유압관로의 주파수변화 따른 압력전파특성

유영태,나기대,김지환 한국공작기계학회 2002 한국생산제조학회지 Vol.11 No.2

In this paper, an oil hydraulic pipeline is terminated by both rotary sinusoidal flow generator at upstream and oriffice at down stream. The pulsating pressure wave form, generated by the rotary sinusoidal flow generator, is measured by pressure sensor. In the analysis of this paper, a component of the fundamental frequency is obtained by using Laplace transformation. The experimental and analytical results make clear that (1) viscosity is significant role in hydraulic pipe. (2) When pulsating frequency is matched with the natural frequency, resonance frequency occurred periodically. According to the study proposed here, dynamic pressure in a circular oil pipe is expressed in propagation of pressure wave with respect to frequency and Bessel function. The resonance frequency is 108Hz at oil temperature 20℃ in this study. The abrupt change of gain value id due to effect of resonance frequency. The results of experiment are compared with the calculated results, and agreement of both results is fairly good.

유압관로의 임피던스 전달특성

유영태,나기대,모양우,김지환 朝鮮大學校 機械技術硏究所 2003 機械技術硏究 Vol.6 No.2

Design for quite operation of fluid power system requires t h understanding of noise and vibration characteristics of t h system This paper presents a dynamic response of design of hydraulic circuit. Experimental investigations on the attenuation characteristics of pressure ripple in automotive power steering hydraulic pipe with dynamic response of hydraulic pipe line is examined.

경계조건변화에 따른 동력전달관로의 동특성

나기대,유영태,김지환 한국공작기계학회 2002 한국생산제조학회지 Vol.11 No.6

Design for a quiet operation of fluid power system requires the understanding of noise and vibration characteristics of the system. It's not easy to analyze noise problem in hydraulic cylinder used in typical actuator Because they've got complex fluid dynamics. One of the fundamental problems associated with the hydraulic system is the pulsating flow in pipe lines, which can e tackled by the analysis under simplifying assumptions. The present study focuses on theoretic analysis and experimental study on the dynamics of laminar pulsating flow in a circular pipe. We analyze the propagation characteristics of the pressure pulse within a hydraulic pipe line taking into account the pulsating flow frequency variation. We also measure instantaneous pressure pulses within pipe line to identify the transfer functions. We conduct series of experiments to investigate the propagation characteristics of pressure pulse for various pressure of pulsating flow. The working fluid of the present study is ISO VG46 and the temperature ranges from 20 to 60℃ with normal pressure at 4000kPa. The flow rate is measured by using an ultrasonic flow meter. Pressures at fixed upstream and downstream positions are measured concurrently. The electric signals of the pressure sensor are stored and analyzed using a system analyzer(PKE 983 series). The frequency is varied in the range of 10~500Hz. The Reynolds number is kept below 2,000. In the present study, boundary condition was varied by installing a surge tank and an orifice at the end of pipe. Experimental and theoretical results were compared each other under various boundary conditions.

유압관로에서 비정상 압력측압공의 동특성에 관한 연구

나기대,유영태,김지환 조선대학교 에너지.자원신기술연구소 2000 에너지·자원신기술연구소 논문지 Vol.22 No.2

In this study, the analysis of the dynamics characteristics and performance investigation of the pressure measurement in the hydraulic pipe. The exact solution of the frequency response is obtained by using the complicated transfer function. The discrepancy with the exact and the approximate is small, so the approximation solution is adopted to compare the experimental result with the theoretical analysis. The pressure measurement in the hydraulic pipe is caused by length of capillary and according to the end volume size. The experimental and calculate result show that characteristic of the pressure .measurement in the hydraulic pipe varies with the length of capillary and volume size. Therefore present theoretical formulation and experimental result can be used generally in designing and performance evaluation of all the hydraulic pressure measurement in the hydraulic pipe

D-Amphetamine이 니코틴성 흥분작용에 의한 카테콜아민 분비작용에 미치는 영향

임건한,서유석,민선영,임지연,김용직,나광문,임동윤 朝鮮大學校 附設 醫學硏究所 2005 The Medical Journal of Chosun University Vol.30 No.1

본 연구의 목적은 d-arphetamine이 흰쥐의 적출부신 관류모델에서 니코틴 수용체 흥분에 의한 카테콜아민(CA) 유리작용에 미치는 영향을 검색하여 그 작용기전을 규명하고자 하였다. D-amphetamine은 흰쥐 부신정맥내로 60분간 관류시 d-amphetamine자체는 약한 CA 분비작용을 나타내었으나, d-amphetamine (30 μM)을 비롯한 강력한 neuronal nicotine 수용체 작용제인 cytisine (50 μM) 및 epibatidine (30 μM)에 의한 CA 유리작용을 처음 4-10분 동안만 유의하게 증강시켰다. 또한, d-amphetamine (30 μM)은 60분간 부신정맥 내로 관류한 상태에서 dihydropyridine L-형 칼슘통로 개방약물인 Bay-K-8644 (10 μM)과 세포질내 칼슘저장고에서 Ca^(2+) ATPase 억제제인 cyclopiazonic acid (10 μM)의 CA 유리작용을 처음 4분간만 유의하게 증강시켰다. 그러나, 고농도의 d-amphetamine (500 μM)은 상기한 모든 분비촉진제의 CA분비작용을 오히려 억제하였다. 이와 같은 연구결과로 보면, 흰쥐 관류 부신수질에서 d-amphetamine은 낮은 농도에서는 콜린성 니코틴 수용체 흥분에 의한 카테콜아민 분비반응을 증강시키지만, 고농도에서는 오히려 억제적으로 작용함을 시사한다. 따라서, d-amphetamine은 용량에 따라서 흰쥐 적출 관류부신수질의 니코틴 수용체의 작용제 및 길항제로 이중 작용(dual action)을 나타내는 것으로 생각된다. 이러한 d-amphetamine의 작용은 흰쥐 부신수질 크롬친화세포의 dihydropyridine계 L-형 칼슘통로의 활성화 및 세포 내 칼슘저장고로부터 칼슘유리작용과 관련성이 있는 것으로 사료된다. The purpose of the present study was to examine the effect of d-amphetamine on CA release evoked by nocotinic receptor stimulation from the isolated perfused model of the rat adrenal gland, and to establish its mechanism of action. D-amphetamine(30 μM), when perfused into an adrenal vein of the rat adrenal gland for 60 min, enhanced the CA secretory responses evoked by ACh (5.32 mM), nicotine (30 μM), cytisine (50 μM, a selective neuronal nicotinic Nn-receptor agonist) and epibatidine (30 nM, a selective neuronal nicotinic Nn receptor agonist) only for the first period (4~10 min), although it alone has weak effect on CA secretion. Moreover, d-amphetamine (30 μM) in to an adrenal vein for 60 min also augmented the CA release evoked by BAY-K-8644, an activator of the dihydropyridine L-type Ca^(2+) channels, and cyclopiazonic acid, an inhibitor of cytoplasmic Ca^(2+) ATPase only for the first peroid (4 min). However, in the presence rather inhibited the CA secretory responses evoked by the above all of secretagogues. Taken together, these experimental results suggest that d-amphetamine at a low concentration enhances the CA secretion from the rat adrenal medulla evoked by stimulation of cholinergic nicotininc receptors, but at a high concentration it rather inhibits them. It semms that d-amphetamine has dual action acting as both agonist and antagonist at nicotinic receptors of the isolated perfused rat adrenal medulla, which are might be dependent on the concentration. It is also thought that these actions of d-amphetamine are probably relevant to the activation of the dihydropyridine L-type Ca^(2+) channels located on the rat adrenomedullary chromaffin cell membrane and release of Ca^(2+) from the cytoplasmic store.

원심압축기의 선회실속특성에 관한 연구

모양우,나기대,유영태,김지환 朝鮮大學校 機械技術硏究所 2003 機械技術硏究 Vol.6 No.2

In the present study, the performance characteristics and the number of stall cell during rotating stall of a centrifugal air compressor were experimentally investigated. Rotating stall in the vaneless diffuser were investigated by measuring unsteady pressure fluctuations at several different diffuser radius using a high frequency pressure transducer. The number of stall cell and their rotational speeds are distinctive features of the rotating stall phenomenon. The present study is mainly forced on the analysis for the stall cell number and its propagation speed unstable operating region of the compressor. The interpretation method of visualization is based on the pressure distribution in the circumference pressure fields while plotting the pressure and its harmonics variations in time in polar coordinates. To obtain the visualize the existence rotating stall, auto-correlation function and the frequency spectra of the pressure fluctuations were measured at rh-2 = 1.52. When the flow coefficient is lower than 0.150, the static pressure at impeller inlet is higher than that at inlet duct of the Compressor. And the flow coefficient is lower than 0.086, several stall cell groups of discrete frequencies are observed.

유압관로의 비정상유동에 따른 임피던스 전달특성

모양우,유영태,나기대,김지환 한국공작기계학회 2004 한국생산제조학회지 Vol.13 No.6

Design for quite operation of fluid power system requires the understanding of noise and vibration characteristics of the system. This paper presents a dynamic response of design of hydraulic circuit. Experimental investigations on the attenuation of pressure ripple in automotive power steering hydraulic pipe line is examined. Also, a mathematical model of hydraulic pipe is proposed to support a design of the hydraulic circuit. and the impedance characteristics of pressure ripple is analyzed. It is experimentally shown that power steering hydraulic pipe attenuates pressure ripple with high frequency.

Chitosan/oleamide Nanofluid for Enhancing Gas Utilization Efficiency in C1-gas Bioconversion

Eungsu KANG,Hyunsuk CHOI,Ji Yeong LEE,Min-sik KIM,Jeong Geol NA,Yoo Seong CHOI 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10

Microbial biotransformation using C1-gases (CH₄, CO) is a notable technique for sustainable, carbon-neutral chemical and fuel production. However, the low mass transfer coefficient (KLa) of C1-gases in biological processes has hampered the efficient production of value-added materials, despite efficient, nonnative strains having been recently developed. Here, we constructed a nanofluid material mainly composed of chitosan and oleamide (CS/OA), which was stably suspended with a particle size of 120.7 ± 39.0 ㎚ in aqueous culture media below pH 7.5. The kLa value was enhanced more than 1.5-fold with a reduction of surface tension even in the 0.0001 % (w/v) CS/OA nanofluid. In addition, when the nanofluid was applied into media for seed-cultivation of three C1-gas utilizing strains such as Methylomonas sp. DH-1, M. trichosporium OB3b, and Thermococcus onnurineus NA1 156T, the CS/OA nanoparticles attached to the cell surface, leading to a morphological change in the cell surface at extended lag-phase, and enhanced the specific cell growth rates (μmax), gas utilization efficiency in log-phase. Remarkably, the adapted strains from the seed culture using the CS/OA nanofluid media also had enhanced μmax in a subsequent subculture and the main culture using conventional culture media, resulting in higher C1 gas consumption, cell growth, and metabolite production such as formate and succinate. These results showed that the CS/OA nanofluid could be an effective medium component to enhance the gas utilization efficiency in C1-gas microbial bioconversion.Microbial biotransformation using C1-gases (CH₄, CO) is a notable technique for sustainable, carbon-neutral chemical and fuel production. However, the low mass transfer coefficient (KLa) of C1-gases in biological processes has hampered the efficient production of value-added materials, despite efficient, nonnative strains having been recently developed. Here, we constructed a nanofluid material mainly composed of chitosan and oleamide (CS/OA), which was stably suspended with a particle size of 120.7 ± 39.0 ㎚ in aqueous culture media below pH 7.5. The kLa value was enhanced more than 1.5-fold with a reduction of surface tension even in the 0.0001 % (w/v) CS/OA nanofluid. In addition, when the nanofluid was applied into media for seed-cultivation of three C1-gas utilizing strains such as Methylomonas sp. DH-1, M. trichosporium OB3b, and Thermococcus onnurineus NA1 156T, the CS/OA nanoparticles attached to the cell surface, leading to a morphological change in the cell surface at extended lag-phase, and enhanced the specific cell growth rates (μmax), gas utilization efficiency in log-phase. Remarkably, the adapted strains from the seed culture using the CS/OA nanofluid media also had enhanced μmax in a subsequent subculture and the main culture using conventional culture media, resulting in higher C1 gas consumption, cell growth, and metabolite production such as formate and succinate. These results showed that the CS/OA nanofluid could be an effective medium component to enhance the gas utilization efficiency in C1-gas microbial bioconversion.

Correlations among Motor Function, Quality of Life, and Caregiver Depression Levels in Children with Cerebral Palsy

( Ji-na Yoo ) 대한물리치료학회 2016 대한물리치료학회지 Vol.28 No.6

Purpose: This study aimed to evaluate the relationships among quality of life, caregiver depression levels, and disease severity, especially motor function, in children with cerebral palsy. Methods: Data were collected through questionnaires using survey and interview from 80 caregivers of children with cerebral palsy. The caregivers` quality of life was measured using medical outcomes study 36-item short form health survey, and level of depression was scored using the beck depression inventory. In addition, children`s motor function was evaluated using gross motor function measure-88 and functional independence measure scores. Results: Among 8 domains of medical outcomes study 36-item short form health survey, “physical functioning,” “physical role functioning,” “mental health,” and “bodily pain” domains were significantly correlated to “total” percentage scores of gross motor function measure-88. In addition, “mental health” and “bodily pain” domains were correlated to each sub-dimension, including “lying and rolling,” “sitting,” “crawling and kneeling,” “standing,” and “walking, running, and jumping.” Similarly, the “running” and “jumping” dimensions including motor function measures correlated with “transfer,” “locomotion,” and “motor subtotal” of functional independence measure scores. The beck depression inventory scores were negatively correlated to “lying and rolling,” “sitting,” “crawling and kneeling,” and the “total” percentage scores of gross motor function measure-88. The beck depression inventory scores were negatively correlated to “sphincter control,” “communication,” “social cognition,” “cognitive subtotal,” and “total” functional independence measure scores. Conclusion: It is necessary to consider the quality of life and emotional problems of caregivers of CP children and support them both physically and psychologically with comprehensive rehabilitation.

Tea time in the library

Yoo, Ji Na 한국콘텐츠학회 2022 ICCC International Digital Design Invitation Exhib Vol.2022 No.12