The protein puzzle : the consumption and production of meat, dairy and fish in the European Union

In het rapport 'The protein puzzle. The consumption and production of meat, dairy and fish in the European Union' brengen onderzoekers van het Planbureau voor de Leefomgeving (PBL) in kaart wat de gevolgen van de productie en consumptie van dierlijke eiwitten zijn voor milieu, natuur en gezondheid. Vervolgens schetst het PBL welke opties er in Europees verband zijn om de negatieve effecten te verminderen. Met deze studie verschaft het PBL relevante feiten en cijfers ten behoeve van het debat over eiwitconsumptie, inclusief een indicatie van de onzekerheden daarbij

Nanosecond repetitively pulsed discharges in N2-O2 mixtures: Inception cloud and streamer emergence

We evaluate the nanosecond temporal evolution of tens of thousands of positive discharges in a 16 cm point-plane gap in high purity nitrogen 6.0 and in N2–O2 gas mixtures with oxygen contents of 100 ppm, 0.2%, 2% and 20%, for pressures between 66.7 and 200 mbar. The voltage pulses have amplitudes of 20 to 40 kV with rise times of 20 or 60 ns and repetition frequencies of 0.1 to 10 Hz. The discharges first rapidly form a growing cloud around the tip, then they expand much more slowly like a shell and finally after a stagnation stage they can break up into rapid streamers. The radius of cloud and shell in artificial air is about 10% below the theoretically predicted value and scales with pressure p as theoretically expected, while the observed scaling of time scales with p raises questions. We find characteristic dependences on the oxygen content. No cloud and shell stage can be seen in nitrogen 6.0, and streamers emerge immediately. The radius of cloud and shell increases with oxygen concentration. On the other hand, the stagnation time after the shell phase is maximal for the intermediate oxygen concentration of 0.1% and the number of streamers formed is minimal; here the cloud and shell phase seem to be particularly stable against destabilization into streamers

Probing photo-ionization: simulations of positive streamers in varying N2:O2 mixtures

Photo-ionization is the accepted mechanism for the propagation of positive streamers in air though the parameters are not very well known; the efficiency of this mechanism largely depends on the presence of both nitrogen and oxygen. But experiments show that streamer propagation is amazingly robust against changes of the gas composition; even for pure nitrogen with impurity levels below 1 ppm streamers propagate essentially with the same velocity as in air, but their minimal diameter is smaller, and they branch more frequently. Additionally, they move more in a zigzag fashion and sometimes exhibit a feathery structure. In our simulations, we test the relative importance of photo-ionization and of the background ionization from pulsed repetitive discharges, in air as well as in nitrogen with 1 ppm O2 . We also test reasonable parameter changes of the photo-ionization model. We find that photo- ionization dominates streamer propagation in air for repetition frequencies of at least 1 kHz, while in nitrogen with 1 ppm O2 the effect of the repetition frequency has to be included above 1 Hz. Finally, we explain the feather-like structures around streamer channels that are observed in experiments in nitrogen with high purity, but not in air.Comment: 12 figure

Probing photo-ionization: Experiments on positive streamers in pure gasses and mixtures

Positive streamers are thought to propagate by photo-ionization whose parameters depend on the nitrogen:oxygen ratio. Therefore we study streamers in nitrogen with 20%, 0.2% and 0.01% oxygen and in pure nitrogen, as well as in pure oxygen and argon. Our new experimental set-up guarantees contamination of the pure gases to be well below 1 ppm. Streamers in oxygen are difficult to measure as they emit considerably less light in the sensitivity range of our fast ICCD camera than the other gasses. Streamers in pure nitrogen and in all nitrogen/oxygen mixtures look generally similar, but become somewhat thinner and branch more with decreasing oxygen content. In pure nitrogen the streamers can branch so much that they resemble feathers. This feature is even more pronounced in pure argon, with approximately 10^2 hair tips/cm^3 in the feathers at 200 mbar; this density could be interpreted as the free electron density creating avalanches towards the streamer stem. It is remarkable that the streamer velocity is essentially the same for similar voltage and pressure in all nitrogen/oxygen mixtures as well as in pure nitrogen, while the oxygen concentration and therefore the photo-ionization lengths vary by more than five orders of magnitude. Streamers in argon have essentially the same velocity as well. The physical similarity of streamers at different pressures is confirmed in all gases; the minimal diameters are smaller than in earlier measurements.Comment: 28 pages, 14 figures. Major differences with v1: - appendix and spectra removed - subsection regarding effects of repetition frequency added - many more smaller change