Cyclical Unemployment: Sectoral Shifts or Aggregate Disturbances?

Recent work by David Lilien has argued that the existence of a strong positive correlation between the dispersion of employment growth rates across sectors (G) and the unemployment rate implies that shifts in demand from some sectors to others are responsible for a substantial fraction of cyclical variation in unemployment. This paper demonstrates that, under certain empirically satisfied conditions, aggregate demand movements alone can produce a positive correlation between G and the unemployment rate. Two tests are developed which permit one to distinquish between a pure sectoral shift interpretation and a pure aggregate demand interpretation of this positive correlation. The finding that G and the volume of help wanted advertising are negatively related and the finding that G is directly associated with the change in unemployment rather than with the level of unemployment both support an aggregate demand interpretation. A proxy for sectoral shifts that is purged of the influence of aggregate demand is then developed. Models which allow sectoral shifts in the composition of demand and fluctuations in the aggregate level of demand to affect the unemployment rate independently are estimated using this proxy. The results support the view that pure sectoral shifts have not been an important source of cyclical fluctuations in unemployment.

Development of a magneforming process for the fabrication of thin-wall tungsten cylinders final report

Magneforming process - high energy rate metal forming technique for fabrication of thin wall tungsten cylinder

Cyclical Unemployment: Sectoral Shifts or Aggregate Disturbances?

Recent work by David Lilien has argued that the positive correlation between the dispersion of employment growth rates across sectors (a) and the unemployment rate implies that sectoral shifts in labor demand are responsible for a substantial fraction of cyclical variation in unemployment. This paper demonstrates that, under empirically satisfied conditions, traditional single-factor business-cycle models will produce a positive correlation between (sigma) and the unemployment rate. Information on the job vacancy rate permits one to distinguish between a pure sectoral shift and a pure aggregate demand interpretation of this positive correlation. The finding that a and the volume of help wanted advertising (a job vacancy proxy) are negatively related supports an aggregate demand interpretation.Economic

A IMPORTÂNCIA DA INTEGRAÇÃO REGIONAL E A QUESTÃO DAS DESIGUALDADES DO PROCESSO DE DESENVOLVIMENTO

O presente trabalho tem como objetivo debater a consolidação de Blocos Econômicos,especificamente do MERCOSUL. Neste contexto, propõe-se a abertura de nova frente dediscussão baseada na hipótese de o Brasil romper amarras do subdesenvolvimento. Explora-seinicialmente o tema de modelos alternativos de desenvolvimento, sob a ótica das Relações EconômicasInternacionais, nomeadamente, os Modelos cognominados Voltado para fora e Voltadopara dentro. Em seguida, procura-se explicitar formas de Relações Econômicas Internacionaisem seus efeitos sobre o Desenvolvimento, principalmente o chamado “livre-comércio” e a IntegraçãoRegional a um bloco econômico. Conclui-se que a integração regional é a opção mais indicada para os periféricos. Observa-se então que as possibilidades de desenvolvimento do capitalismo em país periférico são analisadas na literatura, com raras exceções, tomando como fundamentação a Teoria da Dependência e supondo que as economias periféricas constituem, em relação aos aspectos relevantes, um conjunto homogêneo. Discorda-se de aspecto dessa visão e ressalta-se a possibilidade de casos isolados de ruptura, podendo um país como o Brasil superar a condição de subdesenvolvido. Chama-se a atenção da importância da estruturação demodelo de integração regional para travessia deste tipo. Para tal, ressaltam-se as potencialidades e, mais especificamente, as condições e obstáculos para a consolidação do Mercosul

Supernova Shock Breakout Through a Wind

The breakout of a supernova shock wave through the progenitor star's outer envelope is expected to appear as an X-ray flash. However, if the supernova explodes inside an optically-thick wind, the breakout flash is delayed. We present a simple model for estimating the conditions at shock breakout in a wind based on the general observable quantities in the X-ray flash lightcurve: the total energy E_X, and the diffusion time after the peak, t_diff. We base the derivation on the self-similar solution for the forward-reverse shock structure expected for an ejecta plowing through a pre-existing wind at large distances from the progenitor's surface. We find simple quantitative relations for the shock radius and velocity at breakout. By relating the ejecta density profile to the pre-explosion structure of the progenitor, the model can also be extended to constrain the combination of explosion energy and ejecta mass. For the observed case of XRO08109/SN2008D, our model provides reasonable constraints on the breakout radius, explosion energy, and ejecta mass, and predicts a high shock velocity which naturally accounts for the observed non-thermal spectrum.Comment: Accepted for publication in MNRAS (v3: minor changes in the discussion of XRO08109/SN2008D, conclusions unchanged

Can long-term periodic variability and jet helicity in 3C 120 be explained by jet precession?

Optical variability of 3C 120 is discussed in the framework of jet precession. Specifically, we assume that the observed long-term periodic variability is produced by the emission from an underlying jet with a time-dependent boosting factor driven by precession. The differences in the apparent velocities of the different superluminal components in the milliarcsecond jet can also be explained by the precession model as being related to changes in the viewing angle. The evolution of the jet components has been used to determine the parameters of the precession model, which also reproduce the helical structure seen at large scales. Among the possible mechanisms that could produce jet precession, we consider that 3C 120 harbours a super-massive black hole binary system in its nuclear region and that torques induced by misalignment between the accretion disc and the orbital plane of the secondary black hole are responsible for this precession; we estimated upper and lower limits for the black holes masses and their mean separation.Comment: 10 pages, 4 figures, accepted for publication in MNRA

Precessing microblazars and unidentified gamma-ray sources

The recent discovery by Paredes et al. (2000) of a persistent microquasar that is positionally coincident with an unidentified gamma-ray source has open the possibility that other sources in the Third EGRET Catalog could be interpreted as microquasars as well. In this letter we show that some variable unidentified EGRET sources in the galactic plane could be produced by faint, otherwise undetected microquasars with precessing jets. When the jet points towards the observer, gamma-ray emission resulting from upscattered stellar photons could be detectable yielding a variable source with weak or undetectable counterpart at longer wavelengths. Strategies for detecting these``microblazars'' with forthcoming satellites are briefly discussed.Comment: 4 pages, 3 figures, Astronomy & Astrophysics Letters in press, typing errors correctio

Photometric and dynamic evolution of an isolated disc galaxy simulation

We present a detailed analysis of the evolution of a simulated isolated disc galaxy. The simulation includes stars, gas, star formation and simple chemical yields. Stellar particles are split in two populations: the old one is present at the beginning of the simulation and is calibrated according to various ages and metallicities; the new population borns in the course of the simulation and inherits the metallicity of the gas particles. The results have been calibrated in four wavebands with the spectro-photometric evolutionary model GISSEL2000 (Bruzual & Charlot 1993). Dust extinction has also been taken into account. A rest-frame morphological and bidimensional photometric analysis has been performed on simulated images, with the same tools as for observations. The effects of the stellar bar formation and the linked star formation episode on the global properties of the galaxy (mass and luminosity distribution, colours, isophotal radii) have been analysed. In particular, we have disentangled the effects of stellar evolution from dynamic evolution to explain the cause of the isophotal radii variations. We show that the dynamic properties (e.g. mass) of the area enclosed by any isophotal radius depends on the waveband and on the level of star formation activity. It is also shown that the bar isophotes remain thinner than mass isodensities a long time (> 0.7 Gyr) after the maximum of star formation rate. We show that bar ellipticity is very wavelength dependent as suggested by real observations. Effects of dust extinction on photometric and morphological measurements are systematically quantified.Comment: 14 pages, 16 figures (13 in eps, 3 in jpg format). Accepted for publication in A&

Future Evolution of the Intergalactic Medium in a Universe Dominated by a Cosmological Constant

We simulate the evolution of the intergalactic medium (IGM) in a universe dominated by a cosmological constant. We find that within a few Hubble times from the present epoch, the baryons will have two primary phases: one phase composed of low-density, low-temperature, diffuse, ionized gas which cools exponentially with cosmic time due to adiabatic expansion, and a second phase of high-density, high-temperature gas in virialized dark matter halos which cools much more slowly by atomic processes. The mass fraction of gas in halos converges to ~40% at late times, about twice its calculated value at the present epoch. We find that in a few Hubble times, the large scale filaments in the present-day IGM will rarefy and fade away into the low-temperature IGM, and only islands of virialized gas will maintain their physical structure. We do not find evidence for fragmentation of the diffuse IGM at later times. More than 99% of the gas mass will maintain a steady ionization fraction above 80% within a few Hubble times. The diffuse IGM will get extremely cold and dilute but remain highly ionized, as its recombination time will dramatically exceed the age of the universe.Comment: 22 pages, 10 figures. Accepted to New Astronomy. Movies and a higher resolution version of the paper are available at http://cfa-www.harvard.edu/~knagamine/FutureIG