350 research outputs found
Flore des Mascareignes : La Réunion, Maurice, Rodrigues : 64. Balsaminacées à 68. Burséracées
Long Range Magnetic Order and the Darwin Lagrangian
We simulate a finite system of confined electrons with inclusion of the
Darwin magnetic interaction in two- and three-dimensions. The lowest energy
states are located using the steepest descent quenching adapted for velocity
dependent potentials. Below a critical density the ground state is a static
Wigner lattice. For supercritical density the ground state has a non-zero
kinetic energy. The critical density decreases with for exponential
confinement but not for harmonic confinement. The lowest energy state also
depends on the confinement and dimension: an antiferromagnetic cluster forms
for harmonic confinement in two dimensions.Comment: 5 figure
Taxonomic relevance of seed and seedling morphology in two Amazonian species of Entada (Leguminosae)
The open-loop discounted linear quadratic differential game for regular higher order index descriptor systems
Primary carbonatite melt from deeply subducted oceanic crust
Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here we provide experimental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.4 page(s
I Going Away. I Going Home. : Austin Clarke\u27s Leaving this Island Place
Austin Clarkeâs âLeaving This Island Placeâ is one of scores of Caribbean autobiographical works that focus on a bright, young, lower-class islander leaving his/her small island place and setting out on âEldorado voyages.â The narrative of that journey away from home to Europe or Canada or the United States and the later efforts to return may be said to be the Caribbean story, as suggested in the subtitle of Wilfred Carteyâs study of Caribbean literature, Whispers from the Caribbean: I Going Away, I Going Home, which argues that while in Caribbean literature there is much movement away, there is also a body of literature in which âthe notion of âawayâ and images of movement out are replaced by images of returnâ (xvi). Traditionally, however, the first autobiographical works, such as George Lammingâs In the Castle of My Skin, V. S. Naipaulâs A House for Mr. Biswas, Merle Hodgeâs Crick Crack, Monkey, Jamaica Kincaidâs Annie John, Michelle Cliffâs No Telephone to Heaven, Edwidge Danticatâs Breath, Eyes, Memory, and Elizabeth Nunezâs Beyond the Limbo Silence, have focused on the childhood in the Caribbean and the journey awayâor at least the preparation for that journey. Such is the case with Clarkeâs âLeaving This Island Place.
Platinum-group elements, S, Se and Cu in highly depleted abyssal peridotites from the Mid-Atlantic Ocean Ridge (ODP Hole 1274A): Influence of hydrothermal and magmatic processes
Highly depleted harzburgites and dunites were recovered from ODP Hole 1274A, near the intersection between the Mid-Atlantic Ocean Ridge and the 15°20âČN Fracture Zone. In addition to high degrees of partial melting, these peridotites underwent multiple episodes of melt-rock reaction and intense serpentinization and seawater alteration close to the seafloor. Low concentrations of Se, Cu and platinum-group elements (PGE) in harzburgites drilled at around 35-85 m below seafloor are consistent with the consumption of mantle sulfides after high degrees (>15-20 %) of partial melting and redistribution of chalcophile and siderophile elements into PGE-rich residual microphases. Higher concentrations of Cu, Se, Ru, Rh and Pd in harzburgites from the uppermost and lowest cores testify to late reaction with a sulfide melt. Dunites were formed by percolation of silica- and sulfur-undersaturated melts into low-Se harzburgites. Platinum-group and chalcophile elements were not mobilized during dunite formation and mostly preserve the signature of precursor harzburgites, except for higher Ru and lower Pt contents caused by precipitation and removal of platinum-group minerals. During serpentinization at low temperature (<250 °C) and reducing conditions, mantle sulfides experienced desulfurization to S-poor sulfides (mainly heazlewoodite) and awaruite. Contrary to Se and Cu, sulfur does not record the magmatic evolution of peridotites but was mostly added in hydrothermal sulfides and sulfate from seawater. Platinum-group elements were unaffected by post-magmatic low-temperature processes, except Pt and Pd that may have been slightly remobilized during oxidative seawater alteration
Genome-wide interaction study of smoking and bladder cancer risk
Bladder cancer is a complex disease with known environmental and genetic risk factors. We performed a genome-wide interaction study (GWAS) of smoking and bladder cancer risk based on primary scan data from 3002 cases and 4411 controls from the National Cancer Institute Bladder Cancer GWAS. Alternative methods were used to evaluate both additive and multiplicative interactions between individual single nucleotide polymorphisms (SNPs) and smoking exposure. SNPs with interaction P values < 5 x 10(-) (5) were evaluated further in an independent dataset of 2422 bladder cancer cases and 5751 controls. We identified 10 SNPs that showed association in a consistent manner with the initial dataset and in the combined dataset, providing evidence of interaction with tobacco use. Further, two of these novel SNPs showed strong evidence of association with bladder cancer in tobacco use subgroups that approached genome-wide significance. Specifically, rs1711973 (FOXF2) on 6p25.3 was a susceptibility SNP for never smokers [combined odds ratio (OR) = 1.34, 95% confidence interval (CI) = 1.20-1.50, P value = 5.18 x 10(-) (7)]; and rs12216499 (RSPH3-TAGAP-EZR) on 6q25.3 was a susceptibility SNP for ever smokers (combined OR = 0.75, 95% CI = 0.67-0.84, P value = 6.35 x 10(-) (7)). In our analysis of smoking and bladder cancer, the tests for multiplicative interaction seemed to more commonly identify susceptibility loci with associations in never smokers, whereas the additive interaction analysis identified more loci with associations among smokers-including the known smoking and NAT2 acetylation interaction. Our findings provide additional evidence of gene-environment interactions for tobacco and bladder cancer
Mantle Pb paradoxes : the sulfide solution
Author Posting. © Springer, 2006. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Contributions to Mineralogy and Petrology 152 (2006): 295-308, doi:10.1007/s00410-006-0108-1.There is growing evidence that the budget of Pb in mantle peridotites is largely
contained in sulfide, and that Pb partitions strongly into sulfide relative to silicate melt. In
addition, there is evidence to suggest that diffusion rates of Pb in sulfide (solid or melt)
are very fast. Given the possibility that sulfide melt âwetsâ sub-solidus mantle silicates,
and has very low viscosity, the implications for Pb behavior during mantle melting are
profound. There is only sparse experimental data relating to Pb partitioning between
sulfide and silicate, and no data on Pb diffusion rates in sulfides. A full understanding of
Pb behavior in sulfide may hold the key to several long-standing and important Pb
paradoxes and enigmas. The classical Pb isotope paradox arises from the fact that all
known mantle reservoirs lie to the right of the Geochron, with no consensus as to the
identity of the âbalancingâ reservoir. We propose that long-term segregation of sulfide
(containing Pb) to the core may resolve this paradox. Another Pb paradox arises from the fact that the Ce/Pb ratio of both OIB and MORB
is greater than bulk earth, and constant at a value of 25. The constancy of this âcanonical
ratioâ implies similar partition coefficients for Ce and Pb during magmatic processes
(Hofmann et al. 1986), whereas most experimental studies show that Pb is more
incompatible in silicates than Ce. Retention of Pb in residual mantle sulfide during
melting has the potential to bring the bulk partitioning of Ce into equality with Pb if the
sulfide melt/silicate melt partition coefficient for Pb has a value of ~ 14. Modeling shows
that the Ce/Pb (or Nd/Pb) of such melts will still accurately reflect that of the source, thus
enforcing the paradox that OIB and MORB mantles have markedly higher Ce/Pb (and
Nd/Pb) than the bulk silicate earth. This implies large deficiencies of Pb in the mantle
sources for these basalts. Sulfide may play other important roles during magmagenesis:
1). advective/diffusive sulfide networks may form potent metasomatic agents (in both
introducing and obliterating Pb isotopic heterogeneities in the mantle); 2). silicate melt
networks may easily exchange Pb with ambient mantle sulfides (by diffusion or
assimilation), thus âsamplingâ Pb in isotopically heterogeneous mantle domains
differently from the silicate-controlled isotope tracer systems (Sr, Nd, Hf), with an
apparent âde-couplingâ of these systems.Our intemperance
should not be blamed on the support we gratefully acknowledge from NSF: EAR-
0125917 to SRH and OCE-0118198 to GAG
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