2,388 research outputs found
Algebraic Aspects of Abelian Sandpile Models
The abelian sandpile models feature a finite abelian group G generated by the
operators corresponding to particle addition at various sites. We study the
canonical decomposition of G as a product of cyclic groups G = Z_{d_1} X
Z_{d_2} X Z_{d_3}...X Z_{d_g}, where g is the least number of generators of G,
and d_i is a multiple of d_{i+1}. The structure of G is determined in terms of
toppling matrix. We construct scalar functions, linear in height variables of
the pile, that are invariant toppling at any site. These invariants provide
convenient coordinates to label the recurrent configurations of the sandpile.
For an L X L square lattice, we show that g = L. In this case, we observe that
the system has nontrivial symmetries coming from the action of the cyclotomic
Galois group of the (2L+2)th roots of unity which operates on the set of
eigenvalues of the toppling matrix. These eigenvalues are algebraic integers,
whose product is the order |G|. With the help of this Galois group, we obtain
an explicit factorizaration of |G|. We also use it to define other simpler,
though under-complete, sets of toppling invariants.Comment: 39 pages, TIFR/TH/94-3
Biocomposites of poly(lactic acid) and lactic acid oligomer-grafted bacterial cellulose: It's preparation and characterization
This work demonstrates the synthesis of lactic acid oligomer-grafted-untreated bacterial cellulose (OLLA-g-BC) by in situ condensation polymerization which increased compatibilization between hydrophobic poly(lactic acid) (PLA) and hydrophilic BC, thus enhancing various properties of PLA-based bionanocomposites, indispensable for stringent food-packaging applications. During the synthesis of OLLA-g-BC, hydrophilic BC is converted into hydrophobic due to structural grafting of OLLA chains with BC molecules. Subsequently, bionanocomposites films are fabricated using solution casting technique and characterized for structural, thermal, mechanical, optical, and gas-barrier properties. Morphological images showed uniform dispersion of BC nanospheres in the PLA matrix, which shows strong filler–matrix interaction. The degradation temperatures for bionanocomposites films were above PLA processing temperature indicating that bionanocomposite processing can be industrially viable. Bionanocomposites films displayed decrease in glass transition (T g ) and ~20% improvement in elongation with 10 wt % fillers indicating towards plasticization of PLA. PLA/OLLA-g-BC films showed a slight reduction in optical transparency but had excellent UV-blocking characteristics. Moreover, dispersed BC act as blocking agents within PLA matrix, reducing the diffusion through the bionanocomposite films which showed ~40% improvement in water-vapor barrier by 5 wt % filler addition, which is significant. The reduced T g , improved elongation combined with improved hydrophobicity and water-vapor barrier make them suitable candidate for flexible food-packaging applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47903. © 2019 Wiley Periodicals, Inc
Rolling tachyon solution of two-dimensional string theory
We consider a classical (string) field theory of matrix model which was
developed earlier in hep-th/9207011 and subsequent papers. This is a
noncommutative field theory where the noncommutativity parameter is the string
coupling . We construct a classical solution of this field theory and show
that it describes the complete time history of the recently found rolling
tachyon on an unstable D0 brane.Comment: 19 pages, 2 figures, minor changes in text and additional references,
correction of decay time (version to appear in JHEP.
Conservation Laws and Integrability of a One-dimensional Model of Diffusing Dimers
We study a model of assisted diffusion of hard-core particles on a line. The
model shows strongly ergodicity breaking : configuration space breaks up into
an exponentially large number of disconnected sectors. We determine this
sector-decomposion exactly. Within each sector the model is reducible to the
simple exclusion process, and is thus equivalent to the Heisenberg model and is
fully integrable. We discuss additional symmetries of the equivalent quantum
Hamiltonian which relate observables in different sectors. In some sectors, the
long-time decay of correlation functions is qualitatively different from that
of the simple exclusion process. These decays in different sectors are deduced
from an exact mapping to a model of the diffusion of hard-core random walkers
with conserved spins, and are also verified numerically. We also discuss some
implications of the existence of an infinity of conservation laws for a
hydrodynamic description.Comment: 39 pages, with 5 eps figures, to appear in J. Stat. Phys. (March
1997
Magnetic structure of EuFe2As2 determined by single crystal neutron diffraction
Among various parent compounds of iron pnictide superconductors, EuFe2As2
stands out due to the presence of both spin density wave of Fe and
antiferromagnetic ordering (AFM) of the localized Eu2+ moment. Single crystal
neutron diffraction studies have been carried out to determine the magnetic
structure of this compound and to investigate the coupling of two magnetic
sublattices. Long range AFM ordering of Fe and Eu spins was observed below 190
K and 19 K, respectively. The ordering of Fe2+ moments is associated with the
wave vector k = (1,0,1) and it takes place at the same temperature as the
tetragonal to orthorhombic structural phase transition, which indicates the
strong coupling between structural and magnetic components. The ordering of Eu
moment is associated with the wave vector k = (0,0,1). While both Fe and Eu
spins are aligned along the long a axis as experimentally determined, our
studies suggest a weak coupling between the Fe and Eu magnetism.Comment: 7 pages, 7 figure
Exact solutions for a mean-field Abelian sandpile
We introduce a model for a sandpile, with N sites, critical height N and each
site connected to every other site. It is thus a mean-field model in the
spin-glass sense. We find an exact solution for the steady state probability
distribution of avalanche sizes, and discuss its asymptotics for large N.Comment: 10 pages, LaTe
Distribution of sizes of erased loops of loop-erased random walks in two and three dimensions
We show that in the loop-erased random walk problem, the exponent
characterizing probability distribution of areas of erased loops is
superuniversal. In d-dimensions, the probability that the erased loop has an
area A varies as A^{-2} for large A, independent of d, for 2 <= d <= 4. We
estimate the exponents characterizing the distribution of perimeters and areas
of erased loops in d = 2 and 3 by large-scale Monte Carlo simulations. Our
estimate of the fractal dimension z in two-dimensions is consistent with the
known exact value 5/4. In three-dimensions, we get z = 1.6183 +- 0.0004. The
exponent for the distribution of durations of avalanche in the
three-dimensional abelian sandpile model is determined from this by using
scaling relations.Comment: 25 pages, 1 table, 8 figure
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