In an attempt to develop a better understanding of the effect of knottiness on the yield of logs for sawn timber products, the present study examines the position and geometrical characteristics of 429 knots found in seven Norway spruce (Picea abies (L.) Karst) middle logs from southern Finland. The raw data used in this study were in the form of coordinates of points located on the knot surface recorded in a cylindrical (R, L, T) reference frame. The data were smoothed using a non linear three-dimensional model. A curvature analysis of the knot pith was used to differentiate the curved and straight portions of the knots. This analysis made possible calculation of knot angles, symmetry, ovality and volume. The major finding of this study is the uneven distribution of knots around the log circumference. Nearly 50% of the total knot volume was concentrated in one-third of the log facing the south-east. Knots were also more prominent in higher portions of the logs studied. These observations support the argument that the uneven distribution of knots offers potential for improving the grade yield of timber sawn from trees harvested in high-latitude countries.
It often takes one single event to interest teenagers in a topic that will become a passion or a career. It is in this spirit that the SPIE and OSA Student Chapters at Université Laval created the Photonic Games three years ago, to kindle an interest in teenagers towards studies and careers in optics. The activity, offered each year to more than a hundred grade 11 students, is divided in two parts. First, we offer a hands-on workshop in their classrooms about reflection, refraction, dispersion, birefringence and polarization. A few days later, all the students come to the Centre d'optique, photonique et laser (COPL) at Université Laval for a day of competition where a volunteer physics student accompanies each team of four students. Challenges are various to promote the qualities that make great scientists: creativity, teamwork, knowledge, inquisitiveness, self-confidence and perseverance. The first two editions of the Photonic Games have proven to be beneficial for the students, teachers and volunteers, and we endeavor to improve it as we construct on our experience with the past editions to fine-tune and improve the Photonic Games concept.
As energy efficiency becomes more and more important, light-emitting diodes (LEDs) are a promising alternative to traditional lighting. Indeed, the energy efficiency of LEDs is still improving as their luminosity is modulated by current. Moreover, for applications such as exterior lamp posts, their small size, directionality, colors and high frequency response allow to combine them and provide design possibilities which are impossible with any other light source. However, as any lamp, LEDs have a lumen depreciation which is a function of both current and temperature. Thus, to take advantage of the full characteristics of LEDs, LED luminaire longevity strategies must be carefully studied and planned, especially since the IES and CIE guidelines state clearly that the luminaire must maintain the rated recommended light level until the end of the system's operating life. The recommended approach for LED luminaire specification is therefore to use the end-of-life light level when evaluating the luminaire. Different power supply strategies have been simulated to determine which one maximizes energy saving and lifetime. With these results, it appears that active control can save at least 25% in energy, but the best strategy cannot be determined because of uncertainties in luminosity degradation models.
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