The effect of incorporation of steatite wastes on the mechanical properties of cementitious composites

The recycling of mineral wastes is considered today an activity of utmost importance, contributing in the diversification of products, reduction of final costs, besides promoting alternative raw materials for some industrial sectors. This work focuses on the incorporation of steatite wastes in cementitious composites. A full design of experiment was carried out in order to investigate the effect of the experimental factors: fraction and particle size of steatite and compaction pressures (10 and 30 MPa) on the mechanical properties of the ceramic composites. The increase of the steatite fraction provided an increase of the bulk density and apparent porosity of the composites. Large particles of steatite provided an increase of the apparent porosity decreasing the mechanical strength. The increase of the pressing compaction decreased the apparent porosity, increasing the bulk density and the mechanical strength of the composites.     

Strength improvement of LPS–SiC ceramics by oxidation treatment

In this work, SiC ceramics were liquid phase sintered (LPS), using AlN–Y₂O₃ as additives, and oxidized at 1400 °C in air for up to 120 h. Oxidation was monitored by the weight gain of the samples as function of exposition time and temperature. A parabolic growth of the oxidation layer has been observed and the coefficient of the growth rate has been determined by relating the weight gain and the surface area. The effect of oxidation on strength has been determined by 4-point bending tests. Phase analysis by X-ray diffraction and microstructural observation by scanning electron microscopy indicated the formation of a uniform and dense oxidation layer. The elimination of surface flaws and pores and the generation of compressive stresses in the surface resulted in a strength increase of the oxidized samples.     

Distortion-free laser beam shaping for material processing using a digital micromirror device

Digital micromirror devices (DMD) are increasingly used in laser-based manufacturing for a maskless beam shaping in order to realize simultaneous 2D/3D material processing. Thereby, the DMD has to be irradiated under a sharp angle to achieve acceptable projection quality with negligible distortion phenomena. In this article, we present a novel setup for DMD-based laser material processing. It enables the irradiation under large angles (up to 60\(^{\circ }\)), the reduction of optical elements as well as machine size. Occurring optical distortions during the amplitude-based laser beam shaping are characterized. To eliminate these phenomena, we implement an optical modelling of the DMD patterns, taking into account the propagation through the tilted interfaces. The resulting imaging of different desired shapes is verified experimentally for its geometrical properties such as length, radius and aspect ratio. Thereby, an angle-dependent correction and high shape accuracy of the image projection is shown. This novel arrangement may have applications in direct laser writing and photochemical machining.     

Bioactivity and cytotoxicity of glass and glass–ceramics based on the 3CaO·P2O5–SiO2–MgO system

The mechanical strength of bioactive glasses can be improved by controlled crystallization, turning its use as bulk bone implants viable. However, crystallization may affect the bioactivity of the material. The aim of this study was to develop glass–ceramics of the nominal composition (wt%) 52.75(3CaO·P₂O₅)–30SiO₂–17.25MgO, with different crystallized fractions and to evaluate their in vitro cytotoxicity and bioactivity. Specimens were heat-treated at 700, 775 and 975 °C, for 4 h. The major crystalline phase identified was whitlockite, an Mg-substituted tricalcium phosphate. The evaluation of the cytotoxicity was carried out by the neutral red uptake methodology. Ionic exchanges with the simulated body fluid SBF-K9 acellular solution during the in vitro bioactivity tests highlight the differences in terms of chemical reactivity between the glass and the glass–ceramics. The effect of crystallinity on the rates of hydroxycarbonate apatite (HCA) formation was followed by Fourier transformed infrared spectroscopy. Although all glass–ceramics can be considered bioactive, the glass–ceramic heat-treated at 775 °C (V775-4) presented the most interesting result, because the onset for HCA formation is at about 24 h and after 7 days the HCA layer dominates completely the spectrum. This occurs probably due to the presence of the whitlockite phase (3(Ca,Mg)O·P₂O₅). All samples were considered not cytotoxic.     

Fatigue and subcritical crack growth in ZrO2–bioglass ceramics

This work investigates the characteristics of ZrO₂ based ceramics (Y-TZP) doped with bioglass developed for dental prostheses. Powder mixtures composed of zirconia and 3 or 5 wt% of 3CaO·P₂O₅–SiO₂–MgO bioglass were sintered at 1300 °C for 2 h. The samples were characterized by their phase composition using X-Ray diffraction (XRD) and analysis of their microstructure by scanning electronic microscopy (SEM). Hardness and fracture toughness were evaluated using the Vickers indentation method, while bending strength and fatigue resistance were determined using the four-point bending testing. The mechanical properties indicate that the samples achieved high density under the applied sinter conditions. X-ray diffraction analysis revealed tetragonal ZrO₂ as a major crystalline phase. Hardness, fracture toughness and bending strength of the sintered samples containing 3% or 5% bioglass were 1167and 1134 HV, 6.3 and 6.1 MPa m^1/2 and 453 and 636 MPa, respectively. The fatigue results presented large scattering, which is attributed to a heterogeneous distribution of the secondary glassy phase in the zirconia matrix. The non-uniform dispersion of the glass may result in the formation of stress gradients, possibly responsible for crack initiation and their respective subcritical growth during fatigue testing. The fatigue limit determined was superior to stresses developed during mastication, turning its use in dental prostheses viable. Weibull statistics were applied on the fatigue results obtained at average stress levels of 255, 270 and 285 MPa in order to calculate the subcritical crack growth. A life expectancy of over 20 years under severe cyclic pressure conditions has been calculated.     

Analysis of the renal transplant waiting list: application of a parametric competing risk method

BACKGROUND: The strong competition for scarce renal graft resources jeopardizes an individual patient's chances of a transplantation within a reasonable time scale. This study was undertaken to quantify these chances of receiving a transplant. METHODS: All patients registered for their first renal allograft between January 1980 and December 1993 (n=40,636) in Eurotransplant were selected. The influence of patient characteristics, such as age, HLA phenotype frequency, % panel-reactive antibodies, period of registration, and ABO blood group, on the waiting list outflow was studied. The competing risk method was applied, and Poisson models were built to estimate the risk factor effects. RESULTS: The chance of transplantation within 10 years after registration was overestimated by Kaplan-Meier (84%); using the competing risk method it was only 74%. The predicted chance for death on the waiting list was overestimated by 33% (45% Kaplan-Meier vs. 12% competing risk). A time-varying covariate effect on the chances of waiting list outflow was observed. Favorable factors for quick transplantation, such as blood group AB or a common HLA phenotype, were no longer seen to be driving forces for transplantation once 5 to 6 years of waiting time had been accrued. CONCLUSION: When multiple outcomes exist, Kaplan-Meier estimates should not be interpreted as survival rates, while competing risk estimates yield appropriate chances. A significantly decaying effect of the usual allocation parameters is observed with ongoing waiting time. This phenomenon is the statistical basis for redesigning allocation strategies. Organ exchange algorithms should have the potential to adapt to these time-varying effects.     

Characterization of an N-acetylglucosamine-6-O-sulfotransferase from human respiratory mucosa active on mucin carbohydrate chains

A microsomal GlcNAc-6-O-sulfotransferase activity from human bronchial mucosa, able to transfer a sulfate group from adenosine 3'-phosphate 5'-phosphosulfate onto methyl-N-acetylglucosaminides or terminal N-acetylglucosamine residues of carbohydrate chains from human respiratory mucins, has been characterized. The reaction products containing a terminal HO3S-6GlcNAc were identified by high performance anion-exchange chromatography. Using methyl-beta-N-acetylglucosaminide as a substrate, the optimal activity was obtained with 0.1% Triton X-100, 30 mM NaF, 20 mM Mn2+, 5 mM AMP in a 30 mM MOPS (3-(N-morpholino) propanesulfonic acid) buffer at pH 6.7. The apparent Km values for adenosine 3'-phosphate 5'-phosphosulfate and methyl-beta-N-acetylglucosaminide were observed at 9.1 x 10(-6) M and 0.54 x 10(-3) M, respectively. The enzyme had more affinity for carbohydrate chains with a terminal GlcNAc residue than for methyl-beta-N-acetylglucosaminide; it was unable to catalyze the transfer of sulfate to position 6 of the GlcNAc residue contained in a terminal Galbeta1-4GlcNAc sequence. However, oligosaccharides with a nonreducing terminal HO3S-6GlcNAc were substrates for a beta1-4 galactosyltransferase from human bronchial mucosa. These data point out that GlcNAc-6-O-sulfotransferase must act before beta1-4 galactosylation in mucin-type oligosaccharide biosynthesis.     

Towards formalising AADL in Proof Assistants

This paper presents first steps towards a formalisation of the Architecture Analysis and Design Language, mainly concentrating on a representation of its data model. For this, we contrast two approaches: one set-based (using the B modelling framework) and one in a higher-order logic (using the Isabelle proof assistant). We illustrate a transformation on a simplified part of the AADL metamodel concerning flows.     

LPE growth of crack-free PbSe layers on Si(100) using MBE-Grown PbSe/BaF2CaF2 buffer layers

Crack-free PbSe on (100)-oriented Si has been obtained by a combination of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) techniques. MBE is employed first to grow a PbSe/BaF₂/CaF₂ buffer structure on the (100)-oriented Si. A 2.5 μm thick PbSe layer is then grown by LPE. The LPE-grown PbSe displays excellent surface morphology and is continuous over the entire 8×8 mm² area of growth. This result is surprising because of the large mismatch in thermal expansion coefficients between PbSe and Si. Previous attempts to grow crack-free PbSe by MBE alone using similar buffer structures on (100)-oriented Si have been unsuccessful. It is speculated that the large concentration of Se vacancies in the LPE-grown PbSe layer may allow dislocation climb along higher order slip planes, providing strain relaxation.