Sharif Digital Repository

Helium is a valuable substance that is widely used in industry and medicine because of its unique properties. Due to the increasing demand for helium in the global market, several helium extraction units have been launched in the world in recent years; Nevertheless, there is still a significant gap between projected global helium production capacity and demand. Today, natural gas is known as the main source of helium on the earth. The method of industrial extraction of helium from natural gas is cryogenic. Due to the low temperature of this process, relatively high power consumption is used to extract helium from natural gas. Therefore, the optimization of this process is of great... 

In the last few years, the most important problem to find a solution for the COVID-19 disease, and tests show that many factors are effective in the health and recovery of people with this disease. Therefore, scientists all over the world are looking to prevent the spread of this disease by identifying the effective factors in the recovery of corona patients and finding solutions for their health. The proposed algorithm is hybrid deep learning model CNN+GRU and appeal them to the laboratory test data from hospital. In this research, the goal is to be able to diagnose this disease in time with routine laboratory test, which consist of three main stages. In the first stage: initial... 

In the field of cancer diagnosis, particularly brain tumors, the priority is to achieve highly accurate tumor detection. Deep learning has shown remarkable potential in object detection tasks, making it a valuable tool for identifying brain tumors. We have proposed a new method for combining the strength of Faster R-CNN in detecting objects and the ability of Vision Transformer’s (Faster-VIT) ability to extract essential features. The proposed method significantly improves the accuracy and efficiency of brain tumor detection in MRI images. We have called the proposed combination Faster-VIT. To assess the effectiveness of the proposed method, we have utilized the Br35H dataset, comprising... 

Recent researches show inefficient use of frequency spectrum such that there is shortage of frequency in operation. In order to overcome this problem cognitive radio are introduced that opportunist usage of frequency band is their prominent characteristic. Problems and challenges caused by using these networks are wide and increasing. In this thesis we focus on improving resource management algorithms in cognitive radio. In this study in order to have a dynamic and efficient management in choosing reliable and quality channels, reinforcement learning algorithms are used based upon existing data and experiences. Since this tool has the learning capability and analysis in dynamic situation of... 

Moving towards a sustainable energy system in the evolving society requires the utilization of new applications like Electrical Vehicles (EVs) and integration of Renewable Energy Sources (RESs) which will make new challenges for today’s power grids. To address these challenges, it is essential for emerging demand control paradigm to not only adapt the required demand with available supply but also consider the comfort and the level of lifestyle each customer may have in practice. In this research, due to the ever-growing interconnectivity of the grids, a distributed Commodity Market (CM) framework is proposed in which intelligent agents embedded in Demand Control Entity (DCE) units in... 

Network management includes a wide range of topics such as performance, security, monitoring, debugging and so on. The network monitoring plays a vital role and can cover a wide range of network management requirements. Monitoring is the only way to know the correct network performance in accordance with the network design. In order to understand what is happening on the network and how network performance over time, the network should have a reporting system. Today, the reporting is done using network monitoring tools. In traditional networks, network monitoring is done using additional hardware which imposes high costs, complexity and also additional traffic overheads to the network. But... 

Inhencemant of automobile radiator heat performance is the purpose of this study. Radiator fin shape, coolant fluid properties and influence of nanofluid studied in this research. Plain fin, louvered fin and vortex generator fin is choosen and design. With flow simulation influence of fin shape on heat performance is studied. After that, with considering radiator coolant fluid, the effect of antifreezing on fin heat transfer is evaluated. Then by addin nanoparticles to water and antifreezing solution, effect of nanofluid on heat transfer is evaluated. Results show that with increasing the air velocity for all geometries in the study , heat transfer and pressure drop is increased. But heat... 

Heart is a muscular organ, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste to the lungs. Heart is sort of like a pump, or two pumps in one. The right side of heart receives blood from the body and pumps it to the lungs. The left side of the heart does the exact opposite: It receives blood from the lungs and pumps it out to the body. However, in end-stage heart failure, the heart can no longer pump enough blood to meet the body’s needs, in which case implantable left ventricular assist devices provide support for patients at risk of death from end-stage heart failure.Centrimag... 

Wing grids are among devices used for increasing wing performance. Wing grids decrease wing induced drag by breaking the wing main tip vortex to smaller vortices with lower turbulence intensity value. These devices are mostly used in low Reynolds regimes, and their effectiveness decreases as the Reynolds number increases. In most researches around the world, wing grids have simple design configurations, but in this research wing grids are designed in such a way that each grid has a minimum value of induced drag respectively. So, in addition to reducing baseline wing induced drag by breaking the main vortex to smaller vortices by means of wing grid, each grid has a minimum value of induced... 

In recent years, the increase of particulate matter concentration due to frequent dust storms has become one of the most important dilemmas of people around the world. The high concentration of dust particles causes irreparable respiratory diseases, premature death, economic and social damages. Because of placement in the vicinity of the main sources of dust, Iran has been severely affected by the phenomenon of dust storms and damage caused by it.In this research, two dust storms occurred in Tehran are simulated using WRF-Chem and HYSPLIT models. The first event took place on February 2, 2016, and the second event took place on May 22, 2018. In order to determine the empirical parameters of... 

Since traffic lights are the only mechanized system at street level, their operation mode affects traffic congestion. Since traffic lights organize vehicles at crossways, the target of traffic light smartification is to reduce waiting time based on the density of traffic flows. There are many topics that work in this field to recognize traffic before making any decision based on traffic. Hence, if it is possible to introduce an algorithm for change static timing and predetermined timing of the traffic lights, it can affect the density of traffic at the large scale. This dissertation introduces an algorithm to reduce traffic congestion using traffic lights and correct timing. In this case,... 

Smoke must be exhausted, as the first action, in probable fire in subways, underground transportation systems and mines in order to survive people exposed to it. To achieving this purpose, the axial fan should be used to move the smoke to the exit lines. These fans should be had same performances in suction and discharge directions (main and reverse directions). This means flow rate should be the same at main and reverse directions. Therefore, fully reversible axial flow fans should be used in emergency ventilations. The fully reversible axial flow fans have same efficiencies in suction and discharge directions. The symmetric profiles should be used in manufacturing of the blades of these... 

The use of MANETs in many areas is rapidly spreading. Due to dynamic nature,and limited energy of this networks, they are vulnerable to some attacks including blackhole attack. Blackhole attack can disrupt the commiunication between hosts and cause denial of service. One of countermeasures to this attack which has been recently proposed is the ActiveTrust. ActiveTrust is a routing protocol which relys on malicious node detection using trust calculations; this scheme has been proposed for WSNs. In this work we adopt the ActiveTrust’s idea and try to apply it into MANETs. Then we simulate the resulting proposal in NS-3 and compare the results  

Transverse Vortex-Induced Vibration(VIV) and Flow-Induced Vibration(FIV) of a rigid, circular, elastically mounted single degree of freedom cylinder is scrutinized in range 3×104≤ Re ≤12×104 by means of Computational Fluid Dynamics(CFD). ANSYS CFX, based on FV, is employed to simulate VIV and FIV in different system parameters such as stiffness and mass ratio. Firstly, the minimum structured, hexahedron computational cell required to simulate VIV and FIV by means of Finite Volume (FV) method is provided. Then, the appropriate size for computational domain to simulate VIV and FIV accurately is discussed concisely. Approximated amplitude and frequency ratio are compared to experimental data... 

Heat exchangers are one of the most important components used in liquefaction cycles and overall efficiency of the cycle mainly depends on the heat exchangers effectiveness. It has been shown that the effectiveness of these equipments should be high enough to be able to liquefy a gas. Spiral heat exchangers are used frequently in cryogenic industry and specially in Helium liquefaction industry due to their specific characteristics, however according to literature review it turns out that little study is done in the field of simulation and geometrical parameter investigation of these kind of heat exchangers, so in this study the design and simulation of these cryogenics heat exchangers are... 

Liquefaction of gases is one of the applications of cryogenic science. Among the gases, Helium has the lowest boiling point, which at a pressure of 1atm is approximately 4.2K. Liquid helium can be used to cool superconductors in transportation equipment, military radars, and medical imaging equipment. For helium liquefaction, various cycles are used; these cycles have different parameters in their structure such as of input mass fraction to expanders, heat exchanger effectiveness, expander arrangement and ... which their analysis for improving the performance of the cycle is important. In this research, the aim is to study 2, 3 and 4 expander cycle with various parameters and structure. For... 

Gas liquefaction is one of the main applications of Cryogenics science. Due to the unique properties of Helium, it is a strategic product in the world. Therefore, appropriate and applicable analysis should be used to investigate and optimize the Helium liquefaction cycles. In the current study, the goal is to find the optimal point with the help of energy and exergy analysis based on economic criterion, for the various parameters of Collins’ cycle. In order to simulate the cycle, a computer code is developed. First, sensitivity analysis of different parameters affecting the exergy efficiency and liquid fraction of the cycle has been done. Then, Artificial Neural Network and Genetic Algorithm... 

Helium is known as a strategic material due to its unique properties and applications in the development of advanced industries. Currently, natural gas is the only source from which helium can be produced economically. The United States, Qatar, Algeria, and Russia have the largest share of helium production, respectively. In this research, the process of helium extraction from natural gas and its liquefaction, independent of LNG production based on helium in South Pars gas of Iran, which is the largest helium reservoir in the world, were designed and simulated.In the helium liquefaction section, the speed and accuracy of the process simulation were improved by developing a home code based on... 

In this thesis, an identified dynamic model of a fixed wing UAV, known as WAYO, is presented. To do so, frequency domain system identification technique is utilized. Due to physical and environmental constraints, it was impossible to carry out precise flight tests of the aircraft in all flight phases. Instead, a small-sized UAV, called Twin Star-BL was selected to carry out the tests and to validate the simulation model. In both cases (WAYO and Twin Star-BL) transfer functions were obtained using frequency responses and employing extensive identification process. Identified models were then assessed using time domain data for different test records. Finally, handling qualities of both aerial... 

Introducing a new paradigm, cognitive radio, for spectrum utilization of unlicensed users, new research on spectrum utilization of licensed users was planned. The results show inefficiency of spectrum usage, so cognitive radio network was introduced. Cognitive radio network should not have any affect on primary users activity, so these networks face with some chalenges and the important ones is the supporting of the QoS.
In this thesis after analyzing of the proposed routing metrics for finding best end-to-end path, the important ones of them were selected for more precise analyzing. After analyzing we find some disadvantage, can be improved by multi-radio. Although all of these metrics...