2,245 research outputs found

    Trellises for stabilizer codes: definition and uses

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    Trellises play an important theoretical and practical role for classical codes. Their main utility is to devise complexity-efficient error estimation algorithms. Here, we describe trellis representations for quantum stabilizer codes. We show that they share the same properties as their classical analogs. In particular, for any stabilizer code it is possible to find a minimal trellis representation. Our construction is illustrated by two fundamental error estimation algorithms.Comment: 5 pages, 2 figure

    Conformal dimension and random groups

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    We give a lower and an upper bound for the conformal dimension of the boundaries of certain small cancellation groups. We apply these bounds to the few relator and density models for random groups. This gives generic bounds of the following form, where ll is the relator length, going to infinity. (a) 1 + 1/C < \Cdim(\bdry G) < C l / \log(l), for the few relator model, and (b) 1 + l / (C\log(l)) < \Cdim(\bdry G) < C l, for the density model, at densities d<1/16d < 1/16. In particular, for the density model at densities d<1/16d < 1/16, as the relator length ll goes to infinity, the random groups will pass through infinitely many different quasi-isometry classes.Comment: 32 pages, 4 figures. v2: Final version. Main result improved to density < 1/16. Many minor improvements. To appear in GAF

    Transdet: a matched-filter based algorithm for transit detection - application to simulated COROT light curves

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    We present a matched-filter based algorithm for transit detection and its application to simulated COROT light curves. This algorithm stems from the work by Bord\'e, Rouan & L\'eger (2003). We describe the different steps we intend to take to discriminate between planets and stellar companions using the three photometric bands provided by COROT. These steps include the search for secondary transits, the search for ellipsoidal variability, and the study of transit chromaticity. We also discuss the performance of this approach in the context of blind tests organized inside the COROT exoplanet consortium.Comment: 6 pages, 4 figures, in Transiting Extrasolar Planets Workshop, meeting held in Heidelberg, 25-28 September 200

    Two-Type Age-Dependent Branching Processes with Inhomogeneous Immigration as Models of Renewing Cell Population

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    2000 Mathematics Subject Classification: primary 60J80; secondary 60J85, 92C37.Two-type reducible age-dependent branching processes with inhomogeneous immigration are considered to describe the kinetics of renewing cell populations. This class of processes can be used to model the generation of oligodendrocytes in the central nervous system in vivo or the kinetics of leukemia cells. The asymptotic behavior of the first and second moments, including the correlation, of the process is investigated.This research was supported by NIH grants 2R01 NS039511, R01 CA134839, and 1R01 AI069351

    Managing Operating Procedures in Distributed Collaborative Projects

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    In recent years, large distributed collaborative projects have become very prominent in scientific research, allowing exchanges between laboratories located in different institutions and countries and between various domains of competence. Particularly the work on nanotoxicity – a field which has only been under investigation for a few years and is still lacking regulatory framework – highlighted the need for well-controlled methods, as well as rules for the handling and disposal of used materials. To obtain comparable and reproducible results of experiments conducted in a distributed context, the standardisation and proper documentation of the applied methods is crucial. The European project NanoDiaRA, whose aim is to develop nanoparticles and biomarkers for the early diagnosis of inflammatory disease, faces this situation as it involves 15 European partners and brings together different scientific cultures and professional backgrounds. Protocols especially developed for Superparamagnetic Iron Oxide Nanoparticles and a management system were designed and implemented within the NanoDiaRA project to fulfil those needs. The main goals were the establishment of standardised Standard Operating Procedures assuring transparency and reproducibility and the provision of access to these protocols to every project partner, as well as their clear allocation to carry out precise measurements and production steps

    Environment as a Witness: Selective Proliferation of Information and Emergence of Objectivity in a Quantum Universe

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    We study the role of the information deposited in the environment of an open quantum system in course of the decoherence process. Redundant spreading of information -- the fact that some observables of the system can be independently ``read-off'' from many distinct fragments of the environment -- is investigated as the key to effective objectivity, the essential ingredient of ``classical reality''. This focus on the environment as a communication channel through which observers learn about physical systems underscores importance of quantum Darwinism -- selective proliferation of information about ``the fittest states'' chosen by the dynamics of decoherence at the expense of their superpositions -- as redundancy imposes the existence of preferred observables. We demonstrate that the only observables that can leave multiple imprints in the environment are the familiar pointer observables singled out by environment-induced superselection (einselection) for their predictability. Many independent observers monitoring the environment will therefore agree on properties of the system as they can only learn about preferred observables. In this operational sense, the selective spreading of information leads to appearance of an objective ``classical reality'' from within quantum substrate.Comment: New figures, to appear in PR

    Reaction-induced surface reconstruction of silver in contact with zirconium

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    When two solid metals are in contact at high temperature, interdi usion occurs leading in some cases to the growth of intermetallic compounds. The study of nucleation, growth and properties of these intermetallic compounds are of interest since it can be critical for many applications in industries. Yet, the e ect of these reactions on the initial surfaces of both metals is not well understood and particularly when surfaces are not perfectly flat and for short contact time. The purpose of the present study is to demonstrate that the growth of an intermetallic compound layer between to solid metals can lead to the surface reconstruction of one of them. The silver–zirconium system will be presented in order to illustrate this new phenomenon. The e ect of contact point on the di usion- reaction process has been modelled by patterning the Zr surface. The nucleation and growth of the intermetallic compounds occur along the contact points which leads to silver surface reconstruction with the growth of the preferential crystal planes f 111 g ad f 100 g . A model explaining this new phenomenon is developed based on the minimisation of Gibbs energy and the di usion rates af both Ag & Zr atoms in the binary system Ag / Zr

    Haydeeite: a spin-1/2 kagome ferromagnet

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    The mineral haydeeite, alpha-MgCu3(OD)6Cl2, is a S=1/2 kagome ferromagnet that displays long-range magnetic order below TC=4.2 K with a strongly reduced moment. Our inelastic neutron scattering data show clear spin-wave excitations that are well described by a Heisenberg Hamiltonian with ferromagnetic nearest-neighbor exchange J1=-38 K and antiferromagnetic exchange Jd=+11 K across the hexagons of the kagome lattice. These values place haydeeite very close to the quantum phase transition between ferromagnetic order and non-coplanar twelve-sublattice cuboc2 antiferromagnetic order. Diffuse dynamic short-range ferromagnetic correlations observed above TC persist well into the ferromagnetically ordered phase with a behavior distinct from critical scattering

    Consistent quantum mechanics admits no mereotopology

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    It is standardly assumed in discussions of quantum theory that physical systems can be regarded as having well-defined Hilbert spaces. It is shown here that a Hilbert space can be consistently partitioned only if its components are assumed not to interact. The assumption that physical systems have well-defined Hilbert spaces is, therefore, physically unwarranted.Comment: 10 pages; to appear in Axiomathe

    Аргументация как лингвистический элемент в полемике. Виды аргументов

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    Thermoanaerobacter brockiifermented serine to acetate and ethanol. It oxidized leucine to isovalerate, isoleucine to 2-methylbutyrate, and valine to isobutyrate only in the presence of thiosulfate, or when co-cultured withMethanobacteriumsp. This oxidative deamination was rendered thermodynamically possible by the ability ofT. brockiito reduce thiosulfate to sulfide or the transfer of reducing equivalents to the hydrogenotrophic methanogen. The results suggest thatT. brockiimay be of ecological significance in thermal environments in the turnover of amino acids, especially with thiosulfate or H2-utilizing methanogens are present
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