1,573 research outputs found
Translation-Rotation Coupling in Transient Grating Experiments : Theoretical and Experimental Evidences
The results of a Transient Grating experiment in a supercooled molecular
liquid of anisotropic molecules and its theoretical interpretation are
presented. These results show the existence of two distinct dynamical
contributions in the response function of this experiment, density and
orientation dynamics. These dynamics can be experimentally disentangled by
varying the polarisation of the probe and diffracted beams and they have been
identified and measured in a Heterodyne Detected experiment performed on
m-toluidine. The results of the theory show a good qualitative agreement with
the measurements at all temperatures.Comment: PDF format, 14 pages including 4 figures, accepted for publication in
EPL. minor modification
Is there something of the MCT in orientationally disordered crystals ?
Molecular Dynamics simulations have been performed on the orientationally
disordered crystal chloroadamantane: a model system where dynamics are almost
completely controlled by rotations. A critical temperature T_c = 225 K as
predicted by the Mode Coupling Theory can be clearly determined both in the
alpha and beta dynamical regimes. This investigation also shows the existence
of a second remarkable dynamical crossover at the temperature T_x > T_c
consistent with a previous NMR and MD study [1]. This allows us to confirm
clearly the existence of a 'landscape-influenced' regime occurring in the
temperature range [T_c-T_x] as recently proposed [2,3].Comment: 4 pages, 5 figures, REVTEX
A low density of 0.8 g/cc for the Trojan binary asteroid 617 Patroclus
The Trojan population consists of two swarms of asteroids following the same
orbit as Jupiter and located at the L4 and L5 Lagrange points of the
Jupiter-Sun system (leading and following Jupiter by 60 degrees). The asteroid
617 Patroclus is the only known binary Trojan (Merline et al. 2001). The orbit
of this double system was hitherto unknown. Here we report that the components,
separated by 680 km, move around the system centre of mass, describing roughly
a circular orbit. Using the orbital parameters, combined with thermal
measurements to estimate the size of the components, we derive a very low
density of 0.8 g/cc. The components of Patroclus are therefore very porous or
composed mostly of water ice, suggesting that they could have been formed in
the outer part of the solar system.Comment: 10 pages, 3 figures, 1 tabl
Main Belt Binary Asteroidal Systems With Circular Mutual Orbits
In 2003, we initiated a long-term adaptive optics campaign to study the orbit
of various main-belt asteroidal systems. Here we present a consistent solution
for the mutual orbits of four binary systems: 22 Kalliope, 45 Eugenia, 107
Camilla and 762 Pulcova. With the exception of 45 Eugenia, we did not detect
any additional satellites around these systems although we have the capability
of detecting a loosely-bound fragment (located at 1/4 x RHill) that is ~40
times smaller in diameter than the primary. The common characteristic of these
mutual orbits is that they are roughly circular. Three of these binary systems
belong to a C-"group" taxonomic class. Our estimates of their bulk densities
are consistently lower (~1 g/cm3) than their associated meteorite analogs,
suggesting an interior porosity of 30-50% (taking CI-CO meteorites as analogs).
22 Kalliope, a W-type asteroid, has a significantly higher bulk density of ~3
g/cm3, derived based on IRAS radiometric size measurement. We compare the
characteristics of these orbits in the light of tidal-effect evolution.Comment: 72 pages, 9 tables, 4 figure
Main Belt Binary Asteroidal Systems With Eccentric Mutual Orbits
Using 8m-10m class telescopes and their Adaptive Optics (AO) systems, we
conducted a long-term adaptive optics campaign initiated in 2003 focusing on
four binary asteroid systems: (130) Elektra, (283) Emma, (379) Huenna, and
(3749) Balam. The analysis of these data confirms the presence of their
asteroidal satellite. We did not detect any additional satellite around these
systems even though we have the capability of detecting a loosely-bound
fragment (located at 1/4 x RHill) ~40 times smaller in diameter than the
primary. The orbits derived for their satellites display significant
eccentricity, ranging from 0.1 to 0.9, suggesting a different origin. Based on
AO size estimate, we show that (130) Elektra and (283) Emma, G-type and P-type
asteroids respectively, have a significant porosity (30-60% considering CI-CO
meteorites as analogs) and their satellite's eccentricities (e~0.1) are
possibly due to excitation by tidal effects. (379) Huenna and (3749) Balam, two
loosely bound binary systems, are most likely formed by mutual capture. (3749)
Balam's possible high bulk density is similar to (433) Eros, another S-type
asteroid, and should be poorly fractured as well. (379) Huenna seems to display
both characteristics: the moonlet orbits far away from the primary in term of
stability (20% x RHill), but the primary's porosity is significant (30-60%).Comment: 60 pages, 7 tables, 4 figures, in press to Icaru
Triplicity and Physical Characteristics of Asteroid (216) Kleopatra
To take full advantage of the September 2008 opposition passage of the M-type
asteroid (216) Kleopatra, we have used near-infrared adaptive optics (AO)
imaging with the W.M. Keck II telescope to capture unprecedented high
resolution images of this unusual asteroid. Our AO observations with the W.M.
Keck II telescope, combined with Spitzer/IRS spectroscopic observations and
past stellar occultations, confirm the value of its IRAS radiometric radius of
67.5 km as well as its dog-bone shape suggested by earlier radar observations.
Our Keck AO observations revealed the presence of two small satellites in orbit
about Kleopatra (see Marchis et al., 2008). Accurate measurements of the
satellite orbits over a full month enabled us to determine the total mass of
the system to be 4.64+/-0.02 10^18 Kg. This translates into a bulk density of
3.6 +/-0.4 g/cm3, which implies a macroscopic porosity for Kleopatra of ~
30-50%, typical of a rubble-pile asteroid. From these physical characteristics
we measured its specific angular momentum, very close to that of a spinning
equilibrium dumbbell.Comment: 35 pages, 3 Tables, 9 Figures. In press to Icaru
Avian cholera, a threat to the viability of an Arctic seabird colony?
© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS One 7 (2012): e29659, doi:10.1371/journal.pone.0029659.Evidence that infectious diseases cause wildlife population extirpation or extinction remains anecdotal and it is unclear whether the impacts of a pathogen at the individual level can scale up to population level so drastically. Here, we quantify the response of a Common eider colony to emerging epidemics of avian cholera, one of the most important infectious diseases affecting wild waterfowl. We show that avian cholera has the potential to drive colony extinction, even over a very short period. Extinction depends on disease severity (the impact of the disease on adult female survival) and disease frequency (the number of annual epidemics per decade). In case of epidemics of high severity (i.e., causing >30% mortality of breeding females), more than one outbreak per decade will be unsustainable for the colony and will likely lead to extinction within the next century; more than four outbreaks per decade will drive extinction to within 20 years. Such severity and frequency of avian cholera are already observed, and avian cholera might thus represent a significant threat to viability of breeding populations. However, this will depend on the mechanisms underlying avian cholera transmission, maintenance, and spread, which are currently only poorly known.The study was supported by the Canadian Wildlife Service-Environment Canada (http://www.ec.gc.ca/), Nunavut Wildlife Management Board (http://
www.nwmb.com/), Greenland Institute of Natural Resources (http://www.natur.gl/), Polar Continental Shelf Project (http://polar.nrcan.gc.ca/), Fonds Que´be´cois de
la Recherche sur la Nature et les Technologies (http://www.fqrnt.gouv.qc.ca/), Canadian Network of Centres of Excellence ArcticNet (http://www.arcticnet.ulaval.
ca/), Natural Sciences and Engineering Research Council of Canada (http://www.nserc-crsng.gc.ca/), and the Department of Indian Affairs and Northern Canada
(http://www.ainc-inac.gc.ca/)
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