198 research outputs found
A two-parameter family of double-power-law biorthonormal potential-density expansions
Biorthonormal basis function expansions are widely used in galactic dynamics,
both to study problems in galactic stability and to provide numerical
algorithms to evolve collisionless stellar systems. They also provide a compact
and efficient description of the structure of numerical dark matter haloes in
cosmological simulations. We present a two-parameter family of biorthonormal
double-power-law potential-density expansions. Both the potential and density
are given in closed analytic form and may be rapidly computed via recurrence
relations. We show that this family encompasses all the known analytic
biorthonormal expansions: the Zhao expansions (themselves generalizations of
ones found earlier by Hernquist & Ostriker and by Clutton-Brock) and the
recently discovered Lilley, Sanders, Evans & Erkal expansion. Our new
two-parameter family includes expansions based around many familiar spherical
density profiles as zeroth-order models, including the models and the
Jaffe model. It also contains a basis expansion that reproduces the famous
Navarro-Frenk-White (NFW) profile at zeroth order. The new basis expansions
have been found via a systematic methodology which has wide applications in
finding further examples. In the process, we also uncovered a novel integral
transform solution to Poisson's equation
The super-NFW model: An analytic dynamical model for cold dark matter haloes and elliptical galaxies
An analytic galaxy model with at small radii and at large radii is presented. The asymptotic density fall-off is
slower than the Hernquist model, but faster than the Navarro-Frenk-White (NFW)
profile for dark matter haloes, and so in accord with recent evidence from
cosmological simulations. The model provides the zeroth-order term in a
biorthornomal basis function expansion, meaning that axisymmetric, triaxial and
lopsided distortions can easily be added (much like the Hernquist model itself
which is the zeroth-order term of the Hernquist-Ostriker expansion). The
properties of the spherical model, including analytic distribution functions
which are either isotropic, radially anisotropic or tangentially anisotropic,
are discussed in some detail. The analogue of the mass-concentration relation
for cosmological haloes is provided.EJL and JLS acknowledge financial support from the Science and Technology Facilities Council
Galaxy halo expansions: a new biorthogonal family of potential-density pairs
Efficient expansions of the gravitational field of (dark) haloes have two
main uses in the modelling of galaxies: first, they provide a compact
representation of numerically-constructed (or real) cosmological haloes,
incorporating the effects of triaxiality, lopsidedness or other distortion.
Secondly, they provide the basis functions for self-consistent field expansion
algorithms used in the evolution of -body systems. We present a new family
of biorthogonal potential-density pairs constructed using the Hankel transform
of the Laguerre polynomials. The lowest-order density basis functions are
double-power-law profiles cusped like at small
radii with asymptotic density fall-off like .
Here, is a parameter satisfying . The family therefore
spans the range of inner density cusps found in numerical simulations, but has
much shallower -- and hence more realistic -- outer slopes than the
corresponding members of the only previously-known family deduced by Zhao
(1996) and exemplified by Hernquist & Ostriker (1992). When , the
lowest-order density profile has an inner density cusp of
and an outer density slope of , similar to the famous
Navarro, Frenk & White (1997) model. For this reason, we demonstrate that our
new expansion provides a more accurate representation of flattened NFW haloes
than the competing Hernquist-Ostriker expansion. We utilize our new expansion
by analysing a suite of numerically-constructed haloes and providing the
distributions of the expansion coefficients.JLS and EJL acknowledge the support of the STFC
Models of Distorted and Evolving Dark Matter Halos
We investigate the ability of basis function expansions to reproduce the evolution of a Milky Way-like dark matter halo, extracted from a cosmological zoom-in simulation. For each snapshot, the density of the halo is reduced to a basis function expansion, with interpolation used to recreate the evolution between snapshots. The angular variation of the halo density is described by spherical harmonics, and the radial variation either by biorthonormal basis functions adapted to handle truncated haloes or by splines. High fidelity orbit reconstructions are attainable using either method with similar computational expense. We quantify how the error in the reconstructed orbits varies with expansion order and snapshot spacing. Despite the many possible biorthonormal expansions, it is hard to beat a conventional Hernquist-Ostriker expansion with a moderate number of terms ( radial and angular). As two applications of the developed machinery, we assess the impact of the time-dependence of the potential on (i) the orbits of Milky Way satellites, and (ii) planes of satellites as observed in the Milky Way and other nearby galaxies. Time evolution over the last 5 Gyr introduces an uncertainty in the Milky Way satellites' orbital parameters of per cent, comparable to that induced by the observational errors or the uncertainty in the present-day Milky Way potential. On average, planes of satellites grow at similar rates in evolving and time-independent potentials. There can be more, or less, growth in the plane's thickness, if the plane becomes less, or more, aligned with the major or minor axis of the evolving halo
A global class reunion with multiple groups feasting on the declining insect smorgasbord
We report a detection of a surprising similarity in the diet of predators across distant phyla. Though just a first glimpse into the subject, our discovery contradicts traditional aspects of biology, as the earliest notions in ecology have linked the most severe competition of resources with evolutionary relatedness. We argue that our finding deserves more research, and propose a plan to reveal more information on the current biodiversity loss around the world. While doing so, we expand the recently proposed conservation roadmaps into a parallel study of global interaction networks
Next Generation Sequencing of Fecal DNA Reveals the Dietary Diversity of the Widespread Insectivorous Predator Daubenton's Bat (Myotis daubentonii) in Southwestern Finland
Understanding predator-prey dynamics is a fundamental task in the evaluation of the adaptive capacities of species. However, direct observations or morphological identification of fecal remains do not offer an effective way to study the dietary ecology of elusive species, such as nocturnal insectivorous bats. However, recent advances in molecular techniques have opened a new method for identifying prey species from fecal samples. In this study, we amplified species-specific mitochondrial COI fragments from fecal DNA extractions from 34 individual Daubenton's bats (Myotis daubentonii) collected between 2008 and 2010 from southwestern Finland. Altogether, 128 different species of prey were identified based on a comprehensive local DNA reference library. In our study area, Daubenton's bats feed most frequently on insects of the orders Diptera (found in the diet of 94% individuals), Trichoptera (69%) and Lepidoptera (63%). The most frequent dipteran family in the diet was Chironomidae, which was found in 31 of 34 individuals. Most common prey species were chironomids Microtendipes pedellus (found in 50% of bats), Glyptotendipes cauliginellus (44%), and Procladius ferrugineus (41%). For the first time, an accurate species level list of the diet of the insectivorous Daubenton's bat (Myotis daubentonii) in Finland is presented. We report a generally applicable method for describing the arthropod diet of vertebrate predators. We compare public databases to a national database to highlight the importance of a local reference database
Bats and Wind Farms: The Role and Importance of the Baltic Sea Countries in the European Context of Power Transition and Biodiversity Conservation
Although labeled as environmentally friendly, wind power can have negative impacts on the environment, such as habitat destruction or wildlife fatalities. Considering the distribution and migratory characteristics of European bats, the negative effects of wind power should be addressed on an appropriate scale. This review summarizes the current state of knowledge on interactions between wind farms and bats in Europe, and compares it with the situation in the countries of the European boreal biogeographic region. We analyzed data from papers published in international and national scientific journals, focusing on studies conducted in Europe. The issue of the impacts wind power has on bats is clearly overlooked in most of the countries of the European boreal region, with low volumes of research available on the topic. This is probably due to fewer wind farms in the area, making this recent issue a less-prioritized topic. However, the Baltic Sea, and the countries surrounding it, are of extreme importance with regards to bat migration, especially for the Pipistrellus nathusii. Therefore, more research on wind power and bats is needed in this region, as well as more cooperation between all the stakeholders
Refining rodent models of spinal cord injury.
This report was produced by an Expert Working Group (EWG) consisting of UK-based researchers, veterinarians and regulators of animal experiments with specialist knowledge of the use of animal models of spinal cord injury (SCI). It aims to facilitate the implementation of the Three Rs (Replacement, Reduction and Refinement), with an emphasis on refinement. Specific animal welfare issues were identified and discussed, and practical measures proposed, with the aim of reducing animal use and suffering, reducing experimental variability, and increasing translatability within this critically important research field
Threats from the air: Damselfly predation on diverse prey taxa
To understand the diversity and strength of predation in natural communities, researchers must quantify the total amount of prey species in the diet of predators. Metabarcoding approaches have allowed widespread characterization of predator diets with high taxonomic resolution. To determine the wider impacts of predators, researchers should combine DNA techniques with estimates of population size of predators using mark-release-recapture (MRR) methods, and with accurate metrics of food consumption by individuals.Herein, we estimate the scale of predation exerted by four damselfly species on diverse prey taxa within a well-defined 12-ha study area, resolving the prey species of individual damselflies, to what extent the diets of predatory species overlap, and which fraction of the main prey populations are consumed.We identify the taxonomic composition of diets using DNA metabarcoding and quantify damselfly population sizes by MRR. We also use predator-specific estimates of consumption rates, and independent data on prey emergence rates to estimate the collective predation pressure summed over all prey taxa and specific to their main prey (non-biting midges or chironomids) of the four damselfly species.The four damselfly species collectively consumed a prey mass equivalent to roughly 870 (95% CL 410-1,800) g, over 2 months. Each individual consumed 29%-66% (95% CL 9.4-123) of its body weight during its relatively short life span (2.1-4.7 days; 95% CL 0.74-7.9) in the focal population. This predation pressure was widely distributed across the local invertebrate prey community, including 4 classes, 19 orders and c. 140 genera. Different predator species showed extensive overlap in diets, with an average of 30% of prey shared by at least two predator species.Of the available prey individuals in the widely consumed family Chironomidae, only a relatively small proportion (0.76%; 95% CL 0.35%-1.61%) were consumed.Our synthesis of population sizes, per-capita consumption rates and taxonomic distribution of diets identifies damselflies as a comparatively minor predator group of aerial insects. As the next step, we should add estimates of predation by larger odonate species, and experimental removal of odonates, thereby establishing the full impact of odonate predation on prey communities
BAT3 Guides Misfolded Glycoproteins Out of the Endoplasmic Reticulum
Secretory and membrane proteins that fail to acquire their native conformation within the lumen of the Endoplasmic Reticulum (ER) are usually targeted for ubiquitin-dependent degradation by the proteasome. How partially folded polypeptides are kept from aggregation once ejected from the ER into the cytosol is not known. We show that BAT3, a cytosolic chaperone, is recruited to the site of dislocation through its interaction with Derlin2. Furthermore, we observe cytoplasmic BAT3 in a complex with a polypeptide that originates in the ER as a glycoprotein, an interaction that depends on the cytosolic disposition of both, visualized even in the absence of proteasomal inhibition. Cells depleted of BAT3 fail to degrade an established dislocation substrate. We thus implicate a cytosolic chaperone as an active participant in the dislocation of ER glycoproteins.United States. National Institutes of HealthBoehringer Ingelheim Fond
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