2,725 research outputs found
Nonlocal symmetries of integrable two-field divergent evolutionary systems
Nonlocal symmetries for exactly integrable two-field evolutionary systems of
the third order have been computed. Differentiation of the nonlocal symmetries
with respect to spatial variable gives a few nonevolutionary systems for each
evolutionary system. Zero curvature representations for some new nonevolution
systems are presented
Production of para-- and orthopositronium at relativistic heavy ion colliders
We consider the ortho-- and parapositronium production in the process Ps where A is a nucleus with the charge number Z. The inclusive cross
section and the energy distribution of the relativistic Ps are calculated which
are of primary interest from the experimental point of view. The accuracy of
the corresponding cross sections is given by omitting terms for the para--Ps and for the ortho--Ps production
where and 16 for the RHIC and the LHC. Within this
accuracy the multiphoton (Coulomb) corrections are taken into account. We show
that the RHIC and the LHC will be Ps factories with a productions rate of about
relativistic Ps per day. The fraction of the ortho--Ps is
expected to be of the same order as that of the para--Ps for Au--Au and Pb--Pb
collisions.Comment: 22 pages, 5 figures, RevTeX, misprint correcte
Thermodynamics of a mixed quantum-classical Heisenberg model in two dimensions
We study the planar antiferromagnetic Heisenberg model on a decorated
hexagonal lattice, involving both classical spins (occupying the vertices) and
quantum spins (occupying the middle of the links). This study is motivated by
the description of a recently synthesized molecular magnetic compound. First,
we trace out the spin 1/2 degrees of freedom to obtain a fully classical model
with an effective ferromagnetic interaction. Then, using high temperature
expansions and Monte Carlo simulations, we analyse its thermal and magnetic
properties. We show that it provides a good quantitative description of the
magnetic susceptibility of the molecular magnet in its paramagnetic phase.Comment: Revtex, 6 pages, 4 included postscript figures, fig.1 upon request to
[email protected] . To appear in J. of Physic C (condensed matter
Photoconductivity of CdS-CdSe granular films: influence of microstructure
We study experimentally the photoconductivity of CdS-CdSe sintered granular
films obtained by the screen printing method. We mostly focus on the
dependences of photoconductivity on film's microstructure, which varies with
changing heat-treatment conditions. The maximum photoconductivity is found for
samples with compact packing of individual grains, which nevertheless are
separated by gaps. Such a microstructure is typical for films heat-treated
during an intermediate (optimal) time. In order to understand whether the
dominant mechanism of charge transfer is identical with the one in
monocrystals, we perform temperature measurements of photoresistance.
Corresponding curves have the same peculiar nonmonotonic shape as in CdSe
monocrystals, from which we conclude that the basic mechanism is also the same.
It is suggested that the optimal heat-treatment time appears as a result of a
competition between two mechanisms: improvement of film's connectivity and its
oxidation. Photoresistance is also measured in vacuum and in helium atmosphere,
which suppress oxygen and water absorption/chemisorption at intergrain
boundaries. We demonstrate that this suppression increases photoconductivity,
especially at high temperatures.Comment: 12 pages, 8 figures, final versio
Binary collisions of charged particles in a magnetic field
Binary collisions between charged particles in an external magnetic field are
considered in second-order perturbation theory, starting from the unperturbed
helical motion of the particles. The calculations are done with the help of an
improved binary collisions treatment which is valid for any strength of the
magnetic field, where the second-order energy and velocity transfers are
represented in Fourier space for arbitrary interaction potentials. The energy
transfer is explicitly calculated for a regularized and screened potential
which is both of finite range and non-singular at the origin, and which
involves as limiting cases the Debye (i.e., screened) and Coulomb potential.
Two distinct cases are considered in detail. (i) The collision of two identical
(e.g., electron-electron) particles; (ii) and the collision between a
magnetized electron and an uniformly moving heavy ion. The energy transfer
involves all harmonics of the electron cyclotron motion. The validity of the
perturbation treatment is evaluated by comparing with classical trajectory
Monte--Carlo calculations which also allows to investigate the strong
collisions with large energy and velocity transfer at low velocities. For large
initial velocities on the other hand, only small velocity transfers occur.
There the non-perturbative numerical classical trajectory Monte--Carlo results
agree excellently with the predictions of the perturbative treatment.Comment: submitted to Phys. Rev.
Quantum circuits for spin and flavor degrees of freedom of quarks forming nucleons
We discuss the quantum-circuit realization of the state of a nucleon in the
scope of simple symmetry groups. Explicit algorithms are presented for the
preparation of the state of a neutron or a proton as resulting from the
composition of their quark constituents. We estimate the computational
resources required for such a simulation and design a photonic network for its
implementation. Moreover, we highlight that current work on three-body
interactions in lattices of interacting qubits, combined with the
measurement-based paradigm for quantum information processing, may also be
suitable for the implementation of these nucleonic spin states.Comment: 5 pages, 2 figures, RevTeX4; Accepted for publication in Quantum
Information Processin
A Possibility of Detecting Fast Neutrons in a 10B Solid-gas Detector
The possibility of detecting thermal and fast neutrons in 10B solid-gas detector is considered. The simulation of the neutron detection process shows a significant difference in the detector signals caused by neutrons of different energies. An experimental verification of the detector’s operation was performed using W-Be photoneutron source with different ratio of fast and thermal neutrons incident on the detector. The measured amplitude spectra of the signals for different neutron energies were compared with the simulation results. The qualitative agreement between experimental and calculated data indicates the possibility of using this detector for recording thermal and fast neutrons
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