Inter- and Intra-granular flux Pinning in Ba(Fe0.91Co0.09)2As2 Superconductors

AbstractThermally assisted flux flow (TAFF) and flux pinning energiesare studied in a Ba(Fe0.91Co0.09)2As2 (Tc = 25.3K) sample via resistivity and AC susceptibility measurements in magnetic fields up to 18T. The flux pinning energy U(T,H) is determined from the Arrhenius law. The pinning maxima well determined by resistivity measurements ranged from 1724K at 0 T to 585K at 18 T with a sharp drop off so that U(T=Tc) varied with the applied field H as . The pinning activation energies determined from the AC susceptibility data but were by a factor of three higher, which is explained here. Both inter- and intra-granular pinning energies are determined in low fields. The onset of TAFF temperature and the crossover temperature Tx from TAFF to flux flow are determined, showing the limitations of the Anderson-Kim model

Frequency Dependent Flux Dynamics and Activation Energies in Pnictide Bulk (Ba0.56K0.44)Fe2As2 Superconductor

AbstractThermally activated flux de-pinning and flux activation de-pinning energies are studied in a (Ba0.56K0.44)Fe2As2 (Tc=38.5K) bulk superconductor in DC magnetic fields up to 18 T. Ac susceptibility was measured as a function of temperature, DC and AC magnetic fields, and frequency. Ac susceptibility curves shift to higher temperatures as the frequency is increased from 75 to 1997Hz in all fields. We model this data by Arrhenius law to determine flux activation energies as a function of AC and DC magnetic fields. The activation energy ranges from 8822K at μ0 Hdc = 0 T to 1100K at 18 T for Hac =80 A/m. The energies drop quickly in a non-linear manner as DC field rises above 0 T and around 1 T, which we describe as pinning transition field, the drop levels and continues more slowly in a linear like manner as DC field approaches to 18 T. Furthermore, the activation energy drops quickly as AC field increases from 80 A/m to 800 A/m at 0 DC field. As the DC field rises above 0, the activation energy has significantly weaker dependence on the AC field amplitude. Extensive map of the de-pinning, or irreversibility, lines shows broad dependence on the magnitude of the small AC field, frequency, in addition to the DC field

Disorder Induced Effects on the Critical Current Density of Iron Pnictide BaFe_1.8 Co_0.2 As_2 single crystals

Investigating the role of disorder in superconductors is an essential part of characterizing the fundamental superconducting properties as well as assessing potential applications of the material. In most cases, the information available on the defect matrix is poor, making such studies difficult, but the situation can be improved by introducing defects in a controlled way, as provided by neutron irradiation. In this work, we analyze the effects of neutron irradiation on a Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystal. We mainly concentrate on the magnetic properties which were determined by magnetometry. Introducing disorder by neutron irradiation leads to significant effects on both the reversible and the irreversible magnetic properties, such as the transition temperature, the upper critical field, the anisotropy, and the critical current density. The results are discussed in detail by comparing them with the properties in the unirradiated state.Comment: accepted for Ph

Fast Li ionic conduction in solid solutions of the system Li4GeO4-Li2ZnGeO4-Li3PO4

A wide range of solid solution formation in the Li4GeO4-Li2ZnGeO4-Li3PO4 system was observed to occur with a structure based on γII-Li3PO4. This includes the fast Li conductor lisicon (Li14Zn(GeO4)4). The ionic conductivities of solid solutions in this systems are reported. Much of the solid solution range is structually metastable at room temperature; however, the decomposition kinetics are appreciable only at elevated temperatures (>350°C). The evolution of low Li4GeO4 on decomposing causes an irreversible decrease in the conductivity. At 200°C, the bulk ionic conductivity of several of these solid solutions is higher than that of lisicon. Solid solutions along the Li4GeO4-Li3PO4 tie line are structurally stable and have a higher bulk ionic conductivity than lisicon, and also of the corresponding Li4SiO4-Li3PO4 solid solutions at 200°C

Silver ionic and electronic conductivity in Ag9GaS6

Electrical measurements on the mixed ionic, electronic conductor Ag9GaS6, which undergoes a phase transition at 303 K, were performed. The silver ionic conductivity in the low-temperature α-form measured using an ionic 4-probe method, is given by σT = 4.3 × 106 exp [(-29.8kJ/mol)/ RT] S m-1 K. The establishment of a fixed, reproducible thermodynamic state in this three-component, single-phase material is discussed. Experiments with Ag9GaS6 equilibrated with Ag + Ag2S and S + Ag2S revealed n-type conductivity in both equilibrium states. The electronic conductivity of β-Ag9GaS6 equilibrated with Ag + Ag2S is given by σ = 1.2 × 105 exp[(-30.4 kJ/mol)/RT] S m-1. The electron density and Hall mobility were determined from van der Pauw and Hall effect measurements

Gender differences in adrenergic regulation of lipid mobilization during exercise.

Gender differences in adrenergic regulation of lipid mobilization during exercise. Hellstrom L, Blaak E, Hagstrom-Toft E. Department of Medicine, Huddinge Hospital, Karolinska Institute, Sweden. Gender differences in adrenergic regulation of glycerol levels in subcutaneous, abdominal adipose tissue were investigated during submaximal exercise in non-obese, healthy men and women, using microdialysis. During exercise, glycerol levels in venous plasma and venous serum concentrations of free fatty acids increased more in women and reached about two-fold higher values than in men (p < 0.005 or less). Plasma noradrenaline and insulin did not differ between the sexes, whereas plasma adrenaline was two-fold higher in men than in women during exercise (p < 0.01). The glycerol levels in adipose tissue increased during exercise and decreased in the post-exercise period in either sex. When the non-selective beta adrenoceptor blocking agent propranolol was added to the microdialysis perfusate before exercise was initiated, the subsequent increase in dialysate glycerol was significantly diminished in both sexes (p < 0.05). A similar addition of the alpha adrenoceptor blocking agent phentolamine, however, caused a significant further rise in tissue glycerol in men (p < 0.05), whereas the exercise induced increase in glycerol levels remained unaffected by phentolamine in women. Adipose tissue blood flow did not change during exercise in either men or women. In either sex, dialysate lactate levels increased during exercise. This increase was not altered if alpha- or beta-blocking agents were added to the perfusate. In summary, during short term submaximal work, women have a higher increase in circulating lipid than men. This appears, at least in part, to be due to a sex difference in the adrenergic regulation of lipid mobilization during exercise. In men exercise activates beta- as well as alpha-adrenergic receptors in adipose tissue, whereas only beta receptors are activated in adipose tissue of women. Finally, methodological investigations indicate that microdialysis is a valid method for short-term exercise experiments

Rectal nitric oxide and fecal calprotectin in inflammatory bowel disease.

OBJECTIVE: The assessment of intestinal inflammation in patients with inflammatory bowel disease (IBD) remains a difficult challenge. Both rectal nitric oxide (NO) and fecal calprotectin can be measured using non-invasive methods and are emerging as promising inflammatory markers in IBD. In this study the aim was to compare calprotectin and NO levels in IBD patients. MATERIAL AND METHODS: Rectal NO was measured tonometrically in 23 healthy volunteers and 32 patients with IBD. In addition, we collected stool samples from all subjects for measurement of fecal calprotectin and nitrate/nitrite (NO metabolites). RESULTS: Patients with IBD had greatly increased NO and calprotectin levels compared to healthy volunteers (p <0.001). In addition, the nitrate levels were slightly increased in IBD patients. A weak correlation was found between rectal NO levels, disease activity and number of loose stools in IBD patients (Spearman's rho 0.37 and 0.51, respectively; p <0.05). Fecal calprotectin correlated only with age (Spearman's rho 0.51; p <0.01). However, no correlation was found between NO and calprotectin. CONCLUSIONS: Both rectal NO and fecal calprotectin are greatly increased during bowel inflammation, but they may reflect different parts of the inflammatory process. Future studies will elucidate the clinical usefulness of these two markers