Sharif Digital Repository

Classical continuum mechanics fails to give an accurate solution near the crack tip, moreover, it implies that a solid is able to sustain an infinite stress at the Griffith-Inglis crack tips. Among other critical issues is the inability of classical approach to sense the size effect. For these reasons, for more in-depth understanding and accurate behavioral predictions, it is essential to develop some atomistic methods which properly accounts, not only for the structure but also the long and short range atomic interactions effectively. In this work the interaction of coated inhomogeneity and crack under polynomial loading is simulated by using the many body Rafii-Tabar and Sutton potential... 

Meshless Methods using kernel approximation like Reproducing Kernel Particle Method (RKPM) are methods for solving partial differential equations that require only nodal data and a description of the geometry without requiring element connectivity data and mesh producing. An innovative method of nonplanar material partitioning method (NMPM) with implementation of RKPM is employed to calculate the stress intensity factor (SIF) at the tip of an anticrack sited in an isotropic plate under a remote applied loading. Numerical examples in comparison with the exact closed form expressions show that accurate SIF for mode I can be obtained.

 

Nowadays, the excellent technological applications of composites have attracted the attentions of industry and numerous scientists. They are advantageous for their high tensile modulus, strength, and promising electrical and thermal properties. In applying the approach of lamellar inhomogeneity to real composites, the micro-geometries of the reinforcement must be considered such that they can be approximated as limiting case of an ellipsoid. In vapor grown carbon nanofiber, the fiber may have a diameter of about 150nm and length of 10-20 µm [1]. The modulus of carbon nanofiber is normally in the range of 100-600 GPa and sometimes even higher, whereas the modulus of some polymers is usually... 

A brief overview of the proposed research, its aims, engineering relevance and applications Underground space has long been exploited through the history to fulfill different human necessities. Underground facilities built in areas subject to earthquake activity must withstand both seismic and static loads. Some underground structures have experienced significant damage in recent large earthquakes. Tehran is located in seismic zone and investigation and research on the subject has significant role in design and construction of underground spaces for earthquake loads. Underground structures are complex structures which consist of different parts Such as passage way and platform space. Passage... 

Recently, considerable efforts have been devoted to evaluation of seismic dynamic response of a circular tunnel. Conventional approaches have considered integral liners embedded in an elastic medium. In this study, we model a circular tunnel driven by TMB in homogeneous soil. Tunnel lining with 6 pieces of segments is analyzed by software in three dimensions. The results demonstrate that the stiffness difference between the segment and joints can enhance the internal forces of the segment significantly, which is crucial for the design of segments. The design of tunnel segment joints and joints between tunnels and portal structures are investigated by comparing with different parameters of... 

With the popular choice of using underground structures and tunnel in big cities and with significant damage in recent large earthquake; therefore more attention is given to the behavior of the underground structure in seismic area. The purpose of this thesis is to present the Soil-Tunnel-Structure Interaction analysis performed for different dynamic load condition. Therefore we modeled a 3D intersection part of two different tunnels in homogeneous soil by ABAQUS software. The soil and concrete structure of tunnel is modeled by three dimensional solid finite elements and the boundary of soil is modeled by three dimensional infinite elements with 8 nodes. The results demonstrate the geostatic... 

Quality of Experience (QoE) indicates the overall quality of one service such as Voice over IP (VoIP) from users' point of view by considering several systems, human, and contextual factors. QoE measurement and prediction are more challenging than Quality of Service (QoS) which is only related to network parameters. There exist various objective and subjective methods for QoE prediction. This research investigates various features affecting QoE by proposing a comprehensive subjective evaluation by employing a large number of users. We show that many unconsidered factors including speaker specifications and signal properties, such as signal-to-noise ratio (SNR), can affect QoE so that the SNR... 

Frequently using Personal Identification Information has escalated the security concerns of bank accounts, emails, daily transactions, and other activities. Therefore, user access to such apps must be controlled. Traditional personal verification methods offer limited security because they might need to be remembered or stolen. Therefore, Biometric authentication, which identifies persons by their unique biological information, is gaining popularity. However, palm vein identification is highly secure because the vein patterns are not duplicated in other people, even in monozygotic twins. Moreover, it has a liveness detection and is convenient since the vein pattern cannot be faked,... 

Coming to the generation of technology, where everything is possible through the Internet contributes a significant proportion to privacy protection. Several Privacy protection technologies have been launched to maintain the confidentiality of user information. Tor, also known as an Onion Router, is indeed the largest global anonymized network technology, including over 7000 distinct domain controller endpoints located all over the globe. Various kinds of wrongdoings are increasing day by day such as terrorism, abuse of the child is increasing using the network. To stop this monitoring plan is needed to develop. To enable this all the hacking mechanisms along with the architecture were... 

Iris segmentation is an essential step in a medical imaging-based automated diagnosis system. The operation of dividing a digital image into areas with different characteristics and setting objectives is known as image segmentation. The extraction of the iris from unnecessary sections of the image is very important for any biometric device. Eyelid / eyelash obstruction, special reflections, intensity heterogeneity, and an irregular iris border, are considered as noise which affect the iris segmentation process. Focusing on Fuzzy C-Means (FCM) clustering and Grasshopper Optimization Algorithm (GOA), we present a new and efficient method for dividing iris-filled, annoying, and iris limits that... 

Simulation of biophysical neural networks enables the interpretation and integration of fast-growing and different experimental datasets. The widely used NEURON simulator allows molecular-to-network simulation. However, it is still a very hard challenge to create large-scale models and operate parallel simulations applying NEURON. SUNY Downstate developed the NetPyNE means networks using Python and NEURON, which was funded by the New York State Department of Health and some other institutions. NetPyNE is a Python-based tool that enables the development of data-driven multi-scale network models in NEURON through both programmatic and graphical interfaces. It is a powerful tool for parallel... 

Today, with the development of technology, cyberattacks are on the rise. Personal and corporate computer systems can be exposed to various threats and dangers of hackers and malware, including information theft, forgery, and denial of service, which can cause great material and moral damage to individuals and organizations. So, it is necessary to take security measures in this regard. Many security mechanisms are available to prevent security vulnerabilities against various threats. In this study, first, after carefully studying network attacks, we identify the criteria for identifying attacks that can be executed in network traffic and explain how to calculate them. The current research... 

Classification of Traffic Internet obtained early interest in the computer science community. Various methods have been presented for classifying the traffic of Internet to manage both security and Quality of Service (QoS). Nonetheless, traditional methods of classification including scheme of Transmission Control Protocol/Internet Protocol (TCP/IP) have not been accepted because of their complicated management. Classification method of network through learning algorithms of machine is the most popular classification method of traffic at this time. ELM was proposed as a modern algorithm of learning for the Single-hidden Layer Feed Forward Neural Networks (SLFNs). Meanwhile, learning process... 

Flash Crowd traffic generation can be used as a metrics for measuring the resiliency and performance of a server. Also, it can provide a framework for verification and test of Intrusion detection systems (IDS) and Intrusion protection systems (IPS). Common traffic generation methods mimic timing and content of input traffic or regenerate input traffic by extracting its statistic distribution. So all of them need input traffic, while properties of Flash Crowd are different in the various servers and situations and there is no guaranty in existence of such samples of traffic for all servers. In this thesis, we introduce and use a new method for traffic generation without the need for input... 

With the expansion of network equipment including routers and wireless modems, these equipment have become more susceptible to backdoors and hacker attacks. One way to cause troubles to these systems is through backdoor insertion. Recently, several attacks via backdoor insertions have been reported by some of the major router companies. In this project, a complete description of routers, ways of intrusion to routers and how to change settings in routers in order to measure traffic intensity are explained. In this thesis we manually setup a backdoor in a router in order to observe its effects on local networks. Furthermore, we purposely attack a router in order to find the followings: 1. Ways... 

Today Ethernet is the predominant technology for implementing Local Area Networks. Its privileges encourage service providers to extend Ethernet from Local Area Networks to Metropolitan Area Networks or even Wide Area Networks. Ethernet benefits such as low operational costs, well interoperability, plug-n-paly characteristic and rapid provisioning on demand make Ethernet ideal for Metropolitan Area Networks.But Ethernet by itself has some weakness like flat structure that makes it unfit for use in Metropolitan Area Networks. A suitable solution for taking advantages of Ethernet benefits in service provider network is using Ethernet in access network and applying multi-point to multi-point... 

The 60 GHz high speed technology, is the interesting category in network world nowadays. In this study, we consider one of the 60 GHz technologies as it is called WiGig. WiGig works under IEEE802.11ad standard, one of the WLAN standards that works at 60 GHz frequency band. We have surveyed the total MAC and physical layer of this standard to find the way to enhance the MAC protocol. This MAC protocol is applying the CSMA/CA and TDMA methods to access the channel. We have applied the CSMA/CA in our thesis that is a contention based access method. We found that with this method our network is not fair. Since there are not any studies about the value of Fairness in this standard, we... 

Today road accidents take the lives of millions of people on a yearly basis through the world. Also, numerous attempts have been proposed to increase safety on the roads. Vehicular Ad hoc Network (VANET) is a subclass of mobile ad hoc networks (MANET); the main goal of which is to increase the safety and efficiency of road traffics and trips. However, like other networks, routing protocols are one of the most important parts of VANET. But, due to the unique characteristics of VANET (high mobility, short radio coverage area, etc.), the process of data dissemination is a more challenging task than other networks. Therefore, the need for efficient, reliable and safe routing protocols which can... 

Deduplication is a data reduction technique, which eliminates redundant data by storing only a single copy of each file or block, along with a reference to the unique copy of data. Deduplication reduces the storage space and bandwidth requirements of data storage systems, and becomes more effective when applied across multiple users. All deduplication techniques use cryptographic algorithms to detect duplication instead of byte-by-byte comparison between input data and all previously stored data. In this manner, the data stream is divided into non-overlapping chunks of data. Then, the hash values of non-overlapping chunks create an exclusive criterion to identify duplicates. In this thesis,... 

There are several applications of wireless sensor networks wherein the data collected by the sensors in the network are critical and hence have to be reliably transported to the sink, example of such applications are fire detection in a forest or controlling vibration on body of dam. Reliable communication in wireless sensor networks is hard to achieve efficiently using methods in conventional systems like Internet. End-to-end retransmission is inefficient, or in some cases impossible. It is well-known that Reed-Solomon codes may be used to provide error correction for multiple failures in RAID-like systems. To the coding theorists, this technique is a straight forward extension to a basic...