• Journal of Gifted/Talented Education
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• v.24 no.1
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• pp.17-43
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• 2014

On the subjects of elementary 3rd grade three child prodigies who had learned the four fundamental arithmetic operations and primary concepts of fraction, this study conducted a qualitative case research to examine how they composed schema of addition and multiplication of fractions and transformed schema through recognition of precise concepts and linking of concepts with addition and multiplication of fractions as the contents. That is to say, this study investigates what schema and transformed schema child prodigies form through composition of primary mathematic concepts to succeed in relational understanding of addition and multiplication of fractions, how they use their own formed schema and transformed schema for themselves to approach solutions to problems with addition and multiplication of fractions, and how the subjects' concept formation and schema in their problem solving competence proceed to carry out transformations. As a result, we can tell that precise recognition of primary concepts, schema, and transformed schema work as crucial factors when addition of fractions is associated with multiplication of fractions, and then that the schema and transformed schema that result from the connection among primary mathematic concepts and the precise recognition of the primary concepts play more important roles than any other factors in creative problem solving with respect to addition and multiplication of fractions.

• Journal of Microbiology
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• v.39 no.1
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• pp.67-73
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• 2001

A validation study was conducted to evaluate the efficacy and mechanism of the cryo-precipitation, monoclonal anti-FVIIIc antibody (mAb) chromatography, Q-Sepharose chromatography, and lyophilization steps involved in the manufacture of high purity factor VIII (GreenMono) from human plasma, in the removal and/or inactivation of hepatitis A virus (HAV). Samples from the relevant stages of the production process were spiked with HAV and subjected to scale-down processes mimicking the manufacture of the high purity factor VIII concentrate. Samples were collected at each step and immediately titrated using a 50% tissue culture infectious dose (TCID$\_$50/) and then the virus reduction factors were evaluated. HAV was effectively partitioned from factor VⅢ during cryo-precipitation with the log reduction factor of 3.2. The mAb chromatography was the most effective step far removal of HAV with the log reduction factor of $\geq$4.3. HAV infectivity was not detected in the fraction of factor VⅢ, while most of HAV infectivity was recovered in the fractions of flow through and wash during mAb chromatography. Q-Sepharose chromatography showed the lowest efficacy for partitioning HAV with the log reduction factor of 0.7. Lyophilization was an effective step in inactivating HAV with the log reduction factor of 2.3. The cumulative lag reduction factor, $\geq$10.5, achieved for tile entire manufacturing process was several magnitudes greater than the potential HAV load of current plasma pools.

• Korean Management Science Review
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• v.24 no.1
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• pp.113-126
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• 2007

This paper deals with a mathematical approach for finding the time-fractions for the time-fraction based scheduling method in multimedia wireless networks. By introducing a constraint that regulates the performance fairness amongst users, we present a systematic method for harmonizing both the system and user performance. Numerical results show that the time-fraction based scheduling method reinforced with our scheme is very effective especially in multimedia environments.

• Journal of the Korean School Mathematics Society
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• v.12 no.2
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• pp.151-170
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• 2009

The purpose of the study is to analyze the sixth graders' understanding of concepts and operation about fraction. The test was administered and analyzed to 707 sixth graders' performance on fractions after the fraction instructions in elementary schools in Seoul, Korea. The participants are asked to answer two sets of questions for 40 minutes. First, they are asked to answer to 16 problems about the concepts of fraction with respect to part-whole, ratio, operator, measure, quotient, equivalent, and operations. Second, specially, to investigate sixth graders' ability of drawing and describing the situation of division including fraction, the descriptive problem asked students (1) to describe $3\;{\div}\;\frac{1}{2}$ into pictorial representation and (2) to write the solving process. The participants of this study didn't show deep understandings about the concepts and operation of fraction. The degree of understanding of subconstructs of fraction shows that their knowledge of ratio concept with respect to fraction was highest while their understanding of measure with respect to fraction was lowest. Considering their wrong answers, about 59% of participants showed misconception to the question of naming one fraction that appears between $\frac{1}{5}$ and $\frac{1}{6}$. Further, they didn't explain their understanding with drawing about the division of fraction ($3\;{\div}\;\frac{1}{2}$).

• Journal for History of Mathematics
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• v.25 no.4
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• pp.1-10
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• 2012

In Chinese mathematics, there have been two numeral systems, namely one in spoken language for recording and the other by counting rods for computations. They concerned with problems dealing with practical applications, numbers in them are concrete numbers except in the process of basic operations. Thus they could hardly develop a pure theory of numbers. In Song dynasty, 0 and TianYuanShu were introduced, where the coefficients were denoted by counting rods. We show that in this process, counting rods took over the role of the numeral system in spoken language and hence counting rod numeral system plays the role of that for abstract numbers together with the tool for calculations. Decimal fractions were also understood as denominate numbers but using the notions by counting rods, decimals were also admitted as abstract numbers. Noting that abacus replaced counting rods and TianYuanShu were lost in Ming dynasty, abstract numbers disappeared in Chinese mathematics. Investigating JianJie YiMing SuanFa(簡捷易明算法) written by Shen ShiGui(沈士桂) around 1704, we conclude that Shen noticed repeating decimals and their operations, and also used various rounding methods.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.24 no.4
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• pp.462-470
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• 2014

Objectives: The purpose of this study was to evaluate quartz concentrations in airborne respirable dust and particle size-related quartz concentrations. Methods: Respirable dust samples were collected using a 10 mm Dorr-Oliver nylon cyclone equipped with a 37 mm, $5{\mu}m$ pore size PVC filter. Dust samples were collected with a Marple's personal cascade impactor from stone grinding operations in five stone-related business located in the Gyeongsangbuk-do area. Results: The geometric mean of quartz concentration in the respirable dust was $0.170mg/m^3$, and the rate of exceeding the Korean Occupational Exposure Limit(KOEL) was 93.3%. The quartz concentration by particle size shows that it was the highest($0.115mg/m^3$) in stage 5($3.50-6.00{\mu}m$), which corresponds with the size of respirable particle. The smaller the particle sizes were, the higher quartz the content became. The mass fractions of inhalable, thoracic, and respirable dust were 72.1%, 36.0%, and 14.4%. Conclusions: The rate of the quartz concentration in respirable dust from stone grinding operations exceeding the American Conference of Governmental Industrial Hygienists Threshold Limit Values was 100%, which means proper work environmental management is required through regular working environmental measurements. Given that the stone grinding operations had a higher small size dust concentrations, there is a need to reduce respirable dust, such as through wet operation and local exhaust ventilation.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.644-645
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• 2006

TiC-and Ti(C,N)-based cermets are excellent in semi-and final finishing of work piece during cutting operations. Typical microstructure of the cermets is a core/rim structure. The undissolved Ti(C,N) cores contribute to their high hardness while the rim phases, (Ti,M1,M2)(C,N)-type solid solutions, play great roles in enhancing the toughness. In this paper, various ultrafine pre-mixed MeC-Ni powders were synthesized and the powders were sintered or hot pressed after mixing in order to control the size and volume fractions of core and rim phases in the system. This paper will present the factors determining the microstructure along with mechanical properties.

• School Mathematics
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• v.14 no.1
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• pp.45-64
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• 2012

The purpose of the present study was to investigate middle grades (Grade 5-7) mathematics teachers' knowledge of partitive fraction division. The data were derived from a part of 40-hour professional development course on fractions, decimals, and proportions with 13 in-service teachers. In this study, I attempted to develop a model of teachers' way of knowing partitive fraction division in terms of two knowledge components: knowledge of units and partitioning operations. As a result, teachers' capacities to deal with a sharing division problem situation where the dividend and the divisor were relatively prime differed with regard to the two components. Teachers who reasoned with only two levels of units were limited in that the two-level structure they used did not show how much of one unit one person would get whereas teachers with three levels of units indicated more flexibilities in solving processes.

• School Mathematics
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• v.17 no.2
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• pp.157-178
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• 2015

The purpose of this study was to investigate the role of calculators as a cognitive tool rather than calculating tool in learning elementary school mathematics. The calculator activities on multiplying two numbers ending with 0s or two decimal fractions and mixed four operations were developed, and exploratory lessons with the activities were implemented to three 3rd graders and two 5th graders. The results were shown that calculators provided an alternative effective learning environment: students were able to use heuristic thinking, reason inductively and successfully investigate principles of mathematics through the pattern recognition. And finally, we discussed the heuristic method through utilizing calculators.

• Advances in concrete construction
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• v.15 no.1
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• pp.23-39
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• 2023

One of the important problems of concrete placing is the concrete compaction, which can affect the strength, durability and apparent quality of the hardened concrete. Therefore, vibrating operations might be accompanied by much noise and the need for training the involved workers, while inappropriate functioning can result in many problems. One of the most important methods to solve these problems is to utilize self-compacting cementitious composites instead of the normal concrete. Due to their benefits of these new materials, such as high tensile, compressive, and flexural strength, have drawn the researchers' attention to this type of cementitious composite more than ever. In this experimental investigation, six mixing designs were selected as a base to acquire the best mechanical properties. Moreover, forty-eight rectangular composite panels with dimensions of 300 mm × 400 mm and two thickness values of 30 mm and 50 mm were cast and tested to compare the flexural and impact energy absorption. Steel fibers with volume fractions of 0%, 0.5% and 1% and with lengths of 25 mm and 50 mm were imposed in order to prepare the required cement composites. In this research, the composite panels with two thicknesses of 30 mm and 50 mm, classified into 12 different groups, were cast and tested under three-point flexural bending and repeated drop weight impact test, respectively. Also, the examination and comparison of flexural energy absorption with impact energy absorption were one of the other aims of this research. The obtained results showed that the addition of fibers of longer length improved the mechanical properties of specimens. On the other hand, the findings of the flexural and impact test on the self-compacting composite panels indicated a stronger influence of the long-length fibers.