Archive for the ‘Magnetism’ Category

Since the 1930s scientists have been searching for particles that are simultaneously matter and antimatter. Now physicists have found strong evidence for one such entity inside a superconducting material. The discovery could represent the first so-called Majorana particle, and may help researchers encode information for quantum computers.

Physicists think that every particle of matter has an antimatter counterpart with equal mass but opposite charge. When matter meets its antimatter equivalent, the two annihilate one another. But some particles might be their own antimatter partners, according to a 1937 prediction by Italian physicist Ettore Majorana. For the first time researchers say they have imaged one of these Majorana particles, and report their findings in the October 3 Science.

The new Majorana particle showed up inside a superconductor, a material in which the free movement of electrons allows electricity to flow without resistance. The research team, led by Ali Yazdani of Princeton University, placed a long chain of iron atoms, which are magnetic, on top of a superconductor made of lead. Normally, magnetism disrupts superconductors, which depend on a lack of magnetic fields for their electrons to flow unimpeded. But in this case the magnetic chain turned into a special type of superconductor in which electrons next to one another in the chain coordinated their spins to simultaneously satisfy the requirements of magnetism and superconductivity. Each of these pairs can be thought of as an electron and an antielectron, with a negative and a positive charge, respectively. That arrangement, however, leaves one electron at each end of the chain without a neighbor to pair with, causing them to take on the properties of both electrons and antielectrons—in other words, Majorana particles.

As opposed to particles found in a vacuum, unattached to other matter, these Majoranas are what’s called “emergent particles.” They emerge from the collective properties of the surrounding matter and could not exist outside the superconductor.

The new study shows a convincing signature of Majorana particles, says Leo Kouwenhoven of the Delft University of Technology in the Netherlands who was not involved in the research but previously found signs of Majorana particles in a different superconductor arrangement. “But to really speak of full proof, unambiguous evidence, I think you have to do a DNA test.” Such a test, he says, must show the particles do not obey the normal laws of the two known classes of particles in nature—fermions (protons, electrons and most other particles we are familiar with) and bosons (photons and other force-carrying particles, including the Higgs boson). “The great thing about Majoranas is that they are potentially a new class of particle,” Kouwenhoven adds. “If you find a new class of particles, that really would add a new chapter to physics.”

Physicist Jason Alicea of California Institute of Technology, who also did not participate in the research, said the study offers “compelling evidence” for Majorana particles but that “we should keep in mind possible alternative explanations—even if there are no immediately obvious candidates.” He praised the experimental setup for its apparent ability to easily produce the elusive Majoranas. “One of the great virtues of their platform relative to earlier works is that it allowed the researchers to apply a new type of microscope to probe the detailed anatomy of the physics.”

The discovery could have implications for searches for free Majorana particles outside of superconducting materials. Many physicists suspect neutrinos—very lightweight particles with the strange ability to alter their identities, or flavors—are Majorana particles, and experiments are ongoing to investigate whether this is the case. Now that we know Majorana particles can exist inside superconductors, it might not be surprising to find them in nature, Yazdani says. “Once you find the concept to be correct, it’s very likely that it shows up in another layer of physics. That’s what’s exciting.”

The finding could also be useful for constructing quantum computers that harness the laws of quantum mechanics to make calculations many times faster than conventional computers. One of the main issues in building a quantum computer is the susceptibility of quantum properties such as entanglement (a connection between two particles such that an action on one affects the other) to collapse due to outside interference. A particle chain with Majoranas capping each end would be somewhat immune to this danger, because damage would have to be done to both ends simultaneously to destroy any information encoded there. “You could build a quantum bit based on these Majoranas,” Yazdani says. ”The idea is that such a bit would be much more robust to the environment than the types of bits people have tried to make so far.”

http://www.scientificamerican.com/article/majorana-particle-matter-and-antimatter/

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salmon

When migrating, sockeye salmon typically swim up to 4,000 miles into the ocean and then, years later, navigate back to the upstream reaches of the rivers in which they were born to spawn their young. Scientists, the fishing community and lay people have long wondered how salmon find their way to their home rivers over such epic distances.

A new study, published in this week’s issue of Current Biology and partly funded by the National Science Foundation, suggests that salmon find their home rivers by sensing the rivers’ unique magnetic signature.

As part of the study, the research team used data from more than 56 years of catches in salmon fisheries to identify the routes that salmon had taken from their most northerly destinations, which were probably near Alaska or the Aleutian Islands in the Pacific Ocean, to the mouth of their home river–the Fraser River in British Columbia, Canada. This data was compared to the intensity of Earth’s magnetic field at pivotal locations in the salmon’s migratory route.

Earth has a magnetic field that weakens with proximity to the equator and distance from the poles and gradually changes on a yearly basis. Therefore, the intensity of the magnetosphere in any particular location is unique and differs slightly from year to year.

Because Vancouver Island is located directly in front of the Fraser River’s mouth, it blocks direct access to the river’s mouth from the Pacific Ocean. However, salmon may slip behind Vancouver Island and reach the river’s mouth from the north via the Queen Charlotte Strait or from the south via the Juan De Fuca Strait.

Results from this study showed that the intensity of the magnetic field largely predicted which route the salmon used to detour around Vancouver Island; in any given year, the salmon were more likely to take whichever route had a magnetic signature that most closely matched that of the Fraser River years before, when the salmon initially swam from the river into the Pacific Ocean.

“These results are consistent with the idea that juvenile salmon imprint on (i.e. learn and remember) the magnetic signature of their home river, and then seek that same magnetic signature during their spawning migration,” said Nathan Putman, a post-doctoral researcher at Oregon State University and the lead author of the study.

It has long been known that some animals use Earth’s magnetic field to generally orient themselves and to follow a straight course. However, scientists have never before documented an animal’s ability to “learn” the magnetic field rather than to simply inherit information about it or to use the magnetic field to find a specific location.

This study provides the first empirical evidence of magnetic imprinting in animals and represents the discovery of a major new phenomenon in behavioral biology.

In addition, this study suggests that it would be possible to forecast salmon movements using geomagnetic models–a development that has important implications for fisheries management.

Putman says scientists don’t know exactly how early and how often salmon check Earth’s magnetic field in order to identify their geographic locations during their trip back home. “But,” he says, “for the salmon to be able to go from some location out in the middle of the Pacific 4,000 miles away, they need to make a correct migratory choice early–and they need to know which direction to start going in. For that, they would presumably use the magnetic field.”

Putman continues, “As the salmon travel that route, ocean currents and other forces might blow them off course. So they would probably need to check their magnetic position several times during this migration to stay on track. Once they get close to the coastline, they would need to hone in on their target, and so would presumably check in more continuously during this stage of their migration.”

Putman says that once the salmon reach their home river, they probably use their sense of smell to find the particular tributary in which they were born. However, over long distances, magnetism would be a more useful cue to salmon than odors because magnetism–unlike odors–can be detected across thousands of miles of open ocean.

Like other Pacific Salmon, sockeye salmon spawn in the gravel beds of rivers and streams. After the newly hatched salmon emerge from these beds, they spend one to three years in fresh water, and then they migrate downstream to the ocean.

Next, the salmon travel thousands of miles from their home river to forage in the North Pacific for about two more years, and then, as well-fed adults, they migrate back to the same gravel beds in which they were born.

When migrating, salmon must transition from fresh water to sea water, and then back again. During each transition, the salmon undergo a metamorphosis that Putman says is almost as dramatic as the metamorphosis of a caterpillar into a butterfly. Each such salmon metamorphosis involves a replacement of gill tissues that enables the fish to maintain the correct salt balance in its environment: the salmon retains salt when in fresh water and pumps out excess salt when in salt water.

Salmon usually undertake their taxing, round-trip migration, which may total up to 8,000 miles, only once in their lives; they typically die soon after spawning.

http://www.sciencedaily.com/releases/2013/02/130207131713.htm

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Scientists are studying the Earth’s magnetic field using the stones that line Maori steam ovens.

The cooking process generates so much heat that the magnetic minerals in these stones will realign themselves with the current field direction.

An archaeological search is under way in New Zealand to find sites containing old ovens, or hangi as they are known.

Abandoned stones at these locations could shed light on Earth’s magnetic behaviour going back hundreds of years.

“We have very good palaeomagnetic data from across the world recording field strength and direction – especially in the Northern Hemisphere,” said Gillian Turner from Victoria University, Wellington, New Zealand.

“The southwest Pacific is the gap, and in order to complete global models, we’re rather desperate for good, high-resolved data from our part of the world,” she told BBC News.

Dr Turner was speaking here at the American Geophysical Union (AGU) Fall meeting, the world’s largest annual gathering of Earth scientists.

The NZ researcher is working on a project to retrieve information about changes in the Earth’s magnetic field stretching back over the past 10,000 years.

For data on the last few centuries, she would ordinarily have turned to pottery.

When these objects are fired, the minerals in their clay are heated above the Curie temperature and are demagnetised.

Then, as the pots cool down, those minerals become magnetised again in the direction of the prevalent field. And the strength of the magnetisation is directly related to the strength of that field.

Unfortunately for Dr Turner, the first settlers on New Zealand 700-800 years ago – the Maori – did not use pottery. However, the researcher has hit upon a fascinating alternative.

She is now exploiting the Maori cooking tradition of the steam oven.

These were pits in the ground into which were placed very hot stones, covered with baskets of food and layers of fern fronds soaked in water.

The whole construction was then topped with soil and left to cook for several hours.

Dr Turner and colleagues experimented with a modern-day hangi to see if the stones at the base of the pit could achieve the necessary Curie temperatures to reset their magnetisation – to prove they could be used as an alternative data source for their study.

“The Maori legend is that the stones achieve white hot heat,” she explained.

“Well, red hot is about 700 degrees and so white hot would be a good deal more than that. But by putting some thermocouples in the stones we were able to show they got as high as 1,100C, which of itself is quite surprising. At that temperature, rock-forming minerals start to become plastic if not melt.”

By placing a compass on top of the cooled hangi stones Dr Turner’s team was able to establish that a re-magnetisation had indeed taken place.

It turns out that hangi stones were carefully chosen, and one of the most popular types was an andesite boulder found in Central North Island.

“The Maori prefer these volcanic boulders because they don’t crack and shatter in the fire, and from our point of view they’re the best because magnetically they behave better – they’re formed with a high concentration of magnetite,” the Wellington scientist said. “But there are some sedimentary rocks which we can use also.”

Dr Turner’s team is now scouring New Zealand for archaeological digs that have uncovered hangi ovens. It is crucial that a date is recovered with the stones. This can be provided by a radiocarbon analysis of the charcoal left from the firewood used to light the oven.

Hangi stones are only likely to take Dr Turner back to the 1200s. For magnetic data deeper in time, she needs to go to other sources.

“We’re also studying volcanic rocks because they’re erupted above the Curie temperature. And the other source of information is lake sediments. Long-core sediments can give us a continuous record at specific places.”

http://www.bbc.co.uk/news/science-environment-20520454

Thanks to Kebmodee for bringing this to the attention of the It’s Interesting community.

121205200057

 

Carp stored in large tubs at Czech Christmas markets align themselves in the north-south direction, suggesting they possess a previously unknown capacity to perceive geomagnetic fields, according to a new study published December 5 in the open access journal PLOS ONE, led Hynek Burda from the University of Life Sciences (Prague), Czech Republic and colleagues from other institutions.

Their study included over 14,000 fish in 25 markets, and the majority of these fish were found to align themselves along the north-south axis. The fish were accustomed to human onlookers, and street lights and other potential disturbances seemed to have no effect on the orientation of the fish.

In the absence of other common stimuli for orientation like light, sound or the flow of water, the authors suggest that the fish most likely align themselves to geomagnetic cues.

http://www.sciencedaily.com/releases/2012/12/121205200057.htm

 

A HAMSTER spent the Easter break recovering with its owners from the unusual ordeal of eating a Spider-Man magnet and becoming stuck to the metal bars of its cage.

Kate Meech and her four children returned to their Bugbrooke home last Thursday afternoon to find four month-old Smurf quite distressed, attached to the outside of its cage.

Kate said: “When I saw the small circular shape from inside her cheek I realised she was attached by a magnet.

“It took a bit of a tug to pull her away from it and then we had to keep her in a plastic box, for obvious reasons.

“She seemed to be fine so I thought she would just spit it out if she was left alone.

“But after checking on her for a few days I realised that, instead, her body started to push it out of her cheek, treating it as a foreign body.

“It made me feel quite queasy.

“We found the magnet and she just has a little graze on her cheek. But she’s back to her normal, loopy self.”

Mrs Meech said the magnet was understood to have come from the foot of her 10-year-old son Thomas’s toy Spider-Man figure.

She added: “I’ve warned the children to keep their toys away from the cage from now on.”

http://www.northamptonchron.co.uk/news/local/spider-man-magnet-swallowing-hamster-recovering-after-sticking-itself-to-bars-of-metal-cage-1-3719398#