No description available.

No description available.

No description available.

In order to quantitatively examine the crustal structure of the Panama Basin without the benefit of local seismic refraction data, the following assumptions were made: (1) No significant lateral changes in density take place below a depth of 50 km. (2) The densities of the crustal layers are those of a 50-km standard section derived by averaging the results of 11 seismic refraction stations located in normal oceanic crust 10 to 40 million years (m. y. ) in age. (3) The density of the upper mantle is constant to a depth of SO km. (4) The thickness of the oceanic layer is normal in that region of the basin undergoing active spreading, exclusive of aseismic ridges. (5) The thickness of the transition layer is 1. 1 kin everywhere in the basin. Subject to these assumptions, the following conclusions are drawn from the available gravity, bathymetry, and sediment-thickness data: (1) Structurally, the aseismic ridges are surprisingly similar, characterized by a blocky, horst-like profile, an average depth of less than 2 km, an average depth to the Mohorovicic discontinuity of 17 km, and an average free-air anomaly of greater than +20 mgal. The fact that their associated free-air anomalies increase from near zero at their seaward ends to greater than +40 mgal at their landward ends suggests that the Cocos and Carnegie ridges are uplifted at their landward ends by lithospheric bending. (2) The centers of sea-floor spreading and fracture zones are characterized by a shoaling of the bottom and an apparent deepening of the Mohorovicic discontinuity. The only exception to this generalization is the northern end of the Panama fracture zone between the Cocos and Coiba ridges. (3) The Panama fracture zone and the fracture zone at 85°20'W longitude divide the Panama Basin into three provinces of different crustal thickness. Between these two fracture zones the crustal thickness is normal; west of 85°20W longitude it is greater than normal; and east of the Panama fracture zone it is less than normal. (4) In that part of the Panama Basin east of the Panama fracture zone there is a major discontinuity at 3°N latitude between a smooth, isostatically compensated crust to the south and an extremely rugged, uplifted crust to the north. An explanation for this discontinuity is the effect of the inflection in the shape of the continental margin at 3°N latitude on the eastward subductiori of the Nazca plate. / Graduation date: 1974

The Carnegie Ridge is a linear, aseismic, submarine ridge lying between the Galapagos Islands and the coast of South America. A 2300 meter deep saddle near 86°W. longitude divides the ridge into western and eastern segments. Surface ship, near bottom, and grain size studies from the saddle have been used to delineate the present geological environment and history of the ridge. Structurally the Carnegie Ridge is rather simple in profile, being bounded by east-west trending scarps which give the ridge a block-faulted appearance. Acoustic basement over the ridge appears smooth on reflection profiles and is composed of chert. The sedimentary sequence above the chert horizon contains a lower chalk unit overlain by calcareous ooze. Where erosion has exposed the chalk a karst-like micro-topography is present which is characterized by steep walled channels and cliffs and consolidated bed forms undergoing erosion and dissolution. The ridge crest has been stripped of almost its entire sediment cover. Thick sequences of sediment are found only in areas protected from north or south flowing bottom currents. Evidence of erosion is provided by extensive channeling on both the north and south flanks of the ridge. Near bottom observations in one channel on the north flank revealed a large field of sand dunes indicating northward, downslope sediment transport. These dunes are found on a manganese-encrusted chalk which floors the channel. Hydrographic data suggest that the northward flow across the ridge may be produced by the spillover of bottom water. Near bottom and surface ship observations are consistent with a southward sediment transport on the south flank of the ridge. The mechanism responsible for this southward flow remains unresolved. Current meters deployed on the north and south flanks recorded only low speed currents, opposite in direction to the inferred sediment transport. Apparently the bottom water flow responsible for erosion and sediment transport over the ridge is episodic in nature and was not recorded during the present survey. The grain size characteristics of surface sediments respond to the same processes which control sediment distribution. Where erosion is evident over the ridge crest, coarse lag deposits of foraminiferal sand are found. Apparently the erosion is most pronounced at the sill depth on the ridge since the sediments tend to become finer both upslope and downslope from that point. Three dominant modes are present in the sand fraction from the ridge. These modes record the initial input and fragmentation of foraminiferal tests. Continued fragmentation and dissolution of these tests creates a large number of finer modes. The age of true basaltic crust over the ridge is between 10 and 26 million years. This crust was probably created during a period of very slow spreading on the Galapagos Rift Zone during the Miocene. Unconformities on the ridge indicate that erosion dates only from the mid-Pliocene. The initiation of erosion was probably in response to further uplift of the ridge. This uplift may have been related to slight southward underthrusting along the north flank of the ridge. / Graduation date: 1975 / Best scan available for figures on p.67, 96. The original is a black and white photocopy.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1983. / Grant provided by NASA under Grant NAG 6-9. Includes bibliographical references (p. 187-193).

Traditional dissolution models are based in the analyses of bulk solution compositions and ignore the fact that different sites of a surface dissolve at different rates. Consequently, the variation of surface area and surface reactivity during dissolution are not considered for the calculation of the overall dissolution rate, which is expected to remain constant with time. The results presented here show the limitations of this approach suggesting that dissolution rates should be calculated as a function of an overall surface reactivity term that accounts for the reactivity of each of the sites that constitute the surface. In contrast to previous studies, here the focus is put on studying the surface at different dissolution times. Significant changes in surface topography of CaF2 were observed during the initial seconds and up to 3200 hours of dissolution. The observed changes include the increase of surface area and progressive exposure of the most stable planes, with consequent decrease in overall reactivity of the surface. The novelty of a proposed dissolution model for fluorite surfaces, when compared with traditional dissolution models, is that it differentiates the reactivity of each characteristic site on a surface, e.g. plane or step edge, and considers the time dynamics. The time dependency of dissolution rates is a major factor of uncertainty when calculating long term dissolution rates using equations derived from dissolution experiments running for short periods of time and using materials with different surface properties. An additional factor of uncertainty is that the initial dissolution times are the most dynamic periods of dissolution, when significant variations of surface area and reactivity occur. The results are expected to have impact in the field of nuclear waste management and to the larger geological and material science community. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Submitted.</p>

Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 47-49). Also available by World Wide Web.

Thesis (Ph. D. in Physical Oceanography)--Naval Postgraduate School, March 2003. / Dissertation supervisor: Mary L. Batteen. Includes bibliographical references (p. 167-168). Also available online.

This thesis describes the examination and characterisation of semiconductor silicon by the various methods of X-Ray Diffraction Topography. A brief introduction is given to the dynamical theory of X-ray diffraction and its relevance to the formation of contrast in X-ray topographs. The experimental methods used and contrast formation mechanisms are introduced. The design and construction of an inexpensive Automated Bragg Angle Controller (ABAC) is described, based around a microcomputer and using many of the existing features of the Lang camera. This enables Lang topographs of the whole of distorted crystals to be taken. Using the ABAC, the contrast of defects in Lang topographs of cylindrically bent silicon wafers is explored. A comparison is made between this data and images in Hirst topographs and contrast differences between the techniques are attributed to the presence of an inhomogeneous bending moment. The change in contrast in section and Lang topographs upon homogeneous bending for asymmetric reflections is also investigated and mechanisms for the contrast changes are suggested. A bipolar device wafer is examined with double crystal topography using synchrotron radiation and a highly asymmetric reflection with a glancing angle of incidence. By exploiting the wavelength tuneability of the synchrotron radiation, the depth penetration of the X-rays is varied and the optimum experimental conditions for observing both defects and devices determined. Using this technique it is possible to image both devices and process related defects to a high resolution and contrast. The Lang, section and glancing angle double crystal topography techniques are compared for the examination of a CMOS device wafer. The relative strengths and weaknesses of each technique are highlighted and many defects are imaged and characterised. Finally, results showing the appearance of fringes in the double crystal topographs for low angles of incidence are presented. These are attributed to the' presence of along range strain, and the dependence of the fringes upon curvature is explored for moderate bending conditions (R ~35m).