9,391 research outputs found

    Semileptonic decays of the Higgs boson at the Tevatron

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    We examine the prospects for extending the Tevatron reach for a Standard Model Higgs boson by including the semileptonic Higgs boson decays h --> WW --> l nu jj for M_h >~ 2 M_W, and h --> W jj --> l nu jj for M_h <~ 2 M_W, where j is a hadronic jet. We employ a realistic simulation of the signal and backgrounds using the Sherpa Monte Carlo event generator. We find kinematic selections that enhance the signal over the dominant W+jets background. The resulting sensitivity could be an important addition to ongoing searches, especially in the mass range 120 <~ M_h <~ 150 GeV. The techniques described can be extended to Higgs boson searches at the Large Hadron Collider.Comment: 68 pages, 19 figure

    Frictional resistance of aesthetic orthodontic arch wires compared to traditional arch wires before and after toothbrush abrasion

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    Our objective was to compare frictional resistance evident in aesthetic archwires to traditional (non-aesthetic) archwires. Methods: Archwires ligated with elasatics to fixed brackets were pulled through these brackets while frictional resistance (in lbf) was measured. Results: There were no confirmed significant differences between the frictional resistance of the aesthetic arch wires compared to the traditional non-coated wires for all wire sizes tested Conclusions: Our data suggests that a sacrifice of clinical performance with these aesthetic archwires as compared to traditional archwires is not likel

    The Iodine Satellite (iSAT) Propellant Feed System - Design and Development

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    The development, modeling, and testing of components and subsystems required to feed iodine propellant to a 200-W Hall thruster and cathode are described. This work aims to address design deficiencies and issues associated with the propellant feed system that were revealed by an integrated thruster-cathode-feed system test. The feed system design is modified to use materials that are more resistant to the highly-reactive nature of iodine propellant. Dynamic modeling indicates that the inclusion of additional constraints on feed system tubing will reduce the vibrationally-induced stresses that occur during launch. Full spacecraft thermal modeling show that the feed system heater power levels are sufficient to heat the tank and propellant lines to operating temperatures, where iodine in the tank is sublimed to supply propellant for operation and the tubing is elevated in temperature to keep propellant from redepositing to block the flow. Experiments are conducted to demonstrate that is it possible through the application of heating to clear an iodine deposit blocking the flow. Deposits in the low-pressure portion of the system near the exit to vacuum are shown to be relatively easy to remove in this manner while blockages forming upstream nearer to the higher-pressure propellant tank require significantly more effort to remove. Fluid flow modeling of the feed system is performed, exhibiting some qualitative agreement with experimental data. However, the highly viscous nature of the fluid flow and the dependence of the component flow coefficients on the Reynolds number are likely causes of the generally-poor quantitative agreement between the modeling results and experimentally-measured fluid flow properties

    Vented Chill / No-Vent Fill of Cryogenic Propellant Tanks

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    Architectures for extended duration missions often include an on-orbit replenishment of the space vehicle's cryogenic liquid propellants. Such a replenishment could be accomplished via a tank-to-tank transfer from a dedicated tanker or a more permanent propellant depot storage tank. Minimizing the propellant loss associated with transfer line and receiver propellant tank thermal conditioning is essential for mass savings. A new methodology for conducting tank-to-tank transfer while minimizing such losses has been demonstrated. Charge-Hold-Vent is the traditional methodology for conducting a tank-to-tank propellant transfer. A small amount of cryogenic liquid is introduced to chill the transfer line and propellant tank. As the propellant absorbs heat and undergoes a phase change, the tank internal pressure increases. The tank is then vented to relieve pressure prior to another charge of cryogenic liquid being introduced. This cycle is repeated until the transfer lines and tank are sufficiently chilled and the replenishment of the propellant tank is complete. This method suffers inefficiencies due to multiple chill and vent cycles within the transfer lines and associated feed system components. Additionally, this system requires precise measuring of cryogenic fluid delivery for each transfer, multiple valve cycling events, and other complexities associated with cycled operations. To minimize propellant loss and greatly simplify on-orbit operations, an alternate methodology has been designed and demonstrated. The Vented Chill / No Vent Fill method is a simpler, constant flow approach in which the propellant tank and transfer lines are only chilled once. The receiver tank is continuously vented as cryogenic liquid chills the transfer lines, tank mass and ullage space. Once chilled sufficiently, the receiver tank valve is closed and the tank is completely filled. Interestingly, the vent valve can be closed prior to receiver tank components reaching liquid saturation temperature. An incomplete fill results if insufficient energy is removed from the tank's thermal mass and ullage space. The key to successfully conducting the no vent fill is to assure that sufficient energy is removed from the system prior to closing the receiver tank vent valve. This paper will provide a description of the transfer methodology and test article, and will provide a discussion of test results

    Ventricular endocardial tissue geometry affects stimulus threshold and effective refractory period

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    Background: Understanding the biophysical processes by which electrical stimuli applied to cardiac tissue may result in local activation is important in both the experimental and clinical electrophysiology laboratory environments, as well as for gaining a more in-depth knowledge of the mechanisms of focal-trigger-induced arrhythmias. Previous computational models have predicted that local myocardial tissue architecture alone may significantly modulate tissue excitability, affecting both the local stimulus current required to excite the tissue and the local effective refractory period (ERP). In this work, we present experimental validation of this structural modulation of local tissue excitability on the endocardial tissue surface, use computational models to provide mechanistic understanding of this phenomena in relation to localized changes in electrotonic loading, and demonstrate its implications for the capture of afterdepolarizations. Methods and Results: Experiments on rabbit ventricular wedge preparations showed that endocardial ridges (surfaces of negative mean curvature) had a stimulus capture threshold that was 0.21 ± 0.03 V less than endocardial grooves (surfaces of positive mean curvature) for pairwise comparison (24% reduction, corresponding to 56.2 ± 6.4% of the energy). When stimulated at the minimal stimulus strength for capture, ridge locations showed a shorter ERP than grooves (n = 6, mean pairwise difference 7.4 ± 4.2 ms). When each site was stimulated with identical-strength stimuli, the difference in ERP was further increased (mean pairwise difference 15.8 ± 5.3 ms). Computational bidomain models of highly idealized cylindrical endocardial structures qualitatively agreed with these findings, showing that such changes in excitability are driven by structural modulation in electrotonic loading, quantifying this relationship as a function of surface curvature. Simulations further showed that capture of delayed afterdepolarizations was more likely in trabecular ridges than grooves, driven by this difference in loading. Conclusions: We have demonstrated experimentally and explained mechanistically in computer simulations that the ability to capture tissue on the endocardial surface depends upon the local tissue architecture. These findings have important implications for deepening our understanding of excitability differences related to anatomical structure during stimulus application that may have important applications in the translation of novel experimental optogenetics pacing strategies. The uncovered preferential vulnerability to capture of afterdepolarizations of endocardial ridges, compared to grooves, provides important insight for understanding the mechanisms of focal-trigger-induced arrhythmias

    Tumour necrosis factor-stimulated gene (TSG)-6-mediated interactions with the inter-alpha-inhibitor heavy chain 5 facilitate TGF beta1-dependent fibroblast to myofibroblast differentiation.

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    Fibroblasts are central to wound healing and fibrosis through Transforming Growth Factor-beta (TGF-beta1)-triggered differentiation into contractile, alpha_smooth muscle actin (alpha_sma)-positive myofibroblasts. This is mediated by accumulation of a pericellular matrix of hyaluronan (HA) and the HA-dependent co-localisation of CD44 with the Epidermal Growth Factor Receptor (EGFR). Interactions of HA with hyaladherins, such as Inter-alpha-Inhibitor (IalphaI) and Tumour Necrosis Factor-stimulated gene_6 (TSG_6) are also essential for differentiation. This study investigated the mechanisms involved. TSG6 and alpha_sma had different kinetics of induction by TGFbeta1, with TSG6 peaking before alphasma. siCD44 or EGFR inhibition prevented differentiation but had no effect on TSG-6 expression. TSG-6 was essential for differentiation, and mAb A38 (preventing IalphaI heavy chain [HC] transfer), HA-oligosaccharides, Cobalt, or siBikunin prevented TSG-6 activity, preventing differentiation. A38 also prevented the EGFR/CD44 association. This suggested that TSG6/IalphaI HC interaction was necessary for the effect of TSG-6 and that HC-stabilisation of HA initiated the CD44/EGF-R association. The newly-described HC5 was shown to be the principal HC expressed and its cell surface expression was prevented by siRNA inhibition of TSG6 or Bikunin. HC5 was released by hyaluronidase treatment, confirming its association with cell surface HA. Finally, HC5 knock down by siRNA confirmed its role in myofibroblast differentiation. The current study describes a novel mechanism linking the TSG-6 transfer of the newly-described HC5 to the HA-dependent control of cell phenotype. The interaction of HC5 with cell surface HA was essential for TGFbeta1-dependent differentiation of fibroblasts to myofibroblasts, highlighting its importance as a novel potential therapeutic target

    Viscoelasticity near the gel-point: a molecular dynamics study

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    We report on extensive molecular dynamics simulations on systems of soft spheres of functionality f, i.e. particles that are capable of bonding irreversibly with a maximum of f other particles. These bonds are randomly distributed throughout the system and imposed with probability p. At a critical concentration of bonds, p_c approximately equal to 0.2488 for f=6, a gel is formed and the shear viscosity \eta diverges according to \eta ~ (p_c-p)^{-s}. We find s is approximately 0.7 in agreement with some experiments and with a recent theoretical prediction based on Rouse dynamics of phantom chains. The diffusion constant decreases as the gel point is approached but does not display a well-defined power law.Comment: 4 pages, 4 figure

    Selection criteria for immediate implant placement and immediate loading for single tooth replacement in the maxillary esthetic zone: A systematic review and meta-analysis.

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    OBJECTIVES The aim of this study was to review available evidence for Type 1A (immediate implant placement and immediate loading) of single tooth replacement in the maxillary esthetic zone. MATERIALS AND METHODS An electronic search was conducted utilizing the databases of MEDLINE, Embase, and Cochrane to identify publications reporting on the outcomes of Type 1A for single tooth replacement in the maxillary esthetic zone. The success and survival rates of the included articles were reported, which were further categorized according to the clinical criteria reported in Type 1A. Mean survival rates were univariately compared between risk groups and additionally between studies published before and since 2012 using bias-corrected and study size-weighed bootstrap tests. A study time-correcting meta-analysis was then performed to obtain an overall effect for the study pool. RESULTS A total of 3118 publications were identified in the search, with a total of 68 articles included. A mean number of implants per study were 37.2 and mean follow-up was 2.8 years. All the included studies utilizing Type 1A report highly selective inclusion and exclusion criteria. Univariate risk group comparison determined that studies before 2012 report a significantly lower mean survival rate (difference of -1.9 percentage points [PP], 95% CI: [-0.3, -4.0], p = .02), facial gap dimension had an impact on survival rates (+3.1 PP [0.2, 5.3] for width >2 mm, p = .04), as well as presence of endodontic infection (+2.6 PP [0.9, 5.1], p = .004). CONCLUSIONS Type 1A has a high survival rate in studies reporting strict patient and site selection criteria. Further research is required to assess esthetic and functional success with Type 1A treatments
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