1,778 research outputs found
Controlled nanochannel lattice formation utilizing prepatterned substrates
Solid substrates can be endued with self-organized regular stripe patterns of
nanoscopic lengthscale by Langmuir-Blodgett transfer of organic monolayers.
Here we consider the effect of periodically prepatterned substrates on this
process of pattern formation. It leads to a time periodic forcing of the
oscillatory behavior at the meniscus. Utilizing higher order synchronization
with this forcing, complex periodic patterns of predefined wavelength can be
created. The dependence of the synchronization on the amplitude and the
wavelength of the wetting contrast is investigated in one and two spatial
dimensions and the resulting patterns are discussed. Furthermore, the effect of
prepatterned substrates on the pattern selection process is investigated
Dynamics of a thin liquid film with surface rigidity and spontaneous curvature
The effect of rigid surfaces on the dynamics of thin liquid films which are
amenable to the lubrication approximation is considered. It is shown that the
Helfrich energy of the layer gives rise to additional terms in the
time-evolution equations of the liquid film. The dynamics is found to depend on
the absolute value of the spontaneous curvature, irrespective of its sign. Due
to the additional terms, a novel finite wavelength instability of flat rigid
interfaces can be observed. Furthermore, the dependence of the shape of a
droplet on the bending rigidity as well as on the spontaneous curvature is
discussed.Comment: 4 pages, 5 figure
Creating novel specificities in a fungal nonself recognition system by single step homologous recombination events
In many organisms, two component systems have evolved to discriminate self from nonself. While the molecular function of the two components has been elucidated in several systems, the evolutionary events leading to the large number of different specificities for self–nonself recognition found in most systems remain obscure.
We have investigated the variation within a multiallelic nonself recognition system in the phytopathogenic basidiomycete Ustilago maydis by means of sequence analysis and functional studies.
The multiallelic b mating type locus of U. maydis ensures outbreeding during sexual development. Nonself recognition is specified by the two homeodomain proteins, bE and bW, encoded by the b locus. While bE–bW combinations from the same allele do not dimerize, bE and bW proteins originating from different alleles form a heterodimeric complex that functions as master regulator for sexual and pathogenic development.
We show that novel specificities of the b mating type locus have arisen by single homologous recombination events between distinct b alleles that lead to a simultaneous exchange of subdomains involved in dimerization in both bE and bW, altering the specificity of both proteins in a single step
Complementary Sensory and Associative Microcircuitry in Primary Olfactory Cortex
The three-layered primary olfactory (piriform) cortex is the largest component of the olfactory cortex. Sensory and intracortical inputs converge on principal cells in the anterior piriform cortex (aPC).Wecharacterize organization principles of the sensory and intracortical microcircuitry of layer II and III principal cells in acute slices of rat aPC using laser-scanning photostimulation and fast two-photon population Ca²⁺ imaging. Layer II and III principal cells are set up on a superficial-to-deep vertical axis. We found that the position on this axis correlates with input resistance and bursting behavior. These parameters scale with distinct patterns of incorporation into sensory and associative microcircuits, resulting in a converse gradient of sensory and intracortical inputs. In layer II, sensory circuits dominate superficial cells, whereas incorporation in intracortical circuits increases with depth. Layer III pyramidal cells receive more intracortical inputs than layer II pyramidal cells, but with an asymmetric dorsal offset. This microcircuit organization results in a diverse hybrid feedforward/recurrent network of neurons integrating varying ratios of intracortical and sensory input depending on a cell’s position on the superficial-to-deep vertical axis. Since burstiness of spiking correlates with both the cell’s location on this axis and its incorporation in intracortical microcircuitry, the neuronal output mode may encode a given cell’s involvement in sensory versus associative processing
Testing the implications of a permanent or seasonal marine reserve on the population dynamics of Eastern Baltic cod under varying environmental conditions
In order to test the implications of the establishment of a marine reserve in the Baltic Sea, a spatially disaggregated, discrete time, age-structured model for the Eastern Baltic cod (Gadus morhua callarias L.) stock was constructed. Functional relationships for recruitment and predation mortality were developed by multiple regression analyses. The resultant model output compares well with observed data from the fishery. The model was then applied to simulate stock development over a 50 year time period using different management policies and a variety of environmental conditions. The investigated management policies reduce fishing mortality and range from a moratorium on the Eastern Baltic cod fishery via the establishment of a permanent or a seasonal marine reserve in ICES subdivision 25 to a fishing as usual scenario. The environmental conditions incorporated were based on the size of the reproductive volume (RV) and comprise a best case and a worst case of reproductive conditions, and two more realistic scenarios, where we assumed that a historic series of RV-sizes reoccurs over the simulation period. Our results show a strong dependence of stock dynamics on the environmental conditions. Under prevailing low RV, our model projects stock extinction by the year 2020, if fishing continues as usual. Under the restrictive scenarios, where fishing mortality is reduced either directly or by implementation of a marine reserve, the stock benefits from an increase in stock size and an improved age-structure. A seasonal closure of SD 25 as opposed to a closure of the entire Baltic Sea appears to be sufficient to prevent the Eastern Baltic cod stock from falling below safe biological limits.Baltic cod, management, age-structured model, population dynamics, MPA, environmental variability, reproductive volume
Struktur und räumliche Verteilung mikrobieller Gemeinschaften im Verdauungstrakt ausgewählter Boden-Invertebraten
Boden-Makroinvertebraten sind entscheidend an der
Transformation organischer Substanz beteiligt, die für viele
Schlüsselfunktionen des Bodens verantwortlich ist. An den
Transformationsprozessen, die während der Darmpassage
ingestierter organischer Substanz ablaufen, sind intestinale
Mikroorganismen beteiligt, die auch für die Ernährung ihrer
Wirte von entscheidender Bedeutung sind. Über die
Zusammensetzung der mikrobiellen Gemeinschaften im
Verdauungstrakt der meisten Boden-Invertebraten sowie ihre
räumliche Verteilung innerhalb verschiedener Darmabschnitte ist
allerdings nur wenig bekannt. Gerade die Topologie mikrobieller
Gemeinschaften wird aber als eine wichtige Voraussetzung zum
tieferen Verständnis ihrer Funktion in Verdauungstrakten von
Invertebraten angesehen, die von ausgeprägten axialen und
radialen Gradienten physiko-chemischer Parameter geprägt sind.
Im Rahmen dieser Arbeit wurden daher Struktur und räumliche
Verteilung mikrobieller Gemeinschaften im Verdauungstrakt der
Larven zweier Scarabaeiden (Pachnoda ephippiata
[Kongo-Rosenkäfer] und Melolontha melolontha [Feldmaikäfer])
und von Regenwürmern (Lumbricus terrestris) mit Methoden der
molekularen mikrobiellen Ökologie untersucht. Während der
Untersuchungen wurde zudem ein neuartiger PCR-Artefakt, die
Bildung sog. pseudo-T-RFs, mit bedeutenden Auswirkungen für die
T-RFLP-Analyse mikrobieller Gemeinschaften entdeckt,
beschrieben und mögliche Ansätze zu seiner Vermeidung
aufgezeigt.
In einer T-RFLP-Studie mit Regenwürmern wurde
gezeigt, dass sich die Darmmikrobiota dieser Tiere aus der
Nahrung rekrutiert, d.h. ihnen im Gegensatz zu vielen anderen
Boden-Invertebraten eine spezifische Darmflora fehlt. Es wurde
deutlich, dass die mit dem gefressenen Boden aufgenommene
mikrobielle Gemeinschaft während der Darmpassage signifikante
Veränderungen ihrer relativen Zusammensetzung erfährt und dass
die Unterschiede zwischen den mikrobiellen Gemeinschaften von
Futter, Darm und Losung stark von der Diät der Regenwürmer
beeinflusst werden.
Die hier präsentierten Ergebnisse zur
Intestinalmikrobiologie von Scarabaeidenlarven stellen die
ersten ihrer Art für Käferlarven und mit die ersten für andere
Boden-Arthropoden als Termiten dar. Es konnte gezeigt werden,
dass sich die ausgeprägten Unterschiede physiko-chemischer
Parameter (pH-Wert, Redoxpotential, Fettsäurespektren), die
zwischen den Haupt-Darmabschnitten (Mittel- und Enddarm) der
Larven herrschen, in einer deutlich unter-schiedlichen
Besiedlung mit Mikroorganismen widerspiegeln. Im Gegensatz zu
den untersuchten Regenwürmern ist die Darmmikrobiota der
Scarabaeidenlarven als spezifische Darmflora anzusehen, da sie
deutlich verschieden zur Mikrobiota der aufgenommenen Nahrung
war. Bei beiden Larven war der Mitteldarmabschnitt weniger
dicht besiedelt als der als Gärkammer angesehene Enddarm. Die
Methanogenese war stets auf den Enddarm beschränkt; bei den
Maikäferlarven wurden Methanobrevibacter-Arten, bei den
Rosenkäferlarven zusätzlich Methanomicrococcus-Arten als
verantwortliche Methanogene identifiziert. Im Vergleich zu den
Bacteria war aber sowohl die Diversität als auch die relative
Häufigkeit der Archaea sehr gering. Die phylogenetische Analyse
der Bakteriengemeinschaften zeigte eine sehr große Diversität
auf, die offensichtlich viele bislang unkultivierte Arten
umfasst. Die überwiegende Mehrheit aller Sequenzen ließ sich
den Actinobacteria, Bacillales, Bacteroidetes, Clostridiales,
Lactobacillales und Proteobacteria zuordnen; viele Klone
gruppierten mit Klonen und Isolaten aus anderen
Intestinalsystemen, ein weiterer Beleg für die Darmspezifität
der Scarabaeiden-Mikrobiota. Die Verwandtschaft vieler Klone zu
hydrolytischen, cellulolytischen und gärenden Isolaten stand in
Einklang mit den Fettsäureprofilen der Darmabschnitte (v.a.
Acetat und Lactat) und deutet die Beteiligung von
Mikroorganismen an der Transformation organischer Substanz nach
dem Modell einer anaeroben Nahrungskette zumindest im Enddarm
an. Ob dies auch für den Mitteldarmabschnitt gilt, ist noch
unklar, da bei den Maikäferlarven keine stabile Darmmikrobiota
in diesem Kompartiment nachgewiesen werden konnte.
Am Enddarm
der Maikäferlarven wurde erstmals für Arthropoden eine
umfassende Analyse der mikrobiellen Gemeinschaften in den
Unterfraktionen Wand und Lumen eines Darmabschnittes
durchgeführt. Hierbei wurden ausgeprägte Unterschiede in der
Besiedlung dieser beiden Fraktionen festgestellt, die als
Anpassungen an morphologische (Chitinbäumchen an der
Enddarmwand) und eventuell auch physiko-chemische Unterschiede
(Gradient eindringenden Sauerstoffs) zwischen Darmwand und
-lumen interpretiert werden können. Der auffälligste
Unterschied war eine hohe Abundanz (10 - 15% aller Bakterien)
Desulfovibrio-verwandter Bakterien an der Enddarmwand, die
sowohl mit PCR-abhängigen als auch PCR-unabhängigen Methoden
abgesichert werden konnte. In seiner Eindeutigkeit ist dieser
Befund für Arthropoden bislang einmalig
Sulfate-Reducing Microorganisms in Wetlands – Fameless Actors in Carbon Cycling and Climate Change
Freshwater wetlands are a major source of the greenhouse gas methane but at the same time can function as carbon sink. Their response to global warming and environmental pollution is one of the largest unknowns in the upcoming decades to centuries. In this review, we highlight the role of sulfate-reducing microorganisms (SRM) in the intertwined element cycles of wetlands. Although regarded primarily as methanogenic environments, biogeochemical studies have revealed a previously hidden sulfur cycle in wetlands that can sustain rapid renewal of the small standing pools of sulfate. Thus, dissimilatory sulfate reduction, which frequently occurs at rates comparable to marine surface sediments, can contribute up to 36–50% to anaerobic carbon mineralization in these ecosystems. Since sulfate reduction is thermodynamically favored relative to fermentative processes and methanogenesis, it effectively decreases gross methane production thereby mitigating the flux of methane to the atmosphere. However, very little is known about wetland SRM. Molecular analyses using dsrAB [encoding subunit A and B of the dissimilatory (bi)sulfite reductase] as marker genes demonstrated that members of novel phylogenetic lineages, which are unrelated to recognized SRM, dominate dsrAB richness and, if tested, are also abundant among the dsrAB-containing wetland microbiota. These discoveries point toward the existence of so far unknown SRM that are an important part of the autochthonous wetland microbiota. In addition to these numerically dominant microorganisms, a recent stable isotope probing study of SRM in a German peatland indicated that rare biosphere members might be highly active in situ and have a considerable stake in wetland sulfate reduction. The hidden sulfur cycle in wetlands and the fact that wetland SRM are not well represented by described SRM species explains their so far neglected role as important actors in carbon cycling and climate change
Structure and dynamics of iron pentacarbonyl
The dynamics of CO ligand scrambling in Fe(CO)5 has been investigated by linear infrared spectroscopy in supercritical xenon solution. The activation barrier for the Berry pseudorotation in Fe(CO)5 was determined experimentally to be Ea = 2.5 ± 0.4 kcal mol–1 by quantitative analysis of the temperature-dependent spectral line shape. This compares well with the range of Ea/(kcal mol–1) = 2.0 to 2.3 calculated by various DFT methods and the value of 1.6 ± 0.3 previously obtained from 2D IR measurements by Harris et al. ( Science 2008, 319, 1820). The involvement of Fe(CO)5···Xe interactions in the ligand scrambling process was tested computationally at the BP86-D3/AE2 level and found to be negligible
Staged Concept for Treatment of Severe Postsaphenectomy Wound Infection
The saphenous vein remains the most commonly used conduit in coronary artery bypass surgery. Vein harvest is a critical component with significant morbidity associated with leg wounds from open technique. Occurring complications are hematoma, postoperative pain, skin changes, neuropathy, and septic or nonseptic wound complications. Within the context of a recent case, we present our approach to postsaphenectomy wound management
Mediterranean radiocarbon offsets and calendar dates for prehistory
A single Northern Hemisphere calibration curve has formed the basis of radiocarbon dating in Europe and the Mediterranean for five decades, setting the time frame for prehistory. However, as measurement precision increases, there is mounting evidence for some small but substantive regional (partly growing season) offsets in same-year radiocarbon levels. Controlling for interlaboratory variation, we compare radiocarbon data from Europe and the Mediterranean in the second to earlier first millennia BCE. Consistent with recent findings in the second millennium CE, these data suggest that some small, but critical, periods of variation for Mediterranean radiocarbon levels exist, especially associated with major reversals or plateaus in the atmospheric radiocarbon record. At high precision, these variations potentially affect calendar dates for prehistory by up to a few decades, including, for example, Egyptian history and the much-debated Thera/Santorini volcanic eruption
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