Nonlinear elastic polymers in random flow

Polymer stretching in random smooth flows is investigated within the framework of the FENE dumbbell model. The advecting flow is Gaussian and short-correlated in time. The stationary probability density function of polymer extension is derived exactly. The characteristic time needed for the system to attain the stationary regime is computed as a function of the Weissenberg number and the maximum length of polymers. The transient relaxation to the stationary regime is predicted to be exceptionally slow in the proximity of the coil-stretch transition.Comment: 10 pages, to be published in J. Fluid Mec

Renormalized transport of inertial particles in surface flows

Surface transport of inertial particles is investigated by means of the perturbative approach, introduced by Maxey (J. Fluid Mech. 174, 441 (1987)), which is valid in the case the deflections induced on the particle trajectories by the fluid flow can be considered small. We consider a class of compressible random velocity fields, in which the effect of recirculations is modelled by an oscillatory component in the Eulerian time correlation profile. The main issue we address here is whether fluid velocity fluctuations, in particular the effect of recirculation, may produce nontrivial corrections to the streaming particle velocity. Our result is that a small (large) degree of recirculation is associated with a decrease (increase) of streaming with respect to a quiescent fluid. The presence of this effect is confirmed numerically, away from the perturbative limit. Our approach also allows us to calculate the explicit expression for the eddy diffusivity, and to compare the efficiency of diffusive and ballistic transport.Comment: 18 pages, 13 figures, submitted to JF

The radio spectra of reddened 2MASS QSOs: evidence for young radio jets

Multifrequency radio continuum observations (1.4-22 GHz) of a sample of reddened QSOs are presented. We find a high incidence (13/16) of radio spectral properties, such as low frequency turnovers, high frequency spectral breaks or steep power-law slopes, similar to those observed in powerful compact steep spectrum (CSS) and gigahertz-peaked spectrum (GPS) sources. The radio data are consistent with relatively young radio jets with synchotron ages <1e6-1e7yr. This calculation is limited by the lack of high resolution (milli-arcsec) radio observations. For the one source in the sample that such data are available a much younger radio age is determined, <2e3yr, similar to those of GPS/CSS sources. These findings are consistent with claims that reddened QSOs are young systems captured at the first stages of the growth of their supermassive black holes. It also suggests that expanding radio lobes may be an important feedback mode at the early stages of the evolution of AGN.Comment: 9 pages, to appear in MNRA

The Macroeconomic Effects of Fiscal Policy in Portugal: a Bayesian SVAR Analysis

In the last twenty years Portugal struggled to keep public finances under control, notably in containing primary spending. We use a new quarterly dataset covering 1979:1-2007:4, and estimate a Bayesian Structural Autoregression model to analyze the macroeconomic effects of fiscal policy. The results show that positive government spending shocks, in general, have a negative effect on real GDP; lead to important “crowding-out” effects, by impacting negatively on private consumption and investment; and have a persistent and positive effect on the price level and the average cost of financing government debt. Positive government revenue shocks tend to have a negative impact on GDP; and lead to a fall in the price level. The evidence also shows the importance of explicitly considering the government debt dynamics in the model. Finally, a VAR counter-factual exercise confirms that unexpected positive government spending shocks lead to important “crowding-out” effects..B-SVAR, fiscal policy, debt dynamics, Portugal.

Assessing Long-Term Fiscal Developments: Evidence from Portugal

Drawing on quarterly data for Portugal, we use a Three-Stage Least Square method and a system of equations to recursively estimate two components of fiscal policy – responsiveness and persistence – and to infer about the sources of fiscal deterioration (improvement). The results suggest that: (i) government spending exhibits higher persistence than government revenue; and (ii) government revenue is more responsive to the business cycle than government spending.Fiscal deterioration; Portugal.

The Macroeconomic Effects of Fiscal Policy

We investigate the macroeconomic effects of fiscal policy using a Bayesian Structural Vector Autoregression approach. We build on a recursive identification scheme, but we: (i) include the feedback from government debt (ii); look at the impact on the composition of output; (iii) assess the effects on asset markets (via housing and stock prices); (iv) add the exchange rate; (v) assess potential interactions between fiscal and monetary policy; (vi) use quarterly data, particularly, fiscal data; and (vii) analyze empirical evidence from the U.S., the U.K., Germany, and Italy. The results show that government spending shocks, in general, have a small effect on GDP; lead to important “crowding-out” effects; have a varied impact on housing prices and generate a quick fall in stock prices; and lead to a depreciation of the real effective exchange rate. Government revenue shocks generate a small and positive effect on both housing prices and stock prices that later mean reverts; and lead to an appreciation of the real effective exchange rate. The empirical evidence also shows that it is important to explicitly consider the government debt dynamics in the model.fiscal policy; Bayesian Structural VAR; debt dynamics.

The Macroeconomic Effects of Fiscal Policy

We investigate the macroeconomic effects of fiscal policy using a Bayesian Structural Vector Autoregression approach. We build on a recursive identification scheme, but we: (i) include the feedback from government debt (ii); look at the impact on the composition of output; (iii) assess the effects on asset markets (via housing and stock prices); (iv) add the exchange rate; (v) assess potential interactions between fiscal and monetary policy; (vi) use quarterly data, particularly, fiscal data; and (vii) analyze empirical evidence from the U.S., the U.K., Germany, and Italy. The results show that government spending shocks, in general, have a small effect on GDP; lead to important “crowding-out” effects; have a varied impact on housing prices and generate a quick fall in stock prices; and lead to a depreciation of the real effective exchange rate. Government revenue shocks generate a small and positive effect on both housing prices and stock prices that later mean reverts; and lead to an appreciation of the real effective exchange rate. The empirical evidence also shows that it is important to explicitly consider the government debt dynamics in the model.fiscal policy, Bayesian Structural VAR, debt dynamics.

Consumption, Wealth, Stock and Government Bond Returns: International Evidence

In this paper, we show, from the consumer’s budget constraint, that the residuals of the trend relationship among consumption, aggregate wealth, and labour income should predict both stock returns and government bond yields. We use data for several OECD countries and find that when agents expect future stock returns to be higher, they will temporarily allow consumption to rise. Regarding government bond yields, when bonds are seen as a component of asset wealth, then investors react in the same way. If, however, the increase in the yields is perceived as signalling a future rise in taxes, then they will temporarily reduce their consumption.consumption, wealth, stock returns, bond returns.

Fiscal Policy, Housing and Stock Prices

This paper investigates the link between fiscal policy shocks and movements in asset markets using a Fully Simultaneous System approach in a Bayesian framework. Building on the works of Blanchard and Perotti (2002), Leeper and Zha (2003), and Sims and Zha (1999, 2006), the empirical evidence for the U.S., the U.K., Germany, and Italy shows that it is important to explicitly consider the government debt dynamics when assessing the macroeconomic effects of fiscal policy and its impact on asset markets. In addition, the results from a VAR counter-factual exercise suggest that: (i) fiscal policy shocks play a minor role in the asset markets of the U.S. and Germany; (ii) they substantially increase the variability of housing and stock prices in the U.K..; and (iii) government revenue shocks have apparently contributed to an increase of volatility in Italy.Bayesian Structural VAR; fiscal policy; housing prices; stock prices.

Consumption, Wealth, Stock and Government Bond Returns: International Evidence

In this paper, we show, from the consumer’s budget constraint, that the residuals of the trend relationship among consumption, aggregate wealth, and labour income should predict both stock returns and government bond yields. We use data for several OECD countries and find that when agents expect future stock returns to be higher, they will temporarily allow consumption to rise. Regarding government bond yields, when bonds are seen as a component of asset wealth, then investors react in the same way. If, however, the increase in the yields is perceived as signalling a future rise in taxes, then they will temporarily reduce their consumption.consumption, wealth, stock returns, bond returns.