148 research outputs found
DMRG studies of the effect of constraint release on the viscosity of polymer melts
The scaling of the viscosity of polymer melts is investigated with regard to
the molecular weight. We present a generalization of the Rubinstein-Duke model,
which takes constraint releases into account and calculate the effects on the
viscosity by the use of the Density Matrix Renormalization Group (DMRG)
algorithm. Using input from Rouse theory the rates for the constraint release
are determined in a self consistent way. We conclude that shape fluctuations of
the tube caused by constraint release are not a likely candidate for improving
Doi's crossover theory for the scaling of the polymer viscosity.Comment: 6 pages, 8 figure
Field Driven Pairing State Phase Transition in d_x^2-y^2+id_xy-Wave Superconductors
Within the framework of the Ginzburg-Landau theory for
-wave superconductors, we discuss the pairing state phase
transition in the absence of the Zeeman coupling between the Cooper pair
orbital angular momentum and the magnetic field. We find that above a
temperature , the pairing state in a magnetic field is pure
-wave. However, below , the pairing state is
-wave at low fields, and it becomes pure
-wave at higher fields. Between these pairing states there
exists a field driven phase transition . The transition field increases with
decreasing temperature. In the field-temperature phase diagram, the phase
transition line is obtained theoretically by a combined use of a variational
method and the Virial theorem. The analytical result is found to be in good
agreement with numerical simulation results of the Gingzburg-Landau equations.
The validity of the variational method is discussed. The difference to the case
with the Zeeman coupling is discussed, which may be utilized to the detection
of the Zeeman coupling.Comment: 5 pages, 2 figures, submitted to PRB Brief Repor
Impurity and interface bound states in and superconductors
Motivated by recent discoveries of novel superconductors such as
NaCoOHO and SrRuO, we analysize features of
quasi-particle scattering due to impurities and interfaces for possible gapful
and Cooper pairing. A bound state appears near
a local impurity, and a band of bound states form near an interface. We
obtained analytically the bound state energy, and calculated the space and
energy dependent local density of states resolvable by high-resolution scanning
tunnelling microscopy. For comparison we also sketch results of impurity and
surface states if the pairing is nodal p- or d-wave.Comment: 4 pages, 4 figure
Mining Contrast Subspaces
In this paper, we tackle a novel problem of mining contrast subspaces. Given a set of multidimensional objects in two classes C+  and C− and a query object o, we want to find top-k subspaces S that maximize the ratio of likelihood of o in C+  against that in C−. We demonstrate that this problem has important applications, and at the same time, is very challenging. It even does not allow polynomial time approximation. We present CSMiner, a mining method with various pruning techniques. CSMiner is substantially faster than the baseline method. Our experimental results on real data sets verify the effectiveness and efficiency of our method
Barrier effects on the collective excitations of split Bose-Einstein condensates
We investigate the collective excitations of a single-species Bose gas at T=0
in a harmonic trap where the confinement undergoes some splitting along one
spatial direction. We mostly consider onedimensional potentials consisting of
two harmonic wells separated a distance 2 z_0, since they essentially contain
all the barrier effects that one may visualize in the 3D situation. We find,
within a hydrodynamic approximation, that regardless the dimensionality of the
system, pairs of levels in the excitation spectrum, corresponding to
neighbouring even and odd excitations, merge together as one increases the
barrier height up to the current value of the chemical potential. The
excitation spectra computed in the hydrodynamical or Thomas-Fermi limit are
compared with the results of exactly solving the time-dependent
Gross-Pitaevskii equation. We analyze as well the characteristics of the
spatial pattern of excitations of threedimensional boson systems according to
the amount of splitting of the condensate.Comment: RevTeX, 12 pages, 13 ps figure
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