220 research outputs found
Metadata for describing learning scenarios under European Higher Education Area paradigm
In this paper we identify the requirements for creating formal descriptions of learning scenarios designed under the European Higher
Education Area paradigm, using competences and learning activities as the basic pieces of the learning process, instead of contents and learning resources, pursuing personalization. Classical arrangements of content based courses are no longer enough to describe all the richness of this new learning process, where user profiles, competences and complex hierarchical itineraries need to be properly combined. We study the intersection with the current IMS Learning Design specification and the
additional metadata required for describing such learning scenarios. This new approach involves the use of case based learning and collaborative
learning in order to acquire and develop competences, following adaptive learning paths in two structured levels
Topological quantum chemistry
The past decade's apparent success in predicting and experimentally
discovering distinct classes of topological insulators (TIs) and semimetals
masks a fundamental shortcoming: out of 200,000 stoichiometric compounds extant
in material databases, only several hundred of them are topologically
nontrivial. Are TIs that esoteric, or does this reflect a fundamental problem
with the current piecemeal approach to finding them? To address this, we
propose a new and complete electronic band theory that highlights the link
between topology and local chemical bonding, and combines this with the
conventional band theory of electrons. Topological Quantum Chemistry is a
description of the universal global properties of all possible band structures
and materials, comprised of a graph theoretical description of momentum space
and a dual group theoretical description in real space. We classify the
possible band structures for all 230 crystal symmetry groups that arise from
local atomic orbitals, and show which are topologically nontrivial. We show how
our topological band theory sheds new light on known TIs, and demonstrate the
power of our method to predict a plethora of new TIs.Comment: v1: 8 pages + 40 pages supplemenetary material. Previously submitted
v2: ~ Published version. 11 pages + 79 pages supplementary material.
Descriptions of the data used in this paper can be found in arXiv:1706.08529
and arXiv:1706.09272. All data can be accessed via the Bilbao
Crystallographic Server (http://cryst.ehu.es). Two additional papers
elaborating on the general theory currently in pre
Band Connectivity for Topological Quantum Chemistry: Band Structures As A Graph Theory Problem
The conventional theory of solids is well suited to describing band
structures locally near isolated points in momentum space, but struggles to
capture the full, global picture necessary for understanding topological
phenomena. In part of a recent paper [B. Bradlyn et al., Nature 547, 298
(2017)], we have introduced the way to overcome this difficulty by formulating
the problem of sewing together many disconnected local "k-dot-p" band
structures across the Brillouin zone in terms of graph theory. In the current
manuscript we give the details of our full theoretical construction. We show
that crystal symmetries strongly constrain the allowed connectivities of energy
bands, and we employ graph-theoretic techniques such as graph connectivity to
enumerate all the solutions to these constraints. The tools of graph theory
allow us to identify disconnected groups of bands in these solutions, and so
identify topologically distinct insulating phases.Comment: 19 pages. Companion paper to arXiv:1703.02050 and arXiv:1706.08529
v2: Accepted version, minor typos corrected and references added. Now
19+epsilon page
Building Blocks of Topological Quantum Chemistry: Elementary Band Representations
The link between chemical orbitals described by local degrees of freedom and
band theory, which is defined in momentum space, was proposed by Zak several
decades ago for spinless systems with and without time-reversal in his theory
of "elementary" band representations. In Nature 547, 298-305 (2017), we
introduced the generalization of this theory to the experimentally relevant
situation of spin-orbit coupled systems with time-reversal symmetry and proved
that all bands that do not transform as band representations are topological.
Here, we give the full details of this construction. We prove that elementary
band representations are either connected as bands in the Brillouin zone and
are described by localized Wannier orbitals respecting the symmetries of the
lattice (including time-reversal when applicable), or, if disconnected,
describe topological insulators. We then show how to generate a band
representation from a particular Wyckoff position and determine which Wyckoff
positions generate elementary band representations for all space groups. This
theory applies to spinful and spinless systems, in all dimensions, with and
without time reversal. We introduce a homotopic notion of equivalence and show
that it results in a finer classification of topological phases than approaches
based only on the symmetry of wavefunctions at special points in the Brillouin
zone. Utilizing a mapping of the band connectivity into a graph theory problem,
which we introduced in Nature 547, 298-305 (2017), we show in companion papers
which Wyckoff positions can generate disconnected elementary band
representations, furnishing a natural avenue for a systematic materials search.Comment: 15+9 pages, 4 figures; v2: minor corrections; v3: updated references
(published version
Graph Theory Data for Topological Quantum Chemistry
Topological phases of noninteracting particles are distinguished by global
properties of their band structure and eigenfunctions in momentum space. On the
other hand, group theory as conventionally applied to solid-state physics
focuses only on properties which are local (at high symmetry points, lines, and
planes) in the Brillouin zone. To bridge this gap, we have previously [B.
Bradlyn et al., Nature 547, 298--305 (2017)] mapped the problem of constructing
global band structures out of local data to a graph construction problem. In
this paper, we provide the explicit data and formulate the necessary algorithms
to produce all topologically distinct graphs. Furthermore, we show how to apply
these algorithms to certain "elementary" band structures highlighted in the
aforementioned reference, and so identified and tabulated all orbital types and
lattices that can give rise to topologically disconnected band structures.
Finally, we show how to use the newly developed BANDREP program on the Bilbao
Crystallographic Server to access the results of our computation.Comment: v1: 29 Pages, 13 Figures. Explains how to access the data presented
in arXiv:1703.02050 v2: Accepted version. References updated, figures
improve
Accuracy in Rating and Recommending Item Features
This paper discusses accuracy in processing ratings of and
recommendations for item features. Such processing facilitates featurebased user navigation in recommender system interfaces. Item features, often in the form of tags, categories or meta-data, are becoming important hypertext components of recommender interfaces. Recommending features would help unfamiliar users navigate in such environments. This work explores techniques for improving feature recommendation accuracy. Conversely, it also examines possibilities for processing user ratings of features to improve recommendation of both features and items. This work’s illustrative implementation is a web portal for a museum collection that lets users browse, rate and receive recommendations for both artworks and interrelated topics about them. Accuracy measurements compare proposed techniques for processing feature ratings and recommending features. Resulting techniques recommend features with relative accuracy. Analysis indicates that processing ratings of either features or items does not improve accuracy of recommending the other
A Survey of Multi-Agent Human-Robot Interaction Systems
This article presents a survey of literature in the area of Human-Robot
Interaction (HRI), specifically on systems containing more than two agents
(i.e., having multiple humans and/or multiple robots). We identify three core
aspects of ``Multi-agent" HRI systems that are useful for understanding how
these systems differ from dyadic systems and from one another. These are the
Team structure, Interaction style among agents, and the system's Computational
characteristics. Under these core aspects, we present five attributes of HRI
systems, namely Team size, Team composition, Interaction model, Communication
modalities, and Robot control. These attributes are used to characterize and
distinguish one system from another. We populate resulting categories with
examples from recent literature along with a brief discussion of their
applications and analyze how these attributes differ from the case of dyadic
human-robot systems. We summarize key observations from the current literature,
and identify challenges and promising areas for future research in this domain.
In order to realize the vision of robots being part of the society and
interacting seamlessly with humans, there is a need to expand research on
multi-human -- multi-robot systems. Not only do these systems require
coordination among several agents, they also involve multi-agent and indirect
interactions which are absent from dyadic HRI systems. Adding multiple agents
in HRI systems requires advanced interaction schemes, behavior understanding
and control methods to allow natural interactions among humans and robots. In
addition, research on human behavioral understanding in mixed human-robot teams
also requires more attention. This will help formulate and implement effective
robot control policies in HRI systems with large numbers of heterogeneous
robots and humans; a team composition reflecting many real-world scenarios.Comment: 23 pages, 7 figure
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