Sharif Digital Repository

the theses is composed of two main parts related to the nonlinearity of vectorial functions. The first part is devoted to maximally nonlinear vectorial function (bent vectorial functions) which contribute to an optimal resistance to both linear and differential attacks on symmetric cryptosystems. They can be used in block ciphers at the cost of additional diffusion-compression-expansion layers, or as building blocks for the construction on substitution boxes (S-boxes) and they are also useful for construction robust codes and algebraic manipulation detection codes. A main issue on bent vectorial bent functions is to characterize bent monomial trace functions leading to a classification of... 

Fuel cells convert the chemical energy of hydrogen and oxygen directly into the electricity. Their high efficiency and low emissions have made them a prime candidate for powering the next generation electric vehicles. Polymer electrolyte membrane is a key component of the PEM fuel cells. One of the critical problems to overcome in some PEM fuel cells is the water management because If there is not enough water, the membrane becomes dehydrated which leads to a rapid increase in ohmic resistance. On the other hand, if too much water is present, flooding may occur resulting in the pores of the gas diffusion filled by water and the available passage for reactant gases is decreased. In this work...