2,264 research outputs found
Characterizing dynamic length scales in glass-forming liquids
Reply to Comment by Flenner and Szamel on our paper in Nature Physics 8, 164
(2012).Comment: 1 pag
A random walk description of the heterogeneous glassy dynamics of attracting colloids
We study the heterogeneous dynamics of attractive colloidal particles close
to the gel transition using confocal microscopy experiments combined with a
theoretical statistical analysis. We focus on single particle dynamics and show
that the self part of the van Hove distribution function is not the Gaussian
expected for a Fickian process, but that it reflects instead the existence, at
any given time, of colloids with widely different mobilities. Our confocal
microscopy measurements can be described well by a simple analytical model
based on a conventional continuous time random walk picture, as already found
in several other glassy materials. In particular, the theory successfully
accounts for the presence of broad tails in the van Hove distributions that
exhibit exponential, rather than Gaussian, decay at large distance.Comment: 13 pages, 5 figs. Submitted to special issue "Classical and Quantum
Glasses" of J. Phys.: Condens. Matter; v2: response to refere
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
Subdiffusion and intermittent dynamic fluctuations in the aging regime of concentrated hard spheres
We study the nonequilibrium aging dynamics in a system of quasi-hard spheres
at large density by means of computer simulations. We find that, after a sudden
quench to large density, the relaxation time initially increases exponentially
with the age of the system. After a surprisingly large crossover time, the
system enters the asymptotic aging regime characterized by a linear increase of
the relaxation time with age. In this aging regime, single particle motion is
strongly non-Fickian, with a mean-squared displacement increasing
subdiffusively, associated to broad, non-Gaussian tails in the distribution of
particle displacements. We find that the system ages through temporally
intermittent relaxation events, and a detailed finite size analysis of these
collective dynamic fluctuations reveals that these events are not spanning the
entire system, but remain spatially localized.Comment: 11 pages; 10 fig
Field-induced magnetic behavior in quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8: A single-crystal neutron diffraction study
BaCo2V2O8 is a nice example of a quasi-one-dimensional quantum spin system
that can be described in terms of Tomonaga-Luttinger liquid physics. This is
explored in the present study where the magnetic field-temperature phase
diagram is thoroughly established up to 12 T using single-crystal neutron
diffraction. The transition from the N\'eel phase to the incommensurate
longitudinal spin density wave (LSDW) phase through a first-order transition,
as well as the critical exponents associated with the paramagnetic to ordered
phase transitions, and the magnetic order both in the N\'eel and in the LSDW
phase are determined, thus providing a stringent test for the theory.Comment: 17 pages with 15 figure
Cascading water underneath Wilkes Land, East Antarctic ice sheet, observed using altimetry and digital elevation models
We describe a major subglacial lake drainage close to the ice divide in
Wilkes Land, East Antarctica, and the subsequent cascading of water
underneath the ice sheet toward the coast. To analyse the event, we combined
altimetry data from several sources and subglacial topography. We estimated
the total volume of water that drained from Lake Cook<sub>E2</sub> by differencing
digital elevation models (DEM) derived from ASTER and SPOT5 stereo imagery
acquired in January 2006 and February 2012. At 5.2 ± 1.5 km<sup>3</sup>, this
is the largest single subglacial drainage event reported so far in
Antarctica. Elevation differences between ICESat laser altimetry spanning
2003–2009 and the SPOT5 DEM indicate that the discharge started in November
2006 and lasted approximately 2 years. A 13 m uplift of the surface,
corresponding to a refilling of about 0.6 ± 0.3 km<sup>3</sup>, was observed
between the end of the discharge in October 2008 and February 2012. Using
the 35-day temporal resolution of Envisat radar altimetry, we monitored the
subsequent filling and drainage of connected subglacial lakes located
downstream of Cook<sub>E2</sub>. The total volume of water traveling within the
theoretical 500-km-long flow paths computed with the BEDMAP2 data set is
similar to the volume that drained from Lake Cook<sub>E2</sub>, and our
observations suggest that most of the water released from Lake Cook<sub>E2</sub>
did not reach the coast but remained trapped underneath the ice sheet. Our
study illustrates how combining multiple remote sensing techniques allows
monitoring of the timing and magnitude of subglacial water flow beneath the
East Antarctic ice sheet
Real space application of the mean-field description of spin glass dynamics
The out of equilibrium dynamics of finite dimensional spin glasses is
considered from a point of view going beyond the standard `mean-field theory'
versus `droplet picture' debate of the last decades. The main predictions of
both theories concerning the spin glass dynamics are discussed. It is shown, in
particular, that predictions originating from mean-field ideas concerning the
violations of the fluctuation-dissipation theorem apply quantitatively,
provided one properly takes into account the role of the spin glass coherence
length which plays a central role in the droplet picture. Dynamics in a uniform
magnetic field is also briefly discussed.Comment: 4 pages, 4 eps figures. v2: published versio
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