Experimental and numerical study of residual stresses caused by cold expansion of adjacent holes

Cold expansion is a useful process for imposing compressive residual stresses around the holes in riveted and bolted connections. These stresses increase the fatigue life of holed parts. Distribution and amount of exerted residual stress dependent on various parameters as material, distance of adjacent holes, hole diameter, cold expansion ratio and plate thickness. In this study, experimental and numerical results for two different aluminum alloys and various holes distances are investigated and compared. Effects of mentioned parameters on the residual stress are studied.     

Relationship of nanostructure and thermo-chemical response/thermal ablation of carbon aerogels

In this work, the interfacial mass balance relations combined with the non-parametric kinetic (NPK) analysis results were used for evaluating the thermo-chemical ablation process and oxidation mechanism of carbon aerogels with various porous structure. It was found that the two-parameter model of Nomen–Sempereis was able to describe the kinetics of the oxidation reaction and to reveal the structure-dependent contribution of two main processes with chemical and physical nature. The porosity of the carbon aerogel, rather than the other microstructural features, was realized more effective on the rate of ablation.     

A Constant-Potential Infeasible-Start Interior-Point Algorithm with Computational Experiments and Applications

We present a constant-potential infeasible-start interior-point (INFCP) algorithm for linear programming (LP) problems with a worst-case iteration complexity analysis as well as some computational results.The performance of the INFCP algorithm is compared to those of practical interior-point algorithms. New features of the algorithm include a heuristic method for computing a good starting point and a procedure for solving the augmented system arising from stochastic programming with simple recourse. We also present an application to large scale planning problems under uncertainty.     

Evaluation of magnetically recyclable nano-Fe3O4 as a green catalyst for the synthesis of mono- and bis-tetrahydro-4H-chromene and mono and bis 1,4-dihydropyridine derivatives

Research on Chemical Intermediates - Magnetically separable Fe3O4 nanoparticles were used as an environmental friendly catalyst for the synthesis of mono- and bis-tetrahydro-4H-chromene and mono-...     

Maximizing working pressure of autofrettaged three layer compound cylinders with considering Bauschinger effect and reverse yielding

One of the most effective methods for increasing capacity of thick-walled cylindrical pressure vessels is creating compressive residual stress in their walls. This can be applied by using multilayer shrink fitted or autofrettaged cylinders or combination of these methods. In this study, for a three layer compound cylinder, effects of interference fit values and their locations and autofrettage pressure were studied on the working pressure. Analytical and numerical results show that proper values and locations of the applied interferences can increase the capacity up to two times versus simple cylinder. Applying low-pressure autofrettage (less than one quarter of full autofrettage) on the compound cylinder can more increase the working pressure.     

Dermal Tattoo Biosensors for Colorimetric Metabolite Detection

Tattooing is a ubiquitous body modification involving the injection of ink and/or dye pigments into the dermis. Biosensors in the form of tattoos can be used to monitor metabolites in interstitial fluid. Here, minimally invasive, injectable dermal biosensors were developed for measuring pH, glucose, and albumin concentrations. The dermal pH sensor was based on methyl red, bromothymol blue, and phenolphthalein, which responded to a pH range from 5.0 to 9.0. The dermal glucose sensor consisted of glucose oxidase, 3,3′,5,5′‐tetramethylbenzidine, and peroxidase that detected concentrations up to 50.0 mmol L^?1. The dermal albumin sensor consisted of 3′,3′′,5′,5′′‐tetrachlorophenol‐3,4,5,6‐tetrabromosulfophthalein to measure concentrations up to 5.0 g L^?1. The sensors were multiplexed in ex vivo skin tissue and quantitative readouts were obtained using a smartphone camera. These sensors can be used to manage of acid–base homeostasis, diabetes, and liver failure in point‐of‐care settings.     

Solving a system of nonlinear fractional partial differential equations using homotopy analysis method

In this article, the homotopy analysis method (HAM) has been employed to obtain solutions of a System of nonlinear fractional partial differential equations. This indicates the validity and great potential of the homotopy analysis method for solving system of fractional partial differential equations. The fractional derivative is described in the Caputo sense.     

Synthesis and comparative study of optical and electrical properties of Au-doped carbon nanotubes prepared in different reaction media

We introduce the synthesis, characterization and physical properties of gold (Au) doped multiwalled carbon nanotubes (MWCNTs) in different reaction media. In order to dope MWCNTs with Au nanoparticles (NPs), first functionalized carbon nanotubes (f-MWCNTs) were prepared. The reduction of gold (III) chloride trihydrate for synthesizing Au NPs in the presence of f-MWCNTs was performed by using sodium citrate as a reducing agent. The produced nanocomposites were characterized using FTIR, XRD and TEM analyses to explore their chemical structures and morphologies. All of the samples have been characterized by TGA and resultantly, the composite made into ethylene glycol exhibited the most concentration of Au NPs into the composite network. This work probes the optical characteristics, such as UV–vis absorption, and optical band gap. Hall effect analyses declared some pleasing variations in electrical characteristics. Remarkably, the n-type doping of Au NPs in the p-type MWCNTs’ network led to a downshift of the Fermi level. This process increased the doped samples electrical conductivity. The results indicated that modification of MWCNTs with Au NPs has generally an important role in decreasing the band gap and increasing the electrical activity of MWCNTs. Our research outcomes provide a new vision into how different reaction media could affect the characteristics of MWCNT/Au nanocomposites. We discovered that ethylene glycol could be considered as a perfect reaction medium for preparation of high-quality doped CNTs with excellent physical properties. Our effort opens up the door to far more investigations on the role of the reaction medium in products’ characteristics.     

Study the effect of acetic acid on structural,optical and mechanical properties of PVA/chitosan/MWCNT films

Polyvinyl alcohol (PVA)/chitosan/multiwalled carbon nanotube (MWCNT) films were successfully prepared by using solution-casting method. Structural properties were studied using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectroscopies. The effect of acetic acid (AA) concentration on the films optical parameters was studied by using absorbance and transmittance data recorded during ultraviolet-visible (UV–Vis) spectroscopy. The results indicated that increasing the AA concentration in MWCNT-reinforced PVA films caused an increase in their optical capability. We also evaluated mechanical properties such as stress-strain behavior, Young's modulus, tensile strength, elongation at break, etc. Mechanical indices have been modified by introducing carbon nanotubes, even though enhancing the AA concentration meets significant restrictions on higher percentages of AA concentration, which needs to be delicately considered. The porous structure of the films, such as porous pattern, materials’ diameter, and shape was examined by field emission electron microscopy (FESEM). Engineering analyses showed that the films reinforced with MWCNTs exhibited an interconnected homogenous structure in various acid concentrations.     

Mechanical properties of two-dimensional graphyne sheet under hydrogen adsorption

In the present work, the mechanical properties of graphyne, a class of graphene allotropes with carbon triple bonds, subjected to the hydrogen chemisorption are studied using a first-principles density functional approach. Two configurations for the maximum of hydrogen adsorption are considered: (I) adsorption of hydrogen atoms on carbon atoms at the two opposite sides of graphyne sheet and (II) adsorption of hydrogen atoms on carbon atoms at the same side of graphyne sheet. Formation energy for hydrogenated graphyne (H-graphyne) corresponding to these states of adsorption is calculated and it is indicated that state (I) is more stable than state (II). Density functional calculations within the generalized gradient approximation (GGA) in the harmonic elastic deformation range are performed to obtain the elastic constants of graphyne and H-graphyne in state (I). This study shows that H-graphyne has an in-plane stiffness of 125 N/m and a Poisson's ratio of 0.23. It is observed that the in-plane stiffness of H-graphyne is lower than that of graphyne. This clearly reveals the destructive effect of hydrogen adsorption on the mechanical properties of graphyne. The results of this paper are helpful for the design of future nanodevices in which H-graphyne acts as their basic element.