In 2011, Internet users spent almost 23% of their time on social media sites such as Twitter and Facebook. Twitter alone was estimated to have over 200 million active users. With social media being such a popular online pastime, a tremendous amount of information becomes available from the posts that users put on social media sites. This information has the potential to reveal details about the social media users, such as the relationship between characteristics of the users and what they post. This relationship is a hot research topic and one of the most frequently studied characteristic is the gender of a user. Feature frequency is often included in such a task, but this thesis shows that for Twitter tweets it either does not contribute significantly to gender classification or hinders classification. / McAnulty College and Graduate School of Liberal Arts; / Computational Mathematics / MS; / Thesis;

The objective of this project was to design and implement an experimental hydraulic system that simulates joint flexibility of a single rigid link flexible joint robot manipulator, with the ability of changing the joint flexibilitys parameters. Such a system could facilitate future control studies of robot manipulators by reducing investigation time and implementation cost of research. It could also be used to test the performance of different strategies to control the movement of flexible joint manipulators.<p>A hydraulic rotary servo motor was used to simulate the action of a flexible joint robot manipulator. It was a challenging task, since the control of angular acceleration was required. <p>A single-rigid-link, elastic-joint robot manipulator was mathematically modeled and implemented using Matlab. Joint flexibility parameters such as stiffness and damping, could be easily changed. This simulation was considered as a function generator to drive the hydraulic flexible joint robot. In this study the desired angular acceleration of the manipulator was used as the input to the hydraulic rotary motor and the objective was to make the hydraulic system follow the desired acceleration in the frequency range specified. The hydraulic system consisted of a servovalve and rotary motor. <p>A hydraulic actuator robot was built and tested. The results indicated that if the input signal had a frequency in the range of 5 to 15 Hz and damping ratio of 0.1, the experimental setup was able to reproduce the input signal with acceptable accuracy. Because of the inherent noise associated with the measurement of acceleration and some severe non-linearities in the rotary motor, control of the experimental test system using classical methods was not as successful as had been anticipated. This was a first stage in a series of studies and the results provide insight for the future application of more sophisticated control schemes.<p>

A class of hippocampal interneurons in CA1, bordering the lacunosum-moleculare and radiatum hippocampal layers (the LM/R cell), has been shown to exhibit membrane potential oscillations (MPOs) subthreshold to action potential generation. MPOs occur at theta frequency (4-12 Hz) and are of interest because of their putative role in promoting network level theta activity. MPOs arise without synaptic input suggesting that they originate through interactions in the cell’s repertoire of currents. To investigate the generation of MPOs we develop a single compartment model of the cell based on the physiological characterization of its currents. The model includes both deterministic current models and white noise. Our analysis allows for a complete characterization of the cell’s dynamics over the subthreshold range and shows that MPOs arise through the interaction between current dynamics and system noise. We find that MPOs show a particular dependency on the A-type potassium and persistent sodium current magnitudes.

One of the most famous problem of finding optimal weight to maximize an agent's expected terminal utility in finance literature is Merton's optimal portfolio problem. Classic solution to this problem is given by stochastic Hamilton-Jacobi-Bellman Equation where we briefly review it in chapter 1. Similar idea has found many applications in other finance literatures and we will focus on its application to the high-frequency trading using limit orders in this thesis. In [1], major analysis using the constant volatility arithmetic Brownian motion stock price model with exponential utility function is described. We re-analyze the solution of HJB equation in this case using different asymptotic expansion. And then, we extend the model to the regime-switching volatility model to capture the status of market more accurately.

One of the most famous problem of finding optimal weight to maximize an agent's expected terminal utility in finance literature is Merton's optimal portfolio problem. Classic solution to this problem is given by stochastic Hamilton-Jacobi-Bellman Equation where we briefly review it in chapter 1. Similar idea has found many applications in other finance literatures and we will focus on its application to the high-frequency trading using limit orders in this thesis. In [1], major analysis using the constant volatility arithmetic Brownian motion stock price model with exponential utility function is described. We re-analyze the solution of HJB equation in this case using different asymptotic expansion. And then, we extend the model to the regime-switching volatility model to capture the status of market more accurately.

A class of hippocampal interneurons in CA1, bordering the lacunosum-moleculare and radiatum hippocampal layers (the LM/R cell), has been shown to exhibit membrane potential oscillations (MPOs) subthreshold to action potential generation. MPOs occur at theta frequency (4-12 Hz) and are of interest because of their putative role in promoting network level theta activity. MPOs arise without synaptic input suggesting that they originate through interactions in the cell’s repertoire of currents. To investigate the generation of MPOs we develop a single compartment model of the cell based on the physiological characterization of its currents. The model includes both deterministic current models and white noise. Our analysis allows for a complete characterization of the cell’s dynamics over the subthreshold range and shows that MPOs arise through the interaction between current dynamics and system noise. We find that MPOs show a particular dependency on the A-type potassium and persistent sodium current magnitudes.

Surface properties of polymers and competition adsorption of toluene and heptane on silica were studied using IR-visible sum frequency generation (SFG) vibrational spectroscopy. SFG is intrinsically surface sensitive because the second-order optical process is forbidden in media with inversion symmetry, such as bulk polymers and liquids. This nonlinear optical technique provides surface vibrational spectra under ambient conditions without the need of an ultra-high vacuum environment. Polymer surface properties, including surface relaxation temperature of poly(methyl methacrylate) (PMMA) and surface electronic states of poly[2-methoxy, 5-ethyl (2’-hexyloxy) para phenylenevinylene] (MEH-PPV), were investigated. It was found that there are significant differences between the surface and bulk properties for these polymers. For PMMA, a new surface structure relaxation was identified at 67°C, which does not match any known structure relaxation temperatures for bulk PMMA and is 40°C below the bulk glass transition temperature. For MEH-PPV, SFG electronic spectra, which were obtained by scanning the frequencies of incident visible and JR beams, indicated that the electronic states at the polymer/solid and air/polymer interfaces are red-shifted with respect to that of the bulk. Finally, SFG was employed to study the competition adsorption of toluene and heptane on silica surfaces. Experimental data showed that heptane adsorbed favorably compared to toluene. Using a Langmuir adsorption isotherm, the changes of Gibbs free energy for the adsorption processes were calculated to be —12.1 ± 1.8 (kJ/mol) for toluene and —16.5 ± 2.3 (kJ/mol) for heptane.

The present work contributes to the ongoing discussion of the factors involved in perfecting foreign language learning through a close examination of vocabulary use. Motivated by Laufer’s (1991) argument that the use of less frequent vocabulary items is a sign that a language learner is approximating the lexical competence of a native speaker, I set out to model Laufer and Nation’s (1995) study that assessed lexical frequency. The first goal of this work was to assess the usefulness of the lexical frequency profile (Laufer and Nation, 1995) in evaluating written texts produced by learners of German. This lexical frequency profile had mostly been used to examine vocabulary use of learners of English. Instead of using frequency bands of German, this work relied on three generated word frequency lists. The second goal of this work was to examine how the language repertoire of aspiring bilinguals varies at the lexical level by comparing vocabulary use at three competency levels (Introductory German I, II and Intermediate German). The analysis revealed that the lexical frequency profile is a valuable tool for evaluating lexical use by language learners, although the tool was difficult to adapt for research of texts in German. Furthermore, learners in all three courses relied heavily on vocabulary from learning materials used in their courses, and they were more likely to use less frequent words as they progressed from the introductory to the intermediate language course.

No description available.

The present work contributes to the ongoing discussion of the factors involved in perfecting foreign language learning through a close examination of vocabulary use. Motivated by Laufer’s (1991) argument that the use of less frequent vocabulary items is a sign that a language learner is approximating the lexical competence of a native speaker, I set out to model Laufer and Nation’s (1995) study that assessed lexical frequency. The first goal of this work was to assess the usefulness of the lexical frequency profile (Laufer and Nation, 1995) in evaluating written texts produced by learners of German. This lexical frequency profile had mostly been used to examine vocabulary use of learners of English. Instead of using frequency bands of German, this work relied on three generated word frequency lists. The second goal of this work was to examine how the language repertoire of aspiring bilinguals varies at the lexical level by comparing vocabulary use at three competency levels (Introductory German I, II and Intermediate German). The analysis revealed that the lexical frequency profile is a valuable tool for evaluating lexical use by language learners, although the tool was difficult to adapt for research of texts in German. Furthermore, learners in all three courses relied heavily on vocabulary from learning materials used in their courses, and they were more likely to use less frequent words as they progressed from the introductory to the intermediate language course.