Ultraviolet Light-Responsive Photorheological Fluid for Sensors and Actuators Realized by Phosphorescence Effects and LSTM RNN

A photo-rheological fluid (PRF) is a smart fluid which exhibits different viscosity under UV irradiation. A PRF is comprehensively presented in this work, with particular focus on its responses under UV off/on conditions. The isomeric conversion from SP to MC and vice versa under UV off and on, respectively, showed unequal rates of transformation. As a result, a complex non-linear hysteretic response was observed. To be used indifferent types of sensors and actuators which can exploit its rheological properties, it is essential the PRF have linearized hysteresis behavior. To minimize the asymmetric non-linear hysteresis characteristics under UV on and off conditions, the well-known long-lasting phosphor SAO (SrAl2O4:Eu2+, Dy3+) was incorporated. The incorporation of SAO in the PRF improved the linearity of the PRF response, although the conversion rate was not identical under UV off/on conditions. The SAO particles were observed to settle over time due to phase splitting, undermining the usefulness of the SAO-PRF composite. Instead of improving the PRF response by further adjusting the PRF composite, a software approach based on Long Short-Term Memory Recurrent Neural Networks (LSTM RNN) was employed to model and compensate the asymmetric non-linear hysteresis response, ensuring the realization of sensors and actuators that exploit PRF as hardware.

Polymer Nanocomposite-based Moisture Sensors for Monitoring of the Water Contents in the Natural Gas Pipelines

In this study, the polymer-based humidity sensors were investigated for humidity sensing applications. The key advantages of polymers that have garnered this attraction are their lightweight, easy preparation, and low cost of both materials and fabrication process. Different techniques are used to enhance the surface morphology and sensitivity of polymeric films, which include synthesis of nanocomposites, copolymerization techniques, and blending of polymers. The incorporation of nanoparticles to the polymer matrix improves the electrical and mechanical properties of the polymeric film. We have investigated different polymer nanocomposites based humidity sensors on enhancing the sensitivity of the sensor, on achieving faster response and recovery time and lower hysteresis loss as compared to the polymeric humidity sensors. In the first phase, we investigated the PLA-TiO2 nanocomposite for humidity sensing applications. We have optimized the concentration of TiO2 in the PLA-TiO2 nanocomposite and apply acetone for the surface treatment of the sensing film. In the second phase, we studied the PVDF-TiO2 nanocomposite-based humidity sensor, achieved a linear response of the sensor, and optimized the concentration of PVDF. In the third phase, we incorporated the BaTiO3 nanoparticles within optimized PVDF and studied the dielectric property of the nanocomposite film. PVDF-BaTiO3 sensors show a smaller hysteresis response. In the 4th phase, we blend the PVDF with SPEEK polymer; the optimized concentration of SPEEK improves the sensitivity of the humidity sensors at a lower humidity level.

Comparative Investigation of Phenomenological Modeling for Hysteresis Responses of Magnetorheological Elastomer Devices

Magnetorheological elastomer (MRE) is a type of magnetic soft material consisting of ferromagnetic particles embedded in a polymeric matrix. MRE-based devices have characteristics of adjustable stiffness and damping properties, and highly nonlinear and hysteretic force–displacement responses that are dependent on external excitations and applied magnetic fields. To effectively implement the devices in mitigating the hazard vibrations of structures, numerically traceable and computationally efficient models should be firstly developed to accurately present the unique behaviors of MREs, including the typical Payne effect and strain stiffening of rubbers etc. In this study, the up-to-date phenomenological models for describing hysteresis response of MRE devices are experimentally investigated. A prototype of MRE isolator is dynamically tested using a shaking table in the laboratory, and the tests are conducted based on displacement control using harmonic inputs with various loading frequencies, amplitudes and applied current levels. Then, the test results are used to identify the parameters of different phenomenological models for model performance evaluation. The procedure of model identification can be considered as solving a global minimization optimization problem, in which the fitness function is the root mean square error between the experimental data and the model prediction. The genetic algorithm (GA) is employed to solve the optimization problem for optimal model parameters due to its advantages of easy coding and fast convergence. Finally, several evaluation indices are adopted to compare the performances of different models, and the result shows that the improved LuGre friction model outperforms other models and has optimal accuracy in predicting the hysteresis response of the MRE device.

The Seismic Investigation of Off-Diagonal Steel Braced RC Frames

Steel bracing may be used to enhance the seismic strength of RC frames. Concentric steel bracing generally reduces ductility, which is a key component of seismic design. To overcome the problem, ductile steel brace-RC frame systems are therefore usually introduced in the form of eccentric braces. In the present study, the Off-Diagonal Bracing System (ODBS), which works as a concentric type of bracing, is investigated. In this paper the response of ODBS elements to cyclic loading is first explored and compared with those of other types of bracing such as X-bracing and inverted-V bracing systems. The time history analysis responses and cyclic hysteresis responses of a number of lowrise to mid-rise RC frames retrofitted with different types of bracing systems are then evaluated and compared. It is shown that under seismic excitation, a much reduced base shear is experienced by frames retrofitted with ODBS compared to other bracing systems. The results of time history and cyclic hysteresis response analyses also indicate a far greater energy dissipation capacity and ductility for the ODBS compared to other bracing systems. It is also concluded that ODBS performs best in lowrise frames. The out-of-plane buckling response of the ODBS is also investigated, and it is shown that a double-plated central connection can control such an adverse response.

Loops de histerese na evapotranspiração em área de pastagem no sul do Brasil

One of the main components of water and energy balance in terrestrial ecosystems, the evapotranspiration (ET), was estimated using the eddy covariance technique. To better understand these energy transfer processes it is necessary to know how the ET responds to different meteorological variables. The main objective of this work is to investigate the hysteresis response of ET to environmental variables including air temperature (Temp), vapor pressure deficit (DPV) and net radiation (Rn) at a diel timescale for a pasture area in southern Brazil. ET presents hysteresis with DPV and Temp, responding more strongly to the vapor pressure deficit.