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Turbine : A Distributed-memory Dataflow Engine for High Performance Many-task Applications

Wozniak J. M., Armstrong T. G., Maheshwari K., Lusk E. L., Katz D. S., Wilde M., Foster I. T.

Fundamenta Informaticae

2013

Vol. 128, nr 3

337--366

Efficiently utilizing the rapidly increasing concurrency of multi-petaflop computing systems is a significant programming challenge. One approach is to structure applications with an upper layer of many loosely coupled coarse-grained tasks, each comprising a tightly-coupled parallel function or program. “Many-task” programming models such as functional parallel dataflow may be used at the upper layer to generate massive numbers of tasks, each of which generates significant tightly coupled parallelism at the lower level through multithreading, message passing, and/or partitioned global address spaces. At large scales, however, the management of task distribution, data dependencies, and intertask data movement is a significant performance challenge. In this work, we describe Turbine, a new highly scalable and distributed many-task dataflow engine. Turbine executes a generalized many-task intermediate representation with automated self-distribution and is scalable to multi-petaflop infrastructures. We present here the architecture of Turbine and its performance on highly concurrent systems.

Charge Density Distribution, Electrostatic Properties and Sensitivity of the Highly Energetic Molecule 2,4,6-Trinitro-1,3,5-triazine: A Theoretical Study

Srinivasan P., Maheshwari K., Jothi M., Kumaradhas P.

Central European Journal of Energetic Materials

2012

Vol. 9, nr 1

59-76

Ab initio and density functional theory (DFT) calculations were carried out on the energetic propellant molecule 2,4,6-trinitro-1,3,5-triazine (TNTA) to understand its bond topology and its energetic properties using the theory of atoms in molecules (AIM). The DFT method predicts that the electron density ρ bcp (r) at the bond critical points of ring C-N bonds is ∼ 2.34 e Å -3 and the corresponding Laplacian ∇ 2 ρ bcp(r) is ∼ -24.4 e Å -5 ; whereas these values are found to be very small in the -NO2 group attached to C-N bonds [ρ bcp(r): ∼ 1.73 e Å -3 and Δ 2 ρ bcp (r): ∼ -14.5 e Å -5 ]. The negative Laplacian values of C-NO 2 bonds are significantly lower which indicates that the charges of these bonds are highly depleted. The C-NO2 bonds exhibit low bond order (∼ 0.8), as well as low (∼ 56.4 kcal/mol) bond dissociation energy. As we reported in our earlier studies, we found high bond charge depletion for these bonds, which are considered the weakest bonds in the molecule. The frontier orbital energies exhibit a wide band gap, which is larger than those of existing molecules TATB, TNT and TNB. The impact sensitivity (H 50 %) (4.2 m) and oxygen balance (2.77%) were calculated and compared with related structures. Large negative electrostatic potential regions were found near the nitro groups where reaction is expected to occur. The relation between charge depletion ∇ 2 ρ bcp(r) and the electrostatic potential at the bond midpoints V mid reveals the sensitive areas of the molecule.