16,407 research outputs found
Flight measured and calculated exhaust jet conditions for an F100 engine in an F-15 airplane
The exhaust jet conditions, in terms of temperature and Mach number, were determined for a nozzle-aft end acoustic study flown on an F-15 aircraft. Jet properties for the F100 EMD engines were calculated using the engine manufacturer's specification deck. The effects of atmospheric temperature on jet Mach number, M10, were calculated. Values of turbine discharge pressure, PT6M, jet Mach number, and jet temperature were calculated as a function of aircraft Mach number, altitude, and power lever angle for the test day conditions. At a typical test point with a Mach number of 0.9, intermediate power setting, and an altitude of 20,000 ft, M10 was equal to 1.63. Flight measured and calculated values of PT6M were compared for intermediate power at altitudes of 15500, 20500, and 31000 ft. It was found that at 31000 ft, there was excellent agreement between both, but for lower altitudes the specification deck overpredicted the flight data. The calculated jet Mach numbers were believed to be accurate to within 2 percent
On local Fourier analysis of multigrid methods for PDEs with jumping and random coefficients
In this paper, we propose a novel non-standard Local Fourier Analysis (LFA)
variant for accurately predicting the multigrid convergence of problems with
random and jumping coefficients. This LFA method is based on a specific basis
of the Fourier space rather than the commonly used Fourier modes. To show the
utility of this analysis, we consider, as an example, a simple cell-centered
multigrid method for solving a steady-state single phase flow problem in a
random porous medium. We successfully demonstrate the prediction capability of
the proposed LFA using a number of challenging benchmark problems. The
information provided by this analysis helps us to estimate a-priori the time
needed for solving certain uncertainty quantification problems by means of a
multigrid multilevel Monte Carlo method
Wing and body motion during flight initiation in Drosophila revealed by automated visual tracking
The fruit fly Drosophila melanogaster is a widely used model organism in studies of genetics, developmental biology and biomechanics. One limitation for exploiting Drosophila as a model system for behavioral neurobiology is that measuring body kinematics during behavior is labor intensive and subjective. In order to quantify flight kinematics during different types of maneuvers, we have developed a visual tracking system that estimates the posture of the fly from multiple calibrated cameras. An accurate geometric fly model is designed using unit quaternions to capture complex body and wing rotations, which are automatically fitted to the images in each time frame. Our approach works across a range of flight behaviors, while also being robust to common environmental clutter. The tracking system is used in this paper to compare wing and body motion during both voluntary and escape take-offs. Using our automated algorithms, we are able to measure stroke amplitude, geometric angle of attack and other parameters important to a mechanistic understanding of flapping flight. When compared with manual tracking methods, the algorithm estimates body position within 4.4±1.3% of the body length, while body orientation is measured within 6.5±1.9 deg. (roll), 3.2±1.3 deg. (pitch) and 3.4±1.6 deg. (yaw) on average across six videos. Similarly, stroke amplitude and deviation are estimated within 3.3 deg. and 2.1 deg., while angle of attack is typically measured within 8.8 deg. comparing against a human digitizer. Using our automated tracker, we analyzed a total of eight voluntary and two escape take-offs. These sequences show that Drosophila melanogaster do not utilize clap and fling during take-off and are able to modify their wing kinematics from one wingstroke to the next. Our approach should enable biomechanists and ethologists to process much larger datasets than possible at present and, therefore, accelerate insight into the mechanisms of free-flight maneuvers of flying insects
Simple one-dimensional quantum-mechanical model for a particle attached to a surface
We present a simple one-dimensional quantum-mechanical model for a particle
attached to a surface. We solve the Schr\"odinger equation in terms of Weber
functions and discuss the behavior of the eigenvalues and eigenfunctions. We
derive the virial theorem and other exact relationships as well as the
asymptotic behaviour of the eigenvalues. We calculate the zero-point energy for
model parameters corresponding to H adsorbed on Pd(100) and also outline the
application of the Rayleigh-Ritz variational method
Modeling Member Responses to the Farmer Owned Cooperative's Alternative Capital Management Strategies
Agricultural Finance, Agribusiness,
Exact solutions of Brans-Dicke wormholes in the presence of matter
A fundamental ingredient in wormhole physics is the presence of exotic
matter, which involves the violation of the null energy condition. Although a
plethora of wormhole solutions have been explored in the literature, it is
useful to find geometries that minimize the usage of exotic matter. In this
work, we find exact wormhole solutions in Brans-Dicke theory where the normal
matter threading the wormhole satisfies the null energy condition throughout
the geometry. Thus, the latter implies that it is the effective stress-energy
tensor containing the scalar field, that plays the role of exotic matter, that
is responsible for sustaining the wormhole geometry. More specifically, we
consider a zero redshift function and a particular choice for the scalar field
and determine the remaining quantities, namely, the stress-energy tensor
components and the shape function. The solution found is not asymptotically
flat, so that this interior wormhole spacetime needs to be matched to an
exterior vacuum solution.Comment: 7 pages, 3 figure
Nonminimal coupling of perfect fluids to curvature
In this work, we consider different forms of relativistic perfect fluid
Lagrangian densities, that yield the same gravitational field equations in
General Relativity. A particularly intriguing example is the case with
couplings of the form , where is the scalar
curvature, which induces an extra force that depends on the form of the
Lagrangian density. It has been found that, considering the Lagrangian density
, where is the pressure, the extra-force vanishes. We argue
that this is not the unique choice for the matter Lagrangian density, and that
more natural forms for do not imply the vanishing of the
extra-force. Particular attention is paid to the impact on the classical
equivalence between different Lagrangian descriptions of a perfect fluid.Comment: 6 pages. V2: minor changes and references adde
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