15,883 research outputs found
The properties of the stellar populations in ULIRGs I: sample, data and spectral synthesis modelling
We present deep long-slit optical spectra for a sample of 36 Ultraluminous
Infrared Galaxies (ULIRGs), taken with the William Herschel Telescope (WHT) on
La Palma with the aim of investigating the star formation histories and testing
evolutionary scenarios for such objects. Here we present the sample, the
analysis techniques and a general overview of the properties of the stellar
populations. Spectral synthesis modelling has been used in order to estimate
the ages of the stellar populations found in the diffuse light sampled by the
spectra in both the nuclear and extended regions of the target galaxies. We
find that adequate fits can be obtained using combinations of young stellar
populations (YSPs,t_YSP<=2 Gyr), with ages divided into two groups: very young
stellar populations (VYSPs, t_VYSP <=100 Myr) and intermediate-young stellar
populations (IYSPs, 0.1 < t_IYSP <= 2 Gyr). Our results show that YSPs are
present at all locations of the galaxies covered by our slit positions, with
the exception of the northern nuclear region of the ULIRG IRAS 23327+2913.
Furthermore, VYSPs are presents in at least 85% of the 133 extraction apertures
used for this study. Old stellar populations (OSPs, t_{OSP} > 2 Gyr) do not
make a major contribution to the optical light in the majority of the apertures
extracted. In fact they are essential for fitting the spectra in only 5% (7) of
the extracted apertures. The estimated total masses for the YSPs (VYSPs+IYSPs)
are in the range 0.18 x 10^{10} <= M_YSP <= 50 x 10^{10} Msun. We have also
estimated the bolometric luminosities associated with the stellar populations
detected at optical wavelengths, finding that they fall in the range 0.07 x
10^{12} < L_bol < 2.2 x 10^{12} Lsun. In addition, we find that reddening is
significant at all locations in the galaxies.Comment: accepted for publication in MNRA
Effect of Maternal Hypoxia on Fetal Development: Programming of HIE Phenotype in Neonatal Rat Brain
Developmental programming of health and disease correlates the adverse intrauterine environment and the risk of disease later in life as cardiovascular disease, metabolic diseases, renal dysfunction or neurobehavioral disorders among others. Maternal hypoxia is one of the most common intrauterine growth restricted environment during pregnancy. Perinatal hypoxic-ischemic encephalopathy is an important cause of brain injury in the newborn due to a systematic asphyxia. Our study aims to test the hypothesis that maternal hypoxia affect the organogenesis of the kidney by affecting the kidney structure and focusing on the roles of AT1R and AT2R, while the brain development will also be affected by this maternal insult increasing the vulnerability of this to HIE brain injury and the role of GR and the epigenetic modification that regulate the expression of the GR will be assessed. Finally, the MAPK/ERK pathway as part of the downstream of the neuroprotective mechanism of the GR against neonate HIE brain injury will be evaluated. To address these issues two rats model were established: perinatal hypoxia exposure model in time-dated pregnant rats and hypoxic-ischemic encephalopathy in 10-day-old rat pups. Through these studies we found that maternal hypoxia decrease the number of glomeruli in offspring rat kidneys and a down-regulation on the expression of AT1R was observed in the kidneys of the adult rats in a sex dimorphism way, affecting more the females than the males. In addition, we observed that maternal hypoxia increased the vulnerability of the brain to HIE on P-10 pups by repressing the expression of GR. Epigenetics studies demonstrated that this down-regulation of GR was due to hypermethylation on promoter region of exon variants 17 and 111 of the GR gene. Dexamethasone, a synthetic glucocorticoid, treatment on normoxic P-10 brains increased the expression of LPGDS, and pERK44 and also the level of prostaglandin D2, while, the neuroprotective effect of dexamethasone observed against HIE brain injury on P-10 pups was diminished by MAPK/ERK and LPGDS inhibitor, and by blocking the DP1 receptor. These findings provide a new insight in understanding the pathogenesis of HIE in newborns and may suggest potential targets for the prevention and treatment of HIE brain injury
The Berry-Tabor conjecture for spin chains of Haldane-Shastry type
According to a long-standing conjecture of Berry and Tabor, the distribution
of the spacings between consecutive levels of a "generic'' integrable model
should follow Poisson's law. In contrast, the spacings distribution of chaotic
systems typically follows Wigner's law. An important exception to the
Berry-Tabor conjecture is the integrable spin chain with long-range
interactions introduced by Haldane and Shastry in 1988, whose spacings
distribution is neither Poissonian nor of Wigner's type. In this letter we
argue that the cumulative spacings distribution of this chain should follow the
"square root of a logarithm'' law recently proposed by us as a characteristic
feature of all spin chains of Haldane-Shastry type. We also show in detail that
the latter law is valid for the rational counterpart of the Haldane-Shastry
chain introduced by Polychronakos.Comment: LaTeX with revtex4, 6 pages, 6 figure
Crossover between the Dense Electron-Hole Phase and the BCS Excitonic Phase in Quantum Dots
Second order perturbation theory and a Lipkin-Nogami scheme combined with an
exact Monte Carlo projection after variation are applied to compute the
ground-state energy of electron-hole pairs confined in a
parabolic two-dimensional quantum dot. The energy shows nice scaling properties
as N or the confinement strength is varied. A crossover from the high-density
electron-hole phase to the BCS excitonic phase is found at a density which is
roughly four times the close-packing density of excitons.Comment: Improved variational and projection calculations. 17 pages, 3 ps
figures. Accepted for publication in Int. J. Mod. Phys.
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