604 research outputs found
On the number of lines in the limit set for discrete subgroups of
Given a discret subgroup \Gamma\subset PSL(3,\C), we determine the number
of complex lines and complex lines in general position lying in the complement
of: maximal regions on which acts properly discontinuously, the
Kularni's limit set of and the equicontinuity set of . We also
provide sufficient conditions to ensure that the equicontinuity region agrees
with the Kulkarni's discontinuity region and is the largest set where the group
acts properly discontinuously and we provide a description of he respective
limit set in terms of the elements of the group
Effect of debris size on the tribological performance of thermally sprayed coatings
This research aims to assess the effect of the debris particle size on the tribological performance
and lubrication regime parameters of a Ni-based alloy coating. This is a key industrial problem,
and its resolution can contribute to better machine endurance and proper maintenance.
The debris particles are simulated by hard Al2O3 particles of size ranging from nanometers to 45
μm and dispersed in an oil lubricant. The coating studied is NiCrBSi deposited by flame spraying
technique followed by the Surface Flame Melting (SFM) process. The counterpart disk sample
was fabricated from quenched and tempered F-5220 steel (in line with A681(O1) ASTM). This
pair was tested under linear sliding contact.
Our results show that the addition of alumina particles contributes to a significant increase in
wear, particularly for the largest particles (micrometric size). In the case of micrometric particles,
it is possible to observe the formation of higher surface roughness, numerous microgrooves, and
plastic flow of NiCrBSi coating perpendicular to the sliding direction, resulting in higher loss of
volume.
It was found that the actual surface roughness (obtained as a function of the debris particle size)
allows better identification and prediction of the lubrication regime for wear processes instead of
the traditional approach that uses the initial surface roughness as a parameter
Papel do ferro no mecanismo fungicida mediado pelo óxido nÃtrico de macrófagos murinos ativados com IFN-gama contra conÃdias do Paracoccidioides brasiliensis
Iron is an essential growth element of virtually all microorganisms and its restriction is one of the mechanisms used by macrophages to control microbial multiplication. Paracoccidioides brasiliensis, the agent of paracoccidioidomycosis, an important systemic mycosis in Latin America, is inhibited in its conidia-to-yeast conversion in the absence of iron. We studied the participation of iron in the nitric oxide (NO)-mediated fungicidal mechanism against conidia. Peritoneal murine macrophages activated with 50U/mL of IFN-gamma or treated with 35 µM Deferoxamine (DEX) and infected with P. brasiliensis conidia, were co-cultured and incubated for 96 h in the presence of different concentrations of holotransferrin (HOLO) and FeS0(4). The supernatants were withdrawn in order to assess NO2 production by the Griess method. The monolayers were fixed, stained and observed microscopically. The percentage of the conidia-to-yeast transition was estimated by counting 200 intracellular propagules. IFN-gamma-activated or DEX-treated Mthetas presented marked inhibition of the conidia-to-yeast conversion (19 and 56%, respectively) in comparison with non-activated or untreated Mthetas (80%). IFN-gamma-activated macrophages produced high NO levels in comparison with the controls. Additionally, when the activated or treated-macrophages were supplemented with iron donors (HOLO or FeSO4), the inhibitory action was reversed, although NO production remained intact. These results suggest that the NO-mediated fungicidal mechanism exerted by IFN-gamma-activated macrophages against P. brasiliensis conidia, is dependent of an iron interaction.O ferro é elemento essencial para o crescimento de microrganismos e sua limitação é um dos mecanismos usados por macrófagos para controlar a multiplicação microbiana. Paracoccidioides brasiliensis, o agente da paracoccidioidomicose, uma das micoses sistêmicas mais importantes na América Latina, é inibido em sua conversão de conÃdia-à -levedura na ausência do ferro. Estudamos a participação do ferro no mecanismo fungicida mediado pelo óxido nÃtrico (NO) na sua interação com as conÃdias do fungo. Macrófagos peritoneais murinos ativados com 50U/mL de IFN-gama ou tratados com 35 µM Deferoxamina (DEX) e infectados com conÃdias do P. brasiliensis foram co-cultivados e incubados por 96 h na presença de concentrações diferentes de holotransferrina (HOLO) e FeS0(4). Os sobrenadantes foram retirados a fim de avaliar a produção de NO2 pelo método de Griess. Os macrófagos eram fixados, corados e observados ao microscópio. A porcentagem da transição de conÃdia-à -levedura foi estimada contando 200 propágulos intracelulares. Os macrófagos ativados com citocina ou tratados com DEX apresentaram inibição marcada da conversão de conÃdia-à -levedura (19 e 56%, respectivamente) em comparação com macrófagos controle (80%). Os macrófagos ativados com IFN-gama produziram elevação nos nÃveis de NO em comparação com macrófagos não-tratados ou não-activados. Adicionalmente, quando as monocapas ativadas ou tratadas foram suplementadas com doadores do ferro (HOLO ou FeSO4), a ação inibitória foi revertida embora a produção de NO permanecesse intacto. Estes resultados sugerem que o mecanismo fungicida mediado pelo NO exercido por macrófagos ativados com IFN-gama contra conÃdias do P. brasiliensis é dependente de uma interação do ferro
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