1. Mechanisms of urea adsorption by soils Physically adsorbed urea may be easily desorbed by dilution. Chemisorbed urea existing primarily in the form of relatively stable soil organic matter-urea complexes may, in part, be slowly dissociated upon dilution. Differences between soil types with respect to urea adsorption were primarily related to organic matter contents; the effects of CEC, pH, and clay mineral content were found to be insignificant. Wet soils had a lower capacity for urea adsorption than dry soils. Considering the amounts of urea adsorbed it appears that soils have a weak affinity for the urea molecule. 2. Mechanisms of urea hydrolysis and volatilization in soils The biological or catalytic hydrolysis of urea is rapid and can be related to soil microbial activities. The reaction rate of the chemical hydrolysis of urea is very slow and insignificant in comparison with the biological or catalytic hydrolysis. Urea-nitrogen loss through ammonia volatilization may immediately follow urea hydrolysis and proceeds rapidly. Urea hydrolysis and ammonia volatilization from ammonium carbonate are first order reactions. 3. Mechanism of foliar absorption and subsequent utilization of urea The mechanism of foliar absorption of urea solution is suggested to be a simple physical diffusion phenomenon. The absorbing capacity of the foliage for urea solution is relatively lover during the day than during the night. It is suggested that rapid evaporation at high temperature and low humidity conditions may increase the concentration of the urea solution on the leaf thereby decreasing the rate of diffusion of foliar applied urea into the leaf. The absorbing capacity of the leaf for urea solution is independent of its position, but the younger leaves have a higher capacity to metabolize the absorbed urea. Urea in foliage cannot be translocated, but more than 90%of the absorbed urea can be rapidly and directly transformed into other soluble nitrogenous compound(s). The mechanism of the biochemical reactions and their related enzymatic systems are not yet known. Sucrose does not influence the urease activity, and no urease activity was detected in the tobacco leaves used. The reduction of urea injury from foliar applied urea solutions containing sucrose was associated with decreased urea absorption and increased urea utilization. A relationship was found to exist between the urea concentration in the leaf and the incidence of injury. Plasmolysis resulting from increased urea concentrations in the leaf may be the cause of foliage burning resulting from foliar application of urea. 4. Methodology The principle of the newly developed methods for the determination of urea in fertilizers, urine, and blood and the estimation of urease activity is based on the difference in electric conductivity of urea and ammonium carbonate produced from urea by urease in solution. These methods are rapid, simple and accurate. They have very wide testing ranges, and the values of the standard curves are constant at a specified temperature. Interference due to the presence of colored impurities are eliminated. However, these methods will not be applicable if heavy metal ions such as Ag, Hg, and the protein-destroying substances are present in the testing solution. / Ph. D.

Ph. D.

The main purpose behind this thesis was to study the variations of strength in a soil after it had been stabilized with various percentages of lime, cement, and combinations of the two. In both cases where the additives were added separately to the soil, the percentages used were 5 and 10 per cent by dry weight of soil. In the additive combination study, lime-cement percentage additions were 2-3, 3-2, 4-6, and 6-4 by dry weight of soil. The first two percentages, when added together, amount to 5 per cent stabilizing agent, while the latter two total 10 per cent. Since these two totals were the same as those used in the separate lime and cement studies, an analysis of strength changes when lime, cement, and lime-cement combinations were added to the soil could be made. Strength studies which were made consisted of unconfined compression immediately after compaction and after a four-day curing period in a 100 per cent humidity curing room. Atterberg limit tests were also run at the various percentages of additive. The laboratory test results indicate: 1. For cured specimens containing a stabilizing agent, the greatest four-day strengths will occur at or above OMC, in most cases. This may not always be true in the case of cement, since moisture condition is not as significant in cement stabilization as it is in other types. 2. Control of moisture at or near OMC during field compaction appears to be much more important in lime stabilization than in cement stabilization if maximum strengths are to develop. This statement is supported by a statistical analysis which was performed on the strength data. 3. The variation of' the lime-cement percentage trom 6-4 to 4-6 has no effect on four-day cured strengths. / M.S.

This paper is concerned with the statistical approach to population genetics. The genetical characteristics of the population under consideration are the population size and the gene frequencies. The limitations on the population are (a) the individuals are either all haploids or all diploids; (b) the alleles are only two in number, either A or a; (c) there are no selection and migration pressures occurring in the population. Three main model types, the branching processes, the Markov chains, and the diffusion processes are discussed. Published results on the subject are presented along with some new investigations. Comparable results obtained by various authors are checked, some of which are found to be invalid. Continuous approximations are used to derive some of the results of discrete processes, but a chapter is devoted to the justification of such approximations. / M.S.

M.S.

An analytical study of the dynamics of manned rotating space stations under various steady-state and transient excitation, such as docking impacts, attitude system torques, and crew motions, has been conducted. The basic equations of motion for the spinning station are developed and expressions simulating the applied disturbances are introduced. Two stability systems, a gyroscopic wobble damper and a proportional jet damper are represented mathematically, and the motion of the station under the external disturbances has been determined with and without the effects of these stability systems. Computer results for a toroidal example station are presented, and the effects of a variation in the moment of inertia distribution are discussed. A description of an experimental facility capable of simulating the excitation considered in the theoretical analysis and of determining and recording the resultant station lotion is also included. / M.S.

Using a variance-stabilizing transformation of the non-centralχ² distribution and Wald's sequential probability ratio test, procedures have been developed for sequential analysis of categorical data group-wise. These procedures' enables (i) a simple hypothesis to be used for the alternative hypothesis instead of the composite hypothesis commonly used in goodness-of-fit tests, contingency tables, and Mood's non-parametric generalization of the one-way analysis of variance, (ii) calculation or a power function, and (iii) calculation of the greatest expected ASR's and the non-centrality parameter requiring this sample size in addition to the ASN's when the null or alternative hypothesis is true. Application of these procedures to the three types of analysis given in (i) give the right decisions with sample sizes near the calculated ASN’s. The ASN's for when the expected number of groups equals one compare favorably with those obtained by Jackson (1959) using Bhate’s conjecture and those obtained empirically by Appleby (1960). In general, the sequential approach will require smaller sample sizes than fixed sampling if the non-centrality parameter is equal to or less than the group size and the group size is large enough to meet minimum expectation requirements. / M.S.

Many benz(a)anthracene derivatives are able to produce cancer in the experimental animal. There is a correlation between the calculated total electronic charge of the K-region and this carcinogenic activity. There is also ample proof that benz(a)anthracene derivatives are honed to the skin through quinoid type bonds in the K"region. However, the prediction of physiological activity of benz(a)anthracenes is still unreliable because of the limitations of the theoretical model described by existing theories. The purpose of this work was to synthesize some substituted benz(a)anthracenes with a shielded K-region and with a different L-region electron density than in 7-phenyl-bena(a)anthracene in the hope of increasing our knowledge regarding molecular structure-physiological relationship. / Ph. D.

This study is one phase of a ten-year project designed to evaluate forest-wildlife relationships. The project was initiated in 1958 on the Jefferson National Forest, Broad Run Wildlife Management Area, Craig County, Virginia. The objective of the study was to determine if correlations existed between quantities of available deer browse in the understory of a particular forest cover type and several site quality measurements. The purpose of the study was to determine if weights of browse per acre could be estimated reliably by utilizing easily obtained site quality measurements instead of clipping and weighing browse. Eight site quality measurements (variables) were tested. These were: site index, depth of the A₁ soil horizon, position on slope, basal area per acre, aspect (exposure), percent of slope, elevation, and the number of clipped stems per sampling unit. Fieldwork was conducted in two major forest cover types; the oak, hickory, poplar, white pine type (cove hardwoods type), and the mixed oak-pine type. Sampling units were located randomly, in pairs, within each of these two forest cover types. Each sampling unit consisted of a circular 1/4 acre plot and a square 1/100 acre plot located at the center of the circular plot. A system of double sampling was used to obtain browse weight data and site quality data for comparisons. Data on eight variables recorded at each 1/4 acre sampling unit were compared with the quantity of browse clipped from the 1/100 acre sampling unit located at the center of that particular 1/4 acre plot. A multiple regression analysis was used to determine the degree of correlation between quantities of browse (available browse) clipped from sampling units and all measurements of the eight independent variables (site quality measurements) recorded on sampling units. The final analysis of the oak, hickory, poplar, white pine cover type data indicated that the variables significantly related to browsing weights per acre were the number of stems clipped per sampling unit and the depth of the A₁ soil horizon. These two significant variables explained 48,63 percent of the total variation in browse weights occurring between sampling units. Using only the two significant site quality measurements (independent variables), the final estimating equation was: Y (pounds of browse per acre) = -0.14 + 0.06 (number of stems clipped per sampling unit) + 0.61 (depth of the A₁ horizon, inches). The final estimating equation should not be used for reliable estimates of browse production in the oak, hickory, poplar, white pine forest cover type. A total of 51.37 percent of the variation in browse weights occurring between sampling units is unaccounted for in this equation. The final analysis of the mixed oak-pine cover type data indicated that the only variable significantly related to browsing weights per acre was the number of stems clipped per sampling unit. However, this significant variable explained only 17.97 percent of the total variation in browse weights occurring between sampling units. Using only the one significant site quality measurement (independent variable), the final estimating equation was: Y (pounds of browse per acre) = 2.24 + 0.07 (number of stems clipped per sampling unit). The final estimating equation should not be used for reliable estimates of available browse production in the mixed oak-pine forest cover type. A total of 82.03 percent of the variation in browse weights occurring between sampling units was unexplained in this equation. More research is necessary to determine other easily measured environmental factors (variables) which might bear a significant relationship to quantities of available deer browse produced in the two forest cover types sampled. When several more of these significant variables are discovered, the addition of these variables to the estimating equations for the two cover types might account for a large enough percent of the explained variation to enable the game biologist to use the equations for reliable estimates of browse production. / Master of Science

Master of Science