Informal social support plays a crucial role in post-disaster recovery, but are there systematic patterns of inequality in individuals' mobilization of social support? This study examines the predictors of both the network structure and substantive dimensions of social support in order to understand how different people experience different forms of support. Survey data were collected from 390 tornado-affected households in the US state of Indiana. Personal network analysis and multilevel analysis of dyadic ties show that beyond disaster-specific contexts such as household damage and evacuation status, individual and social status factors played a role. In general, older females and those with low educational level reported receiving support from denser and longer-known ties centered around kin. Dimensions of social support were differentiated by both receivers' and providers' gender, with females having a larger number of multiplex ties (i.e., multiple support types from a single alter) and exchanging emotional support, in contrast to males providing tangible support and information. In addition, people known through social relationships were key links to outside community contacts. Theoretical and practical implications regarding social support in post-disaster recovery are discussed.

The component of ground reaction force (GRF) acting perpendicular to the leg in the sagittal plane during human locomotion (acting in a rotary direction) has not been systematically investigated and is not well understood. In this paper, we investigate this rotary component of the GRF of 11 human subjects (mean age ± s.d.: 26.6 ± 2.9 years) while walking and speed walking on a treadmill, along with eight human subjects (mean age ± s.d.: 26.3 ± 3.1) running on a treadmill. The GRF on both legs was measured, along with estimates of the subject's mass centre and the centre of pressure of each foot to yield total leg lengths and leg angle. Across all steady walking and running speeds, we find that the rotary component of the GRF has significant magnitude (peak values from 5% to 38% of body weight, from slow walking to moderate running, respectively) and implies leg propulsion of the mass centre in the rotary direction. Furthermore, peak rotary force magnitude over stance increases with locomotion speed for both walking and running (p < 0.05), and the time-averaged (mean) rotary force shows a slight increase with walking speed (though the mean force trend is uncertain for running). Also, an estimate of average power input from the rotary force of the leg acting at the mass centre shows moderate and strong positive correlation with locomotion speed for running and walking respectively (p < 0.05). This study also shows that the rotary force acts differently in walking versus running: rotary force is predominantly positive during running, but during walking it exhibits both positive and negative phases with net positive force found over the whole stride.

The relative leg stiffness of most running animals falls in a small range between 7 and 27. Here we present a theoretical study of an established running model, an actuated Spring Loaded Inverted Pendulum model, to determine if the energetic cost and stability of running might be co-optimized over this range of leg stiffness values. The energetic cost of the model is quantified as the energy spent to move a unit mass a unit distance. The stability of the model is based on the system response to perturbations with respect to periodic locomotion solutions, and uses the linearized dynamics of Poincaré return maps and the resulting maximum eigenvalue and singular value decomposition in order to analyze asymptotic stability and the overall system response to perturbations, respectively. We find that there exists a tradeoff between stability and energetic cost in the model with respect to variation in forcing (actuation) level: For a given leg stiffness, the energetic cost tends to be more optimal with smaller forcing, and the opposite for stability. We find that intermediate levels of forcing can achieve near asymptotic stability or complete asymptotic stability while remaining small enough to yield a relatively low energetic cost consistent with human-like values. We demonstrate that this outcome can be achieved in the model with a simple optimization function that balances stability and energetic cost. We then investigate the stability and energetic cost when both leg stiffness and forcing are varied. Overall, the analysis shows that leg stiffness values in or near the biological range offers a good chance of simultaneously achieving both reasonable energetic cost and stability in the model. The results of this study suggest that stability and energetic cost may be interacting factors that have a combined influence on the effective leg stiffness and actuation (forcing) used by running animals.

The factors that explain the speed of recovery after disaster remain contested. While many have argued that physical infrastructure, social capital, and disaster damage influence the arc of recovery, empirical studies that test these various factors within a unified modeling framework are few. We conducted a mail survey to collect data on household recovery in four small towns in southern Indiana that were hit by deadly tornadoes in March 2012. The recovery effort is ongoing; while many of the homes, businesses, and community facilities were rebuilt in 2013, some are still under construction. We investigate how households in these communities are recovering from damage that they experienced and the role of social capital, personal networks, and assistance from emergency responders on the overall recovery experience. We used an ordered probit modeling framework to test the combined as well as relative effects of (a) damage to physical infrastructures (houses, vehicles, etc.); (b) recovery assistance from emergency responders (FEMA) as well as friends and neighbors; (c) personal network characteristics (size, network density, proximity, length of relationship); (d) social capital (civic engagement, contact with neighbors, trust); and (e) household characteristics. Results show that while households with higher levels of damage experienced slower recovery, those with recovery assistance from neighbors, stronger personal networks, and higher levels of social capital experienced faster recovery. The insights gained in this study will enable emergency managers and disaster response personnel to implement targeted strategies in facilitating post-disaster recovery and community resilience.

This chapter provides an overview of simple conceptual models of locomotion at the scale of whole body movements. First, conceptual models of locomotion are introduced along with a few key empirical observations that support the construction of simple conceptual models. Next, a theoretical perspective is offered based on “templates and anchors” theory, where templates are related to simple conceptual models. Commonly used models of legged locomotion are then presented: The Spring-Loaded Inverted Pendulum (SLIP) model of running and the Inverted Pendulum (IP) model of walking. Legged locomotion is next presented in terms of oscillatory behavior and oscillatory-based analysis. Finally, readers are taken on a tour of a “model zoo” featuring many extensions of the SLIP and IP models to more complex and realistic models.

An educational incubator in Purdue University's Polytechnic Institute has been experimenting with highly integrated methods to facilitate, assess, and evaluate student learning. Comprised of transdisciplinary faculty and students, one of the basic covenants is to intentionally and repeatedly balance Humanities and STEM concepts by way of open-ended problems affecting humanity and the planet. The learning experience environment tries to integrate faculty and students from widely different disciplines in scenarios where cognitive and metacognitive development is encouraged and explored. This special session will engage attendees in examples of activities that can help students become self-aware of the power of music on their physiology and imagination while also integrating problem-solving and other STEM related concepts. Participants will take away ideas and techniques that they can add to their own palette for fostering integrated learning and metacognitive development. This session aligns with FIE's focus on innovations in classroom techniques.

This chapter provides an overview of simple conceptual models of locomotion at the scale of whole body movements. First, conceptual models of locomotion are introduced along with a few key empirical observations that support the construction of simple conceptual models. Next, a theoretical perspective is offered based on “templates and anchors” theory, where templates are related to simple conceptual models. Commonly used models of legged locomotion are then presented: The Spring-Loaded Inverted Pendulum (SLIP) model of running and the Inverted Pendulum (IP) model of walking. Legged locomotion is next presented in terms of oscillatory behavior and oscillatory-based analysis. Finally, readers are taken on a tour of a “model zoo” featuring many extensions of the SLIP and IP models to more complex and realistic models.

Gait initiation is an integral and complex part of human locomotion. In this paper, we present a novel compliant-leg model-based approach to understanding the key phases of initiation, the nature of the effective forces involved in initiation, and the importance of the anticipatory postural adjustments (APAs). The results demonstrate that in the presence of APAs, we observe a change in the characteristic of forcing required for initiation, and the energetic cost of gait initiation is also reduced by approximately 58%. APAs also result in biologically relevant leg landing angles and trajectories of motion. Furthermore, we find that a sublinear functional relationship with the velocity error from steady state predicts the required force, consistent with an open loop control law basis for gait initiation.

One of the first artifacts produced by a massive multi-year education transformation effort has been the launching of a one-of-a-kind program focused on transdisciplinary studies that goes well beyond conventional notions of disciplines. One of the main thrusts of the transformation was to intentionally and repeatedly integrate STEM and Humanities learning and outcome assessment of skills and abilities needed for the 21 st century. The challenges of creating and sustaining systemic shifts in culture and operational systems at a large campus have been many, and sometimes controversial. This special session will provide attendees with information and active engagement in a dialog about the motivations, design, and implementation of significant systemic change. Attendees will take away insights not only from what is presented, but also active engagement in transdisciplinary conversations. This session aligns with FIE's focus on innovations in program design and classroom techniques.

Here, we seek to determine how compliantly suspended loads could affect the dynamic stability of legged locomotion. We theoretically model the dynamic stability of a human carrying a load using a coupled spring-mass-damper model and an actuated spring-loaded inverted pendulum model, as these models have demonstrated the ability to correctly predict other aspects of locomotion with a load in prior work, such as body forces and energetic cost. We report that minimizing the load suspension natural frequency and damping ratio significantly reduces the stability of the load mass but may slightly improve the body stability of locomotion when compared to a rigidly attached load. These results imply that a highly-compliant load suspension could help stabilize body motion during human, animal, or robot load carriage, but at the cost of a more awkward (less stable) load.

Here, we introduce and analyze a novel approximation of the well-established and widely used spring-loaded inverted pendulum (SLIP) model of legged locomotion, which has made several validated predictions of the center-of-mass (CoM) or point-mass motions of animal and robot running. Due to nonlinear stance equations in the existing SLIP model, many linear-based systems theories, analytical tools, and corresponding control strategies cannot be readily applied. In order to provide a significant simplification in the use and analysis of the SLIP model of locomotion, here we develop a novel piecewise-linear, time-invariant approximation. We show that a piecewise-linear system, with the only nonlinearity due to the switching event between stance and flight phases, can predict all the bifurcation features of the established nonlinear SLIP model over the entire three-dimensional model parameter space. Rather than precisely fitting only one particular solution, this approximation is made to quantitatively approximate the entire solution space of the SLIP model and capture all key aspects of solution bifurcation behavior and parametric sensitivity of the original SLIP model. Further, we provide an entirely closed-form solution for the stance trajectory as well as the system states at the end of stance, in terms of common functions that are easy to code and compute. Overall, the closed-form solution is found to be significantly faster than numerical integration when implemented using both matlab and c++. We also provide a closed-form analytical stride map, which is a Poincaré return section from touchdown (TD) to next TD event. This is the simplest closed-form approximate stride mapping yet developed for the SLIP model, enabling ease of analysis and numerical coding, and reducing computational time. The approximate piecewise-linear SLIP model presented here is a significant simplification over previous SLIP-based models and could enable more rapid development of legged locomotion theory, numerical simulations, and controllers.

The mechanisms underlying the metabolic cost of running, and legged locomotion in general, remain to be well understood. Prior experimental studies show that the metabolic cost of human running correlates well with the vertical force generated to support body weight, the mechanical work done, and changes in the effective leg stiffness. Further, previous work shows that the metabolic cost of running decreases with decreasing body weight, increases with increasing body weight and mass, and does not significantly change with changing body mass alone. In the present study, we seek to uncover the basic mechanism underlying this existing experimental data. We find that an actuated spring-mass mechanism representing the effective mechanics of human running provides a mechanistic explanation for the previously reported changes in the metabolic cost of human running if the dimensionless relative leg stiffness (effective stiffness normalized by body weight and leg length) is regulated to be constant. The model presented in this paper provides a mechanical explanation for the changes in metabolic cost due to changing body weight and mass which have been previously measured experimentally and highlights the importance of active leg stiffness regulation during human running.

The IEEE Robotics and Automation Society (RAS) Technical Committee (TC) on Biorobotics was formed with the goal of providing a forum and dissemination mechanism for the interaction between biological and artificial (autonomous or semiautonomous) systems and to present biology as a learning tool for novel engineering paradigms.

Despite the neuromechanical complexity and wide diversity of running animals, most run with a center-of-mass motion that is similar to a simple mass bouncing on a spring. Further, when animals׳ effective leg stiffness is measured and normalized for size and weight, the resulting relative leg stiffness that most animals prefer lies in a narrow range between 7 and 27. Understanding why this nearly universal preference exists could shed light on how whole animal behaviors are organized. Here we show that the biologically preferred values of relative leg stiffness coincide with a theoretical minimal energetic cost of locomotion. This result strongly implies that animals select and regulate leg stiffness in order to reduce the energy required to move, thus providing animals an energetic advantage. This result also helps explain how high level control targets such as energy efficiency might influence overall physiological parameters and the underlying neuromechanics that produce it. Overall, the theory presented here provides an explanation for the existence of a nearly universal preferred leg stiffness. Also, the results of this work are beneficial for understanding the principles underlying human and animal locomotion, as well as for the development of prosthetic, orthotic and robotic devices.

Despite the neuromechanical complexity underlying animal locomotion, the steady-state center-of-mass motions and ground reaction forces of animal running can be predicted by simple spring-mass models such as the canonical spring-loaded inverted pendulum (SLIP) model. Such SLIP models have been useful for the fields of biomechanics and robotics in part because ground reaction forces are commonly measured and readily available for comparing with model predictions. To better predict the stability of running, beyond the canonical conservative SLIP model, more recent extensions have been proposed and investigated with hip actuation and linear leg damping (e.g., hip-actuated SLIP). So far, these attempts have gained improved prediction of the stability of locomotion but have led to a loss of the ability to accurately predict ground reaction forces. Unfortunately, the linear damping utilized in current models leads to an unrealistic prediction of damping force and ground reaction force with a large nonzero magnitude at touchdown (TD). Here, we develop a leg damping model that is bilinear in leg length and velocity in order to yield improved damping force and ground reaction force prediction. We compare the running ground reaction forces, small and large perturbation stability, parameter sensitivity, and energetic cost resulting from both the linear and bilinear damping models. We found that bilinear damping helps to produce more realistic, smooth vertical ground reaction forces, thus fixing the current problem with the linear damping model. Despite large changes in the damping force and power loss profile during the stance phase, the overall dynamics and energetics on a stride-to-stride basis of the two models are largely the same, implying that the integrated effect of damping over a stride is what matters most to the stability and energetics of running. Overall, this new model, an actuated SLIP model with bilinear damping, can provide significantly improved prediction of ground reaction forces as well as stability and energetics of locomotion.