Local gravity field modeling using spherical radial basis functions and a genetic algorithm

Spherical Radial Basis Functions (SRBFs) can express the local gravity field model of the Earth if they are parameterized optimally on or below the Bjerhammar sphere. This parameterization is generally defined as the shape of the base functions, their number, center locations, bandwidths, and scale coefficients. The number/location and bandwidths of the base functions are the most important parameters for accurately representing the gravity field; once they are determined, the scale coefficients can then be computed accordingly. In this study, the point-mass kernel, as the simplest shape of SRBFs, is chosen to evaluate the synthesized free-air gravity anomalies over the rough area in Auvergne and GNSS/Leveling points (synthetic height anomalies) are used to validate the results. A two-step automatic approach is proposed to determine the optimum distribution of the base functions. First, the location of the base functions and their bandwidths are found using the genetic algorithm; second, the conjugate gradient least squares method is employed to estimate the scale coefficients. The proposed methodology shows promising results. On the one hand, when using the genetic algorithm, the base functions do not need to be set to a regular grid and they can move according to the roughness of topography. In this way, the models meet the desired accuracy with a low number of base functions. On the other hand, the conjugate gradient method removes the bias between derived quasigeoid heights from the model and from the GNSS/leveling points; this means there is no need for a corrector surface. The numerical test on the area of interest revealed an RMS of 0.48 mGal for the differences between predicted and observed gravity anomalies, and a corresponding 9 cm for the differences in GNSS/leveling points.     

基于神经网络的南太平洋长鳍金枪鱼渔场预报

南太平洋长鳍金枪鱼是我国远洋渔业的重点捕捞对象;对南太平洋长鳍金枪鱼进行准确的渔场预报;可以提高捕捞效率;提高渔业的生产能力。本研究根据1993-2010年南太平洋长鳍金枪鱼的延绳钓生产数据以及海洋卫星遥感数据（海水表面温度;SST;海面高度;SSH）和ENSO（El Niño-Southern Oscillation）指标;采用DPS（data processing system）数据处理系统中的BP人工神经网络模型;以渔获产量（单位时间的渔获尾数）和单位捕捞努力量渔获量（CPUE;Catch per unit of effort）分别作为中心渔场的表征因子;并作为BP模型的输出因子;以月、经度、纬度、SST、SSH和ENSO指标等作为输入因子;分别构建4-3-1;5-4-1;5-3-1;6-5-1;6-4-1;6-3-1等BP模型结构;比较渔场预报模型优劣。研究结果表明;以CPUE作为输出因子的BP人工神经网络结构总体上较优;其中以6-4-1模型结构为最优;相对误差只有0.006 41。研究认为;以CPUE为输出因子的6-4-1结构的人工神经网络模型;能够准确预报南太平洋长鳍金枪鱼的渔场位置。     

Impact of major organophosphate pesticides used in agriculture to surface water and sediment quality (Southern Caspian Sea basin,Haraz River)

Organophosphate pesticides are compounds that are not only toxic to both humans and wildlife but also difficult to degrade under natural environmental conditions. In Iran, agricultural practices are strongly dependent on the use of pesticides due to climatic and soil conditions, thus posing a potential risk to groundwater quality standards. Evaluating the concentration of organophosphate pesticides namely diazinon, fenitrothion, dichlorvos, ethion, profenofos, malathion and azinphos methyl in water samples in May (low precipitation rate), December (high precipitation rate) as well as the concentration in sediments along the Haraz River is taken into consideration in this study. Generally the pesticides concentration in water samples are relatively higher in May in comparison with that in December; this fact may be due to two major reasons: the first reason is attributed to the prompt raining after the treatment period of most orchards and dry farming lands that will terminate in more wash out of such pesticides towards the branches and main river channel, while the second reason may be considered as the less river water dilution rate in May because of lower precipitation rate. Furthermore, the relatively higher concentrations in downstream stations may be contributed to more intensified agricultural (specially rice paddies), urban and rural land uses in this region in comparison with upstream areas which contain mainly dry farming, grazing lands and orchards with relatively lower loads of pesticides. Additionally, as the Henry’s law constant of all pesticides considered in this study are relatively low, volatilization may not be regarded as an important route of dissipation. Diazinon, azinphos methyl and dichlorvos showed the highest water concentrations in comparison with other pesticides that may be justified by their extended use within the basin during last decades. Based on the chemical properties as well as remarkably higher values in sediment samples in comparison with water ones, it is concluded that the two pesticides, ethion and fenitrothion, persist in the environment due to non-degradable tendencies. Although the concentration of mentioned pesticides is not so high in the water samples, more precautions must be considered in their future use. Regarding the sorption coefficient variation alongside the river, the higher values in upstream and central parts may be attributed to the higher potential of different types of erosion regarding deeper slopes and also sand, gravel and carbonate mining activities at the banks and also river bed in such regions which is considered as an anthropogenic disturbance. In case of central parts, in addition to mentioned reasons, the existence of coal outcrops in the geologic texture of the study area may also be considered as a key role in augmentation of the sorption coefficient. Finally, the dominant clayey and loamy soils containing more organics may be attributed as the major reason of sorption tendency in downstream.     

The Maastrichtian-Danian in the SW Zagros Fold-Thrust Belt (S. Iran): An Integration of Planktonic Foraminiferal Biostratigraphy and Gamma-Ray Spectrometry

In this study, the Maastrichtian-Danian boundary was measured and sampled in two stratigraphic sections, the north and south flanks of the Dehnow anticline in Coastal Fars, Southern Iran. This boundary was also investigated in the drilled exploratory well-1 in the same region. The lithology of the Maastrichtian-Danian deposits consists of glauconitic, phosphatic argillaceous limestones and marlstones. 30 genera and 77 species of planktonic foraminifera have been determined. The recognized biozon...     

Clear-water scour around semi-elliptical abutments with armored beds

Experimental study has been carried out under a clear-water scour condition to explore the local scour around semi-elliptical model bridge abutments with armor-layer bed, compared with the local scour process around semi-circular abutment. Two types of model bridge abutments, namely semi-elliptical and semi-circular abutments have been used in this experimental study. The model abutments had a ratio of streamwise length of abutment to the length of abutment transverse to the flow of 2 for semi-circular abutments and 3 for semi-elliptical abutments. In total, 50 Experiments have been designed and conducted under different flow conditions such as bed shear velocities, flow depth, and dimensions of bridge abutment model, as well as grain size of the bed material. Based on these experiments, the scour process around bridge abutments has been assessed. The dependence of the equilibrium scour depth of the scour hole on hydraulic variables has been studied. Empirical equation describing the equilibrium scour depth of the scour hole around bridge abutments has been developed.     

Synergic Impacts of Two Non-ionic Natural Surfactants and Low Salinity Water on Interfacial Tension Reduction,Wettability Alteration and Oil Recovery: Experimental Study on Oil Wet Carbonate Core Samples

Natural Resources Research - Low salinity water (LSW) flooding alters rock surface wettability toward more water wetness, and consequently, oil recovery will be increased from a carbonate oil...     

Performance of the horizontal drains in upstream shell of earth dams on the upstream slope stability during rapid drawdown conditions

Slope stability analysis during rapid drawdown is an important consideration in the design of embankment dams. During rapid drawdown, the stabilizing effect of the water on the upstream face is lost, but the pore water pressures within the embankment may remain high. As a result, the stability of the upstream face of the dam can be much reduced. Installing horizontal drains is a very efficient and cost-effective method for reducing the pore water pressure and increasing the stability of the upstream slope. The theory of horizontal drains in the upstream shell of earth dams is well established, but there seems to be limited resources available for the design of this type of horizontal drains. Hence, this study is focused on the performance of horizontal drains in the upstream shell of the slope of earth dams on the upstream slope stability during rapid drawdown conditions. The parametric study has been conducted on the variation of horizontal drain parameters such as the number of drains, their length, and their location. In this study, ten scenarios were analyzed based on different drainage configurations and the performance of each scenario is investigated on the seepage and the upstream slope stability during rapid drawdown conditions using finite element and limit equilibrium methods. The results demonstrated that the stability of the upstream slope during rapid drawdown conditions increases by increasing the number of drains. The length of drains extending further from its intersection with the critical failure surface does not provide any significant change in the factor of safety. Finally, the study also found that installing drains in the lower region of the upstream shell of earth dams gives more stability than those installed in higher elevations.     

A new ellipsoidal gravimetric, satellite altimetry and astronomic boundary value problem, a case study: The geoid of Iran

A new gravimetric, satellite altimetry, astronomical ellipsoidal boundary value problem for geoid computations has been developed and successfully tested. This boundary value problem has been constructed for gravity observables of the type (i) gravity potential, (ii) gravity intensity (i.e. modulus of gravity acceleration), (iii) astronomical longitude, (iv) astronomical latitude and (v) satellite altimetry observations. The ellipsoidal coordinates of the observation points have been considered as known quantities in the set-up of the problem in the light of availability of GPS coordinates. The developed boundary value problem is ellipsoidal by nature and as such takes advantage of high precision GPS observations in the set-up. The algorithmic steps of the solution of the boundary value problem are as follows:

- Application of the ellipsoidal harmonic expansion complete up to degree and order 360 and of the ellipsoidal centrifugal field for the removal of the effect of global gravity and the isostasy field from the gravity intensity and the astronomical observations at the surface of the Earth.

- Application of the ellipsoidal Newton integral on the multi-cylindrical equal-area map projection surface for the removal from the gravity intensity and the astronomical observations at the surface of the Earth the effect of the residual masses at the radius of up to 55 km from the computational point.

- Application of the ellipsoidal harmonic expansion complete up to degree and order 360 and ellipsoidal centrifugal field for the removal from the geoidal undulations derived from satellite altimetry the effect of the global gravity and isostasy on the geoidal undulations.

- Application of the ellipsoidal Newton integral on the multi-cylindrical equal-area map projection surface for the removal from the geoidal undulations derived from satellite altimetry the effect of the water masses outside the reference ellipsoid within a radius of 55 km around the computational point.

- Least squares solution of the observation equations of the incremental quantities derived from aforementioned steps in order to obtain the incremental gravity potential at the surface of the reference ellipsoid.

- The removed effects at the application points are restored on the surface of reference ellipsoid.

- Application of the ellipsoidal Bruns’ formula for converting the potential values on the surface of the reference ellipsoid into the geoidal heights with respect to the reference ellipsoid.

- Computation of the geoid of Iran has successfully tested this new methodology.

Erosion Rate Prediction Model for Levee-Floodwall Overtopping Applications in Fine-Grained Soils

Characterizing soil erosion and predicting levee erosion rates for various levee soils and storm conditions during floodwall overtopping events is necessary in designing levee-floodwall systems. In this study, a series of laboratory scaled levee-floodwall erosion tests were conducted to determine erosion characteristics of fine grained soils subject to overtopping from different floodwall heights with variable flow-rates. A decreasing rate of erosion was observed as a pool of water was generated in the created scour hole at the crest of the levee model. The erosion rates were also assessed using jet erosion test (JET) and erosion function apparatus (EFA) tests. The results of levee-floodwall overtopping along with soil geotechnical characteristics such as plasticity index, compaction level, and saturation level of the levee soils as well as hydraulic parameters such as water overtopping velocity were used to develop a levee-floodwall erosion rate prediction model. Then, the results of JET and EFA were integrated to develop another prediction model for levee-floodwall erosion rate estimation. Consequently, the prediction models were evaluated by conducting additional tests and comparing the prediction results with the actual measured erosion rates.