5,925 research outputs found

    Immersive front-projection analysis using a radiosity-based simulation method

    Get PDF
    International audienceVideo projectors are designed to project onto flat white diffuse screens. Over the last few years, projector-based systems have been used, in virtual reality applications, to light non-specific environments such as the walls of a room. However, in these situations, the images seen by the user are affected by several radiometric disturbances, such as interreflection. Radiometric compensa tion methods have been proposed to reduce the disturbance caused by interreflection, but nothing has been proposed for evaluating the phenomenon itself and the effectiveness of compensation methods. In this paper, we propose a radiosity-based method to simulate light transfer in immersive environments, from a projector to a camera (the camera gives the image a user would see in a real room). This enables us to evaluate the disturbances resulting from interreflection. We also consider the effectiveness of interreflection compensation and study the influence of several parameters (projected image, projection onto a small or large part of the room, reflectivity of the walls). Our results show that radiometric compensation can reduce the influence of interreflection but is severely limited if we project onto a large part of the walls around the user, or if all the walls are bright

    On the development of a novel detector for simultaneous imaging and dosimetry in radiotherapy

    Get PDF
    Radiotherapy uses x-ray beams to deliver prescribed radiation doses that conform to target anatomy and minimise exposure of healthy tissue. Accuracy of dose delivery is essential, thus verification of dose distributions in vivo is desirable to monitor treatments and prevent errors from compromising patient outcomes. Electronic portal imaging devices (EPIDs) are commonly used x-ray imagers, however their non water-equivalent response complicates use for dosimetry. In this thesis, a Monte Carlo (MC) model of a standard EPID was developed and extended to novel water-equivalent configurations based on prototypes in which the high atomic number components were replaced with an array of plastic scintillator fibres. The model verified that full simulation of optical transport is not necessary to predict the standard EPID dose response, which can be accurately quantified from energy deposited in the phosphor screen. By incorporating computed tomography images into the model, its capacity to predict portal dose images of humanoid anatomy was also demonstrated. The prototype EPID’s water-equivalent dose response was characterised experimentally and with the MC model. Despite exhibiting lower spatial resolution and contrast-to-noise ratio relative to the standard EPID, its image quality was sufficient to discern gross anatomical structures of an anthropomorphic phantom. Opportunities to improve imaging performance while maintaining a water-equivalent dose response were identified using the model. Longer fibres increased efficiency and use of an extra-mural absorber maximised spatial resolution. Optical coupling between the scintillator fibres and the imaging panel may further improve performance. This thesis demonstrates the feasibility of developing a next-generation EPID for simultaneous imaging and dosimetry in radiotherapy. Such a detector could monitor treatment deliveries in vivo and thereby facilitate adaptations to treatment plans in order to improve patient outcomes

    Bulk Laser Material Modification: Towards a Kerfless Laser Wafering Process

    Get PDF
    abstract: Due to the ever increasing relevance of finer machining control as well as necessary reduction in material waste by large area semiconductor device manufacturers, a novel bulk laser machining method was investigated. Because the cost of silicon and sapphire substrates are limiting to the reduction in cost of devices in both the light emitting diode (LED) and solar industries, and the present substrate wafering process results in >50% waste, the need for an improved ingot wafering technique exists. The focus of this work is the design and understanding of a novel semiconductor wafering technique that utilizes the nonlinear absorption properties of band-gapped materials to achieve bulk (subsurface) morphological changes in matter using highly focused laser light. A method and tool was designed and developed to form controlled damage regions in the bulk of a crystalline sapphire wafer leaving the surfaces unaltered. The controllability of the subsurface damage geometry was investigated, and the effect of numerical aperture of the focusing optic, energy per pulse, wavelength, and number of pulses was characterized for a nanosecond pulse length variable wavelength Nd:YAG OPO laser. A novel model was developed to describe the geometry of laser induced morphological changes in the bulk of semiconducting materials for nanosecond pulse lengths. The beam propagation aspect of the model was based on ray-optics, and the full Keldysh multiphoton photoionization theory in conjuncture with Thornber's and Drude's models for impact ionization were used to describe high fluence laser light absorption and carrier generation ultimately resulting in permanent material modification though strong electron-plasma absorption and plasma melting. Although the electron-plasma description of laser damage formation is usually reserved for extremely short laser pulses (<20 ps), this work shows that it can be adapted for longer pulses of up to tens of nanoseconds. In addition to a model describing damage formation of sub-band gap energy laser light in semiconducting and transparent crystalline dielectrics, a novel nanosecond laser process was successfully realized to generate a thin plane of damage in the bulk of sapphire wafers. This was accomplished using high numerical aperture optics, a variable wavelength nanosecond laser source, and three-dimensional motorized precision stage control.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

    On the development of a novel detector for simultaneous imaging and dosimetry in radiotherapy

    Get PDF
    Radiotherapy uses x-ray beams to deliver prescribed radiation doses that conform to target anatomy and minimise exposure of healthy tissue. Accuracy of dose delivery is essential, thus verification of dose distributions in vivo is desirable to monitor treatments and prevent errors from compromising patient outcomes. Electronic portal imaging devices (EPIDs) are commonly used x-ray imagers, however their non water-equivalent response complicates use for dosimetry. In this thesis, a Monte Carlo (MC) model of a standard EPID was developed and extended to novel water-equivalent configurations based on prototypes in which the high atomic number components were replaced with an array of plastic scintillator fibres. The model verified that full simulation of optical transport is not necessary to predict the standard EPID dose response, which can be accurately quantified from energy deposited in the phosphor screen. By incorporating computed tomography images into the model, its capacity to predict portal dose images of humanoid anatomy was also demonstrated. The prototype EPID’s water-equivalent dose response was characterised experimentally and with the MC model. Despite exhibiting lower spatial resolution and contrast-to-noise ratio relative to the standard EPID, its image quality was sufficient to discern gross anatomical structures of an anthropomorphic phantom. Opportunities to improve imaging performance while maintaining a water-equivalent dose response were identified using the model. Longer fibres increased efficiency and use of an extra-mural absorber maximised spatial resolution. Optical coupling between the scintillator fibres and the imaging panel may further improve performance. This thesis demonstrates the feasibility of developing a next-generation EPID for simultaneous imaging and dosimetry in radiotherapy. Such a detector could monitor treatment deliveries in vivo and thereby facilitate adaptations to treatment plans in order to improve patient outcomes

    Solar astronomy

    Get PDF
    An overview is given of modern solar physics. Topics covered include the solar interior, the solar surface, the solar atmosphere, the Large Earth-based Solar Telescope (LEST), the Orbiting Solar Laboratory, the High Energy Solar Physics mission, the Space Exploration Initiative, solar-terrestrial physics, and adaptive optics. Policy and related programmatic recommendations are given for university research and education, facilitating solar research, and integrated support for solar research

    Robust and practical measurement of volume transport parameters in solid photo-polymer materials for 3D printing

    Get PDF
    Volumetric light transport is a pervasive physical phenomenon, and therefore its accurate simulation is important for a broad array of disciplines. While suitable mathematical models for computing the transport are now available, obtaining the necessary material parameters needed to drive such simulations is a challenging task: direct measurements of these parameters from material samples are seldom possible. Building on the inverse scattering paradigm, we present a novel measurement approach which indirectly infers the transport parameters from extrinsic observations of multiple-scattered radiance. The novelty of the proposed approach lies in replacing structured illumination with a structured reflector bonded to the sample, and a robust fitting procedure that largely compensates for potential systematic errors in the calibration of the setup. We show the feasibility of our approach by validating simulations of complex 3D compositions of the measured materials against physical prints, using photo-polymer resins. As presented in this paper, our technique yields colorspace data suitable for accurate appearance reproduction in the area of 3D printing. Beyond that, and without fundamental changes to the basic measurement methodology, it could equally well be used to obtain spectral measurements that are useful for other application areas
    • …
    corecore