629 research outputs found
Probabilistic Fragmentation and Effective Power Law
A simple fragmentation model is introduced and analysed. We show that, under
very general conditions, an effective power law for the mass distribution
arises with realistic exponent. This exponent has a universal limit, but in
practice the effective exponent depends on the detailed breaking mechanism and
the initial conditions. This dependence is in good agreement with experimental
results of fragmentation.Comment: 4 pages Revtex, 2 figures, zipped and uuencode
On-Line Distributed Traffic Grooming
This paper addresses the problem of on-line traffic grooming in WDM paths. Each request consists of a source node, a destination node, and the desired bandwidth for the connection. Connections may be multi-hop, permitting the use of multiple lightpaths. We describe a new distributed on-line algorithm for this problem that is provably wide-sense non-blocking under cer- tain assumptions. Moreover, we use simulations to demonstrate that the algorithm is extremely effective even when some of these assumptions are relaxed
Iterative Temporal Motion Planning for Hybrid Systems in Partially Unknown Environments
This paper considers the problem of motion planning for a
hybrid robotic system with complex and nonlinear dynamics
in a partially unknown environment given a temporal logic
specification. We employ a multi-layered synergistic framework
that can deal with general robot dynamics and combine
it with an iterative planning strategy. Our work allows us
to deal with the unknown environmental restrictions only
when they are discovered and without the need to repeat
the computation that is related to the temporal logic specification.
In addition, we define a metric for satisfaction of
a specification. We use this metric to plan a trajectory that
satisfies the specification as closely as possible in cases in
which the discovered constraint in the environment renders
the specification unsatisfiable. We demonstrate the efficacy
of our framework on a simulation of a hybrid second-order
car-like robot moving in an office environment with unknown
obstacles. The results show that our framework is successful
in generating a trajectory whose satisfaction measure of the
specification is optimal. They also show that, when new obstacles
are discovered, the reinitialization of our framework
is computationally inexpensive
Minimal recipes for global cloudiness
Clouds are primary modulators of Earth’s energy balance. It is thus important to understand the links connecting variabilities in cloudiness to variabilities in other state variables of the climate system, and also describe how these links would change in a changing climate. A conceptual model of global cloudiness can help elucidate these points. In this work we derive simple representations of cloudiness, that can be useful in creating a theory of global cloudiness. These representations illustrate how both spatial and temporal variability of cloudiness can be expressed in terms of basic state variables. Specifically, cloud albedo is captured by a nonlinear combination of pressure velocity and a measure of the low-level stability, and cloud longwave effect is captured by surface temperature, pressure velocity, and standard deviation of pressure velocity. We conclude with a short discussion on the usefulness of this work in the context of global warming response studies
An Electronic Mach-Zehnder Interferometer
Double-slit electron interferometers, fabricated in high mobility
two-dimensional electron gas (2DEG), proved to be very powerful tools in
studying coherent wave-like phenomena in mesoscopic systems. However, they
suffer from small fringe visibility due to the many channels in each slit and
poor sensitivity to small currents due to their open geometry. Moreover, the
interferometers do not function in a high magnetic field, namely, in the
quantum Hall effect (QHE) regime, since it destroys the symmetry between left
and right slits. Here, we report on the fabrication and operation of a novel,
single channel, two-path electron interferometer that functions in a high
magnetic field. It is the first electronic analog of the well-known optical
Mach-Zehnder (MZ) interferometer. Based on single edge state and closed
geometry transport in the QHE regime the interferometer is highly sensitive and
exhibits very high visibility (62%). However, the interference pattern decays
precipitously with increasing electron temperature or energy. While we do not
understand the reason for the dephasing we show, via shot noise measurement,
that it is not a decoherence process that results from inelastic scattering
events.Comment: to appear in Natur
Modulation of functional network properties in major depressive disorder following electroconvulsive therapy (ECT): a resting-state EEG analysis
Electroconvulsive therapy (ECT) is a highly effective neuromodulatory intervention for treatment-resistant major depressive disorder (MDD). Presently, however, understanding of its neurophysiological effects remains incomplete. In the present study, we utilised resting-state electroencephalography (RS-EEG) to explore changes in functional connectivity, network topology, and spectral power elicited by an acute open-label course of ECT in a cohort of 23 patients with treatment-resistant MDD. RS-EEG was recorded prior to commencement of ECT and again within 48 h following each patient’s final treatment session. Our results show that ECT was able to enhance connectivity within lower (delta and theta) frequency bands across subnetworks largely confined to fronto-central channels, while, conversely, more widespread subnetworks of reduced connectivity emerged within faster (alpha and beta) bands following treatment. Graph-based topological analyses revealed changes in measures of functional segregation (clustering coefficient), integration (characteristic path length), and small-world architecture following ECT. Finally, post-treatment enhancement of delta and theta spectral power was observed, which showed a positive association with the number of ECT sessions received. Overall, our findings indicate that RS-EEG can provide a sensitive measure of dynamic neural activity following ECT and highlight network-based analyses as a promising avenue for furthering mechanistic understanding of the effects of convulsive therapies
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