Sharif Digital Repository

Magnesium and its alloys have been used as biodegradable implements in recent years. However Magnesium implements may corrode in the body before the natural healing process of the damaged tissue. MAO process was studied in order to reduce primary corrosion of Magnesium alloy in Simulated Body Fluid (SBF). MAO coating was created on AZ31 alloy in a nontoxic alkaline-silicate solution at DC current densities of 5, 10, 15 and 20 mA/cm2 for 30 minutes and the current was in form of 20-10-5 mA/cm2 steps that each were applied for 10 minutes. The maximum corrosion resistance was observed for the mentioned step applied current in a 30g/l Sodium Silicate solution. Furthermore the effects of adding... 

catalyzed oxidation of organic compounds such as olefins, sulfides, benzylics alcohols and phenolics. Cyanide-catalyzed aldimine coupling was employed to senthesize compounds with a-imineamine structural motifs : 2,3-di-(2-hydroxyphenyl)-1,2-dihydroquinoxaline, that way for synthesized NONO tetra-dentate Schiff-base ligands. With attention to solid geometry these ligands are possible to synthesize homo and hetronuclear mixed-ligand complexes. we are also synthesized homonuclear mixed-ligand Mn(III) and hetronuclear Mn(III)-Fe(III) with tetradentate Schiff-base ligand quinoxaline and acetyl acetone ligand. These complexes and ligands are characterized by FT-IR, 1H NMR, 13C NMR, UV and... 

Orthogonal Frequency Division Multiplexing (OFDM) is a digital transmission method developed to meet the increasing demand for higher data rates in communications which can be used in both wired and wireless environments. This thesis describes the issue of the Peak to Average Power Ratio (PAPR) in OFDM system, based on compressed sensing at the receiver of a peak-reducing sparse clipper applied to an OFDM signal at the transmitter. By choosing proper clipping threshold, clipping signal will be sparse so locations, magnitudes, and phases of the clipping signal can be recovered by compressed sensing method. We demonstrate that in the absence of optimization algorithms at the transmitter,... 

Localization of electrical activity in the brain is one of the major problems in cognitive science and neuroscience. Indeed, Source localization is the inverse processing procedure on brain signals to estimate the location and position of resources in the human brain. Current technics for neurological imaging is included fMRI، PET، MEG and ERP. These methods is not appropriated to answer the question that when does each of different components of the brain begin their activity. The EEG signals could be useful to eliminate some of limitations of above methods. The problem with EEG signals collected from the skull is that they don’t refer directly to the location of active neurons. The... 

When organizations prefer to outsource their data, security protection of data will be more important. Using cryptography in addition to access control techniques is a natural way for saving confidentiality of data against untrusted server. However, encryption and decryption of data result in database performance degradation. In such a situation all the information stored in encrypted form, one cannot make the selection on the database content any more. Data should be decrypted first, so an unwilling tradeoff between the security and performance is normally forced. The appropriate approaches to increase the performance are methods to deal directly with the encrypted data without firstly... 

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... 

Existing Intrusion Detection Systems (IDSs) are not designed to deal with all categories of processing environments. This thesis focuses on IDSs for the Grid computing environment, and concentrates on feature selection and performance. An existing framework, Globus, is used as the basis for the consideration and development of the research issue in Grid computing. The system is based on two engine designs: (a) Signature and (b) Support Vector Machine; SVM has been selected for pattern discovery in traffic analysis. We found that the performance of the system greatly depends on the efficiency of the underlying framework and the number of Intrusion Detection System instances. We demonstrate... 

While intrusion detection systems (IDSs) are widely used, large number of alerts as well as high rate of false positive events make such a security mechanism insufficient. Accordingly, a track of recent security research, focused on alert correlation. This thesis proposes a Hidden Markov Model (HMM) based correlation method of intrusion alerts which have been fired from different IDS sensors across an enterprise. We used HMM to predict the next attack class of the intruder that is also known as plan recognition. Our method has two advantages. Firstly, it does not require any usage or modeling of network topology, system vulnerabilities, and system configurations. Secondly, as we perform high... 

Today many communications take place over asynchronous insecure networks which do not provide any guarantee of security (as Internet); hence there is a must in authenticating party or parties with which we are going to interact. In many cases, more than two parties (entities) are going to interact, resulting in need of group authentication. Since authentication is inseparable from key exchange, we are going to introduce a new authenticated group key exchange protocol in this thesis which benefits from all known features for such a protocol in the literature such as contributiveness and deniability. To overcome the problem of concurrency, we use a framework dedicated to security in concurrent... 

Data outsourcing is considered as a promising approach in today computing and connected world. This approach enables organizations to outsource their data to anexternal third party server which is responsible for storing and propagation of outsourced data. Although data outsourcing offers many benefits, especially for those organizations with limited resources and increaseing data volume, but this approach in security aspects like providing confidentiality and privacy about curious external third party or other threats, is faced by serious challenges. In the recent decade many approaches for solving or at least decreasing the potential threats over providing confidentiality of outsourced... 

Electronic voting refers to voting methods that is done using electronic devices or via the Internet or Web. Helios and Civitas protocols are among the recent protocols introduced in this field. Importance and high sensitivity of electronic voting protocols has led researchers to pay high attention about their security analysis. In recent years, different approaches have been used to inspect and analyze electronic voting protocols. In many of such approaches, analysis had been done in a very abstract environment and without considering the operational requirements.The purpose of this thesis is to evaluate the security features of electronic voting protocols, considering their operational and... 

In this paper, we consider a three-echelon supply chain consisting of a producer, a distributor and a retailer. Generally each echelon tends to minimize his own inventory costs. On the other hand, competitive environment of business market, force companies to develop strategic alliances. In order to boost their partnership, separated echelons must integrate their policies, so that the total cost of the system be minimized. The model, extends the research of Wang et al.(2011) by changing the No shortage assumption into backlog shortage model.
This study assumes different deterioration rates among different echelons, and deterioration rates are time-sensitive, which is very helpful in... 

Inventory control has been always considered important due to its prominent role in managing and better application of resources in the field of operational systems. Ordering system or review stock policy in supply chain management can be mentioned as one of the inventory control study fields of management. A lot of researches have been done in investigating ordering system in supply chain under certainty conditions; however, since the real world is full of uncertainties, parameters such as demand cannot be predicted exactly and we encounter with ambiguity. In this case, using crisp (exact) values can cause to decide wrongly (a wrong decision). On the other hand, due to absence of sufficient... 

End-to-end electronic voting protocols for electronic voting systems are used to hold a secure election with the two features of anonymity and verifiability. Verifiable mixnets are a fundamental element of electronic voting systems, which can keep the voters anonymous by mixing their votes, and provide a verifiability mechanism to prove their performance correctness. As the design of electronic voting protocols is error-prone, researchers consider the use of mathematics-based and systematic methods for their analysis. Therefore, based on formal methods and the process algebra approach, several studies have been conducted to analyze these systems, but none have properly analyzed verifiable... 

This thesis is related to applying survey of scientific inventory control methods in Khoramshahr Oil Extraction Company (KHOEC). KHOEC is the producer of edible oils in I.R of Iran and is a subset of E.T.K.A holding organization. The inventory costs of high consuming items are studied and optimized based on the optimal ordering policy (r, Q). First, the company raw materials are identified and classified based on ABC analysis method. For developing the new method of inventory control, the demand for each item is predicted, and the probability distribution of demand during the lead time is determined. Then according to this information and the desired service level of management, order point... 

This thesis presents a location- inventory model for dual-channel supply chains .Dual-channel supply chains have two channels for sale the traditional in-store (retail) channel and the online (retail) channel.The model assigns online demands to the capacitated stores currently serving in-store demands. Keeping the delivery network of the in-store demands unchanged, the model aims at minimizing the summation of transportation cost, inventory cost, and fixed handling cost in the system while assigning the online demands. We assume that at the beginning of each period a distribution center which just distributes products to the stores, follows an order-up-to policy which increases the total...