Essays in Dynamic Corporate Finance

My dissertation aims at understanding the financing and investment decisions of firms. It contains two chapters. Chapter One studies the currency composition of debt for firms in emerging economies. Using a dataset of traded Mexican firms, I document two stylized facts about firms in the non-tradable sector: (i) they take on large amounts of dollar-denominated debt and (ii) their earnings are not sensitive to the exchange rate. I propose an explanation based on imperfect competition in the domestic goods market that reconciles these seemingly contradictory empirical facts. First I develop a stylized model of production and financing for firms in an open economy. I show that non-exporting firms are exposed to exchange rate risk because of the presence of exporters in the economy, and that they hedge their currency exposure using dollar debt. An extended model is used to quantify how much of the dollar debt in the data can be explained through this channel. A calibrated version of the model can account for all of the dollar debt observed in the data. Chapter Two investigates the relationship between the investment decisions of firms and their cost of financing. Recent empirical work using panel data documents that, while the correlation of investment and Tobin\u27s Q is low, the correlation of investment and credit spreads is high. We propose an explanation for these empirical findings, based on time-varying risk, i.e. stochastic volatility. In our model, firms finance investments using defaultable debt as well as equity issuance, and they are subject to standard profitability shocks as well as shocks to volatility. An increase in volatility leads to an increase in the probability of default and hence the credit spread, while reducing investment and increasing equity value. This shock hence generates a negative correlation between investment and credit spreads, and between investment and Q, helping the model match the data

The Topology ToolKit

This system paper presents the Topology ToolKit (TTK), a software platform designed for topological data analysis in scientific visualization. TTK provides a unified, generic, efficient, and robust implementation of key algorithms for the topological analysis of scalar data, including: critical points, integral lines, persistence diagrams, persistence curves, merge trees, contour trees, Morse-Smale complexes, fiber surfaces, continuous scatterplots, Jacobi sets, Reeb spaces, and more. TTK is easily accessible to end users due to a tight integration with ParaView. It is also easily accessible to developers through a variety of bindings (Python, VTK/C++) for fast prototyping or through direct, dependence-free, C++, to ease integration into pre-existing complex systems. While developing TTK, we faced several algorithmic and software engineering challenges, which we document in this paper. In particular, we present an algorithm for the construction of a discrete gradient that complies to the critical points extracted in the piecewise-linear setting. This algorithm guarantees a combinatorial consistency across the topological abstractions supported by TTK, and importantly, a unified implementation of topological data simplification for multi-scale exploration and analysis. We also present a cached triangulation data structure, that supports time efficient and generic traversals, which self-adjusts its memory usage on demand for input simplicial meshes and which implicitly emulates a triangulation for regular grids with no memory overhead. Finally, we describe an original software architecture, which guarantees memory efficient and direct accesses to TTK features, while still allowing for researchers powerful and easy bindings and extensions. TTK is open source (BSD license) and its code, online documentation and video tutorials are available on TTK's website

A New Antigen Recognized by Cytolytic T Lymphocytes on a Human Kidney Tumor Results from Reverse Strand Transcription

By stimulating blood lymphocytes from a renal cell carcinoma patient in vitro with the autologous tumor cells, we obtained cytolytic T lymphocyte (CTL) clones that killed several autologous and allogeneic histocompatibility leukocyte antigen (HLA)-B7 renal carcinoma cell lines. We identified the target antigen of these CTLs by screening COS cells transfected with the HLA-B7 cDNA and with a cDNA library prepared with RNA from the tumor cells. The antigenic peptide recognized by the CTLs has the sequence LPRWPPPQL and is encoded by a new gene, which we named RU2. This gene is transcribed in both directions. The antigenic peptide is not encoded by the sense transcript, RU2S, which is expressed ubiquitously. It is encoded by an antisense transcript, RU2AS, which starts from a cryptic promoter located on the reverse strand of the first intron and ends up on the reverse strand of the RU2S promoter, which contains a polyadenylation signal. This mechanism of antigen expression is unprecedented and further illustrates the notion that many peptides recognized by T cells cannot be predicted from the primary structure of the major product of the encoding gene. Antisense transcript RU2AS is expressed in a high proportion of tumors of various histological types. It is absent in most normal tissues, but is expressed in testis and kidney, and, at lower levels, in urinary bladder and liver. Short-term cultures of normal epithelial cells from the renal proximal tubule expressed significant levels of RU2AS message and were recognized by the CTLs. Therefore, this antigen is not tumor specific, but corresponds to a self-antigen with restricted tissue distribution

Phylogeography of harbour porpoise (Phocoena phocoena) in the Southeastern North Atlantic and in the Black sea explored by the analyses of nuclear and mitochondrial DNA

19th Annual Conference of the European Cetacean Society and associated workshop, April 2-7, 2005, La Rochelle, FranceIn recent years, a decline in harbour porpoise (Phocoena phocoena) populations in the North Atlantic has been reported and this has raised concern over population sustainabilityN

Photodynamic and Antibiotic Therapy Impair the Pathogenesis of Enterococcus faecium in a Whole Animal Insect Model

Enterococcus faecium has emerged as one of the most important pathogens in healthcare-associated infections worldwide due to its intrinsic and acquired resistance to many antibiotics, including vancomycin. Antimicrobial photodynamic therapy (aPDT) is an alternative therapeutic platform that is currently under investigation for the control and treatment of infections. PDT is based on the use of photoactive dye molecules, widely known as photosensitizer (PS). PS, upon irradiation with visible light, produces reactive oxygen species that can destroy lipids and proteins causing cell death. We employed Galleria mellonella (the greater wax moth) caterpillar fatally infected with E. faecium to develop an invertebrate host model system that can be used to study the antimicrobial PDT (alone or combined with antibiotics). In the establishment of infection by E. faecium in G. mellonella, we found that the G. mellonella death rate was dependent on the number of bacterial cells injected into the insect hemocoel and all E. faecium strains tested were capable of infecting and killing G. mellonella. Antibiotic treatment with ampicillin, gentamicin or the combination of ampicillin and gentamicin prolonged caterpillar survival infected by E. faecium (P = 0.0003, P = 0.0001 and P = 0.0001, respectively). In the study of antimicrobial PDT, we verified that methylene blue (MB) injected into the insect followed by whole body illumination prolonged the caterpillar survival (P = 0.0192). Interestingly, combination therapy of larvae infected with vancomycin-resistant E. faecium, with antimicrobial PDT followed by vancomycin, significantly prolonged the survival of the caterpillars when compared to either antimicrobial PDT (P = 0.0095) or vancomycin treatment alone (P = 0.0025), suggesting that the aPDT made the vancomycin resistant E. faecium strain more susceptible to vancomycin action. In summary, G. mellonella provides an invertebrate model host to study the antimicrobial PDT and to explore combinatorial aPDT-based treatments

New Insight into the Colonization Processes of Common Voles: Inferences from Molecular and Fossil Evidence

Elucidating the colonization processes associated with Quaternary climatic cycles is important in order to understand the distribution of biodiversity and the evolutionary potential of temperate plant and animal species. In Europe, general evolutionary scenarios have been defined from genetic evidence. Recently, these scenarios have been challenged with genetic as well as fossil data. The origins of the modern distributions of most temperate plant and animal species could predate the Last Glacial Maximum. The glacial survival of such populations may have occurred in either southern (Mediterranean regions) and/or northern (Carpathians) refugia. Here, a phylogeographic analysis of a widespread European small mammal (Microtus arvalis) is conducted with a multidisciplinary approach. Genetic, fossil and ecological traits are used to assess the evolutionary history of this vole. Regardless of whether the European distribution of the five previously identified evolutionary lineages is corroborated, this combined analysis brings to light several colonization processes of M. arvalis. The species' dispersal was relatively gradual with glacial survival in small favourable habitats in Western Europe (from Germany to Spain) while in the rest of Europe, because of periglacial conditions, dispersal was less regular with bottleneck events followed by postglacial expansions. Our study demonstrates that the evolutionary history of European temperate small mammals is indeed much more complex than previously suggested. Species can experience heterogeneous evolutionary histories over their geographic range. Multidisciplinary approaches should therefore be preferentially chosen in prospective studies, the better to understand the impact of climatic change on past and present biodiversity

Phylogeographic Study of Apodemus ilex (Rodentia: Muridae) in Southwest China

BACKGROUND: The Mountains of southwest China have complex river systems and a profoundly complex topography and are among the most important biodiversity hotspots in the world. However, only a few studies have shed light on how the mountains and river valleys promote genetic diversity. Apodemus ilex is a fine model for investigating this subject. METHODOLOGY/PRINCIPAL FINDINGS: To assess the genetic diversity and biogeographic patterns of Apodemus ilex, the complete cytochrome b gene sequences (1,140 bp) were determined from 203 samples of A. draco/ilex that were collected from southwest China. The results obtained suggested that A. ilex and A. draco are sistergroups and diverged from each other approximately 2.25 million years ago. A. ilex could be divided into Eastern and Western phylogroups, each containing two sub-groups and being widespread in different geographical regions of the southern Hengduan Mountains and the western Yunnan - Guizhou Plateau. The population expansions of A. ilex were roughly from 0.089 Mya to 0.023 Mya. CONCLUSIONS: Our result suggested that A. ilex is a valid species rather than synonym of A. draco. As a middle-high elevation inhabitant, the phylogenetic pattern of A. ilex was strongly related to the complex geographical structures in southwest China, particularly the existence of deep river valley systems, such as the Mekong and Salween rivers. Also, it appears that the evolutionary history of A. ilex, such as lineage divergences and population expansions were strongly affected by climate fluctuation in the Late Pleistocene

Pan-African Genetic Structure in the African Buffalo (Syncerus caffer): Investigating Intraspecific Divergence

The African buffalo (Syncerus caffer) exhibits extreme morphological variability, which has led to controversies about the validity and taxonomic status of the various recognized subspecies. The present study aims to clarify these by inferring the pan-African spatial distribution of genetic diversity, using a comprehensive set of mitochondrial D-loop sequences from across the entire range of the species. All analyses converged on the existence of two distinct lineages, corresponding to a group encompassing West and Central African populations and a group encompassing East and Southern African populations. The former is currently assigned to two to three subspecies (S. c. nanus, S. c. brachyceros, S. c. aequinoctialis) and the latter to a separate subspecies (S. c. caffer). Forty-two per cent of the total amount of genetic diversity is explained by the between-lineage component, with one to seventeen female migrants per generation inferred as consistent with the isolation-with-migration model. The two lineages diverged between 145 000 to 449 000 years ago, with strong indications for a population expansion in both lineages, as revealed by coalescent-based analyses, summary statistics and a star-like topology of the haplotype network for the S. c. caffer lineage. A Bayesian analysis identified the most probable historical migration routes, with the Cape buffalo undertaking successive colonization events from Eastern toward Southern Africa. Furthermore, our analyses indicate that, in the West-Central African lineage, the forest ecophenotype may be a derived form of the savanna ecophenotype and not vice versa, as has previously been proposed. The African buffalo most likely expanded and diverged in the late to middle Pleistocene from an ancestral population located around the current-day Central African Republic, adapting morphologically to colonize new habitats, hence developing the variety of ecophenotypes observed today

Suppression of Friction-Induced Oscillations through Use of High-Frequency Dither Signals

Friction-induced oscillations occur in many engineering systems, often resulting in noise, vibration, and excessive or uneven wear. This research addresses the suppression of such oscillations, especially with application to braking systems, through the use of high-frequency dither signals. Brake squeal is an annoying and elusive problem too often present in braking systems of automobiles, trucks and aircraft. In previous work, the effectiveness of high-frequency dither to eliminate squeal in an automotive disc brake assembly was demonstrated experimentally. The main features of the dither-squeal cancellation system was the application of a high frequency variation in the brake pressure force accomplished by means of a piezoelectric stack placed behind one of the brake pads. This thesis contains a theoretical and numerical treatment of the application of dither to frictional systems. Two types of systems are investigated. The first is a classic, mass-on-a-moving belt problem, which experiences friction-induced oscillations similar to those encountered in brake applications. The system is first studied using an analytical technique based on the method of averaging. It is shown that, depending on the system, friction, dither-waveform, and belt-speed parameters, dither can stabilize an unstable system. However, in some cases, dither can destabilize an initially stable system. These results are verified numerically using time integration. The second type of system analyzed in this thesis is an annular plate with a rotating frictional device. The method of multiple scales is used to predict subcritical regions of instability; the results are validated using Floquet theory. The thesis treats both tangential and normal dither, the latter being closer to the brake application. It is found that normal dither, in addition to being harder to analyze, is much less effective than tangential dither.Ph.D.Committee Co-Chair: Aldo A. Ferri; Committee Co-Chair: Kenneth A. Cunefare; Committee Member: Jerry H. Ginsberg; Committee Member: Laurence J. Jacobs; Committee Member: Olivier A. Baucha