Sharif Digital Repository

In Mobile Ad hoc Networks (MANETs), nodes depend on each other for routing and forwarding their packets. However, to save power and other resources, nodes belonging to independent authorities may behave selfishly, and not cooperate in network activities. Such selfish behaviour poses a real threat to the proper functioning of MANETs. To cope with this situation, a motivation stimulation mechanism is required to provide sufficient incentives for nodes to forward other nodes’ packets. One Appropriate approach is to have network nodes paid in order to motivate them to cooperate with protocol. To achieve truthfulness, the payment based on the cost of transmission of packets. Since the mentioned... 

Quantum mechanics, in the first place, investigates systems by introducing some principals about Hilbert space, Schrodinger equation etc. which are recognized as closed quantum systems. In principal, this is not possible to separate a system from its surrounding environment. Thus, the implications of the environment on the evolution of the system must be taken into consideration. As a matter of fact, all systems are considered open in a sense that, it is interacting with another system called the environment. In such circumstances, we tend to represent a description of open quantum systems in a way that following the evolution of the total system, i.e. system and the environment, is not... 

The measurement problem is one of the issues that is still under debate about the Quantum theory. A significant part of literature during the recent years includes the standard point of view about this problem (including the separation of microscopic and macroscopic domains) and the criticisms of some major physicists in this context. Among these, alternative theories and interpretations have been getting more attention. Experimental tests of Quantum Mechanics in the macroscopic domain and their comparison with alternative theories have always encountered various difficulties (in particular the decoherence phenomenon). Anyway, towards the end of the last century, with the advances in... 

In contrast to traditional Networks where a designer can specify an action plan for each agent, in a network with strategic agents, every agent acts selfishly and chooses his strategy privately so as to maximize his own objective. In this dissertation, we study problems arising in the design of static and dynamic networks with strategic agents. We consider two classes of design problems. In the first class, the designer utilizes her control over decisions and resources in the system to incentivize the agents via monetary incentive mechanisms to reveal their private information that is crucial for the efficient operation of the system. In this class of problems, we address two main challenges... 

Automatic image annotation is an image retrieval mechanism to extract relative semantic tags from visual contents. The number of digital images uploaded in the virtual world is rapidly growing every day. Most of those images are not assigned with proper tags or labels. Although automatic image annotation methods are developed to assign proper tags to images, most of these methods assign some irrelevant tags and also sometimes a few relevant tags are missing. So far, the improvements of accuracy in newly developed automatic image annotation methods have been about one or two percent in F1-score compared to the previous methods. To reach much better performance, we analyzed most of the... 

Machining in its general concept forms the major part of manufacturing processes regarding time and cost. Therefore any progress in machining techniques would be well beneficial. High speed machining is one of the recent concepts in machining technology which has attracted much attention and effort. But high speed spindles as the main part of high speed machines, have been notorious for their lack of reliability and sudden failure which originates mostly from thermal problems. In order to ensure reliable operation of spindles it is necessary to predict thermo-mechanical behavior of machine-tool spindles. The major sources of heat in a spindle are angular contact ball bearings (the most... 

With the ever-growing use of cloud computing by practitioners and also the emphasis placed by researchers from various backgrounds on this field, collaboration between various clouds has emerged as a new research area garnering a lot of attention in recent years. Cloud Federation, in which different clouds interact for purposes such as increased productivity and decreased costs, is one aspect of this new trend, which although faced with many challenges,has the potential to make cloud computing even more pervasive then before.In this thesis, by focusing on statistical multiplexing in the resource usage behavior of cloud requests, we evaluate the efficient and fair partitioning of requests in... 

Now a days, the ability of measuring the mechanical properties of the living cells in in experiments has been increased. Experiments shows that the stem cells could alter their faith in different mechanical situations, but an integrated model about this phenomenon in literature has not been introduced yet. In this research thesis s minimal cell model (MMC) is developed to capture the behavior of the cells on substrates with varying mechanical properties and morphologies, MMC consists of large scale models for outer membrane of the cell and nuclear envelope, cytoplasmic area, chromatin fibers and Extra cellular matrix. Each component of the MMC will be placed in an integrated software to... 

The probability of crack appearance in soil structures and porous media is not avoidable, which could be the reason of structures collapse. According to the important affects, which they play in the vulnerability of the structures, they should be taking into account. The cracks have different effects on various materials. The most properties that cracks have, is their ability of conveying the fluid flow. For the most accurate analysis of discontinues domains, their governing equations should be taken and solved. Finite Element Method is one of the best solutions of differential governing equations. However, the appearance of some problems in the modeling of discontinues domain, was the... 

In recent years, more attention has been paid to the development of lightweight concrete (LWC). Study of such this material had been marked due to more importance of use of it.It is now well known that in order to model cracks the finite element model is more suitable.The fracture of quasi-brittle material such as concreteincludesthe fracture process zone (FPZ).Cohesive zone model is considered the most common model used for FPZ modeling.Therefore, in this article the propagation of cohesive cracks inLWC is modeled using the extended finite element method (XFEM). In this study, modeling showed fastgrowth and propagation of cracks inLWC. Due to its cavities and pores, LWC shows to be more... 

Crack nucleation and growth is unfavorable in many industrial and every day-life cases. designers’ effort is to prevent or delay it by taking into account safety and maintenance considerations; but in some industrial operations, the main target is to form a crack in a part to achieve a particular shape; and designers’ duty is to control the way it happens. so numerical modeling of this phenomena has many useful applications in preventing the structures’ failure and designing the production processes for industrial goods; and because of this, a great attention has been paid to it in the last two decades. a situation usually encountered in every day-life is the earthquake excitation which... 

Twophase medias are one of the most complicated medias in engineering and because of its importance, its been considered by a lot of researchers ever since. Varaioty of the problems in these medias, has ended in lots of methods for studing them. The primariative efforts in modeling deformable pouros medias was done by Terzaghi and others have improved the primary consepts and have suggested different methods. One of the most common and applicable methods in these medias is u-p formulation. This form is applicable in low frequencies (such as earthquakes) with great accuracy. In this thises, this form is used as primery formulation. Because deformation in multiphase problems can be large, in... 

The main purpose of this study is computational modeling of saturated deformable porous media using multiscale finite element method and explicit modeling of discontinuities such as microcracks at the microscopic scale. The real engineering problems we deal with in the simulation of the phenomenas happening in nature or industrial applications, in contrast to the simplifications being assumed, occur in heterogeneous materials. Although most microscopic heterogeneities are not present in macroscopic scale, they do have their effects on material behavior. In the computational homogenization method, the problem is analyzed coupled in two scales, therefore, the macroscopic behavior of media is... 

In this paper a new multi-scale method is developed for modeling heterogeneous materials, this method is based on homogenization and it is classified as hierarchical multi-scale method. For simulating problems in continues media, finding the elastic tensor is necessity, in homogeneous material this tensor come down from Young’s modulus and poison’s ratio, however in Nano-scale problems specially in heterogeneous material, this solution does not work and need to revise. To deal with heterogeneity in these problems homogenization by a representative volume element is a novel method. The properties of material is imported from RVE in each step of solving problem to larger scale, and by... 

Carbon nanotubes are cylinders in Nano scale formed of carbon atoms with covalent bonds that contain a significant electrical and mechanical features. Carbon nanotubes are divided into two main types: multi-walled carbon nanotubes (MWCNTs) and single walled carbon nanotubes (SWCNTs). A SWCNT is a rolled graphene sheet (graphene is in fact a single sheet of graphite). SWCNTs has lately been considered as one of most interesting research cases. The reason why researchers have been fond of investigating about graphene has been its unconventional quantum hall effects, high room-temperature electrical conductivity and its mechanical stability despite of being composed of single layer atom... 

Gravity drainage is known as the main mechanism for Enhanced Oil Recovery (EOR) in naturally fractured reservoirs. In fact, this mechanism is active in gas invaded zone. In spite of numerous researches in the area, the literature suffers from the lack of a comprehensive model for controlled gravity drainage. Calculating the accurate oil recovery and ultimate recovery factor is inevitable for a successful field development plan as well as enhancing oil recovery. To obtain the accurate values of the aforementioned parameters, an accurate model to solve nonlinear differential equations is necessary. To this end, COMSOL, the well known commercial CFD software, has been used for the modeling of... 

A mathematical model helps to understand any system with any level of complication, such as the human body. The heart, vascular system, and lungs are three important parts of each body that life is impossible without them. The performance of the cardiovascular and respiratory systems is tuned by a group of complex mechanisms which are called regulatory mechanisms. Therefore, a model which describes the behavior of these mechanisms has great importance. The goal of this research is to provide and simulate the newest and most complete model in this field. The presented model should consist of the heart, vascular system, lungs, respiratory system, gas exchange and transport, and finally... 

In this study, a tree-dimensional random pore-scale network model is used to simulate the membrane contactor porous medium. Drainage and imbibition phenomena is simulated to have a better knowledge of liquid and/gas intrusion trough the membrane porous structure. A genetic algorithm is used as an optimization tool. Several variables such as the number, radius and location of pores, the coordination number, as well as the radius and length of the throats are used herein as the optimization parameters. The difference between the binary SEM images and virtual sections on the generated network in conjunction with the permeability and mean pore size data were selected as the objective function.... 

owning to the side effects and disadvantages of conventional methods of cancers treatments such as chemotherapy, currently, scientists are attempting to find new methods to replace them. Furthermore, many human diseases like SCID and Hemophilia are due to genetic disorders and scientists are also seeking to find permanent treatments instead of available temporary ones for them. in recent years, regarding the obtained achievement, Gene Therapy is being considered as a promising method for both cancers and genetic disorders treatment. But due to low efficiency of this method at this stage, there is an endevour among researchers for a more profound comprehension of the basics of gene therapy to... 

Selective laser sintering is a technique which uses a laser as the power source to sintering some selected points at a bed of powder in order to create a solid structure. In this research the SLS mechanisms of powder deposition is simulated and surface smoothness and layer density created by each mechanism is computed. For this purpose roller, blade and hopper mechanisms are simulated. For this simulation, polyamide 12 (PA2200) which is a common material is used. In this simulation at first powder specifications are extracted according to the references and for particle shape instead of using the spherical particle shape we use a certain shape that is more close to reality which created by...