1,620 research outputs found
Equilibrium ultrastable glasses produced by random pinning
Ultrastable glasses have risen to prominence due to their potentially useful
material properties and the tantalizing possibility of a general method of
preparation via vapor deposition. Despite the importance of this novel class of
amorphous materials, numerical studies have been scarce because achieving
ultrastability in atomistic simulations is an enormous challenge. Here we
bypass this difficulty and establish that randomly pinning the position of a
small fraction of particles inside an equilibrated supercooled liquid generates
ultrastable configurations at essentially no numerical cost, while avoiding
undesired structural changes due to the preparation protocol. Building on the
analogy with vapor-deposited ultrastable glasses, we study the melting kinetics
of these configurations following a sudden temperature jump into the liquid
phase. In homogeneous geometries, we find that enhanced kinetic stability is
accompanied by large scale dynamic heterogeneity, while a competition between
homogeneous and heterogeneous melting is observed when a liquid boundary
invades the glass at constant velocity. Our work demonstrates the feasibility
of large-scale, atomistically resolved, and experimentally relevant simulations
of the kinetics of ultrastable glasses.Comment: 9 pages, 5 figure
Sheer shear: weak lensing with one mode
3D data compression techniques can be used to determine the natural basis of
radial eigenmodes that encode the maximum amount of information in a
tomographic large-scale structure survey. We explore the potential of the
Karhunen-Lo\`eve decomposition in reducing the dimensionality of the data
vector for cosmic shear measurements, and apply it to the final data from the
\cfh survey. We find that practically all of the cosmological information can
be encoded in one single radial eigenmode, from which we are able to reproduce
compatible constraints with those found in the fiducial tomographic analysis
(done with 7 redshift bins) with a factor of ~30 fewer datapoints. This
simplifies the problem of computing the two-point function covariance matrix
from mock catalogues by the same factor, or by a factor of ~800 for an
analytical covariance. The resulting set of radial eigenfunctions is close to
ell-independent, and therefore they can be used as redshift-dependent galaxy
weights. This simplifies the application of the Karhunen-Lo\`eve decomposition
to real-space and Fourier-space data, and allows one to explore the effective
radial window function of the principal eigenmodes as well as the associated
shear maps in order to identify potential systematics. We also apply the method
to extended parameter spaces and verify that additional information may be
gained by including a second mode to break parameter degeneracies. The data and
analysis code are publicly available at
https://github.com/emiliobellini/kl_sample.Comment: 15 pages, 16 figures. Accepted version on OJ
Duality for pathwise superhedging in continuous time
We provide a model-free pricing-hedging duality in continuous time. For a
frictionless market consisting of risky assets with continuous price
trajectories, we show that the purely analytic problem of finding the minimal
superhedging price of a path dependent European option has the same value as
the purely probabilistic problem of finding the supremum of the expectations of
the option over all martingale measures. The superhedging problem is formulated
with simple trading strategies, the claim is the limit inferior of continuous
functions, which allows for upper and lower semi-continuous claims, and
superhedging is required in the pathwise sense on a -compact sample
space of price trajectories. If the sample space is stable under stopping, the
probabilistic problem reduces to finding the supremum over all martingale
measures with compact support. As an application of the general results we
deduce dualities for Vovk's outer measure and semi-static superhedging with
finitely many securities
Crossovers in the dynamics of supercooled liquids probed by an amorphous wall
We study the relaxation dynamics of a binary Lennard-Jones liquid in the
presence of an amorphous wall generated from equilibrium particle
configurations. In qualitative agreement with the results presented in Nature
Phys. {\bf 8}, 164 (2012) for a liquid of harmonic spheres, we find that our
binary mixture shows a saturation of the dynamical length scale close to the
mode-coupling temperature . Furthermore we show that, due to the broken
symmetry imposed by the wall, signatures of an additional change in dynamics
become apparent at a temperature well above . We provide evidence that
this modification in the relaxation dynamics occurs at a recently proposed
dynamical crossover temperature , which is related to the breakdown
of the Stokes-Einstein relation. We find that this dynamical crossover at
is also observed for a system of harmonic spheres as well as a WCA liquid,
showing that it may be a general feature of glass-forming systems.Comment: 10 pages, 8 figure
Mass transfer and hydrodynamic characteristics of new carbon carbon packing: Application to CO2 post-combustion capture
A novel structured packing, the 4D packing, has been characterized in terms of hydrodynamics, effective area and gas side mass transfer coefficient. The increase of the 4D opening fraction allows to reduce pressure drop and to get a better capacity than Mellapak 500Y and 750Y, for which the geometric areas are similar. The 50% open 4D packing, 4D-50%, leads to effective areas which are higher than Mellapak 500Y ones, and doubled compared with Mellapak Plus 252Y ones. Effective areas for the 4D do not decrease when the opening fraction increases from 30 to 50%, this indicates that a non-negligible amount of droplets is generated at 50%. Gas side mass transfer coefficient had been measured with an original experimental method: water evaporation. Corresponding results seem to be in agreement with the literature, and with the fact that a large amount of droplets is generated. Correlations are proposed for both effective area and gas side mass transfer coefficient for the 4D-50%.The 4D-50% packing could be very interesting for post-combustion CO2 capture since it generates low pressure drop and a very high interfacial area. This will be further confirmed by an economic study for which the absorber plant will be designed with a rate based model
Modern computational studies of the glass transition
The physics of the glass transition and amorphous materials continues to
attract the attention of a wide research community after decades of effort.
Supercooled liquids and glasses have been studied numerically since the advent
of molecular dynamics and Monte Carlo simulations in the last century. Computer
studies have greatly enhanced both experimental discoveries and theoretical
developments and constitute an active and continually expanding research field.
Our goal in this review is to provide a modern perspective on this area. We
describe the need to go beyond canonical methods to attack a problem that is
notoriously difficult in terms of time scales, length scales, and physical
observables. We first summarise recent algorithmic developments to achieve
enhanced sampling and faster equilibration using replica exchange methods,
cluster and swap Monte Carlo algorithms, and other techniques. We then review
some major recent advances afforded by these novel tools regarding the
statistical mechanical description of the liquid-to-glass transition as well as
the mechanical, vibrational and thermal properties of the glassy solid. We
finally describe some important challenges for future research
Experimental tracking of limit-point bifurcations and backbone curves using control-based continuation
Control-based continuation (CBC) is a means of applying numerical continuation directly to a physical experiment for bifurcation analysis without the use of a mathematical model. CBC enables the detection and tracking of bifurcations directly, without the need for a post-processing stage as is often the case for more traditional experimental approaches. In this paper, we use CBC to directly locate limit-point bifurcations of a periodically forced oscillator and track them as forcing parameters are varied. Backbone curves, which capture the overall frequency-amplitude dependence of the system’s forced response, are also traced out directly. The proposed method is demonstrated on a single-degree-of-freedom mechanical system with a nonlinear stiffness characteristic. Results are presented for two configurations of the nonlinearity — one where it exhibits a hardening stiffness characteristic and one where it exhibits softening-hardening. </jats:p
HYDRODYNAMIC MEASUREMENTS AROUND MOVING PROFILES: FLAPPING FLIGHT, WATER TURBINE, AND OSCILLATING PROFILE
In the field of the fluid mechanics, the team HYDEE (Hydrodynamics and Environmental flow section) of the institute Pprime is involved in the understanding of flows around moving profiles for environmental applications, the maritime transport, the renewable energy production, The research interests cover fundamental aspects of unsteady flows with moving structures, turbulent free-surface flows, environmental flows and mixing through different national and European programs. Fundamental contributions to optical flow measurements include PIV stereoscopy PIV measurement techniques and recently free surface measurement and volumetric measurement techniques have been obtained
SYNCHRONIZATION OF A SLIDE PRESENTATION AND PRESENTATION VIDEO RECORDING
A technique is proposed for assisting a user with presenting and recording a slide based presentation on a cloud-content based platform. A document application provided by the cloud-content based platform receives a request to record a video of a slide presentation. During the slide presentation, the document application generates a set of timestamp bookmarks, where each timestamp bookmark corresponds with a slide of the slide presentation document. At the end of the presentation, the video recording terminates and the slide presentation and the recorded presentation video is made available for consumption by one or more viewers. During consumption, the viewer is able to select a slide of interest and, based on the user selection, the application will present the viewer with the portion of the video recording that has the time stamp associated with the selected slide
Charge separation by photoexcitation in semicrystalline polymeric semiconductors: An intrinsic or extrinsic mechanism?
We probe charge photogeneration and subsequent recombination dynamics in neat
regioregular poly(3-hexylthiophene) films over six decades in time by means of
time-resolved photoluminescence spectroscopy. Exciton dissociation at 10K
occurs extrinsically at interfaces between molecularly ordered and disordered
domains. Polaron pairs thus produced recombine by tunnelling with distributed
rates governed by the distribution of electron-hole radii. Quantum-chemical
calculations suggest that hot-exciton dissociation at such interfaces results
from a high charge-transfer character.Comment: 10 pages, 3 figure
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