110 research outputs found
An integrated approach to rotorcraft human factors research
As the potential of civil and military helicopters has increased, more complex and demanding missions in increasingly hostile environments have been required. Users, designers, and manufacturers have an urgent need for information about human behavior and function to create systems that take advantage of human capabilities, without overloading them. Because there is a large gap between what is known about human behavior and the information needed to predict pilot workload and performance in the complex missions projected for pilots of advanced helicopters, Army and NASA scientists are actively engaged in Human Factors Research at Ames. The research ranges from laboratory experiments to computational modeling, simulation evaluation, and inflight testing. Information obtained in highly controlled but simpler environments generates predictions which can be tested in more realistic situations. These results are used, in turn, to refine theoretical models, provide the focus for subsequent research, and ensure operational relevance, while maintaining predictive advantages. The advantages and disadvantages of each type of research are described along with examples of experimental results
A quantitative variational phase field framework
The finite solid-liquid interface width in phase field models results in
non-equilibrium effects, including solute trapping. Prior phase field modeling
has shown that this extra degree of freedom, when compared to sharp-interface
models, results in solute trapping that is well captured when realistic
parameters, such as interface width, are employed. However, increasing the
interface width, which is desirable for computational reasons, leads to
artificially enhanced trapping thus making it difficult to model departure from
equilibrium quantitatively. In the present work, we develop a variational phase
field model with independent kinetic equations for the solid and liquid phases.
Separate kinetic equations for the phase concentrations obviate the assumption
of point wise equality of diffusion potentials, as is done in previous works.
Non-equilibrium effects such as solute trapping, drag and interface kinetics
can be introduced in a controlled manner in the present model. In addition, the
model parameters can be tuned to obtain ``experimentally-relevant" trapping
while using significantly larger interface widths than prior efforts. A
comparison with these other phase field models suggests that interface width of
about three to twenty-five times larger than current best-in-class models can
be employed depending upon the material system at hand leading to a speed-up by
a factor of , where and denote the interface width and
spatial dimension, respectively. Finally the capacity to model non-equilibrium
phenomena is demonstrated by simulating oscillatory instability leading to the
formation of solute bands.Comment: 51 pages, 9 figures, supplemental material
Scale Development for Perceived School Climate for Girls’ Physical Activity
Objectives: To test an original scale assessing perceived school climate for girls\u27 physical activity in middle school girls. Methods: Confirmatory factor analysis (CFA) and structural equation modeling (SEM). Results: CFA retained 5 of 14 original items. A model with 2 correlated factors, perceptions about teachers\u27 and boys\u27 behaviors, respectively, fit the data well in both sixth and eighth-graders. SEM detected a positive, significant direct association of the teacher factor, but not the boy factor, with girls\u27 self-reported physical activity. Conclusions:School climate for girls\u27 physical activity is a measurable construct, and preliminary evidence suggests a relationship with physical activity
Scale Development for Perceived School Climate for Girls’ Physical Activity
Objectives: To test an original scale assessing perceived school climate for girls\u27 physical activity in middle school girls. Methods: Confirmatory factor analysis (CFA) and structural equation modeling (SEM). Results: CFA retained 5 of 14 original items. A model with 2 correlated factors, perceptions about teachers\u27 and boys\u27 behaviors, respectively, fit the data well in both sixth and eighth-graders. SEM detected a positive, significant direct association of the teacher factor, but not the boy factor, with girls\u27 self-reported physical activity. Conclusions: School climate for girls\u27 physical activity is a measurable construct, and preliminary evidence suggests a relationship with physical activity
Self-Management Strategies Mediate Self-Efficacy and Physical Activity
Self-efficacy theory proposes that girls who have confidence in their capability to be physically active will perceive fewer barriers to physical activity or be less influenced by them, be more likely to pursue perceived benefits of being physically active, and be more likely to enjoy physical activity. Self-efficacy is theorized also to influence physical activity through self-management strategies (e.g., thoughts, goals, plans, and acts) that support physical activity, but this idea has not been empirically tested
Prevention of Adolescent Depression in Primary Care: Barriers and Relational Work Solutions
Background and Purpose: Depression affects millions of adolescents in the United States each year. This population may benefit from targeted preventive interventions. We sought to understand the internal factors that affect the ability of healthcare organizations to implement an intervention that involves mental health screening and depression prevention treatment of at-risk adolescents in primary care settings. Methods: From November 2011 to July 2016 we conducted a study of the implementation of a multisite (N=30) phase 3 randomized clinical trial of an Internet-based depression prevention intervention program (CATCH-IT). We describe the prevalence of internal barriers on the screening and enrollment process by reporting REACH (the proportion of target audience exposed to the intervention). Results: A total of 369 adolescents were randomized into the intervention or control program. Mean REACH values for the study clinics were 0.216 for screening and 0.181 for enrollment to CATCH-IT. Mean REACH enrollment lost due to internal barriers was 0.233. This translated to 4,691 adolescents lost at screening and 2,443 adolescents lost at enrollment due to internal barriers. Conclusion: We propose a model of the implementation process that emphasizes the importance of positive relational work that assists in overcoming internal barriers to REACH. We also provide implications for policy and practice
Decay of isolated surface features driven by the Gibbs-Thomson effect in analytic model and simulation
A theory based on the thermodynamic Gibbs-Thomson relation is presented which
provides the framework for understanding the time evolution of isolated
nanoscale features (i.e., islands and pits) on surfaces. Two limiting cases are
predicted, in which either diffusion or interface transfer is the limiting
process. These cases correspond to similar regimes considered in previous works
addressing the Ostwald ripening of ensembles of features. A third possible
limiting case is noted for the special geometry of "stacked" islands. In these
limiting cases, isolated features are predicted to decay in size with a power
law scaling in time: A is proportional to (t0-t)^n, where A is the area of the
feature, t0 is the time at which the feature disappears, and n=2/3 or 1. The
constant of proportionality is related to parameters describing both the
kinetic and equilibrium properties of the surface. A continuous time Monte
Carlo simulation is used to test the application of this theory to generic
surfaces with atomic scale features. A new method is described to obtain
macroscopic kinetic parameters describing interfaces in such simulations.
Simulation and analytic theory are compared directly, using measurements of the
simulation to determine the constants of the analytic theory. Agreement between
the two is very good over a range of surface parameters, suggesting that the
analytic theory properly captures the necessary physics. It is anticipated that
the simulation will be useful in modeling complex surface geometries often seen
in experiments on physical surfaces, for which application of the analytic
model is not straightforward.Comment: RevTeX (with .bbl file), 25 pages, 7 figures from 9 Postscript files
embedded using epsf. Submitted to Phys. Rev. B A few minor changes made on
9/24/9
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