1,125 research outputs found
A Sulfoxide Reagent for One-Pot, Three-Component Syntheses of Sulfoxides and Sulfinamides
Sulfoxides and sulfinamides represent versatile sulfur functional groups found in ligands, chiral auxiliaries, and bioactive molecules. Canonical two-component syntheses, however, rely on substrates with a preinstalled C-S bond and impede efficient and modular access to these sulfur motifs. Herein is presented the application of an easily prepared, bench-stable sulfoxide reagent for one-pot, three-component syntheses of sulfoxides and sulfinamides. The sulfoxide reagent donates the SO unit upon the reaction with a Grignard reagent (RMgX) as a sulfenate anion (RSO-). While subsequent trapping reactions of this key intermediate with carbon electrophiles provide sulfoxides, a range of tertiary, secondary, and primary sulfinamides can be prepared by substitution reactions with electrophilic amines. The syntheses of sulfinamide analogs of amide- and sulfonamide-containing drugs illustrate the utility of the method for the rapid preparation of medicinally relevant molecules
Microbial metabolisms and calcification in freshwater biofilms
In dieser Arbeit wurden Biofilme zweier
CO2-entgasender KarstwasserbÀche in Deutschland, welche in ihrem
Verlauf fluĂabwĂ€rts hohe Kalziumkarbonat-ĂbersĂ€ttigungen erreichen,
bezĂŒglich der mikrobiellen Effekte auf die CaCO3-FĂ€llung,
Wasserchemie des Mikro- und Makromilieus, Stabile
IsotopenverhĂ€ltnisse und Kalktuff-GefĂŒgebildung untersucht. In situ
und ex situ Mikroelektroden-Messungen an kalzifizierenden
Biofilmen, welche hauptsÀchlich von filamentösen Cyanobakterien
aufgebaut werden, zeigen, daĂ unter Belichtung eine CaCO3-FĂ€llung
durch Photosynthese induziert, unter Dunkelheit dagegen eine
FĂ€llung verhindert wird. Eine Photosynthese-induzierte
CaCO3-FÀllung wurde ebenso bestÀtigt durch 45Ca-Tracer-Experimente
und Massenbilanzrechnungen. Die in den Kalktuff-Stromatolithen
aufgezeichneten stabilen Sauerstoff- und Kohlenstoff-Isotopenwerte
lieĂen keinen Photosynthese-Effekt erkennen, trotz der
offensichtlichen Photosynthese-induzierten FĂ€llung. Entsprechend
kann das Fehlen einer 13C-Anreichungen in Karbonatmineralen nicht
als Indikator fĂŒr ein Fehlen eines Photosynthese-Effektes auf eine
KarbonatfÀllung gewertet werden Ebenso kann das Verkalkungsmuster
von Cyanobakterien nicht zur Unterscheidung von
Photosynthese-induzierter und physikochemisch induzierter
CaCO3-FĂ€llung herangezogen werden. Insbesondere tritt in den
photosynthetisch verkalkten Kalktuff-Biofilmen anstatt
Polysaccharidscheiden-ImprÀgnation eine -Inkrustation auf, sprich
ein Verkalkungsmuster, welches vormals als Indikator fĂŒr
physikochemisch-erzwungene FĂ€llung angesehen wurde. Auch wenn
Kalktuff-Stromatolithen durch Photosynthese-induzierte
KalzitfÀllung gebildet werden, so zeigen doch
Massenbilanzrechnungen, daĂ die Biofilmverkalkung fĂŒr nur etwa
10-20% des Ca2+-Entzuges im Bachwasser verantwortlich ist, wÀhrend
der verbliebene Ca2+-Entzug mit physikochemischer FĂ€llung auf Ăsten
und BlÀttern sowie in Form feinkörnige Kalzitpartikel erklÀrt
werden muĂ. Entsprechend sind die Effekte einer
Photosynthese-induzierten FĂ€llung verdĂŒnnt, und damit mit
herkömmlichen Wasseranalysen kaum nachweisbar, auĂer bei GewĂ€ssern
mit geringen FlieĂgeschwindigkeiten. Auf der anderen Seite können
endolithische Cyanobakterien-Biofilme wie auch Moose aufgrund ihrer
geringeren Photosynthese-Leistung keine KalkfÀllung induzieren, wie
ex situ Mikroelektroden-Messungen belegen. Biofilm-freie
Kalksubstrate fĂŒhren trotz hoher ĂbersĂ€ttigungen des
Umgebungsmilieus zu keiner spontanen KalkfÀllung, wohingegen
Kalktuffbiofilme unter denselben Bedingungen eine FĂ€llung
induzieren. Dies zeigt, daĂ Photosynthese ein entscheidender
Mechanismus zur Ăberwindung kinetischer Barrieren der CaCO3-FĂ€llung
ist, sogar in hochgradig ĂŒbersĂ€ttigten Milieus. Modellrechnungen
des Photosynthese-Effekts unter verschiedenen pH, DIC und
Ca2+-Konzentrationen zeigen, daĂ die Voraussetzungen einer
Photosynthese-induzierten KarbonatfÀllung (1) optimale
pH-DIC-Bedingungen mit niedrigem DIC-Puffereffekt, (2) ausreichende
initiale MineralsÀttigungen, und (3) nicht extrem niedrige
Ca2+-Konzentrationen sind. AuĂerdem können hohe IonenstĂ€rken eine
Photosynthese-induzierte FÀllung beeintrÀchtigen oder verhindern.
Sicherlich muĂ auch die Photosynthese-AktivitĂ€t der Biofilme fĂŒr
eine Verschiebung des Karbonatgleichgewichtes auf oder in den
Biofilmen hoch genug sein. Die meisten dieser Voraussetzungen
lassen sich auch auf KarbonatfĂ€llungen ĂŒbertragen, welche durch
andere Arten mikrobieller StoffwechselaktivitÀt wie
Sulphatreduktion induziert werden. Die SchluĂfolgerung ist daher,
daĂ die oben genannten Voraussetzungen wichtige SchlĂŒssel fĂŒr das
VerstÀndnis der Bildung und generelle Verteilung karbonatischer
Mikrobialithe durch die Erdgeschichte hindurch sind
Information-transfer characteristics in network motifs
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ć ±ćŠçăĄă«ăășă ă«èż«ă--. äșŹéœć€§ćŠăăŹăčăȘăȘăŒăč. 2023-01-30.Information processing in biological systems is realized by the appropriate transmission of information flows over complex networks, such as gene regulatory, signal transduction, and neural networks. These information flows are affected by the input-signal characteristics and structural properties of network systems, such as the network topology, regulation rules, and intrinsic and environmental noise. Many biological networks frequently include several typical patterns called network motifs, which are considered to play important roles in biological functions. However, their information-theoretic properties, particularly the dependence of the information flows in each network on the input signal, remain poorly understood. In our previous study [Mori and Okada, Phys. Rev. Res. 2, 043432 (2020)], we developed a graphical expansion method to describe transfer entropy (TE), a measure of information flow, in Boolean networks in terms of multiple information pathways. There, the input signal was limited to a simple case, and the effect of the input-signal characteristics on TE was not clarified. In this paper, we improve our method to render it applicable to Boolean networks that receive input signals with arbitrary stochastic characteristics. Our formula expresses how TE is determined by the input-signal characteristics, the assignment of Boolean functions, and the noise magnitude. We find that, in both positive and negative feedback loops, TE hardly depends on the signal timescale. In contrast, coherent and incoherent feedforward loops show low- and high-pass filtering properties, respectively, for a time-varying signal, which is consistent with previous reports. The emergence of either low- or high-pass filtering is determined by the Fourier components of the Boolean functions on specific pathways transmitting information flows. Thus our formula reveals the mechanism of information transfer in network motifs and provides insights into the origin of information processing in biological networks
Kinetics of motile solitons in fluid nematics
Solitary waves, dubbed "solitons", are special types of waves that propagate
for an infinite distance under ideal conditions. These waves are ubiquitously
found in nature such as typhoon or neuron signals. Yet, their artificial
generation and the control of their propagation remain outstanding challenges
in materials science owing to an insufficient understanding of the experimental
conditions and theoretical aspects. Herein, a generic strategy for forming
particle-like solitons and controlling their kinetics in nematic fluid media is
reported. The key to the realisation of the generation of solitons and the
control of their kinetics is the coupling between the fluid elasticity and the
background flow flux, as evidenced by experimental observations and theoretical
approaches. The findings of this study enable the exploration of solitons in a
wide range of materials and have technological ramifications for the lossless
transport of energy or structures.Comment: Manuscript 25 pages, 6 figures, Supplementary Information 23 pages,
13 figure
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Semantical-coordinate Terms Detection from Hierarchical Knowledge Using Web Snippets
AbstractIn this paper, we describe a method to detect semantical-coordinate terms. We often use semantical-coordinate terms as objects of comparative validation and examples for the given term, and then linguistic expressions and knowledge processing are enriched. Semantical-coordinate terms should be hyponyms of a same hypernym, and their usage and concepts should be similar. However hierarchical knowledge is useful to view concepts, hierarchically coordinate terms are sometimes inappropriate as semantical-coordinate terms for our suppositions, because some of them might have multiple hypernyms and general perceptions of the terms are not taken in the consideration. On the other hand, using only Web context to detect semantical-coordinate terms, concepts of the terms are not taken in the consideration while public perceptions and their usages might be incorporated. Therefore we propose hybrid method using both hierarchical knowledge and Web snippets. We conducted bench scale tests to detect semantical-coordinate terms of some terms and discuss about the results in this paper. Through the tests and discussions, we confirmed that the semantical-coordinate terms detected by our proposed method were not only hierarchically but also semantically and intuitively appropriate
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