Sharif Digital Repository

We consider a spherical thick shell immersed in two different spherically symmetric space-times. Using the fact that the boundaries of the thick shell with two embedding space-times must be nonsingular hypersurfaces, we develop a scheme to obtain the underlying equation of motion for the thick shell in general. As a simple example, the equation of motion of a spherical dustlike shell in vacuum is obtained. To compare our formalism with the thin shell one, the dynamical equation of motion of the thick shell is then expanded to the first order of its thickness. It is easily seen that the thin shell limit of our dynamical equation is exactly that given in the literature for the dynamics of a... 

Despite all the advancements in tissue engineering, one of the unsolved challenges is the mass transfer limitation. Therefore, the subject of pre-vascularization in the engineered tissues gets more attention to avoid necrotic core formation. In this study, we considered a design for interconnected channels with a muscle tissue-like structure, in silico and in vitro. A sequence of simple steps make it possible for us to use the same material, gelatin, as both a sacrificial material and one of the main components of the scaffold simultaneously. We defined a new approach to quantify the repeatability of a new combination of hydrogels (Partially Oxidized Alginate + Gelatin) for extrusion-based... 

We consider a spherical thick 3-brane immersed in a five-dimensional bulk space-time. We demonstrate how the thick brane equation of motion expanded in powers of the thickness of the brane can be obtained from the expected junction conditions on the boundaries of thick brane with the two embedding space-times. It is shown that the finite thickness corrections lead to a faster collapse of the brane in the vacuum  

Abstract The role of the work function and Fermi level is significant in the performance of the photo-electrochemical cells. We report that a correlation exists between work function and thickness of deposited thin film metals (e.g., Zn, Pb, Co, and Cu). The potential difference between a metal and a reference electrode is used as a rough approach for investigation of work function or the Fermi level. Metal thickness was calculated using faradic current during electrodeposition and further investigated by X-ray diffraction technique. The results show that when thickness decreases the potential also decreases (becomes positive) and the Fermi level of metals electrodeposited on the indium tin... 

In this paper, the advantages of numerical simulation to improve the process of copper electroforming are demonstrated. In this regard, the finite element model of copper electroforming for a rotating cone electrode was first prepared and then, the effect of the key parameters, such as applied current density, solution conductivity, electrode spacing, and anode height, on the uniformity of the thickness was investigated. The model combines tertiary current distribution with Bulter–Volmer electrode kinetics and computational fluid dynamics at the turbulent condition. In order to validate the model, a cone-shaped shell was produced by electroforming method in the laboratory. The obtained... 

In this study, we present results of a mathematical model in which the governing equations of electroforming process were solved using a robust finite element solver (COMSOL Multiphysics). The effects of different parameters including applied current density, solution electrical conductivity, electrode spacing, and anode height on the copper electroforming process have been investigated. An electroforming experiment using copper electroforming cell was conducted to verify the developed model. The obtained results show that by increasing the applied current density, the electroforming process takes place faster, thereby resulting in a higher thickness of the electroformed layer. In addition,... 

Governing equilibrium equations of thick-walled spherical vessels made of material following linear strain hardening and subjected to a steady-state radial temperature gradient using elasto-plastic analysis are derived. By considering a maximum plastic radius and using the concept of thermal autofrettage for the strengthening mechanism, the optimum wall thickness of the vessel for a given temperature gradient across the wall thickness is obtained. Finally, in the case of thermal loading on a vessel, the effect of convective heat transfer on the optimum thickness is studied and a general formula for the optimum wall thickness and design graphs for several different cases are presented. © 2008... 

A three-dimensional elasticity solution for the analysis of functionally graded rotating cylinders with variable thickness profile is proposed. The axisymmetric structure has been divided in several divisions in the radial direction. Constant mechanical properties and thickness profile are assumed within each division. The solution is considered for four different thickness profiles, namely constant, linear, concave, and convex. It is shown that the linear, concave, and convex thickness profiles have smaller stress values compared to a constant thickness profile. The effects of various grading indices as well as different boundary conditions, namely solid, free-free hollow and fixed-free... 

In this study, the effect of through-thickness shear (TTS) stress has been examined on the prediction of forming limit diagrams (FLDs). Determination of the FLD is based on the Marciniak–Kuczynski (M–K) model with some modifications on the stress states for consideration of the TTS stress effects. For solving the equations, the Newton–Raphson method has been used. Furthermore, the Nakazima test has been simulated to investigate the stress state which occurs in the sheet during the test. Results showed that the formability of sheet metal could be better as the through-thickness stress increased. Also, implementation of TTS stress in the present model, the corresponding FLD has better... 

In this study, the effect of through-thickness shear (TTS) stress has been examined on the prediction of forming limit diagrams (FLDs). Determination of the FLD is based on the Marciniak–Kuczynski (M–K) model with some modifications on the stress states for consideration of the TTS stress effects. For solving the equations, the Newton–Raphson method has been used. Furthermore, the Nakazima test has been simulated to investigate the stress state which occurs in the sheet during the test. Results showed that the formability of sheet metal could be better as the through-thickness stress increased. Also, implementation of TTS stress in the present model, the corresponding FLD has better... 

In this study, the effect of through-thickness shear (TTS) stress has been examined on the prediction of forming limit diagrams (FLDs). Determination of the FLD is based on the Marciniak–Kuczynski (M–K) model with some modifications on the stress states for consideration of the TTS stress effects. For solving the equations, the Newton–Raphson method has been used. Furthermore, the Nakazima test has been simulated to investigate the stress state which occurs in the sheet during the test. Results showed that the formability of sheet metal could be better as the through-thickness stress increased. Also, implementation of TTS stress in the present model, the corresponding FLD has better... 

The influence of sheet thickness on sheet metal forming limits is a controversial issue; while some investigations indicate the considerable influence of thickness on forming limit diagrams (FLDs), others suggest that it is of negligible importance. In the present work, it has been demonstrated that if the thickness-reduction process is chosen so as not to alter the micro structure of the material, the forming limits do not change with variations of thickness. A material which has extensive usage in sheet metal forming processes of automotive industry (St14) has been provided. The initial thickness of the sheet is 1.5mm and using grinding process (which does not alter the microstructure) the... 

The main aim of this study was to improve current efficiency and to obtain thicker coatings via aluminum oxide (Al2O3) addition to the chromium (Cr) (III) bath. Design/methodology/approach ‐ Pure Cr and nanocomposite Cr–Al2O3 coatings were electrodeposited from Cr (III) bath onto cathode copper substrates by conventional method. Dependence of current efficiency to current density, Al2O3 content and particle size were investigated. Findings ‐ Current efficiency increased with Al2O3 amount and decreased with Al2O3 particle size. Maximum current efficiency was achieved at 25 A/dm2 for pure Cr and 30 A/dm2 for composite coatings. Al2O3 bath content, current density and stirring rate increased... 

This paper presents a formulation for in-plane modal characteristics of non-uniform thickness annular elliptic and circular plates for all classical boundary conditions. The investigations are performed for elastic and isotropic annular elliptic plates on the basis of two- dimensional linear plane stress theory of elasticity. Two-dimensional boundary characteristic orthogonal polynomials (BCOP) are used in the Rayleigh-Ritz method to obtain the natural frequencies and associated mode shapes. The proposed method, not only can find solution for those simple cases of annular circular plates available in literature as a simplified case study, but also it finds some natural frequencies which can...