A branching process model for sand avalanches

An analytically solvable model for sand avalanches of noninteracting grains of sand, based on the Chapman-Kolmogorov equations, is presented. For a single avalanche, distributions of lifetimes, sizes of overflows and avalanches, and correlation functions are calculated. Some of these are exponentials, some are power laws. Spatially homogeneous distributions of avalanches are also studied. Computer simulations of avalanches of interacting grains of sand are compared to the solutions to the Chapman-Kolmogorov equations. We find that within the range of parameters explored in the simulation, the approximation of noninteracting grains of sand is a good one.     

On the role of heterogeneous and imperfect information in a laboratory financial market

In this paper, we analyze the behavior of a group of heterogeneously informed investors in an laboratory asset market. Our experimental setting is inspired by Huber et al. (On the benefit of information in markets with heterogeneously informed traders: an experimental study, 2004). However, instead of their system of cumulative and exogenously given information structure, we introduce an information market where the traders can buy an imperfect prediction of the future value of the dividend with a maximum anticipation of four periods. The accuracy of the prediction decreases with the chosen time horizon, whereas its price remains constant. Our results confirm a non-strictly monotonic increasing value of the information.     

Development of a capillary electrophoretic method for the separation of diastereoisomers of a new human immunodeficiency virus protease inhibitor

A capillary electrophoretic (CE) method was developed for the separation of diastereoisomers of a new human immunodeficiency virus (HIV) protease inhibitor TMC114. In total 16 isomers of this drug have been synthesized (eight pairs of enantiomers). We succeeded in the separation of the eight diastereoisomers, but no enantiomers could be separated. Because of the high similarity and water-insolubility of these isomers, the separation is a real challenge. Different CE modes were tried out: capillary zone electrophoresis (CZE), nonaqueous capillary electrophoresis (NACE), micellar electrokinetic capillary chromatography (MEKC), and microemulsion electrokinetic capillary chromatography (MEEKC). Only MEEKC offered resolution of these compounds.     

Is the ring conformation the most critical parameter in lipase-catalysed acylation of cycloalkanols?

CAL-B catalysed the resolution of several five and six-membered cyclic beta-hydroxy esters efficiently with the exception of the cis-cyclohexanol (+/-)-4. When employing molecular modelling techniques the conformation turned out to be the most important determinant for their reactivity towards O-acetylation. In all cases, the R enantiomers reacted faster than the S enantiomers since the reactive intermediates of the former can adopt more favourable ring conformations and thus experience less steric hindrance in the active site. Furthermore, the minimised structure for the main conformer of R-4 showed that the axial hydrogens in the 3 and 5-positions with respect to the hydroxyl group prevent the enzymatic reaction.     

Minimal number of chromatographic test parameters for the characterisation of reversed-phase liquid chromatographic stationary phases

This paper focuses on the classification or differentiation of RP-HPLC columns based on measured chromatographic properties. A chemometric study has been conducted on a published data set consisting of 85 RP-HPLC columns and on a data set consisting of 47 self-tested columns. Principal component analysis enables determination of the number of parameters necessary for a rational differentiation. The results show that reducing the number of parameters for such differentiation still allows classification of the columns just as a higher number did. It is shown that three test parameters produce a classification similar to that obtained with five parameters.     

Chiral separation of pyrethroic acids with single isomer permethyl monoamino beta-cyclodextrin selector

Enantiomers and diastereomers of chrysanthemic, permethrinic, and deltamethrinic pyrethroic acids were separated from each other, using positively ionizable permethyl monoamino beta-cyclodextrin (PMMAbetaCD). The highest chiral resolution value was 20.0. The optimum conditions of separation were found to be 16 mM PMMAbetaCD concentration and pH 6.5, where analytes and selector were in oppositely ionized states. Selectivity of PMMAbetaCD proved to be the best among the cyclodextrin derivatives studied.     

Photobiological characteristics and photosynthetic UV responses in two Ulva species (Chlorophyta) from southern Spain

The effect of different wavebands of artificial UV (UVB and UVA) and photosynthetically active radiation (PAR) was assessed in two species of the genus Ulva, U. olivascens and U. rotundata, from southern Spain in order to test for possible differences in acclimation of photosynthesis. Both species share similar morphology but are subject to different light environments: U. rotundata is an estuarine alga, inhabiting subtidal locations, while U. olivascens is an intertidal, sun-adapted organism. Algae were exposed to three different UV conditions, PAR+UVA+UVB, PAR+UVA and PAR for 7 d. Short-term exposure (6 h) was also carried out, using two PAR levels, 150 and 700 micromolm(-2)s(-1). Pigment contents and photosynthesis vs. irradiance curves from oxygen evolution were used to contrast sun- and shade adaptation between these species. O2-based net photosynthesis (Pmax) and PAM-chlorophyll fluorescence (optimal quantum yield, Fv/Fm) were used as parameters to evaluate photoinhibition of photosynthesis in the experiments. The results underline different photobiological characteristics among species: the subtidal U. rotundata had higher contents of pigments (Chl a, Chl b and carotenoids) than the sun-adapted U. olivascens, which resulted in higher thallus absorptance and P-I parameters characterized by higher photosynthetic efficiency at limiting irradiances (alpha) and lower saturating points for photosynthesis (Ek). After 7 d exposure, photoinhibition of Fv/Fm was close to 40-45% in both species. Differences between UV treatments were seen in U. rotundata after 5 d and after 7 d in U. olivascens, in which PAR+UVA impaired strongly photosynthesis (80%). Such patterns were correlated with a progressive decrease in pigment contents, specially chlorophylls. In short-term (6 h) exposures, combinations of UVA+UVB and high PAR level resulted in high rates of photoinhibition of chlorophyll fluorescence (68-92%) in U. rotundata, whereas in U. olivascens photoinhibition ranged between 42% and 53%. Photoinhibition under low PAR combined to UV radiation was lower than observed under high PAR. Net O2-Pmax revealed similar response among the species, with maximal photoinhibition rates close to 60% in algae incubated under high PAR+UVA+UVB. In the case of UV exposure in combination with low PAR, the highest photoinhibition rates were measured in U. rotundata.     

Effect of P2O5 content in phosphogypsum on its thermal decomposition to CaCO and SO2

The effect of P₂O₅ on the thermal decomposition of phosphogypsum to phospholime and sulphur dioxide has been studied.

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Zusammenfassung Es wurde der Einfluß von P₂O₅ auf die thermische Zersetzung von Phosphogips zu Phospholim und Schwefeldioxid untersucht.

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First seco-C oleananes from nature

[structure: see text] The triterpenes 8,14-seco-oleana-8(26),13-dien-3beta-ol (1) and its acetyl derivative 2 were isolated from Stevia viscida and Stevia eupatoria, respectively. Their structures were elucidated by 2D NMR, including carbon-carbon connectivity experiments, and confirmed by X-ray diffraction analysis of ketone 3. The absolute configuration was determined by NMR analysis of the Mosher esters of 1. The biogenetic implications of the new substances are discussed.     

Modification of asbestos by siliconates

The ability of some siliconates to hydrophobize and modify the surface of different kinds of asbestos was studied. A 6 wt% aqueous solution of potassium methylsiliconate was used in various quantities. After treatment, the asbestos samples were analysed by IR-spectroscopy, TG-DTA and electron microscopy. Structural changes were found on the asbestos surface, including the appearance of chemical bonds. The studies revealed that the sorption and lyophilic properties of asbestos are lowered, these being the basic preconditions for its injurious action on health.