2O Concentrations Research Articles

Geochemical Characteristics and Significance of Major Elements, Trace Elements and REE in Mineralized Altered Rocks of Large-Scale Tsagaan Suvarga Cu-Mo Porphyry Deposit in Mongolia

The alteration types of the large-scale Tsagaan Suvarga Cu-Mo porphyry deposit mostly comprise stockwork silicification, argillization, quartz-sericite alteration, K-silicate alteration, and propylitization. The mineralized and altered zones from hydrothermal metallogenic center to the outside successively are Cu-bearing stockwork silicification zone, Cubearing argillized zone, Cu-Mo-bearing quartz-sericite alteration zone, Cu-Mo-bearing K-silicate alteration zone, and propylitization zone. The K-silicate alteration occurred in the early phase, quartz-sericite alteration in the medium phase, and argillization and carbonatization (calcite) in the later phase. Ore-bearing-altered rocks are significantly controlled by the structure and fissure zones of different scales, and NE- and NW-trending fissure zones could probably be the migration pathways of the porphyry hydrothermal system. Results in this study indicated that the less the concentrations of REE, LREE, and HREE and the more the extensive fractionation between LREE and HREE, the closer it is to the center circulatory hydrothermal ore-forming and the more extensive silicification. The exponential relationship between the fractionation of LREE and HREE and the intensity of silicification and K-silicate alteration was found in the Cu-Mo deposit studied. The negative Eu anomaly, normal Eu, positive Eu anomaly and obviously positive Eu anomaly are coincident with the enhancement of Na 2O and K 2O concentrations gradually, which indicated that Eu anomaly would be significantly controlled by the alkaline metasomatism of the circulatory hydrothermal ore-forming system. Therefore, such characteristics as the positive Eu anomaly, the obvious fractionation between LREE and HREE and their related special alteration lithofacies are suggested to be metallogenic prognostic and exploration indications for Tsagaan Suvarga-style porphyry Cu-Mo deposits in Mongolia and China.

Denitrification rate determined by nitrate disappearance is higher than determined by nitrous oxide production with acetylene blockage

A mixed beech and spruce forest soil was incubated under potential denitrification assay (PDA) condition with 10% acetylene (C 2H 2) in the headspace of soil slurry bottles. Nitrous oxide (N 2O) concentration in the headspace, as well as nitrate, nitrite and ammonium concentrations in the soil slurries were monitored during the incubation. Results show that nitrate disappearance rate was higher than N 2O production rate with C 2H 2 blockage during the incubation. Sum of nitrate, nitrite, and N 2O with C 2H 2 blockage could not recover the original soil nitrate content, showing an N imbalance in such a closed incubation system. Changes in nitrite and ammonium concentration during the incubation could not account for the observed faster nitrate disappearance rate and the N imbalance. Non-determined nitric oxide (NO) and N 2 production could be the major cause, and the associated mechanisms could vary for different treatments. Commonly applied PDA measurement likely underestimates the nitrate removal capacity of a system. Incubation time and organic matter/nitrate ratio are the most critical factors to consider using C 2H 2 inhibition technique to quantify denitrification. By comparing the treatments with and without an antibiotic, the results suggest that microbial N uptake probably played a minor role in N balance, and other denitrifying enzymes but nitrate reductase could be substantially synthesized during the incubation.

Seasonal cycle of N 2O vertical distribution and air–sea fluxes over the continental shelf waters off central Chile (∼36°S)

The continental shelf off central Chile is subject to strong seasonal coastal upwelling and has been recognized as an important outgassing area for, amongst others, N 2O, an important greenhouse gas. Several physical and biogeochemical variables, including N 2O, were measured in the water column from August 2002 to January 2007 at a time series station in order to characterize its temporal variability and elucidate the physical and biogeochemical mechanisms affecting N 2O levels. This 4-year time series of N 2O levels reveals seasonal variability associated basically with hydrographic and oceanographic regimes ( i. e., upwelling and non-upwelling). However, a noteworthy temporal evolution of both the vertical distribution and N 2O levels was observed repeatedly throughout the entire study period, allowing us to distinguish three stages: winter/early spring (Stage I), mid-spring/mid-summer (Stage II), and late summer/early autumn (Stage III). Stage I presents low N 2O, the lowest surface saturation ever registered (from 64% saturation) in a period of high O 2, and a homogeneous column driven by strong wind; this distribution is explained by physical and thermodynamic mechanisms. Stage II, with increasing N 2O concentrations, agrees with the appearance of upwelling-favourable wind stress and a strong influence of oxygen-poor, nutrient-rich equatorial subsurface waters (ESSW). The N 2O build-up creates a “hotspot” (up to 2426% N 2O saturation) and enhanced concentrations of NO 2 - (up to 3.97 μM) and NH 4 + (up to 4.6 μM) at the oxycline (4–28 μM) (∼20–40 m depth). Although the dominant N 2O sources could not be determined, denitrification (mainly below the oxycline) appears to be the dominant process in N 2O accumulation. Stage III, with diminishing N 2O concentrations from mid-summer to early autumn, was accompanied by low N/P ratios. During this stage, strong bottom N 2O consumption (from 40% saturation) was suggested to be mainly driven by benthic denitrification. Consistent with the evolution of N 2O in the water column over time, the estimated air–sea N 2O fluxes were low or negative in winter (−9.8 to 20 μmol m −2 d −1, Stage I) and higher in spring and summer (up to 195 μmol m −2 d −1, Stage II), after which they declined (Stage III). In spite of the occurrence of ESSW and upwelling events throughout stages II and III, N 2O behaviour should be a response of the biogeochemical evolution associated with biological productivity and concomitant O 2 levels in the water and even in the sediments. The results presented herein confirm that the study area is an important source of N 2O to the atmosphere, with a mean annual N 2O flux of 30.2 μmol m −2 d −1; however, interannual variability could not yet be properly characterized.

High hydrogen solubility in Al-rich stishovite and water transport in the lower mantle

Stishovite is an important phase in subducting oceanic crust. The post-garnet assemblage from a precursor eclogite lithology contains up to 25% stishovite at pressures above 25 GPa. This stishovite may contain up to 5 wt.% Al 2O 3. We measured the hydrogen contents of stishovite samples synthesized at 20–25 GPa and 1200–1800 °C from several starting materials containing up to 10 wt.% Al 2O 3. FTIR spectra of stishovite show major bands at 3111–3134 cm − 1 , with the frequencies increasing as H 2O and Al 2O 3 contents increase, and several minor bands at 2659–2667, 3240, 3261, 3312–3334, and 3351 cm − 1 . The H 2O content of Al-free stishovite is in the range of 16–30 wt. ppm. The maximum H 2O content of Al-bearing stishovite (4.4 wt.% Al 2O 3) synthesized at 20 GPa and 1400 °C is 3010 ± 300 wt. ppm. Most hydrogen in stishovite is associated with Al 3+ substitutional defects on the octahedral (Si 4+) site. The hydrogen can occupy 40% of vacancies created by incorporation of Al 3+ at 20 GPa. This observation along with some anomalies in the FTIR spectra may indicate an alternative mechanism of Al 3+ incorporation into stishovite via the formation of oxygen vacancies or interstitial Al i defects. We report the highest H 2O concentrations in Al-stishovite to date, and argue that it is the most important carrier of water into the lower mantle post-garnet eclogitic assemblages.

Carbonation of fly ash in oxy-fuel CFB combustion

Oxy-fuel combustion of fossil fuel is one of the most promising methods to produce a stream of concentrated CO 2 ready for sequestration. Oxy-fuel FBC (fluidized bed combustion) can use limestone as a sorbent for in situ capture of sulphur dioxide. Limestone will not calcine to CaO under typical oxy-fuel circulating FBC (CFBC) operating temperatures because of the high CO 2 partial pressures. However, for some fuels, such as anthracites and petroleum cokes, the typical combustion temperature is above 900 °C. At CO 2 concentrations of 80–85% (typical of oxy-fuel CFBC conditions with flue gas recycle) limestone still calcines, but when the ash cools to the calcination temperature, carbonation of fly ash deposited on cool surfaces may occur. This phenomenon has the potential to cause fouling of the heat transfer surfaces in the back end of the boiler, and to create serious operational difficulties. In this study, fly ash generated in a utility CFBC boiler was carbonated in a thermogravimetric analyzer (TGA) under conditions expected in an oxy-fuel CFBC. The temperature range investigated was from 250 to 800 °C with CO 2 concentration set at 80% and H 2O concentrations at 0%, 8% and 15%, and the rate and the extent of the carbonation reaction were determined. Both temperature and H 2O concentrations played important roles in determining the reaction rate and extent of carbonation. The results also showed that, in different temperature ranges, the carbonation of fly ash displayed different characteristics: in the range 400 °C < T ⩽ 800 °C, the higher the temperature the higher the CaO-to-carbonate conversion ratio. The presence of H 2O in the gas phase always resulted in higher CaO conversion ratio than that obtainable without H 2O. For T ⩽ 400 °C, no fly ash carbonation occurred without the presence of H 2O in the gas phase. However, on water vapour addition, carbonation was observed, even at 250 °C. For T ⩽ 300 °C, small amounts of Ca(OH) 2 were found in the final product alongside CaCO 3. Here, the carbonation mechanism is discussed and the apparent activation energy for the overall reaction determined.

The effects of semi-lunar spring and neap tidal change on nitrification, denitrification and N 2O vertical distribution in the intertidal sediments of the Yangtze estuary, China

To explore the influences of semi-lunar spring and neap tidal changes on nitrogen cycling in intertidal sediments, a comparative study among waterlogged, desiccated and reflooded systems was carried out in August 2005 and February 2006 by analyzing nitrification, denitrification and N 2O depth profiles in the intertidal flats of the Yangtze estuary. Laboratory experiments showed that alternating emersion and inundation resulted in the significant changes in nitrification and denitrification rates in the intertidal sediment systems. Due to the desiccation-related effects, lowest nitrification and denitrification rates were observed in the desiccated sediment cores. Highest nitrification and denitrification rates were however detected in the waterlogged and reflooded systems, respectively. It is hypothesized that the highest nitrification rates in the waterlogged sediments were mainly attributed to higher nitrifier numbers and NH 4 + being more available, whereas the availability of NO 3 − might dominate denitrification in the reflooded sediments. In addition, the highest N 2O concentrations were detected in the reflooded sediment cores, and the lowest found in the dried sediment cores. It was also shown that N 2O in the intertidal sediments was mainly from nitrification under the desiccated condition. In contrast, N 2O in the intertidal sediments was produced mainly via denitrification under the waterlogged and reflooded conditions. It is therefore concluded that the semi-lunar tidal cycle has a significant influence on nitrification, denitrification and N 2O production in the intertidal sediment systems.

Electric current induced compositional variation in LiNbO 3 fiber crystal grown by a micro-pulling down method

The electric-field modified partitioning of Li ion species was studied for the growth of LiNbO 3 fiber crystals via a micro-pulling down (μ-PD) method. DC power was applied between the platinum seed and the outlet of a capillary pipe attached to the bottom of the crucible so as to generate a constant electric current. The electric current, passing through the molten zone, the solid–liquid interface and the crystal, induced an electric field near the interface which influences the transport and segregation of ionic species in the melt. The compositional change in terms of mol% Li 2O was examined by measuring the Curie temperature of crystals grown from melts with various compositions. The melt with Li 2O concentration larger than the congruent-melting composition ( k 0 Li 2 O < 1 ) decreased its Li 2O content near the interface by an electric current flowing from the crystal to the melt, while it did not change by the inverse current. In contrast, the melt with Li 2O concentration smaller than the congruent composition ( k 0 Li 2 O > 1 ) increased its Li 2O content by the electric current from the melt to the crystal, while it did not change by the inverse current. The above variation was peculiar to growth via a μ-PD method under an electric field induced by an imposed electric current, which confirmed that the major ionic species driven by the electric field was the Li ion species resulting in a change in the bulk Li 2O concentration both in the melt near the interface and in the grown crystal.

ITO deposited by pyrosol for photovoltaic applications

The goal of this work is to investigate morphology, electrical and optical properties of indium-tin-oxide (ITO) deposited by pyrosol on glass and Si substrates at different temperatures and to implement such layers for the processing of Si-based solar cells. The influence of the methanol/H 2O ratio on general properties of ITO was investigated. Atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission spectra, ellipsometry and resistivity measurements were used for the analysis. It is shown that properties of ITO layers depend dramatically on the substrate used. It is shown that the resistivity of ITO layers deposited on a glass substrate is higher up to 2.5 times, compared to that of ITO layers deposited on a Si substrate at the same conditions, but in both cases decreases if the deposition temperature increases. Moreover, ITO layers deposited on a glass substrate are more flat and their refractive indexes are always lower for all deposition temperatures. An increase of the H 2O concentration in a film-forming solution leads to a decrease of the ITO film resistivity and to a slight increase of the roughness. An application of pyrosol deposited ITO films as the top transparent electrodes for the (p +nn +)Si and heterojunction ITO/n-Si solar cells is demonstrated.

Photocatalytic degradation and mineralization of a malodorous compound (dimethyldisulfide) using a continuous flow reactor

Dimethyldisulfide (DMDS) degradation and mineralization were carried out in a continuous flow reactor using TiO 2-P25 or ZnO as photocatalysts. The efficiency of the disappearance and of the mineralization of the DMDS showed to be very sensitive to the molar flow of the sulphur compounds. In our study, we have evaluated the limit average mineralization rate of DMDS per Watt emitted (for TiO 2-P25). Catalyst deactivation has been observed after several hours of complete DMDS mineralization, which was expressed by the decrease of CO 2 concentration and the appearance of residual DMDS on the outlet side of the reactor. This phenomenon is due to the inhibition of active sites on the catalyst by the formation of sulfates as final sulphur-compounds (determined by ionic chromatography). The FT-IR analysis, performed on catalyst in presence of high DMDS flow, indicated the presence of partial oxidation products such as sulfoxides, sulfones, sulfonates, sulfates and carbonyl groups. All of these disappearing after static irradiation, except for sulfate according to ionic chromatography analysis. The effect of humidity is shown; the data indicated that a detrimental effect occurs depending on the DMDS/H 2O concentration ratio. Comparison of the disappearance and of the mineralization of DMDS in presence of TiO 2-P25, commercial ZnO or home made nano-ZnO catalysts is presented and discussed. Nano-ZnO material, prepared at low temperature, showed an efficiency close to that of TiO 2-P25 while no activity was detected in the presence of commercial ZnO.

Origin of retrograde fluid in ultrahigh-pressure metamorphic rocks: Constraints from mineral hydrogen isotope and water content changes in eclogite–gneiss transitions in the Sulu orogen

By taking advantage of having depth profiles between contrasting lithologies from core samples of the Chinese Continental Scientific Drilling (CCSD) project, a combined study was carried out to examine changes in mineral H isotope, total water and hydroxyl contents in garnet and omphacite across the contacts between ultrahigh-pressure (UHP) eclogite and gneiss in the Sulu orogen, east-central China. The samples of interest were from two continuous core segments from the CCSD main hole at depths of 734.21–737.16 and 929.67–932.86 m, respectively. The results show δD values of −116‰ to − 64‰ for garnet and −104‰ to −82‰ for omphacite, consistent with incorporation of meteoric water into protoliths of UHP metamorphic rocks by high-T alteration. Both equilibrium and disequilibrium H isotope fractionations were observed between garnet and omphacite, suggesting fluid-assisted H isotope exchange at local scales during amphibolite-facies retrogression. While bulk water analysis gave total H 2O concentrations of 522–1584 ppm for garnet and 1170–20745 ppm for omphacite, structural hydroxyl analysis yielded H 2O contents of 80–413 ppm for garnet and 228–412 ppm for omphacite. It appears that significant amounts of molecular H 2O are present in the minerals, pointing to enhanced capacity of water storage in the UHP eclogite minerals. Hydrogen isotope variations in the transition between eclogite and gneiss show correlations with variations in their water contents. Petrographically, the degree of retrograde metamorphism generally increases with decreasing distance from the eclogite–gneiss boundary. Thus, retrograde metamorphism results in mineral reactions and H isotope variation. Because hydroxyl solubility in nominally anhydrous minerals decreases with dropping pressure, significant amounts of water are expected to be released from the minerals during decompression exhumation. Decompression exsolution of structural hydroxyl from 1 m 3 volume of eclogite composed of only garnet and omphacite results in release of a quantitative estimate of 3.07–3.44 kg water that can form 140–156 kg amphibole during exhumation. Therefore, it is concluded that fluid for retrogression of the eclogites away from the eclogite–gneiss boundary was derived from the decompression exsolution of structural hydroxyl and molecular H 2O in nominally anhydrous minerals. For the eclogites adjacent to gneiss, in contrast, the retrograde metamorphism was principally caused by aqueous fluid from the gneiss which is relatively rich in water. Consequently, both the origin and availability of metamorphic fluid during exhumation of deeply subducted continental crust are deciphered by this combined study focusing on the transitions and the retrograde processes between the felsic and mafic UHP rocks.

Vibrational modes of sodium–tellurite glasses: Local structure and Boson peak changes

Raman spectra of xNa 2O−(1− x)TeO 2 glasses were measured and analyzed over a broad composition range. The network structure of the glass consists of a mixture of TeO 4 trigonal bipyramids and TeO 3 trigonal pyramidal units. Increase of alkali content results in conversion of the TeO 4 units into TeO 3 units with a varying number of non-bridging oxygen atoms. This local structure transformation becomes more evident at x=0.2, where rigidity percolation theory predicts a threshold for the rigid-to-floppy transition. However, other spectral features such as the composition dependence of the energy of the Boson peak do not support the occurrence of the stiffness transition. The controversial dependence of dynamical parameters such as the fragility index as a function of Na 2O concentration is also discussed.

Experimental determination of the effect of H 2O on the 410-km seismic discontinuity

Due to the high solubility of H 2O in the mineral wadsleyite it has been recognized that the presence of H 2O in the mantle could influence the pressure and pressure interval of the olivine to wadsleyite phase transformation that is generally considered to be the cause of the 410-km seismic discontinuity. We have performed multianvil experiments in the Mg 2SiO 4–H 2O system in order to quantify the expansion of the wadsleyite stability field as a result of the presence of H 2O. At 1200 °C we find that the wadsleyite stability field expands to lower pressures by approximately 1 GPa under H 2O-rich fluid-saturated conditions. At 1400 °C the expansion is approximately 0.4 GPa and no expansion can be detected at 1600 °C. A thermodynamic model based on recent H 2O solubility measurements and crystallographic observations predicts an expansion of the wadsleyite stability field that is in good agreement with the experimental results. When these results are combined with phase relations in the Mg 2SiO 4–Fe 2SiO 4 system it can be shown that significant effects on the pressure and pressure interval of the olivine to wadsleyite transformation, i.e. on the depth and width of the 410-km discontinuity, are only expected at lower than ambient mantle temperatures (< 1400 °C) and for H 2O concentrations that are substantially greater than 0.2 wt.%. Areas of the mantle where the 410-km discontinuity appears to occur over a depth interval of over 20 km can only be explained if the temperature in these regions is at or below 1200 °C and water concentrations are close to the level where olivine would become H 2O saturated (i.e. > 0.5 wt.%). The presence of ferric Fe in the mantle, however, may also play a role in the broadening of the 410-km discontinuity that is as yet unquantified.

The concept and development of emission spectroscopy for the non-destructive evaluation (NDE) of the failure of thermal barrier coatings

An emission spectroscopy non-destructive evaluation (NDE) method was proposed and developed for in situ monitoring of the degradation of plasma-sprayed thermal barrier coatings (TBCs). Lithium oxide (Li 2O) was chosen as the emission spectroscopic marker material doped in the yttria-stabilized zirconia (YSZ) layer in TBC system. The lithium spectral response was examined in flame in terms of lithium oxide concentration, temperature, exposed area of the doped inner layer and distance from collection port to lithium excitation source. The possible viability of emission spectroscopy as a NDE method for the TBC failure inspection was demonstrated. The Li 2O concentration in YSZ was optimized based on the thermal cycling test for the Li 2O-doped TBCs with different structural configurations. And the durable Li 2O-doped plasma-sprayed TBC structure was generated with the optimized Li 2O concentration and make it potentially applicable in industry.

Effect of Na 2O additions on the sinterability and piezoelectric properties of lead-free 95(Na 0.5K 0.5)NbO 3–5LiTaO 3 ceramics

As a candidate for lead-free piezoelectric materials, Na 2O excess 95(Na 0.5K 0.5)NbO 3–5LiTaO 3 (NKN–5LT) ceramics were developed by conventional sintering process. Sintering temperature was lowered by adding Na 2O as a sintering aid. Abnormal grain growth in NKN–5LT ceramics was observed with varying Na 2O contents. This grain growth behavior was explained in terms of interface reaction-controlled nucleation and growth. The electrical properties of NKN–5LT ceramics were investigated as a function of Na 2O concentration. In the 1 mol% Na 2O excess NKN–5LT samples sintered at 1050 °C for 4 h in air, electromechanical coupling factor and piezoelectric constant of NKN–5LT ceramics were found to reach the highest values of 0.43 and 230 pC/N, respectively.

Experimental determination of H 2O loss from melt inclusions during laboratory heating: Evidence from Raman spectroscopy

Experiments have been conducted to quantify H 2O loss from melt inclusions during laboratory heating using Raman spectroscopy. Quartz-hosted melt inclusions from the early-erupted plinian stage of the Bishop Tuff were heated to 800 °C and 1 kbar for 4 to 1512 h (63 days). Previous studies had shown that unheated melt inclusions from this unit of the Bishop Tuff contain 4.8–6.5 wt.% H 2O. Many Bishop Tuff melt inclusions fluoresce under visible (514 nm) Raman excitation. To minimize fluorescence interference, a method was developed to analyze silicate glasses and melt inclusions using an UV (244 nm) excitation source. The Raman microprobe was calibrated using silicate glass standards with known H 2O contents, and the results indicate that the UV excitation data produce a calibration line with a different slope compared to that produced using visible excitation. The inclusions show insignificant H 2O loss when heated for less than 12 h, while approximately 75% of the original H 2O was lost after 1512 h. The rate of H 2O loss decreases after a few hundred hours, suggesting either a change in H 2O speciation or in the mechanism of H 2O loss. Our results suggest that most silicic melt inclusions maintain their original H 2O concentration if they are not heated for more than about 12 h during laboratory studies.

The effects of variable sources, processes and contaminants on the composition of northern EPR MORB (8–10°N and 12–14°N): Evidence from volatiles (H 2O, CO 2, S) and halogens (F, Cl)

New volatile (H 2O, CO 2, S), halogen (F, Cl) and trace-element data for selected fresh MORB glasses are reported from two geologically and geophysically well-studied regions on the East Pacific Rise (8–10°N and 12–14°N) with distinct differences in spreading rate and magma supply. Sample locations include on-axis and young off-axis eruptions, as well as off-axis fissures, abyssal hills and pillow mounds. H 2O, F, S and trace-element concentrations increase with decreasing MgO content, displaying over-enriched liquid lines of descent consistent with combined fractional and in-situ crystallization. A negative correlation between CO 2/Nb and MgO indicates simultaneous degassing and magma crystallization, while broadening of this correlation to lower CO 2/Nb at constant MgO indicates shallow degassing and CO 2 loss during magma transport to the seafloor. Excess Cl concentrations and associated high Cl/Nb and Cl/K ratios of some northern EPR MORB result from variable pre-eruption contamination by high-salinity brines derived from supercritical phase separation of seawater within deeply-rooted hydrothermal circulation systems. In the faster-spreading 9–10°N and the Siqueiros Transform region magma-brine contamination is limited to off-axis samples, while on-axis samples contain no excess Cl. In the slower-spreading 12–14°N region, on-axis and off-axis samples exhibit similar extents of Cl addition and magma-brine contamination. This contamination appears to affect only Cl, and does not appear to impact concentrations of H 2O or highly incompatible trace elements such as K and Ba. Dissolved H 2O and CO 2 concentrations provide pressure estimates of eruption initiation, and indicate the majority of on-axis samples in the 9–10°N region (including Siqueiros Transform) and 12–14°N region were extracted from crustal depths equivalent to the top of the local axial magma chamber without significant degassing. Samples recovered from off-axis locations in both regions were in magma-vapour equilibrium at eruption depths or at best extracted undegassed from within layer 2B. These results indicate vertical transport of magma leading to eruption is generally faster on-axis than off-axis. Pressure estimates show that Cl addition mainly occurs within or below layer 2B, and rarely at the top of the axial magma chamber. Off-axis Cl contamination occurred similarly in both regions, independent of spreading rate. Uncontaminated samples from both regions yield similar estimates for H 2O and halogen abundances in the northern EPR mantle. Combined estimates (128 ± 5 ppm H 2O, 178 ± 1 ppm F, 1298 ± 6 ppm S, and 5.38 ± 1.1 ppm Cl) are similar to previous estimates based on volumetrically and geographically more-restricted host glass and melt inclusions from Siqueiros Transform samples.

Geochemistry of Neoproterozoic mafic intrusions in the Panzhihua district (Sichuan Province, SW China): Implications for subduction-related metasomatism in the upper mantle

Metasomatism above subduction zones is an important process that produces heterogeneous mantle and thus a diversity of igneous rocks. In the Panzhihua district, on the western margin of the Yangtze Block (SW China), two Neoproterozoic mafic intrusions, one olivine gabbro and one hornblende gabbro, have identical ages of 746 ± 10 and 738 ± 23 Ma. Both of the gabbros are tholeiitic in composition and have arc-like geochemical compositions. The hornblende gabbros have K 2O concentrations ranging from 0.70 to 1.69 wt.% and show enrichment of Rb, Ba, U, Th and Pb and depletion of Nb,Ta and Ti. They have variable 87Sr/ 86Sr ratios (0.7045–0.7070) with constant ɛNd( t) values (−0.12 to −0.93). The olivine gabbros have relatively low K 2O (0.19–0.43 wt.%), are depleted in Rb and Th relative to Ba and U, and have obvious negative Nb–Ta and Zr–Hf anomalies on primitive mantle-normalized trace element diagrams. Their ɛNd( t) values range from −0.64 to −1.73 and initial 87Sr/ 86Sr ratios from 0.7070 to 0.7075. Both types of gabbro experienced fractional crystallization of clinopyroxene, plagioclase, amphibole and minor Fe–Ti oxide. The parental magmas of the olivine and hornblende gabbros were formed by about 20% partial melting of garnet–spinel lherzolite and spinel lherzolite, respectively. According to trace elemental ratios, the hornblende gabbros were probably derived from a source strongly modified by subducted slab fluids, whereas the olivine gabbros came from a mantle source modified by subducted slab melts. The close association of the olivine gabbros and hornblende gabbros suggests that a steep subduction zone existed along the western margin of the Yangtze Block during Neoproterozoic time. Thus, the giant Neoproterozoic magmatic event in South China was subduction-related.

Simulating estuarine nitrous oxide production by means of a dynamic model

We describe a dynamic model developed from a commercially available modeling package (ECoS-III) to simulate estuarine dissolved inorganic nitrogen (DIN) dynamics, and consequent N 2O production and atmospheric flux on the timescale of tidal cycles. Simulated model state variables were NH 4 + , NO 3 - and N 2O concentrations, and salinity. Model outputs were evaluated through comparison with summer field data for the Tyne estuary, UK. The model adequately reproduced the observed axial profiles of NH 4 + , NO 3 - and N 2O concentrations. Nitrification was shown to be the dominant N 2O source and estimates of the ratios nitrification to DIN load and N 2O emission to DIN load are considerably lower than the corresponding values adopted in global scale models of estuarine N 2O emissions based on DIN transformations. Hence our results are consistent with the requirement imposed by atmospheric N 2O growth rate constraints that the amount of atmospheric N 2O arising from agriculturally related sources, including estuarine transformations of N, be revised downward.

Occupational exposure to nitrous oxide – The role of scavenging and ventilation systems in reducing the exposure level in operating rooms

Objectives The aim of this study was to assess the level of occupational exposure to nitrous oxide (N 2O) in operating rooms (ORs), as related to different ventilation and scavenging systems used to remove waste anaesthetic gases from the work environment. Methods The monitoring of N 2O in the air covered 35 ORs in 10 hospitals equipped with different systems for ventilation and anaesthetic scavenging. The examined systems included: natural ventilation with supplementary fresh air provided by a pressure ventilation system (up to 6 air changes/h); pressure and exhaust ventilation systems equipped with ventilation units supplying fresh air to and discharging contaminated air outside the working area (more than 10 air changes/h); complete air-conditioning system with laminar air flow (more than 15 air changes/h). The measurements were carried out during surgical procedures (general anaesthesia induced intravenously and maintained with inhaled N 2O and sevofluran delivered through cuffed endotracheal tubes) with connected or disconnected air scavenging. Air was collected from the breathing zone of operating personnel continuously through the whole time of anaesthesia to Tedlar ® bags, and N 2O concentrations in air samples were analyzed by adsorption gas chromatography/mass spectrometry. Results N 2O levels in excess of the occupational exposure limit (OEL) value of 180 mg/m 3 were registered in all ORs equipped with ventilation systems alone. The OEL value was exceeded several times in rooms with natural ventilation plus supplementary pressure ventilations and twice or less in those with pressure/exhaust ventilation systems or air conditioning. N 2O levels below or within the OEL value were observed in rooms where the system of air conditioning or pressure/exhaust ventilation was combined with scavenging systems. Systems combining natural/pressure ventilation with scavenging were inadequate to maintain N 2O concentration below the OEL value. Conclusion Air conditioning and an efficient pressure/exhaust ventilation (above 12 air exchanges/h) together with efficient active scavenging systems are sufficient to sustain N 2O exposure in ORs at levels below or within the OEL value of 180 mg/m 3.

Rapid measurements of temperature and H 2O concentration in IC engines with a spark plug-mounted diode laser sensor

Crank angle-resolved measurements of gas temperature and water vapor concentration are made during the compression stroke of an internal combustion (IC) engine with a novel diode laser absorption sensor. The temperature is determined from the ratio of optical absorption for two overtone transitions of water vapor in the intake gas mixture, and the H 2O concentration is determined from this inferred temperature and the absorption for one of the transitions. The measurements sample a short-path region (6 mm) of the in-cylinder gases near the spark plug, which has been modified to provide optical access. Hence, the sensor can be installed in nearly any engine via the spark plug port. Wavelength modulation spectroscopy is employed with second harmonic detection (WMS-2 f) to enable the short-path measurements over a range of temperatures and pressures from 500 to 1050 K and 1 to 50 atm at a bandwidth of 7.5 kHz. The accuracy of the sensor is validated in a static cell, giving RMS errors of less than 3% in temperature and less than 3.6% in H 2O concentration over a wide range of conditions. Crank angle-resolved measurements are performed in unfired and fired engine cylinders, illustrating the potential of this sensor for investigating a range of difficult-to-model trends in current and proposed IC engine combustion schemes.