Christos N. Panagopoulos

Sliding wear behaviour of Zinc–Nickel alloy electrodeposits

Abstract The sliding wear behaviour of zinc–nickel electrodeposited coatings on mild steel substrates was investigated using a spherical pin-on-disc apparatus. The pin materials were alumina and hardened steel. The composition of the coatings was the following: 86 wt% zinc–14 wt% nickel. The friction coefficient of zinc–nickel coating against alumina counter spheres was found to be higher than that against hardened steel counter spheres. The weight loss of zinc–nickel coating after sliding against hardened steel counter spheres was found to be lower than that against alumina counter spheres. The main wear mechanism of the zinc–nickel coating sliding against stainless steel was noted to be severe shearing of the surface layers of the coating due to the ploughing action of the steel pins. For the wear experiments of zinc–nickel coatings against alumina spheres, a surface delamination mechanism is proposed to be the predominant wear mechanism of the coatings.

Laser surface-treatment of titanium

Abstract The surface of laser-treated titanium specimens shows a succession of dark and white stripes. The surface roughness of these specimens was observed to be a function of the power density of the laser; the hardness of the top surface layers (35 μm) of the laser-treated titanium specimens being greater than that of the deeper layers of the same specimens.

Heat-treatment of zinc-coated aluminium

Abstract The heat-treatment of zinc-coated aluminium in atmospheric air was studied. The weight gain of the heat-treated zinc-coated aluminium specimens (in the range 250–350°C) was found to increase following a parabolic law with increasing time for constant heating temperature. Zinc oxide (ZnO) of protective nature was found to form on their surface in the range 250–350°C. Heat-treatment at 400°C resulted in the formation of non-protective oxide on the surface of the specimens. Heat-treatment also resulted in the diffusion of zinc into the aluminium substrate and mainly in the diffusion of aluminium into the zinc coating. For high temperatures and large heating times the above procedure resulted in the formation of a two-phase diffusion zone consisting of nearly elemental zinc and aluminium, since the mutual solubility of these two elements is very small.

Reaming versus broaching in cemented hip arthroplasty : Mechanical stability in cadaver femora

Introduction We used an experimental hip model to assess the mechanical stability of a hip prosthesis, and compared the femoral medullary canal preparation techniques of reaming and broaching. Methods 15 pairs of cadaveric femora had a simulated replacement, the right femur with a reaming technique and the left with a broaching technique. Both femurs were radiographed to assess component positioning and cement mantle. The femurs were osteotomized 30 days after the procedure. The shear strength of the interface was studied at 4 different levels along an aluminum rod during push-out tests. Results The overall mean value of the interface failure load was 15% lower with the reaming technique (6.5 kN for the reaming technique versus 7.7 kN for the broaching technique; p = 0.02). Interpretation Broaching was superior to reaming for the preparation of the femoral canal, and should be used in order to increase primary stability. Further in vivo studies are required to account for factors such as intramedullary pressure, bleeding and surgical variations, which could not be accounted for in our study.

UV laser beam/YBCO target interaction for optimum preablation for the growth of YBCO thin films

The morphological and compositional changes which take place during the laser irradiation of YBCO targets are discussed. The understanding of the evolution of target composition, will lead to better control of film quality. In the case stated here, a XeCl excimer laser was used to irradiate rotated and also non-rotated YBa2Cu3O7-x targets. The modified surface of these targets was systematically studied by scanning electron microscopy and energy dispersive x-ray microanalysis. It was observed that some crucial deposition parameters, such as the number of pulses and fluence has a strong effect on the roughening of the target. A comparative study was done on the derived High-Tc superconducting thin films. It was shown that the conditions during the preablation procedure which affect the target surface morphology correlate closely with the appearance of laser droplets on the film surface.

Lap and butt joints of dissimilar stainless steels welded by CO2 laser

This work concerns the lap welding of dissimilar (AISI 304 - 430, AISI 430 - 304, AISI 316 - 430, and AISI 430 - 316) stainless steels and the butt welding of dissimilar (AISI 304 - 316 and AISI 304 - 430) ones using a fast axial flow 2 kW cw CO2 laser (B.O.C. Laser Ltd.). Two covering gases, He and N2, are used fed coaxially to the laser beam through a 12 mm outlet diameter nozzle at a flow rate varying from 1.67 to 1.87 X 10-3)m3/s. The influence of the process parameters, such as power level, covering gas, and speed on the quality of the welded joints is examined. In the second part of the work laser lap and butt welds of dissimilar stainless steels are characterized by macro and micro graphic investigations to enable structural evaluations. Fillet weld morphology and quality of the same specimens is examined for the two different covering gases, He and N2. Moreover, the different structural aspects of the melted zones obtained with laser welds of the same pair of stainless steels, but with the beam impinging first on the austenitic stainless steel (e.g., AISI 304 - 430) and then the ferritic one (e.g., AISI 430 - 304), or vice versa, are also studied and evaluated.

Evaluation of a Mobile Home Care Platform

As the population of the industrialized world is aging, the field that deals with seniors’ adoption of technology has gained ground in the scientific community. Recent advances in technology have allowed the development of sophisticated telecare systems that support the independent living of seniors, with communication, remote health monitoring and emergency response services. However, usability issues often prevent elderly people from enjoying the benefits of modern technology, despite the amount of research to understand their needs in system design. In this work, we have performed a usability assessment of the “BioAssist” system, which is an integrated home care platform that incorporates both communication and health monitoring features. A comparative evaluation with the “iTriage” application, followed by a series of interviews and qualitative analysis have provided us with valuable insights and guidelines for designing home care systems for seniors.

Mechanical behaviour of zinc-coated copper

Abstract The mechanical behaviour of zinc-coated copper was studied in the zinc coating thickness range of 0–50 μm. The microhardness and the adhesion of the zinc coating to the copper substrate were observed to increase with increasing thickness of the zinc coating. The ultimate tensile strength and the fracture strain of the zinc-coated copper were found to increase and to decrease, respectively, with increasing strain rate for a constant value of the zinc coating thickness.

Surface treatment of aluminum with an excimer laser

The irradiation of pure aluminum with a KrF excimer laser revealed that its surface morphology and roughness can be affected. The surface structure of laser treated aluminum was also found to be affected by the laser irradiation procedure. In addition, depending upon the lasing conditions, the corrosion resistance of aluminum in NaCl solution can be improved.

The HealthSign Project: Vision and Objectives

This paper presents the HealthSign project, which deals with the problem of sign language recognition with focus on medical interaction scenarios. The deaf user will be able to communicate in his native sign language with a physician. The continuous signs will be translated to text and presented to the physician. Similarly, the speech will be recognized and presented as text to the deaf users. Two alternative versions of the system will be developed, one doing the recognition on a server, and another one doing the recognition on a mobile device.