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Showing 1 to 20 of 48 for “"collimation"”.
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Super-collimation in a rod-based photonic crystal
Super-collimation is the propagation of a light beam without spreading that occurs when the light beam is guided by the dispersion properties of a photonic crystal, rather than by defects in the photonic crystal. Super-collimation has many potential applications, the most straight-forward of which …
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Optical studies of super-collimation in photonic crystals
… spatial spreading. This effect, called super-collimation (also known as self-collimation), allows diffraction-free propagation of micron-sized beams over centimeter-scale distances. This linear effect is a natural result of the unique dispersive properties of photonic crystals. In this thesis, …
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Digital Waveform Acquisition and Adaptive Collimation Methods for SPECT
Single Photon Emission Computed Tomography (SPECT) is a minimally invasive, functional imaging modality mainly used clinically in cardiology, oncology, and neurology. SPECT has also been particularly useful in preclinical settings because of the ability to perform longitudinal studies on animal …
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Novel Schemes for the Collimation of Neutral Electron-Positron Beams
Electron-Positron beams represent a unique state of matter that present overall charge neutrality and therefore not embedded by self-generated magnetic fields. These beams are believed to be emitted as highly collimated astronomical jets by some of the most powerful and distant astrophysical …
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Applications of Multi-Pinhole Gamma Camera Collimation to Tomography and Image Enhancement
Recently, multi-pinhole gamma camera collimation has been introduced in the field of emission tomography. This collimation process simultaneously produces several images covering a limited angular range, which may then be recombined to obtain tomographic slices of the object imaged. This study has …
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Collimation of deuterium / 3-helium fusion products for advanced spacecraft propulsion and power
… necessary for the IEC fusion core. Numerically, collimation of 300 eV electrons without a stabilization coil was demonstrated to approach 95% at a profile corresponding to Vsolenoid = 20.0V, Ifloating = 2.78A, Isolenoid = 4.05A while collimation of electrons with stabilization coil present was …
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Design and Validation of a Prototype Collimation System with Reduced Applicator Weights for Elekta Electron Therapy Beams
… of this study was to design an electron collimation system for Elekta Infinity accelerators with significantly reduced applicator weights, while maintaining acceptable in-field beam flatness and out-of-field leakage dose. The design was restricted to 6-20 MeV beams for 6x6 to 25x25 cm2 …
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Optical studies of photonic crystals and high index-contrast microphotonic circuits
… and theoretical beam evolution about the super-collimation frequencies, the effects of disorder on beam evolution are pinpointed. Despite the effects of disorder, super-collimation is found to be robust, producing stationary beam-widths over 600 isotropic diffraction-lengths. In addition, …
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Modelling Of Protostellar Jets Using Intense Lasers
… In the first of these, the effects on jet collimation of radiative emission and the presence of a gaseous ambient medium were studied, with a view to learning about the effects of these factors on YSO jets by studying their scaled laboratory counterparts. The second experiment was designed …
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Novel resonant and light-guiding phenomena in photonics
… propose a 2D PhC structure that supports super-collimation over a large frequency range. We theoretically and numerically investigate the collimation mechanism in this 2D structure, in comparison to that of two other frequently used related PhC structures. We also point out the potential …
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Development Of A Supercontinuum Based Photoacoustic Aerosol Light Absorption And Albedo Spectrometer (PALAAS)
… and scattering coefficients of aerosols. Collimation techniques for supercontinuum sources using lens-based and off-axis parabolic mirror-based collimators were evaluated and it was determined that the off-axis mirror had superior collimation abilities for multi-spectral beams. A proof of …
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Fixed and Adaptive Multiple-Pinhole Apertures for Brain SPECT Imaging
… gamma-ray projection images created by physical collimation methods at a sufficient number of angles that the data can be reconstructed into a 3-dimensional representation of the radio-tracer distributions within the patient. In addition to existing applications in cancer and heart disease, SPECT …
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A Q-switched, cavity-dumped YAG laser for use in plasma physics experiments
… configuration to produce higher gain and better collimation than would otherwise be possible. Pulses of light with energies of 18±2 mJ and FWHMs of about 12 ns were produced. It was found that more than 100 mJ of light was being emitted in the form of prelase pulses, due to the Pockels cells used …
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Nuclear resonance fluorescence in Si²⁸
… gamma rays from the reaction. The direction of collimation with reference to the direction of the bombarding protons governs the exact energy of the ground state games available for absorption. The energy deficit which appears in emission and absorption is made up by the kinetic energy of the …
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MONTE CARLO MODELING OF THE GAMMA KNIFE PERFEXION<sup>TM</sup>
… each, and can independently choose one of three collimation sizes for each sector. The largest collimator size is designed to produce a sphere of dose 16 mm in diameter at the focus. The smaller collimators produce dose spheres 8 mm and 4 mm in diameter.
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The Design and Characterization of a Multiple Pinhole Collimator and Its Applications in Biopharmaceutics
… distortion of images caused by multi-pinhole collimation was also investigated. It was concluded that tablet disintegration can only be discerned from visual images under favorable conditions such as short source-to-collimator distances and parallelism of the planes of the object and the …
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A Complete Dosimetric Model of the Gamma Knife Perfexion Using Penelope Monte Carlo Codes
… each; each sector can be set to one of three collimation sizes. The collimators can produce nominal spheres of dose 16 mm, 8 mm, or 4 mm in diameter at the focus. Planning for Gamma Knife stereotactic radiosurgery (GK SRS) is performed using images from computed tomography (CT) and/or magnetic …
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IMPROVING RESOLUTION IN WRIST SPECT WITH CONVERGING COLLIMATORS AND CT ANATOMICAL PRIORS
… These results demonstrated that pinhole collimation or CT prior information, which is now possible with SPECT/CT canneras can improve spatial resolution, however, current count levels are a limiting factor.
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Density measurement of OH radicals in non-thermal plasmas by laser induced fluorescence and time-resolved absorption spectroscopy
… The main advances of the new set up are a better collimation of the UV light and a novel gating scheme. They both significantly reduce the interference of the plasma-induced emission on the absorption measurement. The second setup is dedicated to an improved laser induced fluorescence experiment, …
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Controlling light emission with shaped electron wavefunctions
… wavefunction shaping can greatly enhance the collimation of radiation from electron beams passing through spatially periodic electromagnetic fields, such as those in undulators. Moreover, the radiation from rapidly decelerated shaped electrons can be made directional and monochromatic. Using …
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