612 research outputs found
Hierarchy of protein loop-lock structures: a new server for the decomposition of a protein structure into a set of closed loops
HoPLLS (Hierarchy of protein loop-lock structures)
(http://leah.haifa.ac.il/~skogan/Apache/mydata1/main.html) is a web server that
identifies closed loops - a structural basis for protein domain hierarchy. The
server is based on the loop-and-lock theory for structural organisation of
natural proteins. We describe this web server, the algorithms for the
decomposition of a 3D protein into loops and the results of scientific
investigations into a structural "alphabet" of loops and locks.Comment: 11 pages, 4 figure
Anisotropy parameters of superconducting MgB
Data on macroscopic superconducting anisotropy of MgB are reviewed. The
data are described within a weak coupling two-gaps anisotropic s-wave model of
superconductivity. The calculated ratio of the upper critical fields
increases with decreasing temperature in
agreement with available data, whereas the calculated ratio of London
penetration depths decreases to reach
at T=0. Possible macroscopic consequences of
are discussed.Comment: accepted to Physica C, special MgB2 issu
Determination of superconducting anisotropy from magnetization data on random powders as applied to LuNiBC, YNiBC and MgB
The recently discovered intermetallic superconductor MgB2 appears to have a
highly anisotopic upper critical field with Hc2(max)/Hc2(min} = \gamma > 5. In
order to determine the temperature dependence of both Hc2(max) and Hc2(min) we
propose a method of extracting the superconducting anisotropy from the
magnetization M(H,T) of randomly oriented powder samples. The method is based
on two features in dM/dT the onset of diamagnetism at Tc(max), that is commonly
associated with Hc2, and a kink in dM/dT at a lower temperature Tc(min).
Results for LuNi2B2C and YNi2B2C powders are in agreement with anisotropic Hc2
obtained from magneto-transport measurements on single crystals. Using this
method on four different types of MgB2 powder samples we are able to determine
Hc2(max)(T) and Hc2(min)(T) with \gamma \approx 6
Giant microwave absorption in fine powders of superconductors
Enhanced microwave absorption, larger than that in the normal state, is
observed in fine grains of type-II superconductors (MgB and KC)
for magnetic fields as small as a few of the upper critical field. The
effect is predicted by the theory of vortex motion in type-II superconductors,
however its direct observation has been elusive due to skin-depth limitations;
conventional microwave absorption studies employ larger samples where the
microwave magnetic field exclusion significantly lowers the absorption. We show
that the enhancement is observable in grains smaller than the penetration
depth. A quantitative analysis on KC in the framework of the
Coffey--Clem (CC) theory explains well the temperature dependence of the
microwave absorption and also allows to determine the vortex pinning force
constant
Observational constrains on the DGP brane-world model with a Gauss-Bonnet term in the bulk
Using the data coming from the new 182 Gold type Ia supernova samples, the
baryon acoustic oscillation measurement from the Sloan Digital Sky Survey and
the H(z) data, we have performed a statistical joint analysis of the DGP
brane-world model with a high curvature Gauss-Bonnet term in the bulk.
Consistent parameters estimations show that the Gauss-Bonnet-Induced Gravity
model is a viable candidate to explain the observed acceleration of our
universe.Comment: 11 pages, 6 figures, revised version, accepted for publication in
Phys. Lett.
Anisotropy of superconducting MgB2 as seen in electron spin resonance and magnetization data
We have observed the conduction electron spin resonance (CESR) in fine
powders of MgB2 both in the superconducting and normal states. The Pauli
susceptibility is chi_s=2.0*10^{-5} emu/mole in the temperature range of 450 to
600 K. The spin relaxation rate has an anomalous temperature dependence. The
CESR measured below T_c at several frequencies suggests that MgB_2 is a
strongly anisotropic superconductor with the upper critical field, H_c2,
ranging between 2 and 16 T. The high-field reversible magnetization data of a
randomly oriented powder sample are well described assuming that MgB_2 is an
anisotropic superconductor with H_c2^{ab} / H_{c2}^{c} \approx 6--9.Comment: 4 pages, 4 eps figure
Macroscopic anisotropy in superconductors with anisotropic gaps
It is shown within the weak-coupling model that the macroscopic
superconducting anisotropy for materials with the gap varying on the Fermi
surface cannot be characterized by a single number, unlike the case of clean
materials with isotropic gaps. For clean uniaxial materials, the anisotropy
parameter defined as the ratio of London penetration depths,
, is evaluated for all 's. Within the two-gap model
of MgB, is an increasing function of .Comment: 4 pages, 2 figure
The Kosterlitz-Thouless Phenomenon on a Fluid Random Surface
The problem of a periodic scalar field on a two-dimensional dynamical random
lattice is studied with the inclusion of vortices in the action. Using a random
matrix formulation, in the continuum limit for genus zero surfaces the
partition function is found exactly, as a function of the chemical potential
for vortices of unit winding number, at a specific radius in the plasma phase.
This solution is used to describe the Kosterlitz- Thouless phenomenon in the
presence of 2D quantum gravity as one passes from the ultra-violet to the
infra-red.Comment: 15 pages. This version to appear in Nucl.Phys.B contains less
introductory material (revised
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