Paleoenvironmental interpretations of Quaternary reef deposits based on comparisons of 10 selected modern and fossil larger foraminifera from the Ryukyu Islands, Japan

Abstract A new method for reconstructing depositional environments of larger foraminifera‐bearing limestones is proposed. First, depth and spatial distributions of empty tests of 10 foraminiferal taxa in a 1–2 mm size fraction were examined using 32 surface sediment samples collected from depths shallower than 200 m, located to the west of Miyako Island, Ryukyu Islands, northwest Pacific. Distributional ranges of empty tests in the 1–2 mm size fraction appear to be more limited than those including other size fractions in previous reports, partly because larger empty tests of each taxon are less easily transported than smaller ones. Multivariate analyses (Q‐mode cluster analysis and non‐metric multidimensional scaling ordination) based on binary (presence/absence) data of the 10 taxa delineate four sample groups, each of which corresponds to different depositional environments: nearshore zone/bay inlet; back‐reef to fore‐reef; outer shelf to shelf slope; and shelf slope distant from coral reefs. Next, these modern data were applied to reconstruct the depositional environment of a rock section distributed in the Shiratorizaki area (Irabu Island, Ryukyu Islands), which consists of larger foraminiferal limestone of the Pleistocene Ryukyu Group. Multivariate analyses were performed on the fossil plus the modern foraminiferal data to explore the possible relationship of the fossil associations with variations in modern associations, demonstrating that the fossil foraminiferal associations resemble the modern outer shelf associations. The modern analog technique was also applied to estimate paleobathymetry using fossil foraminiferal data. The results indicate that the section studied was deposited in outer shelf environments at depths between 53.5 and 98.6 m. These paleoenvironmental interpretations are consistent with previous studies based on sedimentary facies and the computer‐based expert system. The modern dataset and methods used in our work would be particularly useful for paleoenvironmental reconstructions of Quaternary reef and shelf carbonates along active margins of the northwest Pacific.     

Small-Amplitude Disturbances In A Radiating And Scattering Grey Medium Ii. Solutions Of Given Real Wave Number <Emphasis Type="BoldItalic">k</Emphasis>

We study the fundamental modes of radiation hydrodynamic waves arising from one-dimensional small-amplitude initial fluctuations with wave number k in a radiating and scattering grey medium using the Eddington approximation. The dispersion relation analyzed is the same as that of Paper I (Kaneko et al., 2000), but is solved as a quintic in angular frequency ω while a quadratic in k ² in Paper I. Numerical results reveal that wave patterns of five solutions are distinguished into three types of the radiation-dominated and type 1 and type 2 matter-dominated cases. The following wave modes appear in our problem: radiation wave, conservative radiation wave, entropy wave, Newtonian-cooling wave, opacity-damped and cooling-damped waves, constant-volume and constant-pressure diffusion modes, adiabatic sound wave, cooling-damped and drag–force-damped isothermal sound waves, isentropic radiation-acoustic wave, and gap mode. The radiation-dominated case is characterized by the gap between the isothermal sound and isentropic radiation-acoustic speeds within which there is not any acoustic wave propagating with real phase speed. One of the differences between type 1 and type 2 matter-dominated cases is the connectivity of the constant-volume diffusion mode, which originates from the radiative mode in the former case, while from the Newtonian-cooling wave in the latter case. Analytic solutions are derived for all wave modes to discuss their physical significance. The criterion, which distinguishes between radiation-dominated and type 1 matter-dominated cases, is given by Γ₀ = 9, where Γ₀ = C _p ^(tot)/C _V ^(tot) is the ratio of total specific heats at constant pressure and constant volume. Waves in a scattering grey medium are also analyzed, which provides us some hints for the effects of energy and momentum exchange between matter and radiation.     

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.     

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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.     

Control algorithm for estimating future responses of active variable stiffness structure

A control algorithm has been developed for controlling Active Variable Stiffness (AVS) structures. This algorithm analyses information of an observed seismic excitation, estimates the future structural responses and determines how to alter the structure stiffness. An objective structure is assumed to possess N on-off elements whose states are controlled by the proposed algorithm. That is, at a given moment t_k, (1) seismic excitation information is expressed by an Auto Regressive (AR) model as the identification model; (2) future excitation information is predicted using the AR model; (3) future responses due to predicted excitation are estimated; (4) based on the initial condition at t_k, the responses of 2^N possible structural states from t_k, to t_k+L are calculated; (5) the state which minimizes the input energy during t_L is selected; and (6) immediately after t_k, on-off elements are set up and subjected to the selected states. The effectiveness of the induced algorithm is confirmed by numerical experiments on a model of a three-storey building under sine and seismic excitations.     

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...     

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.