Search results for "ASTER"
showing 10 items of 2223 documents
The origin of postembryonic neuroblasts in the ventral nerve cord of Drosophila melanogaster.
1991
ABSTRACT Embryonic and postembryonic neuroblasts in the thoracic ventral nerve cord of Drosophila melanogaster have the same origin. We have traced the development of threefold-labelled single precursor cells from the early gastrula stage to late larval stages. The technique allows in the same individual monitoring of progeny cells at embryonic stages (in vivo) and differentially staining embryonic and postembryonic progeny within the resulting neural clone at late postembryonic stages. The analysis reveals that postembryonic cells always appear together with embryonic cells in one clone. Further-more, BrdU labelling suggests that the embryonic neuroblast itself rather than one of its proge…
Stage-specific inductive signals in the Drosophila neuroectoderm control the temporal sequence of neuroblast specification.
2001
One of the initial steps of neurogenesis in the Drosophila embryo is the delamination of a stereotype set of neural progenitor cells (neuroblasts) from the neuroectoderm. The time window of neuroblast segregation has been divided into five successive waves (S1-S5) in which subsets of neuroblasts with specific identities are formed. To test when identity specification of the various neuroblasts takes place and whether extrinsic signals are involved, we have performed heterochronic transplantation experiments. Single neuroectodermal cells from stage 10 donor embryos (after S2) were transplanted into the neuroectoderm of host embryos at stage 7 (before S1) and vice versa. The fate of these cel…
An expeditious synthesis of spinasterol and schottenol, two phytosterols present in argan oil and in cactus pear seed oil, and evaluation of their bi…
2015
International audience; Spinasterol and schottenol, two phytosterols present in argan oil and in cactus pear seed oil, were synthesized from commercially available stigmasterol by a four steps reactions. In addition, the effects of these phytosterols on cell growth and mitochondrial activity were evaluated on 158N murine oligodendrocytes, C6 rat glioma cells, and SK-N-BE human neuronal cells with the crystal violet test and the MTT test, respectively. The effects of spinasterol and schottenol were compared with 7-ketocholesterol (71CC) and ferulic acid, which is also present in argan and cactus pear seed oil. Whatever the cells considered, dose dependent cytotoxic effects of 71CC were obser…
High-order services and spatial change in the central and eastern European countries
2004
This paper examines the level of high-order services in the CEECs. These services are of growing strategic importance across the whole range of production sectors in developed economies (Bailly and Coffey, 1994). They are both the cause and the consequence of globalization, in a cumulative process. It is through high-order services that large cities, and the regions around them, become closely interconnected within global networks. These services are fundamental features both in the changing pattern of regional disparities across an enlarged EU and in the process of metropolization (Bourdeau-Lepage, 2004a and Bourdeau-Lepage Huriot, 2002 and 2004). The development of high-order services wil…
Piano col colore! Mezzo secolo di contraffazioni nei centri storici
2010
The transformation dynamics of the ancient towns are completely changing the urban landscape of the historical countries in Italy in the last fifty years. The most superficial part of material constitutes the image of the architectures and plays a meaningful role in the perception of the historical districts that still characterize the contemporary city, but the aptitude for destroying architectural finishes and deleting superficial patina involves therefore to alter the character of the old towns irreversibly. It had to be obvious it would have been essential to conserve the authentic materials and signs of time that denote the historical authenticity of monuments, but new surfaces of plas…
Levy flights in confining environments: Random paths and their statistics
2013
We analyze a specific class of random systems that are driven by a symmetric L\'{e}vy stable noise. In view of the L\'{e}vy noise sensitivity to the confining "potential landscape" where jumps take place (in other words, to environmental inhomogeneities), the pertinent random motion asymptotically sets down at the Boltzmann-type equilibrium, represented by a probability density function (pdf) $\rho_*(x) \sim \exp [-\Phi (x)]$. Since there is no Langevin representation of the dynamics in question, our main goal here is to establish the appropriate path-wise description of the underlying jump-type process and next infer the $\rho (x,t)$ dynamics directly from the random paths statistics. A pr…
Synthesis and Isolation of Enantiomerically Enriched Cyclopenta[b]benzofurans Based on Products from Anodic Oxidation of 2,4-Dimethylphenol
2015
The anodic treatment of 2,4-dimethylphenol offers a powerful and direct method for the construction of a dehydrotetramer with four contiguous stereocentres on a multigram scale. The installation of propellanes on this scaffold using enantiomerically pure carbonyl compounds leads to a mixture of diastereomers. This mixture is easily separable using standard chromatography and gives rise to optically pure cyclopenta[b]benzofurans which are important scaffolds in a variety of natural products. The synthesis is easy to perform and allows a reliable access to chiral compounds with very high enantiomeric excess. It was possible to determine the absolute configuration of these compounds by compari…
Yttrium Hydrido Complexes that Contain a Less “Constrained Geometry” Ligand: Synthesis, Structure, and Efficient Hydrosilylation Catalysis
2001
σ-Bond metathesis of the new linked amino-cyclopentadiene (C5Me4H)CH2SiMe2NHCMe3 with Y(CH2SiMe3)3(THF)2 gave the alkyl-yttrium complex [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(CH2SiMe3)(THF)] (1) in 66% yield. Compound 1 was characterized by NMR spectroscopy and X-ray crystal structure analysis. By hydrogenolysis, 1 was quantitatively converted into the dimeric hydride [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(THF)(μ-H)]2 (2). X-ray crystal structure analysis revealed a Y2H2 core connected to two [Y(η5:η1-C5Me4CH2SiMe2NCMe3)(THF)] fragments in a skewed manner, with a relatively long yttrium−yttrium distance of 3.7085(8) A. In solution, two diastereomers were observed by 1H NMR spectroscopy at −78 °C. Dimer 2 was s…
Installation of Amine Moieties into a Polycyclic Anodic Product Derived from 2,4-Dimethylphenol
2011
When 2,4-dimethylphenol is anodically treated, a dehydrotetramer with four contiguous stereocentres is readily obtained on a multi-gram scale. The substitution of a 2,4-dimethyl-phenoxy fragment by several amines was demonstrated, and the best results were obtained with primary amines. Optically pure α-chiral aliphatic amines yield diastereomeric mixtures that can be separated in most cases. The basic amine causes a partial hemiketal-opening of the bisbenzofuran moiety leading to an equilibrium within an α,β-unsaturated cyclohexenone. This dynamic behaviour occurs on the time scale of NMR spectroscopy and is also found by X-ray analysis providing a consistent picture.
ChemInform Abstract: Enantioselective Mannich Reaction of β-Keto Esters with Aromatic and Aliphatic Imines Using a Cooperatively Assisted Bifunctiona…
2015
The title reaction tolerates aliphatic and aromatic substituents on both reaction partners, affording products (III) as a mixture of inseparable diastereomers with low or without any diastereoselectivity.