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

Defoemational and physico-chemical properties of cereain sediments, with particular reference to colliery spoil

The present study is placed in the context of the disastrous Aberfan (Wales) colliery tip failure in 1966, particularly with respect to the singular lack of knowledge regarding the consequences of long-term weathering of coal-bearing strata. Initial breakdown of fresh indurated sediments from underground workings (roof and floor measures) is shown to be a function of a) sedimentary structures b) capillarity (air-breakage) c) expandable mixed-layer 10A clay content. A geographical variation in clay mineralogy implies that breakdown should generally be at a minimum in the Durham, Northumberland and Scottish coalfields. An in situ study of a stratigraphic section containing all rock-types likely to be found in British colliery tips shows that chemical (weathering) processes are very restricted. Pyrite is the only mineral species which has completely broken down within the 8ft-deep weathering zone, over a period of about 10,000 years. Cohesion is the strength parameter most susceptible to in situ degradation and the shear strength parameters of the near-surface materials generally conform with those of jointed and fissured rocks, rather than soils The residual (ultimate) strength of weathered- unweathered Coal Measures sediments is shown to be a function of the ratio quartz: clay minerals. Major temperature-time dependent, mineralogical changes in the superficial zone of the very coaly, 100-year-old Brancepeth colliery tip are not matched by a large fall-off in shear strength. The composite internal friction value is similar to shale-fill dams in Britain; there is no statistically significant strength difference between upper slope (younger) and lower slope (older) samples, which are some 27 per cent higher than the residual spoil strength. Convincing chemical, physical and mechanical data from a 50-year-old tip at Yorkshire Main Colliery show that small changes within the heap are more readily attributable to changing colliery practice, rather than to degradation processes. After initially rapid physical breakdowm, the material has changed little after burial. This study has shown that long-term weathering processes have little influence on the overall stability of colliery spoil

Designing, implementing, and evaluating a staff development program on learning styles and teaching styles in an urban junior high school.

This study documented the process of designing, implementing, and evaluating a low-cost, school-based, researcher-conducted staff development program for four voluntary Black seventh and eighth grade science and social studies teachers at Roosevelt Junior Senior High School, New York, during 1987-88. The underlying purpose was to learn more about effective school improvement in low-income school districts. Staff development efforts aimed to expand teachers\u27 teaching styles to accord more closely with urban Black students\u27 diverse learning styles in four homogeneously grouped classes with the intent of (a) improving students\u27 academic achievement, (b) increasing attendance to class, and (c) improving attitudes about school. Five collaboratively planned workshops on teaching styles and learning styles provided opportunities for teachers (a) to expand their repertoire of teaching styles, (b) to recognize students\u27 learning styles, (c) to develop problem-solving techniques for their classes, (d) to work cooperatively with other teachers, and (e) to enhance their professional growth. Based on observations, discussions, interviews, and self-reports, the researcher concluded that teachers (a) utilized different teaching strategies in their classes to address more students\u27 learning styles, (b) provided more opportunities for students to work cooperatively in class, (c) shared ideas with other teachers, (d) planned their lessons with other teachers, (e) incorporated students\u27 suggestions into lessons, (f) utilized a larger variety of teaching aids and materials, and (g) praised their students more often. Their students (a) displayed less inappropriate behavior in class, (b) worked cooperatively with their classmates, (c) offered teachers suggestions to make classes more interesting, and (d) complained less often of boredom. Evidence of positive gains suggests that staff development is feasible in low-income school districts when staff are encouraged to seek support and ideas from students, parents, teachers, and administrators about issues considered important in their setting. Collaborative planning fosters a climate that encourages a variety of school improvement efforts to flourish over time