4,006 research outputs found
The Influence of Culture on ABMP Negotiation Parameters
Negotiations are known to proceed differently across cultures. A realistic agent model of international negotiations has to take cultural differences into account. This paper presents an agent-based model that tackles this challenge. The context is a trade game where commodities with a hidden quality attribute are exchanged. The negotiation model uses the ABMP negotiation architecture. It applies a utility function that includes market value, quality preference, and risk attitude. The indices of the five dimensions of Hofstedeās model of national cultures are used, in combination with agentās group membership and societal status, to differentiate negotiation behavior by adaptation of weight factors in the utility function and ABMP parameters. The paper presents test runs with synthetic cultures and a set of actual national cultures. The present version of the model helps to understand behaviors in international trade networks. It proves that Hofstedeās dimensions can be used to generate culturally differentiated agent
Optical spectroscopy of (candidate) ultra-compact X-ray binaries: constraints on the composition of the donor stars
We present optical spectroscopy of several (candidate) ultra-compact X-ray
binaries (UCXBs) obtained with the ESO VLT and Gemini-North telescopes. In only
one of five observed UCXB candidates did we find evidence for H in its spectrum
(4U 1556-60). For XB 1905+00 the optical counterpart is not detected. For the
known UCXBs 4U 1626-67 and XB 1916-05 we find spectra consistent with a C/O and
a He/N accretion disc respectively, the latter is the first optical spectrum of
a He-rich donor in an UCXB. Interestingly, the C/O spectrum of 4U 1626-67 shows
both similarities as well as marked differences from the optical C/O spectrum
of 4U 0614+09. We obtained phase resolved spectroscopy of 4U 0614+09 and the 44
min transient XTE J0929-314. In neither object were we able to detect clear
orbital periodicities, highlighting the difficulties of period determinations
in UCXBs. We reanalysed the spectra of XTE J0929-314 that were taken close to
the peak of its 2003 X-ray outburst and do not confirm the detection of Halpha
emission as was claimed in the literature. The peak spectra do show strong C or
N emission around 4640A, as has also been detected in other UCXBs. We discuss
the implications of our findings for our understanding of the formation of
UCXBs and the Galactic population of UCXBs. At the moment all studied systems
are consistent with having white dwarf donors, the majority being C/O rich.Comment: Accepted for publication in MNRA
Epitaxial Growth of an n-type Ferromagnetic Semiconductor CdCr2Se4 on GaAs(001) and GaP(001)
We report the epitaxial growth of CdCr2Se4, an n-type ferromagnetic
semiconductor, on both GaAs and GaP(001) substrates, and describe the
structural, magnetic and electronic properties. Magnetometry data confirm
ferromagnetic order with a Curie temperature of 130 K, as in the bulk material.
The magnetization exhibits hysteretic behavior with significant remanence, and
an in-plane easy axis with a coercive field of ~125 Oe. Temperature dependent
transport data show that the films are semiconducting in character and n-type
as grown, with room temperature carrier concentrations of n ~ 1 x 10^18 cm-3.Comment: 12 pages, 3 figure
Characterisation of a candidate dual AGN
We present Chandra and optical observations of a candidate dual AGN
discovered serendipitously while searching for recoiling black holes via a
cross-correlation between the serendipitous XMM source catalog (2XMMi) and
SDSS-DR7 galaxies with a separation no larger than ten times the sum of their
Petrosian radii. The system has a stellar mass ratio M/M. One of the galaxies (Source 1) shows clear evidence for AGN activity in
the form of hard X-ray emission and optical emission-line diagnostics typical
of AGN ionisation. The nucleus of the other galaxy (Source 2) has a soft X-ray
spectrum, bluer colours, and optical emission line ratios dominated by stellar
photoionisation with a "composite" signature, which might indicate the presence
of a weak AGN. When plotted on a diagram with X-ray luminosity vs [OIII]
luminosity both nuclei fall within the locus defined by local Seyfert galaxies.
From the optical spectrum we estimate the electron densities finding n e cm and n e cm. From a 2D
decomposition of the surface brightness distribution we infer that both
galaxies host rotationally supported bulges (Sersic index ). While the
active nature of Source 1 can be established with confidence, whether the
nucleus of Source 2 is active remains a matter of debate. Evidence that a faint
AGN might reside in its nucleus is, however, tantalising.Comment: 16 pages, 9 figures. Accepted for publication on MNRAS. Comments
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Chandra observations of the millisecond X-ray pulsar IGR J00291+5934 in quiescence
In this Paper we report on our analysis of three Chandra observations of the
accretion-powered millisecond X-ray pulsar IGR J00291+5934 obtained during the
late stages of the 2004 outburst. We also report the serendipitous detection of
the source in quiescence by ROSAT during MJD 48830-48839. The detected 0.3-10
keV source count rates varied significantly between the Chandra observations
from (7.2+-1.2)x10^-3, (6.8+-0.9)x10^-3, and (1.4+-0.1)x10^-2 counts per second
for the 1st, 2nd, and 3rd Chandra observation, on MJD 53371.88, 53383.99, and
53407.57, respectively. The count rate for the 3rd observation is 2.0+-0.4
times as high as that of the average of the first two observations. The
unabsorbed 0.5-10 keV source flux for the best-fit power-law model to the
source spectrum was (7.9+-2.5)x10^-14, (7.3+-2.0)x10^-14, and
(1.17+-0.22)x10^-13 erg cm^-2 s^-1 for the 1st, 2nd, and 3rd Chandra
observation, respectively. We find that this source flux is consistent with
that found by ROSAT [~(5.4+-2.4)x10^-14 erg cm^-2 s^-1]. Under the assumption
that the interstellar extinction, N_H, does not vary between the observations,
we find that the blackbody temperature during the 2nd Chandra observation is
significantly higher than that during the 1st and 3rd observation. Furthermore,
the effective temperature of the neutron star derived from fitting an absorbed
blackbody or neutron star atmosphere model to the data is rather high in
comparison with many other neutron star soft X-ray transients in quiescence,
even during the 1st and 3rd observation. If we assume that the source quiescent
luminosity is similar to that measured for two other accretion powered
millisecond pulsars in quiescence, the distance to IGR J00291+5934 is 2.6-3.6
kpc.Comment: 7 pages, 3 Figures, accepted for publication in MNRA
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