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1

Preparation Of Fine Grained SiC At Reduced Temperature By Two-Step Sintering

Kim K.-W., Oh K.-S., Lee H., Kim B. S., Chung T.-J.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1539--1542

EN

Two-step sintering route was applied for the densification SiC by promoting the role of liquid phase. The specimen contained 8 vol% of liquid phase composed of Al2O3 and Y2O3. The heating schedule consisted with initial rapid heating to 2000°C and immediate quenching to 1700 or 1750°C. By heating at elevated temperature, even distribution of the liquid phase was intended. The heat treatment at reduced temperature was to suppress the evaporative loss of the liquid and to secure the time for densification. The two-step sintering effectively suppressed loss of mass and coarsening. The resultant SiC was thus dense and was composed of fine grains exhibiting hardness of 2321 kgf/mm2.

2

A New 3D Sensor System by Using Virtual Camera Model and Stereo Vision for Mobile Robots

Lee H., Kim M. N., Cho H.

Journal of Automation Mobile Robotics and Intelligent Systems

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2008

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Vol. 2, No. 4

38-44

EN

So many researches have been conducted to develop 3D sensing method for mobile robots. Among them, the optical triangulation, a well-known method for 3D shape measurement, is also based on active vision sensing principle for mobile robot sensor system, so that the measurement result is robust to illumination noises from environments. Due to this advantage it has been popularly used. However, to obtain the 3D information of environment needs a special scanning process and scanning actuators need. To omit this scanning process multi-line projection methods have been widely researched. However, they suffer from an inherent limitation: The results of multi-line projection method commonly have measurement errors because of 2 -ambiguity caused by regularly repeated multiline laser pattern. In this paper, to overcome 2 -ambiguity effectively, we introduce a novel sensing method for a 3D sensing system using multi-line projection and stereo cameras, based on the virtual camera model and stereovision algorithm. To verify the efficiency and accuracy of the proposed method, a series of experimental tests is performed.

3

Molecular Clusters to Nanomaterials

Singh N., Lee H., Suh S., Kołaski M., Kim K.

Polish Journal of Chemistry

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2007

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Vol. 81, nr 5-6

1021-1035

EN

Theoretical investigations of gas phase clusters enable the evaluation of intrinsic molecular properties and intermolecular interactions. Based on the microscopic determination of the properties of individual atoms, molecules, or clusters, one can predict the macroscopic properties of bulk matter. With the aid of theoretical insights into the interaction forces holding these clusters and subsequent properties of a large number of cluster systems (ranging from simple water clusters to large pi-systems), we have investigated the properties of various novel molecular systems including endo/exohedral fullerenes, nanotori, nonlinear optical materials, ionophores/receptors, polypeptides, enzymes, organic nanotubes, nanowires, and electronic and nano-mechanical molecular devices. This mini-review highlights some of the interesting results obtained in the course of our extensive theoretical investigations of clusters toward the molecular design approach of nanomaterials.

4

Microstructure evolution modeling of square-diamond pass hot bar rolling of AISI 4135 steel

Lee H., Kwon H., Im Y., Hodgson P.

Computer Methods in Materials Science

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2006

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Vol. 6, No. 3-4

140-149

EN

In this study, kinetics of the static (SRX) and metadynamic recrystallization (MDRX) of AISI4135 steel was investigated using hot torsion tests. Continuous torsion tests were carried out to determine the critical strain for dynamic recrystallization (DRX). The times for 50% recrystallization of SRX and MDRX were determined, respectively, by means of interrupted torsion tests. Furthermore, austenite grain size (AGS) evolution due to recrystallization (RX) was measured by optical microscopy. With the help of the evolution model established, the AGS for hot bar rolling of AISI4135 steel was predicted numerically. The predicted AGS values were compared with the results using the other model available in the literature and experimental results to verify its validity. Then, numerical predictions depending on various process parameters such as interpass time, temperature, and roll speed were made to investigate the effect of these parameters on AGS distributions for square-diamond pass rolling. Such numerical results were found to be beneficial in understanding the effect of processing conditions on the microstructure evolution better and control the rolling processes more accurately.

PL

W pracy badano kinetykę statycznej (SRX) i metadynamicznej (MDRX) rekrystalizacji stali AISI4135 w próbie skręcania. Ciągłe próby skręcania wykonano w celu wyznaczenia krytycznych odkształceń dla dynamicznej rekrystalizacji (DRX). Czasy do 50% rekrystalizacji SRX i MDRX zostały wyznaczone w dwustopniowych próbach skręcania. Dodatkowo, zmiany wielkości ziarna austenitu (AGS) spowodowane rekrystalizacja były mierzone na mikroskopie optycznym. Stosując opracowany model ewolucji mikrostruktury, wyznaczona została wielkość ziania austenitu przy walcowaniu na gorąco prętów ze stali AISI4135. Wyznaczone wartości AGS został}1 porównane z wynikami otrzymanymi z dostępnego w literaturze modelu i z wynikami doświadczeń, które posłużyły do weryfikacji modelu. "Następnie określono wpływ takich parametrów jak czas przerwy, temperatura i prędkość walcowania na rozkład AGS przy walcowaniu w układzie przepustów kwadrat-romb. Wyniki numerycznej symulacji ułatwiły zrozumienie wpływu warunków procesu na rozwój mikrostruktury i bardzie] dokładne sterowanie procesem stało się możliwe.

5

High frequency magneto-impedance effect in glass-coated amorphous Co83.2 B3.3 Si5.9 Mn7.6 microwires

Lee H., Kim Y. S., Yu S. C.

Materials Science

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2003

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Vol. 21, No. 1

115-121

EN

The measurements of the giant magneto-impedance (GMI) were carried out in the amorphous Co83.2B3.3Si5.9Mn7.6 micro-wires at high frequency range from 100 MHz up to 1 GHz of an accurrent flowing along the wire and at varying axial dc-magnetic field in its range of š120 Oe. The wires, about 15žm in diameter, were fabricated by a glass-coated melt spinning technique. The shape of the impedance curves plotted vs. a dc-field is changing dramatically with the frequency. The phase angle was also strongly dependent on this field. The maximum value of GMI, around 250%, was reached at the frequency of about 500 MHz. The external dc-magnetic field changes the circumferential permeability as well as the penetration depth, both in turn change the impedance of the sample. The increments of GMI at high frequency can be understood in terms of the LC- resonance phenomena. The sudden change of the phase angle, as large as 180°, evidenced the occurrence of the resonance at a given intensity of the external dc-field.

6

Design and implementation of infrared readout circuit using a new input circuit of current mirroring direct injection (CMDI)

Yoon N., Kim B., Lee H., Kim C.

Opto-Electronics Review

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1999

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Vol. 7, No. 4

321-326

EN

A new readout structure for infrared (IR) focal plane arrays (FPA) is presented in this paper. By applying a new input circuit of current mirroring direct injection (CMDI), we realised a high-performance readout circuit for IRFPA. It was found from the SPICE simulation that the CMDI inherently makes the detector bias stable as well as has almost 100% injection efficiency to the readout circuit from the detector even for low RDA values because it has almost zero input impedance. Compared with previous other input circuits, it has also many advantages such as small area and low power consumption. A readout chip including the CMDI inputt circuit has been designed and fabricated for MWIR 1x128 staggered linear HgCdTe infrared detector arrays using 1.2 um single-poly-double-metal N-well CMOS technology. From the measurement results of the fabricated chip, the readout function was successfully verified at 77 K with 5 V supply voltage.

7

Interval regression analysis with polynomial and its similarity to rough sets concept

Tanaka H., Lee H.

Fundamenta Informaticae

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1999

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Vol. 37, Nr 1,2

71-87

EN

This paper proposes interval regression analysis with polynomials. For data sets with crisp inputs and interval outputs, three estimation models called as an upper, a lower, and a possi-bility estimation models can be formulated from the concepts of the possibility and necessity measures. Always there exists an upper and a possibility estimation model when a linear sys-tem with interval coefficients is considered, but it is not assured to attain a solution for a lower estimation model in an interval linear system. If we can not obtain the lower estimation model, it might be caused by adopting a model not fitting to the given data. Thus we consider polynomials to find a regression model which fits well to the given observations. The possibility model is used to check the existence of the lower model. If we can find a proper lower model, the estimated upper and lower models deserve more credit than the previous models in the former studies. We also introduce the measure of fitness to gauge the degree of approximation of the obtained models to the given data. The upper and lower estimation models in interval regression analysis can be considered as the upper and lower approximation in rough sets. The similarity between the interval estimation models and the rough sets concept is also discussed. In order to illustrate our approach, numerical examples are shown.