387 research outputs found
Zoneamento de riscos climáticos para a cultura do dendezeiro no Estado do Pará.
Este trabalho mostra os resultados preliminares do zoneamento de riscos climáticos para a cultura do dendezeiro no estado do Pará, maior produtor de óleo de palma do Brasil, onde se concentra mais de 80% da área plantada com dendezeiros no país. O estudo utilizou dois enfoques de zoneamento: o zoneamento agroclimático e o zoneamento de riscos climáticos. O zoneamento agroclimático constou de um refinamento de estudos anteriores para a definição das áreas com boa, moderada e restrita potencialidades para a cultura, utilizando informações de exigências de clima e de solo da cultura, e de dados climatológicos do estado. O zoneamento de riscos climáticos envolveu a identificação de zonas de riscos para as áreas, previamente, identificadas no zoneamento agroclimático. Essas áreas apresentam potencialidades boa e moderada para a cultura, e se concentram no pólo de produção de dendê no Pará. Usou-se modelo de balanço hídrico para período mensal e freqüência de 80% para efetuar simulações de balanço hídrico. Determinou-se níveis de riscos climáticos a partir de análise de déficits hídricos para a fase crítica da cultura com relação a deficiência de água, considerada como o período em que ocorre a diferenciação sexual do botão floral que influencia na quantidade de cachos. Os resultados obtidos foram espacializados utilizando-se o Sistema de Informações Geográficas. Os principais resultados obtidos foram: mapa de aptidão agroclimática do dendê para o estado do Pará, indicando as áreas classificadas como boa, moderada e restrita para a cultura, e a definição de quatro níveis de riscos climáticos no pólo dendezeiro: a) com leve ou nenhum risco climático; b) com pequeno risco climático; c) com moderado risco climático e d) com grande risco climático
Self-tuning to the Hopf bifurcation in fluctuating systems
The problem of self-tuning a system to the Hopf bifurcation in the presence
of noise and periodic external forcing is discussed. We find that the response
of the system has a non-monotonic dependence on the noise-strength, and
displays an amplified response which is more pronounced for weaker signals. The
observed effect is to be distinguished from stochastic resonance. For the
feedback we have studied, the unforced self-tuned Hopf oscillator in the
presence of fluctuations exhibits sharp peaks in its spectrum. The implications
of our general results are briefly discussed in the context of sound detection
by the inner ear.Comment: 37 pages, 7 figures (8 figure files
Inflationary Models Driven by Adiabatic Matter Creation
The flat inflationary dust universe with matter creation proposed by
Prigogine and coworkers is generalized and its dynamical properties are
reexamined. It is shown that the starting point of these models depends
critically on a dimensionless parameter , closely related to the matter
creation rate . For bigger or smaller than unity flat universes
can emerge, respectively, either like a Big-Bang FRW singularity or as a
Minkowski space-time at . The case corresponds to a de
Sitter-type solution, a fixed point in the phase diagram of the system,
supported by the matter creation process. The curvature effects have also been
investigated. The inflating de Sitter is a universal attractor for all
expanding solutions regardless of the initial conditions as well as of the
curvature parameter.Comment: 25 pages, 2 figures(available from the authors), uses LATE
Quantum cosmological perfect fluid models
Perfect fluid Friedmann-Robertson-Walker quantum cosmological models for an
arbitrary barotropic equation of state are constructed using
Schutz's variational formalism. In this approach the notion of time can be
recovered. By superposition of stationary states, finite-norm wave-packet
solutions to the Wheeler-DeWitt equation are found. The behaviour of the scale
factor is studied by applying the many-worlds and the ontological
interpretations of quantum mechanics. Singularity-free models are obtained for
.Comment: Latex file, 12 pages. New paragraphs in the Introduction and
Conclusion, and other minor corrections in the text and in some formulas.
Accepted for publication in General Relativity and Gravitatio
Zoneamento de risco climático para a cultura de dendezeiro - Estado do Pará: resultados preliminares.
bitstream/item/63499/1/Oriental-Doc92.PD
Graviton Production in Elliptical and Hyperbolic Universes
The problem of cosmological graviton creation for homogeneous and isotropic
universes with elliptical (\vae =+1) and hyperbolical (\vae =-1) geometries
is addressed. The gravitational wave equation is established for a
self-gravitating fluid satisfying the barotropic equation of state , which is the source of the Einstein's equations plus a cosmological
-term. The time dependent part of this equation is exactly solved in
terms of hypergeometric functions for any value of and spatial
curvature \vae. An expression representing an adiabatic vacuum state is then
obtained in terms of associated Legendre functions whenever , where n is an integer. This includes most
cases of physical interest such as . The mechanism of
graviton creation is reviewed and the Bogoliubov coefficients related to
transitions between arbitrary cosmic eras are also explicitly evaluated.Comment: 25 pages, uses REVTE
Mutations in protocadherin 15 and cadherin 23 affect tip links and mechanotransduction in mammalian sensory hair cells
Immunocytochemical studies have shown that protocadherin-15 (PCDH15) and cadherin-23 (CDH23) are associated with tip links, structures thought to gate the mechanotransducer channels of hair cells in the sensory epithelia of the inner ear. The present report describes functional and structural analyses of hair cells from Pcdh15av3J (av3J), Pcdh15av6J (av6J) and Cdh23v2J (v2J) mice. The av3J and v2J mice carry point mutations that are predicted to introduce premature stop codons in the transcripts for Pcdh15 and Cdh23, respectively, and av6J mice have an in-frame deletion predicted to remove most of the 9th cadherin ectodomain from PCDH15. Severe disruption of hair-bundle morphology is observed throughout the early-postnatal cochlea in av3J/av3J and v2J/v2J mice. In contrast, only mild-to-moderate bundle disruption is evident in the av6J/av6J mice. Hair cells from av3J/av3J mice are unaffected by aminoglycosides and fail to load with [3H]-gentamicin or FM1-43, compounds that permeate the hair cell's mechanotransducer channels. In contrast, hair cells from av6J/av6J mice load with both FM1-43 and [3H]-gentamicin, and are aminoglycoside sensitive. Transducer currents can be recorded from hair cells of all three mutants but are reduced in amplitude in all mutants and have abnormal directional sensitivity in the av3J/av3J and v2J/v2J mutants. Scanning electron microscopy of early postnatal cochlear hair cells reveals tip-link like links in av6J/av6J mice, substantially reduced numbers of links in the av3J/av3J mice and virtually none in the v2J/v2J mice. Analysis of mature vestibular hair bundles reveals an absence of tip links in the av3J/av3J and v2J/v2J mice and a reduction in av6J/av6J mice. These results therefore provide genetic evidence consistent with PCDH15 and CDH23 being part of the tip-link complex and necessary for normal mechanotransduction
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