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Roshan et al. recently described a "divide-and-conquer" technique for parsimony analysis of large data sets, Rec-I-DCM3, and stated that it compares very favorably to results using the program TNT. Their technique is based on selecting subsets of taxa to create reduced data sets or subproblems, finding most-parsimonious trees for each reduced data set, recombining all parts together, and then performing global TBR swapping on the combined tree. Here, we contrast this approach to sectorial searches, a divide-and-conquer algorithm implemented in TNT. This algorithm also uses a guide tree to create subproblems, with the first-pass state sets of the nodes that join the selected sectors with the rest of the topology; this allows exact length calculations for the entire topology (that is, any solution N steps shorter than the original, for the reduced subproblem, must also be N steps shorter for the entire topology). We show here that, for sectors of similar size analyzed with the same search algorithms, subdividing data sets with sectorial searches produces better results than subdividing with Rec-I-DCM3. Roshan et al.'s claim that Rec-I-DCM3 outperforms the techniques in TNT was caused by a poor experimental design and algorithmic settings used for the runs in TNT. In particular, for finding trees at or very close to the minimum known length of the analyzed data sets, TNT clearly outperforms Rec-I-DCM3. Finally, we show that the performance of Rec-I-DCM3 is bound by the efficiency of TBR implementation for the complete data set, as this method behaves (after some number of iterations) as a technique for cyclic perturbations and improvements more than as a divide-and-conquer strategy.
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PMID:On divide-and-conquer strategies for parsimony analysis of large data sets: Rec-I-DCM3 versus TNT. 1756 72

At the end of November 1914 Lord Moulton (1844-1921) became the director of explosives production in the War Office. A 70-year-old jurist may seem an extraordinary choice, but he was an extraordinary man. He was Senior Wrangler at Cambridge, was elected to the Royal Society for research on electricity, and learned about chemistry as a barrister for dye and explosives manufacturers. He assembled an able team of administrators and chemists who designed and managed mammoth new national explosives factories. They could not make enough TNT and picric acid from obtainable precursors, so Moulton persuaded the reluctant armed services to adopt mixtures of TNT and ammonium nitrate, which enabled them to make even more than was needed. In mid-1915 they moved to the new Ministry of Munitions, where they also became responsible for fertilizers and poison gases. In 1917 they produced explosives at a higher rate than was attained in World War II.
Notes Rec R Soc Lond 2014 Jun 20
PMID:Lord Justice of Appeal John Fletcher Moulton and explosives production in World War I: 'the mathematical mind triumphant'. 2492 Nov 9