Experimental tests of metal extraction from stones sampled from articially contaminated railway ballasts are presented and discussed. Metal extraction was performed by washing with aqueous solutions of disodium ethylenedi- aminetetraacetate (EDTA), at selected concentrations. The eectiveness of the remediation process was evaluated using leaching tests. The results indicate that the washing technology represents a successful and aordable solution for the imple- mentation of an on-site treatment aimed at a reuse process. Adopting a 0.05 M EDTA solution, extraction yields in the range between 40% and 70% were achieved, depending on contact time and pH of the washing solution.
In this study, we report on the activity concentrations of $^{238}$U, $^{232}$Th, $^{40}$K, and $^{137}$Cs in 50 soil samples of Bethlehem Province, West Bank, Palestine. Gamma-ray spectroscopy was employed to perform the measurements using an HPGe detector. On one hand, the activity concentrations of natural radionuclides were found to vary from 12.7 to 122.3 Bq kg$^{-1}$ with an average value of 41.4 Bq kg$^{-1}$ for $^{238}$U, from 2.0 to 32.2 Bq kg$^{-1}$ with an average value of 19.5 Bq kg$^{-1}$ for $^{232}$Th, and from 12.0 to 183.8 Bq kg$^{-1}$ with an average value of 113.3 Bq kg$^{-1}$ for $^{40}$K. On the other hand, the activity concentrations of the artificial $^{137}$Cs radionuclide were found between 1.0 and 12.2 Bq kg$^{-1}$, with an average value of 2.8 Bq kg$^{-1}$. The variations of the assessed radiological hazard parameters indices $Ra_{eq}$, $D_{r}$, $ H_{ex}$, and $I_{\gamma }$ of natural radionuclides were found to be as follows: 16-148, 7-65, 0.04-0.4, and 0.11-1.00, respectively. The results were found to be comparable to or lower than similar reported data worldwide. Accordingly, the investigated soil zones can be considered to have normal levels of natural background radiation.
Clay from Kono-bowe, Nigeria, was activated thermally and chemically and used to remove lead(II) and chromium(III) ions from aqueous solution. The effects of adsorption process variables were studied as well as the kinetics and equilibrium of the process. Analysis of the activated samples showed that the surface area, cation exchange capacity, and adsorption performance were positively favored by both activation processes. It was observed that the adsorption rate increased with an increase in temperature, contact time, adsorbent dosage, initial ion concentration, and solution pH values. The pH$_{PZC}$ of the adsorbents was determined to be 6.5, 7.4, and 7.2, for KBR, KBTA, and KBAA, respectively. It was observed that sample KBAA yielded maximum adsorption efficiency of 99.9% for the removal of chromium(III), and gave maximum adsorption efficiency of 98.7% for lead(II) removal. The results of the kinetics analysis of the adsorption data revealed that adsorption follows pseudo-second-order kinetics. Analysis of the equilibrium data showed that the Langmuir isotherm provided a better fit to the experimental data for KBR, while the Freundlich isotherm fitted the experimental data of KBTA and KBAA. Evaluation of the thermodynamic parameters revealed that the adsorption process is spontaneous and endothermic.
Model-based feedback linearizing control is studied for the control of fed-batch yeast fermentation. For this purpose, the specific growth rate of fed-batch baker's yeast fermentation is controlled with a state feedback linearizing control approach. All control algorithms are constructed on reliable primary measurements, data reconciliation, and state estimations developed previously. The obtained biomass concentrations and specific growth rates are used in the control algorithms. Initially, the results of open-loop specific growth rate controlled fed-batch baker's yeast fermentation are given to show the shortcomings of the existing control method in practice. The state feedback linearizing control of the specific growth rate is then applied to the fed-batch baker's yeast fermentation. Different specific growth rate profiles are investigated and results are presented. The successful implementation of the control of the specific growth rate is shown under the critical specific growth rate value and other limiting factors.
In most geotechnical projects the linear Mohr--Coulomb envelope is used. This envelope is curved for coarse-grained soils and is affected by some factors such as confining pressure, relative density, mineralogy, particle crushing, fine content, and gradation of sand particles. The curved strength envelope could be used to study the behavior of deep foundations, earth dams, soil slopes, and other earth structures in which failure occurs under considerable normal stresses. A deep failure surface may be more critical than a shallow surface when the phenomenon of curved strength envelopes is considered, because the secant friction angle decreases with increasing depth of soil layers and confining pressure. The main purpose of this research is to express the secant friction angle of sands as a function of normal stress and relative compaction. In this study, direct shear tests are performed on air-dried and saturated sand samples at different normal stresses to evaluate the variation of secant friction angle with these factors.
A series of nine experiments was performed in a physical model of an asymmetric compound channel to quantify the boundary shear stress at the interface of the bed of a main channel and floodplain. Commonly used equations of shear stress distributions across the bottoms of the main channel and floodplain interfaces were analyzed and tested for various types of asymmetric compound channels and their flow conditions. The lateral momentum transfer between the deep main channel and the adjoining shallow floodplains was found to greatly affect the shear stress distribution at the bottoms of the main channel and the flood plain subsections. Different dimensionless ratios of shear stress distributions were obtained and related to the relevant parameters. Some important results concerning the uniformity of the shear stress distribution, which is significant in sediment-laden rivers to state the possible locations of erosion and deposition, are presented.
The problem of steady laminar mixed convection heat transfer about a vertical cone embedded in a porous medium with high porosity was studied numerically, taking into account the radiation--conduction effect. The fluid was assumed to be incompressible and dense. The nonlinear coupled parabolic partial differential equations governing the flow were transformed into nonsimilar boundary layer equations, which were then solved numerically using the Keller box method. The effects of the exponent in the power law variation of the free stream velocity m, the mixed convection parameter Ri, the radiation--conduction parameter Rd, the surface temperature parameter qw, and Forchheimer parameter g on the velocity and temperature profiles, as well as on the local skin friction and local heat transfer, are presented and analyzed. The validity of the methodology and analysis was checked by comparing the results obtained for some specific cases with those available in the literature.
This study investigated the effectiveness of screens as energy dissipaters in small hydraulic structures using physical experiments. In the experimental design, the Froude number, screen arrangements, and screen porosity were the major controlling parameters. The experiments covered a range of Froude numbers between 2.5 and 8.5, screen porosity of 40% and 50%, and gaps of double screens between 1 and 5 cm. The main goal of this study was investigation of the screens creating submerged hydraulic jumps. The flow depth was digitally measured in order to perceive the turbulences and validate the results of energy dissipation against those of the methods in the literature. The experimental results show the importance of each parameter on the screen performance. The screens with double arrangement with the imposed hydraulic jump dissipated more energy. The gaps of the double arrangement had an insignificant effect on energy dissipation. The double screen with porosity of 40% had the best performance. Since the Froude number was found to be the most effective parameter, quadratic equations as a function of this number were fitted to the experimental results with high R$^{2}$ and very low RMSE values. The quadratic equations can be employed as interpolators and/or extrapolators.
The effect of different types of surface roughness on a turbulent boundary layer was studied using 1D velocity measurements in a relatively high Reynolds flow. The roughness consisted of trapezoidal ribs with horizontal spacing and roughness height $k$. The roughness elements were aligned in a direction transverse to the flow. A series of 7 tests of fully rough turbulent subcritical flow over two-dimensional transverse repeated trapezoidal ribs was undertaken, in which the ribs were varied to give uniform rib spacing-to-height ratios of p/k = 6--36. Measurements of the velocity were carried out over a range of Reynolds numbers, 81735 $
This paper analyzes the flow and heat and mass transfer characteristics of the free convection on a vertical plate with uniform wall temperature and concentration in a micropolar fluid in the presence of a first-order chemical reaction and radiation. A uniform magnetic field $B_{0}$ is applied normal to the plate. The governing nonlinear partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations using similarity transformations and then solved numerically using the Keller-box method. The numerical results are compared and found to be in good agreement with previously published results as special cases of the present investigation. The coefficient of skin-friction, wall couple stress, the rate of heat transfer in terms of Nusselt number, and the ratio of convective to diffusive mass transport in terms of Sherwood number at the plate are presented graphically for various values of coupling number, magnetic parameter, radiation parameter, chemical reaction parameter, Prandtl number, and Schmidt number.
Among the advanced materials, the $\gamma $-TiAl intermetallic compounds, due to their unique properties, are being gradually employed instead of nickel base super alloys, titanium alloys, and other high temperature alloys in the aerospace and automotive industries. These properties include maintaining high strength and creep resistance at elevated temperatures. Considering the features of this material and the limitations of traditional machining procedures, in this paper the results of utilizing the EDM process for $\gamma $-TiAl and the effects of input parameters, including discharge current and discharge duration, on output characteristics, comprising material removal rate, tool wear ratio, surface texture, and compositions and phases of machined surfaces, are presented. The results show that the EDM process affects surface integrity of $\gamma $-TiAl and causes the formation of surface cracks even at the lowest level of discharged energy. The increase in the discharge energy results in the formation of longer cracks with wider mouths. Due to the ingress of carbon and oxygen on the surface of the specimen, initial compositions and phases of machined surfaces are changed and brittle phases such as Ti$_{3}$Al and TiC are formed on the machined surfaces.
A spur dike is a structure that projects from a stream bank into the river channel and causes a redirection of flow away from the bank toward the tip of the spur dike. Construction of a spur dike against the flow causes significant changes in flow pattern in the channel. In this study, the flow pattern around a 25% submerged T-shaped spur dike in a 90$^{\circ}$ bend with rigid bed and various Froude numbers 0.2, 0.34, 0.45, and 0.6 was examined using FLOW-3D software. Numerical results were compared with experimental results and analyzed. The results indicated that in cross section around the spur dike, when Froude number increases, the formed vortexes decreased by 35%. Longitudinal velocity and lateral velocity increased twice as much as their former values. The highest amount of vertical velocity was observed between the wing of the spur dike and the external bend, and closer to the external bend, with an increase in Froude number, vertical velocity components variations decreased by 33%. Moreover, the results indicated that when the Froude number increases, the width of the separation zone increases, but the change in the length of the separation zone in different levels is negligible.
This research was conducted to investigate the efficacy and feasibility of a UV/H$_{2}$O$_{2}$ process as a posttreatment step for complete treatment of a biologically treated composting leachate. This study was an experimental study and was conducted during April to September 2013. Leachate samples from the effluent of a multistep biological treatment system were used for further treatment by the UV/H$_{2}$O$_{2}$ process. The effectiveness of the pH values (2-10), H$_{2}$O$_{2}$ concentrations (0.5-4 g/L), and reaction times (15-75 min) were evaluated to determine optimum operational conditions. The highest removal efficiencies were 90%, 92%, 90%, and 88% for chemical oxygen demand (COD), biochemical oxygen demand$_{5}$ (BOD$_{5})$, total organic carbon (TOC), and total suspended solids (TSS) respectively, at the optimum operation conditions (pH 4, 3 g/L H$_{2}$O$_{2}$ concentration, and 75 min reaction time). The UV/H$_{2}$O$_{2}$ was found to oxidize preferably COD and BOD$_{5}$ of the leachate samples and, as a consequence, a decrease in the organic loads of the leachate was observed after oxidation treatment. The UV/H$_{2}$O$_{2}$ process proved to be a feasible posttreatment method for a biologically treated composting leachate and effectively reduced the organic loads.
An analytical study on unsteady hydromagnetic free convective flow of a viscous incompressible electrically conducting fluid in the presence of an inclined magnetic field taking Hall currents into account has been presented. The governing equations are solved analytically using the Laplace transform technique. The variations of the fluid velocity components and the fluid temperature are shown graphically and are discussed. The shear stresses and the rate of heat transfer at the channel plates are derived. The results are shown in figures and tables followed by a quantitative discussion.
Time-dependent creep behavior of hollow rotating cylinders made from functionally graded piezoelectric material has been investigated using Mendelson's method of successive approximation. All the mechanical, thermal, and piezoelectric properties are modeled as the power-law distribution of volume fraction. Based on equilibrium, strain displacement, stress-strain, and electric displacement relations, a differential equation containing creep strains for displacement is derived. Creep strains are time-, temperature-, and stress-dependent, and the closed-form solution cannot be found for this constitutive differential equation. A semianalytical method in conjunction with the method of successive approximation has therefore been proposed for this analysis. Similar to the radial stress histories, electric potentials increase with time, because the latter is induced by the former during creep deformation of the cylinder, justifying industrial application of such a material as efficient actuators and sensors.
An analytical solution for a functionally graded two-layer beam subjected to transverse loading is handled based on the theory of elasticity. The upper and lower layers are fully bonded to each other and simply supported at the edges. Poisson's ratios are taken as constant and Young's moduli are assumed to vary exponentially through the thickness of the layers. Numerical results for the normal stresses and shear stress are given as a solution and the effect of grading on the stress distributions is investigated. In the functionally graded beam solution it is required that one side of the beam is stiffer while the other side is softer when Young's modulus is assumed to vary exponentially through the thickness. The exponential variation of the elasticity modulus may be symmetrical about the mid-plane when the beam is designated as layered.
In this study, cerium-based conversion coating was deposited on aluminum 7075-T6 by dip immersion method. Cerium oxide/hydroxide is an environmentally friendly conversion coating. Its corrosion resistance in 3.5 wt.% NaCl solution was investigated by means of electrochemical impedance spectroscopy, potentiodynamic polarization, and surface techniques. The coated samples showed a significant decrease in corrosion rate and the coating resistance increased with increasing immersion time up to 1200 s. In addition, electrochemical impedance data showed that in the presence of cerium oxide/hydroxide conversion coatings, the charge transfer resistance of aluminum increased. Surface morphology and its chemical composition were analyzed by means of scanning electron microscopy and energy dispersive spectroscopy. Aluminum 7075, cerium oxide/hydroxide coatings, impedance, corrosion, scanning electron microscopy, potentiodynamic polarization
Effects of higher order Taylor series terms of the nodal integration-radial point interpolation method (NI-RPIM) are investigated on the solution accuracy of 3D elastostatic problems. The nodal integration technique is based on Taylor series expansion and, generally, its first two terms are used. It is only applied to 2D elastostatic problems in the literature. However, in the current study, terms are used up to the 5th order and it is applied to 3D elastostatic problems. Integration domains are obtained with rectangular prisms. Three different case studies are solved with different support domain sizes and shape parameters. Their results are compared with the finite element method, RPIM with Gauss integration, and available analytical solutions. Results are discussed in detail.
One of the important design considerations for structures situated on sand deposits is the potential for instability caused by the development of excess pore water pressure as a result of earthquake loading. A build-up of excess pore water pressure may lead to initial liquefaction. In this paper, to examine the influence of overburden pressure on liquefaction potential, equivalent loads of several buildings with various stories were loaded on a sandy soil deposit using the FLAC program. The pore water pressure ratio $r_{u}$ was defined for the program by a Fish function. Analyses showed that by increasing the applied loading due to building construction, the values of effective stress and shear stress in the soil mass increased, and this generally can be a factor to influence liquefaction potential. Furthermore, dynamic analyses showed that there was a shallow longitudinal area beneath tall buildings in which liquefaction potential increased due to stress concentration and high confining effective stress; generally, they can be named as the factors to increase liquefaction potential.
