2,136 research outputs found
Can the jamming transition be described using equilibrium statistical mechanics?
When materials such as foams or emulsions are compressed, they display solid
behaviour above the so-called `jamming' transition. Because compression is done
out-of-equilibrium in the absence of thermal fluctuations, jamming appears as a
new kind of a nonequilibrium phase transition. In this proceeding paper, we
suggest that tools from equilibrium statistical mechanics can in fact be used
to describe many specific features of the jamming transition. Our strategy is
to introduce thermal fluctuations and use statistical mechanics to describe the
complex phase behaviour of systems of soft repulsive particles, before sending
temperature to zero at the end of the calculation. We show that currently
available implementations of standard tools such as integral equations,
mode-coupling theory, or replica calculations all break down at low temperature
and large density, but we suggest that new analytical schemes can be developed
to provide a fully microscopic, quantitative description of the jamming
transition.Comment: 8 pages, 6 figs. Talk presented at Statphys24 (July 2010, Cairns,
Australia
Shear localization in a model glass
Using molecular dynamics simulations, we show that a simple model of a glassy
material exhibits the shear localization phenomenon observed in many complex
fluids. At low shear rates, the system separates into a fluidized shear-band
and an unsheared part. The two bands are characterized by a very different
dynamics probed by a local intermediate scattering function. Furthermore, a
stick-slip motion is observed at very small shear rates. Our results, which
open the possibility of exploring complex rheological behavior using
simulations, are compared to recent experiments on various soft glasses.Comment: 4 pages, 4 figures (5 figure files
Prediction of transits of solar system objects in Kepler/K2 images: An extension of the Virtual Observatory service SkyBoT
All the fields of the extended space mission Kepler/K2 are located within the
ecliptic. Many solar system objects thus cross the K2 stellar masks on a
regular basis. We aim at providing to the entire community a simple tool to
search and identify solar system objects serendipitously observed by Kepler.
The SkyBoT service hosted at IMCCE provides a Virtual Observatory (VO)
compliant cone-search that lists all solar system objects present within a
field of view at a given epoch. To generate such a list in a timely manner,
ephemerides are pre-computed, updated weekly, and stored in a relational
database to ensure a fast access. The SkyBoT Web service can now be used with
Kepler. Solar system objects within a small (few arcminutes) field of view are
identified and listed in less than 10 sec. Generating object data for the
entire K2 field of view (14{\deg}) takes about a minute. This extension of the
SkyBot service opens new possibilities with respect to mining K2 data for solar
system science, as well as removing solar system objects from stellar
photometric time-series
Estimation of the normal contact stiffness for frictional interface in sticking and sliding conditions
Modeling of frictional contact systems with high accuracy needs the knowledge of several contact parameters, which are mainly related to the local phenomena at the contact interfaces and affect the complex dynamics of mechanical systems in a prominent way. This work presents a newer approach for identifying reliable values of the normal contact stiffness between surfaces in contact, in both sliding and sticking conditions. The combination of experimental tests, on a dedicated set-up, with finite element modeling, allowed for an indirect determination of the normal contact stiffness. The stiffness was found to increase with increasing contact pressure and decreasing roughness, while the evolution of surface topography and third-body rheology affected the contact stiffness when sliding
Memory effects in classical and quantum mean-field disordered models
We apply the Kovacs experimental protocol to classical and quantum p-spin
models. We show that these models have memory effects as those observed
experimentally in super-cooled polymer melts. We discuss our results in
connection to other classical models that capture memory effects. We propose
that a similar protocol applied to quantum glassy systems might be useful to
understand their dynamics.Comment: 24 pages, 12 figure
Near-infrared spatially resolved spectroscopy of (136108) Haumea's multiple system
The transneptunian region of the solar system is populated by a wide variety
of icy bodies showing great diversity. The dwarf planet (136108) Haumea is
among the largest TNOs and displays a highly elongated shape and hosts two
moons, covered with crystalline water ice like Hamuea. Haumea is also the
largest member of the sole TNO family known to date. A catastrophic collision
is likely responsible for its unique characteristics. We report here on the
analysis of a new set of observations of Haumea obtained with SINFONI at the
ESO VLT. Combined with previous data, and using light-curve measurements in the
optical and far infrared, we carry out a rotationally resolved spectroscopic
study of the surface of Haumea. We describe the physical characteristics of the
crystalline water ice present on the surface of Haumea for both regions, in and
out of the Dark Red Spot (DRS), and analyze the differences obtained for each
individual spectrum. The presence of crystalline water ice is confirmed over
more than half of the surface of Haumea. Our measurements of the average
spectral slope confirm the redder characteristic of the spot region. Detailed
analysis of the crystalline water-ice absorption bands do not show significant
differences between the DRS and the remaining part of the surface. We also
present the results of applying Hapke modeling to our data set. The best
spectral fit is obtained with a mixture of crystalline water ice (grain sizes
smaller than 60 micron) with a few percent of amorphous carbon. Improvements to
the fit are obtained by adding ~10% of amorphous water ice. Additionally, we
used the IFU-reconstructed images to measure the relative astrometric position
of the largest satellite Hi`iaka and determine its orbital elements. An orbital
solution was computed with our genetic-based algorithm GENOID and our results
are in full agreement with recent results.Comment: Accepted for publication in A&
Surfing on a critical line: Rejuvenation without chaos, Memory without a hierarchical phase space
The dynamic behaviour of glassy materials displays strong nonequilibrium
effects, such as ageing in simple protocols, memory, rejuvenation and Kovacs
effects in more elaborated experiments. We show that this phenomenology may be
easily understood in the context of the nonequilibrium critical dynamics of
non-disordered systems, the main ingredient being the existence of an infinite
equilibrium correlation length. As an example, we analytically investigate the
behaviour of the 2D XY model submitted to temperature protocols similar to
experiments. This shows that typical glassy effects may be obtained by `surfing
on a critical line' without invoking the concept of temperature chaos nor the
existence of a hierarchical phase space, as opposed to previous theoretical
approaches. The relevance of this phenomenological approach to glassy dynamics
is finally discussed.Comment: Version to be published in Europhysics Letters. Slight modifs + ref
to "surfing" adde
Highly nonlinear dynamics in a slowly sedimenting colloidal gel
We use a combination of original light scattering techniques and particles
with unique optical properties to investigate the behavior of suspensions of
attractive colloids under gravitational stress, following over time the
concentration profile, the velocity profile, and the microscopic dynamics.
During the compression regime, the sedimentation velocity grows nearly linearly
with height, implying that the gel settling may be fully described by a
(time-dependent) strain rate. We find that the microscopic dynamics exhibit
remarkable scaling properties when time is normalized by strain rate, showing
that the gel microscopic restructuring is dominated by its macroscopic
deformation.Comment: Physical Review Letters (2011) xxx
Spin Configuration in the 1/3 Magnetization Plateau of Azurite Determined by NMR
High magnetic field Cu NMR spectra were used to determine the local
spin polarization in the 1/3 magnetization plateau of azurite,
Cu(CO)(OH), which is a model system for the distorted diamond
antiferromagnetic spin-1/2 chain. The spin part of the hyperfine field of the
Cu2 (dimer) sites is found to be field independent, negative and strongly
anisotropic, corresponding to 10 % of fully polarized spin in a
-orbital. This is close to the expected configuration of the "quantum"
plateau, where a singlet state is stabilized on the dimer. However, the
observed non-zero spin polarization points to some triplet admixture, induced
by strong asymmetry of the diamond bonds and .Comment: Phys. Rev. Lett. 102, in press (2009
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