Carrier-Induced Magnetic Circular Dichloism in the Magnetoresistive Pyrochlore Tl2Mn2O7

Infrared magnetic circular dichloism (MCD), or equivalently magneto-optical Kerr effect, has been measured on the Tl2Mn2O7 pyrochlore, which is well known for exhibiting a large magnetoresistance around the Curie temperature T_C ~ 120 K. A circularly polarized, infrared synchrotron radiation is used as the light source. A pronounced MCD signal is observed exactly at the plasma edge of the reflectivity near and below T_c. However, contrary to the conventional behavior of MCD for ferromagnets, the observed MCD of Tl2Mn2O7 grows with the applied magnetic field, and not scaled with the internal magnetization. It is shown that these results can be basically understood in terms of a classical magnetoplasma resonance. The absence of a magnetization-scaled MCD indicates a weak spin-orbit coupling of the carriers in Tl2Mn2O7. We discuss the present results in terms of the microscopic electronic structures of Tl2Mn2O7.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp

Superconducting properties of the pyrochlore oxide Cd2Re2O7

We report the superconducting properties of the pyrochlore oxide Cd2Re2O7. The bulk superconducting transition temperature Tc is about 1.0 K, and the upper critical field Hc2 determined by the measurement of specific heat under magnetic fields is 0.29 T. The superconducting coherence length is estimated to be 34 nm. Specific heat data measured on single crystals suggest that the superconducting gap of Cd2Re2O7 is nodeless.Comment: 6 pages, 6 figures, 1 table, to be published in J. Chem. Phys. Solid

Unusual T_c variation with hole concentration in Bi_2Sr_{2-x}La_xCuO_{6+\delta}

We have investigated the $T_c$ variation with the hole concentration $p$ in the La-doped Bi 2201 system, Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+\delta}$. It is found that the Bi 2201 system does not follow the systematics in $T_c$ and $p$ observed in other high-$T_c$ cuprate superconductors (HTSC's). The $T_c$ vs $p$ characteristics are quite similar to what observed in Zn-doped HTSC's. An exceptionally large residual resistivity component in the inplane resistivity indicates that strong potential scatterers of charge carriers reside in CuO$_2$ planes and are responsible for the unusual $T_c$ variation with $p$, as in the Zn-doped systems. However, contrary to the Zn-doped HTSC's, the strong scatter in the Bi 2201 system is possibly a vacancy in the Cu site.Comment: RevTeX, 3 figures, to be published in the Physical Review

Quasiparticle Excitation in the Superconducting Pyrochlore Cd2Re2O7 Probed by Muon Spin Rotation

The quasiparticle excitations in the mixed state of Cd2Re2O7 have been studied by means of muon spin rotation/relaxation. The temperature dependence of the magnetic penetration depth (lambda) is consistent with a nearly isotropic superconducting order parameter, although a slight discrepancy which is dependent on the details in the analysis may be present. This is also supported by the relatively weak field dependence of lambda.Comment: 12 pages, 2 figures, to appear in J. Phys. Soc. Jp

Mott-Hubbard quantum criticality in paramagnetic CMR pyrochlores

We present a correlated {\it ab initio} description of the paramagnetic phase of Tl$_2$Mn$_2$O$_7$, employing a combined local density approximation (LDA) with multiorbital dynamical mean field theory (DMFT) treatment. We show that the insulating state observed in this colossal magnetoresistance (CMR) pyrochlore is determined by strong Mn intra- and inter-orbital local electron-electron interactions. Hybridization effects are reinforced by the correlation-induced spectral weight transfer. Our result coincides with optical conductivity measurements, whose low energy features are remarkably accounted for by our theory. Based on this agreement, we study the disorder-driven insulator-metal transition of doped compounds, showing the proximity of Tl$_2$Mn$_2$O$_7$ to quantum phase transitions, in agreement with recent measurements.Comment: 4 pages, 4 figure

Lateral Compartment Contact Pressures Do Not Increase After Lateral Extra-articular Tenodesis and Subsequent Subtotal Meniscectomy

© The Author(s) 2019. Background: Modified Lemaire lateral extra-articular tenodesis (LET) has been proposed as a method of addressing persistent anterolateral rotatory laxity after anterior cruciate ligament (ACL) reconstruction (ACLR). However, concerns remain regarding the potential for increasing lateral compartment contact pressures. Purpose: To investigate changes in tibiofemoral joint contact pressures after isolated ACLR and combined ACLR plus LET with varying states of a lateral meniscal injury. Study Design: Controlled laboratory study. Methods: Eight fresh-frozen cadaveric knee specimens (mean age, 60.0 ± 3.4 years) were utilized for this study, with specimens potted and loaded on a materials testing machine. A pressure sensor was inserted into the lateral compartment of the tibiofemoral joint, and specimens were loaded at 0°, 30°, 60°, and 90° of flexion in the following states: (1) baseline (ACL- and anterolateral ligament–deficient), (2) ACLR, (3) ACLR with LET, (4) partial meniscectomy (removal of 50% of the posterior third of the lateral meniscus), (5) subtotal meniscectomy (removal of 100% of the posterior third of the lateral meniscus), and (6) LET release (LETR). Mean contact pressure, peak pressure, and center of pressure were analyzed using 1-way repeated-measures analysis of variance. Results: Across all flexion angles, there was no statistically significant increase in the mean contact pressure or peak pressure after ACLR plus LET with and without lateral meniscectomy compared with isolated ACLR. There was a significant reduction in the mean contact pressure, from baseline, after subtotal meniscectomy (69.72% ± 19.27% baseline; P =.04) and LETR (65.81% ± 13.40% baseline; P =.003) at 0° and after the addition of LET to ACLR at 30° (61.20% ± 23.08% baseline; P =.031). The center of pressure was observed to be more anterior after partial (0°, 30°) and subtotal (0°, 60°) meniscectomy and LETR (0°, 30°, 60°). Conclusion: Under the loading conditions of this study, LET did not significantly alter lateral compartment contact pressures when performed in conjunction with ACLR in the setting of an intact or posterior horn–deficient lateral meniscus. Clinical Relevance: This study should provide surgeons with the confidence that it is safe to perform LET in this manner in conjunction with ACLR without altering lateral compartment pressures, regardless of the status of the lateral meniscus

Cost-effectiveness of different monitoring strategies in a screening and treatment programme for hepatitis B in The Gambia

Background: Clinical management of chronic hepatitis B virus (HBV) infection is complex and access to antiviral treatment remains limited in sub-Saharan Africa. International guidelines recommend monitoring at least annually for disease progression among HBV-infected people not meeting treatment criteria at initial diagnosis. This study aimed to assess the impact and cost-effectiveness of alternative strategies for monitoring. Methods: We used a mathematical model of HBV transmission and natural history, calibrated to all available West African data, to project the population-level health impact, costs and cost-effectiveness of different monitoring strategies for HBV-infected individuals not initially eligible for antiviral treatment. We assumed that these patients were found in the year 2020 in a hypothetical community-based screening programme in The Gambia. Monitoring frequencies were varied between every 5 and every 1 year and targeted different age groups. Results: The currently recommended annual monitoring frequency was likely to be not cost-effective in comparison with other strategies in this setting. 5-yearly monitoring in 15-45-year olds, at US$338 per disability-adjusted life year averted, had the highest probability of being the most effective cost-effective monitoring strategy. Conclusions: Monitoring less frequently than once a year is a cost-effective strategy in a community-based HBV screening and treatment programme in The Gambia, with the optimal strategy depending on the cost-effectiveness threshold. Efficiencies may be gained by prioritising the 15-45-year age group for more intensive monitoring

Hepatitis B testing and treatment in HIV patients in The Gambia - compliance with international guidelines and clinical outcomes

Background Compliance with WHO guidelines on HBV screening and treatment in HIV-coinfected patients is often challenging in resource limited countries and has been poorly assessed in sub-Saharan Africa. Methods Between 2015 and 2016, we assessed physician’s compliance with WHO guidelines on HIV-HBV coinfection in the largest HIV clinic in The Gambia, and the hepatic outcomes in HIV-HBV coinfected patients as compared to randomly selected HIV-monoinfected controls. Results 870 HIV-infected patients regularly seen in this clinic agreed to participate in our study. Only 187 (21.5%, 95% CI 18.8–24.3) had previously been screened for HBsAg, 23 (12.3%, 95% CI 8.0–17.9) were positive of whom none had liver assessment and only 6 (26.1%) had received Tenofovir. Our HBV testing intervention was accepted by all participants and found 94/870 (10.8%, 95% CI 8.8–13.1) positive, 78 of whom underwent full liver assessment along with 40 HBsAg-negative controls. At the time of liver assessment, 61/78 (78.2%) HIV-HBV coinfected patients received ART with 7 (11.5%) on Tenofovir and 54 (88.5%) on Lamivudine alone. HIV-HBV coinfected patients had higher APRI score compared to controls (0.58 vs 0.42, p = 0.002). HBV DNA was detectable in 52/53 (98.1%) coinfected patients with 14/53 (26.4%) having HBV DNA >20,000 IU/L. 10/12 (83.3%) had at least one detectable 3TC-associated HBV resistance, which tended to be associated with increase in liver fibrosis after adjusting for age and sex (p = 0.05). Conclusions Compliance with HBV testing and treatment guidelines is poor in this Gambian HIV programme putting coinfected patients at risk of liver complications. However, the excellent uptake of HBV screening and linkage to care in our study suggests feasible improvements

Spin Dynamics of the Magnetoresistive Pyrochlore Tl_2Mn_2O_7

Neutron scattering has been used to study the magnetic order and spin dynamics of the colossal magnetoresistive pyrochlore Tl_2Mn_2O_7. On cooling from the paramagnetic state, magnetic correlations develop and appear to diverge at T_C (123 K). In the ferromagnetic phase well defined spin waves are observed, with a gapless ($\Delta <0.04$ meV) dispersion relation E=Dq^{2} as expected for an ideal isotropic ferromagnet. As T approaches T_C from low T, the spin waves renormalize, but no significant central diffusive component to the fluctuation spectrum is observed in stark contrast to the La$_{1-x}$(Ca,Ba,Sr)$_x$MnO$_3$ system. These results argue strongly that the mechanism responsible for the magnetoresistive effect has a different origin in these two classes of materials.Comment: 4 pages (RevTex), 4 figures (encapsulated postscript), to be published in Phys. Rev. Let