Maria Cristina Porcu

Rigid–plastic approximation to predict plastic motion under strong earthquakes

The paper shows that the rigid–plastic oscillator can be used to evaluate the maximum plastic displacement of any elastic–plastic oscillator under any earthquake. Motivated by this result a rigid–plastic response spectrum is introduced, which provides an easy method to calculate the maximum plastic displacement of a rigid–plastic oscillator for any given earthquake. Such a spectrum is easier to construct than the elastic–plastic response spectrum or the classical elastic one. By means of appropriate formulas presented in the paper, the rigid–plastic response spectrum can be used to determine a realistic upper bound to the maximum plastic displacement of any elastic–plastic oscillator under the given earthquake. Copyright

Purification and Characterization of an NAD(P)H:Quinone Oxidoreductase from Glycine Max Seedlings

An NAD(P)H:(quinone acceptor) oxidoreductase (EC 1.6.99.2) was purified from Glycine max seedlings by means of chromatographic procedures. After 1371-fold purification, the enzyme showed a single band in IEF corresponding to an isoelectric point of 6.1. A single band was also found in native-PAGE both by activity staining and Coomassie brilliant blue staining. The molecular mass determined in SDS-PAGE was 21900 Da, while in HPLC gel-filtration it was 61000 Da. The NAD(P)H:quinone oxidoreductase was able to use NADH or NADPH as the electron donor. Among the artificial quinones which are reduced by this enzyme, 6-hydroxydopa- and 6-hydroxydopamine-quinone are of particular interest because of their neurotoxic effects.

Stress stability at the yield surface

Abstract An elastic-plastic material may be unstable at yield under work control, if the values of its free energy at yield are not properly restricted. This is true whether the material is stable in Druckers sense or not. In materials in which plastic volume change is unrestricted, stability under work control requires that the yield surface should be equipotential for free energy. On the other hand, if plastic flow is isochoric, the intersections of the yield surface with planes normal to the hydrostatic axis must be equipotential.

Analysis of elastic nonlinearity for impact damage detection in composite laminates

This paper concerns the experimental analysis of nonlinear response features of a composite laminate plate for impact damage detection. The measurement procedure is based on the Scaling Subtraction Method (SSM) and consists in exciting the damaged specimen with two sinusoidal signals at different amplitude. The linearly rescaled response signal at low amplitude excitation is subtracted from the response at large amplitude excitation to extract the nonlinear signatures. The latter are analysed in the time domain to infer the presence of damage. Results are compared with frequency domain analyses using the nonlinear vibro-acoustic modulation technique (NWMS). Changes in amplitude and phase as well as modulation effects of the acquired responses are also monitored. Surface-bonded, low profile piezoceramic transducers are used for excitation and sensing. Both measurements techniques are applied to detect barely visible impact damage in laminate composite plate. Non-destructive penetrant-enhanced X-ray inspections are carried out to characterize the extent of internal damage. The behavior of the nonlinear features and the sensitivity of each technique are also investigated in the paper.

New mercurated resins for covalent immobilisation

A hydrophilic resin based on cross-linked polyvinyl alcohol and containing appropriate aromatic moieties, suitable for mercuration, was prepared. Such supports were then treated with mercuric salts to obtain hydrophilic materials which showed a high affinity towards thiols and thiol-containing proteins like bovine serum albumin and bovine liver catalase. Some properties of both the mercurated resin and an immobilised catalase preparation were studied.

The ongoing destabilization of the mosul dam as observed by synthetic aperture radar interferometry

We present a detailed survey on the ongoing destabilization process of the Mosul dam. The dam is located on the Tigris river and is the biggest hydraulic structure in Iraq. From a geological point of view the dam foundation is unstable due to the underlying geology that is formed by alternate and variable strata of highly soluble materials such as gypsum, anhydrite, marl and limestone. Here we present the first comprehensive multi-sensor cumulative deformation map for the dam generated from space-based synthetic aperture radar (SAR) measurements from the Italian constellation COSMO-SkyMed and the European Sentinel-1a satellite. We compared 2014–2016 data to an historic dataset spanning 2004–2010 acquired with the Envisat ASAR sensor. We found that deformation was rapid during 2004–2010, slowed down in 2012–2014, and restarted in August 2014 when grouting operations stopped due to the temporary capture of the dam by the self proclaimed Islamic State in Iraq and Syria (ISIS). We took advantage of the availability of data from multiple SAR satellites to infer the deformation at the dam in great spatial and temporal detail and shed new light on the processes of the ongoing destabilization. This study highlights how new constellations of SAR sensors together with the availability of historical datasets are leading to important advances in deformation monitoring of small scale geologic and manmade features.

Excessive pedestrian-induced swaying in code-compliant walkways

Abstract Human-induced dynamic loads may trigger noisy vibrations on slender structures, affecting even their serviceability and compromising their use. This paper shows that current code-based design may not be effective enough in preventing excessive lateral vibrations of footbridges. By referring to the case history of the Assago-Forum walkway (Italy), it is shown that the widely adopted ES-ISO-10137 International Standard may, in fact, lead to underestimating—even significantly—the actual peak lateral accelerations in walkways and, consequently, it may erroneously consider structures safe against human-induced lateral vibrations when they are not actually so. The reason can be found in the extent to which the horizontal load code-based model is affected by the design scenario. By considering the horizontal actions relating to different code-compliant scenarios, a numerical dynamic analysis of the Assago-Forum walkway has been carried out. The results have then been compared with those obtained through a recently published, more advanced study. This investigation provides evidence that the design guidance given by ES-ISO-10137 against pedestrian-induced lateral vibrations of walkways may not be adequate. The paper also advances some suggestions on how code-based design might be improved.