The Impact of the New Earth Gravity Models on the Measurement of the Lense–Thirring Effect

We examine how the new forthcoming Earth gravity models from the CHAMP and, especially, GRACE missions could improve the measurement of the general relativistic Lense–Thirring effect according to the various kinds of observables which could be adopted. In a very preliminary way, we use the first recently released EIGEN2 CHAMP–only and GGM01C GRACE–based Earth gravity models in order to assess the impact of the mismodelling in the even zonal harmonic coefficients of geopotential which represents one of the major sources of systematic errors in this kind of measurement. However, discretion is advised on evaluating the reliability of these results because the Earth gravity models used here, especially EIGEN2, are still very preliminary and more extensive calibration tests must be performed. According to the GGM01C model, the systematic error due to the unmodelled even zonal harmonics of geopotential amounts to 2% for the combination of the nodes of LAGEOS and LAGEOS II and the Perigee of LAGEOS II used up to now by Ciufolini and coworkers in the currently performed LAGEOS-LAGEOS II Lense-Thirring experiment, and to 14% for a combination explicitly presented here which involves the nodes only of LAGEOS and LAGEOS II.     

Pile-up correction in characterizing single-photon avalanche diodes of high dark count rate

Although as a single-photon detector, the single-photon avalanche diode (SPAD) may be applied to multi-photon conditions. At a minimum, SPADs with a high dark count rate (DCR) demand a higher value of photon number per pulse to improve the signal-to-noise ratio. In this case, and without correction, severe pile-up distortion may induce a system error in the measurement of photon detection efficiency (PDE) and timing jitter. In this paper, we study the pile-up distortion in SPAD characterization by numerical simulation and experimentation, and introduce a pile-up correction method for the precise characterization of PDE and timing jitter in immature SPADs with an unintentionally high DCR. The results of this study are useful in the development of future SPADs.     

Surface characterization (XPS and SIMS) of emersed polybithiophene electrodes

Emersed polybithiophene (pbT) films, doped at different levels with ClO₄⁻, have been prepared by both discharging fully charged samples and charging fully discharged samples. The different strengths of two surface techniques, e.g. x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS), have been fully exploited in the analysis of emersed pbT samples. XPS has been used to assess the relative atomic concentrations of species from substratum, dopant and, for the first time, solvent (acetonitrile). Curve analysis has been employed, where necessary, to discern between different chemical environments of the same atom. Different chemical environments for acetonitrile molecules have been observed in different samples. The higher surface sensitivity of static SIMS and variable-angle XPS has been employed to distinguish between double layer and more deeply located mobile species. The participation of all mobile species (anions, cations and solvent molecules) to the charging-discharging process and the direction of migration of them at the different stages of the process have been assessed and found to be in good agreement with previous reports.     

Fluxon dynamics and higher harmonics of a.c. susceptibility in HTSC

Il Nuovo Cimento D - Measurements of fundamental and higher harmonics of a.c. susceptibility on polycrystalline high-T c superconductors were carried out using a new method, involving a 2-channel...     

Surface spectroscopic characterization of advanced polymer materials

The potential of a complementary use of X-ray photoelectron spectroscopy and static ToF-SIMS has been exploited with reference to the characterization of electron conducting polymers (polybithiophene) electrochemically synthetized. Particular attention has been focused on the problem of material stability under electrochemical switching.A coherent picture could be drawn showing that irreversible modifications of the surface chemistry occur, strongly dependent on the dryness of the solvent; moreover, the pathway of doping-undoping process can vary noticeably in dependence on the experimental conditions.