Settlement and growth of copper-tolerantEctocarpus siliculosus (Dillw.) Lyngbye on different copper-based antifouling surfaces under laboratory conditions

The first paper of this series reports the development of an algal culture system suitable for monitoring marine antifouling characteristics of copper-based alloy materials under standardized laboratory conditions, using the marine-fouling algaEctocarpus siliculosus. The physical and chemical conditions necessary for both the formation of corrosion films typical of those formed at sea and vigorous growth of the alga in the incubating medium were investigated using copper-nickel 90/10 as a test material. Preincubation of sample plates in seawater for up to 140 days proved necessary in order to generate passive corrosion films which continued to release copper at sufficiently low rates to permit algal growth, spore production and settlement. Seawater sterilization and addition of supplementary algal nutrients did not significantly affect the equilibrium rates of copper loss or the composition of the corrosion films. Aeration of the medium accelerated the attainment of this equilibrium but the addition of Fe²⁺ ions had no effect. Surface preparation and orientation of sample plates had little effect on rates of copper loss. Corrosion rates recorded in these trials compare favourably with those reported for similar materials exposed at sea.     

Fatigue crack growth of AA2219 under different aging conditions

The fatigue crack growth of commercial AA2219 has been examined under different aging treatments, namely, naturally aged (NA), under aged (UA), peak aged (PA) and over aged (OA) conditions. From the near threshold stress intensity range (ΔK_NTH), the alloy in the NA condition is found to have the highest resistance to fatigue crack initiation. The crack growth rate increases and the near threshold stress intensity range decreases with advancing aging. This observation is found to be consistent with lower levels of crack closure and decreasing levels of tortuosity in crack path for PA and OA tempers. The inhomogeneous transcrystalline slip in the UA condition results in the slower crack growth at low stress intensity range (ΔK). The fracture morphology changes from crystallographic facets near the threshold region to clearly developed ductile striations in the Paris power-law regime to microvoid coalescence in the high ΔK regions.     

Superhydrophobicity of natural and artificial surfaces under controlled condensation conditions

In this paper, we have comparatively investigated the stability of superhydrophobic behaviors of fresh and biomimetic lotus leaf surfaces under controlled water condensation conditions. The binary micro/nano structures of the superhydrophobic surfaces are observed with electron micrographs. Contact and sliding angles are evaluated by syringing water droplets on the substrates with surface temperatures and humidity precisely controlled between -10 and 30 °C, and RH = 10, 30, 60, and 90%. According to the calculations on the solid-liquid contact area fraction in different environmental conditions based on a micro/nano binary structure model, the effects of condensed water on superhydrophobic surfaces are assessed quantitatively. Both the calculated and experimental results indicate that the temperature difference between surface temperature and the dew point during measurement is essential to the occurrence of water condensation while the effect of condensation on the surface wettability also depends on the topology of hierarchical structured surfaces. The loss of water repellency that usually appears on the artificial superhydrophobic surface under low temperature and high humidity conditions is proved to be reversible, showing a bidirectional transition of the equilibrium state between Wenzel and Cassie-Baxter.     

Fatigue crack growth behaviour of gamma base titanium aluminides under different loading conditions

Static and cyclic fatigue crack growth behaviour of gamma base titanium aluminides with three different microstructures were investigated. Influence of cyclic test frequency on fatigue crack growth behaviour was also studied at room temperature under a controlled humidity condition. The crack growth behaviour both under static and cyclic loading was strongly influenced by the microstructure. The threshold stress intensity and crack growth behaviour under cyclic loading were much inferior than that under static loading indicating the ‘true-cyclic fatigue’ effect exhibited in gamma base titanium aluminides. No significant effect of test frequency on the crack growth behaviour was observed for the equiaxed and duplex microstructure materials.     

Studying the growth of carbon nanotubes on carbon fibers surface under different catalysts and electrochemical treatment conditions

A special electrochemical anodic oxidation (EAO) method was applied to modify the surface of carbon fibers (CFs) with fatty alcohol polyoxyethylene ether phosphate (O₃P), triethanolamine (TEA), fatty alcohol polyoxyethylene ether ammonium phosphate (O₃PNH₄), and ammonium bicarbonate (NH₄HCO₃) used as the electrolyte respectively. Then different catalysts, including Ni, Co, and Cu, were used to catalyze the growth of carbon nanotubes (CNTs) on the surface of CFs. The variation regulation of structure and property of CNTs on CFs surface was investigated by different methods. The results showed that the optimal effect of surface modification of CFs was achieved when O₃PNH₄ served as an electrolyte and the optimal electrochemical treatment intensity (ETI) was 100C/g. Also, with temperature variety, there are different microstructure changes for CNTs that adopt different catalysts. Through the experiment, a uniform catalyst coating was obtained on the surface of CFs after reduction process, which laid the foundation for the growth of uniform and regular CNTs.     

The microscopic structure of adsorbed water on hydrophobic surfaces under ambient conditions

The interaction of water vapor with hydrophobic surfaces is poorly understood. We utilize graphene templating to preserve and visualize the microscopic structures of adsorbed water on hydrophobic surfaces. Three well-defined surfaces [H-Si(111), graphite, and functionalized mica] were investigated, and water was found to adsorb as nanodroplets (～10-100 nm in size) on all three surfaces under ambient conditions. The adsorbed nanodroplets were closely associated with atomic-scale surface defects and step-edges and wetted all the hydrophobic substrates with contact angles<～10°, resulting in total water adsorption that was similar to what is found for hydrophilic surfaces. These results point to the significant differences between surface processes at the atomic/nanometer scales and in the macroscopic world.     

Development of crumb rubber reinforced bituminous binder under laboratory conditions

Bituminous binders are widely used in the construction of flexible pavements. However, in some applications, the performance of conventional binders is not considered to be satisfactory. Reinforcing these binders with selected polymers prevents premature failure of a pavement by improving the properties of the binder. Another source of reinforcement comes from crumb (ground) rubber produced from waste tyres. After they have been worn-out during their limited service life, millions of used tyres are discarded every year and are hauled to a dump. The fatigue resistance at temperatures below normal service temperatures (25°C), one of the key engineering properties of crumb rubber reinforced binders, has been found to be lower than that of neat binders. This paper is concerned with the development of a rubber reinforced binder. It was shown that the binder has the potential to be used as an all-weather wearing course in flexible roads, whilst at the same time recycling a considerable amount of waste rubber.     

The generation of free concentrated air vortexes under laboratory conditions

Video filming is used to investigate the dynamics of free concentrated vortexes which arise over a heated underlying surface as a result of unstable stratification of air. Various types of trajectories of motion of the base of vortex structures are revealed. Parameters are analyzed such as the temperature of underlying surface, the region of emergence of vortex structures, the lifetime, and the direction of motion, which define the type of trajectory of vortex base.     

A program of equivalent tests for turbine blades under laboratory conditions

A method of conducting equivalent tests of turbine blades under laboratory conditions, which ensures reproduction of the operational pattern of the loading in its most heavily loaded components, is proposed. A method for construction of the equivalent-test program is analyzed on a stage-I turbine blade of one of the high-temperature aviation gas-turbine engines.Translated from Problemy Prochnosti, No. 7, pp. 89–92, July, 1991.     

Effects of different modified underlayer surfaces on growth and optical properties of InGaN quantum dots

InGaN/GaN quantum dots were grown on the sapphire (0 0 0 1) substrate in a metalorganic chemical vapor deposition system. The morphologies of QDs deposited on different modified underlayer (GaN) surfaces, including naturally as grown, Ga-mediated, In-mediated, and air-passivated ones, were investigated by atomic force microscopy (AFM). Photoluminescence (PL) method is used to evaluate optical properties. It is shown that InGaN QDs can form directly on the natural GaN layer. However, both the size and distribution show obvious inhomogeneities. Such a heavy fluctuation in size leads to double peaks for QDs with short growth time, and broad peaks for QDs with long growth time in their low-temperature PL spectra. QDs grown on the Ga-mediated GaN underlayer tends to coalesce. Distinct transform takes place from 3D to 2D growth on the In-mediated ones, and thus the formation of QDs is prohibited. Those results clarify Ga and In's surfactant behavior. When the GaN underlayer is passivated in the air, and together with an additional low-temperature-grown seeding layer, however, the island growth mode is enhanced. Subsequently, grown InGaN QDs are characterized by a relatively high density and an improved Gaussian-like distribution in size. Short surface diffusion length at low growth temperature accounts for that result. It is concluded that reduced temperature favors QD's 3D growth and surface passivation can provide another promising way to obtain high-density QDs that especially suits MOCVD system.     

Properties of 13KhMF steel after operation and degradation under the laboratory conditions

The influence of cooling rate in the process of thermal treatment on the formation of the microstructure of 13KhMF heat-resistant steel is investigated. The relationships between the microstructure, strength characteristics, crack-resistance characteristics, and creep resistance of the material are determined. The transformations of the structure are modeled by the changes in the duration of tempering. The bainitemartensite structure is characterized by the best combination of properties and the largest period of transformation of the structure. The comparison of the results of laboratory and long-term in-service degradation and their influence on the structure, strength, and crack-resistance characteristics shows that they are similar.     

Microstructural characteristics of HPC under different thermo-mechanical and thermo-hydraulic conditions

The microstructural characteristics of high performance concrete (HPC) samples were analysed using scanning electronic microscopy (SEM) and X-ray diffraction (XRD) following thermo-hydraulic and thermo-mechanical testing. The relationship between engineering behaviour (transport and mechanical properties) and microstructure for HPC was then analysed. The failure mechanism of HPC under thermo-mechanical conditions was also discussed. Lower porosity, a higher content of calcium silicate hydrate (C−S−H) and a lower content of the crystalline-phase calcium hydroxide (CH) in both the cement paste and transition zone all exerted a positive influence on the transport and mechanical properties of HPC. By increasing temperature to 200°C, the evaporation of water led to an increase in capillary porosity as well as to a reduction in the cohesive forces between C−S−H layers, which cause degradation of the concrete’s transport and mechanical properties. Microcracking under thermo-mechanical conditions proved to be the main failure mechanism of HPC.

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Résumé Les propriétés microstructurelles des échantillons de béton à haute performance (BHP) ont été analysées par microscopie électronique à balayage (MEB) et diffraction X, suite aux tests thermo-hydrauliques et thermo-mécaniques. Les relations entre le comportement en matière d’ingénierie du matériau (propriétés mécaniques et de transfert) et les microstructures de BHP ont été ensuite évaluées. Le mécanisme de rupture du BHP sous des conditions thermo-mécaniques a aussi été abordé dans ce papier. Un niveau de porosité plus faible, une plus grande concentration en silicate de calcium hydraté (C−H−S) et une concentration plus faible de l’hydroxyde de calcium (CH) à la fois dans la pate de ciment et dans la zone de transition ont joué une influence positive sur les propriétés mécaniques et de transfert des BHP. En élevant la T° à 200°C, l’évaporation de l’eau a conduit à une augmentation de la porosité capillaire de même qu’à une réduction des forces de cohésion entre les couches de H−S−C, engendrant une dégradation des propriétés mécaniques et de transfert du béton. Les microfissures sous l’effet des conditions thermo-mécaniques se sont avérées être la cause principale de dégradation mécanique du BHP.

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Editorial Note. Prof. Z. Li is a RILEM Senior Member. Prof. G. Ballivy and Prof. K. Khayat work at the CRIB—University of Sherbrooke, a RILEM Titular Member.     

Modification of human polymorphonuclear neutrophilic cell (PMN)-adhesion on biomaterial surfaces by protein preadsorption under static and flow conditions

Biomaterials induce a specific reaction after implantation in the human body. This reaction depends on the chemical and physico-chemical properties of the material as well as on the site and type of implantation. We have used a dynamic model, the parallel-plate flow-chamber, to examine the interactions of different biomaterials with polymorphonuclear neutrophilic cell (PMN) and how these interactions are influenced by protein preadsorption. Our results clearly show that for hydrophobic materials, glass and PE, which induce a prominent adhesion of PMN, the mixture of albumin and fibrinogen induces the best inhibitory effect. On hydrophilic biomaterial surfaces, untreated TCPS and PC-coated TCPS, reveal only a minor influence of adsorbed proteins on PMN adhesion because of a primary low adhesive surface for PMN and proteins as well. Human citrated plasma leads only to a slight inhibition of PMN adhesion. On the hydrophobic materials, glass and PE, bovine serum albumin (BSA) had the best anti-adhesive potential with respect to PMN. The coating using phosphorylcholine is an excellent surface modification to prevent PMN-adhesion and protein adsorption. The results of our experiments suggest that investigations under static and flow conditions are also needed to determine the influence of protein adsorption on other relevant blood cell populations, for example, platelets and monocytes.     

Modification of human platelet adhesion on biomaterial surfaces by protein preadsorption under static and flow conditions

Biomaterial-induced thrombosis remains one of the main complications of vascular implant devices. Preadsorbed proteins on the biomaterial/blood interface will modify the adhesion and activation of platelets (PTLs) during the initial contact-phase. Our results clearly show that PTL-adherence on biomaterials is influenced not only by protein preadsorption, but also by flow conditions. The covalent coating of TCPS and glass by phosphorylcholine (PC) induces a significant decrease of PTL adhesion but leads to a slight, but nevertheless significant activation of PTL, which was detected by the induction of P-selectin expression using FACS analysis. Methodologically, the visualization of PTL adhesion gave more reliable results for measurement of PTL adhesion than the cell-enzyme immunoassay (EIA) for P-selectin. Human citrated plasma caused an inhibition of PTL. It is probable, that the contained sodium citrate may inhibit PTL adhesion by its calcium ion-binding capacity. The flow experiment as dynamic system is in our view absolutely essential for the evaluation of biomaterials for vascular prosthesis, and is in accordance with the international standards. The results of the experiments also suggest that investigations under static and flow conditions are needed to determine the influence of protein adsorption on mixed blood cell populations, for example, on PTL and PMN mixtures/co-cultures in order to achieve a better simulation of the in vivo situation.     

Radiometric calibration of SUMER: refinement of the laboratory results under operational conditions on SOHO

The radiometric calibration of the solar telescope and spectrometer SUMER was carried out in the laboratory before delivery of the instrument for integration into the SOHO (Solar and Heliospheric Observatory) spacecraft. Although this effort led to a reasonable coverage of the wavelength range from 53.70 to 146.96 nm, uncalibrated portions of the sensitivity curves remained before SUMER became operational in early 1996. Thereafter it was possible to perform extrapolations and interpolations of the calibration curves of detector A to shorter, longer, and intermediate wavelengths by using emission line pairs with known intensity ratios. The spectra of the stars alpha and rho Leonis were also observed on the KBr (potassium bromide) photocathode and the bare microchannel plate (MCP) in the range from 120 to 158 nm. In addition, the sensitivity ratios of the KBr photocathode to the bare MCP were determined for many solar lines as well as the H i Lyman and the thermal continua. The results have been found to be consistent with published laboratory data. The uncertainty is +/-15% (1 varsigma) in the wavelength range from 54 to 125 nm.     

不同元件故障状态下滚动轴承的动态特性研究

为探究局部故障状态下滚动轴承内部动态特性的差异性和相似性,以NU306圆柱滚子轴承为研究对象,利用有限元仿真软件ANSYS/LS-DYNA构建正常以及外圈、内圈和滚动体分别故障时的有限元模型,得到不同故障状态下滚动体的应力特性、振动特性及运动特性。结果表明,当滚动轴承的不同元件发生故障时,故障前端应力均会滞后,后端应力均会提前,其中外圈故障时应力的变化最大;外圈故障时滚动体在经过故障区域期间的振动加速度先减小后增大,内圈和滚动体故障时振动加速度先增大后减小;外圈和滚动体故障时滚动体的公转转速均比理论公转转速小,内圈故障时滚动体的公转转速比理论公转转速大。所构建的有限元模型可用于探究不同元件故障时滚动轴承内部的故障机理,可为进一步研究滚动轴承的承载能力和使用寿命提供有力的分析方法。