Browsing by Subject "Polarization"

The Rho GTPase Cdc42 is a master regulator of cell polarity that orchestrates reorganization of the cytoskeleton. During polarity establishment, active GTP-Cdc42 accumulates at a part of the cell cortex that becomes the front of the cell. Localized GTP-Cdc42 orients the cytoskeleton through a set of “effector” proteins that bind specifically to GTP-Cdc42 and not GDP-Cdc42. A family of Cdc42 effectors, called GICs in yeast and BORGs in mammals, have been implicated in regulation of both the actin cytoskeleton and the septin cytoskeleton. Yeast cells lacking both Gic1 and Gic2 are able to polarize and grow at low temperatures, but many mutant cells fail to polarize the cytoskeleton at high temperature. This led to the conclusion that GICs communicate between Cdc42 and different cytoskeletal elements.

To better characterize the role of GIC proteins in yeast, we utilized time-lapse fluorescent microscopy to examine morphogenetic events in living single cells. Surprisingly, we found that not only the cytoskeleton but also Cdc42 itself failed to polarize in many gic1 gic2 mutant cells at high temperature. This observation indicates that GICs may act upstream of polarization rather than downstream.

Polarization of Cdc42 is triggered by cell-cycle progression, and in particular by G1 Cyclin-dependent kinase (CDK) activity. Using a live-cell reporter for G1 CDK activation, we found that cells lacking GICs were not defective in CDK activation, but showed a specific defect in polarization downstream of the CDK. Previous work had implicated the scaffold protein Bem1 in a positive feedback loop important for polarization. Cells lacking GICs failed to polarize Bem1 as well as Cdc42 at high temperature. Future work will be directed at understanding how GICs contribute to polarity establishment. Because many of the mechanisms and proteins involved in polarization are highly conserved, we anticipate our findings will help inform how this process regulated in higher eukaryotes.

The three papers in this dissertation seek to measure more accurately critical concepts in the field of American political institutions so as to inform and enable theory-building. The first paper addresses committee prestige in the U.S. House of Representatives, arguing that the seniority of members transferring off of standing committees reveals important information about the relative prestige of those committees. In response, I import a measure called PageRank which enables me to exploit information on seniority while measuring committee prestige. I then demonstrate that the prestige of a legislator's committee portfolio predicts the political action committee (PAC) contributions she receives for the next campaign cycle. A second paper tackles the theoretical possibility that majority parties may manipulate their control over committee assignments for partisan goals, countering a vast literature which has generally failed to find evidence of partisan manipulation across stage legislatures. I argue that several theoretical and practical constraints render universal stacking impractical and introduce a new measure of partisan stacking called "seats above expectation" (SAE); I find little evidence of universal partisan (or ideological) stacking in state legislatures. I then argue that majority parties should selectively stack committees under two circumstances: (1) when the operations of committees affect the electoral prospects of all legislators, generating so-called "uniform electoral externalities;" and (2) when committees in a polarized setting are endowed with gatekeeping rights. Leveraging SAE, evidence from the states confirms these selective stacking hypotheses. The final paper examines political polarization, offering a more behavioral conception and a network-based measure, called modularity, applicable to collegial courts and legislatures alike. After demonstrating validity, I then measure polarization at the U.S. Supreme Court and in both houses of Congress using opinion-joining and cosponsorship networks. My primary contributions here are to argue that polarization need not be equated with partisan polarization and to develop a measure which permits such a distinction and decomposition. Indeed, I find that while polarization is tantamount to partisan polarization in the present-day Congress, as recently as four decades ago partisanship accounted for just over half of measured polarization.

This dissertation aims to investigate the ways in which culture shape how people perceive, remember, and transmit information to one another and how that information can be shaped by culture. I specifically study: (1) how stigma and stereotypes affect how individuals discern and recall information about an individual with schizophrenia; and (2) how political partisanship may alter one’s perceptions of an ambiguous social interaction that is politically salient. To answer these questions, I conduct two experiments and collect data from online participants. In the first study, I recruit participants from Amazon Mechanical Turk to read a story about an individual with schizophrenia and retell it from memory. In my second study, I recruit participants from Prolific, and I ask them to watch a video and label the characters involved in the interaction they watched. I find that biases about individuals with schizophrenia shape the content participants remember and transmit, leading to narratives that become more stereotype-consistent over time. I also find that political partisanship has a strong relationship with how participants label the characters involved in the video of my second study. These findings contribute to the fields of cultural sociology, medical sociology, and political polarization. While varied in approach, both experiments show that culture, in a variety of forms, shapes not only how individuals interpret the world, but also how they interact with it.

The Duke Free-electron laser (FEL) system, driven by the Duke electron storage ring, has been at the forefront of developing new light source capabilities over the past two decades. In 1999, the Duke FEL demonstrated the first lasing of a storage ring FEL in the vacuum ultraviolet (VUV) region at $194$ nm using two planar OK-4 undulators. With two helical undulators added to the outboard sides of the planar undulators, in 2005 the highest FEL gain ($47.8\%$) of a storage ring FEL was achieved using the Duke FEL system with a four-undulator configuration. In addition, the Duke FEL has been used as the photon source to drive the High Intensity $\gamma$-ray Source (HIGS) via Compton scattering of the FEL beam and electron beam inside the FEL cavity. Taking advantage of FEL's wavelength tunability as well as the adjustability of the energy of the electron beam in the storage ring, the nearly monochromatic $\gamma$-ray beam has been produced in a wide energy range from $1$ to $100$ MeV at the HIGS. To further push the FEL short wavelength limit and enhance the FEL gain in the VUV regime for high energy $\gamma$-ray production, two additional helical undulators were installed in 2012 using an undulator switchyard system to allow switching between the two planar and two helical undulators in the middle section of the FEL system. Using different undulator configurations made possible by the switchyard, a number of novel capabilities of the storage ring FEL have been developed and exploited for a wide FEL wavelength range from infrared (IR) to VUV. These new capabilities will eventually be made available to the $\gamma$-ray operation, which will greatly enhance the $\gamma$-ray user research program, creating new opportunities for certain types of nuclear physics research.

With the wide wavelength tuning range, the FEL is an intrinsically well-suited device to produce lasing with multiple colors. Taking advantage of the availability of an undulator system with multiple undulators, we have demonstrated the first two-color lasing of a storage ring FEL. Using either a three- or four-undulator configuration with a pair of dual-band high reflectivity mirrors, we have achieved simultaneous lasing in the IR and UV spectral regions. With the low-gain feature of the storage ring FEL, the power generated at the two wavelengths can be equally built up and precisely balanced to reach FEL saturation. A systematic experimental program to characterize this two-color FEL has been carried out, including precise power control, a study of the power stability of two-color lasing, wavelength tuning, and the impact of the FEL mirror degradation. Using this two-color laser, we have started to develop a new two-color $\gamma$-ray beam for scientific research at the HIGS.

Using the undulator switchyard, four helical undulators installed in the beamline can be configured to not only enhance the FEL gain in the VUV regime, but also allow for the full polarization control of the FEL beams. For the accelerator operation, the use of helical undulators is essential to extend the FEL mirror lifetime by reducing radiation damage from harmonic undulator radiation. Using a pair of helical undulators with opposite helicities, we have realized (1) fast helicity switching between left- and right-circular polarizations, and (2) the generation of fully controllable linear polarization. In order to extend these new capabilities of polarization control to the $\gamma$-ray operation in a wide energy range at the HIGS, a set of FEL polarization diagnostic systems need to be developed to cover the entire FEL wavelength range. The preliminary development of the polarization diagnostics for the wavelength range from IR to UV has been carried out.

Many cost-effective, evidence-based developmental programs (EBPs) remain inaccessible to children in need. To improve access to care, this dissertation theoretically and then empirically examines different approaches to advocating for dissemination funding in a polarized political context. Section 1 describes recent advances in the use of morally framed messaging to change attitudes. Section 2 reviews research on political polarization with an emphasis on how polarization affects online message processing. Section 3 describes a theoretically informed EBP advocacy strategy that seeks to tailor and target advocacy messages to promote bipartisan support for EBP dissemination.

Sections 4, 5, and 6 describe three studies designed to test whether motivated social cognition (Jost, Glaser, Kruglanski, & Sulloway, 2003) or moral foundations theory (Graham, Haidt, & Nosek, 2009) may be used to tailor message frames to speak to the distinct needs of Liberals and Conservatives. In Section 7, results and limitations are discussed. Although the three studies provide limited support for the hypothesis that theory can be used to design persuasive, tailored messages, message frames were consistently overwhelmed by competition from partisan cues and ideological arguments. The dissertation concludes by arguing that, in order to generate bipartisan support for EBP dissemination, implementation funding and structures that are already highly prioritized by Liberals need to be designed to appeal to Conservatives’ substantive policy preferences.

Climate change is thought to be one of the most pressing environmental problems facing humanity. However, due in part to failures in political communication and how the issue has been historically defined in American politics, discussions of climate change remain gridlocked and polarized. In this dissertation, I explore how climate change has been historically constructed as a political issue, how conflicts between climate advocates and skeptics have been communicated, and what effects polarization has had on political communication, particularly on the communication of climate change to skeptical audiences. I use a variety of methodological tools to consider these questions, including evolutionary frame analysis, which uses textual data to show how issues are framed and constructed over time; Kullback-Leibler divergence content analysis, which allows for comparison of advocate and skeptical framing over time; and experimental framing methods to test how audiences react to and process different presentations of climate change. I identify six major portrayals of climate change from 1988 to 2012, but find that no single construction of the issue has dominated the public discourse defining the problem. In addition, the construction of climate change may be associated with changes in public political sentiment, such as greater pessimism about climate action when the electorate becomes more conservative. As the issue of climate change has become more polarized in American politics, one proposed causal pathway for the observed polarization is that advocate and skeptic framing of climate change focuses on different facets of the issue and ignores rival arguments, a practice known as “talking past.” However, I find no evidence of increased talking past in 25 years of popular newsmedia reporting on the issue, suggesting both that talking past has not driven public polarization or that polarization is occurring in venues outside of the mainstream public discourse, such as blogs. To examine how polarization affects political communication on climate change, I test the cognitive processing of a variety of messages and sources that promote action against climate change among Republican individuals. Rather than identifying frames that are powerful enough to overcome polarization, I find that Republicans exhibit telltale signs of motivated skepticism on the issue, that is, they reject framing that runs counter to their party line and political identity. This result suggests that polarization constrains political communication on polarized issues, overshadowing traditional message and source effects of framing and increasing the difficulty communicators experience in reaching skeptical audiences.

I develop and justify a measure of polarization based on pairwise differences between and within groups, which improves on previous approaches in its ability to account for multiple dimensions and an arbitrary number of partitions. I apply this measure to a roll-call based ideological mapping of U.S. legislators to show that while the contemporary Congress is polarized relative to mid-century levels, the current state is not historically unprecedented.

I then estimate the ideology of public opinion using survey respondent thermometer evaluations of political elites and population subgroups. I find that party affiliation is polarizing in this space, but that alternate partitions of the electorate, along racial, educational, and other socio-demographic lines, are de-polarized.

Finally, I estimate a two-dimensional latent space based on social identity trait co-occurrence. I show that positions in this space are predictive of survey respondent ideology, partisanship, and voting behavior. Further, I show that when conceived in this way, we do observe a polarization of the social space over the last half-century of American politics.

Why do agents react to economic shocks privileging their identities and distrust of elites over their economic interests? This dissertation argues that this paradox can be explained by the logic of democratic representation. In a democracy, citizens delegate their economic interests to elites and institutions and forge a \emph{long-run relationship} with them. It shows that three factors -trust, identity and economic aspirations- regulate this relationship, and the fact that conflicts are processed within it can explain two puzzles: a) why economic disagreements arise while economic conditions remain unchanged and b) why economic shocks result in polarization or populism.

Firstly, it looks at the link between living standards and anti-establishment politics after financial crises. It pools 250 opinion and spending surveys and shows that unfulfilled economic aspirations undermine the trust in elites and institutions. Citizens protect their economic interests making their trust contingent on their economic aspirations. Financial crises undermine their well-being, and the ensuing decline in trust can interact with pre-existing political identities, and polarize politics along lines apparently unrelated to economic deprivations.

Secondly, it examines the link between affective polarization and economic expectations looking at 27 European countries since 1993. It identifies partisan bias looking at how citizens react to cabinet shifts. It shows that citizens with identical fundamentals but different identities update their subjective expectations in opposite directions. It argues that partisan bias is driven by affective polarization: the polarization of elites increases the hostility towards opponents, and citizens express it through their subjective expectations. However, bias does not push citizens to act against their economic self-interest. I reject alternative explanations about the source of bias including (a) lack of information (b) disagreements over the expected effects of government policy or its competence.

These findings suggest that democracy can transform the experience of citizens of economic antagonisms into conflicts with elites or about identity. However, trust and identities do not diminish the impact of economic factors, it only makes it more complex.

Geographic clustering has been linked to contemporary political polarization by jour- nalists and other researchers in recent years, most recently and notably by Bishop and Cushing (2008). In these accounts, clustering is motivated, in part, by shared tastes for combinations of place attributes that attract individuals with interrelated values and similar characteristics or skillsets. In order to test whether political pref- erences aligns with location choice, this paper proposes a sorting model based on the composition of migrants' political preferences.

Sorting is defined as the increase in the variation of a parameter of preference distributions of different location, in the absence of individual preference change. The model estimates the separate prob- abilities of party identification in U.S. congressional districts among migrants and non-migrants.

Based on an empirical application using the 2006 Cooperative Congressional Elec- tion Study, I find that a significant number of district satisfy the sorting condition. Aa multinomial logit model predicts that individual ideology is significant explana- tory variable in the partisanship of destination districts among migrants, even after controlling for the partisanship of originating districts.

The final chapter evaluates sorting and polarization in U.S. congressional districts based on intra-decade changes to population size. I show that overall polarization in high growth districts exceeds sorting, and suggest this results from an increase in electoral bias that could result from heavy migration into districts that begin the decade as very homogenous.

A commonly accepted model of public attitudes toward election rules assumes that citizens follow the cues of their preferred party’s elites and support rules that would benefit that party in elections. However, a separate literature on procedural fairness suggests that the public places a high priority on the fairness of democratic institutions. This dissertation tests which model predominates in the public’s decisions on election rules across a variety of policies and political contexts. It finds that most citizens prefer fair electoral institutions at the expense of partisan interest when that choice is made explicit, and a minority of committed partisans are driven by partisanship. While most partisans are unwilling to manipulate election rules to benefit their own party, they react negatively to attempts at manipulation by the other party. Citizens are susceptible to influence from elite messaging on election law issues but are resistant to attempts to influence their core democratic principles.

Spectral‐domain optical‐coherence tomography (SDOCT) has recently emerged as a powerful new tool for noninvasive human retinal imaging. I have developed a low‐cost, high resolution real‐time Spectral Domain Optical Coherence Tomography (SDOCT) system optimized for rapid 3D imaging of the human retina in vivo. Then functional retinal OCT imaging such as polarization sensitive OCT (PSOCT) and Doppler OCT were also developed based on phase technique. Unique phase unwrapping method in retina is described to extract the total reflectivity, accumulative retardance and fast axis orientation of the retinal nerve fiber layer (RNFL). The polarization scrambling layer of the retinal pigment epithelium was segmented by employing single camera sequential scan bsed PSOCT. As an extension, synthetic wavelength method will be also introduced for phase unwrapping in cell imaging. Finally I present an algorithm for 3D refraction correction based on a vector representation which accounts for refraction of CT light in the cornea. Following 3D refraction correction of volumetric corneal datasets, we can estimate the corneal optical power, thickness and the individual wavefront aberrations of the epithelial and the refraction‐corrected endothelial surfaces by using Zernike spectrum analysis.

Researchers have dedicated substantial effort to investigating important non-material motivations for people to get involved in politics, such as duty, emotions, and identities. Less attention, however, has been paid to the expectations people develop for what governments and politicians will deliver. This dissertation is about what people think elections will do for them, where those expectations come from, and their political consequences.

The first substantive chapter explores the policy changes people expect from elections, and how those expectations influence the decision to vote. There I study voters' beliefs about what candidates would actually do if given political power. I first find that public respondents likely underestimate the impediments that the separation of power poses to policy change. Just before the 2020 election, these general population respondents expected much more legislation than political scientists completing an identical survey. Second, among the general public, there was a 16 percentage point difference between voters and non-voters in expectations for policy change resulting from the election. Most importantly, these high expectations predicted validated voter turnout better than education, identifying as a Democrat or as a Republican (as well as partisan strength and ideology), having voted in 2016, and political interest. These results support explanations for the decision to turnout which center on the benefits, whether individual or social, that people believe their preferred candidate will deliver.

Next, Chapter 3 argues that a psychological bias called focalism contributes to an overestimation of the differences between political candidates, which in turn increases participation and polarization. Focalism causes people to confuse the allocation of attention to things with the importance of those things. Because attention to politics typically centers on conflict, the result is an exaggeration of differences across the partisan divide. I test this intuition using an experimental design that provides all respondents with all of the information they need to estimate how much Joe Biden and Donald Trump objectively disagreed on policy positions just before the 2020 election. I find that shifting attention – towards either those positions the candidates agreed or disagreed with each other on – influences beliefs about the differences between candidates. The effect exceeds that of identifying as a Democrat or as a Republican. Beyond those perceptions, focalism increases turnout intentions, perceptions of election importance, negative feelings towards the out-candidate, and affective polarization.

Finally, Chapter 4 attempts to moderate people's expectations using a series of real-world experiments. That final essay asks: would learning about coverage biases as people learn about the news soften people's beliefs about how different Democrats and Republicans are? To test this question, I use two experiments, one of which recruited participants to consume news covering the full population of partisan and non-partisan sources and the second of which randomized coverage among a sample predisposed to change their minds. I find that giving people the tools to understand media bias does give people the opportunity to choose to consume centrist news. Exploring app-use data, I show that people who explicitly choose to engage with stories favored by these moderate sources stories while avoiding stories favored by partisan sources feel less polarized.