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Spatial Prediction of Soil Aggregate Stability and Aggregate-Associated Organic Carbon Content at the Catchment Scale Using Geostatistical Techniques

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Pedosphere 2011年第3期21卷 389-399页

作者： j.mohammadi M.H.MOTAGHIAN Department of Soil Science Agriculture CollegeShahrekord University

The association of organic carbon with secondary particles （aggregates） results in its storage and retention in soil. A study was carried out at a catchment covering about 92 km2 to predict spatial variability of soil water-stable aggregates （WSA）, mean weight diameter （MWD） of aggregates and organic carbon （OC） content in macro.- （〉 2 mm）, meso- （1-2 mm）, and micro-aggregate （〈 1 mm） fractions, using geostatistical methods. One hundred and eleven soil samples were eSlleeted at the 0 10cm depth and fractionated into macro-, meso-, and mlcro-aggregates by wet sieving. The OC content was determined for each fraction. A greater percentage of water-stable aggregates was found for micro-aggregates, followed by meso-aggregates. Aggregate OC content was greatest in meso-aggregates （9 g kg-1）, followed by micro-aggregates （7 g kg-1）, while the least OC content was found in macro-aggregates （3 g kg-1）. Although a significant effect （P = 0.000） of aggregate size on aggregate OC content was found, however, our findings did not support the model of aggregate hierarchy. Land use had a significant effect （P = 0.073） on aggregate OC content. The coefficients of variation （CVs） for OC contents associated with each aggregate fraction indicated macro-aggregates as the most variable （CV = 71%）. Among the aggregate fractions, the micro-aggregate fraction had a lower CV value of 27%. macro-aggregates to 84% for micro-aggregates. Geostatistical analysis differences in their spatial patterns in both magnitude and space at variance for most aggregate-associated properties was lower than 45%. The mean content of WSA ranged from 15% for showed that the measured soil variables exhibited each aggregate size fraction. The relative nugget The range value for the variogram of water-stable aggregates was almost similar （about 3 km） for the three studied aggregate size classes. The range value for the variogram of aggregate-associated OC contents ranged from about 3 km for macro-aggregates to about

关键词： kriging organic matter variogram water-stable aggregates

Spatial Estimation of Saturated Hydraulic Conductivity from Terrain Attributes Using Regression,Kriging,and Artificial Neural Networks

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Pedosphere 2011年第2期21卷 170-177页

作者： H.R.MOTAGHIAN j.mohammadi Department of Soil Science Agriculture CollegeShahrekord UniversityShahrekord (Iran)

Several methods,including stepwise regression,ordinary kriging,cokriging,kriging with external drift,kriging with varying local means,regression-kriging,ordinary artificial neural networks,and kriging combined with artificial neural networks,were compared to predict spatial variation of saturated hydraulic conductivity from environmental *** methods except ordinary kriging allow for inclusion of secondary *** secondary spatial information used was terrain attributes including elevation,slope gradient,slope aspect,profile curvature and contour curvature.A multiple jackknifing procedure was used as a validation *** mean square error (RMSE) and mean absolute error (MAE) were used as the validation indices,with the mean RMSE and mean MAE used to judge the prediction *** performance by ordinary kriging was poor,indicating that prediction of saturated hydraulic conductivity can be improved by incorporating ancillary data such as terrain *** combined with artificial neural networks performed *** prediction models made better use of ancillary information in predicting saturated hydraulic conductivity compared with the competing *** combination of geostatistical predictors with neural computing techniques offers more capability for incorporating ancillary information in predictive soil *** is great potential for further research and development of hybrid methods for digital soil mapping.

关键词： digital elevation model geostatistics soil hydraulic properties spatial mapping

Geostatistical Assessment of Pb,Zn and Cd Contamination in Near-Surface Soils of the Urban-Mining Transitional Region of Isfahan,Iran

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Pedosphere 2010年第5期20卷 568-577页

作者： M.DAYANI j.mohammadi Department of Soil Science Agriculture FacultyRamin Agriculture and Natural Resources University Department of Soil Science Agriculture FacultyShahrekord University

Due to the lack of regulation and environmental education and awareness, Sepahanshahr located in vicinity of Isfahan City, central Iran, is now a rapid growing residential area suffering from the considerable consequences of poorly regulated mining activities operating in its vicinity. A survey was carried out on soil Pb, Zn and Cd concentrations around Sepahanshahr Town to explore the spatial structure of Pb, Zn and Cd distribution and to map their concentrations using geostatistical techniques. 100 near-surface soil samples were collected and analyzed for Pb, Zn and Cd and some related soil physical and chemical variables such as pH, organic matter content, electrical conductivity, and clay, silt and sand contents. The variography results showed a strong spatial dependency in heavy metals concentration due to the dilution effects of natural factors including atmospheric dispersion and precipitation. The almost same range values calculated for both In-transformed Pb and sand data suggested presence of spatial co-regionalization. However, In-transformed Zn data showed a shorter spatial dependency among the three tested heavy metals. Kriged maps of all three heavy metals showed a strong gradient of contamination around the three mining sites activating in the area. The results of this study provide insight into identification of the extent and spatial variability of Pb, Zn and Cd pollution in the mining sites and surrounding urban areas.

关键词： heavy metals Kriging soil pollution spatial variability variogram

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货车零部件概率统计疲劳安全计算

智慧轨道交通 1986年第3期 30-32页

作者： j.mohammadi 王昶

一、前言铁路货车极易由其零部件中的交变应力引起损坏。这些交变应力的产生是由于轨道的几何条件,特别是由于轨道的不平顺引起的。在正常运行条件下,产生的应力在允许的极限之内,交变应力的循环是导致破坏的主要因素。每一应力循环在... 详细信息

一、前言铁路货车极易由其零部件中的交变应力引起损坏。这些交变应力的产生是由于轨道的几何条件,特别是由于轨道的不平顺引起的。在正常运行条件下,产生的应力在允许的极限之内,交变应力的循环是导致破坏的主要因素。每一应力循环在相应的零件中产生一定程度的损伤。这种损伤累积直到疲劳破坏的产生。这时,累积损伤达到一临界水平。了解货车这个特点并计算这个临界水平是货车“安全运行”设计的必不可少的部分。

关键词：零部件安全计算疲劳寿命车体疲劳力学性质概率密度函数概率论随机变量货运车辆货车

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铁路货车疲劳失效概率分析

智慧轨道交通 1987年第2期 42-47页

作者： j.mohammadi 侯卫星

铁路货车的关键性部件承受的是波动应力,因而易发生疲劳损伤。这种波动应力是由于车辆在轨道上作不同的运动和所经历的各种轨道不平顺引起的。无论是轨道不平顺还是相应的运动都是随机的。因此,它所造成的疲劳损伤只能用概率水平来确定... 详细信息

铁路货车的关键性部件承受的是波动应力,因而易发生疲劳损伤。这种波动应力是由于车辆在轨道上作不同的运动和所经历的各种轨道不平顺引起的。无论是轨道不平顺还是相应的运动都是随机的。因此,它所造成的疲劳损伤只能用概率水平来确定。本文介绍货车疲劳损伤的概率评价方法,还讨论了车辆疲劳损伤计算时不确定的边界条件的影响,同时论述了这种方法在车体设计上的应用和疲劳寿命估算。

关键词：失效概率边界条件危险单元铁路货车概率密度函数波动应力不确定性轨道不平顺

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生命线危险性分析方法

世界地震工程 1983年第3期 12-21页

作者： j.mohammadi A.H-S.Ang 陈达生

序言在地震活动性强烈的地区,生命线系统抗地震威胁的可靠性是需要在其设计中考虑的最重要因素之一。这里所谓"生命线系统"是指复盖很大地表面积的人工或工程系统的网络。按这个定义,油管、供水系统、通讯或交通网络都可认为是生命线系统。

关键词：断层破裂长度破坏概率衰减公式地面震动近震源区震级地震危险性分析震源参数地面运动地壳运动震源模型震源类型

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地震次生火灾危险性分析

世界地震工程 1994年第3期10卷 54-60页

作者： j.mohammadi S.Alyasin D.N.Bak 宋建学

一、概述与背景对地震影响区来说,次生火灾是个重要问题。从财产损失和人员伤亡角度来看,次生火灾有时会成为地震损失的主要部分。加里福尼亚州几乎所有的现代大地震,都在居住区和商业区产生了次生火灾。

关键词：地震次生火灾危险性

Sol-gel derived nanocrystalline and mesoporous barium strontium titanate prepared at room temperature

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Particuology 2011年第3期9卷 235-242页

作者： Mohammad Reza mohammadi Derek j.Fray Department of Materials Science & Engineering Sharif University of Technology Department of Materials Science & Metallurgy University of Cambridge

Perovskite-type barium strontium titanate （BST） thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol-gel route at room temperature. The prepared sol had a narrow particle size distribution of about 20 nm. X-ray diffraction （XRD） revealed that phase composition and preferable orientation growth of BST depended upon the annealing temperature. Transmission electron microscope （TEM） images showed that the crystallite size of the powders decreased with increasing annealing temperature from 8 nm at 25 ℃ down to 5 nm at 800 ℃. Field emission scanning electron microscope （FE-SEM） analysis and atomic force microscope （AFM） images revealed that BST thin films had mesoporous and nanocrystafiine structure with average grain size of 3Onm at 600 ℃. Based on Brunauer-Emmett-Teller （BET） analysis, the synthesized BST showed mesoporous structure containing nnres with needle, and nlate shanes and BET surface area in the range of 49-32 m^2/g at 500-800℃

关键词： Barium strontium titanate Room temperature Sol-gel chemistry Nanostructure

Numerical and experimental study of twin-fluid two-phase internal-mixing atomizer to develop maximum entropy method

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Chinese journal of Aeronautics 2020年第9期33卷 2281-2294页

作者： Alireza mohammadi Fathollah OMMI Department of Mechanical Engineering.Tarbiat Modares University Tehran 14115-111Iran

This paper presents an analytical, numerical, and experimental study on atomization characteristics and droplet distribution of a twin-fluid two-phase internal mixing atomizer to develop a Maximum Entropy Method(MEM). A two-phase Eulerian-Lagrangian method is utilized for atomization modeling of the inside and outside atomizer. In order to modify energy and momentum sources in the MEM, parametric studies are performed, and experimental tests are carried out to verify the results by applying the shadowgraph method. An advanced test stand is developed to prepare a wide range of changes in atomization characteristics and mixing ratios. A high degree of consistency is found between numerical results from the developed MEM and experimental tests with different gas-phase pressures and liquid flow rates. The droplet diameter and velocity distribution are reviewed based on various Weber numbers, sources of energy, and momentum. Turbulence modeling assists to estimate the breakup length and time scale precisely in the developed MEM, and distribution ranges with mean values are achieved. With reference to a strong correlation between upstream turbulence flow and the developed MEM verified by experimental tests, an ideal droplet size and velocity distribution prediction is observed.

关键词： Atomization Droplet distribution Internal-mixing atomizer Maximum entropy method Shadowgraph technique Test stand