3,323 research outputs found
Microwave emission from spinning dust in circumstellar disks
In the high density environments of circumstellar disks dust grains are
expected to grow to large sizes by coagulation. Somewhat unexpectedly, recent
near-IR observations of PAH features from disks around Herbig Ae/Be stars
demonstrate that substantial amount of dust mass in these disks (up to several
tens of per cent of the total carbon content) can be locked up in particles
with sizes ranging from several to tens of nanometers. We investigate the
possibility of detecting the electric dipole emission produced by these
nanoparticles as they spin at thermal rates (tens of GHz) in cold gas. We show
that such emission peaks in the microwave range and dominates over the thermal
disk emission at \nu 5 % of the
total carbon abundance is locked up in nanoparticles. We test the sensitivity
of this prediction to various stellar and disk parameters and show that if the
potential contamination of the spinning dust component by the free-free and/or
synchrotron emission can be removed, then the best chances of detecting this
emission would be in disks with small opacity, having SEDs with steep sub-mm
slopes (which minimizes thermal disk emission at GHz frequencies). Detection of
the spinning dust emission would provide important evidence for the existence,
properties, and origin of the population of small dust particles in
protoplanetary disks, with possible ramifications for planet formation.Comment: 9 pages, 3 figures, submitted to Ap
Front dynamics during diffusion-limited corrosion of ramified electrodeposits
Experiments on the diffusion-limited corrosion of porous copper clusters in
thin gap cells containing cupric chloride are reported. By carefully comparing
corrosion front velocities and concentration profiles obtained by phase-shift
interferometry with theoretical predictions, it is demonstrated that this
process is well-described by a one-dimensional mean-field model for the generic
reaction A + B (static) -> C (inert) with only diffusing reactant (cupric
chloride) and one static reactant (copper) reacting to produce an inert product
(cuprous chloride). The interpretation of the experiments is aided by a
mathematical analysis of the model equations which allows the reaction-order
and the transference number of the diffusing species to be inferred. Physical
arguments are given to explain the surprising relevance of the one-dimensional
mean-field model in spite of the complex (fractal) structure of the copper
clusters.Comment: 26 pages, 10 figures, submitted to J. Phys. Chem. B, high quality eps
figures available at http://www-math.mit.edu/~bazant/paper
Alien Registration- Leger, Mary C E. (Auburn, Androscoggin County)
https://digitalmaine.com/alien_docs/31157/thumbnail.jp
Detection of the buckminsterfullerene cation (C60+) in space
In the early 90s, C60+ was proposed as the carrier of two diffuse
interstellar bands (DIBs) at 957.7 and 963.2 nm, but a firm identification
still awaits gas-phase spectroscopic data. Neutral C60, on the other hand, was
recently detected through its infrared emission bands in the interstellar
medium and evolved stars. In this contribution, we present the detection of
C60+ through its infrared vibrational bands in the NGC 7023 nebula, based on
spectroscopic observations with the Spitzer space telescope, quantum chemistry
calculation, and laboratory data from the literature. This detection supports
the idea that C60+ could be a DIB carrier, and provides robust evidence that
fullerenes exist in the gas-phase in the interstellar medium. Modeling efforts
to design specific observations, combined with new gas-phase data, will be
essential to confirm this proposal. A definitive attribution of the 957.7 and
963.2 nm DIBs to C60+ would represent a significant step forward in the field.Comment: To appear in "Proceedings of IAU 297 symposium on the Diffuse
Interstellar Bands", eds. J. Cami and N. Cox (5 pages
Amaryllis : Valse Lente
https://digitalcommons.library.umaine.edu/mmb-ps/2044/thumbnail.jp
A New Family of Planets ? "Ocean Planets"
A new family of planets is considered which is between rochy terrestrial
planets and gaseous giant ones: "Ocean-Planets". We present the possible
formation, composition and internal models of these putative planets, including
that of their ocean, as well as their possible Exobiology interest. These
planets should be detectable by planet detection missions such as Eddington and
Kepler, and possibly COROT (lauch scheduled in 2006). They would be ideal
targets for spectroscopic missions such as Darwin/TPF.Comment: 15 pages, 3 figures submitted to Icarus notes (10 july 2003
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