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• An arc segmentation algorithm is proposed. • An arc feature extraction method including four feature quantities is proposed. • The feature quantities can serve as critical criteria of arc development stages. Insulator flashover seriously affects the safe operation of power grid. To improve the arc development mechanism and achieve flashover warning, this paper researches the arc evolution characteristics during direct current (DC) flashover process of composite insulator using visible discharge images. Firstly, an arc segmentation algorithm based on edge brightness and local threshold is proposed. It aims to solve the problems of uneven arc brightness, insulator reflection and arc halos in visible discharge images. Then, to quantify segmented arcs, an arc feature extraction method with four feature quantities of arc width, projected length, offset distance and centroid ordinate is proposed. Finally, this paper also extracts and studies the variation characteristics of the four feature quantities in two types of DC flashover processes respectively. The result shows that the proposed feature quantities effectively describe the arc state. Additionally, the arc width change rate k exceeding 1.3 k max , the insulation failure percentage reaching 75%, and the arc offset distance reaching the set threshold can serve as the critical criteria for arc development stages, dividing the two types of DC flashover processes into three stages. Building upon the critical criteria, it is expected to achieve flashover warning. [ABSTRACT FROM AUTHOR]

3–5, 8–14 μm mid-far infrared (MF-IR) coherent lights generated by nonlinear optical (NLO) crystals are crucial for many industrial and military applications. AgGaGe5Se12 (AGGSe) is a promising NLO candidate because of its good optical performance. In this paper, the large AGGSe single crystal of 35 mm diameter and 80 mm length was obtained by the seed-aided Bridgman method. The crystalline quality was characterized with X-ray diffraction, rocking curve, transmission spectrum. The FWHM of the (210) peak was about 0.05° and the IR transmission was about 60% (1–10 μm, 6 mm thick). Additionally, it performed well in 8 μm frequency doubling, with a maximum output power of about 41 mW, corresponding to an optical-to-optical conversion efficiency of 3.2%. The laser induced damage threshold (LIDT) value was about 200 MW/cm2 (1.06 μm, 20 ns, 1 Hz). [ABSTRACT FROM AUTHOR]

A mid-infrared BaGa 4 Se 7 optical parametric oscillator with high conversion efficiency and beam quality is demonstrated, which is pumped by a 2.79-μm electro-optically Q-switched Cr, Er:YSGG laser. A pulse energy of 3.5 mJ with a pulse width of 21 ns at 10 Hz is obtained in the range of 3.94-9.55 μm, and the beam quality factors are measured to be Mx2=5.0 and My2=4.6. The optical-to-optical conversion efficiency is 18.9%, and the slope efficiency is 31.6%, which is a 59% improvement on the best of the previously reported slope efficiencies for BaGa 4 Se 7 -based OPOs.

Recently developed chalcogenides nonlinear optical crystals have potential application in mid- to far-infrared laser fields. However, high-quality single crystals are hard to be prepared because of high vapor pressure of sulfur component and decomposition of chalcogenides during the polycrystalline synthesis and single-crystal growth. A pressure-assisted technique was performed to prepare stoichiometric AgGaS 2 and AgGaGeS 4 polycrystalline materials. On the basis of the synthesized polycrystalline materials, high-quality AgGaS 2 and AgGaGeS 4 single crystals were successfully obtained using the seed directional Bridgman method with a well-designed crucible-capsule technique. These single crystals possess high homogeneity and low absorption coefficient, making it can be applied in nonlinear optical experiments. The pressure-assisted method can also be suitable to prepare other chalcogenide and phosphide compounds. The method of polycrystalline synthesis and single crystals growth described in this work will be helpful for preparing other chalcogenides nonlinear optical crystals.

Objective: To study the relationships between polymorphisms of angiotensin-converting enzyme 1 (ACE-1) gene and N(5),N(10) -methylene-tetra-hydrofolic acid reductase (MTHFR) gene and ischemic stroke (IS)., Methods: The polymorphisms of ACE-1 and MTHFR genes in the peripheral white blood cells of 143 patients with IS and 154 controls were analyzed using PCR- RFLP., Results: The frequencies of II, ID, and DD genotypes of ACE-1 gene were 37.1%, 48.3%, and 14.7% respectively in IS patients,and were 44.2%, 37.7%, and 18.2% respectively in the controls. The relative risk of stroke in IS group was 1.2 times that in the control group. The frequencies of TT, CT, and CC genotypes of MTHFR gene were 14.0%; 45.5%, and 40.5% respectively in the IS group, and 5.2%, 31.8%, and 63.0% respectively in the control group. The frequency of TT genotype was 5.2% in the control group and 1.4% in the IS group (P < 0.05). The frequency of T allele was 21.10% in the control group and 36.65% in the IS group (P < 0.01). The individuals with TT + ID or CT + ID were more susceptible to IS. The individuals with TT + ID were 4.3 times susceptible to IS than the controls, and the individuals with CT + ID were 1.63 times susceptible to IS than the controls. However, the individuals with CC + ID were less susceptable to IS in comparison to the controls (P = 0.003)., Conclusion: TT and CT genotypes of MTHFR gene may be the risk factors of IS. There is a co-effective action between polymorphisms of ACE-1 gene and those of MTHFR gene in the pathogenesis of IS. CC genotype may have a protective effect against IS.