58,822 research outputs found

    A More Precise Extraction of |V_{cb}| in HQEFT of QCD

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    The more precise extraction for the CKM matrix element |V_{cb}| in the heavy quark effective field theory (HQEFT) of QCD is studied from both exclusive and inclusive semileptonic B decays. The values of relevant nonperturbative parameters up to order 1/m^2_Q are estimated consistently in HQEFT of QCD. Using the most recent experimental data for B decay rates, |V_{cb}| is updated to be |V_{cb}| = 0.0395 \pm 0.0011_{exp} \pm 0.0019_{th} from B\to D^{\ast} l \nu decay and |V_{cb}| = 0.0434 \pm 0.0041_{exp} \pm 0.0020_{th} from B\to D l \nu decay as well as |V_{cb}| = 0.0394 \pm 0.0010_{exp} \pm 0.0014_{th} from inclusive B\to X_c l \nu decay.Comment: 7 pages, revtex, 4 figure

    Tribo-corrosion properties of cobalt-based medical implant alloys in simulated biological environments

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    Tribological problems and corrosion degradation have been recognized as essential risks for total joint replacements, especially for all-metal arthroplasty. Few studies have focused on the interactions between tribology and corrosion (tribocorrosion) for implant materials. This paper addresses the importance of understanding tribocorrosion and the evaluation of such materials in simulated biological environments. Due to the complex effect of proteins on tribocorrosion, which has been demonstrated in previous studies, this study focuses towards understanding the effects of amino acids as aspects of material degradation. Dulbecco’s Modified Eagle’s Medium (DMEM) is a cell culture solution. It contains comparable amount and types of amino acids to normal synovial fluid in human joints. 0.36% NaCl solution was employed to isolate the biological species. Three materials were tested; High carbon (HC) CoCrMo (contains 0.19% carbon), low carbon (LC) CoCrMo (widely used materials for total joint replacement) and stainless steel UNS S31603 (316L). Integrated electrochemical tests supported by measurement of friction and near surface chemical analysis were carried out to enable their tribocorrosion behaviour to be fully characterized. As a general conclusion, amino acids were found to react with materials under tribological contacts and form complex organometallic/oxides which lubricate the metallic sample surface. Tribocorrosion plays a very important role in material degradation in the studied environments. HC CoCrMo shows superior wear, corrosion and tribocorrosion resistance – the material characteristics and their effect on the different tribocorrosion processes are discussed

    Synovial joint lubrication – does nature teach more effective engineering lubrication strategies?

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    Nature shows numerous examples of systems which show energy efficiency, elegance in their design and optimum use of materials. Biomimetics is an emerging field of research in engineering and successes have been documented in the diverse fields of robotics, mechanics, materials engineering and many more. To date little biomimetics research has been directed towards tribology in terms of transferring technologies from biological systems into engineering applications. The potential for biomimicry has been recognised in terms of replicating natural lubricants but this system reviews the potential for mimicking the synovial joint as an efficient and durable tribological system for potential engineering systems. The use of materials and the integration of materials technology and fluid/surface interactions are central to the discussion

    |V_ub| and |V_cb|, Charm Counting and Lifetime Differences in Inclusive Bottom Hadron Decays

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    Inclusive bottom hadron decays are analyzed based on the heavy quark effective field theory (HQEFT). Special attentions in this paper are paid to the b\to u transitions and nonspectator effects. As a consequence, the CKM quark mixing matrix elements |V_ub| and |V_cb| are reliably extracted from the inclusive semileptonic decays B\to X_u e \nu and B\to X_c e \nu. Various observables, such as the semileptonic branch ratio B_SL, the lifetime differences among B^-, B^0, B_s and \Lambda_b hadrons, the charm counting n_c, are predicted and found to be consistent with the present experimental data.Comment: 20 pages, Revtex, 4 figures and 2 table

    Lifetime Difference and Endpoint effect in the Inclusive Bottom Hadron Decays

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    The lifetime differences of bottom hadrons are known to be properly explained within the framework of heavy quark effective field theory(HQEFT) of QCD via the inverse expansion of the dressed heavy quark mass. In general, the spectrum around the endpoint region is not well behaved due to the invalidity of 1/mQ1/m_Q expansion near the endpoint. The curve fitting method is adopted to treat the endpoint behavior. It turns out that the endpoint effects are truly small and the explanation on the lifetime differences in the HQEFT of QCD is then well justified. The inclusion of the endpoint effects makes the prediction on the lifetime differences and the extraction on the CKM matrix element Vcb|V_{cb}| more reliable.Comment: 11 pages, Revtex, 10 figures, 6 tables, published versio