455 research outputs found
Augen auf beim Dünger
Ein Landwirt in der Westschweiz hat kürzlich festgestellt, dass ein Dünger, den er gekauft hatte, Fremdkörper wie Kunststoffe, Aluminium und Schnüre enthielt. Er meldete dies seinem Lieferanten und dem FiBL
Specific interactions leading to transgressive overyielding in cover crop mixtures
Growing mixtures of species instead of sole crops is expected to increase the ecosystem services provided by cover crops. This study aimed at understanding the interactions between species and investigating how they affect the performance of the mixture. Four species were combined in six bispecific mixtures in a field experiment. The performance of each species when grown in a mixture was compared to its performance as a sole crop at different sowing densities, to characterise the influence of intra- and interspecific competition for each species. Intra- and interspecific competition coefficients were quantified using a response surface design and the hyperbolic yield-density equation. Interactions between the four species ranged from facilitation to competition. Most of the mixtures exhibited transgressive overyielding. Without nitrogen (N) fertilisation, high complementarity between species allowed to achieve the highest biomass. With N fertilisation, high dominance of one mixture component should be avoided to achieve good performance. A revised approach in the use of the land equivalent ratio for the evaluation of cover crop mixtures is also proposed in this study. It allows to better identify transgressive overyielding in mixtures and to better characterise the effect of one species on the other within the mixture
The Continuous Skolem-Pisot Problem: On the Complexity of Reachability for Linear Ordinary Differential Equations
We study decidability and complexity questions related to a continuous
analogue of the Skolem-Pisot problem concerning the zeros and nonnegativity of
a linear recurrent sequence. In particular, we show that the continuous version
of the nonnegativity problem is NP-hard in general and we show that the
presence of a zero is decidable for several subcases, including instances of
depth two or less, although the decidability in general is left open. The
problems may also be stated as reachability problems related to real zeros of
exponential polynomials or solutions to initial value problems of linear
differential equations, which are interesting problems in their own right.Comment: 14 pages, no figur
La lutte contre le doryphore
Ces dernières années, de plus en plus de dégâts sur les pommes de terre biologiques ont été causés par le doryphore. Un traitement précoce pendant les deux premiers stades larvaires donne les meilleurs résultats
PAC-learning gains of Turing machines over circuits and neural networks
A caveat to many applications of the current Deep Learning approach is the
need for large-scale data. One improvement suggested by Kolmogorov Complexity
results is to apply the minimum description length principle with
computationally universal models. We study the potential gains in sample
efficiency that this approach can bring in principle. We use polynomial-time
Turing machines to represent computationally universal models and Boolean
circuits to represent Artificial Neural Networks (ANNs) acting on
finite-precision digits.
Our analysis unravels direct links between our question and Computational
Complexity results. We provide lower and upper bounds on the potential gains in
sample efficiency between the MDL applied with Turing machines instead of ANNs.
Our bounds depend on the bit-size of the input of the Boolean function to be
learned. Furthermore, we highlight close relationships between classical open
problems in Circuit Complexity and the tightness of these
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