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Reatividade de materiais de moldagem na fundição de precisão de titânio
(Universidade Federal de São Carlos, 2009-04-13) Oliveira, Diego Pedreira de; Bolfarini, Claudemiro; https://lattes.cnpq.br/9231627080617037; https://lattes.cnpq.br/8388790875028551
Investment casting of Titanium parts free of defects is very difficult owing to the reactivity of this element in the liquid state .The objective of this study was to evaluate the reactivity of titanium with refractory oxides of high thermodynamic stability, such as yttria and alumina. Centrifugal castings of small parts were carried out by melting the metal in an yttria coated crucible and pouring the liquid into molds coated with a mixture of yttrium and aluminum oxides. As binder for the powders were added colloidal suspensions of silica, alumina, yttria or zirconium acetate. Only the silica and alumina colloidal bonded the moulds with useful mechanical strength allowing the centrifugal casting trials. Both, yttria colloidal and zirconium acetate were excluded of the trials. By analyzing the hardness profile it could be noted that a similar curve was obtained for different moulds (oxides plus binder) related to the hardened layer thickness. However, the molds using a higher thermodynamic stability combination of binder and oxides presented lower Vicker values. The pair Yttria/Alumina colloidal induced less than 350 Vickers and Alumina/Alumina colloidal less than 720 Vickers on the surface of titanium as cast, for instance. Finally, a mathematical simulation of the process was proposed and it could be well adjusted and compared to the experimental graphics.
Frugivoria por aves e fenologia em Miconia albicans e Miconia ligustroides (Melastomataceae), em fragmento de cerrado na região de São Carlos, SP, Brasil
(Universidade Federal de São Carlos, 2009-04-13) Souza, Natália Allenspach de; Dias Filho, Manoel Martins; https://lattes.cnpq.br/1346547036069954; https://lattes.cnpq.br/0494259674341420
The present study had as objective to characterize the avian guild that consumes Miconia albicans and Miconia ligustroides fruits and also to describe the fenology of these plants. The study was carried out in a 124.68 ha fragment of cerrado vegetation, located in the Universidade Federal de São Carlos, campus São Carlos (21°58´ S, 47° 52´ W), São Paulo state, Brazil. Between March 2008 and February 2009, 30 plants of each species, random selected, were accompanied every 2 weeks and the number of floral buds, flowers, fruits and the percentage of new leaves were registered. During the fruiting periods, 96 hours of focal tree observations were made for each vegetal species, when the visitant birds, time and duration of visits, number of consumed fruits and the treatment given to the fruits were registered. M. ligustroides fruits were given to captive birds, to assess retention time of the seeds in their digestive tract. M. albicans fruited between October and January, coinciding with the wet season. During this period, 212 visits with fruit consumption were observed, performed by 19 bird species from 9 families. Species of the family Emberizidae were responsible for the majority of visits (34.9%), but the treatment given to the fruits allows to infer they are probable seed predators. Mimus saturninus and Patagioenas picazuro consumed the largest parcel of fruits (respectively 23.34 and 19.27%). M. ligustroides fruited between March and June, in the transition between wet and dry seasons. 101 visits performed by 15 bird species from 6 families were observed. Species of genera Elaenia performed the majority of visits (34.65%), followed by Tangara cayana (12.87%) and Schistochlamys ruficapillus (10.89%). Family Thraupidae species were, together, the most representative in number of visits and fruit consumption. Average duration of visits for each bird species was always less than 3 minutes, lower even than the smallest retention time observed at the captive birds experiment (Pitangus sulphuratus: 4.98 ± 1.53 minutes). Adding the fact that birds consumed the whole fruit in all observations made at M. ligustroides trees, it is posible that the observed birds are potential seed dispersers of this plant. M. albicans and M. ligustroides produce a large amount of small fruits with many diminute seeds. Their fruits are consumed by many bird species with generalist diets. Therefore, both elastomataceas utilize an opportunistic frugivore bird dispersion strategy. These data show that both species may be usefull in conservation programs for recuperation of degraded cerrado areas, but future studies are necessary to verify the dispersive potential of the birds here registered, just as to know the germination and seedling establishment characteristics.