3,344 research outputs found
The electromagnetic environment in CFC structures
Extensive measurements of induced voltages and currents were made using a CFC (carbon fiber composites) horizontal stabilizer from the A320 as a test bed. The work was done to investigate the efficacy of various protection schemes to reduce the magnitudes of the induced voltages and validate a computer program INDCAL. Results indicate that a good understanding of the various induced voltage mechanisms including the long wave effect due to current redistribution was obtained
A Quantum Window Onto Early Inflation
Inflation in the early Universe is one of the most promising probes of
gravity in the high-energy regime. However, observable scales give access to a
limited window in the inflationary dynamics. In this essay, we argue that
quantum corrections to the classical dynamics of cosmological fields allow us
to probe much earlier epochs of the inflationary phase and extend this window
by many orders of magnitude. We point out that both the statistics of
cosmological fluctuations at observable scales, and the field displacements
acquired by spectator fields that play an important role in many
post-inflationary processes, are sensitive to a much longer phase of the
inflationary epoch.Comment: 5 pages, 2 figures. Honourable Mention from the Gravity Research
Foundation 2017 Awards for Essays on Gravitation. Version to appear in
October 2017 Special Issue of the International Journal of Modern Physics D.
Updated to match the published versio
Renormalisation group improvement in the stochastic formalism
We investigate compatibility between the stochastic infrared (IR) resummation
of light test fields on inflationary spacetimes and renormalisation group
running of the ultra-violet (UV) physics. Using the Wilsonian approach, we
derive improved stochastic Langevin and Fokker-Planck equations which
consistently include the renormalisation group effects. With the exception of
stationary solutions, these differ from the naive approach of simply replacing
the classical potential in the standard stochastic equations with the
renormalisation group improved potential. Using this new formalism, we
exemplify the IR dynamics with the Yukawa theory during inflation, illustrating
the differences between the consistent implementation of the UV running and the
naive approach.Comment: 18 pages, 1 figure, 1 appendix, matches accepted version in JCA
Measurements of some parameters of thermal sparks with respect to their ability to ignite aviation fuel/air mixtures
A method used to generate thermal sparks for experimental purposes and methods by which parameters of the sparks, such as speed, size, and temperature, were measured are described. Values are given of the range of such parameters within these spark showers. Titanium sparks were used almost exclusively, since it is particles of this metal which are found to be ejected during simulation tests to carbon fiber composite (CFC) joints. Tests were then carried out in which titanium sparks and spark showers were injected into JP4/(AVTAG F40) mixtures with air. Single large sparks and dense showers of small sparks were found to be capable of causing ignition. Tests were then repeated using ethylene/air mixtures, which were found to be more easily ignited by thermal sparks than the JP4/ air mixtures
Surface Structural Disordering in Graphite upon Lithium Intercalation/Deintercalation
We report on the origin of the surface structural disordering in graphite
anodes induced by lithium intercalation and deintercalation processes. Average
Raman spectra of graphitic anodes reveal that cycling at potentials that
correspond to low lithium concentrations in LixC (0 \leq x < 0.16) is
responsible for most of the structural damage observed at the graphite surface.
The extent of surface structural disorder in graphite is significantly reduced
for the anodes that were cycled at potentials where stage-1 and stage-2
compounds (x > 0.33) are present. Electrochemical impedance spectra show larger
interfacial impedance for the electrodes that were fully delithiated during
cycling as compared to electrodes that were cycled at lower potentials (U <
0.15 V vs. Li/Li+). Steep Li+ surface-bulk concentration gradients at the
surface of graphite during early stages of intercalation processes, and the
inherent increase of the LixC d-spacing tend to induce local stresses at the
edges of graphene layers, and lead to the breakage of C-C bonds. The exposed
graphite edge sites react with the electrolyte to (re)form the SEI layer, which
leads to gradual degradation of the graphite anode, and causes reversible
capacity loss in a lithium-ion battery.Comment: 12 pages, 5 figure
The Impact of Speculative Investments on Commodity Price
Speculative investments have always been a component of the marketplace. Their existence is vital for providing liquidity and risk transfer, allowing for an efficiently operating market. The futures market was originally used by farmers and grain buyers to reduce risk. There has been an observable increase of noncommercial (speculative) investment since the inception of the futures market. There is a belief that these investors may be adversely affecting the market, considering their primary view of the market is as a financial instrument with no actual interest in the physical underlying commodity. Agencies such as the Commodity Futures Trading Commission have even gone as far as proposing position limits in an attempt to control speculation. This paper attempts to find if there is any significant evidence that speculation may be causing adverse effects to commodities and their related prices. With a better understanding of the market and market participants, agencies may be able to make informed decisions related to speculative policies
- …