In vitro data from our laboratory demonstrate that vitamin B6 (B6) supplementation of estrogen receptor - positive and - negative breast cancer cells is growth inhibitory. Others have reported that dietary B6 supplementation resulted in increased fibrosarcoma pyridoxal phosphate (PLP) concentrations and a significant inverse relationship between tumor PLP concentration and tumor volume in mice. This suggests that, in contrast to data reported for normal cells, tumor cells are capable of accumulating supplemental B6. In the current study, we investigated the effects of dietary B6 supplementation on 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma in rats. Specifically, we aimed to identify the effect of pyridoxine (PN) supplementation on tumor growth and vitamin uptake by tumor cells. To accomplish this, 50 d old female Sprague Dawley rats were gavaged with 15 mg DMBA and fed a diet containing either 7, 350, or 1050 mg PN-HCl/kg diet, which is the equivalent of 1, 50, or 150x the National Research Council's B6 requirement for rats, respectively. These levels of PN have previously been shown to produce no overt signs of toxicity in rats. Throughout the experiment, the percent of rats with tumors and the average number of tumors per rat remained similar between groups. Mammary tumor growth rates were significantly increased in response to dietary B6 supplementation (P < 0.05). Liver PLP and pyridoxal (PL) concentrations did not differ between dietary treatment groups. Plasma PL and PLP concentrations were significantly higher in the group fed the 150x diet compared with the 1x diet (P < 0.001, P < 0.05). Mammary tissue PL concentrations of the 150x group were significantly higher (P < 0.05) than the 1x group, but no differences were observed in mammary PLP concentrations. Similarly to mammary tissue, no differences between groups were observed in tumor PLP concentration. However, tumor PL concentrations in both the 50x and 150x dietary treatment groups were significantly higher than those from the rats fed the 1x diet (P < 0.002). These data demonstrate that previously reported inhibitory effects of supplemental B6 on breast cancer growth in vitro do not occur in response to dietary supplementation at 50 or 150 times the B6 requirement in vivo. In fact, dietary B6 at 150x the requirement may actually promote mammary tumor growth. In light of these results, investigation of the effects of supplemental B6 on cancer growth in humans is warranted. Supported by American Cancer Society Grant # IRG-99-225-01. / Master of Science

by Chan Hiu Shuen. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (p. 123-135). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Our knowledge of stellar magnetic fields relies almost entirely on circular polarization observations, which has historically limited our understanding of the stellar magnetic field topologies. Recently, it has become possible to obtain phase-resolved high-resolution spectropolarimetric observations in all four Stokes parameters for early-type magnetic stars. Interpretation of such observations with the Magnetic Doppler imaging technique has uncovered a new, previously unknown, level of complexity of surface stellar magnetic fields. This new insight is critical for understanding the origin, evolution and structure of magnetic fields in early-type stars. In this study we observed the magnetic, chemically peculiar Ap stars HD 24712 (DO Eri, HR 1217) and HD 125248 (CS Vir, HR 5355) in all four Stokes parameters with the HARPSpol spectropolarimeter at the ESO 3.6-m telescope. The resulting spectra have high signal-to-noise ratio and superb resolving power, by far surpassing the quality of any existing stellar Stokes parameter observations. We studied variation of the spectrum and magnetic observables of HD 24712 as a function of rotational phase (paper I). In the subsequent magnetic Doppler imaging investigation of this star, we interpreted the phase-resolved Stokes line profile observations (paper II). This analysis showed that HD 24712, unlike more massive Ap stars studied in all four Stokes parameters, has a dominant dipolar field component with a negligible contribution of small-scale magnetic structures. Simultaneously with magnetic mapping we derived surface abundance distributions of Fe, Nd, Na, and Ca. Building upon the technique of Magnetic Doppler imaging, we developed the first three-dimensional abundance inversion code and applied it to reconstruct the abundance distributions of Fe and Ca in three dimensions in the atmosphere of HD 24712 (paper III). We also performed Magnetic Doppler imaging analysis of the spectropolarimetric observations of HD 125248 (paper IV). The reconstructed detailed maps of the surface abundance distribution and magnetic field topology of HD 125248 revealed a magnetic field with significant deviations from the canonical dipolar field geometry, and strong surface abundance inhomogeneities for Cr and several rare earth elements. We assessed our inversion results in the context of magnetic Doppler imaging studies of other magnetic, chemically peculiar Ap stars and latest theoretical research on the evolution and stability of magnetic fields in radiative stellar interiors. Our analysis suggests that old or less massive Ap stars have predominantly dipolar magnetic fields while more massive or younger stars exhibit more complicated field topologies. We also compared our three-dimensional chemical abundance maps of HD 24712 to the predictions of theoretical atomic diffusion calculations in magnetized stellar atmospheres, generally finding a lack of agreement between theory and observations.

Lee Po Yuk. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1987. / Bibliography: leaves 75-81.

Xu Feng. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (p. 205-233). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Mercury-manganese (HgMn) stars belong to the class of chemically peculiar (CP) stars. It was recently discovered that some HgMn stars have spots of chemical elements on their surfaces. According to conventional picture of CP stars, magnetic field facilitates the formation and long term stability of chemical spots by controlling stratification of elements in stellar atmosphere. However, previous attempts to find magnetic field in HgMn stars set an upper limit on its strength at the level of about 20-100 Gauss. Observational evidence suggested that even weaker magnetic fields can be responsible for the formation of chemical spots. The main goal of our work was to verify this possibility. The search for weak magnetic fields requires the use of least-squares deconvolution (LSD) technique.  This method combines information from many spectral lines providing a mean line profile with increased signal-to-noise ratio. Up to now there was no extensive comparison of the LSD profile with real spectral lines. We showed that the LSD profile of the intensity spectrum does not behave like a real spectral line as a function of chemical composition. However, for circular polarization, LSD profile resembles the profile of a spectral line with mean atomic parameters. We performed a comprehensive search for magnetic field in 47 HgMn stars and their companions, based on high-quality spectropolarimetric data obtained with the HARPSpol polarimeter at the ESO 3.6-m telescope. With the help of LSD technique, an upper limit on the mean longitudinal magnetic field was brought down to 2-10 G for most stars. We concluded that magnetic field is not responsible for the spot formation in HgMn stars. We obtained full rotational phase coverage for the HgMn stars φ Phe and 66 Eri. This enabled us to investigate line profile variability, reconstruct surface maps of chemical elements, and perform a search for magnetic field with very high sensitivity. For φ Phe we derived surface maps of Y, Sr, Ti, Cr, and obtained an upper limit of 4 G on the field strength. We also found marginal indication of vertical stratification of Y and Ti. No magnetic field was detected in both components of 66 Eri, with an upper limit of 10-24 G. We discovered chemical spots of Y, Sr, Ba, and Ti, in the primary star. We demonstrated a relation between the binary orbit and the morphology of these spots.

Permanent dielectric materials are integral to the fabrication of microelectronic devices and packaging. Dielectrics are used throughout devices to electrically and mechanically isolate conductive components. As such, they are required to have low electrical permittivity and robust mechanical properties. For packaging applications, dielectrics can be directly photo-definable. Dielectrics need to have excellent lithographic properties. These properties are pivotal for enabling high yield and low cost fabrication of reliable, energy efficient devices. The aim of this work was to develop new positive tone dielectrics which have improved or application-specific lithographic, mechanical, and electrical properties. To this end, several new dielectric polymers and chemistries were evaluated and characterized. Initially, it was desired to develop a positive tone, polynorbornene (PNB) dielectric that utilizes diazonaphthoquinone (DNQ) photochemistry. Cross-linking was achieved with epoxy cross-linkers during a thermal cure. Several DNQ-containing compounds were evaluated, but only one had good miscibility with PNB. The dissolution characteristics of PNB were measured with respect to polymer composition, DNQ loading, and cross-linker loading. PNB films exhibited unique dissolution properties, and these measurements allowed for an optimum formulation to be developed. A formulation with 20 pphr DNQ and 10 pphr epoxy cross-linker had sufficient inhibition in unexposed regions and fast dissolution in exposed regions. The resulting dielectric was the first positive tone, DNQ-based PNB dielectric. After achieving photo-definability, the cross-linking of the cured dielectric was evaluated by characterizing the mechanical properties. It was discovered that DNQ acted as a cross-linker in these films, and this insight was key to achieving good curing of the dielectric. Several experiments were performed to support this conclusions, and the reaction kinetics of this cross-linking reaction were evaluated. This effort produced a functional, positive tone dielectric with a sensitivity of 408 mJ cm-2 and contrast of 2.3. The modulus was 2.0 to 2.6 GPa and the dielectric constant of 3.7 to 3.9, depending on the curing conditions. The DNQ cross-linking results led to the investigation of other cross-linking chemistries for positive tone dielectrics. A chemically amplified (CA) photochemistry was utilized along with a Fischer esterification cross-linking reaction. Patterning and cross-linking were demonstrated with a methacrylate polymer. Successful positive tone lithography was demonstrated at a high sensitivity of 32.4 mJ cm-2 and contrast of 5.2. Cross-linking was achieved at 120°C as shown by residual stress and solubility measurements. The CA photochemistry and Fischer esterification cross-linking were also demonstrated using a PNB dielectric, which was shown to have improved lithographic properties: a sensitivity of 8.09 mJ cm-2 and contrast of ≥ 14.2. Work was performed to evaluate the effect of the polymer composition on the mechanical and electrical properties. A polymer with 60 mol% hexafluoroisopropanol norbornene and 40 mol% tert-butyl ester norbornene exhibited a dielectric constant of 2.78, which is lower than existing positive tone dielectrics. It also outperformed existing dielectrics in several other categories, including dark erosion, volume change, cure temperature, and in-plane coefficient of thermal expansion. However, a limitation of this dielectric was cracking in thick films. The final study was to improve the mechanical properties of this CA PNB dielectric specifically to enable 5 µm thick films. First, a terpolymer was tested that included a non-functional third monomer. The dielectric constant increased to 3.48 with 24 mol% of the third monomer. Second, low molecular weight additives were used to lower the modulus. Only one of the five tested additives enabled high quality, thick films. This additive did not significantly affect the dielectric constant at low loadings. An optimized formulation was made, and processing parameters were studied. The additive decreased the lithographic properties, lowering the sensitivity to 175 mJ cm-2 and lowering the contrast to 4.36. In all, this work produced three functional dielectrics with positive tone photo-definability and good lithographic properties. Each dielectric can serve a variety of purposes in microelectronics packaging.

Debris disks are a fundamental component of exoplanetary systems. Understanding their relationship with host stars and neighboring planets can help contextualize the evolution of exoplanetary systems. In order to further that goal, this thesis addresses some extreme outlier examples of debris disk systems. First, the highly asymmetric debris disk around HD 111520 is resolved and analyzed at multiple wavelengths to create a self-consistent model of the disk thermal emission and scattered light. The best-fit model is proposed to be an asymmetric disk from a recent collision of large, icy bodies on one side of the disk. In contrast, most debris disks are thought to be in a steady collisional cascade and this disk model could represent a relatively rare event in the creation of debris disks. Secondly, an optical spectroscopic survey of stars is conducted on stars where far-infrared observations exist to detect the presence of debris disks. Specifically, AF-type stars are targeted in order to provide context regarding the Lambda Boo phenomenon, where stars are found to be specifically refractory metal-poor. One mechanism for this was hypothesized to be from planetary scattering of debris disks, causing the accretion of volatiles from comets. The findings were that over the entire unbiased sample, stars which were refractory metal poor tended to be the stars with brightest debris disks. This supports a planet-disk hypothesis underlying the accretion of volatile gases, since debris disks undergoing active planetary stirring are brighter. This would mean about 13\% of stars with debris disk are undergoing strong planetary scattering based on the occurrence rate of Lambda Boo stars relative to debris disk stars. These two tacks in our observational understanding of these extreme examples of debris disks provide constraints on the volatility at work. / Graduate

Orientador: Antonio Tallarico Vicente Adorno / Banca: Assis Vicente Benedetti / Banca: Dimas Roberto Vollet / Banca: Sebastião Elias Kuri / Banca: Tomaz Toshimi Ishikawa / Resumo: Neste trabalho a cinética de decomposição da fase martensítica na liga Cu-10%Al com adições de 4, 6, 8 e 10%Ag foi estudada usando calorimetria exploratória diferencial (DSC), análise térmica diferencial (DTA), termodilatometria (TD), microscopia óptica (MO), microscopia eletrônica de varredura (MEV), difratometria de raios X (DRX), análise por dispersão de energias de raios X (EDX), medidas de variação da microdureza com a temperatura de têmpera e o tempo de envelhecimento e medidas de tensão-deformação. Os resultados obtidos indicaram a presença de uma etapa intermediária de reação nas ligas com 4 a 8%Ag, no intervalo de temperaturas de 200 a 300 oC, e essa etapa foi atribuída ao consumo da fase α desordenada. A presença da prata retardou a reação de decomposição eutetóide e intensificou o efeito de estabilização da fase martensítica no intervalo de temperatura e tempo considerados nesse estudo. Esse efeito de estabilização foi atribuído à redistribuição dos átomos de Ag como defeitos de estrutura, aumento do número de pares Cu-Al devido à interação Ag-Al e à redistribuição de átomos de Al ao redor de um átomo de Cu na sub-rede do cristal martensítico. Todos esses efeitos combinados diminuem a energia livre da fase martensítica e contribuem para o aumento da temperatura da transformação reversa. Para as ligas Cu-10%Al com e sem adições de prata a seqüência de reações durante o envelhecimento das amostras é composta das seguintes etapas: consumo da fase α seguida do ordenamento da martensita. A velocidade da reação de consumo da fase α depende da concentração de prata e uma mudança considerável na velocidade da reação de ordenamento da martensita é observada apenas para a liga com 10%Ag. Os valores das energias de ativação para os processos indicaram que a reação (α + β')→β' é a etapa dominante...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this work, the kinetics of martensitic phase decomposition in the Cu-10wt.%Al alloy with additions of 4, 6, 8 and 10 wt.%Ag was studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), thermodilatometry (TD), optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometry (XRD), energy dispersive X-ray analysis (EDX), microhardness changes measurements with temperature and time and stress-strain measurements. The results indicated the presence of an intermediate reaction step for alloys with Ag additions up to 8wt.% in the temperature range between 200 and 300 oC, attributed to the consumption of the disordered α phase. The presence of Ag retarded the eutectoid decomposition reaction and enhanced the stabilization of the martensitic phase, in the time and temperature ranges considered. This stabilization effect was attributed to Ag atoms redistribution as structure defects, increase in the numbers of Cu-Al pairs due to Ag-Al interaction and to the Al atoms redistribution around one Cu atom at the sub-lattice of the martensitic crystal. The combination of these effects decreases the martensitic phase free energy and increases the reverse transformation temperature. The proposed reactions sequence for the aging of Cu-10wt.%Al alloy with and without Ag additions is the consumption of the α phase followed by the martensitic phase ordering. The rate of the α phase consumption reaction depends on the Ag concentration and a remarkable change in the martensitic phase ordering reaction rate is only observed for the addition of 10wt.%Ag. The obtained activation energy values indicated that the (α + β')→β' reaction, assisted by quenched-in vacancies migration, is the dominant step. / Doutor

Rotation has a number of important effects on the evolution of stars. Apart from structural changes because of the centrifugal force, turbulent mixing and meridional circulation can dramatically affect a star's chemical evolution. This leads to changes in the surface temperature and luminosity as well as modifying its lifetime. Rotation decreases the surface gravity, causes enhanced mass loss and leads to surface abundance anomalies of various chemical isotopes all of which have been observed. The replication of these physical effects with simple stellar evolution models is very difficult and has resulted in the use of numerous different formulations to describe the physics. We have adapted the Cambridge stellar evolution code to incorporate a number of different physical models for rotation, including several treatments of angular momentum transport in convection zones. We compare detailed grids of stellar evolution models along with simulated stellar populations to identify the key differences between them. We then consider how these models relate to observed data. Models of rotationally-driven dynamos in stellar radiative zones have suggested that magnetohydrodynamic transport of angular momentum and chemical composition can dominate over the otherwise purely hydrodynamic processes. If this is the case then a proper consideration of the interaction between rotation and magnetic fields is essential. We have adapted our purely hydrodynamic model to include the evolution of the magnetic field with a pair of time-dependent advection--diffusion equations coupled with the equations for the evolution of the angular momentum distribution and stellar structure. This produces a much more complete, though still reasonably simple, model for the magnetic field evolution. We consider how the surface field strength varies during the main-sequence evolution and compare the surface enrichment of nitrogen for a simulated stellar population with observations. Strong magnetic fields are also observed at the end of the stellar lifetime. The surface magnetic field strength of white dwarfs is observed to vary from very little up to 10 9G. As well as considering the main-sequence evolution of magnetic fields we also look at how the strongest magnetic fields in white dwarfs may be generated by dynamo action during the common envelope phase of strongly interacting binary stars. The resulting magnetic field depends strongly on the electrical conductivity of the white dwarf, the lifetime of the convective envelope and the variability of the magnetic dynamo. We assess the various energy sources available and estimate necessary lifetimes of the common envelope.