Sharif Digital Repository

Osseointegrated dental implants are deficient in natural periodontal ligaments. It may therefore, disrupts the natural function of implant and leads to excessive stress and strain in jaw bone. Our new proposed implant has the nonlinear internal component which imitates periodontal ligaments function. A nonlinear finite element analysis developed to investigate the efficiency of utilizing this nonlinear internal layer for three conditions of bone implant interface conditions under vertical and horizontal loading conditions. Our results so far indicate that the use of a class of material exhibiting incompressible hyperelastic behaviour as a internal layer can reduce the peak stress deduced... 

The resonant frequencies and torsional sensitivities of an atomic force microscope (AFM) assembled cantilever probe which comprises a horizontal cantilever, two vertical extensions and two tips located at their free ends are studied. This probe makes the AFM capable of measuring, for instance, the outer/inner diameter, roundness and roughness of microstructures like micro-holes and micro nozzles which leads to a time-saving swift scanning process. In this work, the effects of the sample surface contact stiffness and the geometrical parameters such as the ratio of the vertical extension length to the horizontal cantilever length and the distance of the first vertical extension from the... 

A large number of Wireless Sensor Network (WSN) security schemes have been proposed in the literature, relying primarily on symmetric key cryptography. To enable those, Random Key pre-Distribution (RKD) systems have been widely accepted. However, WSN nodes are vulnerable to physical compromise. Capturing one or more nodes operating with RKD would give the adversary keys to compromise communication of other benign nodes. Thus the challenge is to enhance resilience of WSN to node capture, while maintaining the flexibility and low-cost features of RKD. We address this problem, without any special-purpose hardware, proposing a new and simple idea: key splitting. Our scheme does not increase... 

Embryogenesis, regeneration and cell differentiation in microbiological entities are influenced by mechanical forces. Therefore, development of mechanical properties of these materials is important. Neural network technique is a useful method which can be used to obtain cell deformation by the means of force-geometric deformation data or vice versa. Prior to insertion in the needle injection process, deformation and geometry of cell under external point-load is a key element to understand the interaction between cell and needle. In this paper the goal is the prediction of cell membrane deformation under a certain force, and to visually estimate the force of indentation on the membrane from... 

Embryogenesis, regeneration and cell differentiation in microbiological entities are influenced by mechanical forces. Therefore, development of mechanical properties of these materials is important. Neural network technique is a useful method which can be used to obtain cell deformation by the means of force-geometric deformation data or vice versa. Prior to insertion in the needle injection process, deformation and geometry of cell under external point-load is a key element to understand the interaction between cell and needle. In this paper, the goal is the prediction of cell membrane deformation under a certain force and to visually estimate the force of indentation on the membrane from... 

Many Random Key Distribution (RKD) schemes have been proposed in the literature to enable security applications in Wireless Sensor Networks (WSNs). A main security aspect of RKD schemes is their resistance against node capture attacks, since compromising the sensors and capturing their keys is a common risk in such networks. We propose a new method, based on a 2-Dimensional Hash Chain (2DHC), that can be applied on any RKD scheme to improve their resilience. Our method maintains the flexibility and low cost features of RKD schemes and it doesn't require any special-purpose hardware or extra memory to store keys in the sensors. We demonstrate that our approach significantly increases the... 

The current study was aimed at developing a package of “model + algorithm” for the design of resin in pulp (RIP) and carbon in pulp (CIP) processes of gold, uranium, and base metals. For this purpose, we first formulated a double-resistance model for irreversible adsorption (accompanied by chemical reaction) in CSTRs, and modified the McKay et al. semi-analytical model for reversible uptake in a similar system. We then devised two algorithms for the design and optimization of reversible and irreversible RIP and CIP cascades. The developed algorithms were applied on the extraction of copper, uranium, and gold. The packages are able to specify the optimum number of stages, reactor volume (V),... 

This paper deals with investigation of deformations and pull-in charges of the cantilever and doubly clamped carbon nanotubes (CNTs) with different geometries using molecular dynamics simulation technique. The well-known AIREBO potential for the covalent bonds between carbon atoms, Lennar-Jones potential for the vdW interaction and the Coulomb potential for electrostatic actuation are employed to model the nano electromechanical system. The results reveal that longer CNTs with smaller diameters have smaller pull-in charges in comparison with shorter CNTs possessing larger diameters. Furthermore, the pull-in charges of the doubly clamped CNTs are higher than the pull-in charges of the... 

A large number of random key pre-distribution (RKD) schemes have been proposed in the literature to secure wireless sensor network applications, relying on symmetric key cryptography. However, sensor nodes are exposed to physical compromise by adversaries, who target the symmetric keys stored at each node. With the stolen keys in their possession, the adversaries are then able to compromise communication links between benign nodes. Here, the big challenge arises: how to increase resilience of RKD schemes for wireless sensor networks to node capture, while maintaining the flexibility and low-cost features of RKD? We propose the idea of key splitting to address this problem, without the need... 

In this investigation for Expandable Pattern Casting (EPC) simulation, an algorithm was developed to calculate the gas pressure of the evaporated foam during mould filling. Also, the effect of backpressure evaporative foam on filling behavior was modeled with a new experimental function by adding a Volume Of Fraction (VOF) function. The simulation of molten flow and track free surfaces is based on the (SOLution Algorithm) SOLA-VOF numerical technique. To simulate the three-dimensional incompressible flow of melt in EPC moulds, the pressure boundary conditions, heat transfer and foam gas pressure effect were modified. In order to verify the computational results of simulation melt flow in EPC... 

A new method for position determination of stationary targets from radio bearings, using triangulation, and based on the partial derivative analysis of bearing error has been proposed. Mathematical derivations have been carried out and a simulation illustrating the effectiveness of the method has been run. It turns out that, the method works best when the noise is excessively high and the traversed path is asymmetric. In such conditions, the method illustrates an error reduction of up to 5% with respect to the Least Square algorithm  

Large signal behavior of the Laser Diode is analyzed with the aim of finding a qualitative relationship between modulation amplitude and the change in the shape of its transfer function. It is found that, at quasi-static conditions, increasing the amplitude of the modulating signal smoothes out the original piecewise-linear transfer function of the diode. It further shifts the now smoothed knee point to lower DC currents. As the frequency increases, however, these effects become less and less pronounced. In addition, the transfer function becomes rather wavy due to the failure of current density to reach the saturation level necessary for adequate stimulated emission. At even higher... 

In this paper the root cause failure of a super-heater boiler tube is discovered. The tube has been worked in caustic media (pH = 8.9∼9.6) for virtually 40 months. The working temperature and pressure were recorded in the range of 204-315°C and 43 bar, respectively According to the chemical analysis, it was revealed that the tube is in accordance with ASTM A213 Gr T22. The corrosion products of the tube were characterized by EDS, XRF and XRD techniques. Visual inspection indicated that the macro-cavity was promoted on the inner surface of the tube. Also, a drastic wall thinning with gouging marks were observed. As a result of steam blanketing phenomenon, the sodium ions are locally... 

Optical tweezers provide an accurate measurement technique for evaluating mechanical properties of the living cells and many experimental studies have been done to understand the behavior of cells due to external forces. Numerical studies such as finite element methods have been used in order to simulate mechanical behavior of the Red Blood Cells (RBCs). Recent studies have shown that the particle methods are useful tools to simulate the mechanical behavior of living cells. Since in microscopic scales, using discrete models are preferred than continuum methods, a particle-based method is used to simulate the deformation of RBC which is stretched by optical tweezers. The cytoplasm of RBC is... 

The effect of temper rolling and subsequent annealing on texture development and magnetic properties of semi-processed non grain oriented electrical steel has been investigated. The result shows that 5 % temper rolling and final annealing at 850 8C resulted in strong a-fiber component. The etch-pit technique shows that strain induced boundary migration is responsible for new texture component augmentation. Vibrating sample magnetometery reveals that maximum and minimum magnetic permeability are related to rolling and transverse directions, respectively. Average magnetic permeability is improved to some extent as a result of temper rolling and subsequent annealing. © Carl Hanser Verlag GmbH &... 

The objective of this work is to create an analytical framework to study the problem of squeezed film damping in micromirrors considering the bending of the supporting torsion microbeams. Using mathematical and physical justifications, nonlinear Reynolds equation governing the behavior of the squeezed gas underneath the mirror is linearized. The resulting linearized equation is then nondimensionalized and analytically solved for two cases of the infinitesimal and finite tilting angle of the mirror. The obtained pressure distribution from the solution of the Reynolds equation is then utilized for finding the squeezed film damping force and torque applied to the mirror. The results show that... 

The purpose of this paper is to design and analyze a 3-link micro-device proposed as a micro-manipulator. This micro-manipulator includes 3 micro-beams as links connected to one another with no conventional or flexural joints. While the structure of the micro-manipulator is monolithic, end-effector workspace is achieved through deflection of links which is actuated by piezoelectric layers. By combining static analysis of the links through a multilayer piezoelectric beam model and kinematic analysis of the micro-manipulator, inverse kinematic has been solved utilizing the Taylor series expansion technique and the perturbation method. The obtained results through the present model reveal that... 

Valveless micropumps are widely used due to simple structure, durability and low maintenance. Understanding the fluid-membrane interaction and performance criteria is still a challenging problem for the scientists. In this work, a new model for side mounted valve micropumps is developed to obtain dynamic response of micropump with respect to piezoelectric actuation. The parameters of this model are obtained in terms of actuation frequency and geometrical dimensions of the micropump. Balancing elastic, inertial and damping forces result in the governing equation of the micropump system model. Analytical studies for the bottom mounted valve micropump indicate pump flux is independent of the... 

A problem associated with modeling and control of the power factor correction rectifiers is that the ac variations in duty cycle, as well as in the ac input voltage and current are not small, and hence the traditional small signal analysis is not justified. Nonetheless, the low-frequency components of the converter can be modeled via the circuit averaging technique, but the resulting equivalent circuits are, in general, time varying and highly nonlinear. Nonlinear stability analysis methods are not appropriate for analysis and control design of such complicated circuits. In this paper a piecewise affine approximation is introduced for modeling of switching circuits. This approach makes the...