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Significance of Hertwig’s Epithelial Root Sheath
Siqin Yang,조의식 대한구강해부학회 2015 대한구강해부학회지 Vol.36 No.1
As tooth crown formation completes and root formation begins, the inner and outer enamel epithelial cells proliferate from the cervical loop of the enamel organ to form a continuous sheath containing double layer of cells, which is known as Hertwig's epithelial root sheath (HERS). Through reciprocal epithelial-mesenchymal interactions, HERS plays an important role in root development, including root morphogenesis (root size, shape and number), dentinogenesis and cemetogenesis. However, the precise nature of this role remains unclear. At later stage of root development, following the formation of first radicular mantle dentin, HERS fragments into discrete clusters of cells and migrate away from the root to the region of future periodontal ligament, which form the epithelia cell rests of Malassez (ERM).
Derivation of hypermethylated pluripotent embryonic stem cells with high potency
Bao, Siqin,Tang, Walfred WC,Wu, Baojiang,Kim, Shinseog,Li, Jingyun,Li, Lin,Kobayashi, Toshihiro,Lee, Caroline,Chen, Yanglin,Wei, Mengyi,Li, Shudong,Dietmann, Sabine,Tang, Fuchou,Li, Xihe,Surani, M Azi Nature Publishing Group 2018 Cell research Vol.28 No.1
<P>Naive hypomethylated embryonic pluripotent stem cells (ESCs) are developmentally closest to the preimplantation epiblast of blastocysts, with the potential to contribute to all embryonic tissues and the germline, excepting the extra-embryonic tissues in chimeric embryos. By contrast, epiblast stem cells (EpiSCs) resembling postimplantation epiblast are relatively more methylated and show a limited potential for chimerism. Here, for the first time, we reveal advanced pluripotent stem cells (ASCs), which are developmentally beyond the pluripotent cells in the inner cell mass but with higher potency than EpiSCs. Accordingly, a single ASC contributes very efficiently to the fetus, germline, yolk sac and the placental labyrinth in chimeras. Since they are developmentally more advanced, ASCs do not contribute to the trophoblast. ASCs were derived from blastocysts in two steps in a chemically defined medium supplemented with Activin A and basic fibroblast growth factor, followed by culturing in ABCL medium containing ActA, BMP4, CHIR99021 and leukemia inhibitory factor. Notably, ASCs exhibit a distinct transcriptome with the expression of both naive pluripotency genes, as well as mesodermal somatic genes; <I>Eomes, Eras, Tdgf1, Evx1, hand1, Wnt5a</I> and distinct repetitive elements. Conversion of established ESCs to ASCs is also achievable. Importantly, ASCs exhibit a stable hypermethylated epigenome and mostly intact imprints as compared to the hypomethylated inner cell mass of blastocysts and naive ESCs. Properties of ASCs suggest that they represent cells at an intermediate cellular state between the naive and primed states of pluripotency.</P>
Aimin Fan,Siqin Chang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.2
This paper presents an extended state observer-based backstepping sliding mode control method (ESO-based BSMC) to achieve precise motion control for the electromagnetic valve actuator (EMVA). The extended state observer is introduced to compensate external disturbance and model uncertainties of the system, the backstepping method is used to decompose the system into some subsystems, and the sliding mode control is designed to guarantee the valve to follow the desired valve motion. The stability of the proposed control system is verified through Lyapunov stability theorem. Simulation results demonstrate that the proposed method avoids chattering problem, and it is robust to external disturbance and model uncertainties. Experimental results show the similar behavior as the simulations within an acceptable error. A transition time of 3.9 ms and a seating velocity less than 0.03 m/s are obtained to prove the effectiveness of the proposed method. Moreover, fully flexible valve actuator has been fulfilled and the valve motion profiles are given.
Bulbul Ahmed,Siqin Liu,Hongwei Si 한국식품영양과학회 2017 Journal of medicinal food Vol.20 No.2
Natural bioactive compounds are considered an excellent alternative strategy for developing effective, safe, and cost-effective antiobesity agents. The aim of this study was to investigate if combinations of soy bean genistein (G), green tea epigallocatechin-3-gallate (E), and/or grape resveratrol (R) at low dosages synergistically inhibit preadipocyte differentiation both in 3T3-L1 cells and human primary preadipocytes (HPAs). Our results show that combinations of G, E, and/or R additively inhibited preadipocyte differentiation (39–56% of control) both in 3T3-L1 cells at 30 μM and HPAs at 15 μM, while the individual compounds have no antiadipogenic effect at the selected concentrations. We also observed similar patterns that combinations of G, E, and/or R additively reduced protein expressions of peroxisome proliferator-activated receptor gamma (PPAR-γ) and CCAAT binding proteins alpha (C/EBP-α), the two key preadipocyte differentiation regulators, both in differentiated 3T3-L1 cells and HPAs. Moreover, combined G, E, and/or R attenuated protein expressions of fatty acid binding protein 4 and perilipin, two PPAR-γ/C/EBP-α downstream molecules in fat drop development in a very similar pattern, in inhibiting differentiation in preadipocytes. This combined antiadipogenic effect of G + E + R is additive, not synergistic according to our results and the Median-Effect Principle. In addition, we found that a lower concentration (15 μM) of G, E, and/or R is required in HPAs than the concentration (30 μM) needed in 3T3-L1 cells, to exert the combined antiadipogenic effect. These data suggest that combinations of G, E, and/or R intake or soy bean, green tea, and/or grape simultaneous consumption may prevent obesity in human being.
Yaxuan Xu,Siqin Chang,Liang Liu,Tianbo Wang,Maoyang Hu 한국자동차공학회 2019 International journal of automotive technology Vol.20 No.6
For the multi-cylinder gasoline engine, the consistency among cylinders is an important index to affect the engine emission and the engine power. In this paper, an individual cylinder air-fuel ratio (A/F) control method for a fourcylinder camless engine with the electromagnetic valve train (EMVT) was proposed to reduce the imbalance of engine torque. An individual cylinder A/F estimation algorithm with a single universal exhaust gas oxygen (UEGO) sensor based on fading Kalman filtering was introduced. Four proportional-integral feedback controllers were built to regulate the individual A/F by adjusting the intake valve closing (IVC) timing of each cylinder independently based on the EMVT. The effectiveness of the proposed estimation and control approach was validated by co-simulation of GT-Power and Simulink. The results showed that the proposed estimation method could accurately estimate the individual cylinder A/F, and the maximum estimation error under steady state condition was less than 1 %. With the feedback control, both the individual A/F imbalance and the cylinderto- cylinder torque generation imbalance were decreased.
Point-to-point motions control of an electromagnetic direct-drive gas valve
Jiayu Lu,Siqin Chang,Liang Liu,Xinyu Fan 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.1
Electromagnetic linear actuators are widely used as drives in gas regulating valve, which is the key factor to determine the performance of the gas valve. In order to improve the performance of Electromagnetic direct-drive gas valve (EMDGV), a compound controller for non-repetitive point-to-point motions was proposed in this paper, combining with the advantages of Active disturbance rejection control (ADRC), Time-optimal control (TOC) and Sliding mode control (SMC). Simulation and experimental results show that the proposed method has the characteristics of fast response and high precision, and can achieve soft landing control. The response time is less than 8 ms, the control accuracy is 0.02 mm, and the seating velocity is within 0.04 m/s. The proposed method also has strong robustness to actuator parameter variation and good anti-disturbance ability.
MODEL-BASED CONTROL OF ELECTROMAGNETIC VALVE ACTUATORS FOR ENGINE SPEED CONTROL
Huitao Chen,Siqin Chang,Aimin Fan 한국자동차공학회 2019 International journal of automotive technology Vol.20 No.1
The introduction of electromagnetic valve actuators (EMVA) benefits engine fuel economy, torque performance and reduction of emissions. Meanwhile, it complicates the controller for the purpose of regulating the additional freedom degrees of intake valvetrain, such as valve lift, opening timing and opening duration. In order to address the control issue of EMVA application, a model-based controller is needed to realize that the cylinder air charge is regulated by controlling the EMVA motion directly for controlling the engine speed and output torque. For the development of the controller, a control-oriented model of engine with EMVA that can simulate the intake process of unthrottled operation, torque generation and crankshaft rotational dynamics was first developed. Then a model-based EMVA controller was designed to regulate the actuation of electromagnetic intake valves which consisted of a feedforward and a PID feedback module. According to torque-based concept, engine speed reference was translated into torque demand using optimal control theory and the speed control problem was solved as two parts: torque management that decided torque demand and the torque demand tracking. The simulations carried out in Matlab/Simulink verified the effectiveness of the controller. In addition, a test platform of the EMVA for hardware-in-the-loop (HIL) simulation was established and the practicability of EMVA application to engine intake systems was validated preliminarily.
Haitao Li,Yang Sun,최형진,Siqin Zhao 한국고분자학회 2018 Macromolecular Research Vol.26 No.9
Hierarchical architectures of poly(methyl methacrylate) (PMMA)/aminofunctionalized multi-walled carbon nanotube (MWNT-NH2) particles were prepared, in which the electrical conductive network was constructed on the surface of PMMA microspheres. The morphology, composition, and electrical conductivity of the particles were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and four-probe electrical conductivity measurement. The PMMA/MWNT-NH2 transducers were exposed to each ethanol, water, toluene, and chloroform for volatile organic compounds (VOCs) sensing detection. The particles showed excellent sensitivity, good reversibility, and a strong response compared to the raw MWNTs and MWNT-NH2. This was attributed not only to the formation of a charge transmission path on the particle surface, but also to the interaction between the vapor molecules and functionalized MWNTs. The enhanced sensing performance of the PMMA/MWNT-NH2 particles suggests that it is a good candidate for the preparation of electronic noses for disease diagnostics and VOCs detection.
Xu Jiangtao,Feng Yong,Chang Siqin,Guo Tongjun 한국자동차공학회 2020 International journal of automotive technology Vol.21 No.6
As one of the most common engine types in nowadays, the thermal efficiency of spark-Ignition (SI) engine is limited due to the lower compression ratio. Various technical solutions have been proposed to suppress knock and improve compression ratio of SI engines. In this paper, an new technical solution based on electromagnetic valve train (EMVT) was proposed to suppress knock of spark ignition engines, so that high compression ratio (HCR) engine (13:5) was obtained. Moreover, experimental and numerical analyses were carried out to optimize the proposed EMVT strategy. The result showed that the proposed EMVT strategies could well suppress the engine knock by reducing end-gas temperature and pressure and improving the spark-flame rate, resulting in significantly enhanced power, economic, and emission characteristics of SI engines. This study provides theoretical basis and technical approach for the development of internal combustion engines with high efficiency and high compression ratio.
Nfic regulates tooth root patterning and growth
Tak-Heun Kim,Cheol-Hyeon Bae,Siqin Yang,Joo-Cheol Park,Eui-Sic Cho 대한해부학회 2015 Anatomy & Cell Biology Vol.48 No.3
Molecular interactions between epithelium and mesenchyme are important for root formation. Nuclear factor I-C (Nfic) has been identified as a key regulator of root formation. However, the mechanisms of root formation and their interactions between Hertwig’s epithelial root sheath (HERS) and mesenchyme remain unclear. In this study, we investigated the role of Nfic in root patterning and growth during molar root development. The molars of Nfic knockout mice exhibited an enlarged pulp chamber and apical displacement of the pulpal floor, characteristic features of taurodontism, due to delayed furcation formation. In developing molar roots of mutant mice at P14, BrdU positive cells decreased in the apical mesenchyme of the elongation region whereas those cells increased in the dental papilla of the furcation region. Whereas cytokeratin 14 and laminin were localized in HERS cells of mutant molars, Smoothened (Smo) and Gli1 were downregulated in preodontoblasts. In contrast, cytokeratin 14 and Smo were localized in the cells of the furcation region of mutant molars. These results indicate that Nfic regulates cell proliferation in the dental mesenchyme and affects the fate of HERS cells in a site-specific manner. From the results, it is suggested that Nfic is required for root patterning and growth during root morphogenesis.