10.6 鸡精

billyisfragile!

是原文吗？

第一段：现在流行的几乎所有的显微镜，都有一个缺点：好像是通过镜片什么的来对焦，会有折射衍射之类的（defraction?反正就是测量珠峰那篇里面的那个词）。某个科学家，很早之前提出了一个方法来观察测量精密的atom之类的，但是一直无法实现，因为not until recently，才发现了能够达到那么高精度变化的物质（也就是说你可以让他只膨胀或者缩小1微微米那种，这样材料做出来的显微镜精度高）（这句话好像有题）

第一段说到了, 某种光的波长不在人类可以看到的波长之中, 所以某科学家提出了一个理论跟仪器, 但是在那时候无法制作出该仪器第二段说到了, 现在科技的进步导致该仪器已经产生.

Objects smaller than the wavelengths of visible light are a  staple of contemporary science and technology. Biologists study  single molecules of protein or DNA;  materials scientists examine atomicscale flaws in crystals; microelectronics engineers lay out circuit patterns  only a few tens of atoms thick. Until recently this minute world could  be seen only by cumbersome, often  destructive methods such as electron  microscopy and X-ray diffraction. It lay  beyond the reach of any instrument as  simple and direct as the familiar light  microscope.

A family of new microscopes opens  this realm to direct observation. The  devices can map atomic and molecular shapes, electrical, magnetic and  mechanical properties and even temperature variations at a higher resolution than ever before, without the  need to modify the specimen or expose it to damaging, high-energy radiation. The achievement seems implausible. More than 100 years ago, after  all, the German physicist and lensmaker Ernst Abbe described a fundamental limitation of any microscope  that relies on lenses to focus light or  other radiation: diffraction obscures  details smaller than about one half the  wavelength of the radiation.

第一段：光学显微镜有人说不给力，因为有折射什么会影响，然后1956年（大概是这时候）有人提出了一种理论可以解决这个问题，但还没办法通过这个理论制作新的显微镜，因为缺少能够精确定位的仪器还是技术来着（失忆了。。。但这里有题，看到文章很容易locate）

The new microscopes-typified by  the scanning tunneling microscope, for which Gerd Binnig and Heinrich  Rohrer of the IBM Zurich Research Laboratory received a Nobel prize in 1986-overcome this Abbe barrier with ease. The principle by which they  do so was first described in 1956. In that year]. A. O'Keefe, then of the U. S. Army Mapping Service, proposed a microscope in which light would  shine through a tiny hole in an opaque  screen, illuminating an object directly  in front of the screen. Light transmitted through the specimen or reflected  back through the hole would be recorded as the sample was scanned  back and forth. O'Keefe pointed out  that the resolution of such a "scanning near-field microscope" would be  limited only by the size of the hole and  not by the wavelength of the light. In  principle the device could make superresolving images-images showing  details smaller than half a wavelength.

O'Keefe acknowledged that technology capable of positioning and  moving an object with the needed precision did not exist. By resorting to  long-wavelength radiation, however,  Eric Ash of University College, London,  adopted the O'Keefe strategy in 1972  to circumvent the Abbe barrier. He  passed microwave radiation at a wavelength of three centimeters through a  pinhole-size aperture and scanned an  object in front of it to record an image  with a resolution of 150 microns-one  
two-hundredth of a wavelength.

By that time, means of controlling  sample position and movement with  the precision needed to surpass the  resolution of a conventional light microscope were becoming available. In  the same year as Ash's demonstration,  Russell D. Young of the National Bureau of Standards succeeded in manipulating objects in three dimensions with a precision of about a nanometer (a billionth of a meter). He relied  on piezoelectrics-ceramic materials that change size ever so slightly when  an electrical potential across the material is changed. Piezoelectric controls  opened the way to the development,  in 1981, of the supreme example of  a scanning near-field microscope, the  scanning tunneling microscope, or  STM [see "The Scanning Tunneling Microscope," by Gerd Binnig and Heinrich Rohrer; SCIENTIFIC AMERICAN, August, 1985).

第二段：说这个新型显微镜“XXX tunnelling microscope”的工作原理，这个显微镜就是通过control（大概就是支架）来控制一个probe，由于这种材料能够精密控制大小，这样能够让那个probe尽可能的贴近标本的表面，但是不接触。这样足够近的情况下，两边如果有电压，就会产生一个"tunnel"，实际就是两者的gap中产生电流了。（有题问tunnel是什么，就是the nature of currents between probe and specimen）这个电流的强度，是由probe和标本中物质粒子的距离决定的，probe会在整个标本上移动，当他经过一堆atom上时，电流就强，当他经过atom之间的相对空白的地方（想象两颗石子中间的空当），电流就弱，所以根据电流大小就可以知道这个标本的表面的形状。

In the STM the "aperture" is a tiny tungsten probe, its tip ground so  fine that it may consist of only a single atom and measure just .2 nanometer in width. Piezoelectric controls  maneuver the tip to within a nanometer or two of the surface of a conducting specimen-so close that the electron clouds of the atom at the probe  tip and of the nearest atom of the  specimen overlap. When a small voltage is applied to the tip, electrons  "tunnel" across the gap, generating  a minuscule tunneling current. The  strength of the current is exquisitely  sensitive to the width of the gap; typically it decreases by a factor of 10 each  time the gap is widened by .1 nanometer-half the diameter of an atom.

X and y piezoelectric controls  (which govern motion in the two dimensions of a plane) move the probe  back and forth across the specimen  surface in a raster pattern, its parallel  tracks separated by perhaps a fraction  of a nanometer. If the probe maintained a steady height, the tunneling  current would fluctuate dramatically, increasing as the tip passed over  bumps such as surface atoms and  falling to nothing as it crossed gaps  between atoms. Instead the probe  moves up and down in concert with  the topography. A feedback mechanism senses the variations in tunneling current and varies the voltage applied to a third, Z, control. The Z piezoelectric moves the probe vertically  to stabilize the current and maintain

橘子太软

bzy! 发表于 2018-10-6 16:07
https://forum.chasedream.com/thread-1324887-1-1.html

【考古】植物AP授粉

Mark一下！               

vegetableshu

Akiii 发表于 2018-10-6 15:55
先谢楼主~数学那道题真的是问占B的占比吗。。如果是问A&B占总体的占比，就是1/9
...

怎么算的呀，请问

Cris7

Akiii 发表于 2018-10-6 15:55
先谢楼主~数学那道题真的是问占B的占比吗。。如果是问A&B占总体的占比，就是1/9
...

占总体的比不是1/8吗？

OLIVIAHAN777

感谢分享！