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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.
111

PERCEIVED BRIGHTNESS OF COLORED LIGHT : A study about the perceived brightness of near-monochromatic light in comparison to neutral white light

Albunayah, Razan, C Lindén, Sofia January 2023 (has links)
Recently, there has been a notable rise in the use of colored lighting for both indoor andoutdoor spaces. This trend necessitates a clear understanding of the principles behindselecting lighting levels that are both ergonomic and energy efficient. The objective ofthis study was to establish guidelines for planning colored light. An experiment wasconducted where the perceived brightness of three different near-monochromatic lightswere compared to white light. The stimuli covered a narrow visual field. 33 personsaged 18-40Y participated. Through the measurement of the participants' perception ofthe amount of colored light required -to achieve the same level of brightness as withwhite light- the study was able to determine a percentage-based relationship betweencolored and white light. The result showed that there were clear differences in theperceived brightness of the different colored lights, in line with earlier research withsimilar conditions. This implicates that the results may be used as a foundation whenplanning colored light.
112

Research of appropriate luminance level of monitor screens in workplace

Wang, Mengfei, Shu, Shiqi January 2023 (has links)
MÅL: Huvudsyftet med den här studien är att undersöka hur naturligt ljus påverkar det mänskliga ögats preferens för skärmens ljusstyrka när man tittar på en datorskärm. METODER: Tre experiment genomförs för att mäta i vilken utsträckning solljus förändrar bakgrundsljuset i form av solstrålning. Förexperimentet tar bilder med en kamera som simulerar detmänskliga ögat och en 27-tumsskärm för att simulerabakgrundsmiljön. Förexperimentet varierade skärmens ljusstyrka och efterexperimentet en RGB-bild i enfärgad färg för att få fram intensiteten av det ljus som kommer in i det mänskliga ögat under olika förhållanden. Kontrollförsöket ökade luminansintervallet till 10 och minskade ljusstyrkan till 5 nivåer från 60-100. Vi erhöll 2000 data om förhållandet mellan solljus och solstrålning för att förutsäga förändringen av ljuset i rummet när gardinerna dras för. Intervjutestade 16 vuxna som arbetar på Sogeti för att få fram deras preferenser för olika färger i olika bakgrundsbelysningsförhållanden. RESULTAT: Förexperimentet och kontrollexperimentet visade att varje färg har olika effekt på intensiteten av det ljus som avges av skärmens ljusstyrka när omgivningsljuset förändras. Intervjuresultaten visade att människor har olika preferenser för ljusstyrka. Mörka färger kräver högre ljusintensitet på skärmen när solstrålningen är 0:241, medan ljusa färger kräver lägre ljusintensitet på skärmen när solstrålningen är 430:751. SLUTSATSER: Den viktigaste idén är att upprätthålla ett visst förhållande mellan omgivningens ljusstyrka och skärmens ljusstyrka för att undvika visuell trötthet som orsakas av skärmen. Den här studien ger teoretiskt stöd till tillverkare av elektroniska apparater och ger referensutlåtanden för adaptiv justering av olika färger och ljusstyrka som visas på skärmar. / OBJECTIVE: The main goal of this study is to investigate the impact of natural light on the human eye's preference for screen brightness when viewing a computer screen. METHODS: Three experiments are conducted to measure the extent to which sunlight changes the background light in terms of solar radiation. The Pre-experiment takes pictures with a camera that simulates the human eye and a 27" monitor to simulate the background environment. Pre-experiment varied the brightness of the screen and post-screen of a solid color RGB image to obtain the intensity of light entering the human eye under various conditions. Control Experiment increased the luminance interval to 10 and reduced the brightness level to 5 levels from 60-100. We obtained 2000 data on the relationship between sunlight and solar radiation to predict the change in room light when curtains are drawn. Interview tested 16 adults working at Sogeti to obtain their preference for different colors in different background lighting conditions. RESULTS: Pre-experiment and Control Experiment showed that each color has a different effect on the intensity of light emitted by the screen brightness when the ambient light changes. Interview results showed that people have different preferences for brightness. Dark colors require higher screen light intensity when the solar radiation is 0:241, while bright colors require lower screen light intensity when the solar radiation is 430:751. CONCLUSIONS: The most important idea is to maintain a certain ratio of environmental brightness to screen brightness to avoid visual fatigue caused by the screen. This study provides theoretical assistance for electronic device manufacturers and provides reference opinions for adaptive adjustment of different colors and brightness displayed on screens.
113

Inomhusklimat : En studie om fastigheter uppfyller krav som ställs på inomhus klimatet och hur brukarnas upplevelse av detta / Indoor climate : A study on how real estate complies with the requirements of the indoor climate and how the users experience it

Nilsson, Felix, Johansson, Andreas January 2017 (has links)
Människans välmående och förmåga att prestera optimalt påverkas av inomhusklimatet. de främsta faktorerna som påverkar människans upplevelse av detta är luftkvalitet, ljus och ljudnivåer.I den här rapporten vill vi ta reda på hur en byggnad som vi har valt lever upp till de krav som ställs på inomhusklimatet, ta reda på hur personer i byggbranschen ser på/värderar inomhusklimatet och hur det arbetar för att uppfylla kraven på ett bra inomhusklimat. För att ta reda på detta har vi använt oss av handlingar för det huset vill valt, intervjuer med branschfolk samt en enkätundersökning som delats ut till brukarna av byggnaden.Byggnaden uppfyller de krav som ställs på ljud, ljus, luftkvalité, värmekomfort på vinterhalvåret och värmekomfort på sommarhalvåret enligt miljöbyggnad gulds kriterier för projekterande värden. Enligt vår enkät undersökning med 46 deltagare där frågor som tagits fram av Sweden Green Building Council som handlar om hur nöjda brukarna är med inomhusklimatet klarade ljud, ljus och luftkvalitet kraven på nöjdhet som ska vara minst 80 % av deltagarna. Värmekomforten i byggnaden klarade däremot inte kraven på både vinter och sommarhalvåret.Slutsatsen från den här studien är att i byggnaden överlag håller en hög standard men att det går att göra förbättringar i värmesystemen i form av injusteringar av ventilation och sekundärvärme. Deltagarna var väldigt nöjda med dagsljus och vi kom fram till slutsatsen att på grund av de stora fönsterytorna som skapar detta är det svårt att få en bra värmekomfort i fastigheten då alla typer av öppningar för med sig värmeförluster.De företag och personer vi har varit i kontakt med jobbar alla aktivt med inomhusklimat frågor både i projekteringsstadiet och i brukar stadiet. De ser alla en positiv framtid för den fortsatta utvecklingen av inomhusklimatet och att det är en av de viktigaste frågor man ställs inför vid uppförande av fastigheter. / Human well-being and ability to perform optimally are affected by the indoor climate. The main factors that affect the human experience of this are air quality, light and noise levels.In this report we want to find out how a building we have chosen meets the requirements of the indoor climate, find out how people in the construction industry are looking at/appreciating the indoor climate and how they work to meet the requirements for a good indoor climate. To research this we have used documents from the house we choose, interviews with industry people and a survey conducted to the users of the building.The building meets the requirements for sound, light, air quality, warmth comfort during the winter and heat comfort during the summer months according to the environmental building gold criteria for projected values. According to our survey, a survey of 46 participants where questions raised by the Swedish Green Building Council, which deal with how satisfied the users are with the indoor climate, sound, light and air quality achieved the satisfaction requirements that should be at least 80%. However, the heating comfort in the building did not meet the demands in winter and summertime's.The conclusion from this study is that the building in general has a high standard but that improvements in heating systems can be made in form of adjustments of ventilation and secondary heating. The participants were very happy with daylight and we came to the conclusion that because of the large windows that create this, it is difficult to get a good heating comfort in the property as all types of openings bring heat losses.The companies and people we have been in contact with, all actively work with indoor climate issues, both at the design stage and at the user stage. They all see a positive future for the continued development of the indoor climate and that it is one of the most important issues facing the construction of real estate
114

Design And Fabrication Of Space Variant Micro Optical Elements

Srinivasan, Pradeep 01 January 2009 (has links)
A wide range of applications currently utilize conventional optical elements to individually transform the phase, polarization, and spectral transmission/reflection of the incident radiation to realize the desired system level function. The material properties and the feasibility of fabrication primarily impact the device and system functionality that can be realized. With the advancement in micro/nano patterning, growth, deposition and etching technology, devices with novel and multiplexed optical functionalities have become feasible. As a result, it has become possible to engineer the device response in the near and far field by controlling the phase, polarization or spectral response at the micro scale. One of the methods that have been explored to realize unique optical functionalities is by varying the structural properties of the device as a function of spatial location at the sub-micron scale across the device aperture. Spatially varying the structural parameters of these devices is analogous to local modifications of the material properties. In this dissertation, the optical response of interference transmission filters, guided mode resonance reflection filters, and diffraction gratings operated in Littrow condition with strategically introduced spatial variation have been investigated. Spatial variations in optical interference filters were used to demonstrate wavelength tunable spatial filters. The effect was realized by integrating diffractive and continuous phase functions on the defect layer of a one-dimensional photonic crystal structure. Guided mode resonance filters are free space optical filters that provide narrow spectral reflection by combining grating and waveguide dispersion effects. Frequency dependent spatial reflection profiles were achieved by spatially varying the grating fill fraction in designed contours. Diffraction gratings with space variant fill fractions operating in Littrow condition were used to provide graded feedback profiles to improve the beam quality and spatial brightness of broad area diode lasers. The fabrication of space variant structures is challenging and has been accomplished primarily by techniques such as ruling, electron beam writing or complex deposition methods. In order to vary the desired structural parameter in a designed manner, a novel technique for the fabrication of space variant structures using projection lithography with a fidelity that rivals any of the current technologies was also developed as a part of this work. The devices exhibit wavelength dependent beam shaping properties in addition to spatial and spectral filtering and have potential applications in advanced imaging systems, graded reflectivity laser mirrors, and engineered illumination. The design, modeling, microfabrication and experimental characterization of space variant micro optical elements with novel optical functionalities are presented.
115

Разработка информационной системы для оценки радиояркостной температуры головного мозга на основе модельных данных : магистерская диссертация / Development of an information system for assessing the radio brightness temperature of the brain based on model data

Анвар, П. Г. П., Anvar, P. G. P. January 2020 (has links)
Цель работы: разработка информационной системы для моделирования особенностей распределения радиояркостной температуры головного мозга. Актуальность работы основывается на широком развитии рассматриваемых компонент магистерской. В настоящее время устройства измерения температуры (ИК и контактные методы) в общем случае могут измерять температуру поверхности тела, поэтому важна разработка методов моделирования для неинвазивных измерений температуры внутренних органов, особенно такого сложного объекта как головной мозг. Результаты работы: для оценки изменений распределения радиояркостной температуры разработана информационная система основанная на численном решений уравнений Пеннеса В процессе работы проведено моделирование при разных конфигурациях с помощью алгоритмов, позволяющих последовательно запускать расчет моделей при разных проекциях антенн-аппликаторов на поверхности модели головы. / The relevance of the work is based on the broad development of the considered components of the master's degree. At present, temperature measuring devices (IR and contact methods) can generally measure the temperature of the body surface, therefore, it is important to develop modeling methods for non-invasive measurements of the temperature of internal organs, especially of such a complex object as the brain. Results of the work: to assess changes in the distribution of radio brightness temperature, an information system was developed based on numerical solutions of the Pennes equations. In the process of work, modeling was carried out for different configurations using algorithms that allow sequentially launching the calculation of models with different projections of antenna-applicators on the surface of the head model. Modeling was carried out in Python environment using Paraview software. Figures and diagrams were created using Microsoft Office and Diagram.io software.
116

Die Kleinterzrückung als harmonischer Topos des amerikanischen Musicals

Sprenger, Sebastian 22 September 2023 (has links)
Die aufsteigende Kleinterzrückung des tonalen Zentrums stellt eine im amerikanischen Musical mittlerweile geradezu klischeehafte Wendung zur Erzeugung erhöhter musikalisch-espressiver Intensität dar, die in ungezählten Songs zu beobachten ist. Um ihre spezifische Qualität musiktheoretisch darzustellen, wird im vorliegenden Aufsatz auf das u.a. von Jacques Handschin und Hermann Pfrogner entwickelte Modell der ›relativen Helligkeitswerte‹ der Töne einer diatonischen Skala je nach ihrer Position in der als Quintenkette vorgestellten Diatonik zurückgegriffen. Anhand dreier Beispiele – Leonard Bernsteins Tonight (West Side Story, 1957), Kurt Weills Speak low (One Touch of Venus, 1943) und Alan Menkens Out There (The Hunchback of Notre Dame, 1996) – wird zudem untersucht, wie die Distanz der tonalen Zentren im Rahmen einer primär an diatonischen Verläufen orientierten Melodik im Einzelfall überbrückt wird. / In American musicals the shift of tonal center up by minor-third represents a downright cliché for heightening musical-expressive intensity that can be observed in countless songs. In order to illustrate the specific quality of this shift, the present article employs among other things the model of “relative brightness values” (relative Helligkeitswerte) developed by Jacques Handschin and Hermann Pfrogner, which describes the tones of a diatonic scale according to their position in a diatonic system understood as a chain of fifths. The examination of three examples—Leonard Bernstein’s “Tonight” (West Side Story, 1957), Kurt Weill’s “Speak low” (One Touch of Venus, 1943), and Alan Menken’s “Out There” (The Hunchback of Notre Dame, 1996)—will reveal how, within melodies confined primarily to diatonic processes, the distance between tonal centers can at times be spanned.
117

Robust visual SLAM with compressed image data : A study of ORB-SLAM3 performance under extreme image compression / Robust visuell SLAM med komprimerad bilddata : En studie av ORB-SLAM3-prestanda under extrem bildkomprimering

Wang, Guangzhi January 2023 (has links)
Offloading SLAM to the edge/cloud is now becoming an attractive option to greatly decrease device energy usage. The new SLAM solution involves compressing image data on the device before transmission, allowing a further decrease in the network bandwidth when performing SLAM at the edge/cloud. However, lossy compression affects the quality of images, making image features harder to detect and track during visual SLAM operation, impacting localization accuracy. Current visual SLAM implementations assume that images are non-compressed since SLAM is traditionally executed onboard the device to which a camera is directly connected. This thesis work explores the impact of image compression on the localization accuracy of ORBSLAM3, a representative visual SLAM system, and in what way the ORBSLAM3’s modules for feature detection and matching are affected. Methods are proposed that adapt the image bitrates based on the number of features detected and enhance the image brightness for low-light conditions, plus optimizing the internal parameters in SLAM, to improve the robustness of the overall system to image compression. The experiment results show the detailed influence of the impact brought by compression on ORB-SLAM3 and prove the effectiveness of our methods. Also, integrating these methods yields synergistic improvements. While this thesis work primarily addresses the SLAM system’s front-end, future work can target back-end modifications. / Att avlasta SLAM till kanten/molnet blir nu ett attraktivt alternativ för att markant minska enheters energiförbrukning. Den nya SLAM-lösningen innebär att bilddata komprimeras på enheten innan den överförs, vilket möjliggör ytterligare minskning av nätverksbandbredden vid genomförandet av SLAM vid kanten/molnet. Men förlustkomprimering påverkar bildernas kvalitet och gör det svårare att upptäcka och följa bildfunktioner under visuell SLAM-drift, vilket påverkar lokaliseringsnoggrannheten. Nuvarande implementationer av visuell SLAM förutsätter att bilderna inte är komprimerade eftersom SLAM traditionellt utförs ombord på den enhet till vilken en kamera är direkt ansluten. Denna avhandling utforskar effekten av bildkomprimering på lokaliseringsnoggrannheten hos ORB-SLAM3, en representativ visuell SLAM-system, och på vilket sätt ORB-SLAM3: s moduler för funktionssökning och matchning påverkas. Metoder föreslås som anpassar bildbitarna baserat på antalet detekterade funktioner och förbättrar bildens ljusstyrka för svagt ljusförhållanden, samt optimerar de interna parametrarna i SLAM för att öka hela systemets robusthet mot bildkomprimering. Experimentresultaten visar den detaljerade påverkan som kompression har på ORB-SLAM3 och bevisar effektiviteten hos våra metoder. Dessutom ger integration av dessa metoder synergi och förbättringar. Även om denna avhandling primärt fokuserar på SLAM-systemets framsida, kan framtida arbete rikta sig mot bakkantsmodifieringar.
118

Modeling Confidence and Response Time in Brightness Discrimination: Testing Models of the Decision Process with Controlled Variability in Stimulus Strength

Intermaggio, Victor G. 22 June 2012 (has links)
No description available.
119

Analyse de la modélisation de l'émission multi-fréquences micro-onde des sols et de la neige, incluant les croutes de glace à l'aide du modèle Microwave Emission Model of Layered Snowpacks (MEMLS).

Montpetit, Benoît January 2015 (has links)
Résumé : L'étude du couvert nival est essentielle afin de mieux comprendre les processus climatiques et hydrologiques. De plus, avec les changements climatiques observés dans l'hémisphère nord, des événements de dégel-regel ou de pluie hivernale sont de plus en plus courants et produisent des croutes de glace dans le couvert nival affectant les moeurs des communautés arctiques en plus de menacer la survie de la faune arctique. La télédétection micro-ondes passives (MOP) démontre un grand potentiel de caractérisation du couvert nival. Toutefois, a fin de bien comprendre les mesures satellitaires, une modélisation adéquate du signal est nécessaire. L'objectif principal de cette thèse est d'analyser le transfert radiatif (TR) MOP des sols, de la neige et de la glace a fin de mieux caractériser les propriétés géophysiques du couvert nival par télédétection. De plus, un indice de détection des croutes de glace par télédétection MOP a été développé. Pour ce faire, le modèle Microwave Emission Model of Layered Snowpacks (MEMLS) a été étudié et calibré afin de minimiser les erreurs des températures de brillance simulées en présences de croutes de glace. La première amélioration faite à la modélisation du TR MOP de la neige a été la caractérisation de la taille des grains de neige. Deux nouveaux instruments, utilisant la réflectance dans le proche infrarouge, ont été développés afin de mesurer la surface spécifique de la neige (SSA). Il a été démontré que la SSA est un paramètre plus précis et plus objectif pour caractériser la taille des grains de neige. Les deux instruments ont démontré une incertitude de 10% sur la mesure de la SSA. De plus, la SSA a été calibré pour la modélisation MOP a n de minimiser l'erreur sur la modélisation de la température de brillance. Il a été démontré qu'un facteur multiplicatif [phi] = 1.3 appliqué au paramètre de taille des grains de neige dans MEMLS, paramètre dérivé de la SSA, est nécessaire afin de minimiser l'erreur des simulations. La deuxième amélioration apportée à la modélisation du TR MOP a été l'estimation de l'émission du sol. Des mesures radiométriques MOP in-situ ainsi que des profils de températures de sols organiques arctiques gelés ont été acquis et caractérisés a fin de simuler l'émission MOP de ces sols. Des constantes diélectriques effectives à 10.7, 19 et 37 GHz ainsi qu'une rugosité de surface effective des sols ont été déterminés pour simuler l'émission des sols. Une erreur quadratique moyenne (RMSE) de 4.65 K entre les simulations et les mesures MOP a été obtenue. Suite à la calibration du TR MOP du sol et de la neige, un module de TR de la glace a été implémenté dans MEMLS. Avec ce nouveau module, il a été possible de démontré que l'approximation de Born améliorée, déjà implémenté dans MEMLS, pouvait être utilisé pour simuler des croutes de glace pure à condition que la couche de glace soit caractérisée par une densité de 917 kg m[indice supérieur _􀀀3] et une taille des grains de neige de 0 mm. Il a aussi été démontré que, pour des sites caractérisés par des croutes de glace, les températures de brillances simulées des couverts de neige avec des croutes de glace ayant les propriétés mesurées in-situ (RMSE=11.3 K), avaient une erreur similaire aux températures de brillances simulées des couverts de neige pour des sites n'ayant pas de croutes de glace (RMSE=11.5 K). Avec le modèle MEMLS validé pour la simulation du TR MOP du sol, de la neige et de la glace, un indice de détection des croutes de glace par télédétection MOP a été développé. Il a été démontré que le ratio de polarisation (PR) était très affecté par la présence de croutes de glace dans le couvert de neige. Avec des simulations des PR à 10.7, 19 et 37 GHz sur des sites mesurés à Churchill (Manitoba, Canada), il a été possible de déterminer des seuils entre la moyenne hivernale des PR et les valeurs des PR mesurés indiquant la présence de croutes de glace. Ces seuils ont été appliqués sur une série temporelle de PR de 33 hivers d'un pixel du Nunavik (Québec, Canada) où les conditions de sols étaient similaires à ceux observés à Churchill. Plusieurs croutes de glace ont été détectées depuis 1995 et les mêmes événements entre 2002 et 2009 que (Roy, 2014) ont été détectés. Avec une validation in-situ, il serait possible de confirmer ces événements de croutes de glace mais (Roy, 2014) a démontré que ces événements ne pouvaient être expliqués que par la présence de croutes de glace dans le couvert de neige. Ces mêmes seuils sur les PR ont été appliqués sur un pixel de l'Île Banks (Territoires du Nord-Ouest, Canada). L'événement répertorié par (Grenfell et Putkonen, 2008) a été détecté. Plusieurs autres événements de croutes de glace ont été détectés dans les années 1990 et 2000 avec ces seuils. Tous ces événements ont suivi une période où les températures de l'air étaient près ou supérieures au point de congélation et sont rapidement retombées sous le point de congélation. Les températures de l'air peuvent être utilisées pour confirmer la possibilité de présence de croutes de glace mais seul la validation in-situ peut définitivement confirmer la présence de ces croutes. / Abstract : Snow cover studies are essential to better understand climatic and hydrologic processes. With recent climate change observed in the northern hemisphere, more frequent rain-on-snow and meltrefreeze events have been reported, which affect the habits of the northern comunities and the survival of arctique wildlife. Passive microwave remote sensing has proven to be a great tool to characterize the state of snow cover. Nonetheless, proper modeling of the microwave signal is needed in order to understand how the parameters of the snowpack affect the measured signal. The main objective of this study is to analyze the soil, snow and ice radiative transfer in order to better characterize snow cover properties and develop an ice lens detection index with satellite passive microwave brightness temperatures. To do so, the passive microwave radiative transfer modeling of the Microwave Emission Model of Layered Snowpacks (MEMLS) was improved in order to minimize the errors on the brightness temperature simulations in the presence of ice lenses. The first improvement to passive microwave radiative transfer modeling of snow made was the snow grain size parameterization. Two new instruments, based on short wave infrared reflectance to measure the snow specific surface area (SSA) were developed. This parameter was shown to be a more accurate and objective to characterize snow grain size. The instruments showed an uncertainty of 10% to measure the SSA of snow. Also, the SSA of snow was calibrated for passive microwave modeling in order to reduce the errors on the simulated brightness temperatures. It was showed that a correction factor of φ = 1.3 needed to be applied to the grain size parameter of MEMLS, obtain through the SSA measurements, to minimize the simulation error. The second improvement to passive microwave radiative transfer modeling was the estimation of passive microwave soil emission. In-situ microwave measurements and physical temperature profiles of frozen organic arctic soils were acquired and characterized to improve the modeling of the soil emission. Effective permittivities at 10.7, 19 and 37 GHz and effective surface roughness were determined for this type of soil and the soil brightness temperature simulations were obtain with a minimal root mean square error (RMSE) of 4.65K. With the snow grain size and soil contributions to the emitted brightness temperature optimized, it was then possible to implement a passive microwave radiative transfer module of ice into MEMLS. With this module, it was possible to demonstrate that the improved Born approximation already implemented in MEMLS was equivalent to simulating a pure ice lens when the density of the layer was set to 917 kg m−3 and the grain size to 0 mm. This study also showed that by simulating ice lenses within the snow with there measured properties, the RMSE of the simulations (RMSE= 11.3 K) was similar to the RMSE for simulations of snowpacks where no ice lenses were measured (only snow, RMSE= 11.5 K). With the validated MEMLS model for snowpacks with ice lenses, an ice index was created. It is shown here that the polarization ratio (PR) was strongly affected by the presence of ice lenses within the snowpack. With simulations of the PR at 10.7, 19 and 37 GHz from measured snowpack properties in Chucrhill (Manitoba, Canada), thresholds between the measured PR and the mean winter PR were determined to detect the presence of ice within the snowpack. These thresholds were applied to a timeseries of nearly 34 years for a pixel in Nunavik (Quebec, Canada) where the soil surface is similar to that of the Churchill site. Many ice lenses are detected since 1995 with these thresholds and the same events as Roy (2014) were detected. With in-situ validation, it would be possible to confirm the precision of these thresholds but Roy (2014) showed that these events can not be explained by anything else than the presence of an ice layer within the snowpack. The same thresholds were applied to a pixel on Banks island (North-West Territories, Canada). The 2003 event that was reported by Grenfell et Putkonen (2008) was detected by the thresholds. Other events in the years 1990 and 2000’s were detected with these thresholds. These events all follow periods where the air temperature were warm and were followed by a quick drop in air temperature which could be used to validate the presence of ice layer within the snowpack. Nonetheless, without in-situ validation, these events can not be confirmed.
120

The optical and NIR luminous energy output of the Universe : the creation and utilisation of a 9 waveband consistent sample of galaxies using UKIDSS and SDSS observations with the GAMA and MGC spectroscopic datasets

Hill, David T. January 2011 (has links)
Theories of how galaxies form and evolve depend greatly on constraints provided by observations. However, when those observations come from different datasets, systematic offsets may occur. This causes difficulties measuring variations in parameters between filters. In this thesis I present the variation in total luminosity density with wavelength in the nearby Universe (z<0.1), produced from a consistent reanalysis of NIR and optical observations, taken from the MGC, UKIDSS and SDSS surveys. I derive luminosity distributions, best-fitting Schechter function parameterisations and total luminosity densities in ugrizYJHK, and compare the variation in luminosity density with cosmic star formation history (CSFH) and initial mass function (IMF) models. I examine the r band luminosity distribution produced using different aperture definitions, the joint luminosity- surface brightness (bivariate brightness) distribution in ugrizYJHK, comparing them to previously derived distributions, and how the total luminosity density varies with wavelength when surface brightness incompleteness is accounted for. I find the following results. (1) The total luminosity density calculated using a non-Sersic (e.g. Kron or Petrosian) aperture is underestimated by at least 15%, (2) Changing the detection threshold has a minor effect on the best-fitting Schecter parameters, but the choice of Kron or Petrosian apertures causes an offset between datasets, regardless of the filter used to define the source list, (3) The decision to use circular or elliptical apertures causes an offset in M* of 0.20 mag, and best-fitting Schechter parameters from total magnitude photometric systems have a flatter faint-end slope than Kron or Petrosian photometry, (4) There is no surface brightness distribution evolution with luminosity for luminous galaxies, but at fainter magnitudes the distribution broadens and the peak surface brightness dims. A Choloniewski function that is modified to account for this surface brightness evolution fits the bivariate-brightness distribution better than an unmodified Choloniewski function, (5) The energy density per unit interval, vf(v) derived using MGC and GAMA samples agrees within 90% confidence intervals, but does not agree with predictions using standard CSFH and IMF models. Possible improvements to the data and alterations to the theory are suggested.

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