1,107 research outputs found
Optical Albedo Theory of Strongly-Irradiated Giant Planets: The Case of HD 209458b
We calculate a new suite of albedo models for close-in extrasolar giant
planets and compare with the recent stringent upper limit for HD 209458b of
Rowe et al. using MOST. We find that all models without scattering clouds are
consistent with this optical limit. We explore the dependence on wavelength and
waveband, metallicity, the degree of heat redistribution, and the possible
presence of thermal inversions and find a rich diversity of behaviors.
Measurements of transiting extrasolar giant planets (EGPs) at short wavelengths
by MOST, Kepler, and CoRoT, as well as by proposed dedicated multi-band
missions, can complement measurements in the near- and mid-IR using {\it
Spitzer} and JWST. Collectively, such measurements can help determine
metallicity, compositions, atmospheric temperatures, and the cause of thermal
inversions (when they arise) for EGPs with a broad range of radii, masses,
degrees of stellar insolation, and ages. With this paper, we reappraise and
highlight the diagnostic potential of albedo measurements of hot EGPs shortward
of 1.3 m.Comment: 6 pages, 1 table, 1 color figure; accepted to the Astrophysical
Journa
Radiative Heat Transfer between Neighboring Particles
The near-field interaction between two neighboring particles is known to
produce enhanced radiative heat transfer. We advance in the understanding of
this phenomenon by including the full electromagnetic particle response, heat
exchange with the environment, and important radiative corrections both in the
distance dependence of the fields and in the particle absorption coefficients.
We find that crossed terms of electric and magnetic interactions dominate the
transfer rate between gold and SiC particles, whereas radiative corrections
reduce it by several orders of magnitude even at small separations. Radiation
away from the dimer can be strongly suppressed or enhanced at low and high
temperatures, respectively. These effects must be taken into account for an
accurate description of radiative heat transfer in nanostructured environments.Comment: 22 pages, 9 figures, fully self-contained derivation
Epsilons Near Zero limits in the Mie scattering theory
The classical Mie theory - electromagnetic radiation scattering by the
homogeneous spherical particles - is considered in the epsilon near zero limits
separately for the materials of the particles and the surrounding medium. The
maxima of a scattered transverse electrical (TE) field for the surrounding
medium materials with the epsilon near zero limits are revealed. The effective
multipole polarizabilities of the corresponding scattering particles are
investigated. The possibility to achieve magnetic dipole resonance and
accordingly to construct metamaterials with negative refractive index for the
aggregates spherical particles in surrounding medium with the epsilon near zero
limits is considered.Comment: 8 pages, 6 figure
Universality in scattering by large-scale potential fluctuations in two-dimensional conductors
We study electron propagation through a random array of rare, opaque and
large (compared the de Broglie wavelength of electrons) scatterers. It is shown
that for any convex scatterer the ratio of the transport to quantum lifetimes
\eta=\tau_{tr}/\tau_{tot}$ does not depend on the shape of the scatterer but
only on whether scattering is specular or diffuse and on the spatial
dimensionality (D). In particular, for specular scattering, \eta is a universal
constant determined only by the dimensionality of the system: \eta = 2 for D =
3 and \eta = 3/2 for D = 2. The crossover between classical and quantum regimes
of scattering is discussed.Comment: 4 pages, 3 figures, submitted to PR
Vacuum friction in rotating particles
We study the frictional torque acting on particles rotating in empty space.
At zero temperature, vacuum friction transforms mechanical energy into light
emission and produces particle heating. However, particle cooling relative to
the environment occurs at finite temperatures and low rotation velocities.
Radiation emission is boosted and its spectrum significantly departed from a
hot-body emission profile as the velocity increases. Stopping times ranging
from hours to billions of years are predicted for materials, particle sizes,
and temperatures accessible to experiment. Implications for the behavior of
cosmic dust are discussed.Comment: 4 figures, 10 pages, includes paper and supplementary information in
the appendi
Quantum limited particle sensing in optical tweezers
Particle sensing in optical tweezers systems provides information on the
position, velocity and force of the specimen particles. The conventional
quadrant detection scheme is applied ubiquitously in optical tweezers
experiments to quantify these parameters. In this paper we show that quadrant
detection is non-optimal for particle sensing in optical tweezers and propose
an alternative optimal particle sensing scheme based on spatial homodyne
detection. A formalism for particle sensing in terms of transverse spatial
modes is developed and numerical simulations of the efficacy of both quadrant
and spatial homodyne detection are shown. We demonstrate that an order of
magnitude improvement in particle sensing sensitivity can be achieved using
spatial homodyne over quadrant detection.Comment: Submitted to Biophys
Testing spontaneous localization theories with matter-wave interferometry
We propose to test the theory of continuous spontaneous localization (CSL) in
an all-optical time-domain Talbot-Lau interferometer for clusters with masses
exceeding 1000000 amu. By assessing the relevant environmental decoherence
mechanisms, as well as the growing size of the particles relative to the
grating fringes, we argue that it will be feasible to test the quantum
superposition principle in a mass range excluded by recent estimates of the CSL
effect.Comment: 4 pages, 3 figures; corresponds to published versio
Fast outflow of neutral hydrogen in the radio galaxy 3C293
We report the detection of very broad HI absorption against the central
regions of the radio galaxy 3C293. The absorption profile, obtained with the
Westerbork Synthesis Radio Telescope, has a full width at zero intensity of
about 1400 km/s and most of this broad absorption (~1000 km/s) is blueshifted
relative to the systemic velocity. This absorption represents a fast outflow of
neutral gas from the central regions of this AGN. Possible causes for such an
outflow are discussed. We favour the idea that the interaction between the
radio jet and the rich ISM produces this outflow. Some of the implications of
this scenario are considered.Comment: 11 pages, 4 Figures To be published in: Astrophysical Journal Letter
Infrared dust emission in the outer disk of M51
We examine faint infrared emission features detected in Spitzer Space
Telescope images of M51, which are associated with atomic hydrogen in the outer
disk and tidal tail at R greater than R_25 (4.9', ~14 kpc at d=9.6 Mpc). The
infrared colors of these features are consistent with the colors of dust
associated with star formation in the bright disk. However, the star formation
efficiency (as a ratio of star formation rate to neutral gas mass) implied in
the outer disk is lower than that in the bright disk of M51 by an order of
magnitude, assuming a similar relationship between infrared emission and star
formation rate in the inner and outer disks.Comment: 13 pages in manuscript form, 2 figures; download PDF of manuscript
with original-resolution Figure 1 at
http://www.eg.bucknell.edu/physics/thornley/thornleym51.pd
Cooperative scattering and radiation pressure force in dense atomic clouds
We consider the collective scattering by a cloud of two-level atoms
driven by an uniform radiation field. Dense atomic clouds can be described by a
continuous density and the problem reduces to deriving the spectrum of the
atom-atom coupling operator. For clouds much larger than the optical
wavelength, the spectrum is treated as a continuum, and analytical expressions
for several macroscopic quantities, such as scattered radiation intensity and
radiation pressure force, are derived. The analytical results are then compared
to the exact -body solution and with those obtained assuming a symmetric
timed Dicke state. In contrast with the symmetric timed Dicke state, our
calculations takes account of the back action of the atoms on the driving field
leading to phase shifts due to the finite refraction of the cloud
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