Joohan Kim

Transforming growth factor-β induces epithelial to mesenchymal transition and suppresses the proliferation and transdifferentiation of cultured human pancreatic duct cells†‡

Pancreatic duct cells are considered a potential source of β‐cell regeneration, and transforming growth factor‐β (TGF‐β) has been suggested to perform an important role in these processes, but the underlying mechanism of the signal pathways, especially in humans, remains poorly understood. To evaluate the role of TGF‐β1, pancreatic duct cells were isolated from three brain‐dead organ donors. Pancreatic cell clusters harvested after islet isolation were dispersed to single cells and cultured in monolayers, then treated with TGF‐β1. We analyzed the characteristics of the cultured cells, the TGF‐β1 intracellular signaling pathway, the proliferation, and transdifferentiation rates of the duct cells. We also evaluated the genes and protein expression patterns after TGF‐β1 treatment. After TGF‐β1 treatment, typical morphologic changes representative of EMT were observed and Erk1/2, JNK, and AKT phosphorylation, Ras downstream effectors, were increased. β cell‐specific transcription factors including PDX‐1, Beta2/NeuroD, Ist‐1, and NGN3 were markedly suppressed and the rate of transdifferentiation into β cells was also suppressed. Genomic and proteomic analyses suggested that TGF‐β1 induces marked changes in a variety of structural genes and proteins associated with EMT. In conclusion, TGF‐β1 induces EMT in cultured human pancreatic duct cells, but suppresses its proliferation and transdifferentiation into β cells. Our results are the first report of TGF‐β1 effects for EMT and ductal cell transdifferentiation and proliferation at the protein level in human pancreatic duct cells. J. Cell. Biochem. 112: 179–188, 2011.

Combustion and emission modelling of a direct-injection spark-ignition engine by combining flamelet models for premixed and diffusion flames

The combustion and emission production processes of a DISI (direct-injection spark-ignition) engine were modelled by combining flamelet models for premixed and diffusion flames. A new surrogate fuel was proposed to approximate the complicated composition of real gasoline. In contrast to simpler conventional models, the fuel was modelled as a ternary mixture of three hydrocarbons: iso-octane, n-heptane and toluene. Turbulent flame propagation in a partially premixed field was modelled by a premixed flamelet model. The mass fractions of the detailed composition of species in burnt gas were predicted by a diffusion flamelet model. For the pollutant formation modelling, a two-step oxidation of CO and H2 was used to simulate the secondary diffusion flame. The extended Zeldovich mechanism was used to model NOx formation, while a phenomenological model was used to model soot formation. This model was initially applied to a simple geometry to investigate the fundamentals of the models behaviour, after which three-dimensional computational fluid dynamic (CFD) simulations were performed in a realistic engine geometry.

Temperature Compensation of Hot-Wire Anemometer with Photoconductive Cell

A new temperature compensation technique for hot-wire anemometer is proposed in this article. In contrast to the available compensation techniques, a photoconductive cell is introduced here as a variable resistor in the bridge. The major advantage of adopting an active component such as photoconductive cell is that temperature compensation can be achieved by using any kind of temperature sensors, once the output of temperature sensor is given as a voltage. Validation experiments using a photoconductive cell with a thermocouple-thermometer are conducted in the temperature range from 30 to 50 °C and the velocity ranges from 8 to 18 m/s.

Simple Modification of the Bladder Outlet Obstruction Index for Better Prediction of Endoscopically-Proven Prostatic Obstruction: A Preliminary Study

Purpose The bladder outlet obstruction index (BOOI), also known as the Abrams-Griffiths (AG) number, is the most widely used index for predicting BOO. However, the obstructed prostatic urethra determined by the BOOI is often inconsistent with endoscopically-proven obstruction. We assessed abdominal straining pattern as a novel parameter for improving the prediction of BOO. Materials and Methods We retrospectively reviewed the pressure-flow studies (PFS) and cystourethroscopy in 176 BPH/LUTS patients who were unresponsive to medical therapy. During PFS, some groups of patients tried to urinate with abdominal straining, which can increases intravesical pressure and underestimate BOOI theoretically. Accordingly, the modified BOOI was defined as (PdetQmax+ΔPabd)-2Qmax. Results Ultimately, 130 patients were eligible for the analysis. In PFS, ΔPabd (PabdQmax-initial Pabd) was 11.81±13.04 cmH2O, and it was 0–9 cmH2O in 75 (57.7%), 10–19 cmH2O in 23 (17.7%) and ≥20 cmH2O in 32 (24.6%) patients. An endoscopically obstructed prostatic urethra in 92 patients was correctly determined in 47 patients (51.1%) by the original BOOI versus 72 patients (78.3%) based on the modified BOOI. Meanwhile, an “unobstructed” urethra according to the original BOOI was present in 11 patients (12.0%), whereas according to the modified BOOI, only 2 (2.1%) would be labeled as “unobstructed”. In receiver operating characteristic curves, the area under the curve was 0.906 using the modified BOOI number versus 0.849 in the original BOOI (p<0.05). Conclusions The change in abdominal pressure was correlated with endoscopically-proven obstruction. Our simple modification of the BOOI on the basis of this finding better predicted bladder outlet obstruction and, therefore, should be considered when evaluating BOO in patients with LUTS/BPH.

Laser Micro-Welding Process in which Magnetic Fields are Applied

We have conducted a study on stainless steel laser-welding materials by using a laser beam for the evaluation. Stainless steel used in a rust and excellent thermal deformation has a variety of application. In this study, to improve the mechanical properties of stainless steel, a 50 W laser thermal source is used and magnetic fields are applied, on the basis of suggestions. The mechanical properties and performance are evaluated by performing a numerical analysis, tensile test, and shape, microstructure, and hardness test. The results show that the mechanical properties of improve increased speed the melting pool, tensile strength of 16 kPa rise, run into the melting zone and hardness 7 Hv.

Non-contact Measurement and Analysis of Surface Hardness on Welding Steel using Laser-induced Breakdown Spectroscopy

In this work, effects of plasma on different hardness of welding steel using laser-induced breakdown spectroscopy were investigated. The ratios of ionic to atomic spectrum peaks were related to its material hardness. The major spectrum peak (Fe) and minor spectrum peak (Mn) were considered as monitoring elements. The stronger repulse plasma was generated, the harder material it was. The ratios of ionic to atomic spectrum peaks increased with respect to the material hardness as well. The correlation of minor spectrum peaks was stronger than that of major spectrum peaks. However, the major spectrum peaks indicated a similar trend, which could be used to estimate the hardness, too. Based on this result, the method could be used as a non-contact remote measurement of material properties.

Laser-assisted deposition of Cu bumps for microelectronic packaging

Abstract Cu bump was transferred using a focused laser pulse for microelectronic packaging. An Nd:YAG laser pulse (maximum energy of 500 mJ; wavelength of 1064 nm; fluences of 0.4–2.1 kJ/cm 2 ) was irradiated on a sacrificial absorption layer with copper coating. The focused laser beam induced plasma between the semi-transparent donor slide and the sacrificial layer, causing a shock wave. The shock wave pressure pushed the Cu layer and transferred material to deposit a bump on substrate. A beam-shaper was used to produce uniform pressure at the interface to reduce fragmentation of the transferred material on the substrate. The calculated shock wave pressure with respect to laser fluence was 1–3 GPa. A Cu bump of diameter of 200 μm was successfully deposited at laser fluence of 0.6 kJ/cm 2 . The pressure control at the sacrificial layer using a laser pulse was critical to produce a bump with less fragmentation. The technique can be applied to forming Cu bump for an interconnecting process in electronics.

An Overview of Selective Laser Sintering

레이저는 에너지를 미세하게 조절하여 재료를 가공할 수 있는 장점을 가지고 있기에 레이저가 발명된 다음부 터 많은 관련 응용기술이 연구 발전되어 왔다. 선택적 레이저 소결 (Selective Laser Sintering)은 레이저를 이 용한 재료가공의 한 가지 방법으로 레이저의 선택적 에 너지 전달 기능을 이용해 분말 등의 재료를 선택적으로 고형화시키는 기술을 말한다. 이는 재료의 표면처리를 목적으로 하는 레이저 클래딩(Laser cladding)과 유사한 기술이지만 단순히 표면처리만을 주 목적으로 하는 레 이저 클래딩에서 발전하여 특수한 목적의 형상을 소결 접착의 형식으로 만드는 것을 말한다. 이러한 선택적 레 이저 소결은 부품 및 시작품 제작이 복잡하거나 비싼 장비를 사용하지 않고도 신속하고 경제적인 방법으로 해결하려는 경향이 증가함에 따라, 쾌속조형기술 (Rapid-prototyping)로 연구 발전되어 왔고 이는 3D CAD 도면으로부터 직접 고형의 물리적 모델을 만드는 공정이다. 쾌속조형기술이 소개된 것은 대략 20년 전이 며, layer-by-layer, 3D modeling 가공에 직접 이용되고 있다. 이러한 쾌속조형기술은 스테레오리소그래피 (stereolithography), 3D 프린팅 (3D printing), 레이저 직 접 제작 (Laser direct fabrication), FDM (Fused Deposition Modelding) 등 다양한 다른 용어로 불리우 게 되었지만 기본 원리는 선택적 레이저 소결 (SLS)과 동일하다. 단 선택적 레이저 소결(SLS)의 경우 그 재료 의 선택범위가 금속 또는 세라믹 분말 등으로 제한되어 사용되는 경우도 있으나 넓은 의미에서는 고형분말뿐만 아니라 액체 또는 기체상태의 재료도 그 범위 안에 둘 수 있다. 또한 선택적 레이저 소결 (SLS)은 부분적 용 융이냐 아니면 완전한 용융이냐에 따라 선택적 레이저 용융(SLM) 등의 명칭으로 구분되어 지기도 한다. 본 논문에서는 지금 까지 연구 및 소개된 선택적 레 이저 소결의 기술 개요, 응용 분야 및 현황 등을 제시하 고자 한다.

A Study on the Optimization of IR Laser Flip-chip Bonding Process Using Taguchi Methods

A flip-chip bonding system using IR laser with a wavelength of 1064 nm was developed and associated process parameters were analyzed using Taguchi methods. An infrared laser beam is designed to transmit through a silicon chip and used for transferring laser energy directly to micro-bumps. This process has several advantages: minimized heat affect zone, fast bonding and good reliability in the microchip bonding interface. Approximately 50 % of the irradiated energy can be directly used for bonding the solder bumps with a few seconds of bonding time. A flip-chip with 120 solder bumps was used for this experiment and the composition of the solder bump was Sn3.0Ag0.5Cu. The main processing parameters for IR laser flip-chip bonding were laser power, scanning speed, a spot size and UBM thickness. Taguchi methods were applied for optimizing these four main processing parameters. The optimized bump shape and its shear force were modeled and the experimental results were compared with them. The analysis results indicate that the bump shape and its shear force are dominantly influenced by laser power and scanning speed over a laser spot size. In addition, various effects of processing parameters for IR laser flip-chip bonding are presented and discussed.

Modeling laminar burning velocity of gasoline using an energy fraction-based mixing rule approach

To determine an optimum combustion chamber design and engine operating strategies, computational fluid dynamics simulations of direct-injection spark-ignition engines have become an indispensable step in the powertrain development process. The laminar burning velocity of gasoline is known as an essential input parameter for combustion simulations. In this study, a new methodology for modeling the laminar burning velocity of gasoline for direct-injection spark-ignition engine simulations is proposed. Considering the gasoline as a complex mixture of hydrocarbon fuel, three hydrocarbons, iso-octane, n-heptane, and toluene were incorporated as surrogate fuel components to represent gasoline with distinct aromatic laminar flame characteristics compared to alkane. A mixing rule, based on energy fractions, was adopted to consider the compositional variation of gasoline. The laminar burning velocities of iso-octane, n-heptane, and toluene were calculated under wide thermo-chemical conditions in conjunction with detailed chemical reaction kinetics in the premixed flame simulation. Finally, a set of laminar burning velocity model equations was derived by curve-fitting the flame simulation results of each hydrocarbon component in consideration of the effect of temperature, pressure, and diluent. The laminar burning velocity model was validated against the measurement data of gasoline’s laminar burning velocity found in the literature, and was applied to the computational fluid dynamics simulation of a direct-injection spark-ignition engine under the various operating conditions to explore the prediction capability.