• ALGAE
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• 제35권2호
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• pp.167-176
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• 2020

Iodine exists as a trace element in seawater, with total iodine being generally constant at about 0.45-0.55 μM. Almost all of this iodine occurs in two main forms: iodate and iodide. Iodate is the thermodynamically stable form under normal seawater conditions, and thus should be the only iodine-containing species in the water column. However, iodate concentrations are found to vary considerably, being generally greater at depth and lower at the surface, while iodide concentrations follow the reverse pattern, being anomalously accumulated in the euphotic zone and decreasing with depth. The fact that iodide concentrations follow a depth dependence corresponding to the euphotic zone suggests that biological activity is the source of the reduced iodine. Nonetheless, the nature and source of iodate reduction activity remains controversial. Here, using a combination of field and laboratory studies, we examine some of the questions raised in our and other previous studies, and seek further correlations between changes in iodine speciation and the presence of marine macro- and microalgae. The present results indicate that microalgal growth per se does not seem to be responsible for the reduction of iodate to iodide. However, there is some support for the hypothesis that iodate reduction can occur due to release of cellular reducing agents that accompany cell senescence during phytoplankton bloom declines. In addition, support is given to the concept that macroalgal species such as giant kelp (Macrocystis pyrifera) can take up both iodide and iodate from seawater (albeit on a slower time scale). We propose a mechanism whereby iodate is reduced to iodide at the cell surface by cell surface reductases and is taken up directly as such without reentering the bulk solution.

• 한국토양비료학회지
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• 제48권4호
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• pp.305-311
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• 2015

Both low and high temperatures affect plant growth and development at whole plant level, tissue and even cell level through a variety of metabolic changes. Temperature stress is one of frequently occurring problems in greenhouse crops in summer and winter seasons due to the wide-spread year-round cultivation. In the present study, we investigated the extent of the inhibition of growth, macro-element uptake and soluble carbohydrate production, and the effect of extra-supply of minerals as a means of the recovery from temperature damage. Tomato plants were grown five different growth temperatures (15/8, 20/13, 28/21, 33/23 and $36/26^{\circ}C$), and extra-supply of minerals was composed of 1.5- and 2.0-fold stronger than the standard nutrition (1/2 strength of Hoagland's solution). Temperature stress significantly adversely affected tomato growth and mineral uptake, whereas soluble carbohydrate accumulation represented temperature-dependent response, more accumulation at low temperature and more consumption at high temperature. The soluble sugars in leaves and stems were mostly declined with the supply of extra-minerals at low and optimal temperatures, whereas remained unchanged at high temperature. The starch levels also remained unchanged or slightly decreased.

• 한국재료학회지
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• 제28권11호
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• pp.680-684
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• 2018

We investigate the effect of light intensity and wavelength of a solar cell device using photoconductive atomic force microscopy(PC-AFM). A $POCl_3$ diffusion doping process is used to produce a p-n junction solar cell device based on a polySi wafer, and the electrical properties of prepared solar cells are measured using a solar cell simulator system. The measured open circuit voltage($V_{oc}$) is 0.59 V and the short circuit current($I_{sc}$) is 48.5 mA. Moreover, the values of the fill factors and efficiencies of the devices are 0.7 and approximately 13.6 %, respectively. In addition, PC-AFM, a recent notable method for nano-scale characterization of photovoltaic elements, is used for direct measurements of photoelectric characteristics in limited areas instead of large areas. The effects of changes in the intensity and wavelength of light shining on the element on the photoelectric characteristics are observed. Results obtained through PC-AFM are compared with the electric/optical characteristics data obtained through a solar simulator. The voltage($V_{PC-AFM}$) at which the current is 0 A in the I-V characteristic curves increases sharply up to $18W/m^2$, peaking and slowly falling as light intensity increases. Here, $V_{PC-AFM}$ at $18W/m^2$ is 0.29 V, which corresponds to 59 % of the average $V_{oc}$ value, as measured with the solar simulator. Furthermore, while the light wavelength increases from 300 nm to 1,100 nm, the external quantum efficiency(EQE) and results from PC-AFM show similar trends at the macro scale but reveal different results in several sections, indicating the need for detailed analysis and improvement in the future.

• Structural Engineering and Mechanics
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• 제69권3호
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• pp.257-268
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• 2019

Infills are as important members in structural design as beams, columns and braces. They have significant effect on structural behavior. Because of lots of variables in infills like material non-linear behavior, the interaction between frames and infill, etc., the infills performance during an earthquake is complicated, so have led designers do not consider the effect of infills in designing the structure. However, the experimental studies revealed that the infills have the remarkable effect on structure behavior. As if these effects ignored, it might occur soft-story phenomena, torsion or short-column effects on the structures. One simple and appropriate method for considering the infills effects in analyzing, is replacing the infills with diagonal compression strut with the same performance of real infill, instead of designing the whole infill. Because of too many uncertainties, codes and researchers gave many expressions that were not as the same as the others. The major intent of this paper is calculation the width of this diagonal strut, which has the most characteristics of infill. This paper by comprehensive on different parameters like the modulus of young or moment of inertia of columns presents a new formula for achieving the equivalent strut width. In fact, this new formula is extracted from about 60 FEM analyses models. It can be said that this formula is very efficient and accurate in estimating the equivalent strut width, considering the large number of effective parameters relative to similar relationships provided by other researchers. In most cases, the results are so close to the values obtained by the FEM. In this formula, the effect of out of plane buckling is neglected and this formula is used just in steel structures. Also, the thickness of infill panel, and the lateral force applied to frame are constant. In addition, this new formula is just for modeling the lateral stiffness. Obtaining the nearest response in analyzing is important to the designers, so this new formula can help them to reach more accurate response among a lot of experimental equations proposed by researchers.

• Computers and Concrete
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• 제23권1호
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• pp.61-68
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• 2019

This paper presents a computational rational model to predict the ultimate and optimized load capacity of reinforced concrete (RC) beams strengthened by a combination of longitudinal and transverse fiber reinforced polymer (FRP) composite plates/sheets (flexure and shear strengthening system). Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. A high performance concrete, known as polymer concrete, made up of natural aggregates and an orthophthalic polyester binder, reinforced with non-metallic bars (glass reinforced polymer) has been studied. The material is described at micro and macro level, presenting the key physical and mechanical properties using different experimental techniques. Furthermore, a full description of non-metallic bars is presented to evaluate its structural expectancies, embedded in the polymer concrete matrix. In this paper, the mechanism of mechanical interaction of smooth and lugged FRP rods with concrete is presented. A general modeling and application of various elements are demonstrated. The contact parameters are defined and the procedures of calculation and evaluation of contact parameters are introduced. The method of calibration of the calculated parameters is presented. Finally, the numerical results are obtained for different bond parameters which show a good agreement with experimental results reported in literature.

• Earthquakes and Structures
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• 제16권4호
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• pp.501-512
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• 2019

In this study, seismic vulnerability assessment and seismic isolation retrofit of Bayburt Yakutiye Mosque is investigated. Bayburt Yakutiye Mosque was built in the early 19th century at about 30-meter distance to Coruh river in the center of Bayburt in Turkey. The walls of historical masonry structure were built with regional white and yellow stones and the domes of the mosque was built with masonry bricks. This study is completed in four basic phases. In first phase, experimental determination of the regional white stone used in the historical structure are investigated to determine mechanical properties as modulus of elasticity, poison ratio and compression strengths etc. The required information of the other materials such as masonry brick and the regional yellow stone are obtained from literature studies. In the second phase, three dimensional finite element model (FEM) of the historical masonry structure is prepared with 4738 shell elements and 24789 solid elements in SAP2000 software. In third phase, the vulnerability assessment of the historical mosque is researched under seismic loading such as Erzincan (13 March 1992), Kocaeli (17 August 1999) and Van (23 November 2011) earthquakes. In this phase, the locations where damage can occur are determined. In the final phase, rubber base isolators for seismic isolation retrofit is used in the macro model of historical masonry mosque to prevent the damage risk. The results of all analyses are comparatively evaluated in details and presented in tables and graphs. The results show that the application of rubber base isolators can prevent to occur the destructive effect of earthquakes.

• 산업융합연구
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• 제21권1호
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• pp.87-93
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• 2023

주식 투자에서 매수와 매도의 타이밍을 결정하는 것은 주식 투자의 수익률 올리기 위해 가장 중요한 요인 중에 하나이다. 주식은 싸게 사서 비싸게 팔면 이익이 되지만, 비싸게 사서 싸게 팔면 손해가 된다. 주식의 가격을 결정하는 매수와 매도의 물량에 의해 가격이 결정이 되고, 매수와 매도는 기업실적, 경제지표와도 관련이 있다. CNN에서 제공하는 공포와 탐욕지수는 7가지 요소를 사용하고, 각 요소에 가중치를 부여하여 탐욕과 두려움으로 정의한 가중치 평균을 0~100 사이의 척도로 계산하여 매일 발표하고 있다. 지수가 0에 가까우면 주식시장 심리가 두려운것이고, 100에 가까우면 탐욕스러운 것이다. 따라서 미국 S&P 500 지수를 CNN 공포와 탐욕지수에 따른 매수와 매도를 할 경우 최대 수익률이 발생하는 매매 기준을 분석하여 최적의 매수와 매도 타이밍을 제시하여 주식투자에 수익률을 높일 수 있는 방안을 제시하고자 한다.

• 한국전산구조공학회논문집
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• 제13권1호
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• pp.13-24
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• 2000

교량 바닥판 설계에 대한 현 시방규정은 바닥판 슬래브가 처짐이 구속된 거더에 연속 지지되어 있다고 가정하므로, 바닥판 지간 중앙의 정모멘트와 거더 상단에 발생하는 부모멘트의 크기가 같은 것으로 간주하고 있다. 그러나 바닥판에 발생하는 휨모멘트는 거더의 처짐에 의해서 많은 영향을 받고 있으며, 거더의 처짐을 고려치 않는 현 시방규정에 의해 설계된 바닥판은 상부철근의 부식으로 인한 내구성 저하와 유지보수 비용 증가 등의 문제점을 안고 있다. 따라서 본 연구에서는 매크로 요소를 이용해 거더의 처짐 효과를 고려할 수 있는 해석법을 개발하였고, 이를 유한요소법을 통해 검증하였다. 또한, 이 해석법을 바탕으로 바닥판의 횡방향 휨모멘트에 영향을 미치는 여러 변수에 대한 분석을 수행하였다. 해석 결과, 바닥판의 지점부 모멘트는 거더의 간격뿐만 아니라 거더와 바닥판의 휨강성비 교량의 길이, 하중의 재하위치, 거더의 비틀림 강성, 가로보의 휨강성과 배치 간격 등에 많은 영향을 받고 있는 것을 알 수 있으며, 영향선을 이용해 최대하중 위치를 결정하여 몇 개의 예제교량을 대상으로 지점부의 설계모멘트를 계산해 본 결과, 현 시방규정이 다소 보수적인 값을 나타내고 있다.

• 한국주조공학회지
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• 제35권6호
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• pp.147-154
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• 2015

The effects of Sc and Sr elements on the modification of the eutectic $Mg_2Si$ phase and the castability were investigated in the Al-4wt%Mg-0.9wt%Si-0.3wt%Mn-0.15wt%Fe alloy. Measurements of the cooling curve and microstructure observations were performed to analyze the additional effects of Sc and Sr minor elements during the solidification process. A prominent effect found on the modification of the eutectic $Mg_2Si$ phase with additions of the Sr and Sc elements. Here, a fine eutectic $Mg_2Si$ phase and a decrease in the growth temperature of the eutectic $Mg_2Si$ phase were evident with an addition of Sc element up to 0.2 wt%. The growth temperature of the eutectic $Mg_2Si$ phase decreased and the effect on the modification of the eutectic $Mg_2Si$ phase increased with the addition of Sr element up to 0.02 wt%. The addition of 0.02wt%Sr had the strongest effect on the modification of the eutectic $Mg_2Si$ phase, and the resulting microstructure of the eutectic $Mg_2Si$ phase was found to have a fibrous morphology with a decreased aspect ratio and an increased modification ratio. Fluidity and shrinkage tests were conducted to evaluate the castability of the alloy. The addition of 0.02wt%Sr effectively increased the fluidity of the alloy, while an addition of Sc did not show any effect compared to when nothing was added. The maximum filling length was recorded for 0.01wt%TiB-0.02wt%Sr owing to the effect of the fine ${\alpha}$-Al grains. The macro-shrinkage ratio decreased, while the micro-shrinkage ratio increased with the addition of various eutectic modifiers. The highest ratio of micro-shrinkage was recorded for the 0.02wt%Sr condition. However, the total shrinkage ratio was nearly identical regardless of the amounts added in this study.

• 생물환경조절학회지
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• 제17권4호
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• pp.252-260
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• 2008

본 실험은 장미 식물공장에서 single-node cutting 'Versillia'의 양분흡수 특성을 구명하고 순환식 수경재배 시스템에 적합한 배양액 내 무기이온 조절방식을 구명하고자 수행하였다. 실험 기간동안 각 처리별 배양액 내 무기이온함량 변화를 살펴본 결과 EC 제어구의 경우 $NO_3$-N은 생육 후반이 되면 그 함량이 적정 범위 이상으로 증가 하였고 P와 Mg은 감소하였으며 배양액 첨가구는 전체적인 배양액 내 무기이온 함량이 증가하였다. 이에 비해 무기이온 제어구는 생육 기간동안 근권 내 적정 범위를 유지하였다. 광합성 효율을 나타내는 지표 중 하나인 Fv/Fm는 무기이온제어구와 배양액 첨가구에서 높았고 절화장, 생체중 등은 무기이온 제어구에서 높았다. 그러나 뿌리의 활성 정도를 측정해본 결과 무기이온 제어구에서 높았으나 배양액 첨 가구에서는 생육 초기에 배양액 내 pH 변화폭이 커서 가장 낮게 나타났다. 위의 결과를 종합하였을 때, 무기이온 조절(다량 미량원소 제어구와 다량원소 제어구)을 통해 배양액을 관리하는 것이 생육 전 기간 동안 근권 환경을 적절히 유지해 줄 수 있었고 이에 따라 절화 품질도 향상되므로 장미(single-node cutting) 순환식 수경재배에 적합한 근권 환경 제어방식이라고 할 수 있다.