Nitrogen Fluxes in Silage Maize Production: Relationship between Nitrogen Content at Silage Maturity and Nitrate Concentration in Soil Leachate

A challenge with respect to environmental soundness of agricultural production is the development of suitable indicators, which support an improved understanding and measurement of agricultural activities on environmental quality. The objective of this study was to investigate whether N concentration (Nc) of silage maize at silage maturity, a routinely recorded quality parameter, can serve as an indicator of nitrate concentration in the soil leachate (NO₃C). The study was based on a 5-year experiment (1997–2001), conducted on sandy soil in Northern Germany. The experiment involved four mineral N fertilization rates (0, 50, 100, 150 kg N ha⁻¹) and three slurry treatments (0, 20, 40 m³ ha⁻¹). The water and N balance model HERMES was applied to simulate the N flows within the soil–plant system. The model performed satisfactorily for aboveground biomass accumulation, N uptake, soil mineral N, and nitrate leaching. Statistical analysis of the relationship between measured crop N concentration (Nc, g N kg⁻¹) at silage maturity and simulated mean nitrate concentration (NO₃C, mg NO₃1⁻¹) of the leachate (October–March) revealed a significant impact of rainfall amount during spring/summer. Two exponential functions were estimated to describe the relationship for (i) ℈wet’ years: NO₃C = 3.4253 × exp(0.3426 × Nc), and (ii) ℈dry’ years: NO₃C = 6.8538 × exp(0.1811 × Nc). While in ℈dry’ years nitrate concentration exceeded the drinking water threshold even at very low N concentrations, the risk of high nitrate concentrations was negligible in ℈wet’ years. It is concluded that the newly developed indicator can provide a useful tool for assessing the potential risk of groundwater nitrate contamination in silage maize production.     

Topology optimization of flow domains using the lattice Boltzmann method

We consider the optimal design of two- (2D) and three-dimensional (3D) flow domains using the lattice Boltzmann method (LBM) as an approximation of Navier-Stokes (NS) flows. The problem is solved by a topology optimization approach varying the effective porosity of a fictitious material. The boundaries of the flow domain are represented by potentially discontinuous material distributions. NS flows are traditionally approximated by finite element and finite volume methods. These schemes, while well established as high-fidelity simulation tools using body-fitted meshes, are effected in their accuracy and robustness when regular meshes with zero-velocity constraints along the surface and in the interior of obstacles are used, as is common in topology optimization. Therefore, we study the potential of the LBM for approximating low Mach number incompressible viscous flows for topology optimization. In the LBM the geometry of flow domains is defined in a discontinuous manner, similar to the approach used in material-based topology optimization. In addition, this non-traditional discretization method features parallel scalability and allows for high-resolution, regular fluid meshes. In this paper, we show how the variation of the porosity can be used in conjunction with the LBM for the optimal design of fluid domains, making the LBM an interesting alternative to NS solvers for topology optimization problems. The potential of our topology optimization approach will be illustrated by 2D and 3D numerical examples.     

Biomethane production kinetics of rumen pretreated lignocellulosic wastes

Clean Technologies and Environmental Policy - Bioenergy production from lignocellulosic biomass is challenging due to its complex structure. Therefore, a pretreatment is required before methane...     

Zündung von Wasserstoff-Knallgas im Stoßwellenrohr

Ohne Zusammenfassung Schlu? des Aufsatzes aus Heft 3 (1967) S. 69/76.     

Measurements of convective heat transfer from a horizontal cylinder rotating in a tank of water

The present paper deals with measurements of heat transfer from a horizontal cylinder rotating in water. The experimental results have been correlated by the equation Nu = 0.133Re^2/3 · Pr^1/3 for a range of rotating Reynolds numbers from 1000 to 46 000, and Prandtl numbers from 2.2 to 6.4. This equation compares very well with the experimental and theoretical information available for air, water and oil in published works.

The analogy suggested by Anderson and Saunders between natural convection from a horizontal plate and the present type of flow has been used to predict the Nusselt numbers. The analogy solution and the present experimental results have been found to compare very well with each other.     

Coupling edge and region-based information for boundary finding in biomedical imagery

We propose in this paper a boundary finding scheme for biomedical imagery which integrates a region-based method and an edge-based technique. We show that more accurate and robust results may be obtained through seeking a joint solution to the traditional approach of curve evolution. The approach incorporates an energy model based on prior distribution and likelihood into the curve evolution of the geodesic active contour (GAC) method. During curve evolution, we use a decision function to adjust relevant parameters in the model automatically so that the curve can easily avoid ‘clutter’. For termination of curve evolution, a stability index is proposed which examines curve evolution convergence to ensure that the curve arrives at the boundary robustly and accurately. The experimental results demonstrate that advantages can be achieved using our approach compared to several classical methods.