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921.
Phosphorus-containing Fe and Fe?Mo sulfide catalysts supported on γ-Al2O3 and activated carbon were evaluated for their thiophene HDS activities at atmospheric pressure. The thiophene HDS activity of the carbon-supported catalysts decreased considerably in the presence of phosphorus, while the activity of the alumina-supported catalysts was not affected. It was shown by Mössbauer spectroscopy that in both the oxidic carbon- and alumina-supported catalyst precursors the presence of phosphorus resulted in an improved dispersion of the Fe phase. In the sulfided carbon-supported Fe and Fe?Mo catalysts, the presence of phosphorus resulted in the formation of an “Fe(II)-phosphate” phase, which was held responsible for the decrease in HDS activity. With regard to the sulfided alumina-supported catalysts, it was found that phosphorus did not influence the structure of the metal sulfide species.  相似文献   
922.
Mössbauer spectra of AlTFe-alloys with T=Cr or Mn, show a quadrupole splitting QS≈0.4 mm/s. This shows that the iron atom is not in an icosahedral site. In order to investigate the local symmetry further, we applied an external magnetic field Hext≈5T, so that the asymmetry parameter ν can be obtained. Using a one site approximation the results are: ν=0.7 for decagonal Al7(Mn0.7Fe0.3)2 and ν=0.8 for icosahedral Al6Cr0.7Fe0.3. This means that the iron atoms are in sites with a symmetry lower than axially symmetric. Most of the vertices in a Penrose lattice show such a symmetry.  相似文献   
923.
A double heterostructure NpnP optoelectronic switching device with low holding power has been fabricated. In the static regime a holding power of 20 nW for a device area of 200 mu m*100 mu m was obtained. This value represents a reduction of four orders of magnitude in holding power compared to previous reported PnpN or PnN structures with equivalent device area. A higher optical sensitivity and a lower optical switching intensity is consequently obtained with these devices.<>  相似文献   
924.
925.
The high spin structure of the nucleus129Ba has been investigated using a18O induced reaction. The known bands could be followed up to a maximum spin (55/2) ?. Some 56 states and 78 transitions could be placed in the level scheme. Band crossings were established in both positive and negative parity structures. They display features of strong polarization effects due to the alignment of h11/2 protons.  相似文献   
926.
A very efficient transmission line model for the analysis of arrays of rectangular microstrip antennas is presented. The structure of the model is discussed, and its validity is proved. This is done for the isolated microstrip antenna as well as for the coupling between antennas. Then follows a discussion of the numerical efficiency. And finally a numerical example shows the effect of mutual coupling on the impedance and radiation pattern of a 21 element Chebyshev array at different scanangles.  相似文献   
927.
Spectrophotometry was used with multivariate calibration to simultaneously determine compounds in mixtures. Two antidepressant mixtures were investigated: imipramine hydrochloride and chlordiazepoxide and nortriptyline hydrochloride and fluphenazine hydrochloride. Considerable spectral overlap and large differences in component concentrations were challenges. Since this type of analysis is often performed using complex algorithms, a simple strategy was used here for the simultaneous determination of both mixture components by classical least squares, principal component regression, and partial least squares. Experimental design was used to select the optimum parameters including the wavelength range, sampling interval, software, and derivative order. Accuracy was enhanced by proper wavelength selection. In addition, derivatives of the raw spectra improved the selectivity. The standard deviation, deviation of mean recovery from 100%, and prediction ability of the models were used as the responses. In respect to these terms, first-order derivatization of the spectra and a sampling interval of 1?nm provided the best results. In particular, the low concentration compounds in the mixtures (chlordiazepoxide and fluphenazine) were determined more accurately with precision lower than 3%. The strategy was used for the quality control of pharmaceuticals containing the mixtures without chemical pretreatment.  相似文献   
928.
A novel thiophene attached anthracene (TA) based fluorescent compound was designed and synthesized. The TA showed a high quantum yield (Qy = 0.34) in regard to fluorescence. We applied this TA compound to detect specific metal compound and found that it could identify CuCl2 from other metals through dramatic fluorescence change at λmax = 460 nm. It showed strong quenching fluorescence property with CuCl2 while with other metal compounds it exhibited strong blue fluorescence emission. UV/Vis absorption spectroscopy clearly demonstrated that the quenching property of TA at λmax = 460 nm was due to overlapping of the fluorescence peak of TA at λmax = 460 nm and the absorption band of CuCl2 (from 190 nm to 525 nm). Binding constant (K′), which was 0.0895 mM?2, indicated a complexation ratio between TA and CuCl2 as 1:2 and this interaction induced quenching property.  相似文献   
929.

Pure and complete fractions of neodymium, samarium, europium, gadolinium and dysprosium were isolated by means of high performance ion chromatography, using a cation exchange column and gradient elution with alpha-hydroxyisobutyric acid solutions (α-HIBA). Intermediate precision and robustness of the isolation method was investigated, identifying eluent pH as the most important parameter. Investigation of the elution behaviour of the most important fission and activation products and actinides indicated that preventing the accumulation of cesium on the cation exchange column required further isocratic elution with a higher concentrated α-HIBA solution after elution of the lanthanides. A sample matrix free of carbon was achieved by means of acid digestion, followed by UV photo-oxidation, resulting in samples suitable for mass spectrometric analysis.

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930.
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