Stabilization of microbial residues by co-precipitation with Fe and Al oxyhydroxides

It is now widely accepted that microbial residues are a significant source for soil organic matter (SOM) formation. This material must be stabilised in soil in order to persist. A potential mechanism for stabilisation of organic materials in soil is co-precipitation with metal oxyhydroxides (Fe and Al), which, however, may be affected by redox transitions. We thus evaluated the mineralisation of 14C-labelled bacterial residues (Escherichia coli cells and cell envelope fragments) and their co-precipitates with Fe or Al oxyhydroxide under different redox conditions in a laboratory incubation experiment. The co-precipitates or untreated microbial residues (control) were mixed with soil and incubated in sealed vessels under either fully aerobic or under oxygen-limited conditions for up to 345 days. To achieve oxygen limitation, incubation was conducted under an N2 atmosphere for the first 100 days. The redox potential was further decreased by waterlogging the samples (from day 100) and by substrate and nutrient additions (from day 290), to increase electron acceptor consumption by the soil microbes. Mineralisation of the microbial residues was quantified by liquid scintillation counting. The data were fitted to different types of models, depending on the experimental phase. Co-precipitation with Fe and Al oxyhydroxides decreased mineralisation of both intact cells and cell envelope fragments significantly, indicating strong protection of biomass and its fragments. Mineralisation of intact cells was slightly faster than that of cell envelope fragments, indicating higher recalcitrance of the latter material, which therefore may be enriched in SOM. Strongly reducing conditions resulted reductive dissolution of Fe oxyhydroxide and thus in a loss of the stabilising effect of the co-precipitation. We conclude that co-precipitation with and incrustation of organic material by Fe and Al oxyhydroxides provide significant stabilisation of microbial residues. However, environmental conditions, e.g. the redox potential, modify the extent of this stabilisation. Fitting the mineralisation data to the models indicated that initially mainly pool sizes were affected by the factors studied, whereas later in the experiment the rate constants were more sensitive. The results improved significantly our understanding how organic materials, in particular microbial residues, are stabilised in soil

Tunnelling dominates the reactions of hydrogen atoms with unsaturated alcohols and aldehydes in the dense medium

Hydrogen addition and abstraction reactions play an important role as surface reactions in the buildup of complex organic molecules in the dense interstellar medium. Addition reactions allow unsaturated bonds to be fully hydrogenated, while abstraction reactions recreate radicals that may undergo radical-radical recombination reactions. Previous experimental work has indicated that double and triple C--C bonds are easily hydrogenated, but aldehyde -C=O bonds are not. Here, we investigate a total of 29 reactions of the hydrogen atom with propynal, propargyl alcohol, propenal, allyl alcohol, and propanal by means of quantum chemical methods to quantify the reaction rate constants involved. First of all, our results are in good agreement with and can explain the observed experimental findings. The hydrogen addition to the aldehyde group, either on the C or O side, is indeed slow for all molecules considered. Abstraction of the H atom of the aldehyde group, on the other hand, is among the faster reactions. Furthermore, hydrogen addition to C--C double bonds is generally faster than to triple bonds. In both cases, addition on the terminal carbon atom that is not connected to other functional groups is easiest. Finally, we wish to stress that it is not possible to predict rate constants based solely on the type of reaction: the specific functional groups attached to a backbone play a crucial role and can lead to a spread of several orders of magnitude in the rate constant.Comment: Accepted for publication in A&

Passive remote sensing of columnar water vapour content above land surfaces. Part I: Theoretical algorithm development - Part II: Comparison of OVID measurements with radiosonde and DIAL measurements

Various efforts are currently being made to develop remote sensing techniques for high accuracy determination of atmospheric columnar water vapour content above land surfaces. Most of those algorithms are based on radiative transfer calcu lations, however, which have to be verified by spectral airborne or satellite measurements. Initial verification of a new algorithm with the aid of airborne spectral data using the spectrometer OVID (Optical Visible and near Infrared Detector), an airborne water vapour DIAL (Differential Absorption Lidar), an airc;raft humicap sensor and radiosonde data is performed dUIing a flight experiment over Southern Germany. This water vapour algorithm is also dedicated to the MERIS (MEdium Resolution Imaging Spectrometer) in strument on board ESA's satellite ENVISAT which will be launched 1999. Spatial water vapour gradients of &120 = 0.1 g/cm2 over a distance of 100 km were resolved by applying the OVID measurements. The error estimation of the absolute value of the retrieved water vapour contents poses· some problems due to insufficient additional temporal and spatial radiosonde data. However, the principal feasibility has been prove

Neural Networks Supporting Phoneme Monitoring Are Modulated by Phonology but Not Lexicality or Iconicity: Evidence From British and Swedish Sign Language

Sign languages are natural languages in the visual domain. Because they lack a written form, they provide a sharper tool than spoken languages for investigating lexicality effects which may be confounded by orthographic processing. In a previous study, we showed that the neural networks supporting phoneme monitoring in deaf British Sign Language (BSL) users are modulated by phonology but not lexicality or iconicity. In the present study, we investigated whether this pattern generalizes to deaf Swedish Sign Language (SSL) users. British and SSLs have a largely overlapping phoneme inventory but are mutually unintelligible because lexical overlap is small. This is important because it means that even when signs lexicalized in BSL are unintelligible to users of SSL they are usually still phonologically acceptable. During fMRI scanning, deaf users of the two different sign languages monitored signs that were lexicalized in either one or both of those languages for phonologically contrastive elements. Neural activation patterns relating to different linguistic levels of processing were similar across SLs; in particular, we found no effect of lexicality, supporting the notion that apparent lexicality effects on sublexical processing of speech may be driven by orthographic strategies. As expected, we found an effect of phonology but not iconicity. Further, there was a difference in neural activation between the two groups in a motion-processing region of the left occipital cortex, possibly driven by cultural differences, such as education. Importantly, this difference was not modulated by the linguistic characteristics of the material, underscoring the robustness of the neural activation patterns relating to different linguistic levels of processing

Atomic structure of Ge quantum dots on the Si(001) surface

In situ morphological investigation of the {105} faceted Ge islands on the Si(001) surface (hut clusters) have been carried out using an ultra high vacuum instrument integrating a high resolution scanning tunnelling microscope and a molecular beam epitaxy vessel. Both species of hut clusters--pyramids and wedges--were found to have the same structure of the {105} facets which was visualized. Structures of vertexes of the pyramidal clusters and ridges of the wedge-shaped clusters were revealed as well and found to be different. This allowed us to propose a crystallographic model of the {105} facets as well as models of the atomic structure of both species of the hut clusters. An inference is made that transitions between the cluster shapes are impossible.Comment: 6 pages, 6 figures. Accepted to JETP Letters (publication date 2010-03-25

Field-induced interactions in magneto-active elastomers - a comparison of experiments and simulations

In this contribution, field-induced interactions of magnetizable particles embedded into a soft elastomer matrix are analyzed with regard to the resulting mechanical deformations. By comparing experiments for two-, three- and four-particle systems with the results of finite element simulations, a fully coupled continuum model for magneto-active elastomers is validated with the help of real data for the first time. The model under consideration permits the investigation of magneto-active elastomers with arbitrary particle distances, shapes and volume fractions as well as magnetic and mechanical properties of the individual constituents. It thus represents a basis for future studies on more complex, realistic systems. Our results show a very good agreement between experiments and numerical simulations—the deformation behavior of all systems is captured by the model qualitatively as well as quantitatively. Within a sensitivity analysis, the influence of the initial particle positions on the systems' response is examined. Furthermore, a comparison of the full three-dimensional model with the often used, simplified two-dimensional approach shows the typical overestimation of resulting interactions in magneto-active elastomers

Variability-aware Datalog

Variability-aware computing is the efficient application of programs to different sets of inputs that exhibit some variability. One example is program analyses applied to Software Product Lines (SPLs). In this paper we present the design and development of a variability-aware version of the Souffl\'{e} Datalog engine. The engine can take facts annotated with Presence Conditions (PCs) as input, and compute the PCs of its inferred facts, eliminating facts that do not exist in any valid configuration. We evaluate our variability-aware Souffl\'{e} implementation on several fact sets annotated with PCs to measure the associated overhead in terms of processing time and database size.Comment: PADL'20 pape

Fluctuations and differential contraction during regeneration of Hydra vulgaris tissue toroids

We studied regenerating bilayered tissue toroids dissected from Hydra vulgaris polyps and relate our macroscopic observations to the dynamics of force-generating mesoscopic cytoskeletal structures. Tissue fragments undergo a specific toroid-spheroid folding process leading to complete regeneration towards a new organism. The time scale of folding is too fast for biochemical signalling or morphogenetic gradients which forced us to assume purely mechanical self-organization. The initial pattern selection dynamics was studied by embedding toroids into hydro-gels allowing us to observe the deformation modes over longer periods of time. We found increasing mechanical fluctuations which break the toroidal symmetry and discuss the evolution of their power spectra for various gel stiffnesses. Our observations are related to single cell studies which explain the mechanical feasibility of the folding process. In addition, we observed switching of cells from a tissue bound to a migrating state after folding failure as well as in tissue injury. We found a supra-cellular actin ring assembled along the toroid's inner edge. Its contraction can lead to the observed folding dynamics as we could confirm by finite element simulations. This actin ring in the inner cell layer is assembled by myosin- driven length fluctuations of supra-cellular {\alpha}-actin structures (myonemes) in the outer cell-layer.Comment: 19 pages and 8 figures, submitted to New Journal of Physic

Magic Islands and Barriers to Attachment: A Si/Si(111)7x7 Growth Model

Surface reconstructions can drastically modify growth kinetics during initial stages of epitaxial growth as well as during the process of surface equilibration after termination of growth. We investigate the effect of activation barriers hindering attachment of material to existing islands on the density and size distribution of islands in a model of homoepitaxial growth on Si(111)7x7 reconstructed surface. An unusual distribution of island sizes peaked around "magic" sizes and a steep dependence of the island density on the growth rate are observed. "Magic" islands (of a different shape as compared to those obtained during growth) are observed also during surface equilibration.Comment: 4 pages including 5 figures, REVTeX, submitted to Physical Review

Strong Pinning in High Temperature Superconductors

Detailed measurements of the critical current density jc of YBa2Cu3O7 films grown by pulsed laser deposition reveal the increase of jc as function of the filmthickness. Both this thickness dependence and the field dependence of the critical current are consistently described using a generalization of the theory of strong pinning of Ovchinnikov and Ivlev [Phys. Rev. B 43, 8024 (1991)]. From the model, we deduce values of the defect density (10^21 m^-3) and the elementary pinning force, which are in good agreement with the generally accepted values for Y2O3-inclusions. In the absence of clear evidence that the critical current is determined by linear defects or modulations of the film thickness, our model provides an alternative explanation for the rather universal field dependence of the critical current density found in YBa2Cu3O7 films deposited by different methods.Comment: 11 pages; 8 Figures; Published Phys. Rev. B 66, 024523 (2002