• Title/Summary/Keyword: VSS

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Comparison for the Economic Performance of Control Charts with the VSI and VSS Features (VSI와 VSS 관리도의 경제적 효율 비교)

  • 박창순;이재헌;김영일
    • Journal of Korean Society for Quality Management
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    • v.30 no.2
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    • pp.99-117
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    • 2002
  • Variable sampling interval(VSI) and variable sample size(VSS) control charts vary the sampling rate for the next sample depending on the current chart statistic. This paper develops EWMA charts with the VSI and VSS features, and investigates the effectiveness of these charts in context of an economic model. The economic properties of these charts are evaluated by using Markov chain methods. The model contains cost parameters which allow the specification of the costs associated with sampling, false alarms, and operating off target. This economic model can be used to quantify the cost saving that can be obtained by using control charts with the VSI and VSS features instead of with the fixed sampling rate(FSR) feature, and can also be used to gain insight into the way that control charts with the VSI and VSS features should be designed to achieve optimal economic performance. The economic performance of X charts with the VSI and VSS features is also considered.

A VSR $\bar{X}$ Chart with Multi-state VSS and 2-state VSI Scheme

  • Lee, Jae-Heon;Park, Chang-Soon
    • Journal of Korean Society for Quality Management
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    • v.32 no.4
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    • pp.252-264
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    • 2004
  • Variable sampling Interval (VSI) control charts vary the sampling interval according to value of the control statistic while the sample size is fixed. It is known that control charts with 2-state VSI scheme, which uses only two sampling intervals, give good statistical properties. Variable sample size (VSS) control charts vary the sample size according to value of the control statistic while the sampling interval is fixed. In the VSS scheme no optimal results are known for the number of sample sizes. It is also known that the variable sampling rate (VSR) $\bar{X}$ control chart with 2-state VSS and 2-state VSI scheme leads to large improvements In performance over the fixed sampling rate (FSR) $\bar{X}$ chart, but the optimal number of states for sample size Is not known. In this paper, the VSR Χ charts with multi-state VSS and 2-state VSI scheme are designed and compared to 2-state VSS and 2-state VSI scheme. The multi-state VSS scheme is considered to, achieve an additional improvement by switching from the 2-state VSS scheme. On the other hand, the multi-state VSI scheme is not considered because the 2-state scheme is known to be optimal. The 3-state VSS scheme improves substantially the sensitivity of the $\bar{X}$ chart especially for small and moderate mean shifts.

On parameter identification algorithm using VSS theory (가변구조이론에 의한 파라미터 identification 알고리즘)

  • 심귀보;한동균;전홍태
    • 제어로봇시스템학회:학술대회논문집
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    • 1992.10a
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    • pp.927-930
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    • 1992
  • VSS identification approach is based on following concept, i.e. while in sliding motion, the switching of control inputs refects system uncertainites. Therefore, if there exist some operations that make the information form the switiching control inputs be achievable, then the unknown parameters can be actually identification mechanisms which can fully make use of the available information. Two different types of VSS identifiers are taken into consideration. The first type uses adjustable model whose structure is similar to that of identified systems. From the viewpoint of contro, this type of VSS identifiers may be regraded as direct identifier vecause the identified system is handled as an open loop. On the other hand, if the identified system is controlable in the sense of VSS(sliding mode can be generated through chosing control inputs), the second type of VSS identifier, the indirect VSS identifier, can be constructed according to the linerized system strucutre while staying in sliding mode. Therefroe it can be applied to some nonlinear systems which are not linear in parametric space by general identification algorithms, whereas linear in parametric space when sliding mode is existed.

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VSS control of inverted pendulum (도립진자의 가변 구조 제어)

  • 한문섭;이욱열
    • 제어로봇시스템학회:학술대회논문집
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    • 1988.10a
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    • pp.54-57
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    • 1988
  • In this thesis, after the inverted pendulum being made, its state equation was established with parameters obtained by the state space approach and its position stabilization control was performed with VSS. The switching function of VSS was obtained from pole placement method and as the result of VSS control was compared with that of optimal regulator control, its robustness was clarified in sliding mode. The position and stabilization control of the inverted pendulum Wstem were acomplished with VSS.

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Sewage sludge solubilization using ultrasonic combined with calcium peroxide (초음파/과산화칼슘(US/CaO2)을 이용한 하수슬러지 가용화)

  • Han, Jun-Hyuk;Nam, Se-Yong
    • Journal of the Korea Organic Resources Recycling Association
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    • v.29 no.4
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    • pp.41-46
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    • 2021
  • In order to investigate the degree of sewage sludge solubilizaion using ultrasonic(US) combined with calcium peroxide(CaO2), VSS reduction rate, solubilization rate, SCOD/VSS ratio, SCOD increasing rate, LB-EPS(Loosely-Bound EPS) and TB-EPS(Tightly-bound EPS) were measured. US was compared as a control. Solubilization rate increased by 23.4% under US and increased by 50.7% under US/CaO2(0.05 g CaO2/g VSS). and also, at the same conditions, VSS reduction rate increased by 7.1% and 17.7%, respectively. SCOD increasing rate from 10 to 90 minutes was 0.0151 min-1 under US/CaO2(0.02 g CaO2/g VSS). TB-EPS decreased by 36.4% under US and decreased by 59.0% under US/CaO2(0.05 g CaO2/g VSS). TB-EPS decreased during first 10 minutes and then decreased slowly until 90 minutes. There was no significant difference in TB-EPS decrease according to the dosage of calcium peroxide.

Diagnostic value of the Vesikari Scoring Sys­tem for predicting the viral or bacterial patho­gens in pediatric gastroenteritis

  • Shim, Dong Ho;Kim, Dong Yeon;Cho, Ky Young
    • Clinical and Experimental Pediatrics
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    • v.59 no.3
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    • pp.126-131
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    • 2016
  • Purpose: To evaluate the diagnostic value of the Vesikari Scoring System (VSS) as an early predictor of pathogens in children with acute gastroenteritis (AG). Methods: In this retrospective study, the VSS score, absolute neutrophil count (ANC), and C-reactive protein (CRP) levels were analyzed in 107 hospitalized children with AG, aged 6 months to 17 years. Patients were divided into nonspecific, viral, and bacterial groups according to the pathogens detected using a multiplex polymerase chain reaction (PCR) test. Results: Patients in the bacterial group had significantly higher CRP values and VSS scores compared to those in the viral group and significantly higher VSS scores compared to those in the nonspecific group (P<0.05). Patients in the viral group had significantly higher VSS scores than those in the nonspecific group (P<0.05). Logistic regression analysis revealed that VSS was the most effective diagnostic tool for predicting the type of pathogen (P<0.05). The area under the receiver operating characteristics curve of VSS was significantly greater than that for ANC and CRP (P<0.05). At a cutoff point of 10 in the VSS, an acceptable diagnostic accuracy could be achieved for distinguishing between bacterial and viral pathogens in AG. Conclusion: VSS can be considered a useful and reliable infectious marker for pediatric gastroenteritis. VSS may be a good early predictor of the type of pathogen, enabling development of a treatment plan before results from a stool culture or PCR test are available.

A Study on the Biogas Production and VSS Concentration in Organic Wastewater Treatment Using a Downflow Anaerobic Packed Bed Reactor with HRT Change (하향유식 혐기성 고정상 생물반응기에서 유기성 폐수의 HRT변화에 따른 Biogas 생성 및 VSS 농도에 관한 연구)

  • 김정회;강동수;장인용
    • Journal of Environmental Health Sciences
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    • v.19 no.3
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    • pp.17-21
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    • 1993
  • Characteristics of a downflow anaerobic packed bed reactor with raschig ring ceramics as a packing were measured and discussed for the basic evaluation of the process. A synthesized glucose substrate wastewater were used as a feed and process characteristics such as pH, biogas production, composition of produced gas, COD removal and VSS were measured with the hydraulic retention time (HRT) changing from 0.25 to 2 days. As a result, this type of reactor was applicable in continuous operation within the given HRT range and the transient period approaching the steady state was about 20 days. The content of methane in produced gas increase with HRT was always high above 50% enough to use as energy source. The COD removal efficiency increased gradually as HRT increased. The axial profile of VSS concentration in the reactor usually showed the maximum at the lower region and the minimum at the middle. The VSS concentration at the upper region and the exit appeared similarly. However, at 0.25 day of HRT, the VSS concentration of effluent became higher than that of the upper region. Therefore the optimum HRT of this reactor occurred about 0.5 day, at which the production of methane began to be just stabilized and loss of VSS and COD removal were resonable.

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A Continuous Sliding Surface Transformed VSS by Saturation Function for MIMO Uncertain Linear Plants (다입출력 불확실 선형 플랜트를 위한 포화함수에 의한 연속 슬라이딩 면 변환 가변구조시스템)

  • Lee, Jung-Hoon
    • Journal of the Institute of Electronics and Information Engineers
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    • v.52 no.7
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    • pp.127-134
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    • 2015
  • In this note, a continuous sliding surface transformed variable structure systems by the saturation function is presented for MIMO uncertain linear plants. A discontinuous sliding surface transformed VSS is proposed theoretically. The closed loop exponential stability together with the MIMO existence condition of the sliding mode on the predetermined sliding surface is investigated. For practical applications, a continuous approximation of the discontinuous VSS is made by means of the saturation function. The discontinuity of the control input as the inherent property of the VSS is much improved in view of the practical aspects. Through a design example and simulation studies, the usefulness of the proposed continuous transformed VSS controller is verified.

The Statistical Design of VSS $\bar{X}$ Chart Considering Two Assignable Causes (두 개의 이상원인을 고려한 VSS $\bar{X}$ 관리도의 통계적 설계)

  • 심성보;강창욱
    • Journal of Korean Society for Quality Management
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    • v.28 no.3
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    • pp.44-52
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    • 2000
  • In this paper we apply VSS X chart to the case when two assignable causes effect the process mean shift. We compare the case when two compound assignable causes effect the process mean with another one which effects individually. For the practical use of VSS $\bar{X}$ chart we propose the sample size which minimizes the average number of samples until the signal is given in out-of-control state.

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Statistical Design of VSS $\overline{A}$ Charts for Monitoring an AR(1) Process (AR(l) 공정을 탐지하는 VSS $\overline{A}$ 관리도의 통계적 설계)

  • 이재헌
    • Journal of Korean Society for Quality Management
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    • v.31 no.3
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    • pp.126-135
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    • 2003
  • A basic assumption in standard applications of control charts is that the observations are statistically independent. However, this assumption is often violated from processes in many industries. The presence of autocorrelation has a serious impact on the performance of control charts, causing a dramatic increase in the frequency of false alarms. This paper considers a process in which the observations can be modeled as a first order autoregressive(AR(1)) process, and develops (equation omitted) charts with the variable sample size(VSS) scheme for monitoring the mean of this process.