The temperature fields in electrically heated wires at crisis of boiling

The self-organization processes take place in several phenomena and physical objects and in particular they arise in metals in conditions of charge transfer. At liquid helium temperature in conditions of the increase of direct current flowing through bismuth, indium and tungsten there arise unstabilities of charge carries flux and this process exhibits itself in electromagnetic oscillations generation. This instability the authors refer to the mutual influence of the current flowing through the sample and magnetic field of the current. With this heat flux density through the sample’s surfaces didn’t exceed 0.1 W/sm2. Such a value of heat flux is сlose to the first boiling crisis but the author state that the nature of these phenomena is no case is connected with the heat removal specific features

Optical transparency and local electronic structure of Yb-doped Y 2 O 3 ceramics with tetravalent additives

The results of optical transmission and X-ray core-level spectra measurements of Yb:Y 2 O 3 ceramics with different tetravalent sintering additives (ZrO 2 , CeO 2 and HfO 2 ) fabricated from nanopowders (produced by the laser ablation method) and then annealed at 1400 °C in air for 2 h are presented. It is found that the transmission values for ZrO 2 - and HfO 2 -doped ceramics at the lasing wavelengths are higher than those of CeO 2 -doped samples. The X-ray photoelectron spectra (XPS) O 1s spectra show that the relative intensity of oxygen defect peak detected for 3Yb:Y 2 O 3 + 5CeO 2 ceramics decreases substantially and consistently compared to that of 5Yb:Y 2 O 3 + 5HfO 2 and 3Yb:Y 2 O 3 + 5ZrO 2 samples. This can be attributed to a more complete filling of oxygen vacancies due to annealing-induced oxygen diffusion into the highly defective sintered ceramics. The measurements of XPS Ce 3d spectra showed that the insufficiently complete filling of the oxygen vacancies in the 3Yb:Y 2 O 3 + 5CeO 2 compound is due to the appreciable presence of trivalent cerium ions. © 2019 by the authors.Ministry of Education and Science of the Russian Federation, Minobrnauka: 3.7270.2017/8.9This study was supported by FASO (Theme "Electron" No. AAAA-A18-118020190098-5). The XPS measurements were supported by the Ministry of Education and Science of the Russian Federation (Project No. 3.7270.2017/8.9) and the Government of the Russian Federation (Act 211, agreement No. 02.A03.21.0006). Fabrication of ceramic samples was performed in the framework of the state task of IEP UB RAS

CuO-CeO2 nanocomposite catalysts produced by mechanochemical synthesis

Mechanochemical synthesis based on ball-milling of individual oxides was applied as a one-step preparation technique for CuO-CeO2 catalyst for preferential CO oxidation in H2 excess. The mechanical energy dose transferred to the original powder mixture determines both the catalyst composition and activity. It is found that after 90 min of milling (corresponding to a dose of 372 kJ mol-1), a mixture of 10 wt.% CuO-CeO2 powder exhibits a CO conversion of 97% at 423 K. Four active oxygen states, which are not observed in case of pure CeO2, were detected in the nanocomposite lattice and attributed to the presence of Cu in surface sites as well as in subsurface bulk sites of CeO2, in nearest neighbor and next nearest neighbor positions. Correspondingly, oxidation of CO to CO2 was found to occur in a two-stage process with Tmax = 395/460 K, and oxidation of H2 to H2O likewise in a four-stage process with Tmax = 426/448/468/516 K. The milled powder consists of CeO2 crystallites sized 8-10 nm agglomerated to somewhat larger aggregates, with CuO dispersed on the surface of the CeO2 crystallites, and to a lesser extent present as Cu2O. © 2019 Author(s).This work was partially supported by Russian Foundation for Basic Research [Projects n.n. 16-03-00330a and 16-03-00178a] in theoretical studies and part of experimental research and by FASO [program no. AAAA-A18-118012390374-3]. XPS measurements were supported by FASO (Theme “Electron”). The Alexander von Humboldt foundation is gratefully acknowledged for funding. We also would like to thank N. Berezkina for SEM measurements. We acknowledge support by the Open Access Publication Funds of the Göttingen University. Declarations of interest: none

The use of atomic force microscopy for structural and surface morphological analysis of Fanconi anemia patient fibroblasts before and after exposure to γ-radiation

The surface morphological changes of Fanconi anemia patient fibroblasts after exposure to γ–radiation were investigated by AFM and foci immunofluorescence staining. The reorganization of the actin cytoskeleton was found, having resulted in reduction of the membrane stiffness and increase of adhesion in nuclear and lamellipodial regions of the cell

The structure of Green functions in quantum field theory with a general state

In quantum field theory, the Green function is usually calculated as the expectation value of the time-ordered product of fields over the vacuum. In some cases, especially in degenerate systems, expectation values over general states are required. The corresponding Green functions are essentially more complex than in the vacuum, because they cannot be written in terms of standard Feynman diagrams. Here, a method is proposed to determine the structure of these Green functions and to derive nonperturbative equations for them. The main idea is to transform the cumulants describing correlations into interaction terms.Comment: 13 pages, 6 figure

Unveiling the Atomic and Electronic Structure of Stacked-Cup Carbon Nanofibers

We report results of comprehensive experimental exploration (X-ray photoemission, Raman and optical spectroscopy) of carbon nanofibers (CNFs) in combination with first-principles modeling. Core-level spectra demonstrate prevalence of sp2 hybridization of carbon atoms in CNF with a trace amount of carbon–oxygen bonds. The density functional theory (DFT)-based calculations demonstrated no visible difference between mono- and bilayers because σ-orbitals are related to in-plane covalent bonds. The influence of the distortions on π-peak is found to be significant only for bilayers as a result of π–π interlayer bonds formation. These results are supported by both experimental Raman and XPS valence band spectra. The combination of optical measurements with a theoretical modeling indicates the formation of optically active graphene quantum dots (GQDs) in the CNF matrix, with a radiative relaxation of the excited π* state. The calculated electronic structure of these GQDs is in quantitative agreement with the measured optical transitions and provides an explanation of the absence of visible contribution from these GQDs to the measured valence bands spectra. © 2021, The Author(s).XPS measurements calculations are supported by Ministry of Science and Education of Russian Federation: Theme “Electron” № AAAA-A18-118020190098-5 and Project FEUZ-2020-0059. Optical measurements were additionally supported by RFBR project № 20-42-660012 and RSF project № 21-12-00392. DWB acknowledges the support from Jiangsu innovative and Entrepreneurial Talents Project

Influence of Oxygen Ion Migration from Substrates on Photochemical Degradation of CH3NH3PbI3 Hybrid Perovskite

Measurements of XPS survey, core levels (N 1s, O 1s, Pb 4f, I 3d), and valence band (VB) spectra of CH3NH3PbI3 (MAPbI3) hybrid perovskite prepared on different substrates (glass, indium tin oxide (ITO), and TiO2) aged under different light-soaking conditions at room temperature are presented. The results reveal that the photochemical stability of MAPbI3 depends on the type of substrate and gradually decreases when glass is replaced by ITO and TiO2. Also, the degradation upon exposure to visible light is accompanied by the formation of MAI, PbI2, and Pb0 products as shown by XPS core levels spectra. According to XPS O 1s and VB spectra measurements, this degradation process is superimposed on the partial oxidation of lead atoms in ITO/MAPbI3 and TiO2/MAPbI3, for which Pb–O bonds are formed due to the diffusion of the oxygen ions from the substrates. This unexpected interaction leads to additional photochemical degradation. © 2021 by the author. Licensee MDPI, Basel, Switzerland.Funding: The sample preparation, aging experiments, UV‐vis, XRD, and SEM characterization were supported by Russian Science Foundation (project No. 19‐73‐30020). The XPS measurements were supported by the Ministry of Education and Science of the Russian Federation (project FEUZ‐2020‐0060), Theme ‘Electron’, no. AAAA‐A18‐118020190098‐5 and Russian Foundation for Basic Research (projects No. 21‐52‐52002/21 and 20‐42‐660003). C.‐C.C. acknowledges the financial support from the Ministry of Science and Technology in Taiwan (MOST 110‐2923‐E‐002‐007‐MY3) and the Top University Project from National Taiwan University (110L7836 and 110L7726)

Cu-Site Disorder in CuAl2O4 as Studied by XPS Spectroscopy

The results of full study of X-ray photoelectron spectra (XPS) of spin-liquid candidate CuAl2O4 including the measurements of high-energy resolved core level (Cu 2p, Al 3p, O 1s), Cu LMM Auger and valence band spectra are presented. The comparison of obtained results with spectra of reference samples and specially performed density functional theory calculations has confirmed a finite Cu site-disorder in CuAl2O4, where about 30% of Cu2+ ions occupy the octahedral sites. Obtained valence band spectra can be used in further theoretical studies aimed on the investigation of electronic and magnetic properties of this mysterious ma-terial. © 2021, The Author(s).The DFT calculations were supported by the Russian Science Foundation (project no. 20-62-46047). The XPS measurements were supported by the Ministry of Science and Higher Education of the Russian Federation (theme Electron no. AAAA-A18-118020190098-5 and project FEUZ 2020-0060). I.S. Zhidkov acknowledges the support of the Council of the President of the Russian Federation for State Support of Young Scientists and Leading Scientific Schools (project no. MK-989.2020.2)