Percent H2O Research Articles

Effects of univariate and multivariate regression on the accuracy of hydrogen quantification with laser-induced breakdown spectroscopy

Hydrogen (H) is a critical element to measure on the surface of Mars because its presence in mineral structures is indicative of past hydrous conditions. The Curiosity rover uses the laser-induced breakdown spectrometer (LIBS) on the ChemCam instrument to analyze rocks for their H emission signal at 656.6nm, from which H can be quantified. Previous LIBS calibrations for H used small data sets measured on standards and/or manufactured mixtures of hydrous minerals and rocks and applied univariate regression to spectra normalized in a variety of ways. However, matrix effects common to LIBS make these calibrations of limited usefulness when applied to the broad range of compositions on the Martian surface. In this study, 198 naturally-occurring hydrous geological samples covering a broad range of bulk compositions with directly-measured H content are used to create more robust prediction models for measuring H in LIBS data acquired under Mars conditions. Both univariate and multivariate prediction models, including partial least square (PLS) and the least absolute shrinkage and selection operator (Lasso), are compared using several different methods for normalization of H peak intensities. Data from the ChemLIBS Mars-analog spectrometer at Mount Holyoke College are compared against spectra from the same samples acquired using a ChemCam-like instrument at Los Alamos National Laboratory and the ChemCam instrument on Mars. Results show that all current normalization and data preprocessing variations for quantifying H result in models with statistically indistinguishable prediction errors (accuracies) ca. ±1.5weight percent (wt%) H2O, limiting the applications of LIBS in these implementations for geological studies. This error is too large to allow distinctions among the most common hydrous phases (basalts, amphiboles, micas) to be made, though some clays (e.g., chlorites with ≈12wt% H2O, smectites with 15–20wt% H2O) and hydrated phases (e.g., gypsum with ≈20wt% H2O) may be differentiated from lower-H phases within the known errors. Analyses of the H emission peak in Curiosity calibration targets and rock and soil targets on the Martian surface suggest that shot-to-shot variations of the ChemCam laser on Mars lead to variations in intensity that are comparable to those represented by the breadth of H standards tested in this study.

Competitive sorption of CO2 and H2O in 2:1 layer phyllosilicates

Expandable clays such as montmorillonite have interlayer exchange sites whose hydration state can be systematically varied from near anhydrous to almost bulk-like water conditions. This phenomenon has new significance with the simultaneous implementation of geological sequestration and secondary utilization of CO2 to both mitigate climate warming and enhance extraction of methane from hydrated clay-rich formations. In this study, the partitioning of CO2 and H2O between Na-, Ca-, and Mg-exchanged montmorillonite and variably hydrated supercritical CO2 (scCO2) was investigated using in situ X-ray diffraction (HXRD), infrared (IR) spectroscopic titrations, and quartz crystal microbalance (QCM) measurements. Density functional theory calculations provided mechanistic insights. Structural volumetric changes were correlated to quantified changes in sorbed H2O and CO2 concentrations as a function of percent H2O saturation in scCO2. Intercalation of CO2 is inhibited when the clay is fully collapsed (dehydrated interlayer), peaks sharply with the introduction of some H2O and partial expansion of the interlayer region, and then decreases systematically with further hydration of the clay. This behavior is discussed in the context of recent theoretical calculations of the montmorillonite H2O–CO2 system.

In situ study of CO₂ and H₂O partitioning between Na-montmorillonite and variably wet supercritical carbon dioxide.

Shale formations play fundamental roles in large-scale geologic carbon sequestration (GCS) aimed primarily to mitigate climate change and in smaller-scale GCS targeted mainly for CO2-enhanced gas recovery operations. Reactive components of shales include expandable clays, such as montmorillonites and mixed-layer illite/smectite clays. In this study, in situ X-ray diffraction (XRD) and in situ infrared (IR) spectroscopy were used to investigate the swelling/shrinkage and H2O/CO2 sorption of Na(+)-exchanged montmorillonite, Na-SWy-2, as the clay is exposed to variably hydrated supercritical CO2 (scCO2) at 50 °C and 90 bar. Measured d001 values increased in stepwise fashion and sorbed H2O concentrations increased continuously with increasing percent H2O saturation in scCO2, closely following previously reported values measured in air at ambient pressure over a range of relative humidities. IR spectra show H2O and CO2 intercalation, and variations in peak shapes and positions suggest multiple sorbed types of H2O and CO2 with distinct chemical environments. Based on the absorbance of the asymmetric CO stretching band of the CO2 associated with the Na-SWy-2, the sorbed CO2 concentration increases dramatically at sorbed H2O concentrations from 0 to 4 mmol/g. Sorbed CO2 then sharply decreases as sorbed H2O increases from 4 to 10 mmol/g. With even higher sorbed H2O concentrations as saturation of H2O in scCO2 was approached, the concentration of sorbed CO2 decreased asymptotically. Two models, one involving space filling and the other a heterogeneous distribution of integral hydration states, are discussed as possible mechanisms for H2O and CO2 intercalations in montmorillonite. The swelling/shrinkage of montmorillonite could affect solid volume, porosity, and permeability of shales. Consequently, the results may aid predictions of shale caprock integrity in large-scale GCS as well as methane transmissivity in enhanced gas recovery operations.

CaTiO3 nanobricks prepared from anodized TiO2 nanotubes

Bioactive CaTiO3 nanobricks were synthesized using a two-step anodization–hydrothermal treatment. TiO2 nanotubes (TNTs) on the Ti substrate surface were first prepared by anodization in a glycerol electrolyte with 0.5% NH4F. Two percent H2O in the electrolyte was required to obtain highly ordered TNTs; the regularity of TNTs was indispensible for further formation of CaTiO3 nanostructures. The TNTs were then hydrothermally treated in saturated Ca(OH)2 solution at 150°C for 12h. The TNTs were transformed to crystalline CaTiO3 nanobricks of width 45–75nm and length 125–275nm. A transformation mechanism was proposed based on a combination of dissolution–precipitation and Ostwald ripening. The bioactivity of the CaTiO3 nanobricks was evaluated using simulated body fluid immersion tests. A hydroxyapatite layer with high coverage was formed within 7days, showing the potential for biomedical applications.

Calibration for IR measurements of OH in apatite

In this work, we have calibrated the infrared (IR) method for determining OH concentrations in apatite with absolute concentrations obtained through elastic recoil detection (ERD) analysis. IR spectra were collected on oriented, single-crystal apatite samples using polarized transmission infrared spectroscopy. The weight percent H2O is 0.001199 ± 0.000029 (the error is given at 1σ level hereafter) times A / d , where A is the linear absorbance peak height measured using polarized IR when the light vector E is parallel to the c -axis of the apatite crystal, and d is the sample thickness in centimeters. This corresponds to a linear molar absorptivity, e = 470 ± 11 L/mol/cm−1. The calibration using linear absorbance can be applied when there is only one dominant peak at 3540 cm−1. If other peaks are significant, then the integrated molar absorptivity, e = (2.31 ± 0.06) ×104 L/mol/cm2, should be used. The detection limit of H2O concentration in apatite by IR approaches parts per million level for wafers of 0.1 mm thickness. The accuracy based on our calibration is 5–10% relative.

Effects of Confinement in Carbon Nanotubes on the Activity, Selectivity, and Lifetime of Fischer−Tropsch Co/Carbon Nanotube Catalysts

The effects of electronic properties of the inner and outer surfaces of carbon nanotubes (CNTs) on the deactivation of cobalt Fischer−Tropsch (FT) catalysts were studied. The comparative characterization of the fresh and used 0.20 w (mass fraction) Co/CNT catalysts by transmission electron microscopy (TEM), X-ray diffraction (XRD), temperature-programmed reduction (TPR), Brunnauer−Emmett−Teller analysis (BET), and H2 chemisorption showed that cobalt reoxidation, cobalt-support interactions, and sintering are the main sources of catalyst deactivation. TEM showed that continuous FT synthesis for 480 h increased the average Co particle size located inside the pores from (7 to 8.5) nm, while the average Co particle size located outside of the tubes increased from (11.5 to 25) nm. XRD analysis of the used catalyst confirmed cobalt reoxidation, interaction between cobalt and CNTs, and the creation of carbide phases. At a high percent CO (%CO) conversion and H2O partial pressure, the deactivation rate is zero-order and independent of the number of active catalyst sites. In this case, the main deactivation mechanisms are cobalt reoxidation and metal support interactions. At lower %CO conversion and H2O partial pressure, the deactivation rate can be simulated with power law expressions of the order of 11.4 for the particles outside the tubes and 30.2 for the particles inside the tubes. In this case, the main deactivation mechanism is sintering. Because of the electron deficiency of the inner sides of the CNTs, the interaction between the cobalt oxides and the support is stronger, leading to lower rates of sintering as compared with the particles located on the outer layers of the CNTs. Regeneration recovered the catalyst activity with 9.1 % of the total activity loss.

Evolution of boudins under progressively decreasing pore pressure A case study of pegmatites enclosed in marble deforming at high grade metamorphic conditions, Naxos, Greece

During ductile deformation of marbles under high grade metamorphic conditions on Naxos, Greece, pegmatites enclosed in the marbles were deformed in a brittle fashion forming blocky boudins with quartz crystallized in the interboudin zones. We studied the three-dimensional geometry of the boudins in the field and in two large samples. The first sample was serially sectioned to observe the structural and microstructural evolution; in the second sample we mapped the surface morphology of the deformed pegmatite. In profile, the boudins can be classified as symmetric torn type boudins, evolving towards asymmetric boudins with a later domino boudin component. In three dimensions, however, the morphology of the boudinaged pegma- tite is a simple set of normal faults with mode-I fractures in the fault tips and rotation of the fault blocks to accommodate the extension in the marble. Deformation history was constrained by petrology and microstructures in combi- nation with simple order of magnitude calculations of both the cooling and pore fluid pressure evolution. The dynamically recrystallized, coarse-grained calcite of the marble provides clear evidence that after the pegmatite intruded the marble and solidified, it was deformed at peak conditions of M2b metamorphism (� 670 °C and � 0.6 GPa). Such pegmatitic melts contain � 10 percent H2O which is released during crystalliza- tion. We infer that after crystallization of the pegmatite the pore fluid pressure in the pegmatite remained close to lithostatic due to the very low permeability of the surrounding marble, and the pegmatite was deformed at very low effective stress which led to brittle deformation of feldspar and mode-I fracturing of the pegmatite, forming torn type boudins. With time the pore fluid pressure slowly decreased, increasing the effective stress. Ongoing N-S extension thus resulted in slip along the quartz-filled interboudin zones and in block rotation, producing domino boudins.

Hydrothermal Alteration, Ore Fluid Characteristics, and Gold Depositional Processes along a Trondhjemite-Komatiite Contact at Tarmoola, Western Australia

Tarmoola is a structurally controlled Archean orogenic gold deposit hosted in greenschist facies metamorphosed komatiite and trondhjemite in the Leonora district of the Eastern Goldfields province, Yilgarn craton. High-grade (>1 g/t Au) orebodies are located in komatiite wall rock adjacent to the eastern and northeastern margins of the asymmetrical, north-south–striking, Tarmoola trondhjemite intrusion. Gold-bearing veins postdate trondhjemite emplacement (ca. 2700 Ma), quartz diorite dikes (ca. 2667 Ma), and regional greenschist facies metamorphism. Textures and crosscutting relationships in gold-bearing veins indicate two stages of hydrothermal fluid infiltration associated with a single gold-related hydrothermal event: a volumetrically dominant, but gold-poor, stage I fluid and a gold-rich stage II fluid. Gold-bearing veins contain stage I milky quartz and pyrite that are overprinted by stage II quartz-ankerite-muscovite-chalcopyrite-sphalerite-galena-gold-tellurides ± albite ± chlorite ± fuchsite ± epidote ± scheelite. Stage I hydrothermal alteration assemblages are different in trondhjemite and komatiite due to contrasting reactions between a common ore fluid and disparate wall-rock chemistry. Stage II fluid-wall rock interaction was minor compared to stage I and is indicated by the overprinting of stage I mineral assemblages by stage II microveins. Wall-rock alteration proximal to veins in trondhjemite is characterized by replacement of igneous plagioclase, amphibole, biotite, and metamorphic chlorite by hydrothermal quartz, muscovite, ankerite, calcite, pyrite, chalcopyrite, sphalerite, galena, tellurides, and gold, whereas in proximal alteration in komatiite, metamorphic chlorite and talc are replaced by ankerite, quartz, muscovite, albite, chlorite, fuchsite, pyrite, chalcopyrite, sphalerite, galena, tellurides, and gold. The stage II fluid was enriched in H2O, CO2, Si, Ca, K, Na, S, Au, Ag, Cu, Pb, W, Bi, As, Mo, Zn, and Te. Based on fluid inclusion studies and stage II mineral equilibria, gold deposited from a homogeneous, neutral to slightly alkaline (pH 5.1–5.5), reduced, low-salinity (<5.5 wt % NaCl equiv) fluid that had a bulk composition of 78 mole percent H2O and 21 mole percent CO2, and trace amounts of CH4, C2H6, H2, Ar, H2S, and He. Gold deposition occurred at 300° ± 50°C and 0.5 to 3.0 kbars. Assuming lithostatic fluid pressures, gold precipitated at a 2- to 10-km depth. Stage II gray quartz δ 18Ofluid values range from 5.9 to 7.5 per mil, whereas δ Dfluid values calculated from the dehydration of muscovite grains and measured directly from bulk fluid inclusion analyses of stage II gray quartz have ranges of –9 to –35 and –27 to –28 per mil, respectively. Hydrothermal ore fluids were transported from greater crustal depths to the site of gold deposition during the district-scale D3 event by shallowly W dipping, reverse brittle-ductile shear zones in supracrustal rock and along the steeply east dipping trondhjemite contact. Associated subhorizontal east-west shortening caused the reactivation of the eastern trondhjemite margin and subparallel foliation, which facilitated the transport of hydrothermal fluids and the generation of gold-bearing veins and hydrothermal alteration zones in komatiite. East-west–striking fractures in trondhjemite aided the lateral migration of ore fluids away from trondhjemite margins and the formation of east-west–striking gold-bearing veins and broad alteration zones. Gold was most likely transported in the stage II fluid as bisulfide complexes. The sulfidation of trondhjemite and komatiite wall rock by the stage II fluid caused the destabilization of Au bisulfide complexes and gold deposition. Potassium, Ca, and CO2 metasomatism of komatiite wall rock may have enhanced gold deposition via the acidification of the stage II fluid. The physicochemical characteristics of the Tarmoola ore fluid and relative timing of gold mineralization are consistent with the Yilgarn-wide, 2650 to 2630 Ma gold event. The host-rock chemistry, vein, and proximal wall-rock alteration mineral assemblages, and fluid temperature and pressures during gold deposition are also similar to that of earlier (ca. 2755 Ma) gold deposits in the Leonora district.

Water in Earth's lower mantle.

Secondary ion mass spectrometry measurements show that Earth's representative lower mantle minerals synthesized in a natural peridotitic composition can dissolve considerable amounts of hydrogen. Both MgSiO3-rich perovskite and magnesiowüstite contain about 0.2 weight percent (wt%) H2O, and CaSiO3-rich perovskite contains about 0.4 wt% H2O. The OH absorption bands in Mg-perovskite and magnesiowüstite were also confirmed with the use of infrared microspectroscopic measurements. Earth's lower mantle may store about five times more H2O than the oceans.

Fluid Characteristics of Granitoid-Hosted Gold Deposits in the Birimian Terrane of Ghana: A Fluid Inclusion Microthermometric and Raman Spectroscopic Study

Fluid inclusions in vein quartz from 10 granitoid-hosted gold deposits and prospects in the Birimian terrane of Ghana, as well as from the Sansu mine (Ashanti shear zone type) and quartz veins in the nonmineralized Princess Town granodiorite, were studied by microthermometry and Raman microspectrometry. Fluid inclusions from the granitoid-hosted gold deposits are dominated by aqueous H2O-CO2-NaCl type 1 and liquid CO2-N2 ± CH4 type 2, with minor (<10%) aqueous H2O-NaCl type 3. Type 1 inclusions show large variations in CO2 phase volume proportions (10–90%) at 25°C and have salinities commonly between 0 and 6 wt percent NaCl equiv. Their bulk densities fall in a major range from 0.62 to 1.11 g/cm3. Type 2 inclusions show no visible H2O phase at room temperature and have bulk densities between 0.30 and 0.92 g/cm3. Type 3 inclusions, containing 10 to 20 vol percent H2O vapor, have salinities of 1 to 8 wt percent NaCl equiv and bulk densities of 0.77 to 1.03 g/cm3. In most cases, the three types of fluid inclusions coexist as groups in individual quartz grains of the samples studied. These fluid inclusions are interpreted to be trapped during phase separation of an originally homogeneous H2O-CO2 fluid, with low salinity (<6 wt % NaCl equiv) and moderate to high density (0.65–0.95 g/cm3). The type 1 fluid inclusions are suggested to be heterogeneous mixtures of the two end members of type 2 and 3 inclusions. Fluid immiscibility is documented by petrographic characteristics and microthermometric results of the three types of inclusions. Trapping temperatures and pressures, estimated from microthermometry of type 3 inclusions, equation of state, and the P-T-X nature of the H2O-CO2-NaCl system, are mainly between 200° and 350°Cand 1 and 3 kbars for the gold deposits. By contrast, fluid inclusions in the Sansu mine at Ashanti mostly comprise the liquid CO2-N2 ± CH4 type 2. The inclusions are considered to represent postentrapment modifications of trapped fluids. In addition, fluid inclusions in barren vein quartz from the Princess Town granodiorite comprise the low-salinity (commonly <6 wt % NaCl equiv) H2O-NaCl type 3. Raman microspectrometry shows that gaseous compositions of fluid inclusions from both granitoid- and shear zone-hosted gold deposits are mainly composed of CO2 (80–95 mol %), with significant amounts of N2 (2–20 mol %) and CH4 (0–10 mol %). The distinct low-salinity H2O-CO2-rich fluids from the granitoid-hosted gold deposits are comparable in composition to those from the major Ashanti and Tarkwaian types of gold deposits in the Birimian terrane of Ghana. These fluids are most likely to be metamorphic in origin and associated with the waning stages of the regional Birimian orogeny. Gold deposition within the Birimian granitoids was related to fluid phase separation and sulfidization of host rocks during hydrothermal alteration and mineralization. The present study, together with previous publications, suggests that fluid inclusions are characterized by H2O-CO2-NaCl and/or CO2-N2 ± CH4 types in mineralized areas, whereas H2O-NaCl fluid compositions dominate in barren areas. Fluid inclusion characteristics may, therefore, be a useful tool for regional gold exploration in the Birimian terrane of Ghana.

Performance of a Vacuum Formed Chopped Ceramic Fiber Filter in a Reducing Environment

A laboratory-scale apparatus has been used for unattended, long duration, continuous flow through testing of a vacuum formed chopped ceramic fiber filter under reducing conditions at atmospheric pressure. Four candle specimens were exposed from 150 to 3550 h to 600°C gas containing 4 percent CO, 11 percent H2, 12 percent CO2, 14 percent H2O, 59 percent N2, 1 ppmv NaCl, 50 ppmv H2S, and 1000–2000 ppmw ash from a transport reactor operated in gasification mode. A database was established on pressure drop of the as-received and exposed filter as a function of face velocity and temperature. Tests were conducted to investigate the effects of back-pulse parameters on filter regenerability. Results are reported on the critical reservoir pressure and pulse duration for maintaining a stable saw-tooth profile of pressure drop across the filter element. Data are obtained to characterize the effect of chemical and thermal aging on the apparent bulk density of the filter, pore size distribution, fast fracture strength, and microstructure. It is suggested that the compliant filter undergoes a slow process of rigidization upon exposure to the test environment.

The vegetation and its environments in Maine peatlands

This study is based on relevés from 96 peatlands representing the typologic, environmental, and geographic variation of Maine peatlands, and on peat pore-water chemistry at a representative set of 51 of these peatlands. We give optima and tolerances of pH, Ca, P, NO3-N, NH4-N, and influence of upper on lower vegetational strata for the 73 most common vascular plant species, excluding sedges, which are presented elsewhere. The program TWINSPAN differentiated 30 plant communities. Environments of the first seven TWINSPAN divisions differed largely by Ca, pH, P, NH4, Fe, microrelief, substrate depth, degree of humification, and climate. A canonical correspondence analysis (CCA) with forward selection entered pH, P, Na, Fe, Ca, Mg, and percent H2O as the minimum number of variables which best explains species variation. A CCA of the lower strata vascular plants demonstrated the importance of the upper strata (percent overstory) on species' distributions. Gradients of pH–alkalinity and percent overstory are primary in determining Maine's peatland vegetation. Other important gradients are percent H2O in upper peat, concentrations of lithic elements (P, Fe, Mn, Al, and Si) in pore water, and climate. Although these gradients partially covary, some of the variation in species' distributions can be attributed to independent aspects of individual gradients. Species richness across the range of peatland types is related to pH–alkalinity for vascular plants, and to percent H2O, microrelief, and percent overstory for bryophytes. Key words: plant communities, Maine, multivariate statistical analysis, peatlands, mires, vegetation.

Multiple-Dose Mannitol Reduces Brain Water Content in a Rat Model of Cortical Infarction

Repeated use of mannitol in the setting of ischemic infarction is a controversial and poorly defined therapeutic intervention. The purpose of this study was to examine the effects of repeated mannitol infusions on brain water content and tissue pressure in a well-defined rat model of focal ischemic stroke. Mannitol infusions (0.5, 1.5, or 2.5 g/kg) were given by intravenous bolus 4 or 24 hours after 90-minute transient cortical ischemia in the territory of the right middle cerebral artery in rats and every 4 hours thereafter for a total of 24 hours. Fluid replacement was limited to 0.5 mL i.v. isotonic saline administered immediately after each mannitol dose. Control rats received 0.5 mL i.v. saline at the same intervals and were otherwise under ad libitum conditions. Water contents (percent H2O) of whole hemispheres and of cortical biopsies were measured with the wet-dry method, and blood samples were analyzed for plasma osmolality and chemistries. In a subgroup of rats, tissue pressure was also measured within the hemisphere ipsilateral to the infarct. Repeated mannitol infusions resulted in a dose-dependent increase in plasma osmolality and a dose-dependent decrease in the percent H2O of the ischemic middle cerebral artery cortex and ipsilateral hemisphere. In contrast, percent H2O of the contralateral cortex and hemisphere was significantly decreased only in the groups given the highest dose of mannitol (2.5 g/kg). Mannitol infusions at a dose of 1.5 g/kg begun 24 hours after reperfusion were also associated with a significant reduction of tissue pressure. In a rat model of ischemic cortical infarction, repeated mannitol infusions resulted primarily in a decrease in the percent H2O of the infarct and ipsilateral hemisphere, as well as decreased tissue pressure.

Retrograde mineral reactions: a heat source in the continental crust?

Chemical reactions of water with silicates are strongly exothermic. Therefeore, retrograde metamorphism is also a strongly exothermic process and thus a potentially powerful heat source. Depending on the time scale its contribution to the terrestrial heat flow can be equivalent to, or even exceed, that of radioactive decay. During hydration mafic rocks and gneisses liberate 60 J/cm3 for each weight percent H2O they bind. It is argued that retrograde reactions constitute relatively short-lived, single or repeated episodes during crustal cooling, and that they can influence, or even strongly perturb, the geotherm during thousands to a million years. The thermal effects involved are non-trivial; they should be considered in interpretations of heat flow measurements. They could constitute the main heat source for hydrothermal mineralisations not connected with magmatic intrusions and possibly contribute to the thermal development of sedimentary basins. These effects are large enough to be one of the possible explanations for the difference between the predicted and measured heat flows at the KTB site.

Petrogenesis of the basalt-andesite-dacite association of Grenada, Lesser Antilles island arc, revisited

The basalt-andesite-dacite association of Grenada is produced by fractional crystallization of primary magmas that contain about 15 weight percent MgO and 1–2 weight percent H2O. The compositions of primary magmas indicate that they were last in equilibrium with the mantle at depths greater than about 65 km, indicating that they must ascend rapidly after they segregate from residual mantle. It is inferred that mantle wedge diapirism typically leads to moderately large degrees of batch partial melting in the formation of primary arc magmas (~ 10–30%). The trace-element geochemical diversity of primary magmas mainly reflects variable degrees of source-region enrichment by fluids derived from the subducted slab. The degree to which source regions are enriched is likely related to mantle wedge dynamics.Water pressure suppresses plagioclase crystallization in derivative magmas, leading to development of the calc-alkaline, rather than tholeiitic, differentiation trend. Amphibole crystallization typically occurs only after melt MgO content decreases below about 4 weight percent.The island-arc crust acts as a density filter. As arc crust thickens, parental basaltic magmas will have a greater tendency to stagnate at mid-crustal levels. The observation that basalts predominate in young island arcs while andesites and dacites predominate in more mature arcs is explained by this hydrostatic control: the thicker the arc crust, the more magmas must differentiate by crystal segregation to become buoyant enough to erupt at the surface.

Comparison of Chemiluminescence and Ultraviolet Ozone Monitor Responses in the Presence of Humidity and Photochemical Pollutants

The effect of water vapor and other pollutants on ozone monitoring instruments was investigated. Five UV-type and two chemiluminescence-type monitors were employed in this study. The results of the study indicate that in systems containing ozone, water vapor and zero air only, the UV-based monitors showed negligible effects due to humidity. On average, the UV monitors were within 0.5 percent of independently determined ozone values judged to be extremely accurate. The chemiluminescence-based monitors showed systematically higher readings than the UV monitors with added water vapor. The effect was found to be linear with water vapor concentration with an average positive deviation of 3.0 percent per percent H2O at 25 degrees C. For these measurement, ozone concentrations ranged from 85 to 320 ppbv and water concentrations from 1 to 3 percent (i.e., dew point temperatures from 9 to 24 degrees C). These results are largely in agreement with previous studies conducted to measure this interference, although the present study extends the range of water concentrations tested. Studies were also performed with a smog chamber with simulated polluted air (containing paraffinic, olefinic and aromatic hydrocarbon precursors) and varying relative humidities. Although the presence of water vapor did not appear to represent a substantial interference in these systems, a positive interference was observed with the UV monitors. This interference was likely a result of the presence of toluene and some of its aromatic photooxidation products (e.g., benzaldehyde), which can be partially removed from the reference stream by the ozone scrubber within the UV monitor. If the compound absorbs radiation at 254 nm, it is detected as ozone. However, when the results are scaled back to ambient concentrations of toluene and NO(x), the effect appears to be very minor (ca. 3 percent under the study conditions). It is concluded that under atmospheric conditions at moderate pollution and relative humidity levels, both types of instruments can give accurate measurements of the ozone concentration. These potential effects should be recognized when conducting ambient ozone measurements.

Texturally-early fluid inclusions in garnets: evidence of the prograde metamorphic path?

Well-formed, texturally-early fluid inclusions in garnets from the Archean Pikwitonei granulite domain, Manitoba, Canada, have been analyzed using microthermometric methods. The mean CO2 homogenization temperature (to liquid) for inclusions in 12 of 13 samples from the Cauchon Lake-Nelson River area is +15.2° C (n=125, 2σ=8.2° C), corresponding to a CO2 density of 0.82 g/cm3. Inclusions in the remaining sample have somewhat lower CO2 homogenization temperatures (mean=+5.4° C, n=24). The studied inclusions contain an estimated 10 to 20 vol. percent H2O, with minor amounts of other fluid species such as CH4, N2, and/or H2S. The fluid inclusions were probably trapped during early garnet growth at relatively low pressures (≤5 kbar if at 750° C), and appear to have undergone only limited or possibly no subsequent re-equilibration. This interpretation is consistent with the “anti-clock-wise” P-T-t path (heating before loading) determined for the Pikwitonei region by other workers. For such a prograde path, inclusions entrapped early, at high temperatures but at relatively low pressures, would experience internal underpressures during most of the subsequent prograde and retrograde phases of metamorphism. The texturally-early fluid inclusions in garnets from the Pikwitonei region therefore cannot be used to provide direct information about the highest metamorphic temperature and pressure conditions (750° C and 7 kbar). However, the results obtained in this study suggest that texturally-early fluid inclusions in garnets may, in some cases, retain evidence of the prograde metamorphic path.

Ionic mobilities and hydrophobic interactions in Ph4PCl-NaCl mixtures in hydroorganic solvents

The aim of this work is to correlate the experimental conductimetric ionic behavior with the hydrophobic properties of the Ph4P+ ion. Ionic mobility determinations using radioactive tracers have been extended to Ph4PCl-NaCl mixtures at a constant 0.5 molar total salt concentration over the whole range of electrolyte mixture composition. Molar conductance measurements have been carried out in water and in H2O — 5 mole percent acetonitrile and H2O — 5 mole percent dimethylsulfoxide. Deviations from the additivity law have been found to be maximum for a 0.6 mole fraction of Ph4PCl. Large negative mixture effects, up to −27% in H2O have been measured for the limiting case of a cation in trace amounts. The main experimental result is the decrease of the Ph4P+ mobility with increasing proportion of Na+ ions in the mixture. The unexpected negative sign of the mixture effect for the less mobile cation is interpreted in terms of solute-solvent hydrophobic interactions and solvent structure. A possible dimerization of the Ph4P+ ion is suggested. Densities of NaCl and Ph4PCl in the aquo-organic solvents are also included.

The Application of Multivariate Statistics and Saturation Extract Data to Identify Dispersive Clay Soils

Abstract Soils from a geotechnical project in Oklahoma may be classified as dispersive or nondispersive with a high degree of confidence by substituting selected pore-water data (weight percent H2O at saturation, saturation extract pH, log base 10 of the pore-water conductivity, and log base 10 of the pore-water sodium concentration) into derived discriminant classification functions. The discriminant functions were derived using discriminant analysis, a multivariate statistical classification technique, performed on a 28-sample data set. This statistical procedure was utilized after problems were noted with the currently accepted porewater chemical test for dispersion, suggested by Sherard et al. Suggestions for using the derived discriminant function as the basis of a simple chemical field test and precautions regarding data interpretation are presented.

Changes in Milk Composition during Lactation in the Northern Elephant Seal

Elephant seals, Mirounga angustirostris, are exceptional mammals in that females fast entirely during nursing while their pups may quadruple in weight over the 28-day suckling period. Obviously, all water and nutrients for both pup and mother must be derived from the females' body reserves. Thus one might anticipate changes in milk composition during nursing which reflect the physiological requirements of both parent and offspring. Milk samples were taken from 20 females in the field at known times in their respective nursing cycles during the 1976-77 breeding season on Ano Nuevo Island, California. The milk was analyzed for: percent H₂O, percent protein, percent fat, fatty acid composition, and the presence of reducing sugars. During the first 21 days of lactation, fat and water content of milk changed with mirror-image kinetics; fat rising from approximately 15% to a plateau of approximately 55%, while water content fell from approximately 75% to a constant level of approximately 35%. Plateau values per...