11 research outputs found
Multivalent 1,2,3âTriazoleâLinked Carbohydrate Mimetics by HuisgenâMeldalâSharpless Cycloadditions of an Azidopyran
Starting from an enantiopure 3âazidoâsubstituted pyran derivative and various oligoâalkynes a series of multivalent 1,2,3âtriazoleâlinked carbohydrate mimetics was synthesized. The copperâcatalyzed HuisgenâMeldalâSharpless cycloaddition (CuAAC) served as key coupling reaction. Cu/C in the presence of triethylamine proved to be a good catalytic system in most cases. Triâ, tetraâ, hexaâ, and octavalent compounds with typical rigid or flexible core units were prepared. The most complex compound contains a C60âfullerene center leading to a dodecavalent carbohydrate mimetic. Only a few of the multivalent target compounds could be converted into pure Oâsulfated derivatives that are required for their evaluation as Lâ and Pâselectin ligands. Nevertheless, preliminary experiments suggest that the dodecavalent C60âderived compound may be a promising ligand of these biologically important proteins with IC50 values in the low nanomolar range
Cosmology and Cosmogony in a Cyclic Universe
In this paper we discuss the properties of the quasi-steady state
cosmological model (QSSC) developed in 1993 in its role as a cyclic model of
the universe driven by a negative energy scalar field. We discuss the origin of
such a scalar field in the primary creation process first described by F. Hoyle
and J. V. Narlikar forty years ago. It is shown that the creation processes
which takes place in the nuclei of galaxies are closely linked to the high
energy and explosive phenomena, which are commonly observed in galaxies at all
redshifts.
The cyclic nature of the universe provides a natural link between the places
of origin of the microwave background radiation (arising in hydrogen burning in
stars), and the origin of the lightest nuclei (H, D, He and He). It
also allows us to relate the large scale cyclic properties of the universe to
events taking place in the nuclei of galaxies. Observational evidence shows
that ejection of matter and energy from these centers in the form of compact
objects, gas and relativistic particles is responsible for the population of
quasi-stellar objects (QSOs) and gamma-ray burst sources in the universe.
In the later parts of the paper we briefly discuss the major unsolved
problems of this integrated cosmological and cosmogonical scheme. These are the
understanding of the origin of the intrinsic redshifts, and the periodicities
in the redshift distribution of the QSOs.Comment: 51 pages including 1 figur
Dwarf Elliptical Galaxies
Dwarf elliptical (dE) galaxies, with blue absolute magnitudes typically
fainter than , are the most numerous type of galaxy in the nearby
universe. Tremendous advances have been made over the past several years in
delineating the properties of both Local Group satellite dE's and the large dE
populations of nearby clusters. We review some of these advances, with
particular attention to how well currently available data can constrain 1)
models for the formation of dE's, 2) the physical and evolutionary connections
between different types of galaxies (nucleated and nonnucleated dE's, compact
E's, irregulars, and blue compact dwarfs) that overlap in the same portion of
the mass-spectrum of galaxies, 3) the contribution of dE's to the galaxy
luminosity functions in clusters and the field, 4) the star-forming histories
of dE's and their possible contribution to faint galaxy counts, and 5) the
clustering properties of dE's. In addressing these issues, we highlight the
extent to which selection effects temper these constraints, and outline areas
where new data would be particularly valuable.Comment: 63p, uuencoded compressed postscript, 2/8 figs included, A&A Review
in press, request paper copies from [email protected], STScI 86
Palaeoenvironmental significance of lacustrine stromatolites of the Arnstadt Formation (âSteinmergelkeuperâ, Upper Triassic, N-Germany)
Iterations chaotiques discretes
SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 17660 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc