3,728 research outputs found
Li, B and Be Contents of Harzburgites from the Dramala Complex (Pindos Ophiolite, Greece): Evidence for a MOR-type Mantle in a Supra-subduction Zone Environment
The Pindos ophiolite represents oceanic lithosphere obducted during the Jurassic. The Dramala mantle section mainly consists of highly depleted spinel harzburgite and minor plagioclase-bearing harzburgite. Textural observations and major element compositions of minerals indicate that the harzburgites experienced impregnation by a mafic, depleted melt and subsequent high-temperature (high-T) hydration and cooling (>750°C) forming pargasite and edenitic hornblende. During further cooling (from ≥ 350-400°C to < 100°C), talc + tremolite ± serpentine ± olivine, serpentine + magnetite, and finally plagioclase alteration phases formed. To test the hypothesis of a supra-subduction zone origin for the Dramala mantle, we measured Li, B and Be contents of minerals by secondary ion mass spectrometry. Whole-rock contents were measured using inductively coupled plasma-mass spectrometry and prompt gamma neutron activation analysis. We observe low Li and B contents of primary minerals (olivine, orthopyroxene, clinopyroxene) consistent with values for unmetasomatized mantle minerals; only Li contents of clinopyroxene (up to 3·7 μg/g) are slightly elevated. The bulk Li contents (0·5-1·1 μg/g) are in the upper range of values for unmetasomatized mantle, whereas B contents (<0·04-1·1 μg/g) are variable and slightly elevated compared with the unmetasomatized mantle as a result of serpentinization. Beryllium abundances in all minerals are very low (<0·005 μg/g), except for pargasite, where a maximum Be content of 0·012 μg/g was measured. The selective addition of Li to clinopyroxene can be related to the interaction with a depleted melt, and/or to partitioning of Li into clinopyroxene upon cooling. During high-T hydration and cooling, the fluid calculated to be in equilibrium with the pargasite or edenitic hornblende (based on Li, Be and B) could have been reaction-modified seawater. Low-T hydration may have led to a very minor increase in bulk B content of most samples and to the formation of serpentine with highly variable B contents (0·1-28 μg/g). Low-T hydration decreased the Li content of orthopyroxene, and Li was probably leached from some samples. The lack of correlation between degree of serpentinization and bulk B contents as well as the presence of high- and low-B serpentine can be explained by low fluid-rock ratios, decreasing T during serpentinization and lack of equilibrium as a result of fast obduction-exhumation. The low light-element contents of primary minerals and whole-rock samples clearly argue against a supra-subduction zone (SSZ) origin of the Dramala mantle section, and against the previous hypothesis of hydrous melting of the Pindos mantle above a subduction zone. We therefore conclude that the Dramala harzburgites represent a mid-ocean ridge (MOR)-type mantle, and not an SSZ-type mantle, juxtaposed with MOR-type and SSZ-type oceanic crust, either in a back-arc or in an intra-oceanic subduction zone settin
On the Concept of a Notational Variant
In the study of modal and nonclassical logics, translations have frequently been employed as a way of measuring the inferential capabilities of a logic. It is sometimes claimed that two logics are “notational variants” if they are translationally equivalent. However, we will show that this cannot be quite right, since first-order logic and propositional logic are translationally equivalent. Others have claimed that for two logics to be notational variants, they must at least be compositionally intertranslatable. The definition of compositionality these accounts use, however, is too strong, as the standard translation from modal logic to first-order logic is not compositional in this sense. In light of this, we will explore a weaker version of this notion that we will call schematicity and show that there is no schematic translation either from first-order logic to propositional logic or from intuitionistic logic to classical logic
Fractional Hamiltonian Monodromy from a Gauss-Manin Monodromy
Fractional Hamiltonian Monodromy is a generalization of the notion of
Hamiltonian Monodromy, recently introduced by N. N. Nekhoroshev, D. A.
Sadovskii and B. I. Zhilinskii for energy-momentum maps whose image has a
particular type of non-isolated singularities. In this paper, we analyze the
notion of Fractional Hamiltonian Monodromy in terms of the Gauss-Manin
Monodromy of a Riemann surface constructed from the energy-momentum map and
associated to a loop in complex space which bypasses the line of singularities.
We also prove some propositions on Fractional Hamiltonian Monodromy for 1:-n
and m:-n resonant systems.Comment: 39 pages, 24 figures. submitted to J. Math. Phy
Pair Plasma Dominance in the Parsec-Scale Relativistic Jet of 3C345
We investigate whether a pc-scale jet of 3C345 is dominated by a normal
plasma or an electron-positron plasma. We present a general condition that a
jet component becomes optically thick for synchrotron self-absorption, by
extending the method originally developed by Reynolds et al. The general
condition gives a lower limit of the electron number density, with the aid of
the surface brightness condition, which enables us to compute the magnetic
field density. Comparing the lower limit with another independent constraint
for the electron density that is deduced from the kinetic luminosity, we can
distinguish the matter content. We apply the procedure to the five components
of 3C345 (C2, C3, C4, C5, and C7) of which angular diameters and radio fluxes
at the peak frequencies were obtainable from literature. Evaluating the
representative values of Doppler beaming factors by their equipartition values,
we find that all the five components are likely dominated by an
electron-positron plasma. The conclusion does not depend on the lower cutoff
energy of the power-law distribution of radiating particles.Comment: 17 page
Setting the stage: social-environmental and motivational predictors of optimal training engagement
In this paper, we will firstly explore the central tenets of SDT. Research that has examined the social-environmental and motivation-related correlates of optimal training, performance and health-related engagement through the theoretical lens of SDT will be reviewed. Drawing from SDT-driven work undertaken in educational, sport and dance settings, we will draw conclusions and suggest future directions from a research and applied perspective
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Intersections of Jane Jacobs’ conditions for diversity and low-carbon urban systems: a look at four global cities
Countless cities are rapidly developing across the globe, pressing the need for clear urban planning and design recommendations geared towards sustainability. This article examines the intersections of Jane Jacobs’ four conditions for diversity with low-carbon and low-energy use urban systems in four cities around the world: Lyon (France), Chicago (United-States), Kolkata (India), and Singapore (Singapore). After reviewing Jacobs’ four conditions for diversity, we introduce the four cities and describe their historical development context. We then present a framework to study the cities along three dimensions: population and density, infrastructure development/use, and climate and landscape. These cities differ in many respects and their analysis is instructive for many other cities around the globe. Jacobs’ conditions are present in all of them, manifested in different ways and to varying degrees. Overall we find that the adoption of Jacobs' conditions seems to align well with concepts of low-carbon urban systems, with their focus on walkability, transit-oriented design, and more efficient land use (i.e., smaller unit sizes). Transportation sector emissions seems to demonstrate a stronger influence from the presence of Jacobs' conditions, while the link was less pronounced in the building sector. Kolkata, a low-income, developing world city, seems to possess many of Jacobs' conditions, while exhibiting low per capita emissions - maintaining both of these during its economic expansion will take careful consideration. Greenhouse gas mitigation, however, is inherently an in situ problem and the first task must therefore be to gain local knowledge of an area before developing strategies to lower its carbon footprint
PROviding Better ACcess To ORgans: A comprehensive overview of organ‐access initiatives from the ASTS PROACTOR Task Force
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138905/1/ajt14441_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138905/2/ajt14441.pd
Identifying Critical Roles for the Lamin B Receptor and Additional Nuclear Envelope Proteins in Regulating the Proliferation and Differentiation of Myeloid Progenitors
Neutrophils are blood phagocytes that contain lobulated nuclei, development of which depend on the expression of an inner nuclear membrane (INM) protein called the lamin B receptor (LBR). Loss of LBR expression causes not only hypolobulation of neutrophil nuclei (Pelger-Huët anomaly) but also severe developmental defects in humans (HEM/Greenberg dysplasia) and mice (ichthyosis). LBR is considered a dual function protein: the N-terminal domain contains chromatin and lamin B binding sites, whereas the C-terminal domain anchors LBR to the INM and exhibits C14 sterol reductase activity. Despite our knowledge of these two structural features of LBR, which domain supports normal development is unclear. We recently addressed this issue with regards to myelopoiesis by expressing wild-type and mutant forms of mouse Lbr in myeloid cells derived from an ichthyosis mouse. We demonstrated that expression of the Lbr sterol reductase domain alone can support nuclear morphologic maturation and is critical to both cholesterol biosynthesis and lipid-stressed proliferative responses of myeloid progenitors. In contrast, myeloid progenitors that lack the homologous C14 sterol reductase Tm7sf2 displayed normal nuclear maturation, cholesterol biosynthesis and lipid-stressed proliferation. We have now generated ichthyosis myeloid cells that express forms of Lbr with missense mutations in the sterol reductase domain known to cause HEM/Greenberg dysplasia. Our preliminary results indicate that these sterol reductase missense mutations disrupt cholesterol biosynthesis and lipid-stressed proliferation, but do not appear to affect nuclear maturation. We are also analyzing the expression patterns of Lbr and two additional nuclear envelope (NE) proteins, Lamin A/C and Sun2, during neutrophil vs. macrophage differentiation using both cell line models and ex vivo differentiated mouse bone marrow, and examining how overexpression of either Lamin A/C or Sun2 affects myeloid differentiation. Our studies may reveal new insight into how different NE proteins regulate the complex functions of two professional phagocytes
An asteroseismic test of diffusion theory in white dwarfs
The helium-atmosphere (DB) white dwarfs are commonly thought to be the
descendants of the hotter PG1159 stars, which initially have uniform He/C/O
atmospheres. In this evolutionary scenario, diffusion builds a pure He surface
layer which gradually thickens as the star cools. In the temperature range of
the pulsating DB white dwarfs (T_eff ~ 25,000 K) this transformation is still
taking place, allowing asteroseismic tests of the theory. We have obtained
dual-site observations of the pulsating DB star CBS114, to complement existing
observations of the slightly cooler star GD358. We recover the 7 independent
pulsation modes that were previously known, and we discover 4 new ones to
provide additional constraints on the models. We perform objective global
fitting of our updated double-layered envelope models to both sets of
observations, leading to determinations of the envelope masses and pure He
surface layers that qualitatively agree with the expectations of diffusion
theory. These results provide new asteroseismic evidence supporting one of the
central assumptions of spectral evolution theory, linking the DB white dwarfs
to PG1159 stars.Comment: 7 pages, 3 figures, 3 tables, accepted for publication in A&
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