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ABSTRACTThe Rio Grande Cone is a major fanlike depositional feature in the continental slope of the Pelotas Basin, Southern Brazil. Two representative sediment cores collected in the Cone area were retrieved using a piston core device. In this work, the organic matter (OM) in the sediments was characterized for a continental vs. marine origin using chemical proxies to help constrain the origin of gas in hydrates. The main contribution of OM was from marine organic carbon based on the stable carbon isotope (δ13C-org) and total organic carbon/total nitrogen ratio (TOC:TN) analyses. In addition, the 14C data showed important information about the origin of the OM and we suggest some factors that could modify the original organic matter and therefore mask the “real” 14C ages: (1) biological activity that could modify the carbon isotopic composition of bulk terrestrial organic matter values, (2) the existence of younger sediments from mass wasting deposits unconformably overlying older sediments, and (3) the deep-sediment-sourced methane contribution due to the input of “old” (>50 ka) organic compounds from migrating fluids.

The 3-2-1 fixture design principle is the most used method to locate prismatic workpieces. To further increase location accuracy, the influence of friction and contact stiffness between workpiece and fixture parts should be minimized. This can be achieved by decreasing the structural stiffness of the locators in the tangential direction to the contact. Hence, based on flexure hinges, locators with two different stiffness values are investigated. To analyze the influence of locator stiffness, a special experimental setup is developed to study two locators positioned in the secondary plane of the 3-2-1 fixture. Experiments are carried out to compare the locators with flexure hinges to a rigid one. The displacement and rotation of the workpiece are investigated as a function of the clamping force. The experimental results show that the reduction in the tangential stiffness can improve the position and orientation accuracy of workpieces.