Controlling the kinetic chain length of the crosslinks in photo-polymerized biodegradable networks

Biodegradable polymer networks were prepared by photo-initiated radical polymerization of methacrylate functionalized poly(d,l-lactide) oligomers. The kinetic chains formed in this radical polymerization are the multifunctional crosslinks of the networks. These chains are carbon–carbon chains that remain after degradation. If their molecular weight is too high these poly(methacrylic acid) chains can not be excreted by the kidneys. The effect of the photo-initiator concentration and the addition of 2-mercaptoethanol as a chain transfer agent on the molecular weight of the kinetic chains was investigated. It was found that both increasing the initiator concentration and adding 2-mercaptoethanol decrease the kinetic chain length. However, the effect of adding 2-mercaptoethanol was much larger. Some network properties such as the glass transition temperature and the swelling ratio in acetone are affected when the kinetic chain length is decreased.     

Hydrogeologisches Konzeptmodell von München: Grundlage für die thermische Grundwassernutzung

The Munich Gravel Plain has been studied under various aspects, but there has been no detailed hydrogeological underground model of the entire city area. As a result of the ??urban heat-island?? effect, groundwater temperatures reach 18?°C and locally exceed 20?°C. This aquifer is therefore suitable for systematic and large-scale near-surface geothermal energy exploitation. The goal of this study was to establish the first detailed hydrogeological model of the city of Munich, as a basis for estimating the geothermal potential. A database of more than 20,000 drill holes was available, of which 730 were selected, interpreted and processed. As a result, 26 east-west cross sections were constructed, showing the geometry and structure of the aquifer and the position of the unconfined water table during low, average and high-water conditions. Based on these profiles and basic hydraulic considerations, a groundwater flow rate of about 3?m³/s was established. Results of this study indicate a high potential for thermal groundwater use and corresponding reductions of heating oil consumption and CO₂ emissions. At the same time, thermal rehabilitation of the overheated urban groundwater could be achieved. The quantification of this geothermal potential and the space-time optimisation of thermal groundwater use for heating and cooling require a detailed analysis of groundwater temperatures and numerical groundwater flow and heat transport modelling.     

Oxygen and light sensitive field-effect transistors based on ZnO nanoparticles attached to individual double-walled carbon nanotubes

The attachment of semiconducting nanoparticles to carbon nanotubes is one of the most challenging subjects in nanotechnology. Successful high coverage attachment and control over the charge transfer mechanism and photo-current generation open a wide field of new applications such as highly effective solar cells and fibre-enhanced polymers. In this work we study the charge transfer in individual double-walled carbon nanotubes highly covered with uniform ZnO nanoparticles. The synthetic colloidal procedure was chosen to avoid long-chained ligands at the nanoparticle-nanotube interface. The resulting composite material was used as conductive channel in a field-effect transistor device and the electrical photo-response was analysed under various conditions. By means of the transfer characteristics we could elucidate the mechanism of charge transfer from non-covalently attached semiconducting nanoparticles to carbon nanotubes. The role of positive charges remaining on the nanoparticles is discussed in terms of a gating effect.     

THERMODYNAMIC FUNCTIONS OF THE SOLID-LIQUID TRANSITION OF HYDROCARBON MIXTURES

ABSTRACT

The dependences of the melting temperature and the enthalpy of fusion on the composition are the essential factors for modelling precipitation and solubility of solid hydrocarbons in crude oils and crude oil products. Long-chain iso-alkanes and cyclic alkanes must be considered besides of n-alkanes. Therefore a degree of isomerization and cyclization was defined using the refractive index and the carbon number. The melting temperatures and the enthalpies of fusion of different n-alkanes and fractions of crude oil were determined by differential scanning calorimetry. Both parameters can be correlated with the degree of isomerization and cyclization by a quadratic fuction.     

Phosphorus gettering of iron by screen‐printed emitters in monocrystalline Czochralski silicon wafers

In this paper, we demonstrate single‐sided screen‐printed emitters in thin monocrystalline Czochralski silicon (Cz‐Si) wafers with an improved gettering of iron compared with conventional double‐sided POCl₃ emitters. The phosphorus dopant pastes used have to be chosen carefully to provide a sufficiently low emitter sheet resistance and to avoid iron contamination. The iron concentration is determined in a non‐destructive way from the minority carrier lifetime obtained by quasi‐steady‐state photoconductance measurements, down to levels not yet demonstrated for screen‐printed emitters. In addition, the well‐known metastable boron–oxygen complexes in Cz‐Si have been transferred into a stable state by light‐induced degradation prior to these measurements. Copyright © 2012 John Wiley & Sons, Ltd.     

Schwimmende Architektur: schwimmende Bauten als Aufgabenfeld für die Bauphysik

Schwimmende Architektur, ein nicht eindeutiger Fachbegriff, wird zunehmend auch in Deutschland thematisiert. Punktuell entstehen exklusive Wohnbauten wie auch einfache schwimmende Ferienhäuser. Infolge spezifischer Randbedingungen auf dem Wasser sowohl für die Schwimmkörper als auch für deren Aufbauten ergeben sich zusätzliche Chancen und Risiken. Der Beitrag behandelt beispielhaft bauphysikalische Bezüge. Entwicklungstendenzen der Weltbevölkerung hinsichtlich Wachstum und Verteilung bei gleichzeitig steigendem Meeresspiegel erfordern künftig ein verstärktes wissenschaftliches Interesse und Engagement der Bauphysik auch für schwimmende Bauten. Floating architecture and the responsibility of building physics for floating buildings. Floating architecture, a new and still unambiguous technical term is increasingly being addressed as subject in Germany. Point by popint exclusive buildings are constructed such as simple floating houses for holidays. As a result of specific boundary conditions of the water area for the pontoons as well as for their construction additional chances and risks are given. The paper represents examples with regard to the building physics. Development trends of the world population concerning growth and distribution coupled with rising sea levels call for an increased scientific interest and engagement of the building physics for floating architecture in future too.     

Preparation and mechanical properties of highly-aligned carbon micro-trees

Carbon micro-trees with a diameter of 15-25 μm were synthesized in an acetylene atmosphere by arc-plasma assisted chemical vapor deposition from a coal-based carbon anode using iron as catalyst. The as-obtained carbon micro-trees were studied by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, polarized light microscopy and Raman spectroscopy. It is found that the carbon micro-trees grow on the anode surface as highly-oriented arrays and have an anisotropic yet highly graphitized structure with a solid inner core. The Young’s modulus of the micro-trees was determined to be 0.4 TPa on average, which is comparable to that of carbon nanotubes reported in literature.     

Cleaning robot navigation using panoramic views and particle clouds as landmarks

The paper describes a visual method for the navigation of autonomous floor-cleaning robots. The method constructs a topological map with metrical information where place nodes are characterized by panoramic images and by particle clouds representing position estimates. Current image and position estimate of the robot are interrelated to landmark images and position estimates stored in the map nodes through a holistic visual homing method which provides bearing and orientation estimates. Based on these estimates, a position estimate of the robot is updated by a particle filter. The robot’s position estimates are used to guide the robot along parallel, meandering lanes and are also assigned to newly created map nodes which later serve as landmarks. Computer simulations and robot experiments confirm that the robot position estimate obtained by this method is sufficiently accurate to keep the robot on parallel lanes, even in the presence of large random and systematic odometry errors. This ensures an efficient cleaning behavior with almost complete coverage of a rectangular area and only small repeated coverage. Furthermore, the topological-metrical map can be used to completely cover rooms or apartments by multiple meander parts.