Getting Wired with Nanowires
Nanowires are simply very tiny wires. They are composed of metals such as silver, gold, or iron, or semiconductors such as silicon, zinc oxide, and germanium. Nanoparticles are used to create these little nanowires, which can have a diameter as small as 3 nanometers.
Growing nanowires
The production of nanowires is similar to nanotubes; it requires using a catalyst particle in a heated reaction chamber. To grow nanowires composed of gallium-nitride, researchers at Harvard University flow nitrogen gas and vaporized gallium through the reaction chamber containing an iron target. Iron nanoparticles are vaporized from the target by a laser to act as a catalyst. Both gallium and nitrogen molecules dissolve in the iron nanoparticle. When you get so much
gallium and nitrogen in the particle that it starts to sweat off of the surface, molecules precipitate onto the surface of the particle where they combine to grow the nanowire.
When you grow any nanowire, the materials you use must be soluble in the catalyst nanoparticle. For example, to grow silicon nanowires, a gold catalyst nanoparticle is used because silicon dissolves in gold.
To grow arrays of nanowires — great for making electronic devices or sensors — you can use catalyst nanoparticles positioned on a solid substrate, rather than nanoparticles in a vapor. For example, researchers at the National Institute of Standards and Technology have used gold nanoparticles on a sapphire surface as catalysts to grow arrays of nanowires composed of zinc oxide. By changing the size of the gold nanoparticles, they are abie to control whether the nanowires grow tilted vertically at a 60-degree angle up from the surface, or horizontally along the surface.
Nanowires at work
Several research groups have demonstrated the use of nanowires to create memory devices and transistors. Researchers at Hewlett-Packard and the University of California at Los Angeles have demonstrated that a memory cell can be formed at the intersection of two nanowires. Using a somewhat more complicated array of nanowires, they have also come up with a transistor-like device called a crossbar latch.
Folks at the University of Southern California and the NASA Ames Research Center have demonstrated a memory device that uses indium oxide nanowires. They are predicting that this device will be able to store 40 gigabits per square centimeter, which is a lot of data by anybody's standards.
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Sail E-way: Spacecraft Riding the Solar Wind on Electric-Field Sails Could Cruise at180,000Kph
By Steven Ashley
A sail formed not of material, but by electric fields reaching a diameter of 40 kilometers could tap the solar wind and propel the fastest man-made object ever.
VIRTUAL SAIL: The electric solar wind sail, or e-sail, concept offers the opportunity to field truly enormous virtual sails as much as 40 kilometers across, possibly enabling the development of the fastest man-made objects ever flown perhaps at speeds around 50 kilometers per second, Janhunen says.
It takes large quantities of rocket fuel to power space probes through the cosmos. So much so that many long-range missions, including exploratory voyages to the outer planets and beyond, are typically impractical or too time-consuming to contemplate carrying out using conventional rocket motors. To address the problem, scientists have developed ingenious alternative propulsion systems such as ion-drive technologies that require much less propellant than standard chemical rockets but, nonetheless, travel much faster over time. But even ion thrusters have limitations.
What if spacecraft could traverse our solar system or even interstellar space at yet greater velocities using no propellants at all? Such is the allure of solar sails—large, ultrathin mirrors that harness the faint pressure of the sun's reflected light to move through the vacuum of space. It is no wonder then that engineers at NASA and the Japan Aerospace Exploration Agency (JAXA) are now flight-testing prototypes of these photon- propelled solar sails—dubbed, respectively, NanoSail-D and IKAROS.
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Dark Energy, Dark Matter
In the early 1990's one tiling was fairly certain about the expansion of the Universe. It might have enough energy density to .stop its expansion and recollapse. It might have so little energy density that it would never stop expanding, but gravity was certain to slow the expansion as time went on. Granted, the slowing had not been observed, but theoretically, the Universe had to slow. The Universe is lull of matter and the attractive force of gravity pulls all matter together. Then came 1998 and the Hubble Space Telescope (UST ) observations of very distant supernovae that showed that, a long time ago, the Universe was actually expanding more slowly than it is today. So the expansion of the Universe has not been slowing due to gravity, as everyone thought, it has been accelerating. No one expected this, no one knew how to explain it. Bui something was causing it.
Eventually theorists came up with three sorts of explanations. Maybe it was a result of a long-discarded version of Einstein's theory of gravity, one that contained what was called a "cosmological constant." Maybe there was some strange kind of energy-fluid that filled space. Maybe there is something wrong with Einstein's theory of gravity and a new theory could include some kind of field that creates this cosmic acceleration. Theorists still don't know what the correct explanation is, but they have given the solution a name. It is called dark energy.
What is Dark Energy?
More is unknown than is known. We know how much dark energy there is because we know how it affects the Universe's expansion. Other than that, it is a complete mystery. But it is an important mystery. It turns out that roughly 70% of the Universe is dark energy. Dark matter makes up about 25%. The rest - everything on Earth, everything ever observed with all of our instruments, all normal matter - adds up to less than 5% of the Universe. Come to think of it. Maybe it shouldn't be called "normal" matter at all, since it is such a small fraction of the Universe.
One explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood. The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein's gravity theory, the version that contains a cosmological constant makes a second prediction: "empty space" can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear. As a result, this form of energy would cause the Universe to expand faster and faster. Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the Universe. .Another explanation for how space acquires energy comes from the quantum theory of mailer. In this theory, "empty space" is actually full of temporary ("virtual") particles that continually form and then disappear. But when physicists tried to calculate how much energy this would give empty space, the answer came out wrong - wrong by a lot. The number came out 10120 times too big. That's a 1 with 120 zeros after it. It's hard to get an answer that bad. So the mystery continues.
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