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591.
在高功率光纤放大器实验中,时常发现增益光纤抽运注入熔接点后10—50 cm处容易发生光纤烧毁现象.为了对该现象进行理论预测,基于光纤激光器速率方程模型和增益光纤的热传导模型,从种子功率、抽运功率和抽运吸收三个方面对掺镱双包层光纤放大器中的放大自发辐射(ASE)和温度特性进行研究.结果表明,在放大倍率较高、ASE较为严重等情况下,光纤放大器中的最高温度点一般不在抽运注入的熔接点处,而在距离熔接点10—50 cm处,与实验中发现光纤烧毁的位置基本符合.从光纤放大器的ASE抑制、最高温度点温度控制角度出发,对光纤放大器在种子功率、抽运功率、抽运吸收、放大倍率和抽运波长等方面的设计给出了指导性的建议. 相似文献
592.
First-principles calculations were performed to investigate the magnetic properties of Zn(Mn,Li)O based on the Perdew-Burke-Ernzerhof form of generalized gradient approximation. Antiferromagnetic (AFM) ordering is the ground state in Mn-doped ZnO system without the codopant of Li, while seven different geometrical configurations of Zn(Mn,Li)O prefer stable ferromagnetic (FM) ordering. We found that dopant Li can effectively change the magnetic coupling in the ZnMnO system. The Curie temperature (TC) of FM ordering depends on the geometric configuration, and the highest TC is about 1388 K. The FM stabilization is greatly affected by Mn-Mn distance rather than by the position of dopant Li. We propose that dopant Li mediates FM coupling through a double exchange interaction or an RKKY interaction when Li is located, respectively, near or far from Mn ions. 相似文献
593.
从3个方面阐述了利用"化学信息检索"课程培养学生自主学习能力的做法和体会,包括培养学生自主总结信息检索方法,培养学生利用信息检索自主学习专业课程以及自主培养科研能力。 相似文献
594.
A novel synthetic approach for the preparation of arylacetic acids via the reaction of aldehydes, N-(2,3,4,6-tetra-O-pivaloylated-d-glucopyranosyl)amine and trimethylsilylcyanide was developed, in which the N-(2,3,4,6-tetra-O-pivaloylated-d-glucopyranosyl)amine can be recycled conveniently and reused efficiently. 相似文献
595.
With the insertion of SiO(2) nanoparticles in the oxide layer, near-lasing actions such as threshold behavior and resonance modes are observed at the Si bandgap energy of metal-oxide-silicon (MOS) structure. The threshold current is ~12 mA . The SiO(2) nanoparticles cause simultaneous localization of electrons and holes to enhance phonon-assisted radiative recombination. Electroluminescence at Si bandgap energy is increased to orders of magnitude larger than in similar MOS structures without SiO(2) nanoparticles. The efficient light emission at the Si bandgap energy indicates that a direct bandgap nature is not necessarily the basic requirement for radiative recombination. 相似文献
596.
[reaction: see text]. A novel fluorescent chemosensor (compound 1) containing aminonaphthol, which selectively recognizes fluoride anion with high sensitivity, was synthesized. The fluorescence of compound 1 was quenched rapidly by fluoride ion, and a new peak at a longer wavelength emerged concurrently, which constituted the signature for fluoride detection. The mechanism of exciplex formation was proposed for the interesting observation. 相似文献
597.
Entanglement of a two-qubit anisotropic Heisenberg XYZ chain in nonuniform magnetic fields with intrinsic decoherence 总被引:1,自引:0,他引:1
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Taking the intrinsic decoherence effect into account, this paper investigates the entanglement of a two-qubit anisotropic Heisenberg XYZ model in the presence of nonuniform external magnetic fields by employing the concurrence as entanglement measure. It is found that both the intrinsic decoherence and the anisotropy of the system give a significant suppression to the entanglement. Moreover it finds that the initial state of the system plays an important role in the time evolution of the entanglement, which means that the entanglement of the system is independent of the nonuniformity and uniformity of the magnetic field when the system is in the initial state |ψ (0)) = |00) and [ψ′ (0)) = m |01) + n |10), respectively. 相似文献
598.
599.
AbstractOne new coumarin, muralatin R, was isolated from the leaves of Murraya alata Drake (Rutaceae). Its structure was elucidated by extensive analysis of the NMR and MS data, along with the specific rotation comparison. Muralatin R was found to be capable of activating the transient receptor potential vanilloid 1 (TRPV1) channel through desensitization mechanism. The results supply reference for clarification of the therapeutic basis and mechanism of action of Murraya plants for treating psychogenic pain or somatoform pain disorders. 相似文献
600.
AbstractA novel aromatic compound, grandiuvarone B (5-acetoxy-3-benzoyloxymethyl-5H-oxepin-4-one), along with a known compound grandiuvarone A (5-acetoxy-6-benzoyloxymethyl-5H-oxepin-4-one) were isolated from methanol extracts of Desmos chinensis leaves. Their structures were determined by various spectroscopic techniques including nuclear magnetic resonance (NMR), high-resolution electrospray ionisation mass spectrometry (HR-ESI-MS) and circular dichroism (CD). Grandiuvarone A and grandiuvarone B are isomers and the S configuration of grandiuvarone B was reported for the first time. We then determined their antifungal activity against Aspergillus flavus. Results revealed that grandiuvarone B exhibited better antifungal activity against A. flavus, with MIC values of 0.01?mg/mL compared to grandiuvarone A (MIC values of 0.02?mg/mL). In the presence of each active compound at 160?μg/g of aquafeed, A. flavus growth was completely inhibited. Grandiuvarone B also showed antibacterial activity against the plant pathogen Ralstonia solanacearum. 相似文献