32,253 research outputs found
Multivariable Repetitive-predictive Controllers using Frequency Decomposition
Repetitive control is a methodology for the tracking of a periodic reference signal. This paper develops a new approach to repetitive control systems design using receding horizon control with frequency decomposition of the reference signal. Moreover, design and implementation issues for this form of repetitive predictive control are investigated from the perspectives of controller complexity and the effects of measurement noise. The analysis is supported by a simulation study on a multi-input multi-output robot arm where the model has been constructed from measured frequency response data, and experimental results from application to an industrial AC motor
Differential chemical abundance analysis of a 47 Tuc AGB star with respect to Arcturus
This study resolves a discrepancy in the abundance of Zr in the 47 Tucanae
asymptotic giant branch star Lee 2525. This star was observed using the echelle
spectrograph on the 2.3 m telescope at Siding Spring Observatory. The analysis
was undertaken by calibrating Lee 2525 with respect to the standard giant star
Arcturus. This work emphasises the importance of using a standard star with
stellar parameters comparable to the star under analysis rather than a
calibration with respect to the Sun (Koch & McWilliam 2008). Systematic errors
in the analysis process are then minimised due to the similarity in atmospheric
structure between the standard and programme stars. The abundances derived for
Lee 2525 were found to be in general agreement with the Brown & Wallerstein
(1992) values except for Zr. In this study Zr has a similar enhancement
([Zr/Fe] = +0.51 dex) to another light s-process element, Y ([Y/Fe] = +0.53
dex), which reflects current theory regarding the enrichment of s-process
elements by nuclear processes within AGB stars (Busso et al. 2001). This is
contrary to the results of Brown & Wallerstein (1992) where Zr was
under-abundant ([Zr/Fe] = +0.51 dex) and Y was over-abundant ([Y/Fe] = +0.50
dex) with respect to Fe.Comment: 11 pages, 5 figures Accepted for publication in MNRA
Radiolysis of Macromolecular Organic Material in Mars-Relevant Mineral Matrices
The fate of organic material on Mars after deposition is crucial to interpreting the source of these molecules. Previous work has addressed how various organic compounds at millimeter depths in sediments respond to ultraviolet radiation. In contrast, this study addressed how highenergy particle radiation (200MeV protons, simulating the effect of galactic cosmic rays and solar wind at depths of <45 cm) inuences organic macromolecules in sediments. Specically, we report the generation of organicacid radiolysis products after exposure to radiation doses equivalent to geological time scales (17 Myr). We found that formate and oxalate were produced from a variety of organic starting materials and mineral matrices. Unlike ultravioletdriven reactions that can invoke Fenton chemistry to produce organic acids, our work suggests that irradiation of semiconductor surfaces, such as TiO2 or possible clay minerals found on Mars, forms oxygen and hydroxyl radical species, which can break down macromolecules into organic acids. We also investigated the metastability of benzoate in multiple mineral matrices. Benzoate was added to samples prior to irradiation and persisted up to 500 kGys of exposure. Our ndings suggest that organic acids are likely a major component of organic material buried at depth on Mars
A 2D systems approach to iterative learning control for discrete linear processes with zero Markov parameters
In this paper a new approach to iterative learning control for the practically relevant case of deterministic discrete linear plants with uniform rank greater than unity is developed. The analysis is undertaken in a 2D systems setting that, by using a strong form of stability for linear repetitive processes, allows simultaneous con-sideration of both trial-to-trial error convergence and along the trial performance, resulting in design algorithms that can be computed using Linear Matrix Inequalities (LMIs). Finally, the control laws are experimentally verified on a gantry robot that replicates a pick and place operation commonly found in a number of applications to which iterative learning control is applicable
Quiet Clean Short-haul Experimental Engine (QCSEE) Under-The-Wing (UTW) composite nacelle subsystem test report
The element and subcomponent testing conducted to verify the under the wing composite nacelle design is reported. This composite nacelle consists of an inlet, outer cowl doors, inner cowl doors, and a variable fan nozzle. The element tests provided the mechanical properties used in the nacelle design. The subcomponent tests verified that the critical panel and joint areas of the nacelle had adequate structural integrity
Aerodynamic characteristics of a 1/6-scale model of the rotor systems research aircraft with the rotors removed
A wind-tunnel investigation was conducted to refine the aerodynamic characteristics of the rotor systems research aircraft. For the investigation, a 1/6-scale model without a main rotor or a tail rotor was used. The model provided the capability for testing different engine nacelle sizes, engine pylon fairings, and tail configurations. The engine thrust effects were modeled by small engine simulators (fans). Data were obtained primarily over an angle-of-attack range from -13 deg to 13 deg at several values of sideslip. Stability characteristics and control effectiveness were investigated. The model with the scaled engine nacelles and the combination T-tail and lower horizontal tail displayed longitudinal and lateral-directional stability. Results show that by reducing the horizontal or vertical-tail span the longitudinal stability is decreased. Reducing the engine nacelle size increases the static stability of the model. Effective dihedral is essentially zero at 0 deg angle of attack and 0 deg wing incidence
The planetary nebula population in the halo of M87
We investigate the diffuse light in the outer regions of the nearby
elliptical galaxy M87 in the Virgo cluster, using planetary nebulas (PNs) as
tracers. The surveyed areas (0.43 squared degrees) cover M87 up to a radial
distance of 150 kpc, in the ransition region between galaxy halo and
intracluster light (ICL). All PNs are identified through the on-off band
technique using automatic selection criteria based on the distribution of the
detected sources in the colour-magnitude diagram and the properties of their
point-spread function. We extract a catalogue of 688 objects down to
m_5007=28.4, with an estimated residual contamination from foreground stars and
background Lyalpha galaxies, which amounts to ~35% of the sample. This is one
of the largest extragalactic PN samples in number of candidates, magnitude
depth, and radial extent, which allows us to carry out an unprecedented
photometric study of the PN population in the outer regions of M87. We find
that the logarithmic density profile of the PN distribution is shallower than
the surface brightness profile at large radii. This behaviour is consistent
with the superposition of two components associated with the halo of M87 and
with the ICL, which have different luminosity specific PN numbers, the ICL
contributing three times more PNs per unit light. Because of the depth of this
survey we are also able to study the shape of the PN luminosity function (PNLF)
in the outer regions of M87. We find a slope for the PNLF that is steeper at
fainter magnitudes than the standard analytical PNLF formula and adopt a
generalised model that treats the slope as a free parameter. Comparing the PNLF
of M87 and the M31 bulge, both normalised by the sampled luminosity, the M87
PNLF contains fewer bright PNs and has a steeper slope towards fainter
magnitudes.Comment: 16 pages, 13 figures, 5 tables, accepted for publication in A&
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