A physically based circuit model is proposed for SPICE simulation of thermally assisted reset transitions in resistive switching devices. The model allows the simulation of conductive filaments with complex structures, such as a main filament with several subfilaments attached forming a tree structure, or several filaments interlaced between them. The model has been validated by comparing with experimental data and the simulations obtained with a previously published simulation tool. A study of the influence of different subfilaments configurations on the variability of resistive random access memory I-V reset curves is also presented.

The relevance of the intrinsic series resistance effect in the context of resistive random access memory (RRAM) compact modeling is investigated. This resistance notably affects the conduction characteristic of resistive switching memories so that it becomes an essential factor to consider when fitting experimental data, especially those coming from devices exhibiting the so-called snapback and snapforward effects. A thorough description of the resistance value extraction procedure and an analysis of the connection of this value with the set and reset transition voltages in HfO₂-based valence change memories are presented. Furthermore, in order to illustrate the importance of this feature in the shape of the I–V curve, the Stanford model for RRAM devices is enhanced by incorporating the series resistance as an additional parameter in the Verilog-A model script.

This paper presents a comparison of the acoustic emission (AE) energy and the plastic strain energy released by some reinforced concrete (RC) specimens subjected to cyclic or seismic loadings. AE energy is calculated, after proper filtering procedures, using the signals recorded by several AE low frequency sensors (25–100 kHz) attached on the specimens. Plastic strain energy is obtained by integrating the load displacement curves drawn from the measurements recorded during the test. Presented are the results obtained for: (i) two beams (with and without an artificial notch) and a beam-column connection subjected to several cycles of imposed flexural deformations; (ii) a reinforced concrete slab supported by four steel columns, and a reinforced concrete frame structure, both of the latter are subjected to seismic simulations with a uniaxial shaking table. The main contribution of this paper, which is a review of some papers previously published by the authors, is to highlight that, in all cases, a very good correlation is found between AE energy and plastic strain energy, until the onset of yielding in the reinforcing steel. After yielding, the AE energy is consistently lower than the plastic strain energy. The reason is that the plastic strain energy is the sum of the contribution of concrete and steel, while the AE energy acquired with thresholds higher than 35 dB_AE captures only the contribution of the concrete cracking, not the steel plastic deformation. This good correlation between the two energies before the yielding point also lends credibility to the use of AE energy as a parameter for concrete damage evaluation in the context of structural health monitoring.

This paper proposes the monitoring of old timber beams with natural defects (knots, grain deviations, fissures and wanes), reinforced using carbon composite materials (CFRP). Reinforcement consisted of the combination of a CFRP laminate strip and a carbon fabric discontinuously wrapping the timber element. Monitoring considered the use and comparison of two types of sensors: strain gauges and multi-resonant acoustic emission (AE) sensors. Results demonstrate that: (1) the mechanical behavior of the beams can be considerably improved by means of the use of CFRP (160% in bending load capacity and 90% in stiffness); (2) Acoustic emission sensors provide comparable information to strain gauges. This fact points to the great potential of AE techniques for in-service damage assessment in real wood structures.

In this work, we study the stability behavior of composite magnetorheological fluids consisting of magnetic (iron) and non-magnetic (poly(methylmethacrylate)) particles dispersed in mineral oil. Because of the opacity of the suspensions, optical methods traditionally employed for evaluation of the gravitational settling in colloidal suspensions are not suitable for sedimentation follow-up in this case. For this reason, we use an alternative method based on the evaluation of the resonant frequency of the inductance of a thin coil surrounding the sample. The movement of the coil along the height of the container at specified steps and time intervals allows obtaining information about the local volume fraction of particles inside the tube. The obtained successive profiles for the multi-component suspensions show a decrease of the iron particle settling and of the initial rate of settling as the poly(methylmethacrylate) volume fraction is increased. Finally, the increase of the poly(methylmethacrylate) concentration gives rise to an improvement of the rheological properties upon magnetic field application for a given concentration of iron. Both a strong rheological response and a good colloidal stability are essential for practical applications.