Global ETD Search

11	Functional evidence for cone-specific connectivity in the human retina Whitaker, David J., McGraw, Paul V., McKeefry, Declan J., Vakrou, Chara 09 June 2009 (has links) No / Physiological studies of colour vision have not yet resolved the controversial issue of how chromatic opponency is constructed at a neuronal level. Two competing theories, the cone-selective hypothesis and the random-wiring hypothesis, are currently equivocal to the architecture of the primate retina. In central vision, both schemes are capable of producing colour opponency due to the fact that receptive field centres receive input from a single bipolar cell ¿ the so called `private line arrangement¿. However, in peripheral vision this single-cone input to the receptive field centre is lost, so that any random cone connectivity would result in a predictable reduction in the quality of colour vision. Behavioural studies thus far have indeed suggested a selective loss of chromatic sensitivity in peripheral vision. We investigated chromatic sensitivity as a function of eccentricity for the cardinal chromatic (L/M and S/(L + M)) and achromatic (L + M) pathways, adopting stimulus size as the critical variable. Results show that performance can be equated across the visual field simply by a change of scale (size). In other words, there exists no qualitative loss of chromatic sensitivity across the visual field. Critically, however, the quantitative nature of size dependency for each of the cardinal chromatic and achromatic mechanisms is very specific, reinforcing their independence in terms of anatomy and genetics. Our data provide clear evidence for a physiological model of primate colour vision that retains chromatic quality in peripheral vision, thus supporting the cone-selective hypothesis. Colour vision Chromatic opponency Chromatic sensitivity Cone selective hypothesis Random wiring hypothesis Central vision Peripheral vision
12	Camouflage chez les araignées crabe : approche sensorielle, comportementale et écologique / No title available Defrize, Jérémy 29 June 2010 (has links) Misumena vatia est supposée, depuis plus d‟un siècle, adapter sa couleur à celle de son substrat pour diminuer sa probabilité d‟être détectée par des proies et des prédateurs. Il existe cependant un décalage entre la quantité de travaux sur son écologie, sa notoriété en tant qu‟experte du camouflage, et la connaissance réelle sur son camouflage et le changement de couleur. Le but de cette thèse était d‟aborder le camouflage d‟un point de vue sensoriel, à une échelle communautaire, en combinant plusieurs approches. Il a été ainsi démontré que si M. vatia était indétectable dans l‟achromatique à longue distance, le niveau de contraste chromatique à courte distance était dépendant du substrat et de l‟identité du receveur. Des études électrophysiologiques et comportementales montrent de manière convergente que M. vatia possède la vision des couleurs. Les juvéniles utilisent cette habilité pour choisir des substrats qui les rendent peu détectable pour les proies. Enfin, les résultats de cette thèse sont replacés dans un contexte évolutif et physiologique plus général. / Misumena vatia is assumed for more than a century to adapt its colouration to the colour of its substrate in order to decrease the risk of being detected by prey and predators. However, a discrepancy exists between the large quantity of works on its ecology, its fame as an expert of camouflage and the empirical knowledge about its cryspis and colour change mechanisms. The aim of this thesis was therefore to study crypsis from a community sensory perspective, using an approach combing physiology, behaviour and colour vision models. We showed that if M. vatia was undetectable at long distance through achromatic vision, the chromatic contrast value is quite dependent of both substrates and receiver identities. Electrophysiological recordings and behavioural choices all concur to show that M. vatia is able to see colours. Spiderlings use this ability for making choices among coloured backgrounds diminishing its conspicuousness to potential prey. Finally, the results of this thesis are discussed in an evolutionary and physiological context. Ecologie sensorielle des communautés Sensibilité spectrale Misumena vatia Misumena vatia Crypsis Community sensory ecology Chromatic contrast Achromatic contrast Colour preference Spectral sensitivities
13	Koherencí řízený holografický mikroskop nové generace / New Generation of a Coherence-Controlled Holographic Microscope Slabý, Tomáš January 2015 (has links) This doctoral thesis deals with design of a new generation of coherence-controlled holographic microscope (CCHM). The microscope is based on off-axis holographic configuration using diffraction grating and allows the use of temporally and spatially incoherent illumination. In the theoretical section a new optical configuration of the microscope is proposed and conditions for different parameters of the microscope and its optical components are derived. The influence of different sources of noise on phase detection sensitivity is studied. In the next section design of experimental setup is described and automatable adjustment procedure is proposed. Last section describes experimental verification of the most important optical parameters of the experimental setup. When compared to previous generation of CCHM, the newly proposed configuration uses infinity-corrected objectives and common microscope condensers, allows more space for the specimens, eliminates the limitation of spectral transmittance and significantly simplifies the adjustment procedure so that automation of this procedure is possible.
14	Koherencí řízený holografický mikroskop / COHERENCE-CONTROLLED HOLOGRAPHIC MICROSCOPE Kolman, Pavel January 2010 (has links) ransmitted-light coherence-controlled holographic microscope (CCHM) based on an off-axis achromatic and space-invariant interferometer with a diffractive beamsplitter has been designed, constructed and tested. It is capable to image objects illuminated by light sources of arbitrary degree of temporal and spatial coherence. Off-axis image-plane hologram is recorded and the image complex amplitude (intensity and phase) is reconstructed numerically using fast Fourier transform algorithms. Phase image represents the optical path difference between the object and the reference arms caused by presence of an object. Therefore, it is a quantitative phase contrast image. Intensity image is confocal-like. Optical sectioning effect induced by an extended, spatial incoherent light source is equivalent to a conventional confocal image. CCHM is therefore capable to image objects under a diffusive layer or immersed in a turbid media. Spatial and temporal incoherence of illumination makes the optical sectioning effect stronger compared to a confocal imaging process. Object wave reconstruction from the only one recorded interference pattern ensures high resistance to vibrations and medium or ambience fluctuations. The frame rate is not limited by any component of the optical setup. Only the detector and computer speeds limit the frame rate. CCHM therefore allows observation of rapidly varying phenomena. CCHM makes the ex-post numerical refocusing possible within the coherence volume. Coherence degree of the light source in CCHM can be adapted to the object and to the required image properties. More coherent illumination provides wider range of numerical refocusing. On the other hand, a lower degree of coherence makes the optical sectioning stronger, i.e. the optical sections are thiner, it reduces coherence-noise and it makes it possible to separate the ballistic light. In addition to the ballistic light separation, CCHM enables us to separate the diffused light. Multi-colour-light
15	Vision Beyond Optics: Standardization, Evaluation and Innovation for Fluorescence Microscopy in Life Sciences Huisman, Maximiliaan 01 April 2019 (has links) Fluorescence microscopy is an essential tool in biomedical sciences that allows specific molecules to be visualized in the complex and crowded environment of cells. The continuous introduction of new imaging techniques makes microscopes more powerful and versatile, but there is more than meets the eye. In addition to develop- ing new methods, we can work towards getting the most out of existing data and technologies. By harnessing unused potential, this work aims to increase the richness, reliability, and power of fluorescence microscopy data in three key ways: through standardization, evaluation and innovation. A universal standard makes it easier to assess, compare and analyze imaging data – from the level of a single laboratory to the broader life sciences community. We propose a data-standard for fluorescence microscopy that can increase the confidence in experimental results, facilitate the exchange of data, and maximize compatibility with current and future data analysis techniques. Cutting-edge imaging technologies often rely on sophisticated hardware and multi-layered algorithms for reconstruction and analysis. Consequently, the trustworthiness of new methods can be difficult to assess. To evaluate the reliability and limitations of complex methods, quantitative analyses – such as the one present here for the 3D SPEED method – are paramount. The limited resolution of optical microscopes prevents direct observation of macro- molecules like DNA and RNA. We present a multi-color, achromatic, cryogenic fluorescence microscope that has the potential to produce multi-color images with sub-nanometer precision. This innovation would move fluorescence imaging beyond the limitations of optics and into the world of molecular resolution. microscopy nanoscopy fluorescence cryogenic cryo-fluorescence cryoFM FM 3DSPEED SPEED standardization PSF PSF engineering achromatic dichroic multi-color super-resolution imaging imaging standard optics adaptive optics meta-data meta MetaMax calibration characterization back-projection image reconstruction pseudo-tomography model-based reconstruction chromatic aberrations cryogenic imaging 4D-PSF calibration tool Bioimaging and Biomedical Optics Biological Engineering Biomedical Devices and Instrumentation Biophysics Computer-Aided Engineering and Design Electrical and Electronics Electromagnetics and Photonics Electro-Mechanical Systems Engineering Physics Molecular Biology Nanoscience and Nanotechnology Numerical Analysis and Computation Optics Other Engineering Systems and Integrative Engineering

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