217 research outputs found
Reflectivity Anisotropy Spectra of Cu- and Ag- (110) surfaces from {\it ab initio} theory
We are able to disentagle the effects of the intraband and interband parts of
the bulk dielectric function on the bare dielectric anisotropy of the surface.
We show how the position, sign and amplitude of the structures observed in such
spectra depend on the above quantities. The lineshape of all the calculated
structures agree very well with the ones observed experimentally for samples
treated by suitable surface cleaning. In particular, we reproduce the observed
single peak structure of Ag at high energy, found to represent a state of the
clean surface different from the one giving the originally observed double peak
structure. This results is not reproduced by the 'local field' model.Comment: 4 pages, 3 figures. submitted to Phys. Rev. Let
Reduced pulmonary oxygen diffusion at 36 weeks of postmenstrual age in small-for-gestational-age preterm infants of less than 32 weeks without bronchopulmonary dysplasia
Background: Small-for-gestational-age (SGA) preterm infants are at increased risk of developing bronchopulmonary dysplasia (BPD). There is limited information on pulmonary oxygen diffusion of SGA preterm infants, particularly in those without BPD. Objective: To compare the pulmonary oxygen diffusion of SGA to that of appropriate-for-gestational-age (AGA) preterm infants without BPD. Study Design: Preterm infants with a gestational age (GA) between 24.0 and 31.6 weeks were studied. The oxygen saturation (SpO2), fraction to inspired oxygen (FiO2), and the SpO2 to FiO2 ratio (SFR) were compared between SGA and AGA infants. The association between SGA and SFR at 36 weeks was assessed using a multiple regression analysis. In the subgroup without BPD, SGA were match-paired for GA and gender with AGA infants. Results: We analyzed 1189 infants surviving at 36 weeks: 194 (16%) were SGA and 995 (84%) AGA. The incidence of BPD was significantly higher in SGA than AGA infants (32% vs. 13%; p =.000). Out of the 995 infants without BPD, 132 (13%) were SGA and 863 (87%) AGA. SGA was negatively associated with the SFR value at 36 weeks, independently from BPD. SGA infants without BPD had significantly higher (better) SFR at birth, but lower (worse) SpO2 and SFR and from 33 to 36 weeks than their matched AGA counterpart. At 36 weeks, median SpO2 and SFR values were 97.7 versus 98.4 (p =.006) and 465 versus 468 (p =.010) in match-paired SGA and AGA, respectively. Conclusion: Among preterm infants of less than 32 weeks and without BPD, SGA infants had a reduced pulmonary oxygen diffusion at 36 weeks in comparison with AGA infants
An E-ELT Case Study: Colour-Magnitude Diagrams of an Old Galaxy in the Virgo Cluster
One of the key science goals for a diffraction limited imager on an Extremely
Large Telescope (ELT) is the resolution of individual stars down to faint
limits in distant galaxies. The aim of this study is to test the proposed
capabilities of a multi-conjugate adaptive optics (MCAO) assisted imager
working at the diffraction limit, in IJHK filters, on a 42m diameter ELT to
carry out accurate stellar photometry in crowded images in an Elliptical-like
galaxy at the distance of the Virgo cluster. As the basis for realistic
simulations we have used the phase A studies of the European-ELT project,
including the MICADO imager (Davies & Genzel 2010) and the MAORY MCAO module
(Diolaiti 2010). We convolved a complex resolved stellar population with the
telescope and instrument performance expectations to create realistic images.
We then tested the ability of the currently available photometric packages
STARFINDER and DAOPHOT to handle the simulated images. Our results show that
deep Colour-Magnitude Diagrams (photometric error, 0.25 at I27.2;
H25. and K24.6) of old stellar populations in galaxies, at the
distance of Virgo, are feasible at a maximum surface brightness,
17 mag/arcsec (down to M and M M), and
significantly deeper (photometric error, 0.25 at I29.3; H26.6
and K26.2) for 21 mag/arcsec (down to M and
M M). The photometric errors, and thus also the depth of
the photometry should be improved with photometry packages specifically
designed to adapt to an ELT MCAO Point Spread Function. We also make a simple
comparison between these simulations and what can be expected from a Single
Conjugate Adaptive Optics feed to MICADO and also the James Webb Space
Telescope.Comment: 17 pages, 22 figures, accepted on A&
SMASHing the LMC: A Tidally-induced Warp in the Outer LMC and a Large-scale Reddening Map
We present a study of the three-dimensional (3D) structure of the Large
Magellanic Cloud (LMC) using ~2.2 million red clump (RC) stars selected from
the Survey of the MAgellanic Stellar History. To correct for line-of-sight dust
extinction, the intrinsic RC color and magnitude and their radial dependence
are carefully measured by using internal nearly dust-free regions. These are
then used to construct an accurate 2D reddening map (165 square degrees with
~10 arcmin resolution) of the LMC disk and the 3D spatial distribution of RC
stars. An inclined disk model is fit to the 2D distance map yielding a best-fit
inclination angle i = 25.86(+0.73,-1.39) degrees with random errors of +\-0.19
degrees and line-of-nodes position angle theta = 149.23(+6.43,-8.35) degrees
with random errors of +/-0.49 degrees. These angles vary with galactic radius,
indicating that the LMC disk is warped and twisted likely due to the repeated
tidal interactions with the Small Magellanic Cloud (SMC). For the first time,
our data reveal a significant warp in the southwestern part of the outer disk
starting at rho ~ 7 degrees that departs from the defined LMC plane up to ~4
kpc toward the SMC, suggesting that it originated from a strong interaction
with the SMC. In addition, the inner disk encompassing the off-centered bar
appears to be tilted up to 5-15 degrees relative to the rest of the LMC disk.
These findings on the outer warp and the tilted bar are consistent with the
predictions from the Besla et al. simulation of a recent direct collision with
the SMC.Comment: 25 pages, 15 figures, published in Ap
Slow crossover in YbXCu4 intermediate valence compounds
We compare the results of measurements of the magnetic susceptibility Chi(T),
the linear coefficient of specific heat Gamma(T)=C(T)/T and 4f occupation
number nf(T) for the intermediate valence compounds YbXCu4 (X = Ag, Cd, In, Mg,
Tl, Zn) to the predictions of the Anderson impurity model, calculated in the
non-crossing approximation (NCA). The crossover from the low temperature Fermi
liquid state to the high temperature local moment state is substantially slower
in the compounds than predicted by the NCA; this corresponds to the
''protracted screening'' recently predicted for the Anderson Lattice. We
present results for the dynamic susceptibility, measured through neutron
scattering experiments, to show that the deviations between theory and
experiment are not due to crystal field effects, and we present
x-ray-absorption fine-structure (XAFS) results that show the local crystal
structure around the X atoms is well ordered, so that the deviations probably
do not arise from Kondo Disorder. The deviations may correlate with the
background conduction electron density, as predicted for protracted screening.Comment: Submitted to Physical Review B on June 7, 2000, accepted for
publication November 2, 2000. Changes to the original manuscript include: 1)
a discussion of the relation of the slow crossover to the conduction electron
density; 2) a discussion of the relation of the reported results to earlier
photoemission results; and, 3) minor editorial change
Multi-phonon Resonant Raman Scattering Predicted in LaMnO3 from the Franck-Condon Process via Self-Trapped Excitons
Resonant behavior of the Raman process is predicted when the laser frequency
is close to the orbital excitation energy of LaMnO3 at 2 eV. The incident
photon creates a vibrationally excited self-trapped ``orbiton'' state from the
orbitally-ordered Jahn-Teller (JT) ground state. Trapping occurs by local
oxygen rearrangement. Then the Franck-Condon mechanism activates multiphonon
Raman scattering. The amplitude of the -phonon process is first order in the
electron-phonon coupling . The resonance occurs {\it via} a dipole forbidden
to transition. We previously suggested that this transition (also seen
in optical reflectivity) becomes allowed because of asymmetric oxygen
fluctuations. Here we calculate the magnitude of the corresponding matrix
element using local spin-density functional theory. This calculation agrees to
better than a factor of two with our previous value extracted from experiment.
This allows us to calculate the absolute value of the Raman tensor for
multiphonon scattering. Observation of this effect would be a direct
confirmation of the importance of the JT electron-phonon term and the presence
of self-trapped orbital excitons, or ``orbitons''.Comment: 8 pages and 3 embedded figures. The earlier short version is now
replaced by a more complete paper with a slightly different title. This
version includes a caculation by density-functional theory of the dipole
matrix element for exciting the self-trapped orbital exciton which activates
the multiphonon Raman signal
A tidally induced global corrugation pattern in an external disk galaxy similar to the milky way
We study the two-dimensional (2D) line-of-sight velocity (Vlos) field of the low-inclination, late-type galaxy VV304a. The resulting 2D kinematic map reveals a global, coherent, and extended perturbation that is likely associated with a recent interaction with the massive companion VV304b. We use multiband imaging and a suite of test-particle simulations to quantify the plausible strength of in-plane flows due to nonaxisymmetric perturbations and show that the observed velocity flows are much too large to be driven either by a spiral structure or by a bar. We use fully cosmological hydrodynamical simulations to characterize the contribution from in- and off-plane velocity flows to the Vlos field of recently interacting galaxy pairs like the VV304 system. We show that, for recently perturbed low-inclination galactic disks, the structure of the residual velocity field, after subtraction of an axisymmetric rotation model, can be dominated by vertical flows. Our results indicate that the Vlos perturbations in VV304a are consistent with a corrugation pattern. Its Vlos map suggests the presence of a structure similar to the Monoceros ring seen in the Milky Way. Our study highlights the possibility of addressing important questions regarding the nature and origin of vertical perturbations by measuring the line-of-sight velocities in low-inclination nearby galaxies
Galaxy evolution in compact groups I: Revealing a transitional galaxy population through a multiwavelength approach
Compact groups of galaxies (CGs) show members with morphological
disturbances, mainly products of galaxy-galaxy interactions, thus making them
ideal systems to study galaxy evolution, in high-density environment. To
understand how this environment affects the properties of galaxies, we select a
sample of 340 CGs in the Stripe 82 region, for a total of 1083 galaxies, and a
sample of 2281 field galaxies as a control sample. By performing a
multi-wavelength morphological fitting process using S-PLUS data, we divide our
sample into early-type (ETG), late-type (LTG), and transition galaxies using
the r-band S\'ersic index and the colour (u-r). We find a bimodal distribution
in the plane of the effective radius-S\'ersic index, where a secondary
"peculiar" galaxy population of smaller and more compact galaxies is found in
CGs, which is not observed in the control sample. This indicates that galaxies
are undergoing a morphological transformation in CGs. In addition, we find
significant statistical differences in the distribution of specific Star
Formation Rate (sSFR) when we compare both environments for LTGs and ETGs. We
also find a higher fraction of quenched galaxies and a lower median sSFR in CGs
than in the control sample, suggesting the existence of environmental effects
favoring the cessation of star formation, regardless of galaxy type. Our
results support the notion that CGs promote morphological and physical
transformations, highlighting their potential as ideal systems for galaxy
pre-processing.Comment: 17 pages, 15 figures. Accepted for publication in MNRA
The 2009 L’Aquila (central Italy) MW6.3 earthquake: Main shock
A MW
6.3 earthquake struck on April 6, 2009 the
Abruzzi region (central Italy) producing vast damage in the
L’Aquila town and surroundings. In this paper we present
the location and geometry of the fault system as obtained
by the analysis of main shock and aftershocks recorded
by permanent and temporary networks. The distribution of
aftershocks, 712 selected events with ML 2.3 and 20 with
ML 4.0, defines a complex, 40 km long, NW trending
extensional structure. The main shock fault segment extends
for 15–18 km and dips at 45 to theSW, between 10 and 2 km
depth. The extent of aftershocks coincides with the surface
trace of the Paganica fault, a poorly known normal fault
that, after the event, has been quoted to accommodate the
extension of the area.We observe a migration of seismicity to
the north on an echelon fault that can rupture in future large
earthquakes.PublishedL183083.1. Fisica dei terremotiJCR Journalreserve
The prevalence of pseudo-bulges in the Auriga simulations
We study the galactic bulges in the Auriga simulations, a suite of 30 cosmological magnetohydrodynamical zoom-in simulations of late-type galaxies in Milky Way sized dark matter haloes performed with the moving-mesh code AREPO. We aim to characterize bulge formation mechanisms in this large suite of galaxies simulated at high resolution in a fully cosmological context. The bulges of the Auriga galaxies show a large variety in their shapes, sizes, and formation histories. According to observational classification criteria, such as Sérsic index and degree of ordered rotation, the majority of the Auriga bulges can be classified as pseudo-bulges, while some of them can be seen as composite bulges with a classical component; however, none can be classified as a classical bulge. Auriga bulges show mostly an in situ origin, 21 per cent of them with a negligible accreted fraction (facc < 0.01). In general, their in situ component was centrally formed, with ∼75 per cent of the bulges forming most of their stars inside the bulge region at z = 0. Part of their in situ mass growth is rapid and is associated with the effects of mergers, while another part is more secular in origin. In 90 per cent of the Auriga bulges, the accreted bulge component originates from less than four satellites. We investigate the relation between the accreted stellar haloes and the bulges of the Auriga simulations. The total bulge mass shows no correlation with the accreted stellar halo mass, as in observations. However, the accreted mass of bulges tends to correlate with their respective accreted stellar halo mass
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