2,779 research outputs found
Vortex pinning in high-Tc materials via randomly oriented columnar defects, created by GeV proton-induced fission fragments
Extensive work has shown that irradiation with 0.8 GeV protons can produce
randomly oriented columnar defects (CD's) in a large number of HTS materials,
specifically those cuprates containing Hg, Tl, Pb, Bi, and similar heavy
elements. Absorbing the incident proton causes the nucleus of these species to
fission, and the recoiling fission fragments create amorphous tracks, i.e.,
CD's. The superconductive transition temperature Tc decreases linearly with
proton fluence and we analyze how the rate depends on the family of
superconductors. In a study of Tl-2212 materials, adding defects decreases the
equilibrium magnetization Meq(H) significantly in magnitude and changes its
field dependence; this result is modeled in terms of vortex pinning. Analysis
of the irreversible magnetization and its time dependence shows marked
increases in the persistent current density and effective pinning energy, and
leads to an estimate for the elementary attempt time for vortex hopping, tau ~
4x10^(-9) s.Comment: Submitted to Physica C; presentation at ISS-2001. PDF file only, 13
pp. tota
Functional changes in motor endplates of the target muscle after amputation of the C7 nerve root
There are limited data on structural and functional changes in motor endplates and
muscle fibers in the target muscle following amputation of the 7th cervical nerve root, a
transplantation-related procedure in surgical treatment in the case of avulsions of the brachial
plexus roots. We examined functional changes in these structures using stimulated singlefiber electromyography (sSF-EMG) in an animal model. Unilateral amputation of the 7th
cervical nerve root was performed in 36 male rats, and the m. triceps brachii muscle was
tested by sSF-EMG at different time points. We observed significant differences in the jitter
(mean consecutive difference, MCD, of the latencies between adjacent muscle fibers) at postamputation weeks 1, 2, 4, and 6. The post-operation fiber density (FD) values within the
zone of effective stimulation also gradually increased. At post-amputation weeks 8 and 12,
the jitter values returned to normal levels, whereas FD values continued to rise. Our results
indicate that the post-amputation compensatory processes in the target muscles of the 7th
cervical nerve root are completed at 9-12 weeks after amputation.Дані щодо структурних та функціональних змін у моторних
кінцевих пластинках та м’язових волокнах м’яза-цілі після ампутації сьомого шийного нервового корінця (процедури в рамках трансплантаційного хірургічного лікування
наслідків відриву корінців брахіального сплетіння) поки
що обмежені. Ми досліджували функціональні зміни в згаданих структурах, використовуючи методику стимуляційної „одноволоконної” електроміографії в умовах експериментальної моделі на тваринах. Унілатеральну ампутацію
сьомого цервікального нервового корінця було виконано на
36 щурах-самцях, і триголові м’язи плеча тестувалися за допомогою згаданої ЕМГ-методики в різні часові інтервали.
Ми виявили істотні відмінності середніх варіацій („дрижання”, jitter, різниць між послідовними величинами) латентних періодів, характерних для прилеглих одне до одного
м’язових волокон, у перший, другий, четвертий та шостий
тижні після операційного періоду. В цей час щільність волокон у зоні ефективної стимуляції також поступово зростала.
На восьмий–12-й тижні післяопераційного періоду значення варіацій („дрижання”) поверталися до нормальних, тоді
як значення щільності активованих волокон продовжували
зростати. Наші результати свідчать про те, що післяампутаційні компенсаторні процеси в м’язах-цілях волокон нервового корінця С7 завершуються через дев’ять–12 тижнів після ампутації останнього
Tunneling spectra of submicron BiSrCaCuO intrinsic Josephson junctions: evolution from superconducting gap to pseudogap
Tunneling spectra of near optimally doped, submicron
BiSrCaCuO intrinsic Josephson junctions are presented,
and examined in the region where the superconducting gap evolves into
pseudogap. The spectra are analyzed using a self-energy model, proposed by
Norman {\it et al.}, in which both quasiparticle scattering rate and
pair decay rate are considered. The density of states derived
from the model has the familiar Dynes' form with a simple replacement of
by = ( + )/2. The
parameter obtained from fitting the experimental spectra shows a roughly linear
temperature dependence, which puts a strong constraint on the relation between
and . We discuss and compare the Fermi arc behavior
in the pseudogap phase from the tunneling and angle-resolved photoemission
spectroscopy experiments. Our results indicate an excellent agreement between
the two experiments, which is in favor of the precursor pairing view of the
pseudogap.Comment: 7 pages, 6 figure
The littlest Higgs model and Higgs boson associated production with top quark pair at high energy linear collider
In the parameter space allowed by the electroweak precision measurement data,
we consider the contributions of the new particles predicted by the littlest
Higgs() model to the Higgs boson associated production with top quark pair
in the future high energy linear collider(). We find that the
contributions mainly come from the new gauge bosons and . For
reasonable values of the free parameters, the absolute value of the relative
correction parameter can be significanly large,
which might be observed in the future experiment with .Comment: latex files, 13 pages, 3 figure
Fermion Condensation Quantum Phase Transition versus Conventional Quantum Phase Transitions
The main features of fermion condensation quantum phase transition (FCQPT),
which are distinctive in several aspects from that of conventional quantum
phase transition (CQPT), are considered. We show that in contrast to CQPT,
whose physics in quantum critical region is dominated by thermal and quantum
fluctuations and characterized by the absence of quasiparticles, the physics of
a Fermi system near FCQPT or undergone FCQPT is controlled by the system of
quasiparticles resembling the Landau quasiparticles. Contrary to the Landau
quasiparticles, the effective mass of these quasiparticles strongly depends on
the temperature, magnetic fields, density, etc. This system of quasiparticles
having general properties determines the universal behavior of the Fermi system
in question. As a result, the universal behavior persists up to relatively high
temperatures comparatively to the case when such a behavior is determined by
CQPT. We analyze striking recent measurements of specific heat, charge and heat
transport used to study the nature of magnetic field-induced QCP in
heavy-fermion metal CeCoIn and show that the observed facts are in good
agreement with our scenario based on FCQPT and certainly seem to rule out the
critical fluctuations related with CQPT. Our general consideration suggests
that FCQPT and the emergence of novel quasiparticles near and behind FCQPT and
resembling the Landau quasiparticles are distinctive features intrinsic to
strongly correlated substances.Comment: 10 pages, Revtex, new references and facts are adde
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Balancing the popularity bias of object similarities for personalised recommendation
Network-based similarity measures have found wide applications in recommendation algorithms and made signicant contributions for uncovering users' potential interests. However, existing measures are generally biased in terms of popularity, that the popular objects tend to have more common neighbours with others and thus are considered more similar to others. Such popularity bias
of similarity quantification will result in the biased recommendations, with either poor accuracy or poor diversity. Based on the bipartite network modelling of the user-object interactions, this paper firstly calculates the expected number of common neighbours of two objects with given popularities in random networks. A Balanced Common Neighbour similarity index is accordingly developed
by removing the random-driven common neighbours, estimated as the expected number, from the total number. Recommendation experiments in three data sets show that balancing the popularity bias in a certain degree can significantly improve the recommendations' accuracy and diversity
simultaneously
Harmonic maps from degenerating Riemann surfaces
We study harmonic maps from degenerating Riemann surfaces with uniformly
bounded energy and show the so-called generalized energy identity. We find
conditions that are both necessary and sufficient for the compactness in
and modulo bubbles of sequences of such maps.Comment: 27 page
Analysis of the vertexes , and radiative decays ,
In this article, we study the vertexes and with the light-cone QCD sum rules, then assume the vector meson
dominance of the intermediate , and , and
calculate the radiative decays and .Comment: 28 pages, 4 tables, revised versio
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