7,647 research outputs found

    Zero-energy peak of the density of states and localization properties of a one-dimensional Frenkel exciton: Off-diagonal disorder

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    We study a one-dimensional Frenkel Hamiltonian with off-diagonal disorder, focusing our attention on the physical nature of the zero-energy peak of the density of states. The character of excitonic states (localized or delocalized) is also examined in the vicinity of this peak. It is shown that the state being responsible for the peak is localized. A detailed comparison of the nearest-neighbor approach with the long-range dipole-dipole coupling is performed.Comment: 15 pages with 7 figures (REVTeX). To appear in Physical Review

    High temperature creep of 20 vol.% SiC-HfB2 UHTCs up to 2000 °C

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    High temperature compressive creep of SiC-HfB2 UHTCs up to 2000 °C has been studied. Microstructural analysis after deformation reveals formation of new phases in the Hf-B-Si and Hf-B-Si-C systems, which are responsible for the poor creep resistance. RE oxide additions have a negative effect reducing the creep resistance of SiC-HfB2 UHTCs. A simplistic analysis for the required creep resistance is described, indicating that only SiC-HfB2 UHTCs could withstand re-entry conditions for 5 min in a single use. However, RE oxide addition to SiC-HfB2 UHTCs does not provide the required creep resistance for them to be candidate materials for hypersonic applications

    ETHICS AND AGING: FOCUS ON LIVING WILL FOR PATIENTS WITH DEMENTIA

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    Today dementia certainly represents a public health priority with a huge global impact on wordwide population. However, clinical and social issues related to demen-tia have long been marginalized. The actual high prevalence of dementias requires also to face issues from a bioethical perspective, regarding how to deal with demented patient\u2019s disposition. There are currently no specific guide-lines on the national territory regarding whether to draw up a living will by a patient with dementia, neither about the informa-tive role of physicians during the progres-sive story of the disease
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