Showing papers by "IPG Photonics published in 2000"

Density measurements of liquid Fe-S alloys at high-pressure

Abstract: We present the first static measurements of the density of metallic liquids in the Fe-S system in the pressure and temperature range 1.5 GPa-6.2 GPa and 1500 K - 1780 K. Density is inferred from X-ray absorption experiments carried out with a large volume press at the European Synchrotron Radiation Facility. It is shown that increasing the amount of sulfur in liquid iron decreases the bulk incompressibility by -2.5 GPa per 1 weight% of S. These data are important for constraining the presence and amount of sulfur in the cores of small planetary bodies.

Ørsted Initial Field Model

Abstract: Magnetic measurements taken by the Orsted satellite during geomagnetic quiet conditions around Jan-uary 1, 2000 have been used to derive a spherical harmonic model of the Earth's magnetic field for epoch 2000.0. The maximum degree and order of the model is 19 for internal, and 2 for external, source fields; however, coefficients above degree 14 may not be robust. Such a detailed model exists for only one previous epoch, 1980. Achieved rms misfit is < 2 nT for the scalar intensity and < 3 nT for one of the vector components perpendicular to the magnetic field. For scientific purposes related to the Orsted mission, this model supercedes IGRF 2000.

Runge–Kutta methods and renormalization

Abstract: Rooted trees have been used to calculate the solution of nonlinear flow equations and Runge–Kutta methods. More recently, rooted trees have helped systematizing the algebra underlying renormalization in quantum field theories. The Butcher group and B-series establish a link between these two approaches to rooted trees. On the one hand, this link allows for an alternative representation of the algebra of renormalization, leading to nonperturbative results. On the other hand, it helps to renormalize singular flow equations. The usual approach is extended here to nonlinear partial differential equations. A nonlinear Born expansion is given, and renormalization is used to partly remove the secular terms of the perturbative expansion.

Structural changes in liquid Fe at high pressures and high temperatures from Synchrotron X-ray Diffraction

Abstract: High-energy synchrotron X-ray diffraction measurements on liquid iron in the vicinity of the δ-γ-liquid triple point (to 2300 K and 5 GPa) reveal significant changes in the structure of the liquid upon increasing pressure and temperature. The second and third neighbor shells in the g(r) shift to shorter distances and develop new structure with increasing pressure. The results can be interpreted in terms of the liquid acquiring bcc-like local order which evolves to a mixture of bcc- and fcc-like local order as pressure and/or temperature are raised.

Migration and segregation of sodium under β-irradiation in nuclear glasses

Abstract: Raman, 11B Nuclear Magnetic Resonance (NMR) and X-ray Photoelectron (XPS) spectroscopy investigations have been made on a series of β-irradiated aluminoborosilicate glasses. This work shows the following changes of the glass structure under β-irradiation: (i) an increase of glass polymerization, (ii) an increase of boron in a trigonal environment and (iii) no modification in the aluminum environment during irradiation. These glass modifications under β-irradiation can be correlated with the migration of sodium outside of the Si and B glass network formers. Moreover, XPS experiments show a strong decrease of the sodium concentration at the surface of these irradiated glasses. This study presents therefore strong evidences of migration and segregation processes of sodium during a β-irradiation in the bulk for these simplified aluminoborosilicate glass compositions.

EXAFS and Molecular Dynamics combined study of CaO ? FeO ? 2SiO2 glass. New insight into site significance in silicate glasses

Abstract: A new and coherent view of the local environment of Fe2+ in silicate glasses is derived from a combined study by EXAFS and Molecular Dynamics simulation. Iron is located in distorted sites, whose geometry varies continuously from a tetrahedron to a triangular bipyramid. Iron polyhedra are apex-connected to the silicate network, while edge-linked to each other, matching with a random distribution of iron in the glass. Fe2+ does not have the significance of a network-forming element. Its local structure results from the freezing of dynamical exchange processes occurring in the liquid.

Chicxulub impactites: Geochemical clues to the precursor rocks

Abstract: — The 65 Ma Chicxulub impact structure, Mexico, with a diameter of ∼180 km is the focus of geoscientific research because of its link to the mass extinction event at the Cretaceous-Tertiary (K/T) boundary Chicxulub, now buried beneath thick post-impact sediments, is probably one of the best-preserved terrestrial impact structures known Because of its inaccessibility, only limited samples on the impact lithologies from a few drill cores are available We report major element and Sr-, Nd-, O-, and C-isotopic data for Chicxulub impact-melt lithologies and basement clasts in impact breccias of drill cores C-1 and Y-6, and for melt particles in the Chicxulub ejecta horizon at the K/T boundary in Beloc, Haiti The melt lithologies with SiO2 ranging from 58 to ∼63 wt% show significant variations in the content of Al, Ca, and the alkalies In the melt matrix samples, δ13C of the calcite is about −3%o The δ18O values for the siliceous melt matrices of Y-6 samples range from 99 to 124%o Melt lithologies and the black Haitian glass have rather uniform 87Sr/86Sr ratios (07079 to 07094); only one lithic fragment displays 87Sr/86Sr of 07141 The Sr model ages TSrUR for most lithologies range from 830 to 1833 Ma; unrealistic negative model ages point to an open Rb-Sr system with loss of Rb in a hydrothermal process The 143Nd/144Nd ratios for all samples, except one basement clast with 143Nd/144Nd of 05121, cluster at 05123 to 05124 In an ɛNd-ɛSr diagram, impactites plot in a field delimited by ɛNd of −2 to −6, and ɛSr of 55 to 69 This field is not defined by the basement lithologies described to occur as lithic clasts in impact breccias and Cretaceous sediments At least one additional intermediate to mafic precursor component is required to explain the data

Quantitative Measurement of Paramagnetic Fe3+ in Kaolinite

Abstract: A method is proposed to measure the absolute concentration of paramagnetic Fe3+ ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe3+ signal is calibrated by calculating the powder EPR spectra of Fe3+ ions in corundum and low-defect kaolinite. The paramagnetic Fe3+ concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe3+ ions and other iron species, such as Fe3+ concentrated phases and Fe2+ ions. The concentration of isolated structural Fe3+ ranges between 200–3000 ppm and represents less than half of the total iron within kaolinite crystals.

Modeling of debris avalanche and generated water waves: Application to real and potential events in Montserrat

Abstract: Tsunamis generated by a sudden entry of debris avalanches into the sea have caused some of the worst natural disasters in historic times. The evolution of the Soufriere Hill volcano's activity in Montserrat, Lesser Antilles, could lead to a dome collapse generating a tsunami. Two scenarios have been simulated here. In the first case, the potential entry into the sea of a debris mass of 40 millions of m 3 at the mouth of the Tar River Valley, towards the East has been considered. In this case, the debris avalanche is approximated as a fluid entering the sea with a given front height and a given velocity. Sensitivity tests have shown that the simulated water wave is very sensitive to the imposed initial conditions. In order to have a more accurate source term in the tsunami model, we have developed here a numerical debris avalanche model. This model takes into account a Coulomb-type friction law and solves the vertically integrated long wave equations. A first application of this model has been made to simulate the 26 th December 1997 debris avalanche with an estimated volume of 60 millions of m 3 that occurred in the White River valley, South of Montserrat. Preliminary results show that the debris avalanche path is very sensitive to the considered value of the friction angle 5. An empirical value of 5 lower than 15∘ i. e. less than the value expected for debris avalanches, is required to reproduce the great mobility of this avalanche.

Electrical conductivity and crustal structure beneath the central Hellenides around the Gulf of Corinth (Greece) and their relationship with the seismotectonics

Abstract: A deep magnetotelluric sounding (MTS) investigation in the western part of the Gulf of Corinth has revealed a complex electrical image of the crustal structure. The geotectonic structure of the Parnassos unit and the Transition zone in the central Hellenides, overthrusting the Pindos zone both towards the west and towards the south, has been clearly identified by its higher resistivity and its intrinsic anisotropy related to the N–S strike of the Hellenides range. Subsequent N–S extension of the Gulf introduced another heterogeneous anisotropy characteristic that corresponds to E–W-trending normal faults on both sides of the Gulf. The 2-D modelling of the MTS results reveals the existence of a relatively conductive layer about 4 km thick at a depth greater than 10 km in the middle crust. It corresponds to a ductile detachment zone suggested by microseismic and seismic studies (King et al. 1985; Rigo et al. 1996; Bernard et al. 1997a). It may be attributed to the phyllite series lying between the allochthonous Hellenic nappes and the autochthonous Plattenkalk basement. Towards the east, under the Pangalos peninsula, approaching the internal Hellenides, the detachment zone could root deeply into the lower crust. Some strong local electrical anomalies are observed, reaching the conductive layer in the middle crust, such as that under the Mamousia fault and under the front of the overthrust of the Transition zone on the Pindos zone. Other anomalies affect only the shallower zones such as that beneath the Helike fault and in the Psaromita peninsula. These shallower anomalies provide complementary information to the study of spatial and temporal variations of the seismic anisotropy in relation to the short- and long-term tectonic activity of the Gulf (Bouin et al. 1996; Gamar et al. 1999).

Evidence from 10Be and U series disequilibria on the possible contamination of mid-ocean ridge basalt glasses by sedimentary material

Abstract: [1] It has often been suggested that U series disequilibria measured in mid-ocean ridge basalts (MORB) can be perturbed by contamination with sedimentary or hydrothermal material found near the ridge axis where the basalts are erupted. Here we provide an independent way of estimating the maximum degree of contamination by sediment using constraints from 10Be. Since 10Be is mostly a cosmogenic nuclide and has a half life of 1.5 × 106 years, any 10Be found in a MORB glass must result from contamination by sedimentary material where cosmogenic 10Be is enriched. Four MORB samples with a wide range in Th concentrations (87–550 ppb) were measured for U decay series and 10Be. No 10Be above the detection limit (6 × 104 to 1 × 105 atoms) was measured in the glasses except for one sample that was not picked. Considering that the sedimentary contaminant contains 109 to 1010 atoms/g, the maximum fraction of contaminant in the picked glasses is 10−4 to 10−5. Mass balance calculations between a surficial contaminant and a hypothetical pristine glass with (231Pa/235U) = 1 and (10Be/9Be) = 0 show that only for the unpicked sample, nearly all the measured excess 231Pa can be accounted for by contamination. For the other samples, <15% to <1% of the excess 231Pa and 230Th can be explained by incorporation of sedimentary material. This study reemphasizes the need for careful sample preparation for U series measurements in MORB, especially at low U levels (<50 ppb). It also confirms that the large U series excesses in carefully picked and cleaned MORB samples are magmatic in origin.

On the trees of quantum fields

Abstract: The solution of some equations involving functional derivatives is written as a series indexed by planar binary trees. The terms of the series are given by an explicit recursive formula. Some algebraic properties of these series are investigated. Several examples are treated in the case of quantum electrodynamics: the complete fermion and photon propagators, the two-body Green function and the one-body Green function in the presence of an external source, the complete vacuum polarization, the electron self-energy and the irreducible vertex.

Constraint on the S‐wave velocity at the base of the mantle

Abstract: Some recent seismic studies have suggested the presence of a thin ultra-low P-wave velocity layer (ULVZ) at the base of the mantle, which is interpreted to be due to presence of partial melting. Partial melting would lead to a strong decrease of the S-wave velocity for which there is no seismic evidence. Such a decrease in the S-wave velocity would produce a strong precursor to SKS phase from the conversion of S to P at the upper boundary of the layer. We analyze records of events from the subduction zones in the south-west Pacific region obtained at stations in North America. At the source side, the converted phases propagate in the region, where the ultra-low P-wave velocity has been found earlier. Our analysis demonstrates that either the S-wave velocity drop in this layer is much smaller than predicted by the hypothesis of melting, or the layer is so thin (less than about 10–15 km) that it can not be detected with our technique.

Determination of interatomic distances and coordination numbers by K-XANES in crystalline minerals with distorted local structure

Abstract: The method for quantitative determination of interatomic distances and coordination numbers (CN) from experimental K-XANES of light metallic atoms in crystalline compounds with distorted local structure is proposed, based on the extraction of the first shell term and the multiple-scattering term. In crystalline minerals the extraction of these terms can be obtained under uncertainties of ~0.3 - 0.4 A in the values of the second and more distant shell radii, using the unambiguous diffraction data on cell unit parameters and the type of point symmetry. The fitting of the extracted first shell term by theoretical terms, generated within alternative models for the split of this shell under the local structure distortions in the environment of the absorbing metallic atom, permits one to obtain the interatomic distances and CN in reasonable quantitative agreement with the diffraction data for the reference compounds studied.

Permanence des flux de masse d'une rivière en tresses expérimentales

Abstract: A small-scale experimental braided river system has been reproduced. This experiment shows that: (i) destabilisation of the river occurs through sediment feeding; (ii) for constant input fluxes of mass, transfer by the river evolves towards a steady state in which mass fluxes at each end of the reach remain constant although instable braiding remains inside the box; (iii) instability of the braided river remains both when the system aggrades or degrades.

Renormalization of QED with planar binary trees

Abstract: The renormalized photon and electron propagators are expanded over planar binary trees. Explicit recurrence solutions are given for the terms of these expansions. In the case of massless Quantum Electrodynamics (QED), the relation between renormalized and bare expansions is given in terms of a Hopf algebra structure. For massive quenched QED, the relation between renormalized and bare expansions is given explicitly.