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Internal Geometry (internal + geometry)

Distribution by Scientific Domains

Earth and Environmental Science	60%

Selected Abstracts

Spontaneous Current Oscillations during Hard Anodization of Aluminum under Potentiostatic Conditions

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
Woo Lee
Abstract Nanoporous anodic aluminum oxide is prepared by hard anodization of aluminum under potentiostatic conditions using 0.3,M H2C2O4. Under unstirred electrolyte condition, spontaneous current oscillations are observed. The amplitude and period of these current oscillations are observed to increase with anodization time. As a consequence of the oscillatory behavior, the resulting anodic alumina exhibits modulated pore structures, in which the diameter contrast and the length of pore modulation increase with the amplitude and the period of current oscillations, respectively, and the current peak profile determines the internal geometry of oxide nanopores. The mechanism responsible for the oscillatory behavior is suggested to be a diffusion-controlled anodic oxidation of aluminum. [source]

The sedimentary structure of the Lomonosov Ridge between 88°N and 80°N

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2005
Wilfried Jokat
SUMMARY While the origin of the 1800-km-long Lomonosov Ridge (LR) in the Central Arctic Ocean is believed to be well understood, details on the bathymetry and especially on the sediment and crustal structure of this unique feature are sparse. During two expeditions in 1991 and 1998 into the Central Arctic Ocean several high quality seismic lines were collected along the margin of the ridge and in the adjacent Makarov Basin (MB). The lines collected between 87°36,N and 80°N perpendicular to and along the LR show a sediment starved continental margin with a variety of geological structures. The different features may reflect the different geological histories of certain ridge segments and/or their different subsidence histories. The sediments in the deep MB have thicknesses up to 2.2 km (3 s TWT) close to the foot of the ridge. At least in part basement reflections characteristics suggest oceanic crust. The acoustically stratified layers are flat lying, except in areas close to the ridge. Seismic units on the LR can be divided into two units based on refraction velocity data and the internal geometry of the reflections. Velocities <3.0 km s,1 are considered to represent Cenozoic sediments deposited after the ridge subsided below sea level. Velocities >4.0 km s,1 are associated with faulted sediments at deeper levels and may represent acoustic basement, which was affected by the Late Cretaceous/Early Cenozoic rift events. Along large parts of the ridge the transition of the two units is associated with an erosional unconformity. Close to the Laptev Sea such an erosional surface may not be present, because of the initial great depths of the rocks. Here, the deeper strata are affected by tectonism, which suggests some relative motion between the LR and the Laptev Shelf. Stratigraphic correlation with the Laptev Sea Shelf suggests that the ridge has not moved as a separate plate over the past 10 Myr. The seismic and regional gravity data indicate that the ridge broadens towards the Laptev Shelf. Although the deeper structure may be heavily intruded and altered, the LR appears to extend eastwards as far as 155°E, a consequence of a long-lived Late Cretaceous rift event. The seismic data across LR support the existence of iceberg scours in the central region of the ridge as far south as 81°N. However, no evidence for a large erosional events due to a more than 1000-m-thick sea ice cover is visible from the data. South of 85°N the seismic data indicate the presence of a bottom simulating reflector along all lines. [source]

Description for smooth contact conditions based on the internal geometry of contact surfaces

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003
Alexander Konyukhov Dr.
A kinematical approach, based on the consideration of the contact conditions in the local coordinate system, is proposed for the contact description and for consistent linearization. This leads to a simple structure of the tangent matrix, which is subdivided into main, rotational and curvature parts. Various alternatives neglecting parts of the contact tangent matrix are considered. Representative examples show the effectiveness of the proposed approach for contact problems with arbitrary large deformation. [source]

Erosional vs. accretionary shelf margins: the influence of margin type on deepwater sedimentation: an example from the Porcupine Basin, offshore western Ireland

BASIN RESEARCH, Issue 5 2009
M. C. Ryan
ABSTRACT A 1000 km2 three-dimensional (3D) seismic data survey that extends out from the western margin of the Porcupine Basin, offshore western Ireland reveals the internal geometry and depositional history of a large Palaeogene (Palaeocene,Early Eocene) shelf-margin. Two wells intersect the margin thereby constraining the depositional environments. The 34/19-1 well (landward end) intersects slope, shelf, marginal marine to coastal plain facies. The 35/21-1 well (basinward end) intersects seismically imaged shelf-margin clinoforms where base of slope back up to coastal plain deposits (source-to-sink) are represented. The basin-fill stratal architecture of the Palaeogene succession reveals sediment deposition under two end member, basin physiographic styles: (1) an erosional margin style and (2) an accretionary or progradational margin style. Uplift of the western margin of the basin is suggested as the major cause of the initially oversteepened shelf-slope erosional profile. Key characteristics of an erosional margin include sediment bypass of the shelf, canyon formation, and the development of significant onlapping submarine fan deposits on the lower slope. Failure on the slope is also revealed by several mass,transport complexes (MTCs) that carve out major erosive features across the slope. Three-dimensional seismic analysis illustrates variations in size, geometry and depositional trend and transport mechanisms of the MTCs. Confined, thick chaotic seismic facies, erosional basal scours and syn-depositional thrusting (pressure ridges) at terminus as opposed to thin, high-amplitude discontinuous facies with an unconfined lobate terminus are interpreted to indicate slump- and slide-dominated vs. debris flow-dominated MTCs, respectively. The erosional margin was transformed into an accretionary margin when the gradient of the shelf-slope to basin-floor profile was sufficiently lowered through the infilling and healing of the topographic lows by the onlapping submarine-fan deposits. This shallowing of the basin allowed nearshore systems to prograde across the deepwater systems. The accretionary margin was characterised by a thick sediment prism composed of clinoforms both at the shoreface/delta (tens of metres) and shelf-margin (hundreds of metres) scales. Shelf-margin clinoforms, the focus of this study, are the fundamental regressive to transgressive building blocks (duration 10,100 kyr) of the stratigraphic succession and can be observed on a larger scale (,1 Myr) through the migration and trajectory patterns of the shelf-edge. Trajectory pathways in the accretionary margin are accretionary in a descending or ascending manner. The descending style was characterised by a shelf-slope break that migrated seawards and obliquely downwards as a result of a relative sea-level fall. The descending trajectory geometry is lobate along strike suggestive of a point source progradation. Internally, the descending trajectory consists of downward stepping, steeply dipping shelf-margin clinoforms that display extensive slumping and deposition of sediment on the lower slope indicative of rapid deposition. Furthermore, basin-floor fans and associated ,feeder' channels extend basinwards beyond toe of slope. The ascending trajectory reflects a shelf-slope break that is interpreted to have migrated seawards during steady or rising relative sea level. The ascending trajectory geometry is associated with significant lateral sediment dispersal along the shelf-edge, reflecting distributary systems that were less ,fixed' or a greater reworking and longshore drift of sediment. Accretion involving the ascending shelf-edge trajectory characteristically lacked significant basin-floor deposits. Variable ascending trajectories are recognised in this study, as read from the angle at which the shelf-slope break migrates. Horizontal to high angle ascending trajectories correspond to dominantly progradational and dominantly aggradational shelf-edge trajectories, respectively. The sequence stratigraphic analysis of the Porcupine deltaic complex reveals a long-term relative sea-level rise. [source]

Morphologic variability of exposed mass-transport deposits on the eastern slope of Gela Basin (Sicily channel)

BASIN RESEARCH, Issue 2 2007
Daniel Minisini
ABSTRACT The NE portion of Gela Basin in the Sicily Channel is affected by multiple slope failures originated during the late-Quaternary. Basin sequences show evidence of stacked acoustically transparent and/or chaotic units, characterized by irregular upper surfaces, interpreted as mass-transport deposits. The seafloor morphology also shows evidence of both old, partially buried, as well as recent slide products. Two recent slides exposed at seafloor, only 6 km apart (Twin Slides), are similar in geomorphological parameters, age and multistage evolution. Multistage failure of Twin Slides evolved from mud flows, derived from the extensive failure of less consolidated post-glacial units, to localized slides (second stage of failure) affecting older and more consolidated materials. Although Twin Slides are very close to each other and have similar runout and fall height, they produced very dissimilar organization of the displaced masses, likely reflecting the distinct source units affected by failures. Integrating geophysical, sedimentological, structural and palaeontological data, a detailed investigation was conducted to determine the size and internal geometry of this mass-transport complex, to explain the differentiated product and to shed light on its predisposing factors, triggers and timing. [source]