Sharif Digital Repository

Advances in computing and networking areas lead to advent of malwares with new and sophisticated features. One of these type of malwares are environment sensitive malwares which behave differently when finding out specific signs in the execution environment. They first was considered and defined in the context of malware analysis systems; meaning that these types of malwares stop their malicious behavior when detecting analysis machine as their execution environment. In this way they could challenge and evade analysis process. Afterwards, the domain of environment sensitive malwares went beyond the analysis systems and covered all environmental sensitivities which hinder the progress of... 

Neutron noise equations, which are obtained by assuming small perturbations of macroscopic cross sections around a steady-state neutron field and by subsequently taking the Fourier transform in the frequency domain, have been usually solved by analytical techniques or by resorting to diffusion theory, but in this thesis, in order to increase of accuracy of neutron noise calculation, has been used transport approximation for neutron noise calculation and the Monte Carlo method has been used to solve transport equation of the neutron noise in the frequency domain. Since the transport equation of the neutron noise is a complex equation, a new Monte Carlo technique for treating complex-valued... 

Shock wave–bubble interaction is not yet fully understood, while has many important applications. Such physics for example appears in sonoluminescense phenomenon, wherein a sinusoidal pressure field causes a gas bubble to first become large and then small enough to collapse. In this complex physics, spherical shock wave also appears right before, during, and right after the bubble bursting. On the other hand, modeling the interface between the liquid and gas in such problems, in which the gas becomes compressible is challenging. In this regard, Ghost-Fluid/Front Tracking method has shown to be very practical. In this work, the Euler equations have been computationally solved to simulate the... 

In this thesis we consider the dynamics of a general predator-prey model which generalizes several known predator-prey, assuming that the intrinsic growth rate of the pray, the predation rate, and the removal functions are given in an unspecified form. Using the Lyapunov method, we derive sufficient conditions for the stability of the equilibria. also, we consider a delayed periodic predator- prey model and sufficient conditions are derived for the existence, uniqueness and global asymptotic stability of positive periodic solutions of the model.

 

Nowadays, the use of processed conductive polymers for conducting matrix polymers, as well as improving other properties for planting in the body, is very common. In this project, the fabrication and identification of electrically conductive films and fibers from biocompatible poly lactic acid and conductive polyAniline polymer in the form of nano-fibers or nanoparticles was intended. These fibers and films have been made in form of a plate or tube then, have been used as biosensors. These polymeric prostheses should be sterilized before planting in human body. Gamma rays are the best sterilization methods and are used at low doses (25 kGy) to sterilize plastic medical supplies. On the other...