1,303 research outputs found
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
Synchronization in Weighted Uncorrelated Complex Networks in a Noisy Environment: Optimization and Connections with Transport Efficiency
Motivated by synchronization problems in noisy environments, we study the
Edwards-Wilkinson process on weighted uncorrelated scale-free networks. We
consider a specific form of the weights, where the strength (and the associated
cost) of a link is proportional to with and
being the degrees of the nodes connected by the link. Subject to the
constraint that the total network cost is fixed, we find that in the mean-field
approximation on uncorrelated scale-free graphs, synchronization is optimal at
-1. Numerical results, based on exact numerical diagonalization
of the corresponding network Laplacian, confirm the mean-field results, with
small corrections to the optimal value of . Employing our recent
connections between the Edwards-Wilkinson process and resistor networks, and
some well-known connections between random walks and resistor networks, we also
pursue a naturally related problem of optimizing performance in queue-limited
communication networks utilizing local weighted routing schemes.Comment: Papers on related research can be found at
http://www.rpi.edu/~korniss/Research
Consensus formation on adaptive networks
The structure of a network can significantly influence the properties of the
dynamical processes which take place on them. While many studies have been
devoted to this influence, much less attention has been devoted to the
interplay and feedback mechanisms between dynamical processes and network
topology on adaptive networks. Adaptive rewiring of links can happen in real
life systems such as acquaintance networks where people are more likely to
maintain a social connection if their views and values are similar. In our
study, we consider different variants of a model for consensus formation. Our
investigations reveal that the adaptation of the network topology fosters
cluster formation by enhancing communication between agents of similar opinion,
though it also promotes the division of these clusters. The temporal behavior
is also strongly affected by adaptivity: while, on static networks, it is
influenced by percolation properties, on adaptive networks, both the early and
late time evolution of the system are determined by the rewiring process. The
investigation of a variant of the model reveals that the scenarios of
transitions between consensus and polarized states are more robust on adaptive
networks.Comment: 11 pages, 14 figure
Late-time supernova light curves: The effect of internal conversion and Auger electrons
Energy release from radioactive decays contributes significantly to supernova
light curves. Previous works, which considered the energy deposited by
gamma-rays and positrons produced by 56Ni, 56Co, 57Ni, 57Co, 44Ti and 44Sc,
have been quite successful in explaining the light curves of both core collapse
and thermonuclear supernovae. We point out that Auger and internal conversion
electrons together with the associated X-ray cascade, constitute an additional
heat source. When a supernova is transparent to gamma-rays, these electrons can
contribute significantly to light curves for reasonable nucleosynthetic yields.
In particular, the electrons emitted in the decay of 57Co, which are largely
due to internal conversion from a fortuitously low-lying 3/2- state in the
daughter 57Fe, constitute an additional significant energy deposition channel.
We show that when the heating by these electrons is accounted for, a slow-down
in the lightcurve of SN 1998bw is naturally obtained for typical hypernova
nucleosynthetic yields. Additionally, we show that for generic Type Ia
supernova yields, the Auger electrons emitted in the ground-state to
ground-state electron capture decay of 55Fe exceed the energy released by the
44Ti decay chain for many years after the explosion.Comment: 6 pages, 2 figures, 1 table, MNRAS in press, v2 with updated
reference
Testing the Collective Properties of Small-World Networks through Roughness Scaling
Motivated by a fundamental synchronization problem in scalable parallel
computing and by a recent criterion for ``mean-field'' synchronizability in
interacting systems, we study the Edwards-Wilkinson model on two variations of
a small-worldnetwork. In the first version each site has exactly one random
link of strength , while in the second one each site on average has
links of unit strength. We construct a perturbative description for the width
of the stationary-state surface (a measure of synchronization), in the weak-
and sparse-coupling limits, respectively, and verify the results by performing
exact numerical diagonalization. The width remains finite in both cases, but
exhibits anomalous scaling with in the latter for .Comment: 4 pages, 3 figure
Natural infection of Run1-positive vines by naïve genotypes of Erysiphe necator
The Run1 locus for dominant resistance to powdery mildew (Erysiphe necator) has been successfully introgressed into Euvitis from Vitis rotundifolia. In the current study, Run1 vines were hybridized with breeding lines at Cornell University, and the presence of the locus was assayed using the markers GLP1-12 and VMC8g9. Signs of powdery mildew were observed on 14 of 113 Run1-positive seedlings in October 2010 in Geneva, N.Y. Severity of infection was lower for Run1-positive than for Run1-negative seedlings. Presence of mature cleistothecia suggested infection by at least two pathogen genotypes, which since V. rotundifolia is not grown within 800+ km of Geneva, N.Y., evolved from a pathogen population naïve to Run1 resistance. Therefore, caution in the deployment of the Run1 locus in new resistant cultivars is suggested so the effectiveness of Run1 does not diminish over time.
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