3,894 research outputs found
Synthesis of hover autopilots for rotary-wing VTOL aircraft
The practical situation is considered where imperfect information on only a few rotor and fuselage state variables is available. Filters are designed to estimate all the state variables from noisy measurements of fuselage pitch/roll angles and from noisy measurements of both fuselage and rotor pitch/roll angles. The mean square response of the vehicle to a very gusty, random wind is computed using various filter/controllers and is found to be quite satisfactory although, of course, not so good as when one has perfect information (idealized case). The second part of the report considers precision hover over a point on the ground. A vehicle model without rotor dynamics is used and feedback signals in position and integral of position error are added. The mean square response of the vehicle to a very gusty, random wind is computed, assuming perfect information feedback, and is found to be excellent. The integral error feedback gives zero position error for a steady wind, and smaller position error for a random wind
Multi-input, multi-output regulator design for constant disturbances and non-zero set points with application to automatic landing in a crosswind
Undesirable steady offsets result when a stationary, linear regulator using state feedback is subjected to constant disturbances and/or non-zero setspoints. To eliminate these offsets, the disturbances and non-zero setpoints can be fed forward to the control. Only when the number of outputs is less than or equal to the number of control inputs can the outputs be maintained at arbitrary non-zero setpoints. The state and the disturbance may be estimated using a constant gain Kalman filter or by modeling the constant disturbances as exponentially correlated processes with long correlation times
Competition and the Retreat from Collective Bargaining, NIESR Discussion Paper No. 318
For most of the twentieth century, collective bargaining provided the terms on which labour was commonly employed in Britain. However, the quarter century since 1980
has seen the collapse of collectivism as the main way of regulating employment. Our argument is that the tacit settlement between organized labour and employers was undermined by increasing product market competition. The paper first provides an overview of the changing map of collective bargaining, focusing on the private sector.
It then moves on to ask why the retreat took place, and to explore the part played by product market competition and, in particular, by the profitability of different
industries. The paper concludes with an analysis of the consequences of privatisation
A terminal guidance scheme for lifting body entry vehicles
Perturbation feedback guidance for terminal phase of lifting body entry vehicl
Search complexity and resource scaling for the quantum optimal control of unitary transformations
The optimal control of unitary transformations is a fundamental problem in
quantum control theory and quantum information processing. The feasibility of
performing such optimizations is determined by the computational and control
resources required, particularly for systems with large Hilbert spaces. Prior
work on unitary transformation control indicates that (i) for controllable
systems, local extrema in the search landscape for optimal control of quantum
gates have null measure, facilitating the convergence of local search
algorithms; but (ii) the required time for convergence to optimal controls can
scale exponentially with Hilbert space dimension. Depending on the control
system Hamiltonian, the landscape structure and scaling may vary. This work
introduces methods for quantifying Hamiltonian-dependent and kinematic effects
on control optimization dynamics in order to classify quantum systems according
to the search effort and control resources required to implement arbitrary
unitary transformations
Optimal switching of a nanomagnet assisted by microwaves
We develop an efficient and general method for optimizing the microwave field
that achieves magnetization switching with a smaller static field. This method
is based on optimal control and renders an exact solution for the 3D microwave
field that triggers the switching of a nanomagnet with a given anisotropy and
in an oblique static field. Applying this technique to the particular case of
uniaxial anisotropy, we show that the optimal microwave field, that achieves
switching with minimal absorbed energy, is modulated both in frequency and in
magnitude. Its role is to drive the magnetization from the metastable
equilibrium position towards the saddle point and then damping induces the
relaxation to the stable equilibrium position. For the pumping to be efficient,
the microwave field frequency must match at the early stage of the switching
process the proper precession frequency of the magnetization, which depends on
the magnitude and direction of the static field. We investigate the effect of
the static field (in amplitude and direction) and of damping on the
characteristics of the microwave field. We have computed the switching curves
in the presence of the optimal microwave field. The results are in qualitative
agreement with micro-SQUID experiments on isolated nanoclusters. The strong
dependence of the microwave field and that of the switching curve on the
damping parameter may be useful in probing damping in various nanoclusters.Comment: 9 pages, 8 figure
Multiple Imputation When Rate of Change Is The Outcome of Interest
Little research has been devoted to multiple imputation (MI) of derived variables. We investigated various MI approaches for the outcome, rate of change, when the analysis model is a two-stage linear regression. Our simulations showed that competitive approaches depended on the missing data mechanism and presence of auxiliary terms
Optimal Control of Superconducting N-level quantum systems
We consider a current-biased dc SQUID in the presence of an applied
time-dependent bias current or magnetic flux. The phase dynamics of such a
Josephson device is equivalent to that of a quantum particle trapped in a D
anharmonic potential, subject to external time-dependent control fields, {\it
i.e.} a driven multilevel quantum system. The problem of finding the required
time-dependent control field that will steer the system from a given initial
state to a desired final state at a specified final time is formulated in the
framework of optimal control theory. Using the spectral filter technique, we
show that the selected optimal field which induces a coherent population
transfer between quantum states is represented by a carrier signal having a
constant frequency but which is time-varied both in amplitude and phase. The
sensitivity of the optimal solution to parameter perturbations is also
addressed
A Chebyshev minimax technique oriented to aerospace trajectory optimization problems.
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76822/1/AIAA-6604-910.pd
A Transiting Jupiter Analog
Decadal-long radial velocity surveys have recently started to discover
analogs to the most influential planet of our solar system, Jupiter. Detecting
and characterizing these worlds is expected to shape our understanding of our
uniqueness in the cosmos. Despite the great successes of recent transit
surveys, Jupiter analogs represent a terra incognita, owing to the strong
intrinsic bias of this method against long orbital periods. We here report on
the first validated transiting Jupiter analog, Kepler-167e (KOI-490.02),
discovered using Kepler archival photometry orbiting the K4-dwarf KIC-3239945.
With a radius of , a low orbital eccentricity
() and an equilibrium temperature of K,
Kepler-167e bears many of the basic hallmarks of Jupiter. Kepler-167e is
accompanied by three Super-Earths on compact orbits, which we also validate,
leaving a large cavity of transiting worlds around the habitable-zone. With two
transits and continuous photometric coverage, we are able to uniquely and
precisely measure the orbital period of this post snow-line planet
( d), paving the way for follow-up of this mag
target.Comment: 14 pages, 10 figures. Accepted to ApJ. Posteriors available at
https://github.com/CoolWorlds/Kepler-167-Posterior
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