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We use a spatially resolved cavity ring-down technique to show that the 2D eigenmode of an unstable optical cavity has a fractal pattern, i.e. it looks the same at different length scales. In agreement with theory, we find that this pattern has the maximum conceivable roughness, i.e., its fractal dimension is 3.01 plus\minus 0.04. This insight in the nature of unstable cavity eigenmodes may lead to better understanding of wave dynamics in open systems, for both light and matter waves.
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arxiv:physics/0304046
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Fundamental and vortex solitons in a two-dimensional optically induced waveguide array are reported. In the strong localization regime, the fundamental soliton is largely confined to one lattice site, while the vortex state comprises of four fundamental modes superimposed in a square configuration with a phase structure that is topologically equivalent to the conventional vortex. However, in the weak localization regime, both the fundamental and vortex solitons spread over many lattice sites. We further show that fundamental and vortex solitons are stable against small perturbations in the strong localization regime.
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arxiv:physics/0304047
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Seeing the Earth crust as crisscrossed by faults filled with fluid at close to lithostatic pressures, we develop a model in which its elastic modulii are different in net tension versus compression. In constrast with standard nonlinear effects, this ``threshold nonlinearity'' is non-perturbative and occurs for infinitesimal perturbations around the lithostatic pressure taken as the reference. For a given earthquake source, such nonlinear elasticity is shown to (i) rotate, widen or narrow the different lobes of stress transfer, (ii) to modify the $1/r^2$ 2D-decay of elastic stress Green functions into the generalized power law $1/r^{\gamma}$ where $\gamma$ depends on the azimuth and on the amplitude of the modulii asymmetry. Using reasonable estimates, this implies an enhancement of the range of interaction between earthquakes by a factor up to 5-10 at distances of several tens of rupture length. This may explain certain long-range earthquake triggering and hydrological anomalies in wells and suggest to revisit the standard stress transfer calculations which use linear elasticity. We also show that the standard double-couple of forces representing an earthquake source leads to an opening of the corresponding fault plane, which suggests a mechanism for the non-zero isotropic component of the seismic moment tensor observed for some events.
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arxiv:physics/0304054
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In the study of weakly turbulent wave systems possessing incomplete self-similarity it is possible to use dimensional arguments to derive the scaling exponents of the Kolmogorov-Zakharov spectra, provided the order of the resonant wave interactions responsible for nonlinear energy transfer is known. Furthermore one can easily derive conditions for the breakdown of the weak turbulence approximation. It is found that for incompletely self-similar systems dominated by three wave interactions, the weak turbulence approximation usually cannot break down at small scales. It follows that such systems cannot exhibit small scale intermittency. For systems dominated by four wave interactions, the incomplete self-similarity property implies that the scaling of the interaction coefficient depends only on the physical dimension of the system. These results are used to build a complete picture of the scaling properties of the surface wave problem where both gravity and surface tension play a role. We argue that, for large values of the energy flux, there should be two weakly turbulent scaling regions matched together via a region of strongly nonlinear turbulence.
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arxiv:physics/0304077
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We investigate the experimental spectra of excited NO molecules in the diamagnetic regime and develop a quantitative semiclassical framework to account for the results. We show the dynamics can be interpreted in terms of classical orbits provided that in addition to the geometric orbits, diffractive effects are appropriately taken into account. We also show how individual orbits can be extracted from the experimental signal and use this procedure to reveal the first experimental manifestation of inelastic diffractive orbits.
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arxiv:physics/0304096
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We comment about the general argument given to obtain the rocket equation as it is exposed in standard textbooks. In our opinion, it can induce students to a wrong answer when solving variable mass problems.
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arxiv:physics/0304113
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Two paradoxical aspects of the prevailing kinetic equations are presented. One is related to the usual understanding of distribution function and the other to the usual understanding of the phase space. With help of simple counterexamples and direct analyses, involved paradoxes manifest themselves.
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arxiv:physics/0305006
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Lobster-ISS is a revolutionary astrophysical X-ray all-sky monitor scheduled for deployment as an attached payload on the International Space Station (ISS) in 2009. Using a new wide field-of-view focusing optic, Lobster-ISS provides an order-of-magnitude improvement in the sensitivity of all-sky monitors in the soft X-ray band (0.1-3.0 keV). This lobster-eye optic presents unique challenges to the imaging X-ray detector at its focus. Micro-patterned imaging proportional counters, with thier mechanical simplicity and high performance, are the most practical means of meeting the requirements. We describe our design for the Lobster-ISS imaging detector based on direct-imaging micro-well proportional counters and the expected performance.
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arxiv:physics/0305025
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When developing and assessing density functional theory methods, a finite basis set is usually employed. In most cases, however, the issue of basis set dependency is neglected. Here, we assess several basis sets and functionals. In addition, the dependency of the semiempirical fits to a given basis set for a generalised gradient approximation and a hybrid functional is investigated. The resulting functionals are then tested for other basis sets, evaluating their errors and transferability.
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arxiv:physics/0305060
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We concern ourselves with the self-induced charge currents in electromagnetic materials and some related topics on its effects in the present paper. The contribution of self-induced charge currents of metamaterial media to photon effective rest mass is briefly discussed. We concentrate primarily on the torque, which is caused by the interaction of self-induced charge currents in dilute plasma with interstellar magnetic fields, acting on the torsion balance in the torsion balance experiment. It is shown by our evaluation that the muons and alpha-particles in secondary cosmic rays will contribute an effective rest mass about 10^{-54} Kg to the photon, which is compared to the newly obtained upper limit on photon rest mass in Luo's rotating torsion balance experiment.
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arxiv:physics/0305076
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The vibration stability requirements for the Next Linear Collider (NLC) are far more stringent than for the previous generation of Colliders. To meet these goals, it is imperative that the effects of vibration on NLC Linac components from near-field sources (e.g. compressors, high vacuum equipment, klystrons, modulators, pumps, fans, etc) be well understood. The civil construction method, whether cut-and-cover or parallel bored tunnels, can determine the proximity and possible isolation of noise sources. This paper presents a brief summary and analysis of recently completed and planned studies for characterization of near-field vibration sources under either construction method. The results of in-situ vibration measurements will also be included.
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arxiv:physics/0305115
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We report on a new test of Lorentz invariance performed by comparing the resonance frequencies of two orthogonal cryogenic optical resonators subject to Earth's rotation over 1 year. For a possible anisotropy of the speed of light c, we obtain 2.6 +/- 1.7 parts in 10^15. Within the Robertson-Mansouri-Sexl test theory, this implies an isotropy violation parameter beta - delta - 1/2 of -2.2 +/- 1.5 parts in 10^9, about three times lower than the best previous result. Within the general extension of the standard model of particle physics, we extract limits on 7 parameters at accuracies down to a part in 10^15, improving the best previous result by about two orders of magnitude.
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arxiv:physics/0305117
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It is shown that, in spite of the appearances, the standard expression for the oscillation probability of ultrarelativistic neutrinos is Lorentz invariant.
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arxiv:physics/0305122
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Since its release in 1999, the LHC experiments have been evaluating GEANT4 in view of adopting it as a replacement for the obsolescent GEANT3 transport MonteCarlo. The ALICE collaboration has decided to perform a detailed physics validation of elementary hadronic processes against experimental data already used in international benchmarks. In one test, proton interactions on different nuclear targets have been simulated, and the distribution of outgoing particles has been compared to data. In a second test, penetration of quasi-monoenergetic low energy neutrons through a thick shielding has been simulated and again compared to experimental data. In parallel, an effort has been put on the integration of GEANT4 in the AliRoot framework. An overview of the present status of ALICE GEANT4 simulation and the remaining problems will be presented. This document will describe in detail the results of these tests, together with the improvements that the GEANT4 team has made to the program as a result of the feedback received from the ALICE collaboration. We will also describe the remaining problems that have been communicated to GEANT4 but not yet addressed.
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arxiv:physics/0306025
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This paper analyzes the consequences of electric current generation at the front of the Bow Shock (BS) and the dependence of the direction of this current on the IMF. The conditions of this current closure through the body of the magnetosphere are discussed. It is shown that the process of penetration of the external current into magnetized plasma has a two-stage character. Initially, a change in current on the boundary gives rise to a region of surface charge, the field of which polarizes the near-wall layer with the thickness on the order of one gyroradius of protons. The polarization process involves the formation of the displacement current which produces the Ampere force accelerating the plasma inside the double layer. When the plasma velocity reaches the electric drift velocity (within a time on the order of the inverse gyrofrequency of protons), the electric field in this plasma disappears, whereas in a fixed frame of reference, on the contrary, it reaches equilibrium values. The front of variation of the electric field penetrates the plasma with the velocity of a fast magnetosonic wave. A change in the convection velocity field causes a redistribution of plasma pressure. The appearance of corresponding gradients signifies the penetration of current into plasma. The gradients are changing until a new steady state is reached, to which the new convection velocity field and the new plasma pressure field correspond. This new state is reached in a time which is estimated.
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arxiv:physics/0306041
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Using only lidar or radar an accurate cloud boundary height estimate is often not possible. The combination of lidar and radar can give a reliable cloud boundary estimate in a much broader range of cases. However, also this combination with standard methods still can not measure the cloud boundaries in all cases. This will be illustrated with data from the Clouds and Radiation measurement campaigns, CLARA. Rain is a problem: the radar has problems to measure the small cloud droplets in the presence of raindrops. Similarly, few large particles below cloud base can obscure the cloud base in radar measurements. And the radar reflectivity can be very low at the cloud base of water clouds or in large regions of ice clouds, due to small particles. Multiple cloud layers and clouds with specular reflections can pose problems for lidar. More advanced measurement techniques are suggested to solve these problems. An angle scanning lidar can, for example, detect specular reflections, while using information from the radars Doppler velocity spectrum may help to detect clouds during rain.
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arxiv:physics/0306069
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Despite of their success, the results of first-principles quantum mechanical calculations contain inherent numerical errors caused by various approximations. We propose here a neural-network algorithm to greatly reduce these inherent errors. As a demonstration, this combined quantum mechanical calculation and neural-network correction approach is applied to the evaluation of standard heat of formation $\DelH$ and standard Gibbs energy of formation $\DelG$ for 180 organic molecules at 298 K. A dramatic reduction of numerical errors is clearly shown with systematic deviations being eliminated. For examples, the root--mean--square deviation of the calculated $\DelH$ ($\DelG$) for the 180 molecules is reduced from 21.4 (22.3) kcal$\cdotp$mol$^{-1}$ to 3.1 (3.3) kcal$\cdotp$mol$^{-1}$ for B3LYP/6-311+G({\it d,p}) and from 12.0 (12.9) kcal$\cdotp$mol$^{-1}$ to 3.3 (3.4) kcal$\cdotp$mol$^{-1}$ for B3LYP/6-311+G(3{\it df},2{\it p}) before and after the neural-network correction.
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arxiv:physics/0306075
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The bremsstrahlung energy loss distribution of electrons propagating in matter is highly non Gaussian. Because the Kalman filter relies solely on Gaussian probability density functions, it might not be an optimal reconstruction algorithm for electron tracks. A Gaussian-sum filter (GSF) algorithm for electron track reconstruction in the CMS tracker has therefore been developed. The basic idea is to model the bremsstrahlung energy loss distribution by a Gaussian mixture rather than a single Gaussian. It is shown that the GSF is able to improve the momentum resolution of electrons compared to the standard Kalman filter. The momentum resolution and the quality of the estimated error are studied with various types of mixture models of the energy loss distribution.
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arxiv:physics/0306087
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The ammonia dimer (NH3)2 has been investigated using high--level ab initio quantum chemistry methods and density functional theory (DFT). The structure and energetics of important isomers is obtained to unprecedented accuracy without resorting to experiment. The global minimum of eclipsed C_s symmetry is characterized by a significantly bent hydrogen bond which deviates from linearity by about 20 degrees. In addition, the so-called cyclic C_{2h} structure is extremely close in energy on an overall flat potential energy surface. It is demonstrated that none of the currently available (GGA, meta--GGA, and hybrid) density functionals satisfactorily describe the structure and relative energies of this nonlinear hydrogen bond. We present a novel density functional, HCTH/407+, designed to describe this sort of hydrogen bond quantitatively on the level of the dimer, contrary to e.g. the widely used BLYP functional. This improved functional is employed in Car-Parrinello ab initio molecular dynamics simulations of liquid ammonia to judge its performance in describing the associated liquid. Both the HCTH/407+ and BLYP functionals describe the properties of the liquid well as judged by analysis of radial distribution functions, hydrogen bonding structure and dynamics, translational diffusion, and orientational relaxation processes. It is demonstrated that the solvation shell of the ammonia molecule in the liquid phase is dominated by steric packing effects and not so much by directional hydrogen bonding interactions. In addition, the propensity of ammonia molecules to form bifurcated and multifurcated hydrogen bonds in the liquid phase is found to be negligibly small.
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arxiv:physics/0306154
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A model for a non-Kerr cylindrical nematic fiber is presented. We use the multiple scales method to show the possibility of constructing different kinds of wavepackets of transverse magnetic (TM) modes propagating through the fiber. This procedure allows us to generate different hierarchies of nonlinear partial differential equations (PDEs) which describe the propagation of optical pulses along the fiber. We go beyond the usual weakly nonlinear limit of a Kerr medium and derive an extended Nonlinear Schrodinger equation (eNLS) with a third order derivative nonlinearity, governing the dynamics for the amplitude of the wavepacket. In this derivation the dispersion, self-focussing and diffraction in the nematic are taken into account. Although the resulting nonlinear $PDE$ may be reduced to the modified Korteweg de Vries equation (mKdV), it also has additional complex solutions which include two-parameter families of bright and dark complex solitons. We show analytically that under certain conditions, the bright solitons are actually double embedded solitons. We explain why these solitons do not radiate at all, even though their wavenumbers are contained in the linear spectrum of the system. Finally, we close the paper by making comments on the advantages as well as the limitations of our approach, and on further generalizations of the model and method presented.
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arxiv:physics/0306189
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Cu,Zn superoxide dismutase (SOD1) has been implicated in the familial form of the neurodegenerative disease Amyotrophic Lateral Sclerosis (ALS). It has been suggested that mutant mediated SOD1 misfolding/aggregation is an integral part of the pathology of ALS. We study the folding thermodynamics and kinetics of SOD1 using a hybrid molecular dynamics approach. We reproduce the experimentally observed SOD1 folding thermodynamics and find that the residues which contribute the most to SOD1 thermal stability are also crucial for apparent two-state folding kinetics. Surprisingly, we find that these residues are located on the surface of the protein and not in the hydrophobic core. Mutations in some of the identified residues are found in patients with the disease. We argue that the identified residues may play an important role in aggregation. To further characterize the folding of SOD1, we study the role of cysteine residues in folding and find that non-native disulfide bond formation may significantly alter SOD1 folding dynamics and aggregation propensity.
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arxiv:physics/0306200
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The calculated double differential cross sections for 60eV energy, where the cross sections are also maximum, agree with the measured results of Shyn (1992) in a much better way compaired to other theories for such energies.
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arxiv:physics/0307025
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The attenuation length and refractive index of liquid xenon for intrinsic scintillation light (178nm) have been measured in a single experiment. The value obtained for attenuation length is 364 +- 18 mm. The refractive index is found to be 1.69 +- 0.02. Both values were measured at a temperature of 170 +- 1 K.
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arxiv:physics/0307044
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We find that the function that describes the surface of spherical aberration free lenses can be used for both positive and negative refractive index media. With the inclusion of negative index, this function assumes the form of all the conic sections and expands the theory of aplanatic optical surfaces. There are two different symmetry centers with respect to the index that create an asymmetric relationship between positive and negative index lens profiles. In the thin lens limit the familiar formulas for image position and magnification hold for any index.
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arxiv:physics/0307088
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In the recent article `Conflict between anthropic reasoning and observation'(gr-qc/0303070) Ken D. Olum, using some inflation-based ideas and the anthropic premise that we should be typical among all intelligent observers in the Universe, arrives at the puzzling conclusion that `we should find ourselves in a large civilization (of galactic size) where most observers should be, while in fact we do not'. In this note we discuss the intriguing possibility whether we could be in fact immersed in a large civilization without being aware of it. Our conclusion is that this possibility cannot be ruled out provided two conditions are met, that we call the Subanthropic Principle and the Undetectability Conjecture. ----- En el reciente articulo `Conflicto entre razonamiento antropico y observacion' Ken D. Olum, basandose en algunas ideas sobre la inflacion cosmologica y en la premisa antropica de que tenemos que ser tipicos entre los observadores inteligentes del Universo, llega a la sorprendente conclusion de que `deberiamos encontrarnos en una civilizacion grande (de tamanio galactico) al igual que la mayoria de los observadores, mientras que de hecho no lo estamos'. En este articulo discutimos la posibilidad de que nuestra civilizacion este de hecho inmersa en una civilizacion grande, sin que seamos conscientes de ello. Nuestra conclusion es que esta posibilidad no puede descartarse si se cumplen dos condiciones, que llamamos el Principio Subantropico y la Conjetura de Indetectabilidad.
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arxiv:physics/0308078
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Two-dimensional fluid simulations of interchange turbulence for geometry and parameters relevant for the scrape-off layer of confined plasmas are presented. We observe bursty ejection of particles and heat from the bulk plasma in the form of blobs. These structures propagate far into the scrape-off layer where they are lost due to transport along open magnetic field lines. From single-point recordings it is shown that the blobs have asymmetric conditional wave forms and lead to positively skewed and flat probability distribution functions. The radial propagation velocity may reach one tenth of the sound speed. These results are in excellent agreement with recent experimental measurements.
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arxiv:physics/0309020
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In CLEAN (Cryogenic Low Energy Astrophysics with Noble gases), a proposed neutrino and dark matter detector, background discrimination is possible if one can determine the location of an ionizing radiation event with high accuracy. We simulate ionizing radiation events that produce multiple scintillation photons within a spherical detection volume filled with liquid neon. We estimate the radial location of a particular ionizing radiation event based on the observed count data corresponding to that event. The count data are collected by detectors mounted at the spherical boundary of the detection volume. We neglect absorption, but account for Rayleigh scattering. To account for wavelength-shifting of the scintillation light, we assume that photons are absorbed and re-emitted at the detectors. Here, we develop spatial Maximum Likelihood methods for event reconstruction, and study their performance in computer simulation experiments. We also study a method based on the centroid of the observed count data. We calibrate our estimates based on training data.
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arxiv:physics/0309033
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At the "Domus Galilaeana" in Pisa, many original documents and records are kept, which belong to the scientific activity carried out by Enrico Fermi until 1938. I compared those documentary sources with the supported evidences, the personal recollections, concerning the discovery that hydrogenated substances increase the radioactivity induced by neutrons: such a comparison leads to the conclusion that the discovery occurred on October 20th 1934, i.e., two days before the date that all the accounts that have been supported so far report. That suggests that any historical study to come, and regarding the experiments carried out by Fermi and his group on neutrons, cannot neglect to analyse carefully the accounts regarding those experiments and to compare them with the archive records.
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arxiv:physics/0309046
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Generic wave dislocations (phase singularities, optical vortices) in three dimensions have anisotropic local structure, which is analysed, with emphasis on the twist of surfaces of equal phase along the singular line, and the rotation of the local anisotropy ellipse (twirl). Various measures of twist and twirl are compared in specific examples, and a theorem is found relating the (quantised) topological twist and twirl for a closed dislocation loop with the anisotropy C line index threading the loop.
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arxiv:physics/0309069
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We report on calculations of the elastic cross section and thermalization rate for collision between two maximally spin-polarized chromium atoms in the cold and ultracold regimes, relevant to buffer-gas and magneto-optical cooling of chromium atoms. We calculate ab initio potential energy curves for Cr2 and the van der Waals coefficient C6, and construct interaction potentials between two colliding Cr atoms. We explore the effect of shape resonances on elastic cross section, and find that they dramatically affect the thermalization rate. Our calculated value for the s-wave scattering length is compared in magnitude with a recent measurement at ultracold temperatures.
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arxiv:physics/0309076
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The conjecture is considered that every body induces the wave field which imposes oscillations on the gravitational potential of a body. The function for oscillations is chosen to prevent the gravitational collapse of the matter at the nucleus energy density. Oscillations of the gravitational potential of a body produce effective inertial outward acceleration for a particle orbiting around the body. Footprints of the effective inertial acceleration due to oscillations of the gravitational potentials of the Sun and Earth are investigated. The conjecture allows to explain the anomalous shift of the perihelion of Mercury and Icarus, the anomalous shift of the perigee of LAGEOS II, the anomalous acceleration acting on Pioneer 10, 11, the anomalous increase in the lunar semi-major axis. The advance of the Keplerian orbit for Earth, Jupiter, Neptune, Uranus caused by the effective inertial acceleration due to oscillations of the gravitational potential of the Sun is in agreement with the observational bounds from the planetary ephemeris.
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arxiv:physics/0309099
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A hierarchical approach to the construction of compound distributions for process-induced faults in IC manufacture is proposed. Within this framework, the negative binomial distribution is treated as level-1 models. The hierarchical approach to fault distribution offers an integrated picture of how fault density varies from region to region within a wafer, from wafer to wafer within a batch, and so on. A theory of compound-distribution hierarchies is developed by means of generating functions. A study of correlations, which naturally appears in microelectronics due to the batch character of IC manufacture, is proposed. Taking these correlations into account is of significant importance for developing procedures for statistical quality control in IC manufacture. With respect to applications, hierarchies of yield means and yield probability-density functions are considered.
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arxiv:physics/0310012
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In this paper, the phenomenon of band gaps and Anderson localization of water waves over one-dimensional periodic and random bottoms is investigated by the transfer matrix method. The results indicate that the range of localization in random bottoms can be coincident with the band gaps for the corresponding periodic bottoms. Inside the gap or localization regime, a collective behavior of water waves appears. The results are also compared with acoustic and optical situations.
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arxiv:physics/0310024
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The physio-chemical properties of Nafion 115 and a composite Nafion 115/Zirconium Phosphate (25wt%) membranes are compared. The composite membrane takes up more water than Nafion at the same water activity. However, the proton conductivity of the composite membrane is slightly less than that for Nafion 115. Small angle X-ray scattering shows the hydrophilic phase domains in the composite membrane are spaced further apart than in Nafion 115, and the composite membrane shows less restructuring with water uptake. Despite the lower proton conductivity of the composite membranes they display better fuel cell performance than Nafion 115 when the fuel cell is operated under-humidified. It is suggested that the composite membrane has a greater rigidity that accounts for its improved fuel cell performance.
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arxiv:physics/0310029
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Simultaneous two-dimensional trapping of neutral dipolar molecules in low- and high-field seeking states is analyzed. A trapping potential of the order of 20 mK can be produced for molecules like ND3 with time-dependent electric fields. The analysis is in agreement with an experiment where slow molecules with longitudinal velocities of the order of 20 m/s are guided between four 50 cm long rods driven by an alternating electric potential at a frequency of a few kHz.
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arxiv:physics/0310046
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A simple relativistic treatment of Michelson-Morley type of experiments shows the remarkable internal consistency of 1932 Miller's cosmic solution v_{earth} \sim 208 km/s deduced from the experimental fringe shifts observed with his apparatus. The same analysis of present-day experiments is in good agreement with the existing data.
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arxiv:physics/0310053
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The possibility to derive an equation for the mean velocity field in turbulent flow by using classical statistical mechanics is investigated. An application of projection operator technique available in the literature is used for this purpose. It is argued that the hydrodynamic velocity defined there, in situations where the fluid is turbulent, is to be interpreted as the mean velocity field; in that case, the momentum component of the generalized transport equation derived there is the mean velocity equation. In this paper, stationary incompressible flow for constant mass density and temperature is considered. The stress tensor is obtained as a nonlinear functional of the mean velocity field, the linear part of which is the Stokes tensor. The formula contains a time correlation function in local equilibrium. Presently, there exists a microscopic theory for time correlations in total equilibrium only. For this reason and as a preliminary measure, the formula has been expanded into a power series in the mean velocity; though this limits the applicability to low Reynolds number flow. The second order term has been evaluated in a former paper of the author. For the third order term, the form of the kernel function is derived. Its calculation with the aid of the mode-coupling theory is completed; it will be reported in an separate paper. An numerical application with the data of the circular jet is under way.
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arxiv:physics/0310054
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The linearized Navier-Stokes equations for a system of superposed immiscible compressible ideal fluids are analyzed. The results of the analysis reconcile the stabilizing and destabilizing effects of compressibility reported in the literature. It is shown that the growth rate $n$ obtained for an inviscid, compressible flow in an infinite domain is bounded by the growth rates obtained for the corresponding incompressible flows with uniform and exponentially varying density. As the equilibrium pressure at the interface $p_\infty$ increases (less compressible flow), $n$ increases towards the uniform density result, while as the ratio of specific heats $\gamma$ increases (less compressible fluid), $n$ decreases towards the exponentially varying density incompressible flow result. This remains valid in the presence of surface tension or for viscous fluids and the validity of the results is also discussed for finite size domains. The critical wavenumber imposed by the presence of surface tension is unaffected by compressibility. However, the results show that the surface tension modifies the sensitivity of the growth rate to a differential change in $\gamma$ for the lower and upper fluids. For the viscous case, the linearized equations are solved numerically for different values of $p_\infty$ and $\gamma$. It is found that the largest differences compared with the incompressible cases are obtained at small Atwood numbers. The most unstable mode for the compressible case is also bounded by the most unstable modes corresponding to the two limiting incompressible cases.
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arxiv:physics/0310072
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We show that the acceptance probability for swaps in the parallel tempering Monte Carlo method for classical canonical systems is given by a universal function that depends on the average statistical fluctuations of the potential and on the ratio of the temperatures. The law, called the incomplete beta function law, is valid in the limit that the two temperatures involved in swaps are close to one another. An empirical version of the law, which involves the heat capacity of the system, is developed and tested on a Lennard-Jones cluster. We argue that the best initial guess for the distribution of intermediate temperatures for parallel tempering is a geometric progression and we also propose a technique for the computation of optimal temperature schedules. Finally, we demonstrate that the swap efficiency of the parallel tempering method for condensed-phase systems decreases naturally to zero at least as fast as the inverse square root of the dimensionality of the physical system.
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arxiv:physics/0310101
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A direct method is proposed for reconstruction of the effective atomic number by means of multi-energy radiography of the material. The accuracy of the method is up to 95% . Advantages over conventional radiographic methods, which ensure accuracy of just about 50%, are discussed. A physical model has been constructed, and general expressions have been obtained for description of the effective atomic number in a two-energy monitoring scheme. A universal dependence has been predicted for the effective atomic number as a function of relative (two-energy) radiographic reflex. The established theoretical law is confirmed by the experimental data presented. The proposed development can find multiple applications in non-destructive testing and related fields, including those in the civil sphere as well as anti-terrorist activities.
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arxiv:physics/0310118
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K+(aq) ion is an integral component of many cellular processes, amongst which the most important, perhaps, is its role in transmitting electrical impulses along the nerve. Understanding its hydration structure and thermodynamics is crucial in dissecting its role in such processes. Her we address these questions using both the statistical mechanical quasi-chemical theory of solutions and ab initio molecular dynamics simulations. Simulations predict an interesting hydration structure for K+(aq): the population of about six (6) water molecules within the initial minimum of the observed g_{KO}(r) at infinite dilution involves four (4) inner-most molecules that the quasi-chemical theory suggests should be taken as the theoretical inner shell. The contribution of the 5th and 6th closest water molecules is observable as a distinct shoulder on the principal maximum of the g_{KO}(r). The quasi-chemical estimate of solvation free energy for the neutral pair KOH is also in good agreement with experiments.
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arxiv:physics/0310158
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Semi-classical molecular dynamics simulations of small rare gas clusters in short laser pulses of 100 nm wavelength were performed. For comparison, the cluster response to 800 nm laser pulses was investigated as well. The inner ionization dynamics of the multi-electron atoms inside the cluster was treated explicitly. The simulation results underpin that at XUV wavelengths collisions play an important role in the energy absorption. The generation of the surprisingly high charge states of Xe atoms inside clusters, as they were observed in the free-electron laser experiment at DESY, Hamburg, Germany [Wabnitz et al., Nature 420, 482 (2002)], is due to the reduced ionization potential of atoms inside charged clusters, the ionization ignition mechanism, and collisions.
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arxiv:physics/0310166
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We study the statistical mechanics of grafted polymers of arbitrary stiffness in a two-dimensional embedding space with Monte Carlo simulations. The probability distribution function of the free end is found to be highly anisotropic and non-Gaussian for typical semiflexible polymers. The reduced distribution in the transverse direction, a Gaussian in the stiff and flexible limits, shows a double peak structure at intermediate stiffnesses. We also explore the response to a transverse force applied at the polymer free end. We identify F-Actin as an ideal benchmark for the effects discussed.
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arxiv:physics/0311012
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This paper extends the derivation of the Lagrangian averaged Euler (LAE-$\alpha$) equations to the case of barotropic compressible flows. The aim of Lagrangian averaging is to regularize the compressible Euler equations by adding dispersion instead of artificial viscosity. Along the way, the derivation of the isotropic and anisotropic LAE-$\alpha$ equations is simplified and clarified. The derivation in this paper involves averaging over a tube of trajectories $\eta^\epsilon$ centered around a given Lagrangian flow $\eta$. With this tube framework, the Lagrangian averaged Euler (LAE-$\alpha$) equations are derived by following a simple procedure: start with a given action, Taylor expand in terms of small-scale fluid fluctuations $\xi$, truncate, average, and then model those terms that are nonlinear functions of $\xi$. Closure of the equations is provided through the use of \emph{flow rules}, which prescribe the evolution of the fluctuations along the mean flow.
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arxiv:physics/0311086
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High-energy bremsstrahlung and K X-rays were used to produce nearly background-free K X-ray spectra of up to 87 keV (Pb) via X-ray fluorescence. The fluorescing radiation was produced by electron accelerators, consisting of heated and cooled cylindrical LiTaO3 and LiNbO3 crystals at mTorr pressures. The newly discovered process of gas amplification whereby the ambient gas pressure is optimized to maximize the electron energy was used to produce energetic electrons which when incident on a W/Bi target gave rise to a radiation field consisting of high-energy bremsstrahlung as well as W and Bi K X-rays. These photons were used to fluoresce Ta and Pb K X-rays.
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arxiv:physics/0311090
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Motivated by recent experimental work by Folkenberg et al. we consider the effect of weak disorder in the air-hole lattice of small-core photonic crystal fibers. We find that the broken symmetry leads to higher-order modes which have generic intensity distributions resembling those found in standard fibers with elliptical cores. This explains why recently reported experimental higher-order mode profiles appear very different from those calculated numerically for ideal photonic crystal fibers with inversion and six-fold rotational symmetry. The splitting of the four higher-order modes into two groups fully correlates with the observation that these modes have different cut-offs.
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arxiv:physics/0311106
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GePEToS is a simulation framework developed over the last few years for assessing the instrumental performance of future PET scanners. It is based on Geant4, written in Object-Oriented C++ and runs on Linux platforms. The validity of GePEToS has been tested on the well-known Siemens ECAT EXACT HR+ camera. The results of two application examples are presented : the design optimization of a liquid Xe micro-PET camera dedicated to small animal imaging as well as the evaluation of the effect of a strong axial magnetic field on the image resolution of a Concorde P4 micro-PET camera.
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arxiv:physics/0312019
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The maximum strength of gravity at the surface of an object of a given mass is not attained for a spherical shape, but for a small departure from sphericity.
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arxiv:physics/0312029
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From the equilibrium condition $\delta S=0$ applied to an isolated thermodynamic system of electrically charged particles and the fundamental equation of thermodynamics ($dU = T dS-(\mathbf{f}\cdot d\mathbf{r})$) subject to a new procedure, it is obtained the Lorentz's force together with non-inertial terms of mechanical nature. Other well known ponderomotive forces, like the Stern-Gerlach's force and a force term related to the Einstein-de Haas's effect are also obtained. In addition, a new force term appears, possibly related to a change in weight when a system of charged particles is accelerated.
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arxiv:physics/0312080
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The angular distribution of the emitted electrons, following the two--photon ionization of the hydrogen--like ions, is studied within the framework of second order perturbation theory \textit{and} the Dirac equation. Using a density matrix approach, we have investigated the effects which arise from the polarization of the incoming light as well as from the higher multipoles in the expansion of the electron--photon interaction. For medium-- and high--Z ions, in particular, the non--dipole contributions give rise to a significant change in the angular distribution of the emitted electrons, if compared with the electric--dipole approximation. This includes a strong forward emission while, in dipole approximation, the electron emission always occurs symmetric with respect to the plane which is perpendicular to the photon beam. Detailed computations for the dependence of the photoelectron angular distributions on the polarization of the incident light are carried out for the ionization of the H, Xe$^{53+}$ and U$^{91+}$ (hydrogen--like) ions.
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arxiv:physics/0312111
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We review the analytical methods of solving the stochastic equations for barrier-type dynamical behavior in plasma systems. The path-integral approach is examined as a particularly efficient method of determination of the statistical properties.
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arxiv:physics/0312127
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In the context of the recently developed "equation-free" approach to the computer-assisted analysis of complex systems, we illustrate the computation of coarsely self-similar solutions. Dynamic renormalization and fixed point algorithms for the macroscopic density dynamics are applied to the results of short bursts of appropriately initialized molecular dynamics in a simple diffusion simulation. The approach holds promise for locating coarse self-similar solutions and the corresponding exponents in a variety of multiscale computational contexts.
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arxiv:physics/0312142
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The recent interpretation of the positive resonance frequency shift in dielectric resonators loaded by water is reviewed. Instead of the invoked negative dielectric constant of water surface layer, it is demonstrated that the experimental results are fully reproduced by taking into account the dielectric losses of the sample.
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arxiv:physics/0401023
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We make a comparative study of hard x-ray emission from 15 $\mu$m methanol microdroplets and a plain slab target of similar atomic composition at similar laser intensities. The hard X-ray yield from droplet plasmas is $\simeq$ 35 times more than that obtained from solid plasmas. A prepulse that is about 10ns and about 5% of the main pulse is essential for hard x-ray generation from the droplets. A hot electron temperature of 36 keV is measured from the droplets at 8$\times10^{14}$ W cm$^{-2}$; three times higher intensity is needed to obtain similar hot electron temperature from solid plasmas with similar composition. We use 1D PIC simulation to obtain qualitative correlation to the experimental observations.
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arxiv:physics/0401024
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Numerical algorithm for direct simulation of the gas flow in the Holweck pump is developed. The results illustrating the important features of the flow in the pump are reported. An attention is paid to the problem of the pump design optimization.
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arxiv:physics/0401028
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In 2002, the ATHENA collaboration reported the creation and detection of cold (~15 K) antihydrogen atoms [1]. The observation was based on the complete reconstruction of antihydrogen annihilations, simultaneous and spatially correlated annihilations of an antiproton and a positron. Annihilation byproducts are measured with a cylindrically symmetric detector system consisting of two layers of double sided Si-micro-strip modules that are surrounded by 16 rows of 12 pure CsI crystals (13 x 17.5 x 17 mm^3). This paper gives a brief overview of the experiment, the detector system, and event reconstruction. Reference 1. M. Amoretti et al., Nature 419, 456 (2002).
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arxiv:physics/0401034
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Torsional-space Monte Carlo simulations of flexible molecules are usually based on the assumption that all values of dihedral angles have equal probability in the absence of atomic interactions. In the present paper it is shown that this assumption is not valid. Thermodynamic sampling using dihedral angles or other internal coordinates has to account for both the correct metric in conformational space and the conformation-dependence of the moment of inertia tensor. Metric and moment of inertia terms appear as conformation-dependent factors in the partition function and are obtained by proper separation of internal and rotational degrees of freedom. The importance of both factors is discussed for a number of short peptides as well as for the folded and unfolded states of a protein. It is concluded that thermodynamic Monte Carlo simulations of protein folding that neglect these correction factors tend to underestimate the stability of the folded state.
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arxiv:physics/0401036
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We devise a non-Hermitian Rayleigh-Schroedinger perturbation theory for the single- and the multireference case to tackle both the many-body problem and the decay problem encountered, for example, in the study of electronic resonances in molecules. A complex absorbing potential (CAP) is employed to facilitate a treatment of resonance states that is similar to the well-established bound-state techniques. For the perturbative approach, the full CAP-Schroedinger Hamiltonian, in suitable representation, is partitioned according to the Epstein-Nesbet scheme. The equations we derive in the framework of the single-reference perturbation theory turn out to be identical to those obtained by a time-dependent treatment in Wigner-Weisskopf theory. The multireference perturbation theory is studied for a model problem and is shown to be an efficient and accurate method. Algorithmic aspects of the integration of the perturbation theories into existing ab initio programs are discussed, and the simplicity of their implementation is elucidated.
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arxiv:physics/0401081
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The accurate modeling of the dielectric properties of water is crucial for many applications in physics, computational chemistry and molecular biology. This becomes possible in the framework of nonlocal electrostatics, for which we propose a novel formulation allowing for numerical solutions for the nontrivial molecular geometries arising in the applications mentioned before. Our approach is based on the introduction of a secondary field, $\psi$, which acts as the potential for the rotation free part of the dielectric displacement field ${\bf D}$. For many relevant models, the dielectric function of the medium can be expressed as the Green's function of a local differential operator. In this case, the resulting coupled Poisson (-Boltzmann) equations for $\psi$ and the electrostatic potential $\phi$ reduce to a system of coupled PDEs. The approach is illustrated by its application to simple geometries.
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arxiv:physics/0401086
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Grease ice is an agglomeration of disc-shaped ice crystals, named frazil ice, which forms in turbulent waters of the Polar Oceans and in rivers as well. It has been recognized that the properties of grease ice to damp surface gravity waves could be explained in terms of the effective viscosity of the ice slurry. This paper is devoted to the study of the dynamics of a suspension of disc-shaped particles in a gravity wave field. For dilute suspensions, depending on the strength and frequency of the external wave flow, two orientation regimes of the particles are predicted: a preferential orientation regime with the particles rotating in coherent fashion with the wave field, and a random orientation regime in which the particles oscillate around their initial orientation while diffusing under the effect of Brownian motion. For both motion regimes, the effective viscosity has been derived as a function of the wave frequency, wave amplitude and aspect ratio of the particles. Model predictions have been compared with wave attenuation data in frazil ice layers grown in wave tanks.
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arxiv:physics/0402047
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The linear and nonlinear properties of the Rao-dust-magnetohydrodynamic (R-D-MHD) waves in a dusty magnetoplasma are studied. By employing the inertialess electron equation of motion, inertial ion equation of motion, Amp\`ere's law, Faraday's law, and the continuity equation in a plasma with immobile charged dust grains, the linear and nonlinear propagation of two-dimensional R-D-MHD waves are investigated. In the linear regime, the existence of immobile dust grains produces the Rao cutoff frequency, which is proportional to the dust charge density and the ion gyrofrequency. On the other hand, the dynamics of an amplitude modulated R-D-MHD waves is governed by the cubic nonlinear Schroedinger equation. The latter has been derived by using the reductive perturbation technique and the two-timescale analysis which accounts for the harmonic generation nonlinearity in plasmas. The stability of the modulated wave envelope against non-resonant perturbations is studied. Finally, the possibility of localized envelope excitations is discussed.
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arxiv:physics/0402050
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We used computer simulation to calculate the electric dipole moments of the alpha and beta tubulin monomers and dimer and found those to be |palpha|=552D, |pbeta|=1193D and |palpha-beta|=1740D respectively. Independent surface plasmon resonance (SPR) and refractometry measurements of the high-frequency dielectric constant and polarizability strongly corroborated our previous SPR-derived results giving delta-n/delta-c ~1.800x10^-3 ml/mg. The refractive index of tubulin was measured to be n_tub ~2.90 and the high frequency tubulin dielectric constant kappa_tub ~8.41 while the high-frequency polarizability was found to be alpha_tub ~ 2.1x10^-33 C m^2/V. Methods for the experimental determination of the low-frequency p are explored as well as ways to test the often conjectured quantum coherence and entanglement properties of tubulin. Biobits, bioqubits and other applications to bioelectronics are discussed.
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arxiv:physics/0402053
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Second harmonic optical coherence tomography, which uses coherence gating of second-order nonlinear optical response of biological tissues for imaging, is described and demonstrated. Femtosecond laser pulses were used to excite second harmonic waves from collagen harvested from rat tail tendon and a reference nonlinear crystal. Second harmonic interference fringe signals were detected and used for image construction. Because of the strong dependence of second harmonic generation on molecular and tissue structures, this technique offers contrast and resolution enhancement to conventional optical coherence tomography.
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arxiv:physics/0402060
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One can make the very simple hypothesis that the Universe is the inside of an hypersphere in 4 dimensions, where our 3-dimensional world consists of hypersurfaces at different radii. Based on this assumption it is possible to show that Universe expansion at a rate corresponding to flat comes as a direct geometrical consequence without intervening critical density; any mass density is responsible for opening the Universe and introduces a cosmological constant. Another consequence is the appearance of inertia swirls of expanding matter, which can explain observed velocities around galaxies, again without the intervention of dark matter. When restricted to more everyday situations the model degenerates in what has been called 4-dimensional optics; in the paper this is shown to be equivalent to general relativity in all static isotropic metric situations. In the conclusion some considerations bring the discussion to the realm of 4D wave optics.
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arxiv:physics/0402075
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Throughout all years of study, students of physics are confronted with the question 'what exactly is light?' - a question that is impossible to answer correctly and, therefore, continuously discussed within the framework of models. Numerous models have been introduced for this purpose and subsequently compete with one another for validity. On the one hand, this may lead to learning difficulties. Yet, on the other hand, this may be considered a didactic chance, if thinking about the model is compounded with the consideration of models in general. Research in secondary school level II physics classes and with physics students provides insight into the processes of model construction as well as that of overcoming models, which will be presented and analyzed here. The possibilities which computer simulations provide for the discussion of various models of light are demonstrated and their influence on a structured construction of models will be discussed.
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arxiv:physics/0402080
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We investigate the electronic structure and properties of atoms exposed to a magnetic quadrupole field. The spin-spatial as well as generalized time reversal symmetries are established and shown to lead to a two-fold degeneracy of the electronic states in the presence of the field. Low-lying as well as highly excited Rydberg states are computed and analyzed for a broad regime of field gradients. The delicate interplay between the Coulomb and various magnetic interactions leads to complex patterns of the spatial spin polarization of individual excited states. Electromagnetic transitions in the quadrupole field are studied in detail thereby providing the selection rules and in particular the transition wavelengths and corresponding dipole strengths. The peculiar property that the quadrupole magnetic field induces permanent electric dipole moments of the atoms is derived and discussed.
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arxiv:physics/0402109
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The paper develops a modified geometrical optics (GO) of smoothly inhomogeneous isotropic medium, which takes into account two topological phenomena: Berry phase and the optical Magnus effect. By using the analogy between a quasi-classical motion of a quantum particle with a spin and GO of an electromagnetic wave in smoothly inhomogeneous media, we have introduced the standard gauge potential associated with the degeneracy in the wave momentum space. This potential corresponds to the Dirac-monopole-like field (Berry curvature), which causes the topological spin (polarization) transport of photons. The deviations of waves of right-hand and left-hand helicity occur in the opposite directions and orthogonally to the principal direction of motion. This produces a spin current directed across the principal motion. The situation is similar to the anomalous Hall effect for electrons. In addition, a simple scheme of the experiment allowing one to observe the topological spin splitting of photons has been suggested.
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arxiv:physics/0402110
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Energies of ns[1/2] (n= 6-9), np[j] (n = 6-8), nd[j] (n= 6-7), and 5f[j] states in neutral Au and Au-like ions with nuclear charges Z = 80 - 83 are calculated using relativistic many-body perturbation theory. Reduced matrix elements, oscillator strengths, transition rates and lifetimes are determined for the 30 possible nl[j]-n'l'[j'] electric-dipole transitions. Results for a limited number states ns[1/2], np[j] (n= 6-7) and 6d[j] are obtained in the relativistic single-double (SD) approximation, where single and double excitations of Dirac-Fock wave functions are included to all orders in perturbation theory. Using SD wave functions, accurate values are obtained for energies of the eight lowest states and for the fourteen possible electric-dipole matrix elements between these states. With the aid of the SD wave functions, we also determine transition rates and oscillator strengths for the fourteen transitions together with lifetimes of 6p[j], 7p[j], and 6d[j] levels. We investigate the hyperfine structure in HgII and TlIII. The hyperfine A-values are determined for 6s[1/2] and 6p[j] states in 199Hg+, 201Hg+, and 205Tl++ isotopes. These calculations provide a theoretical benchmark for comparison with experiment and theory.
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arxiv:physics/0402133
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The question what information is necessary for determination of a unique solution of hydrodynamic equations for ideal fluid is investigated. Arbitrary inviscid flows of the barotropic fluid and of incompressible fluid are considered. After integrating hydrodynamic equations, all information on the fluid flow is concentrated in dynamic equations in the form of indefinite functions, whereas the initial and boundary conditions contain information on the fluid particle labeling. It is shown that for determination of the stationary flow of the incompressible fluid the vorticity on any stream line must be given. Giving the velocity on the boundary, one does not determine the vorticity, in general. If there are closed stream lines, the vorticity cannot be given on them via boundary conditions. This circumstance explains existence of different stationary vortical flows under the same boundary conditions.
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arxiv:physics/0403010
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The aim of the Working Group on Single Beam Behaviour was to concentrate on the items limiting the achievement of high luminosity. Some are related to high current and short bunch distance, as electron cloud instability (ECI), the others to the lattice design, as Dynamic Aperture (DA), wigglers, Interaction Region (IR) design, lifetime and background. These arguments have been discussed to explore the feasibility of a very high luminosity Phi-factory.
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arxiv:physics/0403024
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A formal linear vector field representation for scientific equations is developed to rationalize the intuitive methods that are constantly employed. It is shown that unlike mechanical units that appear in the basis of the space, the reduced temperature and Boltzmann parameter cannot be described by the basis set individually and can only be described as a product. Further, the definition and determination of temperature is dependent on theory and not on standard mechanical units. It is shown that there is no reason to reduce the number of degrees of freedom in temperature determination via equipartition since stochastic variables are involved, and this observation is significant in that the temperature variable reported in simulation studies would have a discrepancy to the extent of using the decreased number of freedom, which is most cases is not large nor significant. The standard assignments used in reduced units do not lead to errors because operationally the resulting reduced temperature parameter represents the reduced product of the temperature and Boltzmann parameters. The non-independence of these quantities explains why entropy and other associated functions cannot be calculated directly, but are always scaled in dimensionless increments of the Boltzmann parameter.
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arxiv:physics/0403033
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Aging phenomena constitute one of the most complex and serious potential problems which could limit, or severely impair, the use of gaseous detectors in unprecedented harsh radiation environments. Long-term operation in high-intensity experiments of the LHC-era not only demands extraordinary radiation hardness of construction materials and gas mixtures but also very specific and appropriate assembly procedures and quality checks during detector construction and testing. Recent experimental data from hadron beams is discussed. It is shown that the initial stage of radiation tests, usually performed under isolated laboratory conditions, may not offer the full information needed to extrapolate to the long-term performance of real and full-size detectors at high energy physics facilities. Major factors, closely related to the capability of operating at large localized ionization densities, and which could lead to operation instabilities and subsequent aging phenomena in gaseous detectors, are summarized. Finally, an overview of aging experience with state-of-the-art gas detectors in experiments with low- and high-intensity radiation environments is given with a goal of providing a set of rules, along with some caveat, for the construction and operation of gaseous detectors in high luminosity experiments.
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arxiv:physics/0403055
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The paper formulates Maxwell's equations in 4-dimensional Euclidean space by embedding the electromagnetic vector potential in the frame vector $g_0$. Relativistic electrodynamics is the first problem tackled; in spite of using a geometry radically different from that of special relativity, the paper derives relativistic electrodynamics from space curvature. Maxwell's equations are then formulated and solved for free space providing solutions which rotate the vector potential on a plane; these solutions are shown equivalent to the usual spacetime formulation and are then discussed in terms of the hypersphere model of the Universe recently proposed by the author.
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arxiv:physics/0403058
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The ALICE High-Level Trigger processes data online, to either select interesting (sub-) events, or to compress data efficiently by modeling techniques. Focusing on the main data source, the Time Projection Chamber, the architecure of the system and the current state of the tracking and compression methods are outlined.
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arxiv:physics/0403063
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The distinction between the real positions of moving objects in a single reference frame and the apparent positions of objects at rest in one inertial frame and viewed from another, as predicted by the space-time Lorentz Transformations, is discussed. It is found that in the Rockets-and-String paradox the string remains unstressed and does not break and that the pole in the Barn-and-Pole paradox never actually fits into the barn. The close relationship of the Lorentz-Fitzgerald Contraction and the relativity of simultaneity of Special Relativity is pointed out and an associated paradox, in which causality is apparently violated, is noted.
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arxiv:physics/0403094
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Precise energies of rovibrational states of the exotic hydrogen-like molecule $(dt\mu)Xee$ are of importance for $dt\mu$ resonant formation, which is a key process in the muon-catalyzed fusion cycle. The effect of the internal structure and motion of the $dt\mu$ quasi-nucleus on energy levels is studied using the three-body description of the $(dt\mu)Xee$ molecule based on the hierarchy of scales and corresponding energies of its constituent subsystems. For a number of rovibrational states of $(dt\mu)dee$ and $(dt\mu)tee$, the shifts and splittings of energy levels are calculated in the second order of the perturbation theory.
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arxiv:physics/0403116
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We formulate a quantum Monte Carlo (QMC) method for calculating the ground state of many-boson systems. The method is based on a field-theoretical approach, and is closely related to existing fermion auxiliary-field QMC methods which are applied in several fields of physics. The ground-state projection is implemented as a branching random walk in the space of permanents consisting of identical single-particle orbitals. The method is in principle exact. We illustrate this method with a trapped atomic boson gas, where the atoms interact via an attractive or repulsive contact two-body potential. We choose as the single-particle basis a real-space grid. We compare with exact results in small systems, and arbitrarily-sized systems of untrapped bosons with attractive interactions in one dimension, where analytical solutions exist. We also compare with the corresponding Gross-Pitaevskii (GP) mean-field calculations for trapped atoms, and discuss the close formal relation between our method and the GP approach. Our method provides a way to systematically improve upon GP while using the same framework, capturing interaction and correlation effects with a stochastic, coherent ensemble of non-interacting solutions. We discuss various algorithmic issues, including importance sampling and the back-propagation technique for computing observables, and illustrate them with numerical studies. We show results for systems with up to N ~ 400 bosons.
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arxiv:physics/0403146
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We present observations of VUV transitions between doubly excited sextet states in O IV, F V and Ne VI. Spectra were produced by collisions of an O+, (FH)+ and Ne+ beam with a solid carbon target. Some observed lines are assigned to the 1s2s2p23p 6L-1s2p33p 6P electric-dipole transitions in O IV, F V and Ne VI, and are compared with results of MCHF (with QED and higher-order corrections) and MCDF calculations. 31 new lines have been identified. The sextet systems of boronlike ions are possible candidates for x-ray and VUV lasers.
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arxiv:physics/0404001
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We use the relativistic Hartree-Fock method, many-body perturbation theory and configuration-interaction method to calculate the dependence of atomic transition frequencies on the fine structure constant, alpha. The results of these calculations will be used in the search for variation of the fine structure constant in quasar absorption spectra.
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arxiv:physics/0404008
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A multidimesional function $y(\vec r)$ defined by a sample of points $\{\vec r_i,y_i\}$ is approximated by a differentiable function $\widetilde y(\vec r)$. The problem is solved by using the Gauss-Hermite folding method developed in the nuclear shell correction method by Strutinsky.
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arxiv:physics/0404018
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We study the Bogoliubov-Dirac-Fock model introduced by Chaix and Iracane ({\it J. Phys. B.}, 22, 3791--3814, 1989) which is a mean-field theory deduced from no-photon QED. The associated functional is bounded from below. In the presence of an external field, a minimizer, if it exists, is interpreted as the polarized vacuum and it solves a self-consistent equation. In a recent paper math-ph/0403005, we proved the convergence of the iterative fixed-point scheme naturally associated with this equation to a global minimizer of the BDF functional, under some restrictive conditions on the external potential, the ultraviolet cut-off $\Lambda$ and the bare fine structure constant $\alpha$. In the present work, we improve this result by showing the existence of the minimizer by a variational method, for any cut-off $\Lambda$ and without any constraint on the external field. We also study the behaviour of the minimizer as $\Lambda$ goes to infinity and show that the theory is "nullified" in that limit, as predicted first by Landau: the vacuum totally kills the external potential. Therefore the limit case of an infinite cut-off makes no sense both from a physical and mathematical point of view. Finally, we perform a charge and density renormalization scheme applying simultaneously to all orders of the fine structure constant $\alpha$, on a simplified model where the exchange term is neglected.
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arxiv:physics/0404047
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The distribution of inter-occurrence time between seismic events is a quantity of great interest in seismic risk assessment. We evaluate this distribution for different models of earthquakes occurrence and follow two distinct approaches: The non homogeneous Poissonian and the non Poissonian one. In all cases we obtain either a power law or a power law damped by an exponential factor behaviour. This feature of the distribution makes impossible any prediction of earthquakes occurrence. Nevertheless it suggests the interpretation of the earthquake occurrence phenomenon as due to some non-linear dynamics to be further investigated.
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arxiv:physics/0404068
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A common mechanism for intracellular transport is the use of controlled deformations of the membrane to create spherical or tubular buds. While the basic physical properties of homogeneous membranes are relatively well-known, the effects of inhomogeneities within membranes are very much an active field of study. Membrane domains enriched in certain lipids in particular are attracting much attention, and in this Letter we investigate the effect of such domains on the shape and fate of membrane tubes. Recent experiments have demonstrated that forced lipid phase separation can trigger tube fission, and we demonstrate how this can be understood purely from the difference in elastic constants between the domains. Moreover, the proposed model predicts timescales for fission that agree well with experimental findings.
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arxiv:physics/0404086
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Iterative projection algorithms for phase retrieval are tested on two simple toy models. The result provides useful insights in the behavior of these algorithms.
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arxiv:physics/0404091
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A novel experiment to test special relativity via Lorentz symmetry has become factible thanks to three recent technological achievements: huge Michelson-like set-up with arms 3 km long (Virgo) and 4 km (Ligo) with beam paths respectively reaching 120 km and 200 km through multiple reflections, ultrashort laser pulses of 10-15 s and ultrafast detectors of 10-12 s resolution. The alliance of these three elements would allow checking the equality of the time-of-flight of the two orthogonal beams with a resolution high enough to allow prospecting in a novel way the equivalency of inertial system postulated in special relativity. In effect, for a beam path length of 120 or 200 km and a net drift velocity of earth of 370 km/s relative to the cosmic microwave background CMB), a classical analysis predicts a time-of-flight difference of the order of 10 ns between the two orthogonal beams, while relativity infers them to be equal. So, what is under scrutiny is the exhaustivity of the electromagnetic equivalency of inertial systems. A null time-of-flight difference would strengthen the Lorentz symmetry, while a non null result would bring a threshold to the equivalency of inertial systems and at the same time would provide a tool to define their speed, which should be equal to that relative to the CMB for being congruent.
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arxiv:physics/0404116
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Theoretically predicted linear correlation between the volume coefficient of thermal expansion and the thermal heat capacity was investigated for highly symmetrical atomic arrangements. Normalizing the data of these thermodynamic parameters to the Debye temperature gives practically identical curves from zero Kelvin to the Debye temperature. This result is consistent with the predicted linear correlation. At temperatures higher than the Debye temperature the normalized values of the thermal expansion are always higher than the normalized value of the heat capacity. The detected correlation has significant computational advantage since it allows calculating the volume coefficient of thermal expansion from one experimental data by using the Debye function.
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arxiv:physics/0404117
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The constraint of incompressibility is often used to simplify the magnetohydrodynamic (MHD) description of linearized plasma dynamics because it does not affect the ideal MHD marginal stability point. In this paper two methods for introducing incompressibility are compared in a cylindrical plasma model: In the first method, the limit $\gamma \to \infty$ is taken, where $\gamma$ is the ratio of specific heats; in the second, an anisotropic mass tensor $\mathbf{\rho}$ is used, with the component parallel to the magnetic field taken to vanish, $\rho_{\parallel} \to 0$. Use of resistive MHD reveals the nature of these two limits because the Alfv\'en and slow magnetosonic continua of ideal MHD are converted to point spectra and moved into the complex plane. Both limits profoundly change the slow-magnetosonic spectrum, but only the second limit faithfully reproduces the resistive Alfv\'en spectrum and its wavemodes. In ideal MHD, the slow magnetosonic continuum degenerates to the Alfv\'en continuum in the first method, while it is moved to infinity by the second. The degeneracy in the first is broken by finite resistivity. For numerical and semi-analytical study of these models, we choose plasma equilibria which cast light on puzzling aspects of results found in earlier literature.
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arxiv:physics/0405002
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Corrections of order $\alpha^3(Z\alpha)^5m$ to the Lamb shift and corrections of order $\alpha^3(Z\alpha)E_F$ to hyperfine splitting generated by the insertions of the three-loop one-particle reducible diagrams with radiative photons in the electron line are calculated. The calculations are performed in the Yennie gauge.
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arxiv:physics/0405039
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We present a new Monte Carlo method which couples Path Integral for finite temperature protons with Quantum Monte Carlo for ground state electrons, and we apply it to metallic hydrogen for pressures beyond molecular dissociation. We report data for the equation of state for temperatures across the melting of the proton crystal. Our data exhibit more structure and higher melting temperatures of the proton crystal than Car-Parrinello Molecular Dynamics results. This method fills the gap between high temperature electron-proton Path Integral and ground state Diffusion Monte Carlo methods.
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arxiv:physics/0405056
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A general method is described for finding algebraic expressions for matrix elements of any one- and two-particle operator for an arbitrary number of subshells in an atomic configuration, requiring neither coefficients of fractional parentage nor unit tensors. It is based on the combination of second quantization in the coupled tensorial form, angular momentum theory in three spaces (orbital, spin and quasispin), and a generalized graphical technique. The latter allows us to calculate graphically the irreducible tensorial products of the second quantization operators and their commutators, and to formulate additional rules for operations with diagrams. The additional rules allow us to find graphically the normal form of the complicated tensorial products of the operators. All matrix elements (diagonal and non-diagonal with respect to configurations) differ only by the values of the projections of the quasispin momenta of separate shells and are expressed in terms of completely reduced matrix elements (in all three spaces) of the second quantization operators. As a result, it allows us to use standard quantities uniformly for both diagona and off-diagonal matrix elements.
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arxiv:physics/0405101
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Today, relativistic calculations are known to provide a very successful means in the study of open-shell atoms and ions. But although accurate atomic data are obtained from these computations, they are traditionally carried out in jj-coupling and, hence, do often not allow for a simple LSJ classification of the atomic levels as needed by experiment. In fact, this lack of providing a proper spectroscopic notation from relativistic structure calculations has recently hampered not only the spectroscopy of medium and heavy elements, but also the interpretation and analysis of inner-shell processes, for which the occurrence of additional vacancies usually leads to a very detailed fine structure. Therefore, in order to facilitate the classification of atomic levels from such computations, here we present a program (within the Ratip environment) which help transform the atomic wave functions from jj-coupled multiconfiguration Dirac-Fock computations into a LS-coupled representation. Beside of a proper LSJ assignment to the atomic levels, the program also supports the full transformation of the wave functions if required for (nonrelativistic) computations.
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arxiv:physics/0406006
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The global requirements for energy are increasing rapidly as the global population increases and the under-developed nations become more advanced. The traditional fuels used in their traditional ways will become increasingly unable to meet the demand. The need for a review of the energy sources available is paramount, although the subsequent need to develop a realistic strategy to deal with all local and global energy requirements is almost as important. Here attention will be restricted to examining some of the claims and problems of using nuclear power to attempt to solve this major question.
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arxiv:physics/0406046
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An improved system for creating a pulsed, low-temperature molecular beam of OH radicals has been developed. We use a pulsed discharge to create OH from H$_2$O seeded in Xe during a supersonic expansion, where the high-voltage pulse duration is significantly shorter than the width of the gas pulse. The pulsed discharge allows for control of the mean speed of the molecular packet as well as maintains a low temperature supersonic expansion. A hot filament is placed in the source chamber to initiate the discharge for shorter durations and at lower voltages, resulting in a translationally and rotationally colder packet of OH molecules.
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arxiv:physics/0406151
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It is shown that dynamics of the interface between ideal fluid and light viscous fluid is exactly integrable in the approximation of small surface slopes for two-dimensional flow. Stokes flow of viscous fluid provides a relation between normal velocity and pressure at interface. Surface elevation and velocity potential of ideal fluid are determined from two complex Burgers equations corresponding to analytical continuation of velocity potential at the interface into upper and lower complex half planes, respectively. The interface loses its smoothness if complex singularities (poles) reach the interface.
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arxiv:physics/0407041
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Recent discussions of the origins of the thermodynamical asymmetry ("the arrow of time") by Huw Price and others are critically assessed. This serves as a motivation for consideration of relationship between thermodynamical and cosmological causes. Although the project of clarification of the thermodynamical explanandum is certainly welcome, Price excludes another interesting option, at least as viable as the sort of Acausal-Particular approach he favors, and arguably more in the spirit of Boltzmann himself. Thus, the competition of explanatory projects includes three horses, not two. In addition, it is the Acausal-Particular approach that could benefit enormously from dissociation from fanciful ideas of low-entropy future boundary conditions entertained by Price. Novel revolutionary developments in observational cosmology, as well as in the nascent astrophysical discipline of physical eschatology, have obliterated such hypotheses. Also, the Acausal-Anthropic approach we propose, offers another clear instance of disteleological nature of the anthropic principle.
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arxiv:physics/0407045
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It is important to have experimental methods to estimate the maximum beam intensity for the Fermilab Booster as objective input into long term program commitments. An important existing limit is set by the available rf power. This limit is difficult to set a priori because the real longitudinal impedance is not well known. The synchrotron phase at transition crossing was measured using both the mountain range plot and the direct phase measurement of the RF accelerating voltage relative to the beam, and results were consistent. They were applied to predict 6E12 maximum Booster beam intensity with present running conditions.
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arxiv:physics/0407060
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The periods of the harmonic oscillations of the ion core of charged sodium clusters around the equilibrium shapes are considered. It is found that these periods are of the order of magnitude of the experimentally measured relaxation times of the plasmons, which suggests the importance of the electron-ion coupling and stresses the role played by the electron-phonon interaction in the dissipation of the plasmon energy. The relation of the process to fission is briefly discussed.
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arxiv:physics/0407086
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We reconsider the problem of the stability of the thermohaline circulation as described by a two-dimensional Boussinesq model with mixed boundary conditions. We determine how the stability properties of the system depend on the intensity of the hydrological cycle. We define a two-dimensional parameters' space descriptive of the hydrology of the system and determine, by considering suitable quasi-static perturbations, a bounded region where multiple equilibria of the system are realized. We then focus on how the response of the system to finite-amplitude surface freshwater forcings depends on their rate of increase. We show that it is possible to define a robust separation between slow and fast regimes of forcing. Such separation is obtained by singling out an estimate of the critical growth rate for the anomalous forcing, which can be related to the characteristic advective time scale of the system.
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arxiv:physics/0407147
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We detected phase jumps of the Free Core Nutation (FCN) of the Earth directly from the analysis of the Very Long Baseline Interferometer (VLBI) observation of the Earth rotation for the period 1984-2003 by applying the Weighted Wavelet Z-Transform (WWZ) method and the Short-time Periodogram with the Gabor function (SPG) method. During the period, the FCN had two significant phase jumps in 1992 and 1998. These epochs coincide with the reported occurrence of geomagnetic jerks.
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arxiv:physics/0408026
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The National Ignition Facility (NIF) technology is designed to drive deuterium-tritium (DT) internal confinement fusion (ICF) targets to ignition using indirect radiation from laser beam energy captured in a hohlraum. Hydrodynamical instabilities at interfaces in the ICF capsule leading to mix between the DT fue l and the ablator shell material are of fundamental physical interest and can affect the performance characteristics of the capsule. In this Letter we describe new radiochemical diagnostics for mix processes in ICF capsules with plastic or Be (0.9%Cu) ablator shells. Reactions of high-energy tritons with shell material produce high-energy $\beta$-emitters. We show that mix between the DT fuel and the shell material enhances high-energy prompt beta emission from these reactions by more than an order of magnitude over that expected in the absence of mix.
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arxiv:physics/0408057
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