Graduation date: 1973

The portion of the East Pacific Rise (EPR) between 5° and 12°S can be subdivided into three areas by fracture zones that offset the rise axis at about 6.5°S and 9°S. In all three regions, the spreading axis of the EPR is defined by a topographic block 300 to 350 m high and about 15 km wide. The axial block commonly has subordinate peaks or shoulders on each flank that vary up to 5 km wide. Analysis of linear magnetic anomalies in the southern of the three areas suggests that sea-floor spreading has been occurring at rates of 80 mm/y to the west and 77 mm/y to the east during the last 1.7 million years (my). The rise axis is offset in two places about 10 km. These displacements are interpreted to be the result of discrete jumps of the site of spreading activity. Reconnaissance data from the east flank of the EPR indicate that spreading activity on this portion of the rise began just over 8 my ago when the site of crustal accretion jumped westward from the now dormant Galapagos Rise. About 4.6 my ago the section of rise crest between approximately 10.5°S and the 9°S fracture zone jumped westward a distance of at least 10 km, isolating the pre-existing axial block. By 1.7 my ago, this axial offset no longer existed, implying a relatively westward migration of the rise axis south of 10.5° during the period from 4.6 to 1.7 my ago. The two offsets of the present axis occurred between 1.6 and 0.9 my ago and 0.7 my ago and the present in the north and south, respectively. The formation of the axial block, its associated shoulders and the abyssal topography, apparently consisting of tilted fault blocks with steep sides facing the axis, can be explained by an empirical model. This model combines extrusion of basalt along the spreading axis to form the axial block and rotational faulting to form the shoulders of the block and then lower the shoulders to merge with the abyssal topography of the uppermost rise flanks. In the region north of the 6.5°S fracture zone, seismic activity on the rise crest, combined with topographic information, suggests that the EPR axis is unstable here and that it is in the process of reorienting to a more stable regional trend. Identification and mapping of magnetic anomalies in the vicinity of 6°S reveal a spreading rate of about 77 mm/y, an episode of oblique spreading that occurred 1.7 my ago, and a 10 km westward jump of the axis which occurred since 0.7 my ago. The fracture zone at 6.5°S offsets the EPR axis 55 km right laterally. Both the bathymetric and magnetic expression of this fracture zone are markedly reduced a few tens of kilometers away from its active portion, implying that some change in the processes forming the fracture zone occurred about 0.3 my ago. Between the fracture zones at 6.5° and 9°S, two deactivated segments of the rise axis, each about 40 km long, occur 90 and 65 km west of the currently active axis. These inactive axial segments were isolated by eastward jumps of the spreading center. The more northerly jump, along 6.5°S, occurred 0.3 my ago and spanned 68 km. The other, along 7°S, covered a similar distance and is either just completed or still going on. Reconnaissance data from this part of the EPR suggests that sea-floor spreading began here about 6.5 my ago and has been continuing at a rate of approximately 78 mm/y. / Graduation date: 1975

ABSTRACT For the 3-D system of wave motion consisted of a free-surface progressive gravity wave train propagating over a two side ripple bottom , a perturbation expansion procedure is developed to second order. The mechanism and the properity of the induced wave motion by the effect of the ripple bottom on the free-surface progressive gravity waves , including the resonance and non-resonance case , is described. To the induced resonance wave motion to the second order of the solution , the growth of its energy flux with time , and consequently the growth for the transmission speed of its energy flux are vividly demonstrated. Furthermore , the relation between the transmission speed in time and space is also established. Finally , the growth of the induced resonance wave motion with its propagating distance in the region of the ripple bottom located is emphasized. The variation and growth of the whole flow field of the wave motion system in time and space is therefore presented. To ascertain the accuracy and the generality of the analytical result , it was verified not only to by reducing which the solution of the one side wavy bottom, but also conform to the three kinds of the actual physical situation.

Thesis--University of Tokyo. / Vita. Bibliography: p. 201-209.

Wuppertal, Univ., Diss., 2005. / Computerdatei im Fernzugriff.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 188-199).

Thesis (M.S.) in Geological Sciences--University of Maine, 2002. / Includes vita. Three maps inserted in pocket. Includes bibliographical references (leaves 112-117 ).

Des matériaux denses nanostructurés à base de l’alliage métastable Ni-P ont été élaborés par une stratégie "bottom-up" qui combine deux étapes. La première consiste en la préparation de nanoparticules de l’alliage grâce au procédé polyol modifié par l’ajout d’hypophosphite, un agent réducteur fort. Les nanoparticules obtenues sont de morphologie sphérique et de taille variant de 39 à 220 nm. La deuxième étape consiste en la consolidation de ces nanopoudres par le procédé SPS. Les massifs denses obtenus sont constitués de grains polygonaux de nickel (taille variant de 154 à 650 nm) et de nanoparticules sphériques de Ni₃P localisées aux points de jonction triple et aux joints des grains de nickel. Ces nanoparticules de taille ne dépassant pas 250 nm sont formées par un mécanisme de diffusion du phosphore à travers les grains de nickel. Les matériaux denses élaborés présentent les caractéristiques magnétiques d’un ferromagnétisme doux (faible champ coercitif) mais une aimantation à saturation élevée proche de celle du nickel massif. Les propriétés mécaniques sont fonction de la taille des grains. Quand cette taille est faible, les matériaux manifestent une résistance mécanique et une limite élastique élevées accompagnées d’une faible ductilité. Une augmentation de la taille des grains entraine des évolutions inverses conformément à la loi de Hall-Petch. / Dense nanostructured materials based on the metastable Ni- P alloy were prepared by "bottom- up" strategy. This synthesis pathway is the combination of two steps. The first is to prepare the powder by soft chemistry (reduction in polyol medium modified by the addition of hypophosphite a strong reducing agent). The nanoparticles produced have spherical morphology and size ranging from 39 to 220 nm. These powders are metastable solid solutions Ni- P. The second step is to consolidate these powders by SPS process; it results in dense nanostructured material consisting of polygonal grains of nickel (size ranging from 254 to 650 nm) along with spherical nanoparticles Ni3P located at triple junction points and grain boundaries. These nanoparticles of size no greater than 250 nm are formed by a diffusion mechanism through the phosphorous nickel grains. The as-obtained dense materials have magnetic characteristics of a soft ferromagnetism (low coercivity) but a good saturation magnetization close to that of bulk nickel. These materials also exhibit very interesting mechanical properties depending on the grain size. When the grain size is small, the materials exhibit mechanical strength and high elastic limit accompanied by low ductility. An increase in grain size leads to inverse changes in line with the Hall-Petch law.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

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