Largest Physics Meeting of the Year Convenes
Next Month in Dallas, Texas, March 20-25, 2011
Highlights of the American Physical Society (APS) 2011 March Meeting
100th Anniversary of the Discovery of Superconductivity to be Celebrated
The March Meeting of the American Physical Society (APS) –the largest physics meeting of the year -- will take place from March 20 to 25 at the Dallas Convention Center. Approximately 7000 papers will be delivered in the course of the meeting. Journalists are invited to attend the meeting free of charge. Registration information may be found at the end of this press release. Hotel information can be found at the meeting website.
Traditionally the March APS meeting has been a major venue for presenting the scientific principles and techniques behind many of the high-tech devices of today and tomorrow. The large topic areas at the meeting are condensed matter physics, computer physics, biological physics, chemical physics, polymers, and fluids. Specific hot topic areas include graphene, topological insulators---materials that are insulators on the inside but exceptional conductors on the outside---quantum computing, smart materials, bio-engineering, energy efficiency, spintronics, microfluidics, and ultracold atoms.
Not all the presentations at the meeting are highly technical. Session H8 features talks on the physics of rodeo, singing Tesla coils, and the science behind barbecue. Monday, March 21 at 7:45 pm, Vincent Crespi will talk about the attempt to broaden public understanding and appreciation of science, especially nanoscience, through exhibits at museums.
MEETING HIGHLIGHTS
BEAM ME BACKWARDS, SCOTTY
Rather than send airplanes into the upper atmosphere to detect pollutants or biological weapons, researchers at Texas A&M University, with collaborators from Princeton University and the University of Arizona, have developed a backwards-emitting laser-like beam that could be developed to identify gases and particles in the sky. To create the backwards-emitting beam, the team first shoots laser pulses of different speeds to excite air molecules. The two pulses join to generate a new laser-like pulse, called a backwards-emitting beam, that travels back towards the source. This beam could potentially be exploited for new types of remote sensing and may lead to a novel way to measure components of the atmosphere. Because the researchers are able to control where the laser-like beam is created, they could examine the air at nearly any altitude, searching for anthrax spores or pollution particles miles above the Earth without ever having to the leave the ground.
THE TINIEST ANTENNA
Researchers at the Institute of Photonics Sciences (ICFO) in Barcelona who produced the world’s smallest antennas in August of 2010 have now expanded their collection to include a palette of tiny antennas that can transmit photons in various patterns. The antennas operate much like the old fashioned TV antennas that once sprouted from most rooftops, except that they are millions of times smaller and are constructed of nanoscopic rods that direct the light emitted from a quantum dot. Niek van Hulst of ICFO-Barcelona will describe recent advances in nanoantenna development, and will discuss applications ranging from the detection of signals emitted by biological molecules to the construction of efficient connections between quantum dots for quantum computers and highly secure cryptographic systems.
X-RAY VISION FOR ARCHAEOLOGISTS
Archaeologists studying text carved into stone tablets or painted on pottery struggle to read the ancient markings when they have been eroded or obscured over time. To help them out, a trio of physicists at Cornell University created a way to expose traces of ancient markings, using a technique called X-ray fluorescence (XRF) imaging. XRF imaging reveals chemical traces left behind by tools and paints that are invisible to the naked eye. High resolution images can be created from XRF scans in minutes to hours. After starting with ancient Greek and Roman objects, the physicists turned recently to imaging Mayan artifacts. On one piece of Mayan pottery, black paint was partially obscured by a layer of black crud. Using XRF imaging, the researchers revealed the original pattern of paint by identifying and isolating chemicals specific to the paint. The team can do the same to reveal one layer of paint underneath another. Unlike some other techniques, no special sample environment is required for XRF imaging and objects of different sizes, ranging from a small chip to an eight-foot-tall stone tablet, can be imaged. XRF imaging is also non-destructive because it does not require a sample to be removed from an artifact. The technique allows archaeologists to see what the eye cannot, opening the door to future breakthroughs in understanding ancient civilizations.
NANO-SCALE VIEW COULD AID IN EARLY CANCER DETECTION
A recently-developed technique to analyze swabbed samples of cells could provide early lung, colon, ovarian, pancreatic, and esophageal cancer detection. Vadim Backman of Northwestern University will give a talk about an optical technique, called partial wave spectroscopic (PWS) microscopy, that can reveal the cancerous breakdown of cells at the nano-scale level. By zooming in very close, PWS can detect the signature of cancer in the disarray of a single cell’s nucleus. Like detecting a home’s risk of earthquake damage by spying cracks in the brickwork, PWS can detect the onset of cancer from the disorder at the heart of a cell, which occurs long before other outward signs of cancer develop. A recent small-scale trial showed promise for early detection using PWS when lung cancer was detected in cheek swab samples. The method is currently in the clinical research phase.
HOMELAND SPECTROSCOPY
Explosives in airports can be hard to detect but two new creations could make detection easier and airports safer. Abhishek Kumar and colleagues at the University of Massachusetts Lowell created a new fluorescent polymer developed to respond to trace elements of explosives in the air. A thin film of the polymer solution is smeared on a flat surface, like a glass slide, and exposed to the air being tested. By shining a light on the sample and measuring the amount of fluorescent light emitted, it’s possible to quickly determine whether the film has been exposed to even a tiny amount of a chemical bound to the polymer. The creators are currently working to produce a small commercial device with multiple sensors whose redundancy could help reduce false-positives. The polymer can be mass-manufactured and distributed broadly at a low cost, bringing enhanced explosive detection to airports around the world. Srikanth Singamaneni and colleagues at Washington University developed flexible and durable swabs that will enable security officials to use a more sensitive form of spectroscopy, called surface enhanced Raman scattering, to search for traces of explosives in cars, suitcases, and other containers.
NEW TAKES ON PHYSICS AND EDUCATION
Comic books as educational tools? Rebecca Thompson, of the American Physical Society’s Outreach Department, will talk about the use of comic books to teach physics to children. She’ll discuss three APS comic books including the laser-related adventures of a superhero called Spectra and a book about Nikola Tesla’s professional battle with Thomas Edison. John Fanchi from Texas Christian University will present a new undergraduate program intended to motivate students to work on solutions to our energy problems by becoming the next generation of energy professionals. J. Pedro Ochoa, from the Lawrence Berkeley National Laboratory, will give practical advice on overcoming cultural barriers, speaking from his own experience transitioning from Mexico to the United States and to China. Other topics in the session include a look at the nature of discovery and the pleasure of finding things out, (Joshua Borchardt, North Dakota State University), and an overview of a program at the University of Texas College of Natural Sciences that brings freshman into research laboratories, leading to improved retention, higher GPAs and increased graduate school enrollment. (Rosa Elia Cardenas).
SPIDER-MAN FOR REAL
Spider webs are sticky stuff. Understanding how they trap and retain prey even in wet environments could lead to development of more durable adhesives. A spider-inspired, water-resistant adhesive could be used for anything from tougher bandages to underwater sealants. Vasav Sahni and colleagues at the University of Akron have investigated spider adhesive to reveal how the polymer material is both strong and flexible. The researchers met in the dark of the night when their lab was empty and no vibrations from coworkers’ movement could disturb their work. They measured the force needed to stretch tiny glue droplets, each a third the width of a human hair, from the delicate silk fibers of a spider web. The late night experiments were vital because even a mistimed breath could have ruined their efforts. After gaining an understanding of how the spider glue functions, the team was successful in mimicking the glue in the lab.
NEW GRAPHENE DEVICES AND NOBEL PRIZE LECTURE
Graphene was celebrated last year with the award of the Nobel Prize for physics to Andre Geim and Konstantin Novoselov a scant six years after their discovery of the ultra-thin, strong, and electronically versatile material. Many research groups have now made progress towards practical graphene-based devices that could eventually make conventional silicon electronics obsolete. Among the recently-developed graphene devices being announced in session B37 at the 2011 March Meeting are radio frequency transistors, logic inverters, and transparent and flexible field emission devices, to name just a few. Also in session B37, Walt de Heer of the Georgia Institute of Technology will present an invited talk offering a broad overview of graphene based electronics. In addition, 2010 Nobel Laureate Novoselov will be the featured speaker at a special Nobel Prize Session on Wednesday, March 23 at 5:45 PM.
CARBON NANOTUBE “RUBBER” WITHSTANDS RECORD TEMPERATURE RANGE
A new viscoelastic (or rubber-like) material built entirely of carbon nanotubes retains its properties over a record temperature range, from -196 C to 1000 C. (By comparison, silicone rubber only remains stable from -55 C to 300 C.) The key to the material’s extraordinary resilience comes from relying on a network of carbon nanotubes linked into a random mesh, rather than the polymer molecules that make up most conventional elastics. In order to test the carbon nanotube viscoelasticity, the researchers who developed the material at the Technology Research Association for Single Wall Carbon Nanotubes (TASC) and National Institute of Advanced Industrial Science and Technology (AIST) in Japan conducted impact tests that bombarded samples with steel spheres while the material was at various temperature extremes. The resulting indentations were identical whether the material had been dipped in liquid nitrogen or blasted with a butane torch. Although it’s too early to say for sure what sorts of applications could benefit from such a temperature insensitive viscoelasticity, the researchers who developed it speculate that it may come in handy for craft headed to interstellar space, inside high-temperature furnaces, or perhaps as high performance parts in airplanes and other vehicles. Ming Xu of TASC & AIST will discuss the likely mechanisms behind the viscoelastic’s record-setting temperature range as well as describing new methods the group has developed for creating softer, more elastic and stronger versions of the material.
NANOTUBE FABRIC TOUGHER THAN KEVLAR
Yarns and twines made of carbon nanotubes could lead to the toughest textiles ever made, provided methods to spin them into substantial lengths are successful. Tobin Filleter and colleagues at Northwestern University have developed methods to make nanotube twine tougher still by exposing it to electron beams that cause the fibers to form microscopic mechanical bonds known as crosslinks. The crosslinked fibers are as much as ten times stiffer and stronger than non-irradiated fibers. In the same session, Ray Baughman of the University of Texas at Dallas will consider larger-scale issues of forming carbon nanotube yarns into long enough segments to be woven into fabrics for use in superconductors, Li-ion battery materials, and fuel cells, among other applications.
SUPERCONDUCTIVITY CENTENNIAL
The year 2011 marks a century since the discovery of superconductivity. Session B3 will be devoted to the history of the discovery, including notable superconductivity milestones. Session Q3 looks at research opportunities in superconductivity. Dozens of sessions will cover reports of the latest research findings. The Industrial Physics Forum, a meeting-within-the-meeting sponsored jointly by the American Physical Society and the American Institute of Physics, will look at the latest industrial applications of superconductivity (sessions 1A, 1B, A5). Topics in these sessions include the advent of a comprehensive theory of low-temperature superconductivity, the latest superconductivity applications in the areas of medical imaging, the electric grid, electronics, astrophysical detectors, and sensors for tiny magnetic fields.
MODELING THE DECLINE OF RELIGION
The decline of religion in some modern cultures is a trend reflected in census data. About half of all people in the Netherlands, for instance, identify themselves as having no religious affiliation. Now at Northwestern University and the University of Arizona, researchers have developed a simple mathematical model that accurately describes what is going on. Richard Wiener of the University of Arizona will describe how he and his collaborators used historical census data from a number of countries to track the growth of religious non-affiliation and applied techniques from physics research to analyze the competition for adherents between religious and irreligious segments of modern secular societies. Their model predicts that in many modern secular societies, religions will continue to lose members and be driven toward extinction. The model is also applicable to a variety of competitive social systems, the researchers argue, like smokers vs. non-smokers, vegetarians vs. meat-eaters, obese vs. non-obese people, and Mac vs. PC users.
FRONTIERS IN PHYSICS
As part of the Industrial Physics Forum at the 2011 March Meeting, the Frontiers in Physics session D5 will feature five talks on some of the most dynamic topics in physics. Linda Young of Argonne National Laboratory will speak about the Linac Coherent Light Source, the world’s first hard X-ray laser, based at SLAC National Accelerator Laboratory. Some of the laboratory’s first experimental results are about what happens when an atom’s inner electrons are blasted out with X-rays. National Institute of Standards and Technology (NIST) scientist Joseph Stoscio will describe scanning tunneling microscopes (STMs) that operate at low temperatures and high magnetic fields, making them perfect for exploring quantum mechanical phenomena and conduction in graphene. Stanford physicist Shoucheng Zhang will describe potential applications for topological insulators, materials in which electrons flow easily on their surfaces but not though their interiors. Barbara Jacak, a physicist at Stony Brook University and a leader of a detector group at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory will report on the experiment that created the hottest fireballs ever seen on Earth by smashing gold ions together. The coldest place on Earth, arguably, is the center of Deborah Jin’s atom trap at the University of Colorado in Boulder. She will look at the strange chemistry that occurs among atoms at very cold temperatures.
NEW METHODS FOR READING GENES
A faster, cheaper, and more accurate alternative for analyzing DNA may soon be on the market. Shuo Huang and colleagues at Arizona State University have developed a new approach for determining the components that make up individual molecules of DNA using a scanning tunneling microscope to probe along a piece of DNA and read the electronic signature of each of the bases in a DNA string. The researchers predict that it will eventually be a faster, cheaper, and more accurate alternative to existing methods for sequencing single pieces of DNA, though it is currently limited to reading pieces no longer than 10 bases long. To be commercially viable, the researchers believe that the technique should be able to read DNA segments made up of 1,000 bases or more. They are currently developing a version of the device that they hope will lead to the next generation of rapid and cheap DNA analysis.
TOPOLOGICAL INSULATORS
Topological insulators, materials that allow charge to flow easily on their surfaces but not their interiors, are the one of the fastest-growing subjects of physics research. The insulators are expected to be a boon for the development of spintronics -- circuitry that exploits the spin of electrons as well as their electrical charge. Topological insulators are featured in many sessions including D2, H2, Y2, A35, B35, D35, H35, J35, P35, and others. Some specific new results: Nuh Gedik and his colleagues at MIT will report (papers J35.00008, J35.00010, J35.00012) on the use of light to probe the electron currents, some of them on the surface of the material and some of them perhaps traveling through a buried structure beneath the surface. Kesong Yang (X32.00005) will announce the discovery of some 40 new topological insulating materials.
HIGH-PURITY GERMANIUM CRYSTALS FOR DARK MATTER EXPERIMENTS
More than 80% of the matter in the universe is a mystery to science. We call it dark matter, and though we know it exists, we don't know what it is and we have never been able to detect it directly. A number of new experiments to detect dark matter are underway in Japan, Europe, Canada, and the United States. These experiments are being conducted deep underground, hidden from the interfering radiation produced by cosmic ray showers. Dongming Mei from the University of South Dakota will describe the latest results in preparation of high-purity germanium crystals for the proposed experiments for the Deep Underground Science and Engineering Laboratory (DUSEL). The laboratory is being constructed more than a mile underground in the former Homestake gold mine in Lead, S.D. Mei and his colleagues are studying how to grow large crystals of high-purity germanium up to a few kg in weight in the underground environment at DUSEL in order to detect dark matter and to study neutrinos. Once in place about two years from now, the crystals will be used to detect particles of dark matter, as well as other rare and exotic phenomena. Mei will also present techniques for identifying impurity levels that can degrade the crystals’ performance.
SELF-PROPELLED MINI MACHINES
Rachita Sharma and colleagues at North Carolina State University have developed a technique for remotely steering millimeter-sized machines that are self-propelling when placed in a fluctuating electric field. Like miniature boats, the tiny machines float on water and pump microscopic amounts of fluid across their surface when the electric field is turned on, which propels them forward. Changing the field can make the minuscule machines turn or reverse course. The group is also working on self-propelled particles based on living cells that rely on glucose for power. Such devices may one day precisely deliver drugs in the body, diagnose medical conditions, and detect toxins in the environment, among other applications. Videos of the devices in action are available.
PROTEIN FOLDING SPEED LIMIT
One of the most fundamental problems in modern biophysics is that of protein folding -- how the genetically-defined sequence of a protein completely determines its three-dimensional structure. Milo Lin and colleagues at the California Institute of Technology have determined the speed limit of protein folding by measuring and modeling one of the simplest shortest steps in the process -- the initial formation of a common protein structure called an alpha helix. They modeled this protein component as a collection of connected spheres. They also experimentally observed the same folding process by making a tiny protein of five amino acids and tracking the folding over the course of a few nanoseconds. Comparing the model and experiment allowed them to identify the factors that limit folding speed.
RURAL STOCK EXCHANGES AND PLANETARY-SCALE TRADING
Physicists in Boston are exploring the wisdom of decentralizing stock exchanges. Alexander Wissner-Gross, of MIT and Harvard University, and colleagues analyzed the advantage of coordinating financial transactions from centralized locations, asking whether it would be advantageous to decentralize exchanges, and if so, where the exchanges should be located. Their idea, first presented last year in the journal Physical Review E, is that putting an intermediate trading center between two major centers is advantageous if the trading is rapid and auditable. They found that there is always an optimal trading position located between any two points on the Earth, with some in rural areas. They worked out a formula for calculating where the locations could be. At the 2011 March Meeting, they will present detailed results that examine what happens when there are multiple intermediate trading points located between major centers of commerce. They have worked out some of the most profitable locations on Earth from which to coordinate trading. Rather than consolidate trading at places like the New York Stock Exchange, the analysis calls for treating the planet itself as one giant trading floor -- something they are now speaking to a number of companies about doing.
THE PHYSICS OF ECONOMIC DIVERSITY
Combining statistical physics and economic development theory, physicist Cesar A. Hidalgo of MIT's Media Lab along with Ricard Hausmann, the director of the Center for International Development at Harvard University and former chief economist of the Inter-American Development Bank, has modeled economic data from countries around the world to predict future economic production. There is a predictable aspect to the global economy, Hidalgo said, but the processes operate over periods of 10-15 years, which is much longer than the time scales of political cycles. They found a set of universal rules that create robust economic patterns seen across the globe. The ability of a country to produce a new product in the future, for instance, is highly dependent on the specific mix of products the country currently produces. This makes predicting a country's future industries possible. Moreover, economic diversity itself tends to be "contagious," crossing borders from one country to the next. Countries are 50 percent more likely to begin exporting a new product if a neighboring country is already exporting that product. The work has raised the interest of the World Bank and the United Nations Development Programme. The researchers claim that the rise of China over the last decade and the crash of Greece in the last few years would have been predictable using their model because of the economic diversity of those two countries in the 1990s. Looking forward for the next two decades, they predict that Turkey, Indonesia, and Vietnam should all see stellar growth. They believe Russia, however, will experience more modest and volatile growth.
PHYSICS HISTORY/INTERNATIONAL PHYSICS
Session V24, History of Physics and International Programs, covers a spectrum of historical topics, including an effort just after World War II to control the spread of nuclear weapons, the 1946 Acheson-Lilienthal Report on the International Control of Atomic Energy, the wealth of radio research that originated in wartime radar work at MIT, Willie Hobbs Moore (1934-1994) -- the first female African-American physicist, physics research in sub-Saharan Africa, and talks about research in Finland, Latin America, and East Asia. Session X8, Migrations of Physicists, is about the movement of physicists across international borders. The topics include a look at the International Centre for Theoretical Physics in Trieste, Italy, the forced migration of scientists under the Nazis, the migration of scientists from Central Europe during the Cold War, the migration of German scientists into Russia in the 18th and 19th centuries as well as the emigration of scientists from Russia during the Soviet and post-Soviet eras, and the complex migration patterns of Chinese physicists in America--some of whom stay in the U.S. while others return.
A LIST OF OTHER INTERESTING TALKS BY DAY
MONDAY, MARCH 21
--Gauging a physicist’s success, beyond citation counting
--How do neurons grow?
--A look at Kamerlingh Onnes’ discovery of superconductivity in 1911
--A large quilt, measuring 84 x 84 inches, will be used to illustrate the quantum states of graphene
--Using a quantum dot as a beam splitter for Cooper pairs of electrons as a source of entangled particles
--Qubits in a semiconducting nanowire
--A new approach for high-efficiency water desalination
--New materials that can address the challenges of lithium-ion batteries for energy storage
--Applications of Statistical and Nonlinear Physics to Social Systems
--Bionanotechnology
TUESDAY, MARCH 22
--Fingerless robotic hand
--Clay bubbles and the origin of cellular life
--Quantum magnetic analog of forest fires
--Supercurrents flowing in ferromagnets
--Computational physics’ greatest hits
--The first real single-molecule transistor
--Drowning in Carbon: The Imperative of Nuclear Power
--The physics of cancer
--Financial, social, co-evolving and interdependent networks
WEDNESDAY, MARCH 23
--Electronic properties of graphene change depending on how many layers are stacked up, including effects of twisting one layer relative to another
--Observation of a box-shaped shock wave during the collision of two clouds of fermion atoms
--The physics of evolution
--Theoretical physics in industrials settings: the auto industry, high-tech sector, oil and gas industries
THURSDAY, MARCH 24
--The smallest ever loops of high-temp superconducting films, part of a surface patterned with loops and nanowires, for the purpose of making electronic devices
--Only cryostat where one can directly view a 1-K surface through a room-temperature window http://meetings.aps.org/Meeting/MAR11/Event/143421
--Pressure-assisted ejection of DNA from bacteriophage
--Compressed air or vacuum for moving automobiles and trains
FRIDAY, MARCH 25
--Silicene nanoribbons, silicon analogues of graphene
--Highest electric field strength, 2 x 10^9 V/m, in a plate capacitor gap
--Crystal growth dynamics
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MORE INFORMATION FOR JOURNALISTS
- General Meeting Information
- Searchable Abstracts
PRESS CONFERENCES
Press conferences will be held daily in the Dallas Convention Center rooms A125/136. A press conference schedule, which will include instructions for dialing in remotely, will be issued in early March.
REGISTERING AS A JOURNALIST
Journalists planning to attend the meeting should contact James Riordon about free registration (riordon@aps.org, 301-209-3238).
PRESSROOM INFORMATION
A dedicated and staffed pressroom will operate throughout the meeting at the Dallas Convention Center. Phones, computers, printers, and free wireless Internet access will be available to reporters using the pressroom.
- Location: Dallas Convention Center, rooms A118/119; press conferences in A125/136
- Hours: MON-THU, 7:30 a.m. to 5:30 p.m. and FRI, 7:30 a.m. to noon
- Phone numbers: 214-853-8001, 214-853-8002, 214-853-8003, 214-853-8004
- Fax number: 214-853-8000
- Food service: Both breakfast and lunch will be provided on MON, TUE, and WED. Breakfast only will be served on THU, and coffee/tea will be available on FRI.
Thursday, February 3, 2011
LX12399/Phys. Rev. Lett. 106, 053602 (2011)
Physicists make “sunglasses for atoms” using bizarre quantum effect
Researchers in Barcelona have developed a new, extremely selective
optical filter to protect atomic quantum memories, part of a proposed
quantum Internet, using one of the most paradoxical effects in quantum
physics. In the quantum network, particles of light (photons) would be
sent between distant locations, and stored in quantum memories
(collections of atoms), when they are not in use.
We all know the effect of sunglasses: Sunglasses block dangerous,
invisible UV light in order to protect our eyes, while they let pass
most of the visible light. In principle, this kind of filter could be
used to feed quantum memories the very specific color they can store
while protecting them from light that has not the right color. To have
an idea of the kind of selection we are talking about: Of the light
visible to the human eye, less than one millionth can be stored in an
atomic quantum memory. But there is a problem: it is hard to find a
filter that transmits only this extremely specific color and blocks
all the rest. However, it is easy to find a filter that absorbs a very
specific color.
To solve this problem, researchers led by Prof. Morgan Mitchell at
ICFO have used a paradoxical quantum effect known as “Interaction-Free
Measurement” or IFM. First predicted in the 1990s, IFM uses quantum
interference, in which a particle takes two paths at the same time, to
do something that would seem impossible: IFM can turn transmission
into absorption and vice versa. Through IFM, a collection of atoms can
therefore be made to transmit a specific color, instead of absorbing
it. The researchers took advantage of this and put the same atoms that
are used in a quantum memory into an IFM to implement a filter at the
wavelength at which the atoms are normally absorbing.
The researchers used these “sunglasses for atoms” - that select 1 part
out of 5 million of the visible spectrum - to create pure single
photons of an extremely well-defined color for the first time. These
filtered photons have all requirements that are essential in an
advanced quantum network.
***
LW12091
Why bubbles don’t stick to walls
The next time you watch the bubbles glide elegantly up the side of your champagne glass, consider that you are in fact observing the result of a fundamental physical force, predicted by H. C. Hamaker in 1937, but only now conclusively demonstrated.
The Van der Waals force acts between all bodies, and is almost always attractive, often responsible for strong adhesion, such as the feet of geckos. However, for certain combinations of materials, the force can be a repulsion, which is very strong at small separations. It is possible that in the future it could be used to levitate objects and make devices which are experience no friction.
This work uses a tiny bubble as a probe to measure these forces. The bubble is repelled by solid surfaces in water, and in order to measure such small forces precisely, an Atomic Force Microscope is used. This device measures the movement of a tiny lever the size of a human hair to measure small forces very accurately.
It is found that, as predicted by theory, the strength of the force can be controlled by the material of which the surface is composed, with gold setting the standard for the biggest repulsion.
These results not only demonstrate the presence and magnitude of this unusual force for the first time, but also suggest that we may be able to design micro-scale devices for handling fluids with no friction
Physicists make “sunglasses for atoms” using bizarre quantum effect
Researchers in Barcelona have developed a new, extremely selective
optical filter to protect atomic quantum memories, part of a proposed
quantum Internet, using one of the most paradoxical effects in quantum
physics. In the quantum network, particles of light (photons) would be
sent between distant locations, and stored in quantum memories
(collections of atoms), when they are not in use.
We all know the effect of sunglasses: Sunglasses block dangerous,
invisible UV light in order to protect our eyes, while they let pass
most of the visible light. In principle, this kind of filter could be
used to feed quantum memories the very specific color they can store
while protecting them from light that has not the right color. To have
an idea of the kind of selection we are talking about: Of the light
visible to the human eye, less than one millionth can be stored in an
atomic quantum memory. But there is a problem: it is hard to find a
filter that transmits only this extremely specific color and blocks
all the rest. However, it is easy to find a filter that absorbs a very
specific color.
To solve this problem, researchers led by Prof. Morgan Mitchell at
ICFO have used a paradoxical quantum effect known as “Interaction-Free
Measurement” or IFM. First predicted in the 1990s, IFM uses quantum
interference, in which a particle takes two paths at the same time, to
do something that would seem impossible: IFM can turn transmission
into absorption and vice versa. Through IFM, a collection of atoms can
therefore be made to transmit a specific color, instead of absorbing
it. The researchers took advantage of this and put the same atoms that
are used in a quantum memory into an IFM to implement a filter at the
wavelength at which the atoms are normally absorbing.
The researchers used these “sunglasses for atoms” - that select 1 part
out of 5 million of the visible spectrum - to create pure single
photons of an extremely well-defined color for the first time. These
filtered photons have all requirements that are essential in an
advanced quantum network.
***
LW12091
Why bubbles don’t stick to walls
The next time you watch the bubbles glide elegantly up the side of your champagne glass, consider that you are in fact observing the result of a fundamental physical force, predicted by H. C. Hamaker in 1937, but only now conclusively demonstrated.
The Van der Waals force acts between all bodies, and is almost always attractive, often responsible for strong adhesion, such as the feet of geckos. However, for certain combinations of materials, the force can be a repulsion, which is very strong at small separations. It is possible that in the future it could be used to levitate objects and make devices which are experience no friction.
This work uses a tiny bubble as a probe to measure these forces. The bubble is repelled by solid surfaces in water, and in order to measure such small forces precisely, an Atomic Force Microscope is used. This device measures the movement of a tiny lever the size of a human hair to measure small forces very accurately.
It is found that, as predicted by theory, the strength of the force can be controlled by the material of which the surface is composed, with gold setting the standard for the biggest repulsion.
These results not only demonstrate the presence and magnitude of this unusual force for the first time, but also suggest that we may be able to design micro-scale devices for handling fluids with no friction
Wednesday, February 2, 2011
LS12815E
Reconsidering the Human Genome Structure
The human genome presents compositional features of many different scales and complex long-range correlations. This suggests that compositional fluctuations are scale-invariant, and therefore that there is not a typical dominant scale of genome organization in many orders of magnitude, typically up to orders of 100 kb. At this
scale, it is well-known the existence of isochores, i.e. long DNA tracks of relatively homogeneous G+C content with a typical size of 100 kb. To date, human genome is viewed as a mosaic of isochores harboring the rest of genomic elements. However, first we present evidences showing that isochores are actually organized at much larger scales into gigantic compositional segments or superstructures, with typical sizes of the order of 10 Mb, thus challenging the current view of the human
genome. Second, we introduce a new segmentation algorithm based on rigorous statistical criteria which takes into account the long-range correlations present in
human DNA, and which is able to detect automatically these superstructures: each human chromosome is divided into a few huge segments (15-20 Mb) with homogeneous G+C content. And third, we show that gene pairs embedded in each superstructure, despite that on average they can be very distant , share many functional properties in common (even more than genes contained in the same isochore, one hundred times closer on average). This suggests the existence of a previously unreported very large scale functional organization of the human genome.
***
LW12551
Attosecond control of photoelectron emission
Since the early days of atomic and molecular physics, it is known that
the natural time scale of electron motion in atoms and molecules is
the attosecond -- that is a billionth of a billionth of a second. In
the last ten years, with the advent of controllable sources of
ultrashort light pulses, the attosecond scale has become the finest
time resolution reachable in experiments. It is now possible to
observe electrons as they move that fast, in real time. In this
Letter, we demonstrate how the dynamics of an electron ejected from a
molecule, upon absorption of two photons, can be traced with
attosecond resolution using a technique designed so far to
characterize attosecond light pulses. Furthermore, we show how
electron ejection can be controlled and delayed by several
femtoseconds, marking a new step toward attosecond control of chemical
reactions at the electronic level.
Reconsidering the Human Genome Structure
The human genome presents compositional features of many different scales and complex long-range correlations. This suggests that compositional fluctuations are scale-invariant, and therefore that there is not a typical dominant scale of genome organization in many orders of magnitude, typically up to orders of 100 kb. At this
scale, it is well-known the existence of isochores, i.e. long DNA tracks of relatively homogeneous G+C content with a typical size of 100 kb. To date, human genome is viewed as a mosaic of isochores harboring the rest of genomic elements. However, first we present evidences showing that isochores are actually organized at much larger scales into gigantic compositional segments or superstructures, with typical sizes of the order of 10 Mb, thus challenging the current view of the human
genome. Second, we introduce a new segmentation algorithm based on rigorous statistical criteria which takes into account the long-range correlations present in
human DNA, and which is able to detect automatically these superstructures: each human chromosome is divided into a few huge segments (15-20 Mb) with homogeneous G+C content. And third, we show that gene pairs embedded in each superstructure, despite that on average they can be very distant , share many functional properties in common (even more than genes contained in the same isochore, one hundred times closer on average). This suggests the existence of a previously unreported very large scale functional organization of the human genome.
***
LW12551
Attosecond control of photoelectron emission
Since the early days of atomic and molecular physics, it is known that
the natural time scale of electron motion in atoms and molecules is
the attosecond -- that is a billionth of a billionth of a second. In
the last ten years, with the advent of controllable sources of
ultrashort light pulses, the attosecond scale has become the finest
time resolution reachable in experiments. It is now possible to
observe electrons as they move that fast, in real time. In this
Letter, we demonstrate how the dynamics of an electron ejected from a
molecule, upon absorption of two photons, can be traced with
attosecond resolution using a technique designed so far to
characterize attosecond light pulses. Furthermore, we show how
electron ejection can be controlled and delayed by several
femtoseconds, marking a new step toward attosecond control of chemical
reactions at the electronic level.
Monday, January 31, 2011
LR12245
Chain reaction explosions in vibrated granular matter
One of the characteristic properties of granular materials--e.g.
sand--is that energy is dissipated at collisions so a continuous
energy input is necessary to keep these materials in motion. In this
paper, we show that granular materials can store energy and release it in
the form of energy bursts--like explosions--to the rest of the system
in a chain reaction manner.
This phenomenon that takes place in vibrated mixtures of heavy and
light grains, confined between two close and parallel plates, has been
observed in experiments and simulations. The analysis shows that the
heavy grains store energy in a rapid synchronized vertical motion that
randomly loses its coherence liberating the energy to the whole
system. In the picture, an energy burst sequence taking place in the
cluster of heavy grains (blue) as seen in the simulations (top) and
experiments (bottom).
***
LZ12501
First atom circuit with a tunable weak link
We have created a long-lived (≈ 40 s) persistent current in a toroidal Bose-Einstein condensate held in an all-optical trap. A repulsive optical barrier across one side of the torus creates a tunable weak link in the condensate circuit, which can affect the current around the loop. Super flow stops abruptly at a barrier strength such that the local flow velocity at the barrier exceeds a critical velocity. The measured critical velocity is consistent with dissipation due to the creation of vortex-antivortex pairs. This system is the first realization of an elementary closed-loop atom circuit.
Quantum fluids can exhibit properties such as long range coherence and superfluidity that make them useful for constructing sensors and other devices. For example, superconducting quantum interference devices (SQUIDs)are sensitive magnetic field detectors, and superfluid He circuits have been used to detect rotation. Ultracold atomic-gas analogs of electronic devices and circuits,
or “atomtronics” have been proposed including diodes and transistors. Of particular interest is the realization of an atomic-gas SQUID analog. SQUID circuits
have been realized with either tunnel or weak link junctions. In atomic Bose-Einstein condensates, Josephson junctions have been demonstrated only between
adjacent wells. Here we present the first implementation of a non-trivial, closed-loop atom circuit, and show that it is possible to control the current at the
single-quantum level by changing the strength of a weak link. This is an essential step toward realizing an atomic SQUID analog.
Chain reaction explosions in vibrated granular matter
One of the characteristic properties of granular materials--e.g.
sand--is that energy is dissipated at collisions so a continuous
energy input is necessary to keep these materials in motion. In this
paper, we show that granular materials can store energy and release it in
the form of energy bursts--like explosions--to the rest of the system
in a chain reaction manner.
This phenomenon that takes place in vibrated mixtures of heavy and
light grains, confined between two close and parallel plates, has been
observed in experiments and simulations. The analysis shows that the
heavy grains store energy in a rapid synchronized vertical motion that
randomly loses its coherence liberating the energy to the whole
system. In the picture, an energy burst sequence taking place in the
cluster of heavy grains (blue) as seen in the simulations (top) and
experiments (bottom).
***
LZ12501
First atom circuit with a tunable weak link
We have created a long-lived (≈ 40 s) persistent current in a toroidal Bose-Einstein condensate held in an all-optical trap. A repulsive optical barrier across one side of the torus creates a tunable weak link in the condensate circuit, which can affect the current around the loop. Super flow stops abruptly at a barrier strength such that the local flow velocity at the barrier exceeds a critical velocity. The measured critical velocity is consistent with dissipation due to the creation of vortex-antivortex pairs. This system is the first realization of an elementary closed-loop atom circuit.
Quantum fluids can exhibit properties such as long range coherence and superfluidity that make them useful for constructing sensors and other devices. For example, superconducting quantum interference devices (SQUIDs)are sensitive magnetic field detectors, and superfluid He circuits have been used to detect rotation. Ultracold atomic-gas analogs of electronic devices and circuits,
or “atomtronics” have been proposed including diodes and transistors. Of particular interest is the realization of an atomic-gas SQUID analog. SQUID circuits
have been realized with either tunnel or weak link junctions. In atomic Bose-Einstein condensates, Josephson junctions have been demonstrated only between
adjacent wells. Here we present the first implementation of a non-trivial, closed-loop atom circuit, and show that it is possible to control the current at the
single-quantum level by changing the strength of a weak link. This is an essential step toward realizing an atomic SQUID analog.
Saturday, January 29, 2011
Phys. Rev. E 83, 017101 (2011)
Universal patterns in sound amplitudes of songs and music genres
We report a statistical analysis of more than eight thousand songs. Specifically, we investigated the probability
distribution of the normalized sound amplitudes. Our findings suggest a universal form of distribution that agrees
well with a one-parameter stretched Gaussian. We also argue that this parameter can give information on music
complexity, and consequently it helps classify songs as well as music genres. Additionally, we present statistical
evidence that correlation aspects of the songs are directly related to the non-Gaussian nature of their sound
amplitude distributions.
***
LQ12585
Emergence and Decline of Scientific Paradigms
Scientific paradigms have a tendency to rise fast and decline slowly. This asymmetry reflects the difficulty in developing a truly original idea, compared to the ease at which a concept can be eroded by numerous modifications. Here we formulate a model for the emergence and spread of ideas which deals with this asymmetry by constraining the ability of agents to return to already abandoned concepts. The model exhibits a fairly regular pattern of global paradigm shifts, where older paradigms are eroded and subsequently replaced by new ones. The model sets the theme for a new class of pattern formation models, where local dynamics breaks the detailed balance in a way that prevents old states from defending themselves against new nucleating or invading states. The model allows for frozen events in terms of the coexistence of multiple metastable states.
***
LW12017
MISSING INFORMATION LOCATED EXPERIMENTALLY
There are many physical processes in nature which lead to apparent loss of
information. In the present paper, for the first time, we have
experimentally located the missing information and demonstrated the
validity of quantum no-hiding theorem. To test this we have considered
randomization of a qubit as a prime example of the bleaching process and
reconstructed the missing information from the simplest possible
environment which in our case is a two-qubit system. In the quantum world
if a system interacts with the environment it looses the purity and even
it might end up being in a completely mixed (unpolarized) state that has
no information about the original. Then one may wonder where is the
missing information. The no-hiding theorem is a fundamental result in
quantum information theory which addresses this issue precisely. To put
it simply, the theorem tells us that if any physical process leads to loss
of quantum information, then it must be found in the rest of the
environment with no information being hidden in the correlations. The
result can be applied to many physical scenarios starting from quantum
state randomization, thermalization, decoherence, quantum teleportation,
black hole evaporation and many more. Furthermore, the no-hiding theorem
generalizes the Landauer erasure principle where an arbitrary quantum
state transforms to a fixed mixed state. Indeed, this will have wide
impact whenever one encounters the issue of information loss. The
no-hiding theorem also demonstrates the notion of conservation of quantum
information. Since this is universally valid in quantum world we believe
that its experimental test constitutes an important step.
***
LZ12219
Rotate the multiferroic blues away
For decades, researchers have looked for multiferroic materials in which the
magnetization could be controlled with an electric field. But finding a
material with the right combination of properties for practical applications
- a large polarization and a strong polarization-magnetization coupling -
has proven a difficult challenge. In our Letter, we identify a class of
multiferroics in which combinations of certain atomic displacement patterns
- octahedral rotation distortions - give rise to both a large polarization
and ferromagnetism. This result is remarkable because octahedral rotations
usually cannot individually produce a polarization. Most importantly, the
rotations are coupled to the magnetization in such a way that when an
electric field is used to change the direction of the polarization, the
magnetization also changes direction. This is precisely the type of
electric-field controllable magnetic material that scientists have long
searched for. Our work opens a new direction for the discovery of these
technologically important materials.
Universal patterns in sound amplitudes of songs and music genres
We report a statistical analysis of more than eight thousand songs. Specifically, we investigated the probability
distribution of the normalized sound amplitudes. Our findings suggest a universal form of distribution that agrees
well with a one-parameter stretched Gaussian. We also argue that this parameter can give information on music
complexity, and consequently it helps classify songs as well as music genres. Additionally, we present statistical
evidence that correlation aspects of the songs are directly related to the non-Gaussian nature of their sound
amplitude distributions.
***
LQ12585
Emergence and Decline of Scientific Paradigms
Scientific paradigms have a tendency to rise fast and decline slowly. This asymmetry reflects the difficulty in developing a truly original idea, compared to the ease at which a concept can be eroded by numerous modifications. Here we formulate a model for the emergence and spread of ideas which deals with this asymmetry by constraining the ability of agents to return to already abandoned concepts. The model exhibits a fairly regular pattern of global paradigm shifts, where older paradigms are eroded and subsequently replaced by new ones. The model sets the theme for a new class of pattern formation models, where local dynamics breaks the detailed balance in a way that prevents old states from defending themselves against new nucleating or invading states. The model allows for frozen events in terms of the coexistence of multiple metastable states.
***
LW12017
MISSING INFORMATION LOCATED EXPERIMENTALLY
There are many physical processes in nature which lead to apparent loss of
information. In the present paper, for the first time, we have
experimentally located the missing information and demonstrated the
validity of quantum no-hiding theorem. To test this we have considered
randomization of a qubit as a prime example of the bleaching process and
reconstructed the missing information from the simplest possible
environment which in our case is a two-qubit system. In the quantum world
if a system interacts with the environment it looses the purity and even
it might end up being in a completely mixed (unpolarized) state that has
no information about the original. Then one may wonder where is the
missing information. The no-hiding theorem is a fundamental result in
quantum information theory which addresses this issue precisely. To put
it simply, the theorem tells us that if any physical process leads to loss
of quantum information, then it must be found in the rest of the
environment with no information being hidden in the correlations. The
result can be applied to many physical scenarios starting from quantum
state randomization, thermalization, decoherence, quantum teleportation,
black hole evaporation and many more. Furthermore, the no-hiding theorem
generalizes the Landauer erasure principle where an arbitrary quantum
state transforms to a fixed mixed state. Indeed, this will have wide
impact whenever one encounters the issue of information loss. The
no-hiding theorem also demonstrates the notion of conservation of quantum
information. Since this is universally valid in quantum world we believe
that its experimental test constitutes an important step.
***
LZ12219
Rotate the multiferroic blues away
For decades, researchers have looked for multiferroic materials in which the
magnetization could be controlled with an electric field. But finding a
material with the right combination of properties for practical applications
- a large polarization and a strong polarization-magnetization coupling -
has proven a difficult challenge. In our Letter, we identify a class of
multiferroics in which combinations of certain atomic displacement patterns
- octahedral rotation distortions - give rise to both a large polarization
and ferromagnetism. This result is remarkable because octahedral rotations
usually cannot individually produce a polarization. Most importantly, the
rotations are coupled to the magnetization in such a way that when an
electric field is used to change the direction of the polarization, the
magnetization also changes direction. This is precisely the type of
electric-field controllable magnetic material that scientists have long
searched for. Our work opens a new direction for the discovery of these
technologically important materials.
Tuesday, January 25, 2011
AX10557
ULTRALONG-RANGE CASIMIR FORCE CAN MAKE OBJECTS FLY
The elusive Casimir effect is one of the most intriguing physical
phenomena, which, due to the quantum fluctuations of the electromagnetic
field, results in the attraction or repulsion of uncharged bodies. This
tiny force is only relevant in the nanoscale, since it invariably decays
with the fourth power of the distance between the bodies. Or at least,
that was thought to be the case until some time ago. Indeed, recently it
was suggested that by guiding the quantum fluctuations of the
electromagnetic field with an array of metallic nanorods it is possible
to boost the strength of the Casimir force by several orders of
magnitude. Here, we demonstrate how this ultra-long range force can be
put into work and used to levitate objects! We show that the plane at
which the nanorods are cut acts as a mirror for the waves propagating
inside the nanorods crystal. However, unlike the usual metallic mirrors,
the wave reflected at the tips of the nanorods is in phase with the
impinging wave. Such a crucial property results in a repulsive Casimir
force that pushes conducting bodies embedded into the nanorods crystal
away from the mirror. This purely quantum force may be strong enough to
act against the gravity and lift up metallic pieces. For example, we
show that a 200 nm-thick tungsten film can be lift up to 1 micron within
a crystal composed of silver nanorods of 40 nm in diameter.
***
LY12700
A NEUTRON STAR TURNING SUPERFLUID
Ten years of Chandra observations of the neutron star "Cas A" have revealed
that it is cooling rapidly, an unusual behavior never observed previously.
We present a natural explanation based on neutron superfluidity and proton
superconductivity. These quantum phenomena set in when the temperature drops below some critical value. We propose that neutrons inside Cas A are presently developing a superfluid phase and emitting copius amounts of neutrinos which are cooling the star. Cas A has an age of 330 yrs and no other neutron star is known that is young enough to observe the onset of superfluidity. From Cas A's age, we deduce the neutron p-wave superfluid critical temperature to be a half billion degrees. Furthermore, the combination of the star's high surface temperature, about 2 million degrees, and large cooling rate implies that protons are in an s-wave superconducting state.
The transition to superconductivity has a larger critical temperature because it occurred prior to now when the star's core was warmer. This is the first direct evidence that these phenomena, predicted by theoretical models of high energy-density matter, occur within neutron stars.
***
AY10627
Propagation of relativistic charged particles in ultracold atomic gases with Bose-Einstein condensates
At the present moment the Bose-condensation phenomenon in gases of atoms
and molecules is experimentally realized in extreme physical conditions
(ultralow temperatures). A Bose-Einstein condensate (BEC) is a coherent
state of matter, i.e., the state with practically identical behaviour of
particles that form it. The consequence of the external extreme conditions
and coherent behaviour is the manifestation of different phenomena that
are difficult or impossible to observe in other conditions.
To the vivid effects related to the BEC phase one should also add some
peculiarities of a propagation of the relativistic charged particles
through a condensed gas. Most probably, this sort of problem is considered
for the first time in the framework of the present paper. The main
attention was paid to the energy change of the propagating particles. This
change results from the Cherenkov effect in the gas with a BEC. The most
uncommon result of the consideration is that at the certain conditions the
particle not only emits the energy, but it also can be accelerated by the
ulltracold gas. We define the conditions for the particle acceleration and
discuss also the possibility of defining the spectral characteristics of
atoms forming BEC by registering the Cherenkov radiation.
***
BW11359
Revealing the Carrier density and mobility of the Graphene layers in Graphite
Using an experimentally simple method to obtain the mean free path and density of electrical carriers of the graphene layers inside a thin graphite flake without adjustable parameters, a team from Germany and Spain demonstrated that these carriers can move several micrometers without having scattering whereas their density remains extremely small and all at room temperature. The obtained values overwhelm by orders of magnitude those obtained in single graphene layers of micrometer size revealing that ballistic electronics in graphite is feasible. From the basic research point of view, the results cast now strong doubts on the validity of the commonly used electronic band structure of graphite assuming values for the carrier density that appear to be non-intrinsic of the ideal graphite structure. The figure shows scanning electron microscope pictures of two samples showing the constrictions used to restrict the flow of the carriers and obtain directly their mean free path through the measurement of the electrical resistance.
***
EY10601
Non-classical transport in anisotropic fractal media
Numerous observations show that impurity transport in geologic media, as a rule, is not described by the classical diffusion laws, according to which the mean-square displacement of the particles grows linearly with time. Instead the transport process occurs in the regime of super-diffusion when mean-square displacement grows proportionally to the time in a power greater than unity, or sub-diffusion with the time exponent less than unity. A fractal geometry of fractures leading to long-range correlations of infiltrating moisture velocities may be the physical background of super-diffusion. Researchers have now shown that the presence of anisotropy and directedness of moisture infiltration due to the gravity lead to a number of interesting peculiarities in the impurity transport phenomena in fractal media. Among them are anomalous drift and coexistence of super-diffusive regime in vertical direction and classical diffusion in horizontal plane. In the case of strong anisotropy a considerable contraction of concentration distribution occurs in horizontal plane at large vertical distances. The peculiarities stated above are important for the safety problem of radioactive waste disposal in geologic media.
***
LX12087
Theory of Everything Finding a Way to Describe Life
String theory is said to be the theory of everything. But
until now its realm has been very far away from the life of ordinary
people. Not so anymore, as a group of theoretical physicists at
Uppsala University in Sweden and CNRS in France argue that
amazingly string theory describes even life itself. For this
they develop a string theory depiction of proteins, the workhorses
of all living cells. In order that life as we know it can take place,
proteins in our cells must each become folded into their own, very
specific shape. If misfolded, a protein can not fulfill its mission.
This can lead to a death of cell or cause tormenting diseases
such as Alzmeimer's, Parkinson's and many cancers. By applying
sophisticated string theory techniques originally introduced to explain
properties of elementary particles like the all-elusive Higgs boson,
and using ordinary personal computers they describe folded proteins
reaching accuracies that occasionally exceed even the most precise
experimental measurements. This can pave a way to a deeper understanding
why and how proteins fold, which in turn may eventually lead to cures
to some of the most unrelenting diseases.
ULTRALONG-RANGE CASIMIR FORCE CAN MAKE OBJECTS FLY
The elusive Casimir effect is one of the most intriguing physical
phenomena, which, due to the quantum fluctuations of the electromagnetic
field, results in the attraction or repulsion of uncharged bodies. This
tiny force is only relevant in the nanoscale, since it invariably decays
with the fourth power of the distance between the bodies. Or at least,
that was thought to be the case until some time ago. Indeed, recently it
was suggested that by guiding the quantum fluctuations of the
electromagnetic field with an array of metallic nanorods it is possible
to boost the strength of the Casimir force by several orders of
magnitude. Here, we demonstrate how this ultra-long range force can be
put into work and used to levitate objects! We show that the plane at
which the nanorods are cut acts as a mirror for the waves propagating
inside the nanorods crystal. However, unlike the usual metallic mirrors,
the wave reflected at the tips of the nanorods is in phase with the
impinging wave. Such a crucial property results in a repulsive Casimir
force that pushes conducting bodies embedded into the nanorods crystal
away from the mirror. This purely quantum force may be strong enough to
act against the gravity and lift up metallic pieces. For example, we
show that a 200 nm-thick tungsten film can be lift up to 1 micron within
a crystal composed of silver nanorods of 40 nm in diameter.
***
LY12700
A NEUTRON STAR TURNING SUPERFLUID
Ten years of Chandra observations of the neutron star "Cas A" have revealed
that it is cooling rapidly, an unusual behavior never observed previously.
We present a natural explanation based on neutron superfluidity and proton
superconductivity. These quantum phenomena set in when the temperature drops below some critical value. We propose that neutrons inside Cas A are presently developing a superfluid phase and emitting copius amounts of neutrinos which are cooling the star. Cas A has an age of 330 yrs and no other neutron star is known that is young enough to observe the onset of superfluidity. From Cas A's age, we deduce the neutron p-wave superfluid critical temperature to be a half billion degrees. Furthermore, the combination of the star's high surface temperature, about 2 million degrees, and large cooling rate implies that protons are in an s-wave superconducting state.
The transition to superconductivity has a larger critical temperature because it occurred prior to now when the star's core was warmer. This is the first direct evidence that these phenomena, predicted by theoretical models of high energy-density matter, occur within neutron stars.
***
AY10627
Propagation of relativistic charged particles in ultracold atomic gases with Bose-Einstein condensates
At the present moment the Bose-condensation phenomenon in gases of atoms
and molecules is experimentally realized in extreme physical conditions
(ultralow temperatures). A Bose-Einstein condensate (BEC) is a coherent
state of matter, i.e., the state with practically identical behaviour of
particles that form it. The consequence of the external extreme conditions
and coherent behaviour is the manifestation of different phenomena that
are difficult or impossible to observe in other conditions.
To the vivid effects related to the BEC phase one should also add some
peculiarities of a propagation of the relativistic charged particles
through a condensed gas. Most probably, this sort of problem is considered
for the first time in the framework of the present paper. The main
attention was paid to the energy change of the propagating particles. This
change results from the Cherenkov effect in the gas with a BEC. The most
uncommon result of the consideration is that at the certain conditions the
particle not only emits the energy, but it also can be accelerated by the
ulltracold gas. We define the conditions for the particle acceleration and
discuss also the possibility of defining the spectral characteristics of
atoms forming BEC by registering the Cherenkov radiation.
***
BW11359
Revealing the Carrier density and mobility of the Graphene layers in Graphite
Using an experimentally simple method to obtain the mean free path and density of electrical carriers of the graphene layers inside a thin graphite flake without adjustable parameters, a team from Germany and Spain demonstrated that these carriers can move several micrometers without having scattering whereas their density remains extremely small and all at room temperature. The obtained values overwhelm by orders of magnitude those obtained in single graphene layers of micrometer size revealing that ballistic electronics in graphite is feasible. From the basic research point of view, the results cast now strong doubts on the validity of the commonly used electronic band structure of graphite assuming values for the carrier density that appear to be non-intrinsic of the ideal graphite structure. The figure shows scanning electron microscope pictures of two samples showing the constrictions used to restrict the flow of the carriers and obtain directly their mean free path through the measurement of the electrical resistance.
***
EY10601
Non-classical transport in anisotropic fractal media
Numerous observations show that impurity transport in geologic media, as a rule, is not described by the classical diffusion laws, according to which the mean-square displacement of the particles grows linearly with time. Instead the transport process occurs in the regime of super-diffusion when mean-square displacement grows proportionally to the time in a power greater than unity, or sub-diffusion with the time exponent less than unity. A fractal geometry of fractures leading to long-range correlations of infiltrating moisture velocities may be the physical background of super-diffusion. Researchers have now shown that the presence of anisotropy and directedness of moisture infiltration due to the gravity lead to a number of interesting peculiarities in the impurity transport phenomena in fractal media. Among them are anomalous drift and coexistence of super-diffusive regime in vertical direction and classical diffusion in horizontal plane. In the case of strong anisotropy a considerable contraction of concentration distribution occurs in horizontal plane at large vertical distances. The peculiarities stated above are important for the safety problem of radioactive waste disposal in geologic media.
***
LX12087
Theory of Everything Finding a Way to Describe Life
String theory is said to be the theory of everything. But
until now its realm has been very far away from the life of ordinary
people. Not so anymore, as a group of theoretical physicists at
Uppsala University in Sweden and CNRS in France argue that
amazingly string theory describes even life itself. For this
they develop a string theory depiction of proteins, the workhorses
of all living cells. In order that life as we know it can take place,
proteins in our cells must each become folded into their own, very
specific shape. If misfolded, a protein can not fulfill its mission.
This can lead to a death of cell or cause tormenting diseases
such as Alzmeimer's, Parkinson's and many cancers. By applying
sophisticated string theory techniques originally introduced to explain
properties of elementary particles like the all-elusive Higgs boson,
and using ordinary personal computers they describe folded proteins
reaching accuracies that occasionally exceed even the most precise
experimental measurements. This can pave a way to a deeper understanding
why and how proteins fold, which in turn may eventually lead to cures
to some of the most unrelenting diseases.
Friday, January 21, 2011
LX12358
Pendulum in Fermi liquid
When a pendulum is immersed in a liquid, its oscillation frequency is
generally reduced because of the flow of the liquid around the bob.
This is not necessarily the case in a Fermi liquid. In ordinary
liquids atoms or molecules continuously collide with each other. This
leads to standard hydrodynamic description of the fluid, which is
essentially similar as in water. A Fermi liquid is different because
at low temperatures the bob of the pendulum excites quasiparticles
which are ballistic, i.e. they fly off like a ball hit by a bat. In
spite of being ballistic, the quasiparticles interact with each
other, as argued by Lev Landau in 1957. We show that for attractive
interactions, the frequency of the pendulum is increased by immersing
it in a the Fermi liquid. Such a case is realized in isotopic
mixtures of helium (3He & 4He). Experiments made in this system show
evidence of the frequency increase. This "Landau force" is a new
application of Landau's theory, which is one of the central paradigms
of condensed matter physics.
***
LY12754
A phonodiode for detection of ultrashort acoustic pulses
We describe an all-electrical method for the detection of ultrashort acoustic pulses using a semiconductor device. The device could be named a ‘phonodiode’ in analogy with a photodiode used for detecting light. Such devices could find applications in high speed acoustically-driven switching of electronic circuits, direct conversion of terahertz sound to terahertz electrical signals, and heterodyne mixing of terahertz acoustical and electrical signals.
There has in recent years been a rapid expansion in the area of phononics, which is concerned with the physics and applications of sub-terahertz coherent phonons (the quanta of vibration, or acoustic, energy). This has been driven by development of femtosecond laser-based techniques for generating picosecond-duration acoustic phonon pulses. The traditional method of detecting the acoustic signals is to use an optical probe. We demonstrate high-speed electrical detection of the acoustic pulses using a metal-semiconductor contact (Schottky diode). We show that the device detects, with good sensitivity and temporal resolution, the acoustic pulses generated by femtosecond laser excitation of a metal film. A phonodiode, used in conjunction with an electrical method of generation of coherent phonon pulses, e.g. a saser, could make an integrated all electrical system for manipulations with coherent sub-terahertz phonon pulses.
Pendulum in Fermi liquid
When a pendulum is immersed in a liquid, its oscillation frequency is
generally reduced because of the flow of the liquid around the bob.
This is not necessarily the case in a Fermi liquid. In ordinary
liquids atoms or molecules continuously collide with each other. This
leads to standard hydrodynamic description of the fluid, which is
essentially similar as in water. A Fermi liquid is different because
at low temperatures the bob of the pendulum excites quasiparticles
which are ballistic, i.e. they fly off like a ball hit by a bat. In
spite of being ballistic, the quasiparticles interact with each
other, as argued by Lev Landau in 1957. We show that for attractive
interactions, the frequency of the pendulum is increased by immersing
it in a the Fermi liquid. Such a case is realized in isotopic
mixtures of helium (3He & 4He). Experiments made in this system show
evidence of the frequency increase. This "Landau force" is a new
application of Landau's theory, which is one of the central paradigms
of condensed matter physics.
***
LY12754
A phonodiode for detection of ultrashort acoustic pulses
We describe an all-electrical method for the detection of ultrashort acoustic pulses using a semiconductor device. The device could be named a ‘phonodiode’ in analogy with a photodiode used for detecting light. Such devices could find applications in high speed acoustically-driven switching of electronic circuits, direct conversion of terahertz sound to terahertz electrical signals, and heterodyne mixing of terahertz acoustical and electrical signals.
There has in recent years been a rapid expansion in the area of phononics, which is concerned with the physics and applications of sub-terahertz coherent phonons (the quanta of vibration, or acoustic, energy). This has been driven by development of femtosecond laser-based techniques for generating picosecond-duration acoustic phonon pulses. The traditional method of detecting the acoustic signals is to use an optical probe. We demonstrate high-speed electrical detection of the acoustic pulses using a metal-semiconductor contact (Schottky diode). We show that the device detects, with good sensitivity and temporal resolution, the acoustic pulses generated by femtosecond laser excitation of a metal film. A phonodiode, used in conjunction with an electrical method of generation of coherent phonon pulses, e.g. a saser, could make an integrated all electrical system for manipulations with coherent sub-terahertz phonon pulses.
Tuesday, January 18, 2011
EX10520
NANO-SPIDERS HURRY ALONG TRACKS
We study the movement of nano-scale walkers, called "molecular
spiders" that travel along one-dimensional tracks. Our analysis
reveals a useful transient behavior: the spiders move faster than
ordinary random walkers over significant distances and times. In other
words they travel faster than diffusion. The spiders in our model are
inspired by physical experiments (Pei et al., J. Am. Chem. Soc. 128
12693-12699, 2006; Lund et al., Nature 465 206-210 (2010)), in which
spider molecules are synthesized with a rigid chemically inert body
attached to legs made of single-stranded segments of DNA; they walk on
a surfaces coated with single-stranded DNA complementary to the legs.
The legs attach and detach to the surface strands, causing the spider
to move over the surface. When a leg detaches from a strand for the
first time, it cuts it in half. This change is irreversible and the
legs subsequently bind to cut strands more weakly.
Previous analyses dealt with so-called asymptotic behavior---if time
goes to infinity, the spiders diffuse. Our analysis is based on
stochastic computer simulations, which enable us to predict how the
strand modification affects the motion of spiders in the context of
real experiments that last for a finite time and where spiders cover a
finite distance. This has important applications if spiders walking
along one-dimensional tracks are used as a transport mechanism for molecular
payloads. We hope to use our simulations to help chemists design
faster spiders. In the future spiders might be used for various
medical purposes or to assemble nano-devices built from molecules
which spiders will be able to pick up and carry along tracks.
***
BU11301
Magnetization switched off by crystal vibration
We have connected magnetic phase transition observed in magnetocaloric
MnAs near room temperature (315 K) with particular vibration of crystal
structure. We have shown that excitation of this vibration (with
increasing temperature or stretching the sample) leads to disordering of
magnetic moments and disappearance of total magnetization. Discovery of
such a strong coupling between crystal vibrations and magnetization
enabled us to form a simple explanation of the mechanism of both:
discontinuous magneto-structural phase transition at 315 K as well as
continuous return at 393 K (without magnetic ordering) to the
low-temperature structure. This particular interplay between magnetic
and lattice properties leads to large entropy change around this
discontinuous transition and, consequently, to giant magnetocaloric
effect promising applications in cheap and green refrigeration at room
temperature. Our theoretical predictions agree well with all
experimental findings published earlier.
***
LV12016
SPONTANEOUS RIPPLING OF GRAPHENE MIMICS CONDENSATION OF RELATIVISTIC
HIGGS FIELD
Great part of the current excitement about graphene (the one-atom thick
carbon layer) comes from the fact that it is the only known membrane
(genuine two-dimensional material) with conducting properties. A
remarkable and puzzling property of this material is its strong tendency
to develop ripples (modulations of the vertical displacements) by which
the membrane freezes spontaneously into a corrugated configuration. In
this paper we have shown that the interaction between the membrane
distortions and its conduction electrons places the flat phase of
graphene in unstable equilibrium, closely mimicking the state of the
relativistic Higgs field prior to its decay into a ground-state
condensate filling the space -the mechanism that gives mass to
elementary particles in high-energy physics. We have seen that the
effective potential for both quantum fields (the vertical displacement
in graphene, the Higgs field in relativistic physics) has the same
typical "mexican-hat" shape, which makes the unstable state at the top
to spontaneously decay by rolling down to a lowest-energy state with
broken symmetry (the aggregate of ripples in one case, the Higgs
condensate filling the vacuum in the other). The analogue goes further,
since graphene has a control parameter (the tension of the membrane)
that plays the same role as the bare mass square for the Higgs field,
opening the possibility of investigating the behavior of the Higgs
sector of elementary particle theories at the much smaller energies of a
condensed matter system like graphene.
***
BZ11073
Hours Marked by Neutrons
Small-angle neutron diffraction is a powerful probe for the behavior
of quantized magnetic field lines (and their associated 'vortices' of
screening currents) penetrating into superconductors. Using this
technique, we made the first observation of the so-called 'vortex
lattice' in pure crystals of HgBa2CuO4+d, one of the best
high-temperature superconductors discovered to date. The diffraction
pattern looks exactly like the markings of hours on a clock face
(attached figure), reflecting a simple geometric beauty of nature that
a hexagonal arrangement in two dimensions allows for the largest
nearest-neighbor distance for a given number density -- the vortices
want to stay away from one another, and the presence of two types of
hexagonal domains rotated by 90 degrees relative to each other leads
to the twelve diffraction spots. By further studying the vortex
lattice at various temperatures and magnetic fields, we confirmed a
previously proposed mechanism for long and straight magnetic field
lines to decompose into short segments surrounded by uncorrelated
screening currents (referred to as 'vortex pancakes'), which explains
why the diffraction signal vanishes at high fields. Our work opens the
door for future investigations into the vortex physics in this highly
ideal new family of superconductors.
***
LW12339
Direct observation of superconducting vortex bundles in the critical state
P.W. Anderson proposed in 1962 that motion of flux bundles restores the
critical state in hard superconductors, after a change in temperature or
magnetic field. We now provide first images of vortex bundles, and show how
they accumulate and release stress. We push vortices in a bundle by slightly
increasing the magnetic field, and observe that bundles are not rigid.
Vortex positions inside a bundle can change, accumulating stress, before it
is suddenly released. Data are taken under magnetic fields of some Tesla,
similar to those used in superconducting magnets. Vortex motion in such
devices can, under some conditions, lead to magnet failure. A better
knowledge about the microscopic mechanism behind flux arrangements, directly
imaged in our experiment, could help improving magnet design.
***
LX12217
Jams, Jellies, Creams and Paste: Prediction of long time physical behavior in glasses is now feasible
In our paper we have proposed a procedure to predict a very long time and a very short time physical behavior of glassy materials such as molecular glasses, spin glasses and colloidal glasses (or pastes) by carrying out experiments over practically possible time timescales. We have proposed an effective time approach that adjusts the material clock appropriately to accommodate time dependent change of relaxation time brought about by an aging process in glassy materials. We demonstrate effectiveness of this approach by predicting creep compliance of many soft materials such as aqueous clay suspension, commercial hair gel and acrylic emulsion paint. This Letter demonstrates that the effective time approach successfully predicts a very long and very short time physical behavior of materials showing diverse aging regimes ranging from sub-aging (or slow aging) to hyper-aging (very fast aging) dynamics. This approach can be used to predict behavior of any linear response function in molecular glasses, spin glasses, and variety of soft pasty materials such as pharmaceutical and cosmetic pastes/creams, toothpastes, paints, and variety of high viscosity food materials such as jams and jellies.
NANO-SPIDERS HURRY ALONG TRACKS
We study the movement of nano-scale walkers, called "molecular
spiders" that travel along one-dimensional tracks. Our analysis
reveals a useful transient behavior: the spiders move faster than
ordinary random walkers over significant distances and times. In other
words they travel faster than diffusion. The spiders in our model are
inspired by physical experiments (Pei et al., J. Am. Chem. Soc. 128
12693-12699, 2006; Lund et al., Nature 465 206-210 (2010)), in which
spider molecules are synthesized with a rigid chemically inert body
attached to legs made of single-stranded segments of DNA; they walk on
a surfaces coated with single-stranded DNA complementary to the legs.
The legs attach and detach to the surface strands, causing the spider
to move over the surface. When a leg detaches from a strand for the
first time, it cuts it in half. This change is irreversible and the
legs subsequently bind to cut strands more weakly.
Previous analyses dealt with so-called asymptotic behavior---if time
goes to infinity, the spiders diffuse. Our analysis is based on
stochastic computer simulations, which enable us to predict how the
strand modification affects the motion of spiders in the context of
real experiments that last for a finite time and where spiders cover a
finite distance. This has important applications if spiders walking
along one-dimensional tracks are used as a transport mechanism for molecular
payloads. We hope to use our simulations to help chemists design
faster spiders. In the future spiders might be used for various
medical purposes or to assemble nano-devices built from molecules
which spiders will be able to pick up and carry along tracks.
***
BU11301
Magnetization switched off by crystal vibration
We have connected magnetic phase transition observed in magnetocaloric
MnAs near room temperature (315 K) with particular vibration of crystal
structure. We have shown that excitation of this vibration (with
increasing temperature or stretching the sample) leads to disordering of
magnetic moments and disappearance of total magnetization. Discovery of
such a strong coupling between crystal vibrations and magnetization
enabled us to form a simple explanation of the mechanism of both:
discontinuous magneto-structural phase transition at 315 K as well as
continuous return at 393 K (without magnetic ordering) to the
low-temperature structure. This particular interplay between magnetic
and lattice properties leads to large entropy change around this
discontinuous transition and, consequently, to giant magnetocaloric
effect promising applications in cheap and green refrigeration at room
temperature. Our theoretical predictions agree well with all
experimental findings published earlier.
***
LV12016
SPONTANEOUS RIPPLING OF GRAPHENE MIMICS CONDENSATION OF RELATIVISTIC
HIGGS FIELD
Great part of the current excitement about graphene (the one-atom thick
carbon layer) comes from the fact that it is the only known membrane
(genuine two-dimensional material) with conducting properties. A
remarkable and puzzling property of this material is its strong tendency
to develop ripples (modulations of the vertical displacements) by which
the membrane freezes spontaneously into a corrugated configuration. In
this paper we have shown that the interaction between the membrane
distortions and its conduction electrons places the flat phase of
graphene in unstable equilibrium, closely mimicking the state of the
relativistic Higgs field prior to its decay into a ground-state
condensate filling the space -the mechanism that gives mass to
elementary particles in high-energy physics. We have seen that the
effective potential for both quantum fields (the vertical displacement
in graphene, the Higgs field in relativistic physics) has the same
typical "mexican-hat" shape, which makes the unstable state at the top
to spontaneously decay by rolling down to a lowest-energy state with
broken symmetry (the aggregate of ripples in one case, the Higgs
condensate filling the vacuum in the other). The analogue goes further,
since graphene has a control parameter (the tension of the membrane)
that plays the same role as the bare mass square for the Higgs field,
opening the possibility of investigating the behavior of the Higgs
sector of elementary particle theories at the much smaller energies of a
condensed matter system like graphene.
***
BZ11073
Hours Marked by Neutrons
Small-angle neutron diffraction is a powerful probe for the behavior
of quantized magnetic field lines (and their associated 'vortices' of
screening currents) penetrating into superconductors. Using this
technique, we made the first observation of the so-called 'vortex
lattice' in pure crystals of HgBa2CuO4+d, one of the best
high-temperature superconductors discovered to date. The diffraction
pattern looks exactly like the markings of hours on a clock face
(attached figure), reflecting a simple geometric beauty of nature that
a hexagonal arrangement in two dimensions allows for the largest
nearest-neighbor distance for a given number density -- the vortices
want to stay away from one another, and the presence of two types of
hexagonal domains rotated by 90 degrees relative to each other leads
to the twelve diffraction spots. By further studying the vortex
lattice at various temperatures and magnetic fields, we confirmed a
previously proposed mechanism for long and straight magnetic field
lines to decompose into short segments surrounded by uncorrelated
screening currents (referred to as 'vortex pancakes'), which explains
why the diffraction signal vanishes at high fields. Our work opens the
door for future investigations into the vortex physics in this highly
ideal new family of superconductors.
***
LW12339
Direct observation of superconducting vortex bundles in the critical state
P.W. Anderson proposed in 1962 that motion of flux bundles restores the
critical state in hard superconductors, after a change in temperature or
magnetic field. We now provide first images of vortex bundles, and show how
they accumulate and release stress. We push vortices in a bundle by slightly
increasing the magnetic field, and observe that bundles are not rigid.
Vortex positions inside a bundle can change, accumulating stress, before it
is suddenly released. Data are taken under magnetic fields of some Tesla,
similar to those used in superconducting magnets. Vortex motion in such
devices can, under some conditions, lead to magnet failure. A better
knowledge about the microscopic mechanism behind flux arrangements, directly
imaged in our experiment, could help improving magnet design.
***
LX12217
Jams, Jellies, Creams and Paste: Prediction of long time physical behavior in glasses is now feasible
In our paper we have proposed a procedure to predict a very long time and a very short time physical behavior of glassy materials such as molecular glasses, spin glasses and colloidal glasses (or pastes) by carrying out experiments over practically possible time timescales. We have proposed an effective time approach that adjusts the material clock appropriately to accommodate time dependent change of relaxation time brought about by an aging process in glassy materials. We demonstrate effectiveness of this approach by predicting creep compliance of many soft materials such as aqueous clay suspension, commercial hair gel and acrylic emulsion paint. This Letter demonstrates that the effective time approach successfully predicts a very long and very short time physical behavior of materials showing diverse aging regimes ranging from sub-aging (or slow aging) to hyper-aging (very fast aging) dynamics. This approach can be used to predict behavior of any linear response function in molecular glasses, spin glasses, and variety of soft pasty materials such as pharmaceutical and cosmetic pastes/creams, toothpastes, paints, and variety of high viscosity food materials such as jams and jellies.
Tuesday, January 11, 2011
EX10652
Mechanical model of the ultrafast, carnivorous plant Utricularia
The underwater traps of the carnivorous plants of the
Utricularia species catch their preys through the repetition of an
"active slow deflation / passive fast suction" sequence. In this
paper, we propose a mechanical model that describes both phases and
strongly supports the hypothesis that the trap door acts as a flexible
valve that buckles under the combined effects of pressure forces and
the mechanical stimulation of trigger hairs, and not as a panel
articulated on hinges. This model combines two different approaches,
namely (i) the description of thin membranes as triangle meshes with
strain and curvature energy, and (ii) the molecular dynamics approach,
which consists in computing the time evolution of the position of each
vertex of the mesh according to Langevin equations. The only free
parameter in the expression of the elastic energy is the Young's
modulus E of the membranes. The values for this parameter are
unequivocally obtained by requiring that the trap model fires, like
real traps, when the pressure difference between the outside and the
inside of the trap reaches about 15 kPa. Among other results, our
simulations show that, for a pressure difference slightly larger than
the critical one, the door buckles, slides on the threshold and
finally swings wide open, in excellent agreement with the sequence
observed in high-speed videos.
***
LV11835AR
Interfacing ultracold atoms with quantum electronics
We show that electrons flowing quantum-mechanically through a semiconductor nanostructure can trap and control atoms less than a micron above the chip surface. The temperature of the atoms is eleven orders of magnitude smaller than that of the nanostructure – low enough to form a Bose-Einstein condensate.
This new hybrid quantum system, in which ultracold atoms above the nanostructure couple to electrons within it, has the potential to make microchips whose functionality far exceeds that of existing electron-only devices by offering extreme sensitivity and control. Even the smallest possible quantised chip current can imprint rewritable patterns in the condensate. Conversely, the condensate itself can be used for non-invasive functional imaging of quantum electronic devices.
In previous structures, atoms have been trapped by passing current through thick metal wires on the chip surface. But high current noise, combined with a strong quantum pull that the chip exerts on the atoms, destroyed traps closer than a few microns from the surface.
Our work shows that thin quantum conductors fabricated in a two-dimensional electron gas – already used in mobile telephones – overcome these limitations by reducing the current noise by three orders of magnitude, thus opening the way to creating miniature hybrid atom chips.
Mechanical model of the ultrafast, carnivorous plant Utricularia
The underwater traps of the carnivorous plants of the
Utricularia species catch their preys through the repetition of an
"active slow deflation / passive fast suction" sequence. In this
paper, we propose a mechanical model that describes both phases and
strongly supports the hypothesis that the trap door acts as a flexible
valve that buckles under the combined effects of pressure forces and
the mechanical stimulation of trigger hairs, and not as a panel
articulated on hinges. This model combines two different approaches,
namely (i) the description of thin membranes as triangle meshes with
strain and curvature energy, and (ii) the molecular dynamics approach,
which consists in computing the time evolution of the position of each
vertex of the mesh according to Langevin equations. The only free
parameter in the expression of the elastic energy is the Young's
modulus E of the membranes. The values for this parameter are
unequivocally obtained by requiring that the trap model fires, like
real traps, when the pressure difference between the outside and the
inside of the trap reaches about 15 kPa. Among other results, our
simulations show that, for a pressure difference slightly larger than
the critical one, the door buckles, slides on the threshold and
finally swings wide open, in excellent agreement with the sequence
observed in high-speed videos.
***
LV11835AR
Interfacing ultracold atoms with quantum electronics
We show that electrons flowing quantum-mechanically through a semiconductor nanostructure can trap and control atoms less than a micron above the chip surface. The temperature of the atoms is eleven orders of magnitude smaller than that of the nanostructure – low enough to form a Bose-Einstein condensate.
This new hybrid quantum system, in which ultracold atoms above the nanostructure couple to electrons within it, has the potential to make microchips whose functionality far exceeds that of existing electron-only devices by offering extreme sensitivity and control. Even the smallest possible quantised chip current can imprint rewritable patterns in the condensate. Conversely, the condensate itself can be used for non-invasive functional imaging of quantum electronic devices.
In previous structures, atoms have been trapped by passing current through thick metal wires on the chip surface. But high current noise, combined with a strong quantum pull that the chip exerts on the atoms, destroyed traps closer than a few microns from the surface.
Our work shows that thin quantum conductors fabricated in a two-dimensional electron gas – already used in mobile telephones – overcome these limitations by reducing the current noise by three orders of magnitude, thus opening the way to creating miniature hybrid atom chips.
Monday, January 10, 2011
LM12123E
Towards a fusion between structural sciences and fusion physics.
Ultra-intense and ultra-short radiation pulses from X-ray lasers have allowed scientists to reproduce astrophysical conditions on the face of Earth. An international collaborationdescribes surprising results from the FLASH free-electron laser in Hamburg, Germany. They focused an extremely intense X-ray pulse (lasting only a few millionth of a billionth of a second) on a metallic target, heating it to several million degrees Centigrades. The power density of the radiation reached more than 10^17 W/cm^2, which would be similar to the power density of all the sun light hitting the Earth focused to a spot of only 1 cm^2.
Two unexpected results emerge. Firstly, at the highest intensities, part of the sample suddenly becomes transparent to radiation, and damage becomes less dominant. This is good news for imaging single particles and molecules with ultra-intense X-ray pulses. Secondly, when the sample eventually blew up, some of the ejected ions had high enough energies to facilitate nuclear fusion. Computer simulations show just how the radiation affects the sample long after the pulse had left. The results
indicate that developments at X-ray lasers could, in principle, lead to a fusion between structural sciences and fusion physics.
Towards a fusion between structural sciences and fusion physics.
Ultra-intense and ultra-short radiation pulses from X-ray lasers have allowed scientists to reproduce astrophysical conditions on the face of Earth. An international collaborationdescribes surprising results from the FLASH free-electron laser in Hamburg, Germany. They focused an extremely intense X-ray pulse (lasting only a few millionth of a billionth of a second) on a metallic target, heating it to several million degrees Centigrades. The power density of the radiation reached more than 10^17 W/cm^2, which would be similar to the power density of all the sun light hitting the Earth focused to a spot of only 1 cm^2.
Two unexpected results emerge. Firstly, at the highest intensities, part of the sample suddenly becomes transparent to radiation, and damage becomes less dominant. This is good news for imaging single particles and molecules with ultra-intense X-ray pulses. Secondly, when the sample eventually blew up, some of the ejected ions had high enough energies to facilitate nuclear fusion. Computer simulations show just how the radiation affects the sample long after the pulse had left. The results
indicate that developments at X-ray lasers could, in principle, lead to a fusion between structural sciences and fusion physics.
Friday, January 7, 2011
LS12152
Strangely shaped drops playing the “game of life“
In 1831 Michael Faraday discovered that a liquid bath can present waves on its surface when it is subjected to vertical oscillation. Until now this has been performed in liquids confined in containers of different fixed shapes. We have performed the Faraday experience in an alcohol drop floating on an oil bath. The interplay of the waves with the border of the drop generates two behaviors. In the first one, the drop shape co-evolves with the waves to reach an equilibrium and
becomes elliptical or square , recalling the self-tuning of oscillators as in optical laser cavities and micro-cavities. In the second the drop is extended by the waves, it buckles and breaks in fragments with archetypical shapes: snakes, croissants, horseshoes or rings. These fragments self-propagate, rotate, collide, destroy each other, reorganize etc…Their interplay on the liquid bath recalls the famous Conway's mathematical “game of life“. These behaviors show how a beautiful complex collective behavior can emerge in a very simple experiment.
***
LU12992
Microfluidic Assembly Lines
Microflouidic technology has revolutionized the control of flows at small scales giving rise to new possibilities for assembling complex structures on the microscale. We analyze different possible algorithms for assembling arbitrary structures, and demonstrate that a sequential assembly algorithm can manufacture arbitrary 3D structures from identical constituents. We illustrate the algorithm by showing that a modifed Hele-Shaw cell with 7 controlled flowrates can be designed to construct the entire English alphabet from particles that irreversibly stick to each other.
Strangely shaped drops playing the “game of life“
In 1831 Michael Faraday discovered that a liquid bath can present waves on its surface when it is subjected to vertical oscillation. Until now this has been performed in liquids confined in containers of different fixed shapes. We have performed the Faraday experience in an alcohol drop floating on an oil bath. The interplay of the waves with the border of the drop generates two behaviors. In the first one, the drop shape co-evolves with the waves to reach an equilibrium and
becomes elliptical or square , recalling the self-tuning of oscillators as in optical laser cavities and micro-cavities. In the second the drop is extended by the waves, it buckles and breaks in fragments with archetypical shapes: snakes, croissants, horseshoes or rings. These fragments self-propagate, rotate, collide, destroy each other, reorganize etc…Their interplay on the liquid bath recalls the famous Conway's mathematical “game of life“. These behaviors show how a beautiful complex collective behavior can emerge in a very simple experiment.
***
LU12992
Microfluidic Assembly Lines
Microflouidic technology has revolutionized the control of flows at small scales giving rise to new possibilities for assembling complex structures on the microscale. We analyze different possible algorithms for assembling arbitrary structures, and demonstrate that a sequential assembly algorithm can manufacture arbitrary 3D structures from identical constituents. We illustrate the algorithm by showing that a modifed Hele-Shaw cell with 7 controlled flowrates can be designed to construct the entire English alphabet from particles that irreversibly stick to each other.
Thursday, January 6, 2011
LV12575
Lighthouse lens brightens prospects for quantum computing.
Fresnel lenses, first developed for use in lighthouses, have found a
bright new future in quantum computing. In our experiment a
micro-fabricated Fresnel lens was used to efficiently image the light
emitted from a single atom. Gathering more light results in faster
processing speeds and lower error rates in quantum computers built
from trapped atoms. Light collection is a crucial limit since the
light from a single atom has a maximum brightness less than a
trillionth that of a light bulb. Arrays of many lenses can be
micro-fabricated on a single piece of glass for use in the development
of large-scale quantum computing. Algorithms including database
searching, molecular modeling, and factoring large numbers require
fewer calculations when performed with a quantum computer. A future
large scale quantum computer would be able to solve these problems
when the complexity exceeds the capacity of conventional computers.
Lighthouse lens brightens prospects for quantum computing.
Fresnel lenses, first developed for use in lighthouses, have found a
bright new future in quantum computing. In our experiment a
micro-fabricated Fresnel lens was used to efficiently image the light
emitted from a single atom. Gathering more light results in faster
processing speeds and lower error rates in quantum computers built
from trapped atoms. Light collection is a crucial limit since the
light from a single atom has a maximum brightness less than a
trillionth that of a light bulb. Arrays of many lenses can be
micro-fabricated on a single piece of glass for use in the development
of large-scale quantum computing. Algorithms including database
searching, molecular modeling, and factoring large numbers require
fewer calculations when performed with a quantum computer. A future
large scale quantum computer would be able to solve these problems
when the complexity exceeds the capacity of conventional computers.
Wednesday, January 5, 2011
LX11868
Testing Gravity at the micro scale
Gravity is the weakest of the fundamental interactions but probably the most important one because of its ubiquitous nature which determines the space/time geometry around us. Experiments on gravity have always attracted enormous interest, especially today in the quest of deviations from General Relativity and of possible scenarios beyond the Standard Model. In this work we exploit new microscopic quantum probes of gravity constituted by ultracold Strontium atoms confined in the valleys of a periodic array of potential wells produced by a vertically-aligned laser beam. We perform an accurate measurement of the Earth's gravity and verify that the result obtained with this microscopic quantum system is consistent with the one measured with a macroscopic classical gravimeter. In our new technique atoms exchange quanta of energy with the time-modulated laser field: resonant quantum tunneling, which is observed experimentally, occurs once the energy quanta equal the gravitational potential between neighboring potential wells, which are vertically separated by multiples of the laser wavelength. Our results open interesting prospects for testing gravitational redshift and Newtonian law at micrometer scale and can also find applications for future compact, high precision quantum sensors of gravity and time.
***
LW12140
Classical single-electron dynamics observed on the surface of liquid helium
For the first time, the transport of electrons through a small constriction, or 'point contact', has been measured
in the classical regime. Unlike in metals or semiconductors, where interactions between electrons are compromised by the
surrounding lattice of atoms, the electrostatic interaction between electrons floating above a liquid helium surface
is 'unscreened' and therefore strong. Hence, these surface electrons behave, in general, as a two-dimensional system of
classical charged particles. In this work, we measured the transport of such surface electrons through a small
constriction at the center of a microchannel filled with superfluid helium. The width of the constriction was controlled
using nanofabricated electrodes submerged beneath the helium surface. As the constriction was opened, a step-like
increase in the surface electron current was observed each time an additional electron was able to pass through the constriction.
The first step in the current therefore corresponded to electrons passing through the constriction in single-file.
Remarkably, we find that these dynamics are similar to those observed in crowds of human pedestrians moving through
bottlenecks, rather than in electron transport in metallic or semiconductor point-contact devices.
Testing Gravity at the micro scale
Gravity is the weakest of the fundamental interactions but probably the most important one because of its ubiquitous nature which determines the space/time geometry around us. Experiments on gravity have always attracted enormous interest, especially today in the quest of deviations from General Relativity and of possible scenarios beyond the Standard Model. In this work we exploit new microscopic quantum probes of gravity constituted by ultracold Strontium atoms confined in the valleys of a periodic array of potential wells produced by a vertically-aligned laser beam. We perform an accurate measurement of the Earth's gravity and verify that the result obtained with this microscopic quantum system is consistent with the one measured with a macroscopic classical gravimeter. In our new technique atoms exchange quanta of energy with the time-modulated laser field: resonant quantum tunneling, which is observed experimentally, occurs once the energy quanta equal the gravitational potential between neighboring potential wells, which are vertically separated by multiples of the laser wavelength. Our results open interesting prospects for testing gravitational redshift and Newtonian law at micrometer scale and can also find applications for future compact, high precision quantum sensors of gravity and time.
***
LW12140
Classical single-electron dynamics observed on the surface of liquid helium
For the first time, the transport of electrons through a small constriction, or 'point contact', has been measured
in the classical regime. Unlike in metals or semiconductors, where interactions between electrons are compromised by the
surrounding lattice of atoms, the electrostatic interaction between electrons floating above a liquid helium surface
is 'unscreened' and therefore strong. Hence, these surface electrons behave, in general, as a two-dimensional system of
classical charged particles. In this work, we measured the transport of such surface electrons through a small
constriction at the center of a microchannel filled with superfluid helium. The width of the constriction was controlled
using nanofabricated electrodes submerged beneath the helium surface. As the constriction was opened, a step-like
increase in the surface electron current was observed each time an additional electron was able to pass through the constriction.
The first step in the current therefore corresponded to electrons passing through the constriction in single-file.
Remarkably, we find that these dynamics are similar to those observed in crowds of human pedestrians moving through
bottlenecks, rather than in electron transport in metallic or semiconductor point-contact devices.
Monday, January 3, 2011
EV10570
Experiments on the morphology of icicles
Icicles form when cool water drips from an overhanging support under ambient conditions which are below freezing. Ice growth is controlled by the removal of latent heat, which is transferred into the surrounding air via a thin film of water flowing over the ice surface. We describe laboratory experiments in which icicles were grown under controlled conditions. We used image analysis to probe the evolution of the icicle shape under various conditions. A recent asymptotic theory suggests that, overall, icicles converge to self-similar shapes which are predicted to be attractors. On the other hand, stability theory predicts that the ice-water interface can become unstable to form ripple patterns on the icicle surface. Our experimental results show that the predicted self-similar profile is only found in certain cases, and that icicles can also exhibit unpredicted non-uniformities such as branching near the tip. We find that pure water icicles are more likely to be self-similar than those grown from tap water. Ripples, which are also deviations from the self-similar profile, were observed to climb upward during icicle growth.
***
EU10761
Rotating Liquid Film
In our childhood, colorful soap bubble brought us lots of joys and reveries. Do you know that soap water can also be made into so-called liquid film motor, which was first reported by Iranian scientists. We have constructed a simple theoretical model to systematically explain the working principle of it. Our theory can not only give the relation of threshold fields for the rotation of the liquid film motor, but also can recover the picture observed in experiments: the rotating liquid film is composed of lots of concentric rings among which the rings near the center are rotating faster than those away from it, as shown in figure below. The theory reported here, in addition to its guidance for the potential applications of the liquid film motor (to mix or phase separate liquids or particles in microfluidic chips), can also provide us with a new physical viewpoint for deepening our understanding of water anomalous behaviors and the physics of film flows.
***
LT12213E
Synergistic Rafting
Two and two always do not make four. At least this seems to be the case
for the mechanisms which control the organization of Cholesterol patches,
called Lipid Rafts, in the outer membrane of biological cells. While these
domains dictate pathological events such as viral infection and cancer
progression by modulating their dimension and property, our theoretical
and experimental investigations illustrate that these aspects are, in
turn, determined by the cooperative interactions between lipid-recycling
and interface-pinning. It is found that effect of one is amplified in
presence of other. Results also delineate a dynamic interaction pattern
among membrane constituents against the conventional static perspective.
***
LY11873
Laser creates matter
Ultrarelativistic electron-positron pair plasma with particle density
exceeding the solid-state one can be produced by colliding laser pulses
in vacuum. We calculate the plasma parameters and show that such plasma
can be produced for not extremely high laser intensity 10^24 W/cm^2
achievable in near coming laser facilities. A significant part of laser
energy is scattered and absorbed by the self-generated electron-positron
pair plasma that can limit the attainable intensity of the focused laser
radiation. Furthermore, the plasma can be used as a bright source of
high-energy gamma-quanta. The plasma is produced via development of the
avalanche-like electromagnetic cascade: the electrons or positrons are
accelerated in the laser field and emit energetic photons which decay in
the laser field thereby producing new generation of electron-positron
pairs, etc. The cascade can be initiated by a single pair created
accidentally from the vacuum in the laser field or by external
high-energy photons.
***
LY12352E
Can we cheat the radar as desired?
The optical illusion means that the image of a real object perceived by eyes is deceptive or misleading, i.e., the optical illusion confuses the human sensor – the eyes – to perceive a wrong image of the real target. As a concept extension, a radar illusion will confuse the electromagnetic (EM) sensor – the radar – to perceive the wrong EM image of a real target. Hence, in the radar illusion, the EM image of a target which is gathered by the radar looks like another different target. Metamaterials can provide a powerful tool to design perfectly optical or radar illusions. In this work, we realize the experiment of a radar illusion device which changes the radar image of a metallic target into a dielectric target with pre-designed material parameters and size. Such an illusion device will confuse the radar, hence the real EM properties of the metallic target cannot be perceived. We have designed and fabricated the radar illusion device using artificial metamaterials in the microwave frequency, and good illusion performances are observed in the experimental results. Compared to invisibility cloaks, illusion devices not only make an object invisible, but also could generate one or more virtual images with different shapes and material makeups. Hence such a kind of optical or radar illusion devices could have applications beyond the normal invisibility cloaks.
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DWR1039
Verlinde vs Newton
Recently, E.Verlinde proposed an intriguing idea, according to which the force of gravity does not exist at small distance scales, but emerges from a deeper microscopic reality due to the entropy difference in an empty space between two massive macroscopic objects. This truly revolutionary view on gravity is contrasted with the standard Newtonian approach, according to which gravity is a fundamental potential force. If correct, Verlinde’s theory may lead to many profound conclusions, including those related with the greatest challenge of modern physics – the reconciliation of quantum mechanics and gravity.
We confront Verlinde’s entropic gravity with the empirical evidence for quantum mechanical bound states of neutrons in the Earth’s gravitational field. The observation of these states is in agreement with the predictions of the standard quantum mechanics and the Newtonian potential force of gravity. However, in Verlinde’s approach the gravitational force between neutrons and the Earth is due to the difference of entropy associated with the position of neutrons. This leads to a dramatic modification of quantum mechanical description of the neurton bound states in the way which contradicts the observations. The nature seems to favor the old Newtonian description of gravitation over the Verlinde’s entropic gravity.
Experiments on the morphology of icicles
Icicles form when cool water drips from an overhanging support under ambient conditions which are below freezing. Ice growth is controlled by the removal of latent heat, which is transferred into the surrounding air via a thin film of water flowing over the ice surface. We describe laboratory experiments in which icicles were grown under controlled conditions. We used image analysis to probe the evolution of the icicle shape under various conditions. A recent asymptotic theory suggests that, overall, icicles converge to self-similar shapes which are predicted to be attractors. On the other hand, stability theory predicts that the ice-water interface can become unstable to form ripple patterns on the icicle surface. Our experimental results show that the predicted self-similar profile is only found in certain cases, and that icicles can also exhibit unpredicted non-uniformities such as branching near the tip. We find that pure water icicles are more likely to be self-similar than those grown from tap water. Ripples, which are also deviations from the self-similar profile, were observed to climb upward during icicle growth.
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EU10761
Rotating Liquid Film
In our childhood, colorful soap bubble brought us lots of joys and reveries. Do you know that soap water can also be made into so-called liquid film motor, which was first reported by Iranian scientists. We have constructed a simple theoretical model to systematically explain the working principle of it. Our theory can not only give the relation of threshold fields for the rotation of the liquid film motor, but also can recover the picture observed in experiments: the rotating liquid film is composed of lots of concentric rings among which the rings near the center are rotating faster than those away from it, as shown in figure below. The theory reported here, in addition to its guidance for the potential applications of the liquid film motor (to mix or phase separate liquids or particles in microfluidic chips), can also provide us with a new physical viewpoint for deepening our understanding of water anomalous behaviors and the physics of film flows.
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LT12213E
Synergistic Rafting
Two and two always do not make four. At least this seems to be the case
for the mechanisms which control the organization of Cholesterol patches,
called Lipid Rafts, in the outer membrane of biological cells. While these
domains dictate pathological events such as viral infection and cancer
progression by modulating their dimension and property, our theoretical
and experimental investigations illustrate that these aspects are, in
turn, determined by the cooperative interactions between lipid-recycling
and interface-pinning. It is found that effect of one is amplified in
presence of other. Results also delineate a dynamic interaction pattern
among membrane constituents against the conventional static perspective.
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LY11873
Laser creates matter
Ultrarelativistic electron-positron pair plasma with particle density
exceeding the solid-state one can be produced by colliding laser pulses
in vacuum. We calculate the plasma parameters and show that such plasma
can be produced for not extremely high laser intensity 10^24 W/cm^2
achievable in near coming laser facilities. A significant part of laser
energy is scattered and absorbed by the self-generated electron-positron
pair plasma that can limit the attainable intensity of the focused laser
radiation. Furthermore, the plasma can be used as a bright source of
high-energy gamma-quanta. The plasma is produced via development of the
avalanche-like electromagnetic cascade: the electrons or positrons are
accelerated in the laser field and emit energetic photons which decay in
the laser field thereby producing new generation of electron-positron
pairs, etc. The cascade can be initiated by a single pair created
accidentally from the vacuum in the laser field or by external
high-energy photons.
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LY12352E
Can we cheat the radar as desired?
The optical illusion means that the image of a real object perceived by eyes is deceptive or misleading, i.e., the optical illusion confuses the human sensor – the eyes – to perceive a wrong image of the real target. As a concept extension, a radar illusion will confuse the electromagnetic (EM) sensor – the radar – to perceive the wrong EM image of a real target. Hence, in the radar illusion, the EM image of a target which is gathered by the radar looks like another different target. Metamaterials can provide a powerful tool to design perfectly optical or radar illusions. In this work, we realize the experiment of a radar illusion device which changes the radar image of a metallic target into a dielectric target with pre-designed material parameters and size. Such an illusion device will confuse the radar, hence the real EM properties of the metallic target cannot be perceived. We have designed and fabricated the radar illusion device using artificial metamaterials in the microwave frequency, and good illusion performances are observed in the experimental results. Compared to invisibility cloaks, illusion devices not only make an object invisible, but also could generate one or more virtual images with different shapes and material makeups. Hence such a kind of optical or radar illusion devices could have applications beyond the normal invisibility cloaks.
***
DWR1039
Verlinde vs Newton
Recently, E.Verlinde proposed an intriguing idea, according to which the force of gravity does not exist at small distance scales, but emerges from a deeper microscopic reality due to the entropy difference in an empty space between two massive macroscopic objects. This truly revolutionary view on gravity is contrasted with the standard Newtonian approach, according to which gravity is a fundamental potential force. If correct, Verlinde’s theory may lead to many profound conclusions, including those related with the greatest challenge of modern physics – the reconciliation of quantum mechanics and gravity.
We confront Verlinde’s entropic gravity with the empirical evidence for quantum mechanical bound states of neutrons in the Earth’s gravitational field. The observation of these states is in agreement with the predictions of the standard quantum mechanics and the Newtonian potential force of gravity. However, in Verlinde’s approach the gravitational force between neutrons and the Earth is due to the difference of entropy associated with the position of neutrons. This leads to a dramatic modification of quantum mechanical description of the neurton bound states in the way which contradicts the observations. The nature seems to favor the old Newtonian description of gravitation over the Verlinde’s entropic gravity.
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