Sharif Digital Repository

The low melting and solidification rates of phase change materials, which traces back to their low thermal conductivity coefficient, has led the application of these materials to face limitations. In this study, it is attempted to enhance the energy storage process in phase change materials for a complete charge-discharge cycle using a novel method called SFD-IBF. Throughout this novel technique paraffin and acetone are used as phase change material and intermediate boiling fluid, respectively. In the solidification process, there is no direct contact between the cold source and the molten paraffin, while acetone, as an intermediate fluid, is being boiled via adsorbing paraffin’s heat and... 

Humanoid robots are robots that are similar in appearance and performance to humans. Designing and controlling a humanoid robot to perform such supposedly ordinary tasks as walking, running, writing, talking, driving, riding bikes, and the like is such a difficult task from the control point of view that it seems to be quite ambitious and inaccessible. In this thesis, the previous efforts of scientists and researchers are presented using different intelligent controllers. Additionally, the dynamic analysis of selective biped (seven-link biped robot) is illustrated. In this research, we present a method to control the walking of the biped robot while retaining stability. In this method the... 

Due to the increasing spread of metal industries and the need for raw material as feed for electric furnaces in order to produce cast iron and steel, as well as scrap deficiency and rising prices, the use of sponge iron as a substitute for scrap was considered in this project Therefore, in order to achieve the chemical analysis of the sorel ingot that is special for spherical graphite cast iron production with low manganese and chromium content, the direct reduction process was carried out using tunnel kiln method on low-manganese iron ore concentrate.After the investigation on direct reduction parameters including the saggers and coal grading,the produced sponge iron has melted in... 

The visible growth in usage of computer networks in daily human life has significantly increased the importance of their correct and flawless operation. Various solutions have been offered to evaluate the operation correctness of network equipment. One of the most important issues in this context is evaluating the performance of such equipment. Due to the increase in speed of network ports, design and implementation of performance evaluation tools have become a challenging issue in terms of parameters such as speed, time accuracy, power consumption and cost. In this thesis, a hardware-based system for testing network equipment with 10 Gbps ports has been designed and implemented. This system... 

Punctuation marks in every language, constitute an important part of a text. Not inserting these punctuations in text, makes the text ambiguous. The output text of automatic speech recognition (ASR) system, is typically a raw sequence of words, containing no punctuation marks. This makes the text difficult or even impossible to make sense of for humans, as well as for any further text processing tasks. The goal of this thesis is to perform automatic punctuation insertion in Persian texts lacking punctuation marks. To the best of our knowledge, this is the first work done in this context for the Persian language. For this purpose, firstly, we assembled a state-of-the-art corpus to train and... 

Payload Attribution Systems (PAS) are one of the most important tools of network forensics for detecting offenders and victims after the occurrence of a cybercrime. A PAS stores the network traffic history in order to detect the source and destination pair of a certain data stream in case a malicious activity occurs on the network. The huge volume of information that is daily transferred in the network means that the data stored by a PAS must be as compact and concise as possible. Moreover, the investigation of this large volume of data for a malicious data stream must be handled within a reasonable time. For this purpose, several techniques based on storing a digest of traffic using Bloom... 

These days, the heat transfer phenomena is an important issue in internal combustion engines design because of direct effects on the performance, efficiency and emission of engine. One of the main parts is cylinder head which contacts with hot gases in combustion chamber and expose high heat flux. In this thesis, cylinder head of Tiba engine modeled by three dimensional and transient thermal analysis. In this modeling in order to consideration the effect of fluid flow, different domain of cylinder head (water jacket, intake/exhaust ports) has been simulated and appended to the model. Also combustion phenomena modeled separately, and then the heat transfer coefficient in the surface of... 

Daily improvements in technology and exchanging important information via internet and connection networks make data and connection security a significant problem. Cryptology is the branch of knowledge which concerns secret communications in all of its aspects. Two major areas of cryptology are cryptography and cryptanalysis. Cryptography is a branch of cryptology concerned with protecting communications from being read by unauthorized people.
Cryptologists design and create algorithms to improve cryptography along with finding methods to crack those algorithms. Cryptanalysis is a branch of cryptology concerned with cracking the cryptographic systems used by others.
Cryptographic... 

Following dramatic changes after using deep learning method as a solution for Natural Language Processing tasks, Transformer architecture get popular. Based on that, then BERT Language model presented and get state-of-the-art as a solution for a lot of language processing tasks. It was a turning point in Natural Language Processing field. Also, in cross-lingual methods research line motivated by developing a common space for representation of language units, e.g. words, sentences, in more that one language, get some remarkable improvements. However, for languages distant from English such as Persian or Arabic the methods' performance was not clear. In this work, we performed some innovative... 

From 1384 to 1395, the labor market in Iran has experienced a mysterious behavior in total number of employment, which we call it puzzle of jobless growth and growthless employment. By studying only the net changes in total number of employment, some important information neglected in explaining this phenomenon. To this end, it is common in labor economics to use dynamic labor market indicators such as job flows and labor flows. In this research, we first calculate labor flows from 1384 to 1395 and job flows from 1382 to 1392 by economic sector, firm size, job classification, occupational insurance coverage, gender and job type. Then the following question will be answered: Is the... 

Routers play a key role in transferring information between various Networks. It is very important to make sure about the compatibility of OSPF in a router with its standard description. In this regard, before presenting or applying a router and also evaluating its performance, it is necessary to carry out conformance test with the help of network equipment testers Tester designers extract test cases from protocol standard description through non-formal ways and exam them on network equipment.
In this thesis, a part of OSFP protocol has been modeled through colored Petri nets. In this regard, two sections of OSPF RFC have been model checked: neighbor state machine and data base... 

Cardio Vascular Diseases (CVD) is currently the most important cause of mortality in the world. Coronary artery disease (CAD-with 3 major epicardial vessels) is one of the significant CVD. Coronary angiography remains the gold standard for identifying the presence and absence of stenosis due to CAD. It is performed by inserting a catheter into the coronary artery, directly injecting radiopaque contrast material there and recording radiographic images in different view of arteries. Images of this invasive way show severity and area of stenosis.
A sign of CAD is endothelial dysfunction (inner artery layer) in peripheral arteries like the brachial artery. Due to a significant correlation... 

By expansion of urban areas and increasing in number of vehicles commuting, tunnels are one of the most inevitable part for developing urban areas. Nevertheless, one of the important topics about tunnels is exhaustion of polluted air into its surroundings. Tohid Tunnel, stretching about 2136 meter, is currently the longest urban tunnel in Iran, connecting Chamran and Navvab Highway from north of Fatemi street, to the Shokufeh street. Now, exhausting pollutants is done only by north and south portals beside a middle shaft. The purpose of this project is to analyze pollutant dispersion from south portal of Tohid tunnel which is located in Navvab residential region. This is done by considering... 

Energy crisis is one of the crises which human beings face these days. Optimizing the operation of energy consuming machines is one of the most effective methods in decreasing energy consumption. Gasoline direct injection engines as new achievements in automobile and propulsion industry, reduce fuel consumption by increasing the engine efficiency. In these types of engines, a high pressure injector injects fuel directly into the combustion chamber instead of injecting fuel in intake ports. Thus, because of evaporation cooling, the mixture cools down, so the possibility of achieving higher compression ratios in higher engine speeds and loads, without occurrence of knock is provided. Increase... 

Porous medium is a material consisting of a solid matrix with an interconnected void. A polymer is a large molecule composed of many repeated subunits, known as monomers; Polyurethane is a type of polymer which has many uses. The aim of this research project is to investigate the effective factors in polyurethane polymer injection and the behavior of this material during the foaming in cavities with different soil porosities (0.15 < φ < 0.4). Parameters such as thermal boundary conditions and the soil material that could be effective in solidification of polyurethane are analyzed, numerically using FLUENT software. A simplified model for foaming is presented in this study which can be used... 

Wireless sensor networks (WSNs) are composed of many independent spatially-distributed sensor nodes where communicate their information acquired from environment to shape a uniform view of their managed scope. Using WSNs in places which human can hardly attend uninterruptedly, as well as constraints such as low power consumption, low price, small size, and limited radio range, are the biggest challenges for researchers and WSN designers. Supplying security is yet another common challenge of using these networks. The beginning chapters of this dissertation introduce the most important security mechanisms in WSNs, that is, key management and cryptography. Since each application has its own... 

The main objective of this study is a numerical simulation of flow and mixing behavior of two miscible liquids in a new static mixer over the Reynolds number in the range of 20-160. The performance of the proposed static mixer has been compared with the well-known three different static mixers namely, Kenics, SMX, and Komax. Pressure drop ratio (Z-factor), a coefficient of variation (CoV) and extensional efficiency (α) characteristics were, respectively, used to evaluate power consumption, distributive mixing and dispersive mixing performances in all static mixers. Since there are no experimental data for examined mixers, firstly, the CFD model was validated with measured data of the... 

Auction is one of the most important and oldest institutions in economics, enabling resource allocation and trade of goods in the economy. Investigating the effects of changes in reservation price in auctions is an important question in auction theory research. In this study, focusing on a policy implemented by Yektanet, which involved altering the reservation price in auctions for advertising slots, we assessed its impact on advertiser costs. The implemented policy led to the activation of two distinct mechanisms, resulting in conflicting effects on the company's revenue. The first mechanism involved an increase in bid and intensified competition for ad placements on average, while the... 

The Yazd province is located in the dry and desert region of Iran and is constantly exposed to strong winds and dust storms due to its climatic conditions and geographical location. The first objective of this thesis is to assess the dust storm events that have occurred in Yazd province in order to identify their source and pathways of transport during the long-term period of 2012-2019. A novel multi-criteria framework for identifying the sources of dust storms and dust events in Yazd province has been presented using the HYSPLIT model. In this framework, the numerical results, along with geographical features, observational and satellite data, were used as criteria in the multi-criteria... 

In this study, Al-TiO2 composites layer were produced on Al 1100 substrate using friction stir processing technique. The variation of process parameters such as tool rotational and substrate advancing speed as well as number of FSP passes were adjusted to achieve quite uniform dispersion of Nano-particles in the Al matrix of the fabricated surface layer. Microstructural observations were carried out using optical and scanning electron microscopes. By increasing the FSP passes, uniform distribution of TiO2 particles in the matrix improved. Surface composition layer exhibited a micro-hardness value of 49 HV which was around twice of the as-received substrate. In addition wear resistance of...