4,322 research outputs found
Towards Distributed and Adaptive Detection and Localisation of Network Faults
We present a statistical probing-approach to distributed fault-detection in networked systems, based on autonomous configuration of algorithm parameters. Statistical modelling is used for detection and localisation of network faults. A detected fault is isolated to a node or link by collaborative fault-localisation. From local measurements obtained through probing between nodes, probe response delay and packet drop are modelled via parameter estimation for each link. Estimated model parameters are used for autonomous configuration of algorithm parameters, related to probe intervals and detection mechanisms. Expected fault-detection performance is formulated as a cost instead of specific parameter values, significantly reducing configuration efforts in a distributed system. The benefit offered by using our algorithm is fault-detection with increased certainty based on local measurements, compared to other methods not taking observed network conditions into account. We investigate the algorithm performance for varying user parameters and failure conditions. The simulation results indicate that more than 95 % of the generated faults can be detected with few false alarms. At least 80 % of the link faults and 65 % of the node faults are correctly localised. The performance can be improved by parameter adjustments and by using alternative paths for communication of algorithm control messages
Rigorous statistical detection and characterization of a deviation from the Gutenberg-Richter distribution above magnitude 8 in subduction zones
We present a quantitative statistical test for the presence of a crossover c0
in the Gutenberg-Richter distribution of earthquake seismic moments, separating
the usual power law regime for seismic moments less than c0 from another faster
decaying regime beyond c0. Our method is based on the transformation of the
ordered sample of seismic moments into a series with uniform distribution under
condition of no crossover. The bootstrap method allows us to estimate the
statistical significance of the null hypothesis H0 of an absence of crossover
(c0=infinity). When H0 is rejected, we estimate the crossover c0 using two
different competing models for the second regime beyond c0 and the bootstrap
method. For the catalog obtained by aggregating 14 subduction zones of the
Circum Pacific Seismic Belt, our estimate of the crossover point is log(c0)
=28.14 +- 0.40 (c0 in dyne-cm), corresponding to a crossover magnitude mW=8.1
+- 0.3. For separate subduction zones, the corresponding estimates are much
more uncertain, so that the null hypothesis of an identical crossover for all
subduction zones cannot be rejected. Such a large value of the crossover
magnitude makes it difficult to associate it directly with a seismogenic
thickness as proposed by many different authors in the past. Our measure of c0
may substantiate the concept that the localization of strong shear deformation
could propagate significantly in the lower crust and upper mantle, thus
increasing the effective size beyond which one should expect a change of
regime.Comment: pdf document of 40 pages including 5 tables and 19 figure
Localized quantum walks as secured quantum memory
We show that a quantum walk process can be used to construct and secure
quantum memory. More precisely, we show that a localized quantum walk with
temporal disorder can be engineered to store the information of a single,
unknown qubit on a compact position space and faithfully recover it on demand.
Since the localization occurss with a finite spread in position space, the
stored information of the qubit will be naturally secured from the simple
eavesdropper. Our protocol can be adopted to any quantum system for which
experimental control over quantum walk dynamics can be achieved.Comment: 7 pages, 4 figure
Fault localization based only on failed runs
Fault localization commonly relies on both passed and failed runs, but passed runs are generally susceptible to coincidental correctness and modern software automatically produces a huge number of bug reports on failed runs. FOnly is an effective new technique that relies only on failed runs to locate faults statistically. © 2012 IEEE.published_or_final_versio
Robust Trapped-Ion Quantum Logic Gates by Continuous Dynamical Decoupling
We introduce a novel scheme that combines phonon-mediated quantum logic gates
in trapped ions with the benefits of continuous dynamical decoupling. We
demonstrate theoretically that a strong driving of the qubit decouples it from
external magnetic-field noise, enhancing the fidelity of two-qubit quantum
gates. Moreover, the scheme does not require ground-state cooling, and is
inherently robust to undesired ac-Stark shifts. The underlying mechanism can be
extended to a variety of other systems where a strong driving protects the
quantum coherence of the qubits without compromising the two-qubit couplings.Comment: Slightly longer than the published versio
Mid-ocean ridge exploration with an autonomous underwater vehicle
Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 4 (2007): 52-61.Human-occupied submersibles, towed
vehicles, and tethered remotely operated
vehicles (ROVs) have traditionally been
used to study the deep seafloor. In recent
years, however, autonomous underwater
vehicles (AUVs) have begun to replace
these other vehicles for mapping and
survey missions. AUVs complement the
capabilities of these pre-existing systems,
offering superior mapping capabilities,
improved logistics, and better utilization
of the surface support vessel by allowing
other tasks such as submersible operations,
ROV work, CTD stations, or multibeam
surveys to be performed while the
AUV does its work. AUVs are particularly
well suited to systematic preplanned surveys
using sonars, in situ chemical sensors,
and cameras in the rugged deep-sea
terrain that has been the focus of numerous
scientific expeditions (e.g., those to
mid-ocean ridges and ocean margin settings).
The Autonomous Benthic Explorer
(ABE) is an example of an AUV that has
been used for over 20 cruises sponsored
by the National Science Foundation
(NSF), the National Oceanic and
Atmospheric Administration (NOAA)
Office of Ocean Exploration (OE), and
international and private sources. This
paper summarizes NOAA OE-sponsored
cruises made to date using ABE
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