The mechanisms of water diffusion in polymerized silicate melts     

Harald Behrens  M. Nowak 《Contributions to Mineralogy and Petrology》1997,126(4):377-385

Diffusion of water was experimentally investigated for melts of albitic (Ab) and quartz-orthoclasic (Qz₂₉Or₇₁, in wt %) compositions with water contents in the range of 0 to 8.5 wt % at temperatures of 1100 to 1200 °C and at pressures of 1.0 and 5.0 kbar. Apparent chemical diffusion coefficients of water (D _water) were determined from concentration-distance profiles measured by FTIR microspectroscopy. Under the same P-T condition and water content the diffusivity of water in albitic, quartz-orthoclasic and haplogranitic (Qz₂₈Ab₃₈ Or₃₄, Nowak and Behrens, this issue) melts is identical within experimental error. Comparison to data published in literature indicates that anhydrous composition only has little influence on the mobility of water in polymerized melts but that the degree of polymerization has a large effect. For instance, D_water is almost identical for haplogranitic and rhyolitic melts with 0.5–3.5 wt % water at 850 °C but it is two orders of magnitude higher in basaltic than in haplogranitic melts with 0.2–0.5 wt % water at 1300 °C. Based on the new water diffusivity data, recently published in situ near-infrared spectroscopic data (Nowak 1995; Nowak and Behrens 1995), and viscosity data (Schulze et al. 1996) for hydrous haplogranitic melts current models for water diffusion in silicate melts are critically reviewed. The NIR spectroscopy has indicated isolated OH groups, pairs of OH groups and H₂O molecules as hydrous species in polymerized silicate melts. A significant contribution of isolated OH groups to the transport of water is excluded for water contents above 10 ppm by comparison of viscosity and water diffusion data and by inspection of concentration profiles from trace water diffusion. Spectroscopic measurements have indicated that the interconversion of H₂O molecules and OH pairs is relatively fast in silicate glasses and melts even at low temperature and it is inferred that this reaction is an active step for migration of water. However, direct jumps of H₂O molecules from one cavity within the silicate network to another one can not be excluded. Thus, we favour a model in which water migrates by the interconversion reaction and, possibly, small sequences of direct jumps of H₂O molecules. In this model, immobilization of water results from dissociation of the OH pairs. Assuming that the frequency of the interconversion reaction is faster than that of diffusive jumps, OH pairs and water molecules can be treated as a single diffusing species having an effective diffusion coefficient . The shape of curves of D_water versus water content implies that increases with water content. The change from linear to exponential dependence of D_water between 2 and 3 wt % water is attributed to the influence of the dissociation reaction at low water content and to the modification of the melt structure by incorporation of OH groups. Received: 26 March 1996 / Accepted: 23 August 1996  相似文献   

Basic model of water- and gas-flow through smectite clay buffers     

Roland Pusch  Harald Hkmark 《Engineering Geology》1990,28(3-4):379-389

Canister embedment of highly compacted Na bentonite forms a low-permeable medium of significant homogeneity both macro- and microscopically. However, despite the fact that a large part of the porewater is in interlamellar positions and not mobile by ordinary hydraulic gradients, there are still a number of pore passages that let water and gas through even at very high bulk densities. A preliminary model for flow and diffusion has been outlined on the basis of generalized, quantitative microstructural data and basic physical relationships. It accounts for actually recorded hydraulic and gas conductivities as well as for commonly measured swelling pressures. Qualitatively, it is in agreement also with published ion diffusion data.  相似文献   

Who determines transformational change in development and climate finance?     

Harald Winkler  Navroz K. Dubash 《Climate Policy》2016,16(6):783-791

The language of transformational change is increasingly applied to climate policy, and particularly in climate finance. Transformational change in this context is used with respect to low-carbon development futures, with the emphasis on mitigation and GHG metrics. But, for many developing countries, climate policy is embedded in a larger context of sustainable development objectives, defined through a national process. Viewed thus, there is a potential tension between mitigation-focused transformation and nationally driven sustainable development. We explore this tension in the context of operationalizing the Green Climate Fund (GCF), which has to deal with the fundamental tension between country ownership and transformational change. In relation to climate finance, acceptance of diverse interpretations of transformation are essential conditions for avoiding risk of transformational change becoming a conditionality on development. We further draw lessons from climate governance and the development aid literature. The article examines how in the case of both the Clean Development Mechanism and Nationally Appropriate Mitigation Actions, there has been limited success in achieving both development objectives and ‘nationally appropriate’ mitigation. The development aid literature points to process-based approaches as a possible alternative, but there are limitations to this approach.

Policy relevance

The concept of transformational change has gained prominence in climate finance. The conundrum facing the GCF is that it seeks to support transformational change in the climate realm, in a context where countries may have competing priorities. Balancing or even transcending this tension is a fundamental design challenge for the GCF. A primary focus on mitigation, particularly if metrics of performance are tied exclusively to GHG reduction, raise concerns about diluting ownership by recipient countries and evokes concerns of conditionality or worse. The literature on development assistance has explored options notably conditions on process and adequate capacity, and suggests that there are no short cuts to building domestic ownership. Actors on climate change need to avoid the risk that transformational change is perceived as, and becomes, an imposed condition. The risk that transformation change, operationalized in the context of unequal power relations, becomes an imposition on development, needs to be avoided.  相似文献   

Studying spatial and trophic interactions between capelin and cod using individual-based modelling   总被引：2，自引：0，他引：2  

Huse  Geir; Johansen  Geir Odd; Bogstad  Bjarte; Gjosaeter  Harald 《ICES Journal of Marine Science》2004,61(7):1201-1213

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Effect of internal overpressure on free spanning pipelines     

Geir Moe  Harald Stle Hansen  Terje Overvik 《Ocean Engineering》1986,13(2)

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Exsolution in ternary feldspars     

Harald Carstens 《Contributions to Mineralogy and Petrology》1966,14(1):27-35

It is shown that the microstructures of the antiperthites of the South Norwegian anorthosites strongly suggest an exsolution origin. In addition to the normal exsolution reactions responsible for most antiperthites, exsolution of potash feldspar in plagioclase may occur by a discontinuous mode of precipitation.  相似文献   

Implementation and testing of a lateral boundary scheme as an open boundary condition in a barotropic ocean model     

Eivind A. Martinsen  Harald Engedahl 《Coastal Engineering》1987,11(5-6)

The flow relaxation scheme (FRS) is tested as an open boundary condition (OBC). This scheme was originally designed to relax external solutions (ES) from a large area model towards solutions in a limited area model with a fine mesh. When one uses the FRS as a pure OBC; i.e. the ES are unknown and set equal to zero, the FRS method degenerates to a sponge type OBC. Since a sponge type OBC does not work well in all cases, for instance in the case of an alongshore uniform wind; Chapman (1985) and Røed and Cooper (1987), we introduced local wind induced solutions as a part of the ES.When we also included the tide in the ES, the tests showed that the FRS method handled the tidal input problem very well. Even in the case where noise was added to the tide in the ES, the results were good.The major drawbacks for the FRS method are the required extention of the computer-space and -time.  相似文献   

Results from microseismic monitoring,conventional instrumentation,and tomography surveys in the creation and thinning of a burst-prone sill pillar     

Richard McCreary  John McGaughey  Yves Potvin  Dave Ecobichon  Marty Hudyma  Harald Kanduth  Alain Coulombe 《Pure and Applied Geophysics》1992,139(3-4):349-373

Located in northern Québec, the Lac Shortt Mine was a small gold mine consisting of a thin subvertical orebody which was mined in three main phases. High stress and rockbursting conditions were experienced when ore was extracted in the upper zone between the surface and a depth of 500 metres during the first two phases of mining. Severe rockbursts were experienced in late 1989 near the shaft and in the footwall development following a deepening of the mine shaft to a depth of 830 m and partial development of footwall drift access for the third phase of mining (the mining of the lower zone starting at a depth of 830 m moving upward toward a depth of 500 m). A 16-channel Electrolab MP250 microseismic system, with a Queen's University Full-Waveform piggy-back system, was installed underground at the site due to these problems.It was expected that the thinning sill would be subjected to an ever-increasing load as the thickness of the 500 m sill pillar decreased in the face of the mining excavation from below. A monitoring program consisting of the microseismic monitoring system, a range of conventional geomechanics monitoring tools as well as the undertaking of periodic seismic tomography surveys to assess the ongoing state of stress and rock mass condition within the sill was therefore warranted.The anomalously high-magnitude stress field and the brittle rockmass created a situation in which rockmass failure was common and violent. In the creation and thinning of the sill pillar, the location of banded microseismic activity was crucial in tracing rockmass failure and the associated ground control problems. Reliable source-location determination enabled the identification of areas of stress increase. The movement of the rockmass failure front could be followed, and was responsible for stope dilution, footwall and orebody development deterioration, and caving.Source-mechanism analyses gave accurate double-couple solutions for approximately forty percent of these events having at least ten recognizable polarities. Results suggested movement along vertical north-south striking or vertical east-west striking features. Underground observation of damaged access points showed that vertical north-south striking joints were experiencing failure.The microseismic activity, which was consistently concentrated close to the southwest and northeast corners of current production stopes, could be explained by a stress field oriented obliquely to the strike of the orebody, as measured prior to shrinkage of the sill pillar byin situ stress measurements and observed borehole overbreaks. The orientations of theP andT axes for the microseismic activity further confirmed that the stress field oriented obliquely to strike.While an increase in compressional-wave velocity of 2.3 percent, corresponding to a measured stress increase of approximately 10 MPa could be measured by repeated tomographic surveys, it was relatively small and only a factor of two or so above the velocity measured uncertainty. The relative insensitivity of thein situ rock mass modulus to the applied stress is believed to be largely due to the rockmass discontinuities being relatively closed prior to stress increase, as substantiated by the small deformations seen by the extensometer and borehole camera. This situation existed because of the very high pre-mining stress level.The experimental demonstration that the rock could not absorb substantially increased load through the mechanism of discontinuity closure or tightening (which would be reflected in the modulus) may be evidence in itself of potentially burst-prone ground, such as encountered at Lac Shortt.  相似文献   

Nutrient dynamics in the Sylt-Rømø Bight ecosystem,German Wadden Sea: An ecological network analysis approach     

Dan Baird  Harald Asmus  Ragnhild Asmus 《Estuarine, Coastal and Shelf Science》2008

Carbon, nitrogen, and phosphorus flow networks, consisting of 59 compartments, were constructed for the Sylt-Rømø Bight, a large shallow sea in the German Wadden Sea. These networks were analysed using ecological network analysis. Each network depicts the standing stock of each component in the ecosystem, and the flows between them. The trophic efficiency by which material is utilised in the Bight increase from 3%, to 6% to 17% for C, N and P, respectively. The number of cycles though which these elements pass increase from 1 197 for carbon, to 414?744 and 538?800 for nitrogen and phosphorus, respectively. The Finn Cycling Index, reflecting the amount of material recycled as a fraction of the total system activity, TST, increases from 17% for carbon, to 43% for nitrogen, to 81% for phosphorus. Other system level attributes such as the Average Path Length, the Average Internal Mutual Information, Relative Ascendancy, Relative and Normalized Redundancy, show an increase from the carbon to the nitrogen to the phosphorus networks. Phosphorus is tightly cycled over longer pathways than the other two elements, and also has the longest residence time in the Bight. Postulated differences between the behaviour of energy (or carbon) and biogeochemical networks in coastal ecosystems are evident from the results obtained from ecological network analysis.  相似文献   

Facies architecture and sedimentology of a meandering fluvial system: a Palaeogene example from the Weisselster Basin, Germany   总被引：1，自引：0，他引：1  

Jochen Halfar  Walter Riegel  & Harald Walther 《Sedimentology》1998,45(1):1-17

The Schleenhain open pit coal mine, located 30 km south of Leipzig, Germany, exposes Upper Eocene and Oligocene non-marine strata representing fluvial deposition in the centre of the Weisselster Basin. Active mining and successive cuts provided the rare opportunity to obtain a three-dimensional perspective of laterally extensive surface outcrops. These were used to construct a detailed fence diagram, which provided the basis for recognition of key architectural elements in the weakly consolidated meandering stream deposits. In addition to the eight basic architectural elements of Miall (1985 ), the element SL (shallow lake deposits) was newly defined and the element CH (channel) was subdivided into CHg (palaeo-river system) and CHk (small channel). The profiles contain parts of two fining-upward cycles, which are separated by an unconformity spanning the Early Oligocene. Deposits of the first cycle begin with transverse sand bars (downstream accretion deposits-DA) and point bars (lateral accretion deposits-LA). The upper part of the cycle is represented by overbank fines (OF) and the element SL, which consists of laterally discontinuous lenses of dark, plant-bearing, kaolinite-rich clays, that were deposited in shallow lakes adjacent to the active channel. Coal seams interlayered with palaeosols are the main constituents of element OF. Sheetlike bodies of medium to fine gravels (gravel bars and bedforms-GB) on an erosive coal surface mark the beginning of the second cycle. Dissolution of underlying Permian salts and sulphates prior to, during, and after the deposition of the Palaeogene strata caused the development of two synclines within the outcrop. Coal seams and clay horizons which thicken and dip towards the centre of the synclines, provide evidence for their chronological development.  相似文献