• 대한기계학회논문집A
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• 제21권3호
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• pp.502-510
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• 1997

A disturbance rejection controller using eccentricity filtering and LQ control techniques is proposed to alleviate the effecto of major roll eccentricity in multivariable cold-rolling processes. Fundamental problems in multivariable cold-rolling processes such as process time delay inherent in exit thickness measurement and non-stationary characteristics of roll eccentricity signals can be overcome by the proposed control method. The filtered instantaneous estimate of roll eccentricity may be exploited to improve instantaneous estimate of the exit thickness variation based on roll force and roll gap measurements, and a feedforward compensator is augmented as a reference for a gaugemeter thickness estimator. LQ feedback controller is combined with eccentricity filter for the attenuation of the exit thickness variation due to the entry thickness variation. The simulation results show that the roll eccentricity disturbance is significantly eliminated and other disturbances also are attenuated.

• Journal of Welding and Joining
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• 제28권2호
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• pp.74-78
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• 2010

In this paper, a non-contact method of evaluating the thickness reduction in an aluminum sheet caused by corrosion and friction using SH-EMAT (shear horizontal, electromagnetic acoustic transducer) is described. Since this method is based on the measurement of the time-of-flight and amplitude change of guided waves caused from the thickness reduction, it provides information on the thinning defects. Information was obtained on the changes of the various wave features, such as their time-of-flight and amplitude, and their correlations with the thickness reduction were investigated. The interesting features in the dispersive behavior of selected guided modes were used for the detection of thinning defects. The measurements of these features using SH waves were performed on aluminum specimens with regions thinned by 7.2% to 29.5% of the total thickness. It is shown that the time-of-flight measurement provides an estimation of the thickness reduction and length of the thinning defects.

• Journal of Periodontal and Implant Science
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• 제30권1호
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• pp.179-187
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• 2000

The objectives of this study were to measure keratinized gingival thickness in healthy Korean adults, and to correlate the keratinized gingival thickness with width of keratinized gingiva, probing pocket depth and gingival recession.Thickness measurements were performed in 37 Korean dental students using an ultrasonic device(SDM). Width of keratinized gingiva, gingival recession and probing pocket depth were measured with a Williams periodontal probe.The results showed that the keratinized gingival thickness varied from 0.83 mm(canines) to 1.16 mm(central incisors) in the maxilla and, in the mandible, from 0.68 mm(1st premolars) to 1.69 mm(2nd molars). In a stepwise multiple linear regression analysis, 23% of variation of gingival thickness could be explained by width of keratinized gingiva and probing pocket depth. It could be concluded that the keratinized gingival thickness depends on tooth type and correlates with width of keratinized gingiva and probing pocket depth.

• Tribology and Lubricants
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• 제20권5호
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• pp.225-230
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• 2004

Most studies of elsatohydrodynamic lubrication are oriented only to the measurement of film thickness itself with optical interferometer. In order to exactly investigate the tribological characteristics of a certain lubricant, it is also important to get the information of traction behaviors as well. In this work, we developed a device for measuring the friction force of ehl contact condition as well as the film thickness. To verify the validity of the measuring system, the friction forces and film thicknesses under ehl condition are simultaneously measured with the variations of additive ratios of viscosity index improvers which cause non-linear tendencies of film thickness to contact velocity.

• The Journal of Advanced Prosthodontics
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• 제6권4호
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• pp.309-316
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• 2014

PURPOSE. The color of the ceramic restorations is affected by various factors such as brand, thickness of the layered the ceramic, condensation techniques, smoothness of surface, number of firings, firing temperature and thickness of dentin. The aim of this study was to evaluate the color change and surface roughness in dental porcelain with different thicknesses during repeated firings. MATERIALS AND METHODS. Disc-shaped (N=21) metal-ceramic samples (IPS Classic; Ivoclar Vivadent; Shaar, Liechtenstein) with different thickness were exposed to repeated firings. Color measurement of the samples was made using a colorimeter and profilometer was used to determine surface roughness. ANOVA and Tukey tests with repeated measurements were used for statistical analysis. RESULTS. The total thickness of the ceramics which is less than 2 mm significantly have detrimental effect on the surface properties and color of porcelains during firings (P<.05). CONCLUSION. Repeated firings have effects on the color change and surface roughness of the dental ceramics and should be avoided.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.95-97
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• 2005

Loss in the multi-stacked HTS wires are affected by a number of factor, such as, number of wires used in the stack, direction of external magnetic field and insulation thickness between the wire. This paper examines the effects of the insulation thickness on the magnetization loss of the multi-stacked YBCO coated conductor. Measurements of magnetization loss were performed using 4 different typo of multi-stacked wires and under various angle of external magnetic field. Test results show that loss density per unit volume increased for YBCO coated conductors when thickness of insulation increased. Loss density per unit volume decreased for YBCO coaled conductors when stacking number of tapes increased.

• Current Optics and Photonics
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• 제5권1호
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• pp.52-58
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• 2021

We show that a simple double-slit experimental setup can be used to measure the thickness of a transparent thin film. The phase difference between the light passing through one slit covered with photoresist film and that passing through the other slit without film was estimated using the simple Fraunhofer diffraction formula for a double slit. Our method gave error of a few percent or less for film thicknesses ranging from 0.7 to 1.7 ㎛, demonstrating that a laboratory double-slit experimental setup can be utilized in practical film-thickness measurements.

• 지질공학
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• 제24권1호
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• pp.81-89
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• 2014

국내 터널현장에서는 일차 지보재의 안정성 및 이차라이닝의 두께와 시공 시기 등을 결정하기 위하여 숏크리트에서 응력 측정을 수행하고 있다. 본 연구에서는 국내 여러 지역의 터널 현장에서 수행된 숏크리트 응력 측정 사례의 분석을 통하여 숏크리트 계측 현황 및 숏크리트 안정성 평가 기준의 문제점을 제시하였다. 또한 개선된 숏크리트 응력 계측 방법을 시공 중인 터널현장에 적용한 사례를 제시하였다. 현재와 같이 숏크리트의 안정성 평가를 측정응력의 절대적 크기를 통하여 수행하기 위해서는 숏크리트 응력 측정의 신뢰성 향상이 필요하다.

• Wind and Structures
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• 제34권1호
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• pp.101-113
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• 2022

We experimentally investigate the high-Reynolds flow around a rectangular cylinder of aspect ratio 5:1. This configuration is the object of the international BARC benchmark. Wind tunnel tests have been carried out for the flow at zero angle of attack and a Reynolds number, based on the crossflow cylinder length and on the freestream velocity, equal, to 40 000. Velocity measurements are obtained by using hot-wire anemometry along 50 different cross-flow traverses on the cylinder side and in the near wake. Differential pressure measurements are acquired on multiple streamwise sections of the model. The obtained measurements are in a good agreement with the state-of-the-art experiments. For the first time among the several contributions to the BARC benchmark, detailed flow measurements are acquired in the region near the cylinder side and in the near-wake flow. The edges and the thickness of the shear layers detaching from the upstream edges are derived from velocity measurements. Furthermore, we compute the flow frequencies characterizing the roll-up of the shear layers, the evolution of vortical structures near the cylinder side and the vortex shedding in the wake.

• Imaging Science in Dentistry
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• 제34권3호
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• pp.151-157
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• 2004

Purpose : To evaluate the quantitative accuracy of three-dimensional (3D) images by means of comparing distance measurements on the 3D images with direct measurements of dry human skull according to slice thickness and scanning modes. Materials and Mathods : An observer directly measured the distance of 21 line items between 12 orthodontic landmarks on the skull surface using a digital vernier caliper and each was repeated five times. The dry human skull was scanned with a Helical CT with various slice thickness (3, 5, 7 mm) and acquisition modes (Conventional and Helical). The same observer measured corresponding distance of the same items on reconstructed 3D images with the internal program of V-works 4.0/sup TM/(Cybermed Inc., Seoul, Korea). The quantitative accuracy of distance measurements were statistically evaluated with Wilcoxons' two-sample test. Results: 11 line items in Conventional 3 mm, 8 in Helical 3mm, 11 in Conventional 5mm, 10 in Helical 5mm, 5 in Conventional 7mm and 9 in Helical 7mm showed no statistically significant difference. Average difference between direct measurements and measurements on 3D CT images was within 2mm in 19 line items of Conventional 3mm, 20 of Helical 3mm, 15 of Conventional 5mm, 18 of Helical 5mm, II of Conventional 7mm and 16 of Helical 7mm. Conclusion: Considering image quality and patient's exposure time, scanning protocol of Helical 5mm is recommended for 3D image analysis of the skull in CT.