1,189 research outputs found
Optimal read/write memory system components
Two holographic data storage and display systems, voltage gradient ionization system, and linear strain manipulation system are discussed in terms of creating fast, high bit density, storage device. Components described include: novel mounting fixture for photoplastic arrays; corona discharge device; and block data composer
Modeling of SAR signatures of shallow water ocean topography
A hydrodynamic/electromagnetic model was developed to explain and quantify the relationship between the SEASAT synthetic aperture radar (SAR) observed signatures and the bottom topography of the ocean in the English Channel region of the North Sea. The model uses environmental data and radar system parameters as inputs and predicts SAR-observed backscatter changes over topographic changes in the ocean floor. The model results compare favorably with the actual SEASAT SAR observed backscatter values. The developed model is valid for only relatively shallow water areas (i.e., less than 50 meters in depth) and suggests that for bottom features to be visible on SAR imagery, a moderate to high velocity current and a moderate wind must be present
Consensus formation on coevolving networks: groups' formation and structure
We study the effect of adaptivity on a social model of opinion dynamics and
consensus formation. We analyze how the adaptivity of the network of contacts
between agents to the underlying social dynamics affects the size and
topological properties of groups and the convergence time to the stable final
state. We find that, while on static networks these properties are determined
by percolation phenomena, on adaptive networks the rewiring process leads to
different behaviors: Adaptive rewiring fosters group formation by enhancing
communication between agents of similar opinion, though it also makes possible
the division of clusters. We show how the convergence time is determined by the
characteristic time of link rearrangement. We finally investigate how the
adaptivity yields nontrivial correlations between the internal topology and the
size of the groups of agreeing agents.Comment: 10 pages, 3 figures,to appear in a special proceedings issue of J.
Phys. A covering the "Complex Networks: from Biology to Information
Technology" conference (Pula, Italy, 2007
Scaling in Small-World Resistor Networks
We study the effective resistance of small-world resistor networks. Utilizing
recent analytic results for the propagator of the Edwards-Wilkinson process on
small-world networks, we obtain the asymptotic behavior of the
disorder-averaged two-point resistance in the large system-size limit. We find
that the small-world structure suppresses large network resistances: both the
average resistance and its standard deviation approaches a finite value in the
large system-size limit for any non-zero density of random links. We also
consider a scenario where the link conductance decays as a power of the length
of the random links, . In this case we find that the average
effective system resistance diverges for any non-zero value of .Comment: 15 pages, 6 figure
Non-thermal excitation and ionization in supernovae
We incorporate non-thermal excitation and ionization processes arising from
non-thermal electrons that result from \gamma-ray energy deposition, into our
radiative transfer code CMFGEN. The non-thermal electron distribution is
obtained by solving the Spencer-Fano equation using the procedure of Kozma &
Fransson (1992). We applied the non-thermal calculations to the blue supergiant
explosion model whose early evolution was studied in Dessart & Hillier (2010).
Non-thermal processes generally increase excitation and ionization and decrease
the temperature of the ejecta. We confirm that non-thermal processes are
crucial for modeling the nebular spectra. Both optical HI and HeI lines are
significantly strengthened. While optical HeI lines are not easily discerned in
observational spectra due to severe blending with other lines, HeI 2.058 \mu m
provides an excellent opportunity to infer the influence of non-thermal
processes. We also discuss the processes controlling the formation of the HeI
lines during the nebular epoch. Most lines of other species are only slightly
affected. We also show that the inclusion of FeI has substantial
line-blanketing effects on the optical spectra. Our model spectra and synthetic
light curves are compared to the observations of SN 1987A. The spectral
evolution shows broad agreement with the observations, especially H\alpha. The
uncertainties of the non-thermal solver are studied, and are expected to be
small. With this new addition of non-thermal effects in CMFGEN, we now treat
all known important processes controlling the radiative transfer of a supernova
ejecta, whatever the type and the epoch.Comment: 18 pages, 22 figures, accepted to MNRA
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