12,676 research outputs found
The accuracy of parameters determined with the core-sampling method: application to Voronoi tessellations
The large-scale matter distribution represents a complex network of structure
elements such as voids, clusters, filaments, and sheets. This network is
spanned by a point distribution. The global properties of the point process can
be measured by different statistical methods, which, however, do not describe
directly the structure elements. The morphology of structure elements is an
important property of the point distribution. Here we apply the core-sampling
method to various Voronoi tessellations. Using the core-sampling method we
identify one- and two-dimensional structure elements (filaments and sheets) in
these Voronoi tessellations and reconstruct their mean separation along random
straight lines. We compare the results of the core-sampling method with the a
priori known structure elements of the Voronoi tessellations under
consideration and find good agreement between the expected and found structure
parameters, even in the presence of substantial noise. We conclude that the
core-sampling method is a potentially powerful tool to investigate the
distribution of such structure elements like filaments and walls of galaxies.Comment: 14 pages (Latex) with 6 figures, the complete paper with 8 figures is
available at http://kosmos.aip.de/~got/projects.html {Characteristical scales
in point distributions}, Astronomy and Astrophysics Supplement Series,
accepte
Organic Farming Scenarios: Operational Analysis and Costs of implementing Innovative Technologies
The objective of this study has been to design a number of farm scenarios representing future plausible and internally consistent organic farming enterprises based on milk, pig, and plant production and use these farm scenarios as the basis for the generation of generalised knowledge on labour and machinery input and costs. Also, an impact analysis and feasibility study of introducing innovative technologies into the organic
production system has been invoked.
The labour demand for the production farms ranged from 61 to 253hha1 and from 194 to 396hLU1 (LU is livestock units) for work in the animal houses. Model validation results showed that farm managerial tasks amount to 14–19% of the total labour requirement. The impact of introducing new technologies and work methods related to organic farming was evaluated using two innovative examples of weed control: a
weeding robot and an integrated system for band steaming. While these technologies increased the capital investment required, the labour demand was reduced by 83–85% in sugar beet and 60% in carrots, which would improve profitability by 72–85% if fully utilised. Profitability is reduced, if automation efforts result in insufficient weed removal compared to manual weeding. Specifically, the benefit gained by robotic weeding
was sensitive to the weed intensity and the initial price of the equipment, but a weeding efficiency of under 25% is required to make it unprofitable.
This approach demonstrates the feasibility of applying and testing operational models in organic farming systems in the continued evaluation and documentation of labour and machinery inputs
Observation of force-detected nuclear magnetic resonance in a homogeneous field
We report the experimental realization of BOOMERANG (better observation of magnetization, enhanced resolution, and no gradient), a sensitive and general method of magnetic resonance. The prototype millimeter-scale NMR spectrometer shows signal and noise levels in agreement with the design principles. We present H-1 and F-19 NMR in both solid and liquid samples, including time-domain Fourier transform NMR spectroscopy, multiple-pulse echoes, and heteronuclear J spectroscopy. By measuring a H-1-F-19 J coupling, this last experiment accomplishes chemically specific spectroscopy with force-detected NMR. In BOOMERANG, an assembly of permanent magnets provides a homogeneous field throughout the sample, while a harmonically suspended part of the assembly, a detector, is mechanically driven by spin-dependent forces. By placing the sample in a homogeneous field, signal dephasing by diffusion in a field gradient is made negligible, enabling application to liquids, in contrast to other force-detection methods. The design appears readily scalable to µm-scale samples where it should have sensitivity advantages over inductive detection with microcoils and where it holds great promise for application of magnetic resonance in biology, chemistry, physics, and surface science. We briefly discuss extensions of the BOOMERANG method to the µm and nm scales
A Cosmological Three Level Neutrino Laser
We present a calculation of a neutrino decay scenario in the early Universe.
The specific decay is \nu_{2} \to \nu_{1} + \phi, where \phi is a boson. If
there is a neutrino mass hierarchy, m_{\nu_{e}} < m_{\nu_{\mu}} <
m_{\nu_{\tau}}, we show that it is possible to generate stimulated decay and
effects similar to atomic lasing without invoking new neutrinos, even starting
from identical neutrino distributions. Under the right circumstances the decay
can be to very low momentum boson states thereby producing something similar to
a Bose condensate, with possible consequences for structure formation. Finally,
we argue that this type of decay may also be important other places in early
Universe physics.Comment: 7 pages, RevTex, due for publication in Phys. Rev. D, April 15 issu
Expansion-limited aggregation of nanoclusters in a single-pulse laser-produced plume
Formation of carbon nanoclusters in a single-laser-pulse created ablation plume was studied both in vacuum and in a noble gas environment at various pressures. The developed theory provides cluster radius dependence on combination of laser parameters, properties of ablated material, and type and pressure of an ambient gas in agreement with experiments. The experiments were performed on carbon nanoclusters formed by laser ablation of graphite targets with 12 picosecond 532 nm laser pulses at MHz-range repetition rate in a broad range of ambient He, Ar, Kr, and Xe gas pressures from 2Ă— 10-2 to 1500 Torr. The experimental results confirmed our theoretical prediction that the average size of the nanoparticles depends weakly on the type of the ambient gas used, and is determined exclusively by the single laser pulse parameters even at the repetition rate as high as 28 MHz with the time gap 36 ns between the pulses. The most important finding relates to the fact that in vacuum the cluster size is mainly determined by hydrodynamic expansion of the plume while in the ambient gas it is controlled by atomic diffusion in the gas. We demonstrate that the ultrashort pulses can be used for production of clusters with the size less than the critical value, which separates the particles with properties drastically different from those of a material in a bulk. The presented results of experiments on formation of carbon nanoclusters are in close agreement with the theoretical scaling. The developed theory is applicable for cluster formation from any monatomic material, such as silicon for example
Charge order in Magnetite. An LDA+ study
The electronic structure of the monoclinic structure of FeO is
studied using both the local density approximation (LDA) and the LDA+. The
LDA gives only a small charge disproportionation, thus excluding that the
structural distortion should be sufficient to give a charge order. The LDA+
results in a charge disproportion along the c-axis in good agreement with the
experiment. We also show how the effective can be calculated within the
augmented plane wave methods
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