3,021 research outputs found
Intrinsic Oxygen Vacancy and Extrinsic Aluminium Dopant Interplay: A Route to the Restoration of Defective TiO
Density functional theory (DFT) and DFT corrected for on-site Coulomb
interactions (DFT+U) calculations are presented on Aluminium doping in bulk
TiO and the anatase (101) surface. Particular attention is paid to the
mobility of oxygen vacancies throughout the doped TiO lattice, as a means
by which charge compensation of trivalent dopants can occur. The effect that Al
doping of TiO electrodes has in dye sensitised solar cells is explained as
a result of this mobility and charge compensation. Substitutional defects in
which one Al3+ replaces one Ti4+ are found to introduce valence band holes,
while intrinsic oxygen vacancies are found to introduce states in the band-gap.
Coupling two of these substitutional defects with an oxygen vacancy results in
exothermic defect formation which maintain charge neutrality. Nudged elastic
band calculations have been performed to investigate the formation of these
clustered defects in the (101) surface by oxygen vacancy diffusion, with the
resulting potential energy surface suggesting energetic gains with small
diffusion barriers. Efficiency in- creases observed in dye sensitised solar
cells as a result of aluminium doping of TiO electrodes are investigated by
adsorbing the tetrahydroquinoline C2-1 chromophore on the defective surfaces.
Adsorption on the clustered extrinsic Al3+ and intrinsic oxygen vacancy defects
are found to behave as if adsorbed on a clean surface, with vacancy states not
present, while adsorption on the oxygen vacancy results in a down shift of the
dye localised states within the band-gap and defect states being present below
the conduction band edge. Aluminium doping therefore acts as a benign dopant
for 'cleaning' TiO through oxygen vacancy diffusion.Comment: 32 pages, 15 figures, accepted for publication by J. Phys. Chem.
DSSC Anchoring Groups: A Surface Dependent Decision
Electrodes in dye sensitised solar cells (DSSCs) are typically
nanocrystalline anatase TiO2 with a majority (101) surface exposed. Generally
the sensitising dye employs a carboxylic anchoring moiety through which it
adheres to the TiO2 surface. Recent interest in exploiting the properties of
differing TiO2 electrode morphologies, such as rutile nanorods exposing the
(110) surface and anatase electrodes with high percentages of the (001) surface
exposed, begs the question of whether this anchoring strategy is best,
irrespective of the majority surface exposed. Here we address this question by
presenting density functional theory calculations contrasting the binding
properties of two promising anchoring groups, phosphonic acid and boronic acid,
to that of carboxylic acid. Anchor-electrode interactions are studied for the
pro- totypical anatase (101) surface, along with the anatase (001) and rutile
(110) surfaces. Finally the effect of using these alternative anchoring groups
to bind a typical coumarin dye (NKX- 2311) to these TiO2 substrates is
examined. Significant differences in the binding properties are found depending
on both the anchor and surface, illustrating that the choice of anchor is
necessarily dependent upon the surface exposed in the electrode. In particular
the boronic acid is found to show the potential to be an excellent anchor
choice for electrodes exposing the anatase (001) surface.Comment: 44 pages, 15 figures, accepted by J. Phys.:Condens. Matter.
Coordinates for structures available via figshar
Linear Scaling Density Matrix Real Time TDDFT: Propagator Unitarity \& Matrix Truncation
Real time, density matrix based, time dependent density functional theory
proceeds through the propagation of the density matrix, as opposed to the
Kohn-Sham orbitals. It is possible to reduce the computational workload by
imposing spatial cut-off radii on sparse matrices, and the propagation of the
density matrix in this manner provides direct access to the optical response of
very large systems, which would be otherwise impractical to obtain using the
standard formulations of TDDFT. Following a brief summary of our
implementation, along with several benchmark tests illustrating the validity of
the method, we present an exploration of the factors affecting the accuracy of
the approach. In particular we investigate the effect of basis set size and
matrix truncation, the key approximation used in achieving linear scaling, on
the propagator unitarity and optical spectra. Finally we illustrate that, with
an appropriate density matrix truncation range applied, the computational load
scales linearly with the system size and discuss the limitations of the
approach.Comment: Accepted for publication in J. Chem. Phy
EFFICACY OF ELECTRON BEAM IRRADIATION OF PROCESSED PORK PRODUCTS
The research reported on in this paper was conducted as part of a larger project. That project is on-going and is focused on ascertaining if irradiation of processed meats would be effective and economical. It involved the examination, through modeling, of the irradiation of one of many currently produced ready-to-eat (RTE) convenience-oriented, value-added pork products, sliced boneless ham. The results and findings reported in this paper represent the initial estimates of the cost and potential profitability or economic viability of irradiation of processed meats. The results and findings in this paper should be considered preliminary with extension and verification to be reported in a later paper by the authors. The objective of the portion of that project reported on in this paper was to conduct cost analysis of alternative irradiation methods and to ascertain the cost of each of those methods. Three scenarios were considered for cost analysis. The first scenario was the installation of an X-ray irradiator at an existing meat processing plant. The second scenario was the installation of a Cobalt-60 irradiator at an existing meat processing plant. The third scenario assumed that the meat processor contracted for irradiation services from an off-site company providing such service to a number of clients. For purposes of this study it was assumed that irradiation of sliced boneless ham would result in either a .06/pound increase in willingness to pay [price] or an equivalent combination of reduced costs and increased price. Total cost per pound for the irradiation process applied to sliced boneless ham ranged from 0.069 at the 50 million pound annual throughput rate when contracting with an off-site company.Food Consumption/Nutrition/Food Safety,
Globalization, growth and distribution in Spain 1500-1913
The endogenous growth literature has explored the transition from a Malthusian
world where real wages, living standards and labor productivity are all linked to
factor endowments, to one where (endogenous) productivity change embedded
in modern industrial growth breaks that link. Recently, economic historians
have presented evidence from England showing that the dramatic reversal in
distributional trends – from a steep secular fall in wage-land rent ratios before
1800 to a steep secular rise thereafter – must be explained both by industrial
revolutionary growth forces and by global forces that opened up the English
economy to international trade. This paper explores whether and how the
relationship was different for Spain, a country which had relatively poor
productivity growth in agriculture and low living standards prior to 1800, was a
late-comer to industrialization afterwards, and adopted very restrictive policies
towards imports for much of the 19th century. The failure of Spanish wagerental
ratios to undergo a sustained rise after 1840 can be attributed to the
delayed fall in relative agricultural prices (due to those protective policies) and
to the decline in Spanish manufacturing productivity after 1898
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