Influence of ischemia on the discharge rate in motor units during a sustained submaximal contraction

Motor unit discharge patterns were observed under ischemic and non-ischemic conditions in the tibialis anterior during two sessions approximately 48 hours apart. Ten subjects completed three 5-second maximum voluntary contractions [MVCs) followed by a prolonged, submaximal, isometric contraction to induce fatigue, and three additional MVCs. This fatigue trial was completed under both ischemic and non-ischemic conditions. For the ischemic condition, a pressure cuff was placed above the knee, inflated to 180 mmHg, and arterial occlusion verified via Doppler ultrasound. During the fatigue task, a constant force of 20% MVC was maintained until endurance time. Single motor unit activity was recorded with intramuscular fine wire electrodes. Endurance time during the ischemic fatigue task (3.71 ± 0.58 min) was significantly less than the non-ischemic fatigue task (9.11 ± 0.56 min). Both tasks showed a significant decline in motor unit discharge rate. There was greater variability in the discharge rate during ischemic compared to non-ischemic conditions. Time to minimum discharge rate was greater during ischemic conditions. Overall, ischemic conditions resulted in decreased endurance time, greater rate of decline in discharge rate, and greater variability in discharge rate of motor units.Kinesiology and Health Educatio

Stably Extending Two-Dimensional Bipedal Walking to Three Dimensions

In this paper we develop a feedback control law that results in stable walking gaits on flat ground for a three-dimensional bipedal robotic walker given stable walking gaits for a two-dimensional bipedal robotic walker. This is achieved by combining disparate techniques that have been employed in the bipedal robotic community: controlled symmetries, geometric reduction and hybrid zero dynamics. Controlled symmetries are utilized to obtain stable walking gaits for a two-dimensional bipedal robot walking on flat ground. These are related to walking gaits for a three-dimensional (hipless) bipedal robot through the use of geometric reduction. Finally, these walking gaits in three dimensions are made stable through the use of hybrid zero dynamics

Stable Marriage with Ties and Bounded Length Preference Lists

We consider variants of the classical stable marriage problem in which preference lists may contain ties, and may be of bounded length. Such restrictions arise naturally in practical applications, such as centralised matching schemes that assign graduating medical students to their first hospital posts. In such a setting, weak stability is the most common solution concept, and it is known that weakly stable matchings can have different sizes. This motivates the problem of finding a maximum cardinality weakly stable matching, which is known to be NP-hard in general. We show that this problem is solvable in polynomial time if each man's list is of length at most 2 (even for women's lists that are of unbounded length). However if each man's list is of length at most 3, we show that the problem becomes NP-hard and not approximable within some d > 1, even if each woman's list is of length at most 4

The why's the limit: curtailing self-enhancement with explanatory introspection

Self-enhancement is linked to psychological gains (e.g., subjective well-being, persistence in adversity) but also to intrapersonal and interpersonal costs (e.g., excessive risk taking, antisocial behavior). Thus, constraints on self-enhancement may sometimes afford intrapersonal and interpersonal advantages. We tested whether explanatory introspection (i.e., generating reasons for why one might or might not possess personality traits) constitutes one such constraint. Experiment 1 demonstrated that explanatory introspection curtails self-enhancement. Experiment 2 clarified that the underlying mechanism must (a) involve explanatory questioning rather than descriptive imagining, (b) invoke the self rather than another person, and (c) feature written expression rather than unaided contemplation. Finally, Experiment 3 obtained evidence that an increase in uncertainty about oneself mediates the effect

Multi-Scale Modeling of the Innate Immune System: A Dynamic Investigation into Pathogenic Detection

Having a well-functioning immune system can mean the difference between a mild ailment and a life-threatening infection; however, predicting how a disease will progress has proven to be a significant challenge. The dynamics driving the immune system are governed by a complex web of cell types, signaling proteins, and regulatory genes that have to strike a balance between disease elimination and rampant inflammation. An insufficient immune response will induce a prolonged disease state, but an excessive response will cause unnecessary cell dead and extensive tissue damage. This balance is usually self-regulated, but medical intervention is often necessary to correct imbalances. Unfortunately, these therapies are imperfect and accompanied by mild to debilitating side-effects caused by off-target effects. By developing a detailed understanding of the immune response, the goal of this dissertation is to predict how the immune system will respond to infection and determine how new potential therapies could overcome these threats. Computational modeling provides an opportunity to synthesize current immunological observations and predict response outcomes to pathogenic infections. When coupled with experimental data, these models can simulate signaling pathway dynamics that drive the immune response, incorporate regulatory feedback mechanisms, and model inherent biological noise. Taken together, computational modeling can explain emergent behavior that cannot be determined from experiment alone. This dissertation will unitize two computational modeling techniques: ordinary differential equations (ODEs) and agent-based modeling (ABMs). Ultimately, they are combined in a novel way to model cellular immune responses across multiple length scales, creating a more accurate representation of the pathogenic response. TLR4 and cGAS signaling are prominent in a number of diseases and dysregulations including---but not limited to---autoimmunity, cancer, HIV, HSV, tuberculosis, and sepsis. These two signaling pathways are so prevalent because they are activated extremely early and help drive the downstream immune signaling. Modeling how cells dynamically regulate these pathways is critical for understanding how diseases circumvent feedback mechanisms and how new therapies can restore immune function to combat disease progression. By using ODE and ABM techniques, these studies aim to incrementally expand our knowledge of innate immune signaling and understand how feedback mechanisms control disease severity

Migration Consequences of Welfare Reform

In this paper, we investigate whether or not recent state and federal changes in welfare policy -- the imposition of time-limited benefits, the use of financial sanctions for non-compliance, and the setting of strict work eligibility rules -- affect the migration of low-educated unmarried women. Estimates of welfare's effect on migration reveal that welfare policy does indeed affect migration. Recent changes in policy that have made public assistance a less attractive alternative are associated with greater migration among low-educated unmarried women. Welfare reform has motivated low-educated women to move greater distances more frequently, and to combine such moves with employment. Estimates also indicate that welfare reform is associated with more local (i.e., within county) changes in residential location that are associated with employment, although estimates of this effect were not robust to estimation method. The close link between residential moves and employment in the post-reform period is consistent with the idea that welfare reform has motivated people to move for economic reasons such as better employment opportunities. This evidence suggests that the traditional way of thinking about the effect of welfare on migration -- as a strategic move to obtain higher benefits -- is inadequate.

A geometric approach to three-dimensional hipped bipedal robotic walking

This paper presents a control law that results in stable walking for a three-dimensional bipedal robot with a hip. To obtain this control law, we utilize techniques from geometric reduction, and specifically a variant of Routhian reduction termed functional Routhian reduction, to effectively decouple the dynamics of the three-dimensional biped into its sagittal and lateral components. Motivated by the decoupling afforded by functional Routhian reduction, the control law we present is obtained by combining three separate control laws: the first shapes the potential energy of the sagittal dynamics of the biped to obtain stable walking gaits when it is constrained to the sagittal plane, the second shapes the total energy of the walker so that functional Routhian reduction can be applied to decoupling the dynamics of the walker for certain initial conditions, and the third utilizes an output zeroing controller to stabilize to the surface defining these initial conditions. We numerically verify that this method results in stable walking, and we discuss certain attributes of this walking gait