665 research outputs found
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Variability of the North Atlantic summer storm track: mechanisms and impacts on European climate
The summertime variability of the extratropical storm track over the Atlantic sector and its links to European climate have been analysed for the period 1948â2011 using observations and reanalyses. The main results are as follows. (1) The dominant mode of the summer storm track density variability is characterized by a meridional shift of the storm track between two distinct paths and is related to a bimodal distribution in the climatology for this region. It is also closely related to the Summer North Atlantic Oscillation (SNAO). (2) A southward shift is associated with a downstream extension of the storm track and a decrease in blocking frequency over the UK and northwestern Europe. (3) The southward shift is associated with enhanced precipitation over the UK and northwestern Europe and decreased precipitation over southern Europe (contrary to the behaviour in winter). (4) There are strong oceanâatmosphere interactions related to the dominant mode of storm track variability. The atmosphere forces the ocean through anomalous surface fluxes and Ekman currents, but there is also some evidence consistent with an ocean influence on the atmosphere, and that coupled oceanâatmosphere feedbacks might play a role. The ocean influence on the atmosphere may be particularly important on decadal timescales, related to the Atlantic Multidecadal Oscillation (AMO)
Empirische Shortcuts:Studentische Forschungsprojekte in der Methodenlehre
Die empirische Bildungsforschung hat in den letzten Jahren einen nachhaltigen quantitativen und qualitativen Aufschwung genommen. Erziehungswissenschaftliche Forschung erschöpft sich jedoch nicht im M&E des schulischen Lernstands im nationalen und internationalen Vergleich und seiner Ursachen sondern umfasst ein weites Feld an Fragestellungen aus unterschiedlichsten Bereichen. Dies muss den Studierenden, neben den methodischen Modellen und Instrumentarien exemplarisch vermittelt werden. Das ideale didaktische Modell hierfĂŒr ist zweifellos ein von den Studierenden selbst konzipiertes und durchgefĂŒhrtes Forschungsprojekt, wie es seit Jahren im Programmbereich âEmpirische PĂ€dagogikâ des Instituts fĂŒr Erziehungswissenschaft der WWU MĂŒnster praktiziert. Dadurch werden den Studierenden Dimensionen eröffnet, die im Zeitalter von Modularisierung, OECD-Statistiken und Ressourcenverknappung sich zunehmend verengen. Die damit verbundenen Impulse und Erfahrungsgewinne sind in eine Belebung und Bereicherung des Studiums
Dark Matter and Baryons in the Most X-ray Luminous and Merging Galaxy Cluster RX J1347.5-1145
The galaxy cluster RX J1347-1145 is one of the most X-ray luminous and most
massive clusters known. Its extreme mass makes it a prime target for studying
issues addressing cluster formation and cosmology. In this paper we present new
high-resolution HST/ACS and Chandra X-ray data. The high resolution and
sensitivity of ACS enabled us to detect and quantify several new multiply
imaged sources, we now use a total of eight for the strong lensing analysis.
Combining this information with shape measurements of weak lensing sources in
the central regions of the cluster, we derive a high-resolution,
absolutely-calibrated mass map. This map provides the best available
quantification of the total mass of the central part of the cluster to date. We
compare the reconstructed mass with that inferred from the new Chandra X-ray
data, and conclude that both mass estimates agree extremely well in the
observed region, namely within 400 / h_70 kpc of the cluster center. In
addition we study the major baryonic components (gas and stars) and hence
derive the dark matter distribution in the center of the cluster. We find that
the dark matter and baryons are both centered on the BCG within the
uncertainties (alignment is better than <10 kpc). We measure the corresponding
1-D profiles and find that dark matter distribution is consistent with both NFW
and cored profiles, indicating that a more extended radial analysis is needed
to pinpoint the concentration parameter, and hence the inner slope of the dark
matter profile.Comment: 12 pages, Accepted for publication in ApJ, full-res version
http://www.physics.ucsb.edu/~marusa/RXJ1347.pd
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The roles of static stability and tropical â extratropical interactions in the summer interannual variability of the North Atlantic sector
Summer seasonal forecast skill in the North Atlantic sector is lower than winter skill. To identify potential controls on predictability, the sensitivity of North Atlantic baroclinicity to atmospheric drivers is quantified. Using ERA-INTERIM reanalysis data, North Atlantic storm-track baroclinicity is shown to be less sensitive to meridional temperature-gradient variability in summer. Static stability shapes the sectorâs interannual variability by modulating the sensitivity of baroclinicity to variations in meridional temperature gradients and tropopause height and by modifying the baroclinicity itself. High static stability anomalies at upper levels result in more zonal extratropical cyclone tracks and higher eddy kinetic energy over the British Isles in the summertime. These static stability anomalies are not strongly related to the summer NAO; but they are correlated with the suppression of convection over the tropical Atlantic and with a poleward-shifted subtropical jet. These results suggest a non-local driver of North Atlantic variability. Furthermore, they imply that improved representations of convection over the south-eastern part of North America and the tropical Atlantic might improve summer seasonal forecast skill
VLT observations of the z=6.28 quasar SDSS 1030+0524
We present new VLT spectroscopic observations of the most distant quasar
known, SDSS J1030+0524 at z=6.28 which was recently discovered by the Sloan
Digital Sky Survey. We confirm the presence of a complete Gunn-Peterson trough
caused by neutral hydrogen in the intergalactic medium. There is no detectable
flux over the wavelength range from 8450 to 8710 A. We set an improved limit on
the drop of the flux level blueward of the Ly alpha line: a factor of
> 200. Below 8450 A the spectrum shows a rise in flux, with a large fraction
(> 60 %) of the total emission produced by few narrow features of transmitted
flux. We discuss the obvious proximity effect around this quasar, with the
presence of transmitted flux with many absorption features in a region of about
23h^{-1} comoving Mpc. If assuming the surrounding medium were completely
neutral, the size of this region would imply a quasar lifetime of \~1.3x10^7
years.
We also present near-IR spectroscopy of both SDSS J1030+0524 and of SDSS
J1306+05, the second most distant quasar known at redshift 6.0. We combine
measurements of the CIV line and limits on the HeII emission with the NV line
measurements from the optical spectra to derive line ratios, and by implication
the abundances of these early quasar environments. The results are
indistinguishable from those of lower redshift quasars and indicate little or
no evolution in the abundances from z ~ 6 to z ~ 2. The line ratios suggest
supersolar metallicities, implying that the first stars around the quasars must
have formed at least a few hundreds of Myrs prior to the observation, i.e. at
redshift higher than 8.Comment: Accepted by the Astronomical Journal (scheduled for May 2002).
Proximity effect section revise
Halo shapes constrained from a pure sample of central galaxies in KiDS-1000
We present measurements of fh, the ratio of the aligned components of the projected halo and galaxy ellipticities, for a sample of central galaxies using weak gravitational lensing data from the Kilo-Degree Survey (KiDS). Using a lens galaxy shape estimation that is more sensitive to outer galaxy regions, we find fhâ=â0.50â
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0.20 for our full sample and fhâ=â0.55â
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0.19 for an intrinsically red sub-sample (that therefore has a higher stellar mass), rejecting the hypothesis that round halos and/or galaxies are not aligned with their parent halo at 2.5Ï and 2.9Ï, respectively. We quantify the 93.4% purity of our central galaxy sample using numerical simulations and overlapping spectroscopy from the Galaxy and Mass Assembly survey. This purity ensures that the interpretation of our measurements is not complicated by the presence of a significant fraction of satellite galaxies. Restricting our central galaxy ellipticity measurement to the inner isophotes, we find fhâ=â0.34â
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0.17 for our red sub-sample, suggesting that the outer galaxy regions are more aligned with their dark matter halos than the inner regions. Our results are in agreement with previous studies and suggest that lower mass halos are rounder and/or less aligned with their host galaxy than samples of more massive galaxies, studied in galaxy groups and clusters
Inhibitors of Helicobacter pylori Protease HtrA Found by âVirtual Ligandâ Screening Combat Bacterial Invasion of Epithelia
Background: The human pathogen Helicobacter pylori (H. pylori) is a main cause for gastric inflammation and cancer. Increasing bacterial resistance against antibiotics demands for innovative strategies for therapeutic intervention. Methodology/Principal Findings: We present a method for structure-based virtual screening that is based on the comprehensive prediction of ligand binding sites on a protein model and automated construction of a ligand-receptor interaction map. Pharmacophoric features of the map are clustered and transformed in a correlation vector (âvirtual ligandâ) for rapid virtual screening of compound databases. This computer-based technique was validated for 18 different targets of pharmaceutical interest in a retrospective screening experiment. Prospective screening for inhibitory agents was performed for the protease HtrA from the human pathogen H. pylori using a homology model of the target protein. Among 22 tested compounds six block E-cadherin cleavage by HtrA in vitro and result in reduced scattering and wound healing of gastric epithelial cells, thereby preventing bacterial infiltration of the epithelium. Conclusions/Significance: This study demonstrates that receptor-based virtual screening with a permissive (âfuzzyâ) pharmacophore model can help identify small bioactive agents for combating bacterial infection
Soil fungal community shift evaluation as a potential cadaver decomposition indicator
Fungi metabolise organic matter in situ and so alter both the bio-/physico-chemical properties and microbial community structure of the ecosystem. In particular, they are responsible reportedly for specific stages of decomposition. Therefore, this study aimed to extend previous bacteria-based forensic ecogenomics research by investigating soil fungal community and cadaver decomposition interactions in microcosms with garden soil (20 kg, fresh weight) and domestic pig (Sus scrofa domesticus) carcass (5 kg, leg). Soil samples were collected at depths of 0â10 cm, 10â20 cm and 20â30 cm on days 3, 28 and 77 in the absence (control âPg) and presence (experimental +Pg) of Sus scrofa domesticus and used for total DNA extraction and nested polymerase chain reaction and denaturing gradient gel electrophoresis (PCRâDGGE) profiling of the 18S rRNA gene. The ShannonâWiener (HâČ) community diversity indices were 1.25 ± 0.21 and 1.49 ± 0.30 for the control and experimental microcosms, respectively, while comparable Simpson species dominance (S) values were 0.65 ± 0.109 and 0.75 ± 0.015. Generally, and in contrast to parallel studies of the bacterial 16S rRNA and 16S rDNA profiles, statistical analysis (t-test) of the 18S dynamics showed no mathematically significant shifts in fungal community diversity (HâČ; p = 0.142) and dominance (S; p = 0.392) during carcass decomposition, necessitating further investigations
Average Properties of a Large Sample of z_abs ~ z_em associated Mg II Absorption Line Systems
We have studied a sample of 415 associated (z_ab z_em; relative velocity with
respect to QSO <3000km/s) Mg II absorption systems with 1.0<=z_ab<=1.86, in the
spectra of SDSS DR3 QSOs, to determine the dust content and ionization state in
the absorbers. We studied the dependence of these properties on the properties
of the QSOs and also, compared the properties with those of a similarly
selected sample of 809 intervening systems (apparent relative velocity with
respect to the QSO of >3000km/s), so as to understand their origin. From the
analysis of the composite spectra, as well as from the comparison of measured
equivalent widths in individual spectra, we conclude that the associated Mg II
absorbers have higher apparent ionization, measured by the strength of the C IV
absorption lines compared to the Mg II absorption lines, than the intervening
absorbers. The ionization so measured appears to be related to apparent
ejection velocity, being lower as the apparent ejection velocity is more and
more positive. There is clear evidence, from the composite spectra, for SMC
like dust attenuation in these systems; the 2175AA absorption feature is not
present. The extinction is almost twice that observed in the similarly selected
sample of intervening systems. We reconfirm that QSOs with non-zero FIRST radio
flux are intrinsically redder than the QSOs with no detection in the FIRST
survey. The incidence of associated Mg II systems in QSOs with non-zero FIRST
radio flux is 1.7 times that in the QSOs with no detection in the FIRST survey.
The associated absorbers in radio-detected QSOs which comprise about 12% of our
sample, cause 3 times more reddening than the associated absorbers in
radio-undetected QSOs. This excess reddening possibly suggests an intrinsic
nature for the associated absorbers in radio-detected QSOs.Comment: Accepted for publication in Ap
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