61,773 research outputs found
Analysis and design of planar and non-planar wings for induced drag minimization
Improvements in the aerodynamic efficiency of commercial transport aircraft will reduce fuel usage with subsequent reduced cost, both monetary and environmental. To this end, the current research is aimed at reducing the overall drag of these aircraft with specific emphasis on reducing the drag generated by the lifting surfaces. The ultimate goal of this program is to create a wing design methodology which optimizes the geometry of the wing for lowest total drag within the constraints of a particular design specification. The components of drag which must be considered include profile drag, and wave drag. Profile drag is dependent upon, among other things, the airfoil section and the total wetted area. Induced drag, which is manifested as energy left in the wake by the trailing vortex system is mostly a function of wing span, but also depends on other geometric wing parameters. Wave drag of the wing, important in the transonic flight regime, is largely affected by the airfoil section, wing sweep, and so forth. The optimization problem is that of assessing the various parameters which contribute to the different components of wing drag, and determining the wing geometry which generates the best overall performance for a given aircraft mission. The primary thrust of the research effort to date was in the study of induced drag. Results from the study are presented
Relic density and CMB constraints on dark matter annihilation with Sommerfeld enhancement
We calculate how the relic density of dark matter particles is altered when
their annihilation is enhanced by the Sommerfeld mechanism due to a Yukawa
interaction between the annihilating particles. Maintaining a dark matter
abundance consistent with current observational bounds requires the
normalization of the s-wave annihilation cross section to be decreased compared
to a model without enhancement. The level of suppression depends on the
specific parameters of the particle model, with the kinetic decoupling
temperature having the most effect. We find that the cross section can be
reduced by as much as an order of magnitude for extreme cases. We also compute
the mu-type distortion of the CMB energy spectrum caused by energy injection
from such Sommerfeld-enhanced annihilation. Our results indicate that in the
vicinity of resonances, associated with bound states, distortions can be large
enough to be excluded by the upper limit |mu|<9.0x10^(-5) found by the
COBE/FIRAS experiment.Comment: 10 pages, 6 figures, accepted for publication in Physical Review D.
Corrections to eqs. 9,10,14 and 16. Figures updated accordingly. No major
changes to previous results. Website with online tools for Sommerfeld-related
calculations can be found at
http://www.mpa-garching.mpg.de/~vogelsma/sommerfeld
Coaxial injector spray characterization using water/air as simulants
Quantitative information about the atomization of injector sprays is required to improve the accuracy of computational models that predict the performance and stability of liquid propellant rocket engines. An experimental program is being conducted at NASA-Lewis to measure the drop size and velocity distributions in shear coaxial injector sprays. A phase/Doppler interferometer is used to obtain drop size data in water air shear coaxial injector sprays. Droplet sizes and axial component of droplet velocities are measured at different radii for various combinations of water flow rate, air flow rate, injector liquid jet diameter, injector annular gap, and liquid post recess. Sauter mean diameters measured in the spray center 51 mm downstream of the liquid post tip range from 28 to 68 microns, and mean axial drop velocities at the same location range from 37 to 120 m/s. The shear coaxial injector sprays show a high degree of symmetry; the mean drop size and velocity profiles vary with liquid flow rate, post recess, and distance from the injector face. The drop size data can be used to estimate liquid oxygen/hydrogen spray drop sizes by correcting property differences between water-air and liquid oxygen/hydrogen
The design of an airfoil for a high-altitude, long-endurance remotely piloted vehicle
Airfoil design efforts are studied. The importance of integrating airfoil and aircraft designs was demonstrated. Realistic airfoil data was provided to aid future high altitude, long endurance aircraft preliminary design. Test cases were developed for further validation of the Eppler program. Boundary layer, not pressure distribution or shape, was designed. Substantial improvement was achieved in vehicle performance through mission specific airfoil designed utilizing the multipoint capability of the Eppler program
Against Game Theory
People make choices. Often, the outcome depends on choices other people make. What mental steps do people go through when making such choices? Game theory, the most influential model of choice in economics and the social sciences, offers an answer, one based on games of strategy such as chess and checkers: the chooser considers the choices that others will make and makes a choice that will lead to a better outcome for the chooser, given all those choices by other people. It is universally established in the social sciences that classical game theory (even when heavily modified) is bad at predicting behavior. But instead of abandoning classical game theory, those in the social sciences have mounted a rescue operation under the name of ābehavioral game theory.ā Its main tool is to propose systematic deviations from the predictions of game theory, deviations that arise from character type, for example. Other deviations purportedly come from cognitive overload or limitations. The fundamental idea of behavioral game theory is that, if we know the deviations, then we can correct our predictions accordingly, and so get it right. There are two problems with this rescue operation, each of them is fatal. (1) For a chooser, contemplating the range of possible deviations, as there are many dozens, actually makes it exponentially harder to figure out a path to an outcome. This makes the theoretical models useless for modeling human thought or human behavior in general. (2) Modeling deviations are helpful only if the deviations are consistent, so that scientists (and indeed decision makers) can make predictions about future choices on the basis of past choices. But the deviations are not consistent. In general, deviations from classical models are not consistent for any individual from one task to the next or between individuals for the same task. In addition, peopleās beliefs are in general not consistent with their choices. Accordingly, all hope is hollow that we can construct a general behavioral game theory. What can replace it? We survey some of the emerging candidates
Steps Towards Precise Ar/Ar Chronologies for Fluid-Rock Interaction Throughout the Solar System
Raw Multi-Channel Audio Source Separation using Multi-Resolution Convolutional Auto-Encoders
Supervised multi-channel audio source separation requires extracting useful
spectral, temporal, and spatial features from the mixed signals. The success of
many existing systems is therefore largely dependent on the choice of features
used for training. In this work, we introduce a novel multi-channel,
multi-resolution convolutional auto-encoder neural network that works on raw
time-domain signals to determine appropriate multi-resolution features for
separating the singing-voice from stereo music. Our experimental results show
that the proposed method can achieve multi-channel audio source separation
without the need for hand-crafted features or any pre- or post-processing
Can We Build Behavioral Game Theory?
The way economists and other social scientists model how people make interdependent decisions is through the theory of games. Psychologists and behavioral economists, however, have established many deviations from the predictions of game theory. In response to these findings, a broad movement has arisen to salvage the core of game theory. Extant models of interdependent decision-making try to improve their explanatory domain by adding some corrective terms or limits. We will make the argument that this approach is misguided. For this approach to work, the deviations would have to be consistent. Drawing in part on our experimental results, we will argue that deviations from classical models are not consistent for any individual from one task to the next or between individuals for the same task. In turn, the problem of finding an equilibrium strategy is not easier but rather is exponentially more difficult. It does not seem that game theory can be repaired by adding corrective terms (such as consideration of personal characteristics, social norms, heuristic or bias terms, or cognitive limits on choice and learning). In what follows, we describe new methods for investigating interdependent decision-making. Our experimental results show that people do not choose consistently, do not hold consistent beliefs, and do not in general align actions and beliefs. We will show that experimental choices are inconsistent in ways that prevent us from drawing general characterizations of an individualās choices or beliefs or of the general population\u27s choices and beliefs. A general behavioral game theory seems a distant and, at present, unfulfilled hope
- ā¦