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The Global ETD Search service is a free service for researchers
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Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 1 to 10 of 10 (0.032 seconds)| 1 |
Phase modulating interferometry with stroboscopic illumination for characterization of MEMSRodgers, Matthew T. 22 January 2007 (has links)
This Thesis proposes phase modulating interferometry as an alternative to phase stepping and phase-shifting interferometry for use in the shape and displacement characterization of microelectromechanical systems (MEMS) [Creath, 1988; de Groot, 1995a; Furlong and Pryputniewicz, 2003]. A phase modulating interferometer is developed theoretically with the use of a stroboscopic illumination source and implemented on a Linnik configured interferometer using a software control package developed in the LabVIEWâ„¢ programming environment. Optimization of the amplitude and phase of the sinusoidal modulation source is accomplished through the investigation and minimization of errors created by additive noise effects on the recovered optical phase. A spatial resolution of 2.762 µm over a 2.97x2.37 mm field of view has been demonstrated with 4x magnification objectives within the developed interferometer. The measurement resolution lays within the design tolerance of a 500Ã… ±2.5% thick NIST traceable gold film and within 0.2 nm of data acquired under low modulation frequency phase stepping interferometry on the same physical system. The environmental stability of the phase modulating interferometer is contrasted to the phase stepping interferometer, exhibiting a mean wrapped phase drift of 40.1 mrad versus 91 mrad under similar modulation frequencies. Shape and displacement characterization of failed µHexFlex devices from MIT's Precision Compliant Systems Laboratory is presented under phase modulating and phase stepping interferometry. Shape characterization indicates a central stage displacement of up to 7.6 µm. With a linear displacement rate of 0.75 Ã…/mV under time variant load conditions as compared to a nominal rate of 1.0 Ã…/mV in an undamaged structure [Chen and Culpepper, 2006].
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Development of an optoelectronic holographic otoscope system for characterization of sound-induced displacements in tympanic membranesHulli, Nesim 13 January 2009 (has links)
The conventional methods for diagnosing pathological conditions of the tympanic membrane (TM) and other abnormalities require measuring its motion while responding to acoustic excitation. Current methodologies for characterizing the motion of the TM are usually limited to either average acoustic estimates (admittance or reflectance) or single-point mobility measurements, neither of which is sufficient to characterize the detailed mechanical response of the TM to sound. Furthermore, while acoustic and single-point measurements are useful for the diagnosis of some middle ear disorders, they are not useful in others. Measurements of the motion of the entire TM surface can provide more information than these other techniques and may be superior for the diagnosis of pathology. In this Thesis, the development of an optoelectronic holographic otoscope (OEHO) system for characterization of nanometer scale motions in TMs is presented. The OEHO system can provide full-field-of-view information of the sound-induced displacements of the entire surface of the TM at video rates, allowing rapid quantitative analysis of the mechanical response of normal or pathological TMs. Preliminary measurements of TM motion in cadaveric animals helped constrain the optical design parameters for the OEHO, including the following: image contrast, resolution, depth of field (DOF), laser power, working distance between the interferometer and TM, magnification, and field of view (FOV). Specialized imaging software was used in selecting and synthesizing the various components. Several prototypes were constructed and characterized. The present configuration has a resolution of 57.0 line pairs/mm, DOF of 5 mm, FOV of 10 ´ 10 mm2, and a 473 nm laser with illumination power of 15 mW. The OEHO system includes a computer controlled digital camera, a fiber optic subsystem for transmission and modulation of laser light, and an optomechanical system for illumination and observation of the TM. The OEHO system is capable of operating in two modes. A 'time-averaged' mode, processed at video rates, was used to characterize the frequency dependence of TM displacements as tone frequency was swept from 500 Hz to 25 kHz. A 'double-exposure' mode was used at selected frequencies to measure, in full-field-of-view, displacements of the TM surface with nanometer resolution. The OEHO system has been designed, fabricated, and evaluated, and is currently being evaluated in a medical-research environment to address basic science questions regarding TM function. Representative time-averaged holographic and stroboscopic interferometry results in post-mortem and live samples are herein shown, and the potential utilization discussed.
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Probing Molecular Stoichiometry by Photon Antibunching and Nanofluidics Assisted Imaging in SolutionCheng, Hao 18 May 2017 (has links)
No description available.
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Improving visibility of latent stains on dark fabric: dark adaptation and stroboscopic light sourcesMiller, Yolonda B. 30 January 2024 (has links)
When an item is submitted to a crime laboratory, the first step in analysis is to examine the item under white light. The next step in examination often involves the use of alternate light sources (ALS) to search for potential biological evidence. Dark adaptation has been suggested as a method to maximize benefits from fluorescent evidence examinations. Dark adaptation refers to the ways the human eye adapts to low light conditions through pupil dilation and rod cell activation. This study evaluates the Crime-lite Eye®, a device designed to help forensic scientists determine their level of dark adaptation before commencing an ALS examination. When tested, the use of the Crime-lite Eye® device resulted in 14% more visualization of fluorescence and 11% more accuracy in pattern recognition, though results were not statistically significant. Since results were more accurate overall, however, and because allowing for a period of dark adaptation would not significantly delay investigation efforts, laboratories should consider implementing a dark adaptation period into their workflow during fluorescent examinations.
Additionally, some ALS manufacturers have begun to include a strobing feature in their devices, such as the GlowTorch FN Forensic Light™. It is known from studies on human attention that flickering stimuli are very effective at capturing attention. Any material fluorescing in response to a strobing ALS would look to the examiner to be suddenly appearing and disappearing as a series of sudden onset stimuli, potentially making weak fluorescence easier to see. Participants in this study were asked to examine four plaid shirts in ambient light conditions and dark conditions, while using either a solid ALS or a strobing ALS. Participants were slightly more accurate while using the strobing ALS device (90% vs 82% in ambient light conditions and 93% vs 92% in dark lighting conditions). However, many of them reported feeling eye strain and annoyance while using the strobing feature. As the change in accuracy was not statistically significant, there is no evidence at present that suggests forensic laboratories need to implement a strobing ALS device into their protocols.
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The study of chaotic phase synchronization of nonlinear electronic circuits and solid-state laser systemsLin, Chien-Hui 12 July 2012 (has links)
We study the chaotic phase synchronization (CPS) between the external periodically driving signals and the nonlinear dynamic systems. The periodical signal was applied to drive the Chua circuit system with two-scroll attractor and the four-scroll attractor circuit system. The phase synchronization between the outputs of these two circuit systems and the driving signals were investigated. Besides, the chaotic phase synchronization of the periodically pump-modulated microchip Nd:YVO4 laser and the microchip Nd:YVO4 laser with optical feedback were also examined in this study.
Phase synchronization (PS) transition of these periodically driven nonlinear dynamic systems exhibited via the stroboscopic technique and recurrence probability. The recurrence probability and correlation probability of recurrence were utilized to estimate the degree of PS. In this thesis, the degree of PS was studied by taking into account the amplitude and frequency of the external driving signal. The experimental compatible numerical simulations also reflected the fact that the Arnold tongues are experimentally and numerically exhibited in the periodically driven nonlinear dynamic systems.
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Energy Efficiency and Power Consumption Improvement of IR Illumination for Surveillance CamerasTormo Lluch, Carlos January 2018 (has links)
The power and energy optimization of a device can lead to a reduced cost, smaller area, better temperature performance, and higher lifetime. Furthermore, in systems that have limited power budget, it allows running simultaneously more functionalities or using features that require higher power demand.Therefore, both from the user and the company perspective, the value of a product increases as the energy optimization improves. For nighttime surveillance video recording, it is common to use infrared illumination to light the targetscene, which draws a significant portion of the total camera energy consumption. This master thesis examines and discusses how stroboscopic infrared illumination can enhance the energy efficiency in videorecording cameras with rolling shutter image sensors. This report analyzes LED driver circuits, recommends methodologies, and sorts the most relevant parameters to help to dimension and design the illumination system for a light-strobing system. A promising field of use for this technique has been found to be the license-plate recognition (LPR) scenario, for which this thesis dedicates a chapter in this document. This project has been developed at AXIS Communications, where a prototype has been built for one of their network security cameras. The prototype has been tested for LPR for both strobing light systems and conventional IR lighting systems. The results obtained prove that the energy efficiency of the illumination system can be improved more than 95% when stroboscopic illumination is used. / Effektförbrukning och energioptimering av en produkt kan leda till lägre kostnad, mindre storlek, bättre temperaturprestanda och högre livslängd. I system med begränsad effektbudget möjliggör detta dessutom aktivering av fler funktioner samtidigt, eller användning av funktioner med högre strömförbrukning. Därmed gör energioptimering att produktens värde ökar både för användaren och för företaget som tillverkar den. För videoinspelning med övervakningskamera nattetid är det vanligt att använda infraröd belysning för att belysa scenen, vilket ofta förbrukar en betydande del av kamerans totala effektbudget. Detta examensarbete undersöker och diskuterar hur blixtrande (Eng. strobed) infraröd belysning kan förbättra energieffektiviteten vid videoinspelning med bildsensorer med rullande slutare. I denna rapport analyseras LED-drivkretsarna, metodik rekommenderas samt att de mest relevanta parametrarna för att dimensionera och designa ett belysningssystem baserad på strobed IR-belysning sorteras ut. Ett lovande användningsområde för denna teknik har visat sig vara LPR-scenariot (License Plate Recognition), vilket diskuteras i ett eget kapitel i denna rapport. Projektet har genomförts på AXIS Communications, där en prototyp har byggts baserat på en av dess nätverkskameror. Prototypen har utvärderats LPR-sammanhang med både strobed och konventionellt IR belysningssystem. De erhållna resultaten visar att energieffektiviteten hos belysningssystemet kan förbättras med mer än 95% när blixtrande belysning används.
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Characterization of pico- and nanosecond electron pulses in ultrafast transmission electron microscopy / Caractérisation des impulsions électroniques pico et nanoseconde en microscopie électronique en transmission ultrarapideBücker, Kerstin 10 October 2017 (has links)
Cette thèse présente une étude des impulsions électroniques ultra-brèves en utilisant le nouveau microscope électronique en transmission ultrarapide (UTEM) à Strasbourg. La première partie porte sur le mode d’opération stroboscopique, basé sur l’utilisation d’un train d’impulsions d’électrons de l’ordre de la picoseconde pour l’étude des phénomènes réversibles ultrarapides. L’étude paramétrique effectuée a permis de révéler les dynamiques fondamentales des impulsions électroniques. Des mécanismes inconnus jusqu’alors et décisifs dans les caractéristiques des impulsions ont été dévoilés. Il s’agit des effets de trajectoire, qui limitent la résolution temporelle, et du filtrage chromatique, qui impacte la distribution en énergie et l’intensité du signal. Ces connaissances permettent aujourd’hui un paramétrage affiné de l’UTEM de manière à satisfaire les divers besoins expérimentaux. La deuxième partie concerne l’installation du mode d’opération complémentaire : le mode « singel-shot ». Ce mode fait appel à une impulsion unique d’intensité élevé et d’une durée de l’ordre de la nanoseconde pour l’étude des phénomènes irréversibles. L’UTEM de Strasbourg étant le premier instrument single-shot équipé d’un spectromètre de perte d’énergie des électrons (EELS), l’influence de l’aberration chromatique a pu été étudiée en détail. Elle s’est dévoilée être une limitation majeure pour la résolution en imagerie, nécessitant d’ajuster le bon compromis avec l’aberration sphérique d’une part et l’intensité du signal d’autre part. Enfin, la faisabilité de mener des études en EELS ultrarapide avec une seule impulsion nanoseconde a pu être démontrée, ceci constituant une première mondiale. Ce résultat très prometteur ouvre un tout nouveau domaine d’expériences résolu en temps. / This thesis presents a study of ultrashort electron pulses by using the new ultrafast transmission electron microscope (UTEM) in Strasbourg. The first part focuses on the stroboscopic operation mode which works with trains of picosecond multi-electron pulses in order to study ultrafast, reversible processes. A detailed parametric study was carried out, revealing fundamental principles of electron pulse dynamics. New mechanisms were unveiled which define the pulse characteristics. These are trajectory effects, limiting the temporal resolution, and chromatic filtering, which acts on the energy distribution and signal intensity. Guidelines can be given for optimum operation conditions adapted to different experimental requirements. The second part starts with the setup of the single-shot operation mode, based on intense nanosecond electron pulses for the investigation of irreversible processes. Having the first ns-UTEM equipped with an electron energy loss spectrometer, the influence of chromatic aberration was studied and found to be a major limitation in imaging. It has to be traded off with spherical aberration and signal intensity. For the first time, the feasibility of core-loss EELS with one unique ns-electron pulse is demonstrated. This opens a new field of time-resolved experiments.
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Test-Retest Reliability and Influence of Visual Constraint During Two Novel Reactive-Agility TasksDuncan, Samantha Lynn January 2021 (has links)
No description available.
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Characterization of Quasi-Periodic Orbits for Applications in the Sun-Earth and Earth-Moon SystemsBrian P. McCarthy (5930747) 17 January 2019 (has links)
<div>As destinations of missions in both human and robotic spaceflight become more exotic, a foundational understanding the dynamical structures in the gravitational environments enable more informed mission trajectory designs. One particular type of structure, quasi-periodic orbits, are examined in this investigation. Specifically, efficient computation of quasi-periodic orbits and leveraging quasi-periodic orbits as trajectory design alternatives in the Earth-Moon and Sun-Earth systems. First, periodic orbits and their associated center manifold are discussed to provide the background for the existence of quasi-periodic motion on n-dimensional invariant tori, where n corresponds to the number of fundamental frequencies that define the motion. Single and multiple shooting differential corrections strategies are summarized to compute families 2-dimensional tori in the Circular Restricted Three-Body Problem (CR3BP) using a stroboscopic mapping technique, originally developed by Howell and Olikara. Three types of quasi-periodic orbit families are presented: constant energy, constant frequency ratio, and constant mapping time families. Stability of quasi-periodic orbits is summarized and characterized with a single stability index quantity. For unstable quasi-periodic orbits, hyperbolic manifolds are computed from the differential of a discretized invariant curve. The use of quasi-periodic orbits is also demonstrated for destination orbits and transfer trajectories. Quasi-DROs are examined in the CR3BP and the Sun-Earth-Moon ephemeris model to achieve constant line of sight with Earth and avoid lunar eclipsing by exploiting orbital resonance. Arcs from quasi-periodic orbits are leveraged to provide an initial guess for transfer trajectory design between a planar Lyapunov orbit and an unstable halo orbit in the Earth-Moon system. Additionally, quasi-periodic trajectory arcs are exploited for transfer trajectory initial guesses between nearly stable periodic orbits in the Earth-Moon system. Lastly, stable hyperbolic manifolds from a Sun-Earth L<sub>1</sub> quasi-vertical orbit are employed to design maneuver-free transfer from the LEO vicinity to a quasi-vertical orbit.</div>
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Zeitaufgelöste inelastische Neutronenstreuung an entmischenden Silber-Natriumchlorid-Einkristallen / Time-resolved inelastic neutron scattering from demixing silver-sodium-chloride single crystalsCaspary, Dirk 31 October 2002 (has links)
No description available.
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