Effect of different surface treatments on the shear bond strength of resin cement to zirconia ceramic and metal alloy*

The bonding of resin cement to ceramic materials plays an important role in dentistry. The purpose of this study is to evaluate the effects of various surface treatments on the shear bond strength (SBS) of zirconia ceramic and metal alloy. A total of 60 specimens were prepared from Y-TZP ceramic and metal alloy. The specimens were divided into three subgroups (n = 10) that received different surface treatments for each material. An Er:YAG laser (ER), a femtosecond laser (FS), and air-borne particle abrasion (A) were employed as surface treatments. One specimen from each group was analyzed using a scanning electron microscope (SEM) at 500 x magnification after surface treatments. The self-adhesive resin cement was then bonded to the treated surfaces using a Teflon mold. The specimens were thermocycled for 5,000 cycles at 5–55 °C, and then the SBS test was performed. Kruskal–Wallis and Mann–Whitney U tests were used to determine the differences between the groups (p = 0.05), and failure modes were evaluated for each specimen. Statistical analyses revealed significant differences between the surface treatment methods. The mean SBS values of the air-borne particle-abraded groups were higher than those of the other groups. The femtosecond-irradiated groups of each material showed significantly higher SBS values than the Er:YAG-irradiated groups (p < 0.05). Within the limitations of this study, air-borne particle abrasion and the femtosecond laser were more effective than Er:YAG laser treatment.     

Deep cold rolling with ultrasonic vibrations—a new mechanical surface enhancement technique

The paper presents a newly developed mechanical surface enhancement technique utilising ultrasonic vibrations, namely Ultrasonic Deep Cold Rolling (UDCR) process. UDCR differs from Conventional Deep Cold Rolling (CDCR) by applying static and also dynamic forces resulting from ultrasonic vibrations. The principle and concept of the new process are described. The evaluation and comparison of experimental results (e.g. surface roughness, surface micro-hardness and compressive residual stresses) obtained after treatments of Ti–6Al–4V specimens are discussed. The advantages of proposed technique and its potential applications are also reported. UDCR could be used for treating thin components without deteriorating the component shape as less pressure is being applied on the part surface during UDCR. Compressive residual stresses of about 900 MPa at 0.2 mm depth from the surface can be achieved.     

Integration of variable refrigerant flow and heat pump desiccant systems for the cooling season

Energy saving and indoor air condition enhancing potentials by integrating the variable refrigerant flow (VRF) and heat pump desiccant (HPD) systems were investigated in a field performance test during a cooling season. Three different operating modes: non-ventilated, HPD ventilation assisted and HPD ventilation–dehumidification assisted VRF systems were investigated. The HPD systems operated in the ventilation–dehumidification mode dehumidify the outdoor air and supply it to the indoor air during the ventilation. It was found that the VRF systems provided an average of 97.6% of the total cooling energy for the HPD ventilation assisted mode. The remainder was the recovered cool by the HPD systems during ventilation. The VRF systems provided an average of 78.9% of the total cooling energy for the HPD ventilation–dehumidification assisted mode. The remainder was covered by the HPD systems which provided additional sensible and latent cooling. Overall, among the three operating modes, it is concluded that the HPD ventilation–dehumidification assisted VRF outdoor units consume less energy than the HPD ventilation assisted ones, but more than the non-ventilated ones, while providing the best indoor thermal comfort and indoor air quality conditions. For the total system, the HPD ventilation–dehumidification assisted VRF systems consume less energy than the HPD ventilation assisted ones.     

Estimation of Engine Emissions from Commercial Aircraft at a Midsized Turkish Airport

The estimated atmospheric emissions of aircraft operations at a midsized Turkish airport (Adnan Menderes Airport, AMA) for the year 2004 are presented in this paper. The landing and takeoff (LTO) emissions of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOX) were calculated using the flight data recorded by the State Airports Authority Directorate General. Emission factors from the International Civil Aviation Organization Engine Exhaust Emission Databank were used for different aircraft operation modes such as take-off, climbout, approach, and taxi/idle engine conditions. Total LTO emissions from commercial aircrafts at AMA were estimated as 21?t/y for HC, 138?t/y for CO, and 197?t/y for NOX. Boeing 737-800 type aircrafts have the biggest portions in total emissions (12% for HC, 18% for CO, and 35% for NOX). It is estimated that an increase of 1?min in taxiing time causes an increase of 4.2%, 4.6%, and 0.4% in the amount of HC, CO, and NOX emissions, respectively. Estimations show that the full capacity of aircraft movements at AMA might cause annual emissions to be 176?t/y for HC, 1,184?t/y for CO, and 1,306?t/y for NOX.     

Influence of solutes on hydration and lubricity of dextran brushes

The characteristic lubricity and non-fouling behavior of polymer brushes is critically dependent on the solvation of the polymer chains, as well as the chain-chain interactions. Dextran brushes have shown promise as non-toxic aqueous lubricant films, and are similar in composition to natural lubricating systems, while their comparative simplicity allows for controlled preparation and fine characterization. This project entails measuring the solvation and lubricity of dextran brushes in the presence of additives which modify the inter-chain hydrogen bonding. The thickness and refractive index of the film were measured during adsorption of the brush layer onto a silica substrate and the subsequent immersion in solutions of potassium sulfate and α, α-trehalose. We also studied the lubricity of the system as a function of normal loading using colloidal-probe AFM. Both solutes are shown to have a minimal effect on the hydration of the brush while significantly reducing the brush lubricity, indicating that inter-chain hydrogen bonding supports the load-bearing capacity of polysaccharide brushes.     

Synthesis and thermoluminescence properties of rare earth oxides （Y, Ce-Lu） doped lithium triborate

Lithium triborate (LiB3O5) was synthesized by high temperature solid-state reaction method, and then rare earth oxides were doped into LiB3O5 to enhance its thermoluminescent (TL) properties. The identification and characteristics of the obtained compounds were determined by X-ray diffraction (XRD), Fourier transform infrared (FTIR) analyses, differential thermal analyses (DTA) and scanning electron microscopy (SEM). The glow curves were obtained using a thermoluminescent (TL) reader. The results revealed that all the rare earth oxides were not good activators for lithium triborate and the obtained compounds could not be used for dosimetric applications.     

Variable refrigerant flow systems: A review

This review study presents a detailed overview of the configurations of the outdoor and indoor units of a multi-split variable refrigerant flow (VRF) system, and its operations, applications, marketing and cost. Besides, a detailed review about the experimental and numerical studies associated with the VRF systems is provided. The aim is to put together all the diversified information about the VRF systems in a single source. According to detailed review, it is observed that the compressor frequency and the electronic expansion valve opening should be controlled simultaneously for the control strategies, and it is concluded that VRF system not only consumes less energy than the common air conditioning systems such as variable air volume, fan-coil plus fresh air under the same conditions, but also provides better indoor thermal comfort as long as it is operated in the individual control mode. It is found that even though the main drawback of the VRF system is the high initial cost compared to the common air conditioning systems, due to the energy saving potential of the VRF system, the estimated payback period of the VRF system compared to an air cooled chiller system in a generic commercial building could be about 1.5 year.     

The effects of casting and forging processes on joint properties in friction-welded AISI 1050 and AISI 304 steels

The aim of the present study was to investigate the effects of investment casting and forging process on the microstructure and mechanical properties of friction weldments, AISI 1050–AISI 304. A continuous-drive friction welding device with the automatic control ability of friction time and forging pressure was designed and constructed. Factorial design of experiments was performed to join investment cast AISI 1050 steels and forged AISI 1050 steels with AISI 304 austenitic stainless steel with respect to the optimized process parameters. The joint performance was evaluated by tensile and hardness tests performed parallel and perpendicular to the weld interface. Microstructure of forged parts under friction welding was examined using optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy. Results of microstructural studies were compared with those of friction welding of investment cast parts. The results reveal that a recrystallized region or a mechanically mixed layer was formed on the AISI 304 side near the weld interface, depending on friction time and friction pressure. Friction welding of forged parts always exhibited higher tensile strength, lower hardness, and more upset than the cast parts.     

Nanostructured membrane electrode assemblies from layer‐by‐layer composite/catalyst containing membranes and their fuel cell performances

In this study, two approaches are compared to develop nanostructured membrane electrode assemblies (MEA) using layer‐by‐layer (lbl) technique. The first is based on the direct deposition of polyallylamine hydrochloride (PAH) and sulfonated polyaniline (sPAni) on Nafion support to prepare lbl composite membrane. In the second approach, sPAni is coated on the support in the presence of platinum (Pt) salt, Nafion solution and Vulcan for obtaining catalyst containing membranes (CCMs). SEM and UV–vis analysis show that the multilayers are deposited on both sides of Nafion successfully. Although H₂/O₂ single cell performances of acid doped lbl composite membrane based MEA are found to be at the range of 126 and 160 mW cm^?2 depending on the number of deposited layers, the cell performance of MEA obtained from catalyst containing lbl self‐assembled thin membrane (PAH/sPAni‐H⁺)_10‐Pt is found to be 360 mW cm^?2 with a Pt utilization of 720 mW mgPt^?1. This performance is 82% higher as compared to original Nafion^®117 based MEA (198 mW cm^?2). From the cell performance evaluations for different structured MEAs, it is mainly found out that the use of lbl CCMs instead of composite membranes and fabrication of thinner electrolytes result in a higher H₂/O₂ cell activity due to significant reduction in ohmic resistivity. Also, it is observed that the use of sPAni slightly improves the cell performance due to an increased probability of the triple phase contact and it can lead to superior physicochemical properties such as conductivity and thermal stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40314.