• 한국전산구조공학회논문집
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• 제26권5호
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• pp.351-358
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• 2013

본 논문에서는 Pothead를 지지하는데 사용하는 지그의 고유진동수를 일정 범위로 제한하여 Pothead와 공진을 일으키지 않도록 하는 지그의 최적 설계안을 제시한다. 쿤 터커(Kuhn-Thucker) 조건을 적용한 최적기준법(Optimality criteria method)을 사용하여 위상 최적화를 수행하였고, 이 과정에서 유한요소 크기기 최적 형상에 미치는 영향을 검토하였다. 또한 위상 최적화 결과를 바탕으로 실험 계획법(Design of experiments)과 반응 표면법(Response surface method)을 사용하여 형상 및 치수 최적화를 수행하여 비교용 지그에 비해 전체 질량이 30% 감소되는 결과를 얻었다. 마지막으로 최적화된 지그의 내진 해석을 수행한 Pothead의 응답은 Metal Handbook에서 제시된 내진 응답을 만족하고 있다.

• Steel and Composite Structures
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• 제44권2호
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• pp.155-169
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• 2022

In the present paper an analytical model was developed to study the non-linear vibrations of Functionally Graded Carbon Nanotube (FG-CNT) reinforced doubly-curved shallow shells using the Multiple Scales Method (MSM). The nonlinear partial differential equations of motion are based on the FGM shallow shell hypothesis, the non-linear geometric Von-Karman relationships, and the Galerkin method to reduce the partial differential equations associated with simply supported boundary conditions. The novelty of the present model is the simultaneous prediction of the natural frequencies and their mode shapes versus different curvatures (cylindrical, spherical, conical, and plate) and the different types of FG-CNTs. In addition to combining the vibration analysis with optimization algorithms based on the genetic algorithm, a design optimization methode was developed to maximize the natural frequencies. By considering the expression of the non-dimensional frequency as an objective optimization function, a genetic algorithm program was developed by valuing the mechanical properties, the geometric properties and the FG-CNT configuration of shallow double curvature shells. The results obtained show that the curvature, the volume fraction and the types of NTC distribution have considerable effects on the variation of the Dimensionless Fundamental Linear Frequency (DFLF). The frequency response of the shallow shells of the FG-CNTRC showed two types of nonlinear hardening and softening which are strongly influenced by the change in the fundamental vibration mode. In GA optimization, the mechanical properties and geometric properties in the transverse direction, the volume fraction, and types of distribution of CNTs have a considerable effect on the fundamental frequencies of shallow double-curvature shells. Where the difference between optimized and not optimized DFLF can reach 13.26%.

• 한국음향학회지
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• 제27권1호
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• pp.1-11
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• 2008

기하음향학 방법들을 이용한 중주파수 해석의 어려움을 해결하기 위하여 소리의 전파에서 위상 정보를 고려한 위상 기하음향학 방법이 제안되었다. 위상 기하음향학 방법은 위상정보를 고려하여 중주파수 대역의 간섭 현상을 설명할 수 있는 장점을 가지고 있다. 그러나 이러한 방법들을 이용하여 소리의 파동성으로 대표되는 저주파수 현상들을 모두 설명할 수 없다. 특히 저주파수 대역에서는 모서리나 장애물에 의한 회절현상을 고려하지 못하여 전달함수나 충격응답의 예측시 오차가 발생한다. 또한 실수인 흡음 계수를 사용한 해석 결과는 측정치와 차이를 보이므로 반사 계수의 잘못된 위상 정보는 교정되어야 한다. 본 연구에서는 균일 회절 이론을 병합한 위상 빔 추적법의 결과를 기존의 위상 빔 추적법의 결과와 비교하였다. 또한 벽면 반사계수의 위상을 변화시키며 위상 정보의 영향을 조사하였다. 제안된 오차 보정 방법들을 이용하면, 좀더 낮은 주파수 대역까지 정확성을 향상시켜 위상 빔 추적법을 실내음향 예측에 적용할 수 있다.

• The Korean Journal of Pain
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• 제13권1호
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• pp.8-18
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• 2000

Background: Intraperitoneal (IP) and intrathecal (IT) administration of $\alpha$-amino-3-hydroxy-5-methyl-4-isoxazole-propionic (AMPA) and kainate (KA) receptor antagonist attenuate hyperalgesia in various models of persistent pain. The purpose of this study was to assess the effects of IP and IT LY293558, a novel AMPA/KA receptor antagonist on mechanical hyperalgesia after incision. Methods: Sprague-Dawley rats were anesthetized with halothane and underwent plantar incision. Two hours later, responses to mechanical stimuli were assessed using the response frequency to a nonpunctate mechanical stimulus and withdrawal threshold to calibrated von Frey filaments. One group of rats received vehicle, 5 or 10 mg/kg of LY293558 IP. In the other group, vehicle, 0.2, 0.5 or 2 nmol of LY293558 was administered IT. Ataxia and motor function were also evaluated. Results: Hyperalgesia was persistent in both the vehicle and 5 mg/kg group. IP administration of 10 mg/kg of LY293558 increased withdrawal threshold at 30 and 60 min after incision; deficits in rotorod performance were observed at 30, 60, 90 and 150 min. IT administration of 0.5 nmol of LY293558 increased the median withdrawal threshold at 30 and 60 min. Motor function was only impaired at 30 min. IT administration of 2 nmol produced hemiparesis. Again, inhibition of pain behaviors outlasted the effects on motor function. Conclusions: These data further suggest AMPA/KA receptors are important for the maintenance of pain behaviors caused by incisions. IT administration of LY293558 was more effective than systemic administration and reducing pain behaviors caused by a surgical incision.

• 한국자동차공학회논문집
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• 제21권3호
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• pp.88-97
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• 2013

This paper presents a robust air-to-fuel ratio (AFR) control algorithm for managing exhaust gas recirculation (EGR) systems. In order to handle production tolerance, deterioration and parameter-varying characteristics of the EGR system, quantitative feedback theory (QFT) is applied for designing the robust AFR control algorithm. A plant model of EGR system is approximated by the first order transfer function plus time-delay (FOPTD) model. EGR valve position and AFR of exhaust gas are used as input/output variables of the plant model. Through engine experiments, parameter uncertainty of the plant model is identified in a fixed engine operating point. Requirement specifications of robust stability and reference tracking performance are defined and these are fulfilled by the following steps: during loop shaping process, a PID controller is designed by using a nominal loop transmission function represented on Nichols chart. Then, the frequency response of closed-loop transfer function is used for designing a prefilter. It is validated that the proposed QFT-based AFR control algorithm successfully satisfy the requirements through experiments of various engine operating points.

• 한국정보통신학회논문지
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• 제21권12호
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• pp.2232-2240
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• 2017

국제해상기구는 국제해상인명안전협약을 통해 국제항해 선박에 대하여 AIS와 VHF를 의무화하고, 국내 또한 선박안전법과 선박설비기술기준을 통해 특정 선박에 의무화 하고 있다. 그러나 다양한 통신장비 및 복잡한 사용법으로 인해 오동작이 발생하고 실제 구조신호에 대한 응답지연으로 인하여 인명사고가 발생하는 경우가 많다. 그래서 최근 해상통신장치는 국제해상안전조난시스템 현대화의 일환으로 차세대 해상통신시스템 구축을 위해 여러 종류의 해상통신시스템을 연동 및 통합하려는 시도가 이루어지고 있다. 본 논문에서는 AIS와 VHF의 연동 및 통합을 통한 DSC 기능을 구현하는 기법에 대하여 기술하였다. AIS에서 선박의 정보를 추출하고 VHF의 DSC 기능에 활용할 수 있는 데이터의 연동 알고리즘을 통해 향 후 국내기술기준 및 표준화를 달성하기위한 근거를 제시하고자 한다.

• 생명과학회지
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• 제19권6호
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• pp.825-831
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• 2009

본 연구에서는 저압.저산소환경의 노출을 시켜 30분간의 유산소성 자전거운동이 호흡기계 반응 및 면역기능의 응답에 미치는 영향을 검토하였다. 그 결과 몇 가지 지견을 도출해낼 수 있었다. 첫째로 75 $%HR_{max}$ 강도에서 30분간의 유산소성 운동 중에 저산소성 환기억제 또는 저하(hypoxic ventilatory depression or decline)라고 하는 현상은 평지뿐만이 아니라 3,000 m 고도에서도 나타나고 있고, 둘째 호흡기계의 반응은 축구선들이 특히 고소에서 적응과 감수성이 우수하다고 할 수 있으며, 셋째 면역기능의 항목인 단구(monocyte)는 운동습관의 유무 및 3,000 m의 고도에 따라 서로 다른 양상(상호작용)으로 변화를 하고 있다고 할 수 있다.

• Journal of Gastric Cancer
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• 제19권1호
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• pp.49-61
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• 2019

Purpose: The perigastric vagus nerve may play an important role in preserving function after gastrectomy, and intraoperative neurophysiologic tests might represent a feasible method of evaluating the vagus nerve. The purpose of this study is to assess the feasibility of neurophysiologic evaluations of the function and viability of perigastric vagus nerve branches during gastrectomy. Materials and Methods: Thirteen patients (1 open total gastrectomy, 1 laparoscopic total gastrectomy, and 11 laparoscopic distal gastrectomy) were prospectively enrolled. The hepatic and celiac branches of the vagus nerve were exposed, and grabbing type stimulation electrodes were applied as follows: 10-30 mA intensity, 4 trains, $1,000{\mu}s/train$, and $5{\times}$frequency. Visible myocontractile movement and electrical signals were monitored via needle probes before and after gastrectomy. Gastrointestinal symptoms were evaluated preoperatively and postoperatively at 3 weeks and 3 months, respectively. Results: Responses were observed after stimulating the celiac branch in 10, 9, 10, and 6 patients in the antrum, pylorus, duodenum, and proximal jejunum, respectively. Ten patients responded to hepatic branch stimulation at the duodenum. After vagus-preserving distal gastrectomy, 2 patients lost responses to the celiac branch at the duodenum and jejunum (1 each), and 1 patient lost response to the hepatic branch at the duodenum. Significant procedure-related complications and meaningful postoperative diarrhea were not observed. Conclusions: Intraoperative neurophysiologic testing seems to be a feasible methodology for monitoring the perigastric vagus nerves. Innervation of the duodenum via the celiac branch and postoperative preservation of the function of the vagus nerves were confirmed in most patients.

• 한국자동차공학회논문집
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• 제15권2호
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• pp.50-57
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• 2007

Shocks are excited by impulsive forces and cause discomfort in vehicles. Current standards define means of evaluating shocks and predicting their discomfort, but the methods are based on research with a restricted range of shocks. This experimental study was designed to investigate the discomfort of seated subjects exposed to a wide range of vertical shocks. Shocks were produced from the responses of one degree-of-freedom models, with 16 natural frequencies (from 0.5 to 16 Hz) and four damping ratios (0.05 0.1, 0.2 and 0.4), to a hanning-windowed half-sine force inputs. Each type of shock was presented at five vibration dose values in the range $0.35\;ms^{-1.75}$ to $2.89\;ms^{-1.75}$. Fifteen subjects used magnitude estimation method to judge the discomfort of all shocks. The exponent in Stevens' power law, indicating the rate of growth in discomfort with shock magnitude, decreased with increasing fundamental frequency of the shocks. At all magnitudes, the equivalent comfort contours showed greatest sensitivity to shocks having fundamental frequencies in the range 4 to 12.5 Hz. At low magnitudes the variations in discomfort with the shock fundamental frequency were similar to the frequency weighting $W_b$ in BS 6841, but low frequency high magnitudes shocks produced greater discomfort than predicted by this weighting. At some frequencies, for the same unweighted vibration dose value, there were small but significant differences in discomfort caused by shocks having different damping ratios. The rate of increase in discomfort with increasing shock magnitude depends on the fundamental frequency of the shock. In consequence, the frequency-dependence of discomfort produced by vertical shocks depends on shock magnitude. For shocks of low and moderate discomfort, the current methods seem reasonable, but the response to higher magnitude shocks needs further investigation.

• 생물정신의학
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• 제21권4호
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• pp.168-174
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• 2014

Objectives Sensory gating dysfunctions in patients with schizophrenia and bipolar disorder have been investigated through two similar methods ; P50 suppression and prepulse inhibition paradigms. However, recent studies have demonstrated that the two measures are not correlated but rather constitute as distinct neural processes. Recent studies adopting spectral frequency analysis suggest that P50 suppression reflects the interaction between gamma and other frequency bands. The aim of the present study is to investigate which frequency component shows more significant interaction with gamma band. Methods A total of 108 mood disorder patients and 36 normal subjects were included in the study. The P50 responses to conditioning and test stimuli with an intra-pair interval of 500 msec were measured in the study population. According to P50 ratio (amplitude to the test stimulus/amplitude to the conditioning stimulus), the subjects with P50 ratio less than 0.2 were defined as suppressed group (SG) ; non-suppressed group (NSG) consisted of P50 ratio more than 0.8. Thirty-five and 25 subjects were included in SG and NSG, respectively. Point-to-point correlation coefficients (PPCCs) of both groups were calculated between two time-windows : the first window (S1) was defined as the time-window of one hundred millisecond after the conditioning auditory stimulus and the second window (S2) was defined as the time-window of 100 msec after the test auditory stimulus. Spectral frequency analysis was performed to investigate which frequency band results in the difference of PPCC between SG and NSG. Results Significant reduction of PPCC between S1 and S2 was observed in the SG (Pearson's r = 0.24), compared to PPCC of the NSG (r = 0.58, p < 0.05). In spectral frequency analysis, gamma band showed "phase-reset" and similar responses after the two auditory stimuli in suppressed and non-suppressed group. However in the case of alpha band, comparison showed significantly low PPCC in SG (r = -0.14) compared to NSG (r = 0.36, p < 0.05). This may be reflecting "phase-out" of alpha band against gamma band at approximately 50 msecs after the test stimulus in the SG. Conclusions Our study suggests that normal P50 suppression is caused by phase-out of alpha band against gamma band after the second auditory stimulus. Thus it is demonstrated that normal sensory gating process is constituted with attenuated alpha power, superimposed on consistent gamma response. Implications of preserved gamma and decreased alpha band in sensory gating function are discussed.