601 research outputs found
Hadronic Gamma Rays from Supernova Remnants
A gas cloud near a supernova remnant (SNR) provides a target for
pp-collisions leading to subsequent gamma-ray emission through neutral pion
decay. The assumption of a power-law ambient spectrum of accelerated particles
with index near -2 is usually built into models predicting the spectra of
very-high energy (VHE) gamma-ray emission from SNRs. However, if the gas cloud
is located at some distance from the SNR shock, this assumption is not
necessarily correct. In this case, the particles which interact with the cloud
are those leaking from the shock and their spectrum is approximately
monoenergetic with the injection energy gradually decreasing as the SNR ages.
In the GLAST energy range the gamma-ray spectrum resulting from particle
interactions with the gas cloud will be flatter than expected, with the cutoff
defined by the pion momentum distribution in the laboratory frame. We evaluate
the flux of particles escaping from a SNR shock and apply the results to the
VHE diffuse emission detected by the HESS at the Galactic centre.Comment: 4 pages, 3 figures. Contribution to the 30th ICRC, Merida, Mexico,
2007 (final version
On the mechanism for breaks in the cosmic ray spectrum
The proof of cosmic ray (CR) origin in supernova remnants (SNR) must hinge on
full consistency of the CR acceleration theory with the observations; direct
proof is impossible because of the orbit stochasticity of CR particles. Recent
observations of a number of galactic SNR strongly support the SNR-CR connection
in general and the Fermi mechanism of CR acceleration, in particular. However,
many SNR expand into weakly ionized dense gases, and so a significant revision
of the mechanism is required to fit the data. We argue that strong ion-neutral
collisions in the remnant surrounding lead to the steepening of the energy
spectrum of accelerated particles by \emph{exactly one power}. The spectral
break is caused by a partial evanescence of Alfven waves that confine particles
to the accelerator. The gamma-ray spectrum generated in collisions of the
accelerated protons with the ambient gas is also calculated. Using the recent
Fermi spacecraft observation of the SNR W44 as an example, we demonstrate that
the parent proton spectrum is a classical test particle power law , steepening to at .Comment: APS talk to appear in PoP, 4 figure
Aperiodic Schrodinger Crystals
In 1945, E. Schrödinger predicted the possibility of the existence of "aperiodic crystals,"that is, more and more increasing crystalline aggregates, but without a simple lattice repetition mechanism. In the present work, such structures are experimentally prepared using selenium as an example. By thermal gradient treatment of the amorphous selenium film, we have obtained nano-thin spatial dissipative structures (SDS) of hexagonal selenium, the lattice of which undergoes non-uniform rotational curvature around, in the general case, three mutually perpendicular directions. The formation of these nano-thin SDS of hexagonal selenium occurs as a result of cooperative rotations of selenium macromolecules around, in general, three mutually perpendicular directions. Since nano-thin SDS after hardening in air have all the features of crystals each of the above nano-thin SDS of hexagonal selenium obtained at different annealing temperatures corresponds to the concept of "aperiodic crystals"Thus, "aperiodic crystals"were obtained experimentally, the possibility of the existence of which was predicted by E. Schrödinger. © Published under licence by IOP Publishing Ltd
Study of Physical Properties and Physical Processes in Nano-thin Spatial Dissipative Structures
Two-dimensional geometric object "neutral surface"- successfully used to study thin plates. The use of this two-dimensional geometric object is not possible for the study of physical properties and physical processes in nano-thin SDS (spatial dissipative structures). The SDS lattice undergoes a rotational curvature around three mutually perpendicular directions, and the nano-thin SDS itself remains flat. We have developed a method for the study of nano-thin SDS with rotary lattice curvature. We used as a basis the method of visualizing the rotational curvature of the lattice by constructing a two-dimensional geometric object - the surface of the lattice curvature by nano-thin SDS. This method of investigation involves application of the lattice curvature surface with nano-thin SDS for the selected crystallographic direction as a "neutral surface". The method will find application in nanotechnology. © Published under licence by IOP Publishing Ltd
Nanofine spatial dissipative structures with azimutal lattice curvation
The nanofine spatial dissipative structures (NSDS) were characterized by transmission electron microscopy and electron diffraction. The NSDS obtained by thermogradiently processing an amorphous selenium film by unilateral heating of its lower surface at T = 413 K preliminarily. The results indicate that the NSDS of hexagonal selenium obtained in an amorphous film possess an azimuthal curvature of the lattice and a nonlinear fan-shaped system of flexural contours on their electron microscopic image. The lattice of the above NSDS undergoes elastic - plastic rotational curvature around three mutually perpendicular directions. The lattice rotation angles of hexagonal selenium NSDS reach: around [001], - 25 , around the direction perpendicular [001] and lying in the plane of the amorphous film - 32 , around the direction perpendicular to the first two ones and not lying in the plane of the amorphous film - azimuthal curvature of the lattice, - 35 . Thus, as a result of electron-microscopic and microdiffraction studies, it was found that NSDS of hexagonal selenium with azimuthal curvature of the lattice, causing the curvature of its habitus, are in a nonequilibrium state. © Published under licence by IOP Publishing Ltd
Phenomenon of relaxation of inhomogeneous elastic rotational curvature of the lattice of nanofine spatial dissipative structures of hexagonal selenium
Nanofine rhomboid spatial dissipative structures (NRSDS) of hexagonal selenium were found and studied by means of transmission electron microscopy in amorphous Se films coated with nanofine layers of amorphous carbon, at a temperature of their thermo gradient treatment of 423 K. As a result, pictures were received of fan-shaped linear bending extinction contours on the electron-microscopic images of NRSDS. It was shown that in the above NRSDS take place continuous linear increase in the bend radius of the lattice along [001], due to continuous linear relaxation of the inhomogeneous elastic torsion of the lattice around [001]. The continuous linear relaxation of the elastic rotational curvature of the lattice around [001] in NRSDS of hexagonal selenium with inhomogeneous elastic rotational curvature of the lattice covers the entire nanofine rhomboid spatial dissipative structures, and not its part, as is the case with the formation of interblock boundaries in the nanofine rhomboid spatial dissipative structures. © Published under licence by IOP Publishing Ltd
PREPARATION A SERIES OF ATROPISOMERIC BIPY-DIOXIDES BY OXIDATIVE COUPLING AND THEIR APPLICATION IN ASYMMETRIC CATALYSIS
The authors thank the Russian Science Foundation for Grant No. 18-73-10156
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