This study characterizes the volatile aromatic and metabolite components of domestic native Apocynum lancifolium blossom. The accurate characterization of fragrances collected from the blossom was carried out using gas chromatography-mass. A total of 70 chemical components were identified, including ketones of acetophenone (29.22%), phenylethyl alcohol (10.54%), methyl-benzenemethanol (8.43%), benzyl alcohol (7.97%), natural bicyclic sesquiterpene types of caryophyllene (6.08%), gurjunene (6.20%), humulene (1.90%), and ocimene (1.04%). Overall, the content of ketones, alcohols, and terpenes was higher than that of others. The major metabolite components were pentanoic acid, malic acid, fructofuranoside, quinic acid, tagatose, sorbose, galactose, inositol, galactaric acid, glucopyranoside, and octadecenoic acid.

본 연구의 목적은 코로나 사태로 인해 대학에서 실시된 비상 온라인 영어 수업이 원어민 교수자의 인식과 태도에 미치는 영향과 2020년 1학기와 2학기 사이에 어떠한 인식의 변화가 있었는지 알아보는 것이다. 1학기에는 88명, 2학기에는 106명의 교수자가 설문에 참여 하였으며 그 결과, 두 학기 참여자 대부분은 학생들의 영어 능력과 자신감이 향상되었다고 믿는 것으로 나타났다. 참여자들은 비상 온라인 수업으로 인하여 학생들의 수업 참여도, 소통, 협업, 공동체 의식은 일반 수업에 비해 낮았다고 인식하고 있는 것으로 나타났다. 그러나 1학기에 비하여 2학기에 앞서 언급한 모든 분야에서 현저히 발전된 모습을 보였으며 학생들은 새로운 방식으로 자신을 표현하는 능력을 보였다고 답하였다. 설문에 응답한 교수자들은 대부분 비상 온라인 수업 방식에 대해 비교적 긍정적인 태도를 보였으며 두 학기에 걸쳐 실시된 영어 프로그램이 성공적이라고 인식하고 있는 것으로 나타났다. 그 이유로는 한국의 기존 기술 인프라와 학생들의 전자기기에 대한 숙련도, 교수자들의 수업을 돕기 위해 매주 실시 되었던 교육 프로그램을 들 수 있다. 또한, 소규모 수업이었다는 것과 새로운 프로그램이 아닌 기존의 프로그램을 적용했다는 것도 교수자들이 비상 온라인 영어 수업에 대해 긍정적인 인식을 갖는데 영향을 미쳤다고 할 수 있다.

The solubilities of different multicomponent lanthanide oxide (Ln2O3) solid solutions including binary (Ln1 and Ln2 = La, Nd, Eu, or Tm), ternary (Ln1, Ln2, and Ln3 = La, Nd, Eu, or Tm), and higher systems (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) were studied after aging for four weeks at 60°C. Our recent study revealed that the phase transformations in binary ((La, Nd) and (La, Eu)) and ternary (La, Nd, Eu) systems are responsible for the formation of (La, Nd)(OH)3, (La, Eu)(OH)3, and (La, Nd, Eu)(OH)3 solid solutions, respectively. The variations in the mole fractions of La3+, Nd3+, and Eu3+ in the sample solutions of these hydroxide solid solutions indicated that a thermodynamic equilibrium might account for the apparent La, Nd, and Eu solubilities. Conversely, the binary and ternary systems containing Tm2O3 as the heavy lanthanide oxide retained the oxide-based solid solutions, and their solubility behaviors were dominated by their congruent dissolutions. In the higher multicomponent system, the X-ray diffraction patterns of the solid phases, before and after contact with the aqueous phase indicated the formation of a stable oxide solid solution and their solubility behavior was explained by its congruent dissolution.

A laser scabbling experiment was performed using a high-power fiber laser to investigate the removal rate of the concrete block and the scabbled depth. Concrete specimens with a 28-day compressive strength of 30 MPa were used in this study. Initially, we conducted the scabbling experiment under a stationary laser beam condition to determine the optimum scan speed. The laser interaction time with the concrete surface varied between 3 s and 40 s. The degree of spalling and vitrification on the surface was primarily dependent on the laser interaction time and beam power. Furthermore, thermal images were captured to investigate the spatial and temporal distribution of temperature during the scabbling process. Based on the experimental results, the scan speed at which the optical head moved over the concrete was set to be 300 mm∙min−1 or 600 mm∙min−1 for the 4.8-kW or 6.8-kW laser beam, respectively. The spalling rates and average depth on the concrete blocks were measured to be 87 cm3∙min−1 or 227 cm3∙min−1 and 6.9 mm or 9.8 mm with the 4.8-kW or 6.8-kW laser beams, respectively.

For application in nuclear decommissioning, underwater laser cutting studies were conducted on thick stainless-steel plates for various cutting directions using a 6 kW fiber laser. For cutting along the horizontal direction with horizontal laser irradiation, the maximum cutting speed was 110 mm∙min−1 for a 48 mm thick stainless-steel plate. For cutting along the vertical direction with horizontal laser irradiation, a maximum speed of 120 mm∙min−1 was obtained for the same thickness, which confirmed that the cutting performance was similar but slightly better. Moreover, when cutting with vertically downward laser irradiation, the maximum cutting speed was 120 mm∙min−1 for a plate of the same thickness. Thus, the cutting performance for vertical irradiation was nearly identical to that for horizontal irradiation. In conclusion, it was possible to cut thick stainless-steel plates regardless of the laser irradiation and cutting directions, although the assist gas rose up due to buoyancy. These observations are expected to benefit laser cutting procedures during the actual dismantling of nuclear facilities.

In this study, the well-known non-destructive acoustic emission (AE) and electrical resistivity methods were employed to predict quantitative damage in the silo structure of the Wolsong Low and Intermediate Level Radioactive Waste Disposal Center (WLDC), Gyeongju, South Korea. Brazilian tensile test was conducted with a fully saturated specimen with a composition identical to that of the WLDC silo concrete. Bi-axial strain gauges, AE sensors, and electrodes were attached to the surface of the specimen to monitor changes. Both the AE hit and electrical resistance values helped in the anticipation of imminent specimen failure, which was further confirmed using a strain gauge. The quantitative damage (or damage variable) was defined according to the AE hits and electrical resistance and analyzed with stress ratio variations. Approximately 75% of the damage occurred when the stress ratio exceeded 0.5. Quantitative damage from AE hits and electrical resistance showed a good correlation (R = 0.988, RMSE = 0.044). This implies that AE and electrical resistivity can be complementarily used for damage assessment of the structure. In future, damage to dry and heated specimens will be examined using AE hits and electrical resistance, and the results will be compared with those from this study.

Chemical equilibrium calculations for multicomponent aqueous systems involving the reductive dissolution of magnetite (Fe3O4) with oxalic acid (H2C2O4) were performed using the HSC Chemistry® version 9. They were conducted with an aqueous solution model based on the Pitzer’s approach of one molality aqueous solution. The change in the amounts and activity coefficients of species and ions involved in the reactions as well as the solution pH at equilibrium was calculated while changing the amounts of raw materials (Fe3O4 and H2C2O4) and the system temperature from 25°C to 125°C. In particular, the conditions under which Fe3O4 is completely dissolved at high temperatures were determined by varying the raw amount of H2C2O4 and the temperature for a given raw amount of Fe3O4 fed into the aqueous solution. When the raw amount of H2C2O4 added was small for a given raw amount of Fe3O4, no undissolved Fe3O4 was present in the solution and the pH of the solution increased significantly. The formation of ferrous oxalate complex (FeC2O4) was observed. The equilibrium amount of FeC2O4 decreased as the raw amount of H2C2O4 increased.