Knots in trees: strain distribution in a naturally optimised structure

Electronic speckle pattern interferometry was applied to directly measure the distribution of longitudinal, tangential, and shear strains in small boards of Norway spruce (Picea abies (L.) Karst.) exposed to tensile load in longitudinal direction. A sample with a central intergrown knot and one with an equivalent loose knot were compared with reference samples made of clear wood with an artificial central circular or square hole, respectively. The observed measurements were compared with a finite element (FE) simulation. The FE model was based on a geometric model to quantify the local fibre orientation and a micromechanical model to estimate elastic constants of clear wood and knot tissue. Both the measurements and simulation clearly illustrate a rather homogenous strain distribution around the intergrown knot. In comparison, the natural optimisation of dispersing strain peaks is less efficient in the case of loose knots. The artificial circular and square holes in samples with parallel fibre orientation lead to high gradients in the strain field and peak values in vicinity of the disturbance.     

Electrospinning and mechanical properties of polymeric fibers using a novel gap-spinning collector

Tissue engineering is an interdisciplinary field which combines the basic principles of life sciences and engineering. One promising idea is the combination of scaffolds and living cells in order to produce new functional tissue. The scaffolds play the role of a microenvironment that guides the cells towards tissue formation and regeneration. One of the most frequently used techniques to produce scaffolds is electrospinning. Tissue engineered constructs have to exhibit physiological and mechanical properties comparable to the native tissue they are intended to replace. To create polymeric fibers with controlled orientation, a cylindrical collector that rotates at a certain speed could be used, creating fibers that run longitudinally. The process of gap-spinning enables the production of specifically aligned fibers. Aim of this study was to develop a novel setup capable of producing multilayered structures with controlled fiber angle. The structural, morphological and mechanical characteristics of the fibers were accessed using scanning electron microscopy and uniaxial tensile tests. Longer pre-stretching led to thinner (in the sub-micron scale), more brittle and less elastic fibers. In a nutshell, the results indicated that fiber mats of desired orientation, fiber diameter and mechanical properties could be produced by controlled gap-spinning with a translational collector.     

A soil science renaissance

The renaissance was an intellectually-rich period following a period of stasis in the medieval period. Something analogous appears to be currently taking place in soil science where novel approaches to thought are combined with a revival of ideas from the past. Renewed interest in agriculture (food, feed, fuel) and numerous publications have brought soils back onto the global research agenda. The need for up-to-date and fine resolution soil information and the revival of soil research has been highlighted and prioritised in several recent studies by the UN and other international organizations. Soil erosion, nutrient depletion and pollution are key issues that have been brought up in many recent reports - in most cases in relation to environmental degradation, climate change and world-food production. There is also an increased interest in soils in the popular press and media, and soils have entered the policy arena in many countries and several continents. We guestimate that about €3.2 billion is annually spent on soil research in Europe, North America, and some of the main countries in Asia and Oceania. For the global soil science community, there are challenges ahead to address the questions raised in these reports. There is a whole set of new techniques and methodologies in the wings waiting to take centre stage. There is a direct need to educate a new generation of soil scientists and to increase the influx of soil science students in many universities. The soil science community should benefit from the current upsurge in soil science, but the community has to deliver the goods and information that is wanted and much needed.     

Type-specific reference conditions of fluvial landscapes: A search in the past by 3D-reconstruction

River/floodplain restoration programs are often based on type-specific reference conditions of the respective river section. Most large rivers in the industrialized world are heavily degraded and lack near-natural reference sites. For that reason, historical analyses of the pre-channelization state have been used to define adequate restoration targets at the Austrian Danube section in the Alluvial Zone National Park downstream from Vienna. This study compares new reference data derived from 3D-reconstructions in the form of digital terrain models from two historical Danube river landscapes: the Machland floodplain in 1812 and the former floodplain in Vienna in 1849. The focus is on the original hydrological surface and subsurface connectivity of the river-floodplain systems related to different flow situations. Here, we use water cover, shorelines, depth of the groundwater table and inundation depth as surrogates for measuring connectivity. The results show that the two study sites naturally constituted extreme formations of the Austrian anabranching Danube sections. The Machland section was one of the narrowest floodplains but highly dynamic, and the Vienna/Lobau section was one of the broadest, whereby only the central part close to the main channel originally showed high morphological turnover. The analyses of hydrological surface connectivity relative to total floodplain extension reveal significant differences due to their basic geological and geographical conditions. Despite these basic differences, both study sites – in absolute numbers – showed similar extensions of the water bodies at low and mean flow. The depths of the groundwater table related to mean flow were also comparable. Prior to channelization, the groundwater conditions in both floodplains favored the formation of wet to moist alluvial forest communities.     

Red fluorescence in reef fish: A novel signalling mechanism?

Background  

At depths below 10 m, reefs are dominated by blue-green light because seawater selectively absorbs the longer, 'red' wavelengths beyond 600 nm from the downwelling sunlight. Consequently, the visual pigments of many reef fish are matched to shorter wavelengths, which are transmitted better by water. Combining the typically poor long-wavelength sensitivity of fish eyes with the presumed lack of ambient red light, red light is currently considered irrelevant for reef fish. However, previous studies ignore the fact that several marine organisms, including deep sea fish, produce their own red luminescence and are capable of seeing it.     

CANINE INTRACRANIAL EPIDERMOID CYST

A 7-year-old intact male pitbull presented with a 2-month history of progressive dysequilibrium. Cerebrospinal fluid analysis was indicative of a central inflammatory or neoplastic disorder. A cerebellar cystic structure was identified on magnetic resonance imaging which was found to be an epidermoid cyst on histopathology.     

Die Bestandsänderung der Waldvogelwelt durch Krieg und Kriegsfolgen und der forstliche Vogelschutz

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