7,301 research outputs found
Origin of the high piezoelectric response in PbZr(1-x)TixO3
High resolution x-ray powder diffraction measurements on poled PbZr(1-x)TixO3
(PZT) ceramic samples close to the rhombohedral-tetragonal phase boundary (the
so-called morphotropic phase boundary, MPB) have shown that for both
rhombohedral and tetragonal compositions, the piezoelectric elongation of the
unit cell does not occur along the polar directions but along those directions
associated with the monoclinic distortion. This work provides the first direct
evidence for the origin of the very high piezoelectricity in PZT.Comment: 4 pages, 4 EPS figures embedded. More specific title and abstract. To
appear in Phys. Rev. Let
Theoretical study of molecular electronic excitations and optical transitions of C60
We report results on ab initio calculations of excited states of the
fullerene molecule by using configuration interaction (CI) approach with singly
excited determinants (SCI). We have used both the experimental geometry and the
one optimized by the density functional method and worked with basis sets at
the cc-pVTZ and aug-cc-pVTZ level. Contrary to the early SCI semiempirical
calculations, we find that two lowest electron
optical lines are situated at relatively high energies of ~5.8 eV (214 nm) and
~6.3 eV (197 nm). These two lines originate from two transitions: from HOMO to (LUMO+1) () and from (HOMO--1)
to LUMO (). The lowest molecular excitation, which is the level, is found at ~2.5 eV. Inclusion of doubly excited determinants
(SDCI) leads only to minor corrections to this picture. We discuss possible
assignment of absorption bands at energies smaller than 5.8 eV (or
larger than 214 nm).Comment: 6 pages, 1 figure, 9 Table
The in vivo Effect of Ultraviolet Irradiation (290-350 nm) on Epidermal Chromatin
In vivo ultraviolet radiation (290-350 nm, 800 J/m2
) in the absence of any exogenously added sensitizer induced oross-ltnkirng of DNA to protein in chromatin isolated from guinea pig epidermis.
The chemical properties and the biologic activity of epidermal
chromatin isolated from both irradiated and non-irradiated
specimens were examined. One hour post-irradiation the lesion was
no more detectable, indicating that a repair process was effective
1n the viable mammalian epidermis
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