1,540 research outputs found

    Confinement and the Pion Nucleon Sigma Term

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    Gribov's theory of confinement offers a simple explanaton of the value of the pion nucleon sigma term. There is no need to invoke a large strange quark component in the nucleon.Comment: 4 pages, Cavendish HEP 93/

    Structure of the nucleon in chiral perturbation theory

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    We discuss a renormalization scheme for relativistic baryon chiral perturbation theory which provides a simple and consistent power counting for renormalized diagrams. The method involves finite subtractions of dimensionally regularized diagrams beyond the standard modified minimal subtraction scheme of chiral perturbation theory to remove contributions violating the power counting. This is achieved by a suitable renormalization of the parameters of the most general effective Lagrangian. As applications we discuss the mass of the nucleon, the σ\sigma term, and the scalar and electromagnetic form factors.Comment: Invited talk given by S. Scherer at the Fourth International Conference on Perspectives in Hadronic Physics, Trieste, Italy, 12 -16 May 2003, 8 pages, 7 figure

    The Human Touch

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    Biting insects, inaccessible terrain, impenetrable bamboo thickets and thorn bushes. Mine clearance in Cambodia is a hot, sweaty business at the best of times. Because tripwires hidden in the undergrowth could trigger explosions, the vegetation has to be cleared by hand before mine detection can start. It is a tedious matter and can occupy two-thirds of a mine clearer\u27s working day

    Developing New Technology for Humanitarian Demining

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    Despite the spending of hundreds of millions of dollars on high-tech research over the last few years, local humanitarian deminers still use traditional prodders and metal detectors. The biggest recent technical innovation has been mechanical vegetation clearance which was mostly developed in the field and bypassed the research route

    Virtual Machine and Code Generator for PLC-Systems

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    In the programming of PLC-Systems (PLC = Programmable Logic Controller) in building automation there were no vital changes over the past few years. Most users of PLC-Systems in building automation do the programming in FBD (functional block diagram). The users always start their projects with the programming of the PLC software. After that the HMI (Human Machine Interface) or the SCADA-System (Supervisory Control And Data Acquisition) are added as subsequent Tasks. Programming tools like CoDeSys build on this bottom up approach. Most of the time the user has to cope with different tools for the different tasks and the programming tools are built for a specific hardware. Almost every PLC manufacturer has its own implementation of the IEC 61131 standard with various interpretations. So a change of hardware means that the programming tool, the way how to program the PLC-System, the HMI tool and the SCADA tool changes. The interfaces between the tools are sometimes pretty clumsy and software, generated with these tools, is often not easily transferred to the PLC-System of another PLC-System manufacturer. This investigation proposes a top down approach to a project. For the first time the starting point of a project will be the plant diagram. The programming will be intuitively done in the plant diagram. Template objects (e.g. for pumps) created with the object orientated paradigm will be used to accomplish this task. The created PLC software will run in a virtual machine on the PLC-System and thus will be reusable on PLC-Systems of different manufacturers, which will eliminate the dependency on certain hardware. The merging together of SCADA, HMI development and PLC programming will lead to a more natural way in programming PLC-Systems. In a first step the user draws his plant diagram with template objects (TO) and afterwards binds the template objects on the plant diagram together. With this approach the user only has to cope with a single software tool. The independency from the PLC hardware will be an additional alleviation for the user. The aim of the investigation is to determine the realisability of a generic SCADA-System FBD programming language, a virtual machine and a code generator for PLC-Systems

    Unmet Needs in Dystonia:Genetics and Molecular Biology-How Many Dystonias?

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    Genetic findings of the past years have provided ample evidence for a substantial etiologic heterogeneity of dystonic syndromes. While an increasing number of genes are being identified for Mendelian forms of isolated and combined dystonias using classical genetic mapping and whole-exome sequencing techniques, their precise role in the molecular pathogenesis is still largely unknown. Also, the role of genetic risk factors in the etiology of sporadic dystonias is still enigmatic. Only the systematic ascertainment and precise clinical characterization of very large cohorts with dystonia, combined with systematic genetic studies, will be able to unravel the complex network of factors that determine disease risk and phenotypic expression

    pi(-)p atom in ChPT: strong energy-level shift

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    The general formula of the pi(-)p atom strong energy-level shift in the 1s state is derived in the next-to-leading order in the isospin breaking, and in all orders in chiral expansion. Isospin-breaking corrections to the level shift are explicitly evaluated at order p^2 in ChPT. The results clearly demonstrate the necessity to critically reaccess the values of the piN scattering lengths, extracted from the energy-level shift measurement by means of the potential model-based theoretical analysis.Comment: 16 pages, LaTeX-file, 1 Figur

    Growth description for vessel wall adaptation: a thick-walled mixture model of abdominal aortic aneurysm evolution

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    (1) Background: Vascular tissue seems to adapt towards stable homeostatic mechanical conditions, however, failure of reaching homeostasis may result in pathologies. Current vascular tissue adaptation models use many ad hoc assumptions, the implications of which are far from being fully understood; (2) Methods: The present study investigates the plausibility of different growth kinematics in modeling Abdominal Aortic Aneurysm (AAA) evolution in time. A structurally motivated constitutive description for the vessel wall is coupled to multi-constituent tissue growth descriptions; Constituent deposition preserved either the constituent’s density or its volume, and Isotropic Volume Growth (IVG), in-Plane Volume Growth (PVG), in-Thickness Volume Growth (TVG) and No Volume Growth (NVG) describe the kinematics of the growing vessel wall. The sensitivity of key modeling parameters is explored, and predictions are assessed for their plausibility; (3) Results: AAA development based on TVG and NVG kinematics provided not only quantitatively, but also qualitatively different results compared to IVG and PVG kinematics. Specifically, for IVG and PVG kinematics, increasing collagen mass production accelerated AAA expansion which seems counterintuitive. In addition, TVG and NVG kinematics showed less sensitivity to the initial constituent volume fractions, than predictions based on IVG and PVG; (4) Conclusions: The choice of tissue growth kinematics is of crucial importance when modeling AAA growth. Much more interdisciplinary experimental work is required to develop and validate vascular tissue adaption models, before such models can be of any practical use

    Recent results on nucleon sigma terms in lattice QCD

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    It has proven a significant challenge to experiment and phenomenology to extract precise values of the nucleon sigma terms. This difficulty opens the window for lattice QCD simulations to lead the field in resolving this aspect of nucleon structure. Here we report on recent advances in the extraction of nucleon sigma terms in lattice QCD. In particular, the strangeness component is now being resolved to a precision that far surpasses best phenomenological estimates.Comment: 6 pages, 1 figure; prepared for Proc. 4th Int Symposium on Symmetries in Subatomic Physics (SSP2009), Taipei, Taiwan, June 2-5 200