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Today, the focus lies on the state of the environment and how we can choose more sustainable alternatives to oil based materials. One material of interest is microfibrillated cellulose (MFC).The microfibril exhibits interesting properties, which one is its excellent barrier properties, that is expected to come in good use for the conversion to a more sustainable society. It is believed that the use of biobased barriers will increase with these new materials and MFC is showing promising results. But in order to develop the material to its full potential, it is important to investigate how MFC behaves in different situations, which can be examined with rheological measurements. The aim of the thesis is to examine how the rheological properties of suspensions containing MFC are affected by temperature and time storing and how the learning from this work can be used for influencing dispersion properties. Four samples were investigated, containing different amounts of MFC and modified waxy maize starch. The samples were analyzed with a dynamic rotational rheometer (Kinexus Pro +) with a splined cup and bob. The following steps were included in the method development used in this work: sample preparation, the repeatability, rest time and statistical analysis. An oscillatory shear and steady shear measurement was performed on the samples, and selected samples were studied with microscopy. The results show that the temperature has affected the samples. The shear viscosity of all samples decreased with increasing temperature and the samples followed the temperature dependence of Arrhenius' equation. For samples containing MFC, the structure was affected, and the initial viscosity was not recovered. The complex viscosity did also decrease at the beginning to then suggestively increase, creating a stronger network at higher temperatures. With the raised temperature the bonding between the fibrils became weaker, which in turn made the dispersion less viscous. Then, depending on the applied force, the shear viscosity and complex viscosity acted differently. To conclude, both the shear viscosity and the complex viscosity in these dispersions containing MFC are dependent on the temperature and time storing. By the learnings from this work, a method has been developed to understand how to use temperature and storing time to lower the shear viscosity and lower, or increase, the complex viscosity. / Idag ligger det ett stort fokus på miljöns tillstånd och hur vi kan välja mer hållbara alternativjämfört med oljebaserade material. Ett material av intresse är mikrofibrillerad cellulosa (MFC).Denna mikrofibrill besitter intressanta egenskaper, varav en är enastående barriäregenskaper,som förväntas komma till god användning i omställningen till ett mer hållbart samhälle. Det tros att biobaserade barriärer kommer att användas mer i dessa nya material och här visar MFC lovande resultat. Men för att kunna utveckla materialet till sin fulla potential är det viktigt att undersöka hur MFC beter sig i olika situationer, som kan undersökas genom reologiska mätningar. Syftet med arbetet är att undersöka hur de reologiska egenskaperna för suspensioner innehållande MFC påverkas av temperatur och lagringstid samt hur lärdomen från det här arbetet kan användas för att påverka dispersionsegenskaper. Fyra prover undersöktes,innehållande olika mängd MFC och modifierad majsstärkelse. Proverna analyserades med en dynamisk rotations reometer (Kinexus Pro +) med räfflad kopp och bob. Följande steg ingick i metodutvecklingen som användes i detta arbete: provberedning, repeterbarhet, vilotid och statistisk analys. En oscillerande skjuvning och jämn skjuvmätning utfördes på de olika proverna samt att utvalda prover studerades med mikroskopi. Resultatet visade att temperaturen hade påverkat proverna. Skjuvviskositeten för alla prover minskade med en ökande temperatur och proverna följde temperaturberoendet av Arrhenius ekvation. För prover innehållande MFC påverkades strukturen och startviskositeten återficks inte. Den komplexa viskositeten minskade också till en början för att sedan suggestivt öka, vilket skapade ett starkare nätverk vid högre temperaturer. Med en högre temperatur blev bindningarna mellan fibrillerna svagare, vilket bidrog att dispersionerna blev mindre viskösa. Beroende på den applicerade kraften, verkade skjuvviskositeten och den komplexa viskositeten olika. Slutsatsen var att både skjuvviskositeten och den komplexa viskositeten i dessa prover innehållande MFC beroende av temperaturen och lagringstid. Från lärdomen av arbetet har en metod tagits fram för att kunna använda temperatur och lagringstid för att sänka skjuvviskositeten och sänka, eller öka, den komplexa viskositeten.

Short Large-Amplitude Magnetic Structures (SLAMS) have been observedby spacecraft near Earth’s quasi-parallel bow shock. They arecharacterized by a short and sudden increase of the magnetic field,usually by a factor of 2 or more. SLAMS studies have previously beenlimited to small sample sizes because SLAMS were identified throughmanual inspection of the spacecraft data. This makes it difficult to drawgeneral conclusions and the subjective element complicates collaborationbetween researchers. A solution is presented in this thesis; anautomatic SLAMS detection algorithm. We investigate several movingwindowmethods and measure their performance on a set of manuallyidentified SLAMS. The best algorithm is then used to identify 98406SLAMS in data from the Magnetospheric Multiscale (MMS) mission. Ofthose, 66210 SLAMS were detected when the Fast Plasma Investigation(FPI) instrument was active. Additionally, we are interested in knowingwhether a detected SLAMS is located in the foreshock or magnetosheath.Therefore, we implement a Gaussian mixture model classifier,based on hierarchical clustering of the FPI data, that can separatebetween the four distinct regions of the magnetosphere that MMSencounters; magnetosphere, magnetosheath, solar wind and (ion) foreshock.The identified SLAMS are compiled into a database which holdstheir start and stop dates, positional coordinates, B-field informationand information from the magnetospheric classifier to allow for easyfiltering to a specific SLAMS population. To showcase the potentialof the database we use it to perform preliminary statistical analysison how the properties of SLAMS are affected by its spatial and/ormagnetospheric location. The database and Matlab implementationare available on github: https://github.com/cfognom/MMS_SLAMS_detection_and_magnetospheric_classification. / Korta magnetiska strukturer med hög amplitud (SLAMS) har observeratsav satelliter nära jordens kvasi-parallella bogchock. En kortoch plötslig höjning av magnetfältsstyrkan är ett typiskt drag förSLAMS, vanligtvis med en faktor 2 eller mer. Forskning om SLAMShar tidigare varit begränsad till mindre fallstudier eftersom SLAMSidentifierats genom manuell inspektion av satellitdata. Detta gör detsvårt att dra generella slutsatser och det subjektiva elementet försvårarsamarbetet mellan forskare. En lösning till detta problem presenteras idenna avhandling; en automatisk identifieringsalgoritm för SLAMS. Viundersöker flera metoder och mäter deras prestanda på en uppsättningmanuellt identifierade SLAMS. Den bästa algoritmen används sedan föratt identifiera 98406 SLAMS i data från MMS-uppdraget. Av dessa upptäcktes66210 SLAMS när FPI-instrumentet var aktivt. Vi är dessutomintresserade av att veta om en upptäckt SLAMS finns i förshocken ellermagnetoskiktet. Därför implementerar vi en Gaussisk klassificeraresom bygger på hierarkisk klustring av FPI-data. Den kan separerade fyra distinkta regionerna av magnetosfären som MMS observerar;magnetosfär, magnetoskikt, solvind och (jon) förchock. De identifieradeSLAMS:en sammanställs till en databas som innehåller deras start- ochstoppdatum, positionskoordinater, B-fältsinformation och informationfrån magnetosfärsklassificeraren för att möjliggöra enkel filtrering tillen specifik SLAMS-population. För att visa potentialen av databasenutför vi en preliminär statistisk undersökning av hur egenskapernaav SLAMS påverkas av deras rumsliga och/eller magnetosfäriska position.Databasen och Matlab-implementationen är tillgängliga på Github:https://github.com/cfognom/MMS_SLAMS_detection_and_magnetospheric_classification.

The incorporation of Gallium Nitride (GaN) Power Amplifiers (PAs) into future high power aperture radar systems is certain; however, the introduction of this technology into multifunction radar systems will present new challenges to radar engineers. This dissertation describes a broad investigation into amplitude and phase transients produced by GaN PAs when they are excited with multifunction radar waveforms. These transients are the result of self-heating electrothermal memory effects and are manifested as interpulse instabilities that can negatively impact the coherent processing of multiple pulses. A behavioral model based on a Foster network topology has been developed to replicate the measured amplitude and phase transients accurately. This model has been used to develop a digital predistortion technique that successfully mitigates the impact of the transients. The Moving Target Indicator (MTI) Improvement Factor and the Root Mean Square (RMS) Pulse-to-Pulse Stability are used as metrics to assess the impact of the transients on radar system performance and to test the effectiveness of a novel digital predistortion concept. / Ph. D.

Scintillation of Global Positioning Systems (GPS) signals have been extensively studied at low and high latitude regions of the Earth. It has been shown in past studies that amplitude scintillation is severe at low latitudes and phase scintillation is severe at high latitudes. Unlike low and high latitude regions, mid-latitude scintillation has not been extensively studied. Further, it has been suggested that mid-latitude scintillation is negligible. The purpose of this research is to challenge this belief. A multi-constellation and multi-frequency receiver, that tracks American, Russian, and European satellites, was used to monitor scintillation activity at the Virginia Tech Space Center. Analysis was performed on collected data from various days and compared to past research done at high, mid, and low latitudes. The results are discussed in this thesis. / Master of Science

Cavity ring-down spectroscopy has been used over the last twenty years as a highly sensitive absorption spectroscopic technique to measure light attenuation in gases, liquids, and solid samples. An optical cavity is used as a multi-pass cell, and the decay time of the light intensity in the cavity is measured, thereby rendering the techniques insensitive to light intensity fluctuations. Optical waveguides are used to build the optical cavities presented in this work. The geometries of such waveguides permit the use of very small liquid sample volumes while retaining the advantages of cavity ring-down spectroscopy. In this thesis cavity ring-down measurements are conducted, both, in the time domain and by measuring phase-shifts of sinusoidally modulated light, and the two methods are theoretically connected using a simple mathematical model, which is then experimentally confirmed. A new laser driver, that is compatible with high powered diode lasers, has to be designed to be able to switch from time domain to frequency domain measurements. A sample path length enhancement within the optical cavity is explored with the use of liquid core waveguides. The setup was optimised with respect to the matrix liquid, the geometrical matching of waveguide geometries, and the shape of liquid core waveguide ends. Additionally, a new technique of producing concave lenses at fibre ends has been developed and the output of a general fibre lens is simulated. Finally, liquid core waveguides are incorporated into a fibre-loop ring-down spectroscopy setup to measure the attenuation of two model dyes in a sample volume of <1 µL. The setup is characterized by measuring concentrations of Allura Red AC and Congo Red from 1 µM to a limit of detection of 5 nM. The performance of the setup is compared to other absorption techniques measuring liquid samples. / Thesis (Ph.D, Chemistry) -- Queen's University, 2013-04-23 14:08:16.33