Sharif Digital Repository

In the secure data outsourcing scenario, verification of the reply of an unreliable server includes assessing the authenticity, completeness and it’s integrity. In this thesis, an efficient method, with emphasis on freshness, has been introduced to evaluate the correctness of the replies from a server. It takes in hand different application needs, inherent differences in the data, and different update mechanisms. This method evaluates freshness by using timestamps alongside the data being out sourced. Due to the requirement of verifying not only the freshness of the response, but the correctness of the timestamps as well, two general methods for evaluating and verifying the responses were... 

One of the security issues in database outsourcing scenario is the correctness of the query results. Correctness verification includes integrity, completeness and freshness of the results. Most of the proposed approaches for correctness verification impose high overhead on the components of the scenario which prevents the scenario to implemented in practical applications. In this thesis, we have proposed a probabilistic approach which imposes acceptable overhead for correctness verification of returned results of service provider. The approach uses the previous behavior of the service provider to calculate a trust value toward it which is used to adjust the imposed overhead. In other words,... 

One of the important concepts in cosmology is that all of the observations is done on the past light-cone. In general, cosmological linear perturbation theory is done in a particular gauge and often on spacelike hyperplanes. Then in order to link quantities calculated in perturbation theory with observables, we have to take into account effects coming from projecting these quantities onto past light-cone. We aim in this thesis to study these effects and to calculate corrections over observable quantities such as, two point correlation function and power spectrum of matter perturbations in cosmos. For a particular observational example, in the end we study clustering of structures in... 

Generally to deal with errors in communication systems, two methods have been proposed: FEC and ARQ. In FEC, redundancy bits are added to the data that causes detection and correction of certain error patterns. ARQ method is based on retransmission of information if there is an error in the information. Another method, which is called Hybrid-ARQ, is the combination of these two methods; there are two types of TypeI and TypeII for this category. In typeI, number of redundancy bits in consecutive transmissions of one codeword is constant but in typeII, number of redundancy bits of a codeword increases in subsequent retransmissions.
To deal with burst errors, we can use interleaving along... 

Cloud and distributed storage systems can provide large-scale data storage and high data reliability by adding redundancy to data. Redundant data may get lost due to the instability of distributed systems such as hardware failures. In order to maintain data availability, it is necessary to regenerate new redundant data in another node, referred to as a newcomer and this process reffered to repair process. Repair process is expected to be finished as soon as possible, because the regeneration time can influence the data reliability and availability of distributed storage systems. In this context, the general objective is to minimize the volume of actual network traffic caused by such... 

The objective of this project is to design and control and optimize a single-stage three-phase three-switch unity power factor telecom rectifier. For this purpose, the topology of three-phase three-switch converter has been investigated for both isolated and un-isolated converters. Following a comprehensive investigation on the converter structure, the power dissipation factors have been detected and the quantity of the power dissipation has been calculated by analytical methods and it confirmed by simulation results. To avoid extra power losses some novel soft-switched structures for three-phase three-switched converters have been introduced. the proper operation of the soft-switched... 

During years, supersymmetry has been a candidate for resolution of Higgs mass fine-tuning problem that is quadratic dependence of scalar mass radiative correction to UV-physics. So, supersymmetry phenomenology is of great importance. As accelerators have reached energy of 13 TeV in recent years and sparticles have not yet been observed, it is important to have a theory in hand, describing SUSY breaking dynamics with scale of SUSY breaking above the energies currently accessible to accelerators. As a result of mass-sum-rule constraint which holds in theories with spontaneous SUSY breaking at tree level and leads to light sparticles and even tachyonic directions, there are currently no... 

The spatial diffusion of house prices has been the subject of research for many years. Most of these studies have found a strong relationship between neighboring regions and a weaker relation between nonneighbors. This study uses changes in real house prices within Tehran at the level of municipality zones to illustrate the ripple effect by using quarterly house price data of Tehran’s twenty municipality zones since 1371 to 1391. It also aims to illustrate the heterogeneity in spatial spillovers of house prices development across space and time. We found that a positive shock in house prices diffuse more rapidly that a negative shock; the time shock will diffuse also have a heavier level... 

Scratchpad memory (SPM) is extensively used as the on-chip memory in modern embedded processors alongside of the cache memory or as its alternative. Soft errors in SPM are one of the major contributors to system failures, due to ever-increasing susceptibility of SPM cells to energetic particle strikes. Since a large fraction of soft errors occurs in the shape of Multiple-Bit Upsets (MBUs), traditional memory protection techniques, i.e., Error Correcting Code (ECCs), are not affordable for SPM protection; mainly because of their limited error coverage and/or their high overheads. This thesis proposes a novel recomputation-based algorithm that efficiently protects SPM with high error... 

In this thesis we are going to show various relations between AdS/CFT correspondence and quantum information theory. For this aim we have a brief review about this correspondence and describe how one can derive linearized Einstein's equations using holographic prescription of entanglement entropy. It is explained how the quantum error correction concept can help us to solve the paradoxes due to extrapolate dictionary. After introducing $ T\overline{T} $ deformation and complexity, we use the path integral optimization approach of Takayanagi and collaborators to find the time slice of geometries dual to states in the $ T\overline{T} $-deformed two dimensional conformal field theories... 

In this thesis, new boundary conduction mode boost PFCs are proposed and implemented for different power levels according to the characteristics and requirements of each power level. For medium power applications, we have proposed a new zero voltage switching PFC based on a synchronous boost converter which is controllable with conventional boundary conduction mode PFC control ICs without requiring any additional timing adjustment control circuits other than a special high side driver that consists of only low voltage components. Based on mathematical calculations, we have proposed two sipmle circuit solutions to reduce the high level of line current zero crossing distortion in the proposed... 

In this project the novel zero-voltage-switching topology for power factor correction bridgeless boost rectifier is proposed. By employing an improved ZVS pulse-width-modulation (PWM) switch cell, ZVS of all the main switches is achieved without additional current or voltage stress of main switches. Also for the auxiliary switch the zero-current-switching is provided. In all modes of opretion of this converter, the power path is provided by maximum two semiconductor so the conduction loss of converter is low as in conventional converter. With this features the efficiency of proposed converter is very high  

Recent success of Deep Learning models, resulted in their evergrowing application in many fields. However these models usually require huge datasets, which can sometimes be hard to collect. One of the challenges related to medical data, is the Batch Effect; Medical data is usually gathered through multiple experiments. Each experiment might have a slightly different conditions than the other, resulting a shift in the data related to that batch. Batch effects can have more severe impact during testing time, as the shift in the data distribution could be bigger. Many methods have been proposed to reduce or remove the effect of external conditions on data distribution.Deep Learning models have...