805 research outputs found
Effect of Carbon-Doping in Bulk Superconducting MgB2 Samples
Bulk superconducting samples of MgB2 were prepared by solid state reaction of
stoichiometric quantities of Mg turnings and B in a sealed Ta cylinder at 890 C
for 2 hours. The as-synthesized MgB2 samples had a Tc of 39 K, as defined as
the onset of diamagnetism. The crystal symmetry was found to be hexagonal with
lattice parameters, a=3.0856 A, and c=3.5199 A, similar to the literature
values. To study the effect of carbon doping in MgB2, various C-containing
samples of x varying from 0 to 1.00 in MgB2-xCx were prepared. Magnetic
characterizations indicate that the Tc onset is same for pure and C-doped
samples for x = 0.05, and 0.10. However, the shielding signal decreased
monotonically with C content, apparently due to the presence of carbon on the
grain boundaries that isolates grains and prevents flow of supercurrents on the
perimeter.Comment: 10 pages, 3 figure
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
Wireless Energy Harvesting Assisted Two-Way Cognitive Relay Networks: Protocol Design and Performance Analysis
This paper analyzes the effects of realistic relay transceiver on the outage probability and throughput of a two-way relay cognitive network that is equipped with an energy-harvesting relay. In this paper, we configure the network with two wireless power transfer policies and two bidirectional relaying protocols. Furthermore, the differences in receiver structure of relay node that can be time switching or power splitting structure are also considered to develop closed-form expressions of outage and throughput of the network providing that the delay of transmission is limited. Numerical results are presented to corroborate our analysis for all considered network configurations. This paper facilitates us not only to quantify the degradation of outage probability and throughput due to the impairments of realistic transceiver but also to provide an insight into practical effects of specified configuration of power transfer policy, relaying protocol, and receiver structure on outage and throughput. For instance, the system with multiple access broadcast protocol and the power splitting-based receiver architecture achieves ceiling throughout higher than that of the transmission rate of source nodes. On the contrary, a combination of dual-source energy transfer policy and the time division broadcast protocol is contributed the highest level of limiting factor in terms of transceiver hardware impairments on the network throughput.</p
Ni-Cr textured substrates with reduced ferromagnetism for coated conductor applications
A series of biaxially textured Ni(1-x)Cr(x) materials, with compositions x =
0, 7, 9, 11, and 13 at % Cr, have been studied for use as substrate materials
in coated conductor applications with high temperature superconductors. The
magnetic properties were investigated, including the hysteretic loss in a Ni-7
at % Cr sample that was controllably deformed; for comparison, the loss was
also measured in a similarly deformed pure Ni substrate. Complementary X-ray
diffraction studies show that thermo-mechanical processing produces nearly
complete {100} cube texturing, as desired for applications.Comment: PDF only; 19 pp., incl 10 figure
Unzipping Dynamics of Long DNAs
The two strands of the DNA double helix can be `unzipped' by application of
15 pN force. We analyze the dynamics of unzipping and rezipping, for the case
where the molecule ends are separated and re-approached at constant velocity.
For unzipping of 50 kilobase DNAs at less than about 1000 bases per second,
thermal equilibrium-based theory applies. However, for higher unzipping
velocities, rotational viscous drag creates a buildup of elastic torque to
levels above kBT in the dsDNA region, causing the unzipping force to be well
above or well below the equilibrium unzipping force during respectively
unzipping and rezipping, in accord with recent experimental results of Thomen
et al. [Phys. Rev. Lett. 88, 248102 (2002)]. Our analysis includes the effect
of sequence on unzipping and rezipping, and the transient delay in buildup of
the unzipping force due to the approach to the steady state.Comment: 15 pages Revtex file including 9 figure
Effects of hydrostatic pressure on the magnetic susceptibility of ruthenium oxide Sr3Ru2O7: Evidence for pressure-enhanced antiferromagnetic instability
Hydrostatic pressure effects on the temperature- and magnetic field
dependencies of the in-plane and out-of-plane magnetization of the bi-layered
perovskite Sr3Ru2O7 have been studied by SQUID magnetometer measurements under
a hydrostatic helium-gas pressure. The anomalously enhanced low-temperature
value of the paramagnetic susceptibility has been found to systematically
decrease with increasing pressure. The effect is accompanied by an increase of
the temperature Tmax of a pronounced peak of susceptibility. Thus,
magnetization measurements under hydrostatic pressure reveal that the lattice
contraction in the structure of Sr3Ru2O7 promotes antiferromagnetism and not
ferromagnetism, contrary to the previous beliefs. The effects can be explained
by the enhancement of the inter-bi-layer antiferromagnetic spin coupling,
driven by the shortening of the superexchange path, and suppression, due to the
band-broadening effect, of competing itinerant ferromagnetic correlations.Comment: 11 pages, 4 figure
TeV-scale bileptons, see-saw type II and lepton flavor violation in core-collapse supernova
Electrons and electron neutrinos in the inner core of the core-collapse
supernova are highly degenerate and therefore numerous during a few seconds of
explosion. In contrast, leptons of other flavors are non-degenerate and
therefore relatively scarce. This is due to lepton flavor conservation. If this
conservation law is broken by some non-standard interactions, electron
neutrinos are converted to muon and tau-neutrinos, and electrons - to muons.
This affects the supernova dynamics and the supernova neutrino signal. We
consider lepton flavor violating interactions mediated by scalar bileptons,
i.e. heavy scalars with lepton number 2. It is shown that in case of TeV-mass
bileptons the electron fermi gas is equilibrated with non-electron species
inside the inner supernova core at a time-scale of order of (1-100) ms. In
particular, a scalar triplet which generates neutrino masses through the
see-saw type II mechanism is considered. It is found that supernova core is
sensitive to yet unprobed values of masses and couplings of the triplet.Comment: accepted to Eur.Phys.J.
Optically opaque color-flavor locked phase inside compact stars
The contribution of thermally excited electron-positron pairs to the bulk
properties of the color-flavor locked quark phase inside compact stars is
examined. The presence of these pairs causes the photon mean free path to be
much smaller than a typical core radius ( km) for all
temperatures above 25 keV so that the photon contribution to the thermal
conductivity is much smaller than that of the Nambu-Goldstone bosons. We also
find that the electrons and positrons dominate the electrical conductivity,
while their contributions to the total thermal energy is negligible.Comment: 3 pages, 2 figures. Published versio
Formulation Development and Evaluation of Alginate Microspheres of Ibuprofen
The present study was designed to investigate the effects of different variables on the release profile of ibuprofen microspheres formulated using modified emulsification method. Eight batches of microspheres (F1-F8) were prepared by applying 23 factorial design. The amount of sodium alginate, amount of calcium chloride, and amount of magnesium stearate were selected as formulation variables. All the batches were evaluated in terms of percentage yield, percentage encapsulation efficiency and in vitro release characteristics. The batch F7 was found to be optimum batch and was further characterized via scanning electron microscopy (SEM) and particle size analysis. Multiple linear regression was applied to confirm significant effect of each variable on release characteristics. The model developed in the present study can be effectively utilized to achieve the formulation with desired release characteristics
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