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Design And Fabrication Of Passive Cooling Materials For Sustainable Solar Energy And Building Applications
No full textConventional cooling technologies not only consume substantial energy but increase the heat-trapping gases in the atmosphere. Passive cooling technologies such as radiative cooling and building envelope require little or no additional power input. Thus, they offer the most promising alternatives to address the ever-hot planet by efficiently reducing the energy consumption without adverse environmental impacts. In this dissertation, I have developed two types of passive cooling materials, including solar transparent and mid-infrared (MIR) radiative cooling mesoporous silica nanoparticles (MSNs) and kirigami-based dynamic shading envelope, for solar cells and building applications, respectively. The thermal stress decreases the photovoltaic performance and long-term stability because it induces critical and irreversible damage to the materials of the devices. Conventional cooling methods have been used to decrease the temperature of solar cells. However, they increase the cost because of the external energy input or increase in the system complexity. Here, I develop the innovative radiative cooler to efficiently decrease the temperature of perovskite solar cells (PSCs). In this part, MSNs of different pore diameters are synthesized to fine-tune the refractive index. The diameter of MSNs is controlled by pH, temperature, and reaction time. To manipulate pore diameter and volume, the ratio of the swelling agents and surfactants is controlled. MSNs with different pore diameters are stacked by solution process to fabricate the graded refractive index (GRI) structure on the PSCs, which shows high transmission in the solar wavelength region and high emission in the MIR region. The outdoor test over 20 days shows little change of the crystal structures of the perovskite, methylammonium lead iodide (MAPbI3), or change of the solar performance, whereas that without the coating is completely degraded. This strategy may open the new possibility for efficient cooling of PSCs. In the second approach, I fabricate kirigami-based dynamic shading envelopes with linear cuts from polyethylene naphthalate (PEN) film and analyze the light management of them in the real working condition. The interspace between the cutting lines is varied to fine-tune the degree of the opening of the envelope. Due to different interspaces and variable strains, kirigami envelopes with different opening gap areas are obtained to modulate the amount of light entering the building. The simulation is performed to investigate the effect of kirigami based dynamic envelope on light modulation and hence temperature inside the space. Well-controlled measurement system and in-depth simulation result in high consistency between experimental and simulation data, within the acceptable level (±1.6 oC). This work suggests that kirigami structures have great potentials in the building energy savings
A House’s Speech Divided: Novel Applications Of Text-As-Data For The Study Of Elite Polarization In The U.s. House Of Representatives (1983-2016)
Get PDFCurrent models of elite polarization imply that the behaviors and ideologies of Democrats and Republicans have become increasingly distinct. The congressional roll-call voting record is the most relied-on indicator of congressional polarization, however, voting behavior is limited in its scope, ability to provide deeper insights into the nature of elite polarization, and can be affected by external non-ideological factors. This dissertation leverages the richness of the congressional record and introduces a flexible computational method, the dynamic topic model, to study three unique but related indicators of political polarization across three decades of debate from the floor of the House of Representatives (1983-2016). Using the output of the dynamic topic mode – and through the lens of political communication – this dissertation reveals patterns of increasing polarization in not only what Democrats and Republicans talk about, but also how political issues are discussed. Furthermore, this dissertation interrogates elite ideologies through belief network analysis and finds that the networks of political beliefs held by Democrats and Republicans have not significantly diverged since 1983. This dissertation introduces a novel approach to the study of political polarization in Congress and provides three applied use-cases for studying political polarization through text-as-data and relevant quantities to political communication
The Role Of The T Cell Repertoire In Response To Cancer Immunotherapy
No full textThe advent of immune checkpoint blockade (ICB) and other immunotherapies has been a watershed in the evolution of cancer care. Despite these recent breakthroughs, many patients fail to respond to these therapies or relapse after treatment. Recent studies suggest that the availability of effective anti-tumor T cells is limited by cancer immunoediting, which depletes neoantigens that can be recognized by the immune system. Central tolerance further constrains the tumor-specific T cell repertoire by eliminating T cells with high-affinity T cell receptors (TCRs) against potential tumor self-antigens. Self-antigen specific T cells that escape elimination often succumb to exhaustion after ICB; however, whether high-affinity self-reactive T cells could be effectively mobilized to reject ICB refractory tumors is unknown. Through these studies, we test the hypothesis that treatment with a receptor activator of nuclear factor-κB ligand (RANKL) blocking antibody temporarily disrupts central tolerance leading to the rescue of high-affinity self-reactive T cells that enhance ICB response against neoantigen-poor tumors. We find that transiently interrupting central tolerance through RANKL blockade enabled ICB to durably reject poorly immunogenic tumors. Rejection of ICB refractory B16 melanoma was mediated by CD8 T cells specific for TRP2, a melanoma self-antigen, and coincided with “on-target” autoimmune vitiligo. Murine studies coupled with TCR repertoire analysis revealed that RANKL blockade facilitated the mobilization of a novel population of MFI-high TRP2 tetramer+ CD8 T cells, indicating increased TCR avidity for self-antigen. TRP2 tetramer-high CD8 T cells enriched after RANKL blockade exhibited enhanced TCR signaling, enrichment in NFAT/AP-1 genes, and increased lymph node expansion. In addition, memory-precursor and effector-memory T cells against tumor self-antigens were generated and exhibited transcriptional features associated with clinical ICB response. Furthermore, RANKL blockade enhanced other immunotherapies for cancer, such as therapeutic and prophylactic vaccination. We conclude that RANKL blockade potentiates cancer immunotherapies by expanding the T cell repertoire against tumor self-antigens and thus, facilitates the rejection of otherwise immunotherapy refractory tumors
Disentangling The Reciprocal Causal Relationship Between Political Efficacy And Sharing Traditional And Humorous Political Information
No full textA reciprocal relationship purportedly exists between political efficacy, one’s belief in their ability to effectively participate in democratic activities, and news sharing, such that greater political efficacy may lead to greater news sharing, which might then cultivate or reinforce political efficacy. In this dissertation, we deployed short interventions using online surveys to test whether manipulating political efficacy influences news sharing intentions, and whether manipulating news sharing behavior influences individual political efficacy. We also explore the relationship between news sharing and collective political efficacy, or the perceived belief in the abilities of American citizens to effectively organize for political action. Further, political humor and satire currently occupies a significant media space as an accessible and shareable format of political news information. We deepen our analysis by testing the influence of political humor on the causal relationships between political efficacy and news sharing. In this dissertation, we present findings from three online survey experimental studies. In Study 1 (N=517), building on the idea that political efficacy can be developed by successful personal experiences of political participation, we examined the effect of civic values-based affirmation, Civic Affirmation on increasing political efficacy. In Study 2 (N=397), we tested the intended manipulation of political efficacy via Civic affirmation, on news sharing. Here, we also manipulated humor by sourcing news videos from both traditional news and news comedy programming. Lastly, in Study 3 (N=459), we tested the effect of news sharing and humor on political efficacy. Here, we manipulated news sharing by asking participants to select videos from lists of news videos to share with other participants. Results show that Civic Affirmation led to greater collective political efficacy and news sharing intentions as compared to traditional values-based affirmation, and that sharing news with others did not lead to greater political efficacy. Further, individuals who were not assigned any treatment showed greater collective political efficacy than those who were assigned affirmation tasks, news video sharing or description tasks. These findings suggest further investigation in the role of collective political efficacy on political engagement, and revisiting the role of short psychological interventions in developing civic attitudes and behaviors
Concomitant Suppression Of Both Cox-1 And Cox-2 Is Not Sufficient To Cause Gastroenteropathy Associated With Chronic Nsaid Use
No full textNonsteroidal anti-inflammatory drugs (NSAIDs) are the most widely used nonaddictive medications for the management of chronic pain and inflammation; however, these drugs are associated with many gastrointestinal and cardiovascular adverse events, including intestinal bleeding, ulceration, stenosis, myocardial infarction, and stroke. It has long been accepted that NSAID enteropathy is an unavoidable consequence of simultaneously inhibiting both cyclooxygenases (COX) -1 and -2 to suppress prostaglandin synthesis. Operating under this assumption, I had developed a novel mouse model of inducible COX-1 + COX-2 deletion to complement our lab’s chronic NSAID exposure model. These COX double-knockout mice exhibited substantially suppressed prostaglandin levels comparable to (and often lower than) those of wildtype mice treated with the nonselective NSAID naproxen. Yet surprisingly, the COX double-knockouts never spontaneously developed any gastrointestinal damage when tracked for an entire year, whereas the naproxen mice consistently exhibit gastric and intestinal lesions and bleeding within 3 weeks. Moreover, upon administering naproxen to the COX double-knockout mice, they do develop gastroenteropathy, despite lacking the intended drug target and exhibiting no change in prostaglandin levels from baseline. The same pattern is observed when these mice are treated with phenylpropionic acid, a compound that bears a similar structure to naproxen yet has no COX activity. These results challenge the prevailing dogma that attributes NSAID enteropathy to prostaglandin inhibition, robustly demonstrating that prolonged suppression of prostaglandin synthesis alone is not sufficient to induce gastrointestinal damage. Rather, mechanisms specific to the drug (including topical irritation of the intestinal epithelium, mitochondrial dysfunction, enterohepatic recirculation, and prolonged exposure to bile acids) appear to be required as the dominant insult or a double-hit. With a better understanding of how NSAIDs elicit intestinal damage, these studies ultimately aim to improve enteric NSAID tolerance in patients. They may afford insights that allow for the design of safer pharmaceuticals or drug combinations that widen the therapeutic index of a commonly consumed class of drugs
Effects of Inter-Molecular and Intra-Molecular Factors on the Properties of Simulated Glasses
No full textGlasses of small organic molecules are a ubiquitous material type of wide interest due to their unique amorphous packings. However, their properties can vary widely based on preparation method, aging time, or type of molecule. Stable glasses, prepared via physical vapor-deposition, have been shown to exhibit properties equivalent to those that been aged for thousands of years. Molecular dynamics simulations of coarse-grained molecules provide a simple model for closely examining the relevant properties of glasses, both traditionally liquid-quenched and vapor-deposited. In this dissertation, several projects are presented focusing on systematic changes to inter-molecular interactions and intra-molecular degrees of freedom and how they impact glass properties in silico. In Chapter 2, we study the effects of inter-molecular interactions and microstructure formation on vapor-deposited glass films, using a coarse-grained model of molecules with fluorinated tails. By altering the length of the tail, we can tune the degree of microstructure formation, and we observe how this affects vapor-deposited glass stability, while also proposing, and supporting a mechanism for this behavior. In Chapter 3, models of organic molecules are developed focusing on the strength of the rotational barriers placed on their side groups in order to study intra-molecular degrees of freedom. Here we see the effect this has on vapor-deposited glass stability and make connections to surface mobility and the depth of the mobile region. In Chapter 4, vapor-deposited and liquid-quenched glasses are tested for their mechanical response to shear. The large differences in their properties, as well as the length scales over which they take place, are correlated with local particle mobility. Finally, in Chapter 5, the same molecular models are used to tune fragility behavior. The machine-learned structural property, softness, is implemented for a molecular system for the first time and provides new insight into the origins of glass fragility
Considering the Relationship between Student Satisfaction and Student Engagement on Retention and Completion in Higher Education Institutions
No full textResearch has shown that students who are satisfied with college and more engaged on campus are more likely to graduate (Astin, 1993; Kuh et al., 2008; Pascarella & Terenzini, 2005; Schreiner & Nelson, 2013). Thus, investing in programs or services to engage students and increase satisfaction has been a focus of some institutions (Kezar et al., 2015, 2020; McClure, 2019; Webber, 2018). Despite this, little is known about how the relationship between satisfaction/engagement and completion varies across important contexts, including student subgroups (race, socioeconomic status, or academic ability) or institutional types (level or control), or about how these relationships vary when using simple measures of satisfaction and engagement. Utilizing a sample of approximately 22,500 students in the Beginning Postsecondary Students Longitudinal Study (BPS) 12:17 cohort, I use a multivariate linear regression to provide an updated and more nuanced understanding the relationship between satisfaction and engagement and students’ retention and ultimate degree attainment. Results suggest that the relationship between satisfaction and engagement with retention and completion is stronger for certain student and institutional subgroups
Cognitive Processes in L2 Vocabulary Acquisition: Exploring the Effects of Four Online Vocabulary Tasks for Learners of Different Proficiency Levels
No full textThis study investigates the effects of four online vocabulary tasks on second language (L2) vocabulary acquisition among learners of different proficiency levels. While tasks are widely used to support L2 vocabulary learning, the efficacy of a task depends on the interplay between task and learner factors. Thus, choosing an appropriate task requires not only identifying the task features which may foster cognitive processes that contribute to learning, but also considering how the effects of such features may be moderated by factors outside of the task. The present study aims to provide insights into this issue by exploring the effects of various task features on L2 vocabulary acquisition and the potential moderating role of one learner factor, L2 proficiency. Drawing from the involvement load hypothesis (ILH) and technique feature analysis (TFA), four instructional tasks which varied in their inclusion of features believed to facilitate vocabulary learning were selected for the study: (a) sentence writing (SW), (b) fill-in-the-blank (FIB), (c) fill-in-the-blank with pictures and audio (FIB+PA), and (d) word study with pictures and audio plus fill-in-the-blank (WS+PA+FIB). A total of 75 participants with high intermediate or advanced proficiency in English were randomly assigned to complete one of the four instructional tasks or a control task online. Participants’ vocabulary knowledge was measured through a modified version of the Vocabulary Knowledge Scale (VKS) and a multiple-choice recognition test from which meaning recall, meaning recognition, and total VKS scores were obtained. Findings from multiple regression analyses and ANOVAs indicated that in general, the instructional tasks led to greater learning gains than the control task. Furthermore, among the instructional tasks, SW and WS+PA+FIB tended to be more effective than FIB and FIB+PA in promoting vocabulary learning. However, there was also evidence that the effects of the tasks were moderated by L2 proficiency, as SW and FIB effects were found to be more salient for advanced learners. These results are interpreted from the perspective of different cognitive processing theories, and the implications for L2 vocabulary acquisition theory and pedagogy are discussed
How Does She Do It? Strategies Used and Challenges Faced by Unmarried Student Mothers Enrolled in U.S. Four-Year Universities.
No full textOne in five undergraduate students in the United States is also a parent raising at least one child (Gault et al., 2014), but few will complete a bachelor’s degree within six years. Using Greene’s (2014) Ecological Resiliency Model as a conceptual framework, this phenomenological study examines the persistence of 38 single mothers in the latter half of an undergraduate program at a four-year university. Each woman was in a unique context and with her own particular life experience, but three themes were common across all participants: a clear motivation to achieve economic gains for themselves and their children; the experience of some form of unseen identity; and varying degrees of challenges with single mother stereotypes. Their persistence strategies were dynamic, adaptive management approaches with their own tactics, drawing on various supports over time. Three key supports were university programs, workplace flexibility, and social networks. Without them, participants were more likely to express concerns about meeting fundamental household needs, feelings of loneliness and isolation, and stress over role challenges. Universities should support the growing category of students who are also single mothers as part of their diversity, equity, and inclusion plans
Mechanical Properties of Fibrous Network Materials
No full textWe discuss mechanical behavior of specific fibrous network materials, including the evolution of tension in fibrin clots, compression of pulmonary emboli, and fracture of Whatman filter paper. The first material, fibrin clots, consist of random networks of fibrin fibers. When clots form by polymerization they develop tensile pre-stresses. We construct a mathematical model for the evolution of tension in isotropic fibrin gels. As the fiber diameter grows over time, properties which depend on it, such as the stored energy per unit length of a single fiber, the force-stretch relation of a fiber, and therefore the tension in the network as a whole, also evolve over time. The second fibrous network is pulmonary emboli, which consist of random networks of fibrin fibers with fluid-filled pores and red blood cells (RBCs). Stress-strain responses of human pulmonary emboli under cyclic compression were measured, revealing that emboli exhibit hysteretic stress-strain curves characteristic of foams. We describe the hysteretic response of emboli using a model of phase transitions, in which the compressed embolus is segregated into coexisting rarefied and densified phases whose fractions change as compression progresses. Our model takes into account RBC rupture in compressed emboli and stresses due to fluid flow through their small pores. The mechanical response of emboli is shown to vary depending on their RBC content. The third fibrous network is Whatman filter paper. The effect of humidity on properties such as out-of-plane fracture toughness of Whatman filter paper is studied for a broad range of relative humidities. Crack growth is modeled using traction-separation laws, whose parameters are fitted to experiments. Additionally, a novel model is developed to capture the high peak and sudden drop in the experimental force measurement caused by the existence of an initiation region, an imperfect zone ahead of a nascent crack. The relative effect of each independent parameter is explored to better understand the humidity dependence of the traction-separation parameters. The materials studied have biological, clinical, and industrial applications, and the methods described here are also applicable to other fibrous network materials