Tan, Augustine Tuck Lee

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.

A total of 11 fundamental and 3 overtone bands of the formaldoxime isotopologue 13CD2NOH were identified using its Fourier transform infrared (FTIR) spectra which were recorded with a low resolution (0.50 cm−1) in the 500–4000 cm−1 region, and high resolution (0.00096 cm−1) in the 280–500 cm−1 region. Their relative infrared (IR) band intensities were also measured. Furthermore, a rovibrational analysis of the IR transitions of the band of 13CD2NOH was carried out using its high-resolution FTIR spectrum which was recorded at the Australian Synchrotron. A total of 1077 IR transitions of the C-type band were assigned and fitted using the Watson's A-reduced Hamiltonian in the Ir representation to derive its band center and the = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms for the first time, with a root-mean-square (rms) deviation of 0.00044 cm−1. The band center of the band of 13CD2NOH were found to be 391.054446(36) cm−1. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by fitting 407 ground state combination differences (GSCDs) derived from the assigned IR transitions of the band of 13CD2NOH of this work. The rms deviation of the GSCD fit was 0.00040 cm−1. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the = 1 state of 13CD2NOH 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. Close agreement was found for the calculated and experimental rovibrational constants of 13CD2NOH for both ground and = 1 states. The vibrational anharmonic frequencies of the 12 fundamental bands of 13CD2NOH in the 280–4000 cm−1 region, and their IR band intensities were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data. Finally, the ground state rotational constants and the band center of the band of the cis conformer of 13CD2NOH were calculated and compared with those of the trans conformer of this work.

Black cumin seed oil (BCSO) contains a large number of bioactive compounds and thus has many medicinal health benefits and uses. Its high economic profits in the market lead to the frequent occurrence of adulterating this oil with cheaper edible oils such as grape seed oil, walnut oil. It is difficult to detect adulteration as the oil adulterant has similar physical characteristic and even similar chemical composition to the authentic oil. The development of an accurate and rapid analytical method using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy is of essential importance for determination of authenticity of BCSO and quantification of oil adulterants. In this study, BCSO and grape seed oil (GSO) were mixed in various ratios to mimic the adulteration. A clustering group lasso method was developed by incorporating both the high correlation structure of spectral variables and the underlying group features into the model. Instead of assuming that groups are known a priori as does ordinary group lasso, the clustering group lasso infers groups of spectral features from the data and encourages spectral variables within a group to have a shared association with the response. The model using ATR-FTIR spectroscopy proved to be a powerful tool to quantify BCSO adulteration with high accuracy and can accurately predict the quantity of adulterant at levels as low as 5%. With a substantial reduction in number of spectral features, the clustering group lasso model shows a simple regression coefficient profile with improved interpretability as compared to the ordinary group lasso model and other penalized models. The spectral regions automatically selected for quantification of BCSO adulteration can be helpful for the interpretation of the major chemical constituents of BCSO regarding its anti-cancer and anti-inflammatory effects from a chemometric perspective.

A time resolved imaging study of pulsed laser ablated Fe and Al plasma plumes with specific interest in the splitting of plumes into the slow and fast moving components as they expand through the background argon gas at different pressures is reported. The material ablation was achieved using a Q-switched Nd:YAG yttrium aluminum garnet laser operating at 532 nm with a pulse duration of 8 ns full width at half maximum and a fluence of 30 Jcm−2 at the target surface. Typical time resolved images with low magnification show that the splitting occurs at moderate background gas pressures 0.5 and 1.0 mbar for Fe, and 0.2 mbar for Al plasma plumes. The plume splitting did not occur for higher background gas pressures.

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.

Wild-grown Ganoderma lucidum (G. lucidum), a traditional Chinese herbal medicine, is highly cherished and expensive for its medicinal efficiency. This study targets the development of an accurate and effective analytical method to distinguish wild-grown G. lucidum from cultivated ones, which are of essential importance for the quality assurance and estimation of its medicinal value. Furthermore, different parts of G. lucidum have been studied to examine the differences between wild-grown and cultivated ones. Fourier transform infrared (FTIR) diffuse reflectance spectroscopy combined with the appropriate chemometric method has been proven to be a rapid and powerful tool for discrimination of wild-grown and cultivated G. lucidum with classification accuracy of 98%. The informative spectral absorption bands for discrimination emphasized by the linear diagnostic rule have provided quantitative interpretations of the chemical constituents of wildgrown G. lucidum regarding its anticancer effects.

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.

The effect of laser energy fluence on the onset and growth of Rayleigh–Taylor (RT) instabilities in laser induced Fe plasma is investigated using time-resolved fast gated imaging. The snow plow and shock wave models are fitted to the experimental results and used to estimate the ablation parameters and the density of gas atoms that interact with the ablated species. It is observed that RT instability develops during the interface deceleration stage and grows for a considerable time for higher laser energy fluence. The effects of RT instabilities formation on the surface topography of the Fe thin films grown in pulsed laser deposition system are investigated (i) using different laser energy fluences for the same wavelength of laser radiation and (ii) using different laser wavelengths keeping the energy fluence fixed. It is concluded that the deposition achieved under turbulent condition leads to less smooth deposition surfaces with bigger sized particle agglomerates or network.