Effects of water on strength and failure mode of coarse-grained granites at 300°C   总被引：1，自引：0，他引：1  

E. Althaus  A. Friz-Töpfer  Dr. rer. nat. Ch. Lempp  O. Natau 《Rock Mechanics and Rock Engineering》1994,27(1):1-21

Summary Deformation experiments have been performed in a triaxial compression cell at a temperature of 300°C and confining pressures up to 65 MPa using samples of homogeneous, fresh two-mica-granite (RM) and monzogranite (CM). The cylindrical specimens (d=70 mm, h=140 mm, V=540 cm³) were tested undrained under dry (105°C), as received, and water saturated conditions at deformation rates between and . The mechanical behaviour of the two types of coarse-grained, crystalloblastic granites is critically influenced by mineralogical composition, porosity, and the amount of intergranular water present in the samples. The failure stress of the CM granite is at about 65% of that of the RM granite; in both rocks strength decreases with increasing porosity and water content.The presence of interstitial water causes a failure mode of non-localized, homogeneously distributed microcracking in the central parts of the samples, whereas, in runs with dry granites, strain localization along a single shear fracture was observed. When aqueous fluids are present, the macroscopic style of deformation of granites appears to be ductile even at lowP andT conditions. Strength and angle of internal friction are reduced to very low values. The style of deformation, as well as the reduction of strength of the water-saturated rock samples, is due to mechanical and chemical effects of intergranular water at elevated temperatures.The maximum differential stresses measured for these coarse-grained granites are much lower than the strength commonly reported for other granites, e. g. Westerly and Charcoal granites. Our data suggest that the strength of the granitic crust under differential stress is lower than currently deduced from laboratory experiments.  相似文献   

The Mauritius Radiotelescope     

K. Golap  N. H. Issur  R. Somanah  R. Dodson  M. Modgekar  S. Sachdev  N. Udaya Shankar  Ch. V. Sastry 《Astrophysics and Space Science》1995,228(1-2):373-377

The Mauritius Radiotelescope (MRT) is a T-shaped array of helical antennas with a 2048 m EW arm and a 890 m South arm. The primary objective of the telescope is to produce a sky survey in the declination zone -15° to -65° with a point source sensitivity of 200 mJy and an angular resolution of 4'×4.6'cosec(z) at 151.6 MHz, z being the zenith angle . This paper describes the telescope and the present status  相似文献   

Observations of the Rosette Nebula using the Decameter Wave Radio Telescope at Gauribidanur     

A. A. Deshpande  R. K. Shevgaonkar  Ch. V. Sastry 《Astrophysics and Space Science》1984,102(1):21-27

A map of Rosette Nebula in continuum absorption is made at 34.5 MHz using the Decameter Wave Radio Telescoe at Gauribidanur, India, with a resolution of 26×40, is presented. These observations are combined with the 2700 MHz measurements of Grahamet al. (1982) to derive the electron temperature distribution across the nebula. It is found that the temperatures in the southeastern parts of the nebula are around 5000 K and increase up to 8000 K towards the northwestern regions. It is suggested that the lower electron temperatures in the southeastern regions are due to the presence of more dust there compared to other regions in the nebula.  相似文献   

Determination semi-automatique des diametres de crateres lunaires a partir de plaques photographiques de la Lune     

M. Froeschle  Ch. Ounnas 《Earth, Moon, and Planets》1981,24(1):3-11

Résumé Nous comparons les valeurs des diamètres de cratères lunaires obtenues à partir de mesures visuelles et semi-automatiques de plaques photographiques de la Lune. Nous montrons que le tracé du contour d'un cratère obtenu à partir d'un nouvel algorithme de calcul est équivalent au contour estimé par l'il.

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We compare two methods for the determination of lunar crater diameters: visual and semiautomatic. We show that the lunar crater contour obtained either by application of the new algorithm or by visual measure are equivalent.

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Scattering by nonspherical particles and optical properties of Martian dust     

Petr Chýlek  G.W. Grams 《Icarus》1978,36(2):198-203

Ultraviolet spectral reflectance data obtained from the Mariner 9 during the 1971 Mars dust storm were analyzed at two wavelengths to deduce the complex index of refraction of Martian dust. Martian dust particles were considered to be irregularly shaped and randomly oriented nonspherical particles. The analysis shows that the Mariner 9 data are consistent with the scattering by irregular particles with an index of refraction m = 1.59 ? 0.0015i at λ = 0.305 μm and m = 1.55 ? 0.004i at λ = 0.268 μm. Both the real and the imaginary parts of refractive index found are considerably smaller than previously reported results using a spherical shape model for Martian dust particles.  相似文献   

Présence d'une mangrove à Avicennia au Miocène moyen dans la région de Digne (Alpes-de-Haute-Provence,France) : implications stratigraphiques et paléoclimatiques     

Jean-Jacques Châteauneuf  Hugues Bauer  Isabelle Cojan 《Comptes Rendus Geoscience》2006,338(3):197-205

Avicennia pollen grains have been discovered in marine facies from the Middle Miocene deltaic series of Châteauredon (southeastern France). Based on the local stratigraphy, an age between 15.8 and 16.5 Ma is proposed for these grains. The age and the transgressive context of the Avicennia bearing-levels are in agreement with the maximum extension of the mangrove known in the western Mediterranean during interval N8–NN4 pro parte, in relation with the Langhian highstand. This mangrove occurrence at 42°N latitude during Middle Miocene is a more northern witness of the mangrove sites known in Languedoc and Provence areas. It also implies a lower climatic gradient than today. To cite this article: J.-J. Châteauneuf et al., C. R. Geoscience 338 (2006).  相似文献   

Study of geothermal water intrusion due to groundwater exploitation in the Puebla Valley aquifer system, Mexico   总被引：1，自引：1，他引：1  

E. Leticia Flores-Márquez  Gabriel Jiménez-Suárez  Raymundo G. Martínez-Serrano  René E. Chávez  Daniel Silva Pérez 《Hydrogeology Journal》2006,14(7):1216-1230

Significant intrusion of geothermal water into fresh groundwater takes place in the Puebla Valley aquifer system, Mexico. The decline in the potentiometric surface due to the overexploitation of the groundwater induces this intrusion. This hydrological system comprises three aquifers located in Plio-Quaternary volcanic sediments and Mesozoic calcareous rocks. The hydraulic balance of the aquifer shows that the annual output exceeds the natural inputs by 12 million m³. Between 1973 and 2002, a drop in the potentiometric surface, with an 80 m cone of depression, was identified in a 5-km-wide area located southwest of the city of Puebla. Chemical analyses performed on water samples since 1990 have shown an increase in total dissolved solids (TDS) of more than 500 mg/L, coinciding with the region showing a cone of depression in the potentiometric surface. A three-dimensional flow and transport model, based on the hydrogeological and geophysical studies, was computed by using the MODFLOW and MT3D software. This model reproduces the evolution of the aquifer system during the last 30 years and predicts for 2010 an additional drawdown in the potentiometric surface of 15 m, and an increase in the geothermal water intrusion.  相似文献   

Microclimatological characteristics of a miscanthus (Miscanthus cv. giganteus) stand during stable conditionsat night in the nonvegetative winter period     

J. Eitzinger  Ch. Kössler 《Theoretical and Applied Climatology》2002,72(3-4):245-257

Summary ?Microclimatological data obtained during a field experiment in the nongrowing winter period were used to study the microclimatologically stable night conditions of a 200 × 150 m miscanthus (Miscanthus cv. giganteus) stand and compared to open field conditions. The microclimatological pattern within the miscanthus canopy was characterized by long-wave radiative cooling of the plant stand and by an established temperature inversion within the canopy at calm nights. The results show that there are significant differences in air temperature and energy balance components between the open field and the miscanthus field during calm and clear nights. In general, net radiation difference during the cold and calm nights was relatively constant and about 20 W m⁻² less negative in miscanthus (because of lower surface temperatures) than at the open field. Air temperature differences also remained fairly constant and were up to 3 °C lower than at the open field (at the height of 1 m). Through thermal inversion cold air accumulated in the lower parts of the canopy as shown by the vertical air temperature profiles. They showed a greater amplitude within the diurnal cycle in the miscanthus stand than in the open field. Through the onset of wind, temperature profiles changed rapidly and differences diminished. Vertical katabatic air drainage into the canopy layers was estimated indirectly by using the energy balance approach. It was calculated from the significant energy balance closure gap and showed a mean air exchange rate of up to 22 m³ m⁻² h⁻¹, related to a stand volume of 1 m² area and 4 m height, during the mostly calm and clear nights, depending on the canopy net radiation and turbulent heat exchange forced by slight wind spells. Quantitative uncertainties in calculated cold air drainage which are introduced by the measurement method and certain assumptions in the calculations, were considered in a sensitivity analysis. In spite of these uncertainties evidence of katabatic cold air flow is given. Received July 29, 1999; revised June 11, 2001; accepted March 14, 2002  相似文献   

黄河下游壶穴的研究   总被引：10，自引：0，他引：10       下载免费PDF全文

钟建华  倪晋仁  沈晓华  王冠民  冀国盛  吴孔友  李理  洪梅  李勇  朱光有 《地质学报》2002,76(2):279-286

黄河下游(泺口以下)发育了大量的壶穴(Pothole),按成因可以分为6种:流水侵蚀、风蚀、圆砾铸模、冰压刻、冰融水滴蚀及泄气侵蚀。流水侵蚀形成的圆形Pothole规模不一,小者直径在十余厘米,深数厘米,大者直径达数米,深1 m余;风蚀形成的圆形Pothole规模一般比较小,直径多在二、三十厘米以下,深10 cm以下,大部分穴壁缓斜,状如盘碟;圆砾铸模形成的Pothole规模一般较小,直径多在一、二十厘米以下、穴壁陡倾,状如锅穴;冰融水滴蚀形成的Pothole形态复杂,规模不一,既有穴壁缓斜的盘碟状者,也有穴壁陡倾近乎直立的近圆柱状者,直径从不足1cm到三、四十厘米,其穴缘、穴壁和穴底常有次级构造;泄气侵蚀形成的Pothole更是十分复杂,平面形态可以圆形到近圆形甚至其他复杂形态,穴壁可以非常平缓,也可以陡倾,直径从数厘米到数十厘米,深数毫米到二、三十厘米,穴缘和穴壁也常有次级伴生构造,既可单独产出,也可成群产出,同时还可以多个密集产出,状如蜂巢,这一类Pothole的成因极为独特,主要与黄河断流河床捕获的空气泄漏有关。  相似文献   

Seismic Hazard for Selected Sites in Greece: A Bayesian Estimate of Seismic Peak Ground Acceleration   总被引：1，自引：1，他引：1  

A. A. Lyubushin  T. M. Tsapanos  V. F. Pisarenko  G. Ch. Koravos 《Natural Hazards》2002,25(1):83-98

A procedure for estimating maximum values of seismic peak ground accelerationat the examined site and quantiles of its probabilistic distribution in a future timeinterval of a given length is considered. The input information for the method areseismic catalog and regression relation between peak seismic acceleration at a givenpoint and magnitude and distance from the site to epicenter (seismic attenuation law).The method is based on Bayesian approach, which simply accounts for influenceof uncertainties of seismic acceleration values. The main assumptions for the method are Poissonian character of seismic events flow and distribution law of Gutenberg-Richter's type. The method is applied to seismic hazard estimation in six selected sitesin Greece.  相似文献