3,541 research outputs found
Attitude estimation of earth orbiting satellites by decomposed linear recursive filters
Attitude estimation of earth orbiting satellites (including Large Space Telescope) subjected to environmental disturbances and noises was investigated. Modern control and estimation theory is used as a tool to design an efficient estimator for attitude estimation. Decomposed linear recursive filters for both continuous-time systems and discrete-time systems are derived. By using this accurate estimation of the attitude of spacecrafts, state variable feedback controller may be designed to achieve (or satisfy) high requirements of system performance
Anomalous enhancement of a penguin hadronic matrix element in B->K eta'
We estimate the density matrix element for the pi^0, eta and eta' production
from the vacuum in the large-N_c limit. As a consequence, we find that the QCD
axial anomaly leads to highly non-trivial corrections to the usual flavour
SU(3) relations between B^0-> K^0 pi^0, B^0-> K^0 eta and B^0-> K^0 eta' decay
amplitudes. These corrections may explain why the B-> K eta' branching ratio is
about six times larger than the B-> K pi one.Comment: 5 pages, 1 figur
The Green-function transform and wave propagation
Fourier methods well known in signal processing are applied to
three-dimensional wave propagation problems. The Fourier transform of the Green
function, when written explicitly in terms of a real-valued spatial frequency,
consists of homogeneous and inhomogeneous components. Both parts are necessary
to result in a pure out-going wave that satisfies causality. The homogeneous
component consists only of propagating waves, but the inhomogeneous component
contains both evanescent and propagating terms. Thus we make a distinction
between inhomogenous waves and evanescent waves. The evanescent component is
completely contained in the region of the inhomogeneous component outside the
k-space sphere. Further, propagating waves in the Weyl expansion contain both
homogeneous and inhomogeneous components. The connection between the Whittaker
and Weyl expansions is discussed. A list of relevant spherically symmetric
Fourier transforms is given
AAA gunnermodel based on observer theory
The Luenberger observer theory is used to develop a predictive model of a gunner's tracking response in antiaircraft artillery systems. This model is composed of an observer, a feedback controller and a remnant element. An important feature of the model is that the structure is simple, hence a computer simulation requires only a short execution time. A parameter identification program based on the least squares curve fitting method and the Gauss Newton gradient algorithm is developed to determine the parameter values of the gunner model. Thus, a systematic procedure exists for identifying model parameters for a given antiaircraft tracking task. Model predictions of tracking errors are compared with human tracking data obtained from manned simulation experiments. Model predictions are in excellent agreement with the empirical data for several flyby and maneuvering target trajectories
Computer simulation results of attitude estimation of earth orbiting satellites
Computer simulation results of attitude estimation of Earth-orbiting satellites (including Space Telescope) subjected to environmental disturbances and noises are presented. Decomposed linear recursive filter and Kalman filter were used as estimation tools. Six programs were developed for this simulation, and all were written in the basic language and were run on HP 9830A and HP 9866A computers. Simulation results show that a decomposed linear recursive filter is accurate in estimation and fast in response time. Furthermore, for higher order systems, this filter has computational advantages (i.e., less integration errors and roundoff errors) over a Kalman filter
Network-analysis-guided synthesis of weisaconitine D and liljestrandinine.
General strategies for the chemical synthesis of organic compounds, especially of architecturally complex natural products, are not easily identified. Here we present a method to establish a strategy for such syntheses, which uses network analysis. This approach has led to the identification of a versatile synthetic intermediate that facilitated syntheses of the diterpenoid alkaloids weisaconitine D and liljestrandinine, and the core of gomandonine. We also developed a web-based graphing program that allows network analysis to be easily performed on molecules with complex frameworks. The diterpenoid alkaloids comprise some of the most architecturally complex and functional-group-dense secondary metabolites isolated. Consequently, they present a substantial challenge for chemical synthesis. The synthesis approach described here is a notable departure from other single-target-focused strategies adopted for the syntheses of related structures. Specifically, it affords not only the targeted natural products, but also intermediates and derivatives in the three families of diterpenoid alkaloids (C-18, C-19 and C-20), and so provides a unified synthetic strategy for these natural products. This work validates the utility of network analysis as a starting point for identifying strategies for the syntheses of architecturally complex secondary metabolites
Anomalous Spin Dynamics of Hubbard Model on Honeycomb Lattices
In this paper, the honeycomb Hubbard model in optical lattices is
investigated using O(3) non-linear sigma model. A possible quantum non-magnetic
insulator in a narrow parameter region is found near the metal-insulator
transition. We study the corresponding dynamics of magnetic properties, and
find that the narrow region could be widened by hole doping.Comment: 9 pages, 12 figure
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