9,424 research outputs found
Ionizing radiation exposure of LDEF
The Long Duration Exposure Facility (LDEF) was launched into orbit by the Space Shuttle 'Challenger' mission 41C on 6 April 1984 and was deployed on 8 April 1984. The original altitude of the circular orbit was 258.5 nautical miles (479 km) with the orbital inclination being 28.5 degrees. The 21,500 lb NASA Langley Research Center satellite, having dimensions of some 30x14 ft was one of the largest payloads ever deployed by the Space Shuttle. LDEF carried 57 major experiments and remained in orbit five years and nine months (completing 32,422 orbits). It was retrieved by the Shuttle 'Columbia' on January 11, 1990. By that time, the LDEF orbit had decayed to the altitude of 175 nm (324 km). The experiments were mounted around the periphery of the LDEF on 86 trays and involved the representation of more than 200 investigators, 33 private companies, 21 universities, seven NASA centers, nine Department of Defense laboratories and eight foreign countries. The experiments covered a wide range of disciplines including basic science, electronics, optics, materials, structures, power and propulsion. The data contained in the LDEF mission represents an invaluable asset and one which is not likely to be duplicated in the foreseeable future. The data and the subsequent knowledge which will evolve from the analysis of the LDEF experiments will have a very important bearing on the design and construction of the Space Station Freedom and indeed on other long-term, near-earth orbital space missions. A list of the LDEF experiments according to experiment category and sponsor is given, as well as a list of experiments containing radiation detectors on LDEF including the LDEF experiment number, the title of the experiment, the principal investigator, and the type of radiation detectors carried by the specific experiment
Mass and width of the sigma
I report on recent work done in collaboration with Irinel Caprini and
Gilberto Colangelo. We observe that the Roy equations lead to a representation
of the pion pion scattering amplitude that exclusively involves observable
quantities, but is valid for complex values of s. At low energies, this
representation is dominated by the contributions from the two subtraction
constants, which are known to remarkable precision from the low energy theorems
of chiral perturbation theory. Evaluating the remaining contributions on the
basis of the available data, we demonstrate that the lowest resonance carries
the quantum numbers of the vacuum and occurs in the vicinity of the threshold.
Although the uncertainties in the data are substantial, the pole position can
be calculated quite accurately, because it occurs in the region where the
amplitude is dominated by the subtractions. The calculation neatly illustrates
the fact that the dynamics of the Goldstone bosons is governed by the
symmetries of QCD.Comment: Contribution to the proceedings of MESON 2006 (Krakow
Low relaxation rate in a low-Z alloy of iron
The longest relaxation time and sharpest frequency content in ferromagnetic
precession is determined by the intrinsic (Gilbert) relaxation rate \emph{}.
For many years, pure iron (Fe) has had the lowest known value of for all pure ferromagnetic metals or binary alloys. We show that an
epitaxial iron alloy with vanadium (V) possesses values of which are
significantly reduced, to 355 Mhz at 27% V. The result can be understood
as the role of spin-orbit coupling in generating relaxation, reduced through
the atomic number .Comment: 14 pages, 4 figure
Shear thickening in densely packed suspensions of spheres and rods confined to few layers
We investigate confined shear thickening suspensions for which the sample
thickness is comparable to the particle dimensions. Rheometry measurements are
presented for densely packed suspensions of spheres and rods with aspect ratios
6 and 9. By varying the suspension thickness in the direction of the shear
gradient at constant shear rate, we find pronounced oscillations in the stress.
These oscillations become stronger as the gap size is decreased, and the stress
is minimized when the sample thickness becomes commensurate with an integer
number of particle layers. Despite this confinement-induced effect, viscosity
curves show shear thickening that retains bulk behavior down to samples as thin
as two particle diameters for spheres, below which the suspension is jammed.
Rods exhibit similar behavior commensurate with the particle width, but they
show additional effects when the thickness is reduced below about a particle
length as they are forced to align; the stress increases for decreasing gap
size at fixed shear rate while the shear thickening regime gradually
transitions to a Newtonian scaling regime. This weakening of shear thickening
as an ordered configuration is approached contrasts with the strengthening of
shear thickening when the packing fraction is increased in the disordered bulk
limit, despite the fact that both types of confinement eventually lead to
jamming.Comment: 21 pages, 14 figures. submitted to the Journal of Rheolog
Nährstoffversorgung von Ackerbohnen im Ökologischen Landbau
Inadequate nutrient supply frequently limits biological nitrogen fixation (BNF), plant growth and grain yield of legumes. Under no-till conditions, root growth may be restrained and therefore reduce nutrient uptake. Our studies were carried out to assess the nutrient status of Vicia faba L. (particularly at the onset of bloom) in Germany by using newly created DRIS (Diagnosis and Recommendation Integrated System) norm values, Critical Nutrient Levels (CNL), and the optimum nutrient range.
In a field experiment in 2010 at 4 sites (Klein-Altendorf, Wiesengut & 2 organic farms) the applied fertilizers were fermentation residues, compost, pomace, meat-bone-meal, rock-phosphate, sodium-molybdate, potassium sulphate, and borax. Nutrient elements measured in leaf samples were: C, N, S, K, Ca, P, Mg, Fe, Mn, Zn, Cu, B and Mo. As S was detected to be deficient, K2SO4 (35 kg S/ha) had a significantly positive effect on plant growth, yield and symbiosis
Gene Tree Labeling Using Nonnegative Matrix Factorization on Biomedical Literature
Identifying functional groups of genes is a challenging problem for biological applications.
Text mining approaches can be used to build hierarchical clusters or trees from the information in the biological literature. In particular, the nonnegative matrix factorization (NMF) is examined as one approach to label hierarchical trees. A generic labeling algorithm as well as an evaluation technique is proposed, and the effects of different NMF parameters with regard to convergence and labeling accuracy are discussed. The primary goals of this study are to provide a qualitative assessment of the NMF and its various parameters and initialization, to provide an automated way to classify biomedical data, and to provide a method for evaluating labeled data assuming a static input tree. As a byproduct, a method for generating gold standard trees is proposed
Gilbert Damping in Magnetic Multilayers
We study the enhancement of the ferromagnetic relaxation rate in thin films
due to the adjacent normal metal layers. Using linear response theory, we
derive the dissipative torque produced by the s-d exchange interaction at the
ferromagnet-normal metal interface. For a slow precession, the enhancement of
Gilbert damping constant is proportional to the square of the s-d exchange
constant times the zero-frequency limit of the frequency derivative of the
local dynamic spin susceptibility of the normal metal at the interface.
Electron-electron interactions increase the relaxation rate by the Stoner
factor squared. We attribute the large anisotropic enhancements of the
relaxation rate observed recently in multilayers containing palladium to this
mechanism. For free electrons, the present theory compares favorably with
recent spin-pumping result of Tserkovnyak et al. [Phys. Rev. Lett.
\textbf{88},117601 (2002)].Comment: 1 figure, 5page
- …