Effect of different surface treatments on the repair bond strength of resin composites with titanium

The purpose of this study was to evaluate the effect of different surface treatment combinations on the bonding of composite resins to NiCr and titanium alloys after thermal cycling. Square-shaped specimens (10?mm x 10?mm x 2?mm) were made from NiCr and titanium alloys. The specimens were divided into 6 pretreatment groups (n?=?11): (1) machined titanium (control, no treatment); (2) CoJet sand application; (3) grinding with a diamond bur; (4) metal primer application; (5) CoJet sand?+?metal primer application; and (6) grinding with a diamond bur?+?metal primer application. The surface roughness of the mechanically treated specimens (control, grinding, CoJet sand) was evaluated. The surface morphology of both metals and elemental composition were examined with SEM and EDS. The composite resin was applied to the specimens. Shear bond strength (SBS) was tested after thermal cycling (5000 cycles, 5?°C to 55?°C). Failure modes were determined. The data were analyzed using the Shapiro-Wilk test, two-way ANOVA and post hoc Fisher’s LSD test (p?=?.05). For titanium specimens, the grinding?+?metal primer exhibited higher values than the other groups, and all groups showed higher SBS values than the control group. Combined use of CoJet sand, grinding with a diamond bur, and metal primer application would be useful for enhancing the bond strength of composite resin to titanium. The grinding of the NiCr surface with a diamond bur is the only method that could improve the bond strength of a composite resin compared to the other methods.     

Assessment of the dynamic stability of the portals of the Dorukhan tunnel using numerical analysis

Instability problems may arise during the construction and operation of tunnels depending on the quality of the rock mass. In particular, determining instability problems at the portals of a tunnel is of utmost importance during excavation and operation of the tunnel. Slope instability and rockfalls are the most frequent instability problems that may be encountered at tunnel portals. Such instability problems can be triggered by dynamic effects such as earthquakes, blasting, etc. This study investigates the stability of the portals of the Dorukhan Tunnel connecting the provinces of Zonguldak and Bolu in the close vicinity of the North Anatolian Fault Zone (NAFZ), which is a well-known strike-slip 1500 km long fault. The effect of an earthquake that may occur in the NAFZ on the extent of failure has also been studied by numerical analyses. In the analyses, a three-dimensional dynamic analysis computer code, based on the finite difference method, has been used. According to results of the dynamic numerical analyses, the Devrek portal was found to be more stable than the Mengen portal. Moreover, it was found that, for acceleration values of dynamic wave higher than 0.5g, tunnel portal slopes and the areas as far as 20–50 m from the tunnel entrance may suffer serious damage. Wave propagation perpendicular to the tunnel axis was established to cause more damage around the openings and in the portal slopes as wave compared to propagation parallel to the tunnel axis.     

Determination of the relationship between uniaxial and triaxial swelling equations for clay bearing rocks

Design in swelling mediums is mostly based on uniaxial data since the standards proposed by the International Society for Rock Mechanics Commission on Swelling Rocks for uniaxial tests are in the form of recommendations, triaxial sets are not highly available; and there is no standard developed for triaxial tests. The main purpose of this study is to define the relationship between the uniaxial and the triaxial swelling equations and to predict the triaxial values using the uniaxial data. The other purpose of the study is to contribute to the development of the standards and to expand the data available in the literature about triaxial swelling behavior. Numerous uniaxial and triaxial swelling tests were performed on the samples from seven different locations, in Turkey, in a state of the art swelling laboratory. As a result of the determination of the triaxial swelling behavior of these samples, the relationships between the uniaxial and the triaxial swelling data for the individual samples as well as the whole set of samples are expressed by the equations derived from the statistical analyses.     

Hydrogen is not an utopia for Turkey

The aim of this study was to explore how the future of technological developments in hydrogen will be shaped in Turkey by using a two-round Delphi method undertaken to determine and measure the expectations of the sector representatives through online surveys where a total of 60 experts responded from 18 different locations. The article discusses not only the expert sights on hydrogen technologies but also all bibliometrical approaches. The results showed that the hydrogen economy will enhance innovations as well as economic prosperities with the support of appropriate policies. Formulating such policies requires a timely and detailed understanding of the latest R&D trends and developments in science and technology policy in all developed countries, and the comprehensive analysis of these developments to enable accurate predictions of future science and technology trends. Therefore, we hope that this study can shed a light on the future use of hydrogen technologies, especially for policy makers.     

Dielectric behavior characterization of a fibrous‐ZnO/PVDF nanocomposite

This study is focused on forming a fibrous‐zinc oxide/polyvinylidine fluoride (ZnO/PVDF) nanocomposite and characterizing its dielectric behavior. The nanocomposite is prepared in two steps. First, a network of nanoscale diameter ZnO fibers is produced by sintering electrospun PVA/Zinc Acetate fibers. Second, the ZnO fibrous nonwoven mat is sandwiched between two PVDF thermoplastic polymer films by hot‐press casting. Scanning electron microscope images of the nanocomposite show that hot‐press casting of the fibrous‐ZnO network breaks the network up into short fibers. The in‐plane distribution of the ZnO fillers (i.e., the short fibers) in the PVDF matrix appears to comply with that of the pristine ZnO fibers before hot‐pressing, indicating that the fillers remain well‐dispersed in the polymer matrix. To the authors' knowledge, the work reported herein is the first demonstration of the use of electrospinning to secure the dispersion and distribution of a network of inorganic fillers. Moreover, processing a fibrous‐ZnO/PVDF flexible composite as described in this report would facilitate material handling and enable dielectric property measurement, in contrast to that on a fibrous mat of pure ZnO. Because of the high surface area of the short ZnO fibers and their polycrystalline structure, interfacial polarization is pronounced in the nanocomposite film. The dielectric constant is enhanced significantly‐up to a factor of 10 at low frequencies compared to the dielectric constant of constituent materials (both bulk ZnO and PVDF), and up to a factor of two compared to a bulk‐ZnO/PVDF composite. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

The effect of silicon carbide additives on the stab resistance of shear thickening fluid treated fabrics

Applications of shear thickening fluids (STFs) with ballistic fabrics improve the protection performance of body protective systems. This article presents an innovative view of STF-impregnated ballistic fabrics by integrating silicon carbide (SiC) particles into targets. In this study, SiC particles were added into silica-based STFs, and Twaron fabrics were impregnated with this novel suspension. The effect of the SiC particles in the STFs was investigated with rheological testing. The results show that SiC particles are able to increase the viscosity profile of the suspension. In the stab testing, two types of impactors, such as spikes and knives, were dropped on the composite targets. According to the results, SiC particles enhance the protection performance of the STF-treated ballistic fabrics while keeping the flexibility.     

The effect of different surface pretreatments on the bond strength of veneering resin to polyetheretherketone

The aim of this study was to investigate the effect of different surface pretreatment methods on the bond strength of veneering resin to polyetheretherketone (PEEK) based aesthetic frameworks. Five hundred and forty PEEK disks were fabricated and divided into 6 pretreatment groups (n = 90); (C) untreated control group, (B) airborne-particle abrasion, (S) silica coating, (L) etching with Er:YAG (erbium-doped yttrium aluminium garnet) laser, (LB) etching with Er:YAG laser and airborne-particle abrasion and (LS) etching with Er:YAG laser and silica coating. After topographical surface examinations, specimens were conditioned with adhesive and veneering resin was polymerized onto the PEEK specimens. Twenty-four hours after veneering, specimens were subjected to thermal aging. Afterwards, shear bond strength (SBS) tests were performed and the obtained data were analyzed with one-way ANOVA and Tukey test at a significance level of α = .05. Group B (1.58 ± 0.15 μm), Group L (1.79 ± 0.29 μm), Group LB (2.20 ± 0.23 μm) and Group LS (2.31 ± 0.52 μm) demonstrated significantly higher surface roughness (SR) values compared to Group C (1.03 ± 0.11 μm). Group B (10.97 ± 2.88 MPa), Group S (12.07 ± 2.82 MPa), Group LB (12.09 ± 2.08 MPa) and Group LS (13.14 ± 1.45 MPa) demonstrated significantly higher SBS values compared to Group C (6.35 ± 1.21 MPa). Airborne-particle abrasion, silica coating or their combined use with Er:YAG laser system establish durable bond between PEEK and resin; however, only Er:YAG laser treatment has no positive effect on resin-PEEK bond.     

Air oxidation of aqueous cyanides in a countercurrent fixed bed reactor

This study was conducted to discuss the removal of cyanides from water by air oxidation. Experiments were carried out in a countercurrent fixed bed reactor for three different values of temperature, concentration, gas and liquid flow rates. It was operated at pH 12 by using delrin (formaldehyde polymer) as packing material. Effects of some operating parameters on the conversion were studied, and it was observed that the conversion percent increased by increasing temperature and decreasing gas and liquid flow rates. Effect of concentration was not steady. A conversion of 89% was achieved under optimum conditions while it ranges from 44 to 79% at room temperature.     

Optimum design of multiple positioned tuned mass dampers for structures constrained with axial force capacity

The stories of structure may have different and limited axial force capacity. In order to passively control the translational movement of structures, a tuned mass damper (TMD) positioned on a story may cause to exceed axial force capacity of a story. The optimum performance is achieved when all additional masses are positioned on the top story. Whereas, the top stories of structure may be constructed with lower axial force capacity than the lower stories. In that case, the maximum allowed TMD mass for upper stories may be low. In that situation, several TMDs may be positioned on several stories. In the current study, the optimum tuning of TMDs positioned on multiple stories of structure is investigated. By using small masses, it is also possible to obtain effective passive control with dampers that have small damping coefficients comparing with a single TMD on the top of the structure. The design variables of the optimization problem such as the period and damping ratio of TMD are tuned according to a metaheuristic algorithm called flower pollination algorithm. The TMD is optimized for near‐fault excitations by using impulsive motions during the optimization process. The proposal was applied to four case studies. According to the results, the multiple positioned TMDs may be a practical and effective option comparing with the use of a single heavy TMDs on the top of a structure.     

Technoparks and Technology Transfer Offices as Drivers of an Innovation Economy: Lessons from Istanbul's Innovation Spaces

Universities can significantly contribute to the regional development and innovation capability of a city if the knowledge produced in universities can be appropriately cycled back to the city in the form of technological innovation. Technology parks and technology transfer offices (TTOs), as urban knowledge and innovation spaces, are two important channels of building research platforms with enterprises where universities can disseminate knowledge. While technology parks create space for knowledge generation and innovation within a city, university TTOs play a critical role in enhancing knowledge spillover and creating new start-up firms. This paper highlights the contribution universities can make to Istanbul's potential of becoming an innovative city that houses successful urban knowledge and innovation spaces. By conducting interviews with the managers of technoparks and TTOs in Istanbul, we explore how the existence of technoparks and TTOs within a university affects the success of technology-transfer mechanisms.