Sharif Digital Repository

Recent advancements in technology and the growing human demand for energy have driven researchers towards developing new methods for energy storage and transfer. Lithium-ion batteries are among the most crucial technologies used in this field, requiring heat dissipation for proper operation. When using these batteries, in addition to keeping the maximum temperature within an acceptable range, the maximum temperature difference is also important and must be considered. Given the suitable ability of phase change materials (PCMs) in controlling temperature uniformity, many researchers have explored hybrid battery cooling systems that combine PCMs with other cooling methods. In the current... 

Membrane processes are accounted as the newest technology for gas separation and nowadays are more applicable in different petroleum, gas and petrochemical industries because of abundant advantages. One of important application of membrane gas separation technology is syngas adjustment and hydrogen enrichment. In this research, the appropriate alumina nanocomposite membranes for this purpose are prepared and their gas separation performance is investigated. Therefore the mixed matrix membranes, containing the continues polymeric phase polyethersulfone and dispersed phase alumina nanoparticles is synthesized by using methods of experimental design. As the best of our knowledge, there is no... 

Partial oxidation of methane (POX) is one of the most common processes to produce synthesis gas. In this study the kinetics of this process is examined and some reduced mechanisms are introduced to model it in this study. The experimental data from Research Institute of Petroleum Industry are used as reference experimental data. Inlets of this reactor are oxygen and methane with equivalence ratio between 2.53 and 2.9. Moreover, the experimental results of previous studies with the air as the oxidant in equivalence ration between 2.4 and 2.6 are used as basis for comparison of simulation results. During the first step, partial oxidation of methane in non-catalytic porous media is simulated by... 

The fabrication of potassium sodium niobate piezoceramic with oriented microstructure and study of its piezoelectric properties is one of the main objectives of the present study. For this purpose, first the raw materials were synthesized. solid state reaction and topochemical reaction were used for the synthesis of potassium sodium niobate and sodium niobate respectively. The X-ray diffraction results determined that the powder synthesized by the solid state method in the binary system KNbO3-NaNbO3 is closer to the morphotropic phase boundary compared to the powder synthesized in the ternary system Na2CO3-K2CO3-Nb2O5. Particles morphology also includes coarse cubic shape and small equiaxed... 

Sensor Networks are set of devices which are distributed throughout an environment and are connected to each other, usually wirelessly, to collect environmental information including temperature, aire pressure, moist, pollution and physiological functions of the human body. Each device consists of a microprocessor, converter and power supply, transmitter and a receiver. In this study we intend to investigate such setup and the measured signals assuming they are sparse. A sparse signal is a discrete time signal most of indices of which are equal to zero. With this assumption at hand, we will be able to reduce the sampling rate and take advantage of sparse signal processing techniques. This... 

High-quality online services demand reliable and fast packet delivery at the network layer. However, clear evidence documents the existence of compromised routers in the ISP and enterprise networks, threatening network availability and reliability. A compromised router can stealthily drop, modify, inject, or delay packets in the forwarding path to launch Denial-of-Service, surveillance, man-in-the-middle attacks, etc. So researches tried to create intrusion detection methods to identify adversarial routers and switches. To this end, data-plane fault localization (FL) aims to identify faulty links and is an effective means of achieving high network availability. FL protocols use... 

Confining nematic liquid crystal between two curved boundary conditions while the nematic molecules have a degenerate planar anchoring leads to complex and beautiful textures of molecular disparagement(defect) in the bulk and on the surfaces. Such the liquid crystal shells are made with double-emulsion techniques in microfluidic devices have provided applications for micro-scale colloidal linkers.In this work, we have numerically minimized the elastic energy in one-constant approximation in present of Fournier’s degenerate surface potential with finite element method. The nematic shell is confined between two spherical surfaces that we have studied the final energies and their related... 

A liquid crystal is a state of matter composed of highly anisotropic building blocks. When liquid crystals are exposed to surfaces with given shapes and anchoring conditions, the orientation of their molecules gets spatially disordered and topological defects may form in the system. The interplay between liquid crystals and the geometry and topology of the colloidal particles has motivated extensive recent studies.In this thesis, we present the numerical modeling results for two faceted colloidal particles in a thermotropic nematic liquid crystal. To obtain the equilibrium nematic field with a finiteelement method, we numerically minimize the free energy of the system that based on the... 

Providing high bandwidth network infrastructures for ever increasing need of data transport is of great importance. The underling infrastructure for many communication services such as GSM/3G/4G mobile networks and Internet services is Synchronous Digital Hierarchy (SDH) optical transport systems. SDH are standardized protocols that multiplex multiple lower rate digital bit streams, such as E1 and Ethernet, and transfer them synchronously over optical fiber using lasers or LEDs. In addition to high data transfer rates, flexible network management and protection mechanisms have great importance, hence are part of SDH standards. In order to obtain flexible network architecture and protected... 

Development of Smart Grid and deployment of smart meters in large scale has raised a lot of concerns regarding customers’ privacy. Consequently, several schemes have been proposed to overcome the above mentioned issue. These schemes mainly rely on data aggregation as a method of protecting users’ privacy from the grid operators. However, the main problem with most of these schemes is the fact that they require a large amount of processing power at the meter side. This, together with the fact that smart meters don’t usually have a powerful processor, can cause the unavailability of smart meter data at the required time for operators of the grid, and at the same time disables smart meters from... 

Secure routing is a major key to service maintenance in wireless ad hoc networks. Ad hoc nature exposes the network to several types of node misbehavior or attacks. Wormhole attack is one of the most severe active attacks to mobile ad hoc networks. Noting the resource limitations in such networks, nodes may have a tendency to behave selfishly. Selfish behavior can have drastic impacts on network performance. We have proposed a Misbehavior-Tolerant Multipath Routing protocol (MTMR) which detects and punishes all types of misbehavior such as selfish behavior, wormhole, sinkhole and grey-hole attacks. The protocol utilizes a proactive approach to enforce cooperation. In addition, it uses a... 

Dynamic spectrum access with the aid of cognitive radio (CR) technology is a viable solution to spectrum scarcity. There are many military and emergency applications that require the use of cognitive radio ad-hoc networks (CRAHNs). In these net- works, nodes must first find each other in a wide spectrum and then exchange their desired data. The process of finding each other in a multichannel environment is a challenging task and is usually known as rendezvous. Since rendezvous is the first step in communication, disrupting will disable the nodes from establishing proper communication sessions. That results in a drastic degrade in the performance of the network. Therefore, it is important to... 

Spray-wall impingement is one of the phenomenon that associated in different subject such as spray cooling, combustion chamber and gas turbine. With the impingement of spray to the wall, liquid film begins to form. Wall film characteristics is still an important subject to study. Due to the various stages of liquid film formation from injection of spray till spray-wall impingement, the investigation of this phenomenon is far more complicated. This paper is meant to provide detailed data on spray-wall impingement and wall film formation physics with the help of computational analysis of OpenFOAM . A Lagrangian-Eulerian method based on discrete phase model (DPM) was employed to model...