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Greatest Resistance (greatest + resistance)
Selected AbstractsMaterial stiffness, branching pattern and soil matric potential affect the pullout resistance of model root systemsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2007S. B. Mickovski Summary Understanding of the detailed mechanisms of how roots anchor in and reinforce soil is complicated by the variability and complexity of both materials. This study controlled material stiffness and architecture of root analogues, by using rubber and wood, and also employed real willow root segments, to investigate the effect on pullout resistance in wet and air-dry sand. The architecture of model roots included either no laterals (tap-root) or a single pair at two different locations (herringbone and dichotomous). During pullout tests, data on load and displacement were recorded. These studies were combined with Particle Image Velocimetry (PIV) image analysis of the model root-soil system at a transparent interface during pullout to increase understanding of mechanical interactions along the root. Model rubber roots with small stiffness had increasing pullout resistance as the branching and the depth of the lateral roots increased. Similarly, with the stiff wooden root models, the models with lateral roots embedded deeper showed greatest resistance. PIV showed that rubber model roots mobilized their interface shear strength progressively whilst rigid roots mobilized it equally and more rapidly over the whole root length. Soil water suction increased the pullout resistance of the roots by increasing the effective stress and soil strength. Separate pullout tests conducted on willow root samples embedded in sand showed similar behaviour to the rigid model roots. These tests also demonstrated the effect of the root curvature and rough interface on the maximum pullout resistance. [source] Desert shrub water relations with respect to soil characteristics and plant functional typeFUNCTIONAL ECOLOGY, Issue 3 2002J. S. Sperry Summary 1.,Soil characteristics influence plant communities in part through water relations. Hypothetically, finer textured soils in arid climates should be associated with more negative plant and soil water potentials during drought, greater resistance of xylem to cavitation, and shallower root systems than coarse soils. 2.,These hypotheses were tested by comparing the water relations of Great Basin shrubs growing in sand versus loam soils. The eight study species (Chrysothamnus nauseosus, Chrysothamnus viscidiflorus, Chrysothamnus parryi, Tetradymia glabrata, Atriplex canescens, Atriplex confertifolia, Grayia spinosa and Sarcobatus vermiculatus) varied in typical rooting depth and vegetative phenology. 3.,Xylem pressures for a species were, on average, 1·1 MPa more negative in the loam versus the sand site, despite greater precipitation at the loam site. Root xylem at the loam site was, on average, 0·9 MPa more resistant to cavitation than at the sand site for the same species. There was a strong trend for shallower rooting depths at the loam versus the sand site. Within a species, roots were consistently more vulnerable to cavitation than stems, and experienced more cavitation during the growing season. 4.,Over most of the summer there was much more cavitation at the loam site than at the sand site. More than 80% loss of xylem conductivity (PLC) was estimated in shallow roots of three species at the loam site by the end of July, with two of the three showing extensive leaf drop and branch mortality. Transpiration rate was negatively correlated with PLC, with a tendency for lower gas-exchange rates in loam versus sand. 5.,At the sand site, cavitation resistance was negatively correlated with estimated rooting depth. Drought-deciduous species had the shallowest root systems and greatest resistance to cavitation. In contrast, two species with phreatophytic tendencies were summer-active and were the most vulnerable to cavitation. 6.,The cavitation resistance of roots determines the minimum water potential permitting hydraulic contact with soil. Differences in cavitation resistance of roots between desert species may contribute to differences in sensitivity of gas exchange to soil drought, ability to perform hydraulic lift, and response to late summer rain pulses. [source] Determination of survival, identity and stress resistance of probiotic bifidobacteria in bio-yoghurtsLETTERS IN APPLIED MICROBIOLOGY, Issue 3 2006V.S. Jayamanne Abstract Aims:, To determine the level of bifidobacteria in bio-yoghurts in the UK, identify the species, and compare the resistance of common Bifidobacterium spp. to acidity and oxidative stress. Methods and Results:, A storage trial of bio-yoghurts was carried out to determine the level and survival of bifidobacteria. The 16S rRNA gene targeted PCR was used to identify the species. Acid tolerance was determined by introducing the organisms to pH-adjusted skimmed milk and enumerating during storage at 4°C. Oxidative stress resistance was determined using the H2O2 disc diffusion assay technique. Nine of 10 bio-yoghurts contained bifidobacteria at levels >106 CFU g,1 at the time of purchase. The viability of the organism decreased during storage and on expiry only five products retained viability >106 CFU g,1 while two others were very close to the target population. Bifidobacterium animalis ssp. lactis showed superior survival abilities and stress tolerance compared with Bifidobacterium longum, Bifidobacterium breve, Bifidobacterium bifidum, Bifidobacterium adolescentis and Bifidobacterium longum biotype infantis. Conclusions:,Bifidobacterium animalis ssp. lactis, the only Bifidobacterium spp. found in bio-yoghurts, had the greatest resistance to acidity and oxidative stress. Significance and Impact of the Study:, The technological properties of B. animalis ssp. lactis make it suitable for inclusion in bio-yoghurts although its putative health benefits need further investigation. [source] Evaluation of aluminide diffusion coatings for thermal cyclic oxidation protection of a nickel-base superalloyMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 10 2005A. Elsawy Abstract Active element modified aluminide diffusion coatings on IN738 substrates were produced by a new route using continuously cast, aluminum alloy wires consisting of Al-Y, Al-Ce, Al-La and Al-Si-Y. The cast wires were used as evaporation sources for ion-vapour deposition followed by diffusion heat treatments to form nickel aluminide coatings. In order to examine the oxidation resistance of these coatings at elevated temperatures, thermal cyclic oxidation experiments were carried out in air at 1050°C. While all coatings were found to provide significant protection, the Al-La modified coatings provided the greatest resistance to cyclic oxidation. On the other hand, with coatings based on Al-Si-Y alloys, while silicon has a strong ability to reduce the outward diffusion of aluminum, the adverse effect of silicon on mechanical properties of the coating, together with the formation of volatile silicon monoxide, led to catastrophic localized oxidation of the protective coatings. 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