117 research outputs found
Quantum Phase Transition in the SU(4) Spin-Orbital Model on the Triangular Lattice
Motivated by the absence of cooperative Jahn-Teller effect in LiNiO2 and
BaVS3, two layered oxides with triangular planes, we study the SU(4) symmetric
spin-orbital model on the triangular lattice. Upon reducing the next-nearest
neighbour coupling, we show that the system undergoes a quantum phase
transition to a liquid phase. A variational approach to this liquid phase shows
that simple types of long-range correlations are suppressed, suggesting that it
is stable against lattice distortions.Comment: 5 pages, 5 figures, RevTex
Alzheimer's disease and symbiotic microbiota: an evolutionary medicine perspective
Microorganisms resident in our bodies participate in a variety of regulatory and pathogenic processes. Here, we describe how etiological pathways implicated in Alzheimerâs disease (AD) may be regulated or disturbed by symbiotic microbial activity. Furthermore, the composition of symbiotic microbes has changed dramatically across human history alongside the rise of agriculturalism, industrialization, and globalization. We postulate that each of these lifestyle transitions engendered progressive depletion of microbial diversity and enhancement of virulence, thereby enhancing AD risk pathways. It is likely that the human life span extended into the eighth decade tens of thousands of years ago, yet little is known about premodern geriatric epidemiology. We propose that microbiota of the gut, oral cavity, nasal cavity, and brain may modulate AD pathogenesis, and that changes in the microbial composition of these body regions across history suggest escalation of AD risk. Dysbiosis may promote immunoregulatory dysfunction due to inadequate education of the immune system, chronic inflammation, and epithelial barrier permeability. Subsequently, proinflammatory agentsâand occasionally microbesâmay infiltrate the brain and promote AD pathogenic processes. APOE genotypes appear to moderate the effect of dysbiosis on AD risk. Elucidating the effect of symbiotic microbiota on AD pathogenesis could contribute to basic and translational research
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