Showing papers in "Reviews of Modern Physics in 2002"
TL;DR: In this paper, the authors compare the theoretical and practical aspects of the two approaches and their specific numerical implementations, and present an overview of accomplishments and work in progress, as well as a comparison of both the Green's functions and the TDDFT approaches.
Abstract: Electronic excitations lie at the origin of most of the commonly measured spectra. However, the first-principles computation of excited states requires a larger effort than ground-state calculations, which can be very efficiently carried out within density-functional theory. On the other hand, two theoretical and computational tools have come to prominence for the description of electronic excitations. One of them, many-body perturbation theory, is based on a set of Green’s-function equations, starting with a one-electron propagator and considering the electron-hole Green’s function for the response. Key ingredients are the electron’s self-energy S and the electron-hole interaction. A good approximation for S is obtained with Hedin’s GW approach, using density-functional theory as a zero-order solution. First-principles GW calculations for real systems have been successfully carried out since the 1980s. Similarly, the electron-hole interaction is well described by the Bethe-Salpeter equation, via a functional derivative of S. An alternative approach to calculating electronic excitations is the time-dependent density-functional theory (TDDFT), which offers the important practical advantage of a dependence on density rather than on multivariable Green’s functions. This approach leads to a screening equation similar to the Bethe-Salpeter one, but with a two-point, rather than a four-point, interaction kernel. At present, the simple adiabatic local-density approximation has given promising results for finite systems, but has significant deficiencies in the description of absorption spectra in solids, leading to wrong excitation energies, the absence of bound excitonic states, and appreciable distortions of the spectral line shapes. The search for improved TDDFT potentials and kernels is hence a subject of increasing interest. It can be addressed within the framework of many-body perturbation theory: in fact, both the Green’s functions and the TDDFT approaches profit from mutual insight. This review compares the theoretical and practical aspects of the two approaches and their specific numerical implementations, and presents an overview of accomplishments and work in progress.
3,195 citations
TL;DR: In this article, the authors examined the current understanding of the lives and deaths of massive stars, with special attention to the relevant nuclear and stellar physics, and focused on their post-helium-burning evolution.
Abstract: amount of energy, a tiny fraction of which is sufficient to explode the star as a supernova. The authors examine our current understanding of the lives and deaths of massive stars, with special attention to the relevant nuclear and stellar physics. Emphasis is placed upon their post-helium-burning evolution. Current views regarding the supernova explosion mechanism are reviewed, and the hydrodynamics of supernova shock propagation and ‘‘fallback’’ is discussed. The calculated neutron star masses, supernova light curves, and spectra from these model stars are shown to be consistent with observations. During all phases, particular attention is paid to the nucleosynthesis of heavy elements. Such stars are capable of producing, with few exceptions, the isotopes between mass 16 and 88 as well as a large fraction of still heavier elements made by the r and p processes.
1,981 citations
TL;DR: The holographic principle as mentioned in this paper asserts that the fundamental degrees of freedom involved in a unified description of spacetime and matter must be manifest in an underlying quantum theory of gravity, and it has yet to be explained.
Abstract: There is strong evidence that the area of any surface limits the information content of adjacent spacetime regions, at $1.4\ifmmode\times\else\texttimes\fi{}{10}^{69}$ bits per square meter. This article reviews the developments that have led to the recognition of this entropy bound, placing special emphasis on the quantum properties of black holes. The construction of light sheets, which associate relevant spacetime regions to any given surface, is discussed in detail. This article explains how the bound is tested, and its validity is demonstrated in a wide range of examples. A universal relation between geometry and information is thus uncovered. It has yet to be explained. The holographic principle asserts that its origin must lie in the number of fundamental degrees of freedom involved in a unified description of spacetime and matter. It must be manifest in an underlying quantum theory of gravity. This article surveys some successes and challenges in implementing the holographic principle.
1,706 citations
TL;DR: In this paper, a review of double quantum dot studies for realizing solid state quantum bits is presented and the evolution of discrete energy levels in the magnetic field is studied, where the double-quantum dot geometry allows for an accurate determination of the intrinsic lifetime of discrete states in quantum dots.
Abstract: Electron transport experiments on two lateral quantum dots coupled in series are reviewed. An introduction to the charge stability diagram is given in terms of the electrochemical potentials of both dots. Resonant tunneling experiments show that the double dot geometry allows for an accurate determination of the intrinsic lifetime of discrete energy states in quantum dots. The evolution of discrete energy levels in magnetic field is studied. The resolution allows one to resolve avoided crossings in the spectrum of a quantum dot. With microwave spectroscopy it is possible to probe the transition from ionic bonding (for weak interdot tunnel coupling) to covalent bonding (for strong interdot tunnel coupling) in a double dot artificial molecule. This review is motivated by the relevance of double quantum dot studies for realizing solid state quantum bits.
1,627 citations
TL;DR: The cubic complex Ginzburg-Landau equation is one of the most-studied nonlinear equations in the physics community as mentioned in this paper, it describes a vast variety of phenomena from nonlinear waves to second-order phase transitions, from superconductivity, superfluidity, and Bose-Einstein condensation to liquid crystals and strings in field theory.
Abstract: The cubic complex Ginzburg-Landau equation is one of the most-studied nonlinear equations in the physics community. It describes a vast variety of phenomena from nonlinear waves to second-order phase transitions, from superconductivity, superfluidity, and Bose-Einstein condensation to liquid crystals and strings in field theory. The authors give an overview of various phenomena described by the complex Ginzburg-Landau equation in one, two, and three dimensions from the point of view of condensed-matter physicists. Their aim is to study the relevant solutions in order to gain insight into nonequilibrium phenomena in spatially extended systems.
1,557 citations
TL;DR: In this paper, the properties of quasi-two-dimensional semiconductor quantum dots are reviewed, and the formation of the so-called maximum-density droplet and its edge reconstruction is discussed.
Abstract: The properties of quasi-two-dimensional semiconductor quantum dots are reviewed. Experimental techniques for measuring the electronic shell structure and the effect of magnetic fields are briefly described. The electronic structure is analyzed in terms of simple single-particle models, density-functional theory, and "exact" diagonalization methods. The spontaneous magnetization due to Hund's rule, spin-density wave states, and electron localization are addressed. As a function of the magnetic field, the electronic structure goes through several phases with qualitatively different properties. The formation of the so-called maximum-density droplet and its edge reconstruction is discussed, and the regime of strong magnetic fields in finite dot is examined. In addition, quasi-one-dimensional rings, deformed dots, and dot molecules are considered. (Less)
1,133 citations
TL;DR: In this article, the authors show how quantum information theory extends traditional information theory by exploring the limits imposed by quantum, rather than classical, mechanics on information storage and transmission, and show that quantum computers can achieve enhanced speed over their classical counterparts using information-theoretic arguments.
Abstract: Quantum mechanics and information theory are among the most important scientific discoveries of the last century. Although these two areas initially developed separately, it has emerged that they are in fact intimately related. In this review the author shows how quantum information theory extends traditional information theory by exploring the limits imposed by quantum, rather than classical, mechanics on information storage and transmission. The derivation of many key results differentiates this review from the usual presentation in that they are shown to follow logically from one crucial property of relative entropy. Within the review, optimal bounds on the enhanced speed that quantum computers can achieve over their classical counterparts are outlined using information-theoretic arguments. In addition, important implications of quantum information theory for thermodynamics and quantum measurement are intermittently discussed. A number of simple examples and derivations, including quantum superdense coding, quantum teleportation, and Deutsch's and Grover's algorithms, are also included.
976 citations
TL;DR: A review of recent advances in the physics of strongly interacting charged systems functioning in water at room temperature can be found in this article, which discusses the universal theory of charge inversion based on the idea of a strongly correlated liquid of adsorbed counterions, similar to a Wigner crystal.
Abstract: The authors review recent advances in the physics of strongly interacting charged systems functioning in water at room temperature. In these systems, many phenomena go beyond the framework of mean-field theories, whether linear Debye-H\"uckel or nonlinear Poisson-Boltzmann, culminating in charge inversion---a counterintuitive phenomenon in which a strongly charged particle, called a macroion, binds so many counterions that its net charge changes sign. The review discusses the universal theory of charge inversion based on the idea of a strongly correlated liquid of adsorbed counterions, similar to a Wigner crystal. This theory has a vast array of applications, particularly in biology and chemistry; for example, in the presence of positive multivalent ions (e.g., polycations), the DNA double helix acquires a net positive charge and drifts as a positive particle in an electric field. This simplifies DNA uptake by the cell as needed for gene therapy, because the cell membrane is negatively charged. Analogies of charge inversion to other fields of physics are also discussed.
969 citations
TL;DR: A variety of observations suggest that magnetic fields are present in all galaxies and galaxy clusters as mentioned in this paper, but fundamental questions concerning the nature of the dynamo as well as the origin of the seed fields necessary to prime it remain unclear.
Abstract: A variety of observations suggest that magnetic fields are present in all galaxies and galaxy clusters. These fields are characterized by a modest strength ${(10}^{\ensuremath{-}7}\char21{}{10}^{\ensuremath{-}5}\mathrm{G})$ and huge spatial scale $(\ensuremath{\lesssim}1\mathrm{Mpc}).$ It is generally assumed that magnetic fields in spiral galaxies arise from the combined action of differential rotation and helical turbulence, a process known as the \ensuremath{\alpha}\ensuremath{\omega} dynamo. However, fundamental questions concerning the nature of the dynamo as well as the origin of the seed fields necessary to prime it remain unclear. Moreover, the standard \ensuremath{\alpha}\ensuremath{\omega} dynamo does not explain the existence of magnetic fields in elliptical galaxies and clusters. The author summarizes what is known observationally about magnetic fields in galaxies, clusters, superclusters, and beyond. He then reviews the standard dynamo paradigm, the challenges that have been leveled against it, and several alternative scenarios. He concludes with a discussion of astrophysical and early-Universe candidates for seed fields.
861 citations
TL;DR: A review of single-bubble sonoluminescence can be found in this article, where the authors survey the major areas of research in this field and present an overview of what is known and outlines some directions for future research.
Abstract: Single-bubble sonoluminescence occurs when an acoustically trapped and periodically driven gas bubble collapses so strongly that the energy focusing at collapse leads to light emission. Detailed experiments have demonstrated the unique properties of this system: the spectrum of the emitted light tends to peak in the ultraviolet and depends strongly on the type of gas dissolved in the liquid; small amounts of trace noble gases or other impurities can dramatically change the amount of light emission, which is also affected by small changes in other operating parameters (mainly forcing pressure, dissolved gas concentration, and liquid temperature). This article reviews experimental and theoretical efforts to understand this phenomenon. The currently available information favors a description of sonoluminescence caused by adiabatic heating of the bubble at collapse, leading to partial ionization of the gas inside the bubble and to thermal emission such as bremsstrahlung. After a brief historical review, the authors survey the major areas of research: Section II describes the classical theory of bubble dynamics, as developed by Rayleigh, Plesset, Prosperetti, and others, while Sec. III describes research on the gas dynamics inside the bubble. Shock waves inside the bubble do not seem to play a prominent role in the process. Section IV discusses the hydrodynamic and chemical stability of the bubble. Stable single-bubble sonoluminescence requires that the bubble be shape stable and diffusively stable, and, together with an energy focusing condition, this fixes the parameter space where light emission occurs. Section V describes experiments and models addressing the origin of the light emission. The final section presents an overview of what is known, and outlines some directions for future research.
843 citations
TL;DR: In this article, the authors provide a review of grain boundary properties and their applications in high-Tc superconductivity and high-power and electronic device applications, as well as the theoretical models developed to describe grain boundary behavior.
Abstract: Since the first days of high-Tc superconductivity, the materials science and the physics of grain boundaries in superconducting compounds have developed into fascinating fields of research. Unique electronic properties, different from those of the grain boundaries in conventional metallic superconductors, have made grain boundaries formed by high-Tc cuprates important tools for basic science. They are moreover a key issue for electronic and large-scale applications of high-Tc superconductivity. The aim of this review is to give a summary of this broad and dynamic field. Starting with an introduction to grain boundaries and a discussion of the techniques established to prepare them individually and in a well-defined manner, the authors present their structure and transport properties. These provide the basis for a survey of the theoretical models developed to describe grain-boundary behavior. Following these discussions, the enormous impact of grain boundaries on fundamental studies is reviewed, as well as high-power and electronic device applications.
TL;DR: In this paper, the authors describe the discovery and study of BoseEinstein condensates (BECs) in atomic gases from a personal perspective, and describe how they were used to explore quantum-degenerate gases, such as BECs first realized in 1995.
Abstract: The lure of lower temperatures has attracted physicists for the past century, and with each advance towards absolute zero, new and rich physics has emerged. Laypeople may wonder why ‘‘freezing cold’’ is not cold enough. But imagine how many aspects of nature we would miss if we lived on the surface of the sun. Without inventing refrigerators, we would only know gaseous matter and never observe liquids or solids, and miss the beauty of snowflakes. Cooling to normal earthly temperatures reveals these dramatically different states of matter, but this is only the beginning: many more states appear with further cooling. The approach into the kelvin range was rewarded with the discovery of superconductivity in 1911 and of superfluidity in helium-4 in 1938. Cooling into the millikelvin regime revealed the superfluidity of helium-3 in 1972. The advent of laser cooling in the 1980s opened up a new approach to ultralow-temperature physics. Microkelvin samples of dilute atom clouds were generated and used for precision measurements and studies of ultracold collisions. Nanokelvin temperatures were necessary to explore quantum-degenerate gases, such as Bose-Einstein condensates first realized in 1995. Each of these achievements in cooling has been a major advance, and recognized with a Nobel prize. This paper describes the discovery and study of BoseEinstein condensates (BEC’s) in atomic gases from my personal perspective. Since 1995, this field has grown explosively, drawing researchers from the communities of atomic physics, quantum optics, and condensedmatter physics. The trapped ultracold vapor has emerged as a new quantum system that is unique in the precision and flexibility with which it can be controlled and manipulated. At least 30 groups have now created condensates, and the publication rate on Bose-Einstein condensation has soared following the discovery of the gaseous condensates in 1995 (see Fig. 1).
TL;DR: Bose-Einstein condensation has a long and rich history dating from the early 1920s as mentioned in this paper, and some of the developments in physics that made possible the successful pursuit of BEC in a gas.
Abstract: Bose-Einstein condensation, or BEC, has a long and rich history dating from the early 1920s. In this article we will trace briefly over this history and some of the developments in physics that made possible our successful pursuit of BEC in a gas. We will then discuss what was involved in this quest. In this discussion we will go beyond the usual technical description to try and address certain questions that we now hear frequently, but are not covered in our past research papers. These are questions along the lines of: How did you get the idea and decide to pursue it? Did you know it was going to work? How long did it take you and why? We will review some our favorites from among the experiments we have carried out with BEC. There will then be a brief encore on why we are optimistic that BEC can be created with nearly any species of magnetically trappable atom. Throughout this article we will try to explain what makes BEC in a dilute gas so interesting, unique, and experimentally ${\mathrm{challenging}.}^{1}$
TL;DR: A review of the history, current status, physical mechanisms, experimental methods, and applications of nonlinear magneto-optical effects in atomic vapors can be found in this paper.
Abstract: The authors review the history, current status, physical mechanisms, experimental methods, and applications of nonlinear magneto-optical effects in atomic vapors. They begin by describing the pioneering work of Macaluso and Corbino over a century ago on linear magneto-optical effects (in which the properties of the medium do not depend on the light power) in the vicinity of atomic resonances. These effects are then contrasted with various nonlinear magneto-optical phenomena that have been studied both theoretically and experimentally since the late 1960s. In recent years, the field of nonlinear magneto-optics has experienced a revival of interest that has led to a number of developments, including the observation of ultranarrow (1-Hz) magneto-optical resonances, applications in sensitive magnetometry, nonlinear magneto-optical tomography, and the possibility of a search for parity- and time-reversal-invariance violation in atoms.
TL;DR: In this paper, the authors present the basic formalism underlying ab initio phase diagram calculations, along with the generalization required to account for lattice vibrations, and provide a clear picture of the origin of vibrational entropy differences between phases in an alloy system that goes beyond the traditional bond counting and volume change arguments.
Abstract: A long-standing limitation of first-principles calculations of substitutional alloy phase diagrams is the difficulty in accounting for lattice vibrations. A survey of the theoretical and experimental literature seeking to quantify the effect of lattice vibrations on phase stability indicates that they can be significant. Typical vibrational entropy differences between phases are of the order of 0.1 to 0.2kB/atom, which is comparable to the typical values of configurational entropy differences in binary alloys (at most 0.693kB/atom). This article presents the basic formalism underlying ab initio phase diagram calculations, along with the generalization required to account for lattice vibrations. The authors review the various techniques allowing the theoretical calculation and the experimental determination of phonon dispersion curves and related thermodynamic quantities, such as vibrational entropy or free energy. A clear picture of the origin of vibrational entropy differences between phases in an alloy system is presented that goes beyond the traditional bond counting and volume change arguments. Vibrational entropy change can be attributed to the changes in chemical bond stiffness associated with the changes in bond length that take place during a phase transformation. This so-called “bond stiffness vs bond length” interpretation both summarizes the key phenomenon driving vibrational entropy changes and provides a practical tool to model them.
TL;DR: How quantum physics allows information coding in classically unexpected and subtle nonlocal ways, as well as information processing with an efficiency largely surpassing that of the present and foreseeable classical computers is reviewed.
Abstract: Quantum theory has found a new field of application in the realm of information and computation during recent years. This paper reviews how quantum physics allows information coding in classically unexpected and subtle nonlocal ways, as well as information processing with an efficiency largely surpassing that of the present and foreseeable classical computers. Some notable aspects of classical and quantum information theory will be addressed here. Quantum teleportation, dense coding, and quantum cryptography are discussed as examples of the impact of quanta on the transmission of information. Quantum logic gates and quantum algorithms are also discussed as instances of the improvement made possible in information processing by a quantum computer. Finally the authors provide some examples of current experimental realizations for quantum computers and future prospects.
TL;DR: In this article, the authors review the physics of ultrafast dynamics in semiconductors and their heterostructures, including both the observed experimental phenomena and the theoretical description of the processes.
Abstract: The authors review the physics of ultrafast dynamics in semiconductors and their heterostructures, including both the observed experimental phenomena and the theoretical description of the processes. These are probed by ultrafast optical excitation, generating nonequilibrium states that can be monitored by time-resolved spectroscopy. Light pulses create coherent superpositions of states, and the dynamics of the associated phase relationships can be directly investigated by means of many-pulse experiments. The commonly used experimental techniques are briefly reviewed. A variety of different phenomena can be described within a common theoretical framework based on the density-matrix formalism. The important interactions of the carriers included in the theoretical description are the phonon interactions, the interactions with classical and quantum light fields, and the Coulomb interaction among the carriers themselves. These interactions give rise to a strong interplay between phase coherence and relaxation, which strongly affects the non equilibrium dynamics. Based on the general theory, the authors review the physical phenomena in various semiconductor structures including superlattices, quantum wells, quantum wires, and bulk media. Particular results which have played a central role in understanding the microscopic origins of the relaxation processes are discussed in detail.
TL;DR: In this paper, an overview of the differential geometry of curves and surfaces using examples from soft matter as illustrations is presented, which requires a background only in vector calculus and is otherwise self-contained.
Abstract: This article presents an overview of the differential geometry of curves and surfaces using examples from soft matter as illustrations. The presentation requires a background only in vector calculus and is otherwise self-contained.
TL;DR: The heavy-fermion compound with an order parameter of unconventional symmetry is the only unambiguous case of multiple superconducting phases as mentioned in this paper, however, no single theoretical scenario is completely consistent with all the data.
Abstract: The heavy-fermion compound ${\mathrm{UPt}}_{3}$ is the first compelling example of a superconductor with an order parameter of unconventional symmetry. To this day, it is the only unambiguous case of multiple superconducting phases. Twenty years of experiment and theory on the superconductivity of ${\mathrm{UPt}}_{3}$ are reviewed, with the aim of accounting for the multicomponent phase diagram and identifying the superconducting phases. First, the state above the superconducting critical temperature at ${T}_{c}=0.5\mathrm{K}$ is briefly described: de Haas--van Alphen and other measurements demonstrate that this state is a Fermi liquid, with degeneracy fully achieved at ${T}_{c}.$ This implies that the usual BCS theory of superconductivity should hold, although the strong magnetic interactions suggest the possibility of an unconventional superconducting order parameter. The role of the weak antiferromagnetic order below ${T}_{N}=5\mathrm{K}$ in causing phase multiplicity is examined. A comprehensive analysis of which superconducting states are possible is given, and the theoretical basis for each of the main candidates is considered. The behavior of various properties at low temperature $(T\ensuremath{\ll}{T}_{c})$ is reviewed. The experiments clearly indicate the presence of nodes in the superconducting gap function of all three phases. In particular, the low-temperature low-field phase has a gap with a line node in the basal plane and point nodes along the hexagonal $c$ axis. The phase diagram in the magnetic-field--temperature plane has been determined in detail by ultrasound and thermodynamic measurements. Experiments under pressure indicate a coupling between antiferromagnetism and superconductivity and provide additional clues about the order parameter. Theoretically, Ginzburg-Landau theory is the tool that elucidates the phase diagram, while calculations of the temperature and field dependence of physical quantities have been used to compare different order parameters to experiment. On balance, the data point to a two-component order parameter belonging to either the ${E}_{1g}$ or the ${E}_{2u}$ representation, with degeneracy lifted by a coupling to the symmetry-breaking magnetic order. However, no single theoretical scenario is completely consistent with all the data. The coupling of superconductivity and magnetism may be the weakest link in the current picture of ${\mathrm{UPt}}_{3},$ and full understanding depends on the resolution of this issue.
TL;DR: In this article, all measurements published on the low-temperature thermal conductivity and acoustic attenuation in amorphous solids have been reviewed, on a total of over 60 different compositions.
Abstract: In order to test whether the low-energy excitations explored extensively in amorphous solids are indeed universal, all measurements published on the low-temperature thermal conductivity and acoustic attenuation in these solids have been reviewed, on a total of over 60 different compositions. The ratio of the phonon wavelength \ensuremath{\lambda} to the phonon mean free path l has been found to lie between ${10}^{\ensuremath{-}3}$ and ${10}^{\ensuremath{-}2}$ in almost all cases, independent of chemical composition and frequency (wavelength) of the elastic waves, which varied by more than nine orders of magnitude in the different experiments. When the data were fitted with the tunneling model, which is based on the assumption of atomic or molecular tunneling states with a certain spectral distribution, the tunneling strength C, which describes their coupling to the lattice, was found to range from ${10}^{\ensuremath{-}4}$ to ${10}^{\ensuremath{-}3}$ in almost all cases. The only exceptions reported so far are certain films of amorphous silicon, germanium, and carbon. In these films, low-temperature acoustic attenuations over two orders of magnitude smaller have been observed compared to all other amorphous solids. Another remarkable observation is that a large number of disordered crystals, and even a thermally equilibrated quasicrystal, have low-energy lattice vibrations that are quantitatively indistinguishable from those of amorphous solids. Their tunneling strengths also range from ${10}^{\ensuremath{-}4}$ to ${10}^{\ensuremath{-}3}.$ These measurements have also been reviewed. It is concluded that the absence of long-range order is neither sufficient nor necessary for the existence of the low-energy excitations.
TL;DR: In this article, the authors review the use of core-level resonant photoemission and resonant Auger spectroscopy to study femtosecond charge transfer dynamics.
Abstract: The authors review the use of core-level resonant photoemission and resonant Auger spectroscopy to study femtosecond charge-transfer dynamics. Starting from simple models of the relevant processes, they examine the rationale for this approach and illustrate the approximations and known subtleties for the inexperienced experimentalist. Detailed analysis of case studies of increasing complexity are taken up, as well as the connection to related approaches using both valence excitation and the core-level fluorescent channel.
TL;DR: In this article, the authors present a chronological survey of the main ideas behind the lattice Boltzmann method with special focus on the role played by the $H$ theorem in enforcing compliance of the method with macroscopic evolutionary constraints (the second law) as well as in serving as a numerically stable computational tool for fluid flows and other dissipative systems out of equilibrium.
Abstract: In the last decade, minimal kinetic models, and primarily the lattice Boltzmann equation, have met with significant success in the simulation of complex hydrodynamic phenomena, ranging from slow flows in grossly irregular geometries to fully developed turbulence, to flows with dynamic phase transitions. Besides their practical value as efficient computational tools for the dynamics of complex systems, these minimal models may also represent a new conceptual paradigm in modern computational statistical mechanics: instead of proceeding bottom-up from the underlying microdynamic systems, these minimal kinetic models are built top-down starting from the macroscopic target equations. This procedure can provide dramatic advantages, provided the essential physics is not lost along the way. For dissipative systems, one essential requirement is compliance with the second law of thermodynamics. In this Colloquium, the authors present a chronological survey of the main ideas behind the lattice Boltzmann method, with special focus on the role played by the $H$ theorem in enforcing compliance of the method with macroscopic evolutionary constraints (the second law) as well as in serving as a numerically stable computational tool for fluid flows and other dissipative systems out of equilibrium.
TL;DR: The status of neutrino oscillation searches employing nuclear reactors as sources is reviewed in this article, where the authors present a detailed review of the current state of the art in the field.
Abstract: The status of neutrino oscillation searches employing nuclear reactors as sources is reviewed. This technique, a direct continuation of the experiments that proved the existence of neutrinos, is today an essential tool in investigating the indications of oscillations found in studying neutrinos produced in the sun and in the earth’s atmosphere. The low energy of the reactor νe makes them ideal for exploring oscillations with small mass differences and relatively large mixing angles. In the last several years the determination of the reactor antineutrino flux and spectrum has reached a high degree of accuracy. Hence measurements of these quantities at a given distance L can be readily compared with the expectation at L=0, thus testing the disappearance of νe. Two recent experiments, CHOOZ and PALO VERDE, with baselines of about 1 km and sensitive to the neutrino mass differences associated with the atmospheric neutrino anomaly have collected data and published results recently. An ambitious project with a baseline of more than 100 km, KAMLAND, has now began to take data. This last reactor experiment will have a sensitivity sufficient to explore part of the oscillation phase space relevant to solar neutrino scenarios. It is the only envisioned experiment with a terrestrial source of neutrinos capable of addressing the solar neutrino puzzle.
TL;DR: The first successful experiments at the sodium facilities in Riga and Karlsruhe, and on other experiments which were carried out or planned at various places in the world were reported in this paper.
Abstract: Cosmic magnetic fields, including the fields of planets, stars, and galaxies, are believed to be caused by dynamo action in moving electrically conducting fluids. While the theory and numerics of hydromagnetic dynamos have flourished during recent decades, an experimental validation of the effect was missing until recently. We sketch the long history towards a working laboratory dynamo. We report on the first successful experiments at the sodium facilities in Riga and Karlsruhe, and on other experiments which are carried out or planned at various places in the world.
TL;DR: In this paper, the authors present theoretical understanding of photons and hard photoproduction processes, discussing the production of jets, light and heavy hadrons, quarkonia, and prompt photons in photon-photon and photon-hadron collisions.
Abstract: The author reviews the present theoretical understanding of photons and hard photoproduction processes, discussing the production of jets, light and heavy hadrons, quarkonia, and prompt photons in photon-photon and photon-hadron collisions. Virtual and polarized photons and prompt-photon production in hadron collisions are also discussed. The most important leading-order and next-to-leading-order quantum chromodynamics results are compiled in analytic form. A large variety of numerical predictions is compared to data from TRISTAN, LEP, and HERA and extended to future electron and muon colliders. The sources of all relevant results are collected in an extensive bibliography.
TL;DR: In this article, the atomic structure of carbon nanotubes is deduced from high-resolution electron microscopy and electron diffraction in transmission through a single nanotube, and the principal features of the observed micrographs are interpreted in terms of the cylindrical, chiral geometry of the atomic distribution of single-wall or multi-wall nanotsubes.
Abstract: This colloquium discusses the atomic structure of carbon nanotubes as deduced from high-resolution electron microscopy and electron diffraction in transmission through a single nanotube. The principal features of the observed micrographs are interpreted in terms of the cylindrical, chiral geometry of the atomic distribution of single-wall or multiwall nanotubes. In order to better understand the mechanism of image formation in electron diffraction, the authors propose optical simulation experiments using a laser pointer and a little ``diffraction laboratory on a slide.'' The simulations visibly reproduce all the features of the observed electron micrographs, namely, the quasihexagonal patterns of Bragg spots, the streaked nature of the spots, the doubling of the spot number induced by chirality, etc. The present colloquium should allow a general readership to appreciate the continuing efficiency and power of diffraction methods for the determination of the structure of macromolecules.
TL;DR: In this paper, the development of weak links in superfluid superconductors has been described, and the basic techniques used to study this system are reviewed and the experimental and theoretical milestones that have led to their present understanding.
Abstract: Josephson weak links between samples of macroscopic quantum systems such as superconductors, superfluids, and Bose-Einstein condensates provide a unique tool with which to explore quantum mechanics and an opportunity to create applications based on macroscopic quantum physics. In this review we describe the development of the field of weak links in superfluid ${}^{3}\mathrm{He}.$ We review the basic techniques used to study this system and then describe the experimental and theoretical milestones that have led to our present understanding.
TL;DR: The state of the art and the path to future progress in high-spatial-resolution imaging interferometry is reviewed in this article, with a focus on the problems specific to delay lines, beam recombination, polarization, dispersion, fringe tracking, bootstrapping and cophasing.
Abstract: The present ``state of the art'' and the path to future progress in high-spatial-resolution imaging interferometry is reviewed. The review begins with a treatment of the fundamentals of stellar optical interferometry, the origin, properties, and optical effects of turbulence in the Earth's atmosphere, the passive methods such as speckle interferometry that are applied on a single telescope to overcome atmospheric image degradation, and various other techniques. These topics include differential speckle interferometry, speckle spectroscopy and polarimetry, phase diversity, wave-front shearing interferometry, phase-closure methods, dark speckle imaging, as well as the limitations imposed by the detectors on the performance of speckle imaging. A brief account is given of the technological innovation of adaptive optics to compensate for atmospheric effects on the image in real time. A major advancement involves the transition from single-aperture to dilute-aperture interferometry using multiple telescopes. Therefore the review deals with recent developments involving ground-based and space-based optical arrays. Emphasis is placed on the problems specific to delay lines, beam recombination, polarization, dispersion, fringe tracking, bootstrapping, coherencing and cophasing, and recovery of the visibility functions. The role of adaptive optics in enhancing visibilities is also discussed. The applications of interferometry, such as imaging, astrometry, and nulling, are described. The mathematical intricacies of the various ``postdetection'' image-processing techniques are examined critically. The review concludes with a discussion of the astrophysical importance and the prospects of interferometry.
TL;DR: In this paper, the authors discuss the issues relating to high-average-power light sources and introduce an important new class of light sources, energy-recovering linacs, which leads to high overall efficiency and scales favorably to systems with even higher average power.
Abstract: Free-electron-laser (FEL) oscillators have only recently achieved their original promise as producers of high-power, short-wavelength, tunable radiation. Room-temperature accelerator systems have generally had limited duty factor due to excessive Ohmic losses on cavity walls. The application of superconducting radio-frequency (SRF) technology has now permitted an increase by more than two orders of magnitude in FEL average power due just to increased duty factor in continuous-wave operation. A concurrent technical development that leveraged the high efficiency of SRF linacs was the demonstration of beam energy recovery while lasing. This leads to high overall efficiency and scales favorably to systems with even higher average power. This paper will discuss the issues relating to high-average-power light sources. The planned and demonstrated performance of several FEL facilities will illustrate the sizable advantages that superconducting radio frequency offers for high average flux and output multiplexing for several simultaneous users. An important new class of light sources, energy-recovering linacs, will be introduced.