1,218 research outputs found
A Solution Set-Based Entropy Principle for Constitutive Modeling in Mechanics
Entropy principles based on thermodynamic consistency requirements are widely
used for constitutive modeling in continuum mechanics, providing physical
constraints on a priori unknown constitutive functions. The well-known
M\"uller-Liu procedure is based on Liu's lemma for linear systems. While the
M\"uller-Liu algorithm works well for basic models with simple constitutive
dependencies, it cannot take into account nonlinear relationships that exist
between higher derivatives of the fields in the cases of more complex
constitutive dependencies.
The current contribution presents a general solution set-based procedure,
which, for a model system of differential equations, respects the geometry of
the solution manifold, and yields a set of constraint equations on the unknown
constitutive functions, which are necessary and sufficient conditions for the
entropy production to stay nonnegative for any solution. Similarly to the
M\"uller-Liu procedure, the solution set approach is algorithmic, its output
being a set of constraint equations and a residual entropy inequality. The
solution set method is applicable to virtually any physical model, allows for
arbitrary initially postulated forms of the constitutive dependencies, and does
not use artificial constructs like Lagrange multipliers. A Maple implementation
makes the solution set method computationally straightforward and useful for
the constitutive modeling of complex systems.
Several computational examples are considered, in particular, models of gas,
anisotropic fluid, and granular flow dynamics. The resulting constitutive
function forms are analyzed, and comparisons are provided. It is shown how the
solution set entropy principle can yield classification problems, leading to
several complementary sets of admissible constitutive functions; such problems
have not previously appeared in the constitutive modeling literature
Legehennen in einem mobilen Stallsystem - Auslaufnutzung und FlÀchenzustand -
The use of the free-range area by laying hens housed in a mobile system and the resulting condition of the range were investigated. The free-range was used very intensively. On an average of nine complete observation days 35 % of the birds (23 â 44 % means per day) were outside the house. The maximum of animals in the free range was 77 %. 75 % (60 â 95 %) of the hens outside the house stayed in an area of 20 m around the house. This led to deteriorated conditions of the range in these areas. By moving the mobile house regularly (after 2 weeks in summer and 6 weeks in winter) a destruction of the vegetation could be avoided, while after not moving the house for three months in winter a complementary seeding became necessary.
We conclude that the use of mobile systems for poultry in conjunction with a regular change of position and sufficient area per animal can avoid destruction of the vegetation despite an intensive use of the free-range all year round
Legehennen in einem mobilen Stallsystem - FlÀchenmanagement und resultierende Stickstoffgehalte im Auslauf -
In the last years free range poultry was often criticised for its negative impacts on environment. As the animals do not use the run equally, a big part of the excreted nutrients are accumulated in the area close to the poultry house. This can lead to an increased rate of nutrient loss especially nitrogen by leaching.
Within this study the use of a mobile housing system for 1.000 layers on an organic farm in North Hessia with a mean of 700 mm precipitation per year and an average of 8,9°C (soil texture: loam in the first, silt loam in the second year) was observed for two years. A documentation and optimization of the management and regular investigations into the contents of mineral nitrogen in all parts of the outdoor run were carried out. The aim of the study was to survey, if a well-balanced distribution of nutrients can be reached by moving the house within the free-range and which management is necessary for that.
The results showed a better distribution of mineral nitrogen in the second year, when the house was moved in winter time every six weeks, while the contents were slightly less well-balanced, when it stayed at one position for three months in the first winter . In both years the highest amounts of mineral nitrogen in any part of the hen run with 37 and 24 mg / kg DM were much lower than the contents of up to 160 mg / kg DM close to stationary houses examined in other studies. The results of this study show that a well-balanced distribution of nutrients in free-ranges for poultry can be reached by using mobile housing systems combined with the right management
Samenfeste Sorten oder Hybriden - Untersuchungen an Speisemöhren aus einem Anbauvergleich an zwei Standorten des Ăkologischen Landbaus
An zwei Standorten des Ăkologischen Landbaus (Neu-Eichenberg, Nordhessen: mittlerer bis schwerer Boden; Queck, Osthessen: leichter Boden) wurden Feldversuche mit Möhren durchgefĂŒhrt, um sechs samenfeste Sorten und sechs Hybriden auf ihre Anbautauglichkeit zu prĂŒfen. AuĂer der Roh- und HandelswarenertrĂ€ge wurden die Einheitlichkeit des Erntegutes (cv%) bestimmt und die Gehalte an Mineralstoffen (K, Ca, P, Mg) und Zuckern (D-Glucose, D-Fructose, Saccharose) analysiert. Auch sogenannte Bildschaffende Methoden (Kupferchloridkristallisation, Steigbild, Rundfilterchromatogramm) kamen zur Anwendung. Die untersuchten Hybriden erzielten MehrertrĂ€ge von 25 bis 29% und in den meisten FĂ€llen auch gleichmĂ€Ăiger lange RĂŒben als die Samenfesten. Die Inhaltsstoffuntersuchungen zeigten höhere Mineralstoffgehalte und niedrigere Quotienten von Mono- zu Disaccharide bei den samenfesten Sorten. Mithilfe der Bildschaffenden Methoden konnten die Proben blind klar in zwei unterschiedliche Gruppen differenziert werden: Die Bilder der samenfesten Sorten waren im Vergleich zu denjenigen der Hybriden geprĂ€gt durch einen höheren Grad an FormintensitĂ€t und Reife
SGARFACE: A Novel Detector For Microsecond Gamma Ray Bursts
The Short GAmma Ray Front Air Cherenkov Experiment (SGARFACE) is operated at
the Whipple Observatory utilizing the Whipple 10m gamma-ray telescope. SGARFACE
is sensitive to gamma-ray bursts of more than 100MeV with durations from 100ns
to 35us and provides a fluence sensitivity as low as 0.8 gamma-rays per m^2
above 200MeV (0.05 gamma-rays per m^2 above 2GeV) and allows to record the
burst time structure.Comment: 29 pages, 14 figures, accepted for publication in Astroparticle
Physic
Samenfeste Sorten oder Hybriden - Anbauvergleich von Möhren unter den VerhĂ€ltnissen des Ăkologischen Landbaus
A field trial with carrots was carried out in 1998 at two sites in Hesse (North: loamy soil in Neu-Eichenberg; East: sandy soil in Queck) to compare 6 open pollinating and 6 F1 hybrids under an Organic Farming regime. Characteristics of cultivation, harvest, quality, and longevity were measured. Of the parameters of cultivation and harvest the hybrids showed a more intensive foliage growth, higher marketable yields (plus 29 and 25%), and more homogeneous taproots than the open pollinating cultivars. Picture forming methods clearly separated the samples into the two groups of breeding methods. The open pollinating cultivars were characterized by higher degrees of form intensity and ripeness and a stable vitality. The hybrids of the sandy site had a better keeping quality after 6Âœ months storage, only the open pollinating cultivar âRodelikaâ had a very high ranking similar to the hybrids âKardame F1â and âBolero F1â
Constituent Quarks, Diquarks and the N-Delta Mass Splitting
We analyze hadron as well as quark and diquark correlation functions in
Landau gauge in order to extract information on the spin dependence of the
quark-quark interaction. We find evidence that the N-Delta mass splitting can
be attributed to the spin dependence of the interaction between quarks in a
colour anti-triplet state with spin 0 and 1, respectively. The lightest
excitations are observed in the S=0 channel. However, no evidence for a deeply
bound diquark state is found.Comment: LATTICE98(spectrum), 3 pages, LaTeX2e File, 4 EPS-figures,
espcrc2.st
Simulation of the Flow and Acoustic Field of a Fan
The focus of the present work is the steady and
unsteady numerical simulation of flow field and
flow-induced acoustic field of a fan using a hybrid
approach. The steady simulation of the flow field is
carried out with a realizable k-epsilon turbulence
model. In a second step the result are used for the
evaluation of the acoustic sources, which are used
as input data of the Broadband Noise Model. From
this computational acoustics (CA) we get a
qualitative map of acoustic power level in the entire
computational domain. From steady flow fields
with different mass flows as inlet boundary
condition the characteristic curve of the fan
(pressure vs. mass flow) is evaluated.
In the unsteady simulation, the acoustic noise
propagation is computed using the Ffowcs Williams
and Hawkings (FW-H) analogy. The source term in
the acoustic propagation equation is achieved from
the CFD result. With this unsteady simulation the
transient acoustic power level in every location can
be calculated, which enables a FFT-analysis of the
acoustic field
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