1,396 research outputs found
Hot new directions for quasi-Monte Carlo research in step with applications
This article provides an overview of some interfaces between the theory of
quasi-Monte Carlo (QMC) methods and applications. We summarize three QMC
theoretical settings: first order QMC methods in the unit cube and in
, and higher order QMC methods in the unit cube. One important
feature is that their error bounds can be independent of the dimension
under appropriate conditions on the function spaces. Another important feature
is that good parameters for these QMC methods can be obtained by fast efficient
algorithms even when is large. We outline three different applications and
explain how they can tap into the different QMC theory. We also discuss three
cost saving strategies that can be combined with QMC in these applications.
Many of these recent QMC theory and methods are developed not in isolation, but
in close connection with applications
Pathways From Family Disadvantage via Abusive Parenting and Caregiver Mental Health to Adolescent Health Risks in South Africa
PURPOSE:
Adolescent health is a major concern in low- and middle-income countries, but little is known about its predictors. Family disadvantage and abusive parenting may be important factors associated with adolescent psychological, behavioral, and physical health outcomes. This study, based in South Africa, aimed to develop an empirically based theoretical model of relationships between family factors such as deprivation, illness, parenting, and adolescent health outcomes.
METHODS:
Cross-sectional data were collected in 2009–2010 from 2,477 adolescents (aged 10–17) and their caregivers using stratified random sampling in KwaZulu-Natal, South Africa. Participants reported on sociodemographics, psychological symptoms, parenting, and physical health. Multivariate regressions were conducted, confirmatory factor analysis employed to identify measurement models, and a structural equation model developed.
RESULTS:
The final model demonstrated that family disadvantage (caregiver AIDS illness and poverty) was associated with increased abusive parenting. Abusive parenting was in turn associated with higher adolescent health risks. Additionally, family disadvantage was directly associated with caregiver mental health distress which increased adolescent health risks. There was no direct effect of family disadvantage on adolescent health risks but indirect effects through caregiver mental health distress and abusive parenting were found.
CONCLUSIONS:
Reducing family disadvantage and abusive parenting is essential in improving adolescent health in South Africa. Combination interventions could include poverty and violence reduction, access to health care, mental health services for caregivers and adolescents, and positive parenting support. Such combination packages can improve caregiver and child outcomes by reducing disadvantage and mitigating negative pathways from disadvantage among highly vulnerable families
Stepping onto the unknown: reflexes of the foot and ankle while stepping with perturbed perceptions of terrain
This is the author accepted manuscript. The final version is available from the Royal Society via e the DOI in this recordData availability: The data from this study and the code to generate the figures and statistics are publically available at
10.6084/m9.figshare.12986223Unanticipated variations in terrain can destabilize the body. The foot is the primary interface with
the ground and we know that cutaneous reflexes provide important sensory feedback. However,
little is known about the contribution of stretch reflexes from the muscles within the foot to upright
stability. We used intramuscular electromyography measurements of the foot muscles flexor
digitorum brevis (FDB) and abductor hallucis (AH) to show for the first time how their short latency
stretch reflex response (SLR) may play an important role in responding to stepping perturbations.
The SLR of FDB and AH was highest for downwards steps and lowest for upwards steps, with the
response amplitude for level and compliant steps in between. When the type of terrain was
unknown or unexpected to the participant, the SLR of AH and the ankle muscle soleus tended to
decrease. We found significant relationships between the contact kinematics and forces of the leg
and the SLR, but a person’s expectation still had significant effects even after accounting for these
relationships. Motor control models of short latency body stabilization should not only include local
muscle dynamics, but also predictions of terrain based on higher-level information such as from
vision or memory
Intermittent control models of human standing: similarities and differences
Two architectures of intermittent control are compared and contrasted in the context of the single inverted pendulum model often used for describing standing in humans. The architectures are similar insofar as they use periods of open-loop control punctuated by switching events when crossing a switching surface to keep the system state trajectories close to trajectories leading to equilibrium. The architectures differ in two significant ways. Firstly, in one case, the open-loop control trajectory is generated by a system-matched hold, and in the other case, the open-loop control signal is zero. Secondly, prediction is used in one case but not the other. The former difference is examined in this paper. The zero control alternative leads to periodic oscillations associated with limit cycles; whereas the system-matched control alternative gives trajectories (including homoclinic orbits) which contain the equilibrium point and do not have oscillatory behaviour. Despite this difference in behaviour, it is further shown that behaviour can appear similar when either the system is perturbed by additive noise or the system-matched trajectory generation is perturbed. The purpose of the research is to come to a common approach for understanding the theoretical properties of the two alternatives with the twin aims of choosing which provides the best explanation of current experimental data (which may not, by itself, distinguish beween the two alternatives) and suggesting future experiments to distinguish between the two alternatives
Do horizontal propulsive forces influence the nonlinear structure of locomotion?
<p>Abstract</p> <p>Background</p> <p>Several investigations have suggested that changes in the nonlinear gait dynamics are related to the neural control of locomotion. However, no investigations have provided insight on how neural control of the locomotive pattern may be directly reflected in changes in the nonlinear gait dynamics. Our simulations with a passive dynamic walking model predicted that toe-off impulses that assist the forward motion of the center of mass influence the nonlinear gait dynamics. Here we tested this prediction in humans as they walked on the treadmill while the forward progression of the center of mass was assisted by a custom built mechanical horizontal actuator.</p> <p>Methods</p> <p>Nineteen participants walked for two minutes on a motorized treadmill as a horizontal actuator assisted the forward translation of the center of mass during the stance phase. All subjects walked at a self-select speed that had a medium-high velocity. The actuator provided assistive forces equal to 0, 3, 6 and 9 percent of the participant's body weight. The largest Lyapunov exponent, which measures the nonlinear structure, was calculated for the hip, knee and ankle joint time series. A repeated measures one-way analysis of variance with a t-test post hoc was used to determine significant differences in the nonlinear gait dynamics.</p> <p>Results</p> <p>The magnitude of the largest Lyapunov exponent systematically increased as the percent assistance provided by the mechanical actuator was increased.</p> <p>Conclusion</p> <p>These results support our model's prediction that control of the forward progression of the center of mass influences the nonlinear gait dynamics. The inability to control the forward progression of the center of mass during the stance phase may be the reason the nonlinear gait dynamics are altered in pathological populations. However, these conclusions need to be further explored at a range of walking speeds.</p
Access and utilisation of primary health care services comparing urban and rural areas of Riyadh Providence, Kingdom of Saudi Arabia
The Kingdom of Saudi Arabia (KSA) has seen an increase in chronic diseases. International evidence suggests that early intervention is the best approach to reduce the burden of chronic disease. However, the limited research available suggests that health care access remains unequal, with rural populations having the poorest access to and utilisation of primary health care centres and, consequently, the poorest health outcomes. This study aimed to examine the factors influencing the access to and utilisation of primary health care centres in urban and rural areas of Riyadh province of the KSA
Neurospora from natural populations: Population genomics insights into the Life history of a model microbial Eukaryote
The ascomycete filamentous fungus Neurospora crassa played a historic role in experimental biology and became a model system for genetic research. Stimulated by a systematic effort to collect wild strains initiated by Stanford geneticist David Perkins, the genus Neurospora has also become a basic model for the study of evolutionary processes, speciation, and population biology. In this chapter, we will first trace the history that brought Neurospora into the era of population genomics. We will then cover the major contributions of population genomic investigations using Neurospora to our understanding of microbial biogeography and speciation, and review recent work using population genomics and genome-wide association mapping that illustrates the unique potential of Neurospora as a model for identifying the genetic basis of (potentially adaptive) phenotypes in filamentous fungi. The advent of population genomics has contributed to firmly establish Neurospora as a complete model system and we hope our review will entice biologists to include Neurospora in their research
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