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791.
This paper presents the application of a discrete element technique to the analysis of the dynamic indentation of either a purely brittle or a brittle viscoplastic geomaterial which can experience fragmentation resulting in fragments with size dependent strength characteristics. 相似文献
792.
Prof. Dr. I. D. Ryabchikov Dr. Ch. Miller Prof. Dr. P. W. Mirwald 《Mineralogy and Petrology》1996,58(1-2):101-110
Summary Compositions of the hydrous melts in equilibrium with garnet, omphacitic clinopyroxene and quartz have been investigated experimentally at 28.5 and 35 kbar. They are represented by silica-rich liquids (> 70% SiO2) with low MgO, FeO and CaO contents. The removal of ca 10–15% of the magma of this composition may be sufficient to convert quartz eclogite formed after subduction of altered MORB into a quartz-free bimineralic eclogite assemblage, which is a common type of xenoliths in kimberlites.At 28.5 kbar the solidus temperature is between 700 and 750° C in the system quartz eclogite—water, and the high pressure amphibole-out boundary lies at ca 25 kbar in accord with the previous studies.
With 1 Figures 相似文献
Die Zusammensetzung wasserhältiger Schmelzen im Gleichgewicht mit Quarz-Eklogiten
Zusammenfassung Um Prozesse zu simulieren, die bei der Subduktion von Ozeanbodenbasalten durch partielle Anatexis im Stabilitätsfeld von Eklogiten ablaufen, wurde die Zusammensetzung wasserhältiger Schmelzen in Gleichgewicht mit Granat, Omphacit und Quarz bei 28.5 und 35 Kbar experimentell untersucht. Diese Schmelzen sind reich an SiO2 (> 70 Gew%) und arm an Mg0, Fe0 and CaO. Die Extraktion von ca. 10–15% derartiger Schmelzen würde genügen, um quarzführende Eklogite, die durch die Subduktion von alteriertem MORB Material entstanden sind, in quarzfreie bimineralische Eklogite umzuwandeln wie sie häufig als Xenolithe in Kimberliten beobachtet werden.Im System Quarz-Eklogit-Wasser liegt die Solidustemperatur bei 28.5 Kbar zwischen 700 und 750°C. Die obere Stabilitätsgrenze von Amphibol liegt in diesem Temperaturbereich bei ca. 25 Kbar.
With 1 Figures 相似文献
793.
A cool period from about 11000 to 10 500 BP (11 to 10.5 ka) is recognized in pollen records from the southern Great Lakes area by the return of Picea and Abies dominance and by the persistence of herbs. The area of cooling appears centred on the Upper Great Lakes. A high-resolution record (ca. 9 mm/y) from a borehole in eastern Lake Erie reveals, in the same time interval, this pollen anomaly, isotope evidence of meltwater presence (a — 3 per mil shift in 18O and a +1.1 per mil shift in 13C), increased sand, and reduced detrital calcite content, all suggesting concurrent cooling of Lake Erie. The onset of cooling is mainly attributed to the effect of enhanced meltwater inflow on the relatively large upstream Main Lake Algonquin during the first eastward discharge of glacial Lake Agassiz. Termination of the cooling coincides with drainage of Lake Algonquin, and is attributed to loss of its cooling effectiveness associated with a substantial reduction in its surface area. It is hypothesized that the cold extra inflow effectively prolonged the seasonal presence of lake ice and the period of spring overturn in Lake Algonquin. The deep mixing would have greatly increased the thermal conductive capacity of this extensive lake, causing suppression of summer surface lakewater temperatures and reduction of onshore growing-degree days. Alternatively, a rapid flow of meltwater, buoyed on sediment-charged (denser) lakewater, may have kept the lake surface cold in summer. Other factors such as wind-shifted pollen deposition and possible effects from the Younger Dryas North Atlantic cooling could have contributed to the Great Lakes climatic reversal, but further studies are needed to resolve their relative significance.Contribution to Climo Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate ProgramGeological Survey of Canada Contribution 58 890 相似文献
794.
795.
Sahila Beegum Jiří Šimůnek Adam Szymkiewicz K. P. Sudheer Indumathi M. Nambi 《Ground water》2019,57(3):392-408
The “HYDRUS package for MODFLOW” is an existing MODFLOW package that allows MODFLOW to simultaneously evaluate transient water flow in both unsaturated and saturated zones. The package is based on incorporating parts of the HYDRUS-1D model (to simulate unsaturated water flow in the vadose zone) into MODFLOW (to simulate saturated groundwater flow). The coupled model is effective in addressing spatially variable saturated-unsaturated hydrological processes at the regional scale. However, one of the major limitations of this coupled model is that it does not have the capability to simulate solute transport along with water flow and therefore, the model cannot be employed for evaluating groundwater contamination. In this work, a modified unsaturated flow and transport package (modified HYDRUS package for MODFLOW and MT3DMS) has been developed and linked to the three-dimensional (3D) groundwater flow model MODFLOW and the 3D groundwater solute transport model MT3DMS. The new package can simulate, in addition to water flow in the vadose zone, also solute transport involving many biogeochemical processes and reactions, including first-order degradation, volatilization, linear or nonlinear sorption, one-site kinetic sorption, two-site sorption, and two-kinetic sites sorption. Due to complex interactions at the groundwater table, certain modifications of the pressure head (compared to the original coupling) and solute concentration profiles were incorporated into the modified HYDRUS package. The performance of the newly developed model is evaluated using HYDRUS (2D/3D), and the results indicate that the new model is effective in simulating the movement of water and contaminants in the saturated-unsaturated flow domains. 相似文献
796.
Ashok K. Mishra Mehmet ?zger Vijay P. Singh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(4):517-535
Climate model simulations for the twenty-first century point toward changing characteristics of precipitation. This paper
investigates the impact of climate change on precipitation in the Kansabati River basin in India. A downscaling method, based
on Bayesian Neural Network (BNN), is applied to project precipitation generated from six Global Climate Models (GCMs) using
two scenarios (A2 and B2). Wet and dry spell properties of monthly precipitation series at five meteorologic stations in the
Kansabati basin are examined by plotting successive wet and dry durations (in months) against their number of occurrences
on a double-logarithmic paper. Straight-line relationships on such graphs show that power laws govern the pattern of successive
persistent wet and dry monthly spells. Comparison of power-law behaviors provides useful interpretation about the temporal
precipitation pattern. The impact of low-frequency precipitation variability on the characteristics of wet and dry spells
is also evaluated using continuous wavelet transforms. It is found that inter-annual cycles play an important role in the
formation of wet and dry spells. 相似文献
797.
The least squares collocation algorithm for estimating gravity anomalies from geodetic data is shown to be an application
of the well known regression equations which provide the mean and covariance of a random vector (gravity anomalies) given
a realization of a correlated random vector (geodetic data). It is also shown that the collocation solution for gravity anomalies
is equivalent to the conventional least-squares-Stokes' function solution when the conventional solution utilizes properly
weighted zero a priori estimates. The mathematical and physical assumptions underlying the least squares collocation estimator
are described. 相似文献
798.
Summary Satellite gradiometry is studied as a means to improve the geoid in local areas from a limited data coverage. Least-squares
collocation is used for this purpose because it allows to combine heterogeneous data in a consistent way and to estimate the
integrated effect of the attenuated spectrum. In this way accuracy studies can be performed in a general and reliable manner.
It is shown that only three second-order gradients contribute significantly to the estimation of the geoidal undulations and
that it is sufficient to have gradiometer data in a 5°×5° area around the estimation point. The accuracy of the geoid determination
is strongly dependent on the degree and order of the reference field used. An accuracy of about ±1 m can be achieved with
a reference field of (12, 12). There is an optimal satellite altitude for each reference field and this altitude may be higher
than 300 km for a field of low degree and order. The influence of measuring errors is discussed and it is shown that only
gradiometer data with accuracies better than ±0.05 E will give a significant improvement of the geoid. Finally, some results
on the combination of satellite gradiometry and terrestrial gravity measurements are given.
The proposed method seems to be well suited for local geoid determinations down to the meter range. It is especially interesting
for unsurveyed and difficult areas because no terrestrial measurements are necessary. Furthermore, it has the practical advantage
that only a local data coverage is needed. 相似文献
799.
D. P. Rao 《Journal of the Indian Society of Remote Sensing》1977,5(1):25-30
The use of aerial photo-interpretation technique in preparing an applied hydromorphological map is discussed. The practical utility of the map for ground water exploration in granitic terrain is presented. An attempt to prepare a similar map using LANDSAT CCT by analysis through a Multispectral Data Analysis System and the relative merits of computer aided map and aerial photo map are discussed. The details available in aerial photo map have been found to be lacking in computer aided map. Visual interpretation of LANDSAT imagery can improve the computer aided classification results. 相似文献
800.
Thorium-230 dating on saline of the Lower Salt unit in pluvial Searles Lake, California, shows that this unit was formed between 24,500 and 32,000 years ago. The initial apparent 14C age of the lake is estimated to be about 900 years. After correcting for nonradiogenic 230Th and for the initial 14C age, excellent agreement between 230Th and 14C ages is obtained. The reliability of 230Th dating on salt deposit opens a new way for continuation of absolute chronology below the Lower Salt in Searles Lake. 相似文献