5,016 research outputs found
CVD of CrO2: towards a lower temperature deposition process
We report on the synthesis of highly oriented a-axis CrO2 films onto (0001)
sapphire by atmospheric pressure CVD from CrO3 precursor, at growth
temperatures down to 330 degree Celsius, i.e. close to 70 degrees lower than in
published data for the same chemical system. The films keep the high quality
magnetic behaviour as those deposited at higher temperature, which can be
looked as a promising result in view of their use with thermally sensitive
materials, e.g. narrow band gap semiconductors.Comment: 13 pages, 4 figure
Quantum Monte Carlo Calculations of Pion Scattering from Li
We show that the neutron and proton transition densities predicted by recent
quantum Monte Carlo calculations for A=6,7 nuclei are consistent with pion
scattering from 6Li and 7Li at energies near the Delta resonance. This has
provided a microscopic understanding of the enhancement factors for quadrople
excitations, which were needed to describe pion inelastic scattering within the
nuclear shell model of Cohen and Kurath.Comment: 10 pages, REVTeX, 3 postscript figures; added calculation of elastic
and inelastic pion scattering from 6Li at multiple energie
EAGLE multi-object AO concept study for the E-ELT
EAGLE is the multi-object, spatially-resolved, near-IR spectrograph
instrument concept for the E-ELT, relying on a distributed Adaptive Optics,
so-called Multi Object Adaptive Optics. This paper presents the results of a
phase A study. Using 84x84 actuator deformable mirrors, the performed analysis
demonstrates that 6 laser guide stars and up to 5 natural guide stars of
magnitude R<17, picked-up in a 7.3' diameter patrol field of view, allow us to
obtain an overall performance in terms of Ensquared Energy of 35% in a 75x75
mas^2 spaxel at H band, whatever the target direction in the centred 5' science
field for median seeing conditions. The computed sky coverage at galactic
latitudes |b|~60 is close to 90%.Comment: 6 pages, to appear in the proceedings of the AO4ELT conference, held
in Paris, 22-26 June 200
XMM-Newton observations of the nitrogen-rich Wolf-Rayet star WR 1
We present XMM-Newton results for the X-ray spectrum from the N-richWolf-Rayet (WR) star WR1. The EPIC instrument was used to obtain a medium-resolution spectrum. The following features characterize this spectrum: ( a) significant emission "bumps" appear that are coincident with the wavelengths of typical strong lines, such as MgXI, SiXIII, and SXV; (b) little emission is detected above 4 keV, in contrast to recent reports of a hard component in the stars WR 6 and WR 110 which are of similar subtype; and ( c) evidence for sulfur K-edge absorption at about 2.6 keV, which could only arise from absorption of X- rays by the ambient stellar wind. The lack of hard emission in our dataset is suggestive that WR 1 may truly be a single star, thus representing the first detailed X-ray spectrum that isolates the WR wind alone ( in contrast to colliding wind zones). Although the properties of the S-edge are not well- constrained by our data, it does appear to be real, and its detection indicates that at least some of the hot gas in WR 1 must reside interior to the radius of optical depth unity for the total absorptive opacity at the energy of the edge
Young Planetary Nebulae: Hubble Space Telescope Imaging and a New Morphological Classification System
Using Hubble Space Telescope images of 119 young planetary nebulae, most of
which have not previously been published, we have devised a comprehensive
morphological classification system for these objects. This system generalizes
a recently devised system for pre-planetary nebulae, which are the immediate
progenitors of planetary nebulae (PNs). Unlike previous classification studies,
we have focussed primarily on young PNs rather than all PNs, because the former
best show the influences or symmetries imposed on them by the dominant physical
processes operating at the first and primary stage of the shaping process.
Older PNs develop instabilities, interact with the ambient interstellar medium,
and are subject to the passage of photoionization fronts, all of which obscure
the underlying symmetries and geometries imposed early on. Our classification
system is designed to suffer minimal prejudice regarding the underlying
physical causes of the different shapes and structures seen in our PN sample,
however, in many cases, physical causes are readily suggested by the geometry,
along with the kinematics that have been measured in some systems. Secondary
characteristics in our system such as ansae indicate the impact of a jet upon a
slower-moving, prior wind; a waist is the signature of a strong equatorial
concentration of matter, whether it be outflowing or in a bound Keplerian disk,
and point symmetry indicates a secular trend, presumably precession, in the
orientation of the central driver of a rapid, collimated outflow.Comment: (to appear in The Astronomical Journal, March 2011.) The quality of
the figures as it appears in the arXiv pdf output is not up-to-par; the full
ms with high-quality figures is available by anonymous FTP at
ftp://ftp.astro.ucla.edu/pub/morris/sahai_AJ_360163.pd
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