Chemical shift anisotropy amplification

A new NMR experiment which allows a measurement of the chemical shift anisotropy (CSA) tensor under magic angle spinning (MAS) is described. This correlates a fast MAS spectrum in the omega2 dimension with a sideband pattern in omega1 in which the intensities mimic those for a sample spinning at a fraction of the rate omega r/N, and these sidebands result from an amplification by a factor N of the modulation caused by the CSA. Standard methods can be used to extract the principal tensor components from the omega1 sideband patterns, and the nature of the experiment is such that the use of a large number of t1 increments can be avoided without compromising the resolution of different chemical sites. The new experiment is useful for accurately measuring narrow shift anisotropies.     

Chemical shift anisotropy selective inversion

Magic angle spinning (MAS) is used in solid-state NMR to remove the broadening effects of the chemical shift anisotropy (CSA). In this work we investigate a technique that can reintroduce the CSA in order to selectively invert transverse magnetization. The technique involves an amplitude sweep of the radio frequency field through a multiple of the spinning frequency. The selectivity of this inversion mechanism is determined by the size of the CSA. We develop a theoretical framework to describe this process and demonstrate the CSA selective inversion with numerical simulations and experimental data. We combine this approach with cross-polarization (CP) for potential applications in multi-dimensional MAS NMR.     

Chemical shift anisotropy and offset effects in cross polarization solid-state NMR spectroscopy

The effect of an offset term in the cross-polarization (CP) Hamiltonian of a heteronuclear spin-12 pair due to off-resonant radio frequency (rf) irradiation and/or chemical shift anisotropy on one of the rf channels is investigated. Analytical solutions, simulations, and experimental results are presented. Formulating the CP spin dynamics in terms of an explicit unitary evolution operator enables the CP period to be inserted as a module in a given pulse scheme regardless of the initial density matrix present. The outcome of post-CP manipulation via pulses can be calculated on the resulting density matrix as the phases and amplitudes of all coherence modes are available. Using these tools it is shown that the offset can be used to reduce the rf power on that channel and the performance is further improved by a post-CP pulse whose flip angle matches and compensates the tilt of the effective field on the offset channel. Experimental investigations on single crystalline and polycrystalline samples of peptides confirm the oscillatory nature of CP dynamics and prove the slowing down of the dynamics under offset and/or mismatch conditions.     

Chemical shift anisotropy of27Al in AlPO4-21

Chemical shift anisotropy of²⁷Al in AlPO₄-21 is studied.     

An efficient amplification pulse sequence for measuring chemical shift anisotropy under fast magic-angle spinning

A two-dimensional experiment for measuring chemical shift anisotropy (CSA) under fast magic-angle spinning (MAS) is presented. The chemical shift anisotropy evolution is amplified by a sequence of π-pulses that repetitively interrupt MAS averaging. The amplification generates spinning sideband manifolds in the indirect dimension separated by the isotropic shift along the direct dimension. The basic unit of the pulse sequence is designed based on the magic-angle turning experiment and can be concatenated for larger amplification factors.     

199Hg spin-lattice relaxation and chemical shift anisotropy in diphenylmercury

¹⁹⁹Hg spin-lattice relaxation times (T₁) have been measured for diphenylmercury at magnetic fields of 2.35 and 7.05 T. T₁ was nine times shorter at the higher field (0.033 sec at 310 K) than at the lower field (0.30 sec), showing relaxation by chemical shift anisotropy (CSA) to be the dominant mechanism even at the lower field. Variable-temperature ¹³C T₁ measurements at 6.35 T made it possible to determine a value for the correlation time for motion perpendicular to the axis of the molecule (50 psec at 300 K), which with the ¹⁹⁹Hg data allowed a value of 6800 ± 680 ppm to be calculated for the mercury chemical shift anisotropy. The activation energy for rotational motion was 13.3 kJ · mole⁻¹. Previous data on dimethylmercury have been reassessed and the importance of the CSA mechanism for ¹⁹⁹Hg at high fields is pointed out.     

Properties of carbon films with high conductivity anisotropy

Carbon films with high conductivity anisotropy were obtained via sputtering a graphite target with an accelerated argon ion beam. The film structure was studied using Raman spectroscopy (combination scattering spectroscopy), transmission high-resolution electron microscopy, chemical analysis, X-ray photoelectron spectroscopy, and tunnel spectroscopy. We found conductivity anisotropy along and across the film chains of the order of 10⁴, which is associated with a high content of linear carbon chains with sp hybridization of bonding orbitals.     

Second-generation optical-resolution photoacoustic microscopy with improved sensitivity and speed

We developed second-generation (G2) optical-resolution photoacoustic microscopy (OR-PAM). Incorporation of a novel acoustic detection scheme improved upon the sensitivity of our first-generation (G1) system by 18.4 dB, deepening the in vivo tissue penetration to 1.2 mm at 570 nm. Moreover, translating the imaging head instead of the living object accelerated the scanning speed by a factor of 5, widening the field of view within the same acquisition time. Mouse ears, as well as mouse brains with intact craniums, were imaged in vivo in both total concentration and oxygen saturation of hemoglobin.     

Ferromagnetic resonance in polycrystalline ferrites with high magnetic anisotropy

The ferromagnetic resonance absorption line is computed in polycrystalline ferrites in the independent grain approximation taking account of the magnetic crystallographic and magnetostriction anisotropies. The results obtained show that the influence of elastic stresses on the shape of the absorption line is analogous to the effect of the magnetic crystallographic anisotropy.Translated from Izvestiya VUZ. Fizika, No. 1, pp. 9–16, January, 1972.     

Chemical shift anisotropy edited complete unraveling of overlapped 1H NMR spectra of enantiomers: application to small chiral molecules

The differential values of NMR spectral parameters like chemical shift anisotropies, dipolar couplings and quadrupolar couplings of enantiomers in chiral liquid crystalline media are employed not only for their visualization but also for their quantification. Large differences in chemical shift anisotropies and the quadrupolar couplings between the enantiomers enable the use of 13C and extensive 2H NMR detection for such a purpose. In spite of high magnetic moment, high sensitivity and abundant presence of protons in all the chiral molecules, 1H detection is not routinely employed due to severe overlap of unresolved transitions arising from short and long distance couplings. Furthermore, the doubling of the spectra from two enantiomers and their indistinguishable overlap due to negligible difference in chemical shift anisotropies hampers their discrimination. The present study demonstrates the use of proton chemical shift anisotropy as an exclusive parameter for such a discrimination. The method employs the non-selective excitation of homonuclear Nth quantum coherence of N coupled protons. The simultaneous flipping of all the coupled spins results in a single transition in the multiple quantum dimension at the cumulative sum of their anisotropic chemical shifts for each enantiomer, with the measurable difference between them, resulting in their complete unraveling.     

15N chemical shift anisotropy in protein structure refinement and comparison with NH residual dipolar couplings

Recent methods of aligning proteins which were developed in order to measure residual dipolar couplings (RDCs) in solution can also be used for additional applications such as measuring the 15N CSA in the form of chemical shift differences, Deltadelta. A new XPLOR-NIH module has been developed and implemented for NMR structure refinement using the 15N Deltadelta data as restraints. The results of this refinement are shown using the protein Bax. This method should be amenable to any protein which can be studied by NMR. An analysis comparing the structural information provided by NH RDCs and the 15N Deltadelta is included.     

The Eshelby factor for cubic crystals with arbitrary elastic anisotropy

The Eshelby factor for cubic crystals has been calculated for arbitrary anisotropy. One of the two integrations needed could be performed analytically. An expansion up to 4th order in the anisotropy and exact results for special cases are also given.     

高灵敏度双折射光纤压力传感器

本文报道了一种高灵敏度双折射光纤压力传感器.它的结构简单,环境温度的变化几乎不影响它的灵敏度.压力温度灵敏度比约为53K·bar~(-1).它的温度灵敏度只是“熊猫”光纤的1/7.5.     

Fiber Bragg grating hydrophone with high sensitivity

A fiber Bragg grating （FBG） hydrophone with high sensitivity was demonstrated. This hydrophone used a rubber diaphragm and a copper hard core as the sensing element. To compensate the hydrostatic pressure, a capillary tube was fixed at the end of the hydrophone. Theoretical analysis of the acoustic pressure sensitivity was given in this letter. Experiments were carried out to test the frequency response of the hydrophone. The result shows that when the Young＇s modulus of the diaphragm is higher, a flatter frequency response will be obtained.     

具有大指向性开角及高发射电压响应的发射换能器

应用复合变幅杆及夹心式换能器结构,研制了一种指向性开角较大且发射电压响应较高的发射换能器。应用有限元方法对换能器的工作频率,发射电压响应及指向性进行了理论计算。并与实验结果进行了比较,结果较吻合。本文研制的换能器工作频率为75.6kHz,发射电压响应级达到1 56dB(基准值1V/μPa),-3dB发射指向性开角100°     

Renormalization of anisotropy and glueball masseson tadpole improved lattice gauge action

The Numerical calculations for tadpole-improved U(1) lattice gauge theory in three-dimensions on anisotropic lattices have been performed using standard path integral Monte Carlo techniques. Using average plaquette tadpole renormalization scheme, simulations were done with temporal lattice spacings much smaller than the spatial ones and results were obtained for the string tension, the renormalized anisotropy and scalar glueball masses. We find, by comparing the regular and sideways potentials, that tadpole improvement results in very little renormalization of the bare anisotropy and reduces the discretization errors in the static quark potential and in the glueball masses.Received: 19 March 2003, Revised: 26 August 2003, Published online: 24 October 2003