5,521 research outputs found
Edge-enhanced disruptive camouflage impairs shape discrimination
Disruptive colouration (DC) is a form of camouflage comprised of areas of pigmentation across a targetâs surface that form false edges, which are said to impede detection by disguising the outline of the target. In nature, many species with DC also exhibit edge enhancement (EE); light areas have lighter edges and dark areas have darker edges. EE DC has been shown to undermine not only localisation but also identification of targets, even when they are not hidden (Sharman, Moncrieff, & Lovell, 2018). We use a novel task, where participants judge which âsnakeâ is more âwiggly,â to measure shape discrimination performance for three colourations (uniform, DC, and EE DC) and two backgrounds (leafy and uniform). We show that EE DC impairs shape discrimination even when targets are not hidden in a textured background. We suggest that this mechanism may contribute to misidentification of EE DC targets
Dissociating the effect of disruptive colouration on localisation and identification of camouflaged targets
Disruptive camouflage features contrasting areas of pigmentation across the animalsâ surface that form false edges which disguise the shape of the body and impede detection. In many taxa these false edges feature local contrast enhancement or edge enhancement, light areas have lighter edges and dark areas have darker edges. This additional quality is often overlooked in existing research. Here we ask whether disruptive camouflage can have benefits above and beyond concealing location. Using a novel paradigm, we dissociate the time courses of localisation and identification of a target in a single experiment. We measured the display times required for a stimulus to be located or identified (the critical duration). Targets featured either uniform, disruptive or edge enhanced disruptive colouration. Critical durations were longer for identifying targets with edge enhanced disruptive colouration camouflage even when presented against a contrasting background, such that all target types were located equally quickly. For the first time, we establish empirically that disruptive camouflage not only conceals location, but also disguises identity. This shows that this form of camouflage can be useful even when animals are not hidden. Our findings offer insights into how edge enhanced disruptive colouration undermines visual perception by disrupting object recognition
New H_(2)O masers in Seyfert and FIR bright galaxies: III. The southern sample
Context. A relationship between the water maser detection rate and far infrared (FIR) flux densities was established as a result of two 22 GHz maser surveys in a complete sample of galaxies (Dec > â30°) with flux densities of >50 Jy and >30 Jy.
Aims. We attempted to discover new maser sources and investigate the galaxies hosting the maser spots by extending previous surveys to southern galaxies with particular emphasis on the study of their nuclear regions.
Methods. A sample of 12 galaxies with Dec 50 Jy was observed with the 70-m telescope of the Canberra deep space communication complex (CDSCC) at Tidbinbilla (Australia) in a search for water maser emission. The average 3Ï noise level of the survey was 15 mJy for a 0.42 km s^(â1) channel, corresponding to a detection threshold of âŒ0.1 L_â for the isotropic maser luminosity at a distance of 25 Mpc.
Results. Two new detections are reported: a kilomaser with an isotropic luminosity L_(H_(2)O) ~ 5 L_â in NGC 3620 and a maser with about twice this luminosity in the merger system NGC 3256. The detections have been followed-up by continuum and spectral line interferometric observations with the Australia Telescope Compact Array (ATCA). In NGC 3256, a fraction (about a third) of the maser emission originates in two hot spots associated with star formation activity, which are offset from the galactic nuclei of the system. The remaining emission may originate in weaker centres of maser activity distributed over the central 50". For NGC 3620, the water maser is coincident with the nuclear region of the galaxy. Our continuum observations indicate that the nature of the nuclear emission is probably linked to particularly intense star formation. Including the historical detection in NGC 4945, the water maser detection rate in the southern sample is 15% (3/20), consistent with the northern sample. The high rate of maser detections in the complete all-sky FIR sample (23%, 15/65) confirms the existence of a link between overall FIR flux density and maser phenomena. A relation between H_(2)Oâand OH masers in the FIR sample is also discussed
Energy dependence of non-local potentials
Recently a variety of studies have shown the importance of including
non-locality in the description of reactions. The goal of this work is to
revisit the phenomenological approach to determining non-local optical
potentials from elastic scattering. We perform a analysis of neutron
elastic scattering data off Ca, Zr and Pb at energies MeV, assuming a Perey and Buck or Tian, Pang, and Ma non-local
form for the optical potential. We introduce energy and asymmetry dependencies
in the imaginary part of the potential and refit the data to obtain a global
parameterization. Independently of the starting point in the minimization
procedure, an energy dependence in the imaginary depth is required for a good
description of the data across the included energy range. We present two
parameterizations, both of which represent an improvement over the original
potentials for the fitted nuclei as well as for other nuclei not included in
our fit. Our results show that, even when including the standard Gaussian
non-locality in optical potentials, a significant energy dependence is required
to describe elastic-scattering data.Comment: 6 pages, 3 figures, accepted by Phys. Rev. C Rapid Communicatio
High Resolution VSOP Imaging of a Southern Blazar PKS 1921-293 at 1.6 GHz
We present a high resolution 1.6 GHz VSOP image of the southern blazar PKS
1921-293. The image shows a typical core-jet morphology, consistent with
ground-based VLBI images. However, the addition of data from the space antenna
has greatly improved the angular resolution (especially along the north-south
direction for this source), and thus allowed us to clearly identify the core.
Model fitting reveals an inner jet component ~1.5 mas north of the core. This
jet feature may be moving on a common curved path connecting the jet within a
few parsecs to the 10-parsec-scale jet. The compact core has a brightness
temperature of 2.6*10**12 K (in the rest frame of the quasar), an indication of
relativistic beaming. We analyzed the source in terms of three models,
involving the inverse Compton catastrophe, an inhomogeneous relativistic jet,
and the equipartition of energy between the radiating particles and the
magnetic field. Our analysis of this gamma-ray-quiet blazar shows no preference
to any particular one of these models.Comment: 7 pages including 2 figures and 1 table, PASJLaTeX, accepted for
publication in PAS
A study of high-altitude manned research aircraft employing strut-braced wings of high-aspect-ratio
The effect of increased wing aspect ratio of subsonic aircraft on configurations with and without strut bracing. Results indicate that an optimum cantilever configuration, with a wing aspect ratio of approximately 26, has a 19% improvement in cruise range when compared to a baseline concept with a wing aspect ratio of approximately 10. An optimum strut braced configuration, with a wing aspect ratio of approximately 28, has a 31% improvment in cruise range when compared to the same baseline concept. This improvement is mainly due to the estimated reduction in wing weight resulting from use of lifting struts. All configurations assume the same mission payload and fuel. The drag characteristics of the wings are enhanced with the use of laminar flow airfoils. A method for determining the extent of attainable natural laminar flow, and methods for preliminary structural design and for aerodynamic analysis of wings lifting struts are presented
Space VLBI Observations of 3C 279 at 1.6 and 5 GHz
We present the first VLBI Space Observatory Programme (VSOP) observations of
the gamma-ray blazar 3C 279 at 1.6 and 5 GHz. The combination of the VSOP and
VLBA-only images at these two frequencies maps the jet structure on scales from
1 to 100 mas. On small angular scales the structure is dominated by the quasar
core and the bright secondary component `C4' located 3 milliarcseconds from the
core (at this epoch). On larger angular scales the structure is dominated by a
jet extending to the southwest, which at the largest scale seen in these images
connects with the smallest scale structure seen in VLA images. We have
exploited two of the main strengths of VSOP: the ability to obtain
matched-resolution images to ground-based images at higher frequencies and the
ability to measure high brightness temperatures. A spectral index map was made
by combining the VSOP 1.6 GHz image with a matched-resolution VLBA-only image
at 5 GHz from our VSOP observation on the following day. The spectral index map
shows the core to have a highly inverted spectrum, with some areas having a
spectral index approaching the limiting value for synchrotron self-absorbed
radiation of 2.5. Gaussian model fits to the VSOP visibilities revealed high
brightness temperatures (>10^{12} K) that are difficult to measure with
ground-only arrays. An extensive error analysis was performed on the brightness
temperature measurements. Most components did not have measurable brightness
temperature upper limits, but lower limits were measured as high as 5x10^{12}
K. This lower limit is significantly above both the nominal inverse Compton and
equipartition brightness temperature limits. The derived Doppler factor,
Lorentz factor, and angle to the line-of-sight in the case of the equipartition
limit are at the upper end of the range of expected values for EGRET blazars.Comment: 11 pages, 6 figures, emulateapj.sty, To be published in The
Astrophysical Journal, v537, Jul 1, 200
Water Vapour Effects in Mass Measurement
Water vapour inside the mass comparator enclosure is a critical parameter. In
fact, fluctuations of this parameter during mass weighing can lead to errors in
the determination of an unknown mass. To control that, a proposal method is
given and tested. Preliminary results of our observation of water vapour
sorption and desorption processes from walls and mass standard are reported
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