52 research outputs found
Sufficient enlargements of minimal volume for finite dimensional normed linear spaces
Let denote the unit ball of a normed linear space . A symmetric,
bounded, closed, convex set in a finite dimensional normed linear space
is called a {\it sufficient enlargement} for if, for an arbitrary isometric
embedding of into a Banach space , there exists a linear projection
such that . The main results of the paper: {\bf
(1)} Each minimal-volume sufficient enlargement is linearly equivalent to a
zonotope spanned by multiples of columns of a totally unimodular matrix. {\bf
(2)} If a finite dimensional normed linear space has a minimal-volume
sufficient enlargement which is not a parallelepiped, then it contains a
two-dimensional subspace whose unit ball is linearly equivalent to a regular
hexagon
Theory of spin-polarized bipolar transport in magnetic p-n junctions
The interplay between spin and charge transport in electrically and
magnetically inhomogeneous semiconductor systems is investigated theoretically.
In particular, the theory of spin-polarized bipolar transport in magnetic p-n
junctions is formulated, generalizing the classic Shockley model. The theory
assumes that in the depletion layer the nonequilibrium chemical potentials of
spin up and spin down carriers are constant and carrier recombination and spin
relaxation are inhibited. Under the general conditions of an applied bias and
externally injected (source) spin, the model formulates analytically carrier
and spin transport in magnetic p-n junctions at low bias. The evaluation of the
carrier and spin densities at the depletion layer establishes the necessary
boundary conditions for solving the diffusive transport equations in the bulk
regions separately, thus greatly simplifying the problem. The carrier and spin
density and current profiles in the bulk regions are calculated and the I-V
characteristics of the junction are obtained. It is demonstrated that spin
injection through the depletion layer of a magnetic p-n junction is not
possible unless nonequilibrium spin accumulates in the bulk regions--either by
external spin injection or by the application of a large bias. Implications of
the theory for majority spin injection across the depletion layer, minority
spin pumping and spin amplification, giant magnetoresistance, spin-voltaic
effect, biasing electrode spin injection, and magnetic drift in the bulk
regions are discussed in details, and illustrated using the example of a GaAs
based magnetic p-n junction.Comment: 36 pages, 11 figures, 2 table
Frontend electronics for high-precision single photo-electron timing
The next generation of high-luminosity experiments requires excellent particle identification detectors, which calls for imaging Cherenkov counters with fast electronics to cope with the expected hit rates. A Barrel DIRC will be used in the central region of the Target Spectrometer
of the planned PANDA experiment at FAIR. A single photo-electron timing resolution of better
than 100 ps RMS is required for the Barrel DIRC to disentangle the complicated patterns created
on the image plane. R&D studies have been performed to provide a design based on the TRB3
readout using FPGA-TDCs with a typical precision of 10 ps RMS and custom frontend electronics with high-bandwidth pre-amplifiers and fast discriminators. The discriminators also provide
time-over-threshold information, thus enabling walk corrections to improve the timing resolution.
Two types of frontend electronics cards optimised for reading out 64-channel PHOTONIS Planacon MCP-PMTs were tested: one based on the NINO ASIC and the other, called PADIWA, based
on FPGA discriminators. Promising results were obtained in a full characterisation using a fast
laser setup and in a test experiment at MAMI, Mainz, with a small scale DIRC prototype
Geographical and temporal distribution of SARS-CoV-2 clades in the WHO European Region, January to June 2020
We show the distribution of SARS-CoV-2 genetic clades over time and between countries and outline potential genomic surveillance objectives. We applied three available genomic nomenclature systems for SARS-CoV-2 to all sequence data from the WHO European Region available during the COVID-19 pandemic until 10 July 2020. We highlight the importance of real-time sequencing and data dissemination in a pandemic situation. We provide a comparison of the nomenclatures and lay a foundation for future European genomic surveillance of SARS-CoV-2.Peer reviewe
J/psi production as a function of charged-particle pseudorapidity density in p-Pb collisions at root s(NN)=5.02 TeV
We report measurements of the inclusive J/ψ yield and average transverse momentum as a function of charged-particle pseudorapidity density dNch/dη in p–Pb collisions at sNN=5.02TeV with ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/ψ yield with normalised dNch/dη, measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/ψ production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity
Verifying resource requirements for ontology-driven rule-based agents
Recent efforts towards the Semantic Web have resulted in powerful languages such as Semantic Web Rule Language (SWRL) based on OWL-DL and RuleML. Rule languages and inference engines incorporate reasoning capabilities to Semantic Web application systems. In this paper we present an approach for the design and specification of ontology-driven multi-agent rule-based systems. We use the Maude rewriting system and its Linear Temporal Logic (LTL) model checking tool to verify response time guarantees for the target systems. We present TOVRBA, an extended version of a verification tool developed by the first author, for ontology-driven multi-agent rule-based systems which allows the designer to specify information about agents' interactions, behavior, and execution strategies at different levels of abstraction. TOVRBA generates an encoding of the system for the Maude LTL model checker, allowing properties of the system to be verified. We illustrate the use of the framework on a simple healthcare system. © 2012 Springer-Verlag
- …