Variational Methods for Control and Design of Bipedal Robot Models

This thesis investigates nonsmooth mechanics using variational methods for the modeling, control, and design of bipedal robots. The theory of Lagrangian mechanics is extended to capture a variety of nonsmooth collision behaviors in rigid body systems. Notably, a variational impact model is presented for the transition of constraints behavior that describes a biped switching stance feet at the conclusion of a step. Next, discretizations of the impact mechanics are developed using the framework of variational discrete mechanics. The resulting variational collision integrators are consistent with the continuous time theory and have an underlying symplectic structure. In addition to their role as integrators, the discrete equations of motion capturing nonsmooth dynamics enable a direct method for trajectory optimization. Upon specifically defining the optimal control problem for nonsmooth systems, examples demonstrate this optimization method in the task of determining periodic gaits for two rigid body biped models. An additional effort is made to optimize bipedal walking motions through modifications in system design. A method for determining optimal designs using a combination of trajectory optimization methods and surrogate function optimization methods is defined. This method is demonstrated in the task of determining knee joint placement in a given biped model.</p

Geometry of unsteady fluid transport during fluid–structure interactions

We describe the application of tools from dynamical systems to define and quantify the unsteady fluid transport that occurs during fluid–structure interactions and in unsteady recirculating flows. The properties of Lagrangian coherent structures (LCS) are used to enable analysis of flows with arbitrary time-dependence, thereby extending previous analytical results for steady and time-periodic flows. The LCS kinematics are used to formulate a unique, physically motivated definition for fluid exchange surfaces and transport lobes in the flow. The methods are applied to numerical simulations of two-dimensional flow past a circular cylinder at a Reynolds number of 200; and to measurements of a freely swimming organism, the Aurelia aurita jellyfish. The former flow provides a canonical system in which to compare the present geometrical analysis with classical, Eulerian (e.g. vortex shedding) perspectives of fluid–structure interactions. The latter flow is used to deduce the physical coupling that exists between mass and momentum transport during self-propulsion. In both cases, the present methods reveal a well-defined, unsteady recirculation zone that is not apparent in the corresponding velocity or vorticity fields. Transport rates between the ambient flow and the recirculation zone are computed for both flows. Comparison of fluid transport geometry for the cylinder crossflow and the self-propelled swimmer within the context of existing theory for two-dimensional lobe dynamics enables qualitative localization of flow three-dimensionality based on the planar measurements. Benefits and limitations of the implemented methods are discussed, and some potential applications for flow control, unsteady propulsion, and biological fluid dynamics are proposed

Variational Collision Integrators and Optimal Control

This paper presents a methodology for generating locally optimal control policies for mechanical systems that undergo collisions at point contacts. Principles of nonsmooth mechanics for rigid bodies are used in both continuous and discrete time, and provide impact models for a variety of collision behaviors. The discrete Euler-Lagrange (DEL) equations that follow from the discrete time analyses yield variational integration schemes for the dierent impact models. These DEL equations play a pivotal role in the method of Discrete Mechanics and Optimal Control (DMOC), which generates locally optimal control policies as the solution to equality constrained nonlinear optimization problems. The DMOC method is demonstrated on a 4-link planar walking robot model, generating locally optimal periodic walking gaits

Determinants of HPV vaccine awareness and healthcare providers' discussion of HPV vaccine among females

Two human papillomavirus (HPV) vaccines are available and can prevent 98% of HPV 16 and 18 infections. This study aimed to explore determinants of 1) HPV vaccine awareness among a cohort of low-income women participating in a cancer prevention program in Central Texas and compare them to United States residents; 2) determinants of healthcare providers' discussion of HPV vaccine among female residents of the United States. Bivariate and multivariable analysis of HPV vaccine awareness using survey data (n = 359) collected between 2014 and 2016 in Central Texas, and the Health Information and Nutrition Survey (HINTS) data which is a nationally representative dataset (unweighted n = 1214) collected in 2013 were conducted. Bivariate and multivariable regression analyses of healthcare providers' discussion of the HPV vaccine using the HINTS survey data were also conducted. Compared to non-Hispanic Whites, there was a decreased likelihood of HPV vaccine awareness among non-Hispanic Blacks (OR = 0.50; 95% CI = 0.28–0.90) and Hispanics (OR = 0.55; 95% CI = 0.30–0.99) in the grant funded program, as well as non-Hispanic Blacks (OR = 0.28; 95% CI = 0.14–0.58) and Hispanics (OR = 0.22; 95% CI = 0.12–0.41) in the HINTS data. There was also a decreased likelihood of healthcare providers discussing the HPV vaccine with respondents who were 35–49 years (OR = 0.50; 95% CI = 0.30–0.84), 50–64 years (OR = 0.26; 95% CI = 0.14–0.49) or ≥65 years compared to those who were 18–34 years among the HINTS data respondents. Interventions to increase HPV awareness among non-Hispanic Blacks and Hispanics, as well as encourage healthcare providers' discussion of the HPV vaccination during patient encounters regardless of the patient's age are needed

From Attitudes to Social Representations in Endangered Language Research: Towards an Interactional Framework

International audienceMany language endangerment researchers maintain that language is fundamentally linked to an identifiable ethnic community and identity. However, there is a dearth of in-depth sociolinguistic studies on speakers' own views of these links. Studying speakers' views is essential to understanding why a language is endangered. In this paper, I present a case study in South India focusing on speakers of an endangered language and their views, or social representations, of their linguistic and social reality. Through the use of discursive and conversation analysis techniques, I examine the way in which the participants in an interview jointly construct and position themselves in relation to essentialising social representations similar to those employed by many endangered language researchers. Speakers in the extract discussed use discursive strategies mainly to distance themselves from essentialising views of their linguistic and social reality, though the analysis also shows the dynamic and co-constructed nature of the social representations