Dynamics of Rotation of Super-Earths

We numerically investigate the dynamics of rotation of several close-in terrestrial exoplanet candidates. In our model, the rotation of the planet is disturbed by the torque of the central star due to the asymmetric equilibrium figure of the planet. We model the shape of the planet by a Jeans spheroid. We use surfaces of section and spectral analysis to explore numerically the rotation phase space of the systems adopting different sets of parameters and initial conditions close to the main spin-orbit resonant states. One of the parameters, the orbital eccentricity, is critically discussed here within the domain of validity of orbital circularization timescales given by tidal models. We show that, depending on some parameters of the system like the radius and mass of the planet, eccentricity etc, the rotation can be strongly perturbed and a chaotic layer around the synchronous state may occupy a significant region of the phase space. 55 Cnc e is an example.Comment: In Press. Celestial Mechanics and Dynamical Astronomy. 30 pages, 9 figure

Spin-orbit coupling for tidally evolving super-Earths

We investigate the spin behavior of close-in rocky planets and the implications for their orbital evolution. Considering that the planet rotation evolves under simultaneous actions of the torque due to the equatorial deformation and the tidal torque, both raised by the central star, we analyze the possibility of temporary captures in spin-orbit resonances. The results of the numerical simulations of the exact equations of motions indicate that, whenever the planet rotation is trapped in a resonant motion, the orbital decay and the eccentricity damping are faster than the ones in which the rotation follows the so-called pseudo-synchronization. Analytical results obtained through the averaged equations of the spin-orbit problem show a good agreement with the numerical simulations. We apply the analysis to the cases of the recently discovered hot super-Earths Kepler-10 b, GJ 3634 b and 55 Cnc e. The simulated dynamical history of these systems indicates the possibility of capture in several spin-orbit resonances; particularly, GJ 3634 b and 55 Cnc e can currently evolve under a non-synchronous resonant motion for suitable values of the parameters. Moreover, 55 Cnc e may avoid a chaotic rotation behavior by evolving towards synchronization through successive temporary resonant trappings.Comment: Accepted for publication in MNRA

Utilization of Organic Co-Solvents to Enhance Bacterial Conversion of Poorly Water-Soluble Compounds

Mass transfer of a poorly water-soluble gas in fermentations can reduce the performance of bioreactors. In aerobic fermentations, oxygen often becomes a limiting factor. In the biodegradation of volatile organic contaminants, their poor water solubilities often regulate the process. In fermentations of synthesis gas to fuels and chemicals, the issue of mass transfer is apparent. Since the mass transfer rate of the gaseous substrate to the aqueous phase is often the rate-limiting step in the bacterial conversion, many different reactor configurations have been suggested. An alternative approach could be to incorporate a co-solvent, which has properties that will increase the interfacial mass-transfer area and thereby improve the overall conversion rate. In this thesis work, two bacterial systems were used to illustrate enhancement of the conversion of poorly water-soluble substrates by the addition of co-solvents. The first tested system was anaerobic conversion of synthesis gas by Clostridium ljungdahlii and the second was aerobic conversion of toluene by Pseudomonas putida F1. Clostridium ljungdahlii (ATCC 55383) converts coal synthesis gas (carbon monoxide, hydrogen, and carbon dioxide) into ethanol and acetic acid. A limiting factor in this process is the low solubility of synthesis gas in aqueous media. Different co-solvent systems were evaluated to increase the effective conversion rate of carbon monoxide. The Ostwald coefficient and the octanol-water partition coefficient values were considered when selecting co-solvent systems, and serum bottle experiments were performed to test solvent systems for biocompatibility. Hexadecane proved to the best solvent tested in terms of both gas conversion rate and biocompatibility. Serum bottles with 10% hexadecane (v/v) converted 100% of the available carbon monoxide to products, while in the control serum bottles, only 30% was converted during the same time. Pseudomonas putida F1 (ATCC 700007) was used as a model organism to study the conversion enhancement of toluene in stirred tank reactors. Silicone oil was used as a co-solvent with and without rhamnolipids (biosurfactants) to enhance the mass transfer rate. Batch experiments were conducted in two side-by-side fermentation vessels; one with silicone oil and one without it. Silicone oil was tested at three different concentrations: 10%, 30%, and 50% (v/v). Results showed that the presence of 30% silicone oil resulted in a 20% higher conversion of toluene when compared to the control. Rhamnolipids were tested at two different concentrations: 0.025% (no silicone oil) and 0.0025% (with 30% silicone oil) (w/v). No significant enhancement in conversion was observed when rhamnolipids were only added by themselves or when they were added in conjunction with 30% silicone oil. In subsequent experiments, results showed that increasing the silicone oil from 20% to 35% in a continuous stirred tank reactor increased the conversion rate by 10%

New records of biting midges of the genus Culicoides Latreille from Mexico (Diptera: Ceratopogonidae)

We provide the first records of six species of biting midges (Diptera: Ceratopogonidae) in the genus Culicoides Latreille from Mexico: C. baueri Hoffman, C. castillae Fox, C. debilipalpis Lutz, C. iriartei Fox, C. leoni Barbosa and C. pusilloides Wirth and Blanton. In addition, C. leopoldoi Ortiz is confirmed from Mexico, and new records are included for 25 other species previously recorded in Mexico: C. arubae Fox and Hoffman, C. blantoni Vargas and Wirth, C. crepuscularis Malloch, C. daedalus Macfie, C. diabolicus Hoffman, C. foxi Ortiz, C. furens (Poey), C. gabaldoni Ortiz, C. haematopotus Malloch, C. hylas Macfie, C. insignis Lutz, C. jamaicensis Edwards, C. luteovenus Root and Hoffman, C. neopulicaris Wirth, C. nigrigenus Wirth and Blanton, C. pampoikilus Macfie, C. panamensis Barbosa, C. paraensis (Goeldi), C. phlebotomus (Williston), C. poikilonotus Macfie, C. pusillus Lutz, C. stigmalis Wirth, and all three species in the C. (Monoculicoides) variipennis complex, C. variipennis (Coquillett), C. occidentalis Wirth and Jones, and C. sonorensis Wirth and Jones

Design and Optimization of a Mycoplasma Detection Assay

Mycoplasma are among the smallest free living microorganisms. These bacteria grow slowly, lack a rigid cell wall and are not eliminated by filter sterilization methods used in tissue culture. Mycoplasma infection affects biochemical and genetic aspects of cultured cells, resulting in experimental inconsistency. Therefore, it is necessary to establish routine testing for mycoplasma contamination in tissue culture laboratories. Our goal is to develop a reliable and cost-effective test for mycoplasma in cell culture based on established methods found in literature. We first cloned and sequenced a PCR product from a commercial mycoplasma detection kit. Sequencing revealed the 16s rRNA as the target for mycoplasma detection; we confirmed this target by conducting a literature search. PCR primers were designed using 16s rRNA gene as a target. We set-up reactions and optimized conditions for the real-time PCR assay to detect the target and confirmed amplicon size with agarose gel electrophoresis. We identified that 56oC was the best temperature for the PCR and found that agarose gel electrophoresis was a better detection method because it identified the size to confirm the proper product. The primers we ordered to develop this assay produce the proper band; however, results of several assays have been inconsistent as sometimes a known positive sample fails to amplify. As well, in several PCR reactions the negative showed a signal. The overall reaction needs improvements to have greater reliability and to eliminate all sources of contamination. Research is continuing results are not final

Three Essays in International Finance

In this dissertation, I focus my research on some of the economically significant and current open problems in international finance, specifically the relationship between Credit Default Swaps (CDS) on sovereign debt, the importance of fundamental dyadic distances on the initiation and completion of cross-border mergers and acquisitions, and the impact of domestic and transnational terrorism on cross-border mergers and acquisitions. In the first essay, we study the relationship between sovereign debt ratings and the information contained in CDS spreads regarding the credit risk of the reference entity. Using data for 54 countries over a twelve-year period, we find that the variation in average sovereign ratings in a given year can be explained by average CDS spreads over the previous three years. In a horse race between CDS spreads and sovereign ratings, we find that CDS spread changes can predict sovereign events while rating changes cannot. In the second essay, we study how dyadic distance influences the initiation, completion, and duration of cross-border mergers and acquisitions. Using a sample of 173,616 cross-border deals announced between 1970 and 2016, we find evidence that cross-country cultural, institutional, geographical, religious, and language differences, all play a deciding role in the initiation of mergers and acquisitions. The completion of acquisitions is independent of cultural factors, but largely depends on differences in economy size, language, religion, and bureaucracy of the acquiring and target countries. Finally, the duration of deals is influenced by idiosyncratic factors only. In the third essay, we study whether incidents of domestic and transnational terrorism impact the propensity of firms to acquire cross-border firms. We adopt a theoretical model to show that high levels of terrorism in the target countries are associated with lower cross-border acquisition flows. Empirically, we exploit the exogenous variation induced by differences in genetic diversity, ethnic fractionalization, and religious fractionalization between acquirer and target countries. Our results show that an target from a country with lower terrorist incidents than the acquirer country are associated with more cross-border mergers and acquisitions

The orbit of Aegaeon and the 7:6 Mimas-Aegaeon resonance

Aegaeon (S/2008 S 1) is the last satellite discovered by the Cassini spacecraft at the end of the 2000s. Like the satellites Methone and Anthe, it is involved in mean motion resonance with the mid-sized Mimas. In this work, we give a detailed analysis of the current orbit of Aegaeon identifying the resonant, secular and long-term perturbations due to Mimas and the oblateness of Saturn, and the effects of Tethys. For this task, we perform thousands of numerical simulations of full equations of motion of ensembles of small bodies representing clones of Aegaeon. We have mapped the domain of the 7:6 Mimas-Aegaeon resonance in the phase space of the semi-major axis and eccentricity. It displays a large area dominated by regular motions associated with the 7:6 corotation resonance surrounded by chaotic layers. Aegaeon is currently located very close to the periodic orbit of the resonance, which extends up to eccentricities $\sim0.025$ centered at semi-major axis $\sim168,028$ km. We show that the current orbit of Aegaeon has an important forced component in eccentricity due to the 7:6 resonance. The orbital inclination of Aegaeon has a non-negligible forced value due to long-term perturbations of Mimas. These two forced modes explain the complex perturbed orbit of Aegaeon without requiring the co-existence of multiple resonances.Comment: Published in Celestial Mechanics and Dynamical Astronomy. Due to a journal production problem, two terms have been missed in the second line of Table 1 (e_o and e_o^3