Showing papers on "Field (physics) published in 2003"
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TL;DR: In this paper, the authors present an alternative explanation which allows scalar fields to evolve cosmologically while having couplings to matter of order unity in the solar system, where the mass of the fields depends on the local matter density.
Abstract: The evidence for the accelerated expansion of the universe and the time-dependence of the fine-structure constant suggests the existence of at least one scalar field with a mass of order H_0 If such a field exists, then it is generally assumed that its coupling to matter must be tuned to unnaturally small values in order to satisfy the tests of the Equivalence Principle (EP) In this paper, we present an alternative explanation which allows scalar fields to evolve cosmologically while having couplings to matter of order unity In our scenario, the mass of the fields depends on the local matter density: the interaction range is typically of order 1 mm on Earth (where the density is high) and of order 10-10^4 AU in the solar system (where the density is low) All current bounds from tests of General Relativity are satisfied Nevertheless, we predict that near-future experiments that will test gravity in space will measure an effective Newton's constant different by order unity from that on Earth, as well as EP violations stronger than currently allowed by laboratory experiments Such outcomes would constitute a smoking gun for our scenario
1,388 citations
TL;DR: In this article, the present day and initial mass functions in various components of the Galaxy, disk, spheroid, young and globular clusters, were reviewed and a general IMF determination was examined in the context of star formation theory.
Abstract: We review recent determinations of the present day and initial mass functions in various components of the Galaxy, disk, spheroid, young and globular clusters. As a general feature, the IMF is well described by a power-law form for $m\ga 1 \msol$ and a lognormal form below. The extension of the disk IMF into the brown dwarf (BD) regime is in good agreement with observations and yields a disk BD number-density comparable to the stellar one $\sim 0.1 \pc3$. The IMF of young clusters is found to be consistent with the disk field IMF, providing the same correction for unresolved binaries. The spheroid IMF relies on much less robust grounds. Within all the uncertainties, it is found to be similar to the one derived for globular clusters, and is well represented also by a lognormal form with a characteristic mass slightly larger than for the disk. The IMF characteristic of early star formation remains undetermined, but different observational constraints suggest that it does not extend below $\sim 1 \msol$. These IMFs allow a reasonably robust determination of the Galactic present-day and initial stellar and brown dwarf contents. They also have important galactic implications in yielding more accurate mass-to-light ratio determinations. The M/L ratios obtained with the disk and the spheroid IMF yield values 1.8 and 1.4 smaller than a Salpeter IMF, respectively. This general IMF determination is examined in the context of star formation theory. (shortened)
881 citations
TL;DR: In this article, adaptive spatial binning of Integral-Field Spectroscopic (IFS) data to reach a chosen constant signal-to-noise ratio per bin is presented.
Abstract: We present new techniques to perform adaptive spatial binning of Integral-Field Spectroscopic (IFS) data to reach a chosen constant signal-to-noise ratio per bin. These methods are required for the proper analysis of IFS observations, but can also be used for standard photometric imagery or any other two-dimensional data. Various schemes are tested and compared by binning and extracting the stellar kinematics of the Sa galaxy NGC2273 from spectra obtained with the panoramic IFS SAURON.
770 citations
TL;DR: In this article, a simple treatment for incorporating induced polarization in computer simulations is formulated on the basis of the classical Drude oscillator model, where electronic induction is represented by the displacement of a charge-carrying massless particle attached to a polarizable atom under the influence of the local electric field.
Abstract: A simple treatment for incorporating induced polarization in computer simulations is formulated on the basis of the classical Drude oscillator model. In this model, electronic induction is represented by the displacement of a charge-carrying massless particle attached to a polarizable atom under the influence of the local electric field. The traditional self-consistent field (SCF) regime of induced polarization is reproduced if these auxiliary particles are allowed to relax instantaneously to their local energy minima for any given fixed configuration of the atoms in the system. In practice, such treatment is computationally prohibitive for generating molecular dynamics trajectories because the electric field must be recalculated several times iteratively to satisfy the SCF condition, and it is important to seek a more efficient way to simulate the classical Drude oscillator model. It is demonstrated that a close approximation to the SCF regime can be simulated efficiently by considering the dynamics of a...
599 citations
TL;DR: A theoretical model for the excitation and emission of SH radiation at the tip is developed and it is found that this source can be represented by a single on-axis oscillating dipole.
Abstract: The field near a sharp metal tip can be strongly enhanced if irradiated with an optical field polarized along the tip axis. We demonstrate that the enhanced field gives rise to local second-harmonic (SH) generation at the tip surface thereby creating a highly confined photon source. A theoretical model for the excitation and emission of SH radiation at the tip is developed and it is found that this source can be represented by a single on-axis oscillating dipole. The model is experimentally verified by imaging the spatial field distribution of strongly focused laser modes.
596 citations
TL;DR: In this article, the authors investigated the nonthermal X-ray emission from Cas A, using BeppoSAX, Compton Gamma Ray Observatory OSSE, and Chandra data, and constructed a simple two-zone model.
Abstract: We investigate the nonthermal X-ray emission from Cas A, using BeppoSAX, Compton Gamma Ray Observatory OSSE, and Chandra data. For the hard X-ray continuum we test the model proposed by Laming, which invokes nonthermal bremsstrahlung from electrons accelerated by lower hybrid plasma waves. The justification for this model comes from our determination of a lower limit to the average magnetic field of B > 0.5 mG. For such high magnetic fields, the synchrotron losses are severe enough that most of the electron populations responsible for the radio emission have maximum electron energies well below the limit for which X-ray synchrotron emission is important. However, we do suggest that the rim surrounding Cas A, seen in Chandra continuum images, is X-ray synchrotron emission. The width of this rim of 15-4'' can be used to infer the magnetic field near the shock front, for which we estimate B = 0.08-0.16 mG and electron energies of ~57-40 TeV. This magnetic field strength is lower than the average magnetic field but higher than what may be expected from shocked interstellar medium, suggesting either a high magnetic field in the wind of the progenitor or rapid postshock field amplification by nonlinear growth of plasma waves. Combining the two magnetic field measurements, we have constructed a simple two-zone model. Most of the radio emission comes from inside Cas A, where the magnetic field is strong. In contrast, the inverse Compton emission is dominated by emission from near the shock front. Only for our lower limit on the magnetic field strength near the shock front is it possible to explain the recent detection of TeV emission by the High Energy Gamma Ray Astronomy experiment with inverse Compton emission, for which, in addition, we have to assume a rather high far-infrared photon density that should be twice as high as our best estimate of ~70 cm-3. Pion decay is therefore likely to be the dominant emission from Cas A at TeV energies.
420 citations
TL;DR: In this article, the upscaled groundwater flow and solute transport characteristics of two-dimensional hydraulic conductivity fields with three fundamentally different spatial textures and consider the conditions under which physical mobile-immobile domain mass transfer occurs in these fields.
Abstract: [1] We describe the upscaled groundwater flow and solute transport characteristics of two-dimensional hydraulic conductivity fields with three fundamentally different spatial textures and consider the conditions under which physical mobile–immobile domain mass transfer occurs in these fields. All three fields have near-identical lognormal univariate conductivity distributions, as well as near-identical isotropic spatial covariance functions. They differ in the pattern by which high- or low-conductivity regions are connected: the first field has connected high-conductivity structures; the second is multivariate log-Gaussian and, hence, has connected structures of intermediate value; and the third has connected regions of low conductivity. We find substantially different flow and transport behaviors in the three different fields. Flow and transport in the multivariate log-Gaussian field are consistent with stochastic theory. The field with connected high-conductivity paths has an effective conductivity greater than the geometric mean and large variations in fluid velocity. It produces significant mass transfer behavior (i.e., tailing) when the conductivity variance is large and, depending on the system parameters, this mass transfer is driven by either diffusion or advection. In the field with connected low-conductivity regions, the effective conductivity is below the geometric mean and transport is well characterized by the advection–dispersion model with a dispersivity smaller than that in the multivariate log-Gaussian field. Thus, physical mobile–immobile domain mass transfer may occur in smooth hydraulic conductivity fields with univariate log-Gaussian density functions if the variability in conductivity is sufficient and the high values are more connected than modeled by the multivariate log-Gaussian distribution.
392 citations
TL;DR: In this article, the authors reported the discovery of linear polarization in the prompt gamma-ray emission from GRB021206, which indicates that it is synchrotron emission from relativistic electrons in a strong magnetic field.
Abstract: Observations of the afterglows of gamma-ray bursts (GRBs) have revealed that they lie at cosmological distances, and so correspond to the release of an enormous amount of energy. The nature of the central engine that powers these events and the prompt gamma-ray emission mechanism itself remain enigmatic because, once a relativistic fireball is created, the physics of the afterglow is insensitive to the nature of the progenitor. Here we report the discovery of linear polarization in the prompt gamma-ray emission from GRB021206, which indicates that it is synchrotron emission from relativistic electrons in a strong magnetic field. The polarization is at the theoretical maximum, which requires a uniform, large-scale magnetic field over the gamma-ray emission region. A large-scale magnetic field constrains possible progenitors to those either having or producing organized fields. We suggest that the large magnetic energy densities in the progenitor environment (comparable to the kinetic energy densities of the fireball), combined with the large-scale structure of the field, indicate that magnetic fields drive the GRB explosion.
375 citations
TL;DR: It is determined that N2 molecules are four times more likely to ionize when aligned parallel to the field than when aligned perpendicular to it, which indicates the dependence of strong field ionization of N2 on molecular orientation.
Abstract: We demonstrate a method to measure strong field laser ionization of aligned molecules. The method employs a macroscopic field-free dynamic alignment, which occurs during revivals of rotational wave packets produced by a femtosecond laser pulse. We investigate the dependence of strong field ionization of ${\mathrm{N}}_{\mathrm{2}}$ on molecular orientation. We determine that ${\mathrm{N}}_{\mathrm{2}}$ molecules are four times more likely to ionize when aligned parallel to the field than when aligned perpendicular to it.
373 citations
TL;DR: An overview of properties of polymer-nanoparticle composites in bulk and in solution is presented along with a review of work performed during the last three years in this paper, particularly focused on organic-inorganic materials such as polymer-nospheres, tubes, rods, fibers and nanoplatelets.
Abstract: An overview of properties of polymer–nanoparticle composites in bulk and in solution is presented along with a review of work performed during the last 3 years. The review is particularly focused on organic–inorganic materials such as polymer–nanospheres, tubes, rods, fibers and nanoplatelets. Fundamental studies on flow-induced structures in polymer–particle composites are emphasized. This relatively new area demands sophisticated experiments to augment pragmatic knowledge necessary to support theoretical descriptions of composite structures and properties. The complexity of this area guarantees that this will remain an active field for some time to come.
TL;DR: In this article, a decomposition of the microscopic anelastic strain field on a finite set of transformation fields is proposed to describe the overall behavior of composites with nonlinear dissipative phases.
TL;DR: In this article, a universal expression for the difference of the scale anomalies between the ultraviolet and infrared fixed points, which is of order 1 in the large N expansion, was derived.
TL;DR: In this article, the surface wave equations appropriate to 3D ocean models have been presented in the literature, and expressions for vertically dependent radiation stresses and a definition of the Doppler velocity for a vertically dependent current field are obtained.
Abstract: Surface wave equations appropriate to three-dimensional ocean models apparently have not been presented in the literature. It is the intent of this paper to correct that deficiency. Thus, expressions for vertically dependent radiation stresses and a definition of the Doppler velocity for a vertically dependent current field are obtained. Other quantities such as vertically dependent surface pressure forcing are derived for inclusion in the momentum and wave energy equations. The equations include terms that represent the production of turbulence energy by currents and waves. These results are a necessary precursor for three-dimensional ocean models that handle surface waves together with wind- and buoyancy-driven currents. Although the third dimension has been added here, the analysis is based on the assumption that the depth dependence of wave motions is provided by linear theory, an assumption that is the basis of much of the wave literature.
Book•
01 Jun 2003
TL;DR: In this article, a series of increasingly complex worked examples, emphasizing problems based on physical processes, devices, and models, are presented, with sample problems and solutions for each new concept, using different problem solving methods to demonstrate advantages and limitations of each approach.
Abstract: Develops problem solving confidence through a series of increasingly complex worked examples, emphasizing problems based on physical processes, devices, and models. Covers charges as the source of the electric field coupled to polarizable and conducting media with negligible magnetic field; currents as the source of the magnetic field coupled to magnetizable media with electromagnetic induction generating an electric field; and electrodynamics where the electric and magnetic fields are of equal importance resulting in radiating waves. Presents sample problems and solutions for each new concept, using different problem solving methods to demonstrate advantages and limitations of each approach. Clarifies the rigorous mathematical development by describing systems with linear, constant co-efficient differential and difference equations.
TL;DR: In this paper, the self-forces of a small mass moving through curved spacetime are decomposed into two parts each of which satisfies the perturbed Einstein equations through O(mu) and includes the ''tail term'' which determines the self force effects of the particle interacting with its own gravitational field, including radiation reaction.
Abstract: The gravitational field of a particle of small mass \mu moving through curved spacetime is naturally decomposed into two parts each of which satisfies the perturbed Einstein equations through O(\mu). One part is an inhomogeneous field which, near the particle, looks like the \mu/r field distorted by the local Riemann tensor: it does not depend on the behavior of the source in either the infinite past or future. The other part is a homogeneous field and includes the ``tail term'': it completely determines the self force effects of the particle interacting with its own gravitational field, including radiation reaction. Self force effects for scalar, electromagnetic and gravitational fields are all described in this manner.
TL;DR: In this article, a wave function is specified by partitioning an active space into an unrestricted number of orbital groups and limiting values, in the form of minima and maxima, for the electron occupancies of each group.
Abstract: In order to reduce the number of ineffective configurations in a priori generated configuration spaces, a direct configuration interaction method has been developed which limits the electron occupations of orbital groups making up a total active space. A wave function is specified by first partitioning an active space into an unrestricted number of orbital groups and second by providing limiting values, in the form of minima and maxima, for the electron occupancies of each group. The configuration interaction problem corresponding to all possible determinants satisfying these conditions is solved in a fully direct manner by the use of Slater–Condon expressions in conjunction with single and double replacements. This configuration interaction approach, termed occupation restricted multiple active space-configuration interaction, has also been linked with orbital optimization programs to produce the occupation restricted multiple active space-self consistent field method.
TL;DR: The linear and nonlinear properties of the lower-hybrid drift instability in a thin current sheet with thickness comparable to a thermal ion gyroradius ρi∼L were examined in this paper.
Abstract: The linear and nonlinear properties of the lower-hybrid drift instability are examined in a thin current sheet with thickness comparable to a thermal ion gyroradius ρi∼L. The linear Vlasov stability is calculated using a formally exact technique in which the orbit integrals are treated numerically and the eigenvalue problem for the resulting system of integrodifferential equations is solved using a finite element representation of the eigenfunction. For the fastest growing lower-hybrid modes with wavelength on the electron gyroscale (kyρe∼1), the resulting mode structure is localized on the edge of the current sheet. However, for modes with wavelengths intermediate between the electron and ion gyroscale kyρiρe∼1, the lower-hybrid instability has a significant electromagnetic component to the mode structure which is localized in the central region of the sheet. The addition of a weak guide field complicates the mode structure and gives rise to fluctuations in all three components of the magnetic field. The...
TL;DR: In this paper, a three-axis search coil magnetometer is used to measure magnetic fluctuations at frequencies up to 4 kHz, a waveform unit (up to either 10 Hz or 180 Hz) and a Spectrum Analyser (upto 4 kHz) for the Spatio Temporal Analysis of Field Fluctuations (STAFF) experiment.
Abstract: . The Spatio Temporal Analysis of Field Fluctuations (STAFF) experiment is one of the five experiments, which constitute the Cluster Wave Experiment Consortium (WEC). STAFF consists of a three-axis search coil magnetometer to measure magnetic fluctuations at frequencies up to 4 kHz, a waveform unit (up to either 10 Hz or 180 Hz) and a Spectrum Analyser (up to 4 kHz). The Spectrum Analyser combines the 3 magnetic components of the waves with the two electric components measured by the Electric Fields and Waves experiment (EFW) to calculate in real time the 5 × 5 Hermitian cross-spectral matrix at 27 frequencies distributed logarithmically in the frequency range 8 Hz to 4 kHz. The time resolution varies between 0.125 s and 4 s. The first results show the capabilities of the experiment, with examples in different regions of the magnetosphere-solar wind system that were encountered by Cluster at the beginning of its operational phase. First results obtained by the use of some of the tools that have been prepared specifically for the Cluster mission are described. The characterisation of the motion of the bow shock between successive crossings, using the reciprocal vector method, is given. The full characterisation of the waves analysed by the Spectrum Analyser, thanks to a dedicated program called PRASSADCO, is applied to some events; in particular a case of very confined electromagnetic waves in the vicinity of the equatorial region is presented and discussed. Key words. Magnetospheric physics (magnetopause, cusp and boundary layer) – Space plasma physics (waves and instabilities; shock waves)
TL;DR: The S-PROG model as mentioned in this paper is an advection-based nowcasting system that uses the observations that rain fields commonly exhibit both spatial and dynamic scaling properties, that is, the lifetime of a feature in the field is dependent on the scale of the feature (large features evolve more slowly than small features).
Abstract: Quantitative nowcasts of rainfall are frequently based on the advection of rain fields observed by weather radar. Spectral Prognosis (S-PROG) is an advection-based nowcasting system that uses the observations that rain fields commonly exhibit both spatial and dynamic scaling properties, that is, the lifetime of a feature in the field is dependent on the scale of the feature (large features evolve more slowly than small features), and that features at all scales between the outer and inner observed scales are present in the field. The logarithm of the radar reflectivity field is disaggregated into a set or cascade of fields, in which each field in the set (or level in the cascade) represents the features of the original field over a limited range of scales. The Lagrangian temporal evolution of each level in the cascade is modeled using a simple autoregressive (lag 2) model, which automatically causes the forecast field to become smooth as the structures at the various scales evolve through their life cycles, or can be used to generate conditional simulations if the noise term is included. This paper describes the model and presents preliminary results.
TL;DR: It is explicitly shown that in the adiabatic limit dephasing is due to fluctuations of the dynamical phase.
Abstract: The effect of fluctuations in the classical control parameters on the Berry phase of a spin 1/2 interacting with an adiabatically cyclically varying magnetic field is analyzed. It is explicitly shown that in the adiabatic limit dephasing is due to fluctuations of the dynamical phase.
TL;DR: In this article, negative energy phantom field with quantum CFT supports the creation of deSitter universe, while pure phantom or dust with quantum effects may naturally lead to the occurence of anti-deSitter brane universe but not deSitters one.
Abstract: Five-dimensional braneworld cosmology with deSitter (inflationary) brane universe induced by classical and quantum matter is discussed. It is shown that negative energy phantom field with quantum CFT supports the creation of deSitter universe. On the same time, pure phantom or dust with quantum effects, or Chaplygin gas with quantum effects may naturally lead to the occurence of Anti-deSitter brane universe but not deSitter one. It is also interesting that unlike to four-dimensional gravity, for phantom with (or without) quantum contribution the standard cosmological energy conditions may be effectively satisfied.
TL;DR: In this article, an analysis of the HST images of 82 nearby field late-M and L dwarfs is presented, where the statistics included systems with separations in the range 1.6-16 A.U.
Abstract: We present analysis of Hubble Space Telescope images of 82 nearby field late-M and L dwarfs. We resolve 13 of these systems into double M/L dwarf systems and identify an additional possible binary. Combined with previous observations of 20 L dwarfs, we derive an observed binary fraction for ultracool dwarfs of 17+4-3%, where the statistics included systems with separations in the range 1.6-16 A.U. We argue that accounting for biases and incompleteness leads to an estimated binary fraction 15+-5% in the range 1.6-16 A.U. No systems wider than 16 A.U. are seen, implying that the wide companion frequency is less than 1.7%; the distribution of orbital separation is peaked at ~2-4 A.U. and differs greatly from the G dwarf binary distribution. Indirect evidence suggests that the binary fraction is ~5+-3% for separations less than 1.6 A.U. We find no evidence for differences in the binary fraction between stellar late-M and L dwarfs and substellar L dwarfs. We note, however, that the widest (>10 A.U.) systems in our sample are all of earlier (M8-L0) spectral type; a larger sample is needed determine if this is a real effect. One system with a spectral type of L7 has a secondary that is fainter in the HST F814W filter but brighter in F1042M; we argue that this secondary is an early-T dwarf.
TL;DR: A mechanism by which neocortical ripples during normal network activity could actively participate in the initiation of seizures on reaching a certain threshold amplitude is proposed, which involves a vicious feedback loop in which very fast oscillations in field potentials are a reflection of synchronousaction potentials, and in turn these oscillations help generate and synchronize action potentials in adjacent neurons through electrical interactions.
Abstract: Multi-site field potential and intracellular recordings from various neocortical areas were used to study very fast oscillations or ripples (80–200 Hz) during electrographic seizures in cats under ...
TL;DR: In this paper, the implications of causality on a primordial magnetic field were discussed and it was shown that the residual field on large scales is much more suppressed than usually assumed, and that a helical component is even more reduced.
Abstract: We discuss the implications of causality on a primordial magnetic field. We show that the residual field on large scales is much more suppressed than usually assumed, and that a helical component is even more reduced. Due to this strong suppression, even maximal primordial fields generated at the electroweak phase transition can just marginally seed the fields in clusters, but they cannot leave any detectable imprint on the cosmic microwave background.
TL;DR: Leka et al. as discussed by the authors used photospheric vector magnetic field data from the University of Hawai'i Imaging Vector Magnetograph, with good spatial and temporal sampling, to study the question of identifying a pre-flare signature unique to flare events in parameters derived from the magnetic vector field.
Abstract: Photospheric vector magnetic field data from the University of Hawai'i Imaging Vector Magnetograph, with good spatial and temporal sampling, are used to study the question of identifying a preflare signature unique to flare events in parameters derived from the magnetic vector field, B In this first of a series of papers, we present the data analysis procedure and sample results focusing only on three active regions (NOAA Active Regions 8636, 8771, and 0030), three flares (two M class and one X class), and (most importantly) a flare-quiet epoch in a comparable flare-producing region Quantities such as the distribution of the field morphology, horizontal spatial gradients of the field, vertical current, current helicity, "twist" parameter α, and magnetic shear angles are parameterized using their moments and appropriate summations The time series of the resulting parameterizations are examined one at a time for systematic differences in overall magnitude and evolution between the flare and flare-quiet examples The variations expected due to atmospheric seeing changes are explicitly included In this qualitative approach we find (1) no obvious flare-imminent signatures from the plain magnetic field vector and higher moments of its horizontal gradient or from most parameterizations of the vertical current density; (2) counterintuitive but distinct flare-quiet implications from the inclination angle and higher moments of the photospheric excess magnetic energy; (3) flare-specific or flare-productivity signatures, sometimes weak, from the lower moments of the field gradients, kurtosis of the vertical current density, magnetic twist, current helicity density, and magnetic shear angle The strongest results are, however, that (4) in ensuring a flare-unique signature, numerous candidate parameters (considering both their variation and overall magnitude) are nullified on account of similar behavior in a flare-quiet region, and hence (5) considering parameters one at a time in this qualitative manner is inadequate To address these limitations, a quantitative statistical approach is presented in Paper II by Leka & Barnes
TL;DR: It is shown that the vesicle, which assumes a steady orientation with respect to the shear flow for r identical with eta(in)/eta(out)or=r( c), and develops a powerful method, the advected-field approach.
Abstract: We study dynamics of vesicles with a viscosity contrast between the interior and exterior, and subjected to a linear shear flow. It is shown that the vesicle, which assumes a steady orientation with respect to the shear flow for r identical with eta(in)/eta(out) or=r(c). Tumbling occurs as a saddle-node bifurcation. We present analytical and numerical results. We develop a powerful method, the advected-field approach. This method allows one to treat several different phenomena with great flexibility.
TL;DR: In this article, the power counting for effective field theories with narrow resonances near a two-body threshold is discussed, where the effective field theory is perturbative and only one combination of coupling constants is fine-tuned.
TL;DR: In this article, the authors studied the effect of quantum interference and coupling field on the optical bistability of a three-level atomic system in V-configuration confined in a unidirectional optical ring cavity.
Abstract: The phenomenon of optical bistability is studied for the three-level atomic system in V-configuration confined in a unidirectional optical ring cavity, and the effects of quantum interference and coupling field are investigated. The possibility of obtaining optical multistability in the system by controlling quantum interference and coupling field strength is also discussed.