published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Avhandlingen behandlar de teoretiska och praktiska aspekterna av att använda spektrala vinkelupplösta reflektansmätningar för optisk karakterisering av fiberbaserade material såsom papper och kartong. En spektral goniofotometer används för att mäta det reflekterade ljusets vinkelfördelning. En stor del av arbetet utgörs av att utvärdera instrumentets noggrannhet, samt utreda hur de vinkelupplösta mätningarna skall utföras på bästa sätt för att erhålla en så fullständig karakterisering som möjligt. Det reflekterade ljuset består av tre komponenter; ytreflektans, bulkreflektans samt fluorescens. En fullständig karakterisering förutsätter att dessa tre komponenter kan analyseras separat, vilket i detta arbete görs genom nyutvecklade metoder. En metod har utvecklats för separation av ytreflektans och bulkreflektans. Metoden bygger på att analysera hur den totala reflektansen förändras vid ökande absorption i det reflekterande materialet. Absorptionen kontrolleras genom inkjet-tryckning där tryckfärg appliceras på substratet i sådan mängd att bulkreflektansen helt släcks ut. Genom att kombinera mätningar på tryckt och otryckt substrat kan de båda komponenterna separeras. Trots att ytreflektansen från ett matt papper är liten i förhållande till bulkreflektansen, så visar resultaten att den ökar markant med ökande betraktningsvinkel och kan därmed ha stor inverkan på den totala reflektansen. Bidraget från fluorescens kan kvantitativt analyseras genom att kombinera mätningar utförda med respektive utan UV-filter. Vinkelupplösta mätningar och Monte Carlo-simuleringar av fluorescensens vinkelfördelning visar att dess anisotropi är relaterad till det medeldjup vid vilket fluorescensen emitteras. Resultaten förklarar observerade skillnader och motstridigheter i tidigare rapporterade studier kring huruvida fluorescens kan anses vara Lamberskt fördelad. Samtliga goniofotometriska mätningar är utförda med ett kompakt, kommersiellt tillgängligt, dubbelstråleinstrument. För att undersöka instrumentets lämplighet för absoluta reflektansmätningar utförs en analys av dess mätnoggrannhet. Resultaten visar att instrumentets kompakta storlek i kombination med den anisotropa reflektansen från papper introducerar systematiska fel av samma storleksordning som den totala mätnoggrannheten. Dessa fel uppstår på grund av den relativt stora detektorapertur som måste användas vid mätningar av diffus reflektans, vilket är karakteristiskt för papper och kartong. Resultaten visar även att felen är störst vid flacka mätvinklar och för prover med hög grad av anisotropisk reflektans, och en geometrisk korrektionsmetod för denna typ av systematiska fel föreslås. Spektrala och vinkelupplösta mätningar medför per automatik stora mängder mätdata. Genom att använda strålningstransportteori som en matematisk modell för hur ljus sprids i papper kan mätdatat reduceras till en uppsättning beskrivande materialparameterar. Att uppskatta dessa optiska parametrar utifrån vinkelupplösta reflektansmätningar är i sig ett komplicerat problem, vilket dessutom är känsligt för mätfel och val av mätvinklar. Detta inversa problem analyseras i detalj, och speciellt hur valet av mätvinklar kan reduceras utan att försämra förutsättningarna för estimeringen. Simuleringar visar att mätningarna kan begränsas till infallsplanet, eller till och med enbart framåtriktningen, så länge tillräckligt flacka mätvinklar är inkluderade i mätsekvensen. / This thesis is about measuring and modelling light reflected from paper by using goniophotometric measurements. Measuring bidirectional reflectance requires highly accurate instruments, and a large part of the work in this thesis is about establishing the requirements that must be fulfilled to ensure valid data. A spectral goniophotometer is used for measuring the light reflected from paper and methods are developed for analyzing the different components, i.e. the fluorescence, surface reflectance and bulk reflectance, separately. A separation of the surface and bulk reflectance is obtained by inkjet printing and analyzing the total reflectance in the absorption band of the ink. The main principle of the method is to add dye to the paper until the bulk scattered light is completely absorbed. The remaining reflectance is solely surface reflectance, which is subtracted from the total reflectance of the undyed sample to give the bulk reflectance. The results show that although the surface reflectance of a matte paper is small in comparison with the bulk reflectance, it grows rapidly with increasing viewing angle, and can have a large influence on the overall reflectance. A method for quantitative fluorescence measurements is developed, and used for analyzing the angular distribution of the fluoresced light. The long-standing issue whether fluorescence from turbid (or amorphous) media is Lambertian or not, is resolved by using both angle-resolved luminescence measurements and radiative transfer based Monte Carlo simulations. It is concluded that the degree of anisotropy of the fluoresced light is related to the average depth of emission, which in turn depends on factors such as concentration of fluorophores, angle of incident light and the absorption coefficient at the excitation wavelength. All measurements are conducted with a commercially available benchtop sized double-beam spectral goniophotometer designed for laboratory use. To obtain reliable results, its absolute measurement capability is evaluated in terms of measurement accuracy. The results show that the compact size of the instrument, combined with the anisotropic nature of reflectance from paper, can introduce significant systematic errors of the same order as the overall measurement uncertainty. The errors are related to the relatively large detection solid angle that is required when measuring diffusely reflecting materials. Situations where the errors are most severe, oblique viewing angles and samples with high degree of anisotropic scattering, are identified, and a geometrical correction is developed. Estimating optical properties of a material from bidirectional measurements has proved to be a challenging problem and the outcome is highly dependent on both the quality and quantity of the measurements. This problem is analyzed in detail for optically thick turbid media, and the study targets the case when a restricted set of detection angles are available. This is the case when e.g. an unobstructed view of the sample is not possible. Simulations show that the measurements can be restricted to the plane of incidence (in-plane), and even the forward direction only, without any significant reduction in the precision or stability of the estimation, as long as sufficiently oblique angles are included.

Gamma-ray bursts (GRBs) are the mysterious, short and intense flashes of gamma-rays in the space, and are believed to originate from the rare, explosively devastating, stellar events that happens at cosmological distances. Enormous progress has been made from four decades of GRB research endeavor but the ultimate understanding of their origins has yet to arrive. Recently revealed features in their early afterglows broadened the opportunity space for exploration. We have carried out extensive studies on various physical processes in GRBs. We showed that the distribution of electrons' energy spectral index in GRBs and other relativistic sources is inconsistent with the prediction from the first-order Fermi theory of the shock particle acceleration. We investigated the photon scattering processes within the relativistic outflow that produces the GRB and calculated the resultant emission flux from it. We showed the scattering of the GRB prompt photons by the circum-burst dust, although an attractive possibility, can not explain the puzzling plateau component in the GRB afterglow light curve. We made meaningful constraint on the GRB prompt emission radius, R [greater-than or equal to] 10¹⁴, by studying the synchrotron self absorption for a small sample of bursts with good data. We showed that a late jet, which is thought to be producing the late X-ray flares in GRB afterglows, will produce detectable emissions from its interactions with other components in the explosive event of GRB, and identification of these emissions could verify the existence of the late jet and further prove the massive star origin of long-duration GRBs. / text

This report examines how the neighborhoods along the Metro Blue line have changed over the past two decades, and reflects on the current emerging issue in Transit oriented development (TOD), which is promoting equitable transit neighborhoods. The primary study area includes the route of the Metro Blue line through Los Angeles County where the most economically disadvantaged and marginalized communities are located in the county. In order to investigate the impact of the rail line effectively, the concept of Walksheds are used as the units of analysis, which is defined as the area within a half-mile walking distance from the transit station. Focusing on social equity impact of the transit system operation, the comparison analysis between Los Angeles County and the twenty-two Walksheds of each station in the line evaluates the changes in the close-by neighborhoods while also looking at various social demographic indicators that can reflect demographic shifts using decennial Census data of 1990, 2000, and 2010. While looking at the change through time series data analysis vertically, the performance of each station area is examined horizontally. Therefore, comparative analysis is conducted in four stages to figure out the extent to which the neighborhoods have changed, how rapidly the change occurred and whether the neighborhood change occurred in a positive way or not. The result from the four comparative analyses indicates that the Metro Blue line did not work as a catalyst for promoting economic opportunity in the region in spite of the initial expectations of its advocates. In the beginning of the rail operation of 1990, the neighborhoods along the rail line were excluded and poverty was widespread in the region. However, even after two decades, the twenty-two Walksheds along the Metro Blue Line still remain as undesirable places to live and marginalized as compared to the rest of the county. Moreover, the neighborhood change in the twenty-two Walksheds is negatively linked to the Walksheds based on the result of the comparative analysis. / text

Introduction: Dementia is an age-associated neurodegenerative disorder characterized by a progressive loss of neuro-cognitive function and the emergence of a wide variety of behavioral symptoms. Alzheimer's disease (AD) is the most common types of dementia. Sleep disturbances in patients with Alzheimer's disease is common and previous studies from North America, Europe and Japan reported light therapy could improve the sleep circadian rhythm ( rest-activity) disturbances in AD. However, there was no previous Chinese study on light exposure and sleep quality nor the circadian rhythm in Chinese Alzheimer's disease patients. Objective : The objective of the present study was to investigate the association of light exposure intensity with the quality of sleep and behavioural symptoms in Chinese Alzheimer’s disease (AD) patients Method: This was a cross-sectional observational study. 203 Chinese elderly patients with Alzheimer's disease were recruited from the Memory Clinic in Queen Mary Hospital, the University of Hong Kong, from July 2014 to December 2014. Socio-demographic data and comorbid diseases information were collected from all subjects. Their sleep qualities, quantities and conditions of light exposure were recorded with a sleep logbook and light meter. Their cognitive function, disturbing behaviour, depressive mood and quality of life scales were assessed by a semi-structured questionnaire. Light exposure intensity measured by Light meter (Model SDL 400). Measure for cognitive function were the Abbreviated Mental Test (AMT), Behavioral symptoms measured by the Neuropsychiatric Inventory (NPI) and mood by Geriatric Depression Scale. (GDS-15) The association of outdoor or indoor light exposure with sleep quality and quantities were analyzed by descriptive, bivariate and multivariate analyses. Main outcome measures: The main outcome measure was the sleep quality and quantities of patient, measured by Pittsburgh Sleep Quality Index. (PSQI) Results: 203 subjects (60 males and 143 females) were recruited. 70.4 % of the studied subjects were females. Male to female ratio is 1:2.38. Mean age of them was 81.6 years. The mean (SD) scores of the recruited were: AMT = 4.5 (2.9); PSQI = 6.9 (3.4); NPI =14.4 (17.2); GDS-15= 4.3 (2.8); QOL-AD (patients) = 30.7 (4.9); QOL-AD (caregivers) = 29.5 (4.7) respectively. In bivariate analysis, the Global PSQI score was significantly associated with the morning and afternoon outdoor light exposure. (r = -0.634 and -0.466, respectively) For the total light exposure and mean light exposure, both of them showed strong significant negative correlation with Global PSQI score. (r = -0.769 and -0.769 respectively). Mean (SD) light exposure per day for morning and afternoon outdoor setting were 2372.9 lux (2564.7) and 1090.8 lux (1894.6) respectively. Mean(SD) light exposure per day was 1196.7 lux (866.1) Gender identity showed significant correlation with Global PSQI score (r = 0.034). Global PSQI score was significantly associated with the NPI total score (r = 0.261, p<0.001), the GDS-15 score (r = 0.336, p<0.001), the QOL-AD for patients (r = -0.257, p<0.001), and the QOL-AD for caregivers. (-0.313, p<0.001) In multivariate analyses, using general linear models, the Global PSQI score was highly independent associated with the total light exposure (p=0.000), and significantly associated with the NPI score and Gender (p = 0.011 and 0.021), after adjusting for potential confounders in bivariate analysis. (i.e. gender, activity of daily living status, hypertension and Chronic obstructive airway disease). Confounding factors were NPI and gender. Conclusion: In the present study, We found the intensity of natural light exposure was related to good sleep quality in older Chinese Alzheimer’s disease patients with age 65 years and above in Hong Kong as well as lesser episode of behavioural symptoms. Hence, daily outdoor light exposure is highly recommended for persons with Alzheimer’s disease. / published_or_final_version / Medicine / Master / Master of Medical Sciences

<p>Lättviktsskivor till möbelindustrin har varit ett omskrivet tema i olika branschtidningar den sista tiden.</p><p>Detta examensarbete beskriver och undersöker en ny konstruktion av en lättviktsskiva i massivt trä.</p><p>Lättviktsskivan är uppbyggd som en sandwichkonstruktion i tre skikt. Ytskikten består av 6 mm tjocka</p><p>limfogar och kärnmaterialet av profilerade distanser. Materialet är furu och lättviktsskivan har en</p><p>densitet på 320 kg/m3 vid 39 mm tjocklek. Utifrån kontakter med utvalda tillverkare och användare av</p><p>skivmaterial, samt genom tester, har denna konstruktion granskas och förslag på förbättringar har tagits</p><p>fram. Den ursprungliga distansen som var sammansatt av två halvor med centrumhål har ersatts av en</p><p>massiv distans med en liknande profilering. Vid företagskontakter framkom det en viss tveksamhet till</p><p>synliga fingerskarvar på synliga ytor, vilka den ursprungliga prototypen uppvisade. Med det som</p><p>utgångspunkt presenteras det ett förslag till olika kvaliteter till synliga respektive osynliga och dolda</p><p>ytor vid undersökning av estetiska och produktionstekniska aspekter.</p> / <p>Light-weight panels to the furniture industry have been a well documented task in line papers the last</p><p>time. This work describes and studies a new type of a construction of a light-weight panel in massive</p><p>wood. The light-weight panel in massive wood is built like a sandwich construction in three levels. The</p><p>outer layers are made of 6 mm thick massive wood glue panels and the core material by profiled</p><p>distances. Material is pine and the light-weight panel has a density of 310–332 kg/m3. Out of contacts</p><p>with selected producers and users of board materials, as in combination with tests, has this construction</p><p>been checked and purposes for improvements have been stated. The original distances, which were put</p><p>together by two parts including a centre hole have been replaced by a type of distance in massive wood</p><p>with a similar profiling. In contacts with companies has a slightly reserve been shown to finger-joints</p><p>on visible surfaces, which the originally prototype had. I conclusion with this presents a suggestion for</p><p>different kinds of qualities for visible and not visible respectively and hidden surfaces in conclusion</p><p>with the investigation of aesthetically and production technically aspects.</p>

<p>The purpose of this study is to survey and evaluate if the individual contrast sensitivity and preferences for horizontal and vertical lighting level correspond to the values that standard SS-EN 12464-1 recommends for the workplace- and surrounding light levels.</p><p>This study examines if lighting should be adapted after the individuals’ need or if a general value can be found that will cover every individuals’ need for a workplace and surrounding light level. This study also examines if parameters like sex, age and/or glasses/lenses have an effect on the amount of lighting that the test subjects need. Lastly we compared the values concerning the relationship between workplace- and surrounding light levels with standard SS-EN 12464-1’s recommendations.</p><p>The study is carried out with an experimental design that surveys 220 test subjects who were chosen by a selection of convenience. The test subjects did perform a test where they estimated their individual need for lighting in office environments regarding lighting for workplace and its surroundings. Every test subject carried out the test where they repeated the same attempt three times, to establish if the individual lighting need oscillated or if it was constant, whereupon the results were analyzed, compiled and compared to standard SS-EN 12464-1.</p><p>The results show that the minim- and maxim value for the test subjects is between 70 – 4300 lux. The result varies with different parameters such as sex, age and glasses/lenses. We could also state that the relationship between workplace- and surrounding light levels is slightly higher than what standard SS-EN 12464-1 recommends, which should be taken into consideration when planning future lighting constructions.</p><p>Based on the results in this study, our conclusion is that standard SS-EN 12464-1 does not cover the needs on the comfort levels that the test subjects indicated. The values that the test subjects indicated differ from the values that standard SS-EN 12464-1 recommends.</p><p>Since there is a huge spread of the experienced need for lighting between individuals and age groups, we draw the conclusion that general values of measure can’t be applied as a standard on neither workplace- nor surrounding light levels. To fulfill the needs that users have, the lighting construction should be adapted for the individual and give a lighting flood that will fill the individual needs for workplace lighting.</p>

No description available.

Over the past few years, researchers have directed a significant amount of effort towards realizing tunable all-optical devices using nonlinear optical methods. It is now possible to exercise dynamic control of the group velocity of light traveling through a wide variety of material systems. The slow and fast light refer to situations in which the group velocity íg of an optical pulse through a dispersive material can be made to be smaller and larger, respectively, than the phase velocity vp = c/n. This ability could overcome the remaining challenge in current optical networks of storing and manipulating an optical signal directly in optical domain so as to avoid a bottleneck due to optical-to-electrical (O/E) and electrical-to-optical (E/O) conversions. The overall purpose of the dissertation is to study novel slow-light systems that provide controlled generation of large pulse delays relative to the pulse width with minimal pulse shape distortion by optimally design resonance profiles of such systems. The system design studies utilize several measures of performance such as the fractional delay, power throughput, and signal distortion under the limited system resource constraints. To this end, powerful data fidelity metrics are required to quantify the performance of tunable delay devices. Here, a new framework for measuring an information velocity and throughput is described and implemented using Shannon mutual information concepts. This new technique is used to investigate trends, trade-offs, and limits in slow light devices, which are physically sensible and in good agreement with analyses obtained using a conventional eye-opening(EO) metric. Using these information-theoretic and/or conventional metrics, we present the quantifying performance of gain-based stimulated Brillouin scattering (SBS) system in optical fibers as well as optical passive devices such as Fabry-Perot, fiber Bragg gratings, and ring resonators. It is shown that combining the SBS gain medium with these passive devices can compensate their respective disadvantages and thus increase delay performance without using additional resource of SBS pump power. The results show the possibility of achieving a fractional delay up to 10 at a signal bandwidth up to tens of GHz.