Essays in the economics of uncertainty

Demers, Michel Edward Elgar 1985 국내박사

CD8+ T cell effector function and transcriptional regulation during HIV pathogenesis

Demers, Korey R University of Pennsylvania 2016 해외박사(DDOD)

A detailed understanding of the immune response to human immunodeficiency virus (HIV) infection is needed to inform prevention and therapeutic strategies that aim to contain the AIDS pandemic. The CD8+ Tcell response plays a critical role in controlling viral replication during HIV infection and will likely need to be a part of any vaccine approach. The qualitative feature of the CD8+ Tcell response most closely associated with immunologic control of HIV infection is its cytotoxic capacity. The pore-forming protein, perforin, is a major determinant of the cytotoxic capacity of CD8+ Tcells. In the context of chronic HIV infection, enhanced perforin expression by HIV-specific CD8+ Tcells is associated with greater control over HIV replication. However, individuals experiencing chronic progressive infection (CP) often demonstrate a diminished ability to express this important cytolytic molecule. HIV-specific CD8+ Tcells from CP also express lower levels of the T-box transcription factor T-bet, an upstream regulator of CD8+ Tcell effector differentiation and function. Whether HIV-specific CD8+ Tcells from progressors possess effector capacity during the earliest stages of infection and subsequently lose it remains unclear. The relationship between perforin, T-bet, and the closely related transcription factor eomesodermin (Eomes) also remains largely undefined in the context of acute, chronic, or controlled HIV infection. In this work, we report that CD8+ Tcell responses had high cytotoxic potential during acute HIV infection but perforin expression quickly waned with the resolution of peak viremia. Importantly, perforin was maintained in HIV-specific CD8+ Tcells with high levels of T-bet, but not necessarily in a population of T-betLo HIV-specific CD8 + T cells that expanded as infection progressed. During chronic infection there was a generalized increase in perforin expression for both total memory and HIV-specific CD8+ Tcells that was dissociated from both T-bet and Eomes. Of note, however, individuals in which perforin remained closely associated with T-bet demonstrated greater in vivo control of HIV replication. Collectively, our data imply that loss of transcriptional regulators responsible for driving strong cytotoxic responses, such as T-bet, contributes to CD8+ Tcell dysfunction during chronic progressive HIV infection.

Equity valuation and the determinants of equity risk in the property-casualty insurance industry

Demers, Elizabeth Anne Stanford University 2000 해외박사(DDOD)

This dissertation consists of two empirical studies conducted in the setting of the property-casualty (“P&C”) industry. The first essay documents the relative explanatory power of alternative equity valuation models for the share prices of publicly traded insurers. I develop a dual valuation model that incorporates the underlying economic and accounting characteristics of P&C insurers, and investigate the influence of underwriting profitability on the role of underwriting valuation variables. I hypothesize and find that the dual model provides greater explanatory power for insurers' share prices than asset-only and earnings-only valuation models, suggesting that the stock and flow components in the dual model capture different aspects of equity value. Also as expected, underwriting profitability affects the economic and statistical significance of underwriting-related valuation variables. Consistent with prior studies, my results support the hypothesis that fair values are incrementally value-relevant to historical cost measures, however I do not find evidence that fair values offer relatively greater explanatory power than historical cost measures for P&C share prices. The second empirical essay examines the relations between unpredictable accrual errors, equity risk, executive incentives, and various dimensions of risk management activity in the P&C industry. I empirically capture the endogeneity inherent in firms' risk management activities by modeling the determinants of insurers' equity risk and risk management choice variables in a simultaneous equation system. I extend the accruals literature by exploiting specialized accrual error disclosures in the insurance industry to develop proxies for the uncertainty inherent in firms' underwriting results. As hypothesized, my proxy for the uncertainty in the loss reserve estimation and reporting process is positively associated with insurer equity: risk, and with three corporate risk management choice variables: capital levels, reinsurance activity, and asset portfolio risk. Executives' personal incentives are not found to be incrementally significant after controlling for other economic determinants of equity risk. The results of my study have implications beyond the insurance industry; my findings suggest that simple OLS models that fail to incorporate the simultaneities inherent in firms' risk taking activities may be subject to severely biased coefficient estimates.

Applications of Lie groups in turbulence modeling

DeMers, Louis Joseph University of Illinois at Urbana-Champaign 2000 해외박사(DDOD)

A systematic Lie algebra approach is developed for the dimensional reduction of systems of partial differential equations. Lie algebra analysis utilizes global equations of scaling groups to obtain Lie groups admitted by a system of PDEs. The subsequent Lie group generators are employed in order to obtain similarity variables that may be interpreted as invariant functions of the scaling groups admitted by the system. The similarity variables are used to transform systems of partial differential equations into ordinary differential equations. Since invariance is built into the systematic approach, invariance properties of the original system are not lost in the transformation process. Group analysis is applied to the general two-dimensional k-ϵ turbulence model. Symmetry algebras for the k-ϵ turbulence model have been calculated by Khor'kova. and Verbovetsky. This systematic approach is applied to the specific flow problem of turbulent submerged free plane jets. Similarity solutions obtained through Lie group analysis of the zero-equation turbulence model are equivalent to those obtained through traditional mathematical techniques. Lie groups are then applied to the k-ϵ turbulence model's PDEs for submerged free plane jets. A numerical simulation is performed on the subsequent system of ODEs obtained from this model. The results for the turbulent properties obtained from the numerical computation are in good agreement with the similarity profiles obtained from the zero-equation model. These properties include the axial and transverse velocities, stream function, vorticity and transverse eddy viscosity.

Curvature-driven Pattern Formation in Multicomponent Membranes

Demers, Matthew Francis Northwestern University 2012 해외박사(DDOD)

Multicomponent liquid membranes occur in many important physical systems and offer promise in the rational design of materials. This promise is due in large part to their versatile phase behavior. Under the right circumstances, distinct physical properties of the components can lead to the spontaneous ordering of membrane components into patterns. This thesis contains a study of multicomponent membranes whose patterns arise from component-specific shape preferences. These preferences couple the membrane's extrinsic and intrinsic geometries, since the membrane's degrees of freedom include both its shape in space and its in-membrane component arrangement. A continuum theory is developed for a multicomponent membrane with shape-composition coupling. A general scheme is presented for classifying strongly segregated membrane patterns according to the topology of component domains. This model is studied numerically and analytically. In the numerical study, a discretized model is formulated for the case of a strongly segregated three-phase vesicle. Minimal energy configurations are found using simulated annealing Monte Carlo simulations. Phase diagrams are constructed for a number of control parameter pairs, exhibiting a wide variety of patterns. An effective attraction between components of largest and smallest spontaneous curvature is observed and characterized. In the analytic study, solutions for minimal surface shape in known patterns are computed for select tractable cases. These solutions are applicable to an arbitrary number of phase types, and applied to the case of a three-phase membrane.

Sampling as lineage in hip-hop

Demers, Joanna Teresa Princeton University 2002 해외박사(DDOD)

Sampling is one of the most distinctive features of hip-hop music. Excerpts from earlier recordings (known as “samples”) are reused to create a new work. These excerpts are recontextualized in ways that may be humorous, ironic, or respectful. Sampling began as a process in which multiple turntables were played simultaneously and controlled manually. More recently, hip-hop artists have relied on digital technology that enables precise control and manipulation of sounds. When hip-hop (a multifaceted artistic movement consisting of graffiti, breakdancing, fashion, and rap music) began in the late 1970s, disk jockeys sampled almost exclusively from African-American musical genres such as soul, funk, and rhythm and blues. This sampling “canon” was employed to construct a lineage between hip-hop and older forms of black American popular music, particularly those linked with advances of the Civil Rights era. Hip-hop's need to create lineage can be understood as a form of Signifyin(g), in which well-known musical materials are quoted, critiqued, and parodied. During its first twenty years, hip-hop frequently collided with the mainstream pop industry in litigations concerning the legality and ethicality of sampling. These confrontations reflected inherent differences between the hip-hop community, then largely reliant on traditional African-American understandings of originality, and the pop community, which perpetuates modernist prejudices against borrowing and quotation. Since the mid-1990s, however, these lawsuits have mostly disappeared, due to a curious assimilation of sampling into music industry copyright practice. By recycling of black images from music, fashion, and blaxploitation cinema, hip-hop constructs an “authentic” African-American identity, one which coalesced in urban ghettos during the 1970s. For nearly three decades, sampling has been an effective means of self-assertion for the hip-hop community and has arguably exerted greater influence on racial relations than any other musical genre since rock ‘n’ roll.

Keeping a store: The social and commercial worlds of John Askin in the eighteenth-century Great Lakes, 1763-1796

Demers, Elizabeth Sherburn Michigan State University 2010 해외박사(DDOD)

John Askin arrived in the Great Lakes in 1763 to work as a merchant in the lucrative transatlantic fur trade. By 1796, he had amassed significant personal wealth that included real estate, goods, and slaves. He also achieved social prominence and political influence both locally and within the larger fur trade milieu of the Great Lakes borderland. This dissertation reveals not only how Askin achieved such success in his lifetime, but uses Askin as a case study to examine how merchants used their social and political networks in the course of everyday business. Intermarriage with Indian women and kinship with Native groups were crucial strategies for fur trade success; so was slavery, both Indian and African, which British merchants commonly used to increase labor, capital, and social wealth. The carrying and supply trade, including agriculture, were also significant aspects of the trade. John Askin was a frontier type, whose wealth, influence, and power both created the unique characteristics of the Great Lakes borderland and ultimately helped bring about its demise at the beginning of the nineteenth century.

Markov extensions and natural conditionally invariant measures for dynamical systems with holes

Demers, Mark Francis New York University 2003 해외박사(DDOD)

Consider a piecewise differentiable map <italic>T</italic> of a compact Riemannian manifold <italic>M</italic>. Let <italic>H</italic> be an open set in <italic>M</italic>. We call <italic>H</italic> the hole and keep track of the iterates of a point as long as they do not enter <italic>H</italic>. Once a point enters <italic>H</italic>, it is absorbed and does not return. We study the statistical properties of the escape dynamics of such a system and are interested in the existence and properties of <italic>absolutely continuous conditionally invariant measures</italic> (abbreviated a.c.c.i.m.). We first show that a dynamical system with arbitrarily small holes may have many a.c.c.i.m.s which share the same support even when the corresponding closed system has been shown to have a unique absolutely continuous invariant measure. Many of these measures may not reflect the escape dynamics with respect to the reference measure on <italic>M</italic>. It then becomes essential to establish properties of a conditionally invariant measure, rather than merely prove its existence. We propose some properties that a natural conditionally invariant measure should have in order to shed light on the statistical properties of the system. We introduce to the study of dynamical systems with holes the method of Markov extensions, due to L.-S. Young, which has been used successfully to study a wide variety of dynamical systems without holes. The basic idea of this method is to construct an associated dynamical system with simpler properties than the original, study the properties of this system and then pass the results back to the original system. This method does not require any Markov structure in the original dynamical system and is flexible enough to apply to nonuniformly hyperbolic systems. We first prove results for the of dynamical systems with holes: expanding maps of the interval and certain parameter values of the logistic family <italic>fa</italic>(<italic>x</italic>) = 1 − <italic>ax</italic><super>2</super> on [−1, 1]. This method yields the existence of an a.c.c.i.m. with many of the properties proposed for a natural conditionally invariant measure and has the potential to be extended to other classes of dynamical systems with holes.

Investigating Cholesterol Orientation in Lipid Bilayer by Raman Spectroscopy

Demers, Steven M. E ProQuest Dissertations & Theses Rice University 2020 해외박사(DDOD)

A History of Both Clonality and Recombination Governs the Population Structure of Alternaria Endophyte Communities on Prairie Dalea

DeMers, Mara ProQuest Dissertations & Theses University of Minn 2021 해외박사(DDOD)

Prairie has become one of the most endangered biomes in North America under changing climates engendered by anthropogenic activity. The patterns of diversity we observe of native prairie species in remnant prairie sites are the outcome of both historical and contemporary processes, and understanding these underlying processes will inform the responses of these populations to future environmental changes.The assembly of fungal endophyte communities within plants depends on the complex interactions of fungal taxa, their host plants, and the abiotic environment. Prairie plant communities provide a unique avenue to explore the interplay of biotic and abiotic factors affecting endophyte communities, since the historical distribution of prairies spans a broad range of temperature and precipitation, while the distances between small fragments of contemporary prairie communities may challenge the dispersal capabilities of these otherwise ubiquitous fungi. We sampled foliar fungal endophytes from two native prairie legumes, purple and white prairie clovers (Dalea purpurea and D. candida), in 17 remnant prairie sites across Minnesota in order to evaluate the relative contributions of abiotic factors, host species, and dispersal limitation to the diversity and structure of these communities. We found that similarity of communities was significantly associated with their location along a temperature and precipitation gradient, and we showed a distance-decay relationship that suggests dispersal limitations only over very large spatial scales. Although the effect of host species was small relative to these other factors, the two Dalea species maintained distinct communities within sites where they co-occur. Our results illustrate the capacity of many of these endophyte taxa to disperse over large distances and across heterogeneous biotic and abiotic environments and suggest that the interplay of biotic and abiotic factors maintains high diversity observed in endophyte communities.Our results showed that community composition of endophytic fungi in Dalea spp. varied along a precipitation and temperature gradient, among hosts, and in apparent response to the abundance of Alternaria spp., but left unexplained patterns of genetic variation among the many isolates assigned to Alternaria alternata. We used genotyping-by-sequencing (GBS) to assess population genetic structure of endophytic Alternaria among sampling sites and between host species, and compare levels of recombination and clonality and assess evidence for sexual or parasexual reproduction in these communities. We found cryptic diversity among sequenced samples, as only a subset aligned well to A. alternata reference genomes. Analysis of sequences closely related to reference A. alternata genomes, treated here as a single species, revealed a high level of clonality, and genotypic diversity shared across populations. However, we also detected evidence of recombination events consistent with sexual or parasexual reproduction, as well as two mating types, MAT1-1 and MAT1-2, which were present in roughly equal frequencies in all but one sampled population. Together, the results suggest recent asexual proliferation after rapid colonization of the sampled sites from an ancestral source population. Recombination likely occurred more frequently in the source population, and is now rare.