Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 25 for “"spatial filter"”.
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External cavity laser with coherent amplifier array and multiple slit spatial filter
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1986.
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Spatial filter performance on point-target detection in various clutter conditions using visible images
… point targets in clutter is a challenge because spatial noise in an image can be much greater than temporal noise. Suppression of clutter uses a spatial filter matched to the target size. The goal of filtering is to reduce the spatial noise to the temporal noise limit. In this thesis, the …
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High-power single-mode vertical-cavity surface-emitting lasers
… The devices presented include the metallic spatial filter, the extended pillar design with experimental verification of optimized higher order mode loss, and the surface relief design with an experimentally verified model. The metallic spatial filter is found to show peak output power near …
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Fourier-based optical analysis of a membrane mirror spatial light modulator
… optical system, used to read out a phase-only spatial light modulator (SLM) for phase to intensity conversion. The computational model, based on discrete cosine transforms, is lightweight enough to be run on standard desktop computers, and flexible enough to allow engineering simulations of …
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Transverse mode selection and brightness enhancement in laser resonators by means of volume Bragg gratings
… a diffractive optical element is proposed as a spatial filter, allowing for the design of compact high brightness sources not possible with conventional methods of transverse mode selection. This thesis explores the angular selectivity of volume Bragg gratings (VBGs) and their use as spatial …
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Large eddy simulation of compressible channel flow
… the unresolvable (subgrid) scales by applying a spatial filter to the compressible Navier-Stokes equations. The Leonard and cross terms which appear due to the filtering procedure are modeled based on a Taylor series expansion. The subgrid scale Reynolds terms are modeled using a compressible …
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Vibrational Control of a Cantilever Beam Using Sensor and Actuator Averaging Methods
… and actuator averaging, a method to create a spatial filter that is insensitive to model parameter uncertainty. We develop a controller to actively control cantilever beam vibration using accelerometer input. The controller is a classic single-sensor single-actuator system that achieves a …
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Synthesis Technique of Thickness-Customizable Multilayered Frequency Selective Surface for Plasma-Based Electromagnetic Structures
… used to synthesize the transfer response of the filter given desired characteristics such as filter type, center frequency, and bandwidth. These inverter layers are essentially electromagnetic coupling interlayers that can be adjusted to customize the thickness of multilayered FSS without …
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On the development of a low-cost lithographic interferometer
… is utilized to simplify the construction of a spatial filter. The resulting custom-built interference lithography tool is able to print large-area (~ cm2 ) periodic patterns. The tool has a small footprint (~0.2 M2 ) and can be assembled for less than 6000 USD.
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A Novel Unit Cell Antenna for Highly Integrated Phased Arrays in the SHF Band
… signals to processing electronics. Signals are filtered and amplified to maintain the desired sensitivity and complexly weighted using circuits with reconfigurable amplification gain and phase delay. Finally, all signals are combined. The summation of these complexly weighted spatial samples …
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A VLSI array processor architecture for emulating resistive network filtering
… The work started from a resistive network -type spatial filter that was part of a video image compression algorithm. The functionality of this algorithm, as well as the filter, was described in Cellular Neural/Nonlinear Network (CNN) notations and they will be used throughout this thesis in …
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Ionization of air produced by strong shocks
… a continuously working Helium-Neon laser with a spatial filter was employed. The number of electrons per cubic centimeter behind the shock was measured at Mach numbers of 17.6 and 18.1. The data obtained did not represent accurate quantitative values of electron concentrations due to the unknown …
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Real-time optical intensity correlation using photorefractive BSO
… achieved with a synthetic discriminant function filter displayed by the Epson liquid crystal display in the real-time intensity correlator. The phase and intensity modulation properties of the Epson liquid crystal display are studied.<br/><br/>A further research topic which uses the Epson liquid …
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Moiré interferometry at high temperatures
… at high temperature was enhanced by means of a spatial filter and a narrow band interference filter to minimize the background noise from the glow of the specimen and heater. The system was verified by a free thermal expansion test of an aluminum block. Good agreement demonstrated the validity …
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A Filtered-Wall Formulation for Large -Eddy Simulation of Wall -Bounded Turbulence
… In this approach the wall is treated by 'filtering through it', so that in the LES representation, the wall is not a sharp boundary. A homogeneous (or nearly homogeneous) spatial filter is applied to an extended domain, in which the wall is embedded. By treating the wall in this way, the …
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Discrete-frequency infrared imaging with a quantum cascade laser and diffuse optical Raman tomography: methods toward improving clinically relevant label-free chemical contrast
… conventional sources was observed when using a spatial filter aperture on the order of the wavelength of light (10μm). We further demonstrate this advantage by illustrating supersampling point mapping which is not achievable with conventional sources. Second, we present experimental results and …
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Distributed-effect modal domain optical fiber sensors for flexible structure control
… sensors can be fabricated with spatially varying sensitivity to the distributed measurand and act as spatial filters. The spatial variation in the sensor sensitivity, known as the sensor's weighting function, determines the measurement provided by the spatial filter. Spatial …
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Frequency selective surface (FSS) for cellular signals shelding
… etched on a dielectric substrate which acts as a spatial filter. The proposed FSS is designed as a band-stop filter to attenuate the cellular signals operating at GSM900, GSM1800 and IMT2000 frequency bands. The employment of the FSS is an effective shielding technique as it eliminates the need …
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Theory and application of quasi-elastic equations in terrain-folowing coordinates based on the full pressure field
… ƒã coordinate by White (1989). The equations are filtered of vertically propagating acoustic waves. However, since Lamb waves are present, the equations may be termed quasi-elastic. In contrast to similar quasi-elastic pressure-based models, the equations and the numerical solution procedure …
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Spatial pattern of African Easterly Waves and their Precipitation in Northern Africa
… around 700-850 hPa. This study explores the spatial distribution of AEWs and their precipitation using the Tropical Easterly Waves Climatology and the Integrated Multi-satellite Retrievals for Global Precipitation Measurement (IMERG). First, a spatial filter is used to limit 2001-2021 …
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