Byuna T.,Hansung Science High School |
Lee G.,Seoul National University
American Journal of Physics | Year: 2014
This study investigates the belief that solving a large number of physics problems helps students better learn physics. We investigated the number of problems solved, student confidence in solving these problems, academic achievement, and the level of conceptual understanding of 49 science high school students enrolled in upper-level physics classes from Spring 2010 to Summer 2011. The participants solved an average of 2200 physics problems before entering high school. Despite having solved so many problems, no statistically significant correlation was found between the number of problems solved and academic achievement on either a mid-term or physics competition examination. In addition, no significant correlation was found between the number of physics problems solved and performance on the Force Concept Inventory (FCI). Lastly, four students were selected from the 49 participants with varying levels of experience and FCI scores for a case study. We determined that their problem solving and learning strategies was more influential in their success than the number of problems they had solved. © VC 2014 American Association of Physics Teachers.
Um I.-H.,Ewha Womans University |
Seo J.-Y.,Ewha Womans University |
Kang J.-S.,Ewha Womans University |
An J.-S.,Hansung Science High School
Bulletin of the Chemical Society of Japan | Year: 2012
Pseudo-first-order rate constants (k obsd) have been measured for reactions of phenyl Y-substituted-phenyl carbonates with alkali metal ethoxides (EtOM, M = Li, Na, and K). The plot of k obsd vs. [EtOM] curves upward for the reaction of diphenyl carbonate with EtOM but is linear for that with EtOK in the presence of 18-crown-6-ether (18C6), indicating that the reaction is catalyzed by M + ions and the catalytic effect disappears in the presence of 18C6. The kobsd values for the reactions with EtOK have been dissected into f EtO- and k EtOK, i.e., the second-order rate constants for the reactions with dissociated EtO - and ion-paired EtOK, respectively. The Hammett plots correlated with σ - and σ -0 constants exhibit highly scattered points, while the Yukawa-Tsuno plots result in an excellent linear correlation with p = 2.11 and r = 0.21 for k EtO-, and P = 1.62 and r = 0.26 for k EtOK, implying that the reaction proceeds through a concerted mechanism. The catalytic effect (i.e., the k EtOK/k EtOr ratio) is independent of the electronic nature of the substituent Y. Thus, it has been concluded that K + ion catalyzes the reaction by increasing the electrophilicity of the reaction center. © 2012 The Chemical Society of Japan.
Park H.-J.,Sehwa Girls High School |
Kim M.-S.,Hansung Science High School |
Cho K.,Seoul National University |
Yun J.-H.,Seoul National University |
And 2 more authors.
Acta Pharmacologica Sinica | Year: 2013
Aim: Disulfiram is an aldehyde dehydrogenase inhibitor that was used to treat alcoholism and showed anticancer activity, but its anticancer mechanism remains unclear. The aim of this study was to investigate the effects of disulfiram on the hypoxia-inducible factor (HIF)-driven tumor adaptation to hypoxia in vitro. Methods: Hep3B, Huh7 and HepG2 hepatoma cells were incubated under normoxic (20% O2) or hypoxic (1% O2) conditions for 16 h. The expression and activity of HIF-1α; and HIF-2α; proteins were evaluated using immunoblotting and luciferase reporter assay, respectively. Semi-quantitative RT-PCR was used to analyze HIF-mediated gene expression. Endothelial tubule formation assay was used to evaluate the anti-angiogenic effect. Results: Hypoxia caused marked expression of HIF-1α; and HIF-1α; in the 3 hepatoma cell lines, dramatically increased HIF activity and induced the expression of HIF downstream genes (EPO, CA9, VEGF-A and PDK1) in Hep3B cells. HIF-2α; expression was positively correlated with the induction of hypoxic genes (CA9, VEGF-A and PDK1). Moreover, hypoxia markedly increased VEGF production and angiogenic potential of Hep3B cells. Disulfiram (0.3 to 2 μmol/L) inhibited hypoxia-induced gene expression and HIF activity in a dose-dependent manner. Disulfiram more effectively suppressed the viability of Hep3B cells under hypoxia, but it did not affect the cell cycle. Overexpression of HIF-2α; in Hep3B cells reversed the inhibitory effects of disulfiram on hypoxia-induced gene expression and cell survival under hypoxia. Conclusion: Disulfiram deregulates the HIF-mediated hypoxic signaling pathway in hepatoma cells, which may contribute to its anticancer effect. Thus, disulfiram could be used to treat solid tumors that grow in a HIF-dependent manner. © 2013 CPS and SIMM.
Alkali metal ion catalysis and inhibition in nucleophilic substitution reactions of 3,4-Dinitrophenyl diphenylphosphinothioate with alkali metal ethoxides in anhydrous ethanol: Effect of changing electrophilic center from P=O to P=S
An J.-S.,Hansung Science High School |
Namkoong G.,Hansung Science High School |
Kang J.-S.,Ewha Womans University |
Um I.-H.,Ewha Womans University
Bulletin of the Korean Chemical Society | Year: 2011
Pseudo-first-order rate constants (kobsd) have been measured spectrophotometrically for nucleophilic substitution reactions of 3,4-dinitrophenyl diphenylphosphinothioate 9 with alkali metal ethoxides (EtOM, M = Li, Na, K) in anhydrous ethanol at 25.0 ± 0.1 °C. The plot of kobsd vs. [EtOM] is linear for the reaction of 9 with EtOK. However, the plot curves downwardly for those with EtOLi and EtONa while it curves upwardly for the one with EtOK in the presence of 18-crown-6-ether (18C6). Dissection of kobsd into kEtO- and kEtOM (i.e., the second-order rate constant for the reaction with dissociated EtO - and ion-paired EtOM, respectively) has revealed that the reactivity increases in the order kEtOLi < kEtONa < k EtO- ≈ kEtOK < kEtOK/18C6, indicating that the reaction is inhibited by Li+ and Na+ ions but is catalyzed by 18C6-crowned K+ ion. The reactivity order found for the reactions of 9 contrasts to that reported previously for the corresponding reactions of 1, i.e., kEtOLi > kEtONa < k EtOK > kEtO- ≈ kEtOK/18C6, indicating that the effect of changing the electrophilic center from P=O to P=S on the role of M+ ions is significant. A four-membered cyclic transition-state has been proposed to account for the M+ ion effects found in this study, e.g., the polarizable sulfur atom of the P=S bond in 9 interacts strongly with the soft 18C6-crowned K+ ion while it interacts weakly with the hard Li+ and Na+ ions.
Jung D.H.,Seoul National University |
Kim C.K.,Hansung Science High School |
Oh K.H.,Hansung Science High School |
Lee D.-H.,Hansung Science High School |
And 3 more authors.
Korean Journal of Horticultural Science and Technology | Year: 2014
The large amount of CO2 emitted from mushrooms during incubation and developmental stages can be utilized in plant production systems as a CO2 source. The objectives of this study were to measure the CO2 emission and absorption rates of mushroom and lettuce, respectively, and to analyze the CO2 concentrations at various ratios of mushroom and lettuce in a closed production system. The CO2 emission rate of king oyster mushrooms (Pleurotus eryngii (DC.) Quél) and CO2 absorption rate of lettuces (Lactuca sativa L. cv. Asia Heuk Romaine) were measured by using two closed acryl chambers (1.0 m × 0.8 m × 0.5 m) in which indoor temperatures were maintained at 18°C and 22°C, respectively. The lettuce was grown at a light intensity of PPF 340 mol•m−2•s−1 and with nutrient solution at EC 1.2 dS•m−1. The air was periodically circulated between the two chambers using a diaphragm pump. The CO2 emission rate of the mushroom increased until the 15th day after scratching (DAS) and then decreased. The rate also increased with increased indoor temperature. In particular, the CO2 emission rate per fresh weight of fruit body increased by about 3.1 times after thinning compared to before thinning. In terms of CO2 balance, the CO2 emission rates from a bottle (950 mL) of the mushroom at 9, 12, and 14 DAS were equivalent to those of 3, 4.5, and 5.5 lettuce plants at 7, 10, and 12 DAT (days after transplanting), respectively. This work shows that balance in CO2 concentration could be achieved using an appropriate ratio of the two crops in a closed production system. © 2014 Korean Society for Horticultural Science.