Biomimetic deposition of hydroxyapatite on the surface of silica thin film covered steel tape

The biomimetic deposition of hydroxyapatite (HA) on the surface of SiO₂ thin film coated metal substrates was developed and investigated.     

Staying on your feet: the effectiveness of posture and handles in counteracting balance perturbation

Stairways, public transport and inclined walkways are often considered as sites with higher likelihood of falls due to a sudden loss of balance. Such sites are usually marked with warning signs, equipped with non-slip surfaces and handles or handrails to avert or decrease this likelihood. Especially, handles are supposed to provide additional support in cases of a sudden loss of balance. However, the mechanisms of using handles for balance at different heights are not yet fully disclosed. We simulated full body perturbations by applying an anterior force to the waist and investigated effectiveness and mechanisms of balance recovery in five different postures: step stance and normal stance with or without holding handles at different heights. Results indicate that both step stance and holding handles at different vertical positions sufficiently assist balance recovery, compared to normal stance. While there was no significant effect of handle in CoM displacement, the shoulder height handle required the lowest handle force, indicating a difference in using the handle.

Practitioner summary: To investigate handle use for balance recovery, we perturbed healthy young adults in different standing positions. Even though the use of different handles had a similar effect, the lowest forces were exerted on the shoulder height handle indicating a preferred handle position for balance recovery.

Abbreviation: AP: antero-posterior; CNS: Central nervous system; CoM: Center of Mass; CoMmax: Maximal displacement of the center of mass; CoP: Center of pressure; FHmax: Maximal resultant force exerted on the handle; hFHmax: Maximal horizontal force exerted on the handle; vFHmax; Maximal vertical force exerted on the handle; M1-M8: Perturbation force magnitude     

COUPLED PROBLEM OF THERMODIFFUSION IN VISCOELASTIC BODIES

This paper deals with the effect of the process of thermodiffusion in viscoelastic bodies. The basic linear coupled equations of the problem are derived, and possibilities for their simplification are indicated. A method for their solution is demonstrated and then applied to the case of a viscoelastic layer.     

Finite difference solution of the one-dimensional advection–diffusion equation with variable coefficients in semi-infinite media

One-dimensional advection–diffusion equation with variable coefficients in semi-infinite media is solved using explicit finite difference method for three dispersion problems: (i) solute dispersion along steady flow through inhomogeneous medium, (ii) temporally dependent solute dispersion along uniform flow through homogeneous medium, and (iii) solute dispersion along temporally dependent unsteady flow through inhomogeneous medium. The continuous point source of uniform nature is considered at the origin of the medium. Results are compared to analytical solutions reported in the literature and good agreement was found. We have shown that explicit finite difference method is effective and accurate for solving advection–diffusion equation with variable coefficients in semi-infinite media, which is especially important when arbitrary initial and boundary conditions are required.     

Deposition of Zn–Co by constant and pulsed current

The initial stages of both Zn–Co and Zn electrodeposition were investigated by electrochemical quartz crystal microgravimetry (EQCM). The initial electrode mass growth, determined under both pulse and constant current conditions, was much higher than predicted by Faraday's law. This was explained in terms of the precipitation of scarcely soluble compounds of zinc on an electrode surface. The EQCM data confirm that the hydroxide suppression mechanism explains the anomalous Zn and Co codeposition. A nonuniform adsorption of brightener (benzalaceton) on the profiled surface was concluded on the basis of plating distribution investigations. The additive adsorbs to a greater extent on the surface projections.     

Mechanical Properties and Dislocation Structure Evolution in Ti6Al7Nb Alloy Processed by High Pressure Torsion

Ultrafine-grained biocompatible Ti-6Al-7Nb alloy was produced by high pressure torsion (HPT). Lattice defects—vacancies and dislocations—investigated by positron annihilation spectroscopy, observations by scanning electron microscopy, and microhardness evaluation are linked to the strain imposed by different numbers of HPT revolutions and to the distance from the specimen center. Positron annihilation spectroscopy showed significant increase of dislocation density and concentration of vacancy clusters after ½ of the HPT revolution. Microhardness increases by 20 pct with increasing strain, but it is heterogenous due to duplex microstructure. The heterogeneity of the microhardness increases with increasing strain, suggesting that a heavily deformed and fragmented α + β lamellar microstructure is more hardened than primary alpha grains. The defect structure is homogenous after ½ HPT revolution, while the microhardness becomes homogenous after 3 HPT revolutions only.     

Synthesis and characterization of hafnium carbide fine powders

Hafnium carbide powder was synthesized by sol–gel polycondensation of hafnium chloride with citric acid. The starting materials were dissolved in water and mixed homogeneously on a hot plate until precursor gel was formed. Pyrolysis of this gel resulted in monoclinic hafnia which after subsequent heat treatment transformed into hafnium carbide. The obtained materials were analyzed by means of X-ray diffraction and scanning electron microscopy. The results showed that the obtained carbide powders were composed of nearly equiaxed particles with narrow size distribution. Characterization by nitrogen adsorption showed that the obtained powders were micro- and mesoporous materials with high specific surface area.     

Constructing control rules for a dynamic system: probabilistic qualitative models,lookahead and exaggeration

Dynamic systems have sometimes to be controlled in circumstances that are very inconvenient for classical control methods. In such cases, use of qualitative controllers seems to be a promising alternative, as they can be designed without having an exact mathematical model. A method for synthesizing control rules is presented, in which a probabilistic qualitative model is used together with a decision strategy that takes into account the results of qualitative simulation. As a case study, the problem of the inverted pendulum control is considered. By combining the model simulation lookahead and a decision criterion, an interesting phenomenon of ‘exaggerated simulation’ has emerged. Experimental results show that in certain cases, using an exaggerated force in the process of simulation considerably improves the performance of generated control rules. The exaggeration helps to detect some trends of the system's behaviour that would otherwise have remained hidden. Experiments and mathematical analysis show that the improvement due to the exaggeration is comparable to that achieved by a deeper lookahead in the state transition graph.     

Experimental design for parameter estimation of two time-scale model of photosynthesis and photoinhibition in microalgae

A method for parameter estimation of two time-scale model of photosynthesis and photoinhibition is presented.