With the advent of high-power lasers in recent decades, a unique source of hard X-ray radiation has become availible. This source of collimated, broadband, femtosecond, incoherent and hard X-ray radiation is produced when a focused laser with intensity above 10^18 W/cm^2 collides with a gas target. The strong electric field of the laser pulse ionizes the gas and interacts with the plasma generating a strong plasma wake wave. This space charge separation inside the target generates longitudal electric fields of the order of 100 GV/m. This resulting electrostatic wakefield accelerates the electrons to relativistic velocities and causes them to travel in oscillatory motion behind the laser pulse, producing hard and collimated X-ray radiation. This thesis is focused on a theoretical evaluation and an experimental design of this laser-plasma X-ray source. Furthermore, we consider the source's unique properties for novel imaging applications.

We have conducted a statistical analysis of the ultra-luminous X-ray point sources (ULXs; L X ≥ 10 39 ergs -1) in a sample of galaxies selected from the Arp Atlas of Peculiar Galaxies. We find a possible enhancement of a factor of 2-4 in the number of ULXs per blue luminosity for the strongly interacting subset. Such an enhancement would be expected if ULX production is related to star formation, as interacting galaxies tend to have enhanced star formation rates on average. For most of the Arp galaxies in our sample, the total number of ULXs compared to the far-infrared luminosity is consistent with values found earlier for spiral galaxies. This suggests that for these galaxies, ULXs trace recent star formation. However, for the most infrared-luminous galaxies, we find a deficiency of ULXs compared to the infrared luminosity. For these very infrared-luminous galaxies, active galactic nuclei may contribute to powering the far-infrared; alternatively, ULXs may be highly obscured in the X-ray in these galaxies and therefore not detected by these Chandra observations. We determined local UV/optical colors within the galaxies in the vicinity of the candidate ULXs using Galaxy Evolution Explorer UV and Sloan Digitized Sky Survey optical images. In most cases, the distributions of colors are similar to the global colors of interacting galaxies. However, the u - g and r - i colors at the ULX locations tend to be bluer on average than these global colors, suggesting that ULXs are preferentially found in regions with young stellar populations. In the Arp sample there is a possible enhancement of a factor of 2-5 in the fraction of galactic nuclei that are X-ray-bright compared to more normal spirals.

We present new, contemporaneous Hubble Space Telescope STIS and XMM-Newton observations of the O7 III(n)((f)) star ξ Per. We supplement the new data with archival IUE spectra, to analyze the variability of the wind lines and X-ray flux of ξ Per. The variable wind of this star is known to have a 2.086-day periodicity. We use a simple, heuristic spot model that fits the low-velocity (near-surface) IUE wind line variability very well, to demonstrate that the low-velocity absorption in the new STIS spectra of N iv λ1718 and Si iv λ1402 vary with the same 2.086-day period. It is remarkable that the period and amplitude of the STIS data agree with those of the IUE spectra obtained 22 yr earlier. We also show that the time variability of the new XMM-Newton fluxes is also consistent with the 2.086-day period. Thus, our new, multiwavelength coordinated observations demonstrate that the mechanism that causes the UV wind line variability is also responsible for a significant fraction of the X-rays in single O stars. The sequence of events for the multiwavelength light-curve minima is Si iv λ1402, N iv λ1718, and X-ray flux, each separated by a phase of about 0.06 relative to the 2.086-day period. Analysis of the X-ray fluxes shows that they become softer as they weaken. This is contrary to expectations if the variability is caused by periodic excess absorption. Furthermore, the high-resolution X-ray spectra suggest that the individual emission lines at maximum are more strongly blueshifted. If we interpret the low-velocity wind line light curves in terms of our model, it implies that there are two bright regions, i.e., regions with less absorption, separated by 180°, on the surface of the star. We note that the presence and persistence of two spots separated by 180° suggest that a weak dipole magnetic field is responsible for the variability of the UV wind line absorption and X-ray flux in ξ Per.

The stellar winds of hot stars have an important impact on both stellar and galactic evolution, yet their structure and internal processes are not fully understood in detail. One of the best nearby laboratories for studying such massive stellar winds is the O4I(n)fp star ζ Pup. After briefly discussing existing X-ray observations from Chandra and XMM, we present a simulation of X-ray emission line profile measurements for the upcoming 840 kilosecond Chandra HETGS observation. This simulation indicates that the increased S/N of this new observation will allow several major steps forward in the understanding of massive stellar winds. By measuring X-ray emission line strengths and profiles, we should be able to differentiate between various stellar wind models and map the entire wind structure in temperature and density. This legacy X-ray spectrum of ζ Pup will be a useful benchmark for future X-ray missions.

Using archived data from the Chandra X-ray telescope, we have extracted the diffuse X-ray emission from 49 equal-mass interacting/merging galaxy pairs in a merger sequence, from widely separated pairs to merger remnants. After the removal of contributions from unresolved point sources, we compared the diffuse thermal X-ray luminosity from hot gas (L X(gas)) with the global star formation rate (SFR). After correction for absorption within the target galaxy, we do not see a strong trend of L X(gas)/SFR with the SFR or merger stage for galaxies with SFR > 1 Myr-1. For these galaxies, the median L X(gas)/SFR is 5.5 ×1039 ((erg s-1)/Myr-1)), similar to that of normal spiral galaxies. These results suggest that stellar feedback in star-forming galaxies reaches an approximately steady-state condition, in which a relatively constant fraction of about 2% of the total energy output from supernovae and stellar winds is converted into X-ray flux. Three late-stage merger remnants with low SFRs and high K-band luminosities (L K ) have enhanced L X(gas)/SFR; their UV/IR/optical colors suggest that they are post-starburst galaxies, perhaps in the process of becoming ellipticals. Systems with L K < 1010 L have lower L X(gas)/SFR ratios than the other galaxies in our sample, perhaps due to lower gravitational fields or lower metallicities. We see no relation between L X(gas)/SFR and Seyfert activity in this sample, suggesting that feedback from active galactic nuclei is not a major contributor to the hot gas in our sample galaxies.

No description available.

Nanocrystalline, nanoporous, and heterogeneous functional materials have a range of unique physical and chemical properties at the nanoscale that make them useful in various fields such as gas storage, sensing, catalysis, and construction. However, these materials have complex and varied internal structures make them difficult to analyze using traditional methods. In this work, advanced tools were presented that combine several existing algorithms and techniques to enable efficient and accurate analysis of the structures of these materials. The tools were tested on well-studied systems (TiO2 nanoparticles) and novel materials (multiple metal organic frameworks), and the results showed that they produced accurate and reliable results. These results have contributed to important scientific discoveries, some of which are highlighted in this thesis. First, an automated platform for x-ray scattering experiments and a streaming data pipeline were developed to determine pair distribution functions, which were used to study nanocrystalline, nanoporous, and heterogeneous functional materials. A systematic workflow was then proposed and tested to analyze the phases and morphologies of metal oxide nanoparticles. Using the data pipeline and workflow, the effects of temperature on phases, morphologies, and structure order during the synthesis of titanium oxide (bronze) nanoparticles were demonstrated. Specific tools were then designed to analyze the structures of nanoporous materials based on the disorder in their complex structures. The turbostratic disorder in zirconium phosphates was analyzed, and the potential to tune disorders using phosphoric acid concentration was demonstrated. In addition, the glass transition in metal-organic frameworks was detected, and a reminiscent correlation between metal sites in the glass state was discovered. Furthermore, evidence of polar solvent-induced lattice arrangement in an aluminum metal-organic framework was found using the analysis of pair distribution functions. Finally, a simple but effective algorithm was proposed to study the grain distribution and mosaicity in heterogeneous crystalline materials, moving beyond the study of homogeneous systems. Overall, these studies aim to enable faster and more comprehensive analysis of the disordered structures in nanocrystalline, nanoporous, and heterogeneous materials, which could have applications in fields including photocatalysis, optical or gas sensing, radioactive waste storage, and metallurgical industry.

No description available.

This project was initiated by the Cardcrock Division of the Naval Surface Warfare Center (CDNSWC) and the Office of Naval Research to study the effects of various processing parameters on the residual stress state of HSLA-100 bead-on-plate weldments. Three groups of samples were provided to Virginia Tech by CDNSWC. The first (GPX) was a sample of unwelded, as-received base material; the second group (RS-) consisted of an experimental matrix of differently processed bead-on-plate weldments which were all ground prior to welding in order to prepare the surface for welding; the third group (SR-) was a pair of weldments vacuum annealed at 1200°F for one and two hours, and then welded (without grinding) using welding parameters identical to weldments from the second group. X-ray diffraction was used to measure the surface residual stress state of all samples. It was found that the surface residual stress states of the GPX plate and the unwelded SR-group plates showed no statistically significant difference in magnitude, though the variation of the stress state over the surface of the plates seemed to decrease with increasing annealing time. The severe, non-uniform grinding was determined to play a very large role in the residual stresses generated in the welds, sometimes changing both the magnitude and the shape of the stress patterns. Residual stresses in plates that were ground before welding were always more tensile than those that were not ground. Grinding also caused a large compressive-to-tensile stress gradient in the transverse direction. The grinding made it difficult to determine the effects of different welding parameters on the residual stress state. Assuming that the stresses closest to the weld bead are exclusively residual stresses due to welding, preheat temperature reduced the tensile nature, or increased the compressive nature, of the residual stresses. This is due to the preheat reducing the effect of shrinkage stresses induced after the austenite transformation upon cooling of the weldment. Because of the effects of grinding and the small sample sizes, no definitive conclusions could be drawn about the effects of heat input and plate thickness. It was shown that grinding was the dominant parameter on the residual stress state in these HSLA-100 bead-on-plate weldments. Because the angle and force of grinding are purely at the discretion of the operator, it is very difficult to determine the effects of different welding parameters on the residual stresses generated in bead-on-plate weldments ground prior to welding. / Master of Science

A part of the Ph.D. project focused on growth and characterization of metal multilayers is presented in this licentiate thesis. The main interest in carrying out this research is to develop highly reflective normal-incidence condenser mirrors for soft X-ray microscopy studies in the water window (λ=2.4-4.2 nm) wavelength regime. Transition metals like Sc, Ti V, etc. have been considered because of the presence of their 2p-absorption edges within the water window. An anomalous dispersion at absorption edges has been utilized to get enhanced reflectance of soft X-rays. Since a single surface exhibits a very poor X-ray reflectivity, Cr/Sc, Cr/Ti, and Ni/V multilayers were grown in order to coherently add many reflections from several interfaces. The selection of Cr and Ni, as spacer layer, was made on the basis of their X-ray optical contrasts with the above-mentioned transition metals. The multilayer design, i.e., the individual layer thicknesses and the total number of bilayers, directly influences the resultant reflectance and careful determination was therefore made with the aid of computer simulations. All multilayers were grown on chemically cleaned Si substrates by ion-assisted dual target magnetron sputtering under high vacuum (~10-7 Torr) conditions. The effect of low and high ion-flux bombardment of low energy (&lt;50 eV) Ar ions, on growing surfaces was studied for all material systems. Furthermore, a two-stage deposition of each individual layer with modulated ion-energies was applied in order to obtain smooth and abrupt interfaces with as small intermixing as possible. Ion-surface interactions were also theoretically considered for estimating an appropriate ion-flux and ion-energy range desired for sufficient ad-atom mobilities. X-ray reflectivity and transmission electron microscopy have been the main probes for multilayer characterization in this work. For the Cr/Ti multilayer designed for normal incidence and grown with optimized two-stage ion-energy modulation, a peak reflectance of 2.1% was achieved at the Ti-2p absorption edge (λ=2.74 nm). For a multilayer mirror designed for the Brewster angle a maximum reflectance of 4.3% was accomplished. These measurements were made at the synchrotron radiation source BESSY in Berlin. Specular reflectivity and diffuse scattering scans were utilized for quantitative and qualitative analysis of the vertical and lateral structure of the multilayers. At-wavelength measurements of a series of Cr/Ti multilayers revealed the accumulation of roughness with increasing number of bilayers (N&gt;100) for this material system. Hard X-ray reflectivity and diffractometry were used for quality checks of the multilayers for rapid feedback to the deposition. In-situ annealing using hard X-ray reflectivity was also performed to assess the thermal stability of Cr/Ti multilayers. It was found that probably due to a strong thermal diffusion the degradation of multilayers (with bilayer period of 1.37 nm) in this material system occurs just above the growth temperature (~40°C). The accumulation of a low spatial frequency "waviness" with increasing number of layers in Cr/Ti multilayers was investigated by transmission electron microscopy. The influence of process conditions on multilayer structure with different periodicities was investigated by TEM analyses of a series of three samples for each of the above-mentioned material system. The Cr/Sc multilayers have shown the most flat and abrupt interface structure without any significant roughness evolution when grown with optimum process parameters. / <p>Report code: LiU-TEK-LIC-2005:48. On the day of the defence data the status of article I was: Accepted.</p>