2,812 research outputs found
Role of the self-interaction error in studying chemisorption on graphene from first-principles
Adsorption of gaseous species, and in particular of hydrogen atoms, on
graphene is an important process for the chemistry of this material. At the
equilibrium geometry, the H atom is covalently bonded to a carbon that puckers
out from the surface plane. Nevertheless the \emph{flat} graphene geometry
becomes important when considering the full sticking dynamics. Here we show how
GGA-DFT predicts a wrong spin state for this geometry, namely =0 for a
single H atom on graphene. We show how this is caused by the self-interaction
error since the system shows fractional electron occupations in the two bands
closest to the Fermi energy. It is demonstrated how the use of hybrid
functionals or the GGA+ method an be used to retrieve the correct spin
solution although the latter gives an incorrect potential energy curve
Recent developments in Vorton Theory
This article provides a concise overview of recent theoretical results
concerning the theory of vortons, which are defined to be (centrifugally
supported) equilibrium configurations of (current carrying) cosmic string
loops. Following a presentation of the results of work on the dynamical
evolution of small circular string loops, whose minimum energy states are the
simplest examples of vortons, recent order of magnitude estimates of the
cosmological density of vortons produced in various kinds of theoretical
scenario are briefly summarised.Comment: 6 pages Latex. Contribution to 1996 Cosmology Meeting, Peyresq,
Franc
Locally produced legumes and seaweed. Sustainable protein sources for a self-sufficient European animal production?
The animal feeding industry is looking for new local sources of high quality protein in order to reduce import and ensure sustainable and environmental friendly animal production systems. Local legumes and seaweeds may be alternative sources of protein.
We present in this paper the background for the ongoing Norwegian Research Council project Legumes and seaweeds as alternative protein sources for sheep (AltPro), which aims to investigate the suitability and potential of legumes and seaweeds as new and underutilized protein sources in sheep diets. The project addresses several critical aspects for the future development of the agriculture industry in Norway applicable to other European countries from an integrated social and natural scientific approach:
1. use of protein sources alternative to soya,
2. environmental, climatic, societal and economical sustainability,
3. animal health and welfare
Kinematics of Nearby Subdwarf Stars
We present an analysis of the space motions of 742 subdwarf stars based on
the sample of Carney et al. (1994, CLLA). Hipparcos parallaxes, TYC2+HIP proper
motions and Tycho2 proper motions were combined with radial velocities and
metallicities from CLLA. The kinematical behavior is discussed in particular in
relation to their metallicities. The majority of these sample stars have metal
abundances of [Fe/H] >-1 and represent the thick disk population. The halo
component, with [Fe/H] <-1.6, is characterized by a low mean rotation velocity
and a radially elongated velocity ellipsoid. In the intermediate metallicity
range (-1.6 < [Fe/H] <-1), we find a significant number of subdwarfs with
disklike kinematics. We interpret this population of stars as a metal-weak
thick disk population.Comment: 6 pages, 7 figures, accepted by Astronomy & Astrophysic
The cluster population of the irregular galaxy NGC 4449 as seen by the Hubble Advanced Camera for Surveys
We present a study of the star cluster population in the starburst irregular
galaxy NGC 4449 based on B, V, I, and Ha images taken with the Advanced Camera
for Surveys on the Hubble Space Telescope. We derive the cluster properties
such as size, ellipticity, and total magnitudes. Cluster ages and masses are
derived fitting the observed spectral energy distributions with different
population synthesis models. Our analysis is strongly affected by the
age-metallicity degeneracy; however, if we assume a metallicity of ~1/4 solar,
as derived from spectroscopy of HII regions, we find that the clusters have
ages distributed quite continuously over a Hubble time, and they have masses
from ~10^3 M_sun up to ~2 x 10^6 M_sun, assuming a Salpeters' IMF down to 0.1
M_sun. Young clusters are preferentially located in regions of young star
formation, while old clusters are distributed over the whole NGC 4449 field of
view, like the old stars (although we notice that some old clusters follow
linear structures, possibly a reflection of past satellite accretion). The high
SF activity in NGC 4449 is confirmed by its specific frequency of young massive
clusters, higher than the average value found in nearby spirals and in the LMC
(but lower than in other starburst dwarfs such as NGC 1705 and NGC 1569), and
by the flat slope of the cluster luminosity function (dN(L_V)\propto L_V^{-1.5}
dL for clusters younger than 1 Gyr). We use the upper envelope of the cluster
log(mass) versus log(age) distribution to quantify cluster disruption, and do
not find evidence for the high (90%) long-term infant mortality found by some
studies. For the red clusters, we find correlations between size, ellipticity,
luminosity and mass: brighter and more massive clusters tend to be more
compact, and brighter clusters tend to be also more elliptical.Comment: Accepted for publication on AJ, one data point changed in Fig. 1
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