New energy and helicity bounds for knotted and braided magnetic fields

In this article we present a review of some of the author's most recent results in topological magnetohydrodynamics (MHD), with an eye to possible applications to astrophysical flows and solar coronal structures. First, we briefly review basic work on magnetic helicity and linking numbers, and fundamental relations with magnetic energy and average crossing numbers of magnetic systems in ideal conditions. In the case of magnetic knots, we focus on the relation between their groundstate energy and topology, discussing the energy spectrum of tight knots in terms of ropelength. We compare this spectrum with the one given by considering the bending energy of such idealized knots, showing that curvature information provides a rather good indicator of magnetic energy contents. For loose knots far from equilibrium we show that inflexional states determine the transition to braid form. New lower bounds for tight knots and braids are then established. We conclude with results on energy-complexity relations for systems in presence of dissipation.     

Influence of the Sonic Anemometer Temperature Calibration on Turbulent Heat-Flux Measurements

The speed of sound in moist air is discussed and a more accurate value for the coefficient of the linear dependence of sonic temperature on specific humidity is proposed. An analysis of speed-of-sound data measured by three sonic anemometers in a climate chamber and in the field shows that the temperature response of each instrument significantly influences not only the determination of sonic temperature, but also its fluctuations. The corresponding relative contribution to the error in the evaluation of the temperature fluctuations and the turbulent heat fluxes can be as high as 40%. The calibration procedure is discussed and a method of correction is proposed.     

PCBs and chlorinated pesticides in organisms from the Ligurian Sea

The concentrations of BHCs, DDTs and PCBs have been determined in samples of Engraulis encrasicholus, Mytilus galloprovincialis, Nephrops norvegicus, Mullus barbatus, Euthymnus alletteratus and Sarda sarda, collected in different stations of the Ligurian Sea. Increasing levels of contamination were found in the order: Nephrops, Mytilus and Engraulis, Mullus and Euthymnus, Sarda.A comparison with the data available in the literature relevant to Mytilus samples collected in Genoa in 1973–1974 showed a notable decrease in the concentration of chlorinated residues.     

Heavy metals in mussels (Mytilus galloprovincialis) from the gulf of la spezia and from the promontory of Portofino,Italy

In different samples of Mytilus galloprovincialis Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb and Zn were determined by AAS. The mussels were taken from 11 sites in the Port of La Spezia. Typical concentration ranges (μ/g dry weight) were as follows: Cd, 2.0–6.8; Co, 0.8–3.2; Cr, 5.8–19.5; Cu, 6.9–33.7; Hg, 0.15–0.38; Mn, 11.8–37.8; Ni, 1.3–10.9; Pb, 13.9–44.6 and Zn, 203–379.Other samples were collected at 4 sites on the Promontory of Portofino and the following values were obtained: Cd, 0.8–1.1; Co, 2.6–2.9; Cu, 3.3–4.2; Hg, 0.09–0.15; Mn, 6.3–9.1; Ni, 1.2–2.4; Zn, 120–140.     

Alternative stable states in mountain forest ecosystems: the case of European larch (<Emphasis Type="Italic">Larix decidua</Emphasis>) forests in the western Alps

European larch (Larix decidua) forests of the western Alps form extensive cultural landscapes whose resilience to global changes is currently unknown. Resilience describes the capacity of ecological systems to maintain the same state, i.e., the same function, processes, structure, and composition despite disturbances, environmental changes and internal fluctuations. Our aim is to explore the resilience of larch forests to changes in climate and land use in the western Italian Alps. To do so, we examined whether larch forests can be described as an alternative stable state in mountain forest ecosystems. We used tree basal area data obtained from field forest inventories in combination with topography, forest structure, land use, and climate information. We applied three different probabilistic methods: frequency distributions, logistic regressions, and potential analyses to infer the resilience of larch forests relative to that of other forest types. We found patters indicative of alternative stable states: bimodality in the frequency distribution of the percent of larch basal area, and the presence of an unstable state, i.e., mixed larch forests, in the potential analyses. We also found: (1) high frequency of pure larch forests at high elevation, (2) the probability of pure larch forests increased mostly with elevation, and (3) pure larch forests were a stable state in the upper montane and subalpine belts. Our study shows that the resilience of larch forests may increase with elevation, most likely due to the altitudinal effect on climate. Under the same climate conditions, land use seems to be the main factor governing the dominance of larch forests. In fact, subalpine larch forests may be more resilient, and natural succession after land abandonment, e.g., towards Pinus cembra forests, seems slower than in montane larch forests. In contrast, in the upper montane belt only intense land use regimes characterized by open canopies and forest grazing may maintain larch forests. We conclude that similar approaches could be applied in other forest ecosystems to infer the resilience of tree species.