2,256 research outputs found
A facet is not an island: step-step interactions and the fluctuations of the boundary of a crystal facet
In a recent paper [Ferrari et al., Phys. Rev. E 69, 035102(R) (2004)], the
scaling law of the fluctuations of the step limiting a crystal facet has been
computed as a function of the facet size. Ferrari et al. use rigorous, but
physically rather obscure, arguments. Approaching the problem from a different
perspective, we rederive more transparently the scaling behavior of facet edge
fluctuations as a function of time. Such behavior can be scrutinized with STM
experiments and with numerical simulations.Comment: 3 page
A Number of Quasi-Exactly Solvable N-body Problems
We present several examples of quasi-exactly solvable -body problems in
one, two and higher dimensions. We study various aspects of these problems in
some detail. In particular, we show that in some of these examples the
corresponding polynomials form an orthogonal set and many of their properties
are similar to those of the Bender-Dunne polynomials. We also discuss QES
problems where the polynomials do not form an orthogonal set.Comment: 17pages, Revtex, no figur
Exact Moving and Stationary Solutions of a Generalized Discrete Nonlinear Schrodinger Equation
We obtain exact moving and stationary, spatially periodic and localized
solutions of a generalized discrete nonlinear Schr\"odinger equation. More
specifically, we find two different moving periodic wave solutions and a
localized moving pulse solution. We also address the problem of finding exact
stationary solutions and, for a particular case of the model when stationary
solutions can be expressed through the Jacobi elliptic functions, we present a
two-point map from which all possible stationary solutions can be found.
Numerically we demonstrate the generic stability of the stationary pulse
solutions and also the robustness of moving pulses in long-term dynamics.Comment: 22 pages, 7 figures, to appear in J. Phys.
Folding of Cu, Zn superoxide dismutase and Familial Amyotrophic Lateral Sclerosis
Cu,Zn superoxide dismutase (SOD1) has been implicated in the familial form of
the neurodegenerative disease Amyotrophic Lateral Sclerosis (ALS). It has been
suggested that mutant mediated SOD1 misfolding/aggregation is an integral part
of the pathology of ALS. We study the folding thermodynamics and kinetics of
SOD1 using a hybrid molecular dynamics approach. We reproduce the
experimentally observed SOD1 folding thermodynamics and find that the residues
which contribute the most to SOD1 thermal stability are also crucial for
apparent two-state folding kinetics. Surprisingly, we find that these residues
are located on the surface of the protein and not in the hydrophobic core.
Mutations in some of the identified residues are found in patients with the
disease. We argue that the identified residues may play an important role in
aggregation. To further characterize the folding of SOD1, we study the role of
cysteine residues in folding and find that non-native disulfide bond formation
may significantly alter SOD1 folding dynamics and aggregation propensity.Comment: 16 pages, 5 figure
New Shape Invariant Potentials in Supersymmetric Quantum Mechanics
Quantum mechanical potentials satisfying the property of shape invariance are
well known to be algebraically solvable. Using a scaling ansatz for the change
of parameters, we obtain a large class of new shape invariant potentials which
are reflectionless and possess an infinite number of bound states. They can be
viewed as q-deformations of the single soliton solution corresponding to the
Rosen-Morse potential. Explicit expressions for energy eigenvalues,
eigenfunctions and transmission coefficients are given. Included in our
potentials as a special case is the self-similar potential recently discussed
by Shabat and Spiridonov.Comment: 8pages, Te
Center and representations of infinitesimal Hecke algebras of sl_2
In this paper, we compute the center of the infinitesimal Hecke algebras Hz
associated to sl_2 ; then using nontriviality of the center, we study
representations of these algebras in the framework of the BGG category O. We
also discuss central elements in infinitesimal Hecke algebras over gl(n) and
sp(2n) for all n. We end by proving an analogue of the theorem of Duflo for Hz.Comment: Final form, to appear in "Communications in Algebra"; 35 pages, laTe
Detecting cold gas at intermediate redshifts: GMRT survey using Mg II systems
Intervening HI 21-cm absorption systems at z > 1.0 are very rare and only 4
confirmed detections have been reported in the literature. Despite their
scarcity, they provide interesting and unique insights into the physical
conditions in the interstellar medium of high-z galaxies. Moreover, they can
provide independent constraints on the variation of fundamental constants. We
report 3 new detections based on our ongoing Giant Metrewave Radio Telescope
(GMRT) survey for 21-cm absorbers at 1.10< z_abs< 1.45 from candidate damped
Lyman_alpha systems. The 21-cm lines are narrow for the z_abs = 1.3710 system
towards SDSS J0108-0037 and z_abs = 1.1726 system toward SDSS J2358-1020. Based
on line full-width at half maximum, the kinetic temperatures are <= 5200 K and
<=800 K, respectively. The 21-cm absorption profile of the third system, z_abs
=1.1908 system towards SDSS J0804+3012, is shallow, broad and complex,
extending up to 100 km/s. The centroids of the 21-cm lines are found to be
shifted with respect to the corresponding centroids of the metal lines derived
from SDSS spectra. This may mean that the 21-cm absorption is not associated
with the strongest metal line component.Comment: 13 pages with 5 figures. Accepted for publication in ApJ
Goethite on Mars - A laboratory study of physically and chemically bound water in ferric oxides
Thermogravimetric study of physically and chemically bound water in ferric oxides of limonite with application to goethite on Mar
Domain Wall and Periodic Solutions of Coupled phi4 Models in an External Field
Coupled double well (phi4) one-dimensional potentials abound in both
condensed matter physics and field theory. Here we provide an exhaustive set of
exact periodic solutions of a coupled model in an external field in
terms of elliptic functions (domain wall arrays) and obtain single domain wall
solutions in specific limits. We also calculate the energy and interaction
between solitons for various solutions. Both topological and nontopological
(e.g. some pulse-like solutions in the presence of a conjugate field) domain
walls are obtained. We relate some of these solutions to the recently observed
magnetic domain walls in certain multiferroic materials and also in the field
theory context wherever possible. Discrete analogs of these coupled models,
relevant for structural transitions on a lattice, are also considered.Comment: 35 pages, no figures (J. Math. Phys. 2006
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