A quantum-like description of the planetary systems

The Titius-Bode law for planetary distances is reviewed. A model describing the basic features of this rule in the "quantum-like" language of a wave equation is proposed. Some considerations about the 't Hooft idea on the quantum behaviour of deterministic systems with dissipation are discussed.Comment: LaTex file, 17 pages, no figures. Version published in Foundations of Physics, August 200

Nonlinear Outcome of Gravitational Instability in Cooling, Gaseous Disks

Thin, Keplerian accretion disks generically become gravitationally unstable at large radius. I investigate the nonlinear outcome of such instability in cool disks using razor-thin, local, numerical models. Cooling, characterized by a constant cooling time t_c, drives the instability. I show analytically that, if the disk can reach a steady state in which heating by dissipation of turbulence balances cooling, then the dimensionless angular momentum flux density \alpha = ((9/4) \gamma (\gamma-1) \Omega t_c)^{-1}. Numerical experiments show that: (1) if t_c \gtrsim 3\Omega^{-1} then the disk reaches a steady, gravito-turbulent state in which Q \sim 1 and cooling is balanced by heating due to dissipation of turbulence; (2) if t_c \lesssim 3\Omega^{-1}, then the disk fragments, possibly forming planets or stars; (3) in a steady, gravito-turbulent state, surface density structures have a characteristic physical scale \sim 64 G \Sigma/\Omega^2 that is independent of the size of the computational domain.Comment: 16 pages, 11 figures, aastex 5.0, to appear in Ap

Founders, Feminists, and a Fascist -- Some Notable Women in the Missouri Section of the MAA

In the history of the Missouri Section of the MAA, some of the more interesting people who influenced the growth and development of the section through the years were and are women. In this chapter, we discuss the contributions of a few (certainly not all) of these women to the Missouri Section and mathematics as a whole, including Emily Kathryn Wyant (founder of KME), Margaret F. Willerding (who dealt with sexism in the 1940s), Maria Castellani (an official in Mussolini’s Italy before coming to America), and T. Christine Stevens (co-founder of Project NExT). Without them, and others like them, both mathematics and the Missouri Section of the MAA would be poorer

Antagonismo de isolados de Trichoderma contra fungos fitopatogênicos habitantes do solo.

Para o diminuir os prejuízos na produção de hortaliças causados por patógenos habitantes do solo, uma das alternativas é o controle biológico. Este trabalho teve como objetivo avaliar o antagonismo in vitro de seis isolados amazônicos de Trichoderma spp. provenientes da coleção do INPA que foram avaliados em experimentos anteriores como controladores da queima-da-saia em alface (Rhizoctonia solani) e de podridão-de-Sclerotium (Sclerotium rolfsii) em pimentão e tomate

Seleção de isolados de Trichoderma spp. para controle biológico de Sclerotium rolfsii em tomateiros.

Doenças causadas por patógenos habitantes do solo são de difícil controle e causam sérios prejuízos na produção de espécies olerícolas no Amazonas. A pesquisa objetiva avaliar seis isolados amazônicos de Trichoderma spp. que mostraram potencial em experimentos anteriores no controle de podridão-de-Sclerotium (Sclerotium rolfsii) em tomateiro (Solanum lycopersicum)