EPR studies of (Bi, Pb)-2223 phase substituted by Ruthenium ions

This work studied X-ray powder diffraction (XRD), electrical resistivity and electron paramagnetic resonance (EPR) measurements for Bi_1.8Pb_0.4Sr₂Ca_2.1Cu_3−xRu_xO_10+δ (0.0 ≤ x ≤ 0.4) superconducting samples. XRD analysis and electrical resistivity data showed that the low-content of Ru, x ≤ 0.05, enhanced both the phase formation and the superconducting transition temperature of (Bi, Pb)-2223 phase. A phase change from (Bi, Pb)-2223 phase to (Bi, Pb)-2212 phase was reported for x ≥ 0.15. Two EPR lines were observed for 0.0 ≤ x ≤ 0.075, indicating the presence of both (Bi, Pb)-2223 and (Bi, Pb)-2212 phases. While, one EPR line was observed for x ≥ 0.15, corresponding to the (Bi, Pb)-2212 phase formation. The number of spins (N) participating in the resonance and its spin paramagnetic susceptibility (χ), for the two phases, were calculated as a function of both Ru-content and temperature. In addition, we reported the variation of activation energy (E_a), Curie constant (C), Curie temperature (θ) and effective magnetic moment (μ) with Ru-content.     

Interpolymer radical coupling: A toolbox complementary to controlled radical polymerization

The current review focuses on the relevance and practical benefit of interpolymer radical coupling methods. The latter are developing rapidly and constitute a perfectly complementary macromolecular engineering toolbox to the controlled radical polymerization techniques (CRP). Indeed, all structures formed by CRP are likely to be prone to radical coupling reactions, which multiply the available synthetic possibilities. Basically, the coupling systems can be divided in two main categories. The first one, including the atom transfer radical coupling (ATRC), silane radical atom abstraction (SRAA) and cobalt-mediated radical coupling (CMRC), relies on the recombination of macroradicals produced from a dormant species. The second one, including atom transfer nitroxide radical coupling (ATNRC), single electron transfer nitroxide radical coupling (SETNRC), enhanced spin capturing polymerization (ESCP) and nitrone/nitroso mediated radical coupling (NMRC), makes use of a radical scavenger in order to promote the conjugation of the polymer chains. More than a compilation of macromolecular engineering achievements, the present review additionally aims to emphasize the particularities, synthetic potential and present limitations of each system.     

NEW ALANINE/EPR DOSIMETER USING EVA COPOLYMER/PARAFFIN AS A BINDER FOR HIGH-DOSE RADIATION DOSIMETRY: PERFORMANCE CHARACTERIZATION

Alanine/EPR rods (3 × 10 mm) for routine use in high-dose radiation applications have been prepared by a simple technique in the laboratory where alanine powder was mixed with molten mixture of paraffin wax and ethylene vinyl acetate copolymer (EVA). The binding mixture EVA/Paraffin does not present interference or noise in the EPR signal before or after the irradiation. The rods show good mechanical properties for safe and multi-use handling. The rods can be used with good precision in the dose range from 1 to 125 kGy. The overall uncertainty for calibration of the EVAPA rod dosimeters at 2σ was found to be 4.56%. The dose response, influence of humidity and temperature during irradiation, energy dependence as well as post–irradiation storage at different conditions are discussed.     

Microscopic structure and energy transfer of vacancy-related defect pairs with Erbium in wide-gap semiconductors

Electron Paramagnetic Resonance (EPR) measurements of Erbium-doped 6H-SiC and wurtzite GaN samples are compared to total energy calculations based on density functional theory (DFT) in order to investigate the well-known luminescence of the intra 4f-shell transition at 1540 nm, useful in light-emitting diodes or lasers. The highly correlated f-electrons of Erbium (Er) have been treated within an LDA+U approach. We discus how pairs of an Er-ion with intrinsic defects can be responsible in GaN and SiC for relaxing the selection rules for intra 4f-shell transitions: In GaN our EPR investigation indicates the presence of a nitrogen vacancy next to the Er-ion. Through controlled generation of intrinsic defects in 6H-SiC single crystals and EPR measurements we support the corresponding model in SiC, that predicts defect pairs of an Er-ion and a neighboring carbon vacancy. In other words, low-energy irradiation seems to be a promising way to enhance the Er-luminescence desired for device applications.     

Vacancy defects induced in the track region of 132 MeV C irradiated SiC

Positron annihilation lifetime spectroscopy (PALS) and electron paramagnetic resonance (EPR) have been used in this work to investigate vacancy defects induced in the track region of 132 MeV ¹²C irradiated silicon carbide. Irradiations have been performed at room temperature at a fluence of 2.5 × 10¹⁴ cm⁻² in N-low doped 6H–SiC and 3C–SiC monocrystals. Silicon monovacancies have been detected in both polytypes using EPR. Their charge state and concentration have been determined in the track and cascade region of the C⁺ ions. PALS measurements performed as a function of temperature have shown the presence of V_Si–C divacancies in the track region for both polytypes.     

Electron Paramagnetic Resonance of Tb3+ Ions in YBa2Cu3O6

The first observation of electron paramagnetic resonance (EPR) of Tb³⁺ doped into YBa₂Cu₃O₆ is reported. EPR is used to determine the local symmetry of the rare-earth ion and to study the effect of suppression of high-T _c superconductivity by doping. The distance between the lowest singlets of Tb³⁺ ion 7.1 GHz 0.24 cm^–1 and g-factor g 17.9 have been estimated from measurements. Both these parameters are in a good agreement with the corresponding calculated values. No evidence of Tb⁴⁺ ions was found.     

Tan δ of ethylene-propylene rubber in cryogenic temperature region–effects of additives and sample thickness

The authors have been developing extruded polymer insulated superconducting power cables. Dielectric loss in electrical insulation cannot be ignored in superconducting cables since conductor loss in the cables is minimal. Studies so far show that ethylene-propylene rubber (EPR) is suitable as an electrical insulating material in the extruded polymer insulated superconducting cable design because it demonstrates excellent mechanical and relatively good electrical qualities at a cryogenic temperature. Widely used EPR includes some kinds of additives; however, their effect on tan δ of EPR at cryogenic temperature remains unknown. The effect of additives such as crosslinking agent and fillers on tan δ of EPR was examined at temperatures of between 4.2 K and 300 K. Thickness dependence of tan δ was also measured using EPR films of different thickness and an extruded EPR insulated cable sample. The results show that additives increase tan δ of relatively thin films of EPR even in the cryogenic temperature region; however, they do not have an intolerable dielectric loss in comparison with conductor loss and heat inflow of the superconducting cable. The remedy to tan δ increase due to the polymer contraction relative to shielding wires has been established.     

Polymer Complexes XLV. Spectral Studies on Metal-Ligand Bonding in Novel Poly-Schiff Base Complexes

Polymer complexes derived from cinnamaldehyde and 2-substituted aniline with Cu(II), Pd(II), Pt(II), UO₂(II), Rh(III), Ru(III), and Pd(IV) have been synthesized and characterized by IR, electronic, EPR, ¹H-NMR, and ¹³C-NMR spectra, as well as by elemental analysis, thermogravimetry, and magnetic susceptibility measurements. The important bands in the IR spectra and the main ¹H- and ¹³C-NMR signals are assigned and discussed in relation to molecular structure. The wavelengths of the principal electronic absorption peaks have been accounted for quantitatively in terms of crystal field theory and various parameters were evaluated. The complexes, [Ru(HL _n )Cl₃] _n , are penta-coordinate; and, a trigonal-bipyramidal environment is commensurate for the Ru(III) ion. The presence of a coordinated water molecule in complex the Cu(II) complex (20) was demonstrated by thermogravimetry. The compounds, [N-(3-phenylacrylidene)-2-mercaptoaniline] (HL₁) and cinnamaldehyde-2-aminophenol (HL₂), act as monobasic and neutral bidentate ligands. The B-value suggests a strong covalency in the metal-ligand -bond. Tentative structures of the polymer complexes are proposed.     

Electron transfer processes at the surface of MoOx/SiO2 catalysts

EPR studies using naturally abundant and ⁹⁵Mo-enriched molybdenum have shown that reduced MoO _x /SiO₂catalysts with different dispersion of molybdenum provide a unique opportunity for molecular-level investigations of surface phenomena involved in the bonding to and activation of small molecules by oxide surfaces. Different types of electron transfer (ET) processes accompanying the activation of O₂and N₂O as well as the reactivity of O^-and CH₂OH transients with coadsorbed CH₃OH and O₂, respectively, have been identified. They include nondissociative and dissociative ET, surface intramolecular ET, and electroprotic transformation (ET coupled with proton transfer). In the case of methanol dehydrogenation it was found that if the reaction occurs on the MoO _x cluster centers, ET exhibits a complementary character, in contrast to isolated Mo centers where noncomplementary ET accompanied by migration of the hydroxymethyl intermediate is observed.     

基于XML的电子病历系统的设计

针对电子病历的发展现状以及存在的问题,提出了基于XML的电子病历系统的设计方案,利用HL7和中间件技术实现医疗系统间的信息交换,结合W3C的XML加密标准给出了对电子病历进行部分加密的方法。实现了医疗系统之间无缝连接,并保证了互连系统间交换信息的安全性。