888 research outputs found
Extraction of the Spin Glass Correlation Length
The peak of the spin glass relaxation rate, S(t)=d{-M_{TRM}(t,t_w)}/H/{d ln
t}, is directly related to the typical value of the free energy barrier which
can be explored over experimental time scales. A change in magnetic field H
generates an energy E_z={N_s}{X_fc}{H^2} by which the barrier heights are
reduced, where X_{fc} is the field cooled susceptibility per spin, and N_s is
the number of correlated spins. The shift of the peak of S(t) gives E_z,
generating the correlation length, Ksi(t,T), for Cu:Mn 6at.% and
CdCr_{1.7}In_{0.3}S_4. Fits to power law dynamics, Ksi(t,T)\propto
{t}^{\alpha(T)} and activated dynamics Ksi(t,T) \propto {ln t}^{1/psi} compare
well with simulation fits, but possess too small a prefactor for activated
dynamics.Comment: 4 pages, 4 figures. Department of Physics, University of California,
Riverside, California, and Service de Physique de l'Etat Condense, CEA
Saclay, Gif sur Yvette, France. To appear in Phys. Rev. Lett. January 4, 199
Advancements in Three-Phase Electric Motor Control: The Dual Voltag Motor Controller for Seamless Voltage Switching and Enhanced Efficiency
The primary objective of this research was to create, manufacture, and assess the operational efficiency of a Dual Voltage Motor Controller capable of automatically detecting the source voltage in a three-phase system and regulating the electric motor to function with either 220V or 440V AC. The resulting technology comprises a combination of magnetic contactors and a microcontroller, serving as a switching mechanism that streamlines the reconfiguration of the electric motor's twelve leads in a delta-delta configuration. This research was conducted at Guimaras State University, focusing on the development of a device aimed at eliminating the need for rewiring motor terminals when switching between 220V AC and 440V AC power sources, and vice versa. The device is designed exclusively for operation within a three-phase system and for electric motors utilizing a delta-delta configuration with twelve leads. Upon assessing the results of the technical evaluation, it was evident that the Dual Voltage Motor Controller effectively managed to switch the electric motor between 220V and 440V alternating current. Furthermore, the data revealed that the device allowed the electric motor to operate in both forward and reverse rotations, whether under low or high voltage conditions. By introducing this innovative technology, the research effectively resolved the limitations of existing motor controllers by introducing auto-detection of the source voltage and facilitating the seamless transfer of terminal connections via magnetic contactors. According to the feedback from technical experts, there is potential for expanding the device's applicability beyond delta-delta connected motors to also encompass wye-delta starting and running configurations for three-phase alternating current motors
Linear response in aging glassy systems, intermittency and the Poisson statistics of record fluctuations
We study the intermittent behavior of the energy decay and linear magnetic
response of a glassy system during isothermal aging after a deep thermal quench
using the Edward-Anderson spin glass model as a paradigmatic example. The large
intermittent changes in the two observables are found to occur in a correlated
fashion and through irreversible bursts, `quakes', which punctuate reversible
and equilibrium-like fluctuations of zero average. The temporal distribution of
the quakes it found to be a Poisson distribution with an average growing
logarithmically on time, indicating that the quakes are triggered by record
sized fluctuations. As the drift of an aging system is to a good approximation
subordinated to the quakes, simple analytical expressions (Sibani et al. Phys
Rev B 74, 224407, 2006) are available for the time and age dependence of the
average response and average energy. These expressions are shown to capture the
time dependencies of the EA simulation results. Finally, we argue that whenever
the changes of the linear response function and of its conjugate
autocorrelation function follow from the same intermittent events a
fluctuation-dissipation-like relation can arise between the two in
off-equilibrium aging.Comment: 10 pages, 17 figures. The mproved version now includes a direct
analysis of the intermittent signal. The new title is hopefully more
informative. Accepted for publication in EPJ
Growth of a dynamical correlation length in an aging superspin glass
We report on zero field cooled magnetization relaxation experiments on a
concen- trated frozen ferrofluid exhibiting a low temperature superspin glass
transition. With a method initially developed for spin glasses, we investigate
the field dependence of the relaxations that take place after different aging
times. We extract the typical number of correlated spins involved in the aging
dynamics. This brings important insights into the dynamical correlation length
and its time growth. Our results, consistent with expressions obtained for spin
glasses, extend the generality of these behaviours to the class of superspin
glasses. Since the typical flipping time is much larger for superspins than for
atomic spins, our experiments probe a time regime much closer to that of
numerical simulations
Aging, rejuvenation and memory phenomena in spin glasses
In this paper, we review several important features of the out-of-equilibrium
dynamics of spin glasses. Starting with the simplest experiments, we discuss
the scaling laws used to describe the isothermal aging observed in spin glasses
after a quench down to the low temperature phase. We report in particular new
results on the sub-aging behaviour of spin glasses. We then discuss the
rejuvenation and memory effects observed when a spin glass is submitted to
temperature variations during aging, from the point of view of both energy
landscape pictures and of real space pictures. We highlight the fact that both
approaches point out the necessity of hierarchical processes involved in aging.
Finally, we report an investigation of the effect of small temperature
variations on aging in spin glass samples with various anisotropies which
indicates that this hierarchy depends on the spin anisotropy.Comment: submitted for the Proceedings of Stat Phys 22, Bangalore (India
Field-Shift Aging Protocol on the 3D Ising Spin-Glass Model: Dynamical Crossover between the Spin-Glass and Paramagnetic States
Spin-glass (SG) states of the 3-dimensional Ising Edwards-Anderson model
under a static magnetic field are examined by means of the standard Monte
Carlo simulation on the field-shift aging protocol at temperature . For each
process with (T; \tw, h), \tw being the waiting time before the field is
switched on, we extract the dynamical crossover time, \tcr(T; \tw, h). We
have found a nice scaling relation between the two characteristic length scales
which are properly determined from \tcr and \tw and then are normalized by
the static field crossover length introduced in the SG droplet theory. This
scaling behavior implies the instability of the SG phase in the equilibrium
limit even under an infinitesimal . In comparison with this numerical result
the field effect on real spin glasses is also discussed.Comment: 4 pages, 5 figures, jpsj2, Changed conten
Evidences Against Temperature Chaos in Mean Field and Realistic Spin Glasses
We discuss temperature chaos in mean field and realistic 3D spin glasses. Our
numerical simulations show no trace of a temperature chaotic behavior for the
system sizes considered. We discuss the experimental and theoretical
implications of these findings.Comment: 4 pages in aps format. 6 .ps figures. It is better to print the paper
in colou
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De novo design of a transmembrane Zn²⁺-transporting four-helix bundle.
The design of functional membrane proteins from first principles represents a grand challenge in chemistry and structural biology. Here, we report the design of a membrane-spanning, four-helical bundle that transports first-row transition metal ions Zn(2+) and Co(2+), but not Ca(2+), across membranes. The conduction path was designed to contain two di-metal binding sites that bind with negative cooperativity. X-ray crystallography and solid-state and solution nuclear magnetic resonance indicate that the overall helical bundle is formed from two tightly interacting pairs of helices, which form individual domains that interact weakly along a more dynamic interface. Vesicle flux experiments show that as Zn(2+) ions diffuse down their concentration gradients, protons are antiported. These experiments illustrate the feasibility of designing membrane proteins with predefined structural and dynamic properties
Real spin glasses relax slowly in the shade of hierarchical trees
The Parisi solution of the mean-field spin glass has been widely accepted and
celebrated. Its marginal stability in 3d and its complexity however raised the
question of its relevance to real spin glasses. This paper gives a short
overview of the important experimental results which could be understood within
the mean-field solution. The existence of a true phase transition and the
particular behaviour of the susceptibility below the freezing temperature,
predicted by the theory, are clearly confirmed by the experimental results. The
behaviour of the complex order parameter and of the Fluctuation Dissipation
ratio are in good agreement with results of spontaneous noise measurements. The
very particular ultrametric symmetry, the key feature of the theory, provided
us with a simple description of the rejuvenation and memory effects observed in
experiment. Finally, going a step beyond mean-field, the paper shortly
discusses new analyses in terms of correlated domains characterized by their
length scales, as well as new experiments on superspin glasses which compare
well with recent theoretical simulations.Comment: To appear in the proceedings of "Wandering with Curiosity in Complex
Landscapes", a scientific conference in honour of Giorgio Parisi for his 60th
birthday, Roma, September 8-10 2008 (submitted for the special issue of the
Journal of Statistical Physics, 2009
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