'Hot' Ice Could Lead To Medical Device

Source:

http://www.sciencedaily.com/releases/2007/09/070926122753.htm

Science Daily — Harvard physicists have shown that specially treated diamond coatings can keep water frozen at body temperature, a finding that may have applications in future medical implants.

Doctoral student Alexander Wissner-Gross and Efthimios Kaxiras, physics professor and Gordon McKay Professor of Applied Physics, spent a year building and examining computer models that showed that a layer of diamond coated with sodium atoms will keep water frozen up to 108 degrees Fahrenheit.
In ice, water molecules are arranged in a rigid framework that gives the substance its hardness. The process of melting is somewhat like a building falling down: pieces that had been arranged into a rigid structure move and flow against one another, becoming liquid water.
The computer model shows that whenever a water molecule near the diamond-sodium surface starts to fall out of place, the surface stabilizes it and reassembles the crystalline ice structure.
Simulations show that the process works only for layers of ice so thin they’re just a few molecules wide — three nanometers at room temperature and two nanometers at body temperature. A nanometer is a billionth of a meter.
The layer should be thick enough to form a biologically compatible shield over the diamond surface and to make diamond coatings more useful in medical devices, Wissner-Gross said.
The work is not the first showing that water can freeze at high temperatures. Dutch scientists had shown previously that ice can form at room temperature if placed between a tiny tungsten tip and a graphite surface. Kaxiras and Wissner-Gross’s work shows that ice can be maintained over a large area at body temperature and pressure.
Device manufacturers have been considering using diamond coatings in medical implants because of their hardness. Concerns have been raised, however, because the coatings are difficult to get absolutely smooth, abrasion of the tissue surrounding the implant could result, and that diamond might have a higher chance of causing blood clots than other materials.
Wissner-Gross said a two-nanometer layer of ice would just fill the pits in the diamond surface, smoothing it out and discouraging clotting proteins from attaching to the surface.
“It should be just soft enough and water-friendly enough to smooth out diamond’s disadvantages,” Wissner-Gross said.
Wissner-Gross and Kaxiras are planning experiments to confirm the computerized findings in the real world. Wissner-Gross said they expect results within a year.
“We’re reasonably confident we’ll be able to realize the effect experimentally,” Wissner-Gross said.
Wissner-Gross, who has been a doctoral student at Harvard since 2003, said the research grew out of an interest in the physical interaction of nanostructured surfaces with molecules that are biologically relevant, such as water. Diamond films are growing cheaper, Wissner-Gross said, and as their cost declines the array of possible uses of the material grows wider.
“We both had this notion that it would be very interesting to combine theory with respect to diamond surfaces with what’s going on in cryobiology,” Wissner-Gross said. “We were thinking about how we could leverage this long-term trend [of declining prices] to do something interesting in the medical field.”
Note: This story has been adapted from material provided by Harvard University.

Fausto Intilla

www.oloscience.com

Quantum Device Traps, Detects And Manipulates The Spin Of Single Electrons

Source:

http://www.sciencedaily.com/releases/2007/09/070927135543.htm

Science Daily — A novel device, developed by a team led by University at Buffalo engineers, simply and conveniently traps, detects and manipulates the single spin of an electron, overcoming some major obstacles that have prevented progress toward spintronics and spin-based quantum computing.

Published online recently in Physical Review Letters, the research paper brings closer to reality electronic devices based on the use of single spins and their promise of low-power/high-performance computing.
"The task of manipulating the spin of single electrons is a hugely daunting technological challenge that has the potential, if overcome, to open up new paradigms of nanoelectronics," said Jonathan P. Bird, Ph.D., professor of electrical engineering in the UB School of Engineering and Applied Sciences and principal investigator on the project. "In this paper, we demonstrate a novel approach that allows us to easily trap, manipulate and detect single-electron spins, in a scheme that has the potential to be scaled up in the future into dense, integrated circuits."
While several groups have recently reported the trapping of a single spin, they all have done so using quantum dots, nanoscale semiconductors that can only demonstrate spin trapping in extremely cold temperatures, below 1 degree Kelvin.
The cooling of devices or computers to that temperature is not routinely achievable, Bird said, and it makes systems far more sensitive to interference.
The UB group, by contrast, has trapped and detected spin at temperatures of about 20 degrees Kelvin, a level that Bird says should allow for the development of a viable technology, based on this approach.
In addition, the system they developed requires relatively few logic gates, the components in semiconductors that control electron flow, making scalability to complex integrated circuits very feasible.
The UB researchers achieved success through their innovative use of quantum point contacts: narrow, nanoscale constrictions that control the flow of electrical charge between two conducting regions of a semiconductor.
"It was recently predicted that it should be possible to use these constrictions to trap single spins," said Bird. "In this paper, we provide evidence that such trapping can, indeed, be achieved with quantum point contacts and that it may also be manipulated electrically."
The system they developed steers the electrical current in a semiconductor by selectively applying voltage to metallic gates that are fabricated on its surface.
These gates have a nanoscale gap between them, Bird explained, and it is in this gap where the quantum point contact forms when voltage is applied to them.
By varying the voltage applied to the gates, the width of this constriction can be squeezed continuously, until it eventually closes completely, he said.
"As we increase the charge on the gates, this begins to close that gap," explained Bird, "allowing fewer and fewer electrons to pass through until eventually they all stop going through. As we squeeze off the channel, just before the gap closes completely, we can detect the trapping of the last electron in the channel and its spin."
The trapping of spin in that instant is detected as a change in the electrical current flowing through the other half of the device, he explained.
"One region of the device is sensitive to what happens in the other region," he said.
Now that the UB researchers have trapped and detected single spin, the next step is to work on trapping and detecting two or more spins that can communicate with each other, a prerequisite for spintronics and quantum computing.
Co-authors on the paper are Youngsoo Yoon, Ph.D., a UB doctoral student in electrical engineering; L. Mourokh of Queens College and the College of Staten Island of the City University of New York; T. Morimoto, N. Aoki and Y. Ochiai of Chiba University in Japan; and J. L. Reno of Sandia National Laboratories.
The research was funded by the U.S. Department of Energy. Bird, who also has received funding from the UB Office of the Vice President for Research, was recruited to UB with a faculty recruitment grant from the New York State Office of Science, Technology and Academic Outreach (NYSTAR).
Note: This story has been adapted from material provided by University at Buffalo.

Fausto Intilla

www.oloscience.com

Understanding The Big Bang: Relativistic Heavy Ion Collider Aids Search For Quark-gluon Plasma

Source:

http://www.sciencedaily.com/releases/2007/09/070925171721.htm

Science Daily — A large scale STAR experiment is currently under way at Brookhaven National Laboratory, with the Sun Grid Compute Utility from Sun's Network.com delivering large-scale computing power and related resources on a utility basis as the project requires.

An acronym for Solenoidal Tracker At RHIC -- the laboratory's Relativistic Heavy Ion Collider -- STAR tracks the thousands of particles produced by ion collisions at RHIC, searching for signs of something called the quark-gluon plasma (QGP), a form of matter that is believed to have last existed just after the Big Bang, at the dawn of the universe.
The goal of STAR is to bring about a better understanding of the universe in its earliest stages, by making it possible for scientists to better understand the nature of the QGP. The STAR experiment is a massive collaboration of 570 scientists and engineers representing 60 institutions in 12 countries. The STAR detector captures images at a rate of about 100 per second and has accumulated several hundred million images so far in the course of the experiment.
As the size of the collaboration and the scope of its work continue to grow, so does the challenge of having the computing power and data processing resources to carry out that work efficiently.
Due to the computing and data intensive nature of the project, the Sun Grid Compute Utility has become a part of the STAR distributed computing strategy to allows such computations to be done at a faster rate, leaving more time for physicists' to analyze the large datasets.
"A scientist will look at the initial analysis and then go on to look at the details, which requires even larger data samples," explains Jerome Lauret, RHIC/ STAR Software and Computing Project Leader, "so the more scientists that are involved, the greater the scope of the data and dataset challenge."
Sun Grid Compute Utility has proven useful on the computing side of the equation, as a resource for the simulations of design, collisions, and other models that are essential to the research conducted by the experiment's physics working groups.
Sun™ Grid has also supported simulations associated with ongoing research related to upgrades of the STARdetector -- upgrades that will allow further advances in the experimental physics of heavy ion collisions.
Note: This story has been adapted from material provided by Sun Microsystems.

Fausto Intilla

www.oloscience.com

A New Look At The Proton

Source:

http://www.sciencedaily.com/releases/2007/09/070925092529.htm

Science Daily — Dutch researcher Paul van der Nat investigated more than three million collisions between electrons and protons. In his PhD thesis he demonstrates -for the first time– that the spin contribution of quarks to the proton can be studied by examining collisions in which two particles (hadrons) are produced.

The spin of a particle can most easily be compared to the rotating movement of a spinning top.
In the HERMES experiment at the HERA particle accelerator in Hamburg, physicists are investigating how the spin of protons can be explained by the characteristics of their building blocks: quarks and gluons.
Van der Nat investigated a method to measure the contribution of the spin of the quarks to the total spin of the proton, independent of the contribution of the spin of the gluons. For this a quark is shot out of the proton by an electron from the particle accelerator, as a result of which two hadrons are formed.
The direction and amount of motion of these two hadrons is accurately measured. This method, which Van der Nat applied for the first time, turned out to be successful.
Spin is a characteristic property of particles, just like matter and electrical charge. Spin was discovered in 1925, by the Dutch physicists Goudsmit and Uhlenbeck. In 1987, scientists at CERN in Geneva discovered that only a small fraction of the proton's spin is caused by the spin of its constituent quarks.
The HERMES experiment was subsequently set up to find this missing quantity of spin, and has been running since 1995. It is expected that spin will play an increasingly important role in many applications. The MRI scanner is a well-known example of an application in which the spin of protons plays a key role.
Note: This story has been adapted from a news release issued by Netherlands Organization for Scientific Research.

Fausto Intilla

www.oloscience.com

Portable Atomic Emission Detector Under Development

Source:

http://www.sciencedaily.com/releases/2007/09/070914172642.htm

Science Daily — Brad Jones, a professor of chemistry at Wake Forest University, is leading a team of researchers at four institutions to develop the first handheld, field instrument capable of detecting and identifying radioactive particles at the site of potential contamination.

The device will enable authorities to quickly test dust, soil, water and crops in the event of a terrorist attack such as a “dirty” bomb.
The three-year project is funded by the National Science Foundation in conjunction with the Department of Homeland Security, which asked scientists to submit proposals for radioactivity detection devices. Jones, who specializes in creating spectroscopic instruments, saw the potential to adapt a design he originally conceived years ago to permit rapid field testing for lead in blood samples.
Jones’ “Tungsten Coil Atomic Emission Spectrometer” is constructed using the metal coil filament from a standard slide projector bulb powered by a 12-volt battery, such as the type used to start boats or automobiles. Environmental samples of suspect particles are dissolved in liquid, and droplets are placed on the coil.
The samples are dried at low voltage and the residue vaporized at 3,000 degrees, producing a flash of light. Each metal displays a unique color signature, which is captured by a fiber optic sensor connected to a laptop computer. Test results are then charted on a graph showing each sample’s wavelength and intensity, allowing scientists to identify specific elements and amounts of radioactivity.
“It’s just a natural application,” Jones says, noting that the radioisotopes likely to be stolen from medical or industrial facilities and used by terrorists are also the most brightly emitting elements in atomic spectrometry. “But, the proposed device represents a new way of thinking in the field of nuclear forensics. Atomic emission spectrometry is traditionally a laboratory-based technique using very large, very expensive instruments. With immediate on-site results, residents could be given timely information about a potential threat or reassured that none existed rather than waiting for samples to be transported to laboratories for analysis.”
Portability may also lead to new applications of atomic spectrometry in the field, Jones adds, such as testing for contamination by pesticides and other pollutants.
Instrument manufacturer Teledyne Leeman Labs is interested in the production and marketing of the device once Jones’ research group perfects their prototype. Jones has collaborated with the company for more than a decade.
Other members of the research team include Clifton P. Calloway Jr., associate professor of chemistry at Winthrop University in Rock Hill, S.C.; Arthur L. Salido, assistant professor of chemistry at Western Carolina University in Cullowhee; and Joaquim A. Nobrega, professor of chemistry at the Federal University of Sao Carlos in Brazil.
Note: This story has been adapted from a news release issued by Wake Forest University.

Fausto Intilla

www.oloscience.com

Official Kilogram Losing Mass: Scientists Propose Redefining It As A Precise Number Of Carbon Atoms

Source:

http://www.sciencedaily.com/releases/2007/09/070921110735.htm

Science Daily — How much is a kilogram?

It turns out that nobody can say for sure, at least not in a way that won't change ever so slightly over time. The official kilogram -- a cylinder cast 118 years ago from platinum and iridium and known as the International Prototype Kilogram or "Le Gran K" -- has been losing mass, about 50 micrograms at last check. The change is occurring despite careful storage at a facility near Paris.
That's not so good for a standard the world depends on to define mass.
Now, two U.S. professors -- a physicist and mathematician -- say it's time to define the kilogram in a new and more elegant way that will be the same today, tomorrow and 118 years from now. They've launched a campaign aimed at redefining the kilogram as the mass of a very large -- but precisely-specified -- number of carbon-12 atoms.
"Our standard would eliminate the need for a physical artifact to define what a kilogram is," said Ronald F. Fox, a Regents' Professor Emeritus in the School of Physics at the Georgia Institute of Technology. "We want something that is logically very simple to understand."
Their proposal is that the gram -- 1/1000th of a kilogram -- would henceforth be defined as the mass of exactly 18 x 14074481 (cubed) carbon-12 atoms.
The proposal, made by Fox and Theodore P. Hill -- a Professor Emeritus in the Georgia Tech School of Mathematics -- first assigns a specific value to Avogadro's constant. Proposed in the 1800s by Italian scientist Amedeo Avogadro, the constant represents the number of atoms or molecules in one mole of a pure material -- for instance, the number of carbon-12 atoms in 12 grams of the element. However, Avogadro's constant isn't a specific number; it's a range of values that can be determined experimentally, but not with enough precision to be a single number.
Spurred by Hill's half-serious question about whether Avogadro's constant was an even or odd number, in the fall of 2006 Fox and Hill submitted a paper to Physics Archives in which they proposed assigning a specific number to the constant -- one of about 10 possible values within the experimental range. The authors pointed out that a precise Avogadro's constant could also precisely redefine the measure of mass, the kilogram.
Their proposal drew attention from the editors of American Scientist, who asked for a longer article published in March 2007. The proposal has so far drawn five letters, including one from Paul J. Karol, chair of the Committee on Nomenclature, Terminology and Symbols of the American Chemical Society. Karol added his endorsement to the proposal and suggested making the number divisible by 12 -- which Fox and Hill did in an addendum by changing their number's final digit from 8 to 6. So the new proposal for Avogadro's constant became 84446886 (cubed), still within the range of accepted values.
Fast-forward to September 2007, when Fox read an Associated Press article on the CNN.com Web site about the mass disappearing from the International Prototype Kilogram. While the AP said the missing mass amounted to no more than "the weight of a fingerprint," Fox argues that the amount could be significant in a world that is measuring time in ultra-sub-nanoseconds and length in ultra-sub-nanometers.
So Fox and Hill fired off another article to Physics Archive, this one proposing to redefine the gram as 1/12th the mass of a mole of carbon 12 -- a mole long being defined as Avogrado's number of atoms. They now hope to generate more interest in their idea for what may turn out to be a competition of standards proposals leading up to a 2011 meeting of the International Committee for Weights and Measures.
At least two other proposals for redefining the kilogram are under discussion. They include replacing the platinum-iridium cylinder with a sphere of pure silicon atoms, and using a device known as the "watt balance" to define the kilogram using electromagnetic energy. Both would offer an improvement over the existing standard -- but not be as simple as what Fox and Hill have proposed, nor be exact, they say.
"Using a perfect numerical cube to define these constants yields the same level of significance -- eight or nine digits -- as in those integers that define the second and the speed of light," Hill said. "A purely mathematical definition of the kilogram is experimentally neutral -- researchers may then use any laboratory method they want to approximate exact masses."
The kilogram is the last major standard defined by a physical artifact rather than a fundamental physical property. In 1983, for instance, the distance represented by a meter was redefined by how far light travels in 1/299,792,458 seconds -- replacing a metal stick with two marks on it.
"We suspect that there will be some public debate about this issue," Fox said. "We want scientists and science teachers and others to think about this problem because we think they can have an impact. Public discussion may play an important role in determining how one of the world's basic physical constants is defined."
How important is this issue to the world's future technological development"
"When you make physical and chemical measurements, it's important to have as high a precision as possible, and these standards really define the limits of precision," Fox said. "The lack of an accurate standard leaves some inconsistency in how you state results. Having a unique standard could eliminate that."
While the new definition would do away with the need for a physical representation of mass, Fox says people who want a physical artifact could still have one -- though carbon can't actually form a perfect cube with the right number of atoms. And building one might take some time.
"You could imagine having a lump of matter that actually had exactly the right number of atoms in it," Fox noted. "If you could build it by some kind of self-assembly process -- as opposed to building it atom-by-atom, which would take a few billion years -- you could have new kilogram artifact made of carbon. But there's really no need for that. Even if you built a perfect kilogram, it would immediately be inaccurate as soon as a single atom was sloughed off or absorbed."
Note: This story has been adapted from a news release issued by Georgia Institute of Technology.

Fausto Intilla

www.oloscience.com

'Radio Wave Cooling' Offers New Twist On Laser Cooling

Source:

http://www.sciencedaily.com/releases/2007/09/070914105600.htm

Science Daily — Visible and ultraviolet laser light has been used for years to cool trapped atoms--and more recently larger objects--by reducing the extent of their thermal motion.

Now, applying a different form of radiation for a similar purpose, physicists at the National Institute of Standards and Technology (NIST) have used radio waves to dampen the motion of a miniature mechanical oscillator containing more than a quadrillion atoms, a cooling technique that may open a new window into the quantum world using smaller and simpler equipment.
Described in a forthcoming issue of Physical Review Letters,* this demonstration of radio-frequency (RF) cooling of a relatively large object may offer a new tool for exploring the elusive boundary where the familiar rules of the everyday, macroscale world give way to the bizarre quantum behavior seen in the smallest particles of matter and light. There may be technology applications as well: the RF circuit could be made small enough to be incorporated on a chip with tiny oscillators, a focus of intensive research for use in sensors to detect, for example, molecular forces.
The NIST experiments used an RF circuit to cool a 200 x 14 x 1,500 micrometer silicon cantilever--a tiny diving board affixed at one end to a chip and similar to the tuning forks used in quartz crystal watches--vibrating at 7,000 cycles per second, its natural "resonant" frequency. Scientists cooled it from room temperature (about 23 degrees C, or 73 degrees F) to -228 C (-379 F).
Other research groups have used optical techniques to chill micro-cantilevers to lower temperatures, but the RF technique may be more practical in some cases, because the equipment is smaller and easier to fabricate and integrate into cryogenic systems. By extending the RF method to higher frequencies at cryogenic temperatures, scientists hope eventually to cool a cantilever to its "ground state" near absolute zero (-273 C or -460 F) , where it would be essentially motionless and quantum behavior should emerge.
Laser cooling is akin to using the kinetic energy of millions of ping-pong balls (particles of light) striking a rolling bowling ball (such as an atom) to slow it down. The RF cooling technique, lead author Kenton Brown says, is more like pushing a child on a swing slightly out of synch with its back-and-forth motion to reduce its arc. In the NIST experiments, the cantilever's mechanical motion is reduced by the force created between two electrically charged plates, one of which is the cantilever, which store energy like electrical capacitors.
In the absence of any movement, the force would be stable, but in this case, it is modulated by the cantilever vibrations. The stored energy takes some time to change in response to the cantilever's movement, and this delay pushes the cantilever slightly out of synch, damping its motion.
* K.R. Brown, J. Britton, R.J. Epstein, J. Chiaverini, D. Leibfried, and D.J. Wineland. 2007. Passive cooling of a micromechanical oscillator with a resonant electric circuit. Physical Review Letters. [Forthcoming].
Note: This story has been adapted from a news release issued by National Institute of Standards and Technology.

Fausto Intilla

www.oloscience.com

Nuclear Physicists Examine Oxygen's Limits

Source:

http://www.sciencedaily.com/releases/2007/09/070913170108.htm

Science Daily — Physicists at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University have made a unique measurement of an exotic oxygen nucleus, leading scientists one step closer to deciphering the behavior of the element at its limits of existence.

The finding, published in Physical Review Letters, confirms a relatively new theoretical model that predicts dramatic changes in structure as one looks at heavier and heavier oxygen nuclei.
In the experiment, researchers measured a never-before-seen energy state of oxygen 23 -- one of the heaviest oxygen isotopes that exist.
"It was very exciting to see an experiment that was able to observe this [energy] state very close to where we predicted," said Alex Brown, a professor a NSCL who was involved in the shaping of the theory.
Atomic nuclei are composed of protons and neutrons, only certain combinations of which can exist. Each element -- determined by the number of protons in its nucleus -- comes in a variety of flavors with different numbers of neutrons, creating isotopes. The search for the maximum number of neutrons that can fit into a given element's nucleus lies at the forefront of nuclear physics research.
Moving towards the limit of nuclear stability often leads to strange behavior, such as unexpected changes in nuclear structure.
"We thought we understood the nuclear forces well," said Andreas Schiller, an assistant professor at Ohio University and lead researcher on the study. "But it turns out, when we go to extreme ratios of neutrons and protons, the forces in those areas still hold surprises."
While oxygen 23 contains 8 protons and 15 neutrons, stable form of oxygen, making up the bulk of the oxygen found on Earth, has only 8 neutrons.
A few years ago, scientists tweaked an older version of the theory of atomic nuclei to try to explain some startling phenomena among the heavier oxygen isotopes. The new calculations predicted more dramatic changes in structure among the heavier oxygen isotopes. The experiment, which was conducted at NSCL, confirms these predictions.
Looking at the excited states of a nucleus -- reached by adding extra energy into it -- s a good way to understand the forces inside it, said Michael Thoennessen, associate director of nuclear science at NSCL and co-author of the paper.
The result paves the road to studying the neighboring oxygen 24 -- the heaviest possible oxygen isotope.
Many more mysteries remain to be explored, physicists say. As many as 8,000 nuclei are predicted to exist, but so far only 2,000 have been observed.
The experiment, funded by the National Science Foundation, was the first to yield new information from two tailored NSCL tools, which came on line only recently. One device, the Modular Neutron Array, detects neutrons with high efficiency, and the other, the sweeper magnet, uses NSCL's superconducting magnet technology to allow a higher percentage of sought-after particles to pass.
These devices make it possible to explore isotopes farther towards the extreme edges of existence, by making experimental run times up to seven times shorter.
"Without them you couldn't do the experiments," Thoennessen said.
Note: This story has been adapted from a news release issued by Michigan State University.

Fausto Intilla

www.oloscience.com

Accepted Notion Of Neutron's Electrical Properties Overturned By New Research

Source:

http://www.sciencedaily.com/releases/2007/09/070917151054.htm

Science Daily — For two generations of physicists, it has been a standard belief that the neutron, an electrically neutral elementary particle and a primary component of an atom, actually carries a positive charge at its center and an offsetting negative charge at its outer edge.
The notion was first put forth in 1947 by Enrico Fermi, a Nobel laureate noted for his role in developing the first nuclear reactor. But new research by a University of Washington physicist shows the neutron's charge is not quite as simple as Fermi believed.
Using precise data recently gathered at three different laboratories and some new theoretical tools, Gerald A. Miller, a UW physics professor, has found that the neutron has a negative charge both in its inner core and its outer edge, with a positive charge sandwiched in between to make the particle electrically neutral.
"Nobody realized this was the case," Miller said. "It is significant because it is a clear fact of nature that we didn't know before. Now we know it."
The discovery changes scientific understanding of how neutrons interact with negatively charged electrons and positively charged protons. Specifically, it has implications for understanding the strong force, one of the four fundamental forces of nature (the others are the weak force, electromagnetism and gravity).
The strong force binds atomic nuclei together, which makes it possible for atoms, the building blocks of all matter, to assemble into molecules.
"We have to understand exactly how the strong force works, because it is the strongest force we know in the universe," Miller said.
The findings are based on data collected at the Thomas Jefferson National Accelerator Facility in Newport News, Va., the Bates Linear Accelerator at the Massachusetts Institute of Technology and the Mainz Microtron at Johannes Gutenberg University in Germany.
The three labs examine various aspects of the properties and behavior of subatomic particles, and Miller studied data they collected about neutrons. His analysis was published online Sept. 13 in Physical Review Letters. The work was funded in part by the U.S. Department of Energy.
Since the analysis is based on data gathered from direct observations, the picture could change even more as more data are collected, Miller said.
"A particle can be electrically neutral and still have properties related to charge. We've known for a long time that the neutron has those properties, but now we understand them more clearly," he said.
He noted that the most important aspect of the finding confirms that a neutron carries a negative charge at its outer edge, a key piece of Fermi's original idea.
The strong force that binds atomic nuclei is related to nuclear energy and nuclear weapons, and so it is possible the research could have practical applications in those areas.
It also could lend to greater understanding of the interactions that take place in our sun's nuclear furnace, and a greater understanding of the strong force in general, Miller said.
"We already know that without the strong force you wouldn't have atoms -- or anything else that follows from atoms," he said.
This research was published online Sept. 13 in Physical Review Letters. The work was funded in part by the U.S. Department of Energy.
Note: This story has been adapted from a news release issued by University of Washington.

Fausto Intilla
www.oloscience.com

Physicists Pin Down Spin Of Surface Atoms

Source:

http://www.sciencedaily.com/releases/2007/09/070912170108.htm

Science Daily — Scientists who dream of shrinking computers to the nanoscale look to atomic spin as one possible building block for both processor and memory, yet setting the spin of an atom, let alone measuring it, has been a challenge.

Now, University of California, Berkeley, physicists have succeeded in measuring the spin of a single atom, moving one step closer to quantum computers and "spintronic" devices built from nanoscale transistors based on atomic spin.
"From a technical point of view, this demonstrates a new ability to engineer, fabricate and measure spin-polarized nanostructures at the single atom level," said Michael F. Crommie, UC Berkeley professor of physics. "Now that I can see an atom's spin, I can ask, 'What can I do with that atomic spin" Can I manipulate it" Can I use it, change it"' This means we can now start incorporating it into other structures."
Crommie and his colleagues at UC Berkeley and the Center for Computational Materials Science (CCMS) at the Naval Research Laboratory in Washington, D.C., recently reported their success in the journal Physical Review Letters.
At the core of today's digital computers are billions of tiny transistor circuits that, because they can exist in two states, are used to represent the binary digits, or "bits" 0 and 1, which are the basis of all computer manipulations.
As researchers seek to reduce the size of digital computers, they have been searching for nanoscale materials that can do digital duty, one of them being a single atom whose outer unpaired electron can be in either of two spin states - up or down.
While researchers previously have been able to deduce the spin polarization of an atom in a surface or thin film where the atoms are packed together and the spins are in an orderly arrangement, no one had been able to directly measure the polarization of an individual "adatom" spin until now. Adatoms are atoms that sit on top of a surface and are not incorporated into it.
Crommie, UC Berkeley post-doctoral fellow Yossi Yayon and graduate student Victor W. Brar succeeded by creating islands of cobalt atoms on a cold copper substrate (4.8 Kelvin, or -451 degrees Fahrenheit) and sprinkling these islands with atoms of either iron or chromium.
Employing a relatively new technique called low-temperature spin-polarized scanning tunneling spectroscopy - essentially a scanning, tunneling microscope that can probe the spin and energy-dependent electron density of a surface - they were able to determine the spin of isolated adatoms atop these cobalt nanoislands.
"These magnetic islands are teeny tiny nanomagnets, but from the single-atom perspective they are just large fixed ferromagnets, like a refrigerator magnet," Crommie said. "We took individual atoms and coupled them to these large magnets so we could fix the direction of the spin of an atom and it would stay put."
Crommie's CCMS colleagues, Steve C. Erwin and post-doctoral fellow Laxmidhar Senapati, calculated that in such a situation, iron atoms would assume a spin state parallel to the spins of the atoms in the cobalt island, while chromium would assume an anti-parallel spin, which is exactly what the researchers found.
How spins couple to one another is an important question for a quantum computer, because in a practical device, the spin of an atom would be quantum mechanically intermingled or "entangled" with the spin of other atoms, manipulated in some sort of calculation, and then disentangled to obtain the result. Understanding such interactions also are critical in spintronic devices, where the spin of atoms is used to control the flow of spin-polarized electrons in a circuit.
"We are clearly not yet in a useful regime for quantum computation because the spins we are looking at are very strongly coupled to the environment," Crommie said. "Nevertheless, this measurement is very useful because it shows that we can observe the spin of these atoms and then start to understand the physics of how the surface is influencing the spin of individual atoms. We hope to next control the spin - that is where we are going with this."
This work was supported in part by the National Science Foundation, the U.S. Department of Energy, the Office of Naval Research and the National Research Council.
Note: This story has been adapted from a news release issued by University of California, Berkeley.

Fausto Intilla

www.oloscience.com

Gamma Ray Lasers? Positronium Created In The Lab

Source:

http://www.sciencedaily.com/releases/2007/09/070912154633.htm

Science Daily — Physicists at UC Riverside have created molecular positronium, an entirely new object in the laboratory. Briefly stable, each molecule is made up of a pair of electrons and a pair of their antiparticles, called positrons.

The research paves the way for studying multi-positronium interactions -- useful for generating coherent gamma radiation -- and could one day help develop fusion power generation as well as directed energy weapons such as gamma-ray lasers. It also could help explain how the observable universe ended up with so much more matter than "antimatter."
The researchers made the positronium molecules by firing intense bursts of positrons into a thin film of porous silica, which is the chemical name for the mineral quartz. Upon slowing down in silica, the positrons were captured by ordinary electrons to form positronium atoms.
Positronium atoms, by nature, are extremely short-lived. But those positronium atoms that stuck to the internal pore surfaces of silica, the way dirt particles might cling to the inside surface of the holes in a sponge, lived long enough to interact with one another to form molecules of positronium, the physicists found.
"Silica acts in effect like a useful cage, trapping positronium atoms," said David Cassidy, the lead author of the research paper and an assistant researcher working in the laboratory of Allen Mills, a professor of physics, the research paper's coauthor. "This is the first step in our experiments. What we hope to achieve next is to get many more of the positronium atoms to interact simultaneously with one another -- not just two positronium atoms at a time."
When an electron meets a positron, their mutual annihilation may ensue or positronium, a briefly stable, hydrogen-like atom, may be formed. The stability of a positronium atom is threatened again when the atom collides with another positronium atom. Such a collision of two positronium atoms can result in their annihilation, accompanied by the production of a powerful and energetic type of electromagnetic radiation called gamma radiation, or the creation of a molecule of positronium, the kind Cassidy and Mills observed in their lab.
"Their research is giving us new ways to understand matter and antimatter," said Clifford M. Surko, a professor of physics at UC San Diego, who was not involved in the research. "It also provides novel techniques to create even larger collections of antimatter that will likely lead to new science and, potentially, to important new technologies."
Matter, the "stuff" that every known object is made of, and antimatter cannot co-exist close to each other for more than a very small measure of time because they annihilate each other to release enormous amounts of energy in the form of gamma radiation. The apparent asymmetry of matter and antimatter in the visible universe is an unsolved problem in physics.
Currently, antimatter finds use in medicine where it helps identify diseases with the Positron Emission Tomography or PET scan.
Cassidy and Mills plan to work next on using a more intense positron source to generate a "Bose-Einstein condensate" of positronium -- a collection of positronium atoms that are in the same quantum state, allowing for more interactions and gamma radiation. According to them, such a condensate would be necessary for the development of a gamma-ray laser.
Study results appear in the Sept. 13 issue of Nature.
Their research was funded by the National Science Foundation.
Note: This story has been adapted from a news release issued by University of California - Riverside.

Fausto Intilla

www.oloscience.com

Physicists Establish 'Spooky' Quantum Communication

Source:

http://www.sciencedaily.com/releases/2007/09/070905133621.htm

Science Daily — Physicists at the University of Michigan have coaxed two separate atoms to communicate with a sort of quantum intuition that Albert Einstein called "spooky."
In doing so, the researchers have made an advance toward super-fast quantum computing. The research could also be a building block for a quantum internet.
Scientists used light to establish what's called "entanglement" between two atoms, which were trapped a meter apart in separate enclosures (think of entangling like controlling the outcome of one coin flip with the outcome of a separate coin flip).
"This linkage between remote atoms could be the fundamental piece of a radically new quantum computer architecture," said Professor Christopher Monroe, the principal investigator who did this research while at U-M, but is now at the University of Maryland. "Now that the technique has been demonstrated, it should be possible to scale it up to networks of many interconnected components that will eventually be necessary for quantum information processing."
David Moehring, the lead author of the paper who did this research as a U-M graduate student, says the most important feature of this experiment is the distance between the two atoms. Moehring graduated and now has a position at the Max-Planck-Institute for Quantum Optics in Germany.
"The separation of the qubits in our entangled state is the most important feature," Moehring said. "Localized entanglement has been performed in ion trap qubits in the past, but if one desires to build a scalable quantum computer network (or a quantum internet), the creation of entanglement schemes between remotely entangled qubit memories is necessary."
In this experiment, the researchers used two atoms to function as qubits, or quantum bits, storing a piece of information in their electron configuration. They then excited each atom, inducing electrons to fall into a lower energy state and emit one photon, or one particle of light, in the process.
The atoms, which were actually ions of the rare-earth element ytterbium, are capable of emitting two different types of photon of different wavelengths. The type of photon released by each atom indicates the particular state of the atom. Because of this, each photon was entangled with its atom.
By manipulating the photons emitted from each of the two atoms and guiding them to interact along a fiber optic thread, the researchers were able to detect the resulting photon clicks and entangle the atoms. Monroe says the fiber optic thread was necessary to establish entanglement of the atoms, but then the fiber could be severed and the two atoms would remain entangled, even if one were "(carefully) taken to Jupiter."
Each qubit's information is like a single bit of information in a conventional computer, which is represented as a 0 or a 1. Things get weird on the quantum scale, though, and a qubit can be either a 0, a 1, or both at the same time, Monroe says. Scientists call this phenomenon "superposition." Even weirder, scientists can't directly observe superposition, because the act of measuring the qubit affects it and forces it to become either a 0 or a 1.
Entangled particles can default to the same position once measured, for example always ending in 0,0 or 1,1.
"When entangled objects are measured, they always result in some sort of correlation, like always getting two coins to come up the same, even though they may be very far apart," Monroe said. "Einstein called this 'spooky action-at-a-distance,' and it was the basis for his nonbelief in quantum mechanics. But entanglement exists, and although very difficult to control, it is actually the basis for quantum computers."
Scientists could set the position of one qubit and know that its entangled mate will follow suit.
Entanglement provides extra wiring between quantum circuits, Monroe says. And it allows quantum computers to perform tasks impossible with conventional computers. Quantum computers could transmit provably secure encrypted data, for example. And they could factor numbers incredibly faster than today's machines, making most current encryption technology obsolete (most encryption today is based on the inability for man or machine to factor large numbers efficiently).
A paper on the findings appears in the Sept. 6 edition of the journal Nature. The paper is titled "Entanglement of single atom quantum bits at a distance."
Note: This story has been adapted from a news release issued by University of Michigan.

Fausto Intilla
www.oloscience.com

Two Nanostructures Are Better Than One

Source:

http://www.sciencedaily.com/releases/2007/09/070904114617.htm

Science Daily — Imagine using minuscule structures the size of molecules to harvest sunlight and convert it into electricity. Or employing the same structures to store hydrogen fuel so that it fits into a car's gas tank. Or replacing today's semiconductors with these structures, ushering in the next generation of small, powerful electronics.

These technologies don't exist yet, but the work of a researcher at the University of Wisconsin-Milwaukee (UWM) is bringing them closer to reality with hybrid materials made with carbon nanotubes (CNTs).
Junhong Chen, assistant professor of mechanical engineering, is pioneering better methods of making CNTs more predictable.
CNTs are invisibly thin sheets of graphite that are rolled into a cylindrical shape. Chen's laboratory focuses on new uses for CNTs combined with nanoparticles, bits of matter that are nanoscale in all three dimensions. (A few nanometers are roughly 50,000 times smaller than the width of a human hair.)
"These interesting multi-component structures will open up new opportunities in several interdisciplinary fields," Chen says, "including medical diagnostics, green energy technology, and sensors for everything from food flavor to invisible toxic gas."
Big and small worlds collide
CNTs are the potential superstar structures of molecular engineering because of their remarkable electronic and mechanical properties. Already they are used in making flat panel display screens and sensing devices that can detect substances in very low concentrations.
They conduct electricity like either copper or silicon, are stronger than steel, pliable like polymers (kinds of plastics) and can be made from a range of raw materials.
The challenge is to coax them to behave in predictable ways.
With the help of graduate student Ganhua Lu, Chen has devised a method for creating hybrid structures by coating CNTs with aerosol nanoparticles. His lab also has produced a low-cost way to make "custom" nanoparticles that gives them full control over the structure's final properties.
Manipulating CNTs and nanoparticles is tricky business because so many conditions affect their behavior. Just below nanoscale, at the level of individual atoms, matter acts quite differently than it does lumped together in bulk.
Already they have devised a gas sensor using only nanoparticles of tin oxide.
Their process for producing hybrid structures is far superior to the method currently available, and their work advances understanding of how materials in the quantum world interact with those in the "seen" world.
Surface science cluster at UWM
"My goal is to make something real, that people can see and use and that has tangible results," says Chen, who came to UWM in 2003 after a year as a post-doctoral scholar at the California Institute of Technology.
With two patents pending and funding from sources such as the National Science Foundation and the Xerox Corporation, he is well on his way.
Chen is one of a cluster of UWM scientists -- in engineering, chemistry and physics -- who conduct research into nano- and surface science. In fact, UWM's Laboratory for Surface Studies, a University of Wisconsin System Center of Excellence, brings together the work of 13 faculty who explore the structure and properties of solid surfaces and the interaction of surfaces with atoms and molecules.
The lab's research encompasses topics such as thin films and laminates, spintronics, molecular wires, optical fiber sensing, and properties such as catalysis, corrosion and friction.
New materials, cool features
When it comes to size, there's tiny and then there's tiny all over. Nanostructures can be at nanoscale in either one, two or three dimensions, or any combination. The structure's properties are determined by the number of dimensions at nanoscale, its shape, and the material it's made of.
CNTs, for example, can behave like an electrical conductor or a semiconductor, depending on the diameter and the twist of the tube. Nanoparticles have their own unique characteristics. Once attached to CNTs, they can transfer their abilities to the tube.
Nanoparticles could potentially give an insulator like silicon the ability to conduct electricity.
A happy union of the two structures offers a chance to brainstorm new applications, says Chen. For example, the hybrid can be altered to absorb and emit various wavelengths of light, giving it optical properties.
"You get an opportunity to make a material that could potentially display not only the properties of the CNT and the nanoparticles, but also some additional properties because of the interaction between the two.
"So one plus one may be greater than two," he says. "That's the whole idea."
Molecular building with control
Before Chen's technique for fusing the two nanostructures, the process took hours.
CNTs are produced in a gas phase from carbon precursors, but nanoparticles are made in a solution, he says. "You had to combine the dry with the wet before you can make something out of it," he says. "It's not very compatible."
Also the surface of each structure had to be modified, and the chemistry would be different for each new material involved.
"What you would get at the end could be very different from what you were trying to get," he says.
So Chen and his lab developed a way to make nanoparticles in the gas (dry) phase. Then they applied an electrostatic force to attract any kind of nanoparticle to the CNT. The one-step process takes only minutes.
"It works like an indoor air cleaner, using the electric field to capture dust particles," he says.
Another advantage of the process is Chen can control the size of the nanoparticle that is fastened to the tube, and that determines the final properties of the hybrid structure. The higher the electric field, the larger the particles it will attract.
Chen believes the research has huge potential.
"Many of our projects lie at the intersection of fundamental science and industrial applications with ample opportunities for new discoveries."
Note: This story has been adapted from a news release issued by University of Wisconsin, Milwaukee.

Fausto Intilla

www.oloscience.com