Showing papers in "Physics in 2008"
Journal Article•
TL;DR: In this paper, the authors provide an overview of the rapidly developing field of photoacoustic imaging, which is a promising method for visualizing biological tissues with optical absorbers, compared with optical imaging and ultrasonic imaging.
Abstract: Photoacoustic imaging is a promising method for visualizing biological tissues with optical absorbers. This article provides an overview of the rapidly developing field of photoacoustic imaging. Photoacoustics, the physical basis of photoacoustic imaging, is analyzed briefly. The merits of photoacoustic technology, compared with optical imaging and ultrasonic imaging, are described. Various imaging techniques are also discussed, including scanning tomography, computed tomography and original detection of photoacoustic imaging. Finally, some biomedical applications of photoacoustic imaging are summarized.
618 citations
TL;DR: A new class of high-temperature superconductors has been discovered in layered iron arsenic compounds as mentioned in this paper, which may shed light on the still unsolved problem of high temperature cuprate superconductivity.
Abstract: A new class of high-temperature superconductors has been discovered in layered iron arsenic compounds. Results in this rapidly moving field may shed light on the still unsolved problem of high-temperature cuprate superconductivity.
139 citations
TL;DR: In this article, large-scale quantum computers are hard to construct because quantum systems easily lose their coherence through interaction with the environment, and researchers have tried to avoid this problem by usi...
Abstract: Large-scale quantum computers are hard to construct because quantum systems easily lose their coherence through interaction with the environment. Researchers have tried to avoid this problem by usi ...
130 citations
TL;DR: In this article, the relativistic Dirac equation for massless fermions was used to describe the surface of topological insulators, leading to an exotic metallic surface on an otherwise 'ordinary' insulator.
Abstract: Electrons in graphene can be described by the relativistic Dirac equation for massless fermions and exhibit a host of unusual properties. The surfaces of certain band insulators—called topological insulators—can be described in a similar way, leading to an exotic metallic surface on an otherwise ‘ordinary’ insulator.
87 citations
TL;DR: Vinante et al. as mentioned in this paper used amplifier feedback to cool oscillation modes in a one-metric-ton aluminum bar that forms the active element in the AURIGA gravity wave detector.
Abstract: Researchers have long sought to detect quantum effects in macroscopic objects, analogous to the superposition of states in Schrodinger’s cat that is both dead and alive. The development of ultrasensitive measurement techniques used in quantum computing and gravity wave detection may offer a way to experimentally test these ideas. Vinante et al. have used amplifier feedback to cool oscillation modes in a one-metric-ton aluminum bar that forms the active element in the AURIGA gravity wave detector. The effective temperature was 0.2 mK . Although other experiments have achieved lower temperatures, the AURIGA resonator is orders of magnitude more massive. Such feedback techniques may enable researchers to approach a regime where quantum effects become apparent.
34 citations
TL;DR: In this article, the authors showed that laser-cooled atomic vapors can be photoionized to form plasmas at temperatures as low as 1 K. This may allow the study of very unusual neutral plasms with liquid and even crystalline properties.
Abstract: Laser-cooled atomic vapors can be photoionized to form plasmas at temperatures as low as 1 K. This may allow the study of very unusual neutral plasmas with liquid and even crystalline properties.
24 citations
TL;DR: In this paper, it was shown that a properly designed combination of incident light waves would be almost completely transmitted and this remarkable result has been shown experimentally in the presence of disordered materials such as milk or snow.
Abstract: Thick layers of disordered materials, such as milk or snow, scatter light so that very little of it gets through. Theorists say that a properly designed combination of incident light waves would be almost completely transmitted and we now have experimental proof of this remarkable result.
23 citations
Journal Article•
TL;DR: The 2006 self-consistent set of values of the fundamental physical constants and conversion factors recommended by the Committee on Data for Science and Technology (CODATA) for international use is given in this paper.
Abstract: This paper gives the 2006 self-consistent set of values of the fundamental physical constants and conversion factors recommended by the Committee on Data for Science and Technology(CODATA) for international use.This set replaces the previously recommended 2002 CODATA set.Although only four years have elapsed between the 31 December 2002 and 31 December 2006 closing dates of the two adjustments,a number of advances in experiment and theory have led to significant improvements in our knowledge of the values of the constants.
20 citations
TL;DR: In this paper, the authors show that the information obtained in such single-particle experiments is different from that given by the ensemble-averaged cases, so one has to be careful about interpreting the results, especially the case when the measured motion exhibits subdiffusion that might be nonergodic (the time and ensemble averages give different answers).
Abstract: One hundred years ago, the atomic-molecular theory of matter was having a hard time, and many physicists considered it merely a kind of convenient shorthand rather than a real description of nature; after all, nobody had really seen a molecule, let alone an atom. Today, developments in micromanipulation and in single-molecule tracking have not only made individual molecules visible, but have led to real breakthroughs in understanding of the molecular basis of life. This ability to follow and to manipulate single molecules has opened new perspectives in nanoscience and nanotechnology. Experts in single-molecule tracking often say that observation of individual trajectories gives more information about the system than only looking at ensemble averages, which is the approach taken in statistical thermodynamics. The idea is that the closer one looks, the more information one can get. In a paper published in Physical Review Letters however, Yong He, Stanislav Burov, Ralf Metzler, and Eli Barkai (at Bar Ilan University in Israel and the Technical University of Munich) show that the information obtained in such single-particle experiments is different from that given by the ensemble-averaged cases, so one has to be careful about interpreting the results [1]. This is especially the case when the measured motion exhibits subdiffusion (a process that is slower than normal Fick’s law diffusion) that might be nonergodic (the time and ensemble averages give different answers). This situation is often encountered in both nonliving physical systems such as disordered semiconductors and groundwater motion in geophysical formations, and in the crowded interiors of living cells. He et al. base their theoretical analysis and numerical simulations on the so-called continuous-time random walk (CTRW) model, first introduced by Montroll and Weiss in 1965 [2]. CTRW was developed to handle a variety of complex diffusion processes by considering the motion of particles on lattices (Fig. 1). The importance of the model became clear after Scher and Montroll [3] successfully used it in 1975 to explain dispersive charge carrier transport in strongly disordered semiconductors (the ubiquitous working media of copy machines and laser printers). In the CTRW model, a particle hardly moves most of the time, and only occasionally gets an opportunity to jump to a new location. The motion is therefore described as a sequence of jumps into different directions interrupted by periods during which the particle is just waiting for the next jump.
20 citations
Journal Article•
TL;DR: In this paper, the authors used geometric phase shifts in the design of quantum gates to perform information processing and showed that these gates may be tolerant to certain types of faults, and may therefore be useful for robust quantum computation.
Abstract: Large-scale quantum computers are hard to construct because quantum systems easily lose their coherence through interaction with the environment. Researchers have tried to avoid this problem by using geometric phase shifts in the design of quantum gates to perform information processing. Experiments and simulations have shown that these gates may be tolerant to certain types of faults, and may therefore be useful for robust quantum computation.
19 citations
TL;DR: In this paper, the same physics applied to an unusual class of insulators, called axions, and was used to resolve a puzzle in the description of the strong interaction between quarks.
Abstract: The esoteric concept of “axions” was born thirty years ago as an attempt to resolve a puzzle in the description of the strong interaction between quarks. It appears that the same physics—though in a much different context—applies to an unusual class of insulators.
TL;DR: In this article, the authors proposed a simple idea that may at last explain the results of persistent currents in nonsuperconducting mesoscopic metal rings, but there was no theory that correctly explained the magnitude or direction of the unexpectedly large currents.
Abstract: A decade ago, experimentalists showed that persistent currents can flow in nonsuperconducting mesoscopic metal rings, but there was no theory that correctly explained the magnitude or direction of the unexpectedly large currents. Theorists are now proposing a simple idea that may at last explain these results.
TL;DR: A new phase of matter called a superglass may be possible, as shown by an investigation of the quantum mechanical analog of a classical hard sphere glass as mentioned in this paper, which is called superglass.
Abstract: A new phase of matter called a superglass may be possible, as shown by an investigation of the quantum mechanical analog of a classical hard sphere glass.
TL;DR: In this paper, a dimensionless parameter is proposed to predict whether dispersed particles in a turbulent flow enhance or attenuate the turbulence, and the parameter is used to predict the effect of dispersed particles on the flow.
Abstract: A novel dimensionless parameter allows prediction of whether dispersed particles in a turbulent flow enhance or attenuate the turbulence.
TL;DR: In this article, images of vortex motion in superfluid helium reveal connections between quantum and classical turbulence and may lead to an understanding of complex flows in both superfluid and ordinary fluids.
Abstract: Images of vortex motion in superfluid helium reveal connections between quantum and classical turbulence and may lead to an understanding of complex flows in both superfluids and ordinary fluids.
Journal Article•
TL;DR: In this article, the authors proposed a simple idea that may at last explain the results of persistent currents in nonsuperconducting mesoscopic metal rings, but there was no theory that correctly explained the magnitude or direction of the unexpectedly large currents.
Abstract: A decade ago, experimentalists showed that persistent currents can flow in nonsuperconducting mesoscopic metal rings, but there was no theory that correctly explained the magnitude or direction of the unexpectedly large currents. Theorists are now proposing a simple idea that may at last explain these results.
Journal Article•
TL;DR: It is 20 years since supernova 1987A, the brightest supernova in more than 400 years, was discoveredSeveral international symposiums were held in 2007, NASA released a special and beautiful supernova color photograph taken by the Hubble space telescope, and commemorative stamps were issued by the USA, all for celebrating SN1987A as discussed by the authors.
Abstract: It is 20 years since supernova 1987A,the brightest supernova in more than 400 years,was discoveredSeveral international symposiums were held in 2007,NASA released a special and beautiful SN1987A color photograph taken by the Hubble space telescope,and commemorative stamps were issued by the USA,all for celebrating SN1987AWe present an overview of its discovery,the spectra and character of its progenitor,the rich data accumulated over long term observations by the Hubble telescope,especially the three-ring structure,and the results of the Chandra X-ray observatoryAlthough SN1987A has been observed continuously,its central compact object has still not been discovered and certain mysteries remain unexplainedFinally,we look into the future
TL;DR: In this paper, the model of a spinning liquid drop can describe the physics of a large number of systems, from the nucleus to black holes, and it is possible to accurately study the many shapes a rapidly rotating liquid drop could take and compare the results against theoretical predictions.
Abstract: From the nucleus to black holes, the model of a spinning liquid drop can describe the physics of a large number of systems. With diamagnetic levitation, it is possible to accurately study the many shapes a rapidly rotating liquid drop can take and compare the results against theoretical predictions.
TL;DR: The discovery of superconductivity in iron-based compounds with a similar, but simpler, structure to the iron-pnictides could provide an important testing ground for unconventional superconductivities as discussed by the authors.
Abstract: The discovery of superconductivity in iron-based compounds with a similar, but simpler, structure to the iron-pnictides could provide an important testing ground for unconventional superconductivity.
TL;DR: The optical frequency combs as discussed by the authors are made up of millions of sharply defined and coherently locked optical frequencies, which can provide a way to implement a powerful quantum computer using laser beams.
Abstract: Laser beams made up of millions of sharply defined and coherently locked optical frequencies, called optical frequency combs, may provide a way to implement a powerful quantum computer.
[...]
TL;DR: In this paper, it was shown that contact with a metal layer could greatly increase the transition temperatures of superconductors, in some cases by as much as an order of magnitude.
Abstract: Discovering superconductivity above room temperature is a dream for modern science and technology. Now, theorists propose that for certain types of superconductors, contact with a metal layer could greatly increase the transition temperatures of these materials—in some cases by as much as an order of magnitude.
TL;DR: A physical model originally developed to describe the kinetics of first-order phase transitions is used and shows that, despite the intrinsic stochasticity of the initiation of DNA replication, cells can still control the amount of time it takes to replicate the genome.
Abstract: Complete and timely replication of the genome is a prerequisite to fulfilling the “dream” of every cell to become two cells [1]. So far, biologists have been successful in identifying the processes involved in DNA replication, but they have not been able to explain a fundamental control problem that cells face, the so-called “random-completion” or “random-gap” problem: how do cells ensure that every last piece of the genome is replicated on time [2]? In a paper in Physical Review E, Scott Yang and John Bechhoefer of Simon Fraser University use insights from condensed-matter physics to answer this question [3]. Using a physical model originally developed to describe the kinetics of first-order phase transitions, they show that, despite the intrinsic stochasticity of the initiation of DNA replication, cells can still control the amount of time it takes to replicate the genome. The authors thus provide a rigorous solution to a long-standing problem in cell biology. The elegance of their formal approach bridging physics and biology, and the depth of their analysis, should inspire scientists from both disciplines.
Journal Article•
TL;DR: In this article, the relativistic Dirac equation for massless fermions was used to describe the surface of topological insulators, leading to an exotic metallic surface on an otherwise 'ordinary' insulator.
Abstract: Electrons in graphene can be described by the relativistic Dirac equation for massless fermions and exhibit a host of unusual properties. The surfaces of certain band insulators—called topological insulators—can be described in a similar way, leading to an exotic metallic surface on an otherwise ‘ordinary’ insulator.
TL;DR: In this article, atoms colliding in a magnetic field can form weakly bound states called Feshbach molecules, which are used in combination with advanced laser techniques to create tightly bound ground-state molecules close to quantum degeneracy.
Abstract: Atoms colliding in a magnetic field can form weakly bound states called Feshbach molecules. These states have now been used in combination with advanced laser techniques to create tightly bound ground-state molecules close to quantum degeneracy.
TL;DR: In this article, the authors used an electric current to manipulate and store information in nanoscale domain walls, where magnetism is not compatible with domain walls because it interrupts a homogeneous magnetization.
Abstract: Most applications based on magnetism are incompatible with domain walls, which interrupt a homogeneous magnetization. Scientists are turning this view around as they discover new ways to use an electric current to manipulate and store information in nanoscale domain walls.
Journal Article•
TL;DR: In this paper, experiments with superconducting qubits show that the partial collapse resulting from a weak continuous measurement can be restored, even with the qubits being superconducted.
Abstract: Quantum measurements are conventionally thought of as irretrievably “collapsing” a wave function to the observed state. However, experiments with superconducting qubits show that the partial collapse resulting from a weak continuous measurement can be restored.
TL;DR: In this paper, the authors find clever ways to control the spin-torque effect precisely, both for when it is wanted and when not, both when the magnet is small enough and when the current carrying polarized spins can flip it around.
Abstract: If a magnet is small enough, an electric current carrying polarized spins can flip it around. Scientists are finding clever ways to control this spin-torque effect precisely, both for when it is wanted and when it is not.
TL;DR: In this paper, a flash of laser light briefly excites electrons in graphite into a bonding state similar to diamond, which can lead to new types of nanoscale circuits.
Abstract: A flash of laser light briefly excites electrons in graphite into a bonding state similar to diamond. Making the conversion complete could lead to new types of nanoscale circuits.
TL;DR: In this article, it was shown that mass can flow through solid helium-4 without viscous resistance, thanks to defects in the crystal lattice, as in a superfluid.
Abstract: Experiments indicate that, as in a superfluid, mass can flow through solid helium-4 without viscous resistance. Recent calculations shed light on how this may happen thanks to defects in the crystal lattice.