Administration of adrenal steroids or blocking agents at optimum doses influenced northern fowl mite development on chickens. Corticosterone at 20 ppm or desoxycorticosterone at 30 ppm in feed were most effective in inhibiting mite infestations. High levels of social stress increased resistance of chickens to mites in a manner similar to but more effective than steroid administration. The mechanism of resistance was a decrease in capillary density at the skin surface. Commercial laying hens caged alone had lower plasma corticosterone levels and supported more mites than hens caged in groups. Stress-induced, steroid initiated, or inbred mite resistance was incompatible with maximum production from chickens. Resistant chickens produced poorer weight gains and testes mass than did susceptible birds. Sex hormones were shown to play a supplementary, and antibody a minor role in mite resistance. Carbaryl was shown to be the compound most toxic to northern fowl mites of those registered in Virginia for application to poultry. Malathien resistance was noted in mites from a commercial poultry house. The synthetic pyrethroid permethrin was effective against these mites. / Ph. D.

The purpose of this paper is to study the asymptotic behavior of bounded solutions x(t) of the integrodifferential equation. / Ph. D.

The two-year college system operates primarily under an open-door admission policy which admits many students who are academically deficient in their writing skills. To meet the needs of these students, many colleges have designed and implemented developmental English courses which, unfortunately, have not always shown a high degree of success. Many studies have been made to identify characteristics of the developmental student, but research is limited in the area of competencies needed by those who instruct students taking developmental writing courses. It was the purpose of this study to identify these competencies, and the method chosen to do this was the Delphi Technique. A panel of fifty-three experts listed what they perceived to be needed competencies for teaching developmental composition. They listed forty-two competencies which were itemized into three categories: rhetorical, pedagogical, and human interaction. The panel members then rated these according to their perceived importance. The investigator ranked them in order of importance by using a weighted score. / Ed. D.

The study attempted to determine if library skills in a community college could be taught more effectively within a one-class-period time frame by a video self-instruction unit or by classroom teaching. The experiment also considered the comparative effectiveness of both modes of instruction when used in groups of developmental and degree-program students. The study was conducted at a multi-campus community college in the fall of 1976. Fourteen English classes (seven developmental, and seven degree-program) participated, yielding 120 subjects after attrition. Each class was separately randomized into two groups. The first group reported to the classroom as usual for instruction in library skills; the second group completed a video self-instructional unit on their own during a designated time period. Instructors of the classroom groups administered post-tests to their students immediately after the lesson. For students in the video self-instructional groups, members of the Learning Resources Center staff administered the post-tests individually. Delayed post-tests were administered to students in both types of groups, by the instructor, 12 days after the "classroom teaching" session. The analysis of variance with repeated measures revealed no significant differences between those taught by the classroom method, and those taught by a video self-instruction unit, for both times of testing. / Ed. D.

Much has been written about the potential resource that tutors might represent in our present educational system. However, very little scientific research could be found on this topic in the physical education field. This lack of evidence concerning the potential usefulness and effectiveness of tutors in physical education, particularly at the elementary school level, provided the impetus to conduct the present study. The purposes of this study were: 1) To investigate the effects of four factors, tutee sex, tutor sex, tutor grade level, and tutor tumbling ability, on a cross-age tumbling teaching program for first grade students. In addition, all first order factor interactions were studied for effect. And, 2) To compare the skill gains of those subjects taught by an upper grade tutor, fourth and sixth, to the gains of those taught by a physical education specialist. The data were collected during the spring of the 1976-77 academic year at W. H. Keister Elementary School in Harrisonburg, Virginia. Seventy-two first grade subjects participated in the study, with boys and girls equally represented. Eight upper grade tutors were selected for the study according to the eight various combinations of the three tutor factors studied for effect; male-female, fourth-sixth grade, and low-high tumbling ability. The seventy-two subjects were pretested for the ability to perform the three tumbling skills of forward roll, headstand, and cartwheel through the use of the Jarvis Tumbling Test (1967). The performances were recorded by a video cassette recorder and scored by two judges. Subjects were randomly assigned to either one of the eight tutors' groups or to the specialist's group and given instruction on the three skills three days a week for six weeks. After which, they were post-tested for skill gain. A six-week cross-age instructional program in tumbling skills was found to increase proficiency in performing the skills, with some increases more pronounced than others. For all subjects, the test score increase percentages from pre- to post-test were 38 percent for the forward roll, 155 percent for the headstand, and 209 percent for the cartwheel. A four-way factorial MANCOVA was applied to the data in order to investigate the effects of the four factors upon mean score change from pre- to post-test, using the .05 level of confidence for significance. Factor one was tutee sex, factor two was tutor sex, factor three was tutor grade level, and factor four was tutor tumbling ability. The analysis of data revealed that the only factor to have a significant effect was tutor grade level. Those subjects with a sixth grade tutor scored significantly higher on the tests than those with a fourth grade tutor. None of the first order interactions between the four factors produced any significant effects on the groups' test scores. A one-way ANOVA was used to analyze data for any significant group differences in test score gains between the eight tutors' groups and one specialist's group. No significant difference was found between the tutors' groups' performances and those of the specialist's group. / Ed. D.

Total charge-transfer cross sections have been obtained in the N₂⁺ - N₂ system with relative ion energies at seven different values between 9 and 441 eV. Data is obtained to examine the curvature and structural relation between total cross section versus ion energy. The effect of ion beam excitation on the cross sections was studied by varying the electron ionization energy in the mass spectrometer ion source over electron energies at eight different values, between 11.6 and 32.1 eV. The dependence of total cross section on the neutralization chamber gas pressure was examined by obtaining data at four different pressure values from 9.9 to 19.9 x 10⁻⁵ torr. Subsequent data treatment provided 56 different cross section values that are with and theoretical results of other investigators. / Ph. D.

Northern red oak (Q. rubra L.) seeds were dormant and required 10 weeks of moist, cold stratification before a large percentage of the seeds would germinate. White oak (Q. alba L.) seeds were not dormant and germinated immediately upon falling from the mother tree. A transfer of mass from the cotyledons to the embryos occurred during germination of red and white oak seeds. No detectable transfer of mass occurred during stratification of the red oak seeds. The longer the red oak seeds were kept under stratification conditions, the shorter the period of time required for seeds at 26°C to begin germination. A significant decrease in GA-like activity occurred during the first 5 weeks of stratification of red oak seeds. No transfer of activity from one pH-dependent ethyl acetate-soluble fraction to another occurred. A slight increase in GA-like activity occurred between 5 'and 7-1/2 weeks of stratification. Red oak seeds stratified for 18 weeks contained significantly more GA-like activity than those receiving lesser periods of stratification. When l8-week stratified red oak seeds were warmed to 26°C, germination commenced within 2 days and the levels of GA-like activity decreased. White oak seeds contained substantially less GA-like activity than red oak seeds and amounts of activity in white oak seeds changed little during cold storage of the seeds. Radicle extension growth of white oak seeds began even at 5°C and complete seed germination began within 2 days of warming to 26°C, independent of the time in cold storage. Cytokinin activity was measured in the ethyl acetate and n-butanol fractions of red oak seeds. Concentrations did not change between 0 and 5 weeks of stratification. / Ph. D.

The primary objective of this study was to empirically test J. D. Thompson's proposition that organizations seek to buffer their technical cores from the uncertainty of the environment. Secondary objectives included: to explore the relationship among core technology, perceived environmental uncertainty, size, and buffering; to provide descriptive statistics on the use of part-time and temporary workers in manufacturing firms; and to empirically test the Perceived Environmental Uncertainty Instrument developed by Duncan and modified by Downey. These were accomplished by examining in an applied setting the relationship among one buffering method, two types of core technologies, size, and perceived environmental uncertainty. / Ph. D.

Generally, the model developed in this investigation predicted quite well the values of the parameters measured experimentally. In certain cases, deviations were observed, but these were due to known factors which have been described in the previous section. This model represents the first link in a chain that is just beginning. The end use of the program will be in DOC feed-forward control applications for injection molding cycles. Several improvements can be made on this model. First, a more detailed analysis should yield a better relationship between the volumetric flow rate and the pressure at a given point. This is necessary because the volumetric flow rate should be smoothly decreased in order to keep the runner entrance pressure at the constant preset injection pressure. In this investigation, a power law relationship was used. This exponential relationship proved to decrease the volumetric flow rate faster than it should have. This caused some oscillations in the predicted temperature and pressure values. It was observed from the experimental data that a linear relationship could do the job, and that the volumetric flow rate should be decreased at each time interval as the pressure increased, instead of waiting until the preset injection pressure was reached as it was done in this investigation. Second, a non-linear regression fit should be performed on the experimental data available for heat capacity and thermal conductivity. The regression equations could be used in the model. This will reduce the consistently high temperatures predicted by the model. Third, the model should be extended to take into account the heat transferred to the wall of the channels. In this investigation a constant wall temperature was assumed in order to simplify the initial development of the model. At this point the finite difference grid used in the model could be extended to include the metal containing the cooling channels where the temperature is known. The inclusion of this feature could be accomplished with a small programming effort. Finally better packing and cooling models could be developed. The cooling model proved to be the poorest of the proposed models. An extra effort to develop a better cooling model was not considered to be necessary, because this investigation was more concerned with the filling and packing stages, which are the critical stages for gate design purposes. / Ph. D.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.