Coordination of Mathematics and Physical Resources by Physics Graduate Students

We investigate the dynamics of how graduate students coordinate their mathematics and physics knowledge within the context of solving a homework problem for a plasma physics survey course. Students were asked to obtain the complex dielectric function for a plasma with a specified distribution function and find the roots of that expression. While all the 16 participating students obtained the dielectric function correctly in one of two equivalent expressions, roughly half of them (7 of 16) failed to compute the roots correctly. All seven took the same initial step that led them to the incorrect answer. We note a perfect correlation between the specific expression of dielectric function obtained and the student's success in solving for the roots. We analyze student responses in terms of a resources framework and suggest routes for future research.Comment: 4 page

The Dynamics of Students' Behaviors and Reasoning during Collaborative Physics Tutorial Sessions

We investigate the dynamics of student behaviors (posture, gesture, vocal register, visual focus) and the substance of their reasoning during collaborative work on inquiry-based physics tutorials. Scherr has characterized student activity during tutorials as observable clusters of behaviors separated by sharp transitions, and has argued that these behavioral modes reflect students' epistemological framing of what they are doing, i.e., their sense of what is taking place with respect to knowledge. We analyze students' verbal reasoning during several tutorial sessions using the framework of Russ, and find a strong correlation between certain behavioral modes and the scientific quality of students' explanations. We suggest that this is due to a dynamic coupling of how students behave, how they frame an activity, and how they reason during that activity. This analysis supports the earlier claims of a dynamic between behavior and epistemology. We discuss implications for research and instruction.Comment: 4 pages, PERC 200

Early initiation of antiretroviral therapy and associated reduction in mortality, morbidity and defaulting in a nurse-managed, community cohort in Lesotho.

INTRODUCTION: The latest WHO guidelines recommend initiating antiretroviral therapy (ART) at CD4 cell counts less than 350 cells/μl. However, donors and national governments are reluctant to support implementation owing to uncertainty regarding feasibility and relative benefit. Lesotho has supported earlier initiation since 2008. We assessed outcomes comparing early (CD4 cell counts >200 cells/μl) and late (CD4 cell counts ≤200 cells/μl) initiation. METHODS: We describe survival probability among patients initiating ART at CD4 cell counts 200 or less and more than 200 cells/μl and assess associations between baseline CD4 cell counts and mortality, morbidity, loss to follow-up and hospitalization using Cox regression adjusting for confounders identified a priori. RESULTS: Our analysis included 1177 patients; median age was 38 years and the majority (67%) were women. Median time on ART for the overall cohort was 506 days (interquartile range 396-608). Five hundred and thirty eight patients initiated ART at a CD4 cell count 200 cells/μl or less (interquartile range 54-160) and 639 patients initiated at CD4 cell count more than 200 cells/μl (interquartile range 238-321). In multivariate analysis, we found that patients initiating at CD4 cell count more than 200 cells/μl were 68% less likely to die (adjusted hazard ratio 0.32, 95% confidence interval 0.20-0.50), and 39% less likely to be lost to follow-up (adjusted hazard ratio 0.61, 95% confidence interval 0.43-0.87). Initiating ART at CD4 cell count more than 200 cells/μl was also associated with a 27% reduction in the rate of incident morbidity (adjusted hazard ratio 0.73, 95% confidence interval 0.65-0.82) and a 63% decreased rate of hospitalization (adjusted hazard ratio 0.37, 95% confidence interval 0.19-0.73). CONCLUSION: Earlier initiation is feasible in a low resource, high HIV prevalence setting, and provides important benefits in terms of reduced mortality, morbidity, retention and hospitalization. Donors should fully support the implementation of the latest WHO recommendations

Global-scale comparisons of human land use: developing shared terminology for land-use practices for global change

Although archaeological data are needed to understand the impacts of past human land use on the Earth system, synthesis is hampered by a lack of consistent categories. We develop hierarchical and scalable land-use classifications for use across the globe

Effect of neglecting passive spinal structures : a quantitative investigation using the forward-dynamics and inverse-dynamics musculoskeletal approach

Inverse-dynamics (ID) analysis is an approach widely used for studying spine biomechanics and the estimation of muscle forces. Despite the increasing structural complexity of spine models, ID analysis results substantially rely on accurate kinematic data that most of the current technologies are not capable to provide. For this reason, the model complexity is drastically reduced by assuming three degrees of freedom spherical joints and generic kinematic coupling constraints. Moreover, the majority of current ID spine models neglect the contribution of passive structures. The aim of this ID analysis study was to determine the impact of modelled passive structures (i.e., ligaments and intervertebral discs) on remaining joint forces and torques that muscles must balance in the functional spinal unit. For this purpose, an existing generic spine model developed for the use in the demoa software environment was transferred into the musculoskeletal modelling platform OpenSim. The thoracolumbar spine model previously used in forward-dynamics (FD) simulations provided a full kinematic description of a flexion-extension movement. By using the obtained in silico kinematics, ID analysis was performed. The individual contribution of passive elements to the generalised net joint forces and torques was evaluated in a step-wise approach increasing the model complexity by adding individual biological structures of the spine. The implementation of intervertebral discs and ligaments has significantly reduced compressive loading and anterior torque that is attributed to the acting net muscle forces by −200% and −75%, respectively. The ID model kinematics and kinetics were cross-validated against the FD simulation results. This study clearly shows the importance of incorporating passive spinal structures on the accurate computation of remaining joint loads. Furthermore, for the first time, a generic spine model was used and cross-validated in two different musculoskeletal modelling platforms, i.e., demoa and OpenSim, respectively. In future, a comparison of neuromuscular control strategies for spinal movement can be investigated using both approaches.Deutscher Akademischer AustauschdienstDeutsche Forschungsgemeinschaftthe Australian Research Council (ARC) Industrial Transformation Training Centre for Joint Biomechanic

Work/ family demands and cardiometabolic risk and sleep duration in extended care employees: multilevel findings from the Work, family and Health Network

The study investigates the associations of work-family conflict and other work and family conditions with objectively-measured outcomes cardiometabolic risk and sleep duration in a study of employees in nursing homes. Multilevel analyses are used to assess cross-sectional associations between employee and job characteristics and health in analyses of 1,524 employees in 30 extended care facilities in a single company. We examine work and family conditions in relation to two major study health outcomes: 1) a validated, Framingham cardiometabolic risk score based on measured blood pressure, cholesterol, glycosylated hemoglobin (HbA1c), body mass index (BMI), and self-reported tobacco consumption, and 2) wrist actigraphy-based measures of sleep duration. In fully-adjusted multi-level models, Work-To-Family conflict, but not Family-to-Work conflict was positively associated with cardiometabolic risk. Having a lower-level occupation (nursing assistants vs. nurses) was also associated with increased cardiometabolic risk, while being married and having younger children at home was protective. A significant age by Work-To-Family conflict interaction revealed that higher Work-To-Family conflict was more strongly associated with increased cardiometabolic risk in younger employees. With regard to sleep duration, high Family-To-Work Conflict was significantly associated with shorter sleep duration. In addition, working long hours and having younger children at home were both independently associated with shorter sleep duration. High Work-To-Family Conflict was associated with longer sleep duration. These results indicate that different dimensions of work-family conflict (i.e., Work-To-Family Conflict and Family-To-Work Conflict) may both pose threats to cardiometabolic risk and sleep duration for employees. This study contributes to the research on work- family conflict suggesting that Work-To-Family and Family-To-Work conflict are associated with specific outcomes. Translating theory and our findings to preventive interventions entails recognition of the dimensionality of work and family dynamics and the need to target specific work and family conditions

Toward a Unification of Star Formation Rate Determinations in the Milky Way and Other Galaxies

The star formation rate (SFR) of the Milky Way remains poorly known, with often-quoted values ranging from 1 to 10 solar masses per year. This situation persists despite the potential for the Milky Way to serve as the ultimate SFR calibrator for external galaxies. We show that various estimates for the Galactic SFR are consistent with one another once they have been normalized to the same initial mass function (IMF) and massive star models, converging to 1.9 +/- 0.4 M_sun/yr. However, standard SFR diagnostics are vulnerable to systematics founded in the use of indirect observational tracers sensitive only to high-mass stars. We find that absolute SFRs measured using resolved low/intermediate-mass stellar populations in Galactic H II regions are systematically higher by factors of ~2-3 as compared with calibrations for SFRs measured from mid-IR and radio emission. We discuss some potential explanations for this discrepancy and conclude that it could be allayed if (1) the power-law slope of the IMF for intermediate-mass (1.5 M_sun < m < 5 M_sun) stars were steeper than the Salpeter slope, or (2) a correction factor was applied to the extragalactic 24 micron SFR calibrations to account for the duration of star formation in individual mid-IR-bright H II regions relative to the lifetimes of O stars. Finally, we present some approaches for testing if a Galactic SFR of ~2 M_sun/yr is consistent with what we would measure if we could view the Milky Way as external observers. Using luminous radio supernova remnants and X-ray point sources, we find that the Milky Way deviates from expectations at the 1-3 sigma level, hinting that perhaps the Galactic SFR is overestimated or extragalactic SFRs need to be revised upwards.Comment: Accepted for publication in A

Preventing Chronic Disease in the Workplace: A Workshop Report and Recommendations

Chronic disease is the leading cause of death in the United States. Risk factors and work conditions can be addressed through health promotion aimed at improving individual health behaviors; health protection, including occupational safety and health interventions; and efforts to support the work–family interface. Responding to the need to address chronic disease at worksites, the National Institutes of Health and the Centers for Disease Control and Prevention convened a workshop to identify research priorities to advance knowledge and implementation of effective strategies to reduce chronic disease risk. Workshop participants outlined a conceptual framework and corresponding research agenda to address chronic disease prevention by integrating health promotion and health protection in the workplace