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211.
Reducing the duration of broadband excitation pulses using optimal control with limited RF amplitude
Skinner TE Reiss TO Luy B Khaneja N Glaser SJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,167(1):68-74
Combining optimal control theory with a new RF limiting step produces pulses with significantly reduced duration and improved performance for a given maximum RF amplitude compared to previous broadband excitation by optimized pulses (BEBOP). The resulting pulses tolerate variations in RF homogeneity relevant for standard high-resolution NMR probes. Design criteria were transformation of Iz-->Ix over resonance offsets of +/-20kHz and RF variability of +/-5%, with a pulse length of 500 micros and peak RF amplitude equal to 17.5 kHz. Simulations transform Iz to greater than 0.995 Ix, with phase deviations of the final magnetization less than 2 degrees, over ranges of resonance offset and RF variability that exceed the design targets. Experimental performance of the pulse is in excellent agreement with the simulations. Performance tradeoffs for yet shorter pulses or pulses with decreased digitization are also investigated. 相似文献
212.
We suggest an architecture for quantum computing with spin-pair encoded qubits in silicon. Electron-nuclear spin-pairs are controlled by a dc magnetic field and electrode-switched on and off hyperfine interaction. This digital processing is insensitive to tuning errors and easy to model. Electron shuttling between donors enables multiqubit logic. These hydrogenic spin qubits are transferable to nuclear spin-pairs, which have long coherence times, and electron spin-pairs, which are ideally suited for measurement and initialization. The architecture is scalable to a highly parallel operation. 相似文献
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M.Robin Bendall Thomas E. Skinner 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,134(2):331-349
To provide the most efficient conditions for spin decoupling with least RF power, master calibration curves are provided for the maximum centerband amplitude, and the minimum amplitude for the largest cycling sideband, resulting from STUD+ adiabatic decoupling applied during a single free induction decay. The principal curve is defined as a function of the four most critical experimental input parameters: the maximum amplitude of the RF field,RFmax, the length of the sech/tanh pulse,Tp, the extent of the frequency sweep,bwdth,and the coupling constant,Jo. Less critical parameters, the effective (or actual) decoupled bandwidth,bweff, and the sech/tanh truncation factor, β, which become more important asbwdthis decreased, are calibrated in separate curves. The relative importance of nine additional factors in determining optimal decoupling performance in a single transient are considered. Specific parameters for efficient adiabatic decoupling can be determined via a set of four equations which will be most useful for13C decoupling, covering the range of one-bond13C1H coupling constants from 125 to 225 Hz, and decoupled bandwidths of 7 to 100 kHz, with a bandwidth of 100 kHz being the requirement for a 2 GHz spectrometer. The four equations are derived from a recent vector model of adiabatic decoupling, and experiment, supported by computer simulations. The vector model predicts an inverse linear relation between the centerband and maximum sideband amplitudes, and it predicts a simple parabolic relationship between maximum sideband amplitude and the productJoTp. The ratiobwdth/(RFmax)2can be viewed as a characteristic time scale, τc, affecting sideband levels, with τc≈Tpgiving the most efficient STUD+ decoupling, as suggested by the adiabatic condition. Functional relationships betweenbwdthand less critical parameters,bweffand β, for efficient decoupling can be derived from Bloch-equation calculations of the inversion profile for a single sech/tanh pulse. Residual splitting of the centerband, normally associated with incomplete or inefficient decoupling, is not seen in sech/tanh decoupling and therefore cannot be used as a measure of adiabatic decoupling efficiency. The calibrated experimental performance levels achieved in this study are within 20% of theoretical performance levels derived previously for ideal sech/tanh decoupling at high power, indicating a small scope for further improvement at practical RF power levels. The optimization procedures employed here will be generally applicable to any good combination of adiabatic inversion pulse and phase cycle. 相似文献
215.
Skinner C.H. Dicicco D. Kim D. Meixler L. Nam C.H. Tighe W. Suckewer S. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1988,16(5):512-519
The authors present two approaches to X-ray laser development at Princeton and review progress toward the wavelength region below 10 nm. In addition, they present the first results from the application of the existing soft X-ray laser at 18.2 nm to X-ray microscopy. Particular emphasis is placed on experimentation with Li-like ions, the modeling of Li-like plasmas, cavity development, and a two-laser approach to wavelengths significantly below 10 nm 相似文献
216.
Electric dipole moments of methyl thiobenzoate (1.70 D), thiophthalic anhydride (3.92 D) and dibenzoyl sulphide (3.88 D) have been measured in benzene at 25° C. The predicted moments of these compounds were calculated and the results interpreted in terms of their conformations. 相似文献
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219.
We prove the one-, two-, and three-variable Iwasawa-Greenberg Main Conjectures for a large class of modular forms that are ordinary with respect to an odd prime p. The method of proof involves an analysis of an Eisenstein ideal for ordinary Hida families for GU(2,2). 相似文献
220.
This work presents the separation of model proteins by capillary electrochromatography involving a monolithic stationary phase with C4 functionality. The monolith was fabricated in UV-transparent capillaries by employing a slight modification of a recently published photopolymerization procedure. With the number of theoretical plates per column ranging between 11000 and 33000, the separation efficiency proved to be lower than capillary zone electrophoresis where plate numbers ranged between 18000 and 66000. However, higher resolution was obtained due to the additional chromatographic separation mechanism. Inter- and intra-column reproducibility were evaluated, the latter could be significantly improved when using a rinsing procedure that contained 0.05% sodium dodecylsulfate in the mobile phase. Plate heights became nearly independent of mobile phase velocities higher than 0.5 mm/s indicating that high velocities can be applied without sacrificing efficiency. Furthermore, peak heights showed a dependence on injection times. For proteins, an increase in capacity factors was found when increasing the percentage of organic solvent in the mobile phase. 相似文献