O2‐consumption,blood flow and PO2 in bone

Osteocytes are bone cells encapsulated in a mineralized matrix. Since they are connected to nutrient blood vessels via narrow canaliculii which provide narrow, tortuous and often long diffusion pathways, the question arises as to how osteocytes are sufficiently supplied with O₂ and metabolites. Furthermore, different oxygen partial pressures (PO₂) ‐ resulting from O₂ supply and local oxygen consumption ‐ may influence cellular proliferation and differentiation. In this context, O₂ consumption rates of bone cells were measured and results were related to published blood flow values. This should allow to estimate mean venous PO₂ and PO₂ distribution in bone. O₂ consumption of bone cells inside spongious calvarial fragments of neonatal rats and adult guinea pigs were measured polarographically in a thermostabilized recording chamber containing Hepes‐buffered saline. PO₂ declined linearly as long as the PO₂ ranged above 20 mmHg. At 27°C and 37°C, the O₂ consumption rate of calvarial fragments from adult animals amounted to 0.06 and 0.1 ml/100 g?min, respectively. Calvaria from newborn rats showed 5‐fold higher values. At 45 °C, oxygen consumption was irreversibly abolished. The blood flow to bones amounts to 5–6 ml/100 g?min being equivalent to an oxygen delivery of about 1 ml/100 g?min. Based on the hemoglobin‐oxygen binding curve and on an O₂ consumption of 0.1 ml/100 g ? min, venous PO₂ calculates to ca. 60 mmHg. This appears to be a luxurious oxygen supply in bone. With respect to the long diffusion pathways, however, high PO₂ values appear necessary to ensure sufficiently steep PO₂ gradients for the the supply of cells remote from nutrient vessels. The resulting local oxygen gradients may orchestrate proliferation and differentiation of bone cells via oxygen‐dependent gene expression. Based on these considerations a model is proposed which comprises known factors influencing blood flow and oxygen tension in bone.     

Untersuchungen zur Biegeprüfung dünner Holzwerkstoffe

Testing technique problems arising in the standards related bending strength determination of thin wood based boards (thicknesst< 10 mm) are described. The paper gives recommendations for a future standardization of this bending test method, based on relevant tests with thin fibre hardboard, particleboard and plywood.     

Evaluation of the use of surrogate Laminaria digitata in eco-hydraulic laboratory experiments

Inert surrogates can avoid husbandry and adaptation problems of live vegetation in laboratories. Surrogates are generally used for experiments on vegetation-hydrodynamics interactions, but it is unclear how well they replicate field conditions. Here, surrogates for the brown macroalgae Laminaria digitata were developed to reproduce its hydraulic roughness. Plant shape, stiffness and buoyancy of L. digitata were evaluated and compared to the properties of inert materials. Different surrogate materials and shapes were exposed to unidirectional flow. It is concluded that buoyancy is an important factor in low flow conditions and a basic shape might be sufficient to model complex shaped plants resulting in the same streamlined shape.     

Connecting Algal Polysaccharide Degradation to Formaldehyde Detoxification

Formaldehyde is a toxic metabolite that is formed in large quantities during bacterial utilization of the methoxy sugar 6-O-methyl-d -galactose, an abundant monosaccharide in the red algal polysaccharide porphyran. Marine bacteria capable of metabolizing porphyran must therefore possess suitable detoxification systems for formaldehyde. We demonstrate here that detoxification of formaldehyde in the marine Flavobacterium Zobellia galactanivorans proceeds via the ribulose monophosphate pathway. Simultaneously, we show that the genes encoding the key enzymes of this pathway are important for maintaining high formaldehyde resistance. Additionally, these genes are upregulated in the presence of porphyran, allowing us to connect porphyran degradation to the detoxification of formed formaldehyde.     

Spatial periodicity in molecular switching

The ultimate miniaturization of future devices will require the use of functional molecules at the nanoscale and their integration into larger architectures. Switches represent a prototype of such functional molecules because they exhibit characteristic states of different physical/chemical properties, which can be addressed reversibly. Recently, various switching entities have been studied and switching of single molecules on surfaces has been demonstrated. However, for functional molecules to be used in a future device, it will be necessary to selectively address individual molecules, preferentially in an ordered pattern. Here, we show that azobenzene derivatives in the trans form, adsorbed in a homogeneous two-dimensional layer, can be collectively switched with spatial selectivity, thus forming a periodic pattern of cis isomers. We find that the probability of a molecule switching is not equally distributed, but is strongly dependent on both the surrounding molecules and the supporting surface, which precisely determine the switching capability of each individual molecule. Consequently, exactly the same lattices of cis isomers are created in repeated erasing and re-switching cycles. Our results demonstrate a conceptually new approach to spatially addressing single functional molecules.     

Trade-offs are not exogenous

Trade-offs between competitive priorities are often seen as exogenous – managers accept them as a given downside while simultaneously addressing multiple competitive priorities. However, some companies seem to face fewer trade-offs than others. The question is how companies reduce their trade-offs to successfully compete on multiple competitive priorities simultaneously. We address this question by theorising that bundles of action programmes are needed to reduce trade-offs between competitive priorities. We examine four Swiss manufacturing plants and show how the selection of action programmes influences the simultaneous competition on multiple competitive priorities. We show that successful competition on multiple competitive priorities does not happen by accident but is achieved by aligning competitive priorities, action programmes, infrastructural/structural changes and contextual factors.     

The effect of the platelet-derived glycosaminoglycan serglycin on in vitro proplatelet-like process formation

The formation of proplatelet-like processes on megakaryocytes cultured in vitro has been shown to be inhibited by prothrombin, found residually in human serum, which is converted in culture to thrombin. This study reports that another factor found in human serum will counter this inhibition and permit proplatelet-like process formation to occur in vitro even in the presence of inhibitory concentrations of thrombin. The factor was purified from human platelet lysates and identified by amino acid sequence analysis as the proteoglycan serglycin. A similar, if not identical, factor was found at elevated levels in the plasma of thrombocytopenic rabbits. Serglycin probably functions as a proplatelet potentiator by virtue of a tendency to complex with thrombin. Thrombin in complex with serglycin retains its enzymatic properties, but is apparently sterically hindered from interacting with the megakaryocyte cell surface. In preliminary studies, the in vivo administration of serglycin in mice resulted in an increased number of circulating platelets when given in combination with interleukin-6 (IL-6).     

Deflection gating for time-resolved x-ray magnetic circular dichroism-photoemission electron microscopy using synchrotron radiation

In this paper, we present a newly developed gating technique for a time-resolving photoemission microscope. The technique makes use of an electrostatic deflector within the microscope's electron optical system for fast switching between two electron-optical paths, one of which is used for imaging, while the other is blocked by an aperture stop. The system can be operated with a switching time of 20 ns and shows superior dark current rejection. We report on the application of this new gating technique to exploit the time structure in the injection bunch pattern of the synchrotron radiation source BESSY II at Helmholtz-Zentrum Berlin for time-resolved measurements in the picosecond regime.