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排序方式: 共有512条查询结果,搜索用时 27 毫秒
1.
This paper examines the small-scale solar wind turbulence driven in view of the Alfvén waves subjected to ponderomotive nonlinearity. Filamentation instability is known to take place for the case of dispersive Alfvén wave (DAW) propagating parallel to the ambient magnetic field. The ponderomotive force associated with DAW is responsible for wave localization and these webs of filaments become more intense and irregular as one proceeds along the spatial domain. The ponderomotive force associated with pump changes with pump parameters giving rise to different evolution patterns. This paper studies in detail the nonlinear evolution of filamentation instability introduced by dispersive Alfven waves (DAWs) which becomes dispersive on account of the finite frequency of DAW i.e., pump frequency is comparable to the ion cyclotron frequency. We have explicitly obtained the perturbation dynamics and then examined the impact of pump magnitude on the driven magnetic turbulence using numerical simulation. The results show steepening at small scales with increasing pump amplitude. The compressibility associated with acoustic fluctuations may explain the variation in spectral scaling of solar wind turbulence as observed by Alexandrova et al. (Astrophys. J. 674:1157, 2008). 相似文献
2.
Introducing a concept of equivalent mass depth of flow, this study describes the phenomenon of non‐point source pollutant (metal) transport for pavement (or overland) flow in analogy with wave propagation in wide open channels. Hysteretic and normal mass rating curves are developed for runoff rate and mass of 12 dissolved and particulate‐bound metal elements (pollutants) using the rainfall‐runoff and water quality data of the 15 × 20 m2 instrumented pavement in Cincinnati, USA. Normal mass rating curves developed for easy computation of pollutant load are found to be of a form similar to Manning's, which is valid for open channel flows. Based on the hysteresis analysis, wave types for dissolution and mixing of particulate‐bound metals are identified. The analysis finds that the second‐order partial‐differential equation normally used for metal transport does not have the efficacy to describe fully the strong non‐linear phenomena such as is described for various metal elements by dynamic waves. In addition, the proportionality concept of the popular SCS‐CN concept is extended for determining the potential maximum metal mass Mp of all the 12 elements transported by a rain storm and related to the antecedent dry period (ADP). For the primary metal zinc element, Mp is found to increase with the ADP and vice versa. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
A self-similar solution to the problem of the implosion of a cylindrical shock wave in the presence of a magnetic field has been investigated. A strong shock wave in a cylindrically-symmetric flow travels to the axis of symmetry through a gas of uniform initial density 0 and zero-pressure. A comparative study has been made between the results obtained in ordinary gasdynamics and magnetogasdynamics with transverse and axial components of the magnetic field. The value of similarity exponent has been assigned from that found in the paper of Whitham (1958). 相似文献
4.
Bal Krishna Maheshwari Deepak A. Gunjagi 《Geotechnical and Geological Engineering》2008,26(1):101-107
Geotextile filters are rapidly replacing graded granular filters as the standard of practice in geotechnical design. The objective
of the present study is to predict the behavior of the geotextile filter for the locally (Roorkee—India) available soils using
three different geotextiles (two nonwoven and one woven). Nonwoven geotextiles are commonly used in filtration applications.
This paper evaluates the long-term performance of two needle-punched nonwoven geotextiles and one woven geotextile. Filtration
tests on soil–geotextile filter systems were conducted in the laboratory in order to evaluate the filtration and clogging
behavior. Laboratory test program, include evaluation of performance of two different nonwoven and one woven geotextile filters
in combination with locally available Solani River Sand and Clayey Soil. The paper describes the concept and details of the
Fine Fraction Filtration (F3) test and presents data on three different geotextiles, which were evaluated using three different soil types. It is deduced
that in all filtration applications, the non-woven geotextile would perform better than the woven geotextile. 相似文献
5.
Rahul Ray Deepak Kumar Pijush Samui Lal Bahadur Roy A.T.C.Goh Wengang Zhang 《地学前缘(英文版)》2021,12(1):375-383
This research focuses on the application of three soft computing techniques including Minimax Probability Machine Regression(MPMR),Particle Swarm Optimization based Artificial Neural Network(ANN-PSO)and Particle Swarm Optimization based Adaptive Network Fuzzy Inference System(ANFIS-PSO)to study the shallow foundation reliability based on settlement criteria.Soil is a heterogeneous medium and the involvement of its attributes for geotechnical behaviour in soil-foundation system makes the prediction of settlement of shallow a complex engineering problem.This study explores the feasibility of soft computing techniques against the deterministic approach.The settlement of shallow foundation depends on the parametersγ(unit weight),e0(void ratio)and CC(compression index).These soil parameters are taken as input variables while the settlement of shallow foundation as output.To assess the performance of models,different performance indices i.e.RMSE,VAF,R^2,Bias Factor,MAPE,LMI,U(95),RSR,NS,RPD,etc.were used.From the analysis of results,it was found that MPMR model outperformed PSO-ANFIS and PSO-ANN.Therefore,MPMR can be used as a reliable soft computing technique for non-linear problems for settlement of shallow foundations on soils. 相似文献
6.
3-D seismic structure of the source area of the 1993 Latur, India, earthquake and its implications for rupture nucleations 总被引:1,自引:0,他引:1
The Latur earthquake (Mw 6.1) of 29 September 1993 is a rare stable continental region (SCR) earthquake that occurred on a previously unknown blind fault. In this study, we determined detailed three-dimensional (3-D) P- and S-wave velocity (Vp, Vs) and Poisson's ratio (σ) structures by inverting the first P- and S-wave high-quality arrival time data from 142 aftershocks that were recorded by a network of temporary seismic stations. The source zone of the Latur earthquake shows strong lateral heterogeneities in Vp, Vs and σ structures, extending in a volume of about 90 × 90 × 15 km3. The mainshock occurred within, but near the boundary, of a low-Vp, high-Vs and low-σ zone. This suggests that the structural asperities at the mainshock hypocenter are associated with a partially fluid-saturated fractured rock in a previously unknown source zone with intersecting fault surfaces. This might have triggered the 1993 Latur mainshock and its aftershock sequence. Our results are in good agreement with other geophysical studies that suggest high conductivity and high concentration of radiogenic helium gas beneath the source zone of the Latur earthquake. Our study provides an additional evidence for the presence of fluid related anomaly at the hidden source zone of the Latur earthquake in the SCR and helps us understand the genesis of damaging earthquakes in the SCR of the world. 相似文献
7.
Gravity and magnetic signatures of volcanic plugs related to Deccan volcanism in Saurashtra, India and their physical and geochemical properties 总被引:1,自引:0,他引:1
D.V. ChandrasekharD.C. Mishra G.V.S. Poornachandra RaoJ. Mallikharjuna Rao 《Earth and Planetary Science Letters》2002,201(2):277-292
The Bouguer anomaly and the total intensity magnetic maps of Saurashtra have delineated six circular gravity highs and magnetic anomalies of 40-60 mGal (10−5m/s2) and 800-1000 nT, respectively. Three of them in western Saurashtra coincide with known volcanic plugs associated with Deccan Volcanic Province (DVP), while the other three in SE Saurashtra coincide with rather concealed plugs exposed partially. The DVP represents different phases of eruption during 65.5±2.5 Ma from the Reunion plume. The geochemical data of the exposed rock samples from these plugs exhibit a wide variation in source composition, which varies from ultramafic/mafic to felsic composition of volcanic plugs in western Saurashtra and an alkaline composition for those in SE Saurashtra. Detailed studies of granophyres and alkaline rocks from these volcanic plugs reveal a calc-alkaline differentiation trend and a continental tectonic setting of emplacement. The alkaline plugs of SE Saurashtra are associated with NE-SW oriented structural trends, related to the Gulf of Cambay and the Cambay rift basin along the track of the Reunion plume. This indicates a deeper source for these plugs compared to those in the western part and may represent the primary source magma. The Junagadh plug with well differentiated ring complexes in western Saurashtra shows well defined centers of magnetic anomaly while the magnetic anomalies due to other plugs are diffused though of the same amplitude. This implies that other plugs are also associated with mafic/ultramafic components, which may not be differentiated and may be present at subsurface levels. Paleomagnetic measurements on surface rock samples from DVP in Saurashtra suggest a susceptibility of 5.5×10−2 SI units with an average Koenigsberger ratio (Qn) of almost one and average direction of remanent magnetization of D=147.4° and I=+56.1°. The virtual geomagnetic pole (VGP) position computed from the mean direction of magnetization for the volcanic plugs and Deccan basalt of Saurashtra is 30°N and 74°W, which is close to the VGP position corresponding to the early phases of Deccan eruption. Modeling of gravity and magnetic anomalies along two representative profiles across Junagadh and Barda volcanic plugs suggest a bulk density of 2900 and 2880 kg/m3, respectively and susceptibility of 3.14×10−2 SI units with a Qn ratio of 0.56 which are within the range of their values obtained from laboratory measurements on exposed rock samples. The same order of gravity and magnetic anomalies observed over the volcanic plugs of Saurashtra indicates almost similar bulk physical properties for them. The inferred directions of magnetization from magnetic anomalies, however, are D=337° and 340° and I=−38° and −50° which represent the bulk direction of magnetization and also indicate a reversal of the magnetic field during the eruption of these plugs. Some of these plugs are associated with seismic activities of magnitude ≤4 at their contacts. Based on this analysis, other circular/semi-circular gravity highs of NW India can be qualitatively attributed to similar subsurface volcanic plugs. 相似文献
8.
A core from the Cambay Shale Formation of the Cambay Basin, containing immature Type III organic matter, was pyrolysed at 300°C for different durations of time to different maturation levels. Fractionation effects were studied employing a three-step extraction technique after removal of the expelled pyrolysate. The extractable organic matter (EOM) obtained on extraction of the whole core is assumed to be that present in open pores, while that obtained on finely crushing the sample is assumed to be that present in closed pores. The EOM obtained from 1 cm chips is termed EOM from semi-open pores. The gross composition of the pyrolysates expelled during pyrolysis is not similar to the oils reservoired in the area, and there is no significant fractionation observed between expelled pyrolysates and unexpelled EOM. Our study indicates movement of fluids between closed, semi-open and open pores. In both systems, there is a higher concentration of EOM in open pores than in semi-open and closed pores, and the fraction of EOM in open pores is much greater in the artificial system than in the natural system. Fractionation effects on n-alkane and isoprenoid hydrocarbon-based parameters were also studied. n-Alkenes are present in semi-open and closed pores of the immature core and in the core after it was pyrolysed to 300°C for 6 and 48 h, but are absent in the open pores. n-Alkenes are present in closed pores in the naturally matured core. Presence of n-alkenes in the pyrolysates expelled during the 6 and 48 h experiments, but their absence in the open pores of the core, indicates that expulsion also occurs through temporary microfractures during laboratory pyrolysis, whereas in the natural system expulsion from closed pores seems to be only via semi-open and open pores. 相似文献
9.
Dilip K Mukhopadhyay Bidyut K Bhadra Tamal K Ghosh Deepak C Srivastava 《Journal of Earth System Science》1996,105(2):157-171
Numerous peraluminous and porphyritic granitic bodies and augen gneisses of granitic compositions occur in the nappe sequences
of the Lower Himalaya. They are Proterozoic-to-lower Paleozoic in age and have been grouped into the ‘Lesser Himalaya granite
belt’. The mode of emplacement and tectonic significance of these granites are as yet uncertain but they are generally considered
to be sheet-like intrusions into the surrounding rocks. The small and isolated granite body (the Chur granite) that crops
out around the Chur peak in the Himachal Himalaya is one of the more famous of these granites. Several lines of evidence have
been adduced to show that the Chur granite has a thrust (the Chur thrust) contact with the underlying metasedimentary sequence
(locally called the Jutogh Group). The Chur granite with restricted occurrence at the highest topographic and structural levels
represents an erosional remnant of a much larger sub-horizontal thrust sheet. The contact relations between the country rocks
and many of the other granite and granitic augen gneisses in the Lesser Himalaya belt are apparently similar to that of the
Chur granite suggesting that at least some of them may also represent thrust sheets. 相似文献
10.
A combined gravity map over the Indian Peninsular Shield (IPS) and adjoining oceans brings out well the inter-relationships between the older tectonic features of the continent and the adjoining younger oceanic features. The NW–SE, NE–SW and N–S Precambrian trends of the IPS are reflected in the structural trends of the Arabian Sea and the Bay of Bengal suggesting their probable reactivation. The Simple Bouguer anomaly map shows consistent increase in gravity value from the continent to the deep ocean basins, which is attributed to isostatic compensation due to variations in the crustal thickness. A crustal density model computed along a profile across this region suggests a thick crust of 35–40 km under the continent, which reduces to 22/20–24 km under the Bay of Bengal with thick sediments of 8–10 km underlain by crustal layers of density 2720 and 2900/2840 kg/m3. Large crustal thickness and trends of the gravity anomalies may suggest a transitional crust in the Bay of Bengal up to 150–200 km from the east coast. The crustal thickness under the Laxmi ridge and east of it in the Arabian Sea is 20 and 14 km, respectively, with 5–6 km thick Tertiary and Mesozoic sediments separated by a thin layer of Deccan Trap. Crustal layers of densities 2750 and 2950 kg/m3 underlie sediments. The crustal density model in this part of the Arabian Sea (east of Laxmi ridge) and the structural trends similar to the Indian Peninsular Shield suggest a continent–ocean transitional crust (COTC). The COTC may represent down dropped and submerged parts of the Indian crust evolved at the time of break-up along the west coast of India and passage of Reunion hotspot over India during late Cretaceous. The crustal model under this part also shows an underplated lower crust and a low density upper mantle, extending over the continent across the west coast of India, which appears to be related to the Deccan volcanism. The crustal thickness under the western Arabian Sea (west of the Laxmi ridge) reduces to 8–9 km with crustal layers of densities 2650 and 2870 kg/m3 representing an oceanic crust. 相似文献