Binary formation with different metallicities: dependence on initial conditions

The fragmentation process in collapsing clouds with various metallicities is studied using three-dimensional nested-grid hydrodynamics. Initial clouds are specified by three parameters: cloud metallicity, initial rotation energy and initial cloud shape. For different combinations of these parameters, we calculate 480 models in total and study cloud evolution, fragmentation conditions, orbital separation and binary frequency. For the cloud to fragment during collapse, the initial angular momentum must be higher than a threshold value, which decreases with decreasing metallicity. Although the exact fragmentation conditions depend also on the initial cloud shape, this dependence is only modest. Our results indicate a higher binary frequency in lower metallicity gas. In particular, with the same median rotation parameter as in the solar neighbourhood, a majority of stars are born as members of binary/multiple systems for  <10⁻⁴ Z_⊙  . With initial mass  <0.1 M_⊙  , if fragments are ejected in embryo from the host clouds by multibody interaction, they evolve to substellar-mass objects. This provides a formation channel for low-mass stars in zero- or low-metallicity environments.     

Mass balance and sources of mercury in Tokyo Bay

The mass balance and sources of mercury in Tokyo Bay were investigated on the basis of observations from December 2003 to January 2005. Estimated input terms included river discharge (70 kg yr⁻¹) and atmospheric deposition (37 kg yr⁻¹), and output terms were evasion (49 kg yr⁻¹), export (13 kg yr⁻¹) and sedimentation (495 kg yr⁻¹). Thus, the outputs (557 kg yr⁻¹) considerably exceeded the inputs (107 kg yr⁻¹). In addition, the imbalance between the inputs and outputs of mercury was much larger than that of other trace metals (Cd, Cr, Cu, Pb and Zn), which suggests that there are other major inputs of mercury to Tokyo Bay. The mercury concentrations in rivers correlated significantly with the concentrations of Al and Fe, major components of soil. In Japan, large amounts of organomercurous fungicides (about 2500 tons as Hg) were used extensively in fields in the past, and most of the mercury was retained in the soil. In this study, the mercury concentration in rivers was measured primarily in ordinary runoff. These observations lead to the hypothesis that field soil discharged into stormwater runoff is a major source of mercury in Tokyo Bay. As a preliminary approach to validating this hypothesis, we measured the concentrations of mercury and other trace metals in river water during a typhoon. The mercury concentrations in stormwater runoff increased to 16–50 times the mean value in ordinary runoff, which is much higher than the increases for other metals. This tends to support the hypothesis.     

Residual structural capacity evaluation of steel moment‐resisting frames with dynamic‐strain‐based model updating method

This paper presents a method for evaluating the residual structural capacity of earthquake‐affected steel structures. The method first quantifies the damage severity of a beam by computing the dynamic‐strain‐based damage index. Next, the model used to analyze the structure is updated based on the damage index, to reflect the observed damage conditions. The residual structural capacity is then estimated in terms of changes in stiffness and strength, which can be applied by structural engineers, via a nonlinear static analysis of the updated model. The main contributions of this paper are in performance evaluation of the dynamic‐strain‐based damage index for seismically induced damage using a newly developed substructure testing environment, consideration of various damage patterns in composite beams, and extension of a local damage evaluation technique to a residual capacity estimation procedure by incorporating the model‐updating technique. In laboratory testing, the specimens were damaged quasi‐statically, and vibration tests were conducted as the damage proceeded. First, a bare steel beam–column connection was tested, and then a similar one with a floor slab was used for a more realistic case. The estimated residual structural capacities for these specimens were compared with the static test results. The results verified that the proposed method can provide fine estimates of the stiffness and strength deteriorations within 10% for the specimen without the floor slab and within 30% for that with the floor slab. Copyright © 2017 John Wiley & Sons, Ltd.     

Analysis of historical trend of pollution sources of lead in Tokyo Bay based on lead isotope ratios in sediment core

The historical trend of pollution sources of Pb in Tokyo Bay, Japan was investigated on the basis of Pb isotope ratios in a sediment core. The isotope ratios of anthropogenic Pb decreased gradually with increasing Pb concentration in the 1900s–1970s, suggesting a combination of Pb sources with various isotope ratios. In contrast, the isotope ratios of anthropogenic Pb in the 1980s–2000s showed no significant trend, and corresponded to the Pb isotope ratios in the three principal rivers flowing into the bay. It is probable that river bottom sediments contaminated with Pb are principal sources of anthropogenic Pb in Tokyo Bay.     

Ore Mineralogy and Mineral Chemistry of the Ashanti Gold Deposit at Obuasi, Ghana

Abstract: The gold deposit at Ashanti occurs in the Proterozoic Birimian formation of Ghana. Two main ore types mined from the deposit are gold-bearing quartz veins, and gold-sulfide disseminations in metasediments and metavolcanics. The main sulfide minerals in the gold-sulfide disseminated ores are arsenopyrite, pyrite and pyrrhotite, and to a very minor extent, sphalerite and tetrahedrite. Carbonate alteration and sericitization are prominent in the metavolcanics and the metasediments, respectively. In the quartz veins, pyrite and arsenopyrite commonly occur in small amounts, but gold mostly occurs in contact with tetrahedrite, chalcopyrite, galena, aurostibite, and sphalerite. Pyrrhotite is absent in the quartz veins.
Microprobe studies indicate that As content of homogeneous arsenopyrite grains ranges from 27. 0 to 31. 7 atm%, and gives mineralization temperatures from 170 to 430°C, although mostly from 300 to 400°C. Chlorite geothermometry using temperature dependence of substitution of Al for Si in the tetrahedral site gives formation temeratures of 330 to 400°C, comparable to the arsenopyrite temperatures. Applying sphalerite–pyrite–pyrrhotite geobarometry to sphalerite with FeS contents from 13. 6 to 12. 5 mol%, the pressure was estimated to be in a range from 5. 9 to 7. 0 kb at the stage of elevated temperatures.
Mineralogical observations, especially absence of pyrrhotite in the quartz veins, together with microprobe data for gold and associated minerals suggest that the fluids having ascended through fissures in the Ashanti deposit were reduced by the reaction with carbonaceous materials in the metasediments during the declining stage of the regional metamorphism.     

Subhorizontal boundary between ultrahigh-pressure and low-pressure metamorphic units in the Sulu–Tjube area of the Kokchetav Massif, Kazakhstan

Abstract The Kokchetav Massif of Kazakhstan includes high to ultrahigh-pressure (HP–UHP) metamorphic rocks (some of which were recrystallized at depths in excess of 150 km), juxtaposed against much lower pressure metamorphic components. We investigated the relationship between the HP–UHP metamorphic unit and the low pressure (LP) unit (Daulet Suite) in the Sulu–Tjube area, where the metamorphic rocks have previously been interpreted as constituting a megamelange with subvertical structural attitudes. Analyses of fold structures suggest that the HP–UHP metamorphic unit overlies the LP unit across a west-dipping subhorizontal boundary. In addition, kinematic indicators display top-to-the-north senses of shear along the tectonic contact between the two units, indicating that the HP–UHP unit has been extruded northward onto the LP unit. Following the juxtaposition of the two units, upright folds developed in both units, and these are associated with the previously reported steeply dipping metamorphic foliations. These data have important implications for the mode of exhumation of the UHP rocks from upper mantle to shallow crustal depths.     

Temporal changes in benthic communities of seagrass beds impacted by a tsunami in the Andaman Sea,Thailand

Seagrass beds are susceptible to various natural and human-induced disturbances. Disturbances affect not only seagrasses, but also the abundance and diversity of associated macrofaunal communities. The Andaman Sea coast of Thailand was heavily affected by the tsunami of December 26, 2004. To examine its impact on seagrass macrofaunal communities, we compared the abundance, diversity and taxa composition by quantitative samplings in 2001 (before the tsunami) and in 2005 and 2006 (after the tsunami). Macrobenthic animals and sediments were collected from vegetated and nonvegetated areas of two sites that had received different levels of tsunami disturbances. A large decline in abundance and diversity was observed in the nonvegetated areas after the tsunami, whereas an increase was observed in the vegetated areas. The magnitude of decline and subsequent recovery of abundance and diversity of macrobenthic animals in nonvegetated areas were similar between the two sites, suggesting that their temporal changes were not solely related to the magnitude of the tsunami disturbance. Similarity of the benthic animals differed greatly between 2001 and 2005–2006 at the nonvegetated areas, whereas it varied less among the 3 years at the seagrass-vegetated areas. This study demonstrated that the presence of seagrass vegetation alters the patterns of temporal variation in macrofaunal assemblages and subsequent recovery processes following a tsunami.     

Fractional Determination of Gold in Twenty Six Geological Reference Materials by Sequential Extraction with Graphite Furnace Atomic Absorption Spectrometry

A method is described to estimate the chemical form of gold (Au) in a variety of geological reference samples, combining a sequential extraction scheme with graphite furnace atomic absorption spectrometry, after extraction of Au as iodide or chloride with methyl isobutyl ketone. The fractions dissolved by sequential extraction are empirically defined as the exchangeable, amorphous, metallic, aqua regia-soluble and residual fractions. The amounts of Au in the amorphous fraction have been derived mainly from oxide or amorphous phases, and the chemical forms of Au are considered to be mostly amorphous and partly metallic. The metallic fraction of Au is likely to exist as submicroscopic grains of native metal which are relatively free from the rock-forming minerals, whereas the aqua regia-soluble or residual fraction of Au may be bound more intimately perhaps as inclusions or solid solutions of either native metal or electrum in most cases. Satisfactory agreement was observed between the sum of the Au values from exchangeable to residual fractions and the reported total Au values, except for a few samples which contained a large amount of reducing materials. Analytical results of Au for twenty six geological reference materials are tabulated, and geochemical and mineralogical features are discussed.     

Mineralogical Associations of Arsenic and Antimony in Thirty Five Geochemical Reference Materials by Sequential Extraction with Hydride Generation and Atomic Absorption Spectrometry

A method is described to estimate the chemical forms of arsenic (As) and antimony (Sb) in a variety of geochemical reference materials, combining a sequential extraction scheme with hydride generation and atomic absorption spectrometry (HG-AAS). The fractions dissolved by sequential extraction are empirically defined as the exchangeable, EDTA soluble, oxide, sulfide and residual fractions. The amount of As and Sb in the EDTA soluble fraction have been derived mainly from oxide phases, and partly from carbonate minerals. Most sulfide minerals in common geological samples were considered to be dissolved with the digestion of 0.7 mol l⁻¹ NaOCl, but only small fraction of arsenopyrite and loellingite in ores could be dissolved in this way. Satisfactory agreement was observed between the sum of the As or Sb values from exchangeable to residual fractions and the reported total As or Sb values, with a few exceptions. Analytical results of As and Sb for thirty five geochemical reference materials are tabulated, and geochemical and mineralogical features are discussed.     

The impact of non-Gaussian errors on weak lensing surveys

The weak lensing power spectrum carries cosmological information via its dependence on the growth of structure and on geometric factors. Since much of the cosmological information comes from scales affected by non-linear clustering, measurements of the lensing power spectrum can be degraded by non-Gaussian covariances. Recently, there have been conflicting studies about the level of this degradation. We use the halo model to estimate it and include new contributions related to the finite size of lensing surveys, following Rimes and Hamilton's study of three-dimensional simulations. We find that non-Gaussian correlations between different multipoles can degrade the cumulative signal-to-noise ratio (S/N) for the power spectrum amplitude by up to a factor of 2 (or 5 for a worst-case model that exceeds current N -body simulation predictions). However, using an eight-parameter Fisher analysis, we find that the marginalized errors on individual parameters are degraded by less than 10 per cent (or 20 per cent for the worst-case model). The smaller degradation in parameter accuracy is primarily because: individual parameters in a high-dimensional parameter space are degraded much less than the volume of the full Fisher ellipsoid; lensing involves projections along the line of sight, which reduce the non-Gaussian effect; some of the cosmological information comes from geometric factors which are not degraded at all. We contrast our findings with those of Lee and Pen who suggested a much larger degradation in information content. Finally, our results give a useful guide for exploring survey design by giving the cosmological information returns for varying survey area, depth and the level of some systematic errors.