20,056 research outputs found
The MAJORANA 76Ge neutrino less double-beta decay project: A brief update
At present, MAJORANA is a research and development (R&D) project to
investigate the feasibility and cost of constructing and operating a one ton
decay experiment with ~1000 kg of Ge detectors fabricated from germanium
enriched to 86% in . The study will include three separate cryostats with
various types of detectors: un-segmented, un-segmented point-contact, minimally
segmented, and highly segmented. One cryostat will contain at least 30 kg of
enriched (preferably point-contact) detectors. The performance of the cryostats
and detectors as well as background levels will be investigated. The goal of
the demonstrator project is to reach a discovery sensitivity of ~ 1026 y.Comment: 3 pages, no figure
Polarization of interacting bosons with spin
We demonstrate rigorously that in the absence of explicit spin-dependent
forces one of the ground states of interacting bosons with spin is always fully
polarized -- however complicated the many-body interaction potential might be.
Depending on the particle spin, the polarized ground state will generally be
degenerate with other states, but one can specify the exact degeneracy. For T>0
the magnetization and susceptibility necessarily exceed that of a pure
paramagnet. These results are relevant to recent experiments exploring the
relation between triplet superconductivity and ferromagnetism, and the
Bose-Einstein condensation of atoms with spin. They eliminate the possibility,
raised in some theoretical speculations, that the ground state or positive
temperature state might be antiferromagnetic.Comment: v4: as published in PR
On the density-potential mapping in time-dependent density functional theory
The key questions of uniqueness and existence in time-dependent density
functional theory are usually formulated only for potentials and densities that
are analytic in time. Simple examples, standard in quantum mechanics, lead
however to non-analyticities. We reformulate these questions in terms of a
non-linear Schr\"odinger equation with a potential that depends non-locally on
the wavefunction.Comment: 8 pages, 2 figure
New Wrinkles on an Old Model: Correlation Between Liquid Drop Parameters and Curvature Term
The relationship between the volume and surface energy coefficients in the
liquid drop A^{-1/3} expansion of nuclear masses is discussed. The volume and
surface coefficients in the liquid drop expansion share the same physical
origin and their physical connection is used to extend the expansion with a
curvature term. A possible generalization of the Wigner term is also suggested.
This connection between coefficients is used to fit the experimental nuclear
masses. The excellent fit obtained with a smaller number of parameters
validates the assumed physical connection.Comment: 6 pages, 2 figure
Correlation equalities and upper bounds for the transverse Ising model
Starting from an exact formal identity for the two-state transverse Ising
model and using correlation inequalities rigorous upper bounds for the critical
temperature and the critical transverse field are obtained which improve
effective results.Comment: 8 pages, 1 figur
In-Shoe Pressure Distribution During Ergometer Rowing In Novice And Experienced Rowers
Distribution of foot pressure during rowing has been minimally investigated.
Foot pressure distribution is most likely altered with experience ca using an increase in stability and thus efficiency duirng the rowing stroke. This study evaluated in-shoe pressure distribution differences between novice and experienced collegiate rowers during rowing on the Concept II ergometer. In shoe pressure was measured in ten subjects, five novice and five experienced, while rowing at a stroke rate of 32-34 strokes per minute. The subjects wore the same model shoe with a Tekscan in-shoe pressure measurement system placed inside each shoe, only the dominant foot was studied. Data were sampled at a rate of 100 Hz. The following variables at the shoe-foot interface were investigated during the drive and the recovery of the stroke: peak forefoot pressure, peak rearfoot pressure, and displacement of the mediolateral and longitudinal center of pressure (COP). Peak pressures were investigated to discover how the pressure is distributed during the stroke. Comparison of the COP was used to indicate the stabililty of the foot during the drive phase. The experienced rowers had a high proportion of the total in-shoe pressure in the forefoot during the drive. Generally there was less pressure exerted on the recovery phase in the experienced subjects. These subjects also had a less variable mediolateral COP and an increase in the longitudinal COP plot. To apply force correctly during the drive it seems to be necessary to place a high proportion of the pressure in the forefoot. The trend toward decreased pressure on the recovery in the experienced rowers may reflect an increased efficiency due to experience. The decrease in the mediolateral COP deviation would appear to be related to increased stability. The longitudinal COP plot showed that with experience the plantar surface in contact with the shoe during the drive increases
Competing spin transfer and dissipation at Co/Cu(001) interfaces on femtosecond timescales
By combining interface-sensitive non-linear magneto-optical experiments with
femtosecond time resolution and ab-initio time-dependent density functional
theory, we show that optically excited spin dynamics at Co/Cu(001) interfaces
proceeds via spin-dependent charge transfer and backtransfer between Co and Cu.
This ultrafast spin transfer competes with dissipation of spin angular momentum
mediated by spin-orbit coupling already on sub 100 fs timescales. We thereby
identify the fundamental microscopic processes during laser-induced spin
transfer at a model interface for technologically relevant ferromagnetic
heterostructures.Comment: 5 pages, 4 figure
Experiment K-6-01. Distribution and biochemistry of mineral and matrix in the femurs of rats
Previous analyses of the composition of mineral and matrix in the bone of young rats following space flight has revealed deficits in calcium, phosphorus, and osteocalcin, a non-collagenous protein, without an associated decrease in collagen. To characterize the location and nature of this mineralization defect in a weight bearing long bone, the femur, researchers attempted to relate the spatial distribution of mineral in situ in the proximal, central and distal thirds of the femoral diaphysis to the biochemical composition of bone from the same area. Biochemical analyses revealed lower concentrations of calcium, phosphorus and osteocalcin but not collagen only in the central third of the diaphysis of the flight animals (F) compared to synchronous controls (S). Collagen concentration was reduced only in the proximal third of the diaphysis, where all 3 crosslinks, expressed as nM/mol collagen were higher in F than S. A new technique, x ray microtomography, with a resolution of 26 microns, was used to obtain semi-quantitative data on mineral distribution in reconstructed sections of wet whole bone. To improve the resolution of the mineral density distribution, images of the surfaces of cut sections were analyzed by backscattered electrons in a scanning electron microscope (BSE). There was good agreement between the results of the two stereochemical techniques which revealed distinct patterns of mineralization in transverse and longitudinal directions of the diaphysis. The novel methodology developed for this flight experiment shows considerable promise in elucidating the biochemical nature of what appear to be regional alterations in the mineralization of long bones of animals exposed to spaceflight
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