Global test of seismic static stress triggering model

Seismic static stress triggering model is tested using Harvard centroid moment tensor (CMT) solution catalogue of 1976~2000 and concept of earthquake doublet. Result shows that seismic static stress triggering effect does exist in the view of global earthquakes, but the effect is very weak. Dividing the earthquakes into thrust focal mechanism, normal focal mechanism, strike-slip focal mechanism, we find that non-strike-slip focal mechanism earthquakes have significant triggering effect, whereas, the triggering effect in strike-slip focal mechanism earthquakes is not obvious. Divided the subsequent events delay time of earthquake doublet into 5 classes of t1, t<1, t10, t<10, 1t10 (t is in unit of d), then seismic static stress triggering effect does not change with delay time in short time period after earthquakes. The research on seismic static stress triggering in different regions of the world indicates that triggering effect is significant in subduction belts. Seismic static stress triggering model is tested by using earthquake doublets in China and its adjacent region. The result indicates that seismic static stress triggering effect cannot be observed easily in China and its adjacent region due to the seismic focal mechanism type (most of the earthquakes are strike-slip earthquakes).

Longevity of animals under reactive oxygen species stress and disease susceptibility due to global warming

The world is projected to experience an approximate doubling of atmospheric CO_2 concentration in the next decades. Rise in atmospheric CO_2 level as one of the most important reasons is expected to contribute to raise the mean global temperature 1.4 ℃-5.8 ℃ by that time. A survey from 128 countries speculates that global warming is primarily due to increase in atmospheric CO_2 level that is produced mainly by anthropogenic activities. Exposure of animals to high environmental temperatures is mostly accompanied by unwanted acceleration of certain biochemical pathways in their cells. One of such examples is augmentation in generation of reactive oxygen species(ROS) and subsequent increase in oxidation of lipids, proteins and nucleic acids by ROS. Increase in oxidation of biomolecules leads to a state called as oxidative stress(OS). Finally, the increase in OS condition induces abnormality in physiology of animals under elevated temperature. Exposure of animals to rise in habitat temperature is found to boost the metabolism of animals and a very strong and positive correlation exists between metabolism and levels of ROS and OS. Continuous induction of OS is negatively correlated with survivability and longevity and positively correlated with ageing in animals. Thus, it can be predicted that continuous exposure of animals to acute or gradual rise in habitat temperature due to global warming may induce OS, reduced survivability and longevity in animals in general and poikilotherms in particular. A positive correlation between metabolism and temperature in general and altered O_2 consumption at elevated temperature in particular could also increase the risk of experiencing OS in homeotherms. Effects of global warming on longevity of animals through increased risk of protein misfolding and disease susceptibility due to OS as the cause or effects or both also cannot be ignored. Therefore, understanding the physiological impacts of global warming in relation to longevity of animals will become very crucial challenge to biologists of the present millennium.

Stress Field Changes before the <i>M</i>_S8.0 Wenchuan Earthquake

The apparent lack of pre-seismic crustal deformation preceding the 2008 Ms8.0 Wenchuan earthquake has been the subject of debate. In this study, tiltmeter data recorded close to the earthquake epicenter were analysed using spectrum and wavelet analysis. Changes in the stress field before the earthquake were analyzed based on the Benioff creep release and changes in regional Global Navigation Satellite System (GNSS) baselines. The characteris-tics of far- and near-field seismicity and deformation processes were investigated using rock fracture experiments. The results show that during pre-seismic strain energy accumu-lation, there was a synergy between stress field changes both proximal and distal to the ep-icenter;moreover, we identified a strong correlation between Benioff creep release and shortening of the LUZH-GUAN GNSS baseline. During the sub-instability stage, the de-formation characteristics of different structural sectors differed;faults near the epicenter were in a highly locked state, and the deformation rate and wave spectra of main period waves obviously decreased. This reflects fixed point deformation driven by deep stress. These results are of great significance for understanding geophysical field observations, for clarifying pre-seismic deformation and for earthquake prediction.

Comparison of Surface Wind Stress Anomalies over the Tropical Pacific Simulated by an AGCM and by a Simple Atmospheric Model

In this paper, surface wind stress anomalies over the tropical Pacific simulated by an AGCM and by a simple atmospheric model are compared with observed. The AGCM is the higher resolution global spectral model-COLA R40 model and the simple atmospheric model is the atmospheric component of the Cane-Zebiak coupled ocean-atmosphere model.The results show that the wind stress anomalies simulated by both the COLA R40 and the simple model have captured the main features of observation but the x component in the CZ model is closer to that in observation than that in the COLA model, and the correlation coefficients between simulated SSTA from the CZ model and observed for Nino indices are higher than those from the COLA model.

南北朝·大地变迁的动力--漫步地震五千年(8)

地下应力场是地壳形变、岩体破坏、地震发生的直接力源,岩体的稳定性问题十分重要。通过国际合作已经完成了全球GPS速度场和地应力图的更新,有了动力源的板块就不再是一堆僵化构造体,它们运动的活力和内部的应力状况被第一次揭示出来。本文介绍了地应力原地测量的方法,应力张量结构的划分原则,全球和中国应力图的基本特征。对于地震的震源机制解,作者绘制了多种三维透视图,便于读者以看图识字的方式掌握震源机制解的地质含义。最后,以两个实例对比了实测应力图和震源机制解的异同,分析了当地动力学的背景。

Influence of Patch Side of Heat-Ray Absorbing Film on One-Dimensional Unsteady Thermal Stresses in Window Glass

Heat-ray absorbing film is used to be bonded on the existing sheet glasses of the windows.It is effective for air-conditioning energy saving against the global warming,because it absorbs heat-ray in the thin film and decreases the incoming heat-ray into the room.On the other hand,the sheet glasses increase the temperature at the surface which the sheet is bonded and sometimes yield heat cracks by thermal stresses.It is important to know the state of thermal stresses accurately in order to develop the heat-ray absorbing film with higher performance and without heat cracks.In this paper,the analysis model is treated as the two-layer plate of the conventional soda sheet glass and the heat-ray absorbing film with different absorptivities.The unsteady temperature and thermal stresses are analyzed and calculated numerically.The influence of the patch side,which the heat-ray absorbing film is bonded at the exterior side or the interior side,on the heat-ray absorbing performance and the thermal stresses is discussed.It is found that the alternative patch side has no effect on the heat-ray absorbing performance and that the patch side is recommended to be interior side from a view point of decreasing thermal stresses against the heat crack of glasses.

几何偏差对多螺栓复合材料接头螺栓载荷和应力分布的影响研究

本研究建立了考虑间隙的复合材料双搭接结构的半解析模型,描述了几何偏差对螺栓载荷和应力分布的影响.首先,从典型复合螺栓接头中提取螺栓/孔局部结构作为代表单元,建立考虑随机几何偏差与接触状态的螺栓/孔对的局部刚度模型.基于Reddy高阶剪切板理论,建立复合材料层合板有限元分析模型.将螺栓/孔对的局部刚度模型与层合板全局刚度模型相结合,形成了综合考虑螺栓/孔间隙和孔拉伸变形的多螺栓复合材料接头装配力学分析模型.随机螺栓/孔组合间隙分析结果表明,合理的螺栓间隙设置可以得到更均匀的钉载分布,为多螺栓接头的排孔设计提供理论指导.

高温胁迫对寄生蜂的影响及其适应机制

昆虫作为变温动物类群,极易遭受高温胁迫的影响,寄生蜂也不例外。寄生蜂是害虫生物防治领域中最常用的天敌昆虫,我国已将赤眼蜂广泛用于农林业鳞翅目害虫的防治。研究高温胁迫对寄生蜂的影响,可为全球气候变暖背景下农林害虫生物防治提供新的见解和对策。本文系统综述了高温胁迫对寄生蜂生命活动的影响以及寄生蜂响应高温胁迫的机制,并就温度升高对寄生蜂规模化繁育和应用可能出现的问题和挑战进行了展望,以期为更好地发挥寄生蜂在害虫生物防治中作用提供理论参考。

特大跨度扁平洞室围岩损伤破坏数值模拟研究

文章针对洞库大跨度扁平拱的不利结构特征,运用正交试验设计数值模拟方案,系统研究了岩体等级、埋深、跨度、扁平率等因素影响下的围岩应力、应变等变化特点;利用全局敏感性分析找到应力指标和变形指标的主控因素,确定各级围岩下洞库跨度的分界标准,分析研究了主控因素的影响规律。

边坡稳定性整体分析法中滑面正应力分布研究

边坡稳定性的整体分析法是严格极限平衡法,无严格条分法的不收敛问题,还能实现三维严格极限平衡法。但整体分析法一直居于非主流地位,原因可能是整体分析法无法像Morgenstern-Price法那样产生静力许可力系。针对二维问题,分析了造成这一问题的原因——滑面正应力构造不当,并建议采用双参数滑面应力修正的折线方式和Fourier方式,这2种方式都能满足滑面正应力分布的自然分解和端点条件。对典型边坡案例的分析表明,在产生静力许可力系的能力方面,整体分析法远优于以Morgenstern-Price法为代表的经典条分法。因此建议在边坡稳定性分析中优先采用整体分析法。

不同填土高度下超大直径钢波纹管拱涵的力学性能分析

施工阶段的填土高度对超大直径钢波纹管拱涵的力学性能影响较大.为保障超大直径钢波纹管拱涵的施工安全,建立12个超大直径钢波纹管拱涵的整体结构有限元模型,分别计算其自重与土压力、自重与车辆荷载共同作用下整体结构的变形与所受应力.建立直径8.79 m第1号波纹管和直径11.00 m第6号波纹管的精细化有限元模型,分析这两种直径拱涵在不同施工阶段填土高度下的受力和变形特征.结果表明,随着填土高度增加到7 m,第1号波纹管的竖向位移与应力不断增加,第6号波纹管的位移与应力先减后增,管顶与管底的水平位移很小,但竖向位移很大;在自重与土应力作用下,土体和波纹管的最大竖向位移分别为67.16 mm和39.28 mm,波纹管的最大拉力与压力分别为13.95 MPa和2.95 MPa;在自重与车辆作用下,波纹管的最大竖向位移为10.37 mm,最大拉力与压力分别为26.65 MPa和0.47 MPa.以上结果均满足拱涵结构的变形与受力要求,对于不同填土高度下较大的结构竖向变形,建议提高底层土体的压实度.研究成果对超大直径钢波纹管涵的推广应用具有重要意义.

啤酒发酵过程中酵母环境压力应答机制研究进展

在啤酒发酵过程中,生产高质量的啤酒要求相应的工艺条件以保证啤酒的质量以及酵母的活力。大多数的风味物质都是在后熟的过程中形成,在后熟过程中,啤酒酵母暴露在不同的压力条件下,包括渗透压、pH、酒精浓度、营养以及温度等。在长期的驯化过程中,啤酒酵母自身表现出各种压力应答机制以适应啤酒发酵过程。本论文概述了啤酒发酵过程中啤酒酵母受到的压力,重点探讨了啤酒酵母在后酵期经受的压力以及压力应答的分子机制,并对如何提高啤酒酵母环境压力应答能力进行了展望。

应力约束全局化策略下的连续体结构拓扑优化

利用Mises强度理论,提出了应力约束全局化策略,将局部的应力约束问题转化为结构整体的应变能约束问题．基于ICM(独立、连续、映射)方法,引入了独立、连续的拓扑变量,对单元重量、单元刚度和单元许用应力的过滤函数进行了选择,建立了以重量为目标,以结构应变能代替应力约束的多工况下连续体结构拓扑优化模型,寻找到了多工况下的最佳传力路径．运用对偶二次规划方法对上述优化模型进行了求解．另外,利用PCL语言,在MSC／PATRAN的开发平台上,实现了应用应力约束全局化策略进行连续体结构拓扑优化的模块化处理．数值算例表明了该方法的可行性和有效性．

全球应力场与构造分析

介绍了近年来全球构造应力研究方面的一些新进展并以“世界应力图”提供的资料为背景 ,结合一些最新的研究成果 ,阐述了全球构造应力场的分布特征及其与板块构造运动之间的联系。研究结果表明 :(1)全球存在大尺度的统一性构造应力场 ;(2 )全球大多数板块内部地区为挤压应力作用 ,其应力结构多为逆断型、走滑型或逆走滑型 ;(3)大陆板块内部的扩张区大多位于高海拔异常地区 ,其应力结构为正断型或正走滑型 ,如青藏高原、东非裂谷和贝加尔裂谷等 ;(4)全球大部分地区的地壳上部构造应力作用方向较为均一 ,存在区域统一应力场 ;(5 )全球大部分地区的最大水平主应力方向与板块绝对运动 (角速度 )迹线保持较好的一致性 ,反映出构造应力与板块运动的关系密切 ;(6 )板块汇聚、洋脊扩张可能是产生岩石圈上部构造应力的主要力源。

干旱对陆地生态系统生产力的影响

该文综述了干旱对陆地生态系统生产力的影响,分析了其影响机制,并总结了植被对干旱的响应与适应及其机理机制。干旱通过抑制光合作用来降低陆地生态系统总初级生产力,干旱还可以降低生态系统的自养呼吸和异养呼吸。同时干旱还可以通过影响其它干扰形式来间接影响陆地生态系统生产力,如增加火干扰的发生频率和强度,增加植物的死亡率,增加病虫害的发生等。在生态系统水平上干旱可以降低碳固定,减弱碳汇功能,甚至把生态系统从碳汇改变成碳源。目前生态系统水平上的干旱影响研究主要通过两种方法实现,一种是模型模拟,另一种就是大型模拟实验。作为陆地生态系统生产力的实现者,在干旱胁迫条件下,植物也会采取积极的适应策略以减弱干旱对生态系统生产力的影响,其适应策略主要分以下3种:在一些周期性发生干旱的地区,植物会调整生长期以避开干旱或通过休眠来减弱干旱所造成的伤害;还有一些植物会通过调节体内的代谢过程,改变一些生理特性来抵御干旱;而长期生活在干旱条件下的植物则通过进化来改变了自身的生理生化代谢过程,形成耐旱机制。目前,植物对干旱响应的分子学机制,以及生态系统水平上对干旱的响应和适应仍然是薄弱的领域,也必然成为未来研究的重点。

基于人工智能的三维结构全局应力求解方法研究

针对结构健康监测系统(SHM)中有限数量的应力测点难以监测结构全局应力的问题,提出一种基于人工智能的三维结构全局应力求解方法,通过少量应力测点实现对三维结构物应力场的实时求解。首先,基于有限单元之间对载荷响应的关联性,运用相关性分析找出求解三维结构物应力场的特征单元;其次,利用神经网络建立特征单元与相关单元的求解关系,并将特征单元设为应力测点进而求解结构全局应力;然后,以某海洋平台连接器结构为应用主体,考虑测点数量、神经网络架构、收敛准则等因素对求解精度的影响,建立连接器结构应力场人工智能算法优化模型;最后,开展实尺度模型试验,经比较分析得出该算法模型应力求解精度高达93.6%,该技术可切实提升SHM系统的实用性,将传统的对“点”监测提升为对“场”监测。

应力约束全局化处理的连续体结构ICM拓扑优化方法

由于应力约束按单元计,加之多工况,使得连续体结构拓扑优化由于约束数目太多,导致应力敏度分析计算量太大而无法接受。基于第四强度理论提出了应力约束条件全局化处理的方法,化为全局替代约束——总应变能约束,用ICM方法对总应变能约束条件下的连续体结构拓扑优化进行建模及求解,其过程分为三步:第一步选择最大应变能对应的工况,在给定重量下求出最小结构总应变能;第二步提出一个数值经验公式,借助第一步的结果,计算出各工况下的许用总应变能;第三步以第二步计算出来的各工况的许用总应变能作为约束,以重量为目标建立模型并求解。顺便指出,第二步的处理方法可以处理载荷相差特别大的情况,即病态载荷情况。数值算例表明:全局性应力约束可以更好地得到传力路径,对于处理多工况问题具有优势。

富氢液对大鼠全脑缺血再灌注损伤的影响

目的脑组织缺血缺氧后,过量自由基产生,破坏组织细胞,形成再灌注损伤。最近,学者研究报道氢气溶解在液体中可选择性中和培养细胞中的羟自由基和亚硝酸阴离子。文中观察腹腔注射富氢液对大鼠暂时性全脑缺血再灌注损伤的影响。方法雄性SD大鼠90只,建立四血管阻塞全脑缺血(15 min)再灌注损伤模型,分为3组:假手术组(n=30),模型组(再灌注同时腹腔注射等渗盐水5ml/kg,n=30)和治疗组(再灌注同时腹腔注射0.6mmol/L富氢液5ml/kg,n=30),检测各组再灌注24 h海马丙二醛(malondialdehyde,MDA)浓度、肿瘤坏死因子α(tumor necrosis factor-α,TNF-α)浓度、核因子-κB(nu-clear factor-kappaB,NF-κB)免疫组化阳性细胞数和活化caspase-3的表达水平以及再灌注72 h海马CA1区HE染色未损伤锥体细胞数。结果与模型组相比,治疗组海马MDA浓度、TNF-α浓度和NF-κB阳性细胞数活均显著下降(P<0.01);活化caspase-3蛋白表达显著降低(P<0.05);海马CA1区锥体细胞数显著增多(P<0.01)。结论腹腔注射富氢液能够有效减轻全脑缺血(15 min)后再灌注时大鼠脑的氧化应激和炎症反应,进而缓减再灌注损伤。

基于ICM方法三维连续体结构拓扑优化

基于ICM方法,建立了在应力和位移约束下以重量为目标的多工况下的三维连续体结构拓扑优化模型.利用von Mises强度理论,提出了应力全局化的方法,从而将局部的应力约束转化为全局的应变能约束问题,减少了约束数目,避免了敏度分析的困难;利用单位虚载荷法,将位移约束表示为设计变量的显式关系.为减小由于不同物理量在数量级上相差太大引起数值计算的误差,将应变能约束和位移约束进行无量纲化,由此建立了包含两类约束的无量纲化的优化模型.同时处理了多工况下的最佳传力路径的问题.利用对偶规划理论对模型进行了求解.另外,利用PCL语言在MSC/Patran的开发平台上实现了该文算法.数值算例表明了该方法的可行性和有效性.

地震静态应力触发模型的全球检验

运用 1 976～ 2 0 0 0年哈佛大学矩心矩张量目录 ,采用“地震对”概念对地震静态应力触发模型进行检验 .结果表明 ,从全球角度来看 ,地震静态应力触发效应确实存在 ,但只是一种很弱的效应 .将地震分为正断层、逆断层、走滑断层等分别对静态应力触发模型进行检验 ,发现非走滑断层地震具有明显的触发效应 ,而走滑断层地震触发效应则不明显 .按“地震对”中后续事件的延迟时间分为延迟时间 t≥ 1天、t<1天、t≥ 1 0天、t<1 0天和 1天≤t≤ 1 0天 5个时间段的“地震对”,分别对地震静态应力触发模型进行研究 ,发现静态应力触发效应在地震之后的短时间内不随延迟时间的变化而变化 .对全球不同区域的地震静态应力触发情况的研究表明 ,消减带“地震对”的触发效应较为明显 .为了研究地震静态应力触发模型在中国应用的可能性 ,对中国及邻区的地震进行了检验 ,发现就中国及邻区的地震类型而言 (以走滑断层为主 ) 。