Optimisation of flow schemes for ion-exchange separations by dynamic programming

Summary This article compares two operational research methods for the choice of the optimal flow scheme in separation chemistry. It is concluded that dynamic programming offers more advantages than the application of the theory of graphs.

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Optimierung von Fliediagrammen für Ionenaustauschtrennungen durch dynamische Programmierung

Zusammenfassung 2 Methoden zur Auswahl des optimalen Fließdiagramms für Trennungsverfahren werden verglichen, wobei gezeigt wird, daß die dynamische Programmierung mehr Vorteile bietet als die Anwendung der Graphentheorie.

Lecture presented at Euroanalysis I Conference, 28. 8.–1. 9. 1972 in Heidelberg.     

Forces and energetics of intermittent swimming

Experiments are reported on intermittent swim-ming motions. Water tunnel experiments on a nominally two-dimensional pitching foil show that the mean thrust and power scale linearly with the duty cycle, from a value of 0.2 all the way up to continuous motions, indicating that individ-ual bursts of activity in intermittent motions are independent of each other. This conclusion is corroborated by particle image velocimetry (PIV) flow visualizations, which show that the main vortical structures in the wake do not change with duty cycle. The experimental data also demonstrate that intermittent motions are generally energetically advan-tageous over continuous motions. When metabolic energy losses are taken into account, this conclusion is maintained for metabolic power fractions less than 1.     

High nuclearity manganese(III) compounds containing phenol-pyrazole ligands: the influence of the ligand on the core geometry

Three high-nuclearity manganese(III) clusters have been synthesized and characterized: [Mn?(μ?-O)?(phpzH)?(thf)?] (1), [Mn?(μ?-O)?(phpzH)?(EtOH)?]·2EtOH (2), and [Mn?(μ?-O)?(μ?-Br)?(HphpzEt)?(phpzEt)] (3). Compounds 1 and 2 contain a [Mn?(μ?-O?)(phpzH)?] core in which antiferromagnetic interactions between the manganese(III) ions are found. Compound 3 is a hexanuclear manganese(III) cluster in which weak ferromagnetic interactions appear to be operative. The formation and the stability of the cluster cores in relation to the type of phenol-pyrazole ligand and the reaction conditions are discussed.     

Measurements and calculations on the simple up-down adaptive procedure for speech-in-noise tests

The simple up-down adaptive procedure is a common method for measuring speech reception thresholds. It is used by the Dutch speech-in-noise telephone screening test [National Hearing test; Smits and Houtgast Ear Hear. 26, 89-95 (2005)]. The test uses digit triplets to measure the speech reception threshold in noise by telephone (SRTT(n)). About 66 000 people took this test within four months of its introduction and details were stored of all individual measurements. Analyses of this large volume of data have revealed that the standard deviation of SRTT(n) estimates increases with hearing loss. This paper presents a calculation model which--using an intelligibility function as input--can determine the standard deviation of SRTT(n) estimates and the bias for the simple up-down procedure. The effects of variations in the slope of the intelligibility function, the guess rate, the starting level, the heterogeneity of the speech material, and the possibilities of optimizing SRTT(n) measurements were all explored with this model. The predicted decrease in the standard deviation of SRTT(n) estimates as a result of optimizing the speech material was confirmed by measurements in 244 listeners. The paper concludes by discussing possibilities for optimizing the development of comparable tests.     

Spirastrellolide studies. Synthesis of the C(1)-C(25) southern hemispheres of spirastrellolides A and B, exploiting anion relay chemistry

Construction of the C(1)-C(25) southern fragments of both spirastrellolide A and B are described. Highlights of the syntheses include effective use of the three component anion relay chemistry (ARC) tactic recently introduced by our laboratory, a stereoselective spirocyclization via concomitant Ferrier reaction to elaborate the BC spiroketal and use of two dithiane unions to install the A ring as well as C(22)-C(25) fragment. The synthesis proceeded with longest linear sequences of 33 and 32 steps, respectively for spirastrellolide A and spirastrellolide B.