ENERGY ACCOUNTING: THE CASE OF FARM MACHINERY IN MARYLAND

Resource /Energy Economics and Policy,

Depositional processes in Saldanha Bay and Langebaan Lagoon

Bibliography: pages 147-161.This study deals with the physical aspects of sedimentation in Saldanha Bay and Langebaan Lagoon. On the basis of detailed textural investigations the depositional history of the study area has been established. The sediments in the bay and in the lagoon consist of a fine terrigenous quartz population and a coarser skeletal carbonate population, which have been mixed in various proportions. In order to gain size parameters that are more closely related to the hydraulic nature of depositional processes observed in the marine environment, grain size analyses were performed with an automatically recording settling tube system. The instrument was developed in the course of this study. Construction costs were kept extremely low without, however, impairing the scientific requirements of the instrument. Over 500 sediment samples were recovered on a closely-spaced grid; in each case, a size analysis was performed on the total sample and on the insoluble, terrigenous fraction. By subtracting the terrigenous size distribution from that of the total sediment, the relevant size parameters of the bioclastic component were calculated. In this manner 1500 individual size distributions were available for interpretation

Proton-induced noise in digicons

The Space Telescope, which carries four Digicons, will pass several times per day through a low-altitude portion of the radiation belt called the South Atlantic Anomaly. This is expected to create interference in what is otherwise anticipated to be a noise-free device. Two essential components of the Digicon, the semiconductor diode array and the UV transmitting window, generate noise when subjected to medium-energy proton radiation, a primary component of the belt. These trapped protons, having energies ranging from 2 to 400 Mev and fluences at the Digicon up to 4,000 P+/sec-sq cm, pass through both the window and the diode array, depositing energy in each. In order to evaluate the effect of these protons, engineering test models of Digicon tubes to be flown on the High Resolution Spectrograph were irradiated with low-flux monoenergetic proton beams at the University of Maryland cyclotron. Electron-hole pairs produced by the protons passing through the diodes or the surrounding bulk caused a background count rate. This is the result of holes diffusing over a distance of many diode spacings, causing counts to be triggered simultaneously in the output circuits of several adjacent diodes. Pulse-height spectra of these proton-induced counts indicate that most of the bulk-related counts overlap the single photoelectron peak. A geometrical model will be presented of the charge collection characteristics of the diode array that accounts for most of the observed effects

Zircon U-Pb strain chronometry reveals deep impact-triggered flow

Large (>100km) meteorite impact cratering events play important roles in surface and biosphere evolution, however, their potential for widespread ductile modification of the lithosphere has been difficult to assess, due partly to our inability to isotopically age-correlate deep mineral fabrics with surface records. We have integrated benchmark U-Pb zircon dating methods (ID-TIMS, SHRIMP) with new microstructural techniques (EBSD, XRD) to demonstrate that crystal-plastic deformation can cause rapid out-diffusion of radiogenic Pb and accompanying trace element alteration in crystalline zircon. We have used this phenomenon to directly date fabric in Archean zircons and xenoliths of the lower crust of South Africa at 2023 15 million years, coeval with the 2020 3 million year old Vredefort cratering event at surface, with extent > or =20,000 km2. Our findings indicate that regional exogenic fabrics, similar to high-temperature tectonic fabrics, exist in ancient crust. Moreover, our results establish that crystal-plastic deformation in the lithosphere can now be directly dated and linked to planetary evolution by zircon U-Pb strain chronometry