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István Pomozi

Bio: István Pomozi is an academic researcher from Eötvös Loránd University. The author has contributed to research in topics: Solar eclipse & Polarization (waves). The author has an hindex of 6, co-authored 8 publications receiving 320 citations.

Papers
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Journal ArticleDOI
TL;DR: It is demonstrated quantitatively that the shorter the wavelength, the greater the proportion of celestial polarization that can be used by animals under cloudy-sky conditions, as has already been suggested by others, may solve the ultraviolet paradox of polarization vision in insects.
Abstract: One of the biologically most important parameters of the cloudy sky is the proportion P of the celestial polarization pattern available for use in animal navigation. We evaluated this parameter by measuring the polarization patterns of clear and cloudy skies using 180 degrees (full-sky) imaging polarimetry in the red (650 nm), green (550 nm) and blue (450 nm) ranges of the spectrum under clear and partly cloudy conditions. The resulting data were compared with the corresponding celestial polarization patterns calculated using the single-scattering Rayleigh model. We show convincingly that the pattern of the angle of polarization (e-vectors) in a clear sky continues underneath clouds if regions of the clouds and parts of the airspace between the clouds and the earth surface (being shady at the position of the observer) are directly lit by the sun. The scattering and polarization of direct sunlight on the cloud particles and in the air columns underneath the clouds result in the same e-vector pattern as that present in clear sky. This phenomenon can be exploited for animal navigation if the degree of polarization is higher than the perceptual threshold of the visual system, because the angle rather than the degree of polarization is the most important optical cue used in the polarization compass. Hence, the clouds reduce the extent of sky polarization pattern that is useful for animal orientation much less than has hitherto been assumed. We further demonstrate quantitatively that the shorter the wavelength, the greater the proportion of celestial polarization that can be used by animals under cloudy-sky conditions. As has already been suggested by others, this phenomenon may solve the ultraviolet paradox of polarization vision in insects such as hymenopterans and dipterans. The present study extends previous findings by using the technique of 180 degrees imaging polarimetry to measure and analyse celestial polarization patterns.

199 citations

Journal ArticleDOI
TL;DR: The results of the own celestial polarization measurements and psychophysical laboratory experiments, in which the atmospheric optical prerequisites of possible sky-polarimetric navigation in Tunisia, Finland, Hungary and the high Arctic are studied are summarized.
Abstract: Between AD 900 and AD 1200 Vikings, being able to navigate skillfully across the open sea, were the dominant seafarers of the North Atlantic. When the Sun was shining, geographical north could be determined with a special sundial. However, how the Vikings could have navigated in cloudy or foggy situations, when the Sun's disc was unusable, is still not fully known. A hypothesis was formulated in 1967, which suggested that under foggy or cloudy conditions, Vikings might have been able to determine the azimuth direction of the Sun with the help of skylight polarization, just like some insects. This hypothesis has been widely accepted and is regularly cited by researchers, even though an experimental basis, so far, has not been forthcoming. According to this theory, the Vikings could have determined the direction of the skylight polarization with the help of an enigmatic birefringent crystal, functioning as a linearly polarizing filter. Such a crystal is referred to as ‘sunstone’ in one of the Viking's sagas, but its exact nature is unknown. Although accepted by many, the hypothesis of polarimetric navigation by Vikings also has numerous sceptics. In this paper, we summarize the results of our own celestial polarization measurements and psychophysical laboratory experiments, in which we studied the atmospheric optical prerequisites of possible sky-polarimetric navigation in Tunisia, Finland, Hungary and the high Arctic.

51 citations

Journal ArticleDOI
TL;DR: The stingless bee Plebeia remota (Holmberg): observations and evolutionary implications, and an ethological comparison with other Meliponine taxa (Hymenoptera, Apidae).
Abstract: 1. Michener CD (1974) The social behavior of the bees. Belknap, Cambridge 2. Sakagami SF (1982) Stingless bees. In: Hermann RH (ed) Social insects, vol III. Academic, New York, pp 361–423 3. Michener CD, Grimaldi D (1988) The oldest fossil bee: Apoid history, evolutionary stasis, and antiquity of social behaviour. Proc Natl Acad Sci USA 85:6424–6426 4. Hartfelder KH, Engels W (1989) The composition of larval food in stingless bess: evaluating nutritional balance by chemosystematic methods. Insectes Sociaux 36 :1–14 5. Camargo CA de (1976) Dieta semi-artificial para abelhas da subfamilia. Meliponinae (Hymenoptera, Apidae). Ciencia e Cultura 28 :430–431 6. Sommeijer MJ, van Zeijl M, Dohmen MR (1984) Morphological differences between worker-laid eggs from a queenright colony and a queenless colony of Melipona rufiventris paraensis (Hymenoptera: Apidae). Entomol Ber Amsterdam 44 :91–95 7. Koedam D (1995) Behavioural and physiological implications of queen dominance in stingless bees. Thesis, University of Utrecht 8. Koedam D, Velthausz PH, van der Krift T, Dohmen MR, Sommeijer MJ (1996) Morphology of reproductive and trophic worker eggs and their controlled release by workers in Tetragonisca angustula (Apidae, Meliponinae). Physiol Entomol 21 :289–296 9. Benthem FDJ van, Imperatriz Fonseca VL, Velthuis HHW (1995) Biology of the stingless bee Plebeia remota (Holmberg): observations and evolutionary implications. Insectes Sociaux 42 :71–87 10. Drumond PM, Zucchi R, Mateus S, Bego L (1996) Oviposition behavior of the stingles bees, XVII. Plebeia (Plebeia) droryana and an ethological comparison with other Meliponine taxa (Hymenoptera, Apidae). Jpn J Entomol 64 :385–400 11. Beig D (1972) The production of males in queenright colonies of Trigona (Scaptotrigona) postica. J Apicultural Res 11 :33–39

37 citations

Journal ArticleDOI
TL;DR: In this article, the authors measured the spatiotemporal change of the polarization pattern of the entire celestial hemisphere during the total solar eclipse of 11 August 1999 in Kecel, Hungary and compared these patterns with the normal celestial polarization patterns measured at the same times on the subsequent day of the eclipse.

27 citations

Journal ArticleDOI
TL;DR: The observation of unpolarized (neutral) points in the sky during the total solar eclipse on 11 August 1999 is reported, near the zenith a neutral point was observed at 450 nm at two different points of time during totality.
Abstract: We report here on the observation of unpolarized (neutral) points in the sky during the total solar eclipse on 11 August 1999. Near the zenith a neutral point was observed at 450 nm at two different points of time during totality. Around this celestial point the distribution of the angle of polarization was heterogeneous: The electric field vectors on the one side were approximately perpendicular to those on the other side. At another moment of totality, near the zenith a local minimum of the degree of linear polarization occurred at 550 nm. Near the antisolar meridian, at a low elevation another two neutral points occurred at 450 nm at a certain moment during totality. Approximately at the position of these neutral points, at another moment of totality a local minimum of the degree of polarization occurred at 550 nm, whereas at 450 nm a neutral point was observed, around which the angle-of-polarization pattern was homogeneous: The electric field vectors were approximately horizontal on both sides of the neutral point.

24 citations


Cited by
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Book ChapterDOI
TL;DR: In this article, it was shown that the Poynting vector has features that are not immediately apparent from the intensity alone, nor from global properties of a beam, but can be easily recognized from the analysis of optical vortices and orbital angular momentum.
Abstract: Publisher Summary The widespread availability of spatially and temporally coherent laser sources makes the production of optical vortices inevitable in any experiment involving scattered laser light. The realization of quantized vortices is not specific to optics: these objects occur in all spatial scalar fields. Although optical vortices are often referred to as “points of phase singularity within a cross section of the field,” physical optical fields extend over three dimensions, and the phase singularities are actually lines of perfect destructive interference that are embedded in the volume filled by the light. Optical vortices are examples of the singularity lines within all complicated scalar fields. By comparison, electromagnetic vector fields do not generally have nodes in all components simultaneously. However, vector fields possess singularities associated with the parameterization of elliptical and partial polarization rather than phase. Polarization singularities are present in many situations, ranging from sunlight to the light transmitted by birefringent materials. Their descriptors are more complicated than their scalar counterpart in that they have both handedness and additional categorization. The study of optical vortices and orbital angular momentum has led to a recognition that the energy flow—characterized by the Poynting vector—has features not immediately apparent from the intensity alone, nor from global properties of a beam.

687 citations

Journal ArticleDOI
TL;DR: In this article, the authors present and discuss the state of the art in studies of desert ant (Cataglyphis) navigation using path integration as an egocentric guideline to acquire con- tinually updated spatial information about places and routes.
Abstract: This essay presents and discusses the state of the art in studies of desert ant (Cataglyphis) navigation. In dealing with behavioural performances, neural mechanisms, and ecological functions these studies ultimately aim at an evolutionary understanding of the insect's navigational toolkit: its skylight (polarization) compass, its path integrator, its view-dependent ways of recognizing places and following landmark routes, and its strategies of flexibly interlinking these modes of navigation to generate amazingly rich behavioural out- puts. The general message is thatCataglyphis uses path integration as an egocentric guideline to acquire con- tinually updated spatial information about places and routes. Hence, it relies on procedural knowledge, and largely context-dependent retrieval of such knowledge, rather than on all-embracing geocentred representations of space.

541 citations

Journal ArticleDOI
TL;DR: In this article, the geometry of ellipse fields at these singularities, using the Stokes parameters and others to characterize the singular geometry and morphology, was investigated, and the densities and correlations of the different types of polarization singularities were calculated in random polarization fields, and compared to the statistics of phase singularities and random surfaces.

347 citations

BookDOI
01 Jan 2004

266 citations

Journal ArticleDOI
TL;DR: The hypothesis entertained in this account is that polarization vision comes in various guises, and that the answer to the question posed in the title is most probably no.
Abstract: In this concept paper, three scenarios are described in which animals make use of polarized light: the underwater world, the water surface and the terrestrial habitat vaulted by the pattern of polarized light in the sky. Within these various visual environments, polarized light is used in a number of ways that make quite different demands on the neural circuitries mediating these different types of behaviour. Apart from some common receptor and pre-processing mechanisms, the underlying neural mechanisms may differ accordingly. Often, information about chi (the angle of polarization), d (the degree of polarization) and lambda (the spectral content) might not --and need not--be disentangled. Hence, the hypothesis entertained in this account is that polarization vision comes in various guises, and that the answer to the question posed in the title is most probably no.

221 citations