3,714 research outputs found

    Experimental investigation of peripheral-wall injection techniques in a water vortex tube

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    Effect of peripheral wall injection technique used to drive water vortex tube on structure and thickness of turbulent mixing region and on flow patterns in boundary layer

    Experimental investigation of radial-inflow vortexes in jet-injection and rotating peripheral-wall water vortex tubes

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    Wall injection area and axial bypass effects on flow pattern of stagnation surface in radial inflow vortexe

    The size of the nucleosome

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    The structural origin of the size of the 11 nm nucleosomal disc is addressed. On the nanometer length-scale the organization of DNA as chromatin in the chromosomes involves a coiling of DNA around the histone core of the nucleosome. We suggest that the size of the nucleosome core particle is dictated by the fulfillment of two criteria: One is optimizing the volume fraction of the DNA double helix; this requirement for close-packing has its root in optimizing atomic and molecular interactions. The other criterion being that of having a zero strain-twist coupling; being a zero-twist structure is a necessity when allowing for transient tensile stresses during the reorganization of DNA, e.g., during the reposition, or sliding, of a nucleosome along the DNA double helix. The mathematical model we apply is based on a tubular description of double helices assuming hard walls. When the base-pairs of the linker-DNA is included the estimate of the size of an ideal nucleosome is in close agreement with the experimental numbers. Interestingly, the size of the nucleosome is shown to be a consequence of intrinsic properties of the DNA double helix.Comment: 11 pages, 5 figures; v2: minor modification

    Hardcore classification: identifying play styles in social games using network analysis

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    In the social network of a web-based online game, all players are not equal. Through network analysis, we show that the community of players in a online social game is an example of a scale free small world network and that the growth of the player-base obeys a power law. The community is centred around a minority group of ``hardcore" players who define the social environment for the game, and without whom the social network would collapse. Methods are discussed for identifying this critically important subset of players automatically through analysing social behaviours within the game

    Panning peptide libraries on filamentous phage

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    1996 Spring.Includes bibliographical references.This Ph.D. project involved using the filamentous phage as a tool to express peptide libraries on its external appendage called the pIII protein. The peptide libraries were designed based on a motif of the honeybee toxin Apamin. Apamin is expressed on the end of the pIII protein and a portion of the apamin section is randomized to produce all possible combinations of amino acids to give a peptide library. The library phage are then panned on a derivatized solid support to determine if any library members have an affinity to a target ligand. The target chosen is a portion of the peptidoglycan layer in bacterial cells called L-lysine-D-alanine-D-alanine. This is the site for binding of the antibiotic vancomycin. Library members that bind to this site should have vancomycin-like activity. This project entailed preparing the libraries, synthesizing the ligand, and derivatizing a variety of solid supports for panning. Many different panning experiments were performed on several libraries and the results are described herein

    Diet-induced obesity impairs mammary development and lactogenesis in murine mammary gland

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    We have developed a mouse model of diet-induced obesity that shows numerous abnormalities relating to mammary gland function. Animals ate 40% more calories when offered a high-fat diet and gained weight at three times the rate of controls. They exhibited reduced conception rates, increased peripartum pup mortality, and impaired lactogenesis. The impairment of lactogenesis involved lipid accumulation in the secretory epithelial cells indicative of an absence of copius milk secretion. Expression of mRNAs for -casein, whey acid protein, and -lactalbumin were all decreased immediately postpartum but recovered as lactation was established over 2–3 days. Expression of acetyl-CoA carboxylase (ACC)- mRNA was also decreased at parturition as was the total enzyme activity, although there was a compensatory increase in the proportion in the active state. By day 10 of lactation, the proportion of ACC in the active state was also decreased in obese animals, indicative of suppression of de novo fatty acid synthesis resulting from the supply of preformed fatty acids in the diet. Although obese animals consumed more calories in the nonpregnant and early pregnant states, they showed a marked depression in fat intake around day 9 of pregnancy before food intake recovered in later pregnancy. Food intake increased dramatically in both lean and obese animals during lactation although total calories consumed were identical in both groups. Thus, despite access to high-energy diets, the obese animals mobilized even more adipose tissue during lactation than their lean counterparts. Obese animals also exhibited marked abnormalities in alveolar development of the mammary gland, which may partially explain the delay in differentiation evident during lactogenesis

    First-principles GW calculations for DNA and RNA nucleobases

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    On the basis of first-principles GW calculations, we study the quasiparticle properties of the guanine, adenine, cytosine, thymine, and uracil DNA and RNA nucleobases. Beyond standard G0W0 calculations, starting from Kohn-Sham eigenstates obtained with (semi)local functionals, a simple self-consistency on the eigenvalues allows to obtain vertical ionization energies and electron affinities within an average 0.11 eV and 0.18 eV error respectively as compared to state-of-the-art coupled-cluster and multi-configurational perturbative quantum chemistry approaches. Further, GW calculations predict the correct \pi -character of the highest occupied state, thanks to several level crossings between density functional and GW calculations. Our study is based on a recent gaussian-basis implementation of GW with explicit treatment of dynamical screening through contour deformation techniques.Comment: 5 pages, 3 figure

    Platelet-Activating Factor-Induced Reduction in Contact Hypersensitivity Responses Is Mediated by Mast Cells via Cyclooxygenase-2-Dependent Mechanisms

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    Platelet-activating factor (PAF) stimulates numerous cell types via activation of the G protein-coupled PAF receptor (PAFR). PAFR activation not only induces acute proinflammatory responses, but it also induces delayed systemic immunosuppressive effects by modulating host immunity. Although enzymatic synthesis and degradation of PAF are tightly regulated, oxidative stressors, such as UVB, chemotherapy, and cigarette smoke, can generate PAF and PAF-like molecules in an unregulated fashion via the oxidation of membrane phospholipids. Recent studies have demonstrated the relevance of the mast cell (MC) PAFR in PAFR-induced systemic immunosuppression. The current study was designed to determine the exact mechanisms and mediators involved in MC PAFR-mediated systemic immunosuppression. By using a contact hypersensitivity model, the MC PAFR was not only found to be necessary, but also sufficient to mediate the immunosuppressive effects of systemic PAF. Furthermore, activation of the MC PAFR induces MC-derived histamine and PGE2 release. Importantly, PAFR-mediated systemic immunosuppression was defective in mice that lacked MCs, or in MC-deficient mice transplanted with histidine decarboxylase- or cyclooxygenase-2-deficient MCs. Lastly, it was found that PGs could modulate MC migration to draining lymph nodes. These results support the hypothesis that MC PAFR activation promotes the immunosuppressive effects of PAF in part through histamine- and PGE2-dependent mechanisms

    Making the Most of Interim Assessment Data: Lessons from Philadelphia

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    Under No Child Left Behind, urban school districts have increasingly turned to interim assessments, administered at regular intervals, to help gauge student progress in advance of annual state exams. These assessments have spawned growing debate among educators, assessment experts, and the testing industry: are they worth the significant investment of money and time? In Making the Most of Interim Assessment Data: Lessons from Philadelphia, Research for Action (RFA) weighs in on this issue. The School District of Philadelphia (SDP) was an early adopter of interim assessments, implementing the exams in 2003. Unlike teachers in some other regions, Philadelphia elementary and middle grades teachers rated these 'Benchmark' assessments highly. However, the study found that enthusiasm did not necessarily correlate with higher rates of student achievement. What did predict student success were three factors -- instructional leadership, collective responsibility, and use of the SDP's Core Curriculum. The report underscores the value of investment in ongoing data interpretation that emphasizes teachers' learning within formal instructional communities, such as grade groups of teachers. This research was funded by the Spencer Foundation and the William Penn Foundation