Electron Spin-Lattice Relaxation of doped Yb3+ ions in YBa2Cu3Ox

The electron spin-lattice relaxation (SLR) times T1 of Yb3+‡ ions were measured from the temperature dependence of electron spin resonance linewidth in Y0.99Yb0.01Ba2Cu3Ox with different oxygen contents. Raman relaxation processes dominate the electron SLR. Derived from the temperature dependence of the SLR rate, the Debye temperature (Td) increases with the critical temperature Tc and oxygen content x. Keywords: EPR; ESR; Electron spin-lattice relaxation; Debye temperature; Critical temperatureComment: 5 Pages 4 Figure

Electron Spin-Lattice Relaxation of Er3+ ions in Er0.01Y0.99Ba2Cu3Ox

The temperature dependence of the electron spin-lattice relaxation SLR was studied in Er0.01Y0.99Ba2Cu3Ox compounds. The data derived from the electron spin resonance ESR and SLR measurements were compared to those from inelastic neutron scattering studies. SLR of Er3+ ions in the temperature range from 20 K to 65 K can be explained by the resonant phonon relaxation process with the involvement of the lowest excited crystalline-electric-field electronic states of Er3+. These results are consistent with a local phase separation effects. Possible mechanisms of the ESR line broadening at lower temperatures are discussed. Keywords: YBCO; EPR; ESR; Electron spin-lattice relaxation time, T ; Crystalline-electric-fieldComment: 6 pages, 4 figure

Criteria for Carotid Atherosclerotic Plaque Instability

© 2020 Elsevier Inc. Background: The study aim is to determine the criteria for carotid atherosclerotic plaque instability with the use of an advanced ultrasound technology, immunohistochemical analysis, and electron paramagnetic resonance (EPR) and assess their correlations with histologic results. Methods: A total of 92 patients were included in the study and were examined by ultrasound duplex scanning and ultrasound elastography. Plaques harvested during carotid endarterectomy were obtained for histologic analysis, immunofluorescent assay, and EPR spectroscopic measurements. Results: Multivariate logistic regression analysis showed that plaques with an area >90 mm2 (odds ratio [OR], 4.05; 95% confidence interval [CI], 1.32–13.2; P = 0.006), plaque volume index > 0.6 cm3 (OR, 2.72; 95% CI, 1.05–9.58; P = 0.04), and juxtaluminal black area ≥8 mm2 (OR, 2.82; 95% CI, 1.22–6. 23; P = 0.02) were statistically significant independent predictors of histologically verified unstable plaques. Unstable plaques occurred in 94% of the patients with these indicators. Significant increases in the number of CD68+ and CD36+ cells (inflammatory markers) and CD31+ cells (neovasculogenesis markers) were revealed in unstable plaques by the immunohistochemical assay. EPR data analysis showed that divalent manganese could serve as a marker of plaque instability. Conclusions: Additional ultrasound criteria, verified by histologic studies, significantly increased the information content for identifying patients with unstable plaques, which can be of great importance in stratifying the risk of ischemic stroke, especially in asymptomatic patients. The degree of calcification is not a mandatory criterion for plaque stabilization

Modernization of the x-band epr spectrometer bruker elexsys e580 for dynamic nuclear polarization

To study the effects of dynamic nuclear polarization (DNP) in the X-band (microwave frequency of 9 GHz), using the capabilities provided by commercial EPR equipment, a part of the EPR spectrometer associated with the excitation and detection of double electron-nuclear resonance signals (ENDOR) has been modernized. Using the developed preamplifier of NMR signals, a homemade “Kazan Nova II”NMR spectrometer was implemented into the radio frequency path of the EPR spectrometer. The tuning and matching circuits made it possible to observe the NMR and DNP signals on protons in the frequency range 14.5–15.2 MHz. The performance of the DNP equipment was tested for a solution of the stable nitroxyl radical TEMPOL in benzene and a crude oil sample. The DNP effects caused by the Overhauser and solid effects were observed. The modernization of the existing EPR equipment creates a basis for further expanding its capabilities to study DNP effects in various systems at different conditions (in the pulsed mode of saturation of the EPR lines, with the temperature lowering, under the action of optical excitation, etc)

Using DFT to calculate the parameters of the crystal field in Mn²⁺ doped hydroxyapatite crystals

Crystal field parameters for two nonequivalent positions Ca (I) and Ca (II) for hydroxy-apatite (HAp) crystals from the density functional theory (DFT) are calculated. Calculations are compared with the experimental electron paramagnetic resonance (EPR) spectra (registered at two microwave frequencies) for the synthesized Mn-HAp powders Ca9.995Mn0.005(PO4)6(OH)2. It is found that in the investigated species, the manganese is redistributed between both calcium sites with prevalence in Ca (I). Agreement between the calculated and experimental data proves that crystal field parameters in HAp can be calculated in the classical DFT model using the distributed electron density

Size-dependent concentration of N⁰ paramagnetic centres in HPHT nanodiamonds

Size-calibrated commercial nanodiamonds synthesized by high-pressure high-temperature (HPHT) technique were studied by high-frequency W- and conventional X-band electron paramagnetic resonance (EPR) spectroscopy. The numbers of spins in the studied samples were estimated. The core-shell model of the HPHT nanodiamonds was proposed to explain the observed dependence of the concentration of the N0 paramagnetic centers. Two other observed paramagnetic centers are attributed to the two types of structures in the nanodiamond shell

Multipurpose portable q-band bridge

The paper describes the design, implementation, and technical characteristics of a portable Q-band microwave (mw) bridge based on the Gunn diode with the potential use for electron paramagnetic resonance (EPR) and dynamic nuclear polarization (DNP) spectroscopies. The mw frequency can be electronically adjusted in the range of 36–38 GHz with the maximal mw output of 120 mW and electronic attenuation of 0–60 dB. The value of the mw frequency can be stabilized and changed via automatic frequency control for direct and alternating current. A self-written Matlab-based program allows tuning and operating the bridge through the RS-485 interface. Examples of the EPR spectra implemented into the magnetic system of the Bruker ESP300 commercial spectrometer are shown

Change of the higher education paradigm in the context of digital transformation: From resource management to access control

© 2020, Sciedu Press. All rights reserved. Digitalization and transition to a new technological structure bring humanity to another level of development. The changing technological structures, industry and society progress, enhance the importance of improving the university development model. The existing management system and infrastructure in universities are often outdated and unable to ensure their competitive and adequate functioning. Hence, the need to improve the processes of using the university infrastructure through digital technology. The composition and range of the resources should also be reviewed and supplemented with new components. The purpose of this work is to reveal the principles and requirements for improving the university infrastructure using digital technology. The methodology is based on modeling the university management system, with the concept of infrastructure logic as a core, meant to include new elements in the university management infrastructure: university stakeholders, cultural values, investments and translation. The management model transformation implies a transition from structural to infrastructural approach, from infrastructure management to managing the infrastructure logic. The digital network platform incorporating the information on all the infrastructure facilities, their status, will provide effective user access management to each university resource. The recommendations formulated to improve the university infrastructure using digital technology will make higher education more effective

Effect of the Beryllium Acceptor Impurity upon the Optical Properties of Single-Crystal AlN

© 2020, Pleiades Publishing, Ltd. Abstract: The influence of the high-temperature (T = 1880°C) diffusion of beryllium ions on the properties of single-crystal aluminum nitride is studied. It is shown that the postgrowth doping of AlN with Be brings about the compensation of shallow Si donor centers uncontrollably incorporated into the AlN lattice during growth. It is established that the introduction of Be into the AlN lattice results in a reduction in the optical absorption of AlN in the visible and ultraviolet regions. The set of results is attributed to a shift of the Fermi level to the top of the valence band of AlN upon the introduction of the Be acceptor impurity