11,673 research outputs found
Enzyme reference materials: their place in diagnostic enzyrnology
Estimations of the activities of various enzymes in clinical samples
are routine tasks for clinical chemists. Most of this work is done
by automatic analysis. The reference ranges against which patients'
results are interpreted, however, have generally been defined in terms
of manual methods and the conditions of a manual method cannot
be reproduced in automated systems. This paper describes the
possibility of translating the results of enzyme analysis into a
common currency through the use of enzyme reference materials as
calibrators
Property investigation and sputter deposition of dispersion-hardened copper for fatigue specimen fabrication
Sputter-deposited alloys of dispersion-hardenable Cu-0.25 vol% SiC and Cu-0.50 vol% SiC and precipitation-hardenable Cu-0.15 wt% Zr and Cu-0.05 wt% Mg-0.15 wt% Zr-0.40 wt% Cr were investigated for selection to evaluate fatigue specimen performance with potential application in fabricating regeneratively cooled rocket thrust chambers. Yield strengths in the 700 to 1000-MN/sq m range were observed with uniform elongation ranging from 0.5 to 1.5% and necking indicative of greater ductility. Electrical conductivity measured as an analog to thermal conductivity gave values 90% IACS for Cu-0.15 wt% Zr and Cu-0.05 wt% Mg-0.15 wt% Zr-0.40 wt% Cr. A 5500-g sputtered deposit of Cu-0.15 wt% Zr alloy, 12.29 mm (0.484 in.) average thickness in the fatigue specimen gage length, was provided to NASA on one of their substrates
Fabrication of thick structures by sputtering
Deposit, 5500-gram of Cu-0.15 wt % Zr alloy, sputtered onto copper cylinder to average thickness of 12.29 mm. Structure was achieved with high-rate sputter deposition for about 100 hours total sputtering time. Material had twice the strength of unsputtered material at temperatures to 723 K and equivalent strength at nearly 873 K
Constraints on the anisotropy of dark energy
If the equation of state of dark energy is anisotropic there will be
additional quadrupole anisotropy in the cosmic microwave background induced by
the time dependent anisotropic stress quantified in terms of .
Assuming that the entire amplitude of the observed quadrupole is due to this
anisotropy, we conservatively impose a limit of for any value of assuming that . This is
considerably tighter than that which comes from SNe. Stronger limits, upto a
factor of 10, are possible for specific values of and .
Since we assume this component is uncorrelated with the stochastic component
from inflation, we find that both the expectation value and the sample variance
are increased. There no improvement in the likelihood of an anomalously low
quadrupole as suggested by previous work on an elliptical universe
Combined Gamma Ray/neutron Spectroscopy for Mapping Lunar Resources
Some elements in the Moon can be resources, such as hydrogen and oxygen. Other elements, like Ti or the minerals in which they occur, such as ilmenite, could be used in processing lunar materials. Certain elements can also be used as tracers for other elements or lunar processes, such as hydrogen for mature regoliths with other solar-wind-implanted elements like helium, carbon, and nitrogen. A complete knowledge of the elemental composition of a lunar region is desirable both in identifying lunar resources and in lunar geochemical studies, which also helps in identifying and using lunar resources. The use of gamma ray and neutron spectroscopy together to determine abundances of many elements in the top few tens of centimeters of the lunar surface is discussed. To date, very few discussions of elemental mapping of planetary surfaces considered measurements of both gamma rays and the full range of neutron energies. The theories for gamma ray and neutron spectroscopy of the Moon and calculations of leakage fluxes are presented here with emphasis on why combined gamma ray/neutron spectroscopy is much more powerful than measuring either radiation alone
Boundary conditions and the entropy bound
The entropy-to-energy bound is examined for a quantum scalar field confined
to a cavity and satisfying Robin condition on the boundary of the cavity. It is
found that near certain points in the space of the parameter defining the
boundary condition the lowest eigenfrequency (while non-zero) becomes
arbitrarily small. Estimating, according to Bekenstein and Schiffer, the ratio
by the -function, , we compute
explicitly and find that it is not bounded near those points that signals
violation of the bound. We interpret our results as imposing certain
constraints on the value of the boundary interaction and estimate the forbidden
region in the parameter space of the boundary conditions.Comment: 16 pages, latex, v2: typos corrected, to appear in Phys.Rev.
The etiology and prevention of feeding intolerance paralytic ileus – revisiting an old concept
Gastro-intestinal (G-I) motility is impaired ("paralytic ileus") after abdominal surgery. Premature feeding attempts delay recovery by inducing "feeding intolerance," especially abdominal distention that compromises respiration. Controlled studies (e.g., from Sloan-Kettering Memorial Hospital) have lead to recommendations that patients not be fed soon after major abdominal surgery to avoid this complication
Hamiltonians for Reduced Gravity
A generalised canonical formulation of gravity is devised for foliations of
spacetime with codimension . The new formalism retains n-dimensional
covariance and is especially suited to 2+2 decompositions of spacetime. It is
also possible to use the generalised formalism to obtain boundary contributions
to the 3+1 Hamiltonian.Comment: 18 pages, revtex, 3 postscript figures include
A Cosmological No-Hair Theorem
A generalisation of Price's theorem is given for application to Inflationary
Cosmologies. Namely, we show that on a Schwarzschild--de Sitter background
there are no static solutions to the wave or gravitational perturbation
equations for modes with angular momentum greater than their intrinsic spin.Comment: 9 pages, NCL94 -TP4, (Revtex
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