Topographic preconditioning of open ocean deep convection

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1995Evidence of enhanced oceanic convection over Maud Rise in the Weddell Sea indicates that bottom topography may play a role in selecting the location and scale of deep convecting oceanic chimneys below large scale atmospheric negative buoyancy forcing. Topographic preconditioning of open ocean deep convection is studied using an idealized, three-dimensional, primitive-equation model. A barotropic mean flow impinges on an isolated Gaussian-shaped seamount in a stratified domain with uniform negative surface buoyancy forcing. A region of topographically trapped flow forms over the topography. When this "Taylor cap" is tall enough to interact with the surface mixed-layer, the local isolation from mean horizontal advection forms a conduit into the deep water. The convective penetration depth within this local region is significantly enhanced relative to ambient levels away from the seamount and to similar runs performed without bottom topography. The parameter dependencies for these preconditioning processes are investigated. With uniform background stratification, the doming of isopycnals does not play a major role in the preconditioning process. However, when a surface intensified stratification is included, domed isopycnals associated with the Taylor cap circulation can also play a preconditioning role. In this case, the pycnocline is first ventilated over the seamount, leading to rapid convective deepening into the weakly stratified deep water. An analytical formula for one-dimensional, non-penetrative convection into an exponential stratification profile is derived and compares well with results from the numerical model. Previous modeling studies have often parameterized the mehanism by which the horizontal scale of oceanographic chimneys is set through the use of disk-shaped surface forcing functions. Unlike in such experiments, topographically preconditioned chimneys are not prone to breakup by the growth of baroclinic instabilities. Instead, convection is generally shut down by horizontal fluxes of heat due to the mean flow across the temperature gradients of the chimney walls. The presence of the mean flow, which is neccessary in order for the topographic preconditioning to work, causes instabilities to be advected downstream faster than they can grow locally. These results suggest that the role of baroclinic eddies in shutting down oceanographic convection is probably misrepresented in studies which parameterize the preconditioning mechanism, particularly if the preconditioning mechanism being parameterized is a topographic one.Financial support for the thesis research was provided by NOAA grant number NA16RC0073 and NSF grant number OCE90-04864. Additional financial support was provided by the Office of Naval Research, Physical Oceanography Division under grant number N00014- 86-K-0751 as well as an AASERT fellowship, grant number N00014-89-J-1106

A review of the population structure of yellowfin tuna, Thunnus albacares, in the Eastern Pacific Ocean

ENGLISH: Since its inception in 1950 by agreement between the Republic of Costa Rica and the United States of America, the Inter-American Tropical Tuna Commission has been engaged in studies of the biology, ecology and population dynamics of yellowfin tuna in the eastern Pacific Ocean. Prime consideration has been given to the evaluation of the effects of fishing pressure on the yellowfin tuna in this area in order to estimate the maximum sustainable yield. A portion of the eastern Pacific has been defined by the Inter-American Tropical Tuna Commission (1963) as a regulatory area for yellowfin tuna (Figure 1). SPANISH: Desde su incepción en 1950, por un acuerdo entre la República de Costa Rica y los Estados Unidos de América, la Comisión Interamericana del Atún Tropical ha estado ocupada en los estudios de la biología, ecología y dinámica de las poblaciones del atún aleta amarilla en el Océano Pacífico Oriental. Se consideró primariamente la evaluación de los efectos de la presión de la pesquería sobre el atún aleta amarilla en esta área, para poder estimar el rendimiento máximo sostenible. Una parte del Pacífico Oriental ha sido definida por la Comisión Interamericana del Atún Tropical (1963), como área de reglamentación del atún aleta amarilla (Figura 1). (PDF contains 60 pages.

Enhancing the heavy Higgs signal with jet-jet profile cuts

The jet-jet profile, or detailed manner, in which transverse energy and mass are distributed around the jet-jet system resulting from the hadronic decay of a $Z$ boson in the process Higgs$\to ZZ$ at a proton-proton collider energy of 40\tev is carefully examined. Two observables are defined that can be used to help distinguish the $\ell^+\ell^-$-jet-jet signal from Higgs decay from the ``ordinary'' QCD background arising from the large transverse momentum production of single $Z$ bosons plus the associated jets. By making cuts on these observables, signal to background enhancement factors greater than $100$ can be obtained.Comment: 16 pages, Univ. Florida IFT-93-

Extensive loss of translational genes in the structurally dynamic mitochondrial genome of the angiosperm Silene latifolia

<p>Abstract</p> <p>Background</p> <p>Mitochondrial gene loss and functional transfer to the nucleus is an ongoing process in many lineages of plants, resulting in substantial variation across species in mitochondrial gene content. The Caryophyllaceae represents one lineage that has experienced a particularly high rate of mitochondrial gene loss relative to other angiosperms.</p> <p>Results</p> <p>In this study, we report the first complete mitochondrial genome sequence from a member of this family, <it>Silene latifolia</it>. The genome can be mapped as a 253,413 bp circle, but its structure is complicated by a large repeated region that is present in 6 copies. Active recombination among these copies produces a suite of alternative genome configurations that appear to be at or near "recombinational equilibrium". The genome contains the fewest genes of any angiosperm mitochondrial genome sequenced to date, with intact copies of only 25 of the 41 protein genes inferred to be present in the common ancestor of angiosperms. As observed more broadly in angiosperms, ribosomal proteins have been especially prone to gene loss in the <it>S. latifolia </it>lineage. The genome has also experienced a major reduction in tRNA gene content, including loss of functional tRNAs of both native and chloroplast origin. Even assuming expanded wobble-pairing rules, the mitochondrial genome can support translation of only 17 of the 61 sense codons, which code for only 9 of the 20 amino acids. In addition, genes encoding 18S and, especially, 5S rRNA exhibit exceptional sequence divergence relative to other plants. Divergence in one region of 18S rRNA appears to be the result of a gene conversion event, in which recombination with a homologous gene of chloroplast origin led to the complete replacement of a helix in this ribosomal RNA.</p> <p>Conclusions</p> <p>These findings suggest a markedly expanded role for nuclear gene products in the translation of mitochondrial genes in <it>S. latifolia </it>and raise the possibility of altered selective constraints operating on the mitochondrial translational apparatus in this lineage.</p

The “fossilized” mitochondrial genome of Liriodendron tulipifera: ancestral gene content and order, ancestral editing sites, and extraordinarily low mutation rate

BACKGROUND: The mitochondrial genomes of flowering plants vary greatly in size, gene content, gene order, mutation rate and level of RNA editing. However, the narrow phylogenetic breadth of available genomic data has limited our ability to reconstruct these traits in the ancestral flowering plant and, therefore, to infer subsequent patterns of evolution across angiosperms. RESULTS: We sequenced the mitochondrial genome of Liriodendron tulipifera, the first from outside the monocots or eudicots. This 553,721 bp mitochondrial genome has evolved remarkably slowly in virtually all respects, with an extraordinarily low genome-wide silent substitution rate, retention of genes frequently lost in other angiosperm lineages, and conservation of ancestral gene clusters. The mitochondrial protein genes in Liriodendron are the most heavily edited of any angiosperm characterized to date. Most of these sites are also edited in various other lineages, which allowed us to polarize losses of editing sites in other parts of the angiosperm phylogeny. Finally, we added comprehensive gene sequence data for two other magnoliids, Magnolia stellata and the more distantly related Calycanthus floridus, to measure rates of sequence evolution in Liriodendron with greater accuracy. The Magnolia genome has evolved at an even lower rate, revealing a roughly 5,000-fold range of synonymous-site divergence among angiosperms whose mitochondrial gene space has been comprehensively sequenced. CONCLUSIONS: Using Liriodendron as a guide, we estimate that the ancestral flowering plant mitochondrial genome contained 41 protein genes, 14 tRNA genes of mitochondrial origin, as many as 7 tRNA genes of chloroplast origin, >700 sites of RNA editing, and some 14 colinear gene clusters. Many of these gene clusters, genes and RNA editing sites have been variously lost in different lineages over the course of the ensuing ∽200 million years of angiosperm evolution

Black Stork Down: Military Discourses in Bird Conservation in Malta

Tensions between Maltese hunters and bird conservation NGOs have intensified over the past decade. Conservation NGOs have become frustrated with the Maltese State for conceding to the hunter lobby and negotiating derogations from the European Union’s Bird Directive. Some NGOs have recently started to organize complex field-operations where volunteers are trained to patrol the landscape, operate drones and other surveillance technologies, detect illegalities, and lead police teams to arrest poachers. We describe the sophisticated military metaphors which conservation NGOs have developed to describe, guide and legitimize their efforts to the Maltese public and their fee-paying members. We also discuss why such groups might be inclined to adopt these metaphors. Finally, we suggest that anthropological studies of discourse could help understand delicate contexts such as this where conservation NGOs, hunting associations and the State have ended in political deadlock

Status of the LUX Dark Matter Search

The Large Underground Xenon (LUX) dark matter search experiment is currently being deployed at the Homestake Laboratory in South Dakota. We will highlight the main elements of design which make the experiment a very strong competitor in the field of direct detection, as well as an easily scalable concept. We will also present its potential reach for supersymmetric dark matter detection, within various timeframes ranging from 1 year to 5 years or more.Comment: 4 pages, in proceedings of the SUSY09 conferenc

Evidence for Parton kT Effects in High pT Particle Production

Inclusive pizero and direct-photon cross sections in the kinematic range 3.5 < pT < 12 GeV/c with central rapidities are presented for 530 and 800 GeV/c proton beams and a 515 GeV/c pi- beam incident on beryllium targets. Current Next-to-Leading-Order perturbative QCD calculations fail to adequately describe the data for conventional choices of scales. Kinematic distributions from these hard scattering events provide evidence that the interacting partons carry significant initial-state parton transverse momentum (kT). Incorporating these kT effects phenomenologically greatly improves the agreement between calculations and the measured cross sections.Comment: 11 pages including 6 pages of figures with caption