Papers by Frantisek Kundracik
Journal of Aerosol Science, Dec 1, 2006
The optical properties of composite particles are calculated by means of the discrete dipole appr... more The optical properties of composite particles are calculated by means of the discrete dipole approximation. In particular, efficiency factors for extinction' scattering and absorption, asymmetry parameter, linear polarization, and phase function S 11 are obtained for particles in which (a) the individual components of different materials are distributed randomly within the particle body, and (b) the individual constituents are not distributed randomly over the particle volume, but are clumped together into larger compact blocks. Particles are assumed to have non-spherical forms (ellipsoids, cuboids, and an irregular shape U2015B10 are discussed in detail). Computational results are compared to those obtained for homogeneous particles of the same morphology using an effective medium theory (EMT). The greatest discrepancies between the use of the homogeneous and the inhomogeneous particles are found for polarization when particle size is larger than the wavelength of incident radiation. An important finding for S 11 is that the particles built from compact homogeneous blocks contribute more efficiently to backscattering than other analyzed particles, leading to a consistently lower asymmetry parameter. The homogeneous particles scatter least in the backscatter region, resulting in the highest asymmetry parameters of the three classes of particles. We find that the internal heterogeneities and surface structure have a comparable effect on the asymmetry parameter. It is shown that the efficiency factor for scattering is reduced when the real material configuration is ignored and the optical properties are modeled using the EMT; however, the use of the EMT and homogeneity assumption leads to significantly increased absorption.
Solid State Phenomena, Apr 1, 2003
The purpose of the present study was to obtain a more complete insight into the electrical and me... more The purpose of the present study was to obtain a more complete insight into the electrical and mechanical properties of Yb2O3 - stabilised zirconia systems as determined by their polymorphous structure with regard to the suitable applications.
Journal of Quantitative Spectroscopy & Radiative Transfer, Jul 1, 2008
We examine the light scattering from wet aerosol particles whose core morphology is a random Gaus... more We examine the light scattering from wet aerosol particles whose core morphology is a random Gaussian sphere coated by different amounts of water. We compare the results with those calculated from a concentric-sphere particle and from a homogeneous-sphere particle whose ...
ABSTRACT Available optical measurements indicate that the modal radius rm of a cometary dust popu... more ABSTRACT Available optical measurements indicate that the modal radius rm of a cometary dust population is in the submicron range and that the dust refractive index m changes slightly in the visible region of the spectrum. A realistic instantaneous particle size distribution f(r) may be determined by processing the measured intensity of continuum at several wavelengths. The solution of the inverse problem for particle size distribution is based on rigorous Mie theory. Additionally, an application of the Rayleigh-Gans approximation enables to construct an accelerated solution scheme since the total intensity of the scattered radiation can then be expressed in an analytical form. However, the range of validity of the approximation is strongly limited to very small submicron-sized particles. The numerical simulations of light scattering by Mie cometary dust particles are performed for two model size distributions - power function f(r) µ r-n and modified gamma function f(r) µ ra e-br, which are commonly used to represent real dust populations. It is shown that the cometary dust size distribution may easily be reproduced analysing the spectral behaviour of measured intensity of the scattered radiation IJ(l). The more rapid increasing of continuum with the wavelength of incident radiation the larger particles are contained in cometary dusty environment.
Journal of Quantitative Spectroscopy & Radiative Transfer, Jul 1, 2020
Scattering by aerosols and gases cause a certain fraction of artificial light emitted upwards is ... more Scattering by aerosols and gases cause a certain fraction of artificial light emitted upwards is redirected to the ground. Of all atmospheric constituents just the aerosols are most important modulators of nightsky brightness under cloudless conditions. Unlike most of the previous we highlight a crucial role of solar radiometry for determining the atmospheric optical depth before night-time observation is to be made. Aerosol optical depth at visible wavelengths extracted from the data measured provides then the information on size distribution or mean refractive index of aerosol particles that in turn are both necessary to make night sky brightness prediction more accurate. Therefore, combining daytime and night-time radiometry we can achieve accuracy much higher than ever before. This is due to significantly reduced uncertainty in aerosol properties. The aerosol data are retrieved from a new portable multi-wavelength optical analyzer that operates Ocean Optics spectrometer. The equipment provides the radiance data from 350 nm to 10 0 0 nm with spectral resolution of 1 nm. Due to high sun radiance levels we use a system of mirrors each reducing the signal to about 4%, while keeping the integration time short. The minimum integration time of 3 ms allows for detection of direct sunlight. The system developed is sensitive to small changes in the aerosol system, while showing a good detection limit even under low turbidity conditions. The system performance is demonstrated in field experiment conducted shortly after front passage when most of aerosol particles is effectively removed by rain.
Monthly Notices of the Royal Astronomical Society, Dec 25, 2019
The emission spectrum of a light-pollution source is a determining factor for modelling artificia... more The emission spectrum of a light-pollution source is a determining factor for modelling artificial light at night. The spectral composition of skyglow is normally derived from the initial spectra of all artificial light sources contributing to the diffuse illumination of an observation point. However, light scattering in the ambient atmosphere imposes a wavelengthspecific distortion on the optical signals captured by the measuring device. The nature of the emission, the spectra and the light-scattering phenomena not only control the spectral properties of the ground-reaching radiation, but also provide a unique tool for remote diagnosis and even identification of the emission spectra of the light-polluting sources. This is because the information contained in the night-sky brightness is preferably measured in directions towards a glowing dome of light over the artificial source of light. We have developed a new method for obtaining the emission spectra using remote terrestrial sensing of the bright patches of sky associated with a source. Field experiments conducted in Vienna and Bratislava have been used to validate the theoretical model and the retrieval method. These experiments demonstrate that the numerical inversion is successful even if the signal-to-noise ratio is small. The method for decoding the emission spectra by the light-scattering spectrometry of a night sky is a unique approach that enables for (i) a systematic characterization of the light-pollution sources over a specific territory, and (ii) a significant improvement in the numerical prediction of skyglow changes that we can expect at observatories.
Acta Physica Slovaca, Dec 1, 2005
The films under study were deposited by e-beam evaporation of yttria-stabilized zirconia (YSZ) cr... more The films under study were deposited by e-beam evaporation of yttria-stabilized zirconia (YSZ) crystalline samples on the n-doped Si (111) substrate at 750 • C. The XRD patterns of the films revealed their polycrystalline structure with a mixture of different phases, mainly the face-centered cubic one. The electrical conductivity and the activation energy as the functions of the yttria content indicated the influence of isolated oxygen ion vacancies as well as the associated point defects. The relative permittivities (εr = 17 − 26) measured at room temperature and 1MHz confirmed YSZ as a high-k gate dielectric also in the form of thin film. The measured microhardness data, evaluated according to Jonsson-Hogmark composite hardness model, (H = 5.9-10.8 GPa), as well as a high refractive index (n = 1.96-2.20) render from YSZ a promising material for protective coatings and optical applications, respectively.
Atmospheric Environment, May 1, 2015
h i g h l i g h t s A novel method for inversion of scattering and extinction data is developed. ... more h i g h l i g h t s A novel method for inversion of scattering and extinction data is developed. Size distribution and aspect ratio of nonspherical particles can be retrieved. Aerosol aspect ratio is determined iteratively if refractive index is a-priori known. The method is effective for large scattering angles including side and back scatter.
Planetary and Space Science, Apr 1, 2006
Perihelion motion, i.e. a secular change of longitude of perihelion, of interplanetary dust parti... more Perihelion motion, i.e. a secular change of longitude of perihelion, of interplanetary dust particles is investigated under the action of solar gravity and solar electromagnetic radiation. As for spherical particle [Klačka, J., 2004. Electromagnetic radiation and motion of a particle. Cel. Mech. Dynam. Astron. 89, 1–61]: (i) perihelion motion is of the order v⇒2/c2 (v⇒ is heliocentric velocity of the
Journal of Quantitative Spectroscopy & Radiative Transfer, May 1, 2018
A new portable sky scanner designed for low-light-level detection at night is developed and emplo... more A new portable sky scanner designed for low-light-level detection at night is developed and employed in night sky brightness measurements in a rural region. The fast readout, adjustable sensitivity and linear response guaranteed in 5-6 orders of magnitude makes the device well suited for narrow-band photometry in both dark areas and bright urban and suburban environments. Quasi-monochromatic night-sky brightness data are advantageous in the accurate characterization of spectral power distribution of scattered and emitted light and, also allows for the possibility to retrieve light output patterns from whole-city light sources. The sky scanner can operate in both night and day regimes, taking advantage of the complementarity of both radiance data types. Due to its inherent very high sensitivity the photomultiplier tube could be used in night sky radiometry, while the spectrometer-equipped system component capable of detecting elevated intensities is used in daylight monitoring. Daylight is a source of information on atmospheric optical properties that in turn are necessary in processing night sky radiances. We believe that the sky scanner has the potential to revolutionize night-sky monitoring systems.
Solar Energy, Sep 1, 2011
The luminous intensity solid of hollow light guide is determined using an extended HOLIGILM solut... more The luminous intensity solid of hollow light guide is determined using an extended HOLIGILM solution. The solution concept enables to simulate luminous intensity solids for various light guides and sky luminance patterns. Angular distribution of light emitted from bottom interface of the light guide strongly depends on how the illumination system is designed. Any beam undergoes many reflection events which
Journal of Materials Science, 2009
Solar Energy, Aug 1, 2018
A comprehensive study of straight light pipe efficiency and illuminance distribution below ceilin... more A comprehensive study of straight light pipe efficiency and illuminance distribution below ceiling level is performed using HOLIGILM tool. The recommendations for light guide systems can be made for different latitudes and sky luminance patterns using the data computed here. The computational results show that the light pipe transmittance is a monotonic function of solar altitude, except for low-sun angles. Redistribution of photons at the light pipe base can be characterized by a scalar value called "asymmetry parameter", g. A use of g is an efficient attempt to the classification of a large number of luminous intensity distributions. The minimum value of g is at low solar elevations (between 10°and 30°) because of balanced contribution of diffuse light of a sky and the direct sunbeams. The low values of g indicate the redistribution of light is more uniform. Luminous intensity solid determined by means of HOLIGILM tool is used to compute illuminance distribution at a working plane. The peak intensity and intensity gradient of a bright ring projected onto a working plane can be used to characterize the optical properties of different light pipes in different climatic zones.
Solar Energy, Aug 1, 2010
Hollow light guides with very high reflective inner surfaces are novel daylight systems that coll... more Hollow light guides with very high reflective inner surfaces are novel daylight systems that collect sunlight and skylight available on the roof of buildings transporting it into deep or windowless interiors in building cores. Thus the better utilization of daylight can result in energy ...
Monthly Notices of the Royal Astronomical Society, Aug 19, 2015
The emission function from ground-based light sources predetermines the skyglow features to a lar... more The emission function from ground-based light sources predetermines the skyglow features to a large extent, while most mathematical models that are used to predict the night sky brightness require the information on this function. The radiant intensity distribution on a clear sky is experimentally determined as a function of zenith angle using the theoretical approach published only recently in MNRAS, 439, 3405-3413. We have made the experiments in two localities in Slovakia and Mexico by means of two digital single lens reflex professional cameras operating with different lenses that limit the system's field-of-view to either 180 o or 167 o. The purpose of using two cameras was to identify variances between two different apertures. Images are taken at different distances from an artificial light source (a city) with intention to determine the ratio of zenith radiance relative to horizontal irradiance. Subsequently, the information on the fraction of the light radiated directly into the upward hemisphere (F) is extracted. The results show that inexpensive devices can properly identify the upward emissions with adequate reliability as long as the clear sky radiance distribution is dominated by a largest ground-based light source. Highly unstable turbidity conditions can also make the parameter F difficult to find or even impossible to retrieve. The measurements at low elevation angles should be avoided due to a potentially parasitic effect of direct light emissions from luminaires surrounding the measuring site.
Journal of Quantitative Spectroscopy & Radiative Transfer, Oct 1, 2015
The explicit solution to Maxwell's equations that satisfies the continuity equation is obtained f... more The explicit solution to Maxwell's equations that satisfies the continuity equation is obtained for electrically charged spherical particles. The traditional separation-ofvariables method (SVM) cannot be used to solve the vector wave equation for a nonuniformly charged spherical particle. In addition, a perturbation approach to the electromagnetic scattering problem fails if a spherical particle is occupied by electric charges that are not spatially homogeneous. By incorporating a correction to the conventional surfacecurrent density, we have refined the conductivity model and found that the Rayleigh approximation (for mode n ¼1) is not a valid approach for modelling the optical effects by electrically charged particles much smaller than the wavelength of an incident radiation. Theoretical analyses indicate that peak enhancements of optical signatures are usually relevant in the long-wavelength limit due to the necessity to include higher-order modes of vibration (n 4 1).
Optics Letters, Oct 29, 2015
Scattering of electromagnetic radiation by electrically charged spherical particles is treated th... more Scattering of electromagnetic radiation by electrically charged spherical particles is treated theoretically. A generalization of the approach is performed by incorporating both intraband and interband effects, while a new oscillatory term corresponding to the classical dispersion theory and the semi-quantum approach is considered. It is shown through a set of numerical experiments that interband effects may reduce the amplitude of resonant peaks for scattering, Q<sub>sca</sub>, and absorption, Q<sub>abs</sub>, and cause a shift of peak positions to longer wavelengths. In general, the resonant features due to interband and intraband effects can occur at different frequencies; thus, both together may result in qualitatively and quantitatively new optical signatures of electrically charged particles. This is a motivating factor for experimentalists who can use the particles as targeted probes, for example, in mapping the electric fields in different media based on scattering and/or absorption properties of electrified particulate systems.
Monthly Notices of the Royal Astronomical Society: Letters, Mar 29, 2021
The population of artificial satellites and space debris orbiting the Earth imposes non-negligibl... more The population of artificial satellites and space debris orbiting the Earth imposes non-negligible constraints on both space operations and ground-based optical and radio astronomy. The ongoing deployment of several satellite 'mega-constellations' in the 2020s represents an additional threat that raises significant concerns. The expected severity of its unwanted consequences is still under study, including radio interference and information loss by satellite streaks appearing in science images. In this Letter, we report a new skyglow effect produced by space objects: increased night sky brightness caused by sunlight reflected and scattered by that large set of orbiting bodies whose direct radiance is a diffuse component when observed with the naked eye or with low angular resolution photometric instruments. According to our preliminary estimates, the zenith luminance of this additional light pollution source may have already reached ∼20 µcd m −2 , which amounts to an approximately 10 percent increase over the brightness of the night sky determined by natural sources of light. This is the critical limit adopted in 1979 by the International Astronomical Union for the light pollution level not to be exceeded at the sites of astronomical observatories.
Monthly Notices of the Royal Astronomical Society, May 24, 2023
Atmospheric turbidity is one of the key factors influencing the propagation of artificial light i... more Atmospheric turbidity is one of the key factors influencing the propagation of artificial light into the environment during cloudless nights. High aerosol loading can reduce the visibility of astronomical objects, and thus information on atmospheric pollution is critical for the prediction of the night sky brightness (NSB) distribution. In particular, the aerosol optical depth (AOD) and asymmetry parameter (g) are among the most important aerosol properties influencing the NSB amplitudes. Ho we ver, these two parameters are rarely available at astronomical sites. Here, we develop a method for AOD and g retrie v als from clear-sky radiometry carried out around sunset or sunrise, shortly before or after night-time observation is intended. The method allows for reducing the number of unknowns needed in the processing and interpretation of night sky radiances, and thus provides an efficient tool for gathering input data to present skyglow simulators. The practice of collecting information about aerosols in this way could become a routine part of astronomical observations, much like observing standard stars to obtain extinction coefficients. If the procedure were conducted around sunset and the data were quickly reduced, it could offer an on-the-spot estimate of the NSB for the night ahead. The error analysis is performed using the theoretical model, while taking into account experimental errors of radiance readings. The capability of the method is demonstrated in a field experiment conducted under cloudless conditions.
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Papers by Frantisek Kundracik