279 research outputs found
Convergência para o Equilíbrio no Modelo Keynesiano: algumas considerações
Este trabalho faz, inicialmente, uma revisão do debate que surgiu após a publicação da Teoria Geral do Emprego, do Juro e da Moeda (TG), de Keynes, no que se refere à natureza da posição de equilíbrio assumida pela economia no longo prazo. Na sequência, são apresentados o modelo de Oreiro (1997) e algumas simulações computacionais, sendo incorporados na análise os argumentos apresentados no capítulo 19 da TG. O objetivo é retomar os argumentos de um dos principais debates da história do pensamento econômico, no intuito de demonstrar que a interpretação convencional (síntese neoclássica) é contestável. As conclusões caminham no sentido de mostrar que, quando são considerados na análise os argumentos apresentados por Keynes no referido capítulo da TG, o resultado da síntese neoclássica de convergência e estabilidade do equilíbrio com pleno emprego torna-se altamente questionável. Esse resultado é obtido por intermédio do desenvolvimento de uma estrutura analítica formal com auxílio de simulações computacionais.Síntese Neoclássica, Equilíbrio, Estabilidade, Emprego e Simulações.
EQUILÍBRIO COM PLENO EMPREGO E EQUILÍBRIO COM DESEMPREGO EM UM CONTEXTO DE PREÇOS E SALÁRIOS FLEXÍVEIS: o debate entre Keynes e os (neo) clássicos
O presente trabalho tem por objetivo retomar o debate entre Keynes e os (neo) clássicos sobre os determinantes da posição de equilíbrio de longo prazo da economia. Como mostrou Keynes na Teoria Geral, com base no principio da demanda efetiva, não existem forças endógenas capazes de gerar e manter a plena ocupação dos fatores sendo, portanto, o equilíbrio com capacidade ociosa (abaixo do pleno emprego) - de fato - a condição normal da economia capitalista. A reação do pensamento convencional, naquilo que ficou conhecido como síntese neoclássica, buscou demonstrar que as proposições fundamentais da economia clássica ainda poderiam ser recuperadas por intermédio de uma estrutura analítica Walrasiana. Mais especificamente, o que estes autores buscaram mostrar é que o modelo proposto pela macroeconomia keynesiana era válido somente no curto prazo, onde as flutuações econômicas eram explicadas, principalmente, pela rigidez de preços e de salários. Essa conclusão baseia-se principalmente sobre a hipótese da atuação do efeito riqueza real (efeito Pigou). Entretanto, esta hipótese é altamente contestável, uma vez que a deflação dos salários nominais também gera efeitos recessivos na economia, os quais, se suficientemente forte, podem neutralizar e até mesmo reverter o efeito riqueza real.Equilíbrio, Flexibilidade e Desemprego Involuntário
Study of sdO models. Pulsation Analysis
We have explored the possibility of driving pulsation modes in models of sdO
stars in which the effects of element diffusion, gravitational settling and
radiative levitation have been neglected so that the distribution of iron-peak
elements remains uniform throughout the evolution. The stability of these
models was determined using a non-adiabatic oscillations code. We analysed 27
sdO models from 16 different evolutionary sequences and discovered the first
ever sdO models capable of driving high-radial order g-modes. In one model, the
driving is by a classical kappa-mechanism due to the opacity bump from
iron-peak elements at temperature ~200,000 K. In a second model, the driving
result from the combined action of kappa-mechanisms operating in three distinct
regions of the star: (i) a carbon-oxygen partial ionization zone at temperature
~2 10^6 K, (ii) a deeper region at temperature ~2 10^7 K, which we attribute to
ionization of argon, and (iii) at the transition from radiative to conductive
opacity in the core of the star.Comment: 13 pages, 19 figures, accepted for publication in MNRAS, 2009
September 1
Mode identification for Balloon 090100001 using combined multicolour photometry and spectroscopy
In this paper, we show that method of mode identification using combined
multicolour photometry and spectroscopy can be successfully applied to the
pulsating subdwarf B star Balloon 090100001. The method constrains the
spherical degree, l.We confirm that the dominant mode is radial and we show
that for some other modes the method provides values of l consistent with the
observed rotationally split triplet. Moreover, we derive a radius variation of
1.7 per cent for the dominant mode. The identification opens the possibility
for constraining the internal structure of the star by means of seismic
methods.Comment: MNRAS, in press, already at the online-early stag
J08069+1527: A newly discovered high amplitude, hybrid subdwarf B pulsator
We present our discovery of a new hybrid pulsating subdwarf B star,
J08069+1527. The effective temperature and surface gravity of 28,500400\,K
and 5.370.04\,dex, respectively, place this object inside the instability
strip and also among other pulsating hot subdwarfs of a hybrid nature, right
next to another fascinating star: Balloon\,090100001. From this proximity, we
anticipated this star could pulsate in both high and low frequency modes.
Indeed, our analysis of photometric data confirmed our prediction. We detected
two peaks in the high frequency region and two other peaks at low frequencies.
In addition, the amplitude of the dominant mode is very high and comparable to
the dominant peaks in other hybrid subdwarf B stars. Since this star is bright,
we performed time-series low resolution spectroscopy. Despite a low
signal-to-noise (S/N) ratio, we were able to detect the main peak from these
data. All our results strongly indicate that J08069+1527 is a high amplitude
pulsating hot subdwarf B star of hybrid nature. By analogy to the other
pulsating sdB star, we judge that the dominant mode we detected here has radial
nature. Future stellar modeling should provide us with quite good constrains as
p- and g-modes presented in this star are driven in different parts of its
interior.Comment: 7 pages, 10 figures, accepted for publication in MNRA
Study of sdO models. Pulsation Analysis
We have explored the possibility of driving pulsation modes in models of sdO
stars in which the effects of element diffusion, gravitational settling and
radiative levitation have been neglected so that the distribution of iron-peak
elements remains uniform throughout the evolution. The stability of these
models was determined using a non-adiabatic oscillations code. We analysed 27
sdO models from 16 different evolutionary sequences and discovered the first
ever sdO models capable of driving high-radial order g-modes. In one model, the
driving is by a classical kappa-mechanism due to the opacity bump from
iron-peak elements at temperature ~200,000 K. In a second model, the driving
result from the combined action of kappa-mechanisms operating in three distinct
regions of the star: (i) a carbon-oxygen partial ionization zone at temperature
~2 10^6 K, (ii) a deeper region at temperature ~2 10^7 K, which we attribute to
ionization of argon, and (iii) at the transition from radiative to conductive
opacity in the core of the star.Comment: 13 pages, 19 figures, accepted for publication in MNRAS, 2009
September 1
A survey for pulsating subdwarf B stars with the Nordic Optical Telescope
A search programme for pulsating subdwarf B stars was conducted with the
Nordic Optical Telescope on La Palma over 59 nights between 1999 and 2009. The
purpose of the programme was to significantly extend the number of rapidly
pulsating sdB stars to better understand the properties of this new group of
variable compact stars. Candidates were selected initially from the HS and HE
surveys, but were supplemented with additional objects from other surveys.
Short sequences of time-series photometry were made on the candidates to
determine the presence of rapid pulsations. In total twenty new pulsators were
found in this survey, most of which have already been published and some
extensively studied. We present four new short period pulsators, bringing the
total of such pulsators up to 49. We also give limits on pulsation amplitudes
for 285 objects with no obvious periodic variations, summarise the results of
the survey, and provide improved physical parameters on the composite pulsators
for which only preliminary estimates were published earlier.Comment: 17 pages, accepted for publication in A&
The pulsating hot subdwarf Balloon 090100001: results of the 2005 multisite campaign
We present the results of a multisite photometric campaign on the pulsating
sdB star Balloon 090100001. The star is one of the two known hybrid hot
subdwarfs with both long- and short-period oscillations. The campaign involved
eight telescopes with three obtaining UBVR data, four B-band data, and one
Stromgren uvby photometry. The campaign covered 48 nights, providing a temporal
resolution of 0.36microHz with a detection threshold of about 0.2mmag in
B-filter data.
Balloon 090100001 has the richest pulsation spectrum of any known pulsating
subdwarf B star and our analysis detected 114 frequencies including 97
independent and 17 combination ones. The strongest mode (f_1) in the 2.8mHz
region is most likely radial while the remaining ones in this region form two
nearly symmetric multiplets: a triplet and quintuplet, attributed to
rotationally split \ell=1 and 2 modes, respectively. We find clear increases of
splitting in both multiplets between the 2004 and 2005 observing campaigns,
amounting to 15% on average. The observed splittings imply that the rotational
rate in Bal09 depends on stellar latitude and is the fastest on the equator. We
use a small grid of models to constrain the main mode (f_1), which most likely
represents the radial fundamental pulsation. The groups of p-mode frequencies
appear to lie in the vicinity of consecutive radial overtones, up to the third
one. Despite the large number of g-mode frequencies observed, we failed to
identify them, most likely because of the disruption of asymptotic behaviour by
mode trapping. The observed frequencies were not, however, fully exploited in
terms of seismic analysis which should be done in the future with a larger grid
of reliable evolutionary models of hot subdwarfs.Comment: accepted for publication in MNRA
GALEX J201337.6+092801: The lowest gravity subdwarf B pulsator
We present the recent discovery of a new subdwarf B variable (sdBV), with an
exceptionally low surface gravity. Our spectroscopy of J20136+0928 places it at
Teff = 32100 +/- 500, log(g) = 5.15 +/- 0.10, and log(He/H) = -2.8 +/- 0.1.
With a magnitude of B = 12.0, it is the second brightest V361 Hya star ever
found. Photometry from three different observatories reveals a temporal
spectrum with eleven clearly detected periods in the range 376 to 566 s, and at
least five more close to our detection limit. These periods are unusually long
for the V361 Hya class of short-period sdBV pulsators, but not unreasonable for
p- and g-modes close to the radial fundamental, given its low surface gravity.
Of the ~50 short period sdB pulsators known to date, only a single one has been
found to have comparable spectroscopic parameters to J20136+0928. This is the
enigmatic high-amplitude pulsator V338 Ser, and we conclude that J20136+0928 is
the second example of this rare subclass of sdB pulsators located well above
the canonical extreme horizontal branch in the HR diagram.Comment: 5 pages, accepted for publication in ApJ Letter
Optical Biomarkers for the Diagnosis of Osteoarthritis through Raman Spectroscopy: Radiological and Biochemical Validation Using Ex Vivo Human Cartilage Samples
[Abstract]
Osteoarthritis (OA) is the most common rheumatic disease, characterized by progressive articular cartilage degradation. Raman spectroscopy (RS) has been recently proposed as a label-free tool to detect molecular changes in musculoskeletal tissues. We used cartilage samples derived from human femoral heads to perform an ex vivo study of different Raman signals and ratios, related to major and minor molecular components of articular cartilage, hereby proposed as candidate optical biomarkers for OA. Validation was performed against the radiological Kellgren–Lawrence (K-L) grading system, as a gold standard, and cross-validated against sulfated glycosaminoglycans (sGAGs) and total collagens (Hyp) biochemical contents. Our results showed a significant decrease in sGAGs (SGAGs, A1063 cm−1/A1004 cm−1) and proteoglycans (PGs, A1375 cm−1/A1004 cm−1) and a significant increase in collagen disorganization (ColD/F, A1245 cm−1/A1270 cm−1), with OA severity. These were correlated with sGAGs or Hyp contents, respectively. Moreover, the SGAGs/HA ratio (A1063 cm−1/A960 cm−1), representing a functional matrix, rich in proteoglycans, to a mineralized matrix-hydroxyapatite (HA), was significantly lower in OA cartilage (K-L I vs. III–IV, p < 0.05), whilst the mineralized to collagenous matrix ratio (HA/Col, A960 cm−1/A920 cm−1) increased, being correlated with K-L. OA samples showed signs of tissue mineralization, supported by the presence of calcium crystals-related signals, such as phosphate, carbonate, and calcium pyrophosphate dihydrate (MGP, A960 cm−1/A1004 cm−1, MGC, A1070 cm−1/A1004 cm−1 and A1050 cm−1/A1004 cm−1). Finally, we observed an increase in lipids ratio (IL, A1450 cm−1/A1670 cm−1) with OA severity. As a conclusion, we have described the molecular fingerprint of hip cartilage, validating a panel of optical biomarkers and the potential of RS as a complementary diagnostic tool for OA.Xunta de Galicia; ED431E 2018/03Xunta de Galicia; IN607A2017/1
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