1,966 research outputs found
Space Shuttle Lightning Protection
The technology for lightning protection of even the most advanced spacecraft is available and can be applied through cost-effective hardware designs and design-verification techniques. In this paper, the evolution of the Space Shuttle Lightning Protection Program is discussed, including the general types of protection, testing, and anlayses being performed to assess the lightning-transient-damage susceptibility of solid-state electronics
ASTP simulated lightning test report
A simulated lightning test was conducted on the backup spacecraft for the Apollo Soyuz Test Project mission (CSM-119) to determine the susceptibility of the Apollo spacecraft to damage from the indirect effects of lightning. It is demonstrated that induced lightning effects from low-level injected currents can be scaled linearly to those which are obtained in a full threat lightning stroke. Test results indicate that: (1) many of the power and signal critical circuits would fail if subjected to full-threat lightning, (2) pyrotechnic circuits are safe for full-threat lightning, and (3) common-mode voltages exceeded the failure criteria level for all but three of the circuits tested
A priori Wannier functions from modified Hartree-Fock and Kohn-Sham equations
The Hartree-Fock equations are modified to directly yield Wannier functions
following a proposal of Shukla et al. [Chem. Phys. Lett. 262, 213-218 (1996)].
This approach circumvents the a posteriori application of the Wannier
transformation to Bloch functions. I give a novel and rigorous derivation of
the relevant equations by introducing an orthogonalizing potential to ensure
the orthogonality among the resulting functions. The properties of these,
so-called a priori Wannier functions, are analyzed and the relation of the
modified Hartree-Fock equations to the conventional, Bloch-function-based
equations is elucidated. It is pointed out that the modified equations offer a
different route to maximally localized Wannier functions. Their computational
solution is found to involve an effort that is comparable to the effort for the
solution of the conventional equations. Above all, I show how a priori Wannier
functions can be obtained by a modification of the Kohn-Sham equations of
density-functional theory.Comment: 7 pages, RevTeX4, revise
Topological Insulators with Inversion Symmetry
Topological insulators are materials with a bulk excitation gap generated by
the spin orbit interaction, and which are different from conventional
insulators. This distinction is characterized by Z_2 topological invariants,
which characterize the groundstate. In two dimensions there is a single Z_2
invariant which distinguishes the ordinary insulator from the quantum spin Hall
phase. In three dimensions there are four Z_2 invariants, which distinguish the
ordinary insulator from "weak" and "strong" topological insulators. These
phases are characterized by the presence of gapless surface (or edge) states.
In the 2D quantum spin Hall phase and the 3D strong topological insulator these
states are robust and are insensitive to weak disorder and interactions. In
this paper we show that the presence of inversion symmetry greatly simplifies
the problem of evaluating the Z_2 invariants. We show that the invariants can
be determined from the knowledge of the parity of the occupied Bloch
wavefunctions at the time reversal invariant points in the Brillouin zone.
Using this approach, we predict a number of specific materials are strong
topological insulators, including the semiconducting alloy Bi_{1-x} Sb_x as
well as \alpha-Sn and HgTe under uniaxial strain. This paper also includes an
expanded discussion of our formulation of the topological insulators in both
two and three dimensions, as well as implications for experiments.Comment: 16 pages, 7 figures; published versio
Potencial de producción de forraje durante el año en Puerto Rico y Santa Cruz
Forage production can vary substantially during the annual cycle in the tropical islands of Puerto Rico and St. Croix. Cool temperatures, low levels of solar radiation, and low rainfall in December and January have been hypothesized to cause decrease in forage growth. A forage growth model was used to simulate yield in different environments in order to examine these hypotheses quantitatively. Weather data were obtained over a period of three to six years from three locations in Puerto Rico and one location in St. Croix. Minimum temperatures were always near or above 20° C and, consequently, did not appear to cause serious losses in forage production. The forage model predicted a decrease in forage production during the winter months due to decreased levels of solar radiation; however, yields were estimated to be approximately 70 to 80% of summer yields. Whereas shallow rooting depth of 45 cm could cause decreased yields in some situations, inadequate rainfall could not explain large yield decreases in winter months. This research indicates that a factor in addition to the ones tested contributes to the loss in winter forage yield. It is speculated that short day lengths directly influence the regulation of plant growth such that forage yield is decreased in winter months. La producción de forraje puede variar substancialmente durante el ciclo anual en las islas tropicales de Puerto Rico y Santa Cruz. Se ha hipotetizado que las temperaturas frías, los bajos niveles de radiación solar, y la baja precipitación en diciembre y enero son los causantes de las disminuciones en el crecimiento del forraje. Para examinar cuantitativamente estas hipótesis se utilizó un modelo de crecimiento en forraje para simular el rendimiento bajo diferentes ambientes. Los datos climáticos por un periodo de tres a seis años se obtuvieron para tres localidades en Puerto Rico y una localidad en Santa Cruz. Las temperaturas mínimas estuvieron siempre cerca o por encima de los 20°C; por lo tanto, no parecieron causar serias pérdidas en la producción de forraje. El modelo de forraje predijo una reducción en la producción de forraje en los meses de invierno debido a una disminución en los niveles de radiación solar; sin embargo, los rendimientos estimados fueron un 70 a 80% de los rendimientos del verano. Si bien el enraizamiento superficial a una profundidad menor de 45 cm podría causar disminución de los rendimientos en algunas situaciones, la precipitación inadecuada no podría explicar las grandes disminuciones ocurridas en los meses de invierno. Esta investigación indica que un factor adicional a los evaluados contribuye a la pérdida en el rendimiento del forraje durante el invierno. Se especula que la corta duración del día influye directamente sobre la regulación del crecimiento de la planta de forma tal que el rendimiento de forraje disminuye en los meses de invierno
Odd Parity and Line Nodes in Heavy Fermion Superconductors
Group theory arguments have demonstrated that a general odd parity order
parameter cannot have line nodes in the presence of spin-orbit coupling. In
this paper, it is shown that these arguments do not hold on the
zone face of a hexagonal close packed lattice. In particular, three of the six
odd parity representations vanish identically on this face. This has potential
relevance to the heavy fermion superconductor .Comment: 5 pages, revte
Pediatric Procedural Pain
Reviews the various settings in which infants, children, and adolescents experience pain during acute medical procedures, and issues related to referral of children to pain management teams. In addition, self-report, reports by others, physiological monitoring, and direct observation methods of assessment of pain and related constructs are discussed and recommendations provided. Pharmacological, other medical approaches, and empirically supported cognitive behavioral interventions are reviewed. Salient features of the interventions are discussed and recommendations are made for necessary components of effective treatment interventions
Transport and the Order Parameter of Superconducting UPt3
We calculate the ultrasonic absorption and the thermal conductivity in the
superconducting state of UPt as functions of temperature and direction of
propagation and polarization. Two leading candidates for the superconducting
order parameter are considered: the and representations. Both
can fit the data except for the ultrasonic absorption in the phase. To do
that, it is necessary to suppose that the system has only a single domain, and
that must be chosen as the most favorable one. However, the theory
requires fine-tuning of parameters to fit the low temperature thermal
conductivity. Thus, transport data favor the theory. Measurements of
the thermal conductivity as a function of pressure at low temperature could
help to further distinguish the two theories.Comment: 7 pages, 4 figure
Ubiquitination directly enhances activity of the deubiquitinating enzyme ataxin‐3
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102210/1/emboj2008289-sup-0001.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102210/2/emboj2008289.pd
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