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In recent years, the Brigham Young University (BYU) Radio Astronomy Systems group has developed phased-array feeds and the data acquisition processing systems necessary to perform radio astronomy observations. This thesis describes the development and testing of a real-time digital beamforming system that reduces both the time required to process phased-array feed data and the disk space used to record this data compared to post-processing beamforming systems. A real-data experiment is also discussed in this thesis, which focuses on some of the data post-processing required for one of BYU's data acquisition systems.Radio-frequency interference mitigation techniques for phased-array feed radio astronomy have been studied for several years, but the effect that these techniques have on weak-signal detection is not well understood. This thesis provides analysis of a simulated weak-source observation for the Green Bank 20-meter telescope and BYU 19 element phasedarray feed with radio-frequency interference present. Interference mitigation techniques are shown to reduce the detectability of weak sources compared with the no interference case, but it is also shown that a weak source can be detected that would otherwise be masked by interference.

Composite cascode stages have been used in operational amplifier designs to achieve ultra-high gain at very low power. The flexibility and simplicity of the stage makes it an appealing choice for low power op-amp designs. Op-amp design using the composite cascode stage is often made more difficult through the lack of a design process. A design process to aid in the selection of the MOSFET dimensions is provided in this thesis. This process includes a table-based method for selection of the widths and lengths of the MOSFETs used in the composite cascode stage. Equations are also derived for the gain, bandwidth, and noise of the composite cascode stage with each of the devices operating in the various regions of inversion.

Mu Columbae is a prototypical weak-wind O star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS instrument and a low-resolution spectrum with Suzaku. This allows us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O stars. Therefore, the "weak-wind problem"--identified from cool wind UV/optical spectra--is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma-the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within five stellar radii. Our results challenge the idea that some OB stars are "weak-wind" stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays.

In-situ chain extension of polymers used in the formulation of artificial tears and mild gelation are techniques to increase the residence time of eye drops on cornea. In-situ chain extension also helps to control the stability of ophthalmic emulsions both in the bottle and in the tear film. In this work, the interaction of hydrophobically modified guar and tear proteins as a method of polymer chain extension and mild gelation has been evaluated. Guar and its derivatives have been found to be very effective for ophthalmic applications. The ideal guar gelation agent is the one that turns on the gelation upon introduction onto the eye and that gelation chemistry is biocompatible and biodegradable. Controllable gelation is desirable to have relatively low viscosity eye drops for easy application and the drops form weak gels in the eye. One recent strategy to cure dry eye disease is to include emulsions in lubricant eye drops. The idea is to supplement the natural lipid layer on the exterior surface of the tear film. Formulating artificial tear emulsions is relatively complicated and must satisfy conflicting criteria. Emulsion droplets should be stable over the period of their shelf life without creaming or aggregate formation. On the other hand, in the tear film the emulsion droplets must cream fast enough and deposit onto the water/lipid film interface on the exterior surface of the tear film. Thus, the emulsion must be stable but not too stable. Initially, science-based design rules were proposed for the development of future generations of lubricant eye drops. The effect of guar molecular weight and concentration on emulsion stability was evaluated. According to the concentration-molecular weight plot, polymer solutions can be divided into stable and unstable regions. They are defined based on the critical flocculation concentration (CFC) and critical viscosity concentration (C*). Inverted QCM-D has been proposed as a simple and fast method to define the stability of oil in water emulsion systems. This technique is a promising alternative for time consuming conventional creaming experiments. Low molecular weight guar can be optimized to out-perform high molecular weight guars without the complications of formulating eye drops with high molecular weight polymers. Hydroxypropyl guar samples were oxidized and modified with linear alkyl amines to give a series of hydrophobically modified guars (MGuars). Lysozyme and human serum albumin (HSA), natural tear proteins, are able to extend the effective chain length of MGuar through polymer/protein complex formation. Hydrophobic modifications on guar enable efficient interaction with proteins, through their mutual hydrophobic characteristics. The interaction of proteins with various alkyl chain lengths, degrees of substitution and a range of molecular weights were examined. Binding and rheological measurements were employed to evaluate the interactions efficiency. Our results suggest that higher degrees of substitution and longer alkyl chain length give higher viscosity values. Lowering molecular weight allows for higher concentration, while keeping the initial viscosity constant. Higher viscosity was achieved as the chain extension occurred. The influence of hydrophobic modification and molecular weight variation on lubrication behavior of MGuars has also been determined. Hydrophobic modification enhanced the lubrication between hydrophobic surfaces. However, saturation of hydrophobes with protein abolished the lubricity. / Thesis / Doctor of Philosophy (PhD)

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