3,088 research outputs found
Post-Flight Evaluation of PICA and PICA-X - Comparisons of the Stardust SRC and Space-X Dragon 1 Forebody Heatshield Materials
Phenolic Impregnated Carbon Ablator (PICA) was developed at NASA Ames Research Center. As a thermal protection material, PICA has the advantages of being able to withstand high heat fluxes with a relatively low density. This ablative material was used as the forebody heat shield material for the Stardust sample return capsule, which re-entered the Earths atmosphere in 2006. Based on PICA, SpaceX developed a variant, PICA-X, and used it as the heat shield material for its Dragon spacecraft, which successfully orbited the Earth and re-entered the atmosphere during the COTS Demo Flight 1 in 2010. Post-flight analysis was previously performed on the Stardust PICA heat shield material. Similarly, a near-stagnation core was obtained from the post-flight Dragon 1 heat shield, which was retrieved from the Pacific Ocean. Materials testing and analyses were performed on the core to evaluate its ablation performance and post-flight properties. Comparisons between PICA and PICA-X are made where applicable. Stardust and Dragon offer rare opportunities to evaluate materials post-flight - this data is beneficial in understanding material performance and also improves modeling capabilities
A Pseudo-logarithmic Image Processing Framework for Edge Detection
Abstract. The paper presents a new [pseudo-] Logarithmic Model for Image Processing (LIP), which allows the computation of gray-level ad-dition, substraction and multiplication with scalars within a fixed gray-level range [0;D] without the use of clipping. The implementation of Laplacian edge detection techniques under the proposed model yields superior performance in biomedical applications as compared with the classical operations (performed either as real axis operations, either as classical LIP models).
Central American Subduction System
Workshop to Integrate Subduction Factory and Seismogenic Zone Studies in Central America, Heredia, Costa Rica, 18–22 June 2007 The driving force for great earthquakes and the cycling of water and climate-influencing volatiles (carbon dioxide, sulfur, halogens) across the convergent margin of Central America have been a focus of international efforts for over 8 years, as part of the MARGINS program of the U.S. National Science Foundation, the Collaborative Research Center (SFB 574) of the German Science Foundation, and the Central American science community. Over 120 scientists and students from 10 countries met in Costa Rica to synthesize this intense effort spanning from land to marine geological and geophysical studies
Detecting the (Quasi-)Two-Body Decays of Leptons in Short-Baseline Neutrino Oscillation Experiments
Novel detector schemes are proposed for the short-baseline neutrino
experiments of next generation, aimed at exploring the large-
domain of \omutau oscillations in the appearance mode. These schemes emphasize
good spectrometry for charged particles and for electromagnetic showers and
efficient reconstruction of \ypi_gg decays. The basic elements are a sequence
of relatively thin emulsion targets, immersed in magnetic field and
interspersed with electronic trackers, and a fine-grained electromagnetic
calorimeter built of lead glass. These elements act as an integral whole in
reconstructing the electromagnetic showers. This conceptual scheme shows good
performance in identifying the (quasi-)two-body decays by their
characteristic kinematics and in selecting the electronic decays of the .Comment: 34 pages, 8 figure
Graphene as a quantum surface with curvature-strain preserving dynamics
We discuss how the curvature and the strain density of the atomic lattice
generate the quantization of graphene sheets as well as the dynamics of
geometric quasiparticles propagating along the constant curvature/strain
levels. The internal kinetic momentum of Riemannian oriented surface (a vector
field preserving the Gaussian curvature and the area) is determined.Comment: 13p, minor correction
Magnetic and superconducting instabilities of the Hubbard model at the van Hove filling
We use a novel temperature-flow renormalization group technique to analyze
magnetic and superconducting instabilities in the two-dimensional t-t' Hubbard
model for particle densities close to the van Hove filling as a function of the
next-nearest neighbor hopping t'. In the one-loop flow at the van Hove filling,
the characteristic temperature for the flow to strong coupling is suppressed
drastically around t'_c approx. -0.33t, suggesting a quantum critical point
between d-wave pairing at moderate t'>t'_c and ferromagnetism for t'<t'_c. Upon
increasing the particle density in the latter regime the leading instability
occurs in the triplet pairing channel.Comment: 4 pages, to appear in Physical Review Letter
Avaliação dos resíduos reacionais provenientes da digestão ácida de materiais biológicos assistida por radiação micro-ondas.
Second Hopf map and supersymmetric mechanics with Yang monopole
We propose to use the second Hopf map for the reduction (via SU(2) group
action) of the eight-dimensional N=8 supersymmetric mechanics to
five-dimensional supersymmetric systems specified by the presence of an SU(2)
Yang monopole. For our purpose we develop the relevant Lagrangian reduction
procedure. The reduced system is characterized by its invariance under the N=5
or N=4 supersymmetry generators (with or without an additional conserved BRST
charge operator) which commute with the su(2) generators.Comment: Final version. To appear in Phys. Rev.
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