The recent expansion of Pluto's atmosphere

Stellar occultations--the passing of a relatively nearby body in front of a background star--can be used to probe the atmosphere of the closer body with a spatial resolution of a few kilometres (ref. 1). Such observations can yield the scale height, temperature profile, and other information about the structure of the occulting atmosphere. Occultation data acquired for Pluto's atmosphere in 1988 revealed a nearly isothermal atmosphere above a radius of approximately 1,215 km. Below this level, the data could be interpreted as indicating either an extinction layer or the onset of a large thermal gradient, calling into question the fundamental structure of this atmosphere. Another question is to what extent Pluto's atmosphere might be collapsing as it recedes from the Sun (passing perihelion in 1989 in its 248-year orbital period), owing to the extreme sensitivity of the equilibrium surface pressure to the surface temperature. Here we report observations at a variety of visible and infrared wavelengths of an occultation of a star by Pluto in August 2002. These data reveal evidence for extinction in Pluto's atmosphere and show that it has indeed changed, having expanded rather than collapsed, since 1988.     

A bayesian approach to modelling stochastic cycles

This article deals with a fully Bayesian approach to describe the cyclical behaviour of a univariate time series. A damped sine wave where both the period and the damping factor are time varying is assumed as the underlying mathematical model for the cyclical component. The model is applied to two real data sets; the annual rainfall observations in Fortaleza, Brazil, and the annual Wolf sunspot numbers.     

Electrophoretic variation in esterases in 3 wild-type and respective mutant strains ofAspergillus flavus

Summary Wild-type strains and auxotrophic mutants ofAspergillus flavus, differing regarding aflatoxin production, were tested for esterases isozymes. Esterases variation was found in all strains used, and a possible correlation between the pattern of esterase bands and aflatoxin production is suggested.Acknowledgment. The authors are thankful to the National Council for the development of Science and Technology (CNPq) and Assistance to Research for São Paulo State (FAPESP) for financial assistance.     

Electron microscopy of thin sections of reticulocytes

Zusammenfassung Retikulozyten von Meerschweinchen, in denen Anämie durch Blutentzug hervorgerufen worden war, wurden in Dünnschnitten elektronenmikroskopisch untersucht. Dabei wurden dieselben filamentösen Körper mit charakteristischer Mitochondrienstruktur, die auch nach teilweiser Trocknung hämolysierter Ausstriche von Retikulozyten auftreten, gefunden. Diese Filamente formen die durch Vitalfärbung (Janusgrün B) dargestellte innere Struktur der Retikulozyten und besitzen Affinität zu den spezifischen Mitochondrienfarbstoffen. Auf Grund dieser Feststellungen wird die Natur der «substantia granulo-filamentosa» für mitochondrienartig und somit präexistent gehalten.

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This study has been aided by a grant from the Conselho Nacional de Pesquisas (Brazil).     

Ultrastructure of a mucous gland cell found in the tube feet of the starfishAsterina stellifera

Resumen Es describida la ultraestrutura de un segundo tipo de célula glandular mucosa que es encontrada en el pié ambulacrario de la estrella del marAsterina stellifera. Los gránulos secretores de esta célula tienen en su interior una ultraestrutura en forma de pequeños puntos densos y delicadas fibrillas, mas faltando una organizatión, principalmente comparada con la organizatión del otro tipo de granulo mucoso, también encontrado en el mismo pié ambulacrario.     

Electron diffraction and electron microscopy studies on the crystalline component of enamel of theOdontaspis (selachii)

Résumé L'auteur constate que dans la dent du Requin du genreOdontaspis l'ultrastucture de la substance qui recouvre la dentine est morphologiquement très semblable à celle de l'émail de la dent humaine. Par diffraction électronique le composant cristallin de l'émail du Requin a été déterminé comme étant del'apatite. Ces résultats montrent que le revêtement externe de la dent d'Odontaspis peut être considéré comme un véritable émail.     

Electrophoretic variation in esterases and phosphatases in eleven wild-type strains ofMetarrhizium anisopliae

Summary 11 wild-type strains ofMetarrhizium anisopliae were electrophoretically tested for phosphatases and esterases. Phosphatase was homogeneous for all strains. For esterase it was possible to distinguish 5 different patterns with which it is possible to characterize the strains analyzed.Acknowledgment. The authors are thankful to the Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq) and to the Empresa Brasileira de Pesquisa Agropecuária (EM-BRAPA) for financial assistance.     

The Amazon basin in transition

Agricultural expansion and climate variability have become important agents of disturbance in the Amazon basin. Recent studies have demonstrated considerable resilience of Amazonian forests to moderate annual drought, but they also show that interactions between deforestation, fire and drought potentially lead to losses of carbon storage and changes in regional precipitation patterns and river discharge. Although the basin-wide impacts of land use and drought may not yet surpass the magnitude of natural variability of hydrologic and biogeochemical cycles, there are some signs of a transition to a disturbance-dominated regime. These signs include changing energy and water cycles in the southern and eastern portions of the Amazon basin.