• Journal of the Optical Society of Korea
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• v.20 no.2
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• pp.223-227
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• 2016

The impact of optical receiver configuration on in-band crosstalk-induced penalty has been investigated in both theoretical and experimental analyses, for differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) signals. Previously it has been shown that DPSK signals are ~6 dB more tolerant to in-band crosstalk than on-off keying (OOK) signals. However, we find that the tolerance difference between the two signals is reduced to ~3 dB when the decision threshold of the receiver is optimized to minimize the bit-error rate for each signal. Then we derive simple equations for the in-band crosstalk-induced penalty in DPSK and DQPSK signals with two different optical receiver configurations: balanced and single-ended direct-detection receivers. We confirm that the penalties obtained from our simple equations agree well with the measured results.

• Journal of the Ergonomics Society of Korea
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• v.22 no.3
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• pp.93-111
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• 2003

This research extends a general theory of cognition to address cognitive constraints on complex command production and allows us to make system design recommendations. The research described in this paper addresses the cognitive origins of problems user have producing sequence-dependent command strings while interacting with the UNIX operating system. We describe an empirical and theoretical analysis of user difficulties, and then show how our analyses lead to design recommendations. In addition, we summarize results from testing the impact of our design recommendations on system usability

• English Language & Literature Teaching
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• no.5
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• pp.149-189
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• 1999

Assessment can be defined as any method used to understand the current knowledge that a student possesses. Assessment may influence decisions about grades, placement, instructional needs, and curriculum. Therefore, the purpose of assessment is to identify how the students think and know, to diagnose the difficulties they face, and to reflect the result of assessment on teaching. But the traditional multiple-choice test failed to evaluate and teach higher-level thinking and problem-solving skills. In this context, performance assessment is being required as an alternative assessment to get better understanding about what the students can do as well as what they know. This article points out some weaknesses of traditional assessments, and comments on the theoretical background and necessity of performance assessment. And it presents more specific information about performance assessment and some examples. It is certain that performance assessment is student-centered and future-oriented. But performance assessment can't be the surest and best way of evaluating the students' abilities. We are just on the way of another experimental stage for improving teaching methodology. More supplementary analyses and further improvements are needed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.215-218
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• 2009

A design of a subscale solid propellant rocket motor was conducted to do the similitude experiments for the large scale rocket motor. One of the main factor to subscale was the mach number of the solid propellant flume through a nozzle exit The analysis of the flume flow was done to obtain the mach number for the large and subscale rocket motor. The flume shapes on the non dimensional axises by the nozzle exit diameter was matched each other. The propellant grain of a subscale solid rocket motor was designed by the profile of pressure vs time obtained by the mach number of the flume shape. Some analyses of the theoretical solution were compared with the results of the ground static test.

• Structural Engineering and Mechanics
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• v.10 no.1
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• pp.27-36
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• 2000

The Oktalok nodal connection system is an aesthetic and efficient system. It has been widely used throughout Australia. The paper will briefly introduce the concept and application of the Oktalok nodal system. The existing design method is based on the assumption that the joints are pin-ended, i.e., the rotational stiffness of the joints is zero. However the ultimate capacity of the frame may increase significantly depending on the rotational stiffness of the joints. Stiffness tests and finite element simulations were carried out to determine the rotational stiffness of the Oktalok joints. Column buckling tests and non-linear finite element analyses were performed to determine the member capacity of columns with semi-rigid end conditions. A simple formulae for the effective length factor of column buckling is derived based on the above experimental and theoretical investigations.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.1
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• pp.48-55
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• 2017

This paper proposes a new link structure that transmits power, clock, and data through a single optical fiber for a future automotive network. A pulse-position modulation (PPM) technique is adopted to guarantee a DC-balanced signal for robust power transmission regardless of transmitted data pattern. Further, circuit implementations and theoretical analyses for the proposed PPM transceiver are described in this paper. A prototype transceiver fabricated in 65-nm CMOS technology, is used to verify the PPM signaling part of the proposed system. The prototype achieves a $10^{-13}$ bit-error rate and 0.188-UI high frequency jitter tolerance while consuming 14 mW at 800 Mb/s.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.417-420
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• 2000

The theoretical analyses for stresses induced in axial direction in the buried pipelines are reviewed. The influences of the axially directed stresses on the surface elliptical crack are studied in detail and thus some engineering technical informations are provided to use reliability assessment of buried pipelines. The change in temperature, the effect of inner pressure and soil friction in the buried pipeline constrained in axial direction are included to determine the axial stresses in the buried pipeline. Furthermore, the stress induced by the pipeline bending are also considered. The stress intensity factors calculated by two models such as a simple plane crack and an elliptical surface crack for a circumferential surface elliptical crack are compared.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.2
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• pp.134-145
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• 1998

The purpose of this paper is to construct a computer simulation system which can analyze and design the hydraulic excavator Theoretical analyses are performed on the hydraulic circuit and attachment of excavator with load sensing system. Databases are constructed for control valve opening areas, horsepower control and for load sensing regulator. For hydraulic components modularized programming techniques are applied which is expected to be utilized for software development of fluid power system. Through simulation an information of any point in hydraulic circuit can be obtained.

• Journal of The Korean Association For Science Education
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• v.8 no.2
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• pp.33-41
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• 1988

During the last decade researchers in science education and psychology have emphasized the importance of children's ideas, or "what they already know", which they bring to their related learning situations. Most research reports on the children's prior ideas reject both the traditional epistemologies and the conventional learning theories. Therefore, this study has its objective to analyze the traditional epistemologies as well as post-positivism contemporarily in vogue, to examine both the conventional learning theories and the constructivism of psychology, and then, based on the analyses, to draw the implications for the future science education. The implications are described under such headings as the nature of science, the science curricula, and the science teaching/learning. The implications are drawn in logical relation to the post-positivism and constructivism, and some of which are empirically validated by the research on the children's conceptions.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.239-244
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• 1999

The reduction phenomena of the compressive strength of concrete with respect to the size of specimens have been extensively investigated. However, adequate analysis technique have not been developed until now. Existing researches have shown that the larger member size, the smaller the strength. This indicated the necessity of nonlinear fracture mechanics theory in order to analyze the fracture behaviors of concrete. The are some models that predict the size effect of compressive strength of cylindrical specimens. Theses equations, however, are developed not considering the difference of fracturing mechanism which depends on both geometry of specimen and the strength level of concrete. In this paper, a model to predict compressive strength of cylindrical concrete specimens with respect to diameters, h/d ratios, and the strength level of concrete, is suggested. For this purpose, theoretical and statistical analyses are conducted. Experimental constants used in the model of new size effect are formulated in terms of strength levels of concrete based on existing experimental data.