Publication Search Results

Now showing 1 - 4 of 4
  • (2006) Doran, Michael
    The transplantation of ex vivo expanded mobilized peripheral blood haematopoietic stem cells (PBSC), in place of unmanipulated cells following high dose chemotherapy, reduces the period of cytopenia associated with the therapy’s hemotoxicity. In this thesis the development and optimization of a preclinical prototype hollow fiber bioreactor (HFBR) for the ex vivo expansion of PBSC is described. Mass transport measurements and model of metabolite profiles demonstrate that Cuprophan and Polyflux are suitable membrane material for high-density cell expansion in a HFBR. Materials selected for the HFBR were found to be non-toxic following a 20-day saline extraction. Growth factor (GF) adsorption to the Polyflux membrane makes it unsuitable for expansion of GF dependent cells. However, the GF retention and minimal adsorption characteristics of the Cuprophan membrane are appropriate for this application. Cell-free medium degrades at 37ºC by an oxygen dependent process generating byproducts that inhibit cell growth. This process is relevant to perfusion bioreactors where the bulk of the medium is maintained at 37ºC and is cell-free. Albumin was shown to slow the degradation process but was itself degraded by shear damage inflicted during recirculation. Treating recirculating medium with dialysis against albumin was shown to be a more effective way to mitigate the effects of degradation and lengthen the functional life of albumin over conventional suspension of albumin in the recirculating medium. The preclinical prototype HFBR utilised dialysis against albumin to expand KG-1a cultures from densities as low as 3.5x10^5 cells/ml up to as high as 2x10^8 cells/ml with expansion rates equivalent to T-flask cultures. This process was then applied to PBSC where the targeted 100-fold expansion was achieved. Process optimization was continued using cord blood (CB) CD34+ cells. Growth factor loading sufficient for PBSC expansion in the HFBR was inadequate for CB expansions due to greater than anticipated CB uptake rates. The cell product from the HFBR contained significantly greater yields of CD34+ cells than attained using T-flask cultures. The HFBR platform is suitable for PBSC expansion and appears promising for CB expansion.

  • (2022) Fan, Hui
    The integration of variable distributed energy resources and vehicle electrification has come to focus over the last few years. While much work has been done to address the challenges that arise in modern distribution system planning and operation, continuous improvement to the models with the change is essential. The objective of this thesis is to improve the distribution network planning and operation models in the presence of distributed generation and electric vehicles. It aims to build stochastic models including the power generation and the charging demand, determine the location and sizing of the energy resources and charging stations in the coupled systems, and evaluate the impacts of the new low-carbon technologies on the network. Using a mixed-integer nonlinear programming framework through an optimal power flow analysis, this thesis presents three major methodological contributions including uncertainty modelling, coordinated mathematical formulation, and conflicting objective solutions. First, a multivariate stochastic process based on the notion of copula is applied to derive probabilistic charging patterns and to obtain the stochastic charging profiles. Second, a two-stage stochastic program based on statistical analysis and numerical simulation is introduced to generate synthetic time series of solar and wind power generation. The continuous distributions are discretized to generate the scenarios and the number of scenarios is reduced using Kantorovich metrics. Third, a two-dimensional Pareto front of dominant solutions is given for the competing objectives using a multiobjective Tchebycheff decomposition-based evolutionary algorithm. Case studies are conducted to evaluate the effectiveness of the proposed methods. An optimal charging scheduling problem is formulated to assess the stochastic charging models. The problem is formulated as a conic quadratic optimal power flow model and solved with a convex optimization algorithm. Network expansion planning problems are presented with carsharing and non-carsharing models, as well as the distributed energy generations. Overall, these problems aim to minimize the planning and operational cost of feeder routing, and substation alterations while maximizing the utilization of charging stations. It is found that an accurate estimation of the randomness intrinsic to the network is critical to ensure the secure and economic operation and planning of the distribution system intertwined with the transport network.

  • (2019) Zhang, Weizheng
    Wireless communication has been developed rapidly in recent years with the utilization of multiple-input multiple-output (MIMO) systems. One promising technique to support ultra-high data rate communication is massive MIMO, or large MIMO, where the number of antennas goes to tens or hundreds. Unmanned Aerial Vehicles (UAVs) have the advantages of high mobility and flexibility that can be used as aerial nodes to provide communication to ground users or base stations. In this thesis, the optimization of pilot based channel estimation with limited pilot length is studied for a massive MIMO system. The pilot length is optimized to maximize the system spectral efficiency. Then, the optimal pilot design is discussed under the constraint of finite pilot length. The performance of uplink signal-to-interference-plus-noise ratio (SINR) and the effect of feedback error are also analyzed in time division duplex (TDD) and frequency division duplex (FDD), respectively. Then, a large MIMO system is utilized for UAV communication. In order to provide directional beamforming, the channel estimation in UAV millimeter wave (mmWave) system is studied. A beam training and tracking method is proposed with user mobility. For beam training, a training codebook is designed based on user location distribution. For beam tracking, two tracking methods are proposed based on different types of user mobility to reduce the training overhead. The proposed beam training codebook provides larger average downlink capacity than the conventional codebook. The proposed beam tracking design is also shown to outperform the existing methods. Lastly, a multiple UAV system in mmWave band is considered and studied. Hybrid beamforming is designed for both fully connected antenna array and partially connected subarray structures. Furthermore, a simultaneous beam tracking scheme for multiple UAV users is proposed based on subarray structure, where both UAV mobility and instability effects are taken into consideration. Simulation results show that with the proposed method, the average downlink sum capacity is improved.

  • (2023) Luo, Xiaoxuan
    Complex borohydrides have the potential to act as solid-state electrolytes for all-solid-state batteries. In this respect, sodium borohydride (NaBH4) is of high interest because it is thermally stable (up to 500 degrees celsius), and it has a high deformability and electrochemical stability against sodium anodes. However, its ionic conductivity at room temperature is extremely low ( ~ 10-10 S cm-1). Accordingly, this thesis aimed at investigating means to create defective NaBH4 structures with the intent to significantly enhance its ionic conductivity. To this aim, several strategies were investigated including the creation of intermediate interfaces, partial anionic substitution, the generation of defects and conducting interfaces through partial hydrolysis. By converting the surface of NaBH4 particles into Na2B12H12 of higher Na+ conductivity, to form NaBH4@Na2B12H12 core-shell structures, the resulting interface was found to lead to an ionic conductivity of 4 × 10-4 S cm-1at 115 degrees celsius, i.e., significantly higher to that of pristine Na2B12H12 (10-7 S cm-1). This demonstrates that it was possible to generate disordered interfaces trough anion mixing. The results suggested that the creation of defects may be more prone to lead to high ionic conductivity. Through partial substitution of BH4- anion by I- in NaBH4, defective NaBH4 structures with varied lattice constants could be created. This anion substitution strategy enhanced the ionic conductivity of NaBH4 doped with NaI to 1.6 × 10-3 S cm-1 at 65 degrees celsius. To further improve upon this, the idea of partial hydrolysis was also investigated with the idea to create both conductivity interfaces and defective NaBH4 structures by exposing NaBH4 to controlled amount of water. The disordered trapped interface located between alpha-NaBH4 and NaB(OH)4 showed fast Na+ dynamics, which led to a Na+ conductivity of 2.6 × 10-3 S cm-1 at 75 degrees celsius. Further addition of poly(ethylene oxide) (PEO) was found to help better control the levels of hydrolysis and the hydrolysed NaBH4-PEO composite electrolyte reached an ionic conductivity of 1.6 × 10-3 S cm-1 at 45 degrees celsius. These results indicate that the controlled formation of defects within NaBH4 is key to the conversion of such hydrides into superionic Na conductors.