19,258 research outputs found
The Threebrane Soliton of the M-Fivebrane
We discuss the supersymmetry algebra of the M theory fivebrane and obtain a
new threebrane soliton preserving half of the six-dimensional supersymmetry.
This solution is dimensionally reduced to various D-p-branes.Comment: 10 pages, phyzz
A New Massive Type IIA Supergravity From Compactification
We consider the most general form for eleven dimensional supersymmetry
compatible with on-shell superfields. This allows for the introduction of a
conformal Spin(1,10) connection. In eleven dimensional Minkowski space this
modification is trivial and can be removed by a field redefinition, however,
upon compactification on S^1 it is possible to introduce a non-trivial `Wilson
line'. The resulting ten dimensional supergravity has massive 1-form and 3-form
potentials and a cosmological constant. This theory does not possess a
supersymmetric eightbrane soliton but it does admit a supersymmetric non-static
cosmological solution.Comment: 13 pages, phyzzx. The introduction is clarifed and a reference adde
Dynamic power load simulator
Two independent models simulate dynamic and steady-state responses of electrical and electronic equipment under power load. One is resistance/capacitance/inductance network, and the other is variable resistance analog device. Resistance, inductance, and/or capacitance are selected by iterative process; time-domain response is compared with that of real equipment to select optimal values
Procyon-A and Eta-Bootis: Observational Frequencies Analyzed by the Local-Wave Formalism
In the present analysis of Procyon-A and Eta-Bootis, we use the local-wave
formalism which, despite its lack of precision inherent to any semi-analytical
method, uses directly the model profile without any modification when
calculating the acoustic mode eigenfrequencies. These two solar-like stars
present steep variations toward the center due to the convective core
stratification, and toward the surface due to the very thin convective zone.
Based on different boundary conditions, the frequencies obtained with this
formalism are different from that of the classical numerical calculation. We
point out that (1) the frequencies calculated with the local-wave formalism
seem to agree better with observational ones. All the frequencies detected with
a good confident level including those classified as 'noise' find an
identification, (2) some frequencies can be clearly identified here as
indications of the core limit.Comment: SOHO 18 / GONG 2006 / HELAS I Meetin
Modélisation du devenir des produits organiques industriels en milieu aquatique - Revue bibliographique
La nécessité de connaßtre aussi bien que possible l'impact des produits rejetés dans l'environnement a conduit à la mise au point de modÚles mathématiques permettant de mieux comprendre le devenir des produits et de prédire l'exposition à laquelle pourra étre soumis l'environnement.Le présent article fait le point des différents modÚles publiés pour ce qui concerne le milieu aquatique et suggÚre différents critÚres permettant de classer les modÚles suivant une complexité croissante.Reprenant la terminologie de MACKAY (1979), 4 types de modÚles sont décrits :- modÚles homogÚnes, équilibrés, conservatifs et stationnaires,- modÚles homogÚnes, non-équilibrés, non-conservatifs et stationnaires,- modÚles homogÚnes, non-équilibrés, non-conservatifs et non-stationnaires,- modÚles de dispersion.Assessing the hazard of a chemical to aquatic life is based on comparing the exposure concentration and the « no effects » concentration. The Greater the ratio between these two concentrations, called the margin of safety, the smaller the hazard to aquatic life.For chemicals already in the environment, monitoring programs can lead to an estimate of the exposure concentrations, but for new chemicals, predictive methods are necessary. This leads to the development of mathematical models which give an estimate of the environmental concentrations front the characteristics of the environment, of the chemical and of the quantity released in the environment.This article gives an overview of the different models which have been already published and suggests a classification based on the following criteria :- number of compartments,- closed or open system,- the degradation of the chemical is or is not taken into account,- an equilibrium has or has not been achieved between the compartments,- the situation is or is not at steady-state.Based on these criteria and quoting MACKAY (1979), four types of models are described :- Homogeneous, equilibrium, conservative and steady-state models,- Homogeneous, non-equilibrium, non-conservative and steady-state models,- Homogeneous, non-equilibrium, non-conservative and unsteady-state models,- Dispersion models.A review of these models applied to artificial or natural ecosystems la presented showing the extent to which these models have beau validated.These models are used not only to predict the exposure concentrations but they also help towards understanding the different phenomena which can affect the fate of a chemical. They allow to identify the mort important phenomena and those which have to be extensively studied. They are also useful for organizing experiments.However and though they are more and more used, these models have still to be improved since several fundamental phenomena, such as the sediment/water exchanges, are still badly understood
Suppression of Giant Magnetoresistance by a superconducting contact
We predict that current perpendicular to the plane (CPP) giant
magnetoresistance (GMR) in a phase-coherent magnetic multilayer is suppressed
when one of the contacts is superconducting. This is a consequence of a
superconductivity-induced magneto-resistive (SMR) effect, whereby the
conductance of the ferromagnetically aligned state is drastically reduced by
superconductivity. To demonstrate this effect, we compute the GMR ratio of
clean (Cu/Co)_nCu and (Cu/Co)_nPb multilayers, described by an ab-initio spd
tight binding Hamiltonian. By analyzing a simpler model with two orbitals per
site, we also show that the suppression survives in the presence of elastic
scattering by impurities.Comment: 5 pages, 4 figures. Submitted to PR
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Rochechouart hydrothermal overprint: disentangling the timing of events through Ar-Ar dating
There is a growing interest in the thermal evolution and fluid behavior of impact structures in the context of their possible influence on emergence of life both in the Early Earth and on other Planetary Bodies. This is largely related to hydrothermal mechanisms at work during the cooling of the hot materials produced and deposited in impact craters. Yet most of the research in this field is focused on theoretical approaches and mathematical models. Ground truth data of terrestrial craters are limited, despite the fact that they are by far the most accessible reservoir for testing models. Even on Earth, few of the 185 impact sites are sufficiently well preserved to yield material that can constrain the key processes of temperature evolution and water availability. The Rochechouart impact crater in the Massif Central region of France exposes rocks that recorded the hydrothermal system. Target rocks immediately below the crater floor are widely exposed within the ~24 km Rochechouart impact structure overlaid by the complete sequence of crater fill deposits in an inner zone ~15 km
Probing electron acceleration and X-ray emission in laser-plasma accelerator
While laser-plasma accelerators have demonstrated a strong potential in the
acceleration of electrons up to giga-electronvolt energies, few experimental
tools for studying the acceleration physics have been developed. In this paper,
we demonstrate a method for probing the acceleration process. A second laser
beam, propagating perpendicular to the main beam is focused in the gas jet few
nanosecond before the main beam creates the accelerating plasma wave. This
second beam is intense enough to ionize the gas and form a density depletion
which will locally inhibit the acceleration. The position of the density
depletion is scanned along the interaction length to probe the electron
injection and acceleration, and the betatron X-ray emission. To illustrate the
potential of the method, the variation of the injection position with the
plasma density is studied
Tuning the electron energy by controlling the density perturbation position in laser plasma accelerators
A density perturbation produced in an underdense plasma was used to improve
the quality of electron bunches produced in the laser-plasma wakefield
acceleration scheme. Quasi-monoenergetic electrons were generated by controlled
injection in the longitudinal density gradients of the density perturbation. By
tuning the position of the density perturbation along the laser propagation
axis, a fine control of the electron energy from a mean value of 60 MeV to 120
MeV has been demonstrated with a relative energy-spread of 15 +/- 3.6%,
divergence of 4 +/- 0.8 mrad and charge of 6 +/- 1.8 pC.Comment: 7 pages, 8 figure
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