4,191 research outputs found
Planar channeling and quasichanneling oscillations in a bent crystal
Particles passing through a crystal under planar channeling experience
transverse oscillations in their motion. As channeled particles approach the
atomic planes of a crystal, they are likely to be dechanneled. This effect was
used in ion-beam analysis with MeV energy. We studied this effect in a bent
crystal for positive and negative particles within a wide range of energies in
sight of application of such crystals at accelerators. We found the conditions
for the appearance or not of channeling oscillations. Indeed a new kind of
oscillations, strictly related to the motion of over-barrier particles, i.e.
quasichanneling particles, has been predicted. Such oscillations, named planar
quasichanneling oscillations, possess a different nature than channeling
oscillations. Through computer simulation, we studied this effect and provided
a theoretical interpretation for them. We show that channeling oscillations can
be observed only for positive particles while quasichanneling oscillations can
exist for particles with either sign. The conditions for experimental
observation of channeling and quasichanneling oscillations at existing
accelerators with available crystal has been found and optimized.Comment: 25 pages, 11 figure
CALCULATION OF NEUTRON-CAPTURE REACTIONS CONTRIBUTION TO ENERGY RELEASE IN VVER-1000 USING SERPENT CODE
Calculating the energy release in fuel elements is an important aspect of the modeling and design of nuclear reactors. Most of the energy is produced by fission, but a non-negligible percentage is coming from neutron capture reactions, such as (n, γ) or (n, α). We implement a previously developed method for the calculation of effective energy release using Serpent Monte Carlo code. We investigate the percentage of capture component in effective energy release for various models of VVER-1000 fuel: firstly, an equivalent cell, then fresh fuel assemblies of different compositions, differing in fuel enrichment and the presence of burnable absorbers. The results are compared to similar calculations previously done in MCNP 4 and MCU 5
Prediction of the Material Composition of the VVER-type Reactor Burned Pellet with Use of Neutron-Physical Codes
The purpose of neutron-physical calculations is typically isotopic composition of the fuel elements. However, in solving materials science problems related to nuclear fuel, researchers are usually interested in elemental composition of the fuel pellets, because the chemical and thermal physic properties are the same for differentisotopes of one chemical element. Nevertheless, for modeling of the elemental composition one should perform calculation of the isotopic composition and carry out the summation over all isotopes of a given chemical element. The development of computational tools allows the use of improved methods and codes, which held the consequent solution of tasks of heat conduction, neutron transport, and kinetics ofnuclides transformation. Thus the calculations take into account the dependence of the thermal conductivity from the changing isotopic composition and fuel burnup. This allows to perform neutron-physical and thermal-physical calculations of the reactor with detailed temperature distribution, taking into account temperature dependence of thermal conductivity and other characteristics. This approach was applied to calculations of the fuel pellet of the VVER type reactor and calculation of its elemental composition.
Keywords: materials science, elemental composition, fuel pellet
Models of assessment of the influence of insurance assets securitization on stability of mutual insurance societies
The article reviews approaches to assessing the effectiveness of the mechanism of insurance assets securitization used to enhance the financial stability of the mutual insurance society, determined by the level of probability of its default. The approaches are based on the methods of simulation modeling of the financial flows of the society formed taking into account the patterns of random payments, deterministic premiums, proceeds and securitization costs.
Following the results of a series of simulation experiments, the peculiarities of the influence of securitization on stability of a MIS are identified, and recommendations for its use are justified. The estimates of the costs of structuring the transaction are obtained, based on which a certain minimum volumes of securitization are determined, at which its use is appropriate.peer-reviewe
Space-Time Complexity in Hamiltonian Dynamics
New notions of the complexity function C(epsilon;t,s) and entropy function
S(epsilon;t,s) are introduced to describe systems with nonzero or zero Lyapunov
exponents or systems that exhibit strong intermittent behavior with
``flights'', trappings, weak mixing, etc. The important part of the new notions
is the first appearance of epsilon-separation of initially close trajectories.
The complexity function is similar to the propagator p(t0,x0;t,x) with a
replacement of x by the natural lengths s of trajectories, and its introduction
does not assume of the space-time independence in the process of evolution of
the system. A special stress is done on the choice of variables and the
replacement t by eta=ln(t), s by xi=ln(s) makes it possible to consider
time-algebraic and space-algebraic complexity and some mixed cases. It is shown
that for typical cases the entropy function S(epsilon;xi,eta) possesses
invariants (alpha,beta) that describe the fractal dimensions of the space-time
structures of trajectories. The invariants (alpha,beta) can be linked to the
transport properties of the system, from one side, and to the Riemann
invariants for simple waves, from the other side. This analog provides a new
meaning for the transport exponent mu that can be considered as the speed of a
Riemann wave in the log-phase space of the log-space-time variables. Some other
applications of new notions are considered and numerical examples are
presented.Comment: 27 pages, 6 figure
Topological properties of punctual Hilbert schemes of almost-complex fourfolds (I)
In this article, we study topological properties of Voisin's punctual Hilbert
schemes of an almost-complex fourfold . In this setting, we compute their
Betti numbers and construct Nakajima operators. We also define tautological
bundles associated with any complex bundle on , which are shown to be
canonical in -theory
Experimental evidence of planar channeling in a periodically bent crystal
The usage of a Crystalline Undulator (CU) has been identified as a promising
solution for generating powerful and monochromatic -rays. A CU was
fabricated at SSL through the grooving method, i.e., by the manufacturing of a
series of periodical grooves on the major surfaces of a crystal. The CU was
extensively characterized both morphologically via optical interferometry at
SSL and structurally via X-ray diffraction at ESRF. Then, it was finally tested
for channeling with a 400 GeV/c proton beam at CERN. The experimental results
were compared to Monte Carlo simulations. Evidence of planar channeling in the
CU was firmly observed. Finally, the emission spectrum of the positron beam
interacting with the CU was simulated for possible usage in currently existing
facilities
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