Experimental confirmation of the formation of collective modes of the magnetization motion of paramagnetic particles in dilute solutions due to spin exchange.

Experimental confirmation of the manifestations of new spin exchange paradigm in EPR spectra of 14N nitroxide radical solutions is presented. It was shown that in the region of relatively low concentrations of radicals, the two side components of the spectrum have a mixed shape (the sum of the absorptive line and dispersive line). The dispersion contributions in these two lines have opposite signs. As the concentration of radicals increases, the contribution of dispersion passes through an extremum and in the region of maximum contribution of dispersion, the contribution of absorption to these two lines changes sign. In the region of high concentrations of radicals, when one homogeneously broadened line is practically observed, it turns out that these side components have resonant frequencies that do not coincide with the frequency of the center of gravity of the spectrum.

Experimental confirmation of the formation of a spin polariton in dilute solutions of paramagnetic particles.

Spin exchange during random bimolecular collisions of paramagnetic particles in dilute solutions leads to a surprising effect. Collective modes of motion of the average values of the transverse magnetization components (spin coherences) of subensembles of radicals with different resonant frequencies are formed. The elementary excitations of these modes can be considered as quasiparticles. As a result of interactions with the microwave field, these quasiparticles form spin polaritons. The theoretical prediction for the formation of spin polaritons was made on the basis that the resonance frequencies observed in the EPR experiment depend on the power of the microwave field. In this work, we present an experimental confirmation of the resonant frequency dependence of the spin ensemble on the microwave power for nitroxide radical [15N]-4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl in toluene.

[Treatment of neurotrophic keratopathy in combined lesions of the trigeminal and facial nerves]. / Lechenie neirotroficheskoi keratopatii pri sochetannom porazhenii troinichnogo i litsevogo nervov.

Ocular symptomatology in lesions of the facial nerve is associated with disturbed innervation of the circular muscle of the eye that leads to disruption of the protective function of the eyelids and the development of exposure symptoms, and is accompanied by a breach in corneal tear film integrity. The main clinical manifestation of the trigeminal nerve damage is the loss of sensory innervation of the cornea and disruption of the supply of neurotransmitters to its cells, manifesting as corneal hypo- or anesthesia. This triggers a cascade of pathological processes that lead to the development of neurotrophic keratopathy. In combined pathology of the facial and trigeminal nerves, a number of interrelated and mutually aggravating problems arise that require correction of lagophthalmos and functional restoration of the trigeminal nerve, since there is an interaction between the corneal epithelium and trigeminal neurons through trophic neuromodulators, which normally contribute to the proliferation of epithelial cells, their differentiation, migration and adhesion, and are essential for vital functions, metabolism and healing of surface lesions of the eye. Classical methods of treating neurotrophic keratopathy aim to protect the ocular surface, and are palliative or auxiliary, do not provide radical relief of the symptoms of neurotrophic keratopathy. Modern surgical technique of neurotization of the cornea allows restoring the structural growth of the nerve, which provides nerve trophism and corneal sensitivity, and is the only pathogenetically substantiated method of effective treatment of neurotrophic keratopathy. At the same time, direct neurotization has undeniable advantages over methods involving intercalary donor nerves, since neuropeptides from nerve fibers are immediately released into the recipient tissue and start reparative processes. Taking into account the accumulated positive experience of neurotization surgeries, scientific and clinical research should be continued in order to improve the most effective methods of corneal neurotization and promote their wider implementation into clinical practice.

Free fibula flap for reconstruction of the severely atrophic mandible: a retrospective study.

The purpose of this retrospective study was to assess the feasibility of using a free fibula flap (FFF) for reconstruction of the alveolar region of the severely atrophic mandible, by determining bone stability after dental implant insertion and prosthetic rehabilitation in a series of eight female patients aged 36-65 years. Dental implant insertion was performed 3-4 months after reconstruction. Prosthetic loading was performed 3-4 months after implant insertion. The height of the reconstructed mandible after surgery was 21.20±1.87mm, with an increase of 8.80±1.71mm from the preoperative height. The height of the FFF immediately after reconstruction was 11.24±1.10mm; this showed a vertical loss of 0.99±0.52mm (8.79%) and maintenance of 91.21% of the initial height at a mean 14 months post-reconstruction. Applying the Wical and Swoope formula to estimate the original mandibular body height, it was found that the difference between this calculated height (21.17±3.76mm) and the reconstructed height (21.20±1.87mm) was only 0.03±3.17mm (0.14%). An overall insignificant decrease of 0.46±1.14 cm3 in FFF volume had occurred at 3-4 months after dental implant functional loading, while in two cases an increase in volume was found (1.22cm3 and 1.71cm3). The good and stable results obtained show that the FFF may be used to reconstruct the whole mandibular alveolar region, with the best possible outcomes.

[The use of autogenous free vascularized fibula transplant for the correction of severe mandibular atrophy]. / Primenenie revaskuliarizirovannogo malobertsovogo autotransplantata dlia ustraneniia vyrazhennoi atrofii nizhnei cheliusti.

The purpose of the study was to increase the effectiveness of surgical treatment and rehabilitation of patients with severe mandibular atrophy by means of autogenous free vascularized fibula transplant use with subsequent dental implants placement in the reconstructed mandible and implant-retained fixed dentures. In 2017 5 female patients underwent surgical treatment of severe mandibular atrophy with autogenous free vascularized fibula transplant in Maxillofacial Surgery department of CRID with additional nonvascularized iliac bone grafts and functional rehabilitation with implant-supported constructions in two of the cases. Due to its form, length and vascularization fibular bone represents a good plastic material for full length mandibular alveolar part reconstruction. The inclusion of the skin paddle in the autogenous free vascularized fibula transplant promotes secure primary closure of the surgical wound in the oral cavity. The use autogenous free vascularized fibula transplant in patients with severe mandibular atrophy with demands a thorough presurgical planning and intraoperative modeling.

Bimolecular encounters and re-encounters (cage effect) of a spin-labeled analogue of cholestane in a series of n-alkanes: effect of anisotropic exchange integral.

Electron paramagnetic resonance (EPR) spectra of the nitroxide spin probe 3ß-doxyl-5α-cholestane (CSL) are studied as functions of the molar concentration, c, and the temperature, T, in a series of n-alkanes. The results are compared with a similar study of a much smaller spin probe, perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (pDT). The Heisenberg spin exchange (HSE) rate constants, K(ex), of CSL are similar in hexane, octane, and decane and are about one-half of those for pDT in the same solvents. They are also about one-half of the Stokes-Einstein-Perrin prediction. This reduction in HSE efficiency is attributed to an effective steric factor, f(eff), which was evaluated by comparing the results with the Stokes-Einstein-Perrin prediction or with pDT, and it is equal to 0.49 ± 0.03, independent of temperature. The unpaired spin density in CSL is localized near one end of the long molecule, so the exchange integral, J, leading to HSE, is expected to be large in some collisions and small in others; thus, J is modeled by an ideal distribution of values of J = J(0) with probability f and J = 0 with probability (1 - f). Because of rotational and translation diffusion during contact and between re-encounters of the probe, the effective steric factor is predicted to be f(eff) = f(1/2). Estimating the fraction of the surface of CSL with rich spin density yields a theoretical estimate of f(eff) = 0.59 ± 0.08, in satisfactory agreement with experiment. HSE is well described by simple hydrodynamic theory, with only a small dependence on solvent-probe relative sizes at the same value of T/η, where η is the viscosity of the solvent. This result is probably due to a fortuitous interplay between long- and short-range effects that describe diffusion processes over relatively large distances. In contrast, dipole-dipole interactions (DD) as measured by the line broadening, B(dip), and the mean time between re-encounters within the cage, τ(RE), vary significantly with the solvent-probe size ratio at the same value of T/η. For these phenomena, dominated by short-range diffusion, the reciprocal fractional free volume V(0)/V(f) provides a better description of the diffusion. Thus, B(dip) and τ(RE) form common curves when plotted vs V(0)/V(f). As a result, the fractional broadening by DD occurs at an order of magnitude higher values of T/η for CSL compared with pDT.

[Technical characteristics and diagnostic capabilities of low-field magnetic resonance tomographs TMR-0,06-KFTI].

The construction, performance, technical characteristics, and prospects for upgrading the low-field magnetic resonance tomograph TMR-0,06-KFTI with magnetic field induction 0.06 T developed at the Kazan Institute of Engineering Physics are described. The engineering solutions and software of the tomograph are original developments of the project team. Tomographs TMR-0,06-KFTI have been successfully used in clinical practice in Naberezhnye Chelny since 2002 and Bugulma since 2005.

Peculiar manifestation of the dipole-dipole interaction between non-Kramers paramagnetic centers as studied by tunable high-frequency EPR spectroscopy.

EPR spectral shape of non-Kramers paramagnetic centers (PCs) is theoretically analyzed under conditions of saturation. The analysis is performed in a model that includes the spectral diffusion process induced by a random modulation of the dipole-dipole interaction of the paramagnetic centers, by reorientations of magnetic moments. It is shown that around zero magnetic field, a 'hole' might appear in the EPR spectrum. We have also studied experimentally the saturation behavior of the EPR spectrum in Cr2+: Mg2SiO4. The experimental results are interpreted in the framework of the model considered. By comparing simulated and experimental spectra, the paramagnetic relaxation times and the characteristic rate of the spectral diffusion are estimated.