Sharif Digital Repository

Data are presented on the solidification of aluminum alloys and their macro segregation behavior. Three alloys with different solidification ranges were prepared in two temperatures. Two types of molds were also prepared by sand and metallic materials. The solidification of Al alloys were studied and the effects of four parameters were determined, including cooling rate, casting temperature, degassing and nucleation effects on solidification and a comparison was conducted to Scheil model performance. Three types of aluminum alloys (Al-12.1%Si, Al-6.9%Si and Al-4.4% Cu) with short, medium and wide solidification ranges were studied and the results showed that degassing, nucleation, increasing... 

The equilibrium crystal structure and electronic structure of BaFe2-x Cox As2 (x = 0,1, 2) superconductor have been investigated by using the pseudopotential Quantum Espresso code based on the ab initio density functional theory in the generalized gradient approximation. The equilibrium crystal structure for x = 1.0 has been determined by considering five different Fe/Co configurations. This study shows that the spin calculation is essential to obtain the experimental values at x = 0.0. The total and partial density of states, band structure, and Fermi surfaces of the three compounds has been calculated. Density of states calculation indicates the important... 

In this paper, a new on-line handwritten signature verification system using Hidden Markov Model (HMM) is presented. The proposed system segments each signature based on its perceptually important points and then computes for each segment a number of features that are scale and displacement invariant. The resulted sequence is then used for training an HMM to achieve signature verification. Our database includes 622 genuine signatures and 1010 forgery signatures that were collected from a population of 69 human subjects. Our verification system has achieved a false acceptance rate (FAR) of 4% and a false rejection rate (FRR) of 12%. © 2003 IEEE  

An Artificial Neural Network (ANN) model has been designed for predicting the effects of alloying elements (Fe, Si, Al, Mn) on the recrystallization behavior and microstructural changes of 70/30 brass. The model introduced here considers the content of alloying elements, temperature, and time of recrystallization as inputs while percent of recrystallization is presented as output. It is shown that the designed model is able to predict the effect of alloying elements well. It is also shown that all alloying elements strongly affect the recrytallization kinetics, and all slow down the recrystallization process. The effect of alloying elements on the activation energy for recrystallization has... 

A significant challenge of foam injection is the stability of the foam in formations. In this study, the modeling of liquid drainage and the impact of some parameters (i.e., concentration of surfactants, nano-particles, and monovalent ions) on the liquid drainage rate and foam stability were investigated by using a population balance model. First, foam bubble size distribution was experimentally measured and used as input for the population balance model. The population balance equations were solved numerically, and the number density of bubble size distribution as a function of time was obtained. Then, the liquid drainage rate was calculated using volume balance equations. It is shown that... 

In optoelectronic OTIS multicomputer networks (also known as Swapped networks), electrical and optical interconnects are used for local and global communication, respectively. An interesting instance of the OTIS multicomputers is the OTIS-mesh. Pancyclicity is of great importance in the implementation of a variety of parallel algorithms in multicomputers. This paper addresses the Pancyclicity problem of OTIS-mesh. More precisely, we prove that if the factor graph G of an OTIS network is a 2-D or 3-D mesh with at least one even radix, OTIS-G can embed any cycle of length l, l?{4,6,7,8,9,...,|G|2}  

The communication between control centers, contact centers, field technicians and customers have been changed in previous decade and traditional analogue communication devices have been being replaced by integrated digital systems. Nowadays communication and computer network substructures are vital to distribution companies because communication system interruption can disrupt majority of services. Therefore, it is necessary to control any situation which can threat communication system. Alborz province power distribution company uses data mining methods like classification and clustering in addition to quantitative statistics for analyzing historical fault data. The result of this study is... 

In this work, sessile drop and low-bond axisymmetric drop shape analysis methods were coupled to provide some new aspects on stick-slip behavior as well as stick time of a drop on calcite surfaces. Slightly hydrophobic calcite surfaces typified with three irregular roughnesses were used to create irregular surfaces to mimic defects for the water-calcite-air systems. Polishing papers of 200, 600, and 1200 grit and a polishing machine were used to prepare surfaces. X-ray diffraction, energy dispersive X-ray spectroscopy, Fourier transform infrared, and atomic force microscopy techniques were employed to evaluate the chemical and physical properties of surfaces. A model was developed to predict... 

Electrophoretic motion of hydrophobic particles has been scrutinized numerically in solid-state nanopores. The Poisson, Stokes, and Nernst-Planck equations are solved simultaneously, and the Newton-Raphson algorithm is used to compute the correct velocity at each point. For the hydrophobic surface characterization, the Navier-slip boundary condition with a wide range of slip lengths is applied to the nanoparticle's surface. The effects of the electric field intensity, the electrolyte concentration, and the particle's size on the electrophoretic velocity are examined. Then, the nanopore's size and surface charge density are manipulated to achieve the configuration for separating hydrophobic... 

A new model is developed for the structure of nanocrystalline materials. Based on the developed model, a new approach for investigating the effect of grain size on the elastic moduli of nanocrystalline materials is introduced. The predictions of the model are strongly correlated with the experimental results reported in the existing literature  

In optoelectronic OTIS multicomputer networks (also known as Swapped networks), electrical and optical interconnects are used for local and global communication, respectively. An interesting instance of the OTIS multicomputers is the OTIS-mesh. Pancyclicity is of great importance in the implementation of a variety of parallel algorithms in multicomputers. This paper addresses the Pancyclicity problem of OTIS-mesh. More precisely, we prove that if the factor graph G of an OTIS network is a 2-D or 3-D mesh with at least one even radix, OTIS-G can embed any cycle of length l, l∈{4,6,7,8,9,...,|G|2}  

A new experimental facility was designed, fabricated and tested to model and study the possibility of applying the bidirectional swirl flow on the combustion chamber of airbreathing subsonic ramjet engine. Appropriate intake was designed to convert axial external air to tangential swirl flow inside the combustion chamber. Inlets with appropriate angles conduct the swirl flow into the chamber and create bidirectional swirl flow field in the combustion chamber. This flow field has been modeled theoretically to determine the velocity field characteristics by previous researchers. Bidirectional swirl flow in liquid fuel ramjet engines has the proven advantage of keeping the combustion chamber... 

Kinematic mismatch between exoskeletons and human body results in excess internal forces/torques and hence discomfort as well as increase the power consumption. The connection stiffness has been shown to have potentials for minimizing the kinematic mismatch effects. However, realization of a desired stiffness in the connection element seems difficult if not impractical. In this work, adding controlled backlash to the exoskeleton-body connection is investigated as a possible solution for the kinematic mismatch challenge. A stiffness model which includes backlash parameters was formulated and identified experimentally using three male subjects on a typical lower extremity exoskeleton. A... 

Network marketing is a business model that depends upon a network of distributors for growth, such as in multilevel marketing. A direct selling method features independent agents that make up a distribution network for goods and services. This paper provides a framework to study the network marketing by adopting the traditional channel. To motivate all distributers in network marketing as well as retailers, it is required to design a well-balanced distribution and pricing system. The allocated commission for distributers in different layers of network marketing is part of pricing system, which is vital. In this paper, we develop an approach to determine all elements of system, including... 

In this study, some new aspects of adsorption of a fluorochemical onto carbonate rocks as a wettability alteration agent to a gas wetting condition with the potential application for reduction of condensate blockage in gas condensate reservoirs are presented. To achieve this, kinetics, equilibrium, and thermodynamic of the adsorption process besides contact angle, imbibition, and characterization tests are investigated. Results of adsorption experiments revealed that kinetics behavior of the utilized fluorochemical–calcite system obeyed the pseudo-second order kinetics model. There was no change in adsorption after about 20 h. Also, the intraparticle diffusion mechanism was not the only rate... 

Standpoints about atrium design have been revolutionized. Nowadays, design of atrium is not only for shine of light, but is also for natural ventilation as well. In high rise building, residents have not a same advantage of buoyancy-driven ventilation that arising from existence of atrium. One strategy to more equalize ventilation and thermal comfort in different levels, is designing building with various opening area in different heights. Present study aims to overcome the problem by changing the atrium shape. Thus, the atrium's wall angularity is changed in different case studies and these shapes are compared with each other in order to find the relations between atrium wall angularity and... 

In the present article, a new model for inverse Hall-Petch relation in nanocrystalline materials has been proposed. It is assumed that lattice distortion along grain boundaries can cause internal stresses and high internal stresses along grain boundaries can promote the grain boundary yielding. The designed model was then verified using the nanocrystalline-copper data. The minimum grain size for inverse Hall-Petch relation is determined to be about 11 nm for Cu. © 2008 ASM International