The Expanded Very Large Array

In almost 30 years of operation, the Very Large Array (VLA) has proved to be a remarkably flexible and productive radio telescope. However, the basic capabilities of the VLA have changed little since it was designed. A major expansion utilizing modern technology is currently underway to improve the capabilities of the VLA by at least an order of magnitude in both sensitivity and in frequency coverage. The primary elements of the Expanded Very Large Array (EVLA) project include new or upgraded receivers for continuous frequency coverage from 1 to 50 GHz, new local oscillator, intermediate frequency, and wide bandwidth data transmission systems to carry signals with 16 GHz total bandwidth from each antenna, and a new digital correlator with the capability to process this bandwidth with an unprecedented number of frequency channels for an imaging array. Also included are a new monitor and control system and new software that will provide telescope ease of use. Scheduled for completion in 2012, the EVLA will provide the world research community with a flexible, powerful, general-purpose telescope to address current and future astronomical issues.Comment: Added journal reference: published in Proceedings of the IEEE, Special Issue on Advances in Radio Astronomy, August 2009, vol. 97, No. 8, 1448-1462 Six figures, one tabl

Mass and heat transfer processes in magmatic orogens driven by magmatism, tectonic deformation, and surface erosion

Magmatic orogens are continental arcs and collisional belts that are associated with syn-tectonic magmatism. They record heat and mass transfer processes acting from the mantle to the surface. While magmatism, deformation, and surface erosion each take place at various depth levels, they are dynamically linked processes through interaction in the lithosphere. This dissertation presents an investigation of how heat and mass transfer processes in the lithosphere affect the evolution of magmatic orogens. I first present an evaluation of magma genesis resulting from partial melting of underthrusted lower crust. The causes of episodic magmatism in the Mesozoic Sierra Nevada continental magmatic arc and the sources of high-magma flux (flare-ups) are under debate. Here, I use the results of numerical modeling and scaling analysis to assess the mass balance and thermodynamic feasibility of generating arc magma as a result of partial melting of underthrusted lower crust. I show with a constant underthrusting rate of 5 km/Myr, the magmatic thickening rate is 0.1-0.3 km/Myr, accounting for 10-30% of the magmatic thickening rate during a flare-up. The cumulative volume of magma generated from the partial melting of a 20-km-thick underthrusted lower crust is on the order of 105 km3, ~10-40% of the estimated magma volume generated during a flare-up. Therefore, the results show that partial melting of underthrusted lower crust plays a subsidiary role in driving a magmatic flare-up event. Additional magma derived from the mantle and/or other crustal sources are needed to achieve the observed magmatic output during flare-ups. However, the arc root developed by partial melting of the underthrusted crust reduces the time needed to obtain the critical thickness for root foundering, thus influencing the tempo of arc magmatism. As magma ascends into the crust, its interactions with the deforming crust are recorded in the exhumation history of a tilted crustal section and fabrics in plutons. The Gangdese Batholith is well exposed in southern Tibet and presents a unique opportunity to investigate the evolution of a continental arc from subduction to collision. I applied Al-in-hornblende barometry across the eastern Gangdese Batholith to obtain pluton emplacement pressures to identify potential spatial trends in bedrock pressure. The results reveal a regional paleo-depth pattern with plutons emplaced at 1-2 kbar in the west near Lhasa that deepens to 6-12 kbars in the east, near Nyingchi. By coupling the pressure data with U-Pb zircon ages, I estimate the exhumation history of the Gangdese Batholith since 100 Ma and show a sequence of exhumation and burial phases as well as the expected changes in crustal thickness, reflecting major tectonic events including the development of a continental arc and the India-Asia continent-continent collision. I hypothesize that the Gangdese Batholith was tilted due to differential exhumation along the E-W direction since ~10 Ma, associated with the formation of the eastern Himalayan syntaxis. Along with the exhumation history, I also studied fabrics recorded by the Gangdese plutons and report magmatic fabric measurements from the eastern Gangdese Batholith, aimed to decipher the crustal response to changes in India-Asia convergence style from subduction to collision. Results show magmatic fabric orientations are variable through time and represent: (1) a pre-collision Late Cretaceous subduction phase of orogen-perpendicular contraction and crustal thickening. (2) Transitional Paleocene-Eocene crustal thinning and a change in crustal contraction stress from ~N-S to ~E-W. (3) Post-Eocene crustal thickening without a clear, dominant principal stress direction. The pre-collision Late Cretaceous fabrics are interpreted to record approximate head-on subduction of the Neo-Tethyan oceanic plate beneath the Asian continent, while the post-collision fabrics reflect the enigmatic nature of the India-Asia collision, as well as the complexity of the post-collisional processes. Motivated by the recognition of the tilted Gangdese crust, I explored the role of surface erosion in driving solid earth processes. Particularly, whether erosion-driven rock uplift is responsible for the rapid exhumation of the eastern Himalayan syntaxis (EHS). Results of numerical simulations show that localized surface erosion (5 km/Myr) is able to exhume lower crust from depths of >40 km on timescale of ~10 Myr, produce high topography, and generate partial melt in the lower crust. Erosion-driven advection elevates the local geothermal gradient and reduces crustal viscosity, promoting deformation. Exhumation is sustained by isostatic flow resulting from lithostatic pressure difference and amplified by crustal diapirism, associated with the presence of hot and buoyant molten rocks in the weakened advection channel. Such diapiric upwellings trigger a rapid acceleration in rock uplift rates to values greater than the driving erosional forcing and cause localized surface uplift, resulting in topography higher than surrounding regions. The erosion-driven exhumation model demonstrates the intricate coupling between surface erosion and rock uplift, as well as the active role of surface erosion in driving orogenic evolution

Metamorphosis Imposes Variable Constraints on Genome Expansion through Effects on Development

Genome size varies ∼100,000-fold across eukaryotes and has long been hypothesized to be influenced by meta- morphosis in animals. Transposable element accumulation has been identified as a major driver of increase, but the nature of constraints limiting the size of genomes has remained unclear, even as traits such as cell size and rate of development co-vary strongly with genome size. Salamanders, which possess diverse metamorphic and non-metamorphic life histories, join the lung- fish in having the largest vertebrate genomes—3 to 40 times that of humans—as well as the largest range of variation in genome size. We tested 13 biologically-inspired hypotheses exploring how the form of metamorphosis imposes varying constraints on genome expansion in a broadly representative phylogeny containing 118 species of salamanders. We show that metamorphosis during which animals undergo the most extensive and synchronous remodeling imposes the most severe constraint against genome expansion, with the severity of constraint decreasing with reduced extent and synchronicity of remodeling. More generally, our work demonstrates the potential for broader interpretation of phylogenetic comparative analysis in exploring the balance of multiple evolutionary pressures shaping phenotypic evolution

7th Annual Jackson School of Geosciences Student Research Symposium, February 3, 2018

ConocoPhillipsGeological Science

A computational model approach to assess the effect of climate change on the growth and development of tadpoles

All of the environmental conditions in nature act on an organism simultaneously. However, in experimental studies of the factors influencing metamorphosis, each factor needs to be examined individually in order to disentangle its specific effects. However, it is challenging to then build properly integrated models which include data on all of the different factors evaluated in different experiments. This study set out to develop a predictive model which could synthesize the results of several experiments on survival, development and growth of Natterjack toad (Epidalea calamita) tadpole guilds. The proposed Population Dynamic P System (PDP) model enables estimates of growth and development during the larval phase, under different environmental conditions, weather conditions, predator density, and pond characteristics and management. The architecture of the model allows the inclusion of an indefinite number of parameters and interactions, with all inputs interacting in parallel, and enables solutions to complex modeling approaches. Using the model with a range of field data, we found that the importance of predation pressure on Natterjack toad tadpole guilds exceeds the potential effects of variations in temperature and precipitation. The impact of introduced invasive predators therefore arguably poses the greatest threat to this species. This type of model holds promise as a reliable management and conservation tool for this and other species, especially where interactions between environmental factors make the impacts of individual factors difficult to predict

Control-Theoretical Perspective in Feedback-Based Systems Testing

Self-Adaptive Systems (SAS) and Cyber-Physical Systems (CPS) have received significant attention in recent computer engineering research. This is due to their ability to improve the level of autonomy of engineering artefacts. In both cases, this autonomy increase is achieved through feedback. Feedback is the iteration of sens- ing and actuation to respectively acquire knowledge about the current state of said artefacts and steer them toward a desired state or behaviour. In this thesis we dis- cuss the challenges that the introduction of feedback poses on the verification and validation process for such systems, more specifically, on their testing. We highlight three types of new challenges with respect to traditional software testing: alteration of testing input and output definition, and intertwining of components with different nature. Said challenges affect the ways we can define different elements of the test- ing process: coverage criteria, testing set-ups, test-case generation strategies, and oracles in the testing process. This thesis consists of a collection of three papers and contributes to the definition of each of the mentioned testing elements. In terms of coverage criteria for SAS, Paper I proposes the casting of the testing problem, to a semi-infinite optimisation problem. This allows to leverage the Scenario Theory from the field of robust control, and provide a worst-case probabilistic bound on a given performance metric of the system under test. For what concerns the definition of testing set-ups for control-based CPS, Paper II investigates the implications of the use of different abstractions (i.e., the use of implemented or emulated compo- nents) on the significance of the testing. The paper provides evidence that confutes the common assumption present in previous literature on the existence of a hierar- chy among commonly used testing set-ups. Finally, regarding the test-case gener- ation and oracle definition, Paper III defines the problem of stress testing control- based CPS software. We contribute to the generation and identification of stress test cases for such software by proposing a novel test case parametrisation. Leveraging the proposed parametrisation we define metamorphic relations on the expected be- haviour of the system under test. We use said relations for the development of stress testing approach and sanity checks on the testing results

Continental collision and slab break-off: numerical models and surface observables

Collision zones worldwide show a vast array of complexity that is difficult to relate to simple collision dynamics. Here we address the problem of linking surface observables to collision dynamics through the use of two and three-dimensional numerical models. We will focus on two specific observables, topography and the presence of ultra-high pressure metamorphic terranes. Our model topography predictions are used to explain the uplift and subsidence history for the Arabia-Eurasia collision. This allows us to relate the post-collisional marine deposits, found on the overriding plate, to a steepening of the subduction interface. Our three-dimensional model is used to explore possible exhumation mechanisms for the Western Gneiss Complex in Norway. From these models we show how an asymmetric collision can help drive exhumation of material that has experienced comparable conditions to the Western Gneiss Complex. The linking of upper mantle and lithosphere dynamics to both topography observation and exhumation patterns allow better understanding of the subduction and collision process