• 한국진공학회지
• /
• 제16권3호
• /
• pp.192-196
• /
• 2007

Hot wall epitaxy 방법으로 우물층의 두께를 바꾸어가며 ZnSe/CdSe/ZnSe 단일 양자우물을 성장하였다. 양자우물층의 두께는 TEM을 이용하여 측정하였다. 광발광의 세기와 반치폭의 변화로부터 양자우물층의 임계두께는 약 $9{\AA}$임을 알 수 있었다. 우물층의 두께가 임계두께 보다 작을 때 광발광과 PLE 스펙트럼의 비교로부터 stoke's shift를 확인하였고, 이는 엑시톤 결합 에너지에 의한 것임을 알 수 있었다. 우물층의 두께에 대한 광발광 피크의 에너지 이동은 이론치와 잘 일치하였다.

• 한국전문물리치료학회지
• /
• 제25권1호
• /
• pp.31-38
• /
• 2018

Background: Patient-centered care has recently become highly recommended, because it can improve health outcomes more effectively than problem-oriented care. The goal attainment scale (GAS) is one of the methods used for patient-centered care. It was originally developed as an outcome measurement tool, but it can also be used as a therapeutic intervention when setting quantifiable patient-centered goals. Objects: We sought to identify the effect of setting patient-centered goals on rehabilitation outcomes in patients with subacute stoke using GAS. Methods: Overall, 46 subjects with subacute stroke were divided into experimental ($n_1=23$) and control ($n_2=23$) groups. Subjects in both groups attended physical therapy sessions five times a week for four weeks. Those in the experimental group set goals using goal-attainment scaling. The mobility of each subject was evaluated using the Rivermead mobility index (RMI); daily-living activities, using the K-modified Barthel index (K-MBI); participation, using the Hopkins rehabilitation-engagement rating scale (HRERS); satisfaction, using the patient-satisfaction scale (PSS). Results: Subjects in the experimental group experienced more significant increases in RMI, HRERS, and PSS than those in the control group (p<.05, p<.05 and p<.01, respectively). After four weeks, GAS scores of the experimental group had increased more significantly than those of baseline (p<.01). Conclusion: Setting patient-centered goals is effective in improving the mobility and satisfaction of patients with subacute stoke. Setting patient-centered goals needs to be performed more frequently in clinical settings.

• 대한기계학회논문집 C: 기술과 교육
• /
• 제3권3호
• /
• pp.233-240
• /
• 2015

본 연구에서는 다양한 형상변수들이 봅슬레이의 공력성능에 미치는 영향을 평가하기 위하여 삼차원 Reynolds-averaged Navier-Stoke 해석을 수행하였으며, 난류모델로는 표준 k-${\varepsilon}$ 모델이 사용하였다. 격자계로는 비정렬 사면체 격자를 사용하였다. 성능 평가를 위한 형상변수로는 전방범퍼의 장축의 길이, 범퍼의 높이, 그리고, 카울링 측면과 정면 각각에서의 곡률반경 등 네가지 변수를 설정하였으며. 이들이 공력성능으로 선정된 항력계수에 미치는 영향을 평가하였다. 해석결과, 범퍼의 높이와 카울링 측면의 곡률반경이 항력계수에 민감한 영향을 미침을 알 수 있었다.

• 한국기계가공학회지
• /
• 제18권2호
• /
• pp.65-72
• /
• 2019

In long freight trains, there is a brake time delay in neighboring freight cars, which causes damage and fractures in the couplers, especially at their knuckle. A problem in the couplers of the cars can cause derailment and damages of human life and property. In this study, maximum forces on the couplers are studied when a long freight car brakes with the brake delay time and coupler gap. We make a dynamic model of 50 freight cars and couplers, applying contact between the couplers and a characteristic curve to express the force and displacement of the buffers using SIMPACK, which is a multi-body dynamics program. We use EN 14531-2, which is a standard of freight car brakes, to verify the dynamic model. Then, we compare the analyzed impact force with the coupler knuckle standard after applying the two carriages of a locomotive in the model based on the dispersed double head control system. The result shows that all coupler gap conditions satisfy the infinite lifetime of the material when the brake delay time is 0.1 second.

• 한국전산유체공학회지
• /
• 제13권1호
• /
• pp.14-20
• /
• 2008

The flow characteristics around a rudder in open water condition is analyzed by the computational method. Reynolds averaged Navier-Stoke's equation is utilized for the computation. The computational hydrodynamic force coefficients are verified through comparing with the experimental results. The information of these flow characteristics is necessary to predict cavitation and maneuvering performances, to estimate steering gear capacitance, and to get the bending moment which is useful for the structural analysis. The pressure distribution, the three-dimensional flow separation, and the tip vortices are investigated. The pattern of the three-dimensional flow separation is analyzed utilizing a topological rule. The tip vortices are also investigated through a visualization technique.

• 한국조명전기설비학회:학술대회논문집
• /
• 한국조명전기설비학회 2009년도 추계학술대회 논문집
• /
• pp.327-329
• /
• 2009

A first short stoke current which has a 10/350 ${\mu}s$ waveform is able to be generated by using the crowbar switch in R-L-C circuit. In this paper, a peaking circuit has been applied to make crowbar switch. Operate effective for generating 10/350 ${\mu}s$ waveform. According to simulation with PSpice, we have found that some value of inductance were more effective to trigger a crowbar switch. As a result of experimental test using crowbar switch with peaking circuit, the success rate of triggering crowbar switch is higher than the normal crowbar switch without peaking circuit.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2000년도 춘계 학술대회논문집
• /
• pp.178-183
• /
• 2000

An efficient Newton-GMRES algorithm is presented for computing two-dimensional steady compressible viscous flows on unstructured hybrid meshes. The scheme is designed on cell-centered finite volume method which accepts general polygonal meshes. Steady-state solution is obtained with pseudo-transient continuation strategy. The preconditioned, restarted general minimum residual(GMRES) method is employed in matrix-free form to solve the linear system arising at each Newton iteration. The incomplete LU fartorization is employed for the preconditioning of linear system. The Spalart-Allmars one equation turbulence model is fully coupled with the flow equations to simulate turbulence effect. The accuracy, efficiency and robustness of the presently developed method are demonstrated on various test problems including laminar and turbulent flows over flat plate and airfoils.

• 대한기계학회논문집B
• /
• 제24권10호
• /
• pp.1335-1342
• /
• 2000

Three-dimensional flow analysis and numerical optimization methods are presented for the design of an axial-flow fan. Steady, incompressible, three-dimensional Reynolds-averaged Navier-Stokes equations are used as governing equations, and standard k- ${\varepsilon}$ turbulence model is chosen as a turbulence model. Governing equations are discretized using finite volume method. Steepest descent method, conjugate gradient method and BFGS method are compared to determine the searching directions. Golden section method and quadratic fit-sectioning method are tested for one dimensional search. Objective function is defined as a ratio of generation rate of the turbulent kinetic energy to pressure head. Two variables concerning sweep angle distribution are selected as the design variables. Performance of the final fan designed by the optimization was tested experimentally.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
• /
• pp.88.2-88.2
• /
• 2011

본 연구는 아연/공기전지 설계기술 개발을 위한 기초 연구로서 전산해석을 이용하여 전해질 유동에 따른 아연/공기전지의 성능 예측에 관한 것이다. 전산해석모델은 전기화학 방정식과 유체유동 방정식으로 구성하였으며, 화학종 반응에 관한 지배방정식으로는 Nernst-Planck식을 이용하였고 전극표면의 전기화학반응은 Butler-Volmer식을 이용하였다. 또한 유체유동 방정식은 Navier-Stoke식을 적용하여 전해질 유동에 따른 전기화학적 성능 변화를 모사하였다. 아연/공기전지 성능 평가 실험으로부터 얻은 I-V 곡선과 전산해석결과와의 비교/분석을 통하여 전기화학모델의 타당성을 검증하였으며, 유체 유동 방정식과의 연동해석을 적용하여 전해질 유입 위치 및 유입 속도에 따른 아연/공기전지의 성능 변화를 조사하였다. 아연/공기전지의 성능은 전해질 유입 위치가 아연극에 가까울수록, 유입 속도가 빠를수록 향상되는 것을 확인할 수 있었다.

• 한국자동차공학회논문집
• /
• 제18권3호
• /
• pp.95-103
• /
• 2010

This paper presents a simulation model of a double-acting high-speed pneumatic cylinder with a relief valve type cushion mechanism. The model predicts piston motion, mass flow rate, pressure and temperature time histories of cushion chamber. Of interest here is to investigate the cushioning effect of varying the piston and piston-rod diameter, cushion ring diameter and length, and stoke in cushion mechanism. As a result, this cushion mechanism is found to be adequate under high-speed driving of pneumatic cylinders. The simulation model proposed here will be very useful to analyze the dynamic characteristics and to improve or design the better cushion mechanism in high-speed pneumatic cushion cylinders.