3D numerical investigation of ZnO/Zn hydrolysis for hydrogen production

The current research is focused on the hydrogen production through a two‐step ZnO/Zn thermochemical water splitting cycle. In the present paper, numerical modeling of the second step is conducted using Computational Fluid Dynamics (CFD)2, where steam reacts with zinc to produce hydrogen. The parametric study shows that the hydrogen yield is relatively insensitive to the steam/zinc molar ratio and inversely proportional to the argon/steam molar ratio. For large argon to steam molar ratios, hydrogen yield is relatively insensitive to the inlet temperature of zinc and steam, and increases marginally with an increase in the argon inlet temperature. Five different reactor configurations were evaluated comprehensively. Among all configurations, a cylindrical reactor with a tangential inlet for argon and zinc, and a radial inlet for steam (both in the bottom plane of the reactor) and a tangential outlet in the top plane of the reactor produced the highest hydrogen yield of 88%. Copyright © 2013 John Wiley & Sons, Ltd.     

Oxidase-Peroxidase sequential polymerization for removal of a dye from contaminated water by horseradish peroxidase (HRP)/glucose oxidase (GOx)/polyurethane hybrid catalyst

Horseradish peroxidase (HRP) and glucose oxidase (GOx) were co-immobilized on polyurethane, and the resulting HRP/GOx/polyurethane biocatalyst was characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDAX) mapping techniques. The prepared biocatalyst was used for removal of acid orange 7 as model azo dye. The required H₂O₂ for activation of HRP was in-situ produced using GOx to prevent deactivation of HRP in the presence of excess chemical H₂O₂. Central composite design (CCD) was applied for modeling and optimization of parameters affecting the activity of prepared biocatalyst. Under the optimum conditions, removal efficiency of the azo dye was predicted to be 87.47%, which was in good agreement with the experimental value (89.69%). In addition, the performance of the prepared biocatalyst for removal of two other dyes with different structure was investigated at the optimum conditions, and a removal efficiency of 91.56% and 95.25% was obtained for removal of methylene blue and malachite green, respectively. The results demonstrated that the resultant HRP/GOx/Polyurethane biocatalyst was able to decrease the chemical oxygen demand (COD) of a textile effluent from 740mg/L to 96mg/L, indicating that the prepared biocatalyst is an effective enzymatic system for treatment of real wastewater.     

Synthesis,Corrosion and Bioactivity Evaluation of Gelatin/Silicon and Magnesium Co-Doped Fluorapatite Nanocomposite Coating Applied on AZ31 Mg Alloy

In this study, a nano-composite composed of gelatin as the matrix and Si-Mg-FA nano-particles as an additive was deposited on the AZ31 Mg alloy via dip coating method. In addition, a coating composed of MgO, MgSiO₃ and Mg₂SiO₄ phases was applied on the AZ31 Mg alloy by anodizing process. It was found that the Nano-composite coating with a uniform distribution of nano-particles within the gelatin matrix with the thickness of about 9 µm was dense, crack-free and uniform whereas the surface of anodized layer was relatively coarse due to the presence of flaws and micro-cracks. The surface morphology, EDS analysis and FTIR results revealed the ability of nano-composite coated specimen to form the bone-like apatite. Due to the presence of aforementioned phases and special surface features, the anodized specimen possessed higher and lower corrosion resistance than uncoated and nano-composite coated specimens, respectively. The passive coating resistances (R_CT) of nano-composite, anodized specimen and uncoated samples were 2164, 1449 and 1024 Ω cm², respectively.     

The harp: a vehicle crash test apparatus for full-scale crash test experiments

The current paper describes an apparatus for full-scale vehicle crash test experimentation. This apparatus is referred to as the harp. In brief, the harp may either accelerate a trolley which is impacted into a test vehicle or the test vehicle itself may be accelerated and impacted into an object such as a barrier, a pole, or another vehicle. If a trolley is accelerated, it is equipped with load cells to record the axial crushing force. If a test vehicle is accelerated, it is equipped with a three-axis accelerometer to record the crushing force. At the impact site, high-speed cameras and instrumentation record vital data during the crash.     

Material and velocity effects on cavitation erosion pitting

Cavitation erosion during the incubation period was investigated via pitting tests conducted on three different materials: an Aluminum alloy, a Nickel Aluminum Bronze alloy and a Duplex Stainless Steel. Pitting tests were conducted in a cavitation tunnel in the velocity range 45–90 m/s at a constant cavitation number. The test section was made of a straight nozzle 16 mm in diameter discharged into the radial 2.5 mm space between two flat walls. Cavitation appears in the form of a toroidal cavity attached to the nozzle exit and damage on the samples facing the nozzle is concentrated in a circular ring centered in the cavity closure region. The exposure time was adjusted to avoid pit overlapping. The material surface was examined using a conventional contact profilometer which allowed us to identify the pits, count them, and measure their main characteristics such as depth, surface area, and volume. From these the pitting rate, the coverage rate, and the depth of deformation rate were defined. Pits were classified according to their diameter. For all materials and operating conditions, pitting rate appears to follow an exponential law in relation to the pit diameter. This law depends upon two parameters only, which were identified as the coverage time τ (i.e. the time required for the surface to be covered by erosion pits) and a characteristic pit diameter δ, which corresponds to the pits whose contribution to the coverage process is the highest. Scaling laws for pitting were derived accounting for both material properties and flow velocity, and a procedure to make pitting test results non-dimensional is proposed. The influence of the material on pitting test results was analyzed. It is shown that the damage is not correlated in simple terms with the elastic limit determined from conventional tensile tests and it is conjectured that other parameters such as the strain rate might play a significant role and should be included in the analysis. The effect of flow velocity on both parameters τ and δ was analyzed and a classical power law was found for the influence of the flow velocity on pitting rate for all three materials. Finally, some analysis and discussion is given concerning distributions of pit volume and pit depth.     

A novel symmetric/asymmetric multilevel current source inverter topology with lower number of components and lowest power rating of switches

A novel multilevel current source inverter (MCSI) configuration is introduced in this paper. The ability of handling with asymmetrical DC sources is one of the substantial advantages of the proposed inverter. In asymmetric mode, by appropriate selection of DC sources magnitude, a considerable increase can be obtained in the number of output levels without any manipulation on inverters’ hardware. In MCSIs, the number of required circuit devices is very important because the overall costs, circuit size, reliability and control complexity are dependent on them directly. The proposed inverter can generate all desired current levels using a lower number of elements. Besides, it is known that reduction of number of switches from conventional inverters imposes an undesired increase in total semiconductor device power (SDP). But, the total SDP of the proposed inverter is kept equal to conventional inverter. To validate the superiority of the proposed inverter, a full comparison is provided. Also, the computer simulation and experimental results are presented.     

Current and Temperature Dependent Matching Fields in Nb Film of Rectangular Array of Holes

Nanoengineered periodic array of holes on superconducting thin films have a great interest due to their excellence for the studies of the vortex pinning mechanisms in the type-II superconductors. Rectangular array of holes has been fabricated over a microbridge of Nb superconducting thin film by e-beam lithography. Rectangular array of holes have two type of scenario, at low magnetic fields matching effects are sharp and narrow while at high fields wide and shallower. In this work, we study the matching pinning effect by the artificial hole array in superconducting Nb thin films. We observed that as the inter distance between holes is decreased; the sharp matching effects become dominant and vice versa.     

Effect of Shot Peening Operation on the Microstructure and Wear Behavior of AZ31 Magnesium Alloy

Protection of Metals and Physical Chemistry of Surfaces - Shot peening is a treatment used to increase surface hardness and wear resistance. In this study, the effect of shot peening on the...     

Urban expansion modeling using an enhanced decision tree algorithm

Decision tree (DT) algorithms have been applied for classification and change detection in various geospatial studies and more recently, for urban expansion and land use/land cover (LULC) change modeling. However, these studies have not elaborated on specification of DT algorithms regarding data sampling, predictor variables, model configuration, and model evaluation. The focus of this study is to explore several balanced and unbalanced sampling methods, various predictor variables, different configurations of stopping rules, and reliable evaluation metrics to enhance the performance of classification and regression tree (CART), one of the most efficacious DT algorithms, for urban expansion modeling. The implementation of the model in the Triangle Region, North Carolina (NC) State, over the period of 2001 to 2011 demonstrates a striking performance with the training accuracy of 97%, the testing accuracy of 94%, and the Kappa value of 0.80. This performance was achieved using a training dataset containing all changed land cells and three times of that randomly selected from unchanged land cells and regulating the minimum number of records in a leaf node equal to 1, the minimum number of records in a parent node equal to 2, and the value of 10,000 for the maximum number of splits. The CART DT algorithm indicates that proximity to built areas, proximity to highways, current LULC type, elevation, and distance to water bodies are the most significant predictor variables for the urban expansion prediction in the study area.