长江的经济账

长江中上游是我国第二大林区,更是这条大江的众水之源,而长江流域的森林,近30年来减少了一半以上,森林覆盖率由22‰下降到不足10‰。四川省上世纪50年代森林覆盖率还有40‰,到80年代就只有14‰了。从金沙江到     

Continuum damage mechanics based modeling progressive failure of woven-fabric composite laminate under low velocity impact

A continuum damage mechanics （CDM） meso-model was derived for both intraply and interply progressive failure behaviors of a 2D woven-fabric composite laminate under a transversely low velocity impact.An in-plane anisotropic damage constitutive model of a 2D woven composite ply was derived based on CDM within a thermodynamic framework,an elastic constitutive model with damage for the fibre directions and an elastic-plastic constitutive model with damage for the shear direction.The progressive failure behavior of a 2D woven composite ply is determined by the damage internal variables in different directions with appropriate damage evolution equations.The interface between two adjacent 2D woven composite plies with different ply orientations was modeled by a traction-separation law based interface element.An isotropic damage constitutive law with CDM properties was used for the interface element,and a damage surface which combines stress and fracture mechanics failure criteria was employed to derive the damage initiation and evolution for the mixed-mode delamination of the interface elements.Numerical analysis and experiments were both carried out on a 2D woven glass fibre/epoxy laminate.The simulation results are in agreement with the experimental counterparts,verifying the progressive failure model of a woven composite laminate.The proposed model will enhance the understanding of dynamic deformation and progressive failure behavior of composite laminate structures in the low velocity impact process.     

Unified analytical solutions for a circular opening based on non-linear unified failure criterion

Unified analytical solutions are presented for the predictions of the stresses and displacements around a circular opening based on nonqinear unified failure criterion and the elastic-brittle-plastic softening model. Unified analytical solutions not only involve generally traditional solutions which are based on the Hock-Brown （H-B） failure criterion or the non-linear twin-shear failure criterion, but also involve other new results. The results of the radius of plastic zone, radial displacements and stresses are obviously different using three rock masses when different values of the unified failure criterion parameter or different material behavior models are used. For a given condition, the radius of plastic zone and radial displacements are reduced by increasing the unified failure criterion parameter. The latent potentialities of rock mass result from considering the effect of intermediate principal stress. It is shown that proper choices of the failure criterion and the material behavior model for rock mass are significant in the tunnel design.     

徽州文化生态保护与利用的四维发展

国家级“徽州文化生态保护实验区”的挂牌。标志着徽州文化保护从此进入了成系列、全生态、全区域保护的新阶段。当前,徽州文化生态的保护与利用发展迅速,表现在广度上：从文物个体-古村落-徽州文化生态保护实验区;深度上：从物质文化-非物质文化-精神文化;高度上：从文保单位-文化景点-生态博物馆;时间跨度上：从历史研究-文化生态系统研究-徽州文化的传承发展。但与此同时,也出现了一些值得警惕的新问题,需要认真思考并加以解决。     

破坏实验的老妈

我的家庭实验室里堆着一些古里古怪的小东西,那是我的宝贝。可妈妈老爱在我的实验室里东动动,西动动,还不时往外扔东西。学校的科学节弄了一个少年诺贝尔奖,得奖同学在巡回演讲时,一位同学讲到了结晶,老师也特别讲了一下什么是结晶。我对结晶很感兴趣,回家也做起了结晶的实验。第二天,那个放着还没结晶的盐水瓶的盒子就不见了。我知道妈妈又犯老毛病了,就第一个问     

沥青砼路面施工接缝处理

一直以来,沥青砼路面施工接缝是施工控制的难点之一.本文根据长期摸索的施工经验,阐述了施工中出现的实际问题和处理方法,并对此略作探讨.     

衔接生活,拓宽语文学习领域

最近,听一位教师上了《特殊的葬礼》一课,这是对学生进行环保教育的一篇好教材。由于本课教学对象是小学四年级学生,他们的环保意识还处于朦胧状态,对环境破坏造成的危害缺乏亲身的体验,因而较难理解人们举行这一特殊葬礼的     

破坏之王

假期作业多吗？心情是不是乱得像窗外的知了声？下面这位阿奇,他也和你有差不多的烦恼!如果生活中能有点魔术．这个假期肯定更精彩！     

计算机主机信息安全问题研究

随着信息技术的迅速发展,信息安全问题越来越受到人们重视。从组成信息服务的层次来看,信息系统一般是由主机、服务器及网络三个层次组成。在这三个层次中,人们往往把过多的注意力放在对服务器和网络的保护和管理上,而忽略了对终端主机的保护和管理,这是不合理的。在信息系统中,主机是人们日常工作的主要平台,用户在主机上进行各种事务处理,存放重要信息,同时绝大多数攻击事件也是从主机发起的。因此,主机的安全保护在系统安全体系结构中居于极其重要的位置。解决安全问题应从主机安全问题入手,增强主机自身的安全性,本文通过分析主机系统结构,提供了一套针对主机安全问题的解决方案。     

《特殊的葬礼》教学设计

一、教学内容 苏教版小学语文教材第八册《特殊的葬礼》第二课时。 二、教材分析 这是一篇有关环保的记叙文。作者描写了巴西著名景观塞特凯达斯瀑布由雄伟壮观到日渐枯萎的过程以及人们失望、震惊、痛心、反思的表现,说明环境破坏给大自然带来的严重危害,告诉我们要珍惜环境,保护环境,爱护我们共同生存的家园——地球。