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.     

Wear behaviour of Al/(Al2O3p+SiCp) hybrid composites

In this study, dry sliding metal–metal and metal–abrasive wear behaviours of the aluminium matrix hybrid composites produced by pressure infiltration technique were investigated. These composites were reinforced with 37 vol% Al₂O₃ and 25 vol% SiC particles and contained up to 8 wt% Mg in their matrixes. While matrix hardness and compression strength increased, amount of porosity and impact toughness decreased with increasing Mg content of the matrix. Metal–metal and metal–abrasive wear tests revealed that wear resistance of the composites increased with increasing Mg addition. On the other hand, abrasive resistance decreased with increasing test temperature, especially above 200 °C.     

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.     

Purkinje Images: Conveying Different Content for Different Luminance Adaptations in a Single Image

Providing multiple meanings in a single piece of art has always been intriguing to both artists and observers. We present Purkinje images, which have different interpretations depending on the luminance adaptation of the observer. Finding such images is an optimization that minimizes the sum of the distance to one reference image in photopic conditions and the distance to another reference image in scotopic conditions. To model the shift of image perception between day and night vision, we decompose the input images into a Laplacian pyramid. Distances under different observation conditions in this representation are independent between pyramid levels and pixel positions and become matrix multiplications. The optimal pixel colour can be found by inverting a small, per‐pixel linear system in real time on a GPU. Finally, two user studies analyze our results in terms of the recognition performance and fidelity with respect to the reference images.     

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.     

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.     

Physico-chemical properties in honey from different regions of Turkey

The present study was undertaken to determine the physico-chemical parameters of honey samples obtained from retailers in Marmara Region (Site 1) and East Anatolia (Site 2) of Turkey. The 70 samples were analysed for parameters including moisture, total acidity, diastase activity, hydroxymethylfurfural (HMF), invert sugar, sucrose, ash, commercial glucose and starch. 10 of 70 (14.3%) honey samples were of unacceptable quality based on recommended criteria of moisture (3 of 70, 4.29%), diastase activity (3 of 70, 4.29%), HMF (2 of 70, 2.86%), invert sugar (4 of 70, 5.71%) and sucrose (2 of 70, 2.86%) by Turkish Food Codex and European Commission Regulation. The results of study indicated that 85.7% of honey samples were at good quality. It is important that the essential precautions should be taken to ensure standardisation and rationalisation of beekeeping techniques, manufacturing procedures and storing processes to improve honey quality.     

On the quality variation impact of returns in remanufacturing

This study considers a two-class production system that is subject to operational and quality failures. A generalized example for such systems is the remanufacturing processes where new and used parts are handled by the same machines. Here the impurities of used parts bring additional load to machines that are shared by new and used parts. In order to analyze the process first the single machine operation is modeled as a Continuous Time Markov Chain. Then based on the single machine model, a model for a two-machine-one-buffer-system is constructed. Here in order to attain computational tractability for systems with larger buffers state aggregation and randomized part type sequencing is considered for both machines. Then using this model the impact of the remanufacturing ratio on the effective throughput rate of the system is numerically analyzed.     

On the dual nature of intra-urban borders: The case of a Romani neighborhood in Istanbul

This essay questions the nature of intra-urban borders from a politico-ethical point of view. Namely: to what extent are intra-urban borders acceptable at a time of proliferating discourses about a borderless world, and open cities? We discuss this through a case study of Sulukule – a historic neighborhood home to a millennium old Roma community located within the historic city center of Istanbul – in the context of the urban renewal project launched by the local municipality. The often cited “humanitarian” pretext for the renewal project is “incorporating” the Sulukule’s poor Roma community into the city and tearing down the borders demarcating their ghetto. Eventually, this discourse of incorporation served to instigate a rapid episode of gentrification in the area. Offering a critical perspective on the municipality’s renewal project, and through a discussion of the often conflicting premises of the discourses of the “right to the city” and the “group right to difference,” this essay argues that intra-urban borders are “undecided” separators and calls for policy tools that are responsive to the enabling aspects of bordering processes.     

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.