Dopamine transporter genotype predicts behavioural and neural measures of response inhibition

The ability to inhibit unwanted actions is a heritable executive function that may confer risk to disorders such as attention deficit hyperactivity disorder (ADHD). Converging evidence from pharmacology and cognitive neuroscience suggests that response inhibition is instantiated within frontostriatal circuits of the brain with patterns of activity that are modulated by the catecholamines dopamine and noradrenaline. A total of 405 healthy adult participants performed the stop-signal task, a paradigmatic measure of response inhibition that yields an index of the latency of inhibition, termed the stop-signal reaction time (SSRT). Using this phenotype, we tested for genetic association, performing high-density single-nucleotide polymorphism mapping across the full range of autosomal catecholamine genes. Fifty participants also underwent functional magnetic resonance imaging to establish the impact of associated alleles on brain and behaviour. Allelic variation in polymorphisms of the dopamine transporter gene (SLC6A3: rs37020; rs460000) predicted individual differences in SSRT, after corrections for multiple comparisons. Furthermore, activity in frontal regions (anterior frontal, superior frontal and superior medial gyri) and caudate varied additively with the T-allele of rs37020. The influence of genetic variation in SLC6A3 on the development of frontostriatal inhibition networks may represent a key risk mechanism for disorders of behavioural inhibition.

Stop-signal task difficulty and the right inferior frontal gyrus

The stop-signal paradigm is increasingly being used as a probe of response inhibition in basic and clinical neuroimaging research. The critical feature of this task is that a cued response is countermanded by a secondary ‘stop-signal’ stimulus offset from the first by a ‘stop-signal delay’. Here we explored the role of task difficulty in the stop-signal task with the hypothesis that what is critical for successful inhibition is the time available for stopping, that we define as the difference between stop-signal onset and the expected response time (approximated by reaction time from previous trial). We also used functional magnetic resonance imaging (fMRI) to examine how the time available for stopping affects activity in the putative right inferior frontal gyrus and presupplementary motor area (right IFG-preSMA) network that is known to support stopping. While undergoing fMRI scanning, participants performed a stop-signal variant where the time available for stopping was kept approximately constant across participants, which enabled us to compare how the time available for stopping affected stop-signal task difficulty both within and between subjects. Importantly, all behavioural and neuroimaging data were consistent with previous findings. We found that the time available for stopping distinguished successful from unsuccessful inhibition trials, was independent of stop-signal delay, and affected successful inhibition depending upon individual SSRT. We also found that right IFG and adjacent anterior insula were more strongly activated during more difficult stopping. These findings may have critical implications for stop-signal studies that compare different patient or other groups using fixed stop-signal delays.

Stop-signal response inhibition in schizophrenia : Behavioural, event-related potential and functional neuroimaging data

Inhibitory control deficits are well documented in schizophrenia, supported by impairment in an established measure of response inhibition, the stop-signal reaction time (SSRT). We investigated the neural basis of this impairment by comparing schizophrenia patients and controls matched for age, sex and education on behavioural, functional magnetic resonance imaging (fMRI) and event-related potential (ERP) indices of stop-signal task performance. Compared to controls, patients exhibited slower SSRT and reduced right inferior frontal gyrus (rIFG) activation, but rIFG activation correlated with SSRT in both groups. Go stimulus and stop-signal ERP components (N1/P3) were smaller in patients, but the peak latencies of stop-signal N1 and P3 were also delayed in patients, indicating impairment early in stop-signal processing. Additionally, response-locked lateralised readiness potentials indicated response preparation was prolonged in patients. An inability to engage rIFG may predicate slowed inhibition in patients, however multiple spatiotemporal irregularities in the networks underpinning stop-signal task performance may contribute to this deficit.

热浸镀钢材在海水中的氢渗透行为及其对材料力学性能的影响

氢渗透和拉应力的联合作用对海洋环境中的热浸镀钢材的安全构成潜在威胁，本文以当前应用最广泛的三种商业化热浸镀钢材（Galvanized、Galfan和Galvalume）为研究对象，采用边界元方法计算了三种镀层缺陷周围的电场分布；设计了专用子母配套双电解池并测试了氢渗透电流密度曲线，比较了镀层氢渗透抑制性能及存在缺陷时的自渗氢倾向，并结合镀层成分及结构进行了分析；推导了氢渗透过程相关公式，建立了适合于评价镀层材料氢渗透行为的TANG-LI模型并计算了控制氢渗透相关过程的动力学参数；通过SSRT比较、分析了镀层材料充氢与无充氢条件下的应力－应变行为，并配合断口的显微分析，探讨了海水中带缺陷镀层的氢渗透行为对钢材基体力学性能的影响，结果表明： ⑴海水中三种镀层钢材缺陷处的阴极电位负于析氢电位，能够发生析氢反应而析出氢原子； ⑵ Galvanized镀层对氢渗透的抑制能力较弱，Galfan镀层完好时能明显抑制外部氢的进入，两者存在缺陷时都能产生额外的氢；Galvalume镀层具有很强的氢渗透抑制能力，而且当其存在缺陷时无自渗氢行为；镀层铝含量越高，完整镀层的氢渗透抑制能力越强，缺陷镀层自渗氢能力越弱。 ⑶Galvanized镀层在海水中的氢渗透能降低基体材料的强度并使得其断裂方式由韧性变为准解理，从而加大了材料发生氢脆的倾向；Galfan镀层的氢渗透行为能降低材料的强度但不会改变其韧性断裂方式；Galvalume缺陷镀层则对材料的强度和韧性断裂方式都不能造成影响。

硫酸盐还原菌和极化电位对海洋结构用钢在海泥中应力腐蚀开裂敏感性的影响

海洋设施长期处于恶劣的腐蚀环境中，如不加以防护，一旦发生应力腐蚀开裂（SCC），损失就会极为惨重。海底泥土区环境十分重要，因为管线和平台桩腿等都埋在海底泥中。海底泥中硫酸盐还原菌（SRB）十分活跃，而且为了防止腐蚀，海泥中的设施无一例外地采取了阴极保护，相当于设施处在长期稳定的充氢状态。因此非常有必要研究海泥中的活性SRB和极化电位对海洋结构用钢在海泥中的氢渗透行为和SCC敏感性造成的影响，弄清SCC发生和发展的过程以便采取相应的措施减缓或防止SCC。 本文通过慢应变速率拉伸实验（SSRT）、电化学阻抗谱（EIS）技术、动电位扫描极化曲线测定实验和氢渗透实验等研究了海泥中SRB和极化电位对16Mn钢和管线钢X56（API X56）的SCC敏感性造成的影响。 从渤海海泥中富集得到SRB菌种，并做出了SRB在海泥中的生长曲线；在荧光显微镜下观察SRB为弧状，可以归为脱硫弧菌属，为革兰氏阴性菌；海泥中活性SRB数量与硫电位等主要腐蚀环境因子具有一定的对应关系。 SSRT结果表明，施加阴极极化电位可以使试样断裂脆性特征明显，SCC敏感性增大；海泥中活性SRB浓度越高，断裂脆性特征越明显，SCC敏感性越大。在含SRB海泥中或阴极极化电位条件下，两种钢都容易发生SCC，氢脆（HIC）起主要作用。 随着浸泡天数的增加，试样在灭菌海泥中的Rp一直增大；在含SRB海泥中Rp先增大，又变小，并呈现出显著的Warburg阻抗特征；在灭菌海泥中，两种试样在阳极电位范围内无SCC敏感区，而在阴极电位范围内有明显的SCC敏感区；在含SRB海泥中，在阳极电位范围和阴极电位范围内均有SCC敏感区；SRB代谢产物既有阳极去极化作用，又有阴极去极化作用，能使腐蚀电流密度增加。 活性SRB的存在能够促进试样在海泥中的氢渗透；在实海工程应用中，两种钢在含SRB海泥中的氢渗透电流密度大约是在不含SRB海泥中的3~4倍。阴极极化电位能够促进试样在灭菌海泥中的氢渗透。在含SRB海泥中对试样施加阴极极化电位，氢渗透电流密度大于不加阴极极化电位时的氢渗透电流密度，也大于在不含SRB的海泥中的氢渗透电流密度。

海洋结构用钢在海洋大气中的氢脆机制研究

氢致开裂以及氢脆现象一直是困扰着石油生产及石油化工的一个重要问题。钢材的氢脆易造成巨大的腐蚀灾难。目前，随着石油开采钻井的深度的加深，石油开采中钢材所处的环境越来越恶劣。硫化氢，二氧化碳以及盐水等腐蚀介质可导致普通腐蚀，硫化物腐蚀，二氧化碳腐蚀，氢的渗透等腐蚀现象。这些腐蚀现象的存在，大大限制了石油工业的发展。硫化氢的存在可引起钢材的氢脆现象，给安全生产带来极大的隐患。然而，研究者对于氢脆现象的研究大部分是在本体溶液中的，对于在大气腐蚀中的氢脆现象的研究并不多见，并且对于动载条件下的氢渗透研究更为鲜见。 本文通过电化学研究方法及慢应变速率拉伸试验（SSRT）研究了从实验室模拟到实际海洋大气环境中，海洋大气对材料渗氢性能的影响及对材料应力腐蚀敏感性的影响，特别是在硫化氢及二氧化硫存在的条件下的影响。结果表明，从实验室模拟到实际海洋大气环境，材料都存在氢渗透现象，硫化氢及二氧化硫的存在可加速材料氢渗透现象，材料应力腐蚀敏感性也随其浓度的增大而增大。结合SEM实验结果，随硫化氢及二氧化硫浓度增大，金属材料由韧性断裂向脆性断裂转变。腐蚀失重实验表明，腐蚀失重与材料氢渗透量之间存在着线性关系。据此研制腐蚀失重传感器，实验结果表明，传感器结果与实际腐蚀失重结果一致，并且该传感器使用方便，可原位、随时、便捷地调查材料腐蚀失重，具有高适应性、高灵敏度的特点。 本文还研究了动载条件下，海洋大气环境中形变对材料氢渗透现象的影响。结果表明，弹性变形阶段，氢渗透电流变化不大，当试样屈服后，氢渗透电流突然下降，然后又回复到一个稳定值，这与氢陷阱的形成有关。

硫酸盐还原菌对热浸镀锌钢材在海水中的氢渗透行为和脆性的影响研究

硫酸盐还原菌(SRB)活动、拉应力和氢的联合作用将对海洋环境中热浸镀锌钢材构筑物的安全带来隐患。本文通过Devanathan－Stachurski双面电解池测试技术，检测了镀层完好及存在缺陷的热浸镀锌钢材在灭菌海水、灭菌培养基及接种SRB的培养基中的氢渗透电流曲线，探讨了镀层缺陷、培养基成分以及SRB对热浸镀锌钢材氢渗透行为的影响；采用电化学阻抗谱测试技术，研究了热浸镀锌钢材在上述介质中的腐蚀机制，并由此讨论了热浸镀锌钢材在不同条件下的氢渗透机制；通过慢应变速率拉伸试验(SSRT)，获得了热浸镀锌钢材在不同腐蚀介质中的应力-应变曲线，比较了其力学性能参数，进而通过断口分析，评价了热浸镀锌钢材在灭菌海水、灭菌培养基及接种SRB培养基中的氢脆敏感性。研究结果表明： (1) 镀层出现缺陷将对热浸镀锌钢材的氢渗透行为起促进作用，这类试样在灭菌海水和灭菌培养基中的平均氢渗透电流密度比镀层完好试样在相同介质中的平均氢渗透电流密度分别提高了250.76%和32.76%；培养基组分对热浸镀锌钢材的氢渗透行为起促进作用，镀层存在缺陷和镀层完好的热浸镀锌钢材试样在灭菌培养基中的平均氢渗透电流密度分别比其在灭菌海水中高181.22%和626.97%；SRB对热浸镀锌钢材的氢渗透行为起抑制作用，镀层存在缺陷及镀层完好的热浸镀锌钢材试样在接种SRB的培养基中的平均氢渗透电流密度分别比灭菌培养基中低90.84%、77.14%。 (2) 电化学测试结果表明，培养基组分能够加速热浸镀锌钢材的腐蚀，使试样表面更容易形成腐蚀缺陷，从而增加其自渗氢能力；活性SRB本身对热浸镀锌钢材的腐蚀和氢渗透起促进作用，但在本文实验条件下，SRB及其代谢产物形成的生物膜以及腐蚀产物组成的致密膜层能够通过阻挡层作用抑制腐蚀，并阻止氢的进入；扫描电镜(SEM)分析结果表明，暴露于接种SRB培养基中的热浸镀锌钢材试样表面有致密的产物膜层，而灭菌培养基中的试样表面没有明显腐蚀产物膜存在。 (3) 培养基组分对热浸镀锌钢材氢渗透行为的促进作用增加了其对氢脆的敏感性，热浸镀锌钢材在灭菌培养基中的断后延伸率和能量密度比在灭菌海水中分别降低了4.97%和5.59%；SRB对热浸镀锌钢材氢渗透行为的抑制作用降低了其对氢脆的敏感性，热浸镀锌钢材在接种SRB的培养基中的断后延伸率和能量密度比其在灭菌培养基中分别高7.78%和8.44%。

35CrMo高强度钢在海洋大气中的氢渗透行为与环境致脆机理研究

海洋大气腐蚀环境是海洋腐蚀环境之一。金属材料在海洋大气环境下会发生环境敏感断裂。在环境敏感断裂中，氢脆是其中的一个重要类型。氢脆是合金中存在过量的氢，并在拉应力协同作用下造成的一种脆断。氢渗透已被证明是金属材料失效的主要原因之一。氢脆导致了材料强度降低，在较低载荷下会导致材料的灾害性破坏，因此研究海洋用钢在海洋大气中的致脆机制与氢渗透行为是十分必要的。本文所做工作主要有以下几点： 一、 采用Devanathan-Stachurski氢渗透技术，研究了35CrMo高强度钢未受 力试样在海洋大气腐蚀环境中的氢渗透及腐蚀失重行为。主要分为两个部分：(1) 干湿循环实验；(2)模拟海洋大气腐蚀实验。实验结果表明，在海洋大气腐蚀环境中，35CrMo 高强度钢存在着明显的氢渗透现象，在不同腐蚀环境中现象有所不同。Cl-离子、H2S、SO2等污染物对氢渗透产生了明显的促进作用。另外，氢渗透量与腐蚀失重存在着明显的线性关系。 二、 采用慢应变速率拉伸实验法(SSRT)，在海洋大气腐蚀环境中对35CrMo试样进行力学性能测试，研究氢渗透对35CrMo应力腐蚀开裂敏感性的影响。实验结果表明，在各种腐蚀条件下，氢渗透会增加35CrMo的应力腐蚀开裂敏感性，使得最大载荷、断裂时间及应变值均减小。 三、 采用Devanathan-Stachurski氢渗透技术与慢应变速率拉伸实验法，进行了35CrMo高强度钢受力试样在海洋大气环境中的氢渗透实验，研究材料形变对氢渗透的影响。实验结果表明，在弹性变形阶段，氢渗透电流逐渐增大，在塑性变形阶段开始后，氢渗透逐渐减小，在塑性变形阶段后期，随着形变的增大，氢渗透电流增大。

Boundary Element Method (BEM) Analysis for Galvanic Corrosion of Hot Dip Galvanized Steel Immersed in Seawater

A numerical analysis of galvanic corrosion of hot-dip galvanized steel immersed in seawater was presented. The analysis was based on the boundary element methods (BEMs) coupled with Newton-Raphson iterative technique to treat the nonlinear boundary conditions, which were determined by the experimental polarization curves. Results showed that galvanic current density concentrates on the boundary of steel substrate and zinc coating, and the sacrificial protection of zinc coating to steel substrate results in overprotection of steel cathode. Not only oxygen reduction but also hydrogen reduction could occur as cathode reactions, which probably led up to the adsorption and absorption of hydrogen atoms. Flat galvanized steel tensile sample shows a brittle behavior similar to hydrogen embrittlement according to the SSRT (show strain rate test) in seawater.

慢性海洛因成瘾者的冲动性和行为抑制缺陷脑机制

In recent years, the deficit of inhibition has become an important reason for explaining addiction. Response inhibition resembles the compulsive drug seeking behavior and it is the basement of addiction inhibition deficits. However, there were no enough evidence for the relationship between addiction and response inhibition deficits and the results of the neuro mechanisms studies remains unclear. Few studies has focused on the exploring the heroin users. Among those paradigms for study response inhibition deficits, stop signal is a very suitable model for the representation of compulsive drug seeking, but only a few researches has worked on this paradigm. In this study, we selected about 100 heroin abusers and had behaviour and neuro imaging scannings for investigating the response inhibition deficits. The behaviour researches found: first, the chronic heroin users had longer reaction time than control group and this reaction time were not affected by stop signals in heroin users. Second, heroin users had less waiting time than control group and they were more impulsive but less flexibility. Their erro monitoring and flexibale adjustment ability decreased. Third, the SSRT of heroin users was significantly longer than control group. These results suggested that the inhibition of heroin users were impaired. Further investigation showed that the SSRT of heroin users had positive correlation of four factor scores of ASI and the macro correlation coefficient was factor three of drug use. This correlation suggested that drug use was the main reason of inhibition deficits. fMRI results mainly focused on the ANOVA analysis for group difference. First, there was no intensity difference in M1 and SMA brain areas between the two groups. Second, heroin users had less activation in right dorsalateral prefrontal cortex, right inferior prefrontal cortex and anterior cingulated cortex, while in bilateral striatum and amygdala, heroin users had more activation than control group. The right prefrontal cortex was indentified as the main inhibition brain area. The anterior cingulated cortex has relationship with erro monitoring and amygdale was an important brain area for impulsivity and emotion control. The network of these brain areas was envovled in impulsivity and inhibition and it was suggested the mainly damaged network for heroin users’ disinhibition. We also investigated the gray matter changes of heroin users and found that chonic heroin use made their gray matter density decreased in prefrontal cortex (including bilateral dorsalateral prefrontal cortex, obital frontal cortex, inferior prefrontal cortex) and anterior cingulated cortex. The gray matter density in these brain regions had negative correlation with drug use duration. In conclusion, we indentified the disinhibition of heroin users and its neuro mechanism. Their compulsivity brain areas had more activation than control group and their inhibition brain areas had less activation than normal control. On the other side, the biological mechanism of this activation changes was the gray matter density decrease in these brain areas.

Susceptibility to environmentally induced cracking of laser-welded NiTi wires in Hanks’ solution at open-circuit potential

In the present study the tensile and super-elastic behaviours of laser-welded NiTi wires in Hanks’ solution at open-circuit potential (OCP) were investigated using tensile and cyclic slow-strain-rate tests (SSRT). In comparison with NiTi weldment tested in oil (non-corrosive environment), the weldment in Hanks’ solution suffered from obvious degradation in the tensile properties as evidenced by lower tensile strength, reduced maximum elongation, and a brittle fracture mode. Moreover, a larger residual strain was observed in the weldment after stress–strain cycles in Hanks’ solution. In addition to the microstructural defects resulting from the welding process, the inferior tensile and super-elastic behaviours of the NiTi weldment in Hanks’ solution could be attributed to the trapping of a large amount of hydrogen in the weld zone and heat-affected zone.

Susceptibility to stress corrosion cracking of NiTi laser weldment in Hanks’ solution

In this study, the susceptibility to stress corrosion cracking (SCC) of laser-welded NiTi wires in Hanks’ solution at 37.5 °C was studied by the slow strain-rate test (SSRT) at open-circuit potential and at different applied anodic potentials. The weldment shows high susceptibility to SCC when the applied potential is near to the pitting potential of the heat-affected zone (HAZ). The pits formed in the HAZ become sites of crack initiation when stress is applied, and cracks propagate in an intergranular mode under the combined effect of corrosion and stress. In contrast, the base-metal is immune to SCC under similar conditions. The increase in susceptibility to SCC in the weldment could be attributed to the poor corrosion resistance in the coarse-grained HAZ.

Reduction of environmentally induced cracking of laser-welded shape memory NiTi wires via post-weld heat-treatment

In this study, the environmentally induced cracking behaviour of the NiTi weldment with and without post-weld heat-treatment (PWHT) in Hanks’ solution at 37.5 °C at OCP were studied by tensile and cyclic slow-strain-rate tests (SSRT), and compared with those tested in oil (an inert environment). Our previous results in the tensile and cyclic SSRT showed that the weldment without PWHT showed high susceptibility to the hydrogen cracking, as evidenced by the degradation of tensile and super-elastic properties when testing in Hanks' solution. The weldment after PWHT was much less susceptible to hydrogen attack in Hanks' solution as no obvious degradation in the tensile and super-elastic properties was observed, and only a very small amount of micro-cracks were found in the fracture surface. The susceptibility to hydrogen cracking of the NiTi weldment could be alleviated by applying PWHT at the optimized temperature of 350 °C after laser welding.

Effect of Post-weld Heat-treatment on the Stress Corrosion Cracking Behaviour of Laser-welded Shape Memory NiTi Wires in Hanks’ Solution

In this study, the stress-corrosion cracking (SCC) behaviour of laser-welded NiTi wires before and after post-weld heat-treatment (PWHT) was investigated. The samples were subjected to slow strain rate testing (SSRT) under tensile loading in Hanks’ solution at 37.5 °C (or 310.5 K) at a constant anodic potential (200 mVSCE). The current density of the samples during the SSRT was captured by a potentiostat, and used as an indicator to determine the susceptibility to SCC. Fractography was analyzed using scanning-electron microscopy (SEM). The experimental results showed that the laser-welded sample after PWHT was immune to the SCC as evidenced by the stable current density throughout the SSRT. This is attributed to the precipitation of fine and coherent nano-sized Ni4Ti3 precipitates in the welded regions (weld zone, WZ and heat-affected zone, HAZ) after PWHT, resulting in (i) enrichment of TiO2 content in the passive film and (ii) higher resistance against the local plastic deformation in the welded regions.

Effects of temperature and strain rate on the tensile behaviors of SIMP steel in static lead bismuth eutectic

In order to assess the susceptibility of candidate structural materials to liquid metal embrittlement, this work investigated the tensile behaviors of ferritic-martensitic steel in static lead bismuth eutectic (LBE). The tensile tests were carried out in static lead bismuth eutectic under different temperatures and strain rates. Pronounced liquid metal embrittlement phenomenon is observed between 200 °C and 450 °C. Total elongation is reduced greatly due to the liquid metal embrittlement in LBE environment. The range of ductility trough is larger under slow strain rate tensile (SSRT) test.