Sharif Digital Repository

In the present investigation, the mechanical alloying (MA) technique was employed to produce nanocrystalline Al-Ti alloys. Elemental Al and Ti powders were mixed with different compositions (0, 5, 10, and 20 wt.% Ti) and then, milled in a planetary ball-mill up to 40 h. The variations of powder morphology and particle size, apparent and tap densities, microstructure, grain size, lattice strain, and microhardness were studied with increasing the milling time. While dissolution of Ti in the Al matrix resulted to the formation of supersaturated Al-Ti solid solution in the samples containing 5 and 10 wt.% Ti, the specimen with 20 wt.% Ti, eventually, led to nanocomposite powder with different... 

In this thesis, we investigate the effects of topological constraints in catenanes composed of interlinked ring polymers on their size in a good solvent as well as on the location of their θ-point when the solvent quality is worsened. We mainly focus on poly[n]catenanes consisting of n ring polymers each of length m interlocked in a linear fashion. We study the scaling of the poly[n]catenane’s radius of gyration assuming that R ~ m^μ n^ν with µ = 16/25 and ν = 3/5 in a good solvent, with these values of µ and ν obtained by means of a Flory-like theory and further confirmed by numerical simulations. We show that individual rings within catenanes feature a surplus swelling due to the presence... 

A variety of early universe models predict the formation of primordial black holes. Primordial black holes can be a candidate for a fraction or total dark matter in the universe. Moreover, mergers of these black holes can produce gravitational waves. After re-entering the horizon, having a sufficiently large amplitude, the initial fluctuations of cosmic matter can collapse to primordial black holes. This thesis studies an inflationary potential that can amplify the power spectrum of curvature perturbations up to several orders of magnitude via imposing some features on the potential. This power amplification on small scales can lead to the formation of primordial black holes. For simplicity,... 

Decision making for planning a petrochemical plant is a difficult task, particularly when decisions are required to be made under constraints and different objectives. Final purpose of current research is to develop a reliable model for selecting limited petrochimal products among all potential alternatives under different constraints, considering two desired objective functions; Maximizing economic gain and minimizing safety risk. The powerful tool of multi objective decision making has been used for solving the proposed model. The developed model has been applied to Jam Petrochemical Company as a case study and the acquired results found to be successful.

 

Storage of the spent nuclear fuels is one of the topics of interest in recent years and many researches have been conducted in this field in order to design storage casks for spent nuclear fuels. In this study, thermal-hydraulic analysis of a dry storage cask for Bushehr Nuclear Power Plant spent nuclear fuels is carried out. Geometry of the analyzed cask is taken from a Russian transportation cask TK-13. Drawing of the geometry is achieved with SolidWorks and it’s meshing is completed in Gambit. 3 different cases were considered for cask’s geometry and design: cask without spacers inside, cask with spacers inside, and cask with spacers inside and fins on the outside surface of the cask.... 

Shoreline monitoring and predicting has a very important role for policymakers and managers of coastal areas in future planning and achieving sustainable development. In this regard, to monitor the shorelines and predict its changes, a study has been conducted considering the effect of tides. In this study, the shoreline obtained from satellite images has been modified by using slope maps, slope direction and tidal data. Then these lines were monitored using the Digital Shoreline Analysis System (DSAS) and finally Bruun's rule along with the RCP scenario was used to predict changes in the shoreline. In this research, the coastlines of Bushehr Province in the Persian Gulf have been selected... 

Accurate modeling of clutter and detection of low observable targets within clutter are the major problems in radar signal processing applications. Recently, fractal geometry is applied to the analysis of high range resolution radar sea clutters. The intrinsic difference in the fractal dimension between sea clutter and the echoes from targets is extracted and used to detect targets. The box-counting method is widely used to estimate fractal dimension but it has some drawbacks never or rarely considered in literature. We explain the drawbacks and propose a new fractal dimension based detector to increase detection performance in comparison with traditional detectors. Both statistically... 

The synthetic aperture radar (SAR) is a microwave imaging radar that achieves high resolution while taking advantage of pulse compression technology and the Doppler effect. In typical radar systems, in order to obtain a good azimuth resolution, one should use an antenna with big aperture. However this is not possible in many cases. SAR has overcome this problem by moving the antenna and so making a synthetic aperture. In inverse SAR (ISAR) the radar antenna is static and synthetic aperture is created by the movement of target. Typical SAR imaging aims at the static targets and when the target is moving, it does not operate well. When detecting moving targets by SAR, both radar and target are... 

Shallow geothermal energy is a renewable and sustainable form of energy that has the potential to help alleviate the growing climate and energy crisis. The most common system used to extract shallow geothermal energy is the ground source heat pump (GSHP) system. The concept of using underground structures in exploiting shallow geothermal energy for space heating and cooling has received increasing attention. This study focuses on the use of geothermal tunnels as a means of extracting shallow geothermal energy.This research examines the effects of different heat transfer mechanisms, and highlights the effects of this phenomenon by focusing on the effects of natural convection around the... 

This study aims to propose a new correlation between in-situ horizontal stress and cone tip resistance in soils. Knowing the field in-situ stress state condition has an important role in stability assessment and stress-deformation analysis in a common geotechnical system. Although vertical stress could be measured easily, horizontal stress is still known as challenging work. Due to the difficulty in sampling undisturbed sand specimens, in-situ tests have been proposed in the previous literature to investigate the different characteristics of this soil. Cone Penetration Test (CPT) is one of the most used and accepted soil methods for soil investigation, identifying different soil parameters... 

This thesis presents turbulent partially premixed combustion modeling behind a bluff-body by using the Flamelet Generated Manifold. The objective of the present work is to develop a 4D FGM program to simulate partially premixed combustion at a reasonable computational cost. Pre-tabulated data of this manifold is obtained by using a correlated joint PDF. An in-house code is developed to build a pre-tabulated library in conjunction with a correlated PDF. Also, an exclusive OpenFOAM solver is created by employing the PIMPLE algorithm. This solver provides the link of the computational domain with the pre-tabulated chemistry. This program is used to simulate Cambridge-Sandia stratified burner... 

While Cloud providers face problems during providing services to their clients, such as lack of resources or increasing idle resources in low workload; they can share their resources with other providers by participating in Cloud Federations, and take advantage of Cloud Computing benefits like high scalability and resource extension. Moreover collaborating Cloud Federations expands Geographical area of providers. The Resource Allocation Problem has been considered in many researches, but in fields like Cloud environment and Federated Clouds it comes with complications. This thesis analyzes an optimized mechanism based on game theoretic approach for Resource Allocation Problem in Federated... 

Token offerings, one of the new methods of financing in the blockchain industry, have provided startups with significant opportunities. In previous studies, most of the factors that determine the success of an initial offering have been examined, and operational performance has been less studied. In this study, the relationship between environmental, social, and corporate governance activities on operational performance and adoption has been presented. Previous studies have shown that more attention to environmental, social, and corporate issues leads to a higher amount of capital raised in the offering. We also address these issues among crowdfunding platforms, which attract more... 

In recent years, with the growth of industrial societies, the amount of energy consumption in the world has been increasing. On the other hand, the most consumed energy sources in the world are non-renewable energy sources. For this reason, governments and industries have invested to facilitate and make renewable energy sources cheaper. One of these renewable energies is geothermal energy, which is one of the most economical ways to use this energy, using heat exchange systems in piles and foundations. Using a heat exchange fluid, energy piles transfer the heat of the earth's surface to the ground with a lower temperature in the hot seasons of the year and use the thermal energy of the... 

DNA is big protein molecule consisting of two strands intertwining each others. Recently DNA molecule has drawn attention of researchers to be used in electronic circuits and molecule electronic field. Therefore, many experiments have been carried out to measure DNA conductivity in different temperature in single molecule or bundle mode with varying size and shape. In this thesis, metallic bundle DNA at normal room temperature is studied and their resistance characteristic is obtained and compared. In order to improve DNA conductivity Metal Ions like zinc are adulterated to each of its structure period. DNAs with these metallic impurities are called metallic DNAs.
Thus, golden electrodes... 

In this thesis, a new passive method suitable for Geolocating LPI radars is introduced. The method uses two Electronic Support (ES) receivers placed on a fast moving platform (e.g., an airplane or a satellite). The proposed method has a high processing gain, which makes it highly suitable for very weak LPI signals. The processing gain of the method was analytically derived and illustrated with simulation to determine if the proposed method can detect LPI radars in much lower SNRs compared to regular time-frequency LPI detection methods. Also, the resolution of the proposed method in both range and cross-range direction in radar location finding was analyzed. Furthurmore, the effect of the... 

In the current situation, kidney transplantation is the most appropriate and least costly treatment for patients with end-stage renal disease (ESRD). Related or altruistic living donors, as well as deceased donors, are considered as a supply source for donated kidneys. Researches have shown deceased donor kidney may not work as well as a living donor kidney because the deceased donor kidney is outside the donor's body for a longer time. If the donor has an incompatibility with the patient (in terms of the blood group, HLA, etc.), a kidney exchange between the pairs can be used to resolve the issue and make the transplantation possible. Pairs with blood group compatibility have also... 

Considering the environmental pollution caused by the consumption of fossil fuels, replacing clean and renewable energies instead of fossil fuels has become one of the most critical issues across the world. The use of energy geostructures, especially energy piles, to exchange the heat between the superstructures and the ground is one of the approaches for taking advantage of clean energy. In order to maintain the safety and the serviceability of structures built on energy piles, it is necessary to study the effects of heat exchange between energy piles and the ground on the mechanical behavior of energy piles, as well as the effects of various parameters on the interaction between energy... 

The Piezocone penetration test is a common geotechnical field test used to assess soil properties. In interpreting the CPTu field measurements, soil drainage conditions are mostly considered completely drained or undrained; however, partial drainage conditions govern such soils as silts or clayey sand mixtures. The studies show that neglecting partial drainage conditions causes soil consolidation characteristics to be underestimated. Most studies have been conducted using calibration chambers and centrifuge tests on clayey soils. Due to the complications in modeling the piezocone test, few numerical studies have been performed in partially drained conditions, especially on coarse-grained...