Showing papers by "IPG Photonics published in 2009"

Determination of rapid Deccan eruptions across the Cretaceous-Tertiary boundary using paleomagnetic secular variation: 2. Constraints from analysis of eight new sections and synthesis for a 3500-m-thick composite section

Abstract: [1] The present paper completes a restudy of the main lava pile in the Deccan flood basalt province (trap) of India. Chenet et al. (2008) reported results from the upper third, and this paper reports the lower two thirds of the 3500-m-thick composite section. The methods employed are the same, i.e., combined use of petrology, volcanology, chemostratigraphy, morphology, K-Ar absolute dating, study of sedimentary alteration horizons, and as the main correlation tool, analysis of detailed paleomagnetic remanence directions. The thickness and volume of the flood basalt province studied in this way are therefore tripled. A total of 169 sites from eight new sections are reported in this paper. Together with the results of Chenet et al. (2008), these data represent in total 70% of the 3500-m combined section of the main Deccan traps province. This lava pile was erupted in some 30 major eruptive periods or single eruptive events (SEE), each with volumes ranging from 1000 to 20,000 km3 and 41 individual lava units with a typical volume of 1300 km3. Paleomagnetic analysis shows that some SEEs with thicknesses attaining 200 m were emplaced over distances in excess of 100 km (both likely underestimates, due to outcrop conditions) and up to 800 km. The total time of emission of all combined SEEs could have been (much) less than 10 ka, with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence (so-called “big red boles”). The number of boles, thickness of the pulses, and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end. On the basis of geochronologic results published by Chenet et al. (2007) and paleontological results from Keller et al. (2008), we propose that volcanism occurred in three rather short, discrete phases or megapulses, an early one at ∼67.5 ± 1 Ma near the C30r/C30n transition and the two largest around 65 ± 1 Ma, one entirely within C29r just before the K-T boundary, the other shortly afterward spanning the C29r/C29n reversal. We next estimate sulfur dioxide (likely a major agent of environmental stress) amounts and fluxes released by SEEs: they would have ranged from 5 to 100 Gt and 0.1 to 1 Gt/a, respectively, over durations possibly as short as 100 years for each SEE. The chemical input of the Chicxulub impact would have been on the same order as that of a very large single pulse. The impact, therefore, appears as important but incremental, neither the sole nor main cause of the Cretaceous-Tertiary mass extinctions.

Tomography of the Alpine region from observations of seismic ambient noise

Abstract: We use correlations of the ambient seismic noise to study the crust in western Europe. Cross correlation of 1 year of noise recorded at 150 three components broadband stations yields more than 3 000 Rayleigh wave group velocity measurements. These measurements are used to construct Rayleigh group velocity maps of the Alpine region and surrounding area in the 5–80 s period band. In the 5–10 s period band, the seismic noise recorded in Europe is dominated by surface waves originating from the Northern Atlantic ocean. This anisotropy of the noise and the uneven station distribution affect the azimuthal distribution of the paths where we obtain reliable group velocity measurements. As a consequence our group velocity models have better resolution in the northeast direction than in the southwest direction. Finally we invert the resulting Rayleigh wave group velocity maps to determine the Moho depth. Our results are in good agreement with the result of the numerous active experiments in the Alps and provide a continuous image of the Alpine structure.

Ab initio study of gap opening and screening effects in gated bilayer graphene

Abstract: The electronic properties of doped bilayer graphene in presence of bottom and top gates have been studied and characterized by means of density-functional theory (DFT) calculations. Varying independently the bottom and top gates it is possible to control separately the total doping charge on the sample and the average external electric field acting on the bilayer. We show that, at fixed doping level, the band gap at the $K$ point in the Brillouin zone depends linearly on the average electric field, whereas the corresponding proportionality coefficient has a nonmonotonic dependence on doping. We find that the DFT-calculated band gap at $K$, for small doping levels, is roughly half of the band gap obtained with standard tight-binding (TB) approach. We show that this discrepancy arises from an underestimate, in the TB model, of the screening of the system to the external electric field. In particular, on the basis of our DFT results we observe that, when bilayer graphene is in presence of an external electric field, both interlayer and intralayer screenings occur. Only the interlayer screening is included in TB calculations, while both screenings are fundamental for the description of the band-gap opening. We finally provide a general scheme to obtain the full band structure of gated bilayer graphene for an arbitrary value of the external electric field and of doping.

The structure of GeO2–SiO2 glasses and melts: A Raman spectroscopy study

Abstract: We have investigated a series of glasses and melts along the GeO2–SiO2 join using in situ Raman spectroscopy. The results for both the glasses and melts are consistent with a continuous random network in which there are ‘regions’ that are SiO2-like, GeO2-like and mixed GeO2–SiO2-like. Incorporation of GeO2 into the SiO2 network is initially accommodated via the 3- and 4-membered SiO4 rings which are lost as they convert to larger mixed Ge/Si rings. The LO–TO mode behavior is also consistent with a network that is composed of different ‘regions’ and is similar to that expected from the Bruggeman effective media model. At the highest temperatures there are indications that the mixed Ge/Si rings convert back to small 3-membered GeO4 rings and large SiO4 rings; the small 3- and 4-membered SiO4 rings are not reformed.

Seismic velocities in Southern Tibet lower crust: a receiver function approach for eclogite detection

Abstract: SUMMARY Beneath the Tibet plateau, the deficit of crustal thickening with respect to what is expected from the plate tectonic constraints is thought to be absorbed either by lateral extrusion or by vertical rock-mass transfer. To nourish the unsettled debate of the relative importance of these two processes, we propose a new approach, based on the S-to-P and the P-to-S wave conversions, enabling the precise determination of the seismic velocities. The weighted amplitudes of the direct conversion and of reverberations are stacked at their predicted arrival times for various values of layer thickness and vP/vS ratio separately for two sets of P- and S-receiver functions. For each set of receiver functions, coherent stack gives the vP/ vS ratio and thickness for the considered layer (the grid search stacking method). The values of vP/vS ratio and layer thickness are functions of the velocity used for stacking the set of receiver functions, but using the P- and S-receiver functions allows us to solve this indetermination and to find the effective parameters of the layer: velocity vS, vP/ vS ratio and thickness. We use a bootstrap resampling of the receiver function data sets to estimate the parameters uncertainties. For the Southern Lhasa Block, the migrated sections of both P- and S-receiver functions (Hi-CLIMB experiment data) show a layer in the lower crust that may be related to the lower Indian crust underplated beneath Tibet. With the grid search stacking method, high shear wave velocities (vS ∼ 4.73 km s –1 ) and low vP/vS ratios (∼1.69) are detected in this layer. Such values are typical for high-grade eclogites, and the low vP/vS ratio precludes the confusion with mafic granulites. There is no evidence for partial eclogitization near and south of the Yarlung–Tsangpo Suture, and the about 19 km thick eclogitic layer extends northwards only to about the middle of the Lhasa terrane.

Experimental and theoretical study of the structural environment of magnesium in minerals and silicate glasses using X-ray absorption near-edge structure

Abstract: X-ray absorption spectroscopy at the Mg K-edge is used to obtain information on magnesium environment in minerals, silicate and alumino-silicate glasses. First-principles XANES calculations are performed for minerals using a plane-wave density functional formalism with core-hole effects treated in a supercell approach. The good agreement obtained between experimental and theoretical spectra provides useful information to interpret the spectral features. With the help of calculation, the position of the first peak of XANES spectra is related to both coordination and polyhedron distortion changes. In alumino-silicate glasses, magnesium is found to be mainly 5-fold coordinated to oxygen whatever the aluminum saturation index value. In silicate glasses, magnesium coordination increases from 4 in Cs-, Rb- and K-bearing glasses to 5 in Na- and Li-bearing glasses but remains equal as the polymerization degree of the glass varies. The variation of the C feature (position and intensity) is strongly related to the alkali type providing information on the medium range order.

Quantitation of sulfate solubility in borosilicate glasses using Raman spectroscopy

Abstract: Raman spectroscopy is used here as an innovative technique to investigate sulfate content in borosilicate glasses. Using Raman spectroscopy after having heated the material, the evolution of sulfate amounts can be followed as a function of temperature, time and chemical composition of the starting matrix. The accu- racy of this technique was verified using electron probe micro analysis (EPMA), on two systems of glasses (SiO2-B2O3-Na2O (SBNa) and SiO2-B2O3-BaO (SBBa)) in order to compare the effect of alkaline or alka- line-earth elements on sulfur speciation and incorporation. To quantitate sulfate content with Raman spectroscopy, the integrated intensity of the sulfate band at 990 cm � 1 was scaled to the sum of the inte- grated bands between 850 and 1250 cm � 1 , bands that are assigned to Q n silica units. Calibration curves were then determined for different samples. The determination of sulfate contents with Raman spectros- copy analysis is possible with an accuracy of approximately 0.1 wt% depending on the composition of the glass. It mainly allows us to follow sulfate removal during the elaboration process and to establish kinetic curves of sulfate release as a function of the viscosity of the borosilicate glass.

Phonon surface mapping of graphite: Disentangling quasi-degenerate phonon dispersions

Abstract: The two-dimensional mapping of the phonon dispersions around the $K$ point of graphite by inelastic x-ray scattering is provided. The present work resolves the longstanding issue related to the correct assignment of transverse and longitudinal phonon branches at $K$. We observe an almost degeneracy of the three TO-, LA-, and LO-derived phonon branches and a strong phonon trigonal warping. Correlation effects renormalize the Kohn anomaly of the TO mode, which exhibits a trigonal warping effect opposite to that of the electronic band structure. We determined the electron-phonon coupling constant to be $166\text{ }{(\text{eV}/\text{\AA{}})}^{2}$ in excellent agreement to GW calculations. These results are fundamental for understanding angle-resolved photoemission, double-resonance Raman and transport measurements of graphene-based systems.

High-resolution spectroscopy on an X-ray absorption beamline.

Abstract: A bent-crystal spectrometer based on the Rowland circle geometry has been installed and tested on the BM30b/FAME beamline at the European Synchrotron Radiation Facility to improve its performances. The energy resolution of the spectrometer allows different kinds of measurements to be performed, including X-ray absorption spectroscopy, resonant inelastic X-ray scattering and X-ray Raman scattering experiments. The simplicity of the experimental device makes it easily implemented on a classical X-ray absorption beamline. This improvement in the fluorescence detection is of particular importance when the probed element is embedded in a complex and/or heavy matrix, for example in environmental sciences.

Post‐rift volcanism and high heat‐flow at the ocean‐continent transition of the eastern Gulf of Aden

Abstract: A high heat-flow (∼900 mW m−2) has been observed over a volcanic structure at the Ocean-Continent Transition in the Eastern Gulf of Aden (Oman margin). The anomaly is superposed to a progressive increase of heat-flow across the margin and can be interpreted either by (1) heat refraction, (2) fluid discharge or (3) cooling magma. The two first explanations cannot be ruled out definitely by modelling analysis, but require unlikely thermal conductivity or permeability values. The third one implies that the latest activity of the volcano was about 100 000 years old and therefore continued c. 18 Ma after the break-up of Africa and Arabia. This potential mechanism is consistent with other lines of evidence of post-rifting activity in the Gulf of Aden and could invalidate the conventional assumption that rifted-margins become passive after the break-up of continents.

Structure and CO2 budget of Merapi volcano during inter-eruptive periods

Abstract: Soil temperature and gas (CO2 concentration and flux) have been investigated at Merapi volcano (Indonesia) during two inter-eruptive periods (2002 and 2007). Precise imaging of the summit crater and the spatial pattern of diffuse degassing along a gas traverse on the southern slope are interpreted in terms of summit structure and major caldera organization. The summit area is characterized by decreasing CO2 concentrations with distance from the 1932 crater rim, down to atmospheric levels at the base of the terminal cone. Similar patterns are measured on any transect down the slopes of the cone. The spatial distribution of soil gas anomalies suggests that soil degassing is controlled by structures identified as concentric historical caldera rims (1932, 1872, and 1768), which have undergone severe hydrothermal self-sealing processes that dramatically lower the permeability and porosity of soils. Temperature and CO2 flux measurements in soils near the dome display heterogeneous distributions which are consistent with a fracture network identified by previous geophysical studies. These data support the idea that the summit is made of isolated and mobile blocks, whose boundaries are either sealed by depositional processes or used as pathways for significant soil degassing. Within this context, self-sealing both prevents long-distance soil degassing and controls heat and volatile transfers near the dome. A rough estimate of the CO2 output through soils near the dome is 200–230 t day−1, i.e. 50% of the estimated total gas output from the volcano summit during these quiescent periods. On Merapi’s southern slope, a 2,500 m long CO2 traverse shows low-amplitude anomalies that fit well with a recently observed electromagnetic anomaly, consistent with a faulted structure related to an ancient avalanche caldera rim. Sub-surface soil permeability is the key parameter that controls the transfer of heat and volatiles within the volcano, allowing its major tectonic architecture to be revealed by soil gas and soil temperature surveys.

Tailored pulse burst

Abstract: Output pulses from an optical system having a seed source and an optical amplifier coupled to the seed source may be controlled by controlling a power of a seed signal from the seed source. The seed signal may be varied between a minimum value and a maximum value in a way that the seed signal exhibits one or more pulse bursts. Each pulse burst may contain one or more pulses. During an inter-pulse period between successive pulses within a pulse burst or between successive pulse bursts, the power of the seed signal may be adjusted to an intermediate value that is greater than the minimum value and less than the maximum value. The intermediate value is chosen to control a gain in the optical amplifier such that a pulse or pulse burst that follows the period exhibits a desired behavior.

Incorporation of water in iron-free ringwoodite: A first-principles study

Abstract: The structures, infrared active OH stretching modes, and relative energies of OH-defects in ringwoodite (γ-Mg 2 SiO 4 ) have been studied by first-principles calculations based on density functional theory (DFT). Two types of fully protonated cationic defects in normal spinel were considered at 0 and 20 GPa, i.e., [ V Mg (OH) 2 ] x , [ V Si OH) 4 ] x defects. In addition, two defects associated with the partial inversion of the spinel structure have been investigated. The first one corresponds to two protons compensating a Mg substituted for Si in tetrahedral site, [Mg Si (OH) 2 ] x , whereas the second defect corresponds to a Mg vacancy located nearby a Mg-Si substitution, [ V Mg (OH) 2 Mg Si Si Mg ] x . The infrared spectrum and evolution with pressure of these OH-defects make it possible to interpret the major IR absorption bands experimentally observed. The main absorption band at ~3150 cm −1 corresponds to protons located between the O-O pairs shared by 16 c and 16 d octahedra, instead of OH along the tetrahedral edges as usually proposed in the literature. The large width of this band is most likely related to the association of OH defects with the various cationic configurations related to the partial inversion of a vacancy-bearing spinel structure. The less intense band at ~3675 cm −1 is assigned to hydrogarnet-type defects with a protonation of the tetrahedral edges. This interpretation is consistent with an Mg/Si ratio lower than 2 and its weak variation as a function of water concentration, as experimentally observed. These results emphasize the importance of taking into account the structural relaxation experienced by defects, instead of using empirical correlation, to assign OH stretching bands to specific O-O pairs of the structure.

Power Scaling of SM Fiber Lasers toward 10kW

Abstract: The physical and engineering challenges in scaling fiber lasers toward 10kW include 1) avoiding non-linear thresholds, particularly SRS, 2) obtaining sufficient pump brightness, and 3) overcoming thermal issues. The methods to overcome these barriers are reviewed and results >6kW SM are provided. Article not available.