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991.
The solubility of silver sulphide (acanthite/argentite) has been measured in aqueous sulphide solutions between 25 and 400°C at saturated water vapour pressure and 500 bar to determine the stability and stoichiometry of sulphide complexes of silver(I) in hydrothermal solutions. The experiments were carried out in a flow-through autoclave, connected to a high-performance liquid chromatographic pump, titanium sampling loop, and a back-pressure regulator on line. Samples for silver determination were collected via the titanium sampling loop at experimental temperatures and pressures. The solubilities, measured as total dissolved silver, were in the range 1.0 × 10−7 to 1.30 × 10−4 mol kg−1 (0.01 to 14.0 ppm), in solutions of total reduced sulphur between 0.007 and 0.176 mol kg−1 and pHT,p of 3.7 to 12.7. A nonlinear least squares treatment of the data demonstrates that the solubility of silver sulphide in aqueous sulphide solutions of acidic to alkaline pH is accurately described by the reactions0.5Ag2S(s) + 0.5H2S(aq) = AgHS(aq) Ks,1110.5Ag2S(s) + 0.5H2S(aq) + HS− = Ag(HS)2− Ks,122Ag2S(s) + 2HS− = Ag2S(HS)22− Ks,232where AgHS(aq) is the dominant species in acidic solutions, Ag(HS)2− under neutral pH conditions and Ag2S(HS)22− in alkaline solutions. With increasing temperature the stability field of Ag(HS)2− increases and shifts to more alkaline pH in accordance with the change in the first ionisation constant of H2S(aq). Consequently, Ag2S(HS)22− is not an important species above 200°C. The solubility constant for the first reaction is independent of temperature to 300°C, with values in the range logKs,111 = −5.79 (±0.07) to −5.59 (±0.09), and decreases to −5.92 (±0.16) at 400°C. The solubility constant for the second reaction increases almost linearly with inverse temperature from logKs,122 = −3.97 (±0.04) at 25°C to −1.89 (±0.03) at 400°C. The solubility constant for the third reaction increases with temperature from logKs,232 = −4.78 (±0.04) at 25°C to −4.57 (±0.18) at 200°C. All solubility constants were found to be independent of pressure within experimental uncertainties. The interaction between Ag+ and HS− at 25°C and 1 bar to form AgHS(aq) has appreciable covalent character, as reflected in the exothermic enthalpy and small entropy of formation. With increasing temperature, the stepwise formation reactions become progressively more endothermic and are accompanied by large positive entropies, indicating greater electrostatic interaction. The aqueous speciation of silver is very sensitive to fluid composition and temperature. Below 100°C silver(I) sulphide complexes predominate in reduced sulphide solutions, whereas Ag+ and AgClOH− are the dominant species in oxidised waters. In high-temperature hydrothermal solutions of seawater salinity, chloride complexes of silver(I) are most important, whereas in dilute hydrothermal fluids of meteoric origin typically found in active geothermal systems, sulphide complexes predominate. Adiabatic boiling of dilute and saline geothermal waters leads to precipitation of silver sulphide and removal of silver from solution. Conductive cooling has insignificant effects on silver mobility in dilute fluids, whereas it leads to quantitative loss of silver for geothermal fluids of seawater salinity. 相似文献
992.
The standard thermodynamic properties and Helgeson-Kirkham-Flowers (HKF) parameters for Sb(OH)3(aq) have been estimated. For this purpose, the available solubility data for senarmontite, valentinite, stibnite, and native Sb in a wide range of temperatures (15 to 450°C) and pressures (1 to 1000 bar), and thermodynamic properties of Sb oxides (senarmontite and valentinite) have been critically analyzed. Published data were complimented by results from new experiments performed by solubility and solid-state galvanic cell methods. Both experimental data and thermodynamic calculations show that the hydroxide complex Sb(OH)3(aq) is primarily responsible for hydrothermal transport of antimony, especially at temperatures above 250°C. 相似文献
993.
Geoid determination using adapted reference field, seismic Moho depths and variable density contrast 总被引:4,自引:0,他引:4
The traditional remove-restore technique for geoid computation suffers from two main drawbacks. The first is the assumption
of an isostatic hypothesis to compute the compensation masses. The second is the double consideration of the effect of the
topographic–isostatic masses within the data window through removing the reference field and the terrain reduction process.
To overcome the first disadvantage, the seismic Moho depths, representing, more or less, the actual compensating masses, have
been used with variable density anomalies computed by employing the topographic–isostatic mass balance principle. In order
to avoid the double consideration of the effect of the topographic–isostatic masses within the data window, the effect of
these masses for the used fixed data window, in terms of potential coefficients, has been subtracted from the reference field,
yielding an adapted reference field. This adapted reference field has been used for the remove–restore technique. The necessary
harmonic analysis of the topographic–isostatic potential using seismic Moho depths with variable density anomalies is given.
A wide comparison among geoids computed by the adapted reference field with both the Airy–Heiskanen isostatic model and seismic
Moho depths with variable density anomaly and a geoid computed by the traditional remove–restore technique is made. The results
show that using seismic Moho depths with variable density anomaly along with the adapted reference field gives the best relative
geoid accuracy compared to the GPS/levelling geoid.
Received: 3 October 2001 / Accepted: 20 September 2002
Correspondence to: H.A. Abd-Elmotaal 相似文献
994.
Summary ?One hundred and thirty six years (1856–1991) of monthly sea-surface temperature (SST) data in the Tropical Atlantic Ocean
are used to investigate the propagating signals of the SST at a decadal (DD) time scale. The first and the third evolving
modes show a relationship between the equatorial and the inter-hemispheric patterns, one evolving into the other mode and
vice-versa. These modes describe two different evolutions of the SST at DD time-scale. The first EEOF features a 12-year period
oscillatory regime with a strong 2-year duration inter-hemispheric pattern evolving into a weak 1-year duration equatorial
pattern and vice-versa. This mode exhibits also a northward displacement of the anomalies in the band 15° S–15° N. The third
EEOF also shows an oscillatory regime, but with a period of 10 years and with a relatively strong 2-year duration equatorial
pattern evolving into a weak 1-year duration inter-hemispheric pattern and vice-versa. For this mode, the SST anomalies show
a southward displacement in the band 15° S–15° N. These results have not yet been documented in previous works and explain
some of the previous findings on the DD variability in the Tropical Atlantic.
Received December 31, 2001; revised April 9, 2002; accepted September 4, 2002
Published online: March 20, 2003 相似文献
995.
Ü. Rannik T. Markkanen J. Raittila P. Hari T. Vesala 《Boundary-Layer Meteorology》2003,109(2):163-189
Observations of wind statistics within and above a Scots pine forest are comparedwith those predicted from an analytical second-order closure model. The roughnesssublayer (RSL) effects, and the influence of stability on similarity functions, arestudied using observations. The commonly accepted forms of similarity functionsdescribe the influence of diabatic effects above the RSL well. According to earlierstudies they are expected also to apply within the RSL. As an exception, the averagewind speed normalised with friction velocity was found to be invariant with stabilityclose to the canopy top under unstable conditions. Lagrangian stochastic trajectorysimulations were used to evaluate the influence of canopy turbulence profiles onfootprint prediction. The main uncertainty was found to arise from parameterisationof the random forcing term in the Lagrangian velocity equation. The influence ofdiabatic conditions was studied, and it was found that thermal stability affectssignificantly the footprint function above the forest canopy, but significantuncertainty exists because of uncertainties in the formulation of stability functions. 相似文献
996.
T. Furevik M. Bentsen H. Drange I. K. T. Kindem N. G. Kvamstø A. Sorteberg 《Climate Dynamics》2003,21(1):27-51
A new coupled atmosphere–ocean–sea ice model has been developed, named the Bergen Climate Model (BCM). It consists of the atmospheric model ARPEGE/IFS, together with a global version of the ocean model MICOM including a dynamic–thermodynamic sea ice model. The coupling between the two models uses the OASIS software package. The new model concept is described, and results from a 300-year control integration is evaluated against observational data. In BCM, both the atmosphere and the ocean components use grids which can be irregular and have non-matching coastlines. Much effort has been put into the development of optimal interpolation schemes between the models, in particular the non-trivial problem of flux conservation in the coastal areas. A flux adjustment technique has been applied to the heat and fresh-water fluxes. There is, however, a weak drift in global mean sea-surface temperature (SST) and sea-surface salinity (SSS) of respectively 0.1 °C and 0.02 psu per century. The model gives a realistic simulation of the radiation balance at the top-of-the-atmosphere, and the net surface fluxes of longwave, shortwave, and turbulent heat fluxes are within observed values. Both global and total zonal means of cloud cover and precipitation are fairly close to observations, and errors are mainly related to the strength and positioning of the Hadley cell. The mean sea-level pressure (SLP) is well simulated, and both the mean state and the interannual standard deviation show realistic features. The SST field is several degrees too cold in the equatorial upwelling area in the Pacific, and about 1 °C too warm along the eastern margins of the oceans, and in the polar regions. The deviation from Levitus salinity is typically 0.1 psu – 0.4 psu, with a tendency for positive anomalies in the Northern Hemisphere, and negative in the Southern Hemisphere. The sea-ice distribution is realistic, but with too thin ice in the Arctic Ocean and too small ice coverage in the Southern Ocean. These model deficiencies have a strong influence on the surface air temperatures in these regions. Horizontal oceanic mass transports are in the lower range of those observed. The strength of the meridional overturning in the Atlantic is 18 Sv. An analysis of the large-scale variability in the model climate reveals realistic El Niño – Southern Oscillation (ENSO) and North Atlantic–Arctic Oscillation (NAO/AO) characteristics in the SLP and surface temperatures, including spatial patterns, frequencies, and strength. While the NAO/AO spectrum is white in SLP and red in temperature, the ENSO spectrum shows an energy maximum near 3 years. 相似文献
997.
We compare flux and concentration footprint estimates of athree-dimensional Lagrangian stochastic dispersion modelapplying backward trajectories with the results of ananalytical footprint model by Kormann and Meixner.The comparison is performed for varying stability regimesof the surface layer as well as for different measurementheights. In general, excellent correspondence is found. 相似文献
998.
Cloud type and cloud cover effects on the surface radiative balance at several Polar sites 总被引:1,自引:0,他引:1
Summary ?The present work concerns measurements performed at five Polar sites in order to study the influence of cloud type and cloud
cover on the surface radiative balance. Cloud cover index was retrieved with the Kasten and Czeplak formula (1980), and comparison
with observed values showed the possibility of applying this formula in Polar regions. The Duchon and O’Malley (1999) methodology
was adopted to estimate the cloud types present during the measurement period for each site. The results show that during
the Antarctic summer clouds have a warming effect on the surface, while during a melting event recorded in the Arctic site
clouds have a net cooling effect on the surface. This result allows us to conclude that, during a melting period a different
cloud type formation, and a lower surface albedo, modify the effects of clouds on the surface radiation balance.
Received April 5, 2002; revised August 1, 2002; accepted August 17, 2002 相似文献
999.
N. Mölders U. Haferkorn J. Döring G. Kramm 《Meteorology and Atmospheric Physics》2003,84(1-2):137-156
Summary ¶Various water budget elements (water supply to the atmosphere, ground water recharge, change in storage) are predicted by HTSVS for a period of 2050 days. The predicted water budget elements are evaluated by routine lysimeter data. The results show that land surface models need parameterizations for soil frost, snow effects and water uptake to catch the broad cycle of soil water budget elements. In principle, HTSVS is able to simulate the general characteristics of the seasonal changes in these water budget elements and their long-term accumulated sums. Compared to lysimeter data, there is a discrepancy in the predicted water supply to the atmosphere for summer and winter which may be attributed to the hardly observed plant physiological parameters like root depth, LAI, shielding factor, etc., the lack of measured downward long-wave radiation, and some simplifications made in the parameterizations of soil frost and snow effects. The fact that high resolution data for the evaluation of model results are missing and evaluation is made on the basis of the data from routine stations of a network is typical for the results of long-term studies on climate. Taking into account the coarse resolution of climate models, the coarse vertical resolution that is used in their LSMs, and the lack of suitable parameters needed, it seems that discrepancies in the order of magnitude found in this study are a general uncertainty in the results of land surface modeling on typical spatial and temporal scales of the climate system.Received October 8, 2001; revised February 15, 2002; accepted September 20, 2002
Published online: April 10, 2003 相似文献
1000.
T. Soler 《Journal of Geodesy》1997,71(3):176-188
The exploits of the multifaceted scientist (engineer-geodesist-metrologist) General Carlos Ibá?ez e Ibá?ez de Ibero (1825–1891),
Marqués de Mulhacén, are recounted. A bibliography of his relevant work is included.
Received 27 September 1996; Accepted 2 October 1996 相似文献