347 research outputs found
Collisional Velocities and Rates in Resonant Planetesimal Belts
We consider a belt of small bodies around a star, captured in one of the
external or 1:1 mean-motion resonances with a massive perturber. The objects in
the belt collide with each other. Combining methods of celestial mechanics and
statistical physics, we calculate mean collisional velocities and collisional
rates, averaged over the belt. The results are compared to collisional
velocities and rates in a similar, but non-resonant belt, as predicted by the
particle-in-a-box method. It is found that the effect of the resonant lock on
the velocities is rather small, while on the rates more substantial. The
collisional rates between objects in an external resonance are by about a
factor of two higher than those in a similar belt of objects not locked in a
resonance. For Trojans under the same conditions, the collisional rates may be
enhanced by up to an order of magnitude. Our results imply, in particular,
shorter collisional lifetimes of resonant Kuiper belt objects in the solar
system and higher efficiency of dust production by resonant planetesimals in
debris disks around other stars.Comment: 31 pages, 11 figures (some of them heavily compressed to fit into
arxiv-maximum filesize), accepted for publication at "Celestial Mechanics and
Dynamical Astronomy
Peter Liddel & Polly Low (éd.), Inscriptions and their uses in Greek and Latin literature
Dans ce volume, issu d’un colloque éponyme qui a eu lieu à l’Université de Manchester en 2009, P. Liddel et P. Low explorent la réception des inscriptions chez les auteurs grecs et latins. Dans une ample introduction ils explicitent les prémisses du colloque et de leur démarche scientifique en les inscrivant dans un projet de recueil et d’analyse de données épigraphiques transmises par les textes anciens, qu’ils ont commencé en 2003 en vue de la constitution du Database of inscriptions in Gre..
Recent collisional jet from a primitive asteroid
Here we show an example of a young asteroid cluster located in a dynamically
stable region, which was produced by partial disruption of a primitive body
about 30 km in size. We estimate its age to be only 1.9 +/- 0.3 Myr, thus its
post-impact evolution should have been very limited. The large difference in
size between the largest object and the other cluster members means that this
was a cratering event. The parent body had a large orbital inclination, and was
subject to collisions with typical impact speeds higher by a factor of 2 than
in the most common situations encountered in the main belt. For the first time
we have at disposal the observable outcome of a very recent event to study
high-speed collisions involving primitive asteroids, providing very useful
constraints to numerical simulations of these events and to laboratory
experiments.Comment: Accepted for publication by MNRA
Visualisation of semantic shifts: the case of modal markers
Poster submission for DH2020. This poster discusses the adequacy of semantic maps for the representation of semantic shifts and how previous models can be enriched by using visual cues to add more information. The poster presents a visualisation proposal applied to the diachronic study of modal markers in Latin
Collisions, Cosmic Radiation and the Colors of the Trojan Asteroids
The Trojan asteroids orbit about the Lagrangian points of Jupiter and the
residence times about their present location are very long for most of them. If
these bodies originated in the outer Solar System, they should be mainly
composed of water ice, but, in contrast with comets, all the volatiles close to
the surface would have been lost long ago. Irrespective of the rotation period,
and hence the surface temperature and ice sublimation rate, a dust layer exists
always on the surface. We show that the timescale for resurfacing the entire
surface of the Trojan asteroids is similar to that of the flattening of the red
spectrum of the new dust by solar-proton irradiation. This, if the cut-off
radius of the size distribution of the impacting objects is between 1mm and 1m
and its slope is -3, for the entire size-range. Therefore, the surfaces of most
Trojan asteroids should be composed mainly of unirradiated dust.Comment: In press in Icaru
Post Hoc Analysis of a Randomized Controlled Trial on Fasting and Plant-Based Diet in Rheumatoid Arthritis (NutriFast): Nutritional Supply and Impact on Dietary Behavior
This study aimed at comparing the nutrient supply and dietary behaviors during a plant-based diet (PBD) combined with time-restricted eating (TRE) to standard dietary recommendations in rheumatoid arthritis patients. In this open-label, randomized, controlled clinical trial, patients were assigned to either a 7-day fast followed by an 11-week PBD including TRE (A) or a 12-week anti-inflammatory diet following official German guidelines (German Nutrition Society, DGE) (B). Dietary habits were assessed by 3-day food records at weeks -1, 4 and 9 and food frequency questionnaires. 41 out of 53 participants were included in a post-hoc per protocol analysis. Both groups had similar energy, carbohydrate, sugar, fiber and protein intake at week 4. Group A consumed significantly less total saturated fat than group B (15.9 +/- 7.7 vs. 23.2 +/- 10.3 g/day; p = 0.02). Regarding micronutrients, group B consumed more vitamin A, B-12, D, riboflavin and calcium (each p <= 0.02). Zinc and calcium were below recommended intakes in both groups. Cluster analysis did not show clear group allocation after three months. Hence, dietary counselling for a PBD combined with TRE compared to a standard anti-inflammatory diet does not seem to lead to two different dietary clusters, i.e., actual different dietary behaviors as expected. Larger confirmatory studies are warranted to further define dietary recommendations for RA
A Peculiar Family of Jupiter Trojans: the Eurybates
The Eurybates family is a compact core inside the Menelaus clan, located in
the L4 swarm of Jupiter Trojans. Fornasier et al. (2007) found that this family
exhibits a peculiar abundance of spectrally flat objects, similar to
Chiron-like Centaurs and C-type main belt asteroids. On the basis of the
visible spectra available in literature, Eurybates family's members seemed to
be good candidates for having on their surfaces water/water ice or aqueous
altered materials. To improve our knowledge of the surface composition of this
peculiar family, we carried out an observational campaign at the Telescopio
Nazionale Galileo (TNG), obtaining near-infrared spectra of 7 members. Our data
show a surprisingly absence of any spectral feature referable to the presence
of water, ices or aqueous altered materials on the surface of the observed
objects. Models of the surface composition are attempted, evidencing that
amorphous carbon seems to dominate the surface composition of the observed
bodies and some amount of silicates (olivine) could be present.Comment: 23 pages, 2 figures, paper accepted for publication in Icaru
The CUORE Cryostat: A 1-Ton Scale Setup for Bolometric Detectors
The cryogenic underground observatory for rare events (CUORE) is a 1-ton
scale bolometric experiment whose detector consists of an array of 988 TeO2
crystals arranged in a cylindrical compact structure of 19 towers. This will be
the largest bolometric mass ever operated. The experiment will work at a
temperature around or below 10 mK. CUORE cryostat consists of a cryogen-free
system based on pulse tubes and a custom high power dilution refrigerator,
designed to match these specifications. The cryostat has been commissioned in
2014 at the Gran Sasso National Laboratories and reached a record temperature
of 6 mK on a cubic meter scale. In this paper, we present results of CUORE
commissioning runs. Details on the thermal characteristics and cryogenic
performances of the system will be also given.Comment: 7 pages, 2 figures, LTD16 conference proceedin
Families among high-inclination asteroids
We present a new classification of families identified among the population
of high-inclination asteroids. We computed synthetic proper elements for a
sample of 18,560 numbered and multi-opposition objects having sine of proper
inclination greater than 0.295. We considered three zones at different
heliocentric distances (inner, intermediate and outer region) and used the
standard approach based on the Hierarchical Clustering Method (HCM) to identify
families in each zone. In doing so, we used slightly different approach with
respect to previously published methodologies, to achieve a more reliable and
robust classification. We also used available SDSS color data to improve
membership and identify likely family interlopers. We found a total of 38
families, as well as a significant number of clumps and clusters deserving
further investigation.Comment: Accepted by Icaru
P/2006 VW139: A Main-Belt Comet Born in an Asteroid Collision?
In this paper we apply different methods to examine the possibility that a
small group of 24 asteroids dynamically linked to main-belt comet P/2006 VW139,
recently discovered by the Pan-STARRS1 survey telescope, shares a common
physical origin. By applying the Hierarchical Clustering and Backward
Integration methods, we find strong evidence that 11 of these asteroids form a
sub-group which likely originated in a recent collision event, and that this
group includes P/2006 VW139. The objects not found to be part of the 11-member
sub-group, which we designate as the P/2006 VW139 family, were either found to
be dynamically unstable, or these are likely interlopers which should be
expected due to the close proximity of the Themis family. As we demonstrated,
statistical significance of P/2006 VW139 family is >99 per cent. We determine
the age of the family to be 7.5 +/- 0.3 Myr, and estimate the diameter of the
parent body to be about 11 km. Results show that the family is produced by an
impact which can be best characterized as a transition from catastrophic to
cratering regime. The dynamical environment of this family is studied as well,
including the identification of the most influential mean motion and secular
resonances in the region. Our findings make P/2006 VW139 now the second
main-belt comet to be dynamically associated with a young asteroid family, a
fact with important implications for the origin and activation mechanism of
such objects.Comment: Accepted for publication in MNRA
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