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81.
82.
Marc Rütschlin Johannes H. Cloete Iain M. Mason Keith D. Palmer 《Journal of Applied Geophysics》2007,62(4):354-360
A new measurement technique enables the complex dielectric properties of the geological strata comprising the UG1–UG2 (Upper Group 1–Upper Group 2) unit of the Bushveld Complex in South Africa to be determined with unprecedented detail at radio frequencies (RF). Results of non-destructive laboratory measurements of representative diamond drill core samples from the UG1–UG2 unit are presented at 25 MHz. These data establish that the UG1 and UG2 chromitite layers are embedded in rock strata (norite, pyroxenite and anorthosite) which are translucent in the HF spectral band, whereas the chromitite layers themselves exhibit significant velocity contrast, making them good radar reflectors. The data presented here is useful for calibration of the radar system, and for predicting the range and resolution performance of borehole radars operating in both the hanging and footwalls of the economically important platiniferous UG2 reef. 相似文献
83.
Wolfram Wobrock Andrea I. Flossmann Marie Monier Jean-Marc Pichon Laurent Cortez Jean-Franois Fournol Alfons Schwarzenbck Stephan Mertes Jost Heintzenberg Paolo Laj Giordano Orsi Loretta Ricci Sandro Fuzzi Harry Ten Brink Piet Jongejan Ren Otjes 《Atmospheric Research》2001,58(4):7907
The second field campaign of the Cloud Ice Mountain Experiment (CIME) project took place in February 1998 on the mountain Puy de Dôme in the centre of France. The content of residual aerosol particles, of H2O2 and NH3 in cloud droplets was evaluated by evaporating the drops larger than 5 μm in a Counterflow Virtual Impactor (CVI) and by measuring the residual particle concentration and the released gas content. The same trace species were studied behind a round jet impactor for the complementary interstitial aerosol particles smaller than 5 μm diameter. In a second step of experiments, the ambient supercooled cloud was converted to a mixed phase cloud by seeding the cloud with ice particles by the gas release from pressurised gas bottles. A comparison between the physical and chemical characteristics of liquid drops and ice particles allows a study of the fate of the trace constituents during the presence of ice crystals in the cloud.In the present paper, an overview is given of the CIME 98 experiment and the instrumentation deployed. The meteorological situation during the experiment was analysed with the help of a cloud scale model. The microphysics processes and the behaviour of the scavenged aerosol particles before and during seeding are analysed with the detailed microphysical model ExMix. The simulation results agreed well with the observations and confirmed the assumption that the Bergeron–Findeisen process was dominating during seeding and was influencing the partitioning of aerosol particles between drops and ice crystals. The results of the CIME 98 experiment give an insight on microphysical changes, redistribution of aerosol particles and cloud chemistry during the Bergeron–Findeisen process when acting also in natural clouds. 相似文献
84.
Paolo Laj Andrea I. Flossmann Wolfram Wobrock Sandro Fuzzi Giordano Orsi Loretta Ricci Stephan Mertes Alfons Schwarzenbck Jost Heintzenberg Harry Ten Brink 《Atmospheric Research》2001,58(4):256
We investigated the partitioning of trace substances during the phase transition from supercooled to mixed-phase cloud induced by artificial seeding. Simultaneous determination of the concentrations of H2O2, NH3 and black carbon (BC) in both condensed and interstitial phases with high time resolution showed that the three species undergo different behaviour in the presence of a mixture of ice crystals and supercooled droplets. Both H2O2 and NH3 are efficiently scavenged by growing ice crystals, whereas BC stayed predominantly in the interstitial phase. In addition, the scavenging of H2O2 is driven by co-condensation with water vapour onto ice crystals while NH3 uptake into the ice phase is more efficient than co-condensation alone. The high solubility of NH4+ in the ice could explain this result. Finally, it appears that the H2O2–SO2 reaction is very slow in the ice phase with respect to the liquid phase. Our results are directly applicable for clouds undergoing limited riming. 相似文献
85.
Broadband synthetic aperture borehole radar interferometry 总被引:1,自引:0,他引:1
Trials in mines have established that wideband VHF borehole radars (BHR), working in the 10–100-MHz band, can be used to probe the rockmass between boreholes over ranges from <5 m to as much as 150 m with submeter resolution. There is evidence that ore bodies reflect these radar signals both specularly and diffusely, much as the ground/air interface does when overflown by synthetic aperture radar (SAR). In both SAR and BHR, multiple flight lines, together with diffuse reflections admit the possibility of developing interferometric 3D images of the object. This paper examines the possibility of imaging buried objects in three dimensions by interferometrically combining broadband VHF borehole radar profiles shot in adjacent pairs of boreholes. Broadbanding in BHR has the advantage of releasing the image from 2nπ phase ambiguities, but practically, interferometric borehole radar (InBHR) needs high signal-to-noise ratios (SNR) to avoid noise capture. This means that 3D InBHR is limited to ranges in wavelengths which are less than the rock's attenuation factor Q. Interferometric methods are developed which are capable of mapping ore bodies and other structures in three dimensions. Tangent plane migration methods are developed here in order to reconstruct surfaces that lie in the near-field of sparse interferometric arrays. 相似文献
86.
Free cupric ion concentrations and Cu complexation in selected Swiss lakes and rivers 总被引:1,自引:0,他引:1
Hanbin Xue Andrea Oestreich David Kistler Laura Sigg 《Aquatic Sciences - Research Across Boundaries》1996,58(1):69-87
[Cu2+] and Cu complexation parameters in some selected freshwater systems in Switzerland were determined by the technique of ligand-exchange and DPCSV. Results from the water columns of some eutrophic and oligotrophic lakes are presented and compared to small acid lakes. Cu is strongly complexed by organic ligands which with very high stability constants at low concentrations are probably biologically produced, as indicated by the seasonal variations in the eutrophic lakes and by the relationship between Cu complexation and algal activity in the eutrophic (pCu=15–16), oligotrophic (pCu=13–14) and acidic (pCu=9–10) lakes. The extent of Cu complexation in river waters was generally lower than in the eutrophic lakes, at similar DOC levels. No obvious correlation between Cu complexation and DOC was observed, indicating that Cu complexing ligands are specific organic compounds. 相似文献
87.
88.
The sources and composition of mercury in Pacific Ocean rain 总被引:1,自引:0,他引:1
Here we report measurements of total Hg (HgT), reactive Hg (HgR), and methylmercury (MMHg) in precipitation from the equatorial Pacific Ocean, collected during a cruise in January and February 1990, and from a mid-continental location in the rural temperate lacustrine northcentral Wisconsin environs. The concentrations of HgT (14.4±6.5 pM), HgR (8.9±4.5 pM) and MMHg (<50 fM) found in equatorial Pacific rain were less than the average concentrations found in Wisconsin. In general, the results indicate that although particulate Hg is a small fraction of the total atmospheric Hg burden, it is the major contributor to Hg in precipitation. Furthermore, deposition could be an important source of HgR to the equatorial Pacific Ocean. In contrast, deposition is not a significant source of MMHg to either the equatorial Pacific Ocean or the remote seepage lakes of Wisconsin. This implies that methylated mercury is formedin situ in these systems. 相似文献
89.
A model is proposed describing the mechanical evolution of a shear zone along compressional and extensional plate boundaries, subject to constant strain rate. The shear zones are assumed as viscoelastic with Maxwell rheology and with elastic and rheological parameters depending on temperature and petrology. Stress and strain are computed as functions of time and depth. For both kinds of boundaries the model reproduces the existence of a shallow seismogenic zone, characterized by a stress concentration. The thickness of the seismogenic layer is evaluated considering the variations of shear stress and frictional strength on faults embedded in the shear zone. Assuming that a fault dislocation takes place, the brittle-ductile transition is assumed to occur at the depth at which the time derivative of total shear stress changes from positive to negative values. The effects of different strain rates and geothermal gradients on the depth of the brittle-ductile transition are studied. The model predictions are consistent with values inferred from seismicity data of different boundary zones. 相似文献
90.
ABSTRACTExperimental work in hydrology is in decline. Based on a community survey, Blume et al. showed that the hydrological community associates experimental work with greater risks. One of the main issues with experimental work is the higher chance of negative results (defined here as when the expected or wanted result was not observed despite careful experimental design, planning and execution), resulting in a longer and more difficult publishing process. Reporting on negative results would avoid putting time and resources into repeating experiments that lead to negative results, and give experimental hydrologists the scientific recognition they deserve. With this commentary, we propose four potential solutions to encourage reporting on negative results, which might contribute to a stimulation of experimental hydrology. 相似文献