27,875 research outputs found
Multi-chord fiber-coupled interferometer with a long coherence length laser
This paper describes a 561 nm laser heterodyne interferometer that provides
time-resolved measurements of line-integrated plasma electron density within
the range of 10^15-10^18 cm^(-2). Such plasmas are produced by railguns on the
Plasma Liner Experiment (PLX), which aims to produce \mu s-, cm-, and
Mbar-scale plasmas through the merging of thirty plasma jets in a spherically
convergent geometry. A long coherence length, 320 mW laser allows for a strong,
sub-fringe phase-shift signal without the need for closely-matched probe and
reference path lengths. Thus only one reference path is required for all eight
probe paths, and an individual probe chord can be altered without altering the
reference or other probe path lengths. Fiber-optic decoupling of the probe
chord optics on the vacuum chamber from the rest of the system allows the probe
paths to be easily altered to focus on different spatial regions of the plasma.
We demonstrate that sub-fringe resolution capability allows the interferometer
to operate down to line-integrated densities of order 10^15 cm^(-2).Comment: submitted to Rev. Sci. Instrum. (2011
Tendency of spherically imploding plasma liners formed by merging plasma jets to evolve toward spherical symmetry
Three dimensional hydrodynamic simulations have been performed using smoothed
particle hydrodynamics (SPH) in order to study the effects of discrete jets on
the processes of plasma liner formation, implosion on vacuum, and expansion.
The pressure history of the inner portion of the liner was qualitatively and
quantitatively similar from peak compression through the complete stagnation of
the liner among simulation results from two one dimensional
radiationhydrodynamic codes, 3D SPH with a uniform liner, and 3D SPH with 30
discrete plasma jets. Two dimensional slices of the pressure show that the
discrete jet SPH case evolves towards a profile that is almost
indistinguishable from the SPH case with a uniform liner, showing that
non-uniformities due to discrete jets are smeared out by late stages of the
implosion. Liner formation and implosion on vacuum was also shown to be robust
to Rayleigh-Taylor instability growth. Interparticle mixing for a liner
imploding on vacuum was investigated. The mixing rate was very small until
after peak compression for the 30 jet simulation.Comment: 28 pages, 16 figures, submitted to Physics of Plasmas (2012
Bounce-free spherical hydrodynamic implosion
In a bounce-free spherical hydrodynamic implosion, the post-stagnation hot
core plasma does not expand against the imploding flow. Such an implosion
scheme has the advantage of improving the dwell time of the burning fuel,
resulting in a higher fusion burn-up fraction. The existence of bounce-free
spherical implosions is demonstrated by explicitly constructing a family of
self-similar solutions to the spherically symmetric ideal hydrodynamic
equations. When applied to a specific example of plasma liner driven
magneto-inertial fusion, the bounce-free solution is found to produce at least
a factor of four improvement in dwell time and fusion energy gain.Comment: accepted by Phys. Plasmas (Nov. 7, 2011); for Ref. 11, please see
ftp://ftp.lanl.gov/public/kagan/liner_evolution.gi
MAGIC observations of Mkn 421 in 2008, and related optical/X-ray/TeV MWL study
The HBL-type blazar Markarian 421 is one of the brightest TeV gamma-ray
sources of the Northern sky. From December 2007 until June 2008 it was
intensively observed in the VHE (E>100 GeV) band by the MAGIC gamma-ray
telescope. The source showed intense and prolonged activity during the whole
period. In some nights the integral flux rose up to 3.6 Crab units (E>200 GeV).
Intra-night rapid flux variations were observed. We compared the optical (KVA)
and X-ray (RXTE-ASM, Swift-XRT) data with the MAGIC VHE data, investigating the
correlations between different energy bands.Comment: 4 pages,4figures, Contribution to the 31st ICRC, Lodz, Poland, July
200
Avalanche-Induced Current Enhancement in Semiconducting Carbon Nanotubes
Semiconducting carbon nanotubes under high electric field stress (~10 V/um)
display a striking, exponential current increase due to avalanche generation of
free electrons and holes. Unlike in other materials, the avalanche process in
such 1D quantum wires involves access to the third sub-band, is insensitive to
temperature, but strongly dependent on diameter ~exp(-1/d^2). Comparison with a
theoretical model yields a novel approach to obtain the inelastic optical
phonon emission length, L_OP,ems ~ 15d nm. The combined results underscore the
importance of multi-band transport in 1D molecular wires
Changes of Forages Fed to Dairy Cows in the Whole Year in Taiwan
Objectives of this study were to determine the kinds and the percents of forages fed to dairy cows in the whole year. Data were taken weekly by the dairy farmers for one year, including kinds and weights of forages fed to dairy cows, the heads of milking cows, dry cows and heifers. Dairy farmer A used napiergrass (Pennisetum purpureum) green chop 68.2%, napiergrass silage 15.3%, pangolagrass (Digitaria decumbens) hay 3.2% and imported bermudagrass (Cynodon dactylon) hay 13.3% to feed cows. Dairy farmer B fed cows with napiergrass green chop 65.1%, pangolagrass 13.0% and imported hays 21.9%, i.e., bermudagrass, alfalfa (Medicago sativa), redtop (Agrostis giantea), oat (Avena sativa) and ryegrass (Lolium perenne). Dairy farmer C fed dairy cows on corn (Zea mays) silage 24.0% and green chop 33.5%, pangolagrass hay 9.1% and imported hays 33.4%, i.e., bermudagrass, alfalfa and timothy (Phleum pratense). Dairy farmer D purchased total mixed ration 58.6% to feed cows. The other forages were corn green chop 14.0%, bermudagrass hay 11.6% and timothy hay 8.6%. Dairy farmer E used corn silage 38.7%, pangolagrass hay 36.5% and hayladge 8.1%, alfalfa hay 14.1%, oat hay and agricultural by-product to feed cows. The forages could be provided steadily when forage crops grew vigorously from April to November. Forage yield decreased after November. Thus, the forages were not available enough to feed cows and the imported hays increased. It was suggested that dairy farmers might make hay or silage during forage growth seasons to keep forages available enough in the whole year
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