Unit 8
Mixing and Flocculation
混合与絮凝
Clearly, if the chemical reactions in coagulating and softening a water are going to take place, the chemical must be mixed with the water.
显然，如果在水的混凝与软化过程中的化学反应将要发生的话，那么化学药剂必须与水进行混合。
In this section we will begin to look at the physical methods necessary to accomplish the chemical processes of coagulation and softening.
在这一章节我们将要开始关注必要的物理方法以完成混凝与软化的过程。
The basis of what will be presented applies to any operation of mixing, flocculating, settling, or filtering.
下面将要提出的基本原理对于混合、絮凝以及过滤的操作都是适用的。
Mixing, or rapid mixing as it is called, is the process whereby the chemicals are quickly and uniformly dispersed in the water.
或者，或者称为快速混合，是由此化学药剂快速均匀的分布到水中的过程。
Ideally, the chemicals would be instantaneously dispersed
throughout the water.
理想状态下，化学药剂会迅速分散到水中。
During coagulation and softening the chemical reactions that take place in rapid mixing form precipitates.
在混凝和软化的过程中，在快速混合中发生的化学反应形成了沉淀。Either aluminum hydroxide or iron hydroxide form during the case of coagulation , while calcium carbonate and magnesium hydroxide form during the case of softening.
在混凝过程中形成氢氧化铝或氢氧化铁，而在软化过程中形成碳酸钙和氢氧化镁。
After forming the precipitates, it is necessary to bring them into contact with one another so that they can agglomerate and form larger particles, called flocs.
在形成沉淀后，有必要使它们互相碰触，以使得它们能够聚集，然后形成更大的颗粒，叫做絮体。
This contacting process is called flocculation and is accomplished by slow, gentle mixing.
这个接触的过程叫做絮凝，它是通过缓慢、柔和的混合完成的。
In the treatment of water and wastewater the degree of mixing is measured by the velocity gradient, G.
在给水处理与污水处理的过程中，混合的程度是通过速度梯度G来衡
量的。
The velocity gradient is best thought of as the amount of mixing
taking place; that is, the higher the G value the more violent
the mixing.
速度梯度被认为是混和发生的最好的指标，也就是说，G 值越高，混
合越剧烈。
The velocity gradient is a function of the power input into a
unit volume of water
速度梯度是单位体积的水输入功率的函数。 It is given by
V
P G μ= where G —velocity gradient (s-1);
P —power input (W);
V —volume of water (m3);
μ—dynamic viscosity (Pa.s).
它由下式给出：
其中 G -速度梯度（- 1）;
的P -输入功率（瓦）;
V 型体积的水（立方米）;
μ-动力粘度（Pa.s ）。
From literature, experience, laboratory, or pilot plant work
it is possible to select an optimal G value for a particular application.
通过文献、经验、图书馆或者中试装置的工作，对于某特殊应用选择一个最近的G值是可能的。
The total number of particle collisions is proportional to G?t0, where t0 is the detention time in the basin.
碰撞离子的总数与G?t0 成正比，其中t0是在池子中的停留时间。Typical design values for G and G?t0 will be discussed elsewhere.
对G和G?T0代的典型设计值将在别处讨论。
Rapid Mix Rapid mixing is probably the most important physical operation affecting coagulant dose efficiency.
快速混合快速混合可能是影响混凝剂剂量效率的最重要的物理操作。
The chemical reaction in coagulation is completed in less than 0.1s; therefore, it is imperative that mixing be as instantaneous and complete as possible.
混凝中的化学反应，不到0.1秒即可完成；因此，必须使得混合尽可能瞬间之内完成。
Rapid mixing can be accomplished within a tank utilizing a vertical shaft mixer, within a pipe using an in-line mixer, Or
in a pipe using a static mixer.
快速搅拌即可利用垂直轴的搅拌器、在管道内用一个管道混合器,在反应池内完成，或者在管道内采用一个静态混合器。一些效率不高的方法有时候也可以采用，如巴氏计量槽，水跃，或者空气混合。Less efficient methods are sometimes used, Such as Parshall flumes, hydraulic jumps, baffled channels, or air mixing. 一些效率不高的方法有时候也可以采用，如巴氏计量槽，水跃，或者空气混合。
Rapid mix tanks usually have detention times of 10 to 30 s with velocity gradients of 600 to 1000 s-1.
快速混合池的停留时间是10～30s，速度梯度是600～1000s-1.
The volume of the rapid mix tank seldom exceeds 8 m3 because of mixing equipment and geometry constraints.
由于混合设备与几何的限制,快速混合池的体积很少超过8m3。
The mixing equipment consists of an electric motor, gear-type speed reducer, and either a turbine or axial flow impeller as shown in Fig. 2-4.
混合设备包括一个电动机，齿轮减速器，一个涡轮或者轴向的水流推进器，如图2-4所示。
The turbine impeller provides more turbulence and is preferred for rapid mixing.
涡轮叶轮提供更多的紊流，是快速混合的首选。
The tanks should be horizontally baffled into at least two and preferably three compartments in order to provide sufficient residence time.
反应池应该水平的阻隔成至少两个，最好三个隔间，以提供足够的停留时间。
They are also baffled vertically to minimize vortexing.
它们也可以被垂直的阻隔以使得涡旋最小化。
Chemicals should be added below the impeller, the point of the most mixing.
化学药剂应该投加都叶轮的下方，这是混合最剧烈的点。
Some common rules-of-thumb are that the design liquid depth is 0.5 to 1.1 times the basin diameter or width; that the impeller diameter be between 0.30 and 0.50 times the tank diameter or width; and that the vertical baffles extend into the tank about 10 percent of the tank width or diameter.
有些常规的经验法则是设计水深等于0.5～1.1×反应池的直径或宽度；叶轮直径介于0.3～0.5×反应池的直径或宽度；垂直的挡流板超过反应池大约反应池的直径或宽度的10％。
Although they may be larger, impeller diameters normally do not exceed 1 m in diameter.
尽管它们可能更大，叶轮直径通常不会超过直径1m。
The liquid depth may be increased to between 1.1 and 1.6 times the tank diameter if dual impellers on the shaft are employed. 如果轴采用双叶轮的话，水深可以增加到1.1和1.6倍的反应池直径。
When dual impellers are employed on gear driven mixers, they are spaced approximately two impeller diameters apart.
当齿轮驱动的搅拌器采用双叶轮时，它们直接距离约两个叶轮直径。Two straight blade turbines impart about 1.9 times as much power
to the water as one turbine alone for the same motor power. 在相同的电机功率条件下，两个直页涡轮可以输出至多单个涡轮1.9倍的功率至水中。
Flocculation While rapid mix is the most important physical factor affecting coagulant efficiency, flocculation is the most important factor affecting particle-removal efficiency. 快速混合是影响混凝效率的最重要影响因子，而絮凝是影响颗粒去除效率的最重要影响因素。
The objective of flocculation is to bring the particles into contact so that they will collide, stick together, and grow to a size that will readily settle.
絮凝的目标是让颗粒接触，使得它们可以碰撞、粘结，然后长成能够容易沉降的大小。
Enough mixing must be provided to bring the floc into contact and to keep the floc from settling in the flocculation basin. 必须提够足够的混合，以使得絮体接触，并使絮体在絮凝池中不要沉淀。
Too much mixing will shear the floc particles so that the floc is small and finely dispersed.
过于剧烈的混合会剪切絮体颗粒，导致絮体变小而被均匀分布。Therefore, the velocity gradient must be controlled within a
relatively narrow range.
因此，速度梯度必须控制在一个相当狭窄的范围内。
Flexibility should also be built into the flocculator so that the plant operator can vary the G value by a factor of two to three.
絮凝池必须具有灵活性，这样可使得水厂操作者能够通过一个因素的两到三倍改变G值。
The heavier the floc and the higher the suspended solids concentration, the more mixing is required to keep the floc in suspension.
絮体越重，SS越高，就需要更多的混合以避免絮体沉降。
Softening floc is heavier than coagulation floc and therefore requires a higher G value.
软化的絮体要比混凝的絮体重，因此需要一个更高的G值。
An increase in the floc concentration (as measured by the suspended solids concentration) also increases the required G. 絮体浓度（通过衡量ss浓度）的增加，也会导致需要的G值的增加。
Flocculation is normally accomplished with an axial flow impeller(轴流式叶轮) , a paddle flocculator, or a baffled chamber.
絮凝通常通过一个轴流式叶轮，带桨的絮凝池，或者阻隔间完成的。
Axial flow impellers have been recommended over the other types of flocculators because they impart a nearly constant G throughout the tank.
轴向流叶轮被建议超过其它形式的絮凝池，因为它们在整个反应池中几乎提供了一个不变的G值。
The flocculator basin should be divided into at least three compartments.
絮凝池应至少被分隔为三个池子。
The velocity gradient is tapered so that the G values decrease from the first compartment to the last.
速度梯度逐渐降低，使得G值从第一个池子至最后一个池子逐渐降低。
Some common rules-of-thumb for axial flow impellers are that the diameter of the impeller is between 0.2 and 0.5 times the width of the chamber and that the maximum impeller diameter is about 3 m.
一些关于轴向流叶轮的直径介于隔间宽度的0.2～0.5倍，叶轮最大直径约是3m。
Unit 8 Section A Animals or children?—A scientist's choice 动物还是孩子？——一位科学家的选择 1 I am the enemy! I am one of those cursed, cruel physician scientists involved in animal research. These rumors sting, for I have never thought of myself as an evil person. I became a children's doctor because of my love for children and my supreme desire to keep them healthy. During medical school and residency, I saw many children die of cancer and bloodshed from injury — circumstances against which medicine has made great progress but still has a long way to go. More importantly, I also saw children healthy thanks to advances in medical science such as infant breathing support, powerful new medicines and surgical techniques and the entire field of organ transplantation. My desire to tip the scales in favor of healthy, happy children drew me to medical research. 1 我就是那个敌人！我就是那些被人诅咒的、残忍的、搞动物实验的医生科学家之一。这些谣言刺痛了我，因为我从来没想到自己是一个邪恶的人。我成为一位儿科医生，因为我爱孩子，也因为我的最大愿望是让他们保持健康。在医学院学习和住院医生实习时，我看到了许多儿童死于癌症和受伤流血——虽然对此医学正取得很大进步，但远非完善。更重要的是，我还看到孩子们能保持健康得益于医学的进步，如婴儿呼吸支持器，功效强大的新药物和外科手术技术及整个器官移植领域的发展。我希望孩子们健康快乐，这促使我从事医学研究。 2 My accusers have twisted the truth into a fable and cast me as the devil. They claim that I have no moral compass, that I torture innocent animals for the sole purpose of career advancement, and that my experiments have no relevance to medicine. Meanwhile, an uncaring public barely watches, convinced that the issue has no significance, and publicity-conscious senators and politicians increasingly give way to the lobbying of animal rights activists. 2 控诉我的人把真相歪曲成一则神话，并把我描写成恶魔。他们声称我没有道德界限，我折磨那些无辜动物的唯一目的就是为了自己的职业升迁，而我的实验根本与医药毫不相关。与此同时，无动于衷的公众几乎不闻不问，相信这个议题毫无意义，而具有宣传意识的参议员和政治家们却对动物权利活动家的游说不断作出让步。 3We,in medical research,have also been unbelievably uncaring.We have allowed the most extr eme animal rights protesters to creep in and frame the issue as one of"animal fraud"and hatred. We have persisted in our belief that a knowledgeable public would consent to the importance of animal research for public health.Perhaps we have been mistaken in not responding to the emoti onal tone of the argument.Perhaps we should have responded to those sad slogans and posters of animals by waving equally sad posters of children dying of cancer or external wounds. 3我们这些从事医学研究的人也显得令人难以置信的冷漠。我们允许最极端的动物权利活动家渐渐侵入，任凭他们把此类研究诬陷为“动物欺诈”和对动物的仇恨。我们一直坚信，有知识的公众会赞同动物研究对公众健康的重要性。也许我们的错误是没有对这场争论的感性基调作出反应。也许我们早应该挥动着儿童死于癌症或外伤的同样令人伤心的海报，来回应那些关于动物受害的伤感标语及海报。 4In the animal rights forum,much is made of the volume of pain these animals experience in the name of medical science.Activists deny that we are trying to help and say it is evidence of our ev il and cruel nature.A more reasonable argument,however,can be advanced in our defense.Life i
Test for Unit 8 （时间：120分钟，满分：120分） 听力部分（25分） Ⅰ.听句子，选择最佳答语。(5分) ()1.A.Sure.Here you are.B．It's an English book.C．It's mine. ()2.A.Yes，I did. B．No，I haven't. C．It's great! ()3.A.Pop music is my favorite. B．I like listening to music. C．Music can help me relax. ()4.A.I read it in the library. B．I have read it before. C．It's interesting. ()5.A.Yes，I will. B．No，I don't like it. C．Yes，it's The Eagles. Ⅱ.听短对话及问题，选择正确答案。(5分) ()6.A.Tom Sawyer. B．Harry Potter. C．Robinson Crusoe. ()7.A.French. B．English. C．German. ()8.A.8：15. B．8：00. C．7：45. ()9.A.Because he had a bad cold and had to see the doctor. B．Because he felt cold and went to buy a coat. C．Because he had to go to see his sister. ()10.A.At school. B．In the hotel. C．At home. Ⅲ.听长对话，选择正确答案。(5分) 听第一段对话，回答第11－12小题。 ()11.What is coming? A．National Day. B．The teacher's birthday. C．Teachers' Day. ()12.What will they buy? A．Some flowers. B．A new CD. C．A bag. 听第二段对话，回答第13－15小题。 ()13.What is the girl worrying about? A．She can't invite her friends to the party. B．She can't go to her friend's party. C．She can't find a good place for the Thanksgiving dinner. ()14.How long will the party last? A．For four hours. B．For five hours. C．For six hours. ()15.Who can help the girl? A．The boy. B．Kevin. C．The boy's father. Ⅳ.听短文，完成下面的表格。每空一词。(10分)
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A fable for tomorrow (Rachel Carson) There was once a town in the heart of America where all life seemed to live in harmony with its surroundings. The town lay in the midst of a checkerboard of prosperous farms, with fields of grain and hillsides of orchards where, in spring, white clouds of bloom drifted above the green fields. In autumn, oak and maple and birch set up a blaze of color that flamed and flickered across a backdrop of pines. Then foxes barked in the hills and deer silently crossed the fields, half hidden in the mists of the fall mornings. 从前在美国中心有一个小镇，那里的万物看上去都与其四周的环境融洽相处。小镇的四周是像棋盘交错的生意盎然的农庄，还有一块块的田地和一座座遍布山坡的果园。春天来了，白色的鲜花云彩般地漂浮在田野上；秋天到了，橡树、枫树和桦树色彩斑斓，在一片松树林间火焰般地燃烧与跳跃。小山上狐狸吠叫，田野间小鹿静静地跃过，所有的一切都在秋天清晨的薄雾中半隐半现。 Along the roads, laurel, viburnum and alder, great ferns and wildflowers delighted the traveler's eye through much of the year. Even in winter the roadsides were places of beauty, where countless birds came to feed on the berries and on the seed heads of the dried weeds rising above the snow. The countryside was, in fact, famous for the abundance and variety of its bird life, and when the flood of migrants was pouring through in spring and fall people traveled from great distances to observe them. Others came to fish the streams, which flowed clear and cold out of the hills and contained shady pools where trout lay. So it had been from the days many years ago when the first settlers raised their houses, sank their wells, and built their barns. 在路的两旁，一年中许多时候，月桂树、荚莲、桤木、蕨类植物和各样的野花都能让过往的行人赏心悦目。即使是冬天，路边的景色依旧是美不胜收，那里无数的小鸟来觅取浆果莓和露在雪地上的枯枝上的种子。事实上，这乡村正是由于鸟类的数量和种类之繁多而出名的。在候鸟群潮涌而来的春秋季节，人们从大老远的地方慕名前来欣赏。还有的人来这里的小溪垂钓。清冽的溪水从山中流出，溪水中有许多鳟鱼藏身的背阴的水潭。所以，从许多年前开始，第一批居住者就在这里盖房挖井，搭起了自己的谷仓。 Then a strange blight crept over the area and everything began to change. Some evil spell had settled on the community: mysterious maladies swept the flocks of chickens; the cattle and sheep sickened and died. Everywhere was a shadow of death. The farmers spoke of much illness among their families. In the town the doctors had become more and more puzzled by new kinds of sickness appearing among their patients. There had been several sudden and unexplained deaths, not only among adults but even among children, who would be stricken suddenly while at play and die within a few hours. 后来，一种奇怪的摧毁力悄然袭击了这个地区，所有的一切都开始变了。某种邪恶的符咒笼罩了这个社区：神秘的疾病攻击了鸡群，牛、羊也纷纷病死，到处都有一层死亡的阴影。农夫们谈论
Unit 8单元测试卷 一根据句意及首字母提示完成单词 1.He can’t wait to o_____ the box to see what present it is. 2.He usually d _____to work, but sometimes he takes a bus. 3.We didn’t go swimming yesterday. I____,we went hiking. 4.She s____an English song for us at the party last Sunday. 5.He didn’t m_____what happened to him in the letter. 6.I want to give a _____（特殊的）gift to my father for his birthday. 7.The computer is the best gift Tony has ever _____(收到) 8.Whom shall we _________(挑选) as our team leader? 9.More than twenty singers ________(参加) in the contest. 10.The program _______(建议) ways for students to communicate with their parents. 11. Mr Li told his little son to answer teachers' questions __________(有礼貌). 12. It's ________________(危险) to swim alone in the river. 13. --I want to report a traffic ___________(事故). --Yes，go ahead. 14. --I thought I'd buy James a new bike for his birthday. --That's a _____________(精彩) idea. 15. Harbin is in the ______________(东北) of China. 二单项选择.( ) 1. _______ should I get Mary for her birthday? A. How B. When C. Where D. What ( ) 2. How about ______ to a concert tonight? A. go B. to go C. going D. to going ( )3. I got the gift _____ my ______ birthday. A. on, ten B. on, tenth C. at, ten D. by, tenth ( ) 4. She lives ______ but she doesn’t feel _______. A. alone, lonely B. alone, alone B. C. lonely, alone D. lonely, lonely ( ) 5. They have ____ eight-year-old child _____Ted. A. an, names B. an, named C. a, name D. a, named ( ) 6. Xiaoli doesn’t work ____ Maomao. A. as harder as B. as hard as C. so harder as D. so hardly as ( ) 7. Our English teacher was ill. So Mr Wang gave us a lesson _____ her. A. instead B. instead of C. beside D. except ( ) 8. I think the story is too hard for the boy________. A. read B. to be read C. to read D. reading ( ) 9. ______ working as a doctor, he also writes novels in his spare time. A. Beside B. Except C. Expect D. Besides ( ) 10. “What about seeing movies?”“_____. I’m tired of staying at home.”
Uｎiｔ8 课文翻译 课文A Refleｃtｉonｓof ａChｉnｅse ｍother iｎｔhe West 一位西方华裔母亲得思考 1.很多人想了解中国父母就是如何培养出如此成功得孩子得。她们想知道,为什么这些中国父母能养育出那么多天分极佳得孩子,她们就是否也能培养出这样得孩子呢? 2.事实就是,中国父母得做法,对固执己见得西方人来说,令人愤慨,难以想象,甚至就是违法得、中国母亲可以不客气地对正在狼吞虎咽得肥胖孩子说:“喂,小胖子,您要减肥了。”与此相反,西方父母必须体谅地、小心翼翼而拐弯抹角地谈及“健康”,而且永远都不会提及“胖"字、结果,孩子还就是因为饮食紊乱与消极得自我评价得去求医问药。长期以来我一直苦思冥想,中国父母这样做就是如何能够全身而退得,我认为中西方得父母之间存在三种意识形态上得差异。 3.首先,我注意到西方父母呵护子女得自尊,使她们免受一切批评。她们担心孩子失败后得感受,于就是不断尽其所能解除子女得忧虑,而不管其表现如何糟糕。西方父母认为孩子就是娇弱得,不够坚强,因此她们得行为也就与中国父母大相径庭了。 4.举个例子,如果一个孩子考试得了个Aˉ回家,西方父母很可能会表扬孩子。而对中国母亲来说, Aˉ根本不算什么好成绩;她还会不快地叹气,问到底出了什么问题。如果孩子得了Ｂ回家,一些西方父母尽管十分不情愿,仍然会表扬孩子。其她西方父母会表达出不满,但不会质疑孩子得智力,或贸然说孩子“笨蛋”、“一文不值”或“太可恶了”、而私下里,西方父母可能会感到担心,但绝不会让孩子们知道、 5.如果中国孩子得了B,不管什么科目,首先面临得就就是一声尖叫与恼怒得爆发、中国母亲会更加不遗余力地找来几十也许几百套得测验题,不惜采取手头任何办法来让自己孩子得成绩提高到Ａ。 6.中国父母要求完美得成绩,因为她们理所当然地认为孩子完全可以做到,而且分数就是比“自尊”更为重要得衡量成功得标准、如果孩子没拿到全A,中国父母就认为这就是因为孩子不够努力。这就就是为什么对表现欠佳得孩子,父母总就是会施以惩罚与辱骂。中国家长相信孩子足够坚强,能够承受羞辱,并会由此进步。 7.其次,中国父母认为孩子欠她们一切。这种瞧法得原因尚不清楚,也许就是儒家“忠”得信条,再加上父母为子女牺牲诸多这一事实。因此,中国孩子必须听从父母教导,使她们自豪,终其一生回报她们。 8.中西方理念碰撞得另一领域就是,西方人大多认为子女无须永远感激父母。我丈夫就是个西方人,实际上就持有这种相反观点。“孩子又不能选择自己得父母,”她曾对我说过、“她们
A fable for tomorrow (Rachel Carson) There was once a town in the heart of America where all life seemed to live in harmony with its surroundings. The town lay in the midst of a checkerboard of prosperous farms, with fields of grain and hillsides of orchards where, in spring, white clouds of bloom drifted above the green fields. In autumn, oak and maple and birch set up a blaze of color that flamed and flickered across a backdrop of pines. Then foxes barked in the hills and deer silently crossed the fields, half hidden in the mists of the fall mornings. 从前在美国中心有一个小镇，那里的万物看上去都与其四周的环境融洽相处。小镇的四周是像棋盘交错的生意盎然的农庄，还有一块块的田地和一座座遍布山坡的果园。春天来了，白色的鲜花云彩般地漂浮在田野上；秋天到了，橡树、枫树和桦树色彩斑斓，在一片松树林间火焰般地燃烧与跳跃。小山上狐狸吠叫，田野间小鹿静静地跃过，所有的一切都在秋天清晨的薄雾中半隐半现。 Along the roads, laurel, viburnum and alder, great ferns and wildflowers delighted the traveler's eye through much of the year. Even in winter the roadsides were places of beauty, where countless birds came to feed on the berries and on the seed heads of the dried weeds rising above the snow. The countryside was, in fact, famous for the abundance and variety of its bird life, and when the flood of migrants was pouring through in spring and fall people traveled from great distances to observe them. Others came to fish the streams, which flowed clear and cold out of the hills and contained shady pools where trout lay. So it had been from the days many years ago when the first settlers raised their houses, sank their wells, and built their barns. 在路的两旁，一年中许多时候，月桂树、荚莲、桤木、蕨类植物和各样的野花都能让过往的行人赏心悦目。即使是冬天，路边的景色依旧是美不胜收，那里无数的小鸟来觅取浆果莓和露在雪地上的枯枝上的种子。事实上，这乡村正是由于鸟类的数量和种类之繁多而出名的。在候鸟群潮涌而来的春秋季节，人们从大老远的地方慕名前来欣赏。还有的人来这里的小溪垂钓。清冽的溪水从山中流出，溪水中有许多鳟鱼藏身的背阴的水潭。所以，从许多年前开始，第一批居住者就在这里盖房挖井，搭起了自己的谷仓。 Then a strange blight crept over the area and everything began to change. Some evil spell had settled on the community: mysterious maladies swept the flocks of chickens; the cattle and sheep sickened and died. Everywhere was a shadow of death. The farmers spoke of much illness among their families. In the town the doctors had become more and more puzzled by new kinds of sickness appearing among their patients. There had been several sudden and unexplained deaths, not only among adults but even among children, who would be stricken suddenly while at play and die within a few hours. 后来，一种奇怪的摧毁力悄然袭击了这个地区，所有的一切都开始变了。某种邪恶的符咒笼罩了这个社区：神秘的疾病攻击了鸡群，牛、羊也纷纷病死，到处都有一层死亡的阴影。农夫们谈论着家中的许多疾病；镇上的医生也越来越因病人中出现的新的病症而感到迷惑。在成人和孩子中发生了好几起突发的不明其由的死亡，那些孩子在玩耍中突然病倒，几小时后就死去了。 There was a strange stillness. The birds, for example - where had they gone? Many people spoke of them, puzzled and disturbed. The feeding stations in the backyards were deserted. The few birds seen anywhere were moribund; they trembled violently and could not fly. It was a spring without voices. On the mornings that had once throbbed with the dawn chorus of robins, catbirds, doves, jays, wrens, and scores of other bird voices there was now no sound; only silence lay over the fields and woods and marsh 这里是一派奇怪的寂静。就说鸟儿们吧---它们都去哪儿了？许多人说起鸟儿的时候都充满了迷惑与不安。他们后院的饲养站已经没有鸟儿光顾了。随处能见到的几只鸟都奄奄一息。他们猛烈地颤抖，却飞不起来。这是一个无声的春天。曾经是震动着画眉鸟、猫鸟、鸽子、樫鸟、欧鹪和许多鸟儿的黎明合唱声的清晨如今却寂然无声。田野间、树林中和沼泽地里也是一片寂静。 On the farms the hens brooded, but no chicks hatched. The farmers complained that they were unable to raise any pigs - the litters were small and the young survived only a few days. The apple trees were coming into bloom but no bees droned among the blossoms, so there was no pollination and there would be no fruit. 在农庄，母鸡下蛋却孵不出小鸡。农夫们抱怨无法养猪，因为刚生下的猪崽太小了，小猪也只能活几天的功夫。苹果树开花了，可是没有蜜蜂在花丛中嗡嗡地采蜜，没有蜜蜂的授粉，也就没有任何果子。 The roadsides, once so attractive, were now lined with browned and withered vegetation as though swept by fire. These, too, were silent, deserted by all living things. Even the streams were now lifeless. Anglers no longer visited them,
八年级上册英语Unit8 单元测试卷 一、单项选择（共25小题；共25分） ( )1. the medical help first, then make her comfortable and call her parents. A. Getting B. Get C. To get ( )2. oranges do you want and orange would you like? A. How many; how many B. How much; how much C. How many; how much D. How much; how many ( )3. I t is sunny. What weather! A. a good B. an awful C. great D. bad ( )4. T here are two and six in the zoo. A. kangaroos; wolfs B. kangaroos; wolves C. kangarooes; wolves D. kangarooes; wolfs ( )5. S ome visited our school last Wednesday. A. German B. Germen C. Germans D. Germens ( )6. S wimming is in summer. A. a great fun B. great fun C. great funs D. great a fun ( )7. --- What can I do for you? --- I want to buy for my daughter. A. a clothing B. a piece clothing C. a piece of clothing D. the piece of clothing ( )8. I want to buy . A. two bottles of milks B. two bottles of milk C. two bottle of milk D. two bottle milks ( )9. T he room was dark, so she asked me to the lights. A. turn up B. turn down C. turn off D. turn on ( )10. —butter do we need for a sandwich? —Two teaspoons should be enough. A. How many B. How much C. How long D. How far ( )11. --- Maria, the dog, will you? --- Why ask me? Tom is playing there. A. to feed B. feed C. feeding ( )12. “exercise every day, my son. It’s good for your health. ”Dad often said to him. A. Takes B. Taking C. Take D. To take ( )13. Thanksgiving is always the fourth Thursday in November. A. in B. on C. at D. for ( )14.—The banana is too big. —You can _______ first. A. cut up them B. cut them up C. cut it up D. cut up it ( )15. Don’t forget to the light when you leave the room. A. turn on B. turn off C. turn up D. turn down ( )16. Don’t _______ the milk into the cup. It’s full (满了). A. peel B. pour C. leave D. drink ( )17. Tom, please add some salt _______ the noodles. A. on B. in C. to D. at ( )18. I had _______ for breakfast yesterday.
第八单元 Grinding is a manufacturing process that involves the removal of metal by employing a rotating abrasive wheel. The latter simulates a milling cutter with an extremely large number of miniature cutting edges. 磨削是通过采用旋转磨轮去除金属的制造工艺。磨轮用非常大量的微型切削刃模仿铣刀进行切削。Generally, grinding is considered to be a finishing process that is usually used for obtaining high-dimensional accuracy and better surface finish. Grinding can be performed on flat, cylindrical, or even internal surfaces by employing specialized machine tools, which are referred to as grinding machines. 一般而言，磨削被认为是一种通常用于获得高尺寸精度和较好表面光洁度的精加工作业。磨削通过采用被称为磨床的特殊机床能在平面、圆柱面甚至内表面上进行。 Obviously, grinding machines differ in construction as well as capabilities, and the type to be employed is determined mainly by the geometrical shape and nature of the surface to be ground, e.g., cylindrical surfaces are ground on cylindrical grinding machines. 显然，磨床根据结构和功能的不同有所区别，使用何种形式的磨床主要取决于被磨削表面的几何形状和物理性质。例如，圆柱面在外圆磨床上磨削。 ?Type of Grinding Operations 磨削作业的类型 1. Surface grinding. As the name surface grinding suggests, this operation involves grinding of flat or plane surfaces. Fig.8.1 indicates the two possible variations, either a horizontal or vertical machine spindle. 1.表面磨削：就像其名称暗示的那样，表面磨削和平面磨削直接有关。图8.1表示了两种可能的变化：卧式磨床主轴或立式磨床主轴。 In the first case (horizontal spindle), the machine usually has a planer-type reciprocating table on which the workpiece is held. However, grinding machines with vertical spindles can have either a planer type table like that of the horizontal-spindle machine or a rotating worktable. 在第一种情况(卧式主轴)，卧式磨床通常具有安装工件的刨床式往复工作台。而立式主轴磨床既可以像卧式主轴磨床那样具有刨床式工作台也可以具有旋转工作台。 Also, the grinding action in this case is achieved by the end face of the grinding wheel (Fig.8.1b), contrary to the case of horizontal-spindle machines, where the workpieces ground by the periphery of the grinding wheel. 而且在这种情况下，磨削动作是通过砂轮端面完成的(图8.1b)，这与通过砂轮周边磨削工件的卧式主轴磨床正好相反。 Fig.8.1a and b also indicate the equations to be used for estimating the different parameters of the grinding operation, such as the machining time and the rate of metal removal. 图8.1a和b同时简述了用于估计诸如加工时间和金属去除率之类的磨削作业不同参数的方程式。 During the surface-grinding operations, heavy workpieces are either held in fixtures or clamped on the machine table by strap clamps and the like, whereas smaller workpieces are usually held by magnetic chucks. 在平面磨削时，重的工件用夹具固定或用压板等夹紧在磨床工作台上，而小的工件则通常是用电磁卡盘固定的。2. Cylindrical grinding. In cylindrical grinding, the workpiece is held between centers during the grinding operation, and the wheel rotation is the source and cause for the rotary cutting motion, as shown in Fig.8.2. In fact, cylindrical grinding can be carried out by employing any of the following methods: 2. 圆柱面磨削：在圆柱面磨削中，作业时工件支撑在两顶尖之间，砂轮转动是导致回转切削运动的动力源，如图8.2所示。实际上，圆柱面磨削能通过采用下列任意方法来实现： (1) The transverse method, in which both the grinding wheel and the workpiece rotate and longitudinal linear feed is applied to enable grinding of the whole length. The depth of cut is adjusted by the cross feed of the grinding wheel into the workpiece. (1) 横向方法：这种方法中砂轮与工件均旋转且采用线性纵向进给以保证能磨削整个长度。切削深度通过改变砂轮