3,563 research outputs found
Improved Current Densities in MgB2 By Liquid-Assisted Sintering
Polycrystalline MgB2 samples with GaN additions were prepared by reaction of
Mg, B, and GaN powders. The presence of Ga leads to a low melting eutectic
phase which allowed liquid phase sintering and produces plate-like grains. For
low-level GaN additions (5% at. % or less), the critical transition
temperature, Tc, remained unchanged and in 1T magnetic field, the critical
current density, Jc was enhanced by a factor of 2 and 10, for temperatures of
\~5K and 20K, respectively. The values obtained are approaching those of hot
isostatically pressed samples.Comment: 12 pages, 1 table, 4 figures, accepted in Applied Physics Letter
Effects Of Post-Deposition Annealing Temperature And Time On Physical Properties Of Metal-Organic Decomposed Lanthanum Cerium Oxide Thin Film.
Lanthanum cerium oxide (LaxCeyOz) precursor was prepared using metal-organic decomposition method. The effects of post-deposition annealing temperatures (400-1000 °C) and annealing time (15-120 minutes) in argon ambient on physical properties of the deposited film were investigated
Growth Mechanism of Cubic-Silicon Carbide Nanowires
Cubic-SiC nanowires were synthesized using activated carbon powder and Si substrate in vacuum at 1200–1350°C for 1–4 hours. The nanowires were grown according to the following proposed mechanisms: (1) diffusion of C/CO into Si substrate, (2) weakening of Si bond and atomic kick-out, (3) formation of Si-C in vapor phase, (4) formation of saturated SiC layer, (5) formation of pyramid-like SiC nanostructure, and (6) formation of SiC nanowires
Effective Vortex Pinning in MgB2 thin films
We discuss pinning properties of MgB2 thin films grown by pulsed-laser
deposition (PLD) and by electron-beam (EB) evaporation. Two mechanisms are
identified that contribute most effectively to the pinning of vortices in
randomly oriented films. The EB process produces low defected crystallites with
small grain size providing enhanced pinning at grain boundaries without
degradation of Tc. The PLD process produces films with structural disorder on a
scale less that the coherence length that further improves pinning, but also
depresses Tc
Growth of Strongly Biaxially Aligned MgB2 Thin Films on Sapphire by Post-annealing of Amorphous Precursors
MgB2 thin films were cold-grown on sapphire substrates by pulsed laser
deposition (PLD), followed by post-annealing in mixed, reducing gas, Mg-rich,
Zr gettered, environments. The films had Tcs in the range 29 K to 34 K, Jcs
(20K, H=0) in the range 30 kA/cm2 to 300 kA/cm2, and irreversibility fields at
20 K of 4 T to 6.2 T. An inverse correlation was found between Tc and
irreversibility field. The films had grain sizes of 0.1-1 micron and a strong
biaxial alignment was observed in the 950C annealed film.Comment: 12 Pages, 5 figures, submitted to Applied Physics Letter
Carbon Recombination Lines from the Galactic Plane at 34.5 & 328 MHz
We present results of a search for carbon recombination lines in the Galaxy
at 34.5 MHz (C) made using the dipole array at Gauribidanur near
Bangalore. Observations made towards 32 directions, led to detections of lines
in absorption at nine positions. Followup observations at 328 MHz
(C) using the Ooty Radio Telescope detected these lines in emission.
A VLA D-array observation of one of the positions at 330 MHz yielded no
detection implying a lower limit of 10' for the angular size of the line
forming region.
The longitude-velocity distribution of the observed carbon lines indicate
that the line forming region are located mainly between 4 kpc and 7 kpc from
the Galactic centre. Combining our results with published carbon recombination
line data near 76 MHz (\nocite{erickson:95} Erickson \et 1995) we obtain
constraints on the physical parameters of the line forming regions. We find
that if the angular size of the line forming regions is , then
the range of parameters that fit the data are: \Te K, \ne \cm3 and pathlengths pc which may correspond to thin
photo-dissociated regions around molecular clouds. On the other hand, if the
line forming regions are in extent, then warmer gas (\Te K) with lower electron densities (\ne \cm3) extending
over several tens of parsecs along the line of sight and possibly associated
with atomic \HI gas can fit the data. Based on the range of derived parameters,
we suggest that the carbon line regions are most likely associated with
photo-dissociation regions.Comment: To appear in Journal of Astrophysics & Astronomy, March 200
Study of CP violation in Dalitz-plot analyses of B0 --> K+K-KS, B+ --> K+K-K+, and B+ --> KSKSK+
We perform amplitude analyses of the decays , , and , and measure CP-violating
parameters and partial branching fractions. The results are based on a data
sample of approximately decays, collected with the
BABAR detector at the PEP-II asymmetric-energy factory at the SLAC National
Accelerator Laboratory. For , we find a direct CP asymmetry
in of , which differs
from zero by . For , we measure the
CP-violating phase .
For , we measure an overall direct CP asymmetry of
. We also perform an angular-moment analysis of
the three channels, and determine that the state can be described
well by the sum of the resonances , , and
.Comment: 35 pages, 68 postscript figures. v3 - minor modifications to agree
with published versio
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