7,805 research outputs found
Solenoid valve performance characteristics studied
Current and voltage waveforms of a solenoid coil are recorded as the valve opens and closes. Analysis of the waveforms with respect to time and the phase of the valve cycle accurately describes valve performance
Projecting the continental accumulation of alien species through to 2050
Biological invasions have steadily increased over recent centuries. However, we still lack a clear expectation about future trends in alien species numbers. In particular, we do not know whether alien species will continue to accumulate in regional floras and faunas, or whether the pace of accumulation will decrease due to the depletion of native source pools. Here, we apply a new model to simulate future numbers of alien species based on estimated sizes of source pools and dynamics of historical invasions, assuming a continuation of processes in the future as observed in the past (a business‐as‐usual scenario). We first validated performance of different model versions by conducting a back‐casting approach, therefore fitting the model to alien species numbers until 1950 and validating predictions on trends from 1950 to 2005. In a second step, we selected the best performing model that provided the most robust predictions to project trajectories of alien species numbers until 2050. Altogether, this resulted in 3,790 stochastic simulation runs for 38 taxon–continent combinations. We provide the first quantitative projections of future trajectories of alien species numbers for seven major taxonomic groups in eight continents, accounting for variation in sampling intensity and uncertainty in projections. Overall, established alien species numbers per continent were predicted to increase from 2005 to 2050 by 36%. Particularly, strong increases were projected for Europe in absolute (+2,543 ± 237 alien species) and relative terms, followed by Temperate Asia (+1,597 ± 197), Northern America (1,484 ± 74) and Southern America (1,391 ± 258). Among individual taxonomic groups, especially strong increases were projected for invertebrates globally. Declining (but still positive) rates were projected only for Australasia. Our projections provide a first baseline for the assessment of future developments of biological invasions, which will help to inform policies to contain the spread of alien species
High magnetic field studies of the Vortex Lattice structure in YBa2Cu3O7
We report on small angle neutron scattering measurements of the vortex
lattice in twin-free YBa2Cu3O7, extending the previously investigated maximum
field of 11~T up to 16.7~T with the field applied parallel to the c axis. This
is the first microscopic study of vortex matter in this region of the
superconducting phase. We find the high field VL displays a rhombic structure,
with a field-dependent coordination that passes through a square configuration,
and which does not lock-in to a field-independent structure. The VL pinning
reduces with increasing temperature, but is seen to affect the VL correlation
length even above the irreversibility temperature of the lattice structure. At
high field and temperature we observe a melting transition, which appears to be
first order, with no detectable signal from a vortex liquid above the
transition
Simulations of laser-driven strong-field QED with Ptarmigan: Resolving wavelength-scale interference and -ray polarization
Accurate modelling is necessary to support precision experiments
investigating strong-field QED phenomena. This modelling is particularly
challenging in the transition between the perturbative and nonperturbative
regimes, where the normalized laser amplitude is comparable to unity and
wavelength-scale interference is significant. Here we describe how to simulate
nonlinear Compton scattering, Breit-Wheeler pair creation, and trident pair
creation in this regime, using the Monte Carlo particle-tracking code
Ptarmigan. This code simulates collisions between high-intensity lasers and
beams of electrons or rays, primarily in the framework of the locally
monochromatic approximation (LMA). We benchmark our simulation results against
full QED calculations for pulsed plane waves and show that they are accurate at
the level of a few per cent, across the full range of particle energies and
laser intensities. This work extends our previous results to linearly polarized
lasers and arbitrarily polarized rays.Comment: 19 pages, 6 figures; additional discussion of validity and updated
figures; to appear in Physics of Plasma
Application of the Socio-Economic Impact Classification for Alien Taxa (SEICAT) to a global assessment of alien bird impacts
We use a recently proposed framework, the Socio-Economic Impact Classification for Alien Taxa (SEICAT) to undertake the first global assessment of the impacts of alien birds on human well-being. A review of the published literature and online resources was undertaken to collate information on the reported socio-economic impacts of 415 bird species with self-sustaining alien populations worldwide. These data were then categorised following the SEICAT guidelines. Impact data were found for 57 (14%) of the 415 alien bird species in this study. All but two of these species were found to have minor impacts on human well-being. The most significant threat to human well-being posed by alien birds may be associated with their impacts on aviation safety. About two-thirds of the impact data found described agricultural impacts. No data were found describing disease transmission impacts on humans. We lack data for developing regions of the world: this is of concern as alien species can threaten livelihoods in developing countries, particularly by affecting agricultural production and hence food security. Most assessments were allocated a ‘Low’ confidence score. This may be because SEICAT is a new framework, requiring data on the way in which alien species affect human well-being, as measured by changes to human activities: even where we do have data describing an alien bird impact, information on how profoundly this impact affects people’s activities is currently rarely available
No Evidence for Orbital Loop Currents in Charge Ordered YBaCuO from Polarized Neutron Diffraction
It has been proposed that the pseudogap state of underdoped cuprate
superconductors may be due to a transition to a phase which has circulating
currents within each unit cell. Here, we use polarized neutron diffraction to
search for the corresponding orbital moments in two samples of underdoped
YBaCuO with doping levels and 0.123. In contrast to
some other reports using polarized neutrons, but in agreement with nuclear
magnetic resonance and muon spin rotation measurements, we find no evidence for
the appearance of magnetic order below 300 K. Thus, our experiment suggests
that such order is not an intrinsic property of high-quality cuprate
superconductor single crystals. Our results provide an upper bound for a
possible orbital loop moment which depends on the pattern of currents within
the unit cell. For example, for the CC- pattern proposed by Varma,
we find that the ordered moment per current loop is less than 0.013 for
.Comment: Comments in arXiv:1710.08173v1 fully addresse
A hilbert-style axiomatisation for equational hybrid logic
This paper introduces an axiomatisation for equational hybrid logic based on previous axiomatizations and natural deduction systems for propositional and first-order hybrid logic. Its soundness and completeness is discussed. This work is part of a broader research project on the development a general proof calculus for hybrid logics
Charged particle motion and radiation in strong electromagnetic fields
The dynamics of charged particles in electromagnetic fields is an essential
component of understanding the most extreme environments in our Universe. In
electromagnetic fields of sufficient magnitude, radiation emission dominates
the particle motion and effects of nonlinear quantum electrodynamics (QED) are
crucial, which triggers electron-positron pair cascades and counterintuitive
particle-trapping phenomena. As a result of recent progress in laser
technology, high-power lasers provide a platform to create and probe such
fields in the laboratory. With new large-scale laser facilities on the horizon
and the prospect of investigating these hitherto unexplored regimes, we review
the basic physical processes of radiation reaction and QED in strong fields,
how they are treated theoretically and in simulation, the new collective
dynamics they unlock, recent experimental progress and plans, as well as
possible applications for high-flux particle and radiation sources.Comment: 62 pages, 35 figures; as submitted to Rev. Mod. Phy
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