Sharif Digital Repository

In the recent years, popularity and number of users of mobile social networks have grown significantly. Due to different types of communication on these networks, users share a lot of information with each other. One of the most critical challenges of social networks is disclosure and unauthorized access to information, data, and communication between users that is a kind of violation of their privacy, which can be done by social network providers, especially unauthorized users. One way to protect one's privacy is using encryption. Therefore, in the present paper, an improved secure design was presented for mobile social network using ciphertext-policy attribute-based encryption (CP-ABE) and... 

As requirements and environments become much more complex, the need for self-adaptive and self-healing software system grows. There are several existing works which present such systems by using different approaches. Using alternative solutions to provide a service or requirement is one of the most important approaches among existing works. In this paper an alternative-based approach for adding self-adaptive capabilities to software systems is proposed. In this approach a group of autonomic elements will be constructed based on different design or implementations that could be considered for a specific service or requirement. By using this approach, a highly adaptive software system could be... 

Different attacks on routing protocols in ad hoc networks occur that one of the most dangerous types is called wormhole attack. This attack happens with the assistance of at least two or more malicious nodes. In this attack nodes create a private tunnel which if a packet comes to one of them, it will be guided to other pair of these malicious nodes by this tunnel and that node broadcasts it into network. This action provides a short connection in the network that is controlled by these malicious nodes. Hence they control all Packets that come to them and threaten the security of data within packets or delete them. Totally, what a wormhole does is an incorrect understanding of network... 

Secure routing is one of the most important topics in the wireless MANETs networks. MANETs networks don't have a central infrastructure for the management of routing in the networks. Each node independently routes and sends packets, so many attacks such as forging, modifying, and denial of service (DoS), Occur in these networks. In this paper, we present the new protocol, SEAODV; Secure Efficient Ad-hoc on Demand Routing Protocol for MANETs networks. SEAODV is based on the AODV algorithm and in comparison with existing secure AODV protocols such as SAODV, ARAN and SEAR have improved security and performances. SEAODV uses HEAP authentication Scheme with symmetric cryptography and one-way hash... 

Different attacks on routing protocols in ad hoc networks occur that one of the most dangerous types is called wormhole attack. This attack happens with the assistance of at least two or more malicious nodes. In this attack nodes create a private tunnel which if a packet comes to one of them, it will be guided to other pair of these malicious nodes by this tunnel and that node broadcasts it into network. This action provides a short connection in the network that is controlled by these malicious nodes. Hence they control all Packets that come to them and threaten the security of data within packets or delete them. Totally, what a wormhole does is an incorrect understanding of network... 

In recent years, mobile social networks have largely been developed and gained considerable popularity. An approach to protecting privacy on mobile social networks is the use of encryption and access control. Good alternatives for use on mobile social networks are the Public Broadcast Encryption approach for appropriate concordance and consistency with the structure of social networks as well as the Attribute-Based Encryption owing to its capability and proper implementation of the access control policy. Accordingly, in this paper, a framework was presented based on the Public Broadcast Encryption and Attribute-Based Encryption. Using proxies, we outsourced some of these operations in the... 

Nanocrystalline lead zirconate titanate (PZT) powders have been synthesized using microemulsion processing route. Microemulsion is one of the major processing techniques to synthesize a nanosize, homogenous, and almost agglomerate free ceramic powders. The ternary microemulsion system is consisted of cyclohexane as the oil phase, Triton X100 as the nonionic surfactant phase, and an aqueous phase containing 0.619MPb 2+, 0.325MZr 4+, and 0.3MTi 4+, representing a Pb 2+: Zr 4+: Ti 4+ molar ratio of 1:0.52:0.48. The ratio of these cations has been adjusted using Inductively Coupled Plasma (ICP) technique. After coprecipitation of metallic hydroxides by adding ammonia solution in microemulsion... 

Dealing with crosscutting requirements in software development usually makes the process more complex. Modeling and analyzing of these requirements in the software architecture facilitate detecting architectural risks early. Distributed systems have more complexity and so these facilities are much useful in development of such systems. Aspect oriented Architectural Description Languages(ADL) have emerged to represent solutions for discussed problems; nevertheless, imposing radical changes to existing architectural modeling methods is not easily acceptable by architects. Software architecture analysis methods, furthermore, intend to verify that the quality requirements have been addressed... 

In this research, (X)PZT-(1-X)PMN ceramics (where X is 0.25, 0.5 and 0.75) were achieved from a conventional mixed-oxide method. Lead Zirconate titanate (PZT) powders with composition near the morphotropic phase boundary have been synthesized via a microemulsion processing route. Modified mixed oxides method was used for obtaining single phase Lead Magnesium niobate (PMN) powder with high relative density (98% of T.D.) and good electrical properties (dielectric constant of ≈10 4 at room temperature). Two-step sintering (TSS) has been applied to suppress the accelerated grain growth of PZT-PMN composite compacts in the last sintering stage. The produced samples with high PZT content showed... 

The inertial microfluidic technique, as a powerful new tool for accurate cell/particle separation based on the hydrodynamic phenomenon, has drawn considerable interest in recent years. Despite numerous microfluidic techniques of particle separation, there are few articles in the literature on separation techniques addressing external outlet geometry to increase the throughput efficiency and purity. In this work, we report on a spiral inertial microfluidic device with high efficiency (>98%). Herein, we demonstrate how changing the outlet geometry can improve the particle separation throughput. We present a complete separation of 4 and 6 μm from 10 μm particles potentially applicable to... 

Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) have been widely applied in fixed partial prostheses as well as dental uses i.e. a substructure for crowns. However, Y-TZP has limited applications, which is due to the presence of defects in its microstructure introduced during the manufacturing process. Accordingly, due to Y-TZP limitations, the novel (X)Y-TZP- 20Al2O3-(80-X) SiO2 (X = 65, 70 and 75) ceramic nanocomposites were successfully fabricated via the powder metallurgy method. X-ray diffraction (XRD) patterns of commercial powders showed the stabilization of monoclinic zirconia (ZM) by increasing the silica content. In order to determine the fracture load and micro-bending... 

Secure routing is a major key to service maintenance in ad hoc networks. Ad hoc nature exposes the network to several types of node misbehavior or attacks. As a result of the resource limitations in such networks nodes may have a tendency to behave selfishly. Selfish behavior can have drastic impacts on network performance. We have proposed a Misbehavior-Tolerant Multipath Routing protocol (MTMR) which detects and punishes all types of misbehavior such as selfish behavior, wormhole, sinkhole and grey-hole attacks. The protocol utilizes a proactive approach to enforce cooperation. In addition, it uses a novel data redirection method to mitigate the impact of node misbehavior on network...