44,604 research outputs found
Scaling Properties of Paths on Graphs
Let be a directed graph on finitely many vertices and edges, and assign a
positive weight to each edge on . Fix vertices and and consider the
set of paths that start at and end at , self-intersecting in any number
of places along the way. For each path, sum the weights of its edges, and then
list the path weights in increasing order. The asymptotic behaviour of this
sequence is described, in terms of the structure and type of strongly connected
components on the graph. As a special case, for a Markov chain the asymptotic
probability of paths obeys either a power law scaling or a weaker type of
scaling, depending on the structure of the transition matrix. This generalizes
previous work by Mandelbrot and others, who established asymptotic power law
scaling for special classes of Markov chains.Comment: 23 pages, 2 figure
Algorithm based comparison between the integral method and harmonic analysis of the timing jitter of diode-based and solid-state pulsed laser sources
AbstractA comparison between two methods of timing jitter calculation is presented. The integral method utilizes spectral area of the single side-band (SSB) phase noise spectrum to calculate root mean square (rms) timing jitter. In contrast the harmonic analysis exploits the uppermost noise power in high harmonics to retrieve timing fluctuation. The results obtained show that a consistent timing jitter of 1.2ps is found by the integral method and harmonic analysis in gain-switched laser diodes with an external cavity scheme. A comparison of the two approaches in noise measurement of a diode-pumped Yb:KY(WO4)2 passively mode-locked laser is also shown in which both techniques give 2ps rms timing jitter
Outer planets probe testing
An atmospheric entry Probe is being developed by NASA Ames Research Center (ARC) to conduct in situ scientific investigations of the outer planets' atmospheres. A full scale engineering model of an MDAC-E Probe configuration, was fabricated by NASA ARC. Proof-of-concept test validation of the structural and thermal design is being obtained at NASA ARC. The model was successfully tested for shock and dynamic loading and is currently in thermal vacuum testing
Chiral Condensate in the Deconfined Phase of Quenched Gauge Theories
We compute the low lying spectrum of the overlap Dirac operator in the
deconfined phase of finite-temperature quenched gauge theory. It suggests the
existence of a chiral condensate which we confirm with a direct stochastic
estimate. We show that the part of the spectrum responsible for the chiral
condensate can be understood as arising from a dilute gas of instantons and
anti-instantons.Comment: Revtex, 16 pages, 3 postscript figure
Volume fluctuations and geometrical constraints in granular packs
Structural organization and correlations are studied in very large packings
of equally sized acrylic spheres, reconstructed in three-dimensions by means of
X-ray computed tomography. A novel technique, devised to analyze correlations
among more than two spheres, shows that the structural organization can be
conveniently studied in terms of a space-filling packing of irregular
tetrahedra. The study of the volume distribution of such tetrahedra reveals an
exponential decay in the region of large volumes; a behavior that is in very
good quantitative agreement with theoretical prediction. I argue that the
system's structure can be described as constituted of two phases: 1) an
`unconstrained' phase which freely shares the volume; 2) a `constrained' phase
which assumes configurations accordingly with the geometrical constraints
imposed by the condition of non-overlapping between spheres and mechanical
stability. The granular system exploits heterogeneity maximizing freedom and
entropy while constraining mechanical stability.Comment: 5 pages, 4 figure
The use of computer-generated color graphic images for transient thermal analysis
Color computer graphics techniques were investigated as a means of rapidly scanning and interpreting large sets of transient heating data. The data presented were generated to support the conceptual design of a heat-sink thermal protection system (TPS) for a hypersonic research airplane. Color-coded vector and raster displays of the numerical geometry used in the heating calculations were employed to analyze skin thicknesses and surface temperatures of the heat-sink TPS under a variety of trajectory flight profiles. Both vector and raster displays proved to be effective means for rapidly identifying heat-sink mass concentrations, regions of high heating, and potentially adverse thermal gradients. The color-coded (raster) surface displays are a very efficient means for displaying surface-temperature and heating histories, and thereby the more stringent design requirements can quickly be identified. The related hardware and software developments required to implement both the vector and the raster displays for this application are also discussed
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