Sharif Digital Repository

The acceleration acting on apex seals, and engine speed fluctuations together with the leading and trailing cells gas pressure forces are analyzed in the present work using the second Newton law. The research shows that cell gas pressure effects are important and inclusion of these effects will provide results which are more compatible with the reality and lead to a much more accurate analysis of the system. Theoretical calculations reveal that gas cell pressure forces represent about 78% of the overall calculated force and ignoring these pressure forces lead to the same magnitude of inaccuracy in predictions  

Well deliverability is an important issue in forecasting the performance of many gas condensate reservoirs. Condensate accumulation near the wellbore can cause a significant reduction in productivity, even in reservoirs where the fluid is very lean. Generally, the well deliverability is affected by two pressure-drop sources due to depletion and condensate buildup. Recently Rapid spreadsheet tools have developed to evaluate the well performance using material balance equation for depletion and two-phase pseudo pressure integral for well inflow performance. Most of them account for the effects of negative inertia and positive coupling in the calculation of gas relative permeability. This paper... 

Well deliverability is an important issue in forecasting the performance of many gas condensate reservoirs. Condensate accumulation near the wellbore can cause a significant reduction in productivity, even in reservoirs where the fluid is very lean. Generally, the well deliverability is affected by two pressure-drop sources due to depletion and condensate buildup. Recently Rapid spreadsheet tools have developed to evaluate the well performance using material balance equation for depletion and two-phase pseudo pressure integral for well inflow performance. Most of them account for the effects of negative inertia and positive coupling in the calculation of gas relative permeability. This paper... 

A non-Markovian generalization of a one-dimensional contact process is being introduced in which every particle has an age and will be annihilated at its maximum age τ. There is an absorbing state phase transition which is controlled by this parameter. The model can demonstrate oscillatory behavior in its approach to the stationary state. These oscillations are also present in the mean-field approximation, which is a first-order differential equation with time delay. Studying dynamical critical exponents suggests that the model belongs to the direct percolation universality class. © 2002 The American Physical Society  

Finite element (FE) method is used to model radial deformation of single-walled carbon nanotube (SWCNT) under hydrostatic pressure. Elastic deformation of the nanostructure is simulated via elastic beams. Properties of the beam element are calculated by considering the stiffness of the covalent bonds between the carbon atoms in the hexagonal lattice. By applying the beam elements in a three-dimensional space, elastic properties of the SWCNT in transverse direction are obtained. In this regard, influences of diameter and tube wall thickness on the radial and circumferential elastic moduli of zigzag and armchair SWCNTs are considered. It is observed that there is a good agreement between the... 

Aspect-Oriented Software Development (AOSD) concentrates on determination and modularization of orthogonal concerns that cut across system modules. An aspect-oriented extension framework helps transform existing methodologies into processes which support AOSD. The authors propose a framework for extending agile methodologies with AOSD features. The stages required for constructing the framework have been identified by scrutinizing existing aspect-oriented methodologies and practices in order to extract the AOSD-specific stages required in each phase of the agile development process. Analysis shows that a methodology extended through this framework can be superior in agility in comparison to... 

A non-Markovian stochastic predator-prey model is introduced in which the prey are immobile plants and predators are diffusing herbivors. The model is studied by both mean-field approximation (MFA) and computer simulations. The MFA results a series of bifurcations in the phase space of mean predator and prey densities, leading to a chaotic phase. Because of emerging correlations between the two species distributions, the interaction rate alters and if it is chosen to be the value which is obtained from the simulation, then the chaotic phase disappears  

A dense membrane of La0.6Sr0.4Co0.8Fe0.2O3- δ (LSCF) perovskite was prepared by a new chelating agent, ethylene diamine N,N,N′,N′-tetra N-acetyl diamine (EDTNAD). As a potent ligand, EDTNAD provided a facile one-step method to form complexes of the four metal ions, simultaneously. The oxygen permeation flux through the pure perovskite LSCF dense membrane was measured over temperature range of 1073-1223 K, thickness of 0.7-1.0 mm and oxygen partial pressure of 0.1-1.0 bar. Oxidative coupling of methane (OCM) reaction using LSCF disk in the atmospheric membrane reactor and over the temperature range of 1073-1173 K showed a C2 selectivity of 100% and C2 yield of 5.01% at 1153 K. Furthermore,... 

Ways to reduce an airline's cost has been studied for years. In fact, in order to achieve this goal, ones need to know different types of airline's costs including; fuel and oil, maintenance, Ticketing, passenger services, etc. and their impact on the total cost of an airline. According to announcement of ICAO [1], "maintenance cost (about 11% of total cost) is the second major cost after fuel and oil". Therefore, this may attract airline owners' attention to find ways to control maintenance cost and eventually the total cost of an airline. Though, there are many systematic approaches to analyze cost reduction and making policies, in this article, SD modeling is applied to develop a... 

This paper presents an approach that integrates clinical methods with Neuro-Fuzzy system in order to diagnose Neonatal Jaundice in newborns. First, a fuzzy logic system designed with medical rules to model the uncertainty that exists in medical diagnosis. Then a fuzzy neural network with an evolutionary learning helps the system to learn the new data gained from the patient and to help the fuzzy system to update itself in an online manner. By combining the aforementioned systems, the proposed approach can help physicians to diagnose jaundice with low risk cost associated with this disease. © 2006 IEEE  

In this article, we presented a numerical solution of steady-state magnetohydrodynamic (MHD) flow of an incompressible, electrically conducting Casson hybrid nanofluid through a stretching surface under the incitement of viscous dissipation, heat generation and induced magnetism. A viscous mixture of water and ethylene glycol (Formula presented.) is considered as a base fluid. Enhanced thermal aspects of the working fluid due to suspended manganese zinc ferrite ((Formula presented.)) and silver ((Formula presented.)) nanoparticles are analyzed by successive over relaxation iterative method. A self-similar procedure is adopted to obtain dimensionless system of governing equations. Order... 

This paper presents a comparison of analytical and experimental results of an investigation on the diagonally stiffened steel plate shear walls (SPWs). Experimental studies were carried out on three 1/3-scaled, one story single bay shear walls. The first specimen was a control specimen which was unstiffened and the other two specimens were diagonally stiffened using different stiffener configurations. Finite-element models of full SPWs are developed using finite element model. The results are compared with experimental results to investigate the influence of stiffeners on the behavior of the specimens. Good agreement between analytical and experimental models is found in point of failure... 

Morphological computation (MC) has revolutionized robotic systems employing morphological properties (MP). Thus far, morphology has been mostly used to analyze morphological functionalities qualitatively after design phase of robotic systems. Furthermore, morphology has verified qualitative requirements, not modeled quantitative specifications. To fill this gap, we present a distributed algorithm to monitor module reconfiguration for homogeneous self-reconfigurable robots (HSRs) considering the size of modules. In this method, neighboring modules of a particular module occupy a spatial region called adjacency configuration (AC), whose size depends on the module size; then, we monitor... 

We consider the problem of learning causal models from observational data generated by linear non-Gaussian acyclic causal models with latent variables. Without considering the effect of latent variables, the inferred causal relationships among the observed variables are often wrong. Under faithfulness assumption, we propose a method to check whether there exists a causal path between any two observed variables. From this information, we can obtain the causal order among the observed variables. The next question is whether the causal effects can be uniquely identified as well. We show that causal effects among observed variables cannot be identified uniquely under mere assumptions of... 

This paper introduces a novel, cost effective visual cryptography scheme suitable for color image transmission over bandwidth constraint channels. Unlike previously proposed schemes, the solution offers perfect reconstruction while producing shares with size smaller than that of the input image. The maximum distance separable (MDS) code principle used in the design allows for the introduction of a flexible framework that compares favorably to competing solutions as it can be seen by examining the experimental results included in this paper. ©2008 IEEE  

This paper presents an analytical approach to design a continuous time-invariant two-level control scheme for asymptotic stabilization of a desired period-one trajectory for a hybrid model describing walking by a planar biped robot with noninstantaneous double-support phase and point feet. It is assumed that the hybrid model consists of both single- and double-support phases. The design method is based on the concept of hybrid zero dynamics. At the first level, parameterized continuous within-stride controllers, including single- and double-support-phase controllers, are employed. These controllers create a family of 2-D finite-time attractive and invariant submanifolds on which the dynamics...