1,943 research outputs found
Wind velocity probing device and method Patent
Free-fall body for obtaining wind velocity profiles by radar trackin
First-principles modeling of electrostatically doped perovskite systems
Macroscopically, confined electron gases at polar oxide interfaces are
rationalized within the simple "polar catastrophe" model. At the microscopic
level, however, many other effects such as electric fields, structural
distortions and quantum-mechanical interactions enter into play. Here we show
how to bridge the gap between these two length scales, by combining the
accuracy of first-principles methods with the conceptual simplicity of model
Hamiltonian approaches. To demonstrate our strategy, we address the equilibrium
distribution of the compensating free carriers at polar LaAlO3/SrTiO3
interfaces. Remarkably, a model including only calculated bulk properties of
SrTiO3 and no adjustable parameters accurately reproduces our full
first-principles results. Our strategy provides a unified description of charge
compensation mechanisms in SrTiO3-based systems.Comment: 4 pages, 4 figures. Supplementary notes:
http://www.icmab.es/dmmis/leem/stengel/supp.pd
Prediction of pilot-aircraft stability boundaries and performance contours
Control-theoretic pilot models can provide important new insights regarding the stability and performance characteristics of the pilot-aircraft system. Optimal-control pilot models can be formed for a wide range of flight conditions, suggesting that the human pilot can maintain stability if he adapts his control strategy to the aircraft's changing dynamics. Of particular concern is the effect of sub-optimal pilot adaptation as an aircraft transitions from low to high angle-of-attack during rapid maneuvering, as the changes in aircraft stability and control response can be extreme. This paper examines the effects of optimal and sub-optimal effort during a typical 'high-g' maneuver, and it introduces the concept of minimum-control effort (MCE) adaptation. Limited experimental results tend to support the MCE adaptation concept
Stability and control of maneuvering high-performance aircraft
The stability and control of a high-performance aircraft was analyzed, and a design methodology for a departure prevention stability augmentation system (DPSAS) was developed. A general linear aircraft model was derived which includes maneuvering flight effects and trim calculation procedures for investigating highly dynamic trajectories. The stability and control analysis systematically explored the effects of flight condition and angular motion, as well as the stability of typical air combat trajectories. The effects of configuration variation also were examined
Longitudinal flying qualities criteria for single-pilot instrument flight operations
Modern estimation and control theory, flight testing, and statistical analysis were used to deduce flying qualities criteria for General Aviation Single Pilot Instrument Flight Rule (SPIFR) operations. The principal concern is that unsatisfactory aircraft dynamic response combined with high navigation/communication workload can produce problems of safety and efficiency. To alleviate these problems. The relative importance of these factors must be determined. This objective was achieved by flying SPIFR tasks with different aircraft dynamic configurations and assessing the effects of such variations under these conditions. The experimental results yielded quantitative indicators of pilot's performance and workload, and for each of them, multivariate regression was applied to evaluate several candidate flying qualities criteria
Technical notes and correspondence: Stochastic robustness of linear time-invariant control systems
A simple numerical procedure for estimating the stochastic robustness of a linear time-invariant system is described. Monte Carlo evaluations of the system's eigenvalues allows the probability of instability and the related stochastic root locus to be estimated. This analysis approach treats not only Gaussian parameter uncertainties but non-Gaussian cases, including uncertain-but-bounded variation. Confidence intervals for the scalar probability of instability address computational issues inherent in Monte Carlo simulation. Trivial extensions of the procedure admit consideration of alternate discriminants; thus, the probabilities that stipulated degrees of instability will be exceeded or that closed-loop roots will leave desirable regions can also be estimated. Results are particularly amenable to graphical presentation
Flexibility and development of mirroring mechanisms
The empirical support for the SCM is mixed. We review recent results from our own lab and others supporting a central claim of SCM that mirroring occurs at multiple levels of representation. By contrast, the model is silent as to why human infants are capable of showing imitative behaviours mediated by a mirror system. This limitation is a problem with formal models that address neither the neural correlates nor the behavioural evidence directly
Cosmological Constraints on Unstable Particles: Numerical Bounds and Analytic Approximations
Many extensions of the Standard Model predict large numbers of additional
unstable particles whose decays in the early universe are tightly constrained
by observational data. For example, the decays of such particles can alter the
ratios of light-element abundances, give rise to distortions in the cosmic
microwave background, alter the ionization history of the universe, and
contribute to the diffuse photon flux. Constraints on new physics from such
considerations are typically derived for a single unstable particle species
with a single well-defined mass and characteristic lifetime. In this paper, by
contrast, we investigate the cosmological constraints on theories involving
entire ensembles of decaying particles --- ensembles which span potentially
broad ranges of masses and lifetimes. In addition to providing a detailed
numerical analysis of these constraints, we also formulate a set of simple
analytic approximations for these constraints which may be applied to generic
ensembles of unstable particles which decay into
electromagnetically-interacting final states. We then illustrate how these
analytic approximations can be used to constrain a variety of toy scenarios for
physics beyond the Standard Model. For ease of reference, we also compile our
results in the form of a table which can be consulted independently of the rest
of the paper. It is thus our hope that this work might serve as a useful
reference for future model-builders concerned with cosmological constraints on
decaying particles, regardless of the particular model under study.Comment: 41 pages, LaTeX, 12 figures, 4 table
The design of digital-adaptive controllers for VTOL aircraft
Design procedures for VTOL automatic control systems have been developed and are presented. Using linear-optimal estimation and control techniques as a starting point, digital-adaptive control laws have been designed for the VALT Research Aircraft, a tandem-rotor helicopter which is equipped for fully automatic flight in terminal area operations. These control laws are designed to interface with velocity-command and attitude-command guidance logic, which could be used in short-haul VTOL operations. Developments reported here include new algorithms for designing non-zero-set-point digital regulators, design procedures for rate-limited systems, and algorithms for dynamic control trim setting
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