acta physica slovaca

Abstract: This paper presents a computer simulation of the electrical breakdown and influence of the insulator parameters (length, thickness, dielectric constant) on the discharge in a small Plasma Focus device. This model has been used to study the evolution of a discharge and especially its different character depending on the insulator parameters.

Abstract: Application of non-thermal plasma produced by pulsed corona discharge in water for degradation of 2-chlorophenol has been investigated in reactor with the needle-plate geometry of electrodes. It was shown that decomposition of 2-chlorophenol by the discharge can be refer\mbox{}red essentially to the oxidation by hydroxyl radical and it can be described by the first order kinetics. The complete removal of $500~\rm{\mu}mol.l^{-1}$ 2-chlorophenol by the discharge was attained in the presence of ferrous ions with the energy efficiency of $3.5\times10^{-3} ~\rm{\mu}mol.J^{-1}$. Chlorohydroquinone, chlorobenzoquinone, 3-chlorocatechol and catechol were detected as the primary decomposition products.

Abstract: It can be said that Maxwell's equations are one of the well-known equations of Physics. Despite the fact that this equations are more than hundred years old (1865), they still are the cornerstone of electrodynamics. Although they have several notations in the literature, this paper gives new representational method that based on dual quaternions. We have aimed the reformulation of classical electrodynamics. Therefore new dual quaternionic equations related with electromagnetism are derived.

Abstract: We present a stochastic non-perturbative analysis of the `rod model' of the theory of radiative transfer treating the `rods' of lengths $L$ as random media. The cross-section function $\sigma(x)$ (per unit length) is defined as a Gaussian random function with the mean value $\bar\sigma$, correlation length $\ell$ and variance $\eta_\sigma^2$. To characterize the random media, we introduce the parameter $\beta=\eta_\sigma\ \sqrt{\ell/{\bar\sigma}}$. If $L$ is fixed, the optical length $X=\int_0^L{\rm d}x\:\sigma(x)$ becomes random. Then also the values of the transmission and reflection coefficient, ${\cal T}(X)$ and ${\cal R}(X)$, are random. Since $X>0$ for physical reasons, we define the probability density of $X$ as a Gaussian only for $X>0$; if $X<0$, we define it as zero. (We show that if such a cut off were not considered and if the Gaussian distribution were extrapolated on the negative semiaxis of $X$, the stochastic analysis of the albedo problem would bear non-physical divergencies.) With this probability density, we carry out (both analytical and numerical) calculations of the first-order and second-order statistical moments of $\cal T$ and $\cal R$, as well as of the variances of $\cal T$ and $\cal R$, as functions of the averaged optical length ${\bar\sigma}L$ and of the parameter $\beta$. We calculate also the correlation function between the stochastic values of $\cal T$ and the stochastic values of $\cal R$.

Abstract: We discribe a model of jet quenching in nuclear collisions at RHIC energies. In the model, jet quenching is to be caused by interruption of jet formation by nucleons arriving at the position of jet formation in a time shorter than the jet formation time. Our mechanism predicts suppression of high-$\pt$ spectra also in d+Au reactions.

Abstract: The dissociative electron attachment to chloro and fluoro derivatives of ethane have been measured using swarm technique. The rate coefficients have been estimated for first time for many of them and the values of the rate coefficients have been correlated to the DEA energies.

Abstract: We study the long wavelength limit of a spin-$s$ Heisenberg antiferromagnetic chain with nearest neighbour interaction, via the nonlinear $\sigma $ model (NL$\sigma $M). We show by mean of Liouville theorem, that the topological term emerges naturally during the passage to a continuum limit field theory. The difference between bosonic and fermionic chains emerges only after the Heisenberg model is mapped onto a NL$\sigma $% M. The latter is developed further and tested for Heisenberg Hamitonian with first and second neighbour coupling, using Non abelian osonization and renormalization group argument. This gives a qualitative explanation of the so-called Haldane's conjecture.

Abstract: The problem of two-dimensional charge density waves is discussed in the context of the van Hove singularity located at the Fermi level. Exact analytical expressions for the CDW-transition temperature $T_{CDW}$, the isotope coefficient $\alpha_{CDW} $, CDW-order parameter at zero temperature $G\left(0\right) $ and discontinuity in the specific heat at critical temperature $\Delta C$ was derived. Our results show that in the presence of the van Hove singularity the isotope coefficient can have small values despite the fact that CDW originates from phonon-induced pairing. The ratio $2G\left( 0\right)/k_BT_{CDW}$ varies very little, whereas the temperature dependence of $\Delta C$ can be different from standard result.

Abstract: Results of polycarbonate plasma treatment in argon r.f. glow discharges as concern the chemical structure and surface free energy are presented. The oxygen-to-carbon ratio increased after the treatment indicating an increase of oxygen containing functional groups on the polycarbonate surface. Small amount of silicon as a result of previous depositions of organosilicon thin films in the same reactor and small amount of nitrogen coming probably from an exposure of the reactive surface to the atmosphere were found on the surface. The surface free energy increased after the treatment from the original value of 35~mJ/m$^2$ to 63--74~mJ/m$^2$. Effect of treatment time, gas flow rate, pressure and aging on the surface free energy was studied too. In order to study an improvement of adhesion between the polycarbonate and an additional coatings the organosilicon thin films were deposited on the untreated and plasma treated polycarbonate. The interfacial fracture resistance of such a system was qualitatively tested by ``cross-hatch peel test''. The initiation and propagation stage of the fracture were studied by depth sensing indentation method followed by an observation of the samples with an optical microscope.