544 research outputs found
Evidence of an interaction from resolved stellar populations: The curious case of NGC1313
The galaxy NGC1313 has attracted the attention of various studies due to the
peculiar morphology observed in optical bands, although it is classified as a
barred, late-type galaxy with no apparent close-by companions. However, the
velocity field suggests an interaction with a satellite companion. Using
resolved stellar populations, we study different parts of the galaxy to
understand further its morphology. Based on HST/ACS images, we estimated star
formation histories by means of the synthetic CMD method in different areas in
the galaxy. Incompleteness limits our analysis to ages younger than ~100Myr.
Stars in the red and blue He burning phases are used to trace the distribution
of recent star formation. Star formation histories suggest a burst in the
southern-west region. We support the idea that NGC1313 is experiencing an
interaction with a satellite companion, observed as a tidally disrupted
satellite galaxy in the south-west of NGC1313. However, we do not observe any
indication of a perturbation due to the interaction with the satellite galaxy
at other locations across the galaxy, suggesting that only a modest-sized
companion that did not trigger a global starburst was involved.Comment: 10 pages, 4 figures, accepted for publication in MNRA
NGC 7331: the Galaxy with the Multicomponent Central Region
We present the results of the spectral investigation of the regular Sb galaxy
NGC 7331 with the Multi-Pupil Field Spectrograph of the 6m telescope. The
absorption-line indices H-beta, Mgb, and are mapped to analyse the
properties of the stellar populations in the circumnuclear region of the
galaxy. The central part of the disk inside ~3" (200 pc) -- or a separate
circumnuclear stellar-gaseous disk as it is distinguished by decoupled fast
rotation of the ionized gas -- is very metal-rich, rather young, ~ 2 billion
years old, and its solar magnesium-to-iron ratio evidences for a very long
duration of the last episode of star formation there. However the gas
excitation mechanism now in this disk is shock-like. The star-like nucleus had
probably experienced a secondary star formation burst too: its age is 5 billion
years, much younger than the age of the circumnuclear bulge. But [Mg/Fe]=+0.3
and only solar global metallicity imply that the nuclear star formation burst
has been much shorter than that in the circumnuclear disk. The surrounding
bulge is rather old, 9--14 billion years old, and moderately metal-poor. The
rotation of the stars and gas within the circumnuclear disk is axisymmetric
though its rotation plane may be slightly inclined to the global plane of the
galaxy. Outside the circumnuclear disk the gas may experience non-circular
motions, and we argue that the low-contrast extended bulge of NGC 7331 is
triaxial.Comment: LATEX, 27 pages, + 15 Postscript figures. Accepted to Astronomical
Journal, July issu
Prevalence of resistance mutations related to integrase inhibitor S/GSK1349572 in HIV-1 subtype B raltegravir-naive and -treated patients
Objectives To compare the frequency of previously in vitro-selected integrase mutations (T124A, T124A/S153F, S153Y, T124A/S153Y and L101I/T124A/S153Y) conferring resistance to S/GSK1349572 between HIV-1 subtype B integrase inhibitor (INI)-naive and raltegravir-treated patients. Methods Integrase sequences from 650 INI-naive patients and 84 raltegravir-treated patients were analysed. Results The T124A mutation alone and the combination T124A/L101I were more frequent in raltegravir-failing patients than in INI-naive patients (39.3% versus 24.5%, respectively, P = 0.005 for T124A and 20.2% versus 10.0%, respectively, P = 0.008 for T124A/L101I). The S153Y/F mutations were not detected in any integrase sequence (except for S153F alone, only detected in one INI-naive patient). Conclusions T124A and T124A/L101I, more frequent in raltegravir-treated patients, could have some effect on raltegravir response and their presence could play a role in the selection of other mutations conferring S/GSK1349572 resistance. The impact of raltegravir-mediated changes such as these on the virological response to S/GSK1349572 should be studied further
Dorsoventral differences in intrinsic properties in developing CA1 pyramidal cells.
The dorsoventral and developmental gradients of entorhinal layer II cell grid properties correlate with their resonance properties and with their hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channel current characteristics. We investigated whether such correlation existed in rat hippocampal CA1 pyramidal cells, where place fields also show spatial and temporal gradients. Resonance was absent during the first postnatal week, and emerged during the second week. Resonance was stronger in dorsal than ventral cells, in accord with HCN current properties. Resonance responded to cAMP in ventral but not in dorsal cells. The dorsoventral distribution of HCN1 and HCN2 subunits and of the auxiliary protein tetratricopeptide repeat-containing Rab8b-interacting protein (TRIP8b) could account for these differences between dorsal and ventral cells. The analogous distribution of the intrinsic properties of entorhinal stellate and hippocampal cells suggests the existence of general rules of organization among structures that process complementary features of the environment
Electrochemical investigation on localised corrosion under silica sand deposit layers of carbon steel within a bespoke test cell
The corrosion behaviour of deep pit-like features on carbon steel under silica sand deposits has been evaluated using a bespoke localised corrosion cell. Local pH and electrochemical measurements were performed, including impedance spectroscopy and galvanic coupling. The corrosion rate of X65 carbon steel at four different recession depths up to 9 mm was evaluated in the presence and absence of a ∼8 mm-thick silica dioxide deposit layer, in a carbon dioxide-saturated environment. The deposit reduced corrosion rates to approximately 1 mm·yr−1 and iron carbonate formed on the steel surface under the deposit due to an increase in local pH
Efficacy of once daily darunavir/ritonavir 800/100 mg in PI/r-experienced HIV-1 infected patients with suppressed HIV-1 replication: the RADAR study
International audiencen.
Differential dorso-ventral distributions of Kv4.2 and HCN proteins confer distinct integrative properties to hippocampal CA1 pyramidal cell distal dendrites.
The dorsal and ventral regions of the hippocampus perform different functions. Whether the integrative properties of hippocampal cells reflect this heterogeneity is unknown. We focused on dendrites where most synaptic input integration takes place. We report enhanced backpropagation and theta resonance and decreased summation of synaptic inputs in ventral versus dorsal CA1 pyramidal cell distal dendrites. Transcriptional Kv4.2 down-regulation and post-transcriptional hyperpolarization-activated cyclic AMP-gated channel (HCN1/2) up-regulation may underlie these differences, respectively. Our results reveal differential dendritic integrative properties along the dorso-ventral axis, reflecting diverse computational needs
HI in Arp72 and similarities with M51-type systems
We present neutral hydrogen (H{\sc i}) observations with the Giant Metrewave
Radio Telescope ({\it GMRT}) of the interacting galaxies NGC5996 and NGC5994,
which make up the Arp72 system. Arp72 is an M51-type system and shows a complex
distribution of H{\sc i} tails and a bridge due to tidal interactions. H{\sc i}
column densities ranging from 0.8 atoms cm in the
eastern tidal tail to 1.7 atoms cm in the bridge
connecting the two galaxies, are seen to be associated with star-forming
regions. We discuss the morphological and kinematic similarities of Arp72 with
M51, the archetypal example of the M51-type systems, and Arp86, another
M51-type system studied with the {\it GMRT}, and suggest that a multiple
passage model of Salo & Laurikainen may be preferred over the classical single
passage model of Toomre & Toomre, to reproduce the H{\sc i} features in Arp72
as well as in other M-51 systems depicting similar optical and H{\sc i}
features.Comment: 8 pages, 6 figures, accepted for publication in MNRA
The Hubble Space Telescope Extragalactic Distance Scale Key Project. X. The Cepheid Distance to NGC 7331
The distance to NGC 7331 has been derived from Cepheid variables observed
with HST/WFPC2, as part of the Extragalactic Distance Scale Key Project.
Multi-epoch exposures in F555W (V) and F814W (I), with photometry derived
independently from DoPHOT and DAOPHOT/ALLFRAME programs, were used to detect a
total of 13 reliable Cepheids, with periods between 11 and 42 days. The
relative distance moduli between NGC 7331 and the LMC, imply an extinction to
NGC 7331 of A_V = 0.47+-0.15 mag, and an extinction-corrected distance modulus
to NGC 7331 of 30.89+-0.14(random) mag, equivalent to a distance of 15.1 Mpc.
There are additional systematic uncertainties in the distance modulus of +-0.12
mag due to the calibration of the Cepheid Period-Luminosity relation, and a
systematic offset of +0.05+-0.04 mag if we applied the metallicity correction
inferred from the M101 results of Kennicutt et al 1998.Comment: To be published in The Astrophysical Journal, 1998 July 1, v501 note:
Figs 1 and 2 (JPEG files) and Fig 7 (multipage .eps file) need to be
viewed/printed separatel
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