Mechanistic modeling of architectural vulnerability factor

Reliability to soft errors is a significant design challenge in modern microprocessors owing to an exponential increase in the number of transistors on chip and the reduction in operating voltages with each process generation. Architectural Vulnerability Factor (AVF) modeling using microarchitectural simulators enables architects to make informed performance, power, and reliability tradeoffs. However, such simulators are time-consuming and do not reveal the microarchitectural mechanisms that influence AVF. In this article, we present an accurate first-order mechanistic analytical model to compute AVF, developed using the first principles of an out-of-order superscalar execution. This model provides insight into the fundamental interactions between the workload and microarchitecture that together influence AVF. We use the model to perform design space exploration, parametric sweeps, and workload characterization for AVF

Direct simulation of electrorheological suspensions subjected to pressure driven flow and spatially non-uniform electric field

A numerical method based on the distributed Lagrange Multiplier method is developed for direct simulation of electrorheological (ER) suspensions subjected to pressure driven flows and spatially non-uniform electric fields. The flow inside particle boundaries is constrained to be rigid body motion by the distributed Lagrange multiplier method and the point-dipole approximation is used to model the electrostatic forces acting on the polarized particles. Simulations show that the particles move to the regions of high electric field when the value of β, the Clausius-Mossotti factor is positive and they move to the regions of low electric field when the value of β is negative. Also, dielectrophoretic force can be used for separating particles with different β values. Using the simulation method the evolution of the microstructure under the influence of electrostatic forces (particle-particle interaction force and dielectrophoretic force) and hydrodynamic forces is analyzed. The different microstructures formed are explained on the basis of non-dimensional parameters that determine the relative strength of the various forces. Simulations show that even when the particle-particle interaction force, dielectrophoretic force and hydrodynamic force coexists, the parameters can be judiciously manipulated so that either the yield stress and viscosity of the ER fluid increases or the particles get collected in the regions of low or high electric fields

Direct numerical simulations and experimental investigation of dielectrophoresis

This dissertation deals with the numerical and experimental studies of the phenomenon of dielectrophoresis, i.e., the motion of neutral particles in nonuniform electric fields. Dielectrophoresis is the translatory motion of neutral particles suspended in a dielectric medium when they are subjected to an external nonuniform electric field. The translatory motion occurs because a force called the dielectrophoretic force, which depends on the spatial variation of the electric field, acts on the particles. As the generation of force involves no moving parts and the particles can be moved without touching them, dielectrophoresis can be used in many applications, including manipulation and separation of biological particles, manipulation of nanoparticles, etc. In the present study, the numerical simulations of the fluid-particle system are performed using a direct numerical simulation scheme based on the distributed Lagrange multiplier method. In this scheme, the fluid flow equations are solved both inside and outside the particle boundaries and flow inside the particle boundary is forced to be a rigid body motion by using the distributed Lagrange multiplier. The electrostatic force acting on the particles is computed using the point dipole method. The scheme is used to study the behavior of particles in the suspension under the influence of a nonuniform electric field. The numerical scheme is used to study the influence of a dimensionless parameter, which is the ratio of electrostatic particle-particle interactions and dielectrophoretic force, in the dynamics of particle structure formation and the eventual particle collection. When this parameter is of order one or greater, which corresponds to the regime where particle-particle interactions are comparable in magnitude to the dielectrophoretic force, simulations reveal that the particles form interparticle chains and the chains then move to the electrode edges in the case of positive dielectrophoresis. When this parameter is of order ten the particles collect in the form of chains extending from one electrode to the opposite one clogging the entire domain. On the other hand, when this parameter is less than order one, particles move to the electrode edges individually and agglomerate at the edges of the electrodes. The results of numerical simulations are verified experimentally using a suspension of viable yeast cells subjected to dielectrophoresis using microelectrodes. The experiments show that at frequencies much smaller than the crossover frequency where the value of the above parameter is greater than order one, the yeast particles form chains and then move and collect at the electrode edges. Where as, at frequencies closer to the crossover frequency where the value of the parameter is less than order one, particles move individually without forming chains and agglomerate at the electrode edges. The numerical simulation scheme is also used to study the dielectrophoresis of nanoparticles. Simulations show that in a uniform electric field the Brownian force is dominant and results in the random scattering of the particles. In the case of nonuniform electric field, it is possible to overcome the Brownian force and collect the particles at pre-determined locations, even though the trajectories of the particles are influenced by Brownian motion. Finally, the method of images is used to improve the electric field solution when the particles are close to the domain walls. Simulations performed for uniform electric fields with the method of images shows that when the distance between the particle and domain boundary is of the order of particle diameter the influence of the particles on the electric field boundary conditions is significant