1,053 research outputs found
Charged Current Neutrino Cross Section and Tau Energy Loss at Ultra-High Energies
We evaluate both the tau lepton energy loss produced by photonuclear
interactions and the neutrino charged current cross section at ultra-high
energies, relevant to neutrino bounds with Earth-skimming tau neutrinos, using
different theoretical and phenomenological models for nucleon and nucleus
structure functions. The theoretical uncertainty is estimated by taking
different extrapolations of the structure function F2 to very low values of x,
in the low and moderate Q2 range for the tau lepton interaction and at high Q2
for the neutrino-nucleus inelastic cross section. It is at these extremely low
values of x where nuclear shadowing and parton saturation effects are unknown
and could be stronger than usually considered. For tau and neutrino energies
E=10^9 GeV we find uncertainties of a factor 4 for the tau energy loss and of a
factor 2 for the charged current neutrino-nucleus cross section.Comment: 20 pages and 11 figure
Drebrin is a novel connexin-43 binding partner that links gap junctions to the submembrane cytoskeleton
AbstractBackground: Connexins form gap junctions that mediate the transfer of ions, metabolites, and second messengers between contacting cells. Many aspects of connexin function, for example cellular transport, plaque assembly and stability, and channel conductivity, are finely tuned and likely involve proteins that bind to connexins' cytoplasmic domains. However, little is known about such regulatory proteins. To identify novel proteins that interact with the COOH-terminal domain of Connexin-43 (Cx43), the most widely expressed connexin family member, we applied a proteomics approach to screen fractions of mouse tissue homogenates for binding partners.Results: Drebrin was recovered as a binding partner of the Cx43 COOH-terminal domain from mouse brain homogenate. Drebrin had previously been described as an actin binding protein that diminishes in brains during Alzheimer's disease. The novel Drebrin-Cx43 interaction identified by proteomics was confirmed by colocalization of endogenous proteins in astrocytes and Vero cells, coimmunoprecipitation, electron microscopy, electrophysiology, coexpression of both proteins with fluorescent tags, and live-cell FRET analysis. Depletion of Drebrin in cells with siRNA results in impaired cell-cell coupling, internalization of gap junctions, and targeting of Cx43 to a degradative pathway.Conclusions: We conclude that Drebrin is required for maintaining Cx43-containing gap junctions in their functional state at the plasma membrane. It is thus possible that Drebrin may interact with gap junctions in zones of cell-cell contacts in a regulated fashion in response to extracellular signals. The rearrangement or disruption of interactions between connexins and the Drebrin-containing submembrane cytoskeleton directs connexins to degradative cellular pathways
Limiting transport steps and novel interactions of Connexin-43 along the secretory pathway.
Matter Effects in Atmospheric Neutrino Oscillations
The Kamiokande II and IMB data on contained events induced by atmospheric
neutrinos exhibit too low a ratio of muons to electrons, which has been
interpreted as a possible indication of neutrino oscillations. At the same
time, the recent data on upward--going muons in underground detectors have
shown no evidence for neutrino oscillations, strongly limiting the allowed
region of oscillation parameter space. In this paper we confront different
types of neutrino oscillation hypotheses with the experimental results. The
matter effects in and in oscillations are discussed and shown to affect
significantly the upward--going muons.Comment: LaTeX, 13 pages, 4 figures (appended as postscript file in the end of
the paper, one should cut them and process separately), Roma n. 91
Measuring the BFKL Pomeron in Neutrino Telescopes
We present a new method for obtaining information on the small x behavior of
the structure function F2 outside the kinematic range of present acelerators
from the mean inelasticity parameter in UHE neutrino-nucleon DIS interactions
which could be measured in neutrino telescopes.Comment: 12 pages, Latex, figures as 7 postscript file
Uniformity in the Wiener-Wintner theorem for nilsequences
We prove a uniform extension of the Wiener-Wintner theorem for nilsequences
due to Host and Kra and a nilsequence extension of the topological
Wiener-Wintner theorem due to Assani. Our argument is based on (vertical)
Fourier analysis and a Sobolev embedding theorem.Comment: v3: 18 p., proof that the cube construction produces compact
homogeneous spaces added, measurability issues in the proof of Theorem 1.5
addressed. We thank the anonymous referees for pointing out these gaps in v
Neutrino Interactions at Ultrahigh Energies
We report new calculations of the cross sections for deeply inelastic
neutrino-nucleon scattering at neutrino energies between 10^{9}\ev and
10^{21}\ev. We compare with results in the literature and assess the
reliability of our predictions. For completeness, we briefly review the cross
sections for neutrino interactions with atomic electrons, emphasizing the role
of the -boson resonance in interactions for neutrino
energies in the neighborhood of 6.3\pev. Adopting model predictions for
extraterrestrial neutrino fluxes from active galactic nuclei, gamma-ray
bursters, and the collapse of topological defects, we estimate event rates in
large-volume water \v{C}erenkov detectors and large-area ground arrays.Comment: 32 pages, 11 figures, uses RevTeX and boxedep
Neutrino Quasielastic Scattering on Nuclear Targets: Parametrizing Transverse Enhancement (Meson Exchange Currents)
We present a parametrization of the observed enhancement in the transverse
electron quasielastic (QE) response function for nucleons bound in carbon as a
function of the square of the four momentum transfer () in terms of a
correction to the magnetic form factors of bound nucleons. The parametrization
should also be applicable to the transverse cross section in neutrino
scattering. If the transverse enhancement originates from meson exchange
currents (MEC), then it is theoretically expected that any enhancement in the
longitudinal or axial contributions is small. We present the predictions of the
"Transverse Enhancement" model (which is based on electron scattering data
only) for the differential and total QE cross sections
for nucleons bound in carbon. The dependence of the transverse
enhancement is observed to resolve much of the long standing discrepancy in the
QE total cross sections and differential distributions between low energy and
high energy neutrino experiments on nuclear targets.Comment: Revised Version- July 21, 2011: 17 pages, 20 Figures. To be published
in Eur. Phys. J.
Lepton Fluxes from Atmospheric Charm
We reexamine the charm contribution to atmospheric lepton fluxes in the
context of perturbative QCD. We include next-to-leading order corrections and
discuss theoretical uncertainties due to the extrapolations of the gluon
distributions at small-x. We show that the charm contribution to the
atmospheric muon flux becomes dominant over the conventional contribution from
pion and kaon decays at energies of about 10^5 GeV. We compare our fluxes with
previous calculations.Comment: 19 pages, latex, revtex, psfi
Single neutral pion production by charged-current interactions on hydrocarbon at 3.6 GeV
Single neutral pion production via muon antineutrino charged-current
interactions in plastic scintillator (CH) is studied using the \minerva
detector exposed to the NuMI low-energy, wideband antineutrino beam at
Fermilab. Measurement of this process constrains models of neutral pion
production in nuclei, which is important because the neutral-current analog is
a background for appearance oscillation experiments. The
differential cross sections for momentum and production angle, for
events with a single observed and no charged pions, are presented and
compared to model predictions. These results comprise the first measurement of
the kinematics for this process.Comment: 6 pages, 5 figures, submitted to Physics Letters
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