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

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