4,161 research outputs found
Internal agent states : experiments using the swarm leader concept
In recent years, an understanding of the operating principles and stability of natural swarms has proven to be a useful tool for the design and control of artificial robotic agents. Many robotic systems, whose design or control principals are inspired by behavioural aspects of real biological systems such as leader-follower relationship, have been developed. We introduced an algorithm which successfully enhances the navigation performance of a swarm of robots using the swarm leader concept. This paper presents some applications based on that work using the simulations and experimental implementation using a swarming behaviour test-bed at the University of Strathclyde. Experimental and simulation results match closely in a way that confirms the efficiency of the algorithm as well as its applicability
A Physical Limit to the Magnetic Fields of T Tauri Stars
Recent estimates of magnetic field strengths in T Tauri stars yield values
--. In this paper, I present an upper limit to the
photospheric values of by computing the equipartition values for different
surface gravities and effective temperatures. The values of derived from
the observations exceed this limit, and I examine the possible causes for this
discrepancy
ASCA and ROSAT observations of nearby cluster cooling flows
We present a detailed analysis of the X-ray properties of the cooling flows
in a sample of nearby, X-ray bright clusters of galaxies using high-quality
ASCA spectra and ROSAT X-ray images. We demonstrate the need for multiphase
models to consistently explain the spectral and imaging X-ray data for the
clusters. The mass deposition rates of the cooling flows, independently
determined from the ASCA spectra and ROSAT images, exhibit reasonable
agreement. We confirm the presence of intrinsic X-ray absorption in the
clusters using a variety of spectral models. We also report detections of
extended m infrared emission, spatially coincident with the cooling
flows, in several of the systems studied. The observed infrared fluxes and flux
limits are in good agreement with the predicted values due to reprocessed X-ray
emission from the cooling flows. We present precise measurements of the
abundances of iron, magnesium, silicon and sulphur in the central regions of
the Virgo and Centaurus clusters. Our results firmly favour models in which a
high mass fraction (70-80 per cent) of the iron in the X-ray gas in these
regions is due to Type Ia supernovae. Finally, we present a series of methods
which may be used to measure the ages of cooling flows from the X-ray data. The
results for the present sample of clusters indicate ages of between 2.5 and 7
Gyr. If the ages of cooling flows are primarily set by subcluster merger
events, then our results suggest that in the largest clusters, mergers with
subclusters with masses of approximately 30 per cent of the final cluster mass
are likely to disrupt cooling flows.Comment: Final version. MNRAS, in press. 36 pages, 9 figs, 14 tables in MNRAS
LaTex styl
Concordant cues in faces and voices: testing the backup signal hypothesis
Information from faces and voices combines to provide multimodal signals about a person. Faces and voices may offer redundant, overlapping (backup signals), or complementary information (multiple messages). This article reports two experiments which investigated the extent to which faces and voices deliver concordant information about dimensions of fitness and quality. In Experiment 1, participants rated faces and voices on scales for masculinity/femininity, age, health, height, and weight. The results showed that people make similar judgments from faces and voices, with particularly strong correlations for masculinity/femininity, health, and height. If, as these results suggest, faces and voices constitute backup signals for various dimensions, it is hypothetically possible that people would be able to accurately match novel faces and voices for identity. However, previous investigations into novel face–voice matching offer contradictory results. In Experiment 2, participants saw a face and heard a voice and were required to decide whether the face and voice belonged to the same person. Matching accuracy was significantly above chance level, suggesting that judgments made independently from faces and voices are sufficiently similar that people can match the two. Both sets of results were analyzed using multilevel modeling and are interpreted as being consistent with the backup signal hypothesis
New bird records for the island of Lombok
Seventeen species are recorded for the first time from the island of Lombok. Nine of these are maritime birds on passage and four are widely occurring migrant shore and land birds. Gallirallus striatus may be a local migrant, Chrysococcyx basalis is a visitor from Australia, and Anthreples malaccensis is presumed to be either a previously overlooked resident or a recent colonist. Hemiprocne longipenis, previously unrecorded from the Lesser Sundas, appears to be a recent colonist
Measuring the difference between actual and reported food intakes in the context of energy balance under laboratory conditions
Acknowledgements The present study was funded by the Food Standards Agency, UK. The Food Standards Agency had no role in the design, analysis or writing of this article. The authors’ responsibilities were as follows: R. J. S., L. M. O’R. and G. W. H. designed the research; L. M. O’R. and Z. F. conducted the research and analysed the data; G. W. H. performed the statistical analyses; P. R. carried out the DLW analysis; R. J. S. had primary responsibility for the final content; R. J. S., L. M. O’R., Z. F., S. W. and M. B. E. L. wrote the paper.Peer reviewedPublisher PD
Large Area Mapping at 850 Microns. V. Analysis of the Clump Distribution in the Orion A South Molecular Cloud
We present results from a 2300 arcmin^2 survey of the Orion A molecular cloud
at 450 and 850 micron using the Submillimetre Common-User Bolometer Array
(SCUBA) on the James Clerk Maxwell Telescope. The region mapped lies directly
south of the OMC1 cloud core and includes OMC4, OMC5, HH1/2, HH34, and L1641N.
We identify 71 independent clumps in the 850 micron map and compute size, flux,
and degree of central concentration in each. Comparison with isothermal,
pressure-confined, self-gravitating Bonnor-Ebert spheres implies that the
clumps have internal temperatures T_d ~ 22 +/- K and surface pressures log
(k^-1 P cm^-3 K) = 6.0 +/- 0.2. The clump masses span the range 0.3 - 22 Msun
assuming a dust temperature T_d ~ 20 K and a dust emissivity kappa_850 = 0.02
cm^2 g^-1. The distribution of clump masses is well characterized by a
power-law N(M) propto M^-alpha with alpha = 2.0 +/- 0.5 for M > 3.0 Msun,
indicating a clump mass function steeper than the stellar Initial Mass
Function. Significant incompleteness makes determination of the slope at lower
masses difficult. A comparison of the submillimeter emission map with an H_2
2.122 micron survey of the same region is performed. Several new Class 0
sources are revealed and a correlation is found between both the column density
and degree of concentration of the submillimeter sources and the likelihood of
coincident H_2 shock emission.Comment: 44 pages, 17 figures, accepted by Ap
Real time measurement of intramuscular pH during routine knee arthroscopy using a tourniquet
Funding statement This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.Peer reviewedPublisher PD
A Deep Look at the Emission-Line Nebula in Abell 2597
The close correlation between cooling flows and emission-line nebulae in
clusters of galaxies has been recognized for over a decade and a half, but the
physical reason for this connection remains unclear. Here we present deep
optical spectra of the nebula in Abell 2597, one of the nearest strong
cooling-flow clusters. These spectra reveal the density, temperature, and metal
abundances of the line-emitting gas. The abundances are roughly half-solar, and
dust produces an extinction of at least a magnitude in V. The absence of [O
III] 4363 emission rules out shocks as a major ionizing mechanism, and the
weakness of He II 4686 rules out a hard ionizing source, such as an active
galactic nucleus or cooling intracluster gas. Hot stars are therefore the best
candidate for producing the ionization. However, even the hottest O stars
cannot power a nebula as hot as the one we see. Some other nonionizing source
of heat appears to contribute a comparable amount of power. We show that the
energy flux from a confining medium can become important when the ionization
level of a nebula drops to the low levels seen in cooling-flow nebulae. We
suggest that this kind of phenomenon, in which energy fluxes from the
surrounding medium augment photoelectric heating, might be the common feature
underlying the diverse group of objects classified as LINERS.Comment: 33 Latex pages, including 16 Postscript figures, to appear in 1997
September 1 Astrophysical Journa
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