599 research outputs found
The axonally secreted protein axonin-1 is a potent substratum for neurite growth
Axonin-1 is a neuronal glycoprotein occurring both as a membrane-bound and a secreted form. Membrane-bound axonin-1 is predominantly located in membranes of developing nerve fiber tracts and has recently been characterized as a cell adhesion molecule; the soluble form is secreted from axons and accumulates in the cerebrospinal fluid and the vitreous fluid of the eye. In the present study, we addressed the question as to whether secreted axonin-1 was released in a functionally competent form and we found that it strongly promotes neurite outgrowth when presented to neurons as an immobilized substratum. Neurite lengths elaborated by embryonic dorsal root ganglia neurons on axonin-1 were similar to those on the established neurite-promoting substrata L1 and laminin. Fab fragments of axonin-1 antibodies completely inhibited neurite growth on axonin-1, but not on other substrata. In soluble form, axonin-1 had an anti-adhesive effect, as revealed by perturbation of neurite fasciculation. In view of their structural similarity, we conclude that secreted and membrane-bound axonin-1 interact with the same growth-promoting neuritic receptor. The fact that secreted axonin-1 is functionally active, together with our previous findings that it is secreted from an internal cellular pool, suggests a functional dualism between membrane-bound and secreted axonin-1 at the site of secretion, which is most likely the growth cone. The secretion of adhesion molecules could represent a powerful and rapidly acting regulatory element of growth cone-neurite interactions in the control of neurite elongation, pathway selection, and possibly target recognition
The XMM-LSS Survey: A well controlled X-ray cluster sample over the D1 CFHTLS area
We present the XMM-LSS cluster catalogue corresponding to the CFHTLS D1 area.
The list contains 13 spectroscopically confirmed, X-ray selected galaxy
clusters over 0.8 deg2 to a redshift of unity and so constitutes the highest
density sample of clusters to date. Cluster X-ray bolometric luminosities range
from 0.03 to 5x10^{44} erg/s. In this study, we describe our catalogue
construction procedure: from the detection of X-ray cluster candidates to the
compilation of a spectroscopically confirmed cluster sample with an explicit
selection function. The procedure further provides basic X-ray products such as
cluster temperature, flux and luminosity. We detected slightly more clusters
with a (0.5-2.0 keV) X-ray fluxes of >2x10^{-14} erg/s/cm^{-2} than we expected
based on expectations from deep ROSAT surveys. We also present the
Luminosity-Temperature relation for our 9 brightest objects possessing a
reliable temperature determination. The slope is in good agreement with the
local relation, yet compatible with a luminosity enhancement for the 0.15 < z<
0.35 objects having 1 < T < 2 keV, a population that the XMM-LSS is identifying
systematically for the first time. The present study permits the compilation of
cluster samples from XMM images whose selection biases are understood. This
allows, in addition to studies of large-scale structure, the systematic
investigation of cluster scaling law evolution, especially for low mass X-ray
groups which constitute the bulk of our observed cluster population. All
cluster ancillary data (images, profiles, spectra) are made available in
electronic form via the XMM-LSS cluster database.Comment: 12 pages 5 figures, MNRAS accepted. The paper with full resolution
cluster images is available at
http://vela.astro.ulg.ac.be/themes/spatial/xmm/LSS/rel_pub_e.htm
Structure detection in the D1 CFHTLS deep field using accurate photometric redshifts: a benchmark
We investigate structures in the D1 CFHTLS deep field in order to test the
method that will be applied to generate homogeneous samples of clusters and
groups of galaxies in order to constrain cosmology and detailed physics of
groups and clusters. Adaptive kernel technique is applied on galaxy catalogues.
This technique needs none of the usual a-priori assumptions (luminosity
function, density profile, colour of galaxies) made with other methods. Its
main drawback (decrease of efficiency with increasing background) is overcame
by the use of narrow slices in photometric redshift space. There are two main
concerns in structure detection. One is false detection and the second, the
evaluation of the selection function in particular if one wants "complete"
samples. We deal here with the first concern using random distributions. For
the second, comparison with detailed simulations is foreseen but we use here a
pragmatic approach with comparing our results to GalICS simulations to check
that our detection number is not totally at odds compared to cosmological
simulations. We use XMM-LSS survey and secured VVDS redshifts up to z~1 to
check individual detections. We show that our detection method is basically
capable to recover (in the regions in common) 100% of the C1 XMM-LSS X-ray
detections in the correct redshift range plus several other candidates.
Moreover when spectroscopic data are available, we confirm our detections, even
those without X-ray data.Comment: 14 pages, 22 additionnal jpeg figures, accepted in A&
Highly stable perylenediimide based self-assembled monolayers studied by spectroelectrochemistry
Perylenediimide (PDI) based self-assembled monolayers (SAMs) have been studied by quartz crystal microbalance, X-ray photoelectron spectroscopy, cyclic voltammetry and spectroelectrochemistry (SEC). The high stability of PDI based SAMs has allowed probing very low signals by absorption and emission SEC and extracting voltabsorptograms. The wavelengths of absorption maxima of PDI, anion radical and dianion species. In contrast, the magnitudes of the molar extinction coefficient of the reduced forms were not preserved in SAM. The quenching of PDI fluorescence was confirmed on gold substrate
The XMM-LSS catalogue: X-ray sources and associated optical data. Version I
Following the presentation of the XMM-LSS X-ray source detection package by
Pacaud et al., we provide the source lists for the first 5.5 surveyed square
degrees. The catalogues pertain to the [0.5-2] and [2-10] keV bands and contain
in total 3385 point-like or extended sources above a detection likelihood of 15
in either band. The agreement with deep logN-logS is excellent. The main
parameters considered are position, countrate, source extent with associated
likelihood values. A set of additional quantities such as astrometric
corrections and fluxes are further calculated while errors on the position and
countrate are deduced from simulations. We describe the construction of the
band-merged catalogue allowing rapid sub-sample selection and easy
cross-correlation with external multi-wavelength catalogues. A small optical
CFHTLS multi-band subset of objects is associated wich each source along with
an X-ray/optical overlay. We make the full X-ray images available in FITS
format. The data are available at CDS and, in a more extended form, at the
Milan XMM-LSS database.Comment: 13 pages, 7 figures and 11 tables (fig. 1 and 6 are enclosed in
reduced resolution), MNRAS Latex, accepted by MNRA
Expressing Belief Flow in Assertion Networks
Abstract. In the line of some earlier work done on belief dynamics, we propose an abstract model of belief propagation on a graph based on the methodology of the revision theory of truth. A modal language is developed for portraying the behavior of this model, and its expressiveness is discussed. We compare the proposal of this model as well as the language developed with some of the existing frameworks for modelling communication situations.
Galaxy Collisions - Dawn of a New Era
The study of colliding galaxies has progressed rapidly in the last few years,
driven by observations with powerful new ground and space-based instruments.
These instruments have used for detailed studies of specific nearby systems,
statistical studies of large samples of relatively nearby systems, and
increasingly large samples of high redshift systems. Following a brief summary
of the historical context, this review attempts to integrate these studies to
address the following key issues. What role do collisions play in galaxy
evolution, and how can recently discovered processes like downsizing resolve
some apparently contradictory results of high redshift studies? What is the
role of environment in galaxy collisions? How is star formation and nuclear
activity orchestrated by the large scale dynamics, before and during merger?
Are novel modes of star formation involved? What are we to make of the
association of ultraluminous X-ray sources with colliding galaxies? To what do
degree do mergers and feedback trigger long-term secular effects? How far can
we push the archaeology of individual systems to determine the nature of
precursor systems and the precise effect of the interaction? Tentative answers
to many of these questions have been suggested, and the prospects for answering
most of them in the next few decades are good.Comment: 44 pages, 9 figures, review article in press for Astrophysics Update
Vol.
Large easy-axis anisotropy in the one-dimensional magnet BaMo(PO4)(2)
We present an extensive experimental and theoretical study on the low-temperature magnetic properties of the monoclinic anhydrous alum compound BaMo(PO4)(2). The magnetic susceptibility reveals strong antiferromagnetic interactions theta(CW) = -167 K and long-range magnetic order at T-N = 22 K, in agreement with a recent report. Powder neutron diffraction furthermore shows that the order is collinear, with the moments near the ac plane. Neutron spectroscopy reveals a large excitation gap Delta = 15 meV in the low-temperature ordered phase, suggesting a much larger easy-axis spin anisotropy than anticipated. However, the large anisotropy justifies the relatively high ordered moment, Neel temperature, and collinear order observed experimentally and is furthermore reproduced in a first-principles calculations by using a new computational scheme. We therefore propose BaMo(PO4)(2) to host S = 1 antiferromagnetic chains with large easy-axis anisotropy, which has been theoretically predicted to realize novel excitation continua
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