The mode coupling theory for the ideal liquid glass transition which was worked out for simple liquids mainly by Götze, Sjögren and their coworkers, is extended to a molecular liquid of linear and rigid molecules. By use of the projection formalism of Zwanzig and Mori an equation of motion is derived for the correlators S m m l l , ' ' (q,t) of the tensorial one-particle density ρ lm (q,t), which contains the orientational degrees of freedom for l > 0. Application of the mode coupling approximation to the memory kernel results into a closed set of equations for S m m l l , ' ' (q,t), which requires the static correlators S m m l l , ' ' (q) as the only input quantities. The corresponding MCT-equations for the non-ergodicity parameters () f q f m m m l l l ≡ , (qe 3) are solved for a system of dipolar hard spheres by restricting the values for l to 0 and 1. Depending on the packing fraction ϕ and on the temperature T, three different phases exist: a liquid phase, where translational (TDOF) (l = 0) and orientational (ODOF) (l = 1) degrees of freedom are ergodic, a phase where the TDOF are frozen into a (non-ergodic) glassy state whereas the ODOF remain ergodic, and finally a glassy phase where both, TDOF and ODOF, are non-ergodic. From the non-ergodicity parameters

The contribution of power production from PV systems to the electricity supply is constantly increasing. An efficient use of the fluctuating solar power production will highly benefit from forecast information on the expected power production, as a basis for management of the electricity grids and trading on the energy market. We present and evaluate the regional PV power prediction system of University of Oldenburg and Meteocontrol GmbH providing forecasts of up to 2 days ahead with hourly resolution. The proposed approach is based on forecasts of the global model of the European Centre for Medium‐Range Forecasts (ECMWF). It includes a post‐processing procedure to derive optimised, site‐specific irradiance forecasts and explicit physical modelling steps to convert the predicted irradiances to PV power. Finally, regional power forecasts are derived by up‐scaling from a representative set of PV systems. The investigation of proper up‐scaling is a special focus of this paper. We introduce a modified up‐scaling approach, modelling the spatial distribution of the nominal power with a resolution of 1° × 1°. The operational PV power prediction system is evaluated in comparison to the modified up‐scaling approach for the control areas of the two German transmission system operators ‘transpower’ and ‘50 Hertz’ for the period 2.7.2009–30.4.2010. rmse values of the operational forecasts are in the range of 4–5% with respect to the nominal power for intra‐day and day‐ahead forecast horizons. Further improvement is achieved with the modified up‐scaling approach. Copyright © 2010 John Wiley & Sons, Ltd.

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The second quantum technological revolution started around 1980 with the control of single quantum particles and their interaction on an individual basis. These experimental achievements enabled physicists, engineers, and computer scientists to utilize long-known quantum features—especially superposition and entanglement of single quantum states—for a whole range of practical applications. We use a publication set of 54,598 papers from Web of Science, published between 1980 and 2018, to investigate the time development of four main subfields of quantum technology in terms of numbers and shares of publications, as well as the occurrence of topics and their relation to the 25 top contributing countries. Three successive time periods are distinguished in the analyses by their short doubling times in relation to the whole Web of Science. The periods can be characterized by the publication of pioneering works, the exploration of research topics, and the maturing of quantum technology, respectively. Compared to the USA, China’s contribution to the worldwide publication output is overproportionate, but not in the segment of highly cited papers.

Studying the history of research fields by analyzing publication records and topical and/or keyword searches with reference publication year spectroscopy (RPYS) has been introduced as a powerful tool to identify the corresponding root publications. However, for some research fields (e.g., rather new and interdisciplinary fields) like solar energy meteorology, encompassing such research fields via a keyword- or topic-based search query is not feasible to get a reasonably exhaustive publication set. Therefore, we apply its variant RPYS-CO to all publications co-cited with two highly important marker papers, using the cited references explorer for inspecting the RPYS-CO results. We obtain two lists of seminal papers, which are able to adequately tell us the story of solar energy meteorology up to the 1990s, respectively in its subfield using satellite-based methods for solar irradiance estimation even to very recent years. Consequently, we recommend this method to gain valuable insights in (new) research fields.

With the announcement of the retirement of Microsoft Academic Graph (MAG), the non-profit organization OurResearch announced that they would provide a similar resource under the name OpenAlex. Thus, we compare the metadata with relevance to bibliometric analyses of the latest MAG snapshot with an early OpenAlex snapshot. Practically all works from MAG were transferred to OpenAlex preserving their bibliographic data publication year, volume, first and last page, DOI as well as the number of references that are important ingredients of citation analysis. More than 90% of the MAG documents have equivalent document types in OpenAlex. Of the remaining ones, especially reclassifications to the OpenAlex document types journal-article and book-chapter seem to be correct and amount to more than 7%, so that the document type specifications have improved significantly from MAG to OpenAlex. As another item of bibliometric relevant metadata, we looked at the paper-based subject classification in MAG and in OpenAlex. We found significantly more documents with a subject classification assignment in OpenAlex than in MAG. On the first and second level, the classification structure is nearly identical. We present data on the subject reclassifications on both levels in tabular and graphical form. The assessment of the consequences of the abundant subject reclassifications on field-normalized bibliometric evaluations is not in the scope of the present paper. Apart from this open question, OpenAlex seems to be overall at least as suited for bibliometric analyses as MAG for publication years before 2021 or maybe even better because of the broader coverage of document type assignments.

We present a historical study of Quantum Technology 2.0 using more than 66,000 papers from 1980 to 2020 that had been assigned to four subfields. We applied the method reference publication year spectroscopy to respective publication sets of the subfields in order to identify their historical roots and seminal papers. We found 126 of them in total, 43 in quantum metrology and sensing, 46 in quantum communication and cryptography, 42 in quantum computing, and 33 in quantum information science–with a significant overlap between subfields–which are all discussed in their relevance for the respective subfield. We compared the subfields regarding their interrelationship and distinctiveness in terms of their most influential papers and were able to deduce a common core set of five seminal publications in all four subfields.

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