Bi-directional association between Spanish-speaking preschoolers' English oral proficiency and student-teacher relationship qualities, The

2012 Summer.Includes bibliographical references.This study examined the bi-directional association between Spanish-speaking preschoolers' (N = 137) English use tendencies and vocabulary skills and the quality of the student-teacher relationship (e.g., close, conflictive, and dependent). Results revealed that children who began preschool in the fall with high English expressive vocabulary skills and a high tendency to use English were more likely to develop close relationships with their teachers the following spring. Further, children with dependent relationships with their teachers in the fall of preschool were more likely to exhibit low English receptive vocabulary skills in the spring. These findings highlight the importance of Spanish-speaking children's English oral proficiency upon school entrance for the development of positive student-teacher relationships, which might be one avenue to foster their school achievement and help close the academic performance gap between Spanish-speaking students and monolingual English speaking peers

A Wind Tunnel Technique for the Identification of Ship Airwake/Rotor Downwash Coupling

A wind tunnel study is performed to analyze the interaction between ship airwakes and helicopter rotor downwash. This interaction is of interest to naval aviators and researchers as this phenomenon is thought to limit helicopter flight envelopes and increase the overall difficulty of maritime rotorcraft operations. In this study, a 1/50th scale simplified naval frigate model and appropriately scaled rotor model are used for all experimental work. A rotor thrust survey was conducted in the immediate vicinity of the landing deck. Two dimensional and stereo particle image velocimetry surveys and rotor thrust measurements with various rotor and ship configurations were conducted. Finally, a velocity based coupling analysis technique was developed and applied. In addition, extensive systems were developed to control wind tunnel conditions, accurately position wind tunnel models, manage data, and ultimately facilitate an efficient experimental process. The developed coupling technique quantifies aerodynamic coupling by examining the component-wise velocity discrepancies between the experimentally observed flowfield and the flowfield generated by superposition. Significant aerodynamic coupling was found below a rotor-over-deck height of Z/D=1.2 for a wind tunnel speed of 5 m/s and zero wind-over-deck angle

The Digital Twin Paradigm for Future NASA and U.S. Air Force Vehicles

Future generations of NASA and U.S. Air Force vehicles will require lighter mass while being subjected to higher loads and more extreme service conditions over longer time periods than the present generation. Current approaches for certification, fleet management and sustainment are largely based on statistical distributions of material properties, heuristic design philosophies, physical testing and assumed similitude between testing and operational conditions and will likely be unable to address these extreme requirements. To address the shortcomings of conventional approaches, a fundamental paradigm shift is needed. This paradigm shift, the Digital Twin, integrates ultra-high fidelity simulation with the vehicle s on-board integrated vehicle health management system, maintenance history and all available historical and fleet data to mirror the life of its flying twin and enable unprecedented levels of safety and reliability

EXPERIMENTAL AND NUMERICAL INVESTIGATION INTO THE EFFECTS OF PANEL CURVATURE ON THE HIGH VELOCITY BALLISTIC IMPACT RESPONSE OF ALUMINUM AND COMPOSITE PANELS

Determining how a material responds to a ballistic impact is important for designing improved penetration-resistant structures. Historically, the majority of research into the effects of ballistic impact has been for flat geometries. However, in aerospace applications, the surfaces that would most likely be subjected to high velocity impacts, the fuselage and the wing sections, are not flat. A need therefore exists to systematically examine and understand the effect, if any, of panel curvature on the ballistic response of both aluminum and composite panels. For this dissertation, a hybrid combination of experimental testing and numerical modeling which was employed to examine the effects of panel curvature on the ballistic limit, the dynamic panel response, and the impact-induced damage in the target material is discussed. Panels of varying curvature were impacted by ½-inch diameter steel spheres for a range of impact velocities that bracketed the experimentally-determined ballistic limit. AS4-3501-6 graphite-epoxy composite panels with two varying curvatures, a 4.4-inch radius of curvature and a 12-inch radius of curvature, and 2024-T3 aluminum panels with four varying curvatures, a 4.4-inch radius of curvature, an 8-inch radius of curvature, a 12-inch radius of curvature, and an infinite radius of curvature (flat plate), were tested. Non-linear finite element models consistently and reliably modeled the ballistic impact event, for both the flat and the curved panels, when the specified elastic modulus correctly captured the characteristics of the wave propagation behavior for the panel material being modeled. For the composite panels, dynamic deformation measurements and strain-gage-instrumented impact tests indicated that an effective elastic modulus on the order of the tensile modulus of the matrix material was more appropriate than a "rule-of-mixtures" effective modulus. The combined experimental-numerical results also identified a parabolic relationship between the panel curvature and the ballistic limit. More importantly, an optimal panel curvature with respect to maximizing the ballistic limit was shown for both the aluminum and the composite panels. Preliminary results from non-destructive and destructive post-impact evaluations suggest that the severity of impact damage may also vary with panel curvature

Response of curved carbon composite panels to shock loading

Dynamic experiments were conducted using a shock tube facility coupled with high speed digital image correlation system to understand the effect of plate curvature on blast response of 32 layered carbon fiber-epoxy panels. Three different geometries of carbon fiber panels were evaluated. These panels had a radii of curvatures of infinity (panel A), 304.8 mm (panel B), and 111.76 mm (panel C). Panels with dimensions of 203.2 mm x 203.2 mm x 2 mm were held with clamped boundary conditions during the shock loading. The input and reflected pressure profiles from the shock loading were carefully analyzed to obtain the impulse and energy during the loading process. As a result of shock loading, Panel A had a mid-point deflection of 14 mm before failure initiated, whereas it was 18 mm for the panel B and 10 mm in panel C. Macroscopic postmortem analysis was also performed to comprehend and compare the different mechanisms of failure observed in the three panels, which showed types of failure mechanism in all the three panels: fiber breakage and inter-layer delamination. The fiber breakage was induced on the face exposed to shock loading and continued inside. The delamination was visible on the side of the specimen as well as on the face exposed to the shock loading. The study showed that panel C can mitigate the highest intensity (pressure) shock waves without the initiation of catastrophic damage in the panel. In regards to the other two panels investigated, panel B could sustain the least shock wave intensity before failure. Panel A could mitigate the blast pressure having intensity in between the intensities impinging on the other two panels. © The Society for Experimental Mechanics, Inc. 2013