16,133 research outputs found
Effects of Bulk Viscosity on Cosmological Evolution
The effect of bulk viscisity on the evolution of the homogeneous and
isotropic cosmological models is considered. Solutions are found, with a
barotropic equation of state, and a viscosity coefficient that is proportional
to a power of the energy density of the universe. For flat space, power law
expansions, related to extended inflation are found as well as exponential
solutions, related to old inflation; also a solution with expansion that is an
exponential of an exponential of the time is found.Comment: 8 pages, latex, no figure
Commensurate-Incommensurate Magnetic Phase Transition in Magnetoelectric Single Crystal LiNiPO
Neutron scattering studies of single-crystal LiNiPO reveal a spontaneous
first-order commensurate-incommensurate magnetic phase transition. Short- and
long-range incommensurate phases are intermediate between the high temperature
paramagnetic and the low temperature antiferromagnetic phases. The modulated
structure has a predominant antiferromagnetic component, giving rise to
satellite peaks in the vicinity of the fundamental antiferromagnetic Bragg
reflection, and a ferromagnetic component giving rise to peaks at small
momentum-transfers around the origin at . The wavelength of the
modulated magnetic structure varies continuously with temperature. It is argued
that the incommensurate short- and long-range phases are due to
spin-dimensionality crossover from a continuous to the discrete Ising state.
These observations explain the anomalous first-order transition seen in the
magnetoelectric effect of this system
Impact of noise on a dynamical system: prediction and uncertainties from a swarm-optimized neural network
In this study, an artificial neural network (ANN) based on particle swarm
optimization (PSO) was developed for the time series prediction. The hybrid
ANN+PSO algorithm was applied on Mackey--Glass chaotic time series in the
short-term . The performance prediction was evaluated and compared with
another studies available in the literature. Also, we presented properties of
the dynamical system via the study of chaotic behaviour obtained from the
predicted time series. Next, the hybrid ANN+PSO algorithm was complemented with
a Gaussian stochastic procedure (called {\it stochastic} hybrid ANN+PSO) in
order to obtain a new estimator of the predictions, which also allowed us to
compute uncertainties of predictions for noisy Mackey--Glass chaotic time
series. Thus, we studied the impact of noise for several cases with a white
noise level () from 0.01 to 0.1.Comment: 11 pages, 8 figure
Landscape features associated with the passive recovery of Mediterranean sclerophyllous woodlands of central Chile
Cooling Curve Analysis Method using a Simplified Energy Balance
In this work is described a new cooling curve analysis method focused on the experimental determination of the latent heat of phase changes and phase transformation kinetics.The method analyses the cooling process of a metallic sample, initially liquid that is contained into a cylindrical metallic mold, both of known weight, thermally isolated at its top and bottom. The method is based on a simplified energy balance associated with the experimental measurement of the temperature change of the sample during its cooling process. The method was applied experimentally to zinc and tin of commercial purity, initially liquids and contained into stainless steel molds in order to determine its ability to determine the latent heat of solidification. In order to validate the method, the obtained values of latent heat were compared with the values reported in thermochemical databases. The obtained results suggest that this method can be used to characterize the solidification of metals..Keywords: Solidification, Kinetics; Cooling curve analysis
Empirical evidence on the relationships between concentration and profitability in Latin American banking
There has been growth in globalization as a result of increased liberalization. This has also resulted in an increase in the role of financial institutions, such as banks. It is the purpose of this study to test Classenâs (2001) hypothesis that increase foreign bank presence has positive welfare implications and that the functioning of national banking markets are improved as a result. Using financial data for 2003 this paper will examine the influence of foreign bank entry on Latin American domestic markets.Latin American banking; Concentration and Profitability; Foreign Bank Influence
Discordant voting processes on finite graphs
We consider an asynchronous voting process on graphs which we call discordant voting, and which can be described as follows. Initially each vertex holds one of two opinions, red or blue say. Neighbouring vertices with different opinions interact pairwise. After an interaction both vertices have the same colour. The quantity of interest is T, the time to reach consensus, i.e. the number of interactions needed for all vertices have the same colour. An edge whose endpoint colours differ (i.e. one vertex is coloured red and the other one blue) is said to be discordant. A vertex is discordant if its is incident with a discordant edge. In discordant voting, all interactions are based on discordant edges. Because the voting process is asynchronous there are several ways to update the colours of the interacting vertices. Push: Pick a random discordant vertex and push its colour to a random discordant neighbour. Pull: Pick a random discordant vertex and pull the colour of a random discordant neighbour. Oblivious: Pick a random endpoint of a random discordant edge and push the colour to the other end point. We show that ET, the expected time to reach consensus, depends strongly on the underlying graph and the update rule. For connected graphs on n vertices, and an initial half red, half blue colouring the following hold. For oblivious voting, ET = n2/4 independent of the underlying graph. For the complete graph Kn, the push protocol has ET = =(n log n), whereas the pull protocol has ET = =(2n). For the cycle Cn all three protocols have ET = =(n2). For the star graph however, the pull protocol has ET = O(n2), whereas the push protocol is slower with ET = =(n2 log n). The wide variation in ET for the pull protocol is to be contrasted with the well known model of synchronous pull voting, for which ET = O(n) on many classes of expanders
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