Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 238-250.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2006. / Härtill 6 uppsatser.

Mémoire (M.Eng.)--Université du Québec à Chicoutmi, 1998. / Document électronique également accessible en format PDF. CaQCU

Thesis (M.S.)--Ohio University, August, 2004. / Includes bibliographical references (p. 71-73).

Thesis (M. Eng.(Geotechnical Engineering))--University of Pretoria, 2003. / Includes bibliographical references.

Thesis (M.S.)--Ohio University, August, 2004. / Title from PDF t.p. Includes bibliographical references (p. 71-73)

Thesis (M.S.P.H.)--Uniformed Services University of the Health Sciences, 2006 / Typescript (photocopy)

Thesis (MEng)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: A desire to increase the efficiency of the comminution process in mineral process systems has led to the need of determining the size distribution of ore particles at various stages in the system. The objective of this research is to investigate the feasibility of the use of an acoustic sensor for measuring particle size distribution. The acoustic signal generated when the particles impact on a cantilever bar is analysed using digital signal processing techniques. As rocks fall onto a metal bar, the bar vibrates. The vibrations contain information th a t is extracted to determine the size of particles tha t impacted on the bar. The bar is modelled as a linear system which is excited by impulses (impact of particles). The response of the bar is deconvolved from the acoustic signal to obtain an impulse whose amplitude is proportional to the energy of the impact. In order to improve size estimates, deconvolution is performed using a statistical model of the impulse sequence (Bernoulli-Gaussian) and then estimated using MAP estimation. Size estimates are not only a function of the mass of particles, but also on the exact position of impact on the bar. Since there is always a variation in the position of impact, size estimates are erroneous. It was found that the position of impact can be determined as to reduce variances dramatically. Due to physical sampling in space, the sensor has a bias towards larger particles. We show how this can be represented mathematically and removed. This project is mainly concerned with rocks in the +8-25mm (+0,7-22 gram) size range. / AFRIKAANSE OPSOMMING: Vergruising van erts in die mineraalbedryf verg groot hoeveelhede energie. Daar is ’n behoefte gei'dentifiseer orn hierdie proses meer effektief te maak. Aangesien die effektiwiteit van ’n meul ’n funksie is van die ertsgroottes wat gemaal word, kan partikel grootte inligting aangewend word om effektiwiteit te bevorder. Die doel van hierdie tesis is om die lewensvatbaarheid van ’n akoestiese sensor vir die doel van partikelgrootte estimasie, te ondersoek. Erts partikels wat val vanaf ’n vervoerband op ’n kantelbalk, veroorsaak dat die balk vibreer. Deur hierdie vibrasies te meet en verwerk, kan inligting aangaande partikel grootte verkry word. Die stelsel word gemodelleer as ’n lineere sisteem met impulse as intree. Die geobserveerde sein is die konvolusie tussen die intree impulse en die impulsweergawe van die sisteem. Deur gebruik te maak van ’n statistiese model en MAP-estimasie, word die effek van die sisteem gedekonvuleer vanaf die geobserveerde sein om ’n benadering van die intree impuls sein te verkry. Die amplitudes van die impulse word gebruik as ’n aanduiding van partikel massa. Partikelgroottes soos benader deur die stelsel, is ’n funksie van die die posisie waar die partikel die balk tref. Deur van patroonherkenning tegnieke gebruik te maak, word die posisie van impak bepaal om sodoende grootte benaderings aan te pas en die variansie van grootte verspreidings te verminder. As gevolg van die feit dat partikels gemonster word deurdat slegs ’n klein persentasie van die hele omvang van partikels ondersoek word, onstaan daar ’n oorhelling ( “bias” ) na groter partikels. Die kans dat groter partikels die balk tref is groter as vir klein partikels. ’n Wiskundige model vir hierdie verskynsel word voorgestel en gewys hoe die die oorhelling geneutraliseer kan word. Hierdie projek het te doen met ertsgroottes +8-25mm (+0,7-22 gram).

Solid substrate cultivation (SSC) using lignocellulosic non-food feedstock, such as switchgrass, is an alternative for advanced biofuel production. Acetone-Butanol-Ethanol (ABE) fermentation in two stages using a sequential culture of microorganisms from the class Clostridia is an approach proposed to increase the butanol production. The goal was to test the efficacy of a sequential culture on high solid substrate cultivation in batch and continuous cultivation, and to evaluate conditions to optimize butanol production using switchgrass as substrate. Initial batch experiments were used to determine particle size effect, choice of solvent producer and pretreatment evaluation: The effect of particle size on gas production was surface area-dependent, 2 mm particle size of switchgrass was better fermented by clostridia than the other particle sizes. C. thermocellum improved switchgrass fermentation by C. beijerinckii. Moreover, C. saccharoperbutylacetonicum produced the highest butanol yield on glucose as substrate. The Fenton reaction was studied as a potential pretreatment for switchgrass. C. beijerinckii grew better on Fenton-treated material, but solvent production was low. The major conclusion of the continuous flow on SSC experiment was that there is no statistical difference in the effect of flow rate within the flow range tested.

Com a crescente diminuição de recursos minerais e o alto custo envolvido na construção da estrutura de uma mina, a recuperação máxima possível de uma jazida vem se tornando fundamental. Para isso além da escolha do método de lavra ter a necessidade de ser feito cautelosamente, é possível lançar mão de métodos adicionais de recuperação, como por exemplo, a recuperação de pilares. Essa pesquisa foi baseada na determinação da caracterização do enchimento (backfill cimentado) utilizado nas câmaras vazias que possibilita a posterior recuperação dos pilares. A caracterização do enchimento é composta da determinação da resistência simples do backfill necessária para que o enchimento cumpra com seu objetivo, desenvolvimento da classificação granulométrica ótima para os agregados e dosagem de cimento e água para alcançar a resistência proposta. A metodologia desenvolvida para obter a nova caracterização é composta de várias etapas que incluem pesquisas em campo e trabalhos em laboratório. Primeiramente, foram obtidos através de análise em campo os parâmetros de dosagem de cimento e classificação granulométrica dos agregados já utilizados na planta de fabricação do enchimento, bem como sua resistência correspondente. Em seguida definições teóricas da dosagem de cimento ideal e classificação granulométrica ótima foram realizadas com base na resistência à compressão simples que foi identificada como necessária para cumprir com as solicitações geomecânicas do maciço rochoso, então posteriormente, a nova caracterização definida teoricamente foi posta à prova através da confecção de corpos de prova de backfill, seguido de execuções de ensaios de compressão. Durante a primeira etapa da metodologia, já se pôde identificar que os agregados possuíam um alto índice de partículas tamanho argila que estavam afetando os resultados de resistência obtidos com a caracterização empregada inicialmente. A partir disso se optou por construir a curva granulométrica ótima sem essa fração. A resistência à compressão simples calculada de 2,69 MPa, foi obtida com base no planejamento de longo prazo que prevê a total recuperação dos pilares existentes na mina. Dessa maneira toda a área que será minerada foi considerada como um único bloco. Finalmente, foi identificada a dosagem de cimento sendo de 4% em peso, que juntamente com a granulometria ótima é capaz de alcançar os valores esperados de resistência. Para que o planejamento da produção da mina durante os próximos anos de vida útil seja efetivamente cumprido, o enchimento deverá prover à mina estabilidade geomecânica local a nível de câmaras abertas com paredes verticais de backfill estáveis e também estabilidade global a nível de contato entre níveis e galerias de acesso. Isso somente será alcançado se a nova caracterização for corretamente aplicada. / As a consequence of the ongoing reduction of mineral resources and the high cost involved in the construction of a mine, the maximum recovery of a mineral deposit becomes a fundamental issue. Therefore, besides the need of caution on the choice of the mining method, it is possible to make use of additional recovery methods, such as the recovery of pillars. This research was based on the determination of the characterization of the fill (cemented backfill) used in avoid stopes that allows the subsequent recovery of adjacent pillars. The characterization of the fill consists of determining the uniaxial compressive strength of the backfill required for an efficient filling, developing an optimal particle-size distribution for the aggregates and finding the cement-water ratio necessary to reach the desired resistance. The methodology developed to obtain the new characterization is comprised of several steps which include field work and laboratory tests. First, cement dosing parameters and particle size of the aggregates (already used at the filling manufacturing plant), as well as their corresponding strength, were obtained through analyses in the field work. Then, theoretical definitions of the ideal cement dosing and optimal particle-size analysis were carried out based on the uniaxial compressive strength that has been identified as necessary to comply with the geomechanical requests from the rock mass, and then later, the new theoretical characterization was tested by making backfill samples, followed by execution of compression tests. During the first stage of this methodology, it has been identified a high proportion of clay particle size for the aggregates, that have affected the strength results obtained from the characterization used initially. From this point, we decided to build the optimal particle-size curve without this fraction. Uniaxial compressive strength, calculated as 2.69 MPa, was obtained from the long-term planning that determines the full recovery of the existing pillars in the mine. In this way, the entire area to be mined was considered as a single block. Finally, the cement dosing has been identified as 4% by weight, which together with the optimal particle size, is able to achieve the expected strength values. In order to effectively fulfill the mine production planning over the next years of lifespan, the filling should provide the mine local geomechanical stability at open stopes level, with vertical walls of stable backfill, and also global stability at the contacts between levels and access galleries. This will only be achieved if the new characterization is correctly applied.