2,415 research outputs found
Quasi-isometric rigidity of subgroups and Filtered ends
Let and be quasi-isometric finitely generated groups and let ; is there a subgroup (or a collection of subgroups) of whose left
cosets coarsely reflect the geometry of the left cosets of in ? We
explore sufficient conditions for a positive answer.
The article consider pairs of the form where is a
finitely generated group and a finite collection of subgroups,
there is a notion of quasi-isometry of pairs, and quasi-isometrically
characteristic collection of subgroups. A subgroup is qi-characteristic if it
belongs to a qi-characteristic collection. Distinct classes of
qi-characteristic collections of subgroups have been studied in the literature
on quasi-isometric rigidity, we list in the article some of them and provide
other examples.
The first part of the article proves: if and are finitely generated
quasi-isometric groups and is a qi-characteristic collection of
subgroups of , then there is a collection of subgroups of
such that and are quasi-isometric pairs.
The second part of the article studies the number of filtered ends of a pair of groups, a notion introduced by Bowditch, and provides an
application of our main result: if and are quasi-isometric groups and
is qi-characterstic, then there is such that .Comment: 24 pages. All comments are welcome! Version 2. Correction in Example
3.4, updated some citations, and correction of minor typo
Quasi-isometry invariance of relative filling functions
For a finitely generated group and collection of subgroups
we prove that the relative Dehn function of a pair is
invariant under quasi-isometry of pairs. Along the way we show quasi-isometries
of pairs preserve almost malnormality of the collection and fineness of the
associated coned off Cayley graphs. We also prove that for a cocompact simply
connected combinatorial --complex with finite edge stabilisers, the
combinatorial Dehn function is well-defined if and only if the -skeleton of
is fine.Comment: 24 pages, 2 figure
Improving scope sensitivity in contingent valuation: joint and separate evaluation of health states
We present data of a contingent valuation survey, testing the effect of evaluation mode on the monetary valuation of preventing road accidents. Half of the interviewees was asked to state their willingness to pay (WTP) to reduce the risk of having only 1 type of injury (separate evaluation, SE), and the other half of the sample was asked to state their WTP for 4 types of injuries evaluated simultaneously (joint evaluation, JE). In the SE group, we observed lack of sensitivity to scope while in the JE group WTP increased with the severity of the injury prevented. However, WTP values in this group were subject to context effects. Our results suggest that the traditional explanation of the disparity between SE and JE, namely, the so-called “evaluability,” does not apply here. The paper presents new explanations based on the role of preference imprecision
Reinforcement and Curriculum Learning for Off-Road Navigation of an UGV with a 3D LiDAR
This paper presents the use of deep Reinforcement Learning (RL) for autonomous navigation
of an Unmanned Ground Vehicle (UGV) with an onboard three-dimensional (3D) Light Detection
and Ranging (LiDAR) sensor in off-road environments. For training, both the robotic simulator
Gazebo and the Curriculum Learning paradigm are applied. Furthermore, an Actor–Critic Neural
Network (NN) scheme is chosen with a suitable state and a custom reward function. To employ the
3D LiDAR data as part of the input state of the NNs, a virtual two-dimensional (2D) traversability
scanner is developed. The resulting Actor NN has been successfully tested in both real and simulated
experiments and favorably compared with a previous reactive navigation approach on the same UGV.Partial funding for open access charge: Universidad de Málag
Pure-Pursuit reactive Path Tracking for Nonholonomic Mobile Robots with a 2D Laser Scanner
Due to its simplicity and efficiency, the pure-pursuit path tracking method has been widely employed for planned navigation of
nonholonomic ground vehicles. In this paper, we investigate the application of this technique for reactive tracking of paths that
are implicitly defined by perceived environmental features. Goal points are obtained through an efficient interpretation of range
data from an onboard 2D laser scanner to follow persons, corridors, and walls. Moreover, this formulation allows that a robotic
mission can be composed of a combination of different types of path segments. These techniques have been successfully tested in the tracked mobile robot Auriga-α in an indoor environment
Using high-density protein microarrays to define a molecular signature of autoantibodies in colorectal cancer
Comunicaciones a congreso
La valoración monetaria de los costes humanos de la siniestralidad vial en España
ResumenLos análisis coste-beneficio en el ámbito de la seguridad vial han de computar la totalidad de los costes, y dentro de ellos ocupan un lugar clave los costes humanos. En esta nota se da cuenta de dos estudios promovidos por la Dirección General de Tráfico orientados a la obtención de valores oficiales para España de los costes asociados a las víctimas mortales y no mortales de los accidentes de tráfico. Mediante la combinación del enfoque de la valoración contingente con la técnica de la lotería estándar (modificada), y con muestras amplias (n1=2020, n2=2000) representativas de la población española, se estimó en 1,4 millones de euros el valor monetario de prevenir un fallecido por accidente de tráfico. Para las lesiones graves y leves, los valores estimados fueron de 219.000 y 6100 euros, respectivamente. Las cifras obtenidas tienen un orden de magnitud similar al de los países de nuestro entorno.AbstractCost-benefit analyses in the field of road safety compute human costs as a key component of total costs. The present article presents two studies promoted by the Directorate-General for Traffic aimed at obtaining official values for the costs associated with fatal and non-fatal traffic injuries in Spain. We combined the contingent valuation approach and the (modified) standard gamble technique in two surveys administered to large representative samples (n1=2,020, n2=2,000) of the Spanish population. The monetary value of preventing a fatality was estimated to be 1.4 million euros. Values of 219,000 and 6,100 euros were obtained for minor and severe non-fatal injuries, respectively. These figures are comparable to those observed in neighboring countries
Practical Lessons from the Deployment and Management of a Smart City Internet-of-Things Infrastructure: The SmartSantander testbed case
The smart cities vision is inexorably turning into a reality. Among the different approaches used to realize more intelligent and sustainable environments, a common denominator is the role that information and communication technologies will play. Moreover, if there is one of these technologies that emerges among the rest, it is the Internet-of-Things (IoT). The ability to ubiquitously embed sensing and actuating capabilities that this paradigm enables is at the forefront of the technologies driving the urban environments transformation. However, there are very little practical experiences of the IoT infrastructure deployment at a large scale. This paper presents practical solutions to the main challenges faced during the deployment and management of a city-scale IoT infrastructure, which encompasses thousands of sensors and other information sources. The experience we have gained during the deployment and operation of the IoT-based smart city infrastructure carried out at Santander (Spain) has led to a number of practical lessons that are summarized in this paper. Moreover, the challenges and problems examples, excerpted from our own real-life experience, are described as motivators for the adopted solutions.This work was supported in part by the research project SmartSantander through the 7th Framework Programme of the European Commission under Grant FP7-ICT-2009-5 and in part by the Spanish Government by means of the project ADVICE "Dynamic provisioning of connectivity in high density 5G wireless scenarios" under Grant TEC2015-71329-C2-1-R
Supervised learning of natural-terrain traversability with synthetic 3D laser scans
Autonomous navigation of ground vehicles on natural environments requires looking for traversable terrain continuously. This paper develops traversability classifiers for the three-dimensional (3D) point clouds acquired by the mobile robot Andabata on non-slippery solid ground. To this end, different supervised learning techniques from the Python library Scikit-learn are employed. Training and validation are performed with synthetic 3D laser scans that were labelled point by point automatically with the robotic simulator Gazebo. Good prediction results are obtained for most of the developed classifiers, which have also been tested successfully on real 3D laser scans acquired by Andabata in motion.Andalusian project UMA18-FEDERJA-090 and Spanish project RTI2018-093421-B-I0
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