Purpose: The purpose of this work was to evaluate the ability of a treatment delivery verification system to detect clinically significant mechanical errors in VMAT delivery utilizing data contained within a commercial record and verify (RV) system, and to test whether the system can be used to reconstruct dose distributions that agree more closely with measured dose distributions than do the original treatment plans. Methods: VMAT treatment plans from five prostate patients, five head and neck patients, and five post-mastectomy chest wall patients treated at our clinic were selected for this study. Known mechanical errors were introduced into each plan, and the dosimetric effect of each error was evaluated by a radiation oncologist to determine mechanical error thresholds for clinical acceptability. Next, shifted plans were delivered on an Elekta linear accelerator, and the resulting dose distribution was measured with a two-dimensional diode array. During delivery, positions of the gantry, multi-leaf collimator (MLC), and jaws were captured in both the RV system and the linac verification interface (LVI). Following plan delivery, recorded delivery data were analyzed to characterize the ability of the recording systems to recognize true mechanical error. Finally, delivery parameters from both recording systems were imported to the treatment planning system and used to recalculate the dose delivered to the measurement phantom to test whether the system can be used to reconstruct dose distributions that agree more closely with measured dose distributions than do the original treatment plans. Results: Minimum mechanical error thresholds over all fifteen cases were found to be 1 mm for systematic MLC error, 2 mm for Gaussian-random MLC error, 3 mm for uniform-random MLC error, 3 mm for central leaf pair error and 2° for gantry error. Analyzing delivery data yielded p-values less than 0.05 for both RV and LVI systems for all central leaf pair and gantry shifts (1, 2, and 3 mm central leaf pair shifts and 1, 2, 3, and 5° rotations), which means that each system could reliably detect errors at threshold values. Reconstruction of delivery data by both RV and LVI systems failed to yield p-values less than 0.05 for prostate, head and neck, and chest wall cases. Conclusion: Both delivery verification systems examined were capable of detecting mechanical errors of 1 mm of the MLC and 2° of the gantry that produce clinically unacceptable changes in the planned dose distribution. However, dose reconstructed using the recorded delivery parameters showed no significant improvement in agreement with measured values. Thus, while the delivery verification system can detect mechanical errors, it cannot more accurately estimate the daily delivered dose than the original plans do.

The Chandra Galactic Bulge Survey (GBS) undertakes to find and classify X-ray sources in the Galactic Bulge. Of these X-ray sources, there is likely a significant minority which are Low Mass X-ray Binaries: systems containing either a neutron star or black hole that is accreting matter from a roughly stellar mass companion via Roche-Lobe overflow. I use optical time-series photometry from the Mosaic-II instrument on the Blanco 4m telescope at the Cerro Tololo Inter-American Observatory to identify counterparts to new X-ray sources in the GBS. Of those that are variable in brightness, I use the morphology of the changes and the relative proportion of optical and X-ray light, to identify high inclination systems through eclipses, to determine what periodicity, if any, is present in the optical light, and use these properties to partially or fully classify X-ray sources. The GBS contains a variety of X-ray sources, including Low Mass X-ray Binaries, Cataclysmic Variables, Intermediate Polars, Active Galactic Nuclei, W Ursa Ma joris stars, RS Canum Venaticorum stars, active stars, and flare stars. Spectroscopy greatly aids the classification of the X-ray source and is used, where available, to distinguish between source types and identify promising ob jects for further study. Only a handful of sources are identified as potential new Low Mass X-ray Binaries in quiescence, which places limits on the number of such systems in the Galaxy and on their outburst duty cycle. In addition to the GBS, I have done work on echo-tomography of Scorpius X-1, the brightest extra-solar X-ray source in the sky. I have found that reprocessing is dominated by the accretion disk in all observations, and that the companion is not reliably distinguishable in reprocessing of continuum light. I also found that reprocessing mainly occurs in the Flaring Branch of the Z-diagram, turning off in other X-ray states.

Purpose: Ultra-short echo time (UTE) imaging is a magnetic resonance imaging (MRI) technique that uses very short echo times (on the order of microseconds) to measure rapid T2 relaxation. An application of UTE is the visualization of magnetic susceptibility-induced shortening of T2 in tissues adjacent to metal, such as prostate tissue with implanted brachytherapy seeds. This study assessed UTE imaging of prostate brachytherapy seeds on a clinical 3T MRI scanner to provide images for post-implant dosimetry. Methods: A prostate tissue phantom was made of gelatin mixed with Gd and other materials to mimic the prostate peripheral zones T1 and T2 relaxation times; this phantom was used to investigate the effect of UTE acquisition parameters on brachytherapy seed visibility. A second phantom was made to model prostate tissue surrounded by muscle tissue; this pelvic phantom was implanted with 85 titanium brachytherapy seeds (STM1251, Bard Medical). Both phantoms were scanned on a 3T GE scanner with a 3D UTE pulse sequence and a fast spin echo (FSE) pulse sequence. The average seed SNR, the CNR between seed and prostate material, and visual characteristics of the seeds were assessed. A seed counting procedure was developed based on the visual seed characteristics, and subsequently used by two physicists to locate seeds in UTE images of the pelvic phantom. Results: On 3D UTE images, the metal seeds caused a bright ring-link artifact in adjacent prostate tissue due to susceptibility-induced T2 shortening. The average seed SNR was 15.99±1.52 for UTE compared to 32.32±22.43 for FSE; CNR between seed and prostate was 6.73±1.85 for UTE vs. 23.76±12.87 for FSE. The ring was larger in diameter than a seed itself; apparent seed diameters were 4.65±0.363 mm for UTE compared to 1.46±0.38 mm for FSE. The 3D spatial ring pattern facilitated differentiation of seeds from needle tracks and seed spacers. The two physicists counted 83 and 86 seeds respectively in the UTE images. Prostate boundaries were less well visualized with UTE compared to FSE. Conclusion: With its ability to visualize brachytherapy seeds, UTE imaging appears to provide an alternative approach to CT for seed identification. Compared to fusion of separately-acquired CT images and T2-weighted MR images (for delineation of prostate boundaries), UTE and T2-weighted MR can be acquired in a single imaging session a convenience to patients while potentially minimizing inter-modality image registration issues. A study in prostate brachytherapy patients of the quality of post-implant dosimetry with UTE imaging compared to CT imaging is recommended.

In this dissertation we begin with a brief introduction to quantum optics concentrating on the topics of the noise of quantum optical states, quantum estimation theory, quantum interferometry and the atom-field interaction. This background is necessary for understanding the discussions in later chapters. In particular, quantum interferometry, which is optical interferometry when the light source is a quantum mechanical state, plays a central role in this dissertation. In Chapter 2 we discuss the phase estimation sensitivity of quantum metrology when photon loss is present. In Chapter 3 we extend the discussion to include the phase fluctuation of the system caused by the environment. We model our metrological system with the Mach-Zehnder interferometer (MZI) and use a light field in the symmetric number-path entangled state as the source. In both chapters we use the parity operator as the detection scheme and show that it is optimal under pure dephasing. In Chapter 4 we discuss the application of quantum optical states in remote sensing and propose a new scheme for a quantum radar. Again, our scheme consists of a MZI and a coherent light source. It is shown that using only coherent states of light and quantum homodyne detection, super-resolving ranging and angle determination are achievable. Chapter 5 is devoted to the generation of a super-resolving single-photon number-path entangled state which may serve as a proof-of-principle prototype for quantum lithography. The repeated implementation of MZIs is shown to be able to remove photons coherently from both modes of a symmetric number-path entangled state with arbitrarily high photon number. Lastly, in Chapter 6 we introduce the phenomenon known as polarization self-rotation and discuss its potential in generating a squeezed vacuum state, which has a huge impact in quantum interferometry.

In highly excited Rydberg atoms, the excited electron is in a large, loosely bound orbit. Hence, in contrast with the ground states, the Rydberg states are very sensitive to external electric field and can be ionized in rather weak fields. The low ionization threshold of Rydberg states results in effective state-specific detection by the selective field ionization technique. In this thesis, high-resolution spectroscopy of Rydberg states of Rubidium using millimeter wave transitions and selective field ionization has been used as a probe of external electric and magnetic fields. Laser cooling and trapping techniques in a magneto-optical trap (MOT) are employed to have a high density and narrow velocity distribution for the atomic sample. In this work the magnetic field inhomogeneity inherent in a MOT is minimized and the stray electric field present at the trap region is compensated in order to have resolved spectra. The Stark line broadening of the spectra obtained in this work may be used to determine the electric field distribution in an expanding ultra-cold neutral plasma.

We demonstrate the capabilities of a new hybrid scheme for simulating dynamical fluid flows in which cylindrical components of the momentum are advected across a rotating Cartesian coordinate mesh. This hybrid scheme allows us to conserve angular momentum to machine precision while capitalizing on the advantages offered by a Cartesian mesh, such as mesh refinement. The work presented here focuses on measuring the real and imaginary parts of the eigenfrequency of unstable axisymmetric modes that naturally arise in massless polytropic tori having a range of different aspect ratios, and quantifying the uncertainty in these measurements. Our measured eigenfrequencies show good agreement with the results obtained from the linear stability analysis of Kojima (1986) and from nonlinear hydrody- namic simulations performed on a cylindrical coordinate mesh by Woodward et al. (1994). When compared against results conducted with a traditional Cartesian advection scheme, the hybrid scheme achieves qualitative convergence at the same or, in some cases, much lower grid resolutions and conserves angular momentum to a much higher degree of precision. As a result, this hybrid scheme is much better suited for simulating astrophysical fluid flows, such as accretion disks and mass-transferring binary systems.

In this thesis the author reports his collaborative efforts on two distinct areas of research that has been conducted. The first part of the thesis pertains to the author and his collaborators research on a particular class of organic magnets called the bimetallic oxalates. The main theme of this research was to predict magnetic compensation (magnetization reversal) in unsynthesized bimetallic oxalate structures, motivated by experiments which showed that Fe(II)Fe(III) exhibited magnetic compensation. In addition it was known that a large amount of anisotropy was present in the bimetallic oxalate structure which resulted from the intermediate oxalate molecules between the transition metal ions which would drastically change the angular momentum of the transition metals. Consequently, because of the large anisotropy, we predicted that, if neutron diffraction measurements were performed on these materials, a spin-wave gap would exist of the order of 7.8 meV. The second half of this thesis is devoted to the author's and his collaborators' research on the cerium volume collapse. Until 2004 the collapse was largely believed to be understood as the result of Kondo screening of the local moment in cerium. However in 2004 it was realized that, in addition to a large Kondo effect driving the cerium volume collapse, the phonon frequency was very different between the large and small volume phases, and consequently the change in phonon frequency was the direct result of large electron-phonon correlations. This upset the apple cart of Kondo correlation being solely responsible for the volume collapse in cerium, and the change in phonon frequency must be accounted for to accurately describe the cerium volume collapse. To this end the author and his collaborators' developed a model which would include both of the correlations (Kondo and phononic) in the volume collapse. To analyze this model we used Dynamical Mean Field Theory in conjunction with Continuous Time Quantum Monte Carlo. What we found in our simulations was that the small volume Kondo phase was drastically influenced by the presence of the electron-phonon correlations.

Complex Materials, such as transition-metal oxides (TMOs) with exotic properties provide immense opportunities in condensed matter and materials science. The signature and challenge of these materials is the multitude of competing ground states that can be tuned or manipulated by doping, structural modification, strain induction, or the application of external stimulus. In the past few years, it is becoming increasingly clear that surfaces/interfaces, thin films, and heterostructures of TMOs, display a rich diversity of fascinating properties that are related to, but not identical to, the bulk phenomena. The fundamental issues for the understanding of these emergent phenomena include the structure and chemical composition in the proximity of surface/interface. In the thesis, I have developed a method using angle resolved X-ray photoelectron spectroscopy (ARXPS) to characterize the surface structure and chemical composition. In particular, I have considered the photoelectron diffraction effects on the relative intensities of different core electron levels which are essential to reveal the variation of chemical composition. I developed the basic methodology for the data analysis of the ARXPS spectra and used the well-known crystal surface of Sr2RuO4 (100) to verify our methodology. Using the angle-dependence of Sr 3d/ Ru 3p core level intensity ratio, our method clearly confirms that the termination layer of the surface is SrO-layer with minor amount of oxygen vacancies. The diffraction pattern matches very well with the theoretical calculation of forward scattering peaks. Then I have used the developed ARXPS method coupled with low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) to investigate the surface structure and chemical composition of a widely used crystal surface: SrTiO3(100). I found that, although maintaining in-plane unreconstructed: primary p(1×1), the surface exhibits out-of-the-plane bulking relaxation. More importantly, the systematic analysis of ARXPS spectra show that the surface is TiO2-layer terminated and has significant oxygen vacancies. These results confirm the conjecture from LEED-I(V) refinement on structure. The existence of surface oxygen-vacancies may explain the observed surface metallicity of SrTiO3. Finally, I have studied the chemical composition of the ultrathin crystalline films of La2/3Sr1/3MnO3 on SrTiO3 (100), especially focusing on the Sr surface segregation. I found that Sr concentration at the surface is appreciably higher than the corresponding bulk value. Such an off-stoichiometric behavior should link to the different physical properties such as nonmetallic/nonmagnetic dead layer behavior in the ultrathin films compared with the bulk crystal. To conclude, by considering the photoelectron diffraction effects, I have developed a method of ARXPES to characterize the surface chemical composition, which is essential for the understanding of emergent phenomena at surface, interface and thin film of complex materials.

Understanding and controlling the complexity that develops in complex transition metal compounds such as high-Tc superconductivity, "colossal" magnetoresistance in manganites, and heavy-fermion compounds, is one of the grand challenges of the 21st century. The exotic properties displayed by these compounds are closely related to the coexistence of nearly degenerate states, coupling simultaneously several active degrees of freedom such as the charge, lattice, orbital, and spin. In this work, we have focused on two systems, one is the newly discovered Fe-based superconducting compounds ((Ba, Ca)(Fe1-xCox)2As2, FeTe1-xSex) and the other one is the doped Ruddleden-Popper (RP) ruthenates (Sr3(Ru1-xMnx)2O7). The materials community was astonished by the discovery of superconductivity with a critical temperature exceeding 55 K in the iron-based superconductors in 2008. This new family of high Tc superconductors with layered structure without Cu has opened up a completely new venue for understanding not only high Tc superconductors but in general the coupling between lattice, charge, orbital and spin. While ruthenates is a prototype of strong correlated electron materials (CEMs) and Mn-doping in Sr3(Ru1-xMnx)2O7 have induced a rich coupled phase diagrams. We approach from the surface to study their geometric and electronic structure because the symmetry breaking offers great opportunities to tune the balance of the coupling. We applied Low energy electron diffraction (LEED) and its Intensity-voltage (I-V) analysis to quantitatively characterize the detail surface structure from momentum space. Then we used low and variable temperature scanning tunneling microscopy/spectroscopy (STM/S) to study surface electronic structure from real space. At last, spin-polarized density functional theory (DFT) calculations were utilized to enhance our understanding of the experimental data, thus providing a new prospective of our discovery. Our results on the domain surface of BaFe2As2 show that the strong spin-lattice coupling at the surface results in the coexistence of structure and spin antiphase domain boundaries with C2 symmetry. For the stripe surface of (Ba, Ca)(Fe1-xCox)2As2, we determined the surface structure which is proved to be stabilized by bulk spin ordering through spin-lattice-charge coupling. Superconductivity has also been observed on stripe surface indicating a spatial-resolved coexisting of anti-ferromagnetic and superconducting order. On FeTe1-xSex system, we observed a nano-scale chemical phase separation of Te and Se atoms thus the optimally doped superconductor is chemically inhomogeneous but electronically homogeneous, in contrast to many CEMs. However, using STM on a different system, Mn-dopants in Sr3(Ru1-xMnx)2O7 were shown to homogeneously (random) distribute on the surface in micro-scale but maybe phase separated in macro-scale.We also discovered a left- and right- chirality of the structural rotation of MnO6, thus to understand the correlation between the magnetic dopants. Our approach of using state-of-the-art surface techniques to study the manifestation of broken symmetry in these complex transition metal compounds, especially the iron pnictides and ruthernate offered the community a fresh look at the underlying physics.

The Kerr rotation and Kerr ellipticity of thin films can be measured using an AC magneto-optic Kerr effect (AC-MOKE) system. The longitudinal MOKE measurements were taken for a series of Co2MnSixAl1-x thin films with values of x= 0.00, 0.25, 0.50, 0.75, 1.00. The films were fabricated using ultra high vacuum, pulsed laser deposition (PLD) techniques. The PLD targets were made using conventional arc-melting techniques. Using a Jones matrix analysis, it was shown that the Kerr rotation and Kerr ellipticity can be measured separately using two optical setups by taking advantage of a photoelastic modulator and lock-in techniques. Co2MnAl and Co2MnSi are both in a class of materials known as Heusler alloys and are predicted to have a high degree of spin polarization. The crystal structure was confirmed as the L21 using powder x-ray diffraction. The lattice constants were shown to be 5.61Å and 5.77 Å for Co2MnSi andCo2MnAl, respectively. For each film, the DC-MOKE, AC-Kerr rotation, and AC- Kerr ellipticity were measured. The DC-MOKE loops were used to estimate the total Kerr rotation. There was no noticeable trend in the values of the total Kerr rotation as calculated using a technique based on Malus law. The Kerr rotation showed a decreasing trend with concentration (x). The sample with x=0.50 was calculated to be the same as the one with x=0.00 value. The Kerr ellipticity also decreased as x was increased. There have been no reports in the literature on direct measurements of the Kerr rotation or ellipticity for Co2MnSixAl1-x for any values of x. The measurements gave values that were comparable to reported calculations and measured values of similar Heusler alloys.