在拉压试验中，试件会被拉长或者缩短，伸长量用△L表示（负值代表缩短）。为了方便对不同长度的试件进行对比，我们将伸长量（△L）除以试件初始长度（L0），记为“应变”（Strain ε）。

为了方便对不同尺寸试件的力学性能进行对比，将单位面积上受到的力作为统一的量化指标，即“应力”（Stress σ）。

We’ve had teams doing the “just in case” scenario. And our rules have been that our designs for OS X must be processor independent, and that every project must be built for both the PowerPC and Intel processors. And so today, for the first time, I can confirm the rumors that every release of Mac OS X has been compiled for both PowerPC and Intel. This has been going on for the last five years.我们有团队在做“以防万一”的场景。我们的规则是我们的 OS X 设计必须独立于处理器，并且每个项目都必须为 PowerPC 和 Intel 处理器构建。所以今天，我第一次可以证实有关 Mac OS X 的每个版本都针对 PowerPC 和 Intel 进行编译的传言。这已经持续了五年。

All of the major tech players, companies from other industries and startups whose names we don’t know yet are working away on some or all of the new major building blocks of the future. They are: Artificial intelligence / machine learning, augmented reality, virtual reality, robotics and drones, smart homes, self-driving cars, and digital health / wearables. All of these things have dependencies in common. They include greater and more distributed computing power, new sensors, better networks, smarter voice and visual recognition, and software that’s simultaneously more intelligent and more secure.

    习近平在主持学习时发表了讲话。他指出，加快实施自由贸易区战略，是我国新一轮对外开放的重要内容。党的十七大把自由贸易区建设上升为国家战略，党的十八大提出要加快实施自由贸易区战略。党的十八届三中全会提出要以周边为基础加快实施自由贸易区战略，形成面向全球的高标准自由贸易区网络。这次中央政治局集体学习安排这个内容，目的是分析我们加快实施自由贸易区战略面临的

    习近平指出，加快实施自由贸易区战略是一项复杂的系统工程。要加强顶层设计、谋划大棋局，既要谋子更要谋势，逐步构筑起立足周边、辐射“一带一路”、面向全球的自由贸易区网络，积极同“一带一路”沿线国家和地区商建自由贸易区，使我国与沿线国家合作更加紧密、往来更加便利、利益更加融合。要努力扩大数量、更要讲质量，大胆探索、与时俱进，积极扩大服务业开放，加快新议题谈判。要坚持底线思维、注重防风险，做好风险评估，努力排除风险因素，加强先行先试、科学求证，加快建立健全综合监管体系，提高监管能力，筑牢安全网。要继续练好内功、办好自己事，加快市场化改革，营造法治化营商环境，加快经济结构调整，推动产业优化升级，支持企业做大做强，提高国际竞争力和抗风险能力。