515 research outputs found
Ideal barriers to polarization reversal and domain-wall motion in strained ferroelectric thin films
The ideal intrinsic barriers to domain switching in c-phase PbTiO_3 (PTO),
PbZrO_3 (PZO), and PbZr_{1-x}Ti_xO_3 (PZT) are investigated via
first-principles computational methods. The effects of epitaxial strain on the
atomic structure, ferroelectric response, barrier to coherent domain reversal,
domain-wall energy, and barrier to domain-wall translation are studied. It is
found that PTO has a larger polarization, but smaller energy barrier to domain
reversal, than PZO. Consequentially the idealized coercive field is over two
times smaller in PTO than PZO. The Ti--O bond length is more sensitive to
strain than the other bonds in the crystals. This results in the polarization
and domain-wall energy in PTO having greater sensitivity to strain than in PZO.
Two ordered phases of PZT are considered, the rock-salt structure and a (100)
PTO/PZO superlattice. In these simple structures we find that the ferroelectric
properties do not obey Vergard's law, but instead can be approximated as an
average over individual 5-atom unit cells.Comment: 9 pages, 13 figure
Uso da modelagem matemática para simulação da dinâmica da matéria orgânica em solos tropicais.
Neutral high-generation phosphorus dendrimers inhibit macrophage-mediated inflammatory response in vitro and in vivo
Inflammation is part of the physiological response of the organism
to infectious diseases caused by organisms such as bacteria,
viruses, fungi, or parasites. Innate immunity, mediated by mono nuclear phagocytes, including monocytes and macrophages, is a
first line of defense against infectious diseases and plays a key role
triggering the delayed adaptive response that ensures an efficient
defense against pathogens. Monocytes and macrophages stimu lation by pathogen antigens results in activation of different
signaling pathways leading to the release of proinflammatory cyto kines. However, inflammation can also participate in the pathogenesis
of several diseases, the autoimmune diseases that represent a relevant
burden for human health. Dendrimers are branched, multivalent
nanoparticles with a well-defined structure that have a high potential
for biomedical applications. To explore new approaches to fight
against the negative aspects of inflammation, we have used neutral
high-generation phosphorus dendrimers bearing 48 (G3) or 96 (G4)
bisphosphonate groups on their surface. These dendrimers show no
toxicity and have good solubility and chemical stability in aqueous
solutions. Here, we present data indicating that neutral phosphorus
dendrimers show impressive antiinflammatory activities both in
vitro and in vivo. In vitro, these dendrimers reduced the secretion
of proinflammatory cytokines from mice and human monocyte derived macrophages. In addition, these molecules present efficient
antiinflammatory activity in vivo in a mouse model of subchronic
inflammation. Taken together, these data suggest that neutral G3-
G4 phosphorus dendrimers have strong potential applications in the
therapy of inflammation and, likely, of autoimmune diseases.info:eu-repo/semantics/publishedVersio
Uso da modelagem matemática para simulação da dinâmica da matéria orgânica em solos tropicais.
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