Double shield TBM performance analysis in difficult ground conditions: a case study in the Gerede water tunnel,Turkey

The performance analysis of double shield TBMs in difficult ground conditions in the Gerede tunnel is presented in this study. The strength of the encountered formations along the tunnel route varied from medium strength (sandstone, limestone) to high strength (basalt). The total length of tunnels is 31.6 km, which was excavated by three double shield TBMs having diameter of 5.57 m. Literature studies are first carried out in order to review the difficult ground conditions and their impacts on mechanized tunnelling. Later, the project, geology, and the characteristics of the TBMs are given in detail. Then the factors affecting the performance of the TBMs, machine utilization, and operational parameters (torque, thrust) are discussed in detail. In the light of these facts, the main objective of this study is to describe the possible improvement methods to reduce the effect of these difficulties on TBM performance.     

Au/Porous silicon‐based sodium borohydride fuel cells

The Au/Porous silicon structure (Au/PS) was developed as hydrogen fuel cell. The use of a porous silicon filled with hydrochloric acid as a proton‐conducting membrane and thin gold film as a catalyst in Au/PS/Si fuel cell is demonstrated. The devices were fabricated by first creating 10–20 µm thick porous silicon layer by anodization etching in a standard silicon wafer and then depositing the gold catalyst film onto the porous silicon. Using sodium borohydride (NaBH₄) solution as the fuel, generation of the open‐circuit voltage of 0.55 V and the fuel cell peak power density of 13 mW cm⁻² at room temperature was achieved. Moreover production of hydrogen by evolution (out‐diffusion) of hydrogen from solid sodium borohydride during thermal annealing at 30–120°C was investigated. Data on the effective diffusion coefficient of the hydrogen in NaBH₄ were determined from intensity changes of infrared vibration peaks of B–H bond (2280 and 3280 cm⁻¹), as a result of thermal annealing of NaBH₄ samples. The relatively high values of the diffusion coefficient of hydrogen, increasing from 1×10⁻⁶ cm² s⁻¹ to 2×10⁻⁴ cm² s⁻¹ suggest that a thermo‐stimulated evolution process can be used for producing hydrogen from NaBH₄. Copyright © 2010 John Wiley & Sons, Ltd.     

Polymers for medical and tissue engineering applications

Recent decades have seen great advancements in medical research into materials, both natural and synthetic, that facilitate the repair and regeneration of compromised tissues through the delivery and support of cells and/or biomolecules. Biocompatible polymeric materials have become the most heavily investigated materials used for such purposes. Naturally‐occurring and synthetic polymers, including their various composites and blends, have been successful in a range of medical applications, proving to be particularly suitable for tissue engineering (TE) approaches. The increasing advances in polymeric biomaterial research combined with the developments in manufacturing techniques have expanded capabilities in tissue engineering and other medical applications of these materials. This review will present an overview of the major classes of polymeric biomaterials, highlight their key properties, advantages, limitations and discuss their applications. © 2014 Society of Chemical Industry     

The TeO2-Na2O System: Thermal Behavior,Structural Properties,and Phase Equilibria

Thermal behavior, structural properties, and phase equilibria of the (100−x)TeO₂-xNa₂O system were studied in the 5 ≤ x ≤ 50 mol% composition range. Investigation of glass formation behavior in the binary system was realized, and the glass formation range was determined as 7.5 ≤ x ≤ 40 mol%. Differential thermal analysis (DTA) and Fourier transform infrared (FTIR) spectroscopy techniques were used for thermal and structural characterization of the glasses. Influence of Na₂O content on glass transition temperature (T_g), glass stability (∆T), density (ρ), molar volume (V_M), oxygen molar volume (V_O), and oxygen packing density (OPD) values of sodium tellurite glasses was evaluated considering the structural transformations in the glass network. For the phase equilibria studies, DTA, X-ray diffraction (XRD), and scanning electron microscopy/energy dispersive X-ray (SEM/EDS) techniques were utilized to characterize the heat-treated samples. According to the phase equilibria studies, three eutectic regions were detected in the 0 < x < 50 mol% composition range of the (100−x)TeO₂-xNa₂O system. A new invariant endothermic reaction was detected for the compositions between 40 ≤ x ≤ 45 mol%. Na₂O.8TeO₂ (11.11 mol% Na₂O) compound that was claimed to exist in the binary system in the literature was found to be the metastable δ-TeO₂ phase.     

The effect of combined use of chitosan and PIPS on push-out bond strength of root canal filling materials

Adhesion of root canal filling materials to root dentin is important for the long-term success of the treatment. Push-out bond strength test is used to evaluate the adhesion capacity of root canal filling materials to root canal walls. The aim of the present study is to compare the bond strength of root canal filling materials to root dentin after irrigation with EDTA, chitosan and the combination of chitosan and PIPS irridation using push-out bond strength test. Forty-eight extracted teeth were resected until 13-mm long roots were obtained. Root canals were prepared with a size-25 OneShape instrument. Samples were divided into three groups each including 15 roots. Group 1: Canals were rinsed with 0.2% chitosan and subjected to laser irridation with PIPS at the same time. Group 2: Canals were rinsed with 0.2% chitosan. Group 3: Canals were rinsed with EDTA. All canals were filled with .06 tapered gutta-percha and AH-plus sealer. One-mm thick slices were taken from coronal, middle and apical one-thirds of the roots. Push-out bond strength was determined using a Universal Testing Machine. One root from each group was observed under SEM to evaluate the degree of smear removal. Statistical analysis was performed with Kruskall-Wallis test. Results showed that bond strength values were statistically similar in overall evaluation for all groups (p > .05). In segmental evaluation, group 1 revealed the highest bond strength in apical one-third compared to other groups (p < .05).     

A simplified method for instability and second‐order load effects of framed structures: Story‐based approach

Several building codes such as ANSI/AISC 360‐16 and EC3 EN 1993‐1‐1 require the use of a proper design method to consider instability and second‐order load effect problems for individual system elements and the entire structural system. Various methods are available to assess stability. All of these methods should consider P‐Δ and P‐δ effects (second‐order effects). The following calculation procedures are presented in this study: (a) a simplified method is developed for P‐Δ and P‐δ analysis in regular frames under the effect of constant axial loads to obtain story drifts and end moments; (b) this method can be applied to an entire building or any individual story, that is, story‐based design is possible; and (c) column effective length factors are obtained for individual columns. In addition, design tables are presented.     

Stretchable poly(glycerol-sebacate)/β-tricalcium phosphate composites with shape recovery feature by extrusion

There has been a great interest in research towards elastomers and their composites with an attempt to obtain the desired biological and mechanical response to scaffold materials in bone tissue engineering. Composites made of ceramic-thermoplastic mixtures have been shown success to deliver the inorganic component while fail to provide replacement of an elastic protein, that is, collagen, of the target bone tissue. Thus, in order to match up with the inherent elasticity of the native tissue, it is proposed an alternative to well-known thermoplastic-containing matrices by using a poly(glycerol-sebacate) (PGS)–beta-tricalcium phosphate elastomeric composite to offer flexibility and mechanical integrity. This study reports for the first time a successful extrusion of PGS containing biodegradable composites with shape-memory feature. The resulting structures are physically and chemically characterized. In vitro cell culture performance of the obtained materials is investigated by using an MC3T3-E1 mouse preosteoblast cell line. The materials obtained in this study can be shaped into the desired size and various forms via temperature stimuli. Resulting materials have been proposed for craniofacial tissue engineering as a bone filler in which surgeons need to shape biomaterials during the surgical procedure due to the complex geometry of the bones. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48689.     

Preparation of nanocoatings in the presence of precipitated CaCO3 fillers by UV-curing

Various methods were employed to prepare precipitated calcium carbonate (PCC) particles. Particle size and morphology were dependent on reaction conditions as well as temperature, reagents and stirring, either mechanical or by ultrasound probe sonication. Sonication helped to reduce the size of CaCO₃ particles as well as the precipitation time. Sonication was also used to disperse PCC particles in the UV-curable formulations as well as for preparation of the PCC. Formulations containing precipitated calcium carbonates and ground calcium carbonates in various grades were cured by a Mini UV-Cure device. Mechanical and thermal properties of films were characterized with a Dynamic Mechanical Analyzer (DMA). SEM analysis was also used to determine the shape and the size of the PCCs. Sonication decreased the precipitation time of calcium carbonate at least four times more than that of conventional precipitation procedures and the dispersion of particles in the formulations increased to a great extent.     

Rheological analysis of ceramic pastes

This paper is concerned with a number of means of characterising the rheological properties of a ceramic paste. The intrinsic flow behaviour of the paste, during upsetting, is studied experimentally by using multi coloured paste samples, as well as by a finite element numerical computation. The flow behaviour of the paste is approximated by an elasto-viscoplastic material constitutive model and implemented by using an established finite element code. The material flow properties, which are necessary for the implementation of the numerical model, were obtained using the squeeze film and hardness indentation test configurations. The flow fields generated by the simulation are shown to be a good accord with the experimental observations. The experimental procedure for selecting the material parameters which are necessary for the implementation of the numerical model is described. The accuracy of the numerical method described is also evaluated by comparing the simulation results with experimental data obtained from the net upsetting force against the imposed relative displacement behaviour and the flow visualisation of deformed coloured layers. In these respects, a comparison of the finite element model predictions and the experimental results demonstrates a good mutual agreement.