Influence of Se and Te substitutions at Tl-site of Tl(Ba,Sr)CaCu2O7 superconductor on the AC susceptibility and electrical properties

The Sr and Ba bearing Tl-1212 phase, Tl(Ba,Sr)CaCu₂O₇ is an interesting superconductor. The Sr only bearing TlSr₂CaCu₂O₇ is not easily prepared in the superconducting form. The Ba only bearing TlBa₂CaCu₂O₇ on the other hand does not show improvement in the transition temperature with elemental substitution. In this work the influence of multivalent Se (non-metal) and Te (metalloid) substitutions at the Tl-site of Tl_1-xM_x(Ba,Sr)CaCu₂O₇ (M = Se or Te) superconductors for x = 0–0.6 was studied. The samples were prepared via the conventional solid-state reaction method. XRD patterns showed a single Tl-1212 phase for x = 0 and 0.1 Se substituted samples. The critical current density at the peak temperature, T_p of the imaginary (χ”) part of the AC susceptibility (χ = χ’ +χ”), J_c-inter(T_p) for all samples was between 15 and 21 A cm⁻². The highest superconducting transition temperature was shown by the x = 0.3 Se-substituted sample (T_c-onset = 104 K, T_c-zero = 89 K, T_cχ’ = 104 K and T_p = 80 K). Te suppressed the superconductivity of Tl-1212 phase. The order of highest transition temperatures are as follows: Tl_1-xTe_x(Ba,Sr)CaCu₂O₇<Tl(Ba,Sr)CaCu₂O₇<Tl_1-xSe_x(Ba,Sr)CaCu₂O₇. This work showed that Se was better than Te in improving the transition temperature and flux pinning of the Tl-1212 phase. The roles of ionic radius of Se and Te on the superconductivity of Tl(Ba,Sr)CaCu₂O₇ are discussed in this paper.     

Antimicrobial susceptibility of isolated pathogens from patients with contact lens-related bacterial keratitis in Crete,Greece: A ten-year analysis

PurposeTo evaluate the bacterial spectrum and antimicrobial susceptibilities of pathogens isolated from contact lens-related bacterial keratitis cases in a large academic Greek hospital.MethodsAll adult patients with positive corneal scrapings or contact lens culture between 2007 and 2016 at the University Hospital of Heraklion, Greece, were retrospectively identified through a local microbiology database and their medical records were reviewed.ResultsA total of 240 isolates were recovered from 131 patients with culture-proven contact lens-associated bacterial keratitis. The most common microorganism identified was Serratia marcescens (17.1% of total isolates), followed by Pseudomonas aeruginosa, Klebsiella spp. and coagulase-negative staphylococci (CoNS). Rates of aztreonam-resistant P. aeruginosa and erythromycin-resistant CoNS decreased in recent years, while the decrease in oxacillin-resistant CoNS was statistically significant (p=0.009). More than 90% of the isolated organisms (S. marcescens, P. aeruginosa, Klebsiella spp. and CoNS) were susceptible to ciprofloxacin or gentamicin.ConclusionGram-negative microorganisms are the most common causative pathogens of contact lens-related keratitis in the region of Crete. Topical antibacterials containing quinolones or gentamicin represent an effective empirical treatment for the majority of the cases. This is quite encouraging, considering that the present study was conducted in a country characterised by high antimicrobial resistance rates. However, culture-driven antimicrobial treatment is mandatory for this sight-threatening infection.     

Development rates of Callosobruchus maculatus (Coleoptera: Chrysomelidae) in landrace cowpea varieties occurring in southwestern Amazonia

Cowpea, Vigna unguiculata (L.), constitutes an important source of protein in various parts of the world, and landrace varieties are widespread in the southwestern Amazon. The population growth of insects is related to survival strategies in response to the feeding substrate. Thus, the development of Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae: Bruchinae) in four landrace varieties of cowpea (VBRL 02, VSNA 02 VRDR 02 and VRBC 02) was determined through daily and accumulated emergence rates. These varieties were selected for this study because they are well distributed throughout the Amazonian communities. Cowpea samples (150 g) of each variety were infested with 50 unsexed adults, and the insects were removed 13 days after beginning the bioassays. To determine the daily emergence rates in the varieties, the adult progeny obtained from the feeding substrate was counted and removed on alternate days after the first emergence, until the end of the emergence period (45 days after the beginning of bioassays). The sum of the daily emergence was accumulated since the initial emergence and resulted in the sum of accumulated emergence (SEa, % day), calculated by SEa = ∑ SEd. We found variations in daily and accumulated emergence rates between the four varieties, and the lowest rates of daily emergence of C. maculatus occurred in the varieties VBRL 02 and VSNA 02. The accumulated emergence was delayed in the variety VBRL 02. These results indicate that landrace varieties of cowpea occurring in the southwestern Amazon are a source of features of resistance to bruchids.     

Co-substitution of zirconium and neodymium on hyperfine interactions and AC susceptibility of SrFe_(12)O_(19) nanohexaferrites

This study presents the influence of Zn and Nd co-substitution on structure,morphology,AC susceptibility and ZFC-FC magnetizations of Sr nanohexaferrites(NHFs),SrFe_(12-x)(Zn,Nd)_xO_(19)(0.0≤x≤1.0),which was produced by sol-gel approach.XRD powder patterns,scanning electron microscopy(SEM) and high-resolution transmission electron spectroscopy(HR-TEM) approve the synthesis of Sr M-type hexaferrite.Mossbauer spectra show that Zn~(2+)ions occupy 2 b and 4f_1 sites while Nd~(3+)ions locate at 2 a,4f_2 and 12 k sites.The magnetic properties of the produced Sr-NHFs were investigated also by ZFC-FC magnetizations and AC susceptibility.According to the M_(FC)-M_(ZFC) results(between 2 and 400 K),no blocking temperature was detected which indicates the ferromagnetic(FM) behavior of NHFs.At lower temperatures,a super-spin glass like behavior is discerned.The AC susceptibility indicates that the magnetic interactions are improved due to the inclusion of low content(x=0.1) of Nd~(3+)and Zn~(2+)ions into the Sr-NHFs.However,with further increasing the Nd~(3+)and Zn~(2+)contents(x=0.9),the magnetic interactions are weakened.     

Using a pulsed electric current to reduce the susceptibility of high-strength steel to the stress corrosion cracking caused by hydrogen

Under the tensile loading, the damage of metals in the corrosive medium is the most destructive and harmful. In this study, the stress corrosion cracking behavior of H-charged high-strength steel in 3.5 wt% NaCl solution after electropulsing treatment was investigated. The experimental results from elongation, yield strength, fracture morphology, and polarization curves all demonstrate the positive effect of the pulsed processing, as it reduced the susceptibility of steel to stress corrosion cracking by removing hydrogen by electropulsing. The reduction in hydrogen content of the pulsed high–strength steels was attributed to electromigration and increased system free energy, which drove the hydrogen atoms in the steel to de–trap and reduced the susceptibility to stress corrosion cracking.     

Thermal and structural modification in transparent and magnetic germanoborate glasses induced by Gd2O3

A series of new transparent and magnetic germanoborate glasses in the system (100-x)[60GeO₂–25B₂O₃–10Na₂O–4Al₂O₃–1PbO] – (x) Gd₂O₃, with x = 0, 1, 2, 5, 10, 15 and 20 mol%, was prepared and studied with respect to their thermal and structural changes in the presence of Gd₂O₃. Based on Differential Scanning Calorimetre (DSC) analysis, a glass with 5% of Gd₂O₃ showed a high thermal stability, which progressively decreases for samples with higher content of Gd₂O₃. By the analysis of Raman and Fourier Transform Infrared (FTIR) spectra, it was possible to identify that by increasing the amount of Gd₂O₃, a progressive depolymerization of 6-membered Ge^[IV] rings is promoted, concomitant with an increase of Ge^[IV] tetrahedra units with non-briding oxygens. The structural analysis through the local-sensitive techniques EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure) showed that the short-range structural modification around the elements Ge and Gd³⁺ does not change with the addition of Gd₂O₃ and the presence of germanium four-fold coordination [Ge^IV] and Gd³⁺ states, respectively. A simulation of the coordination number (N), the interatomic distance (R) of Ge–O and Gd–O bonds and the Debye-Waller factor was also carried out. The microstructure_, after crystallization, of the sample with 15 mol% of Gd₂O₃ was evaluated using optical and electron microscopes. Finally, the paramagnetic behaviour and ion probe quantification of Gd³⁺ ions were obtained based on magnetic susceptibility measurements.     

Effects of Zn and Y on hot-tearing susceptibility of Mg–xZn–2xY alloys

The effect of Zn and Y on hot-tearing susceptibility (HTS) of Mg–xZn–2xY (x?=?1, 1.67, 2.67) alloys is investigated. It is found that the microstructure of the alloys is mainly composed of α-Mg, long-period stacking-ordered (LPSO) phase and W-phase. Both theoretical and experimental results illustrated that HTS of the investigated alloys is in the following order: Mg–1Zn–2Y > Mg–1.67Zn–3.34Y > Mg–2.67Zn–5.34Y. For Mg–2.67Zn–5.34Y alloy, LPSO phase content reaches at the maximum and its grain size reaches at minimum of 16.4 µm, and the pinning effect of the LPSO phase on grain boundaries is considered to be an important reason for reducing HTS of the alloy.     

AC susceptibility and hyperfine interactions of vanadium substituted barium nanohexaferrites

Vanadium ions substituted BaFe₁₂O₁₉ nanohexaferrites, BaFe_12-xV_xO₁₉ (0.0?≤x?≤?0.1), were produced through the sol-gel auto-combustion route. The structure, morphology and the elemental compositions of various products were examined using X–ray powder diffraction, scanning electron microscopy coupled with EDX and EDS elemental mapping. These techniques confirmed the formation of the desired Ba-nanohexaferrite phases. The crystallites size was found to be 55–58?nm range for all products. The magnetic properties of BaFe_12-xV_xO₁₉ nanohexaferrites were investigated by Mossbauer spectroscopy, ZFC-FC magnetizations and AC susceptibility. The evolutions in the values of hyperfine magnetic field, isomer shift, quadrupole splitting, and line width were deduced via Mossbauer analysis. The experiments of ZFC and FC magnetizations indicated that no blocking temperature is observed in the temperature interval 2–400?K, which signals the typical ferromagnetic (FM) behavior for the produced nanohexaferrites. A super-spin glass like behavior is noticed at lower temperatures. The experiments AC susceptibility confirmed that the strength of magnetic interactions is enhanced for lower content of V³⁺ (x?=?0.02). For higher amount of V³⁺, the magnetic interactions are weakened. The obtained results are mainly accredited to the substitutions of Fe³⁺ ions by V³⁺ ions.     

溶解氧变化对阴极极化下10Ni5CrMo钢氢脆敏感性的影响

摘要：为研究溶解氧质量浓度对10Ni5CrMo钢在阴极极化条件下氢脆敏感性影响规律，对10Ni5CrMo钢进行了阴极极化下的电化学交流阻抗谱测试﹑并采用慢应变速率拉伸实验和断口分析方法研究了海水中溶解氧质量浓度变化和不同阴极极化下10Ni5CrMo钢的氢脆敏感性。结果表明：溶解氧质量浓度变化对10Ni5CrMo钢强度几乎没有影响；同一溶解氧质量浓度下，随极化电位负移，断裂时间、伸长率、断面收缩率明显降低，氢脆系数增加，氢脆敏感性显著提高，极化电位达到-1000mV时，氢脆系数已超过安全区允许的最高值25%，进入危险区；同一极化电位下，随着海水中溶解氧质量浓度减少，材料塑性变差，断裂时间、伸长率和断面收缩率不断降低，氢脆系数增加，氢脆敏感性提高。