Mechanical Properties of Bacterially Synthesized Nanocellulose Hydrogels

The mechanical characteristics of bacterially synthesized nano-cellulose (BNC) were studied with uniaxial compression and tensile tests. Compressive loads result in a release of water and the deformation of the water-saturated network corresponds approximately to the volume of released water. The BNC hydrogel exhibits a mainly viscous response under compression. The strain response under tensile loads has an elastic and a viscous component. This can be described with a Maxwell model, where the viscosity is strain rate-dependent. When the aqueous phase of the BNC hydrogel is stabilized with an additional alginate hydrogel matrix, the system exhibits an elastic response under compressive loads. The analysis of the ‘alginated’ BNC network with the Maxwell model shows that the alginate matrix increases the viscosity of the composite system. The results of the mechanical tests show that the water absorbed in the BNC hydrogel strongly influences its mechanical behavior.     

Thrust performance of unsteady propulsors using a novel measurement system,and corresponding wake patterns

An apparatus is described for the measurement of unsteady thrust and propulsive efficiency produced by biologically inspired oscillating hydrodynamic propulsors. Force measurement is achieved using a strain-gauge-based force transducer, augmented with a lever to amplify or attenuate the applied force and control the measurement sensitivity and natural frequency of vibration. The lever can be used to tune the system to a specific application and it is shown that, using the lever, the stiffness can be made to increase more rapidly than the measurement sensitivity decreases. Efficiency is computed from measurements of the time-averaged power imparted to the fluid. The apparatus is applied to two different propulsors, demonstrating the versatility of the system; wake visualizations are examined, which provide insight into the physical mechanisms of efficient propulsion.

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Nanocelluloses: a new family of nature-based materials

Cellulose fibrils with widths in the nanometer range are nature-based materials with unique and potentially useful features. Most importantly, these novel nanocelluloses open up the strongly expanding fields of sustainable materials and nanocomposites, as well as medical and life-science devices, to the natural polymer cellulose. The nanodimensions of the structural elements result in a high surface area and hence the powerful interaction of these celluloses with surrounding species, such as water, organic and polymeric compounds, nanoparticles, and living cells. This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants.     

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Ohne Zusammenfassung     

Matrixunabh?ngige kontinuierliche Dampfraum-Gas-Chromatographie

Zusammenfassung Ausgehend von systematischen Untersuchungen des Matrixeinflusses bei der gas-chromatischen Dampfraum-Analyse und aufgrund prinzipieller Überlegungen wird ein neues Arbeitsverfahren vorgestellt, das es erlaubt, sehr viele Stoffe matrixunabhängig zu bestimmen. Dieses wird durch eine fast quantitative Überführung der flüchtigen Komponenten in das Strip-Gas durch Zusatz von Salzlösungen und durch eine kontinuierliche multiple Gegenstromextraktion über einem strömenden Flüssigkeitsfilm erreicht. Die daraus erwachsenden Vorteile dieses Verfahrens gegenüber der herkömmlichen Technik werden anhand von Beispielen erläutert und aufgezeigt.

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Matrix-independent continuous Head-Space gas-chromatography

Summary A new Head-Space gas-chromatography is presented by means of which it is possible to perform a continuous and selective measurement of numerous organic components dissolved in water. By addition of salt solutions to the sample and a continuous multiple distribution between a thin film of the fluid sample and an inert strip-gas, organic components are nearly quantitatively transferred from the water sample to the strip-gas. The transfer is widely unaffected by the matrix components. The strip-gas, containing more then 95% of the organic components, is analyzed by gas-chromatography. The advantages of the new method as against the hitherto used techniques are demonstrated by means of several examples.

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Die vorliegende Arbeit wurde mit Mitteln des Ministers für Wissenschaft und Forschung des Landes Nordrhein-Westfalen gefördert. Dafür sei an dieser Stelle herzlich gedankt.     

Charge screening and mass spectrum in abelian gauge theories

We give a rigorous proof confiriming a statement of Swieca on a connection between the charge and the mass spectrum in Abelian gauge theories. Our argument is based on a detailed analysis of the momentum-space behavior of form factors in the absence of local charge-carrying fields.