Low-level and ultralow-volume hollow waveguide based carbon monoxide sensor

We demonstrate an ultralow sample volume optical carbon monoxide sensor with detection sensitivity of 180 parts in 10(9) (1σ at 1 Hz). The utilization of a 2.3 μm surface-emitting laser directly coupled to a 3 m hollow capillary fiber as the gas cell is proven to be a compact, sensitive, and cost-efficient gas sensing concept. By mechanical vibration of the fiber, an absorbance resolution of 10(-5) is achieved, which is comparable to single-reflective (double-pass) cells. An improvement of sensitivity over the conventional single-reflective cell is thus approximately linearly scaled with the enhancement of the optical path length, which is usually more than 1 order of magnitude.     

Optimal portfolios of a small investor in a limit order market: a shadow price approach

We study Merton’s portfolio optimization problem in a limit order market. An investor trading in a limit order market has the choice between market orders that allow immediate transactions and limit orders that trade at more favorable prices but are executed only when another market participant places a corresponding market order. Assuming Poisson arrivals of market orders from other traders we use a shadow price approach, similar to Kallsen and Muhle-Karbe (Ann Appl Probab, forthcoming) for models with proportional transaction costs, to show that the optimal strategy consists of using market orders to keep the proportion of wealth invested in the risky asset within certain boundaries, similar to the result for proportional transaction costs, while within these boundaries limit orders are used to profit from the bid–ask spread. Although the given best-bid and best-ask price processes are geometric Brownian motions the resulting shadow price process possesses jumps.     

On the Role of the Excitation/Inhibition Balance of Homeostatic Artificial Neural Networks

Homeostatic models of artificial neural networks have been developed to explain the self-organization of a stable dynamical connectivity between the neurons of the net. These models are typically two-population models, with excitatory and inhibitory cells. In these models, connectivity is a means to regulate cell activity, and in consequence, intracellular calcium levels towards a desired target level. The excitation/inhibition (E/I) balance is usually set to 80:20, a value characteristic for cortical cell distributions. We study the behavior of these homeostatic models outside of the physiological range of the E/I balance, and we find a pronounced bifurcation at about the physiological value of this balance. Lower inhibition values lead to sparsely connected networks. At a certain threshold value, the neurons develop a reasonably connected network that can fulfill the homeostasis criteria in a stable way. Beyond the threshold, the behavior of the artificial neural network changes drastically, with failing homeostasis and in consequence with an exploding number of connections. While the exact value of the balance at the bifurcation point is subject to the parameters of the model, the existence of this bifurcation might explain the stability of a certain E/I balance across a wide range of biological neural networks. Assuming that this class of models describes the self-organization of biological network connectivity reasonably realistically, the omnipresent physiological balance might represent a case of self-organized criticality in order to obtain a good connectivity while allowing for a stable intracellular calcium homeostasis.     

Konversionsmaterialien für die Energiespeicherung

Conversion materials seem to be the only option at the moment to achieve considerably higher gravimetric and volumetric storage capacities of H storage materials and batteries. Although some technical problems exist with the current materials they are a rewarding field for research and development, with the perspective to achieve significant progress in the development of energy storage systems. It has been shown that new approaches for synthesis of complex nanostructures with a high functionality may open the door to this exciting new class of energy storage materials.     

Comparison of Experimental Techniques for Measuring Isosteric Heat of Adsorption

Experimental measurements of heats of adsorption published in the literature are often in disagreement; differences of 10–20% are common. The three most widely used experimental methods are: (1) differentiation of adsorption isotherms at constant loading; (2) measurement of adsorption isosteres; (3) calorimetry. Results from these methods were compared for the systems nitrogen on CaA, oxygen on CaA, and carbon dioxide on NaX. Although the same materials and similar degassing procedures were used for all experiments, calorimetric heats are about 2 kJ/mol higher than the heats from isoteric measurements. Additional experiments are needed to bring these methods into exact agreement.     

Recent advances in CO2/epoxide copolymerization—New strategies and cooperative mechanisms

The catalytic copolymerization of CO₂ with epoxides has been known for over 40 years. Even though many heterogeneous and homogeneous catalyst systems have been developed, catalyst activity and selectivity still remain too low for large scale industrial application.Recent investigations have identified new copolymerization pathways with strong evidence for cooperative (bifunctional) mechanisms. At high dilutions, traditional discrete mononuclear single-site catalyst systems generally show a loss in activity. This effect can be overcome with the help of recently developed dinuclear and binary linked systems that involve cooperative mechanisms and thus permit high catalyst efficiency.This review gives an overview on the most recent advances in CO₂/epoxide copolymerization, new mechanistic studies and strategies for future catalyst developments.     

Reaction of phenolic mannich bases with enamines. General synthesis of pyran-containing fused ring systems

The reaction of o-phenolic Mannich bases with enamines yields cyclic O,N-acetals having a 2-aminodihydropyran or a spiropyranopiperidine structure in common. The 2-aminodihydro-pyrans are easily converted to 2-hydroxydihydropyrans and to pyrans. The preparation of a large variety of pyran-containing fused ring systems is reported.     

Ueber das Oel der Samen von Jatropha Curcas

Ohne ZusammenfassungAssistent an der K. K. technischen Hochschule in Wien.