Sharif Digital Repository

The aggressive device scaling and exponential increase in transistor counts on a chip have increasingly made the modern integrated circuits more susceptible to soft errors. Soft errors are caused by strikes from energetic particles such as neutrons and alpha particles. These errors are making a significant impact in the microelectronics industry. An essential step to design a highly reliable digital system with minimal performance and power penalty is Soft Error Rate (SER) estimation of system components.We propose a very fast and accurate analytical approach to estimate the overall SER and to identify the most vulnerable gates, flip-flops, and paths of a circuit. Our proposed approach fully... 

The present research was conducted to numerical simulation and phenomenology of the pressure fluctuations and instability of the diffuser with the ratio of the diffuser inlet to the nozzle outlet of 1.91. The numerical simulation has been done with k-ω-SST and k-ω-GEKO turbulence models with both steady and unsteady methods for the nozzle with an expansion ratio of 30. Validation of the numerical solution has been done with the help of the experimental test data of the high-altitude test simulator available in the Research Institute of Space Transportation Systems. Tests were conducted by cold gas. Investigations indicate that two types of start occur in the system, stable and unstable... 

In order to test the performance of engines used at high altitudes, a vacuum simulator system is used. In the vacuum test stand the supersonic exhaust diffuser is used to create the vacuum conditions and the automatic discharge of combustion gases into the atmosphere. usually, the exhaust gas temperature of the engine nozzle is much higher than the temperature that steel body of diffuser can stand (above 2500 K). The purpose of this study is to design and analyze a cooling system to protect the diffusers body. In this study, first by comparing different cooling methods, a spray-cooled water treatment method has been selected for the problem. A new algorithm for designing a spray cooling... 

Depending on the geometry and nozzle pressure, increasing the ratio of the diffuser inlet area to the nozzle outlet area can lead to instability in the high-altitude simulator vacuum chamber startup process. This instability results in the formation of harmonic pressure oscillations throughout the diffuser and the vacuum chamber. In this study, a scaled down second throat diffuser with compressed air has been utilized. The performance of the diffuser has been investigated using four conical nozzles with different expansion ratios to simulate instability at area ratios of 1.27, 1.91, 4.1, and 7.81 with rapid nozzle pressure rise. Experiments were conducted by measuring wall pressures along... 

In this work, a high-order accurate gas kinetic scheme based on the compact finite-difference Boltzmann method (CFDBM) is developed and applied for simulating the compressible rarefied gas flows. Here, the Shakhov model of the Boltzmann equation is considered and the spatial derivative term in the resulting equation is discretized by using the fourth-order compact finite-difference method and the time integration is performed by using the third-order TVD Runge-Kutta method. A filtering procedure with three discontinuity-detecting sensors is applied and examined for the stabilization of the solution method especially for the problems involving the discontinuity regions such as the shock. The... 

Often in a vacuum test facility, a supersonic exhaust diffuser uses the energy of the outflow from the nozzle to create and maintain a vacuum condition in the engine test chamber. In this system, the temperature of the motor exhaust gas, which directly hits the diffuser walls, is much higher than the tolerance of the metal body of the diffuser. The purpose of this research is to design a cooling system for thermal protection of diffuser walls of a vacuum simulator using a water-jacket tool. At the beginning of this study, the effective parameters in the design of the water-jacket cooling system were identified. Then, a new algorithm to design and optimize the water-jacket cooling system was... 

In the present study, the effect of the diffuser inlet-to-nozzle exit area ratio (A_d/A_e ) on the gradual starting performance of a second throat exhaust diffuser has been investigated experimentally. Experiments have been carried out with four conical nozzles with different expansion ratios and considering two approaches of gradual increase and gradual decrease of nozzle chamber pressure by a high-pressure air tank. Investigations show that at high area ratios before starting the diffuser, oscillations in the pressure of the test chamber are created due to the instability of the flow at the diffuser inlet. By frequency analysis of the vacuum chamber pressure, it is observed that as A_d/A_e... 

Molecularly imprinted polymers (MIPs) with synthetic recognition sites are capable of detecting and separating chemical species in complex environments. These characteristics are of increasing interest for bioanalytical applications. The chief advantages of MIPs are mechanical and chemical stability, low cost, and ease of preparation. Recently, imprinting technology has been used for fabrication polymer thin films with recognition sites of proteins, plant viruses, and yeasts. Also few investigations applied lithography for synthesis of cell imprinted polymers targeting cell detection and observation of cell morphology.
For the first time, we demonstrate surface imprinting for the... 

Porous polymeric particles have the extensive application in various sciences and various methods have been introduced for production of these particles. Depending on method of production, porous polymeric beads can be produced in diverse shapes, pore size, pores interconectivity, surface morphology and chemical properties. In common methods for production of porous polymeric particles, tuning the size and porosity is difficult or even impossible. Porous polymeric beads with the vast surface area and good functionality have been applied for adsorption of various materials. The purpose of this study is therefore to investigate a new procedure for the production of porous polymeric...