats (VNTR) in exon 3] has been proposed as an etiological factor in attentional deficits manifested in some children diagnosed with this disorder. In the current study, we evaluated ADHD subgroups defined by the presence or absence of the 7-repeat allele of the DRD4 gene, using neuropsychological tests with reaction time measures designed to probe attentional networks with neuroanatomical foci in D4-rich brain regions. Despite the same severity of symptoms on parent and teacher ratings for the ADHD subgroups, the average reaction times of the 7-present subgroup showed normal speed and variability of response whereas the average reaction times of the 7-absent subgroup showed the expected abnormalities (slow and variable responses). This was opposite the primary prediction of the study. The 7-present subgroup seemed to be free of some of the neuropsychological abnormalities thought to characterize ADHD.

Neutrality tests using DNA polymorphism from multiple samples

The polymorphism of a gene or a locus is studied with increasing frequency by multiple laboratories or the same group at different times. Such practice results in polymorphism being revealed by different samples at different regions of the locus. Tests of neutrality have been widely conducted for polymorphism data but commonly used statistical tests cannot be applied directly to such data. This article provides a procedure to conduct a neutrality test and details are given for two commonly used tests. Applying the two new tests to the chemokine-receptor gene (CCR5) in humans, we found that the hypothesis that all mutations are selectively neutral cannot explain the observed pattern of DNA polymorphism.

New double-ceramic-layer thermal barrier coatings based on zirconia-rare earth composite oxides

A series of La2O3-ZrO2-CeO2 composite oxides were synthesized by solid-state reaction. The final product keeps fluorite structure when the molar ratio Ce/Zr >= 0.7/0.3, and below this ratio only mixtures of La2Zr2O7 (pyrochlore) and La2O3-CeO2 (fluorite) exist. Averagely speaking, the increase of CeO2 content gives rise to the increase of thermal expansion coefficient and the reduction of thermal conductivity, but La-2(Zr0.7Ce0.3)(2)O-7 has the lowest sintering ability and the lowest thermal conductivity which could be explained by the theory of phonon scattering. Based on the large thermal expansion coefficient of La2Ce3.25O9.5, the low thermal conductivities and low sintering abilities of La2Zr2O7 and La-2(Zr0.7Ce0.3)(2)O-7, double-ceramic-layer thermal barrier coatings were prepared. The thermal cycling tests indicate that such a design can largely improve the thermal cycling lives of the coatings. Since no single material that has been studied so far satisfies all the requirements for high temperature thermal barrier coatings, double-ceramic-layer coating may be an important development direction of thermal barrier coatings.

维持性血液透析患者认知功能特点研究

Objective: To study the episodic memory, semantic memory, cognitive planning ability and inhibition ability in MHD patients. Method: Neuropsychological research methods such as Action memory of verb-object phrase, Trail Making Test (A and B), Verbal Fluency Test, Go-No/Go test and Stroop Color Naming Task were used to investigate Episodic Memory 、Semantic Memory、Executive Function of 40 MHD and 40 NC. Self-Rating Anxiety Scale (SAS), Self-Rating Depression Scale(SDS), Social Support Scale, Life Satisfaction Scale, and biochemical examination were applied and their relationships with cognitive function were analized. The mean age and education level of MHD group and NC group have no significant difference. Result: 1.Action memory of verb-object phrase differed significantly between MHD group and NC group. 2.Two tests of Verbal Fluency differed significantly between MHD group and NC group. 3.Trail Making Test A, Trail Making Test B, the baseline condition of Go-No/Go Test and Stroop Color Naming Test differed significantly between MHD group and NC group. 4.There is no significant difference between MHD group and NC group on the correct rate of No/Go Test and the baseline condition. Both groups showed Stroop Effect in Go-No/Go test, but MHD group performed significantly worse. 5.In Stroop Color Naming Task Test, NC group showed Stroop Effect, significant Repeated Distraction Promotion Effect and significant Negative Priming Effect,while MHD group showed only Stroop Effect and no Repeated Distraction Promotion Effect and no Negative Priming Effect. There is significant difference in Stroop Effect between MHD group and NC group. Conclusion: 1.Comparing with NC group, episodic memory, semantic memory, cognitive planning ability, and inhibition ability of MHD group were impaired significantly. 2.The pathological aging of Executive Function in MHD group showed: executive Function should be a unitary system. 3.Cognitive impairment is negatively correlated with serum creatinine, blood pressure and anxiety score in MHD patients; and is related with hemoglobin, hematocrit, social support and life satisfaction. Keyword: maintenance hemodialysis, episodic memory, semantic memory, cognitive planning, inhibition ability.

心理测验中项目表述效应的特点、机制和预测因素研究

心理测验中项目的表述效应是测量误差的一个重要来源。本研究借助焦虑控制问卷，探讨心理量表中项目表述效应的心理测量学特点和其产生的方法学上的原因。研究首先考察了项目表述效应在不同的群体间的交互效度验证；然后通过反转项目表述方向的方法，构造出原问卷项目的相反表达的项目，进而通过不同组合形成四个版本的问卷，经过量表层面和项目层面的分析，考查了项目表述效应的心理测量学特点。然后通过项目反应理论分析和实验研究，考查了项目反应理论产生的作用机制。研究最后还考查了人格因素对项目表述效应的影响。主要研究结果如下： 1． 焦虑控制问卷（ACQ）中项目表述效应稳定的存在，中文版问卷的主要结构是一个特质性因子，另外还有两个方法因子。这一结构很好的拟合了中国被试的数据，不管是单个量表验证的结果还是两组被试交互验证的结果都支持这一结构； 2． 通过反ACQ问卷，构造了四个版本的量表，对四个版本验证性因素分析的结果表明，全正向表述项目量表和全反向表述项目量表没有项目表述效应出现，而同时存在正向和反向表述项目的原文卷和反转问卷都出现了方法效应；正向项目和反向项目得分分析的结果表明，总分上只有原量表和全反向量表没有显著差异，原量表和全正量表与全反量表都有显著的差异，表明项目表述效应的出项只和反向表述项目的反向记分有关； 3． 基于项目层面的研究中，用Rasch模型中的Rating Scale Model和full information Bifactor item Analysis 分别去拟合数据，发现Rasch模型对数据的拟合不好，而Bifactor items Analysis 对数据的拟合稍好一些，说明焦虑控制问卷中的项目表述效应因子与特质因子确实不是在同一个水平上的因子，表述效应因子是次级因子； 4． 项目表述效应的产生机制是由于人们只对与自己特质水平最近的项目作是的反应，而对与自己实际特质水平较远的项目作否的反应模式特点造成的； 5． 关于人格对项目表述效应出现的预测作用研究表明，自尊、社会赞许性对反向表述效应因子的产生具有正向预测作用，而行为抑制、行为激活和负向评价恐惧对反向表述因子的出现具有负向的预测作用。 总而言之，本研究得出的结论是，项目表述效应是一种人为造成的方法效应，它是被试只对与自己特质水平最近的项目作是的反应，而对与自己实际特质水平较远的项目作否的反应模式特点造成的。但同时，它又不是完全没有意义的“讨厌”因子，一些人格因素可以预测它的出现，即它的出现受到一些人格因素的影响。