This work is aimed at developing a high sensitivity salinity (conductivity) sensor for marine applications. The principle of sensing involves the use of parallel plate capacitors, which minimizes the proximity effects associated with inductive measurement techniques. The barrier properties of two different materials, AZ5214 and Honeywell's ACCUFLO T3027, were investigated for use as the insulation layer for the sensor. Impedance analysis performed on the two coatings using Agilent's 4924A Precision Impedance Analyzer served to prove that ACCUFLO was a better dielectric material for this application when compared to AZ5214.Two separate detection circuits have been proposed for the salinity sensor. In the Twin-T filter method, a variation in capacitance tends to shift the resonant frequency of a Twin-T oscillator, comprising the sensor. Simulations of the oscillator circuit were performed using Pspice. Experiments were performed on calibrated ocean water samples of 34.996 psu and a shift of 410 Hz/psu was obtained. To avoid the problems associated with the frequency drift in the oscillator, an alternate detection scheme is proposed which employs frequency-to-voltage converters. The sensitivity of this detection scheme was observed to be 10 mV/psu.

This dissertation investigates how presidents build successful legislative coalitions and enact their agenda into law in the United States Congress. It argues that constituencies and electoral incentives cause members of Congress to respond to the president’s agenda in a systematic manner. The president’s strength in members’ constituencies interacts with members’ electoral incentives to determine whether members will vote for or against the president. The theoretical claims presented in this dissertation are supported by a combination of case studies and quantitative analysis. The empirical analysis utilizes a dataset with observations for every member of Congress from 1957 to the present. I find that constituency-level presidential strength causes systematic variance in members’ response to the president’s agenda. Vulnerable members of Congress are particularly sensitive to the president’s strength in their constituencies, while safe members of Congress are a bit less attentive to their constituencies. These findings contribute to our understanding of American politics by showing that the president’s ability to enact agenda items into law is affected by much more than mere party politics. This conclusion is especially relevant in the modern, polarized era in American politics. / text

In this dissertation, I explain why scholars are unable to conclusively find evidence that divided government is the main determinant of legislative gridlock. I argue this unsettled debate is largely attributable to an imprecise conceptual view of inter-branch tensions, and that these conceptual limitations are exacerbated by unrefined measurement practices. I argue refined measures such as party polarization and gridlock intervals better explain institutional behavior than divided government. Using unique datasets estimating legislator preferences on domestic and foreign policy, findings show that when compared to more refined measures, split-party government is not the sole or even the most important source of partisan conflict. In addition, compared to other studies on divided government, I argue the reason the distinction between unified and divided government is often blurred is that a number of underlying political and institutional pressures make sweeping policy change difficult even for most unified governments. These factors contribute to the public’s growing dissatisfaction with government’s inability to solve many economic and social problems. / text

This dissertation studies determinants of the U.S. labor market structure and human capital development, with a focus on technological change. A key feature of the U.S. labor market since 1980 is the substantial growth of the employment in high skill occupations and there is a substantial literature attributing this change to technological change. However, since 1999, the employment growth of high skill occupations has decelerated markedly despite continued rapid growth in technology. The first essay documents this novel trend and examines the role of technological change in explaining this phenomenon. It shows that technological advancements since the late 1990s, such as the onset of Internet, have expanded what computers can do and become substitutes for high skill occupations. This change can explain a substantial portion of the stagnancy in employment growth for high skill occupation in the 2000s. The second essay examines the role of computer adoption in explaining the differences in the change of gender wage gap between 1980 and 2000 across cities in the United States. It uses the city-level routine task intensity in 1980 to predict the subsequent increase in computer adoption and shows that cities with one percent greater increase in computer adoption experienced a 0.7 percent more decrease in the change of male-female wage ratio between 1980 and 2000. Computerization explains about 50 percent of the decline in the male-female wage gap between 1980 and 2000. The third essay studies the causal effect of maternal education on the gender gap in children’s non-cognitive skills. It shows that maternal education reduces boys’ disadvantage in non-cognitive behaviors relative to girls at age 7. To explain the mechanism of this effect, it provides suggestive evidence that better educated mothers spend more time going outings with boys while reading to girls at age 7, and going outings could be more closely related to non-cognitive development than reading.

This dissertation describes the investigation of the fouling of a reverse osmosis membrane under different operating conditions. A mass transfer model to predict the permeate flux decline is defined. These studies used kaolin clay and bentonite clay as the fouling particles. As the membranes, thin film Low fouling Composite 1 polyamide reverse osmosis flat sheet membranes were used. Baseline experiments using only kaolin in D.I. water were conducted. At an operating pressure of approximately 1,380 kPa, no flux decline was observed. These results established the effects of a membrane-particle interaction. For the fouling experiments with kaolin clay, experiments show a linear relationship between the mass of the deposited foulant layer and total permeate flux decline. The increased concentration of scale forming salts such as calcium chloride and sodium carbonate combined with clay particles has been found to increase flux decline. It also leads to the formation of a less porous cake layer on the membrane surface, which may be due to the particle surface charge. The increase in transmembrane pressure leads to the formation of a well compacted, less porous, cake layer on the membrane surface. The reduced porosity results in the deterioration of the permeate quality, which is a direct result of reduced back diffusion of the salt solution.A fouling model that combines a resistance-in-series model and a simplified-mass-transport relationship were used to predict the transient stage permeate flux of a reverse osmosis membrane. This model contains a constant which is a function of the operating condition and the ionic species in the feed solution. It was found that the results from the model agreed with the experimental results.

The goal of this dissertation research is to develop and demonstrate a functioning snapshot imaging spectropolarimeter for the long wavelength infrared region of the electromagnetic spectrum (wavelengths from 8-12 microns). Such an optical system will be able to simultaneously measure both the spectral and polarimetric signatures of all the spatial locations/targets in a scene with just a single integration period of a camera. This will be accomplished by combining the use of computed tomographic imaging spectrometry (CTIS) and channeled spectropolarimetry. The proposed system will be the first instrument of this type specifically designed to operate in the long wavelength infrared region, as well as being the first demonstration of such a system using an uncooled infrared focal plane array. In addition to the design and construction of the proof-of-concept snapshot imaging spectropolarimeter LWIR system, the dissertation research will also focus on a variety of methods on improving CTIS system performance. These enhancements will include some newly proposed methods of system design, calibration, and reconstruction aimed at improving the speed of reconstructions allowing for the first demonstration of a CTIS system capable of computing reconstructions in 'real time.'

One of the biggest quests in nuclear and particle physics in the last three decades is to unravel the spin structure of hadrons like protons and neutrons. Spin not only plays a central role in the strong force connecting the elementary constituents of matter, but is also responsible for many of its fundamental properties including the magnetic moment which defines the magnetic properties, the different phases in low temperature physics, and the stability of the universe in general. The origin of the spin of particles like protons and neutrons, which make up to 99.9% of the visible universe, has been the focus of experimental and theoretical efforts. Experiments at European Muon Collaboration (EMC) found that our knowledge of how the spin of the nucleon is derived from its elementary constituents is naive, and our interpretations are not valid. This was termed the spin crisis, an outstanding puzzle for more than three decades and is still not solved. Deciphering the spin puzzle requires knowing the spin of elementary constituents of these particles, quarks and gluons. One of the major objectives of the Relativistic Heavy Ion Collider (RHIC) spin program at Brookhaven National Laboratory is the measurement of the gluon helicity contribution to the proton spin via measuring the double helicity asymmetry (ALL) in various channels. In Pioneering High Energy Nuclear Interaction eXperiment (PHENIX) we measure ALL in π0 meson production. The π0 meson is reconstructed through its di-photon decay channel. The photons are detected by the PHENIX Electromagnetic Calorimeter, which consists of lead glass and lead scintillator detectors and covers a rapidity of |η|< 0.35 and azimuthal angle of 180°. In this dissertation, the results of ALLin π0 production from the data collected in 2013 at center of mass energy = 510 GeV are presented. In 2013, the total integrated luminosity is 150 pb-1 which is almost ten times the total luminosity recorded in 2009 at center of mass energy = 200 GeV. Due to the increase in the center of mass energy and integrated luminosity, these measurements cover the Bjorken x range down to ~0.01. A non-zero ALL result is observed that is consistent with positive gluon polarization in the probed kinematics.

The phenomenon of directed cell motion in response to external directional cues has drawn significant interest for more than a century, with the first recorded observations of bacterial chemotaxis at the end of the 19th century. Furthermore, movies generated by David Rogers while at Vanderbilt University of a peripheral blood neutrophil tracking a bacterium are a staple of any college biology class to demonstrate the phenomenon of eukaryotic chemotaxis. In just the last decade, our understanding of the biochemical mechanisms underlying the process of directed eukaryotic cell migration. As a result, several generalized processes have been identified, connecting multiple phenomena from cancer metastasis to axon guidance. Making further sense of the complex biochemical pathways requires both quantitative mathematical models and fine control over the external cellular environment. To this end, microfluidics has proven extremely useful, allowing for precise quantification of both the external environment and the cellular response.

Inflation, which posits an exponential expansion in the early universe, is well motivated since it resolves questions that are left unexplained by standard LCDM cosmology, such as the flatness and homogeneity of the universe. The exponential expansion of universe during inflation explains the structure in the universe by freezing out the quantum fluctuations of space. These quantum fluctuations are also expected to generate a background of gravitational waves which would then imprint a B-mode polarization signal on the Cosmic Microwave Background. The Bicep2 and Keck Array experiments search for B-mode polarization from inflationary gravitational waves in the Cosmic Microwave Background. Bicep2 and the Keck Array use small aperture, cold, on-axis refracting optics optimized to target the degree angular scales at which the inflationary B-mode polarization is expected to peak. In this thesis we describe the optical design of Bicep2 and the Keck Array. The small aperture design allows us to fully characterize the far-field performance of the instrument on site at the South Pole using thermal and amplified sources on the ground. We describe the efforts taken to characterize the main beam shapes of each polarization sensitive bolometer, as well as the differential beam paramters of each co-located orthogonally polarized detector pair. We study the residual temperature to polarization leakage induced by the beam mismatches after the principle modes have been mitigated in the analysis. / Physics

Conventional image sensors achieve color imaging using absorptive organic dye filters. These face considerable challenges however in the trend toward ever higher pixel densities and advanced imaging methods such as multispectral imaging and polarization-resolved imaging. In this dissertation, we investigate the optical properties of vertical silicon nanowires with the goal of image sensor applications. First, we demonstrate a multispectral imaging system that uses a novel filter that consists of vertical silicon nanowires embedded in a transparent medium. Second, we demonstrate pixels consisting of vertical silicon nanowires with integrated photodetectors. We show that their spectral sensitivities are governed by nanowire radius, and perform color imaging. In addition, we demonstrate polarization-resolving photodetectors consisting of silicon nanowires with elliptical cross sections. Finally, we discuss a dual detector device. Each pixel consists of vertical silicon nanowires (incorporating photodetectors) formed above a silicon substrate (that also incorporates a photodetector). Our method is very practical from a manufacturing standpoint because all filter functions are defined at the same time through a single lithography step. In addition, our approach is conceptually different from current filter-based methods, as absorbed light in our device is converted to photocurrent, rather than discarded. This ultimately presents the opportunity for very high photon efficiency. / Engineering and Applied Sciences