Topological Susceptibility and Zero Mode Size in Lattice QCD

We use the overlap formalism to define a topological index on the lattice. We study the spectral flow of the hermitian Wilson-Dirac operator and identify zero crossings with topological objects. We determine the topological susceptibility and zero mode size distribution, and we comment on the stability of our results.Comment: 3 pages latex with 2 postscript figures. Talk presented at LATTICE98(confine

Dynamic mechanical response of polymer networks

The dynamic-mechanical response of flexible polymer networks is studied in the framework of tube model, in the limit of small affine deformations, using the approach based on Rayleighian dissipation function. The dynamic complex modulus G* is calculated from the analysis of a network strand relaxation to the new equilibrium conformation around the distorted primitive path. Chain equilibration is achieved via a sliding motion of polymer segments along the tube, eliminating the inhomogeneity of the polymer density caused by the deformation. The characteristic relaxation time of this motion separates the low-frequency limit of the complex modulus from the high-frequency one, where the main role is played by chain entanglements, analogous to the rubber plateau in melts. The dependence of storage and loss moduli, G' and G'', on crosslink and entanglement densities gives an interpolation between polymer melts and crosslinked networks. We discuss the experimental implications of the rather short relaxation time and the slow square-root variation of the moduli and the loss factor tan at higher frequencies.Comment: Journal of Chemical Physics (Oct-2000); Lates, 4 EPS figures include

Active actuator fault-tolerant control of a wind turbine benchmark model

This paper describes the design of an active fault-tolerant control scheme that is applied to the actuator of a wind turbine benchmark. The methodology is based on adaptive filters obtained via the nonlinear geometric approach, which allows to obtain interesting decoupling property with respect to uncertainty affecting the wind turbine system. The controller accommodation scheme exploits the on-line estimate of the actuator fault signal generated by the adaptive filters. The nonlinearity of the wind turbine model is described by the mapping to the power conversion ratio from tip-speed ratio and blade pitch angles. This mapping represents the aerodynamic uncertainty, and usually is not known in analytical form, but in general represented by approximated two-dimensional maps (i.e. look-up tables). Therefore, this paper suggests a scheme to estimate this power conversion ratio in an analytical form by means of a two-dimensional polynomial, which is subsequently used for designing the active fault-tolerant control scheme. The wind turbine power generating unit of a grid is considered as a benchmark to show the design procedure, including the aspects of the nonlinear disturbance decoupling method, as well as the viability of the proposed approach. Extensive simulations of the benchmark process are practical tools for assessing experimentally the features of the developed actuator fault-tolerant control scheme, in the presence of modelling and measurement errors. Comparisons with different fault-tolerant schemes serve to highlight the advantages and drawbacks of the proposed methodology

The first bent double lobe radio source in a known cluster filament: Constraints on the intra-filament medium

We announce the first discovery of a bent double lobe radio source (DLRS) in a known cluster filament. The bent DLRS is found at a distance of 3.4 Mpc from the center of the rich galaxy cluster, Abell~1763. We derive a bend angle alpha=25deg, and infer that the source is most likely seen at a viewing angle of Phi=10deg. From measuring the flux in the jet between the core and further lobe and assuming a spectral index of 1, we calculate the minimum pressure in the jet, (8.0+-3.2)x10^-13 dyn/cm^2, and derive constraints on the intra-filament medium (IFM) assuming the bend of the jet is due to ram pressure. We constrain the IFM to be between (1-20)x10^-29 gm/cm^3. This is consistent with recent direct probes of the IFM and theoretical models. These observations justify future searches for bent double lobe radio sources located several Mpc from cluster cores, as they may be good markers of super cluster filaments.Comment: 13 pages, 4 figures, accepted in ApJ Letter

A comprehensive, multi-process box-model approach to glacial-interglacial carbon cycling

The canonical question of which physical, chemical or biological mechanisms were responsible for oceanic uptake of atmospheric CO2 during the last glacial is yet unanswered. Insight from paleo proxies has led to a multitude of hypotheses but none so far have been convincingly supported in three dimensional numerical modelling experiments. The processes that influence the CO2 uptake and export production are inter-related and too complex to solve conceptually while complex numerical models are time consuming and expensive to run which severely limits the combinations of mechanisms that can be explored. Instead, an intermediate inverse box model approach is used here in which the whole parameter space is explored. The glacial circulation and biological production states are derived from these using proxies of glacial export production and the need to draw down CO2 into the ocean. We find that circulation patterns which explain glacial observations include reduced Antarctic Bottom Water formation and high latitude mixing and to a lesser extent reduced equatorial upwelling. The proposed mechanism of CO2 uptake by an increase of eddies in the Southern Ocean, leading to a reduced residual circulation, is not supported. Regarding biological mechanisms, an increase in the nutrient utilization in either the equatorial regions or the northern polar latitudes can reduce atmospheric CO2 and satisfy proxies of glacial export production. Consistent with previous studies, CO2 is drawn down more easily through increased productivity in the Antarctic region than the sub-Antarctic, but that violates observations of lower export production there

Stock Market Cycles, Financial Liberalization and Volatility

In this paper we analyze the behavior of stock markets in six emerging countries. More specifically, we describe the bull and bear cycles of four Latin American and two Asian countries, comparing their characteristics during both phases and the degree of concordance of bullish periods. We divide our sample in two subperiods in order to account for differences induced by the financial liberalization processes that these countries went through in the early 1990's. We find that cycles in emerging countries tend to have shorter duration and larger amplitude and volatility than in developed countries. However, after financial liberalization Latin American stock markets have behaved more similarly to stock markets in developed countries whereas Asian countries have become more dissimilar. Concordance of cycles across markets has increased significantly over time, especially for Latin American countries after liberalization.