8,726 research outputs found
Pion Charge Exchange on Deuterium
We investigate quantum corrections to a classical intranuclear cascade
simulation of pion single charge exchange on the deuteron. In order to separate
various effects the orders of scattering need to be distinguished and, to that
end, we develop signals for each order of scattering corresponding to
quasi-free conditions. Quantum corrections are evaluated for double scattering
and are found to be large. Global agreement with the data is good.Comment: 30 pages, 12 figure
Anisotropic imbibition on surfaces patterned with polygonal posts
We present and interpret lattice Boltzmann simulations of thick films
spreading on surfaces patterned with polygonal posts. We show that the
mechanism of pinning and depinning differs with the direction of advance, and
demonstrate that this leads to anisotropic spreading within a certain range of
material contact angles.Comment: DSFD Proceedings 201
The evaluation of waste tyre pulverised fuel for NOx reduction by reburning
The combustion of coal for power generation will continue to play a major role in the future, however, this must be achieved using cleaner technologies than we use at present. Scrap tyre arisings in the UK are 400,000 tonnes per year amounting to 30 million tyres and in the EU as a whole, more than 2.5 million tonnes of tyres per year are scrapped. The recent EC Waste Landfill Directive (1999) sets a deadline for the banning of whole and shredded tyres from landfill sites by 2006. Consequently, there is an urgent need to find a mass disposal route for tyres. We describe, in this paper, a novel use for tyre rubber pulverised fuel in a NOx reburning process which may have an application in power station boilers. This method of disposal could represent a way of combining waste disposal, energy recovery and pollution control within one process. A preliminary study of micronised tyre combustion was undertaken to identify the suitable size ranges for application in NOx reduction by reburning. Tests were performed in a down-fired, pulverised fuel combustor (PFC) operating at about 80 kW. Superior combustion characteristics, i.e. burnout were achieved with particle sizes less than 250 μm. A South African coal was used as the primary fuel in the reburn tests and the tyre was fed pneumatically via a separate feed system. Parameters studied, were, reburn zone stoichiometry and reburn fuel fraction. Additionally, the carbon content of the ash was carefully monitored for any effect on burnout at the fuel rich reburn stoichiometries. The NOx reductions achieved with tyres are compared with reburning with coal. NOx reductions up to 80% were achieved with tyres at half of the reburn fuel feed rate required to achieve the same reductions by coal. The results have been evaluated within the context of other studies available in the literature on NOx reburning by bituminous coal, brown coal, gas and biomass
Pion double charge exchange on 4He
The doubly differential cross sections for the He
reaction were calculated using both a two-nucleon sequential single charge
exchange model and an intranuclear cascade code. Final state interactions
between the two final protons which were the initial neutrons were included in
both methods. At incident pion energies of 240 and 270 MeV the low-energy peak
observed experimentally in the energy spectrum of the final pions can be
understood only if the contribution of pion production is included. The
calculated cross sections are compared with data.Comment: 25 pages, 9 figure
Thermophysical Phenomena in Metal Additive Manufacturing by Selective Laser Melting: Fundamentals, Modeling, Simulation and Experimentation
Among the many additive manufacturing (AM) processes for metallic materials,
selective laser melting (SLM) is arguably the most versatile in terms of its
potential to realize complex geometries along with tailored microstructure.
However, the complexity of the SLM process, and the need for predictive
relation of powder and process parameters to the part properties, demands
further development of computational and experimental methods. This review
addresses the fundamental physical phenomena of SLM, with a special emphasis on
the associated thermal behavior. Simulation and experimental methods are
discussed according to three primary categories. First, macroscopic approaches
aim to answer questions at the component level and consider for example the
determination of residual stresses or dimensional distortion effects prevalent
in SLM. Second, mesoscopic approaches focus on the detection of defects such as
excessive surface roughness, residual porosity or inclusions that occur at the
mesoscopic length scale of individual powder particles. Third, microscopic
approaches investigate the metallurgical microstructure evolution resulting
from the high temperature gradients and extreme heating and cooling rates
induced by the SLM process. Consideration of physical phenomena on all of these
three length scales is mandatory to establish the understanding needed to
realize high part quality in many applications, and to fully exploit the
potential of SLM and related metal AM processes
Many-Body Dynamics and Exciton Formation Studied by Time-Resolved Photoluminescence
The dynamics of exciton and electron-hole plasma populations is studied via
time-resolved photoluminescence after nonresonant excitation. By comparing the
peak emission at the exciton resonance with the emission of the continuum, it
is possible to experimentally identify regimes where the emission originates
predominantly from exciton and/or plasma populations. The results are supported
by a microscopic theory which allows one to extract the fraction of bright
excitons as a function of time.Comment: 11 pages, 5 figure
Wall-liquid and wall-crystal interfacial free energies via thermodynamic integration: A molecular dynamics simulation study
A method is proposed to compute the interfacial free energy of a
Lennard-Jones system in contact with a structured wall by molecular dynamics
simulation. Both the bulk liquid and bulk face-centered-cubic crystal phase
along the (111) orientation are considered. Our approach is based on a
thermodynamic integration scheme where first the bulk Lennard-Jones system is
reversibly transformed to a state where it interacts with a structureless flat
wall. In a second step, the flat structureless wall is reversibly transformed
into an atomistic wall with crystalline structure. The dependence of the
interfacial free energy on various parameters such as the wall potential, the
density and orientation of the wall is investigated. The conditions are
indicated under which a Lennard-Jones crystal partially wets a flat wall.Comment: 15 pages, 11 figure
Description of the fluctuating colloid-polymer interface
To describe the full spectrum of surface fluctuations of the interface
between phase-separated colloid-polymer mixtures from low scattering vector q
(classical capillary wave theory) to high q (bulk-like fluctuations), one must
take account of the interface's bending rigidity. We find that the bending
rigidity is negative and that on approach to the critical point it vanishes
proportionally to the interfacial tension. Both features are in agreement with
Monte Carlo simulations.Comment: 5 pages, 3 figures, 1 table. Accepted for publication in Phys. Rev.
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Low-energy Antiproton Interaction with Helium
An ab initio potential for the interaction of the neutral helium atom with
antiprotons and protons is calculated using the Born-Oppenheimer approximation.
Using this potential, the annihilation cross section for antiprotons in the
energy range 0.01 microvolt to 1 eV is calculated.Comment: 13 pages, 7 figures, LaTe
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