The polar bear is much older than previously louis vuitton shoes thought, according to new genetic evidence.
DNA studies suggest the Arctic predator split from its ancestor, the brown bear, about 600,000 years ago.
Previous estimates put the polar bear at about 150,000 years old, suggesting the mammal adapted very rapidly to Arctic life.
Conservationists say the new study, published in Science, has implications for bear conservation.
Polar bears are listed as threatened under the US gucci sunglasses Endangered Species Act.
Conservationists say their survival is at risk, mainly due to the loss of the Arctic sea ice on which they spend much of their lives.
Dr Frank Hailer of the German Biodiversity and Climate Research Centre in Frankfurt, who led the international study, said the genetic information shed new light burberry outlet on conservation issues.
"It fundamentally changes our understanding of polar bears and their conservation today," he told BBC News.
"They have survived previous warm phases but they carry scars from these times - they must have been close to extinction at times."
Nuclear DNA
The researchers looked at DNA from modern bears to study the history of the species, analysing genetic information from the cell nucleus of more than 40 brown, black and polar bears.
Past work has relied mainly on mitochondrial DNA, the burberry bags fragments of genetic material contained within tiny cell components called mitochondria.
The latest findings suggest the polar bear evolved in the mid Pleistocene, about 600,000 years ago. This scenario paints a new picture of the bear's evolutionary history.
The mammal would have had more time to colonise and adapt to life in the high Arctic, and lived through various cycles of warming and cooling.
The polar bear's lack of genetic louis vuitton handbags diversity suggests that changes in the environment, such as warm phases, led to dramatic falls in numbers at times.
The researchers say polar bears face many other threats to their survival today, including habitat destruction, hunting and the effects of environmental pollutants.
Writing in Science, they explain: "Although polar bears oakley sunglasses have persisted through previous warm phases, multiple human-mediated stressors (eg habitat conversion, persecution, and accumulation of toxic substances in the food chain) could magnify the impact of current climate change, posing a novel and likely profound threat to polar bear survival."
Commenting on the research, Dr Steven Amstrup, chief scientist of Polar Bears International, said he suspected the age of the polar bear was Cheapest louis vuitton men t shirts sale white 2012 not entirely settled yet.
Even if they did split from their ancestor 600,000 years ago, they would have lived through only two periods noticeably warmer than today, he said, and spent most of their existence in cooler times.
He added: "It's continuing evidence that polar bears are monster beats solo adapted to a cold environment and they haven't experienced anything of the warming that we are likely to experience in the next 100 years."
2012年4月19日星期四
2012年4月18日星期三
Active galactic nuclei are big
The mystery of the origin of the strongest cosmic rays louis vuitton shoes has deepened as new clues into key suspects, the most powerful explosions in the universe, suggest they are likely not potential culprits, researchers say.
Cosmic rays are charged subatomic particles that streak to Earth from deep in outer space. A few rare cosmic rays are extraordinarily powerful, with energies up to 100 million times greater than any attained by human-made particle colliders, such as CERN's Large Hadron Collider. The sources of these cosmic rays are a mystery.
"Nature is capable of accelerating elementary particles to gucci sunglasses macroscopic energies," said study co-author Francis Halzen at the University of Wisconsin-Madison, principal investigator at the IceCube Neutrino Observatory, a massive telescope designed to find the tiny subatomic particles. "There are basically only two ideas on how she does this — in gravitationally driven particle flows near the supermassive black holes at the centers of active galaxies, and in the collapse of stars to a black hole, seen by astronomers as gamma-ray bursts."
Gamma-ray bursts are the most powerful explosions in the universe. They can emit as much energy as our sun during its entire 10-billion-year lifetime in anywhere from milliseconds to minutes.
"Some gamma-ray bursts are thought to be collapses of supermassive stars — hypernovas — while others are thought to be collisions of black holes with other black holes burberry outlet or neutron stars," said study co-author Spencer Klein of the U.S. Department of Energy's Lawrence Berkeley National Laboratory. "Both types produce brief but intense blasts of radiation."
New evidence may now rule out gamma-ray bursts as sources of these ultra-high-energy cosmic rays.
Researchers employed the IceCube neutrino detector, an array of thousands of detectors encompassing a cubic kilometer of clear Antarctic ice at the South Pole. Neutrinos are ghostly particles that often pass right through matter, only rarely striking atoms.
"This is a coming-of-age for neutrino astronomy burberry bags — the first time we're able to use neutrino data as a new way of looking at astrophysical objects and say something substantive about them," said study co-author Nathan Whitehorn, a physicist at the University of Wisconsin-Madison, who led the recent gamma-ray burst research with Peter Redl of the University of Maryland.
The investigators focused on neutrinos whose energy levels suggest they are linked with gamma-ray bursts. The fireballs that give rise to the gamma rays seen in gamma-ray bursts were thought to potentially hurl particles at very high energies, generating both cosmic rays and energetic neutrinos.
After analyzing data on 307 gamma-ray bursts in 2008 and 2009, the scientists discovered the levels of these neutrinos were at least 3.7 times lower than expected. This suggests louis vuitton handbags gamma-ray bursts are probably not the sources of the most powerful cosmic rays.
"After observing gamma-ray bursts for two years, we have not detected the telltale neutrinos for cosmic-ray acceleration," Halzen said.
Still, it could be that current models of neutrino production from these events might be off.
"We're not entirely clear yet as to what this neutrino flux we're not seeing might mean," Whitehorn told SPACE.com. "Our understanding of oakley sunglasses gamma-ray bursts is not complete — there's a lot of theoretical uncertainty. I suspect what will happen now is that there'll be a lot of efforts in the theory community of how to get neutrino fluxes compatible with the results."
Instead of gamma-ray bursts, researchers note that black holes at the centers or nuclei of active galaxies may be responsible for these ultra-high-energy cosmic rays, Cheapest louis vuitton men t shirts sale white 2012 sucking in matter and spitting out enormous particle jets as they gorge.
"Active galactic nuclei are big — great big accelerators that may be able to accelerate particles to very high energies," said Klein, a long-time member of the IceCube Collaboration.
IceCube has looked for neutrinos from active monster butterfly galactic nuclei, but as yet the data is inconclusive.
The scientists detailed their findings in tomorrow's (April 19) issue of the journal Nature.
Cosmic rays are charged subatomic particles that streak to Earth from deep in outer space. A few rare cosmic rays are extraordinarily powerful, with energies up to 100 million times greater than any attained by human-made particle colliders, such as CERN's Large Hadron Collider. The sources of these cosmic rays are a mystery.
"Nature is capable of accelerating elementary particles to gucci sunglasses macroscopic energies," said study co-author Francis Halzen at the University of Wisconsin-Madison, principal investigator at the IceCube Neutrino Observatory, a massive telescope designed to find the tiny subatomic particles. "There are basically only two ideas on how she does this — in gravitationally driven particle flows near the supermassive black holes at the centers of active galaxies, and in the collapse of stars to a black hole, seen by astronomers as gamma-ray bursts."
Gamma-ray bursts are the most powerful explosions in the universe. They can emit as much energy as our sun during its entire 10-billion-year lifetime in anywhere from milliseconds to minutes.
"Some gamma-ray bursts are thought to be collapses of supermassive stars — hypernovas — while others are thought to be collisions of black holes with other black holes burberry outlet or neutron stars," said study co-author Spencer Klein of the U.S. Department of Energy's Lawrence Berkeley National Laboratory. "Both types produce brief but intense blasts of radiation."
New evidence may now rule out gamma-ray bursts as sources of these ultra-high-energy cosmic rays.
Researchers employed the IceCube neutrino detector, an array of thousands of detectors encompassing a cubic kilometer of clear Antarctic ice at the South Pole. Neutrinos are ghostly particles that often pass right through matter, only rarely striking atoms.
"This is a coming-of-age for neutrino astronomy burberry bags — the first time we're able to use neutrino data as a new way of looking at astrophysical objects and say something substantive about them," said study co-author Nathan Whitehorn, a physicist at the University of Wisconsin-Madison, who led the recent gamma-ray burst research with Peter Redl of the University of Maryland.
The investigators focused on neutrinos whose energy levels suggest they are linked with gamma-ray bursts. The fireballs that give rise to the gamma rays seen in gamma-ray bursts were thought to potentially hurl particles at very high energies, generating both cosmic rays and energetic neutrinos.
After analyzing data on 307 gamma-ray bursts in 2008 and 2009, the scientists discovered the levels of these neutrinos were at least 3.7 times lower than expected. This suggests louis vuitton handbags gamma-ray bursts are probably not the sources of the most powerful cosmic rays.
"After observing gamma-ray bursts for two years, we have not detected the telltale neutrinos for cosmic-ray acceleration," Halzen said.
Still, it could be that current models of neutrino production from these events might be off.
"We're not entirely clear yet as to what this neutrino flux we're not seeing might mean," Whitehorn told SPACE.com. "Our understanding of oakley sunglasses gamma-ray bursts is not complete — there's a lot of theoretical uncertainty. I suspect what will happen now is that there'll be a lot of efforts in the theory community of how to get neutrino fluxes compatible with the results."
Instead of gamma-ray bursts, researchers note that black holes at the centers or nuclei of active galaxies may be responsible for these ultra-high-energy cosmic rays, Cheapest louis vuitton men t shirts sale white 2012 sucking in matter and spitting out enormous particle jets as they gorge.
"Active galactic nuclei are big — great big accelerators that may be able to accelerate particles to very high energies," said Klein, a long-time member of the IceCube Collaboration.
IceCube has looked for neutrinos from active monster butterfly galactic nuclei, but as yet the data is inconclusive.
The scientists detailed their findings in tomorrow's (April 19) issue of the journal Nature.
2012年4月17日星期二
SpaceX has one more launch simulation to complete
SpaceX and NASA are moving ahead with the scheduled April 30 launch date of the Dragon spacecraft and its historic docking with the International Space Station louis vuitton shoes after the flight readiness review was approved at the Johnson Space Center in Houston, Texas.
The comprehensive evaluation of the SpaceX mission is one of the last major steps before the company becomes the first commercial carrier to deliver payloads to the ISS. Although SpaceX founder and chief designer Elon Musk was careful to remind everybody that the flight is a test and success is far from guaranteed.
“I think we’ve got a pretty good shot, but it is worth emphasizing that there’s a lot that can go wrong in a mission like this,” Musk told reporters after the review.
The Falcon rocket being used to launch the Dragon has been used twice, once inserting a Dragon capsule into low earth orbit. But Musk and NASA did emphasize that this is not an actual mission. The goal is to demonstrate SpaceX’s capabilities to launch, rendezvous with the ISS and return to earth. And while there will be some cargo on board and some cargo will be carried back from the space station, nothing on board is considered critical or irreplaceable. Musk reminded reporters of the difficulty of the mission, but he remains confident SpaceX will succeed.
“I think it would be a mistake to put too much weight burberry outlet on this flight because there are hopefully going to be two more flights later this year to the space station, which will be almost identical configuration,” Musk said during the press conference. “So if this one doesn’t succeed in getting to the space station, I’m confident that one of the other two will. There should be no doubt about our resolve. We will get to the space station.”
The mission will take roughly four days until the Dragon will dock with the space station in orbit and combines two separate tests into a single flight. The capsule will then remain attached to the station for 18 days. The first demonstration test will be a flight around the space station to test and verify maneuverability, navigation and communication capabilities.
On flight day three, the Dragon spacecraft will begin a series of maneuvers that will take it on a lap around the ISS beginning with a relatively close 2.5-kilometer (1.5-mile) pass underneath the station. During this close pass the Dragon and the ISS will communicate with each other for the first time. “An absolute requirement for proximity operations,” according to NASA flight director Holly Ridings.
The crew on board the space station will send a test command to Dragon to confirm those on the ISS have the ability to control the capsule when necessary. The gucci sunglasses communication tests are to make sure the crew would be able to command the Dragon to hold or abort if needed when it is in close proximity to the station.
After the 2.5 km pass, the Dragon will move out to 200 km as it continues the lap. It will then again maneuver closer as it passes over the top of the station, this time getting as close as 7 km. The entire lap should take a full day, 22-24 hours according to Ridings.
On flight day four, the Dragon will once again be guided to 2.5 km underneath the station as preparations are made for the final tests before finally docking with the ISS. Once inside this 2.5 km zone, Ridings says the NASA team in Houston has final authority over the mission due to the proximity to the station and the safety of the crew on board.
The next parking spot will be at 1.4 km as the Dragon prepares for the approach initiation. Once everybody agrees for a go, the Dragon will maneuver to a point just 250 meters (820 feet) from the station, which will serve as its hold point for the final tests in very close proximity to the station. According to NASA, the hold point is outside the critical KOS, the acronym-happy agency’s simply named “Keep Out Sphere.”
The next demonstration objectives include interaction with the crew on orbit. From the 250 m hold point, the Dragon team at SpaceX’s Hawthorne, California headquarters burberry bags will issue a command to slowly begin approaching the station, after which the ISS crew will issue a retreat command as the first test. The demonstration will be repeated, this time with the ISS crew issuing a hold command at 220 m.
“That will be the last of our go/no go objectives in terms of the demonstration objective,” according to Ridings.
After these demonstrations are complete and everybody at NASA and SpaceX are satisfied, the Dragon will then make the final maneuvers towards the station. With all the functionality of the Dragon checked out, the spacecraft will be commanded by the SpaceX team to cross the KOS boundary for the first time.
The Dragon will then stop at 30 m, where the go/no-go decision will be made by everybody on the ground as well as the crew on the station to make the final approach. Though the Dragon is an automated spacecraft and is capable of performing the entire mission autonomously, Ridings louis vuitton handbags emphasized that the station crew will be heavily involved and is there as a safety net, especially on the first flight.
After maneuvering to just 10 m from the station, the Dragon will park in its final hold position, known as the capture point. Once a final decision is made for capture, the station crew takes over the final steps using the robotic arm to reach out and grab the Dragon and move into its berthing spot on the station.
The final step of the mission from the 2.5 km point to docking is expected to take around seven to eight hours. On the following day, the station crew begins the laborious cargo transfer as 521 kilograms (1,146 pounds) are offloaded from the Dragon, and 660 kilograms (1,452 pounds) of cargo from the station are placed into the capsule to be returned to earth. Thankfully, it’s mostly the motions that are laborious and not heavy lifting.
Representatives from the NASA side of the review oakley sunglasses meeting also reminded reporters of the test nature of the mission. But all sounded confident based on the preparation, simulations and tests that have been completed. NASA space station program manager Mike Sufferdini told reporters there are still some verifications that need to be done, but everything is looking good.
Sufferdini said the past few years has been a positive learning experience for both organizations and he’s excited to see a new vehicle arrive at the station. One of the differences during the flight readiness review he pointed to compared to past NASA missions is the bottom line. “There were no requirements for mission success,” he said. The simple comment in many ways marks NASA’s transition from shouldering the responsibility to deliver payloads to orbit, to a consumer of space delivery services. This point is driven home as today marks the last flight of the space shuttle discovery as it was flown to Washington, D.C., where it will be handed over to the Smithsonian.
SpaceX has one more launch simulation to complete before the launch. Sufferdini said there are some verifications that still need to be completed, but nothing that indicates there should be any issues.
The mission is part of NASA’s Commercial Orbital Transportation Services program to develop a less expensive way to deliver payloads to orbit. As part of the program Cheapest louis vuitton men t shirts sale white 2012 NASA has invested $381 million in SpaceX. Musk didn’t give a specific number, but he estimated the SpaceX program has cost around $1 billion in total to date. SpaceX and Orbital Sciences are the two companies selected by NASA to provide commercial cargo delivery to the ISS.
The comprehensive evaluation of the SpaceX mission is one of the last major steps before the company becomes the first commercial carrier to deliver payloads to the ISS. Although SpaceX founder and chief designer Elon Musk was careful to remind everybody that the flight is a test and success is far from guaranteed.
“I think we’ve got a pretty good shot, but it is worth emphasizing that there’s a lot that can go wrong in a mission like this,” Musk told reporters after the review.
The Falcon rocket being used to launch the Dragon has been used twice, once inserting a Dragon capsule into low earth orbit. But Musk and NASA did emphasize that this is not an actual mission. The goal is to demonstrate SpaceX’s capabilities to launch, rendezvous with the ISS and return to earth. And while there will be some cargo on board and some cargo will be carried back from the space station, nothing on board is considered critical or irreplaceable. Musk reminded reporters of the difficulty of the mission, but he remains confident SpaceX will succeed.
“I think it would be a mistake to put too much weight burberry outlet on this flight because there are hopefully going to be two more flights later this year to the space station, which will be almost identical configuration,” Musk said during the press conference. “So if this one doesn’t succeed in getting to the space station, I’m confident that one of the other two will. There should be no doubt about our resolve. We will get to the space station.”
The mission will take roughly four days until the Dragon will dock with the space station in orbit and combines two separate tests into a single flight. The capsule will then remain attached to the station for 18 days. The first demonstration test will be a flight around the space station to test and verify maneuverability, navigation and communication capabilities.
On flight day three, the Dragon spacecraft will begin a series of maneuvers that will take it on a lap around the ISS beginning with a relatively close 2.5-kilometer (1.5-mile) pass underneath the station. During this close pass the Dragon and the ISS will communicate with each other for the first time. “An absolute requirement for proximity operations,” according to NASA flight director Holly Ridings.
The crew on board the space station will send a test command to Dragon to confirm those on the ISS have the ability to control the capsule when necessary. The gucci sunglasses communication tests are to make sure the crew would be able to command the Dragon to hold or abort if needed when it is in close proximity to the station.
After the 2.5 km pass, the Dragon will move out to 200 km as it continues the lap. It will then again maneuver closer as it passes over the top of the station, this time getting as close as 7 km. The entire lap should take a full day, 22-24 hours according to Ridings.
On flight day four, the Dragon will once again be guided to 2.5 km underneath the station as preparations are made for the final tests before finally docking with the ISS. Once inside this 2.5 km zone, Ridings says the NASA team in Houston has final authority over the mission due to the proximity to the station and the safety of the crew on board.
The next parking spot will be at 1.4 km as the Dragon prepares for the approach initiation. Once everybody agrees for a go, the Dragon will maneuver to a point just 250 meters (820 feet) from the station, which will serve as its hold point for the final tests in very close proximity to the station. According to NASA, the hold point is outside the critical KOS, the acronym-happy agency’s simply named “Keep Out Sphere.”
The next demonstration objectives include interaction with the crew on orbit. From the 250 m hold point, the Dragon team at SpaceX’s Hawthorne, California headquarters burberry bags will issue a command to slowly begin approaching the station, after which the ISS crew will issue a retreat command as the first test. The demonstration will be repeated, this time with the ISS crew issuing a hold command at 220 m.
“That will be the last of our go/no go objectives in terms of the demonstration objective,” according to Ridings.
After these demonstrations are complete and everybody at NASA and SpaceX are satisfied, the Dragon will then make the final maneuvers towards the station. With all the functionality of the Dragon checked out, the spacecraft will be commanded by the SpaceX team to cross the KOS boundary for the first time.
The Dragon will then stop at 30 m, where the go/no-go decision will be made by everybody on the ground as well as the crew on the station to make the final approach. Though the Dragon is an automated spacecraft and is capable of performing the entire mission autonomously, Ridings louis vuitton handbags emphasized that the station crew will be heavily involved and is there as a safety net, especially on the first flight.
After maneuvering to just 10 m from the station, the Dragon will park in its final hold position, known as the capture point. Once a final decision is made for capture, the station crew takes over the final steps using the robotic arm to reach out and grab the Dragon and move into its berthing spot on the station.
The final step of the mission from the 2.5 km point to docking is expected to take around seven to eight hours. On the following day, the station crew begins the laborious cargo transfer as 521 kilograms (1,146 pounds) are offloaded from the Dragon, and 660 kilograms (1,452 pounds) of cargo from the station are placed into the capsule to be returned to earth. Thankfully, it’s mostly the motions that are laborious and not heavy lifting.
Representatives from the NASA side of the review oakley sunglasses meeting also reminded reporters of the test nature of the mission. But all sounded confident based on the preparation, simulations and tests that have been completed. NASA space station program manager Mike Sufferdini told reporters there are still some verifications that need to be done, but everything is looking good.
Sufferdini said the past few years has been a positive learning experience for both organizations and he’s excited to see a new vehicle arrive at the station. One of the differences during the flight readiness review he pointed to compared to past NASA missions is the bottom line. “There were no requirements for mission success,” he said. The simple comment in many ways marks NASA’s transition from shouldering the responsibility to deliver payloads to orbit, to a consumer of space delivery services. This point is driven home as today marks the last flight of the space shuttle discovery as it was flown to Washington, D.C., where it will be handed over to the Smithsonian.
SpaceX has one more launch simulation to complete before the launch. Sufferdini said there are some verifications that still need to be completed, but nothing that indicates there should be any issues.
The mission is part of NASA’s Commercial Orbital Transportation Services program to develop a less expensive way to deliver payloads to orbit. As part of the program Cheapest louis vuitton men t shirts sale white 2012 NASA has invested $381 million in SpaceX. Musk didn’t give a specific number, but he estimated the SpaceX program has cost around $1 billion in total to date. SpaceX and Orbital Sciences are the two companies selected by NASA to provide commercial cargo delivery to the ISS.
2012年4月15日星期日
The findings open up the possibility of creating
Computer scientists at Kobe University louis vuitton shoes in Japan have built a computer that draws inspiration from the swarming behavior of soldier crabs.
The computer is based on theories from the early 1980s that studies how it could be possible to build a computer out of billiard balls. Proposed by Edward Fredkin and Tommaso Toffoli, the mechanical computer was based on Newtonian dynamics and relied on the motion of billiard balls in an idealized, friction-free environment instead of electronic signals like a conventional computer.
The model was developed to investigate the relation between computation and reversible processes in physics. A channel in this computational system gucci sunglasses would carry information encoded in the form of the presence or absence of billiard balls. The information is processed through a series of gates which the balls either bump into and emerge in a predictable direction based on the ballistics of the collision or which they don’t bump into and emerge with the same velocity.
Picking up where Fredkin and Toffoli left off, Yukio-Pegio Gunji and colleagues at Kobe University have essentially built a billiard ball computer using soldier crabs. In their report (.pdf), they demonstrate that “swarms of soldier burberry outlet crabs can crabs can implement logical gates when placed in a geometrically constrained environment.”
Soldier crabs or Mictyris guinotae live in flat lagoons and form huge colonies of hundreds of thousands of individuals. When they emerge during low tides and form enormous swarms, the crabs exhibit two different behaviors. Individuals on the edge of the swarm show aggressive leadership, keeping a solid edge to the group as they move forwards (or, more likely, sideways) in unison. Those in the middle of the swarm just follow their neighbors and so move in burberry bags a more dynamic way. The crabs on the edge of the swam tend to continually fold back into the body of the swarm, only to be replaced by another.
When a swarm of crabs is placed into a corridor with walls on each side, the crabs will closely follow the wall like a rolling billiard ball. This sort of behavior can be easily controlled, for example, by casting a shadow from above on the swarm to mimic the presence of crab-eating birds. The soldier crabs will move away from any shadowed areas for louis vuitton handbags fear of being munched on. When two swarms of crabs — or “crab balls” — collide, they appear to merge and continue in a direction that is the sum of their respective velocities.
Based on these observations of crab behavior, the team built a pattern of channels that act like logic gates. They first simulated the soldier crab swarming behavior in special patterns of channels. They then created a real system of channels in their lab and unleashed groups of 40 real crabs, which were guided using the fake bird shadow.
They found that they could build a decent OR gate oakley sunglasses using the crabs — this was the place where one or two crab swarms are merged into a single one. However, the more complicated AND-gate required the combined swarm heading down one of three paths. This was found to be less reliable. However, the team believe that they could improve the results by creating a more crab-friendly environment.
The findings open up the possibility of creating an unconventional computing model where the zeros and 1s are represented by the absence or presence of Cheapest louis vuitton men t shirts sale white 2012 a swarm of crabs.
The computer is based on theories from the early 1980s that studies how it could be possible to build a computer out of billiard balls. Proposed by Edward Fredkin and Tommaso Toffoli, the mechanical computer was based on Newtonian dynamics and relied on the motion of billiard balls in an idealized, friction-free environment instead of electronic signals like a conventional computer.
The model was developed to investigate the relation between computation and reversible processes in physics. A channel in this computational system gucci sunglasses would carry information encoded in the form of the presence or absence of billiard balls. The information is processed through a series of gates which the balls either bump into and emerge in a predictable direction based on the ballistics of the collision or which they don’t bump into and emerge with the same velocity.
Picking up where Fredkin and Toffoli left off, Yukio-Pegio Gunji and colleagues at Kobe University have essentially built a billiard ball computer using soldier crabs. In their report (.pdf), they demonstrate that “swarms of soldier burberry outlet crabs can crabs can implement logical gates when placed in a geometrically constrained environment.”
Soldier crabs or Mictyris guinotae live in flat lagoons and form huge colonies of hundreds of thousands of individuals. When they emerge during low tides and form enormous swarms, the crabs exhibit two different behaviors. Individuals on the edge of the swarm show aggressive leadership, keeping a solid edge to the group as they move forwards (or, more likely, sideways) in unison. Those in the middle of the swarm just follow their neighbors and so move in burberry bags a more dynamic way. The crabs on the edge of the swam tend to continually fold back into the body of the swarm, only to be replaced by another.
When a swarm of crabs is placed into a corridor with walls on each side, the crabs will closely follow the wall like a rolling billiard ball. This sort of behavior can be easily controlled, for example, by casting a shadow from above on the swarm to mimic the presence of crab-eating birds. The soldier crabs will move away from any shadowed areas for louis vuitton handbags fear of being munched on. When two swarms of crabs — or “crab balls” — collide, they appear to merge and continue in a direction that is the sum of their respective velocities.
Based on these observations of crab behavior, the team built a pattern of channels that act like logic gates. They first simulated the soldier crab swarming behavior in special patterns of channels. They then created a real system of channels in their lab and unleashed groups of 40 real crabs, which were guided using the fake bird shadow.
They found that they could build a decent OR gate oakley sunglasses using the crabs — this was the place where one or two crab swarms are merged into a single one. However, the more complicated AND-gate required the combined swarm heading down one of three paths. This was found to be less reliable. However, the team believe that they could improve the results by creating a more crab-friendly environment.
The findings open up the possibility of creating an unconventional computing model where the zeros and 1s are represented by the absence or presence of Cheapest louis vuitton men t shirts sale white 2012 a swarm of crabs.
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