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In most real-time systems, tasks use remote operations that are executed upon dedicated processors. External operations introduce selfsuspension delays in the behavior of tasks. This paper presents several negative results concerning scheduling independent hard real-time tasks with self-suspensions. Our main objective is to show that well-known scheduling policies such as fixed-priority or Earliest Deadline First are not efficient to schedule such task systems. We prove the scheduling problem to be NP-hard in the strong sense, even for synchronous task systems with implicit deadlines. We also show that scheduling anomalies can occur at run-time: reducing the execution requirement or the suspension delay of a task can lead the task system to be infeasible under EDF. Lastly, we present negative results on the worst-case performances of well-known scheduling algorithms (EDF, RM, DM, LLF, SRPTF) to maximize tasks completed by their deadlines. Complexity of the Run-Time Scheduling ProblemWe next show that the feasibility problem of scheduling synchronously released tasks, with implicit deadlines having at most one selfsuspension each, is NP-hard in the strong sense. We also prove that scheduling anomalies can occur under EDF.

The conditions of laser-driven shock wave loading lead to the study of the dynamic fracture in an unusual range of stress and strain rates: 20–200 GPa and more than 107 s−1. A cumulative damage criterion for the spallation process has been included in a one-dimensional finite difference hydrodynamic code. Numerical studies show the effect of different parameters: laser-pulse duration, peak induced pressure related to the incident intensity, and target thickness. The simulation results are in agreement with spallation shock-laser experiments on aluminum targets of various thicknesses irradiated by laser pulses of durations between 0.6 and 25 ns with an incident intensity of about 1012 W/cm2 .

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Laser driven shocks can lead to the dynamic failure, called spallation, of materials which undergo a dynamic tension at the crossing of two rarefaction waves. We present here a numerical and experimental study of ductile material scabbing with the particular laser shock conditions (very short durations and very high induced pressure levels). A cumulative damage criterion is implemented into both numerical codes shylac and radioss■. Experiments have been carried out by laser irradiation of thin foils of pure aluminum, copper, and iron by laser pulses with the three durations at medium height 0.6, 2.5, and 27 ns, generating an incident flux ranging from 5×1011 to 5×1012 W/cm2. The validity of the cumulative damage criterion is asserted by the consistency of numerical and experimental results for aluminum whose criterion parameters are known. The unknown constants for copper are determined by fitting the numerical simulations to the experimental data. The material influence on the scab thickness and on the spallation threshold is analyzed. Experimental laser induced spallation data given by irradiation of a rear stepped target have been validated experimentally and numerically.