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991.
F. Rotermund C.J. Yoon K. Kim H. Lim S. Kurimura K. Kitamura 《Applied physics. B, Lasers and optics》2006,85(1):17-20
The first praseodymium-ytterbium up-conversion ZBLAN fiber laser in an all-fiber ring configuration is reported. The laser
operates at 635 nm, is pumped at 835 nm, and consists of only the active ZBLAN fiber and two-fused-fiber couplers.
PACS 42.55.Wd; 42.60.By 相似文献
992.
S.Z. Wang S.F. Yoon T.K. Ng W.K. Loke W.J. Fan 《Applied Physics A: Materials Science & Processing》2005,80(3):631-635
It is demonstrated that a nitrogen supply, manifested as both a direct nitrogen beam from a rf-activated plasma source and dispersive nitrogen radicals from the growth-chamber background, is appropriate for the growth of GaAs-based nitrides. The nitrogen incorporation efficiency shows a linear relationship with increasing rf power when the nitrogen is supplied dispersively, and a saturation behavior when the nitrogen is supplied as a direct nitrogen beam. The indium composition causes a decrease in the nitrogen incorporation efficiency, which is suspected to be brought about by the increase of the growth rate due to the indium flux, because our experiments have proven that the nitrogen composition of GaAsN epilayers apparently decreases as the growth rate increases. It is more controllable to fix the indium flux first than to fix the nitrogen source condition, so as to facilitate wavelength control. The temperature window for the growth of quality nitride is concluded to be between 440 °C and 500 °C. For a quantum well with a certain well width, it is better to add more indium and less nitrogen to reach the desired wavelength in order that the quality of the InGaAs material is kept acceptable. PACS 81.15.Hi; 81.05.Ea; 42.70.-a 相似文献
993.
J.‐T. Hong N.‐S. Cho H.‐S. Yoon T.‐H. Kim D.‐H. Lee W.‐G. Kim 《Journal of polymer science. Part A, Polymer chemistry》2005,43(13):2790-2799
A series of poly(trimethylenecarbonate‐ε‐caprolactone)‐block‐poly(p‐dioxanone) copolymers were prepared with varying feed rations by using two step polymerization reactions. Poly(trimethylenecarbonate)(ε‐caprolactone) random copolymer was synthesized with stannous‐2‐ethylhexanoate and followed by adding p‐dioxanone monomer as the other block. The ring opening polymerization was carried out at high temperature and long reaction time to get high molecular weight polymers. The monofilament fibers were obtained using conventional melting spun methods. The copolymers were identified by 1H and 13C NMR spectroscopy and gel permeation chromatography (GPC). The physicochemical properties, such as viscosity, molecular weight, melting point, glass transition temperature, and crystallinity, were studied. The hydrolytic degradation of copolymers was studied in a phosphate buffer solution, pH = 7.2, 37 °C, and a biological absorbable test was performed in rats. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2790–2799, 2005 相似文献
994.
Su-Dong Cho Joo-Wha Chung Sung-Kyu Kim Deok-Heon Kweon Ki-Hoon Park Yong-Jin Yoon 《Journal of heterocyclic chemistry》1996,33(2):315-318
Some novel benzotriazole, benzothiazinone and pyridooxazinone acyclonucleosides containing 4-hydroxybutyl, 4-hydroxybutoxy, 4-iodobutyl, 2-oxopropyl and 2,3-epoxypropoxy groups as a side chain was prepared. 相似文献
995.
Poly(L ‐lactide) (PLLA)/poly(butylene succinate‐co‐butylene adipate) (PBSA) blends were compounded with Cloisite 25A® (C25A) and C25A functionalized with epoxy groups, respectively. Epoxy groups on the surface of C25A were introduced by treating C25A with (glycidoxypropyl)trimethoxy silane (GPS) to produce so called Twice Functionalized Organoclay (TFC). Variation of morphology and properties of PLLA/PBSA/C25A composites was investigated before and after the treatment with GPS. The morphological structure of the composites was analyzed by using X‐ray diffractometry (XRD) and transmission electron microscopy (TEM). The silicate layers of PLLA/PBSA/TFC were exfoliated to a larger extent than PLLA/PBSA/C25A. Incorporation of the epoxy groups on C25A improved significantly elongation at break as well as tensile modulus and tensile strength of PLLA/PBSA/C25A. The larger amount of exfoliation of the silicate layers in PLLA/PBSA/TFC as compared with that in PLLA/PBSA/C25A was attributed to the increased interfacial interaction between the polyesters and the clay due to chemical reaction. Thermo gravimetric analysis revealed that both T5%, which was the temperature corresponding to 5% weight loss, and activation energy of thermal decomposition of PLLA/PBSA/TFC were far superior to those of PLLA/PBSA/C25A as well as to those of PLLA/PBSA, indicating that the composites with exfoliated silicate layers were more thermally stable than those with intercalated silicate layers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 478–487, 2005 相似文献
996.
The mechanical properties, i.e., Young's modulus, elongation, and tensile stress, were determined as functions of the molecular weight for films of poly(oxydi-p-phenylene pyromellitimide) prepared by thermal cyclization of the precursor poly(amic acid). The molecular weights of the samples were controlled by the monomer stoichiometry employed for the solution condensation of pyromellitic dianhydride and p,p′-oxydianiline. Weight-average molecular weights were determined by light scattering of the precursor poly(amic acid) as well as the fully cyclized polyimide. The elongation-at-break is most sensitive to the molecular weight, undergoing a rapid increase at M w ? 8000 and reaching a limiting value of about 60% for M w > 20,000. 相似文献
997.
Ki-Min Park Il Yoon Shim Sung Lee Green Choi Jeong Sook Lee 《Analytical sciences》2003,19(8):1219-1220
Crystals of C.I. Disperse Blue 354, a commercial methine disperse dye, were grown from an ethyl acetate and the crystal structure was determined. Results show that two aromatic planes are effectively coplanar with the dihedral angle of 10.61(11) degrees. The dicyanomethylene group is slightly twisted and two n-hexyl groups tend to be separated with one alkyl group being at the level of the aromatic plane, and another one below it. The intermolecular hydrogen bonds and the interlayer pi-pi stacking stabilize the crystal packing. 相似文献
998.
A model has been developed to provide a comprehensive simulation of a spray formed by a high‐speed liquid jet. The primary atomization process is simulated in a completely nonlinear fashion using the boundary element method under the assumption of axisymmetric, inviscid flow. The presence of the orifice boundary layer is simulated with a ring vortex whose strength and location are uniquely determined from boundary layer properties at the orifice exit plane. Droplet and axisymmetric ligament tracking models have been developed to provide more comprehensive spray simulations. The breakup of the axisymmetric ligaments shed from the parent surface is assessed both in a nonlinear fashion as well as using the linear stability analysis of Ponstein. Using this latter approach, drop size distributions have been generated from first principles and compared with the popular Rosin–Rammler model. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
999.
Roe Hoan Yoon Talat Salman Gabrielle Donnay 《Journal of colloid and interface science》1979,70(3):483-493
Pauling's electrostatic valence principle has been applied to describe the surface-charging mechanism of oxides in an aqueous environment. This approach has led to the development of an equation with which one can predict the points of zero charge (PZC) of oxides and hydroxides from crystallographic data. The equation proposed in the present work is an improved version of Parks' PZC equation. The improvements are the following: (i) The equation does not incorporate correction terms to take the cation coordination numbers into account; (ii) the PZC of a complex oxide can be predicted directly from crystallographic data instead of from “assumed” PZCs of its component oxides; and (iii) one can use the mean metal-oxygen bond distance of a crystal instead of the ionic radii tabulated by Parks, which are not consistent with the up-to-date values. 相似文献
1000.
Do Yeung Yoon Catherina Chang Richard S. Stein 《Journal of Polymer Science.Polymer Physics》1974,12(10):2091-2110
A model is proposed to account for the orientation of crystals in spherulites upon deforming a polymer. The model assumes affine deformation of the spherulite accompanied by three processes of crystal reorientation within the spherulite. These are tilting of molecular chains with respect to the plane of the lamellae, characterized by a parameter K, twisting of the lamallae about the spherulite radii described by η, and rotation of the b crystal axis about the c axis characterized by a third parameter, P. Values of these parameters are fitted to measured orientation functions and compared with experimental measurements of the azimuthal variation of the intensities of the 110 and 200 crystal reflections from low-density polyethylene. Good agreement is found between the experimental and theoretically predicted intensity variation. Time-dependent experiments under relaxational and vibrational conditions are also treated by the theory. 相似文献