Showing papers by "IPG Photonics published in 2003"

Introduction to U-series Geochemistry

Abstract: During the last century, the Earth Sciences underwent two major revolutions in understanding. The first was the recognition of the great antiquity of the Earth and the second was the development of plate tectonic theory. These leaps in knowledge moved geology from its largely descriptive origins and established the modern, quantitative, Earth Sciences. For any science, and particularly for the Earth Sciences, time scales are of central importance. Until recently, however, the study of time scales in the Earth Sciences was largely restricted to the unraveling of the ancient history of our planet. For several decades, Earth scientists have used a variety of isotope chronometers to unravel the long-term evolution of the planet. A fuller understanding of the physical and chemical processes driving this evolution often remained elusive because such processes occur on time scales (1–105 years) which are simply not resolvable by most conventional chronometers. The U-series isotopes, however, do provide tools with sufficient time resolution to study these Earth processes. During the last decade, the Earth Sciences have become increasingly focused on fundamental processes and U-series geochemistry has witnessed a renaissance, with widespread application in disciplines as diverse as modern oceanography and igneous petrology. The uranium and thorium decay-series contain radioactive isotopes of many elements (in particular, U, Th, Pa, Ra and Rn). The varied geochemical properties of these elements cause nuclides within the chain to be fractionated in different geological environments. while the varied half-lives of the nuclides allows investigation of processes occurring on time scales from days to 105 years. U-series measurements have therefore revolutionized the Earth Sciences by offering some of the only quantitative constraints on time scales applicable to the physical processes that take place on the Earth. The application of U-series geochemistry to the Earth Sciences was thoroughly summarized in 1982 …

DWDM 40 G transmission over trans-Pacific distance (10,000 km) casing CSRZ-DPSK, enhanced FEC and all-Raman amplified 100 km UltraWave/spl trade/ fiber spans

Abstract: We demonstrate error-free dense-wavelength-division multiplexing (DWDM) transmission of 40 40-Gb/s channels with 100-GHz spacing over 10 000 km dispersion-managed fiber using carrier-suppressed return-to-zero differential-phase-shift keying (CSRZ-DPSK), enhanced foward-error correction, and all-Raman-amplified spans with 100-km terrestrial length.

Insights into Magma Genesis at Convergent Margins from U-series Isotopes

Abstract: Convergent margins (oceanic and continental arcs) form one of the Earth’s key mass transfer locations, being sites where melting and transfer of new material to the Earth’s crust occurs and also where crustal materials, including water, are recycled back into the mantle. Volcanism in this tectonic setting constitutes ~15% (0.4–0.6 km3/yr) of the total global output (Crisp 1984) and the composition of the erupted magmas is, on average, similar to that of the continental crust (Taylor and McLennan 1981). Moreover, many arc volcanoes have been responsible for the most hazardous, historic volcanic eruptions. Yet, despite their importance, many fundamental aspects of convergent margin magmatism remain poorly understood. Key among these are the rates of processes of fluid addition from the subducting plate. Furthermore, in stark contrast to the ocean ridges, where adiabatic decompression provides a simple and robust physical model for partial melting, no consensus has yet been reached about the physics of the partial melting process and the mechanism of melt extraction beneath arcs. Preceding chapters concerned with partial melting in this volume (Lundstrom 2003; Bourdon and Sims 2003) have discussed how the differing half-lives and distribution coefficients of the various U-series nuclides result in disequilibria through in-growth. This provides important information on the nature and timing of mantle partial melting processes. In convergent margin settings the differential fluid mobility of U and Ra relative to Th and Pa provides an additional source of fractionation leading to in-growth and this is crucial to understanding the timing and mechanisms of fluid addition. Here we review the role that the proliferation of high quality U-series isotope data, over the last decade, have had in obtaining precise information on time scales and the development of quantitative physical models for convergent margin magmatism. Our approach is to use trace element …

Coseismic and early post-seismic slip associated with the 1999 Izmit earthquake (Turkey), from SAR interferometry and tectonic field observations

Abstract: SUMMARY We use combined tectonic field observations and SAR data to determine an improved model of the slip associated with the 1999 Izmit earthquake, which ruptured the North Anatolian Fault at the eastern end of the Sea of Marmara. The leading goal is to understand the main features of the coseismic and post-seismic deformation, which are captured together in the SAR data. To achieve this, we make a critical analysis of the ERS1-2 SAR data, which allows atmospheric effects to be identified and removed. We also use detailed field mapping and measurements of the earthquake surface rupture. Dislocations in elastic half-space and a forward modelling strategy allow us to obtain a slip model by steps. A trial-and-error approach is combined with conventional inversion techniques to determine the slip in the different regions of the fault. The SAR data are well explained with three main zones of high slip along the fault, releasing a total moment of 2.3 × 10 20 Nm( Mw = 7.6), which is higher than the seismological estimates (1.7‐2.0 × 10 20 N m). The inhomogeneous slip distribution correlates with fault segments identified at the surface. The Izmit rupture appears to have extended 30 km west of the Hersek peninsula into the Sea of Marmara with slip tapering fro m2mt ozero. The western end of the rupture is located 40 km SSE from Istanbul. We show that some features seen near to Mudurnu and Gevye and previously interpreted as slip on secondary faults are explained mostly as atmospheric effects correlated with the topography. Using our approach and the available GPS data we obtain a slip model that represents the coseismic slip alone, which suggests that the moment release during the main shock was 1.9 × 10 20 Nm( Mw = 7.5), consistent with the seismological estimates. We conclude that the SAR data include the effects of 2 m of fast after-slip during the month following the main shock, within a zone of the fault located 12‐ 24 km below the epicentral region. Near the hypocentre at a depth of 18 km, the fault appears to have experienced dynamic slip of 1 m associated with the main shock, followed by 2 m of rapidly decelerating post-seismic shear during the following month. We suggest that the distribution of heterogeneous slip and loading along the different fault segments may be important factors controlling the propagation of large earthquake ruptures along the North Anatolian Fault.

Long-term elasticity in the continental lithosphere; modelling the Aden Ridge propagation and the Anatolian extrusion process

Abstract: SUMMARY The evolution of the Gulf of Aden and the Anatolian Fault systems are modelled using the principles of elastic fracture mechanics usually applied to smaller scale cracks or faults. The lithosphere is treated as a plate, and simple boundary conditions are applied that correspond to the known plate boundary geometry and slip vectors. The models provide a simple explanation for many observed geological features. For the Gulf of Aden the model predicts why the ridge propagated from east to west from the Owen Fracture Zone towards the Afar and the overall form of its path. The smaller en echelon offsets can be explained by upward propagation from the initially created mantle dyke while the larger ones may be attributed to the propagating rupture interacting with pre-existing structures. For Anatolia the modelling suggests that the East Anatolian Fault was created before the North Anatolian Fault could form. Once both faults were formed however, activity could switch between them. The time scales over which this should take place are not known, but evidence for switching can be found in the historical seismicity. For Aden and Anatolia pre-existing structures or inhomogeneous stress fields left from earlier orogenic events have modified the processes of propagation and without an understanding of the existence of such features the propagation processes cannot be fully understood. Furthermore a propagating fault can extend into an active region where it would not have initiated. The North Anatolian Fault encountered slow but active extension when it entered the Aegean about 5 Ma and the stress field associated with the extending fault has progressively modified Aegean extension. In the central Aegean activity has been reduced while to the north-west on features such as the Gulfs of Evvia and Corinth activity has been increased. The field observation that major structures propagate and the success of simple elastic models suggest that the continental crust behaves in an elastic-brittle or elastic-plastic fashion even though laboratory tests may be interpreted to suggest viscous behaviour. There are major problems in scaling from the behaviour of small homogeneous samples to the large heterogeneous mantle and large-scale observations should be treated more seriously than extrapolations of the behaviour of laboratory experiments over many orders of magnitude in space and time. The retention of long-term elasticity and localised failure suggests a similar gross rheology for the oceanic and continental lithospheres. Even though it is incorrect to attribute differences in behaviour to the former being rigid (i.e. elastic) and the latter viscous, oceanic and continental lithosphere behave in different ways. Unlike oceanic crust, continental crust is buoyant and cannot be simply created or destroyed. The process of thickening or thinning works against gravity preventing large displacements on extensional or contractional features in the upper mantle. The equivalents of ridge or subduction systems are suppressed before they can accommodate large displacements and activity must shift elsewhere. On the other hand, strike-slip boundaries and extrusion processes are favoured.

Immobilization of Arsenite and Ferric Iron by Acidithiobacillus ferrooxidans and Its Relevance to Acid Mine Drainage

Abstract: Weathering of the As-rich pyrite-rich tailings of the abandoned mining site of Carnoules (southeastern France) results in the formation of acid waters heavily loaded with arsenic. Dissolved arsenic present in the seepage waters precipitates within a few meters from the bottom of the tailing dam in the presence of microorganisms. An Acidithiobacillus ferrooxidans strain, referred to as CC1, was isolated from the effluents. This strain was able to remove arsenic from a defined synthetic medium only when grown on ferrous iron. This A. ferrooxidans strain did not oxidize arsenite to arsenate directly or indirectly. Strain CC1 precipitated arsenic unexpectedly as arsenite but not arsenate, with ferric iron produced by its energy metabolism. Furthermore, arsenite was almost not found adsorbed on jarosite but associated with a poorly ordered schwertmannite. Arsenate is known to efficiently precipitate with ferric iron and sulfate in the form of more or less ordered schwertmannite, depending on the sulfur-to-arsenic ratio. Our data demonstrate that the coprecipitation of arsenite with schwertmannite also appears as a potential mechanism of arsenite removal in heavily contaminated acid waters. The removal of arsenite by coprecipitation with ferric iron appears to be a common property of the A. ferrooxidans species, as such a feature was observed with one private and three collection strains, one of which was the type strain.

Dehydration and partial melting in subduction zones: Constraints from U-series disequilibria

Abstract: [1] We present a critical reappraisal of U-series data from arc volcanoes to constrain slab dehydration and melting processes using a global subduction zone data set. There is no clear evidence for significant mobilization of Th or Pa in dehydration fluids while the source region of arc rocks is relatively oxidized and mobility of U is strongly enhanced. It is argued that along-arc U/Th and U/Pa isotope data reflect time-integrated addition of U from the slab to the mantle wedge. The presence of large Ra-Th disequilibrium correlated with Ba/Th ratios provides evidence for some very recent fluid addition and fast magma ascent. This is consistent with radiogenic Os isotope signatures in arc lavas that can only be preserved if there is no melt-peridotite equilibration during melt transport. The 231Pa excesses found in most arc lavas provide clear evidence for a melting signature and require that the timescale of melt production cannot be as short as the timescale of melt migration (<100 annum). We propose a dynamic model in which melting is initiated by fluid fluxing and where melt is rapidly extracted out of the mantle via high-velocity channels while 231Pa excess is produced at melting rates consistent with literature estimates of melt productivity. An alternative model with continuous flux melting would require a long melting timescale (1–5 Ma), a large melting region and the mobility of Th and Pa in fluids. A model with a time lag between melting and initial dehydration is more consistent with a thermal structure where the wet solidus is not reached before an intermediate depth.

U-series Constraints on Intraplate Basaltic Magmatism

Abstract: Intraplate magmatism represents approximately one tenth of the flux of magma to the Earth’s surface (Sleep 1990). This type of magmatism has received considerable attention from petrologists and geochemists as it generally exhibits a wider range of chemical compositions than the more uniform mid-ocean ridge basalts. Hence, it is rather paradoxical that our understanding of intraplate magmatism is rather poor. In this chapter, we review the insights that have been gained from using U-series measurements (combined with other chemical and isotopic constraints) to better understand the sources and processes related to intraplate volcanism. Several unique constraints can be obtained from measurement of U-series disequilibria in basalts. First, U-series fractionation can tell us about the residual phases present during melting as small differences in partitioning behavior between the nuclides will induce distinct signatures. Second, as has been shown by the earlier work of Allegre and Condomines (1982), Th isotope ratios can be used to infer the Th/U ratio of the mantle source providing another useful probe for mapping mantle heterogeneities. Lastly, as detailed below, the time-dependence of U-series fractionation during melting and melt migration can place constraints on several rate-dependent parameters such as the melt production rate, and melt velocities. An important feature of hotspot magmatism is that in many cases, the timing of hotspot activity seems to be decoupled from the motion of the lithospheric plate. This observation, which has been the basis for proposing the existence of mantle plumes, suggests that magmas erupted at hotspots should reveal something about the nature of the deeper mantle. Understanding the processes of hotspot magmatism should also tell us about the nature of convective motion responsible for hotspots. In the following section, we first review some of the outstanding issues that need to be resolved to better understand intraplate magmatism. We then …

Dissolution of strontianite at high P-T conditions: An in-situ synchrotron X-ray fluorescence study

Abstract: In-situ measurements of the amount of dissolution of carbonate minerals at high pressures (up to 3.6 GPa) and temperatures (up to 523 K) are reported. Using an externally heated diamond anvil cell (DAC) and synchrotron X-ray fluorescence (SXRF), the extent of dissolution of strontianite (SrCO3) has been followed as a function of time by monitoring the fluorescence of Sr cations in the fluid surrounding the crystal. This work demonstrates that Sr2+ concentrations as low as 1000 ppm can be detected and measured in-situ in a DAC, using a forward transmission geometry. The preliminary data presented here indicate that this technique has high potential for determining solution composition in high-pressure and high-temperature geochemical studies.

400 W low-noise single-mode CW ytterbium fiber laser with an integrated fiber delivery

Abstract: 400 W CW output power at 1080 nm from an industrial grade ytterbium fiber laser with M/sup 2/<1.05 and <1.5% intensity noise was demonstrated. We expect to scale fiber laser output power to the levels far exceeding 500 W.

Modeling of morphogenesis of polyolefin particles: Catalyst fragmentation

Abstract: The growth of polyolefin particles in heterogeneous catalyzed polymerization reactors is simulated often by reaction-transport models that introduce certain ad hoc effective spatial scales to the description of particle morphology and transport processes inside the particles. Because predictive capabilities of such models with respect to particle morphogenesis are limited, a multiscale model of a growing particle is developed. Maximum relevant information can be systematically extracted from particle microscopy images using the method of reconstructed porous media. The spatially 3-D replicas of the particle pore space allow to calculate the effective transport and mechanical properties. Two new modeling techniques approximate catalyst particle fragmentation: Delaunay triangulation generalized into a 3-D space with non-Euclidean metrics and disconnection of the skeleton representation of the solid phase. Predictive mesoscopic modeling of particle morphogenesis is also discussed.

Surface wave higher-mode phase velocity measurements using a roller-coaster-type algorithm

Abstract: SUMMARY In order to solve a highly non-linear problem by introducing the smallest a priori information, we present a new inverse technique called the 'roller coaster' technique and apply it to measure surface wave mode-branch phase velocities. The fundamental mode and the first six overtone parameter vectors, defined over their own significant frequency ranges, are smoothed average phase velocity perturbations along the great circle epicentre-station path. These measurements explain well both Rayleigh and Love waveforms, within a maximum period range included between 40 and 500 s. The main idea of this technique is to first determine all possible configurations of the parameter vector, imposing large-scale correlations over the model space, and secondly to explore each of them locally in order to match the short-wavelength variations. The final solution which achieves the minimum misfit of all local optimizations, in the least- squares sense, is then hardly influenced by the reference model. Each mode-branch a posteriori reliability estimate turns out to be a very powerful instrument in assessing the phase velocity measurements. Our Rayleigh results for the Vanuatu-California path seem to agree correctly with previous ones.

Electrical Resistivity Index in Multiphase Flow through Porous Media

Abstract: The simultaneous flow of two phases through a three-dimensional porous medium is calculated by means of a Lattice-Boltzmann algorithm. The time-dependent phase configurations can be derived and also macroscopic quantities such as the relative permeabilities. When one phase only is supposed to be conductive, the Laplace equation which governs electrical conduction can be solved in each phase configuration; an instantaneous value of the macroscopic conductivity is obtained and it is averaged over many configurations. The influence of saturation on the resistivity index is studied for six different samples and two viscosity ratios. The saturation exponent is systematically determined. The numerical results are also compared to other possible models and also to experimental results; finally, they are discussed and criticized.

Mono Lake or Laschamp geomagnetic event recorded from lava flows in Amsterdam Island (southeastern Indian Ocean)

Abstract: SUMMARY We report a survey carried out on basalt flows from Amsterdam Island (Southeastern Indian Ocean) in order to check the presence of intermediate directions interpreted as belonging to a geomagnetic field excursion within the Brunhes epoch, completing this palaeomagnetic record with palaeointensity determinations and radiometric dating. Because the palaeomagnetic sampling was done over a few hours during the resupply of the French scientific base Martin du Viviers by the Marion Dufresne vessel, we could collect only 29 samples from four lava flows. The directional results corroborate the findings by Watkins & Nougier: normal polarity is found for two units and an intermediate direction, with associated virtual geomagnetic poles (VGPs) close to the equator, for the other two units. A notable result is that these volcanic rocks are well suited for absolute palaeointensity determinations. 50 per cent of the samples yields reliable intensity values with high-quality factors. An original element of this study is that we made use of the thermomagnetic criterion PTRM-tail test of Shcherbakova et al. to help in the interpretation of the palaeointensity measurements. Doing this, only the high-temperature intervals, beyond 400 ◦ C, were retained to obtain the most reliable estimate of the strength of the ancient magnetic field. However, not applying the PTRM-tail test does not change the flow-mean values significantly because the samples we selected by conventional criteria for estimating the palaeointensity carry only a small proportion of their remanence below 400 ◦ C. The normal units yield virtual dipole moments (VDM) of 6.2 and 7.7 (10 22 Am 2 ) and the excursional units yield values of 3.7 and 3.4 (10 22 Am 2 ). These results are quite consistent with the other Thellier determinations from Brunhes excursion records, all characterized by a decrease of the VDM as the VGP latitude decreases. 40 Ar/ 39 Ar isotopic age determinations provide an estimate of 26 ± 15 and 18 ± 9 kyr for the transitional lava flows, which could correspond to the Mono Lake excursion. However, the large error bars associated with these ages do not exclude the hypothesis that this event is the Laschamp.

Quantum field theory and Hopf algebra cohomology

Abstract: We exhibit a Hopf superalgebra structure of the algebra of field operators of quantum field theory (QFT) with the normal product. Based on this we construct the operator product and the time-ordered product as a twist deformation in the sense of Drinfeld. Our approach yields formulas for (perturbative) products and expectation values that allow for a significant enhancement in computational efficiency as compared to traditional methods. Employing Hopf algebra cohomology sheds new light on the structure of QFT and allows the extension to interacting (not necessarily perturbative) QFT. We give a reconstruction theorem for time-ordered products in the spirit of Streater and Wightman and recover the distinction between free and interacting theory from a property of the underlying cocycle. We also demonstrate how non-trivial vacua are described in our approach solving a problem in quantum chemistry.