周期性机械拉伸对人肺上皮细胞增殖的影响

为了研究周期性拉伸应变对人肺上皮细胞DNA合成的影响，应用流式细胞术对拉伸应变下的细胞增殖动力学变化进行了分析。结果表明：在应变为15％，频率为20次／min、40次／min的拉伸刺激下，在24h，正常人支气管上皮细胞H727的增殖活性指数明显降低，细胞的DNA合成受到显著抑制；48h后，人肺腺癌细胞A549的增殖活性明显降低，且拉伸时间越长，抑制作用越强。提示周期性拉伸应变抑制人肺上皮细胞的增殖。     

加载频率与应变比对10CrNi5Mo高强钢低周疲劳寿命的影响

通过对圆形横截面光滑试样进行轴向应变控制的低周疲劳试验,研究了加载频率与应变比对10CrNi5Mo高强钢疲劳寿命的影响。结果表明:在较低频率(0.05～0.1 Hz)范围内,频率对疲劳寿命的影响不明显,随着加载频率的增加(0.1～0.8 Hz),疲劳寿命显著提高,当加载频率增加到0.8 Hz时,疲劳寿命达到最大值,随着加载频率的继续增加(0.8～1.0 Hz),疲劳寿命反而有所下降;在最大应变不变条件下,随着应变比的增加(-1～-0.3),疲劳寿命平稳上升,当应变比增加到-0.30时,随着应变比的继续增加,材料的疲劳寿命急剧升高。研究结果为10CrNi5Mo高强钢的工程应用提供了依据。     

双向拉伸Hopkinson斜杆加载方法的探索与研究EI北大核心CSCD

为了实现对材料的双轴同步拉伸加载,现已有通过双向电磁脉冲驱动,以及对称双曲杆产生的双向拉伸波的方式,对试样进行双向动态拉伸加载。试图探索一种结构简单,造价低廉,加工难度小的双向拉伸Hopkinson斜杆加载装置。为了理解斜杆对弹性压缩波传播规律的影响,对斜杆撞击进行了ABAQUS有限元仿真计算和理想验证试验分析。结果发现,斜杆夹角在低于60°和高于90°时,方波平台段出现前高后低的情形,导致波形失真,同时在夹角大于105°之后,失真更为严重。还对多轴加载的同步性问题和双轴加载的数据获取进行了讨论和分析。结果表明,加载波的不同步会导致试样上加载阶跃,从而加载应变率阶跃,这会影响率敏感材料的试验准确性。为了验证该装置的有效性,搭建验证装置对双向拉伸杆上的拉伸波形进行试验验证,取得了较好的试验结果。     

直接拉伸循环荷载作用下混凝土滞回特性实验研究及定量分析

由于直接拉伸试验较为困难,可靠的数据十分少有。采用液压闭环伺服材料试验机MTS322试验装置(MTS)对混凝土进行了高应力轴拉往复试验,试验采用正弦波进行加载。对混凝土应力和应变的相位差引起的滞回现象进行研究。加载时应变波和应力波的相位差与卸载时不同,加载与卸载的相位差导致了一个不对称的滞后回路。随着加载频率的增加,混凝土的耗散角减小,约为其切线模量的“X”形夹角的一半。     

机械应力等环境对体外培养动物细胞的影响

本文介绍了生物力学领域中不同力学环境对体外培养的动物细胞分裂与增殖方面的研究进展.着重阐述了机械应力对细胞黏附、生长及增殖的影响;基底拉伸时频率、周期数及应变大小对细胞生长与增殖的影响;失重、超重环境等刺激对细胞增殖及分泌的影响.     

基于ARM微处理器的气动变载荷摩擦磨损试验机测控系统

针对不同固体材料在不同条件下的摩擦磨损实验要求,设计了一种基于ARM微处理器的气动变载荷摩擦磨损试验机测控系统。采用气动加载方式,加载形式包括正弦波、方波、锯齿波、三角波、随机波等。气动加载采用Fuzzy-PID闭环控制,提高了动态加载性能。可通过测量实验中的摩擦力、摩擦系数、磨损量、温度、振动等参数来研究变载荷对材料摩擦磨损性能的影响。最后对A3钢材料的摩擦磨损性能进行试验,证明该试验机性能稳定,测控系统准确可靠。     

基于AD9833函数信号发生器的设计

介绍一种以直接数字频率合成器（DDS）为核心信号发生器的设计,采用AVR单片机（ATmegal28）作为控制器,实现对DDS芯片AD9833的控制,使它能够输出信号稳定度优于10-3的正弦波、方波和三角波信号,输出信号频率在1Hz～100kHz范围内可调,具有步进和范围可调的扫频功能。     

加载路径对5A06铝合金力学性能和微观组织的影响

目的 通过力学性能测试和微观组织表征等手段研究预加载方向和双向加载对5A06铝合金组织性能的影响。方法 分别沿轧制方向(RD)和垂直于轧制方向(TD)施加预变形,然后沿RD进行拉伸试验,对比研究预加载方向对合金力学性能的影响。通过双向拉伸试验研究合金在双向加载时力学性能的变化情况;采用透射电镜观察预加载和双向加载条件下典型试样内的位错组态,分析加载路径对位错组态的影响。结果 预加载使5A06铝合金的屈服强度提高,伸长率下降。与RD预加载相比,TD预加载对屈服强度和伸长率的影响更小,TD预加载试样的抗拉强度更高。不同预加载方向下试样的位错组态不同:预加载与二次加载方向一致会使位错沿单一方向塞积;预加载与二次加载方向垂直时会出现平行位错列交错缠结现象。双向加载时,不同加载比例下合金的应力–应变关系不同,加载比例越接近等比例双向拉伸情况,加工硬化系数越大,在等比例双轴拉伸时达到最大。在应力状态从单拉状态变化到等双拉状态的过程中,不同阶段屈服点间隔不同,在等比例双轴拉伸时达到最大,在单向拉伸时最小。对于不同加载比例的试样,其位错密度随中心区应变量的增大而增大。结论 预加载方向会显著影响5A06铝合金的力学性能和位错组态。不同比例的双向加载会影响5A06铝合金的应力–应变关系。     

800MPa级低合金高强度钢的循环软硬化特性

在不同应变级别控制下,研究了800MPa级低合金高强度钢10CrNiSMoV轴向加载低周循环软硬化特性,研究结果表明：应变加载级别不同,材料表现出不同的循环软硬化特性,当应变幅在0．4％～1．0％范围变化时,材料表现出循环软化的特性,且应变幅越大,循环软化速率越高;当应变幅在0．30％-0．40％范围变化时,材料表现出先硬化,再趋于循环饱和,再轻微循环软化直至断裂的特性。采用透射电镜观察了不同应变级别下试样断口的位错形态,用位错理论解释了产生上述现象的原因。     

基于DDS9834的函数发生器设计与实现

本函数信号发生器运用最新的频率合成技术,以专用DDS芯片AD9834为核心,实现多种函数信号的输出,其中包括正弦波、方波、三角波;输出的函数信号的频率在10Hz到1MHz范围可调;具有带宽广、噪声低的良好性质。以STC89C52单片机系统作为控制部分,可以轻松的实现输出波形的选择、输出频率的设定等功能。并采用液晶显示,操作提示明了,人机界面友好。     

Differences in coagulation in clotting of vascular access in hemodialysis patients

Arteriovenous graft (AVG) thrombosis is a frequent cause of graft failure. We evaluated coagulation protein concentrations, platelet function, and viscoelasticity factors in 20 hemodialysis (HD) patients with AVGs. The goal was to determine whether significant differences in protein concentrations, platelet function, and viscoelasticity factors exist among dialysis patients requiring frequent AVG declot procedures vs. those who do not. Twenty HD patients were enrolled: 10 frequent clotters (>3 declots in the previous year) and 10 were nonclotters. Patients on antiplatelets or chronic anticoagulation were excluded. Laboratories were drawn pretreatment and heparinase was added to counteract any potential heparin effect. Coagulation protein concentrations including tissue factor (TF), thrombin/antithrombin III complex (TAT), and prothrombin fragment 1 + 2 (F₁₊₂) were assayed. The time to clot onset was measured by force onset time (FOT). Platelet contractile force (PCF) measured the force produced by platelets during clot retraction, whereas clot rigidity was measured as clot elastic modulus (CEM). FOT, CEM, and PCF were measured by Hemodyne. Both groups had upregulation of the TF pathway, as TF, TAT, and F₁₊₂ levels were similarly increased over baseline levels. Hemodialysis patients with frequent AVG clotting had higher levels of both PCF and CEM compared with nonclotters. Additionally, the frequent clotters had a lower FOT relative to nonclotters, although both were considered in the normal range. Our study suggests that HD patients with recurrent AVG thrombotic events form clots with higher tensile strength compared with HD patients without recurrent graft thrombosis.     

Flow-Induced Instabilities in Pump-Turbines in China

The stability of pump-turbines is of great importance to the operation of pumped storage power (PSP) stations. Both hydraulic instabilities and operational instabilities have been reported in PSP stations in China. In order to provide a reference to the engineers and scientists working on pump-turbines, this paper summarizes the hydraulic instabilities and performance characteristics that promote the operational instabilities encountered in pump-turbine operations in China. Definitions, analytical methods, numerical and experimental studies, and main results are clarified. Precautions and countermeasures are also provided based on a literature review. The gaps between present studies and the need for engineering practice are pointed out.     

Trends in alcohol-impaired driving in Canada

While a general decreasing trend in the number of persons killed in a traffic crash involving a drinking driver has occurred in Canada since the 1980s, it is evident that much of this decrease occurred in the 1990s. Since 2002, less progress has been made as the number of persons killed in crashes involving drinking drivers remains high. To better understand the current situation, this paper describes trends in drinking and driving in Canada from 1998 to 2011 using multiple indicators based on data collected for the Traffic Injury Research Foundation's (TIRF) Road Safety Monitor (RSM), the National Opinion Poll on Drinking and Driving, and trends in alcohol-related crashes based on data collected for TIRF's national Fatality Database in Canada. There has been a continued and consistent decrease in the number of fatalities involving a drinking driver in Canada. This remains true when looking at the number of fatalities involving a drinking driver per 100,000 population and per 100,000 licensed drivers. This decreasing trend is also still apparent when considering the percentage of persons killed in a traffic crash in Canada involving a drinking driver although less pronounced. Data from the RSM further show that the percentage of those who reported driving after they thought they were over the legal limit has also declined. However, regardless of the apparent decreasing trend in drinking driving fatalities and behaviour, reductions have been relatively modest, and fatalities in crashes involving drivers who have consumed alcohol remain high at unacceptable levels.     

Gender differences in publication productivity in psychology in India

An analysis of gender differences in psychology in India provides quantitative and qualitative assessment of R&D output contributed by psychologists with the indication of the trend of growth, skewness, relatedness, co-authorship pattern of productivity.     

铁电陶瓷中电畴翻转研究进展

电畴为铁电陶瓷固有的独特微观组织特征之一,铁电陶瓷的许多性能均与其密切有关.综述了铁电陶瓷中的电畴结构,系统介绍了电场、机械作用引起的电畴翻转,概述了电畴翻转对铁电陶瓷断裂韧性的影响及其研究进展.     

Metrology in Chemistry in Germany

The system for Metrology in Chemistry in Germany is described. At the national standards level, a network of high-level chemistry institutes coordinated by the national metrology institute, PTB, provides the primary references for chemical measurements. A dissemination mechanism employs chemical calibration laboratories accredited within the framework of the German Calibration Service (DKD). They act as “multipliers” between the national standards level and the user level by providing the user with calibration means which are traceable to the SI via national standards. Traceability structures in clinical chemistry, electrochemistry, elemental analysis and gas analysis are described     

陶瓷超塑性的研究进展

本文综述了氧化锆及其复相陶瓷超塑性的研究现状，论述了陶瓷超塑性的变形机理，微观特征和断裂特性。同时，分析和对比了陶瓷超塑性与金属超塑性的特点。目前，对于正确理解超塑性陶瓷的变形机理，还需进行大量工作。     

Standardization in the Cultural Heritage in China

China has begun its standardization process in the cultural heritage since 1960.The standards contributed a lot to the development of the heritage conservation practices. In this paper, the author summaries the existing condition of standardization in the cultural heritages and museums field in China, and presents Standards for the Classification of Collected Cultural Heritages. Also this paper points out the problems which exist in the standardization in the cultural heritage, and gives the advice to solve these problems.