356 research outputs found
Vortical amplification of magnetic field at inward shock of supernova remnant Cassiopeia A
We present an interpretation of the time variability of the -ray flux
recently reported from a multi-epoch campaign of years observations of the
supernova remnant Cassiopeia A by {\it Chandra}. We show for the first time
quantitatively that the keV non-thermal flux increase up to
traces the growth of the magnetic field due to vortical amplification mechanism
at a reflection inward shock colliding with inner overdensities. The fast
synchrotron cooling as compared with shock-acceleration time scale
qualitatively supports the flux decrease.Comment: 5 pages, 2 figures, PRL in pres
Intrinsic non-symbiotic and truncated haemoglobins and heterologous Vitreoscilla haemoglobin expression in plants
To date, haemoglobins (Hbs) have been shown to exist in all kingdoms of life. The least studied and understood groups are plant non-symbiotic haemoglobins (nsHbs) and the recently found plant truncated Hbs (trHbs). From a biotechnological point of view, the best characterized and almost exclusively applied Hb is the bacterial Vitreoscilla haemoglobin (VHb). In this review, the present state of knowledge of structural features and ligand binding kinetics of plant nsHbs and trHbs and their proposed roles as oxygen carriers, oxygen sensors, and for oxygen storage, in nitric oxide (NO) detoxification, and in peroxidase activity are described. Furthermore, in order to predict the functioning of plant Hbs, their characteristics will be compared with those of the better known bacterial globins. In this context, the effects of heterologous applications of VHb on plants are reviewed. Finally, the challenging future of plant Hb research is discusse
Endogenous PttHb1 and PttTrHb, and heterologous Vitreoscilla vhb haemoglobin gene expression in hybrid aspen roots with ectomycorrhizal interaction
Present knowledge on plant non-symbiotic class-1 (Hb1) and truncated (TrHb) haemoglobin genes is almost entirely based on herbaceous species while the corresponding tree haemoglobin genes are not well known. The function of these genes has recently been linked with endosymbioses between plants and microbes. In this work, the coding sequences of hybrid aspen (Populus tremulaĂtremuloides) PttHb1 and PttTrHb were characterized, indicating that the key residues of haem and ligand binding of both genes were conserved in the deduced amino acid sequences. The expression of PttHb1 and PttTrHb was examined in parallel with that of the heterologous Vitreoscilla haemoglobin gene (vhb) during ectomycorrhiza/ectomycorrhizal (ECM) interaction. Both ECM fungi studied, Leccinum populinum and Xerocomus subtomentosus, enhanced root formation and subsequent growth of roots of all hybrid aspen lines, but only L. populinum was able to form mycorrhizas. Real-time PCR results show that the dual culture with the ECM fungus, with or without emergence of symbiotic structures, increased the expression of both PttHb1 and PttTrHb in the roots of non-transgenic hybrid aspens. PttHb1 and PttTrHb had expression peaks 5âh and 2âd after inoculation, respectively, pointing to different functions for these genes during interaction with root growth-improving fungi. In contrast, ECM fungi were not able to enhance the expression of hybrid aspen endogenous haemoglobin genes in the VHb lines, which may be a consequence of the compensating action of heterologous haemoglobi
Fine-structure in the nonthermal X-ray emission of SNR RX J1713.7-3946 revealed by Chandra
We present morphological and spectroscopic studies of the northwest rim of
the supernova remnant RX J1713.7-3946 based on observations by the Chandra
X-ray observatory. We found a complex network of nonthermal (synchrotron) X-ray
filaments, as well as a 'void' type structure -- a dim region of a circular
shape -- in the northwest rim. It is remarkable that despite distinct
brightness variations, the X-ray spectra everywhere in this region can be well
fitted with a power-law model with photon index around 2.3. We briefly discuss
some implications of these results and argue that the resolved X-ray features
in the northwest rim may challenge the perceptions of standard (diffusive
shock-acceleration) models concerning the production, propagation and radiation
of relativistic particles in supernova remnants.Comment: 8 pages, 9 figures; accepted for publication in A&A; significant
additions for publication in Main journal (previous version was for A&A
Letter); a manuscript (as a single PDF file, 501kb) including all figures is
available at http://www.astro.isas.ac.jp/~uchiyama/publication/h4106.pd
On the escape of cosmic rays from radio galaxy cocoons
(Abridged) A model for the escape of CR particles from radio galaxy cocoons
is presented here. It is assumed that the radio cocoon is poorly magnetically
connected to the environment. An extreme case of this kind is an insulating
boundary layer of magnetic fields, which can efficiently suppress particle
escape. More likely, magnetic field lines are less organised and allow the
transport of CR particles from the source interior to the surface region. For
such a scenario two transport regimes are analysed: diffusion of particles
along inter-phase magnetic flux tubes (leaving the cocoon) and cross field
transport of particles in flux tubes touching the cocoon surface. The cross
field diffusion is likely the dominate escape path, unless a significant
fraction of the surface is magnetically connected to the environment. Major
cluster merger should strongly enhance the particle escape by two complementary
mechanisms. i) The merger shock waves shred radio cocoons into filamentary
structures, allowing the CRs to easily reach the radio cocoon boundary due to
the changed morphology. ii) Also efficient particle losses can be expected for
radio cocoons not compressed in shock waves. There, for a short period after
the sudden injection of large scale turbulence, the (anomalous) cross field
diffusion can be enhanced by several orders of magnitude. This lasts until the
turbulent energy cascade has reached the microscopic scales, which determine
the value of the microscopic diffusion coefficients.Comment: A&A in press, 12 pages, 5 figures, minor language improvement
Constraints On the Diffusive Shock Acceleration From the Nonthermal X-ray Thin Shells In SN1006 NE Rim
Characteristic scale lengths of nonthermal X-rays from the SN1006 NE rim,
which are observed by Chandra, are interpreted in the context of the diffusive
shock acceleration on the assumption that the observed spatial profile of
nonthermal X-rays corresponds to that of accelerated electrons with energies of
a few tens of TeV. To explain the observed scale lengths, we construct two
simple models with a test particle approximation, where the maximum energy of
accelerated electrons is determined by the age of SN1006 (age-limited model) or
the energy loss (energy loss-limited model), and constrain the magnetic field
configuration and the diffusion coefficients of accelerated electrons. When the
magnetic field is nearly parallel to the shock normal, the magnetic field
should be in the range of 20-85 micro Gauss and highly turbulent both in
upstream and downstream, which means that the mean free path of accelerated
electrons is on the order of their gyro-radius (Bohm limit). This situation can
be realized both in the age-limited and energy loss-limited model. On the other
hand, when the magnetic field is nearly perpendicular to the shock normal,
which can exist only in the age-limited case, the magnetic field is several
micro Gauss in the upstream and 14-20 micro Gauss in the downstream, and the
upstream magnetic field is less turbulent than the downstream.Comment: 9 pages, 4 figures, accepted for publication in A&
Analytical view of diffusive and convective cosmic ray transport in elliptical galaxies
Context: An analytical solution of the generalized diffusive and convective
transport equation is derived to explain the transport of cosmic ray protons
within elliptical galaxies. Aims: Cosmic ray transport within elliptical
galaxies is an interesting element in understanding the origin of high
energetic particles measured on Earth. As probable sources of those high
energetic particles, elliptical galaxies show a dense interstellar medium as a
consequence of activity in the galactic nucleus or merging events between
galaxies. Thus it is necessary for an appropriate description of cosmic ray
transport to take the diffusive and convective processes in a dense
interstellar environment into account. Here we show that the transport
equations can be solved analytically with respect to the given geometry and
boundary conditions in position space, as well as in momentum space. Results:
The spatial solution is shown using a generalized source of cosmic rays.
Additionally, the special case of a jet-like source is illustrated. We present
the solution in momentum space with respect to an escape term for cosmic ray
protons depending on the spatial shape of the galaxy. For a delta-shape
injection function, the momentum solution is obtained analytically. We find
that the spectral index measured on Earth can be obtained by appropriately
choosing of the strength of Fermi I and Fermi II processes. From these results
we calculate the gamma-ray flux from pion decay due to proton-proton
interaction to give connection to observations. Additionally we determine the
escape-spectrum of cosmic rays. The results show that both spectra are harder
than the intrinsic power-law spectrum for cosmic rays in elliptical galaxies.Comment: 23 pages, 7 figures, accepted for publication in A&
Formation, Propagation, and Decay of Coherent Pulses of Solar Cosmic Rays
We have performed numerical simulations of the interplanetary transport of
solar cosmic rays. The particles form a coherent pulse within AU
after their injection. The gradual decrease of a pulse's speed and anisotropy
can be understood in terms of an equilibrium between pitch-angle scattering and
focusing. The results should be useful for estimating times of particle
injection.Comment: 4 pages (LaTeX) + 4 uuencoded-tarred-compressed postscript figures,
uses agupp.sty (available from ftp://xxx.lanl.gov/macros or
ftp://kosmos.agu.org/agutex), one 3D surface plot FAXed upon request.
Accepted by Geophysical Research Letter
The effect of heterologous VHb expression to the functioning of stress-related genes in hybrid aspen lines exposured to biotic stress
Particle scattering in turbulent plasmas with amplified wave modes
High-energy particles stream during coronal mass ejections or flares through the plasma of the solar wind. This causes instabilities, which lead to wave growth at specific resonant wave numbers, especially within shock regions. These amplified wave modes influence the turbulent scattering process significantly. In this paper, results of particle transport and scattering in turbulent plasmas with excited wave modes are presented. The method used is a hybrid simulation code, which treats the heliospheric turbulence by an incompressible magnetohydrodynamic approach separately from a kinetic particle description. Furthermore, a semi-analytical model using quasilinear theory (QLT) is compared to the numerical results. This paper aims at a more fundamental understanding and interpretation of the pitch-angle scattering coefficients. Our calculations show a good agreement of particle simulations and the QLT for broad-band turbulent spectra; for higher turbulence levels and particle beam driven plasmas, the QLT approximation gets worse. Especially the resonance gap at Îź = 0 poses a well-known problem for QLT for steep turbulence spectra, whereas test-particle computations show no problems for the particles to scatter across this region. The reason is that the sharp resonant wave-particle interactions in QLT are an oversimplification of the broader resonances in test-particle calculations, which result from nonlinear effects not included in the QLT. We emphasise the importance of these results for both numerical simulations and analytical particle transport approaches, especially the validity of the QLT.
Appendices A-D are available in electronic form at http://www.aanda.or
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