Fretting wear behaviour of plasma nitrided Ti-6Al-4V fretted against unnitrided Ti-6Al-4V and alumina counterbodies

Ti-6Al-4V samples were plasma nitrided at 520°C in two environments (nitrogen and a mixture of nitrogen and hydrogen in the ratio of 3:1) for two different time periods (4 h and 18 h). Fretting wear tests were conducted on unnitrided and nitrided samples for 50,000 cycles using two counterbody materials (unnitrided Ti-6Al-4V and alumina). Gross slip prevailed at a normal load of 4.9 N while mixed stick-slip prevailed at 9.8 N. Tangential force coefficient values of plasma nitrided samples were lower than those of unnitrided samples. The tangential force coefficient nearly stabilised after thousand cycles in case of samples tested against Ti-6Al-4V counterbody. On the other hand, it showed a continuously increasing trend in case of specimens tested against alumina counterbody. The samples nitrided for 4 h exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided for 18 h. The samples nitrided in nitrogen-hydrogen mixture environment exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided in nitrogen. The samples plasma nitrided in nitrogen-hydrogen mixture for 4 h exhibited the highest hardness and the lowest tangential force coefficient. The wear volume of the plasma nitrided samples was lower than that of the unnitrided samples. Owing to tribochemical reactions, the wear volume of unnitrided and nitrided samples fretted against alumina ball was higher than that of the samples fretted against Ti-6Al-4V. A consistent trend was not observed regarding which nitriding condition would result in lower wear volume at different loads.     

Effect of various agents on rheological properties of carrot cells and protoplasts

It is known that cell turgor pressure affects the rigidity of plant cells and plays a major role in determining the texture of some plant tissues. The role of cell components in maintaining this turgor pressure (and therefore rigidity) during processing was studied by using agents that affect principal components of cell walls and cell membranes. Cells were prepared from carrot tissue by an enzymic method which removed the middle lamella; further treatment yielded protoplasts. Measurement of the rigidity of carrot cells and protoplasts (related to the complex dynamic modulus G^*) showed that cells were more rigid and lost rigidity more slowly on heating than protoplasts. The effect of osmotic pressure on cell rigidity was examined by treating cells with mannitol solutions (0.1–1.0 M) and measuring G^* at 20°C and during heating from 20 to 90°C. Cells treated with 0.1 and 0.2 M mannitol had higher initial values of G^* compared with the control sample and G^* increased with temperature. Cells treated with mannitol solutions above 0.4 M showed lower G^* values than the control and little change in G^* during heating. Carrot cells and protoplasts were treated with enzymes and the effect of the treatments on rigidity measured. Pronase (a protease) treatment of cells gave a higher initial G^* value than the controls and G^* also increased with temperature but lipase (EC3.1.1.34) had no effect on cells. Both Pronase and lipase had a marked effect on the rigidity of protoplasts causing a reduction in the initial G^* value which decreased further on heating. Cells treated with detergents (dodecyl sulphate and Triton X-100) showed higher initial G^* values compared with controls and G^* increased with temperature. Microscopic studies indicated that degergents caused flocculation of the cells. With protoplasts, dodecyl sulphate caused a complete loss of rigidity and Triton X-100 also reduced the rigidity significantly. There were no signs of flocculation with protoplasts.     

Stress-strain characteristics of concrete confined in steel spirals under repeated loading

Repeated loadings tests have been conducted on 150 mm dia.×300 mm high concrete cylinders with circular steel spiral confining the concrete. Stress-strain curves obtained in the experiments are presented. Equations are proposed for the envelope, unloading and reloading curves of the stress-strain curves and compared with test results.

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Résumé Des essais de chargement répété ont été réalisés sur des cylindres de béton de 150 mm (diamètre)×300 mm (hauteur) confinés dans une hélice d'acier. On présente ici les courbes expérimentales de contrainte/déformation. On propose des équations pour l'enveloppe des courbes obtenues par chargement répété, et l'on procède à une comparaison avec les résultats d'essai.

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Effect of Purity and Substrate on Field Emission Properties of Multi-walled Carbon Nanotubes

Multi-walled carbon nanotubes (MWNT) have been synthesized by chemical vapour decomposition (CVD) of acetylene over Rare Earth (RE) based AB₂ (DyNi₂) alloy hydride catalyst. The as-grown carbon nanotubes were purified by acid and heat treatments and characterized using powder X-ray diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, Thermo Gravimetric Analysis and Raman Spectroscopy. Fully carbon based field emitters have been fabricated by spin coating a solutions of both as-grown and purified MWNT and dichloro ethane (DCE) over carbon paper with and without graphitized layer. The use of graphitized carbon paper as substrate opens several new possibilities for carbon nanotube (CNT) field emitters, as the presence of the graphitic layer provides strong adhesion between the nanotubes and carbon paper and reduces contact resistance. The field emission characteristics have been studied using an indigenously fabricated set up and the results are discussed. CNT field emitter prepared by spin coating of the purified MWNT–DCE solution over graphitized carbon paper shows excellent emission properties with a fairly stable emission current over a period of 4 h. Analysis of the field emission characteristics based on the Fowler–Nordheim (FN) theory reveals current saturation effects at high applied fields for all the samples.     

Baicalein inhibits formation of α-synuclein oligomers within living cells and prevents Aβ peptide fibrillation and oligomerisation

Abnormal protein aggregation in the brain is linked to the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Recent studies revealed that the oligomeric form of aggregates is most likely the toxic species, and thus could be a good therapeutic target. To screen for potent inhibitors that can inhibit both oligomerisation and fibrillation of α-synuclein (α-syn), we systematically compared the antioligomeric and antifibrillar activities of eight compounds that were extracted from Chinese herbal medicines through three platforms that can monitor the formation of α-syn fibrils and oligomers in cell-free or cellular systems. Our results revealed that baicalein, a flavonoid extracted from the Chinese herbal medicine Scutellaria baicalensis Georgi ("huang qin" in Chinese), is a potent inhibitor of α-syn oligomerisation both in cell-free and cellular systems, and is also an effective inhibitor of α-syn fibrillation in cell-free systems. We further tested the protective effect of baicalein against α-syn-oligomer-induced toxicity in neuronal cells. Our data showed that baicalein inhibited the formation of α-syn oligomers in SH-SY5Y and Hela cells, and protected SH-SY5Y cells from α-syn-oligomer-induced toxicity. We also explored the effect of baicalein on amyloid-β peptide (Aβ) aggregation and toxicity. We found that baicalein can also inhibit Aβ fibrillation and oligomerisation, disaggregate pre-formed Aβ amyloid fibrils and prevent Aβ fibril-induced toxicity in PC12 cells. Our study indicates that baicalein is a good inhibitor of amyloid protein aggregation and toxicity. Given the role of these processes in neurodegenerative diseases such as AD and PD, our results suggest that baicalein has potential as a therapeutic agent for the treatment of these devastating disorders.     

Enhanced convective heat transfer using graphene dispersed nanofluids

Nanofluids are having wide area of application in electronic and cooling industry. In the present work, hydrogen exfoliated graphene (HEG) dispersed deionized (DI) water, and ethylene glycol (EG) based nanofluids were developed. Further, thermal conductivity and heat transfer properties of these nanofluids were systematically investigated. HEG was synthesized by exfoliating graphite oxide in H2 atmosphere at 200°C. The nanofluids were prepared by dispersing functionalized HEG (f-HEG) in DI water and EG without the use of any surfactant. HEG and f-HEG were characterized by powder X-ray diffractometry, electron microscopy, Raman and FTIR spectroscopy. Thermal and electrical conductivities of f-HEG dispersed DI water and EG based nanofluids were measured for different volume fractions and at different temperatures. A 0.05% volume fraction of f-HEG dispersed DI water based nanofluid shows an enhancement in thermal conductivity of about 16% at 25°C and 75% at 50°C. The enhancement in Nusselts number for these nanofluids is more than that of thermal conductivity.