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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the 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.
1

Using Hyperopia Measurements to Predict Need for Surgery in Children with Accommodative Esotropia

Jones, Nathan 30 March 2018 (has links)
A Thesis submitted to The University of Arizona College of Medicine - Phoenix in partial fulfillment of the requirements for the Degree of Doctor of Medicine. / Background: Esotropic strabismus is a condition in which the eyes are not properly aligned with each other. In children, uncorrected esotropia may result in permanent loss of vision due to amblyopia, a condition where the nonpreferred, crossing eye is suppressed. Early identification and treatment of esotropia in children is critical, as doing so may prevent permanent loss of vision.
2

Modeling of a Retrodirective Channel With Active Antenna Arrays for Cross-Eye Jamming

Petersson, Björn January 2017 (has links)
Cross-Eye (CE) jamming is a technique aimed at inducing false target angles in radar measurements. The potential to deceive monopulse radar, a radar type commonly used due to its angular accuracy and resilience against jamming, has captured the interest of Electronic Warfare (EW) system manufacturers. CE jamming may increase the capability of self-defense against radar guided missiles. In this thesis, a CE jammer, based on the retrodirective channel design, for use in an EW systems is modeled and analyzed. The focus of the analysis is on the non-reciprocal Active Electronically Scanned Arrays (AESA). An electrical model of the jammer system and the AESA, including variations in the electrical properties, together with three different system correction methods are used. A simulation procedure, using single frequency (CW) signals, is defined and used for estimating total level of reciprocity, which is a primary contributor to jammer performance. Reciprocity error sensitivity for variations in model parameters is simulated to indicate which AESA aspects are essential for performance. Further, the influence of characterization and calibration noise is investigated. The usability of the model is demonstrated in different types of simulations, which highlights the differences between the system correction methods. Simulations show that a relatively high level of reciprocity can be achieved when using system correction, if measurement noise and model limitations are disregarded. The expected degradation in reciprocity from differences in electrical properties between the reception and transmission branch of the AESA has been confirmed. The effect of characterization and calibration noise, for realistic levels of noise, seems to be a dominating factor in the total reciprocity error. A significant increase in reciprocity error can likely be expected when non-CW signals are used and when realistic levels of noise and non-linear effects are added. / Cross-eye (CE) är en störprincip som har potential att inducera vinkelmätfel i radar. Dess möjlighet att störa monopulsradar, en vanligt förekommande typ av radar som är motståndskraftig mot många störformer, har skapat ett intresse för metoden hos tillverkare av system för elektronisk krigföring (EW-system). Användning av CE störning i ett EW-system skulle kunna öka möjligheten till självskydd vid attack från en monopulsradarstyrd robot. Avhandlingen analyserar en modell av en retrodirektiv CE störare som är avsedd för integration i ett multifunktionellt EW-system. Fokus i analysen är på de aktiva gruppantennerna (AESA) som används i systemet. En elektrisk modell av systemet används, vilken inkluderar variationer i parametrar hos AESA samt tre olika systemkorrektionsmetoder. En simuleringsprocedur som ger möjlighet att uppskatta reciprocitetsfel och känslighet för parametervariationer i AESA är definierad. Vidare undersöks inverkan av karaktäriserings och kalibreringsbrus. Modellens användningsområden visas i olika typer av prestandasimulering där effekter av de olika systemkorrektionsmetoderna tydliggörs. Simuleringsresultat för enkelfrekvens (CW) signaler visar en relativt hög nivå av reciprocitet om brus och olinjäriteter ignoreras. Det förväntade resultatet, att elektriska skillnader mellan mottagar- och sändargrenarna orsakar en försämring i reciprocitet, bekräftas. Inverkan av karaktäriserings och kalibreringsbrus verkar vara en dominerande faktor i det totala reciprocitetsfelet då rimliga brusnivåer används. En signifikant höjning av reciprocitetsfelet kan sannolikt förväntas då signaler med en viss bandbredd används och då rimliga nivåer av brus samt olinjäriteter inkluderas. / <p>QC 20171102</p>

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