Isotopic analysis of early solar system objects by an ion microprobe: Parametric studies and initial results     

J N Goswami  G Srinivasan 《Journal of Earth System Science》1994,103(1):57-82

Magnesium, potassium and calcium isotope compositions in terrestrial samples and refractory phases from primitive meteorites are determined using an ion microprobe. A thorough investigation of the different instrument parameters is carried out to ensure that conditions necessary for high mass resolution and high precision isotopic studies are adequately satisfied. The instrument can be tuned to achieve mass resolution (M/ΔM) of up to 10,000 (M≤60); it has a very good dynamic stability (ΔB/B≤10 ppm over durations of ≤40 minutes) and the counting system has an effective dead-time of ≤25 nsec and a dynamic background of ≤0·01 c/s. Reproducibility and precision of isotopic measurements are checked by analyzing magnesium and titanium isotopic compositions in terrestrial standards and isotopically doped silicate glasses. A precision of 2‰ (2σ _m ) was achieved during magnesium isotopic analysis in samples with low Mg content (200 ppm). Results from studies of magnesium and potassium isotopic compositions in several Ca−Al-rich refractory inclusions (CAIs) from the primitive meteorites Efremovka and Grosnaja, representing some of the early solar system objects, are presented. The well-behaved Mg−Al isotopic systematics confirm the pristine nature of the Efremovka CAIs inferred earlier from petrographic and trace element studies. The Grosnaja CAIs that have experienced secondary alterations show disturbed magnesium isotopic systematics. Observation of excess²⁶Mg in several of the analyzed CAIs confirms the presence of the now extinct²⁶Al (t _1/2=7×10⁵ years) in the solar nebula at the time of CAI formation. Our data also suggest a relatively uniform distribution of²⁶Al in the solar nebula. Several Efremovka CAIs with excess²⁶Mg also have excess⁴¹K resulting from the decay of⁴¹Ca (t _1/2≃10⁵ years). This observation constrains the time interval between cessation of nucleosynthetic input to the solar nebula and the formation of some of the first solar system solids (CAIs) to less than a million years.  相似文献   

Mapping of wastelands of Kolar district using false colour composites of thematic mapper (TM) data     

C. R. Shiva Prasad  R. S. Reddy  T. R. Srinivasan  Prabhakara 《Journal of the Indian Society of Remote Sensing》1988,16(4):37-42

This study deals with the technique of remote sensing for identifying and deliniating wastelands in Kolar district of Karnataka. False colour composites of thematic mapper (TM) data supplemented by aerial photographs and toposheets wrere utiliesd for mapping wastelands. A map showing the geographic distribution of the wastelands in the districts was prepared on 1∶250,000 scales by compiling the individual wasteland sheets of 1∶50,000 scale. The seven different catagories of wastelands identified and mapped cover about 11.7% of the area in the district. A procedure for mapping wastelands has been worked out based on the experience gained in Kolar district which is a three phase system comprising image intrepretation of false colour composite of TM data, aerial photo interpretation and limited ground truth verification in the selected doubtful areas. This procedure was found to be adequate enough for mapping wastelands accurately in the shortest possible time with least expense and as such are recommended for mapping wastelands in other districts of the country.  相似文献   

Simulation of Biodegradation and Sorption Processes in Ground Water     

P. Srinivasan  James W. Mercer 《Ground water》1988,26(4):475-487

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Dynamic instability of frames having thin-walled columns     

Srinivasan Sridharan  M. Ashraf Ali 《地震工程与结构动力学》1988,16(5):705-717

Dynamic instability of single storey frames having thin-walled columns has been investigated. The lateral loads sustained by the frame are dynamic in character, while the axial loads are deemed to be quasi-statically applied. The analytical model employed by the authors has the capability of modelling the combined action of the two ‘companion’ local modes whose amplitudes are variable along the length of the column and any type of end conditions of the members. For given levels of axial loads sustained by the columns, the magnitudes of lateral loads causing instability can be significantly smaller than those corresponding to static buckling, provided the dynamic load is of sufficient duration. There exists, however, a threshold value of axial force carried by the columns, below which there is no elastic instability—static or dynamic. For columns with overall critical loads several times greater than the local critical load, there is no danger of elastic instability, but the deflections under dynamic lateral loads of less than 1 per cent of the axial load may reach such huge values that there is a serious danger of localized plastic collapse. It is also shown that moment frames having thin-walled columns such as those fabricated out of cold formed steel are extremely vulnerable to moderate seismic excitations.  相似文献   

Dynamic response of skew bridge decks     

R. S. Srinivasan  K. Munaswamy 《地震工程与结构动力学》1978,6(2):139-156

In this paper the dynamic response of a skew bridge deck has been investigated, treating it as an orthotropic plate and using the finite strip method. Employing the normal mode method, the response of the deck due to a moving force has been calculated. Williams' method has been used to accelerate the convergence of the solution. Numerical work has been done for different skew angles and speed ranges. In this study, the history curves and the maximum amplification spectra for deflection and bending moment are presented.  相似文献   

Studies on the morphological changes in the mahanadi estuary and hukitola barrier island with the aid of photo interpretation techniques     

R. Srinivasan  K. Subba Rao  P. S. Kapileshwar 《Journal of the Indian Society of Remote Sensing》1982,10(2):39-44

Hukitola Bay, situated north of Mahanadi River Delta system in Orissa State is ptotected by a barrier island. This island also provides protection to the coastline in this region from the onslogunt of high waves during southwest monsoon. As such, the changes in the Mahanadi estuary governs the stability of this island to a considerable extent. From the examination of hydrographic charts as well as the toposheets prior to the year 1952 it is observed that the Mahanadi river had a long northerly course along a sandspit six km long prior to its confluence with the sea. With the breach in the sandspit at its southern extrem ty during October 1 51, the mouth of the river shifted southwards by about six km. Photographs taken during 1973 have indicated that the mouth of this river has again migrated northwards by about four Km between 1952 and 1973. The development of a new barrier isiand towards east of the existing Hukitola island is also in evidence. As a sequel to these studies it is inferred that despite the changes in the morphology of the barrier island over the past three decades, the barrier island at this region would be a permanent feature and continue to provide protection to the main coastline in this reach.  相似文献   

Seismic analysis of a rotor-bearing system     

V. Srinivasan  A. H. Soni 《地震工程与结构动力学》1984,12(3):287-311

The seismic analysis of a rotor-bearing system is presented in the time domain. The governing equations of motion for the rotor are derived including the effects of rotatory inertia, shear deformation, gyroscopic effects, axial force, axial torque, stiffness and damping provided by the lubricants in the bearings, base translation and base rotation. A simple and efficient finite rotor element based on a Galerkin formulation is proposed to model the rotor. The effects of disks and flywheels mounted on the rotor are also included in the analysis. An example problem for a rotor-bearing system is solved using El Centro earthquake data. Four cases are investigated that will permit one to study the influence of spin, base rotation, comparison between rigid body model and beam model and the influence of axial force and axial torque. The results of the above study show that the gyroscopic effects amplify the response of the rotor-bearing system. The base rotations of the rotor-bearing system under seismic excitation contribute significantly to the response.  相似文献   

Flood basalts from dharwars of Mysore,India     

R. Srinivasan  B. L. Sreenivas 《Bulletin of Volcanology》1971,35(4):824-840

The term flood basalt is redefined emphasizing the importance of the subaerial environment. Using the well established physical criteria of aerial extent, internal structures, time of extrusion and associations, flood basalt activity is distinguished in the Archeans (Dharwars) of Mysore from the geosynclinal volcanics. Study of chemical composition of the Dharwar and other Archean volcanics in the light ofSugimura’s (1968) SWS index, and plotting of the chemical analyses on theMacdonald andKatsura’s (1964) alkali-silica diagram,Kuno’s (1968) alkali-alumina-silica diagram and Scheynamann’s silica-Niggli qz diagram shows both geosynclinal and subaerial volcanics are mainly tholeiitic. Therefore in deciphering the environment of volcanism, it is suggested that the physical criteria take precedence over chemical composition.  相似文献   

Studies of the electrical activity of thunderstorms with lightning flash-counters     

Dr. G. P. Srivastava  Dr. V. Srinivasan  Dr. C. P. Joseph 《Meteorology and Atmospheric Physics》1973,22(2-3):297-310

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Seasonal discharge and chemical flux variations of rivers flowing into the Bayhead canal of Durban Harbour,South Africa     

Kavandren Moodley  Srinivasan Pillay  Keshia Pather  Hari Ballabh 《中国地球化学学报》2016,35(4):340-353

The u Mhlatuzana, u Mbilo and a Manzimnyama river catchments located on the eastern seaboard of the Kwa Zulu-Natal province, South Africa, form the core of urbanization and industrialization, contributing the only natural freshwater inflows to the Bayhead Canal portion of the Durban Harbour. In this study, seasonal discharges and physico–chemical water properties were used to quantitatively determine the material mass transport capacity of the river systems on the basis of hydrographic inputs and chemical loading from the surrounding land use sectors.The mass transport of the total dissolved solids（TDS）,ammonia（NH₄）, phosphorous（P）, aluminum（Al）, calcium（Ca）, copper（Cu）, chromium（Cr）, mercury（Hg）, potassium（K）, magnesium（Mg）, sodium（Na）, nickel（Ni）, lead（Pb）, sulphur（S） and vanadium（V） was determined for each river. Results indicated that land use, seasonality and river flow were significant determinants for the material loading in the rivers and the receiving port waters. The spatio-temporal distribution patterns of chemical fluxes indicated that industrial activity associated with the a Manzimnyama canal contributed the most, with regards to TDS, NH₄, Ca, K, Mg, Na, S and V, loading in both wet and dry seasons, as well as Al, Cu, Hg and Pb during the dry season. Similarly, industrial activity associated with the u Mbilo/u Mhlatuzana Canal at the lower reaches accounted for the highest P, Al, Cu and Pb fluxes in the wet season alone. Fluxes of these parameters are used to explain theobserved elemental concentrations and patterns of the receiving port waters of the Bayhead Canal.  相似文献