Experimental evidence of s-wave superconductivity in bulk CaC6_{6}

The temperature dependence of the in-plane magnetic penetration depth, $\lambda_{ab}(T)$, has been measured in a c-axis oriented polycrystalline CaC$_{6}$ bulk sample using a high-resolution mutual inductance technique. A clear exponential behavior of $\lambda_{ab}(T)$ has been observed at low temperatures, strongly suggesting isotropic s-wave pairing. Data fit using the standard BCS theory yields $\lambda_{ab}(0)=(720\pm 80)$ Angstroem and $\Delta(0)=(1.79\pm 0.08)$ meV. The ratio $2\Delta(0)/k_{_B}T_{c}=(3.6\pm 0.2)$ gives indication for a conventional weakly coupled superconductor.Comment: To appear in Phys. Rev. Let

Linear and nonlinear electrodynamic response of bulk CaC6 in the microwave regime

The linear and nonlinear response to a microwave electromagnetic field of two c-axis oriented polycrystalline samples of the newly discovered superconductor CaC6 (Tc = 11.5 K) is studied in the superconducting state down to 2 K. The surface resistance Rs and the third order intermodulation distortion, arising from a two-tone excitation, have been measured as a function of temperature and microwave circulating power. Experiments are carried out using a dielectrically loaded copper cavity operating at 7 GHz in a "hot finger" configuration. The results confirm recent experimental findings that CaC6 behaves as a weakly-coupled, fully gapped, superconductor. The weak power dependence of Rs encourages a further investigation of this novel superconductor as a possible alternative to Nb in specific microwave applications.Comment: 8 pages, 4 figures, submitted to Appl. Phys. Let

Intrinsic nonlinearity probed by intermodulation distortion microwave measurements on high quality MgB2 thin films

The two tone intermodulation distortion arising in MgB2 thin films synthesized by hybrid physical-chemical vapour deposition is studied in order to probe the influence of the two bands on the nonlinear response of this superconductor. The measurements are carried out by using a dielectrically loaded copper cavity operating at 7 GHz. Microwave data on samples having critical temperatures above 41 K, very low resistivity values, and residual resistivity ratio larger than 10, are shown. The dependence of the nonlinear surface losses and of the third order intermodulation products on the power feeding the cavity and on the temperature is analyzed. At low power, the signal arising from distortion versus temperature shows the intrinsic s-wave behavior expected for this compound. Data are compared with measurements performed on Nb and YBCO thin films using the same technique.Comment: Revised version. Submitted to APL on October 7th 200

Microwave losses of bulk CaC6

We report a study of the temperature dependence of the surface resistance RS in the graphite intercalated compound (GIC) CaC6, where superconductivity at 11.5 K was recently discovered. Experiments are carried out using a copper dielectrically loaded cavity operating at 7 GHz in a "hot finger" configuration. Bulk CaC6 samples have been synthesized from highly oriented pyrolytic graphite. Microwave data allows to extract unique information on the quasiparticle density and on the nature of pairing in superconductors. The analysis of RS(T) confirms our recent experimental findings that CaC6 behaves as a weakly-coupled, fully gapped, superconductor.Comment: 2 pages, submitted to Physica C (M2S-HTSC 2006 Proceedings

Pharmacological Blockade of Serotonin 5-HT7 Receptor Reverses Working Memory Deficits in Rats by Normalizing Cortical Glutamate Neurotransmission

The role of 5-HT7 receptor has been demonstrated in various animal models of mood disorders; however its function in cognition remains largely speculative. This study evaluates the effects of SB-269970, a selective 5-HT7 antagonist, in a translational model of working memory deficit and investigates whether it modulates cortical glutamate and/or dopamine neurotransmission in rats. The effect of SB-269970 was evaluated in the delayed non-matching to position task alone or in combination with MK-801, a non-competitive NMDA receptor antagonist, and, in separate experiments, with scopolamine, a non-selective muscarinic antagonist. SB-269970 (10 mg/kg) significantly reversed the deficits induced by MK-801 (0.1 mg/kg) but augmented the deficit induced by scopolamine (0.06 mg/kg). The ability of SB-269970 to modulate MK-801-induced glutamate and dopamine extracellular levels was separately evaluated using biosensor technology and microdialysis in the prefrontal cortex of freely moving rats. SB-269970 normalized MK-801 -induced glutamate but not dopamine extracellular levels in the prefrontal cortex. Rat plasma and brain concentrations of MK-801 were not affected by co-administration of SB-269970, arguing for a pharmacodynamic rather than a pharmacokinetic mechanism. These results indicate that 5-HT7 receptor antagonists might reverse cognitive deficits associated with NMDA receptor hypofunction by selectively normalizing glutamatergic neurotransmission

Blocco tematico: Gli studi slavistici in Italia nell’ultimo trentennio (1991-2021): questioni specifiche. Parte I

vol. 20 (2023)

Influence of retinal vessel printings on metamorphopsia and retinal architectural abnormalities in eyes with idiopathic macular epiretinal membrane

"\"To investigate whether the presence of retinal vessel printings (RVPs) in eyes having idiopathic epiretinal membrane (ERM) is associated with a higher degree of metamorphopsia or with more prominent abnormalities in the retinal architecture compared with eyes not having RVPs.. METHODS:. A cross-sectional study of 36 eyes in 36 patients was conducted. The patients were divided into two groups (18 eyes per group) on the basis of the presence or absence of RVPs on fundus autofluorescence (FAF) imaging. Metamorphopsia was assessed using M-CHARTS. The optical coherence tomography (OCT) and FAF images were recorded using the Spectralis HRA+OCT. The macula was divided into 15 squares, and the areas between the displaced retinal vessels and the corresponding RVPs were calculated.. RESULTS:. Vertical, horizontal, and average metamorphopsia scores did not differ between the two groups. However, only two patients in the group with RVPs had an average metamorphopsia score of 0.6 or less versus nine patients in the group without RVPs (P = 0.029). There was no correlation between the area of displacement and vertical (P = 0.44), horizontal (P = 0.8), or average (P = 0.38) metamorphopsia scores. The eyes with RVPs manifested a higher degree of irregularity of the external limiting membrane (ELM) and the photoreceptor inner segment\\\/outer segment (IS\\\/OS) lines (P = 0.042 and P = 0.014, respectively). The presence of RVPs was the only independent variable associated with an average metamorphopsia score of 0.6 or higher.. CONCLUSIONS:. The presence of RVPs in eyes with idiopathic macular ERM is usually associated with an average metamorphopsia score of 0.6 or higher using M-CHARTS and with a higher degree of irregularity of the ELM and IS\\\/OS lines at the fovea.\"