Sharif Digital Repository

Using database encryption to protect data in some situations where access control is not soleley enough is inevitable. Database encryption provides an additional layer of protecton to conventional access control techniques. It prevents unauthorized users, including intruders breaking into a network, from viewing the sensitive data. As a result data remains protected even in the event that database is successfully attacked or stolen. However, encryption and decryption of data result in database performance degradation. In the situation where all the information is stored in encrypted form, one cannot make the selection on the database content any more. Data should be decrypted first, so an... 

This thesis aims to discuss matters in the area of non-symmetrical contact. Problems have been solved by the use of different numerical methods and their precision has been determined. In most projects which have been conducted in regards with contact's studies, Indenter has been considered vertical on the other object and particles of two objects are moving in the vertical direction of the free surface. This matter has resulted in obtaining symmetrical functions relevant to the point of beginning contact which helps distributing contact pressure, stresses and movements. In addition, mostly profiles of two involved objects are considered symmetrical that this matter greatly contributes... 

Quorum Sensing is a cell-to-cell communication pr°Cess depending on cell concentration. Communication among bacterial cells °Ccurs through small molecular signals called autoinducers. The consequences of quorum sensing include the activation of pathogenic properties and activation of the gene for biofilm formation. Biofilms are aggregations of bacteria that adhere to surfaces through extracellular polymeric substances. Bacteria in the biofilm phase are much more resistant to antimicrobial agents than their free-swimming counterparts (i.e. the bacteria in planktonic form). In this study, first a series of coumarin derivatives were synthesized; but due to low solubility of the synthesized... 

In the early days of quantum mechanics it seemed that, this theory is presented to describe atoms and molecules. As the time went on, by distinguishing different applications of quantum mechanics a question raised in scientists minds. Is it possible to see strange quantum effects in every day life. In this regard several attempt have been made to see such properties. One of these phenomena is observing interference effects for Fulleren molecules. In this thesis we investigate different properties of a macroscopic quantum system in different situations. We showed that an asymmetric double well potential, which is a macroscopic quantum system in interaction with environment violates... 

This study presents a novel perspective on pressure-transient analysis (PTA) of downhole-pressure and flow-rate data by use of system-identification (SI) techniques as widely used in advanced process engineering. Key features of the algorithm are that it considers the classic PTA process from a system-theoretical perspective; derives the causal structure of the flow dynamics; proposes a method to deal with continuously varying pressure and flow-rate signals contaminated with correlated noise, which estimates physical reservoir parameters through a systematic matching procedure in the frequency domain; and can cope with arbitrary (i.e., not necessarily piecewise constant) flow-rate signals.... 

PMMA bone cement lacks biodegradability and the ability to bond with surrounding bone tissue. Therefore, the development of a new generation of bioactive bone cements that are biodegradable and possess adequate mechanical properties as well as desirable setting time is receiving remarkable interest.In this study, we have developed novel mineral-based bioactive bone cements. Our mineral bioactive bone cements were composed of Calcium Sulfate Hemihydrate, Bioactive Glass, and Tricalcium Silicate. Firstly, a binary system composed of Calcium Sulfate Hemihydrate and Bioactive Glass was optimized based on mechanical and setting behavior. Secondly, Tricalcium Silicate was added to the powder phase...