376 research outputs found

    Task 4 supporting technology. Part 1: Detailed test plan for leading edge tile development. Leading edge material development and testing

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    This task develops two alternative candidate tile materials for leading edge applications: coated alumina enhanced thermal barrier (AETB) tile and silicone impregnated reusable ceramic ablator (SIRCA) tile. Upon reentry of the X-33/RLV space vehicle, the leading edges experience the highest heating rates and temperatures. The wing leading edge and nose cap experience peak temperatures in the range 2000 to 2700 F. Replacing reinforced carbon-carbon (RCC) with tile-based thermal protection system (TPS) materials is the primary objective. Weight, complexity, coating impact damage, and repairability are among the problems that this tile technology development addresses. The following subtasks will be performed in this development effort: tile coating development; SIRCA tile development; robustness testing of tiles; tile repair development; tile operations/processing; tile leading edge configuration; and life cycle testing

    Special Moduli of Continuity and the Constant in the Jackson-Stechkin Theorem

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    We consider a special 2k-order modulus of continuity W 2k(f,h) of 2π-periodic continuous functions and prove an analog of the Bernstein-Nikolsky-Stechkin inequality for trigonometric polynomials in terms of W 2k. We simplify the main construction from the paper by Foucart et al. (Constr. Approx. 29(2), 157-179, 2009) and give new upper estimates of the Jackson-Stechkin constants. The inequality W2k(f,h)≤3∥f∥∞ and the Bernstein-Nikolsky-Stechkin type estimate imply the Jackson-Stechkin theorem with nearly optimal constant for approximation by periodic splines. © 2013 The Author(s)

    Inverted and horizontal impacted third molars in an Early Modern skull from Wroclaw, Poland: a case report

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    Background: An impacted tooth is one of the most commonly occurring dental anomalies, although some types of impaction (i.e. inverted angulation) may be considered rare finding. There are many hypotheses regarding impaction aetiology. One of the most popular hypotheses suggested that this condition may result from insufficient space in retromolar space, other: improper angulation of tooth bud, malposition of the tooth germ or hereditary factors, insufficient interproximal attrition, ectopy or dysfunction of genes necessary for proper tooth eruption. This study aims to present the odontological and paleopathological assessment of the impacted molars observed within the skull excavated from an early modern cemetery in Wroclaw.  Materials and methods: The skull used in the study was complete and in a good state of preservation. It belonged to an adult individual whose body was buried at the former Salvator Cemetery (currently Czysty Square). The individual’s dentition was almost completely lost antemortem. Only second molars preserved within the maxillae (bilaterally) and the mandible was almost edentulous as well. The morphometric traits have been taken according to standards established by R. Martin. Macroscopic observations were supported by X-rays and computed tomography imaging.  Results: The age at death was estimated at 20–35 years. Comparison of the metric characteristics of skull with the reference material reveals that it is much smaller than the average female skull from this series. Morphometric indices calculated for both splanchocranium and neurocranium allow defining the skull and jaw as short, which could be an important factor involved in the teeth impaction.  Conclusions: Atypical impaction of the third molars could result from small size of skull and could have significantly deteriorated the quality of life of the individual.

    Why Wait?: Early Enteral Feeding After Pediatric Gastrostomy Tube Placement

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    Purpose Early initiation of feedings after gastrostomy tube (GT) placement may reduce associated hospital costs, but many surgeons fear complications could result from earlier feeds. We hypothesized that, irrespective of placement method, starting feedings within the first 6 h following GT placement would not result in a greater number of post-operative complications. Methods An IRB-approved retrospective review of all GTs placed between January 2012 and December 2014 at three academic institutions was undertaken. Data was stratified by placement method and whether the patient was initiated on feeds at less than 6 h or after. Baseline demographics, operative variables, post-operative management and complications were analyzed. Descriptive statistics were used and P-values < 0.05 were considered significant. Results One thousand and forty-eight patients met inclusion criteria. GTs were inserted endoscopically (48.9%), laparoscopically (44.9%), or via an open approach (6.2%). Demographics were similar in early and late fed groups. When controlling for method of placement, those patients who were fed within the first 6 h after gastrostomy placement had shorter lengths of stay compared to those fed greater than 6 h after placement (P < 0.05). Total post-operative outcomes were equivalent between feeding groups for all methods of placement (laparoscopic (P = 0.87), PEG (P = 0.94), open (P = 0.81)). Conclusions Early initiation of feedings following GT placement was not associated with an increase in complications. Feeds initiated earlier may shorten hospital stays and decrease overall hospital costs

    Gamma-ray observations of Tycho's SNR with VERITAS and Fermi

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    High-energy gamma-ray emission from supernova remnants (SNRs) has provided a unique perspective for studies of Galactic cosmic-ray acceleration. Tycho's SNR is a particularly good target because it is a young, type Ia SNR that is well-studied over a wide range of energies and located in a relatively clean environment. Since the detection of gamma-ray emission from Tycho's SNR by VERITAS and Fermi-LAT, there have been several theoretical models proposed to explain its broadband emission and high-energy morphology. We report on an update to the gamma-ray measurements of Tycho's SNR with 147 hours of VERITAS and 84 months of Fermi-LAT observations, which represents about a factor of two increase in exposure over previously published data. About half of the VERITAS data benefited from a camera upgrade, which has made it possible to extend the TeV measurements toward lower energies. The TeV spectral index measured by VERITAS is consistent with previous results, but the expanded energy range softens a straight power-law fit. At energies higher than 400 GeV, the power-law index is 2.92±0.42stat±0.20sys2.92 \pm 0.42_{\mathrm{stat}} \pm 0.20_{\mathrm{sys}}. It is also softer than the spectral index in the GeV energy range, 2.14±0.09stat±0.02sys2.14 \pm 0.09_{\mathrm{stat}} \pm 0.02_{\mathrm{sys}}, measured by this study using Fermi--LAT data. The centroid position of the gamma-ray emission is coincident with the center of the remnant, as well as with the centroid measurement of Fermi--LAT above 1 GeV. The results are consistent with an SNR shell origin of the emission, as many models assume. The updated spectrum points to a lower maximum particle energy than has been suggested previously.Comment: Accepted for publication in The Astrophysical Journa
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