Applied physicists discover that migrating cells flow like glass

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The research, led by investigators at Harvard's School of Engineering and Applied Sciences (SEAS) and the University of Florida, advances scientists' understanding ofwound healing,cancer metastasis, and embryonic development.

The finding was published online February 14 inProceedings of the National Academy of Sciences.

Cellsoften move from one part of the body to another. In a developing embryo, for example, cells in the three germ layers have to arrange themselves spatially so that the cells that will become skin are all on the outside. Similarly, as acancerous tumorexpands, the cells proliferate and push others aside. In wound healing, too, new cells have to move in to replace damaged tissue.

It is well known that cells accomplish these movements through internal cytoskeletal rearrangements that allow them to extend, retract, and divide. At some point during the migration, though, the new tissue settles into place and stops.

"We're trying to understand it from a fundamental point of view,"says principal investigator David Weitz, Mallinckrodt Professor of Physics and Applied Physics at SEAS."What we're really trying to get at is, why do things stop moving?"

The glass under discussion here is not the kind used in windows—though that is part of the larger category. Glasses include any amorphous materials that are viscous enough to remain solid for a reasonable period of time (often considered to be 24 hours) but which flow over longer periods (see sidebar).

Cream that is churned into butter goes through a sort of glass transition, as the increasing density of particles in the fatty emulsion forces it to become solid. Like any glass, butter will lose its form if the temperature rises.

As supercooled fluids and colloids (like cream) become more dense and approach the glass transition, the particles exhibit certain characteristic motions.

"We study this extensively,"says Weitz, who leads the Experimental Soft Condensed Matter Group at SEAS."We take small particles, and we increase their concentration more and more until they stop moving and they become a glass—and we understand how that behaves very well."

Living cells, though, add several levels of complexity to the system: they vary in size, shape, and rigidity; they divide; they sense their environment; and they exert their own forces on their surroundings.

"What is really surprising to us in this research with tissues,"says Weitz,"is that many of the features that inert particles exhibit as their concentration increases are also exhibited by cells. The real qualitative difference is that small particles move only because of thermal motion, whereas cells actually move themselves."

This is an artist's representation of epithelial cells (black) approaching the glass transition (blue). Increasingly large groups of cells (green, purple, red) are able to move together more rapidly than the surrounding cells. Credit: Image courtesy of Thomas E. Angelini, University of Florida.

To simulate and study the migration of living tissue, Weitz's team deposited thousands of epithelial cells—specifically, canine kidney cells—onto a polyacrylamide gel containing the protein collagen. The researchers watched them grow and move under a microscope while measuring the individual and collective cellular movements, as well as the changes in density caused by proliferation.

The researchers found that when the cells are in a confluent layer (meaning that the cells are close enough to be touching), they flow like a liquid. However, when cell density increases past a certain threshold, the tightly packed cells begin to inhibit each other's movement. As a result, some cells are able to travel in groups, while others hardly get to move at all.

In other words, they behave just like a supercooled fluid or colloidal suspension transitioning into a glass.

"The implications for biological processes are very surprising,"says lead author Thomas E. Angelini, formerly a postdoctoral researcher at SEAS and now an Assistant Professor at the University of Florida.

"Imagine a model wound in which a large group of cells are removed from the middle of a confluent layer,"he says."Cells will migrate inward to fill the void. Our results demonstrate that the low density of cells in the center of the wound is analogous to a raised temperature in the center of a molecular glass, causing flow within the hotter region."

"You could say that a wound is melted glass."

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Gas rich galaxies confirm prediction of modified gravity theory

Modern cosmology says that for the universe to behave as it does, the mass-energy of the universe must be dominated bydark matteranddark energy. However, direct evidence for the existence of these invisible components remains lacking. An alternate, though unpopular, possibility is that the currenttheory of gravitydoes not suffice to describe the dynamics of cosmic systems.

A few theories that would modify our understanding of gravity have been proposed. One of these is Modified Newtonian Dynamics (MOND), which was hypothesized in 1983 by Moti Milgrom a physicist at the Weizmann Institute of Science in Rehovot, Israel. One of MOND's predictions specifies the relative relationship between the mass of any galaxy and its flat rotation velocity. However, uncertainties in the estimates of masses of stars in star-dominated spiral galaxies (such as our own Milky Way) previously had precluded a definitive test.

To avoid this problem, McGaugh examined gas rich galaxies, which have relatively fewer stars and a preponderance of mass in the form ofinterstellar gas."We understand the physics of the absorption and release of energy by atoms in the interstellar gas, such that counting photons is LIKE counting atoms. This gives us an accurate estimate of the mass of such galaxies,"McGaugh said.

Using recently published work that he and other scientists had done to determine both the mass and flat rotation velocity of many gas rich galaxies, McGaugh compiled a sample of 47 of these and compared each galaxy's mass AND rotation velocity with the relationship expected by MOND. All 47 galaxies fell on or very close to the MOND prediction. No dark matter model performed as well.

"I find it remarkable that the prediction made by Milgrom over a quarter century ago performs so well in matching these findings for gas rich galaxies,"McGaugh said."

MOND vs. Dark Matter - Dark Energy

Almost everyone agrees that on scales of large galaxy clusters and up, the Universe is well described by dark matter - dark energy theory. However, according to McGaugh this cosmology does not account well for what happens at the scales of galaxies and smaller.

"MOND is just the opposite,"he said."It accounts well for the 'small' scale of individual galaxies, but MOND doesn't tell you much about the larger universe.

Of course, McGaugh said, one can start from the assumption of dark matter and adjust its models for smaller scales until it fits the current finding."This is not as impressive as making a prediction ahead of {new findings}, especially since we can't see dark matter. We can make any adjustment we need."This is rather like fitting planetary orbits with epicycles,"he said. Epicycles were erroneously used by the ancient Greek scientist Ptolemy to explain observed planetary motions within the context of a theory for the universe that placed the earth in its center.

"If we're right about dark matter, why does MOND work at all?"asks McGaugh."Ultimately, the correct theory - be it dark matter or a modification of gravity - needs to explain this."

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Large Hadron Collider powers up to unravel mysteries of nature

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On Monday, theCERNControl Center turned on the LHC beams to begin the next two-year run of the particle collider. CERN directors decided to extend the run through the end of 2012, instead of shutting down in 2011 for repairs as previously planned, and spirits are running high among scientists working in the field of new physics.

Researchers from across the world engineer detectors and seek to solve the mysteries of matter in an international collaboration that reaches from Chicago to Mumbai.

“Recently there was a convention in Chamonix,” said Georgios Choudalakis, a Greek physicist on the ATLAS experiment at the LHC.“The heads of the experiments and the director of the laboratory decided that we will take data for 2 years. And the decisive criterion for this was the sensitivity to the Higgs, so we’re optimistic.”

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The search is on for the Higgs! The international team of scientists at CERN recalls the bumpy history of the Large Hadron Collider, from disastrous delays to recent results that are exceeding expectations. The physicists anticipate breakthroughs in the next two years that will change our fundamental understanding of the universe. Video credit: Chelsea Whyte and Justin Eure/MEDILL.

This comes on the heels of the news that 2011 will be the end of the run for the Tevatron, the second most powerful particle collider in the world located at the Fermi National Laboratory in Batavia. After setbacks and shutdowns, the LHC had collisions in 2010 that went even better than expected.“We made it clear even to ourselves that the page has turned,” said Choudalakis.“The energy frontier is not at the Tevatron anymore. We are cutting more ice here.”

Now, the hunt for the Higgs is on at CERN, the Conseil Européen pour la Recherche Nucléaire.

The elusive Higgs particle is, according to the theory, a fundamental building block of matter and the reason everything has mass.

“Nobody can explain where mass comes from, but we know it’s there,” said Pauline Gagnon, a French physicist at theATLAS experiment. This conundrum is the most important question physicists have to answer, she said.

“If you think of a one pound bag of salt and you add up the weights of each grain of salt, they will logically equal one pound,” said Gagnon. But, when physicists break down atoms in this way and try to determine the weight of the pieces inside, the calculations of the weight of atomic building blocks such as quarks and electrons don’t add up, she said. Here’s where the Higgs comes in.

The proposed Higgs particle is a part of a field that permeates everything. According to theory, it is a particle’s interaction with the Higgs field that creates drag on a particle, giving it mass. Picture a business man walking through a pool in a suit. The water in the pool is like the Higgs field and, as it soaks into his clothing, it will weigh him down and he will move more slowly. He becomes massive.

Although it has been predicted as the final puzzle piece that completes the Standard Model of physics– the leading explanation for atomic interaction– the existence of the Higgs has never been proven. If such a particle exists, experiments at the LHC should be able to detect it.

“We have indirect suggestions of where it should be if the Higgs exists,” said Choudalakis.“But that is if it exists.” If it can’t be found, the Standard Model will have to be rewritten.

In the next two years, the LHC will resume collisions at 7 TeV, or tera electron volts, between the two beams– the highest energy levels achieved in recent years. The decision at Chamonix mandates that energy in the beams will be kept at this conservative level to avoid the types of machine failures that shut down the LHC in 2008, Gagnon said.

At those energy levels, the two particle beams travel through miles of tubes surrounded by 1,700 superconducting magnets that force bunches of charged particles around the ring and through accelerators designed to increase their speed to within a percentage of the speed of light.

The particle beams, each made up of hundreds of billions of protons, began making their way around a series of underground tubes Monday, guided magnetically and gaining speed and energy. The beams start out about as big around as an index finger and, within microseconds they complete their journey through the four accelerator rings into the LHC and are compressed down to the size of a human hair.

“The beams, at 7 TeV, will have an energy which is the same kinetic energy of a 747 landing, so imagine a big airplane which is landing and smashing against a wall– this is the energy of the LHC beams,” said Mirko Pojer, an Italian and the engineer in charge of the CERN Control Center.

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The sections of beam tube that make up the main ring of the LHC are surrounded superconducting magnets that each weigh 27 tons. Credit: Justin Eure/MEDILL

The two beams, moving in opposite directions, collide at 4 points along the ring where the separate LHC experiments house their detectors, which gather data to analyze the collisions that occur every 25 nanoseconds.

Two of the experiments at CERN are designed to detect a possible Higgs particle. Though they have the same goal, the ATLAS and CMS detectors are designed to look at particle collisions differently.

ATLAS, the larger of the two detectors, stands 82 feet high and houses an enormous magnet system that bends the paths of charged particles after collisions in order to measure their momentum, which identifies them.

CMS, the Compact Muon Solenoid, as its name suggests, is more compact than ATLAS. The CMS detector is designed around a large coiled magnet, which creates a uniform magnetic field that is 100,000 stronger than the Earth’s. CMS measures the subatomic debris of the collisions, hunting for signs of the Higgs.

The 3,000 scientists at ATLAS and the 2,000 scientists at CMS are in a race to be the first to make the biggest scientific discovery of the century.

The next two years of operation will provide enough particle collisions for a groundbreaking discovery. If the Higgs exists, the physicists at CMS or ATLAS will see evidence of the particle. With the amount of data that the LHC will be able to gather in the next two years, scientists expect to confirm the existence or absence of the Higgs, said Gigi Rolandi, an Italian and the physics coordinator for the CMS.

These detectors are truly wonders of the modern age. Like the Acropolis or the Great Wall of China, the LHC is just as incredible a feat of engineering, though it cannot be seen as readily.“It’s a real pity that these detectors are underground,” said Choudalakis.“If they were on the surface, everybody would be very proud of what mankind has done.”

At CERN, the discovery of the fundamental building blocks of nature are just around the corner.“People are thrilled by this, and well deservedly,” said Choudalakis.“What is beautiful about science, especially on a big scale like this, is that it makes you feel like you have a little chance in your life, from your humble starting point, to touch your finger on history and leave a fingerprint on it. Imagine history as a big piece of glass. Most people don’t even get close, and you have a chance to leave your fingerprint on it. I think it’s one of the noblest missions a person can have.”

While the discovery of the Higgs would indeed be a milestone for the world of physics, and a tidy completion of the Standard Model, sometimes messy is far more interesting.

“Like we say, if we do not discover the Higgs particle, it will be even more interesting to find out what else is there in the physics and in nature which then controls the amplitudes of interactions of the particles,” said Slawomir Tkaczyk, a Polish physicist on the CMS experiment.“So, after 10 or 15 years of hard work, the most exciting times are still ahead of us.”

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This story is republished courtesy of Medill Reports.Medill Reportsis written and produced by graduate journalism students at Northwestern University's Medill school.

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Outside the small village of Meyrin, Switzerland, horses graze quietly in fields lined by the Jura mountains. You'd never know it by the idyllic landscape, but 300 feet below the Swiss-French border, the Large ...

Physics/General Physics

13 hours ago |4.6/ 5 (10) |8|

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Small particle means big research for international physics project

They're looking atneutrinos,tiny particleswith a major influence on physics research.

Glenn Horton-Smith, associate professor of physics, is leading the K-State exploration on the Double Chooz neutrino detector, located in the Ardennes region of northern France. The detector measures neutrinos from the nearby Chooznuclear power plant.

More than 38 universities and research institutes from eight countries are working on the neutrino detector. K-State is one of 14 U.S. organizations involved.

Neutrinos are neutralelementary particlesthat come from nuclear reactions orradioactive decay, and large detectors are needed to capture and measure them.

The detector is buried more than 300 feet inside a hill a little more than a half of a mile away from the nuclear reactor and is the site of a previous neutrino experiment. Construction on the first of two new neutrino detectors finished in late 2010.

"It's exciting because we're in a data-taking stage right now,"Horton-Smith said."We're looking at the first data that is coming out and making sure everything is working correctly."

K-State scientists, along with K-State's Electronics Design Lab, designed and built the hardware for the detector's monitoring system, which measures the magnetic field and temperature throughout the detector. Horton-Smith wrote the first computer simulation of the detector, and he leads the group of researchers who work on offline data processing and simulation software.

The hardware and software help the detector measure neutrino oscillations, which are the transformations of neutrinos into different types. Neutrinos come in three different types, each an overlapping of three different mass states. As these states oscillate, a neutrino's type changes.

"It is very analogous to a musical chord, where you hear two or three frequencies at the same time,"Horton-Smith said.

While two mass states have been detected in the neutrinos from reactors, the third state is either weak or absent. Researchers in the Double Chooz collaboration want to discover more about this third mass state.

To capture and measure neutrinos, the detector includes a central cylinder 10.5 cubic meters in size that is surrounded by larger cylinders. The cylinders are filled with a clear liquid scintillating oil that glows when neutrinos interact and measures energy deposited by radiation and subatomic particles. Several layers of buffer liquid and steel act as protection.

"We're really checking to see whether all three mass states are in the electron neutrino, or if one of them is missing,"Horton-Smith said."If one of them is missing, there are all sorts of theories about why that may be."

Researchers will collect data throughout the year from the first detector. The second detector, scheduled to be completed in 2012, will be even closer to thenuclear reactor-- more than 1,300 feet. By comparing data from both detectors at two different distances, researchers hope to have more accurate measurements of neutrino oscillations.

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'Fingerprints' match molecular simulations with reality

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ORNL's Jeremy Smith collaborated on devising a method -- dynamical fingerprints -- that reconciles the different signals between experiments andcomputer simulationsto strengthen analyses of molecules in motion. The research will be published in theProceedings of the National Academy of Sciences.

"Experiments tend to produce relatively simple and smooth-looking signals, as they only 'see' a molecule's motions at low resolution,"said Smith, who directs ORNL's Center forMolecular Biophysicsand holds a Governor's Chair at the University of Tennessee."In contrast, data from a supercomputer simulation are complex and difficult to analyze, as the atoms move around in the simulation in a multitude of jumps, wiggles and jiggles. How to reconcile these different views of the same phenomenon has been a long-standing problem."

The new method solves the problem by calculating peaks within the simulated and experimental data, creating distinct"dynamical fingerprints."The technique, conceived by Smith's former graduate student Frank Noe, now at the Free University of Berlin, can then link the two datasets.

Supercomputer simulations and modeling capabilities can add a layer of complexity missing from many types of molecular experiments.

"When we started the research, we had hoped to find a way to use computer simulation to tell us which molecular motions the experiment actually sees,"Smith said."When we were finished we got much more -- a method that could also tell us which other experiments should be done to see all the other motions present in the simulation. This method should allow major facilities like the ORNL's Spallation Neutron Source to be used more efficiently."

Combining the power of simulations and experiments will help researchers tackle scientific challenges in areas like biofuels, drug development, materials design and fundamental biological processes, which require a thorough understanding of how molecules move and interact.

"Many important things in science depend on atoms and molecules moving,"Smith said."We want to create movies of molecules in motion and check experimentally if these motions are actually happening."

View asupercomputer simulationof a protein in motion here: http://www.ornl.gov/ornlhome/hg_mer.htm

"The aim is to seamlessly integrate supercomputing with the Spallation Neutron Source so as to make full use of the major facilities we have here at ORNL for bioenergy and materials science development,"Smith said.

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The Year of the Higgs?

The search will take place at theLarge Hadron Collider(LHC) at CERN, the world's largest particle accelerator at the European Organization for Nuclear Research in Geneva, Switzerland.

The Higgs boson is the only remainingStandard Modelparticle that has not been observed in particle physics experiments. But using two separate and complimentary experiments, the A Toroidal LHC Apparatus (ATLAS) and Compact Muon Solenoid (CMS), scientists hope to prove its existence.

Both ATLAS and CMS are particle physics detectors. They are located on opposite sides of the 27-kilometer (17-mile) LHC ring circling the countryside on the outskirts of Geneva, buried deep below ground.

The LHC has been offline during a winter break, which temporarily halted the experiments.

"The research program over this past year was essentially to commission the accelerator and the experiments to make sure that they work and they are giving us sensible results,"said physicist Aaron Dominguez of the University of Nebraska and the US CMS experiment, whose work is supported by the National Science Foundation.

The University of Nebraska researchers played an important role in building the LHC detectors and analyzing data that comes from the experiments.

Confident that everything is functioning properly, the LHC research community recently announced a decision to delay a planned shutdown of theparticle acceleratoruntil the end of 2012. If the machine continues to function at the current level, researchers believe they can explore the entire"allowed region"--the ranges of mass in which the standard model Higgs boson could exist--by the end of 2012.

"This was one of the reasons to run in 2012 and not just this year,"said Gustaaf Brooijmans of Columbia University and the US ATLAS experiment."Our projections now say that with the 2012 run we should be able to probe about 90-95 percent of the 'allowed region' for the existence of the Higgs boson."

Brooijmans' team at Columbia develops and operates the electronics that read out part of the detector.

"If theacceleratoris performing according to plan, we should have a very good first picture of this whole 'allowed range' of the standard modelHiggs boson,"said Dominguez.

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Physicists build bigger 'bottles' of antimatter to unlock nature's secrets

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While physicists routinely produce antimatter with radioisotopes and particle colliders, cooling these antiparticles and containing them for any length of time is another story. Once antimatter comes into contact with ordinary matter it"annihilates"—or disappears in a flash of gamma radiation.

Clifford Surko, a professor of physics at UC San Diego who is constructing what he hopes will be the world's largest antimatter container, said physicists have recently developed new methods to make special states of antimatter in which they can create large clouds of antiparticles, compress them and make specially tailored beams for a variety of uses.

He described the progress made in this area, including his own efforts, at the annual meeting in Washington, DC, of the American Association for the Advancement of Science. His talk,"Taming Dirac's Particle,"led off the session entitled"Through the Looking Glass: Recent Adventures in Antimatter,"on February 18.

Surko said that since"positrons"—the anti-electrons predicted by English physicist Paul Dirac some 80 years ago—disappear in a burst of gamma rays whenever they come in contact with ordinary matter, accumulating and storing these antimatter particles is no small feat. But over the past few years, he added, researchers have developed new techniques to store billions of positrons for hours or more and cool them to low temperatures in order to slow their movements so they can be studied.

Surko said physicists are now able to slow positrons from radioactive sources to low energy and accumulate and store them for days in specially designed"bottles"that have magnetic and electric fields as walls rather than matter. They have also developed methods to cool them to temperatures as low as that of liquid helium and to compress them to high densities.

"One can then carefully push them out of the bottle in a thin stream, a beam, much like squeezing a tube of toothpaste,"said Surko, adding that there are a variety of uses for such positrons.

A familiar positron technique that does not use this new technology is the PET scan, also known as Positron Emission Tomography, which is now used routinely to study human metabolic processes and help design new drugs.

In the new methods being developed by physicists, beams of positrons will be used in other ways."These beams provide new ways to study how antiparticles interact or react with ordinary matter,"said Surko."They are very useful, for example, in understanding the properties of material surfaces."

Surko and his collaborators at UC San Diego are studying how positrons bind to ordinary matter, such as atoms and molecules."While these complexes only last a billionth of a second or so,"he said,"the 'stickiness' of the positron is an important facet of the chemistry of matter and antimatter."

Surko and his colleagues are building the world's largest trap for low-energy positrons in his laboratory at UC San Diego, capable of storing more than a trillion antimatter particles at one time.

"We are now working to accumulate trillions of positrons or more in a novel 'multi-cell' trap—an array of magnetic bottles akin to a hotel with many rooms, with each room containing tens of billions of antiparticles,"he said.

"These developments are enabling many new studies of nature. Examples include the formation and study of antihydrogen, the antimatter counterpart of hydrogen; the investigation of electron-positron plasmas, similar to those believed to be present at the magnetic poles of neutron stars, using a device now being developed at Columbia University; and the creation of much larger bursts of positrons which could eventually enable the creation of an annihilation gamma ray laser."

"An exciting long-term goal of the work is the creation of portable traps forantimatter,"added Surko."This would increase greatly the ability to use and exploit antiparticles in our matter world in situations where radioisotope- or accelerator-based positron sources are inconvenient to arrange."

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A new high-resolution method for imaging below the skin using a liquid lens

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Rolland will be presenting her findings at the 2011 annual meeting of the American Association for the Advancement of Science in Washington, D.C., on Feb. 19.

"My hope is that, in the future, this technology could remove significant inconvenience and expense from the process of skin lesion diagnosis,"Rolland says."When a patient walks into a clinic with a suspicious mole, for instance, they wouldn't have to have it necessarily surgically cut out of their skin or be forced to have a costly and time-consuming MRI done. Instead, a relatively small, portable device could take an image that will assist in the classification of the lesion right in the doctor's office."

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This prototype device developed by University of Rochester Professor of Optical Engineering Jannick Rolland can take high-resolution images under the skin's surface without removing the skin. Researchers say that in the future it may eliminate the need for many biopsies to detect skin cancer. Credit: J. Adam Fenster

The device accomplishes this using a unique liquid lens setup developed by Rolland and her team for a process known asOptical CoherenceMicroscopy. In a liquid lens, a droplet of water takes the place of the glass in a standard lens. As theelectrical fieldaround the water droplet changes, the droplet changes its shape and therefore changes the focus of the lens. This allows the device to take thousands of pictures focused at different depths below the skin's surface. Combining these images creates a fully in-focus image of all of the tissue up to 1 millimeter deep in human skin, which includes importantskin tissuestructures. Because the device uses nearinfrared lightinstead of ultrasounds, the images have a precise, micron-scale resolution instead of a millimeter-scale resolution.

The process has been successfully tested in in-vivo human skin and several papers on it have been published in peer-reviewed journals. Rolland says that the next step is to start using it in a clinical research environment so its ability to discriminate between different types of lesions may be assessed.

Rolland joined the faculty of the Hajim School of Engineering and Applied Science's Institute of Optics in 2009. She is the Brian J. Thompson Professor of Optical Engineering and is also a professor of biomedical engineering and associate director of the R.E. Hopkins Center for Optical Design and Engineering.

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The physics of a sustainable society revolution

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Innovative physics will lead the way

“I decided to become a scientist when I was a second-grade student at elementary school. Reading biographies of Nobel laureates, I admired scientists for contributing to society through their work. When I was young, the most famous scientists in Japan were the physicists Hideki Yukawa and Shinichiro Tomonaga, who inspired me to become a physicist,” says Tokura.“Physicshas led to major revolutions in human society,” he points out.“A good example is electromagnetic induction discovered by the British physicist Michael Faraday in the nineteenth century.”

Electromagnetic induction is the phenomenon by which an electric current flows through a coil when a magnet is inserted into the coil and pulled out again. Its discovery led to the development of power generators, thus laying the foundation for our electricity-powered modern society. Modern civilization is critically reliant on ubiquitous supply of electrical power, all of which has been built on the discovery of electromagnetic induction.“The recent spread of information technology devices, including mobile phones, personal computers and the Internet, has dramatically changed society and economies, and even our lifestyles. This major revolution began with the emergence of semiconductor electronics, with the development of the transistor about 60 years ago. Such breakthroughs are based on physics.”

Tokura has a vision for another revolution, which he calls‘Innovation 4’. He believes that four key technological breakthroughs could once again change society as we know it: an increase in solar cell conversion efficiency to 40% or more, an increase in the thermoelectric conversion figure of merit to 4 or more, an increase in the critical temperature of superconductivity to 400 K or well above room temperature, and an in increase in battery energy density to 400 watt-hours per kilogram or more.“These numerical targets represent a tripling of existing performance indexes. Another goal is to achieve electronic information processing with minimal power consumption to conserve energy. If realized,‘Innovation 4’ will lead to a sustainable society revolution, but it is difficult to achieve these breakthroughs merely by improving existing technologies. We need to develop electronic technologies based on new principles.”

Tokura and his colleagues have been researching electronic technologies based on principles that are totally different from the mainstream semiconductor electronics of today.“It is assumed that electrons are sparse in conventional semiconductor devices, so the entanglement of electrons is weak. A group of many densely packed electrons, however, interact strongly with each other in what is known as‘a strongly correlated electron system’. In such a system, non-charge properties that are not important in semiconductors, such as electron spin and orbital, also play important roles. We are seeking to create new functions that are not possible using independent electrons alone by utilizing the features of strongly correlated electron systems. High-temperature superconductivity is another phenomenon that occurs in strongly correlated electron systems. Electronic engineering still has infinite potential.

“The electron state in strongly correlated electron systems can be described as a solid produced by electrons. The electron state is like a dilute gas in semiconductors or a liquid in metals. Just as a liquid flows when the container is inclined, electricity flows when a voltage is applied to a metal. In a strongly correlated electron system, where the electron state is‘solid’, electrons are unable to move because of mutual electrical repellence due to their dense packing. Even when a voltage is applied, no electricity flows. Hence, a strongly correlated electron system is an insulator, or specifically, a Mott insulator. When a minor stimulus such as heat, light or an electric field is applied from outside, a phase change from solid to liquid occurs instantaneously, allowing the electrons to move. In strongly correlated electron systems, this state can be changed at ultra-high speed on a nanometer scale.”

A bridge across electron functions

“In a strongly correlated electron system, cross-correlation is possible,” continues Tokura.“When a voltage is applied, an electric current flows. When a magnetic field is applied, the system becomes magnetized. These are the usual responses. By bridging different functions of the electron, unusual responses are induced. We call this phenomenon‘cross-correlation’.”

A typical example of cross-correlation (Fig. 1) is the‘colossal’ magnetoresistance effect, which was achieved with manganese oxide by Tokura in the 1990s. In this phenomenon, electric resistance decreases dramatically by a factor of one-thousand when a magnetic field is applied. This unusual response—a change in electrical resistance when a magnetic field is applied—is an example of cross-correlation. By utilizing a strongly correlated electron system, it is possible to produce a state in which an insulator lacking magnetization and a metal having magnetization compete with each other (Fig. 2). Cross-correlation allows two different functions of the electron to compete in a pair-like manner. When a magnetic field is applied to an insulator, it becomes magnetized and metallic, resulting in a dramatic drop in electric resistance.

Low-energy information processing

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Figure 2: The principle of‘colossal’ magnetoresistance. A state is created in which an insulator lacking magnetization and a metal with magnetization compete in a pair-like manner. When a magnetic field is applied to the insulator, it becomes magnetized and turns metallic, resulting in a dramatic decrease in electrical resistance. This rapid phase change can also be achieved by exposure to light or application of an electric field.

In 2007, Tokura established his own research group, the Cross-Correlated Materials Research Group, at RIKEN, and has since been conducting research on Innovation 4.“We aim to develop electronic technologies based on new principles for processing and recording information without conducting electrons.”

Existing semiconductor devices process information by conducting electrons. However, this involves the use of electrical power, and energy is wasted in the form of waste heat generated due to electric resistance. The same applies to information recording. In hard disks, for example, an electric current is passed through a coil to generate a magnetic field to reverse the orientation of magnetization in a storage bit during information recording. This also requires a electrical power, generating waste heat and wasting energy, and in large computers, the waste heat generated must be cooled using air-conditioners, consuming additional electrical power.

“If cross correlation, that is, the unusual inversion of magnetization using an electric field, rather than the inversion of magnetization using a magnetic field, could be achieved, it will be possible to record information without wasting energy and with minimal power consumption. We are working on using multiferroics to achieve this.”

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Figure 3: Ferroelectrics and ferromagnetics. Ferroelectrics and ferromagnetics permit the orientations of electrical polarization and magnetization to be reversed by applying an electric field and magnetic field, respectively.

Multiferroics exhibit both ferroelectricity and ferromagnetism. A ferroelectric (Fig. 3) exhibits polarization, with one end positively charged and the other end negatively charged, even in the absence of an external electric field. When an electric field is applied to a ferroelectric, the two poles (+ and–) reverse themselves, allowing information to be rewritten. This phenomenon is used in some prepaid‘e-money’ card systems for transport and shopping. A ferromagnetic, on the other hand, exhibits magnetization in the absence of a magnetic field, and the orientation of magnetization can be reversed by applying a magnetic field. Ferromagnetics are utilized in hard disks and other data recording devices.“In multiferroics, it is possible to realize the unusual response of reversing magnetization and simultaneously reversing the electrical polarization using an electric field by linking the orientations of electrical polarization and magnetization.”

Polarization is caused by a bias in the distribution of electrons in a material, whereas magnetization occurs when electron spins line up, which otherwise can have either upward or downward orientations, become aligned in a given orientation. Electron spin thus serves as the origin of magnetization.

“The orientation of polarization can be reversed by deforming the orbital in which the electron is accommodated. By utilizing a strongly correlated electron system of multiferroics, the orientation of electron spins can be reversed by deforming the orbital or electron cloud, which would make it possible to link the polarization and magnetization.”

In 2009, Tokura and his colleagues succeeded in experimentally changing the orientation of magnetization at temperatures below–271°C using an electric field.“If we can improve on this and simultaneously reverse the orientations of magnetization and polarization at room temperature using an electric field, then we will be able to create large-capacity memory that consumes almost no electrical power.”

More recently in June 2010, Tokura’s research group became the first in the world to directly observe skyrmion crystallization, the phenomenon by which electron spin vortices are regularly arranged like a crystal. The result attracted worldwide attention.“It is thought that these electron spin vortices can be moved with a small amount of electric current. Hence, by merely changing the orientation of electron spins one after another, it is possible to move the electron spin vertexes to achieve information processing. This has potential for information processing with minimal power consumption.”

New principles for highly efficient solar cells

“We also have an idea for dramatically improving the power efficiency of solar cells,” says Tokura. In conventional solar cells, a medium such as a semiconductor absorbs photons and generates a free pair of negative and positive charges. By separating the negative electron and positive‘hole’ and transporting them to opposite electrodes, a voltage can be produced. The light-to-electricity conversion efficiencies of modern solar cells is just over 10%, but it should be possible to improve on this efficiency.“Solar radiation contains a broad range of wavelengths. Semiconductor solar cells actually achieve nearly 100% conversion efficiency at particular wavelengths of light, because electron–hole pair can be produced from a single photon at a particular wavelength in each semiconductor with nearly 100% probability. However, an electron–hole pair is also produced when a photon with a shorter wavelength and higher energy level is absorbed, in which case the excess energy is wasted as heat. This accounts for the low power efficiency. If we use a strongly correlated electron system, the wasted energy could be used to create a metallic state and produce a large number of electrons and holes by another mechanism, which could dramatically improve conversion efficiency. Strongly correlated electron systems are being actively studied worldwide, but Tokura and his colleagues are the only group researching their use in highly efficient solar cells.

Basic science will build a bright future

“Physics will continue to yield major revolutions in human society. In recent years, however, it has become increasingly difficult for a single scientist to make a breakthrough alone.”

The Japanese government this year established the Quantum Science on Strong Correlation project with the support of the Funding Program for World-Leading Innovative R&D on Science and Technology. RIKEN is responsible for providing research support, and Tokura serves as key investigator. For this project, he has established a dedicated research group, the Correlated Electron Research Group.“This project aims to set groundbreaking principles for realizing Innovation 4 through integrated joint research among outstanding researchers in a broad range of fields, including physics theory, thin-film growth, structural analysis and instrumentation measurement technology. However, if someone ordered me to produce results that could be used in practical applications within several years, I would struggle. Faraday, when asked about why his discovery ofelectromagnetic inductionwas so important, answered,”Who can predict what a newborn baby will become?” The usefulness of the results of basic research like ours is sometimes unpredictable. In the long term, 50 or 100 years, however, they have the potential to produce major revolutions and contribute greatly to future society.”

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Ice offers possible explanation for Death Valley's mysterious 'self-moving' rocks

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In the remote, almost totally dry lakebed called Racetrack Playa, some of the rocks move themselves across the desert floor when people aren't watching.

Scientists know the rocks move because they leave narrow tracks trailing behind them, but they haven't actually seen it happen. And although one can't entirely rule out the possibility of some prank being played, at least some of the rocks appear to be moving under natural circumstances.

It doesn't rain often in Racetrack Playa, and when it does the lakebed can flood. The rocks don't float exactly, but the main explanation for their movement is that moisture can make the mud on which the rocks sit more slick, making it easier for high winds to push the rocks along. Another explanation offered is that the temporary deposit of water, chilled to form extensive sheets of ice, might help to reflect and focus the winds, making it easier for the rocks to move.

The winds required to move rocks in this way would seem to be at the level of 100 mph or more. That's why the rocks are sometimes referred to as"sailing stones."They are rare but they have been noticed in Racetrack Playa and a few other arid places around the world subject to occasional floods

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The track left from a"self-moving"rock. Credit: Courtesy of Ralph Lorenz

Ralph Lorenz, a scientist at Johns Hopkins University, offers a new explanation. The rocks are actually lifted up by the ice, or at least made more buoyant by the ice, making it easier for the rocks to migrate. If the rocks are moving about on ice rafts, the ground below cannot offer as muchresistanceagainst their motion and the winds needed for movement wouldn't have to be as great, he argued.

So why hasn't the motion been observed?

"Movement happens for only tens of seconds, at intervals spaced typically by several years,"said Lorenz."This would demand exceptional patience as well as luck."

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So, the rocks are probably traveling on the coldest and windiest days that occur over a period of several years. The most likely time would be in the very early dawn. Little wonder no one is around to witness the event.

Lorenz and his colleagues would like to install inexpensive time-lapse monitoring of the Playa area, using digital cameras. The lakebed is about 2.5 miles long and 1.25 miles wide. They have also performed some laboratory tests by blowing on ice-assisted rocks. These simple tests support the ice-raft hypothesis. The results appear in the January 2011 issue of theAmerican Journal of Physics.

An additional reason for studying the rocks of Racetrack Playa is that its qualities resemble those at a drying-up lake on Saturn's moon Titan. Pictures taken by the Cassini-Huygens mission reveal what look like river channels, cobblestones, and lake beds or mud flats. Only at Titan's"Ontario Lacus,"as one interesting site is called, the runoff consists of liquid hydrocarbons, not water. Some pictures even seem to be showing a"bathtub ring"left by what is probably a drying lake.

One of Lorenz's colleagues, Brian K. Jackson, who works at NASA's Goddard Space Flight Center, also likes the idea that their research at Racetrack Playa has a dual purpose.

"It's been exciting trying to solve a mystery that has resisted solution for sixty years,"Jackson said."Scientific accounts of the Racetrack Playa rocks go back to at least 1948, and there were certainly stories about the playa long before that."

And Jackson also believes discoveries in Death Valley, here on Earth, will help us to better understand similar real estate on Titan or Mars.

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The Daya Bay Reactor Neutrino Experiment: On track to completion

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What the researchers find at Daya Bay will bear on some of the most intriguing questions in basicphysics: how much do different kinds ofneutrinosweigh? And which kind is the heaviest? By weighing neutrinos scientists hope to learn how electrons and their cousins, muons and tau particles, came into existence in the moments after the big bang. The answers could explain why there is more matter than antimatter in the universe– and indeed why there is any matter at all.

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The heart of the Near Hall is a pool of ultrapure water in which the antineutrino detectors will be submerged, shielded from radioactive decays in the surrounding rock by more than two meters of water on all sides. The pool is lined with PMTs to track any“stiff” (highly energetic) cosmic rays that make it all the way through the overlying rock. The blue supports beyond the pool indicate where a different kind of detector is being constructed, which will roll over the water pool like a roof and help locate the position of any cosmic rays that enterthe water.

Clues to neutrino mass lie in measuring how one“flavor” of neutrino changes into another. (Electron neutrinos, muon neutrinos, and tau neutrinos, the three flavors, are named after the leptons with which each is associated.) The crucial value, writtenθ₁₃, is a term known as“neutrino mixing angle theta one three”– and the Daya Bay experiment is intended to measure it to within a few degrees. The following tour of the experimental site shows how the researchers hope to do it.

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Unique new probe of proton spin structure at Relativistic Heavy Ion Collider

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“Exploring the mystery of protonspinhas been one of the key scientific research goals at RHIC,” said Steven Vigdor, Brookhaven’s Associate Laboratory Director for Nuclear and Particle Physics.“Like many scientific mysteries, this one turns out to be more complex the more we learn about it. The W boson measurements were enabled by new detection techniques at RHIC’s STAR and PHENIX experiments and by extending RHIC’s world-record energies for the acceleration of proton beams with a distinct spin orientation preference. The results will allow us to tease apart subtle details that were previously inaccessible, and should move the field closer to a quantitative understanding of proton spin structure and dynamics.”

Spin is a quantum property that describes a particle’s intrinsic angular momentum. Like charge and mass, it’s part of a particle’s identity, whose magnitude is the same for all particles of a given type. But unlike charge and mass, spin has a direction that can be oriented differently for individual particles of a given species. The interactions among particles inside atoms, nuclei, and protons depend critically on their relative spin orientations, with influence on a wide range of electrical, magnetic, optical, and other properties of matter. Yet despite the fact that proton spin is used in everyday applications like magnetic resonance imaging (MRI), exactly how— and how much— the individual particles that make up protons contribute to spin remains a mystery.

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PHENIX Detector

Scientists know that the quarks inside a proton each have their own intrinsic spin. But numerous experiments have confirmed that a directional preference among all these quark spins can account for only about 25 percent of the proton’s total spin. RHIC was built with the ability to collide polarized protons— protons whose spins could be aligned in a controlled way— so scientists could probe other factors that might account for the“missing” spin. Much of the equipment needed to realize this unique capability was provided by the RIKEN Institute of Physical and Chemical Research of Japan, whose researchers form a critical part of the international collaborations carrying out this work.

After beginning polarized proton collisions at RHIC late in 2001, the first place the scientists looked for the missing spin was the gluons, the particles that hold a proton’s quarks together via the strong force.

“The shock so far has been that we haven’t found gluons carrying much of the spin,” said PHENIX spokesperson Barbara Jacak, a physicist at Stony Brook University. Measurements from the STAR detector agree. After several polarized proton runs at various energies, RHIC data suggest with more and more certainty that gluons contribute much less than originally speculated to proton spin, so the source of the spin still remains a mystery.

The scientists acknowledge that they haven’t been able to look at all the gluons, particularly those that carry tiny fractions of the proton’s overall momentum.“It’s like we’re looking for missing keys under a narrow-focus street lamp, and we’d like a lamp with broader illumination,” Jacak said.

But as they continue to work on that part of the puzzle, they also have a new way to look at spin.

Thanks to new detection techniques and the ability to run polarized proton collisions at very high energies— 500 GeV, or 500 billion electron volts— RHIC scientists at both PHENIX and STAR are able to directly probe the polarization contributions from different flavored quarks (known by the names“up” and“down”) inside protons for the first time.

“All of the earlier measurements that attempted to separate quark spin contributions according to flavor were done indirectly, and they looked primarily at the contribution of the three leading, or valence, quarks in the proton,” said Bernd Surrow, a Massachusetts Institute of Technology physicist and deputy spokesperson of the STAR collaboration.“This new method of measuring W bosons gives us direct access to quarks known as‘sea quarks,’ which wink in and out of existence as gluons split and reform within the protons.”

Sea quarks are always produced in quark/antiquark pairs and have exceedingly short lifetimes. But at the very high energies achieved in RHIC’s colliding proton beams, these fleeting quarks and antiquarks can collide, or interact, to produce relatively heavy W bosons. So far, RHIC’s experiments have detected Ws by looking for electrons and positrons (positively charged electrons) that form as the Ws decay. The charge of the decay products— whether electrons or positrons— directly reflects the charge of the Ws, which in turn tells what flavor of antiquarks were involved in the collision— whether anti-up or anti-down.

By comparing the number of Ws produced when bunches of RHIC’s colliding protons are polarized in the direction of the beam’s motion with the number produced when the protons are polarized in the opposite direction, the scientists can directly measure the degree to which the antiquark spins point in a preferred direction with respect to the overall proton spin. This robust measurement technique relies on a fundamental, and very well understood, property of the weak interaction by which the Ws are produced, namely, its extreme violation of mirror symmetry.

“Observation of this extreme effect in weak interactions for the first time in polarized proton-proton collisions at RHIC is itself a major milestone,” said Hideto En’yo, director of the RIKEN Nishina Center for Accelerator-Based Science, which established the RIKEN-BNL Research Center (RBRC) to nurture a new generation of physicists interested in studying the strong force and spin physics at RHIC.“It is gratifying to see our large investments in polarization equipment pay off with such large and cleanly interpretable spin effects.”

“You would think you would get equal numbers of anti-up and anti-down quarks inside a proton. But previous experiments have shown that they are very different,” Surrow said.“That means there is a lot of uncertainty about the underlying mechanism of how these sea quarks pop in and out of existence. It also indicates that the different flavors may behave differently in terms of how they contribute to spin.”

Added Jacak,“Understanding these differences won’t by itself solve the spin mystery, but it will give us a clearer picture of one piece of the puzzle, the sea quark contribution.”

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Ground-based lasers vie with satellites to map Earth's magnetic field

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University of California, Berkeley, physicists have now come up with a much cheaper way to measure the Earth's magnetic field using only a ground-basedlaser.

The method involves exciting sodium atoms in a layer 90 kilometers above the surface and measuring the light they give off.

"Normally, the laser makes the sodium atom fluoresce,"said Dmitry Budker, UC Berkeley professor of physics."But if you modulate the laser light, when the modulation frequency matches the spin precession of the sodium atoms, the brightness of the spot changes."

Because the local magnetic field determines the frequency at which the atoms precess, this allows someone with a ground-based laser to map the magnetic field anywhere onEarth.

Budker and three current and former members of his laboratory, as well as colleagues with the European Southern Observatory (ESO), lay out their technique in a paper appearing online this week in the journalProceedings of the National Academy of Sciences.

Various satellites, ranging from the Geostationary Operational Environmental Satellites, or GOES, to an upcoming European mission called SWARM, carry instruments to measure the Earth's magnetic field, providing data to companies searching for oil or minerals, climatologists tracking currents in the atmosphere and oceans, geophysicists studying the planet's interior and scientists tracking space weather.

Ground-based measurements, however, can avoid several problems associated with satellites, Budker said. Because these spacecraft are moving at high speed, it's not always possible to tell whether a fluctuation in the magnetic field strength is real or a result of the spacecraft having moved to a new location. Also, metal and electronic instruments aboard the craft can affect magnetic field measurements.

"A ground-based remote sensing system allows you to measure when and where you want and avoids problems of spatial and temporal dependence caused by satellite movement,"he said."Initially, this is going to be competitive with the best satellite measurements, but it could be improved drastically."

Laser guide stars

The idea was sparked by a discussion Budker had with a colleague about of the lasers used by many modern telescopes to remove the twinkle from stars caused by atmospheric disturbance. That technique, called laser guide star adaptive optics, employs lasers to excite sodium atoms deposited in the upper atmosphere by meteorites. Once excited, the atoms fluoresce, emitting light that mimics a real star. Telescopes with such a laser guide star, including the Very Large Telescope in Chile and the Keck telescopes in Hawaii, adjust their"rubber mirrors"to cancel the laser guide star's jiggle, and thus remove the jiggle for all nearby stars.

It is well known that these sodium atoms are affected by the Earth's magnetic field. Budker, who specializes in extremely precise magnetic-field measurements, realized that you could easily determine the local magnetic field by exciting the atoms with a pulsed or modulated laser of the type used in guide stars. The method is based on the fact that the electron spin of each sodium atom precesses like a top in the presence of a magnetic field. Hitting the atom with light pulses at just the right frequency will cause the electrons to flip, affecting the way the atoms interact with light.

"It suddenly struck me that what we do in my lab with atomic magnetometers we can do with atoms freely floating in the sky,"he said.

Budker's former post-doctoral fellow James Higbie now an assistant professor of physics and astronomy at Bucknell University– conducted laboratory measurements and computer simulations confirming that the effects of a modulated laser could be detected from the ground by a small telescope. He was assisted by Simon M. Rochester, who received his Ph.D. in physics from UC Berkeley last year, and current post-doctoral fellow Brian Patton.

Portable laser magnetometers

In practice, a 20- to 50-watt laser small enough to load on a truck or boat tuned to the orange sodium line (589 nanometer wavelength) would shine polarized light into the 10 kilometer-thick sodium layer in the mesosphere, which is about 90 kilometers overhead. The frequency with which the laser light is modulated or pulsed would be shifted slightly around this wavelength to stimulate a spin flip.

The decrease or increase in brightness when the modulation is tuned to a"sweet spot"determined by the magnitude of themagnetic fieldcould be as much as 10 percent of the typical fluorescence, Budker said. The spot itself would be too faint to see with the naked eye, but the brightness change could easily be measured by a small telescope.

"This is such a simple idea, I thought somebody must have thought of it before,"Budker said.

He was right. William Happer, a physicist who pioneered spin-polarized spectroscopy and the sodium laser guide stars, had thought of the idea, but had never published it.

"I was very, very happy to hear that, because I felt there may be a flaw in the idea, or that it had already been published,"Budker said.

While Budker's lab continues its studies of how spin-polarized sodium atoms emit and absorb light, Budker's co-authors Ronald Holzlöhner and Domenico Bonaccini Calia of the ESO in Garching, Germany, are building a 20-watt modulated laser for the Very Large Array in Chile that can be used to test the theory.

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Laser welding in the right light

It's a quick process, generates almost no waste and is extremely precise: within a few seconds, alaser beamhas welded the casing and speedometer cover together– without any screws, clamps or glues whatsoever. The result is a perfect weld seam scarcely visible to the naked eye. There are no sparks or particles flying through the air during welding. What's more: the resulting heat is confined to a minimal area. This protects the material. Many industries have now turned to welding plastics with a laser.

Still, the technology has its limits; when it comes to fusing twoplastic componentstogether, for instance, there is little freedom of choice. Up until now, the upper joining part had to be transparent to permit the laser to shine through unimpeded while the lower joining part absorbed the radiation. This usually meant soot particles had to be blended into the plastic. These particles absorb the energy of the laser beam and transmit the fusion heat generated to the upper joining part."Up until now, you usually had to choose a single plastic combination: transparent and black. There are lots of applications– in medical technology, for instance– where what's needed is a combination of two transparent plastics,"explains Dr.-Ing. Alexander Olowinsky, project manager at the Fraunhofer Institute for Laser Technology ILT in Aachen, Germany. The researcher and his team have now managed to erase the previous boundaries of laser welding.

"The industry now also makes infrared absorbers that are nearly transparent, but these are not only very expensive but also have a green, yellowish tint to them,"Olowinsky elaborates."So our goal was to find a way to get the job done completely free of absorber materials."To accomplish this, researchers studied the absorption spectra of a range of transparent polymers in search of wavelength ranges within which plastic absorbs laser radiation. Then the scientists tested and perfected the laser systems to match: systems that emit light of the right wavelengths."Before, you didn't have the right light source,"Olowinsky adds."It was only during the past few years that laser sources have been developed that emit light in these wavelength ranges."To deliver the light energy to the joining level– to the seam along the border between the two transparent plastics– the experts at ILT came up with special lens systems. These systems focus the beam so that the highest energy density occurs at the beam waist– where the beam diameter is the smallest– so that the highest temperature is delivered precisely to the joining level.

The researchers' most promising results were achieved at awavelengthof around 1700 nanometers."This is the peak welding-efficiency range,"Olowinsky summarizes. Nevertheless, the researchers are also continuing work on the EU Commission-sponsored"PolyBright"project in search of the combination of the right absorption bands with the matching light sources."The result has to be the most cost-effective laser system possible that can execute high-precision welding tasks at the highest possible speed."

Medical technology and bioanalytics in particular are among the main beneficiaries of the new welding process: The magic word is"lab on a chip."This refers to automatic, miniature-sized laboratory analysis on the surface of a chip. Whether fluids, protein or DNA analyses– the spectrum of applications is a broad one.

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Cracking the children's fingerprint disappearing act

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Forensic scientists often use techniques like magnetic filings dusting, iodine, and cyanoacrylate fuming to see otherwise invisible, or latent,fingerprints. Although efficient, inexpensive, and relatively fast, these methods make it difficult to preserve trace evidence found in a fingerprint. This is particularly difficult with aged fingerprints left by children, which have been shown to fade faster than those of adults, making them almost impossible to capture.

"Previous research has linked the difference in the longevity of fingerprints to the type of oil found in a person's skin,"said NSLS biophysicist Lisa Miller, one of the authors of the study."This oil, known as sebum, is just one of the components of a fingerprint, which also can contain small pieces of skin and sweat residue. We wanted to determine how these fingerprint components change over time in adults and children, and how these changes alter our ability to predict someone's age based on their fingerprint."

Using a collection of latent fingerprints given by six father (ages 35-45) and son (ages 7-10) pairs, the researchers watched for chemical changes over the course of four weeks. Twice a week, one fingerprint from each participant was dusted, lifted, and analyzed based on the number of features, or minutiae, visible. At the same time, a non-invasive synchrotron technique called Fourier transform infrared microspectroscopy (FTIRM) mapped the location and makeup of the skin and sebum in the prints.

"FTIRM is a very useful tool in this case because it allows us to examine individual fingerprint components— namely, skin and sebum— separately,"Miller said.

At all points in time, the fathers' prints dusted darker than those from their sons. In fact, the fathers' prints remained virtually unchanged during the four-week study, while the fine minutiae of their children became increasingly more difficult to see.

The NSLS study, which was carried out at beamline U10B, helps researchers understand this disappearing act. As predicted by previous studies, FTIRM showed that adults produce more sebum than children, which leads to darker prints."The more oily and moist your skin is, the better print you leave behind to be dusted and lifted,"Miller said.

Researchers also found that the composition of the lipids, or fats, in sebum differ significantly between adults and children.

Adult sebum has higher concentrations of stable lipids such as squalene and wax esters, which are less likely to vaporize over time. Conversely, the sebum of children contains higher levels of cholesterol and branched chain free fatty acids— unstable lipids that break down more quickly.

The results, which appeared in the March 2010 edition of the Journal of Forensic Sciences, indicate that children's prints may disappear faster because they contain different oils. This could pave the path toward more advanced fingerprint detection techniques.

"Based on the differences in chemical composition, children's prints can still be distinguished from adults' prints with FTIRM even when the dusted copies are barely identifiable,"Miller said."To accurately determine the age of the print's individual, FTIRM should be used as a complementary tool to conventional forensic methods."

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Read-write device offers new architecture for information processing

"Right now, information in computers has to be transferred between logic and memory,"Molenkamp continues."But with memory becoming so big, the process is becoming cumbersome."In order to remedy this problem, Molenkamp and his colleagues in Würzburg have developed a device that allows for memory storage and logic processing in the same structure. A description of their device can be found inPhysical Review Letters:"Fully Electrical Read-Write Device Out of a Ferromagnetic Semiconductor."

Traditionally, information processing is based on different components. Metallic ferromagnets can be used to store information in a remanent manner, such as in a hard disk. Semiconductors are used for logic functions and for volatile memory (RAM). There must communication between memory and logic in order to get the type of computing we are used to. However, there are limitations to this.“Heat dissipationis a problem,” Molenkamp points out.“Additionally, the communication takes time and an enormous amount of interconnects, and there is only so much that can be done when logic and memory are separated in information processing architecture.”

The solution, then, is to create a new information processing architecture that puts logic and memory in the same device.“We have a sample device that we have shown works as a read-write device, putting logic and memory together to create the basis for a new information processing architecture,” Molenkamp says.

In order to create the device, Molenkamp and his fellows used the ferromagnetic semiconductor (Ga, Mn)As.“Our device allows you to perform logic operation with the same circuits where you store info,” he explains.“You can do away with the transfer between logic and memory parts.” This would cut down on heat dissipation, as well as making information processing much faster.

So far, the team at Würzburg has created a one bit device.“There is a little disc in the middle of the device which is the logical bit,” Molenkamp says.“However, in order for our design to be a full logic device, to actually make it programmable, we need two discs touching on each other.” This is what the group is working on now.

In order to take the device further, Molenkamp says that a different set up might be needed.“We were able to show that we could use this device. It is more of a principle of operation,” he points out.“Next, we will have to transfer to a different material that is magnetic at room temperature. We think that our new information processing architecture can carry over to metals.” In order to accomplish this, Molenkamp continues,“one needs to grow crystalline metal layers to use as starting material.” Once that is done, it is possible to begin developing devices that can operate at room temperature, as well as more advanced circuits.

“The adoption of our device could lead to much smaller computers,” Molenkamp says.“Because the type of memory we describe stays encoded, you wouldn’t need RAM, and that would help with heat dissipation and size. We hope that, now that we have shown that you can integratememoryand logic in this new information processing architecture, that there will be interest in creating devices that use this technology.”

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Microwave photons can nullify the conductivity of electrons confined to the surface of liquid helium

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Two-dimensional electron gases form naturally at the surface of helium because an intrinsic energy barrier preventselectronsfrom penetrating any deeper into the liquid. These gases vary markedly from their three-dimensional counterparts because the electron motion in one direction becomes quantized—that is, their velocity in this direction is governed by quantum mechanics and is restricted to a range of discrete values.

Konstantinov and Kono cooled liquid helium-3 to 0.3 kelvin. They supplied electrons from a nearby hot filament, and applied voltage to a plate below the helium to control the number of electrons per unit area. Then, they fired microwave radiation at the 2DEG (Fig. 1) and measured the longitudinal conductivity— the current induced by an electric field applied along one direction—as a function of external magnetic field. They saw that the conductivity periodically fell to zero as they increased the magnetic field. When they switched off the source of microwave photons, however, this effect ceased.

This previously unidentified nullifying effect of microwave photons onconductivityis a consequence of energy-conserved scattering of theliquid helium’s electrons between different energy states—specifically, the first excited and ground sub-bands.“When the electrons stay in the ground sub-band, the effects are rather dull,” says Kono.“In our experiment, absorption of microwave photons transfers electrons to a higher energy sub-band,” Konstantinov adds.“As we change the magnetic field, the energies of states in two subbands cross, and scattering redistributes electrons between the sub-bands.”

Kono and Konstantinov believe that the result will lead to the observation of more novel phenomena in these two-dimensional systems when they are shifted out of their equilibrium state.“The study of nonequilibrium transport in the extremely clean helium system will complement studies of electron transport in semiconductors,” explains Konstantinov.

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The 'new' kilogram is approaching: Avogadro constant determined with enriched silicon-28

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The crucial phase of the long-term Avogadro project - which is coordinated by PTB - started in 2003: In that year, several national metrology institutes launched - together with the Bureau International des Poids et Mesures (BIPM) and in cooperation with Russian research institutes - the ambitious project of having approximately 5 kg of highly enriched²⁸Si (99.99 %) be manufactured as a single crystal, of measuring the Avogadro constant with it and of achieving - by the year 2010 - a measurement uncertainty of approx. 2• 10^-8. Meanwhile, the first measurements have been completed on the two 1 kg spheres of²⁸Si - which had been polished in Australia - and their density, lattice parameter and surface quality have been determined.

The single steps: After an extensive check of the crystal perfection, the influence of the crystal lattice defects was assessed. Then, the lattice parameter was determined at the Italian metrology institute (INRIM) by means of an X-ray interferometer, and confirmed by comparison measurements with a natural Si crystal at the American NIST. At BIPM, NMIJ (Japan) and PTB, the masses of the two silicon spheres were linked up in vacuum to the international mass standards. In the respective Working Groups of NMIJ, NMI-A (Australia) and PTB, the sphere volume was measured optically - with excellent agreement - by means of interferometers with different beam geometries. The surface layer (basically composed of silicon dioxide) was spectroscopied with electron radiation, X-ray radiation and synchrotron radiation in accordance with different procedures, analyzed and taken into account for the determination of thesilicondensity. The unexpectedly high metallic contamination of the sphere surfaces with copper and nickel silicides which occurred during the polishing process was measured, and its influence on the results of the sphere volume and of the sphere mass was assessed. This resulted in a higher measurement uncertainty.

What was decisive for the success achieved - i.e. a relative overall measurement uncertainty of 3• 10^-8- was the development of a new mass-spectrometric method for the determination of the molar mass at PTB.

The result is a milestone on the way towards a successful realization of the new kilogram definition on the basis of fundamental constants whose values have been fixed. At present, the agreement of this value with other realizations of the kilogram is not good enough to change the existing definition of the mass unit. The present state of the Avogadro project is, however, so promising that - on the basis of new measurements with improved sphere interferometers - the measurement uncertainty of 2• 10^-8demanded by the Consultative Committee for the Mass (CCM) will in the near future be achieved on contamination-free spheres and will probably even be undercut.

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