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ABSTRACT In wooden boards, knots and the resulting fibre deviations in their vicinities are mainly responsible for qualitative downgrading of timber elements. Thus, the development of reliable numerical simulation tools for the determination of effective strength and stiffness properties of timber elements and, in a next step, for the development and evaluation of grading criteria is highly desirable. Due to the complexity of such tools, a comprehensive validation is required. Within this work, the suitability of full-field deformation measurements for four-point bending tests on wooden boards with knots is evaluated first. Next, the test series is used to validate a previously developed three-dimensional numerical simulation tool, which combines a geometrical model for the grain course and a micromechanical model for a density and moisture dependent characterisation of the clear-wood material. The digital image correlation technique proved to be capable to reproduce the strain fields in the vicinity of knots under bending load. Moreover, a very good correlation between numerical and experimental results was obtained. [ABSTRACT FROM AUTHOR]

Outward and inward currents, mainly carried by K(+), were detected in protoplasts of pollen grains (PG) and pollen tubes (PT) of Lilium longiflorum Thunb. by using the whole-cell configuration of the patch-clamp technique. The outward K(+) current (I(K+ out)) was similar in both protoplast types, while the inward K(+) current (I(K+ in)) was higher in pollen tube protoplasts. In PT but not in PG protoplasts, inward K(+) currents were already detectable at negative membrane voltages usually monitored in lily pollen. I(K+ in) consisted of a slow and a fast current component, as revealed by fitting a sum of two exponential functions to the time-dependent current. The contribution of the fast component to the total inward current was higher in PT than in PG protoplasts, which was even more evident at acidic pH of the external medium. Therefore, based on the measured characteristics, the I(K+ in) of PT protoplasts may contribute to the endogenous K(+) currents surrounding a growing pollen tube. [ABSTRACT FROM AUTHOR]