4,469 research outputs found
Generalization of color by chickens: experimental observations and a Bayesian model
Sensory generalization influences animals' responses to novel stimuli. Because color forms a perceptual continuum, it is a good subject for studying generalization. Moreover, because different causes of variation in spectral signals, such as pigmentation, gloss, and illumination, have differing behavioral significance, it may be beneficial to have adaptable generalization. We report on generalization by poultry chicks following differential training to rewarded (T+) and unrewarded (Tâ) colors, in particular on the phenomenon of peak shift, which leads to subjects preferring stimuli displaced away from Tâ. The first three experiments test effects of learning either a fine or a coarse discrimination. In experiments 1 and 2, peak shift occurs, but contrary to some predictions, the shift is smaller after the animal learned a fine discrimination than after it learned a coarse discrimination. Experiment 3 finds a similar effect for generalization on a color axis orthogonal to that separating T+ from Tâ. Experiment 4 shows that generalization is rapidly modified by experience. These results imply that the scale of a âperceptual rulerâ is set by experience. We show that the observations are consistent with generalization following principles of Bayesian inference, which forms a powerful framework for understanding this type of behavior
Superconducting/magnetic three state nanodevice for memory and reading applications
We present a simple nanodevice that can operate in two modes: i) three-state
memory and ii) reading device. The nanodevice is fabricated with an array of
ordered triangular-shaped nanomagnets embedded in a superconducting thin film.
The input signal is ac current and the output signal is dc voltage. Vortex
ratchet effect in combination with out of plane magnetic anisotropy of the
nanomagnets is the background physics which governs the nanodevice performance.Comment: 10 pages, 4 figure
Keck NIRC Observations of Planetary-mass Candidate Members in the sigma Orionis Open Cluster
We present K-band photometry and low-resolution near-infrared spectroscopy
from 1.44 to 2.45 micron of isolated planetary-mass candidate members in the
sigma Orionis cluster found by Zapatero Osorio et al. The new data have been
obtained with NIRC at the Keck I telescope. All of our targets, except for one,
are confirmed as likely cluster members. Hence, we also confirm that the
planetary-mass domain in the cluster is well populated. Using our deep K-band
images we searched for companions to the targets in the separation range 0.3"
to 10" up to a maximum faint limit of K=19.5 mag. One suspected companion seems
to be an extremely red galaxy. The near-infrared colors of the sigma Orionis
substellar members indicate that dust grains condense and settle in their
atmospheres. We estimate that the surface temperatures range from 2500 K down
to 1500 K. The spectroscopic sequence covers the full range of L subclasses,
and the faintest object is tentatively classified as T0. These targets provide
a sequence of substellar objects of known age, distance and metallicity, which
can be used as benchmark for understanding the spectral properties of ultracool
dwarfs.Comment: Accepted for publication in ApJ Letters. 9 pages, 4 figures include
Primeval very low-mass stars and brown dwarfs - VI. Population properties of metal-poor degenerate brown dwarfs
© 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.We presented 15 new T dwarfs that were selected from UKIRT Infrared Deep Sky Survey, Visible and Infrared Survey Telescope for Astronomy, and Wide-field Infrared Survey Explorer surveys, and confirmed with optical to near infrared spectra obtained with the Very Large Telescope and the Gran Telescopio Canarias. One of these new T dwarfs is mildly metal-poor with slightly suppressed -band flux. We presented a new X-shooter spectrum of a known benchmark sdT5.5 subdwarf, HIP 73786B. To better understand observational properties of brown dwarfs, we discussed transition zones (mass ranges) with low-rate hydrogen, lithium, and deuterium burning in brown dwarf population. The hydrogen burning transition zone is also the substellar transition zone that separates very low-mass stars, transitional, and degenerate brown dwarfs. Transitional brown dwarfs have been discussed in previous works of the Primeval series. Degenerate brown dwarfs without hydrogen fusion are the majority of brown dwarfs. Metal-poor degenerate brown dwarfs of the Galactic thick disc and halo have become T5+ subdwarfs. We selected 41 T5+ subdwarfs from the literature by their suppressed -band flux. We studied the spectral-type - colour correlations, spectral-type - absolute magnitude correlations, colour-colour plots, and HR diagrams of T5+ subdwarfs, in comparison to these of L-T dwarfs and L subdwarfs. We discussed the T5+ subdwarf discovery capability of deep sky surveys in the 2020s.Peer reviewe
On the nature of the deeply embedded protostar OMC-2 FIR 4
We use mid-infrared to submillimeter data from the Spitzer, Herschel, and
APEX telescopes to study the bright sub-mm source OMC-2 FIR 4. We find a point
source at 8, 24, and 70 m, and a compact, but extended source at 160, 350,
and 870 m. The peak of the emission from 8 to 70 m, attributed to the
protostar associated with FIR 4, is displaced relative to the peak of the
extended emission; the latter represents the large molecular core the protostar
is embedded within. We determine that the protostar has a bolometric luminosity
of 37 Lsun, although including more extended emission surrounding the point
source raises this value to 86 Lsun. Radiative transfer models of the
protostellar system fit the observed SED well and yield a total luminosity of
most likely less than 100 Lsun. Our models suggest that the bolometric
luminosity of the protostar could be just 12-14 Lsun, while the luminosity of
the colder (~ 20 K) extended core could be around 100 Lsun, with a mass of
about 27 Msun. Our derived luminosities for the protostar OMC-2 FIR 4 are in
direct contradiction with previous claims of a total luminosity of 1000 Lsun
(Crimier et al 2009). Furthermore, we find evidence from far-infrared molecular
spectra (Kama et al. 2013, Manoj et al. 2013) and 3.6 cm emission (Reipurth et
al 1999) that FIR 4 drives an outflow. The final stellar mass the protostar
will ultimately achieve is uncertain due to its association with the large
reservoir of mass found in the cold core.Comment: Accpeted by ApJ, 17 pages, 11 figure
Membership and Multiplicity among Very Low-Mass Stars and Brown Dwarfs in the Pleiades Cluster
We present near-infrared photometry and optical spectroscopy of very low-mass
stars and brown dwarf candidates in the Pleiades open cluster. The membership
status of these objects is assessed. Eight objects out of 45 appear to be
non-members. A search for companions among 34 very low-mass Pleiades members
(M0.09 M) in high-spatial resolution images obtained with the
Hubble Space Telescope and the adaptive optics system of the
Canada-France-Hawaii telescope produced no resolved binaries with separations
larger than 0.2 arcsec (a ~ 27 AU; P ~ 444 years). Nevertheless, we find
evidence for a binary sequence in the color-magnitude diagrams, in agreement
with the results of Steele & Jameson (1995) for higher mass stars. We compare
the multiplicity statistics of the Pleiades very low-mass stars and brown
dwarfs with that of G and K-type main sequence stars in the solar neighborhood
(Duquennoy & Mayor 1991). We find that there is some evidence for a deficiency
of wide binary systems (separation >27 AU) among the Pleiades very low-mass
members. We briefly discuss how this result can fit with current scenarios of
brown dwarf formation. We correct the Pleiades substellar mass function for the
contamination of cluster non-members found in this work. We find a
contamination level of 33% among the brown dwarf candidates identified by
Bouvier et al. (1998). Assuming a power law IMF across the substellar boundary,
we find a slope dN/dM ~ M^{-0.53}, implying that the number of objects per mass
bin is still rising but the contribution to the total mass of the cluster is
declining in the brown dwarf regime.Comment: to be published in The Astrophysical Journa
Electrical manipulation of spin states in a single electrostatically gated transition-metal complex
We demonstrate an electrically controlled high-spin (S=5/2) to low-spin
(S=1/2) transition in a three-terminal device incorporating a single Mn2+ ion
coordinated by two terpyridine ligands. By adjusting the gate-voltage we reduce
the terpyridine moiety and thereby strengthen the ligand-field on the Mn-atom.
Adding a single electron thus stabilizes the low-spin configuration and the
corresponding sequential tunnelling current is suppressed by spin-blockade.
From low-temperature inelastic cotunneling spectroscopy, we infer the
magnetic excitation spectrum of the molecule and uncover also a strongly
gate-dependent singlet-triplet splitting on the low-spin side. The measured
bias-spectroscopy is shown to be consistent with an exact diagonalization of
the Mn-complex, and an interpretation of the data is given in terms of a
simplified effective model.Comment: Will appear soon in Nanoletter
Duality in Non-Trivially Compactified Heterotic Strings
We study the implications of duality symmetry on the analyticity properties
of the partition function as it depends upon the compactification length. In
order to obtain non-trivial compactifications, we give a physical prescription
to get the Helmholtz free energy for any heterotic string supersymmetric or
not. After proving that the free energy is always invariant under the duality
transformation and getting the zero temperature
theory whose partition function corresponds to the Helmholtz potential, we show
that the self-dual point is a generic singularity
as the Hagedorn one. The main difference between these two critical
compactification radii is that the term producing the singularity at the
self-dual point is finite for any . We see that this behavior at
actually implies a loss of degrees of freedom below that point.Comment: (Preprint No. FTUAM-92/12) 17 page
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