3 research outputs found
Power-control design of resonant converters
No full textNovel design techniques are presented for load-resonant and quasi-resonant converters for
use in, for example, arc-welding and fan-load power supplies. Both converters are capable of
very high switching frequency over a wide range of output power, with high efficiency and the
presentation of near-unity power factor to the primary power supply.
Previous work, by the author and his colleagues, has produced. a frequency-domain approach
to produce circuit-designs for use in load-resonant converter applications. This design technique,
although simple and straight-forward to understand, suffers by requiring some rather tedious
trial-and-error algebraic and arithmetic manipulations albeit computer assisted. In this thesis, a
systematic way of designing such circuits, based on Gr6bner Basis ideas, is explained, developed
and compared with the previous best-practice design method. By employing the Gr6bner Basis
techniques to synthesize electrical circuits, an entirely novel approach to the design of series-parallel
load-resonant converter circuits is presented. This has led to the formulation of a new
output-power control methodology in the design of the converters. These techniques produce
output-power-control designs that have superior properties, compared with other established
methods, in the sense of their simplicity, robustness and flexibility.
It is found that the methodology can be further extended to alter any resonant circuits and,
hence enables multilevel-output power to be controlled without involving complex control and
advanced mathematical theories, while still preserving the desirable characteristics of resonant
switching. The technique is, in fact, far more generally useful in the circuit-design/synthesis
arena than the specific load-resonant-converter application for which it was developed.
The novel technique used to vary the speed of an induction motor is found to be promising.
Various test results are presented based on an experimental system
The evolution of citizenship education in nation-building in Singapore and Hong Kong
No full textCitizenship Education is a highly political agenda for politicians and governments, especially those of the emerging nations studied in transitology. Political circumstances that surround the birth of ล nation are inextricably tied up with the unique economic, social and even globalisation contexts that shape the formation of that particular nation. Citizenship education mirrors the political climate of such circumstances. A ruling government's policies and ideologies are often transmitted to the masses through education in the form of citizenship education in its evolving forms that take after the political orientations of the nation. A historical-comparative study of Singapore and Hong Kong is the focus of the thesis and a combined case in point. This historical-comparative approach presents a chronological and qualitative analysis of Singapore and Hong Kong that links the past to the present, and points to future direction on how citizenship education has transformed in its focus, dimensions, content, message and values. Theories of nationalism, nation-state and national identity provide a basis for the understanding of the political, economic and social factors that impact nation- building and the subsequent evolvement of Civic and Moral Education in Singapore and Hong Kong after independence. In an analysis of the content-domain of citizenship education, Singapore’s curriculum is shown to reflect the ruling party's ideologies infused through National Education, where the Singapore story is sacrosanct and has to be mastered by all students so that the continual survival instinct is preserved at ill times. Hong Kong covers more breadth with a curriculum that includes the history of China that can be taught critically and a Chinese cultural heritage element that is infused into all the Key Learning subjects. The Life Event Approach is also more practical and relevant to the students' appreciation of the more individual-growth values learnt. Singapore is identified as an Objective/Globalised nation-state with a parallel Objective/Globalised National Identity that has a predominantly strong political leadership and economic priority in its nation-building foundation. It recognizes the need to rise up to the global challenges ahead. Hong Kong has a combination of Objective/Subjective/Globalised region-state with a parallel Objective/Subjective/Globalised National Identity with China due to its cultural heritage component inherited from China and also the need to meet global challenges. The thesis demonstrates how education can be used as a channel to serve the ideologies of the politicians who have a direct stake in shaping the focus of the political content in citizenship education in building national identity. It also illustrates how the respective political circumstances, economic reasons, social contexts and globalisation challenges drive the evolvement of the citizenship education in both Singapore and Hong Kong
Assessment of nasopharyngeal swab impact on a 3D-Printed cavity model with SISMA epithelial and mucosal layers carrying viruses and optimization of synthesis of liposomes loaded with carbon dots using low-cost microfluidics for controlled drug release
No full textThis research addresses critical challenges in the management of upper respiratory tract infections (URTIs) by developing bioengineering platforms for both diagnostic validation and therapeutic delivery. Addressing the lack of standardized protocols for nasopharyngeal sampling, the first phase of this study established an anatomically accurate 3D-printed nasopharyngeal cavity model derived from computed tomography scans. The model utilized VeroBlue and Agilus30 resins to replicate bone and soft tissue mechanics, respectively, and incorporated a functionalized porcine small intestinal submucosa (SISMA) hydrogel to mimic the mucosal extracellular matrix. Rheological characterization confirmed the hydrogel's physiological relevance, exhibiting a storage modulus (G') of 870 Pa and shear-thinning behavior. This platform validated the performance of a novel injection-manufactured swab (Heicon) against commercial flocked swabs. The Heicon swab demonstrated superior efficiency, achieving a sample release mass of 15.34 ± 1.25 µL compared to 10.31 ± 2.97 µL for the commercial control (p = 0.0439), with an effective release percentage of 91.52 ± 8.13% versus 69.67 ± 28.76%. The model further supported a viable Vero cell epithelial layer with a physiological thickness of approximately 60.71 µm.
Complementing these diagnostic advances, the second phase optimizes carbon dot-liposome (CDLiposome) synthesis using four microfluidic geometries (Serpentine, SARS, CF, Chambers) by validating COMSOL multiphysics models (Mixture/Euler-Euler) against experimental data. For encapsulation, we demonstrate that the Flow Rate Ratio (FRR) of 2:1 is the dominant parameter, while Total Flow Rate (TFR) is statistically insignificant, allowing high-throughput production (150 mL/h). The Chambers device consistently yields the highest efficiency (≈ 90%). Model validation reveals a critical TFR-dependent conflict: custom-damped RANS models (Custom 2) best predict highTFR scalar mixing, whereas the Laminar model best predicts the low-TFR PIV kinematics. This highlights the limitations of using a single RANS closure for both regimes. Finally, in vitro assays on Vero cells confirm the CDLiposomes are highly biocompatible. Confocal microscopy and pharmacological inhibition studies demonstrate successful internalization primarily via the clathrin-mediated pathway (inhibited by Dynasore), with subsequent trafficking to lysosomal compartments (high Mander's M1 coefficient).Maestrí
