Determination of characteristic muon precession and relaxation signals in FeAs and FeAs2, possible impurity phases in pnictide superconductors

We report muon-spin relaxation measurements of highly homogeneous samples of FeAs and FeAs2, both previously found as impurity phases in some samples of recently synthesized pnictide superconductors. We observe well defined muon precession in the FeAs sample with two precession frequencies of 38.2(3) and 22.7(9) MHz at 7.5 K, with the majority of the amplitude corresponding to the lower frequency component. In FeAs2 we confirm previous measurements showing that no long-ranged magnetic order occurs above 2 K and measure the muon spin relaxation rate, which increases on cooling. Our results exclude the possibility that previous muon-spin relaxation measurements of pnictide superconductors have been measuring the effect of these possible impurities.Comment: 4 pages, 3 figures, corrected Figure

Enhancement of Superfluid Stiffness, Suppression of Superconducting T_c and Field-induced Magnetism in the Pnictide Superconductor LiFeAs

Transverse-field muon-spin rotation measurements performed on two samples of LiFeAs demonstrate that the superfluid stiffness of the superconducting condensate in relation to its superconducting transition temperature is enhanced compared to other pnictide superconductors. Evidence is seen for a field-induced magnetic state in a sample with a significantly suppressed superconducting transition temperature. The results in this system highlight the role of direct Fe-Fe interactions in frustrating pairing mediated by antiferromagnetic fluctuations and suggest that, in common with other pnictide superconductors, the system is close to a magnetic instability.Comment: 4 pages, 5 figure

Charge carrier localization induced by excess Fe in the Fe1+y(Te,Se) superconductor system

We have investigated the effect of Fe nonstoichiometry on properties of the Fe1+y(Te, Se) superconductor system by means of resistivity, Hall coefficient, magnetic susceptibility, and specific heat measurements. We find that the excess Fe at interstitial sites of the (Te, Se) layers not only suppresses superconductivity, but also results in a weakly localized electronic state. We argue that these effects originate from the magnetic coupling between the excess Fe and the adjacent Fe square planar sheets, which favors a short-range magnetic order.Comment: 15 pages, 6 figures accepted for publication in PR

Superconductivity up to 30 K in the vicinity of quantum critical point in BaFe2_{2}(As1−x_{1-x}Px_{x})2_{2}

We report bulk superconductivity induced by an isovalent doping of phosphorus in BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$. The P-for-As substitution results in shrinkage of lattice, especially for the FeAs block layers. The resistivity anomaly associated with the spin-density-wave (SDW) transition in the undoped compound is gradually suppressed by the P doping. Superconductivity with the maximum $T_c$ of 30 K emerges at $x$=0.32, coinciding with a magnetic quantum critical point (QCP) which is evidenced by the disappearance of SDW order and the linear temperature-dependent resistivity in the normal state. The $T_c$ values were found to decrease with further P doping, and no superconductivity was observed down to 2 K for $x\geq$ 0.77. The appearance of superconductivity in the vicinity of QCP hints to the superconductivity mechanism in iron-based arsenides.Comment: 9 pages, 4 figures; more data; to appear in Journal of Physics: Condensed Matte

Efficacy of miniaturized imacor trans-esophageal echocardiografm (TEE) prove in mechanical circulatory support.

Application of the miniaturized ImaCor Trans-Esophageal Echocardiogram (TEE) probe in Heart Transplant/Mechanical Cardiac Support Patients In the surgical cardiac care unit (SCCU), therapeutic interventions often need to be done at the bedside, necessitating the need for a rapidly employable diagnostic tool for the cardiac intensivist. We report the clinical utility of the miniature ImaCor TEE-probe in guiding management of post heart transplant (H-Txp) and mechanical cardiac support patients (MCS) and describe the economic benefit of such a device. This is an IRB approved retrospective review of MCS/H-Txp patients who had ImaCor TEE monitoring in the SCCU of our institution in 2011. The effect on management was stratified into 3 categories; Major (tamponade/device selection/RV failure), Moderate (weaning support device guidance/ inotrope management/fluid management/hemodynamic instability) and Minor (line placement/useful data). The ImaCor TEE-Probe was utilized in a total of 34 patients, of which 21 were either supported by MCS or were post H-Txp. Of these, 13 were on ECMO, 9 were post-VAD, 3 supported by the Impella device and 4 were post-H-Txp. 6 patients were placed on more than 1 method of MCS and 1 patient was supported by ECMO after a H-Txp. The device had a Major effect on management in 4 patients (19%), Moderate effect in 13 (62%) and a Minor effect in 4 (19%). The cost difference between this new device and the traditional TEE is also significant (900 USD vs 4000 USD). Our institution saved in excess of 150,000 USD with the use of this device instead of traditional TEE. This figure did not include the ability of this probe to be used repeatedly within a 72-hour time frame, and the potential cost of going to the operating theatre for further management. This device has proven to be an invaluable new adjunct in the SCCU by allowing previously unobtainable continuous real time monitoring of the MCS/H-Txp patient. Use of the ImaCor TEE-probe provides the cardiac intensivist with timely important clinical data that improves patient care and is economically advantageous

Contrasting Pressure Effects in Sr2VFeAsO3 and Sr2ScFePO3

We report the resistivity measurements under pressure of two Fe-based superconductors with a thick perovskite oxide layer, Sr2VFeAsO3 and Sr2ScFePO3. The superconducting transition temperature Tc of Sr2VFeAsO3 markedly increases with increasing pressure. Its onset value, which was Tc{onset}=36.4 K at ambient pressure, increases to Tc{onset}=46.0 K at ~4 GPa, ensuring the potential of the "21113" system as a high-Tc material. However, the superconductivity of Sr2ScFePO3 is strongly suppressed under pressure. The Tc{onset} of ~16 K decreases to ~5 K at ~4 GPa, and the zero-resistance state is almost lost. We discuss the factor that induces this contrasting pressure effect.Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jpn. No.12 (2009

Effect of the tetrahedral distortion on the electronic properties of iron-pnictides

We study the dependence of the electronic structure of iron pnictides on the angle formed by the arsenic-iron bonds. Within a Slater-Koster tight binding model which captures the correct symmetry properties of the bands, we show that the density of states and the band structure are sensitive to the distortion of the tetrahedral environment of the iron atoms. This sensitivity is extremely strong in a two-orbital (d_xz, d_yz) model due to the formation of a flat band around the Fermi level. Inclusion of the d_xy orbital destroys the flat band while keeping a considerable angle dependence in the band structure.Comment: 5 pages, including 5 figures. Fig. 5 replaced. Minor changes in the tex

Do national resources have to be centrally managed? Vested interests and institutional reform in Norwegian fisheries governance

Corporatism -with its privileged access, restricted participation and centralized structures - has a long history in Norwegian fisheries governance. Co-management – understood as a decentralized, bottom-up and more inclusive form of fisheries governance - has not been considered a relevant alternative.. Why does corporatism still prevail in a context where stakeholder status in fisheries governance globally – both in principle and practice - has been awarded environmental organizations, municipal authorities and even consumer advocacy groups? Why then have alternatives to the corporatist system of centralized consultation and state governance never been seriously considered in Norway, in spite of the growing emphasis on fish as a public resource and fisheries management as human intervention in geographically confined and complex ecosystems? We suggest that thismay have to do with the fundamental assumptions behind Norwegian fisheries governance that since fish is a national resource, it must be centrally managed. We argue that this is an assumption that may be contested

On our own terms : the working conditions of internet-based sex workers in the UK

The sex industry is increasingly operated through online technologies, whether this is selling services online through webcam or advertising, marketing or organising sex work through the Internet and digital technologies. Using data from a survey of 240 internet-based sex workers (members of the National Ugly Mug reporting scheme in the UK), we discuss the working conditions of this type of work. We look at the basic working patterns, trajectories and everyday experiences of doing sex work via an online medium and the impact this has on the lives of sex workers. For instance, we look at levels of control individuals have over their working conditions, prices, clientele and services sold, and discuss how this is mediated online and placed in relation to job satisfaction. The second key finding is the experience of different forms of crimes individuals are exposed to such as harassment and blackmail via the new technologies. We explore the relationship internet-based sex workers have with the police and discuss how current laws in the UK have detrimental effects in terms of safety and access to justice. These findings are placed in the context of the changing landscape of sex markets as the digital turn determines the nature of the majority of commercial sex encounters. These findings contribute significantly to the populist coercion/choice political debates by demonstrating levels and types of agency and autonomy experienced by some sex workers despite working in a criminalized, precarious and sometimes dangerous context

Changes of plasma cGP/IGF-1 molar ratio with age is associated with cognitive status of Parkinson disease

Objective: Cognitive impairment is a common feature of Parkinson disease (PD), for which age is a major contributing factor. Insulin-like growth factor-1 (IGF-1) declines with age and contributes to age-related cognitive impairment in PD. Cyclic glycine-proline (cGP) is a metabolite of IGF-1 and normalizes bioavailable IGF-1. Plasma cGP/IGF-1 molar ratio that represents bioactive IGF-1 in circulation, may associate with the cognitive status in PD. Methods: We examined the association of plasma cGP/IGF-1 molar ratio with the cognitive scores or age in PD patients with normal cognition (PD-N, n = 74), mild cognitive impairment (PD-MCI, n = 71), or dementia (PD-D, n = 33), and with the cognitive scores in 23 age-matched healthy controls. Plasma concentrations of IGF-1, IGF binding protein-3, and cGP were evaluated using enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography-mass spectrometry (HPLC-MS), respectively. Results: The cGP/IGF-1 molar ratio was positively correlated with the age of PD-N group, negatively correlated with the age of PD-D group, and not associated with the age of PD-MCI group. Independent of age, the cGP/IGF-1 molar ratio was positively correlated with the cognitive scores of healthy controls, but not in PD groups. Conclusion: Old healthy people with a higher cGP/IGF-1 molar ratio showed better preserved cognition, possibly due to improved IGF-1 function. Increased cGP/IGF-1 molar ratio with age may contribute to cognitive retention in the PD-N group. The absence or reversal of such association with age in the PD-MCI and PD-D groups may indicate the conversion of cognitive status in PD, if confirmed through longitudinal investigations within the individuals with advancing cognitive impairment