740 research outputs found
Lattice-Spin Mechanism in Colossal Magnetoresistant Manganites
We present a single-orbital double-exchange model, coupled with cooperative
phonons (the so called breathing-modes of the oxygen octahedra in manganites).
The model is studied with Monte Carlo simulations. For a finite range of doping
and coupling constants, a first-order Metal-Insulator phase transition is
found, that coincides with the Paramagnetic-Ferromagnetic phase transition. The
insulating state is due to the self-trapping of every carrier within an oxygen
octahedron distortion.Comment: 4 pages, 5 figures, ReVTeX macro, accepted for publication in PR
Crystal structure and electronic states of tripotassium picene
The crystal structure of potassium doped picene with an exact stoichiometry
(K3C22H14, K3picene from here onwards) has been theoretically determined within
Density Functional Theory allowing complete variational freedom of the crystal
structure parameters and the molecular atomic positions. A modified herringbone
lattice is obtained in which potassium atoms are intercalated between two
paired picene molecules displaying the two possible orientations in the
crystal.Along the c-axis, organic molecules alternate with chains formed by
three potassium atoms. The electronic structureof the doped material resembles
pristine picene, except that now the bottom of the conduction band is occupied
by six electrons coming from the ionized K atoms (six per unit cell).
Wavefunctions remain based mainly on picene molecular orbitals getting their
dispersion from intralayer edge to face CH/pi bonding, while eigenenergies have
been modified by the change in the electrostatic potential. The small
dispersion along the c-axis is assigned to small H-H overlap. From the
calculated electronic density of states we expect metallic behavior for
potassium doped picene.Comment: Published version: 8 twocolumn pages, 7 color figures, 2 structural
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Assessment of the application of advanced technologies to subsonic CTOL transport aircraft
Design studies of the application of advanced technologies to future transport aircraft were conducted. These studies were reviewed from the perspective of an air carrier. A fundamental study of the elements of airplane operating cost was performed, and the advanced technologies were ranked in order of potential profit impact. Recommendations for future study areas are given
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