Sharif Digital Repository

Payment channel networks (PCNs) are a promising technology to improve the scalability of cryptocurrencies. Users can send instant and almost free transactions via payment channel networks and, at the same time, enjoy the security guarantees of Blockchains. In order to open a mutual payment channel, two users should send a ``channel creation" transaction to the underlying Blockchain. Through this transaction, two parties deposit some money on the Blockchain. This money, which we call the channel's capacity, can be used to send off-chain transactions between the two users. After the channel creation, the channel-holders can send each other off-chain transactions by forwarding the money back... 

In this thesis, we argue that in many basic algorithms for machine learning, including support vector machine (SVM) for classification, principal component analysis (PCA) for dimensionality reduction, and regression for dependency estimation, we need the inner products of the data samples, rather than the data samples themselves. Motivated by the above observation, we introduce the problem of private inner product retrieval for distributed machine learning, where we have a system including a database of some files, duplicated across some non-colluding servers. A user intends to retrieve a subset of specific size of the inner products of the data files with minimum communication load, without... 

Nowadays we are witnessing the emergence of machine learning in various applications. One of the key problems in data science and machine learning is the problem of dimensionality reduction, which deals with finding a mapping that embeds samples to a lower-dimensional space such that, the relationships between the samples and their properties are preserved in the secondary space as much as possible. Obtaining such mapping is essential in today's high-dimensional settings. Moreover, due to the large volume of data and high-dimensional samples, it is infeasible or insecure to process and store all data in a single machine. As a result, we need to process data in a distributed manner.In this... 

Nowadays, with the development of machine learning and deep learning on one hand, and the dramatic increase in the amount of information available and the complexity of models on the other hand, it is practically impossible to implement learning algorithms on a single node. Thus it is inevitable to distribute learning algorithms on several machines. In a distributed system, the main operations are divided into smaller tasks and performed by different nodes. The final result is then calculated by exchanging messages among the existing nodes.In this thesis, a method is introduced to compute the gradient of a massive data set in a distributed system. In this problem, there are a number of... 

This thesis contains experimental studies on mechanical properties of adobe and mud material and investigating seismic performance of a conventional adobe house using shake table tests. Mechanical properties of adobe and mud material were studied experimentally based on ASTM and BS standard tests. These experiments were designed to evaluate compressive strength of adobe sun-dried blocks and mud mortar cubes. Besides, shear behavior and tensile bond strength of adobe assemblages were under consideration and shear tests were done on adobe panels. As next part of the research, several shaking table tests were conducted on a dome-roof adobe house as a conventional representative of arch-roof... 

Settlement and tilt of structures due to liquefaction of subsoil layers is a major cause of damage during earthquake. One of the main approaches to reduce terrible effects of liquefaction on shallow foundations is ground improvement. Among the variety of ground improvement methods, the densification-based methods have been more paid attention for liquefaction mitigation. For liquefaction hazard mitigation using densification methods, three basic values should be determined i.e. depth, lateral extent, and degree of improvement (percent increase in Dr). In the current design practice, the need for ground improvement is usually decided based on the semi-empirical methods for assessment of... 

Adobe structures are considered as masonry structures which are out of scope of 2800 Iranian code. Due to this code, since these structures are made of weak materials, they do not have a considerable resistance to earthquakes. Since these structures can be found all around Iran; therefore, seismic study of walls as an important component of these structures, is, indeed, necessary. During this study, cyclic tests on three types of adobe walls, without opening, with window-opening, and with door-and-window-opening with a scale of 2:3 were done to study their in-plane behavior and also their failure modes. Based on our observations, in these walls, because of small ratio of height to length,... 

Statistical studies indicate the fact that in Iran, like many other developing countries, a considerable percentage of houses are in the form of traditional buildings, and major losses due to recent earthquakes are because of masonry building collapse. In the early twentieth century in Iran every ten years a destructive earthquake has been occurred which has resulted in huge human casualties and economic losses. After the Bam 2003 earthquake, a team project was defined to investigate the behavior of rural houses with the aim of providing solutions to lessen seismic hazards, and the current study is the fifth phase of the following line of investigations. Among the existing kinds of rural... 

In this thesis, we introduce limited-sharing multi-party computation; in which there is a network of workers (processors) and a set of sources, each having access to a massive matrix as a private input. These sources aim to offload the task of computing a polynomial function of the matrices to the workers, while preserving the privacy of data. We also assume that the load of the link between each source and each worker is upper bounded by a fraction of each input. The objective is to minimize the number of workers needed to perform the computation, such that even if an arbitrary subset of t 1 workers, for some t 2 N, collude, they cannot gain any information about the input matrices. This... 

In the present study, the buckling of generally laminated truncated conical shells having thickness variation expressed by a linear function, subjected to axial compression with simply or clamped supports has been considered. To begin with, the fundamental relations for a conical shell with variable thickness have been derived applying thin-walled shallow shell theory of Donnell-type and theorem of minimum potential energy; non-linear terms of Donnell equations by the help of adjacent-equilibrium criterion are linearized. Governing equations are solved using power series method and are applicable for all combinations of classical boundary conditions. The results are validated with Galerkin... 

One of usual criterion which detrimines how much two polynomials are close to each other is smallness of the norm of vector that is formed from subtraction of their corresponding coefficients. Using this criterion, in this dissertation we become involved in investigation of two similar problems. First one is determination of the closest non-Hurwitz polynomial to a Hurwitz one. During this activity, the robustness margin of Hurwitz polynomial whose coefficients are subject to uncertainty is determined. The second problem is determination of the closest Hurwitz polynomial to another polynomial which is not Hurwitz. Unlike to the first problem, this problem is extremely hard. The solution of... 

Observed performance of nonstructural components and building contents during recent earthquakes demonstrated their significance to control economic seismic losses and downtime. Since a large portion of nonstructural equipments installed in buildings are acceleration sensitive devices, reasonable estimation of the acceleration they undergo during an earthquake has an important role in rational design of secondary systems and subsequently in reducing the earthquake damages. Although a comprehensive amount of research studies have been conducted to date to approximate the floor acceleration demands of a multistory building subjected to the earthquake ground motion, in most work, the soil... 

Nowadays with development of applications that stream video over internet, compression efficiency of video has become very important. On the other hand, Watermarking and video coding are two conflicting technologies. One adds redundancy and other tries to remove it. We have proposed a H.264 watermarking method that does not increases the bit rate. Unlike most of watermarking schemes, this methods embeds the watermark in inter coded frames. Abundance of these frames in video is impressively more than intra frames, so a lot of capacityis eventuated. But these frames are highly compressed using motion compensation, and are very sparse. To avoid from bit rate increment, this method only embeds... 

Islanding detection methods are divided into three main groups as remote, active and passive. Although passive schemes have larger Non Detection Zones (NDZ) relative to other schemes, they are more used in utilities due to their low costs and less PQ problems than in other schemes. Passive Schemes are based on the measurements of passive system parameters. These parameters are measured at the point of common coupling (PCC). A new approach in passive techniques is the use of data-mining to classify the system parameters which affect the islanding detection. Therefore, by finding an efficient and robust data-mining algorithm, the inherent problem of passive schemes, which is their relatively... 

The wide-area damping controller (WADC) has been proposed to enhance the damping of inter-area oscillations. The most challenging deficiencies to make this controller practical are the power system operating condition changes and the inherent time delay of remote signals. They can deteriorate the controller performance and the whole system stability if not properly accounted for in the design procedure. This thesis presents an adaptive delay compensator (ADC) on the basis of the latest development in the wide-area measurement system (WAMS) to cater to varying latencies. The proposed compensator can effectively reciprocate the phase deviation resulting from varying delays to improve the... 

In this work, we consider the problem of secure multi-party computation (MPC). This system includes Γ sources, N processing nodes or workers and one data collector or master. Each node has a constraint on its storage,such that it can store 1/m fraction of size of each input matrices from each node. In addition, up to t of these workers are adversary and may collude to gain information about the private inputs or can do malicious actions to make the final result incorrect. The objective is to calculate an arbitrary polynomial of some massive private matrices as inputs while the privacy is preserved. The main concern in these kind of systems is to reduce the minimum number of workers needed... 

Adobe buildings on one hand are very heavy and hence generate great amounts of inertia loads during earthquakes. Their response is also amplified in the high-frequency earthquake waves due to great stiffness. On the other hand, these structures proved vulnerable during past earthquakes because of low strength and ductility. Considering the fact that there are too many structures of this kind throughout the country and a majority of their residents are the poor, seismic retrofitting of these building should be taken as a priority rather than reconstruction. It is obvious that the proposed retrofitting technique should be simple, feasible and economical, as well. Among possible retrofitting... 

After the heart-rending earthquake in Bam and its severe losses, the engineering community forced to pay special attention to the seismic vulnerability of traditional structures. Therefore, with the aim of reducing of such devastations to minimum, a multi-phase research project was defined at Sharif University of Technology to study the vulnerability and retrofitting of these structures which the current study is the eighth phase of that series research. In the third and fourth phases of this project, a typical adobe building with dome roof was chosen for study making use of shaking table facilities. The tests included both un-retrofitted and retrofitted states and considerable seismic...