Yet another approach to the Gough-Stewart platform forward kinematics

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The forward kinematics of the Gough-Stewart platform, and their simplified versions in which some leg endpoints coalesce, has been typically solved using variable elimination methods. In this paper, we cast doubts on whether this is the easiest way to solve the problem. We will see how the indirect approach in which the length of some extra virtual legs is first computed leads to important simplifications. In particular, we provide a procedure to solve 30 out of 34 possible topologies for a Gough-Stewart platform without variable elimination.Peer ReviewedPostprint (author's final draft

Path planning for active tensegrity structures

This paper presents a path planning method for actuated tensegrity structures with quasi-static motion. The valid configurations for such structures lay on an equilibrium manifold, which is implicitly defined by a set of kinematic and static constraints. The exploration of this manifold is difficult with standard methods due to the lack of a global parameterization. Thus, this paper proposes the use of techniques with roots in differential geometry to define an atlas, i.e., a set of coordinated local parameterizations of the equilibrium manifold. This atlas is exploited to define a rapidly-exploring random tree, which efficiently finds valid paths between configurations. However, these paths are typically long and jerky and, therefore, this paper also introduces a procedure to reduce their control effort. A variety of test cases are presented to empirically evaluate the proposed method. (C) 2015 Elsevier Ltd. All rights reserved.Peer ReviewedPostprint (author's final draft

A bayesian approach to simultaneously recover camera pose and non-rigid shape from monocular images

© . This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/In this paper we bring the tools of the Simultaneous Localization and Map Building (SLAM) problem from a rigid to a deformable domain and use them to simultaneously recover the 3D shape of non-rigid surfaces and the sequence of poses of a moving camera. Under the assumption that the surface shape may be represented as a weighted sum of deformation modes, we show that the problem of estimating the modal weights along with the camera poses, can be probabilistically formulated as a maximum a posteriori estimate and solved using an iterative least squares optimization. In addition, the probabilistic formulation we propose is very general and allows introducing different constraints without requiring any extra complexity. As a proof of concept, we show that local inextensibility constraints that prevent the surface from stretching can be easily integrated. An extensive evaluation on synthetic and real data, demonstrates that our method has several advantages over current non-rigid shape from motion approaches. In particular, we show that our solution is robust to large amounts of noise and outliers and that it does not need to track points over the whole sequence nor to use an initialization close from the ground truth.Peer ReviewedPostprint (author's final draft

Pour faciliter l´alphabétisation scolaire au foyer. Le ¨conte-rimé¨ comme recours littéraire

Se describe y fundamenta el uso de estrategias para que padres y/o cuidadores promuevan desde el hogar habilidades lingüísticas en niños de nivel inicial y primer año de la escuela primaria, a fin de facilitar el aprendizaje primero de la lectura. Estas estrategias están dise- ñadas para que los padres obtengan mayor entendimiento y competencia en desarrollar habilidades lingüísticas en los niños a partir de la lectura de versi-cuentos. Se detallan fundamentos teóricos y lineamientos prácticos para crear un ambiente hogareño rico en experiencias lingüísticas y literarias.Fil: Porta, Maria Elsa. Universidad Nacional de Cuyo. Facultad de Filosofia y Letras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mendoza; Argentin

Pre-reading evaluation skills in pedagogic intervention projects: Methodological and pedagogic purposes in the initial level

En cada una de las etapas evaluativas que componen los diseños cuasi-experimentales de tipo pre / post, dirigidos a evaluar efectos de programas de intervención para promover habilidades lingüísticas predictivas de la lectura en niños de nivel inicial, es posible distinguir no solo una finalidad metodológica, sino también una finalidad pedagógica. El propósito de este artículo es difundir la experiencia adquirida en la selección de una batería de evaluación de habilidades prelectoras como herramienta de valoración y de detección, durante la implementación de proyectos de investigación que evalúan los efectos de programas de intervención dirigidos a desarrollar habilidades lingüísticas en niños de jardín de infantes de escuelas urbano-marginales, con el objetivo de facilitar el aprendizaje de la lectura en primer grado, al mismo tiempo y ritmo que sus pares, disminuyendo así el riesgo de fracaso escolar. El desarrollo de tales habilidades no solo influye de manera significativa en el futuro rendimiento lector, sino que también reduce el riesgo de presentar dificultades en el proceso de adquisición de la lectura. De allí que las instancias de evaluación que componen los diseños dirigidos a evaluar los efectos de los programas de intervención pedagógica permiten comparar rendimientos y, además, constituyen una instancia de detección estratégica de niños en riesgo de presentar dificultades en el proceso de adquisición de la lectura, y de valoración de su respuesta a las distintas condiciones de intervención.Em cada uma das etapas avaliativas que compõem os planejamentos quase experimentais do tipo pré/pós, dirigidos a avaliar efeitos de programas de intervenções para promover habilidades linguísticas preditivas da leitura em crianças de nível inicial, é possível distinguir não somente uma finalidade metodológica, como também uma finalidade pedagógica. O propósito deste artigo é difundir a experiência adquirida na seleção de uma bateria de avaliação de habilidades pré-leitoras como ferramenta de valorização e de detecção, durante a implementação de projetos de pesquisa que avaliam os efeitos de programas de intervenção dirigidos a desenvolver habilidades linguísticas em crianças de jardim de infância de escolas urbano-marginais, com o objetivo de facilitar a aprendizagem da leitura em primeiro grau, ao mesmo tempo e ritmo que seus pares, diminuindo assim o risco de fracasso escolar. O desenvolvimento de tais habilidades não somente influí de maneira significativa no futuro rendimento leitor, como também reduz o risco de apresentar dificuldades no processo de aquisição da leitura. Daí que as instâncias de avaliação que compõem os planejamentos dirigidos a avaliar os efeitos dos programas de intervenção pedagógica permitem comparar rendimentos e, ademais, constituem uma instancia de detecção estratégica de crianças em risco de apresentar dificuldades no processo de aquisição da leitura e de valorização de sua resposta às diferentes condições de intervenção.In each of the evaluative stage that compose the pre/post quasi-experimental designs addressed to evaluate the intervention programs effects to promote linguistic predictive reading skills of children in initial level, it is possible to distinguish not only a methodological purpose, but also a pedagogic purpose. The intention of this article is to spread the acquired experience in the selection of a battery of pre-reading skills evaluation as a valuation and detection tool, during the investigation implementation project which evaluates the effects of intervention programs directed to developing linguistic skills in children in urban-marginal infant schools,with the aim to facilitate the learning of reading in first degree, at the same time as their pairs, diminishing tthis way the risk of school failure.  The development of such skills not only influences in a significant way the future reading performance, but also it reduces the risk of presenting difficulties in the process of reading acquisition, that is why the evaluation instances that compose the designs directed to evaluating the effects of pedagogic programs intervention to compare performances and, in addition, they constitute an instance of children’s strategic risk detection presenting difficulties in the acquisition process of reading, and valuating their respone to different conditions of intervention.Fil: Porta, Maria Elsa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentina. Universidad Nacional de Cuyo. Facultad de Filosofia y Letras; Argentin

Luttinger parameter of quasi-one-dimensional para- H2

We have studied the ground-state properties of para-hydrogen in one dimension and in quasi-one-dimensional configurations using the path-integral ground-state Monte Carlo method. This method produces zero-temperature exact results for a given interaction and geometry. The quasi-one-dimensional setup has been implemented in two forms: the inner channel inside a carbon nanotube coated with H2 and a harmonic confinement of variable strength. Our main result is the dependence of the Luttinger parameter on the density within the stable regime. Going from one dimension to quasi-one dimension, keeping the linear density constant, produces a systematic increase of the Luttinger parameter. This increase is, however, not enough to reach the superfluid regime and the system always remain in the quasicrystal regime, according to Luttinger liquid theory.Postprint (author's final draft

A randomized kinodynamic planner for closed-chain robotic systems

Kinodynamic RRT planners are effective tools for finding feasible trajectories in many classes of robotic systems. However, they are hard to apply to systems with closed-kinematic chains, like parallel robots, cooperating arms manipulating an object, or legged robots keeping their feet in contact with the environ- ment. The state space of such systems is an implicitly-defined manifold, which complicates the design of the sampling and steering procedures, and leads to trajectories that drift away from the manifold when standard integration methods are used. To address these issues, this report presents a kinodynamic RRT planner that constructs an atlas of the state space incrementally, and uses this atlas to both generate ran- dom states, and to dynamically steer the system towards such states. The steering method is based on computing linear quadratic regulators from the atlas charts, which greatly increases the planner efficiency in comparison to the standard method that simulates random actions. The atlas also allows the integration of the equations of motion as a differential equation on the state space manifold, which eliminates any drift from such manifold and thus results in accurate trajectories. To the best of our knowledge, this is the first kinodynamic planner that explicitly takes closed kinematic chains into account. We illustrate the performance of the approach in significantly complex tasks, including planar and spatial robots that have to lift or throw a load at a given velocity using torque-limited actuators.Peer ReviewedPreprin

A Methodological Proposal to Evaluate the Sinergical Industry Concentration

This study deals with the firms’ competitiveness in traditional industries. We understand traditional industry as the one that has transmitted its knowledge generation after generation, and it also has some specific characteristics, such as not being a new industry because its activities have been carried out for many years, to have small and medium sized businesses with little or no presence of transnational firms or having little investment on technology and activities of research and development. The objective of this paper is to present a methodological process for the study and evaluation of the impact of the sinérgic geographical concentration of an industry in its competitiveness. The geographical concentration is a factor of great importance, facilitates the exchange and the cooperation among research centers, among the clients and the suppliers of the region, and it promotes research in the industry (Porter, 1998). On the other hand, the specific concentration of activities in a concrete zone attracts the specialized knowledge. The importance of the geographical concentration and the evidence of the existence of industrial clusters has been studied in an extensive manner through time; Saxenian (1996) analyzed the organization and the characteristics of the electronic firms of Sillicon Valley, Glasmeier (1991) the Swiss clocks, Faulkner and Anderson (1987) the film industry in Hollywood, Scott (1991) the electronic-aeroespacial industry in the south of California, and Abrupt (1982) studied the organization of firms in the north of Italy. Following Kaplan (1986), it turns out to be difficult to imagine that theories in the field of management can be verified, if the test is not carried out inside its context. These tests should serve not only to describe the existence or not of procedures, but also to deduce and to contrast how and why certain practices have to be carried out. If the intention of the researcher is to generate a theory, taking into account the theoretical framework and the key questions to answer are how they are created and how they influence the geographical concentration in the competitiveness of an industry, the most appropiate would be to carry out an explanatory type case study. Some cases will be studied according to Rouse and Daellenbach, (1999). The study of cases to be carried out follows the model proposed by Pérez (1998). The method that will be used in this study, interviews in depth, is classified as direct obtaining of data. The type of interview used is the so call interview of open answers (King, 1994). This technique combines the advantages of the use of closed questionnaires along the qualitative interviews. In the paper, we present an instrument to evaluate the impact of the geographical concentration.

Closure polynomials for strips of tetrahedra

The final publication is available at link.springer.comA tetrahedral strip is a tetrahedron-tetrahedron truss where any tetrahedron has two neighbors except those in the extremes which have only one. Unless any of the tetrahedra degenerate, such a truss is rigid. In this case, if the distance between the strip endpoints is imposed, any rod length in the truss is constrained by all the others to attain discrete values. In this paper, it is shown how to characterize these values as the roots of a closure polynomial whose derivation requires surprisingly no other tools than elementary algebraic manipulations. As an application of this result, the forward kinematics of two parallel platforms with closure polynomials of degree 16 and 12 is straightforwardly solved.Peer ReviewedPostprint (author's final draft

Closed-form position analysis of variable geometry trusses

© . This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Variable geometry trusses are composed, in general, of unit cells which can be modeled as bars connected by spherical joints. Under mild conditions, it has been shown that the only feasible cells are topologically equivalent to bipyramids. Unfortunately, using standard formulations, the closed-form position analysis of bipyramids is not a trivial task. Actually, it has only been achieved for bipyramids with up to 7 vertices, whose closure polynomial has been shown to be of order 24. In this paper, using a distance-based formulation and a kinematic inversion for fans of tetrahedra, the problem is solved for bipyramids with up to 11 vertices, whose closure polynomial is of degree 896. No other position analysis problem leading to such a high-order closure polynomial has been previously solved.Peer ReviewedPostprint (author's final draft