当前位置:黑龙江地方站首页 > 龙江新闻 > 正文


2020年02月24日 20:55:17    日报  参与评论()人

四川大学附属医院四维彩超预约达州市妇幼保健医院男科医生Youre hiking through the Rockies one day when you hear a low, ominous rumble. Landslide! Hundreds of tons of rock and soil are careening toward you at enormous speed.一天,你徒步在岩石堆中穿行,这时你听到一阵低低的隆隆声,势头不妙。是山体滑坡!上百吨的岩石和泥土以极快的速度朝你倾泻下来.Fortunately, theres a helicopter nearby and you lift off just in time to escape unharmed. But now you notice something odd. After the landslide has gone by, in its tracks little dainty flowers are still standing. Blades of grass are unbent. How is this possible?幸运的是,附近有架直升飞机,你及时乘飞机起飞,逃过了这一劫。但你却注意到了一些奇怪的现象。滑坡结束后,美丽的花朵依旧挺立在石块冲刷过的地方,小草也没有被低下头来,是什么让这些植物还能生存下来呢?Before we tell you the answer, heres another question. What happens when you drop a book flat onto a table?在我告诉你之前,先问你另一个问题。如果你将一本书水平扔到桌面上,会发生什么呢?If you try it, youll see that the book doesnt hit the table unimpeded, but lands on a little cushion of compressed air. If you dont believe us, try putting some little pieces of paper on the table before dropping the book. The whoosh of compressed air escaping will blow them off.试一下,你会发现书在撞击桌子的时候遇到了阻碍,落在了压缩空气形成的缓冲垫上。如果你不相信,你可以先在桌上放一些小纸片,再将书抛下去。受压的空气向外逃出,呼啸着将纸片吹走.Thats the same phenomenon that happens with landslides. When an enormous sheet of rocks and dirt gets moving, it acts like a solid object. It traps the air underneath it and actually rides downhill on a cushion of air. Strange as it may seem, much of the landslide never touches the ground at all.这与山体滑坡时发生的现象相同。当巨大的泥石移动的时候,它们的行动就像一个固体。它将空气压在下面。实际上,其实它是在一个气垫上滚下去的。尽管看上去有点怪,但大多数山体滑坡从不会接触到地面。Because the cushion of air stays underneath it, the rocks and dirt arent slowed down by friction much and continue picking up speed as they fall. Large landslides have been clocked in excess of 100 miles an hour.由于空气垫的作用,岩石和泥土并没有受到很大擦力而减速下滑,相反它们会不停地加速。规模大的山体滑坡时速超过100英里每小时.So—could you just lie down and let the landslide whoosh over you? No, unless you are about the size of a blade of grass. People who are bigger than that should keep a helicopter handy. 因此,你会躺下来,让滑坡从你身上越过吗?绝对不行。除非你只有草叶般大小。比草叶体积大的人类应该保身边有一架直升飞机。201206/185527四川省骨科医院治疗前列腺疾病多少钱 Science and Technology Three-dimensional printing An image of the future科技 3D印刷 印刷未来One of the biggest manufacturers in the world gives 3D printing a go世界龙头机器制造商用3D印刷术进行了一次格外成功的应用ULTRASOUND scanners are used for tasks as diverse as examining unborn babies and searching for cracks in the fabric of aircraft.超声波扫描器的应用领域很广,小到用于检查胎儿,大到飞行器机体瑕疵检测等。They work by sending out pulses of high-frequency sound and then interpreting the reflections as images.机理过程是,通过发射高频声波脉冲信号对反射信号进行成像解读。To do all this, though, you need a device called a transducer.但完成该过程,你不能缺少一台叫做‘压电式换能器的设备。Transducers are made from arrays of tiny piezoelectric structures that convert electrical signals into ultrasound waves by vibrating at an appropriate frequency.压电式换能器是由具有‘压电效应的一系列敏感元件机构组成。敏感元件机构通过‘定频震荡将电信号转换成超声波。Their shape focuses the waves so that they penetrate the object being scanned.机构的特定外形可聚焦超声波,对被扫描的物体产生穿透作用。The waves are then reflected back from areas where there is a change in density and on their return the transducer works in reverse, producing a signal which the scanner can process into a digital image.超声波会从密度发生变化的介质反射回来,这时压电式换能器会反向操作产生信号,再经过扫描器的处理,最后进行数字成像。To make a transducer by painstakingly micro-machining a brittle block of ceramic material can take many hours of work, though.压电式换能器需要用到陶瓷材料,而精密地加工一块精细的陶瓷材料就要耗费几个小时的工作时间。As a result, even as the size and cost of the console that controls the scanner has fallen with advances in microelectronics (some are now small enough to fit in a doctors pocket and cost a few hundred dollars), the cost of making the probe itself remains stubbornly high—as much as ten times that of the console.随着微电子领域中,技术的突飞猛进,控制扫描仪的电路板无论从体积还有成本都有很大程度的优化变小和降低。有些电路板小到可以装进医生口袋里面,成本也不过几百美元的价格。而制作换能器探头的成本却一直居高不下,跟电路板相比,探头的制作成本大概是一块电路板的10倍左右。At least, it does if you use traditional ;subtractive; manufacturing techniques like cutting and drilling.即使不考虑体积及成本的情况下,传统的‘对比相减式加工流程技术也能完成这些工作,比如切割,机钻等。However GE, a large American conglomerate, is now proposing to make ultrasound transducers by ;additive; manufacturing—or three-dimensional printing, as it is also known.而GE作为美国的一个庞大的企业集团正考虑采用‘对比添加式的加工流程(或者又称大家所熟悉的‘3D印刷)来加工超声波压电式换能器。A new laboratory at the firms research centre in Niskayuna, New York, is taking a hard-headed look at the technique, which some see as a fad and others as the future,GE在纽约Niskayuna地区的研发中心新成立了一个实验室,目前该实验室正本着理性实际的态度(非一时狂热)对该项技术进行研发,力图找到哪些产品用‘对比添加式而非‘对比相减式的技术流程加工生产更加适合。一些人认为,对该项技术的研发只不过是一时狂热。and working out which products might be made more efficiently by addition rather than subtraction.还有一些人声称,目前的时机并不成熟,对该项技术的研发仅仅具有‘将来时的意义罢了。Ultrasound transducers were an early pick both because of the complicated geometry needed to focus the sound waves and because ceramics are harder than metals to cut and drill accurately.最初选择超声波压电式换能器来作为‘3D印刷术的对象原因有两点。一是该换能器用来聚焦声波的机体外形非常复杂,二是它用到的陶瓷材料比金属的硬度要高很多,很难进行精准地切割和机钻。But they are easy to print.而用‘3D印刷术却很容易解决这两个难题。The GE process for making a transducer begins by sping onto the print table a thin layer of ceramic slurry containing a light-sensitive polymer.GE对加工换能器的方法是首先在印刷台上撒上薄薄的一层陶瓷粘土,其中混入一种光敏聚合体。This layer is exposed to ultraviolet light through a mask that represents the required pattern.然后用紫外线通过露光模板的光孔照射到印刷台的粘土层,以此塑造出需要的模型图案。Wherever the light falls on the polymer it causes it to solidify, binding the particles in the slurry together.光敏聚合体一经被紫外线照射就会立即变得坚硬,粘土中的粒子随即凝结固化。The print table is then lowered by a fraction of a millimetre and the process repeated, with a different mask if required.接下来,印刷台会以不超过一毫米的距离向下位移,然后重复整个上面这一过程,如果有必要,需要重新更换一个新的露光模板。And so on. Once finished, the solidified shape is cleaned of residual slurry and heated in a furnace to sinter the ceramic particles together.以此反复处理直到整个过程结束,再进行清理成模上的残余粘土,最后把成模放入熔炉,以低于熔点的温度进行焙烧,最终完成陶瓷粒子的凝固收缩聚合。More work will be needed to turn the process into a production-y system.该处理流程在具有批量生产体系能力之前,还需要做很多的工作。But Prabhjot Singh, who leads the project, hopes that it will be possible to use it to make not just cheaper ultrasound probes, but also more sensitive ones that can show greater detail.但项目负责人Prabhjot Singh表示,希望不仅仅制造出成本相对低廉的超声波探头,最好探头的灵敏性也会更高,这样可以让我们通过成像看到更加细节化的信息。Although researchers have had new transducer designs in mind for years, it has been impractical to construct them subtractively. Additive manufacturing could change that.多年以来,压电式换能器的研究者们一直都有新型设计的想法,但应用‘对比相减式的加工流程实际上很难能把这样的构想变为现实,而‘对比添加式很可能会使这种困顿得到改善。The new laboratory will look at other forms of additive manufacturing, too.GE的新实验室还将研究其它‘对比添加式的加工流程。Some 3D printers sp metal powders on the print table and sinter the pattern with lasers or electron beams, rather than using masks.比如一些3D印刷机在印刷台铺撒金属粉末之后,采用露光模板以外的激光或电子束方式进行热凝处理来产生样模。Others deposit thin filaments of polymer in order to build structures up.其它流程,如混入聚合体热敏细丝通过自加固原理进行聚合以产生成模。GE is interested in how the technology could be used right across the firms businesses, from aerospace to power generation and consumer products, according to Luana Iorio, head of manufacturing technologies at GE Global Research.GE全球研发中心‘制造技术中心主任Luana Iorio指出,GE旨在为各种商业形式,包括象航空航天、能源及消费产品等领域提供令人满意的‘3D印刷技术。The gains include less waste and the ability to make bespoke parts more easily.这种技术的获益在于节约耗材和使第三方定制个性化零部件变得更加容易。But one of the most compelling advantages is freeing designers from the constraints of traditional production.但最无可争辩的优势之一是让设计者从传统工艺的桎梏中解脱出来。Those constraints include having to design things not in their optimal shape but to be machined, often as a series of pieces.这些限制包括,设计者不得不用多个零部件去实现一个功能,不能从最优化的外形尺寸来设计产品。Additive manufacturing can combine parts into a single item, so less assembly is needed. That can also save weight—a particular advantage in aerospace.‘对比添加式可以整合零部件,避免了一些繁琐的机械组装过程,同时减轻了重量,这点对航空航天领域尤为有利。These new production opportunities mean manufacturers, big and small, are about to become a lot more inventive.在这种新的生产有利背景下,意味着制造商们,无论规模大小,都将变得更加具有创造性。 /201212/213562成都体育学院附属医院产科

绵阳治疗妇科炎症多少钱They get these tables and they realize the next total solar eclipse will occur in the Crimere,他们研究这些表格并且意识到下一次日全食会发生在厄喀德那,which is in Russian territory, on the 21st of August, 1914.那是俄罗斯的领土,而具体时间是1914年8月21日。Freundlich goes to his boss, says, look, lets go to Russia, Im collaborating with Einstein, would you put the money out?弗雷德里希找到他的老板,说,你看,咱们去俄罗斯吧,我在与爱因斯坦合作,你会出这笔费用吗?Then he says, no way. Just refuses.他说道,没门。断然拒绝。Einstein is absolutely furious.爱因斯坦感到非常的愤怒。Reaching beyond the European scientific establishment,弗雷德里希找到欧洲科研机构以为的部门,Freundlich enquires to the director of the Lick Observatory,他询问予天文台的台长,,near San Jose of California, a rugged outpost of American astronomy.它坐落在加州圣·何塞附近,一条崎岖的道路中。It was a community thatve been on the mountain.它位于一个社区,在一座山上。They all had their families, their wives were there, their kid were all there.他们都有家庭,他们的妻子在那里,他们的孩子都在那里。They were depending on each other for survival.他们相互依存才得以生存。For many years it had the largest reflecting telescope in the world.多年来,这座天文台一直拥有世界上最大的反射望远镜。But the most importantly, it has William Wallace Campbell, a pioneer of eclipse photography.但最重要的是,威廉·华莱士·坎贝尔这位日蚀摄影的先驱也在其中。注:听力文本来源于普特201204/177600青白江区龟头炎症 金牛区中医院门诊部

四川省华西医院治疗宫颈糜烂多少钱And fishing can be dangerous. A southern sea lion. It uses the speed of a breaking wave to catch up the gentoos. Sea lions normally eat fish. So he is used to catching stream-line swimmers. But the gentoos seem more than his match-up at sea. He must change tactics. Perhaps it would be easier in the shallows. But, no, it seems penguins are uncatchable in water. How about on land? The penguins wings are so powerful for swimming, but of no help when it comes to running. Now surely the sea lion has a chance. But on the beach both are like fish out of water. Rarely do hunter unhunted play their roles with so little skill. The outcome is anyones guess.无疑异常危险。南方的海狮用其无与伦比的速度追上了巴布亚企鹅。海狮通常吃鱼。所以他会捕捉流线型的游泳者。但是巴布亚企鹅似乎更符合其要求。他必须改变战术。也许在浅滩会比较容易。但是,不,看情况企鹅是在水里是不可能被抓住的。但在陆地上会如何呢?企鹅的翅膀看似就是天生为游泳而准备,但它在跑的时候却根本不起一点作用。现在机会降临到了这只海狮身上。但在地面上都喜欢离开水的鱼。很少有猎人不用一点点技巧打猎。结果则仁者见仁,智者见智。注:听力文本来源于普特201202/169943 Blackcaps are small songbirds that breed in Central Europe. Fifty years ago, most blackcaps went south for the winter to Spain or Portugal. But since the 1960s more and more blackcaps have started wintering in Britain and Ireland. By 2003, blackcaps were seen perched at one in every three backyard bird feeders in Britain! But why did so many blackcaps change their winter vacation location?黑头莺是一种体型较小的鸟类,主要生活在欧洲中部。50年前,大多数黑头莺每到冬季就会迁徙到南部的西班牙或者葡萄牙。但是自20世纪60年代起,越来越多的黑头莺开始飞往英国和爱尔兰过冬。到2003年,有三分之一的英国家庭后院里的喂食器上出现过黑头莺。然而是什么促使如此多的黑头莺另择越冬地呢?The direction birds migrate is coded in their genes. Each population of birds has an average direction they will go, but individuals can vary as much as forty degrees from the average. Although historically, the average direction for blackcaps was towards Portugal, a few birds genes pointed them in a slightly different direction and they ended up in Britain.鸟类迁徙的方向由基因决定。每个鸟群迁徙时都有个平均方向,但个体可以在偏离这个方向40度范围内活动。尽管历史上黑头莺迁徙的平均方向是朝着葡萄牙,但还是有不少黑头莺定位稍有偏差,结果就来到了英国。But for the numbers of blackcaps wintering in Britain to change so dramatically, there must be some significant advantage to fly north rather than south. Perhaps the benefit is simply from the shorter, less taxing flight to Britain. Or maybe it’s because Britain has many bird lovers that stock backyard birdfeeders.在英国过冬的黑头莺数量激增,至于它们选择飞往北方而不是南方,其中肯定有一些显著的优势。也许是因为英国比较近,不必大费周折飞那么远,也许是因为英国有许多鸟类爱好者,在后院到处悬挂喂食器。But researchers from Germany and the UK believe the key difference is the shorter winter days in Britain. Shorter days affect migration and breeding behavior, so British birds return to summer breeding grounds about ten days earlier than birds that went south.但来自德国和英国的研究人员认为关键区别在于英国冬季的白昼较短。白昼短这一点可以影响到鸟类的迁移和繁殖行为,所以,在英国过冬的鸟类会比飞往南方的鸟类提前十天返回夏日的繁殖场所。This ten-day head start lets British migrants claim the best territories and start breeding sooner. Females paired with British males laid more eggs and hatched more chicks than those mated to southern birds. Each year, blackcaps with genes orienting them towards Britain pass on those genes to more chicks. And so the number of blackcaps with the disposition to fly to Britain steadily increases.开头的十天会保这些候鸟们占领最好的领地,迅速开始育下一代。并且,与在南方配对的雌鸟相比,与英国的雄鸟配对的雌鸟产蛋更多,孵出的雏鸟也更多。年复一年,黑头莺会把向英国迁徙的基因一代代传下去。因此,飞往英国过冬的黑头莺数量急剧增长。原文译文属!201212/215976成都都江堰市引产哪家医院最好的成都省第一医院妇科医生



青白江区中医院客服中心 达州市中心医院是公立医院吗?爱共享 [详细]
新都区做人流多少钱 成都市第九人民医院官网 [详细]
雅安人民医院治疗包皮包茎多少钱 度大全龙泉驿区处女膜修复手术多少钱华专家 [详细]
问医健康眉山市第二人民医院投诉电话 成都省第七人民医院做人流好吗医苑活动四川第十医院等级 [详细]