[en] The data recorded by the Rome room temperature gravitational-wave antenna during the Supernova SN 1987a have been analysed in connection with the Mont Blanc neutrino event. An energy innovation is observed which precedes by (1.4±0.5)s the first observed neutrino arrival time with the probability of being accidental of 3 per cent. An estimation of the energy emitted as g.w. distributed over 4π and a frequency bandwidth of 1 kHz gives the figure of 2400 solar mass which is abnormal according to standard views on g.w. Under the hypothesis that the time delay δt between the antenna signal and the first neutrino detected in the Mont Blanc tunnel is due only to the neutrino mass, the following mass value is derived from the observed δt=(1.4±0.5)s: m_νe ≤ (7.2±1.3)eV

[en] A toroidal point-contact dc SQUID has been successfully operated. A large input coil with Lsub(i) = 64 μH was coupled with α² = 0.34 without increasing the rf inductance of the dc SQUID by means of 'capacitive shunt'. The observed valued of Isub(c)R = 200 μV, vertical stroke dV/dphi vertical stroke approx. equal to 400 μV/phisub(o) and R/Lsub(rf) approx. equal to 3 x 10¹¹s^-1 are close to those required for quantum-limited sensitivity. Noise characteristics of this SQUID are being investigated using an rf SQUID readout. (orig.)

[en] The research being performed at the University of Rome on transducers concerns two different kinds of resonant transducers: a capacitive transducer coupled to a low noise cooled FET amplifier and an inductive superconducting transducer coupled to a DC SQUID. Both types of transducer are briefly described. (Auth.)

[en] The detailed analysis of the behaviour of a gravitational-wave antenna coupled to a passive resonant transducer has been performed for short bursts of gravitational radiation. An expression for the noise temperature of the system is given for the general case of a transducer with resonant frequency and mechanical quality factor different from those of the antenna. The analysis of the optimum noise temperature obtainable for a given system shows that the optimum performance is obtained when the frequency of the transducer is slightly different from that of the antenna

[en] The dc-superconducting quantum interference device (SQUID) is a low-noise converter from magnetic flux to voltage which can have, in principle, an energy sensitivity near the quantum limit of ℎ/2. A critical parameter for the ideal performance is the device inductance, which must be kept as small as possible. Minimizing the SQUID inductance, however, is a major concern for a practical device; this requirement implies a small SQUID ring and hence magnetic coupling with an external signal is more difficult to achieve. Here we present an original scheme (called multiwasher) to circumvent this problem, and its implementation in an all-refractory thin-film device. Our scheme not only provides good magnetic coupling with a large input coil (0.5 μH) and very low SQUID inductance, but also shielding from outside uniform fields, such as those generated by ambient disturbances. The measured coupled spectral energy sensitivity in the white region at about 1 kHz is 28ℎ at 4.2 K and 5.5ℎ in a pumped helium bath at 0.9 K. The flux noise spectral density at 0.1 Hz and 0.9 K is Φ_n=1x10^-6Φ₀/√ (Hz) . copyright 1998 American Institute of Physics

[en] We report on measurements on superconductor-insulator-normal tunnel junctions at temperatures below 1 K. The junctions have been fabricated by shadow mask technique and e-beam lithography and have submicron dimensions. The measurements on our junctions show that their characteristics are very sensitive to temperature changes making them suitable for sensing temperature in a bolometer. Measurements on arrays of junctions designed to test the on chip electronic refrigeration will be also shown. (orig.)

[en] The analysis described in this paper, made on the bases of two a priori assumptions derived from the results of the authors' work, shows that the Kamioka data support the previously found correlation between the g.w. data and the Mont Blanc data. The probability that this support be accidental is of the order of 3.3 x 10^-4 or 4.7 x 10^-4 and, in all cases, it is smaller than 5.1 x 10^-3. To this, it should be added the fact that the Kamioka contribution is due to events concentrated near the 5νMont Blanc event

[en] We report the first measurements on a dc superconducting quantum interference device (dc-SQUID) coupled to a gravitational wave detector cooled down to liquid-helium temperature. The overall system is composed of a 2.3-ton aluminum bar and a resonant capacitive transducer coupled to the dc-SQUID amplifier by means of a high-ratio superconducting transformer. The SQUID used in this experiment is a planar device with a multiple-loop geometry having both low noise and good coupling with the external world. The electromechanical equivalent circuit of the system, which is essentially a set of three coupled oscillators, is analyzed in detail in its normal modes and an expression for the effective noise temperature for each mode is given. Measurements are reported on the SQUID alone, on the SQUID plus the high-ratio transformer, and on the SQUID coupled to the antenna in parallel with a field-effect transistor preamplifier

[en] YBa₂Cu₃O_7-x bicrystal dc-superconducting quantum interference devices (SQUIDs) and single layer magnetometers working at 77 K have been fabricated and analyzed. Samples have been made in situ by cylindrical magnetron dc sputtering on [001] SrTiO₃ bicrystal substrates. Magnetic flux noise levels and magnetic field sensitivities by standard flux-locked-loop electronics have been measured out on dc-SQUIDs and magnetometers, respectively. Flux noise levels as low as a few μΦ₀Hz^-1/2 in the white noise regime have been measured in SQUIDs, whereas the magnetic field sensitivity of the magnetometers was influenced by external sources. A comparison of experimental data with analytical expressions modelling the behavior of high T_c SQUIDs has been carried out, with special reference to the flux-to-voltage transfer parameter and noise characteristics. Finally, a reduction of 1/f noise of the SQUIDs has been achieved by a wide band bias reversal electronics. copyright 1997 American Institute of Physics

[en] NAUTILUS, a third generation Cryogenic Gravitational Radiation Detector, now being tested at CERN by the Rome group, uses a dc SQUID as low noise amplifier. For such a system we have developed a superconducting transformer to realize the noise matching between the SQUID and the gravitational detector, and an OFHC holder for the SQUID to be cooled at T ≅ 100 mK. Some preliminary measurements has been made on the SQUID connected to a small dilution refrigerator obtaining a flux noise of Φ_n = 7.10^-7Φ₀/√Hz at 0.2 K. Further measurements show that this noise is not due to the SQUID but to a noise source associated to the SQUID holder. (orig.)