908 research outputs found
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 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
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