32,931 research outputs found
The Helios mechanical despin drive assembly for the high-gain antenna reflector
Helios is the German-American solar probe which comes within 0.31 Astronomical Units of the sun. A special thermal design and a dry lubrication system have resulted in successful operation up to now, with Helios having finished its first orbit around the sun
Structural mechanics of deformation and fracture Quarterly progress report
Structural mechanics of deformation and fracture - responses of model viscoelastic materials to impac
Two-body recombination in a quantum mechanical lattice gas: Entropy generation and probing of short-range magnetic correlations
We study entropy generation in a one-dimensional (1D) model of bosons in an
optical lattice experiencing two-particle losses. Such heating is a major
impediment to observing exotic low temperature states, and "simulating"
condensed matter systems. Developing intuition through numerical simulations,
we present a simple empirical model for the entropy produced in this 1D
setting. We also explore the time evolution of one and two particle correlation
functions, showing that they are robust against two-particle loss. Because of
this robustness, induced two-body losses can be used as a probe of short range
magnetic correlations.Comment: 6 pages, 3 figures - v4, published versio
Pairing, Ferromagnetism, and Condensation of a normal spin-1 Bose gas
We theoretically study the stability of a normal, spin disordered, homogenous
spin-1 Bose gas against ferromagnetism, pairing, and condensation through a
Random Phase Approximation which includes exchange (RPA-X). Repulsive
spin-independent interactions stabilize the normal state against both
ferromagnetism and pairing, and for typical interaction strengths leads to a
direct transition from an unordered normal state to a fully ordered single
particle condensate. Atoms with much larger spin-dependent interaction may
experience a transition to a ferromagnetic normal state or a paired superfluid,
but, within the RPA-X, there is no instability towards a normal state with
spontaneous nematic order. We analyze the role of the quadratic Zeeman effect
and finite system size.Comment: 4 pages, 3 figures, 1 table. Supplementary materials attache
Interpretation of the northern boundary of Ishtar Terra from Magellan images and altimetry
Part of the controversy on the origin of western Ishtar Terra (IT) concerns the nature of Uorsar Rupes (UR), the northern boundary of IT. In the hypothesis of lithospheric convergence and underthrusting, UR is held to be the main boundary thrust fault at the toe of an accretionary wedge. A topographic rise parallel to the scarp was interpreted as a flexural bulge similar to those of terrestrial subduction zones, and quantitative models of this feature seemed broadly consistent with the expected lithospheric structure of Venus. In the alternative mantle upwelling hypothesis for western IT, the outer margins of the highland are thought to be collapsing, and UR has been interpreted as a normal fault. Herein, Magellan images and altimetry are interpreted for this region and the hypothesis that a flexural signature can be distinguished is reassessed. The Magellan images of IT show evidence of crustal shortening adjacent to UR, but extension and burial dominate northwards. Altimetric profiles display the same long wavelength trends visible in Venera data, but no clear evidence of the lithospheric flexure. A model of regional extension and burial is herein favored, but regional compression cannot be ruled out
Parton Saturation-An Overview
The idea of partons and the utility of using light-cone gauge in QCD are
introduced. Saturation of quark and gluon distributions are discussed using
simple models and in a more general context. The Golec-Biernat W\usthoff model
and some simple phenomenology are described. A simple, but realistic, equation
for unitary, the Kovchegov equation, is discussed, and an elementary derivation
of the JIMWLK equation is given.Comment: Cargese Lectures, 34 pages, 19 figure
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