253 research outputs found
Tri-critical behavior in rupture induced by disorder
We discover a qualitatively new behavior for systems where the load transfer
has limiting stress amplification as in real fiber composites. We find that the
disorder is a relevant field leading to tri--criticality, separating a
first-order regime where rupture occurs without significant precursors from a
second-order regime where the macroscopic elastic coefficient exhibit power law
behavior. Our results are based on analytical analysis of fiber bundle models
and numerical simulations of a two-dimensional tensorial spring-block system in
which stick-slip motion and fracture compete.Comment: Revtex, 10 pages, 4 figures available upon reques
Scale relativity and fractal space-time: theory and applications
In the first part of this contribution, we review the development of the
theory of scale relativity and its geometric framework constructed in terms of
a fractal and nondifferentiable continuous space-time. This theory leads (i) to
a generalization of possible physically relevant fractal laws, written as
partial differential equation acting in the space of scales, and (ii) to a new
geometric foundation of quantum mechanics and gauge field theories and their
possible generalisations. In the second part, we discuss some examples of
application of the theory to various sciences, in particular in cases when the
theoretical predictions have been validated by new or updated observational and
experimental data. This includes predictions in physics and cosmology (value of
the QCD coupling and of the cosmological constant), to astrophysics and
gravitational structure formation (distances of extrasolar planets to their
stars, of Kuiper belt objects, value of solar and solar-like star cycles), to
sciences of life (log-periodic law for species punctuated evolution, human
development and society evolution), to Earth sciences (log-periodic
deceleration of the rate of California earthquakes and of Sichuan earthquake
replicas, critical law for the arctic sea ice extent) and tentative
applications to system biology.Comment: 63 pages, 14 figures. In : First International Conference on the
Evolution and Development of the Universe,8th - 9th October 2008, Paris,
Franc
Rupture Pressure Prediction for Composite High Pressure Tanks Using Acoustic Emission
The French Aerospace company AEROSPATIALE manufactures high pressure tanks for helium gas storage. Because these tanks are critical elements for rockets and satellites, a new approach has been developed to have a better knowledge of the structure reliability. Although numerical tools such as finite elements codes are used for the design of such structures and. quality rules are imposed to insure that the tanks manufactured are in accordance to the definition, it is conceivable that even a successful proof test could actually damage the composite and lead to a residual SF less than 2
Dragon-kings: mechanisms, statistical methods and empirical evidence
This introductory article presents the special Discussion and Debate volume
"From black swans to dragon-kings, is there life beyond power laws?" published
in Eur. Phys. J. Special Topics in May 2012. We summarize and put in
perspective the contributions into three main themes: (i) mechanisms for
dragon-kings, (ii) detection of dragon-kings and statistical tests and (iii)
empirical evidence in a large variety of natural and social systems. Overall,
we are pleased to witness significant advances both in the introduction and
clarification of underlying mechanisms and in the development of novel
efficient tests that demonstrate clear evidence for the presence of
dragon-kings in many systems. However, this positive view should be balanced by
the fact that this remains a very delicate and difficult field, if only due to
the scarcity of data as well as the extraordinary important implications with
respect to hazard assessment, risk control and predictability.Comment: 20 page
Mutations in BHD and TP53 genes, but not in HNF1β gene, in a large series of sporadic chromophobe renal cell carcinoma
BHD, TP53, and HNF1β on chromosome 17 were studied in 92 cases of renal cell carcinoma (46 chromophobe, 19 clear cell, 18 oncocytoma, and nine papillary). Six, thirteen, and zero cases had, respectively BHD, TP53, and HNF1β mutations, (84% mutations involved chromophobe), suggesting a role for BHD and TP53 in chromophobe subtype
Mantle Pb paradoxes : the sulfide solution
Author Posting. Š 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
The composition of a disrupted extrasolar planetesimal at SDSS J0845+2257 (Ton 345)
We present a detailed study of the metal-polluted DB white dwarf SDSS J0845+2257 (Ton 345). Using high-resolution Hubble Space Telescope/Cosmic Origins Spectrograph and Very Large Telescope spectroscopy, we have detected hydrogen and 11 metals in the atmosphere of the white dwarf. The origin of these metals is almost certainly the circumstellar disc of dusty and gaseous debris from a tidally disrupted planetesimal, accreting at a rate of 1.6 Ă 1010âgâsâ1. Studying the chemical abundances of the accreted material demonstrates that the planetesimal had a composition similar to the Earth, dominated by rocky silicates and metallic iron, with a low water content. The mass of metals within the convection zone of the white dwarf corresponds to an asteroid of at least âź130â170 km in diameter, although the presence of ongoing accretion from the debris disc implies that the planetesimal was probably larger than this. While a previous abundance study of the accreted material has shown an anomalously high mass fraction of carbon (15 per cent) compared to the bulk Earth, our independent analysis results in a carbon abundance of just 2.5 per cent. Enhanced abundances of core material (Fe, Ni) suggest that the accreted object may have lost a portion of its mantle, possibly due to stellar wind stripping in the asymptotic giant branch. Time series spectroscopy reveals variable emission from the orbiting gaseous disc, demonstrating that the evolved planetary system at SDSS J0845+2257 is dynamically active
Mantle and crustal sources in the genesis of late-hercynian granitoids (NW Portugal) : geochemical and Sr-Nd isotopic constraints
Large volumes of granitoids were emplaced in the Hercynian Central Iberian Zone during the last ductile deformation phase (D3, 300-320 Ma). The biotite-rich granitoids are the most abundant: (1) syn-D3 granodiorites-monzogranites (313-319 Ma) with calc-alkaline and aluminopotassic affinities; (2) late-D3 granodiorites-monzogranites (306-311 Ma), related to subalkaline and aluminopotassic series. These granitoids are associated with coeval gabbro-norite to granodiorite bodies and/or mafic microgranular enclaves. Both granitoids and basic-intermediate rocks show petrological, geochemical and isotopic evidence of interaction between felsic and mafic magmas.
The mantle-derived melts, represented by shoshonitic gabbro-norites, were probably derived from an enriched and isotopically homogeneous source (Srl = 0.7049 to 0.7053, eNd= -2.1 to -2.5). In some syn- and late-D3 plutons there are evidences of essentially crustal granites, represented by moderately peraluminous monzogranites of aluminopotassic affinity. They have similar Nd model ages (1.4 Ga) but different isotopic compositions (Srl = 0.7089 to 0.7106, eNd= -5.6 to -6.8), revealing a heterogeneous crust. Potential protoliths are metasedimentary (immature sediments) and/or fclsic meta-igneous lower crust materials. Large amounts of hybrid magmas were generated by the interaction of these coeval mantle- and crust-derived liquids, giving rise to slightly peraluminous monzogranites/granodiorites of calc-alkaline and subalkaline affinities, which display more depleted isotopic compositions than the crustal end-members (Sr, = 0.7064 to 0.7085, eNd = -4.4 to -6.2). Petrogenetic processes involving mingling and/or mixing and fractional crystallization (at variable degrees) in multiple reservoirs are suggested.
A major crustal growth event occurred in late-Hercynian times (305-320 Ma) related to the input of juvenile mantle magmas and leading to the genesis of composite calc-alkaline and subalkaline plutons, largely represented in the Central Iberian Zone.Financial support was provided by FCT (project PRAXIS 2/2.1/391/94), France-Portugal Scientific Cooperation Programs and by the University of Minho
Seismic and geochemical evidence for large-scale mantle upwelling beneath the eastern Atlantic and western and central Europe
Seismic tomography and the isotope geochemistry of Cenozoic volcanic rocks suggest the existence of a large, sheet-like region of upwelling in the upper mantle which extends from the eastern Atlantic Ocean to central Europe and the western Mediterranean. A belt of extension and rifting in the latter two areas appears to lie above the intersection of the centre of the upwelling region with the base of the lithosphere. Lead, strontium and neodymium isotope data for all three regions converge on a restricted composition, inferred to be that of the upwelling mantle
- âŚ