4,123 research outputs found
Improved limits on photon velocity oscillations
The mixing of the photon with a hypothetical sterile paraphotonic state would
have consequences on the cosmological propagation of photons. The absence of
distortions in the optical spectrum of distant Type Ia supernov\ae allows to
extend by two orders of magnitude the previous limit on the Lorentz-violating
parameter associated to the photon-paraphoton transition, extracted
from the abscence of distortions in the spectrum of the cosmic microwave
background. The new limit is consistent with the interpretation of the dimming
of distant Type Ia supernov\ae as a consequence of a nonzero cosmological
constant. Observations of gamma-rays from active galactic nuclei allow to
further extend the limit on by ten orders of magnitude.Comment: 10 pages, 4 Postscript figures, use epsfig, amssym
The Histone 3'-Terminal Stem-Loop-Binding Protein Enhances Translation through a Functional and Physical Interaction with Eukaryotic Initiation Factor 4G (eIF4G) and eIF3
Metazoan cell cycle-regulated histone mRNAs are unique cellular mRNAs in that they terminate in a highly conserved stem-loop structure instead of a poly(A) tail. Not only is the stem-loop structure necessary for 3'-end formation but it regulates the stability and translational efficiency of histone mRNAs. The histone stem-loop structure is recognized by the stem-loop-binding protein (SLBP), which is required for the regulation of mRNA processing and turnover. In this study, we show that SLBP is required for the translation of mRNAs containing the histone stem-loop structure. Moreover, we show that the translation of mRNAs ending in the histone stem-loop is stimulated in Saccharomyces cerevisiae cells expressing mammalian SLBP. The translational function of SLBP genetically required eukaryotic initiation factor 4E (eIF4E), eIF4G, and eIF3, and expressed SLBP coisolated with S. cerevisiae initiation factor complexes that bound the 5' cap in a manner dependent on eIF4G and eIF3. Furthermore, eIF4G coimmunoprecipitated with endogenous SLBP in mammalian cell extracts and recombinant SLBP and eIF4G coisolated. These data indicate that SLBP stimulates the translation of histone mRNAs through a functional interaction with both the mRNA stem-loop and the 5' cap that is mediated by eIF4G and eIF3
Higher-order conservative interpolation between control-volume meshes: Application to advection and multiphase flow problems with dynamic mesh adaptivity
© 2016 .A general, higher-order, conservative and bounded interpolation for the dynamic and adaptive meshing of control-volume fields dual to continuous and discontinuous finite element representations is presented. Existing techniques such as node-wise interpolation are not conservative and do not readily generalise to discontinuous fields, whilst conservative methods such as Grandy interpolation are often too diffusive. The new method uses control-volume Galerkin projection to interpolate between control-volume fields. Bounded solutions are ensured by using a post-interpolation diffusive correction. Example applications of the method to interface capturing during advection and also to the modelling of multiphase porous media flow are presented to demonstrate the generality and robustness of the approach
Maximum velocities in flexion and extension actions for sport
Speed of movement is fundamental to the outcome of many human actions. A variety of techniques can be
implemented in order to maximise movement speed depending on the goal of the movement, constraints, and the time
available. Knowing maximum movement velocities is therefore useful for developing movement strategies but also as
input into muscle models. The aim of this study was to determine maximum flexion and extension velocities about the
major joints in upper and lower limbs. Seven university to international level male competitors performed
flexion/extension at each of the major joints in the upper and lower limbs under three conditions: isolated; isolated with
a countermovement; involvement of proximal segments. 500 Hz planar high speed video was used to calculate
velocities. The highest angular velocities in the upper and lower limb were 50.0 rad·s-1 and 28.4 rad·s-1, at the wrist
and knee, respectively. As was true for most joints, these were achieved with the involvement of proximal segments,
however, ANOVA analysis showed few significant differences (p<0.05) between conditions. Different segment masses,
structures and locations produced differing results, in the upper and lower limbs, highlighting the requirement of
segment specific strategies for maximal movements
Photometry of supernovae in an image series : methods and application to the Supernova Legacy Survey (SNLS)
We present a technique to measure lightcurves of time-variable point sources
on a spatially structured background from imaging data. The technique was
developed to measure light curves of SNLS supernovae in order to infer their
distances. This photometry technique performs simultaneous PSF photometry at
the same sky position on an image series. We describe two implementations of
the method: one that resamples images before measuring fluxes, and one which
does not. In both instances, we sketch the key algorithms involved and present
the validation using semi-artificial sources introduced in real images in order
to assess the accuracy of the supernova flux measurements relative to that of
surrounding stars. We describe the methods required to anchor these PSF fluxes
to calibrated aperture catalogs, in order to derive SN magnitudes. We find a
marginally significant bias of 2 mmag of the after-resampling method, and no
bias at the mmag accuracy for the non-resampling method. Given surrounding star
magnitudes, we determine the systematic uncertainty of SN magnitudes to be less
than 1.5 mmag, which represents about one third of the current photometric
calibration uncertainty affecting SN measurements. The SN photometry delivers
several by-products: bright star PSF flux mea- surements which have a
repeatability of about 0.6%, as for aperture measurements; we measure relative
astrometric positions with a noise floor of 2.4 mas for a single-image bright
star measurement; we show that in all bands of the MegaCam instrument, stars
exhibit a profile linearly broadening with flux by about 0.5% over the whole
brightness range.Comment: Accepted for publication in A&A. 20 page
Sex adjusted standardized prevalence ratios for celiac disease and other autoimmune diseases in patients with postural orthostatic tachycardia syndrome (POTS) : a systematic review and meta-analysis
Standardised sex-adjusted prevalence ratios (SSPRs) have not been published for any autoimmune diseases (ADs) in patients with Postural Orthostatic Tachycardia Syndrome (POTS), who are predominantly young females. We performed a systematic review according to PRISMA guidelines of POTS cohorts reporting the prevalence of at least one AD. Only four studies were found: two providing data on celiac disease; and two with data on ‘any AD’, Hashimoto’s thyroiditis, rheumatoid arthritis, systemic lupus erythematosus (SLE), Sjogren ¨ ’s syndrome and celiac disease and (one study) antiphospholipid syndrome. All studies were assessed as being at high risk of bias for estimating AD prevalence in POTS patients, with under-reporting of ADs likely due to the lack of rigorous prospective screening for ADs. A literature search found a ‘gold standard’ general population (GP) comparator only for celiac disease in the United States, leading to a pooled SSPR in POTS patients of 2.75 with 95% confidence interval (1.06–4.40). The lack of recent high-quality studies on GP prevalence for the other ADs was noteworthy. Exploratory pooled SSPRs were calculated for ‘any AD’ and for the other five ADs using GP comparator data from a comprehensive review. All pooled SSPRs were greater than one and statistically significant, implying a higher prevalence of these ADs, and any AD, in POTS patients. The magnitude of the exploratory SSPRs was very large for SLE, Sjogren ¨ ’s syndrome and antiphospholipid syndrome, perhaps reflecting the use of non-gold standard GP comparators, which may underestimate AD prevalence. Further research in a large POTS cohort with an appropriately age- and sex-matched GP control group is recommended, to confirm the SSPR for celiac disease and to determine whether SLE, Sjogren’s syndrome and antiphospholipid syndrome are indeed many times more prevalent in POTS patients than in the GP. The findings are consistent with POTS itself being an AD
Productive tensions - engaging geography students in participatory action research with communities
ArticleCopyright © 2013 copyright Taylor & Francis.This study discusses the benefits and challenges of an undergraduate module on participatory geographies, involving students in co-producing research with community partners. The module challenges the knowledge production model predominant in Geography curricula. We argue that it develops students' skills and understanding through engaging them intellectually, socially and emotionally outside the university. As a student, two community partners and a professor, we offer our perspectives on the opportunities and conflicts that arose. We do not gloss over tensions in achieving the module's diverse aims, but suggest that these are productive for teaching, learning, research and the needs of community organizations
Two-dimensional evaluation of atham-fluidity, a nonhydrostatic atmospheric model using mixed continuous/discontinuous finite elements and anisotropic grid optimization
AbstractThis paper presents the first attempt to apply the compressible nonhydrostatic Active Tracer High-Resolution Atmospheric Model–Fluidity (ATHAM-Fluidity) solver to a series of idealized atmospheric test cases. ATHAM-Fluidity uses a hybrid finite-element discretization where pressure is solved on a continuous second-order grid while momentum and scalars are computed on a first-order discontinuous grid (also known as ). ATHAM-Fluidity operates on two- and three-dimensional unstructured meshes, using triangular or tetrahedral elements, respectively, with the possibility to employ an anisotropic mesh optimization algorithm for automatic grid refinement and coarsening during run time. The solver is evaluated using two-dimensional-only dry idealized test cases covering a wide range of atmospheric applications. The first three cases, representative of atmospheric convection, reveal the ability of ATHAM-Fluidity to accurately simulate the evolution of large-scale flow features in neutral atmospheres at rest. Grid convergence without adaptivity as well as the performances of the Hermite–Weighted Essentially Nonoscillatory (Hermite-WENO) slope limiter are discussed. These cases are also used to test the grid optimization algorithm implemented in ATHAM-Fluidity. Adaptivity can result in up to a sixfold decrease in computational time and a fivefold decrease in total element number for the same finest resolution. However, substantial discrepancies are found between the uniform and adapted grid results, thus suggesting the necessity to improve the reliability of the approach. In the last three cases, corresponding to atmospheric gravity waves with and without orography, the model ability to capture the amplitude and propagation of weak stationary waves is demonstrated. This work constitutes the first step toward the development of a new comprehensive limited area atmospheric model.This research has received funding from the European Union Seventh Framework Program (FP7/2007-2013) under Grant agreement 603663 for the research project PEARL (Preparing for Extreme And Rare events in coastaL regions). The EPSRC multiphase program grant MEMPHIS is also acknowledged.This is the author accepted manuscript. The final version is available from the American Meteorological Society via http://dx.doi.org/10.1175/MWR-D-15-0398.
Self-consistent modelling of hot plasmas within non-extensive Tsallis' thermostatistics
A study of the effects of non-extensivity on the modelling of atomic physics
in hot dense plasmas is proposed within Tsallis' statistics. The electronic
structure of the plasma is calculated through an average-atom model based on
the minimization of the non-extensive free energy.Comment: submitted to "Eur. Phys. J. D
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