Efficient Operation of Modular Grid-Connected Battery Inverters for RES Integration

Grid-connected battery storage systems on megawatt-scale play an important role for the integration of renewable energies into electricity markets and grids. In reality, these systems consist of several batteries and inverters, which have a lower energy conversion efficiency in partial load operation. In renewable energy sources (RES) applications, however, battery systems are often operated at low power. The modularity of grid-connected battery storage systems thus allows improving system efficiency during operation. This contribution aims at quantifying the effect of segmenting the system into multiple battery-inverter subsystems on reducing operating losses. The analysis is based on a mixed-integer linear program that determines the system operation by minimizing operating losses. The analysis shows that systems with high modularity can meet a given schedule with lower losses. Increasing modularity from one to 32 subsystems can reduce operating losses by almost 40%. As the number of subsystems increases, the benefit of higher efficiency decreases. The resulting state of charge (SOC) pattern of the batteries is similar for the investigated systems, while the average SOC value is higher in highly modular systems

Wavenumber-explicit continuity and coercivity estimates in acoustic scattering by planar screens

We study the classical first-kind boundary integral equation reformulations of time-harmonic acoustic scattering by planar sound-soft (Dirichlet) and sound-hard (Neumann) screens. We prove continuity and coercivity of the relevant boundary integral operators (the acoustic single-layer and hypersingular operators respectively) in appropriate fractional Sobolev spaces, with wavenumber-explicit bounds on the continuity and coercivity constants. Our analysis is based on spectral representations for the boundary integral operators, and builds on results of Ha-Duong (Jpn J Ind Appl Math 7:489--513 (1990) and Integr Equat Oper Th 15:427--453 (1992)).Comment: v2 has minor corrections compared to v1. arXiv admin note: substantial text overlap with arXiv:1401.280

Brand champion behaviour: Its role in corporate branding

yesBrand champions are responsible for encouraging employee commitment to the corporate brand strategy. They strongly believe in and identify with the brand concept—the company’s selected brand meaning, which underpins corporate brand strategy implementation. We conducted research to explore why and how brand champion behaviour operates within companies implementing a new corporate brand strategy. Against a backdrop of growing interest in brand champion behaviour in corporate branding research, we grounded our study in social identity theory and rhetorical theory from change management literature. Our findings show that articulating a compelling brand vision, taking responsibility, and getting the right people involved are the most widely used strategies by brand champions. We uncover how rhetorical strategies within brand champion behaviour generate employee commitment to a new corporate brand strategy. The dimension of brand champion behaviour that is effective depends on the type of brand evolution, involving shifts in the brand concept. We make suggestions for further studies underpinned by social identity theory and rhetorical theory to investigate brand champion behaviour processes within companies introducing a new corporate brand strategy

Optimizing Trading Decisions for Hydro Storage Systems using Approximate Dual Dynamic Programming

We propose a new approach to optimize operations of hydro storage systems with multiple connected reservoirs whose operators participate in wholesale electricity markets. Our formulation integrates short-term intraday with long-term interday decisions. The intraday problem considers bidding decisions as well as storage operation during the day and is formulated as a stochastic program. The interday problem is modeled as a Markov decision process of managing storage operation over time, for which we propose integrating stochastic dual dynamic programming with approximate dynamic programming. We show that the approximate solution converges towards an upper bound of the optimal solution. To demonstrate the efficiency of the solution approach, we fit an econometric model to actual price and in inflow data and apply the approach to a case study of an existing hydro storage system. Our results indicate that the approach is tractable for a real-world application and that the gap between theoretical upper and a simulated lower bound decreases sufficiently fast. (authors' abstract

Magnetization switching of submicrometer Co dots induced by a magnetic force microscope tip

We have applied magnetic force microscopy (MFM) with an in situ electromagnet to study the switching of the magnetization of submicrometer Co dots fabricated by means of electron-beam lithography. By using the MFM tip as a local-field source, the magnetization of individual single-domain Co dots could be reversed. Micromagnetic simulations show that the switching process is induced by the stray field of the MFM tip. Furthermore, the external field that is necessary to support switching of the dot depends on the tip-dot separation

Quantifying aspects of antonym canonicity in English and Swedish: textual and experimental

This paper highlights the potential usefulness of combining corpus methods and experimental methods to gain new theoretical insights into the role of antonymy as an organizing lexicosemantic principle in human thinking and languages ’ vocabularies. We are intrigued by what distinguishes so-called canonical antonyms such as good-bad, long-short, thin-thick from other types of contrasts such as cold-scorching, pale-dark and speedy-slow. There are probably various converging reasons for perceptions of ‘goodness of antonymy’, e.g. frequency of co-occurrence, co-occurrence in certain constructions, e.g. whether slow or fast, stylistic co-occurrence preferences and pairwise acquisition (e.g. Muehleisen 1997, Willners 2001, Jones 2002, Murphy 2003). The research reported in this paper forms part of an international collaborative project on antonymy in discourse. 1 This paper proposes (i) a principled method for creating a foundation for cross-linguistic comparisons of adjectival antonym pairings, using corpus methods and (ii) subsequently using the corpus data for the design of experiments on antonym canonicity. Since our investigations concern the nature of antonymy as a semantic relation and the patterns of lexicalization in English and Swedish, it is important to make sure that there is