Frequency-Domain Analysis of Linear Time-Periodic Systems

In this paper, we study convergence of truncated representations of the frequency-response operator of a linear time-periodic system. The frequency-response operator is frequently called the harmonic transfer function. We introduce the concepts of input, output, and skew roll-off. These concepts are related to the decay rates of elements in the harmonic transfer function. A system with high input and output roll-off may be well approximated by a low-dimensional matrix function. A system with high skew roll-off may be represented by an operator with only few diagonals. Furthermore, the roll-off rates are shown to be determined by certain properties of Taylor and Fourier expansions of the periodic systems. Finally, we clarify the connections between the different methods for computing the harmonic transfer function that are suggested in the literature

A Harmonic Transfer Function Model for a Diode Converter Train

A method for analysis of electric networks with nonlinear and switching components is presented. The method is based on linearization around the nominal AC voltage, which results in linear time periodic (LTP) models. For nonlinear and switching components, there is coupling between different frequencies, which may cause stability and resonance problems. The models capture this coupling and can thus be used for small signal stability and robustness analysis. A short introduction to transfer functions for LTP systems is given. To illustrate the method, an LTP model for the Adtranz locomotive Re 4/4 is derived. The system consists of an AC-side with a transformer, and a DC-side with a DC motor and a smoothing choke. The AC-side and the DC-side are connected by a diode bridge rectifier. The model clearly shows the coupling between frequencie

ANN-Benchmarks: A Benchmarking Tool for Approximate Nearest Neighbor Algorithms

This paper describes ANN-Benchmarks, a tool for evaluating the performance of in-memory approximate nearest neighbor algorithms. It provides a standard interface for measuring the performance and quality achieved by nearest neighbor algorithms on different standard data sets. It supports several different ways of integrating $k$-NN algorithms, and its configuration system automatically tests a range of parameter settings for each algorithm. Algorithms are compared with respect to many different (approximate) quality measures, and adding more is easy and fast; the included plotting front-ends can visualise these as images, $\LaTeX$ plots, and websites with interactive plots. ANN-Benchmarks aims to provide a constantly updated overview of the current state of the art of $k$-NN algorithms. In the short term, this overview allows users to choose the correct $k$-NN algorithm and parameters for their similarity search task; in the longer term, algorithm designers will be able to use this overview to test and refine automatic parameter tuning. The paper gives an overview of the system, evaluates the results of the benchmark, and points out directions for future work. Interestingly, very different approaches to $k$-NN search yield comparable quality-performance trade-offs. The system is available at http://ann-benchmarks.com .Comment: Full version of the SISAP 2017 conference paper. v2: Updated the abstract to avoid arXiv linking to the wrong UR

MIMO Encoder and Decoder Design for Signal Estimation

We study the joint design of optimal linear MIMO encoders and decoders for filtering and transmission of a vector- valued signal over parallel Gaussian channels subject to a real- time constraint. The objective is to minimize the sum of the estimation error variances at the receiving end. The design problem is nonconvex, but it is shown that a global optimum can be found by solving a related two-stage problem. The first stage consists of a mixed norm minimization problem, where the 2-norm corresponds to the error variance in a corresponding Wiener-Kolmogorov filtering problem and the 1-norm is induced by the channel noise. The second stage consists of a matrix spectral factorization

En kvalitativ studie om anhörigkontakten på LSS-boenden ur ett professionellt perspektiv

Syftet med undersökningen är att få en förståelse för hur kontakten med anhöriga till brukare vid LSS- boenden ser ut ur de professionellas perspektiv. Genom att fokusera på de professionellas perspektiv, vill vi ta reda på de handlingsstrategier och utgångspunkter för dessa som utmynnar i kommunikation. - Hur ser kontakten med anhöriga ut vad gäller kontinuitet, form och innehåll? - Vad finns det för riktlinjer vad gäller kontakt och kommunikation med anhöriga? - Hur integrerar personalen riktlinjer, arbetsgruppens synsätt och individuell syn i kontakten med anhöriga? - Vad har personalen att säga om förväntningarna från andra professionella och brukarnas anhöriga? - Hur ser personalen på gränsdragningen mellan personligt och privat i kontakten med anhöriga? - Vilka svårigheter upplever personalen när det gäller att planera arbetet med brukarna i samförstånd med anhöriga? Studien har genomförts i form av kvalitativa forskningsintervjuer, med en intervjuguide som fokuserar på centrala teman inom ämnet. I resultatet framgår att samtliga intervjupersoner på olika vis uttrycker att det finns en problematik som utgår från att de upplever att de anhörigas förväntningar inte stämmer överens med den egna synen på den professionella arbetsrollen, vilket försvårar kommunikationen. Resultatet har analyserats utifrån symbolisk interaktionism och rollteori. I analysen har dessa olika förväntningar diskuterats utifrån de olika positioner, roller och sociala identiteter som de professionella och de anhöriga till brukarna befinner sig i