Interconnection of thermal parameters, microstructure, macrosegregation and microhardness of unidirectionally solidified Zn-rich Zn–Ag peritectic alloys

In this work, the microstructural evolution of Zn–3.2 wt%Ag (hypoperitectic) and Zn–8 wt%Ag (hyperperitectic) alloys during transient unidirectional solidification is investigated. The experimental results include solidification thermal parameters such as the growth rate (VL), thermal gradient (GL) and tip cooling rate (), which are related to the microstructural interphase spacing (λ) by proposed experimental growth laws. It is shown that, the classical lamellar eutectic growth law λ2V = constant, applies to the growth of the peritectic Zn–Ag alloys examined, despite the different values of the constant associated with each alloy composition. In contrast, it is shown that identical functions of the form λ = constant (GL)−14 (VL)−1/8, and λ = constant () can be applied to both alloys examined. Positive solute macrosegregation was observed in regions close to the bottom of the castings. The dependence of microhardness (HV) on the length scale of the microstructures (including that of a single phase Zn 0.8 wt%Ag alloy: λC− cellular spacing) is examined. An experimental Hall–Petch type power law is proposed relating the resulting microhardness to λC for the single phase alloy, and despite the segregation profiles and the alloying differences of the hypoperitectic and hyperperitectic alloys, the average microhardnesses of these alloys is shown to be essentially constant and similar along the castings lengths63848855CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão tem2013/09267-0; 2012/08494-0; 2012/16328-

Profile of Central and Effector Memory T Cells in the Progression of Chronic Human Chagas Disease

Chagas disease is a parasitic infection caused by protozoan Trypanosoma cruzi that affects approximately 11 million people in Latin America. The involvement of the host's immune response on the development of severe forms of Chagas disease has not been fully elucidated. Studies on the immune response against T. cruzi infection show that the immunoregulatory mechanisms are necessary to prevent the deleterious effect of excessive immune response stimulation and consequently the fatal outcome of the disease. A recall response against parasite antigens observed in in vitro peripheral blood cell culture clearly demonstrates that memory response is generated during infection. Memory T cells are heterogeneous and differ in both the ability to migrate and exert their effector function. This heterogeneity is reflected in the definition of central (TCM) and effector memory (TEM) T cells. Our results suggest that a balance between regulatory and effectors T cells may be important for the progression and development of the disease. Furthermore, the high percentage of central memory CD4+ T cells in indeterminate patients after stimulation suggests that these cells may modulate host's inflammatory response by controlling cell migration to tissues and their effector role during chronic phase of the disease