26,088 research outputs found
Data base for crack growth properties of materials
A computerized data base of crack growth properties of materials was developed for use in fracture control analysis of rocket engine components and other NASA space hardware. The software system has files of basic crack growth rate data, other fracture mechanics material properties such as fracture toughness and environmental crack growth threshold values, and plotting and fitting routines for deriving material properties for use in fracture control analysis. An extensive amount of data was collected and entered, and work is continuing on compiling additional data. The data base and software codes are useful both for fracture control analysis and for evaluation or development of improved crack growth theories
The Scientific Reach of Multi-Ton Scale Dark Matter Direct Detection Experiments
The next generation of large scale WIMP direct detection experiments have the
potential to go beyond the discovery phase and reveal detailed information
about both the particle physics and astrophysics of dark matter. We report here
on early results arising from the development of a detailed numerical code
modeling the proposed DARWIN detector, involving both liquid argon and xenon
targets. We incorporate realistic detector physics, particle physics and
astrophysical uncertainties and demonstrate to what extent two targets with
similar sensitivities can remove various degeneracies and allow a determination
of dark matter cross sections and masses while also probing rough aspects of
the dark matter phase space distribution. We find that, even assuming dominance
of spin-independent scattering, multi-ton scale experiments still have
degeneracies that depend sensitively on the dark matter mass, and on the
possibility of isospin violation and inelasticity in interactions. We find that
these experiments are best able to discriminate dark matter properties for dark
matter masses less than around 200 GeV. In addition, and somewhat surprisingly,
the use of two targets gives only a small improvement (aside from the advantage
of different systematics associated with any claimed signal) in the ability to
pin down dark matter parameters when compared with one target of larger
exposure.Comment: 23 pages; updated to match PRD versio
Overcoming the boundary layer turbulence at Dome C: ground-layer adaptive optics versus tower
The unique atmospheric conditions present at sites such as Dome C on the Antarctic plateau are very favorable for high spatial resolution astronomy. At Dome C, the majority of the optical turbulence is confined to a 30 to 40 m thick stable boundary layer that results from the strong temperature inversion created by the heat exchange between the air and the ice-covered ground. To fully realize the potential of the exceptionally calm free atmosphere, this boundary layer must be overcome. In this article we compare the performance of two methods proposed to beat the boundary layer: mounting a telescope on a tower that physically puts it above the turbulent layer, and installing a telescope at ground level with a ground-layer adaptive optics system. A case is also made to combine these two methods to further improve the image quality
Using Full Information When Computing Modes of Post-Newtonian Waveforms From Inspiralling Compact Binaries in Circular Orbit
The increasing sophistication and accuracy of numerical simulations of
compact binaries (especially binary black holes) presents the opportunity to
test the regime in which post-Newtonian (PN) predictions for the emitted
gravitational waves are accurate. In order to confront numerical results with
those of post-Newtonian theory, it is convenient to compare multipolar
decompositions of the two waveforms. It is pointed out here that the individual
modes can be computed to higher post-Newtonian order by examining the radiative
multipole moments of the system, rather than by decomposing the 2.5PN
polarization waveforms. In particular, the dominant (l = 2, m = 2) mode can be
computed to 3PN order. Individual modes are computed to as high a
post-Newtonian order as possible given previous post-Newtonian results.Comment: 15 page
Fruit and Seed Project of the Cedar Creek Natural History Area
The program was initiated with the support of the Graduate School of the University of Minnesota in May, 1960 through the interest of Dean T. C. Blegen. There are four major objectives: (1) To establish a collection of ripe fruits and seeds to provide a permanent reference file of the entire seed plant flora of the area newly mapped through a grant from the National Science Foundation. (2) To prepare duplicate sets of standard herbarium mounts of material with ripe disseminules, one set for the laboratory at Cedar Creek, the other for the Herbarium of the Department of Botany of the University at Minneapolis. (3) To photograph the various fruits and seeds in Kodachrome and black and white showing both external and internal morphology. ( 4) To prepare eventually an illustrated manual with keys for identification of fruits and seeds
Anharmonicity of flux lattices and thermal fluctuations in layered superconductors
We study elasticity of a perpendicular flux lattice in a layered
superconductor with Josephson coupling between layers. We find that the energy
contains ln(flux displacement) terms, so that elastic constants cannot be
strictly defined. Instead we define effective elastic constants by a thermal
average. The tilt modulus has terms with ln(T) which for weak fields, i.e.
Josephson length smaller than the flux line spacing, lead to displacement
square average proportional to T/ln(T). The expansion parameter indicates that
the dominant low temperature phase transition is either layer decoupling at
high fields or melting at low fields.Comment: 15 pages, 2 eps figures, Revtex, submitted to Phys. Rev. B.
Sunj-class: superconductivit
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