10,057 research outputs found
Special studies of AROD system concepts and designs
Signal to noise ratios in airborne range and orbit determination system, and carrier and range loop performance analyse
Self-sustained spatiotemporal oscillations induced by membrane-bulk coupling
We propose a novel mechanism leading to spatiotemporal oscillations in
extended systems that does not rely on local bulk instabilities. Instead,
oscillations arise from the interaction of two subsystems of different spatial
dimensionality. Specifically, we show that coupling a passive diffusive bulk of
dimension d with an excitable membrane of dimension d-1 produces a
self-sustained oscillatory behavior. An analytical explanation of the
phenomenon is provided for d=1. Moreover, in-phase and anti-phase
synchronization of oscillations are found numerically in one and two
dimensions. This novel dynamic instability could be used by biological systems
such as cells, where the dynamics on the cellular membrane is necessarily
different from that of the cytoplasmic bulk.Comment: Accepted for publication in Physical Review Letter
Conceptualizing community resilience to natural hazards - the emBRACE framework
Abstract. The level of community is considered to be vital for building disaster resilience. Yet, community resilience as a scientific concept often remains vaguely defined and lacks the guiding characteristics necessary for analysing and enhancing resilience on the ground. The emBRACE framework of community resilience presented in this paper provides a heuristic analytical tool for understanding, explaining and measuring community resilience to natural hazards. It was developed in an iterative process building on existing scholarly debates, on empirical case study work in five countries and on participatory consultation with community stakeholders, where the framework was applied and ground-tested in different contexts and for different hazard types. The framework conceptualizes resilience across three core domains: resources and capacities; actions; and learning. These three domains are conceptualized as intrinsically conjoined within a whole. Community resilience is influenced by these integral elements as well as by extra-community forces, comprising disaster risk governance and thus laws, policies and responsibilities on the one hand and on the other, the general societal context, natural and human-made disturbances and system change over time. The framework is a graphically rendered heuristic, which through application can assist in guiding the assessment of community resilience in a systematic way and identifying key drivers and barriers of resilience that affect any particular hazard-exposed community
Routes towards Anderson-Like localization of Bose-Einstein condensates in disordered optical lattices
We investigate, both experimentally and theoretically, possible routes
towards Anderson-like localization of Bose-Einstein condensates in disordered
potentials. The dependence of this quantum interference effect on the nonlinear
interactions and the shape of the disorder potential is investigated.
Experiments with an optical lattice and a superimposed disordered potential
reveal the lack of Anderson localization. A theoretical analysis shows that
this absence is due to the large length scale of the disorder potential as well
as its screening by the nonlinear interactions. Further analysis shows that
incommensurable superlattices should allow for the observation of the
cross-over from the nonlinear screening regime to the Anderson localized case
within realistic experimental parameters.Comment: 4 pages to appear in Phys. Rev. Let
Self-organization and Mechanical Properties of Active Filament Bundles
A phenomenological description for active bundles of polar filaments is
presented. The activity of the bundle results from crosslinks, that induce
relative displacements between the aligned filaments. Our generic description
is based on momentum conservation within the bundle. By specifying the internal
forces, a simple minimal model for the bundle dynamics is obtained, capturing
generic dynamic behaviors. In particular, contracted states as well as solitary
and oscillatory waves appear through dynamic instabilities. The introduction of
filament adhesion leads to self-organized persistent filament transport.
Furthermore, calculating the tension, homogeneous bundles are shown to be able
to actively contract and to perform work against external forces. Our
description is motivated by dynamic phenomena in the cytoskeleton and could
apply to stress-fibers and self-organization phenomena during cell-locomotion.Comment: 19 pages, 10 figure
The Camassa-Holm equation as the long-wave limit of the improved Boussinesq equation and of a class of nonlocal wave equations
In the present study we prove rigorously that in the long-wave limit, the
unidirectional solutions of a class of nonlocal wave equations to which the
improved Boussinesq equation belongs are well approximated by the solutions of
the Camassa-Holm equation over a long time scale. This general class of
nonlocal wave equations model bidirectional wave propagation in a nonlocally
and nonlinearly elastic medium whose constitutive equation is given by a
convolution integral. To justify the Camassa-Holm approximation we show that
approximation errors remain small over a long time interval. To be more
precise, we obtain error estimates in terms of two independent, small, positive
parameters and measuring the effect of nonlinearity and
dispersion, respectively. We further show that similar conclusions are also
valid for the lower order approximations: the Benjamin-Bona-Mahony
approximation and the Korteweg-de Vries approximation.Comment: 24 pages, to appear in Discrete and Continuous Dynamical System
Reverberation Mapping Measurements of Black Hole Masses in Six Local Seyfert Galaxies
We present the final results from a high sampling rate, multi-month,
spectrophotometric reverberation mapping campaign undertaken to obtain either
new or improved Hbeta reverberation lag measurements for several relatively
low-luminosity AGNs. We have reliably measured thetime delay between variations
in the continuum and Hbeta emission line in six local Seyfert 1 galaxies. These
measurements are used to calculate the mass of the supermassive black hole at
the center of each of these AGNs. We place our results in context to the most
current calibration of the broad-line region (BLR) R-L relationship, where our
results remove outliers and reduce the scatter at the low-luminosity end of
this relationship. We also present velocity-resolved Hbeta time delay
measurements for our complete sample, though the clearest velocity-resolved
kinematic signatures have already been published.Comment: 52 pages (AASTeX: 29 pages of text, 8 tables, 7 figures), accepted
for publication in the Astrophysical Journa
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