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31.
Alfred Kepiński 《Aquatic Sciences - Research Across Boundaries》1962,24(2):272-290
Ohne Zusammenfassung 相似文献
32.
Dr. Alfred Leube 《International Journal of Earth Sciences》1963,52(2):721-744
Zusammenfassung Der südafrikanische Subkontinent kann genetisch in drei Einheiten verschiedenen Alters und unterschiedlicher Entwicklung gegliedert werden. Der älteste Teil wurde etwa vor 3000×106 Jahren stabiler Schelf. Die folgende Geosynklinalbildung — nicht so eindeutig umrissen wie die erste — erlebte ihre Hauptdeformation etwa eine Milliarde Jahre später. Der jüngste Deformationsgürtel erstreckt sich parallel zum Atlantischen Ozean und dürfte ans Ende des Präkambriums zu stellen sein.Präkambrische Geosynklinalen scheinen ausgedehnter und langsamer in ihrer Entwicklung gewesen zu sein als jüngere analoge Einheiten. Früharchaische, kaum deformierte und nur schwachmetamorphe Einheiten werden aus dem östlichen Südafrika beschrieben.
According to the structural evolution of South Africa the subcontinent can be divided into three major units of different age and historical development. The oldest part became a stable shelf about 3000×106 years ago. The following geosyncline, not as well defined as the first unit, was subjected to its major folding about 1000×106 years later. The youngest belt, parallel to the Atlantic Ocean, is of late Pre-Cambrian age.Pre-Cambrian geosynclines apparently have not only been considerably larger, but also required much longer time for the completion of one geotectonic cycle than during younger, post-Cambrian periods of the earth's history. The existence of hardly folded and very slightly metamorphosed early Archean rocks is described of the eastern part of South Africa.
Résumé Conformément à l'évolution structurale de l'Afrique du Sud, cette partie du continent peut être divisée en trois unités principales d'âges et de développement historique différents. La partie la plus ancienne devint un massif stable il y a quelque 3.000×106 années. Le géosynclinal suivant, qui n'était pas aussi bien défini que le premier, a subi son plissement principal quelque 1000×106 années plus tard. Le segment le plus jeune, parallèle à l'Océan atlantique, est d'âge précambrien récent.Les géosynclinaux précambriens non seulement semblent avoir été considérablement plus vastes, mais ont pris également pour accomplir un cycle géotectonique un temps plus long que lors des périodes plus récentes de l'histoire de la terre, postérieures au Cambrien. L'existence de roches archéennes anciennes à peine plissées et très faiblement métamorphosées est décrite dans la partie orientale de l'Afrique méridionale.
, .相似文献
33.
Two classes of volcanic plumes on Io 总被引:1,自引:0,他引:1
Comparison of Voyager 1 and Voyager 2 images of the south polar region of Io has revealed that a major volcanic eruption occured there during the period between the two spacecraft encounters. An annular deposit ~1400 km in diameter formed around the Aten Patera caldera (311°W, 48°S), the floor of which changed from orange to red-black. The characteristics of this eruption are remarkably similar to those described earlier for an eruption centered on Surt caldera (338°W, 45°N) that occured during the same period, also at high latitude, but in the north. Both volcanic centers were evidently inactive during the Voyager 1 and 2 encounters but were active sometime between the two. The geometric and colorimetric characteristics, as well as scale of the two annular deposits, are virtually identical; both resemble the surface features formed by the eruption of Pele (255°W, 18°S). These three very large plume eruptions suggest a class of eruption distinct from that of six smaller plumes observed to be continously active by both Voyagers 1 and 2. The smaller plumes, of which Prometheus is the type example, are longer-lived, deposit bright, whitish material, erupt at velocities of ~0.5 km sec?1, and are concentrated at low latitudes in an equatorial belt around the satellite. The very large Pele-type plumes, on the other hand, are relatively short-lived, deposit darker red materials, erupt at ~1.0 km sec?1, and (rather than restricted to a latitudinal band) are restricted in longitude from 240° to 360°W. Both direct thermal infrared temperature measurements and the implied color temperatures for quenched liquid sulfur suggest that hot spot temperatures of ~650°K are associated with the large plumes and temperatures <400°K with the small plumes. The typical eruption duration of the small plumes is at least several years; that of the large plumes appears to be of the order of days to weeks. The two classes therefore differ by more than two orders of magnitude in duration of eruption. Based on uv, visible, and infrared spectra, the small plumes seem to contain and deposit SO2 in their annuli whereas the large plumes apparently do not. Two other plumes that occur at either end of the linear feature Loki may be intermediate or hybrid between the two classes, exhibiting attributes of both. Additionally, Loki occurs in the area of overlap in the regional distributions of the two plume classes. Two distinct volcanic systems involving different volatiles may be responsible for the two classes. We propose that the discrete temperatures associated with the two classes are a direct reflection of sulfur's peculiar variation in viscosity with temperature. Over two temperature ranges (~400 to 430°K and >650°K), sulfur is a low-viscosity fluid (orange and black, respectively); at other temperatures it is either solid or has a high viscosity. As a result, there will be two zones in Io's crust in which liquid sulfur will flow freely: a shallow zone of orange sulfur and a deeper zone of black sulfur. A low-temperature system driven by SO2 heated to 400 to 400°K by the orange sulfur zone seems the best model for the small plumes; a system driven by sulfur heated to >650°K by hot or even molten silicates in the black sulfur zone seems the best explanation for the large plume class. The large Pele-type plumes are apparently concentrated in a region of the satellite in which a thinner sulfur-rich crust overlies the tidally heated silicate lithosphere, so the black sulfur zone may be fairly shallow in this region. The Prometheus-type plumes are possibly confined to the equatorial belt by some process that concentrates SO2 fluid in the equatorial crust. 相似文献
34.
Alfred Clark Jr. 《Solar physics》1968,4(4):386-400
Some theoretical models are given which illustrate the structure of chromospheric magnetic fields associated with supergranulation. It is found that the chromospheric fields depend critically on whether or not there are large-scale vertical motions at the level where the horizontal supergranule motions are observed. In the absence of such motions, the concentration of field produced in the photosphere does not persist more than a few scale heights into the chromosphere; however, the chromospheric mass density is increased above the supergranule boundaries in this case. Completely different results-such as a chromospheric potential field-may be obtained by the inclusion of vertical motions. It is concluded that a rather wide range of chromospheric-field structures is consistent with present observational knowledge of the supergranulation. 相似文献
35.
Martin?SchmidEmail author Andreas?Lorke Alfred?Wüest Michel?Halbwachs Gregory?Tanyileke 《Ocean Dynamics》2003,53(3):288-301
To prevent the recurrence of a disastrous eruption of carbon dioxide (CO2) from Lake Nyos, a degassing plan has been set up for the lake. Since there are concerns that the degassing of the lake may reduce the stability of the density stratification, there is an urgent need for a simulation tool to predict the evolution of the lake stratification in different scenarios. This paper describes the development of a numerical model to predict the CO2 and dissolved solids concentrations, and the temperature structure as well as the stability of the water column of Lake Nyos. The model is tested with profiles of CO2 concentrations and temperature taken in the years 1986 to 1996. It reproduces well the general mixing patterns observed in the lake. However, the intensity of the mixing tends to be overestimated in the epilimnion and underestimated in the monimolimnion. The overestimation of the mixing depth in the epilimnion is caused either by the parameterization of the k-epsilon model, or by the uncertainty in the calculation of the surface heat fluxes. The simulated mixing depth is highly sensitive to the surface heat fluxes, and errors in the mixing depth propagate from one year to the following. A precise simulation of the mixolimnion deepening therefore requires high accuracy in the meteorological forcing and the parameterization of the heat fluxes. Neither the meteorological data nor the formulae for the calculation of the heat fluxes are available with the necessary precision. Consequently, it will be indispensable to consider different forcing scenarios in the safety analysis in order to obtain robust boundary conditions for safe degassing. The input of temperature and CO2 to the lake bottom can be adequately simulated for the years 1986 to 1996 with a constant sublacustrine source of 18 l s–1 with a CO2 concentration of 0.395 mol l–1 and a temperature of 26 °C. The results of this study indicate that the model needs to be calibrated with more detailed field data before using it for its final purpose: the prediction of the stability and the safety of Lake Nyos during the degassing process.Responsible Editor: Hans Burchard 相似文献
36.
Aspects of GLONASS Carrier-Phase Differencing 总被引:2,自引:0,他引:2
37.
38.
Hideyuki Saio Norman H. Baker & Alfred Gautschy 《Monthly notices of the Royal Astronomical Society》1998,294(4):622-634
Properties of the so-called strange modes occurring in linear stability calculations of stellar models are discussed. The behaviour of these modes is compared for two different sets of stellar models, for very massive zero-age main-sequence stars and for luminous hydrogen-deficient stars, both with high luminosity-to-mass ratios. We have found that the peculiar behaviour of the frequencies of the strange modes with the change of a control parameter is caused by the pulsation amplitude of a particular eigenmode being strongly confined to the outer part of the envelope, around the density inversion zone. The frequency of a strange mode changes because the depth of the confinement zone changes with the control parameter. Weakly non-adiabatic strange modes tend to be overstable because the amplitude confinement quenches the effect of radiative damping. On the other hand, extremely non-adiabatic strange modes become overstable because the perturbation of radiation force (gradient of radiation pressure) provides a restoring force that can be out of phase with the density perturbation. We discuss this mechanism by using a plane-parallel two-zone model. 相似文献
39.
Steven C. Schimmel James M. Patrick Linda F. Faas Jerry L. Oglesby Alfred J. Wilson 《Estuaries and Coasts》1979,2(1):9-15
Two long-term studies were conducted to determine toxicity, uptake and depuration of Kepone in blue crabs (Callinectes sapidus). In the first, Kepone was administered to crabs in seawater (0.03 or 0.3 μg Kepone/I) or food (eastern oyster,Crassostrea virginica, containing 0.25 μg/g Kepone). Uptake of Kepone in 28 days was primarily through the contaminated oysters. When these crabs were held in Kepone-free seawater and fed Kepone-free oysters for 28 days, no loss of the insecticide was evident. There were adverse effects on molting and survival in crabs fed oysters that contained 0.25 μg/g Kepone. A second study was conducted to determine: (1) the depuration of Kepone over a 90-day period in blue crabs fed oysters from the James River, Virginia (containing 0.15 μg/g Kepone); and (2) the effects of Kepone on molting and survival of blue crabs fed James River oysters or laboratory-contaminated oysters that contained 0.15 or 1.9 μg/g Kepone. Crabs fed Kepone-contaminated oysters followed by a diet of Kepone-free oysters for 90 days had detectable concentrations of the insecticide in tissues. Also, blue crabs that ate oysters containing Kepone in concentrations similar to those found in oysters from the James River, died or molted less frequently than crabs fed Kepone-free oysters meats. 相似文献
40.
István Gábor Hatvani Norbert Magyar Matthias Zessner József Kovács Alfred Paul Blaschke 《Hydrogeology Journal》2014,22(4):779-794
Water protection is one of the most important goals in environmental protection. The Clean Water Act in the USA and the Water Framework Directive (WFD) in Europe are the legal frameworks to facilitate the achievement of this goal. The question is raised of whether more information can be extracted from WFD-related groundwater data. To answer it, a methodology has been developed that is easy to use and could be implemented into official practice. A case study is presented in which the groundwater data of a sodic area in Austria (Seewinkel) is assessed. Eighteen parameters in groundwater sampled from 23 wells (1991–2011) were analyzed. With basic statistics, trend-, cluster-, Wilks’ λ and spatial sampling density analysis, local phosphorus and boron phenomena were described, along with the determining role of sulphate, groundwater flow, and the oxygen gradient in the area. As a final step, the spatial sampling density was determined. Regarding the current set of parameters, all the sampling sites are necessary and only in the case of certain parameters (Ca2+, Mg2+, K+, NO3 ?, pH) could one sampling site be abandoned. The methodology applied brings a new perspective to exploring groundwater data collected according to the requirements of the WFD. 相似文献