1,498 research outputs found
Catering for sustainability: building a dialogue on organic milk
To boost perspective taking on organic milk among caterers, a co-developmental dialogue in terms of organic milk was employed by researchers and practitioners
Systemic sustainability characteristics of organic farming: a review
Agriculture for food production has come to crossroads: while conventional agriculture needs to improve environmental and social performance, organic agriculture needs to increase the production volumes and to re-establish the connctedness between producers and consumers. Through re-localising the food production there is an increasing convergence of the farming practices towards sustainable agriculture acknowledging the prospects, advantages and limitations of the different production systems. The aim is to find combination of production methods that is optimal in given circumstances and to adapt the production system accordingly. Assessment of the environmental impacts should be integrated into assessment of the overall sustainability. Formulation of the management strategies requires evaluation and integration of reaseach results from many different disciplines, and the focus of the interdisciplinary research should be on food systems bioregions rather than on the level of farms or farming systems.
The present article is a review on today's discussion and research dealing with conventional, organic and local farming for food production. The future prospects of organic production to respond to the challenges of advancing global food security and to contribute to overall sustainable development are discussed. It seems that as a developing production mode organic agriculture has a role to play in the green global network of local food systems
Mapping the three-body system - decay time and reversibility
In this paper we carry out a quantitative analysis of the three-body systems
and map them as a function of decaying time and intial conguration, look at
this problem as an example of a simple deterministic system, and ask to what
extent the orbits are really predictable. We have investigated the behavior of
about 200 000 general Newtonian three body systems using the simplest initial
conditions. Within our resolution these cover all the possible states where the
objects are initially at rest and have no angular momentum. We have determined
the decay time-scales of the triple systems and show that the distribution of
this parameter is fractal in appearance. Some areas that appear stable on large
scales exhibit very narrow strips of instability and the overall pattern,
dominated by resonances, reminds us of a traditional Maasai warrior shield.
Also an attempt is made to recover the original starting conguration of the
three bodies by backward integration. We find there are instances where the
evolution to the future and to the past lead to different orbits, in spite of
time symmetric initial conditions. This implies that even in simple
deterministic systems there exists an Arrow of Time.Comment: 8 pages, 9 figures. Accepted for publication in MNRAS. Includes
low-resolution figures. High-resolution figures are available as PNG
Long-Term Evolution of Massive Black Hole Binaries. III. Binary Evolution in Collisional Nuclei
[Abridged] In galactic nuclei with sufficiently short relaxation times,
binary supermassive black holes can evolve beyond their stalling radii via
continued interaction with stars. We study this "collisional" evolutionary
regime using both fully self-consistent N-body integrations and approximate
Fokker-Planck models. The N-body integrations employ particle numbers up to
0.26M and a direct-summation potential solver; close interactions involving the
binary are treated using a new implementation of the Mikkola-Aarseth chain
regularization algorithm. Even at these large values of N, two-body scattering
occurs at high enough rates in the simulations that they can not be simply
scaled to the large-N regime of real galaxies. The Fokker-Planck model is used
to bridge this gap; it includes, for the first time, binary-induced changes in
the stellar density and potential. The Fokker-Planck model is shown to
accurately reproduce the results of the N-body integrations, and is then
extended to the much larger N regime of real galaxies. Analytic expressions are
derived that accurately reproduce the time dependence of the binary semi-major
axis as predicted by the Fokker-Planck model. Gravitational wave coalescence is
shown to occur in <10 Gyr in nuclei with velocity dispersions below about 80
km/s. Formation of a core results from a competition between ejection of stars
by the binary and re-supply of depleted orbits via two-body scattering. Mass
deficits as large as ~4 times the binary mass are produced before coalescence.
After the two black holes coalesce, a Bahcall-Wolf cusp appears around the
single hole in one relaxation time, resulting in a nuclear density profile
consisting of a flat core with an inner, compact cluster, similar to what is
observed at the centers of low-luminosity spheroids.Comment: 21 page
Small-N Collisional Dynamics: Pushing Into the Realm of Not-So-Small-N
In this paper, we study small-N gravitational dynamics involving up to six
objects. We perform a large suite of numerical scattering experiments involving
single, binary, and triple stars. This is done using the FEWBODY numerical
scattering code, which we have upgraded to treat encounters involving triple
stars. We focus on outcomes that result in direct physical collisions between
stars, within the low angular momentum and high absolute orbital energy regime.
The dependence of the collision probability on the number of objects involved
in the interaction, N, is found for fixed total energy and angular momentum.
Our results are consistent with a collision probability that increases
approximately as N^2. Interestingly, this is also what is expected from the
mean free path approximation in the limit of very large N. A more thorough
exploration of parameter space will be required in future studies to fully
explore this potentially intriguing connection. This study is meant as a first
step in an on-going effort to extend our understanding of small-N collisional
dynamics beyond the three- and four-body problems and into the realm of
larger-N.Comment: 11 pages, 6 figures, 2 tables; accepted for publication in MNRAS;
updated to match published versio
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