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91.
92.
The Planar Shape of Rock Joints 总被引:1,自引:1,他引:0
Knowing the planar shape of discontinuities is important when characterizing discontinuities in a rock mass. However, the
real discontinuity shape is rarely known, since the rock mass is usually inaccessible in three dimensions. Information on
discontinuity shape is limited and often open to more than one interpretation. This paper discusses the planar shape of rock
joints, the most common discontinuities in rock. First, a brief literature review about the shape of joints is presented,
including some information on joint-surface morphology, inferences from observed trace lengths on different sampling planes,
information based on experimental studies, and joint shapes assumed by different researchers. This review shows that joints
not affected by adjacent geological structures such as bedding boundaries or pre-existing fractures tend to be elliptical
(or approximately circular but rarely). Joints affected by or intersecting such geological structures tend to be rectangular.
Then, using the general stereological relationship between trace length distributions and joint size distributions developed
by Zhang et al. (Geotechnique 52(6):419–433, 2002) for elliptical joints, the effect of sampling plane orientation on trace lengths is investigated. This study explains why
the average trace lengths of non-equidimensional (elliptical or similar polygonal) joints on two sampling planes can be about
equal and thus the conclusion that rock joints are equidimensional (circular) drawn from the fact that the average trace lengths
on two sampling planes are approximately equal can be wrong. Finally, methods for characterizing the shape and size of joints
(elliptical or rectangular) from trace length data are recommended, and the appropriateness of using elliptical joint shapes
to represent polygonal, especially rectangular, joints is discussed. 相似文献
93.
Alexander?BorisovEmail author Frank?Brenker Herbert?Palme 《Contributions to Mineralogy and Petrology》2004,148(1):69-78
We have determined the stability of rutile and karrooite on the liquidus of pseudobinary silicate melts of anorthite–diopside eutectic composition with, in addition, of up to 32 wt% TiO2 at one atm total pressure and at wide range of oxygen fugacities. At 1,300°C and at an fO2 below 10–11.2 atm rutile (TiO2) is replaced as liquidus phase by the pseudobrookite-type MgTi2O5–Ti3O5 solid solution with some Al in the crystal structure. The composition of karrooite was found to be strongly dependent on oxygen fugacity. Crystalline phases were identified by transmission electron microscopy (TEM). The results obtained in this study are relevant for understanding the chemistry of lunar armalcolites. Using excess rutile solubility at reducing conditions, we estimated the Ti4+ /Ti3+ ratio in silicate melts at 1,300°C as function of fO2. 相似文献
94.
95.
Christopher A. Gellasch Herbert F. Wang Kenneth R. Bradbury Jean M. Bahr Lauren L. Lande 《Ground water》2014,52(1):105-117
Reverse water‐level fluctuations (RWFs), a phenomenon in which water levels rise briefly in response to pumping, were detected in monitoring wells in a fractured siliciclastic aquifer system near a deep public supply well. The magnitude and timing of RWFs provide important information that can help interpret aquifer hydraulics near pumping wells. A RWF in a well is normally attributed to poroelastic coupling between the solid and fluid components in an aquifer system. In addition to revealing classical pumping‐induced poroelastic RWFs, data from pressure transducers located at varying depths and distances from the public supply well suggest that the RWFs propagate rapidly through fractures to influence wells hundreds of meters from the pumping well. The rate and cycling frequency of pumping is an important factor in the magnitude of RWFs. The pattern of RWF propagation can be used to better define fracture connectivity in an aquifer system. Rapid, cyclic head changes due to RWFs may also serve as a mechanism for contaminant transport. 相似文献
96.
Climate change effects on hydrological system conditions influencing generation of storm runoff in small Alpine catchments 总被引:1,自引:0,他引:1 下载免费PDF全文
Gertraud Meißl Herbert Formayer Klaus Klebinder Florian Kerl Friedrich Schöberl Clemens Geitner Gerhard Markart David Leidinger Axel Bronstert 《水文研究》2017,31(6):1314-1330
Floods and debris flows in small Alpine torrent catchments (<10 km2) arise from a combination of critical antecedent system state conditions and mostly convective precipitation events with high precipitation intensities. Thus, climate change may influence the magnitude–frequency relationship of extreme events twofold: by a modification of the occurrence probabilities of critical hydrological system conditions and by a change of event precipitation characteristics. Three small Alpine catchments in different altitudes in Western Austria (Ruggbach, Brixenbach and Längentalbach catchment) were investigated by both field experiments and process‐based simulation. Rainfall–runoff model (HQsim) runs driven by localized climate scenarios (CNRM‐RM4.5/ARPEGE, MPI‐REMO/ECHAM5 and ICTP‐RegCM3/ECHAM5) were used in order to estimate future frequencies of stormflow triggering system state conditions. According to the differing altitudes of the study catchments, two effects of climate change on the hydrological systems can be observed. On one hand, the seasonal system state conditions of medium altitude catchments are most strongly affected by air temperature‐controlled processes such as the development of the winter snow cover as well as evapotranspiration. On the other hand, the unglaciated high‐altitude catchment is less sensitive to climate change‐induced shifts regarding days with critical antecedent soil moisture and desiccated litter layer due to its elevation‐related small proportion of sensitive areas. For the period 2071–2100, the number of days with critical antecedent soil moisture content will be significantly reduced to about 60% or even less in summer in all catchments. In contrast, the number of days with dried‐out litter layers causing hydrophobic effects will increase by up to 8%–11% of the days in the two lower altitude catchments. The intensity analyses of heavy precipitation events indicate a clear increase in rain intensities of up to 10%. 相似文献
97.
Rutger de Wit Lucas J. Stal Bente Aa. Lomstein Rodney A. Herbert Hans van Gemerden Pierluigi Viaroli Victor-Ugo Cecherelli Francisco Rodríguez-Valera Marco Bartoli Gianmarco Giordani Roberta Azzoni Bart Schaub David T. Welsh Andrew Donnelly Ana Cifuentes Josefa Antn Kai Finster Lise B. Nielsen Anne-Grethe Underlien Pedersen Anne Turi Neubauer Marina A. Colangelo Sander K. Heijs 《Continental Shelf Research》2001,21(18-19)
“Buffer capacities” has been defined in ecology as a holistic concept (e.g., Integration of Ecosystem Theories: A Pattern, second ed. Kluwer, Dordrecht, 1997, 388pp), but we show that it can also be worked out in mechanistic studies. Our mechanistic approach highlights that “buffering capacities” can be depleted progressively, and, therefore, we make a distinction between current and potential “buffering capacities”. We have applied this concept to understand the limited “local stability” in seagrass ecosystems and their vulnerability towards structural changes into macro-algal dominated communities. We explored the following processes and studied how they confer buffering capacities to the seagrass ecosystem: (i) net autotrophy is persistent in Zostera noltii meadows where plant assimilation acts as a sink for nutrients, this contrasted with the Ulva system that shifted back and forth between net autotrophy and net heterotrophy; (ii) the Z. noltii ecosystem possesses a certain albeit rather limited capacity to modify the balance between nitrogen fixation and denitrification, i.e., it was found that in situ nitrogen fixation always exceeded denitrification; (iii) the nitrogen demand of organoheterotrophic bacteria in the sediment results in nitrogen retention of N in the sediment and hence a buffer against release of nitrogen compounds from sediments, (iv) habitat diversification in seagrass meadows provides shelter for meiofauna and hence buffering against adverse conditions, (v) sedimentary iron provides a buffer against noxious sulfide (note: bacterial sulfide production is enhanced in anoxic sediment niches by increased organic matter loading). On the other hand, in the coastal system we studied, sedimentary iron appears less important as a redox-coupled buffer system against phosphate loading. This is because most inorganic phosphate is bound to calcium rather than to iron. In addition, our studies have highlighted the importance of plant–microbe interactions in the seagrass meadows. 相似文献
98.
Richard Titmuss’ classical 1970 study of blood donation has provided a powerful conceptual model for characterising transactions involving human bodily materials. This now paradigmatic model suggests that such transactions are typically organised in accordance with one or other of two dichotomous, and mutually exclusive, modes of exchange: gifting or commodification. In this paper I utilise findings from my own and others’ empirical research to illustrate the range of complex, multiply constituted, and contested modes of commodification that now typically attend the exchange of human body parts and tissues of which Titmuss’ model can take no effective account. Drawing on work by Radin, Callon, and Miller I illustrate the complex justificatory work that those involved must perform to fit their lived experiences of tissue exchange into this now outmoded paradigm. I then consider how the protagonists themselves ontologise their practices and with what effects. In the second part of the paper I consider how neo-liberal ideologies and instruments are being employed to suborn a variety of highly differentiated and geographically distinct practices of bodily commodification to the ‘logic of the market’. I explore here what the operative effects of defining the global circulation of body parts and tissues as a new ‘economy’ might be. I then consider how, if at all, a market logic could ‘Value’ all those ‘calculations of interest’ and ‘values’ that underpin exchanges of human body parts and tissues in specific national, communal or institutional settings. I conclude by reflecting on the desirability or possibility of performing normative assessments of the ethicacy of highly geographically and culturally differentiated practices of bodily commodification. 相似文献
99.
100.
Herbert J. Wiehl David A. Batchelor Carol Jo Crannell Brian R. Dennis Phillip N. Price Andreas Magun 《Solar physics》1985,96(2):339-356
The microwave and hard X-ray characteristics of 13 solar flares that produced microwave fluxes greater than 500 solar flux units have been analyzed. These Great Microwave Bursts were observed in the frequency range from 3 to 35 GHz at Bern, and simultaneous hard X-ray observations were made in the energy range from 30 to 500 keV with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission spacecraft. The principal aim of this analysis is to determine whether or not the same distribution of energetic electrons can explain both emissions. The temporal and spectral behaviors of the microwaves as a function of frequency and the X-rays as a function of energy were tested for correlations, with results suggesting that optically thick microwave emission, at a frequency near the peak frequency, originates in the same electron population that produces the hard X-rays. The microwave emission at lower frequencies, however, is poorly correlated with emission at the frequency which appears to characterize this common source. A single-temperature and a multitemperature model were tested for consistency with the coincident X-ray and microwave spectra at microwave burst maximum. Four events are inconsistent with both of the models tested, and neither of the models attempts to explain the high-frequency part of the microwave spectrum. A source area derived on the basis of the single-temperature model agrees to within the uncertainties with the observed area of the one burst for which spatially resolved X-ray images are available.Swiss National Science Foundation Fellow from the University of Bern.Also Energy/Environmental Research Group, Incorporated, Tucson, Arizona, and Department of Physics and Astronomy, University of North Carolina, Chapel Hill. Present address: Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland. 相似文献