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Doctor of Philosophy / Department of Physics / Bharat Ratra / High precision cosmological observations in last decade suggest that about 70% of our universe's energy density is in so called "Dark Energy" (DE). Observations show that DE has negative effective pressure and therefore unlike conventional energy sources accelerates the cosmic expansion instead of decelerating it. DE is highly uniform and has become a dominant component only recently. The simplest candidate for DE is the time-independent cosmological constant. Although successful in fitting available data, the cosmological constant model has a number of theoretical shortcomings and because of that alternative models of DE are considered. In one such scenario a cosmological scalar field that slowly rolls down its potential acts like a time-dependent cosmological constant. I have used different independent cosmological data sets to constrain the time dependence of DE's energy density in the framework of the slowly-rolling cosmological scalar field model. Present data favors a time-independent cosmological constant, but the time-dependent DE can not be ruled out at high confidence level. Ongoing and planned cosmological probes and surveys will provide more and better quality data over the next decade. When the new data sets are available we will be able to either detect the time dependence of DE or constrain it to a very small physically uninteresting value.

<p> X-ray absorption spectromicroscopy combines microscopy and spectroscopy to provide rich information about the chemical organization of materials down to the nanoscale. But with richness also comes complexity: natural materials such as biological or environmental science specimens can be composed of complex spectroscopic mixtures of different materials. The challenge becomes how we could meaningfully simplify and interpret this information. Approaches such as principal component analysis and cluster analysis have been used in previous studies, but with some limitations that we will describe. This leads us to develop a new approach based on a development of non-negative matrix approximation (NNMA) analysis with both sparseness and spectra similarity regularizations. We apply this new technique to simulated spectromicroscopy datasets as well as a preliminary study of the large-scale biochemical organization of a human sperm cell. NNMA analysis is able to select major features of the sperm cell without the physically erroneous negative weightings or thicknesses in the calculated image which appeared in previous approaches.</p>

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Astronomical images are found on monumental structures and decorative art, and metaphorically in seasonal myths, and are documented by calendars. In Israel and the southern Levant, images of the sun, the moon, and the stars were common decorating motifs. They were found on walls, pottery, and seals and date to as early as the Chalcolithic period; for example, the wall painting of a star at Teleilat Ghassul (North 1961). This dissertation establishes that the people of the Levant were aware of the apparent movement of the sun, and this will be discussed in Chapter 4. They began recording through representation drawings, astronomical phenomena no later than the Chalcolithic/Early Bronze Age and continued to do so late into the Middle Bronze Age. The argument moves beyond the simple use of symbols to the use of images to represent constellations, with the focus on the constellation Leo in Chapter 5. Furthermore, the use of astronomy as a power and political tool is also suggested in Chapter 6. Nonetheless, the primary purpose that is addressed here is the tendency in Syro-Palestinian archaeology has been to attribute technological evidence found in the northern and southern Levant as diffused from Egypt or Assyria, particularly astronomy. This dissertation firmly establishes that astronomy was used in the southern Levant before any significant contact with the civilizations of Egypt or Assyria.

In this work the problem of actuator and sensor mapping and controller design for the flexible structure control is approached as minimization of the residual deformations index (Hinfinity norm of the closed-loop disturbance - deformation path) over the set of non-destabilizing feedback controllers and over the set of possible actuator and sensor mappings. Computational load associated with this approach is reduced by restricting the search to the mapping areas where an inexpensive lower estimate of residual deformations index (derived as a part of this study) is less than the desired value of this index. Further improvement is achieved by including statistical description of the difference between the actual and the estimated performance index over the set of mappings, in order to adjust the level of the mapping acceptance/rejection in such a way that the number of rejected mappings is increased. Serial and parallel optimization procedures based on exhaustive search and genetic algorithms are discussed. These concepts and algorithms are applied to test cases of simply supported beam, the UCLA Large Space Structure, and a telescope mirror model: a hinged round plate.

Decipherment is the tool used to uncover several types of hand signs that played vital roles in the creation of hidden messages in classic artwork. A 3,100 B.C. bas-relief of The 'Kaph' Telescope, formerly named The Narmer Palette, and Michaelangelo Buonarrotte's Battle of Cascina of 1506 were two key works of art that show certain similarities even though separated by 4,500 years. It is evident that Renaissance humanists provided artists with certain knowledge of the ancients. Results of incorporating a number of minor works of art showed that the competence of ancient Egyptians, Cretans and Australian Aboriginals, to name a few, as astronomers, was underestimated. Some deciphered Indus seals attested to a global understanding of the universe, with Gemini and the star of Thuban at the center of their attention. Certain forms of secrecy had to be undertaken for various reasons throughout the millennia. Three examples are: (1) In Italy, to keep controversial and truthful teachings discreet and hidden, artists embedded them in artwork long before the plight of Galileo Galilei and his discoveries. (2) Among Jewish Kabbalists, a well-known design was obscured in The Arnolfini Wedding painting for fear it would be lost due to persecution. (3) Michaelangelo Buonarrotte indicated several meanings through the hands of The Statue of Moses. They were overlooked by several societies, including the gesticulating culture of Italy, because they oppressed the value of signed languages. Spatial decipherment may testify to a need for the restoration of a spatial writing system for expanded linguistic accessibility. A 21st century model community for sign language residents and employees will benefit visual learners, particularly visual artists and non-phonetic decipherers, to better uncover, understand and perhaps use ancient hand forms to restore ancient knowledge. Moreover, the National Association of Teaching English (NATE) has recently endorsed the addition of two skills, viewing and visual representing, to the traditional list of reading, writing, speaking and listening. Students will master these two new skills far more effectively when they are exposed to such a signing community.

In order to increase sky coverage, adaptive optics (AO) systems for large telescopes will require laser systems to provide artificial reference beacons. The most prominent method for creating an artificial beacon is to project laser light tuned to the 589nm, D2 line of sodium onto the mesospheric sodium atoms at an altitude of 90km. When correcting with AO, the best wavefront measurements are obtained when the image of the sodium beacon is as bright and sharp as possible. Blurring occurs due to spot elongation, as a result of sub-aperture displacement from the projector axis, and from diffraction and seeing effects on the projected beam. Mounting the projector in the center of the telescope minimizes the effect of elongation. Simulations were conducted that show that matching the beam waist to ∼2 times the atmospheric turbulence parameter r₀ minimizes the beacon size. For r₀ = 15cm and a 48cm projector, calculations show the optimum projected waist is 29cm. A prototype projector has been built and operated. Recent experiments have shown that this projector is capable of producing 0.75arcsec beacons under good seeing. In addition, spot elongation of 0.5arcsec was observed corresponding to a sodium layer thickness of 10km. The first experimental evidence for optical pumping in the mesospheric layer were obtained. They show a non-thermal profile for the sodium hyperfine structure (3.5:1 line ratio as opposed to 5:3) when projecting circularly polarized light. This profile indicates that the maximum return per watt is obtained by pumping the F = 2 level with a narrow bandwidth compared with pumping both F = 2 and F = 1 with a broad bandwidth. In addition, evidence shows a 30% increase in beacon brightness when pumping the sodium layer with circularly polarized light over linear. A projector for the 6.5m MMT conversion has been designed based on experience gained with the prototype. Analysis of the Strehl reduction due to wavefront reconstruction error shows a reduction in Strehl of < 1% for the optimal operating parameters at the MMT. This less than the fundamental limit of 0.79 for focus anisoplanatism.