Ab initio calculation of the neutron-proton mass difference

The existence and stability of atoms rely on the fact that neutrons are more massive than protons. The measured mass difference is only 0.14\% of the average of the two masses. A slightly smaller or larger value would have led to a dramatically different universe. Here, we show that this difference results from the competition between electromagnetic and mass isospin breaking effects. We performed lattice quantum-chromodynamics and quantum-electrodynamics computations with four nondegenerate Wilson fermion flavors and computed the neutron-proton mass-splitting with an accuracy of $300$ kilo-electron volts, which is greater than $0$ by $5$ standard deviations. We also determine the splittings in the $\Sigma$, $\Xi$, $D$ and $\Xi_{cc}$ isospin multiplets, exceeding in some cases the precision of experimental measurements.Comment: 57 pages, 15 figures, 6 tables, revised versio

Factors affecting the availability of plant nutrients on an Antarctic island

An examination of material from Signy Island, in the South Orkney group, shows that large amounts of plant nutrients are moving through the ecosystem of the island. Physical weathering is a dominant process and the rocks are an important source of potassium and calcium. The ocean provides a steady supply of sodium and magnesium distributed via the atmosphere whilst the fauna provide a large reservoir of phosphorus, nitrogen and cations. Atmospheric distribution of nitrogen from the fauna sites is important but phosphorus appears to depend more on direct droppings and drainage for distribution. The capacity of the bryophyte vegetation to retain ions was demonstrated by experiment. It is suggested that this pattern of nutrient supply applies to much of the Antarctic perimeter zone

Development and application of a resin-bag method to determine available nitrogen in forest soils

SIGLEAvailable from British Library Document Supply Centre- DSC:5682.262(107) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Functional traits of woody plants: correspondence of species rankings between field adults and laboratory-grown seedlings?

Research into interspecific variation in functional traits is important for our understanding of trade-offs in plant design and function, for plant functional type classifications and for understanding ecosystem responses to shifts in species composition. Interspecific rankings of functional traits are a function of, among other factors, ontogenetic or allometric development and environmental effects on phenotypes. For woody plants, which attain large size and long lives, these factors might have strong effects on interspecific trait rankings. This paper is the first to test and compare the correspondence of interspecific rankings between laboratory grown seedlings and field grown adult plants for a wide range of functional leaf and stem traits. It employs data for 90 diverse woody and semiwoody species in a temperate British and a (sub)Mediterranean Spanish flora, all collected according to a strict protocol. For 12 out of 14 leaf and stem traits we found significant correlations between the species ranking in laboratory seedlings and field adults. For leaf size and maximum stem vessel diameter > 50 % of variation in field adults was explained by that in laboratory seedlings. Two important determinants of plant and ecosystem functioning, specific leaf area and leaf N content, had only 27 to 36 and 17 to 31 % of variation, respectively, in field adults explained by laboratory seedlings, owing to subsets of species with particular ecologies deviating from the general trend. In contrast, interspecific rankings for the same traits were strongly correlated between populations of field adults on different geological substrata. Extrapolation of interspecific trait rankings from laboratory seedlings to adult plants in the field, or vice versa, should be done with great cautio