661 research outputs found
Ionized gas velocity dispersion in nearby dwarf galaxies: looking at supersonic turbulent motions
We present the results of ionized gas turbulent motions study in several
nearby dwarf galaxies using a scanning Fabry-Perot interferometer with the 6-m
telescope of the SAO RAS. Combining the `intensity-velocity dispersion'
diagrams (I-sigma) with two-dimensional maps of radial velocity dispersion we
found a number of common patterns pointing to the relation between the value of
chaotic ionized gas motions and processes of current star formation. In five
out of the seven analysed galaxies we identified expanding shells of ionized
gas with diameters of 80-350 pc and kinematic ages of 1-4 Myr. We also
demonstrate that the I-sigma diagrams may be useful for the search of supernova
remnants, other small expanding shells or unique stars in nearby galaxies. As
an example, a candidate luminous blue variable (LBV) was found in UGC 8508. We
propose some additions to the interpretation, previously used by Munoz-Tunon et
al. to explain the I-sigma diagrams for giant star formation regions. In the
case of dwarf galaxies, a major part of the regions with high velocity
dispersion belongs to the diffuse low surface brightness emission, surrounding
the star forming regions. We attribute this to the presence of perturbed low
density gas with high values of turbulent velocities around the giant HII
regions.Comment: 21 pages, 8 figures. Accepted by MNRAS. The high-resolution version
locates at http://www.sao.ru/hq/moisav/MoisLoz_full.pd
The L-sigma Relation of Local HII Galaxies
We present for the first time a new data set of emission line widths for 118
star-forming regions in HII galaxies (HIIGs). This homogeneous set is used to
investigate the L-sigma relation in conjunction with optical spectrophotometric
observations. Peculiarities in the line profiles such as sharp lines, wings,
asymmetries, and in some cases more than one component in emission were
verified. From a new independent homogeneous set of spectrophotometric data we
derived physical condition parameters and performed the statistical principal
component analysis. We have investigated the potential role of metallicity
(O/H), Hbeta equivalent width (WHbeta) and ionization ratio [OIII]/[OII] to
account for the observational scatter of L-sigma relation. Our results indicate
that the L-sigma relation for HIIGs is more sensitive to the evolution of the
current starburst event (short-term evolution) and dated by WHbeta or even the
[OIII]/[OII] ratio. The long-term evolution measured by O/H also plays a
potential role in determining the luminosity of the current burst for a given
velocity dispersion and age as previously suggested. Additionally, galaxies
showing Gaussian line profiles present more tight correlations indicating that
they are best targets for the application of the parametric relations as an
extragalactic cosmological distance indicator. Best fits for a restricted
homogeneous sample of 45 HIIGs provide us a set of new extragalactic distance
indicators with an RMS scatter compatible with observational errors of
Delta_log(LHalpha) = 0.2 dex or 0.5 mag. Improvements may still come from
future optimized observational programs to reduce the observational
uncertainties on the predicted luminosities of HIIGs in order to achieve the
precision required for the application of these relations as tests of
cosmological models.Comment: 53 pages, 15 figures, 4 complete tables Accepted for publication in
The Astrophysical Journa
Screening of fluoroquinolones in environmental waters using disk-based solid-phase extraction combined to microplate fluorimetric determination and LC-MS/MS
Fluoroquinolones are in the order of the day concerning environmental contamination through anthropogenic activities, resulting in increased risk for antibiotic resistance dissemination. In this context, accessible, low-cost analytical methods are required for implementation of comprehensive surveillance and screening schemes. In this work, we propose a down-scaled disk-based solid-phase extraction system from which the eluate can be first screened by miniaturized fluorimetric reading, followed by individual determination of target fluoroquinolones (ciprofloxacin, norfloxacin, and enrofloxacin) by liquid chromatography combined to tandem mass spectrometry. The fluorimetric measurement is based on the intrinsic fluorescence of fluoroquinolones. Disk-based retention was performed after sample acidification (pH 4.0) by mixed-mode cation exchange using polystyrene divinylbenzene sulphonated sorbent. Sample loading was precisely controlled in a dedicated flow system operating at 4.0 mL min−1. Different eluent compositions were tested, with elution performed by 1.00 mL of methanol-ammonium hydroxide (98:2, v/v), with subsequent reading of eluate in both detectors. Quantification was attained for 2–25 µg L−1 range, with LOD values at 1 µg L−1. The proposed approach was successfully applied to estuarine waters from the Douro River, with comparable results to a conventional SPE-LC-MS/MS procedure.info:eu-repo/semantics/publishedVersio
Development of a flow method for the determination of phosphate in estuarine and freshwaters - Comparison of flow cells in spectrophotometric sequential injection analysis
A sequential injection system with dual analytical line was developed and applied in the comparison of two different detection systems viz; a conventional spectrophotometer with a commercial flow cell, and a multi-reflective flow cell coupled with a photometric detector under the same experimental conditions. The study was based on the spectrophotometric determination of phosphate using the molybdenum-blue chemistry. The two alternative flow cells were compared in terms of their response to variation of sample salinity, susceptibility to interferences and to refractive index changes. The developed method was applied to the determination of phosphate in natural waters (estuarine, river, well and ground waters). The achieved detection limit (0.007 mu M PO43-) is consistent with the requirement of the target water samples, and a wide quantification range (0.024-9.5 mu M) was achieved using both detection systems.info:eu-repo/semantics/submittedVersioninfo:eu-repo/semantics/acceptedVersio
Generalised permutation branes
We propose a new class of non-factorising D-branes in the product group GxG
where the fluxes and metrics on the two factors do not necessarily coincide.
They generalise the maximally symmetric permutation branes which are known to
exist when the fluxes agree, but break the symmetry down to the diagonal
current algebra in the generic case. Evidence for the existence of these branes
comes from a Lagrangian description for the open string world-sheet and from
effective Dirac-Born-Infeld theory. We state the geometry, gauge fields and, in
the case of SU(2)xSU(2), tensions and partial results on the open string
spectrum. In the latter case the generalised permutation branes provide a
natural and complete explanation for the charges predicted by K-theory
including their torsion.Comment: 33 pages, 6 figures, v2: Extended discussion of K-theory
interpretation of our branes for products of higher rank groups in the
conclusions; v3: Correction of formula (35) and adjustment of the discussion
below equation (45) (no change of result). Footnote 9 points out a previously
unnoticed subtlety and provides a reference to a more detailed discussio
Loop Operators and the Kondo Problem
We analyse the renormalisation group flow for D-branes in WZW models from the
point of view of the boundary states. To this end we consider loop operators
that perturb the boundary states away from their ultraviolet fixed points, and
show how to regularise and renormalise them consistently with the global
symmetries of the problem. We pay particular attention to the chiral operators
that only depend on left-moving currents, and which are attractors of the
renormalisation group flow. We check (to lowest non-trivial order in the
coupling constant) that at their stable infrared fixed points these operators
measure quantum monodromies, in agreement with previous semiclassical studies.
Our results help clarify the general relationship between boundary transfer
matrices and defect lines, which parallels the relation between
(non-commutative) fields on (a stack of) D-branes and their push-forwards to
the target-space bulk.Comment: 22 pages, 2 figure
Very metal-poor galaxies: ionized gas kinematics in nine objects
The study of ionized gas morphology and kinematics in nine eXtremely
Metal-Deficient (XMD) galaxies with the scanning Fabry-Perot interferometer on
the SAO 6-m telescope is presented. Some of these very rare objects (with
currently known range of O/H of 7.12 < 12+log(O/H) < 7.65, or Zo/35 < Z <
Zo/10) are believed to be the best proxies of `young' low-mass galaxies in the
high-redshift Universe. One of the main goals of this study is to look for
possible evidence of star formation (SF) activity induced by external
perturbations. Recent results from HI mapping of a small subsample of XMD
star-forming galaxies provided confident evidence for the important role of
interaction-induced SF. Our observations provide complementary or new
information that the great majority of the studied XMD dwarfs have strongly
disturbed gas morphology and kinematics or the presence of detached components.
We approximate the observed velocity fields by simple models of a rotating
tilted thin disc, which allow us the robust detection of non-circular gas
motions. These data, in turn, indicate the important role of current/recent
interactions and mergers in the observed enhanced star formation. As a
by-product of our observations, we obtained data for two LSB dwarf galaxies:
Anon J012544+075957 that is a companion of the merger system UGC 993, and SAO
0822+3545 which shows off-centre, asymmetric, low SFR star-forming regions,
likely induced by the interaction with the companion XMD dwarf HS 0822+3542.Comment: Accepted to MNRAS, 20 pages, 3 tables, 7 figure
Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high
We measured the longitudinal double spin asymmetries for single
hadron muo-production off protons and deuterons at photon virtuality <
1(GeV/) for transverse hadron momenta in the range 0.7
GeV/ to 4 GeV/ . They were determined using COMPASS data taken
with a polarised muon beam of 160 GeV/ or 200 GeV/ impinging on
polarised or targets. The experimental
asymmetries are compared to next-to-leading order pQCD calculations, and are
sensitive to the gluon polarisation inside the nucleon in the range
of the nucleon momentum fraction carried by gluons
Interplay among transversity induced asymmetries in hadron leptoproduction
In the fragmentation of a transversely polarized quark several left-right
asymmetries are possible for the hadrons in the jet. When only one unpolarized
hadron is selected, it exhibits an azimuthal modulation known as Collins
effect. When a pair of oppositely charged hadrons is observed, three
asymmetries can be considered, a di-hadron asymmetry and two single hadron
asymmetries. In lepton deep inelastic scattering on transversely polarized
nucleons all these asymmetries are coupled with the transversity distribution.
From the high statistics COMPASS data on oppositely charged hadron-pair
production we have investigated for the first time the dependence of these
three asymmetries on the difference of the azimuthal angles of the two hadrons.
The similarity of transversity induced single and di-hadron asymmetries is
discussed. A new analysis of the data allows to establish quantitative
relationships among them, providing for the first time strong experimental
indication that the underlying fragmentation mechanisms are all driven by a
common physical process.Comment: 6 figure
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