Showing papers by "IPG Photonics published in 2007"

Processing seismic ambient noise data to obtain reliable broad-band surface wave dispersion measurements

Abstract: SUMMARY Ambient noise tomography is a rapidly emerging field of seismological research. This paper presents the current status of ambient noise data processing as it has developed over the past several years and is intended to explain and justify this development through salient examples. The ambient noise data processing procedure divides into four principal phases: (1) single station data preparation, (2) cross-correlation and temporal stacking, (3) measurement of dispersion curves (performed with frequency‐time analysis for both group and phase speeds) and (4) quality control, including error analysis and selection of the acceptable measurements. The procedures that are described herein have been designed not only to deliver reliable measurements, but to be flexible, applicable to a wide variety of observational settings, as well as being fully automated. For an automated data processing procedure, data quality control measures are particularly important to identify and reject bad measurements and compute quality assurance statistics for the accepted measurements. The principal metric on which to base a judgment of quality is stability, the robustness of the measurement to perturbations in the conditions under which it is obtained. Temporal repeatability, in particular, is a significant indicator of reliability and is elevated to a high position in our assessment, as we equate seasonal repeatability with measurement uncertainty. Proxy curves relating observed signal-to-noise ratios to average measurement uncertainties show promise to provide useful expected measurement error estimates in the absence of the long time-series needed for temporal subsetting.

Breakdown of the adiabatic Born-Oppenheimer approximation in graphene.

Abstract: The adiabatic Born-Oppenheimer approximation (ABO) has been the standard ansatz to describe the interaction between electrons and nuclei since the early days of quantum mechanics. ABO assumes that the lighter electrons adjust adiabatically to the motion of the heavier nuclei, remaining at any time in their instantaneous ground state. ABO is well justified when the energy gap between ground and excited electronic states is larger than the energy scale of the nuclear motion. In metals, the gap is zero and phenomena beyond ABO (such as phonon-mediated superconductivity or phonon-induced renormalization of the electronic properties) occur. The use of ABO to describe lattice motion in metals is, therefore, questionable. In spite of this, ABO has proved effective for the accurate determination of chemical reactions, molecular dynamics and phonon frequencies in a wide range of metallic systems. Here, we show that ABO fails in graphene. Graphene, recently discovered in the free state, is a zero-bandgap semiconductor that becomes a metal if the Fermi energy is tuned applying a gate voltage, Vg. This induces a stiffening of the Raman G peak that cannot be described within ABO.

Ambient noise Rayleigh wave tomography across Europe

Abstract: SUMMARY We extend ambient noise surface wave tomography both in bandwidth (10‐50 s period) and in geographical extent (across much of Europe) compared with previous applications. 12 months of ambient noise data from 2004 are analysed. The data are recorded at about 125 broadband Seismic stations from the Global Seismic Network and the Orfeus Virtual European Broad-band seismic Network. Cross-correlations are computed in daily segments, stacked over 1 yr, and Rayleigh wave group dispersion curves from 8 to 50 s period are measured using a phase-matched filter, frequency time analysis technique. We estimate measurement uncertainties using the seasonal variation of the dispersion curves revealed in 3 month stacks. On average, uncertainties in group delays increase with period from ∼ 3t o∼7 s from periods of 10 to 50 s, respectively. Group speed maps at periods from 10 to 50 s are estimated. The resulting path coverage is denser and displays a more uniform azimuthal distribution than from earthquake-emitted surface waves. The fit of the group speed maps to the ambient noise data is significantly improved below 30 s compared to the fit achieved with earthquake data. Average resolution is estimated to be about 100 km at 10 s period, but degrades with increasing period and toward the periphery of the study region. The resulting ambient noise group speed maps demonstrate significant agreement with known geological and tectonic features. In particular, the signatures of sedimentary basins and crustal thickness are revealed clearly in the maps. These results are evidence that surface wave tomography based on crosscorrelations of long time-series of ambient noise data can be achieved over a broad period band on nearly a continental scale and yield higher resolution and more reliable group speed maps than based on traditional earthquake-based measurements.

Phonon anharmonicities in graphite and graphene.

Abstract: We determine from first principles the finite-temperature properties-linewidths, line shifts, and lifetimes-of the key vibrational modes that dominate inelastic losses in graphitic materials. In graphite, the phonon linewidth of the Raman-active E(2g) mode is found to decrease with temperature; such anomalous behavior is driven entirely by electron-phonon interactions, and does not appear in the nearly degenerate infrared-active E(1u) mode. In graphene, the phonon anharmonic lifetimes and decay channels of the A(1)' mode at K dominate over E(2g) at Gamma and couple strongly with acoustic phonons, highlighting how ballistic transport in carbon-based interconnects requires careful engineering of phonon decays and thermalization.

Exponential localization of Wannier functions in insulators.

Abstract: The exponential localization of Wannier functions in two or three dimensions is proven for all insulators that display time-reversal symmetry, settling a long-standing conjecture Our proof relies on the equivalence between the existence of analytic quasi-Bloch functions and the nullity of the Chern numbers (or of the Hall current) for the system under consideration The same equivalence implies that Chern insulators cannot display exponentially localized Wannier functions An explicit condition for the reality of the Wannier functions is identified

Dynamic control on serpentine crystallization in veins: Constraints on hydration processes in oceanic peridotites

Abstract: Deformation and hydration processes are intimately linked in the oceanic lithosphere, but the feedbacks between them are still poorly understood, especially in ultramafic rocks where serpentinization results in a decrease of rock density that implies a volume increase and/or mass transfer. Serpentinization is accompanied by abundant veining marked by different generations of vein-filling serpentines with a high variety of morphologies and textures that correspond to different mechanisms and conditions of formation. We use these veins to constrain the role of deformation and mass transfer processes during hydration of oceanic peridotites at slow-spreading ridges. We have selected a representative set of veins from ocean floor serpentinites of the Mid-Atlantic Ridge near Kane transform fault (23°N) and characterized these in detail for their microstructures and chemistry by coupling optical and electron microscopy (SEM, TEM) with electron microprobe analyses. Four main veining episodes (V1 to V4) accompany the serpentinization. The first episode, identified as vein generation V1, is interpreted as the tectonically controlled penetration of early seawater-dominated fluid within peridotites, enhancing thermal cracking and mesh texture initiation at 3–4 km up to 8 km depth and at T <300–350°C. The two following vein stages (V2 and V3) formed in a closed, diffusive system and accommodate volume expansion required to reach almost 50% serpentinization of the protolith. The cracks exploited by these veins were caused by the progressive unroofing at depths of ∼4 to ∼2 km along a detachment fault. Degree and rate of serpentinization seem to be controlled by the capacity of the system to create space and to drive the mass transfer needed for ongoing serpentinization, and this capacity is in turn linked to the exhumation rate and local tectonics. During this period, water consumed by hydration may prevent the establishment of convective hydrothermal cells. The onset of an open hydrothermal system in the shallow lithosphere (<2 km), where brittle fracturing and advective transfer dominate and enable the completion of serpentinization, is marked by the last vein generation (V4). These results show a complete history of alteration, with the crystallization of different types of serpentine recording different tectonic events, chemical conditions, and modes of hydrothermal alteration of the lithosphere.

Surface wave tomography of the western United States from ambient seismic noise: Rayleigh wave group velocity maps

Abstract: We have applied ambient noise surface wave tomography to data that have emerged continuously from the EarthScope USArray Transportable Array (TA) between October 2004 and January 2007 Estimated Green's functions result by cross-correlating noise records between every station-pair in the network The 340 stations yield a total of more than 55,000 interstation paths Within the 5- to 50-s period band, we measure the dispersion characteristics of Rayleigh waves using frequency-time analysis High-resolution group velocity maps at 8-, 16-, 24-, 30-, and 40-s periods are presented for the western United States The footprint of the TA encloses a region with a resolution of about the average interstation spacing (∼70 km) Velocity anomalies in the group velocity maps correlate well with the dominant geological features of the western United States Coherent velocity anomalies are associated with the Sierra Nevada, Peninsular, and Cascade Ranges, Great Valley, Salton Trough, and Columbia basins, the Columbia River flood basalts, the Snake River Plain and Yellowstone, and mantle wedge features associated with the subducting Juan de Fuca plate

Feasibility study of rock identification at the surface of Mars by remote laser-induced breakdown spectroscopy and three chemometric methods

Abstract: The ChemCam instrument that will equip the Mars Science Laboratory (MSL) rover uses laser-induced breakdown spectroscopy (LIBS) to remotely identify Martian rocks in the proximity of the rover, and to quantitatively assess their composition. Sample identification is then the first step of the chemical analysis, as a decision aid for monitoring the rover and/or before a subsequent composition measurement. In this paper we analyze our experimental spectra obtained in the laboratory by three chemometric methods—principal components analysis (PCA), soft independent modeling of class analogy (SIMCA) and partial least-squares discriminant analysis (PLS-DA)—to investigate the feasibility of rocks classification by remote LIBS. If PCA is very interesting for data visualization, SIMCA and PLS-DA enable the making of automatic predictions. We show that SIMCA is less sensitive than PLS-DA, but also more robust when it encounters spectra of an unknown rock. The instrument accuracy during MSL operations will benefit from a combination of the two approaches.

Complete in situ stress determination in an argillite sedimentary formation

Abstract: Andra has conducted a very comprehensive investigation on the in situ stress field within an argillite formation interbeded between two stiffer limestone formations, for the development of its underground research laboratory. A series of hydraulic tests has been conducted in boreholes located in the vicinity of the future site. Borehole and shaft convergence measurements were also carried out to analyse the mechanical behaviour of the rock. Throughout the stress measurement campaign, several borehole images have shown breakouts or induced fractures, that have been analysed in terms of in situ stress field, both in the argillite and in the limestone layers. All these reliable data highlight the high dependency of the state of stress on the rheology of the formation. A high ratio between the two horizontal principal stress components – ranging from 1.3 to 2.0 – has been observed in the limestones, whereas the maximum horizontal principal stress component has been found to be close to the lithostatic stress in the clay formation at the main level of the laboratory; i.e. at the 490 m depth.

Doping in Carbon Nanotubes Probed by Raman and Transport Measurements

Abstract: In situ Raman experiments together with transport measurements have been carried out on carbon nanotubes as a function of gate voltage. In metallic tubes, a large increase in the Raman frequency of the $G^-$ band, accompanied by a substantial decrease of its linewidth, is observed with electron or hole doping. In addition, we see an increase in the Raman frequency of the $G^+$ band in semiconducting tubes. These results are quantitatively explained using ab initio calculations that take into account effects beyond the adiabatic approximation. Our results imply that Raman spectroscopy can be used as an accurate measure of the doping of both metallic and semiconducting nanotubes.

Traveltime measurements from noise correlation: stability and detection of instrumental time-shifts

Abstract: We test the feasibility of using Green's functions extracted from records of ambient seismic noise to monitor temporal changes in the Earth crust properties by repeated measurements at regional distances. We use about 11 yr of continuous recordings to extract surface waves between three pairs of stations in California. The correlations are computed in a moving 1-month window and we analyse the temporal evolution of measured interstation traveltimes. The comparison of the arrival times in the positive and negative correlation time of Rayleigh and Love waves allows us to separate time-shifts associated with any form of physical change in the medium, those resulting from clock drift or other instrumental errors, and those due to change in the localization of the noise sources. This separation is based on the principle of time symmetry. When possible, we perform our analysis in two different period bands: 5–10 and 10–20 s. The results indicate that significant instrumental time errors (0.5 s) are present in the data. These time-shifts can be measured and tested by closure relation and finally corrected independently of any velocity model. The traveltime series show a periodic oscillation that we interpret as the signature of the seasonal variation of the region of origin of the seismic noise. Between 1999 and 2005, the final arrival time fluctuations have a variance of the order of 0.01 s. This allows us to measure interstation traveltimes with errors smaller than 0.3 per cent of the interstation traveltime and smaller than 1 per cent of the used wave period. This level of accuracy was not sufficient to detect clear physical variation of crustal velocity during the considered 11 yr between the three stations in California. Such changes may be more easily detectable when considering pairs of stations more closely located to each other and in the vicinity of tectonically active faults or volcanoes.

Local Al site distribution in aluminosilicate glasses by 27Al MQMAS NMR

Abstract: Coordination and local environment around Al in glasses and liquids is a long-standing question, which has been a controversial issue in geochemistry and glass science. Nuclear magnetic resonance at high-field (750 MHz) was employed to investigate the geochemically and industrially important CaO–Al2O3–SiO2 system. We show that Al remains mainly in tetrahedral position in glasses, however, the presence of five-fold coordinated aluminum is the general rule throughout the ternary CaO–SiO2–Al2O3 system, except for the low silica percalcic region. The proportion of five-fold (AlV) and six-fold (AlVI) coordinated Al was quantified to determine the effects of composition overall the peralkaline part. Moreover our results indicate that Al may occupy more polymerized positions than Si. These two findings do put new questions to the modeling/understanding of these glasses and their parent liquids.

Fault interactions in the Sea of Marmara pull‐apart (North Anatolian Fault): earthquake clustering and propagating earthquake sequences

Abstract: SUMMARY Knowledge on large earthquakes (M ≥ 7.0), geology and fault kinematics is used to analyse conditions that favour isolated seismicity, clustered earthquakes or propagating sequences along the North Anatolian Fault (NAF) and the Sea of Marmara pull-apart. The overall NAF‐ Marmara fault system is one of the most appropriate on Earth to document fault interactions because reliable information covers almost completely two seismic cycles (the past ∼500 yr). Coulomb stress analysis is used to characterize loading evolution in well-identified fault segments, including secular loading from below and lateral loading imposed by the occurrence of previous earthquakes. Earthquakes along the NAF tend to occur where previous events have increased the stress, but significant isolated events in the Sea of Marmara region (1894, 1912) have occurred, suggesting the secular loading has been the determining factor. Present-day loading appears to be particularly high along the 70-km-long segment located in the central Marmara Sea, southwest of Istanbul. For the 18th century M ≥ 7.0 earthquake clusters, we construct scenarios consistent with the tectonic and historical data. We find that scenarios consistent with slip deficit and secular loading distributions (from below) clearly involve a sequence that propagates westward through the Sea of Marmara, despite the structural complexity. However, the inference of a propagating sequence implies that each event has occurred in a segment previously stressed by lateral Coulomb stress interactions. The most likely scenarios for the propagating sequence are also consistent with Coulomb stress interactions between faults with significant normal slip across the Cinarcik basin. Propagating earthquake sequences do not occur every seismic cycle along the NAF. The loading has to be in a particular state of stress close to failure and uniform all along the fault segments to experience propagating earthquake sequences. Non-uniform stress relief during the 18th century sequence explains the occurrence of isolated events in Marmara in 1894 and 1912. As a consequence, the wellknown 20th century sequence along the NAF has not propagated as a sequence across the Sea of Marmara. The most linear part of the NAF across northern Turkey behaves as a single fault segment, accumulating stress during hundreds of years and rupturing entirely during very short periods. The Marmara pull-apart fault system behaves as a major geometric complexity, stopping or delaying the progression of earthquake clustering and propagating sequences. Fault zones interact with each other at a very large scale.

Sulfur behavior in silicate glasses and melts: Implications for sulfate incorporation in nuclear waste glasses as a function of alkali cation and V2O5 content

Abstract: The presence of sulfur in radioactive waste to be incorporated in borosilicate glasses entails difficulties mainly due to the relatively low solubility of sulfates in the vitreous phase. In this work a study is presented on the effects of the ratio R = [Na2O]/[B2O3], the type of sulfate added and the addition of V2O5 on the incorporation of sulfates in borosilicate glasses. Glass samples were prepared at the laboratory scale (up to 50–100 g) by melting oxide and sulfate powders under air in Pt/Au crucibles. XRF and ICP/AES chemical analysis, SEM/EDS, microprobe WDS and Raman spectroscopy were employed to characterize the fabricated samples. The main experimental results confirm that the incorporation of sulfates in borosilicate glasses is favored by the network depolymerization, which evolves with the ratio R. The addition of V2O5 seems to accelerate the kinetics of sulfur incorporation in the glass and, probably, increase the sulfate solubility by modifying the borate network and fostering the formation of voids of shape and size compatible with the sulfur coordination polyhedron in the glassy network. The kinetics of X2SO4 incorporation in the glass seems to be slower when X = Cs.

Decoupling of arsenic and iron release from ferrihydrite suspension under reducing conditions: a biogeochemical model

Abstract: High levels of arsenic in groundwater and drinking water are a major health problem. Although the processes controlling the release of As are still not well known, the reductive dissolution of As-rich Fe oxyhydroxides has so far been a favorite hypothesis. Decoupling between arsenic and iron redox transformations has been experimentally demonstrated, but not quantitatively interpreted. Here, we report on incubation batch experiments run with As(V) sorbed on, or co-precipitated with, 2-line ferrihydrite. The biotic and abiotic processes of As release were investigated by using wet chemistry, X-ray diffraction, X-ray absorption and genomic techniques. The incubation experiments were carried out with a phosphate-rich growth medium and a community of Fe(III)-reducing bacteria under strict anoxic conditions for two months. During the first month, the release of Fe(II) in the aqueous phase amounted to only 3% to 10% of the total initial solid Fe concentration, whilst the total aqueous As remained almost constant after an initial exchange with phosphate ions. During the second month, the aqueous Fe(II) concentration remained constant, or even decreased, whereas the total quantity of As released to the solution accounted for 14% to 45% of the total initial solid As concentration. At the end of the incubation, the aqueous-phase arsenic was present predominately as As(III) whilst X-ray absorption spectroscopy indicated that more than 70% of the solid-phase arsenic was present as As(V). X-ray diffraction revealed vivianite Fe(II)3(PO4)2.8H2O in some of the experiments. A biogeochemical model was then developed to simulate these aqueous- and solid-phase results. The two main conclusions drawn from the model are that (1) As(V) is not reduced during the first incubation month with high Eh values, but rather re-adsorbed onto the ferrihydrite surface, and this state remains until arsenic reduction is energetically more favorable than iron reduction, and (2) the release of As during the second month is due to its reduction to the more weakly adsorbed As(III) which cannot compete against carbonate ions for sorption onto ferrihydrite. The model was also successfully applied to recent experimental results on the release of arsenic from Bengal delta sediments.

415W Single-Mode CW Thulium Fiber Laser in all-fiber format

Abstract: High power Tm lasers at 2um region is a great source of interest for many application including optical pumping of hybrid (fiber-solid state) lasers, bio-medical, remote sensing and plastic welding. Cladding-pumped single-mode Tm-doped fiber lasers demonstrate significant advantages over solid state Tm lasers. Over last several years multiple groups [1,2] using different techniques demonstrated power scaling of fiber bas ed Tm laser to above 100W level. In this paper, we report a development of a single mode all-fiber format Tm fiber laser with M -value of < =1.1, emission linewidth of <1 nm at 1940nm and output power exceeding 400W CW. This is a highest CW output power for a single-mode Tm fiber laser reported up to date.

The biogeochemistry of mercury at the sediment–water interface in the Thau lagoon. 1. Partition and speciation

Abstract: Solid sediment, pore and epibenthic waters were collected from the Thau lagoon (France) in order to study the post-depositional partition and mobility of mercury in organic rich sediment. Total Hg (HgT) and monomethylmercury (MMHg) profiles were produced in both dissolved and solid phases. The distribution of HgT in the solid phase appeared to be related to the historical changes in the Hg inputs into the lagoon. HgT was in equilibrium between solid and solution phases in the sulfidic part of the cores, with a mean log Kd of 4.9 ± 0.2. The solid phase appeared to be a source of HgT for pore water in the upper oxic to suboxic parts of the cores. The MMHg represented a small fraction of HgT: 3–15% and 0.02–0.80% in the dissolved and solid phases, respectively. Its distribution was characterized by a main peak in the superficial sediments, and another deeper in the core within the sulfide-accumulating zone. In addition, high dissolved MMHg concentrations and methylated percentage were found in the epibenthic water. Ascorbate (pH 8) dissolution of the sediments and analyses of the soluble fraction suggest that the amorphous oxyhydroxides played a major role in controlling total and methylmercury mobility throughout the sediment–water interface. These features are discussed in terms of sources, transfer and transformations. Diffusive fluxes of HgT and MMHg from sediment to the water column for the warm period were estimated to be 40 ± 15 and 4 ± 2 pmol m−2 d−1, respectively.

Interplay between faults and lava flows in construction of the upper oceanic crust : the East Pacific Rise crest 9°25′–9°58′N

Abstract: The distribution of faults and fault characteristics along the East Pacific Rise (EPR) crest between 9°25′N and 9°58′N were studied using high-resolution side-scan sonar data and near-bottom bathymetric profiles. The resulting analysis shows important variations in the density of deformational features and tectonic strain estimates at young seafloor relative to older, sediment-covered seafloor of the same spreading age. We estimate that the expression of tectonic deformation and associated strain on “old” seafloor is ∼5 times greater than that on “young” seafloor, owing to the frequent fault burial by recent lava flows. Thus the unseen, volcanically overprinted tectonic deformation may contribute from 30% to 100% of the ∼300 m of subsidence required to fully build up the extrusive pile (Layer 2A). Many longer lava flows (greater than ∼1 km) dam against inward facing fault scarps. This limits their length at distances of 1–2 km, which are coincident with where the extrusive layer acquires its full thickness. More than 2% of plate separation at the EPR is accommodated by brittle deformation, which consists mainly of inward facing faults (∼70%). Faulting at the EPR crest occurs within the narrow, ∼4 km wide upper crust that behaves as a brittle lid overlying the axial magma chamber. Deformation at greater distances off axis (up to 40 km) is accommodated by flexure of the lithosphere due to thermal subsidence, resulting in ∼50% inward facing faults accommodating ∼50% of the strain. On the basis of observed burial of faults by lava flows and damming of flows by fault scarps, we find that the development of Layer 2A is strongly controlled by low-relief growth faults that form at the ridge crest and its upper flanks. In turn, those faults have a profound impact on how lava flows are distributed along and across the ridge crest.

Pits, rifts and slumps: the summit structure of Piton de la Fournaise

Abstract: A clear model of structures and associated stress fields of a volcano can provide a framework in which to study and monitor activity. We propose a volcano-tectonic model for the dynamics of the summit of Piton de la Fournaise (La Reunion Island, Indian Ocean). The summit contains two main pit crater structures (Dolomieu and Bory), two active rift zones, and a slumping eastern sector, all of which contribute to the actual fracture system. Dolomieu has developed over 100 years by sudden large collapse events and subsequent smaller drops that include terrace formation. Small intra-pit collapse scars and eruptive fissures are located along the southern floor of Dolomieu. The western pit wall of Dolomieu has a superficial inward dipping normal fault boundary connected to a deeper ring fault system. Outside Dolomieu, an oval extension zone containing sub-parallel pit-related fractures extends to a maximum distance of 225 m from the pit. At the summit the main trend for eruptive fissures is N80°, normal to the north–south rift zone. The terraced structure of Dolomieu has been reproduced by analogue models with a roof to width ratio of approximately 1, suggesting an original magma chamber depth of about 1 km. Such a chamber may continue to act as a storage location today. The east flank has a convex–concave profile and is bounded by strike-slip fractures that define a gravity slump. This zone is bound to the north by strike-slip fractures that may delineate a shear zone. The southern reciprocal shear zone is probably marked by an alignment of large scoria cones and is hidden by recent aa lavas. The slump head intersects Dolomieu pit and may slide on a hydrothermally altered layer known to be located at a depth of around 300 m. Our model has the summit activity controlled by the pit crater collapse structure, not the rifts. The rifts become important on the mid-flanks of the cone, away from pit-related fractures. On the east flank the superficial structures are controlled by the slump. We suggest that during pit subsidence intra-pit eruptions may occur. During tumescence, however, the pit system may become blocked and a flank eruption is more likely. Intrusions along the rift may cause deformation that subsequently increases the slump’s potential to deform. Conversely, slumping may influence the east flank stress distribution and locally control intrusion direction. These predictions can be tested with monitoring data to validate the model and, eventually, improve monitoring.

Thermochemistry and melting properties of basalt

Abstract: The heat capacities of the liquid, glassy and crystalline phases of an alkali basalt have been determined from relative enthalpies measured between 400 and 1,800 K. Values given by available models of calculation generally agree to within 2% of these results. As derived from the new data and the enthalpy of vitrification measured at 973 K by oxide-melt drop solution calorimetry for the same sample, the enthalpy of fusion of this basalt increases from 15.4 kJ/mol at 1,000 K to 33.6 kJ/mol at 1,800 K. Comparisons between the enthalpies of fusion of basalt and model compositions confirm the small magnitude of the enthalpy of mixing between the molten mineral components of the liquids. Minor variations in the chemical composition have only a small effect in the heat capacity and the enthalpy of melting of basalt. The enthalpies of formation at 298 K from the oxides of the crystallized and glass phases of this alkali basalt are −112.2 and −98.5 kJ/mol, respectively, for a gram formula weight based on one mole of oxide components.

Rheological characterization of a sedimentary formation from a stress profile inversion

Abstract: SUMMARY Detailed stress measurements have been carried out within a sedimentary sequence composed of a hard-clay formation laying horizontally between two limestone units, in the eastern Paris basin (France). Orientations of the minor and major horizontal principal stresses are found to be in good agreement with the direction of major shortening that prevailed during the last tectonic stage. However, their magnitudes exhibit an intriguing evolution with depth. While the magnitude of the maximum horizontal stress slowly but regularly increases with depth, the magnitude of the minimum horizontal one is larger in the hard-clay formation than in the surrounding limestone units, contrary to expectation from simple elastic considerations. An analytical calculation demonstrates that the genesis of the current stress state may be reproduced by taking into account horizontal strains in two different directions and simulating erosion of part of the overburden with a viscoelastic model for the hard clay and an elastic behaviour for the limestone. However, the elastic constants that are derived for the limestone in order to fit the measured stress field correspond to a material that is more deformable and has a lower Poisson's ratio than predicted by laboratory tests. This discrepancy may be explained by a slow, long-term, deformation process in the limestone, possibly associated with pressure solution.

Powerful fiber laser system

Abstract: A powerful fiber laser system is configured with at least one large-area multi-clad rare-earth doped fiber, which is configured with a MM core capable of propagating a single mode laser emission at a first wavelength, and with at least one pumping assembly capable of generating an optical pump output at a wavelength shorter than the first wavelength of the rare-earth doped fiber. The pumping assembly has a plurality SM fiber lasers coupled to a SM-MM combiner which is operative to lunch the pump output into the cladding of the rare-earth doped fiber so that the powerful fiber laser system is operative to deliver a power of up to 20 kW.

Creating Habitable Zones, at all Scales, from Planets to Mud Micro-Habitats, on Earth and on Mars

Abstract: The factors that create a habitable planet are considered at all scales, from planetary inventories to micro-habitats in soft sediments and intangibles such as habitat linkage. The possibility of habitability first comes about during accretion, as a product of the processes of impact and volatile inventory history. To create habitability water is essential, not only for life but to aid the continual tectonic reworking and erosion that supply key redox contrasts and biochemical substrates to sustain habitability. Mud or soft sediment may be a biochemical prerequisite, to provide accessible substrate and protection. Once life begins, the habitat is widened by the activity of life, both by its management of the greenhouse and by partitioning reductants (e.g. dead organic matter) and oxidants (including waste products). Potential Martian habitats are discussed: by comparison with Earth there are many potential environmental settings on Mars in which life may once have occurred, or may even continue to exist. The long-term evolution of habitability in the Solar System is considered.

Multiyear validation of the NRL-G2S wind fields using infrasound from Yasur

Abstract: The Yasur volcano in the Vanuatu archipelago is an outstanding source of infrasonic waves due to its regular activity. This volcano is permanently monitored by the IS22 infrasound station located in New Caledonia, about 400 km from it, and by one microbarometer installed close to its crater. A multiyear monitoring of Yasur is proposed to validate consistently the Naval Research Laboratory Ground to Space (NRL-G2S) semiempirical atmospheric model up to the stratosphere. The results of propagation modeling accurately explain seasonal changes as well as small short-timescale variations of the infrasonic observables. The azimuthal deviation is predicted with an uncertainty in general lower than 0.5°. The fluctuations of the trace velocity and the celerity are simulated with errors as large as 5 m/s. This study demonstrates that the use of appropriate propagation tools along with the NRL-G2S specifications provides accurate enough results for most of the long-range observations for the purpose of operational infrasound monitoring.

Method and device for controlling optical output of laser diode

Abstract: A method of controlling an optical output of a laser diode includes applying a bipolar current pulse to the laser diode, thereby substantially suppressing the emission tail of the optical output of the laser diode. A device for generating sub-nanosecond intense optical pulses includes a driver unit operative to generate a plurality of bipolar current pulses, and a semiconductor laser diode driven by the bipolar current pulses and operative to emit the intense optical pulses each of which has a substantially suppressed or completely eliminated emission tail.