University of Sannio

About: University of Sannio is a education organization based out in Benevento, Italy. It is known for research contribution in the topics: Gravitational wave & LIGO. The organization has 1278 authors who have published 6125 publications receiving 167577 citations. The organization is also known as: Università degli Studi del Sannio & Universita degli Studi del Sannio.

Nanoscale mechanical characterization of polymers by atomic force microscopy (AFM) nanoindentations: viscoelastic characterization of a model material

Abstract: The atomic force microscope (AFM), apart from its conventional use as a microscope, is also used for the characterization of the local mechanical properties of polymers. In fact, the elastic characterization of purely elastic materials using this instrument can be considered as a well-assessed technique while the characterization of the viscoelastic mechanical properties remains the challenge. In particular, one finds the mechanical behavior changing when performing indentations at different loading rates, i.e. on different time scales. Moreover, this apparent viscoelastic behavior can also be due to complex contact mechanics phenomena, with the onset of plasticity and long-term viscoelastic features which cannot be identified by the force curve alone. For this reason, a viscoelastic characterization, and thus the study of the effects of indentation rate and temperature, was done on model materials where such additional phenomena are not observed. Another time dependence originating from the instrument itself has also been identified and decoupled. In fact, the viscoelastic behavior has been found to be reproducible even if one changes the experimental set-up as far as the preliminary determinations concerning AFM nanoindentations are well performed. The effects of temperature and time scales on the mechanical behavior have also been undertaken. A check on time–temperature superposition is also attempted through the WLF equation and the apparent activation energies for the elementary motions in the rubbery and in the glass transition regions are in good agreement with the expected values.

Soil–pile–structure interaction: experimental outcomes from shaking table tests

Abstract: Summary An effective way to study the complex seismic soil-structure interaction phenomena is to investigate the response of physical scaled models in 1-g or n-g laboratory devices. The outcomes of an extensive experimental campaign carried out on scaled models by means of the shaking table of the Bristol Laboratory for Advanced Dynamics Engineering, University of Bristol, UK, are discussed in the present paper. The experimental model comprises an oscillator connected to a single or a group of piles embedded in a bi-layer deposit. Different pile head conditions, that is free head and fixed head, several dynamic properties of the structure, including different masses at the top of the single degree of freedom system, excited by various input motions, e.g. white noise, sinedwells and natural earthquake strong motions recorded in Italy, have been tested. In the present work, the modal dynamic response of the soil–pile–structure system is assessed in terms of period elongation and system damping ratio. Furthermore, the effects of oscillator mass and pile head conditions on soil–pile response have been highlighted, when the harmonic input motions are considered. Copyright © 2015 John Wiley & Sons, Ltd.

Constraints on Cosmic Strings Using Data from the Third Advanced LIGO–Virgo Observing Run

Abstract: We search for gravitational-wave signals produced by cosmic strings in the Advanced LIGO and Virgo full O3 dataset Search results are presented for gravitational waves produced by cosmic string loop features such as cusps, kinks, and, for the first time, kink-kink collisions A template-based search for short-duration transient signals does not yield a detection We also use the stochastic gravitational-wave background energy density upper limits derived from the O3 data to constrain the cosmic string tension Gμ as a function of the number of kinks, or the number of cusps, for two cosmic string loop distribution models Additionally, we develop and test a third model that interpolates between these two models Our results improve upon the previous LIGO-Virgo constraints on Gμ by 1 to 2 orders of magnitude depending on the model that is tested In particular, for the one-loop distribution model, we set the most competitive constraints to date: Gμ≲4×10^{-15} In the case of cosmic strings formed at the end of inflation in the context of grand unified theories, these results challenge simple inflationary models