The onset of shock wave in an electrically conducting and radiating gas     

A. Kumar  L. P. Singh  R. Shyam 《Astrophysics and Space Science》1985,111(1):131-137

The present work applies the method of characteristics to study the behaviour of planar and cylindrical wave-heads propagating through a perfectly electrically conducting and thermally radiating inviscid gas under the optically thin limit in the presence of a transverse magnetic field. The true nonlinear progress of the flow variable gradients at the wavefront is predicted and the critical distance at which the characteristics pile up at the wavefront to form a shock wave is obtained. It is investigated as to how the effects of radiative flux, the magnetic field strength and the specific heat ratio influence the process of steepening or flattening of the characteristic wavefront.  相似文献   

Analytical investigations on loop-manoeuvre of underwater towed cable-array system   总被引：3，自引：0，他引：3  

Srivastava Shyam Kishore  C. Ganapathy 《Applied Ocean Research》1996,18(6):353-360

The paper reports on analytical case studies on the loop manoeuvre of an underwater towed cable-array system to give an insight into the tactical aspects of their naval applications. The analytical formulation and the solution procedure adopted for this three dimensional dynamic problem is also described. The case studies have been carried out for different loop radii, tow lengths, tow speeds and truncated loops. The resulting X,Y,Z co-ordinates of the towed cable-array and tow-point tensions have been computed. Based on these results, the tow-length to loop radii ratio, leading to cable-array system looping, has been found. The values of speed reduction and turning radius, causing dangerous relaxation in tow-point tension have been worked out. After exit from the loop, the timing required for realignment of the cable-array system with the ship's heading can be obtained from plots of the results. These timings help to plan ship manoeuvres to optimise reestablishment of stable listening conditions during underwater surveillance.  相似文献   

Distribution analysis of salt affected soils under canal and non-canal command area in a part of Etah district,U. P., using remote sensing technique     

A. K. Singh  P. K. Singh  B. Lal  A. N. Singh  A. Mathur 《Journal of the Indian Society of Remote Sensing》2008,36(2):183-188

A World Bank-aided project on sodic land reclamation in Uttar Pradesh is being executed by U.P. Bhumi Sudhar Nigam, Lucknow, and Remote Sensing Applications Centre, U.P., Lucknow has the responsibility of sodic land mapping for the execution of land reclamation programme at the cadastral level. Sodic lands are mainly concentrated in the Gangetic alluvial plains but the problem of sodicity is particularly acute in the canal-irrigated areas. A study of the distribution pattern of sodic lands in canal and noncanal command areas in a reclamation site (covering 60 villages out of which sodic lands were mapped in 51 villages) of Etah district in Uttar Pradesh, indicates that 18.39 per cent area of the canal command villages was barren sodic which was 13.41 per cent of the total geographical area of the site (15417 ha), however, 11.69 per cent area was recorded to be barren sodic in the non-canal command villages which was only 3.16 per cent of the geographical area of the site. The results of soil chemical analysis indicate that barren sodic lands of canal command area are saline-sodic with higher concentration of soluble salts (pH₂ >8.5, EC₂ >4 dSm⁻¹), however, those of non-canal command area are sodic (pH₂ >8.5, EC₂ <4 dSm⁻¹). The post-monsoon ground level in the canal-irrigated areas was in the critical and semicritical zone (< 3.0 mbgl) whereas it was well below the semi-critical zone in the non-canal command area, which indicates that the high ground water level is a major factor to higher the area under sodicity.  相似文献   

Application of soft computing techniques for shallow foundation reliability in geotechnical engineering     

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   

Production of selected cosmogenic radionuclides by muons: 2. Capture of negative muons   总被引：1，自引：0，他引：1  

B. Heisinger  D. Lal  A. J. T. Jull  P. Kubik  S. Ivy-Ochs  K. Knie  E. Nolte   《Earth and Planetary Science Letters》2002,200(3-4):357-369

We have determined the production yields for radionuclides in Al₂O₃, SiO₂, S, Ar, K₂SO₄, CaCO₃, Fe, Ni and Cu targets, which were irradiated with slow negative muons at the Paul Scherrer Institute in Villigen (Switzerland). The fluences of the stopped negative muons were determined by measuring the muonic X-rays. The concentrations of the long-lived and short-lived radionuclides were measured with accelerator mass spectrometry (AMS) and γ-spectroscopy, respectively. Special emphasis was put on the radionuclides ¹⁰Be, ¹⁴C and ²⁶Al produced in quartz targets, ²⁶Al in Al₂O₃ and S targets, ³⁶Cl in K₂SO₄ and CaCO₃ targets, and ⁵³Mn in Fe₂O₃ targets. These targets were selected because they are also the naturally occurring target minerals for cosmic ray interactions in typical rocks. We also present results of calculations for depth-dependent production rates of radionuclides produced after cosmic ray μ⁻ capture, as well as cosmic ray-induced production rates of geologically relevant radionuclides produced by the nucleonic component, by μ⁻ capture, by fast muons and by neutron capture.  相似文献   

Perceptive of the pyroxene-bearing micrometeorites and their relation to chondrites          下载免费PDF全文

N. G. Rudraswami  D. Fernandes  Agnelo De Araujo  M. Shyam Prasad  S. Taylor 《Meteoritics & planetary science》2018,53(10):2035-2050

We studied 149 pyroxenes from 69 pyroxene-bearing micrometeorites collected from deep-sea sediments of the Indian Ocean and South Pole Water Well at Antarctica, Amundsen-Scott South Pole station. The minor elements in pyroxenes from micrometeorites are present in the ranges as follows: MnO ~0.0–0.4 wt%, Al₂O₃ ~0.0–1.5 wt%, CaO ~0.0–1.0 wt%, Cr₂O₃ ~0.3–0.9 wt%, and FeO ~0.5–4 wt%. Their chemical compositions suggest that pyroxene-bearing micrometeorites are mostly related to precursors from carbonaceous chondrites rather than ordinary chondrites. The Fe/(Fe+Mg) ratio of the pyroxenes and olivines in micrometeorites shows similarities to carbonaceous chondrites with values lying between 0 and 0.2, and those with values beyond this range are dominated by ordinary chondrites. Atmospheric entry of the pyroxene-bearing micrometeorites is expected to have a relatively low entry velocity of <16 km s⁻¹ and high zenith angle (70–90°) to preserve their chemical compositions. In addition, similarities in the pyroxene and olivine mineralogical compositions between carbonaceous chondrites and cometary particles suggest that dust in the solar system is populated by materials from different sources that are chemically similar to each other. Our results on pyroxene chemical compositions reveal significant differences with those from ordinary chondrites. The narrow range in olivine and pyroxene chemical compositions are similar to those from carbonaceous chondrites, and a small proportion to ordinary chondrites indicates that dust is largely sourced from carbonaceous chondrite-type bodies.  相似文献   

Estimation of the source parameters of the Nepal earthquake from strong motion data     

A. Joshi  Monu Tomer  Sohan Lal  Sumer Chopra  Sandeep Singh  Sanjay Prajapati  M. L. Sharma  Sandeep 《Natural Hazards》2016,83(2):867-883

  相似文献   

A critical analysis of processes governing the nutrient profiles in the ocean     

R Ramesh  D Lal 《Journal of Earth System Science》1994,103(1):1-15

We have theoretically considered the problem of interpretation of nutrient profiles in the upper ocean (100–2000m). We compare the experimental depth profiles of nonconservative tracers, both stable and radioactive, with solutions of one-dimensional steady state transport equations of increasing complexity including situations not encountered in the real oceans. Apart from gaining insight into the nutrient transport processes, this analysis is useful in offering a way to obtain operational estimates of depth dependent/independent eddy diffusivity and dissolution fluxes in the ocean. These parameters are essential for estimating new production, total production and burial of carbon in the sediments.  相似文献   

Trace gas measurements during aircraft flights in the tropopause region over Europe and North Africa     

M. Schmidt  R. Borchers  P. Fabian  G. Flentje  W. A. Matthews  A. Szabo  S. Lal 《Journal of Atmospheric Chemistry》1984,2(2):133-143

During aircraft flights in May 1981 from Munich (40°N) to north of the Spitsbergen Islands (82°N) and to Monrovia, Liberia (6°N), air samples were obtained in the altitude range of 8 to 11 km and during the ascents and descents near the airports. These samples have been analyzed for the trace gas mixing ratios of CH₄, CO and N₂O. The results of these analyses are presented and discussed.The results provide new evidence of tropospheric-stratospheric exchange events in the vicinity of the subpolar and subtropical tropopause foldings and possibly show a case of transport of CO-enriched air in the upper troposphere above the North Atlantic Ocean.  相似文献   

The Indus-Tsangpo suture zone in Ladakh, northwest Himalaya: Further palaeomagnetic data and implications     

Chris Klootwijk  Madan Lal Sharma  Jozef Gergan  S.K. Shah  Biras Tirkey 《Tectonophysics》1984,106(3-4)

A total of 81 samples (244 specimens) from Upper Cretaceous Indus Molasse and Middle to Upper Cretaceous Dras Flyschoids of the Indus-Tsangpo suture zone in Ladakh (northwest Himalaya) has been studied by thermal demagnetization methods.Both formations showed a characteristic magnetization component indicative for equatorial to low northern palaeolatitudes of acquisition. Similar palaeolatitudes have been obtained before from secondary magnetization components of Early Tertiary age in the Ladakh Intrusives and in the Tibetan Sedimentary Series of central Nepal. The present characteristic components are interpreted likewise as secondary magnetizations which stabilized between 50 and 60 m.y. ago, during Greater India's collision with Asia's southern margin.The Dras Flyschoids show another magnetic component which, in case of primary origin, indicates acquisition at a low southern palaeolatitude. If correct, this interpretation supports recent suggestions for Late Cretaceous obduction of an island arc on Greater India's northern margin.  相似文献