A Hard X-ray Two-Ribbon Flare Observed with Yohkoh/HXT

The Yohkoh hard X-ray telescope (HXT) observed hard X-rays from the impulsive phase of a long-duration event (LDE) occurring on 14 July 2000. The Yohkoh soft X-ray telescope (SXT) and other instruments observed a large arcade, with width and length ∼30 000 km and ∼120 000 km, respectively. In hard X-rays, for the first time, a two-ribbon structure was clearly observed in the energy range above 30 keV. This result suggests that electrons are in fact accelerated in the whole system of this arcade, not merely in a particular dominant loop. We analyzed the motions of bright kernels in the two hard X-ray ribbons in detail. Assuming these bright kernels to be footpoints of newly reconnected loops, we infer from their motions that the loops reconnecting early are highly sheared, while the loops reconnecting later are less sheared. We have also analyzed the hard X-ray spectra of the two ribbons independently. At the outer edge of a ribbon, the spectrum tends to be harder than that in the inner edge. This suggests that higher-energy electrons precipitate at the footpoints of outer loops and lower ones do at those of inner loops. We discuss what kind of model can support this tendency.     

Seismic return motion

Possibilities of backswing of fault displacement are investigated on the basis of a simple crack model. Although it has been suggested that the backswing would not occur in real earthquakes because of friction, there is evidence that some earthquakes might have caused return motion “locally” on the fault surface. This paper attempts to derive conditions for such local return motion. Spatial extension of the crack beyond the stress-filled region into the stress-deficient region gives a favorable site for the return motion, the site being just outside the stress-filled region. In our model the return motion occurs at this site when the frictional stress is less than about 30% of the regional stress in the stress-filled region. The overall return motion, on the other hand, would not occur unless the frictional stress is less than 10% of the regional stress.     

Sulphide and oxide minerals from the Ohmine granitic rocks in Kii Peninsula,central Japan,and their primary paragenetic relations

In the Ohmine granitic rocks of Kii Peninsula, central Japan, ilmenite, rutile, pyrrhotite, pyrite and chalcopyrite commonly occur, but no magnetite is present. Their primary paragenetic relations were confirmed by examining their mode of occurrences as inclusion species in major silicate minerals and the phase relations in the Cu-Fe-S system, though their parageneses changed in cooling of the rocks. This makes it possible to estimate the fugacities of oxygen and sulfur in the granitic rocks based upon their paragenetic relations, and to discuss the nature of volatiles in the granitic rocks. Significant subsolidus reactions for sulfide minerals continued until the rocks cooled below 300° C and took place in two types of mineral grains, in groundmass and as inclusions. The removal of sulfur and copper through the silicate crystals was too easy to preserve the chemistry of sulfides included in silicates.     

Tectonoelectricity

Anomalous earth-current changes in association with an earthquake occurrence have often been reported since the 19th century. Changes reported in classical as well as recent literature are reviewed, although it is hard to say that any physically clear relationship between earth-current changes and earthquakes has been established. Even though a strong correlation between precursory earthcurrent changes and earthquakes has often been reported in the U.S.S.R. and the People's Republic of China in recent years, it appears that a general rule governing the earthquake-related earth-current changes is still very much unknown, partly because of contamination by artificial and natural noise.In contrast to the difficulty in understanding earth-current changes, monitoring of earth-resistivity seems to provide a much clearer means for interpreting geoelectric phenomena in association with tectonic processes in the Earth. Soviet and American work showed that the resistivity decreases to a considerable extent in the focal region prior to an earthquake. Such a change seems to be closely correlated to dilatancy generation in the Earth's crust. This finding doubtless provides an important means for earthquake prediction.An ususual, highly sensitive resistivity variometer, developed by the writer, disclosed that a resistivity change takes place at a teleseismic distance when an earthquake of large and medium magnitude occurs. Many of the resistivity changes thus observed are preceded by a premonitory change, which is supposed to reflect the preliminary rupture at a focal region.     

Fine structures of mutually normalized rare-earth patterns of chondrites

REE abundances in ten chondrites (nine falls and one find) were determined very accurately by mass-spectrometric stable isotope dilution techniques. All of the chondrites have different relative and absolute REE patterns. Except for Eu and, rarely, for Ce, the REE abundances in chondrites are smoothly fractionated from sample to sample. Notwithstanding differences in the abundances of common REE, four of five L6 chondrites have very similar absolute Eu abundances; their mutually-normalized REE patterns are not curved, but are composed of two rectilinear segments.The Leedey-normalized REE pattern for St. Séverin (LL6) is composed of two concave curves. Yonozu's (H4,5) pattern shows negligibly concave curvature on both sides of Eu. Kesen's (H4) pattern is unusual in its overall pattern but also in irregularities for particular elements. The irregularity may be connected with the unusually high vapor pressure of metallic Yb. The REE pattern for the Allende bulk sample shows a discontinuity, presumably reflecting its considerable heterogeneity of composition and structure. It is evident that any pattern of ordinary chondrites cannot be produced from the Allende bulk pattern. A comparison is also made with the results on the chondrite composites previously investigated.     

Assembling “Japantown”? A critical toponymy of urban dispossession in Vancouver,Canada

Geographic scholarship in critical toponymy has highlighted the importance of place naming as a form of discursive power within processes of urbanization. This paper builds on such literature and advances a novel theory of toponymic assemblage to interpret findings from a participatory research project in the Downtown Eastside of Vancouver, Canada. We foreground neighborhood history in the form of a Japanese Canadian enclave and its wartime uprooting and dispossession, and trace the historical antecedents of a resurrected toponymy of “Japantown” that has appropriated and renarrated Japanese Canadian history to facilitate further rounds of dispossession. Using a genealogical method, we highlight three “moments” of Japanese Canadian uprooting, return, presence, and activism, demonstrating how toponymies are assembled in place in heterogeneous and historically contiguous ways. This approach expands on current research in critical toponymy, offering a novel methodology for exploring the enrolment of toponymy, discourse, and materiality in the formation of place.     

Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses

Climate Dynamics - The interannual-decadal variability of the wintertime mixed layer depths (MLDs) over the North Pacific is investigated from an empirical orthogonal function (EOF) analysis of an...     

Study of the structure of silica film by infrared spectroscopy and electron diffraction analyses

Amorphous silicon oxide films have been studied on the basis of electron diffraction (ED) analyses and infrared (IR) spectroscopy in order to elucidate the relationship between the structures. After the heat treatment of the film in air at 300 and 500°C, the ED pattern showed halo rings, and the IR spectra clearly changed. Intensity analysis of the ED pattern provided evidence for the structural change of the amorphous film. It was concluded that the spectral changes in the ranges of 9.2–10.2, 12.5–13.5 and 19.5–22.5 μm were the result of phase transitions of the microcrystallites of α-cristobalite to β-cristobalite, and α- or β-quartz. Astrophysical implications have been discussed.     

Precise Determination of the Coordinate Systems for the Yohkoh Telescopes and the Application of a Transit of Mercury

The Yohkoh solar X-ray observatory carries two telescopes that require coalignment at a level better than the minimum pixel size of 2_45. This coalignment is needed both internally within Yohkoh and for many scientific applications involving data from ground-based radio and optical observatories. We describe the methods successfully developed for this purpose and now incorporated in the Yohkoh software. Soft X-ray observations of the 1993 transit of Mercury across the solar disk provided key information for the calibration of the coalignment procedures.