No description available.

No description available.

The purpose of this study was twofold: 1) to present experimental data on changes in permeability of fibers during irradiation using Na22 as the tracer isotope, and 2) to attempt to correlate these findings with the electrical changes observed.

Thesis (M.A.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / In work reported by Lichtin, Rosenberg, and Imamuras it was found that water added before irradiation of aerated methanol had a surprising effect on peroxide yields. In the absence of water, no hydrogen peroxide was produced during radiolysis, but in the presence of about 0.5 weight-percent water the yield of peroxide increased abruptly from zero to a plateau G value of 2.8. Attempts to reproduce these data were unsuccessful, however, and it was discovered that the observed effect of water on hydrogen peroxide yields is post-radiolytic in nature. Identical peroxide yields were produced during radiolysis of both dry methanol samples and samples to which water was added before radiolysis. In the dry samples, however, hydrogen peroxide was found to decompose with approximately first-order kinetics. Addition of water subsequent to irradiation inhibited decay. No significant change was noted in the concentration of radiolytically-generated formaldehyde during the period of peroxide decay. The average G(H2o2), obtained by extrapolation of the decomposition curve of radiolytically-generated hydrogen peroxide in dry methanol back to the time of the removal ofthe sample from the 60Co source, was 3.28 + 0.12. Half-decay times varied widely due to the variable dryness of the methanol. It was found that solutions of non-radiolytic hydrogen peroxide in dry methanol likewise underwent first-order decay. The rate of decomposition in these solutions could be accelerated by an increase in temperature or by subsequent radiolysis. The addition of formaldehyde was also found to accelerate peroxide decomposition, although no significant change was noted in the formaldehyde concentration. Methyl hydroperoxide was tentatively identified as a radiation product with a G value of about 0.2. Analysis of a radiolytic sample in which hydrogen peroxide had decomposed completely indicated that methyl hydroperoxide had not undergone similar decay. The nature of the hydrogen peroxide decomposition process is still unknown. Speculation concerning the decay inhibiting effect of water has been developed from several points of view: medium effects, specific interactions, and the possible effects of impurity. Influences of added sulfuric acid and methyl borate on radiolytic peroxide yields were also studied briefly. / 2031-01-01

L’appendicite aiguë est la pathologie abdominale aiguë courante et la plus fréquente parmi celles qui nécessitent une intervention chirurgicale rapide. L’imagerie occupe une place croissante dans son diagnostic parce qu’elle tente d’éviter simultanément les appendicectomies inutiles et les perforations appendiculaires compliquées de péritonite tout en recherchant des pathologies alternatives. Si plusieurs techniques d’imagerie sont disponibles – dont la radiographie sans préparation de l’abdomen (dont la performance est faible) et l’imagerie par résonance magnétique (peu disponible, en particulier en urgence) – l’ultrasonographie (US) et la tomodensitométrie (TDM) occupent des positions centrales. Nos études ont investigué la performance de ces dernières, en considérant notamment la réduction de la dose d’irradiation et le recours aux contrastes artificiels. En effet, l’irradiation liée à l’usage de la TDM est à considérer puisque les patients souffrant d’appendicite aiguë sont jeunes (en moyenne 30 ans) tout comme le recours aux contrastes associé à des coûts, de l’inconfort et des risques. Enfin, la performance de ces techniques étant susceptibles d’être influencée par la corpulence des patients et leur quantité de graisse intra-abdominale, l’influence de ces paramètres sur la performance a été évaluée. A travers quatre études, nous avons montré que l’US et la TDM sans contraste IV ou entérique ont des performances similaires quant au diagnostic d’appendicite aiguë et de pathologies alternatives, indépendamment de l’expérience du radiologue et de la corpulence du patient. Néanmoins, les examens non concluants (sans diagnostic d’appendicite aiguë ni de pathologie alternative mais où l’appendice n’est pas vu) sont plus fréquents en US qu’en TDM. L’appendice normal, dont la visualisation permet d’exclure le diagnostic d’appendicite aiguë, est plus fréquemment visible en TDM qu’en US, mais en TDM la reproductibilité quant à considérer la même structure comme étant l’appendice dépend du lecteur. L’injection IV de contraste iodé n’augmente pas la proportion d’appendices détectés mais la reproductibilité d’un lecteur particulier. Aucune caractéristique du sujet ni de son appendice, y compris son environnement abdominal, ne permet de prédire cette reproductibilité. La performance de la TDM est constante quelle que soit la dose d’irradiation ou le recours au contraste IV et/ou entérique, indépendamment de la corpulence du patient. La hiérarchie de l’information apportée par les signes évocateurs d’appendicite aiguë n’est pas influencée par la dose; l’infiltration de la graisse péri-appendiculaire et le diamètre appendiculaire en étant les signes les plus prédictifs, malgré le moindre rapport signal/bruit de l’image générée à faible dose. La fréquence de visualisation de l’appendice est aussi indépendante de cette dose. L’exactitude du diagnostic dépend principalement du lecteur mais pas du contraste – quelle qu’en soit la voie d’administration (orale ou IV) – ni de la dose d’irradiation. Le genre du patient influence cependant cette exactitude, le diagnostic étant plus fréquemment correct chez l’homme que chez la femme, en particulier dans les pathologies alternatives. En conclusion, comme les techniques US et TDM que nous avons investiguées ont des performances équivalentes, les risques associés à l’irradiation et au contraste doivent intervenir dans leur choix. L’US, utilisée en première intention, devrait être complétée par la TDM si son résultat n’est pas concluant. Dans ce cas, la TDM devrait être réalisée, toujours à basse dose d’irradiation, d’abord sans puis, si nécessaire, avec contraste IV et/ou oral.

Newts, such as Notophthalmus viridescens, can regenerate many structures after amputation or injury and have also shown a refractory response to the formation of cancer in tissues that have regenerative capabilities. The mechanisms behind this latter ability have surprisingly not been studied. In the current study, N. viridescens were exposed to a variety of carcinogens in tissue that cannot regenerate with the intention of inducing tumour formation. After testing multiple carcinogens, multiple sites of injection, and two different modes of delivery, no tumours were generated. Consequently, in vitro assays were developed in order to better understand this ability of newt cells to evade transformation. Mouse and newt muscle cells were exposed to DNA damaging agents, such as irradiation and carcinogens, in culture and their response was monitored with respect to the DNA damage response proteins γ-H2AX, p53, and phospho-p53. These proteins are important as they help prevent mutations in the genome from being passed on to daughter cells and potentially generating cells that proliferate uncontrollably, a hallmark of cancer. Preliminary results suggest that after irradiation, γ-H2AX is present in newt cells for a considerably longer period of time in comparison to mouse cells. p53, as well as phospho-p53, appear to be present at a basal level before and after irradiation in newt cells, whereas mouse cells have a distinct increase upon damage and decrease upon repair. The carcinogen treatments also suggest that newt cells have basal levels of expression of these proteins prior to treatment. These studies suggest that newt cells may have a unique profile of these DNA damage response proteins and may be “primed” to repair any future damage. This is a good first step in understanding what is likely a very complicated explanation for newts’ refractory response to cancer formation.

No description available.

Newts, such as Notophthalmus viridescens, can regenerate many structures after amputation or injury and have also shown a refractory response to the formation of cancer in tissues that have regenerative capabilities. The mechanisms behind this latter ability have surprisingly not been studied. In the current study, N. viridescens were exposed to a variety of carcinogens in tissue that cannot regenerate with the intention of inducing tumour formation. After testing multiple carcinogens, multiple sites of injection, and two different modes of delivery, no tumours were generated. Consequently, in vitro assays were developed in order to better understand this ability of newt cells to evade transformation. Mouse and newt muscle cells were exposed to DNA damaging agents, such as irradiation and carcinogens, in culture and their response was monitored with respect to the DNA damage response proteins γ-H2AX, p53, and phospho-p53. These proteins are important as they help prevent mutations in the genome from being passed on to daughter cells and potentially generating cells that proliferate uncontrollably, a hallmark of cancer. Preliminary results suggest that after irradiation, γ-H2AX is present in newt cells for a considerably longer period of time in comparison to mouse cells. p53, as well as phospho-p53, appear to be present at a basal level before and after irradiation in newt cells, whereas mouse cells have a distinct increase upon damage and decrease upon repair. The carcinogen treatments also suggest that newt cells have basal levels of expression of these proteins prior to treatment. These studies suggest that newt cells may have a unique profile of these DNA damage response proteins and may be “primed” to repair any future damage. This is a good first step in understanding what is likely a very complicated explanation for newts’ refractory response to cancer formation.

The aim of this study is to evaluate the variation of solar radiation data between different data sources that will be free and available at the Solar Energy Research Center (SERC). The comparison between data sources will be carried out for two locations: Stockholm, Sweden and Athens, Greece. For the desired locations, data is gathered for different tilt angles: 0°, 30°, 45°, 60° facing south. The full dataset is available in two excel files: “Stockholm annual irradiation” and “Athens annual irradiation”. The World Radiation Data Center (WRDC) is defined as a reference for the comparison with other dtaasets, because it has the highest time span recorded for Stockholm (1964–2010) and Athens (1964–1986), in form of average monthly irradiation, expressed in kWh/m2. The indicator defined for the data comparison is the estimated standard deviation. The mean biased error (MBE) and the root mean square error (RMSE) were also used as statistical indicators for the horizontal solar irradiation data. The variation in solar irradiation data is categorized in two categories: natural or inter-annual variability, due to different data sources and lastly due to different calculation models. The inter-annual variation for Stockholm is 140.4kWh/m2 or 14.4% and 124.3kWh/m2 or 8.0% for Athens. The estimated deviation for horizontal solar irradiation is 3.7% for Stockholm and 4.4% Athens. This estimated deviation is respectively equal to 4.5% and 3.6% for Stockholm and Athens at 30° tilt, 5.2% and 4.5% at 45° tilt, 5.9% and 7.0% at 60°. NASA’s SSE, SAM and RETScreen (respectively Satel-light) exhibited the highest deviation from WRDC’s data for Stockholm (respectively Athens). The essential source for variation is notably the difference in horizontal solar irradiation. The variation increases by 1-2% per degree of tilt, using different calculation models, as used in PVSYST and Meteonorm. The location and altitude of the data source did not directly influence the variation with the WRDC data. Further examination is suggested in order to improve the methodology of selecting the location; Examining the functional dependence of ground reflected radiation with ambient temperature; variation of ambient temperature and its impact on different solar energy systems; Im pact of variation in solar irradiation and ambient temperature on system output.

The irradiation of metallic glasses to induce nanocrystallization was studied in two metallic glass compositions, Cu50Zr45Ti5 and Zr55Cu30Al10Ni5. Atomic mobility was described using a model based on localized excess free volume due to displace- ment cascades created by energetic particle irradiation. Due to the di erence in cascade size among di erent masses of projectiles, a mass-dependent study was per- formed. Metallic glass ribbon samples produced by melt-spinning were bombarded with electron, He, Ar, and Cu particles. Electron irradiation and characterization was performed "in-situ" by means of transmission electron microscopy. The di erent metallic glasses showed dissimilar levels of radiation stability under electron irradi- ation by Cu50Zr45Ti5 forming crystals 1-10 nm in diameter embedded in the amor- phous matrix after about 30 minutes of irradiation, while Zr55Cu30Al10Ni5 showed no such crystallization. Increasing projectile mass caused an increase in the maximum nanocrystal diameter up to approximately 100 nm in Cu irradiated Zr55Cu30Al10Ni5. Studies of di raction patterns of irradiated specimens showed nucleation of Cu10Zr7 phases in both specimens, as well as evidence of CuZr2 in Cu50Zr45Ti5 and both CuZr2 and NiZr2 in Zr55Cu30Al10Ni5. Crystal sizes in irradiated Zr55Cu30Al10Ni5 specimens showed bimodal distribution with many large (50-100 nm) crystals and many small (1-5 nm) crystals. The small crystals in irradiated Zr55Cu30Al10Ni5 were determined to be NiZr2 phase because of the low abundance of Ni. After exposure to 2 keV Ar ions, areas of composition roughly Cu10Zr7 were found by energy-dispersive X-ray spectroscopy but no crystallization was found. Further crystallization was achieved in decomposed specimens after electron irradiation. This shows that atomic segregation is a necessary step before nucleation in metallic glasses.