M.Tech. (Chemical Engineering) / Please refer to full text to view abstract

The objective of this investigation was to determine the influence of work roll cooling on roll thermal behavior. The investigation has been conducted utilizing a previously developed computer model [1]. Three industrial operations were evaluated and features of an optimum configuration have been identified. The magnitude of the thermal zone near the roll surface within which the cyclic temperature variation is confined has been evaluated for different roll cooling conditions. A two dimensional thermal model of a work roll has been developed to predict the thermal field inside the roll, based on which the thermal crown of the roll was calculated under an assumption of axi-symmetric deformation. The heat transfer equation was solved by the numerical finite difference method, the Alternating Direction Implicit (ADI) method. This method makes it possible to solve the problem on a personal computer making it suitable for industrial application due to the minimum requirements of computer storage and time. Also because the thermal model simulates operating conditions including the cooling configuration it is of value in studying a variety of industrial rolling conditions. The influence of roll spray arrangement, roll gap heat transfer and mill pacing on roll thermal crown has been investigated. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Understanding the dynamic behavior of particulate materials is extremely important to many industrial processes with a wide range of applications ranging from hopper flows in agriculture to tumbling mills in the mining industry. Thus simulating the dynamics of particulate materials is critical in the design and optimization of such processes. The mechanical behavior of particulate materials is complex and cannot be described by a closed form solution for more than a few particles. A popular and successful numerical approach in simulating the underlying dynamics of particulate materials is the discrete element method (DEM). However, the DEM is computationally expensive and computationally viable simulations are typically restricted to a few particles with realistic particle shape or a larger number of particles with an often oversimplified particle shape. It has been demonstrated for numerous applications that an accurate representation of the particle shape is essential to accurately capture the macroscopic transport of particulates. The most common approach to represent particle shape is by using a cluster of spheres to approximate the shape of a particle. This approach is computationally intensive as multiple spherical particles are required to represent a single non-spherical particle. In addition spherical particles are for certain applications a poor approximation when sharp interfaces are essential to capture the bulk transport behavior. An advantage of this approach is that non-convex particles are handled with ease. Polyhedra represent the geometry of most convex particulate materials well and when combined with appropriate contact models exhibit realistic transport behavior to that of the actual system. However detecting collisions between the polyhedra is computationally expensive, often limiting simulations to only a few thousand of particles. Driven by the demand for real-time graphics, the Graphical Processor Unit (GPU) offers cluster type performance at a fraction of the computational cost. The parallel nature of the GPU allows for a large number of simple independent processes to be executed in parallel. This results in a significant speed up over conventional implementations utilizing the Central Processing Unit (CPU) architecture, when algorithms are well aligned and optimized for the threading model of the GPU. This thesis investigates the suitability of the GPU architecture to simulate the transport of particulate materials using the DEM. The focus of this thesis is to develop a computational framework for the GPU architecture that can model (i) tens of millions of spherical particles and (ii) millions of polyhedral particles in a realistic time frame on a desktop computer using a single GPU. The contribution of this thesis is the development of a novel GPU computational frame- work Blaze-DEM, that encompasses collision detection algorithms and various heuristics that are optimized for the parallel GPU architecture. This research has resulted in a new computational performance level being reached in DEM simulations for both spherical / Thesis (PhD)--University of Pretoria, 2015. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / The core objectives of the study are: i)to choose an appropriate methodology to evaluate the performance of public enterprises, such as the sugar mills of Bangladesh; ii) to empirically measure the performance of these mills; iii) to build a model to explain the variation in the performance of these enterprises; iv) to measure managerial performance thereform, adjustment having been made for variables beyond the control of the manager; and v) to recommend measures to improve the performance of the sugar mills. / 2031-01-01

Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in ful lment of the requirements for the degree of Master of Science. Johannesburg, 2017. / In this dissertation we tackle the question: is there an emergent Yang-Mills theory coming from the low energy description of branes and open strings? This new Yang-Mills theory has no connection to the original gauge symmetry of the CFT. We thus explore a large N but non-planar limit of the theory. This is done with new methods developed in group representation theory. A study the dilatation operator D in N = 4 SYM theory is done since its eigenvalue, the anomalous dimension, is mapped to the energy of the open string in the IIB string theory. The construction of the spherical harmonics from the harmonic expansion on the 3-sphere, S3, is done to understand the theory of the giant graviton's worldvolume. The light-front parton picture is examined, since it explains how one can \glue" single momentum modes together to obtain higher momentum modes, and we believe that this procedure is described dynamically using magnon bound states. Following from this, we work on determining the exact magnon bound state spectrum. Finally, we test our hypothesis and see if the spectrum of the bound states matches the harmonic spectrum from the harmonic expansion on the 3-sphere, S3. A non-trivial check is also performed to show that the bound state spectrum does indeed match the spectrum coming from N = 4 SYM. / LG2018

Random matrix models have found numerous applications in both Theoretical Physics and Mathematics. In the gauge-gravity duality, for example, the dynamics of the half- BPS sector can be fully described by the holomorphic sector of a single complex matrix model. In this thesis, we study the large-N limit of multi-matrix models at strong-coupling. In particular, we explore the significance of rescaling the matrix fields. In order to investigate this, we consider the matrix quantum mechanics of a single Hermitian system with a quartic interaction. We “compactify” this system on a circle and compute the first-order perturbation theory correction to the ground-state energy. The exact ground-state energy is obtained using the Das-Jevicki-Sakita Collective Field Theory approach. We then discuss the multi-matrix model that results from the compactification of the Higgs sector of N = 4 SYM on S4 (or T S3). For the radial subsector, the saddle-point equations are solved exactly and hence the radial density of eigenvalues for an arbitrary number of even Hermitian matrices is obtained. The single complex matrix model is parametrized in terms of the matrix valued polar coordinates and the first-order perturbation theory density of eigenstates is obtained. We make use of the Harish-Chandra- Itzykson-Zuber (HCIZ) formula to write down the exact saddle-point equations. We then give a complementary approach - based on the Dyson-Schwinger (loop) equations formalism - to the saddle-point method. We reproduce the results obtained for the radial (single matrix) subsector. The two-matrix integral does not close on the original set of variables and thus we map the system onto an auxiliary Penner-type two matrix model. In the absence of a logarithmic potential we derive a radial hemispherical density of eigenvalues. The system is regulated with a logarithm potential, and the Dobroliubov-Makeenko-Semenoff (DMS) loop equations yield an equation of third degree that is satisfied by the generating function. This equation is solved at strong coupling and, accordingly, we obtain the radial density of eigenvalues.

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A series of process design and economics models have been created which calculate the process cost for several scenarios in steam-explosion/fractionation of wood. Steam -explosion pulping may prove to be an alternative to currently practiced standard pulping processes which require large capital investments, cause significant environmental problems, and produce a narrow range of products. In addition, steam-explosion/fractionation technology may offer the opportunity to produce chemicals and materials from biomass at a lower raw material and process cost than the alternative petrochemical feedstocks. The models are a series of modular computer simulations, where each module summarizes a particular group of unit operations with respect to mass balance, energy requirements, and process cost including utilities, capital, labor, and other related costs. These modules are compiled into 3 groups of scenarios: 1) unprocessed steam-exploded wood for use as enzyme! acid hydrolysis feedstock, hardboard production, or as unbleached pulp, 2) water extracted steam-exploded wood for recovery of pentosan polysaccharides and a lignocellulosic fiber, and 3) water and aqueous solvent (alkali or ethanol) extracted steam -exploded wood for recovery of pentosan polysaccharides, lignin polymers, and a cellulose -rich, unbleached fiber. For the base case evaluated, the cost of producing a 50% moisture, based on total weight, steam-exploded fiber is the raw material cost, dry basis, plus 3.5 cents! Lb of raw material consumed, dry basis. For Southwestern Virginia hardwoods at 2 cents/Lb ($40 per ton), dry basis, the total process cost is 5.5 cents/ Lb. / Master of Science

In South Africa there is a need within the milling industry for controlling food safety especially due to customer's demands and government's regulations. The best way to ensure food safety is with the implementation of a HACCP based food safety system. Therefore, the principal aim of this study was to develop a generic HACCP model for the flour milling industry. Afterwards this generic model can then be adapted for each specific mill and its needs.

Esta tese estuda as contribuições proporcionais a In(T) da função de três pontos na teoria de Yang-Mills no calibre axial temporal na ordem de um loop no limite de altas temperaturas. Nós provamos que tais contribuições satisfazem uma identidade de Ward abeliana que as relaciona com o tensor de polarização do glúon, concluindo que são invariantes de Lorentz e têm a mesma estrutura dos pólos ultravioleta que ocorrem a temperatura zero. Usando uma simples prescrição para as constantes de renormalização e as equações do grupo de renormalização a temperatura finita, foi possível mostrar que a constante de acoplamento efetiva decai logaritmicamente em função da temperatura, de acordo com a liberdade assintótica, e é idêntica ao resultado obtido numa classe geral de calibres covariantes. / This thesis studies the In(T) contributions of the three-point function in the Yang-Mills theory in the temporal axial gauge at one-loop level in high-temperature limit. We proved that such contributions satisfy an abelian Ward identity which relates them with the gluon polarization tensor, concluding that they are Lorentz invariant and have the same structure of the ultraviolet poles which occur at zero temperature. Using a simple prescription for the renormalization constants and the finite-temperature renormalization group equations, it was possible to show that the effective coupling constant decreases logarithmically as a function of temperature, in accordance with asymptotic freedom, and is identical to the results obtained in a general class of covariant gauges.