1,999 research outputs found
CHEETAH: Circuit-Switched High-Speed End-to-End Transport Architecture Testbed
We propose a circuit-switched high-speed end-to-end transport architecture (CHEETAH) as a networking solution to provide high-speed end-to-end circuit connectivity to end hosts on a dynamic call-by-call basis. Not only is it envisioned as a complementary service to the basic connectionless service provided by today’s Internet; it also relies on and leverages the presence of this service. Noting the dominance of Ethernet in LANs and SONET/SDH in WANs, CHEETAH circuits will consist of Ethernet segments at the ends and Ethernet-over-SONET segments in the wide area. In this article we explain the CHEETAH concept and describe a wide-area experimental network testbed we have deployed based on this concept. The network testbed currently extends between Raleigh, North Carolina, Atlanta, Georgia, and Oak Ridge, Tennessee, and uses off-the-shelf switches. We have created CHEETAH software to run on end hosts to enable automated use of this network by applications. Our first users of this network testbed and software will be the Terascale Supernova Initiative (TSI) project researchers, who plan to use this network for large file transfers and remote visualizations
Hyperfine interaction and magnetoresistance in organic semiconductors
We explore the possibility that hyperfine interaction causes the recently
discovered organic magnetoresistance (OMAR) effect. Our study employs both
experiment and theoretical modelling. An excitonic pair mechanism model based
on hyperfine interaction, previously suggested by others to explain magnetic
field effects in organics, is examined. Whereas this model can explain a few
key aspects of the experimental data, we, however, uncover several fundamental
contradictions as well. By varying the injection efficiency for minority
carriers in the devices, we show experimentally that OMAR is only weakly
dependent on the ratio between excitons formed and carriers injected, likely
excluding any excitonic effect as the origin of OMAR.Comment: 10 pages, 7 figures, 1 tabl
GBM Volumetry using the 3D Slicer Medical Image Computing Platform
Volumetric change in glioblastoma multiforme (GBM) over time is a critical factor in treatment decisions. Typically, the tumor volume is computed on a slice-by-slice basis using MRI scans obtained at regular intervals. (3D)Slicer – a free platform for biomedical research – provides an alternative to this manual slice-by-slice segmentation process, which is significantly faster and requires less user interaction. In this study, 4 physicians segmented GBMs in 10 patients, once using the competitive region-growing based GrowCut segmentation module of Slicer, and once purely by drawing boundaries completely manually on a slice-by-slice basis. Furthermore, we provide a variability analysis for three physicians for 12 GBMs. The time required for GrowCut segmentation was on an average 61% of the time required for a pure manual segmentation. A comparison of Slicer-based segmentation with manual slice-by-slice segmentation resulted in a Dice Similarity Coefficient of 88.43 ± 5.23% and a Hausdorff Distance of 2.32 ± 5.23 mm
Conservation Laws and Cosmological Perturbations in Curved Universes
When working in synchronous gauges, pseudo-tensor conservation laws are often
used to set the initial conditions for cosmological scalar perturbations, when
those are generated by topological defects which suddenly appear in an up to
then perfectly homogeneous and isotropic universe. However those conservation
laws are restricted to spatially flat (K=0) Friedmann-Lema\^\i tre spacetimes.
In this paper, we first show that in fact they implement a matching condition
between the pre- and post- transition eras and, in doing so, we are able to
generalize them and set the initial conditions for all . Finally, in the
long wavelength limit, we encode them into a vector conservation law having a
well-defined geometrical meaning.Comment: 15 pages, no figure, to appear in Phys. Rev.
Back reaction in the formation of a straight cosmic string
A simple model for the formation of a straight cosmic string, wiggly or
unperturbed is considered. The gravitational field of such string is computed
in the linear approximation. The vacuum expectation value of the stress tensor
of a massless scalar quantum field coupled to the string gravitational field is
computed to the one loop order. Finally, the back-reaction effect on the
gravitational field of the string is obtained by solving perturbatively the
semiclassical Einstein's equations.Comment: 29 pages, LaTeX, no figures. A postcript version can be obtained from
anonymous ftp at ftp://ftp.ifae.es/preprint.f
Deep Neural Networks for Energy and Position Reconstruction in EXO-200
We apply deep neural networks (DNN) to data from the EXO-200 experiment. In
the studied cases, the DNN is able to reconstruct the relevant parameters -
total energy and position - directly from raw digitized waveforms, with minimal
exceptions. For the first time, the developed algorithms are evaluated on real
detector calibration data. The accuracy of reconstruction either reaches or
exceeds what was achieved by the conventional approaches developed by EXO-200
over the course of the experiment. Most existing DNN approaches to event
reconstruction and classification in particle physics are trained on Monte
Carlo simulated events. Such algorithms are inherently limited by the accuracy
of the simulation. We describe a unique approach that, in an experiment such as
EXO-200, allows to successfully perform certain reconstruction and analysis
tasks by training the network on waveforms from experimental data, either
reducing or eliminating the reliance on the Monte Carlo.Comment: Accepted version. 33 pages, 28 figure
CMB Anisotropy Induced by a Moving Straight Cosmic String
We showed that the part of strings could be detected by optical method is
only 20% from the total available amount of such objects, therefore the
gravitational lensing method has to be "completed" by CMB one. We found the
general structure of the CMB anisotropy generated by a cosmic string for simple
model of straight string moving with constant velocity. For strings with
deficit angle 1-2 arcsec the amplitude of generated anisotropy has to be 15-30
muK (the corresponding string linear density is (G mu) ~ 10^{-7} and energy is
GUT one, 10^{15} GeV). To use both radio and optical methods the deficit angle
has to be from 0.1 arcsec to 5-6 arcsec. If cosmic string can be detected by
optical method, the length of corresponding brightness spot of anisotropy has
to be no less than 100 degrees.Comment: 6 pages, 1 Postscript figure, will be published in proceedings of
QUARKS-2008, 15th International Seminar on High Energy Physics, Sergiev
Posad, Russia, 23-29 May, 200
Measurement of the Spectral Shape of the beta-decay of 137Xe to the Ground State of 137Cs in EXO-200 and Comparison with Theory
We report on a comparison between the theoretically predicted and
experimentally measured spectra of the first-forbidden non-unique -decay
transition ^{137}\textrm{Xe}(7/2^-)\to\,^{137}\textrm{Cs}(7/2^+). The
experimental data were acquired by the EXO-200 experiment during a deployment
of an AmBe neutron source. The ultra-low background environment of EXO-200,
together with dedicated source deployment and analysis procedures, allowed for
collection of a pure sample of the decays, with an estimated
signal-to-background ratio of more than 99-to-1 in the energy range from 1075
to 4175 keV. In addition to providing a rare and accurate measurement of the
first-forbidden non-unique -decay shape, this work constitutes a novel
test of the calculated electron spectral shapes in the context of the reactor
antineutrino anomaly and spectral bump.Comment: Version as accepted by PR
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