198,157 research outputs found
Mass Hierarchy and Trapping of Gravity
We construct a model consisting of many D3-branes with only positive tension
in a five-dimensional anti-de Sitter space-time geometry. It is shown that this
type of model naturally realizes not only exponential mass hierarchy between
the Planck scale and the electroweak scale but also trapping of the graviton on
the D3-branes. It is pointed out that our model may have a flexibility to
explain the existence of more than one disparate mass scales, such as the
electroweak scale and the GUT scale, on the same D3-brane.Comment: 11 pages, LaTex 2
Modified Slim-Disk Model Based on Radiation-Hydrodynamic Simulation Data: The Conflict Between Outflow and Photon Trapping
Photon trapping and outflow are two key physics associated with the
supercritical accretion flow. We investigate the conflict between these two
processes based on two-dimensional radiation-hydrodynamic (RHD) simulation data
and construct a simplified (radially) one-dimensional model. Mass loss due to
outflow, which is not considered in the slim-disk model, will reduce surface
density of the flow, and if very significant, it will totally suppress photon
trapping effects. If the photon trapping is very significant, conversely,
outflow will be suppressed because radiation pressure force will be reduced. To
see what actually occurs, we examine the RHD simulation data and evaluate the
accretion rate and outflow rate as functions of radius. We find that the former
monotonically decreases, while the latter increases, as the radius decreases.
However, the former is kept constant at small radii, inside several
Schwarzschild radii, since the outflow is suppressed by the photon trapping
effects. To understand the conflict between the photon trapping and outflow in
a simpler way, we model the radial distribution of the accretion rate from the
simulation data and build up a new (radially) one-dimensional model, which is
similar to the slim-disk model but incorporates the mass loss effects due to
the outflow. We find that the surface density (and, hence, the optical depth)
is much reduced even inside the trapping radius, compared with the case without
outflow, whereas the effective temperature distribution hardly changes. That
is, the emergent spectra do not sensitively depend on the amount of mass
outflow. We conclude that the slim-disk approach is valid for interpreting
observations, even if the outflow is taken into account.Comment: 15 pages, 5 figures, accepted for publication in PAS
Variations on a theme of AGN-driven outflows: luminosity evolution and ambient density distribution
Galactic outflows are now commonly observed in starburst and active galactic
nuclei (AGN) host galaxies. Yet, there is no clear consensus on their physical
driving mechanism(s). We have previously shown that AGN radiative feedback,
driven by radiation pressure on dust, can account for the observed dynamics and
energetics of galactic outflows, provided that radiation trapping is taken into
account. Here we generalise our model results by explicitly considering the
temporal evolution of the central AGN luminosity, and the shell mass evolution
in different ambient density distributions. In the case of fixed-mass shells,
the high observed values of the momentum ratio () and
energy ratio () may be attributed to either
radiation trapping or AGN luminosity decay. In contrast, for expanding shells
sweeping up mass from the surrounding environment, a decay in AGN luminosity
cannot account for the observed high energetics, and radiation trapping is
necessarily required. Indeed, strong radiation trapping, e.g. due to high
dust-to-gas ratios, can considerably boost the outflow energetics. We obtain a
distinct radial dependence for the outflow energetics (,
) in the case of radiation trapping and luminosity decay, which
may help discriminate between the two scenarios. In this framework, the
recently discovered `fossil' outflows, with anomalously high values of the
energetics, may be interpreted as relics of past AGN activity. The observed
outflow properties may therefore provide useful constraints on the past history
of AGN activity and/or the physical conditions of the outflow launch region.Comment: accepted for publication in MNRA
Efficient single photon absorption by a trapped moving atom
The influence of the center of mass motion of a trapped two level system on
efficient resonant single photon absorption is investigated. It is shown that
this absorption process depends strongly on the ratio between the
characteristic time scales of spontaneous photon emission and of the two level
system's center of mass motion. In particular, if the spontaneous photon
emission process occurs almost instantaneously on the time scale of the center
of mass motion coherent control of the center of mass motion offers interesting
perspectives for optimizing single photon absorption. It is demonstrated that
this way time dependent modulation of a harmonic trapping frequency allows to
squeeze the two level system's center of mass motion so strongly that high
efficient single photon absorption is possible even in cases of weak
confinement by a trapping potential.Comment: 9 pages, 5 figure
The Electrostatic Ion Beam Trap : a mass spectrometer of infinite mass range
We study the ions dynamics inside an Electrostatic Ion Beam Trap (EIBT) and
show that the stability of the trapping is ruled by a Hill's equation. This
unexpectedly demonstrates that an EIBT, in the reference frame of the ions
works very similar to a quadrupole trap. The parallelism between these two
kinds of traps is illustrated by comparing experimental and theoretical
stability diagrams of the EIBT. The main difference with quadrupole traps is
that the stability depends only on the ratio of the acceleration and trapping
electrostatic potentials, not on the mass nor the charge of the ions. All kinds
of ions can be trapped simultaneously and since parametric resonances are
proportional to the square root of the charge/mass ratio the EIBT can be used
as a mass spectrometer of infinite mass range
High resolution threshold photoelectron spectroscopy by electron attachment
A system is provided for determining the stable energy levels of a species ion, of an atomic, molecular, or radical type, by application of ionizing energy of a predetermined level, such as through photoionization. The system adds a trapping gas to the gaseous species to provide a technique for detection of the energy levels. The electrons emitted from ionized species are captured by the trapping gas, only if the electrons have substantially zero kinetic energy. If the electrons have nearly zero energy, they are absorbed by the trapping gas to produce negative ions of the trapping gas that can be detected by a mass spectrometer. The applied energies (i.e. light frequencies) at which large quantities of trapping gas ions are detected, are the stable energy levels of the positive ion of the species. SF6 and CFCl3 have the narrowest acceptance bands, so that when they are used as the trapping gas, they bind electrons only when the electrons have very close to zero kinetic energy
Pheromones in pest control on currants : experiences of monitoring, disruption and mass trapping
Pheromones; current practice for monitoring of moths in Finland, control experiments in Finland: mating disruption and mass trapping
Self-Trapping of Polarons in the Rashba-Pekar Model
We performed quantum Monte Carlo study of the exciton-polaron model which
features the self-trapping phenomenon when the coupling strength and/or
particle momentum is varied. For the first time accurate data for energy,
effective mass, the structure of the polaronic cloud, dispersion law, and
spectral function are available throughout the crossover region. We observed
that self-trapping can not be reduced to hybridization of two states with
different lattice deformation, and that at least three states are involved in
the crossover from light- to heavy-mass regimes.Comment: 5 pages, 5 figures, Accepted to Phys. Rev. B Rapid Communication
Coherent molecule formation in anharmonic potentials near confinement-induced resonances
We perform a theoretical and experimental study of a system of two ultracold
atoms with tunable interaction in an elongated trapping potential. We show that
the coupling of center-of-mass and relative motion due to an anharmonicity of
the trapping potential leads to a coherent coupling of a state of an unbound
atom pair and a molecule with a center of mass excitation. By performing the
experiment with exactly two particles we exclude three-body losses and can
therefore directly observe coherent molecule formation. We find quantitative
agreement between our theory of inelastic confinement-induced resonances and
the experimental results. This shows that the effects of center-of-mass to
relative motion coupling can have a significant impact on the physics of
quasi-1D quantum systems.Comment: 7 pages, 4 figure
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