10,614 research outputs found
An Economic and Environmental Analysis of Slurry Separation
With increased pressure to redistribute animal manure in order to lower the environmental pressure from agriculture, it seems obvious to consider processing slurry into nutrient rich fractions which can easily be transported. In this paper, an overall analysis of four different separation technologies is presented. The four technologies are Decanter, Funki Manura 2000, Green Farm Energy and Staring. These technologies are all implemented on a full scale in Denmark. In this paper both the economic and environmental aspects are considered, looking at the entire chain from stable to the field. The total investments range from 50,000 to 4 million Euros and the total net costs are from 1 to 7 Euros per tonne for the four different technologies. One of the clear environmental benefits is a better utilisation of phosphorus, but using phytase in feeding is a cheaper first step when reducing phosphorus surplus. Improved nitrogen utilisation is only apparent with the Staring and Green Farm Energy concepts. The conclusion is that the Funki Manura 2000 system is too expensive and the Decanter system a fairly cheap way to reduce phosphorus levels, but other benefits are limited. Staring and Green Farm Energy show the greatest potential, but these systems have not been running long enough to validate the expected results included in this paper.Resource /Energy Economics and Policy,
Dynamic rotor mode in antiferromagnetic nanoparticles
We present experimental, numerical, and theoretical evidence for a new mode
of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering
experiments on 8 nm particles of hematite display a loss of diffraction
intensity with temperature, the intensity vanishing around 150 K. However, the
signal from inelastic neutron scattering remains above that temperature,
indicating a magnetic system in constant motion. In addition, the precession
frequency of the inelastic magnetic signal shows an increase above 100 K.
Numerical Langevin simulations of spin dynamics reproduce all measured neutron
data and reveal that thermally activated spin canting gives rise to a new type
of coherent magnetic precession mode. This "rotor" mode can be seen as a
high-temperature version of superparamagnetism and is driven by exchange
interactions between the two magnetic sublattices. The frequency of the rotor
mode behaves in fair agreement with a simple analytical model, based on a high
temperature approximation of the generally accepted Hamiltonian of the system.
The extracted model parameters, as the magnetic interaction and the axial
anisotropy, are in excellent agreement with results from Mossbauer
spectroscopy
Bi spectral extraction through elliptic neutron guides
In this paper we present the results of investigating a suggested guide extraction system utilizing both a thermal and a cold moderator at the same time, the so called bi spectral extraction. Here, the thermal moderator has line of sight to the sample position, and the neutrons from the cold source are reflected by a supermirror towards the sample. The work is motivated by the construction of the European Spallation Source ESS but the results are general and can be used at any neutron source. Due to the long pulse structure, most instruments at ESS will be long, often exceeding 50 m from moderator to detector. We therefore investigate the performance of bi spectral extraction for instrument lengths of 30 m, 56 m, 81 m and 156 m. In all these cases, our results show that we can utilize both moderators and thus high intensity in a wide wavelength band in the same instrument at a cost of flux of 5 30 for neutrons with wavelength larger than 1 . In general, the divergence distribution is smooth at the sample position for all wavelength
Construction of transferable spherically-averaged electron potentials
A new scheme for constructing approximate effective electron potentials
within density-functional theory is proposed. The scheme consists of
calculating the effective potential for a series of reference systems, and then
using these potentials to construct the potential of a general system. To make
contact to the reference system the neutral-sphere radius of each atom is used.
The scheme can simplify calculations with partial wave methods in the
atomic-sphere or muffin-tin approximation, since potential parameters can be
precalculated and then for a general system obtained through simple
interpolation formulas. We have applied the scheme to construct electron
potentials of phonons, surfaces, and different crystal structures of silicon
and aluminum atoms, and found excellent agreement with the self-consistent
effective potential. By using an approximate total electron density obtained
from a superposition of atom-based densities, the energy zero of the
corresponding effective potential can be found and the energy shifts in the
mean potential between inequivalent atoms can therefore be directly estimated.
This approach is shown to work well for surfaces and phonons of silicon.Comment: 8 pages (3 uuencoded Postscript figures appended), LaTeX,
CAMP-090594-
Transforum system innovation towards sustainable food. A review
Innovations in the agri-food sector are needed to create a sustainable food supply. Sustainable food supply requires unexpectedly that densely populated regions remain food producers. A Dutch innovation program has aimed at showing the way forward through creating a number of practice and scientific projects. Generic lessons from the scientific projects in this program are likely to be of interest to agricultural innovation in other densely populated regions in the world. Based on the executed scientific projects, generic lessons across the whole innovation program are derived. We found that the agricultural sector requires evolutionary rather than revolutionary changes to reshaping institutions. Measuring sustainability is possible against benchmarks and requires stakeholder agreement on sustainability values. Results show the importance of multiple social views and multiple stakeholder involvement in agricultural innovation. Findings call for flexible goal rather than process-oriented management of innovation. Findings also emphasise the essential role of profit in anchoring sustainable development in business. The results agree with concepts of evolutionary innovation. We conclude that there is no single best solution to making the agri-food sector more sustainable densely populated areas, but that the combination of a range of solutions and approaches is likely to provide the best way forward
A real-space grid implementation of the Projector Augmented Wave method
A grid-based real-space implementation of the Projector Augmented Wave (PAW)
method of P. E. Blochl [Phys. Rev. B 50, 17953 (1994)] for Density Functional
Theory (DFT) calculations is presented. The use of uniform 3D real-space grids
for representing wave functions, densities and potentials allows for flexible
boundary conditions, efficient multigrid algorithms for solving Poisson and
Kohn-Sham equations, and efficient parallelization using simple real-space
domain-decomposition. We use the PAW method to perform all-electron
calculations in the frozen core approximation, with smooth valence wave
functions that can be represented on relatively coarse grids. We demonstrate
the accuracy of the method by calculating the atomization energies of twenty
small molecules, and the bulk modulus and lattice constants of bulk aluminum.
We show that the approach in terms of computational efficiency is comparable to
standard plane-wave methods, but the memory requirements are higher.Comment: 13 pages, 3 figures, accepted for publication in Physical Review
Inelastic Scattering in Metal-H2-Metal Junctions
We present first-principles calculations of the dI/dV characteristics of an
H2 molecule sandwiched between Au and Pt electrodes in the presence of
electron-phonon interactions. The conductance is found to decrease by a few
percentage at threshold voltages corresponding to the excitation energy of
longitudinal vibrations of the H2 molecule. In the case of Pt electrodes, the
transverse vibrations can mediate transport through otherwise non-transmitting
Pt -channels leading to an increase in the differential conductance even
though the hydrogen junction is characterized predominately by a single almost
fully open transport channel. In the case of Au, the transverse modes do not
affect the dI/dV because the Au d-states are too far below the Fermi level. A
simple explanation of the first-principles results is given using scattering
theory. Finally, we compare and discuss our results in relation to experimental
data.Comment: Accepted in Phys. Rev.
Loop Model with Generalized Fugacity in Three Dimensions
A statistical model of loops on the three-dimensional lattice is proposed and
is investigated. It is O(n)-type but has loop fugacity that depends on global
three-dimensional shapes of loops in a particular fashion. It is shown that,
despite this non-locality and the dimensionality, a layer-to-layer transfer
matrix can be constructed as a product of local vertex weights for infinitely
many points in the parameter space. Using this transfer matrix, the site
entropy is estimated numerically in the fully packed limit.Comment: 16pages, 4 eps figures, (v2) typos and Table 3 corrected. Refs added,
(v3) an error in an explanation of fig.2 corrected. Refs added. (v4) Changes
in the presentatio
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