Now showing 1 - 10 of 22
  • Publication
    Open Access
      174  121
  • Publication
    Open Access
    D(3He,p)4He and D(d,p)3H fusion in a small plasma focus operated in a deuterium helium-3 gas mixture
    A 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.
      390  121
  • Publication
    Open Access
    Repetitive operation of a dense plasma soft x-ray source for micromachining
    (2005-07)
    Wong, D.
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    Patran, Alin Constantin
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    Hassan, S. M.
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    Zhang, T.
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    ;
    Lee, Sing
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    ;
    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.
      133  121
  • Publication
    Open Access
    Electronic, structural and magnetic characterization of bulk (ZnO)1−x(MnO2)x system and their PLD synthesized thin films at room temperature
    (ZnO)1−x(MnO2)x thin films for x 0.07 were deposited by pulsed laser deposition (PLD) at room temperature. Rietveld refinement for XRD of bulk samples confirmed the Mn ions substitution in ZnO lattice as inferred by the change in lattice parameters. The as-deposited thin film samples are found to be polycrystalline with the preferred orientation along (110) diffraction plane. No impurity phase was seen to form in thin film sample. Information about different valance states of doping elements is deduced from XPS data with the help of peak fittings of corresponding core peak observed in XPS survey scan. The deposited (ZnO)1−x(MnO2)x thin films exhibit room temperature ferromagnetism for different compositions.
    WOS© Citations 3Scopus© Citations 5  333  112
  • Publication
    Metadata only
    Fourier transform infrared (FTIR) spectrum (250-3800 cmˉ¹) of formaldoxime -¹³C (¹³CH₂NOH) and rovibrational analysis of its ν₁₂ band
    (2022)
    Andre Jusuf
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    ;
    Wu, Marlene Qianyi
    The Fourier transform infrared (FTIR) spectrum of formaldoxime-13C (13CH2NOH) was recorded in the 600–3800 cm−1 region with a resolution of 0.50 cm−1 to identify its fundamental and overtone bands and to measure their relative infrared band intensities. Furthermore, the high-resolution (0.00096 cm−1) FTIR spectrum of the ν12 band of 13CH2NOH was recorded at the Australian Synchrotron in the 250–600 cm−1 region for a rovibrational analysis. A total of 1506 infrared (IR) transitions of the C-type ν12 band were fitted using the Watson's A-reduced and S-reduced Hamiltonians in the Ir representation with a root-mean-square (rms) deviation of 0.000364 cm−1 for both fits. From the rovibrational analysis, the ν12= 1 state rovibrational constants up to one sextic centrifugal distortion term were derived for the first time. The band center of the ν12 band of 13CH2NOH were found to be 397.365846(32) cm−1 in the A-reduced Hamiltonian. The ground state rovibrational constants up to one sextic term were improved with higher accuracy by fitting 1374 ground state combination differences (GSCDs) derived from the IR transitions of the ν8 and ν12 bands of 13CH2NOH, together with two previously reported microwave frequencies. Furthermore, a comparison of the experimental vibrational frequencies, IR band intensities, rovibrational constants (ν12 = 1 and ground states) of 13CH2NOH and those derived from theoretical calculations at two levels of theory: B3LYP and MP2 with cc-pVTZ basis set were made. Close agreement was found for the calculated and experimental rovibrational constants of 13CH2NOH for both ground and ν12 = 1 states.
    WOS© Citations 3Scopus© Citations 2  113
  • Publication
    Restricted
    Developing a framework for assessing students’ construction of scientific explanations in physics
    (Office of Education Research, National Institute of Education, Singapore, 2020)
    Yeo, Jennifer Ai Choo
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    Tan, Jennifer Pei-Ling
    The 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.
      160  8
  • Publication
    Open Access
    Producing a scientific explanation in physics: What it entails and challenges students face
    (National Institute of Education (Singapore), 2017) ;
    Tan, Jennifer Pei-Ling
    ;
    Yeo, Jennifer Ai Choo
      183  125
  • Publication
    Open Access
    Laser shadowgraphic study of the influence of krypton-seeding, switch synchronization and electrode geometry on plasma dynamic in plasma focus device
    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  363  132
  • Publication
    Open Access
    Spectroscopic study of deep level emissions from acceptor defects in ZnO thin films with oxygen rich stoichiometry
    This paper reports the tailoring of acceptor defects in oxygen rich ZnO thin films at different post-deposition annealing temperatures (500–800°C) and Mn doping concentrations. The XRD spectra exhibited the nanocrystalline nature of ZnO thin films along with inconsistent variation in lattice parameters suggesting the temperature-dependent activation of structural defects. Photoluminescence emission spectra revealed the temperature dependent variation in deep level emissions (DLE) with the presence of acceptors as dominating defects. The concentration of native defects was estimated to be increased with temperature while a reverse trend was observed for those with increasing doping concentration. A consistent decrease in DLE spectra, with increasing Mn content, revealed the quenching of structural defects in the optical band gap of ZnO favorable for good quality thin films with enhanced optical transparency.
      367  238
  • Publication
    Metadata only
    Rovibrational analysis of the ν12 and 2ν12- ν12 bands of deuterated formaldoxime (CH2NOD) by high-resolution synchrotron FTIR spectroscopy
    (2021) ;
    Wu, Marlene Qianyi
    The high-resolution Fourier transform infrared (FTIR) spectrum of the band and its hot band 2ν12- ν12 of deuterated formaldoxime (CH2NOD) was recorded at the far-IR beamline of Australian Synchrotron with an unapodized resolution of 0.00096 cm−1 in the 230–350 cm−1 region. A total of 1456 infrared transitions of the ν12 band was fitted using the Watson's A-reduced and S-reduced Hamiltonians in the Ir representation with root-mean-square (rms) deviations of 0.000237 and 0.000262 cm−1 respectively. Furthermore, 483 infrared transitions of the 2ν12- ν12 band were fitted using both A-reduced and S-reduced Hamiltonians in the Ir representation with rms deviation of 0.000186 cm−1. From this rovibrational analysis, the rovibrational constants of the ν12 = 1 state up to sextic terms were derived for the first time. The band centers of the ν12 band of CH2NOD were found to be 303.319556(15) and 303.319553(18) cm−1 in the A-reduced and S-reduced Hamiltonians respectively, while band centers of were 296.620976(67) and 296.620976(67) cm−1 respectively. The rovibrational constants of the ground state of CH2NOD in the A-reduced and S-reduced Hamiltonians were obtained for the first time through the fitting of 608 ground state combination differences (GSCDs) derived from the infrared transitions of the ν12 band, together with 11 previously reported microwave frequencies. The rms deviations of the GSCD fit was 0.000318 and 0.000319 cm−1 in the A-reduced and S-reduced Hamiltonians respectively. Additionally, rotational constants and higher order centrifugal distortion terms of the ground, ν12 = 1, and ν12 = 2 states of CH2NOD were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. The calculated and experimental rovibrational constants of CH2NOD for the ground, = 1, and = 2 states are in close agreement.
    WOS© Citations 3Scopus© Citations 3  73