Comprehensive Modeling of Multimode Fiber Sensors for Refractive Index Measurement and Experimental Validation

We propose and develop a comprehensive model for estimating the refractive index (RI) response over three potential sensing zones in a multimode fiber. The model has been developed based on a combined ray optics, Gaussian beam, and wave optics analysis coupled to the consideration of the injected interrogating lightwave characteristics and validated experimentally through the realization of three sensors with different lengths of stripped cladding sections as the sensing region. The experimental results highly corroborate and validate the simulation output from the model for the three RI sensing zones. The sensors can be employed over a very wide dynamic RI range from 1.316 to over 1.608 at a wavelength of 1550 nm, with the best resolution of 2.2447 × 10−5 RI unit (RIU) obtained in Zone II for a 1-cm sensor length

Sensors and technologies for in situ dissolved methane measurements and their evaluation using Technology Readiness Levels

Dissolved methane measurements rely on the time-consuming collection of discrete water samples followed by gas-chromatography analysis. To date, this approach has proved useful for broad interpretation of environmental processes. However, it limits comprehension of environmental processes that are highly variable in space and or time. This has led to increased interest in in situ dissolved methane sensors to augment data from point sampling.So far, three sensing strategies have been explored using:1) gas-phase measurements after gas extraction through semi-permeable silicon membranes;2) measurements using biosensors; and,3) optical measurements (e.g., surface-plasmon resonance and surface-enhanced Raman spectroscopy).Optical measurements may represent the future for in situ dissolved methane sensing.We review and evaluate different in situ methane sensors and technologies using Technology Readiness Levels

CH4 versus H2 dominated gas venting during serpentinisation reactions. The example of Oman, Voltri and New Caledonia ophiolites

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Characterization of hyperalkaline fluids produced by low-temperature serpentinization of mantle peridotites in the Oman and Ligurian ophiolites

International audienceA regional survey of alkaline springs in Oman and Ligurian ophiolites shows that the alkaline water compositions significantly vary from one ophiolite to the other and within the same ophiolite. The first-order correlation between the Na (and K) and Cl concentrations points to fluid compositions only partly due to evaporation. The scatter around the evaporation line implies that Na and Cl may not be conservative during the alteration of the ultramafic rocks. Mg is almost entirely depleted at pH > 10.5 as a result of serpentine formation within the ultramafic body and of brucite (and minor hydrotalcite) precipitation at the springs. Ca accumulates in the high-pH fluids and is consumed by Ca-carbonate formation at the springs, by mixing with river waters or by the CO2 supply from the atmosphere. Thermodynamic calculations show that brucite saturation is reached at pH values around 10.5 which triggers major changes in the water composition. The waters evolve from a quartz-saturated low-pH continental environment to a brucite-dominated high-pH serpentinizing system at low temperature. The highest water salinities are found in springs located along the basal thrust plane of the ophiolite. The highest Al concentrations are found in some springs located on the crustal side of the mantle/crust boundary. This poses the question of the hydrologic pathways and of the role of the mineralogical composition of the altered formations. Key Points New temperature and composition of the alkaline waters Brucite formation at pH 10.5 triggers major chemical and mineralogical changes Relationship between the water compositions and the hydrologic pathway

Mineralogical assemblages forming at hyperalkaline warm springs hosted on ultramafic rocks: A case study of Oman and Ligurian ophiolites

International audienceWe report on the mineralogical assemblages found in the hyperalkaline springs hosted on Liguria and Oman ophiolites based on exhaustive X-ray diffraction and scanning electron microprobe analyses. In Liguria, hyperalkaline springs produce a thin brownish calcite precipitate that covers the bedrock due to the concomitant atmospheric CO2 uptake and neutralization of the hyperalkaline waters. No brucite and portlandite minerals are observed. The discharge of alkaline waters in Oman ophiolite forms white-orange precipitates. Calcium carbonate minerals (calcite and/or aragonite) are the most abundant and ubiquitous precipitates and are produced by the same mechanism as in Liguria. This process is observed as a thin surface crust made of rhombohedral calcite. Morphological features of aragonite vary from needle-, bouquet-, dumbbell-, spheroidal-like habitus according to the origin of carbon, temperature, and ionic composition of the hyperalkaline springs, and the biochemical and organic compounds. Brucite is observed both at hyperalkaline springs located at the thrust plane and at the paleo-Moho. The varying mixing proportions between the surface runoff waters and the hyperalkaline ones control brucite precipitation. The layered double hydroxide minerals occur solely in the vicinity of hyperalkaline springs emerging within the bedded gabbros. Finally, the dominant mineralogical associations we found in Oman (Ca-bearing carbonates and brucite) in a serpentinizing environment driven by the meteoric waters are surprisingly the same as those observed at the Lost City hydrothermal site in a totally marine environment. Key Points Distinct mineralogical association between Oman and liguria alkaline springs There is no Mg-bearing carbonate similar mineral assemblage in marine and surface serpentinizing environmen

Low Power Hydrogen Sensors Using Electrodeposited PdNi Schottky Diodes

The use of electrodeposited PdNi Schottky barriers as low power Hydrogen sensors is investigated. Electrodeposited PdNi Schottky barriers exhibit very low reverse bias current and the Palladium content of the film causes the Hydrogen molecules to dissociate and be absorbed by the film, changing the metal work function and device current. The Schottky diodes were fabricated on 0.5-1.5 Ohmcm (100) n-type Si by electrodeposition of PdNi followed by evaporation of Aluminium contact pads. Electrical measurements at different Hydrogen pressures were performed on back to back Schottky diodes in a vacuum chamber using pure Nitrogen and a 5% Hydrogen-Nitrogen mixture. Very low currents of 1nA were measured in the absence of Hydrogen. Large increases in the currents, upto a factor of 100, were observed upon exposure to different Hydrogen partial pressures. The highest sensitivity was estimated to be 17.27 nA/mbar. The low idle current, simplicity of fabrication process and ability to easily integrate with conventional electronics proves the suitability of electrodeposited PdNi Schottky barriers as low power Hydrogen sensors

Genetic susceptibility to alcoholic liver disease

A new method for in-situ detection and measurement of dissolved methane in aqueous media/environments with a limit of detection of 0.2 nM (3?, and t90~110s) and range (1-300 nM) is presented. The detection method is based on refractive index (RI) modulation of a modified PolyDiMethylSiloxane (PDMS) layer incorporating molecules of cryptophane-A [1] which have a selective and reversible affinity for methane [2]. The refractive index is accurately determined using surface plasmon resonance (SPR) [3]. A prototype sensor has been repeatedly tested, using a dissolved gas calibration system under a range of temperature and salinity regimes. Laboratory-based results show that the technique is specific, sensitive, and reversible. The method is suitable for miniaturization and incorporation into in situ sensor technology

Fluid circulation along an oceanic detachment fault: insights from fluid inclusions in silicified brecciated fault rocks (Mid-Atlantic Ridge at 13°20'N)

International audienceThe MAR 13°20′N corrugated detachment fault is composed of pervasively silicified mafic cataclastic breccias, instead of ultramafics and gabbros commonly found at other detachments. These breccias record overplating of hangingwall diabases, with syntectonic silicification due to important influx of silica‐iron‐rich fluids, able to leach alkalis and calcium. Fluids trapped in quartz inclusions show important salinity variations (2.1–10 wt.% NaCl eq.) indicating supercritical phase separation. Fluid inclusions also contain minor amounts of H2 ± CO2 ± CH4 ± H2S, with high H2/CO2 and H2/H2S ratios, signatures typical of ultramafic‐hosted vent fluids. We propose that seawater infiltrated the hangingwall upper crust at the axis adjacent to the active detachment, reaching a reaction zone at the dyke complex base (∼2 km). At >500°C, fluids become Si‐rich during diabase alteration (amphibolite‐facies alteration in clasts), and undergo phase separation. Brines, preferentially released in the nearby detachment fault during diabase brecciation, mix with serpentinite‐derived fluids bearing H2 and CH4. Cooling during detachment deformation and fluid upward migration triggers silica precipitation at greenschist‐facies conditions (quartz + Fe‐rich‐chlorite ± pyrite). Important variations in fluid inclusion salinity and gas composition at both sample and grain scales record heterogeneous fluid circulation at small spatial and short temporal scales. This heterogeneous fluid circulation operating at <2 km depth, extending both along‐axis and over time, is inconsistent with models of fluids channeled along detachments from heat sources at the base of the crust at the fault root. Present‐day venting at detachment footwall, including Irinovskoe, is instead likely underlain by fluid circulation within the footwall, with outflow crossing the inactive detachment fault near‐surface

Fluid chemistry of the low temperature hyperalkaline hydrothermal system of Prony Bay (New Caledonia)

The terrestrial hyperalkaline springs of Prony Bay (southern lagoon, New Caledonia) have been known since the nineteenth century, but a recent high-resolution bathymetric survey of the seafloor has revealed the existence of numerous submarine structures similar to the well-known Aiguille de Prony, which are also the location of high-pH fluid discharge into the lagoon. During the HYDROPRONY cruise (28 October to 13 November 2011), samples of waters, gases and concretions were collected by scuba divers at underwater vents. Four of these sampling sites are located in Prony Bay at depths up to 50 m. One (Bain des Japonais spring) is also in Prony Bay but uncovered at low tide and another (Rivière des Kaoris spring) is on land slightly above the seawater level at high tide. We report the chemical composition (Na, K, Ca, Mg, Cl, SO4, dissolved inorganic carbon, SiO2(aq)) of 45 water samples collected at six sites of high-pH water discharge, as well as the composition of gases. Temperatures reach 37 °C at the Bain des Japonais and 32 °C at the spring of the Kaoris. Gas bubbling was observed only at these two springs. The emitted gases contain between 12 and 30% of hydrogen in volume of dry gas, 6 to 14% of methane, and 56 to 72% of nitrogen, with trace amounts of carbon dioxide, ethane and propane. pH values and salinities of all the 45 collected water samples range from the seawater values (8.2 and 35 g L−1) to hyperalkaline freshwaters of the Ca-OH type (pH 11 and salinities as low as 0.3 g L−1) showing that the collected samples are always a mixture of a hyperalkaline fluid of meteoric origin and ambient seawater. Cl-normalized concentrations of dissolved major elements first show that the Bain des Japonais is distinct from the other sites. Water collected at this site are three component mixtures involving the high-pH fluid, the lagoon seawater and the river water from the nearby Rivière du Carénage. The chemical compositions of the hyperalkaline endmembers (at pH 11) are not significantly different from one site to the other although the sites are several kilometres away from each other and are located on different ultramafic substrata. The very low salinity of the hyperalkaline endmembers shows that seawater does not percolate through the ultramafic formation. Mixing of the hyperalkaline hydrothermal endmember with local seawater produces large ranges and very sharp gradients of pH, salinity and dissolved element concentrations. There is a major change in the composition of the water samples at a pH around 10, which delimitates the marine environment from the hyperalkaline environment. The redox potential evolves toward negative values at high pH indicative of the reducing conditions due to bubbling of the H2-rich gas. The calculation of the mineral saturation states carried out for the Na-K-Ca-Mg-Cl-SO4-DIC-SiO2-H2O system shows that this change is due to the onset of brucite formation. While the saturation state of the Ca carbonates over the whole pH range is typical of that found in a normal marine environment, Mg- and Mg-Ca carbonates (magnesite, hydromagnesite, huntite, dolomite) exhibit very large supersaturations with maximum values at a pH of around 10, very well marked for the Bain des Japonais, emphasizing the role of water mixing in mineral formation.The discharge of high-pH waters of meteoric origin into the lagoon marine environment makes the hydrothermal system of Prony Bay unique compared to other low temperature serpentinizing environments such as Oman (fully continental) or Lost City (fully marine)

Production d’hydrogène dans les systèmes hydrothermaux hyperalcalins des ophiolites (Oman, Ligurie, Nouvelle Calédonie)

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