1,476 research outputs found
Magnetic helicity in magnetohydrodynamic turbulence with a mean magnetic field
A computational investigation of magnetic helicity of the fluctuatingmagnetic fieldHm in ideal and freely decaying three‐dimensional (3‐D) magnetohydrodynamics (MHD) in the presence of a uniform mean magnetic field is performed. It is shown that for ideal 3‐D MHDHm, which is a rugged invariant in the absence of a mean magnetic field [Frisch et al., J. Fluid Mech. 77, 796 (1975)], decays from its initial value and proceeds to oscillate about zero. The decay of Hm is shown to result from the presence of a new ‘‘generalized’’ helicity invariant, which includes contributions from the uniform magnetic field. The loss of invariance of Hm will diminish the effects of inverse transfer of Hm on freely decaying turbulence. This is demonstrated in a discussion of the selective decay relaxation process
HLA-G: expression in human keratinocytes in vitro and in human skin in vivo
Classical, polymorphic major histocompatibility complex class I molecules are
expressed on most nucleated cells.They present peptides at the cell surface and,
thus, enable the immune system to scan peptides for their antigenicity. The
function of the other, nonclassical class I molecules in man is controversial.
HLA-G which has been shown by transfection experiments to be expressed at the
cell surface, is only transcribed in placental tissue and in the fetal eye.Therefore, a
role of HLA-G in the control of rejection of the allogeneic fetus has been
discussed. We found that HLA-G expression is induced in keratinocytes by
culture in vitro. Three different alternative splicing products of HLA-G can be
detected: a full length transcript, an mRNA lacking exon 3 and a transcript devoid
of exon 3 and 4. Reverse transcription followed by polymerase chain reaction also
revealed the presence of HLA-G mRNA in vivo in biopsies of either diseased or
healthy skin
Measurement of the electric fluctuation spectrum of magnetohydrodynamic turbulence
Magnetohydrodynamic (MHD) turbulence in the solar wind is observed to show
the spectral behavior of classical Kolmogorov fluid turbulence over an inertial
subrange and departures from this at short wavelengths, where energy should be
dissipated. Here we present the first measurements of the electric field
fluctuation spectrum over the inertial and dissipative wavenumber ranges in a
plasma. The inertial subrange is observed and
agrees strikingly with the magnetic fluctuation spectrum; the wave phase speed
in this regime is shown to be consistent with the Alfv\'en speed. At smaller
wavelengths the electric spectrum is softer and is consistent
with the expected dispersion relation of short-wavelength kinetic Alfv\'en
waves. Kinetic Alfv\'en waves damp on the solar wind ions and electrons and may
act to isotropize them. This effect may explain the fluid-like nature of the
solar wind.Comment: submitted; 4 pages + 3 figure
Deflection of ultra high energy cosmic rays by the galactic magnetic field: from the sources to the detector
We report the results of 3D simulations of the trajectories of ultra-high
energy protons and Fe nuclei (with energies and ) propagating through the galactic magnetic field from the
sources to the detector. A uniform distribution of anti-particles is
backtracked from the detector, at the Earth, to the halo of the Galaxy. We
assume an axisymmetric, large scale spiral magnetic field permeating both the
disc and the halo. A normal field component to the galactic plane () is
also included in part of the simulations. We find that the presence of a large
scale galactic magnetic field does not generally affect the arrival directions
of the protons, although the inclusion of a component may cause
significant deflection of the lower energy protons (
eV). Error boxes larger than or equal to are most expected in
this case. On the other hand, in the case of heavy nuclei, the arrival
direction of the particles is strongly dependent on the coordinates of the
particle source. The deflection may be high enough () as to make
extremely difficult any identification of the sources unless the real magnetic
field configuration is accurately determined. Moreover, not every incoming
particle direction is allowed between a given source and the detector. This
generates sky patches which are virtually unobservable from the Earth. In the
particular case of the UHE events of Yakutsk, Fly's Eye, and Akeno, they come
from locations for which the deflection caused by the assumed magnetic field is
not significant.Comment: LaTeX + 2 postscript figures - Color versions of both figures (highly
recommended) available via anonymous ftp at
ftp://capc07.ast.cam.ac.uk/pub/uhecr_gmf as fig*.g
The xSAP Safety Analysis Platform
This paper describes the xSAP safety analysis platform. xSAP provides several
model-based safety analysis features for finite- and infinite-state synchronous
transition systems. In particular, it supports library-based definition of
fault modes, an automatic model extension facility, generation of safety
analysis artifacts such as Dynamic Fault Trees (DFTs) and Failure Mode and
Effects Analysis (FMEA) tables. Moreover, it supports probabilistic evaluation
of Fault Trees, failure propagation analysis using Timed Failure Propagation
Graphs (TFPGs), and Common Cause Analysis (CCA). xSAP has been used in several
industrial projects as verification back-end, and is currently being evaluated
in a joint R&D Project involving FBK and The Boeing Company
Multiscaling of galactic cosmic ray flux
Multiscaling analysis of differential flux dissipation rate of galactic
cosmic rays (Carbon nuclei) is performed in the energy ranges: 56.3-73.4
Mev/nucleon and 183.1-198.7 MeV/nucleon, using the data collected by ACE/CRIS
spacecraft instrument for 2000 year. The analysis reveals strong
(turbulence-like) intermittency of the flux dissipation rate for the short-term
intervals: 1-30 hours. It is also found that type of the intermittency can be
different in different energy ranges
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