1,004 research outputs found
Particle models from orientifolds at Gepner-orbifold points
We consider configurations of stacks of orientifold planes and D-branes
wrapped on a non trivial internal space of the structure {(Gepner model)^{c=3n}
x T^{2(3-n)}}/Z_N, for n=1,2,3. By performing simple moddings by discrete
symmetries of Gepner models at orienti fold points, consistent with a Z_N
orbifold action, we show that projection on D-brane configurations can be
achieved, generically leading to chiral gauge theories. Either supersymmetric
or non-supersymmetric (tachyon free) models can be obtained. We illustrate the
procedure through some explicit examples.Comment: 36 pages, no figures Corrected sign of eq. 6.26 references added,
minor correction
The alpha-7 nicotinic acetylcholine receptor is involved in a direct inhibitory effect of nicotine on GnRH release : In vitro studies
The activation of nicotinic cholinergic receptors (nAChR) inhibits the reproductive axis; however, it is not clear whether nicotine may directly modulate the release of hypothalamic gonadotropin-releasing hormone (GnRH). Experiments carried out in GT1-1 immortalized GnRH neurons reveal the presence of a single class of high affinity \u3b14\u3b22 and \u3b17 nAchR subtypes. The exposure of GT1-1\ua0cells to nicotine does not modify the basal accumulation of GnRH. However, nicotine was found to modify GnRH pulsatility in perifusion experiments and inhibits, the release of GnRH induced by prostaglandin E1 or by K(+)-induced cell depolarization; these effects were reversed by D-tubocurarine and \u3b1-bungarotoxin. In conclusion, the results reported here indicate that: functional nAChRs are present on GT1-1\ua0cells, the activation of the \u3b1-bungarotoxin-sensitive subclass (\u3b17) produces an inhibitory effect on the release of GnRH and that the direct action of nicotine on GnRH neurons may be involved in reducing fertility of smokers
The AMANDA Neutrino Telescope and the Indirect Search for Dark Matter
With an effective telescope area of order 10^4 m^2, a threshold of ~50 GeV
and a pointing accuracy of 2.5 degrees, the AMANDA detector represents the
first of a new generation of high energy neutrino telescopes, reaching a scale
envisaged over 25 years ago. We describe its performance, focussing on the
capability to detect halo dark matter particles via their annihilation into
neutrinos.Comment: Latex2.09, 16 pages, uses epsf.sty to place 15 postscript figures.
Talk presented at the 3rd International Symposium on Sources and Detection of
Dark Matter in the Universe (DM98), Santa Monica, California, Feb. 199
Exposure-Based Cash-Flow-At-Risk for Value-Creating Risk Management Under Macroeconomic Uncertainty
Age at menopause and lung function: a Mendelian randomisation study
In observational studies, early menopause is associated with lower forced vital capacity (FVC) and a higher risk of spirometric restriction, but not airflow obstruction. It is, however, unclear if this association is causal. We therefore used a Mendelian randomisation (MR) approach, which is not affected by classical confounding, to assess the effect of age at natural menopause on lung function.We included 94\u200a742 naturally post-menopausal women from the UK Biobank and performed MR analyses on the effect of age at menopause on forced expiratory volume in 1\u2005s (FEV1), FVC, FEV1/FVC, spirometric restriction (FV
Measurement of the multi-TeV neutrino cross section with IceCube using Earth absorption
Neutrinos interact only very weakly, so they are extremely penetrating.
However, the theoretical neutrino-nucleon interaction cross section rises with
energy such that, at energies above 40 TeV, neutrinos are expected to be
absorbed as they pass through the Earth. Experimentally, the cross section has
been measured only at the relatively low energies (below 400 GeV) available at
neutrino beams from accelerators \cite{Agashe:2014kda, Formaggio:2013kya}. Here
we report the first measurement of neutrino absorption in the Earth, using a
sample of 10,784 energetic upward-going neutrino-induced muons observed with
the IceCube Neutrino Observatory. The flux of high-energy neutrinos transiting
long paths through the Earth is attenuated compared to a reference sample that
follows shorter trajectories through the Earth. Using a fit to the
two-dimensional distribution of muon energy and zenith angle, we determine the
cross section for neutrino energies between 6.3 TeV and 980 TeV, more than an
order of magnitude higher in energy than previous measurements. The measured
cross section is (stat.) (syst.)
times the prediction of the Standard Model \cite{CooperSarkar:2011pa},
consistent with the expectation for charged and neutral current interactions.
We do not observe a dramatic increase in the cross section, expected in some
speculative models, including those invoking new compact dimensions
\cite{AlvarezMuniz:2002ga} or the production of leptoquarks
\cite{Romero:2009vu}.Comment: Preprint version of Nature paper 10.1038/nature2445
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