6,959 research outputs found
Experimental combustor study program
Advanced combustor concepts are evaluated as a means of accommodating possible future broad specification fuels. The three advanced double annular combustor concepts consisted of (1) a concept employing high pressure drop fuel nozzles for improved atomization, (2) a concept with premixing tubes in the main stage, and (3) a concept with the pilot stage on the inside and the main stage on the sideout, which is the reverse of the other two concepts. All of the advanced concepts show promise for reduced sensitivity to fuel hydrogen content. Some hardware problems were encountered, but these problems could be quickly resolved if refinement tests were conducted. The design with the premixing main stage was selected for a parametric test because of its low NOx emissions level, carbon free dome, and very low dome temperatures which were essentially independent of fuel type. The other advanced designs also had low done temperatures. The premixing dome design liner temperatures exhibited less sensitivity to fuel type than did the base-line combustor, although more sensitivity than observed for concept 1. The inner liner hot spot and the observed smoke results for the premixing design suggest that the fuel-air mixture was not as uniform as desired
Are periodic solar wind number density structures formed in the solar corona?
[1] We present an analysis of the alpha to proton solar wind abundance ratio (AHe) during a period characterized by significant large size scale density fluctuations, focusing on an event in which the proton and alpha enhancements are anti-correlated. In a recent study using 11 years (1995–2005) of solar wind observations from the Wind spacecraft, N. M. Viall et al. [2008] showed that periodic proton density structures occurred at particular radial length-scales more often than others. The source of these periodic density structures is a significant and outstanding question. Are they generated in the interplanetary medium, or are they a relic of coronal activity as the solar wind was formed? We use AHe to answer this question, as solar wind elemental abundance ratios are not expected to change during transit. For this event, the anti-phase nature of the AHe variations strongly suggests that periodic solar wind density structures originate in the solar corona
Schwinger pair production with ultracold atoms
We consider a system of ultracold atoms in an optical lattice as a quantum
simulator for electron-positron pair production in quantum electrodynamics
(QED). For a setup in one spatial dimension, we investigate the nonequilibrium
phenomenon of pair production including the backreaction leading to plasma
oscillations. Unlike previous investigations on quantum link models, we focus
on the infinite-dimensional Hilbert space of QED and show that it may be well
approximated by experiments employing Bose-Einstein condensates interacting
with fermionic atoms. The calculations based on functional integral techniques
give a unique access to the physical parameters required to realize the QED
phenomena in a cold atom experiment. In particular, we use our approach to
consider quantum link models in a yet unexplored parameter regime and give
bounds for their ability to capture essential features of the physics. The
results suggest a paradigmatic change towards realizations using coherent
many-body states rather than single atoms for quantum simulations of
high-energy particle physics phenomena.Comment: 5 pages, 4 figures, PLB versio
Investigation of the effect of ceramic coatings on rocket thrust chamber life
Cylindrical rocket thrust chamber cylinders were coated with a 0.203 mm (0.008 in.) layer of zirconium oxide using a process that employed electrodeposition of metal to a spray coated mandrel. The cylinders were cyclically tested using hydrogen oxygen propellants at a nominal chamber pressure of 4.14 MN/sq m (600 psia) to show the effect of the coating on life. Both cylinders failed prematurely due to causes unrelated to the coatings. Post destructive analysis showed no cooling passage wall deformation. Where erosion of the coating occurred, the coating thickness stabilized at 0.061 mm (0.0024 in.) within 80 cycles and remained well adhered throughout the tests
Experimental evaluation of combustor concepts for burning broad property fuels
A baseline CF6-50 combustor and three advanced combustor designs were evaluated to determine the effects of combustor design on operational characteristics using broad property fuels. Three fuels were used in each test: Jet A, a broad property 13% hydrogen fuel, and a 12% hydrogen fuel blend. Testing was performed in a sector rig at true cruise and simulated takeoff conditions for the CF6-50 engine cycle. The advanced combustors (all double annular, lean dome designs) generally exhibited lower metal temperatures, exhaust emissions, and carbon buildup than the baseline CF6-50 combustor. The sensitivities of emissions and metal temperatures to fuel hydrogen content were also generally lower for the advanced designs. The most promising advanced design used premixing tubes in the main stage. This design was chosen for additional testing in which fuel/air ratio, reference velocity, and fuel flow split were varied
Implementing quantum electrodynamics with ultracold atomic systems
We discuss the experimental engineering of model systems for the description
of QED in one spatial dimension via a mixture of bosonic Na and
fermionic Li atoms. The local gauge symmetry is realized in an optical
superlattice, using heteronuclear boson-fermion spin-changing interactions
which preserve the total spin in every local collision. We consider a large
number of bosons residing in the coherent state of a Bose-Einstein condensate
on each link between the fermion lattice sites, such that the behavior of
lattice QED in the continuum limit can be recovered. The discussion about the
range of possible experimental parameters builds, in particular, upon
experiences with related setups of fermions interacting with coherent samples
of bosonic atoms. We determine the atomic system's parameters required for the
description of fundamental QED processes, such as Schwinger pair production and
string breaking. This is achieved by benchmark calculations of the atomic
system and of QED itself using functional integral techniques. Our results
demonstrate that the dynamics of one-dimensional QED may be realized with
ultracold atoms using state-of-the-art experimental resources. The experimental
setup proposed may provide a unique access to longstanding open questions for
which classical computational methods are no longer applicable
The IT-Productivity Linkage at the Country Level for Developing Economies
Recent evidence suggests that information technology (IT) investments have a positive impact on productivity and economic growth for developed countries. However, for developing countries the relationship between IT investment and economic growth remains unclear. This paper draws on the resource-based view (RBV) theory with its notion of resource complementarity to propose a theoretical model of how factors interact with IT investment to influence economic productivity. The proposed model posits a number of factors effecting the productivity of IT investment in developing economies
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