Sharif Digital Repository

The compressibility behavior of Al-SiC nanocomposite powders was examined and the density-pressure data were analyzed by linear and non-linear compaction equations. SiC particles with an average size of 50 nm were mixed with gas-atomized aluminum powder (40 μm average size) at different volume fractions (up to 20 vol%) and compacted in a rigid die at various pressures. In order to highlight the effect of reinforcement particle size, the compressibility of micrometric SiC particles of two sizes (1 and 40 μm) was also examined. Analysis of the compressibility data indicated hindering effect of the hard ceramic particles on the plastic deformability of soft aluminum matrix, particularly at high... 

The compactification of 6 dimensional Salam-Sezgin model in the presence of 3-form flux H is investigated. We find a torus topology for this compactification with two cusps which are the places of branes, while at the limit of large size L of the compact direction we also obtain sphere topology. This resembles the Randall-Sundrum I,II model. This compactification also provides an example for the so-called 'time warp' solution, [0812.5107 [hep-th]]. According to a no-go theorem in d6, the time warp compactification violates the null energy condition. While the theorem is quiet for d = 6, our model gives a time warp compactification which satisfies the null energy condition. We also derive the... 

TiO 2 -rGO nanocomposite coatings were obtained by electrophoretic deposition (EPD) technique of TiO 2 nanoparticles and graphene oxide (GO) on stainless steel substrate. First, GO particles were synthesized using a modified Hummers' method. GO was reduced electrochemically to form a coating in the presence of nano-sized TiO 2 particles. The influences of different parameters such as GO concentration, coupling co-electro-deposition parameters (electrophoretic duration and voltage) on thickness, surface morphology and, corrosion behavior of the as-synthesized TiO 2 -rGO nanocomposite coatings were systematically surveyed. The morphology and microstructure were investigated by field emission... 

Motivated by realizing open/closed string duality in the work by Gopakumar [Phys. Rev. D 70, 025009 (2004)], we study two- and three-point correlation functions of R-current vector fields in script N = 4 super-Yang-Mills theory. These correlation functions in free field limit can be derived from the worldline formalism and are written as heat kernel integrals in the position space. We show that reparametrizing these integrals converts them to the expected AdS supergravity results which are known in terms of bulk to boundary propagators. We expect that this reparametrization corresponds to transforming open string moduli parametrization to the closed string ones. © 2008 World Scientific... 

We study type IIA superstring theory on a PP-wave background with 24 supercharges. This model can exactly be solved up to quadratic fermionic action and then quantized. The open string in this PP-wave background is also studied. We observe that the theory has supersymmetric Dp-branes for p=2,4,6,8. © 2003 Elsevier Science B.V  

In the present research, different weld layers were deposited on a 1.2714 steel die by gas tungsten arc (GTA) welding with the weld wire of Udimet 520, and effects of welding parameters on microstructure and mechanical properties of Udimet 520 superalloy were investigated. The results showed Udimet 520 weld with cellular-dendritic and rarely dendritic structure including γ matrix rich of Cr, Mo and W, low percentage associated with order morphology and relative uniform distribution of MC type carbides. Udimet 520 alloy showed high resistance against hot cracking during welding and hot cracking occurred only at high input heat values. Also, cracking during welding occurred at the places that...