46,355 research outputs found
SIMLA: Simulating laser-particle interactions via classical and quantum electrodynamics
We present the Fortran code SIMLA, which is designed for the study of charged
particle dynamics in laser and other background fields. This can be done
classically via the Landau-Lifshitz equation, or alternatively, via the
simulation of photon emission events determined by strong-field
quantum-electrodynamics amplitudes and implemented using Monte-Carlo type
routines. Multiple laser fields can be included in the simulation and the
propagation direction, beam shape (plane wave, focussed paraxial, constant
crossed, or constant magnetic), and time envelope of each can be independently
specified.Comment: Submitted to Comp. Phys. Comm. The associated computer program and
corresponding manual will be made available on the CPC librar
Transverse spreading of electrons in high-intensity laser fields
We show that for collisions of electrons with a high-intensity laser,
discrete photon emissions introduce a transverse beam spread which is distinct
from that due to classical (or beam shape) effects. Via numerical simulations,
we show that this quantum induced transverse momentum gain of the electron is
manifest in collisions with a realistic laser pulse of intensity within reach
of current technology, and we propose it as a measurable signature of
strong-field quantum electrodynamics.Comment: 5 pages, 3 figures. Accepted for publication in Physical Review
Letter
Assessment of casting filling by modeling surface entrainment events using CFD
The reliability of cast components is dependent on the quality of the casting process. During this highly transient filling phase the prevention of free surface turbulence and consequential oxide entrainment is critical to ensure the mechanical integrity of the component. Past research has highlighted a number of events that lead to entrainment of surface oxides. Using FLOW-3D, flow structures that result in surface entrainment events have been simulated and an algorithm developed that allows entrainment and defect motion to be tracked. This enables prediction of the quantity and motion of oxide film generated from each event. The algorithm was tested experimentally and compared to experimental data from previously published work. A quantitative criterion is proposed to assess the damage of each type of event. Complete running systems have also been studied to understand how they could be assessed for quality of filling based on the flows within them
The modelling of oxide film entrainment in casting systems using computational modelling
As Campbell stated in 2006, “the use of entrainment models to optimise filling systems designs for castings has huge commercial potential that has so far being neglected by modellers”. In this paper a methodology using computational modelling to define entraining events and track the entrained oxide films is presented. Research has shown that these oxide films present within the casting volume are highly detrimental to casting integrity, thus their entrainment during mould filling is especially undesirable. The method developed for the modelling of oxide entrainment has been validated against previously published data by Green and Campbell (1994) [31]. The validation shows good quantitative correlation with experimental data. However there is scope for further development which has the potential to both improve the accuracy and further validate the technique
A sub-regional management framework for South Pacific longline fisheries
The principal objective of this study was to determine if additional net benefits can be derived from the sub-regional longline fishery by the introduction of a new management agreement that would centre on the provision of licensing arrangements that would allow access by eligible
longline vessels to multiple Exclusive Economic Zones, i.e. Multi-zone Access. [90pp.
COVID-19 and the difficulty of inferring epidemiological parameters from clinical data
Knowing the infection fatality ratio (IFR) is of crucial importance for
evidence-based epidemic management: for immediate planning; for balancing the
life years saved against the life years lost due to the consequences of
management; and for evaluating the ethical issues associated with the tacit
willingness to pay substantially more for life years lost to the epidemic, than
for those to other diseases. Against this background Verity et al. (2020,
Lancet Infections Diseases) have rapidly assembled case data and used
statistical modelling to infer the IFR for COVID-19. We have attempted an
in-depth statistical review of their approach, to identify to what extent the
data are sufficiently informative about the IFR to play a greater role than the
modelling assumptions, and have tried to identify those assumptions that appear
to play a key role. Given the difficulties with other data sources, we provide
a crude alternative analysis based on the Diamond Princess Cruise ship data and
case data from China, and argue that, given the data problems, modelling of
clinical data to obtain the IFR can only be a stop-gap measure. What is needed
is near direct measurement of epidemic size by PCR and/or antibody testing of
random samples of the at risk population.Comment: Version accepted by the Lancet Infectious Diseases. See previous
version for less terse presentatio
Pure Spinor Superspace Identities for Massless Four-point Kinematic Factors
Using the pure spinor formalism we prove identities which relate the
tree-level, one-loop and two-loop kinematic factors for massless four-point
amplitudes. From these identities it follows that the complete supersymmetric
one- and two-loop amplitudes are immediately known once the tree-level
kinematic factor is evaluated. In particular, the two-loop equivalence with the
RNS formalism (up to an overall coefficient) is obtained as a corollary.Comment: 10 pages, harvmac TeX. v2: Updated affiliation and Report-no
Impacts of igneous intrusions on source reservoir potential in prospective sedimentary basins along the western Australian continental margin
Coulomb screening in mesoscopic noise: a kinetic approach
Coulomb screening, together with degeneracy, is characteristic of the
metallic electron gas. While there is little trace of its effects in transport
and noise in the bulk, at mesoscopic scales the electronic fluctuations start
to show appreciable Coulomb correlations. Within a strictly standard Boltzmann
and Fermi-liquid framework, we analyze these phenomena and their relation to
the mesoscopic fluctuation-dissipation theorem, which we prove. We identify two
distinct screening mechanisms for mesoscopic fluctuations. One is the
self-consistent response of the contact potential in a non-uniform system. The
other couples to scattering, and is an exclusively non-equilibrium process.
Contact-potential effects renormalize all thermal fluctuations, at all scales.
Collisional effects are relatively short-ranged and modify non-equilibrium
noise. We discuss ways to detect these differences experimentally.Comment: Source: REVTEX. 16 pp.; 7 Postscript figs. Accepted for publication
in J. Phys.: Cond. Ma
D-Brane Interactions in a Gravitational Shock Wave Background
We study D-branes in the background of a gravitational shock wave. We
consider the case of parallel D-branes located on opposite sides with respect
to the shock wave. Their interaction is studied by evaluating the cylinder
diagram using the boundary states technique. Boundary states are defined at
each D-brane and their scalar product is evaluated after propagation through
the shock wave. Taking the limit where the gravitational shock wave vanishes we
show that the amplitude evaluated is consistent with the flat space-time
result.Comment: To be published in Modern Physics Letters A, revised version with
references added, 12 page
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