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Tan, Augustine Tuck Lee
Preferred name
Tan, Augustine Tuck Lee
Email
augustine.tan@nie.edu.sg
Department
Natural Sciences & Science Education (NSSE)
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ORCID
22 results
Now showing 1 - 10 of 22
- PublicationOpen Access
202 172 - PublicationOpen AccessD(3He,p)4He and D(d,p)3H fusion in a small plasma focus operated in a deuterium helium-3 gas mixture(Institute of Nuclear Chemistry and Technology, 2006)
; ; ; ; ; Lee, SingA 3 kJ plasma focus was operated with a 3He-D2 gas mixture, with partial pressures in the ratio of 2:1, corresponding to an atomic number ratio of 1:1 for 3He and D atoms. The fusion reactions D(3He,p)4He and D(d,p)3H were measured simultaneously using CR-39 polymer nuclear track detectors placed inside a pinhole camera positioned on the forward plasma focus axis. A sandwich arrangement of two 1000 μm thick CR-39 detectors enabled the simultaneous registration of two groups of protons with approximate energies of 16 MeV and 3 MeV arising from the D(3He,p)4He and D(d,p)3H reactions, respectively. Radial track density distributions were obtained from each CR-39 detector and per-shot average distributions were calculated for the two groups of protons. It is found that the D(3He,p)4He and D(d,p)3H proton yields are of similar magnitude. Comparing the experimental distributions with results from a Monte Carlo simulation, it was deduced that the D(3He,p)4He fusion is concentrated close to the plasma focus pinch column, while the D(d,p)3H fusion occurs relatively far from the pinch. The relative absence of D(d,p)3H fusion in the pinch is one significant reason for concluding that the D(3He,p)4He fusion occurring in the plasma focus pinch is not thermonuclear in origin. It is argued that the bulk of the D(3He,p)4He fusion is due to energetic 3He2+ ions incident on a deuterium target. Possible explanations for differing spatial distributions of D(3He,p)4He and D(d,p)3H fusion in the plasma focus are discussed.408 199 - PublicationOpen AccessRepetitive operation of a dense plasma soft x-ray source for micromachining(2005-07)
; ; ; The NX2 device, a low energy plasma focus, at the Nanyang Technological University in Singapore, was used as a soft X-ray (SXR) source for micromachining. The gas used was neon which produced SXRs in a narrow spectral range of 0.9 - 1.6 keV. The SXR yield from repetitive operation of the NX2 device was monitored and measured using a cost effective multi-channel SXR spectrometric system. The system consists of filtered BPX65 PIN diodes, with the associated electronics --- an integrator, sample and peak holder, analogue switch, an A/D converter and a microcontroller. The system enables easy shot-to-shot statistical analysis under repetitive operation at adjustable preset trigger frequencies. A total of 4000 shots were fired at 0.5 Hz, using the same gas filling. The SXR production was at an average yield of 60 J/shot and a maximum single-shot yield of more than 100 J. The SXRs emitted by the NX2 device was used for contact micromachining, producing structures with an excellent aspect ratio of up to 20:1 on 25 μm SU-8 resist.151 165 - PublicationRestrictedDeveloping a framework for assessing students’ construction of scientific explanations in physics(Office of Education Research, National Institute of Education, Singapore, 2020)
; Tan, Jennifer Pei-LingThe ability to produce scientific explanations is an important learning goal in our local physics curriculum. Yeo and Gilbert (2014) showed that its production entails attending to its function, form (structural organisation of meanings) and level (of precision [model used], abstractness and complexity [use of representations]). These multi-dimensions might explain why students find producing an “acceptable” scientific explanation difficult. There are also few studies that examines the kinds of explanations students need to construct, the process of constructing one and the difficulties encountered. There is also an absence of a comprehensive framework for teachers to assess students’ explanations. The goals of this study are thus to (a) develop a framework of scientific explanations that is comprehensive and parsimonious, and (b) produce a characterisation of the process that students undergo in producing scientific explanations.164 8 - PublicationOpen AccessProducing a scientific explanation in physics: What it entails and challenges students face(National Institute of Education (Singapore), 2017)
; 204 176 - PublicationOpen AccessOrder of magnitude enhancement in neutron emission with deuterium-krypton admixture operation in miniature plasma focus device(American Institute of Physics, 2008)
; ; ; ; Krishnan, M.The effect of varied concentrations of deuterium-krypton (D2 - Kr) admixture on the neutron emission of a fast miniature plasma focus device was investigated. It was found that a judicious concentration of Kr in D2 can significantly enhance the neutron yield. The maximum average neutron yield of (1 ± 0.27) x 104 n/shot for pure D2 filling at 3 mbars was enhanced to (3.14 ± 0.4) x 105 n/shot with D2 + 2% Kr admixture operation, which represents a ˃ 30-fold increase. More than an order of magnitude enhancement in the average neutron yield was observed over the broader operating range of 1–4 mbars for D2 + 2 % Kr and D2 + 5% Kr admixtures.
WOS© Citations 28Scopus© Citations 50 404 264 - PublicationOpen AccessChemometric feature selection and classification of Ganoderma lucidum spores and fruiting body using ATR-FTIR spectroscopyGanoderma lucidum (G. lucidum) spores as a valuable Chinese herbal medicine have vast marketable prospect for its bioactivities and medicinal efficacy. This study aims at the development of an effective and simple analytical method to distinguish G. lucidum spores from its fruiting body, which is of essential importance for the quality control and fast discrimination of raw materials of Chinese herbal medicine. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy combined with the appropriate chemometric methods including penalized discriminant analysis, principal component discriminant analysis and partial least squares discriminant analysis has been proven to be a rapid and powerful tool for discrimination of G. lucidum spores and its fruiting body with classification accuracy of 99%. The model leads to a well-performed selection of informative spectral absorption bands which improve the classification accuracy, reduce the model complexity and enhance the quantitative interpretations of the chemical constituents of G. lucidum spores regarding its anticancer effects.
416 431 - PublicationOpen AccessLaser shadowgraphic study of the influence of krypton-seeding, switch synchronization and electrode geometry on plasma dynamic in plasma focus device(Springer Nature, 2015)
; ; ; Laser shadowgraphy has been used to investigate the plasma sheath dynamics in a miniature plasma focus device (FMPF-3, 14 kV/235 J). The occurrence of magneto-hydro-dynamics instabilities are compared for pure deuterium versus deuterium–krypton admixture operation, over the range of gas pressures 2–12 mbar. A cathode-less geometry was also tested to study the influence of cathode configuration on current sheath formation and compression. The average neutron yield, measured using 3He proportional counters, is compared for different geometries and gas pressures. The synchronization of the four pseudo-spark-gap switches was found to be a major factor influencing the plasma sheath dynamics and neutron yield. To make a fair comparison of operation with different gas pressures or admixture proportions, the level of switch synchronization must be in the same range. Laser shadowgraphs of early stage dynamics show that poorly synchronized discharges result in asymmetric plasma sheath formation, and asymmetries in the accelerated sheath typically persist till the end of the final compression.WOS© Citations 3Scopus© Citations 5 376 221 - PublicationOpen AccessOxygen rich p-type ZnO thin films using wet chemical route with enhanced carrier concentration by temperature-dependent tuning of acceptor defects(American Institute of Physics, 2011)
; ; ; This paper reports the temperature-dependent tailoring of acceptor defects in oxygen rich ZnO thin films, for enhanced p-type conductivity. The oxygen rich p-type ZnO thin films were successfully grown by pulsed laser deposition on silicon substrate at different postdeposition annealing temperatures (500–800 °C). The oxygen rich ZnO powder was synthesized by wet chemical method using zinc acetate dihydrate [Zn(CH3COO)2·2H2O] and potassium hydroxide (KOH) as precursors. The powder was then compressed and sintered to make pellets for pulsed laser deposition system. The x-ray diffraction analysis exhibits an improved crystallinity in thin films annealed at elevated temperatures with a temperature-dependent variation in lattice constants. An analysis of Auger Zn L 3 M 4,5 M 4,5 peak reveals a consistent decrease in interstitial zinc (Zni ) exhibiting its temperature-dependent reversion to zinc lattice sites. Room temperature photoluminescence of the p-type ZnO shows a dominant deep level emission peak at ∼3.12 eV related to oxygen interstitials (acceptors). The relative concentration of oxygen interstitials (Oi) increases with increase in annealing temperature, resulting in enhanced hole carrier concentration. The maximum hole carrier concentration of 6.8 × 1014 cm−3 (indicating p-type conductivity) was estimated using Hall probe measurements for the thin film sample annealed at 700 °C.
WOS© Citations 87Scopus© Citations 96 225 329 - PublicationOpen AccessIron oxide magnetic nanoparticles synthesized by atmospheric microplasmas(World Scientific, 2014)
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