298 research outputs found
Magnetic domain structure and dynamics in interacting ferromagnetic stacks with perpendicular anisotropy
The time and field dependence of the magnetic domain structure at
magnetization reversal were investigated by Kerr microscopy in interacting
ferromagnetic Co/Pt multilayers with perpendicular anisotropy. Large local
inhomogeneous magnetostatic fields favor mirroring domain structures and domain
decoration by rings of opposite magnetization. The long range nature of these
magnetostatic interactions gives rise to ultra-slow dynamics even in zero
applied field, i.e. it affects the long time domain stability. Due to this
additionnal interaction field, the magnetization reversal under short magnetic
field pulses differs markedly from the well-known slow dynamic behavior.
Namely, in high field, the magnetization of the coupled harder layer has been
observed to reverse more rapidly by domain wall motion than the softer layer
alone.Comment: 42 pages including 17 figures. submitted to JA
Arylamines suppress their own activation and that of nitroarenes in V79 Chinese hamster cells by competing for acetyltransferases.
The effect of 2-aminofluorene (2-AF) on the toxicity of 2-aminoanthracene (2-AA) and 1,6-dinitropyrene (1,6-DNP) was studied in N-acetyltransferase-proficient V79-NHr1A2 cells genetically engineered for the expression of cytochrome P4501A2, and in wild-type V79-NH cells. 2-AA inhibited the growth of V79-NHr1A2 cells and induced the formation of micronuclei at concentrations of 0.1 to 1.0 microM, but was virtually without toxic effects at a concentration of 10 microM. Addition of 2-AF protected against the cytotoxic and genotoxic effects elicited by low concentrations of 2-AA. Half-maximum protection was observed at 0.2 to 0.5 microM 2-AF. The arylamine also prevented the cytotoxicity caused by 1,6-DNP in V79-NH cells and completely suppressed the formation of 1-acetylamino-6-nitropyrene from 1,6-DNP in these cells. The results indicate that arylamines and related N-hydroxyarylamines are substrates for the same acetyltransferase in V79-NH cells. In consequence, arylamines are capable of suppressing the activation of their proximate cytotoxic and genotoxic products in these cells and, presumably, in vivo
Simulation of neutrino and charged particle production and propagation in the atmosphere
A precise evaluation of the secondary particle production and propagation in
the atmosphere is very important for the atmospheric neutrino oscillation
studies. The issue is addressed with the extension of a previously developed
full 3-Dimensional Monte-Carlo simulation of particle generation and transport
in the atmosphere, to compute the flux of secondary protons, muons and
neutrinos. Recent balloon borne experiments have performed a set of accurate
flux measurements for different particle species at different altitudes in the
atmosphere, which can be used to test the calculations for the atmospheric
neutrino production, and constrain the underlying hadronic models. The
simulation results are reported and compared with the latest flux measurements.
It is shown that the level of precision reached by these experiments could be
used to constrain the nuclear models used in the simulation. The implication of
these results for the atmospheric neutrino flux calculation are discussed.Comment: 11 pages, 9 figure
Rigidity-dependent cosmic ray energy spectra in the knee region obtained with the GAMMA experiment
On the basis of the extensive air shower (EAS) data obtained by the GAMMA
experiment, the energy spectra and elemental composition of the primary cosmic
rays are derived in the 1-100 PeV energy range. The reconstruction of the
primary energy spectra is carried out using an EAS inverse approach in the
framework of the SIBYLL2.1 and QGSJET01 interaction models and the hypothesis
of power-law primary energy spectra with rigidity-dependent knees. The energy
spectra of primary H, He, O-like and Fe-like nuclei obtained with the SIBYLL
interaction model agree with corresponding extrapolations of the balloon and
satellite data to ~1 PeV energies. The energy spectra obtained from the QGSJET
model show a predominantly proton composition in the knee region. The
rigidity-dependent knee feature of the primary energy spectra for each
interaction model is displayed at the following rigidities: ~2.5+/-0.2 PV
(SIBYLL) and ~3.1-4.2 PV (QGSJET). All the results presented are derived taking
into account the detector response, the reconstruction uncertainties of the EAS
parameters, and fluctuations in the EAS development.Comment: 28 pages, 18 figures, accepted for publication in Astroparticle
Physic
Structural Relaxation and Mode Coupling in a Simple Liquid: Depolarized Light Scattering in Benzene
We have measured depolarized light scattering in liquid benzene over the
whole accessible temperature range and over four decades in frequency. Between
40 and 180 GHz we find a susceptibility peak due to structural relaxation. This
peak shows stretching and time-temperature scaling as known from
relaxation in glass-forming materials. A simple mode-coupling model provides
consistent fits of the entire data set. We conclude that structural relaxation
in simple liquids and relaxation in glass-forming materials are
physically the same. A deeper understanding of simple liquids is reached by
applying concepts that were originally developed in the context of
glass-transition research.Comment: submitted to New J. Phy
Turbulent diffusion and drift in galactic magnetic fields and the explanation of the knee in the cosmic ray spectrum
We reconsider the scenario in which the knee in the cosmic ray spectrum is
explained as due to a change in the escape mechanism of cosmic rays from the
Galaxy from one dominated by transverse diffusion to one dominated by drifts.
We solve the diffusion equations adopting realistic galactic field models and
using diffusion coefficients appropriate for strong turbulence (with a
Kolmogorov spectrum of fluctuations) and consistent with the assumed magnetic
fields. We show that properly taking into account these effects leads to a
natural explanation of the knee in the spectrum, and a transition towards a
heavier composition above the knee is predicted.Comment: 17 pp., 6 figures; revised version with minor changes. To appear in
JHE
Energy spectra of cosmic-ray nuclei at high energies
We present new measurements of the energy spectra of cosmic-ray (CR) nuclei
from the second flight of the balloon-borne experiment Cosmic Ray Energetics
And Mass (CREAM). The instrument included different particle detectors to
provide redundant charge identification and measure the energy of CRs up to
several hundred TeV. The measured individual energy spectra of C, O, Ne, Mg,
Si, and Fe are presented up to eV. The spectral shape looks
nearly the same for these primary elements and it can be fitted to an power law in energy. Moreover, a new measurement of the absolute
intensity of nitrogen in the 100-800 GeV/ energy range with smaller errors
than previous observations, clearly indicates a hardening of the spectrum at
high energy. The relative abundance of N/O at the top of the atmosphere is
measured to be (stat.)(sys.) at 800
GeV/, in good agreement with a recent result from the first CREAM flight.Comment: 32 pages, 10 figures. Accepted for publication in Astrophysical
Journa
The giant organelles in beige and Chediak-Higashi fibroblasts are derived from late endosomes and mature lysosomes.
Primary Proton Spectrum of Cosmic Rays measured with Single Hadrons
The flux of cosmic-ray induced single hadrons near sea level has been
measured with the large hadron calorimeter of the KASCADE experiment. The
measurement corroborates former results obtained with detectors of smaller size
if the enlarged veto of the 304 m^2 calorimeter surface is encounted for. The
program CORSIKA/QGSJET is used to compute the cosmic-ray flux above the
atmosphere. Between E_0=300 GeV and 1 PeV the primary proton spectrum can be
described with a power law parametrized as
dJ/dE_0=(0.15+-0.03)*E_0^{-2.78+-0.03} m^-2 s^-1 sr^-1 TeV^-1. In the TeV
region the proton flux compares well with the results from recent measurements
of direct experiments.Comment: 13 pages, accepted by Astrophysical Journa
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