Architectural development and dry matter production in a multisite trial on single and multiaxis apple trees (Malus domestica Borkh) grafted on different rootstocks

In two Italian sites, multiaxis trees slightly reduced primary axis length and secondary axis length of newly grafted trees, and increased the number of secondary shoots. The total length, node production, and total dry matter gain were proportional to the number of axis. Growth of both primary and secondary shoots, and dry matter accumulation, have been found to be also well related to rootstock vigour. A great variability in axillary shoot production was recorded among different environments. Grafted trees had higher primary growth, secondary axis growth, and dry matter gain than chip budded trees. Stem water potential measured in the second year after grafting was not affected by rootstocks or number of leaders. Measurements performed in New Zealand (Hawke’s Bay) during the second year after grafting revealed that both final length and growth rate of primary and secondary axis were related to the rootstock rather than to the training system. Dwarfing rootstocks reduced the number of long vegetative shoots and increased the proportion of less vigorous shoots.

High-Speed Laser Processing of Thin Single and Multi-Layer Films

Theoretical models are developed for the continuous-wave and pulsed laser incision and cut of thin single and multi-layer films. A one-dimensional steady-state model establishes the theoretical foundations of the problem by combining a power-balance integral with heat flow in the direction of laser motion. In this approach, classical modelling methods for laser processing are extended by introducing multi-layer optical absorption and thermal properties. The calculation domain is consequently divided in correspondence with the progressive removal of individual layers. A second, time-domain numerical model for the short-pulse laser ablation of metals accounts for changes in optical and thermal properties during a single laser pulse. With sufficient fluence, the target surface is heated towards its critical temperature and homogeneous boiling or "phase explosion" takes place. Improvements are seen over previous works with the more accurate calculation of optical absorption and shielding of the incident beam by the ablation products. A third, general time-domain numerical laser processing model combines ablation depth and energy absorption data from the short-pulse model with two-dimensional heat flow in an arbitrary multi-layer structure. Layer removal is the result of both progressive short-pulse ablation and classical vaporisation due to long-term heating of the sample. At low velocity, pulsed laser exposure of multi-layer films comprising aluminium-plastic and aluminium-paper are found to be characterised by short-pulse ablation of the metallic layer and vaporisation or degradation of the others due to thermal conduction from the former. At high velocity, all layers of the two films are ultimately removed by vaporisation or degradation as the average beam power is increased to achieve a complete cut. The transition velocity between the two characteristic removal types is shown to be a function of the pulse repetition rate. An experimental investigation validates the simulation results and provides new laser processing data for some typical packaging materials.