Biomechanics of pollen pellet removal by the honey bee

Honey bees (Apis mellifera) carry pollen back to their hive by mixing it with nectar and forming it into a pellet. The pellet must be firmly attached to their legs during flight, but also easily removable when deposited in the hive. How does the honey bee achieve these contrary aims? In this experimental study, we film honey bees removing pollen pellets and find they peel them off at speeds 2–10 times slower than their typical grooming speeds. Using a self-built pollen scraper, we find that slow removal speeds reduce the force and work required to remove the pellet under shear stress. Creep tests on individual pollen pellets revealed that pollen pellets are viscoelastic materials characterized by a Maxwell model with long relaxation times. The relaxation time enables the pellet to remain a solid during both transport and removal. We hope that this work inspires further research into viscoelastic materials in nature.     

A Thermoelectric Generator Concept Using a p–n Junction: Experimental Proof of Principle

Conventional thermoelectric generators (TEGs) use single p- and n-doped legs for thermoelectric energy harvesting. We explore a concept using thermoelectric p–n junctions made from densified silicon nanoparticles. The nanoparticle powder was synthesized in a microwave plasma reactor using silane, diborane, and phosphine as precursors. To achieve a bulk sample with a p–n junction, a layer of boron-doped nanoparticle powder was stacked on a layer of phosphorus-doped powder and compacted by current-activated pressure- assisted densification. To use the p–n structure as a TEG, a temperature gradient was applied along the p–n junction. It is expected that this temperature gradient leads to electron–hole pair generation and separation in the junction, and diffusion of the charge carriers. A reference method was used to characterize the open-circuit voltage of the p–n junction TEG.     

Evaluation of an Accounting Model for Dynamic Virtual Organizations

Accounting of Grid resource and service usage determines the central support activity for Grid systems to be adopted as a means for service-oriented computing in Dynamic Virtual Organizations (DVO). An all-embracing study of existing Grid accounting systems has revealed that these approaches focus primarily on technical precision, while they lack a foundation of appropriate economic accounting principles and the support for multi-provider scenarios or virtualization concepts. Consequently, a new, flexible, resource-based accounting model for DVOs was developed, combining technical and economic accounting by means of Activity-based Costing. Driven by a functional evaluation, this paper pursues a full-fledged evaluation of the new, generically applicable Grid accounting model. This is done for the specific environment of the Leibniz Supercomputing Centre (LRZ) in Garching, Germany. Thus, a detailed evaluation methodology and evaluation environment is outlined, leading to actual model-based cost calculations for a defined set of considered Grid services. The results gained are analyzed and respective conclusions on model applicability, optimizations, and further extensions are drawn.     

Investigations of SU-8 removal from metallic high aspect ratio microstructures with a novel plasma technique

First promising investigations of SU-8 removal experiments with a novel plasma etching technique are presented. The basic idea of this technique is to separate the highly effective generation of chemical radicals (e.g. oxygen radicals) using a traveling wave reactor (TWR) microwave source with water cooled plasma zone from the chemical reaction with the resist polymer. The etching tool operates in a remote and downstream mode with very high radical density allowing precise thermal management of the substrates on the chuck giving controlled process conditions without deviation in temperature, and generally preventing ion bombardment, at least resulting in gentle processing without jeopardizing the integrity of the metal structures. Very good removal of SU-8 with very few residues and very high etching rates up to 10 μm per minute are observed in first experiments which are offering chances to get even more than 20 μm per minute. The etching process is isotropic, and the rate stays stable during the whole removing process even for very thick films of 1 mm and more. First application examples of SU-8 removal are demonstrating the great potential of the presented microwave plasma based technique not only for the cleaning of metallic microparts but also for other more sensitive materials which is demonstrated by SU-8 removal from graphite X-ray mask substrates.     

Oxide nanocrystal based nanocomposites for fabricating photoplastic AFM probes

We report on the synthesis, characterization and application of a novel nanocomposite made of a negative tone epoxy based photoresist modified with organic-capped Fe(2)O(3) nanocrystals (NCs). The mechanical properties of the nanocomposite drastically improve upon incorporation of a suitable concentration of NCs in the polymer, without deteriorating its photolithography performance. High aspect ratio 3D microstructures made of the nanocomposite have been fabricated with a uniform surface morphology and with a resolution down to few micrometres. The embedded organic-capped Fe(2)O(3) NCs drastically increase the stiffness and hardness of the epoxy based photoresist matrix, making the final material extremely interesting for manufacturing miniaturized polymer based mechanical devices and systems. In particular, the nanocomposite has been used as structural material for fabricating photoplastic Atomic Force Microscopy (AFM) probes with integrated tips showing outstanding mechanical response and high resolution imaging performance. The fabricated probes consist of straight cantilevers with low stress-gradient and high quality factors, incorporating sharp polymeric tips. They present considerably improved performance compared to pure epoxy based photoresist AFM probes, and to commercial silicon AFM probes.