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31.
An effective method for achieving a room-temperature multiwavelength erbium-doped fiber ring laser is presented. Simultaneous multiwavelength lasing with 0.5-nm intervals is achieved both experimentally and theoretically by addition of sinusoidal phase modulation in the ring cavity to prevent single-wavelength oscillation. 相似文献
32.
Nam Quoc Ngo Rui Tao Zheng Ng J.H. Tjin S.C. Binh L.N. 《Lightwave Technology, Journal of》2007,25(3):799-802
A new hybrid optimization algorithm is proposed for the design of a fiber Bragg grating (FBG) with complex characteristics. The hybrid algorithm is a two-tier search that employs a global optimization algorithm (i.e., the staged continuous tabu search (SCTS) algorithm) and a local optimization method (i.e., the quasi-Newton method). First, the SCTS global optimization algorithm is used to find a "promising" FBG structure that has a spectral response as close as possible to the targeted spectral response. Then, a local optimization method, namely, the quasi- Newton method, is applied to further optimize the promising FBG structure obtained from the SCTS algorithm to arrive at a targeted spectral response. To demonstrate the effectiveness of the method, the design and fabrication of an optical bandpass filter are presented. 相似文献
33.
We study the nature of the smectic–isotropic phase transition using a mobile 6-state Potts model. Each Potts state represents a molecular orientation. We show that with the choice of an appropriate microscopic Hamiltonian describing the interaction between individual molecules modeled by a mobile 6-state Potts spins, we observe the smectic phase dynamically formed when we cool the molecules from the isotropic phase to low temperatures (T). In order to elucidate the order of the transition and the low-T properties, we use the high-performance Wang–Landau flat energy-histogram technique. We show that the smectic phase goes to the liquid (isotropic) phase by melting/evaporating layer by layer starting from the film surface with increasing T. At a higher T, the whole remaining layers become orientationally disordered. The melting of each layer is characterized by a peak of the specific heat. Such a succession of partial transitions cannot be seen by the Metropolis algorithm. The successive layer meltings/evaporations at low T are found to have a first-order character by examining the energy histogram. These results are in agreement with experiments performed on some smectic liquid crystals. 相似文献
34.
A novel dynamic survivable routing in WDM optical networks with/without sparse wavelength conversion
Vinh Trong Le Xiaohong Jiang Son Hong Ngo Susumu Horiguchi Yasushi Inoguchi 《Optical Switching and Networking》2006,3(3-4):173-190
In this paper, we study the dynamic survivable routing problem, both in optical networks without wavelength conversion and in optical networks with sparse wavelength conversion, and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and genetic algorithms (GA). By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously report cycles (that are formed by two disjoint-link routes) into the routing tables, our new hybrid algorithm can promptly determine the first population of cycles for a new request based on the routing table of its source node, without the time consuming process associated with current GA-based lightpath protection schemes. We further improve the performance of our algorithm by introducing a more advanced fitness function that is suitable for both the above networks. Extensive simulation studies on the ns-2 network simulator show that our hybrid algorithm achieves a significantly lower blocking probability than the conventional survivable routing algorithms for all the cases we studied. 相似文献
35.
An oxacalix[2]arene[2]pyrimidine-bis(ZnII-porphyrin) conjugate was readily prepared via nucleophilic aromatic substitution of a phenolic AB3-Zn-porphyrin on the upper rim of a (1,3-alternate) 5,17-bis(methylsulfonyl)oxacalix[4]arene precursor. Efficient 1:1 complex formation between the ‘jaws’ bisporphyrin tweezer and fullerene C70 was evidenced by 1H NMR titrations (K = 3.0 × 104 M−1), while no detectable complexation could be observed with C60. On the other hand, an analogous oxacalix[4]arene-bis(Cu-corrole) conjugate did not show any measurable (C60 or C70) fullerene binding. 相似文献
36.
Helen L. Ngo 《Tetrahedron letters》2005,46(4):595-597
Polar bisphosphonic acid-derived Ru(BINAP)(DPEN)Cl2 precatalysts were synthesized and immobilized in room temperature ionic liquids (RTILs) for asymmetric hydrogenation of aromatic ketones with ee values of up to 98.7%. The performance of the Ru catalysts is highly dependent on the nature of imidazolium ILs. For the imidazolium ILs without acidic protons, both ILs and Ru catalysts were recycled by simple extraction and reused. Such a simple immobilization approach also prevented the leaching of Ru (and Ru catalysts) into the chiral secondary alcohol products, and should prove desirable for the production of pharmaceutical intermediates that are free from metal contaminants. 相似文献
37.
Ngoc Binh Vo Le Anh Nguyen Tung Lam Pham Duy Tien Doan Thanh Binh Nguyen Quoc Anh Ngo 《Tetrahedron letters》2017,58(25):2503-2506
A procedure to exclusively obtain 3′S-cyanoanhydrovinblastine 12 from two naturally occurring vinca-alkaloids (catharanthine and vindoline) in one step with good yield is described. Stereoselective reductions of 12, providing straightforward access to three new vinca-alkaloids, including two diastereomers 3′S-cyano-(4′R,5′-dihydro)-anhydrovinblastine and 3′S-cyano-(4′S,5′-dihydro)-anhydrovinblastine as well as (3′S-aminomethyl)-(4′S,5′-dihydro)-anhydrovinblastine in good yields is also reported. 相似文献
38.
39.
We propose and experimentally demonstrate a novel switchable and discretely tunable comb filter based on a thermally induced linearly chirped fiber Bragg grating. Experimentally we achieved a thermally induced optical bandpass filter that has eight switchable passband peaks with peak separations of 1.6 and 3.2 nm, a very narrow bandwidth (as small as 10 pm) of each peak, a tunable range of 16.5 nm, and a greater than 25 dB rejection ratio. Two spectral peaks separated by only 0.8 nm were also obtained with this comb filter. This filter provides the unique advantages of an all-fiber structure, switchable spectral peaks, independent tuning of the center wavelength and wavelength spacing of the spectral peaks, low polarization sensitivity, simple structure, ease of fabrication, and low cost. 相似文献
40.
Melinda Fekete Pál Kolonits Ngo Thi Hien Lajos Novák 《Central European Journal of Chemistry》2005,3(4):792-802
New tryptamine 5, 7 and β-carboline derivatives 3 were preparated by palladium-catalyzed coupling reaction of 5-bromotryptamine 1 with aryl boronic acids.
Dedicated to Professor András Lipták on his 70th birthday. 相似文献