6,859 research outputs found
Potential function of simplified protein models for discriminating native proteins from decoys: Combining contact interaction and local sequence-dependent geometry
An effective potential function is critical for protein structure prediction
and folding simulation. For simplified models of proteins where coordinates of
only atoms need to be specified, an accurate potential function is
important. Such a simplified model is essential for efficient search of
conformational space. In this work, we present a formulation of potential
function for simplified representations of protein structures. It is based on
the combination of descriptors derived from residue-residue contact and
sequence-dependent local geometry. The optimal weight coefficients for contact
and local geometry is obtained through optimization by maximizing margins among
native and decoy structures. The latter are generated by chain growth and by
gapless threading. The performance of the potential function in blind test of
discriminating native protein structures from decoys is evaluated using several
benchmark decoy sets. This potential function have comparable or better
performance than several residue-based potential functions that require in
addition coordinates of side chain centers or coordinates of all side chain
atoms.Comment: 4 pages, 2 figures, Accepted by 26th IEEE-EMBS Conference, San
Francisc
Statistical Properties of Multiple Optical Emission Components in Gamma-Ray Bursts and Implications
Well-sampled optical lightcurves of 146 gamma-ray bursts (GRBs) are complied
from the literature. Multiple optical emission components are extracted with
power-law function fits to these lightcurves. We present a systematical
analysis for statistical properties and their relations to prompt gamma-ray
emission and X-ray afterglow for each component. We show that peak luminosity
in the prompt and late flares are correlated and the evolution of the peak
luminosity may signal the evolution of the accretion rate. No tight correlation
between the shallow decay phase/plateau and prompt gamma-ray emission is found.
Assuming that they are due to a long-lasting wind injected by a compact object,
we show that the injected behavior favors the scenarios of a long-lasting wind
after the main burst episode. The peak luminosity of the afterglow onset is
tightly correlated with Eiso, and it is dimmer as peaking later. Assuming that
the onset bump is due to the fireball deceleration by the external medium, we
examine the Gamma_0-Eiso relation and find that it is confirmed with the
current sample. Optical re-brightening is observed in 30 GRBs in our sample. It
shares the same relation between the width and the peak time as found in the
onset bump, but no clear correlation between the peak luminosity and Eiso as
observed in the onset bumps is found. Although its peak luminosity also decays
with time, the slope is much shallower than that of the onset peak. We get L
t^{-1}_{p}$, being consistent with off-axis observations to an expanding
external fireball in a wind-like circum medium. The late re-brightening may
signal another jet component. Mixing of different emission components may be
the reason for the observed chromatic breaks in different energy bands.Comment: 10 pages, 5 figures, to be published by IJMPD (Proceedings of "The
Third Galileo - Xu Guangqi meeting", Beijing, October 11-15, 2011
Effects of tensor forces in nuclear spin-orbit splittings from ab initio calculations
A systematic and specific pattern due to the effects of the tensor forces is
found in the evolution of spin-orbit splittings in neutron drops. This result
is obtained from relativistic Brueckner-Hartree-Fock theory using the bare
nucleon-nucleon interaction. It forms an important guide for future microscopic
derivations of relativistic and nonrelativistic nuclear energy density
functionals.Comment: 14 pages, 3 figure
Fully self-consistent relativistic Brueckner-Hartree-Fock theory for finite nuclei
Starting from the relativistic form of the Bonn potential as a bare
nucleon-nucleon interaction, the full Relativistic Brueckner-Hartree-Fock
(RBHF) equations are solved for finite nuclei in a fully self-consistent basis.
This provides a relativistic ab initio calculation of the ground state
properties of finite nuclei without any free parameters and without three-body
forces. The convergence properties for the solutions of these coupled equations
are discussed in detail at the example of the nucleus O. The binding
energies, radii, and spin-orbit splittings of the doubly magic nuclei He,
O, and Ca are calculated and compared with the earlier RBHF
calculated results in a fixed Dirac Woods-Saxon basis and other
non-relativistic ab initio calculated results based on pure two-body forces.Comment: 22 pages, 13 figure
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