RESUMO
Electrical resistivity experiments show superconductivity atTc=1.1K in a high-quality single crystal of trigonalγ-PtBi2, with an enhanced critical magnetic fieldµ0Hc2(0)â³1.5Tesla and a low critical current-densityJc(0)≈40 A cm-2atH = 0. BothTcandHc2(0)are the highest reported values for stoichiometric bulk samples at ambient pressure. We found a weakHc2anisotropy withΓ=Hc2ab/Hc2c<1, which is unusual among superconductors. Under a magnetic field, the superconducting transition becomes broader and asymmetric. Along with the low critical currents, this observation suggests an inhomogeneous superconducting state. In fact, no trace of superconductivity is observed through field-cooling-zero-field-cooling magnetization experiments.
RESUMO
We report on results of electrical resistivity and structural investigations on the cubic modification of FeGe under high pressure. The long-wavelength helical order (T(C) = 280 K) is suppressed at a critical pressure p(c) approximately 19 GPa. An anomaly at T(X)(p) and strong deviations from a Fermi-liquid behavior in a wide pressure range above p(c) suggest that the suppression of T(C) disagrees with the standard notion of a quantum critical phase transition. The metallic ground state persisting at high pressure can be described by band-structure calculations if zero-point motion is included. The shortest FeGe interatomic distance display discontinuous changes in the pressure dependence close to the T(C)(p) phase line.
RESUMO
The aim of our study was to assess whether acute variations in portal vein Doppler sonographic parameters induced by administration of a single beta-blocker agent are predictive of the long-term effects of these drugs in the prevention of a first episode of variceal bleeding. In 30 patients with liver cirrhosis at high risk for variceal bleeding, duplex Doppler sonographic parameters (maximal portal flow velocity, portal blood flow, and congestion index) were measured before and 4 h after the administration of 40 mg of propranolol. Twenty-three of these patients started chronic therapy with propanolol and were evaluated periodically (seven patients were excluded because they did not continue the therapy). The percentage of patients free from bleeding was 86.9% at the first year and 77.8% at the second year. Among a series of clinical, laboratory, and instrument-based parameters, the only one related to first bleeding, selected by the Cox regression model, was the percentage decrease in maximal portal flow velocity observed after initial administration of propranolol (P < 0.01). The best cutoff value for the percentage decrease in portal flow velocity (portal flow velocity test) was 12%. The prevalence of bleeding had been 25% (3 of 12) in patients with positive portal flow velocity test results (12% decrease or more), versus 64% (7 of 11) in patients with negative portal flow velocity test results. The actuarial probability of remaining free from bleeding (Kaplan-Meier analysis) was different in these two groups (log rank P < 0.01). The portal flow velocity test represents a safe and feasible method to predict the efficacy of beta-blockers in the prevention of a first bleeding episode in patients with cirrhosis. In patients with negative results on the portal flow velocity test, an alternative therapeutic approach should be considered.
