Authors:M. S. Kuznetsova Pages: 635 - 655 Abstract: This work presents an overview of investigations of the nuclear spin dynamics in nanostructures with negatively charged InGaAs/GaAs quantum dots characterized by strong quadrupole splitting of nuclear spin sublevels. The main method of the investigations is the experimental measurements and the theoretical analysis of the photoluminescence polarization as a function of the transverse magnetic field (effect Hanle). The dependence of the Hanle curve profile on the temporal protocol of optical excitation is examined. Experimental data are analyzed using an original approach based on separate consideration of behavior of the longitudinal and transverse components of the nuclear polarization. The rise and decay times of each component of the nuclear polarization and their dependence on transverse magnetic field strength are determined. To study the role of the Knight field in the dynamic of nuclear polarization, a weak additional magnetic field parallel to the optical axis is used. We have found that, only taking into account the nuclear spin fluctuations, we can accurately describe the measured Hanle curves and evaluate the parameters of the electron–nuclear spin system in the studied quantum dots. A new effect of the resonant optical pumping of nuclear spin polarization in an ensemble of the singly charged (In,Ga)As/GaAs quantum dots subjected to a transverse magnetic field is discussed. Nuclear spin resonances for all isotopes in the quantum dots are detected in that way. In particular, transitions between the states split off from the ±1/2 doublets by the nuclear quadrupole interaction are identified. PubDate: 2017-07-01 DOI: 10.1007/s00723-017-0883-z Issue No:Vol. 48, No. 7 (2017)
Authors:Maxim Dolgushev; Sebastian Schnell; Denis A. Markelov Pages: 657 - 671 Abstract: We study the role of hydrodynamic interactions for the relaxation of segments’ orientations in dendrimers. The dynamics is considered in the Zimm framework. It is shown that inclusion of correlations between segments’ orientations plays a major role for the segments’ mobility, which reveals itself in the nuclear magnetic resonance relaxation functions. The enhancement of the reorientation dynamics of segments due to the hydrodynamic interactions is more significant for the inner segments. This effect is clearly pronounced in the reduced spectral density \(\omega J(\omega )\) , maximum of which shifts to higher frequencies when the hydrodynamic interactions are taken into account. PubDate: 2017-07-01 DOI: 10.1007/s00723-017-0897-6 Issue No:Vol. 48, No. 7 (2017)
Authors:Vytautas Klimavicius; Laurynas Dagys; Vladimir Chizhik; Vytautas Balevicius Pages: 673 - 685 Abstract: The high data point density measurements of 1H→11B cross-polarization (CP) kinetics upon magic-angle spinning (MAS) of [bmim][BF4] confined in mesoporous SBA-15 and MCM-41 were carried out. The complex shaped 11B CP MAS signals were observed in both silica and decomposed into two Lorentz components. This points towards the possibility of bimodal distribution of [bmim][BF4] in the studied confinements. The convergence of classical and non-classical spin coupling models was deduced processing CP kinetic curves. A good fit of the theoretical curves to the experimental data was achieved using both models without any non-random deviations between theory and experiment to appear. The convergence of spin coupling models was discussed in terms of relatively high mobility of BF4 − anion respect to the cation and the dynamics of anions in pores. These factors delete the borders between spin clusters. The spin diffusion along the pore surfaces in MCM-41 is more than twice faster than in SBA-15. PubDate: 2017-07-01 DOI: 10.1007/s00723-017-0891-z Issue No:Vol. 48, No. 7 (2017)
Authors:S. V. Ievleva; N. V. Luzhetckaia; K. V. Tyutyukin; V. V. Frolov Pages: 699 - 706 Abstract: Magnetic resonance imaging is well known as a highly effective technique of medical visualization. One of its relatively new approaches is diffusion imaging. As a rule, the majority of magnetic resonance investigations in biology and medicine tends to be carried out in high magnetic fields (1.5 T and higher), but there are some advantages of the same experiments in low magnetic fields. It can be strongly useful, for example, for designing and testing new pulse sequences, training operators of magnetic resonance imagers, making new phantoms (model objects). In this study, diffusion-weighted imaging experiments in a low magnetic field 7 mT are performed in the first time. Nevertheless, this field is about two orders of magnitude bigger than an extremely low Earth field, and so concomitant gradients and polarization problems do not arise. In particular, diffusion weighted images of combined model samples (phantoms) are presented. PubDate: 2017-07-01 DOI: 10.1007/s00723-017-0895-8 Issue No:Vol. 48, No. 7 (2017)
Authors:Yu. V. Bogachev; A. V. Nikitina; A. A. Kostina; V. A. Sabitova; V. V. Pankov; T. G. Shutava; E. G. Petrova; D. A. Kotsikau; V. O. Natarov; K. S. Livanovich Pages: 715 - 722 Abstract: The results of proton nuclear magnetic resonance (NMR) relaxation measurements in aqueous solutions of Mg x Zn y Fe3−x−y O4 magnetite-based composite magnetic nanoparticles (MNPs) are discussed. It is shown that their transverse relaxivity (relaxation efficiency) r 2 is significantly higher than the longitudinal relaxivity r 1 and depends on the magnetic nanoparticles composition and preparation method. A polyelectrolyte layer adsorbed on the nanoparticle surface increases both relaxivity values. The carbonate-synthesized MNPs possess higher values of r 2 and r 1 as compared with base-precipitated complex oxides. Relaxivity r 2 is shown to be affected by stability of MNPs in aqueous solutions and the aggregation behavior apparently can be assessed through the NMR relaxation measurements. PubDate: 2017-07-01 DOI: 10.1007/s00723-017-0889-6 Issue No:Vol. 48, No. 7 (2017)
Authors:D. S. Mazing; A. V. Nikiforova; A. S. Osinin; V. A. Moshnikov; Yu. V. Bogachev; S. M. Sukharzhevskii Pages: 731 - 737 Abstract: Colloidal nanocrystals of ZnSe doped with Mn2+ were synthesized in non-polar medium using hot-injection technique. Obtained samples were characterized by means of photoluminescence and absorption spectroscopies. To confirm the incorporation of Mn2+ impurity and to reveal its state and localization, electron paramagnetic resonance (EPR) spectroscopy was employed. As a result, EPR spectra were analyzed and hyperfine splitting constant and g-factor for Mn2+ dopant were determined. PubDate: 2017-07-01 DOI: 10.1007/s00723-017-0898-5 Issue No:Vol. 48, No. 7 (2017)
Authors:Peter Niedbalski; Christopher Parish; Qing Wang; Andhika Kiswandhi; Lloyd Lumata Abstract: The nitroxide-based 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) free radical is widely used in 13C dynamic nuclear polarization (DNP) due to its relatively low cost, commercial availability, and effectiveness as polarizing agent. While a large number of TEMPO derivatives are available commercially, so far, only few have been tested for use in 13C DNP. In this study, we have tested and evaluated the 13C hyperpolarization efficiency of eight derivatives of TEMPO free radical with different side arms in the 4-position. In general, these TEMPO derivatives were found to have slight variations in efficiency as polarizing agents for DNP of 3 M [1-13C] acetate in 1:1 v/v ethanol:water at 3.35 T and 1.2 K. X-band electron paramagnetic resonance (EPR) spectroscopy revealed no significant differences in the spectral features among these TEMPO derivatives. 2H enrichment of the ethanol:water glassing matrix resulted in further improvement of the solid-state 13C DNP signals by factor of 2 to 2.5-fold with respect to the 13C DNP signal of non-deuterated DNP samples. These results suggest an interaction between the nuclear Zeeman reservoirs and the electron dipolar system via the thermal mixing mechanism. PubDate: 2017-07-08 DOI: 10.1007/s00723-017-0916-7
Authors:Irina G. Agafonova; Vladimir N. Kotelnikov; Boris I. Geltcer; Natalya G. Kolosova; Valentin A. Stonik Abstract: The morpho-functional reorganization of regional vascular arteries is greatly altered after the induction of arterial hypertension (AH) in experimental rats. These changes can be examined using magnetic resonance imaging methods. In our experiment, induced AH caused arteriostenosis of cerebral arteries in two strains of rats—Wistar and OXYS (p < 0.05). In addition, we studied the changes in renal arteries in the same experiment. Compensatory vasodilatation was found in the extrarenal part of arteries. Arteriostenosis was detected in the intrarenal part of arteries, which was due to cytotoxic hypostasis of renal parenchyma. We proposed a cerebral vascular index and applied this index for precise analysis of changes in the studied arteries. This index is calculated as the ratio of the diameter of cerebral arteries to the diameter of renal arteries. The degree of differences in vasoconstriction between cerebral and renal arteries was established. Our results showed a moderate degree of differences in the vasoconstriction of cerebral arteries. In addition, the degree of differences in the vasoconstriction of intrarenal arteries revealed deeper vasoconstriction. These distinctions are 28.1% (p < 0.05) and 60.9% (p < 0.05) for Wistar and OXYS rats, respectively. Arterial morphometry revealed reduced sizes of all OXYS rat arteries compared with those of Wistar rat arteries. These pathological changes were associated with excessive stiffness (rigidity) of vascular walls due to accelerated aging. The accelerated aging of OXYS rat arteries led to a decrease in their vasodilatation potential and a decrease in the blood supply of cerebral and renal arteries. Comparative morphometry of the status of all arteries in both groups after AH revealed multiple specific changes in the remodeled arteries. PubDate: 2017-07-08 DOI: 10.1007/s00723-017-0914-9
Authors:Marija Jovanovic; Milica Selmic; Dragana Macura; Slobodan Lavrnic; Svetlana Gavrilovic; Marko Dakovic; Sandra Radenkovic; Ivan Soldatovic; Tatjana Stosic-Opincal; Ruzica Maksimovic Abstract: Artificial neuronal network (ANN) in classification of glioblastoma multiforme (GBM) recurrence from treatment effects using advanced magnetic resonance imaging techniques was evaluated. In 56 patients with treated GBM, normalised minimal and mean apparent-diffusion coefficient (ADC) values, vessels number on susceptibility-weighted images (SWI) and Cho/Cr ratio were analysed statistically and by ANN. Significant correlation exists between normalised minimal and mean ADC values, and no correlation between ADC and Cho/Cr values. Cut-off values for tumour presence were: 1.14 for normalised minimal ADC (54% sensitivity, 71% specificity), 1.13 for normalised mean ADC (51% sensitivity, 71% specificity), 1.8 for Cho/Cr ratio (92% sensitivity, 82% specificity), grade 2 for SWI (87% sensitivity, 82% specificity). An accurate prediction of ANN to classify patients into GBM progression or treatment effects group was 99% during the training and 96.8% during the testing phase. Multi-parametric ANN allows distinction between GBM recurrence and treatment effects, and can be used in clinical practice. PubDate: 2017-07-06 DOI: 10.1007/s00723-017-0913-x
Authors:I. Gimazov; Yu. Talanov; V. Sakhin; T. Adachi; T. Noji; Y. Koike Abstract: The superconducting fluctuations above the critical temperature in Bi2Sr2Ca1−x Y x Cu2O8+δ (x = 0–0.3) single crystals are studied by microwave absorption (MWA). The maximum in the MWA temperature dependence was observed close to the critical temperature. Its formation is explained by the change of the quasiparticle density of states due to superconducting fluctuations. The fluctuation area boundary is plotted on the phase diagram using the variation of the MWA temperature dependence with the hole density and is compared with the pseudogap phase behavior. PubDate: 2017-07-04 DOI: 10.1007/s00723-017-0912-y
Authors:Jian-ping Huang; Liang-kuan Zhu; Li-hui Wang; Wen-long Song Abstract: Magnetic resonance imaging (MRI) is widely adopted for clinical diagnosis due to its non-invasively detection. However, acquisition of full k-space data limits its imaging speed. Compressed sensing (CS) provides a new technique to significantly reduce the measurements with high-quality MR image reconstruction. The sparsity of the MR images is one of the crucial bases of CS-MRI. In this paper, we present to use sparsity averaging prior for CS-MRI reconstruction in the basis of that MR images have average sparsity over multiple wavelet frames. The problem is solved using a Fast Iterative Shrinkage Thresholding Algorithm (FISTA), each iteration of which includes a shrinkage step. The performance of the proposed method is evaluated for several types of MR images. The experiment results illustrate that our approach exhibits a better performance than those methods that using redundant frame or a single orthonormal basis to promote sparsity. PubDate: 2017-06-27 DOI: 10.1007/s00723-017-0910-0
Authors:Abdul Haseeb Ahmed; Ijaz M. Qureshi; M. Habib Mahmood Abstract: Motion correction is a challenging problem in free breathing undersampled cardiac perfusion magnetic resonance images. It is due to aliasing artifacts in the reconstructed images and the rapid contrast changes in the perfusion images. In addition to the reconstruction limitations, many registration algorithms underperforms in the presence of the rapid intensity changes. In this paper, we propose a novel motion correction technique that reconstructs the motion-free images from the undersampled cardiac perfusion MR data. The technique utilizes the robust principal component analysis along with the periodic decomposition to separate the respiratory motion component that can be registered, from the unchanged contrast intensity variations. It was tested on synthetic data, simulated data, and the clinically acquired data. The performance of the method was qualitatively assessed and validated by comparing manually acquired time–intensity curves of the myocardial sectors to automatically generated curves before and after registration. PubDate: 2017-06-22 DOI: 10.1007/s00723-017-0907-8
Authors:Ae Ran Lim Abstract: The resonance frequencies and relaxation mechanisms of Cs2CuBr4 and Cs2ZnBr4 were examined by static nuclear magnetic resonance (NMR) method. Here, the two inequivalent Cs(1) and Cs(2) sites surrounded by Br ions were distinguished. The saturation recovery traces for 133Cs nuclei in Cs2CuBr4 with the paramagnetic ions, and those in Cs2ZnBr4 without the paramagnetic ions were each fitted by four exponential functions. From these results, the spin–lattice relaxation times T1 in the laboratory frame of 133Cs nuclei in the two crystals were obtained, and Cs(1) surrounded by 11 bromide ions has a longer relaxation time than Cs(2) surrounded by 9 bromide ions. PubDate: 2017-06-22 DOI: 10.1007/s00723-017-0911-z
Authors:Vladimir Chizhik; Vyacheslav Frolov; Pavel Kupryanov; Konstantin Tyutyukin Abstract: The effect of concomitant magnetic fields emerging in conjunction with encoding gradients, which is important in the process of the magnetic resonance imaging in low fields, has been considered. The manifestations of concomitant magnetic fields in a concrete gradient system, namely in the system of two coaxial gradient coils, have been thoroughly analyzed. It has been suggested to improve the gradient system via optimization of the interspace between coils on the basis of the standard criterion of the minimum of root-mean-square deviation of the encoding field dependence from a linear one. It has been shown that the optimal interspace is not the Maxwell condition. PubDate: 2017-06-17 DOI: 10.1007/s00723-017-0909-6
Authors:Baosong Wu; Stephen A. Altobelli; Eiichi Fukushima Abstract: We describe and apply a scheme to obtain nuclear magnetic resonance (NMR) signals from multiple regions in space with a single pulse sequence in systems with strong, usually unavoidable, gradient magnetic fields. This is accomplished with multiple frequency irradiation and reception. Applications described include dual-slice NMR of a fluid to enhance S/N, T 2 measurements of two different samples, and efficient T 1 measurement sequence by interleaving shorter delays within a longer delay for different slices. PubDate: 2017-06-15 DOI: 10.1007/s00723-017-0899-4
Authors:Yu. M. Bunkov; A. V. Klochkov; T. R. Safin; K. R. Safiullin; M. S. Tagirov Abstract: The coherent quantum state of magnons—Bose–Einstein condensate (BEC) has been observed in several types of antiferromagnets. According to the Bose statistics of magnons, BEC appears when the magnon density exceeds the critical density N BEC and the magnon gas condenses to a quantum liquid. The BEC state is characterized by a coherent precession of the magnetization. In this paper, the first experiments showing the suppression of the spin echo signal by the magnon BEC is presented. These experiments confirm the coherence of magnetic excitations in the BEC state. PubDate: 2017-06-07 DOI: 10.1007/s00723-017-0906-9
Authors:A. A. Bogdan; G. V. Kataeva; J. G. Khomenko; A. G. Ilves; L. N. Prakhova Abstract: The quality of the signal received from metabolites in 1H-magnetic resonance spectroscopy (MRS) directly depends on physical parameters of the impulse sequence used, namely on Time of Echo (TE). We compare MRS (Achieva 3T PRESS 1H-MRS (TE = 53 and 144 ms, TR = 2000 ms) data acquired in supraventricular white matter and medial cortex at two various TE (53 and 144 ms) for patients with the multiple sclerosis (25 patients with the confirmed diagnosis of relapsing-remitting multiple sclerosis and 20 patients with the diagnosis of secondary progressive multiple sclerosis) and control group (21 healthy volunteers, comparable on age), to evaluate advantages and disadvantages of these two Echo Time in clinical practice. PubDate: 2017-06-06 DOI: 10.1007/s00723-017-0900-2
Authors:Egor Alakshin; Rasul Gazizulin; Alex Klochkov; Ekaterina Kondratyeva; Artem Laskin; Murat Tagirov Abstract: Geological samples of calcium carbonates (CaCO3) were investigated by 3He NMR, nitrogen porosimetry, X-ray diffraction and electron microscopy methods. The integral porosity of the samples was obtained by 3He nuclear magnetic resonance method and compared with nitrogen adsorption isotherms data. The advantages of 3He porometry method are discussed. PubDate: 2017-06-01 DOI: 10.1007/s00723-017-0904-y
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