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91.
Skinner TE Kobzar K Luy B Bendall MR Bermel W Khaneja N Glaser SJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,179(2):241-249
An optimal control algorithm for generating purely phase-modulated pulses is derived. The methodology is applied to obtain broadband excitation with unprecedented tolerance to RF inhomogeneity. Design criteria were transformation of Iz-->Ix over resonance offsets of +/-25 kHz for constant RF amplitude anywhere in the range 10-20 kHz, with a pulse length of 1 ms. Simulations transform Iz to greater than 0.99 Ix over the targetted ranges of resonance offset and RF variability. Phase deviations in the final magnetization are less than 2-3 degrees over almost the entire range, with sporadic deviations of 6-9 degrees at a few offsets for the lowest RF (10 kHz) in the optimized range. Experimental performance of the new pulse is in excellent agreement with the simulations, and the robustness of the excitation pulse and a derived refocusing pulse are demonstrated by insertion into conventional HSQC and HMBC-type experiments. 相似文献
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95.
Chi-Chang Chiang Gordon B. Skinner 《Journal of Quantitative Spectroscopy & Radiative Transfer》1980,24(6):525-528
Absorption cross sections of molecular oxygen were measured at the H and D Ly-α wavelengths (1215.67 and 1215.34 Å) between 800 and 1700°K, the cross sections being given by the equation σ (cm2) = 4.2E-18 exp(-3070/T) (4.2E-18 = 4.2 × 10-18). The absorption cross section for v = 1 is (9±2)E-19 cm2 and that for v = 2 is (7±3)E-18 cm2, compared to 1.E-20 cm2 for v = 0. Vibrational relaxation times were found to be in agreement with literature data over the range of common temperatures. 相似文献
96.
The origin of the signal seen in response to glucose in a polyaniline|glucose oxidase system is explored by immittance spectroscopy, by comparing data from an equivalent circuit model and the parameters obtained from a solution of the faradaic branch of the frequency dispersion for a coupled chemical—electrochemical reaction mechanism. It was shown that an RC subcircuit in the equivalent circuit model was sensitive to peroxide concentration, and the interaction of peroxide with polyaniline at potentials where it either oxidised or reduced the polyaniline was discussed. This information was used to compare the data obtained in a bulk and entrapped glucose oxidaselglucose system, and it was seen that the origin of the response could not be fully attributed to peroxide interaction in the latter case. Under anaerobic conditions with entrapped enzyme, it was proposed that a complex between the gluconolactone product of the enzyme reaction and the polymer leads to a more conducting polymer, with inherent charge compensation, and this results in the observed enhanced current signal. 相似文献
97.
Nielsen MB Schreiber M Baek YG Seiler P Lecomte S Boudon C Tykwinski RR Gisselbrecht JP Gramlich V Skinner PJ Bosshard C Günter P Gross M Diederich F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(15):3263-3280
A selection of dimeric tetraethynylethenes (TEEs) and perethynylated expanded radialenes, containing different donor/acceptor substitution patterns, have been prepared and fully characterized. The first X-ray crystal structure of an expanded [6]radialene, with twelve peripheral 3,5-di(tert-butyl)phenyl substituents, is presented. This macrocycle, the all-carbon core of which is isomeric with fullerene C60, adopts a non-planar, "chair-like" conformation. Also a TEE dimer, carrying N,N-dimethylaniline donor substituents, has been subjected to an X-ray crystallographic analysis. The electronic properties were studied by UV/Vis spectroscopy and electrochemistry, providing fundamental insight into mechanisms of pi-electron delocalization in the acyclic and macrocyclic chromophores. Donor or donor-acceptor-substituted dimeric TEE derivatives show very strong absorptions extending over the entire UV/Vis region; their longest wavelength absorption bands have high charge-transfer character. Macrocyclic cross-conjugation in the expanded radialenes becomes increasingly efficient with increasing donor-acceptor polarization. A dual, strongly solvent-polarity-dependent fluorescence was observed for a tetrakis(N,N-dimethylaniline)-substituted dimeric TEE; this interesting emission behavior is explained by the twisted intramolecular charge-transfer (TICT) state model. Donor-substituted expanded radialenes display huge resonance-enhanced third-order nonlinear optical coefficients. 相似文献
98.
Molecular-dynamics simulations of a neat atomic fluid, coupled with a simple model for vibrational frequency perturbations, are used to investigate vibrational line broadening near the liquid-gas critical point. All features of our simulations are in qualitative agreement with recent Raman experiments on nitrogen. We also use our simulation results to assess the validity of the mode-coupling theories that have been used to analyze experiment. We find that the theoretical results are not in good agreement with simulation, both for the temperature dependence of the linewidth, and for the frequency time-correlation functions. However, the mode-coupling prediction that critical line broadening is due to the diverging correlation time of the frequency fluctuations is shown to be correct. 相似文献
99.
Volker Batroff Wilhelm Flitsch Wilfried Lübisch Derek Leaver David Skinner 《Tetrahedron letters》1982,23(18):1947-1950
[2.2.3]Cyclazines are obtained in moderate yields by reaction of 3-pyrrolizines bearing conjugative substituents (Ph or CO2Me) with vinamidinium salts in the presence of strong bases. Syntheses of the previously unknown 2-phenyl-3-pyrrolizine and 1-methoxycarbonylcyclopenta [] [2.2.4] cyclazine are also described. 相似文献
100.
An automatic ultraviolet absorptiometric method has been developed for the determination of potassium. The method involves precipitation of potassium by addition of a known excess of sodium tetraphenylborate, removal of the potassium tetraphenylborate precipitate by filtration, and measurement of the excess of sodium tetraphenylborate in the filtrate by means of its absorbance at 254 mμ;. Most of the apparatus, including a continuous filter, is standard AutoAnalyzer equipment but a Uvicord ultraviolet absorptiometer replaces the conventional colorimeter. Build-up of precipitate in the system is eliminated by immersing the mixing coils in an ultrasonic bath which is actuated intermittently by a simple timing mechanism. The method is especially suitable for potassium analysis in production plant where flame photometer results are sometimes affected by fertilizer dust in the air surrounding the burner. 相似文献