We developed a basal area growth model for recovery of advance growth of Norway spruce trees after clear-cutting. Stem diameter growth at ground level and needle-mass characteristics were measured on permanent sample plots in Estonia. Both tree ring analysis (destructive sampling on one sample plot) and yearly repeated measurement data (two plots) were used to quantify advance growth. Basal area growth of small trees was estimated by multiple regression analysis. Previous-year basal area of the tree and basal area growth explained tree performance the next year. Tree needle-mass variables characterizing the acclimation status of the tree were included in the model as explanatory factors. Needle samples (one shoot from the upper third of each tree crown) were collected each year after the growth period from all sample trees. Needle masses of shoots from consecutive years were correlated and this variable was used as a predictor in the simulation model. Accelerating growth was observed in trees that exceeded the growth threshold in the year after release: the greater the needle mass per shoot, the greater the acceleration in growth. Competition among advance regeneration trees was included in the model: small trees under taller neighbors exhibited reduced growth. We found that trees released from a long period of heavy shade can survive, but the time needed for acclimation and resumption of competitive growth rates is considerably longer than for trees released from light shade. Such trees can be used for forest regeneration, but competition control (particularly reducing the proportion of fast-growing hardwoods) is required.

No abstract

In the last years, we assisted to the development of new high precision machine tools: the hexapod machines. We tried to use the hexapod machine as an artefact for CMM's calibration. However, given their cost and their resolution, they are not the best solution for a transportable artefact. By modifying the hexapod structure, we develop two different artefacts: one for local CMM's calibration and another one for global calibration. Local calibration allows us the determination of the transfer function characterizing the sensor displacement of the CMM. This local calibration is based on the measurement of a rigid artefact of a known geometry, derived from hexapod geometry, which allows us to determine the errors of displacement of the sensor of the CMM. The artefact for global calibration uses a self-calibrated method, based on measurements from three miniature laser interferometers, measuring the position of a sphere in the volume of the CMM. The paper describes the patented artefacts for local and global calibration, as well as the referring mathematical problems resulting from self-calibration of global artefact and the method of interpretation of the measurement results of the artefact used in the measure of local errors.

A new kind of artefact, based on a modification of the hexapod machine's well-known structure, has been introduced by Antunes, S. D. et al in [1], in order to determine the global errors of coordinate measuring machines. Here we are presenting results from validation of the technique: using a self-calibrated method and modeling the reference value for calibration based on laser trilateration.

No abstract