Nonlinear finite-element modeling of graphene and single- and multi-walled carbon nanotubes under axial tension

An effective finite-element (FE) approach for modeling the structure and the deformation of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) is presented. An individual tube was modeled using a frame-like structure with beam elements. The effect of van der Waals forces, crucial in MWCNTs, was modeled by spring elements. The success of this new carbon nanotube (CNT) modeling approach was verified by comparing the simulation results for single- and multi-walled nanotubes and graphene with other experimental and computational results available in the literature. Simulations of final deformed configurations were in excellent agreement with the atomistic models for various deformations. The proposed approach successfully predicts the experimentally observed values for mechanical behavior of SWCNTs and MWCNTs. The results demonstrated that the proposed FE technique could provide a valuable tool for studying the mechanical behavior of different types of nanotubes, as well as their effectiveness as load-bearing entities in nanocomposite materials.     

A study on the optimization of the angle of curvature for a Ranque–Hilsch vortex tube,using both experimental and full Reynolds stress turbulence numerical modelling

The working tube is a main part of vortex tube which the compressed fluid is injected into this part tangentially. An appropriate design of working tube geometry leads to better efficiency and performance of vortex tube. In the experimental investigation, the parameters are focused on the working tube angle, inlet pressure and number of nozzles. The effect of the working tube angle is investigated in the range of θ = 0–120°. The experimental tests show that we have an optimum model between θ = 0 and θ = 20°. The most objective of this investigation is the demonstration of the successful use of CFD in order to develop a design tool that can be utilized with confidence over a range of operating conditions and geometries, thereby providing a powerful tool that can be used to optimize vortex tube design as well as assess its utility in the field of new applications and industries. A computational fluid dynamics model was employed to predict the performances of the air flow inside the vortex tube. The numerical investigation was done by full 3D steady state CFD-simulation using FLUENT6.3.26. This model utilizes the Reynolds stress model to solve the flow equations. Experiments were also conducted to validate results obtained for the numerical simulation. First purpose of numerical study in this case was validation with experimental data to confirm these results and the second was the optimization of experimental model to achieve the highest efficiency.     

Investigation on surface properties of superhydrophobic nanocomposites based on polyvinyl chloride and correlation with cell adhesion behavior

The main aim was to study the roles of structural homogeneity and superhydrophobicity on the adhesion of SW colon cancer cells on the surface of polyvinyl chloride (PVC) nanocomposites. Concurrent use of a proper nonsolvent (ethanol) and silica nanoparticles resulted in superhydrophobic behavior and also different surface structures. The effect of added‐ethanol content on the surface properties of PVC nanocomposites was also studied. The synergetic combination of silica and ethanol has led to the formation of a porous surface layer resulting in a considerable boost in the hydrophobic behavior. The scanning electron microscopy, roughness, and X‐ray photoelectron spectroscopy (XPS) analysis results were all in total agreement indicating the substantial change in surface morphology, topography, and composition once the ethanol content was increased to 50 vol.%. The surface structure was notably changed by the addition of polyhedral oligomeric silsesquioxanes (POSS) nanoparticles. It was found that the induced inhomogeneity as a result of POSS addition had an adverse effect on the surface properties. In conclusion, superhydrophobicity could be regarded as a prerequisite for achieving cell‐repellent behavior, but it cannot guarantee a cell repellent surface especially if the surface layer possesses structural inhomogeneity.     

Synthesis of recoverable palladium composite as an efficient catalyst for the reduction of nitroarene compounds and Suzuki cross-coupling reactions using sepiolite clay and magnetic nanoparticles (Fe3O4@sepiolite-Pd2+)

Clays are nontoxic, inexpensive, abundant, and have great potential as catalytic carriers because of their special structure, surface, and suitability for supporting transition metals. In this study, sepiolite was used as a ligand for the heterogenization of palladium chloride on Fe₃O₄ nanoparticle surface as a novel, high temperature stable, and recoverable green catalyst (Fe₃O₄@sepiolite-Pd²⁺). The catalytic activity of this system was tested in the reduction of nitroarene compounds and the Suzuki cross-coupling reaction. The catalyst structure was characterized using spectroscopic data and magnetic and thermal techniques such as Fourier transform infrared, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, vibrating sample magnetometer (VSM), and thermogravimetric analysis.     

A novel ternary GO@SiO2‐HPW nanocomposite as an efficient heterogeneous catalyst for the synthesis of benzazoles in aqueous media

A new solid acid catalyst, consisting of 12‐phosphotungstic heteropoly acid (HPW) supported on graphene oxide/silica nanocomposite (GO@SiO₂), has been developed via immobilizing HPW onto an amine‐functionalized GO/SiO₂ surface through coordination interaction (GO@SiO₂‐HPW). The GO@SiO₂‐HPW nanocomposite was characterized by Fourier transform infrared (FT‐IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and powder X‐ray diffraction (XRD). The prepared nanocomposite could be dispersed homogeneously in water and further used as a heterogeneous, reusable, and efficient catalyst for the synthesis of benzimidazoles and benzothiazoles by the reaction of 1,2‐phenelynediamine or 2‐aminothiophenol with different aldehydes.     

Structural and chromotropism properties of copper(II) complexes with 3,3′-((pyridin-2-ylmethyl)azanediyl)dipropanamide ligand

Transition Metal Chemistry - A tetra-dentate ligand L [3,3′-((pyridin-2-ylmethyl)azanediyl)dipropanamide] was synthesized and characterized by spectroscopic and structural methods. The...     

Using nucleators to control freckles in unidirectional solidification

Buoyancy-induced fluid flow, which is responsible for most forms of macro-segregation and channel-type segregates in castings, is not directly controllable. If left uncontrolled, natural convection will contribute to non-uniform distribution of alloy constituents and grain structure during solidification of a casting. Non-uniform distribution of chemical composition and physical structure in an alloy casting can significantly affect the reliability of mechanical components. Therefore, materials with acceptable defects can be produced only by trial-and-error and their acceptability is determined by costly inspections. We present a novel technique to control the formation of chimneys and resulting freckles in the mushy zone during the solidification of ammonium chloride that is cooled from below. This is done by placing metallic nucleators in particular arrangements on the bottom cooling plate. With this technique, freckles in a casting might be avoided and/or be forced to form where stresses are expected to be lower during use of the part.The objective of this study is to investigate the effects of the arrangement, spacing, and size of the nucleators on finger formation, plume structure, and the solidification process. Results showed that it is possible to obtain a relatively large area free of channel-segregates in a metal analog directionally solidified upward by placing nucleators in certain arrangements at the bottom of the casting. The outcomes of this study will serve as a baseline for subsequent investigations that will examine the solidification of binary alloys, and could be used to test and develop mathematical and numerical models.     

Assessment of four inflow conditions on large-eddy simulation of a gently curved backward-facing step

In this study, we investigated the impact of four different inflow generation methods used in large-eddy simulation on the spatially developing boundary-layer before a recirculation bubble is formed over a gently curved backward-facing step at a Reynolds number 13,700 based on the step height. The configuration under study is very challenging because the separation is caused by a weak adverse pressure gradient, thus making a very sensitive and reliable assessment for evaluating the different inflow conditions used. The first method is a precursor-based simulation in which the velocity data on a certain plane is recorded in a library and then used as the inlet condition for the primary simulation. The second method used is the random noise generation method. The third method is based on generation of turbulent spots which incorporates the distribution of Reynolds stress tensor, and the last one is the so-called rescaling/recycling method proposed by Lund and colleagues. All these methods are compared together in terms of separation and reattachment locations of the recirculation bubble. The flow structures are represented by qualitative criteria, and also streamwise Reynolds stresses and production of turbulent kinetic energy of the flow are assessed and compared together at different stations before and after separation to illuminate how the developing structures within the boundary-layer can affect the locations of separation and reattachment. Distribution of pressure coefficient for different methods showed that there is a relation between production of turbulent kinetic energy and favourable pressure gradient of each method before the separation occurs. Finally, spectra of pressure fluctuation revealed how each inflow condition influences the shedding-instability frequencies.     

Preparation of Highly Biocompatible ZnSe Quantum Dots Using a New Source of Acetyl Cysteine as Capping Agent

In this paper, we describe a facile method for preparation of ZnSe quantum dots (QDs) using an inexpensive and biocompatible source of acetyl cysteine in aqueous media. The structural properties of the ZnSe QDs have been characterized using XRD, FT-IR, and TEM techniques. The optical properties of the as-prepared QDs were found to be size-dependent, due to the strong confinement regime at relatively low refluxing time. Effect of solution pH and refluxing temperature on absorption and emission characteristics of the ZnSe QDs was studied. The empirical effective mass approximation also reveals that, both solution pH and refluxing temperature parameters would effect on ZnSe QDs growth, and increase their size. However, the influence of the solution pH was found to be more prominent. Water-solubility, high emission intensity and sub-10 nm nanocrystals size are the most essential features that suggest our synthesized aqueous-based ZnSe QDs (with a very cost-effective and biocompatible capping agent) can be utilized for biological intentions.