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Based on the adhesion mechanism of polydopamine, the mussel-inspired hydrogel was prepared on the surface of the Ti6Al4V (Ti) with polydopamine (PDA), polyvinyl alcohol (PVA), hydroxyapatite (HA) and polyacrylic acid (PAA) as raw materials in this study, and the Ti-hydrogel artificial cartilage material was constructed. The hydrogel exhibited a tensile strength of 11.76 MPa, an elongation of 988.76%, and a creep deformation of only 0.035 mm under a 20 N load. The friction coefficient of the Ti6Al4V-hydrogel (Ti-hydrogel) artificial cartilage material decreased and the friction performance was improved. After the substrate was modified by the PDA, the bonding strength of the substrate to the hydrogel up to 6.64 MPa. Therefore, the mussel-inspired hydrogel is an ideal high-strength biomimetic cartilage material.

TiO 2 films of different thickness were prepared with the additives of acetylacetone (ACAC) and diethanolamine (DEA), respectively. The results showed that not only the additives but also the film thickness affected the optical properties, surface roughness, absorption and laser-induced damage threshold (LIDT) of TiO 2 films. The LIDT of the film with DEA was higher than that with ACAC, which was attributed to the lower defect density. With the film thickness increase, the significant decrease in LIDT of the film with ACAC was mainly due to the reduced band gap. It indicated that the amount of ACAC or the film thickness should be reduced as much as possible for preparing high LIDT TiO 2 films. After laser damage, the films with ACAC showed cracks, whereas the films with DEA showed spalling. The difference between the damage morphologies was discussed in details.

Superhydrophobic nano Cu/Al 2 O 3 Ni–Cr composited coating with a low adhesive force was deposited onto the Q345 carbon steel via electro-brush plating. Surface morphologies of nano Cu/Al 2 O 3 Ni–Cr composited coating were investigated by scanning electron microscope (SEM). Chemical compositions were characterized by energy dispersive spectroscopy (EDS). First of all, by adjusting different process parameters such as working voltage, relative velocity, Cu particles concentration and plating time, we obtain the most optimal parameters: working voltage is 15 V, relative velocity is 4.8 m/min, Cu particles concentration is 5 g/L and plating time is 60 s. Under the best process parameters, the water contact angle reaches to 156° and a sliding angle is less than 2° on the nano Cu/Al 2 O 3 Ni–Cr coating. Then the mechanism of the superhydrophobic and low adhesion characteristic of this surface were explained by Cassie's model. Low adhesive force can be characterized by max rebound height of water droplet. As a result, to achieve low adhesive surface it is necessary to decrease the fraction of the solid/liquid interface under the water droplet. Finally the coating was proved to have an excellent self-cleaning performance.

In this study, Ta 2 O 5 sol was synthesized from TaCl 5 precursor, and its time dependence of the viscosity, particle size distribution and photoluminescence spectra were studied. Then, Ta 2 O 5 films were prepared using this sol and were succeeding annealed at different temperatures without carbonization and cracks. It was found that the films had good properties such as high transparency, small absorption and high laser-induced damage threshold (LIDT). The LIDT decreased with the increase of the annealing temperature probably due to the acetylacetone in the films. The laser-induced damage morphologies of the films after annealing were different. With the annealing temperature increase, the dominant factor of the laser-induced damage transformed gradually from the stress to the thermal. According to the LIDT and damage morphologies, a structure evolution model of the films annealed at different temperatures was proposed.

Ta2O5 films deposited by ion beam sputtering were post-treated with different methods. The optical properties, microstructures, surface morphologies, absorption and laser-induced damage threshold (LIDT) at 1064 nm and 12 ns of the films were comparatively studied. Annealing conduced to larger changes of optical transmittance and surface morphologies whereas it led to smaller changes of absorption and LIDT than laser conditioning. As it was shown, all the three post-treatment methods in this study were beneficial to the laser damage resistance of the films, yet the details of the defect elimination caused by these methods were different. A defect evolution model was proposed, which revealed the different effects of post-treatment methods on the defect repair of the films. The highest LIDT achieved by the combination of annealing and laser conditioning was due to their complementary effect which resulted in the lowest defect density and the smallest defect size of the film.

High laser-induced damage threshold (LIDT) Ta 2 O 5 films were prepared by the sol–gel method using TaCl 5 as a new precursor. The optical properties, surface morphologies, chemical composition, absorption and LIDT of the films were investigated. The results showed that the transparent and homogenous Ta 2 O 5 films had small surface roughness, low absorption and high LIDT even with large number of layers. The maximum LIDT at 1064 nm and 12 ns of the films was 24.8 J/cm 2 . The ion chromatograph and Fourier transform infrared spectrum were used to reveal the functions of the addition of H 2 O 2 in the sol formation. It was shown that H 2 O 2 had two important functions, which were the decrease of Cl element content and the rapid generation of tantalum oxide. The high LIDT achieved was mainly due to the nearly free of defects in the films.

A third-order non-autonomous memristor-based FitzHugh-Nagumo (FHN) circuit is proposed through introducing a memristor emulator to realize the nonlinear function of the membrane voltage in the FHN model. This memristive FHN model possesses two slow time-scales, i.e. the external forcing current and the memristor inner state variable, and quasi-periodic, periodic bursting, and periodic behaviors are numerically revealed. The mechanism of the two-slow-time-scale-dependent periodic bursting dynamics is explored through using graphical method. Moreover, with the evolution of time, the equilibrium point of the memristive FHN circuit evolves between no equilibrium and line equilibrium point, and the stabilities of the line equilibrium point are highly related to the memristor initial condition. Consequently, the exhibited dynamics can be adjusted not only by tuning the system parameters, i.e. the forcing amplitude and frequency, but also by changing the memristor initial condition. The coexistence of multiple bifurcation modes are also found in some system parameter regions. Finally, a simulated circuit model is designed and PSIM circuit simulations are performed to confirm the numerical simulations. The presented memristive FHN circuit can enrich the family of memristor-based FHN circuits and their exhibited firing dynamics.

Graphite-like carbon (GLC) coatings were fabricated by unbalanced magnetron sputtering technique. Raman spectroscopy and XPS analysis confirmed the nanostructured GLC coatings have high concentration of sp2-hybridized carbon. HRTEM analysis demonstrated that the microstructure of GLC coatings was composed of nanocrystalline graphite, fcc-center cubic (fcc) diamond and amorphous carbon. The tribological performance of GLC coatings combined with five types of liquid lubricants (PFPE, PAO, SO, IL and MAC) has been investigated under the conditions without and with sand-dust particles. Experimental results showed that the obtained excellent low friction and wear-resistance was attributed to the synergistic effect of liquid lubricants and GLC coatings. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.

Ta 2 O 5 , ZrO 2 and HfO 2 films are deposited on BK7 substrates by electron beam evaporation method. The effects of oxygen deficiency on the optical properties and laser-induced damage threshold (LIDT) are investigated by the combination of experimental methods and first principles calculations. The results show that the oxygen deficiency weakens the transmittance, whereas it enhances the absorption of all the films. Once the oxide vacancy appears, the band gaps decrease greatly, which seriously decrease the LIDT. The calculated negative vacancy energies indicate that, when the oxygen vacancy exists, Ta 2 O 5 is most easily to be damaged, next is ZrO 2 and the last is HfO 2 . It is consistent with the LIDT results that Ta 2 O 5 increases 64.8%, ZrO 2 increases 19.4% and HfO 2 increases 12.9% when the oxygen vacancy is eliminated.

Combination of solid and liquid lubricants to meet emission or environmental requirements of future tribological systems while providing the levels of desired friction and wear performance have received considerable research attention in the near term. The aim of the present work was to investigate the tribological behavior of oil-lubricated (PAO, PFPE, SO, IL and MAC) DLC coated surfaces under the conditions without and with sand-dust particles. The effects of applied load, frequency, and sand-dust particles on the tribological performance of DLC coating were systemically studied. The analysis results showed that solid–liquid lubricating coatings including SO and IL exhibited excellent anti-friction (∼0.026) but relative poor wear-resistance performances under the conditions without and with sand-dust environments. But for PFPE and PAO, they demonstrated the worst tribological behaviors with high friction coefficient and wear rates. The added sand-dust particles lead to the wear rates to the one order of magnitude large than that without sand-dust conditions for all the selected liquid lubricants. The viscosity, contact angle and work of adhesion played an important part in affecting the tribological performances. The lubrication regimes in Stribeck curve for the five kinds of liquid lubricants were affected obviously by the sand-dust particles in different way. The formed transfer films on the coating surface and pin have much influence on the tribological behavior and the transition between lubrication regimes.

Solid lubricant films have received considerable research attention in the last decades owing to their remarkable improved tribological characteristics. In this paper, the abrasive wear behaviour of five types of solid lubricant films (magnetron-sputtered diamond-like carbon, magnetron-sputtered molybdenum disulfide, bonded molybdenum disulfide, bonded polytetrafluoroethylene and bonded graphite) in sand-dust environment has been investigated using a reciprocating pin-on-disc test rig. The effects of applied load, amount of sand and particle size on the tribological performance of these films were systemically studied. Experimental results show that magnetron-sputtered films give excellent anti-friction and wear-resistance performances under sand-dust environments compared to bonded solid lubricant films. The significant differences of surface roughness, hardness, microstructure and intrinsic lubricating property directly lead to the different tribological performances and worn morphology. The formed composite transfer layer plays a vital role in reducing friction and wear due to its anti-friction and shielding action of the film surface from the hard metal asperities. Two main abrasive wear mechanisms (three-body rolling wear and two-body grooving wear) occur simultaneously in the tribological process under sand-dust environments. A transfer layer-hardening composite wear modeling was established to further explain the anti-wear mechanisms and friction-reducing capacity of these solid lubricant films under sand-dust environments.

Magnetization force caused by a magnetic field gradient (F m ) is a body force and can cause buoyancy. We numerically simulate the natural convection arising from the depletion of protein concentration around a growing protein crystal when an upward magnetization force acts on the solution. The numerical predictions reveal that an upward magnetization force can damp convection. When a magnetic field gradient μ 2 0 H(dH/dz) = -685 T 2 /m is applied, the maximum flow velocity is reduced by about 50% and the velocity in the vicinity of the crystal is reduced by about 24%. Due to the low electric conductivity of the solution, the contribution of the Lorentz force is negligible. When μ 2 0 H(dH/dz) = -1370 T 2 /m, the upward magnetization force (F m ρg) damps convection completely. Our study shows a new method of controlling convection in the process of protein crystal formation.

An inhomogeneous magnetic field exerts a magnetization force on all materials, including electrically conducting and non-conducting fluids. A recent experiment demonstrated that this force can enhance or suppress convection in a paramagnetic aqueous solution heated from either below or above. In this paper, to clarify the mechanism of the observed phenomena, we numerically simulated the effect of a vertical magnetic field gradient on thermal convection in paramagnetic fluids. These simulated results agree with experimental observations. Our study shows that the magnetic buoyancy force has potential applications for controlling convection and enhancing the heat transfer efficiency in either electrically non-conducting or low-conducting fluids.

We numerically simulated sedimentation flow and buoyancy-driven convection during protein crystal growth in which the crystal size changes from 0.1 to 100 μm and clarified how gravitational fields affect the various stages of crystal growth. When the crystal size is below a few μm, most crystals are suspended in solution and solute transport near the crystal is mainly limited by diffusive transport. When the crystal size is above a few μm, sedimentation flow dominates near the crystal, but solute transport is still mainly limited to diffusive transport. When crystals grow to several μm, most of them settle to the bottom and continue to grow there. When the size is above several 10 μm, buoyancy-driven convection dominates solute transport near growing crystals at the bottom, and the contribution from buoyancy induced convection to crystal interfacial growth rate appears on Earth in comparison with that under zero-gravity condition and increases with increasing crystal size. During the whole crystal growth process, the crystal interface growth rate shows the tendency to decrease as the crystal grows under both normal and zero-gravity conditions. Moreover, our simulations of crystal sedimentation are consistent with experimental observations of lysozyme crystallization that most crystals settle to the bottom when their size reaches several μm.

We present numerical simulations of the velocity and temperature distributions of a nonconducting fluid (water) heated from below in the presence of an imposed, nonuniform magnetic field, generated with a solenoid-type magnet. The vertically placed magnet induces horizontal and vertical magnetic forces due to the gradient of magnetic strength, and the horizontal force is found to play an important role to damp natural convection. When an imposed magnetic field of strength H 0 in the middle of the magnet, is less than a critical value, H 0c , the damping effect increases with increasing H 0 . For H 0 > H 0c , natural convection is completely replaced by convection induced by the magnetic field. Our results indicate a novel method to control convection of nonconducting fluids, especially in crystal formation processes.