Effects of TiN coating on the corrosion of nanostructured Ti-30Ta-xZr alloys for dental implants

Electrochemical characteristics of a titanium nitride (TiN)-coated/nanotube-formed Ti-Ta-Zr alloy for biomaterials have been researched by using the magnetic sputter and electrochemical methods. Ti-30Ta-xZr (x = 3, 7 and 15 wt%) alloys were prepared by arc melting and heat treated for 24 h at 1000 °C in an argon atmosphere and then water quenching. The formation of oxide nanotubes was achieved by anodizing a Ti-30Ta-xZr alloy in H₃PO₄ electrolytes containing small amounts of fluoride ions at room temperature. Anodization was carried out using a scanning potentiostat, and all experiments were conducted at room temperature. The microstructure and morphology of nanotube arrays were characterized by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The TiN coatings were obtained by the radio-frequency (RF) magnetron sputtering technique. The depositions were performed from pure Ti targets on Ti-30Ta-xZr alloys substrates. The corrosion properties of the specimens were examined using potentiodynamic test in a 0.9% NaCl solution by using potentiostat. The microstructures of Ti-30Ta-xZr alloys were changed from an equiaxed to a needle-like structure with increasing Zr content. The interspace between the nanotubes was approximately 20, 80 and 200 nm for Zr contents of 3, 7 and 15 wt%, respectively. The corrosion resistance of the TiN-coated on the anodized Ti-30Ta-xZr alloys was higher than that of the untreated Ti alloys, indicating a better protective effect.     

计量逻辑学中的雪崩逻辑公式

将密码学中满足严格雪崩准则的布尔函数的概念引入到计量逻辑学之中,提出了雪崩逻辑公式的概念,并研究了雪崩逻辑公式的真度及其性质。证明了至少含有三个原子公式的雪崩逻辑公式的真度之集为H1={k/2n-12n-3≤k≤3×2n-3;n=3,4,…},在此基础上,通过引入函数ξ建立了n(n≥3)元雪崩布尔函数个数的表达式,给出了雪崩逻辑公式的构造方法。最后,研究了反射变换下k阶雪崩逻辑公式的性质。     

Quantitative stability of full random two-stage problems with quadratic recourse

ABSTRACT

In this paper, we discuss quantitative stability of two-stage stochastic programs with quadratic recourse where all parameters in the second-stage problem are random. By establishing the Lipschitz continuity of the feasible set mapping of the restricted Wolfe dual of the second-stage quadratic programming in terms of the Hausdorff distance, we prove the local Lipschitz continuity of the integrand of the objective function of the two-stage stochastic programming problem and then establish quantitative stability results of the optimal values and the optimal solution sets when the underlying probability distribution varies under the Fortet–Mourier metric. Finally, the obtained results are applied to study the asymptotic behaviour of the empirical approximation of the model.     

Incorporating human behaviour in simulation models of screening for breast cancer

Simulation modelling is widely used in many industries in order to assess and evaluate alternative options and to test strategies or operating rules which are too complex to be modelled analytically. Simulation software has developed its capability in parallel with the growth in computing power since the 1980s. However in practice, the results from the most sophisticated and complex simulation model may not truly reflect what happens in the real world, because such models do not account for human behaviour. For example, in the domain of healthcare simulation is often used to evaluate the outcomes from medical interventions such as new drug treatments. However in reality patients may not complete the course of a prescribed medication, perhaps because they find the side-effects unpleasant. A simulation study designed to evaluate this medication which ignores such behavioural factors may give unreliable results. In this paper we describe a model for screening for breast cancer which includes behavioural factors to model women’s decisions to attend for mammography. The model results indicate that increasing attendance through education or publicity campaigns can be equally as effective as decreasing the intervals between screens. This would have considerable cost implications for healthcare providers.     

Study on the Influence of Melt Processing on Segmented Polyurethanes Morphology

A study on thermoplastic polyurethanes (TPU) is described. The investigation focuses on morphology of TPU parts depending on processing conditions and its relation with mechanical and thermal properties. It was found that TPU materials present different crystalline structures depending on chemical composition and melt processing conditions during part manufacturing. Due to that fact, strong variations in mechanical and tribological properties are expected.     

Global existence,blow up and asymptotic behaviour of solutions for nonlinear Klein–Gordon equation with dissipative term

We study the Cauchy problem of nonlinear Klein–Gordon equation with dissipative term. By introducing a family of potential wells, we derive the invariant sets and prove the global existence, finite time blow up as well as the asymptotic behaviour of solutions. In particular, we show a sharp condition for global existence and finite time blow up of solutions. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance of short-chain alcohols versus acetonitrile in the surfactant-mediated reversed-phase liquid chromatographic separation of β-blockers

Organic solvents are traditionally added to micellar mobile phases to achieve adequate retention times and peak profiles, in a chromatographic mode which has been called micellar liquid chromatography (MLC). The organic solvent content is limited to preserve the formation of micelles. However, at increasing organic solvent contents, the transition to a situation where micelles do not exist is gradual. Also, there is no reason to neglect the potentiality of mobile phases containing only surfactant monomers instead of micelles (high submicellar chromatography, HSC). This is demonstrated here for the analysis of β-blockers. The performance of four organic solvents (methanol, ethanol, 1-propanol, and acetonitrile) was compared in mobile phases containing the anionic surfactant sodium dodecyl sulphate in the MLC and HSC modes. The association of the organic solvent molecules with micelles gives rise to a significant loss in the elution strength of the organic solvent; whereas upon disruption of micelles, it tends to that observed in the hydro-organic mode. The elution behaviour of the β-blockers was modelled to predict the retention times. This allowed the detailed exploration of the selectivity and resolution of the chromatographic systems in relatively wide ranges of concentration of surfactant and organic solvent. The best performance in terms of resolution and analysis time was achieved using HSC with acetonitrile, being able to base-line resolve a mixture of eight β-blockers. Ethanol also provided a good separation performance, significantly improved with respect to methanol and 1-propanol. In contrast, the hydro-organic mode using acetonitrile or any of the short-chain alcohols could not succeed with the separation of the β-blockers, owing to the poorer selectivity and wider peaks.     

The crystal structures,molecular spectra and thermal behaviour of carbamoylferrocene and ferrocenecarbonylhydrazide

Carbamoylferrocene (1) and ferrocenecarbonylhydrazide (2) were synthesised by modified literature procedures and studied by a combination of the conventional spectroscopic methods (IR, MS and NMR), X-ray crystallography and thermal analysis. The crystal structures of two new polymorphs of amide 1 and the structure of hydrazide 2 were determined, revealing extensive hydrogen bonding interactions of the polar ferrocene substituents and supportive π?$?$π stacking interactions. Whereas the thermal behaviour of hydrazide 2 was relatively complicated, thermolysis of amide 1 in the presence of air oxygen led to a complete elimination of the organic constituents in a single step under mild conditions affording essentially pure hematite (α-Fe₂O₃). Mössbauer spectra, powder X-ray diffraction and high-resolution transmission electron microscopy indicated the pyrolytic hematite to result in the form of random aggregates of well crystalline nanoparticles.     

Physico-mechanical, thermal and morphological behaviour of polyurethane/poly(methyl methacrylate) semi-interpenetrating polymer networks

Semi-interpenetrating polymer networks (SIPNs) of polyurethane (PU) and poly(methyl methacrylate) (PMMA) in different weight ratios viz., 90/10, 70/30, 60/40 and 50/50 were prepared. The SIPNs were characterized for physico-mechanical properties like density, tensile strength and elongation at break. Thermal stability of IPNs was measured using thermogravimetric analysis (TGA). From the TGA thermograms it was noticed that all IPNs are stable up to 325 °C and undergo three-step thermal degradation in the temperature ranges 251-400, 378-508 and 445-645 °C for first, second and third steps, respectively. Thermal degradation kinetic parameters like activation energy (E_a) were calculated using Broido, Coats-Redfern and Horowitz-Metzger models. The values obtained by Broido and Horowitz-Metzger methods showed concurrency, whereas Coats-Redfern method showed relatively lower values. Surface morphology measured using scanning electron microscope (SEM) showed two-phase morphology for all the IPNs.     

Effect of chemical structure on combustion and thermal behaviour of polyurethane elastomer layered silicate nanocomposites

The effect of polyol molecular weight and functionality on nanodispersion of clay in PU/clay nanocomposites and the investigation of their thermal and combustion properties are reported and discussed. Lamellar elastomer polyurethane nanocomposites were synthesized using polyols with different molecular weight and functionality and according to these parameters they show several degrees of dispersion which affect their thermal and combustion behaviour. A barrier effect of clay layer is shown in TGA experiments by a delay of thermal degradation products release in nanocomposite materials compared to the virgin polymer; this barrier effect also leads to formation of char during combustion which lowers the peak of rate of heat release in cone calorimeter tests and eliminates fire-induced dripping of the nanocomposite sample during UL 94 test. However, in order to achieve non-burning behaviour nanocomposite technology must be combined with conventional flame retardant technology.