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991.
Seung Tae Hong Dal Ryung Park Seung-Joon Yoo Jae-Duck Kim Hyung Sang Park 《Research on Chemical Intermediates》2006,32(9):857-870
The active phase of the NiMo/Al2O3 catalyst for hydrodesulfurization reactions has been investigated in this work. Special attention has been focused on the
effect of the order of metal impregnation on the formation of the active phase in the reaction. The Mo and Ni oxides and their
sulfides on the alumina were investigated by XPS and DRS analyses. The Ni-Mo oxides or precursor of the active phase which
are chemically bonded between Mo and Ni were also confirmed from the binding energy shifts of the XPS peaks. The amount of
Ni-Mo oxides was determined after the formation of metal oxides during calcination. The Ni-Mo sulfide (active phase) was then
induced through sulfidation. It was important that Mo should be located at the tetrahedral sites on the alumina with a high
Mo dispersion. These results indicated that there are two important factors in preparing highly efficient Ni-Mo catalysts;
one is that Mo should be located at the tetrahedral coordination on Al2O3 in high dispersion (Mo/Al2O3) and the other is that the Ni species should be supported on MoAl2O4 to form Ni-Mo oxides which change into the Ni-Mo sulfide active sites by sulfidation. 相似文献
992.
The optical properties of an one-dimensional photonic crystal containing graded materials are studied theoretically. The graded layers have space dispersive permittivity and magnetic permeability which vary along the direction perpendicular to the surface of the layer. The gradation profiles of permittivity are studied in detail. We show that the structure possesses forbidden band gaps in its transmission spectra and the gradation profiles of permittivity affect the band gaps significantly. For the exponential gradation profile ε1(x) = α eβx, the number of the band gaps increases and the total frequency region corresponding to the gaps becomes large with increasing parameter β. On the other hand, the position of band gaps can be changed by the adjustment of the gradation profiles even if possessing same volume-average permittivity in the graded layers. Therefore, we can achieve suitable photonic band gaps by choosing gradation profiles of permittivity. 相似文献
993.
Soo‐Young Park Sang‐Cheol Moon N. Venkatasubramanian Thuy D. Dang Jar‐Wha Lee B. L. Farmer 《Journal of Polymer Science.Polymer Physics》2006,44(14):1948-1957
The rigid‐rod polymers, poly(2,6‐naphthalenebenzobisoxazole) (Naph‐2,6‐PBO) and poly(1,5‐naphthalenebenzobisoxazole) (Naph‐1,5‐PBO) were synthesized by high temperature polycondensation of isomeric naphthalene dicarboxylic acids with 4,6‐diaminoresorcinol dihydrochloride in polyphosphoric acid. Expectedly, these polymers were found to have high thermal as well as thermooxidative stabilities, similar to what has been reported for other polymers of this class. The chain conformations of Naph‐2,6‐PBO and Naph‐1,5‐PBO were trans and the crystal structures of Naph‐2,6‐PBO and Naph‐1,5‐PBO had the three‐dimensional order, although the axial disorder existed for both Naph‐2,6‐PBO and Naph‐1,5‐PBO. Naph‐2,6‐PBO exhibited a more pronounced axial disorder than Naph‐1,5‐PBO because of its more linear shape. The repeat unit distance for Naph‐2,6‐PBO (14.15 Å) was found to be larger compared with that of Naph‐1,5‐PBO (12.45 Å) because of the more kinked structure of the latter. The extents of staggering between the adjacent chains in the ac projection of the crystal structure were 0.25c and 0.23c for Naph‐2,6‐PBO and Naph‐1,5‐PBO, respectively. Naph‐1,5‐PBO has a more kinked and twisted chain structure relative to Naph‐2,6‐PBO. The kinked and twisted chain structure of Naph‐1,5‐PBO in the crystal seems to prevent slippage between adjacent chains in the crystal structure. The more perfect crystal structure of Naph‐1,5‐PBO may be due to this difficulty in the occurrence of the slippage. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1948–1957, 2006 相似文献
994.
Young Hun Yu Sang Chill Lee Doo Chul Kim Chao Zhang P. Harrison 《Optics & Laser Technology》2004,36(7):535-580
The resonant wavelength and mode radius of the fundamental modes supported by an oxide apertured terahertz vertical surface emitting laser are determined from Gaussian resonant theory and scalar variational method. The reflectivity of the Bragg mirror is calculated for the lowest modes and it decreases as the aperture size decreases. The aperture radius, thickness, and axial position in the cavity are shown to be an important factor for high efficiency vertical cavity surface emitting lasers and single mode operation. When the aperture size is much larger than the emitting wavelength, the optical loss is negligible. However, the optical loss strongly depends on the aperture size and thickness when aperture size is similar to or smaller than emitting wavelength. 相似文献
995.
Jin‐Woong Kim Jung‐Eun Lee Jee‐Hyun Ryu Jong‐Suk Lee Su‐Jin Kim Sang‐Hoon Han Ih‐Seop Chang Hak‐Hee Kang Kyung‐Do Suh 《Journal of polymer science. Part A, Polymer chemistry》2004,42(10):2551-2557
A new colloidal silver system is presented in which a fine colloidal silver is in situ deposited onto functionalized porous poly(ethylene glycol dimethacrylate) [poly(EGDMA)] microspheres. The effectiveness of the silver deposition has been investigated through an examination of the surface characteristics of poly(EGDMA) microspheres. The result reported in this study demonstrate that the control of the surface area and surface functionality (in this study, a hydroxyl group) of poly(EGDMA) microspheres is an important factor that practically determines the degree of deposition of colloidal silver. X‐ray analysis has shown that silver nanoparticles are dispersed evenly on inner and outer surfaces and have a face center cubic phase. Preservation testing has shown that silver‐containing poly(EGDMA) microspheres have powerful antibacterial properties and, therefore, have significant potential as new preservatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2551–2557, 2004 相似文献
996.
997.
Chun Xi Zhai Hai Ning Gu Da Yong Sang Juan Tian Qi Zhong Zhou 《中国化学快报》2008,19(6):720-724
The deaggregating ability of β-CD and α-CD against the aggregated n-hexadecyl β-naphthoate (A16) and n-dodecyl β-naphthoate (A12) depended not only on the aggregating tendency of A16 and A12 but also on the initial concentration of the aggregated A16 or A12. The inclusive ability of β-CD with the substrates is greater than that of α-CD under hydrophobiclipophilic interaction. 相似文献
998.
999.
1000.
Let M be the moduli space of semistable rank 2 Higgs pairs (V, ϕ) with trivial determinant over a smooth projective curve X of genus g ≥ 2. We provide an explicit formula for the stringy E‐function of M . (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献