Obtaining higher depth of imaging is an important goal in Optical Coherence Tomography (OCT) systems. One of the main factors that affect the depth of OCT imaging is the presence of noise. That’s why the study of noise statistics is an important problem. In the first part of this thesis we obtain an empirical estimate of the second order statistics of noise by using a sequence of Time domain (TD) OCT images. These estimates confirm the non-stationary nature of noise in TD-OCT. In the second part of the thesis these estimates are used to design a depth-dependent matched filter to maximize the Signal-to-Noise Ratio (SNR) and increase the Contrast-to-Noise Ratio (CNR) in TD-OCT. By applying our filter to TD-OCT images of both vascular rabbit tissue and a human tooth, both SNR and CNR were increased and a higher imaging depth was achieved.

Stress är i dagens samhälle ett vanligt förekommande fenomen inom många domäner där individer på olika vis drabbas. Högskolestuderande är en av grupperna. Tidigare forskning visar att olika faktorer bidrar till stress och att stress kan leda till allvarliga konsekvenser för individer. Studiens syfte var att undersöka vilka faktorer som relaterar till högskolestudenters upplevda stress. Till grund för studien låg fem frågeställningar. En enkätundersökning genomfördes för att besvara frågeställningarna. Enkäten bestod av en demografisk del, Antonovskys KASAM-formulär och Cohens perceived stress scale. Respondenterna var 302 studerande vid en högskola i Mellansverige, varav 205 kvinnor och 96 män. Databearbetning skedde med korrelationer, t-test, variansanalys och regressionsanalys. Resultatet mynnade ut i slutsatsen att högskolestudenternas KASAM och könstillhörighet relaterar till upplevd stress, men att delaktighet inte relaterar till upplevd stress. Förslag för framtida forskning inom ämnet ges.

This dissertation explores the neural coding and mechanisms associated with consciousness by analyzing electrical rhythms of the brain under altered states of consciousness, namely epilepsy and anesthesia. First, transformation of neural coding under epileptogenic conditions is examined by computing the Volterra kernels in a rodent epilepsy model, where the epileptogenic condition is induced by altering the concentrations of Mg2+ and K+ of the perfusate for different levels of excitability. Principal dynamic modes (PDMs) are further deduced from the Volterra kernels to compare the changes in neural dynamics under epileptogenic conditions. The integrating PDMs are shown to dominate at all levels of excitability in terms of their relative contributions to the overall response, whereas the dominant frequency responses of the differentiating PDMs shift to higher ranges under epileptogenic conditions, from ripple activities (75 - 200 Hz) to fast ripple activities (200 - 500 Hz). Second, markers of anesthetic states are explored by analyzing amplitude and phase of brain rhythms as well as their interaction and modulation, utilizing electroencephalogram (EEG) recorded from patients undergoing anesthesia. Anesthesia shifts the power to low frequency rhythms, especially alpha rhythms. Additionally anesthesia increases the coupling between alpha rhythms and gamma rhythms while disrupting the coupling between alpha rhythms and ripples (70 - 200 Hz). The results also indicate that the dose responses (i.e. depth of anesthesia) are not necessarily monophasic or linear. The commonality and differences of the changes in brain rhythms associated with these conditions are discussed to elucidate on the possible underlying mechanisms involved in producing consciousness.

This dissertation explores the neural coding and mechanisms associated with consciousness by analyzing electrical rhythms of the brain under altered states of consciousness, namely epilepsy and anesthesia. First, transformation of neural coding under epileptogenic conditions is examined by computing the Volterra kernels in a rodent epilepsy model, where the epileptogenic condition is induced by altering the concentrations of Mg2+ and K+ of the perfusate for different levels of excitability. Principal dynamic modes (PDMs) are further deduced from the Volterra kernels to compare the changes in neural dynamics under epileptogenic conditions. The integrating PDMs are shown to dominate at all levels of excitability in terms of their relative contributions to the overall response, whereas the dominant frequency responses of the differentiating PDMs shift to higher ranges under epileptogenic conditions, from ripple activities (75 - 200 Hz) to fast ripple activities (200 - 500 Hz). Second, markers of anesthetic states are explored by analyzing amplitude and phase of brain rhythms as well as their interaction and modulation, utilizing electroencephalogram (EEG) recorded from patients undergoing anesthesia. Anesthesia shifts the power to low frequency rhythms, especially alpha rhythms. Additionally anesthesia increases the coupling between alpha rhythms and gamma rhythms while disrupting the coupling between alpha rhythms and ripples (70 - 200 Hz). The results also indicate that the dose responses (i.e. depth of anesthesia) are not necessarily monophasic or linear. The commonality and differences of the changes in brain rhythms associated with these conditions are discussed to elucidate on the possible underlying mechanisms involved in producing consciousness.

This project initiated with the aim for improving the ultrahigh resolution optical coherence tomography (UHR-OCT) system performance by considering the limitations to the axial OCT resolution for in vivo imaging of human and animal retina. To this end, a computational model was developed to simulate the effect of wavelength-dependant water absorption on the detected spectral shape of the broad-bandwidth light source used in UHR-OCT at 1060nm wavelength region, which effectively determines the axial OCT resolution in the retina. For experimental verification of the computational model, a custom built light source with a re-shaped spectrum (Superlum Inc.) was interfaced to the state-of-the-art UHR-OCT system. About 30% improvement of the axial OCT resolution in the rat retina and ~12% improvement of the axial OCT resolution in the human retina was achieved compared to the case of the almost Gaussian shaped spectrum of the standard, commercially available SLD. Although water absorption in the 1060nm spectral region strongly affects the sample beam, selecting a suitable light source with specific spectral shape can compensate for the undesired water absorption effect and thus result in significantly improved axial resolution in in vivo OCT retinal images. To demonstrate the advantages of the state-of-the-art OCT technology for non invasive retinal imaging, an established animal model of outer retina degeneration (sodium iodate (NaIO3)-induced retina degeneration) was employed for longitudinal monitoring of the degeneration and investigation of possible early and dynamic signs of damage undetected by other imaging modalities. The long-term (up to 3 months) and short-term (up to 12 hours) effect of sodium iodate toxicity on the layered structure of retina was monitored longitudinally and in vivo for the first time using OCT. An initial acute swelling of the retina, followed by progressive disruption and degeneration of outer retina was observed as a result of sodium iodate-induced damage. Changes in the thickness and optical reflectivity of individual retinal layers were extracted from the OCT images to quantify the changes occurring at different stages of the disease model. Results from this project present the theoretical and practical limits to the highest axial OCT resolution achievable for retina imaging in the 1060nm spectral range both in small animals and humans, and provided a framework for future development of novel light sources. Furthermore, UHR-OCT imaging was shown to be an effective and valuable modality for in vivo, non invasive investigation of retina degenerative disease.

USING GRICE&rsquo / S COOPERATIVE PRINCIPLE AND ITS MAXIMS FOR ANALYZING COHERENCE: A STUDY ON ACADEMIC WRITING &Ouml / zhan, Didem M.A., Program in English Language Teaching Supervisor: Assoc. Prof. Dr. S&uuml / kriye Ruhi September 2004, 95 pages Coherence in written discourse is considered to be a complex and a fuzzy concept but it is, at the same time, a crucial feature of any well-written text. The present study aims to contribute to the field of the teaching of the concept of coherence by proposing an approach to analyzing coherence in students&rsquo / essays in the context of the Department of Modern Languages (DML) at Middle East Technical University (METU) and to the teaching of the concept. The study suggests an approach involving Gricean maxims for analyzing coherence in freshman student argumentative essays at DML at METU. In order to achieve this aim, 50 essays were rated for coherence by two raters and the same essays were analyzed by the researcher for maxim violations. Next, the correlation between the raters&rsquo / judgments and the number of maxim violations in each essay and the correlation between raters&rsquo / judgments and the number of violations for each maxim in each essay was calculated. The findings revealed a significant negative correlation between the variables and a negative correlation between the violation of Quantity maxim most frequently and the raters&rsquo / judgments. The findings suggest that Gricean maxims can be used as a tool for analyzing coherence in student argumentative essays. The implications of this finding for the analysis of the essays, for the teaching, learning and assessment processes are discussed.

Sammanfattning Huvudsyftet med föreliggande kvantitativa studie var att undersöka om polisstudenter på Linnéuniversitetet i Växjö har ett högre genomsnittligt värde av känsla av sammanhang ( Kasam) i jämförelse med en slumpmässig tillfrågad kontrollgrupp av studenter på Linnéuniversitetet i Växjö. Det sekundära syftet var att utröna om det föreligger några könskillnader. Studenterna fick besvara 29 frågor på en Likertskala 1-7, i livsfrågeformuläret Kasam-29. Resultatet visade på att polisstudenter har en högre genomsnittlig grad av Kasam, men att kön inte har någon betydelse. Antalet tillfrågade respondenter var sammanlagt 92, fördelat på 54 polisstudenter varav 37 var män och 17 var kvinnor. Kontrollgruppen bestod av   38 slumpmässigt tillfrågade studenter, 16 män och 22 kvinnor. Det ojämna antalet respondenter mellan grupperna och könsfördelningen hade ingen signifikant påverkan. / Abstract The main purpose of this quantitative survey was to investigate if police students at Linné University of Växjö would have a higher degree of Sense of Coherence (SOC) in comparison to a random control group of other students at Linné University. The secondary purpose was to determine if there are any gender differences. The students answered 29 questions on the Likert scale 1-7 from the Kasam-29 questionnaire. The result showed that police students had an average higher degree of Sense of Coherence, but that gender had no effect. The total of respondents was 92, distributed on 54 police students; 37 men and 17 women. The control group consisted of  38 randomly chosen students, 16 men and 22 women. The uneven quantity of respondents between the groups and genders did not have any significant influence.

Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [197]-201).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.