Magnesium substitution in Nd0.7Sr0.3MnO3

Magnesium substitution in Nd_0.7Sr_0.3MnO₃ has been studied by neutron powder diffraction. Polycrystalline samples of nominal compositions Nd_0.7Sr_0.3Mn_1−yMg_yO₃ with y=0.0, 0.1, 0.2 and 0.3 were synthesized by the standard solid-state reaction method. Rietveld refinements of the neutron powder diffraction data showed that all samples had distorted perovskite structure of orthorhombic symmetry. Mg initially preferred to substitute for Nd and only at Mg concentration greater than 0.1, a substantial substitution for Mn occurred. Our study also showed that Mg-substitution did not change the crystal structure of Nd_0.7Sr_0.3MnO₃.     

A novel method for crack detection in beam-like structures by measurements of natural frequencies

A novel method is proposed for calculating the natural frequencies of a multiple cracked beam and detecting unknown number of multiple cracks from the measured natural frequencies. First, an explicit expression of the natural frequencies through crack parameters is derived as a modification of the Rayleigh quotient for the multiple cracked beams that differ from the earlier ones by including nonlinear terms with respect to crack severity. This expression provides a simple tool for calculating the natural frequencies of the beam with arbitrary number of cracks instead of solving the complicated characteristic equation. The obtained nonlinear expression for natural frequencies in combination with the so-called crack scanning method proposed recently by the authors allowed the development of a novel procedure for consistent identification of unknown amount of cracks in the beam with a limited number of measured natural frequencies. The developed theory has been illustrated and validated by both numerical and experimental results.     

Spectral probing of carrier traps in Si–Ge alloy nanocrystals

Photogenerated carriers in Si–Ge alloy nanocrystals (NCs) prepared by co‐sputtering method were investigated by mean of transient induced absorption. The carrier relaxation features multiple components, with three decay life times of τ ≈ 600 fs, 12 ps, and 15 ns, established for Si_0.2Ge_0.8 alloy NCs of a mean crystal size of 9 nm and standard deviation of 3 nm. Deep carrier traps, identified at the boundary between the NCs and the SiO₂ host with the ionization energy of about 1 eV, are characterized by a long‐range Coulombic potential. These are responsible for rapid depletion of free carrier population within a few picoseconds after the excitation, which explains the low emissivity of the investigated materials, and also sheds light on the generally low luminescence of Si/Ge and Ge NCs. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Oxidation of 9-β-d-ribofuranosyl uric acid by one-electron oxidants versus singlet oxygen and its implications for the oxidation of 8-oxo-7,8-dihydroguanosine

Uric acid, a cellular antioxidant, undergoes oxidation in the presence of one-electron oxidants as well as singlet oxygen. In the present work, the oxidation pathways and products formed from oxidation of the uric acid nucleoside are compared to the more commonly studied uric acid free base. A wider distribution of products, including allantoin, urea, caffolide, and 5-carboxamido-5-hydroxyhydantoin nucleosides, are formed when the N9 position of uric acid is glycosylated. The oxidation pathways share some features in common with the oxidation of 8-oxo-7,8-dihydroguanosine, but the additional spectrum of products implies that the combination of oxidative and deaminative damage to guanosine may lead to a more complex set of DNA lesions than originally described.     

An experimental study of the expansion process of the vapour cloud in open atomizers

Using an oscilloscope the absorbance above a filament atomizer has been measured as a function of the position of the optical axis with respect to the sample position. For the elements investigated (Cd, Pb and Ag) an asymmetrical distribution of the atoms has been found. The vertical velocity of the sample cloud border was constant for each element and twice the horizontal velocity. The experiments have shown that the extension in an open atomizer at atmospheric pressure cannot be described by a pure diffusion process.     

Observation of mixed-phase behavior in the Mn-doped cobaltite La0.7Sr0.3Co1−xMnxO3 (x=0-0.5)

Studies on La_0.7Sr_0.3Co_1−xMn_xO₃ (x=0-0.5) compounds evidence that the interaction between Mn and Co ions in this system is antiferromagnetic super-exchange and not ferromagnetic (FM) double-exchange (DE). As a result, antiferromagnetism and magnetic glassiness develop steadily with increasing Mn content and the system becomes a spin glass at x∼0.1. Analyses of high-field magnetization data indicate that the system consists of two major phases: a metallic FM phase which magnetically saturates in rather low field, and an insulating non-FM phase which has a linear dependence of magnetization on magnetic field. In the low doping regime, the fraction of the non-FM component expands with temperature at the expense of the FM phase and becomes maximal at T_C. Ferromagnetism reappears in highly doped (x≥0.2) compounds due to the presence of DE interaction between the Mn ions. The small volume fraction of the FM phase derived from the M(H) data in high-field region supports the coexistence of insulating and FM behaviors in the highly doped samples.     

General one-loop formulas for $$H\rightarrow f\bar{f}\gamma $$ H → f f ¯ γ and its applications

The European Physical Journal C - Considering supergravity theory is a natural step in the development of gravity models. This paper follows the “algebraic“ path and constructs possible...     

Electrical transport of (1−x)La0.7Ca0.3MnO3+xAl2O3 composites

We report the resistivity (ρ)-temperature (T) patterns in (1-x)La_0,7Ca_0,3MnO₃+xAl₂O₃ composites (0≤x≤0.05) over a temperature regime of 50-300 K. Al₂O₃ addition has increased the resistivity of these composites. The Curie temperature (T_C) is almost independent on the Al₂O₃ content and is about 250 K for all the samples, while the metal-insulator transition temperature (T_MI) decreases with increasing Al₂O₃ content. Based on the phenomenological equation for conductivity under a percolation approach, which is dependent on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions, we fitted the experimental data (ρ−T) from 50 to 300 K and find that the activation barrier increases as Al₂O₃ content increases.     

Experimental estimates on radiative strength function of low-energy γ-quanta following even-odd heavy nuclei decay

The applicability of the method of summed amplitudes of coinciding pulses to determine radiative strength functions of heavy nuclei by measuring two-step cascade-ray spectra is discussed. Experiments based on thermal neutron capture in¹³⁶Ba and¹⁸⁰Hf were carried out to test this method. The values obtained for the radiative strength functions of a wide range of primary transitions were compared with the predictions of two modifications of the giant dipole resonance model. Some insight into the characteristics of the-decay of compound-states is provided by analyzing the information obtained on the two-step-decay of a number of nuclei in the mass region 137A187.Authors' thanks are due to Mrs. T.F. Drozdova and Dr. M.A. Ali for their help in the preparation of the English version of this paper.     

Method for detector calibration in radiation measurement of large samples

A method for detector calibration in radiation measurements of large samples by Monte-Carlo calculation is presented. This method is useful in the absolute radioactivity measurements when the relative method cannot be applied as suitable large standard samples are not available.