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rashidi-mehrabadi--farid
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Effects of heat treatment on the mechanical properties of 3D-printed polylactic acid: Study of competition between crystallization and interlayer bonding
, Article Materials Today Communications ; Volume 39 , 2024 ; 23524928 (ISSN) ; Pircheraghi, G ; Rashidi Mehrabadi, N ; Eshraghi, A ; Sharif University of Technology
2024
Abstract
Fused deposition modeling (FDM) is a popular additive manufacturing technique because of its flexibility, customization, cost-effectiveness, and eco-friendliness. However, due to the layer-by-layer fabrication process and the formation of voids, the mechanical properties of printed parts are lower than other manufacturing techniques. As a solution, heat treatments can effectively mitigate additive manufacturing limitations and improve the mechanical properties of printed parts. The interlayer bonding and subsequently mechanical properties of 3D-printed PLA were affected by the competition between crystallization and chain diffusion of 3D-printed polylactic acid during the heat treatment...
Learning of Alternative Splicing from RNA-seq Data
, M.Sc. Thesis Sharif University of Technology ; Rabiee, Hamid Reza (Supervisor) ; Motahari, Abolfazl (Co-Advisor)
Abstract
We construct and analyse a computational model that predicts the outcome of alternative splicing by recognizing features in RNA sequences. The computational model can be viewed as a “splicing simulator” for a range of healthy human tissues. It takes as input a pre-mRNA sequence surrounding a possibly alternatively spliced exon and estimates the inclusion level of that exon in mature RNA, after splicing occurs. The model is trained using a supervised machine learning framework where the training examples are the alternatively spliced exons, the feature vectors are derived RNA sequences near these exons, and the targets are their corresponding splicing outcomes in healthy individuals. The...
Chromatic Sum in Graphs
, Ph.D. Dissertation Sharif University of Technology ; Mahmudian, Ebadolah (Supervisor)Investigation and Modeling of Polymer Electrolyte Membranes in PEM Fuel Cells
, M.Sc. Thesis Sharif University of Technology ; Roshandel, Ramin (Supervisor)
Abstract
Fuel cells convert the chemical energy of hydrogen and oxygen directly into the electricity. Their high efficiency and low emissions have made them a prime candidate for powering the next generation electric vehicles. Polymer electrolyte membrane is a key component of the PEM fuel cells. One of the critical problems to overcome in some PEM fuel cells is the water management because If there is not enough water, the membrane becomes dehydrated which leads to a rapid increase in ohmic resistance. On the other hand, if too much water is present, flooding may occur resulting in the pores of the gas diffusion filled by water and the available passage for reactant gases is decreased. In this work...
Actuator/sensor modeling for vibration of FGM solid circular plate using Reissner-Mindlin plate theory
, Article ZAMM Zeitschrift fur Angewandte Mathematik und Mechanik ; Volume 90, Issue 4 , 2010 , Pages 287-308 ; 00442267 (ISSN) ; Kargarnovin, M. H ; Najafizadeh, M. M ; Sharif University of Technology
2010
Abstract
In this paper, the vibration of a constant thickness circular plate made of functionally graded material (FGM) is controlled by implementing two piezoelectric layers as a sensor and an actuator. Assuming that the material properties of FGM plate vary only in the thickness direction according to the power law manner, the governing differential equations are derived based on the Reissner-Mindlin plate theory (RMPT). Moreover, in a parallel work another set of differential equations are also derived using classical plate theory (CPT). Then for two different kinds of plate boundary conditions these coupled differential equations are solved using separation of variable technique and obtained...
Free vibration analysis of functionally graded coupled circular plate with piezoelectric layers
, Article Journal of Mechanical Science and Technology ; Volume 23, Issue 8 , 2009 , Pages 2008-2021 ; 1738494X (ISSN) ; Kargarnovin, M. H ; Najafizadeh, M. M ; Sharif University of Technology
2009
Abstract
Based on classical plate theory (CLPT), free vibration analysis of a circular plate composed of functionally graded material (FGM) with its upper and lower surfaces bounded by two piezoelectric layers was performed. Assuming that the material properties vary in a power law manner within the thickness of the plate the governing differential equations are derived. The distribution of electric potential along the thickness direction in piezoelectric layers is considered to vary quadratically such that the Maxwell static electricity equation is satisfied. Then these equations are solved analytically for two different boundary conditions, namely clamped and simply supported edges. The validity of...
Model Based Testing in Software Product Line
, M.Sc. Thesis Sharif University of Technology ; Mirian-Hosseinabadi, Hassan (Supervisor)
Abstract
Software product line (SPL) engineering offers several advantages such as reduced costs, high quality and less time to market in development of family of software products. The goal of software product line is systematic and effective development of a set of software products which share common and managed set of features. Software product line testing has its special challenges such as scalability and variability, and has significant importance due to the importance of quality in software product line and enormous number of possible products. Most of the popular methods in this domain have shortcomings such as having seam between development and testing processes, limited application scope...
Throughput Analysis in Multi Hop Cellular Networks
, M.Sc. Thesis Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
OFDMA multi-hop cellular network (MCN) is the topic of a wide range of research today. In this thesis, we analyse this type of networks, regarding shadowing status, mobility patterns and different service requirements. In the multi-hop (MH) scenario, six fixed relays are set up in each cell, which split the cell into seven subcells. For mobility modeling, each subcell is split into several sub-regions. Mobile nodes are able to maintain at each sub-region with a random time distribution and migrate from it to one of its neighboring sub-regions. We also consider three types of services requiring specific number of subcarriers with specific BERs. The set of subcarriers is distributed among...
Throughput Analysis of a Cognitive Multi-hop Wireless Network Overlaid on a Cellular Network
, M.Sc. Thesis Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
In this thesis, we evaluate the maximum stable throughput of a cognitive multi-hop IEEE 802.11-based WLAN overlaid on a cellular network. In the considered scenario, the secondary users operate in the downlink or uplink frequency band of primary network and transmit their data in free primary channels using OFDM technique. The activity of primary nodes is modeled independently by ON-OFF alternating states. To model the scenario, each secondary user is modeled with an open queueing network. The queueing network can model the transmission of data as well as the effect of primary users. By writing the traffic equations of the queueing network and applying the stability conditions, we are able...
Analysis of the Effect of Frame Aggregation in IEEE 802.11 Standard
, M.Sc. Thesis Sharif University of Technology ; Ashtiyani, Farid (Supervisor)
Abstract
In this thesis the effect of frame aggregation mechanism in maximizing throughput in Wireless Local Area Networks (WLANs) have been investigated. Frame aggregation has become a part of the IEEE 802.11 standard as the amendment IEEE 802.11n. First, we have a quick review on access control layer in IEEE 802.11 standard then illustrate the necessity of frame aggregation. Afterwards, we propose an analytical model for the analysis of an IEEE 802.11n network comprised of an Access Point (AP) and several conventional nodes, all in the coverage area of each other. This analytical model focuses on downlink throughput; therefore only AP uses frame aggregation and the other nodes use basic IEEE 802.11...
Network Coding-based Packet Relaying in Wireless Networks
, M.Sc. Thesis Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
In this thesis, we propose two new network coding-based packet relaying schemes suitable for multiple unicast scenarios in a random access network. In such networks the channels may have memory dependent upon the random access scheme. Thus, the optimal scheme for memoryless channels reported recently in the literature is not necessarily optimal in random access networks. In our proposed schemes, we convert a multiple unicast scenario to a combination of multiple anycast and a few multicast scenarios. By such an approach, we exploit the channels between relay node and the other nodes, instead of using only one channel at each packet transmission, for as many as possible. By simple analytical...
Content Distribution Service Analysis in Vehicular Ad-Hoc Networks
, M.Sc. Thesis Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
Car accident damages take about 7 percent of GPD of Iran every year. As a result of car accidents, the economy of the country is damaging irreparably. The amount of road casualties equals casualties in a complete war. Considering the aforementioned conditions, the researchers are thinking about new technologies to reduce the cost of the accidents. So the use of Vehicular ad-hoc Networks (VANET) is inevitable in the near future. Content distribution service is one of the emerging services of VANETs. This service is used in both safety and comfort related applications. Content distribution describes delivery of media content such as Video, Audio, Image, Text, Software, and Video Games over...
Performance Analysis of Cognitive Radio Networks With Capability of Spectrum Mobility
, M.Sc. Thesis Sharif University of Technology ; Ashtinani, Farid (Supervisor)
Abstract
In cognitive radio networks, secondary users try to use empty channels that primary users provide for transmitting data. First, the secondary users sense the target channels. If the selected channel is empty, they send their data. When the primary user returns, the secondary user has to find another empty channel for transmitting data. The process of changing channel is called hand off. In recent years, there are challenges in the spectrum mobility of for reducing delay time of secondary users packet. In this thesis, we assume that the secondary users network is an ad-hoc network. We use contestation based method for reducing collision between secondary users. In this thesis, we present an...
Energy Harvesting in Wireless Communication Networks
, Ph.D. Dissertation Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
In this dissertation, we focus on two types of EH cooperative networks. In the first type, the source and relay nodes access a shared channel according to a random access protocol. Also, they harvest energy from non-RF environmental resources. The relay node has data and energy buffers to store the packets of the source and the harvested energy, respectively. Our main goal is to find the optimal relaying protocol at the relay node. In this regard, the first type of the EH cooperative networks are investigated in two different scenarios. In the first one, the MAC channels of the nodes are independent of the applied policy at the relay node, and thus the throughput of the network is fixed....
Analysis of Age of Information in Multisource Communication Networks
, M.Sc. Thesis Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
In this thesis, we investigate the age of information in multisource networks. To this end, in the first phase of this thesis, we evaluate the Age of Information (AoI) in slotted ALOHA network. Regarding the interactions among the nodes in such a network, we model the memory of this network with a Trellis and find the peak Age of Information (PAoI) by using this Trellis. Then, we evaluate Age of Information-constrained regions and achievable throughput regions in the slotted ALOHA network and optimize Age of information in a symmetric case. In the second phase, we propose an efficient prioritizing scheme from AoI point of view and find the distribution of AoI and PAoI in such a scheme with...
Cooperative Networks from the MAC Layer Viewpoint
, Ph.D. Dissertation Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
Cooperative networks have attracted much attention in the last decade. Being introduced to mitigate the inefficiencies in the physical layer, cooperation can also be beneficial in upper layers, such as MAC layer. Using cooperative communications is specifically more challenging in the random access networks, where collision is a main concern. Delay, as one of the main performance metrics in random access networks, can decrease significantly by using cooperative communications. Transmission delay, i.e., the required time for delivering one packet form its source to destination, is an important metric in many communication networks, such as the networks in which each node generates and...
Latency Analysis and Improvement in Distributed Storage Systems
, M.Sc. Thesis Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
Today, with the proliferation of smart devices and the advent of various innovative applications, there has been an exponential surge in the number of users in telecommunication networks. Consequently, the data traffic rate is escalating considerably. This has created a major predicament for wireless networks due to the limited frequency spectrum. Therefore, the conventional centralized architecture makes it difficult for the network to address these numerous simultaneous requests. This issue can be solved by designing new architectures. In a way, network information is disseminated to the network's periphery and the contents of the primary data center are provided temporarily in closer...
Traffic Analysis in Cellular Networks based on OFDMA Access
, M.Sc. Thesis Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
OFDMA modulation method is a multiple access technique that is resistant to fading effect in cellular communication systems. In OFDMA, multiple access is performed both in time and frequency, so more users can be served with less delay than other protocols. In this thesis, based on queuing theory, we seek to present a traffic model for OFDMA system traffic analysis in single-cell mode and in the next section in multi-cell mode. Then, by examining and comparing the analytical results and the simulation results, we show that our proposed model for traffic analysis of the OFDMA system is a suitable and effective model. Also, since users in the multimedia environment need different types of...
Analysis and Reduction of the Age of Information in a Random Access Relay Network
, M.Sc. Thesis Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
In data transmission from a transmitter to a receiver, in some applications receiving updated data is crucial. To this end, a metric called Peak Age of Information has been introduced, the minimum of which is equivalent to having more updated packets. In this thesis, a method for calculating the probability distribution function of this random variable in a random access network with a transmitter, a relay, and a receiver in which the error probability of the channels between the transmitter and the relay and also the relay and the receiver is less than the error probability of the channel between the transmitter and the receiver, is proposed. The transmitter and the relay send their packets...
Modeling Dependent Requests in Caching Mechanisms and Its Effect on Delay and Age of Information
, M.Sc. Thesis Sharif University of Technology ; Ashtiani, Farid (Supervisor)
Abstract
In many communication scenarios, dependent requests are commonly observed, such as caching networks. In this thesis, we propose a new analytical model to examine the impact of dependent arrivals on the average response time in a simple queue with exponential service time. We examine two dependency scenarios: batch arrivals and the arrival of one customer after another with a random delay with a known distribution. To accurately model the effect of dependency between arrivals, we define redundant customers in our model to compensate for the existing dependency effects. We demonstrate the validity of our modeling approach analytically in the first scenario and through simulation in the second...