Enhanced scavenging ofPb andPo by processes associated with the East Pacific Rise near 8°45′N

In 1977 and 1981 a hydrothermal plume was detected at the East Pacific Rise (EPR) near 8°45′N and at MANOP Site M, 25 km east of the EPR, by anomalous²²²Rn and Mn concentrations. In 1981, samples were also taken for²¹⁰Pb,²¹⁰Po and²²⁶Ra analyses to determine if enhanced scavenging of these elements occurred in the plume. At both the ridge crest and at Site M, the ²¹⁰Pb/²²⁶Ra ratios range from 0.09 to 0.35, which are among the lowest values ever measured. It appears that removal of the²¹⁰Pb is occurring by processes operating at or near the seafloor. There is also significant ²¹⁰Po/²¹⁰Pb disequilibrium at both locations, which appears to increase away from the seafloor towards the plume (as indicated by elevated Mn concentrations). An in-situ water column scavenging process is suggested by correlation of [²¹⁰Pb-²¹⁰Po] and Mn concentrations in the plume. The residence time of the²¹⁰Po is only about 1 year, which is close to its residence time in surface waters but quite short compared to typical deep sea values. Thus rapid scavenging of the polonium in the plume and relatively rapid settling of particles from the plume is suggested.     

Controlled failure of hollow rock cylinders in uniaxial compression

SummaryControlled Failure of Hollow Rock Cylinders in Uniaxial Compression Detailed consideration is given to the behavior of hollow rock cylinders loaded in uniaxial compression. Elastic stress distributions calculated by the finite element method show that radial stresses are considerably lower in hollow than in solid cylinders, and that the uniformity of the stresses can be improved considerably by using loading platens having the same cross-section as the specimen. Servo-controlled uniaxial compression tests carried out on solid and thick-walled cylinders of white Tennessee marble show no essential differences in the behavior of the two specimen types with similar strengths and fracture phenomena being observed. In tests carried out in servo-controlled, stiff, and conventional machines, the progressive formation of large numbers of short subaxial cracks is followed by the development of macrofractures such as slabbing and shearing well past the peak of the stress-strain curve.

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ZusammenfassungDer gesteuerte Bruch hohler Gesteinszylinder unter einachsigem Druck Das Verhalten hohler Gesteinszylinder unter einachsigem Druck ist eingehend beschrieben. Die Methode der endlichen Elemente ermöglicht die Berechnung der elastischen Spannungsverteilung und zeigt, daß die radialen Spannungen im Hohlzylinder bedeutend geringer sind als im massiven. Der Gebrauch von Druckplatten vom gleichen Querschnitt wie dem der Probe verbessert die Gleichförmigkeit der Spannungen wesentlich.Servo-gesteuerte einachsige Druckversuche an dichtwandigen hohlen und an massiven Proben von weißem Tennessee-Marmor lassen keine wesentlichen Unterschiede zwischen dem Verhalten der beiden Probenarten erkennen. Ähnliche Festigkeiten und Brucherscheinungen sind im hohlen und massiven Zylinder beobachtet worden. In Versuchen mit servo-gesteuerten starren und in konventionellen Maschinen folgt der progressiven Bildung einer großen Anzahl kurzer, etwa axialer Risse die Entstehung von größeren Brucherscheinungen, wie z. B. Abschalungen und Scherbrüche, und zwar deutlich nach dem Scheitelpunkt der Arbeitslinie.

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RésuméFracturation contrôlée de cylindres rocheux creux en compression uniaxiale Une étude détaillée du comportement de cylindres rocheux creux soumis à une compression uniaxiale est faite ici. La répartition des contraintes en milieu élastique déterminée par la méthode des éléments finis a montré que les contraintes radiales étaient beaucoup plus petites dans les cylindres creux que dans les cylindres pleins et que l'uniformité des contraintes pouvait être considérablement améliorée en utilisant des platines de mise en charge ayant la même section que l'éprouvette.Des essais de compression simple effectués avec une presse asservie sur des cylindres de marbre du Tennessee soit pleins soit à paroi épaisse ne montrent aucune différence notable quand au comportement des deux types d'éprouvettes. La résistance à la rupture et les phénomènes de fracturation se sont avérés comparables dans les deux cas. Au cours des essais effectués avec une presse raide asservie et une presse classique, la formation progressive d'un grand nombre de courtes fissures sub axiales est suivie par le développement de macrofractures telles qu'écaillage et cisaillements une fois dépassé le pic de la courbe effort déformation.

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With 11 Figures     

Dynamics of ecosystems and anthropogenic drivers in the Yellow Sea Large Marine Ecosystem

<正>In the developed world, governance of marine ecological environment is the important part of the national ecological and economic outcome. The Yellow Sea is one of large marine ecosystems in the seas of East Asia, which is an extension of one of the largest continental shelf areas, and forms a huge but shallow sediment body in its south area which is geographically unique in the world. As a region with the most fragile natural environment, unparalleled global ecological significance and...     

Rise of Buoyant Emissions from Low-Level Sources in the Presence of Upstream and Downstream Obstacles

Field and laboratory studies have been conducted to investigate the effect of surrounding buildings on the plume rise from low-level buoyant sources, such as distributed power generators. The field experiments were conducted in Palm Springs, California, USA in November 2010 and plume rise from a 9.3 m stack was measured. In addition to the field study, a laboratory study was conducted in a water channel to investigate the effects of surrounding buildings on plume rise under relatively high wind-speed conditions. Different building geometries and source conditions were tested. The experiments revealed that plume rise from low-level buoyant sources is highly affected by the complex flows induced by buildings stationed upstream and downstream of the source. The laboratory results were compared with predictions from a newly developed numerical plume-rise model. Using the flow measurements associated with each building configuration, the numerical model accurately predicted plume rise from low-level buoyant sources that are influenced by buildings. This numerical plume rise model can be used as a part of a computational fluid dynamics model.