Collision Process (collision + process)

Distribution by Scientific Domains

Selected Abstracts

Time domain characteristics of hoof-ground interaction at the onset of stance phase

Summary Reasons for performing study: Little is known about the interaction of the hoof with the ground at the onset of stance phase although is it widely believed that high power collisions are involved in the aetiopathology of several conditions causing lameness. Objectives: To answer 3 questions regarding the fundamental nature of hoof-ground collision: (1) is the collision process deterministic for ground surfaces that present a consistent mechanical interface (2) do collision forces act on the hoof in a small or large range of directions and (3) Is the hoof decelerated to near-zero velocity by the initial deceleration peak following ground contact? Methods: Hoof acceleration during the onset of stance phase was recorded using biaxial accelerometry for horses trotting on a tarmac surface and on a sand surface. Characteristics of the collision process were identified both from vector plots and time series representations of hoof acceleration, velocity and displacement. Results: The response of the hoof to collision with smooth tarmac was predominantly deterministic and consistent with the response of a spring-damper system following shock excitation. The response to collision with sand was predominantly random. The deceleration peak following ground contact did not decelerate the hoof to near-zero velocity on tarmac but appeared to on sand. On both surfaces, collision forces acted on the hoof in a wide range of directions. Conclusions: The study suggests the presence of stiff, visco-elastic structures within the foot that may act as shock absorbers isolating the limb from large collision forces. Potential relevance: The study indicates objectives for future in vivo and in vitro research into the shock absorbing mechanism within the equine foot; and the effects of shoe type and track surface properties on the collision forces experienced during locomotion. Studies of this nature should help to establish a link between musculoskeletal injury, hoof function and hoof-ground interaction if, indeed, one exists. [source]

Seismotectonics of the Sinai subplate , the eastern Mediterranean region

Amos Salamon
SUMMARY We define the Sinai subplate, from a seismotectonic perspective, as a distinct component in the plate tectonics of the eastern Mediterranean region. This is based on the tectonic characteristics of a comprehensive listing of all ML, 4 recorded seismicity in the region during the 20th century, on newly calculated and recalculated fault plane mechanisms of first P -wave arrivals and on published solutions based on waveform inversion of broad-band data. The low seismicity level and scarcity of strong events in the region required a thorough search for useful data and a careful examination of the reliability of the focal solutions. We gathered all available records of first P -wave onsets from the ISS and ISC Bulletins and the local seismic networks. Altogether, we were able to calculate 48 new focal mechanisms and 33 recalculated ones of events that occurred during the years 1940,1992. With the increasing number of teleseismic and regional broad-band stations in the later years, we added 37 solutions based on teleseismic and regional waveform inversions of events that occurred during 1977,2001. These mechanisms enabled us to examine the seismotectonic character of the Sinai subplate. The strike and rake directions of the calculated mechanisms usually reflect the geometry and the large-scale type of deformation observed along the boundaries of the Sinai subplate,the Dead Sea Transform, the Cypriot Arc convergent zone and the Suez Rift. Nevertheless, along each of these boundaries we found anomalous solutions that attest to the complexity of the deformation processes along plate margins. Earthquakes along the Dead Sea Transform exhibit mainly sinistral transtension and transpression, reflecting its leaky manner and local change in the transform geometry. The presence of other unexpected mechanisms near the transform, however, reflects the heterogeneous deformation it induces around. As expected, thrust mechanisms along the Cypriot Arc mirror its convergent nature and typical curved geometry. Transtension and transpressional solutions in the eastern segment of the arc reflect the sinistral shear motion between Anatolia and Sinai there. However, shear mechanisms found between Cyprus and the Eratosthenes Seamount pose a problem regarding its collision process. Most intriguing of all are ML, 4 thrust and shear solutions found in the Gulf of Suez. They are associated with predominantly normal mechanisms within a rift zone and therefore constitute a unique phenomenon, yet to be deciphered. [source]

Cretaceous and Paleogene boundary strata in southern Tibet and their implication for the India-Eurasia collision

LETHAIA, Issue 2 2002
Recent stratigraphic studies in southern Tibet provide new information about the timing of the initial collision between the India and Eurasia continental blocks. The stratigraphic and paleontological evidence document dramatic changes in sedimentary facies and microfauna content across the Cretaceous-Paleogene (K/Pg) boundary. In the Zhongba and Gamba areas in southern Tibet, the K/Pg boundary is marked by a major disconformity, separating platform carbonates from overlying terrigenous conglomerates and sandstones. The stratigraphy of the boundary sequences has recently been improved with the recognition of three foraminiferal assemblages. They are: Maastrichtian Orbitoides-Omphalocyclus, Danian Rotalia-Smoutina-Lockhartia and Thanetian Miscellanea-Daviesina microfaunal assemblages. The K/Pg boundary at the Gamba area is placed between the Orbitoides-Omphalocyclus and Rotalia-Smoutina-Lockhartia faunas. In Tingri, Cretaceous Globotruncana and tertiary Globigerina-Globorotalia microfauna demark the position of the K/Pg boundary. The occurrence of terrigenous sandstones and boulder-size conglomerates in the early Paleocene is compelling evidence for tectonic uplift and emergence of the southern margin of the Lhasa block and of the northern margin of the Indian plate. Therefore, supported by biostratigraphic evidence, we argue that the uplift is caused by the onset of continental collision during the earliest Danian. Progressing plate collision resulted in deformation and fragmentation of the Paleocene carbonate platform and deposition of limestone breccias, which we consider as further evidence for tectonic compression as a result of early continental collision during the Thanetian, earlier than indicated by previous studies in the Himalayas. It is the change in the sedimentary facies and depositional environment that provides the earliest evidence and dating of the initiation of the collision process. From studies of sedimentary strata in southern Tibet, the collision of the India and Lhasa continental blocks was initiated at ,K/Pg boundary time (,65Ma). If that is the case, than the major lithofacies changes at the K/Pg boundary observed in the western Tethys, mostly referred to as intrinsic to the eustatic sea level change, has been driven by continental convergence and collision of the Indian and Eurasian plates. [source]

Analysis of Particle Pumping Using SOLDOR/NEUT2D Code in the JT-60U Tokamak

H. Kawashima
Abstract In order to understand the particle pumping on JT-60U, we analyze the roles of atomic and molecular processes using SOLDOR/NEUT2D code. A case of short strike point distance shows that most of neutrals produced on the targets go toward the exhaust slot directly. Whereas, neutrals are scattered in the spherically at random for the long distance case by collision processes and a few of them go toward the slot. It is clarified that the incident neutrals to the slot at low ne/high Te divertor plasma condition are dominated by atoms. Those at high ne/low Te condition are dominated by molecules due to elastic collision. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]