Drag reduction in bubbly Taylor-Couette turbulence

In Taylor-Couette flow the total energy dissipation rate and therefore the drag can be determined by measuring the torque on the system. We do so for Reynolds numbers between Re=7 x 10(4) and Re=10(6) after having injected (i) small bubbles (R=1 mm) up to a volume concentration of alpha=5% and (ii) buoyant particles (rhop/rhol=0.14) of comparable volume concentration. In case (i) we observe a crossover from little drag reduction at smaller Re to strong drag reduction up to 20% at Re=10(6). In case (ii) we observe at most little drag reduction throughout. Several theoretical models for bubbly drag reduction are discussed in view of our findings.     

Anomalous thermopower in the metalliclike phase of a 2D hole system

We report very low temperature ( T) thermopower and resistivity ( rho) measurements on variable-density, two-dimensional hole systems confined to GaAs quantum wells. As the hole density is lowered from 1.49x10(11) cm(-2) to 0.14x10(11) cm(-2), the system crosses from an insulating ( drho / dT less, similar0) to a metallic regime ( drho / dT>0) and finally displays insulating behavior ( drho / dT<0). Diffusion thermopower shows a striking sign reversal in a narrow range of density in the metallic regime, suggesting a qualitative change in the conduction or the scattering mechanism.     

Bacterial growth response to photoactive quinones

Quinones are known producers of reactive oxygen species (ROS) that may be toxic in natural aquatic environments. In this study, the effects of parent quinones and their photodegradation products on bacterial growth were determined, and photochemical ROS formation rates were measured. Using (3)H-leucine incorporation to measure growth of the bacterium Pseudomonas aeruginosa and natural seawater bacterioplankton, growth inhibition was observed when samples were exposed to dichlone, chloranil and sodium anthraquinone-2-sulfonate (AQ2S). For seawater, compared with other quinones tested, dichlone showed the greatest toxicity in the dark, and AQ2S toxicity was greatest during simultaneous exposure to sunlight. Photodegraded chloranil and dichlone showed decreased toxicity compared with nonirradiated samples. For P. aeruginosa, AQ2S and its photodegradation products showed the greatest toxicity during simultaneous exposure to sunlight. Chloranil photodegradation products showed reduced toxicity compared with the parent compound during simultaneous exposure to sunlight. Dichlone was the only compound to show any toxicity to P. aeruginosa in the dark, and its photodegradation products were more toxic than the parent compound. Based on the results of dark and light controlled experiments measuring bacterial growth and estimated ROS production rates, ROS alone does not account for relative differences in toxicity between these quinones.     

Verified convex hull and distance computation for octree-encoded objects

This paper discusses algorithms for computing verified convex hull and distance enclosure for objects represented by axis-aligned or unaligned octrees. To find a convex enclosure of an octree, the concept of extreme vertices of boxes on its boundary has been used. The convex hull of all extreme vertices yields an enclosure of the object. Thus, distance algorithms for convex polyhedra to obtain lower bounds for the distance between two octrees can be applied. Since using convex hulls makes it possible to avoid the unwanted wrapping effect that results from repeated decompositions, it also opens a way to dynamic distance algorithms for moving objects.     

Simultaneous determination of soluble manganese(III), manganese(II) and total manganese in natural (pore)waters

A new spectrophotometric protocol was developed for the simultaneous determination of soluble Mn(III), Mn(II) and total Mn [sum of soluble Mn(III) and Mn(II)] in sediment porewaters using a water soluble meso-substituted porphyrin [α,β,γ,δ-tetrakis(4-carboxyphenyl)porphine (T(4-CP)P)]. A simple kinetic rate model is used to quantify soluble Mn(II), Mn(III) and total Mn concentrations during a metal substitution reaction. Under optimized conditions, the method accurately determines soluble Mn(II) and Mn(III) within a concentration range of 100 nM-10 μM. The detection limit of total soluble Mn is 50 nM. Using this method, soluble Mn(II) and Mn(III) concentrations were determined in standard solutions within 0.4-2% of the known values and agreed closely with results of inductively coupled plasma mass spectrometric and voltammetric analyses. The procedure was successfully applied to determine soluble Mn(II), Mn(III) and total Mn in sediment porewaters of the Lower St. Lawrence Estuary. Mn(III) represented up to 85% of the total soluble Mn pool in surface sediments.     

Nachweis und Bestimmung der Halogensauerstoffverbindungen

Ohne Zusammenfassung     

Representation,interpolation, and reiteration theorems for generalized approximation spaces

We show that the representation theorem for classical approximation spaces can be generalized to spaces A(X,l ^q (ℬ))={f∈X:{E _n (f)}∈l ^q (ℬ)} in which the weighted l ^q -space l ^q (ℬ) can be (more or less) arbitrary. We use this theorem to show that generalized approximation spaces can be viewed as real interpolation spaces (defined with K-functionals or main-part K-functionals) between couples of quasi-normed spaces which satisfy certain Jackson and Bernstein-type inequalities. Especially, interpolation between an approximation space and the underlying quasi-normed space leads again to an approximation space. Together with a general reiteration theorem, which we also prove in the present paper, we obtain formulas for interpolation of two generalized approximation spaces. Received: December 6, 2001; in final form: April 2, 2002?Published online: March 14, 2003     

The NO- and NO2-catalyzed decomposition of I2 in shock waves

Measurements of the NO-catalyzed dissociation of I₂ in Ar in incident shock waves were carried out in the temperature range of 700°-1520°K and at total concentrations of 5 × 10^?6-6 × 10^?5 mol/cm³, using ultraviolet-visible absorption techniques to monitor the disappearance of I₂. It was shown that the main reaction responsible for the disappearance under these conditions is I₂ + NO → INO + I, for which a rate coefficient of (2.9 ± 0.5) × 10¹³ exp[-(18.0 ± 0.6 kcal/mol)/RT] cm²/mol·sec was determined. The INO formed dissociates rapidly in a subsequent reaction. The reaction, therefore, constitutes a “chemical model” for a “thermal collisional release mechanism.” Preliminary measurements of the rate coefficient for I₂ + NO₂ → INO₂ + I are also presented. Combined with information on the reverse reactions obtained in earlier room temperature experiments, these results lead to accurate values of ΔH°_f for INO and INO₂ equal to 29.7 ± 0.5 and 15.9 ± 1 kcal/mol, respectively.