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BREAKUP MODELING OF A LIQUID JET IN CROSS FLOW
K.-S. IM,K.-C. LIN,M.-C. LAI,M. S. CHON 한국자동차공학회 2011 International journal of automotive technology Vol.12 No.4
We propose a novel breakup model to simulate the catastrophic breakup regime in a supersonic cross flow. A developed model has been extended from an existing Kelvin-Helmholtz/Rayleigh-Taylor (K-H/R-T) hybrid model. A new mass reduction rate equation, which has critical effects on overall spray structure, is successfully adopted, and the breakup length, which is an important parameter in existing model, is replaced by the breakup initiation time. Measured data from the supersonic wind tunnel with a dimension of 762×152×127 mm was employed to validate the newly developed breakup model. A nonaerated injector with an orifice diameter of 0.5 mm is used to inject water into a supersonic flow prescribed by the momentum flux ratio of the liquid jet to free stream air, q0. The conservation-element and solution-element (CE/SE) method, a novel numerical framework for the general conservation law, is applied to simulate the supersonic compressible flow. The spray penetration height and average droplet size along with a spray penetration axis are quantitatively compared with data. The shock train flow structures induced by the presence of a liquid jet are further discussed.
K. H. Loo,Y. M. Lai,Chi K. Tse 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
Most commercial white LEDs are made from blue LEDs coated with YAG phosphor. They generally produce emission spectra that shift in opposite directions under the influences of current amplitude and junction temperature changes. By using a commercial white LED sample, LUXEON K2, the effects of current amplitude and junction temperature on the chromaticity shift of white LEDs over dimming, during which both parameters are known to assert their influences simultaneously, are studied experimentally. The impact of driving/dimming by dc current is discussed through a graphical analysis and verified by experimental measurement. Due to the counteracting influences of current amplitude and junction temperature changes, driving/dimming white LEDs by dc current offers a more superior chromaticity stability compared to PWM. By means of selection of a heat sink’s thermal resistance estimated from an analytical equation derived in this paper, it is found that the overall chromaticity shift of white LEDs over dimming can be minimized at low cost.
Nishiyama, N.,Nakagishi, Y.,Morimoto, Y.,Lai, P.S.,Miyazaki, K.,Urano, K.,Horie, S.,Kumagai, M.,Fukushima, S.,Cheng, Y.,Jang, W.D.,Kikuchi, M.,Kataoka, K. Elsevier Science Publishers 2009 Journal of controlled release Vol.133 No.3
Photodynamic therapy (PDT) is a promising method for the localized treatment of solid tumors. In order to enhance the efficacy of PDT, we have recently developed a novel class of photosensitizer formulation, i.e., the dendrimer phthalocyanine (DPc)-encapsulated polymeric micelle (DPc/m). The DPc/m induced efficient and unprecedentedly rapid cell death accompanied by characteristic morphological changes such as blebbing of cell membranes, when the cells were photoirradiated using a low power halogen lamp or a high power diode laser. The fluorescent microscopic observation using organelle-specific dyes demonstrated that DPc/m might accumulate in the endo-/lysosomes; however, upon photoirradiation, DPc/m might be promptly released into the cytoplasm and photodamage the mitochondria, which may account for the enhanced photocytotoxicity of DPc/m. This study also demonstrated that DPc/m showed significantly higher in vivo PDT efficacy than clinically used Photofrin<SUP>(</SUP>R) (polyhematoporphyrin esters, PHE) in mice bearing human lung adenocarcinoma A549 cells. Furthermore, the DPc/m-treated mice did not show skin phototoxiciy, which was apparently observed for the PHE-treated mice, under the tested conditions. These results strongly suggest the usefulness of DPc/m in clinical PDT.
Comparison of Axi-symmetric Single-Hole Nozzle with Multi-Hole Sac Nozzles
( M. C. Lai ),( Y. Zheng ),( X. Xie ),( K. Im ),( S. Moon ),( Z. Liu ),( J. Gao ),( J. Wang ),( J. M. Shi ),( R. E. Winsor ) 한국액체미립화학회 2010 한국액체미립화학회 학술강연회 논문집 Vol.2010 No.-
It is well know that the internal flow field and nozzle geometry affect the spray behavior, but without high-speed microscopic visualization, it is difficult to characterize the spray structure in details. Single-hole Diesel injectors have been used in fundamental spray research, while most direct-injection engines use multi-hole nozzle to tailor the fuel spray to the combustion chamber geometry. Recent engine trends also use smaller orifice and higher injection pressure. This paper discussed the quasi-steady near-nozzle Diesel spray structures of an axisymmetric single-hole nozzle and a symmetric two-hole nozzle configuration, with a nominal nozzle size of 130 ㎛. Both nozzle holes originate from a sac of identical geometry, but different flow structure inside the nozzle cause significant difference in the observed flow structure near the nozzle exit. The ultrafast fast Phase-contrast X-ray images revealed unique surface and internal morphology of the fuel sprays that can be identified. The two-hole nozzle produces much more unstable jet structure under same injection conditions. The early wavelength developed in the jet is measured to be 30~80 ㎛, depending on the injection conditions. The differences between the nozzle configurations are investigated using CFD simulation. The results show that the three-dimensional fluid flow entering the two-hole nozzle generates stronger streamline curvature and stream-wise vortices which are by default absent in the axisymmetric single-hole nozzle. It also produces thicker shear layer and higher turbulence. The interactions of downwash entrance flow with turbulence potentially enhance the instability and produce wider spray cone angles. The number of holes also has interesting effects on the strength of the vortices and the downwash.
Edge perturbation on electronic properties of boron nitride nanoribbons
K.L. Wong,K.W. Lai,M.W. Chuan,Y. Wong,A. Hamzah,S. Rusli,N.E. Alias,S. Mohamed Sultan,C.S. Lim,M.L.P. Tan Techno-Press 2023 Advances in nano research Vol.15 No.5
Hexagonal boron nitride (h-BN), commonly referred to as Boron Nitride Nanoribbons (BNNRs), is an electrical insulator characterized by high thermal stability and a wide bandgap semiconductor property. This study delves into the electronic properties of two BNNR configurations: Armchair BNNRs (ABNNRs) and Zigzag BNNRs (ZBNNRs). Utilizing the nearest-neighbour tight-binding approach and numerical methods, the electronic properties of BNNRs were simulated. A simplifying assumption, the Hamiltonian matrix is used to compute the electronic properties by considering the self-interaction energy of a unit cell and the interaction energy between the unit cells. The edge perturbation is applied to the selected atoms of ABNNRs and ZBNNRs to simulate the electronic properties changes. This simulation work is done by generating a custom script using numerical computational methods in MATLAB software. When benchmarked against a reference study, our results aligned closely in terms of band structure and bandgap energy for ABNNRs. However, variations were observed in the peak values of the continuous curves for the local density of states. This discrepancy can be attributed to the use of numerical methods in our study, in contrast to the semi-analytical approach adopted in the reference work.
Variable Bi-Level Phase-Shifted Driving Method for High-Power RGB LED Lamps
S. K. Ng,K. H. Loo,Y. M. Lai,K. T. Mok,Chi K. Tse 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
Based on the recently proposed bi-level driving method, this paper presents an extended version of the existing method, which is aimed at maximizing the luminous output of high-power LED lamps by piecewise-linear tracing of their luminous output curves under AM (amplitude modulation) driving. The proposed driving method divides the luminous output curve of an AM-driven LED into a multiple sections, where each section is approximated by a straight line with two predefined end-points acting as the lower and upper current levels as used in the existing bi-level driving method. The intermediate current and luminosity values lying between the upper and lower current levels are obtained by duty cycle mixing of the two current levels. The joined multiple sections has enabled a near-maximum luminous output to be extracted from the LED while a linear dimming is realized within each section. The proposed driving method is verified by implementation in a single-driver RGB color LED lighting system with the red, green, and blue LED driven in a time-sequential manner (or shifted in phase). Experimental results show that a significant gain in luminous efficacy, hence energy saving, is achieved compared to the commonly used pulse-width modulation (PWM) driving.
Prabhakar, A.K.,Lai, H.Y.,Potroz, M.G.,Corliss, M.K.,Park, J.H.,Mundargi, R.C.,Cho, D.,Bang, S.I.,Cho, N.J. Korean Society of Industrial and Engineering Chemi 2017 Journal of industrial and engineering chemistry Vol.53 No.-
Pine pollen is widely used in traditional Chinese medicine and has been consumed as a food product for thousands of years. Owing to wind pollination, its pollen grains are composed of a sporoplasmic central cavity along with two empty air sac compartments. While this architectural configuration is evolutionarily optimized for wind dispersal, such features also lend excellent potential for encapsulating materials, especially in the context of preparing sporopollenin exine capsules (SECs). Herein, we systematically evaluated one-pot acid processing methods in order to generate pine pollen SECs that support compound loading. Morphological properties of the SECs were analysed by scanning electron microscopy (SEM) and dynamic imaging particle analysis (DIPA), and protein removal was evaluated by CHN elemental analysis and confocal laser scanning microscopy (CLSM). It was identified that 5-h acidolysis with 85% w/v phosphoric acid at 70<SUP>o</SUP>C yielded an optimal balance of high protein removal and preservation of microcapsule architecture, while other processing methods were also feasible with an additional enzymatic step. Importantly, the loading efficiency of the pine pollen SECs was three-times greater than that of natural pine pollen, highlighting their potential for microencapsulation. Taken together, our findings outline a successful strategy to prepare intact pine pollen SECs and demonstrate for the first time that SECs can be prepared from multi-compartmental pollen capsules, opening the door to streamlined processing approaches to utilize pine pollen microcapsules in industrial applications.