2,808 research outputs found
Analytical study of the optimum geometric configuration of a space shuttle materials laboratory
A steady state, collisionless flow analysis was made of the density distribution within a hemisphere-disc system due to independent, uniformly distributed internal gas sources. The model was used to estimate the density within a molecular shield, deployed from the shuttle orbiter, which contained internal experiments having a prescribed gas source. Contour plots of the density distribution within the system were presented for disc-to-hemisphere radius ratios of .1, .3, .5, .7, and for disc-to-hemisphere surface emission flux density ratios of .01, 1, 100. The hemisphere-disc system was compared to the empty hemisphere, and it was found that if the disc emission flux density was the same as the hemisphere and the disc radius was not greater than 1/3 of the hemisphere radius, the increase in density at the center of the hemisphere-disc system was less than 50%
An OSI architecture for the deep space network
The flexibility and robustness of a monitor and control system are a direct result of the underlying inter-processor communications architecture. A new architecture for monitor & Control at the Deep Space Network Communications Complexes has been developed based on the Open System Interconnection (OSI) standards. The suitability of OSI standards for DSN M&C has been proven in the laboratory. The laboratory success has resulted in choosing an OSI-based architecture for DSS-13 M&C. DSS-13 is the DSN experimental station and is not part of the 'operational' DSN; it's role is to provide an environment to test new communications concepts can be tested and conduct unique science experiments. Therefore, DSS-13 must be robust enough to support operational activities, while also being flexible enough to enable experimentation. This paper describes the M&C architecture developed for DSS-13 and the results from system and operational testing
Avoided Antiferromagnetic Order and Quantum Critical Point in CeCoIn
We measured specific heat and resistivity of heavy fermion CeCoIn5 between
the superconducting critical field and 9 T, with field in the
[001] direction, and at temperatures down to 50mK. At 5T the data show Non
Fermi Liquid behavior down to the lowest temperatures. At field above 8T the
data exhibit crossover from the Fermi liquid to a Non Fermi Liquid behavior. We
analyzed the scaling properties of the specific heat, and compared both
resistivity and the specific heat with the predictions of a spin-fluctuation
theory. Our analysis leads us to suggest that the NFL behavior is due to
incipient antiferromagnetism (AF) in CeCoIn5, with the quantum critical point
in the vicinity of the . Below the AF phase which competes
with the paramagnetic ground state is superseded by the superconducting
transition.Comment: 5 pages, 3 figure
Magnetic-Field Induced Quantum Critical Point in YbRhSi
We report low-temperature calorimetric, magnetic and resistivity measurements
on the antiferromagnetic (AF) heavy-fermion metal YbRhSi ( 70
mK) as a function of magnetic field . While for fields exceeding the
critical value at which the low temperature resistivity
shows an dependence, a divergence of upon
reducing to suggests singular scattering at the whole Fermi
surface and a divergence of the heavy quasiparticle mass. The observations are
interpreted in terms of a new type of quantum critical point separating a
weakly AF ordered from a weakly polarized heavy Landau-Fermi liquid state.Comment: accepted for publication in Phys. Rev. Let
PATAXÓ: A Framework to Allow Updates Through XML Views
XML has become an important medium for data exchange, and is frequently used as an interface to (i.e., a view of) a relational database. Although a lot of work has been done on querying relational databases through XML views, the problem of updating relational databases through XML views has not received much attention. In this work, we map XML views expressed using a subset of XQuery to a corresponding set of relational views. Thus, we transform the problem of updating relational databases through XML views into a classical problem of updating relational databases through relational views. We then show how updates on the XML view are mapped to updates on the corresponding relational views. Existing work on updating relational views can then be leveraged to determine whether or not the relational views are updatable with respect to the relational updates, and if so, to translate the updates to the underlying relational database
The population of white dwarf binaries with hot subdwarf companions
Hot subdwarfs (sdBs) are core helium-burning stars, which lost almost their
entire hydrogen envelope in the red-giant phase. Since a high fraction of those
stars are in close binary systems, common envelope ejection is an important
formation channel. We identified a total population of 51 close sdB+WD binaries
based on time-resolved spectroscopy and multi-band photometry, derive the WD
mass distribution and constrain the future evolution of these systems. Most WDs
in those binaries have masses significantly below the average mass of single
WDs and a high fraction of them might therefore have helium cores. We found 12
systems that will merge in less than a Hubble time and evolve to become either
massive C/O WDs, AM\,CVn systems, RCrB stars or even explode as supernovae type
Ia.Comment: 5 pages, 2 figures, to appear in the proceedings of the 19th European
White Dwarf Workshop, ASP Conf. Se
Theories of non-Fermi liquid behavior in heavy fermions
I review our incomplete understanding of non-Fermi liquid behavior in heavy
fermion systems at a quantum critical point. General considerations suggest
that critical antiferromagnetic fluctuations do not destroy the Fermi surface
by scattering the heavy electrons- but by actually breaking up the internal
structure of the heavy fermion. I contrast the weak, and strong-coupling view
of the quantum phase transition, emphasizing puzzles and questions that recent
experiments raise.Comment: Overview talk, SCES Paris 1998. References to Sachdev and Ye adde
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