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Technical note: assessment of observation quality for data assimilation in flood models
The assimilation of satellite-based water level observations (WLOs) into 2D hydrodynamic models can keep flood forecasts on track or be used for reanalysis to obtain improved assessments of previous flood footprints. In either case, satellites provide spatially dense observation fields, but with spatially correlated errors. To date, assimilation methods in flood forecasting either incorrectly neglect the spatial correlation in the observation errors or, in the best of cases, deal with it by thinning methods. These thinning methods result in a sparse set of observations whose error correlations are assumed to be negligible. Here, with a case study, we show that the assimilation diagnostics that make use of statistical averages of observation-minus-background and observation-minus-analysis residuals are useful to estimate error correlations in WLOs. The average estimated correlation length scale of 7km is longer than the expected value of 250m. Furthermore, the correlations do not decrease monotonically; this unexpected behaviour is shown to be the result of assimilating some anomalous observations. Accurate estimates of the observation error statistics can be used to support quality control protocols and provide insight into which observations it is most beneficial to assimilate. Therefore, the understanding gained in this paper will contribute towards the correct assimilation of denser datasets
Coupling the dynamics and the molecular chemistry in the Galactic center
The physical conditions of the Galactic center (GC) clouds moving with
non-circular velocities are not well-known. We have studied the physical
conditions of these clouds with the aim of better understanding the origin of
the outstanding physical conditions of the GC molecular gas and the possible
effect of the large scale dynamics on these physical conditions.Using published
CO(1-0) data, we have selected a set of clouds belonging to all the kinematical
components seen in the longitude-velocity diagram of the GC. We have done a
survey of dense gas in all the components using the J=2-1 lines of CS and SiO
as tracers of high density gas and shock chemistry. We have detected CS and SiO
emission in all the kinematical components. The gas density and the SiO
abundance of the clouds in non-circular orbits are similar those in the nuclear
ring (GCR). Therefore, in all the kinematical components there are dense clouds
that can withstand the tidal shear. However, there is no evidence of star
formation outside the GCR. The high relative velocity and shear expected in the
dust-lanes along the bar major axis could inhibit the star formation process,
as observed in other galaxies. The high SiO abundances derived in the
non-circular velocity clouds are likely due to the large-scale shocks that
created the dust lanesComment: One figure as an independent PDF file. Accepted by A&
Sulfur chemistry and isotopic ratios in the starburst galaxy NGC 253
Based on observations of the most abundant sulfur-bearing molecules (H2S, CS,
NS, SO, H2CS, OCS, and SO2) carried out with the IRAM 30m telescope and SEST,
we present the first analysis of the sulfur chemistry of an extragalactic
source, the nuclear region of the starburst galaxy NGC 253. This is the first
time that H2S and, tentatively, H2CS are detected towards the nucleus of a
starburst galaxy. Source averaged fractional abundances of these molecules are
a few 10^-9, except for CS and OCS which are more abundant (10^-8). Sulfur
isotopic ratios, 32S/34S~8+-2 and 34S/33S>9, are measured through observations
of 13CS, C34S, and C33S. A comparison with the observed relative abundances
towards different prototypical Galactic sources suggests that the chemical
composition of NGC 253 is similar to that found towards the molecular clouds
complexes like Sgr B2 in the nuclear region of the Milky Way. The large
overabundance of OCS compared to the predictions of time-dependent sulfur
chemistry models supports the idea that OCS is likely injected into the gas
phase from the grain mantles by low velocity shocks.Comment: Accepted for publication in ApJ. 19 pages, 3 figure
Molecular gas chemistry in AGN. II. High-resolution imaging of SiO emission in NGC1068: shocks or XDR?
This paper is part of a multi-species survey of line emission from the
molecular gas in the circum-nuclear disk (CND) of the Seyfert 2 galaxy NGC1068.
Single-dish observations have provided evidence that the abundance of silicon
monoxide(SiO) in the CND of NGC1068 is enhanced by 3-4 orders of magnitude with
respect to the values typically measured in quiescent molecular gas in the
Galaxy. We aim at unveiling the mechanism(s) underlying the SiO enhancement. We
have imaged with the IRAM Plateau de Bure interferometer the emission of the
SiO(2-1) and CN(2--1) lines in NGC1068 at 150pc and 60pc spatial resolution,
respectively. We have also obtained complementary IRAM 30m observations of HNCO
and methanol (CH3OH) lines. SiO is detected in a disk of 400pc size around the
AGN. SiO abundances in the CND of (1-5)xE-09 are about 1-2 orders of magnitude
above those measured in the starburst ring. The overall abundance of CN in the
CND is high: (0.2-1)xE-07. The abundances of SiO and CN are enhanced at the
extreme velocities of gas associated with non-circular motions close to the AGN
(r<70pc). Abundances measured for CN and SiO, and the correlation of CN/CO and
SiO/CO ratios with hard X-ray irradiation, suggest that the CND of NGC1068 has
become a giant X-ray dominated region (XDR). The extreme properties of
molecular gas in the circum-nuclear molecular disk of NGC1068 result from the
interplay between different processes directly linked to nuclear activity.
Whereas XDR chemistry offers a simple explanation for CN and SiO in NGC1068,
the relevance of shocks deserves further scrutiny. The inclusion of dust grain
chemistry would help solve the controversy regarding the abundances of other
molecular species, like HCN, which are under-predicted by XDR models.Comment: 18 pages, 13 figures, 2 tables; accepted for publication in A&
First detections of extragalactic SO2, NS and NO
We report the first detections of SO_2, NS and NO in an extragalactic source,
the nucleus of the starburst galaxy NGC 253. Five SO_2 transitions, three
groups of hyperfine components of NO and five of NS were detected. All three
species show large abundances averaged over the inner 200 pc of NGC 253. With a
relative abundance of a few 10^-7, the emission of the NO molecule is similar
or even larger than that found in Galactic star forming regions. The derived
relative molecular abundances for each molecule have been compared with those
of prototypical Galactic molecular clouds. These results seem to confirm that
large scale shocks dominate the chemistry of these molecules in the nucleus of
NGC 253, ruling out a chemistry dominated by PDRs for the bulk of the gas.Comment: Accepted by A&A, 4 pages, 6 figure
Fabrication and characterization of superficially modified porous dental implants
Stress-shielding and loosening compromise the success of dental implants under real-life service conditions. This work evaluates the mechanical behavior of superficially modified porous titanium dental implants fabricated by two different routes: conventional powder metallurgy and space-holder techniques. A novel, feasible and repetitive protocol of micro-milling of the implant thread (before sintering), as well as surface modification treatments (after sintering) are also implemented. The discussion is conducted in terms of the influence of porosity and surface roughness on the stiffness and yield strength of implants. The macro-pores concentrate stress locally, and, at the same time, they could act as a barrier to the propagation of micro-cracks. Higher rugosity was observed for virgin implants obtained with spacer particles. Concerning superficially modified implants, while bioglass 1393 was the most effective coating due to its greater infiltration and adhesion capacity, chemical etching could improve osteoblast adhesion because modifies the roughness of the implant surface.Ministry of Science and Innovation of Spain PID2019-109371GB-I00Junta de AndalucĂa–FEDER (Spain) US-125977
Photodissociation chemistry footprints in the Starburst galaxy NGC 253
We report the first detection of PDR molecular tracers, namely HOC+, and CO+,
and confirm the detection of the also PDR tracer HCO towards the starburst
galaxy NGC 253, claimed to be mainly dominated by shock heating and in an
earlier stage of evolution than M 82, the prototypical extragalactic PDR. Our
CO+ detection suffers from significant blending to a group of transitions of
13CH3OH, tentatively detected for the first time in the extragalactic
interstellar medium. These species are efficiently formed in the highly UV
irradiated outer layers of molecular clouds, as observed in the late stage
nuclear starburst in M 82. The molecular abundance ratios we derive for these
molecules are very similar to those found in M 82. This strongly supports the
idea that these molecules are tracing the PDR component associated with the
starburst in the nuclear region of NGC 253. A comparison with the predictions
of chemical models for PDRs shows that the observed molecular ratios are
tracing the outer layers of UV illuminated clouds up to two magnitudes of
visual extinction. Chemical models, which include grain formation and
photodissociation of HNCO, support the scenario of a photo-dominated chemistry
as an explanation to the abundances of the observed species. From this
comparison we conclude that the molecular clouds in NGC 253 are more massive
and with larger column densities than those in M 82, as expected from the
evolutionary stage of the starbursts in both galaxies.Comment: 32 pages, 4 figures, Published in Ap
Tracing high density gas in M 82 and NGC 4038
We present the first detection of CS in the Antennae galaxies towards the NGC
4038 nucleus, as well as the first detections of two high-J (5-4 and 7-6) CS
lines in the center of M 82. The CS(7-6) line in M 82 shows a profile that is
surprisingly different to those of other low-J CS transitions we observed. This
implies the presence of a separate, denser and warmer molecular gas component.
The derived physical properties and the likely location of the CS(7-6) emission
suggests an association with the supershell in the centre of M 82.Comment: 10 pages, 3 figures, ApJ Letter - ACCEPTE
Widespread HCO emission in the M82's nuclear starburst
We present a high-resolution (~ 5'') image of the nucleus of M82 showing the
presence of widespread emission of the formyl radical (HCO). The HCO map, the
first obtained in an external galaxy, reveals the existence of a structured
disk of ~ 650 pc full diameter. The HCO distribution in the plane mimics the
ring morphology displayed by other molecular/ionized gas tracers in M82. More
precisely, rings traced by HCO, CO and HII regions are nested, with the HCO
ring lying in the outer edge of the molecular torus. Observations of HCO in
galactic clouds indicate that the abundance of HCO is strongly enhanced in the
interfaces between the ionized and molecular gas. The surprisingly high overall
abundance of HCO measured in M82 (X(HCO) ~ 4x10^{-10}) indicates that its
nuclear disk can be viewed as a giant Photon Dominated Region (PDR) of ~ 650 pc
size. The existence of various nested gas rings, with the highest HCO abundance
occurring at the outer ring (X(HCO) ~ 0.8x10^{-9}), suggests that PDR chemistry
is propagating in the disk. We discuss the inferred large abundances of HCO in
M82 in the context of a starburst evolutionary scenario, picturing the M82
nucleus as an evolved starburst.Comment: 13 pages, 3 figures, to appear in ApJ Letters; corrected list of
author
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