Master Operators Govern Multifractality in Percolation

Using renormalization group methods we study multifractality in percolation at the instance of noisy random resistor networks. We introduce the concept of master operators. The multifractal moments of the current distribution (which are proportional to the noise cumulants $C_R^{(l)} (x, x^\prime)$ of the resistance between two sites x and $x^\prime$ located on the same cluster) are related to such master operators. The scaling behavior of the multifractal moments is governed exclusively by the master operators, even though a myriad of servant operators is involved in the renormalization procedure. We calculate the family of multifractal exponents ${\psi_l}$ for the scaling behavior of the noise cumulants, $C_R^{(l)} (x, x^\prime) \sim | x - x^\prime |^{\psi_l /\nu}$, where $\nu$ is the correlation length exponent for percolation, to two-loop order.Comment: 6 page

Riding a Spiral Wave: Numerical Simulation of Spiral Waves in a Co-Moving Frame of Reference

We describe an approach to numerical simulation of spiral waves dynamics of large spatial extent, using small computational grids.Comment: 15 pages, 14 figures, as accepted by Phys Rev E 2010/03/2

Non-perturbative renormalisation using dimensional regularisation: applications to the ε expansion

We give a prescription for the one-loop renormalisation of the imaginary parts of vertex functions in gø4, which are generated when gR \u3c 0 is non-perturbative in ɛ. This fixed point determines the imaginary parts of the critical exponents which are generated when ɛ \u3c 0, and allows us to determine the high-order behaviour of the perturbation series in E for these exponents. The generalisation of these ideas to the O(n) symmetric g(ø2)2 model is also given

Logarithmic Corrections for Spin Glasses, Percolation and Lee-Yang Singularities in Six Dimensions

We study analytically the logarithmic corrections to the critical exponents of the critical behavior of correlation length, susceptibility and specific heat for the temperature and the finite-size scaling behavior, for a generic $\phi^3$ theory at its upper critical dimension (six). We have also computed the leading correction to scaling as a function of the lattice size. We distinguish the obtained formulas to the following special cases: percolation, Lee-Yang (LY) singularities and $m$-component spin glasses. We have compared our results for the Ising spin glass case with numerical simulations finding a very good agreement. Finally, and using the results obtained for the Lee-Yang singularities in six dimensions, we have computed the logarithmic corrections to the singular part of the free energy for lattice animals in eight dimensions.Comment: 18 pages. We have extended the computation to lattice animals in eight dimensions. To be published in Journal of Physics

Fertilidade do solo em sistemas agroflorestais agroecológicos no Cerrado brasileiro.

Dentre os sistemas produtivos que mais se adéquam a aplicação dos princípios agroecológicos estão os sistemas agroflorestais (SAF´s), que apresentam um componente arbóreo ou lenhoso e permitem o cultivo de plantas alimentícias ou para produção de energia em suas entrelinhas. O manejo do solo nesses sistemas pode ser feito com o plantio de adubos verdes, especialmente leguminosas, para suprir os nutrientes necessários às culturas, seja pela fixação biológica de nitrogênio, seja pela reciclagem de nutrientes presentes nas camadas mais profundas do solo. Este trabalho objetivou avaliar a fertilidade de um solo tropical e altamente intemperizado durante seis anos de condução de dois SAF´s, sendo um para segurança alimentar, em que foram cultivados feijão e milho, e outro para produção energética, onde foram cultivados girassol, gergelim e amendoim. Amostras de solo (0-0,20 m) coletadas no primeiro (condição inicial), no terceiro e no sexto anos foram analisadas para atributos químicos. Nos dois SAF´s, as combinações de adubos verdes e culturas principais e os arranjos arbóreos elevaram o teor de matéria orgânica e reduziram a acidez potencial em relação à condição inicial. No entanto, a reciclagem feita pelos adubos verdes não foi suficiente para a manutenção do teor dos macro e micronutrientes do solo, com exceção de Mg e K, demonstrando a necessidade de se associar a adubação verde com a aplicação de fertilizantes orgânicos ou organominerais, de forma a repor nutrientes ao solo, exportados pela colheita dos grãos das diferentes culturas.Congreso SEAE

Machine learning classification of breeding protocol descriptions from Canadian Holsteins.

Dairy farmers are motivated to ensure cows become pregnant in an optimal and timely manner. Although timed artificial insemination (TAI) is a successful management tool in dairy cattle, it masks an animal's innate fertility performance, likely reducing the accuracy of genetic evaluations for fertility traits. Therefore, separating fertility traits based on the recorded management technique involved in the breeding process or adding the breeding protocol as an effect to the model can be viable approaches to address the potential bias caused by such management decisions. Nevertheless, there is a lack of specificity and uniformity in the recording of breeding protocol descriptions by dairy farmers. Therefore, this study investigated the use of 8 supervised machine learning algorithms to classify 1,835 unique breeding protocol descriptions from 981 herds into the following 2 classes: TAI or other than TAI. Our results showed that models that used a stacking classifier algorithm had the highest Matthews correlation coefficient (0.94 ± 0.04, mean ± SD) and maximized precision and recall (F1-score = 0.96 ± 0.03) on test data. Nonetheless, their F1-scores on test data were not different from 5 out of the other 7 algorithms considered. Altogether, results presented herein suggest machine learning algorithms can be used to produce robust models that correctly identify TAI protocols from dairy cattle breeding records, thus opening the opportunity for unbiased genetic evaluation of animals based on their natural fertility

Exchange narrowing of NMR line shapes in randomly diluted magnetic systems

An analysis of 19F NMR linewidths in the randomly diluted magnetic system KMnxMg1-xF3 is presented. It is shown that good agreement with measured linewidths can be obtained if in the usual asymptotic spin-diffusion assumption for the spin autocorrelation function 〈Siα(τ)Siα(0)〉avατ-d(x)/2, d(x) is taken to be independent of x above the percolation concentration. Experimental results in the system KNixMg1-xF3 are also presented. These data exhibit striking differences with the behavior of isostructural KMnxMg1-xF3 whose origin is discussed

Doses de nitrogenio no crescimento e producao inicial do mamoeiro, sob gotejamento, no litoral piauiense.

Com objetivo de avaliar o efeito de doses de nitrogenio no crescimento e producao inicial do mamoeiro irrigado, instalou-se um experimento na estacao experimental da Embrapa Meio-Norte, em Parnaiba, PI, em solo pertencente a Unidade de Mapeamento Areias Quartzosas alicas e distroficas A fraco e moderado fase caatinga litoranea, relevo plano.bitstream/item/83331/1/CT970001.pd

Diluted Networks of Nonlinear Resistors and Fractal Dimensions of Percolation Clusters

We study random networks of nonlinear resistors, which obey a generalized Ohm's law, $V\sim I^r$. Our renormalized field theory, which thrives on an interpretation of the involved Feynman Diagrams as being resistor networks themselves, is presented in detail. By considering distinct values of the nonlinearity r, we calculate several fractal dimensions characterizing percolation clusters. For the dimension associated with the red bonds we show that $d_{\scriptsize red} = 1/\nu$ at least to order {\sl O} (\epsilon^4), with $\nu$ being the correlation length exponent, and $\epsilon = 6-d$, where d denotes the spatial dimension. This result agrees with a rigorous one by Coniglio. Our result for the chemical distance, d_{\scriptsize min} = 2 - \epsilon /6 - [ 937/588 + 45/49 (\ln 2 -9/10 \ln 3)] (\epsilon /6)^2 + {\sl O} (\epsilon^3) verifies a previous calculation by one of us. For the backbone dimension we find D_B = 2 + \epsilon /21 - 172 \epsilon^2 /9261 + 2 (- 74639 + 22680 \zeta (3))\epsilon^3 /4084101 + {\sl O} (\epsilon^4), where $\zeta (3) = 1.202057...$, in agreement to second order in $\epsilon$ with a two-loop calculation by Harris and Lubensky.Comment: 29 pages, 7 figure