40 research outputs found
Bootstrapping movement primitives from complex trajectories
Lemme A. Bootstrapping movement primitives from complex trajectories. Bielefeld: Bielefeld University; 2014
Movement primitives as a robotic tool to interpret trajectories through learning-by-doing
Articulated movements are fundamental in many human and robotic tasks. While humans can learn and generalise arbitrarily long sequences of movements, and particularly can optimise them to fit the constraints and features of their body, robots are often programmed to execute point-to-point precise but fixed patterns. This study proposes a new approach to interpreting and reproducing articulated and complex trajectories as a set of known robot-based primitives. Instead of achieving accurate reproductions, the proposed approach aims at interpreting data in an agent-centred fashion, according to an agent's primitive movements. The method improves the accuracy of a reproduction with an incremental process that seeks first a rough approximation by capturing the most essential features of a demonstrated trajectory. Observing the discrepancy between the demonstrated and reproduced trajectories, the process then proceeds with incremental decompositions and new searches in sub-optimal parts of the trajectory. The aim is to achieve an agent-centred interpretation and progressive learning that fits in the first place the robots' capability, as opposed to a data-centred decomposition analysis. Tests on both geometric and human generated trajectories reveal that the use of own primitives results in remarkable robustness and generalisation properties of the method. In particular, because trajectories are understood and abstracted by means of agent-optimised primitives, the method has two main features: 1) Reproduced trajectories are general and represent an abstraction of the data. 2) The algorithm is capable of reconstructing highly noisy or corrupted data without pre-processing thanks to an implicit and emergent noise suppression and feature detection. This study suggests a novel bio-inspired approach to interpreting, learning and reproducing articulated movements and trajectories. Possible applications include drawing, writing, movement generation, object manipulation, and other tasks where the performance requires human-like interpretation and generalisation capabilities
Neural Learning of Stable Dynamical Systems based on Data-Driven Lyapunov Candidates
Neumann K, Lemme A, Steil JJ. Neural Learning of Stable Dynamical Systems based on Data-Driven Lyapunov Candidates. Presented at the Int. Conference Intelligent Robotics and Systems, Tokio
A multimodal corpus for the evaluation of computational models for (grounded) language acquisition
Gaspers J, Panzner M, Lemme A, Cimiano P, Rohlfing K, Wrede S. A multimodal corpus for the evaluation of computational models for (grounded) language acquisition. In: EACL Workshop on Cognitive Aspects of Computational Language Learning. 2014
A Survey for Infall Motions toward Starless Cores. II. and Mapping Observations
We present the results of an extensive mapping survey of 53 `starless' cores
in the optically thick line of CS 2-1 and the optically thin lines of N2H+ 1-0
and C18O 1-0. The purpose of this survey was to search for signatures of
extended inward motions.
This study finds 10 `strong' and 9 `probable' infall candidates, based on
analysis and on the spectral shapes of CS lines.
From our analysis of the blue-skewed CS spectra and the
parameter, we find typical infall radii of 0.06-0.14 pc. Also, using a simple
two layer radiative transfer model to fit the profiles, we derive
one-dimensional infall speeds, half of whose values lie in the range of
0.05-0.09 km s. These values are similar to those found in L1544 by
Tafalla et al., and this result confirms that infall speeds in starless cores
are generally faster than expected from ambipolar diffusion in a strongly
sub-critical core. In addition, the observed infall regions are too extended to
be consistent with the `inside-out' collapse model applied to a very low-mass
star. In the largest cores, the spatial extent of the CS spectra with infall
asymmetry is larger than the extent of the core by a factor of
2-3. All these results suggest that extended inward motions are a common
feature in starless cores, and that they could represent a necessary stage in
the condensation of a star-forming dense core.Comment: Two tex files for manuscript and tables, and 38 figures. To appear in
ApJ
Rare neural correlations implement robotic conditioning with delayed rewards and disturbances
Neural conditioning associates cues and actions with following rewards. The environments in which robots operate, however, are pervaded by a variety of disturbing stimuli and uncertain timing. In particular, variable reward delays make it difficult to reconstruct which previous actions are responsible for following rewards. Such an uncertainty is handled by biological neural networks, but represents a challenge for computational models, suggesting the lack of a satisfactory theory for robotic neural conditioning. The present study demonstrates the use of rare neural correlations in making correct associations between rewards and previous cues or actions. Rare correlations are functional in selecting sparse synapses to be eligible for later weight updates if a reward occurs. The repetition of this process singles out the associating and reward-triggering pathways, and thereby copes with distal rewards. The neural network displays macro-level classical and operant conditioning, which is demonstrated in an interactive real-life human-robot interaction. The proposed mechanism models realistic conditioning in humans and animals and implements similar behaviors in neuro-robotic platforms
Dense Cores in Dark Clouds. XIV. N2H+(1-0) maps of dense cloud cores
We present results of an extensive mapping survey of N2H+(1-0) in about 60
low mass cloud cores already mapped in the NH3(1,1) inversion transition line.
The survey has been carried out at the FCRAO antenna with an angular resolution
about 1.5 times finer than the previous ammonia observations. Cores with stars
typically have map sizes about a factor of two smaller for N2H+ than for NH3,
indicating the presence of denser and more centrally concentrated gas compared
to starless cores. Significant correlations are found between NH3 and N2H+
column densities and excitation temperatures in starless cores, but not in
cores with stars, suggesting a different chemical evolution of the two species.
Velocity gradients range between 0.5 and 6 km/s/pc, similar to what has been
found with NH3 data. ``Local'' velocity gradients show significant variation in
both magnitude and direction, suggesting the presence of complexmotions not
interpretable as simple solid body rotation. Integrated intensity profiles of
starless cores present a ``central flattening'' and are consistent with a
spherically symmetric density law n ~ r^{-1.2} for r < ~0.03 pc and n ~ r^{-2}
at larger r. Cores with stars are better modelled with single density power
laws with n ~ r^{-2}. Line widths change across the core but we did not find a
general trend. The deviation in line width correlates with the mean line width,
suggesting that the line of sight contains ~ 10 coherence lengths. The
corresponding value of the coherence length, ~ 0.01 pc, is similar to the
expected cutoff wavelength for MHD waves. This similarity may account for the
increased ``coherence'' of line widths on small scales. Despite of the finer
angular resolution, the majority of N2H+ and NH3 maps show a similar ``simple''
structure, with single peaks and no elongation.Comment: 62 pages, 11 figures, ApJ, in pres
A Spherical Model for "Starless" Cores of Magnetic Molecular Clouds and Dynamical Effects of Dust Grains
In the standard picture of isolated star formation, dense ``starless'' cores
are formed out of magnetic molecular clouds due to ambipolar diffusion. Under
the simplest spherical geometry, I demonstrate that ``starless'' cores formed
this way naturally exhibit a large scale inward motion, whose size and speed
are comparable to those detected recently by Taffala et al. and Williams et al.
in ``starless'' core L1544. My model clouds have a relatively low mass (of
order 10 ) and low field strength (of order 10 G) to begin with.
They evolve into a density profile with a central plateau surrounded by a
power-law envelope, as found previously. The density in the envelope decreases
with radius more steeply than those found by Mouschovias and collaborators for
the more strongly magnetized, disk-like clouds.
At high enough densities, dust grains become dynamically important by greatly
enhancing the coupling between magnetic field and the neutral cloud matter. The
trapping of magnetic flux associated with the enhanced coupling leads, in the
spherical geometry, to a rapid assemblage of mass by the central protostar,
which exacerbates the so-called ``luminosity problem'' in star formation.Comment: 27 pages, 4 figures, accepted by Ap
Comparative evaluation of approaches in T.4.1-4.3 and working definition of adaptive module
The goal of this deliverable is two-fold: (1) to present and compare different approaches towards learning and encoding movements us- ing dynamical systems that have been developed by the AMARSi partners (in the past during the first 6 months of the project), and (2) to analyze their suitability to be used as adaptive modules, i.e. as building blocks for the complete architecture that will be devel- oped in the project. The document presents a total of eight approaches, in two groups: modules for discrete movements (i.e. with a clear goal where the movement stops) and for rhythmic movements (i.e. which exhibit periodicity). The basic formulation of each approach is presented together with some illustrative simulation results. Key character- istics such as the type of dynamical behavior, learning algorithm, generalization properties, stability analysis are then discussed for each approach. We then make a comparative analysis of the different approaches by comparing these characteristics and discussing their suitability for the AMARSi project
Systematic Molecular Differentiation in Starless Cores
(Abridged) We present evidence that low-mass starless cores, the simplest
units of star formation, are systematically differentiated in their chemical
composition. Molecules including CO and CS almost vanish near the core centers,
where the abundance decreases by one or two orders of magnitude. At the same
time, N2H+ has a constant abundance, and the fraction of NH3 increases toward
the core center. Our conclusions are based on a study of 5 mostly-round
starless cores (L1498, L1495, L1400K, L1517B, and L1544), which we have
mappedin C18O(1-0), C17O(1-0), CS(2-1), C34S(2-1), N2H+(1-0), NH3(1,1) and
(2,2), and the 1.2 mm continuum. For each core we have built a model that fits
simultaneously the radial profile of all observed emission and the central
spectrum for the molecular lines. The observed abundance drops of CO and CS are
naturally explained by the depletion of these molecules onto dust grains at
densities of 2-6 10^4 cm-3. N2H+ seems unaffected by this process up to
densities of several 10^5, while the NH3 abundance may be enhanced by reactions
triggered by the disappearance of CO from the gas phase. With the help of our
models, we show that chemical differentiation automatically explains the
discrepancy between the sizes of CS and NH3 maps, a problem which has remained
unexplained for more than a decade. Our models, in addition, show that a
combination of radiative transfer effects can give rise to the previously
observed discrepancy in the linewidth of these two tracers. Although this
discrepancy has been traditionally interpreted as resulting from a systematic
increase of the turbulent linewidth with radius, our models show that it can
arise in conditions of constant gas turbulence.Comment: 25 pages, 9 figures, accepted by Ap