1,227 research outputs found
CFD Investigation of Flow Past Idealized Engine Nacelle Clutter /// Computational fluid dynamics investigation of flow past idealized engine nacelle clutter
This research modeled low-speed flow past idealized engine nacelle clutter in support of aircraft re suppression research. The idealized clutter was comprised of three vertical rows of staggered circular cylinders approximating typical nacelle obstructions such as fuel lines and wire bundles. Single-phase, Detached-Eddy Simulations (DES) were conducted using the commercial CFD solver, Fluentâą, to resolve the flow-field dynamics inside the clutter element and determine mechanisms accounting for the failure of suppressant spray droplets from traversing the array under low-speed, free-stream conditions (ReD = 1, 575). The numerical models provided no evidence that span-wise vorticity or non-uniform shedding was responsible for transporting dispersed-phase particles towards the tunnel walls for deposition. However, the simulations demonstrated that suppressant droplets would likely follow a path governed by the vector sum of the local carrier fluid velocity and the velocity imposed by gravity. Additionally, the Stokes number was computed from time-accurate data to determine the ability of dispersed particles to negotiate the clutter element without impinging on a cylinder. For slower free-stream velocities, U(infinity) = 1 m/s, suppressant droplets (D = 90 m/) will likely be entrained in vortices shed from the intermediate row of cylinders and subsequently deposited on the last row of cylinders as the Karman vortex directly collides with the clutter. At free-stream velocities, U(INFINITY) = 5 m/=s, the droplet particles will likely fail to track the carrier fluid streamlines in the cylinder wake and remain free of any shed vortices. Thus, the suppressant will conceivably transit the cylinder array without impact. These findings imply that a bluff-body turbulent diffusion flame in a cylinder wake could be nearly impossible to extinguish under high-speed, co-flow conditions
First results of the CERN Resonant WISP Search (CROWS)
The CERN Resonant WISP Search (CROWS) probes the existence of Weakly
Interacting Sub-eV Particles (WISPs) like axions or hidden sector photons. It
is based on the principle of an optical light shining through the wall
experiment, adapted to microwaves. Critical aspects of the experiment are
electromagnetic shielding, design and operation of low loss cavity resonators
and the detection of weak sinusoidal microwave signals. Lower bounds were set
on the coupling constant GeV for axion like
particles with a mass of eV. For hidden sector photons, lower
bounds were set for the coupling constant at a mass
of eV. For the latter we were probing a previously
unexplored region in the parameter space
Photochemical colour change for traditional watercolour pigments in low oxygen levels
An investigation for light exposure on pigments in low-oxygen environments (in the range 0â5% oxygen) was conducted using a purpose-built automated microfadometer for a large sample set including multiple samples of traditional watercolour pigments from nineteenth-century and twentieth-century sources, selected for concerns over their stability in anoxia. The pigments were prepared for usage in watercolour painting: ground and mixed in gum Arabic and applied to historically accurate gelatine glue-sized cotton and linen-based papers. Anoxia benefited many colorants and no colorant fared worse in anoxia than in air, with the exception of Prussian blue and Prussian green (which contains Prussian blue). A Prussian blue sampled from the studio materials of J.M.W. Turner (1775 â 1851) was microfaded in different environments (normal air (20.9% oxygen) 0, 1, 2, 3.5, or 5% oxygen in nitrogen) and the subsequent dark behaviour was measured. The behaviour of the sample (in normal air, anoxia, and 5% oxygen in nitrogen) proved to be consistent with the 55 separately sourced Prussian blue samples. When exposed to light in 5% oxygen in nitrogen, Prussian blue demonstrated the same light stability as in air (at approximately 21°C and 1 atmosphere). Storage in 5% oxygen is proposed for âanoxicâ display of paper-based artworks that might contain Prussian blue, to protect this material while reducing light-induced damage to other components of a watercolour, including organic colorants and the paper support
Fast Chopper Structure for the CERN Superconducting Proton Linac
The SPL chopper is a travelling wave device, which deflects a slow beam (b = v/c = 0.08) by its transverse electric field. We discuss the chopper deflecting structure based on a meander line printed on an alumina substrate. This concept profits from the radiation resistance of alumina, its excellent out-gassing properties and its good thermal conductivity. The use of well established MIC (microwave integrated circuit) thick film technology allows easy implementation of prototypes; the thickness of the printed layer should be increased by means of an electrochemical deposition method. The topology of the structure has been chosen from standard MIC layouts and was subsequently optimized using numerical simulations. Several prototypes have been manufactured and measurements have shown encouraging results
Demonstration of W Signal Detection Methods in the Microwave Range at Ambient Temperature
The detection of a very faint signal in a noisy environment is of considerable interest in different applications including antihydrogen spectroscopy and also microwave axion and âhidden photonâ detection. We demonstrate with a very simple setup using a commercial signal generator and an FFT signal analyzer the detection of a microwave signal of 10**-22 W at ambient temperature
Generalised Shastry-Sutherland Models in three and higher dimensions
We construct Heisenberg anti-ferromagnetic models in arbitrary dimensions
that have isotropic valence bond crystals (VBC) as their exact ground states.
The d=2 model is the Shastry-Sutherland model. In the 3-d case we show that it
is possible to have a lattice structure, analogous to that of SrCu_2(BO_3)_2,
where the stronger bonds are associated with shorter bond lengths. A dimer mean
field theory becomes exact at d -> infinity and a systematic 1/d expansion can
be developed about it. We study the Neel-VBC transition at large d and find
that the transition is first order in even but second order in odd dimensions.Comment: Published version; slightly expande
Interface Engineering to Create a Strong Spin Filter Contact to Silicon
Integrating epitaxial and ferromagnetic Europium Oxide (EuO) directly on
silicon is a perfect route to enrich silicon nanotechnology with spin filter
functionality.
To date, the inherent chemical reactivity between EuO and Si has prevented a
heteroepitaxial integration without significant contaminations of the interface
with Eu silicides and Si oxides.
We present a solution to this long-standing problem by applying two
complementary passivation techniques for the reactive EuO/Si interface:
() an hydrogen-Si passivation and () the
application of oxygen-protective Eu monolayers --- without using any additional
buffer layers.
By careful chemical depth profiling of the oxide-semiconductor interface via
hard x-ray photoemission spectroscopy, we show how to systematically minimize
both Eu silicide and Si oxide formation to the sub-monolayer regime --- and how
to ultimately interface-engineer chemically clean, heteroepitaxial and
ferromagnetic EuO/Si in order to create a strong spin filter contact to
silicon.Comment: 11 pages of scientific paper, 10 high-resolution color figures.
Supplemental information on the thermodynamic problem available (PDF).
High-resolution abstract graphic available (PNG). Original research (2016
Integration over the quantum diagonal subgroup and associated Fourier-like algebras
By analogy with the classical construction due to Forrest, Samei and Spronk
we associate to every compact quantum group a completely
contractive Banach algebra , which can be viewed as a
deformed Fourier algebra of . To motivate the construction we first
analyse in detail the quantum version of the integration over the diagonal
subgroup, showing that although the quantum diagonal subgroups in fact never
exist, as noted earlier by Kasprzak and So{\l}tan, the corresponding
integration represented by a certain idempotent state on makes
sense as long as is of Kac type. Finally we analyse as an explicit
example the algebras , , associated to Wang's free
orthogonal groups, and show that they are not operator weakly amenable.Comment: Minor updates; Remark 5.7 has been added; 31 page
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