7 research outputs found
Probabilistic ballistic annihilation with continuous velocity distributions
We investigate the problem of ballistically controlled reactions where
particles either annihilate upon collision with probability , or undergo an
elastic shock with probability . Restricting to homogeneous systems, we
provide in the scaling regime that emerges in the long time limit, analytical
expressions for the exponents describing the time decay of the density and the
root-mean-square velocity, as continuous functions of the probability and
of a parameter related to the dissipation of energy. We work at the level of
molecular chaos (non-linear Boltzmann equation), and using a systematic Sonine
polynomials expansion of the velocity distribution, we obtain in arbitrary
dimension the first non-Gaussian correction and the corresponding expressions
for the decay exponents. We implement Monte-Carlo simulations in two
dimensions, that are in excellent agreement with our analytical predictions.
For , numerical simulations lead to conjecture that unlike for pure
annihilation (), the velocity distribution becomes universal, i.e. does
not depend on the initial conditions.Comment: 10 pages, 9 eps figures include
Enfermidades digitais em vacas de aptidĂŁo leiteira: associação com mastite clĂnica, metrites e aspectos epidemiolĂłgicos Foot diseases in dairy cows: association with clinical mastitis, metrites and predisposed factors
Utilizaram-se nesse estudo 5300 vacas de aptidĂŁo leiteira, provenientes de 80 propriedades rurais, que adotavam manejo intensivo ou semi-extensivo, com o objetivo de averiguar a existĂȘncia de possĂvel associação entre enfermidades digitais, mastite clĂnica e/ou metrite e identificar possĂveis fatores de risco das enfermidades digitais. Em 325 (6,13%) vacas foram diagnosticados apenas enfermidades digitais, em 35 (0,66%) enfermidades digitais e mastite clĂnica, em 52 (0,98%) enfermidades digitais e metrite, em 28 (0,53%) enfermidades digitais, mastite clĂnica e metrite, em 128 (2,42%) apenas metrite, em 165 (3,11%) somente mastite clĂnica, e em 89 (1,68%) vacas metrite e mastite clĂnica. As mudanças bruscas na alimentação, o excesso de sujidades nas instalaçÔes, os pisos irregulares e abrasivos, a nĂŁo utilização ou uso incorreto de pedilĂșvio, a falta de casqueamento preventivo, a ausĂȘncia de quarentena, e a aquisição de animais sem a preocupação com o aspecto sanitĂĄrio foram considerados os fatores de risco de maior ocorrĂȘncia. Foi constatada diferença significativa entre a ocorrĂȘncia de enfermidades digitais, mastite clĂnica e metrite, alĂ©m de associação fraca entre tais enfermidades, concluindo-se que nĂŁo houve relação expressiva entre enfermidades podais, mastite clĂnica e metrite em vacas lactantes.<br>With the objective to investigate a possible association between foot diseases, clinical mastitis and/or metritis and predisposing factors for foot diseases, 5300 dairy cows from 80 intensive and semi-intensive farms were used. In 325 (6.13%) cows only foot disease was diagnosed, in 35 (0.66%) foot disease and clinical mastitis, in 52 (0.98%) foot disease and metritis, in 28 (0.53%) foot disease, clinical mastitis and metritis, in 128 (2.42%) only metritis, in 165 (3.11%) only clinical mastitis, and in 89 (1.68%) cows metritis and clinical mastitis. Rapid changes in the diet, high exposure time of hoof horn to slurry and wet conditions, concrete floors, use of footbaths, low frequency of claw trimming, irregular quarantine, and no attention to health aspects during acquisition of the animals were considered as major risk factors for the occurrence of those diseases. The McNemar test for dependent samples showed significant statistical differences between the occurrence of foot disease, clinical mastitis and metritis, in spite of the poor association between those diseases. It was concluded that there was no expressive relationship between foot diseases, clinical mastitis and metritis in lactent cows