3,464 research outputs found
Traffic matrix estimation on a large IP backbone: a comparison on real data
This paper considers the problem of estimating the point-to-point
traffic matrix in an operational IP backbone. Contrary to previous studies, that have used a partial traffic matrix or demands estimated from aggregated Netflow traces, we use a unique data set of complete traffic matrices from a global IP network measured over five-minute intervals. This allows us to do an accurate data analysis on the time-scale of typical link-load measurements and enables us to make a balanced evaluation of different traffic matrix estimation techniques. We describe the data collection infrastructure, present spatial and temporal demand distributions, investigate the stability of fan-out factors, and analyze the mean-variance relationships between demands. We perform a critical evaluation of existing and novel methods for traffic matrix estimation, including recursive fanout estimation, worst-case bounds, regularized estimation techniques, and methods that rely on mean-variance relationships. We discuss the weaknesses and strengths of the various methods, and highlight differences in the results for the European and American subnetworks
An efficient new route to dihydropyranobenzimidazole inhibitors of HCV replication.
A class of dihydropyranobenzimidazole inhibitors was recently discovered that acts against the hepatitis C virus (HCV) in a new way, binding to the IRES-IIa subdomain of the highly conserved 5' untranslated region of the viral RNA and thus preventing the ribosome from initiating translation. However, the reported synthesis of these compounds is lengthy and low-yielding, the intermediates are troublesome to purify, and the route is poorly structured for the creation of libraries. We report a streamlined route to this class of inhibitors in which yields are far higher and most intermediates are crystalline. In addition, a key variable side chain is introduced late in the synthesis, allowing analogs to be easily synthesized for optimization of antiviral activity
Experimental implementation and proof of principle for a radionuclidic purity test solely based on half-life measurement
Deep combinatorial optimisation for optimal stopping time problems : application to swing options pricing
A new method for stochastic control based on neural networks and using
randomisation of discrete random variables is proposed and applied to optimal
stopping time problems. The method models directly the policy and does not need
the derivation of a dynamic programming principle nor a backward stochastic
differential equation. Unlike continuous optimization where automatic
differentiation is used directly, we propose a likelihood ratio method for
gradient computation. Numerical tests are done on the pricing of American and
swing options. The proposed algorithm succeeds in pricing high dimensional
American and swing options in a reasonable computation time, which is not
possible with classical algorithms
Non-invasive Scanning Raman Spectroscopy and Tomography for Graphene Membrane Characterization
Graphene has extraordinary mechanical and electronic properties, making it a
promising material for membrane based nanoelectromechanical systems (NEMS).
Here, chemical-vapor-deposited graphene is transferred onto target substrates
to suspend it over cavities and trenches for pressure-sensor applications. The
development of such devices requires suitable metrology methods, i.e.,
large-scale characterization techniques, to confirm and analyze successful
graphene transfer with intact suspended graphene membranes. We propose fast and
noninvasive Raman spectroscopy mapping to distinguish between freestanding and
substrate-supported graphene, utilizing the different strain and doping levels.
The technique is expanded to combine two-dimensional area scans with
cross-sectional Raman spectroscopy, resulting in three-dimensional Raman
tomography of membrane-based graphene NEMS. The potential of Raman tomography
for in-line monitoring is further demonstrated with a methodology for automated
data analysis to spatially resolve the material composition in micrometer-scale
integrated devices, including free-standing and substrate-supported graphene.
Raman tomography may be applied to devices composed of other two-dimensional
materials as well as silicon micro- and nanoelectromechanical systems.Comment: 23 pages, 5 figure
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