2 resultados para Hitsauksen suurtehomenetelmät, High productive welding processes
em DRUM (Digital Repository at the University of Maryland)
Resumo:
The academic achievement of African American adolescents is a national concern for educators and researchers especially since current reports depict the underachievement of African American students as continuing to lag behind their European American peers. Determining what factors within the school environment that contributes to the achievement gap and how it can be reduced remains an important issue in alleviating disparities seen in educational achievement and attainment. This study examined the relation between characteristics of the close friendships of high-achieving African American adolescents and students’ identity development and motivation in school. Data were collected from 217 high-achieving African American students within 10th to 12th grade from 5 public and private high schools. Each student self-reported on their ethnicity, gender, parents’ education level, grade, FARMs, GPA, perceived teacher support (emotional, academic, and instrumental support), their perception of their ethnic identity, and their perception of their achievement values. Through the use of nomination procedures, students also identified their close friends and responded to questions concerning how supportive (emotional, academic, and instrumental support) they each were. Results from multiple regression analyses showed that the provision of instrumental support from close friends related to the exploration process of the high-achieving students’ ethnic identity. In addition, there was a strong relation between the ethnic identity of close friends and that of the individual. Furthermore, although friend support was not a significant predictor of achievement values, demographic (mother’s education level, grade, and FARMS) and control (teacher support) variables predicted students’ importance and utility of school respectively. These findings add to the literature on age and socioeconomic status as they relate to student’s motivation to achieve. Overall, this study provides some evidence highlighting ways in which close friendships might relate to the self-development of high-achieving African American adolescents. This study provides a starting point for additional ways in which to explore how peer processes relate to the academic behaviors of high-achieving African American adolescents.
Resumo:
The first part of this study examines the relative roles of frontogenesis and tropopause undulation in determining the intensity and structural changes of Hurricane Sandy (2012) using a high-resolution cloud-resolving model. A 138-h simulation reproduces Sandy’s four distinct development stages: (i) rapid intensification, (ii) weakening, (iii) steady maximum surface wind but with large continued sea-level pressure (SLP) falls, and (iv) re-intensification. Results show typical correlations between intensity changes, sea-surface temperature and vertical wind shear during the first two stages. The large SLP falls during the last two stages are mostly caused by Sandy’s moving northward into lower-tropopause regions associated with an eastward-propagating midlatitude trough, where the associated lower-stratospheric warm air wraps into the storm and its surrounding areas. The steady maximum surface wind occurs because of the widespread SLP falls with weak pressure gradients lacking significant inward advection of absolute angular momentum (AAM). Meanwhile, there is a continuous frontogenesis in the outer region during the last three stages. Cyclonic inward advection of AAM along each frontal rainband accounts for the continued expansion of the tropical-storm-force wind and structural changes, while deep convection in the eyewall and merging of the final two survived frontal rainbands generate a spiraling jet in Sandy’s northwestern quadrant, leading to its re-intensification prior to landfall. The physical, kinematic and dynamic aspects of an upper-level outflow layer and its possible impact on the re-intensification of Sandy are examined in the second part of this study. Above the outflow layer isentropes are tilted downward with radius as a result of the development of deep convection and an approaching upper-level trough, causing weak subsidence. Its maximum outward radial velocity is located above the cloud top, so the outflow channel experiences cloud-induced long-wave cooling. Because Sandy has two distinct convective regions (an eyewall and a frontal rainband), it has multiple outflow layers, with the eyewall’s outflow layer located above that of the frontal rainband. During the re-intensification stage, the eyewall’s outflow layer interacts with a jet stream ahead of the upper-level trough axis. Because of the presence of inertial instability on the anticyclonic side of the jet stream and symmetric instability in the inner region of the outflow layer, Sandy’s secondary circulation intensifies. Its re-intensification ceases when these instabilities disappear. The relationship between the intensity of the secondary circulation and dynamic instabilities of the outflow layer suggests that the re-intensification occurs in response to these instabilities. Additionally, it is verified that the long-wave cooling in the outflow layer helps induce symmetric instability by reducing static stability.