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31.
Kim CK Han IS Ryu WS Lee HW Lee BS Kim CK 《The journal of physical chemistry. A》2006,110(7):2500-2504
The pi-donating effects of pi-accepting X-substituents in substituted benzylic cations, X-C(6)H(5)-CHR(+) where R = CF(3), H and OCH(3), and X = p-NH(2), p-OCH(3), p-CH(3), H, p-F, p-Cl, p-CHO, m-CN, p-CN, m-NO(2) or p-NO(2), have been studied theoretically by using isodesmic hydride transfer reactions at various levels of theory. It might be difficult to determine the pi-donating effects of pi-acceptors using the simple Hammett-type linear equation, because it is not sensitive enough to include small pi-donating effects. Therefore, this effect was estimated using the NBO deletion energy (DeltaE(D)) of the second-order charge-transfer interaction (DeltaE(ct)) between the pi-orbitals (or lone pair orbitals) of the X-substituent and the pi-orbitals of phenyl ring. The extents of pi-donating effects increased in the order X = p-NO(2) < p-CHO < p-CN < p-Cl for both neutral and cationic species, and these effects were found to be more important for para- than for meta-substituents. Moreover, this could represent a general trend for pi-donation by pi-acceptors. On the other hand, the effects of R-substituents on this pi-donating effect were found to be in the order R = OCH(3) < H congruent with CF(3), as predicted by natural resonance theory (NRT) analyses. 相似文献
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34.
Heui Seob Jeong Jeong Hyun Seo Cha Keun Yoon Joong Kyun Kim Ki-Woong Whang 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1999,27(1):12-13
A direct observation of two-dimensional, time dependent behavior of 147 nm and 173 nm vacuum ultra violet emission from a single surface discharge type AC plasma display panel cell were obtained using a gated, image intensified charge-coupled device (ICCD). The images on the ICCD are formed by a pinhole. The two lines show similar spatial profile but quite different temporal behavior 相似文献
35.
Yu-Nung Hsieh Richard S. Horng Wen-Yueh Ho Ping-Chih Huang Ching-Yun Hsu Thou-Jen Whang Chun-Hsiung Kuei 《Chromatographia》2008,67(5-6):413-420
Six polyvinylimidazolium based ionic liquids were prepared for use as stationary phases for gas chromatography. The influences
of the attached side-chains (hexyl-, octyl- and phenylpropyl-) on the vinylimidazolium cations and of different counter ions
(bromide, hexafluorophosphate, bis-trifluoromethanesulfonlyimide, and bis-trifluoroethanesulfonylimide) were studied. Linear
solubility parameter experiments were conducted to characterize the specific interactions of these stationary phases. Some
of the polymerized ionic liquid stationary phases exhibited unique structural selectivity. m-, and p-xylenes could be distinguished. The preparation of the polymerized ionic liquid column is simple and reliable. This work provides
detailed information for designing polymerized ionic liquids, and shows that these materials have great potential extending
the range of options for stationary phases in gas chromatography. 相似文献
36.
Allen Jong-Woei Whang Shih-Min Chao Cheng-Nan Chen Yi-Yung Chen Horng-Ching Hsiao Xi-Duo Hu 《Optical Review》2011,18(2):218-223
Light-emitting-diode (LED) sources will play a very important role in the future. Nowadays, there are many traditional light
sources gradually being replaced by LED sources. From the viewpoint of illumination, different environments have the same
requirement uniformity of illumination. The basic reason for this is to insure human comfort. Therefore, the promotion of
illumination uniformity is an especially important key issue. In this article, we propose one effective design to improve
the uniformity of illumination of LEDs with Lambertian radiation profiles by inserting into the lighting system, multiple-curvature
lens. The enhanced illumination uniformity of LEDs, in this system, is due to energy redistribution by controlling the direction
of incident light, using geometrical optics theory. Ray tracing was applied for the simulations required. Finally, the uniformity
of illumination is 76.17% in LEDs using multiple-curvature lens, which is twice the uniformity of conventional LEDs. Furthermore,
the phenomenon of overload in the multiple-curvature lens is reduced by increasing the numbers of rings on the lens. The overload
is less than 0.02 lm in the case of lens designed with 23 rings. 相似文献
37.
Based on data representing standard Korean male adults, a mathematical anthropomorphic phantom was developed to calculate the specific absorbed fraction for several organs. The results were then compared against values calculated with other phantoms (OTOKO of Japan, MIRD of the U.S. and GOLEM of Germany). We compared the specific absorbed fractions of six organs (the adrenals, kidneys, liver, lungs, pancreas and spleen) for two cases: when the source and target organs are the same, and when they are different. When both the source and target organs are the same the organ with the highest specific absorbed fraction regardless of energy level was found to be the adrenals in all phantoms. In comparing phantoms, the phantom developed on the basis of standard Koreans produced the highest specific absorbed fraction. Also, as a result of conducting an assessment by separating source organs from target organs, the phantom developed on the basis of standard Koreans displayed relatively high specific absorbed fractions although there were slight differences per organ. 相似文献
38.
S. Alves C. Boekema C. Halim J. Lam E. Whang D. W. Cooke M. Leon 《Hyperfine Interactions》1994,86(1):513-518
A maximum-entropy (ME) method has been applied to TFSR vortex data of RBa2Cu3O7 (R1237; R=Er, Gd and Eu). The obtained information on the field distribution is of much better quality than that resulting from Fourier transformation and curve-fitting of the same data. ME application to R1237 TFSR data taken below Tc at LAMPF show asymmetrical, nearly triangular, field distributions, which broaden with decreasing temperature. Significant deviations from Abrikosov predictions have been observed for the estimated R1237-vortex field distributions. Below 10 K, for Er1237 and Gd1237, the non-Abrikosov features appear to be influenced by the rare-earth magnetism. The low-field tail in the field distribution and the ME-intensity anomaly near Tc suggest glassy features in the 1/2/3 cuprate vortex states. 相似文献
39.
Kinetic studies of the pyridinolysis (XC(5)H(4)N) of aryl dithioacetates (CH(3)C(=S)SC(6)H(4)Z) are carried out in acetonitrile at 60.0 degrees C. A biphasic Br?nsted plot is obtained with a change in slope from a large value (beta(X) congruent with 0.9) to a small value (beta(X) congruent with 0.4) at pK(a) degrees = 5.2, which is attributed to a change in the rate-limiting step from breakdown to formation of a zwitterionic tetrahedral intermediate, T(+/-), in the reaction path as the basicity of the pyridine nucleophile increases. A clear-cut change in the cross-interaction constants rho(XZ) from a large positive value (rho(XZ) = +1.34) to a small negative value (rho(XZ) = -0.15) supports the mechanistic change proposed. 相似文献
40.
Kim S.M. Chakrabarti K. Oh E.O. Whang C.M. 《Journal of Sol-Gel Science and Technology》2003,27(2):149-155
Poly(dimethylsiloxane) (PDMS) modified silica xerogels were prepared by two-step acid/base catalyzed sol-gel process. By keeping the acid amount and hydrolysis period in acidic environment fixed, and adding different amounts of base to the sol afterwards, attempts had been made to study the effect of the different amounts of base catalyst on the micro-structure and physical properties of the prepared ORMOSILs. DTA, SEM, BET, FTIR were performed to characterize the derived specimens. The microstructure and physical properties are greatly influenced by the amount of base added to the sol. With increasing base content the crystallite size and porosity increase and the pore size distribution takes a broad spectrum. Whereas, the glass transition temperature seems to decrease with increasing of base catalyst amount. This is explained in terms of the change in the relative amounts of hydrolysis and condensation reactions due to the addition of different amount of base catalyst, which predominantly influences the condensation reactions. The results are reported in this communication along with possible explanations behind the observations. 相似文献