The Effect of Carboxylates on the Mg Content of Calcites that Transform from ACC

AbstractIn some skeletal-forming and sedimentary environments, calcite and other CaCO3 polymorphs are produced from an amorphous calcium carbonate (ACC) phase. This experimental study determined the Mg content of calcites that grew in the presence of ACC with/without carboxylated biomolecules. The Mg content of the initial ACC obeys a simple fractionation for all conditions except in the presence of oxydiacetate. For all solution compositions, this ACC transforms into calcite crystallites that contain zero to 38 mole %MgCO3, without evidence of secondary polymorphs (Mg/Ca = 0-15). Mg is in the calcite structure within the resolution of the XRD method. The biomolecules slow the ACC to calcite transformation in proportion to their selectivity for Ca over Mg. Citrate, tartarate, and oxydiacetate increase the amount of Mg in both ACC and the resulting calcite. When the Mg2+/Ca2+ ratios of initial solutions are less than ∼5-8, the Mg content of the ACC and calcite products are similar

Observations of Coronal Mass Ejections with the Coronal Multichannel Polarimeter

The Coronal Multichannel Polarimeter (CoMP) measures not only the polarization of coronal emission, but also the full radiance profiles of coronal emission lines. For the first time, CoMP observations provide high-cadence image sequences of the coronal line intensity, Doppler shift and line width simultaneously in a large field of view. By studying the Doppler shift and line width we may explore more of the physical processes of CME initiation and propagation. Here we identify a list of CMEs observed by CoMP and present the first results of these observations. Our preliminary analysis shows that CMEs are usually associated with greatly increased Doppler shift and enhanced line width. These new observations provide not only valuable information to constrain CME models and probe various processes during the initial propagation of CMEs in the low corona, but also offer a possible cost-effective and low-risk means of space weather monitoring.Comment: 6 figures. Will appear in the special issue of Coronal Magnetism, Sol. Phy

Atomic X-ray Spectroscopy of Accreting Black Holes

Current astrophysical research suggests that the most persistently luminous objects in the Universe are powered by the flow of matter through accretion disks onto black holes. Accretion disk systems are observed to emit copious radiation across the electromagnetic spectrum, each energy band providing access to rather distinct regimes of physical conditions and geometric scale. X-ray emission probes the innermost regions of the accretion disk, where relativistic effects prevail. While this has been known for decades, it also has been acknowledged that inferring physical conditions in the relativistic regime from the behavior of the X-ray continuum is problematic and not satisfactorily constraining. With the discovery in the 1990s of iron X-ray lines bearing signatures of relativistic distortion came the hope that such emission would more firmly constrain models of disk accretion near black holes, as well as provide observational criteria by which to test general relativity in the strong field limit. Here we provide an introduction to this phenomenon. While the presentation is intended to be primarily tutorial in nature, we aim also to acquaint the reader with trends in current research. To achieve these ends, we present the basic applications of general relativity that pertain to X-ray spectroscopic observations of black hole accretion disk systems, focusing on the Schwarzschild and Kerr solutions to the Einstein field equations. To this we add treatments of the fundamental concepts associated with the theoretical and modeling aspects of accretion disks, as well as relevant topics from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian Journal of Physics, in pres

Flux Phase as a Dynamic Jahn-Teller Phase: Berryonic Matter in the Cuprates?

There is considerable evidence for some form of charge ordering on the hole-doped stripes in the cuprates, mainly associated with the low-temperature tetragonal phase, but with some evidence for either charge density waves or a flux phase, which is a form of dynamic charge-density wave. These three states form a pseudospin triplet, demonstrating a close connection with the E X e dynamic Jahn-Teller effect, suggesting that the cuprates constitute a form of Berryonic matter. This in turn suggests a new model for the dynamic Jahn-Teller effect as a form of flux phase. A simple model of the Cu-O bond stretching phonons allows an estimate of electron-phonon coupling for these modes, explaining why the half breathing mode softens so much more than the full oxygen breathing mode. The anomalous properties of $O^{2-}$ provide a coupling (correlated hopping) which acts to stabilize density wave phases.Comment: Major Revisions: includes comparisons with specific cuprate phonon modes, 16 eps figures, revte

Extended search for the invisible axion with the axion dark matter experiment

This Letter reports on a cavity haloscope search for dark matter axions in the Galactic halo in the mass range 2.81–3.31μeV. This search utilizes the combination of a low-noise Josephson parametric amplifier and a large-cavity haloscope to achieve unprecedented sensitivity across this mass range. This search excludes the full range of axion-photon coupling values predicted in benchmark models of the invisible axion that solve the strong CP problem of quantum chromodynamics

Changes in meltwater chemistry over a 20-year period following a thermal regime switch from polythermal to cold-based glaciation at Austre Broggerbreen, Svalbard

Our long-term study gives a rare insight into meltwater hydrochemistry following the transition of Austre Brøggerbreen from polythermal to cold-based glaciation and its continued retreat. We find that the processes responsible for ion acquisition did not change throughout the period of records but became more productive. Two regimes before and after July/August 2000 were identified from changes in solute concentrations and pH. They resulted from increased chemical weathering occurring in ice-marginal and proglacial environments that have become progressively exposed by glacier retreat. Carbonate carbonation nearly doubled between 2000 and 2010, whilst increases in the weathering of silicate minerals were also marked. In addition, the end of ablation season chemistry was characterized by reactions in long residence time flow paths like those in subglacial environments, in spite of their absence in the watershed. Furthermore, the retreat of the glacier caused the sudden re-routing of meltwaters through its immediate forefield during 2009, which more than doubled crustal ion yields in this particular year and influenced chemical weathering in 2010 regardless of a low water flux. Such a “flush” of crustally derived ions can be meaningful for downstream terrestrial and marine ecosystems. We therefore find that, during glacier retreat, the recently exposed forefield is the most chemically active part of the watershed, making high rates of weathering possible, even when ice losses have caused a switch to cold-based conditions with no delayed subglacial drainage flowpaths. In addition, the drainage system reorganization events result in significant pCO2 depletion in an otherwise high pCO2 system

Quantifying silica reactivity in subsurface environments: Reaction affinity and solute matrix controls on quartz and SiO{sub 2} glass. 1997 annual progress report

'The author reports the preliminary results of the experiments on the dissolution behavior of vitreous silica (v-SiO{sub 2}) into aqueous solutions of variable pH and ionic strength. The experiments are being conducted in mixed flow reactors with a high circulation rate that simulates constant-stirred conditions, the efficacy of which the authors discuss below. The preliminary results indicate that v-SiO{sub 2} dissolves into aqueous solutions approximately two orders of magnitude more quickly than crystalline silica (e.g., quartz). With additional experiments, they will utilize the dissolution rate data as a framework for understanding the behavior of waste glass compositions in the subsurface. In other work related to the studies of glass reactivity, the author has written one book chapter that will be published as part of a proceedings for the CEA/VALRHO international nuclear waste disposal conference held in Mejannes le Clap, France. In separate work, she is presently writing a second book chapter for the volume entitled Adsorption on Silica Surfaces.

Biomineralization: Systematics of organic-directed controls on carbonate growth morphologies and kinetics determined by in situ AFM. Final report

During the three years of this project, tremendous progress has been made in understanding the microscopic kinetic controls on calcite growth and in investigations of amino acid controls on modifying crystal growth and dissolution. The project began with a focus on the aspartate-calcite system because previous studies have found that acidic matrix macromolecules involved in the regulation of biological crystal growth usually contain aspartic acid-rick domains. Indeed, several studies have shown that aspartate (Asp) modifies the growth morphology of calcite. Aspartate-rich proteins and {beta}-sheet polyaspartate adsorbed on sulfonated polystyrene surfaces were shown to stabilize {l_brace}0001{r_brace} growth surfaces. It was also shown that aspartate also stabilizes the prismatic {l_brace}1{bar 1}00{r_brace} growth forms. For the first time, the author has an understanding of the microscopic controls of aspartate on growth and dissolution