HY Gan - Academia.edu (original) (raw)

Papers by HY Gan

Proceedings of SPIE, Jan 21, 2006

Fluid flow in microfluidic systems can be achieved by electroosmosis (EO) pumping, with its own u... more Fluid flow in microfluidic systems can be achieved by electroosmosis (EO) pumping, with its own unique characteristics and advantages. In practice, multi-fluid (one fluid displacing another fluid) flows are frequently encountered. Understanding of multi-fluid EO flow associated with non-uniform liquid properties is of importance to precise flow control. This paper reports an EO-driven, two-fluid displacement flow in a microcapillary. The

Corrosion Engineering Science and Technology, Jan 15, 2023

Urban rail transit, Sep 28, 2022

A study has been conducted to measure uniform corrosion due to the tunnel environment in the mass... more A study has been conducted to measure uniform corrosion due to the tunnel environment in the mass rapid transit North East Line (NEL) in Singapore. The study was aimed at investigating the corrosivity of the atmospheric environment in the NEL to enhance understanding on the maintenance of metallic components in a tunnel. The corrosivity levels at the buffer areas of ten stations along the NEL were monitored over a period of two years. The measurements were based on physical metal coupons as well as real-time monitoring systems using electrical resistance sensors. The corrosivity levels measured at different exposure sites showed differences, but were generally low and could be generally categorised as G1 according to ISA standard 71.04:2013. The reason for the low corrosivity levels was likely to be due to the relatively mild temperature and low (\60%) average relative humidity.

Scientific Reports, Jan 10, 2023

This in vitro study evaluated the effects of the infiltration of Fand Ca 2+ ions into human ename... more This in vitro study evaluated the effects of the infiltration of Fand Ca 2+ ions into human enamel by electrokinetic flow (EKF) on the enamel microhardness and Fcontent. Sound human enamel ground sections of unerupted third molars were infiltrated with de-ionized water by EKF and with Fion by EKF respectively. All samples were submitted to two successive transverse acid-etch biopsies (etching times of 30 s and 20 min) to quantify Fion infiltrated deep into enamel. Remarkably, sound enamel showed a large increase in microhardness (MH) after infiltration of NaF (p < 0.00001) and CaCl 2 (p = 0.013) by EKF. Additionally, NaF-EKF increased the remineralization in the lesion body of artificial enamel caries lesions compared to controls (p < 0.01). With the enamel biopsy technique, at both etching times, more Fions were found in the EKF-treated group than the control group (p << 0.05), and more fluoride was extracted from deeper biopsies in the NaF-EKF group. In conclusion, our results show that EKF treatment is superior in transporting Ca 2+ and F − ions into sound enamel when compared to molecular diffusion, enhancing both the mineralization of sound enamel and the remineralization of artificial enamel caries. Our modern way of living has greatly reduced oral mechanical forces, which are used to perform natural tooth cleaning, and provided higher sugar consumption, responsible for cariogenic acid formation in oral biofilms. These have contributed to the surge of dental caries as the most prevalent chronic disease in human worldwide 1-4. It has been shown that caries prevalence in adults is tenfold higher than that experienced by children, even in developed countries 1,2. In addition, enamel can be affected by the process of chemical dissolution by acids that are not produced by oral bacteria (dental erosion), which is also quite prevalent (4-83% in European adults) 5. Together with the increasingly aging population, the maintenance of enamel integrity during a lifetime is a challenging and unsolved clinical problem in dentistry. As the first layer of defense against dental caries, dental enamel is known as the most mineralized tissue of the human body, mostly composed of long and thin hydroxyapatite crystallites (70 nm × 30 nm in cross-section, extending from the enamel-dentine junction to the enamel surface). The narrow nanochannels separating those crystallites (2-3 nm in both prismatic and interprismatic regions, and 4-10 nm in the prism sheath; the latter is the main transport route) impose a serious challenge to the transport of materials. This is particularly challenging for negatively charged materials (e.g. fluoride ions) because their transport is hampered by the electric double layer that covers hydroxyapatite crystallites' surfaces and accounts for most of the inter-crystalline space in narrow nanochannels 6-8. The dissolution of enamel due to caries and erosion could be hindered by transporting relevant ions to hydroxyapatite solubility (such as Ca 2+ and F −) deep into normal (sound) enamel sublayers. Nevertheless, existing caries prevention methods are limited to a diffusion process that delivers ions very slowly, at unpredicted rates, and to the outermost enamel layer only 9-12 .

This in vitro study evaluated the effects of the infiltration of F- and Ca2+ ions into human enam... more This in vitro study evaluated the effects of the infiltration of F- and Ca2+ ions into human enamel by electrokinetic flow (EKF) on the mechanical property and F- content of enamel. Sound human enamel ground sections of unerupted third molars were infiltrated with de-ionized water by EKF and with F- ion by EKF respectively. All samples were submitted to two successive transverse acid-etch biopsies (etching times of 30 s and 20 mins) to quantify F- ion infiltrated deep into enamel. Remarkably, sound enamel showed a large increase in microhardness (MH) after infiltration of NaF (p < 0.00001) and CaCl2 (p = 0.013) by EKF. NaF-EKF increased AEC-LB remineralization compared to controls (p < 0.01). With enamel biopsy technique, at both etching times, more F- ions were found in EKF-treated group than the control group (p << 0.05) and more fluoride was extracted from deeper biopsies in the NaF-EKF group. In conclusion, our results show that EKF treatment is a superior in transpo...

2009 11th Electronics Packaging Technology Conference, 2009

ABSTRACT Printed electronics generally refers to the creation of electronic functionality, e.g. c... more ABSTRACT Printed electronics generally refers to the creation of electronic functionality, e.g. conducting circuitry, electrical components, by means of conventional printing techniques on common media such as plastics and paper. The main benefit of printed electronics is the simplified fabrication process, because of the elimination of the complex photolithography process. This means lower cost and shorter cycle time. However, several challenges must still be addressed, such as reliability, electrical performance and peripheral interfacing. Hereby peripheral interfacing was addressed, in particular the manufacturing process of the printed interconnects was studied. The study was conducted following the 2(7-4) fractional factorial design of experiment (DOE) method. Experimental parameters were curing temperature, curing time, pad thickness, pad sizes, solder alloys, cleaning time and number of reflows. Results of the study include effects of the parameters on shear strength of the printed interconnects and the recommendation of values to best employ.

Journal of Dental Research, 2019

As the outermost layer of the tooth crown, dental enamel is the most mineralized tissue in mammal... more As the outermost layer of the tooth crown, dental enamel is the most mineralized tissue in mammals, consisting of hydroxyapatite crystallites separated by long and narrow nanochannels. A major challenge in dentistry is how various molecules can be infiltrated into these nanopores in an efficient and controlled way. Here we show a robust method to transport various ions of interest, such as fluoride (F−), potassium (K+), calcium (Ca++), and sodium (Na+), into these nanopores by electrokinetic flows. It is verified by fluorescence microscopy, laser-scanning confocal microscopy, mass spectrometry, and ion selective electrode technique. Different ions are demonstrated to infiltrate through the entire depth of the enamel layer (~1 mm), which is significantly enhanced penetration compared with diffusion-based infiltration. Meanwhile, transport depth and speed can be controlled by infiltration time and applied voltage. This is the first demonstration of reliably delivering both anions and ...

Encyclopedia of Microfluidics and Nanofluidics, 2014

Dental Materials, 2019

Significance. The demonstrated nanofluidic transport of hydrogen peroxide into enamel has a poten... more Significance. The demonstrated nanofluidic transport of hydrogen peroxide into enamel has a potential to be applied for enhancing tooth whitening, compared to simple diffusion, without heating the hard dental tissues.

Overview of group Nanofluidic BioMEMS group in RLE (Han group) is exploring various ways that the... more Overview of group Nanofluidic BioMEMS group in RLE (Han group) is exploring various ways that the micro/nanofabrication techniques can be used for advanced biomolecule manipulation and separation applications. It is now possible to reliably fabricate nanofluidic gaps and filters that have regular, controllable structures, with near-molecular dimensions (10-100nm). One can take advantage of these nanofluidic structures for advanced separation and manipulation of various biomolecules and bioparticles, including cell, cellular organelles, DNA, protein, and carbohydrates. The research of Nanofluidic BioMEMS group is currently actively designing, fabricating and testing the new kinds of molecular sieves and filters that can be essential for the next-generation biomolecule assays in the new era of genomics, proteomics and glycomics. At the same time, the subject of molecular stochastic motion and molecular interaction with nanostructure is actively studied, in order to provide firm theore...

La presente invention a trait a un systeme electrochimique dote d'un comportement de courant ... more La presente invention a trait a un systeme electrochimique dote d'un comportement de courant limite reduit. Le systeme electrochimique est utile pour les piles a combustible et les biocapteurs. En partie, l'invention a trait a un procede permettant de reduire ou de supprimer le comportement de courant limite dans le fonctionnement de systemes electrochimiques, en particulier ceux dotes d'une membrane selective ou d'electrodes electrochimiques, en reduisant spatialement la convection a proximite de la membrane ou de l'electrode. La presente invention a egalement trait a des systemes electrochimiques utilisant des micropores, des puces a ADN ou des reseaux en colonne de maniere a reduire la convection par rapport aux systemes classiques sans puces a ADN, micropores ou reseaux en colonne.

Encyclopedia of Microfluidics and Nanofluidics, 2015

Microfluidics and Nanofluidics, 2006

In this paper, we examined mixing of various two-fluid flows in a silicon/glass microchannel base... more In this paper, we examined mixing of various two-fluid flows in a silicon/glass microchannel based on the competition of dominant forces in a flow field, namely viscous/elastic, viscous/viscous and viscous/inertial. Experiments were performed over a range of Deborah and Reynolds numbers (0.36 &amp;amp;amp;amp;amp;amp;amp;lt; De &amp;amp;amp;amp;amp;amp;amp;lt; 278, 0.005 &amp;amp;amp;amp;amp;amp;amp;lt; Re &amp;amp;amp;amp;amp;amp;amp;lt; 24.2). Fluorescent dye and microshperes were used to characterize the flow kinematics. Employing abrupt convergent/divergent channel geometry, we

Journal of the Mechanical Behavior of Biomedical Materials

Tooth enamel has an important mechanical function for human dental health, yet characterizing its... more Tooth enamel has an important mechanical function for human dental health, yet characterizing its mechanical properties is not trivial due to its complex nanoporous structures. We examined the distribution of hardness and modulus across the lingual-buccal enamel cross-section by nanoindentation. At the occlusal surface, the hardness and modulus of enamel were found to be 5.00 ± 0.22 GPa and 97.12 ± 2.95 GPa, respectively. At the area close to the enamel-dentine-junction (EDJ), the hardness and modulus were 3.72 ± 0.35 GPa and 76.83 ± 5.71 GPa, respectively. At the middle region in between the EDJ and the outer enamel layer, the hardness and modulus were found to be 4.23 ± 0.18 GPa and 87.62 ± 2.50 GPa, respectively. The surface and area underneath the nanoindent were analyzed using the following microscopy tools: Scanning Electron Microscopy, Focused Ion Beam imaging, and Transmission Electron Microscopy. The deformation mechanisms of enamel were found to be location dependent and influenced by changes in the chemical composition within enamel. The EDJ forms the interface between enamel and dentin. The deformation behavior differed at the EDJ, due to the increased organic phase at the interface. Within the intermediate enamel region, intra-rod cracks were formed at the center of enamel rods and propagated into the neighboring inter-rod region at deviated directions along the orientation of the local crystallites. At the outer enamel layer, crack propagation was constrained by the rigid structure surrounding the indented site. Most of the cracks were formed close to the surface. A significant amount of material was also pushed upwards and delaminated from the enamel surface of the indentation area.

I would like to thank my advisor, Professor LAM Yee Cheong, for his guidance during this work. Hi... more I would like to thank my advisor, Professor LAM Yee Cheong, for his guidance during this work. His patience and constant encouragement have made working under him a very memorable and enjoyable experience. I feel deeply gratified to be his student. I thank Agency for Science, Technology and Research (A*STAR) for its financial support through the A*STAR Graduate Scholarship, and the support received from my co-adviser, Dr. LIM Gnian Cher, and A*STAR's affiliated research institute, SIMTech. I would also like to thank Associate Professor NGUYEN Nam Trung and Associate Professor YANG Chun for their valuable time and discussions. My appreciations to Hilda LIE for her help with clean room processing and DRIE fabrication. I thank all my friends in the MAE Thermal Fluid Research Lab for their time and help in all kinds. It has been great pleasure working with these wonderful individuals. In addition, I wish to thank Professor Boger, D.V. (The University of Melbourne, Australia) for the stimulating discussions and guidance. Lastly and most importantly, I thank my mother KERK Giok Hong, my sister Valerie, my brother Jolvin and my wife Kitty, for being there for me, encouraging, and supporting me. I wish to dedicate this work to them.

Encyclopedia of Microfluidics and Nanofluidics, 2008

Journal of Physics: Conference Series, 2006

Multi-liquid flow, such as one liquid displacing another liquid, is frequently encountered in pra... more Multi-liquid flow, such as one liquid displacing another liquid, is frequently encountered in practice. This can be achieved by electroosmotic (EO) pumping, which has its own unique characteristics and advantages. This investigation is on EO-driven, two-liquid displacement flow in a microcapillary. A theoretical model was developed to take into consideration the axial step change of velocity flow fields at the