Effects of a Physical Activity Intervention on the Stress Reduction of Underserved Adolescent Youth

Stress levels of American teenagers are rising. Studies show that teens are reporting higher stress levels than what they perceive to be healthy and that these levels are higher than the levels of perceived stress reported by adults (APA, 2013). In addition to reporting unhealthy levels of stress, adolescents are reporting feeling overwhelmed and depressed due to their stress (APA, 2013). These findings are especially true for underserved adolescents who are more likely to have exposure to violence, discrimination, racism and conditions of poverty in addition to experiencing the typical stressors associated with adolescence (American Academy of Child and Adolescent Psychiatry, 2019; APA, 2013; CDC, 2017 Youth Risk Behavior Surveillance). Underserved youth also face barriers that prevent them from engaging in PA such as a lack of support and safety concerns (Dubow et al., 1997). Physical activity (PA) has long been known to benefit physical health and has more recently been shown to improve mental health, specifically stress. However, little research has examined how an intervention to increase youth PA can reduce perceived stress and related internalizing symptoms among adolescents. The current study set out to 1) examine the degree to which youth within underserved communities are stressed and experiencing internalizing symptomology considering variations by key youth characteristics (i.e., race, gender, age) and 2) to examine whether youth in the PA intervention have greater reductions in stress and internalizing symptoms as compared to youth in the control from baseline to post-intervention, controlling for individual variances in race, gender, age, and program site. With alarmingly high rates of stress among adolescents, particularly among underserved youth, implementation of a PA intervention within after school programs (ASPs) offers potential to reduce youth stress through improving adolescent PA engagement. ASPs offer a safe, educational and positive environment for students after normal school hours. Findings from the present study determined that in a sample of 338 adolescent youth from underserved communities in the southeast region, baseline stress levels were at similarly high levels compared to national averages and that there were no statistically significant differences by gender, age, race or intervention versus control. However, findings from the study found no differences in students perceived stress or internalizing symptoms between the control and interventions at baseline and endpoint

A static investigation of the thrust vectoring system of the F/A-18 high-alpha research vehicle

A static (wind-off) test was conducted in the static test facility of the Langley 16-foot Transonic Tunnel to evaluate the vectoring capability and isolated nozzle performance of the proposed thrust vectoring system of the F/A-18 high alpha research vehicle (HARV). The thrust vectoring system consisted of three asymmetrically spaced vanes installed externally on a single test nozzle. Two nozzle configurations were tested: A maximum afterburner-power nozzle and a military-power nozzle. Vane size and vane actuation geometry were investigated, and an extensive matrix of vane deflection angles was tested. The nozzle pressure ratios ranged from two to six. The results indicate that the three vane system can successfully generate multiaxis (pitch and yaw) thrust vectoring. However, large resultant vector angles incurred large thrust losses. Resultant vector angles were always lower than the vane deflection angles. The maximum thrust vectoring angles achieved for the military-power nozzle were larger than the angles achieved for the maximum afterburner-power nozzle

Effects of internal yaw-vectoring devices on the static performance of a pitch-vectoring nonaxisymmetric convergent-divergent nozzle

An investigation was conducted in the static test facility of the Langley 16-Foot Transonic Tunnel to evaluate the internal performance of a nonaxisymmetric convergent divergent nozzle designed to have simultaneous pitch and yaw thrust vectoring capability. This concept utilized divergent flap deflection for thrust vectoring in the pitch plane and flow-turning deflectors installed within the divergent flaps for yaw thrust vectoring. Modifications consisting of reducing the sidewall length and deflecting the sidewall outboard were investigated as means to increase yaw-vectoring performance. This investigation studied the effects of multiaxis (pitch and yaw) thrust vectoring on nozzle internal performance characteristics. All tests were conducted with no external flow, and nozzle pressure ratio was varied from 2.0 to approximately 13.0. The results indicate that this nozzle concept can successfully generate multiaxis thrust vectoring. Deflection of the divergent flaps produced resultant pitch vector angles that, although dependent on nozzle pressure ratio, were nearly equal to the geometric pitch vector angle. Losses in resultant thrust due to pitch vectoring were small or negligible. The yaw deflectors produced resultant yaw vector angles up to 21 degrees that were controllable by varying yaw deflector rotation. However, yaw deflector rotation resulted in significant losses in thrust ratios and, in some cases, nozzle discharge coefficient. Either of the sidewall modifications generally reduced these losses and increased maximum resultant yaw vector angle. During multiaxis (simultaneous pitch and yaw) thrust vectoring, little or no cross coupling between the thrust vectoring processes was observed

Behavioural Plasticity in an Ecological Generalist: Microhabitat Use by Western Fence Lizards

Question: What is the basis for geographic variation in microhabitat use in fence lizards? Hypothesis: Population differences in microhabitat use reflect behavioural plasticity rather than genetic or experiential differences. Organisms: Western fence lizards (Sceloporus occidentalis). Field site: Three sites (desert, valley, and mountain) in southern California, USA. Methods: We compared habitat use by free-ranging lizards in three field populations. We also collected lizards from these three populations and studied their microhabitat use in experimental enclosures at a single field site. Results: In the wild, lizards chose higher and shadier perches at the hottest (desert) site, lower and sunnier perches at the coolest (mountain) site, and intermediate perches at the thermally intermediate valley site. However, lizards collected from the three source populations did not differ in microhabitat use in experimental enclosures at a common field site, supporting our hypothesis. Microhabitat choice is an important thermoregulatory mechanism in this species

Experimental and Computational Investigation of a Translating-Throat Single-Expansion-Ramp Nozzle

An experimental and computational study was conducted on a high-speed, single-expansion-ramp nozzle (SERN) concept designed for efficient off-design performance. The translating-throat SERN concept adjusts the axial location of the throat to provide a variable expansion ratio and allow a more optimum jet exhaust expansion at various flight conditions in an effort to maximize nozzle performance. Three design points (throat locations) were investigated to simulate the operation of this concept at subsonic-transonic, low supersonic, and high supersonic flight conditions. The experimental study was conducted in the jet exit test facility at the Langley Research Center. Internal nozzle performance was obtained at nozzle pressure ratios (NPR's) up to 13 for six nozzles with design nozzle pressure ratios near 9, 42, and 102. Two expansion-ramp surfaces, one concave and one convex, were tested for each design point. Paint-oil flow and focusing schlieren flow visualization techniques were utilized to acquire additional flow data at selected NPR'S. The Navier-Stokes code, PAB3D, was used with a two-equation k-e turbulence model for the computational study. Nozzle performance characteristics were predicted at nozzle pressure ratios of 5, 9, and 13 for the concave ramp, low Mach number nozzle and at 10, 13, and 102 for the concave ramp, high Mach number nozzle

An Experimental and Computational Investigation of a Translating Throat Single Expansion-Ramp Nozzle

A translating throat single expansion-ramp nozzle (SERN) concept was designed to improve the off-design performance of a SERN with a large, fixed expansion ratio. The concept of translating the nozzle throat provides the SERN with a variable expansion ratio. An experimental and computational study was conducted to predict and verify the internal performance of this concept. Three nozzles with expansion ratios designed for low, intermediate, and high Mach number operating conditions were tested in the Jet-Exit Test Facility at the NASA Langley Research Center. Each nozzle was tested with a concave and a convex geometric expansion ramp surface design. Internal nozzle performance, paint-oil flow and focusing Schlieren flow visualization were obtained for nozzle pressure ratios (NPR's) up to 13. The Navier-Stokes code, PAB3D, with a k-epsilon turbulence model was utilized to verify experimental results at selected NPR's and to predict the performance at conditions unattainable in the test facility. Two-dimensional simulations were computed with near static free-stream conditions and at nozzle pressure ratios of 5, 9, and 13 for the concave ramp, low Mach number configuration and at the design NPR of 102 for the concave ramp, high Mach number configuration. Remarkable similarities between predicted and experimental flow characteristics, as well as performance quantities, were obtained

Multiaxis Thrust-Vectoring Characteristics of a Model Representative of the F-18 High-Alpha Research Vehicle at Angles of Attack From 0 deg to 70 deg

An investigation was conducted in the Langley 16-Foot Transonic Tunnel to determine the multiaxis thrust-vectoring characteristics of the F-18 High-Alpha Research Vehicle (HARV). A wingtip supported, partially metric, 0.10-scale jet-effects model of an F-18 prototype aircraft was modified with hardware to simulate the thrust-vectoring control system of the HARV. Testing was conducted at free-stream Mach numbers ranging from 0.30 to 0.70, at angles of attack from O' to 70', and at nozzle pressure ratios from 1.0 to approximately 5.0. Results indicate that the thrust-vectoring control system of the HARV can successfully generate multiaxis thrust-vectoring forces and moments. During vectoring, resultant thrust vector angles were always less than the corresponding geometric vane deflection angle and were accompanied by large thrust losses. Significant external flow effects that were dependent on Mach number and angle of attack were noted during vectoring operation. Comparisons of the aerodynamic and propulsive control capabilities of the HARV configuration indicate that substantial gains in controllability are provided by the multiaxis thrust-vectoring control system

An experimental and computational investigation of a translating throat single expansion-ramp nozzle

A translating throat single expansion-ramp nozzle (SERN) concept was designed to improve the off-design performance of a SERN with a large, fixed expansion ratio. The concept of translating the nozzle throat provides the SERN with a variable expansion ratio. An experimental and computational study was conducted to predict and verify the internal performance of this concept. Three nozzles with expansion ratios designed for low, intermediate, and high Mach number operating conditions were tested in the Jet-Exit Test Facility at the NASA Langley Research Center. Each nozzle was tested with a concave and a convex geometric expansion ramp surface design. Internal nozzle performance, paint-oil flow and focusing Schlieren flow visualization were obtained for nozzle pressure ratios (NPR's) up to 13. The Navier-Stokes code, PAB3D, with a k-epsilon turbulence model was utilized to verify experimental results at selected NPRs and to predict the performance at conditions unattainable in the test facility. Two-dimensional simulations were computed with near static free-stream conditions and at nozzle pressure ratios of 5, 9, and 13 for the concave ramp, low Mach number configuration and at the design NPR of 102 for the concave ramp, high Mach number configuration. Remarkable similarities between predicted and experimental flow characteristics, as well as performance quantities, were obtained

Two-dimensional converging-diverging rippled nozzles at transonic speeds

An experimental investigation was performed in the Langley 16-Foot Transonic tunnel to determine the effects of external and internal flap rippling on the aerodynamics of a nonaxisymmetric nozzle. Data were obtained at several Mach numbers from static conditions to 1.2 over a range of nozzle pressure ratios. Nozzles with chordal boattail angles of 10, 20, and 30 degrees, with and without surface rippling, were tested. No effect on discharge coefficient due to surface rippling was observed. Internal thrust losses due to surface rippling were measured and attributed to a combination of additional internal skin friction and shock losses. External nozzle drag for the baseline configurations were generally less than that for the rippled configurations at all free-stream Mach numbers tested. The difference between the baseline and rippled nozzle drag levels generally increased with increasing boat tail angle. The thrust-minus-drag level for each rippled nozzle configuration was less than the equivalent baseline configuration for each Mach number at the design nozzle pressure ratio

Transportation Beyond 2000: Technologies Needed for Engineering Design

The purpose of the workshop was to acquaint the staff of the NASA Langley Research Center with the broad spectrum of transportation challenges and concepts foreseen within the next 20 years. The hope is that the material presented at the workshop and contained in this document will stimulate innovative high-payoff research directed towards the efficiency of future transportation systems. The workshop included five sessions designed to stress the factors that will lead to a revolution in the way we will travel in the 21st century. The first session provides the historical background and a general perspective for future transportation, including emerging transportation alternatives such as working at a distance. Personal travel is the subject of Session Two. The third session looks at mass transportation, including advanced rail vehicles, advanced commuter aircraft, and advanced transport aircraft. The fourth session addresses some of the technologies required for the above revolutionary transportation systems to evolve. The workshop concluded with a wrap-up panel discussion, Session Five. The topics presented herein all have viable technical components and are at a stage in their development that, with sufficient engineering research, one or more of these could make a significant impact on transportation and our social structure