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21.
We provide closed-form approximate solutions to models of horizontal infiltration described by the Boussinesq equation in a semi-infinite aquifer that is initially dry. The approximations preserve such important qualitative properties as scaling and wetting fronts. They are applicable to four types of boundary conditions, two on head and two on flux, enumerated in the paper. All the considered problems admit self-similar variables that allow reduction to boundary value problems for a nonlinear ordinary differential equation. This work extends recent results by Lockington et al. [Lockington DA, Parlange J-Y, Parlange MB, Selker J. Similarity solution of the Boussinesq equation. Adv Water Resour 2000;23(7):725–9] and Telyakovskiy et al. [Telyakovskiy AS, Braga GA, Furtado F. Approximate similarity solutions to the Boussinesq equation. Adv Water Resour 2002;25(2):191–4], with new approximations developed for two of the four cases and a new extension of a previously existing method for a third case. Numerical results extending the work of Shampine [Shampine LF. Some singular concentration dependent diffusion problems. ZAMM 1973;53:421–2] provide a basis for assessing the accuracy of the new methods. 相似文献
22.
Agashev Aleksey M. Nakai Shun&#;ichi Serov Ilya V. Tolstov Aleksander V. Garanin Konstantin V. Kovalchuk Oleg E. 《Mineralogy and Petrology》2018,112(2):597-608
Here we present new data from a systematic Sr, Nd, O, C isotope and geochemical study of kimberlites of Devonian age Mirny field that are located in the southernmost part of the Siberian diamondiferous province. Major and trace element compositions of the Mirny field kimberlites show a significant compositional variability both between pipes and within one diatreme. They are enriched in incompatible trace elements with La/Yb ratios in the range of (65–300). Initial Nd isotope ratios calculated back to the time of the Mirny field kimberlite emplacement (t = 360 ma) are depleted relative to the chondritic uniform reservoir (CHUR) model being 4 up to 6 ɛNd(t) units, suggesting an asthenospheric source for incompatible elements in kimberlites. Initial Sr isotope ratios are significantly variable, being in the range 0.70387–0.70845, indicating a complex source history and a strong influence of post-magmatic alteration. Four samples have almost identical initial Nd and Sr isotope compositions that are similar to the prevalent mantle (PREMA) reservoir. We propose that the source of the proto-kimberlite melt of the Mirny field kimberlites is the same as that for the majority of ocean island basalts (OIB). The source of the Mirny field kimberlites must possess three main features: It should be enriched with incompatible elements, be depleted in the major elements (Si, Al, Fe and Ti) and heavy rare earth elements (REE) and it should retain the asthenospheric Nd isotope composition. A two-stage model of kimberlite melt formation can fulfil those requirements. The intrusion of small bodies of this proto-kimberlite melt into lithospheric mantle forms a veined heterogeneously enriched source through fractional crystallization and metasomatism of adjacent peridotites. Re-melting of this source shortly after it was metasomatically enriched produced the kimberlite melt. The chemistry, mineralogy and diamond grade of each particular kimberlite are strongly dependent on the character of the heterogeneous source part from which they melted and ascended.
相似文献23.
Abandoned rivers (large paleochannels and meanders) are common on river floodplains and low terraces on the East European and West Siberian plains. They are 10–15 times greater in size than the present-day river channels. The large paleochannels are dated back to 11–15 thousand radiocarbon years B.P. (the Late Glacial period). Based on the hydraulic and morphometric relationships for present-day rivers and the method of paleogeographic analogs, the surface runoff during the Late Glacial period was quantitatively reconstructed by the morphometric parameters of large paleochannels. The reconstructed surface runoff exceeded the present values by 1.4 times on the northern mega-slope of the East European Plain (the Northern Dvina, Mezen, and Pechora river basins), by 2.3 times on its southern mega-slope (the Volga, Don, and Dnepr basins), and twofold in West Siberia (the Ob basin). The large surface runoff volumes can be explained by the landscape and climate conditions, including the high coefficients of runoff (due to the permafrost), the increased proportion (and, conceivably, the amount) of snowfall, and, hence, the respective increased intensity of spring floods. The transformation of large Late-Glacial paleorivers due to climate warming at the beginning of the Holocene is a likely scenario of the surface runoff development within the present-day permafrost zone at the ongoing human-induced climate warming. A general decrease in surface runoff and its more uniform intra-annual distribution would result in the reduced size of rivers in the middle Siberia, Yakutia, and northeastern Russia. 相似文献
24.
S.YA. Braude S.L. Rashkovsky K.M. Sidorchuk M.A. Sidorchuk K.P. Sokolov N.K. Sharykin S.M. Zakharenko 《Astrophysics and Space Science》2002,280(3):235-300
This paper presents results and describes the improved data processing algorithm of the low frequency sky survey of discrete
sources carried out with the UTR-2 radio telescope. The measurements were conducted within the frequency range 10 to25 MHz.
Coordinates and flux densities of the sources detected were obtained. Identification with sources from the 4C survey has been
done. The resulting catalogue contains parameter estimates for 483 sources on a set of frequencies within the UTR-2 range.
This revised version was published online in July 2006 with corrections to the Cover Date.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
25.
We present some results of observations on the X-raytransients XTE J1859+226 and XTE J1118+480 by means of the 0.7-metretelescope at the Kalinenkov Astronomical Observatory of Nikolaev StateUniversity. The observations of XTE J1859+226 were obtained inNovember 1999 and April 2000. The observations of theXTE J1118+480 started in April 2000. The light curves are presented here. 相似文献
26.
Igor V. Pekov Natalia V. Zubkova Vasiliy O. Yapaskurt Dmitriy I. Belakovskiy Nikita V. Chukanov Anatoly V. Kasatkin Aleksey M. Kuznetsov Dmitry Y. Pushcharovsky 《Mineralogy and Petrology》2013,107(2):201-210
A new mineral kobyashevite, Cu5(SO4)2(OH)6·4H2O (IMA 2011–066), was found at the Kapital’naya mine, Vishnevye Mountains, South Urals, Russia. It is a supergene mineral that occurs in cavities of a calcite-quartz vein with pyrite and chalcopyrite. Kobyashevite forms elongated crystals up to 0.2 mm typically curved or split and combined into thin crusts up to 1?×?2 mm. Kobyashevite is bluish-green to turquoise-coloured. Lustre is vitreous. Mohs hardness is 2½. Cleavage is {010} distinct. D(calc.) is 3.16 g/cm3. Kobyashevite is optically biaxial (?), α 1.602(4), β 1.666(5), γ 1.679(5), 2 V(meas.) 50(10)°. The chemical composition (wt%, electron-microprobe data) is: CuO 57.72, ZnO 0.09, FeO 0.28, SO3 23.52, H2O(calc.) 18.39, total 100.00. The empirical formula, calculated based on 18 O, is: Cu4.96Fe0.03Zn0.01S2.01O8.04(OH)5.96·4H2O. Kobyashevite is triclinic, $ P\overline{\,1 } $ , a 6.0731(6), b 11.0597(13), c 5.5094(6)?Å, α 102.883(9)°, β 92.348(8)°, γ 92.597(9)°, V 359.87(7)?Å3, Z?=?1. Strong reflections of the X-ray powder pattern [d,Å-I(hkl)] are: 10.84–100(010); 5.399–40(020); 5.178–12(110); 3.590–16(030); 2.691–16(20–1, 040, 002), 2.653–12(04–1, 02–2), 2.583–12(2–11, 201, 2–1–1), 2.425–12(03–2, 211, 131). The crystal structure (single-crystal X-ray data, R?=?0.0399) сontains [Cu4(SO4)2(OH)6] corrugated layers linked via isolated [CuO2(H2O)4] octahedra; the structural formula is CuCu4(SO4)2(OH)6·4H2O. Kobyashevite is a devilline-group member. It is named in memory of the Russian mineralogist Yuriy Stepanovich Kobyashev (1935–2009), a specialist on mineralogy of the Urals. 相似文献
27.
A series of subflares in active region NOAA 9077 (July 2000) and in the activity complex NOAA 0039 + NOAA 0050 were investigated. The structure functions and their characteristics for sets of images of active regions in the hydrogen-alpha line (H-line) were calculated. The ranges of the spatial scales of different scaling behavior of the structure functions were revealed. The existence of intermittent turbulence (multi-fractal structure) in active regions of the chromosphere is shown. Peculiarities of the scaling parameters variations of the structure functions at pre-flare stage are investigated. It was found that on average 20 min before a subflare onset considerable deviation of these variations from the mean occurs, which may be of importance for predictions. It was discovered that maximum variations of scaling parameters with an accuracy to 15 min (on average), in a number of cases coincide with variations of the elongated chromospheric structures in an active-region area. We used H_ filtergrams obtained with the chromospheric telescope of the Baikal observatory operated by ISTP SD RAS. The telescope is coupled with a Halle birefringent filter with a 0.05 nm bandpass, and a Princeton Instruments 2048 × 2048 pixel CCD camera with 16-bit amplitude resolution. 相似文献
28.
Empirical prediction equations of the form W = aQb have been reported for rills and rivers, but not for ephemeral gullies. In this study six experimental data sets are used to establish a relationship between channel width (W, m) and flow discharge (Q, m3 s?1) for ephemeral gullies formed on cropland. The resulting regression equation (W = 2·51 Q0·412; R2 = 0·72; n = 67) predicts observed channel width reasonably well. Owing to logistic limitations related to the respective experimental set ups, only relatively small runoff discharges (i.e. Q < 0·02 m3s?1) were covered. Using field data, where measured ephemeral gully channel width was attributed to a calculated peak runoff discharge on sealed cropland, the application field of the regression equation was extended towards larger discharges (i.e. 5 × 10?4m3s?1 < Q < 0·1 m3s?1). Comparing W–Q relationships for concentrated flow channels revealed that the discharge exponent (b) varies from 0·3 for rills over 0·4 for gullies to 0·5 for rivers. This shift in b may be the result of: (i) differences in flow shear stress distribution over the wetted perimeter between rills, gullies and rivers, (ii) a decrease in probability of a channel formed in soil material with uniform erosion resistance from rills over gullies to rivers and (iii) a decrease in average surface slope from rills over gullies to rivers. The proposed W–Q equation for ephemeral gullies is valid for (sealed) cropland with no significant change in erosion resistance with depth. Two examples illustrate limitations of the W–Q approach. In a first example, vertical erosion is hindered by a frozen subsoil. The second example relates to a typical summer situation where the soil moisture profile of an agricultural field makes the top 0·02 m five times more erodible than the underlying soil material. For both cases observed W values are larger than those predicted by the established channel width equation for concentrated flow on cropland. For the frozen soils the equation W = 3·17 Q0·368 (R2 = 0·78; n = 617) was established, but for the summer soils no equation could be established. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
29.
The operation of a railway track in cold regions results in the premature deformation of subgrade soils caused by significant temperature fluctuations and ecological imbalance. Identification and calculation of the thawing degree of permafrost soils, frost heaving of clays, and groundwater flooding require careful engineering and geological surveying. The paper describes the unique, long-standing experience of the university scientists connected with maintaining the Russian East-Siberian and Trans-Baikal Railways'' facilities. Specific features of and requirements for the surveying, depending on the geological and climatic conditions, are identified. 相似文献
30.
Aleksey I. Sharov 《Geo-Marine Letters》2005,25(2-3):153-166
The present extent of European ice coasts, their spatial changes in the past 50 years and the velocities of ice flow in marginal parts of tidewater glaciers were determined and mapped at a regional scale using space-borne image data, both optical and radar. The methods of satellite photogrammetry and radar interferometry provided efficient solutions to the integral estimation of ice-coast dynamics in the Franz Josef Land, Novaya Zemlya and Svalbard archipelagos. Studies revealed significant degradation of the ice coasts (–7.7% by length) compared to the situation represented in the available maps. The results obtained in the laboratory were verified during several field campaigns. 相似文献