Explosive Crystal: Chemists Reveal Molecular Structure Of Dynamite Detonator, Mercury Fulminate

Source:

http://www.sciencedaily.com/releases/2007/08/070824102049.htm

Science Daily — Known to the alchemists and long used as a detonator to set off dynamite--mercury fulminate has a checkered past. Now, more than 300 years after the discovery of this explosive compound, German researchers have been able to characterize its crystal structure and thus finally reveal the molecular structure of mercury fulminate.
As Wolfgang Beck, Thomas Klapötke and their team report in the journal ZAAC -- Journal of Inorganic and General Chemistry, the orthorhombic crystals consist of separate, nearly linear Hg(CNO)2 molecules.
The alchemists of the seventeenth century were already aware that mixtures of "spiritus vini" (ethanol) and mercury in "aqua fortis" (nitric acid) made for an explosive brew. In his book Laboratorium Chymicum, Johann Kunckel von Löwenstern describes the vigorous reaction of mercury nitrate with alcohol to form mercury fulminate (Hg(CNO)2). In 1799, the English chemist Edward Howard isolated the compound by chance, which was produced a sensation in the nascent scientific field of chemistry.
Mercury fulminate is very sensitive to shock, friction, and sparks. It explosively decomposes to form mercury, carbon monoxide, and nitrogen. This explosive power was used extensively: Alfred Nobel put mercury fulminate into blasting caps for detonating dynamite. This relatively safe new detonator was what allowed for the huge success of dynamite. In Germany alone, the annual production of mercury fulminate in the early 20th century reached about 100,000 Kg.
The first investigations of the crystal structure of mercury fulminate by X-ray structure analysis date from 1931. Now Beck, Klapötke and their team have finally succeeded in fully solving the structure. To do this, they irradiated small crystals with a uniform crystal lattice, known as single crystals, with X-rays. The resulting X-ray diffraction pattern allowed the researchers to precisely calculate the positions of the individual atoms within the crystal and the distances between them.
Mercury fulminate crystals are orthorhombic and the crystal consists, as expected, of separate Hg(CNO)2 molecules. Each mercury atom is surrounded by two carbon atoms. The measured positions and bond lengths confirm a molecular structure of O−N≡C−Hg−C≡N−O.
Says Beck: "In addition, we can unambiguously show that the molecules in the crystal have a stretched-out, nearly linear form. They are not bent, and each mercury atom is not bound to two oxygen atoms, as they are amazingly still occasionally depicted in the literature."
Reference: The Crystal and Molecular Structure of Mercury Fulminate (Knallquecksilber), Wolfgang Beck, Jürgen Evers, Michael Göbel, Gilbert Oehlinger, Thomas M. Klapötke, Z. anorg. allg. Chem. 2007, vol. 633, no. 9, pp. 1417-1422 doi: 10.1002/zaac.200700176
Note: This story has been adapted from a news release issued by John Wiley & Sons, Inc..

Fausto Intilla
www.oloscience.com

Low-energy Neutrinos Detected Inside Sun

Source:

http://www.sciencedaily.com/releases/2007/08/070827123245.htm

Science Daily — In collaboration with scientists from institutions in the United States and Europe, researchers from Virginia Tech have observed tell-tale signals of neutrinos emitted by thermonuclear fusion reactions that power the sun deep in its interior.
At approximately 15 million degrees, protons -- the nuclei of hydrogen atoms -- and light elements can fuse to form new nuclei. Several such steps eventually convert the hydrogen in the sun into helium, releasing about 25 million times more energy per gram than TNT, oil, or coal.
"While the neutrinos, which are uncharged elementary particles, only take about eight minutes to reach the earth, the thermal energy produced at the center of the sun only appears as sunlight some 50 thousand years later, after diffusing to the sun's surface," said Bruce Vogelaar professor of physics and leader of Virginia Tech's research team for this project.
"The only way to prove the validity of this model of solar energy generation is to observe these neutrinos which easily travel right through the sun because of their weak interaction with matter," Vogelaar said. "Of special interest are those neutrinos from the decay of 7Be, a critical step in the energy chain of the sun."
It is these neutrinos that the Virginia Tech team and their colleagues have observed directly for the first time in the Borexino detector, located under the Gran Sasso peak in the Apennine mountain range about 100 miles east of Rome. Borexino is a massive detector that contains some 350,000 gallons of organic liquid. Its central region detects neutrinos by seeing the light given off when a neutrino collides with an electron, using some 2,200 photosensors arrayed around the detector.
"The sun emits copious amounts of neutrinos in a wide range of energies," Vogelaar said. "About 10 billion pass through your thumbnail each second."
In the last decade, the much rarer high-energy fraction (one part in ten thousand) has been seen in many experiments, he said. The vast majority of the flux, however, is at much lower energies and had not been directly observed until now. This is because previous detector technologies were unable to discriminate low-energy neutrino signals from formidable backgrounds due to radioactivities normally present in the environment. These include the detector itself and cosmic rays. To avoid the latter, the detector was shielded by placing it deep underground at Gran Sasso. The Borexino Collaboration has developed and employed a new technology that virtually eliminated even trace contaminations, allowing successful measurement of the low-energy solar neutrinos.
The required purities are unprecedented -- several million times lower than levels normally achievable, even with the development of ultra-clean technologies for the semiconductor industry. Another major problem with detecting low-energy neutrinos was the inescapable carbon in the detector's organic liquid, which normally contains a million times more radioactive 14C than tolerable for Borexino. 14C is normally used in radiocarbon dating studies.
Raju Raghavan, professor of physics at Virginia Tech and formerly with Bell Laboratories, made the first breakthrough in methods for reducing radioactive contamination sufficiently as well as discovering how to avoid the radiocarbon. With colleagues from University of Pavia, Italy, he invented new methods of purification and material characterization that explicitly showed for the first time that the solubility of heavy metals, such as radioactive Uranium and Thorium, in non-polar liquids were a million times lower than thought earlier, and thus suitable for Borexino.
Since radiocarbon cannot be chemically purified from normal carbon, Raghavan side-stepped the problem by postulating that petrochemicals derived organic liquids ought to contain much less radiocarbon than normal, due to their residence deep in the earth for geological times. Raghavan and colleagues from the University of Toronto developed a method to show this was the case, and that indeed, the purities reached Borexino levels, which are parts per million billion.
"These results on the laboratory scale showed the potential for low-energy neutrino spectroscopy in Borexino and paved the way to large scale investments for the experiment," Raghavan said. "These new techniques have also impacted commercial technology needed today," For example, he solved the sodium contamination problem in photolithographic chemistry in the fabrication of chips in the microelectronic industry using these techniques.
Showing that these results were valid at the ton, and then kiloton, scales was accomplished over the next 10 years by the Borexino collaboration, including exhaustive field tests using a five-ton prototype detector constructed in Gran Sasso.
The Borexino collaboration consists of more than 100 scientists, post-doctoral fellows, and students from Tech and Princeton University in the U.S., and groups from Italy, France, Germany, Russia, and Poland. In addition to Vogelaar and Raghavan, other members of the Virignia Tech team were Henning Back (currently at NCSU), Christian Grieb, Steven Hardy, Matthew Joyce, Derek Rountree, and. Szymon Manecki, along with several undergraduates. The collaboration is led by Gianpaolo Bellini of the University of Milan, Italy. Essential support for the 20-year effort was provided by the Laboratori Nazionali del Gran Sasso, the INFN (Italy), the National Science Foundation, and other funding agencies in Europe and Russia.
"The scientific and technological achievement of Borexino is a testament to the value of international collaboration and the ingenuity and tenacity of the Borexino collaboration over 20 years to achieve the present success." Vogelaar said. "We expect that information on the 7Be solar neutrinos will clarify the sun's energy cycle in great detail and throw light on the nature of the neutrino itself"
Note: This story has been adapted from a news release issued by Virginia Tech.

Fausto Intilla
www.oloscience.com

Photon-transistors For The Supercomputers Of The Future

Source:

http://www.sciencedaily.com/releases/2007/08/070826162731.htm

Science Daily — Scientist from the Niels Bohr Institute at University of Copenhagen and from Harvard University have worked out a new theory which describe how the necessary transistors for the quantum computers of the future may be created.

Researchers dream of quantum computers. Incredibly fast super computers which can solve such extremely complicated tasks that it will revolutionise the application possibilities. But there are some serious difficulties. One of them is the transistors, which are the systems that process the signals.
Today the signal is an electrical current. For a quantum computer the signal can be an optical one, and it works using a single photon which is the smallest component of light.
"To work, the photons have to meet and "talk", and the photons very rarely interact together" says Anders Søndberg Sørensen who is a Quantum Physicist at the Niels Bohr Institute at Copenhagen University. He explains that light does not function like in Star Wars, where the people fight with light sabres and can cross swords with the light. That is pure fiction and can't happen. When two rays of light meet and cross, the two lights go right through each other. That is called linear optics.
What he wants to do with the light is non-linear optics. That means that the photons in the light collide with each other and can affect each other. This is very difficult to do in practice. Photons are so small that one could never hit one with the other. Unless one can control them -- and it is this Anders Sørensen has developed a theory about.
Light collisions at the quantum level
Instead of shooting two photons at each other from different directions and trying to get them to hit each other, he wants to use an atom as an intermediary. The atom can only absorb one photon (such are the laws of physics). If you now direct two photons towards the atom it happens that they will collide on the atom. It is exactly what he wants.
The atom is however very small and difficult to hit. So the photons have to be focussed very precisely. In a previous experiment researchers had discovered that microwaves could be focussed on an atom via a superconducting nano-wire. They got the idea that the same could happen with visible light.
The theoretical model shows that it works. The atom is brought close to the nanowire. Two photons are sent towards the atom and when they hit it an interaction occurs between them, where one imparts information to the other. The information is sent in bits which are either a one or zero digit, and the order of digits produces the message. (Today we can send information via an optic cable and each bit is made up of millions of photons.) In quantum optics each bit is just one photon. The photon has now received its message and the signal continues on its way. It is a step on the way to building a photon-transistor for a quantum computer.
The research has just been published in the scientific journal Nature Physics.
Note: This story has been adapted from a news release issued by University of Copenhagen.

Fausto Intilla

www.oloscience.com

Scientists Shed Light On Molecules In Living Cells

Source:

http://www.sciencedaily.com/releases/2007/08/070821081423.htm

Science Daily — Clemson University chemists have developed a method to dramatically improve the longevity of fluorescent nanoparticles that may someday help researchers track the motion of a single molecule as it travels through a living cell.

The chemists are exploiting a process called "resonance energy transfer," which occurs when fluorescent dye molecules are added to the nanoparticles.
If scientists could track the motion of a single molecule within a living cell it could reveal a world of information. Among other things, scientists could determine how viruses invade a cell or how proteins operate in the body. Such technology also could help doctors pinpoint the exact location of cancer cells in order to better focus treatment and minimize damage to healthy tissue. Outside the body, the technology could help speed up detection of such toxins as anthrax.
The key to developing single-molecule tracking technology may be the development of better fluorescent nanoparticles.
Fluorescent nanoparticles are thousands of times smaller than the width of a human hair and are similar in size to protein molecules, to which they can be attached. When illuminated by a laser beam inside a light microscope equipped with a sensitive digital camera, the nanoparticle attached to a protein will light up, allowing scientists to get a precise fix on the position of the protein and monitor its motion inside a cell.
Until now, nanoparticles have been too dim to detect inside cells, but Clemson chemists have developed a novel type of nanoparticles containing materials called conjugated polymers that light up and stay lit long enough for scientists to string together thousands of images, as in a movie.
Conjugated polymers share many properties with semiconductors like silicon but have the flexibility of plastic. While initial efforts at preparing nanoparticles out of conjugated polymers resulted in particles that were very bright, their brightness quickly faded under the bright glare of a laser beam.
"When a conjugated polymer is in a high energy state, it is vulnerable to attack by oxygen," says principal investigator and chemist Jason McNeill. "The dye efficiently removes the energy from the molecule and re-emits the energy as light, which greatly improves the brightness and longevity of the nanoparticles."
McNeill says other possible targets of investigation include the formation of plaques and fibrils in the brain associated with Alzheimer's disease and mad cow disease. Graduate students Changfeng Wu, Craig Szymanski, Jennifer Grimland and Yueli Zheng contributed to the study, which the National Science Foundation funded.
Clemson University chemists are presenting 40 papers on a wide range of subjects at the society meeting. Other topics include detection and quantification of uranium in groundwater, conversion of lipid feedstocks such as poultry fat to biodiesel and a new mechanism for antioxidants that fight DNA damage.
These findings were reported at the 234th annual national American Chemical Society meeting Aug.19-24 in Boston.
Note: This story has been adapted from a news release issued by Clemson University.

Fausto Intilla

www.oloscience.com

Hydrogen Economy? Organic Polymer Stores Hydrogen Safely

Source:

http://www.sciencedaily.com/releases/2007/08/070824111031.htm

Science Daily — Cardiff scientists exploring the safe storage of hydrogen to power vehicles as an environmentally friendly alternative to petrol have made a promising new discovery.

Having already developed an organic polymer capable of storing 1.7 per cent hydrogen by weight, Professors Neil McKeown from the School of Chemistry together with Peter Budd of the University of Manchester and David Book from the University of Birmingham can now report the creation of an organic polymer able to store around three per cent hydrogen by weight.
The figure is almost double the amount of hydrogen the group’s preliminary polymers could store last year, and offers hope of producing an organic polymer in the future capable of storing enough hydrogen to successfully power a vehicle.
Commenting on the development, Professor McKeown said: “We are excited to report this recent discovery by our research team of a polymer which can hold around three per cent hydrogen by weight. Although we still have a long way to go, it is clear that we are moving in the right direction, especially as we also have a number of promising new polymers to test. ”
In order to make hydrogen a viable alternative to petrol, a material which can store hydrogen at a weight of over six per cent is required. This figure is estimated by the American Department of Energy as the minimum required to make a fuel tank for hydrogen to power a vehicle for 300 miles.
“In order to obtain a polymer that can store useful quantities of hydrogen we need to make a much more porous material,” said Professor McKeown, “but one in which the holes are very small so as to fit snugly the small hydrogen molecules.”
Professor McKeown and his team are investigating a number of promising methods to enhance pororosity as they attempt to build on their current success and produce a material that can store and release hydrogen safely and effectively. They are also collaborating with Professor Kenneth Harris within the School of Chemistry to develop other types of hydrogen storage materials.
Cardiff is the lead University in the research project, which is funded by the Engineering and Physical Sciences Research Council.
Note: This story has been adapted from a news release issued by Cardiff University.

Fausto Intilla

www.oloscience.com

Explaining a 21st Century Version of Young's Experiment

Source:

http://www.sciencedaily.com/releases/2007/08/070823113344.htm

Science Daily — When light strikes a metallic array of tiny openings, smaller than the wavelength of the light itself, interesting entities known as plasmons may be created. An electromagnetic phenomenon like light itself, the plasmons are waves of electrons that move on the surface of a material like ripples on a pond, but they can oscillate back and forth at the frequency of the incoming light. Like water ripples on a pond surface, plasmons travel in the plane of the metal but with a wavelength smaller, sometimes considerably smaller, than the original light.
Just as light can interact with plasmons, these plasmons traveling between the openings, or "apertures," can be reconstituted as light at the apertures. The overall effect is that "large" light can pass through tiny holes.
Scientists are now running experiments to find how the plasmons appear and reform into light by passing light through apertures in various ways. One way is to do the plasmon version of a common high school physics lab experiment: passing waves through two slits, and watching how they interact on the other side. In a high school lab, the waves would be made of water; in the latest experiments, physicists examined the intermediary step in which the plasmons are created near the aperture, pass through, and then reform into a light wave on the other side. This kind of test results in interference patterns from which the coherence altering influence of surface plasmons can be deduced.
C.H. Gan of the University of North Carolina (UNC), Charlotte will report on some new theoretical predictions about the coherence properties of light transmitted through the slits. The theoretical predictions were done by computer simulations of the plasmons' action. The detailed simulations, done with collaborators Greg Gbur of UNC Charlotte and T.D. Visser of the Free University of Amsterdam, show how surface plasmons traveling between the apertures result in a correlation of the light fields emitted from the apertures.
Gan shows how this effect can be tuned (such as by varying the size or spacing of the slits). This tunability in turn has the potential to be exploited in new, potentially high-resolution, high-quality forms of coherence-related imaging.
Paper FTuS3, "Surface Plasmons in Young's Experiment Modulate the Spatial Coherence of Light"
Note: This story has been adapted from a news release issued by Optical Society of America.

Fausto Intilla
www.oloscience.com

Using Life's Building Blocks To Control Nanoparticle Assembly

Source:

http://www.sciencedaily.com/releases/2007/08/070822093124.htm

Science Daily — Using DNA, the molecule that carries life's genetic instructions, researchers at the U.S. Department of Energy's Brookhaven National Laboratory are studying how to control both the speed of nanoparticle assembly and the structure of its resulting nanoclusters.

Learning how to control and tailor the assembly of nanoparticles, which have dimensions on the order of billionths of a meter, could potentially lead to applications ranging from more efficient energy generation and data storage to cell-targeted systems for drug delivery.
Mathew Maye is a chemist in Brookhaven's newly opened Center for Functional Nanomaterials. "We can synthesize nanoparticles with very well controlled optical, catalytic, and magnetic properties," Maye said. "They are usually free-flowing in solution, but for use in a functional device, they have to be organized in three dimensions, or on surfaces, in a well-controlled manner. That's where self assembly comes into play. We want the particles to do the work themselves."
Using optical measurements, transmission electron microscopy, and x-ray scattering at Brookhaven's National Synchrotron Light Source, Maye and his colleagues have shown how to control the self assembly of gold nanoparticles with the assistance of various types of DNA. Their technique takes advantage of this molecule's natural tendency to pair up components called bases, known by the code letters A, T, G and C. The synthetic DNA used in the laboratory is capped onto individual gold nanoparticles and customized to recognize and bind to complementary DNA located on other particles. This process forms clusters, or aggregates, which contain multiple particles.
The research group previously used rigid, double-stranded DNA to speed up and slow down the speed of nanoparticle assembly. Most recently, they also perfected a method for regulating the size of the resulting particle clusters by incorporating multiple types of DNA strands.
On August 22, 2007 Maye will discuss how these two methods provide researchers with precise control of nanoparticle assembly at the 234th National Meeting of the American Chemical Society.
"Self-assembly is really a frontier of nanoscience," Maye said. "Learning how to take a solution of nanomaterials and end up with a functional device is going to be a great achievement."
Note: This story has been adapted from a news release issued by DOE/Brookhaven National Laboratory.

Fausto Intilla

www.oloscience.com

Computational Actinide Chemistry: Are We There Yet?

Source:

http://www.sciencedaily.com/releases/2007/08/070821143617.htm

Science Daily — Ever since the Manhattan project in World War II, actinide chemistry has been essential for nuclear science and technology. Yet scientists still seek the ability to interpret and predict chemical and physical properties of actinide compounds and materials using first principle theory. Computational actinide chemistry may bring that goal closer to achievement.

PNNL scientist Jun Li will provide an overview of developments in computational actinide chemistry at the national meeting of the American Chemical Society.
Progress in relativistic quantum chemistry, computer hardware and computational chemistry software has enabled computational actinide chemistry to emerge as a powerful and predictive tool for research in actinide chemistry.
"These discoveries will have deep impact for heavy-element science and will greatly improve the fundamental understanding of actinides essential to develop advanced nuclear energy systems, atomic weapons and environmental remediation technologies," Li said. Li's presentation will focus on applications of relativistic ab initio and density functional theory (DFT) methodologies to actinide complexes. Special emphasis will be given to applications of DFT methods to the geometries, electronic structures, spectroscopy and excited-state properties of various actinide compounds, from small actinide-containing molecules to large organoactinide systems.
Researchers are identifying molecules such as the so-called Klaui ligand that can effectively extract uranium and other actinides from their natural environment.
Note: This story has been adapted from a news release issued by DOE/Pacific Northwest National Laboratory.

Fausto Intilla

www.oloscience.com

New Finding Bubbles To Surface, Challenging Old View

Source:

http://www.sciencedaily.com/releases/2007/08/070820144237.htm

Science Daily — Chemical engineers have discovered a fundamental flaw in the conventional view of how liquids form bubbles that grow and turn into vapors, which takes place in everything from industrial processes to fizzing champagne.

The findings cast into doubt some aspects of a theory dating back to the 1920s that attempts to describe the underlying molecular mechanism behind a phenomenon called "homogeneous nucleation," said David S. Corti, an associate professor of chemical engineering at Purdue University.
The research could lead to a more precise understanding of the "phase transition" that takes place when bubbles form, grow and then become a vapor, which could, in turn, have implications for industry and research, Corti said.
In the conventional view, a liquid boiling and turning into a vapor takes place in a systematic process known as "nucleation and growth." The liquid first forms tiny "nuclei," or microscopic bubbles, that eventually grow as they pick up particles like a snowball gaining size as it rolls down a hillside. This conventional view is described by "classical nucleation theory," which was originally proposed in the 1920s.
"Our findings indicate that this is not what's going on," Corti said. "The bubble grows via a mechanism very different from classical nucleation theory."
As water is heated in a pot on a stovetop, it begins boiling when the temperature reaches 100 degrees Celsius, or 212 degrees Fahrenheit.
"You get little microscopic bubbles that form on the surfaces of the pot," Corti said.
This bubble formation on a surface is called heterogeneous nucleation. Bubbles also may form, however, by homogeneous nucleation, in which they appear not on surfaces, but within the liquid itself. The new findings specifically apply to homogeneous nucleation.
"A common example is when you heat water in a microwave oven," Corti said. "It heats liquid from the inside as opposed to on the surface, so you can actually raise the temperature of the water above 100 degrees Celsius and it doesn't boil. Sometimes when you microwave water in a mug you can superheat it and, if you put a spoon in there after removing it from the microwave, you introduce nucleation sites and it boils off and sprays hot water. The transition happens rapidly, causing a vapor explosion."
The conventional nucleation theory uses the same mechanism for how liquid droplets condense from a vapor in attempts to describe how bubbles form in a liquid. The Purdue researchers found, however, that bubbles do not form by the same mechanism as condensing droplets, Corti said.
According to the conventional theory, the pathway going from a liquid to a vapor is narrow, strictly defining the molecular mechanism by which the liquid becomes a vapor.
"You could think of this pathway as a mountain pass," Corti said. "In order to get from the liquid to the vapor, you have to go over this mountain pass. If you climb up and you're not quite at the top, sometimes you can roll back down, but if you get to the top, you can roll down to the other side and get to the vapor phase."
The new research has shown that this metaphorical mountain pass is actually more broad and flat than previously thought, meaning there are several possible pathways responsible for the phase transition.
"At the same time, what we found is that once you get over this mountain pass, which is called the free energy surface of bubble formation, the surface disappears," Corti said. "You look at one side and you see the mountain and think everything is OK, but once you climb over, it's as if the mountain disappears on the other side."
In the conventional view, the forming bubbles moving down the mountain pass could, in principle, reverse direction back toward the liquid phase.
"But in our view, as soon as you get over the top of the mountain, the mountain disappears," Corti said. "You have no choice but to plummet to something else, the vapor phase."The findings were based on research using new theoretical methods and verified by computational simulations developed by the Purdue engineers.
Nucleation occurs when a liquid is heated above its boiling temperature or when the pressure exerted on a liquid is decreased below the so-called saturation pressure, which is the case when the lid is removed from the bottle of a carbonated beverage such as champagne, beer or a soft drink.
"This also occurs in the chemical industry and in other work environments where liquids flow through pipes, sometimes with undesirable consequences," Corti said. "Depending on the diameter of the pipes, the pressure of the liquid can drop very rapidly, causing it to become superheated, and before the pressure recovers you can get this phase transition."
The bubbles that form can then collapse when the pressure increases again, sometimes causing significant damage to equipment.
In other industrial processes involving propeller blades, bubbles can form or undergo "cavitation" and then suddenly implode, producing high temperatures and extreme pressures and damaging equipment.
"There are tons of examples, but the real fundamental mechanism underlying what's going on is not that well understood, even for very simple systems," Corti said.
New insights into phase transition could translate into practical and safety benefits for industry. Such insights also could result in a better understanding of the mechanisms responsible for initiating "sonochemistry" and "sonoluminescence" processes in which sound waves are used to form tiny bubbles in liquids. As the bubbles collapse, they emit flashes of light and generate high pressures and temperatures that could be used to enhance chemical reactions.
Another potential practical benefit is to improve the manufacture of foams made of plastic polymers that depends on the formation and distribution of bubbles.
Although the new findings indicate current theory does not adequately describe the molecular mechanism for bubble formation and phase transition from a liquid to vapor, the Purdue researchers do not yet know precisely what that mechanism is.
"We are still working out the full implications of this ourselves," Corti said.
Findings are detailed in a research paper appearing online in August in the journal Physical Review Letters. The paper was written by Corti and chemical engineering doctoral student Mark Uline.
Article: Mark J. Uline and David S. Corti, Activated Instability of Homogeneous Bubble Nucleation and Growth
Note: This story has been adapted from a news release issued by Purdue University.

Fausto Intilla

www.oloscience.com

What, Oh, What Are Those Actinides Doing? Heavy Metals In the Environment

Source:

http://www.sciencedaily.com/releases/2007/08/070819174206.htm

Science Daily — Researchers at Pacific Northwest National Laboratory are uniting theory, computation and experiment to discover exactly how heavy elements, such as uranium and technetium, interact in their environment.

As part of that effort, scientists have combined sensitive experimental measurements with first principle electronic structure calculations to measure, and to really understand, the structural and bonding parameters of uranyl, the most common oxidation state of uranium in systems containing water.
The insights were achieved by PNNL scientist Bert de Jong and associates Gary Groenewold of Idaho National Laboratory and Michael Van Stipdonk of Wichita State University, employing the supercomputing resources of the William R. Wiley Environmental Molecular Sciences Laboratory, a Department of Energy national scientific user facility located at PNNL.
The large number and behavior of electrons in heavy elements makes most of them extremely difficult to study. De Jong said that advancements in computing power and theory are enabling computational actinide chemistry to contribute significantly to the understanding and interpretation of experimental chemistry data, as well as to predicting the chemical and physical properties of heavy transition metal, lanthanide and actinide complexes.
"Now we can make sure we get the right answer for the right reason," de Jong said, adding that results obtained from the calculations are an invaluable supplement to current, very expensive and often hazardous experimental studies.
Researchers are discovering how actinides such as uranium in solution interact with magnetite and other mineral surfaces.
Discoveries made using the new capabilities available to the growing field of computational actinide chemistry could have wide impact, from radioactive waste and cleanup challenges to the design and operation of future nuclear facilities.
Bert De Jong presented this research at the 234th American Chemical Society National Meeting in Boston, Mass., on Aug. 19.
Note: This story has been adapted from a news release issued by DOE/Pacific Northwest National Laboratory.

Fausto Intilla

www.oloscience.com

Could Physicists Make A Time Machine? It All Depends On Curving Space-time

Source:

http://www.sciencedaily.com/releases/2007/08/070822164415.htm

Science Daily — Technion researchers have developed a theoretical model of a time machine that, in the distant future, could possibly enable future generations to travel into the past.

“In order to travel back in time, the spacetime structure must be engineered appropriately,” explains Prof. Amos Ori of the Technion’s Faculty of Physics. “This is what Einstein’s theory of general relativity deals with. It says that spacetime can be flat. That is – it has a trivial, simple structure. But it can also be curved with various configurations. According to the theory of relativity, the essence of gravitational fields is in the curving of spacetime. The theory of relativity also defines how space is curved and how this curvature develops over time.”
The main question is: if, according to the principles of curvature development in the theory of relativity, can a time machine be created? In other words, can we cause spacetime to curve in such a way as to enable travel back in time? Such a journey requires a significant curvature of spacetime, in a very special form.
Traveling back in time is actually closing time-like curves so we can go back to an event at which we were present in the past. In flat space, it is not possible to close curves and go back in time. In order for closed time-like curves to exist, there has to be a curvature of a specific form on spacetime.
The question Prof. Ori is investigating is: do the laws of gravity permit the development of spacetime with the required curvature (closed time-like curves)? In the past, scientists raised a number of objections to this possibility. Now, Prof. Ori is proposing a theoretical model for spacetime that could develop into a time machine.
The model overcomes some of the questions, which, until now, scientists have not succeeded in solving. One of the difficult claims against a time machine was that, in order to create a time machine, it would be necessary for it to contain material with negative density. And since we do not have such material – and it is also not clear if the laws of nature enable the existence of such material in the quantities required - it is not possible to build a time machine. Now, Prof. Ori comes along and proposes a theoretical model that does not require material with negative density. The model that he proposes is, essentially, a vacuum space that contains a region field with standard positive density material.
“The machine is spacetime itself,” he explains. “Today, if we were to create a time machine – an area with a warp like this in space that would enable time lines to close on themselves – it might enable future generations to return to visit our time. We, apparently, cannot return to previous ages because our predecessors did not create this infrastructure for us.”
Prof. Ori emphasizes that we still do not have the technology to control gravitational fields at will, despite the fact that the theoretical principles of how to do this exist. “The model that we developed at the Technion is a significant step but there still remains a number of non-trivial open questions,” he stresses. “It may be that some of these questions also will not be solved in the future. This is still not clear.” As an example, he brings up the problem of instability according to which in spacetime with a time machine there could be disturbances with increasing strength so that spacetime would be disrupted to such an extent that it would cancel out the time machine. Prof. Ori, one of the few scientists in the world investigating this issue, hopes that continued research will present a clearer picture with respect to these questions.
An article on this model was published recently in the journal “Physical Review.”
Note: This story has been adapted from a news release issued by Technion, Israel Institute Of Technology.

Fausto intilla

www.oloscience.com

Working Toward New Energy With Electrochemistry

Source:

http://www.sciencedaily.com/releases/2007/08/070820112829.htm

Science Daily — In an effort to develop alternative energy sources such as fuel cells and solar fuel from "artificial" photosynthesis, scientists at the U.S. Department of Energy's Brookhaven National Laboratory are taking a detailed look at electrons -- the particles that set almost all chemical processes in motion.

Electron transfer plays a vital role in numerous biological processes, including nerve cell communication and converting energy from food into useful forms. It's the initial step in photosynthesis as well, where charges are first separated and the energy is stored for later use -- one of the concepts behind energy production using solar cells. Understanding and controlling the movement of electrons through individual molecules also could allow for the development of new technologies such as extremely small circuits, or help scientists find catalysts that give fuel cells a much-needed boost in efficiency and affordability. Three Brookhaven chemists will discuss how these applications are related to their most recent findings at the 234th National Meeting of the American Chemical Society.
A Different Way to Turn Water into Fuel
Brookhaven chemist James Muckerman works with a team of researchers to design catalysts inspired by photosynthesis, the natural process by which green plants convert sunlight, water, and carbon dioxide into oxygen and carbohydrates. The goal is to design a bio-inspired system that can produce fuels like methanol or hydrogen directly from carbon dioxide or water, respectively, using renewable solar energy.
To replicate one of the important steps in natural photosynthesis, Muckerman uses molecular complexes containing the metal ruthenium as catalysts to drive the conversion of water into oxygen, protons, and electrons. Specifically, Muckerman's group has set out to determine the electronic activity of a catalyst recently developed in Japan. Unlike previous ruthenium catalysts, which have a very short life, this catalyst has quinone ligands attached to each of its ruthenium centers. These electron-accepting molecules appear to make the catalyst very active and stable. The challenge is to determine exactly how the catalyst works.
"It was a controversial result," said Muckerman, who compares the lab results to calculations based on theory. "I believe that the reaction occurs by ruthenium-mediated electron transfer from water molecules bound to the metal centers to the quinone ligands. These electron transfers are initiated by proton transfers from the bound water moieties to the aqueous solution. The ruthenium atoms maintain the same charge state during the entire catalytic cycle, indicating that this catalyst works in a totally different way than the other catalysts."
This result could open up a new direction for designing future catalysts.
Revealing a Jumpstart in Organic Electron Transfer
Using organic molecules as electronic components in nanoscale devices could lead to various technological advances including small-scale circuits for improving solar cells. One of the most important issues in this field is the role of molecule-metal contact and the electron transfer that occurs between the two. With this idea in mind, Brookhaven chemist Marshall Newton and former Brookhaven research associate Vasili Perebeinos studied the electronic activity involved in the self-assembly of sulfur-capped organic molecules supported on a gold surface.
Their results were surprising: "The bottom line is that the electrical action in the formation of this interface has already happened within the organic layer, without direct involvement of the metal," said Newton, who develops models to understand these interactions in molecular systems. "That's somewhat unexpected because people typically say that the big electrical action involves charge moving from or between the organic part and the metal surface. But in this case, the electronic rearrangement occurs internally during the process of bringing all of these organic chains together before they are in contact with the metal."
Newton believes this phenomenon is caused by the need to reduce electrical repulsions between the side-by-side organic chains.
An Affordable Alternative for Fuel Cells
Platinum is the most efficient metal electrocatalyst for accelerating chemical reactions in fuel cells. However, the reactions caused by the expensive metal are slow, and undesired side reactions often degrade the electrode. In an effort to find an affordable alternative with high activity and stability, Brookhaven chemist Ping Liu and her research group are introducing ruthenium oxide to the electronic system.
By carefully forming just one thin layer of platinum on a ruthenium-oxide surface, Ping has calculated that the oxidation-reduction reaction (the driving force for fuel cells) happens almost as quickly as with a pure platinum catalyst, while using much less of the pricey metal and preventing its dissolution.
"Theoretically, when there's one monolayer of platinum on ruthenium-oxide, it has very close activity to pure platinum," Liu said. "It's not quite as good, but it's very close. This surface should be one of the alternatives we consider for oxidation-reduction catalysts."
Future research plans include looking for ways to modify the surface, adding other elements or metals, and further reducing the cost by searching for a surface material less expensive than ruthenium oxide.
The research by Muckerman and Liu is funded through the U.S. Department of Energy's Hydrogen Program, which implements the President's Hydrogen Fuel Initiative, a five-year program that began in 2003 to sponsor research, development, and demonstration of hydrogen and fuel cell technologies. Specifically, the funding derived from DOE's Office of Basic Energy Sciences within the Office of Science, which also funds Newton's work.
Note: This story has been adapted from a news release issued by DOE/Brookhaven National Laboratory.

Fausto Intilla

www.oloscience.com

Cheap And Easy Technique To Produce Hydrogen From Visible Light Is Almost Ready

Source:

http://www.sciencedaily.com/releases/2007/08/070817211908.htm

Science Daily — The prospect for the wide spread use of hydrogen as a portable energy carrier is dependent on finding a clean, renewable method of production. At Penn State University, a research group headed by professor of electrical engineering Craig Grimes in the Materials Research Institute is “only a couple of problems away” from developing an inexpensive and easily scalable technique for water photoelectrolysis - the splitting of water into hydrogen and oxygen using light energy – that could help power the proposed hydrogen economy.

Most current methods of hydrogen production split hydrogen from natural gas in a process that produces climate changing greenhouse gas while consuming a nonrenewable resource. A more environmentally friendly approach would produce hydrogen from water using the renewable energy of sunlight.
In a paper published online in Nano Letters on July 3, 2007, lead author Gopal K. Mor, along with Haripriya E. Prakasam, Oomman K. Varghese, Kathik Shankar, and Grimes, describe the fabrication of thin films made of self-aligned, vertically oriented titanium iron oxide (Ti-Fe-O) nanotube arrays that demonstrate the ability to split water under natural sunlight.
Previously, the Penn State scientists had reported the development of titania nanotube arrays with a photoconversion efficiency of 16.5% under ultraviolet light. Titanium oxide (TiO2), which is commonly used in white paints and sunscreens, has excellent charge-transfer properties and corrosion stability, making it a likely candidate for cheap and long lasting solar cells. However, as ultraviolet light contains only about 5% of the solar spectrum energy, the researchers needed to finds a means to move the materials band gap into the visible spectrum.
They speculated that by doping the TiO2 film with a form of iron called hematite, a low band gap semiconductor material, they could capture a much larger portion of the solar spectrum. The researchers created Ti-Fe metal films by sputtered titanium and iron targets on fluorine-doped tin oxide coated glass substrates. The films were anodized in an ethylene glycol solution and then crystallized by oxygen annealing for 2 hours. They studied a variety of films of differing thicknesses and varying iron content. In this paper they report a photocurrent of 2 mA/cm2, and a photoconversion rate of 1.5%, the second highest rate achieved with an iron oxide related material.
The team is now looking into optimizing the nanotube architecture to overcome the low electron-hole mobility of iron. By reducing the wall thickness of the Ti-Fe-O nanotubes to correspond to the hole diffusion length of iron which is around 4nm, the researchers hope to reach an efficiency closer to the 12.9% theoretical maximum for materials with the band gap of hematite.
“As I see it, we are a couple of problems away from having something that will revolutionize the field of hydrogen generation by use of solar energy,” Grimes says.
Note: This story has been adapted from a news release issued by Penn State Materials Research Institute.

Fausto Intilla

www.oloscience.com

New Clues To Mechanism For 'Colossal Resistance' Effects

Source:

http://www.sciencedaily.com/releases/2007/08/070817145222.htm

Science Daily — Experiments at the U.S. Department of Energy's Brookhaven National Laboratory shed new light on some materials' ability to dramatically change their electrical resistance in the presence of an external magnetic or electric field. Small changes in resistance underlie many electronic devices, including some computer data storage systems.

Understanding and applying dramatic resistance changes, known as colossal magnetoresistance, offers tremendous opportunities for the development of new technologies, including data-storage devices with increased data density and reduced power requirements.
"This is an extremely important piece of work with broad potential application in developing the next generation of electronic and data-storage devices," said Brookhaven physicist Yimei Zhu, one of the lead authors on a paper appearing in the August 21, 2007 Proceedings of the National Academy of Sciences.
The Brookhaven scientists were studying crystalline perovskite manganites that had been doped with extra charge carriers - electrons or "holes" (the absence of electrons) - using various state-of-the-art electron microscopy techniques. In an unprecedented experiment, the scientists used a scanning-tunneling microscope that was built inside an electron microscope to apply an electric stimulus to the sample while observing its response at the atomic scale.
Using this technique, the scientists obtained, for the first time, direct evidence that a small electric stimulus can distort the shape of the crystal lattice, and also cause changes in the way charges travel through the lattice. The lattice distortions accompanied the charge carrier as it moved through the lattice, producing a particle-like excitation called a polaron. "Polarons can be pictured as a charge carrier surrounded by a 'cloth' of the accompanying lattice vibrations," Zhu said.
Zhu's group observed polarons melting and reordering - that is, undergoing a transition from solid to liquid to solid again - in response to the applied current, which the scientists have identified as the key mechanism for colossal mangetoresistance. The technique also allowed the scientists to study polaron behavior, i.e., how variations in electric field, current, and temperature affected this transition.
"We show that static long-range ordering of polarons forms a polaron solid, which represents a new type of charge and orbital ordered state," said Zhu. "The related lattice distortions connect this phenomenon to colossal resistance effects, and suggest ways of modifying charge density and electronic interactions at the vicinity of electric interfaces and electrodes."
Colossal resistance effects could result in miniaturization of electric circuits that operate at lower power. This work therefore has direct impact on the application of these materials in the development of new electronic and spintronic devices (devices that use 'a combination of electron spin and charge). Such devices include new forms of "nonvolatile" computer memory (memory that can retain stored information even when not powered) such as resistive random access memory (RRAM).
This work was done in collaboration with Christian Jooss, a Brookhaven visiting scientist, and colleagues from the University of Goettingen, Germany. The work was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy's Office of Science and by the German Research Foundation.
Note: This story has been adapted from a news release issued by DOE/Brookhaven National Laboratory.

Fausto Intilla

www.oloscience.com

Physicists Discover 'Super Crystals' In A Semiconductor

Source:

http://www.sciencedaily.com/releases/2007/08/070816094653.htm

Science Daily — University of Arizona physicists have discovered that "super crystals" -- crystals which are hundreds to thousands times larger than conventional crystals -- exist in certain organic semiconducting solids.

Pure super-crystalline organic semiconductors will conduct electricity much differently than conventional solids. Super-crystalline semiconductors, for example, could create splashes of current on electrical contacts, even in a uniform electric field, say UA physicist Andrei Lebed and graduate student Si Wu.
Most people understand how liquids freeze as solid crystals when temperatures become cold enough, like water droplets crystallizing into snowflakes or molten glass hardening into solid glass. Snowflakes are homogenous solids formed by a repeating, three-dimensional pattern of molecules that have fixed distances between the repeating molecular units. Solid glass approaches a perfect crystalline pattern, too, after a few hundred years, Lebed said.
Latter 20th-century physicists realized that at low enough temperatures, most liquids that exist in nature become energetically unstable as they solidify. Scientists discovered solids that don't have the commonly known, regular crystalline and glass phases - things like liquid crystals, quasi-crystals and charge-density waves. Charge-density waves are systems that display interesting physics, such as metals becoming insulators.
Understanding the physical nature of a solid phase is one of the most important problems in condensed matter physics, both from a fundamental point of view and from an applications point of view, Lebed and Wu said.
Leading American and Soviet physicists first predicted more than 25 years ago that some organic metals should be made up of "super crystals," Lebed said. Nobel laureate Robert Schrieffer, physicist Lev Gor'kov, who is a pioneer in superconductivity, and other members of the National Academy of Sciences were among the first to predict super crystals.
In super crystals, not only do the patterns of atoms or molecules repeat, there is also a periodically repeating super-structure of plane traps for electrons, Lebed said. "The distance between these plane traps, which are called soliton walls, are typically hundreds to thousands times greater than the distances between the organic molecules." (See the accompanying graphic, above, that illustrates this concept.)
U.S., Soviet and Japanese scientists, including Lebed, collaborated in research to discover the soliton wall superlattices, or super crystals, in organic metals. "Unfortunately, so far no one has discovered super crystals in organic metals," Lebed said.
Lebed and Wu are among the solid state theorists who collaborate with experimentalists in studying other materials that might possibly be super-crystalline.
"Our hopes for a discovery of a long awaited super-crystalline phase were raised after we started to analyze experimental data of James Brooks' group," Lebed said.
Brooks directs condensed matter experiments at the National High Magnetic Field Laboratory in Tallahassee, Fla. Three years ago, physicists there discovered a mysterious solid-state phase in a semiconductor made up of very complicated organic molecules, molecules of perylene (Per) and maleonitriledithiolate (mnt), in high magnetic fields.
"When Wu and I, who are theorists, analyzed the experimental data, what we found was a complete surprise to us," Lebed said. "Our theoretical calculations showed that the only way to explain the appearance of a mysterious high magnetic field state was to suggest that it appears inside a super-crystalline phase."
Lebed and Wu published their study in the July 13 issue of Physical Review Letters.
Future experiments are needed to confirm the theoretical discovery, Lebed added.
If experiments do confirm Lebed's and Wu's results, the novel, exotic solid phase in organic semiconductors promises important technological applications. Such semiconductors will conduct electricity in novels ways. Another striking feature of the super-crystalline semiconductor is that its period and electronic properties might be tuned by changing the strength of the external magnetic field, Lebed said.
Note: This story has been adapted from a news release issued by University of Arizona.

Fausto Intilla

www.oloscience.com

A Sound Way To Turn Heat Into Electricity

Source:

http://www.sciencedaily.com/releases/2007/06/070603225026.htm

Science Daily — University of Utah physicists developed small devices that turn heat into sound and then into electricity. The technology holds promise for changing waste heat into electricity, harnessing solar energy and cooling computers and radars."We are converting waste heat to electricity in an efficient, simple way by using sound," says Orest Symko, a University of Utah physics professor who leads the effort. "It is a new source of renewable energy from waste heat."

Five of Symko's doctoral students recently devised methods to improve the efficiency of acoustic heat-engine devices to turn heat into electricity. They will present their findings on Friday, June 8 during the annual meeting of the Acoustical Society of America at the Hilton Salt Lake City Center hotel.Symko plans to test the devices within a year to produce electricity from waste heat at a military radar facility and at the university's hot-water-generating plant.The research is funded by the U.S. Army, which is interested in "taking care of waste heat from radar, and also producing a portable source of electrical energy which you can use in the battlefield to run electronics" he says.Symko expects the devices could be used within two years as an alternative to photovoltaic cells for converting sunlight into electricity. The heat engines also could be used to cool laptop and other computers that generate more heat as their electronics grow more complex. And Symko foresees using the devices to generate electricity from heat that now is released from nuclear power plant cooling towers.How to Get Power from Heat and SoundSymko's work on converting heat into electricity via sound stems from his ongoing research to develop tiny thermoacoustic refrigerators for cooling electronics.In 2005, he began a five-year heat-sound-electricity conversion research project named Thermal Acoustic Piezo Energy Conversion (TAPEC). Symko works with collaborators at Washington State University and the University of Mississippi.The project has received $2 million in funding during the past two years, and Symko hopes it will grow as small heat-sound-electricity devices shrink further so they can be incorporated in micromachines (known as microelectromechanical systems, or MEMS) for use in cooling computers and other electronic devices such as amplifiers.Using sound to convert heat into electricity has two key steps. Symko and colleagues developed various new heat engines (technically called "thermoacoustic prime movers") to accomplish the first step: convert heat into sound.Then they convert the sound into electricity using existing technology: "piezoelectric" devices that are squeezed in response to pressure, including sound waves, and change that pressure into electrical current. "Piezo" means pressure or squeezing.Most of the heat-to-electricity acoustic devices built in Symko's laboratory are housed in cylinder-shaped "resonators" that fit in the palm of your hand. Each cylinder, or resonator, contains a "stack" of material with a large surface area -- such as metal or plastic plates, or fibers made of glass, cotton or steel wool -- placed between a cold heat exchanger and a hot heat exchanger.When heat is applied -- with matches, a blowtorch or a heating element -- the heat builds to a threshold. Then the hot, moving air produces sound at a single frequency, similar to air blown into a flute."You have heat, which is so disorderly and chaotic, and all of a sudden you have sound coming out at one frequency," Symko says.Then the sound waves squeeze the piezoelectric device, producing an electrical voltage. Symko says it's similar to what happens if you hit a nerve in your elbow, producing a painful electrical nerve impulse.Longer resonator cylinders produce lower tones, while shorter tubes produce higher-pitched tones.Devices that convert heat to sound and then to electricity lack moving parts, so such devices will require little maintenance and last a long time. They do not need to be built as precisely as, say, pistons in an engine, which loses efficiency as the pistons wear. Symko says the devices won't create noise pollution. First, as smaller devices are developed, they will convert heat to ultrasonic frequencies people cannot hear. Second, sound volume goes down as it is converted to electricity. Finally, "it's easy to contain the noise by putting a sound absorber around the device," he says.Studies Improve Efficiency of Acoustic Conversion of Heat to ElectricityHere are summaries of the studies by Symko's doctoral students:-- Student Bonnie McLaughlin showed it was possible to double the efficiency of converting heat into sound by optimizing the geometry and insulation of the acoustic resonator and by injecting heat directly into the hot heat exchanger.She built cylindrical devices 1.5 inches long and a half-inch wide, and worked to improve how much heat was converted to sound rather than escaping. As little as a 90-degree Fahrenheit temperature difference between hot and cold heat exchangers produced sound. Some devices produced sound at 135 decibels -- as loud as a jackhammer.-- Student Nick Webb showed that by pressurizing the air in a similar-sized resonator, it was able to produce more sound, and thus more electricity.He also showed that by increasing air pressure, a smaller temperature difference between heat exchangers is needed for heat to begin converting into sound. That makes it practical to use the acoustic devices to cool laptop computers and other electronics that emit relatively small amounts of waste heat, Symko says.-- Numerous heat-to-sound-to-electricity devices will be needed to harness solar power or to cool large, industrial sources of waste heat. Student Brenna Gillman learned how to get the devices -- mounted together to form an array -- to work together.For an array to efficiently convert heat to sound and electricity, its individual devices must be "coupled" to produce the same frequency of sound and vibrate in sync.Gillman used various metals to build supports to hold five of the devices at once. She found the devices could be synchronized if a support was made of a less dense metal such as aluminum and, more important, if the ratio of the support's weight to the array's total weight fell within a specific range. The devices could be synchronized even better if they were "coupled" when their sound waves interacted in an air cavity in the support.-- Student Ivan Rodriguez used a different approach in building an acoustic device to convert heat to electricity. Instead of a cylinder, he built a resonator from a quarter-inch-diameter hollow steel tube bent to form a ring about 1.3 inches across.In cylinder-shaped resonators, sound waves bounce against the ends of the cylinder. But when heat is applied to Rodriguez's ring-shaped resonator, sound waves keep circling through the device with nothing to reflect them.Symko says the ring-shaped device is twice as efficient as cylindrical devices in converting heat into sound and electricity. That is because the pressure and speed of air in the ring-shaped device are always in sync, unlike in cylinder-shaped devices.-- Student Myra Flitcroft designed a cylinder-shaped heat engine one-third the size of the other devices. It is less than half as wide as a penny, producing a much higher pitch than the other resonators. When heated, the device generated sound at 120 decibels -- the level produced by a siren or a rock concert."It's an extremely small thermoacoustic device -- one of the smallest built -- and it opens the way for producing them in an array," Symko says.

Note: This story has been adapted from a news release issued by University of Utah.

Fausto Intilla

www.oloscience.com

Discovery Of 'Hidden' Quantum Order Improves Prospects For Quantum Super Computers

Source:

http://www.sciencedaily.com/releases/2007/07/070726142010.htm

Science Daily — An international team, including scientists from the London Center for Nanotechnology, has detected a hidden magnetic "quantum order" that extends over chains of 100 atoms in a ceramic without classical magnetism. The findings, which are published July 26 in the journal Science, have implications for the design of devices and materials for quantum information processing.

In quantum information processing, data is recorded and manipulated as quantum bits or 'qubits', generalizations of the classical '0' and '1' bits which are traditionally represented by the 'on' and 'off' states of conventional switches. It is widely believed that if large-scale quantum computers can be built, they will be able to solve certain problems, such as code breaking, exponentially faster than classical computers.Theoretically, the spin of an individual electron is an excellent qubit, but in a real material it interacts with other electrons and its useable quantum properties are rapidly lost. The new research is important because it explicitly demonstrates, using a practical material, that a large number of electron spins can be coupled together to yield a quantum mechanical state with no classical analog. In addition, the team has also established the factors that affect the distance over which the hidden 'quantum order' can be maintained."We had two objectives," explains Professor Gabriel Aeppli, Director of the London Centre for Nanotechnology and the paper's senior author. "The first was to show that we could actually image the quantum order, which is sometimes referred to as phase coherence. The second aim was to manipulate the distance over which it can be maintained." This distance - and how sensitive it is to changes in temperature or chemical impurities in the material - can be essential in determining whether a material will have real-life applications, where it would be crucial to control and maintain quantum order over predetermined extents in space and time.The team studied a ceramic material consisting of chains of nickel-centered oxygen octahedra laid end-to-end. The chains are not ordinary magnets such as those used to fix reminders onto refrigerator doors, but an exotic quantum spin liquid in which the electron spins (analogous to tiny bar magnets) point in random directions with no particular order, even at very low temperatures.To measure the quantum order throughout this classically disordered liquid, the scientists used neutrons to image the magnetic excitations - "flips" or fluctuations of the spins - and the distances over which they could propagate. The experiments were performed at the National Institute of Standards and Technology (NIST) Center for Neutron Research in the US and at the ISIS particle accelerator of the Rutherford Appleton Laboratory in the UK.The scientists found that despite the apparent classical disorder, magnetic excitations could propagate over long chains of atoms at low temperature - in the otherwise magnetically disordered material. Other examples of large-scale quantum phase coherence include superconductors and superfluids where quantum physics leads to fascinating properties.The team also discovered that they could limit the coherence or make it disappear altogether by introducing defects into the material either by adding chemical impurities (doping) or heating. These defects break the chains into independent sub-chains, each with its own, hidden order. This part of the reported research is the first step towards engineered spin-based quantum states in ceramics.Aeppli and other members of the team note that their work was initially not intended to have direct applications, but that they later realized that what they are learning could be applied in a range of fields from nanotechnology to quantum computing.Collaborators on this research include: Guangyong Xu, of John Hopkins University and Brookhaven National Laboratory; Collin L. Broholm, Ying Chen, and Michel Kenzelmann of Johns Hopkins University and the NIST Center for Neutron Research; Yeong-Ah Soh of Dartmouth College; Gabriel Aeppli of the London Centre for Nanotechnology and University College London; John. F. DiTusa of Louisiana State University; Christopher D. Frost from the ISIS Facility, Rutherford Appleton Laboratory, U.K.; Toshimitsu Ito and Kunihiko Oka of the National Institute of Advanced Industrial Science and Technology (AIST), Japan; and Hidenori Takagi from AIST and University of Tokyo.The work was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy's Office of Science, the National Science Foundation, a Wolfson-Royal Society Research Merit Award (UK), and by the Basic Technologies programme of the UK Research Councils.

Note: This story has been adapted from a news release issued by University College London.

Fausto Intilla

www.oloscience.com

Scientists Assemble Single Atoms Into Predefined Nanostructures

Source:

http://www.sciencedaily.com/releases/2007/04/070407163428.htm

Science Daily — Scientists at the Paul Drude Institute for Solid State Electronics in Berlin, Germany, have assembled single atoms of different elements, thus forming nanostructures of predefined size and composition. The team lead by Stefan Foelsch used copper (Cu) and cobalt (Co) atoms to produce pairs or various chains of atoms on a substrate surface made of crystalline copper. “We manipulated the atoms in a low-temperature scanning tunneling microscope”, says Stefan Foelsch. He adds: “We found that the quantum effects in these structures can be understood within the framework of textbook physics describing the electronic properties of simple molecules.”

Thus, it is possible to taylor “artificial molecules” supported by a solid surface made of magnetic and non-magnetic elements. The nanostructures engineered and characterized constitute a promising model for future investigations in order to gain insight into the magnetism of the smallest structures. Stefan Foelsch says that this is an issue of utmost technological relevance.The scientists report on their work in Physical Review Letters (J. Lagoute et al.: „Doping of monatomic Cu chains with single Co atoms“, published online on April 6).

Note: This story has been adapted from a news release issued by Forschungsverbund Berlin.

Fausto Intilla

www.oloscience.com

Laser-cooling Brings Large Object Near Absolute Zero

Source:

http://www.sciencedaily.com/releases/2007/04/070406171036.htm

Science Daily — Using a laser-cooling technique that could one day allow scientists to observe quantum behavior in large objects, MIT researchers have cooled a coin-sized object to within one degree of absolute zero.This study marks the coldest temperature ever reached by laser-cooling of an object of that size, and the technique holds promise that it will experimentally confirm, for the first time, that large objects obey the laws of quantum mechanics just as atoms do.Although the research team has not yet achieved temperatures low enough to observe quantum effects, "the most important thing is that we have found a technique that could allow us to get (large objects) to ultimately show their quantum behavior for the first time," said MIT Assistant Professor of Physics Nergis Mavalvala, leader of the team.

Quantum theory was developed in the early 20th century to account for unexpected atomic behavior that could not be explained by classical mechanics. But at larger scales, objects' heat and motion blur out quantum effects, and interactions are ruled by classical mechanics, including gravitational forces and electromagnetism. "You always learn in high school physics that large objects don't behave according to quantum mechanics because they're just too hot, and the thermal energy obscures their quantum behavior," said Thomas Corbitt, an MIT graduate student in physics and lead author of the paper. "Nobody's demonstrated quantum mechanics at that kind of (macroscopic) scale."To see quantum effects in large objects, they must be cooled to near absolute zero. Such low temperatures can only be reached by keeping objects as motionless as possible. At absolute zero (0 Kelvin, -273 degrees Celsius or -460 degrees Fahrenheit), atoms lose all thermal energy and have only their quantum motion. In their upcoming paper, the researchers report that they lowered the temperature of a dime-sized mirror to 0.8 degrees Kelvin. At that temperature, the 1 gram mirror moves so slowly that it would take 13 billion years (the age of the universe) to circle the Earth, said Mavalvala, whose group is part of MIT's LIGO (Laser Interferometer Gravitational-wave Observatory) Laboratory.The team continues to refine the technique and has subsequently achieved much lower temperatures. But in order to observe quantum behavior in an object of that size, the researchers need to attain a temperature that is still many orders of magnitude colder, Mavalvala said.To reach such extreme temperatures, the researchers are combining two previously demonstrated techniques-optical trapping and optical damping. Two laser beams strike the suspended mirror, one to trap the mirror in place, as a spring would (by restoring the object to its equilibrium position when it moves), and one to slow (or damp) the object and take away its thermal energy.Combined, the two lasers generate a powerful force--stronger than a diamond rod of the same shape and size as the laser beams--that reduces the motion of the object to near nothing.Using light to hold the mirror in place avoids the problems raised by confining it with another object, such as a spring, Mavalvala said. Mechanical springs are made of atoms that have their own thermal energy and thus would interfere with cooling.As the researchers get closer and closer to reaching the cold temperature they need to see quantum behavior, it will get more difficult to reach the final goal, Mavalvala predicted. Several technical issues still stand in the way, such as interference from fluctuations in the laser frequency."That last factor of 100 will be heroic," she said.Once the objects get cold enough, quantum effects such as squeezed state generation, quantum information storage and quantum entanglement between the light and the mirror should be observable, Mavalvala said.The MIT researchers and colleagues at Caltech and the Albert Einstein Institute in Germany will report their findings in an upcoming issue of Physical Review Letters.Other authors on the paper are Christopher Wipf, MIT graduate student in physics; David Ottaway, research scientist at MIT LIGO; Edith Innerhofer (formerly a postdoctoral fellow at MIT); Yanbei Chen, leader of the Max Planck (Albert Einstein Institute) group; Helge Muller-Ebhardt and Henning Rehbein, graduate students at the Albert Einstein Institute; and research scientists Daniel Sigg of LIGO Hanford Observatory and Stanley Whitcomb of Caltech.The research was funded by the National Science Foundation and the German Federal Ministry of Education and Research.

Note: This story has been adapted from a news release issued by Massachusetts Institute of Technology.

Fausto Intilla

www.oloscience.com

Physicists Find Way To 'See' Extra Dimensions

Source:

http://www.sciencedaily.com/releases/2007/02/070203103355.htm

Science Daily — Peering backward in time to an instant after the big bang, physicists at the University of Wisconsin-Madison have devised an approach that may help unlock the hidden shapes of alternate dimensions of the universe. A new study demonstrates that the shapes of extra dimensions can be "seen" by deciphering their influence on cosmic energy released by the violent birth of the universe 13 billion years ago.

The method, published today (Feb. 2) in Physical Review Letters, provides evidence that physicists can use experimental data to discern the nature of these elusive dimensions - the existence of which is a critical but as yet unproven element of string theory, the leading contender for a unified "theory of everything."Scientists developed string theory, which proposes that everything in the universe is made of tiny, vibrating strings of energy, to encompass the physical principles of all objects from immense galaxies to subatomic particles. Though currently the front-runner to explain the framework of the cosmos, the theory remains, to date, untested.The mathematics of string theory suggests that the world we know is not complete. In addition to our four familiar dimensions - three-dimensional space and time - string theory predicts the existence of six extra spatial dimensions, "hidden" dimensions curled in tiny geometric shapes at every single point in our universe. Don't worry if you can't picture a 10-dimensional world. Our minds are accustomed to only three spatial dimensions and lack a frame of reference for the other six, says UW-Madison physicist Gary Shiu, who led the new study. Though scientists use computers to visualize what these six-dimensional geometries could look like (see image), no one really knows for sure what shape they take.The new Wisconsin work may provide a long-sought foundation for measuring this previously immeasurable aspect of string theory.According to string theory mathematics, the extra dimensions could adopt any of tens of thousands of possible shapes, each shape theoretically corresponding to its own universe with its own set of physical laws. For our universe, "Nature picked one - and we want to know what that one looks like," explains Henry Tye, a physicist at Cornell University who was not involved in the new research.Shiu says the many-dimensional shapes are far too small to see or measure through any usual means of observation, which makes testing this crucial aspect of string theory very difficult. "You can theorize anything, but you have to be able to show it with experiments," he says. "Now the problem is, how do we test it?"He and graduate student Bret Underwood turned to the sky for inspiration.Their approach is based on the idea that the six tiny dimensions had their strongest influence on the universe when it itself was a tiny speck of highly compressed matter and energy - that is, in the instant just after the big bang."Our idea was to go back in time and see what happened back then," says Shiu. "Of course, we couldn't really go back in time."Lacking the requisite time machine, they used the next-best thing: a map of cosmic energy released from the big bang. The energy, captured by satellites such as NASA's Wilkinson Microwave Anisotropy Probe (WMAP), has persisted virtually unchanged for the last 13 billion years, making the energy map basically "a snapshot of the baby universe," Shiu says. The WMAP experiment is the successor to NASA's Cosmic Background Explorer (COBE) project, which garnered the 2006 Nobel Prize in physics. Just as a shadow can give an idea of the shape of an object, the pattern of cosmic energy in the sky can give an indication of the shape of the other six dimensions present, Shiu explains.To learn how to read telltale signs of the six-dimensional geometry from the cosmic map, they worked backward. Starting with two different types of mathematically simple geometries, called warped throats, they calculated the predicted energy map that would be seen in the universe described by each shape. When they compared the two maps, they found small but significant differences between them. Their results show that specific patterns of cosmic energy can hold clues to the geometry of the six-dimensional shape - the first type of observable data to demonstrate such promise, says Tye.Though the current data are not precise enough to compare their findings to our universe, upcoming experiments such as the European Space Agency's Planck satellite should have the sensitivity to detect subtle variations between different geometries, Shiu says. "Our results with simple, well-understood shapes give proof of concept that the geometry of hidden dimensions can be deciphered from the pattern of cosmic energy," he says. "This provides a rare opportunity in which string theory can be tested."Technological improvements to capture more detailed cosmic maps should help narrow down the possibilities and may allow scientists to crack the code of the cosmic energy map - and inch closer to identifying the single geometry that fits our universe. The implications of such a possibility are profound, says Tye. "If this shape can be measured, it would also tell us that string theory is correct."The new work was funded by grants from the National Science Foundation, the U.S. Department of Energy, and the Research Corp.

Note: This story has been adapted from a news release issued by University of Wisconsin-Madison.

Fausto Intilla

www.oloscience.com