171 research outputs found
Surface magnetism in ZnO/Co3O4 mixtures
We recently reported the observation of room temperature ferromagnetism in
mixtures of ZnO and Co3O4 despite the diamagnetic and antiferromagnetic
character of these oxides respectively. Here we present a detailed study on the
electronic structure of this material in order to account for this unexpected
ferromagnetism. Electrostatic interactions between both oxides lead to a
dispersion of Co3O4 particles over the surface of ZnO larger ones. As a
consequence, the reduction of Co+3 to Co2+ at the particle surface takes place
as evidenced by XAS measurements and optical spectrocopy. This reduction allows
to xplain the observed ferromagnetic signal within the well established
theories of magnetism.Comment: Accepted in Journal of Applied Physic
AquaData and AquaGIS: Two computer utilities for temporal and spatial simulations of water-limited yield with AquaCrop.
The crop simulation model AquaCrop, recently developed by FAO can be used for a wide range of purposes. However, in its present form, its use over large areas or for applications that require a large number of simulations runs (e.g., long-term analysis), is not practical without developing software to facilitate such applications. Two tools for managing the inputs and outputs of AquaCrop, named AquaData and AquaGIS, have been developed for this purpose and are presented here. Both software utilities have been programmed in Delphi v. 5 and in addition, AquaGIS requires the Geographic Information System (GIS) programming tool MapObjects. These utilities allow the efficient management of input and output files, along with a GIS module to develop spatial analysis and effect spatial visualization of the results, facilitating knowledge dissemination. A sample of application of the utilities is given here, as an AquaCrop simulation analysis of impact of climate change on wheat yield in Southern Spain, which requires extensive input data preparation and output processing. The use of AquaCrop without the two utilities would have required approximately 1000 h of work, while the utilization of AquaData and AquaGIS reduced that time by more than 99%. Furthermore, the use of GIS, made it possible to perform a spatial analysis of the results, thus providing a new option to extend the use of the AquaCrop model to scales requiring spatial and temporal analyses
Insights into the room temperature magnetism of ZnO/Co3O4 mixtures
The origin of room temperature (RT) ferromagneticlike behavior in ZnO-based
diluted magnetic semiconductors is still an unclear topic. The present work
concentrates on the appearance of RT magnetic moments in just mixed ZnO/Co3O4
mixtures without thermal treatment. In this study, it is shown that the
magnetism seems to be related to surface reduction of the Co3O4 nanoparticles,
in which, an antiferromagnetic Co3O4 nanoparticle (core) is surrounded by a
CoO-like shell. This singular superficial magnetism has also been found in
other mixtures with semiconductors such as TiO2 and insulators such as Al2O3
Drag reduction on a blunt body by self-adaption of rear flexibly hinged flaps
We study the aerodynamics of a blunt-based body with rear flexibly-hinged rigid flaps,
subject to a turbulent flow of Reynolds number Re = 12000, under aligned and cross
flow conditions with yaw angle β = 0◦ and β = 4◦. To that aim, different values of
the equivalent torsional stiffness are considered, to cover the range of reduced velocity
U∗ = (0, 3.48] in water tank experiments. The effect of the angular deflection of
plates on the drag and near wake flow is analyzed, experimentally and numerically.
The results show that, in the range of U∗ herein considered, the plates undergo an
inwards quasi-static, self-adaptive deflection, which is symmetric for yaw angles β = 0◦
and asymmetric for β = 4◦. In particular, the plates feature small mean deformation
angles for values of U∗ < 1, whereas a sharp and monotonic increase of such deflection
occurs for U∗ > 1, i.e. for lower values of the hinge’s stiffness, with an asymptotic
trend towards the larger values of U∗. A critical value of reduced velocity of U∗ ≃ 0.96
is obtained as the instability threshold above which plates depart from their initial
equilibrium position. The progressive streamlining of the trailing edge translates into
significant reductions of the associated mean drag coefficients. Thus, reductions close
to 19% with respect to reference static plates configurations are obtained for the most
flexible case of U∗ = 3.48 for both β = 0◦ and β = 4◦. A close inspection of the
near wake reveals that the inwards progressive mean displacement of the plates yields
a reduction in the recirculation bubble size. A symmetric evolution of the recirculating
bubble is observed for β = 0◦, whereas the bubble becomes asymmetric for β = 4◦,
with a larger leeward clockwise vortex. In both cases, the drag coefficient is shown
to vary linearly with the global aspect ratio of the recirculating bubble. The analysis
of the numerical results shows that the reduced extension of the recirculating bubble
significantly alters the formation length and intensity of the eddies size and associated
pressure. It is observed that despite the local pressure decrease in the vortices shed from
the trailing edges, the plates self adaption reduces their size and prevents the eddies
from entering the cavity, thus, creating a dead flow region with a consequent pressure
increase at the body base.Junta de Andalucia FEDER-UJA 1262764Universidad de JaenEuropean CommissionSpanish MCIN/AEI PDC2021-121288-I00European Union Next Generation EU/PRT
Impact of climate change on irrigation management for olive orchards at southern Spain
The irrigation management for olive orchards under future weather conditions requires the development of advanced
tools for considering specific physiological and phenological components affected by the foreseen changes
in climate and atmospheric [CO2]
Study of the Negative Magneto-Resistance of Single Proton-Implanted Lithium-Doped ZnO Microwires
The magneto-transport properties of single proton-implanted ZnO and of
Li(7\%)-doped ZnO microwires have been studied. The as-grown microwires were
highly insulating and not magnetic. After proton implantation the Li(7\%) doped
ZnO microwires showed a non monotonous behavior of the negative
magneto-resistance (MR) at temperature above 150 K. This is in contrast to the
monotonous NMR observed below 50 K for proton-implanted ZnO. The observed
difference in the transport properties of the wires is related to the amount of
stable Zn vacancies created at the near surface region by the proton
implantation and Li doping. The magnetic field dependence of the resistance
might be explained by the formation of a magnetic/non magnetic heterostructure
in the wire after proton implantation.Comment: 6 pages with 5 figure
Quantifying the effect of Tmax extreme events on local adaptation to climate change of maize crop in Andalusia for the 21st century
Extreme events of Tmax can threaten maize production on Andalusia (Ruiz-Ramos et al., 2011). The objective of this work is to attempt a quantification of the effects of Tmax extreme events on the previously identified
(Gabaldón et al., 2013) local adaptation strategies to climate change of irrigated maize crop in Andalusia for the
first half of the 21st century
- …