2,824 research outputs found
Finite-size scaling of helix-coil transitions in poly-alanine studied by multicanonical simulations
We report results from multicanonical simulations of poly-alanine.
Homopolymers of up to 30 amino acids were considered and various thermodynamic
quantities as a function of temperature calculated. We study the nature of the
observed helix-coil transition and present estimates for critical exponents.Comment: to appear in J.Chem.Phys. (Jan 99
Successive phase transitions to antiferromagnetic and weak-ferromagnetic long-range orders in quasi-one-dimensional antiferromagnet CuMoO
Investigation of the magnetism of CuMoO single crystal, which has
antiferromagnetic (AF) linear chains interacting with AF dimers, reveals an AF
second-order phase transition at K. Although weak
ferromagnetic-like behavior appears at lower temperatures in low magnetic
fields, complete remanent magnetization cannot be detected down to 0.5 K.
However, a jump is observed in the magnetization below weak ferromagnetic (WF)
phase transition at K when a tiny magnetic field along
the a axis is reversed, suggesting that the coercive force is very weak. A
component of magnetic moment parallel to the chain forms AF long-range order
(LRO) below , while a perpendicular component is disordered above
at zero magnetic field and forms WF-LRO below .
Moreover, the WF-LRO is also realized with applying magnetic fields even
between and . These results are explainable by both
magnetic frustration among symmetric exchange interactions and competition
between symmetric and asymmetric Dzyaloshinskii-Moriya exchange interactions.Comment: 7 pages, 7 figure
Characteristic Temperatures of Folding of a Small Peptide
We perform a generalized-ensemble simulation of a small peptide taking the
interactions among all atoms into account. From this simulation we obtain
thermodynamic quantities over a wide range of temperatures. In particular, we
show that the folding of a small peptide is a multi-stage process associated
with two characteristic temperatures, the collapse temperature T_{\theta} and
the folding temperature T_f. Our results give supporting evidence for the
energy landscape picture and funnel concept. These ideas were previously
developed in the context of studies of simplified protein models, and here for
the first time checked in an all-atom Monte Carlo simulation.Comment: Latex, 6 Figure
Generalized-ensemble Monte carlo method for systems with rough energy landscape
We present a novel Monte Carlo algorithm which enhances equilibrization of
low-temperature simulations and allows sampling of configurations over a large
range of energies. The method is based on a non-Boltzmann probability weight
factor and is another version of the so-called generalized-ensemble techniques.
The effectiveness of the new approach is demonstrated for the system of a small
peptide, an example of the frustrated system with a rugged energy landscape.Comment: Latex; ps-files include
How to distinguish the Haldane/Large-D state and the intermediate-D state in an S=2 quantum spin chain with the XXZ and on-site anisotropies
We numerically investigate the ground-state phase diagram of an S=2 quantum
spin chain with the and on-site anisotropies described by , where denotes the XXZ anisotropy parameter of the
nearest-neighbor interactions and the on-site anisotropy parameter. We
restrict ourselves to the and case for simplicity. Our main
purpose is to obtain the definite conclusion whether there exists or not the
intermediate- (ID) phase, which was proposed by Oshikawa in 1992 and has
been believed to be absent since the DMRG studies in the latter half of 1990's.
In the phase diagram with and there appear the XY state, the
Haldane state, the ID state, the large- (LD) state and the N\'eel state. In
the analysis of the numerical data it is important to distinguish three gapped
states; the Haldane state, the ID state and the LD state. We give a physical
and intuitive explanation for our level spectroscopy method how to distinguish
these three phases.Comment: Proceedings of "International Conference on Frustration in Condensed
Matter (ICFCM)" (Jan. 11-14, 2011, Sendai, Japan
Charmed meson decay constants in three-flavor lattice QCD
We present the first lattice QCD calculation with realistic sea quark content
of the D^+ meson decay constant f_{D^+}. We use the MILC Collaboration's
publicly available ensembles of lattice gauge fields, which have a quark sea
with two flavors (up and down) much lighter than a third (strange). We obtain
f_{D^+} = 201 +/- 3 +/- 17 MeV, where the errors are statistical and a
combination of systematic errors. We also obtain f_{D_s} = 249 +/- 3 +/- 16 MeV
for the D_s meson.Comment: note added on recent CLEO measurement; PRL versio
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