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91.
92.
A series of di-, tri-, and tetra-tetrazoloalkanes were synthesized from the corresponding nitrile and sodium azide. These were alkylated to give hydroxy terminated chains for possible use as high energy oligomers. 相似文献
93.
P. A. Kendall N. J. Mason 《Journal of Electron Spectroscopy and Related Phenomena》2001,120(1-3):27-31
Electron energy loss spectroscopy (EELS) has been used to study the photo-absorption spectrum of trifluoromethyl sulphur pentafluoride (SF5CF3) for the first time. Comparison is made with the EELS spectrum of sulphur hexafluoride (SF6). The photolysis of the compound is discussed with relevance to estimated lifetimes in the atmosphere. It is estimated that the lifetime of SF5CF3 is of the order of 1000 years. 相似文献
94.
Three diverse rough surfaces have been studied using inelastic He scattering. The first is an ion bombarded Ag(110) surface where a broadened specular peak remains visible but scattering remains entirely elastic as viewed by the incoherent component. The second is a cleaved Te(10
) surface composed of helical chains where the roughness originates from thermal oscillations and scattering is almost entirely inelastic. Thirdly, a glass (7740) disc is shown to be physically rough but the surface is sufficiently rigid to yield largely elastic incoherent scattering. 相似文献
95.
R P Mason P P Antich E E Babcock J L Gerberich R L Nunnally 《Magnetic resonance imaging》1989,7(5):475-485
Multiresonance perfluorocarbon emulsions (Oxypherol and Fluosol-DA) were imaged in tumor-bearing mice using 19F spin-echo magnetic resonance imaging in vivo. Multiple thin-slice fluorine images free of chemical shift artifacts were obtained in 13 minutes and these were correlated with proton images obtained during the same experiment to delineate the anatomic distribution of perfluorocarbons. Sequential images were used to determine the time course of the distribution and the retention of the compounds in tumors and organs. 19F MR spectroscopy was used ex vivo to determine with high sensitivity the relative concentration of perfluorocarbons in different tissues and organs and to confirm the results obtained from imaging experiments. The fluorine images visually demonstrated the preferential localization of the perfluorocarbons in the liver and spleen; shortly after injection, the images also revealed the highly vascularized tumor-chest wall interface. Imaging and spectroscopy together showed that the perfluorocarbons were removed from the blood pool within hours and remained sequestered in tissues at later times; the highest concentrations were found in the spleen and liver, where the agents were retained without spectral changes for the duration of these studies. The perfluorocarbons accumulated within tumors at dose-dependent concentrations, one to two orders of magnitude smaller than those observed in the spleen and liver. 相似文献
96.
Listeners with sensorineural hearing loss are poorer than listeners with normal hearing at understanding one talker in the presence of another. This deficit is more pronounced when competing talkers are spatially separated, implying a reduced "spatial benefit" in hearing-impaired listeners. This study tested the hypothesis that this deficit is due to increased masking specifically during the simultaneous portions of competing speech signals. Monosyllabic words were compressed to a uniform duration and concatenated to create target and masker sentences with three levels of temporal overlap: 0% (non-overlapping in time), 50% (partially overlapping), or 100% (completely overlapping). Listeners with hearing loss performed particularly poorly in the 100% overlap condition, consistent with the idea that simultaneous speech sounds are most problematic for these listeners. However, spatial release from masking was reduced in all overlap conditions, suggesting that increased masking during periods of temporal overlap is only one factor limiting spatial unmasking in hearing-impaired listeners. 相似文献
97.
A. Albinati E. Cesarotti S.A. Mason I. Rimoldi S. Rizzato D. Zerla 《Tetrahedron: Asymmetry》2010,21(9-10):1162-1165
We describe an efficient and convenient route for the preparation of enantiomerically pure d-labelled histidine by asymmetric hydrogenation with a Rh–diphosphine complex in the presence of strong non-coordinating acids. A single-crystal neutron diffraction study of the selectively dideuterated N-benzoyl-histidine methyl ester, tetrafluoroborate salt determined the absolute stereochemistry. This allowed us to clarify the role of H+ in the whole reduction process. 相似文献
98.
99.
H Iwahashi C E Parker R P Mason K B Tomer 《Rapid communications in mass spectrometry : RCM》1990,4(9):352-354
Radical adducts of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) with hydroxyl, methanol-derived, and ethanol-derived radicals were detected by a combination of liquid chromatography with either electron paramagnetic resonance or thermospray mass spectrometry (LC/EPR or LC/TSP-MS) in the Fenton system (with methanol or ethanol). One radical adduct was observed in the reaction of DMPO with the hydroxyl radical or the methanol-derived radical, while two adducts were detected in the reaction of DMPO with ethanol-derived radicals. The LC/TSP-MS spectra showed quasi-molecular ions [M + H]+ at m/z 146 and m/z 160 for the methanol-derived and ethanol-derived radical adducts, respectively, and an apparent molecular ion M+ at m/z 130 for the hydroxyl radical adduct. Use of methyl-D3 alcohol (CD3OH) and ethyl-D5 alcohol (CD3CD2OH) indicated that carbon-centered radicals are formed. Experiments with partially deuterated ethanol (CD3CH2OH and CH3CD2OH) indicated that the two adducts observed in the reaction of DMPO with ethanol-derived radicals correspond to the two diastereomeric adducts of DMPO with the alpha-hydroxyethyl free radical. 相似文献
100.
Leon Glass Theodore J. Perkins Jonathan Mason Hava T. Siegelmann Roderick Edwards 《Journal of statistical physics》2005,121(5-6):969-994
We consider dynamics in a class of piecewise-linear ordinary differential equations and in an electronic circuit that model
genetic networks. In these models, gene activity varies continuously in time. However, as in Boolean or discrete-time switching
networks, gene activity is driven high or low based only on whether the activities of the regulating genes are high or low
(i.e., above or below certain thresholds). Depending on the “regulatory logic”, these models can exhibit simple dynamics,
like stable fixed points or oscillation, or chaotic dynamics. The observed qualitative and quantitative differences between
the dynamics in the idealized equations and the dynamics in the electronic circuit lead us to focus attention on the analysis
of the dynamics as a function of parameter values. We propose new techniques for solving the inverse problem – the problem
of inferring the regulatory logic and parameters from time series data. We also give new symbolic and statistical methods
for characterizing dynamics in these networks. 相似文献