2,905 research outputs found
New Paradigms For Asteroid Formation
Asteroids and meteorites provide key evidence on the formation of
planetesimals in the Solar System. Asteroids are traditionally thought to form
in a bottom-up process by coagulation within a population of initially km-scale
planetesimals. However, new models challenge this idea by demonstrating that
asteroids of sizes from 100 to 1000 km can form directly from the gravitational
collapse of small particles which have organised themselves in dense filaments
and clusters in the turbulent gas. Particles concentrate passively between
eddies down to the smallest scales of the turbulent gas flow and inside
large-scale pressure bumps and vortices. The streaming instability causes
particles to take an active role in the concentration, by piling up in dense
filaments whose friction on the gas reduces the radial drift compared to that
of isolated particles. In this chapter we review new paradigms for asteroid
formation and compare critically against the observed properties of asteroids
as well as constraints from meteorites. Chondrules of typical sizes from 0.1 to
1 mm are ubiquitous in primitive meteorites and likely represent the primary
building blocks of asteroids. Chondrule-sized particles are nevertheless
tightly coupled to the gas via friction and are therefore hard to concentrate
in large amounts in the turbulent gas. We review recent progress on
understanding the incorporation of chondrules into the asteroids, including
layered accretion models where chondrules are accreted onto asteroids over
millions of years. We highlight in the end ten unsolved questions in asteroid
formation where we expect that progress will be made over the next decade.Comment: Chapter to appear in the book ASTEROIDS IV, (University of Arizona
Press) Space Science Series, edited by P. Michel, F. DeMeo and W. Bottk
Mid-infrared sub-wavelength grating mirror design: tolerance and influence of technological constraints
High polarization selective Si/SiO2 mid-infrared sub-wavelength grating
mirrors with large bandwidth adapted to VCSEL integration are compared. These
mirrors have been automatically designed for operation at \lambda = 2.3 m
by an optimization algorithm which maximizes a specially defined quality
factor. Several technological constraints in relation with the grating
manufacturing process have been imposed within the optimization algorithm and
their impact on the optical properties of the mirror have been evaluated.
Furthermore, through the tolerance computation of the different dimensions of
the structure, the robustness with respect to fabrication errors has been
tested. Finally, it appears that the increase of the optical performances of
the mirror imposes a less tolerant design with severer technological
constraints resulting in a more stringent control of the manufacturing process.Comment: The final publication is available at
http://iopscience.iop.org/2040-8986/13/12/125502
Effect of Beam Dynamics Processes in the Low Energy Ring ThomX
As part of the R\&D for the 50 MeV ThomX Compton source project, we have
studied the effect of several beam dynamics processes on the evolution of the
beam in the ring. The processes studied include among others Compton
scattering, intrabeam scattering, coherent synchrotron radiation. We have
performed extensive simulations of a full injection/extraction cycle (400000
turns). We show how each of these processes degrades the flux of photons
produced and how a feedback system contributes to recovering most of the flux.Comment: Submitted to IPAC'14, WEPRO00
Recherche et titrage des antibiotiques présents dans le lait et les produits laitiers I. — Observations sur la méthode des disques
Jacquet Jean, Riquier N. Recherche et titrage des antibiotiques présents dans le lait et les produits laitiers. I. Observations sur la méthode des disques. In: Bulletin de l'Académie Vétérinaire de France tome 121 n°6, 1968. pp. 227-235
Recherche et titrage des antibiotiques dans le lait et les produits laitiers II. — Utilisation de la méthode des cavités
Jacquet Jean, Riquier N. Recherche et titrage des antibiotiques dans le lait et les produits laitiers. II. Utilisation de la méthode des cavités. In: Bulletin de l'Académie Vétérinaire de France tome 121 n°6, 1968. pp. 237-247
Exhausting domains of the symmetrized bidisc
We show that the symmetrized bidisc may be exhausted by strongly linearly
convex domains. It shows in particular the existence of a strongly linearly
convex domain that cannot be exhausted by domains biholomorphic to convex ones.Comment: 6 page
Uniqueness of Bessel models: the archimedean case
In the archimedean case, we prove uniqueness of Bessel models for general
linear groups, unitary groups and orthogonal groups.Comment: 22 page
The complexity of pluralistic ignorance in Republican climate change policy support in the United States
Most Americans fail to recognize widespread public support for climate change action. Here we investigate how this phenomenon differs for Republican supporters versus opponents of several climate change policies. Surveying a representative sample of Republican voters (N = 1000), we find that misperception of in-group support for climate action is primarily restricted to Republicans already opposed to action. Specifically, those in the minority (i.e., Republicans opposed to climate action) were more likely to erroneously perceive other Republicans as holding views on climate change policy similar to their own. While Republican supporters recognize that most Republicans support climate change policy, they may be discouraged from expressing their support due to an information environment disproportionately portraying Republicans as opposed to climate change action
A continuous rating method for preferential voting. The complete case
A method is given for quantitatively rating the social acceptance of
different options which are the matter of a complete preferential vote.
Completeness means that every voter expresses a comparison (a preference or a
tie) about each pair of options. The proposed method is proved to have certain
desirable properties, which include: the continuity of the rates with respect
to the data, a decomposition property that characterizes certain situations
opposite to a tie, the Condorcet-Smith principle, and a property of clone
consistency. One can view this rating method as a complement for the ranking
method introduced in 1997 by Markus Schulze. It is also related to certain
methods of one-dimensional scaling or cluster analysis.Comment: This is part one of a revised version of arxiv:0810.2263. Version 3
is the result of certain modifications, both in the statement of the problem
and in the concluding remarks, that enhance the results of the paper; the
results themselves remain unchange
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