Stroemungskarten und Modelle fuer transiente Zweiphasenstroemungen Abschlussbericht

Experiments with novel measurement instrumentation delivered data on the structure of transient gas-liquid flows used for the development and validation of microscopic, i.e. geometry-independent constitutive equations for the description of momentum exchange between the phases as well as for characterising the frequency of bubble coalescence and fragmentation. For this purpose a vertical test section of the two-phase facility MTLoop in Rossendorf was used, whereas wire-mesh sensors with a resolution of 2-3 mm and a sampling frequency of up to 10 kHz were applied for the first time. This allowed to record the evolution of gas fraction and velocity profiles as well as bubble size distributions along the flow path and during fast transients, i.e. to obtain the data necessary for the modelling. For the test of the model equations, a simplified solver for the fluid-dynamic equations along the test pipe was developed, which considers a large number of bubble size classes. The numerical solutions have shown that the transition from bubble flow with a wall peak of the gas fraction to a flow with central peak and further to a slug flow at increasing gas velocities can be modelled on basis of a unified set of physically reasonable and geometry-independent constitutive laws. These model equations have proven to be generalising for a certain region of superficial velocities and are ready for an implementation in CFD codes. Furthermore, experiments on steam condensation were performed, which have a direct relation to condensation models in thermal hydraulic system codes. The investigations gained experimental data for the model validation, including the behaviour and the effect of non-condensible gases. A special kind of probes for the detection of the non-condensible gas and the replacement of plugs of it were developed and applied in transient condensation tests in slightly inclined heat exchanger pipes. (orig.)Experimente mit neuartigen Messverfahren lieferten Daten ueber die Struktur von trasienten Fluessigkeits-Gas-Stroemungen fuer die Entwicklung und Validierung von mikroskopischen, d.h. geometrieunabhaengigen Konstitutivbeziehungen zur Beschreibung des Impulsaustauschs zwischen Fluessigphase und Gasblasen sowie zur Quantifizierung der Haeufigkeit von Blasenkoaleszenz und -zerfall. Hierzu wurde eine vertikale Testsektion der Zweiphasentestschleife MTLoop in Rossendorf genutzt, wobei erstmals Gittersensoren mit einer Aufloesung von 2-3 mm bei einer Messfrequenz von bis zu 10 kHz angewandt wurden. Dabei wurde die Evolution von Gasgehalts-, Geschwindigkeits- und Blasengroessenverteilungen entlang des Stroemungsweges und bei schnellen Uebergangsprozessen aufgenommen und so die fuer die Modellbildung erforderlichen Daten bereitgestellt. Fuer den Test der Modellbeziehungen wurde ein vereinfachtes Verfahren zur Loesung der Stroemungsgleichungen entlang des Stroemungswegs erstellt. Es basiert auf der Betrachtung einer groesseren Anzahl von Blasengroessenklassen. Die erhaltenen numerische Loesungen haben erstmals gezeigt, dass der bei Erhoehung der Gasvolumenstromdichte stattfindende Uebergang von einer Blasenstroemung mit Randmaximum zu einem Profil mit Zentrumsmaximum und anschliessend zu einer Pfropfenstroemung ausgehend von einem einheitlichen Satz physikalisch begruendeter und geometrieunabhaengiger Konstitutivgleichungen modelliert werden kann. Die Modellbeziehungen haben sich in einem abgegrenzten Gebiet der Volumenstromdichten als generalisierungsfaehig erwiesen und sind fuer den Einbau in CFD-Modelle geeignet. Weiterhin wurden Arbeiten zur Kondensation durchgefuehrt, die direkten Bezug zu den Kondensationsmodellen haben, die in Thermohydraulik-Codes enthalten sind. Die Untersuchung liefert darueber hinaus experimentelle Daten fuer die Modellvalidierung hinsichtlich des Verhaltens und des Einflusses nichtkondensierbarer Gase. Hierfuer wurden spezielle Sonden fuer die Bestimmung der Konzentration und fuer die Lokalisierung von Pfropfen nichtkondensierbarer Gase entwickelt und bei transienten Kondensationsversuchen in einem leicht geneigten Waermeuebertragerrohr eingesetzt. (orig.)Available from TIB Hannover: RR 1847(379) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung und Forschung, Berlin (Germany); Gesellschaft fuer Anlagen- und Reaktorsicherheit mbH (GRS), Koeln (Germany)DEGerman

Comparison of four commercial, automated antigen tests to detect SARS-CoV-2 variants of concern.

A versatile portfolio of diagnostic tests is essential for the containment of the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) pandemic. Besides nucleic acid-based test systems and point-of-care (POCT) antigen (Ag) tests, quantitative, laboratory-based nucleocapsid Ag tests for SARS-CoV-2 have recently been launched. Here, we evaluated four commercial Ag tests on automated platforms and one POCT to detect SARS-CoV-2. We evaluated PCR-positive (n = 107) and PCR-negative (n = 303) respiratory swabs from asymptomatic and symptomatic patients at the end of the second pandemic wave in Germany (February–March 2021) as well as clinical isolates EU1 (B.1.117), variant of concern (VOC) Alpha (B.1.1.7) or Beta (B.1.351), which had been expanded in a biosafety level 3 laboratory. The specificities of automated SARS-CoV-2 Ag tests ranged between 97.0 and 99.7% (Lumipulse G SARS-CoV-2 Ag (Fujirebio): 97.03%, Elecsys SARS-CoV-2 Ag (Roche Diagnostics): 97.69%; LIAISON® SARS-CoV-2 Ag (Diasorin) and SARS-CoV-2 Ag ELISA (Euroimmun): 99.67%). In this study cohort of hospitalized patients, the clinical sensitivities of tests were low, ranging from 17.76 to 52.34%, and analytical sensitivities ranged from 420,000 to 25,000,000 Geq/ml. In comparison, the detection limit of the Roche Rapid Ag Test (RAT) was 9,300,000 Geq/ml, detecting 23.58% of respiratory samples. Receiver-operating-characteristics (ROCs) and Youden’s index analyses were performed to further characterize the assays’ overall performance and determine optimal assay cutoffs for sensitivity and specificity. VOCs carrying up to four amino acid mutations in nucleocapsid were detected by all five assays with characteristics comparable to non-VOCs. In summary, automated, quantitative SARS-CoV-2 Ag tests show variable performance and are not necessarily superior to a standard POCT. The efficacy of any alternative testing strategies to complement nucleic acid-based assays must be carefully evaluated by independent laboratories prior to widespread implementation

Tomographisches Messverfahren fuer die Gasverteilung in einer Axialpumpe bei Zweiphasenbetrieb Aktueller Abschlussbericht zum Vorhaben 7531.50-03-0370-99/3. Berichtszeitraum: 01.07.1999 - 31.12.2000

A new method is described for measuring the local phase distribution in rotating pump rotors or similar objects by gamma tomography. Tomographic projections are made in intervals of only about 100 #mu#s. At a relevant speed of about 25 s"1, this means a comparatively high angular resolution of 0.9 , which provides more detailed information on gas distribution. The transport processes in the rotor of an axial pump during pumping of an air/water mixture were visualized by the tomograph. The effects of changes in the external flow parameters and of variations of the working point on the spatial phase distribution inside the rotor were shown. (orig.)SIGLEAvailable from TIB Hannover: RR 1847(336) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSaechsisches Staatsministerium fuer Wissenschaft und Kunst, Dresden (Germany)DEGerman

Linguistic Situation in Twenty sub-Saharan African Countries: A Survey-based Approach

Data on second languages in sub-Saharan Africa are hard to come by. Consequently, any source that contributes to our knowledge beyond the level of primary languages should be appreciated and exploited. This article utilises Round 4 of the Afrobarometer Survey that collects information on ethnicity, home, and additional languages in 20 sub-Saharan African countries. The study has three main contributions. First, it overviews and compares some widely used sources that contain linguistic data and investigates why they show such a diverse picture on language use patterns. Second, it applies the ICP which, according to the author’s knowledge, is the first linguistic measure that takes multilingualism into account. Third, it shows how a simple graphic representation of the ICP can be used to visualise the most important dimensions of a country’s linguistic situation including the order of languages according to their size, the presence of monolingual speakers, and the relation between vernaculars and the former colonisers’ languages. The study findings are expected to be of interest to scholars engaged in language policy and planning and language-related development issues