Torsional stiffness of viscoelastic spheres in contact

The theory of elastic contact between two spherical bodies according to Hertz, Mindlin and others is used as a basis for an extension to include the contribution of the viscous effects to the total stress for viscoelastic spheres subjected to twisting moments. Expressions relating twisting moment to the radius of a stick region of the contact surface and the radius of the stick region to twist angle are derived. Two term power series truncations of the relations are then used to derive approximate expressions for torsional stiffness of the bodies. Validation of the model was by experiments utilising a rheometer device. Applications for the model in post-harvest agriculture include extraction of material surface properties for use in discrete element modelling of mechanical interactions of fruits and other spheroidal produce during machine handling.Received: 6 January 2004, Published online: 18 June 2004PACS: 46.35. + z Viscoelasticity, plasticity, viscoplasticity - 46.55. + d Tribology and mechanical contacts - 62.20.Dc Elasticity, elastic constants     

Heritability of Stroop and flanker performance in 12-year old children

Background  

There is great interest in appropriate phenotypes that serve as indicator of genetically transmitted frontal (dys)function, such as ADHD. Here we investigate the ability to deal with response conflict, and we ask to what extent performance variation on response interference tasks is caused by genetic variation. We tested a large sample of 12-year old monozygotic and dizygotic twins on two well-known and closely related response interference tasks; the color Stroop task and the Eriksen flanker task. Using structural equation modelling we assessed the heritability of several performance indices derived from those tasks.     

Buffer-gas cooling of NH via the beam loaded buffer-gas method

NH radicals from a molecular beam are cooled using a novel beam-loaded buffer gas method. The radicals are produced in a glow discharge beam source and injected into cryogenic helium gas. Up to 10¹² molecules in their ground electronic, vibrational, and rotational state are detected in the buffer gas and translational temperatures under 6 K are achieved. The cooling method presented is general and can be applied to any molecules in a molecular beam.Received: 20 July 2004, Published online: 26 October 2004PACS: 33.80.Ps Optical cooling of molecules; trapping - 34.50.Ez Rotational and vibrational energy transfer - 39.10. + j Atomic and molecular beam sources and techniquesB. Friedrich: Present address: Department of Molecular Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany.     

Thermodynamic stability of clusters of molybdenum oxide

We show that a single geometrical rule underlies the stability of "polyoxomolybdates", the variety of clusters of molybdenum(VI) oxide in (acidified) aqueous solution that are found experimentally. We predict that upon increasing the proton or total molybdenum oxide concentration, the average size of the clusters increases. We compare our predictions with results from ultracentrifugation experiments and with data in the literature. Finally, it is shown that the formation of metal oxide clusters is thermodynamically equivalent to the formation of surfactant micelles.     

The German bakery waste incident; use of a combined approach of screening and confirmation for dioxins in feed and food

During the last six years several incidents have occurred with dioxins in feed, stressing the need for rapid screening methods for these compounds. The most recent incident was the contamination of bakery waste used for animal feed due to the use of waste wood for drying of the material. In addition to Germany, the material was also shipped to the Netherlands. Levels up to 12 ng TEQ/kg have been detected, being about 15 times over the current limit of 0.75 ng TEQ/kg. In the Netherlands a combined strategy of screening with the CALUX-bioassay and the HRGC/HRMS confirmatory method was used to rapidly control the incident. Pigs were contaminated by the incident but only to a very limited extent. Despite the rather low limits for pig meat, the CALUX bioassay showed excellent performance, once again confirming the value of this assay.     

Even-tempered Slater-type orbitals revisited: from hydrogen to krypton

Even-tempered Slater-type orbital basis sets were developed in 1973, based on total atomic energy optimization. Here, we revisit ET STOs and propose new sets based on past experience and recent computational studies. From preliminary atomic and molecular tests, these sets are shown to be very well balanced and to perform, at lower cost, almost as well as a very large (close to complete) basis set.     

Facile synthesis of a chiral polymeric helix; folding by intramolecular hydrogen bonding

In a single condensation step, a poly-ureidophthalimide is synthesized, which folds into a chiral, helical architecture according to circular dichroism spectroscopy.     

Synthesis of 4-amino-5-H-2,3-dihydroisothiazole-1,1-dioxide ring systems on sugar templates via carbanion-mediated sulfonamide intramolecular cyclization reactions (CSIC protocols) of glyco-alpha-sulfonamidonitriles

The carbanion-mediated sulfonate intramolecular cyclizations (CSIC protocols) of glyco-alpha-sulfonamidonitriles derived from readily available monosaccharides have been extensively investigated using potassium carbonate, cesium carbonate, n-BuLi, and LDA as bases. As a result, a series of enantiomerically pure spiro(4-amino-5-H-2,3-dihydroisothiazole-1,1-dioxide) derivatives have been prepared efficiently and isolated in good yield. The synthesis of these new bicyclic systems is key to accessing a novel range of aza analogues of TSAO nucleosides (ATSAOs).     

A practical synthesis of gramicidin s and sugar amino Acid containing analogues

A practical gram-scale and high-yielding synthesis of the antimicrobial peptide gramicidin S is presented. An Fmoc-based solid-phase peptide synthesis protocol is employed for the generation of the linear decapeptide precursor, which is cyclized in solution to afford the target compound. The versatility of our method is demonstrated by the construction of eight gramicidin S analogues (15a-h) having nonproteinogenic sugar amino acid residues (4-7) incorporated in the turn regions.     

Effect of inhibitors on the catalyzed dehydration of HCO3- by copper(II) complexes re-evaluated

In a recent paper by Cheng and co-workers (Sun, Y.-J.; Zang, L. Z.; Cheng, P.; Lin, H.-K.; Yan, S.-P.; Sun, W.; Liao, D.-Z.; Jiang, Z.-H.; Shen, P.-W. Inorg. Chem. 2003, 42, 508-515), kinetic evidence for inhibitor effects of specific ligands on the catalyzed dehydration of HCO3- by copper(II) complexes of the type [Tp(Ph)]CuX (X- = OH-, N3-, and NCS-) was reported. The analysis of the kinetic data is not correct, and a re-evaluation shows that the claimed catalytic activity of the studied complexes on the dehydration reaction of bicarbonate is indeed questionable. Furthermore, the apparent inhibitor effect of specific selected ligands in the Cu(II) complexes does not seem to exist at all and is based on a wrong interpretation of the kinetic data.