Electrical and thermal transport properties in high T_c superconductors : effects of a magnetic field

Experimental studies of the electric and heat currents in the normal, superconducting and mixed states of high T$_c$ superconductors (HTcS) lead to characterization, complementary to data obtained from equilibrium property based techniques. A magnetic field superimposed on the superconducting sample generates {\it magneto-transport phenomena}, from which an excess electrical resistivity, an excess thermoelectric power, the Hall or the Nernst effect. Different behavioral effects allow one to distinguish various dissipation mechanisms, like quasi particle scattering, vortex motion dissipation and superconductivity fluctuations, in particular when the Corbino geometry is used. Moreover bulk measurements of the thermal conductivity and the electrothermal conductivity in a magnetic field give us sure indications of the order parameter symmetry. The location of the mixed state phase transition lines in the technological phase diagram of HTcS are briefly pointed out through precise measurements performed over broad temperature and magnetic field ranges. The results are mainly reviewed with the aim of defining further investigation lines.Comment: 9 pages, no figures; to appear in Physica

Monetary Union in West Africa and Asymmetric Shocks: A Dynamic Structural Factor Model

The Ghana cocoa market has been extensively liberalised over the period since the mid 1980s. Three issues have been prominent in microeconomic research on the effects of liberalisation on agriculture. The first has been the size of any supply response, the second has been the effect on producers of reduced subsidies on inputs, and the third whether innovation has occurred. In this paper we investigate these issues by estimating a production function for cocoa in Ghana drawing on two household surveys covering the period from 1991 to 1998. The estimated production function allows identifying the factors underlying the change in output. The analysis of the micro data shows that the increase in household output has been very modest at 6 per cent. While the effect of liberalisation has been to raise the price of inputs we find that the contribution of such inputs to cocoa production has increased both relative to land and, very substantially, relative to labour. The ratio of both land and nonlabour inputs to labour rose implying a rise in labour productivity of 39 while land productivity was unchanged. We find no evidence that reforms have led to innovation in techniques which raise total factor productivity. Possible reasons for these outcomes are suggested.

Spatial Propagation of Macroeconomic Shocks in Europe

This paper develops a Spatial Vector Auto-Regressive (SpVAR) model that takes into account both the time and the spatial dimensions of economic shocks. We apply this framework to analyze the propagation through space and time of macroeconomic (inflation, output gap and interest rate) shocks in Europe. The empirical analysis identifies an economically and statistically significant spatial component in the transmission of macroeconomic shocks in Europe.Macroeconomics, Spatial Models, VAR

Monetary Union in West Africa and Asymmetric Shocks: a Dynamic Structural Factor Model

We analyse the costs of a monetary union in West Africa by means of asymmetric aggregate demand and aggregate supply shocks. Previous studies have estimated the shocks with the VAR model. We discuss the limitations of this approach and apply a new technique based on the dynamic factor model. The results suggest the presence of economic costs for a monetary union in West Africa because aggregate supply shocks are poorly correlated or asymmetric across these countries. Aggregate demand shocks are more correlated between West African countries.

Identification of macroeconomic factors in large panels

This paper presents a dynamic factor model in which the extracted factors and shocks are given a clear economic interpretation. The economic interpretation of the factors is obtained by means of a set of over-identifying loading restrictions, while the structural shocks are estimated following standard practices in the SVAR literature. Estimators based on the EM algorithm are developped. We apply this framework to a large panel of US monthly macroeconomic series. In particular, we identify nine macroeconomic factors and discuss the economic impact of monetary policy stocks. The results are theoretically plausible and in line with other findings in the literature. The first part of this paper uses quantitative methods to assess the success of party affiliation, personal interests and the economic profile of the constituencies in predicting voting behavior. Thanks to the detailed censuses of 1846 on agriculture, industry and population, it is possible to typify the economic make-up of the electoral districts in much more detail than in the British case. However, the analysis of roll-call voting proves that party affiliation and personal and constituency economic interests are insufficient to explain the shift towards free trade. The second part of the paper then discusses the role played by political strategy and ideas in the liberalization of corn tariffs, using a qualitative analysis of the debates on tariff policy. The large number of votes over a forty year period allows us to document the relationship between ideas and interests in a new way.Monetary policy, Business Cycles, Factor Models, EM Algorithm.

Identification of macroeconomic factors in large panels.

This paper presents a dynamic factor model in which the extracted factors and shocks are given a clear economic interpretation. The economic interpretation of the factors is obtained by means of a set of overidentifying loading restrictions, while the structural shocks are estimated following standard practices in the SVAR literature. Estimators based on the EM algorithm are developped. We apply this framework to a large panel of US monthly macroeconomic series. In particular, we identify nine macroeconomic factors and discuss the economic impact of monetary policy stocks. The results are theoretically plausible and in line with other findings in the literature.

Identification of Macroeconomic Factors in Large Panels

This paper presents a dynamic factor model where the extracted factors and shocks are given a clear economic interpretation. The economic interpretation of the factors is obtained by means of a set of over-identifying loading restrictions, while the structural shocks are estimated following standard practices in the SVAR literature. Estimators based on the EM algorithm are developed. We apply this framework to a large panel of US monthly macroeconomic series. In particular, we identify five macroeconomic factors and discuss the economic impact of monetary policy shocks. The results are theoretically more plausible than those implied by standard SVAR models and indicate a significant role for monetary policy shocks in macroeconomic dynamics.Monetary policy, Business Cycles, Factor Models, EM Algorithm.

Spatial propagation of macroeconomic shocks in Europe

This paper develops a Spatial Vector Auto-Regressive (SpVAR) model that takes into account both the time and the spatial dimensions of economic shocks. We apply this framework to analyze the propagation through space and time of macroeconomic (inflation, output gap and interest rate) shocks in Europe. The empirical analysis identifies an economically and statistically significant spatial component in the transmission of macroeconomic shocks in Europe.Macroeconomics, Spatial Models, VAR

Aging process of electrical contacts in granular matter

The electrical resistance decay of a metallic granular packing has been measured as a function of time. This measurement gives information about the size of the conducting cluster formed by the well connected grains. Several regimes have been encountered. Chronologically, the first one concerns the growth of the conducting cluster and is identified to belong to diffusion processes through a stretched exponential behavior. The relaxation time is found to be simply related to the initial injected power. This regime is followed by a reorganisation process due to thermal dilatation. For the long term behavior of the decay, an aging process occurs and enhances the electrical contacts between grains through microsoldering.Comment: 11 pages, 4 figure