Critical Fields and Anisotropy of NdO0.82F0.18FeAs Single Crystals

The newly discovered iron-based superconductors have stimulated enormous interests in the field of superconductivity. Since the new superconductor is a layered system, the anisotropy is a parameter with the first priority to know. Meanwhile any relevant message about the critical fields (upper critical field and irreversibility line) are essentially important. By using flux method, we have successfully grown the single crystals NdO0.82F0.18FeAs at ambient pressure. Resistive measurements reveal a surprising discovery that the anisotropy \Gamma = (mc/mab)^{1/2} is below 5, which is much smaller than the theoretically calculated results. The data measured up to 400 K show a continuing curved feature which prevents a conjectured linear behavior for an unconventional metal. The upper critical fields determined based on the Werthamer-Helfand-Hohenberg formula are H_{c2}^{H||ab}(T=0 K) = 304 T and H_{c2}^{H||c}(T=0 K)=62-70 T, indicating a very encouraging application of the new superconductors.Comment: 12 pages, 4 figures, Submitted on 26 May, 200

Microstructure, tensile behavior and oxidation resistance of the two step heat treated Nb- Ti-Si based alloy

Although the temperatures of the hottest section of advanced turbine engines are approaching the limit of nickel-based superalloys, the desire for continued performance improvements for gas turbine engines continues [1]. Nb-Ti-Si based alloys have attracted much attention for their high temperature melting points, relatively low densities and excellent high temperature mechanical properties [2]. In this alloy system, the constitute phases are niobium solid solution (NbSS), silicides (Nb5Si3 and / or Nb3Si) and with / without Cr2Nb. Among these phases, NbSS ensures room temperature fracture toughness and tensile strength, silicides offers high temperature strength, and Cr2Nb provides the oxidation resistance [3].In this study, the Nb-Ti-Si based alloy was firstly prepared by arc-melting and then directional solidification at a rapid speed. Two-step heat treatments were carried out on the directionally solidified Nb-Ti-Si based alloy. The first-step heat treatment was performed at 1375, 1400, 1425 and 1450 °C for 10hours, respectively. According to the microstructure characteristic and their resulting tensile strength, the best condition for the first-step heat treatment is 1425 °C/10 h. Then the second step heat treatment was conducted at 1000, 1100, 1200 and 1300 °C for 50 hours, respectively. The precipitation of nano-scale Cr2Nb particles in the NbSS matrix substantially improved the tensile strength from 850 MPa to 950 MPa, and reduced the weight gain of the alloy from 218.27 to 144.41mg/cm2 by the second step heat treatment at 1000 °C. References [1] B. P. Bewlay, M. R. Jackson, P. R. Subramanian, J. C. Zhao, Metall. Mater. Trans., 34A (2003) 2043-2052 [2] L.N. Jia, J.F. Weng, Z. Li, Z. Hong, L.F. Su, H. Zhang. Mater. Sci. Eng., 623A (2015) 32-37 [3] L. F. Su, L. N. Jia, Y. B. Feng, H. R. Zhang, S. N. Yuan, H. Zhang, Mater. Sci. Eng., 560A(2013) 672-67

Molecular identification of endophytic fungi from Aquilaria sinensis and artificial agarwood induced by pinholes-infusion technique

Agarwood, the resinous portions of Aquilaria plants, have been used as medicines and incenses. Aquilaria sinensis is the major producer of agarwood in China. Agarwood are generally viewed as pathological products formed as defense symptom against fungal infection. In this study, microbial communities inhabiting the leaves of non-resinous and agarwood-producing wounded A. sinensis tree were investigated by cultivation-independent approaches, such as PCR, restriction fragment length polymorphism (RFLP) analysis and sequencing of rDNA internal transcribed spacer (ITS) library. Molecular phylogenetic analysis demonstrated that Botryosphaeria, Colletotrichum gloeosporioides, Phomopsis and Cylindrocladium species are members of the agarwood-producing wounded tree, while Phoma, Mycosphaerella, Sagenomella, Alternaria and Ramichloridium species is able to colonize the non-resinous tree internally. C. gloeosporioides was the only fungus shared by the two rDNA ITS libraries. C. gloeosporoides, Botryosphaeria, and Cylindrocladium were considered to be related to agarwood formation. A pinholes-infusion method to induce the generation of agarwood by chemically stimulated and/or inoculate combined method was established. One to two years after the artificial inoculation, resinous wood were collected and the inoculating effects were detected by ethanol extraction content, thin layer chromatography (TLC) and gas chromatography-mass spectrometry (GCMS) techniques. The results reveal that chemically stimulated with formic acid and infected by Botryosphaeria dothidea produced high yield and high quality artificial agarwood in a relatively short time.Keywords: Agarwood, endophytic fungi, Aquilaria sinensis, molecular identification, artificial induce of agarwoodAfrican Journal of Biotechnology Vol. 12(21), pp. 3115-313

A Calculation Method for Quantitative X-Ray Microanalysis for Microparticle Specimens by Monte Carlo Simulation

A calculation method for quantitative X-ray microanalysis (QXMA) for microparticle specimens of a compound with various shapes is proposed in this paper. On the basis of a simplified physical model, the scattering of electrons in particles is calculated by Monte Carlo simulation. We have derived a series of evaluation formulae of the absorption and fluorescence of characteristic X-rays for the particles with regular shapes. With the use of these theories, along with an iteration calculation, compositions of microparticle specimens can be obtained from the measured X-ray intensity ratios. In order to examine the reliability of the method, a large number of electron probe experiments and analysis calculations were carried out for the microparticle specimens of a variety of geometric shapes, dimensions and compositions. Agreement of calculated concentrations using our method with known compositions of the analyzed particle specimens is fairly good. In practical work, calculation formulae for particle specimens with irregular shapes can be replaced by those of particles with approximate regular shapes

Superconductivity at 22.3 K in SrFe2-xIrxAs2

By substituting the Fe with the 5d-transition metal Ir in SrFe2As2, we have successfully synthesized the superconductor SrFe2-xIrxAs2 with Tc = 22.3 K at x = 0.5. X-ray diffraction indicates that the material has formed the ThCr2Si2-type structure with a space group I4/mmm. The temperature dependence of resistivity and dc magnetization both reveal sharp superconducting transitions at around 22 K. An estimate on the diamagnetization signal reveals a high Meissner shielding volume. Interestingly, the normal state resistivity exhibits a roughly linear behavior up to 300 K. The superconducting transitions at different magnetic fields were also measured yielding a slope of -dHc2/dT = 3.8 T/K near Tc. Using the Werthamer-Helfand-Hohenberg (WHH) formula, the upper critical field at zero K is found to be about 58 T. Counting the possible number of electrons doped into the system in SrFe2-xIrxAs2, we argue that the superconductivity in the Ir-doped system is different from the Co-doped case, which should add more ingredients to the underlying physics of the iron pnictide superconductors.Comment: 4 pages, 4 figure

Hall effect and magnetoresistance in single crystals of NdFeAsO1−x_{1-x}Fx_{x}

Hall effect and magnetoresistance have been measured on single crystals of $NdFeAsO_{1-x}F_{x}$ with x = 0 ($T_c$ = 0 $$K) and x = 0.18 ($T_c$ = 50 $$K). For the undoped samples, strong Hall effect and magnetoresistance with strong temperature dependence were found below about 150 K. The magnetoresistance was found to be as large as 30% at 15 K at a magnetic field of 9 T. From the transport data we found that the transition near 155 K was accomplished in two steps: first one occurs at 155 K which may be associated with the structural transition, the second one takes place at about 140 K which may correspond to the spin-density wave like transition. In the superconducting sample with $T_c$ = 50 $$K, it is found that the Hall coefficient also reveals a strong temperature dependence with a negative sign. But the magnetoresistance becomes very weak and does not satisfy the Kohler's scaling law. These dilemmatic results (strong Hall effect and very weak magnetoresistance) prevent to understand the normal state electric conduction by a simple multi-band model by taking account the electron and hole pockets. Detailed analysis further indicates that the strong temperature dependence of $R_H$ cannot be easily understood with the simple multi-band model either. A picture concerning a suppression to the density of states at the Fermi energy in lowering temperature is more reasonable. A comparison between the Hall coefficient of the undoped sample and the superconducting sample suggests that the doping may remove the nesting condition for the formation of the SDW order, since both samples have very similar temperature dependence above 175 K.Comment: 8 pages, 9 figure

Enteral supplementation of alanyl–glutamine attenuates the up-regulation of beta-defensin-2 protein in lung injury induced by intestinal ischemia reperfusion in rats

AbstractBackground: Beta-defensin-2 (BD-2), an endogenous antimicrobial peptide, plays a key role in immune response against microbial invasion. This study aimed to observe the effect of Alanyl–Glutamine (Ala–Gln) on BD-2 protein expression in pulmonary tissues after intestinal ischemia reperfusion (IIR) in rats and to investigate its correlations to pulmonary inflammatory and oxidative injury. Methods: Rats in IIR and the two treatment groups were subjected to intestine ischemia for 60 min and those in the treatment groups were administered orally with Ala–Gln or alanine (Ala) respectively. Lung tissues were harvested to detect the BD-2 protein expression. Concentrations of Tumor necrosis factor (TNF)-α and malondialdehyde (MDA) as well as superoxide dismutase (SOD) activity in lung tissues were determined simultaneously. Results: Ala–Gln attenuated the up-regulation of BD-2 expression (p < 0.05) and TNF-α (p < 0.05), MDA (p < 0.05) levels, as well as the reduction of SOD activity (p < 0.05) in lung tissues after IIR. But Ala did not exert significant effects. BD-2 protein in lung tissues was positively correlated to local TNF-α level (p < 0.01) and MDA concentration (p < 0.01) with statistical significance. Conclusion: Ala–Gln can relieve the IIR-induced up-regulation of BD-2 protein expression in the lung of rats, which involves anti-inflammation and anti-oxidation mechanisms

Optical orbital-angular-momentum-multiplexed data transmission under high scattering

Multiplexing multiple orbital angular momentum (OAM) channels enables high-capacity optical communication. However, optical scattering from ambient microparticles in the atmosphere or mode coupling in optical fibers significantly decreases the orthogonality between OAM channels for demultiplexing and eventually increases crosstalk in communication. Here, we propose a novel scattering-matrix-assisted retrieval technique (SMART) to demultiplex OAM channels from highly scattered optical fields and achieve an experimental crosstalk of –13.8 dB in the parallel sorting of 24 OAM channels after passing through a scattering medium. The SMART is implemented in a self-built data transmission system that employs a digital micromirror device to encode OAM channels and realize reference-free calibration simultaneously, thereby enabling a high tolerance to misalignment. We successfully demonstrate high-fidelity transmission of both gray and color images under scattering conditions at an error rate of <0.08%. This technique might open the door to high-performance optical communication in turbulent environments

Analysis of the genetic diversity and population structure of Salix psammophila based on phenotypic traits and simple sequence repeat markers

Salix psammophila (desert willow) is a shrub endemic to the Kubuqi Desert and the Mu Us Desert, China, that plays an important role in maintaining local ecosystems and can be used as a biomass feedstock for biofuels and bioenergy. However, the lack of information on phenotypic traits and molecular markers for this species limits the study of genetic diversity and population structure. In this study, nine phenotypic traits were analyzed to assess the morphological diversity and variation. The mean coefficient of variation of 17 populations ranged from 18.35% (branch angle (BA)) to 38.52% (leaf area (LA)). Unweighted pair-group method with arithmetic mean analysis of nine phenotypic traits of S. psammophila showed the same results, with the 17 populations clustering into five groups. We selected 491 genets of the 17 populations to analyze genetic diversity and population structure based on simple sequence repeat (SSR) markers. Analysis of molecular variance (AMOVA) revealed that most of the genetic variance (95%) was within populations, whereas only a small portion (5%) was among populations. Moreover, using the animal model with SSR-based relatedness estimated of S. psammophila, we found relatively moderate heritability values for phenotypic traits, suggesting that most of trait variation were caused by environmental or developmental variation. Principal coordinate and phylogenetic analyses based on SSR data revealed that populations P1, P2, P9, P16, and P17 were separated from the others. The results showed that the marginal populations located in the northeastern and southwestern had lower genetic diversity, which may be related to the direction of wind. These results provide a theoretical basis for germplasm management and genetic improvement of desert willow