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521.
真空度被认为是影响GaAs阴极寿命的最重要参数之一,电子束在阴极附近的壁损失会导致真空度下降。基于高斯分布模型,研究了中国工程物理研究院自由电子激光相干强太赫兹源(FEL-THz)直流光阴极注入器电子束在束线管壁上的损失情况。通过理论分析、数值计算、束流动力学模拟、热力学分析及电子束初步出束实验研究,证明了FEL-THz电子束壁损失能达到W量级,必然引起真空度下降和阴极寿命缩短,这是目前限制出束的重要原因之一。研究表明,为维持电子束持续稳定工作,应将注入器阳极后的管道尺寸扩大到至少45mm。 相似文献
522.
In Zhao et al. (Electron J Combin 19: \({\sharp}\) P19, 2012), we determined the minimum number of vertices of one-realizations of a given finite set S, and constructed the corresponding mixed hypergraphs. In this paper, by finding some of their spanning sub-hypergraphs, we determine the minimum number of \({\mathcal{D}}\) -deges (resp. \({\mathcal{C}}\) -edges) of one-realizations of S. As a result, we partially solve an open problem proposed by Tuza and Voloshin (Bolyai Society Mathematical Studies, vol. 17, pp. 235–255. Springer, Berlin, 2008). 相似文献
523.
Xin Zhang Weifeng Diao Yuan Liu Jiqiao Liu Xia Hou Weibiao Chen 《Applied physics. B, Lasers and optics》2014,115(1):123-127
An all-fiber, single-frequency, linearly polarized, high peak-power, pulsed laser at 1,540 nm for Doppler wind lidar is presented. This laser is composed of a single-frequency, narrow-linewidth external cavity diode laser, and multistage fiber amplifiers. A peak power of 1.08 kW and a pulse width of 500 ns at 10 kHz repetition rate are achieved, which is the highest peak power with a linewidth of 800 kHz in erbium-doped silica fiber to our knowledge. The beam quality of M 2 < 1.3 and a polarization extinction ratio over 16 dB are obtained. This laser will be employed in a compact long-range coherent Doppler wind lidar. 相似文献
524.
实验中首先通过增大四极磁场梯度、提高背景真空度、缩小冷却俘获激光光束直径的方法获得了磁光阱中单原子的装载.其次,通过减小冷却光失谐量、适当增加其光强、同时使用偏振光谱锁频技术抑制冷却光噪声的方法得到了磁光阱中高信号背景比的单原子荧光信号.此外,通过实时反馈控制磁光阱四极磁场梯度的方法,在实验中实现了单原子98%的装载概率.使用Hamburg Brown-Twiss方案测量了磁光阱中的单原子在连续光激发下所辐射荧光的光子统计特性,得到二阶关联度g(2)(τ=0)=0.09. 相似文献
525.
Tingting Guo Guobo Dong Qiang Chen Xungang Diao Fangyuan Gao 《Journal of Physics and Chemistry of Solids》2014
Based on first-principles calculations, (Sb, N) codoped ZnO are investigated. We find that SbZn–4NO have lower formation energy and can form p-type conduction with smaller hole effective mass. In comparation to monodoping of Sb, SbZn–4NO complex can form better p-type conductivity than SbZn–2VZn, which may be strongly compensated by SbZn defect and result in a decrease of p-type conduction. So we inferred that (Sb, N) codoping in ZnO under O-poor condition should be a realizable candidate of p-type conduction. 相似文献
526.
In this paper, we propose an ultra narrow band fiber grating filter which is composed of two optical circulators and two fiber Bragg gratings (FBG). Through numerical simulation and experiment investigation, a narrow-band output spectrum with 1064 nm center wavelength and 0.017 nm bandwidth is obtained. It may find a certain application in the fields of free space optic communication, laser tuning and so on as we believe. 相似文献
527.
Aluminum doped zinc oxide (ZAO) films were deposited by direct current (DC) reactive magnetron sputtering from a ZnO:Al2O3 (3 wt.% Al2O3) ceramic target at room temperature. In order to explore the inhomogeneous property distribution across the substrate, the films were deposited with varied substrate-target distances (Ds) ranging from 2 cm to 9 cm. The experimental results obtained from four-point probe, spectrophotometer, scanning electron microscope, X-ray diffractometer and Auger electronic spectrometer were analyzed to explore the nonuniform property distribution of the obtained ZAO films. The results confirmed that the films’ optoelectronic properties, crystallinity and surface morphology, etc., which were obtained from different substrate areas facing the target were remarkably different. It was revealed that the inhomogeneous property distribution was noticeably dependent on the Ds. It was also suggested that the great difference of electrical conductivity among films from different substrate areas could not be ascribed to the difference of chemical composition, but might be explained by the distinctive crystallinity correspondingly. Films from different substrate regions with distinctive electrical characteristics were either (0 0 2) or (1 1 0) textured. 相似文献
528.
Chunsrivirot S Diao Y Trout BL 《Langmuir : the ACS journal of surfaces and colloids》2011,27(20):12381-12395
Crystallization is commonly used in a separation and purification process in the production of a wide range of materials in various industries. In industry, crystallization usually starts with heterogeneous nucleation on a foreign surface. The complicated mechanism of heterogeneous nucleation is not well understood; however, we hypothesize that there might be a possible correlation between binding affinity to a surface and enhancement of nucleation. Recent studies show that amorphous polymers can be used to control crystallization, selectively produce pharmaceutical polymorphs, and discover novel pharmaceutical polymorphs. To investigate the possible correlation between the binding affinity of one molecule to key binding sites (local binding) and heterogeneous nucleation activity as well as the possibility of using this binding affinity to help guide the selection of polymers that promote heterogeneous nucleation, we computed the free energy of binding of aspirin to four nonporous cross-linked polymers in an ethanol-water 38 v% mixture. These cross-linked polymers are poly(4-acryloylmorpholine) (PAM), poly(2-carboxyethyl acrylate) (PCEA), poly(4-hydroxylbutyl acrylate) (PHBA), and polystyrene (PS); all of them were cross-linked with divinylbenzene (DVB). These systems were used because their heterogeneous nucleation activities are available in literature, and the ranking is PAM > PCEA > PHBA ≈ PS. We generated three independent surfaces for each polymer and computed the free energy of binding of aspirin to the best binding site that we found on each surface. The average free energies of binding to the best sites of PAM, PCEA, PHBA, and PS are -20.4 ± 1.0, -16.7 ± 1.0, -14.4 ± 1.1, and -13.6 ± 1.1 kcal/mol, respectively. We found that the trend of the magnitudes of the average free energies of binding to the best sites is PAM > PCEA > PHBA ≈ PS. This trend is very similar to that of heterogeneous nucleation activity. Our results suggest the importance of the free energy of binding to key sites (local binding) and the possibility of using this quantity to help guide the selection of polymers that promote heterogeneous nucleation. 相似文献
529.
Dong Hong Li Jun Lin Diao Ke Gui Yu Cheng He Zhou 《中国化学快报》2007,18(11):1331-1334
In view of the property of porphyrin's accumulation selectively in tumor,the ftorafur was modified by binding a porphyrin block to improve its tumor targeting and reduce its side effects.These novel porphyrin derivatives and metal compounds were synthesized under mild conditions with satisfactory yield,and the constructions of all these new compounds were characterized by UV,IR,MS, ~1H NMR spectra and elementary analysis.Their anticancer activities were evaluated by MTT assay;the results indicated that the anticancer activities of compounds 4a-c were twice as high as that of ftorafur. 相似文献
530.
A simple and sensitive chemiluminescence method was developed for the determination of fenfluramine. The chemiluminescence signal arising from the reaction between alkaline luminol and N‐bromosuccinimide was found to be greatly enhanced by fenfluramine in the presence of gold nanoparticles. But fenfluramine alone slightly inhibited the CL signal of N‐bromosuccinimide‐luminol in the absence of gold nanoparticles. The experimental parameters that affected the chemiluminescence signal were thoroughly investigated. Under the optimum experimental conditions, the enhanced chemiluminescence intensity was proportional to the concentration of fenfluramine in the range of 0.005‐1.0 mg/L. The detection limit was 0.9 μg/L fenfluramine with a relative standard deviation of 2.5% for 0.1 mg/L fenfluramine solution (n = 11). The method was applied to the determination of fenfluramine in some weight‐reducing tonics and in spiked human urine. A possible CL reaction mechanism was proposed. 相似文献