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이대수 한국물리학회 2021 새물리 Vol.71 No.10
Flexoelectricity describes the generation of electric polarization in response to strain gradients in all materials. Recently, nanoscale flexoelectricity has attracted a wide range of scientific and technological interest. Importantly, flexoelectric effects can be greatly enhanced on a reduced nanoscale due to increased strain gradients, as strain gradients are inversely proportional to the length scale. Beyond this, however, there is the possibility of a greater, previously hidden potential for nanoscale flexoelectricity. In particular, the flexocoupling coefficient itself may also be greatly improved under huge strain gradients on a nanoscale, which may possibly be due to a nonlinear response and/or a surface effect. This review discusses this possibility and introduces recent experimental results for enhanced flexoelectricity on a nanoscale, emphasizing that nanoscale flexoelectricity may be more powerful than previously expected. 변전성 (flexoelectricity) 은 변형률 기울기 (strain gradient) 에 의해서 모든 물질에 전기 분극이발생하는 보편적 현상을 말한다. 최근, 나노 단위 변전성은 광범위한 과학적, 기술적 관심을 끌고 있다. 중요한 점은, 변형률 기울기는 길이 단위에 반비례하기 때문에 나노 단위로 물질 크기가 줄어들면 변형률기울기가 크게 증가하여서 변전 효과 또한 크게 향상될 수 있다는 것이다. 그러나 이러한 점 이외에도 나노단위 변전성은 더 큰 잠재력이 가질 수 있다. 특별히, 거대 변형률 기울기를 가지는 나노 단위 물질에서비선형 반응 및 표면 효과에 의해서 변전결합 (flexocoupling) 계수 자체가 크게 향상될 수 있다. 이총설논문에서는 이러한 가능성에 대해 논의하고 나노 단위에서 향상된 변전성에 대한 최근 실험 결과를 소개한다. 이러한 결과는 나노 단위 변전성이 그동안 기대했던 것보다 더 큰 잠재력을 가질 수 있음을 의미한다.
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Value at Risk의 사후검증을 통한 다변량 시계열자료의 차원축소 방법의 비교: 사례분석
이대수,송성주,Lee, Dae-Su,Song, Seong-Joo 한국통계학회 2011 응용통계연구 Vol.24 No.4
Value at Risk(VaR) is being widely used as a simple tool for measuring financial risk. Although VaR has a few weak points, it is used as a basic risk measure due to its simplicity and easiness of understanding. However, it becomes very difficult to estimate the volatility of the portfolio (essential to compute its VaR) when the number of assets in the portfolio is large. In this case, we can consider the application of a dimension reduction technique; however, the ordinary factor analysis cannot be applied directly to financial data due to autocorrelation. In this paper, we suggest a dimension reduction method that uses the time-series factor analysis and DCC(Dynamic Conditional Correlation) GARCH model. We also compare the method using time-series factor analysis with the existing method using ordinary factor analysis by backtesting the VaR of real data from the Korean stock market.
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P-600 : Promising Substituted of Molybdenum Carbides in Applications for Catalytic Removal of NO
이대수,김극태,최정길 한국화학공학회 2007 화학공학의이론과응용 Vol.10 No.2
The catalytic NO removal reactions were investigated using a series of Mo carbides. Mo carbides were synthesized using Mo oxide (MoO3) and methane gas (CH4) with different heating rates and space velocity. Various characterization techniques such as BET surface area and oxygen uptake measurements were employed to characterize different Mo carbides synthesized in this study. Depending on the preparative conditions, BET surface areas ranged from 1 m2/gr to 28 m2/gr and oxygen uptake values varied from 0.46 ㎛ol/g to 5.41 ㎛ol/g. The Mo carbides were found to be active for NO removal reactions. Although some Mo carbide catalysts were exceeded by Pt/Al2O3 catalyst, the steady state reaction activities of other Mo carbide catalysts were comparable to or even higher than that of the Pt/Al2O3 catalyst. These results implied that Mo carbides could be one of the promising catalysts that might be able to replace platinum group noble metal catalysts in the NO removal reactions.
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이대수,홍순영,Lee, Dae-Soo,Hong, Soon-Yung 대한화학회 1962 대한화학회지 Vol.6 No.2
The waters throughout Taegu area for 87 points were analysed and according to the analytical data, following unfavorable characteristics for industrial uses were given: (1)Shows strong hardness, (2)Has high ratio of ignition residue to evaporation residue, (3) pH value is over 7, (4) Contains considerable quntities of iron.And then investigated the exchange rate and regeneration level of iron ion using cation exchange resin, Lewatit KS.When the hard water containing 2.2 ppm of iron with 18.4 ppm of calcium and 6.2 ppm of magnesium was passed through the ion exchange resin under $3cc/cm^2/min$ in exhaustant flow rate, exchange rate of iron reached to 42% after 300 hours flow. The exchange efficiency shows abrupt decreasing in initial stage of flow up to 100 hours flow. The exchanger which contains iron was regenerated with 10% sodium hydroxide aqua solution under SV (space velocity) 4. By this method, 57% of iron was eliminated from exchanger while calcium and magnesium are removed as much as 85% and 87% respectively.
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2,2-bis(2-methoxy-5-chlorophenyl) 1,1,1-trichloroethane의 合成 과 殺蟲能에 관하여
이대수,김재항,최달형,최영연,Lee, Dae-Soo,Kim, Jae-Hang,Choi, Won-Hyung,Choi, Young-Euion 대한화학회 1966 대한화학회지 Vol.10 No.4
鹽素置換 anisol과 chloral hydrate를 縮合하면 D.D.T 類의 合成에서와 같이 bis compound의 化合物이 生成될 것이고 D.D.T 系統의 化合物처럼 殺蟲能이 있으리라고 豫測되므로 4-chloro anisol 과 chloral hydrate를 縮合하여 生成物의 構造를 檢討하였던 바 2,2 bis(2-methoxy-5-chlorophenyl) 1.1.1-trichloroethane임을 確認하였으며 反應條件과 「국화꼬마수염진딧물」 및 「귤응애」에 대한 殺충能을 檢討한 結果 前報文$^{(67)}$에서 發表한 바 있는 化合物들의 殺蟲能에 比하여 5培나 强한 殺蟲能을 가졌다는 事實을 알았다. An insecticide was obtained by condensation of chloral hydrate with p-chloroanisole. The structure of the insecticide was found to be 2,2-bis(2-methoxy-5-chlorophenyl)1,1,1-trichloroethane(M.C.T.). The best conditions for this condensation reaction were as follows: 1) The sulfuric acid concentration: 93% 2) The mole ratio of sulfuric acid to p-chloroanisole: 8 3) The mole ratio of chloral hydrate to p-chloroanisole: 0.7 4) The reaction time and reaction temperature: 12 hrs and 25-30$^{\circ}C$ The insecticidal effects of M.C.T against the Citrus Red Mite and Chrysanthemum Aphid were five times as strong as D.D.T.
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