Thesis: B.S., Massachusetts Institute of Technology, Department of Biology, 1976 / Includes bibliographical references. / by Ann B. Mansfield. / B.S. / B.S. Massachusetts Institute of Technology, Department of Biology

Thesis (Ph.D.)--Boston University / The formation, evolution and eruption of solar active regions is a main theme in solar physics. Ultimately the goal is predicting when, where and how an eruption will occur, which will greatly aid space weather forecasting. Special kinds of S-shaped active regions (sigmoids) facilitate this line of research, since they provide conditions that are easier to disentangle and have a high probability for erupting as flares and/or coronal mass ejections (CME). Several theories have been proposed for the formation, evolution, and eruption of solar active regions. Testing these against detailed models of sigmoidal regions can provide insight into the dominant mechanisms and conditions required for eruption. This thesis explores the behavior of solar sigmoids via both observational and magnetic modeling studies. Data from the most modern space-based solar observatories are utilized in addition to state-of-the-art three-dimensional data-driven magnetic field modeling to gain insight into the physical processes controlling the evolution and eruption of solar sigmoids. We use X-ray observations and the magnetic field models to introduce the reader to the underlying magnetic and plasma structure defining these regions. By means of a large comprehensive observational study we investigate the formation and evolution mechanism. Specifically, we show that flux cancellation is a major mechanism for building the underlying magnetic structure associated with sigmoids, namely magnetic flux ropes. We make use of topological analysis to describe the complicated magnetic field structure of the sigmoids. We show that when data-driven models are used in sync with MHD simulations and observations we can arrive at a consistent picture of the scenario for CME onset, namely the positive feedback between reconnection at a generalized X-line and the torus instability. In addition we show that topological analysis is of great use in analyzing the post-eruption flare- and CME-associated observational features. Such analysis is used to extend the standard 2D flare/CME models to 3D and to find potentially large implications of topology to understanding 3D reconnection and the seed populations of energetic particles in CMEs.

In this research, some fundamental aspects of surface growth processes are investigated through in-situ synchrotron based x-ray techniques, including a new coherent x-ray technique developed as part of this work, as well as ex-situ Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and simulation. The first part of this dissertation focuses on careful examination of early-time kinetics of indium (In) island growth via real-time Grazing Incidence Small Angle X-ray Scattering (GISAXS) since it is a good example of simple growth systems allowing the results to be directly compared to surface growth theories and also because of its technical relevance for III–V semiconductor deposition. The results are compared with Family-Meakin (FM) droplet growth and coalescence theory through Monte Carlo simulations. In addition, room temperature deposition of amorphous silicon (a-Si) through DC magnetron sputtering onto a silicon (Si) substrate has been investigated via real-time GISAXS. The deposition conditions are optimized to create an idealized growth environment so that the results can be directly compared to surface growth models. Performing the deposition at room temperature results in adatoms having limited surface mobility, which causes formation of correlated mound-like structures on the surface at the early stages of the growth. The correlation distance between the mount-like structures is found to grow linearly with time. The results are compared to a ballistic deposition model including self-shadowing and desorption effects. The second half of this study focuses on investigation of the kinetic roughening dynamics of thin film growth, where the local dynamics are measured after the overall kinetic evolution of the surface roughness reach a steady-state saturation. Coherent X-ray GISAXS (Co-GISAXS) has been developed as a new approach to investigate surface dynamics during thin film deposition. Room temperature deposition of a-Si and amorphous tungsten disilicide (a-WSi2) through DC magnetron sputtering onto respectively Si and SiO2 substrates has been examined. The overall dynamics are complex, but power law behavior is observed for the structure factor and correlation times at the most surface sensitive section of the data. This research demonstrated that Co-GISAXS is a powerful new approach to investigate the correlated dynamics between surface and sub-surface structures. / 2016-10-27T00:00:00Z

We present high-resolution X-ray imaging data from the ACIS-S instrument on the Chandra telescope of the nearby interacting galaxy group NGC 4410. Four galaxies in the inner portion of this group are clearly detected by Chandra, including the peculiar low-luminosity radio galaxy NGC 4410A. In addition to a nuclear point source, NGC 4410A contains diffuse X-ray emission, including an X-ray ridge extending out to about 12″ (6 kpc) to the northwest of the nucleus. This ridge is coincident with an arc of optical emission-line gas, which has previously been shown to have optical line ratios consistent with shock ionization. This structure may be due to an expanding superbubble of hot gas caused by supernovae and stellar winds or by the active nucleus. The Chandra observations also show four or five possible compact ultraluminous X-ray (ULX) sources (L X ≥ 10 39 ergs s -1) associated with NGC 4410A. At least one of these candidate ULXs appears to have a radio counterpart, suggesting that it may be due to an X-ray binary with a stellar-mass black hole, rather than an intermediate-mass black hole. In addition, a faint diffuse intragroup X-ray component has been detected between the galaxies (L X ∼ 10 41 ergs s -1). This supports the hypothesis that the NGC 4410 group is in the process of evolving via mergers from a spiral-dominated group (which typically has no X-ray-emitting intragroup gas) to an elliptical-dominated group (which often has a substantial intragroup medium).

(Chemical Equation Presented) Torn genes: DNA tetramers containing the 2-deoxyribonolactone (dL) lesion have been isolated by HPLC from d(CGCG) and d(pCGCG) films irradiated with X-rays. Upon treatment with spermine as a catalyst, the dL-containing tetramers decompose to 5-methylene-2-furanone (5-MF; see scheme), a characteristic product of dL decomposition. Hence, 5-MP can be used to quantify dL lesions in DNA.

WR 25 is a colliding-wind binary star system comprising a very massive O2.5If∗/WN6 primary and an O-star secondary in an eccentric orbit with a 208 day period. These hot stars have strong, highly supersonic winds that interact to form a bright X-ray source from wind-collision shocks whose conditions change with stellar separation. Different views through the winds of Wolf-Rayet and O stars are afforded with orbital phase as the stars move about their orbits, allowing for exploration of wind structure in ways not easy or even possible for single stars. We have analyzed an on-axis Chandra/HETGS spectrum of WR 25 obtained shortly before periastron when the X-rays emanating from the system are the brightest. From the on-axis observations, we constrain the line fluxes, centroids, and widths of various emission lines, including He triplets of Si xiii and Mg xi. We have also been able to include several serendipitous off-axis HETG spectra from the archive and study their flux variation with phase. This is the first report on high-resolution spectral studies of WR 25 in X-rays.

Using archival data from the Chandra X-ray telescope, we have measured the spatial extent of the hot interstellar gas in a sample of 49 nearby interacting galaxy pairs, mergers, and merger remnants. For systems with SFR > 1 M yr-1, the volume and mass of hot gas are strongly and linearly correlated with the star formation rate (SFR). This supports the idea that stellar/supernovae feedback dominates the production of hot gas in these galaxies. We compared the mass of X-ray-emitting hot gas M X(gas) with the molecular and atomic hydrogen interstellar gas masses in these galaxies (MH2 and MH i, respectively), using published carbon monoxide and 21 cm H i measurements. Systems with higher SFRs have larger M X(gas)/(MH2 + M H i) ratios on average, in agreement with recent numerical simulations of star formation and feedback in merging galaxies. The M X(gas)/( MH2 + M H i) ratio also increases with dust temperature on average. The ratio M X(gas)/SFR is anticorrelated with the Infrared Astronomical Satellite 60-100 μm flux ratio and with the Spitzer 3.6-24 μm color. These trends may be due to variations in the spatial density of young stars, the stellar age, the ratio of young to old stars, the initial mass function, and/or the efficiency of stellar feedback. Galaxies with low SFR (<1 M ⊙ yr-1) and high K band luminosities may have an excess of hot gas relative to the relation for higher SFR galaxies, while galaxies with low K band luminosities (and therefore low stellar masses) may have a deficiency in hot gas, but our sample is not large enough for strong statistical significance.

We propose a novel method for generating synthetic X-rays from atypical inputs. This method creates approximate X-rays for use in non-diagnostic visualization problems where only generic cameras and sensors are available. Traditional methods are restricted to 3-D inputs such as meshes or Computed Tomography (CT) scans. We create custom synthetic X-ray datasets using a custom generator capable of creating RGB images, point cloud images, and 2-D pose images. We create a dataset using natural hand poses and train general-purpose Conditional Generative Adversarial Networks (CGANs) as well as our own novel network pix2xray. Our results show the successful plausibility of generating X-rays from point cloud and RGB images. We also demonstrate the superiority of our pix2xray approach, especially in the troublesome cases of occlusion due to overlapping or rotated anatomy. Overall, our work establishes a baseline that synthetic X-rays can be simulated using inputs such as RGB images and point cloud.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18080号 / 理博第3958号 / 新制||理||1570(附属図書館) / 30938 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 上田 佳宏, 准教授 岩室 史英, 教授 長田 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Recent hardware developments of automated, high speed, portable X-ray diffraction instrumentation have not yet resulted in widespread use of the technique in industry despite its potentials. We suggest that these hardware developments require an equivalent development in the training of instrument operators in order to guarantee the integrity of the resulting data, as well as to enhance the understanding of such materials characterization data. The hurdle to date is the variety of skills necessary in a wide range of scientific and engineering disciplines and which are not commonly found in a single individual. We suggest that a computer-based system, integrating visualization tools, knowledge bases and analysis-capabilities and which is focused on the operator performance can provide an efficient solution to this problem, as it changes the enactment of the stress determination work process. / Master of Science