117,458 research outputs found
STARFISH SAPONINS .23. STEROIDAL GLYCOSIDES FROM THE STARFISH HALITYLE-REGULARIS
No full textEight new steroidal glycosides were isolated from the starfish H. regularis. Three compds. contain the 2,4-di-O-methyl-β-D-xylopyranosyl-(1→2)-α-L-arabinofuranosyl disaccharide moiety, which is attached at C-24 of polyhydroxysteroid aglycons. Another 3 glycosides have polyhydroxylated 24-(β-hydroxyethyl) steroid aglycons with the disaccharide moieties, 2-O-methyl-β-D-xylopyranosyl-(1→2)-β-D-xylopyranosyl or 2,4-di-O-methyl-β-D-xylopyranosyl-(1→2)-α-L-arabinofuranosyl, located at the primary hydroxyl group at C-29. Unlike the other compds., the other 2 glycosides have a sulfate group. These glycosides are accompanied by 2 nonglycosidated polyhydoxylated sterols, i.e., (25S)-5α-cholestane-3β,6α,8,15β,26-hexol and (25S)-5α-cholestane-3β,4β,6α,8,15β,26-heptol. The structures of the new metabolites were detd. by interpretation of spectral data, comparison with related glycosides described previously, and chem. transformations
STARFISH SAPONINS .18. STEROIDAL GLYCOSIDE SULFATES FROM THE STARFISH LINCKIA-LAEVIGATA
No full textThe asterosaponins of the Pacific starfish L. laevigata were sepd. into 5 compds. Four of them are known: thornasteroside A, marthasteroside A1, ophidianoside F, and maculatoside. The 5th minor component, named laevigatoside, is new and was characterized as 6α-O-[β-fucopyranosyl-(1 → 2)-α-arabinopyranosyl-(1 → 4)-[(β-quinovopyranosyl-(1 → 2)]-β-quinovopyranosyl-(1 → 3)-β-quinovopyranosyl]-20-hydroxy-23-oxo-5α-cholest-9(11)-en-3β-yl Na sulfate
Physical interactions promote Turing patterns
No full textTuring's mechanism is often invoked to explain periodic patterns in nature,
although direct experimental support is scarce. Turing patterns form in
reaction-diffusion systems when the activating species diffuse much slower than
the inhibiting species, and the involved reactions are highly non-linear. Such
reactions can originate from co-operativity, whose physical interactions should
also affect diffusion. We here take direct interactions into account and show
that they strongly affect Turing patterns. We find that weak repulsion between
the activator and inhibitor can substantially lower the required differential
diffusivity and reaction non-linearity. In contrast, strong interactions can
induce phase separation, but the resulting length scale is still typically
governed by the fundamental reaction-diffusion length scale. Taken together,
our theory connects traditional Turing patterns with chemically active phase
separation, thus describing a wider range of systems. Moreover, we demonstrate
that even weak interactions affect patterns substantially, so they should be
incorporated when modeling realistic systems.Comment: 5 pages, 5 figures, and appendi
STARFISH SAPONINS .16. COMPOSITION OF THE STEROIDAL GLYCOSIDE SULFATES FROM THE STARFISH LUIDIA-MACULATA
No full textThornasteroside A, maculatoside (I), marthasteroside A2, marthasteroside B, and marthasteroside C were isolated from L. maculata by extn. and chromatog. on Amberlite XAD-2, Sephadex LH-60, Sephadex LH-20, and anal. HPLC on μ-Bondapack C18. The structures of the saponins were detd. by 1H- and 13C-NMR and chem. analyses. Thornasteroside A was previously isolated from Acanthaster planci, whereas the marthasterosides were previously isolated from Marthasterias glacialis
Axinellins A and B: new proline-rich cyclopeptides from the Vanuatu sponge Axinella carteri
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Square Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
New Polyhydroxylated Sterols from the Starfish Luidia maculata
No full textThree new polyhydroxylated sterols, 5α-cholestane-3β,5,6β,15α,16β,26-hexol; 5α-cholestane-3β,6β,7α,15α,16β,26-hexol; and 5α-cholestane-3β,5,6β,7α,15α,16β,26-heptol, were isolated from the Pacific starfish L. maculata
STARFISH SAPONINS .22. ASTEROSAPONINS FROM THE STARFISH HALITYLE-REGULARIS - A NOVEL 22,23-EPOXYSTEROIDAL GLYCOSIDE SULFATE
No full textA new sulfated asterosaponin, regularoside A (I), contg. the (20R,22R,23S,24S)-22,23-epoxy-24-methyl-5α-cholesta-9(11)-ene-3β,6α,20-triol aglycon, was isolated from the Pacific starfish H. regularis. The sulfate residue is at C-3, and the oligosaccharide chain, β-D-fucopyranosyl(1→2)-β-D-quinovopyranosyl(1→4)[β-D-quinovopyranosyl(1→2)]-β-D-quinovopyranosyl(1→3)-β-D-glucopyranosyl, is at C-6. I co-occurs with the common thornasteroside A (II) and the novel regularoside B (III). III also has thornasterol A as its aglycon and the oligosaccharide chain is β-D-fucopyranosyl(1→2)-β-D-fucopyranosyl(1→4)[β-D-quinovopyranosyl(1→2)]-β-D-xylopyranosyl(1→3)-β-D-quinovopyranosyl. The structures of I and III were detd. by 3H- and 13C-NMR combined with chem. degrdn. anal
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