Optimisation and adaptation of synchronisation controllers for networked second-order infinite-dimensional systems

ABSTRACT

The adaptation and optimisation of synchronisation control for networked second-order distributed parameter systems are considered. The objective is to design output feedback controllers guaranteeing agreement between the states of the N systems that individually track a reference model. The controller structure involves feedback terms consisting of the pairwise difference of the measurements of the second-order systems as well as coupling terms that enforce consensus. Placing the closed-loop networked systems in aggregate form allows for further optimisation of the synchronisation gains. Using the aggregate systems ‘closed-loop energy’ as a suitable optimisation measure, the search for the synchronisation gains reduces to the minimisation of the optimisation index, which eventually is described by the trace of the solution to a parameterised Lyapunov operator equation. Considering the adaptation of the synchronisation gains offers an alternative to optimisation. The adaptation is based on Lyapunov redesign-methods and utilises a parameter-dependent Lyapunov functional to extract them. Due to its structure, all network topology information is handled at the local level, thereby relaxing the graph topology conditions in the adaptive case. Numerical studies are included to provide an insight on the effects of synchronisation control of networked second-order distributed parameter systems.     

Efficient tunability and circuit model of nested-U nanoresonators in optical metasurfaces

Tunable metasurfaces can be employed to physically or mechanically engineer and control electromagnetic wave properties like reflection and transmission and their associated spectral characteristics like resonance frequency. Here, we propose highly tunable and sensitive metasurfaces composed of an array of a nested double U-shaped (NDU) nanoresonators on elastic polydimethylsiloxane substrate, operating in infrared region. The mechanical deformation varies the spaces between the coupled resonator elements which in turn leads to corresponding variations in the equivalent capacitance and inductance between the U-shaped elements causing efficient tunability. In addition to the higher signal strengths, it is also reported that the resonant frequency of the proposed metasurface exhibits substantial spectral shift. The observed remarkable trends are adequately verified by the developed equivalent circuit model for the proposed NDU-structure.     

Fabrication of Ta nanoparticles induced by nanosecond laser ablation in ethanol: the study of laser fluence effects

Tantalum nanoparticles (Ta NPs) were synthesized in ethanol solution by ablation with a 1064 nm Nd:YAG laser. Prepared NPs were investigated by UV-visible absorption spectroscopy, Transmission electron microscopy, X-ray diffraction and Photoluminescence measurement. The average sizes of NPs were calculated to be in the range of 12–18 nm. From the UV-visible studies, the plasmon peak position of Ta NPs was observed in the spectral range of 206–208 nm. The XRD spectra clearly showed the crystalline structure of NPs and various peaks of Ta and Ta₂O₅. Moreover, the UV region in the PL spectrum included the free exciton and the bound exciton emission correlated with the defect concentration. In fact, the laser ablation in the organic and inorganic solvents is a strong technique to obtain some NPs with particular structures, which are impossible to produce by conventional methods.     

Laser-induced anisotropy in Ag<Superscript>+</Superscript>-doped glasses

An induced optical anisotropy is observed as a result of interaction of a high-power CW Ar⁺ laser beam, with silver-ion-exchanged glasses. We have shown that the absorption of the beam by the thin layer of Ag⁺ produces a temperature gradient resulting in a radial stress on the surface of the sample. The induced anisotropy makes the sample behave as a thin uniaxial optical medium with axis along the direction of the beam propagation. For the polarized light, the induced anisotropy restricts the application of micro-lenses, which are made by this method. The average refraction index of the interaction area is measured.     

Preparation of acrylonitrile-butadiene-styrene membrane: Investigation of solvent/nonsolvent type and additive concentration

In the present study, preparation of acrylonitrile-butadiene-styrene (ABS) membrane was investigated via phase inversion method. ABS membrane is sensitive to preparation conditions. Therefore, the effect of solvent/nonsolvent type and concentration of additive and ABS was evaluated on the morphology, tensile strength and car wash wastewater treatment. Polyethylene glycol was used as an additive. The results show that nonsolvent type significantly affects the morphology and consequently the flux and rejections of the pollution indices. Increasing concentration of additive and ABS in the casting solution leads to formation of denser and thinner membranes that have lower flux and higher rejections of the pollution indices.     

Dynamic bake hardening of interstitial-free steels

Two types of dynamic strain aging (DSA) strengthening methods were investigated to determine their potentials for industrial use. They are referred to here as dynamic-static bake hardening (DSBH) and dynamic bake hardening (DBH). For this purpose, a 0.06 pct Ti interstitial-free (IF) steel was reheated to 900 °C and cooled at 12 °C/s to room temperature. It was then dynamically bake hardened in the temperature range 100 °C to 250 °C to strains of 2 to 8 pct at a strain rate of 10⁻³ s⁻¹. The tensile properties were determined before and after these treatments. It was found that the occurrence of DSA during dynamic baking led to significant increases in work-hardening rate as well as in the final strength. The results indicate that, for a given solute carbon level, the dynamically and then statically aged samples have higher strengths than those that are bake hardened in the conventional way.     

Modeling the thermomechanical effects on baking behavior of low carbon steels using response surface methodology

Response surface methodology (RSM) was used to study and optimize the effect of thermomechanical treatment on the bake hardening process of low carbon (LC) steels. RSM is a unique modeling approach to replace the costly and time-consuming laboratory simulations to predict the optimal condition for industrial processes. In this study, the RSM based on central composite design (CCD) was used to predict the baking response of low carbon steels. Two models were developed to predict the effects of thermomechanical treatments on the bake hardenability (BH) and final yield stress (FYS) of baked LC steels.