2,534 research outputs found
A Combined EIS-NVSS Survey Of Radio Sources (CENSORS) III: Spectroscopic observations
The Combined EIS-NVSS Survey Of Radio Sources (CENSORS) is a 1.4GHz radio
survey selected from the NRAO VLA Sky Survey (NVSS) and complete to a
flux-density of 7.2mJy. It targets the ESO Imaging Survey (EIS) Patch D, which
is a 3 by 2 square degree field centred on 09 51 36.0, -21 00 00 (J2000). This
paper presents the results of spectroscopic observations of 143 of the 150
CENSORS sources. The primary motivation for these observations is to achieve
sufficient spectroscopic completeness so that the sample may be used to
investigate the evolution of radio sources.
The observations result in secure spectroscopic redshifts for 63% of the
sample and likely redshifts (based on a single emission line, for example) for
a further 8%. Following the identification of the quasars and star-forming
galaxies in the CENSORS sample, estimated redshifts are calculated for the
remainder of the sample via the K-z relation for radio galaxies. Comparison of
the redshift distribution of the CENSORS radio sources to distributions
predicted by the various radio luminosity function evolution models of Dunlop &
Peacock 1990, results in no good match. This demonstrates that this sample can
be used to expand upon previous work in that field.Comment: Accepted for publication in MNRAS. This version has some reduced
resolution figures and 13 associated gif files. A version with all figures
incorporated (at full resolution) is available at
http://www.roe.ac.uk/~pnb/papers/censors_spectro.pd
Single 3 transition metal atoms on multi-layer graphene systems: electronic configurations, bonding mechanisms and role of the substrate
The electronic configurations of Fe, Co, Ni, and Cu adatoms on graphene and
graphite have been studied by x-ray magnetic circular dichroism and charge
transfer multiplet theory. A delicate interplay between long-range interactions
and local chemical bonding is found to influence the adatom equilibrium
distance and magnetic moment. The results for Fe and Co are consistent with
purely physisorbed species having, however, different 3-shell occupancies on
graphene and graphite ( and , respectively). On the other hand,
for the late 3 metals Ni and Cu a trend towards chemisorption is found,
which strongly quenches the magnetic moment on both substrates.Comment: 7 pages, 4 figure
Exchange bias in GeMn nanocolumns: the role of surface oxidation
We report on the exchange biasing of self-assembled ferromagnetic GeMn
nanocolumns by GeMn-oxide caps. The x-ray absorption spectroscopy analysis of
this surface oxide shows a multiplet fine structure that is typical of the Mn2+
valence state in MnO. A magnetization hysteresis shift |HE|~100 Oe and a
coercivity enhancement of about 70 Oe have been obtained upon cooling (300-5 K)
in a magnetic field as low as 0.25 T. This exchange bias is attributed to the
interface coupling between the ferromagnetic nanocolumns and the
antiferromagnetic MnO-like caps. The effect enhancement is achieved by
depositing a MnO layer on the GeMn nanocolumns.Comment: 7 pages, 5 figure
Heights of one- and two-sided congruence lattices of semigroups
The height of a poset is the supremum of the cardinalities of chains in
. The exact formula for the height of the subgroup lattice of the symmetric
group is known, as is an accurate asymptotic formula for the
height of the subsemigroup lattice of the full transformation monoid
. Motivated by the related question of determining the heights
of the lattices of left- and right congruences of , we develop a
general method for computing the heights of lattices of both one- and two-sided
congruences for semigroups. We apply this theory to obtain exact height
formulae for several monoids of transformations, matrices and partitions,
including: the full transformation monoid , the partial
transformation monoid , the symmetric inverse monoid
, the monoid of order-preserving transformations
, the full matrix monoid , the partition
monoid , the Brauer monoid and the
Temperley-Lieb monoid
Sperm morphology, adenosine triphosphate (ATP) concentration and swimming velocity: unexpected relationships in a passerine bird.
The relationship between sperm energetics and sperm function is poorly known, but is central to our understanding of the evolution of sperm traits. The aim of this study was to examine how sperm morphology and ATP content affect sperm swimming velocity in the zebra finch Taeniopygia guttata We exploited the high inter-male variation in this species and created extra experimental power by increasing the number of individuals with very long or short sperm through artificial selection. We found a pronounced quadratic relationship between total sperm length and swimming velocity, with velocity increasing with length up to a point, but declining in the very longest sperm. We also found an unexpected negative association between midpiece length and ATP content: sperm with a short midpiece generally contained the highest concentration of ATP. Low intracellular ATP is therefore unlikely to explain reduced swimming velocity among the very longest sperm (which tend to have a shorter midpiece)
Exchange Splitting and Charge Carrier Spin Polarization in EuO
High quality thin films of the ferromagnetic semiconductor EuO have been
prepared and were studied using a new form of spin-resolved spectroscopy. We
observed large changes in the electronic structure across the Curie and
metal-insulator transition temperature. We found that these are caused by the
exchange splitting of the conduction band in the ferromagnetic state, which is
as large as 0.6 eV. We also present strong evidence that the bottom of the
conduction band consists mainly of majority spins. This implies that doped
charge carriers in EuO are practically fully spin polarized.Comment: 4 pages, 5 figure
Orbital occupation and magnetic moments of tetrahedrally coordinated iron in CaBaFe4O7
CaBaFe4O7 is a mixed-valent transition metal oxide having both Fe2+ and Fe3+
ions in tetrahedral coordination. Here we characterize its magnetic properties
by magnetization measurements and investigate its local electronic structure
using soft x-ray absorption spectroscopy at the Fe L2,3 edges, in combination
with multiplet cluster and spin-resolved band structure calculations. We found
that the Fe2+ ion in the unusual tetrahedral coordination is Jahn-Teller active
with the high-spin e^2 (up) t2^3 (up) e^1 (down) configuration having a
x^2-y^2-like electron for the minority spin. We deduce that there is an
appreciable orbital moment of about L_z=0.36 caused by multiplet interactions,
thereby explaining the observed magnetic anisotropy. CaBaFe4O7, a member of the
'114' oxide family, offers new opportunities to explore charge, orbital and
spin physics in transition metal oxides
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