1,229 research outputs found
Mechanistic Links Between the Sedimentary Redox Cycle and Marine Acid-Base Chemistry
The redox state of Earth's surface is controlled on geological timescales by the flow of electrons through the sedimentary rock cycle, mediated largely by the weathering and burial of CāSāFe phases. These processes buffer atmospheric pOā. At the same time, COā influxes and carbonate burial control seawater acidābase chemistry and climate over long timescales via the carbonateāsilicate cycle. However, these two systems are mechanistically linked and impact each other via charge balance in the hydrosphere. Here, we use a lowāorder Earth system model to interrogate a subset of these connections, with a focus on changes that occur during perturbations to electron flow through the sedimentary rock cycle. We show that the net oxidation or reduction of the Earth's surface can play an important role in controlling acidābase processes in the oceans and thus climate, and suggest that these links should be more fully integrated into interpretive frameworks aimed at understanding Earth system evolution throughout Precambrian and Phanerozoic time
Dynamically induced scalar quark confinement
We employ a functional approach to investigate the confinement problem in
quenched Landau gauge QCD. We demonstrate analytically that a linear rising
potential between massive quarks is generated by infrared singularities in the
dressed quark-gluon vertex. The selfconsistent mechanism that generates these
singularities is driven by the scalar Dirac amplitudes of the full vertex and
the quark propagator. These can only be present when chiral symmetry is broken.
We have thus uncovered a novel mechanism that directly links chiral symmetry
breaking with confinement.Comment: 12 pages, 2 figures; v2: clarifications added and typos corrected,
version to be published by MPL
Lower dimensional Yang-Mills theory as a laboratory to study the infrared regime
Lattice studies of the infrared regime of gauge theories are complicated by
the required extensive limits, the performed gauge fixing and the demand for
high statistics. Using a general power counting scheme for the infrared limit
of Landau gauge SU(N) Yang-Mills theory in arbitrary dimensions we show that
the infrared behavior of Greens functions is both qualitatively and
quantitatively similar in two, three and four spacetime dimensions. Therefore,
lower dimensional lattice simulations can serve as a simplified laboratory to
analyze the presently applied approximations and to obtain first results for
higher correlation functions.Comment: 7 pages, 6 figures; talk presented at Lattice 200
Establishment of Arthrobotrys flagrans as biocontrol agent against the root pathogenic nematode Xiphinema index
Plant-parasitic nematodes cause devastating agricultural damage worldwide. Only a few synthetic nematicides can be used and their application is limited in fields. Therefore, there is a need for sustainable and environment-friendly alternatives. Nematode-trapping fungi (NTF) are natural predators of nematodes. They capture and digest them with their hyphae and are starting to being used as bio-control agents. In this study, we applied the NTF Arthrobotrys flagrans (Duddingtonia flagrans) against the wine pathogenic nematode Xiphinema index. A. flagrans reduced the number of X. index juveniles in pot cultures of Ficus carica, an alternative host plant for X. index, significantly. Sodium-alginate pellets with A. flagrans spores were produced for vineyard soil inoculation under laboratory conditions. The NTF A. conoides, A. musiformis and A. superba were enriched from several soil samples, showing their natural presence. Trap formation is an energy-consuming process and depends upon various biotic and abiotic stimuli. Here, we show that bacteria of the genus Delftia, Bacillus, Pseudomonas, Enterobacter and Serratia induced trap formation in NTF like A. conoides and A. oligospora but not in A. flagrans in the absence of nematodes. The application of NTF along with such bacteria could be a combinatorial way of efficient biocontrol in nematode-infested soil
KugoāOjimaov kriterij ograniÄenja i infracrvena svojstva Landauove baždarne QCD
Recent investigations of the Dyson-Schwinger equations and Monte-Carlo lattice calculations resulted in a coherent description of the fully dressed gluon, ghost and quark propagators in Landau gauge QCD. In the Dyson-Schwinger approach, the infrared behaviour of these propagators is determined analytically. For finite spacelike momenta the gluon, ghost and quark propagators are compared to available corresponding results of lattice Monte-Carlo calculations. For all three propagators, an almost quantitative agreement is found. These results for the non-perturbative propagators allow an analytical verification of the Kugo-Ojima confinement criterion. Our numerical analysis clearly reveals positivity violation for the gluon propagator generated by a cut in the complex momentum plane. The non-perturbative strong running coupling resulting from these propagators possesses an infrared fixed point. The quark propagator obtained from quenched and unquenched calculations displays dynamical chiral symmetry breaking with quark masses close to "phenomenological" and lattice values. We confirm that linear extrapolations of the quark propagator for different bare masses to the chiral limit are inaccurate.Nedavna istraživanja DysonāSchwingerovih jednadžbi i MonteāCarlo raÄuna na reÅ”etki dali su usklaÄen opis potpuno obuÄenih propagatora gluona, duhova i kvarkova u Landauovoj baždarnoj QCD. U DysonāSchwingerovom pristupu, infracrvena svojstva tih propagatora odreÄena su analitiÄki. Za konaÄne vremenske impulse, propagatori gluona, duhova i kvarkova usporeÄuju se dostupnim odgovarajuÄim ishodima MonteāCarlo raÄuna na reÅ”etki. Gotovo kvantitativno slaganje nalazi se za sva tri propagatora. Ti ishodi za neperturbativne propagatore dopuÅ”taju analitiÄku provjeru KugoāOjimaovog kriterija ograniÄenja. NaÅ”a numeriÄka analiza jasno pokazuje krÅ”enje pozitivnosti za gluonski propagator uzrokovan rezom u ravnini kompleksnog impulsa. Neperturbativno jako vezanje, koje je posljedica tih propagatora, ima infracrvenu Ävrstu toÄku. Kvarkovski propagator koji se dobije gaÅ”enim i negaÅ”enim raÄunima pokazuje lomljenje dinamiÄke kiralne simetrije s kvarkovskim masama koje su blizu āfenomenoloÅ”kimā i reÅ”etkinskim vrijednostima. Utvrdili smo da su linearne ekstrapolacije kvarkovskih propagatora za razne gole mase vrlo netoÄne u kiralnoj granici
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