名词解释题
机车的粘着重量
发布日期：2021-03-22
试题解析
粘着系数
粘着系数是指有关计算机车粘着牵引力的系数，指机车粘着牵引力与机车粘着重量之比。由于机车轮周牵引力为机车动轮与钢轨间的静摩擦力，因而粘着系数实质上属于动轮与钢轨间的最大静摩擦系数。但两者之间又不完全相同，因机车振动、轮对蛇行运动、轮对与轨两非点接触和各动轮轮径的差异等原因，轮轨间实际上存在着微小滑动。影响粘着系数的因素很多，如机车类型、轴重、轴重转移、轮箍与钢轨的材料以及它们的表面状态等。粘着系数的变化范围相当大，在干燥清洁的钢轨面上撒上一薄层细砂，牯着系数可高达0.6，而轨面不清洁且潮湿时，粘着系数仅0.15，甚至更小。粘着系数数值通过大量试验来确定。
- 中文名
- 粘着系数
- 定义
- 踏面和钢轨接触面间的摩擦阻力
- 外文名
- Adhesion coefficient
- 实质
- 最大轮周牵引力与粘着重量的比值
黏着系数
机车动轮不空转时的最大轮周牵引力与粘着重量的比值。
货运机车
货运机车是专门用于牵引货物列车的机车。对货物列车的主要要求是，能够以普通的速度牵引较重的列车。因此，这种机车一般动轮较多，动轮直径比客运机车的小，汽缸直径较大，具有较大的牵引力和粘着重量。为了使机车易于安全通过曲线，一般均装有单轴导轮转向架。
- 中文名
- 货运机车
- 作用
- 牵引货物列车
- 外文名
- Goods locomotive
- 分类
- 交通工程
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Passage1In recent years，however，society has come to understand the limitations of schools that merely sort and rank students. We have discovered that students in the bottom one-third to one-half of the rank order-plus all who drop out before being ranked-fail to develop the foundational reading，writing，and mathematical proficiencies needed to survive in，let alone contribute to，an increasingly technically complex and ethnically diverse culture. So today，in asking schools to leave no child behind，society is asking that educators raise up the bottom of the rank-order distribution to a specified level of competence. We call those expectations our "academic achievement standards".Every state has them，and，as a matter of public policy，schools are to be held accountable for making sure that all students meet them.To be clear，the mission of sorting has not been eliminated from the schooling process. Forthe foreseeable future, students will still be ranked at the end of high school. However, society now dictates that such a celebration of differences in amount learned must start at a certain minimum level of achievement for all.The implications of this change in mission for the role of assessment are profound. Assessment and grading procedures designed to permit only a few students to succeed (those at the top of the rank-order distribution) must now be revised to permit the possibility that all students could succeed at some appropriate level. Furthermore, procedures that permitted (perhaps even encouraged) some students to give up in hopelessness and to stop trying must now be replaced by others that promote hope and continuous effort. In short, the entire emotional environment surrounding the prospect of being evaluated must change, especially for perennial low achievers.The students' mission is no longer merely to beat other students in the achievement race. At least part of their goal must be to become competent. Teachers must believe that all students can achieve a certain level of academic success, must bring all of their students to believe this of themselves, must accommodate the fact that students learn at different rates by making use of differentiated instruction, and must guide all students toward the attainment of standards.The driving dynamic force for students cannot merely be competition for an artificial scarcity of success. Because all students can and must succeed in meeting standards, cooperation and collaboration must come into play. The driving forces must be confidence, optimism, and persistence-for all, not just for some. All students must come to believe that they can succeed at learning if they try. They must have continuous access to evidence of what they believe to be credible academic success, however small. This new understanding has spawned increased interest in formative assessment in recent years.Which of the following is closest in meaning to the underlined word "accommodate" in Paragraph 4?
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