831 research outputs found
Solar cell research, phase 2 Semiannual report
Radiation effects on properties of lithium solar cell
VLBI observations of jupiter with the initial test station of LOFAR and the nancay decametric array
AIMS: To demonstrate and test the capability of the next generation of
low-frequency radio telescopes to perform high resolution observations across
intra-continental baselines. Jupiter's strong burst emission is used to perform
broadband full signal cross-correlations on time intervals of up to hundreds of
milliseconds. METHODS: Broadband VLBI observations at about 20 MHz on a
baseline of ~50000 wavelengths were performed to achieve arcsecond angular
resolution. LOFAR's Initial Test Station (LOFAR/ITS, The Netherlands) and the
Nancay Decametric Array (NDA, France) digitize the measured electric field with
12 bit and 14 bit in a 40 MHz baseband. The fine structure in Jupiter's signal
was used for data synchronization prior to correlation on the time-series data.
RESULTS: Strong emission from Jupiter was detected during snapshots of a few
seconds and detailed features down to microsecond time-scales were identified
in dynamic spectra. Correlations of Jupiter's burst emission returned strong
fringes on 1 ms time-scales over channels as narrow as a hundred kilohertz
bandwidth. CONCLUSIONS: Long baseline interferometry is confirmed at low
frequencies, in spite of phase shifts introduced by variations in ionospheric
propagation characteristics. Phase coherence was preserved over tens to
hundreds of milliseconds with a baseline of ~700 km. No significant variation
with time was found in the correlations and an estimate for the fringe
visibility of 1, suggested that the source was not resolved. The upper limit on
the source region size of Jupiter Io-B S-bursts corresponds to an angular
resolution of ~3 arcsec. Adding remote stations to the LOFAR network at
baselines up to thousand kilometers will provide 10 times higher resolution
down to an arcsecond.Comment: 6 pages, 4 figures. Nigl, A., Zarka, P., Kuijpers, J., Falcke, H.,
Baehren, L., VLBI observations of Jupiter with the Initial Test Station of
LOFAR and the Nancay Decametric Array, A&A, 471, 1099-1104, accepted on
31/05/200
Metabolic responses of osteochondral allografts to re-warming after MOPS(TM) preservation versus standard of care storage
Osteoarthritis (OA) affects ~90% of people older than 65, and associated costs top $100 billion annually in the U.S. One treatment available for large cartilage defects seen in osteoarthritis is osteochondral allograft (OCA) transplantation. Currently, tissue banks store OCAs at 4 degree C and implantation is recommended within 28 days after procurement due to significant loss in chondrocyte viability after this time. Because mandatory disease screening protocols typically take 14 days to complete, the window for surgical implantation is narrow, which severely limits clinical use. The MOPS(TM) protocol can maintain OCAs for 56 days. In this study, OCAs stored using MOPS(TM) and SOC protocol were assessed for cell viability and metabolic biomarker production
Cooperative Evaluation of Inner Mongolia, PRC, Grassland Germplasm in the Western USA
Replicated dryland studies were established at three USDA, NRCS, Plant Materials Centers in the USA northern intermountain west by Chinese and American scientists. Forty-six Asian and 16 USA grasses, legumes, and shrubs were included. These plantings were evaluated for vigor, percent stand, and foliage height in 1994 and 1995, and for biomass production in 1995. Generally, USA grasses outperformed Asian grasses, while Inner Mongolian legumes show the highest potential for use in the intermountain west
Random and ordered phases of off-lattice rhombus tiles
We study the covering of the plane by non-overlapping rhombus tiles, a
problem well-studied only in the limiting case of dimer coverings of regular
lattices. We go beyond this limit by allowing tiles to take any position and
orientation on the plane, to be of irregular shape, and to possess different
types of attractive interactions. Using extensive numerical simulations we show
that at large tile densities there is a phase transition from a fluid of
rhombus tiles to a solid packing with broken rotational symmetry. We observe
self-assembly of broken-symmetry phases, even at low densities, in the presence
of attractive tile-tile interactions. Depending on tile shape and interactions
the solid phase can be random, possessing critical orientational fluctuations,
or crystalline. Our results suggest strategies for controlling tiling order in
experiments involving `molecular rhombi'.Comment: Supp. Info. and version with high-res figures at
http://nanotheory.lbl.gov/people/rhombus_paper/rhombus.htm
Nonequilibrium dynamics of fully frustrated Ising models at T=0
We consider two fully frustrated Ising models: the antiferromagnetic
triangular model in a field of strength, , as well as the Villain
model on the square lattice. After a quench from a disordered initial state to
T=0 we study the nonequilibrium dynamics of both models by Monte Carlo
simulations. In a finite system of linear size, , we define and measure
sample dependent "first passage time", , which is the number of Monte
Carlo steps until the energy is relaxed to the ground-state value. The
distribution of , in particular its mean value, , is shown to
obey the scaling relation, , for both models.
Scaling of the autocorrelation function of the antiferromagnetic triangular
model is shown to involve logarithmic corrections, both at H=0 and at the
field-induced Kosterlitz-Thouless transition, however the autocorrelation
exponent is found to be dependent.Comment: 7 pages, 8 figure
Competition of stress corrosion crack branches observed in-situ using time-lapse 3D x-ray synchrotron computed tomography
The progress of a stress corrosion crack in a sensitized AA7075 alloy was studied by in-situ x-ray synchrotron computed tomography. A load was applied to a pre-cracked specimen inside an environmental cell containing moist air and the propagation of the stress corrosion crack was observed. Measurements from the 3D image of the crack have already been shown to provide better quantification compared to observations of the crack from the outer surface. In this paper we study in detail the progress of the stress corrosion crack as it propagates through the material. We reveal how the formation of metal ligaments occurs and the competition of the ‘main’ crack and its branches. We have visualized these features to show the complexity of the local variation in crack morphology in a way that brings new insight into the interaction of the stress corrosion crack with the microstructure of the material
Broken symmetry and the variation of critical properties in the phase behaviour of supramolecular rhombus tilings
The degree of randomness, or partial order, present in two-dimensional
supramolecular arrays of isophthalate tetracarboxylic acids is shown to vary
due to subtle chemical changes such as the choice of solvent or small
differences in molecular dimensions. This variation may be quantified using an
order parameter and reveals a novel phase behaviour including random tiling
with varying critical properties as well as ordered phases dominated by either
parallel or non-parallel alignment of neighbouring molecules, consistent with
long-standing theoretical studies. The balance between order and randomness is
driven by small differences in the intermolecular interaction energies, which
we show, using numerical simulations, can be related to the measured order
parameter. Significant variations occur even when the energy difference is much
less than the thermal energy highlighting the delicate balance between entropic
and energetic effects in complex self-assembly processes
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