Volunteer computing is being used successfully for large scale scientific computations. This research is in the context of Volpex, a programming framework that supports communicating parallel processes in a volunteer environment. Redundancy and checkpointing are combined to ensure consistent forward progress with Volpex in this unique execution environment characterized by heterogeneous failure prone nodes and interdependent replicated processes. An important parameter for optimizing performance with Volpex is the frequency of checkpointing. The paper presents a mathematical model to minimize the completion time for inter-dependent parallel processes running in a volunteer environment by finding a suitable checkpoint interval. Validation is performed with a sample real world application running on a pool of distributed volunteer nodes. The results indicate that the performance with our predicted checkpoint interval is fairly close to the best performance obtained empirically by varying the checkpoint interval.
Batch sorption study was performed using used black tea leaves (UBTL) as a low-cost adsorbent for the removal of lead (II) from aqueous solutions. Experiments were conducted as a function of contact time, initial metal ion concentration, solution pH and temperature. The sorption of Pb(II) on used tea leaves increases with increase of initial pH of solution upto a certain limit which corresponds to the pH nearly 5. The sorption isotherms follow Langmuir equation better than Freundlich equation. Again the Langmuir equation is more applicable at higher temperatures compared to those at low temperature at all pH. The monolayer sorption capacity decreases with increase in processing temperature but the overall sorbed amount increased with the increase in temperature at all pH. The positive value of estimated heat of sorption suggests the activated sorption. A probable mechanism of the sorption of Pb(II) on used tea leaves was proposed based on the surface charge of used tea leaves and the change of charge of Pb(II) with the pH of solution.
A finite-element multigrid scheme for elliptic Nash-equilibrium multiobjective optimal control problems with control constraints is investigated. The multigrid computational framework implements a nonlinear multigrid strategy with collective smoothing for solving the multiobjective optimality system discretized with finite elements. Error estimates for the optimal solution and two-grid local Fourier analysis of the multigrid scheme are presented. Results of numerical experiments are presented to demonstrate the effectiveness of the proposed framework.
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