Methods in soil micromorphology : a technique for the preparation of large thin sections

Stiboka onderzoe

Structural Analysis of a Dragonfly Wing

Dragonfly wings are highly corrugated, which increases the stiffness and strength of the wing significantly, and results in a lightweight structure with good aerodynamic performance. How insect wings carry aerodynamic and inertial loads, and how the resonant frequency of the flapping wings is tuned for carrying these loads, is however not fully understood. To study this we made a three-dimensional scan of a dragonfly (Sympetrum vulgatum) fore- and hindwing with a micro-CT scanner. The scans contain the complete venation pattern including thickness variations throughout both wings. We subsequently approximated the forewing architecture with an efficient three-dimensional beam and shell model. We then determined the wing’s natural vibration modes and the wing deformation resulting from analytical estimates of 8 load cases containing aerodynamic and inertial loads (using the finite element solver Abaqus). Based on our computations we find that the inertial loads are 1.5 to 3 times higher than aerodynamic pressure loads. We further find that wing deformation is smaller during the downstroke than during the upstroke, due to structural asymmetry. The natural vibration mode analysis revealed that the structural natural frequency of a dragonfly wing in vacuum is 154 Hz, which is approximately 4.8 times higher than the natural flapping frequency of dragonflies in hovering flight (32.3 Hz). This insight in the structural properties of dragonfly wings could inspire the design of more effective wings for insect-sized flapping micro air vehicles: The passive shape of aeroelastically tailored wings inspired by dragonflies can in principle be designed more precisely compared to sail like wings —which can make the dragonfly-like wings more aerodynamically effective

Rules and Insights: Connecting the Mathematical and Linguistic Abilities of C.S. Lewis

While most biographical works on C.S. Lewis give passing reference to Lewis\u27 problems with elementary mathematics, few have made an attempt at diagnosing the difficulty or exploring its impact on his writing. A careful study of family correspondence, however, makes it clear that his learning difficulties were not with mathematics alone and suggests connections between attitudes toward and abilities in both mathematics and language. This paper will make these connections clear and will illustrate their ties to Lewis\u27 effective mathematical references

Oudere broers en zussen van mensen met een verstandelijke beperking : een groepsportret.

This study investigated the experiences of elderly brothers and sisters of living with a mentally retarded sibling. As a child, respondents helped their parents with their mentally retarded sibling. The respondents suffered from this caretaking in their youth. In adulthood, the parents passed on the responsibility for the handicapped child mostly to the youngest child in the family. They now act as contacts for the institutions where the mentally retarded sibling lives. The other brothers and sisters are less in touch with their handicapped sibling. The respondents do not discuss explicitly with their children who will take over this role once they themselves are no longer able to do so

Mathematics

Inspired by the song Memories from the musical Cats, this work describes some of the frustrations and joys inherent in mathematical work