102 research outputs found
The vulnerability of nuclear plants during military conflict: Ukraine technical briefing
Nuclear power plants present unique hazards in terms of the potential consequences resulting from a severe accident. Nuclear reactors and their associated high level spent fuel stores are vulnerable to natural disasters, as Fukushima Daiichi showed, but they are also vulnerable in times of conflict.This brief seeks to explain some of the hazards and potential consequences that exist today in Ukraine
A spectroscopic search for faint secondaries in cataclysmic variables
The secondary in cataclysmic variables (CV's) is usually detected by
cross-correlation of the CV spectrum with that of a K or M dwarf template, to
produce a radial velocity curve. Although this method has demonstrated its
power, it has its limits in the case of noisy spectra, such as are found when
the secondary is faint. A method of co-adding spectra, called skew mapping, has
been proposed in the past. Gradually, examples of its application are being
published. Nonetheless, so far no journal article has described the technique
in detail. To answer this need, this paper explores in detail the capabilities
of skew mapping when determining the amplitude of the radial velocity for faint
secondaries. It demonstrates the method's power over techniques that are more
conventional, when the signal-to-noise (s/n) ratio is poor. The paper suggests
an approach to assessing the quality of results. This leads in the case of the
investigated objects to a first tier of results, where we find K2=127+-23 km/s
for SY Cnc, K2=144+-18 km/s for RW Sex, and K2=262+-14 km/s for UX UMa. These
we believe to be the first direct determinations of K2 for these objects.
Furthermore, we also obtain K2=263+-30 km/s for RW Tri, close to a skew mapping
result obtained elsewhere. In the first three cases, we use these results to
derive the mass of the white dwarf companion. A second tier of results includes
UU Aqr, EX Hya, and LX Ser, for which we propose more tentative values of K2.
Clear failures of the method are also discussed (EF Eri, VV Pup, SW Sex).Comment: 23 pages, 22 figures, 10 tables; translated to pdf from a Word file -
no TeX version available. Accepted for publication in MNRA
The birthplace and age of the isolated neutron star RX J1856.5-3754
X-ray observations unveiled various types of radio-silent Isolated Neutron
Stars (INSs), phenomenologically very diverse, e.g. the Myr old X-ray Dim INS
(XDINSs) and the kyr old magnetars. Although their phenomenology is much
diverse, the similar periods (P=2--10 s) and magnetic fields (~10^{14} G)
suggest that XDINSs are evolved magnetars, possibly born from similar
populations of supermassive stars. One way to test this hypothesis is to
identify their parental star clusters by extrapolating backward the neutron
star velocity vector in the Galactic potential. By using the information on the
age and space velocity of the XDINS RX J1856.5-3754, we computed backwards its
orbit in the Galactic potential and searched for its parental stellar cluster
by means of a closest approach criterion. We found a very likely association
with the Upper Scorpius OB association, for a neutron star age of 0.42+/-0.08
Myr, a radial velocity V_r^NS =67+/- 13$ km s^{-1}, and a present-time
parallactic distance d_\pi^NS = 123^{+11}_{-15} pc. Our result confirms that
the "true" neutron star age is much lower than the spin-down age (tau_{sd}=3.8
Myrs), and is in good agreement with the cooling age, as computed within
standard cooling scenarios. The mismatch between the spin-down and the
dynamical/cooling age would require either an anomalously large breaking index
(n~20) or a decaying magnetic field with initial value B_0 ~ 10^{14} G.
Unfortunately, owing to the uncertainty on the age of the Upper Scorpius OB
association and the masses of its members we cannot yet draw firm conclusions
on the estimated mass of the RX J1856.5-3754 progenitor.Comment: 6 pages, accepted for publication on Monthly Notices of the Royal
Astronomical Societ
A kinematic study of Open Clusters: implications for their origin
The Galactic population of open clusters provides an insight into star
formation in the Galaxy. The open cluster catalogue by Dias et al.(2002b) is a
rich source of data, including kinematic information. This large sample made it
possible to carry out a systematic analysis of 481 open cluster orbits, using
parameters based on orbit eccentricity and separation from the Galactic plane.
These two parameters may be indicative of origin, and we find them to be
correlated. We also find them to be correlated with metallicity, another
parameter suggested elsewhere to be a marker for origin in that high values of
any of these two parameters generally indicates a low metallicity ([Fe/H]
Solar0.2 dex). The resulting analysis points to four open clusters in the
catalogue being of extra-Galactic origin by impact of high velocity cloud on
the disk: Berkeley21, 32, 99, and Melotte66, with a possible further four due
to this origin (NGC2158, 2420, 7789, IC1311). A further three may be due to
Galactic globular cluster impact on the disk i.e of internal Galactic origin
(NGC6791, 1817, and 7044).Comment: 14 pages, 816 figures, accepted for publication in MNRAS 14-May-201
Anal canal duplication in an 11-year-old-child
Anal canal duplication (ACD) is the least frequent digestive duplication. Symptoms are often absent but tend to increase with age. Recognition is, however, important as almost half of the patients with ACD have concomitant malformations. We present the clinical history of an eleven-year-old girl with ACD followed by a review of symptoms, diagnosis, treatment, and prognosis based on all the reported cases in English literature
- …