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421.
The similarity solutions of the equations of kinematic flow on a cone-shaped surface, provide a means for checking the numerical models used for converging and diverging flows. These models can be further improved if the initial excess rainfall curve can be described as a power of time. Illustration of this improvement and assessment of numerical models are given for a constant excess rainfall and for excess rainfall proportional to the inverse of the square root of time. 相似文献
422.
A thick blanket of Holocene alluvium lies over southwestern lowland Amazonia, and may possibly occur throughout much of the Amazon Basin. These deposits resulted from massive, seasonal flooding from about 11,000 to about 5000 yr B.P. that was followed by two cycles of erosion and deposition. Interpretations based on these geologic data suggest that southwestern lowland Amazonia is ecologically an “island” in a state of supersaturated disequilibrium as a result of colonization from Pleistocene refugia on its perimeter, and that habitats of highest diversity may be the most recent in origin. Conservation efforts and studies of Amazonian biogeography, soils, and paleoethnography should be reevaluated in light of the geologic data. 相似文献
423.
Wallace H. Campbell 《Surveys in Geophysics》1986,8(3):239-259
Electric currents in long pipelines can contribute to corrosion effects that limit the pipe's lifetime. One cause of such electric currents is the geomagnetic field variations that have sources in the Earth's upper atmosphere. Knowledge of the general behavior of the sources allows a prediction of the occurrence times, favorable locations for the pipeline effects, and long-term projections of corrosion contributions. The source spectral characteristics, the Earth's conductivity profile, and a corrosion-frequency dependence limit the period range of the natural field changes that affect the pipe. The corrosion contribution by induced currents from geomagnetic sources should be evaluated for pipelines that are located at high and at equatorial latitudes. At midlatitude locations, the times of these natural current maxima should be avoided for the necessary accurate monitoring of the pipe-to-soil potential. 相似文献
424.
Campbell M. J. Farmer J. C. Fitzner C. A. Henry M. N. Sheppard J. C. Hardy R. J. Hopper J. F. Muralidhar V. 《Journal of Atmospheric Chemistry》1986,4(4):413-427
Radiochemical techiques have many untapped applications in atmospheric chemistry, especially when great sensitivity is required. We describe the application of these techniques to the measurement of hydroxyl radical concentrations in the troposphere. 相似文献
425.
Wallace H. Campbell 《Pure and Applied Geophysics》1987,125(2-3):427-457
The electrical conductivity of the Earth's upper mantle can be inferred from geomagnetic quiet-day,Sq, variations recorded at the world's observatories using the, coefficients of a spherical harmonic analysis (SHA) that separate the external (source) and internal (induced) parts of the surface field. The conductivity profile determined from such an analysis can be sensitive to special characteristics of the quiet field itself as well as the separation techniques employed. This review of the Sq-analysis features critical to a conductivity derivation is pictorially presented along with the equations for application of theSchmucker (1970) technique to theSHA coefficients for a conductivity determination. Three examples illustrate the use of these equations with differentSq models. 相似文献
426.
The equations of motion are derived for the first mode response of a linear multistorey structure having a linear vibration absorber attached to the roof. Furthermore, the variance of the first mode response to a gaussian white noise lateral base acceleration (as a model of earthquake excitation) is determined. Smallest possible values of the variance of the response along with corresponding absorber parameters are established using an optimization program. It is demonstrated that the absorber is quite effective in reducing first mode response for 5- and 10-storey structures even with relatively small values of the absorber mass. Moreover, minimal responses for the randomly excited single-degree-of-freedom system have been determined, and a design example is presented. The absorber system has potential application not only in earthquake engineering but also in aerospace and terrestrial vehicle design. 相似文献
427.
Particulate trace metal speciation in stream sediments and relationships with grain size: Implications for geochemical exploration 总被引:1,自引:0,他引:1
Sediment samples were collected from streambeds in an undisturbed watershed in eastern Quebec (Gaspé Peninsula). Two sampling sites were located on a stream draining an area of known mineralization (Cu, Pb, Zn) and two on a control stream. The sediment samples were separated into 8 distinct size classes in the 850 μm to <1 μm size range by wet sieving, gravity sedimentation or centrifugation. Each sediment subsample was then subjected to a sequential extraction procedure designed to partition the particulate heavy metals into five fractions: (1) exchangeable; (2) specifically adsorbed or bound to carbonates; (3) bound to Fe-Mn oxides; (4) bound to organic matter; (5) residual. The following metals were analyzed in each extract: Cu, Pb, Zn; Fe, Mn.Comparison of samples from the mineralized area with control samples revealed the expected increase in total concentrations for Cu, Pb and Zn. Non-detrital metals were mainly associated with Fe oxides (specifically adsorbed; occluded) and with organic matter or resistant sulfides. For a given sample, variation of trace metal levels in fractions 2 and 3 with grain size reflected changes in the available quantities of the inorganic scavenging phase (FeOx/MnOx); normalization with respect to Fe and Mn content in fraction 3 greatly reduced the apparent dependency on grain size.The results of this study suggest that a single reducing extraction (NH2OH.HCl) could be used advantageously to detect anomalies in routine geochemical surveys. A second leaching step with acidified H2O2 could also be included, as the trace metal concentrations in fraction 4, normalized with respect to organic carbon content, also showed high {anomaly/background} ratios. 相似文献
428.
Alfons Zehnder Dr. J. Komárek Prof. Dr. S. Golubić Prof. Dr. R. Y. Stanier Dr. J. Komárek Dr. J. Ludvík Dr. L. Kováčik Dr. Asta Almestrand Prof. Dr. P. Compère Dr. D. Mollenhauer Dr. F. Hindák Dr. T. P. Chang Dr. Nagaraj Jeeji Bai C. V. Seshadri Dr. M. -E. Meffert Dr. R. Oberhäuser Dr. J. Overbeck Dr. F. Hindák Susan E. Campbell Dr. Jaroslava Komárková Dr. U. Uehlinger Dr. F. Schanz Dr. Alfons Zehnder 《Aquatic Sciences - Research Across Boundaries》1983,45(1):267-310
The 8th Symposium of the International Association for Cyanophyte Research IAC was attended by 29 specialists from 11 countries.
The 19 oral presentations and discussions centered on the following themes: The basic principles of cyanophyte taxonomy (3
lectures), systematic problems of certain taxonomic groups (5 lectures), morphology (6 lectures) and ecology (5 lectures).
The intensive discussions between representatives of the classical (european) taxonomic treatment of cyanophytes (based on
morphological and ecological characteristics) and those representing the bacteriological study of ‘cyanobacteria’ were especially
valuable. The central theme of the meeting was, however, the mutual microscopic study and discussion of problematic blue-greens
from natural habitats, that were mostly collected during the three field trips into different areas of central Switzerland
(Grimsel-Gotthard-Nufenen. Klewenalp. Gerzensee).
相似文献
429.
Sean W. Campbell John C. Dixon Colin E. Thorn & Robert G. Darmody 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):179-185
This study examines the spatial and temporal variability of chemical denudation rates in Kärkevagge, northern Sweden. The chemical flux rates within the valley are strongly influenced by the local geology. Chemical denudation rates determined for the study period are more than double those previously reported in the literature for this valley. Rates of greater than 46t km−2 a−1 were measured at the valley mouth over the course of the melt season. This difference is likely due to differences in measurement technique compared to that used by past researchers. This rate is also much higher than for other arctic and alpine watersheds. Chemical denudation in Kärkevagge is comparable to larger temperate rivers. The rapid chemical denudation in Kärkevagge is likely due to sulfide weathering creating acid solutions. 相似文献
430.
D. A. Senske D. B. Campbell E. R. Stofan P. C. Fisher J. W. Head N. Stacy J. C. Aubele A. A. Hine J. K. Harmon 《Earth, Moon, and Planets》1991,55(2):163-214
New radar images (resolution 1.5–2.0 km) obtained from the Arecibo Observatory are used to assess the geology of a portion of the equatorial region of Venus (1 S to 45 N and from 270 eastward to 30). Nine geologic units are mapped on the basis of their radar characteristics and their distribution and correspondences with topography are examined. Plains are the most abundant unit, make up 80%; of the area imaged, and are divided into bright, dark, and mottled. Mottled plains contain abundant lava flows and domes suggesting that volcanism forming plains is a significant process in the equatorial region of Venus. Tesserae are found primarily on Beta Regio and its eastern flank and are interpreted to be locally stratigraphically older units, predating episodes of faulting and plains formation. Isolated regions of tesserae concentrated to the north of Western Eistla Regio are interpreted to predate the formation of plains in this area. The volcanoes Sif Mons, Gula Mons, Sappho, Theia Mons, and Rhea Mons, are found exclusively in highland regions and their deposits are interpreted as contributing only a small percentage to the overall volume of the regional topography. The northern 15 of the image data overlap with Venera 15/16 images making it possible to examine the characteristics of geologic units mapped under various illumination directions and incidence angles. Surface panoramas and geochemical data obtained from Venera landers provide ground truth for map units, evidence that plains are made up of basaltic lava flows, and that linear deformation zones contain abundant blocks and cobbles. On the basis of spatial and temporal relationships between geologic units, the highlands of Beta Regio and Western Eistla Regio are interpreted to have formed in association with areas of mantle upwelling which uplift plains, cause rifting, and in the case of Beta Regio, disrupt a large region of tessera. Zones of linear belt deformation in Beta Regio and Western Eistla Regio are interpreted to be extensional and indicate that at least limited extension has occurred in both regions. The images reveal for the first time that southern Devana Chasma is a region of overlapping rift valleys separated by a distance of 600 km. Linear deformation zones in Guinevere Planitia, separating Beta Regio and Eistla Regio, converge at a region of ovoids forming a discontinuous zone of disruption and completes an equatorial encompassing network of highlands and tectonic features. The similarity between ovoids and coronae suggests a mechanism of formation associated with hotspots or mantle plumes. Analysis of the distribution and density of impact craters suggests a surface age for this part of the planet similar to or slightly less than that determined for the northern high latitudes from Venera 15/16 data (0.3 to 1.5 by) and comparable to that calculated for the southern hemisphere. 相似文献