Sharif Digital Repository

The aim of this study was to compare the effect of different cooling conditions (dry, flood, mql) on machined surface parameters (smoothness and protrusion of fibers) and tool erosion in carbon fiber reinforced plastic composite materials (CFRP) in the presence of ultrasonic vibrations or without it. Is. Today, carbon fiber reinforced plastic composite materials or CFRP have become one of the most widely used materials in industry due to their strength and light properties. For example, these materials have been used in the manufacture of products from commercial aircraft to shoes, tennis rackets, golf clubs, fishing rods, etc. The combination of carbon fibers woven with resin in alternating... 

Nowadays, processes with the ability to machine advanced materials are very much needed by industries. Therefore, compare of a rotary ultrasonic-assisted machining process with a conventional machining process is carried out in this study. In order to evaluate this process, the milling and drilling processes are conducted on the carbon fiber-reinforced polymer composite and titanium materials where cutting forces, surface roughness, and fiber pull-out are selected as critical factors for analysis. As a result, it is seen that rotary ultrasonic-assisted machining has a good performance in the milling and drilling of advanced materials. In particular, it is shown that fiber pull-out is... 

The aim of this thesis is to provide a correct explanation of technological determinism. According to this theory, technology has changed our lifestyle and we have to adapt ourselves to it, which is obvious to us even without knowing about this theory. But is this really the essence of technology? Or does the user community act like this when faced with technology? This is the question that we seek to answer in this thesis. For this purpose, we first express different readings of technological determinism, and some theories aligned and not aligned with it. Then we address the dual nature of technology and show that "physical structure" and "the function intended by the designer" together... 

In this project formation of MgO & Mg2Cu reinforcement particle in Magnesium matrix was investigated. Firstly Mg & CuO powders mixture in different weight percentage (4, 8%wt CuO) in 20:1 and 30:1 BPR were milled. Finally, according to XRD result 30:1 BPR was selected for milling. Variations in powders morphology, particles size, crystallite size, lattice strain and phase transformation were investigated by X-ray diffraction, scanning electron microscopy and laser particle size analyzer in different milling time. Result showed that during reaction between Mg and CuO, MgO & Mg2Cu reinforcement particles were formed in matrix. Matrix crystallite size was determined about 35-40 nm. Mg-6.3%wt Cu... 

In recent years membrane bioreactors (MBR) were widely used as an advanced process for industrial wastewater treatment. But fouling issue causes some restrictions in these systems. So for fouling reduction many researches were done.In this study for fouling improvement, blending of hydrophilic polymer (PAN) with main polymer PVDF was used. Blending membrane in phase inversion process with DMAC as solvent and water as non-solvent was made. For pore-forming in membranes, PVP as hydrophilic additive with three different composition was added and then for more enhancement of antifouling property of membrane, TiO2 nanoparticles with four different composition were added to polymeric... 

In the presence project by using of hydrophilic polymer, Cellulose acetate (CA), we tried to modify the membrane made of Polyvinylidine fluoride (PVDF). The membranes were made by phase inversion method. In five levels, at least 10% and at most 30%, CA was added to casting solution. The hydrophilicity of membranes’ surface and pore size was increased. The permeation of the neat membrane of PVDF was less than 10 , on the other hand the permeation of the membranes, which were made by adding CA, was increased up to 500 . The increment of CA more than 20% reduced the porosity of membrane. In the next step to reduce the irreversibility fouling tried to reduce the pore size by adding some... 

Although technological specialization has been recognized as a stimulating factor of international trade (Ricardian theory), new approaches emphasize the endogeneity of technological heterogeneity across countries. Following them, we proceed to examine the effect of free trade on technological differences among 20 OECD members during 1996-2008. We first use the model of Eaton and Kortum (2002) to obtain an annual estimate of technological heterogeneity within the OECD group. We then analyze the behavior of this index facing international trade statistics in the same period. The results show that the OECD countries have been experienced a technological convergence, thanks to a boost in the... 

In this thesis we examine and study the transmission of Ultra Wide Band (UWB) signals over single mode fiber in a radio over fiber system. We begin by developing mathematical model for the key optical components employed in radio over fiber systems. The authenticity of these models is verified with experimental results. Following the above models as well as experiment results, the transmission of UWB signals over optical fiber is investigated. The impact of limited operating bandwidth and nonlinearity of the electrical to optical transfer function on UWB signals is examined. Two types of UWB signals, namely, multi-band orthogonal frequency division multiplexing (MB-OFDM) and impulse radio... 

Despite the relative weakness of exchange rate structural models in determination short term fluctuations, observations show that real exchange rate respond to some fundamental economic variables. Due to the growing foreign sector of national economies, recent studies pay special attention to the impact of terms of trade on currency exchange rate. In this study, a structural model of the real exchange rate between the 70 currencies and during the period 1980-2010 has been developed in the context of panel data. Empirical micro-founded model are based on theoretical general equilibrium. Important features of such study are stationary of variables and causality test. Determination the effect... 

As the Internet traffic grows, the energy efficiency gains more attention as a design factor for the planning and operation of telecommunication networks. Therefore, researchers begin to devise solutions for energy conservation in many scientific disciplines. In this thesis, we focus on the study of energy efficiency in optical transport networks, specially, the newly proposed Spectrum sLICed Elastic optical path (SLICE) networks architecture. First of all, we will introduce energy consuming elements in SLICE networks and their power consumption model. Next, we present a dynamic energy efficient routing and spectrum assignment algorithm (EE-RSA) with regenerator placement (RP) capability for... 

Concentration brings a twofold result to the market. From one side, it reduces the competition and then the number of varieties in the market, which discourages consumption; from another side, however, it reduces the price of goods due to increasing returns to scale and so encourages consumption. This controversial role of concentration raises the question that which degree of concentration might be, say, optimum for the market. Based on the Krugman approach, this study makes a relation between the number of firms, export volume, marginal and average fixed cost of production. We show that when number of firms reduces in the market, export volume could increase because of a reduction in... 

Technology introduces different possibilities to different contexts. Educational milieu is one of those situations where technology plays a crucial role. Computer as an outstanding technological feature has changed our daily life. Computer in the educational contexts has affected the way we learn. Every new innovation has its specifications and problems. Computer like other innovations has aspects that should be investigated. In some cases, computer can distort the tests results and be a source of threat for test validity (construct irrelevant variance). Therefore, the researcher chose to analyze the role of this phenomenon in the assessing procedure. Gender, age, mother tongue, and field of... 

This study investigates the application of ionic liquids as a lubricant in the minimal lubrication system for P20 steel drilling. due to the wide use of cutting fluids in machining processes, it is important to research in this regard to reduce emissions of pollutants, reduce friction, and consequently reduce energy consumption and machining costs. in recent years, ionic liquids have been considered as a new lubricant due to the structure and composition of the special chemical in the fields of: bearings, metal forming, etc. however, in the application of ionic liquids as fluids In the process of machining, very little research has been done. Therefore, deserves that examining the effect of... 

Traditional tool life models and wear prediction do not take into account the variation inherent in metal cutting processes. These lead to additional manufacturing costs. This research presents a stochastic method for both tool life and tool wear prediction. In the first part, Bayesian inference is applied to estimate the two model constants of Taylor tool life prediction model using a discrete grid method. Tool wear tests are performed using an uncoated M42 HSS tool and AISI 1018 carbon steel work material. Test results are used to update initial beliefs about the constants and the updated beliefs are then used to predict tool life using a probability density function (pdf). Finally, the... 

One of the main arguments between scientific realists and scientific anti-realists is about observability. As a prominent anti-realist, van Fraassen and his theory of constructive empiricism and his views on observability and the use of scientific instruments, have been the subject of many debates. He believes that observation is the sole path to knowledge and observation is only possible through unaided human eye, so seeing through scientific instruments like microscopes does not count as observation, therefore the information gained from these procedures are not necessarily true.This thesis not only examines van Fraassen’s outlooks on the matter, but also examines his opponents’ view and... 

Nowadays, piezoelectric motors are used as one of the suitable options in the modern motion control field and precise positioning systems due to their suitable functional characteristics such as high power to weight ratio, fast dynamic response, direct drive motion, integrated structure without backlash and possibility of miniature design. Accordingly, the present dissertation is defined in order to develop a comprehensive path for modeling, analysis and optimization of the ultrasonic piezoelectric motors. In this study, the focus is on the ultrasonic motors with an elliptical structure, but the results can be used for other structures as well. In the present work, the process of modeling of... 

Titanium is the most widely used material in medical implants. One of the drawbacks of utilizing titanium in implants, is its biologically inert surface; which hinders the creation of the optimal bond between the implant and the surrounding tissue. This limitation can be addressed by altering the surface texture. As a technology, applying vibration to the tool or workpiece during machining operations is a practical method to create surface micro textures. Upon reviewing the existing literature, it is evident that the impact of the surface texture achieved by vibration-assisted milling, on the interaction of bone cells with the titanium surface has not been investigated. Therefore, this...