Numerical investigation of natural convection heat transfer of nanofluids in a Γ shaped cavity

This paper analyzes the heat transfer and fluid flow of natural convection in a Γ shaped enclosure filled with Al₂O₃/Water nanofluid that operates under differentially heated walls. The Navier–Stokes and energy equations are solved numerically. Heat transfer and fluid flow are examined for parameters of non-uniform nanoparticle size, mean nanoparticle diameter, nanoparticle volume fraction, Grashof number and different geometry of enclosure. Finite volume method is used for discretizating positional expressions, and the forth order Rung-Kuta is used for discretizating time expressions. Also an artificial compressibility technique was applied to couple continuity to momentum equations. Results indicate that using nanofluid causes an increase in the heat transfer and the Nusselt number so that for R = 0.001 in Gr = 10³, the Nusselt number 25%, in Gr = 10⁴ 26%, and in Gr = 10⁵ 28% increases. Furthermore; by decreasing the mean diameters of nanoparticles, Nusselt number increases. By increasing R parameter (d_p,min/d_p,max) and nano particle volume fraction, Nusselt number increases.     

A Modified Dark Energy Model and Quintessence

The observational data indicate that about 70 % of the total energy density of the current state universe has been occupied by Dark Energy. This is said to be the cause of the accelerated expansion of universe. In this letter we shall use a curvature constant as a scalar field in the quintessence Dark Energy model, for an isotropic universe. Connected to the so-called model, we will specify a definite dynamical field equation from the initial action of the theory.     

Effect of 2D Image Resolution on 3D Stochastic Reconstruction and Developing Petrophysical Trend

Multi-resolution digital rock physics (DRP) makes it possible to up-scale petrophysical properties from micron size to core sample size using two-dimensional (2D) thin section images. Resolution of 3D images and sample size are challenging problems in DRP where high-resolution images are acquired from small samples using inefficient and expensive micro-CT facilities. Three-dimensional stochastic reconstruction is an alternative approach to overcome these challenges. In this paper, we use multi-resolution images and investigate effect of 2D image resolution on 3D stochastic reconstruction and development of petrophysical trends for our two sandstone and carbonate original representative volume elements (RVEs). The proposed method includes three steps. In the first step, the spatial resolution of our original RVEs is decreased synthetically. In the second step, stochastic RVEs are realized for each resolution using two perpendicular images, correlation functions, and phase recovery algorithm. In the reconstruction method, a full set of two-point correlation functions (TPCFs) is extracted from two perpendicular 2D images. Then TPCF vectors are decomposed and averaged to realize 3D stochastic RVEs. In the third step, petrophysical properties like relative and absolute permeability as well as porosity and formation factor are computed. The output is used to develop trends for petrophysical properties in different resolutions. Experimental results illustrate that the proposed method can be used to predict petrophysical properties and reconstruct 3D RVEs for resolutions unavailable in the acquired 2D or 3D data.     

Novel material tailoring method for internally pressurized FG spherical and cylindrical vessels

A new material tailoring method for spherical and cylindrical vessels made of functionally graded materials (FGMs) is presented. It is assumed that the FG material is composed of an Al–SiC metallic-matrix composite. A uniform ratio of in-plane shear stress to yield strength [\(\varphi \left( r \right) \)] is used as the design criterion to utilize the maximum capacity of the vessel. The aim is to find a distribution of SiC particles in the radial direction, i.e., \(f\left( r \right) \), that achieves a uniform index \(\varphi \left( r \right) =\hbox {const}.\) through the wall thickness of the internally pressurized spherical or cylindrical vessel. Both the Mori–Tanaka and rule-of-mixtures homogenization schemes are used to express the effective elastic module and Poisson’s ratio. Moreover, the strength of the composite is expressed based on the rule of mixtures. Besides, finite element simulation is carried out to verify the accuracy of the analytical solution. The effects of input parameters such as the internal pressure, strength of the SiC particles, ratio of in-plane shear stress to effective yield strength, and choice of homogenization scheme on the tailored distribution of the SiC volume fraction in the radial direction are also investigated.     

Systematically engineered electrospun conduit based on PGA/collagen/bioglass nanocomposites: The evaluation of morphological,mechanical, and bio‐properties

Peripheral nerve injury can considerably affect the daily life of affected people through reduced function and permanent deformation of the nerve. One of the conventional treatments used for the management of the disease is the application of autograft, which is recognized as a golden standard method; however, the process of gaining access to autograft has posed a significant challenge to its use. Nerve guidance channels (conduits), which are made in different methods, can act as an alternative therapy for patients that have undergone nerve injury; but, achieving these conduits has always been a major dilemma to be applied for patients with nerve injury. In this study, a novel conduit based on polymer blend nanocomposites of polyglycolic acid (PGA), collagen, and nanobioglass (NBG) were prepared by electrospinning technique and then compared with PGA/collagen and PGA conduits that were made in previous studies. Additionally, their various properties were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), contact angle, dynamic mechanical thermal analysis (DMTA), tensile strength, Fourier‐transform infrared (FTIR), and the porosity and degradation. The results showed that the mechanical, chemical, biocompatibility, and biodegradability properties of PGA/collagen/NBG conduits were more favorable in comparison with other materials. According to 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay and 4′,6‐diamidino‐2‐phenylindole (DAPI) staining technique, nanofibrous electrospun PGA/collagen/NBG conduits are more suitable for cell adhesion and proliferation in comparison with either PGA or PGA/collagen conduits and can have potential for nerve regeneration.     

A robust negative obstacle detection method using seed-growing and dynamic programming for visually-impaired/blind persons

Though a significant amount of work has been done on detecting obstacles, not much attention has been given to the detection of drop offs, e.g., sidewalk curbs, downward stairs, and other hazards. In this paper, we propose algorithms for detecting negative obstacles in an urban setting using stereo vision and two-stage dynamic programming (TSDP) technique. We are developing computer vision algorithms for sensing important terrain features as an aid to blind navigation, which interpret visual information obtained from images collected by cameras mounted on camera legs nearly as high as young person. This paper focuses specifically on a novel computer vision algorithm for detecting negative obstacles (i.e. anything below the level of the ground, such as holes and drop-offs), which are important and ubiquitous features on and near sidewalks and other walkways. The proposed algorithm is compared to other algorithms such as belief propagation and random growing correspondence seeds (GCS). According to the results, the proposed method achieves higher speed, more accurate disparity map and lower RMS errors. The speed of the proposed algorithm is about 28% higher than the random GCS algorithm. We demonstrate experimental results on typical sidewalk scenes to show the effectiveness of the proposed method.     

Titanium Dioxide/Multi-walled Carbon Nanotubes Composite Modified Pencil Graphite Sensor for Sensitive Voltammetric Determination of Propranolol in Real Samples

A very effective electrochemical sensor for the analysis of propranolol was constructed using TiO₂/MWCNT film deposited on the pencil graphite electrode as modifier. The modified electrode represented excellent electrochemical properties such as fast response, high sensitivity and low detection limit. The proposed sensor showed an excellent selective response to propranolol in the presence of foreign species and other drugs. The electrochemical features of the modified electrode were investigated by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) technique which indicated a decrease in resistance of the modified electrode versus bare PGE and MWCNT/PGE. The surface morphology for the modified electrode was determined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FT-IR). Differential pulse technique (DPV) was used to determine propranolol which showed a good analytical response in the linear range of 8.5×10⁻⁸-6.5×10⁻⁶ M with a limit of detection 2.1×10⁻⁸ M. The TiO₂/MWCNT/PGE sensor was conveniently applied for the measurement of propranolol in biological and pharmaceutical media.     

Investigation of thermo-elasto-plastic behavior of thick-walled spherical vessels with inner functionally graded coatings

Having high corrosion and thermal resistance characteristics, Functionally Graded Materials have been found wide range of applications in engineering fields. The analytical elasto-plastic solution for spherical vessels composed of outer homogenous part and inner FG coating under combined pressure and thermal loading is presented in this paper. Furthermore, the loading conditions resulted into onset of yielding from inner radius and fully plastic vessel are obtained. Material constituents in both homogenous and FG parts are assumed to be aluminum and SiC as metal matrix and ceramic particles, respectively. Although the amount of SiC particles in the homogenous part of vessel is assumed to be constant, it is varying in the radial direction of FG part based on the power law function. The results concerning two types of vessels with harder and softer FG coatings are also compared with those from homogenous vessel. Moreover, two dimensional finite element model was applied to simulate the process while the results were considered to verify the accuracy of the analytical solution. Generally, the results demonstrate that coating and grading behavior can really affect the stress distribution and yield pattern in the homogenous vessel with an inner FG coating.