- New Compass Uses Light Beams to Detect Magnetic Field
- Gigantic Spider Webs Made of Silk Tougher Than Kevlar
- Adaptive Traffic Lights Could Achieve ‘The Green Wave’
Posted: 20 Sep 2010 03:22 PM PDT
A compass made of light promises to be more sensitive than anything in a Boy Scout's wildest dreams. A light beam shot through a blob of rubidium atoms can directly and reliably measure the size and orientation of a magnetic field, a team of physicists reports in the Sept. 13 Physical Review A.
These compasses are very good at finding the size of a magnetic field, but typically have to be tweaked to include a built-in local reference magnetic field so that they can also find the field's direction. This comparison of the external field to an internal reference allows the compass to reconstruct the magnetic field, but the quality of the data can vary greatly, says study co-author Alexander Zibrov of Harvard University.
Zibrov and his colleagues wanted to create a compass that could directly pinpoint the direction and the size of a magnetic field. To do that, they relied on a technique that used a magnetically sensitive cloud of atoms and a laser. In their experiment, the team trapped rubidium-87 atoms at 113 degrees Fahrenheit in a domino-sized chip and shined linearly polarized light into the atoms. The light was filtered so that it had the same direction, like the light that makes it through polarized sunglasses.
In the presence of a magnetic field, the atoms' orientation changed in a particular way, and this change was detectable in the light that came through the atom cloud, the team found. This change in transmission allowed the researchers to find the size and direction of the magnetic field at the same time.
Other compasses based on lasers and atoms exist, Zibrov says, but those rely on circularly polarized light and other ways to excite the atoms, and require fancy mathematical models to reconstruct the magnetic field after the measurement has been taken.
In the experiment, the compass detected magnetic fields with a strength between 0.1 gauss, which is less than the Earth's magnetic field, and 200 gauss, which is stronger than a small iron magnet. The authors write that the performance can be adjusted with design tweaks such as changes to the temperature and size of the chip.
The new study is "a nice piece of work," says physicist Szymon Pustelny of Jagiellonian University in Kraków, Poland. Although the physics behind the new compass is largely known, "they succeeded in showing its nice application," he says.
Compared to earlier models, the new compass is more robust against interfering noise coming from random collisions between the atoms and other sources, says study co-author Valera Yudin of the Institute of Laser Physics in Novosibirsk, Russia. What's more, these compasses would be small and would consume very little energy.
But before the optical compass appears strapped to Scouts' belts, the lab prototype must be tested in the field. "To talk about real applications," Pustelny cautions, "a lot of work needs to be done."
Posted: 20 Sep 2010 12:42 PM PDT
A spider discovered deep in the jungles of Madagascar spins the largest webs in the world, using silk that's tougher than any known biological substance.
Named Caerostris darwini, or Darwin's bark spider, the inch-wide arachnid's webs can cover 30-square-foot areas, hanging in midair from 80-foot-long anchor lines.
The webs' size generates enormous structural stresses, magnified by the struggles of trapped prey. Strands must "absorb massive kinetic energy before breaking," and are "10 times better than Kevlar," wrote University of Puerto Rico zoologist Igni Agnarsson in Public Library of Science One.
Agnarsson and Slovenian Academy of Sciences biologist Matjaž Kuntner discovered C. darwini in 2008. It's similar in many ways to Caerostris species found in Africa, but those spiders live at the edges of forest clearings. In Madagascar, where animals have taken kaleidoscopic forms since the island split from mainland Africa 165 million years ago, C. darwini evolved to exploit the airspace above streams and rivers.
A few other spiders build stream-side webs, but none "routinely utilize as habitat the air column immediately above sizeable rivers and up to several meters above water," wrote Agnarsson and Kuntner in an August Journal of Arachnology article. The spiders' superior gossamer likely evolved in tandem with C. darwini's migration to Madagascar's rivers, and is twice as elastic as silk from other web-weaving spiders.
That elasticity is key to the silk's toughness, and its molecular underpinnings remain to be studied. The researchers also plan to study how C. darwini build their webs, likely by casting threads that drift over water and catch branches on distant shores, providing a central structural element.
Another intriguing question is how these relatively small spiders maintain such immense, energetically taxing structures. The webs certainly provide rich sources of food; Agnarsson and Kuntner witnessed catches of dozens of insects at a time. They didn't see the spiders catch birds or bats, but say it's possible.
By the time these questions are answered, some other spider may hold the World's Toughest Material title. The researchers point out that there are more than 40,000 arachnid species, manufacturing some 200,000 types of silk. Scientists have studied only a few dozen.
Images: 1) Man looking at C. darwini web and a C. darwini female./Journal of Arachnology. 2) C. darwini webs spanning a Madagascar river./Public Library of Science One.
Citations: "Bioprospecting Finds the Toughest Biological Material: Extraordinary Silk from a Giant Riverine Orb Spider." By Ingi Agnarsson, Matjaž Kuntner, Todd A. Blackledge. PLoS One, Vol. 5 No. 9, September 16, 2010.
"Web gigantism in Darwin's bark spider, a new species from Madagascar (Araneidae: Caerostris)." By Matjaž Kuntner and Ingi Agnarsson. Journal of Arachnology, Vol. 38 Issue 2, August 2010."
Posted: 20 Sep 2010 07:46 AM PDT
Traffic lights that act locally can improve traffic globally, new research suggests. By minimizing congestion, the approach could save money, reduce emissions and perhaps even quash the road rage of frustrated drivers.
The new approach makes traffic lights go with the flow, rather than enslaving drivers to the tyranny of timed signals. By measuring vehicle inflow and outflow through each intersection as it occurs and coordinating lights with only their nearest neighbors, a system-wide smoothness emerges, scientists report in a September Santa Fe Institute working paper.
"It's very interesting — the approach is adaptive and the system can react," says mechanical engineer Gábor Orosz of the University of Michigan in Ann Arbor. "That's how it should be — that's how we can get the most out of our current system."
An ultimate goal in traffic regulation is "the green wave," the bam, bam, bam of greens that allows platoons of vehicles to move smoothly through intersection after intersection. When that happens, no drivers have to wait very long and sections of road don't become so filled with cars that there's no room for entering vehicles when the light does go green.
To achieve this rare bliss, traffic lights usually are controlled from the top down, operating on an "optimal" cycle that maximizes the flow of traffic expected for particular times of day, such as rush hour. But even for a typical time on a typical day, there's so much variability in the number of cars at each light and the direction each car takes leaving an intersection that roads can fill up. Combine this condition with overzealous drivers, and intersections easily become gridlocked. Equally frustrating is the opposite extreme, where a driver sits at a red light for minutes even though there's no car in sight to take advantage of the intersecting green.
"It is actually not optimal control, because that average situation never occurs," says complex-systems scientist Dirk Helbing of the Swiss Federal Institute of Technology Zurich, a co-author of the new study. "Because of the large variability in the number of cars behind each red light, it means that although we have an optimal scheme, it's optimal for a situation that does not occur."
Helbing and his colleague Stefan Lämmer from the Dresden University of Technology in Germany decided to scrap the top-down approach and start at the bottom. They noted that when crowds of people are trying to move through a narrow space, such as through a door connecting two hallways, there's a natural oscillation: A mass of people from one side will move through the door while the other people wait, then suddenly the flow switches direction.
"It looks like maybe there's a traffic light, but there's not. It's actually the buildup of pressure on the side where people have to wait that eventually turns the flow direction," says Helbing. "We thought we could maybe apply the same principle to intersections, that is, the traffic flow controls the traffic light rather than the other way around."
Their arrangement puts two sensors at each intersection: One measures incoming flow and one measures outgoing flow. Lights are coordinated with every neighboring light, such that one light alerts the next, "Hey, heavy load coming through."
That short-term anticipation gives lights at the next intersection enough time to prepare for the incoming platoon of vehicles, says Helbing. The whole point is to avoid stopping an incoming platoon. "It works surprisingly well," he says. Gaps between platoons are opportunities to serve flows in other directions, and this local coordination naturally spreads throughout the system.
"It's a paradoxical effect that occurs in complex systems," says Helbing. "Surprisingly, delay processes can improve the system altogether. It is a slower-is-faster effect. You can increase the throughput — speed up the whole system — if you delay single processes within the system at the right time, for the right amount of time."
The researchers ran a simulation of their approach in the city center of Dresden. The area has 13 traffic light–controlled intersections, 68 pedestrian crossings, a train station that serves more than 13,000 passengers on an average day and seven bus and tram lines that cross the network every 10 minutes in opposite directions. The flexible self-control approach reduced time stuck waiting in traffic by 56 percent for trams and buses, 9 percent for cars and trucks, and 36 percent for pedestrians crossing intersections. Dresden is now close to implementing the new system, says Helbing, and Zurich is also considering the approach.
Traffic jams aren't just infuriating, they cost time and money, says Orosz. Estimates suggest that in one year, the U.S. driving population spends a cumulative 500,000 years in traffic at a cost of about $100 billion. And the roads are just going to get more congested. The optimal way of dealing with such congestion is to take an approach like Helbing's and combine it with technologies that deal with driver behavior, Orosz says. Car sensors that detect the distance between your bumper and the car in front of you can prevent a sweep of brake-slamming that can tie up traffic, for example.
"In general these algorithms improve traffic, but maybe not as much as they do on paper because we are still human," he says. "It is still humans driving the cars."
|You are subscribed to email updates from Johnus Morphopalus's Facebook notes |
To stop receiving these emails, you may unsubscribe now.
|Email delivery powered by Google|
|Google Inc., 20 West Kinzie, Chicago IL USA 60610|