An Improved NMR Permeability Model for Macromolecules Flowing in Porous Medium Abstract The extraction of macromolecules from nano-self-assembled material can be used as a laboratory model for enhancing oil recovery in reservoirs. By combining Darcy’s law and Poiseuille equation, an improved nuclear magnetic resonance (NMR) permeability model, suitable for macromolecular flow in mesopores is obtained. The calibration coefficients in the Coates equation are expressed in terms of the physical parameters of pore throat ratio rb/rt, tortuosity, and thickness of bond film in the improved model. The results show that the proportion of irreducible fluid to total fluid obtained through NMR characterization can reflect the variation tendency of irreducible macromolecule and water. By simplifying the pores of the extracted samples, the thickness model of irreducible macromolecule and water is established with the total thicknesses calculated as 1.482 nm, 1.585 nm, 1.674 nm, and 1.834 nm. The corresponding permeability results obtained from the NMR characterization (KNMR) are 7.39 mD, 6.02 mD, 5.27 mD, and 6.25 mD. The permeability results obtained from mercury intrusion experiment (KHG) are 5.10 mD, 4.73 mD, 5.82 mD, and 5.56 mD, and those from the Darcy flow experiment (KD) are 4.1 mD and 5.19 mD. The absolute deviation between KNMR and KHGvaries from 0.69 to 2.29 mD, while that between KNMR and KD is 1.58 mD. This method can be applied to the enhanced recovery of shale oil.

Occurrence of Mixed Phase in $$\text {Bi}_{0.5}\text {Sr}_{0.5}\text {Mn}_{0.9}\text {Cr}_{0.1}\text {O}_3$$ Bi 0.5 Sr 0.5 Mn 0.9 Cr 0.1 O 3 Bulk Sample: Electron Paramagnetic Resonance and Magnetization Studies Abstract We study the effects of 10% Cr substitution in Mn sites of Bi \(_{0.5}\) Sr \(_{0.5}\) MnO \(_3\) on the antiferromagnetic (AFM) ( \(T_{\text {N}} \sim \) 110 K) transition using structural, magnetic and electron paramagnetic resonance (EPR) techniques. Field cooled (FC) and zero field cooled (ZFC) magnetization measurements done from 400 K down to 4 K show that the compound is in the paramagnetic (PM) phase till 50 K where it undergoes a transition to a short-range ferromagnetic phase (FM). Electron paramagnetic resonance measurements performed in the temperature range of 300 K to 80 K conform with the magnetization measurements as symmetric signals are observed owing to the paramagnetic phase. Below 80 K, signals become asymmetric. Electron paramagnetic resonance intensity peaks at \(\sim \) 110 K, the decreasing intensity below this temperature confirming the presence of antiferromagnetism. We conclude that below 50 K the magnetization and EPR results are consistent with a cluster glass phase of BSMCO, where ferromagnetic clusters coexist with an antiferromagnetic background.

Spectral Convolution for Quantitative Analysis in EPR Spectroscopy Abstract A method for the determination of number of spins from EPR spectra with a high level of noise is proposed. The method is based on a convolution of the experimental spectrum with the spectrum of the same shape characterized by a high signal-to-noise ratio. It was shown that the convolution technique is rather robust to the presence of additive noise in examined EPR spectrum.

Hyperfine Interaction Promoted Intersystem Crossing Abstract The mechanism of the intersystem crossing (ISC) in planar aromatic hydrocarbons is revised by considering hyperfine interaction promoted singlet–triplet transitions. The density matrix of the spin system of the metastable triplet state is derived. Extra terms including the electron-nuclear ordering, the ordering between the magnetic nuclei of the molecule, and the coherence between the nuclear spin sublevels are shown to be developed during the ISC. Several peculiarities of the spin system are predicted. The results are compared with the properties generated by the optical nuclear polarization. The proposed mechanism is examined by a qualitative analysis of the available experimental data on photoexcited pentacene in p-terphenyl.

Development of High-Field and High-Pressure ESR System and Application to Triangular Antiferromagnet $$\hbox {CsCuCl}_{3}$$ CsCuCl 3 Abstract We have developed a new hybrid-type pressure cell for the high-pressure and high-field electron spin resonance (ESR) measurement using a widely used Oxford 15 T superconducting magnet with the variable temperature insert (VTI). The size of the pressure cell was optimized and a probe was also specially designed so as to be fitted to the VTI. We confirmed that the new pressure cell can generate the pressure up to at least 2.0 GPa repeatedly. Using this new ESR system, high-pressure and high-field ESR measurement was performed on the triangular antiferromagnet \(\hbox {CsCuCl}_{3}\) for \(H \parallel c\) at 4.2 K in the frequency region 60 GHz–420 GHz. We succeeded in observing the significant pressure effect of this compound. Moreover, a new ESR mode which is expected to correspond to the 1/3 magnetization plateau was observed at 0.80 GPa.

Design and Simulation of a Helmholtz Coil for Magnetic Resonance Imaging and Spectroscopy Experiments with a 3T MR Clinical Scanner Abstract Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) are non-invasive techniques for tissue characterization. MRI/MRS in small phantoms with a clinical magnetic resonance scanner requires the design and development of dedicated radiofrequency coils. This paper describes the simulation, design, and application of a 1H transmit/receive Helmholtz coil, suitable for MRI/MRS studies in small phantoms with a clinical 3T scanner. Coil inductance and resistance were analytically calculated by taking into account the conductors cross geometry while magnetic field and sample-induced resistance were calculated with magnetostatic approaches. Finally, the coil sensitivity was measured with the perturbing sphere method. Successively, a coil prototype was built and tested on the workbench and by acquisition of MRI and MRS data. Results show that such coil could provide a low cost and easy to build device for MRI/MRS experiments with a clinical scanner in small specimens.

Supplemental Shimming for HR-μMAS NMR Spectroscopy Abstract Occasionally in proton high-resolution magic angle spinning nuclear magnetic resonance spectroscopy (1H HR-MAS NMR), the standard field shimming across the region-of-interest with the active shims is not sufficient in the presence of substantial magnetic susceptibility gradients. This can be ascribed to the presence of large air pocket within the sample, the proximity between sample and probehead (especially with micro-sized probes), or data acquisition at high magnetic fields. Herein, the study demonstrates a simple approach to enhance the capacity of the shim fields—by supplementing a specific passive ferro-shim—for unifying the field distributions across the sample. Qualitative field numerical analyses were carried out to illustrate the effectiveness of the applied passive shims together with the active shims.

Charge Transfer State in the Composite DTS(FBTTh 2 ) 2 :PC 71 BM: Dynamics of Electron–Hole Distance Distribution After Light Absorption Abstract Light-induced charge separation in an organic photovoltaic (OPV) composite DTS(FBTTh2)2:PC71BM was studied. DTS(FBTTh2)2 or DTS is a non-polymer electron donor and PC71BM is a fullerene-based electron acceptor. Electron spin echo (ESE) technique has been developed to separate the signal of interfacial charge transfer state (CTS) from that of trapped charges. Pronounced out-of-phase ESE signal was observed within first few microseconds after a laser flash exciting the composite at cryogenic temperatures. This implies correlation of unpaired electron spins of DTS+ and PC71BM– species constituting CTS. The distribution of distances between these species is derived from out-of-phase ESE envelope modulation (ESEEM). Out-of-phase ESEEM traces were numerically simulated by the model assuming both magnetic dipolar and electron–hole exchange interactions within CTS. The most probable distance between DTS+ and PC71BM– within CTS increases from 4.9 nm and 5.7 nm with delays after the laser flash increase from 200 ns to 30 µs at the lowest temperature studied 20 K. This is caused by faster recombination of CTS with shorter electron–hole distance. The electron–hole exchange interaction is about J/h = 1.15 MHz for the smallest interspin distance obtained r0 = 2.5 nm. The overall similarity of the initial electron–hole distance and CTS recombination rate for DTS:PC71BM and polymer/fullerene OPV composites studied previously points to similar photoinduced charge separation mechanisms for these systems.

Detection of Magnetosome-Like Structures in Eukaryotic Cells Using Nonlinear Longitudinal Response to ac Field Abstract Although magnetosomes have been discovered in bacteria since several decades, until today the question remains open whether such biomineralized structures do exist in eukaryotic cells. Herein, evidence was provided for the existence of magnetosome-like Fe-based structures in different viable eukaryotic cells by the registration of second harmonic of magnetization M2(H) of longitudinal nonlinear response to weak ac field. The behavior of the field hysteresis of the M2 response from cells in suspension and/or in pellet indicated a multi-domain state of magnetosome-like structures in certain type of cells, and a single-domain state in other cell lines. The amounts of magnetosomes in cells range from ≤ 1÷2 to 5÷8 per cell. The presence of magnetosome-like structures was analyzed in normal tissue samples obtained from Wistar rats and C57/Bl6 mice. Additionally, the tumor tissue (orthotopic rat C6 glioma and mouse GL261 glioma) were assessed for magnetosomes. Detected magnetosomes in certain tissues (i.e., brain, heart, lungs) matched to a single-domain magnetite nanoparticle, whereas in other organs they exhibited characteristics attributable to a multi-domain state, better corresponding to Fe(0) composition of their magnetic cores. Subsequent studies are necessary to elucidate the role of the Fe-based magnetosome-like structures in the biology and physiology of eukaryotic cells.

Golden-Angle Radial Sparse Parallel MR Image Reconstruction Using SC-GROG Followed by Iterative Soft Thresholding Abstract Golden-angle radial sparse parallel (GRASP) magnetic resonance imaging (MRI) is a recent MR image reconstruction technique which integrates parallel imaging, compressed sensing and golden-angle radial scheme to reconstruct the dynamic contrast-enhanced MRI (DCE-MRI) data. Conventionally, GRASP exploits non-uniform fast Fourier transform to grid and de-grid the golden-angle radial data and employs nonlinear conjugate gradient method to recover the unaliased images. GRASP performs gridding and de-gridding operations of golden-angle radial data in every iteration which increases the computational complexity of the conventional GRASP and takes a long image reconstruction time. In this paper, self-calibrated GRAPPA operator gridding (SC-GROG) followed by iterative soft thresholding (IST) is proposed for faster GRASP reconstruction of the golden-angle radial DCE-MRI data. In the proposed method, firstly SC-GROG maps the undersampled golden-angle radial data to a Cartesian grid and then reconstructs the solution image using the IST technique. The proposed method does not require gridding and de-gridding in each iteration; therefore, it is computationally less expensive as compared to the conventional GRASP reconstruction approach. The proposed method is tested for undersampled DCE golden-angle radial liver perfusion data (at acceleration factors 11.8, 19.1 and 30.9). The reconstruction results are assessed visually as well as using mean square error, line profiles and reconstruction time. The reconstruction results are compared with the conventional GRASP reconstruction. The results show that the proposed method provides better quality reconstruction results in terms of reconstruction time and spatio-temporal resolution than the conventional GRASP approach.