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141.
R. K. Mall Ranjeet Singh Akhilesh Gupta G. Srinivasan L. S. Rathore 《Climatic change》2006,78(2-4):445-478
During the recent decade, with the growing recognition of the possibility of climate change and clear evidence of observed
changes in climate during 20th century, an increasing emphasis on food security and its regional impacts has come to forefront of the scientific community.
In recent times, the crop simulation models have been used extensively to study the impact of climate change on agricultural
production and food security. The output provided by the simulation models can be used to make appropriate crop management
decisions and to provide farmers and others with alternative options for their farming system. It is expected that in the
coming decades with the increased use of computers, the use of simulation models by farmers and professionals as well as policy
and decision makers will increase. In India, substantial work has been done in last decade aimed at understanding the nature
and magnitude of change in yield of different crops due to projected climate change. This paper presents an overview of the
state of the knowledge of possible effect of the climate variability and change on food grain production in India.
An erratum to this article can be found at 相似文献
142.
Linfeng Rao Thandankorai G. Srinivasan PierLuigi Zanonato Arturo Bismondo 《Geochimica et cosmochimica acta》2004,68(23):4821-4830
Neptunium is one of the few radioactive elements that are of great concern in the disposal of nuclear wastes in the geological repository, due to its hazards and the long half-life of the isotope, 237Np (t1/2 = 2.14 × 106 years). To understand and predict the migration behavior of neptunium in the geological media, it is of importance to study its hydrolysis at elevated temperatures, because the temperature in the waste package and the vicinity of the repository could be high. Moreover, the chemical analogy between neptunium(V) and plutonium(V) adds even greater value to this investigation, because the latter could exist at tracer levels in neutral and slightly oxidizing waters but is difficult to study due to its rather labile redox behavior.In this work, the hydrolysis of neptunium(V) was studied at variable temperatures (10 to 85°C) in tetramethylammonium chloride (1.12 mol kg−1). Two hydrolyzed species of neptunium(V), NpO2OH(aq) and NpO2(OH)2−, were identified by potentiometry and Near-IR absorption spectroscopy. The hydrolysis constants (*βn) and enthalpy of hydrolysis (ΔHn) for the reaction NpO2+ + nH2O = NpO2(OH)n(1−n)+ + nH+ (n = 1 and 2) were determined by titration potentiometry and microcalorimetry. The hydrolysis constants, *β1 and *β2, increased by 0.8 and 3.4 orders of magnitude, respectively, as the temperature was increased from 10 to 85°C. The enhancement of hydrolysis at elevated temperatures is mainly due to the significant increase of the degree of ionization of water as the temperature is increased. The hydrolysis reactions are endothermic but become less endothermic as the temperature is increased. The heat capacities of hydrolysis, ΔCp1 and ΔCp2, are calculated to be −(71 ± 17) J K−1 mol−1 and −(127 ± 17) J K−1 mol−1, respectively. Approximation approaches to predict the effect of temperature, including the constant enthalpy approach, the constant heat capacity approach and the DQUANT equation, have been tested with the data. 相似文献
143.
The term flood basalt is redefined emphasizing the importance of the subaerial environment. Using the well established physical criteria of aerial extent, internal structures, time of extrusion and associations, flood basalt activity is distinguished in the Archeans (Dharwars) of Mysore from the geosynclinal volcanics. Study of chemical composition of the Dharwar and other Archean volcanics in the light ofSugimura’s (1968) SWS index, and plotting of the chemical analyses on theMacdonald andKatsura’s (1964) alkali-silica diagram,Kuno’s (1968) alkali-alumina-silica diagram and Scheynamann’s silica-Niggli qz diagram shows both geosynclinal and subaerial volcanics are mainly tholeiitic. Therefore in deciphering the environment of volcanism, it is suggested that the physical criteria take precedence over chemical composition. 相似文献
144.
Magnesium, potassium and calcium isotope compositions in terrestrial samples and refractory phases from primitive meteorites
are determined using an ion microprobe. A thorough investigation of the different instrument parameters is carried out to
ensure that conditions necessary for high mass resolution and high precision isotopic studies are adequately satisfied. The
instrument can be tuned to achieve mass resolution (M/ΔM) of up to 10,000 (M≤60); it has a very good dynamic stability (ΔB/B≤10
ppm over durations of ≤40 minutes) and the counting system has an effective dead-time of ≤25 nsec and a dynamic background
of ≤0·01 c/s. Reproducibility and precision of isotopic measurements are checked by analyzing magnesium and titanium isotopic
compositions in terrestrial standards and isotopically doped silicate glasses. A precision of 2‰ (2σ
m
) was achieved during magnesium isotopic analysis in samples with low Mg content (200 ppm). Results from studies of magnesium
and potassium isotopic compositions in several Ca−Al-rich refractory inclusions (CAIs) from the primitive meteorites Efremovka
and Grosnaja, representing some of the early solar system objects, are presented. The well-behaved Mg−Al isotopic systematics
confirm the pristine nature of the Efremovka CAIs inferred earlier from petrographic and trace element studies. The Grosnaja
CAIs that have experienced secondary alterations show disturbed magnesium isotopic systematics. Observation of excess26Mg in several of the analyzed CAIs confirms the presence of the now extinct26Al (t
1/2=7×105 years) in the solar nebula at the time of CAI formation. Our data also suggest a relatively uniform distribution of26Al in the solar nebula. Several Efremovka CAIs with excess26Mg also have excess41K resulting from the decay of41Ca (t
1/2≃105 years). This observation constrains the time interval between cessation of nucleosynthetic input to the solar nebula and
the formation of some of the first solar system solids (CAIs) to less than a million years. 相似文献
145.
Ushijima-Mwesigwa Hayato Hyman Jeffrey D. Hagberg Aric Safro Ilya Karra Satish Gable Carl W. Sweeney Matthew R. Srinivasan Gowri 《Mathematical Geosciences》2021,53(8):1977-1978
Mathematical Geosciences - The publication of this article unfortunately contained a mistake. The assignment to the affiliations of author Satish Karra was not correct 相似文献
146.
Mathematical Geosciences - Inverse modeling techniques for estimating reservoir parameters (e.g., transmissivity, permeability) utilize some dynamic (secondary) information (e.g., hydraulic head or... 相似文献
147.
Evaluation of global optimization algorithms for parameter calibration of a computationally intensive hydrologic model 总被引:1,自引:0,他引:1
With the popularity of complex hydrologic models, the time taken to run these models is increasing substantially. Comparing and evaluating the efficacy of different optimization algorithms for calibrating computationally intensive hydrologic models is becoming a nontrivial issue. In this study, five global optimization algorithms (genetic algorithms, shuffled complex evolution, particle swarm optimization, differential evolution, and artificial immune system) were tested for automatic parameter calibration of a complex hydrologic model, Soil and Water Assessment Tool (SWAT), in four watersheds. The results show that genetic algorithms (GA) outperform the other four algorithms given model evaluation numbers larger than 2000, while particle swarm optimization (PSO) can obtain better parameter solutions than other algorithms given fewer number of model runs (less than 2000). Given limited computational time, the PSO algorithm is preferred, while GA should be chosen given plenty of computational resources. When applying GA and PSO for parameter optimization of SWAT, small population size should be chosen. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
148.
Possible Impacts of Global Warming on the Hydrology of the Ogallala Aquifer Region 总被引:11,自引:0,他引:11
Norman J. Rosenberg Daniel J. Epstein David Wang Lance Vail Raghavan Srinivasan Jeffrey G. Arnold 《Climatic change》1999,42(4):677-692
The Ogallala or High Plains aquifer provides water for about 20% of the irrigated land in the United States. About 20 km3 (16.6 million acre-feet) of water are withdrawn annually from this aquifer. In general, recharge has not compensated for withdrawals since major irrigation development began in this region in the 1940s. The mining of the Ogallala has been pictured as an analogue to climate change in that many GCMs predict a warmer and drier future for this region. In this paper we attempt to anticipate the possible impacts of climate change on the sustainability of the aquifer as a source of water for irrigation and other purposes in the region. We have applied HUMUS, the Hydrologic Unit Model of the U.S. to the Missouri and Arkansas-White-Red water resource regions that overlie the Ogallala. We have imposed three general circulation model (GISS, UKTR and BMRC) projections of future climate change on this region and simulated the changes that may be induced in water yields (runoff plus lateral flow) and ground water recharge. Each GCM was applied to HUMUS at three levels of global mean temperature (GMT) to represent increasing severity of climate change (a surrogate for time). HUMUS was also run at three levels of atmospheric CO2 concentration (hereafter denoted by [CO2]) in order to estimate the impacts of direct CO2 effects on photosynthesis and evapotranspiration. Since the UKTR and GISS GCMs project increased precipitation in the Missouri basin, water yields increase there. The BMRC GCM predicts sharply decreased precipitation and, hence, reduced water yields. Precipitation reductions are even greater in the Arkansas basin under BMRC as are the consequent water yield losses. GISS and UKTR climates lead to only moderate yield losses in the Arkansas. CO2-fertilization reverses these losses and yields increase slightly. CO2 fertilization increases recharge in the base (no climate change) case in both basins. Recharge is reduced under all three GCMs and severities of climate change. 相似文献
149.
Multi-species reactive transport equations coupled through sorption and sequential first-order reactions are commonly used to model sites contaminated with radioactive wastes, chlorinated solvents and nitrogenous species. Although researchers have been attempting to solve various forms of these reactive transport equations for over 50 years, a general closed-form analytical solution to this problem is not available in the published literature. In Part I of this two-part article, we derive a closed-form analytical solution to this problem for spatially-varying initial conditions. The proposed solution procedure employs a combination of Laplace and linear transform methods to uncouple and solve the system of partial differential equations. Two distinct solutions are derived for Dirichlet and Cauchy boundary conditions each with Bateman-type source terms. We organize and present the final solutions in a common format that represents the solutions to both boundary conditions. In addition, we provide the mathematical concepts for deriving the solution within a generic framework that can be used for solving similar transport problems. 相似文献
150.
Application of a temperature-index melt model incorporated into the Soil and Water Assessment Tool (SWAT) is presented to simulate mass balance (MB) and equilibrium line altitude (ELA) of three glaciers. The snow accumulation/melt parameters were adjusted to glacierized and free glacier areas, respectively. The SWAT snow algorithm enabled us to consider spatial variation of snow parameters by elevation bands across the sub-basins, while in the previous studies using SWAT, the related parameters were constant for an entire basin. The results show slight improvement in runoff simulation and significant improvement in simulated MB when considering ELA in model calibration. The results showed that SWAT can be applied to simulate MB, vertical MB distribution and annual ELA, with light calibration efforts for data-scarce catchments. The accuracy of the results depends on the modelled area of ablation zone from which most of the meltwater is released. 相似文献