Sharif Digital Repository

In this study, a novel multiscale analysis is proposed to utilize atomistic properties of crystalline nano-materials as an input to continuum problems in the range of large deformation. The main purpose of presented work is investigating the capability of different hyperelasticity models based on molecular statics (MS) and molecular dynamics methods to attain proper hyperelastic strain energy density function to illustrate atomistic information under various types of deformation loadings. Also, the proficiency of hyperelastic model is investigated for nano-structure including different percentages of voids. The material parameters of hyperelastic strain energy density can be obtained from... 

Block ciphers are one of the most necessary primitives for security protocols, and so, cryptanalysis of them is also essential as well. On the other hand, the security assessment of block ciphers is usually manual work with various specific-idea according to the target block cipher type and algorithm. Some basic known methods for cryptanalysis of block ciphers include linear, differential, meet in the middle, and integral attacks. However, cryptanalysis methods are not limited to them, and many new hybrid or innovative methods are employed to provide better results. Recently, automated cryptanalysis of block ciphers and proposing new methods for analyzes of these ciphers are in the... 

Telecommunications operators look forward to network virtualization to reduce capital and operational expenditures. Optimal performance of the virtualized networks requires efficient resource allocation. On the other hand, in recent years, traffic growth and its dynamic behavior are two main drivers for the development of elastic optical networks. In this research, the problem of resource allocation for virtualized network function requests over an elastic optical network is investigated. Due to the high cost of energy consumption, energy efficiency is considered as the objective of the resource allocation problem. Conventional pure static and dynamic solutions are not suitable for efficient... 

Ferrofluids are special stable suspensions of magnetic nanoparticles dispersed in liquid phase. These materials have numerous biological applications such as drug delivery, magnetic hyperthermia and magnetic resonance imaging due to their special magnetic properties and fluidity. Particle size and magnetic properties of ferrofluids have an important role in these applications. In this work, magnetite-based ferrofluids have been synthesized via coprecipitation and hydrothermal methods. In the coprecipitation process, cysteine and dextran surfactants have been used as ferrofluid stabilizer and effect of synthesize temperature, time, pH and surfactant concentration have been investigated on... 

Single floor facility layout problem (FLP) is related to finding the arrangement of a given number of departments within a facility; in multi-floor FLP, the departments should be imbedded on some floors which are inside the facility. The significant influence of layout design on effectiveness of any organization has made FLP an important issue. This paper presents a three (two) stage mathematical programming method to find competitive solutions for multi (single) floor problems. The first stage assigns the departments to the floors by using a mixed integer programming model (the single floor version does not require this stage). The second stage uses a nonlinear programming model to specify... 

Along with the proliferation of pervasive systems such as RFID systems and sensor networks, the demand for the low-cost, secure-enough primitives has continued to rise. Symmetric-key algorithms especially block ciphers still play an important role as secure ciphers that can be also consistent with the inherent restrictions of pervasive systems. Recently, a lot of block ciphers tailored for these conditions have been designed, such as Present, PrintCipher, Piccolo, and Twine. Biclique attack introduced in AsiaCrypt 2011 is the first and the only method that could break all versions of AES faster than brute-force attack in the single key model. Afterwards, the efficiency of this attack on some... 

With the continuous development of networks and communication technologies, security evaluation of cryptographic primitives, including block ciphers, which serve as the foundation for securing numerous communication protocols in these networks and technologies, has become more crucial than ever before. Inadequate security at block ciphers endures a risk to the overall security architecture of a system. Therefore, significant attention has been devoted to the development of methods for breaking and evaluating the security of block ciphers, known as cryptanalysis. In this thesis, we investigate division property-based integral cryptanalysis, which is one of the latest distinguisher-based... 

Damage detection in all kinds of human-made structures has been given serious attention as one of the main branches of engineering sciences, and significant progress has been made in this field, especially in the field of civil engineering, aerospace and heavy industries. However, although this topic is discussed academically in the field of offshore structures for two decades, not much development has happened in practice and it is still in the stage of knowledge development. One of the most important characteristics of practical online damage detection methods is the ability to be used knowing little information about the modal characteristics of the structure. In this research, an attempt... 

One of the newest methods of rapid prototyping is SLS . In this day, SLS is more common in compare others methods, because it uses little time and man does not nearly interfere in the producing stages of part which is made by SLS method. Also, sophisticated parts, which cannot be built by other methods, can be produced by SLS method. One of the disadvantages of SLS method is low dimensions accuracy of parts produced in this way. This problem has two major reasons: Shrinkage and Warpage. These two phenomena are created because of ununiformed temperature distribution. Others features which have effect on dimensions accuracy are residual stress, porosity and removing space of between powder... 

With the spread of threats against industrial control systems, preserving the security of these systems faces serious challenges. On the other hand, with the increase of communication between industrial control networks and external communication networks, the entry points of these networks have also increased and this exposes them to IP network threats. Beside that, traditional attacks on these systems, which generally occur by infiltrating the internal network, are also constantly changing and becoming more complex. These attacks mainly have a phase of hiding the attack from the monitoring systems, which eliminates the possibility of identifying the attacker's operations to a great extent... 

Carbon nitride is a compound that has the proper energy gap (2.7 eV) for activities in the visible light. In this research, photocatalysts based on nanoporous Carbon nitride sheets was synthesized with three primary ingredient (urea, melamine and melamine hydrochloride) by pyrolysis method. Ag, Cu, Fe2O3 and Fe3O4 were added to the system to prevent the electron-hole recombination as well as increscent the photocatalytic activity. The chemical bonding state properties and microstructure of the synthesized photocatalysts were investigated by means of XRD, SEM, BET, FTIR, DRS and PL methods. In the first step of the research, the activity of prepared compounds was analyzed by visible light for... 

Majority of the oil and gas reservoirs, in the main hydrocarbon production regions around the world, are naturally fractured reservoirs. Fractures play an important role in reservoir fluid flow either in the form of high permeable complex conduits or strong permeability anisotropies. Realistic characterization of naturally fractured reservoirs requires an exhaustive understanding of fracture connectivity and fracture pattern geometry. These subsequently demand description of many fracture parameters such as density (intensity), spacing, orientation, size and aperture. Therefore, a first step in fractured reservoirs characterization is the static geometric modeling of the subsurface fracture... 

Lithium has two stable isotopes, 6Li and 7Li. Abundance of these isotopes are 7.53% and 92.43% respectively. Each isotope has an important role in nuclear industry. For example, 6Li compounds is used in production of tritium in nuclear fusion reactors coated with DT fuel and as fuel in nuclear fusion reactors that operate with laser inertial confinement method applied. 7LiOH is used to adjust the pH of the fluid coolant in light water reactors and also in Breeding Reactors. Lithium isotope separation in different ways so far been brought into operation. The other aspect to this work, it can be both continuous and batch for action. Lithium isotopes for the first time by electrolysis using... 

One of the most important considerations in the vehicle design procedure is the durability of the components. Among different parts of a vehicle, the body is the main load-bearing component and as a result, its durability is critical. Due to the expensive and time-consuming nature of fatigue tests, finite element based durability analysis is of great interest among automotive industry. The aim of this research is to provide an algorithm for a more accurate and efficient durability analysis of the vehicle body by considering inertia effects. By using the multi-body dynamics model of the full vehicle and the finite element model of the vehicle body, the vehicle body structure is analyzed from... 

In recent years, due to urban expansion and population growth, number of floors and excavations depth has increased. Stabilization of excavations is one of the most important issues in geotechnical engineering. Today, one of the most widely used methods that is used in deep excavations is brace soil by steels and pretension them. In this thesis tries to evaluate static behavior of flexible supporting structures with pretension anchors by using PLAXIS2D, FLAC3D and GEOSTUDIO softwares. The objective of this modeling is better understanding the static behavior of walls, comparing the two and three dimensional modeling and the effect of corners of excavation on deformation. The results shows...