Sharif Digital Repository

The use of nanofluids to improve the heat transfer has a special attention in the industry. researches focus on the efficiency of heat transfer nanofluids dates back to 1998. Ferrofluids are a particular type of nanofluids which their nanoparticles have magnetic effect and heat transfer can be increased by applying magnetic field to them. In this work, thermal and hydrodynamic performance of ferromagnetic fluid which flows through a copper tube in thermal entrance region has been studied. The flow in the tube is laminar and is affected by constant heat flux. Part of the tube contains a porous medium with paramagnetic properties and porosity of 0.46. Ferrofluid is composed of F e3O4 and water... 

In this thesis, the multidisciplinary design of liquid propellant satellite launch vehicle has been done by taking into consideration the effects of fuel sloshing. At first, the theory of multidisciplinary design and one-level architecture with the label of multidisciplinary feasibility have been used. In the following, Gravitational Search Algorithm (GSA) and Particle swarm optimization (PSO) have been developed. Then, the multidisciplinary design cycle began with the design of the liquid propellant system. In the propulsion section, the selection of the optimal fuel, the design of the nozzle, motor and the selection of the optimal engine cycle considering the geometric and mass... 

In this research sequence-dependent flowshop and flexible flowshop group scheduling problems are investigated. Several upper and lower bounding methods are proposed for the research problems. Permutation flowshop sequence-dependent group scheduling problem with minimization of total completion time is considered. Since the problem is shown to be strongly NP-hard, a Memetic algorithm (MA) is proposed. A lower bounding method base on the Branch-and-Price algrithm is also proposed. A statistical comparison shows that both the proposed MA and the proposed lower bounding method have better performance than the other methods from the literature with an average 5.96% percentage gap. Flexible... 

Due to the use of rotor dynamics, in the rotating systems such as pumps, turbines and machine tool spindle gained special significance in recent decades and a growing need for rotating machines with high speed, leading to extensive research in this area. Due to instability in the dynamics of these systems, check the stability of the rotor system has been given special emphasis, so that studies and research in terms of models and methods allocated to this topic. The project analyzed the stability of a rotor that includes an elastic shaft is placed on the bearings as it is objective. From point of modeling, the rotor is modeled using Timoshenko beam theory and the rotor mounted on bearing with... 

This research intends to analysis the determinants of child work and schooling in Iran. To do this we use the Household’s Income and Expenditure survey of Iran in 2009. There are two competing theoretical base of household’s time allocation, the unitary and collective bargaining decision approaches. We use the later to consider the differences in preferences of parents toward the child’s time allocation. Making use of Bivariate Probit and Tobit, we examined the effects of parents’ bargaining power and child’s birth order on his/her schooling and work decision. Our finding, confirm that, mother’s bargaining power has negative association with the work participation of her son and daughter but... 

Institutional investors are among the main players of capital market and stock market. These investor’s activities on the one hand affect directly on indices, and on the other hand on transactions of other players in the stock market. In case the transactions of stockholders are not based on sufficient information and merely based on imitation of other investors, herding behavior would be taken place within them.In this study, using two methods of Lakonishok (1992) & Sias (2004), we consider herding behavior amongst the Institutional investors of Iran stock market.In both methods, weekly and monthly data are used for testing herding behavior in the short-run and quarterly data for the... 

Many studies on hybrid vehicles have been done in the past few years. The Full hybrid vehicles need a large number of batteries creating up to 300V to meet the required voltage of electric motor. The size and weight of the batteries cause some problems. This research investigates the mild hybrid vehicle. This vehicle includes a small electric motor and a high power internal combustion engine. In most cases the car’s driving force is created by internal combustion part. A small electric motor, which can operate as engine starter, generator and traction motor, is located between the engine and automatically shifted multi-gear transmission (gearbox). The clutch is used to disconnect the gearbox... 

Working in second job is one the fact in labor market. based on the data of Statistical center of Iran. In Iran approximately 18 % of worker have second job. This trend fluctuate around 20%. That increase from 18% in 1372 into 19% in 1382. This research examines effective factor on secondary job market panel data from statistical surveys conducted by Statistics Centre of Iran from 1380 to 1382 .We apply three step Multiple selection method. Because of existence of censoring data & sample selection problem We use of probit method for panel data for modeling of existence in labor market and second job. Then we use of Tunali (1985) Method for estimate hours in second job. Result of research... 

Due to its extensive applications in financial analysis, stock market volatility modeling is a considerably important issue for stock market practitioners and academics. Using GARCH models to formulate the conditional variance heteroskedasticity with respect to the advantages of panel data technique such as higher degrees of freedom, more flexibility in the control of the omitted or unobserved variables effects, lead to a significant increase in the accuracy of estimations. In this thesis, in order to examine the similarities and differences between the conditional variance structure of stocks in the inter and intra industries, we have used a general to specific methodology of nested tests... 

This paper provides and empirical investigation of individual labor supply of Iranian spouses in a collective framework in which gender ratio and plays a central role in the decision process in household. The data set is taken from the socioeconomic characteristics of panel survey over 2001-2004 and ten yearly headcount of Iran. We have conducted the parameters estimation and hypothesis testing by Semykina, A. and Wooldridge, J.M., (2005) generalized procedure of sample selection in panel data model. Our findings explore that females’ labor supply is affected significantly and strongly by the gender ratio, (total number of males over the females in provinces, both in urban and rural areas).... 

We study stochastically perturb the classical Lotka-Volterra model x ̇(t)=diag(x_1 (t),…,x_n (t))[b+Ax(t)] Into the stochastic differential equation dx(t)=diag(x_1 (t),…,x_n (t))[b+Ax(t)dt+σ(t)dw(t)]. The main aim is to study the asymptotic properties of the solution. We will show that if the noise is too large then the population may become extinct with probability one. We find out a sufficient condition for stochastic differential equation such that it has a unique global positive solution. Moreover, we will establish some new asymptotic properties for the moments as well as for the sample paths of the solution. In particular, we discuss ultimate boundedness and extinction in population...