1,763 research outputs found
Particle Transport in intense small scale magnetic turbulence with a mean field
Various astrophysical studies have motivated the investigation of the
transport of high energy particles in magnetic turbulence, either in the source
or en route to the observation sites. For strong turbulence and large rigidity,
the pitch-angle scattering rate is governed by a simple law involving a mean
free path that increases proportionally to the square of the particle energy.
In this paper, we show that perpendicular diffusion deviates from this behavior
in the presence of a mean field. We propose an exact theoretical derivation of
the diffusion coefficients and show that a mean field significantly changes the
transverse diffusion even in the presence of a stronger turbulent field. In
particular, the transverse diffusion coefficient is shown to reach a finite
value at large rigidity instead of increasing proportionally to the square of
the particle energy. Our theoretical derivation is corroborated by a dedicated
Monte Carlo simulation. We briefly discuss several possible applications in
astrophysics.Comment: (9 pages, 6 figures, revised version with minor changes
Food neophobia is associated with scarce olfactory performances and specific signatures on oral microbiota
Galactic Cosmic Rays from Supernova Remnants: II Shock Acceleration of Gas and Dust
This is the second paper (the first was astro-ph/9704267) of a series
analysing the Galactic Cosmic Ray (GCR) composition and origin. In this we
present a quantitative model of GCR origin and acceleration based on the
acceleration of a mixture of interstellar and/or circumstellar gas and dust by
supernova remnant blast waves. We present results from a nonlinear shock model
which includes (i) the direct acceleration of interstellar gas-phase ions, (ii)
a simplified model for the direct acceleration of weakly charged dust grains to
energies of order 100keV/amu simultaneously with the gas ions, (iii) frictional
energy losses of the grains colliding with the gas, (iv) sputtering of ions of
refractory elements from the accelerated grains and (v) the further shock
acceleration of the sputtered ions to cosmic ray energies. The calculated GCR
composition and spectra are in good agreement with observations.Comment: to appear in ApJ, 51 pages, LaTeX with AAS macros, 9 postscript
figures, also available from ftp://wonka.physics.ncsu.edu/pub/elliso
ALLELIC VARIANTS OF CYP2E1 GENE IN HEPATOCARCINOMA PATIENTS AND IN HEPATIC TUMOR CELL LINES
Background and Aims: Hepatic enzyme CYP2E1 is involved in the
metabolism of a number of exogenous and endogenous substances
(i.e. ethanol, drugs and chemical carcinogens). Being polymorphic,
CYP2E1 gene can give different xeno-metabolic capabilities in a
population and it is well known that inadequate or no enzymatic
deactivation of xenobiotics could induce an increased susceptibility
to disease and cancer. In particular, one of the 5 -flanking region
polymorphisms, able to differentiate CYP2E1 gene transcriptional
activity, is caused by the appearance/disappearance of RsaI and
PstI restriction sites, which generates two different alleles, namely
*C1(Rsa+/Pstâ) and *C2(Rsaâ/Pst+) respectively, reported to be in
complete linkage disequilibrium.
Methods: To confirm the existence of a correlation between some
particular CYP2E1 genotypes/haplotypes and hepatocarcinoma, we
determined CYP2E1 PstI/RsaI genotypes/haplotypes by RFLP-PCR in
a cohort of central western Sicily hepatocarcinoma patients and in
a population of healthy students from the same geographic area.
Results: In hepatocarcinoma patients, modal genotype association
was Rsa++/Pstââ, corresponding to CYP2E1 *C1/*C1 haplotype,
whereas the Rsa+â/Pstâ+ association, equivalent to CYP2E1 *C1/*C2
haplotype, resulted to have the lowest frequency both in patients
and in controls. Moreover, both in patients and in controls, noncanonical
genotype associations were frequent and arose from
a no-linkage disequilibrium between the two polymorphic sites.
Other authors reported this finding as a rare occurrence. Thus,
from analysis of only one restriction site, Rsa++ genotype was
approximately 1.5-fold more frequent in patients than in controls,
and the non-canonical Rsa+â genotype was found relatively
frequent in patients. Moreover, HuH7 and HA22T transformed
hepatocarcinoma cell lines also showed the Rsa+â genotype.
Conclusions: These results suggest that the presence in CYP2E1
genotype of at least one allele with an Rsa I restriction site is
correlated with hepatocarcinoma. As this site is known a consensus
sequence for some specific CYP gene transcription factors, like
HNF-1, it may be supposed that a single nucleotide polymorphism
can alter the possibility of HNF-1 to bind CYP2E1 promoter. This
could determine a marked change in the transcriptional activity
of the gene, incompetence in xenobiotic metabolism or in toxic
substance deactivation and an increased susceptibility to neoplastic
diseases, such as hepatocarcinoma
How efficient are coronal mass ejections at accelerating solar energetic particles?
The largest solar energetic particle (SEP) events are thought to be due to particle acceleration at a shock driven by a fast coronal mass ejection (CME). We investigate the efficiency of this process by comparing the total energy content of energetic particles with the kinetic energy of the associated CMEs. The energy content of 23 large SEP events from 1998 through 2003 is estimated based on data from ACE, GOES, and SAMPEX, and interpreted using the results of particle transport simulations and inferred longitude distributions. CME data for these events are obtained from SOHO. When compared to the estimated kinetic energy of the associated coronal mass ejections (CMEs), it is found that large SEP events can extract ~10% or more of the CME kinetic energy. The largest SEP events appear to require massive, very energetic CMEs
Use of Hydroacoustic Methods for the Identification of Potential Seabed Habitats for Small Pelagic Fish Schools in the Strait of Sicily
Hybrid viscosity and the magnetoviscous instability in hot, collisionless accretion disks
We aim to illustrate the role of hot protons in enhancing the
magnetorotational instability (MRI) via the ``hybrid'' viscosity, which is due
to the redirection of protons interacting with static magnetic field
perturbations, and to establish that it is the only relevant mechanism in this
situation. It has recently been shown by Balbus \cite{PBM1} and Islam & Balbus
\cite{PBM11} using a fluid approach that viscous momentum transport is key to
the development of the MRI in accretion disks for a wide range of parameters.
However, their results do not apply in hot, advection-dominated disks, which
are collisionless. We develop a fluid picture using the hybrid viscosity
mechanism, that applies in the collisionless limit. We demonstrate that viscous
effects arising from this mechanism can significantly enhance the growth of the
MRI as long as the plasma \beta \gapprox 80. Our results facilitate for the
first time a direct comparison between the MHD and quasi-kinetic treatments of
the magnetoviscous instability in hot, collisionless disks.Comment: To appear in the proceedings of the first Kodai-Trieste workshop on
Plasma Astrophysics (Aug 27-Sept 07 2007), Springer Astrophysics and Space
Science Proceedings serie
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Small, Low-energy, Dispersive Solar Energetic Particle Events Observed by Parker Solar Probe
The Energetic Particle InstrumentâLow Energy (EPI-Lo) experiment has detected several weak, low-energy (~30â300 keV nucleonâ»Âč) solar energetic particle (SEP) events during its first two closest approaches to the Sun, providing a unique opportunity to explore the sources of low-energy particle acceleration. As part of the Parker Solar Probe (PSP) Integrated Science Investigation of the Sun (ISâIS) suite, EPI-Lo was designed to investigate the physics of energetic particles; however, in the special lowest-energy "time-of-flight only" product used in this study, it also responds to solar photons in a subset of approximately sunward-looking apertures lacking special light-attenuating foils. During the first three perihelia, in a frame rotating with the Sun, PSP undergoes retrograde motion, covering a 17° heliographic longitudinal range three times during the course of the ~11-day perihelion passes, permitting a unique spatial and temporal study into the location, correlation, and persistence of previously unmeasurable SEPs. We examine the signatures of these SEPs (during the first PSP perihelion pass only) and the connection to possible solar sources using remote observations from the Solar Dynamics Observatory (SDO), the Solar TErrestrial RElations Observatory (STEREO), and the ground-based Global Oscillation Network Group (GONG). The orientation of the Sun relative to STEREO, SDO, and GONG makes such identifications challenging, but we do have several candidates, including an equatorial coronal hole at a Carrington longitude of ~335°. To analyze observations from EPI-Lo, which is a new type of particle instrument, we examine instrumental effects and provide a preliminary separation of the ion signal from the photon background
Solar interacting protons versus interplanetary protons in the core plus halo model of diffusive shock acceleration and stochastic re-acceleration
With the first observations of solar Îł-rays from the decay of pions, the relationship of protons producing ground level enhancements (GLEs) on the Earth to those of similar energies producing the Îł-rays on the Sun has been debated. These two populations may be either independent and simply coincident in large flares, or they may be, in fact, the same population stemming from a single accelerating agent and jointly distributed at the Sun and also in space. Assuming the latter, we model a scenario in which particles are accelerated near the Sun in a shock wave with a fraction transported back to the solar surface to radiate, while the remainder is detected at Earth in the form of a GLE. Interplanetary ions versus ions interacting at the Sun are studied for a spherical shock wave propagating in a radial magnetic field through a highly turbulent radial ray (the acceleration core) and surrounding weakly turbulent sector in which the accelerated particles can propagate toward or away from the Sun. The model presented here accounts for both the first-order Fermi acceleration at the shock front and the second-order, stochastic re-acceleration by the turbulence enhanced behind the shock. We find that the re-acceleration is important in generating the Îł-radiation and we also find that up to 10% of the particle population can find its way to the Sun as compared to particles escaping to the interplanetary space
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