Showing papers by "David W. Johnson published in 1982"

Effects of cooperative, competitive, and individualistic learning on students' achievement in science class

Abstract: The effects on students' achievement and attitudes of cooperative, competitive, and individualistic instruction were compared in ninth-grade physical science classes. Forty-four students were included in the study. Students were randomly assigned to conditions stratifying for sex. The results indicate that cooperative learning experiences promoted greater mastery and retention of the material being taught as well as more positive attitudes toward the experience than did competitive and individualistic learning experiences.

The Effects of Cooperative and Individualistic Instruction on Handicapped and Nonhandicapped Students

Abstract: Summary Comparisons were made of the effects of cooperative and individualistic learning experiences on interpersonal attraction between handicapped and nonhandicapped eleventh-grade students and their achievement. Thirty-one students were assigned to conditions on a stratified random basis, with control held for handicap, ability, and sex. They participated in one instructional unit for 55 minutes a day for 16 instructional days. A behavioral measure was employed for cross-handicapped interaction within the instructional situation. A number of attitude and achievement measures were also given. The results indicate that cooperative learning experiences, compared with individualistic ones, promote more cross-handicapped interaction during instruction, more interpersonal attraction between handicapped and nonhandicapped students, and higher achievement on the part of both handicapped and nonhandicapped students.

Effects of Cooperative, Competitive, and Individualistic Learning Experiences on Cross-Ethnic Interaction and Friendships

Abstract: Summary The effects of cooperative, competitive, and individualistic learning experiences were compared on interethnic interaction and attitudes among 4th-grade boys and girls. Seventy-six students were assigned to conditions on a stratified random basis controlling for ethnic membership, ability, and sex. They participated in two instructional units for 45 minutes a day for 15 instructional days. Behavioral and attitudinal measures were taken for cross-ethnic interaction during the instructional sessions and during daily free-time periods. The results indicate that cooperative learning experiences, compared with competitive and individualistic ones, promoted more cross-ethnic interaction and more positive cross-ethnic attitudes.

Nutrient cycling in forests of the Pacific Northwest

Abstract: Ecosystem analysis has established nutrient cycling as an important area of ecology involving biological, chemical, and geological interactions. Studying the flow of elements through ecosystems provides us with a tool for understanding the functioning of ecosystems. For example, if an ecosystem component has a rapid flux of elements through it, or if it stores large amounts of an element, that component is clearly important in ecosystem function. Nutrient cycling strongly influences ecosystem productivity since nutrient flows are closely linked with transfers of carbon and water. In addition nutrient cycling may also affect succession and evolution in forest ecosystems. Various distinct processes are involved in nutrient cycling, such as decomposition, weathering, uptake, leaching, and so on. Each is a precursor to another and the flow of nutrients follows a set of interconnected steps. Although the basic nutrient cycling processes are common to all ecosystems, the rates of the processes vary from one forest ecosystem to another. This variation plays an important role in forest succession and evolution. For example, long-term foliage retention by conifers may allow a species to exist where only a marginal nutrient supply is available from the soil. Nitrogen-fixing species, on the other hand, can occupy sites where nitrogen availability is low because they can provide their own nitrogen. An understanding of nutrient cycling is thus essential for the rational management of forest ecosystems. Nitrogen is recognized as the most limiting element for forest growth in the Pacific Northwest, particularly in Douglas-fir (Pseudotsuga menziesii) ecosystems (Gessel and Walker 1956; Gessel et al. 1969). For this reason this chapter focuses largely on nitrogen cycling. Cycling of other elements such as potassium and calcium are compared with that of nitrogen, where contrasting behavior may provide insight into nutrient-cycling processes. The objectives of this chapter are to (1) briefly describe the important nutrient cycling processes; (2) contrast nutrient cycles in different forest eco-

Effects of group and individual contingencies on academic performance and social relations of special needs students.

Abstract: Summary The effects of individual and group contingencies were studied on achievement, appropriate classroom behavior, acceptance of handicapped peers, and self-esteem of academically and socially handicapped students. Four studies are reported, focusing on the following: four first-graders, 11 seventh-graders, five ninth-graders, and five first-graders. All were low-achieving, special needs students, many of whom were seeing special education teachers due to their disruptive classroom behavior and alienation of their peers. In all studies, group-contingency procedures were compared to individual-contingency procedures or no-contingency procedures. Different operationalizations of group-contingency procedures were used in each study. The studies were conducted in different school districts at different times of the year. Variations of A-B-A designs were used in the studies. The results are consistent, indicating that group contingencies (compared with individual contingencies or no contingencies at all) p...

Effects of cooperative and individualistic instruction on the achievement of handicapped, regular, and gifted students

Abstract: Summary The effects of cooperative and individualistic learning experiences were compared on achievement of academically handicapped, normal-progress, and gifted sixth-grade students. Fifty-five students were assigned to conditions on a stratified random basis controlling for ability and sex. They participated in one instructional unit for 65 minutes a day for five instructional days. The results indicate that cooperative learning experiences promoted higher achievement, greater retention, more positive attitudes among students, and higher self-esteem than did individualistic learning experiences.

Effects of cooperative and competitive learning experiences on interpersonal attraction between handicapped and nonhandicapped students.

Abstract: Summary The effects of cooperative and competitive learning experiences on interpersonal attraction between handicapped and nonhandicapped, fourth-grade students were compared. Fifty-one students were assigned to conditions on a stratified random basis controlling for handicap, ability, and sex. They participated in two instructional units for 45 minutes a day for 15 instructional days. Cross-handicap interaction during daily free-time periods and a number of attitudes were measured. The results indicate that cooperative learning experiences, compared with competitive ones, promote more interpersonal attraction between handicapped and nonhandicapped students.

Changes in tokamak plasma properties during impurity injection

Abstract: Certain applications of laser blow‐off impurity injection, such as ion temperature measurement and spectral line identification, may require the ratio of injected ions‐to‐plasma electron density to exceed 0.001. To achieve these concentrations we have relied on injection of micron‐sized clusters as well as monatomic species. In these cases the injected impurity can no longer be regarded as a nonperturbing trace sourced at the plasma edge. We therefore have studied the variation of plasma parameters in PLT and PDX as a function of the amount of injected impurities, the species mix, and the type of impurity. We find that for ohmically‐heated plasmas, impurity injection can increase ?e more than 4×1012 cm−3 without causing disruptions. During Ge‐injection experiments where Δne/ne ∠0.05, Te initially rises ∠5% on axis and decreases ∠20% at the edge. The plasma current drops 1–3 % and the loop voltage and radiated power both double. Varying the amount of injected impurities changes the peaking and decay times ...

Ion heating with high-power perpendicular neutral-beam injection in the Poloidal Divertor Experiment (PDX)

Abstract: Plasma heating by near-perpendicular injection of up to 7.2 MW of neutral-beam power has been studied in the PDX tokamak. Collisionless plasmas with central ion temperatures up to 6 keV have been obtained. The total plasma energy, which is dominated by contributions from beam and thermal ions, rises linearly with increasing beam power. The ion heating efficiency in PDX is comparable to that measured in PLT with tangential injection.