Experimental Investigation of Viscosity of Glycerol Based Nanofluids Containing Carbon Nanotubes

The addition of solid nanoparticles to liquids provide significant enhancement of heat transfer and hydrodynamic flow. The viscosity of nanofluids is important for nanofluid transport related to flow dynamics and heat transfer. The aim of the paper is to investigate experimentally the viscosity of nanofluids prepared with glycerol base and nitrogen-doped bamboo shaped multi-walled carbon nanotubes (MWCNTs). The samples are prepared with 0.1, 0.2, 0.5 and 1.0 wt.% MWCNTs. The viscosity of glycerol and MWCNTs nanofluid suspensions are measured at various temperatures and rotational speeds (shear rates). The influence of nanotubes amount, temperature and rotational speed on the viscosity is investigated

Corrosion Behavior of the As-cast and Heat-treated ZA27 Alloy

Corrosion behaviour of the as-cast and heat-treated ZA27 alloy was examined. The alloy was prepared by conventional melting and casting route and then thermally processed by applying T4 heat treatment regime (solutionizing at 370 °C for 3 hours followed by water quenching and natural aging). Corrosion rate of the as-cast and heat-treated ZA27 alloy was determined in 3.5 wt. % NaCl solution through immersion test using both weight loss method and polarization resistance measurements. It was shown that applied thermal treatment resulted in increased ductility of the heat-treated alloy and had a small beneficial effect on the corrosion resistance of ZA27 alloy

Abrasive Wear Resistance of the Iron- and WC-based Hardfaced Coatings Evaluated with Scratch Test Method

Abrasive wear is one of the most common types of wear, which makesabrasive wear resistance very important in many industries. Thehard facing is considered as useful and economical way to improve theperformance of components submitted to severe abrasive wear conditions, with wide range of applicable filler materials. The abrasive wear resistance of the three different hardfaced coatings (two iron‐based and one WC‐based), which were intended to be used for reparation of the impact plates of the ventilation mill, was investigated and compared. Abrasive wear tests were carried‐out by using the scratch tester under the dry conditions. Three normal loads of 10, 50 and 100 N and the constant sliding speed of 4 mm/s were used. Scratch test was chosen as a relatively easy and quick test method. Wear mechanism analysis showed significant influence of the hardfaced coatings structure, which, along with hardness, has determined coatings abrasive wear resistance

Tribological Properties of WC-Co/NiCrBSi and Mo/NiCrBSi Plasma Spray Coatings under Boundary Lubrication Conditions

The tungsten carbide based WC-Co/NiCrBSi (50/50) and molybdenum based Mo/NiCrBSi (75/25) coatings were investigated under boundary lubricated sliding conditions, and their tribological properties were analysed and compared. These two coatings are in service for a long time, but there are very few papers dealing with their tribological properties, especially in lubricated sliding conditions. The NiCrBSi self-fluxing alloy is one of the popularly used materials for thermal sprayed coating, with relatively high hardness, reasonable wear resistance and high temperature corrosion. Tungsten carbide (WC) is one of the most widely used commercial hard coating materials, and is added to the NiCrBSi coating to improve its hardness and wear resistance. Molybdenum (Mo) is added to the NiCrBSi coating to reduce its coefficient of friction, i.e. to improve its dry sliding wear resistance. The results showed that WC-Co/NiCrBSi coating was more wear resistant, but caused higher wear of the counter-body material. Coefficients of friction were similar for both coatings

Experimental investigation and statistical analysis of surface roughness parameters in milling of PA66-GF30 glass-fibre reinforced polyamide

A multi-parameter analysis of surface finish imparted to PA66-GF30 glass-fibre reinforced polyamide by milling is presented. The interrelationship between surface texture parameters is emphasized. Surface finish parameters studied include arithmetic mean deviation of the assessed profile Ra; maximum height of profile, Rt; ten point height Rz; mean width of the profile elements Rsm; skewness of the assessed profile, Rsk and kurtosis of the assessed profile, Rku. The correlation of these parameters with the machining conditions was investigated. By applying analysis of variance and regression analysis to the experimental data close correlation was obtained among certain surface finish parameters and the machining conditions. To facilitate industrial operations full quadratic prediction models were developed for capturing trends for machining quality in advance

The Chlorophyll Catabolite, Pheophorbide a, Confers Predation Resistance in a Larval Tortoise Beetle Shield Defense

Larval insect herbivores feeding externally on leaves are vulnerable to numerous and varied enemies. Larvae of the Neotropical herbivore, Chelymorpha alternans (Chrysomelidae:Cassidinae), possess shields made of cast skins and feces, which can be aimed and waved at attacking enemies. Prior work with C. alternans feeding on Merremia umbellata (Convolvulaceae) showed that shields offered protection from generalist predators, and polar compounds were implicated. This study used a ubiquitous ant predator, Azteca lacrymosa, in field bioassays to determine the chemical constitution of the defense. We confirmed that intact shields do protect larvae and that methanol-water leaching significantly reduced shield effectiveness. Liquid chromatography-mass spectrometry (LC-MS) of the methanolic shield extract revealed two peaks at 20.18 min and 21.97 min, both with a molecular ion at m/z 593.4, and a strong UV absorption around 409 nm, suggesting a porphyrin-type compound. LC-MS analysis of a commercial standard confirmed pheophorbide a (Pha) identity. C. alternans shields contained more than 100 μg Pha per shield. Shields leached with methanol-water did not deter ants. Methanol-water-leached shields enhanced with 3 μg of Pha were more deterrent than larvae with solvent-leached shields, while those with 5 μg additional Pha provided slightly less deterrence than larvae with intact shields. Solvent-leached shields with 10 μg added Pha were comparable to intact shields, even though the Pha concentration was less than 10% of its natural concentration. Our findings are the first to assign an ecological role for a chlorophyll catabolite as a deterrent in an insect defense

The bashful and the boastful : prestigious leaders and social change in Mesolithic Societies

The creation and maintenance of influential leaders and authorities is one of the key themes of archaeological and historical enquiry. However the social dynamics of authorities and leaders in the Mesolithic remains a largely unexplored area of study. The role and influence of authorities can be remarkably different in different situations yet they exist in all societies and in almost all social contexts from playgrounds to parliaments. Here we explore the literature on the dynamics of authority creation, maintenance and contestation in egalitarian societies, and discuss the implications for our interpretation and understanding of the formation of authorities and leaders and changing social relationships within the Mesolithic

The Tri-Trophic Interactions Hypothesis: Interactive Effects of Host Plant Quality, Diet Breadth and Natural Enemies on Herbivores

Several influential hypotheses in plant-herbivore and herbivore-predator interactions consider the interactive effects of plant quality, herbivore diet breadth, and predation on herbivore performance. Yet individually and collectively, these hypotheses fail to address the simultaneous influence of all three factors. Here we review existing hypotheses, and propose the tri-trophic interactions (TTI) hypothesis to consolidate and integrate their predictions. The TTI hypothesis predicts that dietary specialist herbivores (as compared to generalists) should escape predators and be competitively dominant due to faster growth rates, and that such differences should be greater on low quality (as compared to high quality) host plants. To provide a preliminary test of these predictions, we conducted an empirical study comparing the effects of plant (Baccharis salicifolia) quality and predators between a specialist (Uroleucon macolai) and a generalist (Aphis gossypii) aphid herbivore. Consistent with predictions, these three factors interactively determine herbivore performance in ways not addressed by existing hypotheses. Compared to the specialist, the generalist was less fecund, competitively inferior, and more sensitive to low plant quality. Correspondingly, predator effects were contingent upon plant quality only for the generalist. Contrary to predictions, predator effects were weaker for the generalist and on low-quality plants, likely due to density-dependent benefits provided to the generalist by mutualist ants. Because the TTI hypothesis predicts the superior performance of specialists, mutualist ants may be critical to A. gossypii persistence under competition from U. macolai. In summary, the integrative nature of the TTI hypothesis offers novel insight into the determinants of plant-herbivore and herbivore-predator interactions and the coexistence of specialist and generalist herbivores

Thermal cycling behaviour of plasma sprayed nicr-al-co-y2o3 bond coat in thermal barrier coating system

The aim of this study was to investigate the thermal cycling behaviour of NiCr-Al-Co-Y2O3 bond coating in thermal barrier coating (TBC) system with ZrO2-MgO as a top coating. The coatings were deposited by atmospheric plasma spraying (APS) on stainless steel X15Cr13 (EN 1.4024) substrate. The used composite powder NiCr-Al-Co-Y2O3 was mechanically cladded, and the steel substrates were preheated to 160-180 degrees C. The thermal cycling performance of the obtained bond coat and the effect of formed complex ceramic oxides of the Al2O3-Y2O3 system were tested by heating to 1200 degrees C and cooling in air to 160-180 degrees C. The number of performed thermal cycles was 7, 32 and 79. The quality of the obtained coating, as well as its thermal cycling behaviour, was assessed through the microstructural analysis, microhardness and tensile bond strength measurements, and change in chemical composition and microhardness. The obtained results showed that the steel substrate, bond coat oxidation and interdiffusion at bond coat/substrate interface have a significant influence on changes in chemical composition and microhardness of the bond coat. The correlation between oxidation behaviour of NiCr-Al-Co-Y2O3 bond coat and number of thermal cycles was also discussed