328 research outputs found
Frequency-dependent and correlational selection pressures have conflicting consequences for assortative mating in a color-polymorphic lizard, Uta stansburiana
Acknowledgments We would like to thank the numerous undergraduate researchers involved with this project for their invaluable assistance in lizard rearing and data collection. We also thank D. Haisten, A. Runemark, Y. Takahashi, and M. Verzijden for insightful comments on the manuscript. This project was funded by National Science Foundation DEBOS-15973 to A.G.M. and B.R.S.Peer reviewedPublisher PD
Experimental study of partitioning of trace elements and rare earth elements between immiscible silicate liquids-titanite-zircon at the atmospheric pressure
第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月17日(木) 国立極地研究所 2階大会議室前フロ
Partitioning of trace elements and rare earth elements between titanite and major rock-forming minerals in eclogite and clinopyroxenite from the northeastern Shandong Peninsula, eastern China
第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月17日(木) 国立極地研究所 2階大会議
Origin of magnetic moments in carbon nanofoam
A range of carbon nanofoam samples was prepared by using a high-repetition-rate laser ablation technique under various Ar pressures. Their magnetic properties were systematically investigated by dc magnetization measurements and continuous wave (cw) as well as pulsed EPR techniques. In all samples we found very large zero-field cooled-field-cooled thermal hysteresis in the susceptibility measurements extending up to room temperature. Zero-field cooled (ZFC) susceptibility measurements also display very complex behavior with a susceptibility maximum that strongly varies in temperature from sample to sample. Low-temperature magnetization curves indicate a saturation magnetization MS ≈0.35 emu g at 2 K and can be well fitted with a classical Langevin function. MS is more than an order of magnitude larger than any possible iron impurity, proving that the observed magnetic phenomena are an intrinsic effect of the carbon nanofoam. Magnetization measurements are consistent with a spin-glass type ground state. The cusps in the ZFC susceptibility curves imply spin freezing temperatures that range from 50 K to the extremely high value of >300 K. Further EPR measurements revealed three different centers that coexist in all samples, distinguished on the basis of g -factor and relaxation time. Their possible origin and the role in the magnetic phenomena are discussed
Effect of lone-pair stereoactivity on polyhedral volume and structural flexibility: Application to TeIVO6 octahedra
The Distortion Theorem implies that the irregularity of bond distances in a distorted coordination polyhedron causes an increase of mean bond distance. Examination of 40 polyhedra containing the lone-pair cation Te shows that this does not imply an increase in polyhedral volume. Volumes of these polyhedra are 10.3-23.7-Å, compared with the 12.83-Å expected for a hypothetical regular octahedron. There is little correlation between volume and measures of polyhedral distortion such as quadratic elongation, bond-angle variance or vector bond valence. However, the oxygens of our polyhedra lie very close to a sphere of best fit, centred at ∼-1-Å from the Te atom. The Te-centre distance is an index of lone-pair stereoactivity and is linearly related to the radius R sph of the sphere; this is explained by a more localized lone pair repelling the anions more strongly, leading to a longer non-bonded distance between the lone pair and anions. Polyhedral volume still varies considerably for a given R sph, because the oxygen ligands may be distributed over the whole sphere surface, or confined to a small portion of it. The uniformity of this distribution can be estimated from the distance between the sphere centre and the centroid of the O6 polyhedron. Te-centre and centroid-centre distances alone then account for 95% of the variation observed in volume for polyhedra which are topologically octahedral. Six of the polyhedra studied that are outliers are closer in shape to pentagonal pyramids than octahedra. These have short distances from the central Te cation to other Te and/or to large, polarizable cations, suggesting additional weak bonding interactions between these species and the central lone pair. The flexibility of lone-pair polyhedra is further enhanced by the ability of a single polyhedron to accommodate different cations with different degrees of lone-pair activity, which facilitates more diverse solid solution behaviour than would otherwise be the case
Crystal structure and revised chemical formula for burckhardtite, Pb_2(Fe^(3+)Te^(6+))[AlSi_3O_8]O_6: a double-sheet silicate with intercalated phyllotellurate layers
The crystal structure of burckhardite from the type locality, Moctezuma, Sonora, Mexico, has been refined to R_1 = 0.0362 and wR_2 = 0.0370 for 215 reflections with I > 2σ(I). Burckhardtite is trigonal, space group P3lm, with the unit-cell parameters ɑ = 5.2566(5) Å, c = 13.0221(10) Å, V = 311.62(5) Å3 and Z = 1 for the ideal formula unit Pb_2(Fe^(3+)Te^(6+))[AlSi_3O_8]O_6. There is no long-range order of (Fe^(3+), Te^(6+)) or (Al^(3+), Si^(4+)). New microprobe data were used to estimate site scattering factors, and Raman spectroscopic data showed no evidence of O–H stretching bands. Burckhardtite is not closely related to the micas, as supposed previously, but is a double-sheet silicate in which the aluminosilicate anion resembles that of minerals such as cymrite and kampfite. The [(Fe^(3+)Te^(6+))O_6]^(3−) part of the structure is not bonded directly to the aluminosilicate layer, but forms a discrete anionic phyllotellurate layer that alternates with the [AlSi_3O_8]^− double sheets. Similar phyllotellurate layers are known from several synthetic phases. In burckhardtite, Pb^(2+) cations intercalate between phyllosilicate and phyllotellurate layers, forming a Pb_2[FeTeO_6] module that is topologically similar to a slab of the structure of rosiaite, Pb[Sb_2O_6]. The crystal symmetry, structure, classification as a double-sheet silicate and chemical formula, including the determination of the 6+ valence of Te and absence of essential H_2O, are all new findings for the mineral
The crystal structure of ceruleite, CuAl4[AsO4]2(OH)8(H2O)4, from Cap Garonne, France
The crystal structure of ceruleite, CuAl[AsO](OH)(HO), has been solved to an R of 0.0307, using the world's largest crystals from the Cap Garonne mine, France. Ceruleite crystallizes in space group P2/n, with the unit cell a = 7.2000(14), b = 11.345(2), c = 9.856(2) Å, β = 105.57(3)°, V = 775.6(3) Å and Z = 1. Ceruleite has a unique structure that consists of Al(O,OH) octahedra that are sharing edges to form rhombus-shaped tetramers. AsO tetrahedra share two corners with one such rhombus and the other two corners with each of two other rhombi, linking them into a very open mesoporous framework. Cu(OH)(HO) squares lie in the channels and link Al rhombi along || b. HO molecules are also located in the channels
Petrology, geochemistry and tectonic significance of serpentinized ultramafic rocks from the South Arm of Sulawesi, Indonesia
Serpentinized ultramafic rocks occur in two separate basement complexes in the South Arm of Sulawesi, the Bantimala and Barru Blocks. We present petrographic, mineral chemical and geochemical data for these rocks, and interpret them in terms of petrogenesis and tectonic setting. The rocks of both blocks show strong serpentinization of original anhydrous silicates. The Bantimala ultramafics consist mainly of peridotite (harzburgite and dunite) and clinopyroxenite, with lenses of podiform chromitite. Metamorphism is evidenced by the occurrence of amphibolite-facies tremolite schist. In contrast, the Barru ultramafics consist of harzburgite peridotite and podiform chromitite, which also show an amphibolite-facies overprint that in this case may be related to intrusion by a large dacite/granodiorite body. Whole-rock trace element analyses and spinel compositions show that the Barru harzburgite is depleted relative to primitive mantle, and has had some melt extracted. In contrast, the Bantimala dunite, harzburgite and clinopyroxenite are cumulates. Both are derived from a supra-subduction zone environment, and were obducted during the closure of small back-arc basins. If there has been no rotation of the blocks, then the Bantimala ultramafics were emplaced from an ENE direction, while the Barru ultramafics were emplaced from the WNW. The ultramafic suites from these two blocks are juxtaposed with metamorphic assemblages, which were later intruded by younger volcanics, particularly in the Barru Block
The relationship between mineral composition, crystal structure and paragenetic sequence: the case of secondary Te mineralization at the Bird Nest drift, Otto Mountain, California, USA
An unusually diverse array of 25 secondary Te oxysalt minerals has been documented from Otto Mountain, California, and 18 of these from the Bird Nest drift sublocality. A paragenetic sequence for these minerals is proposed, using observed overgrowth relationships plus spatial association data and data from other localities. Apart from Te and O, the components Pb, Cu and H are essential in the majority of the minerals. The atomic Cu/Te ratio decreases through the paragenetic sequence. This, and the occurrence of minerals with additional components such as Cl^–, CO_3^(2–), SO_4^(2–) and Fe^(3+) at an intermediate stage, suggests nonmonotonic evolution of the parent fluids, reflecting differing access to or spatial distribution of various components.
For the minerals with known crystal structures, two alternative 'structural units' were identified, one consisting only of the Te^(4+) or Te^(6+) oxyanion, while the other also included small, strongly-bound cations such as Cu^(2+). The degree of polymerization for the Te oxyanion correlated with the paragenetic sequence: the monomeric tellurate anions of early minerals were replaced progressively by dimers, chains and sheet structures, which may relate to a decreasing abundance of the 'network modifying' Cu^(2+) cation, analogous to Bowen's discontinuous reaction series in igneous rock-forming silicates.
No relationship was seen between paragenetic order and the larger type of structural unit, or structural complexity as defined by information content. This contrasts with results in the literature for evaporite sulfates and pegmatite phosphates. While structure–paragenesis relationships may be widespread, the exact nature of such relationships may be different for different chemical systems and different paragenetic environments
Uterine Weight as a Modifier of Black/White Racial Disparities in Minimally Invasive Hysterectomy Among Veterans with Fibroids in the Veterans Health Administration
INTRODUCTION: Uterine fibroids are the most common indication for hysterectomy. Minimally invasive hysterectomy (MIH) confers lower risk of complications and shorter recovery than open surgical procedures; however, it is more challenging to perform with larger fibroids. There are racialized differences in fibroid size and MIH rates. We examined the role of uterine size in black-white differences in MIH among Veterans in the Department of Veterans Affairs (VA).
METHODS: Using VA clinical and administrative data, we conducted a cross-sectional study among black and white Veterans with fibroids who underwent hysterectomy between 2012 and 2014. We abstracted postoperative uterine weight from pathology reports as a proxy for uterine size. We used a generalized linear model to estimate the association between race and MIH and tested an interaction between race and postoperative uterine weight (≤250 g vs. \u3e250 g). We estimated adjusted marginal effects for racial differences in MIH by postoperative uterine weight.
RESULTS: The sample included 732 Veterans (60% black, 40% white). Postoperative uterine weight modified the association of race and MIH (p for interaction=0.05). Black Veterans with postoperative uterine weight ≤250 g had a nearly 12-percentage point decrease in MIH compared to white Veterans (95% CI -23.1 to -0.5), with no difference by race among those with postoperative uterine weight \u3e250 g.
DISCUSSION: The racial disparity among Veterans with small fibroids who should be candidates for MIH underscores the role of other determinants beyond uterine size. To eliminate disparities in MIH, research focused on experiences of black Veterans, including pathways to treatment and provider-patient interactions, is needed
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