[Katrin Show 1 Polar Lightsl
Virginie Fayad
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This paper reviews the directional orientation of birds with the help of the geomagnetic field under various light conditions. Two fundamentally different types of response can be distinguished. (i) Compass orientation controlled by the inclination compass that allows birds to locate courses of different origin. This is restricted to a narrow functional window around the total intensity of the local geomagnetic field and requires light from the short-wavelength part of the spectrum. The compass is based on radical-pair processes in the right eye; magnetite-based receptors in the beak are not involved. Compass orientation is observed under 'white' and low-level monochromatic light from ultraviolet (UV) to about 565 nm green light. (ii) 'Fixed direction' responses occur under artificial light conditions such as more intense monochromatic light, when 590 nm yellow light is added to short-wavelength light, and in total darkness. The manifestation of these responses depends on the ambient light regime and is 'fixed' in the sense of not showing the normal change between spring and autumn; their biological significance is unclear. In contrast to compass orientation, fixed-direction responses are polar magnetic responses and occur within a wide range of magnetic intensities. They are disrupted by local anaesthesia of the upper beak, which indicates that the respective magnetic information is mediated by iron-based receptors located there. The influence of light conditions on the two types of response suggests complex interactions between magnetoreceptors in the right eye, those in the upper beak and the visual system.
Dashboard reflections are a big problem when we take pictures inside a car, especially with action cams (because of the very large FOV).
I ordered a 37mm circular polarized filter to mount on my Xiaomi Yi. Here is my first test (car stopped) :
Without CPL :
YDXJ0618.jpg1200900 183 KB
What I do know is, that they reduce the amount of light getting into the camera, so only use them when there is a lot of light. They also only works if rotated correctly. If you just set it at a random rotation, it will most likely only remove light in general.
Thanks @katrin. Yes, the black felt works really well. I clean the inside and outside of the glass first with a window cleaner and microfiber cloth, then I lay a large piece of black felt on the dash. The felt prevents the reflection from my ugly gray dashboard from being reflected on the window.
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To understand the structure and function of the brain, we need to study the highly complex, 3D neuronal connections. To enable a correct reconstruction of the nerve fiber pathways, it is crucial to know the detailed substructure of the tissue, especially in regions with crossing fibers. Neuroimaging techniques such as 3D polarized light imaging (3D-PLI) reveal the fiber pathways with micrometer resolution, but fiber crossings still pose a major problem. Here, we show how light scattering can be used to detect fiber crossings in 3D-PLI images and to reveal their substructure.
In various experimental and simulation studies, we find that the transmitted light intensity strongly depends on the angle between the fibers and the direction of light propagation. It can be used not only to reveal 3D information but also to identify crossing fibers. Furthermore, we demonstrate that optical scattering reveals the substructure of brain tissue such as the crossing angles of nerve fibers. To explain our experimental observations, we develop a simulation framework for polarization microscopy that allows us to study light scattering on fibrous tissue models using high-performance computing.
Transmittance of inclined fiber bundles. (a) Mean normalized transmittance values IT,N plotted against the nerve fiber inclination angles α determined, respectively, from 3D-PLI and TPFM measurements of nerve fiber bundles in a mouse brain section (see Fig. S2 in Supplemental Material [55]). The values in blue belong to regions with similar (maximum) fiber density, and the values in orange belong to regions with variable fiber density in which the transmittance might be overestimated. The error bars indicate the standard error of the mean for the evaluated transmittance values. (b) Simulated transmittance curves (mean transmittance IT,N vs inclination α) for a bundle of densely grown fibers (i) and a bundle with broad fiber orientation distribution (ii) for NA=1 (purple curves) and NA=0.15 (green curves). The transmittance curves are normalized by the mean transmittance values of the horizontal bundles, respectively. The simulations are performed with the parameters specified in Appendix pp6, using normally incident light with 550 nm wavelength. Both experimental and simulated data show that the transmittance decreases with an increasing fiber inclination (for NA=0.15).
Simulated scattering patterns for different artificial nerve fiber constellations: (a) densely grown fiber bundle [cf. Fig. 3] with different inclination angles α and (b) in-plane crossing fibers [separate and interwoven bundles; cf. Figs. 5 and 5] with different crossing angles χ. The scattering patterns show the underlying substructure, e.g., the crossing angle of the fibers (indicated by the black lines around the patterns).
Modeling of the 3D-PLI measurement. The figure and table on the left-hand side show the optical components of the polarimeter (the order of the polarizing filters is different than in the measurement, but the setup is mathematically equivalent): light source (green), polarizer and retarder (dark gray), sample (light gray), and objective lens, detector, and camera (blue). The table and figure on the right-hand side show how the optical elements are modeled by FDTD simulations: The incoherent and diffusive light source (LED) with peak wavelength λ^ and full width at half maximum (FWHM) is modeled by performing several simulation runs with plane waves that have different wavelengths (λ) and angles of incidence (φ, θ). The modeled light source emits coherent light that is circularly polarized. The tissue sample is represented by an artificial fiber architecture, the rotating analyzer by a rotated Jones matrix [with rotation matrix R(ρ)]. The numerical aperture (NA) of the imaging system is modeled by considering only wave vector angles θk
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The Radical Pair model proposes that magnetoreception is a light-dependent process. Under low monochromatic light from the short-wavelength part of the visual spectrum, migratory birds show orientation in their migratory direction. Under monochromatic light of higher intensity, however, they showed unusual preferences for other directions or axial preferences. To determine whether or not these responses are still controlled by the respective light regimes, European robins, Erithacus rubecula, were tested under UV, Blue, Turquoise and Green light at increasing intensities, with orientation in migratory direction serving as a criterion whether or not magnetoreception works in the normal way.
The birds were well oriented in their seasonally appropriate migratory direction under 424 nm Blue, 502 nm Turquoise and 565 nm Green light of low intensity with a quantal flux of 81015 quanta s-1 m-2, indicating unimpaired magnetoreception. Under 373 nm UV of the same quantal flux, they were not oriented in migratory direction, showing a preference for the east-west axis instead, but they were well oriented in migratory direction under UV of lower intensity. Intensities of above 361015 quanta s-1 m-2 of Blue, Turquoise and Green light elicited a variety of responses: disorientation, headings along the east-west axis, headings along the north-south axis or 'fixed' direction tendencies. These responses changed as the intensity was increased from 361015 quanta s-1 m-2 to 54 and 721015 quanta s-1 m-2.
The specific manifestation of responses in directions other than the migratory direction clearly depends on the ambient light regime. This implies that even when the mechanisms normally providing magnetic compass information seem disrupted, processes that are activated by light still control the behavior. It suggests complex interactions between different types of receptors, magnetic and visual. The nature of the receptors involved and details of their connections are not yet known; however, a role of the color cones in the processes mediating magnetic input is suggested.
The nature of the observed responses is unclear and raises the question about the factors controlling this behavior. Exposing European robins to a broad-band oscillating magnetic field (0.1 to 10 MHz) indicated that their orientation under high intensity turquoise light was no longer based on the radical pair mechanism underlying the normal magnetic compass [4]. A case that might involve a similar phenomenon has been described in amphibians: after pre-treatment with certain light regimes, salamanders showed an axial preference that in some animals was associated with the orientation of magnetite crystals in their heads [15]. So it seemed possible that the behavior of the robins under monochromatic light of higher intensities was no longer controlled by light, but instead by magnetite or magnetite-based receptors.
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