1,433 research outputs found
Many-body wave scattering by small bodies
Scattering problem by several bodies, small in comparison with the
wavelength, is reduced to linear algebraic systems of equations, in contrast to
the usual reduction to some integral equations
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
Benchmarking Burgerzaken : een empirisch onderzoek naar de kostendoelmatigheid van burgerzaken
De noodzaak van productiviteitsgroei in de publieke sector is nu groter dan ooit. Aan deze noodzaak liggen twee ontwikkelingen ten grondslag. In de eerste plaats staan de financiën van de publieke sector onder druk als gevolg van bezuinigingen. In de tweede plaats worden er op de langere termijn knelpunten op de arbeidsmarkt verwacht als gevolg van vergrijzing en ontgroening van de bevolking. In de marksector dwingen concurrentieoverwegingen organisaties ertoe om voortdurend aandacht te hebben voor productiviteitsverbetering en deze waar mogelijk te realiseren. In de publieke sector ontbreken de prikkels van de markt en lijken productiviteitsverbeteringen moeizaam tot stand te komen
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
An Interacting Galaxy System Along a Filament in a Void
Cosmological voids provide a unique environment for the study of galaxy
formation and evolution. The galaxy population in their interior have
significantly different properties than average field galaxies. As part of our
Void Galaxy Survey (VGS), we have found a system of three interacting galaxies
(VGS_31) inside a large void. VGS_31 is a small elongated group whose members
are embedded in a common HI envelope. The HI picture suggests a filamentary
structure with accretion of intergalactic cold gas from the filament onto the
galaxies. We present deep optical and narrow band H_alpha data, optical
spectroscopy, near-UV and far-UV GALEX and CO(1-0) data. We find that one of
the galaxies, a Markarian object, has a ring-like structure and a tail evident
both in optical and HI. While all three galaxies form stars in their central
parts, the tail and the ring of the Markarian object are devoid of star
formation. We discuss these findings in terms of a gravitational interaction
and ongoing growth of galaxies out of a filament. VGS_31 is one of the first
observed examples of a filamentary structure in a void. It is an important
prototype for understanding the formation of substructure in a void. This
system also shows that the galaxy evolution in voids can be as dynamic as in
high density environments.Comment: 17 pages, 8 figures, accepted for publication in A
KK246, a dwarf galaxy with extended H I disk in the Local Void
We have found that KK 246, the only confirmed galaxy located within the
nearby Tully Void, is a dwarf galaxy with an extremely extended H I disk and
signs of an H I cloud with anomalous velocity. It also exhibits clear
misalignment between the kinematical major and minor axes, indicative of an
oval distortion, and a general misalignment between the H I and optical major
axes. We measure a H I mass of 1.05 +- 0.08 x 10^8 M_sun, and a H I extent 5
times that of the stellar disk, one of the most extended H I disks known. We
estimate a dynamical mass of 4.1 x 10^9 M_sun, making this also one of the
darkest galaxies known, with a mass-to-light ratio of 89. The relative
isolation and extreme underdense environment make this an interesting case for
examining the role of gas accretion in galaxy evolution.Comment: 15 pages, 8 figures, 2 tables, accepted for publication in A
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
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
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
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