Abstract This study examines the in vitro growth and ex vitro establishment of Brassavola tuberculata in relation to the micropropagation system and sucrose concentration employed in the in vitro culture. A completely randomized experimental design was utilized, employing a 2 x 5 factorial arrangement. The experimental period began with seedlings cultivated in vitro for 180 days, which were subsequently transferred to Murashige and Skoog culture media containing sucrose concentrations of 0, 15, 30, 45, or 60 g L-1. The cultures were subjected to two micropropagation systems: conventional and gas exchange. After 90 days of in vitro cultivation, the plants were evaluated, transplanted into a substrate, and placed in a screened nursery for ex vitro cultivation. After 300 days of ex vitro cultivation, the survival and initial characteristics of the plants were assessed. The micropropagation system allowing gas exchange and sucrose concentrations up to 30 g L-1 enhanced the shoot and root growth of in vitro propagated plants. No noticeable anatomical differences were observed after 90 days of in vitro culture among the different sucrose concentrations and micropropagation systems used. In the ex vitro establishment, irrespective of sucrose concentration, the micropropagation system facilitating gas exchange positively influenced all evaluated characteristics.

Resumo Objetivou-se com este trabalho avaliar o crescimento in vitro e estabelecimento ex vitro de Brassavola tuberculata em função do sistema de micropropagação e da concentração de sacarose utilizados no cultivo in vitro. Foi utilizado o delineamento inteiramente casualizado e os tratamentos arranjados em esquema fatorial 2 x 5. Para o início do período experimental, foram utilizadas plântulas cultivadas in vitro por 180 dias, sendo transferidas para meios de cultivo Murashige e Skoog contendo 0, 15, 30, 45 ou 60 g L-1 de sacarose, e as culturas submetidas a dois sistemas de micropropagação: convencional ou com troca gasosa. Após 90 dias de cultivo in vitro, as plantas foram avaliadas e na sequência plantadas em substrato e acondicionadas em viveiro telado para o cultivo ex vitro. Após 300 dias de cultivo ex vitro, as plantas foram avaliadas quanto à sobrevivência e às mesmas características iniciais. A utilização do sistema de micropropagação que permite trocas gasosas, em conjunto com concentrações de sacarose de até 30 g L-1, proporcionou aumento no crescimento de parte aérea e do sistema radicular das plantas propagadas in vitro. As diferentes concentrações de sacarose e os sistemas de micropropagação utilizados não apresentaram diferenças anatômicas perceptíveis aos 90 dias de cultivo in vitro. Já no estabelecimento ex vitro, independente da utilização de sacarose, o sistema de micropropagação que permite trocas gasosas influenciou positivamente todas as características avaliadas.

In this work, we present our preliminary ab initio results for the structural and electronic properties of both Si- and C-terminated SiC (100) surfaces in (2×1) and c(2×2) reconstruction patterns. Based on our results, we found that the Si-terminated surfaces are dominated by weak bonded Si-dimers, which are stabilized only at Si-rich conditions, leading to (3×2) or more complex reconstruction patterns, as verified experimentally. Also, our results show that the C-terminated surfaces is characterized by strong triply-bonded C-dimers, in a c(2×2) reconstruction pattern, which consists of C2 pairs over Si bridge sites, in agreement with experimental results.

In this work, we presented our preliminary ab initio results for the vibrational modes and the phonon frequencies of the SiC (100) surfaces. Our results are in good agreement with the available experimental data whenever this comparison is possible. For the accepted models of the C-terminated surfaces in the c(2×2) reconstruction, while in the bridge-dimer model there is an acetylene-like vibrational A1 mode at 2031 cm-1, which is infrared active, in the staggered-dimer model, there is a Füchs-Kliewer (FK) mode at 1328 cm-1, which is experimentally detected. For Si-terminated surfaces in the p(2×1) reconstruction, instead, no FK was obtained, in contradiction with the HREELS experimental results for the Si-terminated surfaces, but they are in consonance with the fact that this surface should be described by a (3×2) or more complex models.