Further investigations of oblique hypervelocity impact phenomena

The results of a continuing investigation of the phenomena associated with the oblique hypervelocity impact of spherical projectiles onto multi-sheet aluminum structures are described. A series of equations that quantitatively describes these phenomena is obtained through a regression of experimental data. These equations characterize observed ricoshet and penetration damage phenomena in a multi-sheet structure as functions of the geometric parameters of the structure and the diameter, obliquity, and velocity of the impacting projectile. Crater damage observed on the ricochet witness plates is used to determine the sizes and speeds of the ricochet debris particles that caused the damage. It is shown that, in general, the most damaging ricochet debris particle is approximately 0.25 cm (0.10 in) in diameter and travels at the speed of approximately 2.1 km/sec (6,890 ft/sec). The equations necessary for the design of shielding panels that will protect external systems from such ricochet debris damage are also developed. The dimensions of these shielding panels are shown to be strongly dependent on their inclination and on their circumferential distribution around the spacecraft. It is concluded that obliquity effects of high-speed impacts must be considered in the design of any structure exposed to the meteoroid and space debris environment

Pressure wall hole size and maximum tip-to-tip crack length following orbital debris penetration

The threat of damage from high speed meteoroid and orbital debris particle impacts has become a significant design consideration in the development and construction of long duration earth-orbiting spacecraft. Historically, significant amounts of resources have been devoted to developing shielding for such structures as a means of reducing the penetration potential of high speed on-orbit impacts. These efforts have typically focused on simply whether or not the inner (or 'pressure') walls of candidate multi-wall structural systems would be perforated. Only recently the nature and extent of pressure wall penetration damage have begun to be explored. This report presents the results of a study whose objective was to characterize the hole formation and cracking phenomena associated with the penetration of the multi-wall systems being considered for the International Space Station Alpha (ISSA)

Bridging Institutions to Cross the Quantitative/Qualitative Divide

Considering qualitative and quantitative student response data and comparing those data cross-institutionally improves writing center policies locally and helps define broader objectives of the writing center as a campus institution. As writing center practitioners, it can be difficult to determine whether we should focus our research and assessment energies on gathering quantitative or qualitative data. Few of us are trained as “numbers people,” yet most of us regularly collect masses of quantitative data in the form of user statistics, exit surveys measuring student satisfaction, and demographic information about the writers who use our centers. Still, qualitative data often feels like the best illustration of our pedagogy to us, our tutors, and our faculty and administrators. When we do collect qualitative data, it frequently reflects recurrent themes in our scholarship. Even if our qualitative data manifests cross-institutional similarities, it is difficult to compare across different schools. [1] Convinced that both quantitative and qualitative feedback is essential to effective assessment of writing center work, we - three very different writing center practitioners from three very different institutions - set out to create a collaborative research project that would allow us to harness the strengths of both quantitative and qualitative methods.University Writing Cente

Educational achievement and ethnicity in compulsory schooling

This paper analyzes the evolution of the attainment gap between white British born and ethnic minority pupils throughout compulsory schooling, from the age of 5 to 16. At the start of school, pupils from most ethnic groups substantially lag behind White British pupils, but these gaps decline for all groups throughout primary and secondary school. Language is the single most important factor why most ethnic minority pupils improve relative to White British pupils. Although poverty explains part of the differences in levels, it cannot explain why ethnic minority pupils gain relative to or even overtake White British pupils. All ethnic minority groups initially attend worse performing schools than White British pupils. However, more than 20 percent of the subsequent relative improvement can be attributed to ethnic minority pupils moving up to better schools relative to White British pupils. Finally, our results suggest the possibility that the relative improvement of ethnic minority pupils may be related to teacher incentives to concentrate attention on particular pupils, caused by the publication of school league tables at the end of secondary school

Revisiting the German wage structure

This paper shows that wage inequality in West Germany has increased over the past three decades, contrary to common perceptions. During the 1980s, the increase was concentrated at the top of the distribution; in the 1990s, it occurred at the bottom end as well. Our findings are consistent with the view that both in Germany and in the United States, technological change is responsible for the widening of the wage distribution at the top. At the bottom of the wage distribution, the increase in inequality is better explained by episodic events, such as supply shocks and changes in labor market institutions. These events happened a decade later in Germany than in the United States

Repeatability and uncertainty analyses of NASA/MSFC light gas gun test data

This Final Report presents an overview of the impact tests performed at NASA/MSFC in the time period 1985 to 1991 and the results of phenomena repeatability and data uncertainty studies performed using the information obtained from those tests. An analysis of the data from over 400 tests conducted between 1989 and 1991 was performed to generate a database to supplement the Hypervelocity Impact Damage Database developed under a previous effort

Oblique hypervelocity impact response of dual-sheet structures

The results of a continuing investigation of the phenomena associated with the oblique hypervelocity impact of spherical projectiles onto multi-sheet aluminum structures are given. A series of equations that quantitatively describes these phenomena is obtained through a regression of experimental data. These equations characterize observed ricochet and penetration damage phenomena in a multi-sheet structure as functions of geometric parameters of the structure and the diameter, obliquity, and velocity of the impacting projectile. Crater damage observed on the ricochet witness plates is used to determine the sizes and speeds of the ricochet debris particles that caused the damage. It is observed that the diameter of the most damaging ricochet debris particle can be as large as 40 percent of the original particle diameter and can travel at speeds between 24 percent and 36 percent of the original projectile impact velocity. The equations necessary for the design of shielding panels that will protect external systems from such ricochet debris damage are also developed. The dimensions of these shielding panels are shown to be strongly dependent on their inclination and on their circumferential distribution around the spacecraft

RISK FACTORS FOR BOY'S CONDUCT PROBLEMS WITHIN AND ACROSS NEIGHBORHOODS

This study had three aims. The first was to examine whether there is a relationship between children's developmental histories of conduct problems (CP) and neighborhood risk. A second aim was to examine whether children from poorer neighborhoods are exposed to more environmentally-based CP risk factors (e.g., peer deviance, rejecting parenting) than children from more prosperous neighborhoods. Finally, a third aim was to compare the developmental histories of CP youth across communities that varied in SES (e.g., lower-middle-class and more deprived neighborhoods) and within such communities (e.g., high-CP vs. low-CP boys from lower-middle-class communities). Raine's (Raine & Venables, 1984) social push hypothesis proposes that CP youth from more prosperous communities are more likely to demonstrate biologically-based risk factors for CP (e.g., ADHD) and less likely to be exposed to environmentally-based risk factors. These issues were investigated in two samples of ethnically diverse boys, one that included younger children and another that included adolescents. Children were assigned to groups based on their trajectories of CP and neighborhood SES using Nagin's (1999, 2005) semiparametric group based approach to modeling trajectories. Results revealed weak support for a relationship between children's trajectories of CP and neighborhood SES. Also, children from poorer neighborhoods were consistently found to have greater exposure to environmentally-based CP risk factors than children from more prosperous communities. However, contrary to the social push hypothesis, the results did not generally support the notion that CP youth from more prosperous communities had less exposure to environmentally-based CP risk factors or demonstrate more biologically-based risk factors for CP

Geophysical and Biological Reconnaissance of Rock Habitats in Western Camden Bay, Beaufort Sea, Alaska

This report presents the results of a 10-day geophysical and biological survey in western Camden Bay, in the Alaskan Beaufort Sea. The primary objective of this survey was to confirm the existence of boulders and cobbles on the seafloor as reported by Barnes (1981, 1982). The survey area extended from the eastern edge of the Canning River (mud flat area) to Kangigivik Point and seaward to the 14m contour line (Fig. 1). A solid boundary of pack ice prevented any survey work seaward of the 14m contour. We had proposed to examine the seabed to the 18m contour.This work was supported by the Bureau of Land Management through an interagency agreement with the National Oceanic and Atmospheric Administration, under which a multiyear program responding to needs of petroleum development of the Alaskan Continental Shelf is managed by the Outer Continental Shelf Environmental Assessment Program (OCSEAP) office