Contourite or turbidite?: magnetic fabric of fine-grained Quaternary sediments, Nova Scotia continental rise

Samples of three piston cores and one gravity core from the Nova Scotia continental rise (depths 4210-4925 m) have been examined to differentiate parallel-to-slope and downslope depositional processes in Quaternary deposits from a region presently influenced by a strong contour current. Measurement of anisotropy of magnetic susceptibility of samples of a red-brown, silt-laminated lutite 'contourite' facies shows grain alignments which are consistent with both parallel-to-slope (contour current) flow and downslope (turbidity current) flow. We believe that these results provide support for the hypothesis that 'geologically significant' contour currents have influenced continental rise deposition during the Pleistocene. However, our observation that both alongslope and downslope alignments are present in lithologically similar units clearly demonstrates the need for studies on the relationship between lithofacies and process in this geological setting

The magnetic fabric of surficial deep-sea sediments in the HEBBLE area (Nova Scotian continental rise)

The anisotropy of magnetic susceptibility (AMS) of surficial sediments in the HEBBLE area (depth 4820 m, Nova Scotian continental rise) has been measured to study the fabric of these sediments and to relate the sediment fabric to depositional conditions. Previous investigators have established that strong but variable bottom currents are important agents in redistributing bottom sediments in the area. We observe that the upper 1.5 cm of the sediments has a primary fabric (dominantly foliar with horizontal bedding) created by bottom-current activity while sediments deeper than 2.5 cm have a predominantly secondary fabric due to bioturbation. The magnitude of the AMS signal in these sediments is generally low making it difficult to measure some of the fabric elements, especially the direction of the lineated fabric. In the upper 1.5 cm magnetic grains are predominantly oriented parallel to the regional bathymetric contours, but there is also a significant grouping of alignments perpendicular to the contours. Primary fabrics are observed in a few of the samples from the bioturbated sediments with the magnetic grains oriented parallel to the contours. Some of the variability observed between box cores in the magnetic fabric may reflect the variability of depositional conditions within the region. An analysis of the magnitude of the AMS fabric suggests that the parameter Fs, often used to denote bottom-current fabrics, is strongly dependent on the total anisotropy and only weakly dependent on the lineated nature of the fabric. Both primary and secondary fabrics can have relatively large Fs values. Thus Fs does not appear sufficient for delineating bottom current activity in the deep sea

A cell lineage analysis of segmentation in the chick embryo

We have studied the lineage history of the progenitors of the somite mesoderm and of the neural tube in the chick embryo by injecting single cells with the fluorescent tracer, rhodamine-lysine-dextran. We find that, although single cells within the segmental plate give rise to discrete clones in the somites to which they contribute, neither the somites nor their component parts (sclerotome, dermatome, myotome or their rostral and caudal halves) are `compartments' in the sense defined in insects. Cells in the rostral two thirds or so of the segmental plate contribute only to somite tissue and divide about every 10 h, while those in the caudal portions of this structure contribute both to the somites and to intermediate and lateral plate mesoderm derivatives. In the neural tube, the descendants of individual prospective ventral horn cells remain together within the horn, with a cycle time of 10 h. We have also investigated the role of the cell division cycle in the formation and subsequent development of somites. A single treatment of 2-day chick embryos with heat shock or a variety of drugs that affect the cell cycle all produce repeated anomalies in the pattern of somites and vertebrae that develop subsequent to the treatment. The interval between anomalies is 6-7 somites (or a multiple of this distance), which corresponds to 10 h. This interval is identical to that measured for the cell division cycle. Given that cell division synchrony is seen in the presomitic mesoderm, we suggest that the cell division cycle plays a role in somite formation. Finally, we consider the mechanisms responsible for regionalization of derivatives of the somite, and conclude that it is likely that both cell interactions and cell lineage history are important in the determination of cell fates

A comparison of agricultural systems at the Allee Research Center

The petrochemical-dependent agriculture that developed in the export-oriented economy of the 1970\u27s proved vulnerable to high energy costs and volatile export markets as well as detrimental to soil and water resources. This project was designed to compare a petrochemical-based, high-tillage, low-management cropping system (System I) with two alternative systems: a ridge-till, reduced fertilizer and pesticide, high-management system (System II) and a rotational, low-pesticide, low-fertilizer conventional tillage system (System III)

Elastic waves push organic fluids from reservoir rock

Elastic waves have been observed to increase productivity of oil wells, although the reason for the vibratory mobilization of the residual organic fluids has remained unclear. Residual oil is entrapped as ganglia in pore constrictions because of resisting capillary forces. An external pressure gradient exceeding an ‘‘unplugging’’ threshold is needed to carry the ganglia through. The vibrations help overcome this resistance by adding an oscillatory inertial forcing to the external gradient; when the vibratory forcing acts along the gradient and the threshold is exceeded, instant ‘‘unplugging’’ occurs. The mobilization effect is proportional to the amplitude and inversely proportional to the frequency of vibrations. We observe this dependence in a laboratory experiment, in which residual saturation is created in a glass micromodel, and mobilization of the dyed organic ganglia is monitored using digital photography.We also directly demonstrate the release of an entrapped ganglion by vibrations in a computational fluid-dynamics simulation

Air Flow and Pressure Drop Measurements Across Porous Oxides

This report summarizes the results of air flow tests across eight porous, open cell ceramic oxide samples. During ceramic specimen processing, the porosity was formed using the sacrificial template technique, with two different sizes of polystyrene beads used for the template. The samples were initially supplied with thicknesses ranging from 0.14 to 0.20 in. (0.35 to 0.50 cm) and nonuniform backside morphology (some areas dense, some porous). Samples were therefore ground to a thickness of 0.12 to 0.14 in. (0.30 to 0.35 cm) using dry 120 grit SiC paper. Pressure drop versus air flow is reported. Comparisons of samples with thickness variations are made, as are pressure drop estimates. As the density of the ceramic material increases the maximum corrected flow decreases rapidly. Future sample sets should be supplied with samples of similar thickness and having uniform surface morphology. This would allow a more consistent determination of air flow versus processing parameters and the resulting porosity size and distribution

A cell lineage analysis of segmentation in the chick embryo

We have studied the lineage history of the progenitors of the somite mesoderm and of the neural tube in the chick embryo by injecting single cells with the fluorescent tracer, rhodamine-lysine-dextran. We find that, although single cells within the segmental plate give rise to discrete clones in the somites to which they contribute, neither the somites nor their component parts (sclerotome, dermatome, myotome or their rostral and caudal halves) are `compartments' in the sense defined in insects. Cells in the rostral two thirds or so of the segmental plate contribute only to somite tissue and divide about every 10 h, while those in the caudal portions of this structure contribute both to the somites and to intermediate and lateral plate mesoderm derivatives. In the neural tube, the descendants of individual prospective ventral horn cells remain together within the horn, with a cycle time of 10 h. We have also investigated the role of the cell division cycle in the formation and subsequent development of somites. A single treatment of 2-day chick embryos with heat shock or a variety of drugs that affect the cell cycle all produce repeated anomalies in the pattern of somites and vertebrae that develop subsequent to the treatment. The interval between anomalies is 6-7 somites (or a multiple of this distance), which corresponds to 10 h. This interval is identical to that measured for the cell division cycle. Given that cell division synchrony is seen in the presomitic mesoderm, we suggest that the cell division cycle plays a role in somite formation. Finally, we consider the mechanisms responsible for regionalization of derivatives of the somite, and conclude that it is likely that both cell interactions and cell lineage history are important in the determination of cell fates

An Archaeological Survey on the Xoxocotlan Piedmont, Oaxaca, Mexico

Surface survey on the piedmont near the present village of Xoxocotlan, Oaxaca, Mexico, has revealed the pattern of prehistoric settlement around an irrigation canal that distributed water from a dammed reservoir located on the flanks of Monte Alban. Intensive systematic collection techniques have permitted quantitative statements to be made about the density of occupation and the contribution of the irrigation system to the food supply of Monte Alban

A Scientific Name for Pacific Oysters

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