Identification of an extended Bouc–Wen model with application to seismic protection through hysteretic devices

In this paper is proposed an extended Bouc–Wen model for improving its capability to approximate experimental symmetric hysteretic loops. On the basis of the generalized equation there are defined integral and differential conditions that describe the essential geometric properties of a hysteretic curve. Next, a new method based on Genetic Algorithms is developed to identify the Bouc–Wen model parameters from experimental hysteretic loops obtained from periodic loading tests. The performance of presented approach is illustrated for two types of seismic protection devices with hysteretic characteristics: elastomeric base isolators and buckling restrained dissipative braces. The applicability of proposed method is highlighted by using the derived models to analyse by numerical simulation the efficiency of these devices for reducing seismic response of a three stories civil structure.     

Formation of silicon hollow spheres via electromagnetic levitation method under static magnetic field in hydrogen–argon mixed gas

A formation mechanism of a silicon hollow sphere via electromagnetic levitation method under high static magnetic field in hydrogen atmosphere is discussed in this paper. Since the convection in the levitated silicon melt which is caused by the electromagnetic field is restrained by a high static magnetic field, it is possible to examine a solidification of silicon from an equilibrium silicon melt with hydrogen except an effect of convection. The solidified silicon sphere has an extrusion which is formed during the solidification due to reduced stress in the melt. When a nucleation of pore occurs before the formation of the extrusion, a silicon hollow sphere is formed. Since the chance to form the nucleation of pore increases with increasing hydrogen concentration in the melt, a silicon hollow sphere is formed when the solidification is performed in higher hydrogen partial pressure. In the present case, a silicon hollow sphere is formed by the solidification in 50%H₂–50%Ar atmosphere. However, non-porous silicon spheres are formed by the solidification in 25%H₂–75%Ar or 100%Ar atmosphere.     

Synthesis of nanocrystalline carbonated hydroxyapatite powder via nonalkoxide sol–gel method

Nanocrystalline hydroxyapatite powder was synthesized via nonalkoxide sol–gel method. Ca(NO₃)₂·4H₂O and P₂O₅ were mixed in ethanol, which led to a stable sol. STA, XRD and FTIR were used to characterize the calcined powders. The degrees of crystallinity and crystallite sizes were thereafter calculated from XRD patterns. The microscopic observations of the powder were performed using SEM and TEM. Results showed that a nanocrystalline hydroxyapatite powder was obtained after being heated at 450 °C for 6 h. Furthermore, increasing the calcining temperature caused both the formation of carbonate bonds and the increase in the crystallite sizes, and the degree of crystallinity.     

Permanently disentangled states of atom–field system via spontaneously generated coherence

Abstract

The effect of spontaneously generated coherence on evolution of the entanglement between a driven four-level Y-type atom and its spontaneous emission field is studied. We have shown that the atom will be entangled to its spontaneous emission field due to spontaneously generated coherence and coherent population trapping at the steady state. It is found that the degree of entanglement strongly depends on the initial atomic state. So, it can be controlled by the pumping laser pulses used for preparing an initial atomic system. More interestingly, the atom–field system can be found in a permanently disentangled state for a properly prepared atom.     

A system–analogue method of identification of geometric shape of the abrasive grain projection

An advanced method of identification and quantitative estimation of geometric shape of the projection of abrasive powder grains has been proposed. The method is based on a system–analogue approach. For analogues the two-dimensional geometric figures (circles, ellipses, triangles, canonical forms of tetragons, regular pentagons, hexagons, and octagons) that admit a nonadditive analytical representation of the area in terms of generating parameters (whose number does not exceed three) have been taken. A differential and integral characteristics of the shape similarity have been introduced and an analytical apparatus has been put forward to determine the values of these characteristics. The results of appraisal (testing) of the method on synthetic diamond and cBN grits are discussed.     

Extended harmonic input method for response spectrum determination of vehicle–bridge systems

The calculation of response power spectral densities (PSDs) from the excitation PSDs of vehicle–bridge (VB) systems is crucial for the safety evaluation of operating vehicles, bridge fatigue analysis, and vibration control optimization. However, calculations using the available methods result in considerable computational errors when applied to evaluate the response PSDs of VB systems. Hence, an extended harmonic input method (HIM) is proposed to compute the time-varying response spectrum in VB systems. First, the unique characteristics of VB systems that may cause the inapplicability of conventional methods are systematically analyzed. Subsequently, an extended version of the HIM is mathematically established to calculate the time-varying response spectrum of VB systems via the representation of inputs and decomposition of responses. Finally, a numerical example of an actual high-speed railway bridge subjected to track irregularities or seismic excitations is presented to illustrate the efficacy of the novel method.     

Formation mechanism of zirconia nano-particles containing pores prepared via sol–gel-hydrothermal method

Zirconia single crystal nano-particles containing pores were prepared by a sol–gel-hydrothermal method. The unique character of the particles is that some irregular pores are embedded within the single crystals. The results of XRD, TEM and FT-IR show that the gaseous hydrolysates of the superstoichiometric urotropine are the origin of the pores. The gel structure and the hydrothermal treatment are the required conditions resulting in the pores in crystals. The formation mechanism was proposed: zirconia gel was formed after the reaction of ZrOCl₂ with urotropine. The superstoichiometric urotropine was dissolved and distributed uniformly in the gel. The small pores were generated because gaseous hydrolysates of urotropine were constrained in the gel during the hydrothermal treatment. During the process of the amorphous gel transferred into the crystals, some of the pores coarsened with the crystals growth. Big pores disappeared due to the break of the crystals. And only the small pores were remained in the interior of crystals, which could hardly be eliminated by the subsequent crystal growth if the calcination temperature is below 550 °C. Thus, the zirconia nano-particles containing pores were generated.     

Optimization of composition and heat treatment design of Mg–Sn–Zn alloys via the CALPHAD method

This work is focused on the application of the calculation of phase diagrams method for alloy and heat treatment design. We analyzed the influence of Zn content on the precipitation of Mg₂Sn in Mg–Sn–Zn alloys. A comparison with previous studies in the Mg–Sn–Zn system was made according to the published results and computational thermochemistry simulations. The phase evolution in the Mg–Sn–Zn system was evaluated for the different compositions, and the simulations were used for precise alloy and heat treatment design. The composition of the ternary alloy was set as Mg–8wt%Sn–1.25wt%Zn. The Sn and Zn content was designed and confirmed to be within the α-Mg solubility limit at the solution treatment temperature. The addition of Zn and the heat treatment applied resulted in the enhancement and refinement of the Mg₂Sn precipitation. Three Vickers micro-hardness maxima were detected: precipitation of metastable Mg–Zn phases, heterogeneous precipitation of Mg₂Sn on the Mg–Zn precipitates, and Mg₂Sn precipitation in the α-Mg matrix. The CT simulations were found to be a valuable alloy design tool.     

Thermomechanics of the joint–synovial fluid system under periodic and impulse actions

The thermomechanical reaction of the joint–synovial fluid system to periodic and impulse actions has been investigated. The behavior of the body of the joint near the articular surface — resistance of the bone material of the joint to periodic mechanical actions — has been established. It has been shown that the most destructive actions for the joint are instantaneous impulse shock mechanical actions.     

Microstructure characteristics of products in Ti–Si system via combustion synthesis reaction

The products of combustion synthesis reaction in Ti–Si system with molar ratios of Ti:Si = 3:1, 5:3, 5:4, 1:1, and 1:2 were investigated. The phase composition of products and degree of completion in the reaction considerably depend on the initial stoichiometric ratios of reactants. During the SHS reaction of Ti–Si system, the degree of completion follows the order of 5Ti + 3Si > Ti + Si > Ti + 2Si > 5Ti + 4Si > 3Ti + Si. Besides, the micro-structural morphology of Ti–Si compounds, i.e., TiSi₂, TiSi, Ti₅Si₄, and Ti₅Si₃ were also characterized in this study.     

Nucleation and crystallization behaviors of nano-crystalline lithium–mica glass–ceramic prepared via sol–gel method

The paper investigates the effects of nucleation and crystallization treatments on nano-crystalline lithium–mica glass–ceramics, taking the composition LiMg₃AlSi_3(1+x)O_10+6xF₂ (x = 0.5) and 8 mass% MgF₂ synthesized by sol–gel technique. Here, X-ray diffraction, thermal analysis and transmission electron microscopy were used to assess the structural evolutions of as-synthesized nano-crystalline lithium–mica glass–ceramics. It was found that MgF₂ crystals perform as nuclei centers for the mica crystallization hence; a large quantity of mica crystallites obtained following the nucleation process at 400 °C for 12 h. For both the un-nucleated and nucleated samples, the crystallization activation energy was measured as 400.2 and 229.6 kJ mol^?1, respectively. Consequently, the calculated Avrami exponents demonstrated that the growth mechanism of mica crystallites, while applying appropriate nucleation treatment, changes from needle-like to three-dimensional growth.     

Fast response time alcohol gas sensor using nanocrystalline F-doped SnO2 films derived via sol–gel method

Pure and fluorine-modified tin oxide (SnO₂) thin films (250–300 nm) were uniformly deposited on corning glass substrate using sol–gel technique to fabricate SnO₂-based resistive sensors for ethanol detection. The characteristic properties of the multicoatings have been investigated, including their electrical conductivity and optical transparency in visible IR range. Pure SnO₂ films exhibited a visible transmission of 90% compared with F-doped films (80% for low doping and 60% for high doping). F-doped SnO₂ films exhibited lower resistivity (0· 12 × 10^???4 Ω  cm) compared with the pure (14·16 × 10^???4 Ω  cm) one. X-ray diffraction and scanning electron microscopy techniques were used to analyse the structure and surface morphology of the prepared films. Resistance change was studied at different temperatures (523–623 K) with metallic contacts of silver in air and in presence of different ethanol vapour concentrations. Comparative gas-sensing results revealed that the prepared F-doped SnO₂ sensor exhibited the lowest response and recovery times of 10 and 13 s, respectively whereas that of pure SnO₂ gas sensor, 32 and 65 s, respectively. The maximum sensitivities of both gas sensors were obtained at 623 K.     

Study of the growth process of magnetic nanoparticles obtained via the non-aqueous sol–gel method

The growth process of iron oxide nanoparticles during synthesis via the non-aqueous sol–gel method has been analyzed. Samples obtained after reaching reaction temperature T _R = 200 °C and during the following 23 h of synthesis were characterized in detail by X-ray diffraction measurements, transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, Mössbauer spectroscopy, and magnetization measurements. The results show that the iron oxide nanocrystals are majorly composed of maghemite and grow in a faceted shape. The particle size increases gradually during the synthesis, and the structural and magnetic properties improve primarily during the first 6 h of reaction.     

Fabrication of superhydrophobic coating from non-fluorine siloxanes via a one-pot sol–gel method

To fabricate a superhydrophobic and durable coating, non-fluorine siloxane solution for the coating was successfully synthesized via a facile one-pot method. The wetting properties and morphology of coatings with different concentration and adding time of additives were studied. Under condition of low water content, the coatings’ superhydrophobicity was improved with the increasing amount of ammonia content, water content, and low-surface-energy material (HTMS) content. However, too more ammonia or water or HTMS would sacrifice the coating’s integrality and lead to the cracking of it. The obtained coatings showed good superhydrophobicity and anti-UV property on plain and even curved substrates, including glass, metal, and polymer. Contact angle and sliding angle of the coating could reach 158° and 1.8°, respectively. What is more, coating on PET filter could be used for oil/water separation with an efficiency of 80%.     

Bonding of Al to Al2O3 via Al–Cu eutectic method

The Al oxidation layer in the manufactures of direct aluminum bonded Al₂O₃ substrates (DAB) has been a long-term trouble for industries. In this work we propose a new method for fabricating the DAB substrates with no requirement of high vacuum or active O₂-getters. The new method comprises two stages: (i) Cu-film is bonded onto Al₂O₃ ceramic surface via DBC method; (ii) Al foil is joined to the DBC substrate by Al–Cu eutectic method at 600 °C in pure N₂ atmosphere. KF–AlF₃ flux was used to disrupt the Al–oxide layer on the surface of Al foil. The wetting ability was significantly enhanced due to the diffusion of Cu into Al and the dissolving of Al. The final contact angle is achieved of 22.10°. Microstructure and composition of the interface between Al and Al₂O₃ substrate were analyzed. The XRD, SEM and EDS results show that two new phases Al₂Cu and CuAlO₂ were formed, leading to a strong bonding along the interface. The thermal cycling reliability and adhesion strength of DAB substrates were also evaluated. The results show that the DAB substrates can satisfy application requirements completely.     

Failure analysis of transformer liquid — solid insulation system under selective environmental conditions using Weibull statistics method

The failure free operation of transformers is a main factor on economic and safety aspects as per the industrial consumer's point of view. Basically, the transformer is one of the prime equipment in power system network because of its unkind operating condition at different circumstances like higher operating temperature, overloading and continuous operation under uneven outdoor environmental conditions. Above said operating conditions lead to unpredicted failure in the transformer and this directly has an effect on reliability of the power system network. This work aims to investigate the failure rate of transformer liquid insulation (LI)–solid insulation (SI) system at various selective environmental conditions, by considering relative humidity of the air as a frequently variable environmental factor. For investigation, mineral oil (MO) and natural ester like sunflower oil (SFO) and rapeseed oil (RSO) are chosen as the LI system and Kraft paper is chosen as the SI system. The humidified samples are aged at 140 °C up to 1000 h at closed condition. Critical parameters of both LI and SI are periodically measured at an interval of 200 h. Weibull distribution statistics method is used to predict the failure rate of the insulation system with respect to time and relative humidity of the air. From the analysis, it is inferred that the degradation rate of the transformer LI–SI increases with an increase in relative humidity of the air. It is also noted that the LI-MO degrades rapidly when compared with other natural esters.     

Mechanical response of barium-titanate/polymer 0–3 ferroelectric nano-composite film under uniaxial tension

Ferroelectric polymer based 0–3 composite films are attractive for applications such as capacitors and electric energy storage devices. In this paper, deformation and fracture behavior under uniaxial tension is characterized for BaTiO₃/poly(vinyledene fluoride-trifluoroethylene) (abbreviated as BT/P(VDF-TrFE)) ferroelectric composite film. Compared with the pure P(VDF-TrFE) copolymer film, the composite film with a small volume fraction of BT powders shows an enhanced ductility in accompany with reduced stiffness and fracture strength. Scanning electron microscope (SEM) observation and X-ray diffraction (XRD) analysis are carried out to examine the morphology and microstructure change during uniaxial tension. It is demonstrated that addition of a small amount of BaTiO₃ powders into the copolymer matrix inhibits the growth of the crystallite size, causes reduction in the crystalline content and a loosely packed molecular chain structure. Consequently, the fracture strain increases while the stiffness and fracture strength decreases for the composite films.