220 research outputs found
Correct extrapolation of overlap distribution in spin glasses
We study in d=3 dimensions the short range Ising spin glass with Jij=+/-1
couplings at T=0. We show that the overlap distribution is non-trivial in the
limit of large system size.Comment: 6 pages, 3 figure
The Immunity of Polymer-Microemulsion Networks
The concept of network immunity, i.e., the robustness of the network
connectivity after a random deletion of edges or vertices, has been
investigated in biological or communication networks. We apply this concept to
a self-assembling, physical network of microemulsion droplets connected by
telechelic polymers, where more than one polymer can connect a pair of
droplets. The gel phase of this system has higher immunity if it is more likely
to survive (i.e., maintain a macroscopic, connected component) when some of the
polymers are randomly degraded. We consider the distribution of the
number of polymers between a pair of droplets, and show that gel immunity
decreases as the variance of increases. Repulsive interactions
between the polymers decrease the variance, while attractive interactions
increase the variance, and may result in a bimodal .Comment: Corrected typo
Equilibrium valleys in spin glasses at low temperature
We investigate the 3-dimensional Edwards-Anderson spin glass model at low
temperature on simple cubic lattices of sizes up to L=12. Our findings show a
strong continuity among T>0 physical features and those found previously at
T=0, leading to a scenario with emerging mean field like characteristics that
are enhanced in the large volume limit. For instance, the picture of space
filling sponges seems to survive in the large volume limit at T>0, while
entropic effects play a crucial role in determining the free-energy degeneracy
of our finite volume states. All of our analysis is applied to equilibrium
configurations obtained by a parallel tempering on 512 different disorder
realizations. First, we consider the spatial properties of the sites where
pairs of independent spin configurations differ and we introduce a modified
spin overlap distribution which exhibits a non-trivial limit for large L.
Second, after removing the Z_2 (+-1) symmetry, we cluster spin configurations
into valleys. On average these valleys have free-energy differences of O(1),
but a difference in the (extensive) internal energy that grows significantly
with L; there is thus a large interplay between energy and entropy
fluctuations. We also find that valleys typically differ by sponge-like space
filling clusters, just as found previously for low-energy system-size
excitations above the ground state.Comment: 10 pages, 8 figures, RevTeX format. Clarifications and additional
reference
Lack of Ultrametricity in the Low-Temperature phase of 3D Ising Spin Glasses
We study the low-temperature spin-glass phases of the Sherrington-Kirkpatrick
(SK) model and of the 3-dimensional short range Ising spin glass (3dISG). For
the SK model, evidence for ultrametricity becomes clearer as the system size
increases, while for the short-range case our results indicate the opposite,
i.e. lack of ultrametricity. Our results are obtained by a recently proposed
method that uses clustering to focus on the relevant parts of phase space and
reduce finite size effects. Evidence that the mean field solution does not
apply in detail to the 3dISG is also found by another method which does not
rely on clustering
Discrete energy landscapes and replica symmetry breaking at zero temperature
The order parameter P(q) for disordered systems with degenerate ground-states
is reconsidered. We propose that entropy fluctuations lead to a trivial P(q) at
zero temperature as in the non-degenerate case, even if there are zero-energy
large-scale excitations (complex energy landscape). Such a situation should
arise in the 3-dimensional +-J Ising spin glass and in MAX-SAT. Also, we argue
that if the energy landscape is complex with a finite number of ground-state
families, then replica symmetry breaking reappears at positive temperature.Comment: 7 pages; clarifications on valley definition
State Hierarchy Induced by Correlated Spin Domains in short range spin glasses
We generate equilibrium configurations for the three and four dimensional
Ising spin glass with Gaussian distributed couplings at temperatures well below
the transition temperature T_c. These states are analyzed by a recently
proposed method using clustering. The analysis reveals a hierarchical state
space structure. At each level of the hierarchy states are labeled by the
orientations of a set of correlated macroscopic spin domains. Our picture of
the low temperature phase of short range spin glasses is that of a State
Hierarchy Induced by Correlated Spin domains (SHICS). The complexity of the low
temperature phase is manifest in the fact that the composition of such a spin
domain (i.e. its constituent spins), as well as its identifying label, are
defined and determined by the ``location'' in the state hierarchy at which it
appears. Mapping out the phase space structure by means of the orientations
assumed by these domains enhances our ability to investigate the overlap
distribution, which we find to be non-trivial. Evidence is also presented that
these states may have a non-ultrametric structure.Comment: 30 pages, 17 figure
Discreteness and entropic fluctuations in GREM-like systems
Within generalized random energy models, we study the effects of energy
discreteness and of entropy extensivity in the low temperature phase. At zero
temperature, discreteness of the energy induces replica symmetry breaking, in
contrast to the continuous case where the ground state is unique. However, when
the ground state energy has an extensive entropy, the distribution of overlaps
P(q) instead tends towards a single delta function in the large volume limit.
Considering now the whole frozen phase, we find that P(q) varies continuously
with temperature, and that state-to-state fluctuations of entropy wash out the
differences between the discrete and continuous energy models.Comment: 7 pages, 3 figure, 2 figures are added, the volume changes from 4
pages to 7 page
Pores in Bilayer Membranes of Amphiphilic Molecules: Coarse-Grained Molecular Dynamics Simulations Compared with Simple Mesoscopic Models
We investigate pores in fluid membranes by molecular dynamics simulations of
an amphiphile-solvent mixture, using a molecular coarse-grained model. The
amphiphilic membranes self-assemble into a lamellar stack of amphiphilic
bilayers separated by solvent layers. We focus on the particular case of
tension less membranes, in which pores spontaneously appear because of thermal
fluctuations. Their spatial distribution is similar to that of a random set of
repulsive hard discs. The size and shape distribution of individual pores can
be described satisfactorily by a simple mesoscopic model, which accounts only
for a pore independent core energy and a line tension penalty at the pore
edges. In particular, the pores are not circular: their shapes are fractal and
have the same characteristics as those of two dimensional ring polymers.
Finally, we study the size-fluctuation dynamics of the pores, and compare the
time evolution of their contour length to a random walk in a linear potential
Evidence for the double degeneracy of the ground-state in the 3D spin glass
A bivariate version of the multicanonical Monte Carlo method and its
application to the simulation of the three-dimensional Ising spin glass
are described. We found the autocorrelation time associated with this
particular multicanonical method was approximately proportional to the system
volume, which is a great improvement over previous methods applied to
spin-glass simulations. The principal advantage of this version of the
multicanonical method, however, was its ability to access information
predictive of low-temperature behavior. At low temperatures we found results on
the three-dimensional Ising spin glass consistent with a double
degeneracy of the ground-state: the order-parameter distribution function
converged to two delta-function peaks and the Binder parameter
approached unity as the system size was increased. With the same density of
states used to compute these properties at low temperature, we found their
behavior changing as the temperature is increased towards the spin glass
transition temperature. Just below this temperature, the behavior is consistent
with the standard mean-field picture that has an infinitely degenerate ground
state. Using the concept of zero-energy droplets, we also discuss the structure
of the ground-state degeneracy. The size distribution of the zero-energy
droplets was found to produce the two delta-function peaks of .Comment: 33 pages with 31 eps figures include
酸化物ガラスの塩基度と XPS による O1s 化学シフトの相関に関する考察
O1s binding energy measured by X-ray photoelectron spectroscopy (XPS) is candidate as a new tool to determine a new scale of Lewis basicity of oxide ions in glass. Some mathematical expressions for the basicity or XPS chemical shift, such as charge parameter and optical basicity, were compared with the experimental O1s binding energy in binary alkali oxide glasses. The expressions so far in use needed some modification in parameters. A new empirical expression introduced in this paper gives a new concept and universal scale of basicity
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