Honors Projects
Showing 131 - 140 of 298 Items
Aortic pressure and heart rate in the lobster Homarus americanus are modulated by mechanical feedback and neuropeptides
Date: 2021-01-01
Creator: Grace Marie Hambelton
Access: Open access
- Baroreceptors are stretch receptors located in the aorta of mammals; in response to increased afterload, they elicit a decrease in heart rate, creating a negative feedback loop that lowers blood pressure. Although lobsters (Homarus americanus) do not have baroreceptors like mammals, closely related land crabs have been shown to have baroreceptor-like responses. Heart contraction is also regulated by the Frank-Starling response, where increasing stretch or preload increases the contractile force of the heart. In addition to these types of biomechanical modulations, lobsters use a central pattern generator, the cardiac ganglion, to maintain synchronicity of the heartbeat. The heart is also controlled by the central nervous system via neuromodulators, such as myosuppressin, which has been shown to increase active force and decrease frequency in isolated lobster hearts. We performed experiments on a lobster heart with the main arteries still intact, and varied the preload by stretching anterior arteries, and the afterload by elevating the dorsal abdominal artery. We added myosuppressin to modulate the cardiac ganglion output and muscle contraction. We found that the baroreceptor-like response is most directly modulated by active force, whereas frequency could be a secondary control. Increasing preload does increase active force, but that does not correlate to a higher cardiac output, which shows that how hard the heart pumps is not what determines how effectively it is pumping. Additionally, we found that myosuppressin has a much stronger effect on frequency than active force, and so with myosuppressin, frequency becomes the main determinant of cardiac output.
Extreme Value Theory and Backtest Overfitting in Finance
Date: 2015-05-01
Creator: Daniel C Byrnes
Access: Open access
- In order to identify potentially profitable investment strategies, hedge funds and asset managers can use historical market data to simulate a strategy's performance, a process known as backtesting. While the abundance of historical stock price data and powerful computing technologies has made it feasible to run millions of simulations in a short period of time, this process may produce statistically insignificant results in the form of false positives. As the number of configurations of a strategy increases, it becomes more likely that some of the configurations will perform well by chance alone. The phenomenon of backtest overfitting occurs when a model interprets market idiosyncrasies as signal rather than noise, and is often not taken into account in the strategy selection process. As a result, the finance industry and academic literature are rife with skill-less strategies that have no capability of beating the market. This paper explores the development of a minimum criterion that managers and investors can use during the backtesting process in order to increase confidence that a strategy's performance is not the result of pure chance. To do this we will use extreme value theory to determine the probability of observing a specific result, or something more extreme than this result, given that multiple configurations of a strategy were tested.
Stuck in Limbo: Temporary Protected Status, Climate Migrants and the Expanding Definition of Refugees in the United States
Date: 2021-01-01
Creator: Noelia Calcaño
Access: Open access
- There will be 1.2 billion climate refugees by 2050 as ecological disasters precipitate mass migrations around the world. The U.S. does not legally recognize climate migrants as refugees, instead adhering to the 1951 UN Refugee Convention that limits the definition of a refugee to individuals facing political persecution. Despite failing to expand the definition of a refugee, the U.S. has accommodated migrants displaced by natural disasters through a series of ad hoc fixes, most notably “Temporary Protected Status.” In Central American countries that were granted TPS, we encounter the paradox of the U.S. employing environmental disasters to justify continued extensions of this temporary protection, while addressing chronic conditions in the region. The central question of this thesis is, has employing the environment as a catch-all tool for Temporary Protected Status protection expanded the de facto definition of a “refugee,” for Central American migrants impacted by climate catastrophes and if so, how? Though TPS fills a gap in US law by providing de facto protections to migrants fleeing environmental disasters, the environment is being used as a catch-all tool for more systemic economic and political vulnerabilities in Central America. The environment is a catch-all tool for continued protection only insofar as it is not recognized as political, yet it is getting harder to employ the environment as an apolitical driver of migration. The precarious foundation of TPS threatens the hundreds of thousands of Central Americans that depend on this program to live and work legally in the United States.
Who We Are: Incarcerated Students and the New Prison Literature, 1995-2010
Date: 2013-05-01
Creator: Reilly Hannah N Lorastein
Access: Open access
- This project focuses on American prison writings from the late 1990s to the 2000s. Much has been written about American prison intellectuals such as Malcolm X, George Jackson, Eldridge Cleaver, and Angela Davis, who wrote as active participants in black and brown freedom movements in the United States. However the new prison literature that has emerged over the past two decades through higher education programs within prisons has received little to no attention. This study provides a more nuanced view of the steadily growing silent population in the United States through close readings of Openline, an inter-disciplinary journal featuring poetry, essays, fiction, and visual art created by incarcerated students enrolled in the College Program at San Quentin State Prison. By engaging the first person perspective of the incarcerated subject, this project will reveal how incarcerated individuals describe themselves, how they maintain and create intimate relationships from behind bars, and their critiques of the criminal justice system. From these readings, the project outlines conventions of “the incarcerated experience” as a subject position, with an eye toward further research analyzing the intersection of one's “incarcerated status” with one’s race, class, gender, and sexuality.
A Time for Every Purpose: Race, Medical Professionalism, and the Physicians’ Dilemma
Date: 2022-01-01
Creator: Reuben Mindlin Schafir
Access: Open access
- This thesis examines the intersection of race and professionalism in healthcare as they relate specifically to the debate over universal healthcare. It begins with the National Medical Association (NMA), a professional organization for Black physicians founded in 1895. The first two chapters follow the NMA as they attempt to navigate the two allegiances they have: one to be "race men," and work for racial equity in healthcare, and one to be professionals, and work towards affirming their professional sovereignty. The narrative begins in 1945, when President Harry Truman backed the first substantial proposal for a system of nationalized healthcare. Chapter two discusses the 1960s and how the confluence of the Great Society and the civil rights movement provided Black doctors with an opportunity to successfully serve both aspects of their identities. The third chapters explores the 1970s and the events following the passage of Medicare and Medicaid. The NMA began to align itself more closely with the American Medical Association (AMA), which had long-embodied the medical establishment. When this alignment occurred, the Black Panther party offered an alternative method of addressing racial health inequities that rejected not only the notion of healthcare as a commodity, but the entire national identity associated with the free market within which physicians sold care. This thesis considers how the interests of patients and the interests of doctors do and do not align, using race to bring this tension into high relief.
Natural variation in chromatin conformation among populations of Drosophila melanogaster
Date: 2021-01-01
Creator: Utku Ferah
Access: Open access
- The role of polymorphisms in protein-coding and non-coding regions of the genome during adaptive evolution has been a long-debated subject in evolutionary biology. Although the importance of coding-sequence polymorphisms during evolution has been well-documented, the influence of non-coding regions of the genome on phenotypic diversity and adaptive evolution remains less clear. Enhancers are cis-regulatory elements that dictate gene transcription rates, times, and locations; enhancers are located in noncoding regions and, when active, exhibit an open-chromatin conformation. In the current study, we identified putative enhancers that differ in chromatin conformation among three natural isolates of Drosophila melanogaster from different parts of the world. The genome-wide numbers of enhancers active in some natural isolates—but inactive in others—will provide insight into the amount of raw material available for evolution due to transcriptional regulatory variation.
Characterizing and Investigating the Electrophysiological Properties of the Plastic Cricket Auditory System in Response to Cooling
Date: 2022-01-01
Creator: Hannah Tess Scotch
Access: Open access
- The auditory system of the Mediterranean field cricket (Gryllus bimaculatus) is capable of profound compensatory plasticity. Following deafferentation due to the loss of an auditory organ, the dendrites of intermediate auditory neuron Ascending Neuron 2 (AN-2) grow across the midline and functionally connect to contralateral afferents. The loss of the auditory organ can be mimicked with reversible cold-deactivation, in which cooled Peltier elements silence the auditory organ and its afferents. Though this would presumably prevent AN-2 from firing, cooling instead induces a novel firing pattern called DOPE (delayed-onset, prolonged-excitation). In this study, intracellular physiological recordings were completed before, during, and after cooling in response to “chirp” and “pulse” sounds. Analysis was performed within and across crickets to characterize DOPE. Results revealed expected variability across individuals, as well as a wider spread of onset delay and a decrease in spike frequency and number of spikes per burst relative to baseline within individuals during cooling. Generally, subsequent warming only partially restored the neuronal responses to baseline as measured by all three parameters. This was particularly true in response to “pulse” stimuli. Future experiments will investigate if DOPE is caused by synaptic inputs or intrinsic properties of AN-2, as well as the role of inhibition in the circuit. Eventually, we hope to develop a complete model of the auditory circuit for future investigations of plasticity, with ramifications for treating human neuronal injury.
Context-specific effects of vasotocin on social approach in the male common goldfish, Carassius auratus
Date: 2019-05-01
Creator: Katharine Torrey
Access: Open access
- The peptide vasotocin (VT) and its mammalian homologue, vasopressin (VP), produce effects on social behavior that are highly species- and context-specific. We recently sequenced two genes for V1a-like receptors (VTR) in the goldfish brain, one that encodes for a fully-functioning canonical receptor and one that encodes for a non-functional truncated receptor. The current study is an investigation of whether social context may alter expression of these receptor types and thus, potentially, behavioral responses to VT. We used western blotting and immunohistochemistry with custom anti-VTR antibodies to characterize the distribution of VTR throughout the forebrain and the hindbrain. Western blot results showed bands close to the predicted sizes for truncated and canonical VTR constructs, suggesting that both genes are translated into protein in the brain, but the presence of additional bands suggested potential nonspecific binding. Immunohistochemistry data revealed VTR signal throughout the brain in regions associated with social behavior. We additionally examined whether visual and olfactory context alters behavioral responsiveness to VT, potentially by altering the expression of one or both receptors. Behavioral tests suggested that VT inhibits approach to males, but its effect on response to females in reproductive contexts is still undetermined, likely due to interference from a stress response during testing. Further characterization of VTR throughout the brain will clarify how social context might alter VT signaling through context-dependent modulation of its receptors. Additionally, future work should examine the behavioral consequences of such modulation by further studying whether VT’s effect on social approach behavior depends on context.
Responses of central pattern generators in the American lobster STNS to multiple members of a novel neuropeptide family
Date: 2020-01-01
Creator: Benjamin Harley Wong
Access: Open access
- Neuropeptides are important modulators of neural activity, allowing neural networks, such as the central pattern generators (CPGs) that control rhythmic movements, to alter their output and thus generate behavioral flexibility. Isoforms of a neuropeptide family vary in physical structure, allowing potentially distinct functional neuromodulatory effects on CPG systems. While some familial neuropeptide isoforms can differentially affect a system, others in the same family may elicit indistinguishable effects. Here, we examined the effects elicited by members of a novel family of six peptide hormone isoforms (GSEFLamides: I-, M-, AL-, AM-, AV-, and VM-GSEFLamide) on the pyloric filter and gastric mill CPGs in the stomatogastric nervous system (STNS) of the American lobster, Homarus americanus. Recent unpublished work from the Dickinson lab found that five of the six GSEFLamides elicited similar increases in contraction amplitude when perfused through the isolated lobster heart, while one (AVGSEFLamide) had virtually no effect. Using extracellular recordings, we found the pattern of GSEFLamide effects on the STNS gastric mill to be similar to the pattern observed in the lobster cardiac system; the gastric mill circuit was fairly consistently activated by all isoforms except AVGSEFLamide. The intrinsically active pyloric pattern was also significantly enhanced by three out of five peptide isoforms, and nearly significantly enhanced by two more, but was likewise non-responsive to AVGSEFLamide. While the reason AVGSEFLamide had no effect on either pattern is unknown, the similar phenomenon noted in the isolated whole heart potentially indicates that this isoform lacks any function in the lobster.
Survival Strategies: Historic Preservation, Jewish Community, and the German Democratic Republic
Date: 2020-01-01
Creator: Emily Ann Cohen
Access: Open access
- Following the Second World War, as German Communists worked to establish a new socialist East German state, Jews who survived persecution and imprisonment by the Nazis worked to reestablish a Jewish community at the same time. Though many scholars dismiss the relationship between Jews and the Socialist Unity Party, the ruling party of the German Democratic Republic, as one characterized only by neglect and occasional political exploitation, it was much more nuanced, shaped in large part by the Cold War. Both the party and the Jewish community relied on the other to accomplish their goals, namely, survival in a new world order: The Socialist Unity Party relied on the Jewish community to maintain the German Democratic Republic's claim to legitimacy, and the Jews, few in number, relied on the party for financial support. Despite mutual benefits, however, the state and party nearly always had the upper hand. The power imbalance led Jews to find creative ways to fulfill their needs and, at several points, even prompted protest of the party’s treatment of its Jewish citizens. This paper follows the course of this relationship by focusing on the German Democratic Republic's management of sites of historical significance—which vacillated between outright destruction and dedicated protection—returning particularly to the Jewish cemetery in Berlin-Weissensee, one of the largest Jewish cemeteries in Europe. With this particular lens, this project addresses questions about memory, mythology, and agency in a socialist dictatorship and challenges assumptions about Jewish life in East Germany.