Exploring the phase diagram of the two-impurity Kondo problem

A system of two exchange-coupled Kondo impurities in a magnetic field gives rise to a rich phase space hosting a multitude of correlated phenomena. Magnetic atoms on surfaces probed through scanning tunnelling microscopy provide an excellent platform to investigate coupled impurities, but typical high Kondo temperatures prevent field-dependent studies from being performed, rendering large parts of the phase space inaccessible. We present an integral study of pairs of Co atoms on insulating Cu2N/Cu(100), which each have a Kondo temperature of only 2.6 K. In order to cover the different regions of the phase space, the pairs are designed to have interaction strengths similar to the Kondo temperature. By applying a sufficiently strong magnetic field, we are able to access a new phase in which the two coupled impurities are simultaneously screened. Comparison of differential conductance spectra taken on the atoms to simulated curves, calculated using a third order transport model, allows us to independently determine the degree of Kondo screening in each phase.Comment: paper: 14 pages, 4 figures; supplementary: 3 pages, 1 figure, 1 tabl

Large angle magnetization dynamics measured by time-resolved ferromagnetic resonance

A time-resolved ferromagnetic resonance technique was used to investigate the magnetization dynamics of a 10 nm thin Permalloy film. The experiment consisted of a sequence of magnetic field pulses at a repetition rate equal to the magnetic systems resonance frequency. We compared data obtained by this technique with conventional pulsed inductive microwave magnetometry. The results for damping and frequency response obtained by these two different methods coincide in the limit of a small angle excitation. However, when applying large amplitude field pulses, the magnetization had a non-linear response. We speculate that one possible cause of the nonlinearity is related to self-amplification of incoherence, known as the Suhl instabilities.Comment: 23 pages, 8 figures, submitted to PR

Measuring forest floor interception in a beech forest in Luxembourg

International audienceIn hydrological models evaporation from interception is often disregarded, combined with transpiration, or taken as a fixed percentage of rainfall. In general interception is not considered to be a significant process in rainfall-runoff modelling. However, it appears that on average interception can amount to 20?50% of the precipitation. Therefore, knowledge about the process of interception is important. Traditional research on interception mainly focuses on canopy interception and almost completely denies forest floor interception, although this is an important mechanism that precedes infiltration or runoff. Forest floor interception consists partly of interception by dry soil, partly of interception by short vegetation (mosses, grasses and creeping vegetation) and partly of interception by litter. This research concentrates on litter interception: to measure its quantities at point scale and subsequently to upscale it to the scale of a hydrotope. A special measuring device has been developed, which consists of a permeable upper basin filled with forest floor and a watertight lower basin. Both are weighed continuously. The device has been tested in the Huewelerbach catchment (Luxembourg). The preliminary measuring results show that the device is working properly. For November 2004, evaporation from interception is calculated to be 34% of the throughfall in the Huewelerbach catchment

Short communication:Supplementation of fructo-oligosaccharides does not improve insulin sensitivity in heavy veal calves fed different sources of carbohydrates

Heavy veal calves (4–6 mo old) often develop problems with insulin sensitivity. This could lead to metabolic disorders and impaired animal growth performance. Studies in various animal species have shown that the supplementation of short-chain fructo-oligosaccharides (scFOS) can improve insulin sensitivity. We therefore studied the effects of scFOS supplementation on insulin sensitivity in heavy veal calves. Forty male Holstein-Friesian calves (BW = 190 ± 2.9 kg; age = 162 ± 1.4 d at the start of the trial) were fed either a control milk replacer (MR) diet or a diet in which one-third of the lactose was replaced by glucose, fructose, or glycerol for 10 wk prior to the start of the trial. At the start of the trial, calves were subjected to a frequently sampled intravenous glucose tolerance test to assess whole-body insulin sensitivity (muscle and hepatic insulin sensitivity). Calves within each dietary treatment group were ranked based on their insulin sensitivity value. Half of the calves received scFOS (12 mg/kg of BW) with the MR for 6 wk (supplementation was equally distributed over the insulin sensitivity range). Subsequently, a second frequently sampled intravenous glucose tolerance test was conducted to assess the effect of scFOS. In addition, fasting plasma levels of glucose, insulin, triglycerides, and cholesterol were determined to calculate the quantitative insulin sensitivity check index and triglyceride:high-density lipoprotein cholesterol ratio (fasting indicators of insulin sensitivity). Whole-body insulin sensitivity was low at the start of the trial and remained low in all groups [1.0 ± 0.1 and 0.8 ± 0.1 (mU/L)−1 · min−1 on average, respectively]. Supplementation of scFOS did not improve insulin sensitivity in any of the treatment groups. The quantitative insulin sensitivity check index and the triglyceride:high-density lipoprotein cholesterol ratio also did not differ between scFOS and non-scFOS calves and averaged 0.326 ± 0.003 and 0.088 ± 0.004, respectively, at the end of the trial. We conclude that scFOS supplementation does not improve insulin sensitivity in heavy veal calves regardless of the carbohydrate composition of the MR. This is in contrast to other animals (e.g., dogs and horses), where scFOS supplementation did improve insulin sensitivity. The absence of an effect of scFOS might be related to the dosage or to metabolic differences between ruminants and nonruminants. Increasing evidence indicates that dietary interventions in veal calves have little or no effect on insulin sensitivity, possibly because of low levels of insulin sensitivity