241 research outputs found
Why didn't the Global Financial Crisis hit Latin America?
Latin America has a rich history of financial crises. However, it was relatively unharmed by the 2007-2009 Global Financial Crisis (GFC). This paper investigates why, and in particular the role of commodity prices and its institutional framework - in line with the fourth generation financial crisis model. We set up Early Warning Systems (EWS) for Argentina, Brazil and Mexico. These consist of an ordered logit model for currency crises for the period 1990-2007 with a dynamic factor model to deal with the large number of explanatory variables. We present forecasts for the period 2008-2009.
We find that international indicators play an important role in explaining currency crises in Mexico, while banking indicators and commodities explain the currency crisis in Argentina and Brazil. Furthermore, debt and domestic economy indicators are relevant for Argentina and Mexico. Finally, we observe that currency crises in all three countries are related to institutional indicators. For none of the countries the Early Warning System would have issued an early warning for the GFC.Financial crises, Early Warning Systems, Latin America, dynamic factor models, ordered logit model,
Infrared Observations of Hot Gas and Cold Ice toward the Low Mass Protostar Elias 29
We have obtained the full 1-200 um spectrum of the low luminosity (36 Lsun)
Class I protostar Elias 29 in the Rho Ophiuchi molecular cloud. It provides a
unique opportunity to study the origin and evolution of interstellar ice and
the interrelationship of interstellar ice and hot core gases around low mass
protostars. We see abundant hot CO and H2O gas, as well as the absorption bands
of CO, CO2, H2O and ``6.85 um'' ices. We compare the abundances and physical
conditions of the gas and ices toward Elias 29 with the conditions around
several well studied luminous, high mass protostars. The high gas temperature
and gas/solid ratios resemble those of relatively evolved high mass objects
(e.g. GL 2591). However, none of the ice band profiles shows evidence for
significant thermal processing, and in this respect Elias 29 resembles the
least evolved luminous protostars, such as NGC 7538 : IRS9. Thus we conclude
that the heating of the envelope of the low mass object Elias 29 is
qualitatively different from that of high mass protostars. This is possibly
related to a different density gradient of the envelope or shielding of the
ices in a circumstellar disk. This result is important for our understanding of
the evolution of interstellar ices, and their relation to cometary ices.Comment: 18 pages and 14 figures, accepted for publication in A&
Influence of UV radiation from a massive YSO on the chemistry of its envelope
We have studied the influence of far ultraviolet (UV) radiation from a
massive young stellar object (YSO) on the chemistry of its own envelope by
extending the models of Doty et al. (2002) to include a central source of UV
radiation. The models are applied to the massive star-forming region AFGL 2591
for different inner UV field strengths. Depth-dependent abundance profiles for
several molecules are presented and discussed. We predict enhanced column
densities for more than 30 species, especially radicals and ions. Comparison
between observations and models is improved with a moderate UV field incident
on the inner envelope, corresponding to an enhancement factor G0~10-100 at 200
AU from the star with an optical depth tau~15-17. Subtle differences are found
compared with traditional models of Photon Dominated Regions (PDRs) because of
the higher temperatures and higher gas-phase H2O abundance caused by
evaporation of ices in the inner region. In particular, the CN/HCN ratio is not
a sensitive tracer of the inner UV field, in contrast with the situation for
normal PDRs: for low UV fields, the extra CN reacts with H2 in the inner dense
and warm region and produces more HCN. It is found that the CH+ abundance is
strongly enhanced and grows steadily with increasing UV field. High-J lines of
molecules like CN and HCN are most sensitive to the inner dense region where UV
radiation plays a role. Thus, even though the total column density affected by
UV photons is small, comparison of high-J and low-J lines can selectively trace
and distinguish the inner UV field from the outer one. In addition, future
Herschel-HIFI observations of hydrides can sensitively probe the inner UV
field.Comment: Accepted for publication in A&A. 13 pages, 10 figure
Astrochemistry of Sub-Millimeter Sources in Orion: Studying the Variations of Molecular Tracers with Changing Physical Conditions
Cornerstone molecules (CO, H_2CO, CH_3OH, HCN, HNC, CN, CS, SO) were observed
toward seven sub-millimeter bright sources in the Orion molecular cloud in
order to quantify the range of conditions for which individual molecular line
tracers provide physical and chemical information. Five of the sources observed
were protostellar, ranging in energetics from 1 - 500L_sun, while the other two
sources were located at a shock front and within a photodissociation region
(PDR).
Statistical equilibrium calculations were used to deduce from the measured
line strengths the physical conditions within each source and the abundance of
each molecule. In all cases except the shock and the PDR, the abundance of CO
with respect to H_2 appears significantly below (factor of ten) the general
molecular cloud value of 10^-4. {Formaldehyde measurements were used to
estimate a mean temperature and density for the gas in each source. Evidence
was found for trends between the derived abundance of CO, H_2CO, CH_3OH, and CS
and the energetics of the source, with hotter sources having higher
abundances.} Determining whether this is due to a linear progression of
abundance with temperature or sharp jumps at particular temperatures will
require more detailed modeling. The observed methanol transitions require high
temperatures (T>50 K), and thus energetic sources, within all but one of the
observed protostellar sources. The same conclusion is obtained from
observations of the CS 7-6 transition. Analysis of the HCN and HNC 4-3
transitions provides further support for high densities n> 10^7 cm^-3 in all
the protostellar sources.Comment: 36 pages, 8 figures, Astronomy and Astrophysics in pres
Water destruction by X-rays in young stellar objects
We study the H2O chemistry in star-forming environments under the influence
of a central X-ray source and a central far ultraviolet (FUV) radiation field.
The gas-phase water chemistry is modeled as a function of time, hydrogen
density and X-ray flux. To cover a wide range of physical environments,
densities between n_H = 10^4-10^9 cm^-3 and temperatures between T = 10-1000 K
are studied. Three different regimes are found: For T < 100 K, the water
abundance is of order 10^-7-10^-6 and can be somewhat enhanced or reduced due
to X-rays, depending on time and density. For 100 K < T < 250 K, H2O is reduced
from initial x(H2O) ~ 10^-4 following ice evaporation to x(H2O) ~ 10^-6 for F_X
> 10^-3 ergs s-1 cm^-2 (t = 10^4 yrs) and for F_X > 10^-4 ergs s^-1 cm^-2 (t =
10^5 yrs). At higher temperatures (T > 250 K) and hydrogen densities, water can
persist with x(H2O) ~ 10^-4 even for high X-ray fluxes. The X-ray and FUV
models are applied to envelopes around low-mass Class 0 and I young stellar
objects (YSOs). Water is destroyed in both Class 0 and I envelopes on
relatively short timescales (t ~ 5000 yrs) for realistic X-ray fluxes, although
the effect is less prominent in Class 0 envelopes due to the higher X-ray
absorbing densities there. FUV photons from the central source are not
effective in destroying water. The average water abundance in Class I sources
for L_X > 10^27 ergs s^-1 is predicted to be x(H2O) < 10^-6.Comment: 12 pages, 14 figures, Accepted for publication in A&
Magnetic stress as a driving force of structural distortions: the case of CrN
We show that the observed transition from rocksalt to orthorhombic P
symmetry in CrN can be understood in terms of stress anisotropy. Using local
spin density functional theory, we find that the imbalance between stress
stored in spin-paired and spin-unpaired Cr nearest neighbors causes the
rocksalt structure to be unstable against distortions and justifies the
observed antiferromagnetic ordering. This stress has a purely magnetic origin,
and may be important in any system where the coupling between spin ordering and
structure is strong.Comment: 4 pages (two columns) 4 figure
Infrared spectroscopy of solid CO-CO2 mixtures and layers
The spectra of pure, mixed and layered CO and CO2 ices have been studied
systematically under laboratory conditions using infrared spectroscopy. This
work provides improved resolution spectra (0.5 cm-1) of the CO2 bending and
asymmetric stretching mode, as well as the CO stretching mode, extending the
existing Leiden database of laboratory spectra to match the spectral resolution
reached by modern telescopes and to support the interpretation of the most
recent data from Spitzer. It is shown that mixed and layered CO and CO2 ices
exhibit very different spectral characteristics, which depend critically on
thermal annealing and can be used to distinguish between mixed, layered and
thermally annealed CO-CO2 ices. CO only affects the CO2 bending mode spectra in
mixed ices below 50K under the current experimental conditions, where it
exhibits a single asymmetric band profile in intimate mixtures. In all other
ice morphologies the CO2 bending mode shows a double peaked profile, similar to
that observed for pure solid CO2. Conversely, CO2 induces a blue-shift in the
peak-position of the CO stretching vibration, to a maximum of 2142 cm-1 in
mixed ices, and 2140-2146 cm-1 in layered ices. As such, the CO2 bending mode
puts clear constraints on the ice morphology below 50K, whereas beyond this
temperature the CO2 stretching vibration can distinguish between initially
mixed and layered ices. This is illustrated for the low-mass YSO HH46, where
the laboratory spectra are used to analyse the observed CO and CO2 band
profiles and try to constrain the formation scenarios of CO2.Comment: Accepted in A&
Water and ammonia abundances in S140 with the Odin satellite
We have used the Odin satellite to obtain strip maps of the ground-state
rotational transitions of ortho-water and ortho-ammonia, as well as CO(5-4) and
13CO(5-4) across the PDR, and H218O in the central position. A physi-chemical
inhomogeneous PDR model was used to compute the temperature and abundance
distributions for water, ammonia and CO. A multi-zone escape probability method
then calculated the level populations and intensity distributions. These
results are compared to a homogeneous model computed with an enhanced version
of the RADEX code. H2O, NH3 and 13CO show emission from an extended PDR with a
narrow line width of ~3 kms. Like CO, the water line profile is dominated by
outflow emission, however, mainly in the red wing. The PDR model suggests that
the water emission mainly arises from the surfaces of optically thick, high
density clumps with n(H2)>10^6 cm^-3 and a clump water abundance, with respect
to H2, of 5x10^-8. The mean water abundance in the PDR is 5x10^-9, and between
~2x10^-8 -- 2x10^-7 in the outflow derived from a simple two-level
approximation. Ammonia is also observed in the extended clumpy PDR, likely from
the same high density and warm clumps as water. The average ammonia abundance
is about the same as for water: 4x10^-9 and 8x10^-9 given by the PDR model and
RADEX, respectively. The similarity of water and ammonia PDR emission is also
seen in the almost identical line profiles observed close to the bright rim.
Around the central position, ammonia also shows some outflow emission although
weaker than water in the red wing. Predictions of the H2O(110-101) and
(111-000) antenna temperatures across the PDR are estimated with our PDR model
for the forthcoming observations with the Herschel Space Observatory.Comment: 13 pages, 14 figures, 10 tables. Accepted for publication in
Astronomy & Astrophysics 14 November 200
Redundant roles of photoreceptors and cytokinins in regulating photosynthetic acclimation to canopy density
The regulation of photosynthetic acclimation to canopy density was investigated in tobacco canopies and in tobacco and Arabidopsis plants with part of their foliage experimentally shaded. Both species acclimated to canopy light gradients and partial shading by allocating photosynthetic capacity to leaves in high light and adjusting chloroplast organization to the local light conditions. An investigation was carried out to determine whether signalling mediated by photoreceptors, sugars, cytokinin, and nitrate is involved in and necessary for proper photosynthetic acclimation. No evidence was found for a role for sugars, or for nitrate. The distribution of cytokinins in tobacco stands of contrasting density could be explained in part by irradiance-dependent delivery of cytokinins through the transpiration stream. Functional studies using a comprehensive selection of Arabidopsis mutants and transgenics showed that normal wild-type responses to partial shading were retained when signalling mediated by photoreceptors or cytokinins was disrupted. This indicates that these pathways probably operate in a redundant manner. However, the reduction of the chlorophyll a/b ratio in response to local shade was completely absent in the Arabidopsis Ws-2 accession mutated in PHYTOCHROME D and in the triple phyAphyCphyD mutant. Moreover, cytokinin receptor mutants also showed a reduced response, suggesting a previously unrecognized function of phyD and cytokinins
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