Paleomagnetic of basalts from ODP Site 145-883 on Detroit Seamount

Paleomagnetic data were measured from basaltic flows cored by the Ocean Drilling Program (ODP) at Site 883 on the summit of Detroit Seamount, located in the northernmost Emperor seamounts. These data are important because they reflect the paleolatitude of Hawaiian volcanism for the Late Cretaceous and bear upon geodynamic models of hotspot drift. A total of 143 samples were measured, from cores acquired at two ~20-30 m apart. Most samples gave apparently reliable magnetic directions that were analyzed in a tiered fashion to compute a composite inclination vs. depth curve. One hole gave 13 distinct inclination groups, the other 10, and the two were combined into nine groups thought to represent independent measurements of paleofield direction. These data indicate normal magnetic polarity and give a mean inclination of 61.5+10.6°/-6.4° and paleolatitude of 42.8+13.2°/-7.6° (95% confidence limits). This paleolatitude is 6.2° higher than results from another ODP site (884) drilled on the lower flank of the same seamount. The difference is thought to result partly from an age difference (1-3 Myr) and partly from incomplete averaging of paleosecular variation at both drill sites. Together, the data from the two sites reinforce the conclusion that the northern Emperor seamounts were formed far north of the present-day hotspot latitude (~19.5°N) and suggest prior estimates of the amount and rate of southward drift may have been low. This analysis also illustrates uncertainties in determining paleolatitude from a small number of lava flow units from a single drill site.

Accumulation rates of volcanic glass and ice-rafted debris in sediments of the North Pacific Ocean

Mass accumulation rates (MAR) of different components of North Pacific deep-sea sediment provide detailed information about the timing of the onset of major Northern Hemisphere glaciation that occurred at 2.65 Ma. An increase in explosive volcanism in the Kamchatka-Kurile and Aleutian arcs occured at this same time, suggesting a link between volcanism and glaciation. Sediments recovered by piston-coring techniques during ODP Leg 145 provide a unique opportunity to undertake a detailed test of this possibility. Here we use volcanic glass as a proxy for explosive volcanism and ice-rafted debris (IRD) as a proxy for glaciation. The MAR of both glass and IRD increase markedly at 2.65 Ma. Further, the flux of the volcanic glass increased just prior the flix of ice-radted material, suggesting that the cooling resulting from explosive volcanic eruptions may have been the ultimate trigger for the mid-Pliocene glacial intensification.

Early Cenozoic Atlantic and Pacific benthic foraminiferal isotopes from 12 sites

Oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions, with those of benthic foraminifera providing information on the deep oceans. Reconstructions are complicated by interspecies isotopic offsets that result from microhabitat preferences (carbonate precipitation in isotopically distinct environments) and vital effects (species-specific metabolic variation in isotopic fractionation). We provide correction factors for early Cenozoic benthic foraminifera commonly used for isotopic measurements (Cibicidoides spp., Nuttallides truempyi, Oridorsalis spp., Stensioina beccariiformis, Hanzawaia ammophila, and Bulimina spp.), showing that most yield reliable isotopic proxies of environmental change. The statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies. Interspecies isotopic offsets appear to have changed through the Cenozoic, either (1) as a result of evolutionary changes or (2) as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies. Regardless of the reason, the assumption that isotopic offsets have remained constant through the Cenozoic has introduced an 1-2°C uncertainty into deep sea paleotemperature calculations. In addition, we compare multiple species isotopic data from a western North Atlantic section that includes the Paleocene-Eocene thermal maximum to determine the most reliable isotopic indicator for this event. We propose that Oridorsalis spp. was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time; it may be the best recorder at other locations and for other extreme events also.

Gasification of wood particles in a co-current packed bed: Experiments and model analysis

This study focuses on addressing the propagation front movement in a co-current downdraft gasification system. A detailed single particle modeling analysis extended to the packed bed reactor is used to compare with the experimental measurement as well those available in the literature. This model for biomass gasification systems considered pyrolysis process, gas phase volatile combustion, and heterogeneous char reactions along with gas phase reactions in the packed bed. The pyrolysis kinetics has a critical influence on the gasification process. The propagation front has been shown to increase with air mass flux, attains a peak and then decreases with further increase in air mass flux and finally approaches negative propagation rate. This indicates that front is receding, or no upward movement() bra her it is moving downward towards the char bed. The propagation rate correlates with mass flux as (m) over dot `'(0.883) during the increasing regimes of the front movement The study clearly identifies that bed movement is an important parameter for consideration in a co-current configuration towards establishing the effective bed movement. The study also highlights the importance of surface area to volume ratio of the particles in the packed bed and its influence on the volatile generation. Finally, the gas composition for air gasification under various air mass fluxes is compared with the experimental results. (C) 2016 Elsevier B.V. All rights reserved.

Sapientia, 1982, Vol. XXXVII, nº 145 (número completo)

Contenido: La participación del ser III : la participación del acto de ser o existencia / Octavio N. Derisi – La metafísica cristiana en el desarrollo del pensamiento occidental / Alberto Caturelli – El “principium essendi” del hombre y su conocimiento / Julio R. Méndez – El intelecto en el De Anima de Aristóteles : comentario a los capítulos cuarto y quinto del libro III / Ciro Schmidt Andrade – La formación metafísica cristiana en la universidad / Octavio N. Derisi – Rasgos actuales del pensamiento político de Aristóteles / Alberto Buela – Notas y comentarios -- Bibliografía