51,463 research outputs found
Atomistic origins of the phase transition mechanism in Ge2Sb2Te5
Combined static and molecular dynamics first-principles calculations are used
to identify a direct structural link between the metastable crystalline and
amorphous phases of Ge2Sb2Te5. We find that the phase transition is driven by
the displacement of Ge atoms along the rocksalt [111] direction from the
stable-octahedron to high-energy-unstable tetrahedron sites close to the
intrinsic vacancy regions, which give rise to the formation of local 4-fold
coordinated motifs. Our analyses suggest that the high figures of merit of
Ge2Sb2Te5 are achieved from the optimal combination of intrinsic vacancies
provided by Sb2Te3 and the instability of the tetrahedron sites provided by
GeTe
The class of n-entire operators
We introduce a classification of simple, regular, closed symmetric operators
with deficiency indices (1,1) according to a geometric criterion that extends
the classical notions of entire operators and entire operators in the
generalized sense due to M. G. Krein. We show that these classes of operators
have several distinctive properties, some of them related to the spectra of
their canonical selfadjoint extensions. In particular, we provide necessary and
sufficient conditions on the spectra of two canonical selfadjoint extensions of
an operator for it to belong to one of our classes. Our discussion is based on
some recent results in the theory of de Branges spaces.Comment: 33 pages. Typos corrected. Changes in the wording of Section 2.
References added. Examples added. arXiv admin note: text overlap with
arXiv:1104.476
Non(anti)commutative superspace with coordinate-dependent deformation
We consider non(anti)commutative superspace with coordinate dependent
deformation parameters . We show that a chiral
supersymmetry can be defined and that chiral and antichiral superfields are
still closed under the Moyal-Weyl associative product implementing the
deformation. A consistent Super Yang-Mills deformed theory can
be constructed provided satisfies a suitable condition which
can be connected with the graviphoton background at the origin of the
deformation. After adding matter we also discuss the Konishi anomaly and the
gluino condensation.Comment: References added. Accepted for publication in PR
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