Using Lorentz forces to control the distribution of bubbles in a vertical tube filled with liquid metal

In this work, a method to increase the residence time of bubbles in tubes or pipes filled with liquid metal is investigated. Imposing a horizontal electric current and a perpendicular horizontal magnetic field generates an upward-directed Lorentz force. This force can counteract gravity and cause floating of bubbles. Even with homogeneous electric fields these float in the mean but fluctuate randomly within the swarm due to mutual interactions. In the present case the cylindrical shape of the container furthermore creates inhomogeneous electric currents and an inhomogeneous force distribution resulting in a macroscopic convection pattern stirring the bubbles and further homogenising the spatial distribution of the bubbles.LIMTECHDFG/HE 7529/1-

A comparative analysis of two conserved motifs in bacterial poly(A) polymerase and CCA-adding enzyme

Showing a high sequence similarity, the evolutionary closely related bacterial poly(A) polymerases (PAP) and CCA-adding enzymes catalyze quite different reactions—PAP adds poly(A) tails to RNA 3′-ends, while CCA-adding enzymes synthesize the sequence CCA at the 3′-terminus of tRNAs. Here, two highly conserved structural elements of the corresponding Escherichia coli enzymes were characterized. The first element is a set of amino acids that was identified in CCA-adding enzymes as a template region determining the enzymes' specificity for CTP and ATP. The same element is also present in PAP, where it confers ATP specificity. The second investigated region corresponds to a flexible loop in CCA-adding enzymes and is involved in the incorporation of the terminal A-residue. Although, PAP seems to carry a similar flexible region, the functional relevance of this element in PAP is not known. The presented results show that the template region has an essential function in both enzymes, while the second element is surprisingly dispensable in PAP. The data support the idea that the bacterial PAP descends from CCA-adding enzymes and still carries some of the structural elements required for CCA-addition as an evolutionary relic and is now fixed in a conformation specific for A-addition

Repeat Composition of CenH3-chromatin and H3K9me2-marked heterochromatin in Sugar Beet (Beta vulgaris)

Kowar T, Zakrzewski F, Macas J, et al. Repeat Composition of CenH3-chromatin and H3K9me2-marked heterochromatin in Sugar Beet (Beta vulgaris). BMC Plant Biology. 2016;16(1): 120.Background Sugar beet (Beta vulgaris) is an important crop of temperate climate zones, which provides nearly 30 % of the world’s annual sugar needs. From the total genome size of 758 Mb, only 567 Mb were incorporated in the recently published genome sequence, due to the fact that regions with high repetitive DNA contents (e.g. satellite DNAs) are only partially included. Therefore, to fill these gaps and to gain information about the repeat composition of centromeres and heterochromatic regions, we performed chromatin immunoprecipitation followed by sequencing (ChIP-Seq) using antibodies against the centromere-specific histone H3 variant of sugar beet (CenH3) and the heterochromatic mark of dimethylated lysine 9 of histone H3 (H3K9me2). Results ChIP-Seq analysis revealed that active centromeres containing CenH3 consist of the satellite pBV and the Ty3-gypsy retrotransposon Beetle7, while heterochromatin marked by H3K9me2 exhibits heterogeneity in repeat composition. H3K9me2 was mainly associated with the satellite family pEV, the Ty1-copia retrotransposon family Cotzilla and the DNA transposon superfamily of the En/Spm type. In members of the section Beta within the genus Beta, immunostaining using the CenH3 antibody was successful, indicating that orthologous CenH3 proteins are present in closely related species within this section. Conclusions The identification of repetitive genome portions by ChIP-Seq experiments complemented the sugar beet reference sequence by providing insights into the repeat composition of poorly characterized CenH3-chromatin and H3K9me2-heterochromatin. Therefore, our work provides the basis for future research and application concerning the sugar beet centromere and repeat rich heterochromatic regions characterized by the presence of H3K9me2

Application of Positron Emission Particle Tracking (PEPT) to measure the bubble-particle interaction in a turbulent and dense flow

In a flotation cell, turbulence influences the motion of solid particles relative to the bubble surface, and, thus, affects the recovery rate. But, the impact of turbulence on the probability of a bubble-particle aggregation is still difficult to measure, especially in a dense flow. Therefore, the focus of this work was to apply Positron Emission Particle Tracking (PEPT) as a method to investigate the effect of turbulence on the particle movement and bubble-particle interaction in an opaque flow. Single air bubbles (db = 2.5 mm) were generated on a needle in a water flow channel. Upstream, a grid produced an isotropic turbulent flow with 5 % to 15 % turbulence intensity and a Kolmogorov microscale of 20 µm. Depending on the distance to the grid, the flow near the captive bubble (Reb ≈ 450) was characterized by eddies of different length scales and magnitude with tomographic Particle Image Velocimetry (PIV). The solid suspension contained up to 0.3 % polymethylmethacrylate (PMMA) particles (dp = 200 µm–400 µm) and up to six radiolabelled particles (dp = 300 µm–400 µm) coated with PMMA. The trajectories of the labelled particles were used to determine the average particle distribution in the turbulent field and describe the bubble-particle interactions. These results provide valuable information on the applicability of PEPT in turbulent and dense flow fields as well as on particle trajectories close to bubbles, enhancing our understanding of key flotation phenomena

Influence of magnetic fields on the behavior of bubbles in liquid metals

The paper reviews numerical and experimental investigations concerned with the physics of rising bubbles in conducting liquid metals under the action of a magnetic field. Different situations, characterized by different void fractions ranging from single bubbles to bubble swarms, are considered. The impact of the geometrical arrangement is addressed covering large containers with bubbles far from the walls and narrow containers with bubbles interacting with the walls. It is demonstrated that magnetic fields offer a convenient means to influence bubble dynamics, which makes them interesting for technological applications

Influence of magnetic fields on the behavior of bubbles in liquid metals

The paper reviews numerical and experimental investigations concerned with the physics of rising bubbles in conducting liquid metals under the action of a magnetic field. Different situations, characterized by different void fractions ranging from single bubbles to bubble swarms, are considered. The impact of the geometrical arrangement is addressed covering large containers with bubbles far from the walls and narrow containers with bubbles interacting with the walls. It is demonstrated that magnetic fields offer a convenient means to influence bubble dynamics, which makes them interesting for technological applications