44,803 research outputs found
Overview of NASA CTOL program
Technology generated by NASA and specifically oriented toward advanced commercial air transport is reviewed. Results of the Aircraft Energy Efficiency program and of related disciplinary areas are reported. The CTOL research efforts are put into perspective relative to the total NASA aeronautics program
THE EVOLVING PHILOSOPHERS PROBLEM - DYNAMIC CHANGE MANAGEMENT
Published versio
Wave packet approach to transport in mesoscopic systems
Wave packets provide a well established and versatile tool for studying
time-dependent effects in molecular physics. Here, we demonstrate the
application of wave packets to mesoscopic nanodevices at low temperatures. The
electronic transport in the devices is expressed in terms of scattering and
transmission coefficients, which are efficiently obtained by solving an initial
value problem (IVP) using the time-dependent Schroedinger equation. The
formulation as an IVP makes non-trivial device topologies accessible and by
tuning the wave packet parameters one can extract the scattering properties for
a large range of energies.Comment: 12 pages, 4 figure
TRACTABLE DATA-FLOW ANALYSIS FOR DISTRIBUTED SYSTEMS
Automated behavior analysis is a valuable technique in the development and maintainence of distributed systems. In this paper, we present a tractable dataflow analysis technique for the detection of unreachable states and actions in distributed systems. The technique follows an approximate approach described by Reif and Smolka, but delivers a more accurate result in assessing unreachable states and actions. The higher accuracy is achieved by the use of two concepts: action dependency and history sets. Although the technique, does not exhaustively detect all possible errors, it detects nontrivial errors with a worst-case complexity quadratic to the system size. It can be automated and applied to systems with arbitrary loops and nondeterministic structures. The technique thus provides practical and tractable behavior analysis for preliminary designs of distributed systems. This makes it an ideal candidate for an interactive checker in software development tools. The technique is illustrated with case studies of a pump control system and an erroneous distributed program. Results from a prototype implementation are presented
Spherical Orbifolds for Cosmic Topology
Harmonic analysis is a tool to infer cosmic topology from the measured
astrophysical cosmic microwave background CMB radiation. For overall positive
curvature, Platonic spherical manifolds are candidates for this analysis. We
combine the specific point symmetry of the Platonic manifolds with their deck
transformations. This analysis in topology leads from manifolds to orbifolds.
We discuss the deck transformations of the orbifolds and give eigenmodes for
the harmonic analysis as linear combinations of Wigner polynomials on the
3-sphere. These provide new tools for detecting cosmic topology from the CMB
radiation.Comment: 17 pages, 9 figures. arXiv admin note: substantial text overlap with
arXiv:1011.427
Nanometer lithography on silicon and hydrogenated amorphous silicon with low-energy electrons
We report the local oxidation of hydrogen terminated silicon (Si) surfaces induced with the scanning-tunneling microscope (STM) operating in air and by a beam of free low-energy electrons. With STM, oxide lines were written in Si(100) and Si(110) and transferred into the substrate by wet etching. In case of Si(110) trenches with a width as small as 35 nm and a depth of 300 nm were made. The same process has also successfully been applied to the patterning of hydrogenated amorphous silicon (a-Si:H) thin films. We demonstrate the fabrication of metallic ‘nanowires’ using a-Si:H as resist layer. With regard to the process of oxidation, it is found that the oxide written with STM is apparently not proportional to the electron current, in contrast to results obtained with a beam of free electrons in an oxygen gas-environment. The dose needed to remove the hydrogen was determined as a function of electron energy. This dose is minimal for 100 eV electrons amounting to 4 mC/cm2
GRAPHICAL CONFIGURATION PROGRAMMING - THE STRUCTURAL DESCRIPTION, CONSTRUCTION AND EVOLUTION OF SOFTWARE SYSTEMS USING GRAPHICS
Published versio
Theoretical Framework for Microscopic Osmotic Phenomena
The basic ingredients of osmotic pressure are a solvent fluid with a soluble
molecular species which is restricted to a chamber by a boundary which is
permeable to the solvent fluid but impermeable to the solute molecules. For
macroscopic systems at equilibrium, the osmotic pressure is given by the
classical van't Hoff Law, which states that the pressure is proportional to the
product of the temperature and the difference of the solute concentrations
inside and outside the chamber. For microscopic systems the diameter of the
chamber may be comparable to the length-scale associated with the solute-wall
interactions or solute molecular interactions. In each of these cases, the
assumptions underlying the classical van't Hoff Law may no longer hold. In this
paper we develop a general theoretical framework which captures corrections to
the classical theory for the osmotic pressure under more general relationships
between the size of the chamber and the interaction length scales. We also show
that notions of osmotic pressure based on the hydrostatic pressure of the fluid
and the mechanical pressure on the bounding walls of the chamber must be
distinguished for microscopic systems. To demonstrate how the theoretical
framework can be applied, numerical results are presented for the osmotic
pressure associated with a polymer of N monomers confined in a spherical
chamber as the bond strength is varied
Tungsten-rhenium alloy thermocouples effective for high-temperature measurement
Tungsten-rhenium alloy thermocouples, specifically, insulated, sheathed W/W plus 26Re and W plus 5 Re/W plus 26 Re thermocouples, are effective for temperature measurement in excess of 2920 degrees C. These thermocouples have a high thermoelectric output and excellent relationship to temperatures up to 2760 degrees C
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