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排序方式: 共有575条查询结果,搜索用时 15 毫秒
1.
2.
Bending of optical fiber leads to an induced-anisotropy in the index profile that influences many important guiding fiber parameters. An analytical method is described for the measurement of refractive-index-wavelength dispersion in bent optical fibers. Multiple-beam Fizeau fringes technique at transmission is used to analyze the opto-mechanical properties and induced-index anisotropy in a standard single-mode fiber undergoes pure mechanical macrobending. The shift in Fizeau fringes is employed to evaluate the dispersion of the cladding material of the bent fiber. The radial variations in Cauchy’s coefficients and the associated variations of some fiber parameters due to macrobending are carried out. The radial profiles of some material parameters such as oscillation energy, dispersion energy, lattice energy and material dispersion are measured as well. The presented method is capable to achieve quantitative and qualitative measurements, which is not available with other methods. The method has a good index resolution in the order of 10−4 and spatial resolution of 1.3 μm. 相似文献
3.
Mohamed Hilmy Elnagdi Ramadan Maawad Abdel-Motaleb Mona Mustafa Mohamed Foad Zayed Eman Moustafa Kamel 《Journal of heterocyclic chemistry》1987,24(6):1677-1681
The behaviour of several 2-amino-3-cyano-4H-pyran derivatives toward a variety of nucleophilic reagents is reported. 相似文献
4.
A. Mahoui J. Lapasset D. G. Sannikov J. Moret P. Saint Grégoire 《Zeitschrift für Physik B Condensed Matter》1995,99(4):543-549
The crystal structure [(C2H5)4N]2CuCl4 has been determined by X-ray diffraction at 243K. The room temperature phase (phase I) belongs to the space group P42/nm [1] whereas the low temperature phase (phase II) is orthorhombic and belongs to the space group Pnna. The phase transition at Tc=258K is of improper ferroelastic type and it is associated with the ordering of the CuCl4 2? and a partial ordering of the [(C2H5)4N]+ ions which are disordered in the high temperature tetragonal phase. At lower temperature, there occurs another instability which could correspond to a complete ordering in the crystal. 相似文献
5.
L. Raimondo M. Campione M. Moret P. Spearman S. Tavazzi 《Applied Surface Science》2006,253(1):271-274
We propose optical absorption technique at oblique incidence as one of the spectroscopic tools that allow experimentally recognizing the macroscopic order and structural features of molecular solids of conjugated molecules, from single crystals to polycrystalline or twinned samples. We apply this spectroscopy to quaterthiophene as representative of a wide class of materials that usually possess optical transitions of Frenkel exciton origin with strong directional dispersion. The comparison between experimental and simulated data gives evidence of the high sensitivity of this technique for determining quantitatively the polycrystallinity of the measured samples, whose domains may show mirror-like orientation of the unit cell with respect to one of its faces.Frenkel exciton; Oligothiophene, Optical properties 相似文献
6.
Abdel -Aziz M. Wahbi Mona M. Bedair Shereen M. Galal Mohamed H. Abdel-Hay Azza A. Gazy 《Mikrochimica acta》1993,111(1-3):83-91
A sensitive and rapid Spectrofluorimetric method for the determination of guanethidine sulphate, guanfacine hydrochloride, guanoclor sulphate and guanoxan sulphate in tablets and spiked human serum and urine samples is described. The method is based on the reaction of monosubstituted guanidino compounds in an aqueous potassium hydroxide solution with benzoin, in the presence of -mercaptoethanol and sodium sulphite. Highly fluorescent derivatives were obtained, with excitation and emission maximum wavelengths around 325 and 430 nm, respectively. In optimal reaction conditions, the linearity ranges were 0.04–0.28 g/ml, with relative standard deviations less than 2%. The method has been successfully applied to the determination of these drugs in tablets. The results are highly correlated with the B.P. method. Chloroform (or for guanoxan dichloromethane) was used to extract the drugs from serum and urine at basic pH, followed by the proposed fluorimetric method. The limit of detection is 0.02 g/ml for the selected drugs. 相似文献
7.
8.
Dr. Pradip Ghosh Sander de Vos Dr. Martin Lutz Dr. Frederic Gloaguen Prof. Dr. Philippe Schollhammer Dr. Marc-Etienne Moret Prof. Dr. Robertus J. M. Klein Gebbink 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(55):12560-12569
Homogeneous electrocatalytic proton reduction is reported using cobalt complex [ 1 ](BF4)2. This complex comprises two bis(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methane (HBMIM ) ligands that contain an acidic methylene moiety in their backbone. Upon reduction of [ 1 ](BF4)2 by either electrochemical or chemical means, one of its HBMIM ligands undergoes deprotonation under the formation of dihydrogen. Addition of a mild proton source (acetic acid) to deprotonated complex [ 2 ](BF4) regenerates protonated complex [ 1 ](BF4)2. In presence of acetic acid in acetonitrile solvent [ 1 ](BF4)2 shows electrocatalytic proton reduction with a kobs of ≈200 s−1 at an overpotential of 590 mV. Mechanistic investigations supported by DFT (BP86) suggest that dihydrogen formation takes place in an intramolecular fashion through the participation of a methylene C−H bond of the HBMIM ligand and a CoII−H bond through formal heterolytic splitting of the latter. These findings are of interest to the development of responsive ligands for molecular (base)metal (electro)catalysis. 相似文献
9.
Investigations to eliminate defects in the incommensurate phase BaMnF4, led to a method of preparation at a temperature lower than the melting point of BaMnF4. Qualitative studies of the systems BaF2 -H2O -HF and MnF2 -H2O -HF showed that very pure single crystals of BaMnF4 could be grown at a temperature lower than 300°C. Several new phases could be isolated as single crystals, in particular: BaF2′HFSingle crystal X-ray analysis revealed the compound to be monoclinic (Space Group P21 and Z = 2) and confirmed the formula found by chemical analysis. However, because of the difficulty to distinguish between fluorine and oxygen atoms, some problems remain, which will be solved by neutron diffraction studies. Infrared analysis indicate the presence of HF?2 and suggest the following representation: (Ba2+)2(HF?2)2(F?)2.It is possible to extend this method of synthesis to the preparation of other fluorides and related compounds, in particular to those of europium and strontium. 相似文献
10.
Mona Wells Michael Gösch Hauke Harms Jan Roelof van der Meer 《Mikrochimica acta》2005,151(3-4):209-216
This paper describes the development of an analytical technique for arsenic analyses that is based on genetically-modified
bioreporter bacteria bearing a gene encoding for the production of a green fluorescent protein (gfp). Upon exposure to arsenic
(in the aqueous form of arsenite), the bioreporter production of the fluorescent reporter molecule is monitored spectroscopically.
We compared the response measured as a function of time and concentration by steady-state fluorimetry (SSF) to that measured
by epi-fluorescent microscopy (EFM). SSF is a bulk technique; as such it inherently yields less information, whereas EFM monitors
the response of many individual cells simultaneously and data can be processed in terms of population averages or subpopulations.
For the bioreporter strain used here, as well as for the literature we cite, the two techniques exhibit similar performance
characteristics. The results presented here show that the EFM technique can compete with SSF and shows substantially more
promise for future improvement; it is a matter of research interest to develop optimized methods of EFM image analysis and
statistical data treatment. EFM is a conduit for understanding the dynamics of individual cell response vs. population response, which is not only a matter of research interest, but is also promising in the practical terms of developing
micro-scale analysis. 相似文献