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421.
A new formula for dispersion from continuous sources in light wind conditions is derived, which takes account of along-wind dispersion. Thisis achieved by integrating over puffs released at different times and byassuming that the puffs grow with a size that is proportional totravel time at small travel times, and proportional to the square rootof travel time at large times. The results are compared with theGaussian plume formula and with two previous formulae that assumeeither linear growth or growth proportional to the square root of traveltime throughout the puff evolution. The conditions under which thevarious solutions are good approximations to each other or to anyresults that might be obtained with a more realistic puff growthformula are investigated. Finally the relevance of these idealisedresults to more realistic atmospheric flows is discussed and alternativemodelling approaches are considered. 相似文献
422.
In kriging, parametric approaches to covariance (or variogram) estimation require that unknown parameters be inferred from a single realization of the underlying random field. An approach to such an estimation problem is to assume the field to be Gaussian and iteratively minimize a (restricted) negative loglikelihood over the parameter space. In doing so, the associated computational burden can be considerable. Also, it is usually not easy to check whether or not the minimum achieved is global. In this note, we show that in many practical cases, the structure of the covariance (or variogram) function can be exploited so that iterative minimizing algorithms may be advantageously replaced by a procedure that requires the computation of the roots of a simple rational function and the search for the minimum of a function depending on one variable only. As a consequence, our approach allows one to observe in a straightforward fashion the presence of local minima. Furthermore, it is shown that insensitivity of the likelihood function to changes in parameter value can be easily detected. The note concludes with numerical simulations that illustrate some key features of our estimation procedure. 相似文献
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426.
The geological conditions for coal mining in China are complex, with various structural issues such as faults and collapsed columns seriously compromising the safety of coal mine production. In-seam wave exploration is an effective technique for acquiring detailed information on geological structures in coal seam working faces. However, the existing reflected in-seam wave imaging technique can no longer meet the exploration precision requirements, making it imperative to develop a new reflected in-seam wave imaging technique. This study applies the Gaussian beam summation (GBS) migration method to imaging coal seams'' reflected in-seam wave data. Firstly, with regard to the characteristics of the reflected in-seam wave data, methods such as wavefield removal and enveloped superposition are employed for the corresponding wavefield separation, wave train compression and other processing of reflected in-seam waves. Thereafter, imaging is performed using the GBS migration technique. The feasibility and effectiveness of the proposed method for reflected in-seam wave imaging are validated by conducting GBS migration tests on 3D coal-seam fault models with different dip angles and throws. By applying the method to reflected in-seam wave data for an actual coal seam working face, accurate imaging of a fault structure is obtained, thereby validating its practicality. 相似文献
427.
An important aim of modern geostatistical modeling is to quantify uncertainty in geological systems. Geostatistical modeling
requires many input parameters. The input univariate distribution or histogram is perhaps the most important. A new method
for assessing uncertainty in the histogram, particularly uncertainty in the mean, is presented. This method, referred to as
the conditional finite-domain (CFD) approach, accounts for the size of the domain and the local conditioning data. It is a
stochastic approach based on a multivariate Gaussian distribution. The CFD approach is shown to be convergent, design independent,
and parameterization invariant. The performance of the CFD approach is illustrated in a case study focusing on the impact
of the number of data and the range of correlation on the limiting uncertainty in the parameters. The spatial bootstrap method
and CFD approach are compared. As the number of data increases, uncertainty in the sample mean decreases in both the spatial
bootstrap and the CFD. Contrary to spatial bootstrap, uncertainty in the sample mean in the CFD approach decreases as the
range of correlation increases. This is a direct result of the conditioning data being more correlated to unsampled locations
in the finite domain. The sensitivity of the limiting uncertainty relative to the variogram and the variable limits are also
discussed. 相似文献
428.
偏心支撑结构是一种高烈度地震区高层建筑钢结构合理的抗侧力体系,本文针对目前偏心支撑结构存在的不足,提出一种新型的框架支撑形式——耗能器偏心支撑;并将该单斜杆(D型)耗能器偏心支撑与支撑斜杆上不加设耗能器的D型偏心支撑结构进行了对比试验。验证了该新型框架支撑形式不仅可以减少耗能梁段吸收的地震能量,而且可以减小耗能梁段的破坏程度,从而减少震后修复工作量;它具有很好的变形能力和足够的抗侧移能力。文中同时给出了设计方法,并提出了改进措施。 相似文献
429.
Jacqueline A. MacDonald Mitchell J. Small 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(2):203-214
This paper summarizes the findings of a statistical analysis of the locations of metallic anomalies detected at the Pueblo
Precision Bombing Range Number 2 in Otero County, Colorado, and at the Victorville Precision Bombing Range in San Bernardino
County, California. The purpose of the study is to explore whether statistical properties of the pattern of anomaly locations
can be used to discriminate areas likely to contain unexploded ordnance (UXO) left over from previous bombing practice from
those unlikely to contain UXO. Techniques for discriminating areas with and without UXO are needed because historic records
have left an incomplete account of previous military training activities, so that locations historically used for target practice
are often unknown. This study differs from previous research on metallic anomaly data at former military training ranges in
that it analyzes the spatial pattern of the discrete locations of the anomalies, rather than the average number of anomalies
per unit area. The results indicate that differences in spatial pattern may be a distinguishing feature between areas that
were used for target practice and those that are unlikely to contain UXO, even when a large number of ferrous rocks and other
inert metallic anomalies are present. We found that at both of the former bombing ranges, the anomaly patterns in sample areas
that are distant from all known bombing targets are consistent with a complete spatial randomness pattern, while those near
the target areas fit a radially symmetric, bivariate Gaussian pattern. Furthermore, anomaly location patterns generated by
surveys with airborne metal detectors have the same statistical properties as the patterns generated by surveys with on-ground
detectors, even though the airborne systems detect only a subset of the anomalies found by the ground-based detectors. Thus,
pattern information revealed by airborne surveys with metal detectors may be useful in identifying areas where careful searches
for UXO are needed.
相似文献
Jacqueline A. MacDonaldEmail: |
430.
Some of the considerable statistical content of modified Bessel functions of the second kind and of Tricomi's confluent hypergeometric
function is illustrated. Moment solutions for the parameters of exponential class distribution functions based on both are
derived. Unlike the generalised inverse Gaussian, the Tricomi exponential distribution is little known but it emerges that
it is of wide applicability, highly flexible and has the gamma distribution as a special case. 相似文献