• Proceedings of the Acoustical Society of Korea Conference
• /
• 1992.06a
• /
• pp.107-110
• /
• 1992

We investigate the influence of individual properties of piezoceramics such as elastic, dielectric, piezoelectric constants, and the coupling factor on the performance of the transducer operating in thickness mode oscillation. The investigation employs equivalent circuit analysis techniques. Appropriate transfer functions are obtained and discussed which suggest optimum selection guides of piezoelectric ceramics for each purpose, i.e. a transmitter, a receiver, and a pulse-echo transducer. The guides can help ceramic scientists find the direction to proceed in new material development.

• Publications of The Korean Astronomical Society
• /
• v.12 no.1
• /
• pp.197-212
• /
• 1997

The general photometric, spectroscopic, and kinematic properties of the late type halo stars are investigated from a sample of known true halo stars. Halo stars are distributed in a lower left region of infrared (J-H) vs (H-K) color-color diagram, which is recomfirmed to be useful for selection of halo stars. They move with average velocity components of 9 km/sec, -14 km/sec, and 5 km/sec in U, V, and W directions respectively. They are distributed seperately from disk stars in a diagram of metallicity index, CaH1/TiO5 vs (R-I).

• Journal of the Microelectronics and Packaging Society
• /
• v.22 no.4
• /
• pp.1-5
• /
• 2015

In high temperature aircraft electronics, aluminium based brazing filler is the prime choice today. Aluminium and its alloys have compatible properties like weight minimization, thermal conductivity, heat dissipation, high temperature precipitation hardening etc. suitable for the aerospace industry. However, the selection of brazing filler for high temperature electronics requires high temperature joint strength properties which is crucial for the aerospace. Thus the selection of proper brazing alloy material, the composition and brazing method play an important role in deciding the final reliability of aircraft electronic components. The composition of these aluminium alloys dependent on the addition of the various elements in the aluminium matrix. The complex shapes of aluminium structures like enclosures, heat dissipaters, chassis for electronic circuitry, in avionics are designed from numerous individual components and joined thereafter. In various aircraft applications, the poor strength caused by the casting and shrinkage defects is undesirable. In this report the effect of various additional elements on Al based alloys and brazing fillers have been discussed.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.21 no.4
• /
• pp.593-600
• /
• 2012

Thixomolding of Mg-alloy is a semi-solid injection molding process utilizing thixotropic phenomenon. Using this process, higher strength, thinner wall section and tighter tolerance without porosity are obtained. It has been applied for production of near-net-shape magnesium component. To design optimal thixomolding process of Mg-alloy part, molding conditions such as slurry temperature, mold temperature and injection time should be determined properly. Selection of these parameters has been dependent upon engineers' experience and intuitiveness. In this paper, to improve mechanical properties of the thixomolded product, optimal selection of process variables such as injection velocity, barrel temperature and die temperature in the process has been studied through microstructural analysis and Taguchi method. Performance of the process is verified through experiments.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.724-727
• /
• 2005

Material selection is one of the important activities in design and manufacturing. A selected material at the conceptual design stage affects material properties of the designed part as well as manufacturability and cost of the final product. Unfortunately there are not many accessible material databases that can be used for design. In this research, a web-based material database was constructed. In order to assist designers to compare different materials, two-dimensional and three-dimensional graphs were provided. Using these graphical tools, multi-dimensional comparison was available in more intuitive manner. To provide environmental safety of materials, the database included National Fire Protection Association publication Standard No.704. The web-based tool is available at http://fab.snu.ac.kr/matdb.

• Journal of Advanced Marine Engineering and Technology
• /
• v.32 no.6
• /
• pp.915-922
• /
• 2008

The gas separation technology using membrane is widely used to refine various gases in many industry fields and recently is being applying in $CO_2$ recovery technology. In the gas and chemical tanker. nitrogen generators for inerting, purging and padding are on board and most of them have membrane modules of hollow fiber type with long life and vibration resisting properties. Because a membrane module is a key component accounting for 50% of total manufacturing cost of nitrogen generator, adequate selection for it is an important problem. In this paper, the flow performance coefficient based on dimension and specification data of membrane module was relatively selected to compare nitrogen generating capacity of module and various performance tests about the selected PARKER ST6010 membrane module were conducted. As a result, the useful coefficient and basic data in selecting a membrane module were achieved.

• The Korean Journal of Applied Statistics
• /
• v.3 no.1
• /
• pp.79-87
• /
• 1990

The problem of selecting a nonempty subset of K(>2) normal means with unknown variances has been studies by many authors. But the comparisions of the properties and the efficiencies of the proposed subset selection procedures have not been carried out. Thus we investigate properties of the proposed procedures and compare their performances for various cases.

• Communications for Statistical Applications and Methods
• /
• v.25 no.5
• /
• pp.453-470
• /
• 2018

We study how to distinguish the parameters of the sparse autoregressive (AR) process from zero using a non-convex penalized estimation. A class of non-convex penalties are considered that include the smoothly clipped absolute deviation and minimax concave penalties as special examples. We prove that the penalized estimators achieve some standard theoretical properties such as weak and strong oracle properties which have been proved in sparse linear regression framework. The results hold when the maximal order of the AR process increases to infinity and the minimal size of true non-zero parameters decreases toward zero as the sample size increases. Further, we construct a practical method to select tuning parameters using generalized information criterion, of which the minimizer asymptotically recovers the best theoretical non-penalized estimator of the sparse AR process. Simulation studies are given to confirm the theoretical results.

• Proceedings of the IEEK Conference
• /
• 2002.07c
• /
• pp.1893-1896
• /
• 2002

Remediation Selection Expert System (RSES) is a rule-based expert system which is used far the selection of remediation techniques fur petroleum contaminated sites. In this paper, we describe a fuzzy logic-based sub-system: Site Characterization Sub-System (SCSS). It is an enhancement of the RSES, which is used to analyze the hydraulic properties of contaminated sites. This paper focuses on an explanation on how to apply fuzzy set theory for identification of soil types and hydraulic properties of a contaminated site. To illustrate application of fuzzy set theory to the problem, two sample cases are presented in detail.

• Culinary science and hospitality research
• /
• v.12 no.3 s.30
• /
• pp.32-48
• /
• 2006

Korean Traditional Confectionary is a part of our traditional culture taking a great part in our food culture for a while. However, it is now barely maintaining its name. In this research, a new consumption trend 'Well-being' is adopted to suggest the ways to develop the Korean Traditional Confectionary industry. This research intends to find out what effects the 'Well-being' trend, which originated from interest in health, have on Korean Traditional Confectionary selection. A survey includes the questions about the Well-being trend, selection and uses of Korean Traditional Confectionary, and demographic data. This research conducted analysis on 249 people who have used Korean Traditional Confectionary in Busan and Kyeongnam Province to find out effects of the Well-being trend on Korean Traditional Confectionary selection. This empirical study showed that the Well-being trend has some effects on Korean Traditional Confectionary selection while it has the greatest effects on healthy properties and commercial values of Korean Traditional Confectionary.