The shotgun marriage of chemistry and engineering called \"Nanotechnology\" is ushering in the era of self-replicating machinery and self-assembling consumer goods made from cheap raw atoms.
Nanotechnology is molecular manufacturing or, more simply, building things one atom or molecule at a time with programmed nanoscopic robot arms. A nanometer is one billionth of a meter ( 3-4 atoms wide ). Utilizing the well understood chemical properties of atoms and molecules ( how they \" stick\" together) , nanotechnology proposes the construction of novel molecular devices possessing extraordinary properties. The trick is to manipulate atoms individually and place them exactly where needed to produce the desired structure. This ability is almost in our grasp. The anticipated payoff for mastering this technology is far beyond any human accomplishment so far. Technical feasibilities include:
• Self-assembling consumer goods •Computers billions of times faster
• Extremely novel inventions (impossible today) • Safe and affordable space travel
• Medical Nano... virtual end to illness, aging, death
• No more pollution and automatic cleanup of already existing pollution • Molecular food syntheses... end of famine and starvation • Access to a superior education for every child on Earth • Reintroduction of many extinct plants and animals • Terra forming here and the Solar System By treating atoms as discrete, bit-like objects, molecular manufacturing will bring a digital
revolution to the production of material objects. Working at the resolution limit of matter, it will enable the ultimate in miniaturization and performance. By starting with cheap, abundant t
components - molecules - and processing them with small, high-frequency, high-productivity machines, it will make products inexpensive. Design computers that each executes more
What Is Nanotechnology?
The shotgun marriage of chemistry and engineering called \"Nanotechnology\" is ushering in the era of self-replicating machinery and self-assembling consumer goods made from cheap raw atoms.
Nanotechnology is molecular manufacturing or, more simply, building things one atom or molecule at a time with programmed nanoscopic robot arms. A nanometer is one billionth of a meter ( 3-4 atoms wide' ). Utilizing the well understood chemical properties of atoms and molecules ( how they \"stick\" together), nanotechnology proposes the construction of novel molecular devices possessing extraordinary properties. The trick is to manipulate atoms individually and place them exactly where needed to produce the desired structure. This ability is almost in our grasp. The anticipated payoff for mastering this technology is far beyond any human accomplishment so far. Technical feasibilities include:
• Self-assembling consumer goods • Computers billions of times faster
• Extremely novel inventions (impossible today) • Safe and affordable space travel
• Medical Nano... virtual end to illness, aging, death
• No more pollution s and automatic cleanup of already existing pollution • Molecular food syntheses... end of famine and starvation • Access to a superior education for every child on Earth • Reintroduction of many extinct plants and animals • Terra forming here and the Solar System By treating atoms as discrete, bit-like objects, molecular manufacturing will bring a digital
revolution to the production of material objects. Working at the resolution limit of matter, it will enable the ultimate in miniaturization and performance. By starting with cheap, abundant components --
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molecules -- and processing them with small, high-frequency, high-productivity machines, it will make products inexpensive. Design computers that each executes more instructions per second than all of the semiconductor CPUs in the world combined. Nanotechnology will reverse the harm done by the industrial revolution. Imagine being able to cure cancer by drinking a medicine stirred into your favorite fruit juice. Imagine a supercomputer no bigger than a human cell. Imagine a four-person, surface-to-orbit spacecraft no larger or more expensive than the family car. These are just a few products expected from nanotechnology.
Humanity will be faced with a powerful, accelerated social revolution as a result of nanotechnology. In the near future, a team of scientists will succeed in constructing the first nano-sized' robot capable of self-replication. Within a few short years, and five billion trillion nano-robots later, virtually all present industrial processes will be obsolete as well as our contemporary concept of labor. Consumer goods will become plentiful, inexpensive, smart, and durable. Medicine will take a quantum leap forward. Space travel and colonization will become safe and affordable.
For these and other reasons, global life styles will change radically and human behavior will be drastically impacted. The world is on the brink of a new technological revolution beyond any human experience. A new, more powerful industrial revolution capable of bringing wealth, health, and education, without pollution, to every person on the planet. No longer will forest need to be cut or smoke spewed into the air. This is the promise of nanotechnology.
A nanometer is one billionth of a meter. That's a thousand, million times smaller than a meter. If you blew up a baseball to the size of the earth, the atoms would become visible, about the size of grapes. Some 3-4 atoms fit lined up inside a nanometer.
Nanotechnology is about building things atom by atom, molecule by molecule. The trick is to be able to manipulate atoms individually, and place them where you wish on a structure. Nature uses molecular machines to create life. If you want to see a nanotechnology machine, just look in the mirror. Scientists from several fields including chemistry, biology. physics, and electronics are driving towards the precise manipulation of matter on the atomic scale.
How do we get to nanotechnology? Several approaches seem feasible. Ultimately a combination may be the key.
悬索桥
人们常常愿意修建悬桥以代替其他类型的桥梁,特别是在那些运输量比较小而桥的跨度又大的地方。因为悬桥不仅节约材料,而且强度也非常大。现在已经有了主跨超过3000英尺的悬桥,而整个桥面的重量都是由从河的两岸的桥塔悬挂下来的钢缆(一般只有两到四根)从上方来支持的。。
钢缆由几千根具有很高抗拉强度的钢丝组成,这种钢丝均经过了电镀以防止锈蚀。这种钢丝每根直径0.19英寸左右,两三百根夹紧扎在一起,成为一股钢丝绳,而整个钢缆可能是由相当数量的这样的钢丝绳紧密结合并用钢丝捆在一起而组成的。在制造钢缆时,可以采用两种不同的方法:一种是把钢丝绞合成股绳,然后再把这些股绳缠绕在中心股绳上面而形成完整的钢缆;另一种是把钢丝绳相互平行地编起来,然后每隔一段距离把它们夹在一起。后面这种办法显然需要涉及更长的编排操作,因为每根钢丝或每小股钢丝都必须加以编排,并且一股股一根根地调整到适当的下垂度。而绞合的钢丝股绳则可以作为整体一次性安装起来,只要它们不至于重得难以处理。但是相对大跨度的桥梁而言,用平行编排法编制钢缆也有某些优点。
钢缆一般是连续不断的,通过桥塔塔顶,向下穿过侧塔(在有侧塔的那些地方),然后再从侧塔,穿越到缆桩。。钢缆支放在桥塔上专门建造的鞍座上,鞍座的形状造得适合钢缆使用。鞍座可以是固定的,这样钢缆可以在它上面滑动,也可以安装在滚柱上,这样鞍座就会随着钢缆的移动而移动。。考虑到重型钢缆施加的巨大的拉力,它们的末端必须固定在牢固的缆墩上,而且除非钢缆末端埋置在坚固的天然岩石里,否则就必须建造圬工或混凝土桩,其强度要足以承受加在它上面的沉重的压力,钢缆股绳通常是绕套在股绳桩靴上,而桩靴又用键条连接到埋置在缆墩底部的锚定板上。
沿着主桥跨,每隔一段距离,就在钢缆上加上铸钢缆箍,紧紧地夹住钢缆,防止钢缆受潮,而且从缆箍悬下钢丝绳或链条组成的吊索。由于这些吊索必须承受它们所连接的桥面的重量,因此它们必须具有很大的抗拉强度。之所以使用这种加固链条的吊索是因为它们大多可以省除加劲装置,因为这种吊索本身刚度很大。一般说来,防止桥面由于车辆货物的运动和风侧吹而变形是很有必要的。而在使用钢丝绳吊索的情况下,必须在桥面上建造桁架进行加劲.桁架的高度随桥跨的长度而定.
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