A condensed multigroup formulation is developed which maintains direct consistency with the continuous energy or fine-group structure, exhibiting the accuracy of the detailed energy spectrum within the coarse-group calculation. Two methods are then developed which seek to invert the condensation process turning the standard one-way condensation (from fine-group to coarse-group) into the first step of a two-way iterative process. The first method is based on the previously published Generalized Energy Condensation, which established a framework for obtaining the fine-group flux by preserving the flux energy spectrum in orthogonal energy expansion functions, but did not maintain a consistent coarse-group formulation. It is demonstrated that with a consistent extension of the GEC, a cross section recondensation scheme can be used to correct for the spectral core environment error. A more practical and efficient new method is also developed, termed the "Subgroup Decomposition (SGD) Method," which eliminates the need for expansion functions altogether, and allows the fine-group flux to be decomposed from a consistent coarse-group flux with minimal additional computation or memory requirements. In addition, a new whole-core BWR benchmark problem is generated based on operating reactor parameters in 2D and 3D, and a set of 1D benchmark problems is developed for a BWR, PWR, and VHTR core.

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Thesis: Sc. D., Massachusetts Institute of Technology, Department of Nuclear Engineering, 1977 / Vita. / Includes bibliographical references. / Sc. D. / Sc. D. Massachusetts Institute of Technology, Department of Nuclear Engineering

The analytical solution to a model time-dependent continuous lethargy photon transport equation is evaluated numerically to obtain a benchmark solution using the Laplace transforms coupled with the multiple collision expansion method. The benchmark solution is then used to check the accuracy of the multigroup approximation. Excellent agreement between continuous lethargy benchmarks and multigroup approximation is obtained.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Transport of low energy neutrons associated with the galactic cosmic ray cascade is analyzed in this dissertation. A benchmark quality analytical algorithm is demonstrated for use with B scRYNTRN, a computer program written by the High Energy Physics Division of N scASA Langley Research Center, which is used to design and analyze shielding against the radiation created by the cascade. B scRYNTRN uses numerical methods to solve the integral transport equations for baryons with the straight-ahead approximation, and numerical and empirical methods to generate the interaction probabilities. The straight-ahead approximation is adequate for charged particles, but not for neutrons. As N scASA Langley improves B scRYNTRN to include low energy neutrons, a benchmark quality solution is needed for comparison. The neutron transport algorithm demonstrated in this dissertation uses the closed-form Green's function solution to the galactic cosmic ray cascade transport equations to generate a source of neutrons. A basis function expansion for finite heterogeneous and semi-infinite homogeneous slabs with multiple energy groups and isotropic scattering is used to generate neutron fluxes resulting from the cascade. This method, called the F(N) method, is used to solve the neutral particle linear Boltzmann transport equation. As a demonstration of the algorithm coded in the programs M scGSLAB and M scGSEMI, neutron and ion fluxes are shown for a beam of fluorine ions at 1000 MeV per nucleon incident on semi-infinite and finite aluminum slabs. Also, to demonstrate that the shielding effectiveness against the radiation from the galactic cosmic ray cascade is not directly proportional to shield thickness, a graph of transmitted total neutron scalar flux versus slab thickness is shown. A simple model based on the nuclear liquid drop assumption is used to generate cross sections for the galactic cosmic ray cascade. The E scNDF/B V database is used to generate the total and scattering cross sections for neutrons in aluminum. As an external verification, the results from M scGSLAB and M scGSEMI were compared to A scNISN/P scC, a routinely used neutron transport code, showing excellent agreement. In an application to an aluminum shield, the F(N) method seems to generate reasonable results.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. February 16, 2015. / The Adomian decomposition method is an effective procedure for the analytical solution of a wide class of dynamical systems without linearization or weak nonlinearity assumptions, closure approximations, perturbation theory, or restrictive assumptions on stochasticity. Our aim here is to apply the Adomian decomposition method to steady two-dimensional blood flow through a constricted artery in the presence of a uniform transverse magnetic field. Blood flow is the study of measuring blood pressure and determining flow through arteries. Blood flow is assumed to be Newtonian and is governed by the equation of continuity and the momentum balanced equation (which are known as the Navier-Stokes equations). This model is consistent with the principles of ferro-hydrodynamics and magnetohydrodynamics and takes into account both magnetization and electrical conductivity of blood. We apply the Adomian decomposition method to the equations governing blood flow through arteries in the presence of an external transverse magnetic field. The results show that the e ect of a uniform external transverse magnetic field applied to blood flow through arteries favors the physiological condition of blood. The motion of blood in stenosed arteries can be regulated by applying a magnetic field externally and increasing/decreasing the intensity of the applied field.

Colloid detachment and mobilization can be of significant interest to those studying colloid behavior in the environment. The transport of pathogens such as viruses, bacteria, and protozoa can cause health problems in animals and humans. The transport of organics, radionuclides, and other hydrophobic contaminants can be enhanced by adsorption to mobilized colloid surfaces. Research has been done by others quantifying the detachment of colloids from smooth porous media. Real surfaces in the environment and engineered systems are rough. Glass beads were chemically roughened by procedures similar to those from Shellenberger and Logan (2002) and It et al. (2001) using chromic acid and a citric acid/ammonium fluoride solution. Surface asperities were measured using Atomic Force Microscopy (AFM), and the roughness was defined by three parameters: Root Mean Square (RMS) roughness, peak to valley height (P/V height), and peak to peak distance (λ). Detachment from the chemically etched porous media was measured in column tests. The controlling roughness parameter between the two batches of beads was found to be λ. A theoretical model to predict the effect of roughness on detachment was developed. Using a moment balance around the downstream point of contact, the parameters incorporated into the model were particle diameter, P/V height, and λ. The model predicted the shear required for colloid detachment in column tests. Surface roughness was found to significantly inhibit colloid detachment.

Lai Chun Hei Gary = 錳氧化物-鈮摻雜之鈦酸鍶異構結的輸運特性 / 黎鎮禧. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Lai Chun Hei Gary = Meng yang hua wu-ni shan za zhi tai suan si yi gou jie de shu yun te xing / Li Zhenxi. / Acknowledgement --- p.i / Abstract --- p.ii / 論文摘要 --- p.iv / Table of contents --- p.vi / List of Figures --- p.x / List of Tables --- p.xv / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Introduction to perovskite manganites and niobium doped strontium titanate --- p.1-1 / Chapter 1.1.1 --- Structure and properties of perovskite manganites --- p.1-1 / Chapter 1.1.2 --- Structure and properties of niobium doped strontium titanate --- p.1-4 / Chapter 1.1.3 --- Phase transition in perovskite manganites --- p.1-9 / Chapter 1.1.4 --- Charge ordering and small polaron theory in PCMO --- p.1-15 / Chapter 1.1.5 --- Colossal Magnetoresistance (CMR) in perovskite manganites --- p.1-19 / Chapter 1.16 --- Review of semiconducting junction between perovskite manganites and niobium doped strontium titanate --- p.1-23 / Chapter 1.2 --- Research motivation --- p.1-28 / Chapter 1.3 --- Scope of this thesis --- p.1-29 / References --- p.1-31 / Chapter Chapter 2 --- Experimental details / Chapter 2.1 --- Thin film deposition --- p.2-1 / Chapter 2.1.1 --- Facing-target sputtering --- p.2-1 / Chapter 2.1.2 --- Vacuum system --- p.2-3 / Chapter 2.1.3 --- Fabrication and characterization of manganites targets --- p.2-4 / Chapter 2.1.4 --- Substrate --- p.2-7 / Chapter 2.1.5 --- Deposition procedure --- p.2-8 / Chapter 2.1.6 --- Silver electrode coating apparatus --- p.2-10 / Chapter 2.2 --- Annealing systems --- p.2-12 / Chapter 2.2.1 --- Vacuum annealing system --- p.2-12 / Chapter 2.2.2 --- Oxygen annealing system --- p.2-14 / Chapter 2.3 --- Characterization --- p.2-16 / Chapter 2.3.1 --- Profilometer --- p.2-16 / Chapter 2.3.2 --- X-ray diffractometer --- p.2-16 / Chapter 2.3.3 --- Resistance measurement system --- p.2-18 / Chapter 2.3.4 --- Current-voltage characteristics measurement system --- p.2-20 / References --- p.2-23 / Chapter Chapter 3 --- Epitaxial LCMO/STON heterojunction / Chapter 3.1 --- Four point and two point I-V measurement --- p.3-1 / Chapter 3.2 --- Magnetic phase transition of LCMO revealed by four point I-V measurement of LCMO/STON heteroj unction --- p.3-8 / Chapter 3.3 --- Oxygen annealing effect on LCMO/STON heteroj unction --- p.3-14 / Chapter 3.4 --- Positive colossal Magnetoresistance in LCMO/STON heteroj unction --- p.3-16 / References --- p.3-23 / Chapter Chapter 4 --- Epitaxial PCMO/STON heterojunction / Chapter 4.1 --- Ohmic contact for PCMO thin films --- p.4-1 / Chapter 4.2 --- PCMO charge ordering and magnetic phase transition --- p.4-9 / Chapter 4.3 --- Four point I-V measurement of PCMO/STON heterojunction --- p.4-14 / References --- p.4-16 / Chapter Chapter 5 --- Epitaxial LCMO/PCMO/STON junction / Chapter 5.1 --- Tunneling junction fabrication --- p.5-1 / Chapter 5.2 --- Structural characterizations --- p.5-2 / Chapter 5.3 --- PCMO magnetic phase transition revealed by I-V measurement of LCMO/PCMO/STON tunneling junction --- p.5-3 / Chapter 5.4 --- Energy band structure of perovskite manganites --- p.5-11 / Chapter 5.4.1 --- Introduction to energy band of perovskite manganites and STON --- p.5-11 / Chapter 5.4.2 --- Temperature dependent band structure of LCMO explained by diffusion voltage of LCMO/STON heterojunction --- p.5-18 / References --- p.5-22 / Chapter Chapter 6 --- Conclusions / Chapter 6.1 --- Conclusion --- p.6-1 / Chapter 6.2 --- Future outlook --- p.6-3