Thursday, January 6, 2011
1/06/2011 05:02:00 AM Publicado por Alquimia
Just as walkie-talkies transmit and receive radio waves, carbon nanotubes can transmit and receive light at the nanoscale, Cornell researchers have discovered.
Carbon nanotubes, cylindrical rolled-up sheets of carbon atoms, might one day make ideal optical scattering wires -- tiny, mostly invisible antennae with the ability to control, absorb and emit certain colors of light at the nanoscale, according to research led by Jiwoong Park, Cornell assistant professor of chemistry and chemical biology. The study, which includes co-author Garnet Chan, also in chemistry, is published online Dec. 19 in the journal Nature Nanotechnology. The paper's first author is Daniel Y. Joh, a former student in Park's lab.
The researchers used the Rayleigh scattering of light -- the same phenomenon that creates the blue sky -- from carbon nanotubes grown in the lab. They found that while the propagation of light scattering is mostly classical and macroscopic, the color and intensity of the scattered radiation is determined by intrinsic quantum properties. In other words, the nanotubes' simple carbon-carbon bonded molecular structure determined how they scattered light, independent of their shape, which differs from the properties of today's metallic nanoscale optical structures.
"Even if you chop it down to a small scale, nothing will change, because the scattering is fundamentally molecular," Park explained.
They found that the nanotubes' light transmission behaved as a scaled-down version of radio-frequency antennae found in walkie-talkies, except that they interact with light instead of radio waves. The principles that govern the interactions between light and the carbon nanotube are the same as between the radio antenna and the radio signal, they found.
To perform their experiments, the researchers used a methodology developed in their lab that completely eliminates the problematic background signal, by coating the surface of a substrate with a refractive index-matching medium to make the substrate "disappear" optically, not physically. This technique, which allowed them to see the different light spectra produced by the nanotubes, is detailed in another study published in Nano Letters.
The technique also allows quick, easy characterization of a large number of nanotubes, which could lead to ways of growing more uniform batches of nanotubes.
(Photo: Shivank Garg)
1/06/2011 05:01:00 AM Publicado por Alquimia
They're the little white lies we tell to save face or other people's feelings -- the "I'm on my way" text messages or "Got to go, phone's ringing" excuses during online chat sessions.
Cornell communication professors Jeff Hancock and Jeremy Birnholtz call them "butler lies," in honor of the personal assistants of yore who would provide a buffer when unwelcome guests turned up at the door.
Nowadays, we tend to rely on technology to serve this purpose, such as making excuses about needing to get offline when we don't actually have to.
In fact, Hancock has found that up to 10 percent of text messages contain lies, and one-fifth of those are butler lies.
But such lies are hard to hide when GPS cell phone apps publish every movement, and friends post about activities on Facebook for an entire extended network to see. So is technology doing enough to help maintain privacy?
With the help of a $460,000 grant from the National Science Foundation and a small army of student researchers, the Cornell communications duo is studying how people manage their availability using modern technology and whether they can design new ways to help them do so. In their opinion, lying isn't necessarily a bad thing, and some relationships can benefit from a bit of privacy.
And although most of us are aware and accept that we are occasionally being lied to, we are not very good at identifying which messages are lies, he said.
"A lot of the lying that we end up doing is about managing how people interact with us," Hancock said. "We are telling narratives of our lives, and we are telling different narratives to different people. Right now, that narrative is leaky and can get messed up very easily."
So how do we manage it?
Many take advantage of the ambiguity that technology provides to cloak their activities, such as setting their instant messenger status to "away" or "busy" to avoid conversations -- even though that is a lie, and in reality they are sitting inches away from the screen, busy playing solitaire.
Birnholtz believes the widespread use of lies suggests that people are resorting to social solutions because there are insufficient technical solutions. That, in turn, indicates a need for more controls or features to help people manage their personal relationships.
By doing a linguistic analysis of the deceptive messages, Birnholtz said he might be able to design a program that could predict when someone wants information to be shared or protected.
Some of his students are doing related research into how the butler lies vary from country to country, based on the plausibility of particular excuses in different cultures.
And the pair also has funding from Google to study technology-enabled deceptions in the workplace, such as manipulating the "track changes" function in word-processing software to selectively hide or highlight edits in group documents.
"Our social conventions have evolved over 60,000 years. Facebook has been around for six," Hancock said. "I think this is where a lot of the confusion comes from."
(Photo: Cornell U.)
1/06/2011 05:01:00 AM Publicado por Alquimia
If you’ve ever bathed a dog, you know firsthand how quickly a drenched pup can shake water off.
Now researchers at the Georgia Institute of Technology are studying the physics of the wet dog shake to possibly improve the efficiency of washing machines, dryers, painting devices, spin coaters and other machines.
David Hu, assistant professor of mechanical engineering at Georgia Tech, and mechanical engineering graduate student Andrew Dickerson, who led the project, recently captured 40 different animals – 13 species in total – using high-speed videography along with X-ray cinematography to see the details of how a mammal shakes itself dry.
The new research was presented at the 63rd annual meeting of the American Physical Society’s Division of Fluid Dynamics last month.
"We hope the findings from our research will contribute to technology that can harness these efficient and quick capabilities of drying seen in nature,” Dickerson said.
The Georgia Tech researchers found that animals oscillate at frequencies sufficient to lose water droplets and that shaking frequency is a function of animal size.
The larger the animal, the more slowly it shakes dry, Hu and Dickerson said. For example, a mouse moves its body back and forth 27 times per second, but a grizzly bear shakes four times per second. The tinier mammals can experience more than 20 g’s of acceleration.
Mammals with fur, unlike humans, tend to have loose skin that whips around as the animal changes direction, increasing the acceleration. This is crucial to shaking success, and subsequently, body heat regulation, Dickerson said.
“What would you do on a cold day if you were wet and could not towel off or change clothes? Every warm-blooded furry creature faces this dilemma often,” Dickerson said. “It turns out that oscillatory shaking exhibited by mammals is a quite efficient way to dry.”
Hu and Dickerson will continue to look at how animals interact with water in the natural world. Specifically, the researchers want to investigate how animals, such as beavers and otters, have adapted to life in the water and how water droplets interact with hair.
Georgia Institute of Technology
1/06/2011 05:00:00 AM Publicado por Alquimia
A psychology professor has found that the way people perceive the Silhouette Illusion, a popular illusion that went viral and has received substantial online attention, has little to do with the viewers’ personality, or whether they are left- or right-brained, despite the fact that the illusion is often used to test these attributes in popular e-quizzes.
Niko Troje says that a reported preference for seeing the silhouette spinning clockwise rather than counter-clockwise is dependent upon the angle at which the viewer is seeing the image.
“Our visual system, if it has a choice, seems to prefer the view from above,” says Dr. Troje. “It’s a perceptual bias. It makes sense to assume that we are looking down onto objects that are located on the ground below us rather than floating in the air above us.”
In the Silhouette Illusion, a silhouetted woman is seen spinning on one foot, her leg extended. The appeal of the illusion is in the way the woman is spinning – she can be perceived as spinning clockwise or counter-clockwise.
Dr. Troje and his team found that a view-from-above bias (VFA) is what makes the viewer prone to seeing the silhouette in a certain way, not one’s personality or whether the viewer is left- or right-brained. When shown the silhouette illusion, the study’s 24 participants most often reported that the woman was spinning counter-clockwise if viewed from above, and clockwise if viewed from below. Thus, the viewing angle causes the difference in perception.
The theory can also be applied to other popular illusions, including Neckar Cubes, that are often used in online personality tests.
The study was published in i-Perception, the new open-access sister journal of the established British journal Perception.
(Photo: Biomotion Lab.)
1/06/2011 04:59:00 AM Publicado por Alquimia
An asteroid discovered more than 100 years ago my not be an asteroid at all, but an extinct comet that is coming back to life, according to new observations.
The night of Dec. 11, Steve Larson, senior staff scientist with the Catalina Sky Survey, was searching for potentially hazardous asteroids when he came across what looked like a comet: a faint, wispy tail surrounding a bright, star-like core. Four images taken over the course of 30 minutes revealed the object was moving relative to the background stars.
"Its brightness of a total magnitude of 13.4 visual, which is about 900 times fainter than the faintest star you can see in a clear, dark sky, led me to suspect that it was a known comet, but I checked the comet database and got nothing," Larson said.
According to Larson, comets are thought to be a major source of Earth's water, and "extinct" comets may be useful resources for space exploration.
Further investigation revealed that the object was a known asteroid called (596) Scheila, discovered in 1906. The extraterrestrial rock is tumbling through space alongside thousands of similar objects in our solar system's main asteroid belt, roughly between the orbits of Mars and Jupiter, out of the ecliptic plane in which most planets and asteroids travel.
Catalina Sky Survey team member Alex Gibbs checked previous images in the survey's archives but found no activity until Dec. 3. At that time, the object appeared brighter and slightly diffuse.
Previous analysis of (596) Scheila's color indicated that it is composed of primitive carbonaceous material left over from the formation of the solar system and might be an extinct comet.
After the discovery was announced, the astronomical community responded by pointing many of the world's largest telescopes at the object to obtain images and spectra to determine if its tail consists of ice and gases spewing out of the body or if it is dust left behind from a collision with another asteroid. Preliminary spectra of the outburst show that the coma surrounding the asteroid is composed of dust, but more observations will be needed to understand just what is happening with (596) Scheila.
"Most asteroids are collision fragments from larger asteroids and display a range of mineral composition," Larson explained. "But a fraction are thought to be former comets whose volatile ices have been driven off by the sun. If the activity in Scheila proves to be cometary in nature, this will be only the sixth known main-belt comet, and about 100 times larger than previously identified main belt comets."
In 1998, Larson founded the Catalina Sky Survey, a NASA-supported project to discover and catalog Earth-approaching and potentially hazardous asteroids. It operates two telescopes in the Catalina Mountains and one in Australia and is currently discovering 70 percent of the world's known near-Earth objects, including one that fell in northern Sudan in 2008.
(Photo: Alex Gibbs and Steve Larson)
The University of Arizona
1/06/2011 04:59:00 AM Publicado por Alquimia
Innowattech the Israeli company that made news last year when it unveiled a method for harvesting electricity from roads is at it again. This time, the company co-founded by Technion Professor Haim Abramovich is testing its piezoelectric technology on railroad tracks.
In conjunction with Israel’s National Railway Company, the company replaced 32 existing railroad pads with Innowattech’s electricity-generating pads to measure how well they produce electricity. The technology is based upon the piezoelectric effect, the production of electricity that occurs when certain materials - including crystals and some ceramics - are deformed.
“Our pads contain piezoelectric disks, which can transform mechanical stresses into electrical output (voltage),” says Abramovich. “As a result, not only can we harvest energy, we can also gather information that includes train speed, the number of wheels on the train, weight of each wheel, wheel diameter, and wheel perimeter position.
According to Abramovich, preliminary results suggest that areas of railway track that get between 10 and 20 ten-car trains an hour can produce 120 KWh of renewable energy per hour, which could be used to help power trains and/or signals, or be routed to the power grid for use elsewhere.
Innowattech is based in Ra'anana, Israel, with research facilities at the Technion-Israel Institute of Technology. The privately held company specializes in the development of custom piezoelectric generators for specific purposes.