26,606 research outputs found
Two dimensional outflows for cellular automata with shuffle updates
In this paper, we explore the two-dimensional behavior of cellular automata
with shuffle updates. As a test case, we consider the evacuation of a square
room by pedestrians modeled by a cellular automaton model with a static floor
field. Shuffle updates are characterized by a variable associated to each
particle and called phase, that can be interpreted as the phase in the step
cycle in the frame of pedestrian flows. Here we also introduce a dynamics for
these phases, in order to modify the properties of the model. We investigate in
particular the crossover between low- and high-density regimes that occurs when
the density of pedestrians increases, the dependency of the outflow in the
strength of the floor field, and the shape of the queue in front of the exit.
Eventually we discuss the relevance of these results for pedestrians.Comment: 20 pages, 5 figures. v2: 16 pages, 5 figures; changed the title,
abstract and structure of the paper. v3: minor change
Deciding How to Decide: Dynamic Routing in Artificial Neural Networks
We propose and systematically evaluate three strategies for training
dynamically-routed artificial neural networks: graphs of learned
transformations through which different input signals may take different paths.
Though some approaches have advantages over others, the resulting networks are
often qualitatively similar. We find that, in dynamically-routed networks
trained to classify images, layers and branches become specialized to process
distinct categories of images. Additionally, given a fixed computational
budget, dynamically-routed networks tend to perform better than comparable
statically-routed networks.Comment: ICML 2017. Code at https://github.com/MasonMcGill/multipath-nn Video
abstract at https://youtu.be/NHQsDaycwy
Toward transferable interatomic van der Waals interactions without electrons: The role of multipole electrostatics and many-body dispersion
We estimate polarizabilities of atoms in molecules without electron density,
using a Voronoi tesselation approach instead of conventional density
partitioning schemes. The resulting atomic dispersion coefficients are
calculated, as well as many-body dispersion effects on intermolecular potential
energies. We also estimate contributions from multipole electrostatics and
compare them to dispersion. We assess the performance of the resulting
intermolecular interaction model from dispersion and electrostatics for more
than 1,300 neutral and charged, small organic molecular dimers. Applications to
water clusters, the benzene crystal, the anti-cancer drug
ellipticine---intercalated between two Watson-Crick DNA base pairs, as well as
six macro-molecular host-guest complexes highlight the potential of this method
and help to identify points of future improvement. The mean absolute error made
by the combination of static electrostatics with many-body dispersion reduces
at larger distances, while it plateaus for two-body dispersion, in conflict
with the common assumption that the simple correction will yield proper
dissociative tails. Overall, the method achieves an accuracy well within
conventional molecular force fields while exhibiting a simple parametrization
protocol.Comment: 13 pages, 8 figure
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propnet: A Knowledge Graph for Materials Science
Discovering the ideal material for a new application involves determining its numerous properties, such as electronic, mechanical, or thermodynamic, to match those of its desired application. The rise of high-throughput computation has meant that large databases of material properties are now accessible to scientists. However, these databases contain far more information than might appear at first glance, since many relationships exist in the materials science literature to derive, or at least approximate, additional properties. propnet is a new computational framework designed to help scientists to automatically calculate additional information from their datasets. It does this by constructing a network graph of relationships between different materials properties and traversing this graph. Initially, propnet contains a catalog of over 100 property relationships but the hope is for this to expand significantly in the future, and contributions from the community are welcomed
Activity theory: A framework for analysing intercultural academic activity
This article suggests that Activity Theory (AT) can be applied as a holistic framework to analyse the complex sociocultural issues that arise when academics wish to engage in collaborative activity across institutional and cultural boundaries. Attention will initially focus on how Activity Theory, first formulated in the 1930s by Leontâev (1978), and subsequently developed into a second generation by Engeström (1987), can help to analyse and illuminate the inherent complexity within any one community of practice. A more elaborate model of AT (Engeström, 2001) is currently being developed and applied to analyse and illuminate collaborative activity across institutional boundaries, so as to transform discourse communities into speech communities of practice through expansive learning. It is suggested that this âthird generationâ model can be further refined to analyse specific contact zones, within and between activity systems, as a precursor to undertaking collaborative activity. It is suggested that, when discourse communities deriving from different culturally diverse traditions seek to work together, such an a priori analysis would enable potential areas for miscommunication and misconstrual to be identified and possibly resolved before collaborative activity actually commences
The Massive End of the Stellar Mass Function
We derive average flux corrections to the \texttt{Model} magnitudes of the
Sloan Digital Sky Survey (SDSS) galaxies by stacking together mosaics of
similar galaxies in bins of stellar mass and concentration. Extra flux is
detected in the outer low surface brightness part of the galaxies, leading to
corrections ranging from 0.05 to 0.32 mag for the highest stellar mass
galaxies. We apply these corrections to the MPA-JHU (Max-Planck Institute for
Astrophysics - John Hopkins University) stellar masses for a complete sample of
half a million galaxies from the SDSS survey to derive a corrected galaxy
stellar mass function at in the stellar mass range
. We find that the flux corrections and the use
of the MPA-JHU stellar masses have a significant impact on the massive end of
the stellar mass function, making the slope significantly shallower than that
estimated by Li \& White (2009), but steeper than derived by Bernardi et al.
(2013). This corresponds to a mean comoving stellar mass density of galaxies
with stellar masses that is a factor of 3.36
larger than the estimate by Li \& White (2009), but is 43\% smaller than
reported by Bernardi et al. (2013).Comment: 11 pages, 8 figures, Accepted to MNRA
Evolutionary plant breeding for low input systems
Heritable variation is at the heart of the process of evolution. However, variation is restricted in breeding for uniform crop populations using the pedigree line approach. Pedigree lines are successful in agriculture because synthetic inputs are used to raise fertility and control weeds, pests and diseases.
An alternative method promoted for exploring the value of variation and evolutionary fitness in crops is to create composite cross populations. Composite cross populations are formed by assembling seed stocks with diverse evolutionary origins, recombination of these stocks by hybridization, the bulking of F1 progeny, and subsequent natural election for mass sorting of the progeny in successive natural cropping environments. Composite cross populations can provide dynamic gene pools, which in turn provide a means of conserving germplasm resources: they can also allow selection of heterogeneous crop varieties. The value of composite cross populations in achieving these aims is dependent on the outcome of mass trials by artificial and natural selection acting upon the heterogeneous mixture.
There is evidence to suggest that composite cross populations may be an efficient way of providing heterogeneous crops and of selecting superior pure lines for low input systems characterized by unpredictable stress conditions
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