Robust stability analysis of a dc/dc buck converter under multiple parametric uncertainties

Stability studies are a crucial part of the design of power electronic systems, especially for safety critical ap¬plications. Standard methods can guarantee stability under nominal conditions but do not take into account the multiple uncertainties that are inherent in the physical system or in the system model. These uncertainties, if unaccounted for, may lead to highly optimistic or even erroneous stability margins. The structured singular value-based method justifiably takes into account all possible uncertainties in the system. However, the application of the method to power electronic systems with multiple uncertainties is not widely discussed in the literature. This work presents practical approaches to applying the method in the robust stability analysis of such uncertain systems. Further, it reveals the significant impact of various types of parametric uncertainties on the reliability of stability assessments of power electronic systems. This is achieved by examining the robust stability margin of the dc/dc buck converter system, when it is subject to variations in system load, line resistance, operating temperature and uncertainties in the system model. The predictions are supported by time domain simulation and experimental results

Cluster policies of large cities in Russia and Kazakhstan

Relevance. Faced with globalization challenges, large modern cities need to develop their competitive advantages. One source of such advantages is clustering of urban economy. Questions dealing with cluster-based policies and classification of clusters operating on the regional and national levels have attracted much scholarly attention while there is still a research gap regarding urban cluster policies and comparison of city-based clusters.Research objective. The purpose of this study is to analyze the legal framework of cluster policies in Russia and Kazakhstan and to describe the criteria for classification and comparison of city-based clusters.Data and methods. The study used methods of systemic and comparative analysis, formalized methods of analysis of regulatory acts. The selected criteria are universal and can be used for cluster analysis in different countries. We considered strategies for socio-economic development of large cities in Russia and Kazakhstan from the official websites of city administrations as well as the regulatory acts of specific cities.  Results.  In both countries, clusters play a significant role in the development strategies of territories. The Russian and Kazakh governments take similar measures to support cluster initiatives. The regulatory legal acts of both countries emphasize the allocation of subsidies and co-financing of regional programs and RD in clusters. The process of cluster creation in Russia started later than in Kazakhstan but was also more intensive. A popular specialization for clusters in both countries is information technologies and communications, which corresponds to the goals set by the national governments.Conclusions. In both countries, the number of clusters in large cities is increasing annually. Typically, clusters have 11-50 participants. In both countries, there are clusters of different specialization. Strategies for socio-economic development serve as the main documents for devising cluster policies of cities.The practical significance of the study is that it proposes an approach to classification and comparison of clusters that can be used in further analysis and for identification of cluster policy priorities

Focused Crossed Andreev Reflection

We consider non-local transport in a system with one superconducting and two normal metal terminals. Electron focusing by weak perpendicular magnetic fields is shown to tune the ratio between crossed Andreev reflection (CAR) and electron transfer (ET) in the non-local current response. Additionally, electron focusing facilitates non-local signals between normal metal contacts where the separation is as large as the mean free path rather than being limited by the coherence length of the superconductor. CAR and ET can be selectively enhanced by modulating the magnetic field

Double Fe-impurity charge state in the topological insulator Bi2_2Se3_3

The influence of individual impurities of Fe on the electronic properties of topological insulator Bi$_2$Se$_3$ is studied by Scanning Tunneling Microscopy. The microscope tip is used in order to remotely charge/discharge Fe impurities. The charging process is shown to depend on the impurity location in the crystallographic unit cell, on the presence of other Fe impurities in the close vicinity, as well as on the overall doping level of the crystal. We present a qualitative explanation of the observed phenomena in terms of tip-induced local band bending. Our observations evidence that the specific impurity neighborhood and the position of the Fermi energy with respect to the Dirac point and bulk bands have both to be taken into account when considering the electron scattering on the disorder in topological insulators.Comment: 10 pages, accepted for publication in Applied Physics Letters, minor bugs were correcte