PL
 |
EN
Preferencje help
Polish version English version Język
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 10

Liczba wyników na stronie
first rewind previous Strona / 1 next fast forward last
Wyniki wyszukiwania
help Sortuj według:

help Ogranicz wyniki do:
first rewind previous Strona / 1 next fast forward last
1
Content available Microstructure Evolution of Ni-Based ODS Superalloy Powders During Horizontal Rotary Ball Milling
Lee H.-E., Kim Y. S., Park J. K., Oh S.-T.
Archives of Metallurgy and Materials
|
2017
|
Vol. 62, iss. 2B
1253--1255
EN
Microstructure evolution of Ni-based oxide dispersion-strengthened alloy powders with milling time is investigated. The elemental powders having a nominal composition of Ni-15Cr-4.5Al-4W-2.5Ti-2Mo-2Ta-0.15Zr-1.1Y2O3 in wt % were ball-milled by using horizontal rotary ball milling with the change of milling velocity. Microstructure observation revealed that large aggregates were formed in the early stages of ball milling, and further milling to 5 h decreased particle size. The average crystalline size, estimated by the peak broadening of XRD, decreased from 28 nm to 15 nm with increasing milling time from 1 h to 5 h. SEM and EPMA analysis showed that the main elements of Ni and Cr were homogeneously distributed inside the powders after ball milling of 5 h.
2
Content available Fabrication of Cu-Based SiC Composites by Spark Plasma Sintering of Cu-Nitrate Coated SiC Powders
Jeong Y.-K., Kim Y. S., Oh S.-T.
Archives of Metallurgy and Materials
|
2017
|
Vol. 62, iss. 2B
1407--1410
EN
An optimum route to fabricate the Cu-based SiC composites with homogeneous microstructure was investigated. Three methods for developing the densified composites with sound interface between Cu and SiC were compared on the basis of the resulting microstructures. Starting with three powder mixtures of elemental Cu and SiC, elemental Cu and PCS coated SiC or PCS and Cunitrate coated SiC was used to obtain Cu-based SiC composites. SEM analysis revealed that the composite fabricated by spark plasma sintering using elemental SiC and Cu powder mixture showed inhomogeneous microstructure. Conversely, dense microstructure with sound interface was observed in the sintered composites using powder mixture of pre-coated PCS and Cu-nitrate onto SiC. The relationship between powder processing and microstructure was discussed based on the role of coating layer for the wettability.
3
Content available remote Microstructural, optical and electrical properties of Cl-doped CdTe single crystals
Choi H., Kim H. S., Oh J.-H., Kim D. J., Kim Y. S., Chai J.-S., Ha J. H.
Materials Science Poland
|
2016
|
Vol. 34, No. 3
487--493
EN
Microstructural, optical and electrical properties of Cl-doped CdTe crystals grown by the low pressure Bridgman (LPB) method were investigated for four different doping concentrations (unintentionally doped, 4.97 × 1019 cm-3, 9.94 × 1019 cm-3 and 1.99 × 1020 cm-3) and three different locations within the ingots (namely, samples from top, middle and bottom positions in the order of the distance from the tip of the ingot). It was shown that Cl dopant suppressed the unwanted secondary (5 1 1) crystalline orientation. Also, the average size and surface coverage of Te inclusions decreased with an increase in Cl doping concentration. Spectroscopic ellipsometry measurements showed that the optical quality of the Cl-doped CdTe single crystals was enhanced. The resistivity of the CdTe sample doped with Cl at the 1.99 × 1020 cm-3was above 1010cm.
4
Content available remote Characteristics of TlBr single crystals grown using the vertical Bridgman-Stockbarger method for semiconductor-based radiation detector applications
Kim D. J., Oh J.-H, Kim H. S., Kim Y. S., Jeong M., Kang C. G., Jo W. J., Choi H., Kim J. G., Lee S. H., Ha J. H
Materials Science Poland
|
2016
|
Vol. 34, No. 2
297--301
EN
TlBr single crystals grown using the vertical Bridgman-Stockbarger method were characterized for semiconductor based radiation detector applications. It has been shown that the vertical Bridgman-Stockbarger method is effective to grow high-quality single crystalline ingots of TlBr. The TlBr single crystalline sample, which was located 6 cm from the tip of the ingot, exhibited lower impurity concentration, higher crystalline quality, high enough bandgap (>2.7 eV), and higher resistivity (2.5 × 1011 Ω·cm) which enables using the fabricated samples from the middle part of the TlBr ingot for fabricating high performance semiconductor radiation detectors.
5
Content available remote Structural performance of rectangular section confined by squared spirals with no longitudinal bars influencing the confinement
Lee J. M., Kim Y. S., Kim S. W., Park J. H., Kim K. H.
Archives of Civil and Mechanical Engineering
|
2016
|
Vol. 16, no. 4
795--804
EN
Structural performance of rectangular concrete section confined by squared spirals was investigated. Through the uni-axial compression test using concrete prisms with squared spirals and without longitudinal bars, the enhancement of strength and deformation capacity of rectangular concrete section was scrutinized. By the experimental observations on the properties of lateral expansion of concrete prism, a moment of reaching the axial peak stress in section was predicted in a good accuracy. Qualitative relationships between the structural performance (the enhancement of strength and deformation capacity) of concrete prism and confinement efficiency were studied. Also, for the effective use of normal- and high-strength lateral reinforcement, a design implication using the qualitative relationship of the tensile stress in lateral reinforcement at failure of concrete prism with parameters was proposed.
6
Content available remote Numerical and experiment study of residual stress and strain in multi-pass GMA welding
Chand R.R., Kim I.S., Lee J. P., Kim Y.S., Kim D. G.
Journal of Achievements in Materials and Manufacturing Engineering
|
2013
|
Vol. 57, nr 1
31--37
EN
Purpose: Recently, manufacturing industries have been concentrated on selection an optimal of welding parameter and condition that reduces the risk of mechanical failures on weld structures should be required in manufactory industry. In robotic GMA (Gas Metal Arc) welding process, heat and mass inputs are coupled and transferred by the weld arc to the molten weld pool and by the molten metal that is being transferred to the weld pool. The amount and distribution of the input energy are basically controlled by the obvious and careful choices of welding process parameters in order to accomplish the optimal bead geometry and the desired mechanical properties of the quality weldment. The residual stress and welding deformation have the large impact on the failure of welded structures. Design/methodology/approach: To achieve the required precision for welded structures, it is required to predict the welding distortions at the early stages. Therefore, this study represented 2D Finite Element Method (FEM) to predict residual stress and strain on thick SS400 steel metal plate. Findings: The experiment for Gas Metal Arc (GMA) welding process is also performed with similar welding condition to validate the FE results. The simulated and experiment results provide good evidence that heat input is main dependent on the welding parameter and residual stress and distortions are mainly affected by amount on heat input during each weld-pass. Practical implications: This present study on based on the numerical analysis using ansys software, for a thick multi-pass GMA welding. A birth and death technique is employed to control the each weld pass welding. Originality/value: The developed 2D multi-pass model employs Goldak’s heat distribution, to simulate welding on SS400 steel butt-weld joint with a thickness of 16mm. moreover the numerical results are validated with experiment results.
7
Content available remote Computing VaR and AVaR in infinitely divisible distributions
Kim Y. S., Rachev S. T., Bianchi M. L., Fabozzi F. J.
Probability and Mathematical Statistics
|
2010
|
Vol. 30, Fasc. 2
223--245
EN
In this paper we derive closed-form solutions for the cumulative distribution function and the average value-at-risk for five subclasses of the infinitely divisible distributions: classical tempered stable distribution, Kim–Rachev distribution, modified tempered stable distribution, normal tempered stable distribution, and rapidly decreasing tempered stable distribution. We present empirical evidence using the daily performance of the S&P 500 for the period January 2, 1997 through December 29, 2006.
8
Content available remote The modified tempered stable distribution, GARCH models and option pricing
Kim Y. S., Rachev S. T., Chung D. M., Bianchi M. L.
Probability and Mathematical Statistics
|
2009
|
Vol. 29, Fasc. 1
91--117
EN
We introduce a new variant of the tempered stable distribution, named the modified tempered stable (MTS) distribution and we develop a GARCH option pricing model with MTS innovations. This model allows the description of some stylized empirical facts observed in financial markets, such as volatility clustering, skewness, and heavy tails of stock returns. To demonstrate the advantages of the MTS-GARCH model, we present the results of the parameter estimation.
9
Content available remote Control of single-phase to three-phase AC/DC/AC PWM converters for induction motor drives
Lee D.Ch., Kim Y.S.
Przegląd Elektrotechniczny
|
2006
|
R. 82, nr 2
101-106
EN
This paper proposes a control scheme of single-phase to three-phase PWM converters for low power three-phase induction motor drives, where a single-phase half-bridge PWM rectifier and a two-leg inverter are used. With this converter topology, the number of switching devices is reduced to six from ten in case of full-bridge rectifier and three-leg inverter systems. In addition, the source voltage sensor is eliminated with a state observer which controls the deviation between the model current and the system current to be zero. A simple voltage modulation method is used for a two-leg Inverter and a new technique to eliminate the effect of the dc link ripple voltage on the output current is proposed. Though the converter topology itself is of lower cost than the conventional one, it retains such functions as sinusoidal input current, unity power factor, de-link voltage control, bidirectional power flow, and VVVF output voltage. The experimental results for the V/F control of 3Hp induction motor drives controlled by a DSP TMS320C31 chip have verified the effectiveness of the proposed scheme.
PL
W artykule tym została przedstawiona metoda sterowania PWM układem jednofazowego prostownika aktywnego pół-mostkowego w połączeniu z przekształtnikiem trójfazowym dwugałęziowym dla zastosowań w napędach niskiej mocy. Charakterystyczną cechą powyższej topologii jest zredukowana ilość łączników do 6-ciu w porównaniu ze standardową topologią pełnego mostka (4 klucze) oraz dołączonego falownika napięcia (dodatkowe 6 kluczy), gdzie całkowita liczba łączników w konwencjonalnym układzie wynosiłaby 10. W proponowanym sterowaniu, czujnik napięcia został wyeliminowany poprzez wprowadzenie obserwatora stanu, który zmniejsza uchyb pomiędzy prądem zadanym z modelu oraz prądem rzeczywistym do zera. Dodatkowo została zaproponowana nowa prosta metoda sterowania PWM w układzie dwugałęziowym falownika napięcia, która eliminuje wpływ tętnień napięcia obwodu pośredniczącego na prąd falownika. Główną zaletą nowej topologii układu jest niski koszt w porównaniu z konwencjonalną topologią oraz jego cechy takie jak: sinusoidalny prąd falownika, poprawa współczynnika mocy PFC, regulacja napięcia obwodu pośredniczącego, dwukierunkowy przepływ mocy oraz regulowane napięcie wyjściowe falownika. Wyniki eksperymentalne w układzie sterowania skalarnego V/Hz trójfazowym silnikiem indukcyjnym za pomocą procesora sygnałowego DSP TMS320C31 potwierdziły skuteczność proponowanej metody.
10
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
|
2003
|
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.
first rewind previous Strona / 1 next fast forward last
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.