Sharif Digital Repository

In this thesis, we want to present methods that are able to solve the assignment tasks problem in a heterogeneous computing system. These methods are two hybrid methods that are constructed by composing Hopefield Neural Networks with Genetic Algorithms and the Simulated Annealing. First, we solve the relaxed problem by applying Genetic Algorithms and the Simulated Annealing and we compare the results of these ways with other traditional methods. Then, we solve the constrained problem with mentioned hybrid methods. The definition of the problem is as following: Consider a distributed computing system which is comprised of set of processors with different speeds but the same structure. We want... 

In  this  dissertation,  we  investigate  the  frequency  hopped  spread  spectrum  systems  which are extensively used in many communication systems. We derive the capacity region  of  Synchronous  Frequency  Hopped  Multiple  Access  (FHMA)  channels  (for  any  kind of noisy or nonselective fading environment) by using the side information which exists in the multi‐user detection. We assume that random hopping patterns are used by all the transmitters, and the common receiver knows the hopping patterns. We also compute  the  capacities  of  FHMA  with  and  without  power  control  for  AWGN  and  noiseless MFSK (in particular BFSK) modulated systems and compare the ... 

Regarding to the emergence of quantum computers and advances in the large scale implementation of them, exploiting hard problems of coding theory is of great importance.This family of problems, like those of lattices, has an acceptable resistance against classic and quantum attacks. Thus, they can be replaced with hard problems in number theory and algebra. Increasing dominance of cyberspace made us highly dependent to it. Consequently, preparing tools and methods to mitigate future threats is necessary. Digital signatures constitute an important family of cryptographic primitives. Code-based digital signatures are mostly suffering from two main drawbacks: large public key and long time of... 

Image Registration is a fundamental task in numerous applications in medical image processing and is defined as the process of determining the correspondence of between images collected at different times or using different imaging modalities. This correspondence can be used for aligning images so that the pair can be directly compared, combined or analyzed. Image-guided surgery systems use registration for establishing an accurate relation between preoperative and intraoperative image space. There have been several methods for rigid registration which are not easily applicable for soft tissues. Indeed, nonrigid deformation of soft tissues will endanger the accuracy of rigid methods, so it... 

Fire in enclosures is one of the most important disasters due to the presence of human and physical risks, so, investigation of the firefighting scenarios in this case has much importance. In the present study, novel enclosures fire suppression scenarios are simulated using computational fluid dynamics (CFD). The simulations have two major categories. In the first part, performance of different natural ventilation, positive pressure ventilation (PPV) and negative pressure ventilation (NPV) scenarios, which are new methods in firefighting, are evaluated and compared. In this part, the influence of different parameters like geometry, position of inlet and outlets and fire heat release rate... 

In this thesis, we have implemented the quantum renormalization group method to study quantum spin systems. We reviewed the recent progress to calculate the quantum information properties of these models. The recent investigations show that concurrence and entanglement are two quantities which can show quantum critical properties of the quantum systems. More specifically, the derivative of entanglement and the second derivative of ground state energy show divergent behavior at the quantum critical point. Moreover, the ground state fidelity for two different parameters close to quantum critical point shows a drop which leads to a divergent behavior in its corresponding susceptibility. We have... 

Recently magnesium alloys have shown great potential as biodegradable metallic implants. However, due to high corrosion rate in the body environment, these alloys would be degraded before the tissue healing time period. Therefore corrosion resistance of these alloys has to be improved in order to be used in biological environments. In the present work, supposing improvement of corrosion properties of magnesium AZ91D alloy, the alloy has been coated with biocompatible nano-Zirconia particles using Electrophoretic deposition method and the effects of deposition parameters such as bath agitation, Zirconia concentration, current density and duration of deposition process on the properties of the... 

Price and warranty are two powerful marketing tool that can stimulate consumers’ purchase willingness. Therefore, producers must choose the appropriate price and warranty that can stimulate customers to purchase the quantity that will achieve the maximum profit. This study investigates optimal strategies for price and warranty length of a new product to maximize profit of a producer during lifecycle of the product. We consider both durable products and non-durable ones. Customers buy non-durable products many times but if we consider the planning horizon relatively short, each customer buys one product during the period. So, the market for non-durable products is static and for durable ones... 

Foundation which is lowest load-bearing part of structure, transfers load of superstructure to substructure. Because structures are usually placed on soils, the response of the soils influences the motion of the structures and the motion of structures affects the response of the soils. This phenomenon is termed Soil Structure Interaction (SSI). One of these mutual effects is the rocking of shallow foundations in which the base of the foundation under dynamic loading may separate from the underlying ground, by rotating about the longitudinal axis. This rotational mode elongates natural period of the soil-structure system and decreases the base shear demands of the superstructure. Indeed... 

Foot movement is one of the most powerful and adaptable methods of movement in nature. Inspired by humans, the most intelligent creatures on earth, bipedal robots have many uses. In this research, a control method for running a bipedal robot has been designed. In the simulation part of the five-link model, the robot's motion equations for running and walking at different levels are extracted by the Lagrange method. In path generation, using the two-layer optimization method and holonomic and dynamic constraints, optimal paths are produced which are kinematically and dynamically possible (feasible). Additionally, path generation is facilitated by an invariant impact constraint to ensure the... 

The significance of the rail transportation system in the economic, political, and social realms of countries, along with the high costs of managing and maintaining its infrastructure, are among the most significant reasons for the importance of a railway track maintenance management system. Such a system is crucial to maintaining service levels, ensuring reliability and safety of the tracks to an acceptable level, and minimizing maintenance costs. This research focuses is on identifying the optimal maintenance policy for Iranian railway tracks, considering the budget constraints in the maintenance planning. For this purpose, the output of the EM120 machine, which was obtained from the...