1,755 research outputs found
Pressure-Induced Superconductivity in Sc to 74 GPa
Using a diamond anvil cell with nearly hydrostatic helium pressure medium we
have significantly extended the superconducting phase diagram Tc(P) of Sc, the
lightest of all transition metals. We find that superconductivity is induced in
Sc under pressure, Tc increasing monotonically to 8.2 K at 74.2 GPa. The Tc(P)
dependences of the trivalent d-electron metals Sc, Y, La, and Lu are compared
and discussed within a simple s-d charge transfer framework.Comment: to be published in Phys. Rev. B (Brief Reports
An analysis of experts' ratings of ergonomic stress
Experts in the field of industrial ergonomics are frequently called upon to visit workplaces in order to evaluate and rate ergonomic stressors which may cause fatigue, discomfort, or injury. The objective of this study was to evaluate the extent of agreement among experts' perceptions of four categories of ergonomic stress: materials handling (e.g., lifting), upper extremity activities, posture, and energy expenditure.A panel of five experts observed ten jobs in manufacturing and warehouse facilities. A three-point scale (1 = insignificant stress, 2 = moderate stress, 3 = high stress) was used to rate the jobs in each of the four stress categories. In addition, lifting stresses on each job were analyzed using methods described in the NIOSH Work Practices Guide for Manual Lifting. The resulting data were analyzed to determine the level of expert consensus and the level of agreement with the NIOSH results.In general, there was a high level of consensus among the experts. Perfect agreement (identical ratings by all five experts) was obtained for 30 percent of the experts' scores; while consensus agreement (identical ratings by three or more experts) was obtained for 87.5 percent of the scores. In general, the experts' perceptions agreed with the NIOSH ratings of lifting stress. On a few jobs, however, the expert panel considered lifting stresses to be greater than predicted by the NIOSH ratings.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27200/1/0000203.pd
Chiral Lagrangian Parameters for Scalar and Pseudoscalar Mesons
The results of a high-statistics study of scalar and pseudoscalar meson
propagators in quenched lattice QCD are presented. For two values of lattice
spacing, ( fm) and 5.9 ( fm), we
probe the light quark mass region using clover improved Wilson fermions with
the MQA pole-shifting ansatz to treat the exceptional configuration problem.
The quenched chiral loop parameters and are determined
from a study of the pseudoscalar hairpin correlator. From a global fit to the
meson correlators, estimates are obtained for the relevant chiral Lagrangian
parameters, including the Leutwyler parameters and . Using the
parameters obtained from the singlet and nonsinglet pseudoscalar correlators,
the quenched chiral loop effect in the nonsinglet scalar meson correlator is
studied. By removing this QCL effect from the lattice correlator, we obtain the
mass and decay constant of the ground state scalar, isovector meson .Comment: 36 pages, 12 figures, LaTe
Assembling the puzzle of superconducting elements: A Review
Superconductivity in the simple elements is of both technological relevance
and fundamental scientific interest in the investigation of superconductivity
phenomena. Recent advances in the instrumentation of physics under pressure
have enabled the observation of superconductivity in many elements not
previously known to superconduct, and at steadily increasing temperatures. This
article offers a review of the state of the art in the superconductivity of
elements, highlighting underlying correlations and general trends.Comment: Review, 10 pages, 11 figures, 97 references; to appear in Superc.
Sci. Techno
Effect of pressure on the Raman modes of antimony
The effect of pressure on the zone-center optical phonon modes of antimony in
the A7 structure has been investigated by Raman spectroscopy. The A_g and E_g
frequencies exhibit a pronounced softening with increasing pressure, the effect
being related to a gradual suppression of the Peierls-like distortion of the A7
phase relative to a cubic primitive lattice. Also, both Raman modes broaden
significantly under pressure. Spectra taken at low temperature indicate that
the broadening is at least partly caused by phonon-phonon interactions. We also
report results of ab initio frozen-phonon calculations of the A_g and E_g mode
frequencies. Presence of strong anharmonicity is clearly apparent in calculated
total energy versus atom displacement relations. Pronounced nonlinearities in
the force versus displacement relations are observed. Structural instabilities
of the Sb-A7 phase are briefly addressed in the Appendix.Comment: 10 pages, 8 figure
Tunable Electron Multibunch Production in Plasma Wakefield Accelerators
Synchronized, independently tunable and focused J-class laser pulses are
used to release multiple electron populations via photo-ionization inside an
electron-beam driven plasma wave. By varying the laser foci in the laboratory
frame and the position of the underdense photocathodes in the co-moving frame,
the delays between the produced bunches and their energies are adjusted. The
resulting multibunches have ultra-high quality and brightness, allowing for
hitherto impossible bunch configurations such as spatially overlapping bunch
populations with strictly separated energies, which opens up a new regime for
light sources such as free-electron-lasers
Pressure-induced metallization in solid boron
Different phases of solid boron under high pressure are studied by first
principles calculations. The -B structure is found to be stable
up to 270 GPa. Its semiconductor band gap (1.72 eV) decreases continuously to
zero around 160 GPa, where the material transforms to a weak metal. The
metallicity, as measured by the density of states at the Fermi level, enhances
as the pressure is further increased. The pressure-induced metallization can be
attributed to the enhanced boron-boron interactions that cause bands overlap.
These results are consist with the recently observed metallization and the
associated superconductivity of bulk boron under high pressure (M.I.Eremets et
al, Science{\bf 293}, 272(2001)).Comment: 14 pages, 5 figure
Superconductivity in the YIr2Si2 and LaIr2Si2 Polymorphs
We report on existence of superconductivity in YIr2Si2 and LaIr2Si2 compounds
in relation to crystal structure. The two compounds crystallize in two
structural polymorphs, both tetragonal. The high temperature polymorph (HTP)
adopts the CaBe2Ge2-structure type (space group P4/nmm) while the low
temperature polymorph (LTP) is of the ThCr2Si2 type (I4/mmm). By studying
polycrystals prepared by arc melting we have observed that the rapidly cooled
samples retain the HTP even at room temperature (RT) and below. Annealing such
samples at 900C followed by slow cooling to RT provides the LTP. Both, the HTP
and LTP were subsequently studied with respect to magnetism and
superconductivity by electrical resistivity, magnetization, AC susceptibility
and specific heat measurements. The HTP and LTP of both compounds respectively,
behave as Pauli paramagnets. Superconductivity has been found exclusively in
the HTP of both compounds below Tsc (= 2.52 K in YIr2Si2 and 1.24 K in
LaIr2Si2). The relations of magnetism and superconductivity with the electronic
and crystal structure are discussed with comparing experimental data with the
results of first principles electronic structure calculations
Defining Failure of Passive Transfer in South Dakota Beef Calves
Failure of calves to ingest and absorb immunoglobulin from colostrum is a risk factor for illness and decreased performance. Blood samples were taken from 752 calves at three SDSU research units. Total protein in blood, closely correlated to colostral immunoglobulin absorption, was determined and calf health records were collected. Using this data, a classification table of sensitivity and specificity was constructed to determine the relationship between total protein and calf illness and to classify calves as having adequate colostral absorption or inadequate colostral absorption (failure of passive transfer). Along with sensitivity and specificity, positive and negative likelihood ratios were calculated to identify a suitable cutoff point to separate calves that would become ill from those that would remain healthy. The cutoff point selected was a serum total protein level of 5.5 g/dL, which produced a sensitivity of 30% and specificity of 87%. Calves with total protein levels below 5.5 g1dL were 3.07 (95% CI 1.73-5.43, p=0.0002) times as likely to become ill as calves with total protein levels above 5.5 g/dL. In beef production situations similar to those in these herds, producers should be able to limit disease if calves\u27 total protein at 24 hours following birth is equal to or greater than 5.5 g/dL
Low-energy couplings of QCD from current correlators near the chiral limit
We investigate a new numerical procedure to compute fermionic correlation
functions at very small quark masses. Large statistical fluctuations, due to
the presence of local ``bumps'' in the wave functions associated with the
low-lying eigenmodes of the Dirac operator, are reduced by an exact low-mode
averaging. To demonstrate the feasibility of the technique, we compute the
two-point correlator of the left-handed vector current with Neuberger fermions
in the quenched approximation, for lattices with a linear extent of L~1.5 fm, a
lattice spacing a~0.09 fm, and quark masses down to the epsilon-regime. By
matching the results with the corresponding (quenched) chiral perturbation
theory expressions, an estimate of (quenched) low-energy constants can be
obtained. We find agreement between the quenched values of F extrapolated from
the p-regime and extracted in the epsilon-regime.Comment: 20 pages, 5 figure
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