Bioactive double glass coatings for Co-Cr-Mo alloy

Glass compositions for double coatings for a Co-Cr-Mo alloy were developed. The glass compositions were chosen to fulfil such requirements as matching thermal expansion, low glass transition temperature and moderate solubility. For the ground coat a fairly high durability is required, whereas the cover coat must be bioactive, i.e. become attached to living bone by a chemical bond. Two compositions of each type were developed by computer-aided optimization. The glasses were chosen in the Na₂O–CaO–B₂O₃–Al₂O₃–SiO₂–P₂O₅ system. The bioactivity was tested in vitro by immersion in a simulated body fluid. The double coatings on Co–Cr–Mo alloy released hexavalent chromium into the solution as detected by yellow colouration and spectrophotometry. This colouration was strong at the margin between coated and uncoated metal and may be explained by oxidation of trivalent chromium of the alloy in the presence of glass. The released chromium did not have any notable effect on the calcium phosphate formation. After replensihing the solution no coloration was observed. This suggests that the chromate is easily dissolved and that it may be possible to wash it out prior to implantation.     

Vortices in trapped boson-fermion mixtures

No Heading We consider a trapped system of atomic boson-fermion mixture with a quantized vortex. We investigate the density profiles of bosonic and fermionic components as functions of the boson-boson and boson-fermion short-range interaction strengths within the mean-filed approach. Stability of a vortex and conditions for the phase segregation are studied. We compare and contrast our results with the related system of droplets of ³He-⁴He mixtures.PACS numbers: 05.30.–d, 03.75.Ss, 67.60.–g, 67.40. Vs.     

Effect of Al on High-Temperature Oxidation of Cr–W Alloys

The effect of Al on the high temperature oxidation behavior of Cr–10 wt.%W alloy was investigated using a cyclical oxidation test at 1,000 °C in dry air. First, Al was added into the Cr–W alloy as an alloying element up to 8 weight percent. Although alloying with Al reduced the spalling, it did not eliminate it. Secondly, Al was applied to the surface using an aluminizing process. Forming an Al–Cr layer on the Cr–W alloy reduced oxidation rate significantly and eliminated spalling completely.     

Effect of spherical pores on the strength of a polycrystalline ceramic

Bending tests on a ceramic material, lead zirconate-titanate, with varying amounts of porosity, show that the decrease in strength due to spherical pores is much less than would be expected from the stress concentration factor. Using the Weibull probabilistic approach to brittle strength, it is shown that reasonable predictions may be made for the median strength for porosity up to about ten percent.

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Résumé Les essais de flexion sur un matériau céramique: zirconate-titanate de plomb, avec des quantités variables de porosités, montrent que la diminution de la résistance due à la porosité est plus faible que celle donnée par le facteur de concentration de contraintes. En utilisant la méthode statistique de Weibull pour la résistance fragile, il est montré que des prévisions raisonables peuvent être faites pour déterminer la résistance médiane pour une porosité jusqu'aux environs de dix pourcents.

     

Evaluation of the acceptance of glass in bone

Six glasses in the SiO₂-Na₂O-CaO-P₂O₅-Al₂O₃-B₂O₃-system were implanted in rabbit tibia. The bone-implant interfaces were studied by scanning electron microscopy (SEM) and in a push-out test. In SEM it seems possible to distinguish between physical contact and chemical bonding between glass and bone. The measured push-out strength is about 0.5 MPa if no bone contact exists. If physical contact exists the push-out strength is 2–3 MPa. The push-out strength of titanium falls within these limits. Glasses, which on basis of the SEM study are concluded to chemically bond to bone, show push-out strengths of 16–23 MPa. Two non-bonding glasses are compared. One possesses only a silica-rich surface, whereas the other possesses a calcium phosphate-rich surface. Both develop a close contact with bone, but neither bonds chemically. There is no significant difference in their push-out strengths, which are comparable to that of titanium. Even if a calcium phosphate-rich layer forms at the glass surface, bonding may be reduced if Al₂O₃ is included in the glass composition. Further, a phosphate-free bioactive glass is compared with two phosphate-containing bioactive glasses. The phosphate-free glass bonds by incorporating phosphate from the body fluid into its surface. Push-out data indicate that this glass is not as firmly attached to bone as the phosphate-containing ones. The calcium phosphate layer formed is non-uniform, which might explain the lower bonding strength.     

Symmetric and antisymmetric outer plethysms of schur functions

Complete tables are given for the calculations of the outer plethysms of S functions for the symmetric and/or antisymmetric cases {n} ? {m}, {1ⁿ} ? {m}, {n} ? {1^m}, and {1ⁿ} ? {1^m} for all values of m and n with m·n < 30 as well as for m = 3 and n = 10–14, m = 4 and n = 8–10, and m = 5 and n = 6.     

A novel mixing method for powder metallurgy copper-carbon nanotube composites

In this study, copper matrix composite materials with different ratios of carbon nanotubes were produced. The biggest problem faced in the production of carbon nanotube-reinforced composites is that carbon nanotubes do not distribute homogeneously in the matrix. A novel mixing technique was applied to overcome this problem. Hot pressing was used in sample production. A second high-pressure densification process was applied following the hot pressing process for enhancing the properties. The properties of both the hot-pressed specimens and the specimens to which a second high-pressure densification process was applied were characterized with the density measurements, microstructure examinations, and mechanical tests. The microstructure examinations showed that carbon nanotubes could be distributed homogeneously in the copper matrix with the mixing process applied. It was found out that the high-pressure densification process applied following the hot-pressing process increased the relative density and thus, all mechanical properties.     

Robust Adaptive Control of Pulse-width Modulated Rectifiers Based on Adaptive Super-twisting Sliding-mode and State Feedback Controllers

Abstract—This article proposes a new robust adaptive hybrid controller for three-phase pulse-width modulated rectifiers to improve control performance. This hybridization is implemented by combining the second-order sliding mode with the adaptive gain super-twisting control law in the DC bus voltage control loop and state feedback adaptive control in the d-q-axis current control loops. The control objectives are fourfold: (1) driving the DC bus voltage to a reference signal without using a priori knowledge of the plant parameters, (2) forcing the d-q-axis current errors to zero, (3) assuring a satisfactory power factor correction in relation to the AC source, and (4) eliminating the chattering effect. In the closed-loop control system, three-phase source currents and the DC bus voltage are supposed to be available for feedback. As a result, no a priori knowledge of the plant parameters is necessary in the design of the proposed controller. In addition, the proposed controller does not have the disadvantages of singularity, over-parameterization, and chattering phenomenon. Results of experimental studies prove that the proposed control system guarantees the tracking of reference signals with high performance despite all the parameter and external disturbance uncertainties.     

Forced convection heat transfer and pressure drop for a horizontal cylinder with vertically attached imperforate and perforated circular fins

In this study, the effect of holes placed on perforated finned heat exchangers on convective heat transfer experimentally investigated. Six millimeter-diameter holes were opened on each circular fin on a heating tube in order to increase convective heat transfer. These holes were placed on the circular fins in such a way as to follow each other at the same chosen angle. The holes created turbulence in a region near the heating tube surface on the bottom of the fin. Some experiments were then performed to analyze the effect of this turbulence on heat transfer and pressure drop. These experiments were carried out at six different angular locations in order to determine the best angular location. In addition, a perforated finned heater was compared with an imperforate finned heater to observe the differences. In the cases of the Re above the critical value, Nusselt numbers for the perforated finned positions are 12% higher than the Nusselt numbers for the imperforate state. Moreover, a correlation has been obtained between the Re and Nu in the Re number above the critical value and the Re below the critical value. Meanwhile, correlations regarding pressure drops in the flow areas have been obtained.     

Architectural mimicry,spaces of modernity: the Island Casino,Izmir, Turkey

This article looks through the lense of an entertainment building in Izmir, Turkey, within the larger framework of modernity and identity in order to scrutinise ways in which cross-cultural influences are mediated. The programme of the building is conceptualised as a social structure and its aesthetics as a cultural form, which work to connect localities to the processes of modernisation and westernisation in the Turkish context of the 1950s' era. The analysis exposes how the edifice operates as a spatial structure that influences cultural norms and Western behaviour through practices of entertainment and architectural design, simultaneously serving as a medium through which people could perform and express their modernity.