Sharif Digital Repository

Artificial periodic mediums such as metamaterials or photonic crystals have been intensively studied in recent years due to their unique characteristics and the ability to control their effective electromagnetic parameters. Developing accurate methods for the extraction of these parameters is highly desirable, given the potential application of artificial materials in optical and microwave devices. In this thesis a new method is presented for computing the effective bulk and surface parameters of three-dimensional artificial periodic materials. The effective, bulk permeability and permittivity tensors are shown to be directly related to the eigenvectors of the generalized transfer matrix of... 

The frontend stalls caused by instruction cache and branch target buffer (BTB) misses are a well-known source of performance degradation in server processors.To address this limitation, a myriad of hardware prefetchers are proposed. While they can effectively eliminate lots of misses and increase performance, they are impractical solutions due to some shortcomings. In this study, we are looking for effective and practical solutions to address these limitations.Since the considerable fraction of instruction cache misses is sequential misses,sequential prefetchers like next-line prefetcher are simple and effective solutions to remove sequential misses that are used in modern server processors.... 

considering the cosmic web's components as the environment of structure formation or considering them as structures, studying the cosmic web has advantages. But because of the non-linear nature of the cosmic web, extracting information from it has some challenges. The main challenge is that there are several ways of quantifying the cosmic web, in which there is no agreement between them.In this work, by introducing the excursion set of saddle points, we try to find a way for modelling cosmic filaments. By this model, which is an extension of the excursion of peaks, we calculate the critical density contrast of filaments with the help of the ellipsoidal collapse model and then we calculate... 

Abstract: Fault tolerance in computing systems often depends on the precision of fault detection methods, significantly impacting overall reliability. Classic fault tolerance methods, like task replication, struggle to achieve certain reliability targets with imperfect fault detection, which, unlike perfect detection mechanisms, imposes minimal system overheads. Addressing this, our paper introduces Dynamic Task Replication (DTR), a general fault tolerance technique that dynamically determines the number of replicas at runtime to overcome the limitations of classical task replication. Our primary contribution, Optimal Dynamic Task Replication (ODTR), optimizes DTR for a given task, aiming to... 

There is a need to achieve a capability for detailed modeling of the physical processes nano-robots at nano-scales that is driven by the growing demands of nanotechnology.. This is regime where behavior runs contrary to the familiar macroscopic world; optimized engineering design may well benefit from insight gained by emulating some of the multitude of architectures and mechanisms to be found in the biological world. Despite the fact that micro-robotics has long captured the imagination, practical implementations are only now starting to become feasible. One class of nano-robot with potential medical applications was considered that made of single wall carbon nanotube; however, long before... 

Internal combustion (IC) engines are the major source of motive power in the ships. as the severity of the energy dearth and environmental pollution, different researches try to increase the total efficiency and reduce emissions. one of the improvable method is to get waste heat energy and reuse it to produce electricity, cooling and heating. studies of energy balance for marine diesel engine shows that there is potential to recovery waste heat from these motors. in this study a combined electricity, cooling and heating system based on regenerative Rankine cycle with an open feedwater heater and with two open feedwater heater and absorption refrigeration cycle is offered to recover the... 

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... 

The inlet duct is one of the most important components of the waterjet propulsion system, whose hydrodynamic performance is directly related to the capabilities and efficiency of the waterjet propulsion system. In this study, a procedure was proposed to improve the hydrodynamic performance of an inlet duct. According to this proposed procedure, first the basic intake duct geometry of the waterjet propulsion system was prepared using visual programming to simplify the repetition of the design in Rhino design software, and then the numerical analysis of the designed geometry in Star CCM+ commercial software was performed. The simulation results were validated with the results of an... 

One of the common problems in using high voltage network is the occurrence of partial electrical discharge in high voltage equipment such as cables. This problem may not be serious at first, but over time it can cause wear, corrosion, or reduction of equipment life, and eventually, if not prevented in a timely manner, can cause electrical sparks, larger problems, and possibly equipment and network become irreparable. On the one hand, due to very clear reasons, we need the voltage level to be high, and on the other hand, due to the application of high voltage level and the need to optimally design the insulation system to reduce their dimensions and construction costs, there will be the... 

The edge coloring problem is one of the most fundamental problems in graph theory. In this problem, the task is to assign colors to edges so that no two incident edges have the same color. Although finding an optimal edge coloring is NP-hard, Vizing’s theorem asserts that ∆+1 colors are always sufficient, denoting the maximum degree in the graph by ∆.Due to significant increase in the volume of data, for most problems, storing the whole data is not possible. This had led to emergence of new models of processing data such as data streaming model. In semi-streaming model the input graph is represented as a stream of edges, and the storage space of an algorithm is bounded by O(n. polylog n). So... 

Nowadays, science and technology, once again, lead approach to renewable natural resources to access energy due to fossil resources restrictions. Growing need for energy, being concerned about exhaustion of fossil resources, environmental pollution caused by burning fossil materials, climate warming and the greenhouse effect and etc. are obvious evidences of aforesaid fact. On the other hand, oceans and seas are large reservoirs of energy which comes from sunlight, geothermal resources, Earth's rotation and gravity by means of mechanical and hydrothermal processes. During the years, many ideas were conducted to achieve and mine the mentioned enormous energy potential of the oceans and seas.... 

The optimal design of a ground-coupled heat pump (GCHP) system with vertical ground heat exchanger (VGHX) includes thermal modeling of the system and selection of optimal design parameters is presented in this research. Then, by applying Nelder-Mead optimization algorithm, an objective function (Total Annual Cost which is the sum of annual investment and operating costs of the system) is defined and minimized, exposed to specified design constraints. Also, Genetic Algorithm is used to verify the optimal design process. In order to evaluate the accuracy of a presented model, the optimum values of a heat pump design parameters includes saturated temperature/pressure of a condenser and...