• Communications of the Korean Mathematical Society
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• v.33 no.3
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• pp.943-960
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• 2018

Our aim is to introduce the notion of a parametric $N_b-metric$ and study some basic properties of parametric $N_b-metric$ spaces. We give some fixed-point results on a complete parametric $N_b-metric$ space. Some illustrative examples are given to show that our results are valid as the generalizations of some known fixed-point results. As an application of this new theory, we prove a fixed-circle theorem on a parametric $N_b-metric$ space.

• The Research Journal of the Costume Culture
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• v.8 no.2
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• pp.261-271
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• 2000

In order to investigate the function and feature of western men's underclothes in the second half of the 19C, in this study, the historical changes of western men's underclothes are compared the first half of the 19C with the second half of the 19C. In the second half of the 19C, the useful function to ease for body was important. In the 1860's, for day-shirt, the tucked panels was disappeared and the front was pain. But the evening dress-shirt continued to show an expansive front tucked. Coloured shirts was used for country and sporting occasions. Ready-made underwear was used. In the 1870's, the plain breast was introduced and the Gladstone collar was used. Paper collars and dickeys were unfashionable. The drawers was composed a gusset at the back of the waistband. The dress of one generation was became the livery of the next. In the 1880's, a new feature was one stud and the use of pique for the breast. Coloured shirt was composed of stripes across the breast. In the 1890's, height of the collar steadily increased. The coat-shirt and regatta shirt became popular. The nice choice of shirt, collar and tie was a matter of supreme importance .The social status of the white shirt was further threatened by fancy coloured shirts. The mode of relaxation affected sports shirts. By the close of this period, both sexes accepted the hygienic rule of wool next the skin.

• 전자공학회논문지 IE
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• v.47 no.2
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• pp.32-37
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• 2010

In this study, to develop union type SMD inductor core needs to have the desire of super miniaturization and high reliability, it analyzed temperature properties due to electric power value. As the temperature of electronic parts rise, it bring to technical obstacles that parts can not normal operation, it reduce the span of life to raise the fault ratio. Also, it impact to the parts by heat change power and expansive power, it can not behave exactly, and it have an effect on reliability. It measured the difference value between conditional temperature and parts temperature to union type SMD inductor core. As the results of simulation using D.C. current and resistor($R_dc$), it obtained the excellent regular current values at rising temperature of 40[$^{\circ}C$].

• Journal of the Korean Ceramic Society
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• v.38 no.8
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• pp.716-723
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• 2001

시멘트 모르터의 소성수축에 의한 균열을 방지하기 위해 소성수축 특성에 관한 연구를 수행하였다. 우리나라 봄철의 대표적인 기후인 온도 20$\pm$3$^{\circ}C$, 상대습도 55%, 풍속 3.5m/s의 기후조건으로 하였으며, 모르터의 물 시멘트 비, 시멘트 골재 비, 팽창재 사용, 플라이 애쉬 치환, 수분증발을 억제하기 위한 중점제 등을 사용하여 소성수축의 특성을 검토하였다. 연구 결과 소성수축 변형은 응결시간과 밀접한 관계가 있으며 응결시간이 빠를수록 변형은 크게 나타났다. 또한 물시멘트 비에 의해서도 소성수축 변형은 큰 것으로 나타났다. 모르터에서의 골재 비율이 작거나, 플라이 애쉬의 치환율이 클수록 소성수축 변형은 매우 크게 나타났다. 중점제의 사용은 소성수축 변형을 줄이는데 효과가 있었으며, 건조수축 보상용 팽창재의 사용은 소성수축 변형율을 크게 하는데 이는 ettringite 생성에 의한 물 시멘트 비의 감소효과를 가져오기 때문이다.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.209-212
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• 2006

Until now, sulfate attack is not completely understood. The purpose of this study is to provide a fundamental data to understand deterioration mechanism by sulfate attack. Chemical processes for products formed by sulfate attack were explained in this study. ASTM C1012 test and microstructural observations such as XRD and BSE analysis were carried out to manifest behavior and role of the products formed during sulfate attack. Regarding the dominant causes of sulfate attack, the main deterioration modes could be divided into 3 types; (1) expansive type, (2) onion-peeling type, and (3) acidic type.

• Journal of the Korean Ceramic Society
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• v.27 no.5
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• pp.589-596
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• 1990

In this study, the freezing and thawing resistance in sea-water of hardened cement paste was investigated by adding slag, diatomaceous earth and fly ash as blending materials and air entraining agent and superplasticizer as admixtures to the cement paste. The structure of hardened cement pate was densified by potential hydraulic properties and pozzolan reactivities of materials and the freezing and thawing resistance of the paste was improved with the effect blending materials and admixtures. As the blending materials were added to the paste, the quantity of C3A was relatively reduced and the formation of expansive ettringite was suppressed to decrease the penetration of sea-water or Cl-, SO42-ion, and then freeze-thaw resistance was enhanced. Particulary, when 40% of slag was mixed, the resistance was excellent.

• Communications of the Korean Mathematical Society
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• v.34 no.3
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• pp.967-979
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• 2019

Chaotic dynamical systems, preferably on a Cantor-like space with some arithmetic operations are considered as good pseudo-random number generators. There are many definitions of chaos, of which Devaney-chaos and pos itive topological entropy seem to be the strongest. Let $A=\{0,1,{\dots},p-1\}$. We define a continuous map on $A^{\mathbb{Z}}$ using addition with a carry, in combination with the shift map. We show that this map gives rise to a dynamical system with positive entropy, which is also Devaney-chaotic: i.e., it is transitive, sensitive and has a dense set of periodic points.

• Journal of the Korea Institute of Building Construction
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• v.23 no.5
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• pp.547-558
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• 2023

This research delves into the fabrication of an ultra-high-strength concrete, enriched with oxidized graphene nanoplatelet(GO) and hollow glass powder(HGP), notably eschewing the conventional inclusion of silica fume(SF). The primary objective was to scrutinize the autogenous shrinkage characteristics of this innovative formulation. It was discerned that the NewMix specimen, which incorporated the cGO(sourced from Company C) and HGP, and intentionally bypassed SF, showcased a commendable 13% reduction in autogenous shrinkage relative to the benchmark(Ref) specimenthat incorporated SF. Moreover, the proclivity for crack formation owing to autogenous shrinkage in the NewMix was observed to manifested by NewMix at the juncture of cracking emerged as the apex value. Attributed to the expansive specific surface area and exemplary dispersibility of cGO, it was postulated that the concrete's pore structure benefitted from enhanced infill, leading to a reduction in autogenous shrinkage. Additionally, the cGO integration fortified the concrete's resistance to crack initiation. Consequently, such an enhancement is posied to be pivotal in mitigating crack propagation resulting from autogenous shrinkage in ultra-high-strength concrete.

• Computers and Concrete
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• v.16 no.6
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• pp.847-864
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• 2015

This study aimed to develop models of sulfate diffusion and ettringite content profile in cement paste for the predication of the damage behavior in cement paste subject to external sulfate. In the models, multiphase reaction equilibrium between ions in pore solution and solid calcium aluminates phases and the microstructure changes in different positions of cement paste were taken into account. The distributions of expansive volume strain and expansion stress in cement paste were calculated based on the ettringite content profile model. In addition, more sulfate diffusion tests and SEM analyses were determined to verify the reliability and veracity of the models. As the results shown, there was a good correlation between the numerical simulation results and experimental evidences. The results indicated that the water to cement ratio (w/c) had a significant influence on the diffusion of sulfate ions, ettringite concentration profile and expansion properties in cement paste specimens. The cracking points caused by ettringite growth in cement paste specimens were predicted through numerical methods. According to the simulation results, the fracture of cement paste would be accelerated when the specimens were prepared with higher w/c or when they were exposed to sulfate solution with higher concentration.

• Computers and Concrete
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• v.13 no.6
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• pp.739-748
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• 2014

In this article, by using experimental studies and artificial neural network has been tried to investigate the use of nano-silica as concrete admixture to reduce alkali-silica reaction. If there are reactive aggregates and alkali of cement with enough moisture in concrete, a gel will be formed. Then with high reactivity between alkali of cement and existence of silica in aggregates, this gel will expand by absorption of water, and causes expansive pressure and cracks be formed. At the time passes, this gel will reduce both durability and strength of the concrete. By reducing the size of silicate to nano, specific surface area of particles and number of atoms on the surface will be increased, which causes more pozzolanic activity of them. Nano-silica can react with calcium hydroxide ($Ca(OH)_2$) and produces C-S-H gel. In this study, accelerated mortar bar specimens according to ASTM C 1260 and ASTM C 1567, with different mix proportions were prepared using aggregates of Kerman, such as: none admixture and plasticizer, different proportions of nano-silica separately. By opening the moulds after 24 hour and curing in water at $80^{\circ}C$ for 24 hour, then curing in (1N NaOH) at $80^{\circ}C$ for 14 days, length expansion of mortar bars were measured and compared. It was noted that, the lowest length expansion of a specimens shows the best proportion of admixture based on alkali-silica reactivity. Then, prediction of alkali-silica reaction of concrete has been investigated by using artificial neural network. In this study the backpropagation network has been used and compared with different algorithms to train network. Finally, the best amount of nano silica for adding to mix proportion, also the best algorithm and number of neurons in hidden layer of artificial neural network have been offered.