Search

There is presently a general agreement that the simple inter-metallic compound MgB2 is a conventional, phonon mediated, superconductor, and that the anomalies in its behaviour can be consistently explained by the existence of two different gaps. We present a study of the complex conductivity as a function of temperature in pure and Al-doped MgB2 pellets by using a dielectrically loaded resonant cavity at 19 GHz. [Copyright &y& Elsevier]

Abstract: In the graphite–lithium–calcium system, four well-defined intercalation compounds were synthesised. Two of them, CaC6 and Li3Ca2C6, exhibit superconducting properties at 11.5K and 11.15K, respectively, the highest critical temperatures among those of graphite intercalation compounds. The samples are synthesised using a liquid–solid method allowing the preparation of pure bulk samples, auspicious for crystallographic and magnetic measurements. The crystal structure of CaC6 was entirely specified; this compound crystallises in the R-3m space group. The two-dimensional unit cell of Li3Ca2C6 is hexagonal and commensurate with that of graphite and the intercalated sheets, very rich in metal, are seven-layered. The magnetic properties of these phases were studied with an applied field parallel and perpendicular to the graphene sheets. In both cases the magnetic phase diagram indicates that these compounds are type II superconducting materials slightly anisotropic in spite of their lamellar structure. In the case of CaC6, in-plane magnetic penetration depth measurements show a clear exponential behaviour at low temperatures, consistent with an s-wave symmetry of the gap function, well fitted by the standard BCS theory in the dirty limit. [Copyright &y& Elsevier]

We present a study on the power dependence of the microwave surface impedance in thin films of the novel superconductor MgB2. 500 nm thick samples exhibiting critical temperatures ranging between 26 and 38 K are synthesized by an ex situ post-anneal of e-beam evaporated boron in the presence of an Mg vapor at 900 °C. Preliminary results on films grown in situ by a high rate magnetron sputtering technique from stoichiometric MgB2 and Mg targets are also reported. Microwave measurements have been carried out employing a dielectrically loaded niobium superconducting cavity operating at 19.8 GHz and 4 K. The study shows that the electrodynamic response of MgB2 films is presently dominated by extrinsic sources of dissipation, appearing already at low microwave power, likely to be ascribed to the presence of grain boundaries and normal inclusions in the samples. [Copyright &y& Elsevier]

Introduction: In elderly patients treated with chemotherapy for advanced non-small cell lung cancer (NSCLC), frequently an adequate dose intensity (DI) is difficult to be delivered. We therefore performed in this population a study to assess the delivered DI and its impact on clinical outcome. Patients and methods: Inclusion criteria were: age equal or greater than 70 years; cytological or histological diagnosis of NSCLC; stage IIIB or IV; no previous chemotherapy for advanced disease. Total relative dose intensity (RDI) was taken into account for the analysis. An RDI less than 80% was considered as suboptimal for tumor shrinkage. A survival comparison between subgroups (more or less than 80% RDI) was done. Results: 107 patients were eligible for the analysis. Mean age was 74.3 years. PS was 0–1 in 92.5% of subjects. Mean number of comorbidities was 1.86. The most frequently chemotherapy regimens used were single agent vinorelbine and single agent gemcitabine. Overall mean RDI was 68%; 36% of patients received a RDI>80% of the originally planned one. The objective response rate (RR) was 55.2% and 33.3% respectively for patients receiving more or less than 80% of the RDI (p <0.01); a significant difference in overall survival between these two groups (p <0.0001) was also recorded. Baseline hemoglobin and body mass index (BMI) were the variables that significantly influenced the delivered RDI. Conclusions: These data suggest that in elderly patients treated with chemotherapy for advanced NSCLC an adequate dose intensity has a significant positive impact on both response rate and overall survival. [Copyright &y& Elsevier]

We have studied the effect of Nd/Ba substitution on the superconducting properties of R1(NdxBa2−x)Cu3O7 (R=Nd, Y) thin films by using microwave penetration depth and surface resistance measurements. Data on samples characterised by a Nd-excess of 4–5% have been collected by using a microstrip resonator at frequencies of 1.44 and 9.7 GHz and a symmetric dielectric resonator technique in TE0 1 1 mode at 19.8 GHz. A quadratic bT2 low temperature dependence of the penetration depth is observed for the Nd-rich samples, with the coefficient b decreasing with the frequency. The data can be reasonably explained in a d-wave framework supposing that Nd at Ba site behaves, both in Nd1+x Ba2−xCu3O7 and Y1(NdxBa2−x)Cu3O7, as a resonant impurity, as confirmed by scanning tunnelling spectroscopy. The changes of the temperature dependence of the penetration depth with the frequency can be explained with a two fluid approach taking into account the frequency dependence of the complex conductivity. [Copyright &y& Elsevier]