Avalanche statistics of sand heaps

Large-scale computer simulations are presented to investigate the avalanche statistics of sandpiles using molecular dynamics. We show that different methods of measurement lead to contradictory conclusions, presumably due to avalanches not reaching the end of the experimental table.     

Countably many simultaneous random changes of time scales

Simultaneous changes of time scales of the components of a vector Markov process are defined and developed. Measurability properties, Dynkin's lemma, and the strong Markov property are established for the transformed process.     

Surface segregation in alloys: Existence of surface miscibility gaps within regular solution theory

Much attention has been paid to the relationship between the bulk phase diagram and the phenomena of surface segregation. There is no reason to believe, however, that the equilibrium phase boundaries for the surface region are identical to those of the bulk. In this paper, we have derived the surface phase boundaries within the regular solution approximation using pairwise interactions. We find that the concept of phase separation for the surface region is not important if the surface phase is in equilibrium with the bulk and the bulk is in a region of solid solubility. The experimental conditions employed in some studies, however, lead to nonequilibrium states (due to quenching). For these cases, surface phase separation may be expected under typical experimental conditions.     

New studies of the Si-SiO2 interface using auger sputter profiling

We have made new measurements of the morphology and chemistry of “state of the art” thermally grown Si-SiO₂ interfaces using Auger sputter profiling. With improved experimental technique and theoretical treatment of electron escape depth and ion knock-on effects, we find the width of the interface to be about 2.0 nm. This width is probably due to an undulating interface, the period of which is less than 100 μm. Any SiO_x present resides in a connective layer no greater than 0.8 nm thick at any point.     

Organic industrial products

AbstractsParticular products and fields of application

Organic industrial products     

Low-energyπK-scattering

A self-consistent calculation of thes- andp-wave resonance inπK-scattering is attempted using as input the exchanged resonances themselves and the exchange of a?-meson. While this approximation to the left-hand cut fails in thes-wave problem it produces ap-wave resonance but for a much too strong?-coupling. Position and width depend very sensitively on the inelastic region. Suppressing this region by a subtraction at threshold the subtraction constant can be adjusted to yield the observed position. The corresponding width is close to the experimental values for reasonable?-coupling.     

Secoisolariciresinol dehydrogenase: mode of catalysis and stereospecificity of hydride transfer in Podophyllum peltatum

Secoisolariciresinol dehydrogenase (SDH) catalyzes the NAD+ dependent enantiospecific conversion of secoisolariciresinol into matairesinol. In Podophyllum species, (-)-matairesinol is metabolized into the antiviral compound, podophyllotoxin, which can be semi-synthetically converted into the anticancer agents, etoposide, teniposide and Etopophos. Matairesinol is also a precursor of the cancer-preventative "mammalian" lignan, enterolactone, formed in the gut following ingestion of, for example, various high fiber dietary foods, as well as being an intermediate to numerous defense compounds in vascular plants. This study investigated the mode of enantiospecific Podophyllum SDH catalysis, the order of binding, and the stereospecificity of hydride abstraction/transfer from secoisolariciresinol to NAD+. SDH contains a highly conserved catalytic triad (Ser153, Tyr167 and Lys171), whose activity was abolished with site-directed mutagenesis of Tyr167Ala and Lys171Ala, whereas mutagenesis of Ser153Ala only resulted in a much reduced catalytic activity. Isothermal titration calorimetry measurements indicated that NAD+ binds first followed by the substrate, (-)-secoisolariciresinol. Additionally, for hydride transfer, the incoming hydride abstracted from the substrate takes up the pro-S position in the NADH formed. Taken together, a catalytic mechanism for the overall enantiospecific conversion of (-)-secoisolariciresinol into (-)-matairesinol is proposed.