Alteration of the equal settling ratio of fine particles by vertically-oscillating water

An equal settling ratio is an important factor in estimating particle separation accuracy. However, this factor is often calculated using the settling velocity in stationary water, there are no examples of calculation of the equal settling ratio in an actual separator. This is difficult because particle movement in a separator is very complicated, and even simple periodic motions, such as the oscillation field used with many separators, are ignored in many cases. The authors have previously reported on the relation between the equal settling ratio and the oscillation frequency by analysis of particle movement in vertically oscillating water, using spherical particles of glass (average size 435 μm) and zirconia (202 μm) which have the same settling velocity in stationary water. In this study, the influence of particle diameter on the change in the settling velocity in oscillating water was experimentally investigated for three pairs of glass and zirconia particles having different sizes under 0.5 mm, which have the same settling velocity in stationary water. The settling velocities of different-sized particles decreased at different rates in oscillating water, indicating that the equal settling ratio is reduced by water oscillation. We conclude that water oscillation improves the accuracy of size separation for glass particles over 300 μm and zirconia particles over 150 μm when glass and zirconia particles are separated from each other with the difference of these settling velocities.     

Some center-limb statistical trends of impulsive solar bursts at 7 GHz

The more impulsive 7 GHz bursts seem to prefer the solar limb regions, while the degree of polarization decreases with increasing impulsivity.     

Pre-Japan-ARGO: Experimental Observation of Upper and Middle Layers South of the Kuroshio Extension Region Using Profiling Floats

We deployed two profiling floats in the region south of the Kuroshio Extension in March 2000. Temperature and salinity profiles from a depth of 1500 × 10⁴ Pa to the surface are reported every two and four weeks, respectively. The floats performed very well for first four months after deployment. Later they failed in surfacing for a few months when the sea surface temperature in the region was high. The salinity sensors seemed to suffer from some damage during their failure-in-surfacing period. Despite this trouble, the results clearly demonstrate that the profiling float is a very useful and cost-effective tool for physical oceanographic observation in the open sea. This revised version was published online in July 2006 with corrections to the Cover Date.     

Graphitization of carbonaceous matter during metamorphism with references to carbonate and pelitic rocks of contact and regional metamorphisms,Japan

This study is an attempt to correlate the graphitization process of carbonaceous matter during metamorphism with metamorphic grade. Graphitization can be parameterized using crystal structure and chemical and isotopic compositions. The extent of graphitization could be characterized mainly by temperature, duration of metamorphism and rock composition. We compared the graphitization trends for two metamorphic terrains, a contact aureole of the Kasuga area and a regional metamorphic terrain of high-temperature/low pressure type of the Ryoke metamorphic terrain in Northern Kiso area, Central Japan, and for two different lithologies (carbonate and pelite), using X-ray diffractogram, DTA-TG analysis, and chemical and stable isotope analyses. During contact metamorphism, graphitization and carbon isotopic exchange reactions proceeded simultaneously in pelitic and carbonate rocks. The decreases in basal spacing d(002) of the carbonaceous matter in carbonate rocks is greatly accelerated at temperatures higher than about 400° C. Furthermore, carbon isotopic ratios of graphite in carbonate rocks also change to ¹³C-enriched values implying exchange with carbonates. The beginning of this enrichment of ¹³C in the carbonaceous matter coincides with an abrupt increase of the graphitization processes. Carbon isotopic shifting up to 5 in pelites could be observed as metamorphic temperature increased probably by about 400° C. Carbonaceous matter in pelitic rocks is sometimes a mixture of poorly crystallized organic matter and well-crystallized graphite detritus. DTA-TG analysis is an effective tool for the distinction of detrital graphitic material. Two sources for the original carbon isotopic composition of carbonaceous matter in pelites in the Kasuga contact aureole can be distinguished, about-28 and-24 regardless of the presence of detrital graphite, and were mainly controlled by depositional environment of the sediments. Graphitization in limestones and pelitic rocks in regional metamorphism proceeds further than in a contact aureole. In the low-temperature range, the differences in extent of graphitization between the two metamorphic regions is large. However, at temperatures higher than 600° C, the extent of graphitization in both regions is indistinguishable. The degree of graphitization is different in limestones and pelitic rocks from the Ryoke metamorphic terrain. We demonstrate that the graphitization involves a progressive re-construction process of the crystal structure. The sequence of the first appearance of crystal inter planar spacing correlates with the metamorphic grade and indicates the crystal growth of three-dimensional structured graphite.     

An application of a two-layer model to wind driven sub-tidal currents in Puget Sound

A two layer model of an infinitely long channel, with one end closed, is applied to study the sub-tidal response to wind forcing of Puget Sound. The model uses a linear friction parameterization. Data show that the acceleration of current near the surface responds to the wind event almost instantaneously, however, acceleration tends to start decreasing at later times and eventually changes sign even though the wind blows in one direction throughout. Analysis of the model results show that when the forcing frequency is high, the phase lag between forcing and friction causes this phenomena, and as forcing frequency increases, phase lag between forcing and friction approaches /2. When the forcing frequency is low, phase lag between forcing and friction decreases almost linearly with forcing frequency and at extremely low frequency, they almost balance each other. Analysis of the model results show also that the amplitude of baroclinic pressure gradient increases rapidly as forcing frequency decreases and when the forcing frequency is low, the baroclinic pressure gradient becomes important. Effects of baroclinic pressure gradient propagate as a wave from the boundaries and it takes about one day to take effect at the point where the observations were made.     

A high‐T metamorphic complex derived from the high‐P Suo metamorphic complex in the Omuta district,northern Kyushu,southwest Japan

New U–Pb ages of zircons from migmatitic pelitic gneisses in the Omuta district, northern Kyushu, southwest Japan are presented. Metamorphic zonation from the Suo metamorphic complex to the gneisses suggests that the protolith of the gneisses was the Suo metamorphic complex. The zircon ages reveal the following: (i) a transformation took place from the high‐P Suo metamorphic complex to a high‐T metamorphic complex that includes the migmatitic pelitic gneisses; (ii) the detrital zircon cores in the Suo pelitic rocks have two main age components (ca 1900–1800 Ma and 250 Ma), with some of the detrital zircon cores being supplied (being reworked) from a high‐grade metamorphic source; and (iii) one metamorphic zircon rim yields 105.1 ±5.3 Ma concordant age that represents the age of the high‐T metamorphism. The high‐P to high‐T transformation of metamorphic complexes implies the seaward shift of a volcanic arc or a landward shift of the metamorphic complex from a trench to the sides of a volcanic arc in an arc–trench system during the Early Cretaceous. The Omuta district is located on the same geographical trend as the Ryoke plutono‐metamorphic complex, and our estimated age of the high‐T metamorphism is similar to that of the Ryoke plutono‐metamorphism in the Yanai district of western Chugoku. Therefore, the high‐T metamorphic complex possibly represents the western extension of the Ryoke plutono‐metamorphic complex. The protolith of the metamorphic rocks of the Ryoke plutono‐metamorphic complex was the Jurassic accretionary complex of the inner zone of southwest Japan. The high‐P to high‐T transformation in the Omuta district also suggests that the geographic trend of the Jurassic accretionary complex was oblique to that of the mid‐Cretaceous high‐T metamorphic field.     

Spitzer observations of acetylene bands in carbon-rich asymptotic giant branch stars in the Large Magellanic Cloud

We investigate the molecular bands in carbon-rich asymptotic giant branch (AGB) stars in the Large Magellanic Cloud (LMC), using the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope ( SST ) over the 5–38 μm range. All 26 low-resolution spectra show acetylene (C₂H₂) bands at 7 and 14 μm. The hydrogen cyanide (HCN) bands at these wavelengths are very weak or absent. This is consistent with low nitrogen abundances in the LMC. The observed 14 μm C₂H₂  band is reasonably reproduced by an excitation temperature of 500 K. There is no clear dilution of the 14 μm C₂H₂  band by circumstellar dust emission. This 14-μm band originates from molecular gas in the circumstellar envelope in these high mass-loss rate stars, in agreement with previous findings for Galactic stars. The C₂H₂ column density, derived from the 13.7 μm band, shows a gas mass-loss rate in the range 3 × 10⁻⁶ to 5 × 10⁻⁵ M_⊙ yr⁻¹. This is comparable with the total mass-loss rate of these stars estimated from the spectral energy distribution. Additionally, we compare the line strengths of the 13.7 μm C₂H₂  band of our LMC sample with those of a Galactic sample. Despite the low metallicity of the LMC, there is no clear difference in the C₂H₂  abundance among LMC and Galactic stars. This reflects the effect of the third dredge-up bringing self-produced carbon to the surface, leading to high carbon-to-oxygen ratio at low metallicity.