导致物体变形和产生内力的物理因素统称为载荷。根据性质不同，载荷可分为两大类。第一类载荷如重力、惯性力、机械力等，首先可以简化为作用在物体上的外力，外力再引起物体的变形和内力。第二类载荷如温度等物理因素，它们直接引起物体变形，只有当这种变形受到约束时，物体内才产生内力。 作用在物体上的外力分为体力和面力。所谓体力是作用在物体内部体积上的外力。体力作用在物体内充满材料的每一个微小体积上，如重力、惯性力都是体力。面力是作用在物体表面上的外力。如液体对物体表面的压力、风载荷作用在建筑物表面的压力或吸力、汽车车轮作用在路面上的压力。 为了表示物体在坐标系 Oxyz 内的一点 C 所受体力的大小和方向，在 C 点的邻域取一包含 C 在内的微小体积元素 ΔV ，设 ΔV 的体力为 ΔF b ，则当 ΔV 无限缩小而趋于点 C 时，极限 称为 C 点的体力。体力是个矢量，它的量纲为 N/m 3 。 类似可给出面力的定义。作用在物体表面的微小面积上的一点 D 的面力矢量为 式中， ΔS 为包含点 D 的物体表面上的微小面积， ΔF 为作用在该微小面积上的外力。同样，面力是个矢量，它的量纲是 N/m 2 。 在笛卡尔坐标系中，体力和面力可分别写为 式中， i 、 j 、 k 为坐标轴基矢量。 物体在载荷作用下会发生变形，物体各质点间的相对位置发生改变，由于这种变化，产生了企图恢复其初始状态的附加相互作用力，称为内力。在材料力学中，研究杆件的内力采用的“截面法”。截面法是假想地将物体用截面截成两部分，把截面上的内力暴露出来，研究其中一部分物体的静力平衡，从而确定内力。 为了说明应力概念，用截面法假想地把受一组平衡力系作用的物体用一平面 C 分成 A 和 B 两部分，如 图形1.cdr 图 1 所示。将 B 移去，则 B 对 A 的作用应代之以 B 部分的作用力。这种力在 B 移去以前是物体 A 与 B 之间在截面 C 上的内力，且为分布力。如从 C 面上点 P 处取一包含 P 在内的微小面积元素 ΔS ，而 ΔS 上的内力矢量为 Δp ，则内力的平均集度为 Δp/ΔS 。令 ΔS 无限缩小而趋向于点 P ，则在内力连续分布的条件下 Δp/ΔS 趋于一定的极限 σ ，即 图 1 这个极限矢量就是物体在过 C 面上点 P 处的应力。由于 ΔS 是个标量，故应力 σ 的方向与 Δp 的极限方向相同，其大小的量纲为 N/m 2 。 应力矢量 σ 可分解为所在平面的外法线方向和切线方向这两个分量，如图 1 。沿应力所在平面的外法线方向 n 的应力分量称为正应力，记为 σ n 。沿切线方向的应力分量称为切应力，此处下标 n 标明其所在面的外法线方向。 参考文献 陈升平 . 弹性与塑性力学 . 武汉 : 武汉理工大学出版社 .
Exogenous taurine attenuates mitochondrial oxidative stress and endoplasmic reticulum stress in rat cardiomyocytes Yujie Yang, Yue Zhang, Xiaoyu Liu, Ji Zuo, Keqiang Wang, Wen Liu and Junbo Ge Acta Biochim Biophys Sin 2013, 45: 359–367; doi: 10.1093/abbs/gmt034 Department of Cellular and Genetic Medicine, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China Taurine, a conditionally essential amino acid, plays a critical role in cardiovascular function. Here we examined the effect of taurine on mitochondria and endoplasmic reticulum in rat cardiomyocytes during glucose deprivation (GD). Data showed that cell viability, intracellular taurine contents, and taurine transporter expression were decreased during GD. In contrast, an increase in reactive oxygen species and intracellular Ca2+ contents was observed. GD also caused disrupted mitochondrial membrane potential, apoptotic cell death, and dissociation of unfolded protein response (UPR)-relative proteins in cardiomyocytes. Signal transduction analysis showed that Bcl-2 family protein balance was disturbed, caspase-12 was activated and UPR-relative protein levels were up-regulated. Moreover, pre-treatment with 80 mM exogenous taurine attenuated GD effect in cardiomyocytes. Our results suggest that taurine have beneficial effects on inhibiting mitochondria-dependent cell apoptosis and UPR-associated cell apoptosis and might have clinical implications on acute myocardial infarction in future. 图例: Taurine对心肌细胞内质网/肌质网信号通路的影响 全文: http://abbs.oxfordjournals.org/content/45/5/359.full 与此文相关的文献: 1 Taurine protects rat testes against NaAsO2-induced oxidative stress and apoptosis via mitochondrial dependent and independent pathways 2 Potentiation of mitochondrial Ca2+ sequestration by taurine 3 Taurine prevents arsenic-induced cardiac oxidative stress and apoptotic damage: Role of NF-kappa B, p38 and JNK MAPK pathway 4 Taurine suppresses doxorubicin-triggered oxidative stress and cardiac apoptosis in rat via up-regulation of PI3-K/Akt and inhibition of p53, p38-JNK 5 Taurine protected myocardial mitochondria injury induced by hyperhomocysteinemia in rats 6 Taurine prevents tamoxifen-induced mitochondrial oxidative damage in mice 7 Mechanism underlying the antioxidant activity of taurine : prevention of mitochondrial oxidant production
Hippo signaling in stress response and homeostasis maintenance Beibei Mao, Yuhao Gao, Yujie Bai and Zengqiang Yuan Acta Biochim Biophys Sin 2015, Jan, 47(1): 2–9; doi: doi: 10.1093/abbs/gmu109 State Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China Co-ordination of cell proliferation, differentiation, and apoptosis maintains tissue development and homeostasis under normal or stress conditions. Recently, the highly conserved Hippo signaling pathway, discovered in Drosophila melanogaster and mammalian system, has been implicated as a key regulator of organ size control. Importantly, emerging evidence suggests that Hippo pathway is involved in the responses to cellular stresses, including mechanic stress, DNA damage, and oxidative stress, to maintain homeostasis at the cellular and organic levels. The mutation or deregulation of the key components in the pathway will result in degenerative disorder, developmental defects, or tumorigenesis. The purpose of this review is to summarize the recent findings and discuss how Hippo pathway responds to cellular stress and regulates early development events, tissue homeostasis as well as tumorigenesis. 图例: Hippo通路的应激反应 全文: http://abbs.oxfordjournals.org/content/47/1/2.full Go to ABBS Volume 47, Number 1, 2015 : a special issue on Hippo signaling
The induced stress in Li-ion batteries electrode(LIBs) will be discussed in this article, which focus mainly on the modeling and simulating. Two papers from JPS: "Zhang et.al, JPS, 2012, 220-227" and "Haftbaradaran et.al, JPS, 2011, 361-370" are analysed to demonstrate the latest development of this problem. The internal stress will increase the density of defects in batteries, which as a result will affect the capacity and life span of them. The poor cyclic performance of battery could be modeled by strongly coupled diffusion-stress model.Haftbaradaran et.al has developed it to deal with the highly nonlinear behavior of diffusion process in high solute concentration.The validity ofcontinuumhas been proved by comparing with simulation results by Molecular dynamics, one of thecomparisonis demonstrated below, the discrete point are results obtained by MD method while the line represent calculation of thecontinuummodel. Four points concerning the nonlinear behavior of diffusion behavior has been discussed in the work by Haftbaradaran et.al byeliminating their effects one by one in new comparisons between the theoretical and simulating results. In the work of Zhang et.al, more attentions has been paid to the layered structure of electrode in LIBs. Their model has been adapted to discuss the symmetry of of electrode plate, conditions bilayer electrode plate and the effects of charging conditions. The role of current collector in relation with the electrode has been discussed and it has been concluded that the materials of current collector should be as thin as possible and the elastic modulus should be smaller to enhance a much lower stress in the electrode. That is to say, the diffusion induced stress could be well modeled nowadays to predict the performance of new materials in battery electrode. From my perspective, the applicable of models in different kind of materials should be evaluated because the structure and and chemical properties vary between different kind of electrode materials.
I went for an annual check-up this morning. When the male doctor showed up, I practically told him that I saw his father about 3-4 years ago. (This is because the doctor's last name is very unusual.) He looked at me and said: "I saw you 3-4 years ago (while he looked at my medical file), and we are about the same age." I apologized: "I have bad memory these days, due to aging. However, I remember exactly how you looked then..." (He looked like a 60+ years old, a small old man then. I didn't like him, so I tried other doctors after that.) The exam went on, and we chatted about my research on OMZs (oxygen minimum zones). I was surprised that he thought ocean currents have something to do with the OMZs. I guess medical doctors are very smart people. Before he stepped out, I again raised the issue of his appearance, now and then. He said: "Yes, I had a very stressful life then, and lost a lot of weight in one month..." So, I am not crazy and my memory is not always bad, at least not in this case.
Zengsheng Ma, Shiguo Long , Yong Pan, Yichun Zhou Nanoindentation tests in Ni thin films with 3000 nm thickness were performed under the maximum load ranging from 1000 to 9000 m N to investigate the dependence of the Flow stress and Young’s modulus upon the indentation scale under zero and 10% tensile strain. The results show that, the Flow stress and Young’s modulus all display the indentation depth dependence. Furthermore, an analytical relationship between the Young’s modulus E and hardness H for Ni thin films is established based on the conventional depth-sensing indentation method of Oliver and Pharr. ICHMM2008, 195-199, (ISTP) Flow stress and Young's modulus of Ni films in nanoindentation creep.pdf
That's how I feel about today's life in China. Six friends met for dinner on Friday, and three of them needed to go to work on Saturday! I am not talking about scientists who work every day. These three people are doctor, law-enforcement personal, and senior engineer. Stress can cause real harm, if it's not dealt with. I am sure you all know this. Everywhere I visited, my host was on the move. In Guangzhou, my host had to leave for a conference in the US the very next day after our conference ended. In Nanjing, my host stayed for my one-day visit, and left for Beijing the very next morning. I lectured at the NUIST on Friday; my host there was called away in a short notice and called me that morning on his way to the airport, to make sure I was on my way for my lectures. I was going to visit the Shenzhen Campus of Tsinghua University on the 13th, and just received an e-mail to move my visit to the 12th because my host has a meeting on the 13th, again in a short notice. How do you guys (gals) handle life like this? Don't you want some peace and time for yourself?
2010, Proceedings of the 36th International MATADOR Conference , 6 , Pages 227-230 Modeling of hard turning: effect of tool geometry on cutting force Z.Y. Shi, Z.Q. Liu, C.M. Cao Abstract. Hard machining for manufacturing dies and molds offers various advantages, but the productivity is often limited, mainly by tool life. This study investigates the influence of cutting tool geometry on the cutting forces by utilizing finite element simulations (FEM). A set of cutting conditions in numerical FEM were conducted by using four different shaped cutting tools and axial force, radial force and tangential force were found. The results of this research help to explain the conclusion that for cylindrical control, the equation of the actual geometry of the S-shaped inserts involved in cutting is a sphere; that of C-shaped, D-shaped and Tshaped inserts involved in cutting is an ellipsoid with different lengths of short-half axis. Keywords : tool geometry, material flow stress, short-half-axial, cutting force FULL TEXT
标签: stress
