0000000000038469
AUTHOR
W. Olchawa
Pressure Shift and Gravitational Red Shift of Balmer Lines in White Dwarfs. Rediscussion
The Stark-induced shift and asymmetry, the so-called pressure shift (PS) of $H_\alpha$ and $H_\beta$ Balmer lines in spectra of DA white dwarfs (WDs), as masking effects in measurements of the gravitational red shift in WDs, have been examined in detail. The results are compared with our earlier ones from before a quarter of a century (Grabowski et al. 1987, hereafter ApJ'87; Madej and Grabowski 1990). In these earlier papers, as a dominant constituent of the Balmer-line-profiles, the standard, symmetrical Stark line profiles, shifted as the whole by PS-effect, were applied to all spectrally active layers of the WD atmosphere. At present, in each of the WD layers, the Stark-line-profiles (e…
On multi-scale percolation behaviour of the effective conductivity for the lattice model with interacting particles
Recently, the effective medium approach using 2x2 basic cluster of model lattice sites to predict the conductivity of interacting droplets has been presented by Hattori et al. To make a step aside from pure applications, we have studied earlier a multi-scale percolation, employing any kxk basic cluster for non-interacting particles. Here, with interactions included, we examine in what way they alter the percolation threshold for any cluster case. We found that at a fixed length scale k the interaction reduces the range of shifts of the percolation threshold. To determine the critical concentrations, the simplified model is used. It diminishes the number of local conductivities into two main…
Experimental and theoretical Stark broadening studies of the hydrogen Paschen beta line.
Experimental and theoretical Stark broadening studies of the Paschen beta line of hydrogen (lambda=1.28 microm) are reported. Line shape measurements were performed at electron densities of the plasma between 3.5 x 10(15) cm(-3) and 7.5 x 10(15) cm(-3), applying as the light source a wall-stabilized arc operated at atmospheric pressure in a helium-hydrogen gas mixture. The radiation of the plasma, emitted from nearly homogeneous plasma layers in the end-on direction, was registered with the use of a grating spectrometer equipped with a charge coupled device detector. The measured light outputs were calibrated against signals obtained from a tungsten strip radiation standard. The experimenta…
On multi-scale percolation behaviour of the effective conductivity for the lattice model
Macroscopic properties of heterogeneous media are frequently modelled by regular lattice models, which are based on a relatively small basic cluster of lattice sites. Here, we extend one of such models to any cluster's size kxk. We also explore its modified form. The focus is on the percolation behaviour of the effective conductivity of random two- and three-phase systems. We consider only the influence of geometrical features of local configurations at different length scales k. At scales accessible numerically, we find that an increase in the size of the basic cluster leads to characteristic displacements of the percolation threshold. We argue that the behaviour is typical of materials, w…
A new approach to determination of the asymmetry parameter of Stark-broadened isolated spectral lines
A new approach to evaluation of asymmetry parameters of Stark-broadened isolated spectral lines is presented. The procedure is discussed on the example of the N I line at λ = 9822.75 A. Line shape measurements were performed using a wall-stabilized arc, operated at atmospheric pressure. The radiation of the plasma, emitted from homogeneous plasma layers in end-on direction, was measured using a grating spectrometer equipped with a two-dimensional CCD detector. Griem-like profiles, convoluted with the corresponding Doppler and apparatus profiles, were fitted to experimental data. In this way the Stark broadening parameters (electron impact widths, shifts and asymmetry) have been determined. …
Comparison of hydrogen Balmer-alpha Stark profiles measured at high electron densities with theoretical results
Profiles of the H-alpha line calculated using the full computer simulation method (FCSM) and the standard theory (ST) agree excellently with a measured profile (at an electron density of Ne = 9.0 × 1016 cm−3 and temperature T = 12 600 K) in an argon–hydrogen (minority) arc plasma. Calculated widths (FCSM) and shifts (ST) also agree well with experimental data from flash-tube plasmas and gas-linear pinch plasmas. Some discrepancies are probably caused by experimental flaws. Our analysis of the so-called generalized theory (GT) shows that this theory is burdened with un-physical approximations, and consequently so are all subsequent modifications based on GT. It is shown that the so-called ac…
Stark broadening of hydrogen spectral lines with fine structure effects
Formalism and numerical code have been elaborated for calculation of hydrogen line profiles in conditions of plasma in which Stark broadening and fine energy splitting are comparable and it is not possible to neglect either of them. It corresponds to the range of electron densities $10^{11} < N_e ({\rm cm}^{-3}) < 10^{15}$ . Lamb shift and spontaneous emission effects have also been included. Computer simulation method was applied in the calculations. Final results have been compared with experimental and theoretical findings by other authors.
Stark-Broadening Studies of N(I) Multiplet 3p 4P o–3d 4D at 1052.630 nm
Stark-broadening studies of the N(I) multiplet 3p 4P o –3d 4D are reported. Our experimental electron impact widths of spectral lines are compared with the results of our calculations: (i) according to the standard impact theory of Griem with modification, (ii) using a computer simulation method which is based on numerical N-body code (CSM). Line shape measurements were performed using a wallstabilized arc. The radiation of the plasma emitted from homogenous plasma layers was measured using a grating spectrometer equipped with a two-dimensional detector.
Statistical Reconstruction of Microstructures Using Entropic Descriptors
We report a multiscale approach of broad applicability to stochastic reconstruction of multiphase materials, including porous ones. The approach devised uses an optimization method, such as the simulated annealing (SA) and the so-called entropic descriptors (EDs). For a binary pattern, they quantify spatial inhomogeneity or statistical complexity at discrete length-scales. The EDs extract dissimilar structural information to that given by two-point correlation functions (CFs). Within the SA, we use an appropriate cost function consisting of EDs or comprised of EDs and CFs. It was found that the stochastic reconstruction is computationally efficient when we begin with a preliminary synthetic…
Computer simulation and experimental studies of the N I 3p 2S o 1/2 − 3d 2P1/2 spectral line Stark broadening
A computer simulation method, dedicated to lines, which energy levels are influenced only by the quadratic Stark effect, is introduced and tested in this paper. The simulated profiles of the well isolated N I line 3p 2So 1/2 – 3d 2P1/2 are compared with experimental ones.
Sensitivity to Initial Conditions in an Extended Activator--Inhibitor Model for the Formation of Patterns
Despite simplicity, the synchronous cellular automaton [D.A. Young, Math. Biosci. 72, 51 (1984)] enables reconstructing basic features of patterns of skin. Our extended model allows studying the formatting of patterns and their temporal evolution also on the favourable and hostile environments. As a result, the impact of different types of an environment is accounted for the dynamics of patterns formation. The process is based on two diffusible morphogens, the short-range activator and the long-range inhibitor, produced by differentiated cells (DCs) represented as black pixels. For a neutral environment, the extended model reduces to the original one. However, even the reduced model is stat…
Low-cost approximate reconstructing of heterogeneous microstructures
We propose an approximate reconstruction of random heterogeneous microstructures using the two-exponent power-law (TEPL). This rule originates from the entropic descriptor (ED) that is a multi-scale measure of spatial inhomogeneity for a given microstructure. A digitized target sample is a cube of linear size L in voxels. Then, a number of trial configurations can be generated by a model of overlapping spheres of a fixed radius, which are randomly distributed on a regular lattice. The TEPL describes the averaged maximum of the ED as a function of the phase concentration and the radius. Thus, it can be used to determine the radius. The suggested approach is tested on surrogate samples of cer…
Controlling spatial inhomogeneity in prototypical multiphase microstructures
A wide variety of real random composites can be studied by means of prototypes of multiphase microstructures with a controllable spatial inhomogeneity. To create them, we propose a versatile model of randomly overlapping super-spheres of a given radius and deformed in their shape by the parameter p. With the help of the so-called decomposable entropic measure, a clear dependence of the phase inhomogeneity degree on the values of the parameter p is found. Thus, a leading trend in changes of the phase inhomogeneity can be forecast. It makes searching for possible structure/property relations easier. For the chosen values of p, examples of two and three-phase prototypical microstructures show …
Paschen β line shape studies in low-temperature plasmas
Line shape calculations and measurements of the Paschen β line of hydrogen (λ=12818 Å) are reported. Measurements were performed at electron densities of the plasma between 1015 cm-3 and 1016 cm-3. A wall-stabilized arc operated at atmospheric pressure in a helium-hydrogen gas mixture was applied as the excitation source. The radiation of the plasma, originating from nearly homogeneous plasma layers, in the end-on direction, was analyzed. A grating spectrometer equipped with a CCD detector was used for the radiation detection. The measured line profiles are compared with results of available experimental and theoretical Stark broadening data e.g. based on simulation techniques, applied also…
Perturber's charge effect on Stark broadened hydrogen lines in helium plasmas
Abstract The Stark line profiles for hydrogen Ly α , Ly β , Hα, and Hβ are calculated using the computer simulation method for helium plasmas in the range of electron concentration from 1018 to 10 19 cm −3 at increasing temperature values kT from 7 to 10 eV , according to the experimental measurements in dense plasmas (Bochum experiment). The calculation was carried out at two limiting assumptions about the perturbers: (a) in the helium plasma only singly ionized helium ions occur, and (b) in the plasma the doubly ionized ions exclusively exist. In the paper the ratio of the calculated full half-widths, FWHM(b)/FWHM(a), for these lines are presented. The ratio equals about to 1.1 for Lyβ an…
Speeding up of microstructure reconstruction: II. Application to patterns of poly-dispersed islands
We report a fast, efficient and credible statistical reconstruction of any two-phase patterns of islands of miscellaneous shapes and poly-dispersed in sizes. In the proposed multi-scale approach called a weighted doubly-hybrid, two different pairs of hybrid descriptors are used. As the first pair, we employ entropic quantifiers, while correlation functions are the second pair. Their competition allows considering a wider spectrum of morphological features. Instead of a standard random initial configuration, a synthetic one with the same number of islands as that of the target is created by a cellular automaton. This is the key point for speeding-up of microstructure reconstruction, making u…
A critical analysis of the advanced generalized theory: Applicability and applications
Abstract A recent series of theoretical works (“advanced generalized theory”) has been proposed and applied to the analysis of hydrogen lines, particularly H α in plasmas. The “advanced generalized theory” (AGT) [JQSRT 1994;51:129, Phys Rev E 1999;60:R2480, JQSRT 2000; 65:405] is critically examined, both theoretically and in applications to the analysis of experimental data. A number of serious flaws are exposed and discussed. The major flaws include using an inconsistent perturbation theory and erroneous Weisskopf radius-type arguments to access dynamic behavior. Further, the results derived from calculations using the theory are in disagreement with both exact analytic results and benchm…
A Two-Stage Reconstruction of Microstructures with Arbitrarily Shaped Inclusions
The main goal of our research is to develop an effective method with a wide range of applications for the statistical reconstruction of heterogeneous microstructures with compact inclusions of any shape, such as highly irregular grains. The devised approach uses multi-scale extended entropic descriptors (ED) that quantify the degree of spatial non-uniformity of configurations of finite-sized objects. This technique is an innovative development of previously elaborated entropy methods for statistical reconstruction. Here, we discuss the two-dimensional case, but this method can be generalized into three dimensions. At the first stage, the developed procedure creates a set of black synthetic …
Effective electrical conductivity of microstructural patterns of binary mixtures on a square lattice in the presence of nearest-neighbour interactions
Abstract The effective conductivity and percolative behaviour of microstructural patterns of binary mixtures are studied. Microstructure patterns are not entirely random, but result from the presence of attractive or repulsive interactions and thermal fluctuations. The interactions of the particles with one another lead to the formation of correlations between particle positions, while thermal fluctuations weaken these correlations. A simple lattice model is used, where each site is occupied by a single particle, and interactions can occur only between the nearest neighbours. The Kawasaki algorithm is adopted to create 2D microstructure samples. The microstructure is treated as a continuous…
Calculations of Stark-broadened line shapes in phase-conjugate degenerate four-wave mixing laser spectroscopy
The Stark-broadened line shapes for phase-conjugate degenerate four-wave mixing (PCDFWM) laser spectroscopy are studied. The line profiles are calculated for high-density $({N}_{e}g{10}^{21}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{\ensuremath{-}3})$ plasma conditions and for different contributions of the Doppler broadening. Calculations are performed in the limit of low laser intensities using the perturbation approach. The theoretical model takes into account the Stark effect together with the ion dynamics, the electron collisions, and the Doppler effect. The resultant PCDFWM spectral profiles are significantly less broadened and less asymmetric than the emission profiles but shifted by s…
Speeding up of microstructure reconstruction: I. Application to labyrinth patterns
Recently, entropic descriptors based the Monte Carlo hybrid reconstruction of the microstructure of a binary/greyscale pattern has been proposed (Piasecki 2011 Proc. R. Soc. A 467 806). We try to speed up this method applied in this instance to the reconstruction of a binary labyrinth target. Instead of a random configuration, we propose to start with a suitable synthetic pattern created by cellular automaton. The occurrence of the characteristic attributes of the target is the key factor for reducing the computational cost that can be measured by the total number of MC steps required. For the same set of basic parameters, we investigated the following simulation scenarios: the biased/rando…
Computer simulations of hydrogen spectral line shapes in dense plasmas
A new formalism has been elaborated for calculations of hydrogen line profiles emitted by dense plasmas. The main equation of this formalism has a similar form to a set of close-coupled, time-dependent partial differential equations. Calculated line shapes are broadened, shifted and asymmetrical. The formalism yields both shifts and widths of a line calculated within the same theoretical approach. A new basis of the appropriate subspace of the Hilbert space has been built. This basis gives an accurate description of the quadratic Stark effect, and the interaction of the emitter with field gradients. The computer simulation has been used to determine the emitter perturbations by electrons an…
Dispersion of pressure at the inner edge of the neutron star crust
This paper presents a method for estimating the pressure variance at the inner edge of a neutron star crust. The obtained results quantify uncertainty in the estimation of pressure at the core-crust interface, implying that they depend on the selected equation of state and the neutron star’s mass distribution function. The quality of the transition pressure determination depends on the neutron star’s mass, with a significant decrease in accuracy for configurations with masses close to 2M . The method used makes it possible to control the theoretical part of the core-crust pressure dispersion in determining the observational quantities.
Experimental and theoretical studies of Stark profiles of Ar I 696.5 nm spectral line in laser-induced plasma
Abstract We report the results of the Stark profile studies of the 696.543 nm Ar I spectral line in laser-induced plasma generated by a nanosecond Nd:YAG laser radiation at 532 nm in argon at reduced pressure. Plasma diagnostics was performed with the use of the laser Thomson scattering method, free from assumptions about the plasma thermodynamic equilibrium, its composition but also independently of plasma emission spectra. The profiles were investigated in wide range of electron densities and temperatures, from 2.81 · 1022 m − 3 to 5.69 · 1023 m − 3 and from 10 430 K to 73 400 K, respectively. Stark profiles were calculated using a semi-classical method as well as by N-body numerical simu…
Screened Coulomb interaction in insulators with strong disorder
We study the effect of disorder on the excitons in a semiconductor with screened Coulomb interaction. Examples are polymeric semiconductors and/or van der Waals structures. In the screened hydrogenic problem, we consider the disorder phenomenologically using the so-called fractional Scrödinger equation. Our main finding is that joint action of screening and disorder either destroys the exciton (strong screening) or enhances the bounding of electron and hole in an exciton, leading to its collapse in the extreme case. Latter effects may also be related to the quantum manifestations of chaotic exciton behavior in the above semiconductor structures. Hence, they should be considered in device ap…
KINETICS OF CRYSTAL GROWTH LIMITED BY RANDOM VELOCITY FIELDS
A spherical growth process controlled by velocity fluctuations of particles of a saturated solution is investigated. Velocity fluctuations are modeled by a Gaussian random field. The interface evolution is determined by a Langevin-type equation with a multiplicative random field, which in the case of the quasi-homogeneous random Gaussian field is equivalent to Fokker–Planck dynamics. We analyze numerically the Fokker–Planck equation and compare growth kinetics in the case of noisy (i.e. space-independent) fluctuations. It is shown that for a large class of spatially correlated velocity fluctuations, the growth kinetics is universal, i.e. it does not depend on the details of statistics of f…