The Vermilion district of northerneastern Minnesota is a classic example of a lower Precambrian greenstone-granite terrane. It is a complex volcanic-sedimentary pile, characterized by repeated periods of volcanism and the presence of intercalated pyroclastic, volcanoclastic and epiclastic rocks. The volcanic-sedimentary pile is surrounded and intruded by contemporaneous granitic batholiths. Several rock units from the district have been dated by the whole-rock Rb-Sr method. The isochron ages and the corresponding initial Sr87/Sr86 ratios (= I) are:
The Orissa super cyclone which crossed the Orissa coastal region near Paradip on October 29, 1999 proved to be disastrous.
The strong winds, torrential rains with heavy rainfall and high storm surge associated with the cyclone caused havoc that
resulted in the death of thousands of people, cattle and extensive damage to agricultural land, paddy crop, transmission lines,
power supply, roads and buildings. In the present study, a fine resolution finite element model is used to simulate surges
due to this super cyclone. The model results are compared with observed surges available from post-storm survey reports. Comparison
of results show that they are in good agreement with the observed surges, and the finite element model can be used for real
time surge forecasts. 相似文献
Summary The mean monthly precipitable water at four tropical stations Madras (13°00N, 80°11E), Waltair (17°42N, 83°18E), Bombay (18°54N, 72°49E) and Nagpur (21°06N, 79°03E) are evaluated for the layer surface to 500 mb (0–5.4 km) of the atmosphere using radiosonde data available for seven years period (1959–1965). The mean monthly precipitable water for the above four stations is also estimated from dew point temperature.The precipitable water in the air column at any station is examined in relation to monsoon flow. The higher values of precipitable water are found to occur over the regions when there is good supply of moisture by the monsoon flow as well as low level convergence. These studies are believed to provide useful information in forecasting the monsoon circulation over the country. 相似文献
The Palaeo-Proterozoic Ghingee granite is an anatectic granite formed in high grade granulite terrain by ultrametamorphism. The compositional variations both in major and trace elements observed in this granite (SiO2 : 64.16-73.81; Fe2O3 : 0.12-2.19; FeO : 0.12-2.80; MgO : 0.10-2.19; CaO : 1.66-4.71; K2O : 1.09-5.09; Ba: 223-1883 ppm; Cr : 4-60 ppm) are attributed to a) source rock heterogeneity and b) the tectonic disturbances that might have abruptly ended the anatectic melting process. The granite is compositionally similar to Perur, Closepet and Hyderabad granites and is formed during Archaean-Proterozoic transition by anatectic and crustal remelting processes. 相似文献
A study of the formation and movement of sequential Sporadic-E layers observed during the night-time hours at two Indian low-latitude stations, SHAR(dip 10°N) and Waltair (dip 20°N) shows that the layer are formed around 19:00 h. IST at altitudes of ≈180 km. They descend to the normal E-region altitude of about 100 km in three to four hours and becomes blanketing type of Es before they disappear. However, the absence of these descending layers at an equatorial station, Trivandrum (dip 2°N) gives the experimental evidence for wind shear theory. The meridional neutral wind derived from the height variation of the F-layer showed significant poleward wind during the descent of these layers. Hence it is inferred that these layers are formed as a consequence of the convergence of plasma by the poleward wind and the equatorward propagating gravity waves (inferred from the height fluctuations of F-layer). 相似文献
Generation and propagation of internal waves (IWs) in the coastal waters of the extended shelf of the western Bay of Bengal are investigated for late winter by using the Massachusetts Institute of Technology General Circulation Model (MITgcm). The model is forced with astronomical tides and daily winds. Monthly climatological temperature and salinity fields are used as initial conditions. The simulations are compared with time series observations of temperature and currents from acoustic Doppler current profiler (ADCP) and conductivity-temperature-depth (CTD) moored at three locations south of Gopalpur: two at a local depth of 100 m and another at 400-m depth during 19–21 February 2012. The comparison of the spectral estimates for the time series of temperature from the model and observations are in reasonable agreement for the near-tidal frequency waves. The peak of temperature spectra is always found near the shelf break region which steadily lost its intensity over the continental shelf. The calculation of Richardson number reflected the presence of local mixing due to density overturning in the shelf region. To understand further the generation and propagation of internal tides in the region, energy flux and conversion of barotropic-to-baroclinic M2 tidal energy are examined. The model simulations suggest that the internal tide is generated all along the shelf slope. The energy flux analysis shows that the internal tides propagate to either side of the generation sites. 相似文献
Expansive clays swell and shrink seasonally when subjected to changes in the moisture regime causing substantial distress
to the structures built in them. Techniques like sand cushion and cohesive non-swelling soil (CNS) layer have been tried to
arrest heave and consequent damages to structures. Sand cushion has been proved to be counter-productive. Studies have indicated
that even though CNS layer was effective initially, it became less effective after the first cycle of swelling and shrinkage.
Research carried out by the authors, using cement-stabilized fly ash as a cushioning material, has shown that it was quite
effective in arresting heave. Fly ash cushion, stabilized with 10% cement with thickness equal to that of the expansive soil
bed reduces heave by about 75% in the first instance. With subsequent swell-shrink cycles, the performance further improves,
unlike in the case of a black cotton soil provided with a CNS cushion. At the end of fourth cycle of swelling, the reduction
in the amount of heave is as high as 99.1%. 相似文献
Driven by significant technological developments in the hyperspectral imaging, material mapping using reference spectra has received renewed interest of the remote sensing community. The applicability of reference spectral signatures in image classification depends mainly on the material type and its spectral signature behaviour. Identification and spectral characterization of materials which exhibit unique spectral behaviour is the first step in this approach. Consequently there have been active researches for the identification of surface materials which exhibit unique spectral signatures. The uniqueness of reflectance signature of winter rape relative to its co-occurring crop species was reported in this study. Reflectance spectral libraries constructed from field spectral reflectance measurements collected over five agricultural crops (alfalfa, winter barley, winter rape, winter rye, and winter wheat) during four subsequent growing seasons were classified by the linear discriminant analysis (LDA). Further, the reference field spectral database was used for the spectral feature fitting and classification of a historical HyMAP airborne hyperspectral imagery acquired at a separate site, by spectral library search. Results indicate the existence of a meaningful spectral matching between image and field spectra for winter rape and demonstrate the potential for transferring spectral library for hyperspectral image classification. The observed consistency in the discrimination of winter rape demonstrates experimentally the fundamental principle of remote sensing which suggests the theoretical existence of unique spectral signatures for materials which can be incorporated as reference spectral signatures for hyperspectral image classification. 相似文献
The experimental potential energy curves for the different electronic states of molecules like CN, CO and CS observed in comets
are constructed by using the Rydberg-Klein-Rees method as modified by Vanderslice et al. The ground state dissociation energies
are determined by curve fitting technique using the five parameter Hulburt-Hirschfelder (H-H)function. The estimated dissociation
energies are 7.63 ± 0.187, 10.95 ±0.224 and 7.27 ± 0.152 eV for CN, CO and CS respectively. These values are in good agreement
with the literature values. Estimated dissociation energies of CN, CO and CS are used in the relation given by Gaydon and
ionization potentials are evaluated for CO and CS molecules. The estimated ionization potentials are 13.92and 12.15 eV for
CO and CS molecules respectively. The r-centroids and Franck-Condon factors (FC Factors) for the band system of a 3Πr – X1Σ+ (a – X) and A1Π – X 1Σ+ (A -X) of CN, A 2Πi – X2Σ+ (A – X) and B2Σ+-X2Σ+ (B – X) of CO and a 3Πr – X1Σ+ (a – X) of CS molecules have been calculated employing an approximate analytical methods of Jarmain and Fraser and Nicholls
and Jarmain. The absence of the bands in these systems are explained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
High-resolution shipboard geophysical investigations along the Indian Ocean ridge system are sparse especially over the Carlsberg and Central Indian ridges. In the present study, the shipboard gravity and multibeam bathymetry data acquired over a 750 km long section of the Central Indian Ridge between 3 °S and 11 °S have been analysed to understand the crustal structure and the ridge segmentation pattern. The mantle Bouguer anomalies (MBA) and the residual mantle Bouguer anomalies (RMBA) computed in the study area have shown significant variations along the ridge segments that are separated by transform and non-transform discontinuities. The MBA lows observed over the linear ridge segments bounded by well-defined transform faults are attributed to the thickening of the crust at the middle portions of the ridge segments. The estimates of crustal thickness from the RMBA shows an average of 5.2 km thick crust in the axial part of the ridge segments. The MBA and relative RMBA highs along the two non-transform discontinuities suggests a thinner crust of up to 4.0 km. The most significant MBA and RMBA highs were observed over the Vema transform fault suggesting thin crust of 4 km in the deepest part of the transform fault where bathymetry is more than 6000 m. The identified megamullion structures have relative MBA highs suggesting thinner crust. Besides MBA lows along the ridge axis, significant off-axis MBA lows have been noticed, suggesting off-axis mantle upwelling zones indicative of thickening of the crust. The rift valley morphology varies from the typical V-shaped valley to the shallow valley floor with undulations on the inner valley floor. Segments with shallow rift valley floor have depicted well-defined circular MBA lows with persistent RMBA low, suggesting modulation of the valley floor morphology due to the variations in crustal thickness and the mantle temperature. These are supported by thicker crust and weaker lithospheric mantle. 相似文献
