Sharif Digital Repository

Cosmology is a knowledge that deals with the matter of creation of the world, its current structure and its end. This scientific field that was a subject discussed by the scientific, philosophical and religious groups has nowadays taken the attention of many scientists and researchers. The philosophers of science, also, are not exemptions from theses groups and cosmology, as a topic common between philosophy and science, is one of the points that are under discussion in the field of philosophy of science. On the other hand, the religions, also, have noticed this issue. Koran that is the most complete divine book sent from God, has taken account of the creation and the Creator as the axis of... 

Using magnetic torquers as the sole actuator for attitude control of small satellite despite its benefits has a drawback that is lack of controllability. Mechanical torques can be created only perpendicular to the instantaneous magnetic field vector, thus at each time instant the satellite can be controlled only around two axes out of its three perpendicular axes.
Fortunately because of the satellite motion, the direction of uncontrollable axis changes by time, therefore the sufficient attitude control can be achieved along time. Almost all of the present magnetic attitude control methods need more than one orbital period to control and cause the attitude to converge to the desired... 

Humanoid robots are robots that are similar in appearance and performance to humans. Designing and controlling a humanoid robot to perform such supposedly ordinary tasks as walking, running, writing, talking, driving, riding bikes, and the like is such a difficult task from the control point of view that it seems to be quite ambitious and inaccessible. In this thesis, the previous efforts of scientists and researchers are presented using different intelligent controllers. Additionally, the dynamic analysis of selective biped (seven-link biped robot) is illustrated. In this research, we present a method to control the walking of the biped robot while retaining stability. In this method the... 

Congestion is the inseparable part of everyday life in large transportation networks. Expansion of road networks especially in downtown area is next to impossible and it is resulting multiplicative congestion problems. Congestion imposes private and public costs. Therefore, restricting policies on road use through cordon-based or area-based pricing is proposed to reduce the negative impacts of traffic, travel demand management and optimal use of transportation systems. This would produce better resource allocation through transportation network optimization. Implementation of congestion pricing policies induces short-term and long-term effects. In this thesis, it is attempted to determine... 

This research deals with pricing private automobiles entering a congested area in urban CBD to reduce auto-related air pollution. There are two factors affecting the pollution level: car volumes, and the weather condition. A Markov decision process is employed to find the optimal tolls and determine the prices for different states of the system, under several weather conditions. The demand for travel is elastic. It is assumed that users change modes in the short run. In longer terms, the part of the demand with shopping, recreation, or similar flexible trip purposes change the respective demand levels according to the price level. The study attempts to estimate elastic demand functions for... 

Thus far, there has been a great attraction toward the optimal flight path planning problem. Terrain following/avoidance (TF/TA) flight is one of the most significant applications of this issue. To prevent from detection by the radars, fighter aircrafts, cruise missiles and helicopters often have to fly as close as possible to the surface during the operations. Such types of maneuvers are much more demanding and effortful than to be designed and implemented by human. The optimal TF/TA guidance system design comprises three phases: optimal path planning, closed-loop control system design for trajectory tracking and sensor blending to match the onboard and measured terrain data. So far, the... 

Applying spoken dialogue systems (SDS's) is growing in the real life more rapidly because of the advances in the design and management of these systems. The traditional touch tone computer telephony systems are being substituted by the SDS's. In a typical SDS, the user speaks naturally to the system through a phone line and the system provides the required information or performs the required action. Banking and ticket reservation are typical examples of the prevalent SDS's. A spoken dialogue system has four units: automatic speech recognition (ASR), natural language understanding (NLU), dialogue management (DM), and spoken language generation (SLG). In this work, the first spoken dialogue... 

Transportation networks are considered as complex systems, and in many cases they behave in such an irregular and unexpected manner. Such complexities cause problems in studying the behavior of these systems. An example of such complexities is chaos in the network flows. On the other hand, the behavior of these networks is highly affected by the incidents like accidents and bad weather. Such events affect the level of service and travel time reliability of the networks. In this research, a dynamical approach to traffic assignment has been chosen to model chaos and uncertainties in the network. By using this approach for modeling flow evolution, edge of chaos and uncertainty in supply and... 

Pricing users of the network in the congested Central Business District (CBD) will cause change in the travel behavior of the different sectors of these users . The problem of optimal pricing of CBD is formulated in this study as a bilevel optimization . The lower level problem is a joint trip production-distribution-mode choice-assignment problem , which identifies three groups of the users , namely shoppers , retailers and basic employees . The upper level problem maximizes total long-run benefit and minimizes air pollution and changes in attractions of the zones . The demand for shoppers and retailers is elastic , but that of the basic employees is assumed inelastic . The decision... 

Increase of nonlinear loads has led rise of harmonic currents, voltage distortion and imbalance in power system. Those polluted nonsinusuidal environments have made electrical engineer and researchers to define new and more compelet definition of electrical power quantities such as power factor, apparent power, THD and … . The new definitions have resulted in new methods of power quality enhancement technique. IEEE-1459 Std. proposes definitions for electric power in sinusoidal, nonsinusoidal, balanced and unbalanced conditions which can be used for compensation of nonsinusoidal and unbalanced systems. This reaserch introduces a new method to obtain shunt active filter reference signal. This... 

The utilizing language model is one of the most effective methods for improving speech recognition performance. For speech recognition applications, several types of language models have been proposed for speech recognition applications that try to model some parts of language information, such as n-gram models, syntactic models, and semantic models. Although n-gram, syntactic and semantic models are able to model different structures that exist in natural language, they each only capture specific linguistic phenomena. None of them can simultaneously take into account all of language phenomena in a unified probabilistic framework. Recently, a number of semantic models called "latent topic... 

Automatic speech recognition performance degrades significantly when speech is affected by environmental noise. Nowadays, the major challenge is to achieve good robustness in adverse noisy conditions so that automatic speech recognizers can be used in real situations. Spectral subtraction (SS) is a well-known and effective approach; it was originally designed for improving the quality of speech signal judged by human listeners. SS techniques usually improve the quality and intelligibility of speech signal while speech recognition systems need compensation techniques to reduce mismatch between noisy speech features and clean trained acoustic model. Nevertheless, correlation can be expected... 

Automatic Speech Recognition (ASR) engines are too much sensitive to conditions such as noise, transmission line quality, etc. Thus in any real-world application ASR systems should be able to automatically assess reliability or probability of correctness for every decision made by the systems. One technique to increase intelligence of an ASR system is to compute a score, called “confidence measure” to indicate reliability of any recognition decision made by the system. This score can be computed at any required level such as phonemes, syllabi, words or even the whole utterance. Thus a robust and accurate confidence measure results in better detection of recognition errors, Out of Vocabulary... 

Data storage systems are an essential part of any Information Technology (IT) infrastructure. Unavailability of these systems can directly lead to service disruption to customers and can be very costly in enterprise applications such as ebanking, online reservation systems, and mobile services. Modeling availability of disk subsystem is a major step in design of data storage systems. Previous modeling techniques have mainly focused on data unavailability or data loss due to double or multiple disk failures. In this thesis, we present both simulation and analytical modeling techniques to investigate the effect of serviceability on the overall availability of disk subsystems. The proposed... 

Signle-channel speech enhancement using hidden Markov model (HMM) based on minimum mean square error (MMSE) estimator is focused on and an HMM-based speech enhancement in Mel-frequency domain is proposed. The MMSE estimator results in a weighted sum filtering of the noisy signal in which accurate estimation of the filter values and filter weights comprise the main challenges. The cepstral domain modeling for speech enhancement is motivated by accurate filter selection in this domain. In the propsed framework, Mel-frequency spectral (MFS) and Mel-frequency cepstral (MFC) features are studied and experimented. In addition to the spectrum estimator, magnitude spectrum, log-magnitude spectrum... 

Pavement maintenance and rehabilitation is an important problem in road pavement programming. Pavements experience significant distress over its life due to passage of vehicle (particularly heavy trucks), as well as abrupt variation in temperature (freeze and thaw). This would deteriorate pavements and reduces their serviceability. Rise of pavement maintenance costs places higher importance upon the need for maintenance programming. This study employs an evolutionary model to optimize the long-run benefit of the maintenance program. The model is stochastic in nature, and imbeds a Markovian decision procedure in the model to take into account such variabilities. The model is applied on... 

Nowdays, distributed generation (DG) systems based on renewable energy sources have significantly increased around the world as an alternative solution to enhance the power quality and reliability and reduce the need for extensive transmission system as well. An evolved recent concept called microgrid is developed by grouping a cluster of loads and DG units in a common local area which increases the integaration of sustainable energy generation systems. This thesis presents control of a medium voltage (MV) microgrid considering multi-hybrid distributed generation systems (MHGS) and renewable energy resources in island mode. The first part is focused on the development a control strategy for... 

Variation in value and initial cost of construction contracts in many cases lead to considerably increasing the finalized price. These increases are sometimes so big enough that the 25 percent of limitation which could be added to contracts couldn't make them to be finalized and exploitable, so the necessity of a new contract sometimes up to 100 percent or even up to 200 percent of initial cost for completing the same project is inevitable. Although in some specific and rare cases we couldn't avoidance from these changes, but observing the growth of these changes in public construction projects of Iran increase the requirement of special attention in order to find the main causes, prevention... 

Semantic classification of words based on unsupervised learning methods is a challenging issue in computational lexical semantics. The goal of this field of study is to recognize the words that are in the same semantic classes; i.e., can have the same set of arguments. Among all word categories, verb is known as one the most important and is assumed as the central part of the sentence in certain linguistic theories such as case grammar and dependency grammar. Based on Levin’s idea, diathesis alternations and the similarity between these alternations are the clues for the semantic classification of verbs. This idea is verified in languages such as English and German with promising results.... 

The human speech conveys much information such as semantic contents, emotion and even speaker identity. Our goal in this thesis is the task of text-independent speaker identification (SI) in large population applications. Identification (test) time has become one of the most important issues in recent real time systems. Identification time depends on the cost of likelihood computation between test features and registered speaker models. For real time application of SI, system must identify an unknown speaker quickly. Hence the conventional SI methods cannot be used. The main goal in this thesis is to propose several methods that reduced identification time without any loss of identification...