Patterns of pH change inferred from chrysophyte microfossils in Adirondack and northern New England lakes     

John P. Smol  Sushil S. Dixit 《Journal of Paleolimnology》1990,4(1):31-41

The silica-scaled chrysophytes are being used increasingly in paleolimnological studies of lake acidification. This study compares the distribution of scaled chrysophytes in the surface sediment of a calibration set of lakes from the Adirondack Park and from northern New England. With the exception of two taxa, species distributions with respect to pH are similar in the two regions. The stratigraphic distribution of chrysophytes is then compared in five Adirondack and three New England lakes. All the presently acid lakes indicate recent lake acidification, with more acid tolerant chrysophytes increasing in relative frequency in the recent sediments. Because the timing of these species changes is unrelated to any watershed disturbances that may have occurred in the lakes' catchments, atmospheric deposition of acids is believed responsible for these recent pH changes.This is the seventh of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D. F. Charles and D. R. Whitehead are guest editors for this series.  相似文献   

2-D deformation analysis of a half-space due to a long dip-slip fault at finite depth     

Sushil K. Tomar  Naresh K. Dhiman 《Journal of Earth System Science》2003,112(4):587-596

Closed form analytical expressions of stresses and displacements at any field point due to a very long dip-slip fault of finite width buried in a homogeneous, isotropic elastic half-space, are presented. Airy stress function is used to derive the expressions of stresses and displacements which depend on the dip angle and depth of the upper edge of the fault. The effect of dip angle and depth of the upper edge of the fault on stresses and displacements is studied numerically and the results obtained are presented graphically. Contour maps for stresses and displacements are also presented. The results of Rani and Singh (1992b) and Freund and Barnett (1976) have been reproduced.  相似文献   

Some results of night-time scintillations at low latitude     

Sushil Kumar  S K Vijay  A K Gwal 《Journal of Earth System Science》1993,102(2):307-312

Ionospheric scintillation observations of VHF radio signals from FLEETSAT satellite (73°E longitude) at Bhopal from January 1990 to December 1990 have been used to study the characteristic variations of scintillation activity. It is found that scintillation occurrence is essentially a night-time phenomenon and day-time scintillations are very rare. Annual average nocturnal variation of percentage occurrence of scintillations shows maximum at around 2100–2200 hours LT. Seasonally, scintillations are most prominent during equinoxes and least during summer. Geomagnetic disturbances tend to decrease the occurrence of scintillations in the pre-midnight period.  相似文献   

Paleolimnological reconstructions of Rouyn-Noranda lakes within the zone of influence of the Horne Smelter,Québec,Canada     

Aruna S. Dixit  S. Alpay  Sushil S. Dixit  John P. Smol 《Journal of Paleolimnology》2007,38(2):209-226

Diatoms were identified and enumerated from a surface sediment calibration set of 50 lakes in northwestern Québec. The relationship between species composition and environmental variables was examined using canonical correspondence analysis (CCA). Forward selection and Monte Carlo permutation tests in CCA indicated that diatom species distributions in the data set are most strongly correlated to lakewater pH. A strong (r ² _boot = 0.83) weighted averaging calibration model, that includes bootstrapped error estimates, was developed for inferring past lakewater pH. Using this model, temporal changes in pH were reconstructed for two kettle lakes, Lac de la Pépinière and Lac Perron. Based on limnological data, both the study lakes were expected to have recently acidified due to increased acidic precipitation and increases in anthropogenic metal loading. However, our long-term pH inference data indicate that these lakes were naturally acidic during pre-industrial times. Nonetheless, the rate of acidification, particularly in Lac de la Pépinière, has accelerated in the last ∼75 years. These long-term pH records developed for the dilute lakes in northwestern Québec suggest that the region has received increased atmospheric pollutants from the nearby Horne smelter in Rouyn-Noranda. The pH inference profiles are markedly different from many other paleolimnological studies in acid-sensitive regions of Canada that have become acidic primarily as a result of industrial activities. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.  相似文献   

On coda waves of earthquakes     

Sushil Chandra Das Gupta 《Pure and Applied Geophysics》1959,43(1):45-74

Summary Coda waves viz. the tail portion of an earthquake record have been observed and analysed byCarder, Macelwane and others. They showed that the periods of such waves increase with the increase of epicentral distances.Carder observed that these waves have very little transverse component so that these may be considered as of the type of Rayleigh waves. RecentlyOmote showed that the Coda waves contain three periodsT ₁,T ₂,T ₃ of whichT ₁ increases with epi-central distances as observed by previous observers. ButT ₂,T ₃ remain constant for all earthquakes from different epicentral distances.Omote tried to explain this phenomenon by considering that the surface of the earth consists of several layers andT ₂,T ₃ are free oscillation periods of the surface layers.T ₁ period has been explained bySezawa and also byJeffreys which has been shown byGutenberg. The author has attempted to explain the periodsT ₂,T ₃ by considering passage of cracks at the focal region. The Rayleigh wave character of Coda waves and low velocity of such waves have been explained.  相似文献   

Waves and stresses produced in an elastic medium due to impulsive radial forces and twist on the surface of a spherical cavity     

Sushil Chandra Das Gupta 《Pure and Applied Geophysics》1954,27(1):1-6

Summary Displacements and stresses produced by impulsive radial pressure and by impulsive twists have been determined. In the former case total flow of energy across a spherical boundary has been obtained.  相似文献   

Refractive index measurements of ammonia and hydrocarbon ices at 632.8 nm     

Constantin Romanescu  Ajeeta Khatiwada 《Icarus》2010,205(2):695-701

Optical constants in a broad temperature and wavelength range are important input parameters in radiative transfer models used in studies of planetary atmospheres. In the laboratory, the refractive index values of ices at the HeNe laser wavelength (632.8 nm) are often used to monitor the growth rate and thickness of ice films. In this report we present laboratory measurements determining the refractive index at 632.8 nm of ammonia and hydrocarbon ices in the temperature range 80-100 K. Thin ice films are vapor-deposited on a cryogenically cooled mirror located inside a high-vacuum apparatus. The real component of the refractive index of these ice films is determined by a two-angle interferometric technique. Optical modeling calculations of the transmittance and reflectance through the thin ice films assist in the interpretation of the experimental results. We discuss our results and compare them with other measurements available in the literature. The results reported here are relevant to the spectroscopy of icy objects in the solar system; they are needed to perform laboratory characterization of ices, derive optical constants, and model spectra.  相似文献   

Perturbations of a geo-centric synchronous satellite with resonance     

Sushil Yadav  Rajiv Aggarwal 《Astrophysics and Space Science》2014,353(2):417-424

We have investigated the resonances due to the perturbations of a geo-centric synchronous satellite under the gravitational forces of the Sun, the Moon and the Earth including it’s equatorial ellipticity. The resonances at the points resulting from (i) the commensurability between \(\dot{\theta}_{0}\) (steady-state orbital angular rate of the satellite) and \(\dot{\theta}_{m}\) (angular velocity of the moon around the earth) and (ii) the commensurability between \(\dot{\theta}_{0}\) and \(\dot{\psi}_{0}\) (steady-state regression rate of the synchronous satellite) are analyzed. The amplitude and the time period of the oscillation have been determined by using the procedure as given in Brown and Shook (Planetary Theory, Cambridge University Press, Cambridge, 1933). We have observed that as θ _m (0^°≤θ _m ≤45^°) and ψ (0^°≤ψ≤135^°) increase, the amplitude decreases and the time period also decreases. We have also shown the effect of ψ on amplitude and time period for 0^°≤Γ≤45^°, where Γ is the angle measured from the minor axis of the earth’s equatorial ellipse to the projection of the satellite on the plane of the equator.  相似文献   

Resonance in the earth-moon system around the sun including earth’s equatorial ellipticity     

Sushil Yadav  Rajiv Aggarwal 《Astrophysics and Space Science》2013,348(2):367-375

We have investigated the resonances in the earth-moon system around the sun including earth’s equatorial ellipticity. The resonance resulting from the commensurability between the mean motion of the moon and Γ (angle measured from the minor axis of the earth’s equatorial ellipse to the projection of the moon on the plane of the equator) is analyzed. The amplitude and the time period of the oscillation have been determined by using the procedure of Brown and Shook. We have shown the effects of Γ on the amplitude and the time period of the resonance oscillation using the data of the moon. It is observed that the amplitude decreases and the time period also decreases as Γ increases from 0^° to 45^°.  相似文献   

Surfaces and atmospheres of the outer planets, their satellites and ring systems: Part VI     

Athena Coustenis  Sushil Atreya  Patrice Coll 《Planetary and Space Science》2010,58(13):1665-1666

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