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Scientists use light to stitch ‘invisible’ nanoparticles together

gold

At the centre of this new technique are tiny blocks made from ‘metamaterials’ – a special type of artificial material engineered to have properties unlike anything found in nature. These nanoparticle building blocks are just a few billionths of a metre wide, and researchers from the University of Cambridge in the UK have figured out how to control the way light flows through them.

Controlling the way light interacts with a material is a key Read more →

element of any ‘invisibility’ technology, and these metamaterials have been designed to refract light in a direction that renders them invisible to the naked eye.

In order to do this, the researchers needed to ‘stitch’ the metamaterial nanoparticles together into several long strings, which they did by placing the metamaterials in some water and blasting them with an unfocused laser light. “These strings can then be stacked into layers one on top of the other, similar to LEGO bricks,” they say in a press release. ”The method makes it possible to produce materials in much higher quantities than can be made through current techniques.”

Now, what we really want to know is… when do we get our invisibility cloaks? The next step is figuring out how to build bridges between the nanoparticles so they can be produced in larger quantities. “There is a knack to doing this,” says Katie Collins at Wired UK, ”and it involves spacing the material blocks carefully and accurately using barrel-shaped molecules calledcucurbiturils so that it’s as easy as possible to retain control over the process.”

Magnets May Act as Wireless Cooling Agents

The theory describes the motion of magnons — quasi-particles in magnets that are collective rotations of magnetic moments, or “spins.” In addition to the magnetic moments, magnons also conduct heat; from their equations, the MIT researchers found that when exposed to a magnetic field gradient, magnons may be driven to move from one end of a magnet to another, carrying Read more →

heat with them and producing a cooling effect.

“You can pump heat from one side to the other, so you can essentially use a magnet as a refrigerator,” says Bolin Liao, a graduate student in MIT’s Department of Mechanical Engineering. “You can envision wireless cooling where you apply a magnetic field to a magnet one or two meters away to, say, cool your laptop.”

In theory, Liao says, such a magnetically driven refrigerator would require no moving parts, unlike conventional iceboxes that pump fluid through a set of pipes to keep things cool.

Liao, along with graduate student Jiawei Zhou and Department of Mechanical Engineering head Gang Chen, have published a paper detailing the magnon cooling theory in Physical Review Letters.

“People now have a new theoretical playground to study how magnons move under coexisting field and temperature gradients,” Liao says. “These equations are pretty fundamental for magnon transport.”

A cool effect

In a ferromagnet, the local magnetic moments can rotate and align in various directions. At a temperature of absolute zero, the local magnetic moments align to produce the strongest possible magnetic force in a magnet. As temperature increases, a magnet becomes weaker as more local magnetic moments spin away from the shared alignment; a magnon population is created with this elevated temperature.

In many ways, magnons are similar to electrons, which can simultaneously carry electrical charge and conduct heat. Electrons move in response to either an electric field or a temperature gradient — a phenomenon known as the thermoelectric effect. In recent years, scientists have investigated this effect for applications such as thermoelectric generators, which can be used to convert heat directly into electricity, or to deliver cooling without any moving parts.

Liao and his colleagues recognized a similar “coupled” phenomenon in magnons, which move in response to two forces: a temperature gradient or a magnetic field. Because magnons behave much like electrons in this aspect, the researchers developed a theory of magnon transport based on a widely established equation for electron transport in thermoelectrics, called the Boltzmann transport equation.

From their derivations, Liao, Zhou, and Chen came up with two new equations to describe magnon transport. With these equations, they predicted a new magnon cooling effect, similar to the thermoelectric cooling effect, in which magnons, when exposed to a magnetic field gradient, may carry heat from one end of a magnet to the other.

Motivating new experiments

Liao used the properties of a common magnetic insulator to model how this magnon cooling effect may work in existing magnetic materials. He collected data for this material from previous literature, and plugged the numbers into the group’s new model. He found that while the effect was small, the material was able to generate a cooling effect in response to a moderate magnetic field gradient. The effect was more pronounced at cryogenic temperatures.

The theoretical results suggest to Chen that a first application for magnon cooling may be for scientists working on projects that require wireless cooling at extremely low temperatures.

“At this stage, potential applications are in cryogenics — for example, cooling infrared detectors,” Chen says. “However, we need to confirm the effect experimentally and look for better materials. We hope this will motivate new experiments.”

Li Shi, a professor of mechanical engineering at the University of Texas at Austin who was not involved in the research, says the magnetic cooling effect identified by the group is “a highly useful theoretical framework for studying the coupling between spin and heat, and can potentially stimulate ideas of utilizing magnons as a working ‘fluid’ in a solid-state refrigeration system.”

Liao points out that magnons also add to the arsenal of tools for improving existing thermoelectric generators — which, while potentially innovative in their ability to generate electricity from heat, are also relatively inefficient.

“There’s still a long way to go for thermoelectrics to compete with traditional technologies,” Liao says. “Studying the magnetic degree of freedom could potentially help optimize existing systems and improve the thermoelectric efficiency.”

The work was partly supported by the U.S. Department of Energy and the Air Force Office of Scientific Research.

Here’s why your phone and laptop batteries degrade so fast

lithium-batteries

We’ve all experienced the woes of a degraded rechargeable battery, whether it’s a phone that can’t last a day without a charge or a laptop that’s become so reliant on its charger you can barely call it a portable device anymore. It’s a problem that scientists have struggled to solve because they couldn’t figure out what was causing such sudden and rapid battery Read more →

deterioration.

But now researchers at the US Department of Energy have identified why rechargeable batteries lose their ability to hold a charge over time. Working with lithium-ion batteries, which are the most commonly used type of battery in consumer devices, the researchers were able to map their charge and discharge process down to a few billionths of a metre to find exactly how degradation occurs.

Their research appears in a pair of studies published by Nature Communications,and according to Matt Safford at Smithsonian Magazine, two main culprits in battery degradation were identified:

“The first: microscopic vulnerabilities in the structure of the battery material steer the lithium ions haphazardly through the cell, eroding the battery in seemingly random ways, much like rust spreads across imperfections in steel. 

In the second study, focused on finding the best balance between voltage, storage capacity and maximum charge cycles, researchers not only found similar issues with the ion flow, but also tiny accumulations of nano-scale crystals left behind by chemical reactions, which cause the flow of ions to become even more irregular after each charge. Running batteries at higher voltages also led to more ion path irregularities, and thus a more rapidly deteriorating battery.”

While Daniel Abraham, who carries out his own lithium-ion battery research at the Argonne National Laboratory in the US, told Safford at Smithsonian Magazine that there may be more to battery degradation than what was identified by these two studies, the team is optimistic that their research will lead to longer-lasting, more compact and more powerful battery technology.

This will be especially important, said Huolin Xin, a materials scientist at the Brookhaven National Lab in the US and coauthor on both studies, if electric cars are to be more economically viable in the future. It’s generally accepted that we need to replace our phones and laptops every three years to maintain maximum performance, but for an electric car, that rechargeable battery should last for at least 10 to 15 years. The team is hoping that their research will lead to the development of electric car batteries that will last for three decades or more.

 

 

 

 

Saharan dust is key to formation of Bahamas’ Great Bank

UM Rosenstiel School Lewis G. Weeks Professor Peter Swart and colleagues analyzed the concentrations of two trace elements characteristic of atmospheric dust — iron and manganese — in 270 seafloor samples collected along the Great Bahama Bank over a three-year period. The team found that the highest concentrations of these trace elements occurred to the west of Andros Island, an area which has the largest concentration of whitings, white sediment-laden bodies of water produced by Read more →

photosynthetic cyanobacteria.

“Cyanobacteria need 10 times more iron than other photosynthesizers because they fix atmospheric nitrogen,” said Swart, lead author of the study. “This process draws down the carbon dioxide and induces the precipitation of calcium carbonate, thus causing the whiting. The signature of atmospheric nitrogen, its isotopic ratio is left in the sediments.”

Swart’s team suggests that high concentrations of iron-rich dust blown across the Atlantic Ocean from the Sahara is responsible for the existence of the Great Bahama Bank, which has been built up over the last 100 million years from sedimentation of calcium carbonate. The dust particles blown into the Bahamas’ waters and directly onto the islands provide the nutrients necessary to fuel cyanobacteria blooms, which in turn, produce carbonate whitings in the surrounding waters.

Persistent winds across Africa’s 3.5-million square mile Sahara Desert lifts mineral-rich sand into the atmosphere where it travels the nearly 5,000-mile northwest journey towards the U.S. and Caribbean. The paper, titled “The fertilization of the Bahamas by Saharan dust: A trigger for carbonate precipitation?” was published in the early online edition of the journal Geology. The paper’s authors include Swart, Amanda Oehlert, Greta Mackenzie, Gregor Eberli from the UM Rosenstiel School’s Department of Marine Geosciences and John Reijmer of VU University Amsterdam in the Netherlands.

Newly discovered gut virus lives in half the world’s population

 

Robert A. Edwards, a bioinformatics professor at SDSU, and his colleagues stumbled upon the discovery quite by accident. Working with visiting Read more →

researcher and corresponding author on the study Bas E. Dutilh, now at Radboud University Medical Center in The Netherlands, the researchers were using results from previous studies on gut-inhabiting viruses to screen for new viruses.

In the DNA fecal samples from 12 different individuals, they noticed a particular cluster of viral DNA, about 97,000 base pairs long, that the samples all had in common. When Edwards and his colleagues checked this discovery against a comprehensive listing of known viruses, they came up empty.

The researchers then screened for the virus across the database of the National Institute of Health’s Human Microbiome Project (HMP), and Argonne National Laboratory’s MG-RAST database, and again found it in abundance in samples derived from human feces.

To prove that the viral DNA they discovered in their computer data actually exists in nature, fellow SDSU virologist John Mokili used a technique known as DNA amplification to locate the virus in the original samples used to build NIH’s database.

“So we have a biological proof that the virus they found with the computer actually exists in the samples,” Mokili said.

This was a new virus that about half the sampled people had in their bodies that nobody knew about.

“It’s not unusual to go looking for a novel virus and find one,” Edwards said. “But it’s very unusual to find one that so many people have in common. The fact that it’s flown under the radar for so long is very strange.”

An ancient virus

The fact that it’s so widespread indicates that it probably isn’t a particularly young virus, either.

“We’ve basically found it in every population we’ve looked at,” Edwards said. “As far as we can tell, it’s as old as humans are.”

He and his team named the virus crAssphage, after the cross-assembly software program used to discover it.

Some of the proteins in crAssphage’s DNA are similar to those found in other well-described viruses. That allowed Edwards’ team to determine that their novel virus is one known as a bacteriophage, which infects and replicates inside bacteria — and using innovative bioinformatic techniques, they predicted that this particular bacteriophage proliferates by infecting a common phylum of gut bacteria known as Bacteriodetes.

Gut punch

Bacteriodetes bacteria live toward the end of the intestinal tract, and they are suspected to play a major role in the link between gut bacteria and obesity. What role crAssphage plays in this process will be a target of future research.

Further details about crAssphage have been difficult to come by. It’s unknown how the virus is transmitted, but the fact that it was not found in very young infants’ fecal samples suggests that it is not passed along maternally, but acquired during childhood. The makeup of the viral DNA suggests that it’s circular in structure. Further laboratory work has confirmed that the viral DNA is a singular entity, but it’s proven difficult to isolate.

“We know it’s there, but we can’t capture it quite yet,” Edwards said.

Once the virus is isolated, he hopes to delve into its role in obesity. It’s possible the virus in some way mediates the activity of Bacteriodetes colonies, but whether crAssphage promotes or suppresses obesity-related processes in the gut remains to be seen.

The virus might also be used to prevent or mitigate other diseases affected by the gut such as diabetes and gastroenterological maladies.

Once these processes are better understood, Edwards envisions one day the possibility of personalized medicine based on this virus.

“This could be a key to personalized phage medicine,” he said. “In individuals, we could isolate your particular strain of the virus, manipulate it to target harmful bacteria, then give it back to you.”

Key Collaborators

In addition to Edwards, SDSU researchers Katelyn McNair, Savannah Sanchez, Genivaldo G.Z. Silva, Lance Boling, Jeremy J. Barr, Victor Seguritan, Ben Felts, and Elizabeth A. Dinsdale worked on the project, in collaboration with Argonne National Laboratory in Illinois. The study’s corresponding author, Bas E. Dutilh, shares an affiliation with SDSU, Radboud University Medical Center in The Netherlands, and the Federal University of Rio de Janeiro in Brazil. Contributing researcher Ramy K. Aziz shares an affiliation with SDSU and Cairo University in Egypt. Contributing researcher Noriko Cassman was at SDSU during the time of the study and now is at the Netherlands Institute of Ecology.

San Diego State University is a leading institution for bacteriophage research. Its Viromics Information Institute, which has been identified as an SDSU Area of Excellence, is led by biology professors Forest Rohwer, Anca Segall, Edwards and Dinsdale, and takes a cross-disciplinary approach to learning more about bacteriophages and exploring their potential for medical usage.

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