2,189 research outputs found
Superconductivity in hole-doped C60 from electronic correlations
We derive a model for the highest occupied molecular orbital band of a C60
crystal which includes on-site electron-electron interactions. The form of the
interactions are based on the icosahedral symmetry of the C60 molecule together
with a perturbative treatment of an isolated C60 molecule. Using this model we
do a mean-field calculation in two dimensions on the [100] surface of the
crystal. Due to the multi-band nature we find that electron-electron
interactions can have a profound effect on the density of states as a function
of doping. The doping dependence of the transition temperature can then be
qualitatively different from that expected from simple BCS theory based on the
density of states from band structure calculations
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Edible insect processing pathways and implementation of emerging technologies
The processing of insects is paramount to deliver safe and high quality raw materials, ingredients and products for large-scale food and feed applications. Depending upon the nature of the initial material and the desired end product, the processing pathways vary and may include several unit operations currently already used in food and feed processing. Insect processing pathways can involve harvesting, pre-processing, decontamination, further processing, packaging and storage. Several traditional and industrial decontamination methods have been proposed for edible insects, which include smoking, drying, blanching/boiling, marination, cooking, steaming, toasting and their combinations. Further processing steps are employed to produce insect meal, insect flour or extracted insect fractions. Each operation will have a different impact on the chemical and microbiological properties of the final product. Novel food processing technologies (e.g. high pressure processing, pulsed electric field, ultrasound and cold plasma) have shown potential to modify, complement or replace the conventional processing steps in insect processing. These technologies have been tested for microbial decontamination, enzyme inactivation, drying and extraction. Further, these are considered to be environmentally friendly and may be implemented for versatile applications to improve the processing efficiency, safety and quality of insect based products. Future research focuses in insect processing are development of efficient, environmentally friendly and low-cost processes; waste minimisation and incorporation of by-products/co-products
The impact of celestial pole offset modelling on VLBI UT1 Intensive results
Very Long Baseline Interferometry (VLBI) Intensive sessions are scheduled to
provide operational Universal Time (UT1) determinations with low latency. UT1
estimates obtained from these observations heavily depend on the model of the
celestial pole motion used during data processing. However, even the most
accurate precession-nutation model, IAU 2000/2006, is not accurate enough to
realize the full potential of VLBI observations. To achieve the highest
possible accuracy in UT1 estimates, a celestial pole offset (CPO), which is the
difference between the actual and modelled precession-nutation angles, should
be applied. Three CPO models are currently available for users. In this paper,
these models have been tested and the differences between UT1 estimates
obtained with those models are investigated. It has been shown that neglecting
CPO modelling during VLBI UT1 Intensive processing causes systematic errors in
UT1 series of up to 20 microarcseconds. It has been also found that using
different CPO models causes the differences in UT1 estimates reaching 10
microarcseconds. Obtained results are applicable to the satellite data
processing as well.Comment: 8 pp., accepted for publication in Journal of Geodes
Topological analysis of polymeric melts: Chain length effects and fast-converging estimators for entanglement length
Primitive path analyses of entanglements are performed over a wide range of
chain lengths for both bead spring and atomistic polyethylene polymer melts.
Estimators for the entanglement length N_e which operate on results for a
single chain length N are shown to produce systematic O(1/N) errors. The
mathematical roots of these errors are identified as (a) treating chain ends as
entanglements and (b) neglecting non-Gaussian corrections to chain and
primitive path dimensions. The prefactors for the O(1/N) errors may be large;
in general their magnitude depends both on the polymer model and the method
used to obtain primitive paths. We propose, derive and test new estimators
which eliminate these systematic errors using information obtainable from the
variation of entanglement characteristics with chain length. The new estimators
produce accurate results for N_e from marginally entangled systems. Formulas
based on direct enumeration of entanglements appear to converge faster and are
simpler to apply.Comment: Major revisions. Developed near-ideal estimators which operate on
multiple chain lengths. Now test these on two very different model polymers
Оценка экологической опасности отходов горнодобывающих предприятий республики Хакасия с применением метода биотестирования
Представлены результаты геохимического анализа проб отходов горнодобывающих предприятий Республики Хакасия и их биотестирования. При биотестировании в эксперименте с использованием тест-объекта Drosophila melanogaster оценивались: соотношение полов, морфозы, высота подъема куколок, средняя длина тела и крыла по отношению к концентрации пробы в среде. Сделаны выводы о воздействии отходов на живые объекты, выделены химические элементы, оказывающие токсическое действие
Impact of freeze–thaw cycles on soil structure and soil hydraulic properties
The ploughing of soils in autumn drastically loosens the soil structure and, at the same time, reduces its stability against external stresses. A
fragmentation of these artificially produced soil clods during wintertime is often observed in areas with air temperatures fluctuating around the freezing point. From the pore perspective, it is still unclear (i) under which conditions frost action has a measurable effect on soil structure, (ii) what the impact on soil hydraulic properties is, and (iii) how many freeze–thaw cycles (FTCs) are necessary to induce soil structure changes.
The aim of this study was to analyse the cumulative effects of multiple FTC on soil structure and soil hydraulic properties for two different
textures and two different initial structures. A silt clay with a substantial amount of swelling clay minerals and a silty loam with fewer
swell/shrink dynamics were either kept intact in undisturbed soil cores taken from the topsoil from a grassland or repacked with soil clods taken
from a ploughed field nearby. FTCs were simulated under controlled conditions and changes in pore structure ≥ 48 µm were regularly recorded using X-ray µCT. After 19 FTCs, the impact on hydraulic properties were measured, and the resolution of structural characteristics were enhanced towards narrow macropores with subsamples scanned at 10 µm.
The impact of FTC on soil structure was dependent on the initial structure, soil texture, and the number of FTCs. Frost action induced a
consolidation of repacked soil clods, resulting in a systematic reduction in pore sizes and macropore connectivity. In contrast, the macropore
systems of the undisturbed soils were only slightly affected. Independent of the initial structure, a fragmentation of soil clods and
macro-aggregates larger than 0.8 to 1.2 mm increased the connectivity of pores smaller than 0.5 to 0.8 mm. The fragmentation increased the
unsaturated hydraulic conductivity of all treatments by a factor of 3 in by a factor of 3 in a matrix potential range of −100 to −350 hPa, while water retention was only slightly affected
for the silt clay soil. Already 2 to 5 FTCs enforced a well-connected pore system of narrow macropores in all treatments, but it was steadily
improved by further FTCs. The implications of fewer FTCs during milder winters caused by global warming are twofold. In ploughed soils, the
beneficial seedbed consolidation will be less intense. In grassland soils, which have reached a soil structure in dynamic equilibrium that has
experienced many FTCs in the making, there is still a beneficial increase in water supply through increasing unsaturated hydraulic conductivity by
continued FTCs that might also be less efficient in the future.</p
Inlet conditions for large eddy simulation of gas-turbine swirl injectors
Copyright © 2008 American Institute of Aeronautics and AstronauticsIn this paper, we present a novel technique for generating swirl inlets for large eddy simulation. The velocity a short distance downstream of the inlet to the main domain is sampled and the flow velocity data are reintroduced back into the domain inlet, creating an inlet section integrated into the main domain in which turbulence can develop.
Additionally, variable artificial body forces and velocity corrections are imposed in this inlet section, with feedback control to force the flow toward desired swirl, mean, and turbulent profiles. The method was applied to flow in an axisymmetric sudden expansion, with and without swirl at the inlet, and compared against experimental and literature large eddy simulation data and against similar results in the literature. The method generates excellent results for this case and is elegant and straightforward to implement
Broadening the perspective on ocean privatizations: an interdisciplinary social science enquiry
Broadening the perspective on ocean privatizations: an interdisciplinary social science enquiry
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