• 한국산업보건학회지
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• 제16권3호
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• pp.254-263
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• 2006

Manganese has a role as both toxic and essential in humans. Manganese is also an essential component in the welding because it increases the hardness and strength, prevents steel from cracking of welding part and acts as a deoxidizing agent to form a stable weld. In this study, manganese generation rate and its content was determined in flux cored arc welding on stainless steel. Domestic two products and foreign four products of flux cored wires were tested in the well designed fume generation chamber as a function of input power. Welding fume was measured by gravimetric method and metal manganese was determined by inductively coupled plasma-atomic emission spectrophotometer. The outer shell of the flux cored wire tube and inner flux were analyzed by scanning electron microscopy to determine their metal compositions. Manganese generation rate($FGR_{mn}$) was increased as the input power increased. It was 16.3 mg/min at the low input power, 38.1 mg/min at the optimal input power, and up to 55.4 mg/min at the high input power. This means that $FGR_{mn}$ is increased at the work place if welder raise the current and/or voltage for the high productivity. The slope coefficient of $FGR_{mn}$ was smaller than that of the generation rate of total fume(FGR). Also, the correlation coefficient of $FGR_{mn}$ was 0.65 whereas that of FGR is 0.91. $FGR_{mn}$ was equal or higher in the domestic products than that of the foreign products although FGR was similar. From the electron microscopic analytical data, we concluded that outer shell of the wire was composed mainly of iron, chromium, nickel and less than 1.2 % of manganese. There are many metal ingredients such as iron, silica, manganese, zirconium, titanium, nickel, potassium, and aluminum in the inner flux but they were not homogeneous. It was found that both $FGR_{mn}$ and content of manganese was higher and more varied in domestic flux cored wires than those of foreign products. To reduce worker exposure to fumes and hazardous component at the source, further research is needed to develop new welding filler materials that improve the quality of flux cored wire in respect to these points. Welder should keep in mind that the FGR, $FGR_{mn}$ and probably the generation rate of other hazardous metals were increased as the input power increase for the high productivity.

• 한국전기전자재료학회논문지
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• 제36권3호
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• pp.249-254
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• 2023

La_0.7-xCe_xSr_0.3MnO₃ specimens were fabricated by a solid state reaction method and structural and electrical properties with variation of Ce⁴⁺ contents were measured. All specimens exhibited a polycrystalline rhombohedral crystal structure, and the (110) peaks were shifted to low angle side with increasing the amount of Ce⁴⁺ contents. As Ce⁴⁺ ions with different ion radii and charges are substituted with La³⁺ ions, electrical properties are thought to be affected by changes in the double exchange interaction between Mn³⁺-Mn⁴⁺ ions due to distortion of the unit lattice, a decrease in oxygen vacancy concentration, and an increase in lattice defects. Resistivity gradually decrease as the amount of Ce⁴⁺ added increased, and negative temperature coefficient of resistance (NTCR) properties were shown in all specimens. In the La_0.5Ce_0.2Sr_0.3MnO₃ specimens, electrical resistivity, TCR and B-value were 31.8 Ω-cm, 0.55%/℃ and 605 K, respectively.

• Journal of Magnetics
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• 제11권1호
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• pp.55-59
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• 2006

The effect of annealing temperature on the permeability and giant magneto-impedance (GMI) behaviors of $Fe_{68.5}Mn_{5}Si_{13.5}B_9Nb_3Cu_1$ amorphous alloy has been systematically investigated. The nanocrystalline $Fe_{68.5}Mn_{5}Si_{13.5}B_9Nb_3Cu_1$ alloys consisting of ultra-fine $(Fe,Mn)_3Si$ grains embedded in an amorphous matrix were obtained by annealing their precursor alloy at the temperature range from $500^{\circ}C\;to\;600^{\circ}C$ for 1 hour in vacuum. The permeability and GMI profiles were measured as a function of external magnetic field. It was found that the increase of both the permeability and the GMI effect with increasing annealing temperature up to $535^{\circ}C$ was observed and ascribed to the ultrasoft magnetic properties in the sample, whereas an opposite tendency was found when annealed at $600^{\circ}C$ which is due to the microstructural changes caused by high-temperature annealing. The study of temperature dependence on the permeability and GMI effect showed some insights into the nature of the magnetic exchange coupling between nanocrystallized grains through the amorphous boundaries in nanocrystalline magnetic materials.

• 한국물환경학회지
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• 제25권3호
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• pp.404-410
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• 2009

In this study, research for physical and chemical characteristics were conducted through analysis of sediments, grading and heavy metals (e.g., Mn, Cu, Cd, Zn and Pb ) in sewers which are classified by drainage types. After that, cement solidification and yellow soil calcinations made heavy metals stabilized and then, ways of recycling it were examined. The grain size distribution of all sediments was relative graded. When evaluating heavy metal pollution through index of geoaccumulation (Igeo), Cu showed moderately pollution or strong pollution in forest and street site and Zn was assessed by moderately pollution in military, residential, and street site. Analysis of Pearson Correlation coefficient of heavy metal indicated that all items in street site have tight relationship respectively. Especially, Cd-Zn, Cu-Pb, Cu-Mn, and Pb-Mn have relationship at 99% confidence intervals in statistical analysis. Recycling it with cement solidification was satisfied with compressive strength standard under 55% deposit contents and Zn, Pb, Mn were stabilized effectively. If time and temperature plasticity and compressive strength would be standard, it is revealed that yellow soil calcinations is valuable aggregate when it has 50-60 Wt% contents. When considering economic feasibility and stabilization of heavy metals, cement solidification would be more appropriate than yellow soil calcinations as solution to recycling.

• Transactions on Electrical and Electronic Materials
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• 제18권5호
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• pp.261-264
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• 2017

$Ni_{0.79}Co_{0.15-x}Cu_xMn_{2.06}O_4$ ($0{\leq}x{\leq}0.09$) thick films were fabricated using the conventional solid-state reaction method and screen-printing method. Structural and electrical properties of specimens based on the amount of Cu were observed in order to investigate their applicability in the infrared detector. All specimens showed a single spinel phase with a homogeneous cubic structure. As the amount of Cu increased, the average grain size increased and was found to be approximately $5.01{\mu}m$ for the $Ni_{0.79}Co_{0.06}Cu_{0.09}Mn_{2.06}O_4$ specimen. The thickness of all specimens was approximately $55{\sim}56{\mu}m$. As Cu content increased, the resistivity and TCR properties at room temperature decreased, and these values for the $Ni_{0.79}Co_{0.06}Cu_{0.09}Mn_{2.06}O_4$ specimen were $502{\Omega}-cm$ and $-3.32%/^{\circ}C$, respectively. The responsivity and noise properties decreased with an increase in Cu content, with the specimen with a Cu content of x=0.09 showing 0.0183 V/W and $5.21{\times}10^{-5}V$, respectively.

• 한국음향학회지
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• 제6권4호
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• pp.55-63
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• 1987

$PbTiO_3$는 perovskite구조를 가진 강유전체로써 Curie온도가 높고 유전율이 작아 고온. 고주파재료로 주목되어왔으나 curie온도 이하에서 결정이방성(C/a)이 크기 때문에 소결 후 결정립(grain)이 입계(grain boundary)에서 분리되어 치밀하고 기계적으로 강한 세라믹을 얻을 수 없었고, 항전력이 커 분극이 어려위 실용화 되지 않았다. 본 연구에서는 $PbTiO_3$에 Pb일부를 Ca로 치환하고 Mn, Ni, Co및 W의 산화물을 첨가하여 치수가 크고 기계적으로 강한 세라믹을 제조하였고, 그 분극 조건도 PZT의 분극 조건과 같은 정도로 개선하였다. 그리고 결합계수이방성(Kt/Kp)이 $5\sim6$으로 크고, 기계적 품질계수 Qm이 $310\sim480$ 정도로 낮으며, 유전상수가 200대의 값으로 PZT보다 1/5정도 작은 고온, 고주파. 광대역 초음파 발진자 재료로 적합한 압전세라믹을 제조 연구하였다.

• 대한치과의사협회지
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• 제55권5호
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• pp.328-338
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• 2017

Introduction: The aim of the current study was to describe the prevalence and treatment of mandibular first molar eruption disturbances. Methods: A total of 38 mandibular first molars(M1mn) from 36 patients(17 males and 19 females; aged 9 years 2 months?35 years 10 months) were identified from the 13,391 patients that received orthodontic treatment from 1983?2012. The subjects were classified into 3 categories based on panoramic radiographic examination: impaction due to ectopic position of the tooth germ relative to the contra-side same tooth(Group 1), impaction due to obstruction of the eruption path with cyst or calcium mass (Group 2), and primary and secondary retention due to defects in the follicle or periodontal ligament(PDL; Group 3). The treatment outcomes were evaluated into four categories: no treatment(A), orthodontic traction(B), autotransplantation(C), and extraction due to orthodontic traction failure(D). Results: The prevalence rate of M1mn eruption disturbances in this sample was 0.27%. In Groups 1 and 2, most of the impacted M1mn were erupted successfully by orthodontic traction. In Group 3, most of the retained M1mn were failed to erupt and recommended for extraction. Conclusions: Treatment prognosis was favorable on Group 1 & 2 than Group 3. After removing an element of the cause in case of Group 1 & 2, orthodontic traction or periodic observation will be recommended.

• Journal of Magnetics
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• 제17권3호
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• pp.176-184
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• 2012

The structural, magnetic and magnetotransport properties of $La_{0.67}Ca_{0.33}MnO_3$: $Ag_x$ (x = 0, 0.1, 0.2, 0.3 and 0.4) composites were investigated systematically. X-ray and EDX analysis indicated that Ag is not substituted into the main $La_{0.67}Ca_{0.33}MnO_3$ phase and remains an additive to the second phase at the grain boundary. The Curie temperature first decreased from 269 K for x = 0 to 257 K for x = 0.1 and then remained nearly unchanged with increasing Ag content. For the x > 0.1 samples, a second transition temperature ($T_{MI2}$) was observed in the resistance curves. At temperatures below 150 K, a significant enhancement in MR was observed while high temperature MR decreased with increasing Ag content. The maximum MR was observed to be 55% in the x = 0.4 sample at 10 K and a 6T magnetic field, this value is larger than that of pure $La_{0.67}Ca_{0.33}MnO_3$ (53% at 265 K and 6 T). In addition, at low fields (H < 1T), a sharp increase in the MR was observed.

• 한국미생물·생명공학회지
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• 제41권2호
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• pp.145-152
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• 2013

소나무잔나비버섯(Fomitopsis pinicola MKACC 54347)의 균사체로부터 endoglucanase를 생산하기 위한 최적 배양조건을 조사하였다. 복합배지 중 MSM이 가장 높은 endoglucanase 활성을 나타내었으며, MSM의 성분과 농도를 각각 2.0% CMC, 2.0% yeast extract, 0.2% $KH_2PO_4$, 0.03% $MnSO_4$ 및 0.3% trace metal 용액으로 첨가하였을 때 효소활성이 가장 우수하였다. 따라서 F. pinicola로부터 endoglucanase를 생산하기 위한 최적 배지조건은 2.0% CMC, 2.0% yeast extract, 0.2% $KH_2PO_4$, 0.03% $MnSO_4$ 및 0.3% trace metal 용액이다. 이상의 배지를 사용하여 배양온도 $25^{\circ}C$에서 8일 동안 배양하였을 때 최대로 효소 활성이 나타내는 것을 확인하였다. CMC를 기질로 사용한 activity staining의 결과를 통해 F. pinicola 균사체의 endoglucanase 활성여부를 확인할 수 있었으며 그 분자량이 43-70 kDa 임을 확인하였고, 배양액 중의 효소활성의 최적 pH와 온도는 각각 pH 5.0과 $55^{\circ}C$인 것으로 나타났다.

• 자원환경지질
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• 제55권1호
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• pp.29-43
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• 2022

2019년 7월에 얻어진 200개의 지하수 수질자료를 활용하여 보성지역 지하수의 수질 특성을 평가하고, 배경 수질을 도출하였다. 지하수는 질산성질소 농도를 기준으로 Group 1(NO₃^- < 44.3 mg/L)과 Group 2(NO₃^- ≥ 44.3 mg/L)로 구분하였다. t-test 결과, Group 2는 Group 1에 비해 유의성 있게 수온과 Ca 농도가 높았고, F, As, Pb, Zn 등의 농도는 낮게 나타났다. 질산염 농도가 높은 경우에는 낮은 pH, 알칼리도, NH₄, NO₂, F, As, Fe, Mn, Pb, Zn 등의 농도를 보였으며, EC 및 수온은 높아지는 경향을 보였다. 한편, 배경농도는 BRIDGE 방법으로 설정하였다. 본 연구에서 설정된 NO₃, NH₄, PO₄, As, Fe, Mn 항목들에 대한 배경농도 값들은 기존의 환경부 보고서(MOE and KECO, 2018; 2019)에 제시된 중권역별 배경농도 산정 결과보다는 다소 높게 설정되었다. 본 연구에 이용된 수질자료의 수가 훨씬 많다는 점을 감안하면, 본 연구에서 산출된 배경수질 자료의 신뢰성이 더 높은 것이라 판단된다.