Mound formation

Deposits which are forming are frequentiy characterized by venting streams of hot (300°C) mineralized fluid known as smokers. These result in the local formation of metalliferous mud, rock chimneys, or mounds rich in sulfides. In the upper fractured zone or deep in the rock mass beneath the vents, vein or massive sulfide deposits may be formed by the ckculating fluids and preserved as the cmstal plates move across the oceans. These off-axis deposits are potentially the most significant resources of hydrothermal deposits, even though none has yet been located. 

Tubercles are mounds of corrosion product and deposit that cap localized regions of metal loss. Tubercles can choke pipes, leading to diminished flow and increased pumping costs (Fig. 3.1). Tubercles form on steel and cast iron when surfaces are exposed to oxygenated waters. Soft waters with high bicarbonate alkalinity stimulate tubercle formation, as do high concentrations of sulfate, chloride, and other aggressive anions. 

Tuberculation occurs in aqueous solutions. Mounds form over metal surfaces providing for concentration differences, favorable environments for biological growth, and an increase in acidity leading to hydrogen formation. 

The second procedure is different from the previous one in several aspects. First, the metallic substrate employed is Au, which does not show a remarkable dissolution under the experimental conditions chosen, so that no faradaic processes are involved at either the substrate or the tip. Second, the tip is polarized negatively with respect to the surface. Third, the potential bias between the tip and the substrate must be extremely small (e.g., -2 mV) otherwise, no nanocavity formation is observed. Fourth, the potential of the substrate must be in a region where reconstruction of the Au(lll) surface occurs. Thus, when the bias potential is stepped from a significant positive value (typically, 200 mV) to a small negative value and kept there for a period of several seconds, individual pits of about 40 nm result, with a depth of two to four atomic layers. According to the authors, this nanostructuring procedure is initiated by an important electronic (but not mechanical) contact between tip and substrate. As a consequence of this interaction, and stimulated by an enhanced local reconstruction of the surface, some Au atoms are mobilized from the Au surface to the tip, where they are adhered. When the tip is pulled out of the surface, a pit with a mound beside it is left on the surface. The formation of the connecting neck between the tip and surface is similar to the TILMD technique described above but with a different hnal result a hole instead of a cluster on the surface (Chi et al., 2000). 

The effectiveness of the mixing within the vessel. Coning (the formation of a mound of insoluble excipient particles on the bottom of the vessel) may indicate the need for a higher rotation speed or the use of different apparatus (e.g., baskets instead of paddles). 

In the second step the bas is recognized by the receptor site and the bas-rep complex forms. As was noted above, the complex is generally bonded by inter-molecular forces. The bas is transferred from an aqueous phase to the receptor site. The receptor site is very much more hydrophobic than is the aqueous phase. It follows, then, that complex formation depends on the difference in intermolecular forces between the bas-aqueous phase and the bas-receptor site. The importance of a good fit between bas and receptor site has been known for many years. The configuration and conformation of the bas can be of enormous importance. Also important is the nature of the receptor. If the receptor is. a cleft, as is the case in some enzymes, steric effects may be maximal as it may not be possible for a substituent to relieve steric strain by rotating into a more favorable conformation. In such a system, more than one steric parameter will very likely be required in order to account for steric effects in different directions. Alternatively, the receptor may resemble a bowl, or a shallow, fairly flat-bottomed dish. Conceivably it may also be a mound. In a bowl or dish, steric effects are likely to be very different from those in a cleft. Possible examples are shown in Fig. 1, 2, and 3. 

The importance of stratigraphic studies and the identification of sedimentary units at extensively disrupted sites like Hierakonpolis can be illustrated by the excavations at locality II, where there is evidence for habitation (trash mounds and pottery) as well as industry (pottery kilns). This locality ofiered a unique opportunity to study Predynastic ecology because of the excellent state of organic preservation in an area where there was a clustering of multi-functional components (6,14). Four test pits were dug in one area through the site, in the direction NIO °E-SIO °W. The correlation profile is shown in Figure I. The oldest unit identified was Nile silt (Masmas formation). In some areas, this silt was covered by eolian and/or wadi sands, which probably represents a local feature of sand accumulation under arid to semiarid conditions. 

Pache, M., Reitner, J. Arp, G. (2001) Geochemical evidence for the formation of a large Miocene travertine mound at a sublacustrine spring in a soda lake (Wallerstein castle rock, Nordlinger Ries, Germany). Facies 45, 211-230. 

Goulding, H.C., Mills, R.A. and Nesbitt, R.W. (1998) Precipitation of hydrothermal sediments on the active TAG mound implications for ochre formation, in Modem Ocean Floor Processes and the Geological Record (eds R.A. Mills and K. Harrison), Geological Society Special Publication No. 148, pp. 201-216. 

Calcium carbonate is currently more actively studied in aqueous solution. Earth s oceans are saturated with Ca2+ ions, especially near the surface. The calcium is delivered to the oceans mostly by rivers and streams. (As rocks weather, calcium ions are released and attracted to water molecules.) Because there is such a high concentration of calcium ions in the oceans, it easily precipitates out as calcium carbonate or, less commonly, as calcium sulfate. The precipitate contributes to the formation of coral reefs in warm lagoons and shallow tropical seas. Inland salt seas and lakes, such as the Dead Sea in Israel, the Great Salt Lake in Utah, and Mono Lake in eastern California, often have whitish limestone deposits around their shores. (All of these bodies of water are saltier than the oceans.) Softer deposits tend to be called chalk. In locations where spring water bubbles up through the floor of a salty lake, mounds of limestone, called tufas,... 

The Influences of Metal Structure. The formation of a continuous laminar carbon film over extended areas of the surface appears to be a characteristic of precipitation on a well-annealed metal. Structural disorder may be introduced by successive dissolution-precipitation cycles, or may remain as the cold-worked zone on non-annealed material. In both cases, a greater proportion of the mound-type of deposit is expected, which has a carbon overlayer identical to the continuous laminar carbon layer. 

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