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991.
Factors Affecting the Branching Ratio of Photodissociation: Thiophenol Studied through Quantum Wavepacket Dynamics
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Heesun An Dr. Heechol Choi Prof. Yoon Sup Lee Prof. Kyoung Koo Baeck 《Chemphyschem》2015,16(7):1529-1534
The photodissociation dynamics of thiophenol (PhSH) excited to the 11ππ* state was investigated by time‐dependent quantum wavepacket propagation within two‐dimensional (2D) space consisting of the S?H bond and ?SH torsion. We systematically studied the dependence of the branching ratio ${\left( {{{{\rm{\tilde A}}} \mathord{\left/ {\vphantom {{{\rm{\tilde A}}} {{\rm{\tilde X}}}}} \right. \kern-\nulldelimiterspace} {{\rm{\tilde X}}}}} \right)}$ between the two electronic states of the phenylthiyl radical (PhS.) on several factors of the 2D potential energy surfaces (PESs). The effect of a reduced initial barrier to the first ππ*/πσ* conical intersection (CI) was found to be marginal, whereas the effects of a reduced torsional barrier of ?SH on the excited ππ* state and the mitigated slope of the πσ* PES between the first (ππ*/πσ*) and the second (πσ*/S0) CIs were noticeable. The effect of the slope on the branching ratio has never been previously noticed. It was shown that the branching ratio can be sufficiently above unity without pre‐excitation of the torsion mode of ?SH, which has been assumed so far. 相似文献
992.
UV-B irradiation has been used to enhance the secondary metabolite content in plants, but its spatial effect on plants has not been considered. The objective of this study was to compare spatial photosynthetic traits and bioactive compound accumulation in kale (Brassica oleracea L. var Acephala) according to the distribution and length of UV-B exposure near harvest. Plants were exposed to UV-B of 0–3, 3–6 and 6–9 W m−2 for 4 h per day at 5 days (Exp. 1) and 4.2 W m−2 at 5, 4, 3, 2 or 1 days (Exp. 2) before harvest. In spatial distribution, the higher the UV-B intensity, the lower the mean Fv/Fm (maximal photochemical efficiency of PSII) and the higher the concentration of total flavonoid compound (TFC). With UV-B stress, Fv/Fm and fluorescence transient parameters decreased except for DI0/CS (dissipated energy flux per cross section) and PIabs (performance index of PSII). When exposed to UV-B radiation for 2 days before harvest, the total phenolic compounds and TFC per plant were highest, not always proportional to the local Fv/Fm but affected by dry weight. Short-term UV-B stress near harvest would be more efficient for the accumulation of bioactive compounds by minimizing the loss of plant weight. 相似文献
993.
Hyesu Lee Eunmi Jo Dr. Kyung Yoon Chung Prof. Dongjin Byun Dr. Seung Min Kim Dr. Wonyoung Chang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(6):2406-2412
The structural stability of cathode materials during electrochemical reactions, in particular, under high-rate discharge, is pertinent to the design and development of new electrode materials. This study investigates the structural inhomogeneity that develops within a single LiNi0.835Co0.15Al0.015O2 (NCA83) particle during a fast discharging process under different cutoff voltages. Some of the NCA83 particles discharged from a high cutoff voltage (4.8 V) developed surface areas in which the layered structure was recovered, although the interiors retained the degraded spinel structure. These micro- and nano-scale structural inversions from high cutoff voltage seem highly correlated with structural evolutions in the initial charged state, and may ultimately degrade the cycling stability. This study advances understanding of the structural inhomogeneity within primary particles during various electrochemical processes and may facilitate the development of new Ni-rich cathode materials. 相似文献
994.
Analysis of Voice and Quantitative Measurement of Glottal Gap After Thyroplasty Type I in the Treatment of Unilateral Vocal Paralysis 总被引:2,自引:0,他引:2
Thyroplasty type I is one of several surgical treatments in which improving the voice of unilateral vocal fold paralysis is the ultimate objective. The goal of the surgery is the medialization of the paralyzed vocal fold. The purpose of this study is to evaluate the effectiveness of thyroplasty type I through acoustical analysis, aerodynamic measures, and quantitative videostroboscopic measurements. We report on 20 patients with unilateral vocal cord paralysis who underwent thyroplasty type I. We performed preoperative and postoperative video image analysis (normalized glottal gap area) and computer-assisted voice analysis (fundamental frequency, jitter, shimmer, noise-to-harmonic ratio, mean phonation time, mean flow rate, mean subglottic pressure) in all patients. The glottal gap was significantly reduced after thyroplasty type I. Postoperative voice quality was characterized by an improved pitch and amplitude pertubation (jitter and shimmer), phonation time (mean phonation time), and subglottic pressure (mean subglottic pressure). Thyroplasty type I is an effective method for regaining glottal closure and vocal function. 相似文献
995.
Jung-In Yoon Chang-Hyo Son Seung-Moon Baek Hyeon-Ju Kim Ho-Saeng Lee 《Heat and Mass Transfer》2014,50(7):985-996
This paper presents an investigation into the thermal efficiency and main component size of the subcritical ocean thermal energy conversion (OTEC) power cycle using various working fluids under different operation conditions. The analysis procedure was performed with a simulation program written in Engineering Equation Solver. With the given analysis conditions, efficiencies of three types of working fluids were evaluated and compared. It was found that the thermal efficiencies of the subcritical OTEC power cycle depend strongly on the evaporating and condensing temperature, and turbine efficiency, while not roughly depending on superheating degrees and pump efficiencies. With a thorough grasp of these results, an efficient OTEC power cycle can be designed. R717 and R404A yielded the highest and lowest thermal efficiencies among the wet fluids, and R22 showed the largest efficiency among the dry fluids. For the iso-entropic fluids, R245fa provided the highest thermal efficiency. In comparison of main component sizes, R404A and R744 had the largest and smallest condenser size, respectively. Also, R744 exhibited the smallest evaporator size, and R404A and R227ea show the largest size. And R744 and R245fa gave the largest and smallest pump size, respectively. From the results of thermal efficiency and main components for various working fluids in the OTEC power cycle, R717 in the subcritical OTEC power cycle is the preferred working fluid, except for its toxicity and flammability. 相似文献
996.
Yusuf Zuntu Abdullahi Tiem Leong Yoon Mohd Mahadi Halim Md. Roslan Hashim Thong Leng Lim 《哲学杂志》2013,93(24):2077-2088
AbstractMechanical and electronic properties of s-triazine sheet are studied using first-principles calculations based on density functional theory. The in-plane stiffness and bulk modulus for s-triazine sheet are found to be less than that of heptazine. The reduction can be related to the nature of the covalent bonds connecting the adjacent sheets and the number of atoms per unit cell. The Poisson’s ratio of s-triazine sheet is half the value to that of graphene. Additionally, the calculated values of the two critical strains (elastic and yielding points) of s-triazine sheet are in the same order of magnitude to that for heptazine which was calculated using MD simulations in the literature. It is also demonstrated that s-triazine sheet can withstand larger tension in the plastic region. These results established a stable mechanical property for s-triazine sheet. We found a linear relationship of bandgap as a function of bi-axial tensile strain within the harmonic elastic region. The reduced steric repulsion of the lone pairs (px-, py-) causes the pz-like orbital to shift to high energy, and consequently an increase in the bandgap. We find no electronic properties modulation of the s-triazine sheet under electric field up to a peak value of 10 V/nm. Such noble properties may be useful in future nanomaterial applications. 相似文献
997.
998.
Tae-Yeon Cho Kwan-Woo Ko Soon-Gil Yoon Satpal Singh Sekhon Man Gu Kang Young-Sik Hong Chi-Hwan Han 《Current Applied Physics》2013,13(7):1391-1396
We investigated the effect of a Nb2O5 blocking layer formed through the sol–gel method introduced to a titanium metal foil electrode in a flexible dye sensitized solar cell. The blocking layer formed directly on the working electrode physically separates the working electrode from the electrolyte, and prevents back transfer of electrons from the electrode to the electrolyte. The gel processing conditions (sol reaction time) and heat treatment temperature used in formation of the Nb2O5 blocking layer have been shown to affect the performance of the dye sensitized solar cell and optimal values of these parameters have been determined. A sol reaction time of 45 min and heat treatment temperature of 550 °C has been observed to result in optimal cell performance (η = 6.185%, Jsc = 13.233 mA/cm2, Voc = 0.672 V, ff = 0.694). Introduction of an Nb2O5 blocking layer enhances solar cell efficiency by 39.7%, which is much greater than the increase of 24.6% observed in a similar cell containing a TiO2 blocking layer under standard illumination conditions. The results obtained via Nb2O5 have been observed to be superior to those obtained via a TiO2 blocking layer. 相似文献
999.
The 3D scaffold type biocomposites of gelatin/silver nanoparticles were prepared through the silver nanoparticles (Ag NPs) formation in gelatin solution using solution plasma process (SPP) and their antifungal activity was evaluated. The mixture of 3% gelatin solution and silver precursor (AgNO3; 1–10 mM) was subject to discharge at high voltage (1600 V) under the controlled conditions to form the suspension of Ag NPs in the gelatin matrix. The freeze-drying process of lyophilization was employed to fabricate the 3D scaffold type biocomposite of gelatin/Ag NPs from the suspension. The water-insoluble property was improved by cross-linking using UV-irradiation (λ = 254 nm for 15 min). The physical and chemical characteristics of the biocomposite were investigated using UV–vis spectroscopy, EDS, FE-SEM, and TEM. The results indicated that the 3D scaffold biocomposite of gelatin/Ag NPs had spherical shape with approximately 11–12 nm of diameter. The antifungal activity analysis suggested that the biocomposite with Ag NPs could inhibit the growth of Candida albicans as well as that of hyphae and spores of Aspergillus parasiticus significantly. MIC of the biocomposite for C. albicans and A. parasiticus was determined as 80 μg/ml and 240 μg/ml of Ag NPs, respectively. The growth inhibition of 92.8% was observed in the biocomposite with 10 mM Ag against C. albicans. 相似文献
1000.
Ju‐Young Kim Dong Wook Kim Choong Eui Song Dae Yoon Chi Sungyul Lee 《Journal of Physical Organic Chemistry》2013,26(1):9-14
We present a mechanistic study for nucleophilic substitution (SN2) reactions facilitated by multifunctional n‐oligoethylene glycols (n‐oligoEGs) using alkali metal salts MX (M+ = Cs+, K+, X– = F–, Br–, I–, CN–) as nucleophilic agents. Density functional theory method is employed to elucidate the underlying mechanism of the SN2 reaction. We found that the nucleophiles react as ion pairs, whose metal cation is ‘coordinated’ by the oxygen atoms in oligoEGs acting as Lewis base to reduce the unfavorable electrostatic effects of M+ on X–. The two terminal hydroxyl (?OH) function as ‘anchors’ to collect the nucleophile and the substrate in an ideal configuration for the reaction. Calculated barriers of the reactions are in excellent agreement with all experimentally observed trends of SN2 yields obtained by using various metal cations, nucleophiles and oligoEGs. The reaction barriers are calculated to decrease from triEG to pentaEG, in agreement with the experimentally observed order of efficiency (triEG < tetraEG < pentaEG). The observed relative efficiency of the metal cations Cs+ versus K+ is also nicely demonstrated (larger [better] barrier [efficiency] for Cs+ than for K+). We also examine the effects of the nucleophiles (F–, Br–, I–, CN–), finding that the magnitudes of reaction barriers are F– > CN– > Br– > I–, elucidating the observation that the yield was lowest for F–. It is suggested that the role of oxygen atoms in the promoters is equivalent to that of –OH group in bulky alcohols (tert‐butyl or amyl‐alcohol) for SN2 fluorination reactions previously studied in our lab. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献