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- Eastoe, Julian, et al.
(författare)
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Interrogation of a dynamic multi-catalyst ensemble in asymmetric catalysis
- 2010
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640. ; 145, s. 27-47
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Tidskriftsartikel (refereegranskat)abstract
- The Trost Standard Ligand (2) is a chiral diphosphine ligand that distinguishes itself by the high selectivity it induces in the Pd-catalysed reactions of allylic substrates that generate slim cyclic or small linear intermediates. However, a range of unusual features, including memory effects, inverse dependence of selectivity and rate on catalyst concentration, high sensitivity to counter-ion, particularly chloride, and decreasing enantioselectivities at lower temperatures, are often encountered, thus requiring considerable optimisation of reaction conditions to attain optimum selectivity. These features can be accounted for by a model involving a dynamic multi-catalyst ensemble. To gain evidence for this model, the manner in which diphosphine 2 interacts with Pd–allyl cations, and in particular the higher-order systems it generates, has been investigated by use of NMR, isotopic labelling, polarimetry, UV, neutron scattering, X-ray crystallography and molecular modeling. Ligand 2 coordinates to Pd–allyl cations to generate a mononuclear P,P-chelate. This is found to readily form non-chelate oligomers, present in a range of forms, including rings, for which high homochiral selectivity in oligomerisation is demonstrated by the technique of pseudoenantiomers. All of these species are in relatively rapid equilibrium, with half-lives for interconversion in the range 2–6 s. Higher-order aggregation is also detected, and thus at even moderate concentrations (>50 mM) large rod-like aggregates are formed.
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- Tillenius, Martin, et al.
(författare)
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Resource-aware task scheduling
- 2013
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Ingår i: 4th Workshop on Parallel Programming and Run-Time Management Techniques for Many-core Architectures (PARMA). - Germany : Tech. Univ. Berlin. ; , s. 6-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Tillenius, Martin, et al.
(författare)
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Resource-Aware Task Scheduling
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Dependency-aware task-based parallel programming models have proven to be successful for developing efficient application software for multicore-based computer architectures. The programming model is amenable to programmers, thereby supporting productivity, while hardware performance is achieved through a run-time system that dynamically schedules tasks onto cores in such a way that all dependencies are respected. However, even if the scheduling is completely successful with respect to load balancing, the scaling with the number of cores may be sub-optimal due to resource contention. Here we consider the problem of scheduling tasks not only with respect to their inter-dependencies, but also with respect to their usage of resources such as memory and bandwidth. At the software level, this is achieved by user annotations of the task resource consumption. In the run-time system, the annotations are translated into scheduling constraints. Experimental results for different hardware, demonstrating performance gains both for model examples and real applications are presented. Furthermore, we provide a set of tools to detect resource sensitivity and predict the performance improvements that can be achieved by resource-aware scheduling. These tools are solely based on parallel execution traces and require no instrumentation or modification of the application code.
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