Demand-Enhancing Investment in Mixed Duopoly

This paper examines demand-enhancing investment and pricing in mixed duopoly. We analyze a model with differentiated products and reduced-form demand, making no assumptions on the relative efficiency of the public firm. First, we derive sufficient conditions for public investment to crowd out private investment. Second, we characterize the conditions under which individual investments (prices, respectively) in the mixed duopoly are higher (lower) than in the standard duopoly. Third, we show that with linear demand the public firm effectively disciplines the private firm, inducing an improvement in its price-quality ratio relative to the standard duopoly.Mixed oligopoly, price, investment, quality

Curie Point Pyrolysis Gas Chromatography

In Curie Point pyrolysis gas chromatography a ferromagnetic conductor in contact with the sample is heated inside a low volume glass capillary which is inserted into an rf coil with the carrier gas flowing through the capillary. The intrinsic properties of the conductor permit a self-control of the temperature to the Curie Point. The optimum wire diameter for a rapid warm-up is a function of the rf frequency. In order to have a fast temperature drop after cutting the rf field, small wire diameters are preferable. For such conductors relatively high frequencies are inherently necessary for a fast stabilization to the Curie Point. So far no differences in the self-controlled end-temperatures have been detected for wires of different origi

Calculation of thermoacoustic functions with computational fluid dynamics

Thermoacoustic functions are important parameters of one-dimensional codes used for the design of thermoacoustic engines. The thermal and viscous thermoacoustic functions allow the inclusion of three dimensional effects in one-dimensional codes. These functions are especially important in the regenerator of a thermoacoustic engine, where the thermoacoustic heat pumping occurs. Even though analytical solutions were derived for uniform pores, the thermoacoustic functions for complex geometries such as stacked screen or random fiber regenerators cannot be calculated analytically. In order to gain more insight into the geometry induced complex flow fields, the procedure of Udea, et al. (2009) to estimate the thermoacoustic functions was applied in computational fluid-dynamic simulations. By using two measurement locations outside of the regenerator and modeling the regenerator as an array of uniform pores it is possible to estimate the thermoacoustic functions for complex geometries. Furthermore, a correction method is proposed to quantify the entrance effects at the beginning and end of a regular pore. The simulations are first validated for a uniform cylindrical pore with the help of the analytical solution. Then the correction method is successfully applied to a cylindrical pore with the results closely matching the analytical solution

A numerical investigation on the vortex formation and flow separation of the oscillatory flow in jet pumps

A two-dimensional computational fluid dynamics model is used to predict the oscillatory flow through a tapered cylindrical tube section (jet pump) placed in a larger outer tube. Due to the shape of the jet pump, there will exist an asymmetry in the hydrodynamic end effects which will cause a time-averaged pressure drop to occur that can be used to cancel Gedeon streaming in a closed-loop thermoacoustic device. The performance of two jet pump geometries with different taper angles is investigated. A specific time-domain impedance boundary condition is implemented in order to simulate traveling acoustic wave conditions. It is shown that by scaling the acoustic displacement amplitude to the jet pump dimensions, similar minor losses are observed independent of the jet pump geometry. Four different flow regimes are distinguished and the observed flow phenomena are related to the jet pump performance. The simulated jet pump performance is compared to an existing quasi-steady approximation which is shown to only be valid for small displacement amplitudes compared to the jet pump length.Comment: The following article has been accepted by the Journal of the Acoustical Society of America. After it is published, it will be found at: http://scitation.aip.org/JAS

Multi-core Interference-Sensitive WCET Analysis Leveraging Runtime Resource Capacity Enforcement

The performance and power efficiency of multi-core processors are attractive features for safety-critical applications, as in avionics. But increased integration and average-case performance optimizations pose challenges when deploying them for such domains. In this paper we propose a novel approach to compute a interference-sensitive Worst-Case Execution Time (isWCET) considering variable accesses delays due to the concurrent use of shared resources in multi-core processors. Thereby we tackle the problem of temporal partitioning as it is required by safety-critical applications. In particular, we introduce additional phases to state-of-the-art timing analysis techniques to analyse an applications resource usage and compute an interference delay. We further complement the offline analysis with a runtime monitoring concept to enforce resource usage guarantees. The concepts are evaluated on Freescale's P4080 multi-core processor in combination with SYSGO's commercial real-time operating system PikeOS and AbsInt's timing analysis framework aiT. We abstract real applications' behavior using a representative task set of the EEMBC Autobench benchmark suite. Our results show a reduction of up to 75% of the multi-core Worst-Case Execution Time (WCET), while implementing full transparency to the temporal and functional behavior of applications, enabling the seamless integration of legacy applications

Jet pumps for thermoacoustic applications: design guidelines based on a numerical parameter study

The oscillatory flow through tapered cylindrical tube sections (jet pumps) is characterized by a numerical parameter study. The shape of a jet pump results in asymmetric hydrodynamic end effects which cause a time-averaged pressure drop to occur under oscillatory flow conditions. Hence, jet pumps are used as streaming suppressors in closed-loop thermoacoustic devices. A two-dimensional axisymmetric computational fluid dynamics model is used to calculate the performance of a large number of conical jet pump geometries in terms of time-averaged pressure drop and acoustic power dissipation. The investigated geometrical parameters include the jet pump length, taper angle, waist diameter and waist curvature. In correspondence with previous work, four flow regimes are observed which characterize the jet pump performance and dimensionless parameters are introduced to scale the performance of the various jet pump geometries. The simulation results are compared to an existing quasi-steady theory and it is shown that this theory is only applicable in a small operation region. Based on the scaling parameters, an optimum operation region is defined and design guidelines are proposed which can be directly used for future jet pump design.Comment: The following article has been accepted by the Journal of the Acoustical Society of America. After it is published, it will be found at http://scitation.aip.org/JAS

Computational fluid dynamics analysis of the oscillatory flow in a jet pump: the influence of taper angle

A two-dimensional CFD model for predicting the oscillating flow through a jet pump is developed. Various taper angles are investigated and total minor loss coefficients are derived. A good correspondence is achieved with experimental results from the literature. However, at higher taper angles a dramatic decay in the jet pump pressure drop is observed, which serves as a starting point for the improvement of jet pump design criteria for compact thermoacoustic application

On the correlation between the oxygen in hydrogen content and the catalytic activity of cathode catalysts in PEM water electrolysis

Altogether five platinum group metal (PGM) and PGM-free cathode catalysts were investigated in full PEM water electrolysis cells regarding their polarisation behaviour and their hydrogen and oxygen recombination properties. It was shown that the recombination activity of permeated oxygen and evolved hydrogen within the cathodic catalyst layer correlates with the activity of the oxygen reduction reaction (ORR) which was determined ex situ with linear sweep voltammetry. We found that the investigated PGM-free cathode catalysts had a low activity for the ORR resulting in higher measurable oxygen in hydrogen volume fractions compared to the PGM catalysts, which are more active for the ORR. Out of the three investigated PGM-free catalysts, only one commercially available material based on a Ti suboxide showed a similar good polarisation behaviour as the state of the art cathode catalyst platinum, while its recombination activity was the lowest of all catalysts. In addition to the recombination of hydrogen and oxygen on the electrocatalysts, we found that the prevalent carbon-based cathodic porous transport layers (PTL) also offer catalytically active recombination sites. In comparison to an inactive PTL, the measurable oxygen flux using carbon-based PTLs was lower and the recombination was enhanced by microporous coatings with high surface areas. © 2021 The Author(s)