Umbrella species as a conservation planning tool

In northern Europe, a long history of anthropogenic land use has led to profound changes within forest ecosystems. One of the proposed approaches for conservation and restoration of forest biodiversity is the use of umbrella species, whose conservation would confer protection to large numbers of naturally co-occurring species. This thesis aims to evaluate some of the prerequisites to the umbrella species concept, focusing on resident birds in hemiboreal and boreal forests. The study was performed in four areas belonging to the southern Baltic Sea region: central and southern Sweden, south-central Lithuania and northeastern Poland. A review of empirical evaluations of the umbrella species concept performed in various systems suggested that multispecies approaches addressing the requirements of both the umbrellas and the beneficiary species have better potential than approaches based coarsely on the area needs of single species. An analysis of co-occurrence patterns among resident forest birds in landscape units of 100 ha showed that some species reliably indicated high species richness through their presence. For birds of deciduous forests, there was high cross-regional consistency in the identity of the best indicators. Specialised woodpeckers (Picidae) were prominent among the species that performed well as indicators. Their presence in the landscape units was generally linked positively to the degree of naturalness of the forest and to the amounts of resources that have become scarce in intensively managed forests, such as dead wood and large trees. In Sweden, occurrence of the white-backed woodpecker (Dendrocopos leucotos) in bird atlas squares was positively related to species richness among forest birds of conservation concern, as well as to the area of deciduous and mixed forests of high value for conservation. Moreover, the number of red-listed cryptogam species linked to deciduous trees and dead wood was higher where the woodpecker bred. Those results for birds of northern forests suggest that the umbrella species concept may constitute a useful component of conservation planning, especially in the work towards the derivation of quantitative targets. However, umbrella species are not a panacea and should therefore be seen as part of a complementary suite of approaches

Driven waves in a two-fluid plasma

We study the physics of wave propagation in a weakly ionised plasma, as it applies to the formation of multifluid, MHD shock waves. We model the plasma as separate charged and neutral fluids which are coupled by ion-neutral friction. At times much less than the ion-neutral drag time, the fluids are decoupled and so evolve independently. At later times, the evolution is determined by the large inertial mismatch between the charged and neutral particles. The neutral flow continues to evolve independently; the charged flow is driven by and slaved to the neutral flow by friction. We calculate this driven flow analytically by considering the special but realistic case where the charged fluid obeys linearized equations of motion. We carry out an extensive analysis of linear, driven, MHD waves. The physics of driven MHD waves is embodied in certain Green functions which describe wave propagation on short time scales, ambipolar diffusion on long time scales, and transitional behavior at intermediate times. By way of illustration, we give an approximate solution for the formation of a multifluid shock during the collision of two identical interstellar clouds. The collision produces forward- and reverse J shocks in the neutral fluid and a transient in the charged fluid. The latter rapidly evolves into a pair of magnetic precursors on the J shocks, wherein the ions undergo force free motion and the magnetic field grows monotonically with time. The flow appears to be self similar at the time when linear analysis ceases to be valid.Comment: 18 pages including 24 figures, accepted by MNRA

UV Spectroscopy of Star-Grazing Comets within the 49 Ceti Debris Disk

We present analysis of time-variable, shifted absorption features in far-UV spectra of the unusual 49 Ceti debris disk. This nearly edge-on disk is one of the brightest known, and is one of the very few containing detectable amounts of circumstellar gas as well as dust. In our two visits of Hubble Space Telescope STIS spectra, variable absorption features are seen on the wings of lines arising from C II and C IV, but not for any of the other circumstellar absorption lines. Similar variable features have long been seen in spectra of the well-studied $\beta$ Pictoris debris disk and attributed to the transits of star-grazing comets. We calculate the velocity ranges and apparent column densities of the 49 Cet variable gas, which appears to be moving at velocities of tens to hundreds of km s$^{-1}$ relative to the central star. The velocities of the gas in the redshifted variable event in Visit 2 show that the maximum distances of the infalling gas at the time of transit are about 0.05 to 0.2 AU from the central star. A preliminary attempt at a composition analysis of the redshifted event suggests that the C/O ratio in the infalling gas may be super-solar, as it is in the bulk of the stable disk gas.Comment: 6 pages, 7 figures accepted to ApJ, figure 7 updated to most recent versio

High-efficiency Dc to Dc Converter-regulators

High efficiency dc to dc converter regulators for spacecraft power suppl