• Journal of Gastric Cancer
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• 제15권3호
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• pp.151-158
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• 2015

Purpose: Obesity is associated with morbidity following gastric cancer surgery, but whether obesity influences morbidity after laparoscopic gastrectomy (LG) remains controversial. The present study evaluated whether body mass index (BMI) and visceral fat area (VFA) predict postoperative complications. Materials and Methods: A total of 217 consecutive patients who had undergone LG for gastric cancer between May 2003 and December 2005 were included in the present study. We divided the patients into two groups ('before learning curve' and 'after learning curve') based on the learning curve effect of the surgeon. Each of these groups was sub-classified according to BMI (<$25kg/m^2$ and ${\geq}25kg/m^2$) and VFA (<$100cm^2$ and ${\geq}100cm^2$). Surgical outcomes, including operative time, quantity of blood loss, and postoperative complications, were compared between BMI and VFA subgroups. Results: The mean operative time, length of hospital stay, and complication rate were significantly higher in the before learning curve group than in the after learning curve group. In the subgroup analysis, complication rate and length of hospital stay did not differ according to BMI or VFA; however, for the before learning curve group, mean operative time and blood loss were significantly higher in the high VFA subgroup than in the low VFA subgroup (P=0.047 and P=0.028, respectively). Conclusions: VFA may be a better predictive marker than BMI for selecting candidates for LG, which may help to get a better surgical outcome for inexperienced surgeons.

• Industrial Engineering and Management Systems
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• 제10권2호
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• pp.97-103
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• 2011

This paper develops a technology level quantification (TLQ) model by utilizing a learning curve. Original learning curve shows the relationship between cumulative number of units and the required time for the unit. On the other hand, in our developed model, the technology level, such as speed of production and quality of the produced items, is expressed as a function of not cumulative number of units but time, for increasing generality. Furthermore, for expressing each learning that consists of conceptual learning and operational learning, S-curve is utilized in our developed model. By fitting the S-curve and/or decomposing into some activities, our TQL model can be applied to approximate organizational and complicated process. Some variations in time and levels, parameters of our developed model are shown. By using the parameters, the procedure to identify our developed model is proposed. Also, the influential factors for the parameters of our developed model are discussed with classifying the factors into technoware, infoware, humanware, and orgaware. The expected technology level is utilized for expecting the capacity of production system, and the expected capacity can be utilized in predicting various changes in the organization and deciding managerial decision about TT. A case study in manufacturing industry shows the effectiveness of the developed model.

• Journal of Gastric Cancer
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• 제18권2호
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• pp.172-181
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• 2018

Purpose: This study aimed to evaluate the surgical outcomes and investigate the feasibility of reduced-port laparoscopic gastrectomy using learning curve analysis in a small-volume center. Materials and Methods: We reviewed 269 patients who underwent laparoscopic distal gastrectomy (LDG) for gastric carcinoma between 2012 and 2017. Among them, 159 patients underwent reduced-port laparoscopic gastrectomy. The cumulative sum technique was used for quantitative assessment of the learning curve. Results: There were no statistically significant differences in the baseline characteristics of patients who underwent conventional and reduced-port LDG, and the operative time did not significantly differ between the groups. However, the amount of intraoperative bleeding was significantly lower in the reduced-port laparoscopic gastrectomy group (56.3 vs. 48.2 mL; P<0.001). There were no significant differences between the groups in terms of the first flatus time or length of hospital stay. Neither the incidence nor the severity of the complications significantly differed between the groups. The slope of the cumulative sum curve indicates the trend of learning performance. After 33 operations, the slope gently stabilized, which was regarded as the breakpoint of the learning curve. Conclusions: The surgical outcomes of reduced-port laparoscopic gastrectomy were comparable to those of conventional laparoscopic gastrectomy, suggesting that transition from conventional to reduced-port laparoscopic gastrectomy is feasible and safe, with a relatively short learning curve, in a small-volume center.

• Journal of Gastric Cancer
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• 제18권2호
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• pp.182-188
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• 2018

Purpose: Despite the fact that there are several reports of single-port laparoscopic distal gastrectomy (SPDG), no analysis of its learning curve has been described in the literature. The aim of this study was to investigate the favorable factors for SPDG and to analyze the learning curve of SPDG. Materials and Methods: A total of 125 cases of SPDG performed from November 2011 to December 2015 were enrolled. All operations were performed by 2 surgeons (surgeon A and surgeon B). The moving average method was used for defining the learning curve. All cases were divided into 10 cases in a sequence, and the mean operative time and estimated blood loss data were extracted from each group. Results: Surgeon A performed 68 cases (female-to-male sex ratio, 91.1%:8.82%), and surgeon B performed 57 cases (female-to-male sex ratio, 61.4%:38.5%). The operative time of surgeon B significantly decreased after 30 cases ($157.8{\pm}38.4$ minutes vs. $118.1{\pm}34.5$ minutes, P=0.003); that of surgeon A did not significantly decrease before and after around 30 cases ($160.8{\pm}51.6$ minutes vs. $173.3{\pm}35.2$ minutes, P=0.6). The subgroup analysis showed that the operative time significantly decreased in the patients with body mass index (BMI) of <$25kg/m^2$ (<$25kg/m^2$:${\geq}25kg/m^2$, $159.3{\pm}41.7$ minutes: $194.25{\pm}81.1$ minutes; P=0.001). Conclusions: Although there was no significant decrease in the operative time for surgeon A, surgeon B reached the learning curve upon conducting 30 cases of SPDG. BMI of <$25kg/m^2$ was found to be a favorable factor for SPDG.

• 산업공학
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• 제25권4호
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• pp.441-449
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• 2012

Solar PV(photovoltaic) is paid great attention to as a possible renewable energy source to overcome recent global energy crisis. However to be a viable alternative energy source compared with fossil fuel, its market competitiveness should be attained. Grid parity is one of effective measure of market competitiveness of renewable energy. In this paper, we forecast the grid parity timing of solar PV energy in Korea using two factor learning curve model. Two factors considered in the present model are production capacity and technological improvement. As a result, it is forecasted that the grid parity will be achieved in 2019 in Korea.

• 한국수자원학회논문집
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• 제54권spc1호
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• pp.1183-1193
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• 2021

Low flow는 하천수의 공급관리 및 계획, 관개용수 등 다양한 분야에 영향을 미친다. 이러한 유황곡선을 산정하기 위해서는 30년 이상의 충분한 기간의 유량자료의 확보가 필수적이다. 하지만 국가하천 단위 이하의 하천의 경우 장기간의 유량자료가 없거나 중간에 일정기간 동안 결측된 관측소가 있어 하천별 유황 곡선을 산정하기에 한계가 있다. 이에 과거에는 미계측 유역의 유황을 예측하기 위해 다중회귀분석(Multiple Regression Analysis), ARIMA 모형 등 통계학적 기반의 기법들을 사용하였지만, 최근에는 머신러닝, 딥러닝 모형의 수요가 증가하고 있다. 이에 본 연구에서는 최신 패러다임에 맞는 머신러닝 기법인 DNN기법을 제시한다. DNN기법은 ANN기법의 단점인 학습과정에서 최적 매개변수 값을 찾기 어렵고, 학습시간이 느린 단점을 보완한 방법이다. 따라서 본연구에서는 DNN 모형을 이용하여 미계측 유역에 적용 가능한 유황곡선을 산정하고자 한다. 먼저, 유황곡선에 영향을 미치는 인자들을 수집하고 인자들 간의 다중공선성 분석을 통해 통계적으로 유의한 변수를 선정하여, 머신러닝 모형에 입력자료를 구축하였다. 통계적 검증을 통해 머신러닝 기법의 효용성을 검토하였다.

• 대한인간공학회:학술대회논문집
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• 대한인간공학회 1992년도 추계학술대회논문집
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• pp.113-120
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• 1992

In this paper, a mathematical model of learning curve is proposed to study the finger's reaction time. The model is a logarithmic linear type which represents a learning curve appropriately, and parameters are estimated by the linear. The learning coefficient and percentage of a reaction time can be easily computed in the mathematical model. This quantitative approach provides an important information to be used for the working capability qualification for re-employment as well as for the adaptability estimation of aged workers.

• 한국멀티미디어학회논문지
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• 제25권8호
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• pp.991-998
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• 2022

Recently, object recognition using image/video signals is rapidly spreading on autonomous driving and mobile phones. However, the actual input image/video signals are easily exposed to a poor illuminance environment. A recent researches for improving illumination enable to estimate and compensate the illumination parameters. In this study, we propose VE-DCE (video enhancement zero-reference deep curve estimation) to improve the illumination of low-light images. The proposed VE-DCE uses unsupervised learning-based zero-reference deep curve, which is one of the latest among learning based estimation techniques. Experimental results show that the proposed method can achieve the quality of low-light video as well as images compared to the previous method. In addition, it can reduce the computational complexity with respect to the existing method.

• 한국건설관리학회논문집
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• 제14권6호
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• pp.38-48
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• 2013

건설 프로젝트 내의 작업의 반복성에 주목하여 건설산업에의 학습곡선효과 적용에 관한 연구가 꾸준히 이루어졌다. 그러나 충분한 반복 작업을 가지는 초고층 프로젝트에서 학습곡선효과가 실제로 발생하는가에 대한 논란은 지속되고 있다. 이에 관해 기존의 연구들은 실제 건설 현장의 작업 생산성 데이터 분석을 통해 효과의 유무를 검증하였으나 작업 생산성의 향상 여부에만 초점을 맞추고 있을 뿐, 효과가 발생하는 과정에 관한 연구는 이루어지지 않았다. 이에 본 연구는 초고층 프로젝트에서 학습곡선효과가 발현되는 과정에 영향을 미치는 요인들을 분석하여 그 효과를 상쇄시키는 요인들을 찾고, 이를 반영한 작업 생산성 산정 모델을 제시하고자 한다. 이를 통해 기존의 이론을 보완하고 건설산업에서의 학습곡선효과 이론을 재정립하는 데 기여할 수 있다.

• Journal of Korean Neurosurgical Society
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• 제64권3호
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• pp.447-459
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• 2021

Objective : Oblique lateral interbody fusion (OLIF) is becoming the preferred treatment for degenerative lumbar diseases. As beginners, we performed 143 surgeries over 19 months. In these consecutive cases, we analyzed the learning curve and reviewed the complications in our experience. Methods : This was a retrospective study; however, complications that were well known in the previous literature were strictly recorded prospectively. We followed up the changes in estimated blood loss (EBL), operation time, and transient psoas paresis according to case accumulation to analyze the learning curve. Results : Complication-free patients accounted for 43.6% (12.9%, early stage 70 patients and 74.3%, late stage 70 patients). The most common complication was transient psoas paresis (n=52). Most of these complications occurred in the early stages of learning. C-reactive protein normalization was delayed in seven patients (4.89%). The operation time showed a decreasing trend with the cases; however, EBL did not show any significant change. Notable operation-induced complications were cage malposition, vertebral body fracture, injury to the ureter, and injury to the lumbar vein. Conclusion : According to the learning curve, the operation time and psoas paresis decreased. It is important to select an appropriately sized cage along with clear dissection of the anterior border of the psoas muscle to prevent OLIF-specific complications.