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Study on environmental factors influencing the urea content of cow's milk in Wallonia and estimation of nitrogen rejection. In Wallonia (South of Belgium), the urea content of milk produced on farms is assessed by the "Comité du lait". A total of 8,295,337 pieces of data recording the urea content in milk tanks was collected on Walloon farms in 2000 and during the period 2002-2011. These data were analyzed using a linear model. The fixed effects of the agricultural area or vulnerable zone, the month, the year and the interactions between these parameters were included in the model. The levels of fat and protein content in the milk were used as covariates. The average urea content in milk was found to be 255 mg·l-1. Four percent of the observations recorded a urea content of over 350 mg·l-1 and 14% recorded a urea content of over 400 mg·l-1. The models explained 38% and 35% of the variation in milk urea for the agricultural area and the vulnerable area variables, respectively. Within these models, the variables of month, region, year and the month-year interaction were the components that provided the most information. Milk urea content was higher in the summer period – April to October – than during the winter period – November to March – (287 vs 210 mg·l-1). This observation can be explained by the change in the cows' diet. During the summer, most of the cows grazed; ingestion of grass can lead to a nitrogen surplus in the diet. In the so-called "Limoneuse" and "Sablo-limoneuse" agricultural areas, recorded urea content was lower than in "Ardenne" and "Haute-Ardenne" (223 and 220 mg vs 278 and 284 mg·l-1, respectively). This difference can be explained by a greater use of grass in the diet in Ardenne and Haute-Ardenne. In vulnerable areas, urea content was lower (236 vs 273 mg·l-1). Annual nitrogen production calculated using different prediction equations ranged from 82 to 119 kg N per cow depending on the agricultural area.

Improvements after precision dietary management of nitrogen rejection in two commercial dairy farms in Wallonia. Two dairy farms located in Pays de Herve and in Ardennes were followed at regular intervals in order to assess levels of nitrogen rejection. In Farm 1, the cows were divided into two groups: group HP contained high production cows and group BP contained cows with a lower production yield. Each group was offered a specific basal diet. In Farm 2, only one group of cows was assessed. The feed rations on both farms were characterized by a imbalance between the yields allowed by the energy or the nitrogen supplies and by an extremely high OEB balance of 794, 582 and 726 g, respectively, in groups HP and BP and in the Farm 2 group. Dietary changes were proposed in order to balance milk yields and to reduce the hypothesized nitrogen balance. The yield and urea content data from each milk record, along with data regarding nitrogen rejection, were statistically analyzed using a mixed model, which included an autoregressive covariance. The data from records 2, 3, 4 and 5 were then compared to the data from record 1. The advised changes implemented in the feeding management plan maintained milk yields at values similar to the yields observed in record 1 – 36.2, 24.3 and 23.0 l of 4% fat-corrected milk expressed for fixed days in milk produced by groups HP and BP and the Farm 2 group. The changes induced a significant reduction in the milk urea content (220 vs 300 mg·l-1) and a significant reduction in nitrogen rejection, whether expressed in terms of g per day per cow, g·l-1 or kg per year per cow. The cows in the Farm 2 group rejected less nitrogen in absolute terms (217.9 vs 260.1 g per day). However, it is interesting to note that the management approach in Farm 1 was more efficient in terms of nitrogen rejection since the level was on average 9 g·l-1 in comparison with 10 g·l-1 in Farm 2. In conclusion, it appears that, for either farm, whether an intensive or extensive management regime was being employed, the provision of well balanced feed rations led to a reduction in nitrogen rejection. It should, however, be noted that management advice needs to be provided on a farm by farm basis.

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We present a new approach to simulate the transport of charges across organic/organic layer interfaces in organic semiconductor devices. This approach combines the drift-diffusion formalism away from the interface with a hopping description of the charge transport in the vicinity of the interface. It has been implemented in the commercial software SETFOS allowing for fast simulations of the complete device. This new model takes into account both recombination and generation mechanisms across the interface enabling the modeling of charge-generation/recombination interfaces for the numerical simulation of tandem devices. Using this approach, it is also possible to simulate devices using 1,4,5,8,9,11-Hexaazatriphenylenehexacarbonitrile as a hole-injection layer. This particular material has a very deep HOMO level (approximately 9.5 eV), which would seemingly prevent such a layer to be used as a hole-injection material in the framework of traditional drift-diffusion models. [ABSTRACT FROM AUTHOR]

Single-carrier devices are an excellent model system to study charge injection and charge transport properties of (doped) transport layers and to draw conclusions about organic electronics devices in which they are used. By combining steady-state and impedance measurements at varying temperatures of hole-only devices with different intrinsic layer thicknesses, we are able to determine all relevant material parameters, such as the charge mobility and the injection barrier. Furthermore, the correlation and sensitivity analyses reveal that the proposed approach to study these devices is especially well suited to extract the effective doping density, a parameter which cannot be easily determined otherwise. The effective doping density is crucial in organic light-emitting diodes (OLEDs) for realizing efficient injection, charge balance, and lateral conductivity in display or lighting applications. With the fitted drift-diffusion device model, we are further able to explain the extraordinary two-plateau capacitance–frequency curve of these hole-only devices, which originates from charges that flow into the intrinsic layer at zero applied offset voltage. We demonstrate that the observation of this behaviour is a direct indication for ideal charge injection properties and the observed capacitance–frequency feature is linked to the charge carrier mobility in the intrinsic layer. The extracted material parameters may directly be used to simulate and optimize full OLED devices employing the investigated hole-injection and -transport materials. [ABSTRACT FROM AUTHOR]