Study on the performance enhancement of biomedical implants: in vitro test under UV irradiation of titanium anodised in mixed electrolyte

Titanium (Ti) recently has widely been used in the biomedical applications due to its high performance. Therefore, surface modifications of titanium have attracted a lot of interest to provide better osseointegration. Ti was subjected to anodic oxidation process and in vitro testing to assess the bioactivity of titanium oxide (TiO2) coating. TiO2 coating has been anodised at room temperature in different electrolyte; in sulphuric acid (H2SO4); phosphoric acid (H3PO4); and a mixture of H2SO4 and H3PO4 acids. The parameters used in anodization were: concentration of the electrolytes, applied voltage and current density. The coated surface is then evaluated using different testing techniques; the microstructure using scanning electron microscope (SEM); the elemental analysis using Energy-dispersive x-ray spectroscopy (EDX); mineralogical and crystal structure using x-ray diffraction (XRD); absorption analysis using Fourier transform infrared spectroscopy (FT-IR); and the hydrophilicity using water contact angle (WCA). TiO2 was then subjected in vitro testing to assess the bioactivity of TiO2 surface; that is the apatite formation ability. The apatite formation of the TiO2 coating was precipitated by using simulated body fluid (SBF) in the dark and under the ultraviolet (UV) irradiation to mimic the reactions that may occur with the human bone-like cells layer. The testing was done to evaluate the apatite’s microstructure, mineralogy, elements and absorption. From the results it was found that higher apatite was obtained with the increased of the immersion time; higher apatite formation and crystallization was found at earlier time of immersion for the TiO2 that was immersed in SBF under the UV; higher apatite was obtained on the TiO2 coatings that were anodised in H2SO4, H3PO4 and mixture electrolyte at lower electrolyte concentration. The increased apatite on these coatings can be related to the strong Ti-O- functional groups on the coating surface. The highest apatite was obtained on the TiO2 coating that was anodised in a mixture electrolyte that has obtained Ti-OH functional group. The UV has resulted in the increased Ti-O- and Ti-OH groups, thus higher apatite precipitation ability

Analysis of mechanical properties and microstructure of multiple die cavity products produced in vertical and horizontal arrangement by gravity die casting

Multiple cavities die casting (Permanent die casting )in vertical arrangement and horizontal arrangement moulds are widely used in industry. However, manufacturers assume that each product produced in either arrangement would have the same quality. Manufacturers do not have enough information about the properties of each product, i.e. strength, internal defect and the microstructure. Furthermore, in actuality the quality of each product might be affected. It is the problem that we found within the market now (pinholes, cracks, misruns and etc. ), that is the reason investigation and comparison of the multi product in vertical and horizontal arrangement is needed. This investigation is needed to choose which arrangement is preferred to maintain the quality of the product. The methodology used are vickers microhardness test, izod test, ensile test, density and porosity test and optical microscope inspection for all produced sample. Results of this research show that castings produced at vertical arrangement mould have higher mechanical and properties than castings produced in horizontal arrangement mould. Vertical arrangement castings obtained higher density exceeds %1.6117 than horizontal arrangement castings that ranges between (1.156 and 4.8707 percent ). However, vertical arrangement castings obtained higher porosity exceeds %13.3885 than horizontal arrangement castings that ranges between (0.0809 and 7.4629 percent ). The hardness values for vertical castings ranges between (115HV and 78.9HV ), while ranges between (110HV and 79.1HV ) for horizontal castings. Castings in vertical arrangement hardness are %7.5442 higher than hardness for castings in horizontal arrangement. Impact strength values of vertical arrangement casting impact values that ranges between( 6J and 19J ) positions are %118.4615 higher than casting at horizontal arrangement casting positions that range between (2J and 11J ). Ultimate tensile strength for castings produced at vertical arrangement mould ranges between (122-182 MPa ) are %11.81 higher than castings produced at horizontal arrangement castings (101-178 MPa ). The microporosity at vertical arrangement positions are %35 lower than microporoity at horizontal arrangement positions

Constraining Non-thermal and Thermal properties of Dark Matter

We describe the evolution of Dark Matter (DM) abundance from the very onset of its creation from inflaton decay under the assumption of an instantaneous reheating. Based on the initial conditions such as the inflaton mass and its decay branching ratio to DM, reheating temperature, and the DM mass and interaction rate with the thermal bath, the DM particles can either thermalize (fully/partially) with the primordial bath or remain non-thermal throughout their evolution history. In the thermal case, the final abundance is set by the standard freeze-out mechanism for large annihilation rates, irrespective of the initial conditions. For smaller annihilation rates, it can be set by the freeze-in mechanism, also independent of the initial abundance, provided it is small to begin with. For even smaller interaction rates, the DM decouples while being non-thermal, and the relic abundance will be essentially set by the initial conditions. We put model-independent constraints on the DM mass and annihilation rate from over-abundance by exactly solving the relevant Boltzmann equations, and identify the thermal freeze-out, freeze-in and non-thermal regions of the allowed parameter space. We highlight a generic fact that inflaton decay to DM inevitably leads to an overclosure of the Universe for a large range of DM parameter space, and thus poses a stringent constraint that must be taken into account while constructing models of DM. For the thermal DM region, we also show the complementary constraints from indirect DM search experiments, Big Bang Nucleosynthesis, Cosmic Microwave Background, Planck measurements, and theoretical limits due to the unitarity of S-matrix. For the non-thermal DM scenario, we show the allowed parameter space in terms of the inflaton and DM masses for a given reheating temperature, and compute the comoving free-streaming length to identify the hot, warm and cold DM regimes.Comment: 29 pages, 8 figures; some clarifications and references added; published versio

The Artin-Greenberg function of a plane curve singularity

We calculate the Artin-Greenberg function of plane curves. It turns out that this function is a topological invariant of the singularity and that it determines with other invariants the semigroup of the singularity. This generalizes a result of M. Hickel proved for irreductible plane curves

Dynamic Ethnic Fractionalization and Economic Growth in the Transition Economies from 1989 to 2007

In their survey of the literature on ethnic fractionalization and economic performance, Alesina and La Ferrara (JEL 2005) identify two main directions for future research. One is to improve the measurement of diversity and the other to treat diversity as an endogenous variable. This paper tries to address these two issues: it investigates the effects of ethnic fractionalization on economic growth across countries using unique time-varying measures. We first replicate the finding of a weak effect of exogenous diversity on growth and then we show that accounting for how diversity changes over time and treating it as an endogenous variable makes a difference. Once diversity is instrumented (with lagged diversity and latitude), it shows a significant negative impact on economic growth which is robust to different specifications, polarization measures, econometric estimators, as well as to the use of an index of ethnic-religious-linguistic fractionalization.ethnic diversity, fractionalization, polarization, growth