A theoretical scheme of a new device consisting of a lensed fiber and a long period grating (LPG) imprinted in a special single mode gradient-index fiber (SSMGIF) is presented. The SSMGIF consists of the single mode uniform core and the graded-index cladding. The performance of the proposed device is based on specific properties of SSMGIF. For high efficiency coupling between number of cladding modes and co-propagating core mode in this special type of the fiber we can use a number of weak LPGs with the same amplitudes of the refractive index modulation and with almost the same lengths. This scheme provides higher coupling efficiency, relaxed longitudinal alignment tolerance, and smaller device size, than an identical scheme with the LPG imprinted in a step-index (SI) fiber. Two different types of fiber lenses (hemispherical and hyperbolic) are presented for comparison. 相似文献
Photoresponsive gold nanoparticle networks were prepared by functionalizing them with azobenzene derivatives. A network can be formed when a linker molecule constituting the azobenzene moiety suitably derivatized on either side with gold surface sensitive groups such as thiols and amines is added to the nanoparticle solution. It is shown that the interparticle spacing in the networks could be controlled by the reversible trans-cis isomerization of the azobenzene moiety induced by UV and visible light, respectively. The photoinduced variation in the interparticle spacings is inferred by the changes in the optical spectra of the gold nanoparticles which display a red or blue shift in the surface plasmon resonance peak depending on a decrease or increase in the interparticle spacing, respectively. Transmission electron microscopy images are in consonance with the evidence from the optical spectra. 相似文献
The 2,4-dichlorophenoxy acetic acid (2,4-D) is used as a systemic herbicide to control broadleaf weeds in wheat, corn, range land/pasture land, sorghum, and barley. In this study, a fast and efficient method is developed by selection of modified extraction apparatus and high-performance liquid chromatography (HPLC)-UV conditions for the determination of 2,4-D in soil samples. The method is applied to the study of soil samples collected from the agricultural field. The herbicide is extracted from soil samples by acetonitrile in a modified Soxhlet apparatus. The advantages of the apparatus are that it uses small volume of organic solvent, reduced time of extraction, and better recovery of the analyte. The extract is filtered using a very fine microfiber paper. The total extract is concentrated in a rotatory evaporator, dried under ultrahigh pure N2, and finally reconstituted in 1 mL of acetonitrile. HPLC-UV at 228 nm is used for analysis. The herbicide is identified and quantitated using the HPLC system. The method is validated by the analysis of spiked soil samples. Recoveries obtained varied from 85% to 100% for spiked soil samples. The limit of quantitation (LOQ) and the limit of detection (LOD) are 0.010 and 0.005 parts per million (ppm), respectively, for spiked soil samples. The LOQ and LOD are 0.006 and 0.003 ppm for unspiked soil samples. The measured concentrations of 2,4-D in spiked soil samples are between 0.010 and 0.020 ppm with an average of 0.016 +/- 0.003 ppm. For unspiked soil samples it is between 0.006 ppm and 0.012 ppm with an average of 0.009 +/- 0.002 ppm. The measured concentrations of 2,4-D in soil samples are generally low and do not exceed the regulatory agencies guidelines. 相似文献
The stereoselective synthesis of 2,3-unsaturated α-d-glucosides by the SN2′ addition of diverse aglycones onto 4,6-di-O-benzyl-3-O-propargyl glucal was achieved using a catalytic quantity of AuCl3. The Au catalyzed reaction was explored using various aliphatic, aromatic, alicyclic and monosaccharide aglycones. The current protocol tolerates diverse functional groups and is highly stereoselective, fast, catalytic and mild. 相似文献
The reaction of CuCl2·2H2O with 3,5-diisopropylpyrazole (PziPr2H) in the presence of sodium parafluorobenzoate (Na-p-FBz) resulted in the formation of an oxo-chloro-bridged tetranuclear complex [Cu4(PziPr2H)4(μ-O)(μ-Cl)6] 1, whereas the reaction of Cu(NO3)2·3H2O with PziPr2H in the presence of different benzoates gave [Cu(PziPr2H)2(μ-OCH3)]2(NO3)22, [Cu(PziPr2H)3(NO3)(p-ClBz)]·CH3CN 3, [Cu(p-CH3Bz)2(PziPr2H)]2·2CH3CN 4, [Cu(p-OCH3Bz)2(CH3CN)]2·4CH3CN 5 and [Cu(p-CNBz)(CH3CN)]26. Single-crystal X-ray diffraction studies confirmed these formulations. DNA binding studies for these complexes were performed by means of UV-visible absorption titration and viscosity measurements. Gel electrophoresis studies showed that hydroxyl radicals are involved in DNA cleavage in the presence of the complexes. 相似文献
Esaxerenone is a new nonsteroidal mineralocorticoid receptor antagonist utilized to treat high blood pressure. Chemically, esaxerenone is a pyrrole derivative consisting of hindered rotation, which results in stereoisomers named atropisomers. Currently, no methods exist for the separation and quantification of these atropisomers. A new and accurate chiral liquid chromatographic technique was developed and validated to estimate the enantiomeric purity of esaxerenone. Polar organic chiral separation was carried out on an immobilized amylose-based chiral stationary phase (Chiralpak IG) with methanol:acetonitrile:diethylamine (9:1:0.1, v/v/v) mixture as a mobile phase. The total runtime was 15 min, and the resolution (Rs) between the atropisomers was more than 3.0. The detection and quantification thresholds for the R-atropisomer were found to be 0.03 and 0.1 µg mL?1, respectively, for a test concentration of esaxerenone (1000 µg mL?1). Over the range from the limit of quantification to 0.3 percent, the method's linearity for the R-atropisomer was excellent (R2?>?0.999). The R-atropisomer recovery varied from 95 to 102%, confirming the method’s good accuracy. For a 48-h research period, the chemical was shown to be stable.