University of Bremen

About: University of Bremen is a education organization based out in Bremen, Germany. It is known for research contribution in the topics: Population & Context (language use). The organization has 14563 authors who have published 37279 publications receiving 970381 citations. The organization is also known as: Universität Bremen.

Effect of N‐fertilization, plant genotype and environmental conditions on nifH gene pools in roots of rice

Abstract: Terminal restriction fragment length polymorphism (T-RFLP) analysis of PCR-amplified nitrogenase gene (nifH) fragments is a rapid technique for profiling of diazotrophic microbial communities without the necessity of cultures for study. Here, we examined the impact of N-fertilization, plant genotype and environmental conditions on diazotrophic microbial populations in association with roots of rice (Oryza species) by T-RFLP community profiling and found marked effects on the composition of the microbial community. We found a rapid change of the diazotrophic population structure within 15 days after application of nitrogen fertilizer and a strong effect of environmental conditions and plant genotype. Control experiments revealed that phylogenetically distantly related nifH genes were proportionately amplified, and that signal strength reflected the relative abundance of nifH genes in the sample within a 10-fold range of template concentrations. These results clearly demonstrated that our T-RFLP method was suitable to reflect compositional differences in the diazotrophic community in a semiquantitative manner and that the diazotrophic rhizosphere communities of rice are not static but presumably rather highly dynamic.

Magnetite in seafloor serpentinite—Some like it hot

Abstract: Serpentinization of mantle peridotite generates molecular hydrogen that can be exploited by microorganisms to gain metabolic energy; however, the mechanisms that control hydrogen generation and magnetite formation during serpentinization remain poorly understood. We have examined partly to completely serpentinized peridotites recovered during the Ocean Drilling Program and find a remarkable variation in the abundance of magnetite. Some completely serpentinized peridotites have as much as 6.15 wt% magnetite, whereas others are nearly magnetite free (

Capillary driven flow in circular cylindrical tubes

Abstract: Capillary-driven flow of a perfectly wetting liquid into circular cylindrical tubes is studied. Based on an analysis of previous approaches, a comprehensive theoretical model is presented which is not limited to certain special cases. This model considers the meniscus reorientation, the dynamic contact angle as well as inertia, convective, and viscous losses inside the tube and the reservoir. The capillary-driven flow is divided into three successive phases where first inertia then convective losses and finally viscous forces counteract the driving capillary force. This leads to an initial meniscus height increase proportional to the square of time followed by a linear dependence and finally the Lucas–Washburn behavior where the meniscus height is proportional to the square root of time. The three phases are separated by two characteristic transition times which are determined by the Ohnesorge number and the inertia of the liquid. Experiments were carried out under microgravity condition in a carefully chosen range of Ohnesorge numbers and initial liquid heights to cover the complete process from the initial meniscus development to the final Lucas–Washburn behavior. Good agreement of experimental and theoretical data is found throughout the complete range of experiment parameters. The existence of all three flow regimes predicted by the theory is verified by the experiments.

Spatial attention increases performance but not subjective confidence in a discrimination task.

Abstract: Selective attention to a target yields faster and more accurate responses. Faster response times, in turn, are usually associated with increased subjective confidence. Could the decrease in reaction time in the presence of attention therefore simply reflect a shift toward more confident responses? We here addressed the extent to which attention modulates accuracy, processing speed, and confidence independently. To probe the effect of spatial attention on performance, we used two attentional manipulations of a visual orientation discrimination task. We demonstrate that spatial attention significantly increases accuracy, whereas subjective confidence measures reveal overconfidence in non-attended stimuli. At constant confidence levels, reaction times showed a significant decrease (by 15-49%, corresponding to 100-250 ms). This dissociation of objective performance and subjective confidence suggests that attention and awareness, as measured by confidence, are distinct, albeit related, phenomena.

Silicon nanowire band gap modification

Abstract: Band gap modification for small-diameter (1 nm) silicon nanowires resulting from the use of different species for surface termination is investigated by density functional theory calculations. Because of quantum confinement, small-diameter wires exhibit a direct band gap that increases as the wire diameter narrows, irrespective of surface termination. This effect has been observed in previous experimental and theoretical studies for hydrogenated wires. For a fixed cross-section, the functional group used to saturate the silicon surface significantly modifies the band gap, resulting in relative energy shifts of up to an electronvolt. The band gap shifts are traced to details of the hybridization between the silicon valence band and the frontier orbitals of the terminating group, which is in competition with quantum confinement.