2,818 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
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
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
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
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
Mott-Hubbard Transition of Bosons in Optical Lattices with Three-body Interactions
In this paper, the quantum phase transition between superfluid state and
Mott-insulator state is studied based on an extended Bose-Hubbard model with
two- and three-body on-site interactions. By employing the mean-field
approximation we find the extension of the insulating 'lobes' and the existence
of a fixed point in three dimensional phase space. We investigate the link
between experimental parameters and theoretical variables. The possibility to
obverse our results through some experimental effects in optically trapped
Bose-Einstein Condensates(BEC) is also discussed.Comment: 7 pages, 4 figures; to be appear in Phys. Rev.
Top EW couplings at Linear Colliders
In this talk, we present the latest study of e+e− → t¯t, based on a detailed simulation of the ILD detector concept, which assumes a centre-of-mass energy of √s = 500 GeV and a luminosity of L = 500fb−1, equality shared between the incoming beam polarisations of P e−,e+ = (±0.8,∓0.3). The study comprises the cross sections, the forward-backward asymmetry and the slope of the helicity angle asymmetry. The vector and axial vector couplings are separately determined for the photon and the Z component. The tensorial CP-conserving coupling can be also extracted by assuming the other couplings to be the SM values. We show that the sensitivity to new physics would be dramatically improved with respect to what is expected from LHC for electroweak couplings
Coexistence of Itinerant Electrons and Local Moments in Iron-Based Superconductors
In view of the recent experimental facts in the iron-pnictides, we make a
proposal that the itinerant electrons and local moments are simultaneously
present in such multiband materials. We study a minimal model composed of
coupled itinerant electrons and local moments to illustrate how a consistent
explanation of the experimental measurements can be obtained in the leading
order approximation. In this mean-field approach, the spin-density-wave (SDW)
order and superconducting pairing of the itinerant electrons are not directly
driven by the Fermi surface nesting, but are mainly induced by their coupling
to the local moments. The presence of the local moments as independent degrees
of freedom naturally provides strong pairing strength for superconductivity and
also explains the normal-state linear-temperature magnetic susceptibility above
the SDW transition temperature. We show that this simple model is supported by
various anomalous magnetic properties and isotope effect which are in
quantitative agreement with experiments.Comment: 7 pages, 4 figures; an expanded versio
Asset pricing, spatial linkages and contagion in real estate stocks
Following recent methodological developments, we estimate a spatial multi-factor model (SMFM) which combines asset pricing techniques with spatial econometrics to assess systemic implications for REIT index returns. We distinguish between comovement due to market risk exposure (systematic risk) and comovement due to linkages between markets (spillover risk). We find that the spillover risk dramatically increases during the global financial crisis and can explain up to 60% of total asset variation. In the rest of the time, idiosyncratic risks have been the predominant type of risk in real estate stocks. Our results have implications for investors showing that the market can channel asset volatility leading to contagion during crisis periods and therefore residual linkages between country indices need to be accounted for as a means of assessing the diversification benefits of a global portfolio
semileptonic form factors from lattice QCD with M\"obius domain-wall quarks
We calculate the form factors for the decay in 2+1
flavor lattice QCD. For all quark flavors, we employ the M\"obius domain-wall
action, which preserves chiral symmetry to a good precision. Our gauge
ensembles are generated at three lattice cutoffs , 3.6 and 4.5
GeV with pion masses as low as MeV. The physical lattice size
satisfies the condition to control finite volume effects
(FVEs), while we simulate a smaller size at the smallest to directly
examine FVEs. The bottom quark masses are chosen in a range from the physical
charm quark mass to to control discretization effects. We
extrapolate the form factors to the continuum limit and physical quark masses
based on heavy meson chiral perturbation theory at next-to-leading order. Then
the recoil parameter dependence is parametrized using a model independent form
leading to our estimate of the decay rate ratio between the tau ()
and light lepton () channels in the Standard
Model. A simultaneous fit with recent data from the Belle experiment yields
, which is consistent with previous
exclusive determinations, and shows good consistency in the kinematical
distribution of the differential decay rate between the lattice and
experimental data.Comment: 37 pages, 13 figure
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