Dynamic response of rocking cracked masonry walls

The behaviour of masonry constructions results to be very far from the one characterizing ductile structures. In masonry constructions, the seismic action activates a rocking motion rather than a dissipating mechanism. A strength resource of masonry structures, properly reinforced in order to avoid early local failures, consists in exhibiting rocking behaviour, until a failure condition is attained. Aim of the paper is to investigate the dynamic behaviour of masonry single storey walls, according to Housner’s studies and innovatively introducing the effect of diagonal cracks developing from the toes of the piers and shown by typical post-earthquake cracking patterns. The proposed procedure can be easily applied to the case of multi-storey regular masonry walls with openings representing the main resistant structural components of a masonry building. Starting from the evaluation of the incipient rocking acceleration of the system, the free and forced motions of the wall are examined. In the paper, according to the classical Housner’s approach, the energy dissipation occurring during the impact is modelled. Finally, a numerical application, considering a simple constant horizontal acceleration impulse of given duration has been carried out.

     

Initial operation at liquid-helium temperature of the M =2270 kg Al 5056 gravitational-wave antenna of the Rome group

Summary We report on the cooling at liquid-helium temperature of our 2270 kg 5056 Al bar at CERN. The liquid-helium container had been filled up to 1500 liters ensuring to keep the antenna cold for more than one month. The antenna is equipped with a resonant capacitive transducer operating at constant electrical charge with a FET low-noise amplifier. The transducer is tuned to the antenna within less than I Hz and the two normal-mode frequencies are ν₋=908.160 Hz and ν₊=924.234 Hz with an applied electrical field in the transducer of 10⁶ V/m. The corresponding overall merit factors areQ ₋=5.20·10⁶ andQ ₊=7.25·10⁶. The transducer has been tested up to an electrical field of 6·10⁶ V/m: in this condition we have βQ≈10⁴. The antenna has been in operation for several weeks giving, for the Brownian noise, values in agreement with the calculated values. We report also on the results of tests performed on a DC SQUID, whose input was connected to a commercial capacitor via a transformer with turn ratio of 1000. Supported in part by Japan Society for the Promotion of Science.     

Effect of Double-Step Steam Explosion Pretreatment in Bioethanol Production from Softwood

The study investigated the production of bioethanol from softwood, in particular pine wood chip. The steam explosion pretreatment was largely investigated, evaluating also the potential use of a double-step process to increase ethanol production through the use of both solid and liquid fraction after the pretreatment. The pretreatment tests were carried out at different conditions, determining the composition of solid and liquid fraction and steam explosion efficiency. The enzymatic hydrolysis was carried out with Ctec2 enzyme while the fermentation was carried out using Saccharomyces Cerevisiae yeast “red ethanol”. It was found that the best experimental result was obtained for a single-step pretreated sample (10.6 g of ethanol/100 g of initial biomass dry basis) for a 4.53 severity. The best double-step overall performance was equal to 8.89 g ethanol/100 g of initial biomass dry basis for a 4.27 severity. The enzymatic hydrolysis strongly depended on the severity of the pretreatment while the fermentation efficiency was mainly influenced by the concentration of the inhibitors. The ethanol enhancing potential of a double-step steam explosion could slightly increase the ethanol production compared to single-step potential.     

Experimental study of high energy electron interactions in a superconducting aluminum alloy resonant bar

Peak amplitude measurements of the fundamental mode of oscillation of a suspended aluminum alloy bar hit by an electron beam show that the amplitude is enhanced by a factor ∼3.5 when the material is in the superconducting state. This result is consistent with the cosmic ray observations performed by the resonant gravitational wave detector NAUTILUS, made of the same alloy, when operated in the superconducting state. A comparison of the experimental data with the predictions of the model describing the underlying physical process is also presented.     

Bosonic helium clusters doped by alkali metal cations: interaction forces and analysis of their most stable structures

Ab initio potentials are computed for alkali metal cationic partners interacting with ⁴He and an overall many-body potential is constructed for each of the ionic dopants in helium clusters. The structures are then obtained via a genetic algorithm approach and results compared with Basin-Hopping Monte Carlo simulations. The classical arrangements are analyzed and quantum effects discussed in comparison with what has been found with Diffusion Monte Carlo calculations. Further corrections to the classical picture by including three-body forces and radial delocalization of the helium adatoms are also considered and their effects analyzed. This work is dedicated to the late Nando Bernardi, an eclectic and gifted scientist and a dear friend whose early departure has left a sad void in our community.     

Experimental study of the dynamic Newtonian field with a cryogenic gravitational wave antenna

We present an experiment performed to study the behaviour of the dynamic gravitational interaction at laboratory scale. We used as field generator a mass quadrupole rotating in the range of 460 Hz and we detected the acceleration field with the cryogenic gravitational wave antenna Explorer of the Rome group. We report the measurements of this interaction as a function of the distance between the field source and the detector. An upper limit on the parameters of a Yukawa-like potential, modeling an hypotetic deviation from the Newtonian law of gravity, is derived. Received: 14 June 1998 / Published online: 16 September 1998     

Noise measurements on a tunnel junction d.c. SQUID for a gravitational radiation detector at ultralow temperature

Summary We present noise measurements made at temperatures down to 200 mK on a tunnel junction d.c. SQUID, to be used as amplifier for the gravitational-wave experiment Nautilus of the Rome group. We find that the flux noise decreases with temperature, as expected, with a best measured value of at 0.2 K. The presence of an excess noise term independent of temperature is discussed.     

Bosonic helium droplets with cationic impurities: onset of electrostriction and snowball effects from quantum calculations

Variational Monte Carlo and diffusion Monte Carlo calculations have been carried out for cations such as Li(+), Na(+), and K(+) as dopants of small helium clusters over a range of cluster sizes up to about 12 solvent atoms. The interaction has been modeled through a sum-of-potential picture that disregards higher order effects beyond atom-atom and atom-ion contributions. The latter were obtained from highly correlated ab initio calculations over a broad range of interatomic distances. This study focuses on two of the most striking features of the microsolvation in a quantum solvent of a cationic dopant: electrostriction and snowball effects. They are discussed here in detail and in relation with the nanoscopic properties of the interaction forces at play within a fully quantum picture of the cluster features.