Pure iron grains are rare in the universe

The abundant forms in which the major elements in the universe exist have been determined from numerous astronomical observations and meteoritic analyses. Iron (Fe) is an exception, in that only depletion of gaseous Fe has been detected in the interstellar medium, suggesting that Fe is condensed into a solid, possibly the astronomically invisible metal. To determine the primary form of Fe, we replicated the formation of Fe grains in gaseous ejecta of evolved stars by means of microgravity experiments. We found that the sticking probability for formation of Fe grains is extremely small; only several atoms will stick per hundred thousand collisions, so that homogeneous nucleation of metallic Fe grains is highly ineffective, even in the Fe-rich ejecta of Type Ia supernovae. This implies that most Fe is locked up as grains of Fe compounds or as impurities accreted onto other grains in the interstellar medium

O livro eletrônico como marco evolutivo no contexto da história do livro

Monografia (graduação)—Universidade de Brasília, Faculdade de Ciência da Informação, 2011.Esta pesquisa tem por objetivo conhecer aspectos do livro eletrônico, trazendo abordagens referentes ao mesmo, enquanto marco evolutivo dentro do contexto da História do Livro. Assim, com base em uma pesquisa documental e exploratória, busca-se elucidar aspectos que são mais históricos do que propriamente tecnológicos, os quais incluem o livro eletrônico e seu impacto na sociedade, visando contribuir à caracterização do livro eletrônico como instrumento atual de disponibilização de informação, identificar tendências do livro eletrônico como fruto da trajetória ocorrida ao longo da História do Livro, e contribuir à reflexão sobre o futuro do livro impresso dentro de uma sociedade em constante evolução tecnológica, perpassando ainda por questões referentes ao direito autoral. Para tanto foram utilizadas as fontes de informações tradicionais, livros e periódicos, e ainda os blogs, por ser este um instrumento de comunicação amplamente utilizado para livre expressão de opiniões. Discute por fim a coexistência desses dois meios diante de especulações e embates da diversidade de suportes hoje existentes e dos gostos e preferências pessoais. _________________________________________________________________________ ABSTRACTThis research lens to examine in details electronic book aspects, with it self broach as a evolutionary mark in the context of the book history. Therefore, on the bases of one documentary mark in and exploratory research, it trys to elucidate aspects that are more historical than strictly technological, that includes the electronic book and its impact in the society, aiming to contribute to characterize the electronic book as a current instrument to make the information available, to identify the book electronic trends as a result of the progress along the book history and to help the reflection about the future of the printed book in a society that is in a constant technological changing, and some reasons about copyright . So it has been used traditional information sources: books, periodics, and blogs, because they are communication instruments hard used to the free expression of opinions. It discusses, finally, the coexistence of those two ways, among speculation and chars in the diversity of tastes and personal preferences

Sounding-rocket microgravity experiments on alumina dust

Alumina (Al2O3) is believed to be the first major condensate to form in the gas outflow from oxygen-rich evolved stars because of the refractoriness and that alpha-Al2O3. (corundum, most stable polymorph) is a potential origin of a 13 mu m feature that appears close to stars. However, no one has directly reproduced the 13 mu m feature experimentally, and it has remained as a noteworthy unidentified infrared band. Here, we report nucleation experiments on Al2O3 nanoparticles monitored by a specially designed infrared spectrometer in the microgravity environment of a sounding rocket. The conditions approximate to those around asymptotic giant branch (AGB) stars. The measured spectra of the nucleated Al2O3 show a sharp feature at a wavelength of 13.55 mu m and comparable in width to that observed near oxygen-rich AGB stars. Our finding that alpha-Al(2)O(3 )nucleates under certain condition provides a solid basis to elaborate condensation models of dust around oxygen-rich evolved stars