Interactions between the rotifer Euchlanis dilatata and the cladocerans Alona glabra and Macrothrix triserialis in relation to diet type     

Cristian Alberto Espinosa-RodríguezS.S.S. Sarma  S. Nandini 《Limnologica》2012,42(1):50-55

We studied, separately, the effect of the cladocerans Alona glabra and Macrothrix triserialis on the population growth of the rotifer Euchlanis dilatata using three different food types (Chlorella and Scenedesmus, live or dead, offered on a comparable dry weight basis, 3.16 μg C ml⁻¹). Regardless of the presence or absence of competition, E. dilatata cultured using Chlorella (live or dead) showed a higher population growth as compared to Scenedesmus. Compared to heat-killed C. vulgaris, E. dilatata cultured alone and fed on live algae reached higher abundances. Both cladoceran species had an adverse effect on the population growth of Euchlanis, but did not eliminate the rotifers. Of the two cladocerans, M. triserialis had a far more adverse effect on the population densities of E. dilatata as compared to A. glabra. E. dilatata also influenced the population growth of A. glabra and M. triserialis, the former being more adversely affected than the latter. When the egg ratios of E. dilatata were plotted as a function of population density, a significantly inverse relation was obtained only in treatments containing Chlorella but not for other treatments. Statistically the rate of population increase (r) per day of E. dilatata was adversely affected by the diet type and the presence of competing species. The interaction of diet type X competition was also significant. For A. glabra, the presence of E. dilatata and the diet type, but not their interaction, significantly influenced the r. On the other hand for M. triserialis, only the diet type was significant. Our results suggest that the competitive outcome between rotifers and cladocerans was dependent on diet type.  相似文献   

Seasonal dynamics of zooplankton in Lake Huetzalin, Xochimilco (Mexico City, Mexico)     

Cecilia Enríquez García  S. Nandini  S.S.S. Sarma 《Limnologica》2009,39(4):283-291

We quantified the seasonal changes in the zooplankton abundances collected from the Huetzalin Lake (Mexico City, Mexico) for two years (February 2003–January 2004 and then March 2005–February 2006). Selected physicochemical variables (Secchi depth, temperature, pH, conductivity, dissolved oxygen, phosphorus, nitrogen, carbon and chlorophyll a concentration) were also measured at the time of zooplankton collection. The data on zooplankton abundances and the physicochemical variables were subjected to multiple correlation analysis and we also derived Shannon–Wiener species diversity index. Secchi depth ranged from 9 to 65 cm. Generally the lake was alkaline (pH 7–12). The conductivity ranged from 500–1000 mS cm⁻¹, while the mean water temperature was 20.5 °C. Dissolved oxygen levels were generally >3 mg L⁻¹ and were higher in the winter than warmer months. Nitrates (90–95 μg L⁻¹) and phosphates (.2–.5 mg L⁻¹) indicated that the water was eutrophic. Chlorophyll a levels ranged from 143 to 696 μg L⁻¹ during the study period. The zooplankton community was dominated by rotifers (46 species), followed by cladocerans (9 species) and there were only two copepod species. The dominant rotifer species were Brachionus angularis, Brachionus calyciflorus, Brachionus havanaensis, Brachionus quadridentatus, Lecane bulla and Polyarthra vulgaris. Rare rotifer species in Lake Huetzalin were Lecane ohioensis, Dicranophorus forcipatus, Lecane pyriformis, Lindia torulosa, Pleurotrocha petromyzon and Brachionus durgae. Highest densities (occasional peaks of 400 ind L⁻¹) of B. quadridentatus occurred between April and December, while B. havanaensis reached peak densities, during June to October. B. calyciflorus reached densities higher than 1240 ind L⁻¹ during May–September. Cladoceran and copepod densities in Lake Huetzalin were much lower than that of the rotifers. This study confirmed the earlier findings that Xochimilco system of canals is dominated by rotifers and the crustacean zooplankton have much lower abundances possibly due to predation from fish.  相似文献   

Atmospheric noise on the bispectrum in optical speckle interferometry     

S. N. Karbelkar  Rajaram Nityananda 《Journal of Astrophysics and Astronomy》1987,8(3):271-274

Based on a simple picture of speckle phenomena in optical interferometry it is shown that the recent signal-to-noise ratio estimate for the so called bispectrum, due to Wirnitzer (1985), does not possess the right limit when photon statistics is unimportant. In this wave-limit, which is true for bright sources, his calculations over-estimate the signal-to-noise ratio for the bispectrum by a factor of the order of the square root of the number of speckles.  相似文献   

Gravitational lensing by stars in a galaxy halo: Theory of combined weak and strong scattering     

Nityananda  Rajaram  Ostriker  J. P. 《Journal of Astrophysics and Astronomy》1984,5(3):235-250

The theory of gravitational lensing of background quasars by stars in the halo of a galaxy is considered. In the limiting case of small ‘optical depth’, only one star is close enough to the beam to cause strong scattering, and the effect of all the other stars is treated as a perturbation with both systematic and random components. The perturbation coming from weak scattering can increase the number of images and the amplification in those cases where the amplification is already high; such events are preferentially selected in flux limited observations. The theory is applicable to the apparent association of background quasars with foreground galaxies. A comparison with earlier work on the same problem is given. The relevance of these results to gravitational lensing by galaxies as perturbed by random inhomogeneities surrounding the ray path is also briefly discussed.  相似文献   

Structural evolution of a gneiss dome in the axial zone of the proterozoic South Delhi Fold Belt in central Rajasthan     

Dhruba Mukhopadhyay  Nandini Chattopadhyay  Tapas Bhattacharyya 《Journal of the Geological Society of India》2010,75(1):18-31

The structural geometry of the Anasagar gneiss dome in the axial zone of the South Delhi Fold Belt is controlled by polyphase folding. It is classified as a thrust-related gneiss dome and not as a metamorphic core complex. Four phases of deformation have affected both the gneiss and the enveloping supracrustal rocks. D₂ and D₃ deformations probably represent early and late stages of a progressive deformation episode in a simple shear regime combined with compression. The contact between the gneiss and the supracrustal rocks is a dislocation plane (thrust) with top-to-east sense of movement which is consistent with the vergence of the D₂ folds. The thrust had a ramp-and-flat geometry at depth. At the present level of exposure it is a footwall flat (that is, parallel to the gneissosity in the footwall), but it truncates the bedding of the hanging wall at some places and is parallel at others. The thrusting was probably broadly coeval with the D₂ folds and the thrust plane is locally folded by D₂. D₂ and D₃ folds have similar style and orientation as the first and second phases respectively of major folds in the Delhi Supergroup of the South Delhi Fold Belt and these are mutually correlatable. It is suggested that D1 may be Pre-Delhi in age. Available geochronological data indicate that the emplacement of the Anasagar gneiss predated the formation of volcanic rocks in the Delhi Supergroup and also predated the main crust forming event in the fold belt. The Anasagar gneiss and its enveloping supracrustal rocks are probably older than the Delhi Supergroup.  相似文献   

The application of artificial neural networks to magnetotelluric time-series analysis   总被引：4，自引：0，他引：4  

C. Manoj  Nandini Nagarajan 《Geophysical Journal International》2003,153(2):409-423

  相似文献   

Growth of Plankton (Scenedesmus acutus (Chlorophyceae) and Moina macracopa (Cladocera)) on Domestic Wastewater     

S. Nandini  Ricardo Alonso‐Soto  S. S. S. Sarma 《洁净——土壤、空气、水》2013,41(1):11-15

The population growth of the freshwater chlorophyte, Scenedesmus acutus and the cladoceran Moina macrocopa cultured in the laboratory and in microcosms of a wastewater treatment plant was studied. S. acutus was cultured in a defined algal medium and mixed with wastewater. On diets of S. acutus cultured using Bold medium or a mixture with wastewater, the peak densities of M. macrocopa were 6–7 ind. mL^?1, while on a diet of algae cultured on wastewater alone the cladoceran density fluctuated around 2 ind. mL^?1. Population growth rates of M. macrocopa, which ranged from 0.3 to 0.4 d^?1, were significantly lower on alga cultured in wastewater alone. The body size structure of M. macrocopa was larger on algae cultured in Bold medium than in wastewater. Peak densities of M. macrocopa were around 700 ind. L^?1 when the organic matter in the containers was supplemented with algae but it reached lower densities (400 ind. L^?1) when cultured on the organic matter in wastewater alone. Our study indicates that the nutrients in the final stages of wastewater treatment can support the growth of both phytoplankton and zooplankton.  相似文献   

Effect of the presence of a conducting channel between India and Sri Lanka Island on the features of the equatorial electrojet     

Mita Rajaram  B. P. Singh  N. Nityananda  A. K. Agrawal 《Geophysical Journal International》1979,56(1):127-138

Summary. Transient geomagnetic variations like SSCs, Bays, Sq and storm-time variations show anomalously large Z amplitudes at the three permanent magnetic observatories in India under the equatorial electrojet. Our earlier studies have shown that these anomalies cannot be explained in terms of the usual coastal effect. Another unique feature of this area is the small equatorial enhancement of all magnetic fluctuations, which still remains to be completely understood. It is also noticed that Z/H ratio at Annamalainagar is very large for night-time variations but becomes insignificant for day-time fluctuations, whereas no such large difference is seen at Trivandrum, the other coastal station. All the above features have been explained here by introducing the presence of a conducting channel in the lower crust or upper mantle between India and Sri Lanka Island. The anomalies of the equatorial electrojet in the Indian region thus do not necessitate the conducting surface of the mantle to be deeper in this area as has been suggested by earlier workers. A less conducting mantle in the Indian region otherwise could be difficult to incorporate in the present theories of mantle convection when this area is known to be tectonically active. The presence of the conducting channel is further confirmed by analogue model experiments of Papamastorakis. We further observe that the equatorial electrojet does have an associated internal part in the Indian region.  相似文献   

An explanation of induced magnetic variations at Sabhawala,India     

N. Nityananda  A.K. Agarwal  B.P. Singh 《Physics of the Earth and Planetary Interiors》1981,25(3):226-231

Induction vectors calculated for short-period events such as “bays” and “storm sudden commencements” (SSCs) indicate that the conductor causing the anomaly lies to the south of Sabhawala. The nature of vertical transfer functions obtained from spectral analysis of storm-time variations further confirms the presence of such a conductor. The nature of maximum (G_p) and minimum (G₁) response functions suggests that a two-dimensional conductor south of Sabhawala is responsible for anomalies in Z. Invoking a structural model of the Earth's crust beneath the Himalayas, in keeping with accepted orogenic theories, we propose that one structure capable of producing the desired conducting path is a rise of the asthenosphere south of the Himalayan range. Another important factor contributing to the induced variations at Sabhawala is due to a sedimentary trough running parallel to the Himalayas, again to the south. These views are confirmed by a two-dimensional model calculation. It is found that the undulation of the asthenosphere alone does not reproduce the nature of the anomalies in H and Z.  相似文献   

Induction at short periods in the horizontal field variations in the Indian peninsula     

N. Nityananda  A.K. Agarwal  B.P. Singh 《Physics of the Earth and Planetary Interiors》1977,15(1):P5-P9

A study of the horizontal components of certain short-period magnetic-fluctuation events, viz., storm sudden commencements and bays, shows appreciable anomalies at two of the five magnetic observatories in peninsular India. The electric current patterns deduced from the magnetic horizontal induced variations imply channelling of induced currents through the Palk Straits and around the southern tip of the Indian peninsula. An interesting feature of these anomalies is that while the induced magnetic vertical variations are strongly correlated with the horizontal northward magnetic field, the electric current concentrations flow parallel to the coast; southwest, near Annamalainagar, and north near Trivandrum. The observations are interpreted in terms of a regional, east-west, induced electric current pattern which is perturbed in the vicinity of the two observatories by the Indian peninsula.  相似文献