2,341 research outputs found
A New Phenomenology for the Disordered Mixed Phase
A universal phase diagram for type-II superconductors with weak point pinning
disorder is proposed. In this phase diagram, two thermodynamic phase
transitions generically separate a ``Bragg glass'' from the disordered liquid.
Translational correlations in the intervening ``multi-domain glass'' phase are
argued to exhibit a significant degree of short-range order. This phase diagram
differs significantly from the currently accepted one but provides a more
accurate description of experimental data on high and low-T materials,
simulations and current theoretical understanding.Comment: 15 pages including 2 postscript figures, minor changes in published
versio
Vortex Matter Transition in BiSrCaCuO under Tilted Fields
Vortex phase diagram under tilted fields from the axis in
BiSrCaCuO is studied by local magnetization
hysteresis measurements using Hall probes. When the field is applied at large
angles from the axis, an anomaly () other than the well-known
peak effect () are found at fields below . The angular dependence of
the field is nonmonotonic and clearly different from that of
and depends on the oxygen content of the crystal. The results suggest existence
of a vortex matter transition under tilted fields. Possible mechanisms of the
transition are discussed.Comment: Revtex, 4 pages, some corrections are adde
Activity Study of Absorbent Prepared from CaO/CaSO4/Coal Fly Ash for SO2 Removal at Low Temperatures.
This study presents findings from an experimental investigation of the influences of several factors on the desulfurization capacity of absorbent prepared from coal fly ash, CaO, and CaSO4. The absorbent was synthesized using hydrothermal reaction while the sulfation experiments were performed in a fixed-bed reactor under isothermal conditions at low temperature
Investigating The Vortex Melting Phenomenon In BSCCO Crystals Using Magneto-Optical Imaging Technique
Using a novel differential magneto-optical imaging technique we investigate
the phenomenon of vortex lattice melting in crystals of Bi_2Sr_2CaCu_2O_8
(BSCCO). The images of melting reveal complex patterns in the formation and
evolution of the vortex solid-liquid interface with varying field (H) or
temperature (T). We believe that the complex melting patterns are due to a
random distribution of material disorder or inhomogeneities across the sample,
which create fluctuations in the local melting temperature or field value. To
study the fluctuations in the local melting temperature / field, we have
constructed maps of the melting landscape T_m(H,r), viz., the melting
temperature (T_m) at a given location (r) in the sample at a given field (H). A
study of these melting landscapes reveals an unexpected feature: the melting
landscape is not fixed, but changes rather dramatically with varying field and
temperature along the melting line. It is concluded that the changes in both
the scale and shape of the landscape result from the competing contributions of
different types of quenched disorder which have opposite effects on the local
melting transition.Comment: Paper presented at the International Symposium on Advances in
Superconductivity & Magnetism: Materials, Mechanisms & Devices September
25-28, 2001, Mangalore, India. Symposium proceedings will be published in a
special issue of Pramana - Journal of Physic
Global Optimization by Energy Landscape Paving
We introduce a novel heuristic global optimization method, energy landscape
paving (ELP), which combines core ideas from energy surface deformation and
tabu search. In appropriate limits, ELP reduces to existing techniques. The
approach is very general and flexible and is illustrated here on two protein
folding problems. For these examples, the technique gives faster convergence to
the global minimum than previous approaches.Comment: to appear in Phys. Rev. Lett. (2002
Possible new vortex matter phases in BSCCO
The vortex matter phase diagram of BSCCO crystals is analyzed by
investigating vortex penetration through the surface barrier in the presence of
a transport current. The strength of the effective surface barrier, its
nonlinearity, and asymmetry are used to identify a possible new ordered phase
above the first-order transition. This technique also allows sensitive
determination of the depinning temperature. The solid phase below the
first-order transition is apparently subdivided into two phases by a vertical
line extending from the multicritical point.Comment: 11 pages, 3 figures, accepted for publication in PR
c-axis penetration depth in BiSrCaCuO single crystals measured by ac-susceptibility and cavity perturbation technique
The -axis penetration depth in
BiSrCaCuO (BSCCO) single crystals as a function of
temperature has been determined using two techniques, namely, measurements of
the ac-susceptibility at a frequency of 100 kHz and the surface impedance at
9.4 GHz. Both techniques yield an almost linear function
in the temperature range T<0.5 T_c.
Electrodynamic analysis of the impedance anisotropy has allowed us to estimate
m in BSCCO crystals overdoped with oxygen
( K) and m at the optimal doping
level ( K).Comment: 5 pages, 4 figure
Helix vs. Sheet Formation in a Small Peptide
Segments with the amino acid sequence EKAYLRT appear in natural occurring
proteins both in -helices and -sheets. For this reason, we have
use this peptide to study how secondary structure formation in proteins depends
on the local environment. Our data rely on multicanonical Monte Carlo
simulations where the interactions among all atoms are taken into account.
Results in gas phase are compared with that in an implicit solvent. We find
that both in gas phase and solvated EKAYLRT forms an -helix when not
interacting with other molecules. However, in the vicinity of a -strand,
the peptide forms a -strand. Because of this change in secondary
structure our peptide may provide a simple model for the
transition that is supposedly related to the outbreak of Prion diseases and
similar illnesses.Comment: to appear in Physical Review
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