The Formation of Star Clusters II: 3D Simulations of Magnetohydrodynamic Turbulence in Molecular Clouds

(Abridged) We present a series of decaying turbulence simulations that represent a cluster-forming clump within a molecular cloud, investigating the role of magnetic fields on the formation of potential star-forming cores. We present an exhaustive analysis of numerical data from these simulations that includes a compilation of all of the distributions of physical properties that characterize bound cores - including their masses, radii, mean densities, angular momenta, spins, magnetizations, and mass-to-flux ratios. We also present line maps of our models that can be compared with observations. Our simulations range between 5-30 Jeans masses of gas, and are representative of molecular cloud clumps with masses between 100-1000 solar masses. The cores have mass-to-flux ratios that are generally less than that of the original cloud, and so a cloud that is initially highly supercritical can produce cores that are slightly supercritical, similar to that seen by Zeeman measurements of molecular cloud cores. Clouds that are initially only slightly supercritical will instead collapse along the field lines into sheets, and the cores that form as these sheets fragment have a different mass spectrum than what is observed. The spin rates of these cores suggests that subsequent fragmentation into multiple systems is likely. The sizes of the bound cores that are produced are typically 0.02-0.2 pc and have densities in the range 10^4-10^5 cm^{-3} in agreement with observational surveys. Finally, our numerical data allow us to test theoretical models of the mass spectrum of cores, such as the turbulent fragmentation picture of Padoan-Nordlund. We find that while this model gets the shape of the core mass spectrum reasonably well, it fails to predict the peak mass in the core mass spectrum.Comment: Accepted by MNRAS. 28 pages, 16 figures. Substantial revision since last versio

An AI approach for scheduling space-station payloads at Kennedy Space Center

The Payload Processing for Space-Station Operations (PHITS) is a prototype modeling tool capable of addressing many Space Station related concerns. The system's object oriented design approach coupled with a powerful user interface provide the user with capabilities to easily define and model many applications. PHITS differs from many artificial intelligence based systems in that it couples scheduling and goal-directed simulation to ensure that on-orbit requirement dates are satisfied

Dynamics of rapidly rotating Bose-Einstein condensates in a harmonic plus quartic trap

A two-dimensional rapidly rotating Bose-Einstein condensate in a harmonic plus quartic trap is expected to have unusual vortex states that do not occur in a pure harmonic trap. At a critical rotation speed $\Omega_h$, a central hole appears in the condensate, and at some faster rotation speed $\Omega_g$, the system undergoes a transition to a giant vortex state with pure irrotational flow. Using a time-dependent variational analysis, we study the behavior of an annular condensate with a single concentric ring of vortices. The transition to a giant vortex state is investigated by comparing the energy of the two equilibrium states (the ring of vortices and the giant vortex) and also by studying the dynamical stability of small excitation modes of the ring of vortices.Comment: 12pages, 4figure

The green sea turtle: adaptation and resilience to climate change

Sea turtles are a globally distributed migratory species that use a range of habitats during their life cycle, including both land and sea. As egg laying ectotherms they are particularly susceptible to variation in temperature, especially during clutch incubation. Climate change models predict increasing temperatures over the course of the century, along with sea level rise, and changes in weather patterns. Understanding how these factors impact the environment and such ectothermic species is key to their survival. The green sea turtle, Chelonia mydas, is one of the best studied sea turtle species, and like all seven species they are of conservation concern, thus understanding the impact of climate change on this group is of importance for their conservation. In this thesis I seek to investigate the impacts of temperature on offspring sex ratios and hatching success, two key parameters in the reproductive biology of sea turtles, using the Ascension Island rookery as model population. This will infer knowledge on adaptation and resilience to climate change. I first carry out a literature review (Chapter 2) to evaluate the existing knowledge of current primary sex ratios, and find that despite nearly four decades of work on the topic, little progress has been made. Indeed, only four studies have been published on sex determining temperatures in laboratory conditions, and a range of varying methods have been used. I then carried out a laboratory-based study to establish the pivotal temperature, the temperature at which an equal proportion of male and females are produced, (29.3°C) for the Ascension Island green turtle rookery (Chapter 3) and carry out a translocation experiment to determine whether maternal philopatry confers any form of advantage to incubating clutches through localised adaptation (Chapter 4). Neither under laboratory conditions, nor in-situ do I find any evidence of localised thermal adaptation; hatching success drops with increasing temperatures, and clutches from different thermal backgrounds produce equivalent proportions of males and females. Finally, I use this information to evaluate island wide sex ratios and offspring output, based on different climate projection scenarios (Chapter 5). I find that the primary sex ratio will likely be extremely female biased (> 90%) by the end of the century, with hatching success starting to decrease in the most extreme scenarios, especially at the darker beaches where temperatures will exceed thresholds for successful incubation. The geographic isolation of Ascension Island means that there are limited opportunities for dispersal. A full assessment of the impacts of climate change on sea level rise, coastal erosion and changes in weather patterns may provide more information on the treats and opportunities that this population faces. In the meantime, a change in nesting seasonality or nesting distribution within the beaches of Ascension may provide critical to mitigate the impacts of increasing temperatures.Natural Environment Research Council (NERC

Tracking ocean wave spectrum from SAR images

An end to end algorithm for recovery of ocean wave spectral peaks from Synthetic Aperture Radar (SAR) images is described. Current approaches allow precisions of 1 percent in wave number, and 0.6 deg in direction

SSME structural dynamic model development

A mathematical model of the Space Shuttle Main Engine (SSME) as a complete assembly, with detailed emphasis on LOX and High Fuel Turbopumps is developed. The advantages of both complete engine dynamics, and high fidelity modeling are incorporated. Development of this model, some results, and projected applications are discussed

Local contribution of a quantum condensate to the vacuum energy density

We evaluate the local contribution g_[mu nu]L of coherent matter with lagrangian density L to the vacuum energy density. Focusing on the case of superconductors obeying the Ginzburg-Landau equation, we express the relativistic invariant density L in terms of low-energy quantities containing the pairs density. We discuss under which physical conditions the sign of the local contribution of the collective wave function to the vacuum energy density is positive or negative. Effects of this kind can play an important role in bringing about local changes in the amplitude of gravitational vacuum fluctuations - a phenomenon reminiscent of the Casimir effect in QED.Comment: LaTeX, 8 pages. Final journal versio

Gravitational waves in preheating

We study the evolution of gravitational waves through the preheating era that follows inflation. The oscillating inflaton drives parametric resonant growth of scalar field fluctuations, and although super-Hubble tensor modes are not strongly amplified, they do carry an imprint of preheating. This is clearly seen in the Weyl tensor, which provides a covariant description of gravitational waves.Comment: 8 pages, 8 figures, Revte