9,201 research outputs found
Chandra LETGS spectroscopy of the Quasar MR2251-178 and its warm absorber
We present an analysis of our Chandra Low Energy Transmission Grating
Spectrometer (LETGS) observation of the quasar MR2251-178. The warm absorber of
MR2251-178 is well described by a hydrogen column density, N_H~2x10^21 cm^-2,
and an ionization parameter log(xi)~0.6. We find in the spectrum weak evidence
for narrow absorption lines from Carbon and Nitrogen which indicate that the
ionized material is in outflow. We note changes (in time) of the absorption
structure in the band (0.6-1) keV (around the UTAs plus the OVII and OVIII
K-edges) at different periods of the observation. We measure a (0.1-2) keV flux
of 2.58x10^-11 ergs cm^-2 s^-1. This flux implies that the nuclear source of
MR2251-178 is in a relatively low state. No significant variability is seen in
the light curve. We do not find evidence for an extra cold material in the line
of sight, and set an upper limit of N_H~1.2x10^20 cm^-2. The X-ray spectrum
does not appear to show evidence for dusty material, though an upper limit in
the neutral carbon and oxygen column densities can only be set to N_CI~2x10^19
cm^-2 and N_OI~9x10^19 cm^-2, respectively.Comment: 42 pages, 12 figures, Accepted in Apj. Typo in abstract (ver2): "We
do not find evidence for an extra...
Environmental Policies and Mergersâ Externalities
A Cournot oligopolistic setting model of trade is characterized by local and foreign firms competing in the presence of pollution quota and tax. Local firms are foreign-owned (FDI) and repatriate their profits. First, we analyze the impact on welfare given by the merger of the local firms, as a response to external firmsâ competition and pollution abatement costs. Second, when merger is welfare decreasing, we study the best response of the government in order to compensate this negative externality. Finally, we compare the pollution quota and tax in order to determine their efficiency as a policy instrument.environmental policies, mergers, emission permits
Characterization of the known T type dwarfs towards the Sigma Orionis cluster
(Abridged) A total of three T type candidates (SOri70, SOri73, and
SOriJ0538-0213) lying in the line of sight towards Sigma Orionis were
characterized by means of near-infrared photometric, astrometric, and
spectroscopic studies. H-band methane images were collected for all three
sources and an additional sample of 15 field T type dwarfs using LIRIS/WHT.
J-band spectra of resolution of ~500 were obtained for SOriJ0538-0213 with
ISAAC/VLT, and JH spectra of resolution of ~50 acquired with WFC3/HST were
employed for the spectroscopic classification of SOri70 and 73. Proper motions
with a typical uncertainty of +/-3 mas/yr and a time interval of ~7-9 yr were
derived. Using the LIRIS observations of the field T dwarfs, we calibrated this
imager for T spectral typing via methane photometry. The three SOri objects
were spectroscopically classified as T4.5+/-0.5 (SOri73), T5+/-0.5
(SOriJ0538-0213), and T7 (SOri70). The similarity between the
observed JH spectra and the methane colors and the data of field ultra-cool
dwarfs of related classifications suggests that SOri70, 73, and
SOriJ053804.65-021352.5 do not deviate significantly in surface gravity in
relation to the field. Additionally, the detection of KI at ~1.25 microns in
SOriJ0538-0213 points to a high-gravity atmosphere. Only the K-band reddish
nature of SOri70 may be consistent with a low gravity atmosphere. The proper
motions of SOri70 and 73 are measurable and are larger than that of the cluster
by >3.5 sigma. The proper motion of SOriJ0538-0213 is consistent with a null
displacement. These observations suggest that none of the three T dwarfs are
likely Sigma Orionis members, and that either planetary-mass objects with
masses below ~4 MJup may not exist free-floating in the cluster or they may lie
at fainter near-infrared magnitudes than those of the targets (this is H>20.6
mag), thus remaining unidentified to date.Comment: Accepted for publication in A&A (2014), corrected typo
Comment on "Two Phase Transitions in the Fully frustrated XY Model"
The conclusions of a recent paper by Olsson (Phys. Rev. Lett. 75, 2758
(1995), cond-mat/9506082) about the fully frustrated XY model in two dimensions
are questioned. In particular, the evidence presented for having two separate
chiral and U(1) phase transitions are critically considered.Comment: One page one table, to Appear in Physical Review Letter
The frequency map for billiards inside ellipsoids
The billiard motion inside an ellipsoid Q \subset \Rset^{n+1} is completely
integrable. Its phase space is a symplectic manifold of dimension , which
is mostly foliated with Liouville tori of dimension . The motion on each
Liouville torus becomes just a parallel translation with some frequency
that varies with the torus. Besides, any billiard trajectory inside
is tangent to caustics , so the
caustic parameters are integrals of the
billiard map. The frequency map is a key tool to
understand the structure of periodic billiard trajectories. In principle, it is
well-defined only for nonsingular values of the caustic parameters. We present
four conjectures, fully supported by numerical experiments. The last one gives
rise to some lower bounds on the periods. These bounds only depend on the type
of the caustics. We describe the geometric meaning, domain, and range of
. The map can be continuously extended to singular values of
the caustic parameters, although it becomes "exponentially sharp" at some of
them. Finally, we study triaxial ellipsoids of \Rset^3. We compute
numerically the bifurcation curves in the parameter space on which the
Liouville tori with a fixed frequency disappear. We determine which ellipsoids
have more periodic trajectories. We check that the previous lower bounds on the
periods are optimal, by displaying periodic trajectories with periods four,
five, and six whose caustics have the right types. We also give some new
insights for ellipses of \Rset^2.Comment: 50 pages, 13 figure
Chemical (in)homogeneity and atomic diffusion in the open cluster M67
Context. The benchmark open cluster M67 is known to have solar metallicity
and similar age as the Sun. It thus provides us a great opportunity to study
the properties of solar twins, as well as the evolution of Sun-like stars.
Aims. Previous spectroscopic studies reported to detect possible subtle changes
in stellar surface abundances throughout the stellar evolutionary phase, namely
the effect of atomic diffusion, in M67. In this study we attempt to confirm and
quantify more precisely the effect of atomic diffusion, as well as to explore
the level of chemical (in)homogeneity in M67. Methods. We presented a strictly
line-by-line differential chemical abundance analysis of two groups of stars in
M67: three turn-off stars and three sub-giants. Stellar atmospheric parameters
and elemental abundances were obtained with very high precision using the
Keck/HIRES spectra. Results. The sub-giants in our sample show negligible
abundance variations ( 0.02 dex), which implies that M67 was born
chemically homogeneous. We note there is a significant abundance difference
( 0.1 - 0.2 dex) between sub-giants and turn-off stars, which can be
interpreted as the signature of atomic diffusion. Qualitatively stellar models
with diffusion agree with the observed abundance results. Some turn-off stars
do not follow the general pattern, which suggests that in some cases diffusion
can be inhibited, or they might suffered some sort of mixing event related to
planets. Conclusions. Our results pose additional challenges for chemical
tagging when using turn-off stars. In particular, the effects of atomic
diffusion, which could be as large as 0.1 - 0.2 dex, must be taken into account
in order for chemical tagging to be successfully applied.Comment: 19 pages, 21 figures; submitted to A&A on February, 2019, accepted
for publication in A&A on June, 201
Searching for galactic sources in the Swift GRB catalog
Since the early 1990s Gamma Ray Bursts have been accepted to be of
extra-galactic origin due to the isotropic distribution observed by BATSE and
the redshifts observed via absorption line spectroscopy. Nevertheless, upon
further examination at least one case turned out to be of galactic origin. This
particular event presented a Fast Rise, Exponential Decay (FRED) structure
which leads us to believe that other FRED sources might also be Galactic. This
study was set out to estimate the most probable degree of contamination by
galactic sources that certain samples of FREDs have. In order to quantify the
degree of anisotropy the average dipolar and quadripolar moments of each sample
of GRBs with respect to the galactic plane were calculated. This was then
compared to the probability distribution of simulated samples comprised of a
combination of isotropically generated sources and galactic sources. We observe
that the dipolar and quadripolar moments of the selected subsamples of FREDs
are found more than two standard deviations outside those of random
isotropically generated samples.The most probable degree of contamination by
galactic sources for the FRED GRBs of the Swift catalog detected until February
2011 that do not have a known redshift is about 21 out of 77 sources which is
roughly equal to 27%. Furthermore we observe, that by removing from this sample
those bursts that may have any type of indirect redshift indicator and multiple
peaks gives the most probable contamination increases up to 34% (17 out of 49
sources). It is probable that a high degree of contamination by galactic
sources occurs among the single peak FREDs observed by Swift.Comment: Published to A&A, 4 pages, 5 figures, this arXiv version includes
appended table with all the bursts considered in this stud
On the Equivalence of Three-Particle Scattering Formalisms
In recent years, different on-shell scattering
formalisms have been proposed to be applied to both lattice QCD and infinite
volume scattering processes. We prove that the formulation in the infinite
volume presented by Hansen and Sharpe in Phys.~Rev.~D92, 114509 (2015) and
subsequently Brice\~no, Hansen, and Sharpe in Phys.~Rev.~D95, 074510 (2017) can
be recovered from the -matrix representation, derived on the basis of
-matrix unitarity, presented by Mai {\em et al.} in Eur.~Phys.~J.~A53, 177
(2017) and Jackura {\em et al.} in Eur.~Phys.~J.~C79, 56 (2019). Therefore,
both formalisms in the infinite volume are equivalent and the physical content
is identical. Additionally, the Faddeev equations are recovered in the
non-relativistic limit of both representations.Comment: 13 pages, 5 figure
Presence of New Delhi metallo-ÎČ-lactamase gene (NDM-1) in a clinical isolate of Acinetobacter junii in Argentina
Here we report the presence of a clinically significant A. junii blaNDM-1 positive in a 38-year-old woman who was admitted to the emergency department with a fever and leg ulcers with signs of infection. The NDM-1 carbapenemase has been dramatically spread among Gram-negative bacilli, thus imposing a new challenge on the health system to fight bacterial infections.These data expand the number of Acinetobacter species harbouring blaNDM-1. The wide existence of Acinetobacter harbouring and dispersing this carbapenemase emphasizes the importance of non-previously recognized pathogens as reservoirs of dangerous resistance determinants. These resistance determinants can be later easily transferred to other menacing pathogens.Fil: Montaña, Sabrina Daiana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂ©dica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en MicrobiologĂa y ParasitologĂa MĂ©dica; ArgentinaFil: Cittadini, Roxana. Sanatorio Mater Dei; ArgentinaFil: Del Castillo M,. Sanatorio Mater Dei; ArgentinaFil: Uong, S.. California State University; Estados UnidosFil: Lazzaro, T.. California State University; Estados UnidosFil: Almuzara, Marisa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de BioquĂmica ClĂnica; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Hospital de ClĂnicas General San MartĂn; ArgentinaFil: Barberis, Claudia. Sanatorio Mater Dei; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de BioquĂmica ClĂnica; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Hospital de ClĂnicas General San MartĂn; ArgentinaFil: Vay, Carlos Alberto. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de BioquĂmica ClĂnica; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Hospital de ClĂnicas General San MartĂn; ArgentinaFil: RamĂrez, M. S.. California State University; Estados Unido
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