63 research outputs found
Numerical study of barriers and valleys in the free-energy landscape of spin glasses
We study the problem of glassy relaxations in the presence of an external
field in the highly controlled context of a spin-glass simulation. We consider
a small spin glass in three dimensions (specifically, a lattice of size L=8,
small enough to be equilibrated through a Parallel Tempering simulations at low
temperatures, deep in the spin glass phase). After equilibrating the sample, an
external field is switched on, and the subsequent dynamics is studied. The
field turns out to reduce the relaxation time, but huge statistical
fluctuations are found when different samples are compared. After taking care
of these fluctuations we find that the expected linear regime is very narrow.
Nevertheless, when regarded as a purely numerical method, we find that the
external field is extremely effective in reducing the relaxation times.Comment: 22 pages, 10 figures; Published versio
Slow growth of magnetic domains helps fast evolution routes for out-of-equilibrium dynamics
Cooling and heating faster a system is a crucial problem in science, technology, and industry. Indeed, choosing the best thermal protocol to reach a desired temperature or energy is not a trivial task. Noticeably, we find that the phase transitions may speed up thermalization in systems where there are no conserved quantities. In particular, we show that the slow growth of magnetic domains shortens the overall time that the system takes to reach a final desired state. To prove that statement, we use intensive numerical simulations of a prototypical many-body system, namely, the two-dimensional Ising model. © 2021 Published by the American Physical Societ
Scanning Electron Microscope Study of Wohlfahrtia magnifica (Schiner, 1862) (Diptera: Sarcophagidae) I. Structures with Parasitic and Possible Taxonomic Meaning
The larval development of Wohlfahrtia magnifica (the most important dipteran causing sheep myiasis in the Palearctic region) has been studied by means of scanning electron microscopy. The ultrastructure of mouth-hooks, oral ridges, labial lobes, body spines and anterior and posterior peritremes is described for the first time. Their possible adaptations to a parasitic lifeway are also discussed. Thus, the use of new structures in the Sarcophagidae taxonomy is proposed from the point of view of their ultrastructure and adaptative morphology
Scaling Law describes the spin-glass response in theory, experiments, and simulations
The correlation length xi, a key quantity in glassy dynamics, can now be precisely measured for spin glasses both in experiments and in simulations. However, known analysis methods lead to discrepancies either for large external fields or close to the glass temperature. We solve this problem by introducing a scaling law that takes into account both the magnetic field and the time-dependent spin-glass correlation length. The scaling law is successfully tested against experimental measurements in a CuMn single crystal and against large-scale simulations on the Janus II dedicated computer
Temperature chaos is present in off-equilibrium spin-glass dynamics
Experiments featuring non-equilibrium glassy dynamics under temperature changes still await interpretation. There is a widespread feeling that temperature chaos (an extreme sensitivity of the glass to temperature changes) should play a major role but, up to now, this phenomenon has been investigated solely under equilibrium conditions. In fact, the very existence of a chaotic effect in the non-equilibrium dynamics is yet to be established. In this article, we tackle this problem through a large simulation of the 3D Edwards-Anderson model, carried out on the Janus II supercomputer. We find a dynamic effect that closely parallels equilibrium temperature chaos. This dynamic temperature-chaos effect is spatially heterogeneous to a large degree and turns out to be controlled by the spin-glass coherence length ¿. Indeed, an emerging length-scale ¿* rules the crossover from weak (at ¿ « ¿*) to strong chaos (¿ » ¿*). Extrapolations of ¿* to relevant experimental conditions are provided. © 2021, The Author(s)
Temperature chaos is present in off-equilibrium spin-glass dynamics
We find a dynamic effect in the non-equilibrium dynamics of a spin glass that
closely parallels equilibrium temperature chaos. This effect, that we name
dynamic temperature chaos, is spatially heterogeneous to a large degree. The
key controlling quantity is the time-growing spin-glass coherence length. Our
detailed characterization of dynamic temperature chaos paves the way for the
analysis of recent and forthcoming experiments. This work has been made
possible thanks to the most massive simulation to date of non-equilibrium
dynamics, carried out on the Janus~II custom-built supercomputer.Comment: Version accepted for publication in Communication Physics 10 pages, 9
figure
Scaling law describes the spin-glass response in theory, experiments and simulations
The correlation length , a key quantity in glassy dynamics, can now be
precisely measured for spin glasses both in experiments and in simulations.
However, known analysis methods lead to discrepancies either for large external
fields or close to the glass temperature. We solve this problem by introducing
a scaling law that takes into account both the magnetic field and the
time-dependent spin-glass correlation length. The scaling law is successfully
tested against experimental measurements in a CuMn single crystal and against
large-scale simulations on the Janus II dedicated computer.Comment: Revised version, including supplemental materia
Spin-glass dynamics in the presence of a magnetic field: exploration of microscopic properties
The synergy between experiment, theory, and simulations enables a microscopic
analysis of spin-glass dynamics in a magnetic field in the vicinity of and
below the spin-glass transition temperature . The spin-glass
correlation length, , is analysed both in experiments
and in simulations in terms of the waiting time after the spin
glass has been cooled down to a stabilised measuring temperature
and of the time after the magnetic field is changed. This
correlation length is extracted experimentally for a CuMn 6 at. % single
crystal, as well as for simulations on the Janus II special-purpose
supercomputer, the latter with time and length scales comparable to experiment.
The non-linear magnetic susceptibility is reported from experiment and
simulations, using as the scaling variable. Previous
experiments are reanalysed, and disagreements about the nature of the Zeeman
energy are resolved. The growth of the spin-glass magnetisation in zero-field
magnetisation experiments, , is measured from
simulations, verifying the scaling relationships in the dynamical or
non-equilibrium regime. Our preliminary search for the de Almeida-Thouless line
in is discussed.Comment: 49 pages, figures 2
Bacterial siderophores efficiently provide iron to iron-starved tomato plants in hydroponics culture
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