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

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

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 $\gamma$-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

Meson vacuum phenomenology in a three-flavor linear sigma model with (axial-)vector mesons

We study scalar, pseudoscalar, vector, and axial-vector mesons with non-strange and strange quantum numbers in the framework of a linear sigma model with global chiral $U(N_f)_L \times U(N_f)_R$ symmetry. We perform a global fit of meson masses, decay widths, as well as decay amplitudes. The quality of the fit is, for a hadronic model that does not consider isospin-breaking effects, surprisingly good. We also investigate the question whether the scalar $\bar{q}q$ states lie below or above 1 GeV and find the scalar states above 1 GeV to be preferred as $\bar{q}q$ states. Additionally, we also describe the axial-vector resonances as $\bar{q}q$ states.Comment: 29 pages, 4 figures, 3 tables. v2 is the updated version after referee remarks (dilaton field discussed, a new figure added

Stimulation of platelet glycoprotein IIb-IIIa (αIIbβ3-integrin) functional activity by a monoclonal antibody to the N-terminal region of glycoprotein IIIa

AbstractPlatelet glycoprotein (GP) IIb-IIIa complex (αIIbβ3-integrin) changes its conformation upon platelet activation that results in binding of RGD-containing ligands and expression of ligand-induced binding site (LIBS) neoepitopes. Anti-GIIb-IIIa monoclonal antibody (monAB) CRC54 bound to ≤10% of GPIIb-IIIa on resting platelets but binding was enhanced by the occupation of GPIIb-IIIa with RGDS peptide and by platelet activation indicating that CRC54 is directed against LIBS epitope. The epitope was located within the first 100 N-terminal residues of GPIIIa and differed from other LIBS epitopes. CRC54 as well as its Fab fragments were able to induce platelet aggregation. CRC54 also stimulated interaction of GPIIb-IIIa with its ligands (fibrinogen and fibronectin) and conformation-dependent antibodies. The results indicated that changes of GPIIb-IIIa conformation, binding of ligands and platelet aggregation could be stimulated via interaction of anti-LIBS antibody with the N-terminal part of GPIIIa