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Bumsoo Han,Dong Kee Sohn,Joon Sik Lee 대한기계학회 2002 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.16 No.9
An experiment has been conducted on the flow and heat transfer characteristics of film coolant injected from a row of five holes with compound angle orientations of 35° inclination angle and 45° orientation angle. The Reynolds number number based on the mainstream velocity and injection hole diameter 3.58×10⁴. Three-dimensional velocity, film cooling effectiveness and heat transfer coefficient data are presented at three different mass flux ratios of 0.5, 1.0 and 2.0. Flow entrainment has been found between the vortices generated by adjacent injectants. The injectant with compound angle orientation entrains not only the mainstream boundary layer flow but also the adjacent injectant. Because of the flow entrainment, the injectant. With compound angle orientation is characterized by a single vortex while two bound vortices are usually observed in the case of simple angle injection. The strength of the secondary flow depends strongly on the mass flux ratio, which shows significant influence on the film cooling effectiveness and heat transfer coefficient.<br/>
Dropwise gelation-dehydration kinetics during drop-on-demand printing of hydrogel-based materials
Han, Bumsoo,Yun, Gyu Young,Boley, J. William,Kim, Samuel Haidong,Hwang, Jun Young,Chiu, George T.-C.,Park, Kinam Elsevier 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.97 No.-
<P><B>Abstract</B></P> <P>The present study aims to characterize and understand the dropwise gelation-dehydration phenomena during drop-on-demand (DOD) printing of hydrogel-based soft materials. Functional soft materials have broader impacts on many medical and engineering applications, but constructing soft materials into three-dimensional (3D) configuration with spatially varying properties is still extremely challenging. In order to establish a mechanistic understanding, a hypothesis was postulated that the porosity of hydrogel printed is determined by dropwise gelation and dehydration phenomena during the printing process. The underlying rationale is that many functional properties of the printed hydrogels are closely associated with the structural characteristics at the sub-droplet and droplet scales, specifically porosity. The porosity of a hydrogel droplet is thought to be determined by intra-droplet fluid–structure interactions during gelation and dehydration. In this study, thus, we characterized the gelation-dehydration and consequent microstructure of thermally responsive poly(<I>N</I>-isopropylacrylamind-<I>co</I>-acrylamide) (PNIPAM) copolymer droplets as a model hydrogel material. The gelation kinetics was studied by differential scanning calorimetry. Both macroscopic and microscopic structures of DOD printed hydrogels were characterized by a 3D profiler and scanning electron microscopy. Furthermore, a theoretical model to explain this complex transport processes was also developed. The results showed that the gelation is a rapid process and its impact is mainly observed at the deposition of droplets. Significant structural shrinkage of the printed hydrogel droplets was induced by dehydration. This shrinkage resulted in spatially varying intra-droplet porosity. A computational model of intra-droplet fluid–structure interactions was developed to explain this spatial variation of intra-droplet porosity. In addition, a new dimensionless parameter is proposed to gauge the significance of evaporation and interstitial water transport in the fluid–structure interactions. Significance of gelation kinetics, dehydration and complex fluid–structure interaction within the droplets was discussed to design a DOD printing process for 3D additive manufacturing of hydrogel-based soft materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dropwise gelation and dehydration was studied both experimentally and theoretically. </LI> <LI> Dropwise gelation and dehydration during printing process determine the porosity of hydrogel printed. </LI> <LI> An intra-droplet fluid–structure interaction mechanism during printing of hydrogel materials is proposed. </LI> </UL> </P>
Han, Sanghyun,Park, Bumsoo,Lim, Jeong-Wook,Youm, Jin-Young,Choi, Seoung-Won,Kim, Dae Hwan,Ahn, Dong Ki The Korean Neurosurgical Society 2020 Journal of Korean neurosurgical society Vol.63 No.6
The demineralized bone matrix (DBM) as the bone graft material to increase the fusion rate was widely used in spinal fusion. The current study aimed to compare the fusion rate of DBM to the fusion rate of autograft in lumbar spine fusion via meta-analysis of published literature. After systematic search, comparative studies were selected according to eligibility criteria. Checklist (risk of bias assessment tool for non-randomized study) was used to evaluate the risk of bias of the included nonrandomized controlled studies. The corresponding 95% confidence interval (95% CI) were calculated. We also used subgroup analysis to analyze the fusion rate of posterolateral lumbar fusion and lumbar interbody fusion. Eight studies were finally included in this meta-analysis. These eight studies included 581 patients. Among them, 337 patients underwent spinal fusion surgery using DBM (DBM group) and 204 patients underwent spinal fusion surgery with mainly autologous bone and without using DBM (control group). There was no significant differences of fusion rate between the two groups in posterolateral fusion analysis (risk ratio [RR], 1.03; 95% CI, 0.90-1.17; p=0.66) and interbody fusion analysis (RR, 1.13; 95% CI, 0.91-1.39; p=0.27). Based on the available evidence, the use of DBM with autograft in posterolateral lumbar spine fusion and lumbar interbody fusion showed a slightly higher fusion rate than that of autograft alone; however, there was no statistically different between two groups.
15-bit Σ-ΔModulator for ADSL Applications
Suh, Bumsoo,Han, Sang-Chan,Kim, Suwon 연세대학교 아식설계공동연구소 2000 Journal of the Research Institute of ASIC Design Vol.7 No.1
A 550kHz signal bandwidth 15-bit Σ-Δ modulator for ADSL application has been proposed and designed. The most power efficient 2-1-1 cascade structure is selected and the matching of coefficients is optimized properly. The non-idealities introduced by matching and leakage problems have been minimized by a series of fast-settling high-gain fully differential opamps, in which a special gain-boosting scheme named "self-biased gain boosting" is proposed. Also, the popular clock-doubling scheme is used for reducing size of switch TR's and modified for bit-stream feedback usage. The layout of the whole modulator has been packed into 2 x 1 mm area, using 0.35 ㎛ single-poly three-Metal CMOS technology. The simulation results market 97mW for power consumption, that is almost the half of other conventionals.
김유리,한범수,김진규,강호 한국물환경학회 2004 한국물환경학회지 Vol.20 No.4
The use of electron beam irradiation was investigated to disinfect total coliforms in the secondary sewage treatment effluent. Unchlorinated secondary effluent was irradiated at different dose of 0.2~1.0 kGy by 1 MeV, ELV-4 Model electron beam accelerator. It is interesting to note that a 100% reduction in total coliforms and total colonies were achieved until a dose of approximately 0.8 kGy. Even at low dose of 0.2 kGy, the total coliforms and total colonies were successfully inactivated to the level of satisfying the new effluent discharge guideline. Besides disinfection of total coliforms, approximately a 50% removal in biochemical oxygen demand was pronounced at a dose of 0.2 kGy. More than 20% removal in suspended solids and turbidity was also observed at a dose of 1.0 kGy. The application of electron beam irradiation appeared to be one of options to reuse sewage treatment effluent as agricultural or industrial water.