Recent X-ray observations of intermediate BL Lac objects

We present recent ROSAT, ASCA and SAX observations of intermediate BL Lac objects (IBLs), i.e. BL Lacs which are located between high-energy and low-energy peaked BL Lac objects with respect to alpha_rx. Both the statistical properties of IBLs from the RGB sample and a detailed broad band X-ray spectral analysis of two objects (1424+2401, 1055+5644) point towards a continuous distribution of synchrotron emission peak frequencies among BL Lac objects.Comment: 4 pages, 4 figures; to appear in the proceedings of the conference "BL Lac Phenomenon" held in Turku, Finland, June 22-26, 199

Stellar Motion around Spiral Arms: Gaia Mock Data

We compare the stellar motion around a spiral arm created in two different scenarios, transient/co-rotating spiral arms and density-wave-like spiral arms. We generate Gaia mock data from snapshots of the simulations following these two scenarios using our stellar population code, SNAPDRAGONS, which takes into account dust extinction and the expected Gaia errors. We compare the observed rotation velocity around a spiral arm similar in position to the Perseus arm, and find that there is a clear difference in the velocity features around the spiral arm between the co-rotating spiral arm and the density-wave-like spiral arm. Our result demonstrates that the volume and accuracy of the Gaia data are sufficient to clearly distinguish these two scenarios of the spiral arms.Comment: 5 pages, 1 figure, to appear in the proceedings of "The Milky Way Unravelled by Gaia: GREAT Science from the Gaia Data Releases", Barcelona, 1-5 December 2014, eds. N. Walton, F. Figueras, C. Soubira

The Functional Importance of Forbs in Grassland Ecosystems

Herbaceous vegetation in grassland ecosystems is characterised by grass dominance in a species-rich forb-grass mixture. Forbs (i.e. the non-graminoid herbaceous component) represent the largest proportion of total species- and functional richness, which secure important ecosystem functions. Although grasses remain the most important forage source, certain forb species provide nutritious food sources for herbivores. Moreover, forbs provide food- and habitat sources to enhance invertebrate diversity and hence, agricultural food security through the maintenance of healthy pollinator communities. Important food and medicinal sources for human livelihoods in developing countries are also largely contributed by forbs. However, the dynamics and ecology of forb species are poorly understood in rangeland systems. Increasing global pressures are threatening the hyper-diverse grassland ecosystems (including African savannas) and in particular the diversity of the forb flora. The sub-ordinate role of forbs in savanna and grassland rangeland management practices led us to accumulate evidence of important ecosystem functions and services provided by this diverse life form. In this study, we present results that were obtained from several independent studies in which forb data were collected and analysed as an equally important herbaceous life form, to contribute to our current understanding of the ecology of grassland ecosystems. Our results revealed evidence of forbs as important forage for large African mammalian herbivores, including domestic cattle, during periods when other forage resources are severely limited. However, sustained overgrazing can severely deplete forb populations and diversity. Forbs as grazing indicators have been identified as the basis of a proposed forb-condition scoring method for mesic grasslands. Furthermore, the importance of intermediate disturbances, such as moderate grazing and/or the maintenance of crop field margins were identified for invertebrate community conservation. Studies on useful indigenous plants exposed forbs as an important life form to provide food- and medicinal resources to human livelihoods in African grassland ecosystems

Climate Variability in the Woodbush Granite Grasslands of South Africa: Effects on Grassland Diversity

South African old-growth grasslands are hyper-diverse ecosystems which evolved under naturally occurring rainfall variability. It is predicted that future precipitation patterns will become more variable, which could lead to increased frequencies of extreme and prolonged drought events. This study aimed to investigate the effects of climate variability on plant diversity of the fragmented pristine, mistbelt grasslands of the Woodbush Granite Grasslands (WGG) at Haenertsburg, South Africa. It has been reported that species composition has changed substantially in this area, as disturbance-tolerant species enter these systems or existing competitor species become more dominant. A Temporal Beta-diversity Index (TBI) was used to determine the gains and losses in taxonomic and functional diversity, and of endemic and threatened species since 2009. Results show that there was a gain in species from before (2009) to onset of drought (2015) and a loss in species from the onset of the drought (2015) to after the drought (2019), while the overall effect of the drought on species occurrence from 2009 to 2019 was non-significant suggesting ecosystem resilience to drought

Discovery of dumbbell-shaped Cs*He_n exciplexes in solid He 4

We have observed several new spectral features in the fluorescence of cesium atoms implanted in the hcp phase of solid helium following laser excitation to the 6$^{2}$P states. Based on calculations of the emission spectra using semiempirical Cs-He pair potentials the newly discovered lines can be assigned to the decay of specific Cs*He$_{n}$ exciplexes: an apple-shaped Cs$(A\Pi _{3/2})$He$_{2}$ and a dumbbell-shaped Cs$(A\Pi_{1/2})$He$_{n}$ exciplex with a well defined number $n$ of bound helium atoms. While the former has been observed in other enviroments, it was commonly believed that exciplexes with $n>2$ might not exist. The calculations suggest Cs$(A\Pi_{1/2})$He$_{6}$ to be the most probable candidate for that exciplex, in which the helium atoms are arranged on a ring around the waist of the dumbbell shaped electronic density distribution of the cesium atom.Comment: 4 pages, 4 figure

Spiral and bar driven peculiar velocities in Milky Way sized galaxy simulations

We investigate the kinematic signatures induced by spiral and bar structure in a set of simulations of Milky Way-sized spiral disc galaxies. The set includes test particle simulations that follow a quasi-stationary density wave-like scenario with rigidly rotating spiral arms, and $N$-body simulations that host a bar and transient, co-rotating spiral arms. From a location similar to that of the Sun, we calculate the radial, tangential and line-of-sight peculiar velocity fields of a patch of the disc and quantify the fluctuations by computing the power spectrum from a two-dimensional Fourier transform. We find that the peculiar velocity power spectrum of the simulation with a bar and transient, co-rotating spiral arms fits very well to that of APOGEE red clump star data, while the quasi-stationary density wave spiral model without a bar does not. We determine that the power spectrum is sensitive to the number of spiral arms, spiral arm pitch angle and position with respect to the spiral arm. However, it is necessary to go beyond the line of sight velocity field in order to distinguish fully between the various spiral models with this method. We compute the power spectrum for different regions of the spiral discs, and discuss the application of this analysis technique to external galaxies.Comment: 14 pages, 11 figures. Improved and MNRAS Accepte