265 research outputs found
UJM at INEX 2009 Ad Hoc track
7 pagesInternational audienceThis paper1 presents our participation to the INEX 2009 Ad- Hoc track. We have experimented the tuning of various parameters using a âtrainingâ collection (i.e. INEX 2008) quite different than the âtestingâ collection used for 2009 INEX Ad-Hoc track. Several parameters have been studied for article retrieval as well as for element retrieval, especially the two main BM25 weighting function parameters: b and k1
Multiwavelength observations of the supernova remnant G349.7+02 interacting with a molecular cloud
We present molecular-line observations at millimetre, centimetre and infrared
wavelengths of the region containing OH(1720 MHz) masers in the supernova
remnant (SNR) G349.7+0.2, using the Australia Telescope (AT) Mopra antenna, the
Swedish-ESO Submillimeter Telescope, the AT Compact Array and the UNSW Infrared
Fabry-Perot narrow-band filter installed on the Anglo-Australian Telescope.
Several molecular transitions were observed between 1.6 and 3 mm to constrain
the physical parameters of the molecular cloud interacting with the SNR and to
investigate the effects of the SNR shock on the gas chemistry. We detected
shock-excited near-infrared H2 emission towards the centre of the SNR,
revealing highly clumped molecular gas and a good correlation with published
mid-infrared images from the Spitzer Space Telescope. An excellent correlation
between the H2 clumps and OH(1720 MHz) maser positions supports the shock
excitation of the OH(1720 MHz) maser emission. Furthermore, we detected OH
absorption at 1665 and 1667 MHz which shows a good correlation with the shocked
H2 emission and the masers. We found maser emission at 1665 MHz near the
OH(1720 MHz) masers in this SNR, which is found to be associated with a GLIMPSE
source SSTGLMC G349.7294+00.1747. We also detected 1665 and 1667 MHz OH masers,
and weak 4.8 GHz H2CO absorption towards the ultracompact HII region IRAS
17147-3725 located to the southeast of the SNR. We found no 4.7- or 6-GHz
excited-state OH masers or 6-GHz CH3OH maser towards either the SNR or the HII
region.Comment: 25 pages, 13 figures, published in MNRA
A Survey of Hydroxyl Toward Supernova Remnants: Evidence for Extended 1720 MHz Maser Emission
We present the results of GBT observations of all four ground-state hydroxyl
(OH) transitions toward 15 supernova remnants (SNRs) which show OH(1720 MHz)
maser emission. This species of maser is well established as an excellent
tracer of an ongoing interaction between the SNR and dense molecular material.
For the majority of these objects we detect significantly higher flux densities
with a single dish than has been reported with interferometric observations. We
infer that spatially extended, low level maser emission is a common phenomenon
that traces the large-scale interaction in maser-emitting SNRs. Additionally we
use a collisional pumping model to fit the physical conditions under which OH
is excited behind the SNR shock front. We find the observed OH gas associated
with the SNR interaction having columns less than approximately 10^17 per
square cm, temperatures of 20 to 125 K, and densities 10^5 per cubic cm.Comment: 24 pages, 23 figures, Accepted to ApJ, March 26, 2008; v2 - added
Figure 6, minor clarifications to text in Sections 3 and
XMM-Newton observations of the supernova remnant IC443: I. soft X-ray emission from shocked interstellar medium
The shocked interstellar medium around IC443 produces strong X-ray emission
in the soft energy band (E<1.5 keV). We present an analysis of such emission as
observed with the EPIC MOS cameras on board the XMM-Newotn observatory, with
the purpose to find clear signatures of the interactions with the interstellar
medium (ISM) in the X-ray band, which may complement results obtained in other
wavelenghts. We found that the giant molecular cloud mapped in CO emission is
located in the foreground and gives an evident signature in the absorption of
X-rays. This cloud may have a torus shape and the part of torus interacting
with the IC443 shock gives rise to 2MASS-K emission in the southeast. The
measured density of emitting X-ray shocked plasma increases toward the
northeastern limb, where the remnant is interacting with an atomic cloud. We
found an excellent correlation between emission in the 0.3-0.5 keV band and
bright optical/radio filament on large spatial scales. The partial shell
structure seen in this band therefore traces the encounter with the atomic
cloud.Comment: 10 pages, 10 figures, accepted for publication in ApJ (20 September
2006, v649). For hi-res figures, see
http://www.astropa.unipa.it/Library/OAPA_preprints/ic443ele1.ps.g
Radio spectral properties and the magnetic field of the SNR S147
(Abridged) S147 is a large faint shell-type supernova remnant (SNR). Its
remarkable spectral break at cm-wavelengths is an important physical property
to characterize the SNR evolution. However, the spectral break is based on
radio observations with limited precision. We made new radio continuum and
polarization observations of S147 at 11cm and at 6cm with the Effelsberg 100-m
telescope and the Urumqi 25-m telescope, respectively. These new data were
combined with published lower frequency data from the Effelsberg 100-m
telescope and very high frequency data from WMAP to investigate the spectral
turnover and polarization properties of S147. S147 consists of numerous
filaments embedded in diffuse emission. We found that the integrated flux
densities of S147 are 34.8+/-4.0 Jy at 11cm and 15.4+/-3.0Jy at 6cm. These new
measurements confirm the known spectral turnover at ~1.5GHz, which can be
entirely attributed to the diffuse emission component. The spectral index above
the turnover is -1.35+/-0.20. The filamentary emission component has a constant
spectral index over the entire wavelength range up to 40.7GHz of -0.35+/-0.15.
The weak polarized emission of S147 is at the same level as the ambient diffuse
Galactic polarization. The rotation measure of the eastern filamentary shell is
about -70 rad/m2. The filamentary and diffuse emission components of S147 have
different physical properties, which make S147 outstanding among shell type
SNRs.The weak polarization of S147 at 11cm and at 6cm can be attributed to a
section of the S147 shell showing a tangential magnetic field direction.Comment: 11 pages, 17 figures, accepted for publication in Astronomy &
Astrophysics, the resolution of some figures have been reduced. For high
resolution version, see
ftp://ftp.mpifr-bonn.mpg.de/outgoing/p098wre/xiao-etal.pdf,revised following
the language edito
New lambda6cm observations of the Cygnus Loop
Radio continuum and polarization observations of the entire Cygnus Loop at
6cm wavelength were made with the Urumqi 25m telescope. The 6cm map is analysed
together with recently published maps from the Effelsberg 100m telescope at
21cm and 11cm. The integrated flux density of the Cygnus Loop at 6cm is
90+/-9Jy, which implies a spectral index of -0.40+/-0.06 being consistent with
that of Uyaniker et al. (2004) in the wavelength range up to 11cm. This rules
out any global spectral steepening up to 6cm. However, small spectral index
variations in some regions of the source are possible, but there are no
indications for any spectral curvature. The linear polarization data at 6cm
show percentage polarizations up to 35% in some areas of the Cygnus Loop,
exceeding those observed at 11cm. The Rotation Measure is around -21rad/m^2 in
the southern area, which agrees with previous observations. However, the
distribution of Rotation Measures is rather complex in the northern part of the
Cygnus Loop, where the 21cm emission is totally depolarized. Rotation Measures
based on 11cm and 6cm data are significantly larger than in the southern part.
The difference in the polarization characteristic between the northern and
southern part supports previous ideas that the Cygnus Loop consists of two
supernova remnants.Comment: 11 pages, 10 figures, accepted for publication in A&
GBT Observations of IC 443: the Nature of OH(1720 MHz) Masers and OH Absorption
We present results of spectral line observations of the ground state
transitions of hydroxyl(OH) toward supernova remnant IC 443 carried out with
the Green Bank Telescope. At a spatial resolution of 7.2 arcminutes we detect
weak, extended OH(1720 MHz) maser emission with OH(1667/5,1612 MHz) absorption
along the southern extent of the remnant, where no bright compact maser sources
have been observed previously. These newly detected SNR-type masers are
coincident with known molecular clumps and a ridge of shocked molecular
hydrogen indicative of the SNR shock front interacting with the adjacent
molecular cloud. Simultaneous observation of all four ground-state transitions
of OH permits us to fit physical conditions of the shocked gas at the
interaction site. A simple two-component model for the line profiles yields the
physical parameters for detected regions of maser emission including excitation
temperature, OH column density and filling factor. Observed line profiles
suggest the shock is largely propagating toward the line-of-sight in the region
of these newly identified weak masers. The implications of shock geometry and
physical parameters in producing extended OH maser emission in SNRs are
explored. We also present VLA radio continuum observations at 330 MHz for
comparison with OH line observations of the remnant.Comment: 20 pages, 4 figures, 3 tables, submitted to Ap
Promising pre-clinical validation of targeted radionuclide therapy using a [131I] labelled iodoquinoxaline derivative for an effective melanoma treatment
Targeted internal radionuclide therapy (TRT) would be an effective alternative to current therapies for dissemi- nated melanoma treatment. At our institution, a class of iodobenzamides has been developed as potent melanoma- seeking agents. This review described the preclinical vali- dations of a quinoxaline derivative molecule (ICF01012) as tracer for TRT application. It was selected for its high, specific and long-lasting uptake in tumour with rapid clear- ance from non-target organs providing suitable dosimetry parameters for TRT. Extended in vivo study of metabolic profiles confirmed durable tumoural concentration of the unchanged molecule form. Moreover melanin specificity of ICF01012 was determined by binding assay with syn- thetic melanin and in vivo by SIMS imaging. Then, we showed in vivo that [131I] ICF01012 treatment drastically inhibited growth of B16F0, B16Bl6 and M4Beu tumours whereas [131I] NaI or unlabelled ICF01012 treatment was without significant effect. Histological analysis showed that residual tumour cells exhibit a significant loss of aggres- siveness after treatment. This anti-tumoural effect was associated with a lengthening of the treated-mice survival time and an inhibition of lung dissemination for B16Bl6 model. Results presented here support the concept of TRT using a [131I] labelled iodoquinoxaline derivative for an effective melanoma treatment.<br /
Ordering phenomena in quasi one-dimensional organic conductors
Low-dimensional organic conductors could establish themselves as model
systems for the investigation of the physics in reduced dimensions. In the
metallic state of a one-dimensional solid, Fermi-liquid theory breaks down and
spin and charge degrees of freedom become separated. But the metallic phase is
not stable in one dimension: as the temperature is reduced, the electronic
charge and spin tend to arrange themselves in an ordered fashion due to strong
correlations. The competition of the different interactions is responsible for
which broken-symmetry ground state is eventually realized in a specific
compound and which drives the system towards an insulating state.
Here we review the various ordering phenomena and how they can be identified
by optic and magnetic measurements. While the final results might look very
similar in the case of a charge density wave and a charge-ordered metal, for
instance, the physical cause is completely different. When density waves form,
a gap opens in the density of states at the Fermi energy due to nesting of the
one-dimension Fermi surface sheets. When a one-dimensional metal becomes a
charge-ordered Mott insulator, on the other hand, the short-range Coulomb
repulsion localizes the charge on the lattice sites and even causes certain
charge patterns.
We try to point out the similarities and conceptional differences of these
phenomena and give an example for each of them. Particular emphasis will be put
on collective phenomena which are inherently present as soon as ordering breaks
the symmetry of the system.Comment: Review article Naturwissenschaften 200
- âŠ