2,524 research outputs found
Quantification of Cross-coupling and Motion Feedthrough for Multiaxis Controllers Used in an Air Combat Flying Task
A real-time piloted simulation of an air-to-air combat flying task using a wings-level-turn aircraft and various novel controllers was conducted. One objective is to quantify how the pilot interacts with the controllers and control modes, including: (1) controller versus aircraft response; (2) proprioceptive cross-coupling among axes of the controllers; and (3) biodynamic cross-coupling between the aircraft motions and the controllers. In order to aid in identifying the items listed above, both the target aircraft and the large amplitude multimode aerospace research simulator (LAMARS) motion system were distributed with quasi-random sums-of-sinusoids. Since the disturbances were separated in frequency, spectral analysis techniques were used to identify the three items listed. The results of the spectral analysis of controller motions from the two-axis side stick, a twist grip mounted on the side stick, a thumb button mounted on the side stick, and conventional rudder pedals are presented. Conclusions and recommendations for further research are also presented
Study of a safety margin system for powered-lift STOL aircraft
A study was conducted to explore the feasibility of a safety margin system for powered-lift aircraft which require a backside piloting technique. The objective of the safety margin system was to present multiple safety margin criteria as a single variable which could be tracked manually or automatically and which could be monitored for the purpose of deriving safety margin status. The study involved a pilot-in-the-loop analysis of several safety margin system concepts and a simulation experiment to evaluate those concepts which showed promise of providing a good solution. A system was ultimately configured which offered reasonable compromises in controllability, status information content, and the ability to regulate the safety margin at some expense of the allowable low speed flight path envelope
Cosmological Parameters from CMB Maps without Likelihood Approximation
We propose an efficient Bayesian MCMC algorithm for estimating cosmological
parameters from CMB data without use of likelihood approximations. It builds on
a previously developed Gibbs sampling framework that allows for exploration of
the joint CMB sky signal and power spectrum posterior, P(s,Cl|d), and addresses
a long-standing problem of efficient parameter estimation simultaneously in
high and low signal-to-noise regimes. To achieve this, our new algorithm
introduces a joint Markov Chain move in which both the signal map and power
spectrum are synchronously modified, by rescaling the map according to the
proposed power spectrum before evaluating the Metropolis-Hastings accept
probability. Such a move was already introduced by Jewell et al. (2009), who
used it to explore low signal-to-noise posteriors. However, they also found
that the same algorithm is inefficient in the high signal-to-noise regime,
since a brute-force rescaling operation does not account for phase information.
This problem is mitigated in the new algorithm by subtracting the Wiener filter
mean field from the proposed map prior to rescaling, leaving high
signal-to-noise information invariant in the joint step, and effectively only
rescaling the low signal-to-noise component. To explore the full posterior, the
new joint move is then interleaved with a standard conditional Gibbs sky map
move. We apply our new algorithm to simplified simulations for which we can
evaluate the exact posterior to study both its accuracy and performance, and
find good agreement with the exact posterior; marginal means agree to less than
0.006 sigma, and standard deviations to better than 3%. The Markov Chain
correlation length is of the same order of magnitude as those obtained by other
standard samplers in the field.Comment: 9 pages, 3 figures, Published in Ap
Powder alignment system for anisotropic bonded NdFeB Halbach cylinders
A Halbach cylinder, fabricated from pre-magnetized sintered NdFeB magnet segments, is proposed for the powder aligning system during the compression or injection moulding of anisotropic bonded Halbach oriented NdFeB ring magnets. The influence of leading design parameters of the powder aligning system, viz. the number of magnet segments per pole, their axial length and radial thickness, and their clearance from the mould, is investigated by finite element analysis, and validated experimentall
Analysis of anisotropic bonded NdFeB Halbach cylinders accounting for partial powder alignment
An analytical technique is developed for predicting the performance of a bonded Halbach oriented anisotropic magnet, with due account of partial alignment of the NdFeB powder during injection molding. The predicted performance of a 12-pole injection molded, Halbach oriented magnet is compared with measuremen
A Markov Chain Monte Carlo Algorithm for analysis of low signal-to-noise CMB data
We present a new Monte Carlo Markov Chain algorithm for CMB analysis in the
low signal-to-noise regime. This method builds on and complements the
previously described CMB Gibbs sampler, and effectively solves the low
signal-to-noise inefficiency problem of the direct Gibbs sampler. The new
algorithm is a simple Metropolis-Hastings sampler with a general proposal rule
for the power spectrum, C_l, followed by a particular deterministic rescaling
operation of the sky signal. The acceptance probability for this joint move
depends on the sky map only through the difference of chi-squared between the
original and proposed sky sample, which is close to unity in the low
signal-to-noise regime. The algorithm is completed by alternating this move
with a standard Gibbs move. Together, these two proposals constitute a
computationally efficient algorithm for mapping out the full joint CMB
posterior, both in the high and low signal-to-noise regimes.Comment: Submitted to Ap
Marginal distributions for cosmic variance limited CMB polarization data
We provide computationally convenient expressions for all marginal
distributions of the polarization CMB power spectrum distribution
P(C_l|sigma_l), where C_l = {C_l^TT, C_l^TE, C_l^EE, C_l^BB} denotes the set of
ensemble averaged polarization CMB power spectra, and sigma_l = {sigma_l^TT,
sigma_l^TE, sigma_l^EE, sigma_l^BB} the set of the realization specific
polarization CMB power spectra. This distribution describes the CMB power
spectrum posterior for cosmic variance limited data. The expressions derived
here are general, and may be useful in a wide range of applications. Two
specific applications are described in this paper. First, we employ the derived
distributions within the CMB Gibbs sampling framework, and demonstrate a new
conditional CMB power spectrum sampling algorithm that allows for different
binning schemes for each power spectrum. This is useful because most CMB
experiments have very different signal-to-noise ratios for temperature and
polarization. Second, we provide new Blackwell-Rao estimators for each of the
marginal polarization distributions, which are relevant to power spectrum and
likelihood estimation. Because these estimators represent marginals, they are
not affected by the exponential behaviour of the corresponding joint
expression, but converge quickly.Comment: 8 pages, 3 figures; minor adjustment, accepted for publication in
ApJ
Computed Responses of Several Aircraft to Atmospheric Turbulence and Discrete Wind Shears
The computed RMS and peak responses due to atmospheric turbulence and discrete wind shears, respectively, are presented for several aircraft in different flight conditions. The responses are presented with and without the effects of a typical second order washout filter. A complete set of dimensional stability derivatives for each aircraft/flight condition combination evaluated is also presented
Situs inversus with renal neoplasm: a case report
This is a case report of a 43-year male patient who presented at the University Teaching Hospital (UTH), Lusaka, Zambia with a histologically proven renal cell carcinoma and during the course of the investigations, the patient was also found to have situs inversus totalis
Influence of an aperture on the performance of a two-degree-of-freedom iron-cored spherical permanent-magnet actuator
Abstract—This paper describes a computational and experimental study of a two-degree-of-freedom spherical permanent-magnet actuator equipped with an iron stator. In particular, it considers the effect of introducing an aperture in the stator core to facilitate access to the armature. The resultant magnetic field distribution in the region occupied by the stator windings, the net unbalanced radial force, and the resulting reluctance torque are determined by three-dimensional magnetostatic finite-element
analysis. The predicted reluctance torque is validated experimentally, and its implications on actuator performance are described
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