1,721,007 research outputs found
Morphological characterisation of Vitis vinifera L. seeds by image analysis and comparison with archaeological remains
No full textIn archaeobotanical studies, the taxonomic classification of diaspores has usually been done by simple morphological observation and visual comparison with ex situ collections of seeds, although the use of biometric indices has often proved to be a powerful approach in the taxonomic studies of the genus Vitis as well as for the species attribution of archaeological remains. Using image analysis techniques, seeds from two Sardinian archaeological sites, the pre-Nuragic and Nuragic complex of Sa Osa in central-western Sardinia, attested as the oldest Sardinian archaeological site with remains of Vitis seeds, and the Isola di Coltellazzo in southwest Sardinia, were selected and characterized on the basis of morphological features and Elliptic Fourier Descriptors. Moreover, seeds of five modern populations of V. vinifera ssp. sylvestris collected from southwest Sardinia and the seeds of 41 cultivars of V. vinifera ssp. vinifera mainly from southern and central-western Sardinia were also analysed by computer image analysis. The obtained data were used to implement a database of biometric parameters and to compare the unknown archaeological seeds with the characterized recent seeds, using Linear Discriminant Analysis. The similarity of the archaeological seeds to V. vinifera ssp. vinifera cultivars rather than to V. vinifera ssp. sylvestris populations could allow it to be stated that, between the Middle and Final Bronze Age, varieties very close to modern V. vinifera ssp. vinifera were already being used to produce wine and/or to be preserved for foodstuffs. Moreover, the better matching of the archaeological seeds to white grapes rather than black grape cultivars could indicate the origins of the traditional cultivation of white grapes in these regions of Sardinia
Rootstock effects on postharvest physiological and pathological behaviour of ‘Avana’ mandarin
No full textA study on the control of melting ratio to increase mechanical properties of laser welded joints between AISI 440C and AISI 430F
No full textLaser beam welding of dissimilar AISI 440C and AISI 430F stainless steels was investigated in a circular constrained configuration. The beam incidence angle and the offset of the focusing position respect to the contact point between the two materials were used as main control parameters to vary the melting ratio inside the seam. The objective of the study is twofold: to avoid surface microcracks related to the high percentage of carbon of the martensitic steel and to enhance the shear strength of the weld by making it less brittle. To reach this scope the effects of incidence angle and offset on weld bead geometry and melting ratio were studied by means of metallographic analyses, microstructure and microhardness characterization. As last step, the weld mechanical strength was tested by tensile-shear stress test on the whole seam. Experiments demonstrated that varying incidence angle and offsetting the focal position is a reliable method to modify the melting ratio and maintaining the expected resistance length at the material interface, as well. It was found that increasing the percentage of ferritic steel into the joint has beneficial effects on the weld quality and on the shear resistance. The critical carbon content determining the mechanical properties in the fusion zone can be calculated by taking into account the melting ratio
Stress corrosion cracking of tinplated cans for conserved tuna in oil
No full textStress Corrosion Cracking (SCC) is induced by the combined influence of tensile stress and a corrosive environment. SCC can occur for specific metal/environment coupling, and its effect is higher than the sum of environmental corrosiveness and stress state. Usually, the metal surface remains almost unattacked, but with fine cracks penetrating into the material. These cracks can have intergranular or transgranular morphology. SCC is classified as a catastrophic form of corrosion, since the detection of such fine cracks can be very difficult and the damage is not easily predicted. In recent literature, several SCC cases occurring in tinplate cans for the conservation of highly proteic food (meat, tuna or petfood) are reported. In these cases, the specific SCC damage can be very dangerous due to fine cracks that can pass through the can wall, causing the air ingress. The present work is focused on the analysis of stress corrosion damage suffered by two different types of tinplate cans (called A and B) for oil-conserved tuna. Tinplated steel cans came from two different producers, and also the tuna meat came from different companies. Metallic cans are usually produced using low carbon steel, tinplated and then coated with epoxyphenolic resin. From thin strips, the cans are often produced by welding. After welding, both internal and external welding regions are re-protected with epoxyphenolic film; the cans are then filled with tuna meat, filled with oil under low pressure, and finally closed and sterilized around 115-120°C. In both examined cases, fine and branched SCC cracks were observed close to the welding regions. A deep microscopic analysis, performed by Scanning Electron Microscope (SEM) equipped with a energy dispersive system (EDS), highlighted the presence of resin delamination in regions close to SCC cracks. Moreover, inside the microcracks, a mixture of corrosion products and phosphates was detected. A chemico/physical analysis was performed on liquid phases contained in the cans. A large amountof water was present in both can types, higher for sample B than A. Moreover, the chemical analysis of the aqueous phases showed a massive presence of phosphates and bicarbonates, together with chlorides. The typical pH value was around 5.8. Experimental results are discussed in order to explain the occurrence of SCC in the carbon steel. First of all, the occurrence of oil-water separation inside the can is necessary to induce corrosive phenomena. Moreover, the only region prone to SCC is near the welding, as a consequence of residual stresses induced by the thermal treatment. In these regions a water phase comes in contact with the steel surfaces whatever discontinuities are present in the protective epoxy-phenolic deposit. Among possible chemical environment carrying to SCC on low carbon steel, phosphates in deareated water are the most probable in this case. Some experimental evidence suggest that phosphates promote a polarization inversion between steel and tin. A possible way to control SCC damage in these applications is the use of more continuous, thicker and more protective laquers on welding regions, such as powder layers (around 80 m in thickness) obtained with thermoplastic modified polyesters
Study of 13CR-4NI-(MO) (F6NM) steel grade heat treatment for maximum hardness control in industrial heats
Full text linkThe standard NACE MR0175 (ISO 15156) requires a maximum hardness value of 23 HRC for 13Cr-4Ni-(Mo) steel grade for sour service, requiring a double tempering heat treatment at temperature in the range 648–691°C for the first tempering and 593–621°C for the second tempering. Difficulties in limiting alloy hardness after the tempering of forged mechanical components (F6NM) are often faced. Variables affecting the thermal behavior of 13Cr-4Ni-(Mo) during single and double tempering treatments have been studied by means of transmission electron microscopy (TEM) observations, X-ray diffraction measurements, dilatometry, and thermo-mechanical simulations. It has been found that relatively low Ac1 temperatures in this alloy induce the formation of austenite phase above 600°C during tempering, and that the formed, reverted austenite tends to be unstable upon cooling, thus contributing to the increase of final hardness via transformation to virgin martensite. Therefore, it is necessary to increase the Ac1 temperature as much as possible to allow the tempering of martensite at the temperature range required by NACE without the detrimental formation of virgin martensite upon final cooling. Attempts to do so have been carried out by reducing both carbon (<0.02% C) and nitrogen (<100 ppm) levels. Results obtained herein show final hardness below NACE limits without an unacceptable loss of mechanical strength
- …
