An improved Backstepping technique using sliding mode control for transient stability enhancement and voltage regulation of SMIB power system

The problem of transient stability and voltage regulation for a single machine infinite bus (SMIB) system is addressed in this paper. An improved Backstepping design method for transient stability enhancement and voltage regulation of power systems is discussed beginning with the classical Backstepping to designing the nonlinear excitation control of synchronous generator. Then a more refined version of this technique will be suggested incorporating the sliding mode control to enhance voltage regulation and transient stability. The proposed method is based on a standard third-order model of a synchronous generator connected to the grid (SMIB system). It is basically implemented on the excitation side of the synchronous generator and compared to the classical Backstepping controller as well as the conventional controllers which are the automatic voltage regulator and the power system stabiliser. Simulation results prove the effectiveness of the proposed method which ameliorates to a great extent the transient stability compared to the other methods.     

Prediction of the thermal conductivity of metal hydrides – The inverse problem

With sustainability as an important and driving theme, not merely of research, but that of our existence itself, the effort in developing sustainable systems takes many directions. One of these directions is in the transport sector, particularly personal transport using hydrogen as fuel, which logically leads on to the problem of hydrogen storage. This paper deals with the prediction of the effective conductivity of beds of metal hydride for hydrogen storage. To enable modeling of the effective thermal conductivity of these systems, it is necessary to arrive at the functional dependence of the thermal conductivity of the solid hydride on its hydrogen concentration or content. This is the inverse problem in thermal conductivity of multiphase materials. Inverse methods in general are those where we start from known consequences in order to find unknown causes. Using published and known data of the effective thermal conductivity of the hydride–hydrogen assemblage, we arrive at the unknown hydride conductivity by analysis. Among the models available in the literature for determination of the effective conductivity of the bed from the properties of the constituent phases, the model of Raghavan and Martin is chosen for the analysis as it combines simplicity and physical rigor. The result is expected to be useful for predicting the thermal conductivity of hydride particles and determining the optimum heat transfer rates governing the absorption and desorption rates of hydrogen in the storage system.     

Nanofibrous nonwovens based on dendritic‐linear‐dendritic poly(ethylene glycol) hybrids

Dendritic‐linear‐dendritic (DLD) hybrids are highly functional materials combining the properties of linear and dendritic polymers. Attempts to electrospin DLD polymers composed of hyperbranched dendritic blocks of 2,2‐bis(hydroxymethyl) propionic acid on a linear poly(ethylene glycol) core proved unsuccessful. Nevertheless, when these DLD hybrids were blended with an array of different biodegradable polymers as entanglement enhancers, nanofibrous nonwovens were successfully prepared by electrospinning. The pseudogeneration degree of the DLDs, the nature of the co‐electrospun polymer and the solvent systems used for the preparation of the electrospinning solutions exerted a significant effect on the diameter and morphology of the electrospun fibers. It is worth‐noting that aqueous solutions of the DLD polymers and only 1% (w/v) poly(ethylene oxide) resulted in the production of smoother and thinner nanofibers. Such dendritic nanofibrous scaffolds can be promising materials for biomedical applications due to their biocompatibility, biodegradability, multifunctionality, and advanced structural architecture. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45949.     

Multiscale Observation of the Fatigue‐Induced Damage Mechanisms in Carbon‐Black Filled Styrene‐Butadiene Rubber

Filled rubber materials exhibit a complex macroresponse characterized by stress softening, hysteresis, and dissipative heating when they are cyclically loaded. The relationship of these inelastic features to the microstructure changes is far from being fully established. This paper deals with the damage mechanisms in sulfur‐vulcanized styrene‐butadiene rubber (SBR) specimens in the diablo form reinforced with carbon‐black (CB) and zinc‐oxide (ZnO) fillers, and submitted to tension cyclic loading at room temperature. The microstructure alteration is characterized at different relevant scales and at different zones of the diabolo specimen by means of various technologies in the aim to report valuable insights about the mechanisms responsible for the macroresponse of this rubber‐filler material system. IR absorption spectra reveal that increasing filler content induces more interfacial interaction between CB and SBR chains. The environmental scanning electron microscopy (ESEM) observations show relevant altered morphologies of elastomeric chains with a predominant effect of both CB and ZnO fillers. A mesoscale observation of material density variation is presented using X‐ray computed tomography and the results are compared with those issued from ESEM.     

Hybrid 2D nanofibers based on poly(ethylene oxide)/polystyrene matrix and poly(ferrocenylphosphinoboranes) as functional agents

Template smart inorganic polymers within an organic polymeric matrix to form hybrid nanostructured materials are a unique approach to induce novel multifunctionality. In particular, the fabrication of one-dimensional materials via electrospinning is an advanced tool, which has gained success in fulfilling the purpose to fabricate two-dimensional nanostructured materials. We have explored the formation of novel hybrid nanofibers by co-spinning of poly(ferrocenylphosphinoboranes) Fe A [{Fe(C₅H₅)(C₅H₄CH₂PHBH₂)} _n] and Fe B [{Fe(C₅H₅)(C₅H₄PHBH₂)} _n] with poly(ethylene oxide) (PEO) and polystyrene (PS). Fe A and Fe B contain main-group elements and a ferrocene moiety as pendent group and have different properties compared to their only carbon-containing counterparts. The use of PEO and polystyrene provided a matrix to spin those inorganic polymers as hybrid nanofibers which were collected in the form of a nonwoven mat. They were characterized by multinuclear NMR spectroscopy, scanning electron microscopy (SEM), and IR spectroscopy. Thermal properties of the polymers have been checked by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). ¹H, ³¹P, and ¹¹B NMR and IR spectroscopy revealed the nature and types of interactions of the components after co-spinning. The SEM micrographs identify the underlying unidirectional morphology of the generated hybrid nanofibers. Nonetheless, the DSC and TGA confirmed the significant boost toward the thermal stability of the resultant multifunctional fibers. It is believed that these unique types of multifunctional electrospun nanofibers will open new avenues toward the next generation of miniaturized devices.     

Electrospinning of ultrafine non-hydrolyzed silk sericin/PEO fibers on PLA: A bilayer scaffold fabrication

We report the feasibility of electrospinning of protein-polymer multilayered scaffolds with selected materials such as non-hydrolyzed silk sericin (SS), polyethylene oxide (PEO), and polylactic acid (PLA), with tuned fiber size and properties for each layer. We present a new innovative way for the electrospinning (ES) of non-hydrolyzed SS mixed with PEO yielding fibers with an average diameter ranging between 120 and 150 nm. Different SS:PEO ratios have been electrospun to study the effect of the concentration of SS protein on the fibers size and shape, as well and their electrospinnability. Electrospun SS:PEO fibers display weak to no mechanical resistance (non-measurable) and their deposition onto a sturdier scaffold is necessary to allow their use in biomedical and/or pharmaceutical fields. Therefore, bilayer scaffolds have been fabricated consisting of a PLA support and SS:PEO fibers obtained from the optimized SS:PEO ratio (1.2:4). They are composed of a sturdy hydrophobic layer of PLA fibers and a layer of sticky hydrophilic SS:PEO fibers. The scaffolds have been characterized extensively by Fourier transforms infra-red (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and their resistance to mechanical stress. Finally, hydrophobicity of both layers has been determined by measuring the contact angle of water droplets on the scaffolds, further proving the bilayer nature of the scaffolds.     

Application of integrated computational chemistry system to the design of inorganic membranes

Today inorganic membranes attract a lot of interest as a growing field. Main focus of those activities is on the development of membrane materials, which can offer high permselectivities with acceptable high permeances. The need for high permselectivity beyond those limited by Knudsen flow requires the estimation of the factors, which determine the permselectivity. Plausible theoretical models based on physical or chemical reasoning is desirable to guide systematic development efforts for designing next generation inorganic membranes. Here we reviewed our attempts to generate theoretical models based on the molecular dynamics method for this purpose. As a first attempt, simulation was performed at specific conditions where the Knudsen theory can be applied and can be reproduced well by our simulation methodology. Molecular dynamics simulation at 373 K of the permeation of iso- and n-butanes through ZSM-5 type silicalite membrane are presented. After 200 ps of simulation time the permeation of n-butane was observed whereas the permeation of iso-butane was not observed. The calculated permeability of n-butane, which is close to experimental data, is also presented. A study on the affinity membrane for the separation of CO₂ at high temperature is presented and the prospect of permselectivity of CO₂ is demonstrated.     

Experimental Study of the Salt Effect in Vapor/Liquid Equilibria Using Headspace Gas Chromatography

The salt effect on vapor/liquid equilibrium for an ethanol/water system was studied at 70 °C using the Headspace Gas Chromatography technique. The azeotropic point of the system was eliminated in the presence of the salts studied. All the salts investigated in this work exhibited a salting out effect which followed the order of NH₄Cl > NaCl > CaCl₂ and which increased with increasing salt concentration. Good agreement with Furter's equation was observed for the experimental data with unsaturated NaCl salt. The salt effect parameter, determined from Furter's equation, was found to be a function of the liquid concentration.