390 research outputs found
Gravity's Relentless Pull: An interactive, multimedia website about black holes for Education and Public Outreach
We have created a website, called "Black Holes: Gravity's Relentless Pull",
which explains the physics and astronomy of black holes for a general audience.
The site emphasizes user participation and is rich in animations and
astronomical imagery. It won the top prize of the 2005 Pirelli INTERNETional
Awards competition for the best communication of science and technology using
the internet. This article provides a brief overview of the site. The site
starts with an opening animation that introduces the basic concept of a black
hole. The user is then invited to embark on a journey from a backyard view of
the night sky to a personal encounter with a singularity. This journey proceeds
through three modules, which allow the user to: find black holes in the night
sky; travel to a black hole in an animated starship; and explore a black hole
from up close. There are also five "experiments" that allow the user to: create
a black hole; orbit around a black hole; weigh a black hole; drop a clock into
a black hole; or fall into a black hole. The modules and experiments offer
goal-based scenarios tailored for novices and children. The site also contains
an encyclopedia of frequently asked questions and a detailed glossary that are
targeted more at experts and adults. The overall result is a website where
scientific knowledge, learning theory, and fun converge. Despite its focus on
black holes, the site also teaches many other concepts of physics, astronomy
and scientific thought. The site aims to instill an appreciation for learning
and an interest in science, especially in the younger users. It can be used as
an aid in teaching introductory astronomy at the undergraduate level.Comment: STScI Newsletter, 2006, vol. 23, number 2, in press; 5 pages and 2
figures. The black hole website described in this article is located at
http://hubblesite.org/go/blackholes/ . We welcome all feedback and
suggestions, which can be submitted through the "Contact Us" button of the
sit
The Relation Between Unpalatable Species, Nutrients and Plant Species Richness in Swiss Montane Pastures
In agriculturally marginal areas, the control of unpalatable weeds on species rich pastures may become problematic due to agricultural and socio-economic developments. It is unclear how increased dominance of unpalatable species would affect the botanical diversity of these grasslands. We investigated whether there was any relationship between plant species diversity and the abundance of unpalatable species and whether soil conditions affected this relationship. In three species-rich montane pastures in western Switzerland, we related plant species richness to soil attributes, the relative cover of all unpalatable species and the relative cover of the locally dominant, toxic Veratrum album in 25 plots of 4m2. We furthermore determined species richness in small transects through patches of V. album. Species richness was significantly lower in and near (≤ 0.3m) patches of V. album. At the field scale, plant species richness was best described by total soil N:P ratio (positive relation) in one site and the relative abundance of unpalatable species (negative relation) and soil N:P ratio (positive relation) in a second site. In the third site, species richness was not significantly related to any measured variable. Vegetation diversity (Simpson's D) was negatively related to the relative abundance of unpalatable species in one site and positively related to pH in another site. The results suggest that no single factor can explain plant species richness and diversity in montane pastures. At very high densities unpalatable species can have adverse effects but soil nutrient status appears to be a more general determinant of plant species richness. Conservation efforts should give priority to the prevention of intensification of these pasture
Delivery of crop pollination services is an insufficient argument for wild pollinator conservation
There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost- effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost- effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments
The propagation of statistical errors in covariant density functional theory: ground state observables and single-particle properties
Statistical errors in ground state observables and single-particle properties
of spherical even-even nuclei and their propagation to the limits of nuclear
landscape have been investigated in covariant density functional theory (CDFT)
for the first time. In this study we consider only covariant energy density
functionals with non-linear density dependency. Statistical errors for binding
energies and neutron skins significantly increase on approaching two-neutron
drip line. On the contrary, such a trend does not exist for statistical errors
in charge radii and two-neutron separation energies. The absolute and relative
energies of the single-particle states in the vicinity of the Fermi level are
characterized by low statistical errors ( MeV).
Statistical errors in the predictions of spin-orbit splittings are rather
small. Statistical errors in physical observables are substantially smaller
than related systematic uncertainties. Thus, at the present level of the
development of theory, theoretical uncertainties at nuclear limits are
dominated by systematic ones. Statistical errors in the description of physical
observables related to the ground state and single-particle degrees of freedom
are typically substantially lower in CDFT as compared with Skyrme density
functional theory. The correlations between the model parameters are studied in
detail. The parametric correlations are especially pronounced for the and
parameters which are responsible for the density dependence of the model.
The accounting of this fact potentially allows to reduce the number of free
parameters of non-linear meson coupling model from six to five.Comment: 18 pages, 9 figures, submitted to Physical Review C, referee
suggestions are taken into accoun
Managing trap-nesting bees as crop pollinators : Spatiotemporal effects of floral resources and antagonists
The decline of managed honeybees and the rapid expansion of mass-flowering crops increase the risk of pollination limitation in crops and raise questions about novel management approaches for wild pollinators in agroecosystems. Adding artificial nesting sites, such as trap nests, can promote cavity-nesting bees in agroecosystems, but effectiveness could be limited by the availability of floral resources in the surrounding landscape and by natural antagonists. In two European regions, we exposed artificial trap nests in paired field boundaries adjacent to oilseed rape (OSR) fields or non-flowering crops for 2 years within 32 landscapes covering two independent gradients of OSR cover and semi-natural habitat (SNH) cover in the landscape. We analysed the effects of local and landscape-wide floral resource availability, land-use intensity, landscape complexity and natural antagonists on community composition and population dynamics of trap-nesting bees. Numbers of brood cells showed a strong, three-fold increase in response to the additional nesting sites. Species richness and abundance of cavity-nesting bees that were active during OSR flowering increased significantly with increasing amounts of early season landscape-wide floral resource availability, such as the cultivation of OSR. Later foraging species benefited instead from the availability of late-season alternative flower resources or SNH cover once the mass-flowering had ceased. Density-dependent parasitism increased following mass-flowering, while no density-dependent effect was found during mass-flowering. Structural equation modelling revealed that the influence of floral resource availability on community growth rate was mediated by community size. Community size showed a strong negative effect on community growth rate. Despite positive density-dependent parasitism, antagonists had only weak regulating effects on community growth rate. Synthesis and applications. Trap-nesting bee populations grow markedly with the increasing availability of food resources in the landscape and effectiveness of trap nests is only marginally limited by natural antagonists. Thus, trap nests could be a simple pollinator-supporting strategy to accompany the current expansion of mass-flowering crops and to ensure pollination services for insect-pollinated crops. Trap nests benefit, not only early season active generalist bees during oilseed rape flowering, but also species with later phenology if accompanied by other pollinator-supporting practices.</p
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