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Experimental and Numerical Study of Multi-track Laser Cladding to Evaluate Effects of Residual Stress on Fatigue Life
, Ph.D. Dissertation Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Farrahi, Gholam Hossein (Supervisor) ; Shodja Razavi, Reza (Co-Supervisor)
Abstract
Laser cladding is a processing technique of layer-by-layer material deposition which is widely used to repair important components. However, tensile residual stresses generated in this process may result in detrimental effects such as crack, undesirable deformation and reduced fatigue life. A thermo-mechanical finite element model is developed to accurately predict residual stresses of the multiple beads laser cladding process with incorporating the cyclic plasticity into the analysis by utilizing the nonlinear kinematic hardening behavior. FE results are presented for Inconel 718, a material for which the laser cladding process is widely used. The FE results are compared with those of...
Ray Tracing Based on Reinforcement Learning
, M.Sc. Thesis Sharif University of Technology ; Moghadasi, Reza (Supervisor)
Abstract
We show that the equations of reinforcement learning and light transport simulation (rendering equation) are related integral equations. Based on this correspondence, a scheme to learn importance while sampling path space is derived. The new approach is demonstrated in a consistent ray tracing algorithm that uses reinforcement learning to progressively learn where light comes from. As using this information for importance sampling includes information about visibility, too, the number of light transport paths with non-zero contribution is dramatically increased, resulting in much less noisy images within a fixed time budget
Error Rate Analysis and Power Allocation for Cooperative Networks with Imperfect Channel State Information
, M.Sc. Thesis Sharif University of Technology ; Pakravan, Mohammad Reza (Supervisor)
Abstract
Recently, cooperative communications have gained much interest due to its ability to mitigate fading in wireless networks through achieving spatial diversity while resolving the difficulties of installing multiple antennas on small communication terminals. There have been considerable research efforts on the performance analysis of cooperative diversity. This is while most of the current works assume that perfect knowledge of the channel information is available at the destination and/or relay terminals. However, in many practical scenarios, due to the errors caused by Doppler shift or noise on the pilot signals the perfect estimation of channel coefficients is not possible. In this thesis,...
Experimental Study of Various Modes of Electrosprays for Different Liquids
, M.Sc. Thesis Sharif University of Technology ; Morad, Mohammad Reza (Supervisor)
Abstract
In the present study liquid thermophysical properties in electrospray has been studied. Other parameters such as electrical configuration do not change during this study. For this purpose Alcoholic fuels have been chosen because of their high energy density and their polarity that make them suitable for electrospraying. Electrical conductivity, surface tension, viscosity, density and permittivity are the most effective liquid properties in the electrospraying. The visualization method used for this study is shadowgraphy and light scattering method. In this study the range of flow rate and voltage is acquired for each operational mode and Q-V diagram has been obtained for all liquids...
Numerical Modeling and Experimental Investigation of the Efficiency of the Laser-assisted Machining for Ceramics
, Ph.D. Dissertation Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Shoja Razavi, Reza (Co-Supervisor)
Abstract
Laser-assisted machining is nowadays considered as an alternative to conventional machining processes including ceramics grinding, which has provided the basis for extensive experimental and numerical studies in this field. Since the main difference between laser-assisted machining and conventional machining is in the presence of lasers, the main purpose of this study was to investigate the effects of laser on the laser assisted machining process. In this regard, in the first step the process of laser heating to the ceramic workpiece has been studied experimentally and numerically by finite element method. The material used in this research is a slip cast fused silica ceramic. The...
Biosorption of Zinc Ions Using Biomasses Produced From Four Different Types of Microbes Under Batch and Continuous Conditions
, M.Sc. Thesis Sharif University of Technology ; Roostaazad, Reza (Supervisor) ; Razavi, Jalil (Supervisor)
Abstract
Biosorption capacity of zinc (II) by biomasses produced from four species of microorganism including two kinds of bacteria (Pseudomonas putida and Streptomyces rimosus) and two kinds of fungi ( Aspergillus niger and Phanerochate chrysosporium) in batch case were investigated and compared. In all cases dried original bio mass and dried pretreated bio mass with NaOH were used. In all cases biosorption capacity of pretreated biomasses were much higher than non-treated biuomasses to the ratio of 3.8 – 1.4 times. Freundlich and Langmuir equilibrium isotherms were used to match with experimental results of this research. Except S.rimosus, all others were completely matched with Langmuir...
Application of Ultrafiltration to Produce High Solid Content Yogurt
, M.Sc. Thesis Sharif University of Technology ; Roosta Azad, Reza (Supervisor) ; Razavi, Jalil (Supervisor)
Abstract
Labneh is a semisolid product that is produced by concentrating milk to approximately 23% total solids (wt/vol) by the traditional cloth bag method, ultrafiltration and direct reconstitution. For ultrafiltration membrane processing is carried out either before or immediately after fermentation. The effect of storage time on the flow properties of concentrated yogurt (labneh) was investigated using a rotational viscometer. Experiments were performed at after 0, 2, 5 and 14 days after production. The apparent viscosity of fresh sample was then measured as a function of shear rate. For a given shear rate, the apparent viscosity was measured as a function of shearing time. The increase in the...
Machine Learning Based Modeling of Cognitive Performance from Life-style Data
, M.Sc. Thesis Sharif University of Technology ; Razvan, Mohammad Reza (Supervisor) ; Khaligh Razavi, Mahdi (Supervisor)
Abstract
For neurodegenerative diseases like Multiple Sclerosis, Alzheimer’s, or Parkinson’s disease early detection is required to slow progression and prevent disease onset. To do so, identifying early signs and symptoms of the disease as well as modifying lifestyle can play a crucial role. Nowadays, the increasing use of smart gadgets and sensors has paved the way for collecting behavioral data and therefore analyzing and extracting meaningful patterns. In this study, lifestyle and cognitive performance data have been collected via a platform called OptiMind. Previous studies have shown that the Integrated Cognitive Assessment (ICA) can identify patients with neurodegenerative disorders (such as...
Modeling of Damages such as Crack, Inclusions and Areas with Variable Properties in Composite and Metal Structures and then Prediction and Extension of their Life
, M.Sc. Thesis Sharif University of Technology ; Abedian, Ali (Supervisor)
Abstract
Nowadays, some of the major problems of the airplane industry is that airplanes’ fleet are approaching to the end of their defined life, inability to buy new planes and obtaining aircraft’s parts for repairing process. Therefore, in order to increase the life of the aging aircrafts, some essential process such as modeling processes, identify principal structure elements to strengthen and repair them should be done to all these airplanes, all these processes refer as aging process. Aging programs initiated in some countries, such as America, Australia, Britain and Canada from about thirty-five years ago, technological approaches inventing new ways to start repairing worn metallic structures...
Channel Modeling and Assessment of Key Performance Indicators for Wireless Body Area Networks
, Ph.D. Dissertation Sharif University of Technology ; Jahed, Mehran (Supervisor)
Abstract
Wireless Body Area Network (WBAN) is one of the emerging technological trends that paves the way for the next generation medical systems by offering proactive wellness management and early detection of diseases. WBAN, as standardized by IEEE 802.15.6, is a network composed of intelligent, miniaturized, low power sensors that are strategically implanted in, placed on, or in close proximity to the human body. The sensors have responsibility for recording vital physiological signals and wirelessly transmitting them to a central hub for further processing. In this study, we have first investigated the applicable channel models for a typical WBAN. Considering various scenarios with different...
Capacity-outage joint analysis and optimal power allocation for wireless body area networks
, Article IEEE Systems Journal ; 2018 ; 19328184 (ISSN) ; Jahed, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
Wireless body area networks (WBANs) are characterized by short-range wireless communication between inherently resource-limited sensors that operate in the vicinity of the human body for recording certain physiological signals. One of the main limitations of WBANs is in terms of their available power. Since the nodes are typically battery-driven, an efficient power transmission is essential to guarantee long-lasting communications among nodes without the need for frequent battery replacement or charging. In this study, aiming to improve the WBAN performance, we first investigate the power allocation problem by choosing the ergodic capacity and the outage probability as the desired metrics....
Channel modeling and reliability assessment for body-centric wireless communications
, Article 2017 25th Iranian Conference on Electrical Engineering, ICEE 2017, 2 May 2017 through 4 May 2017 ; 2017 , Pages 1-7 ; 9781509059638 (ISBN) ; Jahed, M ; Sharif University of Technology
2017
Abstract
Wireless Body Area Networks (WBANs) are one of the emerging technological trends that have gained a lot of attention both from academic and industrial domains. WBAN, as standardized by IEEE 802.15.6, is a network composed of intelligent, miniaturized, low power nodes that are implanted in, placed on or in close proximity of human body for certain healthcare applications. Sensors send their acquired data to a central hub wirelessly for further processing. In this paper, based on a publicly available channel data set, we investigate the applicable channel models in a typical WBAN. Considering various scenarios with different carrier frequencies, bandwidths, body movements, and transceiver...
Node positioning and lifetime optimization for wireless body area networks
, Article IEEE Sensors Journal ; Volume 17, Issue 14 , 2017 , Pages 4647-4660 ; 1530437X (ISSN) ; Jahed, M ; Sharif University of Technology
2017
Abstract
Wireless communication networks may be categorized based on the extent of the geographical area that they cover. The latest trend in this assortment is wireless body area network (WBAN), which is standardized by IEEE 802.15.6 and is defined as a network composed of intelligent, miniaturized, low-power nodes that are implanted in, placed on, or in close proximity to the human body for certain healthcare applications. In this paper, we will start with some assessments on applicable channel models for a typical WBAN. Considering various scenarios with different carrier frequencies, bandwidths, body movements, and transceiver locations, the well-known Bayesian Information Criterion is used to...
Constrained error rate analysis for wireless body area networks
, Article IET Wireless Sensor Systems ; Volume 9, Issue 6 , 2019 , Pages 366-374 ; 20436386 (ISSN) ; Jahed, M ; Sharif University of Technology
Institution of Engineering and Technology
2019
Abstract
Wireless body area network (WBAN) is composed of miniaturised sensors that operate in the vicinity of the human body for recording the vital physiological signals and wirelessly transmitting them to a central hub for further processing. In this study, a statistical approach is applied to an experimental channel data set to extract the models for the squared channel gain that best describe the characteristics of the transmission medium between the sensors and the central hub. The derived models are then utilised to investigate the error rate performance of WBAN sensors. On the basis thereof, an optimisation problem is formed for which the cost function is the symbol error rate (SER) metric....
Semi Solid Rheocasting of A356 Aluminum Alloy by High Speed Injection
, M.Sc. Thesis Sharif University of Technology ; Ashuri, Hossein (Supervisor)
Abstract
Aluminum is the lightest industrial element after magnesium. As a result, aluminum alloys have many industrial usages because of their high specific strength. Semisolid casting is one of the processes that is capable of producing aluminum alloys with high mechanical properties. In this process, there are a wide variety of methods to prepare semisolid slurry, one of the best ways of which to produce globular structure is electromagnetic stirrer. In this research, the semisolid slurry of A356 aluminum alloy is fabricated by electromagnetic stirrer under different conditions of stirrer intensity current, stirring time and pouring temperature. Then the fabricated semisolid slurry is injected...
Capacity-outage joint analysis and optimal power allocation for wireless body area networks
, Article IEEE Systems Journal ; Volume 13, Issue 1 , 2019 , Pages 635-646 ; 19328184 (ISSN) ; Jahed, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
Wireless body area networks (WBANs) are characterized by short-range wireless communication between inherently resource-limited sensors that operate in the vicinity of the human body for recording certain physiological signals. One of the main limitations of WBANs is in terms of their available power. Since the nodes are typically battery-driven, an efficient power transmission is essential to guarantee long-lasting communications among nodes without the need for frequent battery replacement or charging. In this study, aiming to improve the WBAN performance, we first investigate the power allocation problem by choosing the ergodic capacity and the outage probability as the desired metrics....
Synthesis and Properties of Functional Super Hydrophobic TiO2
, M.Sc. Thesis Sharif University of Technology ; Dolati, Abolghasem (Supervisor)
Abstract
Titanium nano-oxide (TiO2) coatings have been used for self-cleaning, antimicrobial, and dust-proof designs. The degree of wetting of a solid surface with water in humid air depends on how the surface tension of the existing phases relates. The ratio between these tensions estimates the contact angle between a drop of water and the surface on which it is placed. A contact angle above 150 º is essential for surface overflow. In this study, 18 different combinations of titanium oxide and FAS, PDMS and PMS nanoparticles were obtained with a static contact angle of 165 to 150 º and a dynamic contact angle of 7 º.1 to 4.5 º. Following the measurement of water droplet slip speed on a sloping...
The triangular pyramid: Routing and topological properties
, Article Information Sciences ; Vol. 180, issue. 11 , 2010 , p. 2328-2339 ; ISSN: 00200255 ; Sarbazi-Azad, H ; Sharif University of Technology
2010
Abstract
In this paper, a new topology for multicomputer interconnection networks, based on triangular mesh, is proposed. The new network, referred to as the triangular pyramid (or tripy for short), has L levels of triangular mesh. We study some basic important properties of the proposed network as well as introduce a routing algorithm for the tripy network based on the routing of triangular meshes. We prove that this form of pyramidal network is Hamiltonian, Hamiltonian-connected, and pancyclic. We also prove that the proposed network is 6-colorable and conduct a brief comparison of the tripy and its traditional pyramid counterpart. Our results show that the proposed network has higher scalability,...
Symbol error rate analysis and power allocation for decode and forward relaying with channel estimation error
, Article 2012 19th International Conference on Telecommunications, , 23 April 2012 through 25 April 2012, Jounieh ; 2012 ; 9781467307475 (ISBN) ; Pakravan, M. R ; Sharif University of Technology
IEEE
2012
Abstract
In this paper we study the statistical properties of the Signal to Noise Ratio (SNR) of the dual-hop relaying link in a cooperative wireless communication system in the presence of channel estimation errors for Decode and Forward (DF) relaying protocol. Then for assessment of the system performance the Symbol Error Rate (SER) is considered. Two approaches are introduced for SER calculation from which the second one results in a closed form solution. Finally the second approach is used to find an optimum power allocation scheme for transmission of pilot and data symbols at the source and the relay terminals that results in minimizing the SER and considerable amount of power saving. Also Monte...
Study on Thermodynamics of Iodine Vapor Adsorption on Cu Nanoparticles by Different Computational Approach
, M.Sc. Thesis Sharif University of Technology ; Outokesh, Mohammad (Supervisor)
Abstract
Iodine isotopes are among the most significant medical radioisotopes with a wide range of applications in therapy and diagnosis. The I-131 isotope is usually synthesized by irradiation of natural tellurium in atomic reactors. But there is an alternative route in which this isotopes is produced along with two other significant medical radioisotopes (i.e. Mo-99, Xe-131) by neutronic irradiation of uranium in the reactors. To separate iodine isotopes especially in the extraction process of fission fragments, it is necessary to be selective adsorption of iodine on a selective adsorbent. One of the most selective adsorbent for this application is copper. The aim of this study is to compare the...