Sharif Digital Repository

Cooperative communications have been introduced to combat degrading effects of fading in wireless networks and attracted much attention recently. This technique provides distributed spatial diversity that enables energy-efficient transmission of information from source nodes to destination nodes via intermediate relay nodes. Most existing protocols, detection techniques and optimization methods in cooperative networks assume that perfect channel state information is available. While in practical situations, the estimates of the channels may only be known and for acquiring such knowledge, a fraction of power and bandwidth have to be spent for channel estimation using pilot symbols. In this... 

In this study, a numerical investigation of propagation of sound through a fluid-saturated porous column has been proposed so that we can analyze the effects of porous media parameters on decreasing sound amplitude. The mathematical model applied for our simulation is based on Biot equations solved by an explicit finite difference method. Since Biot model is exclusively applicable to porous solids saturated with single fluid phase, in order to simulate a porous solid saturated with two immiscible fluids, we exploited the general Eulerian model instead of Biot model. Efficiency of porous sound absorbers is directly influenced by four major parameters which are porosity, rigidity and thickness... 

Crumb Rubber is one of the main polymer modifiers of binders. This modifier can improve chip seal performance against ravelling (aggregate loss). The most concerning distress in chip seal is ravelling. Aggregate loss is not restricted to the early life of chip seal, but continues throughout the service life. Chip seal can be made with hot binders or emulsion binders. These two type of binder were modified with 7% and 15% of crumb rubber in applicable way. Then, two major environmental effect on chip seal performance, freeze-thaw and asphalt aging, were investigeted based on laboratory test. For this purpose, authors used chip seal bonding test. Chip seal bonding test is developed recently... 

Viscosity is one of the most important properties used in simulating and optimizing transportation design and hydrocarbon reservoirs simulation. In this work, a new model based on the friction theory was used to correlate the viscosity for six different live and dead oil samples taken from the south of the Iranian oil region. As expounded by other researchers, in the friction theory, an equation of state is used to express the intermolecular viscous interactions. In model presented in this work, the standard cubic equations of state such as the SRK and PR were used to correlate the viscosity data for the samples under investigation. In the new model, the effect of critical viscosity on the... 

Landslides, like earthquakes, floods, and volcanoes, are important natural disasters that occur frequently in the mountainous and high regions of our country, especially in the Alborz and Zagros regions, which induce considerable damages. Various factors such as topography, lithology, weather conditions, hydrology, tectonics, earthquakes, and various human activities are effective factors in the instability of natural and man-made slopes. Not one factor can cause instability in slops, however, a combination of the named factors may cause landslides. Therefore, knowing the factors affecting the occurrence of landslides and identifying different areas in terms of sensitivity to their... 

Since the beginning of oil, gas and gas condensate production, the prediction of the formation of mineral scales in different operating conditions has been a serious challenge. Mineral scale are solid particles that are separated from the free water in the reservoir due to changes in the production conditions in terms of temperature and pressure or the fluid composition of the production fluid of reservoir, and there is a possibility of their deposing on the wall of the well column and in the production system, where The way of production from reservoirs faces serious risks. free water, which is permanently entering the pipeline, contains all kinds of salts in the structure of the fluid... 

Shape memory materials are a kind of smart materials which recently have been used in a wide range of fields in particular medicine and aerospace. These materials can be divided to shape memory polymers and shape memory alloys. The basis of shape memory alloys’ properties is a thermoelastic martensitic transformation taking place between a high symmetric phase, called Austenite, and a low symmetric phase, called Martensite. In this project, by means of finite element methods, continuum thermomechanics and selection of appropriate internal variables (such as amount and orientation of volumetric fraction of each phase) and control variables (like strain, stress, temperature and entropy), their...