Sharif Digital Repository

Basically, it is required that the materials used as electrical contacts should have good thermal and electrical conductivity and certain strength. The copper base composites with fine TiO2 particles as reinforcement have almost identical electrical and thermal conductivity with copper; in addition, they have the advantage over pure copper in high strength owing to the dispersion of the fine TiO2 particles, which improve copper matrix strength through impeding dislocation movement. In this present work, at the initial stage, Cu and Ti powders were mechanically alloyed for 60h under Argon atmosphere, and then added Cu2O powders as oxidant. The specimens, containing different amounts of TiO2,... 

Wireless sensor networks have many applications, vary in size, and are deployed in a wide variety of areas. They are often deployed in potentially adverse or even hostile environment so security issues are of much concern in these networks. Key management is a fundamental security issue in sensor networks. In this thesis, we are mainly focusing on key establishment and group rekeying schemes aspects of key management. Due to limited resources of sensor networks, key pre-distribution schemes are currently viewed as the most promising solution. Key predistribution in sensor networks refers to the problem of distributing secret keys among sensor nodes prior to deployment. Recently, many key... 

By increasing speed gap between microprocessors and off-chip Last Level Cache, Optimization in Last Level Cache makes improvement in system performance. With development of new generation of multi-core processors and sharing LLC between these cores, the so called issue of Memory Wall has caused an incremental effect of LLC on system performance. There are three approaches to use this memory more efficiently:
1. Increasing cache capacity
2. Making cache hierarchical and adding different layers to hierarchy
3. Improvement of replacement algorithms in cache memory
The first approach has not been used in regard with limitation of technology and growth of access time due to... 

Considering that automobile weigth reduction in industry is important, improvement the strength of low carbon steel sheets is important. These sheets can be supported the service condition in lower thicknesses. Bulk nano-structured materials have been mostly attracted in materials science due to their unique physical and mechanical properties. Severe plastic deformation (SPD) is one of the most efficient methods to produce ultra fine grained or nano-structured materials. Materials produced by SPD are of great importance because of (1) non-porous structure, (2) great mechanical properties such as high strength and toughness and (3) proper dimension for mechanical and physical testing. ... 

Brazing is a crucial process for repairing and manufacturing high-temperature components made of precipitation-hardened superalloys. Boron-containing filler metals are amongst the most common filler metals used for repairing and joining superalloys. Although boron is an effective MPD in such filler metals, the formation of brittle boride intermetallics in the joining area (Athermal solidification zone and diffusion affected zone), due to the low solubility of boron in the matrix of superalloys, is inevitable. Isothermal Solidification is known as an effective technique for removing boride compounds in the joining area of brazed components. but as the time of isothermal solidification...