322 research outputs found
Connectionist modelling of lexical segmentation and vocabulary acquisition
Adults typically hear sentences in their native language as a sequence of separate words and we might therefeore assume, that words in speech are physically separated in the way that they are perceived. However, when listening to an unfamiliar language we no longer experience sequences of discrete words, but rather hear a continuous stream of speech with boundaries separating individual sentences or utterances. Theories of how adult listeners segment the speech stream into words emphasise the role that knowledge of individual words plays in the segmentation of speech. However, since words can not be learnt until the speech stream can be segmented, it seems unlikely that infants will be able to use word recognition to segment connected speech. For this reason, researchers have proposed a variety of strategies and cues that infants could use to identify word boundaries without being able to recognise the words that these boundaries delimit. This chapter, describes some computational simulations proposing ways in which these cues and strategies for the acquisition of lexical segmentation can be integrated with the infantsÂ’ acquisition of the meanings of words. The simulations reported here describe simple computational mechanisms and knowledge sources that may support these different aspects of language acquisition
A robotic exploration mission to Mars and Phobos
This report discusses the design of a robotic exploration to Mars and Phobos. It begins with the mission's background and objectives, followed by a detailed explanation of various elements of Project Aeneas, including science, spacecraft, probes, and orbital trajectories. In addition, a description of Argos Space Endeavours, management procedures, and overall project costs are presented. Finally, a list of recommendations for future design activity is included
X-ray Polarization from Accreting Black Holes: II. The Thermal State
We present new calculations of X-ray polarization from black hole (BH)
accretion disks in the thermally-dominated state, using a Monte-Carlo
ray-tracing code in full general relativity. In contrast to many previously
published studies, our approach allows us to include returning radiation that
is deflected by the strong-field gravity of the BH and scatters off of the disk
before reaching a distant observer. Although carrying a relatively small
fraction of the total observed flux, the scattered radiation tends to be highly
polarized and in a direction perpendicular to the direct radiation. For
moderately large spin parameters (a/M >~ 0.9), this scattered returning
radiation dominates the polarization signal at energies above the thermal peak,
giving a net rotation in the polarization angle of 90 deg. We show how these
new features of the polarization spectra from BHs in the thermal state may be
developed into a powerful tool for measuring BH spin and probing the gas flow
in the innermost disk. In addition to determining the emission profile,
polarization observations can be used to constrain other properties of the
system such as BH mass, inclination, and distance. New instruments currently
under development should be able to exploit this tool in the near future.Comment: 33 pages, 13 figures, submitted to Ap
The Allen Telescope Array: The First Widefield, Panchromatic, Snapshot Radio Camera for Radio Astronomy and SETI
The first 42 elements of the Allen Telescope Array (ATA-42) are beginning to
deliver data at the Hat Creek Radio Observatory in Northern California.
Scientists and engineers are actively exploiting all of the flexibility
designed into this innovative instrument for simultaneously conducting surveys
of the astrophysical sky and conducting searches for distant technological
civilizations. This paper summarizes the design elements of the ATA, the cost
savings made possible by the use of COTS components, and the cost/performance
trades that eventually enabled this first snapshot radio camera. The
fundamental scientific program of this new telescope is varied and exciting;
some of the first astronomical results will be discussed.Comment: Special Issue of Proceedings of the IEEE: "Advances in Radio
Telescopes", Baars,J. Thompson,R., D'Addario, L., eds, 2009, in pres
Individual differences in reward drive predict neural responses to images of food
A network of interconnected brain regions, including orbitofrontal, ventral striatal, amygdala, and midbrain areas, has been widely
implicated in a number of aspects of food reward. However, in humans, sensitivity to reward can vary significantly from one person to the
next. Individuals high in this trait experience more frequent and intense food cravings and are more likely to be overweight or develop
eating disorders associated with excessive food intake. Using functional magnetic resonance imaging, we report that individual variation
in trait reward sensitivity (as measured by the Behavioral Activation Scale) is highly correlated with activation to images of appetizing
foods (e.g., chocolate cake, pizza) in a fronto–striatal–amygdala–midbrain network. Our findings demonstrate that there is considerable
personality-linked variability in the neural response to food cues in healthy participants and provide important insight into the neurobiological
factors underlying vulnerability to certain eating problems (e.g., hyperphagic obesity)
Feshbach-Stimulated Photoproduction of a Stable Molecular Condensate
Photoassociation and the Feshbach resonance are, in principle, feasible means
for creating a molecular Bose-Einstein condensate from an
already-quantum-degenerate gas of atoms; however, mean-field shifts and
irreversible decay place practical constraints on the efficient delivery of
stable molecules using either mechanism alone. We therefore propose
Feshbach-stimulated Raman photoproduction, i.e., a combination of magnetic and
optical methods, as a viable means to collectively convert degenerate atoms
into a stable molecular condensate with near-unit efficiency.Comment: 5 pages, 3 figures, 1 table; v3 includes few-level diagram of scheme,
and added discussion; transferred to PR
Visualizing the atomic-scale origin of metallic behavior in Kondo insulators
A Kondo lattice is often electrically insulating at low temperatures.
However, several recent experiments have detected signatures of bulk
metallicity within this Kondo insulating phase. Here we visualize the
real-space charge landscape within a Kondo lattice with atomic resolution using
a scanning tunneling microscope. We discover nanometer-scale puddles of
metallic conduction electrons centered around uranium-site substitutions in the
heavy-fermion compound URuSi, and around samarium-site defects in the
topological Kondo insulator SmB. These defects disturb the Kondo screening
cloud, leaving behind a fingerprint of the metallic parent state. Our results
suggest that the mysterious 3D quantum oscillations measured in SmB could
arise from these Kondo-lattice defects, although we cannot rule out other
explanations. Our imaging technique could enable the development of
atomic-scale charge sensors using heavy-fermion probes
X Her and TX Psc: Two cases of ISM interaction with stellar winds observed by Herschel
The asymptotic giant branch (AGB) stars X Her and TX Psc have been imaged at
70 and 160 microns with the PACS instrument onboard the Herschel satellite, as
part of the large MESS (Mass loss of Evolved StarS) Guaranteed Time Key
Program. The images reveal an axisymmetric extended structure with its axis
oriented along the space motion of the stars. This extended structure is very
likely to be shaped by the interaction of the wind ejected by the AGB star with
the surrounding interstellar medium (ISM). As predicted by numerical
simulations, the detailed structure of the wind-ISM interface depends upon the
relative velocity between star+wind and the ISM, which is large for these two
stars (108 and 55 km/s for X Her and TX Psc, respectively). In both cases,
there is a compact blob upstream whose origin is not fully elucidated, but that
could be the signature of some instability in the wind-ISM shock. Deconvolved
images of X Her and TX Psc reveal several discrete structures along the
outermost filaments, which could be Kelvin-Helmholtz vortices. Finally, TX Psc
is surrounded by an almost circular ring (the signature of the termination
shock?) that contrasts with the outer, more structured filaments. A similar
inner circular structure seems to be present in X Her as well, albeit less
clearly.Comment: 11 pages, Astronomy & Astrophysics, in pres
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