FAS Theses and Dissertations

Schizophrenic hallucinations were studied with regard to their phenomenology. A comparison was made with the "model psychoses"-sleep, hallucinogen psychosis, amphetamine psychosis, and the organic psychoses (especially temporal lobe epilepsy). The dopamine theory of schizophrenia was presented, and then the author's own hypothesis for a neurophysiological mechanism for schizophrenic hallucinations was introduced. This hypothesis is an attempt to explain both the etiology and pathogenesis of schizophrenia. It is based on the dopamine theory, and in particular the mesolimbic (A10) dopamine system. Electrical brain stimulation studies, which evoke experiential hallucinations, along with experimental results showing that these hallucinations are dependent upon the subject's psychological state have caused the author to label this phenomenon contextual hallucinations. Recently, dopamine nerve terminals have been discovered in the limbic cortex and it is known that the neuroleptic drugs antipsychotic effects are in the mesolimbic dopamine system. These findings have led the author to propose that schizophrenic hallucinations are very similar to contextual hallucinations and they are elicited by an improper balance of dopamine in the mesolimbic system. It is thought that stress might psychosocially activate this mechanism. The author also suggests that the additional symptoms of schizophrenia are secondary and peripheral to hallucinations.

Although trends and changes in environmental forcing over tropical regions have been recognized, the question remains: how do tropical forests respond to current and future global climate change? Results from long-term studies of permanent forest plots have reported different, and in some cases opposing, trends in tropical forest dynamics in response to climate variability. Researchers remain divided as to whether tropical forests are likely to become net carbon sources or net carbon sinks under ongoing climate change. In this thesis, I use both empirical field measurement data analyses and mathematical modeling approaches to study the structure and dynamics of tropical forests in relation to climate variability. I examine tree growth rates calculated from long-term plot censuses with 5-year intervals and dendrometer band measurements with 3- or 6-month intervals to analyze changes in trees’ growth responses to differences in the mean climate forcing at different sites and to temporal variation in precipitation, temperature and solar radiation at different locations. The results reveal new information about relationships between tree growth and climate variability and offer plausible explanations for conflicting trends in tree growth rates observed across different tropical forests over time. In the modeling studies, I use an integral projection model combined with allometric scaling theories to relate tree demographic rates to differences in forest structure. The ability of this model to predict steady-state stem size-frequency distributions of the forests provides the opportunity to gain insights into the demographic history of the forest. I then develop a new dynamic scaling theory that incorporates the two-way interaction between tree demography and forest structure. It can predict the transient, time-dependent dynamics of forest demography and structure as forests reach their steady-state equilibrium, and can capture the characteristic timescales for these processes. This dynamic scaling theory can also be applied in non-equilibrium situations, such as the dynamics of forest re-growth following natural or human disturbances, or transient changes in forest demography and size distributions following climate change.

The residents of Union City, NJ— a 1.2 square mile metropolis across the Hudson from Manhattan—are fond of taking to the task of adorning their city streets on their own. In the business sector of the city (that is to say, most of it) the business owners garnish their windows with red, white, and blue, and more often than not their decoration is accompanied by the uncomfortably warm smile of a middle-aged bespectacled Irish man. The man, so comically out of place in the majority Spanish-speaking, 82.3% Latino city, is referred to interchangeably as Mayor and State Senator Brian P. Stack. On the city’s border is official proof of his status on the “Welcome to Union City” sign, mirrored by its North Bergen, NJ counterpart and the name Nicholas Sacco: mayor, state senator, assistant superintendent of North Bergen schools, and principal of Horace Mann Elementary. For decades, New Jersey politicians have viewed multiple office holding as an integral part of the urban power structure. To rise up in the totem pole, one must collect public office jobs until rising to one high enough to stand on its own. While not particularly common in the less populated areas of the state, urban centers like the aforementioned Hudson County, Newark, and Camden have a tradition of sending their leaders off to Trenton without making them relinquish their jobs at home. And yet it was these very state legislators that passed a ban on the practice into law in February 2008. Supported by senator-turned-governor Jon Corzine, the ban passed with the support of political leaders like Stack and Sacco. On paper and in the pages of the New York Times it read like a rare and barely believable victory for political morality in what longtime NJ political journalists Bob Ingle and Sandy McClure call “The Soprano State”. If it sounded barely believable, it is probably because in practice it was not. A grandfather clause in the law keeps those currently in two positions of power safe from the wrath of the law. And since elections were held in between the passing of the law and the enacting of it, there are actually more dual office holders in the Legislature today than there were when the law was passed according to state newspaper the Star Ledger. This study intends answer several questions regarding the phenomenon of multiple office holding and its sudden “extinction” in New Jersey. I hypothesize that the introduction of such a law was merely cashing in on a long-standing bit of political credit that, due to the highly salient role of the practice in building machines, could not be touched. As the number of political bosses engaging in this practice diminished, and as the need to hold various offices lessened because of an increase in income and power from other sources, dual office holding became an obsolete relic of the 1990s political machine structures. Thus it became feasible to ban the practice with a grandfather clause for those that had established themselves through this old system, with much credit in the field of ethics to be gained by all involved—every dual office holder, legislator, and the governor himself. On a micro level, it aspires to investigate why early 2008 was an opportune time for such a law and where this grandfather clause arouse from and why. Although the tradition has existed previously in less populated areas of New Jersey, especially in the 1940s, at some point (peaking in the 1990s) dual office holding became an essential component in the structure of an urban political machine. On a macro level, this study seeks to explain the place of such a practice in the creation and maintenance of the traditional urban political machine, a structure with a lush history in New Jersey that is still alive and kicking today. It attempts to begin a dialogue with existing literature on urban politics centered around the practice of dual office holding. To do this, the study needs to paint as vivid a portrait as possible of the modern urban political machine, its bosses, and every gear that moves its structure. For this it will heavily rely on literature describing the initial development of political machines of Tammany Hall and similar structures around the country, paying especial attention to the impact of immigration, given that preliminary research is showing a pronounced impact on the system from the wave of Latino immigrants beginning with the rise of the Cuban Revolution in 1958. This new wave of immigrants appears to have jump-started the machines and replenished them with an entire new wave of fodder ready to be introduced to the patronage system post-naturalization (a matter of five years’ time). Of particular note in this body of urban political research is Steven Erie’s Rainbow’s End, which I have discovered to be the definitive work in the field of immigration and its impact on urban political machines. Working with this broad field of urban politics in mind, I also intend on illustrating in detail the specific political machine structures of the three largest urban communities in New Jersey: Newark, Camden, and the general Hudson County area (as the cities of Hudson County tend to be about 1-2 square miles in area excepting Jersey City, there is little that distinguishes one from another culturally and politically). In order to do this, I must work with data specific to the state, beginning with a database of multiple office holders over time. I have constructed this database over the course of several decades and am currently developing it in the 1930s using biographical sketches in the New Jersey Legislative Manuals published yearly in the New Jersey State Archives of Trenton. Unfortunately, this means that my research is limited to multiple office holders who have one job in the state legislature, but as all signs point to most dual office holders preferring to have a state and local job rather than two of either, I do not believe this will seriously hinder my research. Supplementary research will also come from personal stories, which I plan on gathering from interviews with those deeply involved in urban politics. The study will include interviews with multiple office holders from these regions themselves, as well as those close to them—journalists, chiefs of staff, and those receiving patronage and practicing loyalty to the leaders. The goal of this study is to shed some light on the dark, backroom world of urban politics through the lens of this one common practice among the machine leaders. This one practice, currently a topic of much controversy due to this recent law, could very well be the key to understanding the development of machines, their power over citizens and their ability to maintain themselves over such extended periods of time.

Resilient and exposure-resilient functions are functions whose output appears random even if some portion of their input is either revealed or fixed. We explore an alternative way of characterizing these objects that ties them explicitly to the theory of randomness extractors and simplifies current proofs of basic results. We also describe the inclusions and separations governing the various classes of resilient and exposure-resilient functions. Using this knowledge, we explore the possibility of improving existing constructions of these functions and prove that one specific method of doing so is impossible.

Zero-knowledge protocols enable one party, called a prover, to "convince" another party, called a verifier, the validity of a mathematical statement such that the verifier "learns nothing" other than the fact that the proven statement is true. The different ways of formulating the terms "convince" and "learns nothing" gives rise to four classes of languages having zero-knowledge protocols, which are: statistical zero-knowledge proof systems, computational zero-knowledge proof systems, statistical zero-knowledge argument systems, and computational zero-knowledge argument systems.

We establish complexity-theoretic characterization of the classes of languages in NP having zero-knowledge argument systems. Using these characterizations, we show that for languages in NP:

-- Instance-dependent commitment schemes are necessary and sufficient for zero-knowledge protocols. Instance-dependent commitment schemes for a given language are commitment schemes that can depend on the instance of the language, and where the hiding and binding properties are required to hold only on the YES and NO instances of the language, respectively.

-- Computational zero knowledge and computational soundness (a property held by argument systems) are symmetric properties. Namely, we show that the class of languages in NP intersect co-NP having zero-knowledge arguments is closed under complement, and that a language in NP has a statistical zero-knowledge argument system if and only if its complement has a computational zero-knowledge proof system.

-- A method of transforming any zero-knowledge protocol that is secure only against an honest verifier that follows the prescribed protocol into one that is secure against malicious verifiers. In addition, our transformation gives us protocols with desirable properties like having public coins, being black-box simulatable, and having an efficient prover.

The novelty of our results above is that they are unconditional, meaning that they do not rely on any unproven complexity assumptions such as the existence of one-way functions. Moreover, in establishing our complexity-theoretic characterizations, we give the first construction of statistical zero-knowledge argument systems for NP based on any one-way function.

This work presents optogenetics and real-time computer vision techniques to non-invasively manipulate and monitor neural activity with high spatiotemporal resolution in awake behaving Caenorhabditis elegans. These methods were employed to dissect the nematode's mechanosensory and motor circuits and to elucidate the neural control of wave propagation during forward locomotion. Additionally, similar computer vision methods were used to automatically detect and decode fluorescing DNA origami nanobarcodes, a new class of fluorescent reporter constructs.

Groups often find themselves in a position to self-govern: sometimes a formal governing apparatus is weak or nonexistent; sometimes the legal system is underdeveloped, heavily back-logged or inapplicable; and sometimes groups simply have a preference for informal processes. In such cases, contrary to the Hobbesian vision of a self-help nightmare, groups often fare remarkably well both cooperating internally and coexisting with other groups. Diffuse punishment institutions induce cooperation well in tight-knit groups: the theory is well-understood and empirical examples abound. In many realistic settings, though, groups are imperfectly tight-knit, especially when populations are large or sparse or when communications technology is poor (even Facebook networks with very low-cost links are incomplete). Here I relate cooperation to a group's exact structure of communication to identify the role that networks play in making or breaking cooperation. By generalizing the game-theoretic model in Fearon and Laitin (1996), I present a model flexible enough to account for the various ways that a group may be imperfectly tight-knit.

Field observations show daytime HONO levels in urban, rural and remote environments are greater than those expected at photostationary state, that is, balance between production by (NO+OH) reaction and loss by UV-photolysis and OH-oxidation. Studies have interpreted measurements of ([HONO]{Obs} > [HONO]{PSS}) - or equivalently, the rate of HONO loss exceeding that of production - as evidence of a missing, sunlight-driven HONO source. Formation rate inferred from assuming photostationarity indicate a significant source of HONO, which photolyzes to yield OH. Moreover, depending on the mechanism, it may represent a pathway by which deposited nitrogen oxides are repartitioned back into the atmosphere in reactive form. The accumulation of HONO beneath the nocturnal boundary layer initiates photochemistry in the early morning prior to other (HO_x) precursors. Previous studies have estimated nighttime HONO production rate by attributing the increase in (HONO:NO_x) solely to heterogeneous HONO formation, while treating (NO_x) as an invariant. Moreover, because ambient (HONO:NO_x) exceed what is observed in automobile exhaust, combustion sources are discounted. In May of 2009, we observed HONO and (NO_2) mixing ratios in Houston, Texas during the SHARP campaign. We demonstrate – using a chemical box model – that photostationary state during daytime is not fully established. The reaction/transport time since emission from automobiles is short relative to the lifetime of HONO. The result of assuming PSS is a drastic over-estimation of the magnitude of the so-called missing HONO source. At night, we show that (NO_x) oxidation and emission are significant, thus, (NO_x) cannot be treated as a conservative tracer to infer secondary HONO production. Nearly-continuous observations of HONO and (NO_2) at Harvard Forest from December 2010 to December 2011 reveal daytime HONO levels that are comparable to what is expected from just known chemistry and much lower than has been reported in similar environments by different measurement techniques. Moreover, HONO fluxes are always below detection limit, indicating daytime HONO production contributes negligibly to the (HO_x) and (NO_x) budgets of the overlying atmosphere at Harvard Forest. Nighttime HONO enhancement is observed, but high night-to-night variability in (HONO:NO_2) that is not reasonably explained by the trends in HONO and (NO_2) fluxes, suggest a non-(NO_2), non-ground/canopy-surface related HONO source.

Manipulation of light at the nanoscale has the promise to enable numerous technological advances in biomedical sensing, optical communications, nano-mechanics and quantum optics. As photons have vanishingly small interaction cross sections, their interactions have to be mitigated by matters (i.e. quantum emitters, molecules, electrons etc.). Waveguides and cavities are the fundamental building blocks of the optical circuits, which control or confine light to specific matters of interest. The first half of the thesis (Chapters 2 & 3) focuses on how to design various photonic nanostructures to manipulate light on nano- to micro- scale, especially to modify the light-matter interaction properties. Chapter 2 discusses how nano-slot waveguides and photonic crystal nanobeam waveguides are able to modify the emission of quantum emitters, in a different way that normal ridge waveguides are not able to. Chapter 3 focuses on a more complicated and powerful structure: the photonic crystal nanobeam cavity. The design, fabrication and characterization of the photonic crystal nanobeam cavities are described and demonstrated in detail, which lays out the foundation of the biomedical sensing applications in the second half of the thesis. The second half of the thesis (Chapters 4 & 5) focuses on the application of photonic crystal nanobeam cavities in the label-free sensing of biomedical substances. Chapter 4 demonstrates detection of solutions with different refractive index (aceton, methanol, IPA etc.), glucose concentration, single polystyrene nanoparticles and single streptavidin bio-molecules. Chapter 4 proposes a novel nonlinear optical method to further enhance the sensitivity. Chapter 4 also demonstrates high quality nanobeam cavities fabricated in polymers, that open up a new route to decrease the cost, as well as to achieve novel applications with functional polymers. The broader impact of this technology lies in its potential of commercialization of a new generation of biosensors with high sensitivity and high integration. Chapter 5 discusses progresses towards instrumentation of the nanobeam cavity sensing technology for research & development apparatus, as well as point-of-care diagnostic tools.

This dissertation consists of three essays using economic methods to understand social policy issues. The first chapter uses a regression discontinuity framework to understand how teen birth rates respond to the first college opening in a county. The predicted effect of a college opening on teen births is ambiguous. Teen births could fall if college and motherhood are substitutes, but they could rise if a local college allows teen mothers to attend college or if teen mothers are not on the margin for attending college. Using data on teen births and college openings from 1969-1988, I find that teen births do not fall and may increase following a college opening. The effect is strongest among older teens, lending support to the notion that a local college allows more women to simultaneously become a mother and go to college. The second chapter examines why whites tend not to support welfare programs to the extent that blacks do. I recruited a racially and economically diverse set of subjects in Chicago Heights, IL and Boston and collected an original dataset combining survey questions and preferences for redistribution plans with economic consequences. Black subjects were not systematically more risk or inequity averse than white subjects and were only less confident when the task was a trivia quiz.

This dissertation consists of three empirical essays on distortions in labor market outcomes in developing countries. Chapter 1 tests for downward nominal wage rigidity in markets for casual daily agricultural labor. It examines responses to rainfall shocks in 500 Indian districts from 1956-2008. First, nominal wages rise in response to positive shocks but do not fall during droughts. Second, after transitory positive shocks have dissipated, nominal wages do not fall back down. Third, inflation moderates these effects. Fourth, rigidities lower employment: landless laborers experience a 6% reduction in employment in the year after positive shocks. Fifth, consistent with separation failures, rationing leads to increased labor supply to small farms. New survey evidence suggests that agricultural workers and employers view nominal wage cuts as unfair and believe that they reduce effort. Chapter 2 (with Michael Kremer and Sendhil Mullainathan) describes the results of a field experiment that tests for self-control problems in labor supply. First, we find that workers will choose dominated contracts—which pay less for every output level but have a steeper slope—to motivate themselves. Second, effort increases significantly as workers’ (randomly assigned) payday gets closer. Third, the demand for dominated contracts (and their benefits) is concentrated amongst those with the highest payday effects. Finally, as workers gain experience, they appear to learn about their self control problems: the correlation between the payday effect and the demand for the dominated contract grows with experience. These results together suggest that self-control, in this context at least, meaningfully alters the firm’s contracting problem. Chapter 3 empirically examines the impact of multiple market failures on allocative efficiency in farm production in poor countries. In years when labor rationing is more likely in villages (due to wage rigidity), there is a 63% increase in sharecropped and leased land by small farmers. This is consistent with the prediction that distortions from a failure in one market can be reduced by reallocating other factors of production. In areas with worse credit access, there is less land adjustment in response to labor rationing. These results provide evidence for separation failures resulting from multiple missing markets.

In this dissertation, I explore the implications of the advances in information and communication technology on democracy. In particular, I examine the roles of online institutions—search engines, news aggregators, and social media—in information readership and political outcomes. In Chapter 1, I show that information consumption pattern is more concentrated and polarized in online news traffic than in offline newspaper circulation. I then show that this pattern occurs not because online traffic better reflects people’s demand, but because online institutions generate a cascade. Using this evidence, I argue that online institutions produce a trade-off between the benefits involved when people access information and the costs of the cascade. In Chapter 3, I compare information consumption pattern on various online institutions. In Chapter 2, I explain why the cascade may become increasingly significant over time. An increase in Internet users suggests not only a reduced digital divide but also an even more concentrated and polarized online information consumption pattern as, ceteris paribus, the magnitude of the cascade will increase with an increase in the number of Internet users. I then empirically show a positive association between the traffic to an online institution and the estimated magnitude of the cascade observed on that site. In Chapter 4, I show that the observed concentrated and polarized online information consumption may affect political outcomes. For instance, if such an information consumption pattern affects political behaviors, we can expect the same pattern in measurable political outcomes. I test this prediction by investigating the association between U.S. Representatives using Twitter and their fundraising. Evidence suggests that, after politicians started using Twitter, their individual collected contributions became more concentrated, ideologically polarized, and geographically diverse. Finally, I discuss the implications of these findings for political equality, polarization, and democracy. In sum, online institutions may result in political outcomes becoming more concentrated and polarized. Given that a significant part of the observed concentration and polarization can be attributed to the cascade effect, this paper challenges the notion that Internet-mediated political actions or communications will necessarily promote democracy.

This thesis presents studies of transiting exoplanets using observations gathered in large part from space, with the NASA EPOXI Mission, the Spitzer Space Telescope, and the Kepler Mission. The first part of this thesis describes searches for additional transiting planets in known exoplanet systems, using time series photometry gathered as part of the NASA EPOXI Mission. Using the EPOXI light curves spanning weeks for each star, we searched six exoplanetary systems for signatures of additional transiting planets. These six systems include five hosts to hot Jupiters: HAT-P-4, TrES-3, TrES-2, WASP-3, and HAT-P-7, and one host to a hot Neptune: GJ 436. We place upper limits on the presence of additional transiting planets in the super-Earth radius range for GJ 436 in Chapter 2, and in the Neptune-to-Saturn radius range for the other five systems in Chapter 4. Chapter 3 details a search for additional transits of a hypothesized planet smaller than the Earth, whose presence was suggested by the EPOXI observations of GJ 436. In that study, we demonstrate the sensitivity of Warm Spitzer observations to transits of a sub-Earth-sized planet. The fifth chapter details the characterization and validation of the Kepler-19 system, which hosts a transiting 2.2 (R_{\bigoplus}) planet, Kepler-19b. We demonstrate the planetary nature of the transit signal with an analysis that combines information from high-resolution spectroscopy, the shape of the transit light curve, adaptive optics imaging, and near-infrared transits of the planet. The sinusoidal variation in the transit times of Kepler-19b indicates the presence of an additional perturbing body, and comprises the first definitive detection of a planet using the transit timing variation method. While we cannot uniquely determine the mass and orbital period of Kepler-19c, we establish that its mass must be less than 6 times the mass of Jupiter. The sixth chapter presents evidence for the validation of a 2.0 (R_{\bigoplus}) planet residing in the habitable zone of a low-mass star, Kepler Object of Interest 1361.01. We discuss the theoretical composition of the planet, and address issues specific to habitability of planets orbiting M dwarfs.

This dissertation consists of three essays on income risk and aggregate demand over the business cycle, each addressing an aspect of the Great Recession. The first chapter reframes the standard liquidity trap model to illustrate the costly feedback loop between idiosyncratic risk and aggregate demand. I first show that a liquidity trap can result from excess demand for precautionary savings in times of high uncertainty. Second, I show that the output and welfare costs of the ensuing recession depend crucially on how the drop in demand for output is translated into a reduction in demand for labor. Increased unemployment risk compounds the original rise in idiosyncratic productivity risk and reinforces precautionary motives, deepening the recession. Third, I show that increasing social insurance can raise output and welfare at the zero bound. I decompose these effects to distinguish the component unique to the liquidity trap environment and show that social insurance is most effective at the zero bound when it targets the type of idiosyncratic risk households face, which in turns depends on the labor market adjustment mechanism. The second paper offers a novel model of the connection between the consumer credit and home mortgage markets through an individual’s credit history. This paper introduces a novel justification for the home mortgage interest deduction. In an economy with both housing assets and consumer credit, the mortgage interest deduction is modeled as a subsidy for the accumulation of collateralizable assets by households who have maintained good credit. As such, the subsidy loosens participation constraints and facilitates risk-sharing. Empirical evidence and a calibration exercise reveal that the subsidy has a sizable impact on the availability of credit. The third paper assesses the role of policy uncertainty in the Great Recession. The Great Recession features substantial geographic variation in employment losses, a fact that is often presented as a challenge to uncertainty-based models of the downturn. In this paper we show that there is a substantial correlation between the distribution of employment losses and the increases in local measures of both economic and policy uncertainty. This relationship is robust across a wide range of measures.

This dissertation examines uncertainties about the supernatural among members of the urban middle class in Tehran, Iran. In particular, I attend to the ways in which the category of the supernatural (mavara) has become, for some people, an object of potential scientific (elmi) inquiry that must be distinguished from approaches usually ascribed to the rural, the uneducated, and the poor, often deemed as either superstitions (khorafat) or parochically religious (dini). By examining a range of encounters with the supernatural - such as attempts to explain communications with the souls of the dead, make sense of spirit possession, and differentiate real magic from charlatanism - I highlight the varied modalities through which perspectives and forms of reasoning imagined to be rational and scientific are brought to bear on matters that are understood to lie, at least partially, within the purview of religious knowledge. I situate such supernatural encounters against a backdrop of state disciplinary and coercive measures, thereby illuminating important shifts in Iran's politico-religious landscape in the past two decades, such as the waning of the religious authority of the Shii ulama among certain sections of society. This declining authority does not necessarily imply a weakened interest in Islam (although this is sometimes the case). Rather, it has opened up a space for reception and deliberation of a multiplicity of sources of religious knowledge, both Islamic and non-Islamic. These include forms of Western-imported spirituality and occultism that have been entering Iran for over a century, with their most recent wave consisting of translated texts of New Age spirituality, self-help success literature, and popular psychology that have gained popularity since the end of the war with Iraq. The metaphysical models on offer through these spiritual systems are usually promoted and understood as scientific rather than religious. That is, rather than being seen as contradicting Islamic notions, these formulations are often viewed as parallel to them. By attending to such notions and their everyday manifestations, my project brings into focus various hybrid forms of religious-scientific knowledge, experience, and discourse that have largely been ignored in the study of modern Muslim societies.

The Standard Model of particle physics can account for neither the dark matter dominating the universe's matter density, nor the baryon asymmetry that leads to the visible matter density. This dissertation explores models of new physics that connect dark matter to baryogenesis and can naturally account for the observed quantities of both types of matter. Special emphasis is given to models incorporating new weak-scale physics, as such models often predict signatures at present and upcoming experiments and can potentially be connected to solutions of the hierarchy problem. In one class of models we study, the dark matter abundance is determined by a dark matter asymmetry connected to the baryon asymmetry. In such models, the separate dark matter, baryon, and lepton number global symmetries observed today are individually broken at or above the weak scale and lead to mixing of dark matter and Standard Model fields in the early universe. This can happen generically, with dark matter-visible matter mass mixing induced by large background energies or moduli in the early universe, and can also arise at the electroweak phase transition. Mass mixing models of asymmetric dark matter can readily accommodate dark matter masses ranging from 1 GeV to 100 TeV and expand the scope of possible relationships between the dark and visible sectors. We also consider models of symmetric dark matter in which the annihilation of dark matter particles in the early universe generates the observed baryon asymmetry. This process, called “WIMPy baryogenesis”, naturally accommodates weak-scale dark matter and explains the observed dark matter density with only order-one couplings. WIMPy baryogenesis is a new model of baryogenesis at the weak scale, avoiding problems with high reheat temperatures in supersymmetric theories, and yielding observable consequences in ongoing and future experiments for some models

This study unearths the lost world of early-nineteenth-century Canton. Known today as Guangzhou, this Chinese city witnessed the economic dynamism of global commerce until the demise of the Canton System in 1842. Records of its commercial vitality and global interactions faded only because we have allowed our image of old Canton to be clouded by China's weakness beginning in the mid-1800s. By reviving this story of economic vibrancy, I restore the historical contingency at the juncture at which global commercial equilibrium unraveled with the collapse of the Canton system, and reshape our understanding of China's subsequent economic experience. I explore this story of the China trade that helped shape the modern world through the lens of a single prominent merchant house and its leading figure, Wu Bingjian, known to the West by his trading name of Houqua. I demonstrate that a large measure of Houqua's success stemmed from his ability to maintain an intricate balance between his commercial interests and those of his Western counterparts, all in an era of transnationalism before the imposition of the Western world order. The story of Houqua is at once local, regional, and global. Houqua’s business success certainly amplified the economic vitality in Canton. However, this analysis of his business success is less an examination of the Canton system than a study of the impact of an exceptional operator within this system who, through his personal business endeavors, set in motion changes that had ramifications for China’s development and the global system at large. His success in global business illustrates the construction of networks of trust for the purpose of facilitating economic exchange in the advent of an enforceable, unified international system of arbitration. The experience of his successors tells the story of the diverging economic fortunes of global traders operating formerly on equal footing. This is a story not only of an exceptional individual but also of the dynamic setting of transnational business when regional networks negotiated their connections in the emerging modern world.

Assessment is the primary means of feedback between students and instructors. However, to effectively use assessment, the ability to interpret collected information is essential. We present insights into three unique, important avenues of assessment in the physics classroom and laboratory. First, we examine students’ performance on conceptual surveys. The goal of this research project is to better utilize the information collected by instructors when they administer the Force Concept Inventory (FCI) to students as a pre-test and post-test of their conceptual understanding of Newtonian mechanics. We find that ambiguities in the use of the normalized gain, g, may influence comparisons among individual classes. Therefore, we propose using stratagrams, graphical summaries of the fraction of students who exhibit “Newtonian thinking,” as a clearer, more informative method of both assessing a single class and comparing performance among classes. Next, we examine students’ expressions of confusion when they initially encounter new material. The goal of this research project is to better understand what such confusion actually conveys to instructors about students’ performance and engagement. We investigate the relationship between students’ self-assessment of their confusion over material and their performance, confidence in reasoning, pre-course self-efficacy and several other measurable characteristics of engagement. We find that students’ expressions of confusion are negatively related to initial performance, confidence and self-efficacy, but positively related to final performance when all factors are considered together. Finally, we examine students’ exhibition of scientific reasoning abilities in the instructional laboratory. The goal of this research project is to explore two inquiry-based curricula, each of which proposes a different degree of scaffolding. Students engage in sequences of these laboratory activities during one semester of an introductory physics course. We find that students who participate in the less scaffolded activities exhibit marginally stronger scientific reasoning abilities in distinct exercises throughout the semester, but exhibit no differences in the final, common exercises. Overall, we find that, although students demonstrate some enhanced scientific reasoning skills, they fail to exhibit or retain even some of the most strongly emphasized skills.