Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2006. / Melkote, Shreyes, Committee Chair ; Zhou, Min, Committee Member ; Liang, Steven, Committee Member ; Thadhani, Naresh, Committee Member ; Haj-Ali, Rami, Committee Member. Vita. Includes bibliographical references.

Thesis (Ph.D.)(Metallurgical Engineering)--University of Pretoria, 2005. / Includes summary. Includes bibliographical references.

Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliography.

Thesis (M.Eng.Sc.) - University of Queensland, 1996. / Includes bibliography.

The purpose of this study was to investigate whether ethnicity, gender, grade level and content area mediate the relationship between class size and student achievement. Twenty six educational research studies were collected for this meta-analysis. A meta-analytical approach using like data sets were used to report the most accurate information. Fixed and random effect models were used to ensure the distribution across different studies. A total of three studies were meta-analyzed for this research. The studies included in this research examined class size and student achievement for students in grades K-7. This research examined whether there was a mediating effect on ethnicity, gender, grade level, and content area in the class size and student achievement studies collected and correlated. The results indicate that smaller class size does have a positive impact on student achievement when mediated by ethnicity, grade level, and content area. When examining ethnicity as a mediating factor, a stronger correlation exists for minority students than for whites. When examining grade level as a mediating factor results indicate that a stronger correlation exist for lower grades K-3 than upper grades 4-7. A stronger correlation is present in the content area of reading as compared to other content areas when it was used as a mediating factor. When examining gender as a mediating factor, the largest effect sizes were reported for females in reading as opposed to males in math, both for first grade. These results correlate with those presented in other mediator sections of the study. The results found in this research will contribute to the literature concerning class size and student achievement and will help inform educational policy makers regarding class size as an educational issue.

No description available.

Size-reduction of materials is an important operation in many chemical industries. The purpose of size-reduction are: (a) for specific mesh size product; (b) grinding for release, or unlocking grinding for purposes of surface exposure or locked-in products for chemical or physical attack; (c) specific surface grinding for product; and (d) size modulus, where limited mesh size is needed for specific processing operation. Size-reduction is accomplished by (a) impact, (b) differential movement of adjacent surfaces and (c) by the combination of both. Most size-reduction of a combination of both, whereas swing hammermill grinding is due mainly to impact. Rittingers’ and Kicks’ laws are empirical formulas which do not make an attempt to resolve the forces as applied to grinding into their component parts. Possibly the application of the component forces as applied to impact grinding would give a key to the multiple factors controlling size-reduction. If this can be worked out, the general formula might be obtained that would apply to all phases of size-reduction. The purpose of this investigation is to study the factors as applied to swing hammermill grinding; also, to determine if it is possible to formulate an equation which will hold for the size reduction of various materials. / Master of Science

The grinding models developed previously are concerned with size reduction only. Although they have proven to be useful in the simulation and design of grinding mills, they do not provide information on liberation which is the main objective of most comminution operations. In the present investigation, a population balance model describing the combined processes of size reduction and mineral liberation has been developed for batch grinding operation. The model parameters include conventional breakage rate and breakage distribution functions, along with a new parameter i.e., liberation function that is used to describe changes in particle composition. These parameters have been determined experimentally by examining mill products under optical microscope using a SEM-IPS image analyzer. The areal assays, obtained from the image analysis of monosized particle mounts, have been found to correspond quite closely to the actual chemical assays. It has been found that the method used to prepare particle mounts is critical in achieving accuracy. In the present work, it has been shown that the breakage characteristics of component minerals can be determined by examining the mill feeds and products using an image analyzer. The model parameter analysis has shown that while the breakage rate functions are sensitive to the grinding environment, breakage distribution functions are independent of it. Furthermore, the breakage distribution functions have been found to be normalizable with feed size, thus reducing the number of parameters that must be estimated. The study has also shown that both the breakage rate and the liberation function suggest a preferential breakage of sphalerite over dolomite gangue. The model has been validated by simulating the batch grinding of a sphalerite ore from ASARCO's Young Mine in eastern Tennessee. The model can predict the product size distributions for the total ore and its components, including gangue, sphalerite, and composite particles. An excellent agreement between the model predictions and the experimental results has been observed for both monosized and multisized feed materials. The model is capable of handling multiple classes of composite particles for a binary ore; however, the model has been verified against experimental results by considering only two composite classes. The method of determining liberation functions has also been discussed. The liberation function has been found to be useful for analyzing the liberation mechanisms of composite particles. / Ph. D.

The implications of comminution practices on the planning of a typical open pit mine was investigated in this study by means of computer simulation. The objective was to assess the effects of mining costs as well as processing costs on the production plan of a typical open pit mine. For the purpose of the research, MineLib, an open library of ore body models was consulted. This led to the selection of a copper-gold ore body named “Newman1” for use in the strategic mine optimisation. Various scenarios were considered in order to highlight the contribution of comminution costs to the mine plan. In all the simulated scenarios, the objective function was to maximise the Net Present Value (NPV). And in terms of simulation setup, the comminution costs and cut-off grades were systematically varied from 70 % to 140 %. It was hence possible to investigate their effects on the NPV of the Newman1 ore body using SimSched, a freeware for mine optimisation and planning. Results showed that there is a great opportunity to increase the NPV of the Newman1 block model by adjusting the contribution of processing costs in general and comminution costs in particular. This can be achieved for instance by controlling the policy of cut-off grades, lowering production costs, and increasing throughput. / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)

Call number: LD2668 .T4 1985 S364 / Master of Science