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楼主:城市健康 时间:2019年09月21日 07:22:36 点击:0 回复:0
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Aristotle thought the stars were all exactly the same distance away, stuck to a dark shell that surrounded the Earth like the dome of a planetarium. Now we know that the farthest galaxy is over a billion times more distant than the nearest star. How do astronomers tell how far away the stars are?亚里士多德认为所有星星离我们的距离都是相等的,它们镶嵌在一个环绕在地球四周的,像天文馆的穹顶一样的黑色的硬壳上。现在我们知道最远星系的距离是最近星系的十亿倍。天文学家是如何知道星星离我们有多远呢?One method works like the way your own eyes determine how far away earthbound objects are. Hold a finger upright at arms length, then close an eye as if you were winking. Open that eye and close the other. As you alternate eyes, your finger will seem to change position. Keep winking back and forth, then move your finger closer to your face.有一种方法跟你目测地面上物体的距离一样。竖起一根手指,并保持一段距离,然后闭上眼睛,仿佛你在思考一样。睁开一只眼睛并闭上另一只。当你变换眼睛的时候,手指的位置似乎改变了。继续来来回回地眨眼,然后移动手指,靠近你的脸。The closer your finger is, the more it appears to jump compared to the background. This is the key to one method of measuring how distant the stars are. Closer stars seem to shift more than distant ones do when seen from different places. The farther apart your two observation points are, the more dramatic this shifting becomes.你的手指靠脸越近,相对于背景物它似乎越是有大的跳跃。这是测量星星距离的方法的关键。从不同的地方看时,近一点的星星似乎比远一点的星星跳跃幅度要大。两个观测点相距越远,这种跳跃就更明显。Your eyes are only inches apart, so no matter how much you wink at the stars, you wont be able to shift them with your eyes alone. Astronomers, however, can use telescopes in different parts of the world, thousands of miles apart. Even better, they can photograph a star once, then again six months later. During six months the Earth will have orbited to the other side of the sun, creating a pair of telescopic eyes that are almost two hundred million miles apart. With this distance, the shift becomes quite noticeable. This method has been used to math the location of thousands of nearby stars.你的双眼只相距一英尺远,因此不论你的眼睛眨多少下,光靠眼睛来看星星你是不会产生这种视觉落差的。但是宇航员能在世界上相隔上千英里的不同角落使用望远镜。甚至更好的,他们能给一颗星星拍照,然后六个月后再拍一次。六个月之后,地球就在太阳另一侧的轨道上转动,这样就创造出一对相隔差不多一亿英里的望眼镜“双眼”。在这么远的距离下,跳跃就非常引人注目了。这种方式已被用来演算上千颗附近恒星的位置。原文译文属!201208/195236If youre too busy to remember to eat, your stomach will remind you its time to refuel by growling. Well look at what happens in your gastrointestinal tract, or GI tract, when youre hungry and when youre full.如果你太忙了而忘记了吃饭,你的胃会咕咕叫着提醒你去吃饭。让我们来看看当你饥肠辘辘或者饱餐一顿时,在你的消化道里发生了什么?Your GI tract is an involuntary muscle which is constantly contracting and expanding. After youve eaten, your gastrointestinal muscle contracts and relaxes in order to move food from your stomach into the intestines. When the GI tract has finished digesting a meal, it continues to process the liquids and gasses remaining in the intestines. This process often causes your stomach to rumble when youre hungry.你的消化道是一组非随意肌,它会不停的收缩扩张。吃饭后,你的胃肠肌会收缩与放松,这样就能将食物从胃部移入肠道。当消化道消化完食物后,会继续处理残留在肠道的液体和气体。这个过程经常使你在饥饿时胃部咕咕作响。Stomach growling is caused by intestinal contractions squeezing and popping intestinal gasses. Actually, stomach rumbles are simply flatulence that stays inside the body. The same contractions that cause your stomach to growl also clean out the GI tract. To see how this cleaning movement works, picture a long hose made of a pliable material. If there were an object, say an egg, at the end of the hose, you could push it from that end to the other by squeezing all along the length of the hose. This is how the GI tract keeps itself clean.肠道挤压在它里面的气体使得胃里产生咕咕的低鸣声。实际上,肚子咕咕叫就是体内的肠胃气胀。这种收缩虽然会让肚子咕咕叫,但也会帮助清理消化道。想要了解这个清理运动是如何进行的,就试着幻想一条柔韧型材料做成的长软管。如果软管的末端有一个物体,比如说一个鸡蛋,你可以通过不断挤压软管把鸡蛋推向另一端。这就是消化道如何自我清理的过程。In order to push out bits of food particles left over from a meal, your gastrointestinal tract creates waves of contractions all along the length of the intestines at a rate of two or three per minute. All of this activity in your GI tract when youre hungry can be very noisy, as anyone who has been in the middle of a pre-lunch meeting when stomachs started rumbling can tell you.为了排出餐后少数的食物残渣,你的消化道每2至3分钟就会产生一个沿着肠道传播的收缩运动。当你感到饥饿的时候,消化道里所有的活动都会显得聒噪。在午餐前开会时肚子突然咕咕作响的员工会告诉你这有多么尴尬。原文译文属!201301/219781

Science and Technology Forest conservation Lidartector科技 森林保护 激光雷达探测术How to tell if countries are cheating on their conservation commitments如何判断一个国家在森林保护承诺上是否有舞弊行为IN AN isolated forest in the Sivalik hills of south-western Nepal, intense sun beats down through the treetops.位于尼泊尔西南部西瓦利克山脉一处偏僻的森林内,毒辣的阳光正从树冠强射而入。A sweaty trek up a steep, rocky slope leads to a spot where a team of researchers is busy measuring the trees.经过一段汗流浃背的艰难跋涉,登上一处陡峭怪石嶙峋的斜坡,到达一块区域,就可以看到一组研究人员正忙着对树木进行测量。They are working for Forest Resource Assessment Nepal, a joint venture between the Nepalese and Finnish governments.他们是尼泊尔与芬兰政府森林资源评估合资企业的工作人员。Two global-positioning-system devices guide the researchers to their target.凭借两套全球定位系统就可将研究人员带到目的地。Once there, they use tape measures, callipers and a hand-held laser to measure the heights and girths of all the trees within a 500-square-metre plot.到达目标后,在圈定好的500平方米区域内,他们用卷尺,测径规和手持激光设备对所有树木的高度和树围进行测量。These measurements, and each trees species, are recorded on a clipboard. One plot finished; 959 more to go.测量结果及每棵树的品种都会被记录下来。一块区域测量完成后,他们还要转战其余的959块区域。A classic piece of forestry, then. Boots on the ground. Specimens duly counted.这是当时的一种传统林艺技术,采用人力进行实地考察,准确测量标本。But this is a study with a twist, for its purpose is to calibrate a new approach to the subject—one that will gather information by the bucketload without the need to rely on quite so many boots.但一项新的研究将会使现状产生飞跃的转变,其目标是针对该课题开创一种新的测量方法—即无须动用众多的人力物力就可收集到大量所需信息。This new approach uses a technique called lidar.这项新方法采用的技术称之为;激光雷达术;。Like its cousins radar and sonar, lidar (light detection and ranging), works by broadcasting electromagnetic waves towards a target and then building up a picture from the reflection.与雷达和声纳技术相似,激光雷达(光探测和测距)的工作原理是通过向目标发射电磁波然后根据反射波构建图像。In the case of lidar, the waves are in the form of an infra-red laser beam.拿激光雷达来说,其波形采用的是红外激光束。And in the case of the forests of south-western Nepal, the target is the trees.以尼泊尔西南部的森林为例,被测目标就是树木。During a forest survey, an aircraft-borne lidar sweeps a beam that fires about 70,000 pulses a second over the canopy.在森林探测过程中,载有激光雷达的飞机将每秒产生7万个脉冲的激光束向森林树冠进行扫掠,A sensor on the aircraft records the time it takes to receive the backscattering of pulses, and that is used to compute distances to the forest canopy and to the soil beneath.同时安装在飞机上的探测设备会记录收到脉冲反向散射波的时间,然后分别用于计算到树林冠部及到土壤的距离。The result, when processed through the computers of Arbonaut, a Finnish natural-resource-management company, is a three-dimensional image of the forest that can be correlated with, and calibrated by, the efforts of the chaps with the tape measures.经过芬兰自然资源管理公司的Arbonaut计算机进行数据处理后,便可生成与采用卷尺那帮家伙的测量结果相关并可校验的树林三维图象。And that, in turn, can be used to estimate the amount of carbon stored in the plot examined, and extrapolated to calculate the carbon stored in larger areas of forest that have been scanned by lidar, but not measured with tapes.接下来,它还能用于估算所测森林区域的二氧化碳储存量,以此类推,激光雷达所探测的更大片森林区域的二氧化碳储存量也可以计算出来,但用的可不是卷尺。The point of the project, which should be completed by 2014, is to allow Nepal to participate in international carbon-trading schemes that pay poor countries with lots of trees not to cut them down.该项目预计到2014年完成,其实际意义在于能够让尼泊尔参加国际碳交易计划。该计划向拥有大量树木的贫穷国家付资金,以确保其树木不被砍伐。The Reducing Emissions from Deforestation and Forest Degradation (REDD) scheme agreed at the ed Nations climate-change conference in Cancún last December may eventually be worth billion a year.联合国气候变化会议去年12月在墨西哥坎昆就减少砍伐森林和森林退化产生的排放计划(REDD)达成协议,确定每年最终可用于森林保护的资金达300亿美元。Nepal wants a slice of that.尼泊尔也想参与其中分得一杯羹。Lidar monitoring may provide a way of making sure it is delivering on its side of the bargain.激光雷达监测可能提供了一种方法,表明尼泊尔履行森林保护协议的决心。Until a few years ago, assessing the amount of plant matter in a forest in a cheap and accurate manner seemed an insurmountable problem, according to Eric Dinerstein, chief scientist of the World Wide Fund for Nature, a conservation group that is also involved in the Nepalese lidar project.环保组织世界自然基金会也参与了尼泊尔激光雷达项目的研究。其首席科学家埃里克(Eric Dinerstein)说,几年前,采用经济和准确的方法对植被数量进行评估似乎还是一项无法解决的难题。Although a woodlands area can be worked out from satellite photographs, that gives only a hazy idea of the mass of the plants growing there.尽管林地的面积能从卫星图片上得到,但它只能给提供我们生长在那里的大片植物的粗略情况。If Forest Resource Assessment Nepal and projects like it are successful, that will change.如果象尼泊尔森林资源评估这样的研究项目能够取得成功,情况就会大有不同。It will then be possible, with reasonable confidence, to pay REDD money out only to those countries that deliver the goods—or, rather, the trees—in sufficient, measurable quantities.我们将有充分理由相信REDD计划拨出的资金可能只会流向那些能够提供货真价实,或更确切的说,树木充足且数量可测量的国家。 /201212/213286

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