Crystallisation of sodium sulfate solutions by evaporation under controlled climatic conditions has revealed the existence
of crystalline hydrated sodium sulfate salts not previously reported. The sodium sulfate phase crystallising and the concentration
of the solution at the point of crystallisation depends on the climatic conditions (temperature and evaporation rate). During
the rehydration of the anhydrous sodium sulfate phase, thenardite, another previously unreported phase was formed prior to
the nucleation of the stable phase, mirabilite Na2SO4 · 10H2O. The addition of organic inhibitors changes both the crystallisation and the rehydration behavior in this system. 相似文献
The evolution of fluid chemistry in compacting rock is controlled by coupled chemical processes and rock deformation. In order to characterize this evolution, we conducted water-rock interaction experiments using quartz aggregates at 150 °C and effective pressure of 34.5 MPa. A coupled fluid flow, chemical reaction, and creep compaction model is developed, in which both free-surface reaction and grain-contact dissolution are considered as system volume and porosity evolve.The direct experimental measurement and numerical modeling indicate that effective pressure has significant effects on pore-fluid chemistry. At the early stages of compaction, pore fluids are supersaturated with respect to bulk quartz. With increasing compaction and time, solute concentrations gradually decrease to saturated conditions. Supersaturation is caused mainly by dissolution of ultrafines and high-energy, unstable surfaces which are produced by stress concentrations at grain contacts during the very early stages of compaction. Grain-contact dissolution also contributes to the solute increase in pore fluid in the early stage of compaction, but the effect is small compared to that of ultrafines and unstable surfaces and only slight supersaturation can be produced by it. The gradual decrease in pore-fluid concentration is related to the mechanical removal of ultrafines by pore-fluid flow and the dissolution of ultrafines and unstable surfaces. It also results from the lessening of grain-contact dissolution.Pore fluids in compacting sedimentary basins of quartz sandstone are nearly saturated throughout most of diagenetic processes. Ultrafines and unstable surfaces produced by stress appear not to be the major sources of quartz cement. 相似文献
In mapping the forest–woodland–savannah mosaic of Budongo Forest Reserve, Uganda, four classification methods were compared, i.e. Maximum Likelihood classifier (MLC), Spectral Angle Mapper (SAM), Maximum Likelihood combined with an Expert System (MaxExpert) and Spectral Angle Mapper combined with an Expert System (SAMExpert). The combination of conventional classifiers with an Expert System proved to be an effective approach for forest mapping. This was also the first time that the SAMExpert had been used in the mapping of tropical forests. SAMExpert not only maps with high accuracy, but is also fast and easy to use, making it attractive for use in less developed countries. Another advantage is that it can be executed on a standard PC set up for image processing.Combining the conventional classifiers (MLC and SAM) with the Expert System significantly improved the classification accuracy. The highest overall accuracy (94.6%) was obtained with SAMExpert. The MaxExpert approach yielded a map with an accuracy of 85.2%, which was also significantly higher than that obtained using the conventional MLC approach.The SAMExpert classifier accurately mapped individual classes. Of the four classes of woodland mapped, the Open Woodland (with Terminalia) and Wooded Grassland classes were more accurately mapped using SAMExpert. The Open Woodland had been previously identified by ecologists, but had never been mapped. 相似文献
Glacifluvial deposits along an ice-marginal zone in Småland, southern Sweden, have been dated using post-IR blue OSL. To test for incomplete bleaching, we adopted two strategies: analysis of modern analogues and small-aliquot dose distributions. Samples of modern fluvial sediments show no significant incomplete bleaching; they yield equivalent doses of only 0.5–2 Gy (0.25–4% of our glacifluvial sediment doses). Small-aliquot dose distributions do not provide any evidence for incomplete bleaching.
The sediments are believed to have been deposited during deglaciation and appear to fall into two age groups: 19–25 ka (mainly sandur sediments) and 33–73 ka (mainly deltaic sediments). Compared to the expected ages (13–15 ka), even the younger glacifluvial OSL ages appear up to 10 000 years (25 Gy) too old. The ages are nevertheless stratigraphically consistent and correspond between sites; we deduce that the 19–25 ka ages are true deposition ages. For glacifluvial sedimentation to take place on the South Swedish Upland at this time either a very early deglaciation is required, or alternatively ice-free conditions just prior to the LGM. The deltaic sediments (33–73 ka) were most likely not significantly bleached during deposition and thus they date events prior to the latest ice advance. 相似文献
Infrared-stimulated luminescence (IRSL) dating of feldspars has the potential to date deposits beyond the age range of quartz optical (OSL) dating. Successful application of feldspar IRSL dating is, however, often precluded due to anomalous-fading, the tunnelling of electrons from one defect site to another. In this paper we test procedures proposed for anomalous-fading correction by comparing feldspar IRSL and quartz OSL dating results on a suite of samples from continental deposits from the southeastern Netherlands. We find that even after anomalous-fading correction IRSL ages underestimate the burial age of the deposits and argue that this may be a consequence of a dependency of anomalous fading rate on the dose rate and on the absorbed dose. 相似文献
The transmission and reduction of vibrations in the far-field of the surface of the ground due to a surface load is investigated theoretically and validated with given field measurement data. The performance of a given stabilization column, located directly underneath the load, at a number of receiver positions is studied and measured in terms of insertion loss. A numerical model is presented, which enables the wave-field in the region of the column to be determined, based on an integral equation formulation of the problem which is solved using a boundary element approach. It is shown that the column has a beneficial effect at low frequencies especially in certain frequency bandwidths and is validated with field data. However, when the Rayleigh wavelength becomes short compared with the depth and width of the column adverse effects occur at some frequencies which are also observed in the far-field. Various depths of columns and material properties of the surrounding soil medium are studied and results presented so that some preliminary physical conclusions may be derived. 相似文献
Four K-feldspar samples from the Yidun Arc, eastern Tibetan Plateau, were analysed by the 40Ar/39Ar method with the aim of recovering information on their thermal history using multiple diffusion domain (MDD) theory. Arrhenius plots for each of the samples reveal low retentivity early in the heating experiments, a property that is attributed to their recrystallised nature. This low argon retentivity appears to violate the MDD assumption that volume diffusion is the only mechanism for argon transport within the crystals, thus the thermal histories derived from these analyses are considered suspect. Nevertheless, the age spectra themselves suggest that the majority of samples had cooled below 200 °C prior to the Eocene collision of India with Asia. Thermal history modelling from apatite fission track analyses from the same and nearby samples shows slow cooling through the apatite fission track partial annealing zone during the Cenozoic in samples from the high elevation, low relief areas of the Yidun Arc, while samples from the major Jinsha River valley show rapid cooling through the partial annealing zone beginning in the Miocene. These results suggest that significant Cenozoic denudation has been localised and that most parts of the Yidun Arc have experienced very little denudation during the Cenozoic. 相似文献
To reduce sediment exports discharging to the Great Barrier Reef (GBR), it is essential to identify the sources of exported sediment. We used modelling of spatial sediment budgets (the SedNet model) to identify sources and deposition of sediment as it is transported through river networks. Catchments with high levels of land clearing, cattle grazing and cropping show the largest increases in sediment export compared with natural conditions. Hillslope erosion supplies 63% of sediment to the rivers. Gully erosion and riverbank erosion are lower sources of sediment at the GBR catchment scale, but they are important in some catchments. Overall, 70% of sediment exported from rivers comes from just 20% of the total catchment area, showing that much of the problem can be addressed in a relatively small area. This is a much more manageable problem than trying to reduce erosion across the entire GBR catchment. Areas of high contribution are all relatively close to the coast because of the high erosion and high sediment delivery potential. 相似文献