3,138 research outputs found
On the iterated Crank-Nicolson for hyperbolic and parabolic equations in numerical relativity
The iterated Crank-Nicolson is a predictor-corrector algorithm commonly used
in numerical relativity for the solution of both hyperbolic and parabolic
partial differential equations. We here extend the recent work on the stability
of this scheme for hyperbolic equations by investigating the properties when
the average between the predicted and corrected values is made with unequal
weights and when the scheme is applied to a parabolic equation. We also propose
a variant of the scheme in which the coefficients in the averages are swapped
between two corrections leading to systematically larger amplification factors
and to a smaller numerical dispersion.Comment: 7 pages, 3 figure
Non cell autonomous upregulation of CDKN2 transcription linked to progression of chronic hepatitis C disease
Chronic hepatitis C virus infection (C-HC) is associated with higher mortality arising from hepatic and extrahepatic disease. This may be due to accelerated biological aging; however, studies in C-HC have thus far been based solely on telomere length as a biomarker of aging (BoA). In this study, we have evaluated CDKN2 locus transcripts as alternative BoAs in C-HC. Our results suggest that C-HC induces non-cell-autonomous senescence and accelerates biological aging. The CDKN2 locus may provide a link between C-HC and increased susceptibility to age-associated diseases and provides novel biomarkers for assessing its impact on aging processes in man
Kepler Eclipsing Binary Stars. V. Identification of 31 Eclipsing Binaries in the K2 Engineering Data-set
Over 2500 eclipsing binaries were identified and characterized from the
ultra-precise photometric data provided by the Kepler space telescope. Kepler
is now beginning its second mission, K2, which is proving to again provide
ultra-precise photometry for a large sample of eclipsing binary stars. In the
1951 light curves covering 12 days in the K2 engineering data-set, we have
identified and determined the ephemerides for 31 eclipsing binaries that
demonstrate the capabilities for eclipsing binary science in the upcoming
campaigns in K2. Of those, 20 are new discoveries. We describe both manual and
automated approaches to harvesting the complete set of eclipsing binaries in
the K2 data, provide identifications and details for the full set of eclipsing
binaries present in the engineering data-set, and discuss the prospects for
application of eclipsing binary searches in the K2 mission.Comment: 12 pages, 2 figures, submitted to PAS
Application of Atomic Dielectric Resonance Spectroscopy for the screening of blood samples from patients with clinical variant and sporadic CJD
<p>Abstract</p> <p>Background</p> <p>Sub-clinical variant Creutzfeldt-Jakob disease (vCJD) infection and reports of vCJD transmission through blood transfusion emphasise the need for blood screening assays to ensure the safety of blood and transplanted tissues. Most assays aim to detect abnormal prion protein (PrP<sup>Sc</sup>), although achieving required sensitivity is a challenge.</p> <p>Methods</p> <p>We have used innovative Atomic Dielectric Resonance Spectroscopy (ADRS), which determines dielectric properties of materials which are established by reflectivity and penetration of radio/micro waves, to analyse blood samples from patients and controls to identify characteristic ADR signatures unique to blood from vCJD and to sCJD patients. Initial sets of blood samples from vCJD, sCJD, non-CJD neurological diseases and normal healthy adults (blood donors) were screened as training samples to determine group-specific ADR characteristics, and provided a basis for classification of blinded sets of samples.</p> <p>Results</p> <p>Blood sample groups from vCJD, sCJD, non-CJD neurological diseases and normal healthy adults (blood donors) screened by ADRS were classified with 100% specificity and sensitivity, discriminating these by a co-variance expert analysis system.</p> <p>Conclusion</p> <p>ADRS appears capable of recognising and discriminating serum samples from vCJD, sCJD, non-CJD neurological diseases, and normal healthy adults, and might be developed to provide a system for primary screening or confirmatory assay complementary to other screening systems.</p
Monitoring SO2 emission at the Soufriere Hills Volcano: implications for changes in erruptive conditions
FLWINinfo:eu-repo/semantics/publishe
Functional analysis of epilepsy-associated variants in STXBP1/Munc18-1 using humanised Caenorhabditis elegans
Objective:
Genetic variants in STXBP1 , which encodes the conserved exocytosis protein Munc18â1, are associated with a variety of infantile epilepsy syndromes. We aimed to develop an in vivo Caenorhabditis elegans model that could be used to test the pathogenicity of such variants in a costâeffective manner.
Methods:
The CRISPR/Cas9 method was used to introduce a null mutation into the uncâ18 gene (the C. elegans orthologue of STXBP1 ), thereby creating a paralyzed worm strain. We subsequently rescued this strain with transgenes encoding the human STXBP1/Munc18â1 protein (wildâtype and eight different epilepsyâassociated missense variants). The resulting humanized worm strains were then analyzed via behavioral, electrophysiological, and biochemical approaches.
Results:
Transgenic expression of wildâtype human STXBP1 protein fully rescued locomotion in both solid and liquid media to the same level as the standard wildâtype worm strain, Bristol N2. Six variant strains (E59K, V84D, C180Y, R292H, L341P, R551C) exhibited impaired locomotion, whereas two (P335L, R406H) were no different from worms expressing wildâtype STXBP1. Electrophysiological recordings revealed that all eight variant strains displayed less frequent and more irregular pharyngeal pumping in comparison to wildâtype STXBP1âexpressing strains. Four strains (V84D, C180Y, R292H, P335L) exhibited pentylenetetrazolâinduced convulsions in an acute assay of seizureâlike activity, in contrast to worms expressing wildâtype STXBP1. No differences were seen between wildâtype and variant STXBP1 strains in terms of mRNA abundance. However, STXBP1 protein levels were reduced to 20%â30% of wildâtype in all variants, suggesting that the mutations result in STXBP1 protein instability.
Significance:
The approach described here is a costâeffective in vivo method for establishing the pathogenicity of genetic variants in STXBP1 and potentially other conserved neuronal proteins. Furthermore, the humanized strains we created could potentially be used in the future for highâthroughput drug screens to identify novel therapeutics
Commensurate Scale Relations in Quantum Chromodynamics
We use the BLM method to show that perturbatively-calculable observables in
QCD can be related to each other without renormalization scale or scheme
ambiguity. We define and study the commensurate scale relations. We show that
the commensurate scales satisfy the renormalization group transitivity rule
which ensures that predictions in PQCD are independent of the choice of an
intermediate renormalization scheme. We generalize the BLM procedure to higher
order. The application of this procedure to relate known physical observables
in QCD gives surprisingly simple results. In particular, the annihilation ratio
and the Bjorken sum rule for polarized electroproduction are
related through simple coefficients, which reinforces the idea of a hidden
symmetry between these two observables.Comment: 35 pages (RevTeX), one PostScript figure included at the end.
SLAC-PUB-6481, UMD Preprint #94-13
Asteroseismic determination of obliquities of the exoplanet systems Kepler-50 and Kepler-65
Results on the obliquity of exoplanet host stars -- the angle between the
stellar spin axis and the planetary orbital axis -- provide important
diagnostic information for theories describing planetary formation. Here we
present the first application of asteroseismology to the problem of stellar
obliquity determination in systems with transiting planets and Sun-like host
stars. We consider two systems observed by the NASA Kepler Mission which have
multiple transiting small (super-Earth sized) planets: the previously reported
Kepler-50 and a new system, Kepler-65, whose planets we validate in this paper.
Both stars show rich spectra of solar-like oscillations. From the asteroseismic
analysis we find that each host has its rotation axis nearly perpendicular to
the line of sight with the sines of the angles constrained at the 1-sigma level
to lie above 0.97 and 0.91, respectively. We use statistical arguments to show
that coplanar orbits are favoured in both systems, and that the orientations of
the planetary orbits and the stellar rotation axis are correlated.Comment: Accepted for publication in ApJ; 46 pages, 11 figure
Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
With the unprecedented photometric precision of the Kepler Spacecraft,
significant systematic and stochastic errors on transit signal levels are
observable in the Kepler photometric data. These errors, which include
discontinuities, outliers, systematic trends and other instrumental signatures,
obscure astrophysical signals. The Presearch Data Conditioning (PDC) module of
the Kepler data analysis pipeline tries to remove these errors while preserving
planet transits and other astrophysically interesting signals. The completely
new noise and stellar variability regime observed in Kepler data poses a
significant problem to standard cotrending methods such as SYSREM and TFA.
Variable stars are often of particular astrophysical interest so the
preservation of their signals is of significant importance to the astrophysical
community. We present a Bayesian Maximum A Posteriori (MAP) approach where a
subset of highly correlated and quiet stars is used to generate a cotrending
basis vector set which is in turn used to establish a range of "reasonable"
robust fit parameters. These robust fit parameters are then used to generate a
Bayesian Prior and a Bayesian Posterior Probability Distribution Function (PDF)
which when maximized finds the best fit that simultaneously removes systematic
effects while reducing the signal distortion and noise injection which commonly
afflicts simple least-squares (LS) fitting. A numerical and empirical approach
is taken where the Bayesian Prior PDFs are generated from fits to the light
curve distributions themselves.Comment: 43 pages, 21 figures, Submitted for publication in PASP. Also see
companion paper "Kepler Presearch Data Conditioning I - Architecture and
Algorithms for Error Correction in Kepler Light Curves" by Martin C. Stumpe,
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