External quality assessment of urinary methylmalonic acid quantification - results of a pilot study

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Traffic at the Edge of Chaos

We use a very simple description of human driving behavior to simulate traffic. The regime of maximum vehicle flow in a closed system shows near-critical behavior, and as a result a sharp decrease of the predictability of travel time. Since Advanced Traffic Management Systems (ATMSs) tend to drive larger parts of the transportation system towards this regime of maximum flow, we argue that in consequence the traffic system as a whole will be driven closer to criticality, thus making predictions much harder. A simulation of a simplified transportation network supports our argument.Comment: Postscript version including most of the figures available from http://studguppy.tsasa.lanl.gov/research_team/. Paper has been published in Brooks RA, Maes P, Artifical Life IV: ..., MIT Press, 199

15Nitrogen uptake from shallow- versus deep-rooted plants in multi-species mixtures and monoculture grassland

Only few studies have explored the importance of functional diversity in temperate agricultural grasslands in relation to nitrogen (N) uptake. This study investigates the consequence of growing deep-rooted plants together with grass-clover mixtures in terms of N uptake efficiency from deep soil layers. The objective was to compare the N uptake of the shallow-rooted grassland species Lolium perenne and Trifolium repens; and the deep-rooted species Cichorium intybus and Medicago sativa in monocultures and mixtures. We hypothesized that growing deep-rooted plant species in mixture with shallow-rooted species increases the N uptake from deep soil layers partly through competition. A 15N tracer study was carried out with 15N enriched ammonium-sulphate placed at three different soil depths (40, 80 and 120 cm). To recover 15N, above-ground plant biomass was harvested after 10 days. We described the decline of 15N uptake with depth by using an exponential decay function. The studied plant communities showed the same relative decline in 15N uptake by increasing soil depths, but different capacities in total 15N uptake. Monoculture L. perenne foraged less 15N in all depths compared to the other four plant communities. The relative 15N uptake of individual plant species grown in mixture decreased stronger with depth than in monoculture. Thus, both findings rejected our hypothesis

Puerto Rico and the Netherworld of Sovereign Debt Restructuring

Puerto Rico has incurred debt well beyond its ability to repay. It attempted to address its fiscal woes through legislation allowing the restructuring of some its debt. The Supreme Court put a stop to this effort, holding that Congress in the Bankruptcy Code barred the Commonwealth from enacting its own restructuring regime. Yet all agreed that the Bankruptcy Code did not provide anything in its place. While Congress quickly enacted PROMESA in an attempt to address the Puerto Rico’s fiscal ills, we explore in this paper whether Congress has the power to bar Puerto Rico from enacting a restructuring mechanism and not offer an alternative. We submit that the answer is no. When it comes to a state, the Supreme Court has held that the power to issue debt necessarily implies the power to restructure that debt. Congress can preempt that power, so long as it puts something in its place. To preempt and leave nothing, however, runs afoul of our federal system. The same reasoning, with greater force, applies to Puerto Rico. The federal government entered into a compact with the citizens of Puerto Rico, granting them, among other things, the power to issue debt. Puerto Rico implicitly received the power to restructure this debt. Congress could offer a substitute to any regime that Puerto Rico might enact, but it cannot leave the Commonwealth without any means to address its fiscal affairs

15Nitrogen transfer from legumes to neighbouring plants in multi-species grassland

This study investigates the N transfer from legumes to neighbouring plants, grasses, legumes and herbs in a temperate grassland. In a field experiment white clover (Trifolium repens), red clover (Trifolium pratense) and lucerne (Medicago sativa) were leaf-labelled with 15N enriched urea. The 15N tracer was measured in above-ground plant tissue of eight neighbouring plants in two subsequent harvests in 2008. The three legumes donated 15N to all neighbouring plants, of which grasses, white and red clover were strong receivers. Results show that N transfer increases with N application and from the 1st to the 2nd cut

Non-Data-Aided Parameter Estimation in an Additive White Gaussian Noise Channel

Non-data-aided (NDA) parameter estimation is considered for binary-phase-shift-keying transmission in an additive white Gaussian noise channel. Cramer-Rao lower bounds (CRLBs) for signal amplitude, noise variance, channel reliability constant and bit-error rate are derived and it is shown how these parameters relate to the signal-to-noise ratio (SNR). An alternative derivation of the iterative maximum likelihood (ML) SNR estimator is presented together with a novel, low complexity NDA SNR estimator. The performance of the proposed estimator is compared to previously suggested estimators and the CRLB. The results show that the proposed estimator performs close to the iterative ML estimator at significantly lower computational complexity

Biomass production and N2-fixation in seven grass-legume mixtures

Inclusion of forage legumes in low-input grassland mixtures improves biomass production and soil fertility trough addition of nitrogen (N) from N2-fixation. The impacts of different mixture of legumes and companion grasses on the N production of the forage mixture have rarely been investigated under comparable soil and climatic conditions. We conducted a field experiment on a sandy soil at two nitrogen levels with seven two-species grassland mixtures: alfalfa (Medicago sativa), bird’s-foot trefoil (Lotus corniculatus), red clover (Trifolium pratense), or white clover (Trifolium repens) in mixture with perennial ryegrass (Lolium perenne), and white clover in mixture with meadow fescue (Festuca pratensis), timothy (Phleum pratense), or hybrid ryegrass (Lolium hybridum). Red clover and alfalfa fixed 400-500 kg N ha-1 and bird ’s-foot trefoil just above 100 kg N ha-1 in aboveground biomass. The white clover N fixation was affected by the companion grass species and ranged from 150 to 175 kg N ha-1. Fertilization had different effects on N2-fixation among the legumes, but also significant effects on white clover N2-fixation depending on the companion grass species