3,403 research outputs found
Improved performance of motor-drive systems by SAW shaft torque feedback
The paper describes the application of a non-contact, high bandwidth, low cost, SAW-based torque
measuring system for improving the dynamic performance
of industrial process motor-drive systems. Background to
the SAW technology and its motor integration is discussed
and a resonance ratio control (RRC) technique for the
coordinated motion control of multi-inertia mechanical
systems, based on the measurement of shaft torque via a
SAW-based torque sensor is proposed. Furthermore, a
new controller structure, RRC plus disturbance feedback
is proposed, which enables the controller to be designed to
independently satisfy tracking and regulation
performance. A tuning method for the RRC structure is
given based on the ITAE index, normalized as a function of
the mechanical parameters enabling a direct performance
comparison between a basic proportional and integral (PI)
controller. The use of a reduced-order state observer is
presented to provide a dynamic estimate of the load-side
disturbance torque for a multi-inertia mechanical system,
with an appraisal of the composite closed-loop dynamics.
The control structures are experimentally validated and
demonstrate significant improvement in dynamic tracking
performance, whilst additionally rejecting periodic load
side disturbances, a feature previously unrealisable except
by other, high-gain control schemes that impose small
stability margins
Constriction size distributions of granular filters: a numerical study
The retention capability of granular filters is controlled by the narrow constrictions connecting the voids within the filter. The theoretical justification for empirical filter rules used in practice includes consideration of an idealised soil fabric in which constrictions form between co-planar combinations of spherical filter particles. This idealised fabric has not been confirmed by experimental or numerical observations of real constrictions. This paper reports the results of direct, particle-scale measurement of the constriction size distribution (CSD) within virtual samples of granular filters created using the discrete-element method (DEM). A previously proposed analytical method that predicts the full CSD using inscribed circles to estimate constriction sizes is found to poorly predict the CSD for widely graded filters due to an over-idealisation of the soil fabric. The DEM data generated are used to explore quantitatively the influence of the coefficient of uniformity, particle size distribution and relative density of the filter on the CSD. For a given relative density CSDs form a narrow band of similarly shaped curves when normalised by characteristic filter diameters. This lends support to the practical use of characteristic diameters to assess filter retention capability
The X-ray Emission in Post-Merger Ellipticals
The evolution in X-ray properties of early-type galaxies is largely unconstrained. In particular, little is known about how, and if, remnants of mergers generate hot gas halos. Here we examine the relationship between X-ray luminosity and galaxy age for a sample of early-type galaxies. Comparing normalized X-ray luminosity to three different age indicators we find that L_X/L_B increases with age, suggesting an increase in X-ray halo mass with time after a galaxy's last major star-formation episode. The long-term nature of this trend, which appears to continue across the full age range of our sample, poses a challenge for many models of hot halo formation. We conclude that models involving a declining rate of type Ia supernovae, and a transition from outflow to inflow of the gas originally lost by galactic stars, offers the most promising explanation for the observed evolution in X-ray luminosity
Deep Chandra Observations of HCG 16 - II. The Development of the Intra-group Medium in a Spiral-Rich Group
We use a combination of deep Chandra X-ray observations and radio continuum
imaging to investigate the origin and current state of the intra-group medium
in the spiral-rich compact group HCG 16. We confirm the presence of a faint
(=1.8710 erg/s), low
temperature (0.30 keV) intra-group medium (IGM) extending
throughout the ACIS-S3 field of view, with a ridge linking the four original
group members and extending to the southeast, as suggested by previous Rosat
and XMM-Newton observations. This ridge contains
6.610 solar masses of hot gas and is at least
partly coincident with a large-scale HI tidal filament, indicating that the IGM
in the inner part of the group is highly multi-phase. We present evidence that
the group is not yet virialised, and show that gas has probably been
transported from the starburst winds of NGC 838 and NGC 839 into the
surrounding IGM. Considering the possible origin of the IGM, we argue that
material ejected by galactic winds may have played a significant role,
contributing 20-40% of the observed hot gas in the system.Comment: 11 pages, 6 figures, 1 table, accepted for publication in ApJ;
updated references and fixed typos identified at proof stag
Deep Chandra Observations of HCG 16 - I. Active Nuclei, Star formation and Galactic Winds
We present new, deep Chandra X-ray and Giant Metrewave Radio Telescope
610~MHz observations of the spiral-galaxy-rich compact group HCG 16, which we
use to examine nuclear activity, star formation and the high luminosity X-ray
binary populations in the major galaxies. We confirm the presence of obscured
active nuclei in NGC 833 and NGC 835, and identify a previously unrecognized
nuclear source in NGC 838. All three nuclei are variable on timescales of
months to years, and for NGC 833 and NGC 835 this is most likely caused by
changes in accretion rate. The deep Chandra observations allow us to detect for
the first time an Fe-K emission line in the spectrum of the Seyfert 2
nucleus of NGC 835. We find that NGC 838 and NGC 839 are both
starburst-dominated systems, with only weak nuclear activity, in agreement with
previous optical studies. We estimate the star formation rates in the two
galaxies from their X-ray and radio emission, and compare these results with
estimates from the infra-red and ultra-violet bands to confirm that star
formation in both galaxies is probably declining after galaxy-wide starbursts
were triggered ~400-500 Myr ago. We examine the physical properties of their
galactic superwinds, and find that both have temperatures of ~0.8 keV. We also
examine the X-ray and radio properties of NGC 848, the fifth largest galaxy in
the group, and show that it is dominated by emission from its starburst.Comment: 18 pages, 11 figures, 11 tables, accepted for publication in ApJ;
updated references and fixed typos identified at proof stag
A direct comparison of 2D versus 3D diffusion analysis at nanowire electrodes: A finite element analysis and experimental study
In electroanalysis, the benefits accrued by miniaturisation are a key driver in sensor development. Finite element simulations of electrochemical processes occurring at ultramicro- and nano-electrodes are used to provide key insight into experimental design in relation to diffusion profiles and expected currents. The most commonly used method, the diffusion domain approach (DDA) offers a means of reducing a three dimensional design to two dimensions to ease computational demands. However, the DDA approach can be limited when using basic assumptions which can be incorrect, for example that all electrodes in an array are equivalent. Consequently, to get a more realistic view of molecular diffusion to nanoelectrodes, it is necessary to undertake simulations in 3D. In this work, two and three dimensional models of electrodes comprising of (i) single nanowires, (ii) arrays of nanowires and (iii) interdigitated arrays of nanowires operating in generator-collector mode, were undertaken and compared to experimental results obtained from fabricated devices. The 3D simulations predicted a higher extracted current for a single nanowires and diffusionally independent nanowire arrays when compared to 2D simulations since, unlike the 2D model, they take into account molecular diffusion to and from nanowire termini. These current differences were observed to increase with increasing electrode width and decrease with electrode length. When the nanowire arrays were diffusionally overlapped, they behaved as an electrode of larger width, and the divergence between both models increased further. By contrast, using interdigitated nanowire arrays in generator-collector mode, the differences between extracted current values obtained using the 2D and 3D models were significantly lower. Simulations indicated however, that a higher collection efficiency was predicted by the 2D model when compared to the 3D model. Electrochemical experiments were undertaken to confirm the simulation study and demonstrated that the extracted currents from 3D simulations more closely mapped onto experimentally measured currents
A Catalogue and Analysis of X-ray luminosities of Early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-type galaxies, of
which 136 are based on newly analysed ROSAT PSPC pointed observations. The
remaining luminosities are taken from the literature and converted to a common
energy band, spectral model and distance scale. Using this sample we fit the
L_X:L_B relation for early-type galaxies and find a best fit slope for the
catalogue of ~2.2. We demonstrate the influence of group-dominant galaxies on
the fit and present evidence that the relation is not well modeled by a single
powerlaw fit. We also derive estimates of the contribution to galaxy X-ray
luminosities from discrete sources and conclude that they provide
L_discrete/L_B = 29.5 erg/s/L_solar. We compare this result to luminosities
from our catalogue. Lastly, we examine the influence of environment on galaxy
X-ray luminosity and on the form of the L_X:L_B relation. We conclude that
although environment undoubtedly affects the X-ray properties of individual
galaxies, particularly those in the centres of groups and clusters, it does not
change the nature of whole populations.Comment: 33 pages, 16 postscript figures, accepted for publication in MNRA
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