1,862 research outputs found
Electric field generation by the electron beam filamentation instability: Filament size effects
The filamentation instability (FI) of counter-propagating beams of electrons
is modelled with a particle-in-cell simulation in one spatial dimension and
with a high statistical plasma representation. The simulation direction is
orthogonal to the beam velocity vector. Both electron beams have initially
equal densities, temperatures and moduli of their nonrelativistic mean
velocities. The FI is electromagnetic in this case. A previous study of a small
filament demonstrated, that the magnetic pressure gradient force (MPGF) results
in a nonlinearly driven electrostatic field. The probably small contribution of
the thermal pressure gradient to the force balance implied, that the
electrostatic field performed undamped oscillations around a background
electric field. Here we consider larger filaments, which reach a stronger
electrostatic potential when they saturate. The electron heating is enhanced
and electrostatic electron phase space holes form. The competition of several
smaller filaments, which grow simultaneously with the large filament, also
perturbs the balance between the electrostatic and magnetic fields. The
oscillations are damped but the final electric field amplitude is still
determined by the MPGF.Comment: 14 pages, 10 plots, accepted for publication in Physica Script
Stress and Failure Analysis of Double-Bolted Joints in Douglas-Fir and Sitka Spruce
Stresses in, and strength of, single- and double-bolted mechanical joints in wood members are analyzed experimentally and numerically. The analyses account for the nonlinear geometric and stress-strain responses and the thicknesses of the members. Stresses are obtained using finite elements, strain gages, and moiré techniques. Failure is predicted from assumed strength criteria. Stresses and strength are influenced by end-distance, bolt-spacing, edge-distance, bolt-clearance, and load distribution between bolts of a multiple fastener. Predicted initiation of failure agrees with visible and audible damage initiation in full-scale components. These occur at 10 to 25% of ultimate structural strength
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Navigating Family Involvement in Domestic Violence Fatality Review: Conceptualising Prospects for Systems and Relational Repair
Purpose
Family involvement is a key element of Domestic Homicide Review (DHR), the form of Domestic Violence Fatality Review (DVFR) found in England and Wales. Family involvement is framed as having dual purposes: first, as a benefit to DHRs, enabling a fuller picture of victims’ experiences; second, as a benefit to families themselves, notably as a therapeutic or cathartic opportunity. However, these dual purposes have been little considered. This conceptual article responds to this absence by interrogating the purpose, process and outcomes of family involvement within DHRs.
Method
To explicate purpose, process and outcomes, we synthesise policy, practice and the extant empirical and theoretical literature relating to family involvement in DHRs. We supplement this by engaging with a broader body of emerging research on family involvement in other review systems, analysing this through a lens of citizenship and participation.
Results
Family involvement in DHRs is little explicated and there is a need to better engage with how family are involved in DHRs, as a way of increasing transparency for family rights. By way of response, a tentative conceptual framework is proposed which situates family involvement as demonstrative of systems- and relational-repair.
Conclusions
The article concludes by arguing for greater attention to the Theory(s) of Change underpinning both the place of the family and their testimony, as well as the DHR system as a whole. Such clarity would benefit family, both as the subject of professional interactions but, critically, as agents in the DHR process in their own right
The relationship between dust and [C I] at z = 1 and beyond
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.Measuring molecular gas mass is vital for understanding the evolution of galaxies at high redshifts (z ≳ 1). Most measurements rely on CO as a tracer, but dependencies on metallicity, dynamics, and surface density lead to systematic uncertainties in high-z galaxies, where these physical properties are difficult to observe, and where the physical environments can differ systematically from those at z = 0. Dust continuum emission provides a potential alternative assuming a known dust/gas ratio, but this must be calibrated on a direct gas tracer at z ≳ 1. In this paper, we consider the [C I] 492-GHz emission line, which has been shown to trace molecular gas closely throughout Galactic clouds and has the advantages of being optically thin in typical conditions (unlike CO), and being observable at accessible frequencies at high redshifts (in contrast to the low-excitation lines of CO). We use the Atacama Large Millimetre/submillimetre Array to measure [C I], CO(4–3), and dust emission in a representative sample of star-forming galaxies at z = 1, and combine these data with multiwavelength spectral energy distributions to study relationships between dust and gas components of galaxies. We uncover a strong [C I]–dust correlation, suggesting that both trace similar phases of the gas. By incorporating other samples from the literature, we show that this correlation persists over a wide range of luminosities and redshifts up to z ∼ 4. Finally, we explore the implications of our results as an independent test of literature calibrations for dust as a tracer of gas mass, and for predicting the C I abundance.Peer reviewedFinal Published versio
On the effect of Ti on Oxidation Behaviour of a Polycrystalline Nickel-based Superalloy
Titanium is commonly added to nickel superalloys but has a well-documented
detrimental effect on oxidation resistance. The present work constitutes the
first atomistic-scale quantitative measurements of grain boundary and bulk
compositions in the oxide scale of a current generation polycrystalline nickel
superalloy performed through atom probe tomography. Titanium was found to be
particularly detrimental to oxide scale growth through grain boundary
diffusion
The filamentation instability driven by warm electron beams: Statistics and electric field generation
The filamentation instability of counterpropagating symmetric beams of
electrons is examined with 1D and 2D particle-in-cell (PIC) simulations, which
are oriented orthogonally to the beam velocity vector. The beams are uniform,
warm and their relative speed is mildly relativistic. The dynamics of the
filaments is examined in 2D and it is confirmed that their characteristic size
increases linearly in time. Currents orthogonal to the beam velocity vector are
driven through the magnetic and electric fields in the simulation plane. The
fields are tied to the filament boundaries and the scale size of the
flow-aligned and the perpendicular currents are thus equal. It is confirmed
that the electrostatic and the magnetic forces are equally important, when the
filamentation instability saturates in 1D. Their balance is apparently the
saturation mechanism of the filamentation instability for our initial
conditions. The electric force is relatively weaker but not negligible in the
2D simulation, where the electron temperature is set higher to reduce the
computational cost. The magnetic pressure gradient is the principal source of
the electrostatic field, when and after the instability saturates in the 1D
simulation and in the 2D simulation.Comment: 10 pages, 6 figures, accepted by the Plasma Physics and Controlled
Fusion (Special Issue EPS 2009
PIC Simulations of the Temperature Anisotropy-Driven Weibel Instability: Analyzing the perpendicular mode
An instability driven by the thermal anisotropy of a single electron species
is investigated in a 2D particle-in-cell (PIC) simulation. This instability is
the one considered by Weibel and it differs from the beam driven filamentation
instability. A comparison of the simulation results with analytic theory
provides similar exponential growth rates of the magnetic field during the
linear growth phase of the instability. We observe in accordance with previous
works the growth of electric fields during the saturation phase of the
instability. Some components of this electric field are not accounted for by
the linearized theory. A single-fluid-based theory is used to determine the
source of this nonlinear electric field. It is demonstrated that the magnetic
stress tensor, which vanishes in a 1D geometry, is more important in this
2-dimensional model used here. The electric field grows to an amplitude, which
yields a force on the electrons that is comparable to the magnetic one. The
peak energy density of each magnetic field component in the simulation plane
agrees with previous estimates. Eddy currents develop, which let the amplitude
of the third magnetic field component grow, which is not observed in a 1D
simulation.Comment: accepted by Plasma Physics and Controlled Fusio
Entretien et rétablissement du drain filtrant/tranches d'infiltration : Un problème de gestion des déchets
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