347 research outputs found
Grazing incidence X-ray fluorescence of periodic structures â a comparison between X-ray standing waves and geometrical optics calculations
Grazing incidence X-ray fluorescence spectra of nano-scaled periodic line structures were recorded at the four crystal monochromator beamline in the laboratory of the Physikalisch-Technische Bundesanstalt at the synchrotron radiation facility BESSY II. For different tilt angles between the lines and the plane of incidence of the monochromatic synchrotron radiation, spectral features are observed which can be understood and explained with calculations of the emerging X-ray standing wave (XSW) field. On the other hand, there are structures, i.e., pronounced modulations above the substrate's critical angle of external total reflection, which are not included in the XSW concept. Novel geometrical optics calculations can reproduce these structures taking the sample's specific geometric conditions into account
Langue allemande
Falk Bretschneider Cours de langue appliquĂ©e aux sciences sociales et humaines Compte rendu non communiquĂ©. Falk Bretschneider et Marelke König Lire lâallemand dâhier : introduction aux sources de lâhistoire moderne et contemporaine allemande et Ă la palĂ©ographie (en coopĂ©ration avec lâInstitut historique allemand) Compte rendu non communiquĂ©. Nicole Reinhardt Cours de traduction de lâallemand Enseignement annulĂ©
Extended NJL Model for light and heavy mesons without q-qbar thresholds
We consider the NJL model as an effective quark theory to describe the
interaction which is responsible for the quark flavor dynamics at intermediate
energies. In addition to the usual ultraviolet cut-off which is necessary since
the model is non-renormalizable, we also introduce an infrared cut-off which
drops off the unknown confinement part of the quark interaction, which is
believed to be less important for the flavor dynamics. The infrared cut-off
eliminates all q-qbar thresholds, which plague the application of the usual NJL
model beyond low-energy pion physics. We apply this two-cut-off prescription to
the extended NJL model with chiral and heavy quark symmetries proposed recently
by us. We find a satisfactoring description even of the heavy mesons with
spin/parity J/P = (0+, 1+). Furthermore, the shape-parameters of the Isgur-Wise
function are studied as a function of the residual heavy meson mass.Comment: 9 pages LaTeX, 3 figures included using epsfig.sty, also available
via http://qft3.physik.hu-berlin.de/~feldmann/pub/9608223.ps.Z, Citation [3]
correcte
Identification of disulfiram as a secretase-modulating compound with beneficial effects on Alzheimerâs disease hallmarks
ADAM10 is a metalloproteinase acting on the amyloid precursor protein (APP) as an alpha-secretase in neurons. Its enzymatic activity results in secretion of a neuroprotective APP cleavage product (sAPPalpha) and prevents formation of the amyloidogenic A-beta peptides, major hallmarks of Alzheimerâs disease (AD). Elevated ADAM10 levels appeared to contribute to attenuation of A-beta-Plaque formation and learning and memory deficits in AD mouse models. Therefore, it has been assumed that ADAM10 might represent a valuable target in AD therapy. Here we screened a FDA-approved drug library and identified disulfiram as a novel ADAM10 gene expression enhancer. Disulfiram increased ADAM10 production as well as sAPP-alpha in SH-SY5Y human neuronal cells and additionally prevented A-beta aggregation in an in vitro assay in a dose-dependent fashion. In addition, acute disulfiram treatment of Alzheimer model mice induced ADAM10 expression in peripheral blood cells, reduced plaque-burden in the dentate gyrus and ameliorated behavioral deficits. Alcohol-dependent patients are subjected to disulfiram-treatment to discourage alcohol-consumption. In such patients, enhancement of ADAM10 by disulfiram-treatment was demonstrated in peripheral blood cells. Our data suggest that disulfiram could be repurposed as an ADAM10 enhancer and AD therapeutic. However, efficacy and safety has to be analyzed in Alzheimer patients in the future
A ring of instantons inducing a monopole loop
We consider the superposition of infinitely many instantons on a circle in
R^4. The construction yields a self-dual solution of the Yang-Mills equations
with action density concentrated on the ring. We show that this configuration
is reducible in which case magnetic charge can be defined in a gauge invariant
way. Indeed, we find a unit charge monopole (worldline) on the ring. This is an
analytic example of the correlation between monopoles and action/topological
density, however with infinite action. We show that both the Maximal Abelian
Gauge and the Laplacian Abelian Gauge detect the monopole, while the Polyakov
gauge does not. We discuss the implications of this configuration.Comment: 11 pages, 1 figur
Writhe of center vortices and topological charge -- an explicit example
The manner in which continuum center vortices generate topological charge
density is elucidated using an explicit example. The example vortex
world-surface contains one lone self-intersection point, which contributes a
quantum 1/2 to the topological charge. On the other hand, the surface in
question is orientable and thus must carry global topological charge zero due
to general arguments. Therefore, there must be another contribution, coming
from vortex writhe. The latter is known for the lattice analogue of the example
vortex considered, where it is quite intuitive. For the vortex in the
continuum, including the limit of an infinitely thin vortex, a careful analysis
is performed and it is shown how the contribution to the topological charge
induced by writhe is distributed over the vortex surface.Comment: 33 latex pages, 10 figures incorporating 14 ps files. Furthermore,
the time evolution of the vortex line discussed in this work can be viewed as
a gif movie, available for download by following the PostScript link below --
watch for the cute feature at the self-intersection poin
Distinct phosphatases antagonize the p53 response in different phases of the cell cycle
The basic machinery that detects DNA damage is the same throughout the cell cycle. Here, we show, in contrast, that reversal of DNA damage responses (DDRs) and recovery are fundamentally different in G1 and G2 phases of the cell cycle. We find that distinct phosphatases are required to counteract the checkpoint response in G1 vs. G2. Whereas WT p53-induced phosphatase 1 (Wip1) promotes recovery in G2-arrested cells by antagonizing p53, it is dispensable for recovery from a G1 arrest. Instead, we identify phosphoprotein phosphatase 4 catalytic subunit (PP4) to be specifically required for cell cycle restart after DNA damage in G1. PP4 dephosphorylates KrĂŒppel-associated box domain-associated protein 1-S473 to repress p53-dependent transcriptional activation of p21 when the DDR is silenced. Taken together, our results show that PP4 and Wip1 are differentially required to counteract the p53-dependent cell cycle arrest in G1 and G2, by antagonizing early or late p53-mediated responses, respectively
Search for composite and exotic fermions at LEP 2
A search for unstable heavy fermions with the DELPHI detector at LEP is
reported. Sequential and non-canonical leptons, as well as excited leptons and
quarks, are considered. The data analysed correspond to an integrated
luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV
and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172
GeV and 161 GeV. The search for pair-produced new leptons establishes 95%
confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2,
depending on the channel. The search for singly produced excited leptons and
quarks establishes upper limits on the ratio of the coupling of the excited
fermio
Search for lightest neutralino and stau pair production in light gravitino scenarios with stau NLSP
Promptly decaying lightest neutralinos and long-lived staus are searched for
in the context of light gravitino scenarios. It is assumed that the stau is the
next to lightest supersymmetric particle (NLSP) and that the lightest
neutralino is the next to NLSP (NNLSP). Data collected with the Delphi detector
at centre-of-mass energies from 161 to 183 \GeV are analysed. No evidence of
the production of these particles is found. Hence, lower mass limits for both
kinds of particles are set at 95% C.L.. The mass of gaugino-like neutralinos is
found to be greater than 71.5 GeV/c^2. In the search for long-lived stau,
masses less than 70.0 to 77.5 \GeVcc are excluded for gravitino masses from 10
to 150 \eVcc . Combining this search with the searches for stable heavy leptons
and Minimal Supersymmetric Standard Model staus a lower limit of 68.5 \GeVcc
may be set for the stau mas
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