Gust–Airfoil Coupling with a Loaded Airfoil

The unsteady load response of an airfoil encountering a gust is often modeled using analytical transfer functions, which assume idealized behavior of both the flow and the airfoil. One such transfer function is the Sears function, which models a pure transverse gust interacting with a flat-plate airfoil at zero mean incidence. The function was extended by Goldstein and Atassi (“A Complete Second-Order Theory for the Unsteady Flow About an Airfoil due to a Periodic Gust,” Journal of Fluid Mechanics, Vol. 74, No. 4, 1976, pp. 741–765) to account for camber and incidence, as well as the presence of a streamwise gust component. Atassi (“The Sears Problem for a Lifting Airfoil Revisited-New Results,” Journal of Fluid Mechanics, Vol. 141, April 1984, pp. 109–122) showed that the effects of camber and incidence (that is, nonzero mean airfoil loading) are not negligible when there is a streamwise gust component. In this work, new experimental data are shown for an airfoil with nonzero loading encountering a gust with both streamwise and transverse components. As well as giving validation to the Atassi model, the flow physics behind the model is shown, including the superposition of the gust onto the airfoil potential field and the propagation of the gust along the airfoil surface

Gust–Airfoil Coupling with a Loaded Airfoil

The unsteady load response of an airfoil encountering a gust is often modeled using analytical transfer functions, which assume idealized behavior of both the flow and the airfoil. One such transfer function is the Sears function, which models a pure transverse gust interacting with a flat-plate airfoil at zero mean incidence. The function was extended by Goldstein and Atassi (“A Complete Second-Order Theory for the Unsteady Flow About an Airfoil due to a Periodic Gust,” Journal of Fluid Mechanics, Vol. 74, No. 4, 1976, pp. 741–765) to account for camber and incidence, as well as the presence of a streamwise gust component. Atassi (“The Sears Problem for a Lifting Airfoil Revisited-New Results,” Journal of Fluid Mechanics, Vol. 141, April 1984, pp. 109–122) showed that the effects of camber and incidence (that is, nonzero mean airfoil loading) are not negligible when there is a streamwise gust component. In this work, new experimental data are shown for an airfoil with nonzero loading encountering a gust with both streamwise and transverse components. As well as giving validation to the Atassi model, the flow physics behind the model is shown, including the superposition of the gust onto the airfoil potential field and the propagation of the gust along the airfoil surface

Anatomy of STEM teaching in North American universities

A large body of evidence demonstrates that strategies that promote student interactions and cognitively engage students with content (1) lead to gains in learning and attitudinal outcomes for students in science, technology, engineering, and mathematics (STEM) courses (1, 2). Many educational and governmental bodies have called for and supported adoption of these student-centered strategies throughout the undergraduate STEM curriculum. But to the extent that we have pictures of the STEM undergraduate instructional landscape, it has mostly been provided through self-report surveys of faculty members, within a particular STEM discipline [e.g., (3–6)]. Such surveys are prone to reliability threats and can underestimate the complexity of classroom environments, and few are implemented nationally to provide valid and reliable data (7). Reflecting the limited state of these data, a report from the U.S. National Academies of Sciences, Engineering, and Medicine called for improved data collection to understand the use of evidence-based instructional practices (8). We report here a major step toward a characterization of STEM teaching practices in North American universities based on classroom observations from over 2000 classes taught by more than 500 STEM faculty members across 25 institutions

Metal-Poor Stars Observed with the Magellan Telescope. III. New Extremely and Ultra Metal-Poor Stars from SDSS/SEGUE and Insights on the Formation of Ultra Metal-Poor Stars

We report the discovery of one extremely metal-poor (EMP; [Fe/H]<-3) and one ultra metal-poor (UMP; [Fe/H]<-4) star selected from the SDSS/SEGUE survey. These stars were identified as EMP candidates based on their medium-resolution (R~2,000) spectra, and were followed-up with high-resolution (R~35,000) spectroscopy with the Magellan-Clay Telescope. Their derived chemical abundances exhibit good agreement with those of stars with similar metallicities. We also provide new insights on the formation of the UMP stars, based on comparison with a new set of theoretical models of supernovae nucleosynthesis. The models were matched with 20 UMP stars found in the literature, together with one of the program stars (SDSS J1204+1201), with [Fe/H]=-4.34. From fitting their abundances, we find that the supernovae progenitors, for stars where carbon and nitrogen are measured, had masses ranging from 20.5 M_sun to 28 M_sun and explosion energies from 0.3 to 0.9x10^51 erg. These results are highly sensitive to the carbon and nitrogen abundance determinations, which is one of the main drivers for future high-resolution follow-up of UMP candidates. In addition, we are able to reproduce the different CNO abundance patterns found in UMP stars with a single progenitor type, by varying its mass and explosion energy.Comment: 15 pages, 12 figures; accepted for publication in Ap

Generating high-efficiency swimming kinematics using hydrodynamic eigenmode decomposition

This paper explores the use of hydrodynamic eigenmode decomposition as a means of generating optimal swimming kinematics of slender three-dimensional bodies. The eigenvectors of the unsteady hydrodynamic system are used as basis functions for the response to external forcing, such as perturbations generated by the deformation of the body. Exploiting the orthogonality of the modes, we show that swimming according to a single appropriately selected hydrodynamic eigenmode results in high-efficiency swimming. To demonstrate this result, we use an inviscid three-dimensional vortex lattice model to investigate the hydrodynamic eigenmodes of a selection of geometries. We find that for all of the body geometries tested, hydrodynamic efficiency far exceeding that of pure heaving or pitching can be achieved. All eigenmodes tested produce high-efficiency motion, as long as the beat frequency is higher than the mode's “cut-in” frequency for thrust generation. The eigenmodes show qualitative similarity to swimming patterns observed in nature and also correspond well to the existing classifications of undulatory and oscillatory swimming. This study demonstrates that the hydrodynamic eigenmode analysis can generate high-efficiency swimming kinematics based only on information about the body and wake geometry, and as such, this method has significant potential for further development and application to autonomous underwater vehicle design

Variations in Specialized Policing Response Models as a Function of Community Characteristics- A Survey of Crisis Intervention Team Coordinators

Although a specific program called the Crisis Intervention Team (CIT) has been generally recognized as the best-practice model that addresses the needs of the police officers in responding to mental health calls, many jurisdictions across the country have not only adopted the full CIT model but also have taken the liberty of adding new components and/or removing components of the original model in order to create a unique program that fits the needs of their individual community. The issue of differentiated adaptations of the original CIT model has created a controversy around best practice in the area of police response to individuals with mental health issues who are in crisis. Using an on-line survey and interview methods, this study examined a relationship between the degree of variation within specialized policing response models and their corresponding community characteristics. Previous research shows that the components of the original CIT model have positive influence on officers’ confidence in interacting with people with mental illness. Therefore, this study also hypothesized that a rating of an SPR police officers’ job satisfaction was likely to correlate with the degree to which an SPR program adhered to the original CIT model. The study found that mental health resources, extent of presence of special populations in a community, existence of SPR policies in law enforcement, mental health, and dispatch departments, and how much law enforcement and mental health administrators supported the program, all predicted the degree of total deviation of a program from the original CIT model. Population density, related to a distinction between rural and non-rural communities, did not predict the degree of deviation from the original CIT model. The study also found that the degree of deviation of a program from the original CIT model did not strongly predict the rating of SPR officers’ job satisfaction. The study discusses the possible reasons for the results as well as implications for stakeholders who are considering implementation of a Specialized Policing Response model in their communities. Limitations of the current study’s research design are also discussed

Motivational decline and recovery in higher education STEM courses

Decline in student motivation is a concern for STEM education, especially for underrepresented groups in the sciences. Using the Science Motivation Questionnaire II, 41 foundational STEM courses were surveyed at the beginning and end of each semester in an academic year at a small primarily undergraduate university. Significant pre- to post-semester declines were observed in each of five measured motivational factors (Intrinsic motivation, Career motivation, Self determination, Self-efficacy, and Grade motivation), with effect sizes ranging from 0.21 to 0.41. However, in the second semester pre-survey, four motivational factors rebounded, including three returning to initial levels, suggesting that the observed motivational decline is not long-lasting. Analysis suggests that declines are not related to survey fatigue or student demographics, but rather to grades and, in the case of one motivational factor, to academic field. These findings suggest that a refocus on grading practices across STEM fields may influence student motivation and persistence in STEM

Anatomy of STEM teaching in North American Universities

A large body of evidence demonstrates that strategies that promote student interactions and cognitively engage students with content lead to gains in learning and attitudinal outcomes for students in science, technology, engineering, and mathematics (STEM) courses. Many educational and governmental bodies have called for and supported adoption of these student centered strategies throughout the undergraduate STEM curriculum

Hepatitis B among Pacific Islanders in Southern California: how is health information associated with screening and vaccination?

We measured Hepatitis B virus (HBV) transmission knowledge and self-reported screening/testing behavior among Pacific Islanders (Guamanians/Chamorros, Samoans, and Tongans) in Southern California. We also examined access and trust by Pacific Islanders of varying health information sources. We administered and analyzed survey data (N = 297), using a convenience sample in Los Angeles, Orange, and San Diego Counties in spring 2009. We found that while Pacific Islander respondents reported that they receive health information from physicians, and largely trust this source, information from and trust in physicians were not statistically significant in explaining whether respondents sought HBV screening or vaccination