• Research in Mathematical Education
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• v.18 no.4
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• pp.237-256
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• 2014

This paper reports findings from a written assessment which was designed to investigate Chinese primary school students' understanding of the equal sign and equation structure. The investigation included a sample of 110 Grade 3, 112 Grade 4, and 110 Grade 5 students from four schools in China. Significant differences were identified among the three grades and no gender differences were found. The majority of Grades 3 and 4 students were found to view the equal sign as a place indicator meaning "write the answer here" or "do something like computation", that is, holding an operational view of the equal sign. A part of Grade 5 students were found to be able to interpret the equal sign as meaning "the same as", that is, holding a relational view of the equal sign. In addition, even though it was difficult for Grade 3 students to recognize the underlying structure in arithmetic equation, quite a number of Grades 4 and 5 students were able to recognize the underlying structure on some tasks. Findings in this study suggest that Chinese primary school students demonstrate a relational understanding of the equal sign and a strong structural sense of equations in an earlier grade. Moreover, what found in the study support the argument that students' understanding of the equal sign is influenced by the context in which the equal sign is presented.

• Smart Structures and Systems
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• v.16 no.5
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• pp.937-960
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• 2015

Tuned mass dampers (TMDs) have been a prevalent vibration control device for suppressing excessive vibration because of environmental loadings in contemporary tall buildings since the mid-1970s. A TMD must be tuned to the natural frequency of the primary structure to be effective. In practice, a TMD may be assembled in situ, simultaneously with the building construction. In such a situation, the respective dynamic properties of the TMD device and building cannot be identified to determine the tuning status of the TMD. For this purpose, a methodology was developed to obtain the parameters of the TMD and primary building on the basis of the eigenparameters of any two complex modes of the combined building-TMD system. The theory was derived in state-space to characterize the nonclassical damping feature of the system, and combined with a system identification technique to obtain the system eigenparameters using the acceleration measurements. The proposed procedure was first demonstrated using a numerical verification and then applied to real, experimental data of a large-scale building-TMD system. The results showed that the procedure is capable of identifying the respective parameters of the TMD and primary structure and is applicable in real implementations by using only the acceleration response measurements of the TMD and its located floor.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.4
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• pp.179-187
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• 2020

Seismic qualification of equipment including piping is performed by using floor response spectra (FRS) or in-structure response spectra (ISRS) as the earthquake input at the base of the equipment. The amplitude of the FRS may be noticeably reduced when obtained from coupling analysis because of interaction between the primary structure and the equipment. This paper introduces a method using a modal synthesis approach to generate the FRS in a coupled primary-secondary system that can avoid numerical instabilities or inaccuracies. The FRS were generated by considering the dynamic interaction that can occur at the interface between the supporting structure and the equipment. This study performed a numerical example analysis using a typical nuclear structure to investigate the coupling effect when generating the FRS. The study results show that the coupling analysis dominantly reduces the FRS and yields rational results. The modal synthesis approach is very practical to implement because it requires information on only a small number of dynamic characteristics of the primary and the secondary systems such as frequencies, modal participation factors, and mode shape ordinates at the locations where the FRS needs to be generated.

• Applied Microscopy
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• v.32 no.1
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• pp.31-37
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• 2002

As-cast microstructure of Mg-rich $Mg_{68}Zn_{28}Y_4$ has been investigated by a detailed transmission electron microscopy. The as-cast $Mg_{68}Zn_{28}Y_4$ alloy consisted of three different types of phases: $10{\sim}20{\mu}m$ size primary solidification phase, dendritic phase grown from the primary phase and a eutectic structure formed at the later stage of solidification. The primary solidification phase has an icosahedral structure with a large degree of phason strain. 1/1 rhombohedral approximant phase with lattice parameters: $a=27.2{\AA}\;and\;{\alpha}=63.43^{\circ}$ is first observed in Mg-Zn-Y system. The rhombohedral structure can be obtained by introducing phason strain in the six dimensional face centered hyper-cubic lattice. The decagonal phase nucleates with orientation relationship with the icosahedral phase, and $Mg_4Zn_7$ nucleates with orientation relationship with the decagonal phase, indicating a close structural similarity between the three phases. Gradual depletion of Y during solidification plays an important role in heterogeneous nucleation of decagonal and $Mg_4Zn_7$ phases from icosahedral and decagonal phases respectively.

• Nuclear Engineering and Technology
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• v.31 no.6
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• pp.586-594
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• 1999

To limit both the large displacement and acceleration response of the structure efficiently, the relationships between acceleration and displacement responses of the structure under several earthquakes are investigated for various horizontal stiffness of the base isolation system to determine the effective stiffness of the base isolation system in this paper. An example structure is a five-storey steel frame building as the primary structure and the secondary structures are assumed to be located on the fifth floor of the primary structure. Input motions used in the structural analysis are El Centre 1940, Taft 1952, Mexico 1985, San Fernando 1971 Pacoima Dam, and artificially generated earthquakes. The relationships of the absolute peak acceleration and the displacement at the top of the structure are calculated for various natural periods of base isolators under various earthquakes. The peak acceleration response of the fifth floor in the base isolated structure is significantly reduced by a factor of 2.1 through 6.25. Also, the relative displacement response of the floor to the base of the superstructure is very small. The results of this study can be utilized to determine the effective stiffness of the base isolation system.

• Journal of the korean academy of Pediatric Dentistry
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• v.25 no.4
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• pp.749-760
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• 1998

The main purpose of this study was to evaluate the effect of dentin with various pretreatment application time on the dentin surface structure and the bond strength of glass ionomer restorative matrials between primary and permanent tooth. There are difference of composition, structure and pretreated effect of dentin conditioning between the primary and permanent teeth. Inspite of thease fact, we used the same application time of permanent tooth. This study intends to determine the most effective application time using SEM analysis of the surface change by dentin conditioning. Forty five intact primary and permanent teeth were splited mesiodistally with seperating diamond disk. Each eight specimens were prepared for shear bond strength test. (randomely devided eight group as follows:) group I conditioning for five seconds group II conditioning for ten seconds group III conditioning for fifteen seconds group IV conditioning for twenty seconds Additional specimens were prepared to SEM analysis. The result are as follows: 1. Primary teeth are higher shear bond strength in group I and group II. 2. There was no statistically significant difference between primary and permanent teeth in group III and group IV. 3. In SEM analysis, smear layer removal by dentin pretreatment of primary teeth was faster than permanent teeth. Primary teeth may require shorter pretreatment time of dentin for G-I restoration than that of permanent teeth.

• Journal of KSNVE
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• v.9 no.1
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• pp.97-102
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• 1999

Structure-borne noise is an important aspect to consider during the design and development of a vehicle. In this work. it was desired to identify the primary paths associated with structure-borne noise generated from the engine and front suspension. An experimental source-path-receiver model was used to characterize the system. A variety of primary sources such as engine. tires or exhaust system generate vibrations of the inner surfaces of the passenger compartment of a vehicle which subsequently radiate noise. The source was characterized by the force acting at the engine-to-body interface. and the path was characterized by pressure over force FRF's. The excitation forces were indirectly determined using dynamic stiffness of rubber mount or the system accelerance matrix. Through these analysis, path contribution diagram which is well expressed primary noise path is obtained.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.12
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• pp.27-34
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• 2018

This paper considers the seismic performance of lever-type tuned mass damper(TMD). The lever-type TMD is designed utilizing the seismic-performance of TMD and the control force required for constraining story drift. The TMD is basically designed by tuning the frequency of primary structure. Thus, the TMD plays an important role to reduce the dynamic responses. The lever-type TMD has a merit to control more displacement responses than the existing TMD due to the control forces. It is shown that the optimum design of lever-type TMD is affected by the ratio of the TMD mass with respect to the mass of the primary structure, the damping ration of the primary structure, and the length ratio of the lever. A numerical example exhibits the effectiveness of the dynamic control by the lever-type TMD and its validity is illustrated in a three-story building structure subjected to earthquake.

• Journal of Species Research
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• v.7 no.4
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• pp.340-347
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• 2018

Four psammocinian species(Demospongiae: Dictyoceratida: Irciniidae) are described from Gageodo and Jejudo Islands, Korea. Among them, three are new species, Psammocinia rana, P. massa and P. vermins, which are very different from other recorded species. Secondary fibres of Psammocinia rana are mostly wide platelike shape with large perforation. Primary and secondary fibres of Psammocinia massa are lumped together in a thick mass through numerous areas. Psammocinia vemis is similar to P. mosulpia in skeletal structure, but differs in size of cored sands in primary fibres. The fourth species, we reclassify from Ircinia chupoensis to Psammocinia chupoensis based on more detailed observation of the skeletal structure. Ircinia only has sand cored primary fibres, while the observed species, has sand cored primary and secondary fibres.

• Journal of Korea Society of Industrial Information Systems
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• v.20 no.4
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• pp.75-87
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• 2015

A redundant structure typically consists of primary component and standby component taking over the function of the primary component when the primary component fails. In this research, we consider a redundant structure in which a standby component can take over the function of more than one primary component when primary components fail. And we assume that the system has multi-state according to the states of components while all components have two states. This system is called as the multi-state redundant system with a multi-functional standby component. This type of redundant structure is frequently adapted by the system such as an aircraft in which the weight is an important design factor. In this paper, we propose new reliability model for this multi-state redundant system with a multi-functional standby component in order for evaluating the reliability of the system. Under the assumption that all components have constant failure rate, we evaluate the reliability of the system by applying Markov analysis method. And we investigate the effect of the multi-functional standby component by comparing reliabilities of the parallel system with multi-functional standby component and a simple parallel system and a parallel system with redundant structure.