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121.
122.
气候变暖对中国水稻生产可能影响的研究 总被引:17,自引:0,他引:17
利用随机天气模型,将大气环流模式预测的气候情景与水稻模式相链接,研究了气候变暖对中国水稻生产的可能影响。结果表明,大气中CO2浓度加倍,中国水稻主产区适宜水稻生长的日数将延长6~11d,积温增加220~330℃·d。积温的相对增长率由南向北呈增长趋势。水稻产量形成期低温天气出现频率将减少,而高温天气出现的频率增加。若品种与播种、移栽期不变,水稻产量将下降;而若通过改变品种使作物生育期基本保持目前的状况,减产幅度将比品种不变时明显偏小,部分地区还有可能增产。 相似文献
123.
We investigated the effect of conditioning transient, two-dimensional groundwater flow simulations, where the transmissivity
was a spatial random field, on time dependent head data. The random fields, representing perturbations in log transmissivity,
were generated using a known covariance function and then conditioned to match head data by iteratively cokriging and solving
the flow model numerically. A new approximation to the cross-covariance of log transmissivity perturbations with time dependent
head data and head data at different times, that greatly increased the computational efficiency, was introduced. The most
noticeable effect of head data on the estimation of head and log transmissivity perturbations occurred from conditioning only
on spatially distributed head measurements during steady flow. The additional improvement in the estimation of the log transmissivity
and head perturbations obtained by conditioning on time dependent head data was fairly small. On the other hand, conditioning
on temporal head data had a significant effect on particle tracks and reduced the lateral spreading around the center of the
paths. 相似文献
124.
D. L. Hughson A. Gutjahr 《Stochastic Environmental Research and Risk Assessment (SERRA)》1998,12(3):155-170
We investigated the effect of conditioning transient, two-dimensional groundwater flow simulations, where the transmissivity
was a spatial random field, on time dependent head data. The random fields, representing perturbations in log transmissivity,
were generated using a known covariance function and then conditioned to match head data by iteratively cokriging and solving
the flow model numerically. A new approximation to the cross-covariance of log transmissivity perturbations with time dependent
head data and head data at different times, that greatly increased the computational efficiency, was introduced. The most
noticeable effect of head data on the estimation of head and log transmissivity perturbations occurred from conditioning only
on spatially distributed head measurements during steady flow. The additional improvement in the estimation of the log transmissivity
and head perturbations obtained by conditioning on time dependent head data was fairly small. On the other hand, conditioning
on temporal head data had a significant effect on particle tracks and reduced the lateral spreading around the center of the
paths. 相似文献
125.
P. J. G. Teunissen 《Journal of Geodesy》1997,71(9):541-551
In this contribution we analyse in a qualitative sense for the geometry-free model the dependency of the location, the size
and the shape of the ambiguity search space on different factors of the stochastic model. For this purpose a rather general
stochastic model is used. It includes time-correlation, cross-correlation, satellite elevation dependency and the use of an
a priori weighted ionospheric model, having the ionosphere-fixed model and the ionosphere-float model as special cases. It
is shown that the location is invariant for changes in the cofactor matrix of the phase observables. This also holds true
for the cofactor matrix of the code observables in the ionosphere-float case. As for time-correlation and satellite elevation
dependency, it is shown that they only affect the size of the search space, but not its shape and orientation. It is also
shown that the least-squares ambiguities, their variance matrix and its determinant, for, respectively, the ionosphere-fixed
model, the ionosphere-float model and the ionosphere-weighted model, are all related through the same scalar weighted mean,
the weight of which is governed by the variance ratio of the ionospheric delays and the code observables. A closed-form expression
is given for the area of the search space in which all contributing factors are easily recognized. From it one can infer by
how much the area gets blown up when the ionospheric spatial decorrelation increases. This multiplication factor is largest
when one switches from the ionosphere-fixed model to the ionosphere-float model, in which case it is approximately equal to
the ratio of the standard deviation of phase with that of code. The area gives an indication of the number of grid points
inside the search space.
Received: 11 November 1996 / Accepted: 21 March 1997 相似文献
126.
An evaluation method of hydrocarbon generating potential of highly mature and over-mature marine carbonate 总被引:2,自引:0,他引:2
How to restore the residual organic carbon and residual hydrocarbon-generating potential is discussed based on the hydrocarbon
degradability of source rock. The results indicate there is linear function relationship between the restoring coefficient
of residual organic carbon (Kc) and the vitrinite reflectance (R
o%) of various kinds of source rock, but the relationship is secondary functional between the restoring coefficient of residual
hydrocarbon-generating potential (Ks) and the vitrinite reflectance (R
o%). It is pointed out thatKc = (1 -Dresidual)/(1 -D
primary),Ks= Kc (D
primary/D
residual). The restoration of residual organic carbon and hydrocarbon-generating potential of the Cambrian and Ordovician highly mature
marine carbonate in the Tarim Basin and North China region shows that the lower limit value of hydrocarbon generating potential
and the organic matter abundance of carbonate source rock are basically the same as that of clastic rock. The technical difficulty
in hydrocarbon generating evaluation of highly mature and overmature carbonate is solved. 相似文献
127.
Ching-Min Chang Marian W. Kemblowski 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(2):129-143
Within the framework of stochastic theory and the spectral perturbation techniques, three-dimensional dispersion in partially
saturated soils with a finite correlation scale of log-hydraulic conductivity is analyzed. The effects of spatial variability
of the moisture distribution parameter on the asymptotic spreading behavior of a unsaturated solute plume are assessed. This
is accomplished by comparing two asymptotic macrodispersivities and two variance of solute concentration, obtained for a constant
moisture content and spatially varied moisture, respectively. 相似文献
128.
This series of articles present general applications of functional-analytic theory to the solution of the partial differential equation describing solid transport in aquifers, when either the evolution of the system, the sources, the parameters and/or the boundary conditions are prescribed as stochastic processes in time or in space. This procedure does not require the restricting assumptions placed upon the current particular solutions on which today's stochastic transport theory is based, such as small randomness assumptions (perturbation techniques), Montecarlo simulations, restriction to small spatial stochasticity in the hydraulic conductivity, use of spectral analysis techniques, restriction to asymptotic steady state conditions, and restriction to variance of the concentration as the only model output among others. Functional analysis provides a rigorous tool in which the concentration stochastic properties can be predicted in a natural way based upon the known stochastic properties of the sources, the parameters and/or the boundary conditions. Thus the theory satisfies a more general modeling need by providing, if desired, a systematic global information on the sample functions, the mean, the variance, correlation functions or higher-order moments based on similar information of any size, anywhere, of the input functions. Part I of this series of articles presents the main relevant results of functional-analytic theory and individual cases of applications to the solution of distributed sources problems, with time as well as spatial stochasticity, and the solution subject to stochastic boundary conditions. It was found that the stochastically-forced equation may be a promising model for a variety of random source problems. When the differential equation is perturbed by a time and space stochastic process, the output is also a time and space stochastic process, in contrast with most of the existing solutions which ignore the temporal component. Stochastic boundary conditions seems to quickly dissipate as time increases. 相似文献
129.
P. E. Kloeden E. Platen 《Stochastic Environmental Research and Risk Assessment (SERRA)》1989,3(3):155-178
The development of numerical methods for stochastic differential equations has intensified over the past decade. The earliest methods were usually heuristic adaptations of deterministic methods, but were found to have limited accuracy regardless of the order of the original scheme. A stochastic counterpart of the Taylor formula now provides a framework for the systematic investigation of numerical methods for stochastic differential equations. It suggests numerical schemes, which involve multiple stochastic integrals, of higher order of convergence. We shall survey the literature on these and on the earlier schemes in this paper. Our discussion will focus on diffusion processes, but we shall also indicate the extensions needed to handle processes with jump components. In particular, we shall classify the schemes according to strong or weak convergence criteria, depending on whether the approximation of the sample paths or of the probability distribution is of main interest. 相似文献
130.
S. E. Serrano T. E. Unny 《Stochastic Environmental Research and Risk Assessment (SERRA)》1987,1(4):281-296
Two methods for the solution of partial differential equations (PDE) for the general case of random in time physical parameters are presented and their application to the solution of unsteady regional groundwater flow equations are illustrated. The first method is the semigroup approach which directly offers a solution without resorting to closure approximations (hierarchy techniques), perturbation techniques, or Montecarlo simulation techniques. The semigroup approach can also handle the general stochastic problem when randomness also appears as initial conditions, boundary conditions or forcing terms. The second method is an approximation scheme to obtain the semigroup solution in complex cases and permits the solution of equations with more than one random coefficient. 相似文献