Comparison of linear and nonlinear forms of isotherm models for Zn(II) and Cu(II) sorption on a kaolinite

The most appropriate method in designing the adsorption systems and assessing the performance of the adsorption systems is to have an idea on adsorption isotherms. Comparison analysis of linear least square method and nonlinear method for estimating the isotherm parameters was made using the experimental equilibrium data of Zn(II) and Cu(II) onto kaolinite. Equilibrium data were fitted to Freundlich, Langmuir, and Redlich–Peterson isotherm equations. In order to confirm the best-fit isotherms for the adsorption system, the data set using the chi-square (χ ²), combined with the values of the determined coefficient (r ²) was analyzed. Nonlinear method was found to be a more appropriate method for estimating the isotherm parameters. The best fitting isotherm was the Langmuir and Redlich–Peterson isotherm. The Redlich–Peterson is a special case of Langmuir when the Redlich–Peterson isotherm constant g was unity. The sorption capacity of kaolinite to uptake metal ions in the increasing order was given by Cu (4.2721 mg/g)?<?Zn (4.6710 mg/g).     

Application of a continuum numerical model for pile driving analysis and comparison with a real case

This paper presents the results of a so-called continuum numerical model for wave propagation analysis and soil-pile dynamic response during pile driving. An axisymmetric finite difference numerical model is developed having solid elements for both pile structure and the soil media surrounding and below the pile. Interface elements are used between the pile shaft and the soil to facilitate the sliding between the two media. The performance of the developed model is verified in two stages. First, a simple rod is subjected to a half sine-wave force function at the rod head and the corresponding reflections of force and velocity (multiplied by impedance) are presented for different boundary conditions at the rod tip. The model is then used for signal matching analysis of a real driven pile for which complete information of soil layering, dynamic test signals, and static load test results are available. The signal matching analysis was performed successfully and comparison between several other predicted and measured parameters proved the reasonably good performance of the developed continuum model.     

Shape factor in the drawdown solution for well testing of dual-porosity systems

One of the important parameters in existing commercial dual-porosity reservoir simulators is matrix–fracture shape factor, which is customarily obtained by assuming a constant pressure at the matrix–fracture boundary. In his work, Chang [1] and [2] addressed the impact of boundary conditions at the matrix–fracture interface and presented analytical solutions for the transient shape factor and showed that for a slab-shaped matrix block a constant pressure boundary condition leads to an asymptotic (long-time) shape factor of π²/L², and that a constant volumetric flux leads to an asymptotic shape factor of 12/L². In a recent paper [3], we reconfirmed Chang’s [1] and [2] results using a Laplace transform approach. In this study, we extend our previous analysis and use infinite-acting radial and linear dual-porosity models, where the boundary condition is chosen at the wellbore, as opposed to at the matrix boundary. The coupled equations for fracture and matrix are solved analytically, taking into account the transient exchange between matrix and fracture. The analytical solution that invokes the time dependency of fracture boundary condition under constant rate is then used to calculate the transient shape factors. It is shown that, for a well producing at constant rate from a naturally fractured reservoir, the appropriate value of stabilized shape factor is 12/L². This contrasts with the commonly used shape factor for a slab-shaped matrix block that is subject to a constant pressure boundary condition, which is π²/L². The errors in the matrix–fracture exchange term in a dual-porosity model associated with the use of a shape factor derived based on constant pressure boundary condition at the matrix boundary are then evaluated.     

Evaluating the accuracy of ANN and LR models to estimate the water quality in Zarivar International Wetland,Iran

One of the most important qualitative aspects of wetland ecosystem management is preserving the natural quality of water in such environments. This would not be achievable unless continuous water quality monitoring is implemented. With the recent advances in remote sensing technology, this technology could assist us to produce accurate models for estimating water quality variables in the ecosystem of wetlands. The present study was carried out to evaluate the capability of remote sensing data to estimate the water quality variables [pH, total suspended solids (TSS), total dissolved solids (TDS), turbidity, nitrate, sulfate, phosphate, chloride and the concentration of chlorophyll a] in Zarivar International Wetland using linear regression (LR) and artificial neural network (ANN) models. For this purpose, spectral reflectance of bands 2, 3, 4 and 5 of the OLI sensor of Landsat 8 was utilized as the input data and the collected chemical and physical data of water samples were selected as the objective data for both ANN and LR models. Based on our results overall, ANN model was the proper model compared with LR model. The spectral reflectance in bands 5 and 4 of OLI sensor revealed the best results to estimate TDS, TSS, turbidity and chlorophyll in comparison with other used bands in ANN model, respectively. We conclude that OLI sensor data are an excellent means for studying physical properties of water quality and comparing its chemical properties.     

Viscous-resistive ADAF with a general large-scale magnetic field

We have studied the structure of hot accretion flow bathed in a general large-scale magnetic field. We have considered magnetic parameters , where are the Alfvén sound speeds in three direction of cylindrical coordinate (r,φ,z). The dominant mechanism of energy dissipation is assumed to be the magnetic diffusivity due to turbulence and viscosity in the accretion flow. Also, we adopt a more realistic model for kinematic viscosity (ν=αc _s H), with both c _s and H as a function of magnetic field. As a result in our model, the kinematic viscosity and magnetic diffusivity (η=η ₀ c _s H) are not constant. In order to solve the integrated equations that govern the behavior of the accretion flow, a self-similar method is used. It is found that the existence of magnetic resistivity will increase the radial infall velocity as well as sound speed and vertical thickness of the disk. However the rotational velocity of the disk decreases by the increase of magnetic resistivity. Moreover, we study the effect of three components of global magnetic field on the structure of the disk. We found out that the radial velocity and sound speed are Sub-Keplerian for all values of magnetic field parameters, but the rotational velocity can be Super-Keplerian by the increase of toroidal magnetic field. Also, Our numerical results show that all components of magnetic field can be important and have a considerable effect on velocities and vertical thickness of the disk.     

The evaluation of borehole imaging result comparing with cores in Sarvak fractured and non-fractured reservoir

Core samples are still today considered as the standard measurement against all other measurements which must be compared. Core analysis usually focuses on the worse portion of the reservoir due to the fact that core recovery has rarely been well in a highly fractured zone; hence, permeability measured from core sample is often not representative. Core analysis is a common method to identify small-scale fractures of the well and permeability and porosity; however, there are some limitations in the core procedure such as it is highly expensive and unidirectional and has a low recovery coefficient in fractured zone. In contrast, there tends to be a mistrust and even a suspicion of those logging instruments that make measurements which threaten to replicate or even replace the “sacred core.” Thus, image logs are more useful to study the subsurface fractures in these such cases and the logs which come closest to achieving this are the high-resolution micro resistivity (OBMI) and acoustic geological imaging (UBI). The core and OBMI-UBI result was matched in order to verify the log measurements. Furthermore, FMI data were integrated with other open-hole logs to derive a permeability curve. As demonstrated in the case studies, it is believed that the permeability in the basement could be reasonably evaluated using this method. As a result, this exercise has proven to be very valuable, not only for demonstrating the value of the log data, but also it has also highlighted some significant limitations of the core in water-based mud and oil-based mud systems.     

Near-source attenuation of high-frequency body waves beneath the New Madrid Seismic Zone

Attenuation characteristics in the New Madrid Seismic Zone (NMSZ) are estimated from 157 local seismograph recordings out of 46 earthquakes of 2.6?≤?M?≤?4.1 with hypocentral distances up to 60 km and focal depths down to 25 km. Digital waveform seismograms were obtained from local earthquakes in the NMSZ recorded by the Center for Earthquake Research and Information (CERI) at the University of Memphis. Using the coda normalization method, we tried to determine Q values and geometrical spreading exponents at 13 center frequencies. The scatter of the data and trade-off between the geometrical spreading and the quality factor did not allow us to simultaneously derive both these parameters from inversion. Assuming 1/R ^1.0 as the geometrical spreading function in the NMSZ, the Q _P and Q _S estimates increase with increasing frequency from 354 and 426 at 4 Hz to 729 and 1091 at 24 Hz, respectively. Fitting a power law equation to the Q estimates, we found the attenuation models for the P waves and S waves in the frequency range of 4 to 24 Hz as Q _P?=?(115.80?±?1.36) f ^{(0.495?±?0.129)} and Q _S?=?(161.34?±?1.73) f ^{(0.613?±?0.067)}, respectively. We did not consider Q estimates from the coda normalization method for frequencies less than 4 Hz in the regression analysis since the decay of coda amplitude was not observed at most bandpass filtered seismograms for these frequencies. Q _S/Q _P?>?1, for 4?≤?f?≤?24 Hz as well as strong intrinsic attenuation, suggest that the crust beneath the NMSZ is partially fluid-saturated. Further, high scattering attenuation indicates the presence of a high level of small-scale heterogeneities inside the crust in this region.     

On the number of required response history analyses

This study investigates the number of real ground motions (GMs) required to accurately capture the structural responses when using code-, intensity-, and risk-based seismic assessment frameworks. A key consideration is the use of as-recorded hazard consistent GMs, which appropriately characterize the seismic hazard of the site, for performing response history analysis. A comparison of the structural responses of 3 steel moment resisting buildings using different sets of GMs is made with results obtained using a large set of GMs. The empirical results demonstrate that, in most cases, a risk-based assessment needs a larger number of response history analyses than an intensity-based assessment method to accurately capture the seismic demand on the structural systems. Also, given the same number of GMs, the structural responses from a risk-based assessment are more reliable and stable than those for an intensity-based method. Moreover, the results help to quantify the uncertainty in the structural responses due to using different sample sets of GMs given the applied number of GMs. In addition, the results indicate that a significant bias in structural responses is likely when following the recommendations from several seismic design codes, which suggest utilizing the maximum structural responses if 3 GM pairs are used for response history analysis. A detailed statistical analyses show that the application of 7 GM pairs are sufficient to accurately and reliably estimate structural responses.