Universidade Federal de Minas Gerais

About: Universidade Federal de Minas Gerais is a education organization based out in Belo Horizonte, Minas Gerais, Brazil. It is known for research contribution in the topics: Population & Context (language use). The organization has 41631 authors who have published 75688 publications receiving 1249905 citations.

Family behavior of the optical transition energies in single-wall carbon nanotubes of smaller diameters

Abstract: Using the extended tight-binding model that allows bond lengths and angles to vary, the optical transition energies Eii in single-wall carbon nanotubes are calculated as a function of inverse tube diameter. After geometrical structure optimization, the 2n+m=constant family behavior observed in photoluminescence (PL) experiments is obtained, and detailed agreement between the calculations and PL experiments is achieved after including many-body corrections.

U-Pb Geochronology of Archean magmatism and Proterozoic metamorphism in the Quadrilátero Ferrífero, southern São Francisco craton, Brazil

Abstract: The Quadrilatero Ferrifero is a metallogenic district (Au, Fe, Mn) located in the southernmost Sao Francisco craton in eastern Brazil. It is composed of Archean granitoids, gneisses, and a greenstone belt sequence (Rio das Velhas Supergroup), overlain by a Proterozoic clastic-chemical sedimentary sequence hosting a thick Lake Superior-type banded iron formation (Minas Supergroup). A U-Pb study of the main units leads to the following conclusions: granitoid emplacement was dated at 2776 +7/-6 Ma and 2721 ± 3 Ma; two felsic volcanic rocks from the Rio das Velhas Supergroup yielded ages of 2776 +23/-10 Ma and 2772 ± 6 Ma. These data indicate that greenstone-belt volcanism was coeval with granitoid emplacement, a common feature of greenstone-belt terrains, but so far undocumented in the southern Sao Francisco shield. The younger granitoid intrusion marks the stabilization of the shield in Late Archean time. Zircon cores older than 2776 Ma, together with other data, indicate the presence of continental crust 2.88-3.1 Ga old in the Quadrilatero Ferrifero. A detrital zircon from the uppermost formation in the Minas Supergroup (Sabara Formation) is concordant at 2125 ± 4 Ma and provides the first age constraint on the deposition of the Supergroup. Monazite from two pegmatites and titanite from an amphibolite enclave in gneisses from the Bacao Complex, in central Quadrilatero Ferrifero, yielded ages between 2060 Ma and 2030 Ma. These data may constrain the minimum age for the deposition of the Minas Supergroup. In addition, they indicate that the Early Proterozoic Transamazomian orogeny is represented by amphibolite-facies metamorphism and partial melting of Archean crust.

Cholinergic receptor pathways involved in apoptosis, cell proliferation and neuronal differentiation

Abstract: Acetylcholine (ACh) has been shown to modulate neuronal differentiation during early development. Both muscarinic and nicotinic acetylcholine receptors (AChRs) regulate a wide variety of physiological responses, including apoptosis, cellular proliferation and neuronal differentiation. However, the intracellular mechanisms underlying these effects of AChR signaling are not fully understood. It is known that activation of AChRs increase cellular proliferation and neurogenesis and that regulation of intracellular calcium through AChRs may underlie the many functions of ACh. Intriguingly, activation of diverse signaling molecules such as Ras-mitogen-activated protein kinase, phosphatidylinositol 3-kinase-Akt, protein kinase C and c-Src is modulated by AChRs. Here we discuss the roles of ACh in neuronal differentiation, cell proliferation and apoptosis. We also discuss the pathways involved in these processes, as well as the effects of novel endogenous AChRs agonists and strategies to enhance neuronal-differentiation of stem and neural progenitor cells. Further understanding of the intracellular mechanisms underlying AChR signaling may provide insights for novel therapeutic strategies, as abnormal AChR activity is present in many diseases.