Η Τομογραφία Εκπομπής Ποζιτρονίων, η οποία συχνά αναφέρεται με βάση το ακρωνύμιό της, PET (Positron Emission Tomography), αποτελεί μία πρωτοποριακή τεχνική απεικόνισης η οποία παρέχει εγκάρσιες τομές της λειτουργίας των διαφόρων δομών του ανθρωπίνου σώματος. Η Τομογραφία PET επιτρέπει την μεταβολική απεικόνιση αυτών των δομών (σε αντίθεση με τις ακτίνες-Χ και την Υπολογιστική Τομογραφία (CT – Computer Tomography) οι οποίες παρέχουν ανατομική απεικόνιση), σε μοριακό επίπεδο, και αυτός είναι ο λόγος που συχνά η Τομογραφία PET αναφέρεται ως μοριακή απεικόνιση. Ειδικότερα, οι τομογράφοι PET για μικρά ζώα (Small Animal PET) οι οποίοι απαιτούν ιδιαίτερα υψηλή διακριτική ικανότητα, διαδραματίζουν σημαντικό ρόλο στην βιολογία και στις in-vivo μελέτες της φαρμακοκινητικής των ιχνηθετών και του μεταβολισμού. Σύμφωνα με τη βιβλιογραφία έχουν αναφερθεί διάφοροι τύποι τομογράφων PET, στους οποίους χρησιμοποιήθηκαν διάφοροι τύποι ανιχνευτικών διατάξεων, με διαφορετικό σχεδιασμό σε κάθε περίπτωση. Η τεχνολογία αυτών των τομογράφων βασίζεται στη χρήση μικρών ανόργανων κρυστάλλων, κυρίς αποτελούμενων από BGO, GSO και LSO, οι οποίοι σχηματίζουν ένα block στο οποίο έχει προσαρτηθεί ένας φωτοπολλαπλασιαστής είτε με ευαισθησία θέσης (PS – PMT: Position Sensitive PhotoMultiplier Tube), είτε με πολλαπλές ανόδους (multianode PMT). To BGO (Bismuth Germanate Oxide) είναι το υλικό που χρησιμοποιείται σε αρκετούς εμπορικούς Τομογράφους, έχοντας πλέον αντικαταστήσει το ιωδιούχο νάτριο (ΝαΙ). Ένα πρότυπο σύστημα small animal PET χαμηλού κόστους βρίσκεται υπό ανάπτυξη, προκειμένου να μελετήσουμε τα επιμέρους σχεδιαστικά χαρακτηριστικά του και να μετρήσουμε την απόδοσή του. Ο βασικός block ανιχνευτής αποτελείται από μία 16×16 διάταξη επιμέρους BGO κρυστάλλων διαστάσεων 3.75×3.75×20 mm3, ο οποίος έχει τοποθετηθεί με ειδική διεργασία στην επιφάνεια ενός Hamamatsu R-2486 PSPMT. Με τη χρήση κατάλληλων ηλεκτρονικών διατάξεων και την ανάπτυξη ειδικού λογισμικού πραγματοποιήθηκαν μετρήσεις της απόδοσης των επιμέρους ανιχνευτών καθώς επίσης και μετρήσεις σχετικές με τους φωτοπολλαπλασιαστές. / Positron Emission Tomography, often referred to by its acronym, PET, is an emerging radiologic modality that yields transverse tomographic images of functioning organs in the human body. PET enables the metabolic imaging of organs (as opposed to the anatomic imaging provided by techniques such as the X-ray imaging or the Computerized Tomography (CT)), in molecular level, and this is the reason why it is characterized as molecular imaging. Especially, small animal PET tomographs which require high spatial resolution can play an important role in biology and studies of in vivo tracer pharmacokinetics and metabolism. Various implementations have been reported in the literature using a variety of detector and design technologies. The basic technology for these scanners is based on small inorganic crystals, mainly from BGO, GSO, and LSO, forming detector blocks read out by position sensitive and multianode PMTs. BGO is the material used in a lot of commercial scanners, having replaced NaI, mainly because BGO has higher stopping power and it is not hygroscopic. We have been developing a low-cost small animal PET prototype, in order to study specific design characteristics and measure its performance. The basic block detector design consists of a 16×16 array of 3.75×3.75×20 mm3 individual BGO crystals coupled to a Hamamatsu R-2486 PSPMT. Measurements of the individual detector performance as well as measurements of the PSPMTs have been performed.

A new combustion zone analytical model has been developed in which the combustion front temperature may be calculated. The model describes in the combustion zone, the amount of fuel burned based on reaction kinetics, the fuel concentration and produced gas composition based on combustion stoichiometry, and the amount of heat generated based on a heat balance. Six runs were performed in a 3-inch diameter, 40-inch long steel combustion tube with Jobo crude oil (9-11°API) from the Orinoco Belt in Venezuela. These runs were carried out with air containing three values of oxygen concentration, 21%, 30%, and 40%. The weight percentage of sand, clay, water, and oil in the sand mix was kept constant in all runs at 86.6%, 4.7%, 4.0%, and 4.7% respectively. Injection air rates (3 L/min) as well as the production pressure (300 psig) were kept constant in all runs. The results indicate that the calculated combustion zone temperatures and temperature profiles are in good agreement with the experimental data, for the range of oxygen concentration in the injected air. The use of oxygen-enriched air slightly increased the combustion front temperature from 440°C in a 21 mole % O2 concentration to a maximum of 475°C for air with 40 mole % O2 concentration. Oxygen-enriched air injection also increased the combustion front velocity from 13.4 cm/hr (for 21% oxygen) to 24.7 cm/hr (for 40% oxygen), thus reducing the start of oil production from 3.3 hours (for 21% oxygen) to 1.8 hours (for 40% oxygen). In the field, the use of oxygen-enriched air injection could translate into earlier oil production compared to with not-enriched air injection. The new analytical model for the combustion zone developed in this study will be beneficial to future researchers in understanding the effect of oxygen-enriched in-situ combustion and its implications on the combustion front temperature and combustion front thickness.

Methylenetetrahydrofolate reductase (MTHFR) synthesizes 5-methyltetrahydrofolate, a methyl donor for conversion of homocysteine to methionine. A common thermolabile variant causes mild MTHFR deficiency, induces mild hyperhomocysteinemia when plasma folate levels are low and increases risk for neural tube defects (NTD) and pregnancy loss. To increase our understanding of Mthfr regulation, the 5' and 3' regions of the mouse cDNA and gene were characterized. These studies revealed two major promoters, an internal coding exon in the 5'UTR, alternative transcriptional and translational start sites and alternative splicing and polyadenylation. These data suggest that Mthfr regulation is likely to be complex. To investigate the role of Mthfr in NTD, several approaches were taken. First, folate and MTHFR co-factor, flavin adenine dinucleotide, were shown to stabilize normal and thermolabile MTHFR during heat inactivation, suggesting that folate might prevent hyperhomocysteinemia in individuals with thermolabile enzyme through protein stabilization. Next, in situ hybridization of neurulating mouse embryos showed that Mthfr is expressed in the forebrain, hindbrain, branchial arches, blood vessels, gut, and importantly, in the ventral part of the neural tube. Mthfr+/- mice were then used as a model of mild deficiency to address the effects of maternal and embryonic Mthfr deficiency on development. When combined with inadequate dietary folate, Mthfr +/- pregnant females showed a two-fold higher rate of pregnancy loss than Mthfr+/+ pregnant females. As well, a percentage of day 10.5 embryos from only the Mthfr+/- pregnant females were underdeveloped by 2 days. These effects were not apparent when dietary folate was sufficient, consistent with a genetic-nutritional interactive effect. Finally, folate metabolism was investigated in an NTD model, the curly-tail (ct) mouse, since the ct defect and Mthfr were mapped in close proximity. However, Mthfr sequence in ct mice was simila

El presente es un proyecto investigativo de carácter exploratorio con un enfoque descriptivo alrededor de un fenómeno poco estudiado: el homecasting. Se busca aportar en la construcción, definición y delimitación del fenómeno del homecastig a través de un estudio de caso en el cual se describen y analizan ejemplos específicos relacionados con sujetos, objetos y prácticas particulares, en torno a la producción casera audiovisual alojada en el portal YouTube. El proyecto, realizado entre los años 2009 y 2013 busca aplicar algunos conceptos y metodologías del estudio de la vida cotidiana y la antropología urbana al estudio de las interacciones en Internet, proponiendo un estudio de caso específico (pues los encontrados son más generales o teóricos y no se ocupan de asuntos particulares en relación al homecasting) aportando al campo comunicacional a través de una mirada transversal, que enfatiza en que lo audiovisual está en el centro de los cambios en el sentido de las experiencias estéticas contemporáneas.

Magistriniame darbe pateikta literatūros analizė, tyrimų tikslas ir uždaviniai, tyrimo metodika, tyrimų rezultatai ir jų analizė, išvados. Nustatyta, kad Lietuvoje ežerams valyti naudojamų žemsiurbių pagrindinis trūkumas yra siurbiama skysta pulpa ir mažas jos transportavimo atstumas. Tyrimų tikslas yra įvertinti dažniausiai naudojamos žemsiurbės „Watermaster Classic III“ tinkamumą ežerų valymui Lietuvoje. Tiesioginiais matavimais, trijuose pjūviuose, buvo nustatyti vandens gyliai išvalytose Masčio ežero ir Pakruojo tvenkinio dalyse. Suspenduotų dalelių kiekiui vandenyje nustatyti, iš Masčio ežero buvo paimti buteliu – batometru vandens mėginiai (iš karto baigus siurbimą), tūriniu būdu išmatuotas žemsiurbės našumas. Išmatavus vandens gylius, buvo atlikta aprašomoji stastika, kurios metu buvo pasitelkta „Hydrotech” bei “Microsoft Excel”programinė įranga. Autorius savo jėgomis atliko visus tyrimus. Nustatyta, kad valant Masčio ežero dalį žemsiurbe „Watermaster Classic III“, valymo tolygumas atskiruose pjūviuose siekė 8,1–10,2 %, žymiai prastesnis nei palyginimui Pakruojo tvenkinio dalyje, valant žemsiurbe „3350MK“ (tolygumas sieke 2,9–3,2 %). Esant darbinei konsistencijai 3,7 %, žemsiurbės „Watermaster Classic III“ našumas už 433 m siekė 76 %. Suspenduotų dalelių kiekis tik pirmą dieną prie žemsiurbės buvo žymiai didesnis už foninį lygį, už 10–20 m foninio lygio, o vėliau visur tapo foninio lygmens. Žemsiurbės „Watermaster Classic III“ dienos darbo laiko panaudojimo... [toliau žr. visą tekstą] / This Master's thesis presents the analysis of the literature, the aim and tasks of researches, the methodology, results, analysis and conclusions of the research. It was found that the main drawbacks of dredges which are cleaning lakes in Lithuania are the liquid pulp pumped and its low transportation distance. The aim of this research is to evaluate the most commonly used dredges’ “Watermaster Classic III” suitability for cleaning lakes in Lithuania. The water depths in three sections cleaned in Mastis and Pakruojis lakes were determined by direct measurements, to identify the quantity of suspended particles in the water in Mastis lake (immediately after dredging) water samples were taken with bottle – bathometer and the efficiency of dredge was evaluated using volumetric method. After measuring water death the descriptive statistic was carried out using “Hydrotech“ and “Microsoft Excel” software. All researches were made by author itself. It was found that dredging part of the lake Mastis with “Watermaster Classic III” cleaning uniformity in separate sections was 8.1 to 10.2% while cleaning the part of lake Pakruojis with the dredge „3350MK“ uniformity was significantly lower (2,9 to 3,2 %). In 3.7 % operating consistency “Watermaster Classic III” performance at 433 m was 76 %. The quantity of suspended particles only the first day around the dredge was significantly higher than the background level – 10-20 m above it but later everywhere became equal to background level... [to full text]

A computational and experimental study of the Richtmyer-Meshkov instability is presented here for an inclined interface perturbation. The computational work is composed of simulation studies of the inclined interface RMI performed using the Arbitrary Lagrange Eulerian (ALE) code called ARES. These simulations covered a wide range of Mach numbers (1.2 to 3.5), gas pairs (Atwood numbers 0.23to 0.95), inclination angles (30° to 85°), and explored various perturbation types (both inclined interface and sinusoidal). The computational work included the first parametric study of the inclined interface RMI. This study yielded the first scaling method for the inclined interface RMI mixing width growth rates. It was extended to explore the effect of perturbation linearity and identified that a sharp transition in growth regimes occurs for an initial perturbation inclination angle of 75° with angles below (above) this growing faster (slower). Finally a study of the effects of incident shock strength on the refracted shock wave perturbation decay rate is presented. This study examined how the perturbations induced on the transmitted shock front by the RMI decay with time and found that the decay rates follow a power law model, Alpha=Beta∗S^(Epsilon). When the coefficients from the power law decay model were plotted versus Mach number, a distinct transition region was found which is likely a result of the post-shock heavy gas velocity transitioning from the subsonic to supersonic range. The experimental portion of this work was conducted using the TAMUFMSTF, completed in May of 2012. This facility uses a variable inclination shock tube, with a modular construction design for incident shock strengths of up to Mach 3.0. It employs optical systems for measuring density and velocity fields simultaneously using the planar laser induced fluorescence and particle imaging velocimetry techniques. The design and construction of this facility is reviewed in detail in chapter 4 of this work. The initial experiments performed in the TAMUFMSTF provided the first known extensive experimental data for an inclined interface RMI. Planar laser Mie scattering images and velocity vectors were obtained for a N_(2)/CO_(2) interface at a 60° inclination angle and an incident shock strength of Mach 1.55. These images have been compared with simulations made using the ARES codes and have been shown to have some distinct differences. Some of these differences indicate that the initial conditions in the experiments deviate from the ideal planar interface. Other differences have revealed features which have not been resolved by the simulations due to resolution limitations.

Methylenetetrahydrofolate reductase catalyzes the reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a carbon donor for the remethylation of homocysteine to methionine. Patients with severe MTHFR deficiency have $<$20% residual enzyme activity, moderate hyperhomocysteinemia, vascular lesions and neurological dysfunction. Mildly-deficient individuals with a thermolabile enzyme are at increased risk for developing cardiovascular disease. / Two MTHFR sequence changes were identified. The first was a C to T transition at bp 764 altering a proline to a leucine codon; this change was found in one severely-deficient patient. The second was a C to T transition at bp 677, substituting a valine for a highly-conserved alanine codon. The $ rm A to V$ substitution was identified on 35-40% of chromosomes. Expression of the $ rm A to V$ mutation in prokaryotic cells revealed increased thermolability over the wild-type enzyme. Genotyping for the $ rm A to V$ mutation in three vascular disease studies showed that it was associated with mild hyperhomocysteinemia, a risk factor for vascular disease. / The preventative effects of folate supplementation on the occurrence and recurrence of neural tube defects (NTDs) have been repeatedly demonstrated. The curly-tail (ct) mouse model for NTDs was used to investigate the involvement of MTHFR in these defects. Ct mice had significantly increased homocysteine levels although differences in MTHFR activity were not demonstrated. The mouse MTHFR gene was mapped to distal chromosome 4, close to the major gene for NTDs in ct. MTHFR is suggested as a candidate locus for the ct defect.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Oxygenated volatile organic compounds ((O)VOCs) contribute to ozone formation, affect the oxidising capacity of the troposphere and are sources of growth, and in some cases formation, of aerosols. It is therefore important to identify and quantify sources of (O)VOCs in the troposphere. In the late 1990s a unique technique for quantification of organic trace gas species, proton transfer reaction mass spectrometry (PTR-MS) was developed. PTR-MS potentially offers rapid response and high sensitivity without the need for sample pre-concentration. Concentrations can be derived from the PTR-MS either by calibration or can be calculated from measured ion count rates and kinetic considerations. In this work, the methodology of PTR-MS application is critically assessed. The uncertainties and inaccuracies associated with each parameter employed in the calculation of concentrations are reviewed. This includes a critical appraisal of models for the calculation of the collisional rate constant currently applied in the field of PTR-MS. The use of a model to account for the effects of the electric field, available in the literature but not previously applied to the PTR-MS, is advocated. Collisional rate constants employing each of the models discussed have been calculated for the reactions of H3O+ with over 400 molecules for PTR-MS. In PTR-MS it cannot be assumed that the product ion occurs only at the protonated non-dissociated mass. Few product distributions obtained from PTR-MS are cited in the literature, and even then the reaction chamber conditions (pressure, temperature and electric field strength) are not always specified. A large volume of product distributions for trace gases with H3O+ in select ion flow tube mass spectrometry (SIFT) exists in the literature and is reviewed. In SIFT, no electric field is applied to the reaction chamber and the extent and even nature of fragmentation can differ in PTR-MS. In addition to the application of an electric field, the energy in the reaction chamber can be increased by increasing the temperature or by variation of the reagent ion. In this work, the increase in energy via the three methods is approximated to enable a comparison of product distributions. The review of product distributions in PTR-MS, select ion flow drift tube mass spectrometry (SIFDT), variable temperature select ion flow tube mass spectrometry (VT-SIFT), SIFT, proton transfer reaction time of flight mass spectrometry (PTR-TOF-MS), proton transfer reaction ion trap mass spectrometry (PTR-ITMS) and electron ionisation mass spectrometry (EI-MS) is used alongside thermodynamic considerations to collate a list of potential contributors to a range of mass to charge ratios (m/z) in the PTR-MS. The need for further measurements of product distributions as a function of temperature, pressure and electric field strength for a wider range of (O)VOCs is highlighted. This enables dissociation to be better used as a tool for compound identification rather than being considered a hindrance. The collation of likely product distributions is applied to identify possible contributors to m/z observed during PTR-MS measurements of emission from cattle slurry. Field measurements were made during fertilisation of a grassland site south of Edinburgh in 2004 and 2005 and in laboratory-based measurements in 2006. Contextual reasoning, previous measurements and isotope ratios are used to narrow the list of possible contributors. Large concentrations of m/z cautiously identified as alcohols followed by a latter peak in carboxylic acids were observed during laboratory measurements. Increases in the corresponding m/z were also observed during the fertilisations. Other tentatively identified compounds emitted included phenol, methyl phenol, trimethylamine, and various sulphur containing compounds.