372 research outputs found
Alternativen der Kleegrasnutzung in vieharmen und viehlosen Betrieben
Increasing number of stockless organic farms give reason to search for new forms of clover-grass (CG) utilization in order to maintain or increase soil fertility and productivity. A quantitative study was carried out among 93 organic farms to identify different forms of CG utilization and their assets and drawbacks on organic farms.
Different ways of CG transfer such as direct transfer (cut & carry) and indirect transfer stockless farms. In addition, seven farms were interviewed about their experiences
with CG transfer practices. The farmers rate CG transfer mainly positive, since it may partially compensate the negative effects on soil fertility through the missing manure on stockless organic farms. As less than 0.2 LU/ha is found on more than 34% of all organic farms, there is a high relevance for alternative forms of CG usage in order to
ensure the fertility of organic arable farming. However, we also see a high need for research to improve economic conditions of animal husbandry as an integral part of
sustainable organic farming systems
Alternativen der Kleegrasnutzung in vieharmen und viehlosen Betrieben
Increasing number of stockless organic farms give reason to search for new forms of clover-grass (CG) utilization in order to maintain or increase soil fertility and productivity. A quantitative study was carried out among 93 organic farms to identify different forms of CG utilization and their assets and drawbacks on organic farms.
Different ways of CG transfer such as direct transfer (cut & carry) and indirect transfer stockless farms. In addition, seven farms were interviewed about their experiences
with CG transfer practices. The farmers rate CG transfer mainly positive, since it may partially compensate the negative effects on soil fertility through the missing manure on stockless organic farms. As less than 0.2 LU/ha is found on more than 34% of all organic farms, there is a high relevance for alternative forms of CG usage in order to
ensure the fertility of organic arable farming. However, we also see a high need for research to improve economic conditions of animal husbandry as an integral part of
sustainable organic farming systems
Believing, belonging and volunteerism in adolescence : predictive factors from childhood and confirmation time in a multi-level framework
BKM Lie superalgebras from counting twisted CHL dyons
Following Sen[arXiv:0911.1563], we study the counting of (`twisted') BPS
states that contribute to twisted helicity trace indices in four-dimensional
CHL models with N=4 supersymmetry. The generating functions of half-BPS states,
twisted as well as untwisted, are given in terms of multiplicative eta products
with the Mathieu group, M_{24}, playing an important role. These multiplicative
eta products enable us to construct Siegel modular forms that count twisted
quarter-BPS states. The square-roots of these Siegel modular forms turn out be
precisely a special class of Siegel modular forms, the dd-modular forms, that
have been classified by Clery and Gritsenko[arXiv:0812.3962]. We show that each
one of these dd-modular forms arise as the Weyl-Kac-Borcherds denominator
formula of a rank-three Borcherds-Kac-Moody Lie superalgebra. The walls of the
Weyl chamber are in one-to-one correspondence with the walls of marginal
stability in the corresponding CHL model for twisted dyons as well as untwisted
ones. This leads to a periodic table of BKM Lie superalgebras with properties
that are consistent with physical expectations.Comment: LaTeX, 32 pages; (v2) matches published versio
Micro-plasticity and intermittent dislocation activity in a simplified micro structural model
Here we present a model to study the micro-plastic regime of a stress-strain
curve. In this model an explicit dislocation population represents the mobile
dislocation content and an internal shear-stress field represents a mean-field
description of the immobile dislocation content. The mobile dislocations are
constrained to a simple dipolar mat geometry and modelled via a dislocation
dynamics algorithm, whilst the shear-stress field is chosen to be a sinusoidal
function of distance along the mat direction. The latter, defined by a periodic
length and a shear-stress amplitude, represents a pre-existing micro-structure.
These model parameters, along with the mobile dislocation density, are found to
admit a diversity of micro-plastic behaviour involving intermittent plasticity
in the form of a scale-free avalanche phenomenon, with an exponent for the
strain burst magnitude distribution similar to those seen in experiment and
more complex dislocation dynamics simulations.Comment: 30 pages, 12 figures, to appear in "Modelling and Simulation in
Materials Science and Engineering
Giant segregation transition as origin of liquid metal embrittlement in the Fe-Zn system
A giant Zn segregation transition is revealed using CALPHAD-integrated
density-based modelling of Zn segregation into Fe grain boundaries (GBs). The
results show that above a threshold of only a few atomic percent Zn in the
alloy, a substantial amount of up to 60 at.% Zn can segregate to the GB. We
also found that the amount of segregation significantly increases with
decreasing temperature, while the required Zn content in the alloy for
triggering the segregation transition decreases. Direct evidence of this Zn
segregation transition is obtained using high-resolution scanning transmission
electron microscopy. We trace the origin of the segregation transition and its
temperature dependence back to the low cohesive energy of Zn and a miscibility
gap in Fe-Zn GB, arising from the magnetic ordering effect, which is
demonstrated by ab initio calculations. We show that the massive Zn segregation
resulting from the segregation transition greatly assists with liquid wetting
and reduces the work of separation along the GB. These findings reveal the
fundamental origin of GB weakening and therefore liquid metal embrittlement in
the Fe-Zn system.Comment: Original work, Letter, 14 pages including supplementary material
(SM), 8 figures (3 in SM), 2 tables in S
- …