Orientation preference and fractal character of short fatigue cracks in a weld metal

Short fatigue crack behaviour in a weld metal has been further investigated. The Schmid factor and the fractal dimension of short cracks on iso-stress specimens subjected to reversed bending have been determined and then applied to account for the distribution and orientation characteristics of short fatigue cracks. The result indicates that the orientation preference of short cracks is attributed to the large values of Schmid factor at relevant grains. The Schmid factors of most slip systems, which produced short cracks, are less than or equal to 0.4. Crack length measurements reveal that short crack path, compared to that of long crack, possesses a more stable and relatively larger value of fractal dimension. This is regarded as one of the typical features of short cracks.

Tidal oscillations at the head of Monterey Submarine Canyon and their relation to oceanographic sampling and the circulation of water in Monterey Bay. Annual report, Part 6, September 1972

During a 25-hour hydrographic times series at two stations near the head of Monterey Submarine Canyon, an internal tide was observed with an amplitude of 80 to 115 m in water depths of 120 and 220 m respectively. These large oscillations produced daily variations in hydrographic and chemical parameters that were of the same magnitude as seasonal variations in Monterey Bay. Computed velocities associated with the internal tide were on the order of 10 em/sec, and this tidally induced circulation may have a significant role in the exchange of deep water between Monterey Submarine Canyon and the open ocean. (PDF contains 49 pages)

Seasonal cycles of phytoplankton in relation to the hydrography of Monterey Bay

Annual cycles of relative abundance are described for phytoplankton species collected from Monterey Bay, California, from July 1974 to June 1976, and the population dynamics related to the annual hydrographic cycle. Neritic diatom species dominated the population during the Upwelling and Oceanic periods, with dinoflagellate species becoming numerically more important during the Davidson period. Recurrent species groups identified using Fager's regroup analysis revealed the presence of a large neritic group of overwhelming numerical importance. This group is composed of indigenous species and is present in the bay during most of the year. Conspicuous changes in the phytoplankton population occurred predominantly among species within this group. During the Davidson period, the advection of southern waters into the bay may temporarily displace the endemic species with dinoflagellates becoming numerically more important. A red tide bloom of Gonyaulax polyedra occurred during this period in 1974, which dominated the phytoplankton population for a period of six weeks. The population dynamics of two hydrographically different stations were compared. A station located over the deep waters of the submarine canyon exhibited much lower phytoplankton standing stocks than a station located over the shelf area in the south of the bay, but seasonal changes in relative abundance and species composition were similar. Physical and chemical differences observed between the two stations appear to be the result of the presence of more recently upwelled water in the canyon area, and higher biological utilization in the south of the bay. A close correlation of species diversity with the depth of the mixed layer was observed, with diversity rising with the shoaling of the thermocline. It is suggested that this may reflect the introduction of new species from below the thermocline into the mixed layer as a result of upwelling activity. It is also suggested that this may be an artifact due to sampling problems associated with internal waves. (Document contains 100 pages.)

Time Variation in an Optimal Asymmetric Preference Monetary Policy Model

This paper considers a time varying parameter extension of the Ruge-Murcia (2003, 2004) model to explore whether some of the variation in parameter estimates seen in the literature could arise from this source. A time varying value for the unemployment volatility parameter can be motivated through several means including variation in the slope of the Phillips curve or variation in the preferences of the monetary authority.We show that allowing time variation for the coefficient on the unemployment volatility parameter improves the model fit and it helps to provide an explanation of inflation bias based on asymmetric central banker preferences, which is consistent across subsamples.

Changes In Submersed Macrophytes In Relation To Tidal Storm Surges

We analyzed long-term submersed macrophyte presence-absence data collected from 15 stations in Kings Bay/Crystal River, Florida in relation to three major storm events. The percent occurrence of most species declined immediately after storm events but the recovery pattern after the storm differed among species. Hydrilla (Hydrilla verticillata (L.F.) Royle)and Eurasian watermilfoil (Myriophyllum spicatum L.) exhibited differing recolonization behaviors. Eurasian watermilfoil recolonized quickly after storms but declined in abundance as hydrilla began to increase in abundance. Natural catastrophic events restructure submersed macrophyte communities by eliminating the dominate species, and allowing revegetation and restructuring of communities. Tidal surges may also act to maintain species diversity in the system. In addition, catastrophic events remove dense nuisance plant growth for several years, altering the public's perception of the nuisance plant problem of Kings Bay/Crystal River.