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611.
Biogeochemical records of paleoenvironmental changes in Nainital Lake,Kumaun Himalayas,India 总被引:1,自引:0,他引:1
Preetam Choudhary Joyanto Routh Govind J. Chakrapani Bhishm Kumar 《Journal of Paleolimnology》2009,42(4):571-586
Rapid urbanization and increased tourism around Nainital Lake in the Kumaun Himalayan region in north India has raised concerns
about sediment and water pollution. Lead-210 dated sediment cores from the lake represent ~95 years of accumulation and yield
a mean sedimentation rate of ~4.7 mm year−1. Total organic carbon (TOC), percent N and S and their atomic C/N and C/S ratios, stable isotopes (δ13C, δ15N, and δ34S), and specific biomarkers (n-alkanes and pigments) were measured in the core. Organic matter is primarily derived from in-lake algal production and TOC
flux varies from 1.0 to 3.5 g m−2 year−1. Sediments are anoxic (Eh −328 to −187 mV) and have low (0.10–0.30 g m−2 year−1) N, but high (0.37–1.0 g m−2 year−1) S flux. Shifts in δ13C, δ15N, and δ34S suggest in-lake microbial processes dominated by denitrification and sulfate reduction. The sediments are dominated by short-chain
hydrocarbons with low Carbon Preference Index values. The pigments indicate a gradual shift to cyanobacterial domination of
the phytoplankton community in recent years. Despite an increase in external input of nutrients, the trophic state of the
lake has remained largely unchanged, and the perceived human-induced impacts are limited. 相似文献
612.
Baha Y. Mirghani Kumar G. Mahinthakumar Michael E. Tryby Ranji S. Ranjithan Emily M. Zechman 《Advances in water resources》2009
Groundwater characterization involves the resolution of unknown system characteristics from observation data, and is often classified as an inverse problem. Inverse problems are difficult to solve due to natural ill-posedness and computational intractability. Here we adopt the use of a simulation–optimization approach that couples a numerical pollutant-transport simulation model with evolutionary search algorithms for solution of the inverse problem. In this approach, the numerical transport model is solved iteratively during the evolutionary search. This process can be computationally intensive since several hundreds to thousands of forward model evaluations are typically required for solution. Given the potential computational intractability of such a simulation–optimization approach, parallel computation is employed to ease and enable the solution of such problems. In this paper, several variations of a groundwater source identification problem is examined in terms of solution quality and computational performance. The computational experiments were performed on the TeraGrid cluster available at the National Center for Supercomputing Applications. The results demonstrate the performance of the parallel simulation–optimization approach in terms of solution quality and computational performance. 相似文献
613.
S. Sridharan P. Vishnu Prasanth Y. Bhavani Kumar Geetha Ramkumar S. Sathishkumar K. Raghunath 《Journal of Atmospheric and Solar》2009,71(5):575-582
Resonance lidar observations of sodium density in the upper mesosphere region over Gadanki (13.5°N, 79.2°E) rarely show complex structures with rapid enhancements of sodium density, completely different from normal sporadic sodium structures. The hourly averaged meteor radar zonal winds over Trivandrum (8.5°N, 76.5°E) show an eastward shear with altitude during the nights, when these events are formed. As suggested by Kane et al. [2001. Joint observations of sodium enhancements and field-aligned ionospheric irregularities. Geophysical Research Letters 28, 1375–1378], our observations show that the complex structures may be formed due to Kelvin–Helmholtz instability, which can occur in the region of strong wind shear. 相似文献
614.
615.
This paper presents the effects of soil layering on the characteristics of basin-edge induced surface waves and associated
strain and aggravation factor. The simulated results revealed surface wave generation near the basin-edge. The first mode
of induced Love wave was obtained in models having increasing velocity with depth and a large impedance contrast between the
soil layers. Amplitude amplification or de-amplification of body waves was proportional to the impedance contrast between
the soil layers. The average aggravation factor was inversely proportional to the impedance contrast between the soil layers
in case of increasingvelocity models and proportional in case of decreasing-velocity basinedge models. On the other hand,
the maximum strain was inversely proportional to the impedance contrast between the soil layers in both cases. On the average,
strain was greater in case of increasing-velocity models but the average aggravation factor was greater in case of decreasingvelocity
models. 相似文献
616.
617.
N. Ramaiah V. V. S. S. Sarma Mangesh Gauns M. Dileep Kumar M. Madhupratap 《Journal of Earth System Science》2000,109(4):443-451
Bacterial abundance and production, numbers, sizes and concentrations of transparent exopolymer particles (TEP) and total
organic carbon (TOC) were measured during the 1996 summer monsoon to understand the relationship between TEP, the most labile
particulate organic carbon, and bacteria. While high regional variability in the vertical distribution of TOC was discernible,
TEP concentrations were high in surface waters at 18–20°N along 64°E with concentrations well over 25 mg alginic acid equivalents
I−1 due to upwelling induced productivity. Their concentrations decreased with depth and were lower between 200 and 500 m. Bacterial
concentrations were up to 1.99 × 108 I–1 in the surface waters and decreased by an order of magnitude or more at depths below 500 m. A better relationship has been
found between bacterial abundance and concentrations of TEP than between bacteria and TOC, indicating that bacterial metabolism
is fueled by availability of TEP in the Arabian Sea. Assuming a carbon assimilation of 33%, bacterial carbon demand (BCD)
is estimated to be 1.017 to 4.035 g C m–2 d–1 in the surface waters. The observed TEP concentrations appear to be sufficient in meeting the surface and subsurface BCD
in the northern Arabian Sea. 相似文献
618.
The characteristics of directional spread parameters at intermediate water depth are investigated based on a cosine power ‘2s' directional spreading model. This is based on wave measurements carried out using a Datawell directional waverider buoy in 23 m water depth. An empirical equation for the frequency dependent directional spreading parameter is presented. Directional spreading function estimated based on the Maximum Entropy Method is compared with those obtained using a cosine power ‘2s' parameter model. A set of empirical equations relating the directional spreading parameter corresponding to the peak of wave spectrum to other wave parameters like significant wave height and period are obtained. It shows that the wave directional spreading at peak wave frequency can be related to the non-linearity parameter, which allows estimation of directional spreading without reference to wind information. 相似文献
619.
Interpolation of wave heights 总被引:1,自引:0,他引:1
Remote sensing of waves often necessitates presentation of data in the form of wave height values grouped over large time intervals. This restricts their use to long-term applications only. This paper describes how such data can be made suitable for short-term usage in the field. Weekly mean significant wave heights were derived from their monthly mean observations with the help of different alternative techniques. These include model-free neural network schemes as well as model-based statistical and numerical methods. Superiority of neural networks was noted when the estimations were compared with corresponding observations. The network was trained using three different training algorithms, viz., error back propagation, conjugate gradient and cascade correlation. The technique of cascade correlation took minimum training time and showed better coefficient of correlation between observations and network output. 相似文献
620.
We have obtained empirical relations between the p-mode frequency shift and the change in solar activity indices. The empirical relations are determined on the basis of frequencies obtained from BBSO and GONG stations during solar cycle 22. These relations are applied to estimate the change in mean frequency for the cycle 21 and 23. A remarkable agreement between the calculated and observed frequency shifts for the ascending phase of cycle 23, indicates that the derived relations are independent of epoch and do not change significantly from cycle to cycle. We propose that these relations could be used to estimate the shift in p-mode frequencies for past, present and future solar activity cycles, if the solar activity index is known. The maximum frequency shift for cycle 23 is estimated to be 265±90 nHz, corresponding to a predicted maximum smoothed sunspot number 118.1±35. 相似文献