508 research outputs found
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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Dynamics of Holes and Universality Class of the Antiferromagnetic Transition in the Two Dimensional Hubbard Model
The dynamics of a single hole (or electron) in the two dimensional Hubbard
model is investigated. The antiferromagnetic background is described by a
N\`eel state, and the hopping of the carrier is analyzed within a configuration
interaction approach. Results are in agreement with other methods and with
experimental data when available. All data are compatible with the opening of a
mean field gap in a Fermi liquid of spin polarons, the so called Slater type of
transition. In particular, this hypothesis explains the unusual dispersion
relation of the quasiparticle bands near the transition. Recent photoemission
data for CaCuOCl are analyzed within this context.Comment: New results and comparison with recent data adde
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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Performance of cultivars, hybrids and composites of winter wheat (Triticum aestivum L. em Thell) grown at three locations
The objective of this study was to compare three genetically
different groups of winter wheat for their grain yield. Experimental
material consisted of parental lines grown in pure stands, hybrids, and
1:1 mixtures of the parental combinations. Three sites were employed to
evaluate possible interactions between the different groups across
locations. Phenotypic correlations among selected agronomic traits and
grain yield within each group along with the expression of heterosis
and heterobeltiosis in the hybrids were studied.
Results of this investigation support the general conclusion
reached by other investigators that hybrids and composites are not
consistently superior to the best conventional cultivars of wheat for
grain yield. However, at the Moro site, with the greater environmental
stresses, some hybrids and composites appeared to yield more than the
parental lines grown in pure stands. At Pendleton, the best environment
for yield expression, the hybrids and conventional cultivars did not
differ for grain yield. At this location, the best hybrids and one
composite did significantly outyield the commercial cultivars Stephens,
Malcolm and Hill, but not four advanced parental selections when grown
in pure stands.
Low to moderate values of heterosis and heterobeltiosis for grain
yield were found. The degree of expression being affected by the
specific growing site. Plant height and the number of kernels per spike
showed relatively higher values for heterosis and heterobeltiosis over
locations when compared to the other traits.
Phenotypic correlations suggested that a breeding program to
develop hybrid wheat should combine high number of kernels per spike
with high kernel weight. The positive correlation between grain yield
and plant height indicated that increases in grain yield could be
obtained by increasing plant height if lodging did not present a
problem
Zinc oxide as an ozone sensor
Journal of Applied Physics, Vol. 96, nº3This work presents a study of intrinsic zinc oxide thin film as ozone sensor based on the ultraviolet sUVd photoreduction and subsequent ozone re oxidation of zinc oxide as a fully reversible process performed at room temperature. The films analyzed were produced by spray pyrolysis, dc and rf
magnetron sputtering. The dc resistivity of the films produced by rf magnetron sputtering and constituted by nanocrystallites changes more than eight orders of magnitude when exposed to an UV dose of 4 mW/cm2. On the other hand, porous and textured zinc oxide films produced by spray pyrolysis at low substrate temperature exhibit an excellent ac impedance response where the reactance changes by more than seven orders of magnitude when exposed to the same UV dose,
with a response frequency above 15 kHz, thus showing improved ozone ac sensing
discrimination
Fault-controlled and stratabound dolostones in the Late Aptian-earliest Albian Benassal Formation (Maestrat Basin, E Spain) : petrology and geochemistry constrains
This study was developed under the ExxonMobil FC2 Alliance (Fundamental Controls on Flow in Carbonates). The authors wish to thank ExxonMobil Production Company and ExxonMobil Upstream Research Company for providing funding. The views in this article by Sherry L. Stafford are her own and not necessarily those of ExxonMobil. This research was supported by the Sedimentary Geology Research Group of the Generalitat de Catalunya (2014SGR251). We would like to thank Andrea Ceriani and Paola Ronchi for their critical and valuable reviews, and Associated Editor Piero Gianolla for the editorial work.Peer reviewedPostprin
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