THE USE OF WATERJETS IN CUTTING A MULTIPLE PHASE MATERIAL
The University of Missouri-Rolla is carving a new sculpture. This involves shaping 3 rocks, collectively weighing 100 tons, and cutting figures of a man and a woman from two blocks. The three blocks will then be erected to form a Millennium Arch and the Figures will be polished as a second set. A relatively inexpensive X-Y table and cutting head unit were developed. The cutting waterjet was without abrasive at under 100 MPa. One problem in cutting large blocks (5 m x 2 m by 0.75 m) is that the structure changes. A variety of approaches were taken to solve this problem. The process steps required to cut the rock to shape, and then to carve the rock are described in the paper.
THE EFFECT OF ROCK ANISOTROPY ON THE EXCAVATION RATE IN BARRE GRANITE
The variation in the volume of rock removed when a water jet traverses over a sample of Barre Granite is shown to vary with the angle at which the sample is cut relative to the orientation of the main deposit. For example where the jet impacts perpendicular to a microfissure plane a channel up to 10 times the volume is cut as when the jet is traversed along the microfissure plane. A correlation is shown to exist between the dimensions of the rock volume removed and the angle of impact between the water jet and the two microfissure planes of the Barre Granite.
Pyrite multiple-sulfur isotope evidence for rapid expansion and contraction of the early Paleoproterozoic seawater sulfate reservoir
Abstract Earthʼs oxygenation is often described in terms of two unidirectional steps at the beginning and end of the Proterozoic Eon, separated by a long-lived intermediate redox state. Recent work defines a more complicated path to oxygenation, exemplified by an apparent drop in oxidation state following the early Paleoproterozoic Lomagundi carbon isotope excursion. The timing of this proposed drop in oxidation state is not well constrained, and it is not clear how it relates to redox conditions during the remainder of the Proterozoic. Here we present a study of pyrite multiple-sulfur isotopes, supported by Fe speciation and organic carbon isotopes, from early Paleoproterozoic black shales. We find evidence for the rapid expansion of the seawater sulfate reservoir during the Great Oxidation Event at ca. 2.3 Ga followed by a subsequent contraction in the size of the seawater sulfate reservoir at ca. 2.05 Ga. This scenario is consistent with the emerging view of a rise and fall in surface oxidation state during the early Paleoproterozoic. Comparison of our new data to other records of the seawater sulfate reservoir suggests that the elevated sulfate concentrations that characterize the early Paleoproterozoic did not return until the late Neoproterozoic.