1,333 research outputs found

    Improving the design and operation of a tweedy dough mixer

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    Compared with other cereals, wheat is special because the dough that it makes, when mixed with water and other ingredients, has the following unique properties: 1. It forms a viscoelastic material. 2. It has good gas retention since the diffusion of gases through the dough is small. 3. It sets when cooked to form a solid foam. In the study of dough rheology, mixing and baking, each of these properties generates the need for different types of mathematical considerations. For the Goodman Fielder problem presented at the 1997 Mathematics-In-Industry Study Group (MISG) meeting at Melbourne University, it is the first of these three properties which plays the crucial role in any study of the efficiency of the mixing of wheat flour dough. The group studied the mechanics associated with the mixing of a large 300 kg dough mass within a Tweedy mixer rotating at 360 rpm subject to a cycle time of 4 minutes and concluded: 1. The baffles along the side of the mixing chamber are essential for the elongation strains necessary for dough development. 2. The impeller blades should have a circular rather than rectangular cross section to reduce the stress concentrations in the viscoelastic dough mass that lead to a cutting rather than stretching motion. 3. A series of experimental tests needs to be performed to study the effects of: baffle geometry; mixing speed; and recirculating motions within the mixing chamber

    Soft parton resummation in the current region of semi-inclusive deep inelastic scattering

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    We discuss resummation of large logarithmic terms that appear in the cross-section of semi-inclusive DIS in the case when the final-state hadron follows the direction of the incoming electroweak vector boson in the c.m. frame of the vector boson and the initial-state proton.Comment: Presented at the 8th International Workshop on Deep Inelastic Scattering (DIS2000), Liverpool, U.K., April 2000; 4 pages, 2 fig

    Stability of NLO Global Analysis and Implications for Hadron Collider Physics

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    The phenomenology of Standard Model and New Physics at hadron colliders depends critically on results from global QCD analysis for parton distribution functions (PDFs). The accuracy of the standard next-to-leading-order (NLO) global analysis, nominally a few percent, is generally well matched to the expected experimental precision. However, serious questions have been raised recently about the stability of the NLO analysis with respect to certain inputs, including the choice of kinematic cuts on the data sets and the parametrization of the gluon distribution. In this paper, we investigate this stability issue systematically within the CTEQ framework. We find that both the PDFs and their physical predictions are stable, well within the few percent level. Further, we have applied the Lagrange Multiplier method to explore the stability of the predicted cross sections for W production at the Tevatron and the LHC, since W production is often proposed as a standard candle for these colliders. We find the NLO predictions on sigma_W to be stable well within their previously-estimated uncertainty ranges.Comment: 24 pages, 11 figures. Minor changes in response to JHEP referee repor

    Early LQT2 Nonsense Mutation Generates N-Terminally Truncated hERG Channels with Altered Gating Properties by the Reinitiation of Translation

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    Mutations in the human ether-a-go-go-related gene (hERG) result in long QT syndrome type 2 (LQT2). The hERG gene encodes a K+ channel that contributes to the repolarization of the cardiac action potential. We have previously shown that hERG mRNA transcripts that contain premature termination codon mutations are rapidly degraded by nonsense-mediated mRNA decay (NMD). In this study, we identified a LQT2 nonsense mutation, Q81X, which escapes degradation by the reinitiation of translation and generates N-terminally truncated channels. RNA analysis of hERG minigenes revealed equivalent levels of wild-type and Q81X mRNA while the mRNA expressed from minigenes containing the LQT2 frameshift mutation, P141fs+2X, was significantly reduced by NMD. Western blot analysis revealed that Q81X minigenes expressed truncated channels. Q81X channels exhibited decreased tail current levels and increased deactivation kinetics compared to wild-type channels. These results are consistent with the disruption of the N-terminus, which is known to regulate hERG deactivation. Site-specificmutagenesis studies showed that translation of the Q81X transcript is reinitiated atMet124 following premature termination. Q81X co-assembled with hERG to form heteromeric channels that exhibited increased deactivation rates compared to wild-type channels. Mutant channels also generated less outward current and transferred less charge at late phases of repolarization during ventricular action potential clamp. These results provide new mechanistic insight into the prolongation of the QT interval in LQT2 patients. Our findings indicate that the reinitiation of translation may be an important pathogenic mechanism in patients with nonsense and frameshift LQT2 mutations near the 5′ end of the hERG gene

    Gene Flow Between Great Lakes Region Populations of the Canadian Tiger Swallowtail Butterfly, \u3ci\u3ePapilio Canadensis\u3c/i\u3e, Near the Hybrid Zone With \u3ci\u3eP. Glaucus\u3c/i\u3e (Lepidoptera: Papilionidae)

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    Papilio canadensis were sampled from three locations on either side of Lake Michigan to study gene flow near and through a butterfly hybrid zone. Allele frequencies at four polymorphic enzyme loci, as indicated by allozyme electrophoresis, were similar in all samples. Values for FST were close to zero, indicating that gene flow is high among these populations, even when separated by Lake Michigan. We developed a mitochondrial DNA marker with diagnostic differences between P. canadensis and its parapatric sister species Papilio glaucus, based on PCR-RFLP. P. glaucus haplotypes of this mtDNA marker and P. glaucus alleles of a diagnostic allozyme locus (PGD) were found in P. canadensis populations sampled in Michigan’s Lower Peninsula but not in the Upper Peninsula or Northern Minnesota. The presence of P. glaucus alleles in P. canadensis populations could be due to introgression through hybridization, or could be remnants of a P. glaucus population that was inundated by an influx of P. canadensis alleles

    Getting DNA twist rigidity from single molecule experiments

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    We use an elastic rod model with contact to study the extension versus rotation diagrams of single supercoiled DNA molecules. We reproduce quantitatively the supercoiling response of overtwisted DNA and, using experimental data, we get an estimation of the effective supercoiling radius and of the twist rigidity of B-DNA. We find that unlike the bending rigidity, the twist rigidity of DNA seems to vary widely with the nature and concentration of the salt buffer in which it is immerged

    Multivariate Fitting and the Error Matrix in Global Analysis of Data

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    When a large body of data from diverse experiments is analyzed using a theoretical model with many parameters, the standard error matrix method and the general tools for evaluating errors may become inadequate. We present an iterative method that significantly improves the reliability of the error matrix calculation. To obtain even better estimates of the uncertainties on predictions of physical observables, we also present a Lagrange multiplier method that explores the entire parameter space and avoids the linear approximations assumed in conventional error propagation calculations. These methods are illustrated by an example from the global analysis of parton distribution functions.Comment: 13 pages, 5 figures, Latex; minor clarifications, fortran program made available; Normalization of Hessian matrix changed to HEP standar
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