4,579 research outputs found
Utilisation of underwater acoustic backscatter systems to characterise nuclear waste suspensions remotely
This paper reports application of ABS (Acoustic Backscatter Systems) to address nuclear waste management within the UK. ABS offers a route towards an online monitoring system to characterise wastes safely and remotely in real-time, during pipeline transportation; resulting in reduced hazard reduction timescales and taxpayer cost savings. Here, an ultrasonic velocimetry profiler (UVP) was used to analyse glass dispersions of varying concentrations, to assess online waste monitoring applicability. Acoustic backscatter profiles were collected to establish attenuation coefficients for two glass sizes (âŒ40 and 80â
”m) with 2 and 4â
MHz probes. The 4â
MHz probes were the most highly attenuating while transducer active radius had a negligible effect on probe sensitivity with either glass. A calibration procedure was used to measure sediment attenuation coefficients, which were compared to model estimates and experimental literature. For most systems, measured coefficients were close to estimated values, highlighting improved calibration accuracy, due to the mixing tank used. However, values for the smaller glass and 2â
MHz probes overestimated model predictions, due to additional viscous attenuation. The measured value for the larger glass with 4â
MHz probes was underestimated, this was caused by high attenuation reaching the instrument noise-floor, limiting the region available for analysis
A phase-shift-periodic parallel boundary condition for low-magnetic-shear scenarios
We formulate a generalized periodic boundary condition as a limit of the
standard twist-and-shift parallel boundary condition that is suitable for
simulations of plasmas with low magnetic shear. This is done by applying a
phase shift in the binormal direction when crossing the parallel boundary.
While this phase shift can be set to zero without loss of generality in the
local flux-tube limit when employing the twist-and-shift boundary condition, we
show that this is not the most general case when employing periodic parallel
boundaries, and may not even be the most desirable. A non-zero phase shift can
be used to avoid the convective cells that plague simulations of the
three-dimensional Hasegawa-Wakatani system, and is shown to have measurable
effects in periodic low-magnetic-shear gyrokinetic simulations. We propose a
numerical program where a sampling of periodic simulations at random
pseudo-irrational flux surfaces are used to determine physical observables in a
statistical sense. This approach can serve as an alternative to applying the
twist-and-shift boundary condition to low-magnetic-shear scenarios which, while
more straightforward, can be computationally demanding.Comment: 4 figures, 1 tabl
Evolutionary history of the Nesophontidae, the last unplaced Recent mammal family
The mammalian evolutionary tree has lost several major clades through recent human-caused extinctions. This process of historical biodiversity loss has particularly affected tropical island regions such as the Caribbean, an area of great evolutionary diversification but poor molecular preservation. The most enigmatic of the recently extinct endemic Caribbean mammals are the Nesophontidae, a family of morphologically plesiomorphic lipotyphlan insectivores with no consensus on their evolutionary affinities, and which constitute the only major recent mammal clade to lack any molecular information on their phylogenetic placement. Here, we use a palaeogenomic approach to place Nesophontidae within the phylogeny of recent Lipotyphla. We recovered the near-complete mitochondrial genome and sequences for 17 nuclear genes from a âŒ750-year-old Hispaniolan Nesophontes specimen, and identify a divergence from their closest living relatives, the Solenodontidae, more than 40 million years ago. Nesophontidae is thus an older distinct lineage than many extant mammalian orders, highlighting not only the role of island systems as âmuseumsâ of diversity that preserve ancient lineages, but also the major human-caused loss of evolutionary history
Glueball Spectroscopy in a Relativistic Many-Body Approach to Hadron Structure
A comprehensive, relativistic many-body approach to hadron structure is
advanced based on the Coulomb gauge QCD Hamiltonian. Our method incorporates
standard many-body techniques which render the approximations amenable to
systematic improvement. Using BCS variational methods, dynamic chiral symmetry
breaking naturally emerges and both quarks and gluons acquire constituent
masses. Gluonia are studied both in the valence and in the collective, random
phase approximations. Using representative values for the strong coupling
constant and string tension, calculated quenched glueball masses are found to
be in remarkable agreement with lattice gauge theory.Comment: 12 pages, 1 uuencoded ps figure, RevTe
The Cluster-EAGLE project: Velocity bias and the velocity dispersion-mass relation of cluster galaxies
We use the Cluster-EAGLE simulations to explore the velocity bias introduced when using galaxies, rather than dark matter particles, to estimate the velocity dispersion of a galaxy cluster, a property known to be tightly correlated with cluster mass. The simulations consist of 30 clusters spanning a mass range 14.0 †log 10 (M 200 c /M â ) †15.4, with their sophisticated subgrid physics modelling and high numerical resolution (subkpc gravitational softening), making them ideal for this purpose. We find that selecting galaxies by their total mass results in a velocity dispersion that is 5-10 per cent higher than the dark matter particles. However, selecting galaxies by their stellar mass results in an almost unbiased ( < 5 per cent) estimator of the velocity dispersion. This result holds out to z = 1.5 and is relatively insensitive to the choice of cluster aperture, varying by less than 5 per cent between r 500 c and r 200m . We show that the velocity bias is a function of the time spent by a galaxy inside the cluster environment. Selecting galaxies by their total mass results in a larger bias because a larger fraction of objects have only recently entered the cluster and these have a velocity bias above unity. Galaxies that entered more than 4 Gyr ago become progressively colder with time, as expected from dynamical friction. We conclude that velocity bias should not be a major issue when estimating cluster masses from kinematic methods
Measurement of Spin Transfer Observables in Antiproton-Proton -> Antilambda-Lambda at 1.637 GeV/c
Spin transfer observables for the strangeness-production reaction
Antiproton-Proton -> Antilambda-Lambda have been measured by the PS185
collaboration using a transversely-polarized frozen-spin target with an
antiproton beam momentum of 1.637 GeV/c at the Low Energy Antiproton Ring at
CERN. This measurement investigates observables for which current models of the
reaction near threshold make significantly differing predictions. Those models
are in good agreement with existing measurements performed with unpolarized
particles in the initial state. Theoretical attention has focused on the fact
that these models produce conflicting predictions for the spin-transfer
observables D_{nn} and K_{nn}, which are measurable only with polarized target
or beam. Results presented here for D_{nn} and K_{nn} are found to be in
disagreement with predictions from existing models. These results also
underscore the importance of singlet-state production at backward angles, while
current models predict complete or near-complete triplet-state dominance.Comment: 5 pages, 3 figure
Rapid size change associated with intra-island evolutionary radiation in extinct Caribbean "island-shrews"
Background: The Caribbean offers a unique opportunity to study evolutionary dynamics in insular mammals. However,
the recent extinction of most Caribbean non-volant mammals has obstructed evolutionary studies, and poor DNA
preservation associated with tropical environments means that very few ancient DNA sequences are available for extinct
vertebrates known from the regionâs Holocene subfossil record. The endemic Caribbean eulipotyphlan family
Nesophontidae (âisland-shrewsâ) became extinct ~ 500 years ago, and the taxonomic validity of many Nesophontes species
and their wider evolutionary dynamics remain unclear. Here we use both morphometric and palaeogenomic methods to
clarify the status and evolutionary history of Nesophontes species from Hispaniola, the second-largest Caribbean island.
Results: Principal component analysis of 65 Nesophontes mandibles from late Quaternary fossil sites across Hispaniola
identified three non-overlapping morphometric clusters, providing statistical support for the existence of three sizedifferentiated Hispaniolan Nesophontes species. We were also able to extract and sequence ancient DNA from a ~ 750-yearold specimen of Nesophontes zamicrus, the smallest non-volant Caribbean mammal, including a whole-mitochondrial
genome and partial nuclear genes. Nesophontes paramicrus (39-47 g) and N. zamicrus (~ 10 g) diverged recently during the
Middle Pleistocene (mean estimated divergence = 0.699 Ma), comparable to the youngest species splits in Eulipotyphla and
other mammal groups. Pairwise genetic distance values for N. paramicrus and N. zamicrus based on mitochondrial and
nuclear genes are low, but fall within the range of comparative pairwise data for extant eulipotyphlan species-pairs.
Conclusions: Our combined morphometric and palaeogenomic analyses provide evidence for multiple co-occurring
species and rapid body size evolution in Hispaniolan Nesophontes, in contrast to patterns of genetic and morphometric
differentiation seen in Hispaniolaâs extant non-volant land mammals. Different components of Hispaniolaâs mammal fauna
have therefore exhibited drastically different rates of morphological evolution. Morphological evolution in Nesophontes is
also rapid compared to patterns across the Eulipotyphla, and our study provides an important new example of rapid body
size change in a small-bodied insular vertebrate lineage. The Caribbean was a hotspot for evolutionary diversification as
well as preserving ancient biodiversity, and studying the surviving representatives of its mammal fauna is insufficient to
reveal the evolutionary patterns and processes that generated regional diversity
Characterizing Flocculated Suspensions with an Ultrasonic Velocity Profiler in Backscatter Mode
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