-
Prospective Students
-
Faculty and Staff
-
Current Students
-
Alumni and Friends
Rock weathering, or the mechanical and chemical breakdown of rock over time, creates the landscape on which all terrestrial life is built. Here, I quantify the rates and controls over mechanical weathering [rock cracking/fracturing] f surficial boulder deposits in Eastern California using by collecting rock and crack field measurements, clast size distribution data from the field, and rock elastic properties using laboratory testing. I used a chronosequence or space-for-time approach, whereby data are collected from rocks or sediments that have been exposed to natural weathering conditions for a range of times, using the properties of the stable deposits to represent the amount of weathering that occurs over the time span of exposure. I studied rocks at three sites, with rocks being exposed to Earth surface conditions from 0 to 148,00 years [148 ka].
I manually measured 8763 crack lengths, widths, and orientations from 2221 in situ boulders on Earth’s surface and found that that rock cracking is initially fastest when rocks are exposed to Earth’s surface conditions, with rocks accumulating cracks at a rate of 9-1502 mm of cracks per m^2 rock surface over a thousand years, or 0.1-36 individual cracks per m^2 rock surface over a thousand years. After this point, rocks continue to crack, but the rate of crack growth slows down. After about 30 ka, the growth rate is <36 mm of cracks/m^2 of rock surface per ka, or <1 individual cracks/m^2 of rock surface per ka. Using all rock and crack data I determined that age itself has the most consistent, positive, statistically significant correlation with the number of fractures per rock surface area [fracture number density] and the total length of fractures measured per rock surface area [fracture intensity].
From two sites, I collected a granitic boulder from each dated deposit for rock mechanics testing. These data show that rock compliance increases over time while mechanical weathering leads to an increase in microscale cracks, which alter the rock’s strength and elastic strain response under stress. Using the laboratory analyses and local weather station data, I implemented a simple daily stress model applying Paris’ law of subcritical crack growth to predict single crack growth after each day of weather conditions, for a period of 5000 years. Cracking occurred over only a limited number of unusually intense weather days when the daily range of air temperatures was the largest. In the two semi-arid sites, these cracking days were hot, dry summer days; in the arid site, the day when the most crack growth was predicted coincided with summer monsoonal rains. The model is highly sensitive to rock elastic properties, which supports the theory that a gradual increase in bulk compliance allows rocks to withstand stress without cracking over thousands of years.
Finally, I present clast size data to show that for volcanic and carbonate rocks, there is a correlation between the geometry of cracking observed on the rocks and the shape of sediments on older deposits: when many cracks are parallel to the rock surface, older deposits tend to have more flattened rocks on them. This shows that cracking rates and crack geometries can play a strong role in clast size and shape evolution over geologic time, and mechanical weathering should be considered when interpreting sediments in the geologic record.
These findings are directly applicable to geoscientists attempting to understand weathering, landscape evolution, and geological hazards. More broadly, the decreasing rock cracking rates that accompany slow mechanical property changes represent a real-world example of material fatigue vs. material failure.
In linear dynamics, bounded linear operators over infinite-dimensional Banach spaces have been shown to be able to exhibit interesting characteristics including topological transitivity, topological mixing, and even chaos in the sense of Devaney. This dissertation will examine weighted l^p sequence spaces together with the shift action as the operator. In the case the shift action is over the semi-group N, the above topological properties have been previously characterized by conditions on the weight sequence associated with a given weighted l^p space. This work will present recent results for new characterizations of these properties when the group action over a countable group is instead considered. Additionally, an example choice of the weight sequence in this setting will be presented which yields points which are periodic while having an infinite orbit.
Lastly, new implications for infinite and 0 topological entropy for the weighted l^p space with the shift action over N will be given. In particular, when the weight sequence is summable over a subset of N with positive upper density then infinite entropy may be achieved. Furthermore, when an arbitrary ratio of the weights is bounded above then 0 entropy is guaranteed.
In recent years, there has been an increase in attacks, including advanced persistent threats (APTs), and the techniques used by the attacker in these attacks have reached unprecedented sophistication. Threat hunters use various monitoring tools to monitor and collect all these attack actions (which blend in with benign user activities) for cyber threat hunting—the end devices store monitored activities as generated logs/events. Moreover, Organizations like NIST and CIS provide guidelines (CSC) to enforce cyber security and defend against those attacks.
Although the end hosts and networking devices can record all benign user and adversary actions, it is infeasible to monitor everything. In existing approaches, high memory usage and communication overhead to transfer events to the central server create scalability issues on the monitored network. Single event matching on the end-host devices approach to detect attacks generates false alerts, causing the alert fatigue problem. This dissertation presents a distributed hierarchical monitoring agent architecture to overcome those limitations of existing tools and research works.
Additionally, there are no well-defined automated measures and metrics to validate the enforcement of CSC. Manually analyzing and developing measures and metrics to monitor and implementing those monitoring mechanisms are resource-intensive tasks and massively dependent on the security analyst's expertise and knowledge. To tackle those problems, we use LLM as a knowledge base and reasoner to extract measures, metrics, and monitoring mechanism implementation steps from CSC descriptions to reduce the dependency on security analysts with the help of few-shot learning with chain-of-thought prompting. This dissertation presents CSC enforcement assessment with the help of our distributed hierarchical monitoring agent architecture and prompt engineering.
The orbital angular momentum of light is a promising candidate as an information carrier in optical communication systems to enhance the capacity of data channels. However, the effects of atmospheric turbulence significantly degrade the quality of light beams, thereby imposing limitations on the range of reliable data transmission. To address this issue, researchers have been actively seeking methods to enhance the resilience of light against fluctuations of refractive index due to the atmospheric turbulence. It has long been recognized that partially coherent beams exhibit greater robustness in propagation through turbulence. Consequently, transitioning from full coherence to partial coherence has been suggested as a solution. Conversely, in OAM-based communications, reducing coherence results in broadening of the OAM spectrum, thus increasing cross-talk between adjacent channels. Therefore, utilizing partially coherent beams in free space communications entails both Benefits and drawbacks.
The main objective of this dissertation is to explore various classes of partially coherent beams through analytical approaches in order to identify a robust OAM spectrum in the presence of atmospheric turbulence. The results are presented in three different articles. The first article introduces a simplified version of the extended Huygens-Fresnel principle which is a widely used method of turbulence propagation. The discoveries outlined in the first article substantially alleviate the mathematical complexity associated with propagation in random media, thereby enabling analytical exploration of the propagation of partially coherent beams in random media.
The second article presents an optimization criterion associated with a specific class of partially coherent beams, substantially enhancing their resistance against turbulence. Finally, the third article thoroughly investigates the behavior of three categories of partially coherent beams in interaction with atmosphere, providing a detailed comparison of their respective resistance. The compilation of these three articles presents a comprehensive study of the impact of atmospheric fluctuations on the orbital angular momentum spectrum of partially coherent beams.
The orbital angular momentum of light is a promising candidate as an information carrier in optical communication systems to enhance the capacity of data channels. However, the effects of atmospheric turbulence significantly degrade the quality of light beams, thereby imposing limitations on the range of reliable data transmission. To address this issue, researchers have been actively seeking methods to enhance the resilience of light against fluctuations of refractive index due to the atmospheric turbulence. It has long been recognized that partially coherent beams exhibit greater robustness in propagation through turbulence. Consequently, transitioning from full coherence to partial coherence has been suggested as a solution. Conversely, in OAM-based communications, reducing coherence results in broadening of the OAM spectrum, thus increasing cross-talk between adjacent channels. Therefore, utilizing partially coherent beams in free space communications entails both Benefits and drawbacks.
The main objective of this dissertation is to explore various classes of partially coherent beams through analytical approaches in order to identify a robust OAM spectrum in the presence of atmospheric turbulence. The results are presented in three different articles. The first article introduces a simplified version of the extended Huygens-Fresnel principle which is a widely used method of turbulence propagation. The discoveries outlined in the first article substantially alleviate the mathematical complexity associated with propagation in random media, thereby enabling analytical exploration of the propagation of partially coherent beams in random media.
The second article presents an optimization criterion associated with a specific class of partially coherent beams, substantially enhancing their resistance against turbulence. Finally, the third article thoroughly investigates the behavior of three categories of partially coherent beams in interaction with atmosphere, providing a detailed comparison of their respective resistance. The compilation of these three articles presents a comprehensive study of the impact of atmospheric fluctuations on the orbital angular momentum spectrum of partially coherent beams.
This dissertation explores employee voice behaviors, specifically promotive voice and prohibitive voice. Literature acknowledges that employee voice behaviors are primarily measured at the individual level. However, there is a need for more research on employees' experiences or the potential influence that supervisors have on employees' voices (promotive and prohibitive) through actions such as supervisor incivility. Drawing from Conservation of Resource theory and the resource of Psychological Safety as the theoretical framework. This study reviews the interaction of experiences such as employee resiliency, threats to employee identity, and employee voice behaviors with moderating effects of supervisor incivility. A sample size of employees (N= 294) provides support for the relationship between employee resiliency and promotive voice behaviors. In addition, the study provides insights on practical implementation and future research in academia.
Large cohort studies under simple random sampling could be prohibitive to conduct with a limited budget for epidemiological studies seeking to relate a failure time to some exposure variables that are expensive to obtain. In this case, two-phase studies are desirable. Failure-time-dependent sampling (FDS) is a commonly used cost-effective sampling strategy in such studies. To enhance study efficiency upon FDS, counting the auxiliary information of the expensive variables into both sampling design and statistical analysis is necessary.
In survival analysis, it's commonly assumed that all subjects in a study will eventually experience the event of interest. However, this assumption may not hold in various scenarios. For example, when studying the time until a patient progresses or relapses from a disease, those who are cured will never experience the event. These subjects are often labeled as ``long-term survivors'' or ``cured'', and their survival time is treated as infinite. When survival data include a fraction of long-term survivors, censored observations encompass both uncured individuals, for whom the event wasn't observed, and cured individuals who won't experience the event. Consequently, the cure status is unknown, and survival data comprise a mixture of cured and uncured individuals that can't be distinguished beforehand. Cure models are survival models designed to address this characteristic.
Chapter~2 discusses the semiparametric inference for a two-phase failure-time-auxiliary-dependent sampling (FADS) design that allows the probability of obtaining the expensive exposures to depend on both the failure time and cheaply available auxiliary variables. Chapter~3 considers the generalized case-cohort design for studies with a cure fraction. A few directions for future research are discussed in Chapter~4.
Scholars are particularly interested in understanding effective strategies to turn around business performance as businesses experience periods of decline. As the COVID-19 pandemic has revived the importance of better understanding effective turnaround strategies within organizations, additional research is needed to support businesses as they work to recapture or exceed pre-decline performance. This dissertation's research model suggests that operational and strategic turnaround responses have a relationship with firm performance. It is empirically tested using data collected from 98 top management team members across the United States regarding the operational and strategic turnaround responses implemented to combat the decline caused by COVID-19. The results show that strategic turnaround responses positively impacted firm performance. These findings have practical as well as theoretical implications that suggest the type of turnaround response needed in times of future global phenomena.
The effects of safe sex practice education on knowledge and attitudes among college students. (Under the direction of DR. KATHLEEN JORDAN)
Introduction: Sexual health education is crucial in reducing the burden of STIs among young adults. Comprehensive sexuality education can lead to positive risk reduction outcomes, such as delayed initiation of sex, a decreased number of sexual partners and frequency of sex, and increased use of contraceptives. The purpose of this study was to evaluate the effectiveness of an educational program focused on sexually transmitted infections (STIs) and safe sex practices among college students who are Greek life members. The intervention aimed to enhance the knowledge and attitudes of these students regarding sexual health and promote healthier sexual behaviors. This project is significant as it endeavors to fill the gap in existing literature concerning the effectiveness of sexual health education in college populations who are at heightened risk for STIs.
Design/Methods: The study utilized a pre-post intervention quantitative design. A convenience sample of 23 sorority and fraternity members aged 18-24 participated in the study. The intervention included an educational session focusing on aspects of sexual health, including transmission, screening, prevention of STIs, as well as safe sex practices. Participants were surveyed before and after the educational intervention using the STD Knowledge Questionnaire (STD-KQ).
Results: Of the 55 Greek life members who completed the pre-test, 23 completed the post-test. A paired-sample t-test showed that there was a statistically significant difference in STD-KQ scores pre- and post-intervention, t(22) = 4.51, p < .001, 95%CI [3.36, 9.08]. The average STD-KQ scores significantly increased from 8.65 ± 5.69 pre-intervention to 14.87 ± 5.69 post-intervention, indicating a significant improvement in STI knowledge and attitudes among the participants after the educational program. Additionally, most respondents reported an increased likelihood of using condoms during sexual activity post-intervention. Additionally, the respondents also reported an increased awareness of STDs and safe sex practices.
Discussion:
The findings highlighted the positive impact of targeted sexual health education in a university setting, especially within the Greek life community. These results underscored the need for universities and health educators to prioritize and integrate sexual health education within the curriculum. Lastly, the study also supports adopting a structured, informative approach to improve students’ awareness and practices regarding STI prevention.
ABSTRACT
CHRISTINE SISK. Effectiveness of Cardiac ERAS Multimodal Analgesia on Perioperative Pain in Adult Cardiac Surgery Patients. (Under the direction of Dr. KATHLEEN JORDAN)
Cardiac surgeries often rely on opioid analgesics, which can lead to adverse effects. The implementation of the multimodal analgesic approach, as a part of the ERAS protocol, has the potential to optimize intra- and postoperative pain management, leading to reduced opioid-related complications and improved patient outcomes. The purpose of this study was to evaluate the efficacy of multimodal analgesia within a Cardiac Enhanced Recovery After Surgery (ERAS) program in reducing postoperative pain and opioid consumption in adult cardiac surgery patients. This study compared the effects of cardiac ERAS multimodal analgesia against traditional opioid-based analgesia on postoperative pain and opioid consumption during the operation and the initial 24 hours postoperative.
The study was conducted at a level-one trauma center that had recently implemented the ERAS protocol on all cardiac surgical patients. Data was collected retrospectively from patients undergoing cardiac surgeries before and after the protocol’s implementation. The pre-ERAS group received traditional opioid-based analgesia, while the ERAS group received the ERAS multimodal analgesia protocol.
Data analysis revealed significantly lower intraoperative opioid consumption in the post-ERAS group compared to the pre-ERAS group (U = 1496.00, p = .026, z = -2.30). However, no statistically significant differences were observed in opioid consumption between the groups at 6 hours and 24 hours postoperatively. These findings suggest the ERAS protocol’s effectiveness in reducing intraoperative opioid requirements but limited impact on postoperative opioid consumption within the first 24 hours.
The study demonstrates that cardiac ERAS multimodal analgesia can effectively reduce intraoperative opioid consumption, highlighting its potential as a valuable component of perioperative pain management in cardiac surgery. While the findings did not show a significant reduction in postoperative opioid use, implementing such protocols can still offer benefits for patient care. This includes reducing opioid-related adverse effects and potentially improving patients’ overall recovery. Further research is needed to explore the longer-term impacts of multimodal analgesia on postoperative opioid consumption and patient outcomes in cardiac surgery.
