19 research outputs found
Relating timed and register automata
Timed automata and register automata are well-known models of computation
over timed and data words respectively. The former has clocks that allow to
test the lapse of time between two events, whilst the latter includes registers
that can store data values for later comparison. Although these two models
behave in appearance differently, several decision problems have the same
(un)decidability and complexity results for both models. As a prominent
example, emptiness is decidable for alternating automata with one clock or
register, both with non-primitive recursive complexity. This is not by chance.
This work confirms that there is indeed a tight relationship between the two
models. We show that a run of a timed automaton can be simulated by a register
automaton, and conversely that a run of a register automaton can be simulated
by a timed automaton. Our results allow to transfer complexity and decidability
results back and forth between these two kinds of models. We justify the
usefulness of these reductions by obtaining new results on register automata.Comment: In Proceedings EXPRESS'10, arXiv:1011.601
Expansion of tungsten ions emitted from laser-produced plasma in axial magnetic and electric fields
The experimental results of the investigations on the influence
of external magnetic and electric fields on the characteristics
of a tungsten ion stream emitted from a plasma produced by the
Nd:glass laser (1 J, 1 ns) performed at IPPLM, Warsaw are
presented. A negatively biased target up to −15 kV and
a magnetic field up to 0.45 T were used in the experiment. A
set of ion collectors and an electrostatic cylindrical ion energy
analyzer located at small angles with respect to the laser beam
axis and at large distances from the target were applied for
ion measurements. The effect of an external magnetic field is
essential to plasma expansion, but the effect of the retarding
potential of the target is very weak in our experimental
conditions. The aim of the studies was to prove the possibility
of the optimization of ion beam parameters from laser-produced
plasma for the particular application as a laser ion source
coupled with the electron cyclotron resonance ion source for
particle accelerators
Measurement of ion emission from plasmas obtained with a 600 fs KrF laser
Ion emission from plasmas obtained by the use of a 600 fs, 36 mJ KrF laser operating at 248 nm was measured and analysed for a variety of targets at different laser intensities. The intensity was set by changing the distance between the focusing lens and the target. It was found that the ions emitted originate from impurities and ions from the bulk of the target can be produced only in the subsequent shots. Proton emission was identified from some targets, but the energy of the protons was low (less than 12 keV). A new silicon carbide semiconductor detector proved to be applicable for the collection of the ions
Self-focusing in processes of laser generation of highly-charged and high-energy heavy ions
Laser-beam interaction with expanding plasma was investigated using
the PALS high-power iodine-laser system. The interaction conditions are
significantly changing with the laser focus spot position. The decisive
role of the laser-beam self-focusing, participating in the production of
ions with the highest charge states, was proved
Angular distributions of ions emitted from laser plasma produced at various irradiation angles and laser intensities
AbstractAngular distributions of currents and velocities (energies) of ions produced at various target irradiation angles and laser intensities ranged from 1010 W/cm2 to 1017 W/cm2 were analyzed. It was confirmed that for low laser intensities the ion current distributions are always peaked along the target normal. However, at laser intensities comparable to or higher than 1014 W/cm2, the preferred direction of ion emission strongly depends on the irradiation geometry (laser focus setting, the irradiation angle), and can be off the target normal. This is very likely caused by the non-linear interaction of the laser beam with produced plasma, in particular, by the action of ponderomotive forces and the laser beam self-focusing
Factors influencing parameters of laser ion sources
Various applications demand various kinds of ions. Charge state, energy and the amount of laser produced ions depend, primary, on the wavelength, the energy, the pulse duration, and the focusing ability of the laser used. Angle of the target irradiation, angle of the ion extraction (recording), and mainly the focus setting may significantly influence especially the portion of ions with the highest charge states. The participation of non-linear processes on the generation of ions with extremely high parameters is demonstrated. The observed effects support the idea of a longitudinal structure of the self-focused laser beam with a space period of ∼200 µm
The influence of an intense laser beam interaction with preformed plasma on the characteristics of emitted ion streams
AbstractIntense laser-beam interactions with preformed plasma, preceding the laser-target interactions, significantly influence both the ion and X-ray generation. It is due to the laser pulse (its total length, the shape of the front edge, its background, the contrast, the radial homogeneity) as well as plasma (density, temperature) properties. Generation of the super fast (FF) ion groups is connected with a presence of non-linear processes. Saturated maximum of the charge states (independently on the laser intensity) is ascribed to the constant limit radius of the self-focused laser beam. Its longitudinal structure is considered as a possible explanation for the course of some experimental dependencies obtained
Praca informatyka w ocenie studentów kierunków ekonomicznych
Głównym celem niniejszego artykułu jest przedstawienie preferencji i oczekiwań studentów, związanych z ewentualnym podjęciem w przyszłości pracy w zawodzie informatyka. Analizie poddano postrzeganie przez studentów aktualnej sytuacji i warunków rynkowych, trendów rozwojowych, wyzwań, nadziei i obaw związanych z wykonywaniem pracy związanej z informatyką. Zbadano także bariery i uwarunkowania wyboru tego zawodu. Omówiono ponadto niedociągnięcia w szkolnictwie wyższym w tym zakresie oraz sposoby ich przezwyciężenia w osiąganiu przez studentów pozycji specjalistów IT. Badanie przeprowadzono metodą CAWI wśród studentów wybranych uczelni ekonomicznych w Polsce. Przeprowadzono dyskusję uzyskanych wyników i wyciągnięto wnioski, odnoszące się do poszczególnych aspektów prowadzonych badań. Sformułowano rekomendacje dotyczące oferty edukacyjnej dla studentów wybranych uczelni ekonomicznych pragnących pracować w zawodzie IT
High Power Laser Laboratory at the Institute of Plasma Physics and Laser Microfusion: equipment and preliminary research
The purpose of this paper is to present the newly-opened High Power Laser Laboratory (HPLL) at the Institute of Plasma Physics and Laser Microfusion (IPPLM). This article describes the laser, the main laboratory accessories and the diagnostic instruments. We also present preliminary results of the first experiment on ion and X-ray generation from laser-produced plasma that has been already performed at the HPLL