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351.
--This work deals with computational modelling designed to understand the dynamical mechanism of low frequency monsoonal transients that results from nonlinear divergent-rotational (&gif1;) kinetic energy (KE) conversions due to the effects of Coriolis force, vorticity and divergence during the summer monsoon 1988 over the latitudinal belt 20°S-30°N at 850 hPa and 200 hPa. The results show two distinct spectral peaks spanning 30-45 days and 18-25 days in the energy conversions from the transient divergent motions to rotational motions. Due to the latitudinal variation of the earth's rotational effects, the conversion from the transient divergent to rotational motions, associated mainly with wavenumbers 1 and 2, tend to be more pronounced to the north of 15°N on the 30-45-day and 18-25-day time scales in the upper and lower tropospheres, respectively. The contribution of the stationary waves to maintenance of the low frequency rotational flow due to the effect of divergence through barotropic instability is significant at the upper troposphere. Divergent to rotational KE conversion by wave-wave interaction due to divergence is identified as an important mechanism for maintenance of low frequency oscillations in the lower troposphere. The upper tropospheric planetary scale divergent motions associated with 30-45-day oscillation gain substantial energy through nonlinear &gif1; interaction due to vorticity. 相似文献
352.
Density, δ18O and δ13C were measured along two tracks, one close to the central growth axis and the other, ∼20ℴ off the axis, in a coral (Porites lutea) collected from the Stanley Reef, Central Great Barrier Reef, Australia. The δ18O variations in the coral are well correlated with sea surface temperature changes. The common variances between the two tracks
were about 60% in the δ18O, δ{13}C, and the skeletal density variations. Part of the noise (40%) could be due to the difficulty of sampling exactly
time contemporaneous parts of each band along the two tracks and part of it could be due to genuine intraband variability.
In spite of the intraband variability, the time series obtained from the two tracks are similar, indicating that the dominant
causative factor for the isotopic variations is external, i.e., the environmental conditions that prevail during the growth
of the coral; density band formation does not appear to be directly controlled by the sea surface temperature. 相似文献
353.
S. K. Chaulya M. K. Chakraborty M. Ahmad K. K. K. Singh R. S. Singh B. K. Tewary P. K. Gupta 《Environmental Geology》2000,39(10):1155-1162
A study has been conducted at the Bicholim iron-ore mine, North Goa, India to investigate the hydrogeological continuity
between the mine's open pit and surrounding villages. Water resource accounting by demarcating different watersheds has also
been carried out to analyse the major causes of groundwater scarcity in the region during dry periods. A resistivity survey
and a ground penetrating radar survey were completed around the periphery of open pits, the surrounding village areas and
Mayem Lake. The results of the two independent surveys and other related data confirm that there is no observable hydrogeological
continuity between the pits, nearby villages and Mayem Lake. Hence, there may not be any significant effect on surrounding
water resources due to mining or mine dewatering. Water resource accounting has revealed that only 15–20% of 3500 mm precipitation
per annum becomes part of the groundwater resource. The remainder of the annual precipitation is lost as heavy runoff, evapotranspiration
and subsurface capillary moisture. Closely spaced wells in the region have also aggravated the groundwater scarcity problem
due to draw down effects. Therefore, an effective water resource conservation plan is required for the region to overcome
the problem.
Received: 18 January 1999 · Accepted: 17 May 1999 相似文献
354.
We have presented a spherically symmetric domain wall in five dimensionalspace-time with non-vanishing stress component in the directionperpendicular to the plane of the wall. The general solution to Einstein'sequations for such domain wall is obtained using functional separabilityof metric coefficients. 相似文献
355.
John D. Coates Romy Chakraborty Susan M. OConnor Claudia Schmidt Jürgen Thieme 《洁净——土壤、空气、水》2001,28(7):420-427
As part of a study on microbial redox alteration of humic substances we investigated the potential effect of this metabolism on the fate of heavy metals and hydrocarbons as a result of conformational alteration of the humic molecular structure due to microbial reduction. Our studies indicate that the microbial reduction of humic acids (HA) results in significant morphological and geochemical alterations. X‐ray microscopy analysis indicate that the conformational structure of the humic colloids is altered as a result of the redox change. In the reduced state, the HA appeared as small dense particles, on reoxidation, large loose aggregates were formed. In addition, spectrofluorometric studies indicated that the binding capacity of the HA for naphthalene was decreased by 10% when the HA was reduced. Similarly, the reduced HA yielded higher surface tension values at all concentrations tested which is indicative of a more hydrophilic and less hydrophobic solute. On reoxidation, the surface tension values reverted back to values similar to those obtained for the untreated oxidized HA. These data indicate that the hydrophobicity of the HA is altered on biological reduction of the HA and that this alteration is reversible. In contrast the reduced HA demonstrated a 15% higher affinity for heavy metals such as divalent cobalt than the oxidized HA. In addition to increasing the binding capacity of HA for heavy metals, the reduction of the HA also decreased the bioavailability and toxicity of bound heavy metals such as chromium. When incubated in the presence of Cr(III) and HA, cells of Escherichia coli grew much more rapidly in the presence of the reduced HA suggesting that the higher metal binding capacity of the reduced humic substances resulted in a removal of the Cr(III) from solution and hence reduced its bioavailability and toxicity. These studies demonstrate that HA redox state and reduction of humic acids by microorganisms can have a significant effect on the molecular morphology and binding constants of HA for heavy metals and hydrocarbons and also directly affects the bioavailability of these compounds in the environment. 相似文献