5,739 research outputs found
Magma genesis in the northern Lau Basin, S.W. Pacific
No full textThe northern Lau Basin contains the northeastern-most part of the Tonga arc-basin system. Volcanic rocks associated with the recent-arc have been sampled from Tafahi and Niuatoputapu, and young basalts «1.5Ma) have been dredged from Northern Lau Spreading Centre (NLSC), the northeastern limb of the King's Triple Junction. The 1982 'Kallisto' cruise dredged two ophiolite sections, one containing boninitic, and the other tholeiitic, lavas, from the inner wall of the northern Tonga trench. The magma genesis of these lava suites is related to the structural and geochemical controls imposed during the tectonic evolution of the region. The geochemical controls result from processes related to the mantle dynamics in the northern Lau Basin, and to along-trench variations and the degree of influence of the subduction component. The lavas associated with the Central Lau Spreading Centre are derived from the Lau Basin mantle reservoir, which has Indian MORB mantle (!MM) isotopic characteristics. This reservoir has been present under the region since early-arc magmatism, as indicated by the trace elements and !MM isotopic signatures of the tholeiitic lavas from the eastern ophiolite section, and Eocene lavas from 'Eua. A reservoir with the geochemical characteristics of residual Samoan plume mantle underlies the northern Lau Basin. This mantle has been influxing through the rip in the Pacific plate, at the northern termination of the Tonga trench, since the Lau Basin began to open « 6Ma), as a result of processes relating to subduction roll-back. The north Tongan boninites, the lavas from Tafahi and Niuatoputapu have residual plume mantle sources. However, prior to the opening of the Lau Basin, the proto-Tonga trench formed a barrier to this influx, and therefore, the influence of the plume cannot be detected in lavas associated with the early-arc, such as the tholeiites from one of the ophiolite sections and the Eocene lavas from 'Bua. The variations in the trace element and Pb isotopic compositions of the lavas from the Northern Lau Spreading Centre indicate that mixing has occurred between Lau Basin and residual plume mantle end-members in the central northern Lau Basin. The residual plume mantle sources of the north Tongan boninites and the lavas from Tafahi, Niuatoputapu and the Tofua arc have been enriched by a subduction component, the characteristics of which are enrichment in Lll..E, Ph ± LREE. In the south, the subduction component is made up of fluids derived from subducted Pacific altered oceanic crust and pelagic sediments. However, in the north, it is comprised predominantly of fluids derived from Pacific volcanogenic sediments, with a contribution from altered oceanic crust and possibly subducted plume crust
The development of an endoprosthesis for the metacarpophalangeal joint
No full textRheumatoid arthritis is a painful and debilitating disease which often afflicts the key joint of the hand, the metacarpophalangeal joint. In the worst cases the diseased joint has to be replaced with an artificial joint or prosthesis. The development of the Durham metacarpophalangeal prosthesis as it was taken from prototypes through to production samples, is described in this thesis. Testing of several Durham prostheses to over 70 million cycles has been carried out on a finger function simulator and consistent wear factors of the order of 0.4 x 10(^-) (^6)mm(^3)/Nm have been measured. These wear factors for the prosthesis were also significantly lower than any found previously. Production samples of the prosthesis have been manufactured together with appropriate surgical instrumentation. Tests of the prosthesis material, cross-linked polyethylene, rubbing against itself, have been undertaken on reciprocating pin on plate rigs and again show total wear factors of the order of 0.4 x lO(^-6)mm(^3)/Nm. Interestingly, it was found that pin wear was very much less than plate wear. The pin on plate tests were extended to include ultra-high molecular weight polyethylene (UHMWPE) rubbing against UHMWPE, as well as both polyethylenes against hard counterfaces and the results are reported. A new finger function simulator has been designed, manufactured and a validation test undertaken. Having written the necessary protocol, in conjunction with clinicians and the prosthesis manufacturer, ethical approval was obtained from the local research ethics committee and the Medical Devices Agency, to permit implantation of the prosthesis in human subjects. Lastly a hand strength measurement device for pre and post operation assessment of patients has been developed and manufactured
Grover McCormick, Sr. Letter Unknown Author
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