Sharif Digital Repository

Trust management is a new security solution for situations that there is not enough information about the members of a system. As other security solutions, trust management solutions are not secure against attacks and malicious behaviors. Collusion is one of the most destructive malicious behaviors in these systems. Colluders seek to unfairly affect the trust system. Most of the trust models are vulnerable against this malicious behavior or consider only a limited set of collusion scenarios to resist. Some other mitigation approaches are specific to a trust model and cannot be used by other models. One of the methods to implement trust is exploiting reputation. Reputation systems can be... 

The dynamic behavior of networks largely depends on their structural properties. The information or failures can spread through the links of complex networks constructed by people or agents, and their physical and informational contacts. In this research, the process of network diffusion was investigated in different model and real networks. In particular, we focused on ”cascaded failure” and ”viral marketing” which are among the major topics that have attracted much attention in this context. Firstly, we investigated the robustness of modular complex networks against random and systematic component failures. Many real-world networks have modular structure and they may undergo random errors... 

This study focused on the tolerance of fungi strains including Aspergillus niger, Aspergillus foetidus and Penicillium for different metals (Ni, Co, Mo, V, Mn, Mg, Fe, W and Zn ). Then Aspergillus niger was exposed to mixture of Mo, V and Mn (at a mass ratio of 1:2:6 as approximately present in the spent refinery processing catalyst). The degree of tolerance was measured from the growth rate in the presence of various metals and compared to a control which contained no metals. Effect of type of strains, type of metal and metal concentration on adaptive tolerance of fungus was evaluated. Adaptation experiments with single metals showed Aspergillus niger tolerated up to 1000 mg/l Ni, Zn, 1500... 

Improving the performance of compressors plays a key role in saving energy in industries. The presence of aleatory and epistemic uncertainties, such as dimensional, geometrical and environmental uncertainties, causes the tolerances that are within the allowed ranges in normal assembly conditions to violate the assembly requirements in operational conditions and cause a drop in compressor efficiency. In order to reach the dimensional and geometrical tolerances of the components of a compressor, especially in the design of the rotor and stator blades, that guarantees the optimal and stable performance while not increasi the production costs, there is a need for an optimal and robust tolerance... 

A perturbed lattice is a point process π={x+Y_x ∶x ∈Z^d} where the lattice points in Z^d are perturbed by i.i.d . random variables {Y_x }_(x∈Z^d ). A random point process π is said to be rigid if π∩B_1 (0) , the number of points in a ball , can be exactly determined given π∩B_1^c (0) , the points outside the ball . The process π is called deletion tolerant if removing one point of π yields a process with distribution indistinguishable from that of π . Suppose that Y_x~N_d (0,σ^2 I) are Gaussian vectors with d independent components of variance σ^2 . Holroyd and Soo showed that in dimensions d = 1 , 2 the resulting Gaussian perturbed lattice π is rigid and deletion...