25,888 research outputs found
Obtaining a class of Type N pure radiation metrics using invariant operators
We develop further the integration procedure in the generalised invariant
formalism, and demonstrate its efficiency by obtaining a class of Petrov type N
pure radiation metrics without any explicit integration, and with comparatively
little detailed calculations. The method is similar to the one exploited by
Edgar and Vickers when deriving the general conformally flat pure radiation
metric. A major addition to the technique is the introduction of non-intrinsic
elements in generalised invariant formalism, which can be exploited to keep
calculations manageable.Comment: This work was presented in July 2004, in the Gr17 meeting held in
Dublin-Irelan
An International Comparison of Productivity Change in Agriculture and the Economy as a Whole
A common and longstanding assumption in the economic growth literature has been that total factor productivity growth is lower in the agriculture sector than in the rest of the economy. Using a stochastic production frontier finite mixture model, labor productivity change is decomposed into catch-up, technological change and factor accumulation effects and stochastic shocks. This decomposition is investigated separately in the agriculture sector and the economy as a whole using a balanced panel data set of 45 countries in different development stages during the time period 1967-1992. The impact of labor productivity change components on the evolution of the cross-country counterfactual distribution of labor productivity is also analyzed. For the overall economy, the empirical results indicate that growth and the twin-peak distribution of labor productivity are driven by capital deepening. However, the results for the agriculture sector suggest that labor productivity distribution is brought by total factor productivity changes rather than factor accumulation. Furthermore, the agriculture sector exhibits reductions in capital per worker as well as stronger catch-up and technological change effects. Thus, growth of the rest of the economy appears to owe more to capital deepening and resource reallocation from agriculture than to faster productivity change.Agriculture, Labor Productivity Growth, Catch-Up, Total Factor Productivity, Factor Accumulation, Panel data, Stochastic Production Frontier, Finite Mixture Model.
Phase transition for the frog model
We study a system of simple random walks on graphs, known as frog model. This
model can be described as follows: There are active and sleeping particles
living on some graph G. Each active particle performs a simple random walk with
discrete time and at each moment it may disappear with probability 1-p. When an
active particle hits a sleeping particle, the latter becomes active. Phase
transition results and asymptotic values for critical parameters are presented
for Z^d and regular trees
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Algorithms for network piecewise-linear programs
In this paper a subarea of Piecewise-Linear Programming named network Piecewise-Linear Programming (NPLP) is discussed. Initially the problem formulation, main efinitins and related Concepts are presented. In the sequence of the paper, four specialized algorithms for NPLP, as well as the results of a preliminary computational study, are presented
A Brief Review on Syntheses, Structures and Applications of Nanoscrolls
Nanoscrolls are papyrus-like nanostructures which present unique properties
due to their open ended morphology. These properties can be exploited in a
plethora of technological applications, leading to the design of novel and
interesting devices. During the past decade, significant advances in the
synthesis and characterization of these structures have been made, but many
challenges still remain. In this mini review we provide an overview on their
history, experimental synthesis methods, basic properties and application
perspectives
Static and dynamic properties of vortices in anisotropic magnetic disks
We investigate the effect of the magnetic anisotropy () on the static
and dynamic properties of magnetic vortices in small disks. Our micromagnetic
calculations reveal that for a range of there is an enlargement of the
vortex core. We analyze the influence of on the dynamics of the vortex
core magnetization reversal under the excitation of a pulsed field. The
presence of , which leads to better resolved vortex structures, allows us
to discuss in more details the role played by the in-plane and perpendicular
components of the gyrotropic field during the vortex-antivortex nucleation and
annihilation.Comment: 4 pages, 4 figure
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