Modeling discrete and rhythmic movements through motor primitives: a review

Rhythmic and discrete movements are frequently considered separately in motor control, probably because different techniques are commonly used to study and model them. Yet the increasing interest in finding a comprehensive model for movement generation requires bridging the different perspectives arising from the study of those two types of movements. In this article, we consider discrete and rhythmic movements within the framework of motor primitives, i.e., of modular generation of movements. In this way we hope to gain an insight into the functional relationships between discrete and rhythmic movements and thus into a suitable representation for both of them. Within this framework we can define four possible categories of modeling for discrete and rhythmic movements depending on the required command signals and on the spinal processes involved in the generation of the movements. These categories are first discussed in terms of biological concepts such as force fields and central pattern generators and then illustrated by several mathematical models based on dynamical system theory. A discussion on the plausibility of theses models concludes the wor

Venture Capital Investment Duration: Asia, Europe, and North America

Abstract I apply survival analysis to model the factors that influence venture capital (VC) investment duration. Specifically, I fit a parametric survival model to plot the probability of venture capital exit over time. Given a small number of initial public offering (IPO) exits in the collected sample, the analysis focuses exclusively on exits through mergers and acquisitions (M&A). I fit a Cox proportional hazards model and a parametric model under the generalized Gamma distribution with financing, entrepreneurial firm, and VC firm characteristics. For the first time in the VC investment duration literature, I investigate the time to exit with data of Asian entrepreneurial firms and VC firms. The empirical analysis first draws comparisons between Asian, European, and North American venture capital, and then focuses the analysis to North America. I find that venture capital investments in North America are most likely to exit through M&A, followed by European VC investments and then by Asian VC investments. The region of the VC firm has no effect on the likelihood of an M&A exit

Movement generation using dynamical systems : a humanoid robot performing a drumming task

The online generation of trajectories in humanoid robots remains a difficult problem. In this contribution, we present a system that allows the superposition, and the switch between, discrete and rhythmic movements. Our approach uses nonlinear dynamical systems for generating trajectories online and in real time. Our goal is to make use of attractor properties of dynamical systems in order to provide robustness against small perturbations and to enable online modulation of the trajectories. The system is demonstrated on a humanoid robot performing a drumming task.This work was made possible thanks to the support of the Swiss National Science Foundation (A.I.) and of the European Commissions Cognition Unit, project no. IST-2004-004370 : RobotCub (S.D.

Toward simple control for complex, autonomous robotic applications: combining discrete and rhythmic motor primitives

Vertebrates are able to quickly adapt to new environments in a very robust, seemingly effortless way. To explain both this adaptivity and robustness, a very promising perspective in neurosciences is the modular approach to movement generation: Movements results from combinations of a finite set of stable motor primitives organized at the spinal level. In this article we apply this concept of modular generation of movements to the control of robots with a high number of degrees of freedom, an issue that is challenging notably because planning complex, multidimensional trajectories in time-varying environments is a laborious and costly process. We thus propose to decrease the complexity of the planning phase through the use of a combination of discrete and rhythmic motor primitives, leading to the decoupling of the planning phase (i.e. the choice of behavior) and the actual trajectory generation. Such implementation eases the control of, and the switch between, different behaviors by reducing the dimensionality of the high-level commands. Moreover, since the motor primitives are generated by dynamical systems, the trajectories can be smoothly modulated, either by high-level commands to change the current behavior or by sensory feedback information to adapt to environmental constraints. In order to show the generality of our approach, we apply the framework to interactive drumming and infant crawling in a humanoid robot. These experiments illustrate the simplicity of the control architecture in terms of planning, the integration of different types of feedback (vision and contact) and the capacity of autonomously switching between different behaviors (crawling and simple reaching

Casos importados e autóctones na dinâmica da epidemia de dengue no Brasil

OBJECTIVE: To estimate the basic reproduction number (R0) of dengue fever including both imported and autochthonous cases. METHODS: The study was conducted based on epidemiological data of the 2003 dengue epidemic in Brasília, Brazil. The basic reproduction number is estimated from the epidemic curve, fitting linearly the increase of initial cases. Aiming at simulating an epidemic with both autochthonous and imported cases, a "susceptible-infectious-resistant" compartmental model was designed, in which the imported cases were considered as an external forcing. The ratio between R0 of imported versus autochthonous cases was used as an estimator of real R0. RESULTS: The comparison of both reproduction numbers (only autochthonous versus all cases) showed that considering all cases as autochthonous yielded a R0 above one, although the real R0 was below one. The same results were seen when the method was applied on simulated epidemics with fixed R0. This method was also compared to some previous proposed methods by other authors and showed that the latter underestimated R0 values. CONCLUSIONS: It was shown that the inclusion of both imported and autochthonous cases is crucial for the modeling of the epidemic dynamics, and thus provides critical information for decision makers in charge of prevention and control of this disease.OBJETIVO: Estimar el número de reproducción básica (R0) de la fiebre del dengue incluyendo casos importados y autóctonos. MÉTODOS: El estudio fue realizado basándose en datos epidemiológicos de la epidemia del dengue ocurrida en Brasilia, Districto Federal de Brasil, en el 2003. El número de reproducción básica es estimado de la curva epidémica, fijando el incremento lineal de los casos iniciales. Señalando casos importados y autóctonos en una simulación epidémica, fue diseñado un compartimiento "infeccioso-susceptible-resistente", en el cual los casos importados fueron considerados una fuerza externa. La tasa entre R0 de casos importados versus casos autóctonos fue usado como una estimación real de R0. RESULTADOS: La comparación de ambos números de reproducción (sólo autóctonos versus todos los casos) mostró que considerando todos los casos como autóctonos produjo un R0 por encima de uno, a pesar de que el valor real de R0 era menor que uno. Los mismos resultados fueron obtenidos cuando se aplicó el método a epidemias simuladas con valor fijo de R0. Este método fue también comparado con métodos propuestos anteriormente por otros autores y mostró los mismos valores subestimados de R0. CONCLUSIONES: Fue demostrado que la inclusión de casos importados y autóctonos es crucial para el modelaje de dinámicas epidémicas, y que provee información crítica para aquellos que participan en la toma de decisiones en la prevención y control de esta enfermedad.OBJETIVO: Estimar o número básico de reprodução da dengue (R0), com base nos casos importados, além dos casos autóctones. MÉTODOS: O estudo foi feito sobre dados epidemiológicos da epidemia de dengue em Brasília, 2003. O número básico de reprodução é determinado a partir da curva epidêmica, ajustando uma reta ao crescimento inicial do número de casos. Para simular uma epidemia com casos autóctones e importados, foi criado um modelo compartimentado do tipo "suscetíveis-infectados-resistentes". O R0 real foi estimado pela fração entre R0 dos casos autóctones e dos importados. RESULTADOS: A comparação de ambos valores de reprodução (apenas autóctones versus todos os casos) mostrou que considerando todos casos como autóctones, o valor de R0 foi superior a um, enquanto o R0 real era inferior a um. O mesmo resultado foi obtido com o conjunto de dados simulando uma epidemia com R0 fixo. O método foi também comparado a outros, observando-se que estes últimos subestimaram os valores do R0. CONCLUSÕES: A inclusão de tanto casos autóctones como os importados é essencial para modelar a dinâmica da epidemia, possibilitando informação crítica aos tomadores de decisão, responsáveis pelo controle da doença

Hand placement during quadruped locomotion in a humanoid robot: A dynamical system approach

Locomotion on an irregular surface is a challenging task in robotics. Among different problems to solve to obtain robust locomotion, visually guided locomotion and accurate foot placement are of crucial importance. Robust controllers able to adapt to sensory-motor feedbacks, in particular to properly place feet on specific locations, are thus needed. Dynamical systems are well suited for this task as any online modification of the parameters leads to a smooth adaptation of the trajectories,allowing a safe integration of sensory-motor feedback. In this contribution, as a first step in the direction of locomotion on irregular surfaces, we present a controller that allows hand placement during crawling in a simulated humanoid robot. The goal of the controller is to superimpose rhythmic movements for crawling with discrete (i.e. short-term) modulations of the hand placements to reach specific marks on the ground

Yellow fever virus envelope protein expressed in insect cells is capable of syncytium formation in lepidopteran cells and could be used for immunodetection of YFV in human sera

<p>Abstract</p> <p>Background</p> <p>Yellow fever is an haemorrhagic disease caused by a virus that belongs to the genus Flavivirus (Flaviviridae family) and is transmitted by mosquitoes. Among the viral proteins, the envelope protein (E) is the most studied one, due to its high antigenic potencial. Baculovirus are one of the most popular and efficient eukaryotic expression system. In this study a recombinant baculovirus (vSynYFE) containing the envelope gene (<it>env</it>) of the 17D vaccine strain of yellow fever virus was constructed and the recombinant protein antigenicity was tested.</p> <p>Results</p> <p>Insect cells infected with vSynYFE showed syncytium formation, which is a cytopathic effect characteristic of flavivirus infection and expressed a polypeptide of around 54 kDa, which corresponds to the expected size of the recombinant E protein. Furthermore, the recombinant E protein expression was also confirmed by fluorescence microscopy of vSynYFE-infected insect cells. Total vSynYFE-infected insect extracts used as antigens detected the presence of antibodies for yellow fever virus in human sera derived from yellow fever-infected patients in an immunoassay and did not cross react with sera from dengue virus-infected patients.</p> <p>Conclusions</p> <p>The E protein expressed by the recombinant baculovirus in insect cells is antigenically similar to the wild protein and it may be useful for different medical applications, from improved diagnosis of the disease to source of antigens for the development of a subunit vaccine.</p

On the influence of symbols and myths in the responsibility ascription problem in roboethics - A roboticist’s perspective

Because of the increasing developments of humanoid robots, humans and robots are going to interact more and more often in the near future. Thus, the need for a well-defined ethical framework in which these interactions will take place is very acute. In this article, we will show why responsibility ascription is a key concept to understand today’s and tomorrow’s ethical issues related to human-robot interactions. By analyzing how the myths surrounding the figure of the robot in western societies have been built through centuries, we will be able to demonstrate that the question of responsibility ascription is biased in the sense that it assigns to autonomous robots a role that should be devoted to human