Electric Discharge Machining (EDM) is a process for eroding and removing material by transient action of electric sparks on electrically conductive materials immersed in a dielectric liquid and separated by a small gap. A spark-eroded surface is a surface with matt appearance and random distribution of overlapping craters. It is mechanically hard and stressed close to ultimate tensile strength of the material and sometimes covered with a network of micro cracks. The violent nature of the process leads a unique structure on the machined surface and generates residual stresses due mainly to the non-homogeneity of heat flow and metallurgical transformations. An extensive experimental study is presented to explore the surface and sub-surface characteristics together with the residual stresses induced by the process. Layer removal method is used to measure the residual stress profile in function of depth beneath. A finite element based model is proposed to determine residual stresses and compared with the experimental results. The residual stress pattern is found to be unchanged with respect to machining parameters. Thus, a unit amplitude shape function representing change in curvature with respect to removal depth is proposed. The proposed form is found as a special form of Gauss Distribution, which is the sum of two Gaussian peaks, with the same amplitude and pulse width but opposite center location that is represented by three constant coefficients. In each case, agreement with the proposed form is established with experimental results. Results have shown that these coefficients have a power functional dependency with respect to released energy.

Firm real time system with Poisson arrival process, iid exponential service times and iid deadlines till the end of service of a job, operated under the First Come First Served (FCFS) scheduling policy is well studied. In this thesis, we present an exact theoretical analysis of a similar (M/M/1 + G queue) system with exact admission control (EAC). We provide an explicit expression for the steady state workload distribution. We use this solution to derive explicit expressions for the loss ratio and the sojourn time distribution. An exact theoretical analysis of the performance of an M/M/1 + G queue with preemptive deadlines till the end of service, operating under the Earliest Deadline First (EDF) scheduling policy, appears to be difficult, and only approximate formulas for the loss ratio are available in the literature. We present in this thesis similar approximate formulas for the loss ratio in the present of an exit control mechanism, which discards a job at the epoch of its getting the server if there is no chance of completing it. We refer to this exit control mechanism as the Early job Discarding Technique (EDT). Monte Carlo simulations of performance indicate that the maximum approximation error is reasonably small for a wide range of arrival rates and mean deadlines. Finally, we compare the loss ratios of the First Come First Served and the Earliest Deadline First scheduling policies with or without admission or exit control mechanism, as well as their counterparts with deterministic deadlines. The results include some formal equalities, inequalities and some counter-examples to establish non-existence of an order. A few relations involving loss ratios are posed as conjectures, and simulation results in support of these are reported. These results lead to a complete picture of dominance and non-dominance relations between pairs of scheduling policies, in terms of loss ratios.