Sustainable Syngas Production by High-Temperature Co-electrolysis

High-temperature co-electrolysis shows comparable performance to steam electrolysis. Current densities above 1 A cm⁻² can be reached between 700 °C and 800 °C. Tailor-made syngas is produced, mainly determined by the reactant ratio. The experimental results are supported by modeling. Durability tests with cathode-supported cells show increased voltage degradation rates during electrolysis compared to fuel cell operation. Nickel depletion is found to be the main cause.     

Subspace Clustering for Situation Assessment in Aquatic Drones: A Sensitivity Analysis for State-Model Improvement

Abstract

In this paper, we propose the use of subspace clustering to detect the states of dynamical systems from sequences of observations. In particular, we generate sparse and interpretable models that relate the states of aquatic drones involved in autonomous water monitoring to the properties (e.g., statistical distribution) of data collected by drone sensors. The subspace clustering algorithm used is called SubCMedians. A quantitative experimental analysis is performed to investigate the connections between i) learning parameters and performance, ii) noise in the data and performance. The clustering obtained with this analysis outperforms those generated by previous approaches.     

Study of the catalytic combustion of lean hydrogen-air mixtures in a monolith reactor

This paper presents an experimental study of catalytic hydrogen combustion that used commercial catalysts containing Pt in a honeycomb monolith reactor in a plug flow configuration. The emphasis is on determining global kinetics in the case of low hydrogen content. Measurements of the temperature and composition of the reaction product at the outlet in the steady state condition at the different initial compositions of hydrogen and total volumetric feed rates were performed. The conversion of hydrogen was determined in parallel to the composition of the reaction product at the outlet using GC as well as by means of the thermodynamic approach using material and energy balances. The influence of the flow rate and initial molar fraction of hydrogen on hydrogen conversion is shown. A kinetic expression of the Arrhenius type is proposed with the reaction first order in hydrogen and zero order in oxygen for the overall process of the oxidation of hydrogen in lean hydrogen-air mixtures. The determined activation energy was in good agreement with the desorption activation energy for O₂ from graphene-covered Pt(111) surfaces using temperature-programmed desorption. This result shows transport-limitations for heterogeneous hydrogen conversion in catalytic hydrogen combustion.     

ZigBee与ZigBee PRO:哪个功能集最适合?

ZigBee从问世以来不断改进,这种崭新无线标准革新了家庭自动化市场。对于那些对ZigBee不熟悉,或是没机会了解最新规格的人,本文介绍了ZigBee的现状,概略说明ZigBee与ZigBee PRO的功能集,并讨论不同市场与应用环境下的ZigBee,包括ZigBee在医疗市场中的多方面应用。     

Ausbreitung von Kältefahnen im Grundwasser bei Erdwärmesonden

Shallow geothermal energy installations, especially ground source heat pump (GSHP) systems are increasingly being used for air conditioning and temperature control in buildings. Heating applications, for example, result in cold temperature anomalies (cold plumes) in the subsurface. To avoid interactions between adjacent cold plumes, authorities recommend minimum distances of about 10 m between installations. The length of these plumes can be simulated analytically and numerically. The presented analytical solutions are valid for steady-state conditions and consider conduction, convection and dispersion. The results show that the length depends on different parameters, especially flow velocity. The plumes in gravel aquifers become temporarily longer than in less permeable aquifers. Even under average energy extraction rates, they can exceed 10 m in length after one heating period. In the presented example the plume has a length of 10 m after 100 days under a continuous energy extraction rate of 55 W?m^?1. However, these plumes can regenerate quickly. Finally, the analytical results are discussed in a legal context.     

Universal Portfolios With and Without Transaction Costs

A constant rebalanced portfolio is an investment strategy which keeps the same distribution of wealth among a set of stocks from period to period. Recently there has been work on on-line investment strategies that are competitive with the best constant rebalanced portfolio determined in hindsight (Cover, 1991, 1996; Helmbold et al., 1996; Cover & Ordentlich, 1996a, 1996b; Ordentlich & Cover, 1996). For the universal algorithm of Cover (Cover, 1991),we provide a simple analysis which naturallyextends to the case of a fixed percentage transaction cost (commission ), answering a question raised in (Cover, 1991; Helmbold et al., 1996; Cover & Ordentlich, 1996a, 1996b; Ordentlich & Cover, 1996; Cover, 1996). In addition, we present a simple randomized implementation that is significantly faster in practice. We conclude by explaining how these algorithms can be applied to other problems, such as combining the predictions of statistical language models, where the resulting guarantees are more striking.     

An adaptive spatial diversity receiver for non-Gaussianinterference and noise

Standard linear diversity combining techniques are not effective in combating fading in the presence of non-Gaussian noise. An adaptive spatial diversity receiver is developed for wireless communication channels with slow, flat fading and additive non-Gaussian noise. The noise is modeled as a mixture of Gaussian distributions and the expectation-maximization (EM) algorithm is used to derive estimates for the model parameters. The transmitted signals are detected using a likelihood ratio test based on the parameter estimates. The new adaptive receiver converges rapidly, its bit error rate performance is very close to optimum when relatively short training sequences are used, and it appears to be relatively insensitive to mismatch between the noise model and the actual noise distribution. Simulation results are included that illustrate various aspects of the adaptive receiver performance     

Parabolic Flights @ Home

We developed an unmanned air vehicle (UAV) suitable for small parabolic-flight experiments. The flight speed of 100 m s^− 1 is sufficient for zero-gravity parabolas of 16 s duration. The flight path’s length of slightly more than 1 km and 400 m difference in altitude is suitable for ground controlled or supervised flights. Since this fits within the limits set for model aircraft, no additional clearance is required for operation. Our UAV provides a cost-effective platform readily available for low-g experiments, which can be performed locally without major preparation. A payload with a size of up to 0.9 ×0.3 ×0.3 m³ and a mass of ∼5 kg can be exposed to 0 g ₀–5 g ₀, with g ₀ being the gravitational acceleration of the Earth. Flight-duration depends on the desired acceleration level, e.g. 17 s at 0.17 g ₀ (lunar surface level) or 21 s at 0.38 g ₀ (Martian surface level). The aircraft has a mass of 25 kg (including payload) and a wingspan of 2 m. It is powered by a jet engine with an exhaust speed of 450 m s^− 1 providing a thrust of 180 N. The parabolic-flight curves are automated by exploiting the advantages of sophisticated micro-electronics to minimize acceleration errors.     

On the use of different types of knowledge in metaheuristics based on constructing solutions

Many metaheuristics are either based on neighborhood search or the construction of solutions. Examples for the latter ones include ant colony optimization and greedy randomized adaptive search procedures. These techniques generally construct solutions probabilistically by sampling a probability distribution over the search space. Solution constructions are generally independent from each other. Recent algorithmic variants include two important features that are inspired by deterministic branch and bound derivatives such as beam search: the use of bounds for evaluating partial solutions, and the parallel and non-independent construction of solutions. In this paper we give a theoretical reason of why these algorithms generally work very well in practice. Second, we confirm our theoretical findings by means of practical examples. After the application to artificial problems, we present experimental results concerning the well-known open shop scheduling problem.