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1.	Lindh, Erik L., et al. (författare) Site-resolved H-2 relaxation experiments in solid materials by global line-shape analysis of MAS NMR spectra 2016 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856 .- 1064-1858 .- 1096-0864. ; 268, s. 18-24 Tidskriftsartikel (refereegranskat)abstract We investigate a way one can achieve good spectral resolution in H-2 MAS NMR experiments. The goal is to be able to distinguish between and study sites in various deuterated materials with small chemical shift dispersion. We show that the H-2 MAS NMR spectra recorded during a spin-relaxation experiment are amenable to spectral decomposition because of the different evolution of spectral components during the relaxation delay. We verify that the results are robust by global least-square fitting of the spectral series both under the assumption of specific line shapes and without such assumptions (COmponent-REsolved spectroscopy, CORE). In addition, we investigate the reliability of the developed protocol by analyzing spectra simulated with different combinations of spectral parameters. The performance is demonstrated in a model material of deuterated poly(methacrylic acid) that contains two H-2 spin populations with similar chemical shifts but different quadrupole splittings. In H-2-exchanged cellulose containing two H-2 spin populations with very similar chemical shifts and quadrupole splittings, the method provides new site-selective information about the molecular dynamics.
2.	Johansson, Edvin, et al. (författare) Gradient echo imaging of flowing hyperpolarized nuclei : theory and phantom studies on 129Xe dissolved in ethanol 2002 Ingår i: Journal of Magnetic Resonance. - 1090-7807 .- 1096-0856. ; 159:1, s. 68-75 Tidskriftsartikel (refereegranskat)abstract The influence of flip angle and flow velocity on the signal intensity achieved when imaging a hyperpolarized substance with a spoiled gradient echo sequence was investigated. The study was performed both theoretically and experimentally using hyperpolarized xenon dissolved in ethanol. Analytical expressions regarding the optimal flip angle with respect to signal and the corresponding signal level are presented and comparisons with thermally polarized substances are made. Both experimentally and theoretically, the optimal flip angle was found to increase with increasing flow velocity. Numerical calculations showed that the velocity dependence of the signal differs between the cases of hyperpolarized and thermally polarized substances.
3.	Dvinskikh, Sergey V., et al. (författare) Heteronuclear dipolar recoupling in liquid crystals and solids by PISEMA-type pulse sequences 2003 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 164:1, s. 165-170 Tidskriftsartikel (refereegranskat)abstract A pulse sequence is described for the recoupling of heteronuclear dipolar interactions under MAS. The method is similar to the PISEMA experiment, but employs a well-defined amplitude modulation of one of the two radio-frequency fields. The technique is used for measurements of H-1-C-13 dipolar couplings in unoriented solid and liquid-crystalline samples.
4.	Dvinskikh, Sergey V., et al. (författare) Separated local field spectroscopy of columnar and nematic liquid crystals 2003 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 163:1, s. 46-55 Tidskriftsartikel (refereegranskat)abstract We are in this work comparing the efficiencies of various H-1-C-13 separated local field (SLF) experiments when applied to columnar and nematic liquid crystals. In particular, the performances of the conventional SLF, proton-detected local field (PDLF), and polarization inversion spin exchange at the magic angle (PISEMA) methods in terms of spectral resolution, robustness, and ability to measure long-range couplings are investigated. The PDLF sequence provides in most cases the best dipolar resolution. This is especially obvious for weakly coupled H-1-C-13 spin pairs.
5.	Ivchenko, Nickolay V., et al. (författare) Application of cogwheel phase cycling to sideband manipulation experiments in solid-state NMR 2003 Ingår i: Journal of magnetic resonance. - 1090-7807 .- 1096-0856. ; 164:2, s. 286-293 Tidskriftsartikel (refereegranskat)abstract Cogwheel phase-cycling schemes are applied to sideband suppression and sideband separation experiments in solid-state NMR. It is shown that cogwheel phase cycles lead to the elimination of most pulse imperfection effects, while using far fewer experimental signal acquisitions than conventional phase-cycling methods.
6.	Ivchenko, Nickolay V., et al. (författare) Multiplex phase cycling 2003 Ingår i: Journal of magnetic resonance. - 1090-7807 .- 1096-0856. ; 160:1, s. 52-58 Tidskriftsartikel (refereegranskat)abstract We discuss a new class of phase cycling procedures, in which a set of individual phase-shifted transients are stored separately in the computer and processed afterwards to yield the separated NMR signals from two or more coherence transfer pathways. In the case of two-dimensional double-quantum spectroscopy, this multiplex acquisition procedure allows the acquisition of pure-absorption spectra in only 62.5% of the time needed by previous methods.
7.	Larsson, Erik G., et al. (författare) SNR-optimality of sum-of-squares reconstruction for phased-array magnetic resonance imaging 2003 Ingår i: Journal of magnetic resonance. - : Elsevier. - 1090-7807 .- 1096-0856. ; 163:1, s. 121-123 Tidskriftsartikel (refereegranskat)abstract We consider the commonly used “Sum-of-Squares” (SoS) reconstruction method for phased-array magnetic resonance imaging with unknown coil sensitivities. We show that the signal-to-noise ratio (SNR) in the image produced by SoS is asymptotically (as the input SNR→∞) equal to that of maximum-ratio combining, which is the best unbiased reconstruction method when the coil sensitivities are known. Finally, we discuss the implications of this result.
8.	Price, W. S., et al. (författare) Determination of pore space shape and size in porous systems using NMR diffusometry. Beyond the short gradient pulse approximation 2003 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 160:2, s. 139-143 Tidskriftsartikel (refereegranskat)abstract The influence of finite length gradient pulses on NMR diffusion experiments on liquids confined to diffuse between two parallel planes is investigated. It is experimentally verified that the pore size decreases when determined using finite gradient pulses if the results are analyzed within the short gradient pulse approximation. The results are analyzed using the matrix formulation. The observed minima in the echo decay profiles are considerably less sharp than theoretical analysis would indicate and we suggest that this is due to the presence of a distribution of pore sizes in the sample. In addition, effects due to the presence of background gradients are discussed. It is argued that effects due to the finite length gradient pulses are relatively minor and in realistic applications the effects due to inhomogeneities in pore sizes and effects due to background gradients will constitute more serious problems in pore size determinations by means of NMR diffusometry.
9.	Andersson, P, et al. (författare) An alpha/beta-HSQC-alpha/beta experiment for spin-state selective editing of IS cross peaks 1998 Ingår i: Journal of magnetic resonance (San Diego, Calif. : 1997). - : Elsevier BV. - 1096-0856 .- 1090-7807. ; 133:2, s. 364-367 Tidskriftsartikel (refereegranskat)
10.	Antzutkin, Oleg, et al. (författare) 13C and15N-chemical shift anisotropy of ampicillin and penicillin-V studied by 2D-PASS and CP/MAS NMR 1998 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 135:1, s. 144-155 Tidskriftsartikel (refereegranskat)abstract The principal values of the chemical shift tensors of all13C and15N sites in two antibiotics, ampicillin and penicillin-V, were determined by 2-dimensionalphaseadjustedspinningsideband (2D-PASS) and conventional CP/MAS experiments. The13C and15N chemical shift anisotropies (CSA), and their confidence limits, were evaluated using a Mathematica program. The CSA values suggest a revised assignment of the 2-methyl13C sites in the case of ampicillin. We speculate on a relationship between the chemical shift principal values of many of the13C and15N sites and the β-lactam ring conformation
11.	Antzutkin, Oleg, et al. (författare) Coherence transfer signals in the rotational resonance NMR of a spinning single crystal 2000 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 147:1, s. 147-151 Tidskriftsartikel (refereegranskat)abstract A recent analysis of rotational resonance lineshapes (M. Helmle et al., J. Magn. Reson. 140, 379-403, 1999) predicted the existence of coherence transfer signals, which are generated by mechanically induced coherence transfer during the detection process. These signals correspond to the generation of observable coherences at spin sites that have no magnetization at the beginning of the observation interval but which acquire coherence while the detection is underway. The coherence transfer signals disappear for powder samples in conventional magic-angle-spinning solid-state NMR experiments. In this Communication, we report the successful detection of coherence transfer signals in rotor-synchronized experiments performed on a single crystal of [1,2-13C2]glycine.
12.	Berglund, Anders, et al. (författare) The equilibrium unfolding of MerP characterized by multivariate analysis of 2D NMR data 2005 Ingår i: Journal of magnetic resonance. - San Diego : Academic Press. - 1090-7807 .- 1096-0856. ; 172:1, s. 24-30 Tidskriftsartikel (refereegranskat)abstract A general problem when analysing NMR spectra that reflect variations in the environment of target molecules is that different resonances are affected to various extents. Often a few resonances that display the largest frequency changes are selected as probes to reflect the examined variation, especially in the case, where the NMR spectra contain numerous resonances. Such a selection is dependent on more or less intuitive judgements and relying on the observed spectral variation being primarily caused by changes in the NMR sample. Second, recording changes observed for a few (albeit significant) resonances is inevitably accompanied by not using all available information in the analysis. Likewise, the commonly used chemical shift mapping (CSM) [Biochemistry 39 (2000) 26, Biochemistry 39 (2000) 12595] constitutes a loss of information since the total variation in the data is not retained in the projection into this single variable. Here, we describe a method for subjecting 2D NMR time-domain data to multivariate analysis and illustrate it with an analysis of multiple NNIR experiments recorded at various folding conditions for the protein MerP. The calculated principal components provide an unbiased model of variations in the NNIR spectra and they can consequently be processed as NMR data, and all the changes as reflected in the principal components are thereby made available for visual inspection in one single NMR spectrum. This approach is much less laborious than consideration of large numbers of individual spectra, and it greatly increases the interpretative power of the analysis.
13.	Bielejewski, Michal, et al. (författare) On electrophoretic NMR. Exploring high conductivity samples 2014 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 243, s. 17-24 Tidskriftsartikel (refereegranskat)abstract The performance of a new electrophoretic NMR (eNMR) method that uses a Carr-Purcell-Meiboom-Gill echo train with repeated electric field reversal is investigated. We show that this pulse sequence, with acronym CPMGER, yields strongly reduced artifacts from convective flow effects caused by the simultaneous presence of electroosmotic and thermal driving forces. We demonstrate the achieved improvements in various aqueous solutions. Ultimately, the method can be used for obtaining electrophoretic mobilities by eNMR without relying on uncharged reference molecules, otherwise a significant limitation for electrophoretic experiments performed with nuclei other than 1H.
14.	Björk, Marcus, 1985-, et al. (författare) New approach to phase correction in multi-echo T2 relaxometry 2014 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 249, s. 100-107 Tidskriftsartikel (refereegranskat)abstract Estimation of the transverse relaxation time, T-2, from multi-echo spin-echo images is usually performed using the magnitude of the noisy data, and a least squares (LS) approach. The noise in these magnitude images is Rice distributed, which can lead to a considerable bias in the LS-based T-2 estimates. One way to avoid this bias problem is to estimate a real-valued and Gaussian distributed dataset from the complex data, rather than using the magnitude. In this paper, we propose two algorithms for phase correction which can be used to generate real-valued data suitable for LS-based parameter estimation approaches. The first is a Weighted Linear Phase Estimation algorithm, abbreviated as WELPE. This method provides an improvement over a previously published algorithm, while simplifying the estimation procedure and extending it to support multi-coil input. The algorithm fits a linearly parameterized function to the multi-echo phase-data in each voxel and, based on this estimated phase, projects the data onto the real axis. The second method is a maximum likelihood estimator of the true decaying signal magnitude, which can be efficiently implemented when the phase variation is linear in time. The performance of the algorithms is demonstrated via Monte Carlo simulations, by comparing the accuracy of the estimates. Furthermore, it is shown that using one of the proposed algorithms enables more accurate T-2 estimates; in particular, phase corrected data significantly reduces the estimation bias in multi-component T-2 relaxometry example, compared to when using magnitude data. WELPE is also applied to a 32-echo in vivo brain dataset, to show its practical feasibility.
15.	Carvalho, José P., et al. (författare) Frequency-swept adiabatic pulses for broadband solid-state MAS NMR 2021 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 324 Tidskriftsartikel (refereegranskat)abstract We present a complete description of frequency-swept adiabatic pulses applied to isolated spin-1/2 nuclei with a shift anisotropy in solid materials under magic-angle spinning. Our theoretical framework unifies the existing descriptions of adiabatic pulses in the high-power regime, where the radiofrequency (RF) amplitude is greater than twice the spinning frequency, and the low-power regime, where the RF power is less than the spinning frequency, and so links the short high-powered adiabatic pulse (SHAP) and single-sideband-selective adiabatic pulses (S3AP) schemes used in paramagnetic solid-state NMR. We also identify a hitherto unidentified third regime intermediate between the low- and high-power regimes, and separated from them by rotary resonance conditions. We show that the prevailing benchmark of inversion performance based on (super) adiabatic factors is only applicable in the high- and intermediate-power regimes, but fails to account both for the poor performance at rotary resonance, and the impressive inversion seen in the low-power regime. For low-power pulses, which are non-adiabatic according to this definition of (super) adiabaticity, the effective Floquet Hamiltonian in the jolting frame reveals “hidden” (super) adiabaticity. The theory is demonstrated using a combination of simulation and experiment, and is used to refine the practical recommendations for the experimentalist who wishes to use these pulses.
16.	Carvalho, José P., et al. (författare) Half-integer-spin quadrupolar nuclei in magic-angle spinning paramagnetic NMR : The case of NaMnO2 2022 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 340 Tidskriftsartikel (refereegranskat)abstract A combination of solid-state NMR methods for the extraction of 23Na shift and quadrupolar parameters in the as-synthesized, structurally complex NaMnO2 Na-ion cathode material, under magic-angle spinning (MAS) is presented. We show that the integration of the Magic-Angle Turning experiment with Rotor-Assisted Population transfer (RAPT) can be used both to identify shifts and to extract a range of magnitudes for their quadrupolar couplings. We also demonstrate the applicability of the two-dimensional one pulse (TOP) based double-sheared Satellite Transition Magic-Angle Spinning (TOP-STMAS) showing how it can yield a spectrum with separated shift and second-order quadrupolar anisotropies, which in turn can be used to analyze a quadrupolar lineshape free of anisotropic bulk magnetic susceptibility (ABMS) induced shift dispersion and determine both isotropic shift and quadrupolar products. Combining all these experiments, the shift and quadrupolar parameters for all observed Na environments were extracted and yielded excellent agreement with the density functional theory (DFT) based models that were reported in previous literature. We expect these methods to open the door for new possibilities for solid-state NMR to probe half-integer quadrupolar nuclei in paramagnetic materials and other systems exhibiting large shift dispersion.
17.	Dvinskikh, Sergey V., et al. (författare) C-13 PGSE NMR experiment with heteronuclear dipolar decoupling to measure diffusion in liquid crystals and solids 2000 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 142:1, s. 102-110 Tidskriftsartikel (refereegranskat)abstract A new PGSE NMR experiment, designed to measure molecular diffusion coefficients in systems with nonvanishing static dipolar coupling, is described. The fast static dipolar dephasing of the single-quantum C-13 coherences is removed by multiple-pulse heteronuclear decoupling. The resulting slow dephasing of the C-13 coherences allows for inserting appropriate gradient pulses into the pulse sequence. The presence of the large magnetic field gradient reduces the efficiency of the decoupling sequences which is compensated for by introducing a scheme of sequential slice selection across the sample. The method is demonstrated by F-19-decoupled C-13 PGSE NMR experiments in a lyotropic nematic and lamellar liquid crystal,
18.	Dvinskikh, Sergey V., et al. (författare) Combining PGSE NMR with homonuclear dipolar decoupling 2000 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 144:1, s. 142-149 Tidskriftsartikel (refereegranskat)abstract A new robust approach for combining multiple-pulse homonuclear decoupling and ROSE NMR is introduced for accurately measuring molecular diffusion coefficients in systems with nonvanishing static homonuclear dipolar couplings. Homonuclear decoupling suppresses dipolar dephasing during the gradient pulses but its efficiency and scaling factor for the effective gradient vary across the sample because of the large variation of the frequency offset caused by the gradient. The resulting artifacts are reduced by introducing a slice selection scheme. The method is demonstrated by F-19 PGSE NMR experiments in a lyotropic liquid crystal.
19.	Dvinskikh, Sergey V., et al. (författare) Cross-relaxation effects in stimulated-echo-type PGSE NMR experiments by bipolar and monopolar gradient pulses 2000 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 146:2, s. 283-289 Tidskriftsartikel (refereegranskat)abstract Exchange of longitudinal spin polarization by dipolar cross relaxation between nonequivalent spins results in a modulation of the stimulated echo signal on increasing the encoding/decoding delays and in a multiexponential decap on increasing the diffusion time. These artifacts are suppressed by 180 degrees pulses inserted in the middle of the gradient encoding/decoding periods. The efficiency of the gradient encoding is preserved if bipolar gradient pulses are used instead of monopolar pulses. The behavior of the different pulse sequences is demonstrated by F-19 PGSE NMR experiments in a lyotropic liquid crystal in both isotropic micellar and oriented nematic phases.
20.	Dvinskikh, Sergey V., et al. (författare) Deuterium stimulated-echo-type PGSE NMR experiments for measuring diffusion : Application to a liquid crystal 2001 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 153:1, s. 83-91 Tidskriftsartikel (refereegranskat)abstract The accessibility of molecular self-diffusion coefficients in anisotropic materials, such as liquid crystals or solids, by stimulated-echo-type H-2 PGSE NMR is examined. The amplitude and phase modulation of the signal in the stimulated-echo-type sequence by the static quadrupole coupling during the encoding/decoding delays is suppressed by adjusting the pulse flip angles and the phase cycle. For nuclei that experience both nonnegligible quadrupole and dipole couplings, the application of magic echoes during the evolution periods of stimulated echo is demonstrated as a helpful technique in the case of slow diffusion. These findings are demonstrated by experimental results in the thermotropic liquid crystal of partially deuterated 8CB. The obtained diffusion coefficients are also compared to data obtained by a H-1 homonuclear-decoupling-type PGSE NMR method in the same material.
21.	Dvinskikh, Sergey V., et al. (författare) Frequency offset refocused PISEMA-type sequences 2005 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 175:1, s. 163-169 Tidskriftsartikel (refereegranskat)abstract The popular PISEMA experiment is highly sensitive to the H-1 chemical shift dispersion and the choice of the H-1 carrier frequency. This is due to the off-resonance H-1 irradiation in the FSLG-CP sequence employed during the dipolar evolution period. In the modified approach described in this work, the interfering frequency offset terms are suppressed. In the new pulse schemes, conventional FSLG-CP is intercalated with 180 degrees pulses applied Simultaneously to both frequency channels, and with phases set orthogonal to those of the spin-lock fields. The technique is demonstrated on a nematic liquid-crystalline sample. Extensions to amplitude-modulated FSLG-CP recoupling under MAS are also presented.
22.	Dvinskikh, Sergey V., et al. (författare) Measurement of the principal values of the anisotropic diffusion tensor in an unoriented sample by exploiting the chemical shift anisotropy : F-19 PGSE NMR with homonuclear decoupling 2001 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 148:1, s. 73-77 Tidskriftsartikel (refereegranskat)abstract NMR methods (S. V. Dvinskikh et al. J. Magn. Reson. 142, 102-110 (2000) and S. V. Dvinskikh and I. Furo, J. Magn. Reson. 144, 142-149 (2000)) that combine PGSE with dipolar decoupling are extended to polycrystalline solids and unoriented liquid crystals. Decoupling suppresses dipolar dephasing not only during the gradient pulses but also under signal acquisition so that the detected spectral shape is dominated by the chemical shift tensor of the selected nucleus. The decay of the spectral intensity at different positions in the powder spectrum provides the diffusion coefficient in sample regions with their crystal axes oriented differently with respect to the direction of the field gradient. Hence, one can obtain the principal values of the diffusion tensor. The method is demonstrated by F-19 PGSE NMR with homonuclear decoupling in a lyotropic lamellar liquid crystal.
23.	Dvinskikh, Sergey V., et al. (författare) Measurements of motionally averaged heteronuclear dipolar couplings in MAS NMR using R-type recoupling 2004 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 168:2, s. 194-201 Tidskriftsartikel (refereegranskat)abstract A novel MAS NMR approach is presented for the determination of heteronuclear dipolar couplings in unoriented materials. The technique is based on the proton-detected local field (PDLF) protocol, and achieves dipolar recoupling by R-type radio-frequency irradiation. The experiment, which is called R-PDLF spectroscopy, is demonstrated on solid and liquid-crystalline systems. For mobile systems, it is shown that the R-PDLF scheme provides better dipolar resolution as compared to techniques combining conventional separated local field (SLF) spectroscopy with R-type recoupling.
24.	Dvinskikh, Sergey V., et al. (författare) MRI profiles over very wide concentration ranges : Application to swelling of a bentonite clay 2009 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 198:2, s. 146-150 Tidskriftsartikel (refereegranskat)abstract In MRI investigation of soils, clays, and rocks, mainly mobile water is detected, similarly to that in biological and medical samples. However, the spin relaxation properties of water in these materials and/or low water concentration may make it difficult to use standard MRI approaches. Despite these limitations, one can combine MRI techniques developed for solid and liquid states and use independent information on relaxation properties of water, interacting with the material of interest, to obtain true images of both water and material content. We present procedures for obtaining such true density maps and demonstrate their use for studying the swelling of bentonite clay by water. A constant time imaging protocol provides 1D mapping of the clay distribution in regions with clay concentration above 10 vol%. T-1 relaxation time imaging is employed to monitor the clay content down to 10(-3) vol%. Data provided by those two approaches are in good agreement in the overlapping range of concentrations. Covering five orders of magnitude of clay concentration, swelling of sodium-exchanged bentonite clays from pre-compacted pellets into a gel phase is followed in detail.
25.	Dvinskikh, Sergey V., et al. (författare) Sensitivity and resolution enhancement in solid-state NMR spectroscopy of bicelles 2007 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 184:2, s. 228-235 Tidskriftsartikel (refereegranskat)abstract Magnetically aligned bicelles are becoming attractive model membranes to investigate the structure, dynamics, geometry, and interaction of membrane-associated peptides and proteins using solution- and solid-state NMR experiments. Recent studies have shown that bicelles are more suitable than mechanically aligned bilayers for multidimensional solid-state NMR experiments. In this work, we describe experimental aspects of the natural abundance C-13 and N-14 NMR spectroscopy of DMPC/DHPC bicelles. In particular, approaches to enhance the sensitivity and resolution and to quantify radio-frequency heating effects are presented. Sensitivity of C-13 detection using single pulse excitation, conventional cross-polarization (CP), ramp-CP, and NOE techniques are compared. Our results suggest that the proton decoupling efficiency of the FLOPSY pulse sequence is better than that of continuous wave decoupling, TPPM, SPINAL, and WALTZ sequences. A simple method of monitoring the water proton chemical shift is demonstrated for the measurement of sample temperature and calibration of the radio-frequency-induced heating in the sample. The possibility of using N-14 experiments on bicelles is also discussed.
26.	Edén, Mattias (författare) Two-dimensional MAS NMR correlation protocols involving double-quantum filtering of quadrupolar spin-pairs 2010 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 204:1, s. 99-110 Tidskriftsartikel (refereegranskat)abstract Three two-dimensional (2D) NMR homonuclear correlation techniques invoking double-quantum (2Q) filtration of the central transitions of half-integer spins are evaluated numerically and experimentally. They correlate directly detected single-quantum (1Q) coherences in the t(2) domain with either of 1Q, two-spin 2Q or single-spin multiple-quantum coherence-evolutions in the indirect (t(1)) dimension. We employ experimental Na-23 and Al-22 NMR on sodium sulfite and the natural mineral sillimanite (SiAl2O5), in conjunction with simulated 2D spectra from pairs of dipolar-recoupled spins-3/2 and 5/2 at different external magnetic fields, to compare the correlation strategies from the viewpoints of 2D spectral resolution, signal sensitivity, implementational aspects and their relative merits for establishing internuclear proximities and quadrupolar tensor orientations.
27.	Eriksson, Stefanie, et al. (författare) Isotropic diffusion weighting in PGSE NMR by magic-angle spinning of the q-vector. 2013 Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1096-0856 .- 1090-7807. ; 226, s. 13-18 Tidskriftsartikel (refereegranskat)abstract When PGSE NMR is applied to water in microheterogeneous materials such as liquid crystals, foodstuffs, porous rocks, and biological tissues, the signal attenuation is often multi-exponential, indicating the presence of pores having a range of sizes or anisotropic domains having a spread of orientations. Here we modify the standard PGSE experiment by introducing low-amplitude harmonically modulated gradients, which effectively make the q-vector perform magic-angle spinning (MAS) about an axis fixed in the laboratory frame. With this new technique, denoted q-MAS PGSE, the signal attenuation depends on the isotropic average of the local diffusion tensor. The capability of q-MAS PGSE to distinguish between pore size and domain orientation dispersion is demonstrated by experiments on a yeast cell suspension and a polydomain anisotropic liquid crystal. In the latter case, the broad distribution of apparent diffusivities observed with PGSE is narrowed to its isotropic average with q-MAS PGSE in a manner that is analogous to the narrowing of chemical shift anisotropy powder patterns using magic-angle sample spinning in solid-state NMR. The new q-MAS PGSE technique could be useful for resolving size/orientation ambiguities in the interpretation of PGSE data from, e.g., water confined within the axons of human brain tissue.
28.	Fang, Yuan, et al. (författare) Improved accuracy and precision in electrophoretic NMR experiments. Current control and sample cell design 2020 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 318:106796, s. 1-7 Tidskriftsartikel (refereegranskat)abstract Electrophoretic NMR has the capacity to provide unique physico-chemical information but is limited by avariety of experimental artifacts, such as thermal convection and electrolytic products in the sample.Here we present some simple modifications to the experimental hardware and protocol that, in a signif-icant number of cases, can much improve experimental accuracy and precision. We show that one canstrongly reduce artifacts in a symmetric sample cell with an appropriate feeding of current and with aporous plug suitably inserted. This latter feature requires that the electric field pulses across the sensitivevolume are implemented as current-controlled pulses applied to the sample. Measurements withcurrent-controlled pulses have the additional advantage of not requiring calibration with samples ofknown electrophoretic mobility.
29.	Furo, Istvan, et al. (författare) Noise reduction in quadrupolar echo spectra at short echo times 2001 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 152:2, s. 214-216 Tidskriftsartikel (refereegranskat)abstract The phase cycling scheme Exorcycle embedded into the quadrupolar echo pulse sequence is presented as a tool for reducing ringing effects in broad quadrupolar spectra.
30.	Ghalebani, Leila, et al. (författare) NMR relaxation interference effects and internal dynamics in γ-cyclodextrin 2008 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 195:1, s. 1-8 Tidskriftsartikel (refereegranskat)abstract Multiple-magnetic field (9.4, 14.1 and 21.1 T) measurements of 13C spin–lattice and spin–spin relaxation rates, the heteronuclear Overhauser enhancement and cross-correlated relaxation rates (CCRRs) in the methylene groups are reported for γ-cyclodextrin in water/dimethylsulfoxide solution at 323 and 343 K. The CCRRs are obtained from differences in the initial relaxation rates of the components of the CH2 triplet in the 13C spectra. The relaxation data are analyzed using the Lipari–Szabo approach and a novel modification of the two-site jump model. According to the latter model, inclusion of the dipolar (CH,CH′) cross-correlated longitudinal and transverse relaxation is important for estimating the rate of the conformational jumps in the hydroxymethyl group. Using the dynamic information from the jump model, we have also used the differences in the initial relaxation rates for the triplet components to estimate the anisotropy of the chemical shielding tensor.
31.	Giesecke, Marianne, et al. (författare) Constant-time chemical-shift selective imaging 2013 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 226, s. 19-21 Tidskriftsartikel (refereegranskat)abstract We demonstrate that chemical-shift-selective constant-time imaging (CTI) can be performed by simply inserting selective saturation into the original imaging pulse sequence. The performance of the proposed method is illustrated by 7Li CTI imaging in a battery model that contains both Li metal electrodes and an electrolyte containing a dissolved Li salt.
32.	Grebenkov, Denis, et al. (författare) Exploring diffusion across permeable barriers at high gradients. I. Narrow pulse approximation 2014 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 248, s. 153-163 Tidskriftsartikel (refereegranskat)abstract The adaptive variation of the gradient intensity with the diffusion time at a constant optimal b-value is proposed to enhance the contribution of the nuclei diffusing across permeable barriers, to the pulsed-gradient spin-echo (PGSE) signal. An exact simple formula the PGSE signal is derived under the narrow pulse approximation in the case of one-dimensional diffusion across a single permeable barrier. The barrier contribution to the signal is shown to be maximal at a particular b-value. The exact formula is then extended to multiple permeable barriers, while the PGSE signal is shown to be sensitive to the permeability and to the inter-barrier distance. Potential applications of the protocol to survey diffusion in three-dimensional domains with permeable membranes are illustrated through numerical simulations.
33.	Gudmundson, Erik, 1976-, et al. (författare) Spectral Estimation of Irregularly Sampled Exponentially Decaying Signals with Applications to RF Spectroscopy 2010 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 203:1, s. 167-176 Tidskriftsartikel (refereegranskat)abstract The problem of estimating the spectral content of exponentially decaying signals from a set of irregularly sampled data is of considerable interest in several applications, for example in various forms of radio frequency spectroscopy. In this paper, we propose a new nonparametric iterative adaptive approach that provides a solution to this estimation problem. As opposed to commonly used methods in the field, the damping coefficient, or linewidth, is explicitly modeled, which allows for an improved estimation performance. Numerical examples using both simulated data and data from NQR experiments illustrate the benefits of the proposed estimator as compared to currently available nonparametric methods.
34.	Hallberg, Fredrik, et al. (författare) Sensitive and robust electrophoretic NMR : Instrumentation and experiments 2008 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 192:1, s. 69-77 Tidskriftsartikel (refereegranskat)abstract Although simple as a concept, electrophoretic NMR (eNMR) has so far failed to find wider application. Problems encountered are mainly due to disturbing and partly irreproducible convection-like bulk flow effects from both electro-osmosis and thermal convection. Additionally, bubble formation at the electrodes and rf noise pickup has constrained the typical sample geometry to U-tube-like arrangements with a small filling factor and a low resulting NMR sensitivity. Furthermore, the sign of the electrophoretic mobility cancels out in U-tube geometries. We present here a new electrophoretic sample cell based on a vertically placed conventional NMR sample tube with bubble-suppressing palladium metal as electrode material. A suitable radiofrequency filter design prevents noise pickup by the NMR sample coil from the high-voltage leads which extend into the sensitive sample volume. Hence, the obtained signal-to-noise ratio of this cell is one order of magnitude higher than that of our previous U-tube cells. Permitted by the retention of the sign of the displacement-related signal phase in the new cell design, an experimental approach is described where bulk flow effects by electro-osmosis and/or thermal convection are compensated through parallel monitoring of a reference signal from a non-charged species in the sample. This approach, together with a CPMG-like pulse train scheme provides a superior first-order cancellation of non-electrophoretic bulk flow effects.
35.	Hedin, N., et al. (författare) Accurate intensities of broad NMR lines from composite pulse experiments 2000 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 142:1, s. 32-36 Tidskriftsartikel (refereegranskat)abstract Accurate determination of integral intensities of broad lines is difficult when spin relaxation during the applied pulses cannot be neglected and/or when ringing of the tank circuit interferes with the signal. Here we present an extension of the analytical solution of the generalized Bloch equations (G. A. Morris and P. B. Chilvers, J. Magn. Reson. A 107, 236 (1994)), which is then used to evaluate the signal intensity obtained in a composite pulse experiment designed to cancel ringing effects. Comparing intensities of broad and narrow Br-81 spectral lines tests and proves the accuracy Of this approach.
36.	Hiller, Sebastian, et al. (författare) Chaperone-client complexes: A dynamic liaison. 2018 Ingår i: Journal of magnetic resonance (San Diego, Calif. : 1997). - : Elsevier BV. - 1096-0856 .- 1090-7807. ; 289, s. 142-155 Forskningsöversikt (refereegranskat)abstract Living cells contain molecular chaperones that are organized in intricate networks to surveil protein homeostasis by avoiding polypeptide misfolding, aggregation, and the generation of toxic species. In addition, cellular chaperones also fulfill a multitude of alternative functionalities: transport of clients towards a target location, help them fold, unfold misfolded species, resolve aggregates, or deliver clients towards proteolysis machineries. Until recently, the only available source of atomic resolution information for virtually all chaperones were crystal structures of their client-free, apo-forms. These structures were unable to explain details of the functional mechanisms underlying chaperone-client interactions. The difficulties to crystallize chaperones in complexes with clients arise from their highly dynamic nature, making solution NMR spectroscopy the method of choice for their study. With the advent of advanced solution NMR techniques, in the past few years a substantial number of structural and functional studies on chaperone-client complexes have been resolved, allowing unique insight into the chaperone-client interaction. This review summarizes the recent insights provided by advanced high-resolution NMR-spectroscopy to understand chaperone-client interaction mechanisms at the atomic scale.
37.	Jahangiri, Amir, 1987, et al. (författare) NMR spectrum reconstruction as a pattern recognition problem 2023 Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 346 Tidskriftsartikel (refereegranskat)abstract A new deep neural network based on the WaveNet architecture (WNN) is presented, which is designed to grasp specific patterns in the NMR spectra. When trained at a fixed non-uniform sampling (NUS) schedule, the WNN benefits from pattern recognition of the corresponding point spread function (PSF) pattern produced by each spectral peak resulting in the highest quality and robust reconstruction of the NUS spectra as demonstrated in simulations and exemplified in this work on 2D 1H-15N correlation spectra of three representative globular proteins with different sizes: Ubiquitin (8.6 kDa), Azurin (14 kDa), and Malt1 (44 kDa). The pattern recognition by WNN is also demonstrated for successful virtual homodecoupling in a 2D methyl 1H-13C - HMQC spectrum of MALT1. We demonstrate using WNN that prior knowledge about the NUS schedule, which so far was not been fully exploited, can be used for designing new powerful NMR processing techniques that surpass the existing algorithmic methods.
38.	Kaderavek, Pavel, et al. (författare) Spectral density mapping at multiple magnetic fields suitable for C-13 NMR relaxation studies 2016 Ingår i: Journal of magnetic resonance. - : Elsevier. - 1090-7807 .- 1096-0856. ; 266, s. 23-40 Tidskriftsartikel (refereegranskat)abstract Standard spectral density mapping protocols, well suited for the analysis of N-15 relaxation rates, introduce significant systematic errors when applied to C-13 relaxation data, especially if the dynamics is dominated by motions with short correlation times (small molecules, dynamic residues of macromolecules). A possibility to improve the accuracy by employing cross-correlated relaxation rates and on measurements taken at several magnetic fields has been examined. A suite of protocols for analyzing such data has been developed and their performance tested. Applicability of the proposed protocols is documented in two case studies, spectral density mapping of a uniformly labeled RNA hairpin and of a selectively labeled disaccharide exhibiting highly anisotropic tumbling. Combination of auto- and cross-correlated relaxation data acquired at three magnetic fields was applied in the former case in order to separate effects of fast motions and conformational or chemical exchange. An approach using auto-correlated relaxation rates acquired at five magnetic fields, applicable to anisotropically moving molecules, was used in the latter case. The results were compared with a more advanced analysis of data obtained by interpolation of auto-correlated relaxation rates measured at seven magnetic fields, and with the spectral density mapping of cross-correlated relaxation rates. The results showed that sufficiently accurate values of auto- and cross-correlated spectral density functions at zero and C-13 frequencies can be obtained from data acquired at three magnetic fields for uniformly C-13-labeled molecules with a moderate anisotropy of the rotational diffusion tensor. Analysis of auto-correlated relaxation rates at five magnetic fields represents an alternative for molecules undergoing highly anisotropic motions.
39.	Keyser, Ailsa K.V., et al. (författare) Pulsed electron spin resonance of an organic microcrystal by dispersive readout 2020 Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 321 Tidskriftsartikel (refereegranskat)abstract We establish a testbed system for the development of high-sensitivity Electron Spin Resonance (ESR) techniques for small samples at cryogenic temperatures. Our system consists of a NbN thin-film planar superconducting microresonator designed to have a concentrated mode volume to couple to a small amount of paramagnetic material, and to be resilient to magnetic fields of up to 400mT. At 65mK we measure high-cooperativity coupling (C≈19) to an organic radical microcrystal containing 1012 spins in a pico-litre volume. We detect the spin–lattice decoherence rate via the dispersive frequency shift of the resonator. Techniques such as these could be suitable for applications in quantum information as well as for pulsed ESR interrogation of very few spins to provide insights into the surface chemistry of, for example, the material defects in superconducting quantum processors.
40.	Kharkov, Boris B., et al. (författare) Low rf power high resolution H-1-C-13-N-14 separated local field spectroscopy in lyotropic mesophases 2012 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 223, s. 73-79 Tidskriftsartikel (refereegranskat)abstract Efficiency of the proton detected (encoded) H-1-C-13-N-14 local field spectroscopy technique at low radiofrequency power is examined when applied to concentrated ionic lyotropic mesophases exhibiting heteronuclear and homonuclear dipolar couplings in kHz range. We demonstrate that highly resolved heteronuclear dipolar spectra can be obtained with limited radiofrequency power corresponding to decoupling B-1 field of 20 kHz and with superior spectral resolution and sensitivity provided by standard solution state probes. To maintain sufficiently large spectral window in indirect dimension, power level alternation scheme for homonuclear decoupling was introduced. In anisotropic mesophases of an ionic surfactant, pair-wise coupling constants in the three-spin system H-1-C-13-N-14 were accurately determined. Relative signs of heteronuclear dipolar couplings to nitrogen were obtained employing frequency selective decoupling.
41.	Kolloff, Christopher, 1995, et al. (författare) Motional clustering in supra-τ c conformational exchange influences NOE cross-relaxation rate 2022 Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 338 Tidskriftsartikel (refereegranskat)abstract Biomolecular spin relaxation processes, such as the NOE, are commonly modeled by rotational τc-tumbling combined with fast motions on the sub-τc timescale. Motions on the supra-τc timescale, in contrast, are considered to be completely decorrelated to the molecular tumbling and therefore invisible. Here, we show how supra-τc dynamics can nonetheless influence the NOE build-up between methyl groups. This effect arises because supra-τc motions can cluster the fast-motion ensembles into discrete states, affecting distance averaging as well as the fast-motion order parameter and hence the cross-relaxation rate. We present a computational approach to estimate methyl–methyl cross-relaxation rates from extensive (>100×τc) all-atom molecular dynamics (MD) trajectories on the example of the 723-residue protein Malate Synthase G. The approach uses Markov state models (MSMs) to resolve transitions between metastable states and thus to discriminate between sub-τc and supra-τc conformational exchange. We find that supra-τc exchange typically increases NOESY cross-peak intensities. The methods described in this work extend the theory of modeling sub-μs dynamics in spin relaxation and thus contribute to a quantitative estimation of NOE cross-relaxation rates from MD simulations, eventually leading to increased precision in structural and functional studies of large proteins.
42.	Koptioug, Andrei, 1956-, et al. (författare) New Transmission-Line Resonator for Pulsed EPR 1997 Ingår i: Journal of magnetic resonance. - Amsterdam : Elsiver. - 1090-7807 .- 1096-0856. ; :125, s. 369-371 Tidskriftsartikel (refereegranskat)
43.	Kotsyubynskyy, Dmytro, et al. (författare) Carbon-13 NOESY and equivalent protons : methyl iodide dynamics 2010 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 204:2, s. 239-247 Tidskriftsartikel (refereegranskat)abstract We have shown that proton-coupled carbon-13 2D NOESY experiments, performed on degenerate spin systems, can provide unique quantitative information about anisotropic reorientational motions and molecular geometry. Relevant theory for AX2 and AX3 spin systems is presented, assuming the dipole–dipole and random field relaxation mechanisms of 13C nucleus, and demonstrated on methyl iodide solution in chloroform. Agreement with experimental intensities of all the six independent peaks is very good in the whole range of mixing times (up to 45 s).
44.	Kowalewski, J, et al. (författare) Extensive NMRD studies of Ni(II) salt solutions in water and water-glycerol mixtures 2008 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 195, s. 103-111 Tidskriftsartikel (refereegranskat)abstract Aqueous solutions of simple nickel(II) salts are a classical test case for theories of the paramagnetic relaxation enhancement (PRE) and its dependence on the magnetic field (nuclear magnetic relaxation dispersion, NMRD), going back to late fifties. We present here new experimental data, extending the NMRD range up to 21 T (900 MHz). In addition to salt solutions in (acidified) water, we have also measured on solutions containing glycerol. The aqueous solution data do not show any significant changes compared to the earlier experiments. The interpretation, based on the general ("slow-motion") theory is also similar to the earlier work from our laboratory. The NMRD-data in mixed solvents are qualitatively different, indicating that the glycerol not only changes the solution viscosity, but may also enter the first coordination sphere of the metal ion, resulting in lower symmetry complexes, characterized by non-vanishing averaged zero-field splitting. This hypothesis is corroborated by molecular dynamics simulations. A strategy appropriate for interpreting the NMRD-data for the chemically complicated systems of this type is proposed.
45.	Kowalewski, Jozef, et al. (författare) Field-dependent paramagnetic relaxation enhancement in solutions of Ni(II) : What happens above the NMR proton frequency of 1 GHz? 2020 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 314 Tidskriftsartikel (refereegranskat)abstract An extended set of paramagnetic relaxation enhancement (PRE) data, up to the field of 32.9 Tesla, is reported for protons in an acidified aqueous solution of a Ni(II) salt in the presence and in the absence of added glycerol. For the 55% w/w glycerol sample, a distinct maximum in the PRE vs magnetic field curve is observed for the first time. The data are analysed using the Swedish slow-motion theory, including both the intramolecular (inner-sphere) and intermolecular (outer-sphere) contributions. The results indicate that estimating the outer-sphere part in the presence of the more efficient inner-sphere term is a difficult task.
46.	Larsson, Anna-Carin, et al. (författare) Solid state 31P and 207Pb MAS NMR studies on polycrystalline O,O′-dialkyldithiophosphate lead(II) complexes 2005 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 177:1, s. 56-66 Tidskriftsartikel (refereegranskat)abstract A number of lead(II) O,O′-dialkyldithiophosphate complexes were studied by 13C, 31P, and 207Pb MAS NMR. Simulations of 31P chemical shift anisotropy using spinning sideband analysis reveal a linear relationship between the SPS bond angle and the principal values δ22 and δ33 of the 31P chemical shift tensor. The 31P CSA data were used to assign ligands with different structural functions. In the cases of Adiethyldithiophosphate and di-iso-butyldithiophosphate lead(II) complexes, 2J (31P, 207Pb)-couplings were resolved and used to confirm the suggested assignment of the ligands. The SIMPSON computer program was used to calculate 31P and 207Pb spectral sideband patterns.
47.	Lasic, Samo, et al. (författare) Spectral characterization of diffusion with chemical shift resolution: Highly concentrated water-in-oil emulsion. 2009 Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1096-0856 .- 1090-7807. ; 199, s. 166-172 Tidskriftsartikel (refereegranskat)abstract We present a modulated gradient spin-echo method, which uses a train of sinusoidally shaped gradient pulses separated by 180 degrees radio-frequency (RF) pulses. The RF pulses efficiently refocus chemical shifts and de-phasing due to susceptibility differences, resulting in undistorted, high-resolution diffusion weighted spectra. This allows for the simultaneous spectral characterization of the diffusion of several molecular species with different chemical shifts. The technique is robust against susceptibility artifacts, field inhomogeneity and imperfections in the gradient generating equipment. The feasibility of the technique is demonstrated by measuring the diffusion of water, oil, and water-soluble salt in a highly concentrated water-in-oil emulsion. The diffusion of water and salt reveal precise information about the droplet size distribution below the mum-range. Common droplet size distribution explains both the data for water with finite long-range diffusion and the data for salt with negligible long-range diffusion. The results of water diffusion show that the technique is efficient in deconvolving the effects of molecular exchange between droplets and restricted diffusion within droplets. The effects of water exchange suggest that droplets of different sizes are uniformly distributed within the sample.
48.	Li, Jing-Rebecca, et al. (författare) Numerical study of a macroscopic finite pulse model of the diffusion MRI signal 2014 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 248, s. 54-65 Tidskriftsartikel (refereegranskat)abstract Diffusion magnetic resonance imaging (dMRI) is an imaging modality that probes the diffusion characteristics of a sample via the application of magnetic field gradient pulses. The dMRI signal from a heterogeneous sample includes the contribution of the water proton magnetization from all spatial positions in a voxel. If the voxel can be spatially divided into different Gaussian diffusion compartments with inter-compartment exchange governed by linear kinetics, then the dMRI signal can be approximated using the macroscopic Karger model, which is a system of coupled ordinary differential equations (ODEs), under the assumption that the duration of the diffusion-encoding gradient pulses is short compared to the diffusion time (the narrow pulse assumption). Recently, a new macroscopic model of the dMRI signal, without the narrow pulse restriction, was derived from the Bloch-Torrey partial differential equation (PDE) using periodic homogenization techniques. When restricted to narrow pulses, this new homogenized model has the same form as the Karger model. We conduct a numerical study of the new homogenized model for voxels that are made up of periodic copies of a representative volume that contains spherical and cylindrical cells of various sizes and orientations and show that the signal predicted by the new model approaches the reference signal obtained by solving the full Bloch-Torrey PDE in O(ε(2)), where ε is the ratio between the size of the representative volume and a measure of the diffusion length. When the narrow gradient pulse assumption is not satisfied, the new homogenized model offers a much better approximation of the full PDE signal than the Karger model. Finally, preliminary results of applying the new model to a voxel that is not made up of periodic copies of a representative volume are shown and discussed.
49.	Lips, O., et al. (författare) Magnet design with high B-0 homogeneity for fast-field-cycling NMR applications 2001 Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 149:1, s. 22-28 Tidskriftsartikel (refereegranskat)abstract The design, construction, and performance of a low-inductance solenoidal coil with high B-0 homogeneity for fast-field-cycling NMR is presented. It consists of six concentric layers. The conductor width is varied to minimize the B-0 inhomogeneity in the volume of the sample. This is done using an algorithm which takes the real shape of the conductor directly into account. The calculated coil geometry can be manufactured easily using standard computerized numeric control equipment, which keeps the costs low. The coil is liquid cooled and produces a B-0 field of 0.95 T at 800 A. The field inhomogeneity in a cylindrical volume (diameter 5 mm, length 10 mm) is about 10 ppm, and the inductance is 190 muH. Switching times below 200 mus can be achieved. During 6 months of operation the coil has shown good stability and reliability.
50.	Lund, Anders, et al. (författare) Determination of the g-, hyperfine coupling- and zero-field splitting tensors in EPR and ENDOR using extended Matlab codes 2021 Ingår i: Journal of magnetic resonance. - : Academic Press Inc - Elsevier Science. - 1090-7807 .- 1096-0856. ; 325 Tidskriftsartikel (refereegranskat)abstract The analysis of single crystal electron magnetic resonance (EMR) data has traditionally been performed using software in programming languages that are difficult to update, are not easily available, or are obsolete. By using a modern script-language with tools for the analysis and graphical display of the data, three MatLab (R) codes were prepared to compute the g, zero-field splitting (zfs) and hyperfine coupling (hfc) tensors from roadmaps obtained by EPR or ENDOR measurements in three crystal planes. Schonlands original method was used to compute the g- and hfc-tensors by a least-squares fit to the experimental data in each plane. The modifications required for the analysis of the zfs of radical pairs with S = 1 were accounted for. A non-linear fit was employed in a second code to obtain the hfc-tensor from EPR measurements, taking the nuclear Zeeman interaction of an I = 1/2 nucleus into account. A previously developed method to calculate the g- and hfc -tensors by a simultaneous linear fit to all data was used in the third code. The validity of the methods was examined by comparison with results obtained experimentally, and by roadmaps computed by exact diagonalization. The probable errors were estimated using functions for regression analysis available in MatLab. The software will be published at https://doi.org/10.17632/ps24sw95gz.1, Input and output examples presented in this work can also be downloaded from https://old.liu.se/simarc/downloads?l=en. (C) 2021 The Author(s). Published by Elsevier Inc.

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