68 research outputs found
Space-time Thermodynamics of the Glass Transition
We consider the probability distribution for fluctuations in dynamical action
and similar quantities related to dynamic heterogeneity. We argue that the
so-called "glass transition" is a manifestation of low action tails in these
distributions where the entropy of trajectory space is sub-extensive in time.
These low action tails are a consequence of dynamic heterogeneity and an
indication of phase coexistence in trajectory space. The glass transition,
where the system falls out of equilibrium, is then an order-disorder phenomenon
in space-time occurring at a temperature T_g which is a weak function of
measurement time. We illustrate our perspective ideas with facilitated lattice
models, and note how these ideas apply more generally.Comment: 5 pages, 4 figure
Dynamics and Thermodynamics of the Glass Transition
The principal theme of this paper is that anomalously slow, super-Arrhenius
relaxations in glassy materials may be activated processes involving chains of
molecular displacements. As pointed out in a preceding paper with A. Lemaitre,
the entropy of critically long excitation chains can enable them to grow
without bound, thus activating stable thermal fluctuations in the local density
or molecular coordination of the material. I argue here that the intrinsic
molecular-scale disorder in a glass plays an essential role in determining the
activation rate for such chains, and show that a simple disorder-related
correction to the earlier theory recovers the Vogel-Fulcher law in three
dimensions. A key feature of this theory is that the spatial extent of
critically long excitation chains diverges at the Vogel-Fulcher temperature. I
speculate that this diverging length scale implies that, as the temperature
decreases, increasingly large regions of the system become frozen and do not
contribute to the configurational entropy, and thus ergodicity is partially
broken in the super-Arrhenius region above the Kauzmann temperature . This
partially broken ergodicity seems to explain the vanishing entropy at and
other observed relations between dynamics and thermodynamics at the glass
transition.Comment: 20 pages, no figures, some further revision
Unexpected drop of dynamical heterogeneities in colloidal suspensions approaching the jamming transition
As the glass (in molecular fluids\cite{Donth}) or the jamming (in colloids
and grains\cite{LiuNature1998}) transitions are approached, the dynamics slow
down dramatically with no marked structural changes. Dynamical heterogeneity
(DH) plays a crucial role: structural relaxation occurs through correlated
rearrangements of particle ``blobs'' of size
\cite{WeeksScience2000,DauchotPRL2005,Glotzer,Ediger}. On approaching
these transitions, grows in glass-formers\cite{Glotzer,Ediger},
colloids\cite{WeeksScience2000,BerthierScience2005}, and driven granular
materials\cite{KeysNaturePhys2007} alike, strengthening the analogies between
the glass and the jamming transitions. However, little is known yet on the
behavior of DH very close to dynamical arrest. Here, we measure in colloids the
maximum of a ``dynamical susceptibility'', , whose growth is usually
associated to that of \cite{LacevicPRE}. initially increases with
volume fraction , as in\cite{KeysNaturePhys2007}, but strikingly drops
dramatically very close to jamming. We show that this unexpected behavior
results from the competition between the growth of and the reduced
particle displacements associated with rearrangements in very dense
suspensions, unveiling a richer-than-expected scenario.Comment: 1st version originally submitted to Nature Physics. See the Nature
Physics website fro the final, published versio
Activity phase transition for constrained dynamics
We consider two cases of kinetically constrained models, namely East and
FA-1f models. The object of interest of our work is the activity A(t) defined
as the total number of configuration changes in the interval [0,t] for the
dynamics on a finite domain. It has been shown in [GJLPDW1,GJLPDW2] that the
large deviations of the activity exhibit a non-equilibirum phase transition in
the thermodynamic limit and that reducing the activity is more likely than
increasing it due to a blocking mechanism induced by the constraints. In this
paper, we study the finite size effects around this first order phase
transition and analyze the phase coexistence between the active and inactive
dynamical phases in dimension 1. In higher dimensions, we show that the finite
size effects are also determined by the dimension and the choice of boundary
conditions.Comment: 38 pages, 3 figure
Fragility, Stokes-Einstein violation, and correlated local excitations in a coarse-grained model of an ionic liquid
Dynamics of a coarse-grained model for the room-temperature ionic liquid,
1-ethyl-3-methylimidazolium hexafluorophosphate, couched in the united-atom
site representation are studied via molecular dynamics simulations. The
dynamically heterogeneous behavior of the model resembles that of fragile
supercooled liquids. At or close to room temperature, the model ionic liquid
exhibits slow dynamics, characterized by nonexponential structural relaxation
and subdiffusive behavior. The structural relaxation time, closely related to
the viscosity, shows a super-Arrhenius behavior. Local excitations, defined as
displacement of an ion exceeding a threshold distance, are found to be mainly
responsible for structural relaxation in the alternating structure of cations
and anions. As the temperature is lowered, excitations become progressively
more correlated. This results in the decoupling of exchange and persistence
times, reflecting a violation of the Stokes-Einstein relation.Comment: Published on the Phys. Chem. Chem. Phys. websit
Corresponding States of Structural Glass Formers
The variation with respect to temperature T of transport properties of 58
fragile structural glass forming liquids (68 data sets in total) are analyzed
and shown to exhibit a remarkable degree of universality. In particular,
super-Arrhenius behaviors of all super-cooled liquids appear to collapse to one
parabola for which there is no singular behavior at any finite temperature.
This behavior is bounded by an onset temperature To above which liquid
transport has a much weaker temperature dependence. A similar collapse is also
demonstrated, over the smaller available range, for existing numerical
simulation data.Comment: 6 pages, 2 figures. Updated References, Table Values, Submitted for
Publicatio
Thermodynamic formalism for systems with Markov dynamics
The thermodynamic formalism allows one to access the chaotic properties of
equilibrium and out-of-equilibrium systems, by deriving those from a dynamical
partition function. The definition that has been given for this partition
function within the framework of discrete time Markov chains was not suitable
for continuous time Markov dynamics. Here we propose another interpretation of
the definition that allows us to apply the thermodynamic formalism to
continuous time.
We also generalize the formalism --a dynamical Gibbs ensemble construction--
to a whole family of observables and their associated large deviation
functions. This allows us to make the connection between the thermodynamic
formalism and the observable involved in the much-studied fluctuation theorem.
We illustrate our approach on various physical systems: random walks,
exclusion processes, an Ising model and the contact process. In the latter
cases, we identify a signature of the occurrence of dynamical phase
transitions. We show that this signature can already be unravelled using the
simplest dynamical ensemble one could define, based on the number of
configuration changes a system has undergone over an asymptotically large time
window.Comment: 64 pages, LaTeX; version accepted for publication in Journal of
Statistical Physic
X-ray fluorescence microscopy of light elements in cells: self-absorption correction by integration of compositional and morphological measurements
We present here a new methodology for quantitative mapping of light elements in cells, based on combination of compositional and morphological information, derived respectively by X-ray Fluorescence Microscopy (XRFM), Atomic Force Microscopy and Scanning Transmission X-ray Microscopy (STXM). Since XRFM of light elements (carbon, nitrogen, oxygen, sodium and magnesium), are strongly influenced by self-absorption, we developed an algorithm to correct for this effect, using the morphological and structural information provided by AFM and STXM. Finally, the corrected distributions have been obtained, thus allowing quantitative mapping
First results from the full-scale prototype for the Fluorescence detector Array of Single-pixel Telescopes
The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a design concept for the next generation of ultrahigh-energy cosmic ray (UHECR) observatories, addressing the require- ments for a large-area, low-cost detector suitable for measuring the properties of the highest en- ergy cosmic rays. In the FAST design, a large field of view is covered by a few pixels at the focal plane of a mirror or Fresnel lens. Motivated by the successful detection of UHECRs using a prototype comprised of a single 200 mm photomultiplier-tube and a 1 m2 Fresnel lens system [Astropart.Phys. 74 (2016) 64-72], we have developed a new full-scale prototype consisting of four 200 mm photomultiplier-tubes at the focus of a segmented mirror of 1.6 m in diameter. In October 2016 we installed the full-scale prototype at the Telescope Array site in central Utah, USA, and began steady data taking. We report on first results of the full-scale FAST prototype, including measurements of artificial light sources, distant ultraviolet lasers, and UHECRs.Toshihiro Fujii, Max Malacari, Justin Albury, Jose A. Bellido, John Farmer, Aygul Galimova, Pavel Horvath, Miroslav Hrabovsky, Dusan Mandat, Ariel Matalon, John N. Matthews, Maria Merolle, Xiaochen Ni, Libor Nozka, Miroslav Palatka, Miroslav Pech, Paolo Privitera, Petr Schovanek, Stan B. Thomas, Petr Travnicek (FAST Collaboration
Simulating rare events in dynamical processes
Atypical, rare trajectories of dynamical systems are important: they are
often the paths for chemical reactions, the haven of (relative) stability of
planetary systems, the rogue waves that are detected in oil platforms, the
structures that are responsible for intermittency in a turbulent liquid, the
active regions that allow a supercooled liquid to flow... Simulating them in an
efficient, accelerated way, is in fact quite simple.
In this paper we review a computational technique to study such rare events
in both stochastic and Hamiltonian systems. The method is based on the
evolution of a family of copies of the system which are replicated or killed in
such a way as to favor the realization of the atypical trajectories. We
illustrate this with various examples
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