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排序方式: 共有125条查询结果,搜索用时 500 毫秒
1.
Rolf Dittmann Heinz-Jürgen Feld Wolfgang Samenfink Sigmar Wittig 《Particle & Particle Systems Characterization》1994,11(5):379-384
In utilizing the advantages of extinction measurements in micron and especially submicron particle characterization, the properties of a multiple wavelength extinction technique have been the subject of extended theoretical studies. Furthermore, an experimental set-up was designed which provides high flexibility owing to its modular design. The performance of the technique described is demonstrated by a large variety of applications in aerosol and combustion research and in large-scale industrial systems. It was found to be a reliable tool in characterizing dense particulate systems. 相似文献
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William A. Feld Lucia Serico Beverly G. Genez Linda L. Friar 《Journal of polymer science. Part A, Polymer chemistry》1983,21(3):883-890
The synthesis of two phenylated bifunctional monomers, dimethyl 4-(4-(p-aminophenoxy)phenyl)-3,5,6-triphenylphthalate and dimethyl 4-(4-(4-(p-aminophenoxy)phenoxy)phenyl)-3,5,6-triphenylphthlate, was accomplished. Polymerization in solution or by a bulk polymerization procedure yielded a series of low molecular weight phenylated polyimides. The polymers were soluble in chlorinated hydrocarbons and exhibited thermal stabilities comparable to other polyimide systems. 相似文献
5.
William A. Feld B. Ramalingam Frank W. Harris 《Journal of polymer science. Part A, Polymer chemistry》1983,21(2):319-328
Four aromatic dinitro compounds containing oxyethylene units 1,2-bis(4-nitrophenoxy)ethane, bis(2)-(4-nitrophenoxy)ethyl ether, 1,2-bis(2)-(4-nitrophenoxy)ethoxy)ethane, and bis(2-(2-(4-nitrophenoxy)ethoxy)ethyl) ether were prepared by an aromatic nucleophilic substitution reaction that involved 1-fluoro-4-nitrobenzene and the appropriate oxyethylene glycol. Each of the dinitro compounds could be reduced chemically or catalytically to produce the diamines 1,2-bis(4-aminophenoxy)ethane, bis(2-(4-amino-phenoxy)ethyl ether, 1,2-bis(2-(4-aminophenoxy)ethoxy)ethane, and bis(2-(2-(4-aminophenoxy)ethoxy)ethyl) ether. Polymerization of the diamines was carried out in m-cresol with toluene as an azeotroping agent. Polymides derived from 5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis-1,3-isobenzofuradione exhibited good solubility in chlorinated solvents, glass transition temperatures as low as 140°C, as evidenced by viscous flow, and good thermal stability; a 5% weight loss generally occured at greater than 450°C. Isothermal aging studies conducted at 600°F(315°C) for 200 h indicated that weight loss is directly related to oxyalkylene chain length–10% for the shortest and 50% for the longest chain. 相似文献
6.
Spectroscopic diagnosis of colonic dysplasia. 总被引:4,自引:0,他引:4
R Richards-Kortum R P Rava R E Petras M Fitzmaurice M Sivak M S Feld 《Photochemistry and photobiology》1991,53(6):777-786
We have developed a method for defining diagnostic algorithms for pathologic conditions based on fluorescence spectroscopy. We apply this method to human colon tissue and show that fluorescence can be used to diagnose the presence or absence of colonic adenoma. This method uses fluorescence excitation-emission matrices (EEM) to identify optimal excitation regions for obtaining fluorescence emission spectra which can be used to differentiate normal and pathologic tissues. In the case of normal and adenomatous colon tissue, these were found to be: 330, 370, and 430 nm +/- 10 nm. At these excitation wavelengths, emission wavelengths for use in diagnostic algorithms are identified from average difference and ratio of the spectra from normal and pathologic tissues. In colon tissue, at 370 nm excitation, 404, 480, and 680 nm were found to be useful emission wavelengths for diagnosing the presence of adenoma in vitro. The basis of colon tissue autofluorescence was investigated using EEM of pure molecules and relevant excitation-emission maxima in the literature. 相似文献
7.
Keng Lung Lee Joey Feld Dr. Paul Hume Prof. Tilo Söhnel Dr. Erin Leitao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(2):815-824
A series of ammonium monosubstituted H-phosphonate salts were synthesized by combining H-phosphonate diesters with amines in the absence of solvent at 80 °C. Variation of the ester substituent and amine produced a range of ionic liquids with low melting points. The products and by-products were analyzed by spectroscopic and spectrometric techniques in order to get a better mechanistic picture of the dealkylation and formal dearylation observed. For dialkyl H-phosphonate diesters, (RO)2P(O)H (R=alkyl), the reaction proceeds via direct dealkylation with the reactivity increasing in the order R=iPr<Et<Me corresponding to DFT calculated activation enthalpies of 22.6, 20.8, and 17.9 kcal mol−1. For the diphenyl H-phosphonate diesters, (PhO)2P(O)H, the dearylation was found to proceed via phenol-assisted formation of a 5-coordinate intermediate, (PhO)3PH(OH), from which P(OPh)3 and water were eliminated. The presence of an equivalent of water then facilitated the formation of P(OH)2OPh and the amine, R'NH2, subsequently abstracted a proton from it to yield [(PhO)PH(O)O]-[R'NH3]+. 相似文献
8.
Ten bis(4-aryloxy-3-nitrophenyl) sulfones were synthesized via a phase-transfer catalyzed, nucleophilic displacement reaction involving phenoxides and bis(4-chloro-3-nitrophenyl) sulfone. 相似文献
9.
We report a highly accurate phase-based technique for measuring arbitrarily long optical distance with subnanometer precision. The method employs a Michelson interferometer with a pair of harmonically related light sources, one cw and the other low coherence. By slightly detuning (~2 nm) the center wavelength of the low-coherence source between scans of the target sample, we can use the phase relationship between the heterodyne signals of the cw and the low-coherence light to measure the separation between reflecting interfaces with subnanometer precision. As this technique is completely free of 2pi ambiguity, an issue that plagues most phase-based techniques, it can be used to measure arbitrarily long optical distances without loss of precision. We demonstrate one application of this technique, the high-precision determination of the differential refractive index. 相似文献
10.
Blood analysis by Raman spectroscopy 总被引:1,自引:0,他引:1
Concentrations of multiple analytes were simultaneously measured in whole blood with clinical accuracy, without sample processing, using near-infrared Raman spectroscopy. Spectra were acquired with an instrument employing nonimaging optics, designed using Monte Carlo simulations of the influence of light-scattering-absorbing blood cells on the excitation and emission of Raman light in turbid medium. Raman spectra were collected from whole blood drawn from 31 individuals. Quantitative predictions of glucose, urea, total protein, albumin, triglycerides, hematocrit, and hemoglobin were made by means of partial least-squares (PLS) analysis with clinically relevant precision (r(2) values >0.93). The similarity of the features of the PLS calibration spectra to those of the respective analyte spectra illustrates that the predictions are based on molecular information carried by the Raman light. This demonstrates the feasibility of using Raman spectroscopy for quantitative measurements of biomolecular contents in highly light-scattering and absorbing media. 相似文献