A comparative study of simulated body fluids in the presence of proteins

Simulated body fluid (SBF) is widely used as part of an in vitro method to evaluate implant materials such as their apatite forming ability (AFA), a typical indication of potential bone-bonding ability in vivo. We report the use of carbonate-buffered SBFs as potential solutions for implant evaluation and the effect of proteins, represented by bovine serum albumin (BSA) in SBFs on the nucleation and growth of hydroxyapatite (HA). These solutions are buffered by the thermodynamic equilibrium with 5% CO2 in an incubator, and result in a deposition of carbonated HA. Using several titanium-based surfaces, these solutions were studied in comparison with the widely-used SBF (ISO 23317). The presence of BSA strongly inhibited the formation of HA in traditional SBF, while HA can still be observed in carbonate-buffered SBFs. A kinetic study reveals that the inhibitory effect is concentration dependent with 0.1g/L and 1g/L of BSA having little effect on HA growth but a complete inhibition of HA formation at 5g/L of BSA, as tested using NaOH treated titanium with a known positive AFA. The decrease in solution pH and free calcium concentrations in SBFs due to the addition of BSA is not significant, suggesting other causes for the strong inhibitory effect

Hydrodynamic Collectivity in Proton--Proton Collisions at 13 TeV

In this paper, we investigate the hydrodynamic collectivity in proton--proton (pp) collisions at 13 TeV, using iEBE-VISHNU hybrid model with HIJING initial conditions. With properly tuned parameters, our model simulations can remarkably describe all the measured 2-particle correlations, including integrated and differential elliptic flow coefficients for all charged and identified hadrons ($K_S^0$, $\Lambda$). However, our model calculations show positive 4-particle cumulant $c_{2}\{4\}$ in high multiplicity pp collisions, and can not reproduce the negative $c_{2}\{4\}$ measured in experiment. Further investigations on the HIJING initial conditions show that the fluctuations of the second order anisotropy coefficient $\varepsilon_{2}$ increases with the increase of its mean value, which leads to a similar trend of the flow fluctuations. For a simultaneous description of the 2- and 4- particle cumulants within the hydrodynamic framework, it is required to have significant improvements on initial condition for pp collisions, which is still lacking of knowledge at the moment.Comment: 7 pages, 6 figures, published versio

On the Approximability of the Exemplar Adjacency Number Problem for Genomes with Gene Repetitions

In this paper, we apply a measure, exemplar adjacency number, which complements and extends the well-studied breakpoint distance between two permutations, to measure the similarity between two genomes (or in general, between any two sequences drawn from the same alphabet). For two genomes and drawn from the same set of n gene families and containing gene repetitions, we consider the corresponding Exemplar Adjacency Number problem (EAN), in which we delete duplicated genes from and such that the resultant exemplar genomes (permutations) G and H have the maximum adjacency number. We obtain the following results. First, we prove that the one-sided 2-repetitive EAN problem, i.e., when one of and is given exemplar and each gene occurs in the other genome at most twice, can be linearly reduced from the Maximum Independent Set problem. This implies that EAN does not admit any -approximation algorithm, for any , unless P = NP. This hardness result also implies that EAN, parameterized by the optimal solution value, is W[1]-hard. Secondly, we show that the two-sided 2-repetitive EAN problem has an -approximation algorithm, which is tight up to a constant factor

The band gap and nonlinear optical susceptibility of SrSn1-xVxO3 films

Perovskite-type oxide SrSn1-xVxO3 thin films with different concentrations x = 0.1–0.9 were fabricated by using pulsed-laser deposition, and the effects of V doping on the structure, optical band gap and the third-order optical nonlinearity were systematically investigated. With the increase of x value, the lattice parameters of SrSn1-xVxO3 decrease from 3.997 to 3.862 Å gradually, while the optical band gaps firstly increase and then decrease with boundary at x = 0.3. The third-order nonlinear optical responses were studied via the z-scan technique. The closed-aperture measurements show a negative nonlinear refractive index n2, and the open-aperture measurements demonstrate a saturable absorption β. Both the n2 and β responses vary with the increase of V doping level. The metal-oxygen chemical bond along with the localized V5+Sn2+V5+ complex contribute to the enhancement of optical nonlinearity, and the highest value of third-order susceptibility χ(3) is observed in SrSn0.5V0.5O3 film

Rapid evaluation of bioactive Ti-based surfaces using an in vitro titration method

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Synthesis And Characterization Of Intermetallic Compounds And Transition Metal Nitrides As High-Performance Proton Exchange Membrane Fuel Cell Materials

One of the major challenges in fuel cell technologies, particularly for Proton Exchange Membrane Fuel Cells (PEMFCs), is developing effective catalysts for use in both the anode and cathode. Ordered intermetallic compounds have shown considerable potential for fuel cell applications due to their enhanced catalytic activity, better durability and lower cost. In this work, Pd-Sn intermetallic compounds were investigated. PdSn and Pd3Sn nanoparticles were synthesized under air-free conditions and were tested for their electrochemical properties. Both materials showed poor activities in acidic environment for formic acid and methanol oxidation, but enhanced activities under basic conditions. Various electrochemical tests and structural characterization including high-resolution TEM/STEM and EDX were performed to investigate the changes in these materials that might have resulted in such performance. In this thesis, we also focus on developing stable catalyst supports for fuel cell electrodes, another topic in fuel cell research. Motivated by recent studies which revealed the potential of transition metal nitrides as high performance catalyst supports, we developed a facile synthesis of single-phase, nanocrystalline macroporous chromium nitride and chromium titanium (oxy)nitride with an inverse opal morphology. Characterization using XRD, SEM, HR-TEM/STEM, TGA and XPS is reported. Interconversion of macroporous CrN to Cr2O3 and back to CrN while retaining the inverse opal morphology was also demonstrated. ii

Calcium phosphate formation on titanium-based surfaces: bioactivity evaluated by in vitro methods

The prediction of implant behaviors in vivo by the use of easy-to-perform in vitro methods is of great interest in biomaterials research. In the field of bone implants, it is commonly accepted that a spontaneous formation of a hydroxyapatite (HA) layer on the implant surface under in vivo conditions is a key step for osseointegration that helps to achieve a direct bone-implant bonding. Based on the hypothesis that the formation of this HA layer can also be reproduced in vitro, immersion test in a Simulated Body Fluid (SBF) was proposed and widely used as an in vitro medium to evaluate the Apatite Forming Ability (AFA) of a material, used as an indicator of its bioactivity in vivo. In view of the limitations of the current SBF, carbonate-buffered SBFs were proposed and the effect of proteins on HA formation was investigated using several titanium-based surfaces in comparison with the current SBF (ISO 23317). The presence of bovine serum albumin (BSA), strongly inhibits the formation of HA in conventional SBF on alkaline-etched titanium with a known in vivo bioactivity, whereas HA is still observed in the case of carbonate-buffered SBFs. The inhibitory effect is also found to be concentration-dependent. The insignificant decrease in solution pH and free calcium concentration due to the addition of BSA suggests other causes, such as surface adsorption, for the inhibitory effect. TiO2 rutile powder was also studied and used to investigate the effect of small amino acids on the nucleation and growth of HA. It was found that at a concentration of 10 mM, the amino acids studied including L-Alanine, L-Serine, L-Arginine, L-Cysteine and L-Lysine had little effect on HA growth. Further studies using non-polar L-Alanine and polar L-Serine revealed a stronger effect from L-serine, which is also concentration-dependent. A new, fast in vitro method based on calcium titration is proposed for the evaluation of in vivo bioactivity. In this method, calcium ions are progressively added to a phosphate solution in contact with the test material until the nucleation of HA occurs. The degree of supersaturation of the solution required for the nucleation is used as an indicator of the bioactivity. Using four titanium-based surfaces, same conclusions were obtained compared to the SBF test. However, this method provides a quantitative result in a matter of a few hours. The bioactive materials tested were observed not only to accelerate nucleation but also to change the crystallization pathway. The conclusions drawn from this innovative method were corroborated by in vitro cell culture tests and in vivo animal experiments on a sheep model conducted by other partners of the project. High-resolution in situ techniques were used trying to investigate the mineralization processes. Cryo-TEM revealed the existence of nanometer-sized species in metastable Tris-buffered SBFs. The crystallization process in highly supersaturated solutions was captured in situ by liquid phase TEM. The single crystal rutile (110) surface was found to show a very low AFA. On the contrary, TiO2 powder with a mixture of rutile and anatase was shown to induce HA formation on its surface. In situ AFM revealed both a direct and an indirect pathway to crystalline calcium phosphate species, highlighting the complexity of the process of heterogeneous nucleation of calcium phosphate on bioactive surfaces

Direct access to macroporous chromium nitride and chromium titanium nitride with inverse opal structure

We report a facile synthesis of single-phase, nanocrystalline macroporous chromium nitride and chromium titanium nitride with an inverse opal morphology. The material is characterized using XRD, SEM, HR-TEM/STEM, TGA and XPS. Interconversion of macroporous CrN to Cr2O3 and back to CrN while retaining the inverse opal morphology is also demonstrated

Rapid evaluation of bioactive Ti-based surfaces using an in vitro titration method

The prediction of implant behavior in vivo by the use of easy-to-perform in vitro methods is of great interest in biomaterials research. Simulated body fluids (SBFs) have been proposed and widely used to evaluate the bone-bonding ability of implant materials. In view of its limitations, we report here a rapid in vitro method based on calcium titration for the evaluation of in vivo bioactivity. Using four different titanium surfaces, this method identifies that alkaline treatment is the key process to confer bioactivity to titanium whereas no significant effect from heat treatment is observed. The presence of bioactive titanium surfaces in the solution during calcium titration induces an earlier nucleation of crystalline calcium phosphates and changes the crystallization pathway. The conclusions from this method are also supported by the standard SBF test (ISO 23317), in vitro cell culture tests using osteoblasts and in vivo animal experiments employing a pelvic sheep model

Adaptive Neural Control for an Uncertain 2-DOF Helicopter System with Unknown Control Direction and Actuator Faults

In accordance with the rapid development of smart devices and technology, unmanned aerial vehicles (UAVs) have been developed rapidly. The two-degree-of-freedom helicopter system is a typical UAV that is susceptible to uncertainty, unknown control direction and actuator faults. Hence, a novel adaptive neural network (NN), fault-tolerant control scheme is proposed in this paper. Firstly, to compensate for the uncertainty, a radial-basis NN was developed to approximate the uncertain, unknown continuous function in the controlled system, and a novel weight-adaptive approach is proposed to save on computational cost. Secondly, a class of Nussbaum functions was chosen to solve the unknown-control-direction issue to prevent the effect of an unknown sign for the control coefficient. Subsequently, in response to the actuator faults, an adaptive parameter was designed to compensate for the performance loss of the actuators. Through rigorous Lyapunov analyses, the designed control scheme was proven to enable the states of the closed-loop system to be semi-globally uniformly bounded and the controlled system to be stable. Finally, we conducted a numerical simulation on Matlab to further verify the validity of the proposed scheme