IPG Photonics

About: IPG Photonics is a based out in . It is known for research contribution in the topics: Laser & Fiber laser. The organization has 903 authors who have published 1241 publications receiving 63339 citations.

EXAFS signature of structural Zn at trace levels in natural and synthetic trioctahedral 2:1 phyllosilicates

Abstract: EXAFS spectroscopy has been used to determine the medium-range structural environment (within a radius of 7 A) of trace levels of Zn2+ ions within the octahedral sheets of trioctahedral 2:1 phyllosilicates. EXAFS signatures of trace quantities (800–4000 ppm) of Zn in natural and synthetic trioctahedral 2:1 phyllosilicates (talcs and biotite) were analyzed using ab initio FEFF calculations (FEFF 8.10 code) in which various second-neighbor atomic configurations around a Zn-containing octahedral site were examined. Comparison of the results of these model calculations with observed Zn K -edge EXAFS spectra provides constraints on the distribution of Zn within the octahedral sheet. Zn was found to be randomly distributed within the octahedral sheets of the synthetic talc containing 4000 ppm Zn. In the natural biotite containing 800 ppm Zn, the distribution of Zn could not be determined because of significant Fe content, which precluded unambiguous FEFF analysis. Finally, FEFF analysis of single-scattering and multiple-scattering contributions to the EXAFS data of the Zn-dilute talc sample, followed by comparison with EXAFS data from a natural dioctahedral illite sample containing 140 ppm Zn, allowed unambiguous identification of spectral features characteristic of Zn2+ ions incorporated within the octahedral sheets of trioctahedral phyllosilicates. These results indicate that EXAFS spectroscopy can be used to distinguish between incorporation of trace levels of Zn2+ ions within the octahedral sheet of di- or trioctahedral phyllosilicates. They also provide a strong basis for determining the speciation of Zn at trace concentration levels in natural phyllosilicates from Zn-contaminated soils and sediments using Zn K -edge EXAFS spectroscopy. Because the crystal chemistry of other potentially toxic first-row divalent transition elements (i.e., Co2+, Ni2+, and Cu2+) is similar to that of Zn2+, this FEFF-based EXAFS approach could be used to (1) complement existing FTIR and polarized-EXAFS approaches in assessing the distribution of these elements within the octahedral sheets of di- and trioctahedral plyllosilicates and (2) better determine the speciation of these elements in contaminated soils and sediments.

The November 2002 eruption of Piton de la Fournaise, Réunion: tracking the pre-eruptive thermal evolution of magma using melt inclusions

Abstract: The November 2002 eruption of Piton de la Fournaise in the Indian Ocean was typical of the activity of the volcano from 1999 to 2006 in terms of duration and volume of magma ejected. The first magma erupted was a basaltic liquid with a small proportion of olivine phenocrysts (Fo81) that contain small numbers of melt inclusions. In subsequent flows, olivine crystals were more abundant and richer in Mg (Fo83–84). These crystals contain numerous melt and fluid inclusions, healed fractures, and dislocation features such as kink bands. The major element composition of melt inclusions in this later olivine (Fo83–84) is out of equilibrium with that of its host as a result of extensive post-entrapment crystallization and Fe2+ loss by diffusion during cooling. Melt inclusions in Fo81 olivine are also chemically out of equilibrium with their hosts but to a lesser degree. Using olivine–melt geothermometry, we determined that melt inclusions in Fo81 olivine were trapped at lower temperature (1,182 ± 1°C) than inclusions in Fo83–84 olivine (1,199–1,227°C). This methodology was also used to estimate eruption temperatures. The November 2002 melt inclusion compositions suggest that they were at temperatures between 1,070°C and 1,133°C immediately before eruption and quenching. This relatively wide temperature range may reflect the fact that most of the melt inclusions were from olivine in lava samples and therefore likely underwent minor but variable amounts of post-eruptive crystallization and Fe2+ loss by diffusion due to their relatively slow cooling on the surface. In contrast, melt inclusions in tephra samples from past major eruptions yielded a narrower range of higher eruption temperatures (1,163–1,181°C). The melt inclusion data presented here and in earlier publications are consistent with a model of magma recharge from depth during major eruptions, followed by storage, cooling, and crystallization at shallow levels prior to expulsion during events similar in magnitude to the relatively small November 2002 eruption.

The source motion of 2003 Bam (Iran) earthquake constrained by satellite and ground‐based geodetic data

Abstract: SUMMARY The interpretation of coseismic surface deformation measurements through inversion techniques is of major importance to understand the mechanical behaviour of a seismic fault. Dense geodetic data sets in the vicinity of the ruptured fault provide unique constraints on detailed fault geometry and slip distribution at depth, making them complementary to seismological data. Bam earthquake (Mw 6.6, 2003 December 26) induced surface deformation has been precisely mapped by Envisat ASAR interferometry and by subpixel correlation techniques applied to Spot-5 and ASAR amplitude images. These oblique and horizontal estimations of deformation have been completed with one levelling profile along the main road crossing the rupture from west to east. We process these data (separately and jointly) in a two-step inversion technique, within the elastic half-space theory framework. Our objective is to determine the dislocation model at depth that satisfies simultaneously all the geodetic constraints. Also, we estimate the relative contribution of each geodetic data set to this inversion process. We first use a stochastic direct approach called neighbourhood algorithm in order to estimate the average characteristics of the rupture, and their relative uncertainty. Constraining in this way the geometry of the ruptured fault, we then linearize the inverse problem and compute the slip distribution on the fault using a standard weighted least-square technique, assuming the solution is smooth to some degree. At each step, we discuss the optimal models, their stability as well as the relative influence of each data set on the derived models parameters. Our preferred model reveals a shallow dislocation on a quasi-vertical fault, slightly dipping towards east. The slip vector has a strike-slip component as high as 2 m, while the dip-slip component seems negligible. However, the estimation of the resolution matrices emphasizes the fact that the details of deep fault slip distribution remain out of the scope of this ill-conditioned inverse problem. Yet, our preferred model suggests a main dislocation limited at depth between 1 and 6 km. By contrast, the aftershocks observed in the months following the earthquake are located just beneath the estimated main shock.