Kompetitive Sorption, Diffusionsprozesse und Transport von Kationen in Böden : Experimentelle Erfassung und Modellierung von binären Stoffsystemen

Das Sorptions- und Transportverhalten der Kationenpaare Zn-Ca, Zn-Mg und K-Ca wurde in Batchversuchen mit Reaktionszeiten von 7 min bis 512 h sowie in Säulenperkolationsversuchen unter wassergesättigten Bedingungen an Bodenproben aus dem Ap- und Bv- sowie dem AhBt-Horizont zweier Lößböden des Bonner Raumes untersucht. Für die Auswertung der Meßdaten wurde gemeinsam mit dem Mathematischen Seminar der Landwirtschaftlichen Fakultät das objektorientierte Sorptions-, Diffusions- und Transportmodell OOSDIT entwickelt, das das Sorptionsverhalten von Stoffen durch eine Kombination von Adsorptions- bzw. Kationenaustauschgleichungen und einem Term für die Festkörperdiffusion beschreibt. Das Sorptionsverhalten von Zn in Mg- und Ca-Hintergrundlösung (Batchversuche) ist von einer spontanen Adsorption und einer darauffolgenden diffusionskontrollierten Belegung zusätzlicher Zn-Bindungsplätze an inneren Partikeloberflächen geprägt. Das Modell OOSDIT gibt den zeitlichen Verlauf des Sorptionsgeschehens bei Berücksichtigung von Kationenaustausch, spezifischer Sorption und selektiver Diffusion von Zn sowohl in Ca- als auch Mg-Hintergrundlösungen sehr gut wieder. Die anhand der Meßdaten geschätzten scheinbaren und effektiven Diffusionskoeffizienten für Zn2+ liegen für die verschiedenen Bodenproben bei 512 h Reaktionszeit im Bereich von 10-4 und 10-5 d -1 beziehungsweise 10-20 und 10-22 cm2·s-1. Die geschätzten Diffusionskoeffizienten nehmen mit zunehmender Reaktionszeit ab. Die Modellergebnisse konnten durch unabhängige Messungen validiert werden. Das Adsorptionsverhalten von K+ (Batchversuche) ist durch diffusionsgesteuerte Einlagerung von K+ in die Austauscher geprägt. Im Anschluß an die Adsorption durchgeführte Desorptionsversuche mit Ca-Lösung zeigen, daß der mit zunehmender Adsorptionsdauer festgestellte Rückgang der Extrahierbarkeit durch eine Veränderung der K-Bindungsformen bedingt ist, bei der das zunächst spontan an Tonmineraloberflächen sorbierte K+ nach Diffusion an spezifischen Bindungsstellen in aufgeweiteten Tonmineralzwischenschichten festgelegt wird. Die Modellierung führt nahezu unabhängig von der verwendeten Austauschisotherme zu einer guten Übereinstimmung der errechneten Konzentrationsverläufe mit den Meßdaten. Für die K+-Diffusion werden bei 512 h Reaktionszeit scheinbare und effektive Diffusionskoeffizienten im Bereich von 10-5 bis 10-6 d-1 bzw. 10-19 bis 10-20 cm2·s-1 geschätzt. Die wesentlichen Effekte der Sorption von Zn2+, K+ und Ca2+, wie sie in Batchversuchen auftreten, sind auch bei der Stoffverlagerung in Säulenversuchen zu beobachten. Mit den Sorptions- und Diffusionsparametern, mit denen die Meßwerte aus den Batchversuchen beschrieben werden, können auch die experimentell an Bodensäulen ermittelten Durchbruchskurven von Zn2+, K+ und Ca2+ gut wiedergegeben werden. Die richtige Größenordnung der Modellparameter ergibt sich aber erst bei Rekalibrierung des Austausch- und Diffusionskoeffizienten an den Meßdaten der Säulenversuche. Für das K-Ca-System ist zusätzlich für die Desorption eine am Rücktauschverhalten orientierte Kalibrierung der Austausch- und Diffusionsparameter erforderlich, um die Veränderung der Sorbentenstruktur während der vorangehenden Adsorptionsphase zu berücksichtigen. Mit dem Modell OOSDIT können die für den Stofftransport relevanten Prozesse der Adsorption und Festkörperdiffusion in Batch- wie in Säulenperkolationsversuchen nachvollzogen und erfolgreich für die Vorhersage des Stofftransportes von Zn2+, K+ und Ca2+ in Bodensäulen verwendet werden.Competitive sorption, diffusion processes, and transport of cations in soil - Measuring and modelling binary systems Sorption and transport behaviour of cations in binary systems of Zn-Ca, Zn-Mg, and K-Ca were investigated by batch experiments with reaction times between 7 min and 512 hrs as well as column experiments under conditions of saturated water flow. Three soil samples from the Ap, Bv, and AhBt horizons of loess soils were collected from two locations near Bonn. For the numerical analysis of the measured data the new deterministic simulation model OOSDIT (Objekt Oriented Sorption, Diffusion and Transport Model) was developed in cooperation with the Department of Applied Mathematics of the Agricultural Faculty of the University of Bonn. The time-dependent and diffusion controlled sorption behaviour of substances is described by a combination of various adsorption isotherms and cation-exchange equations with a diffusion term for solid-state diffusion. Refering to the Zn-Ca system (batch experiments), the observed sorption behaviour of Zn is characterised by a rapid and reversible adsorption on outer particle surfaces followed by a diffusional transfer of Zn along micropore walls and defects of the mineral structure to internal sorption sites. Experimental data of Zn sorption in Mg background solution did not show substantial deviations from the Zn-Ca system in the long-term sorption pattern. Considering cation exchange, specific sorption phenomena, and diffusion of Zn into particles, the model OOSDIT describes accurately the time-dependend sorption pattern of Zn, Ca, and Mg in the soil material. The estimated apparent and effective diffusion coefficients for the investigated period of time are in the range of 10-4 to 10-5 d -1 and 10-20 to 10-22cm2·s-1, respectively. Diffusion rates are found to decrease with reaction time. Model results are validated by independent measurements. A sensitivity analysis has shown no improvement of transport description for reactive solutes by using the mobile-immobile approach. The long-term adsorption behaviour of K in Ca-saturated soil samples (batch experiments) is characterised by increasing adsorption and fixation of K in interlattice positions with time. Subsequent desorption experiments have shown a significant decrease in extractability with increasing adsorption time, indicating a change in K binding forms. At sufficiently high K concentrations, the spontaneously bound K on external surface sites of clay minerals was transfered to the fraction of diffusion controlled interlattice bound K. The experimental data were described adequately with OOSDIT. The type of the exchange isotherm did not significantly influence the goodness of fit. The estimated apparent and effective diffusion coefficients for the investigated period of time are in the range of 10-5 to 10-6 d -1 and 10-19to 10-20cm2·s-1, respectively. The main features characterising sorption behaviour of Zn, K, and Ca, as recognised in the batch experiments, have been observed in column transport studies as well. Based on data of batch experiments, the model is able to predict the transport behaviour qualitatively well. Recalibration of sorption and diffusion parameters with data of column experiments also led to quantitatively satisfying descriptions of breakthrough curves. For K transport, recalibration of parameters was necessary for forward and backward exchange considering structural changes of the interlattice space. Considering cation exchange and solid state diffusion, complex sorption and transport patterns of Zn, K, and Ca in batch and column experiments were successfully described

Comparing Frequency Transfer via GNSS and Fiber in a Common-clock Configuration

Realizing a clock-based geodetic network with a relative uncertainty level of 10?18 has been a significant objective for the scientific community. This network can be utilized for realizing more accurate geodetic reference frames and for testing the fundamental laws of physics, such as the theory of relativity. Typically, optical fibers are connecting optical clocks in such a network. For the last decades, Global Navigation Satellite Systems (GNSSs) have built a trustful and easy-setup method for frequency and time transfer. However, recently optical fiber link networks showed better frequency instability. In this study, we investigate the limits of GNSS-based frequency transfer links with the help of an optical fiber link as ground truth. Therefore, we analyze the GNSS data acquired in a dedicated common-clock experiment over a 52 km baseline. We focus on developing two algorithms to estimate the receiver clock differences, hence the frequency instability. These are the single difference (SD) approach with ambiguity fixing as a common view technique, and precise point positioning as an all in-view technique. We discuss the frequency instability achieved by the optical fiber link as well. We evaluate further the performance by computing the modified Allan deviation for both cases. The results show that the ambiguity-fixed solution of SD-CV improves the relative frequency instability via GNSS to reach the order of 3–5 · 10^?17 at one day averaging time. In the optical fiber link, which is the basis of the common clock setup, the round-trip instability shows better performance for all averaging times

The linear chromosome of the plant-pathogenic mycoplasma 'Candidatus Phytoplasma mali'

BACKGROUND: Phytoplasmas are insect-transmitted, uncultivable bacterial plant pathogens that cause diseases in hundreds of economically important plants. They represent a monophyletic group within the class Mollicutes (trivial name mycoplasmas) and are characterized by a small genome with a low GC content, and the lack of a firm cell wall. All mycoplasmas, including strains of 'Candidatus (Ca.) Phytoplasma asteris' and 'Ca. P. australiense', examined so far have circular chromosomes, as is the case for almost all walled bacteria. RESULTS: Our work has shown that 'Ca. Phytoplasma mali', the causative agent of apple proliferation disease, has a linear chromosome. Linear chromosomes were also identified in the closely related provisional species 'Ca. P. pyri' and 'Ca. P. prunorum'. The chromosome of 'Ca. P. mali' strain AT is 601,943 bp in size and has a GC content of 21.4%. The chromosome is further characterized by large terminal inverted repeats and covalently closed hairpin ends. Analysis of the protein-coding genes revealed that glycolysis, the major energy-yielding pathway supposed for 'Ca. P. asteris', is incomplete in 'Ca. P. mali'. Due to the apparent lack of other metabolic pathways present in mycoplasmas, it is proposed that maltose and malate are utilized as carbon and energy sources. However, complete ATP-yielding pathways were not identified. 'Ca. P. mali' also differs from 'Ca. P. asteris' by a smaller genome, a lower GC content, a lower number of paralogous genes, fewer insertions of potential mobile DNA elements, and a strongly reduced number of ABC transporters for amino acids. In contrast, 'Ca. P. mali' has an extended set of genes for homologous recombination, excision repair and SOS response than 'Ca. P. asteris'. CONCLUSION: The small linear chromosome with large terminal inverted repeats and covalently closed hairpin ends, the extremely low GC content and the limited metabolic capabilities reflect unique features of 'Ca. P. mali', not only within phytoplasmas, but all mycoplasmas. It is expected that the genome information obtained here will contribute to a better understanding of the reduced metabolism of phytoplasmas, their fastidious nutrition requirements that prevented axenic cultivation, and the mechanisms involved in pathogenicity

Microparticles globally reprogram Streptomyces albus toward accelerated morphogenesis, streamlined carbon core metabolism, and enhanced production of the antituberculosis polyketide pamamycin

Streptomyces spp. are a rich source for natural products with recognized industrial value, explaining the high interest to improve and streamline the performance of in these microbes. Here, we studied the production of pamamycins, macrodiolide homologs with a high activity against multiresistant pathogenic microbes, using recombinant Streptomyces albus J1074/R2. Talc particles (hydrous magnesium silicate, 3MgO·4SiO2·H2O) of micrometer size, added to submerged cultures of the recombinant strain, tripled pamamycin production up to 50 mg/L. Furthermore, they strongly affected morphology, reduced the size of cell pellets formed by the filamentous microbe during the process up to sixfold, and shifted the pamamycin spectrum to larger derivatives. Integrated analysis of transcriptome and precursor (CoA thioester) supply of particle‐enhanced and control cultures provided detailed insights into the underlying molecular changes. The microparticles affected the expression of 3,341 genes (56% of all genes), revealing a global and fundamental impact on metabolism. Morphology‐associated genes, encoding major regulators such as SsgA, RelA, EshA, Factor C, as well as chaplins and rodlins, were found massively upregulated, indicating that the particles caused a substantially accelerated morphogenesis. In line, the pamamycin cluster was strongly upregulated (up to 1,024‐fold). Furthermore, the microparticles perturbed genes encoding for CoA‐ester metabolism, which were mainly activated. The altered expression resulted in changes in the availability of intracellular CoA‐esters, the building blocks of pamamycin. Notably, the ratio between methylmalonyl CoA and malonyl‐CoA was increased fourfold. Both metabolites compete for incorporation into pamamycin so that the altered availability explained the pronounced preference for larger derivatives in the microparticle‐enhanced process. The novel insights into the behavior of S. albus in response to talc appears of general relevance to further explore and upgrade the concept of microparticle enhanced cultivation, widely used for filamentous microbes

Exchange-correlation effects on quantum wires with spin-orbit interactions under the influence of in-plane magnetic fields

12 pages.-- PACS numbers: 73.63.Nm, 71.70.Ej, 71.15.Mb, 71.70.Gm.-- Final full-text version of the paper available at: http://dx.doi.org/10.1103/PhysRevB.76.115306.Within the noncollinear local spin-density approximation, we have studied the ground state structure of a parabolically confined quantum wire submitted to an in-plane magnetic field, including both Rashba and Dresselhaus spin-orbit interactions. We have explored a wide range of linear electronic densities in the weak (strong) coupling regimes that appear when the ratio of spin-orbit to confining energy is small (large). These results are used to obtain the conductance of the wire. In the strong coupling limit, the interplay between the applied magnetic field irrespective of the in-plane direction, the exchange-correlation energy, and the spin-orbit energy produces anomalous plateaus in the conductance vs linear density plots that are otherwise absent, or washes out plateaus that appear when the exchange-correlation energy is not taken into account.This work has been performed under Grants No. FIS2005-01414 and No. FIS2005-02796 from DGI (Spain), Grant No. 2005SGR00343 from Generalitat de Catalunya, and under Grant No. INFN07-30 from the Italian INFN-Spanish DGI agreement.http://dx.doi.org/10.1103/PhysRevB.76.11530

STING agonism turns human T cells into interferon‐producing cells but impedes their functionality

The cGAS‐STING (cyclic GMP‐AMP synthase‐stimulator of interferon genes) axis is the predominant DNA sensing system in cells of the innate immune system. However, human T cells also express high levels of STING, while its role and physiological trigger remain largely unknown. Here, we show that the cGAS‐STING pathway is indeed functional in human primary T cells. In the presence of a TCR‐engaging signal, both cGAS and STING activation switches T cells into type I interferon‐producing cells. However, T cell function is severely compromised following STING activation, as evidenced by increased cell death, decreased proliferation, and impaired metabolism. Interestingly, these different phenotypes bifurcate at the level of STING. While antiviral immunity and cell death require the transcription factor interferon regulatory factor 3 (IRF3), decreased proliferation is mediated by STING independently of IRF3. In summary, we demonstrate that human T cells possess a functional cGAS‐STING signaling pathway that can contribute to antiviral immunity. However, regardless of its potential antiviral role, the activation of the cGAS‐STING pathway negatively affects T cell function at multiple levels. Taken together, these results could help inform the future development of cGAS‐STING‐targeted immunotherapies