1,246 research outputs found
Effects of C, Cu and Be substitutions in superconducting MgB2
Density functional calculations are used to investigate the effects of
partial substitutional alloying of the B site in MgB2 with C and Be alone and
combined with alloying of the Mg site with Cu. The effect of such substitutions
on the electronic structure, electron phonon coupling and superconductivity are
discussed. We find that Be substitution for B is unfavorable for
superconductivity as it leads to a softer lattice and weaker electron-phonon
couplings. Replacement of Mg by Cu leads to an increase in the stiffness and
doping level at the same time, while the carrier concentration can be
controlled by partial replacement of B by C. We estimate that with full
replacement of Mg by Cu and fractional substitution of B by C, Tc values of 50K
may be attainable.Comment: 5 pages, 4 figure
Linear Stability of Triangular Equilibrium Points in the Generalized Photogravitational Restricted Three Body Problem with Poynting-Robertson Drag
In this paper we have examined the linear stability of triangular equilibrium
points in the generalised photogravitational restricted three body problem with
Poynting-Robertson drag. We have found the position of triangular equilibrium
points of our problem. The problem is generalised in the sense that smaller
primary is supposed to be an oblate spheroid. The bigger primary is considered
as radiating. The equations of motion are affected by radiation pressure force,
oblateness and P-R drag. All classical results involving photogravitational and
oblateness in restricted three body problem may be verified from this result.
With the help of characteristic equation, we discussed the stability. Finally
we conclude that triangular equilibrium points are unstable.Comment: accepted for publication in Journal of Dynamical Systems & Geometric
Theories Vol. 4, Number 1 (2006
Temperature-dependent transformation of the magnetic excitation spectrum on approaching superconductivity in Fe1-x (Ni/Cu)x Te0.5 Se0.5
Spin excitations are one of the top candidates for mediating electron pairing
in unconventional superconductors. Their coupling to superconductivity is
evident in a large number of systems, by the observation of an abrupt
redistribution of magnetic spectral weight at the superconducting transition
temperature, Tc, for energies comparable to the superconducting gap. Here we
report inelastic neutron scattering measurements on Fe-based superconductors,
Fe1-x (Ni/Cu)x Te0.5 Se0.5, that emphasize an additional signature. The overall
shape of the low energy magnetic dispersion changes from two incommensurate
vertical columns at T >> Tc to a distinctly different U-shaped dispersion at
low temperature. Importantly, this spectral reconstruction is apparent for
temperature up to ~3Tc. If the magnetic excitations are involved in the pairing
mechanism, their surprising modification on the approach to Tc demonstrates
that strong interactions are involved
Disordered Boson Systems: A Perturbative Study
A hard-core disordered boson system is mapped onto a quantum spin 1/2
XY-model with transverse random fields. It is then generalized to a system of
spins with an arbitrary magnitude S and studied through a 1/S expansion. The
first order 1/S expansion corresponds to a spin-wave theory. The effect of weak
disorder is studied perturbatively within such a first order 1/S scheme. We
compute the reduction of the speed of sound and the life time of the Bloch
phonons in the regime of weak disorder. Generalizations of the present study to
the strong disordered regime are discussed.Comment: 27 pages, revte
Strange particle production at RHIC in a single-freeze-out model
Strange particle ratios and pT-spectra are calculated in a thermal model with
single freeze-out, previously used successfully to describe non-strange
particle production at RHIC. The model and the recently released data for phi,
Lambda, anti-Lambda, and K*(892) are in very satisfactory agreement, showing
that the thermal approach can be used to describe the strangeness production at
RHIC.Comment: We have added the comparison of the model predictions to the newly
released Lambda and K*(892) pT-spectra from STA
Optical Properties of MFe_4P_12 filled skutterudites
Infrared reflectance spectroscopy measurements were made on four members of
the MFe_4P_12 family of filled skutterudites, with M=La, Th, Ce and U. In
progressing from M=La to U the system undergoes a metal-insulator transition.
It is shown that, although the filling atom induces such dramatic changes in
the transport properties of the system, it has only a small effect on lattice
dynamics. We discuss this property of the compounds in the context of their
possible thermoelectric applications.Comment: Manuscript in ReVTeX format, 7 figures in PostScirpt forma
Impurity-induced transition and impurity-enhanced thermopower in the thermoelectric oxide NaCo_{2-x}Cu_x$O_4
Various physical quantities are measured and analysed for the Cu-substituted
thermoelectric oxide NaCo_{2-x}Cu_xO_4. As was previously known, the
substituted Cu enhances the thermoelectric power, while it does not increase
the resistivity significantly. The susceptibility and the electron
specific-heat are substantially decreased with increasing x, which implies that
the substituted Cu decreases the effective-mass enhancement. Through a
quantitative comparison with the heavy fermion compounds and the valence
fluctuation systems, we have found that the Cu substitution effectively
increases the coupling between the conduction electron and the magnetic
fluctuation. The Cu substitution induces a phase transition at 22 K that is
very similar to a spin-density-wave transition.Comment: 8 pages, 7 figures, submitted to Phys. Rev.
Optical sum rule violation, superfluid weight and condensation energy in the cuprates
The model of hole superconductivity predicts that the superfluid weight in
the zero-frequency -function in the optical conductivity has an
anomalous contribution from high frequencies, due to lowering of the system's
kinetic energy upon entering the superconducting state. The lowering of kinetic
energy, mainly in-plane in origin, accounts for both the condensation energy of
the superconductor as well as an increased potential energy due to larger
Coulomb repulsion in the paired state. It leads to an apparent violation of the
conductivity sum rule, which in the clean limit we predict to be substantially
larger for in-plane than for c-axis conductivity. However, because cuprates are
in the dirty limit for c-axis transport, the sum rule violation is found to be
greatly enhanced in the c-direction. The model predicts the sum rule violation
to be largest in the underdoped regime and to decrease with doping, more
rapidly in the c-direction that in the plane. So far, experiments have detected
sum rule violation in c-axis transport in several cuprates, as well as a
decrease and disappearance of this violation for increasing doping, but no
violation in-plane. We explore the predictions of the model for a wide range of
parameters, both in the absence and in the presence of disorder, and the
relation with current experimental knowledge.Comment: submitted to Phys.Rev.
Rapidity distribution as a probe for elliptical flow at intermediate energies
Interplay between the spectator and participant matter in heavy-ion
collisions is investigated within isospin dependent quantum molecular dynamics
(IQMD) model in term of rapidity distribution of light charged particles. The
effect of different types and size rapidity distributions is studied in
elliptical flow. The elliptical flow patterns show important role of the nearby
spectator matter on the participant zone. This role is further explained on the
basis of passing time of the spectator and expansion time of the participant
zone. The transition from the in-plane to out-of-plane is observed only when
the mid-rapidity region is included in the rapidity bin, otherwise no
transition occurs. The transition energy is found to be highly sensitive
towards the size of the rapidity bin, while weakly on the type of the rapidity
distribution. The theoretical results are also compared with the experimental
findings and are found in good agreement.Comment: 8 figure
Artificial intelligence-based preventive, personalized and precision medicine for cardiovascular disease/stroke risk assessment in rheumatoid arthritis patients: a narrative review
The challenges associated with diagnosing and treating cardiovascular disease (CVD)/Stroke in Rheumatoid arthritis (RA) arise from the delayed onset of symptoms. Existing clinical risk scores are inadequate in predicting cardiac events, and conventional risk factors alone do not accurately classify many individuals at risk. Several CVD biomarkers consider the multiple pathways involved in the development of atherosclerosis, which is the primary cause of CVD/Stroke in RA. To enhance the accuracy of CVD/Stroke risk assessment in the RA framework, a proposed approach involves combining genomic-based biomarkers (GBBM) derived from plasma and/or serum samples with innovative non-invasive radiomic-based biomarkers (RBBM), such as measurements of synovial fluid, plaque area, and plaque burden. This review presents two hypotheses: (i) RBBM and GBBM biomarkers exhibit a significant correlation and can precisely detect the severity of CVD/Stroke in RA patients. (ii) Artificial Intelligence (AI)-based preventive, precision, and personalized (aiP3) CVD/Stroke risk AtheroEdge™ model (AtheroPoint™, CA, USA) that utilizes deep learning (DL) to accurately classify the risk of CVD/stroke in RA framework. The authors conducted a comprehensive search using the PRISMA technique, identifying 153 studies that assessed the features/biomarkers of RBBM and GBBM for CVD/Stroke. The study demonstrates how DL models can be integrated into the AtheroEdge™–aiP3 framework to determine the risk of CVD/Stroke in RA patients. The findings of this review suggest that the combination of RBBM with GBBM introduces a new dimension to the assessment of CVD/Stroke risk in the RA framework. Synovial fluid levels that are higher than normal lead to an increase in the plaque burden. Additionally, the review provides recommendations for novel, unbiased, and pruned DL algorithms that can predict CVD/Stroke risk within a RA framework that is preventive, precise, and personalized. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature
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