Sharif Digital Repository

Recent advances in Micro-Electro-Mechanical Systems (MEMS) technology, wireless communications,and digital electronics have enabled the development of low-cost, low-power,multifunctional sensor nodes that are small in size and communicate untethered in short distances.Wireless Sensor Network (WSN) including these sensors has been utilized in many applications, namely military and environmental applications. Due to unchangeable battery in most WSNs, Power consumption is an important challenge in such systems. A sensor node expends maximum energy in data communication. Control environmental parameter is among the most important applications of WSN. The actual physical environmental information... 

Lots of micro hydropower potentials are spread all around Iran country. They have the capability to produce electricity for workhouses, residential areas, agricultural and animal husbandries and recreational tourism centers. Hence, Sharif University of Technology and Iran Water and Power Resources Development Corporation decided to design and produce three types of hydro micro turbines to cover all range of micro hydropower potentials available in Iran. These three types of micro turbines are Pelton, Banki and Axial and they are designed in order to cover high, middle and low heads in sequence. Frequency control of micro hydropower plants is so vital due to plant off-grid. The most prevalent... 

Separation of speech signals has many applications. For example, it is used human-machine communications. This problem can be divided into three categories: overdetermined, determined and underdetermined. If the number of mixtures is greater than the number of sources, the problem is called overdetermined; if it is equal to the number of sources, the problem is called determined and if it is less than the number of sources that problem is called underdetermined. This MS thesis studies the undertermined case. Moreover, speech signals are sparse in time-frequency domain, meaning that in each time-frequency point, usually only one source is active. So, for separatig the speech signals,the... 

In geotechnical engineering, collapsible soils as a part of problematic soils has an extreme importance since as a mutual effects of applying load and increasing their water content, Soil’s inter-particle forces become weak, and therefore, the soil experiences sudden large volumetric change known as collapse. Foundations built on these soils might experience sudden, large settlement. Collapsible soils exist in almost all continents, and many damages are reported due to the collapse phenomenon of these soils.
Due to the importance of this issue, and lack of comprehensive studies related to the volumetric and shear behavior of these soils, in this study, triaxial wetting test are performed... 

Gallium is a rare and precious metal that is of particular importance in the electronics industry due to its use in semiconductors. This metal is partially present in bauxite ore. Around 70% of gallium go into sodium aluminate solution during the leaching of bauxite in the Bayer process. Gallium can be extracted from this solution, which is also called bayer solution, by several methods. Solvent extraction is one of the most common methods for recovery of gallium from Bayer's solution. Capabilities of this method for metals separation and concentrating of polymetallic solution, makes it suitable for many commercial and operational application. In present work, different substances used to... 

In this essay we focus on the question of whether a 3-manifold (possibly with bound- ary) like M supports a codimension-1 transversely oriented foliation like F , such that F is transverse to ∂M and does not have Reeb components. If such foliation exists, then ∂M is necessarily a (possibly
empty) union of tori and (based on the works of Novikov, Reeb and Rosenberg) M is either S2 × S1(with F being the prod- uct foliation) or M is irreducible. In a paper by David Gabai, which we discuss, the sufficiency of these conditions is proved in case of non-trivial second homology group.Furthermore, from the works of Thurston it is concluded that compact leaves of such foliation are norm minimizing... 

Given a principal bundle a characteristic class is an element of the cohomology al- gebra of the classifying space of structure group of the bundle with coefficients in a commutative ring with unit ,which have a functorial property .When the structure groupe of the bundle is a Lie group and the coefficient ring is the real or complex num- bers , the Chern–Weil approach provides a geometric construction of char-acteristic classes. Classical Chern–Weil formalism relates geometry to topology, assigning to the cur- vature of a connection, de Rham cohomology classes of the underlying manifold.This theory developped in the 40’s by Shiing-ShenChern and Andre Weil which can be seen as a generalisation... 

In the unit clustering problem, given a set of points on the plane, the goal is to group these points into minimum number of clusters of unit size. In the online version, the points arrive one by one and upon each point’s arrival, it must be assigned to some cluster. Another related problem is online unit covering in which moving clusters after opening them is not allowed. In this project, the online clustering and online unit covering problems are studied in two dimensional Euclidean space. An online algorithm with competitive ratio of 5 is presented for the online unit covering problem. In addition, lowerbounds of 2:5 and 4:66 are established for these problems  

The problem of finding the near neighbours is as follows: given a set of npoints, build a data structure that for any query point, can quickly find all points in distancer from the query point. The problem finds applications in various areas of computer science such as data mining, pattern recognition, databases, and search engines. An important factor here is to determine the number of points to be reported. If this number is too small, the answers may be too homogeneous (similar to the query point), and therefore, convey no useful information.On the ther hand, if the number of reported points is too high, again the informativeness decreases because of the large output size. Therefore, in... 

About a century, “Eye Tracking” has been studied, and it has two definitions: • The process of measuring the point of gaze (where one is looking). • The process of measuring the motion of an eye relative to the head. Eye tracking technology has been used in many fields such as psychology. However, applications of this technology has been recently considered in marketing, computer interfacing, entertainment, training and so forth. Since pupil is a distinc area in eye images, pupil detection is one of the effective solutions of eye tracking. In most of the pupil detection approaches, the edge points of the pupil contour are detected firstly, and then the optimal ellipse is fitted to them.... 

Clustering is one of the most well-known fundamental problems in computer science. In this thesis we have focused on a particular version of such problem, called capacititated k-center, and we analyze and survey them in the distributed model, when massive data is given. Our contribution in this research includes a new approximation algorithms with constant approximate factors for such problems in the distributed model, as well as improving the best available algorithm for capacitated k-center problem. Composable coreset as one of the most important techniques in distributed and streaming model is our primary tools in designing these algorithms. This technique gives the opportunity of solving... 

Sparse signal processing (SSP), as a powerful tool and an efficient alternative to traditional complete transforms, has become a focus of attention during the last decade. In this approach, we want to approximate a given signal as a linear combination of as few as possible basis signals. Each basis signal is called an atom and their collection is called a dictionary. This problem is in general difficult and belongs to the Np-hard problems; since it requires a combinatorial search. In recent years however, it has been shown both theoretically and experimentally that the sparset possible representation of a signal in an overcomplete dictionary is unique under some conditions and can be found... 

In this thesis, at first upstream transient error propagation and amplification phenomenon is introduced. Then, the previous methods to attenuate this phenomenon are presented. To overcome this drawback, a new method that is based on feed-forward and off-take disturbance estimation and lost data reconstruction in wireless communication is presented. In this thesis, an estimation of unknown off-take disturbance at the present time is approximated or in fact predicted using the last data. Also, in the presented method, the lost data is reconstructed using two different methods. At the end, the satisfactory performance of the proposed control method is illustrated by many computer simulations  

Blind Source Separation (BSS) is a challenging task in signal processing which aims to separate sources from their mixtures when no information is available about the sources or the mixing system. Different approaches have already been proposed for source separation.However, during the last decade, new approaches based on multimodal nature of phenomena have been proposed for source separation. Different aspects of a multimodal phenomenon can be measured by means of different instruments where each of the measured signals is called a modality of that phenomenon. Although the modalities are different signals with different features, due to the same physical origin, they usually have some... 

Sparse representation has attracted much attention over the past decade. The main idea is that natural signals have information contents much lower than their ambient dimensions,and as such, they can be represented by using only a few basis signals (also called atoms). In other words, a natural signal of length n, which in general needs n atoms to be represented, can be written as a linear combination of s atoms, where s ≪ n. To achieve a sparser representation, i.e., a smaller s, the number of atoms is chosen much larger than n. In this way, there are more choices to represent a signal and we can choose the sparsest possible combination. The set of atoms is called a dictionary. Here, two... 

Sparse representation has been an important problem in recent decade. The main idea in this problem is that natural signals have information contents much lower than their ambient dimensions and as such, they can be represented by using only a few atoms. For example, if the dimension of signal is n, the purpose in sparse representation is to achieve the representation of signal in terms of s atom (s ≪ n). In sparse coding, the dictionary depends on the used signal. In some of the problem, dictionary is specified and sparse representation is obtained by this dictionary. In this case, because the dictionary is known, maybe sparse representation is not suitable for this signal. For this reason,...