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    Dynamical X-ray diffraction imaging of voids in dislocation-free high-purity germanium single crystals
    (Copenhagen : Munksgaard, 2020) Gradwohl, Kevin-P.; Danilewsky, Andreas N.; Roder, Melissa; Schmidbauer, Martin; Janicskó-Csáthy, József; Gybin, Alexander; Abrosimov, Nikolay; Sumathi, R. Radhakrishnan
    White-beam X-ray topography has been performed to provide direct evidence of micro-voids in dislocation-free high-purity germanium single crystals. The voids are visible because of a dynamical diffraction contrast. It is shown that voids occur only in dislocation-free parts of the crystal and do not show up in regions with homogeneous and moderate dislocation density. It is further suggested that the voids originate from clustering of vacancies during the growth process. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection.
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    Survey vs Scraped Data: Comparing Time Series Properties of Web and Survey Vacancy Data
    (Berlin : Springer Nature, 2019) De Pedraza, P.; Visintin, S.; Tijdens, K.; Kismihók, G.
    This paper studies the relationship between a vacancy population obtained from web crawling and vacancies in the economy inferred by a National Statistics Office (NSO) using a traditional method. We compare the time series properties of samples obtained between 2007 and 2014 by Statistics Netherlands and by a web scraping company. We find that the web and NSO vacancy data present similar time series properties, suggesting that both time series are generated by the same underlying phenomenon: the real number of new vacancies in the economy. We conclude that, in our case study, web-sourced data are able to capture aggregate economic activity in the labor market.