Hydrophobic properties of textile materials: robustness of hydrophobicity

Extremely hydrophobic surfaces have been receiving considerable interest, such as in the contexts of self-cleaning glass or clothes, antifouling paintings, and the reduction of friction drag. A large variety of treatments permits the obtainment of (super)hydrophobic textile surfaces. The point here is to investigate the role of different geometrical textile parameters on the hydrophobicity, and more particularly, on the robustness of this property. The influences of solid surface roughness on the wetting behavior are commonly studied for model solid textures while textile roughness is largely deformable. A laboratory test method is suggested to evaluate this robustness. Some hydrophobic fibrous structures were prepared (using classical woven fabrics and pile fabrics) to investigate the influence of textile structures on their static and forced wetting properties. Static contact angles, contact angle hysteresis, and the contact angle after compression were measured. The meso- and micro-structures appeared to influence either the static wetting or the robustness of the hydrophobicity after compression.     

Numerical Analysis of Artificial Electron Heating Effects on Polar Mesospheric Winter Echoes

In this paper, an analytical model is used to analyze the modulated polar mesospheric winter echoes (PMWE). The winter parameters were introduced to simulate the effects of different parameters during the artificial electron heating of PMWE. The important role of the charged dust particle in the creation of PMWE is confirmed again. It is found that during the heating of PMWE, the increases of the dust size, dust charge, electron temperature, initial electron density, and ion-neutral collision frequency cause the increase of the electron density irregularity, and hence the PMWE strength. However, with increasing the dust density, the electron density irregularity and the PMWE strength decrease.     

Hybrid silane-treated glass fabric/epoxy composites: tensile properties by micromechanical approach

The effect of interface modification on the interfacial adhesion and tensile properties of glass fabric/epoxy composites was evaluated in two directions of 0° and +45°. Herein, the glass fabric surface was modified by colloidal nanosilica particles and by a new blend of silane-coupling agents including both reactive and non-reactive silanes. Composite samples with high strength and toughness were obtained. A simultaneous improvement of tensile strength and toughness was observed for an epoxy composite reinforced with a hybrid-sized glass fabric including silane mixture and nanosilica. In fact, the incorporation of colloidal silica into the hybrid sizing dramatically modified the fiber surface texture and created mechanical interlocking between the glass fabric and resin. The results were analyzed by the rule of mixtures (ROM), Halpin–Tsai (H–T), and Chamis equations. It was found that the ROM equations provided approximate upper bound values for all investigated composite samples. In the samples containing nanosilica, the shear and elastic moduli values calculated by the Chamis and ROM equations showed good agreement with those obtained from experiments. However, in other samples, the values calculated by the H–T equation showed a better agreement with the experimental data. The analysis of fracture surfaces indicated that both silane and nanosilica particles had influence on the mode of failures at the interface.     

Cooperative distributed state estimation: resilient topologies against smart spoofers

A network of observers is considered, where through asynchronous (with bounded delay) communications, they cooperativelyestimate the states of a linear time-invariant (LTI) system. In such a setting, a new type of adversary might affect the observationprocess by impersonating the identity of the regular node, which is a violation of communication authenticity. These adversariesalso inherit the capabilities of Byzantine nodes, making them more powerful threats called smart spoofers. We show howasynchronous networks are vulnerable to smart spoofing attack. In the estimation scheme considered in this paper, informationflows from the sets of source nodes, which can detect a portion of the state variables each, to the other follower nodes. Theregular nodes, to avoid being misguided by the threats, distributively filter the extreme values received from the nodes in theirneighborhood. Topological conditions based on strong robustness are proposed to guarantee the convergence. Two simulationscenarios are provided to verify the results.     

Effect of liquid phase on scale formation during high-temperature oxidation of AlSi-transformation-induced plasticity steel surfaces

The oxidation kinetics, and the structural evolution of the resulting surface scale, of cast transformation-induced plasticity (TRIP) steel (0.97 wt pct Al and 1.11 wt pct Si) has been investigated in the temperature range of 850 °C to 1250 °C under atmospheres with oxygen partial pressures close to 0.2 atm. Direct visualization using a high-temperature confocal scanning laser microscope (CSLM) showed that at 1050 °C and higher temperatures, a liquid oxide phase formed beneath the surface, penetrating and liquefying the scale that had formed initially. After a period of time, which was dependent on temperature, the liquid became fully crystallized. A microprobe analysis of the steel/scale interface indicated an Al₂O₃-SiO₂-FeO _n composition in the liquid oxide. This phase formed a network that penetrated the scale. The rest of the outer scale consisted primarily of Fe₂O₃, while Al-Si-rich oxides were observed close to the metal/scale interface. Thermogravimetric analysis indicated a parabolic growth rate below 1000 °C and a linear growth rate at 1000 °C. At higher temperatures, a parabolic rate dominated once again. The scale thickness appears to be limited by the time period during which the liquid oxide could contribute to rapid mass transfer, which resulted in the observed linear oxidation rate. As the upper temperature limit of the linear oxidation region is reached, the liquid oxide becomes enriched with FeO _n , decreasing the stability of the liquid phase. This leads to crystallization of solid Fe oxides at the surface or the formation of appreciable amounts of Al- and Si-rich oxides at the interface. These processes block access of the liquid oxide to the steel.     

Internal stress relaxation based method for elastic stiffness characterization of very thin films

Accurate measurement of the Young's modulus of films with thickness smaller than a few hundreds of nanometers remains extremely challenging. The present method disclosed here is based on the combined measurements of the internal stress using the Stoney method and of the corresponding elastic strain obtained by releasing microstructures. Experimental validation is presented for silicon nitride films. The Young's moduli of the 100, 300, and 500 nm-thick films are equal to 193 ± 20 GPa, 226 ± 22 GPa, and 208 ± 18 GPa, respectively, in good agreement with nanoindentation test results. This very simple method can potentially be used for much thinner films and extended to materials involving no internal stress.     

The relationship between crystal growth behaviour and constitution in the systems LiF-LuF3, LiF-ErF3 and LiF-YF3

The crystal growth behaviour of LiRF₄-type compounds in the systems LiF-LuF₃, LiF-ErF₃ and LiF-YF₃, have been related to the constitution of the respective systems. Crystal growth, differential thermal analysis (DTA) and microstructural studies indicate that the phases Li Lu F₄ and LiErF₄are clearly congruent in nature which is in agreement with previous work on these compounds. Corresponding studies for the compound LiYF₄ are consistent with this phase being either just congruent or just syntectic (but definitely not peritectic) in character, its constitutional behaviour depending critically on the level of contamination.     

Oxidation and Characterization of As‐Cast TRIP Steel Surfaces

This paper presents recent results from a collaborative study between the Department of Ferrous Metallurgy at RWTH‐Aachen University and the Department of Materials Science and Engineering at Carnegie Mellon University on high temperature oxide scale formation of Al and Si containing as cast TRIP steel surfaces under conditions similar to that of continuous casting and hot rolling. A combination of experimental studies consisting of (i) electron microprobe analysis and metallographic studies of the cast steel surface, (ii) direct visualization of the oxide formation through high temperature confocal scanning microscopy and (iii) Tammann furnace oxidation tests were carried out. It was found that internal oxidation of Al and Si takes place along the inter‐dendritic boundaries, where Al and Si were found to have been enriched after casting. The scale formed on the steel surface was a complex mixture of solid fayalite ((FeO_n)₂(SiO₂)), wüstite (FeO_n), magnetite (Fe₃O₄), hematite (Fe₂O₃), and Fe‐particulates and the rate of scale growth appears to have been controlled at high temperatures by the formation of a liquid slag layer that allows for rapid oxygen transport to the steel/scale interface.     

Seismic analysis of Tehran Telecommunication Tower using complex fractional modulus

Seismic response of large concrete tower structures with passive or active damping is important in terms of performance under earthquake loads. The conventional finite element method has been used successfully in linear and nonlinear analyses in large concrete structures. The method can be performed by subdividing the large structure into small uniform elements having approximate shape functions. Although this replaces a single complicated structural system with a number of simple uniform elements, in cases of tall concrete tower structures with cracking and crushing behaviour in the concrete material and yielding in the reinforcement, the computer time and memory can be large. Hence, it is desirable to search for a procedure requiring fewer elements and also less computer time and effort to model the structure. In this respect, attention is paid to the advanced complex damped spectral element method, which benefits from the more accurate and also mathematically complicated shape functions. Use of the advanced spectral element method can help engineers to design a complex structure, such as a tall concrete tower, with lower cost and lower weight. Using a computer program, the proposed formulation has been used to derive the nonlinear dynamic response of the 435‐m Tehran Telecommunication Tower. Copyright © 2002 John Wiley & Sons, Ltd.     

Highly durable macromolecular epoxy resin as anticorrosive coating material for carbon steel in 3% NaCl: Computational supported experimental studies

The purpose of present study is in the direction of development of an anticorrosive coating formulation of high durability for carbon steel corrosion in 3 wt% NaCl medium. The formulation comprises of a macromolecular epoxy coating (DGEDDS-MDA) based bisphenol S diglycidyl ether (DGEDDS) cured with a methylene dianiline (MDA). The formulation was characterized by FT-IR spectroscopy method. Performance of the epoxy coating was represented using PDP and EIS approaches. The formulation acts as effective anticorrosive coating for long durability (180 days). Surfaces of the specimens before and after 180 days exposure to UV radiation were examined using SEM. PDP, SEM, and EIS studies showed that DGEDDS-MDA acted as highly durable and effective anticorrosive formulation. Results also showed that the formulation acts as interface type inhibitor and its presence enhances the polarization resistance (R_p) value. DFT study suggests that the formulation DGEDDS-MDA possesses strong ability to interact with metal surface through its several electron rich centers. MD and MC simulations showed that studied formulation effectively adsorb on the substrate (metallic surface). Results of EIS, PDP, and SEM studies (experimental) were well-supported by DFT, MD, and MC (computational) simulations.