9,603 research outputs found
Cruise aerodynamics of USB nacelle/wing geometric variations
Experimental results are presented on aerodynamic effects of geometric variations in upper surface blown nacelle configurations at high speed cruise conditions. Test data include both force and pressure measurements on two and three dimensional models powered by upper surface blowing nacelles of varying geometries. Experimental results are provided on variations in nozzle aspect ratio, nozzle boattail angle, and multiple nacelle installations. The nacelles are ranked according to aerodynamic drag penalties as well as overall installed drag penalties. Sample effects and correlations are shown for data obtained with the pressure model
X-ray time lags in AGN: inverse-Compton scattering and spherical corona model
We develop a physically motivated, spherical corona model to investigate the
frequency-dependent time lags in AGN. The model includes the effects of Compton
up-scattering between the disc UV photons and coronal electrons, and the
subsequent X-ray reverberation from the disc. The time lags are associated with
the time required for multiple scatterings to boost UV photons up to soft and
hard X-ray energies, and the light crossing time the photons take to reach the
observer. This model can reproduce not only low-frequency hard and
high-frequency soft lags, but also the clear bumps and wiggles in reverberation
profiles which should explain the wavy-residuals currently observed in some
AGN. Our model supports an anti-correlation between the optical depth and
coronal temperatures. In case of an optically thin corona, time delays due to
propagating fluctuations may be required to reproduce observed time lags. We
fit the model to the lag-frequency data of 1H0707-495, Ark 564, NGC 4051 and
IRAS 13224-3809 estimated using the minimal bias technique so that the observed
lags here are highest-possible quality. We find their corona size is ~7-15 r_g
having the constrained optical depth ~2-10. The coronal temperature is ~150-300
keV. Finally, we note that the reverberation wiggles may be signatures of
repeating scatters inside the corona that control the distribution of X-ray
sources.Comment: 15 pages, 10 figures, accepted for publication in MNRA
Exploratory studies of the cruise performance of upper surface blown configurations: Experimental program, high-speed pressure tests
Basic pressure data are presented which was obtained from an experimental study of upper-surface blown configurations at cruise. The high-speed (subsonic) experimental work, studying the aerodynamic effects of wing-nacelle geometric variations, was conducted around semi-span model configurations composed of diversified, interchangeable components. Power simulation was provided by high-pressure air ducted through closed forebody nacelles. Nozzle geometry was varied across size, exit aspect ratio, exit position and boattail angle. Both 3-D force and 2-D pressure measurements were obtained at cruise Mach numbers from 0.5 to 0.8 and at nozzle pressure ratios up to about 3.0. The experimental investigation was supported by an analytical synthesis of the system using a vortex lattice representation with first-order power effects. Results are also presented from a compatibility study in which a short-haul transport is designed on the basis of the aerodynamic findings in the experimental study as well as acoustical data obtained in a concurrent program. High-lift test data are used to substantiate the projected performance of the selected transport design
Exploratory studies of the cruise performance of upper surface blown configuration: Experimental program, high-speed force tests
The work to develop a wing-nacelle arrangement to accommodate a wide range of upper surface blown configuration is reported. Pertinent model and installation details are described. Data of the effects of a wide range of nozzle geometric variations are presented. Nozzle aspect ratio, boattail angle, and chordwise position are among the parameters investigated. Straight and swept wing configurations were tested across a range of nozzle pressure ratios, lift coefficients, and Mach numbers
Exploratory studies of the cruise performance of upper surface blown configurations. Experimental program: Test facilities, model design instrumentation, and lowspeed, high-lift tests
The model hardware, test facilities and instrumentation utilized in an experimental study of upper surface blown configurations at cruise is described. The high speed (subsonic) experimental work, studying the aerodynamic effects of wing nacelle geometric variations, was conducted around semispan model configurations composed of diversified, interchangeable components. Power simulation was provided by high pressure air ducted through closed forebody nacelles. Nozzle geometry was varied across size, exit aspect ratio, exit position and boattail angle. Three dimensional force and two dimensional pressure measurements were obtained at cruise Mach numbers from 0.5 to 0.8 and at nozzle pressure ratios up to about 3.0. The experimental investigation was supported by an analytical synthesis of the system using a vortex lattice representation with first order power effects. Results are also presented from a compatibility study in which a short haul transport is designed on the basis of the aerodynamic findings in the experimental study as well as acoustical data obtained in a concurrent program. High lift test data are used to substantiate the projected performance of the selected transport design
Exploratory studies of the cruise performance of upper surface blown configurations
The data and major conclusions obtained from an experimental/analytical study of upper-surface blown (USB) configurations at cruise are summarized. The high-speed (subsonic) experimental work, studying the aerodynamic effects of wing-nacelle geometric variations, was conducted around semi-span model configurations composed of diversified, interchangeable components. Power simulation was provided by high pressure air ducted through closed forebody nacelles. Nozzle geometry was varied across size, exit aspect ratio, exit position and boattail angle. Both 3-D force and 2-D pressure measurements were obtained at cruise Mach numbers from 0.5 to 0.8 and at nozzle pressure ratios up to about 3.0. The experimental investigation was supported by an analytical synthesis of the system using a vortex lattice representation with first-order power effects. Results are also presented from a compatibility study in which a short-haul transport is designed on the basis of the aerodynamic findings in the experimental study as well as acoustical data obtained in a concurrent program. High-lift test data are used to substantiate the projected performance of the selected transport design
Soft Manifold Dynamics Behind Negative Thermal Expansion
Minimal models are developed to examine the origin of large negative thermal
expansion (NTE) in under-constrained systems. The dynamics of these models
reveals how underconstraint can organize a thermodynamically extensive manifold
of low-energy modes which not only drives NTE but extends across the Brillioun
zone. Mixing of twist and translation in the eigenvectors of these modes, for
which in ZrW2O8 there is evidence from infrared and neutron scattering
measurements, emerges naturally in our model as a signature of the dynamics of
underconstraint.Comment: 5 pages, 3 figure
Indexed induction and coinduction, fibrationally.
This paper extends the fibrational approach to induction and coinduction pioneered by Hermida and Jacobs, and developed by the current authors, in two key directions. First, we present a sound coinduction rule for any data type arising as the final coalgebra of a functor, thus relaxing Hermida and Jacobs’ restriction to polynomial data types. For this we introduce the notion of a quotient category with equality (QCE), which both abstracts the standard notion of a fibration of relations constructed from a given fibration, and plays a role in the theory of coinduction dual to that of a comprehension category with unit (CCU) in the theory of induction. Second, we show that indexed inductive and coinductive types also admit sound induction and coinduction rules. Indexed data types often arise as initial algebras and final coalgebras of functors on slice categories, so our key technical results give sufficent conditions under which we can construct, from a CCU (QCE) U : E -> B, a fibration with base B/I that models indexing by I and is also a CCU (QCE)
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