83 research outputs found
Globaler Isomorphismus versus sozio-kulturelle Konfiguration:: Weltgeschichtliche Curricula im internationalen Vergleich
Myelination in the absence of UDP-galactose:ceramide galactosyl-transferase and fatty acid 2 -hydroxylase
<p>Abstract</p> <p>Background</p> <p>The sphingolipids galactosylceramide (GalCer) and sulfatide are major myelin components and are thought to play important roles in myelin function. The importance of GalCer and sulfatide has been validated using UDP-galactose:ceramide galactosyltransferase-deficient (<it>Cgt</it><sup>-/-</sup>) mice, which are impaired in myelin maintenance. These mice, however, are still able to form compact myelin. Loss of GalCer and sulfatide in these mice is accompanied by up-regulation of 2-hydroxylated fatty acid containing (HFA)-glucosylceramide in myelin. This was interpreted as a partial compensation of the loss of HFA-GalCer, which may prevent a more severe myelin phenotype. In order to test this hypothesis, we have generated <it>Cgt</it><sup>-/- </sup>mice with an additional deletion of the fatty acid 2-hydroxylase (<it>Fa2h</it>) gene.</p> <p>Results</p> <p><it>Fa2h</it><sup>-/-</sup>/Cgt<sup>-/- </sup>double-deficient mice lack sulfatide, GalCer, and in addition HFA-GlcCer and sphingomyelin. Interestingly, compared to <it>Cgt</it><sup>-/- </sup>mice the amount of GlcCer in CNS myelin was strongly reduced in <it>Fa2h</it><sup>-/-</sup>/<it>Cgt</it><sup>-/- </sup>mice by more than 80%. This was accompanied by a significant increase in sphingomyelin, which was the predominant sphingolipid in <it>Fa2h</it><sup>-/-</sup>/<it>Cgt</it><sup>-/- </sup>mice. Despite these significant changes in myelin sphingolipids, compact myelin was formed in <it>Fa2h</it><sup>-/-</sup>/<it>Cgt</it><sup>-/- </sup>mice, and g-ratios of myelinated axons in the spinal cord of 4-week-old <it>Fa2h</it><sup>-/-</sup>/<it>Cgt</it><sup>-/- </sup>mice did not differ significantly from that of <it>Cgt</it><sup>-/- </sup>mice, and there was no obvious phenotypic difference between <it>Fa2h</it><sup>-/-</sup>/<it>Cgt</it><sup>-/- </sup>and <it>Cgt</it><sup>-/- </sup>mice</p> <p>Conclusions</p> <p>These data show that compact myelin can be formed with non-hydroxylated sphingomyelin as the predominant sphingolipid and suggest that the presence of HFA-GlcCer and HFA-sphingomyelin in <it>Cgt</it><sup>-/- </sup>mice does not functionally compensate the loss of HFA-GalCer.</p
Estimating errors reliably in Monte Carlo simulations of the Ehrenfest model
Using the Ehrenfest urn model we illustrate the subtleties of error
estimation in Monte Carlo simulations. We discuss how the smooth results of
correlated sampling in Markov chains can fool one's perception of the accuracy
of the data, and show (via numerical and analytical methods) how to obtain
reliable error estimates from correlated samples
Self-consistent ladder DA approach
We present and implement a self-consistent DA approach for
multi-orbital models and ab initio materials calculations. It is applied to the
one-band Hubbard model at various interaction strengths with and without
doping, to the two-band Hubbard model with two largely different bandwidths,
and to SrVO. The self-energy feedback reduces critical temperatures
compared to dynamical mean-field theory, even to zero temperature in
two-dimensions. Compared to a one-shot, non-self-consistent calculation the
non-local correlations are significantly reduced when they are strong. In case
non-local correlations are weak to moderate as for SrVO, one-shot
calculations are sufficient.Comment: 21 Pages, 20 Figure
Effect of pitchfork bifurcations on the spectral statistics of Hamiltonian systems
We present a quantitative semiclassical treatment of the effects of
bifurcations on the spectral rigidity and the spectral form factor of a
Hamiltonian quantum system defined by two coupled quartic oscillators, which on
the classical level exhibits mixed phase space dynamics. We show that the
signature of a pitchfork bifurcation is two-fold: Beside the known effect of an
enhanced periodic orbit contribution due to its peculiar -dependence at
the bifurcation, we demonstrate that the orbit pair born {\em at} the
bifurcation gives rise to distinct deviations from universality slightly {\em
above} the bifurcation. This requires a semiclassical treatment beyond the
so-called diagonal approximation. Our semiclassical predictions for both the
coarse-grained density of states and the spectral rigidity, are in excellent
agreement with corresponding quantum-mechanical results.Comment: LaTex, 25 pp., 14 Figures (26 *.eps files); final version 3, to be
published in Journal of Physics
Moyal star product approach to the Bohr-Sommerfeld approximation
The Bohr-Sommerfeld approximation to the eigenvalues of a one-dimensional
quantum Hamiltonian is derived through order (i.e., including the
first correction term beyond the usual result) by means of the Moyal star
product. The Hamiltonian need only have a Weyl transform (or symbol) that is a
power series in , starting with , with a generic fixed point in
phase space. The Hamiltonian is not restricted to the kinetic-plus-potential
form. The method involves transforming the Hamiltonian to a normal form, in
which it becomes a function of the harmonic oscillator Hamiltonian.
Diagrammatic and other techniques with potential applications to other normal
form problems are presented for manipulating higher order terms in the Moyal
series.Comment: 27 pages, no figure
Potential climatic transitions with profound impact on Europe
We discuss potential transitions of six climatic subsystems with large-scale impact on Europe, sometimes denoted as tipping elements. These are the ice sheets on Greenland and West Antarctica, the Atlantic thermohaline circulation, Arctic sea ice, Alpine glaciers and northern hemisphere stratospheric ozone. Each system is represented by co-authors actively publishing in the corresponding field. For each subsystem we summarize the mechanism of a potential transition in a warmer climate along with its impact on Europe and assess the likelihood for such a transition based on published scientific literature. As a summary, the ‘tipping’ potential for each system is provided as a function of global mean temperature increase which required some subjective interpretation of scientific facts by the authors and should be considered as a snapshot of our current understanding. <br/
Diametrically opposite methylome-transcriptome relationships in high- and low-CpG promoter genes in postmitotic neural rat tissue
DNA methylation can control some CpG-poor genes but unbiased studies have not found a consistent genome-wide association with gene activity outside of CpG islands or shores possibly due to use of cell lines or limited bioinformatics analyses. We performed reduced representation bisulfite sequencing (RRBS) of rat dorsal root ganglia encompassing postmitotic primary sensory neurons (n = 5, r > 0.99; orthogonal validation p < 10−19). The rat genome suggested a dichotomy of genes previously reported in other mammals: low CpG content (< 3.2%) promoter (LCP) genes and high CpG content (≥ 3.2%) promoter (HCP) genes. A genome-wide integrated methylome-transcriptome analysis showed that LCP genes were markedly hypermethylated when repressed, and hypomethylated when active with a 40% difference in a broad region at the 5′ of the transcription start site (p < 10−87 for -6000 bp to -2000 bp, p < 10−73 for -2000 bp to +2000 bp, no difference in gene body p = 0.42). HCP genes had minimal TSS-associated methylation regardless of transcription status, but gene body methylation appeared to be lost in repressed HCP genes. Therefore, diametrically opposite methylome-transcriptome associations characterize LCP and HCP genes in postmitotic neural tissue in vivo
In situ, satellite measurement and model evidence on the dominant regional contribution to fine particulate matter levels in the Paris megacity
International audiencePublished by Copernicus Publications on behalf of the European Geosciences Union. 9578 M. Beekmann et al.: Evidence for a dominant regional contribution to fine particulate matter levels Abstract. A detailed characterization of air quality in the megacity of Paris (France) during two 1-month intensive campaigns and from additional 1-year observations revealed that about 70 % of the urban background fine particulate matter (PM) is transported on average into the megacity from upwind regions. This dominant influence of regional sources was confirmed by in situ measurements during short intensive and longer-term campaigns, aerosol optical depth (AOD) measurements from ENVISAT, and modeling results from PMCAMx and CHIMERE chemistry transport models. While advection of sulfate is well documented for other megacities, there was surprisingly high contribution from long-range transport for both nitrate and organic aerosol. The origin of organic PM was investigated by comprehensive analysis of aerosol mass spectrometer (AMS), radio-carbon and tracer measurements during two intensive campaigns. Primary fossil fuel combustion emissions constituted less than 20 % in winter and 40 % in summer of carbonaceous fine PM, unexpectedly small for a megacity. Cooking activities and, during winter, residential wood burning are the major primary organic PM sources. This analysis suggests that the major part of secondary organic aerosol is of modern origin , i.e., from biogenic precursors and from wood burning. Black carbon concentrations are on the lower end of values encountered in megacities worldwide, but still represent an issue for air quality. These comparatively low air pollution levels are due to a combination of low emissions per inhabitant , flat terrain, and a meteorology that is in general not conducive to local pollution build-up. This revised picture of a megacity only being partially responsible for its own average and peak PM levels has important implications for air pollution regulation policies
Kommunen gestalten Ernährung: Neue Handlungsfelder nachhaltiger Stadtentwicklung
Kommunen gestalten Ernährung“, lautet der Titel der 153. Dokumentation des Deutschen Städte- und Gemeindebundes und des Verbundforschungsprojekts KERNiG (Kommunale Ernährungssysteme als Schlüssel zu einer umfassend-integrativen Nachhaltigkeitsgovernance), gefördert durch das Bundesministerium für Bildung und Forschung. Für Kommunen spielen Nachhaltigkeit und Klimaschutz eine immer wichtigere Rolle. Dabei wurden die Umweltauswirkungen von Ernährung auf Ebene der Kommunen bisher nur wenig berücksichtigt. Im Themenfeld Ernährung liegen jedoch bedeutende Reduktionspotentiale des ökologischen Fußabdrucks. Wenn Kommunen den Anspruch haben eine nachhaltige Stadtentwicklung zu fördern, kommen sie nicht umhin, sich auch mit ihren Ernährungssystemen auseinanderzusetzen. Das Handbuch soll mit Hilfe von Praxisbeispielen aufzeigen, an welchen Stellen und in welchen Handlungsfeldern sich zentrale Gestaltungspotenziale für Ernährung auf kommunaler Ebene befinden. Kommunen sollen ermutigt werden, das Thema Ernährung als Teil einer nachhaltigen Stadtentwicklung aufzugreifen
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